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Industrial manufacturing process of Acrylonitrile
Book · November 2014
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Ulsan National Institute of Science and Technology
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ABSTRACT
7KHSURMHFWUHSRUWIRUµ$FU\ORQLWULOH¶SUHVHQWHGKHUHLQLVLQWHQGHGWRFRYHUWKHRUHWLFDO
and practical principles associated with manufacture of Acrylonitrile and application
of such principles to a commercial plant scale.
7KH ILUVW FKDSWHU µ,QWURGXFWLRQ¶ GLVFXVVHV LQ EULHI WKH KLVWRU\ DQG GHYHORSPHQW RI
Acrylonitrile and its production. Detailed list of uses of Acrylonitrile as product and
Acetonitrile as byproduct are also included. It includes import and export data for
Acrylonitrile. The chapter contains manufacturer in India and worldwide, their
installed capacities and present production rates.
7KH FKDSWHU µ/LWHUDWXUH VXUYH\¶ LQFOXGHV WKH W\SHV RI OLWHUDWXUH LH LQIRUPDWLRQ
sources that were referred in preparation of this report. A detailed review of
information regarding Acrylonitrile is presented.
µ3URFHVVVHOHFWLRQ¶FKDSWHUFRYHUVYDULRXVDYDLODEOHSURFHVVHVXVHGIRUSURGXFWLRQRI
Acrylonitrile on a worldwide basis. The various processes are used are described
thereafter. The capacity selection and justification for it are presented in this chapter.
A process description of Sohio process i.e. ammoxidation of propylene in fluidized
bed reactor is followed by detail description include in next chapter.
7KH FKDSWHU RQ µ0DWHULDO %DODQFH¶ FRYers an overall material balance for 70000
MTPD Acrylonitrile plant as well as equipment wise material balance.
7KH FKDSWHU RQ µ(QHUJ\ %DODQFH¶ LQFOXGHV WKH HQWKDOS\ FKDQJHV DVVRFLDWHG ZLWK
equipments, cooling or heating requirements and loads on condensers and reboilers
of columns.
7KH FKDSWHU RQ µGHVLJQ RI PDMRU HTXLSPHQWV¶ FRYHUV GHWDLO SURFHVV GHVLJQ DQG
mechanical design of the Fluidized bed reactor and HCN column. The Fluidized bed
reactor and HCN column. The Fluidized bed reactor also includes the design of
bubbling fluidized bed model. The specifications for auxiliary equipments mention in
next chapter.
7KH µ8WLOLW\ UHTXLUHPHQWV¶ FKDSWHU LQFOXGHV WKH FRROLQJ ZDWHU UHIULJHUDQW VWHDP
power, air, nitrogen and other utility requirements for the process in consideration.
1
7KHµ(QYLURQPHQWDODQG6DIHW\&RQVLGHUDWLRQ¶FKDSWHUGLVFXVVHVSROOXWLRQSUREOHPV
as well as safety data and measures for Acrylonitrile plant. It includes safety
measures carry out in Acrylonitrile plant. It also includes biodegradation of waste
FRQWDLQORZF\DQLGH7KHµ0DWHULDOVRIFRQVWUXFWLRQ¶FKDSWHUSUHVHQWVWKHPDWHULDOVRI
construction for various equipments.
7KH µ,QVWUXPHQWDWLRQ DQG 3URFHVV &RQWURO¶ FKDSWHU LQFOXGHV PDMRU SURFHVV FRQWURO
techniques and instruments along with a P & I diagram. In which process control
techniques and instruments provision on reactor is also mention with its significance.
Project & product costs, return of investment and pay-out periods have been
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A comSOHWHOLVWRIFLWHGUHIHUHQFHLVSUHVHQWHGLQWKHµ5HIHUHQFH¶FKDSWHU
At last, properties of Acrylonitrile, various data related to Acrylonitrile and
$FU\ORQLWULOHSODQWDUHLQFOXGHGLQµ$SSHQGLFHV¶
2
CONTENTS
Abstract
01
Contents
03
List of Table
07
List of Figure
08
Nomenclature & Symbols
09
Sr. Chapter
Title
No.
1
1
Introduction
1.1 Introduction
1.2 History
2
2
Market Survey
2.1 Uses of Acrylonitrile
2.2 Uses of Acetonitrile
2.3 Current installed capacity
2.4 Import & export position
3
3
Physical & Chemical Properties
3.1 Physical Properties
3.2 Chemical Properties
4
4
Literature Survey
4.1 Literature Survey
4.2 Acrylonitrile & Sohio process
4.3 Sohio Process Research & Development
4.4 Reaction Kinetics
4.5 Catalyst Development
4.6 Catalyst mechanism
4.7 Synthesis of method
4.8 Economics ± Acrylonitrile
5
5
Process Selection
5.1 Basic manufacturing process
5.2 Selection of best process
5.3 Selection capacity
6
6
Thermodynamics & kinetics
6.1Process selection
6.2 Revamps of Acrylonitrile plant
3
Page
No.
11
11
12
15
15
20
21
22
26
26
29
31
31
32
33
35
36
37
37
38
41
41
51
53
54
54
62
7
7
8
8
9
9
10
10
6.3Auxiliary Chemicals added
62
Material Balance
7.1 Basis
7.2 Catalyst performance
7.3 Molecular weight
7.4 Reactor
7.5 Quench column
7.6 Absorber
7.7 Recovery column &Decanter
7.8 Aceto column
7.9 HCN column
7.10 Product column
Energy Balance
8.1 Preheating of reactor
8.2 Reactor
8.3 Cooler
8.4 Quench column
8.5 Around after cooler
8.6 Heat absorbers and heat exchangers
8.7 Recovery column
8.8 Decanter
8.9 Aceto Stripper
8.10 HCN Column
8.11 ACN column
Design of Equipments
9.1 Fluidized Bed Reactor
9.2 Distillation Column
Process Control & Instrumentation
10.1 Role of P& ID
10.2 Process measurement
10.3 Temperature Control
10.4 Pressure Control
10.5 Level Control
10.6 Flow Control
10.7 Alarms And Safety Trips And Interlocks
10.8 Instrumentation And Process Control For Acrylonitrile
Reactor
10.9 Instrumentation And Process Control For Other
65
65
65
66
67
70
71
72
73
73
74
75
75
75
78
79
81
82
84
86
87
88
89
90
90
95
103
103
104
105
106
106
106
107
107
4
108
Equipments
11
11
12
12
13
13
14
14
Safety and pollution control
11.1 Safety And Pollution Control
11.2 Chemical Hazards
11.3 Fire And Explosion Hazard
11.4 Air And Land Pollution
11.5 Safety In Plant
11.6 Concept of safer side
11.7 Prevention & control of hazards in ACN plant
11.8 Acetonitrile
11.9 ACETONITRILE: Safety Data Sheet
11.10 Hydrogen Cyanide
11.11 Ammonia
11.12 General Safety Aspects In Chemical Plant:
11.13(Effluent Treatment )
Plant location & layout
12.1 Selection of plant location
12.2 Primary factors for plant location
12.3 Specific factors for plant location
12.4 Plant layout
Cost Estimation
13.1 Factors affecting production & investment cost
13.2 Capital investment
13.3 Direct cost
13.4 Indirect cost
13.5 Costing of plants
13.6 Profit Analysis
110
110
110
110
111
111
112
113
117
123
124
125
126
133
137
137
137
139
141
144
144
145
145
146
148
152
Utilities
14.1 Utilities
14.2 Steam systems
14.3 Fuel system
14.4 Water system
14.5 Brine coolant system
14.6 Air system
14.7 Nitrogen system
14.8 Electricity
14.9 Steam generating system
153
153
153
154
154
155
156
157
157
157
5
15
15
16
Auxiliary Equipments
15.1 Column
15.2 Heat Exchangers
15.3 Tanks
Summary
160
160
161
161
162
16
17
17
References
163
18
18
Appendices
18.1 Appendices No. 1
18.2 Appendices No. 2
18.3 Appendices No. 3
166
166
168
170
6
LIST OF TABLES
Table No.
2.1
2.2
2.3
2.4
2.5
2.6
2.7
3.1
3.2
3.3
3.4
3.5
7.1
7.2
7.3
8.1
8.2
8.3
8.4
8.5
8.6
8.7
8.8
8.9
8.10
8.11
9.1
10.1
11.1
13.1
13.2
13.3
13.4
14.1
Description of Tables
Levels of residual acrylonitrile found in various products
,QGLD¶V3HUVSHFWLYH
Uses of acrylonitrile U.S and Europe
Producers of Acrylonitrile
Estimated U.S production of acrylonitrile
Industries in India import acrylonitrile.(in 1983)
Historical data
Physical Properties of Acrylonitrile
Thermodynamic Data:
Solubilities of Acrylonitrile in Water:
Azeotrope of acrylonitrile:
Acrylonitrile vapor Pressure over Aq. solutions at 250C
Molecular weight in kg / kgmole
Material balance over Reactor
Material balance over Quench Column:
Components and its properties
Components and its Heat properties
Enthalpy out with products
Enthalpy out with gases
Enthalpy out with gases [at top]
Enthalpy out with the mixture
Enthalpy out with unabsorbed gases from top
Enthalpy out with bottom stream
Enthalpy out with Distillate: [DHD]
Components and their mole fraction
Enthalpy in Decanter
X-Y composition
Temperature ranges for certain instruments:
COD/BOD table
Purchase equipment cost (PEC)
Direct Production cost
Labor and production supervision
Product selling cost
Utility Requirement:
7
Page No.
18
19
19
21
22
23
25
26
27
27
28
28
66
69
71
75
76
77
78
80
82
83
83
85
85
86
96
105
134
148
150
150
152
158
LIST OF FIGURES
Figure No.
5.1
5.2
5.3
9.1
18.1
Description of Figures
Acrylonitrile by Sohio Process
Acrylonitrile by Ethylene Cyanohydrin route
Acrylonitrile by Acetylene-HCN route
Macabe-Theile method (X-Y plot)
Safety Symbol for Acrylonitrile
8
Page No.
42
45
47
97
171
NOMENCLATURES & SYMBOLS
W
= Weight flow of shell side fluid, (kg/hr)
C
= Heat capacity of shell side fluid, (kJ/kg °C)
µ
= Shell side fluid viscosity, (kg/m.hr)
K
= Thermal conductivity of hot fluid, (kJ/m hr°C)
Rd1, Rd2
= Dirt factor, (hr ft2°F/Btu)
W
= Weight flow of tube side fluid, (kg/hr)
c
= Heat capacity of tube side fluid, (kJ/kg °C)
µ
= tube side fluid viscosity, (kg/m.hr)
k
= Thermal conductivity of cold fluid, (kJ/m hr°C)
LMTD
= Log mean temperature difference, (°C)
R
= Temperature group (dimensionless)
S = s1
= Temperature group (dimensionless)
T1
= Shell side inlet temperature, (°C)
T2
= Shell side outlet temperature, (°C)
t1
= tube side inlet temperature, (°C)
t2
= tube side outlet temperature, (°C)
¨7
= Temperature differences of table, (°C)
IDs = ID
= Internal diameter of shell, (m)
Nt
= Number of tubes
D
= Inside diameter of tubes, (m)
Lt
= Length of tubes, (m)
PT
= Pitch, (m)
Qs
= Shell side heat flow, (kJ/hr)
Qt
= Tube side heat flow, (Btu/hr)
Ft
= Temperature difference factor (dimensionless)
Ta
= Average temperature of hot fluid, (°C)
Tb
= Average temperature of cold fluid, (°C)
¨W
= True temperature difference, (°C)
9
as
= Area of Shell, (m2)
C'
= Clearance,(m)
B
= Baffle spacing, (m)
De
= Equivalent diameter of heat transfer for shell side, (m)
Gs
= Mass velocity, (kg/hr m2)
Res
= Reynolds number for heat transfer (dimensionless)
jH
= Factor for heat transfer (dimensionless)
Øs
= Viscosity ratio (µ/µ w) (dimensionless)
Øt
=Viscosity ratio (µ/µ w) (dimensionless)
ho
= Heat transfer co-efficient for outside fluid, (kJ/m2 hr°C)
at¶
=Area of a tube, (m)
n
= Number of passes
Gt
= Mass velocity, (kg/hr m2)
at
= Area of tube side, (m2)
V
= Velocity, (m/s)
Ro
= Density of cold fluid, (kg/m3)
Ret
= Reynolds number of tube side for heat transfer (dimensionless)
hi
= Heat transfer co-efficient for outside fluid, (kJ/m2 hr°C)
ID
= Inside diameter of tube, (m)
OD
= Outside diameter of tube, (m)
hi o
= Value of hi when referred to tube side diameter, (kJ/m2 hr°C)
Uc
= Clean overall heat transfer co-efficient, (kJ/m2 hr°C)
Ud
= Designed overall heat transfer co-efficient, (kJ/m2 hr°C)
A
= Heat transfer surface, (m2 )
D¶¶
= External surface per linear foot, (m2 )
f1 , f2
= friction factor (dimensionless)
De1
= Equivalent diameter, (m)
S1
= specific gravity (dimensionless)
¨3s
= Allowable pressure drop for shell side, (psi)
¨3t
= Allowable pressure drop for tube side, (psi)
10
CHAPTER-1: INTRODUCTION
1.1 INTRODUCTION
Chemical Name:
Acrylonitrile
Molecular Formula:
CH2CHCN
Structural Formula:
Synonyms:
ACN
Vinyl cyanide
Acrylic nitrile
2 ± propenenitrile
Propenoic acid nitrile
Propylene nitrile
Acrylic acid nitrile
Cyanoethylene
International Classification:
UN No.
1093
CAS Reg No.
107-13-1
EINECS No.
203-466-5
EC No.
608-003-00-4
STCC
4906420
11
HI (Kemler Code)
33
HS Code
2926 10 00
Description
Flammable Liquid, Toxic substance.
WGK
3 (highly polluting substance)
Packing group
1
Emergence action code
3WE
Poison Class
1* (carcinogenic, mutagenic)
Storage Class (VCI)
3 A (Flammable liquid materials)
1.2 HISTORY
In 1983, the French Chemist, CH. MOUREAU, first prepared Acrylonitrile by
dehydrating either acrylamide or ethylene Cyanohydrin with phosphorous
pentoxides. However, no significant technical or commercial applications were
discovered for acrylonitrile until the late 1930s.
Interest in acrylonitrile first developed when I.G. Farben industries introduced a
synthetic rubber, Buna N, based on a copolymer of butadiene and acrylonitrile into
Germany. This synthetic rubber was highly resistant to swelling in gasoline, oils and
other non polar solvents. At about the some time research began in United States on
similar copolymers termed GR-A, NBR or nitrile rubber. During Second World War,
acrylonitrile containing polymers was developed in the US and West Germany due to
its resistance to oils and lack of access to natural rubber. Projects concerning
acrylonitrile containing polymers received special support during Second World War
because of obvious strategic importance, thus establishing acrylonitrile as a monomer
with commercial significance.
Since that time the dramatic increase in demand for acrylonitrile has been attributed
not to nitrile rubber but largely to acrylic fibers, first introduced commercially in
1950 by Du Pont under the trademark Orlon based on ethylene oxide and Hydrogen
cyanide i.e. from ethylene Cyanohydrin,. Spurred efforts to develop improved
process technology for acrylonitrile manufacture to meet the growing market.
Therefore, it found numerous other applications as monomer, co monomer, and
intermediate for fibers, resins, thermoplastic and elastomers. Other significant uses
12
are as an intermediate for organic synthesis, most notably for producing adiponitrile
and acrylamide. This wide range of applications and successful improvements in
production techniques were the essential reasons for the dramatic expansion in
acrylonitrile production.
Acrylonitrile is among the top 50 Chemical produced in the United States as a result
of the tremendous growth in its use as a starting for a wide range of chemical and
polymer products.
Today nearly all acrylonitrile is produced by Ammoxidation of propene. Four major
company groups, Sohio, Nitto, Eni Chem. /UOP & BP Chemicals/Ugine have
developed Ammoxidation processes of commercial importance. Although the first
report of the preparation of acrylonitrile from propene occurred in a patent by the
Allied Chemical and Dye Corporation in 1947, it was a decade later when Standard
Oil of Ohio (Sohio) developed the first commercially viable more effective catalysts
having economically interesting selectivities for this process and it is known as Sohio
Process. Today, all of the United States capacity and approximately 90% of world
capacity for acrylonitrile is based on the Sohio Process. Sohio, now BP chemicals, is
WKHZRUOG¶VODUJHVWOLFHQVRUZLWKLQWKHODWHVRIWRWDl installed capacity.
Other development Related to acrylonitrile are as follows:
The attempt to react olefins with ammonia is by no means new. In 1934 reference
was made by Elllis to the reaction of ethylene and ammonia at 450 oC in the presence
of zinc sulphate on silica gel to give Acetonitrile.
CH2 = CH2 + NH3
CH3CN + 2H2
Sinclair Refining Company carried out a programmed of work on the reaction of
olefins and ammonia after the Second World War. Such reactions were carried out at
high pressure and about 350o C.in the presence of hydrogenation catalysts such as
cobalt. Products from ethylene, propylene, and the n-butenes included the straight
chain amines and nitriles; from propylene, acrylonitrile was obtained but in low
yield.
CH3CH:CH2 + NH3
CH2 = CHCN + 3H2
13
Socony Vacuum Oil Company (now Mobil Oil Co.) also examined this field using
higher temperatures, lower pressures and a less active hydrogenation catalyst.
Acetonitrile was the main product from most olefins. Interest in the specific synthesis
of acetonitrile has waned with the availability of by-product acetonitrile from the
newer acrylonitrile syntheses. Acetonitrile is assuming an increasing significance as a
solvent for extractive distillation.
Approximately stoichiometric quantities of propylene, ammonia and oxygen (as air)
are introduced into a fluidized catalytic reactor at 1-3 atm and 400-500o C. with a
contact time of a few seconds, as a once-through operation. The reactor effluent is
scrubbed with water in a recovery tower to remove the soluble organic products as an
aqueous solution. The solution is taken to a product separator providing a wet
acrylonitrile overhead product which is dried and purified by azeotropic and
conventional distillation. The bottom product from the separator is wet acetonitrile
which is concentrated, dried and purified by distillation. The catalyst is understood to
be bismuth phosphomolybate. Yields, per pound of propylene feed, have been quoted
as follows: acrylonitrile 0.13lb.27 it is understood that this process now uses a
different catalyst not including bismuth, and possibly based on spent uranium.
The SNAM process for propylene ammoxidation indicates a reactor temperature of
520 OC., molar rations 1 propylene 1.1 ammonia, 8 air and 20 steam. With a catalyst
containing 1.1 per cent vanadium. Extractive distillation (using water and
acetophenone) is used to assist in the separation acrylonitrile from acrylonitrile.
4CH3CH = CH2 + 6NO
4CH2 = CHCN + N2 + 6H2O
The nitric oxide may be regarded as a product of ammonia oxidation. The du Pont
process is carried out at about 700oC in the presence of a supported silver catalyst.
Other reaction of olefins with nitrogen compounds have been overshadowed by the
massive developments in the manufacture of acrylonitrile, but are not without
interest.
14
CHAPTER-2: MARKET SURVEY
2.1 USES OF ACRYLONITRILE
For Doing Market Survey we need to find uses of acrylonitrile. Acrylonitrile is a key
monomer for various polymeric consumer products. A such, it is not used directly in
any and use; however it is building monomer for below given polymeric material.
2.1.1 Fibers:
Acrylonitrile most important application is for the production of polymer for textile
fibers. Acrylic textile fibers are by far the largest end use products for ACN. Acrylic
fibers always contain a Comonomer such as methyl acrylates. Fiber containing 85%
wt of more ACN are usually referred to as acrylics whereas fibers containing 35 to 80
% ACN are termed modacrylics.
These fibers are used primarily for the manufacture of apparel, including sweaters,
fleece wear and sportswear as well as for home furnishings, including carpets,
upholstery and draperies. Demand is largely subject to turns in the fashion industry.
Acrylic fibers consume about 65% of the ACN produced worldwide.
The familiar trade names of acrylic fibers are Orlon, acrilan, Courtelle.
2.1.2 Resins:
The production of acrylonitrile butadiene styrene (ABS) and styrene-acrylonitrile
(SAN) resins consumes the second largest quantity ACN and styrene onto polybutadiene or a styrene butadiene copolymer.
ABS is the most widely used engineering (i.e. metal replacing) plastic. It is a two
phase polymer system, with the electrometric butadiene ± acrylonitrile copolymer
dispersed in a rigid styrene ± acrylonitrile matrix. ABS resins contain about 25%
ACN and are characterized by their chemical resistance, mechanical strength and are
RI PDQXIDFWXUH &RQVXPSWLRQ RI $%6 UHVLQV LQFUHDVHG VLJQLILFDQWO\ LQ ¶V ZLWK
its growing application as a specialty performance polymer in construction,
automotive, machine and appliance applications. Opportunities still exist for ABS
resins to replace more traditional material for packaging, building, and automotive
components.
15
SAN resins typically contain 25-30% ACN. Because of their high clarity, they can be
used primarily as a substitute for glass in drinking cups and tumblers, automobile
instrument panels and instrument lenses. Together, ABS and SAN resins account for
about 20% of domestic acrylonitrile consumption.
2.1.3 Intermediated for polymers:
Because of its reactivity, acrylonitrile can be used as a chemical intermediate.
Examples are acrylic acid and acrylamide by hydrolysis, adiponitrile, a nylon
intermediate, by electrolytic coupling and amines by cyanoethylation.
The largest increase among the end-uses for ACN over the past 10 years has come
from chemical intermediates adiponitrile and acrylamide. This has grown to become
the third largest outlet of ACN.
Adiponitrile is used by Monsanto as a precursor for hexamethylenediamine (HMDA,
C6H16N2) and is made by a proprietary ACN electrohydrodimerization process.
HMDA is used exclusively for the manufacture of nulon-6, 6. The growth of this
ACN in recent years stems largely form replacement of adipic acid (C6H10O4) with
ACN in HMDA production rather than from a significant increase in nylon6, 6
demand. A non electrochemical catalytic route has also been developed for ACN
dimerization to adiponitrile. This technology, if it becomes commercial, can provide
additional replacement opportunity for ACN in nylon manufacture.
Acrylamide is produced commercially by heterogeneous copper catalyzed hydration
of ACN. It is used primarily in the form of a polymer, polyacrylamide, in the paper
and pulp industry and in waste water treatment as flocculants to separate solid
material from waste water streams. Other applications include mineral processing,
coal processing and enhanced oil recovery in which polyacrylamide solutions were
found effective for displacing oil from rock. Other growth markets for acrylamide are
in binders, adhesive and absorbents.
2.1.4 Rubber:
Nitrile rubber, the original driving force behind ACN production, have taken a less
significant place as end-use products Nitrile rubber consists of butadiene ACN
cop0olymers with an ACN content of 15-45%. Butadiene ± acrylonitrile rubber was
16
developed in Germany prior to World War II and is still used today. . They find
extensive industrial application because of its excellent resistance to oil and
chemicals, its good flexibility at low temperatures, high abrasions and heat resistance
(up to 1200C) and good mechanical properties.
In addition to the traditional applications of nitrile rubber for hoses, gaskets, seals
and oil well equipment, new applications have merged with the development of
nitrile rubber blends with PVC. These blends combine the chemical resistance and
low temperature flexibility characteristics of nitrile rubber with the stability and
ozone resistance of PVC. This has greatly expanded the use of nitrile rubber in
outdoor applications for hoses, belts and cable jackets, where ozone resistance is
necessary.
2.1.5 Specialty application:
Some ACN copolymers have found specialty applications where good gas barrier
properties are required along with strength and high impact resistance. Examples of
WKHVH DUH %3 FKHPLFDOV¶ %DUH[ $&1 PHWK\O Acrylate butadiene copolymer.
These barrier resins compact directly in the alcoholic and other beverage bottle
market with traditional glass and metal containers as well as with polyethylene
terephthalate [PET] and poly vinyl chloride [PVC] in the beverage bottle market.
Other applications include food, agro-chemicals and medical packaging. Total ACN
consumption for barrier resins application is small, consuming less than about 1% of
the total ACN production.
The acrylonitrile content of containers fabricated from acrylonitrile copolymers and
the possible migration of acrylonitrile into foods and beverages have been reviewed.
The U.S. Federal Drug Administration declared acrylonitrile to be an indirect food
additive and banned its use in beverage containers and other food-packaging
applications in the USA in September, 1977. The Environmental Protection
Agency(EPA) and the German MAK commission has classified acrylonitrile to be a
human carcinogen The Canada Food and Drugs Act and Regulations (1982) prohibit
the sale of any food in packaging containing acrylonitrile, such that the compound
may pass into the food.
17
A growing specialty application for ACN is in the manufacture of carbon fibers.
They are produced by pyrolysis of or oriented PAN fibers and are used to reinforce
composites for high performance application in the air craft, defense, and aerospace
industries. These applications include rocket engine nozzles, rocket nose cones, and
structural components for aircraft and orbital vehicles where light weight and high
strength are needed.
Other small specialty application of ACN are in the production of fatty amines, ion
exchange resins, and fatty amines use in cosmetics, adhesive, corrosion inhibitors
and water treatment resins. Examples of these amines include 2-acrylamido-2methylpropanesulfonic acid (C7H13NSO4), 3-methoxypropionitrile (C4H7NO) and 3methoxypropylamine (C4H11NO).
Other monomers, for example vinyl chloride, vinylidene chloride, vinyl acetate and
acrylates, will copolymerize with acrylonitrile to form resins used in paints, surface
coating and packaging. Acrylonitrile is used in manufacturing of Pesticides. In a
mixture with carbon tetrachloride, acrylonitrile has also been used as a fumigant for
tobacco and for flour milling and bakery equipment.
Table 2.1 shows the levels of residual acrylonitrile in several polymers, some
acrylonitrile derivatives and products fumigated with acrylonitrile (US Consumer
Product Safety Commission).
Table 2.1: Levels of residual acrylonitrile found in various products
Product
Acrylonitrile content
Acrylic and modacrylics fibres
1 mg/kg
Acrylonitrile-butadiene-styrene resins
30-50 mg/kg
Styrene-acrylonitrile resins
15 mg/kg
Nitrile rubber and latex material
0-750 mg/kg
Acrylamide
25-50 mg/kg
Polyether polymer polyols
100-300 mg/kg
18
Table 2.2: Indian Perspective
The trend in consumption of various end products as the percentage of total ACN
produced and import in India as shown below.
