2013
Acrylonitrile by Propylene
Ammoxidation
Submitted by
Guided by
Dr. R.G.Pala
Aman Agrawal
Ankesh Kumar Singh
Pratik Chaplot
Rahul Gupta
Raju Mishra
Sachin Goel
1/5/2013
Table of Contents
1
Introduction ................................................................................................................................... 2
2
Price and Demand ......................................................................................................................... 3
3
Health Effects ................................................................................................................................. 3
4
3.1.1
Sources and Potential Exposure ................................................................................... 4
3.1.2
Assessing Personal Exposure ....................................................................................... 4
Sohio Process ................................................................................................................................. 7
Reactor ............................................................................................................................................... 8
Effect of different variables on Conversion ..................................................................................... 9
5
Aspen Simulation......................................................................................................................... 12
Reactor ............................................................................................................................................. 12
Quencher .......................................................................................................................................... 13
Absorber........................................................................................................................................... 15
Recovery Unit (Re-boiled Stripper) ............................................................................................... 17
Overall .............................................................................................................................................. 19
6
Plant Wide Control System Design ............................................................................................ 21
Pressure Driven Overall Flow Sheet .............................................................................................. 21
Dynamic Stripper: ........................................................................................................................... 22
Dynamic Absorber and Stripper: ................................................................................................... 22
7
Liquid Separation Scheme .......................................................................................................... 23
Materials to be recovered ............................................................................................................... 23
Development of Separation Sequence ........................................................................................... 23
Simplifying Assumptions ................................................................................................................ 26
Simulation of Separation Steps and Equipment Sizing ................................................................ 26
Distillation Columns .................................................................................................................... 28
Overall Process Balance .............................................................................................................. 28
Water Recovery ........................................................................................................................... 29
8
Pollutants And Their Control...................................................................................................... 30
9
Modifications to Design .............................................................................................................. 31
Quench Column (Acidic) ................................................................................................................. 31
10
Plant Location .......................................................................................................................... 36
11
References ................................................................................................................................ 43
12
Appendix .................................................................................................................................. 44
1 | Acrylonitrile by Propene Ammoxidation
1
Introduction
Acrylonitrile is a chemical compound with the formula C3H3N. This colourless liquid often appears yellow
due to impurities. It is an important monomer for the manufacture of useful plastics such
as polyacrylonitrile. In terms of its molecular structure, it consists of a vinyl group linked to a nitrile.
FIGURE 1: Lewis Structure.
Acrylonitrile (AN) is commercially produced by a reaction of propylene and ammonia in the presence
of a catalyst. Having both olefinic (C=C) and nitrile (C-N) groups permits a large variety of reactions
and makes ANa versatile chemical intermediate. The nitrile group can undergo hydrolysis,
hydrogenation, esterification and reduction. Reactions of the carbon double bond include
polymerization, copolymerization, cyanoethylation, cyclization and halogenation. One of the
reasons for the versatility of acrylonitrile is that it can form copolymers with other unsaturated
compounds, such as styrene and butadiene, for example a raw material for acrylic acid, acrylic
esters, acrylic amide in the synthesis of compounds used for the production of adhesives, antioxidants, binders and emulsifiers. In its liquid state, acrylonitrile has a tendency to polymerize, which
is prevented by the addition of phenolic or amine-based stabilizers and small quantities of water.
Most industrial acrylonitrile is produced by catalytic ammoxidation of propene:
2CH3-CH=CH2 + 2NH3 + 3O2 → 2CH2=CH-C≡N + 6H2O
TABLE 1: Chemical properties of Acrylonitrile
Chemical Name
Regulatory Name
Molecular formula
Molecular weight
Density
Boiling point
Melting point
Vapor pressure
Solubility
Conversion factor
DOT Label
Acrylonitrile
2-Propenenitrile, Acrylonitrile
C3H3N
53.1 g/mol
0.81 g/cm3 at 25oC
77.3oC
-82oC
100 torr at 23oC
Soluble in isopropanol, ethanol, ether, acetone, and benzene
1 ppm = 2.17 mg/m3 at 25°C
Flammable Liquid
Acrylonitrile (AN), also known as vinyl cyanide (CH2=CH-C≡N), is a high volume commodity chemical
with worldwide production of more than 10 billion pounds per year. It contributes billions annually to
the U.S. economy. Acrylonitrile is used as a monomer in the production of acrylic and modacrylic fibers,
which accounts for approximately 50% of its global use.