USE
CONSUMPTION (% of ACN produced)
Acrylic fibers
65
ABA/SAN resins
15
Adiponitrile/ acrylamide
12
Nitrile rubber
4
Other
4
Table 2.3: shows the use patterns of acrylonitrile and its products in the USA
and Western Europe
Product
% of acrylonitrile
% of product
production
Acrylic
and
USA
W. Europe
48
68
82 - clothing and home furnishings, 18 -
modacrylic fibers
Acrylonitrile-
export
21
15
88 - pipe fittings, automotive vehicle
Butadiene-styrene
components, 12 - automobile
and Acrylonitrile-
instrument panels, household items etc.
styrene resins
Adiponitrile
12
--
mainly hexamethylenediamine
Other products
19
17
21 - nitrile elastomers, 21 ±
acrylamide, 16 - barrier resins, 42 polyether polymer
19
2.2 USES OF ACRYLONITRILE
Being a volatile highly polar solvent, acrylonitrile finds its greatest use as an
extracting fluid for fatty acids and animal and vegetable oils. Acrylonitrile has been
widely used as an extractive distillation solvent in the petrochemical industry for
separating olefin-diolefin mixtures and for C4-hydrocarbons. When Acrylonitrile is
used in this way, recycling is effected by water dilution of the extract and condensate
with subsequent phase separation, after which the Acrylonitrile is Azeotrope from the
aqueous phase. Acrylonitrile has been used as a solvent for polymer spinning and
casting because of the combination of high solubility and desirable intermediate
volatility. It is also used as a solvent for isolating components from crude products
such as crude wool resin. Acrylonitrile is used as a common laboratory solvent for
recrystallizing various chemicals and is widely used as a solvent in HPLC analysis.
Acrylonitrile is also used in biotechnology research as a solvent in the synthesis of
DNA and peptide sequencing (Borman,1990). Acrylonitrile can be used to remove
tars, phenols and colouring matter from petroleum hydrocarbons that are not soluble
in Acrylonitrile. Acrylonitrile is also used as a starting material for the synthesis of
many chemicals such as acetophenone, alpha-naphthyl acetic acid, thiamine and
acetomidine (Hawley, 1971).
Main use patterns of Acrylonitrile
¾ Extraction of fatty acids and animal and vegetable oils
¾ Extraction of unsaturated petroleum hydrocarbons
¾ Solvent for polymer spinning and casting
¾ Moulding of plastics
¾ Removal of tars, phenols and coloring matter from petroleum hydrocarbons
¾ Purification of wool resin
¾ Recrystallization of steroids
¾ Starting material for synthesis of chemicals
¾ Solvent in DNA synthesis and peptide sequencing
¾ Medium for promoting reactions
¾ Solvent in non-aqueous titrations
20
¾ Non-aqueous solvent for inorganic salts
¾ High-pressure liquid chromatographic analysis
¾ Catalyst and component of transition-metal complex catalysts
¾ Extraction and refining of copper, Stabilizer for chlorinated solvents
¾ Perfume manufacture, Pharmaceutical solvents
2.3 CURRENT INSTALLED CAPACITY
Acrylonitrile is a large-volume commodity chemical. Worldwide capacity is about
5.7 million metric tons. Capacity compared with consumption is in surplus in North
America and in deficit in Asia. World production in 2000 was estimated at about 4.6
million metric tons.
In India:
In India Acrylonitrile only produced by Indian Petrochemicals Corporation Limited
(IPCL), Baroda complex by Sohio Process having capacity of 30000 tons per annum
which consumed in Acrylates plant of IPCL itself.
In USA:
By 2001, the demand for acrylonitrile is expected to be 3.8 billion pounds. Following
is a list of the dominant producers of acrylonitrile in the United States.
Table 2.4: Producers of acrylonitrile and their capacities
Producer
Location
1997 Capacity*
1994 Capacity*
BP Chemicals,
Green Lake, TX
1,000
700
BP Chemicals,
Lima, OH
500
500
Cytec Industries,
Avondale, LA
475
320
DuPont,
Beaumont, TX
385
380
Solutia Monsanto),
Alvin, Tex.
500
480
City, 700
700
Sterling Chemicals, Texas
TX
* millions of pounds of acrylonitrile produced per year
(Source: Mannsville and other websites)
Sterling Chemicals' 750-million-pound-per-year acrylonitrile plant at Texas City,
Tex. has been idled since February 2001 because of poor profitability.
21
Monsanto spun-off its industrial chemicals operations as Solutia, in 1997. In late
2000, Solutia brought a new 550 million-pound per year plant on stream in Alvin,
raising the site's nameplate capacity to more than 1 billion pounds. The plant's output
is shared with Asahi and Bayer, both of which have equity in the facility.
Amoco merged with British Petroleum to become BP Amoco in 1998. In July 2000,
BP Amoco Chemicals reverted to the name BP Chemicals after BP Amoco decided
to adopt a new unified global brand, centered on the name BP. The new name
embraces British Petroleum, Amoco, Arco and Burmah Castrol, all acquired by BP.
Table 2.5: Estimated U.S. production and capacity of Acrylonitrile (Millions of
Pounds)
Year
1991
1992
1993
1994
1996
Capacity
3,080
3,080
3,080
3,080
3,200
Production
2,642
2,823
2,504
2,926
N/A
Exports
1,300
1,365
1,020
1,450
N/A
Demand
1,342
1,458
1,484
1,476
1,550
(Source: USITC and other websites)
Demand for acrylonitrile is expected to grow at an average annual rate of 2 to 3
percent after the 1990/1991 market slowdown. It is estimated that production was
roughly 2,926 million pounds in. Exports were expected to increase from 1,020
million pounds in 1993 to 1,450 million pounds in 1994. U.S. capacity greatly
exceeds domestic demand. About 40 percent of U.S. production of acrylonitrile was
exported in 1993. Increasing worldwide capacity for acrylonitrile production may
limit U.S. exports in the future.
2.4 IMPORT / EXPORT POSITION
The demand for Acrylonitrile in the world is growing. The Asian demand currently
represents about half of the worldwide Acrylonitrile demand of some 5,000,000 tons
per year, and its growth is expected to continue. The export market for acrylonitrile
continues to be driven by strong demand from Asia.
The Acrylonitrile operations, with their strategic position in the rapidly growing
Asian market, have developed in concert with a strong and growing Acrylonitrile
22
demand, and in an overall program of timely restructuring of operations to effectively
anticipate and meet the continuing rise in Acrylonitrile demand.
The world acrylonitrile market grew from 1.9 million tones in 1994 to 2.2 million
tones in 2001. Leading exporters are the USA, Denmark and France, while top
importers include Germany, Taiwan, the UK, Belgium and Japan. The global
acrylonitrile market is worth over US$620 million a year.
In India:
There are large demands of Acrylonitrile in India. But only IPCL produced and
consumed itself. So, no export of Acrylonitrile and large amount of Acrylonitrile
import in India.
Importer of India:
Following are some industries in India import acrylonitrile.(in 1983)
Table 2.6: industries in India import acrylonitrile.(in 1983)
COUNTRY
Austria
QUANTITY
CIF VALUE
Tons
Rs.
NAME OF IMPORTER
14.800
2,95,000
Asian Paints India Ltd.
14.800
2,98,100
Gharda Chemical Limited.
China
24.000
3,83,6000
Kantilal Manilal & Company
F.R.G.
25.000
5,02,800
BASF India Limited.
12.800
2,51,400
Colour Chem Limited.
Export Copr.
29.600
7,13,700
Indian Dyestuff Indust.
Netherland
4.564
89,900
Aditya Organics Pvt. Ltd.
10.106
2,12,200
Colour chem. Limited.
25.428
4,96,800
Standard Organics Limited.
25.428
4,90,800
STC of India Ltd.
S. Korea
10.150
1,92,600
Puneet Resins Pvt. Ltd.
Taiwan
12.800
2,31,600
Ganelex Trading & Fin. Ltd.
12.800
2,31,600
Shankarlal & Sons.
23
COUNTRY-WISE TOTAL IMPORTS
Austria
29.600
5,93,100
China
24.000
3,83,600
F.R.G.
97.080
21,29,800
Netherland
65.526
8,48,600
Taiwan
25.600
4,63,200
Total
241.806
44,18,300
Now number of industries of India manufacturing acrylic fibers, Acrylic resins like
ABS, SAN etc. and other intermediates import Acrylonitrile for their plant raw
material
In USA:
The acrylonitrile business is heavily dependent on exports. From 1990 until the end
of 1997, exports were more than 1 billion pounds per year, serving a rapidly growing
acrylic fiber and styrenics industry in the Far East. In 1997, about 1.5 billion pounds
of acrylonitrile were exported, roughly equivalent to domestic consumption. When
that fell off at the end of 1997 and through 1998 and much of 1999, operating rates
went down in the US by about 15 percent, and suddenly there was over-capacity
based solely on a declining export market. For the past couple of years, exports have
again grown to more than 1.5 billion pounds. But, because most of the anticipated
new acrylonitrile capacity will be built in Asia, long term export market is at risk.
Demand and Growth:
Demand:
2000: 1,690 million pounds; 2001: 1,680 million pounds; 2005: 1,800 million
pounds, projected. Demand equals production plus imports (2000: 17 million pounds;
2001: 5 million pounds) less exports (2000: 1,505 million pounds; 2001: 1,574
million pounds).
24
Table-2.7 Historical data:
Year
Demand
pounds)
1995
1,717
1996
1,712
1997
1,648
1998
1,649
1999
1,690
2000
1,680
25
(million
of
CHAPTER-3: PHYSICAL & CHEMICAL PROPERTIES
3.1 PHYSICAL PROPERTIES
Acrylonitrile (C3H3N, mol wt. = 53.064) is an unsaturated molecule having a carbon
± carbon double bond conjugated with a nitrile group. It is a polar molecule because
of the presence of the nitrogen heteroatom. There is a partial shift in the bonding
electrons towards the more electronegative nitrogen atom, as represented by the
following heterovalent resonance structures.
CH2 = CH-C = N:
CH2 = CH-C = N:
CH2-CH = C = N
Table-3.1 Physical Properties of Acrylonitrile:
Property
Value
Appearance
Clear, colorless liquid
Odor
With faintly pungent odor
o
Boiling point, C
77.3oC
Freezing point oC
83.5oC
Density, 20oCg/cm3
0.806
o
Volatility, 78 C,%
> 99
o
Vapor pressure, 20 C,K Pa
11.5
Vapor density (air = 1)
1.8
o
Solubility in water, 20 C, wt%
7.3
pH (5% aqueous solution)
6.0 ± 7.5
o
Critical Temperatures, C
246oC
Critical Pressure, Mpa
3.54
3
Critical Volume, g/cm
3.798
Refractive index, n 25/D
1.3888
Dielectric constant, 33.5 MHz
38
Ionization potential, eV
10.75
26
Molar refractivity (D line)
15.67
o
Surface tension, 25 C, mN/m (=dyn/cm)
26.6
Dipole moment, Cmc
1.171 x 10-29 ( For Liquid)
1.294 x 10-29 ( For Vapor)
Viscosity, 25oC,mPas (=cP)
0.34
Table-3.2 Thermodynamic Data:
Property
Value
o
Auto ignition temperature. C
481
o
Flammability limits in air, 25 C, vol%
Lower = 3.0
Upper = 17.0
o
Free energy of formation, Gg, 25 C KJ/mol
Enthalpy of formation, 25oC KCal/mol
195
45.37 ( For gas)
36.2( For liquid )
o
Heat of combustion, liquid, 25 C, KJ/mol
1761.5
o
Heat of vaporization, 25 C, KJ/mol
32.65
Molar heat capacity, KJ (kg K)
2.09 ( Liquid)
1.204 (Gas at 50oC, 101.3 KPa )
Molar heat of fusion, KJ/mol
6.61
o
Entropy, S, gas at 25 C, 101.3kPab, KJ/ (mol K)
274
Table-3.3 Solubilities of Acrylonitrile in Water:
Acrylonitrile in Water in
Temperature, oC
Water, wt%
Acrylonitrile, wt%
-50
-
0.4
-30
-
1.0
0
7.1
2.1
10
7.2
2.6
20
7.3
3.1
27
30
7.5
3.9
40
7.9
4.8
50
8.4
6.3
60
9.1
7.7
70
9.9
9.2
80
11.1
10.9
Acrylonitrile is miscible in a wide range of organic solvents, including acetone,
benzene, carbon tetrachloride, diethyl ether, ethyl acetate, ethylene, cyanohydrins,
petroleum ether, toluene, some kerosenes, and methanon. Composition of some
common azeotropes of Acrylonitriel is given in Table below.
Table-3.4 Azeotrope of acrylonitrile:
Boiling point, oC
Azeotrope
Acrylonitrile,
Concentration wt%
Tetrechlorosilane
51.2
89
Water
71.0
88
Isopropyl alcohol
71.6
56
Benzene
73.3
47
Methanol
61.4
39
Carbon tetrachloride
66.2
21
Chloro trimethyl silane
57.0
7
Table-3.5. Acrylonitrile vapor Pressure over Aqueous solutions at 250C
Acrylonitrile, wt%
Vapor pressure, kPa
1
1.3
2
2.9
3
5.3
4
6.9
5
8.1
28
6
10.0
7
10.9
3.2 CHEMICAL PROPERTIES:
Acrylonitrile is a very reactive compound.
The important reactions of Acrylonitrile are as below.
Reactions of the double bond
3.2.1Polymerization:
Acrylonitrile can undergo spontaneous, exothermic polymerization in the absence of
hydroquinone inhibitor to give polyacrylonitrile (PAN).
The homo and copolymerization of Acrylonitrile take place rapidly in the presence of
radiation, anionic initiators or fire radical sources, such as peroxides or diazo
compounds.
H
hv
|
nCH2 = CH-CH
[CH2-C]n
initiator
|
CN
The reaction involves charge transfer complexes between various monomers and can
be produced in the vapor, liquid or solid, in solution and in dual-phase system. Only
the latter two methods have industrial impact.
3.2.2 Hydrogenation:
In the presence metal catalyst hydrogenation of Acrylonitrile gives propionitrile &
propylamine.
(C3H4N)
(C3H9N)
Ni
C3H5N + H2
2H2
C3H5N
410oC
29
C3H9N
3.2.3 Hydrodimerization:
Two molecules of Acrylonitrile react with hydrogen molecule to give adiponitriel
over a metal catalyst.
Metal
2CH2 = CHCN + H2
C6H8N2
Catalyst
3.2.4 Halogenations;
In the presence of light Acrylonitrile react with halogens to produce
dihalopropinitriles.
CH2±CH- CN
CH2 = CHCN + Cl2
|
|
Cl
Cl
|
i) Production of acrylamide:
For years the first step in the commercial production of acrylamide was the partial
hydrolysis with sulfuric acid to acrylamide sulphate. Then it is converted to
acrylamide (C3H5NO) by neutralization with a base.
CH2 = CHCN + H2SO4 (+H2O)
CH3 CH2CNO.H2SO4
+ NaOH
C3H5NO + Na2SO4 + H2O
However, now acrylonitrile is converted directly to acrylamide using various copper
based catalysts.
CH2 = CH-CN + H2O ±Cu
C3H5NO
ii) Production of methylacrylate:
Industrially important acrylic esters can be formed by reaction of acrylamide sulphate
with organic alcohols. Methyl acrylate C4H6O2 has been produced commercially by
the alcoholysis of acrylamide sulphate with methanol.
30
CHAPTER-4: LITERATURE SURVEY
4.1 LITERATURE SURVEY
The Literature Survey is the most import part of the Project Work. The Literature
survey has been done to obtain information concerning Acrylonitrile and its
production from the number of sources. The literature survey yielded a lot of
information on Acrylonitrile
In literature, various available and absolute processes are known and I choose Sohio
as the best process among them. I find the raw materials used, also power and other
utilities required for processes, also by product obtained, also about safety and
environmental consideration. So, one can economically deiced the proper
manufacturing processes which can give maximum product output with lower
operating cost.
As per periodicals, lots of information is available. The periodicals give us the
abstract about articles and its reference. The books related to chemical engineering
and technology, handbooks, encyclopedias, Symposiums, Journals and Plant training
manuals are very useful available sources of most of project work.
The CD-520V VSHFLDOO\ &'V RI ³3HUU\¶V +DQGERRN´ DQG ³%DVLF 3ULQFLSDO DQG
&DOFXODWLRQLQFKHPLFDOHQJLQHHULQJE\+LPPHOEODX´IURP3HUU\µV&'ORWVRIILJXUHV
and required theory as well as date available. The Himmelbau CD Rom is very user
friendly in calculation part of energy valance and designing.
The other source of Literature Survey is the internet websites. From websites it is
very helpful in find out available information related to Acrylonitrile world wide. It
is particularly very helps in find out latest information about price, capacity data
related to Acrylonitrile and also various manufacture of Acrylonitrile.
31
4.2 ACRYLONITRILE AND SOHIO PROCESS:
4.2.1 Early History:
Acrylonitrile, first synthesized in 1893 by Charles Moureu,
did not become important until the 1930s, when industry
began using it in new applications such as acrylic fibers for
textiles and synthetic rubber.
Although by the late 1940s the utility of acrylonitrile was
unquestioned, existing manufacturing methods were expensive, multistep
processes. They seemed reserved for the world's largest and wealthiest principal
manufacturers: American Cyanamid, Union Carbide, DuPont, and Monsanto. At
such high production costs, acrylonitrile could well have remained little more than
an interesting, low-volume specialty chemical with limited applications.
In the late 1950s, however, Sohio's research into selective catalytic oxidation led to
a breakthrough in acrylonitrile manufacture. The people who invented, developed,
and commercialized the process showed as much skill in marketing as in chemistry.
The result was such a dramatic lowering of process costs that all other methods of
producing acrylonitrile, predominantly through acetylene, soon became obsolete.
At this site in 1957, Sohio researchers developed the
"Sohio Acrylonitrile Process," an innovative single-step
method of production that made acrylonitrile available as a
key raw material for chemical manufacturing worldwide.
Sohio as groundbreaking experimentation and bold
engineering brought plentiful, inexpensive, high-purity
acrylonitrile to the market, a principal factor in the evolution and dramatic growth of
the acrylic plastics and fibers industries. Today, nearly all acrylonitrile is produced
by the Sohio process, and catalysts developed at the Warrensville Laboratory are
used in acrylonitrile plants around the world. Sohio became part of The British
Petroleum Company p.l.c. in 1987.
32
4.2.2 Acrylonitrile
Chances are that acrylonitrile touches everyone in some
way every day. Acrylonitrile is the key ingredient in the
acrylic fiber used to make clothing and carpeting; in
acrylonitrile-butadiene-styrene (ABS), a durable material
used in automobile components, telephone and computer
casings, and sports equipment; and in nitrile rubber, which
is used in the manufacture of hoses for pumping fuel.
Acrylonitrile is used to produce plastics that are impermeable to gases and are ideal
for shatterproof bottles that hold chemicals and cosmetics clear "blister packs" that
keep meats fresh and medical supplies sterile, and packaging for many other
products. It is also a component in plastic resins, paints, adhesives, and coatings. The
acrylonitrile in those products was made by a process discovered and developed in
the 1950s by scientists and engineers at The Standard Oil Company, or Sohio, which
became part of British Petroleum (BP) in 1987. The process is a single-step direct
method for manufacturing acrylonitrile from propylene, ammonia, and air over a
fluidized bed catalyst.
The discovery and commercialization of this process were the result of the talent,
imagination, teamwork, and risk-taking by Sohio's employees. Sohio's discovery led
to the production of plentiful and inexpensive acrylonitrile of high purity as a raw
material and to dramatic growth in the thermoplastics, synthetic fiber, and food
packaging industries. Today more than 95% of the world's acrylonitrile is produced
by BP or made under its license.
4.3 SOHIO PROCESS-RESEARCH AND DEVELOPMENT:
Sohio process was extensively tested in operation of a pilot plant unit for several
months at the Sohio Research centre in Cleveland. The product from this unit was
fiber grade and major U.S. consumer specification Substantial quantities were
polymerized, spun into fiber dyed, with complete acceptance.
Some of the special aspects of the Research and development program be of interest.
The initial research work was conducted in small plant of the type shown in Figure 1
33
with steel tubular reactors were employed. Vapor chromatography analytical tool.
The reaction studies were supported by special product recovery and operation
studies. Multiplate glass Oldrshaw distillation columns with an internal design shown
in Figure2 were used to obtain design date. This column resembles a miniature glass
sieve tray complete with down comers. One-and two-inch diameter units of
appropriate plat age were used. Correlation of work done in this equipment with
actual plant operation has been excellent in spite of the tremendous scale-up factors.
The second step in the reactor scale-up was conducted in equipment of the type
FDOOHG³$GYDQFHPHQW´XQLWV7KH\KDGDQLQWHUQDOGLDPHWHURIDERXWWKUHHLQFKHVDQG
employed one to two liters of catalyst charge. Much of the basic plant reactor design
and operating in formation came from units of this size with little or no modification
ensuing from the subsequent larger scale pilot plant operation.
4.3.1 Pilot plant evaluation
The pilot unit operation was not aimed at securing detailed plant design data but
predominantly to give a firm evaluation of catalyst life and to supply market
development samples.
The pilot unit chosen was an 18 in, I.D. reactor with a catalyst charge of several
hundred pounds. The recovery equipment was of the Oldershaw type made
predominantly of glass units in the four and six-inch diameter size range.
It may be of special interest to note that certain phases of the research work, the
process advancement work, the pilot operation, and the detailed plant design were all
conducted simultaneously. This type of simultaneous operation can greatly compress
the time required to get an interesting process to plant stage. It creates a certain
amount of discomfort and occasional back-tracking, but over-all progress can be
speedily made if all groups involved are in close proximity and daily contact.It also
brings t bear at an early stage the tremendous know-how available from the contract
firms and can save substantial amounts of money in eliminating pilot scale work not
needed for actual plant design.
34
4.3.2 Commercial aspects worldwide
The detailed plant design shown it will have a low electrical load, a relatively small
fresh water requirement, will be self-sufficient in steam, and will produce no unusual
water effluent. Detailed economic studies indicate that for essentially all foreseeable
sets of economic conditions and plant sizes, the Sohio process compares favorably
with conventional routes in respect to investment, raw materials, operating costs, and
product quality. It appears that small plants can be fully competitive with the
previous larger facilities which has t he integrated with HCN, C 2H2, or ethylene
oxide production. Plants do not have to be at the raw material site, since both
propylene and anhydrous ammonia are readily transported. Plant construction
materials are conventional and all operations are near atmospheric pressure except
for steam generation.
Sohio has decided to commercialize this process abroad and an active exploitation
program is underway on a world-wide basis. It appears that many for3eign countries
are eager to enter or expand acrylic fiber manufacture. The new raw material picture
supplied by this process enables operation at many sites where production from C 2H2
and HCN would be impossible to uneconomic.
4.4 REACTION KINETICS:
Laboratory has found that the ammoxidation reaction over bismuth molybdate
containing catalysts has first-order dependence with respect t o propylene and a zeroorder dependence on both oxygen and ammonias when they are supplied in at least
stoichiometric amounts.
Kinetic measurements were made up to high digress of conversion in both fixed and
fluidized catalyst beds. Differential reactors, designed with draw-off ports so that a
small portion of the reaction products could be withdrawn for analysis after fixed
reaction times, were employed. The fluidized bed reactor contained sieve trays,
which results in a more nearly plug flow of the gas through the reactor allowing more
accurate control of residence time. Composition of the bismuth-phosphomolybdate
catalysts used in both reactors was 24.1% Bi, 14.8% Mo, 0.4% P, 23.4% Si, and the
35
balance oxygen. A 3/16 inch x 3/16 inch cylindrical pellet was used in the fixed bed,
and a micro spherodal form was used in the fluidized bed.
A PFR is used for producing acrylonitrile from propylene, ammonia and oxygen. The
reaction rates are found to be independent of NH3 or O2 concentrations and can be
represented as
C3H6 + NH3 ------> C2H3CN + 3H2 ..««««««« C3H6 + O2 -------> C2H3CHO + H2O .««««««« C2H3CHO + NH3 -----> C2H3CN + 2H22««««« At 470 deg C, k1 = 0.195 s-1, k2 = 0.005 s-1, and k3 = 0.4 s-1. The feed at the rate of
4200 kg/hr to the reactor contains 6.6% propylene, 86.1% air and 7.3% NH3. Design
the PFR for a desired conversion of 85%.
Activation energies of the ammoxidation reaction were determined from Arrhenius
plots, and the values obtained for propylene were 19 K cal per mole in the fixed bed
and 17 K cal per mole in the fluid bed. This is in agreement with values of 19 to 21 K
cal mole reported by Kolchin and coworkers (1964).
Kinetic measurement under acrylonitrile synthesis conditions follow a first-order
dependence of reaction rate on propylene concentration and essentially zero-order on
propylene concentration and essentially zero-order dependence on both oxygen and
ammonia concentration when these reactants are provide in a t least slight excess. A
common rate limiting step involving abstracting of hydrogen from the methyl group
of propylene appears to be operative in ammoxidation reaction.
4.5 CATALYST DEVELOPMENT FOR SOHIO PROCESS:
The
catalyst
originally
employed
in
the
Sohio
Process
was
bismuth-
phophomolybdate combination. Since that time there has been a continuous search
for alternatives and for superior performance, resulting in patents by more than 30
companies.
Sohio introduce a catalyst 21 basically combination of antimony-uranium in 1967,
then possible to considerably reduce the amount of acetonitrile which was one of the
by products. Further advances were achieved on using modified bismuth molybdate
catalyst containing iron compounds (among others) to increase the selectivity. This
36
modification with iron is based on research work conducted by Knapsack. This
catalyst was introduced by Sohio as catalyst 41 basically combination of ferro
bismuth-phophomolybdate in 1972. In 1978, Sohio introduced catalyst 49 with aimed
at improved efficiency and reduction in by products.
4.6 CATALYST MECHANISM:
The Sohio catalyst, which requires a higher temperature of 4200C, comprises iron,
antimony, molybdenum, vanadium, tellurium, and copper, supported on silica. It
gives an overall acrylonitrile yield of 80% and a hydrogen cyanide yield of 3% with
no acrylonitrile. The ammoxidation reaction is highly exothermic and is carried out
in a fluidized bed to ensure effective heat exchange and temperature control.