2 | Acrylonitrile by Propene Ammoxidation
Acrylic fiber is used for clothing, carpeting and other fabrics and in the production of rugged plastics for
automotive components, computers, and appliances. Acrylic fiber is also used in the manufacture of
polyacrylonitrile (PAN)-base carbon fibers; which are increasingly important materials for lightweight,
high-strength applications in aeronautics, automotive, engineering, etc. Acrylonitrile is used as a comonomer the production of acrylonitrile, butadiene, styrene (ABS) and styrene acrylonitrile (SAN)
polymers, which accounts for an additional 31% of use. These polymers are used in a wide range of oiland chemical-resistant nitrile rubber for industrial hoses, gaskets and seals. Acrylonitrile is also used as
an intermediate in the production of other industrial chemicals, such as adiponitrile and acrylamide.
2 Price and Demand
FIGURE 2: Price of Acrylonitrile (ACN Highlights from 01-15, Feb 2013)
In the first half of the last fortnight, selling offers for ACN went up at slow and steady pace. In the early
first half of the last fortnight, ACN prices firm up in Asian market due to rise in feedstock rates, which
supported the price rise. Prices were stable in European market due to poor energy market. In the early
second half of the last fortnight, ACN prices surged in Asian market due to increase in feedstock value
coupled with improved demand from the downstream market. It is produced in very large amounts (2.5
billion pounds in 1993) by five companies in the United States. U.S. demand is likely to increase 2 to 3
percent per year for the next several years. The largest users of acrylonitrile are companies that make
acrylic and modacrylic fibers. Companies also use AN to make: high impact acrylonitrile-butadienestyrene (ABS) plastics used in business machines, luggage, and
construction material; styreneacrylonitrile (SAN) plastics used in automotives and household goods and in packaging material;
adiponitrile, a chemical used to make nylon; and dyes, drugs, and pesticides.
3 Health Effects
FIGURE 3: MSDS Label
Chemicals can be released to the environment as a result of their manufacture, processing, and use. EPA
has developed information summaries on selected chemicals to describe how you might be exposed to
these chemicals, how exposure to them might affect you and the environment, what happens to them in
3 | Acrylonitrile by Propene Ammoxidation
the environment, who regulates them, and whom to contact for additional information. EPA is committed
to reducing environmental releases of chemicals through source reduction and other practices that
reduce creation of pollutants.
Acrylonitrile is highly flammable & toxic. It undergoes explosive polymerization. The burning material
releases fumes of hydrogen cyanide and oxides of nitrogen. It is classified as a Class 2B
carcinogen (possibly carcinogenic) by the International Agency for Research on Cancer (IARC), and
workers exposed to high levels of airborne acrylonitrile are diagnosed more frequently with lung cancer
than the rest of the population. Exposure to acrylonitrile can occur in the workplace or in the
environment following releases to air, water, land, or groundwater. Exposure can also occur when people
smoke cigarettes or breathe automobile exhaust. Acrylonitrile enters the body when people breathe air
or consume water or food contaminated with AN. It can also be absorbed through skin contact. It does
not remain in the body due to its breakdown and removal.
There are two main excretion processes of acrylonitrile. The primary method is excretion in urine when
acrylonitrile is metabolized by being directly conjugated to glutathione. The other method is when
acrylonitrile is metabolized with 2-cyanoethylene oxide to produce cyanide end products that ultimately
forms thiocyanate, which is excreted via urine, or carbon dioxide and eliminated through the lungs.
Acrylonitrile evaporates when exposed to air. It dissolves when mixed with water. Most releases of
acrylonitrile to the environment are to underground sites or to air. Acrylonitrile evaporates from water
and soil exposed to air. Once in air, AN breaks down to other chemicals. Microorganisms living in water
and in soil can also break down AN. Because it is a liquid that does not bind well to soil, acrylonitrile that
makes its way into the ground can move through the ground and enter groundwater. Plants and animals
are not likely to store acrylonitrile.
Exposure to acrylonitrile is primarily occupational. It is used in the manufacture of acrylic acid and
modacrylic fibers. Acute (short-term) exposure of workers to acrylonitrile has been observed to cause
mucous membrane irritation, headaches, dizziness, and nausea. No information is available on the
reproductive or developmental effects of acrylonitrile in humans. Based on limited evidence in humans
and evidence in rats, EPA has classified acrylonitrile as a probable human carcinogen (Group B1).