The mechanism for the formation of acrylonitrile from ammoxidation of propylene is
shown in figure. The mechanism is illustrated for the original Sohio catalyst, and
oxidized bismuth molybdenum species, which reacts with ammonia to give the
imminium compound (VIII). This bond with an allyl radical resulting from the
abstraction of hydrogen from propylene (II) to give (IX). As indicated in s(X) a
double hydride shift occurs to liberate 1 mol of ammonia and to give the species
(XI). This is oxidized to give(XIII), which forms (XIII) by a hydride shift Compound
(XIII) undergoes the transformation shown in (XIV) to give the desired product
acrylonitrile (XV), and the catalyst species (XVI), which with oxygen regenerates the
initial catalyst species(I)
4.7 SYNTHESIS OF POLY (ACRYLONITRILE):
4.7.1 Polymerization processes include: Bulk Poly(acrylonitrile) is not soluble in its
monomer. The reaction is autocatalytic, and as the viscosity increases, it becomes
increasingly difficult to remove heat. The reaction may run out of control if done by
a batch process.
1. emulsion
2. suspension
3. slurry
4. solution
37
Dimethylformamide is the solvent to use for a solution process. Acrylamide
polymerizes exothermically in the presence of free radical or anionic initiators.
Oxygen is a strong inhibitor, but it forms peroxides, explosion may take place. Once
all the oxygen has reacted, the polymerization begins; the peroxides begin to
thermally degrade.
The solvent must form hydrogen bonds with strength comparable to that of the
polymer chains, but also separate the polymer molecules with a nonpolar segment.
Dimethylformamide
works,
but
form
amide,
methylformamide,
and
Dimethylformamide do not. Glass transition temperature- 105 deg C
4.8 ECONOMICS ± ACRYLONITRILE:
The strongest factors in future Acrylonitrile pricing will be the improvement of
profess technology and the future price of propylene feedstock. For that let us first
look at the approximate sales price breakdown for Acrylonitrile, then at the
propylene market.
From the various information of Capital and operating casts calculations we can
reach several conclusions about Acrylonitrile pricing.
1. Propylene constitutes 35 to 45% of the selling price of Acrylonitrile. Reaction
yield and price of propylene will therefore be very important
2. As usual with commodity [necessary things] petrochemical both scale of plant and
average capacity utilization are important factor in required selling price.
With these economics in mind, we should also observe how sensitive this cost
structure is to changes in the environment or errors in our assum0tions. For example,
As reported by U.S. Tariff Commission if the plant is designed with a 440 million
lb/year capacity (assuming technical feasibility), costs could be 1.0 cents/lb lower
when operating at 90% of capacity. On the other hand, operating at only 75% of
capacity in the above plant would increase unit costs by 0.7 cents/lb. Choosing just
WKH³ULJKW´VL]HRISODQWWRVHUYHDYDLODEOHPDUNHWVZLOOWKXVEHTXLWLPSRUWDQW
Another environmental factor is the forecast increase in costs of both energy and
hydrocarbon feedstock. Price for Gulf Coast natural gas will cause a direct increase
in required Acrylonitrile price. The indirect increase in ammonia prices would add
38
another to Acrylonitrile prices. Propylene is a more complex question, however, and
calls for a detailed analysis because of its nature as a by-product of both refining and
olefins production.
Several recent articles have been published on propylene and the consensus seems to
be that propylene prices will either decline or at least not increase as rapidly as other
basic petrochemicals. While large quantities of propylene are used in making alkylate
fore leaded gasoline, propylene alkylate is inferior to butylenes alkylate in a
nonleaded gasoline pool. After the available isobutane and alkylation capacity are
allocated to butylenes, not enough will be available to expand usage of propylene in
refineries.
At the same time, steam crackers are being built t handle heavier feed stocks
(naphtha, gas oils) instead of the ethane and propane fed in the past. Since these feed
stocks produce 0.4 to 0.65 more kgs of propylene for each kg of ethylene than ethane
feedstock. Olefins producers will have a disproportionate increase in their available
propylene. While propylene markets are expanding, they have generally not been
forecast to grow as rapidly as ethylene markets. However, a relatively lower
propylene price will act to bring an adjustment of the relative growth rates by
encouraging the substitution of propylene derivatives (poly propylene, Acrylonitrile,
propylene oxide) for competing ethylene derivatives (polyethylene, vinyl chloride,
ethylene oxide). This will work to hold down Acrylonitrile prices, especially when
combined with application of 4h e new Sohio catalyst t existing plants and several
large new plants.
In doing he price forecast, a statistical study by Professor Robert Stobaugh and the
author has pointed out 4 factors which underly past declines in petrochemical prices
[4]. The 2 strongest factors in prices declines of 82 petrochemicals over a 17-year
period were: (1) the increasing scale economies of ever-large production facilities;
and (2) the efficiencies resulting from accumulating production experience (e.g., the
recently announced catalyst). These factors will continue to work for lower
Acrylonitrile prices.
39
Slightly less important as factors in the past are trends toward (3) more producers and
(4) more standardized products. Both of this acted t cut profit margins toward a
³FRPPRGLW\´ OHYHO DQG VKRXOG FRQWLQXH WR GR VR LQ WKH IXWXUH :KLOH $FU\ORQLWULOH
has a standardized quality, the present six U.S. producers could be joined by one or
two others in the next decade. The importance of large volume and propylene pricing
suggests that other oil companies may join Sohio in Acrylonitrile production, with
some resultant reduction Acrylonitrile price. This would be quit consistent with the
product life cycle as it applies to petrochemicals. As they mature, many other
petrochemicals have attracted oil companies and exhibited declining real
manufacturing costs. While other petrochemicals will reverse this trend in the next
decade, Acrylonitrile has an excellent position continue the trend of declining real
price.
On balance, then (1) technology improvement, (2) low propylene prices, (3) larger
plants, and (4) competitive threats of new producers should overcome increases in
other production costs to reduce real Acrylonitrile prices or allow for relatively
modest price increase. This price advantage over competing monomers will help to
bring about the continued expansion of Acrylonitrile derivatives through 1983.
40
CHAPTER-05: PROCESS SELECTION
5.1 BASIC MANUFACTURING PROCESSES:
Although a variety of chemical routes to acrylonitrile have been proven, and various
processes developed, present practice concentrates exclusively on the ammoxidation
of propylene. In the great majority of cases the Sohio fluid-bed process is used.
Considering the chemistry first, the more important routes, listed by chronological
development, have been the following:
5.1.1 Ammoxidation of Propylene:There are a number of Ammoxidation of Propylene processes for manufacturing
acrylonitrile among them; the Sohio process has attained the greatest industrial
importance of all the Ammoxidation processes.
Ammoxidation represents the catalytic oxidative reaction of activated methyl groups
with NH3 leading to the formation of a nitrile group and is react with propylene to
obtain acrylonitrile.
H2C = CHCH3 + NH3 + 1.5 O2
H2C = CHCN + 3H2O
[Cat.]
(a) Sohio Process:
Process Principle:
Heterogeneously catalyzed single-step gas-phase oxidation of propylene in presence
of NH3 and air using bismuth phosphomolybate on silica catalysts in fluidized bed
reactor.
Technological Characteristics:
Heat from exothermic main, side and secondary reactions evolved, via fluidized bed
and heat exchanger utilize in steam generation.
H2C = CHCH3 + NH3 + 1.5 O2
H2C = CHCN + 3H2O
[Catalyst = bismuth phosphomolybate]
Process Description:
In the industrial Sohio process, approximately Stochiometrical amounts of Propylene
is reacted with slight excess of NH3 and excess of air in the fluidized bed reactor in
41
42
Figure-5.1 Acrylonitrile by Sohio Process
presence of catalyst at temperature of 400-450 OC and gauge pressure 30-200 KPa
(0.3-2 bar)with residence times of a few second about 20 seconds. The propylene is
converted to acrylonitrile with a yield of 80% obtainable. The principles by products
are acrylonitrile and Hydrogen Cyanide. One Kg of propylene yields 0.8 ± 0.9 kg
acrylonitrile, 0.02 ± 0.11 kg acrylonitrile, and .1 ± 0.15 kg hydrogen Cyanide. The
gases from highly exothermic reaction are cooled by means of internal water coils.
The Reactor effluent is cooled. Unreacted ammonia is removed by water acidified
with sulphuric acid as aqueous ammonia Sulphate, which can be recovered by
crystallization. Scrubbing in on absorber column separates off-gases overhead.
Consisting primarily of nitrogen, is vented.
The reaction products remain in aqueous phase. Acrylonitrile is removed by
extractive distillation and is recovered. The crude acrylonitrile and hydrogen Cyanide
are distilled into the recovery column where it is steam stripped. Hydrogen Cyanide
is removed by distillation as the light impurities which can recover as buy product.
The acrylonitrile is purified to get pure acrylonitrile.
(b) BP (Distillers) ± Ugine route:
The ammoxidation technology initially developing in the 1905s as a result of
collaboration between PCUK (Produits Chimiques Ugine Kuhlmann), BP
(Distillers), and Border Chemicals. In 1965 two plants based on the technology went
into operation. During recent years, Distillers and PCUK have continued developing
and marketing an acrylonitrile process that is the outgrowth of the technology begun
in the 1950s. Plants using the PUCK Technology are now located in Great Britain,
France, Mexico, and Korea. The technology is most notably distinguished from that
of Sohio by the use of fixed bed reactors instead of fluidized bed reactors.
Process Principle:
Two step propene reaction with interim isolation of acrolein.
Process Description:
Using the BP (Distillers) - Ugine process, propene is initially oxidized on a Se/CuO
catalyst to Acrolein which it then converted into acrylonitrile in a second stage
43
employing NH3 and air with a MoO3 fixed-bed catalyst. This two-step conversion
leads to a higher acrylonitrile selectivity of approx. 90% (based on H2C = CHCHO).
(c) UOP - Montedison route:
Montedison became interested in acrylonitrile manufacture in the early 1950s. in
1956 the company commissioned a plant near Venice, Italy that produced
acrylonitriel from acetylene and hydrocyanic acid. By 1967 the company had begun
operating a small semi-industrial fluidized ammoxidation reaction system (i.e., one
operating with propylene, air, and ammonia in a fluidized bed reactor) that had been
developed in their own laboratories. This was followed by construction and operation
of Montedison-type acrylonitrile plants in Priolo, Sicily (1968), and in Puertollano,
Spain (1973).
In 1975 UOP and Montedison entered into an agreement under which UOP acquired
exclusive licensing rights. As a result of the agreement, process improvements have
been made.
(d) Nitto Technology:
For several years the Nitto Chemical Industry Company of Japan has been attempting
to develop improved catalysts for the ammoxidation of propylene to acrylonitrile.
The principal reactions for the ammoxidation step are same as Sohio process Basic
Difference
is
the
different
catalyst.
In
1974
the
company
announced
FRPPHUFLDOL]DWLRQ RI &DWDO\VW 16$ DV ³&DWDO\VW ´ containing Fe, Sb, and
other components. Probably, acrolein, acetone, acetaldehyde, proponaldehyde, and
high boiling cyanohydrins are formed in small amounts.
(e) Based on Propane or Propylene geed Stock:
Lummus has also developed an acrylonitrile manufacturing process based on propane
or propylene; NH3 and O2 in a salt melt of e.g. KCl ± CuCl ± CuCl2. Commercial
processes are not in operation so far.
5.1.2 From Ethylene Cyanohydrin Route:
The first industrial production of acrylonitrile based on ethylene oxide, was
developed by IG Farbenin and Leverkusen in Germany in early 1940s and operated
by Union Carbide in the United States from 1952 onwards and by American
44
45
Figure-5.2 Acrylonitrile by Ethylene Cyanohydrin route
Cyanamid from 1970. During the interim period around mid-1960s both plants have
been shut down.
Process Principle of Ethylene Oxide Route:
Two-step homogeneously catalyzed reaction to intermediate Cyanohydrin with
subsequent homogeneously or heterogeneously Catalyzed dehydration.
C2H4O + HCN
CH2(OH)CH2CN
[Al2O3 Cat.]
CH2(OH)CH2CN
H2C = CHCN + H2O
[Al2O3 Cat.]
Material Required:
Basis
: 1 ton Acrylonitrile (99%)
Ethylene Cyanohydrin : 1400 kg
Catalyst
: Small quantity
Process:
The process involved the base catalyzed addition of HCN to ethylene oxide forming
ethylene cyanohydrin. Acrylonitrile can be manufactured by dehydrated ethylene
Cyanohydrin. Pass continuously refined Cyanohydrin either over a dehydration
catalyst activated reduced pressure between 250 to 350 OC in the vapor phase or in
the liquid phase at 200OC in the presence of alkali m3etal or alkaline earth metal
Salts of Organic acid, Primarily
Magnesium Carbonate. Condense the reaction
products coming out from Reactor and pass into a decanter where water layer and
organic layer i.e. crude acrylonitrile layer separate out. The water layer discard and
crude acrylonitrile layer charge into a fractionating column and return the lowboiling heads to ethylene cyanohydrin still. The bottom consist high boiling
impurities and are generally discarded. Recover 99 % purity dry Acrylonitrile
Substantially from middle of column.
5.1.3 Acetylene- Hydrogen Cyonide:
It is the another industrial pathway developed by Bayer and commercially operated
by American DuPont, Goodrich, Knapsack, and Monsanto involved the CuCl-NH4Cl
catalyzed addition of HCN to acetylene at 70-80 OC: At the end of the sixties, the
46
47
Figure-5.3 Acrylonitrile by Acetylene-HCN route
Monsanto and Cyanamid plants were shut down. Consequently at the beginning of
the seventies less than 1% of the total acrylonitrile production was manufactured
according to this route.
Process Principle of Acetylene Route:
Single-step, homogeneously Catalyzed hydrocyanation in the liquid phase
Reaction
HC=CH + HCN
H2C = CHCN
[Cu2Cl2 Cat.]
80 % yield
Material Requirements:
Basic
: 1ton acrylonitrile (99%)
Acetylene
: 545 kg
Hydrogen Cyanide
: 545 kg
Catalyst loss (contained copper) : Small
Process:
Acrylonitrile is produced by the reaction of acetylene and hydrogen cyanide in the
presence of a catalyst under either liquid or vapor-phase conditions.
Acetylene and hydrogen cyanide in a molar ration of 10 to 1 are feed into a rubberlined cylindrical reactor that is kept about two thirds full of catalyst solution. The
aqueous solution contains 26 per cent cuprous chloride (based on the weight of
dissolved copper). The catalyst may be used to produce approximately 20 kg of
acrylonitrile per kg of dissolved copper before regeneration. This may be
conveniently accomplished by precipitating the copper with zinc and reconverting to
cuprous chloride. The aqueous catalyst solution is maintained at a temperature of
70OC, and the reactor is operated at essentially atmospheric pressure.
The reaction gases from the top of the reactor contain acrylonitrile, unreacted
acetylene, 1 to 3 per cent hydrogen cyanide, and small amounts of numerous byproducts such as acetaldehyde, vinyl acetylene, divinyl acetylene, vinyl chloride,
cyanbutadiene, lactonitrile, and chloroprene. The gases are washed counter currently
48
with water in a scrubber, which removes the acrylonitrile, hydrocyanic acid, and
some of the by-products. The washed gases are recycled to the reactor.
The water solution, containing about 1.5 per cent acrylonitrile, is steam-distilled in a
column to give 80 per cent acrylonitrile. The crude product is fractionated in a series
of columns to yield 99 percent pure acrylonitrile. The yield based on acetylene is
about 80 percent and is somewhat higher (90 to 95 per cent) based on hydrocyanic
acid. The greatest losses in yield arise from formation of vinyl acetylenes and their
derivatives. Various patents cover removal of vinyl acetylenes from the liquid phase
before distilling acrylonitrile and from the gaseous phase prior to recycling acetylene.
The vapor-phase process involves passing a mixture of equal volumes of acetylene
and hydrogen cyanide over a fixed metallic cyanide catalyst (suspended on an inert
carrier) at temperatures of 400 to 500 OC. The gaseous reactants may be diluted with
steam or inert gases to improve the yield, but it is still reported to be rather low. The
addition of an acidic substance, such as phosphoric acid, to the crude reaction product
entering the column is said to reduce secondary reactions and increase the yield of
acrylonitrile.
5.1.4 Acetaldehyde-hydrogen Cyanide Reaction:
Another process by Knapsack-Griesheim remained industrially insignificant.
Acetaldehyde react with HCN froming the nitrile of lactic acid i.e. lactonitrile which
was then dehydrated to acrylonitrile at 600-700OC in presence of H3PO4.
Process Principle of Acetaldehyde Route:
Two-step reaction initially to acetaldehyde cyanohydrin i.e. lactic acid nitrile with
subsequent catalytic dehydration.
Reaction:
CH3CHO + HCN
CH3CHCN
|
OH
CH3CHCN
|
H2C = CHCN
[Cat.]
OH
49
The first stage of this reaction is still operated in Japan today, it serves however to
manufacture lactic acid by hydrolysis of lactonitrile in the presence of H2SO4.
CH3CHCN
CH3CHCOOH
|
|
OH
OH
Lactic acid nitrile presently use only as intermediate in lactic acid manufacture.
Lactic acid is isolated as its methyl ester and purified. Musahino operates a 5,000
ton/annum plant.
5.1.5 Nitrosation of Propylene:
It is the process no longer operated today, provides the transition at the modern
manufacturing routes to acrylonitrile as propane is employed ad feedstock. DuPont
developed propane nitrosation process, then operated it for a period in a pilot plant in
the USA. By means of this process, propane was catalytically reacted with NO using
Ag2O/ SiO2 or alkali metal oxide with thallium or lead compounds:
4H2C = CHCH3 + 6NO
4H2C = CHCN + 6H2O + N2
[catalyst]
A silver oxide on silica catalyst in employed, the reaction temperature being in the
region of 5000C. At one time a Du Pont plant in Beaumont, Texas, employed a
process based on this reaction
5.1.6 Future Processes:
Just like propylene, propane should also be a suitable feed stock for the
Ammoxidation. Monsanto Power Gas, process based on propane or propylene, and
ICI have developed and are doing research work on production of acrylonitrile from
propane as a main raw material along with NH3 & O2, using oxides of the and
tungsten as catalyst at 485-520 OC temperature. It has been claimed on pilot plant
scale that by the use of above catalyst, the formation of highly poisonous Hydrogen
Cyanide as by product could be avoided to large extent. Thus, this process appears to
be technological alterative of future for the production of acrylonitrile. The economic
advantages of the process are claimed to be the price advantage of propane over
propylene not much differ, increased production of Valuable acetonitrile and HCN
50
by products instead of others and lower effluent cost. It is hoped to introduce the
process at the beginning of the Mitsubishi Chemicals and BOC have also developed a
propane-based ammoxidation process which has higher selectivity than typical
propylene-based systems.
5.1.7 Dual Process:
A combination of two process i) propylene ammoxidation and (ii) addition of HCN
acetylene can be used as an economical industrial process. Ammoxidation of
propylene gives HCN as a by product alongwith ACN the main product by following
reaction.
C3H6 + NH3 + 1.5O2
CH2CHCN + 3H2O
(Main reaction)
1/3 C3H6 +NH3 + O2
HCN + 2H2O
(Side reaction)
HCN thus produced is about 8% of total ACN produced, which can be reacted with
acetylene to convert it into ACN.
C2H2 + HCN
CH2CHCN
Thus, in this processes, HCN is totally used up, hence it is and intrinsically safe
process.
5.2 WHY SOHIO PROCESS IS THE BEST?
Propylene ammoxidation using Sohio Process has following advantages over other
processes for production of acrylonitrile.
5.2.1Process:
Sohio process gives highest conversion of propylene (about 98%) with high
selectivity for ACN. It is a once through process, not recycle of reactants is required
The reaction flow diagram is quit simple. It consist of catalytic, vapor phase, one step
conversion operating at a moderate temperature (below 500 0C), ordinary pressures
(below 3 atmospheres), and residence time of a few seconds.
5.2.2 Raw Material
In Sohio process refinery propylene and conversional fertilizer grade anhydrous
ammonia along with air are the only raw materials. Propylene concentration is not
51
critical; with 50 to 90% propylene acceptable is a reactor feed. All the materials cost
less and are more abundant on world wide basis than the previously used raw
materials: ethylene oxide, acetylene, and acetaldehyde, hydrogen cyanide. The older
processes for manufacturing acrylonitrile employ the relatively expensive Raw
Material building
5.2.3 Handling of Hydrogen Cyanide:Acrylonitrile is produced by Ethylene Oxide or acetylene reaction with Hydrogen
Cyanide [HCN]. But HCN is the highly poisonous which is used as raw material and
far large amount of the lethal chemical has to be stored and handled. While in Sohio
process HCN is obtained compare to in small quantity as a by-product.
Thus, in comparison to acetylene or ethylene oxide based process, propylene based
process appears to be for superior technological alternative as the highly poisonous
HCN has to be handled is a far less quantity. Hence Sohio process is safer than other
processes using HCN as a raw material
5.2.4 Catalyst Development:The Sohio process has remained economically advantaged over other process
technologies since the first commercial plant in1960 because of the higher
acrylonitrile yields resulting from the introduction of improved commercial catalysts.
Reported per-pass conversions of propylene to acrylonitrile have increased from
about 65% to over 80% with developed catalyst.
5.2.5 By products:The major by product is Acetonitrile, which sold as two preclude volumes age.
Acetonitrile power full resins and has some other unique associated with the
extremely high polarity of the cyano group. Other by product is HCN widely used
commercially recoverable by product.
5.2.6 Fluidized bed reactor:Because of Fluidized bed reactor, get advantage of it over fixed bed reactor. Although
loss of catalysts is more in fluidized bed reactor than in fixed bed reactor, the higher
yield in fluidizing bed reactor overshadows loss due to catalyst carryover. Moreover,
52
the loss of catalyst can be minimized by providing properly designed internal
cyclones.
5.2.7Other comments:An advantage of Cyanohydrins process is that it produces lesser amount of impurities;
however it is not economically competitive with Sohio process. The drawbacks of
acetylene - HCN process were expensive raw materials, formation of some
undesirable impurities like divinyl acetylene and methyl vinyl ketone which are
difficult to remove and the frequent regeneration required for catalyst. Propane based
processes are more economical than Sohio process due to difference in their prices.
However this price difference is not likely to be great enough in the near future to
dictate change.
6RILQDOO\FRQFOXGHWKDW«««««««
The propylene-based process developed by Sohio was able to displace all other
commercial production technologies because of its advantages of highest conversion
rate of propylene (about 98%) with high selectivity for ACN[80%]., lower raw
material costs, no recycle of unreacted raw materials i.e once through process and
these will result in overall product cost is become lower. Any industry will become
more profitable as it will manufacture product with high conversion and at low cost.
So, the conclusion can be drawn that, acrylonitrile produced by Sohio process is more
feasible, practicable and economical and this can be also proved as in United States
all capacity and about 90% of the world capacity far acrylonitrile production is based
on the Sohio process.
5.3 SELECTION OF CAPACITY:
IPCL, Baroda is the sole producer of acrylonitrile in India with plant capacity of
around 30000 ton per annum. All industries in India required Acrylonitrile is
imported. The current Indian demand is very large and would further increased in
future depend upon the market of its uses as resins, fibers, rubbers and as other
intermediates. So, company has to try to increase acrylonitrile production to
overcome current demand and future regulatory demand. Hence, a capacity of 70000
MTPA is selected for Acrylonitrile plant based on Sohio Process.
53
CHAPTER-06: THERMODYNAMICS & KINETICS
6.1 Process Description:
The reactor section can be divided into three parts.
1. Preparation of feed
2. Mixing and reactions.
3. Heat removal from reactor and gases.
Ammonia, propylene and air are feed material. Liquid ammonia is fed to ammonia
vaporizer in shell side stream via fitter. Ammonia is vaporized by absorbing heat
from the side stream water of the absorber. Vaporized ammonia is then passed
through an entrainment separator to remove and return any liquid ammonia
entertainment.
Vapor ammonia is now passed through super heater where vapor ammonia is heated
to 65 oC using low pressure stream. Superheated ammonia at 65 OC is fed to the
reactor at pressure 2.3 Kg/cm2 g.
Propylene is supplied to plant in liquefied form in pipeline from petrochemicals plant.
Liquid propylene is directly sent to vaporizer by passing it through propylene fitter.
This propylene is vaporized in vaporizer as in case of ammonia. Then, vaporized
propylene is now passed through entrainment separator and super heater as per
ammonia. The temperature of superheated propylene vapor is 65OC and it is fed at 2.5
Kg/cm2G pressure to reactor.
Air is sucked from open atmosphere by using an air compressor. The air compressor
is run by a steam turbine which is fed with high pressure steam obtained by using heat
of reaction in reactor. This saves electricity and it is important from economic point
of vies. The air compressor provides air at 2.5 Kg/cm2 g pressure.
The Acrylonitrile is produced by SOHIO Process using ammoxidation of propylene
in fluidized bed catalytic reactor, can conveniently divided into three section:
1. Reactor section
2. Recovery section
3. Purification section
54
6.1.1 Reactor Section:
The fluidized bed catalytic reactor is the heart of process. Liquid ammonia and liquid
propylene are vaporized and propylene and ammonia vapors are superheated by
passing through super heater. Propylene and ammonia enter the reactor through feed
sparger with mixing. The process air compression provides reaction air at 2.5 Kg/cm2
g., before entering the reactor, the air from the air compressor is passed through start
up heater. Air is admitted to the reactor bottom where it passed into fluidized bed
through a air grid. The air grid is below the propylene ammonia feed sparger.
Feed to Reactor:Ammonia at 2.3 Kg/cm2 g and 65 0C
Propylene at 2.5 Kg/cm2 g and 65 0C
Air at 2.2 Kg/cm2g and 170 0C
The expected feed mole ratios are approximately
Propylene - 1.0
Ammonia - 1.23
Air
- 9.1 to 9.3
Beside the possibility of catalytic reduction the ammonia to propylene ratio is too
low, there will be an excess consumption of sulphuric acid to remove excess
ammonia. The air to propylene ratio mentioned above is design number and the actual
ratio may vary with operation.
Propylene, ammonia and air flowing up through the reactors fluidizing the bed of
catalyst. The catalyst B CM9 MC & C 491 MC is used which is finely divided solid
in the 10 to 100 micron range.
The reactor is normally operated at a pressure 0.75 Kg/cm2 g at top and a temperature
between 430 to 450OC. The reactor gives an 80 mole percentage conversion of
propylene to Acrylonitrile, using catalyst C 491 MC.
Because of the reaction which take place forming acrylonitrile and other products are
exothermic Therefore, cooling is necessary to maintain temperature in reactor. The
reactor contains multiple sets of vertical U-tube coils through which treated
condensed water pass. Heat from reaction is transferred to the circulating water in
55
coils producing steam 41.5 Kg/cm2 g. The saturated steam passes through coil to
produce superheating the steam. Various number of these steam coils can be placed in
service or taken out of service, in order to affect temperature control in reactor.
Temperature control can also be accomplished by adjusting the feed rates.
The catalyst bed level is maintained in reactor. If the bed level is too low, the cooling
coils will be uncovered and not be enough cooling surface available to properly6
control the reactor temperature. If the bed level is too high, catalyst losses may be
excessive.
The Reactor also contains cyclone separators through which the effluent gases must
pass before they leave the reactor. These cyclone separators remove most the catalyst
which has been carried along with the gaseous stream. The catalyst drops into a dip
leg at the bottom of each separator and is returned to the catalyst bed. Each dip leg is
equipped with trickle valve. The trickle valve is constructed with a flapper which
deeps catalyst from backing up to cyclone dips legs. This flapper periodically opens
when the weight of catalyst in the dip leg overcomes the pressure outside the trickle
valve and some catalyst is dumped back into the bed. Each dip leg has air purge to
prevent plugging
During normal operation, catalyst fines are produced in the reactors due to attrition,
fines too small to be retained by the cyclones pass out of the reactor with effluent
gases. The catalyst inventory should be maintained the good reactor temperature
control and maximum conversion to acrylonitrile.
The reactor effluent includes unreacted ammonia and propylene, oxygen, nitrogen,
acrylonitriel, acetonitrile, Hydrogen cyanide, carbon dioxide, carbon monoxide, water
and small quantities of other materials.
The reactor effluent gases pass through the effluent cooler where the heat is
transferred to the make up boiler feed water or which may be used in reactor steam
coils. From the effluent cooler, the partially cooled at 230 OC effluent gases flow to
the hot quench in the recovery section .The reactor section also contains the facilities
for feeding water to the reactor steam coils and handling the steam generated in the
steam coils.
56
Any change in operating conditions in the reactor changes most of the other
conditions. Therefore, the total effect of any change is difficult to predict. For
instance, an increase in pressure in the reactor reduces the volume of the gases in the
reactor, and therefore reduces the velocity of the gases through the catalyst bed. With
increased pressure, carbon dioxide production is increased with a resulting rise in
reactor temperature and drop in the oxygen content of the effluent stream. The
operation of reactor must also be optimized depending on the age and condition of the
catalyst and the production rates in the plant.
In general, however, conversion to acrylonitrile is favored by low pressure, low
temperature, short retention times and good fluidization of the catalyst bed. Proper
distribution of the feeds is very important. Any blockage of feed spargers which can
seriously affect the propylene conversion to acrylonitrile.
6.1.2 Recovery Section:
The major feed stream to recovery section is the reactor effluent gases which is
partially cooled at 232 OC is introduced to the bottom of the quench column through a
sparger and is adiabatically cooled down to 85 OC in the lower stage of quench
column. The quench column is made of two sections. At bottom section, water
circulation through proper distributions helps to settle fine catalyst and polymers.
Where as at top section un reacted ammonia is neutralized by reacting with sulphuric
acid distributed by spray spargers and forms 20-25 weight % Ammonium Sulphate
[(NH4)2SO4] solution and maximum of 3.3 weight % polymers. The amount of acid is
determined by maintaining pH in the range of 3-4.5. liquid droplets carried upward by
effluent gas will knocked down by demister tray above each section and returned to
the bottom through demister tray liquid down comer. Solvent water or DM water is
sparged at the column top to flush demister tray and water recycled from the heads
column decanter and stripper bottom are fed to bottom section for flushing tray.
Antifoam is added in circulating water to prevent foaming in the column. From the
ammonium sulphate tank it is pumped to Acrylates crystallizer for recovery of
ammonium sulphate or incinerated in ACN in incinerator. If ammonia is not
57
neutralized, ammonia may react with acrylonitrile to form various fouling deposits
and acid gives polymerization of hydrogen cyanide.
To minimize any liquid escaped from the quench column will be controlled in a low
flow centrifugal liquid entrainment separator and return to quench column.
Then, the effluent gases pass through series of after coolers. Here the effluent gases
are cooled by passing cooling water in counter current direction with gases. The
cooling water pass through shell side and the gases pass through tube side of after
coolers. Finally the gases are cooled from 85 OC to 38 OC.
The cooled effluent gases in after coolers have soda ash solution injection along with
organic to maintain pH in the range of 6 to 6.5. The oxygen content of the reactor
effluent is an important variable and is continuously monitored in the overhead
stream leaving the quench column, before entering to the absorber.
The product stream exists from the quench column and after cooler coming in the
absorber bottom as a feed. The absorber is a tray tower with short section at top and
bottom which are provided for heat exchanger.
The absorber is tower used to recover acrylonitrile and other organic by absorbing
with counter-current flow of water. The absorber and related heat exchangers and
vaporizers are an integrated system. A change in operating condition in any part of
the absorber system will affect all the other parts. Using less water than this may
result in a less of acrylonitrile as overhead with the inert gas stream. Using more
water than design result in the need more process water to be circulated handled and a
more dilute solution of organics coming from absorber bottom. For this purpose lean
water is used. Lean water for absorption is with drawn from the stripper column as
side stream which is cooled in heads column reboiler or rich-water-lean water
exchanges and then lean water cooler. Lean water temp is controlled approximately
40 OC. The flow of the lean water is controlled by determining the absorber water
requirements. It is controlled according to the level on the collection tray of absorber,
these changes of the flow in absorber upper circulation. This in turn varies the level at
the bottom of the absorber.
58
This warm lean water about 38-40 OC is first enter from the top of the absorber and is
cooled by contact with the cold off gases as it passes downward. From first collection
tray, the water is removed as absorber side stream and cooled with brine in chiller and
passes through ammonia vaporizer where is chilled by Vaporizing ammonia and this
chilled water is return to absorber below collection tray. Then, the chilled water flows
downward to the absorber bottom for absorbing the acrylonitrile and other organics
from gases.
The bottom stream from the absorber is rich water. A portion of rich water is removed
and cooled with brine in chiller and is chilled by vaporizing propylene by passing
through propylene vaporizer. This cold water is return to absorber above feed cooling
section. Flow through this circulating system is regulated to maintain a constant
temperature 21 OC in the absorber bottom.
The unabsorbed gas stream mainly containing unreacted hydrocarbons, oxygen
nitrogen, carbon dioxide, carbon monoxide, water and Small amount of acrylonitrile
in ppm is vented through the absorber vent stack.
The Recovery Column is a tray tower which separates the acrylonitrile from
acrylonitrile by extractive distillation. So, it is also known as Acrylo-Aceto Splitter
this case solvent water is used as solvent. The acrylonitrile goes overhead, preferable
as an acrylonitrile water azeotrope. The acetonitrile goes out at the bottom of the
column in dilute water solution. The hydrogen Cyanide in the feed splits; most of
hydrogen cyanide goes overhead with acrylonitrile and some goes out the bottom
with acetonitrile.
The heat required to make the separation in the Aceto-Acrylo Splitter is supplied by
the vapors from the upper section of stripper/steam.
The overhead product is separated into organic phase and aqueous i.e. water phase in
the decanter. The inhibitor HQ is added to the recovery column overhead vapor line
to inhibit the formation of polymer. The organic layer containing acrylonitrile,
hydrogen Cyanide and water is pumped to the CHN column Acrylo-Aceto Splitter.
The water layer is returned to feed.
59
The bottoms product containing acetonitriel in addition too water, hydrogen cyanide
and polymers are fed to the Aceto stripper where acetonitriel, hydrogen cyanide and
some water are taken as the overhead. The crude acetonitriel is sent to the acetonitriel
purification system.
The Recovery Column Splitter bottom stream is pumped to the Aceto-Stripper. The
stripper is the tray tower which removers acetonitrile and hydrogen cyanide from the
bulk of the circulating water, so this water can be reused in the absorber and
Recovery column Acetonitrile, Hydrogen Cyanide and some water vapors go
overhead to stripper condenser and then to the stripper reflux drum. The reflux drums
of equipped with a inert gas purge and is vented to the flare header. Part of condensed
vapors is used as reflux; the remainder i.e. crude acetonitrile goes to acetonitrile
purification system. Also some part of vapors from upper part of stripper is removed
and supply heat to the Recovery column when steam not available. The heat required
to make the separation in the stripper is supplied by 3.5 kg / cm2.g steam to a
reboiler.
Antifoam is added in stream from stripper Recovery column to control foaming in the
Recovery Section. Sodium carbonate Solution is added to stripper and to Recovery
column overhead line to adjust circulating water pH at these solutions should be
maintained within range of 6.0 to 6.5. Sodium Hydroxide Solution should not be used
to substitute Sodium carbonate Solution, as run-away polymerization may be initiated
by sodium hydroxide.
6.1.3 Purification Section:
HCN Column:
The crude acrylonitrile from the Recovery Column decanter, composed primarily of
acrylonitrile, hydrogen cyanide and water, is pumped too HCN column, as it remove
HCN as by product it also called drying column as large amount of water removed
from acrylonitrile in this column HCN column is tray column, removed both
hydrogen cyanide and water are removed from the acrylonitrile. The overhead
vapour, which is approximately 99% Hydrogen Cyanide, goes to an external
overhead condenser where it is condensed. The condensed liquid is partly refluxed to
60
the column and partly sent to HCN purification. Any uncondensed vapor passes
through a liquid knockout drum and goes to the Incinerator or Flare. Acetic acid is
added to at top of column to prevent formation of hydrogen cyanide polymers. The
hydrogen cyanide vapors are condensed on the tube side in a downward flow. Sulphur
dioxide is added to the HCN vapor line to help minimize hydrogen cyanide
polymerization in the vapor phase.
In order to remove water, a total liquid draw off intermediately and is cooled is sidestream cooler where it is cooled to 40 OC. This stream then goes to decanter when a
phase separation takes place. One phase is predominately water phase the other phase
organic phase i.e. acrylonitriel. The water phase is pumped from decanter to bottom
of quench column and alternately this stream goes with ammonium sulphate stream as
waste water. The acrylonitrile phase is sent back to the HCN column via Heat
exchanger Hydroquinone (HQ) as an acrylonitrile polymerization inhibitor is added
into the organic phase of HCN column decanter.
The lower amount of cyanides in the HCN column decanter, the better will be the
water removal capability of the drying section of this column.
6.1.4 Product Column:
The bottoms of HCN column /drying column are pumped as feed to product column.
The product column is a vacuum column that separates heavier and lighter from the
acrylonitrile. The column is equipped with an overhead condenser and a vent
condenser for removing non-condensable. The vent condenser is equipped with
vacuum ejector with medium pressure steam. Most of the overhead stream is reflux to
the top of the column and the remainder is normally recycled to Recovery column
feed or Recovery column decanter. The recycle to Recovery column decanter
removes low boiling impurities from the product column and prevents them from
accumulating in the top of the column. Heavy products of reaction and polymer in the
purification system are removed via the product column bottoms stream. To remove
solid polymer, the bottom stream is filtered before the bottoms pump. The net
bottoms product flows to the Recovery column for recovery of products.[the overhead
61
product and bottoms of product column again feed to Recovery column for recover
acrylonitrile So it is also known as Recovery column.
The product acrylonitrile is removed from top and is pumped via the cooler to product
rundown tank. Polymerization inhibitors Hydroquinone (HQ) Methyl Ether
Hydroquinone (MEHQ) are added into rundown storage tank ages.
6.1.5 Aceto Column:
Crude acetonitrile coming from stripper top having around 1-2% HCN is taken in
topped crude tank and HCN is killed by digestion by formaldehyde and caustic in
treating kettle. The overhead material is chemically dried by anhydrous calcium
chloride and for the final purification batch distillation is operated.
6.2 REVAMP OF ACRYLONITRILE PLANT:
Revamp of acrylonitrile plant is aimed at
(1) Increasing capacity of plant.
(2) Reducing water consumption of the plant.
(3) Steam saving.
(4)It involve reactor cyclone, air grid, hydrocarbon sprager modification and
change in internals of Quench column and absorber.
6.3 AUXILIARY CHEMICALS ADDED:
Some chemicals added in process streams with their significance are given as below.
6.3.1 Inhibitors:
There are three inhibitor solutions are used for prevention of polymerization of
acrylonitrile MEHQ or Ammonia is used to inhibit the final product acrylonitrile. HQ
is used to inhibit acrylonitrile polymerization in various location in the plant, except I
the final product rundown tank and the tip of product column. These materials are
toxic and must be handled accordingly.
1) Methyl Ether of Hydroqu9oone (MEHQ):
This solution should be weight percent MEHQ in Acrylonitrile. For preparation of
solution, acrylonitrile is added to mixing tank. Then MEHQ is dumped into mixing
tank.
62
2) AQUA Ammonia
This solution should be 30 weight percent ammonia in water. Treated water is
charged to the aqua Ammonia drum. When a definite level has been established in the
drum, the pump is started to circulate the water through the aqua ammonia cooler,
having brine flow, Ammonia vapors are slowly added to the drum. Circulating water
stream will dissolve Ammonia according to vapor pressure of Ammonia t that
temperature. The temperature is adjusted to give 30% Ammonia solution.
As the inhibitor solution is consumed, additional water and ammonia vapors are
slowly and continuously added to the drum for maintaining equilibrium.
3) Hydroquinone (HQ):
This solution should be 6.5 weight percent HQ in acrylonitrile. This solution should
be prepared in similar way as For MEHQ. Hydroquinone is less soluble in
acrylonitrile than MEHQ.
6.3.2 Antifoam Agent:
Antifoam agent used to prevent foaming in the quench column and the recovery
column section circulating water system. Betz foam ± Troll LT or Betz DL -300-82 is
example of such antifoam agent. It is added into water and diluted. It is charged to the
antifoam tank and then supplied with antifoam injection pump.
6.3.3 Soda Ash Solution:
Soda Ash solution should be 10 weight percent sodium carbonate in water.
Condensate is added to the mixing tank. Mixer is turned on and enough sodium
Carbonate is added to make the solution. Soda Ash solution is used to adjust pH of
circulating water and minimizing corrosion in the systems. It is added in stripper tray
and recovery column overhead line down stream of the condenser.
6.3.4 Acetic Acid:
Acetic Acid solution should be 50 weight percent acetic acid in water.
Add concentrated Acetic Acid to mixing tank and then slowly add condensate to the
tank. Mix contents with the agitator. Continue adding condensate until the desired
acid concentration is achieved. Acetic Acid is used in HCN column condenser inlet
for preventing polymerization of hydrogen Cyanide.
63
6.3.5 Sulphur Dioxide:
Sulphur Dioxide is added t the HCN vapor line to help minimize HCN
polymerization in the vapor phase.
64
CHAPTER 07: MATERIAL BALANCE
Material balances are the basis of process design. A material balance taken over
complete process will determine the quantities of raw materials required and products
produced. Balances over Individual process until set the process stream flows and
compositions.
The general conservation equation for any process can be written as
Material out = material in + generation ± consumption + accumulation
For a steady state process the accumulation term is zero. If a chemical reaction is
taking place a particular chemical species may be formed or consumed. But if there is
no chemical reaction, the steady state balance reduces to,
Material out = Material in
A balance equation can be written for each separately identifiable species present,
elements, compounds and for total material.
7.1 BASIS:
Basis: 70, 000 tons/annum.
The process is planned and developed as a continuous process. A plant is operated for
24 Hours per day and 330 per year.
Capacity
= 70,000 tons/annum
= 70,000 / (330 x 24)
= 8838.38 kg/hr
7.2 CATALYST PERFORMANCE:
As using catalyst M9MC given by Sohio, the conversion of C3H6 is taken as,
80%
to
ACN
2.3%
to
Aceto
5.9%
to
HCN
65
1.5%
to
acrylic Acid\
0.7%
to
Acrolein
0.2%
to
Acetic acid
5.1%
to
CO2
2.9%
to
CO2
1.4%
to
Unconverted C3H6
7.3. MOLECULAR WEIGHT: in kg / kgmole
Table-7.1 Molecular weight in kg / kgmole
Acrylonitrile [C2H3CN]
:
53.03
Acetonitrile [CH3CN]
:
41.02
Hydrogen Cyanide [HCN]
:
27.01
Propylene [C3H6]
:
42.03
Ammonia [NH3]
:
17
Oxygen [O3]
:
32
Nitrogen [N2]
:
28
Acrolein [CH2CHCHO]
:
56.03
Carbon monoxide [CO]
:
28.01
Water [H2O]
:
18
Carbon Dioxide [CO2]
:
44.01
Acrylic Acid [CH2CHCOOH]
:
72.03
Acetic Acid [CH3COOH]
:
60.02
Assume there is 1% loss of ACN as in any outlet stream or which may polymerized.
So, actual capacity of plant is 8927.66 kg/hr.
Assume no catalyst mass coming out from the reactor.
Let, Air / C3H6 = 6.75 and NH3 / C3H6 = 0.42
Both ratios are on the weight basis.
66
7.4 REACTOR:
[1]Acrylonitrile:
C3H6 + 3/2 O2 + NH3
(42.03)
(48)
CH2 = CHCN + 3H2O
(17)
(53.03)
(54)
Propylene required (for 80% conversion to ACN)
= (8927.66 x 42.03) / 53.03
= 7075.80 kg/hr (for 80% conversion)
Actual C3H6 used
= 7075.80 / 0.80
= 8844.75 kg/hr
[2] Hydrogen Cyanide:
C3H6 + 3NH3 + 3O2
3HCN + 6H2O
(42.03)
(81.03)
(51)
(96)
(108)
Hydrogen Cyanide produced
= (0.059 x 8844.75) x (81.03) / 42.03
= 1006.06 kg/hr
[3] Acetonitrile:
C3H6 + 3/2 O2 + 3/2 HN3
(42.03)
(48)
3/2CH3CN + 3H2O
(25.5)
(61.53)
Acetonitrile produced
= 297.81 kg/hr
[4] Acrolein:
C3H6 + O2
CH2 = CHCOOH + H2O
(42.03) (32)
(56.03)
(18)
Acrolein produced
= 82.53 kg/hr
[5] Acrylic Acid:
C3H6 + 3/2O2
(42.03)
CH2 = CHCOOH + H2O
(48)
(72.03)
Acrylic Acid produced
=227.37 kg/hr
67
(18)
(54)
[6] Acetic Acid:
C3H6 + 3/2O2
(42.03)
3/2CH3COOH
(48)
(90.03)
Acetic Acid produced
= 37.89 kg/hr
[7] Carbon Dioxide:
C3H6 + 9/2O2
3CO2 + 3H2O
(42.03)
(132.03)
(144)
(54)
Carbon Dioxide produced
= 1417.00 kg/hr
[8] Carbon Monoxide:
C3H6 + 3O2
3CO + 3H2O
(42.03) (96)
(84.03)
Carbon Monoxide produced
= 512.81 kg/hr
[9] Ammonia: From reaction [1], [2] and [3].
Ammonia required = 3618.60 kg/hr
now, NH3 / C3H6 = 0.42
Therefore, NH3 actual input
= (0.42) x (8844.75)
= 3714.80 kg/hr
NH3 consumed
= 3618.60 kg/hr
NH3 excess i.e. unreacted
= 3714.8 ± 3618.60
= 96.20 kg/hr
[10] Water: From reaction [1] to [8]
Water formed
= 11685.68 kg/hr
68
(54)
[11] Air: From reactions [1] to [8]
Oxygen required
= 11855.29 kg/hr
Now, Air contains 23.3% O2 & 76.7% N2 on weight basis.
Air required
= 11855.29 / 0.233
= 50881.17 kg/hr
Now, Air / C3H6
= 6.75
Air in
= (6.75) x (8844.75)
= 59702.06 kg/hr
O2 in = 13910.58 kg/hr
(23.3 wt% of air)
N2 in = 45791.48 kg/hr
(76.7 wt% of air)
O2 consume d
= 11855.29
= 13910.58 ± 11855.29
O2 excess
= 2055.29 kg/hr
N2 out
= 45791.48 kg/hr
ACN
= 8927.66 kg/hr
Table-7.2 Material balance over Reactor:
Component Material in, kg/hr Material out, kg/hr
Propylene
8844.75
--
Ammonia
3714.80
--
O2
13910.58
--
N2
45791.48
45791.48
Acrylonitrile
--
8927.66
Acetonitrile
--
297.81
HCN
--
1006.06
Acrolein
--
82.53
Acetic acid
--
37.89
Acrylic Acid
--
227.37
69
CO2
--
1417.00
CO
--
512.81
Water
--
11685.68
Total
72261.61
72261.61
7.5 QUENCH COLUMN:
Input stream = Effluent from Reaction via effluent cooler
Two section provided in Quench column. Water is circulated over both section from
stripper i.e. water in = Water from Aceto stripper
= 9414.96 kg/hr
Excess NH3 = 96.20 kg/hr
Excess NH3 React with H2SO4:
Reaction:
2NH3 + H2SO4
(34.02)
(NH4)2SO4
(96.06)
(138.08)
H2SO4 in
= (96.20 x 98.06) / 34.02
= 2777.29 kg/hr
let 10% excess
Total H2SO4 added
= 305.02 kg/hr
Excess H2SO4
= 27.73 kg/hr
Other by product like, Acrylics Acid, A.A, Acrolein, some ACN are polymerized and
catalyst carry over also taken out with bottom stream.
70
Table-7.3 Material balance over Quench Column:
Component
Material in, kg/hr
Material out , kg/hr
Acrylonitrile
8927.66
8927.66
Acetonitrile
297.81
297.81
HCN
1006.06
1006.06
Acrolein,Acetic cid,Acrylic Acid
347.79
--
Waste
--
347.79
CO2
1417.00
1417.00
CO
512.81
512.81
Water
11685.68(as feed)
15864.07(at top)
9414.96(as Lean Water)
5236.57(at bottom)
33609.77
33609.77
Total
7.6 ABSORBER:
Assumption:
Off-gases containing CO, CO2, N2, unreacted O2, unreacted C3H6. Not absorbed in
water and are remove from top of column.
Also HCN of 0.5% in is removed in it i.e.,
= (0.005) (1006.06)
= 5.03 kg/hr
ACN out at top as off gases = 54 kg/hr
Off ± gases contains
Some entrained water = 108.59 kg/hr
and all CO2,CO,N2,Unconverted C3H6
Data:
Solubility of Acrylonitriel in water, wt%
At 400C
7.9%
0
7.5%
0
7.3%
At 30 C
At 20 C
71
Top of absorber have temperature 400C and at 400C water added at top. Feed at
bottom also 400C and feed enter at bottom is also at 400C. but about 250C maintain in
column using side stream cooling.
So, take solubility of Acrylonitrile around 7.7 wt% in water
Therefore, for 8927.66 kg/hr ACN is,
Water required for absorb ACN
= (8927.66 x92.3) / 7.7
= 107015.98 kg/hr
Acetonitrile& HCN have infinite solubility in water for absorption.
Lean water added
NJKU«««««««««««>)URP(QHUJ\%DODQFH@
So Total water added for absorption is water with feed and lean water.
7.7 RECOVERY COLUMN AND DECANTER:
RECOVERY COLUMN:
We have Separation of Acetonitrile as bottom and Acrylonitrile as overhead using
extractive distillation using water as solvent.
All Acrylonitrile and all HCN feed separated as overhead. Also, Separation such as,
total Aceto ±98% to bottom (of Inlet feed) and 2% as overhead ( of Inlet feed)
Aceto at bottom
= (297.81) x (0.98)
= 291.85 kg/hr
Aceto at top
= 297.81 x 0.02
= 5.96 kg/hr
Now, bottom has 1.7% dilute solution of Aceto of
Water with Aceto at bottom
= (291.85 x 100) / 1.7
=17167.64 kg/hr
Water as overhead
= 8476.39 kg/hr
DECANTER:
Now, consider top stream have is separated out in decanter in aqueous (water) phase
and organic (ACN) phase. Separate out 95% of aqueous phase as water in decanter.
72
Water goes with organic phase = 5% of top stream
= 0.05 x 8476.39
= 414.5 kg/hr
Water removed
=8476.39 - 414.5
=8061.89 kg/hr
7.8 ACETO COLUMN:
Total Acetonitrile in feed separated as over head
Acetonitriel is overhead
= 291.85 kg/hr
In Aceto-stripper, the total Acetonitrile go as overhead with water and get 70%
acetonitrile as overhead.
Acetonitriel is overhead
= 291.85 kg/hr (70%)
Water with Acetonitrile as overhead
= 125.08 kg/hr (30%)
= 17167.64 ± 125.08
Water out a bottom
= 17042.56 kg/hr
7.9 HCN COLUMN:
The feed of HCN column is generally ACN & HCN with little amount of H2O and
Acetonitrile. Hence, it can be treated as binary distillation considerably HCN & ACN
alone.
From feed, all ACN and 99% pure HCN is recovered from top.
F=D+W
10295.15 = D + W
Where, F related to feed
D related to distillate (overhead) products
W related to bottom products
For HCN Balance:
F XF = D XD+ W XW
1001.03
= D (0.99) + W (0.01)
Solving above two equations for D & W
D
= 1001.02 kg/hr
73
W
= 9294.13 kg/hr
Top product stream:
HCN Recovered from top = 991.02 kg/hr
ACN as to product = 10.0 kg/hr
The bottom crude ACN Stream has,
ACN
= 8863.66 kg/hr
HCN
= 10.01 kg/hr
H2O
= 414.5 kg/hr
Aceto
= 5.96 kg/hr
7.10 PRODUCT COLUMN:
It is the column to get pure ACN from crude ACN. Recover 99.7% of feed as top
stream along as Product Acrylonitrile.
ACN as overhead product
= (8863.66) x (0.997)
= 8838.38 kg/hr
Also, Bottom stream contains Heavy ends Polymer mass which from during the
whole process from the small amount of Acrylonitrile (25.28 kg/hr), Acetonitrile
(5.96 kg/hr), and water (414.5kg/hr).
74
CHAPTER-08: ENERGY BALANCE
Let, the reference temperature = 25oC
8.1 PREHEATING OF REACTOR:
To initiate the exothermic reaction, it is necessary to heat the reactants, i.e. air,
propylene and ammonia is to reactor temperature 425oC before reaction.
[Feed at high pressure/ temperature lower than 425oC assume have same enthalpy at
425oC, atm.]
Energy required for preheat the reactants,
Table-8.1 Components and its properties
Component
Kg/hr
Mole.wt.
Kg
Cp.at
ni.cpi
o
mol/hr
425 C
C3H6
8844.75
42.03
210.44
28.3
5955.42
Ammonia
3714.80
17
218.52
10.05
2196.10
Air
59702.06
29
3300.07
7.21
23793.51
Ȉni Cpi = 31945.04
ǻ7
= 425-25=4200 C
Energy Supplied to preheat reactant Ȉni Cpi. ǻ7
= 13416915 Kcal
This energy supplied by the Heater.
8.2 ENERGY BALANCE AROUND REACTOR:
Reactants in at 4250 C
Products out at 4250 C
At 250 C
At 250 C
(a)Enthalpy in with reactants
= 13416915 Kcal
(b)Total Heat of Reaction:
Assume, Formation of Acrolein, Acetic acid, Acrylic acid is very very small and it is
neglected
75
(i) C3H6 + NH3 + 1.5O2
CH2CHCN + 3H2O
(ii) 2/3C3H6 + NH3 + O2
CH3CN + 2H2O
(iii) 1/3C3H6 + NH3 + O2
HCN + 2H2O
(iv) C3H6 + 4.5O2
3CO2 + 3H2O
(v) C3H6 + 3O2
3CO + 3H2O
Heat of formation at 25oC
Acrylonitrile
liquid
36.2
Acetonitrile
gas
19.81
Hydrogen Cyanide
gas
31.1
Carbon
Table-8.2 Components and its properties
Compound
State
Kcal/gmol
Propylene
gas
4.88
Ammonia
gas
-11.0
Water
gas
-57.8
Acrylonitrile
gas
45.37
Dioxide
gas
-94.05
Carbon Oxide
gas
-32.81
Heat of reaction =
>Ȉ KHDWRIIRUPDWLRQRISURGXFWV @± >Ȉ KHDWRIIRUPDWLRQRIUHDFWDQWV @
Heat of reaction of Acrylonitrile
= [(45.37) + 3(-57.8)] ± [4.88 + (-11.0)]
= - 132.91 Kcal/gmol
= - 132910 Kcal/kgmole
Heat of reaction of Hydrogen Cyanide
= [3(31.1) + 6(-57.8)] ± [4.88 + 3(-11.0)]
= -291.38 Kcal/gmol
= - 291380 Kcal/kgmole
76
Heat of reaction of Acetonitrile
= [1.5(19.80) + 3(-57.8)] ± [4.88+1.5(-11.0)]
= - 165.07 Kcal/gmol
= - 165070 Kcal/kgmole
Heat of reaction of Carbon Dioxide
= [3(- 94.05) + 3(-57.8)] ± [4.88]
= - 460.43 Kcal/gmol
= - 460430 Kcal/kgmole
Heat of reaction of Carbon Oxide
= [3(32.81) + 3(-57.8)] ± [4.88]
= - 276.71 Kcal/gmol
= - 276710 Kcal/kgmole
7RWDOǻ+
Ȉniǻ+R
=57130676.23 Kcal
(c) Enthalpy out with products:
Table-8.3 Enthalpy out with products
Component
Kg/hr
Mol.
K
Wt.
Mol/hr
Cpi at 4250C
ni.cpi
ACN
8927.66
53.03
168.35
24.88
4188.54
Aceto
297.81
41.02
7.26
17.63/19.86
144.58
HCN
1006.06
27.01
37.27
9.95
370.84
CO2
1417.00
44.01
32.2
10.05
323.61
CO
512.81
28.01
8.84
7.44
65.77
H2O
11685.68
18
649.2
8.45/7.25
4706.7
C3H6
123.83
42.03
2.95
28.3
83.38
NH3
96.20
17
5.66
9.28
52.51
O2
2055.29
32
64.23
7.45
478.50
N2
45791.48
28
1635.41
7.1
11611.41
77
Ȉni Cpi = 22025.84
ǻ7 -25=4200 C
Enthalpy out with products:
Ȉni Cpi ǻ7
= 22025.84 x 420
= 9250852.80 Kcal
(d) Enthalpy removed by the coolant
= Enthalpy of Reactant at 250C ± Heat of reactions ±
Enthalpy of product 4250C
= (- 13416915) - (- 57130676.23) - (9250852.80)
= - 61296738.43 Kcal
(e) Coolant required:
This heat is removed using steam at 1100C which is superheated up to 3700C.
Msteam Cpsteam ǻ7 .FDO
[Msteam] x [1] x [370-110] = 61296738.43 Kcal
Msteam = 3064836.92 kg/hr
This is the amount of steam required to removed the heat at evolved in the reactor.
8.3 ENERGY BALANCE OVER PRODUCT GAS COOLER:
Inlet temperature of gases = 4250C
Outlet temperature of gases = 2300C
(a) Enthalpy in with gases
= 9250852.80 Kcal
(b) Enthalpy out with gases:
Table-8.4 Enthalpy out with gases
Component
Kg/hr
Mol.
KMol/hr Cpi at 2300C
ni.cpi
Wt.
ACN
8927.66
53.03
168.35
21.91
3688.55
Aceto
297.81
41.02
7.26
17.43
126.54
HCN
1006.06
27.01
37.27
9.35
348.47
CO2
1417.00
44.01
32.2
10.03
331.66
78
CO
512.81
28.01
8.84
7.13
63.03
H2O
11685.68
18
649.2
7.47
4849.52
C3H6
123.83
42.03
2.95
22.7
66.97
NH3
96.20
17
5.66
9.28
52.53
O2
2055.29
32
64.23
7.27
466.95
N2
45791.48
28
1635.41
7.0
11447.87
Ȉni Cpi = 21773.55
ǻ7 -25=2250C
Enthalpy out with gases
Ȉni Cpi ǻ7
= (21773.55) x (225)
= 4899048.75 Kcal
(c)Coolant Required:
Steam required to cool the effluent at temperature 1100C which is heated upto heated
upto 2000C temperature.
0VWHDP&SVWHDPǻ7
= (Enthalpy out with gases) ± (Enthalpy out with gases )
= (9250852.80) - (4899048.75)
= 4351804.05 Kcal
[Msteam] x [1] x [200-110] = 4351804.05Kcal
Msteam = 48353.38 kg/h
8.4 ENERGY BALANCE AROUND QUENCH COLUMN:
(a) Enthalpy in with product gases:
= 489 9048.75 Kcal
(b) Enthalpy due to heat of reaction:
In the Quench column the neutralization of ammonia using Sulphuric acid take place.
2NH3 + H2SO4
(34.02)
(96.06)
(NH4)2SO4
(138.08)
ǻ+R = -76662 Kcal / Kmol Ammonium Sulphate
Amount of (NH4)2SO4 formed = 390.72 kg/hr[from Material Balance]
Total heat liberated due to reaction
79
= (-76662) x (390.72/138.08)
= - 216927.7 Kcal
(c) Enthalpy out with gases [at top]:
Table-8.5 Enthalpy out with gases [at top]
Component
Kg/hr
Mol.
K
Wt.
Mol/hr
Cpi at 850C
ni.cpi
ACN
8973.66
53.03
167.35
19.78
3309.78
Aceto
297.81
41.02
7.26
17.21
12.94
HCN
1006.06
27.01
37.27
8.88
330.96
CO2
1417.00
44.01
32.2
9.22
296.88
CO
512.81
28.01
8.84
6.98
61.70
O2
2055.29
32
64.23
7.02
450.89
N2
45791.48
28
1635.41
6.96
11382.45
H2O
11864.07
18
881.34
4.73
881.34
C3H6
123.83
42.03
2.95
17.6
51.92
ȈQL&SL ǻ7 -25 = 60 0C
Enthalpy RXWZLWKJDVHV ȈQL&SL ǻ7= 1006731.6 Kcal
(d) Enthalpy out with bottom stream:
ȈQL&SL ǻ7
= (6.5 x 390.72) + (1 x 1762)
[Cp of (NH4)2SO4 =6.5 Kcal /kg]
= 258100.80 Kcal
Heat carried away by H2SO4 polymer neglected in bottom stream as it is very very
small.
(e) Heat required liquefying the water vapor which out from bottom and cool from
230 to 85 0C
= (to cool water vapor to 230 to 100 0C) + (Exchange of latent heat of vaporization)
+ (cool liquid water from 100 to 850C)
= (5236.57 x 1 x 130) + (5236.57 x 550) + (5236.57 x 1 x 15)
80
=3639416.15 Kcal
Enthalpy removed
= (a) - (b) - (c) - (d) - (e)
= 211727.9 Kcal
So, water added
0VWHDP&SVWHDPǻ7
= 211727.9 Kcal
[Msteam] x [1] x [23] = 211727.9 Kcal
Msteam = 9414.96 kg/hr
This is water added to quench column.
8.5 ENERGY BALANCE AROUND AFTER COOLER:
Inlet temperature of gases
= 850C
Outlet temperature for gases
= 400C
Boiling point of ACN
= 780C
Boiling point of Aceto
= 820C
Therefore, at 400C temperature, ACN and Aceto will get condensed.
(a) Heat in with gases
= 1006731.6 K cal
(b) Heat required to condense ACN:
= MACNȜACN
= (8973.66/53.03) x (780)
= 130519.61 Kcal
(c) Heat required to condesese Aceto:
= MACETOȜ ACETO
= (297.81/41.02) X (711)
= 5161.94 Kcal
(d) Enthalpy out with the mixture:
81
Table-8.6 Enthalpy out with the mixture
Component
Kg/hr
Mol.
K
Wt.
Mol/hr
Cpi at 400C
ni.cpi
ACN(L)
8973.66
53.03
167.35
26.87
4496.16
Aceto(L)
297.81
41.02
7.26
21.06
156.82
HCN
1006.06
27.01
37.27
8.66
322.76
CO2
1417.00
44.01
32.2
8.9
286.58
CO
512.81
28.01
8.84
6.97
61.61
C3H6
123.83
42.03
2.95
15.85
46.76
O2
2055.29
32
64.23
7.0
449.61
N2
45791.48
28
1635.41
6.96
13470.45
H2O(L)
11864.07
18
881.34
18
15864.12
Ȉni Cpi = 35154.87
ǻ7 -25=150C
Enthalpy out with gases
Ȉni Cpi ǻ7
= (35154.87) x (15)
= 527323.05 Kcal
(e) Enthalpy absorbed by the water added
= (a) ± (b) ± (c) ± (d)
= 343727.00 Kcal
0ZDWHU&SZDWHUǻ7
Let, cooling water temeperature is 300C is added and out let temperature is 40oC.
Mwater x (1) x (10) = 343727.00
Mwater = 34372.70 kg
So, 34372.70 kg cooling water required.
8.6 ENERGY BALANCE AROUND ABSORBER AND HEAT EXCHANGES:
Inlet temperature of Absorber
= 400C
Outlet temperature of Absorber
= 400C [at top]
Maintain temperature in absorber
= 250C
82
(a) Enthalpy in with feed mixture:
= 527323.05 Kcal
(b) Enthalpy out with unabsorbed gases from top:
Table-8.7 Enthalpy out with unabsorbed gases from top
Component
Kg/hr
Mol.
K
Wt.
Mol/hr
Cpi at 400C
ni.cpi
CO2
1417.00
44.01
32.2
8.9
286.58
CO
512.81
28.01
8.84
6.97
61.61
O2
2055.29
32
64.23
7.0
449.61
N2
45791.48
28
1635.41
6.9
11284.33
123.83
42.03
2.95
15.85
46.76
H2O(G)
11864.07
18
6.03
16.2
97.69
HCN
1006.06
27.01
0.18
8.66
1.56
C3H6
Ȉni Cpi = 1228.14
ǻ7 -25=150C
Enthalpy out with unabsorbed gases
Ȉni Cpi ǻ7
=183422.1 Kcal
(C) Enthalpy out with bottom stream:
Table-8.8 Enthalpy out with bottom stream
Component
Kg/hr
Mol.
K
Wt.
Mol/hr
Cpi at 300C
ni.cpi
CAN (L)
8927.66
53.03
167.33
26.57
4445.96
Aceto (L)
297.81
41.02
7.26
21.34
154.93
HCN
1006.06
27.01
37.27
8.06
320.52
H2O (L)
22644.04
18
1424.66
18
25643.88
Ȉni Cpi = 30565.29
ǻ7 -25 = 50C
Enthalpy out with unabsorbed gases
Ȉni Cpi ǻ7
83
= 152826.45 Kcal
(d) Enthalpy in with lean water:
Mlean water CpH2O ǻ7
= 9888.56 x (1) x (40 -25)
= 148328.4 Kcal
(e) Enthalpy removed by cooling system:
Heat evolved = [Heat in with feed + Heat with lean water]
± [heat out with gases + Heat out with bottom product]
= [(a) + (d) ] ± [ (b) + (c) ]
=339402.90 Kcal
This heat removed by cooling/chilling system. Also this cooling/ chilling system used
by cooling/ chilling side stream from absorber to maintain temperature of absorber
around 250C for better absorption.
Heat exchanger 1:
It is rich water/solvent water exchanger. It increases the temperature of bottom rich
water from 30 to 400C.
Msolvent water CpH2O ǻ7
= Heat out ± Heat in
Msolvent water x (1) x (80-50)
= 459294.3-15826.45
Msolvent water
= 10215.59 kg/hr
Heat exchanger 2:
It is rich water (40oC) /Let water (95oC) exchangers. It preheat the rich water upto
80oC for feeding recovery cooled. (No vaporization assume)
Mlean water CpH2O ǻ7
= Heat out ± Heat in
Mlean water x (1) x (90-85)
= 148328.43
Mlean water
= 9888.56 kg/hr
8.7 ENERGY BALANCE AROUND RECOVERY COLUMN:
(a) Heat in with feed= 148328.43 K cal = F HF
Temperature of column = 85 0C (at top)
(b) Load on reboiler, Qb:
Feed at 800C, It is Saturated liquid.
84
Load on reboiler, Qb = [for vaporization of ACN, Aceto, H2O as distillate]
+ [H.T. in Remaining comp. coming from bottom]
ȈmȜȈni Cpi. ǻT
= [(8873.66 x 147) + (5.96 x 173.68) + (8476.39 x 550)] +
[(177.8+17358.39) x (110-80)]
= 6518895.503 Kcal
/HWVWUHDPLVXVHGLQUHERLOHUDWDWPKDYLQJȜ stream = 550 K cal/kg
Steam required in reboiler
Mstream Ȝ stream = 6518895.503
M stream = 11852.54 kg/hr
(c)Enthalpy out with Distillate: [DHD]
Table-8.9 Enthalpy out with Distillate: [DHD]
Component
Kg/hr
Mol.
K
Wt.
Mol/hr
Cpi at 850C
ni.cpi
CAN (G)
8927.66
53.03
168.35
16.77
2806.12
Aceto (G)
297.81
41.02
0.15
13.5
2.03
HCN (G)
1006.06
27.01
37.27
9.2
320.88
H2O (G)
22644.04
18
470.91
6.19
2914.43
Ȉni Cpi = 6065.97
ǻ7 -25 = 600C
(QWKDOS\RXWZLWKGLVWLOODWH Ȉni Cpi . ǻ7
= 363958.2 Kcal
= D HD
(d) Enthalpy out with Bottoms (W.HW)
Table-8.10 components and their mole fraction
Component
Kg/hr
Mol.
K
Wt.
Mol/hr
Cpi at 850C
ni.cpi
Aceto
291.85
41.02
7.115
24.99
177.8
Water
17167.64
18
955.76
18.02
17358.39
85
Ȉni Cpi = 17536.19
ǻ7 -25 = 85 oC
Enthalpy out with bottoms
Ȉni Cpi . ǻ7
= 1490576.28 Kcal
= W HW
(e) Condenser load:
Top product condensed and then cools upto 40OC
P&Sǻ7PȜP&Sǻ7
Heat removed
O
Boiling point ACN (78 C), Aceto (82OC), So, take 85OC as saturated liquid as
feed.HCN is gas from 85 OC to 40OC and Water 85OC liquid.
Heat removed
= [(8873.66 x 147) + (5.96 x 173.68)+(1001.03 x 210.23)]
+ [(167.33 x 26.3)+(0.15 x 21.91)+(37.27 x 8.7)+(470.91 x 18)] x (85 - 40)
=1737702.92 Kcal
Cooling water required
0FZ&Sǻ7
= 1737702.92
Mcw x (1) x (10) = 1737702.92
Mcw
= 173770.3 kg/hr
8.8 ENERGY BALANCE ON DECANTER:
Enthalpy in Decanter
Table-8.11 Enthalpy in Decanter
Component
Kg/hr
Mol.
K
Wt.
Mol/hr
Cpi at 400C
ni.cpi
CAN (l)
8973.66
53.03
167.33
26.87
2896.16
Aceto (l)
5.95
41.02
0.15
21.6
3.24
HCN (l)
1001.03
27.01
37.27
8.66
322.76
H2O (l)
8476.39
18
470.91
18
8476.38
Ȉni Cpi = 13298.54
0
Enthalpy in Decanter ǻ7 -25 =15 C
86
>Ȉni Cpi @ǻ7
=199478.03 Kcal
Enthalpy out with organic phase
= (4496.16+3.24+322.76+414.5) x (40-25)
= 78987.3 Kcal
Enthalpy out with aqueous phase
= (8061.9 x 15)
= 120928.5 Kcal
8.9 ENERGY BALANCE ON ACETO STRIPPER:
The feed at saturated liquid
(a) Heat in = F HF = 78987.3 K cal
ȈPȜȈni Cpi. ǻ7
(b) Load on reboiler, Qb:
= ((291.85/4 2.03) x 7476.43) + ((125.08/18) x 550) +
(17042.56 x 18 x 10)
= 3123397.9 Kcal
/HWVWUHDPLVXVHGLQUHERLOHUDWDWPKDYLQJȜ stream = 550 K cal/kg
Steam required in reboiler
Mstream Ȝ stream = 31233097.9 Kcal
M stream = 5678.91kg/hr
(c) Enthalpy out with Distillate: [DHD]
R = 1.5
L = 1.5 D
= (1.5) (416.93) kg
= 625.40 kg
G = L+ D
= 1042.33 kg
*Ȝ
= (1042.33) (5398.5)
= 5627019.55 K cal
Mcw.Cp ǻ7
= 5627019.55 kg/hr
Mcw x 1 x 10
= 5627019.55 kg/hr
Mcw
= 562701.96 kg/hr
D HD
>Ȉ0L&pi@ǻ7
87
= [((291.85/42.03) x 17.21) + ((125.08/18) x 18)] x (85-25)
= 14675.02 Kcal
W HW >Ȉ0L&pi@ǻ7
=17042 x 18 x (120-25)
= 29142777.6 Kcal
8.10 ENERGY BALANCES ON HCN COLUMN:Enthalpy input with feed = 78987.3 Kcal
Top temperature= 25oC
Bottom temperature = 80oC
The feed at saturated liquid
(a) Heat in = F.HF = 78987.3 K cal
ȈPȜȈni Cpi. ǻ7
(b) Load on reboiler,Qb:
= [(1001.03 x 210.37) ] + [(1697.33+28.22) + (0.15 x
22.12) + (23 x 17.92)] x (80-40)
= 2143151.90Kcal
/HWVWUHDPLVXVHGLQUHERLOHUDWDWPKDYLQJȜ stream = 550 K cal/kg
Steam required in reboiler
Mstream Ȝ stream = 2143151.90
M stream = 3896.64 kg
(c)Enthalpy out with Distillate: [DHD]
L/D = R
R = 1.1
D = 991.01
L = 1090.11 kg/hr
G=L+D
= 2081.12 kg/hr
mbrine.Cpi ǻ7 *Ȝ
mbrine x (1.6) x (5) = (2081012 x 6008.09)
mbrine = 1562944.53 kg
F HF = 78987.3 K cal
88
D HD = m.Cp ǻ7
ǻ7 , as reference temperature is 25, and distillate has W.HW temperature.)
W.HW = [(167.33 x 29.24)+(0.37 x 8.87) + (23.03 x 19.31)+(0.15 x 23.62)] x (80-25)
= 293934.30 Kcal
8.11 ENERGY BALANCE ON ACN COLUMN:
Feed is saturated liquid at 850C
(a) Heat in = F.HF = K cal
(b) Load on reboiler, Qb: ȈPȜȈni Cpi. ǻ7
= [(167.33 x 7801.29)] + [neglected- as very less ]
= 1305389.85Kcal
/HWVWUHDPLVXVHGLQUHERLOHUDWDWPKDYLQJȜ stream = 550 K cal/kg
Steam required in reboiler
Mstream Ȝ stream = 1305389.85Kcal
M stream = 2373.44 kg/hr
(c)Enthalpy out with Distillate: [DHD]
L/D = 1.7
L = 1.7[8838.38]
= 15025.25
G=L+D
= 23863.63
*Ȝ
= (23863.63) x (7801.29)
= 186167098.1 K cal
mcwCpi ǻ7 .FDO
(mcw) (1) (10) = 186167098.1
mcw= 18616709.80 kg/hr
= Cooling Water flowrate
D.HD >Ȉ0L&pi@ǻ7
= [(8838.38/53.03) x 19.7 x (25)]
= 82083.77 Kcal
W.HW
>Ȉ0L&pi@ǻ7
= [((35.28/53.03) x 19.7) + ((10.01/42.03) x 17.2) + ((414.5/18) x 18)] x
(75) = 32377.5 Kcal
89
Designing for half coil.jacket.
p
= 40 kg/cm2
pd
= 40 x 1.05 kg/cm2
fa
= 980 Kg/cm2
di
= 500 mm
Now,
tc=
pdi
+ Ca
2fa
= 14 mm (standard)
Checking for total circumferential shear :
fps=
p2di
p1Di
+
2ts
4tc+2.5ts
= 610.11 kg/cm2
which is less than 980 Kg/cm2
Hence, it is safe
9.1.2 Checking tower height for various external and internal loads
Data
Height of the reactor
= 13.8 + 2
= 15.8 m
Internal diameter of the reactor = 4.6m
Thickness of shell
= 6mm
Design pressure
= 0.82 Kgf/cm2
J
= 0.85
MOC : Carbon steel
Specific gravity
= 7.7
Corrosion allowance
= 3 mm
(1)
Axial stress due to pressure
fap
=
0.82 x 4600
4x3
= 314.33 Kgf/cm2
92
CHAPTER-10: PROCESS CONTROL & INSTRUMENTATION
10.1 ROLE OF PROCESS INSTRUMENTATION AND CONTROL:
The important feature common to all processes is that process is never in a state of
static equilibrium for more than a very short period of time. A process is dynamic
quantity subject to find to drive it away form the desired state of equilibrium the
process must then be manipulated upon or corrected to drive it back towards the
desired state and thus to maintain the efficiency of the process. Instruments are used
to measure the variable such as temperature, pressure, composition, level, flow rate
etc. In chemical industry it can be operated automatically, semi automatically or
manually.
Now a days must of the plant are controlled automatically by electronic controllers or
by means of computer signals. Now days a DCS plant system is very popular in
industry for controlling the various variables of operations. Plant with DCS system is
highly sophisticated and more accurate result oriented.
Instrument is applied to Acrylonitrile plant involves the use of level controls, flow
rate controllers, temperature controller, pressure controller and automatic control of
process variable. Electronic or pneumatic controller systems are used mostly. The
automatic controller are much more efficient and accurate then manual controller
because it is not possible all the time to controls the variable manually and hence it is
necessary to fix the limit to give the optimum economic operation some of the
operation equipment give alarm with light on the panel. The subsequent control is to
be exercised when temperature, level, pressure, and flow deviates from its operating
sate value.
During the start up and shutdown of the plant and during abnormal and emergency
conditions the plant is operated under manual control when plant becomes steady
state and under normal operation it is operated under auto control.
Automatic control is the norm throughout the chemical industry, and the resultant
savings in labor combined with improved ease and efficiency of operations has more
than offset the added expense of instrumentation.
103
All the operation in a chemical plant depends on the measurement and control of the
process variables. Instruments are used in the chemical industry to measure process
variables, such as temperature, pressure, density, viscosity, humidity, pH, liquid level,
flow rate, chemical composition, specific heat, conductivity and dew point. By use of
instruments having varying degrees of complexity, the values of these variables can
be recorded continuously and controlled within narrow limits.
10.1.1 Instrumentation and Control Objectives:
The primary objectives of the designer when specifying instrumentation & control
schemes are,
(a) Safe plant design:
- To keep the process valuable within known safe operating limit.
- To dictate dangerous situation as they develop in to provide alarms and
automatic shut down systems.
- To provide inter locks and alarms to prevent dangerous operating procedures.
(b) Production rate:
- To achieve the desired production output.
(c) Production quantity:
-To maintain the product consumption within the specified quality
standards.
(d) Cost:
-To operate at the lower production cost, commensurate with the objectives.
But sometimes it may be better strategy to product a better quality at a higher cost.
(e) Labour:
- The process can operate with less labour power and hence lower the operating
cost.
In a typical chemical processing plant, these objectives are achieved by a
combination of control, manual monitoring & laboratory analysis.
10.2 PROCESS MEASUREMENT:
Process measurements encompass the application of the principles of metrology to
the process in question. The objective is to obtain values for the current conditions
within the process and make this information available in a form usable by either the
104
control system or process operators, or any other entity that needs to know. Process
measurements fall in two categories:
10.2.1 Continuous measurements:
Most process control application in continuous processes rely on continuous
measurements. The components of a typical continuous measurement device are
sensor, transmitter and signal processor. The sensor produces a single that is related
in a known manner to the process variable of interest. The single processor linearizes
this relation and compensates for effect of other variables. The transmitter generates a
signal that can be transmitted over some distance.
10.2.2 Discrete measurements:
In batch processes, discrete measurements are more widely used. These
measurements are also used in safety interlock for both continuous as well as batch
processes.
10.3 TEMPERATURE CONTROL:
Measurements of the hotness or coldness of a body or fluid is commonplace in the
process industries. Temperature measuring devices utilize systems with properties
that vary with temperature in a simple, reproducible manner. Temperature can be
determined by measuring several physical properties as the specific volume of fluid,
electrical resistivity of metal, thermoelectric potential at the junction of a pair of
dissimilar metals, colour comparison or light wavelength.
Table-10.1 Temperature ranges for certain instruments:
Thermocouple
200oC to 1820oC
pyrometers
1300oC to 250oC
vapor pressure thermometer
85oC to 425oC
mercury in glass thermometers
27oC to 400oC
Bimetal thermometers
180oC to 580oC
Thermistors
upto + 300oC
Resistance thermometers
200oC to 850oC
105
10.4 PRESSURE CONTROL:
Pressure control will be necessary for most systems handling vapor or gas, the
method of control will depend on the nature of the process.
Safety of chemical plants depends upon the timely measurement of pressure and its
control at a specified level. Any excess pressure development than the design
pressure may damage the equipment in addition to the fire and other explosion
hazard. Pressure can be in absolute, gauge, vacuum or differential form. Process
pressure measurement devices are divided into three groups:
(A) Devices based on measurement of height of a liquid column.
(B) Devices based on measurement of distortion of an elastic pressure chamber.
(C) Electrical sensing devices.
Monometers: (U-tube, Differential, Inclined) fall into first category. Bourdon tubes,
bellows and diaphragm fall into second category. Strain gauges, piezoelectric
transducers etc. fall into third category.
10.5 LEVEL CONTROL:
In any equipment where are interface exists between two phases some means of
maintaining the interface at the required level must be provided.
The measurement of level can be defied as the determination of the location of the
interface between two fluids, separable by gravity, with respect to a fixed datum
plane. The most common level measurement is that of the interface between a liquid
and gas. Other level measurements frequently encountered are the interface between
two liquids, between a granular or fluidized solid and gas, and between a liquid and
its vapor. Float actuated devices, head devices, electrical methods, sonic methods and
thermal methods are used for level measurements.
This may be incorporated in the designing of the equipment, as is usually done for
decanters or storage tanks or by automatic control or the flow from the equipment.
10.6 FLOW CONTROL:
Flow defined as volume per unit time at specified temperature and pressure
conditions, is generally measured by positive displacement of rate meters. The
principal classes of flow measuring instruments used in the process industries are
106
variable head, variable area, positive displacement and turbine instruments, mass
flowmeter, vortex-shedding and ultrasonic flowmeters, magnetic flowmeters, and
more recently, coriolis mass flowmeters.
Orifice meter, venturimeter and pitot tube are the most common head flow meters and
rotameter is an area flowmeter. In head flowmeter, area available for flow is variable
which in area flowmeters, it is a constant quantity.
Flow control is usually associated with inventory control in a storage tank or other
equipment. There must be a reservoir to tank up the change in flow rate. To provide
flow control on a compressor or pump running at a fixed and supplying a near
constant volume out put a by pass control would be used.
10.7 ALARMS AND SAFETY TRIPS AND INTERLOCKS:
Alarms are used to alert operations of serious and potentially hazardous deviations in
process conditions. Key instruments are fitted with switches and relays to operate
audible and visual alarms on the control panels and annuciator penels, where delay or
lack to the rapid development of a hazardous situation, the instrument would be fitted
with a trip system to take action automatically to prevent the hazard, such as shutting
down pumps, closing valves, operating emergency systems.
The basic compounds of the automatic trip system are :
1.
A sensor to monitor the control variable & provide an out put signal when a
present valve is exceed the instrument.
2.
A link to transfer the signal to the actuator usually consisting a system of
pneumatic or electric relays.
3.
An actuator to carry out the required action: close or open valve switch of a
motor.
10.8
INSTRUMENTATION
AND
PROCESS
CONTROL
FOR
ACRYLONITRILE REACTOR:
The reactor is a fluidized bed catalytic gas-solid reactor. The instrument s and
controls provided over and around this reactor are discussed as follows.
The feed to reactor is,
107
Air
= 2.2 kg/cm2 and 170oC
Propylene
= 2.5 kg/cm2 and 56oC
Ammonia
= 2.3 kg/cm2 and 65oC
Air is heated in start-up heater, the outlet temperature recorded by temperature
recording controller (TRC-1) which control he Burner System used for heating
purpose.
Propylene and Ammonia is heated n super heater using steam. The steam flow rate is
controlled by temperature recording controller (TRC-2 & 3).
Air propylene and Ammonia flow rate as feed to reactor is controlled by flow
recording controllers (FRC 4 and 5, 6). The flow rate of air is maintained by venting
air to atmosphere by anti surge flow which is controlled by flow controller (FIC-7).
The pressure of Propylene and Ammonia is controlled by pressure indicating
controllers (PIC-8 & 9). The pressure of air outlet from air compressor is controller
with pressure indicating controller (PIC-10) by regulating the speed of compressor.
The temperature of Reactor is obtained on the temperature indicator and recorder
(TR-11) from a thermocouple mounted on reactor shell.
The pressure of reactor is indicated by pressure indicator and recorder (PR-12)at top
of reactor.
The reactions in reactor exothermic. So temperature of reactor changes as reaction
proceeds. We must provide temperature indication controller (TIC-13) which controls
the inside temperature of reactor by providing proper coolant flowrate into steam
coils in the reactor to remove heat evolved during reaction.Level indicator (LR-14)
indicates the level of fluidized bed in the reactor.
10.9 INSTRUMENTATION AND PROCESS CONTROL FOR OTHER
EQUIPMENTS:
10.9.1Distillation Column Control:The primary objective of distillation column is to maintain the specified composition
of the top & bottom products and side steams co-relating to the Effects of distillation
in:
108
1) Feed flow rate, composition & temp.
2) Stream supply pressure.
3) Cooling water pressure & Heating temp.
4) Ambient conditions, which cause change in internal reflux.
A variety of the control schemes are used to Distillation column control for
continuous, versatile control of distillation column processes, the requirement
generally adopted is the constant temp profile in the column. This ensures
preservation of equilibrium between the liquid & vapour phase in the column. The
relevant variables to maintain this profile is pressure, boil up rate, reflux ratio &
reflux temp. Although composition control by direct analysis of the product streams
is feasible. It is practiced due to the expenses of metering equipment of & because of
the intolerable response lime for accurate control purpose. Product sample be
analyzed by chromatographic or other techniques, however, as a periodic check on
quality.
Any change vapor flow rate upward through the column is due to variation in boil up
rate will alter the press at the top of the column and this provides a basic for control
of the boil up rate by regulation of reboiler steam pressure using a pressure controller.
The reflux rate will be controlled using measurement of liquid level in the reflux
drum to control total condensate flow and measurement of liquid level in the reflux
drum to control total condensate flow and measurement and comparison of both
distillate and reflux rates to ensure that the specified reflux ratio is maintained.
Control of the reflux stream temperature will be achieved by the use of the temp.
Controlled which actuates the cooling water inlet valve of the condenser.
109
CHAPTER-11: SAFETY & POLLUTION CONTROL
11.1 SAFETY AND POLLUTION CONTROL:
Any organization has la legal and moral obligation to safe guard the health and
welfare of its employees and the general public. Safety is also good business; the
good management practice needs to ensure safe operation will also ensure efficient
operation.
All manufacturing processes are to some extent hazardous, but in chemical processes
there are additional, special hazards associated with the chemical include toxicity,
flammability, explosions, sources of ignition, pressure variations, temperature
variations and noise.
Toxic and corrosive chemicals, fires explosions and mechanical equipment are the
major health and safety hazards encountered in the operation of plants in the process
industries. Maximum protection must be provided to the plant personal and there
must be a maximum chance of occurrence of accidents.
11.2 CHEMICAL HAZARDS:Many chemicals can cause dangerous burns if they come in contact with tissues.
Dehydration by strong dehydrating, agents, digestion by strong acids and bases and
oxidation by strong oxidizing agents can destroy living tissues. Eyes and the mucous
membranes of the nose and throat are particularly susceptible to the effects of
corrosive dusts, mists and gases. Tolerance levels of toxic chemicals and explosive
limits for various flammable materials must be known.
11.3 FIRE AND EXPLOSION HAZARD:Careful plant layout and judicious choice of constructional material reduced the
chance of this hazard. Hazardous operation should be designed to meet the
specification and codes. Adequate venting is necessary and it is advisable to provide
protection by using both spring loaded values and rupture disks.
Possible sources of fire are reduced by eliminating all unnecessary ignition sources
such as flames, sparks of heated, materials, matches, smoking, welding, cutting static
110
electricity spontaneous combustion and non explosion proof electrical equipment are
all potential ignition sources.
Fire alarms, temperature alarms, fire fighting equipment and sprinkler system must be
available readily in the plant. First aid stations, protected walk ways and work areas
should be provided in the final plant.
11.4 AIR AND LAND POLLUTION:Electrostatic precipitators, venturi scrubbers cyclones, sonic agglomerators,
scrubbers, washers and many other kinds of equipment and treating methods should
be used to remove atmospheric contaminants from waste gases. Incineration and
burying in concrete encased blocks are possible solution for dangerous solid wastes.
Transportation to uninhibited regions is solution form other types of solid waste.
11.4.1 Water Pollution:Dissolved inorganic slats, acid and alkalis suspended solids and floating matter,
oxygen-consuming materials, other toxic materials taste and color producing
materials etc. must be.
11.5 SAFETY IN PLANT:
There are primarily two types of major hazards in petrochemical industry:
a. The first is due to flammability low flash point and wide explosive limits of the
chemicals handled and
b. Toxic hazard due to toxicity and carcinogenicity of various chemicals.
Complete understanding of the chemicals, their physical and chemical properties,
especially with respect to reactivity, is very important for their safe handling.
Mankind today is used great deal comfort which would have been beyond the
imagination of our ancestors. Today petrochemicals are part and parcel of our daily
lives. The contribution of petrochemicals to modern civilization is immense. We
cannot imagine the chaos that would ensue if petrochemicals suddenly cease to exist.
Hence, despite the hazards, we must continue to produce petrochemical. The industry
has to expand, develop and operate continuously if the growth of civilization is
continuing unabated. The primary objective in achieving the above goals is to tame
111
the hazards. For this it may be necessary to change the work situation, to choose
designs and methods of working which eliminate or reduce these hazards.
Concept of Inherently Safer Plants:
7KH FRQFHSW LQ WKH GHVLJQ SI SHWURFKHPLFDO SODQWV KDV VZLWFKHG IURP ³,QWULQVLFDOO\
6DIH´WR³,QKHUHQWO\6DIHU´3ODQWVWKLVGRHVQRWPHDQWKDWWKHUH should be a ban on
plants which handle hazardous materials or contain large inventories. It is merely
suggested that we should:
Consider the alternative processes while selecting the technology
Innovate in the design of equipment which make s the operations simpler and less
hazardous and
Make low inventory one of our main aims.
,IZHDSSO\WKHDERYHFRQFHSWRI³,QKHUHQWO\6DIHU´SODQWVDWWKHYHU\EHJLQQLQJRID
project, we may be able
To choose a route that avoids the use of hazardous raw materials or intermediates
To choose or develop equipment design which does not require larger quantities of
materials in process.
Alternative Route of Production:
As in Acrylonitrile plant use Sohio Process which handle less quantity of HCN highly
poisonous material compare to other manufacturing process as alternative technology.
11.6 CONCEPT OF SAFER DESIGNS:
In the design of the equipment for hazardous petrochemical plants, it is possible to
reduce the hazards by utilizing certain innovations which will reduce the inventory of
hazardous chemicals. These are simple and help to achieve the required objective.
Below are observations which will help in this direction:11.6.1 Reactor Design:
A tubular reactor is safer than a pot reactor. For a 20,000 MTA plant, a 5 cm diameter
tubular reactor is sufficient with 1 meter per second velocity. In IPCL, Baroda
complex an 80,000 MTPA low density polyethylene plant has a tubular reactor size of
5 cm only. If the rupture disc blows up because of decomposition, the total volume
released into the atmosphere is only about 300-600 kg which is easy to control
112
Vapor phase reactors may be developed to liquid phase reactors.
Sometimes larger reactors are required because the conversion may be low or the
mixing is poor. It may be possible to improve the conversion by changing the
parameters or incorporating better methods of mixing.
11.6.2 Distillation Columns:
Inventory in distillation columns can be reduced by:
Incorporating a narrow base
Internal calendrias.
Combining two distillation stages in one.
11.6.3 Exchangers:
Inventory of hazardous materials can be reduced:
By putting more hazardous materials in tubes.
Use of higher flow rates.
Use of extended surface exchangers
Higher temperature differences.
11.6.4 Storage in Safer Form:
Hazardous chemical can be stored or used in less hazardous forms.
Store materials in less hazardous form using coolant, inhibitor or other additives.
Keep suitable environment to store materials.
11.6.5 Safer Designs:
Overhead condensers and reflux by gravity and withdrawal of product etc. by gravity
will reduce the pressure handling increase safety. Sometimes it may be possible to
dispense with relief valves and all that comes after them by using strong vessels,
strong enough to withstand the highest pressure that can be reached. Similarly instead
of installing vacuum relief valves we can make vessels to withstand full vacuum.
11.7 PREVENTION AND CONTROL OF HAZARDS IN ACRYLONITRILE
PLANT:
Acrylonitrile is produced by ammoxidation of propylene in a fluidized bed reactor
using bismuth molybdenum based catalyst. Hydrocyanic acid (Hydrogen cyanide)
113
and acetonitriel are the co products of ammoxidation of propylene. The extreme
toxicity of hydrocyanic acid is well known. Added to this, the low boiling point and
tendency f HCN to polymerize violently has led us to take extreme care in handling
this hazardous chemical. Of late, Acrylonitrile, once considered a harmless chemical,
is now being designated as carcinogenic.
Safety Aspect at Design Stage:
11.7.1 Fire and explosion:
(1) The reaction is vapor phase reaction, being an oxidation reaction. The reactor
and its associated equipment are very prone to the hazard of explosion. Apart
from normal operation, start-up and shutdown of the reactor are the most
critical stages. Before start-up, the organic content downstream of reactor is
checked in quench column, to avoid formation of explosive mixture when air is
diverted.
(2) The ratio of ammonia to air is fixed in such a way that effluent from the reactor
contains oxygen much below the explosive limit of ammonia and oxygen. Only
when oxygen content falls below seven percent is propylene added to the
reactor. Cooling coils are taken not operation to control the reactor
temperature.
(3) All the safety valves from the column and propylene system are connected to a
hydrocarbon flare which passes through a water seal drum is connected to a
closed toxic sewer system. The safety valves are purged with nitrogen to avoid
stagnancy of acrylonitrile/HCN, which on polymerization block the outlet. The
flare is also provided with a molecular seal to eliminate the chance of flash
back.
11.7.2 Environmental Hazard:
(1) Acrylonitrile, hydrogen cyanide and acetonitriel present environmental
hazards. Detailed engineering is done keeping in view the minimum leakages.
All the pumps handling aqueous stream are provided with single mechanical
seals and those handling organics are provided with double mechanical seals.
114
The outlet of seals is connected to a closed toxic sewer which is reprocessed in
the plant to recover the organics.
(2) All the floor washing including the water from the plant area are collected in
big pits each, and only after testing for cyanide, COD and pH are they sent to
the effluent channel. If needed provision also exist for incinerating the storm
water.
(3) All the column blow downs from the plant are incinerated. The incinerator
temperature is kept at 700-8000C to burn all the organics.
(4) Acrylonitrile plant should have flare as stand by for hydrocyanic acid vapors.
The HCN-rich gases are normally sent to the incinerator. In case of incinerator
stoppage HCN is automatically diverted to flare. Flare tip is provided with
temperature sensing and alarm in the control room to indicate whether pilot
burner is on or not.
(5) HCN purification section is kept running only when there is demand. A policy
decision has been taken not to keep any inventory for HCN.
(6) Fortunately HCN area is provided with water deluge system with two
independent supply sources and can be operated from control room. The deluge
system is placed in such a way as to cover the complete HCN area.
(7) Separate low temperature system is installed to cool HCN to zero or subzero
temperature.
11.7.3 Routine Checks:
The safety systems provided for the plant are periodically checked for healthiness.
(1) The reactor start-up and operation checklist includes the testing of safety
systems connected with reactor.
(2) The oxygen analyzer is calibrated twice a week
(3) The environment air is sampled with draeger tube periodically to detect leaks.
(4) The water deluge system is checked every week.
(5) The safety valves are regularly checked for setting.
115
11.7.4 Manpower Training and Structure:
(1)
An important aspect in reducing the hazards in operation and handling in
the petrochemical industry is educating the people involved and making them
follow certain set procedures by incorporating certain checklists so that
chances of human errors are further eliminated. Periodic training of the
personnel and religious following of the checklists are part of the routine.
(2)
In each plant there should be a separate independent Safety Engineer to
monitor and ensure that the safety procedures are strictly followed. The Safety
Engineer reports to the Safety Department though he is selected from among t
operating personnel.
(3)
Each plant should have a Safety Committee which will meet at least once in
a quarter to identify the hazardous areas in both maintenance and operation.
Suggestions for improving work situations should be discussed and considered.
A list of such suggestions should be making, implemented and monitored by
the Safety Engineer.
(4)
Periodical medical check-ups of the plant personnel should be carried out
and recorded for monitoring.
11.7.5 Other Safety Measures:
As operation of the plant continues many areas where enough attention was not given
during the design stage will be revealed. These areas are then identified and necessary
modifications carried out for improving safety.
Some modifications which are being carried out in ACN Plant:
(1) Low temperature storage with high temperature alarm in control room, for higher
stability of chemicals and reduction of environmental pollution.
(2) Arrangement for short stops as a secondary safety measure in case of failure of the
above.
(3) Scrubber on the vents to reduce pollution and exposure of operating personnel.
(4) Extension of water sprays systems to cover more areas which absorb HCN on
leakage.
116
(5) Seal less pumps for reducing environmental pollution and for safety of operating
personnel.
11.7.6 Conclusion:
We realize and agree that petrochemicals are going to stay with us in various forms.
We cannot discard them just because there are hazards encountered in their
production and handling. We try to change out concept in the design of petrochemical
plants from intrinsically safe to inherently safer plants. The following guidelines have
been given by Kletz for controlling hazardous materials.
a. Avoid them (substitution).
b. Use less of them (intensification).
c. Use them under conditions which make them less hazardous (attenuation).
d. Contain them, so that they do not leak out.
e. Control leaks ± by emergency isoration, open plants to encourage dispersion.
f. Survive leaks ± by fire protection, fire fighting etc.
In short there are three choices before us:
1. We can do without chemical plants and their products and the benefits and
risks they bring to mankind but it would be a journey back in time.
2. We can try to work out the risks and play safe. But the situation will never be
completely safe.
3. We can try to change the work situation, choose designs and methods of
working which eliminate or reduce the hazards and proceed with the venture.
11.8 ACRYLONITRILE (CH2 = CHCN):
11.8.1 Characteristic:
We discussed in chapter 1 about characteristics of acrylonitrile
Odor:
Colorless to pale yellow liquid with a pungent odor which can only be detected at
concentrations above the permissible exposure level, in a range of 13-19 parts
Acrylonitrile per million parts of air (13-19 ppm).
117
11.8.3 Exposure may not exceed either:
1. Two parts Acrylonitrile per million parts of air (2 ppm) averaged over eight-hour
workday; or
2. Ten parts Acrylonitrile per million parts of air (10 ppm) averaged over any 15minute period in the workday.
3. In addition, skin and eye contact with liquid Acrylonitrile is prohibited.
11.8.4 Symptoms:
Dermatitis, lacrimation (flow of tears), headache, weakness, vomiting, diarrhea,
jaundice, suffocation, fatal.
11.8.5 Health Hazard Data:
(a) Acrylonitrile can affect your body if you inhale the vapor (breathing), if it comes
in contact
with your eyes or skin, or if you swallow it. Acrylonitrile is highly toxic
if ingested. It is extremely irritating and corrosive to skin and eyes. It may enter your
body through your skin.
(b) Effects of Overexposure:
1) Short-Term Exposure: Acrylonitrile causes eye irritation, nausea, vomiting,
headache, sneezing, weakness, and lightheadedness. At high concentrations, the
effects of exposure may go on to loss of consciousness and death. When acrylonitrile
is held in contact with the skin after being absorbed into shoe leather or clothing, it
may produce blisters following several hours of no apparent effect. Unless the shoes
or clothing are removed immediately and the area washed, blistering will occur.
Usually there is no pain or inflammation associated with blister formation.
2) Long-Term Exposure: Acrylonitrile is categorized as a cancer hazard by OSHA. It
has been determined to be carcinogenic to laboratory animals and mutagenic in both
mammalian and non-mammalian tests. Genetic transformations and damage have
been reported in tissue cultures exposed to acrylonitrile. Animal tests show that it is a
reproductive toxicant only at maternally toxic doses. Repeated or prolonged exposure
of the skin to acrylonitrile may produce irritation and dermatitis.
118
Permissible exposure limits for acrylonitrile in the United State are 2 ppm for and 8-h
time weighted average concentration and 10 ppm as the ceiling concentration for a 15
min period.
3) Reporting Signs and Symptoms: You should inform your employer if you develop
any signs or symptoms which may be caused by exposure to acrylonitrile.
11.8.6 Emergency First-aid Procedures:
(1) Eye Exposure: If acrylonitrile gets into your eyes, wash your eyes immediately
with large amounts of water, lifting the lower and upper lids occasionally. Get
medical attention immediately. Contact lenses should not be worn when working with
this chemical.
(2) Skin Exposure: If acrylonitrile gets on your skin, immediately wash the
contaminated skin with water. If acrylonitrile soaks through your clothing, especially
your shoes, remove the clothing immediately and wash the skin with water. If
symptoms occur after washing, get medical attention immediately. Thoroughly wash
the clothing before re-using. Contaminated leather shoes or other leather articles
should be discarded.
(3) Inhalation: If you or any other person breathes in large amounts of acrylonitrile,
move the exposed person to fresh air at once. If breathing has stopped, perform
artificial respiration. Keep the affected person warm and at rest. Get medical attention
as soon as possible.
(4) Swallowing: When acrylonitrile has been swallowed, give the person large
quantities of water immediately. After the water has been swallowed, try to get the
person to vomit by having him touch the back of his throat with his finger. Do not
make an unconscious person vomit. Get medical attention immediately.
(5) Rescue: Move the affected person from the hazardous exposure. If the exposed
person has been overcome, notify someone else and put into effect the established
emergency procedures. Do not become a casualty yourself. Understand your
emergency rescue procedures and know the locations of the emergency equipment
before the need arises.
119
(6) Special First-Aid Procedures: First-aid kits containing an adequate supply (at
least two dozen) of amyl nitrite pearls (impulse), each containing 0.3 ml, should be
maintained at each site where acrylonitrile is used. When a person is suspected of
receiving an overexposure to acrylonitrile, immediately remove that person from the
contaminated area using established rescue procedures. Contaminated clothing must
be removed and the acrylonitrile washed from the skin immediately. Artificial
respiration should be started at once if breathing has stopped. If the person is
unconscious, amyl nitrite may be used as an antidote by a properly-trained individual
in accordance with established emergency procedures. Medical aid should be
obtained immediately.
11.8.7 Emergence Treatment and Measures:
(1) Hygienic Precautions: Adequate ventilation. No food and smoking in working
area.
Preclude from exposure those individuals with pulmonary and lever diseases.
(2) Hygienic Treatments (First Aid): Remove immediately the exposed personnel
from the contaminated area. Wash promptly the skin with abundant soap and water.
Irrigate eyes completely with water. Administer artificial respiration followed by
inhalation f amyl nitrile every 5 minutes. Treat the patient with 10 cc of 3% sodium
nitrile dose intramuscularly within 2 minutes followed by administration of 50 cc of
25% sodium thiosulfate in the same way. Hospitalize. Treat accidental swallowing by
inducing vomiting orally using 1% sodium thiosulfate followed by injecting 50cc of
25% sodium thiosulfate intravenously.
11.8.8 Fire Hazards:
It is highly ignitable and flammables. Its ignition point of water solution are (2%) 211
o
C, (3%) 12 oC, (5%) below 9 oC. It is polymerized violently in presence of
concentrated alkalis. Extreme care is needed if it is treated with strong alkali.
Acrylonitrile tends to polymerize even at room temperature by light, gives high heat
and a container may rupture on polymerization.
120
Fire extinguishments:
Fight a fire a safe distance. i) 8VHH[WLQJXLVKHUVRIGU\FKHPLFDO³DOFRKRO´IUDPRU
carbon dioxide. ii) Shut off source of supply. iii) Use dry chemical, CO2 or foam.
iv) Water may be ineffective, but useful to cool fire-exposed containers. Keep
surrounding area cool under water fog.
11.8.9 Respirators and Protective Clothing:
(1) Respirators: You may be required to wear a respirator for non-routine activities,
in emergencies, and while your employer is in the process of reducing acrylonitrile
exposures through engineering controls. If respirators are worn, they must have a
label issued by the National Institute for Occupational Safety and Health (NIOSH)
under the provisions of 42 CFR part 84 stating that the respirators have been
approved for use with organic vapors. For effective protection, respirators must fit
your face and head snugly. Respirators should not be loosened or removed in work
situations where their use is required.
Acrylonitrile does not have a detectable odor except at levels above the permissible
exposure limit. Do not depend on odor to warn you when a respirator cartridge or
canister is exhausted. Cartridges or canisters must be changed daily. Reuse of these
may allow acrylonitrile to gradually filter through the cartridge and cause exposures
which you cannot detect by odor. If you can smell acrylonitrile while wearing a
respirator, the respirator is not working correctly. Go immediately to fresh air. If you
experience difficulty breathing while wearing a respirator, tell your safety officer.
(2) Supplied Air Suits: In some work situations, the wearing of supplied-air suits may
be necessary. Your employer should instruct you in their proper use and operation.
(3) Protective Clothing: You must wear impervious clothing, gloves, face shield, or
other appropriate protective clothing to prevent skin contact with liquid acrylonitrile.
Where protective clothing is required, your employer is required to provide clean
garments to you as necessary to assure that the clothing protects you adequately.
Replace or repair impervious clothing that has developed leaks. Acrylonitrile should
never be allowed to remain on the skin. Clothing and shoes which are not impervious
121
to acrylonitrile should not be allowed to be contaminated with acrylonitrile, and if
they do, the clothing and shoes should be promptly removed and decontaminated. The
clothing should be laundered or discarded after the acrylonitrile is removed. Once
acrylonitrile penetrates shoe leather, or other leather articles, the article should not be
worn again.
(4) Eye Protection: You must wear splash-proof safety goggles or face shields in
areas where liquid acrylonitrile may contact your eyes. In addition contact lenses
should not be worn when working with acrylonitrile.
11.8.10 Precautions for Safe Use, Handling, and Storage:
(1) Temperature: Acrylonitrile is a flammable liquid and its vapors can easily form
explosive mixtures in air. Safe storage temperature is 25oC.
Do not store uninhibited Acrylonitrile. It is not stable unless stabilizer is added (i.e.
Aqua ammonia or MEHQ). It polymerizes fast with exothermic reaction.
(2) Container: Acrylonitrile must be stored in tightly-closed containers in a cool,
well-ventilated area, away from heat, sparks, flames, strong oxidizers (especially
bromine), strong bases, copper, copper alloys, ammonia, and amines. Protect
containers against physical damage.
Store drum on end with bungs up, no more than two layers.
Preferably seal with inert gas such as nitrogen.
(3) Fire protection: Sources of ignition such as smoking and open flames are
prohibited wherever acrylonitrile is handled, used, or stored in a manner that could
create a potential fire or explosion hazard. You should use non-sparking tools when
opening or closing metal containers of acrylonitrile, and containers must be bonded
and grounded when pouring or transferring liquid acrylonitrile.
Fire extinguishers and quick drenching facilities must be readily available, and you
should know where they are and how to operate them.
(4) Body protection: You must immediately remove any non-impervious clothing
that becomes contaminated with acrylonitrile, and this clothing must not be rewash
until the acrylonitrile is removed from the clothing. Impervious clothing wet with
122
liquid acrylonitrile can be easily ignited. This clothing must be washed down with
water before you remove it.
If your skin becomes wet with liquid acrylonitrile; you must promptly and thoroughly
wash or shower with soap or mild detergent to remove any acrylonitrile from your
skin.
If you handle acrylonitrile, you must wash your hands thoroughly with soap or mild
detergent and water before eating, smoking, or using toilet facilities.
You must not keep food, beverages, or smoking materials nor are you permitted to eat
or smoke in regulated areas where acrylonitrile concentrations are above the
permissible exposure limits.
Ask your supervisor where acrylonitrile is used in your work area and for any
additional plant safety and health rules.
(5) Spills and Leakage:
(a) Absorb with papers. Allow to evaporate on a glass or iron dish in a hood. Dispose
by burning the paper.
(b) Add excessive sodium hydroxide and calcium hypochlorite solution on. Transfer
into a large beaker. After one hour, drain in to the sewer with sufficient water and
wash the split site.
(6) Disposal and Waste Treatment: Add by stirring excessive alcohol sodium
hydroxide. After one hour, evaporate alcohol and add sufficient calcium hypochlorite.
After 24 hours drain into the sewer with abundant water.
11.9 ACETONITRILE: Safety data sheet
(A)Characteristics:
1)
Flash point
: 55oC
2)
Auto ignition temperature
: Not Known
3)
Flammable limits
: Lower ± 4.4%, Upper ± 16%
4)
TVL
: 40 ppm
(B) Health Hazards:
Highly toxic when ingested and can be absorbed through skin and respiratory tract.
Inhalation cause headache, nausea, loss of consciousness or dizziness.
123
(C) Fire Hazard:
Dangerous when exposed to heat or flame. When heated to decomposition it emits
highly toxic fumes of cyanides and react with water steam r acids to produces toxic
flammable vapors.
(D) Safe Handling:
Keep away from heat and flame. Use self contained breathing apparatus. War full
protective clothing.
(E) Fire extinguishments:
Use dry FKHPLFDO µ$OFRKRO IRDP¶ RU &22 extinguisher. Wear special protective
clothing.
(F) First Aid:
Remove the patient to the fresh air. In case of skin contact, wash with plenty of water.
In all cases report to Medical Center.
11.10 HYDROGEN CYANIDE:
(A) Characteristics:
1) Flash point
: 0oc
2) Auto ignition temperature
: 535.7oc
3) Flammable limits
: Lower ± 6%, Upper ± 41%
4) TLV
: 10 ppm
(B) Health Hazard:
HCN is one of the most lethal chemical of cyanide group. When HCN is inhaled or
ingested Cyanide group is liberated which combines with hemoglobin in blood and
reduces the capacity of blood to transport oxygen and causes death.
Following special provisions must be kept to handle HCN safely.
1) HCN leak emergency siren is provided. Regular testing of this system is
done once in a week.
2) Water spray deluge system is provided at various locations in the plant.
3) On line HCN leak monitoring system is provided at various points in
piping carrying HCN.
4) The ventilate above HCN incinerator should be high enough.
124
5) In HCN section all lines are sloping so that no HCN accumulates in pipe
lines.
6) All control valves in HCN section are below seal type so that no leakage
from its gland/steam is possible.
11.11 AMMONIA:
(A)Flammability:
: 651oC
Ignition temperature
Explosive limits
NH3 ± O2 mixture (at 20oC, 101.3 KPa) = 15.79 Vol % NH3
NH3 ± Air mixture
At 0oC, 101.3 KPa)
o
At 100 C, 101.3 KPa)
= 16 -27 Vol % NH3
= 15.5 ± 28 Vol % NH3
The presence of oil of other combustible materials will increase the fire hazards.
Readily combines with either silver oxide or mercury to form explosive compounds.
Toxicity:-
TLV ± 50 ppm
TDL: Inhalation ± human (ihl ± hmn) LCL: 1000 ppm/3h
ihl ± hmn TCL : 20 ppm TFX : Irritation
ihl ± hmn TCL : 1000 mg/kg TFX : Carcinogenic
(B) Heath hazards:
Symptoms:
Affects sensitive membranes of the eyes, nose, throat and lungs depending on
concentration. Because of its great attractively to water, it is particularly irritating to
moist skin surfaces. Liquid ammonia may cause severe injury by freezing the tissues
and subjecting it to caustic action. Inhalation in high concentration may cause edema
of respiratory tract, fit of the glottis and suffocation. Highly irritant and erosive to
skin and mucous membranes which may affect deeply into the tissues.
Visual disorder may occur by contact to the eyes. It may cause headache, vomiting,
cough and difficulty in breathing.
(C) Handling and Storage:
Ammonia is stored in liquid state by two methods
125
1.
Pressure storage at ambient temperature in spherical or cylindrical
pressure vessel
Atmospheric storage at 33oC in insulating cylindrical tanks.
2.
Outdoors or detached storage is preferred. Indoor storage should be in a cool, will
ventilated, non combustible location, away from all possible sources of ignition and
separate from other chemicals particularly oxidizing gas, chlorine, bromine, iodine
and acids. Cylinders should be protected from direct sunlight and all possible
precessions.
Hazardous reaction with:
Substance
Condition
Reaction
Remarks
Halogens
Contact
Explosion
Halogenated Nitrogen formed.
Chlorated
Formulates Explosion Ammonium chlorate is liable to explosion.
Wear face shied, chemical cartridge, respirator, rubber gloves and boots.
(D) Emergency Treatment and Measures:(A)Hygienic precaution: preclude from exposure for those individuals affected
with eye and pulmonary diseases.
(B)Hygienic Treatments (First Aid): Irritate eyes with water and instill droplets of
olive oil. Forcible removal of frozen clothing may tear the skin badly hence
proper precaution must be taken while undressing. Wash contaminated area of
body with soap and water. Oxygen should be taken up with sue of intermitted
positive pressure breathing apparatus.
(C)Fire precautions: Use water to keep fire exposed container cool and also to
protect the men affected.
Spills and leakage: Neutralize with HCl, wipe mop or use, water aspirator. Drain into
a sewer with sufficient water.
Disposal and waste Treatment: Pot into large vessel containing water and neutralize
with HCl. Discharge into a sewer with sufficient water.
11.12 GENERAL SAFETY ASPECTS IN CHEMICAL PLANT:
How to handle Chemicals: Be serious!
«DQGEHFDUHIXODURXQGFKHPLFDOVDWDOOWLPHV
126
Presently, the techniques used for the treatment of such a hazardous waste are either
Incineration or Extensive chemical Treatment. Both of these methods are very costly
and hence, an alternative economical method has been suggested in this paper.
Initially, the pretreatment of hazardous waste should be done by hot alkali digestion
and chemical coagulation so the COD/BOD and ACN contents could be reduced
considerably. Such a pretreated waste effluent stream should then, be treated
biologically. This treatment consists of two stages biologically. This treatment
consists of two stage biological extended aeration system, where in bio-oxidation
takes place. Approximately 85 to 90% reduction in COD and Cyanide level is
achieved. By treating toxic cyanide waste by this method, considerable reduction in
operating cost is expected.
Thus, as could be observed from the above data, this stream contains high
concentration of organic cyanides along with high COD/BOD value.
Treatments:
The following treatment can reduce COD/BOD and Acrylonitrile to considerable
extent.
(A) Physico-chemical treatment:
i) Hot alkaly digestion
ii) Chemical coagulation
Hot alkaly digestion with 2 to 4% NaOH at the temperature of 100 to 110 oC for 1 to 3
hrs. Followed by cooling and chemical coagulation by Alum/lime and removal of
sediments reduces CN and COD/BOD to large extent as could be observed from the
following date:
Table-11.1 COD/BOD table
pH
8 to10
COD
20000 to10000 ppm
BOD
10000 to 20000 ppm
Organic Cyanides
10 to 30ppm
Colour
Light Brown
134
To get rid of this pretreated effluent generally incinerated which require huge quantity
of fuel or extensive chemical treatment is the only process. However the cost of
incineration or chemical treatment is quite high, hence and alternative economical
method is necessary.
(B) Activated Sludge biological Process:
Toxic cyanide containing effluent can be treated biologically by two sludge activated
sludge process under specific conditions. A schematic flow sheet for two stage
biological treatment is shown in figure.
Effluent water is collected in collecting chamber, in this for dilution purpose and to
provide minerals and salts to biomass raw water or sanitary waste is added. In
equalization pond it is aerated to equalize the mass as well as to remove volatiles.
In
the next
step
pH
adjustment/coagulation
is
carried
out
by adding
Alum/lime/polyelectrolyte or any other coagulating agents/aids. Settled sludge is
removed through clari floculator and supernatant is fed to 1st stage bioreactor with
constant rate along with required dose of nutrients.
Organic matters in the waste water gets decomposed by bio oxidation by aeration in
the bio-reactor and mixed liquor is sent t clarifier from where with controlled rate
activated sludg3is recycled back to the system and some portion is sent to sludge
thickener and thickened sludge after centrifuging is discarded as cake. Supernatant
from clarifier is retreated biologically in the second stage to have reduction of
COD/BOD and CN up to 80 ± 95%.
Feed
: maximum ACN level 15 ppm max
(To be controlled by dilution)
COD
: 6000 ppm max
Ph
: neutral to alkaline up to 9 pH
Mixed liquor
: 3000 to 4000 ppm Suspended Solids
F/M
: 0.2 to 1.6
O2 supply
: 1.5 to 2.5 kg. O2/kg. COD Removed
Retention time
: 24 hour to 96 hour
135
The above mentioned biological system is of standard norms, however since strong
cyanide decomposing bacteria are of absolute different nature, the initial propagation
and acclimatization is very much an art and considerably different from normal
treatment. Required conditions during treatment.
It must be noted that as ACN has strong toxic property, loading of the system should
be with controlled rate. In order to reduce the influence of toxicity of ACN to
biomass, effluent should be diluted initially by either raw water or sanitary waste t
bring down the level of ACN and COD less than 15 ppm and 6000 ppm respectively.
Also for healthy state of microorganisms 1 to 1.5% of P source and small amount of
nutrients are added based on the BOD loadings.
Thus as per the flow sheet digamma the effluent cyanide waste stream first under foes
physico-chemical treatment where COD/BOD is diluted by digestion and coagulation.
This is further diluted by sanitary and other waste water and as a result of biooxidation and biodegrading sludge is obtained out of bioreactors, 1 and 2. This sludge
is filtered out and the clear liquid is obtained out of the clarifier.
Conclusion: The process is not substantially different than that of standard activated
sludge process, but separation of strong ACN decomposing bacteria, their
propagation, cultivation and acclimatization is an art of this process. However it can
be concluded that with special precautions, waste water containing toxic cyanide and
extended aeration activated sludge biological treatment which reduces COD/BOD
and ACN upto 90-95%. The initial investment may be high by 30 to 40 % more
compared to the chemical process, but operating cost is quite low and operating cost
difference pays off capital investment within about two to three years of time.
136
CHAPTER-12: PLANT LOCATION AND LAYOUT
12.1 SELECTION OF PLANT LOCATION:
The geographical location of the final plant layout can have a strong influence on the
success of an industrial venture. Much care must be taken in choosing the plant site
and many different factors must be considered. Primarily the plant should be located
where the minimum cost of production and distribution can be obtained but other
factors such as room for expansion and general living condition are also important.
An appropriate idea as living reaches the detailed estimate stage and a firm location
should be established upon completion of the detailed estimate design. The choice of
the final site should be first based on a complete survey of the advantage and
disadvantage of available real estate. The following factors should be considered in
choosing a plant site.
12.2 PRIMARY FACTOR FOR PLANT LOCATION:
12.2.1 Raw Material availability:
The source of raw material is one of the most important factors influencing the
selection of plant layout. This is particularly true if large volumes of raw materials are
consumed because location near the raw material sure permits considerable reduction
in transportation and storage charge.
Attention should be given to the purchase price of the raw materials, distance from
the source of supply, freight or transportation expenses, availability and reliability of
supply, purity of raw material and storage requirement. It is necessary that raw
materials should be available in required quality and quantity without delay.
For acrylonitrile, the raw materials are propylene available nearby petroleum refinery,
ammonia available nearby fertilizer plant.
12.2.2 Markets:
The location of market or intermediate distribution centers affects the cost of product
distribution and the time required for shipping. Proximity to the large major markets
is an important factor in the selection of a plant layout because purchasers usually
find it advantageous to purchase from nearby source.
137
It should be noted that markets are needed for by products as well as for major final
product. So, it is beneficial to have a chemical market near to the plant.
12.2.3 Energy Availability:
Power and steam requirements are high in most industrial plants and fuel is ordinarily
required to supply these utilities. Consequently power and fuel can be combined as
one major factor in the choice of plant layout.
The local cost of power can help determine whether power should be purchased or
self generated for economic operation.
12.2.4 Climate:
Weather has a seasonal effect on the economic operation of the plant. The
temperature and humidity should be favorable. It should not be in the region where
have more chances of Hurricanes, torpedo earth quake, Heavy flood and high wind
velocity. Temperature range should be 15-40oC.
If the plant is located in cold climate, costs may be increased by necessity for
construction of protection shelters around the process equipment, and special cooling
towers or air conditioning equipment may be required if the prevailing temperature
are high.
Excess humidity or extreme of hot or cold weather can have a serious effect on the
economic operation of a plant and these factors should be examined when selecting a
plant layout.
12.2.5 Water Supply:
The process industry use large quantities of water for cooling, washing, steam
generation etc. The plant, therefore, must be located where a dependable supply of
water is available. A large river or lake is preferable although deep well or artisans
well may be satisfactory if the amount of water required is not too large.
The level of the existing water table can be checked by consulting the state geological
survey and information on the constancy of the water table and the year round
capacity of local river or lake should be obtained.
138
If the water supply shows seasonal fluctuation, it may desirable to construct a
reservoir or to drill several stand by wells. The temperature, mineral content, salt or
sand contents, bacteriological treatment must also be considered.
Also potable water for staff must be easily available.
12.3 SPECIFIC FACTORS FOR PLANT LOCATION:
12.3.1 Transportation Facilities:
A plant should have easy access to transport facilities. The transport facilities
available to the plant must not be only easily accessible, but they must also be
enough, quick and available at reasonable rates. Water, Rail, Roads and Highways are
the common means of transportation. These facilities are very necessary for the
transfer of raw materials and product transportation.
Water, railroads, and highways are the common means for transportation used by
industrial concerns. The kind and amount of product and raw materials determines the
most suitable type of transportation to local freight rates and existing rail road lines.
The proximity to railroad centers and the possibility of canal, river, lake or ocean
transport must be considered. Motor trucking facilities are widely used and can serve
as a useful supplement to rail and water facilities. If possible, the plant layout should
have access to all three types of transportation and certainly atleast two types should
be available. There is usually need for convenient air and rail transportation between
the plant and the main company headquarters and effective transportation facilities
for the plant personnel are necessary.
12.3.2 Skilled Labour Supply:
Availability of skilled a labour and constant supply should be considered. The type
and supply of labour available in the vicinity of a proposed plant layout must be
examined. Consideration should be given to prevailing pay rated, restrictions on
number of hours worked performance week, competing industries that can case
dissatisfaction or high turnover rates among the workers, raid problems and variations
in the skill and intelligence of the workers. Now a day, labour unions are the main
look out of better site selection. Labour problems should be minimum.
139
12.3.3 Waste Disposal:
The site should be such that it should have the best and adequate facilities for the
waste which is coming out. In recent years many legal restrictions have been placed
on the methods for disposing of waste materials from the process industries.
The layout selected for a plant should have adequate capacity and facility for correct
waste disposal. Even though a given area has minimal restrictions on pollution, it
should not be assumed that these conditions will continue to exist.
In choosing plant layout, the permissible tolerance levels for various methods of
waste disposal should be considered carefully and attentions should be given to
potential requirements for additional waste treatment facilities.
12.3.4 Tax and Legal Restrictions:
State and the local tax rates on property, income, unemployment, insurance and
similar items vary from one location to another. Some incentives are given by state or
central government to particular industry likewise less tax rate or tax free zone in
backward (Tribe) area, octori free for particular time period and subsidy, loan is also
given. All these benefit reduces capital investment, production prices. So preference
should be given to place where this type of facilities are available Similar local
regulation on zoning, building aspects and transportation facilities can have a major
influence on the final choice of a plant layout.
In fact zoning difficulties and obtaining the required permits can often be much more
important in terms of cost and time delay than many of the factors discussed in the
preceding section.
12.3.5 Site Characteristic:
The characteristics of the land at a proposed plant site should be examined carefully.
The topography of the tract of land and soil structure must be considered. Since either
or both may have a pronounced effect on construction cost and living conditions
further changes facilities. Therefore even though no immediate expansions have been
planned; new plant should be constructed at location where additional space is
available.
140
12.3.6 Flood and Fire Protection:
Many industrial plants are located along rivers of near bodies of water and there are
risks of floods or hurricanes damage. Before choosing a plant layout the regional
history of natural events of these types should be examined and consequences of such
occurrences considered.
Protection from losses by fire is another important factor in selecting plant location.
The site should be such that it should have the best possible fire facility. If should
located such that the fire station are nearer and adequate facilities are possible during
the emergency. In case of a major fire, assistance form outside fire departments
should be available. Fire hazards in the immediate area surrounding the plant layout
not are over looked.
12.3.7 Advance Library and Training Center:
To develop, the plant properly, trained staff is very much necessary and for further
research advanced library facilities covering the subjects in detail, is necessary.
12.3.8 Community Factors:
The gates are so placed that the material in and out of plant is systematically recorded
and controlled. Provisions of probable future expansion is also taken into
consideration and space provided for.
The control room and laboratory are attached to plant so as to easy assess to plants.
Attached laboratory allows prompt sampling, analyzing and reporting to control room
of various changes and trouble shooting.
Large cities offer the advantages of factory warehouse facilities so that replacement,
parts of the plant can be readily obtained. The workers prefer to sue public
transportation then such public transportation must be efficient ad economical.
12.4 PLANT LAYOUT:
Once the location of the factory is decided handle the major equipments are at hand,
the immediate step is to have specific plant layout. Layout of a plant in the factory
means the allocation f apace, arrangement of equipment and machinery in such a
manner that maximum utilization of men, machine and materials is done and
141
CHAPTER-13: COST ESTIMATION
A plant design obviously must present a process that is capable of operating under
condition, which will yield a profit. Since net profit equals total income minus all
expenses, it is essential that chemical engineer be aware of the many different types
of costs involved in manufacturing processes. Money must be paid out for direct plant
expenses, such as those for raw materials, labors and equipments. In addition many
other indirect expenses are included, and these must be included if a complete
analysis of the total cost is to be obtained. Some examples of these indirect expenses
are administrative salaries, product distribution costs, and cost for inter plant
communications.
A capital investment is required for any industrial process; the determination of the
necessary investment is an important part of a plant design project. Total investment
for any process consists of the fixed capital investment for the physical equipment
and facilities in the plus the working capital for money which must be available to
pay salaries, keep law materials and product on hand, and handle other special items
requiring a direct cash outlay. Thus, in an analysis of costs in industrial processes,
Capital investment costs, manufacturing costs, and general expenses including
income takes must be taken into consideration.
The detail cost estimation is obviously very much essential for any project to estimate
its profitability and hence feasibility.
13.1 FACTORS AFFECTING INVESTMENT AND PRODUCTION COSTS:
1.
Sources of equipment: - One of the major costs involved in any chemical
process is for the equipment. Standard available equipments are cheaper than
specially design ones.
1) Price fluctuations: - In current scenario, the prices are very quite widely from
period to another hence chemical engineer should consider this point while
estimating the cost.
2) Company policies: - Policies of Individuals Company have a direct effect on
costs.
144
3) Operating time and rate of production: -One of the factors that has important
effect on costs is the variation of the total available time during which the
process is in operation.
4) Governmental policies: - The national government has many regulations and
restrictions, which have a direct effect on industrial costs.
13.2 CAPITAL INVESTMENT:Fixed ± Capital investments: Fixed Capital investment represent the capital necessary,
for the installed process equipment with all auxiliaries that are needed for complete
process design.
Working capital: The working capital for an industrial plant consist of the total
amount of money invested in,
1. Raw materials and supplies carried in stock
2. Finished products in stock and semi finished products in the process of being
manufactured
3. Account receivable
4. Cash kept on hand for monthly payment of operating expenses, such as
salaries, wages and raw material purchases
5. Accounts payable and
6. Taxes Payable.
13.3 ESTIMATION OF TOTAL PRODUCT COST:The total product cost intern is generally divided into the categories of manufacturing
cost and general expenses. Manufacturing costs are also known as operating or
production costs.
Manufacturing costs: All expenses directly connected with the manufacturing
operation or physical equipment of a process plant itself are included in the
manufacturing costs.
These expenses are divided into three classifications as follows:
1)Direct production costs 2) Fixed charges, and 3) Plant overhead costs.
145
General expenses: general expenses are classified as
1) Administrative expenses
1. Distribution and marketing expenses.
2. Research and development expenses.
3. Financial expenses
4. Gross earning expenses.
13.4 BREAKDOWN OF FIXED CAPITAL INVESTMENT ITEMS FOR A
CHEMICAL PROCESS.
13.4.1 Direct costs
1. Purchased equipment
All equipment listed on a complete flow sheet, spare parts and non installed
equipment, supplies and equipment allowance, inflation cost allowance, freight
charges, taxes, insurance, duties, and allowance for modification during startup.
1. Purchased-equipment installation, structural supports, insulation, paints.
2. Instrumentation and controls, purchase, installation, calibration
3. Piping: Process building-carbon steel, alloy, cast iron, lead, lined, aluminum,
copper, asbestos-cement, ceramic, plastic, rubber, reinforced concrete. Piping
hangers, fittings, valves insulation-piping equipment.
4. Electrical equipment and materials: Electrical equipment-switches, motors,
conduit, wire, fittings, feeders, grounding, instrument and control wiring,
lighting, panels.
5. Buildings (including services):Process building-substructures, superstructures,
platforms, supports, stairways, ladders, access ways, cranes, monorails, hoists,
elevators, auxiliary building-administration and office, medial or dispensary,
cafeteria, garage, product warehouse, parts warehouse, guard and safety, fire
station, change house, personal building, shipping office and platform, research
laboratory, control laboratory.
Maintenance shops-electric, piping, sheet metal, machine, welding, carpentry,
instrument.
146
Building services-plumbing, heating, ventilation, dust collection, air condition
systems, painting, sprinkler systems, fire alarm.
6. Yard improvements: Site development-site clearing, grading, roads, walkways,
railroads, fences, parking areas, wharves and piers, recreational facilities,
landscaping.
7. Utilities: Steam, water, power, refrigeration, compressed air, fuel, waste
disposal.
Facilities-boiler plant incinerator, wells, river intake, water treatment, cooling towers,
water storage, electric substation, refrigeration plant, air plant, fuel storage, waste
disposal plant, fire protection, non process equipment, shop equipment, automotive
equipment, yard material-handling equipment, laboratory equipment, locker-room
equipment, large equipment, shelves, bin, pallets, hand trucks, housekeeping
equipment, fire extinguishers, hoses, fire engines, loading stations. Distribution and
packing-raw-material and product storage and handling equipment, product
packaging equipment, blending facilities, loading stations
8. Land
Surveys and fees, property cost
13.4.2 Indirect costs
1) Engineering and supervision
Engineering costs-administrative, process, design and general engineering, drafting,
cost engineering, procuring, expediting, reproduction, communications, scale models,
consultant fees, travel, engineering supervision and inspection.
2) Construction expenses
Construction, operation and maintenance of temporary facilities, offices, roads,
parking lots, electrical, piping, communications, fencing
Construction tools and equipment
Construction supervision, accounting, timekeeping, purchasing, expending
Warehouse personnel and expense, guards
Safety, medical, fringe benefits Permits,
147
field tests, special licensesTaxes, insurance, interest
3) CoQWUDFWRU¶VIHH
4) Contingency.
13.5 COSTING OF THE PLANT:
13.5.1 Fixed Capital Investment
(A) Direct costs:
(1) Purchase equipment cost (PEC)
Table-13.1 PEC
Sr.
Equipment
No.
Nos. of
Cost
Total cost
Units
Rs/unit
Rs.
1.
Ammonia storage tank
1
250000
250000
2.
Propylene storage tank
1
266000
26000
3.
Product storage tanks for HCN,
3
339400
1018200
ACN & AN
4.
Fluidized bet reactor
1
4791000
4791000
5.
Quencher
1
276800
276800
6.
Absorber
1
280000
280000
7.
Recovery column
1
610000
610000
8.
Distillation column
4
332750
1331000
9.
Electrical heater
3
85450
256350
10. Rotary compressor
2
366000
732000
11. Centrifugal pump
30
16000
480000
12. Reciprocating pump
8
36000
732000
13. Heat exchanger
12
246100
2954000
14. Cooler
4
133100
532400
15. Condensers
4
219600
878400
16. Reboiler (Kettle type)
4
166000
664000
17. Centrifugal separtor
1
104000
104000
18. Electrical heater
1
58500
58500
148
19. Cooling tower
2
166000
332000
20. Refrigeration unit
1
618000
618000
Total
17164650
13.5.1(A) Direct Cost
1. Purchased equipment cost (PCE)
= Rs. 17164650
2. Purchased equipment installation cost (0.5 PEC)
= Rs. 8582325
3. Instrumentation and control cost (0.2 PEC)
= Rs. 3432930
4. Insulation and painting cost (0.15 PEC)
=Rs. 2574697
5. Electrical installation (0.2 PEC)
= Rs. 3432930
6. Building cost (0.2 PEC)
= Rs. 3432930
7. Service Facilities (0.1 PEC)
= Rs. 1716465
Total direct cost (TDC) (A)
VXPPDWLRQµ¶WRµ¶
= Rs. 40339628
13.5.1(B) Indirect cost:
1. Engineering and supervision (0.5 TDC)
= Rs. 20168464
2. Construction and contractors fees (0.7 TDC)
= Rs. 2823850
3. Contingencies cost (0.5 TDC)
= Rs. 20168464
TIC = (B) = (1) + (2) + (3)
= Rs. 6857277
Fixed capital investment (FCI)
= TDC + TIC
= Rs. 108909706
Working capital investment WCI = 0.3 FCI
= Rs. 32672912
So Total capital investment TCI = FCI + WCI
= Rs. 141582618
13.5.1.C
Estimation of total product cost:
Manufacturing cost
(A) Direct production cost
(a) Raw material cost
Basis = 330 working days
149
Table-13.2 Direct Production cost
Sr
Raw Material
No.
Qty./year
Rate
Amounts
(Kg.)
Rs. kg
Rs.
1.
C3 ±cut
70 x 106
20
1400 x 106
2.
Ammonia
30 x 106
10
300 x 106
3.
Catalyst
5000
1000
5 x 106
1705 x 106
Total
(b) Labor and production supervision
Table-13.3 Labor and production supervision
Sr. Designation
Number
Rs./month
No.
Total Rs.
Year
1.
M.D.
1
200000
2400000
2.
V.P.
5
150000
9000000
3.
G.M.
8
75000
7200000
4.
Process plant
(i) Production manager
1
30000
360000
(ii) Chief Engineer
5
27800
1668000
(iii) Jr. Engineer
10
12000
1440000
(iv) Operator
15
6000
1080000
(v) Skilled Workers
10
3000
360000
(vi) Unskilled Workers
10
1500
180000
3
4000
144000
Supervisor
3
4000
144000
Workers
12
1500
216000
3
12000
432000
5.
Lab. Section
Chemical
6.
7.
Utility Section
Maintenance Section
Engg. (Mec.)
150
8.
9.
Engg. (Elec.)
3
12000
432000
Technicians
9
3500
378000
Officer
1
15000
18000
Clerical staff
5
5000
300000
Head
1
6000
72000
Security officer
1
3000
36000
Watchman
4
2000
96000
Heat
1
15000
18000
Officer
1
8000
96000
Others
3
2500
9000
Sales Officer
1
12000
144000
Sales man
4
6000
288000
Administration
Safety and security
10. Stores and Purchase
Dept.
11. Marketing Section
Total
26835000
(c) Utility cost
= 0.2 TPC
(d) Maintenance and repairs = 0.1 FCI
= Rs. 10890970
(e) Operating supplies = 0.01 FCI
= Rs. 1089097
(f) Lab. Charges
= 0.025 TPC
(g) Patents and royalties
= 0.02 TPC
A = Direct production cost = (a) + (b) + (c) + (d) + (e) + (f) + (g)
= Rs. 1744 x 106 + 0.245 TPC
(B) Fixed Charges:(a) depreciation = 0.1 FCI + 0.03 (Building cost)
= Rs. 10957300
(b)
Local taxes = 0.04 FCI + Rs. 4356388
151
(c) Insurance premium = 0.025 FCI
So, B = F.C.
= Rs. 2722742
= (a) + (b) + (c)
= Rs. 18036430
(C) Plant overheads
= 0.07 TPC
(D) General Expenses
= 0.07 TPC
(E) Interest = 0.11 TCI
= Rs. 15574087
Then, TPC
= (A) + (B) + (C) + (D) + (E)
So TPC
= Rs. 2462 x 106
13.6 PROFIT ANALYSIS
Table-13.4 Product selling cost
Material
Qty. kg.
6
Rate Rs./kg
Total Rs.
35
2450 x 106
ACN
70 x 10
AN
236 x 104
20
47.2 x 106
HCN
7968 x 103
10
79.68 x 106
TCS
= Rs. 2576.88 x 106
Gross Profit = TCS ±TPC
= Rs. 144.88 x 106
Tax paid = 0.4 x Gross Profit
= Rs. 45952000
Net Profit = Gross Profit ± Tax
= Rs.62.928 x 106
Payout period = Depreciable TCI / (Net Profit/year + Depreciation/year)
= 1.25 years
Rate of return = Net profit x 100 / TCI
= 44.45 %
152
CHAPTER-14: UTILITIES
14.1 UTILITIES:
The word utilities refer to the ancillary services needed in the operation of any
production process. All the streams used in the plant other than reactants come under
the head of utility. These are many streams which are being used by Acrylonitrile
plant as utility.
14.2 STEAM SYSTEM:
The steam is required for supplying heat the process fluid in the various equipments
and for many outer purposes in the plant. For this purpose utilize heat evolved in
reactor by using steam generating system. For extra requirement of steam can be
produced in boiler is just like shell and tube heat exchanger.
14.2.1 Steam:
There are three levels of steam in the plant.
1.
High Pressure Superheated steam.
2.
Medium Pressure Steam
3.
Low Pressure Steam.
The High Pressure saturated steam at 41.5 kg/cm2 and 2530C is generated in reactor
cooling coils in the process of removing the exothermic heat of reaction. A major
portion of the saturated steam produced is superheated in the reactor Superheat
cooling coils. Super heated steam is controlled at 370 0C and used to drive the reactor
air compressor. A small part of the high pressure saturated steam produced in used to
control the temperature of the superheated steam by bypassing, the superheat coils.
Some part of high pressure saturated steam is let down into medium pressure steam
and some part in low pressure steam. Most of low pressure steam comes from the air
compressor turbine.
High Pressure Super Heated Steam:
This steam is used to drive the turbine which drives the reactor air compressor,
exhausting to the low pressure steam header.
153
Medium Pressure Steam:
This steam is used in the catalyst hopper ejector, the product column ejector and the
evacuation ejector for the purification reboilers.
Low Pressure Steam:
This steam is used in reboilers of columns, reactor steam quenches, steam service
stations, deaerator, Start-up heater firebox purges, tower and tank steam purge.
14.2.2 Condensate System:
Condensate is collected from the steam heated reboilers. Part of this condensate is
returned to the reactor cooling system for reuse. A portion of the condensate is cooled
and used to supply as required, water for various pump seals and auxiliary chemical
make up requirements.
14.3 FUEL SYSTEM:
Fuel oil is used as fuel. It is used in start up heater to heat the air from air compressors
to approximately 4800C. Fuel oil is burnt in burners and air in tube is heated directly
with flame. Fuel oil is also used in incinerator for burning ammonium sulphate, waste
water and spent solution.
14.4 WATER SYSTEM:
14.4.1 General purpose Water:
The water used for drinking, washing, flushing etc. purposed is considered as general
purpose water. It is drawn from a river or lake.
14.4.2 DM Water:
The Demineralized water is required as boiler feed water for steam generation. It is
obtained from the DM water plant.
14.4.3 Cooling Water:
The cooling water is drawn from a river or lake in sufficient quantity. It is required
for providing cooling the materials in various heat exchangers for cooling. The hot
water from heat exchangers is taken to cooling tower.
The type of cooling tower is induced type. The temperature of water to cooling tower
is 35-370C. The temperature of water from cooling tower is 25-270C.
154
Hot waters from the plant after the heat exchanging come to the cooling tower
through one single header. There is no need to pump it to top of the tower as pressure
at the discharge side is significant for the circulation of cooling tower through the
piquet and to complete the cycle.
(1) Cooling tower is a induced draft cooling tower where two exhaust fans all rotated.
Majority part of cooling tower is made of wood blocks and cement sheets.
(2) Hot water coming to the tower is sprinkled from the tower using plastic nozzle
which passes through the tower flow metal baffles provided for adequate heat
transfer. Air coming from side ways passes through the tower and due to exhaust fan
carried to the top of the tower.
(3) Flow rate of outgoing water from cooling tower is 2000 m3/hr and make up water
provided is just 20 m3/hr approximately.
(4) Evaporation and windage loses are almost 1% of the total flow rate.
Temperature drop is 8 to 100C (maximum).
(5) Due to continuous operation of cooling tower there are many problems which
arises at the time of operation like to maintain pH of the water, scale formation to
control algal formation etc.
i)
To remove or control algae formation some biocides are added at proper
intervals of time.
ii) If these are more free radicals of chlorine then that leads to corrosion
problems moreover due to recirculation of water problem of scale formation also
arises. Sodium hydrochloride is added in their respective proportion to handle the
problem of scale formation and to maintain chloride level.
iii) 98% H2SO4 is added continuously in very small amounts to maintain the
pH level of the cooling tower.
(6) Blow down system is also there to flush the tower and then to remove it rapidly so
as to remove scale which has been formed at the bottom of the tower.
14.5 BRINE COOLANT ± REFRIGERANT:
In acrylonitrile plant, Ethylene Glycol is used as coolant. Ethylene Glycol is used in
various heater exchangers for cooling other material and thereby it is heated. This hot
155
brine is taken to brine refrigeration section. Here, compressors are working for
refrigeration of brine. The refrigerated brine is at temperature 40C (390F) and it is
taken to heat exchangers again for heat exchange.
Refrigeration is required to maintain the temperature below that of the surroundings
to keep the product in liquid form at low temperature and high pressure.
There are two basic refrigeration cycles.
1)
Vapor-Compression cycle
2)
Absorption refrigeration cycle.
Vapor-Compression cycle: A Liquid evaporating at constant pressure provides a means for heat absorption at
constant temperature Likewise, condensation of vapour, after compression to a high
pressure, provides for the refection of heat at constant temperature. The Liquid from
the condenser is returns to its original state by an expansion process. This can be
carried out in a turbine from which work is obtained.
For lower load, expander is replaced by tower valve which isentropic ally reduces the
pressure.
The refrigerant used is brine or ethylene glycol which is non hazardous and non
poisonous.
14.6 AIR SYSTEM:
14.6.1 Plant Air System:Plant air is provided to all the air service stations throughout the production area.
Plant air is also used for aeration of the catalyst in the catalyst drum during transfer
operations, to pressurize the catalyst storage drum and for purging in various
equipments and to keep tank under some positive air pressure etc.
14.6.2 Instrument Air System:All automatic control instruments are supplied with air if they are pneumatic controls.
The air supplied to these instruments is called Instrument Air. The pressure of
instrument air supply is constant at 1.4 kg/cm2 (20 lb/in2). Instrument air require for
Acrylonitrile plant is generated at instrument air section. For that purpose
atmospheric air filtered and fed to the compressor.
156
14.7 NITROGEN PRODUCTION PLANT:
N2 is separated from air needed for industrial purposes there are basically three
processes by which one can separate oxygen and nitrogen from air they are,
1) Cryogenic distillation.
2) Burning of any fuel with air
3) Adsorption using carbon molecular sieves.
As cryogenic separation using distillation is very expensive hence it is not advisable
to use this method keeping in mind the comparatively low demand of N 2 in the plant.
Secondly N2 we get by distillation is highly pure containing almost no oxygen. For
plant purpose that high purity is not required. Due to this reasons the company has
opted for pressure swing adsorption of oxygen to get nitrogen stream which can be
used for Acrylonitrile plant for various purpose.
14.8 ELECTRICITY:
The electricity is required for motor drives, lighting and general use. It is generated
onsite or purchased from GEB depending on the requirements.
14.9 STEAM GENERATING SYSTEM:
14.9.1 Heat removal from reactor and gases:As ammoxidation reaction of propylene is highly exothermic, heat must be removed
from reactor to run the process smoothly. However, the process is finely adjusted
such that the heat produced during reaction is utilized too run the steam turbine and
thereby air compressor with high savings of electricity. For this purpose, a steam
generation system is working.
Condensate of steam from various heat exchangers reboilers comes to a condensate
tank. With new make up D.M. Water feed. This boiler feed water from condensate
tank flows to the deaerator under action of deaerator level controller. In deaerator,
low pressure steam is added to heat the water and strip out dissolved gases. Hydrazine
(N2H4) is also added to deaerator to react with oxygen dissolved is condensate water.
Nitrogen and other gases are released from deaerator.
Now, deaerated water is pumped by the feed water pump to Reaction Products gas
cooler. Reactor Product gas cooler is a heat exchanger where reaction products gases
157
from reactor are passing through tube side and boiler feed water in shell side in
counter current direction. The cooled gases are now taken to quench column. Water is
heated to approximately 2300C. It comes to the coolant drum and then it is pumped by
reactor coolant pump to the reactor cooling coils. Here, water absorbs heat from
reactor. The steam and water mixture leaving the reactor cooling coils flows back to
the coolant drum for separation of the steam and recirculation of the cooling water.
Water from the discharge of reactor coolant pump is also recirculated to the inlet of
the product gas cooler to control the temperature of product gases at 2320C for
prevention of polymerization. The most of steam from top of coolant drum is taken to
upper reactor cooling coils. Here, this steam is super heated to 370 0C and then it is
used to run steam turbine.
A small part of saturated steam (41.5 kg/cm2s, 2530C) from top of coolant drum islet
down into the low pressure steam heater (3.5 kg/cm2g). However, most of the low
pressure steam consumed in the plant comes from the air compressor turbine. A small
quantity of high pressure steam is let down to medium pressure steam for using in the
vacuum ejectors.
Phosphate solution is added in coolant drum for maintaining pH of circulating water.
Table-14.1 Utility Requirement:
Utility
Saturated steam at 110oC
Process water
Steam
Equipment
Flow rate kg/sec
Reactor coils
851
Product gas cooler
48
Quench Col
2.61
Absorber
9.55
Heat exchanges (Recycle)
2.84
Heat exchange (Recycle)
2.75
Recovery col. Reboiler
3.29
Aceto stripper Reboiler
1.58
HCN column Reboiler
1.08
ACN column Reboiler
0.66
158
Cooling water
Brine
Recovery col. Reboiler
48.27
Aceto stripper rubber
156.31
ACN column rubber
517.13
HCN condenser
434.15
159
CHAPTER-15: AUXILARY EQUIPMENTS
15.1 Columns
1) Quench Column:
M.O.C.
= 316 S.S. clad [column] and Stone ware [Packing]
Type
= packed Tower
--- 2 inch packing
--- Tower divided into two sections.
2) Absorber:
M.O.C.
= 316 S.S. clad [column] and 316 SS [trays]
Type
= Valve tray column
Tray spacing
= 0.6 m
No. of trays
= 40
3) Recovery column:
M.O.C.
= 316 S.S. clad [column] and 316 SS [trays]
Type
= Valve trays
Tray spacing
= 0.5 m
No. of trays
= 60
4) Aceto Column:
M.O.C.
= 316 S.S. clad [column] and 316 SS [trays]
Type
= Sieve tray
Tray spacing
= 0.5 m
No. of trays
= 30
5) HCN Column:
M.O.C.
= 316 S.S. clad [ column and trays both]
Type
= Sieve tray
Tray spacing
= 0.6 m
No. of trays
= 20
6) Product Column:
M.O.C.
= 316 S.S. clad [column] and 316 SS [trays]
160
Type
= Valve tray column
Tray spacing
= 0.6 m
No. of trays
= 40
15.2 Heat Exchangers:
Ammonia and Propylene vaporizers and superheater:
Shell
= Rubber lined
Tubes
= Graphite
Product gas cooler:
Shell and Tubes
= Carbon steel
After coolers, and condenser of HCN column, Reboilers of Aceto and HCN column
and condenser of HCN column:
Shell
= Carbon steel
Tubes
= 316 SS
Rich / Lean water heat exchanger, Rich / Solvent water heat exchanger, Reboiler of
Recovery column and product column:
Shell and Tubes = 316 SS
All Reflux drums, decanters have M.O.C. = 316 SS
15.3 Tanks:
Ammonia storage:
Store in bullets.
M.O.C.
= Carbon Steel
Store in spherical vessel. M.O.C.
= Carbon Steel
Propylene storage:
Acrylonitrile Tank:
Closed vertical tank.
HCN storage tank:
M.O.C.
= Carbon Steel
M.O.C.
= 316 SS
161
CHAPTER-16: SUMMARY
An exhaustive literature survey & market survey was made for the selection of the
process for the manufacture of Acrylonitrile with all the advantages taken in general.
Although this process is not fit for the smaller production, but seeing the growing
demand in the country, at least few units of large scale are required.
The production of Acrylonitrile by propylene ammonia air oxidation reaction process.
Seems to be the most appropriate process.
The process design was based on standard code and practices available in the
literature. The performance of continuous flow fluidized bed reactor has been tented
for the production distribution. Acrylonitrile is the most important industrial product
with its demand growing everyday statistics show that there is a wide gap between
demand and supply in the country and keeping in view the future demand, possibility
of the gap getting wider is envisaged if the few production units are not put.
Acrylonitrile production raw material propylene and ammonia are very hazardous and
requires a safer way for handling, storage and transportation. So lots of care should be
taken for there storage, handling and transportation.So safety is an important factor
and a proper attention is to be paid for keeping its standard high as possible.
Here a high degree of automation with computer aided analyzer is required for
keeping the yieled % higher and also ensuring a better quality product.
Acetonitrile by product has proven a good solvent competitor for acetone, particularly
in the solvent extraction of butadiene and other dienes.
Ultimately from this project report I conclude that from technical and economical
point of view this project of acrylonitrile is viable. This project can pay back all our
invested money in about 1.5yrs. (if than efficiently for 330 days). During running
this project lots of precautions should be taken care of for safety of an organization,
as the materials used in this project are very hazardous and flammable.
162
CHAPTER-17: REFRENCES
1) .LUN 2WKPHU³(QF\FORSHGLDRI&KHPLFDO7HFKQRORJ\´9RO3- 369,
4th Edition, John Wiley & Sons, New York, 1987
2) 8OOPDQQ¶V(QF\FORSHGLDRI,QGXVWULDO&KHPLVWU\9&+SXEOLFDWLRQV*HUPDQ\
Vol. A1, P. 177 - 183, 1985.
3) 0FNHWWD -RKQ - ³(QF\FORSHGLD RI &KHPLFDO 3URFHVVLQJ 'HVLJQ´ 0DUFHO
Dekker
Inc.Publication,
4) Chemical and Process Technology Encyclopedia, D.M. Considine, McGraw
Hill Book Company, P. 30 ± 35, 1974.
5) ³0F*UDZ +LOO (QF\FORSHGLD RI 6FLHQFH DQG 7HFKQRORJ\´9RO )LIWK
edition,McGraw Hill Book Company.
6) 3HUU\ 5REHUW + 'RQ *UHHQ ³3HUU\¶V &KHPLFDO (QJLQHHUV¶ +DQGERRN´
Seventh and Sixth Edition, McGraw-Hill International Editions, Chemical
Engineering Series, New York, 1998.
7) &RXOVRQ -0 DQG 5LFKDUGVRQ -) ³&KHPLFDO (QJLQHHULQJ´ )LUVW HGLWLRQ
Vol.6, Pergamon Press ,Oxford, 1983.
8) 0F&DEH :/ 6PLWK -&
+DUULRW 3 ³8QLW 2SHUDWLRQV RI &KHPLFDO
(QJLQHHULQJ´ )LIWK HGLWLRQ 0F*UDZ +LOO ,QWHUQDWLRQDO (GLWLRQV &KHPLFDO
Engineering Series, New York, ,(1989).
9) 7UH\EDO 5( ³0DVV 7UDQVIHU 2SHUDWLRQV´ 7KLUG HGLWLRQ 0F*UDZ +LOO
International Editions, Chemical Engineering Series, New York, (1981).
10)
SmiWK -0 9DQ 1HVV +& ´,QWURGXFWLRQ WR &KHPLFDO (QJLQHHULQJ
7KHUPRG\QDPLFV´)LIWKHGLWLRQ,QWHUQDWLRQDO(GLWLRQV&KHPLFDO(QJLQHHULQJ
Series, New York, (1987).
Symposiums and Journals:
1) Editing by Mossson Kwauk, Daizo Kunni, Zheng Jiansheng, Mansanodu
+DVXWDQL ³)OXLGL]DWLRQ¶±6FLHFQH DQG 7HFKQRORJ\´-conference Pumps,
Second Chain ± Japan Symposium, 10 to15 April, 1985, Science Press,
Beijing, Chian, 1985.
163
2) ³:RUNVKRSRQGHVLJQDQG2SHUDWLRQRI+HDWWUDQVIHU 6\VWHP´ WR$SULO
1992), At: Seminar Hall, Chemical Engineering Dept., Vadodara, By IIChE,
Baroda Regional Centre.
3) $SSOLHG 3RO\PHU 6\PSRVLD ³$FU\ORQLWULOH LQ 0DFURPROHFXOHV´ $W &KLFDJR
Jllinois, August 27-29, 1973, By the Maconomelecular Secrretariat of
American Chemical Society,
Editor Eli M. Pearce, John Wiley and sons pub.
6HPLQDURQ³+D]DUGVLQ&KHPLFDO,QGXVWU\- Technology, Prevention and
5HPHGLHV´ Organized by IIChE, Baroda and Ahemadabad Regional Center, on
2nd March 1985 at Research Center Auditorium, IPCL, Baroda.
³6DIHW\DQG/RVV3UHYHQWLRQLQWKH&KHPLFDODQGRLO3URFHVVLQJ,QGXVWULHV´
No 120. The Institution of chemical Engineers, Rugby, UK Hemesphere
Publishing Corporation.
6) S.P. Lankhuyzen, P.M. Florack, and H.S. Van Der BAAN, Journal of Catalyst,
Vol. 42, P 20-28, April ±June 1976.
7) W. Keith hall, Frank S. Stone (editors), Journal of Catalyst, Volume87, P 363380, May ± June 1984.
8) A.N. Orlov, S.G. Gaganbn, Kinetic and Catalysis, P 1308-13011, June 1975.
9) J.M. Berty, Chemical Engineering Progress, Vol. 70, No.5, P. 78-84, May
1974.
10)P.R. Prabhu, Chemical Age India, Vol.36, No.9, P 827-829, September 1985.
11)Stobaugh, R.B., Hydrocarbon processing, Vol.50, P. 109-120, January 1971.
12)F. Veatch, J.L. Callahan, J.D. Ideal, Jr. and E.C. Milberger, Chemical
Engineering Process, Vol.50, No.10, P. 65-67, October 1960.
13)J.L. Callahan, E.C. Milaberger, R.K. Grasselli, and H.A. Strecker, Industrial
and Engineering Chemistry Product Research and Development, Vol.9, No.2,
P. 134-142, 1970.
14)R.B. Stobaugh, S.G. Mcti Clark and G.D. Camirand, Hydrocarbon Processing,
Vol.50, P. 109-120, January 1971.
15) Roland Nilsson and Arne Andersson, Industrial and Engineering Chemistry
164
Research and Development, Vol.36, P.5207-5219, 1997.
Websites:www.rockbridgegroup.com
www.chemdat.de
www.ipcl.co.in
www.inchem.org
www.safetyinfo.com
165
CHAPTER-18: APPENDICES
18.1 APPENDICES NO. 1:
Raw Material Specification:
1. Propylene (C3H6):Molecular weight
= 42.03
Purity
: 85% minimum
C2H4
: 5% maximum
C4H6
: 0.1% maximum
C2H2
: 0.1% maximum
Methyl Acetylene/Prop. Butadiene
: 0.75 maximum
H2S
: 10 ppm maximum
S (free)
: 50ppm maximum
2. Ammonia (NH3):Molecular weight
= 17.03
Purity
: 95.5% minimum
3. Air:Molecular Weight
Purity
= 29
: Free of dust, oil and chemicals.
4. Catalyst 49MC:
Typical chemical analysis
Approximate weight
Percent
Potassium
<1
Iron
<3
Nickel
4-9
Bismuth
<3
Molybdenum
20-25
Cesium
<1
Magnesium
<3
Cerium
<3
166
Silicon (And Oxygen)
Balance
Typical Performance of Catalyst C 49MC
Chemical
Conversion%
Acrylonitrile
79.9
Acetonitrile
2.3
Acrolein
0.7
Acrylic acid
1.5
HCN
5.9
CO
2.9
CO2
5.1
Total conversion
98.5
Unconverted Propylene
1.5
Product Specifications:
1. ACRYLONITRRILE (CH2CH = CN)
ACETONE
100 ppm Max.
ACETONITRILE
250 ppm Max.
ACROLEIN
5 ppm Max.
ACIDITY AS AH
30 ppm Max.
ALDEHYDES AS ACETALDEHYDE
5 ppm Max.
COPPER
0.1 ppm Max.
HCN
10 ppm Max.
IRON
0.1 ppm Max.
H2O/PEROXIDES
0.5% / 0.2 ppm Max.
APPEARANCE
Clear and free of suspended matter.
pH
6.0 ± 7.5
COLOUR
5 APHA Max.
REFREACTIVE INDEX
1.3882 ± 1.3892 nd
167
Label for Container or drum Packing:
ACRYLONITRILE
WARNING ! POISON
WARNING ! FLAMMABLE
Figure-18.1 Safety Symbol for Acrylobitrile
AVOID PROLONGED OR REPEATED BREATING OF VAPOR
ABSORPTION THROUGH SKIN IS HARMUFUL
KEEP OUT OF THE REACH OF CHILDREN
KEEP AWAY FROM HEAT, SPARKS, & FIRE, DO NOT LEAVE
CONTAINER OPEN
USE WITH ADEQUATE VENTILATION, AVOID EXPOSURE TO
CONCENTRATED VAPOR AVOID PROLONGED CONTACT WITH SKIN
OR CLOTHING.
171
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