[The main sources of information for this fact sheet are EPA's Integrated Risk Information System (IRIS),
which contains information on inhalation chronic toxicity of acrylonitrile and the RfC and the
carcinogenic effects of acrylonitrile including the unit cancer risk for inhalation exposure, EPA's Health
Effects Assessment for Acrylonitrile, and the Agency for Toxic Substances and Disease Registry's
(ATSDR's) Toxicological Profile for Acrylonitrile.]
3.1.1
Sources and Potential Exposure
 Human exposure to acrylonitrile appears to be primarily occupational, via inhalation.
 Acrylonitrile may be released to the ambient air during its manufacture and use.
3.1.2
Assessing Personal Exposure
 Acrylonitrile can be detected in the blood to determine whether or not exposure has occurred.
 Metabolites may be detected in the urine, but some breakdown products are not specific to
acrylonitrile.
Acute Effects


Workers exposed via inhalation to high levels of acrylonitrile for less than an hour experienced
mucous membrane irritation, headaches, nausea, feelings of apprehension and nervous
irritability; low grade anaemia, leukocytosis, kidney irritation, and mild jaundice were also
observed in the workers, with these effects subsiding with the ending of exposure. Symptoms
associated with acrylonitrile poisoning include limb weakness, laboured and irregular
breathing, dizziness and impaired judgment, cyanosis, nausea, collapse, and convulsions.
A child died after being exposed to acrylonitrile by inhalation, suffering from respiratory
malfunction, lip cyanosis, and tachycardia before death. Several adults exposed to the same
concentration of acrylonitrile exhibited eye irritation, but no toxic effects.
4 | Acrylonitrile by Propene Ammoxidation


Acute dermal exposure may cause severe burns to the skin in humans.
Acute animal tests in rats, mice, rabbits, and guinea pigs have demonstrated acrylonitrile to
have high acute toxicity from inhalation and high to extreme acute toxicity from oral or dermal
exposure.
Chronic Effects (Non-Cancer)
 In one study, headaches, fatigue, nausea, and weakness were frequently reported in chronically
(long-term) exposed workers.
 In rats chronically exposed by inhalation, degenerative and inflammatory changes in the
respiratory epithelium of the nasal turbinates and effects on brain cells have been observed.
 The Reference Concentration (RfC) for acrylonitrile is 0.002 milligrams per cubic meter (mg/m3)
based on degeneration and inflammation of nasal respiratory epithelium in rats. The RfC is an
estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation
exposure to the human population (including sensitive subgroups) that is likely to be without
appreciable risk of deleterious noncancer effects during a lifetime. It is not a direct estimator of
risk but rather a reference point to gauge the potential effects. At exposures increasingly greater
than the RfC, the potential for adverse health effects increases. Lifetime exposure above
the RfC does not imply that an adverse health effect would necessarily occur.
 EPA has medium confidence in the study on which the RfC was based because, although it was a
well-conducted chronic study in an appropriate number of animals, it was performed on only one
species, did not identify a no-observed-adverse-effect level (NOAEL), was confounded by the
early sacrifice of rats with large mammary gland tumors and the target organ (nasal turbinates)
was examined only at the end of the study in relatively few animals; medium to low confidence in
the database because of the lack of chronic or subchronic inhalation data in a second species, the
lack of reproductive data by the inhalation route and the existence of an oral study showing
reproductive effects; and, consequently, medium to low confidence in the RfC.
 EPA has calculated a provisional Reference Dose (RfD) of 0.001 milligrams per kilogram body
weight per day (mg/kg/d) for acrylonitrile based on decreased sperm counts in mice. The
provisional RfD is a value that has had some form of Agency review, but it does not appear on
IRIS.
Reproductive/Developmental Effects
 No information is available on the reproductive or developmental effects of acrylonitrile in
humans.
 Fetal malformations (including short tail, missing vertebrae, short trunk, omphalocele, and
hemivertebra) have been reported in rats exposed to acrylonitrile by inhalation.
 In mice orally exposed to acrylonitrile, degenerative changes in testicular tubules and decreased
sperm count were observed.
Cancer Risk




A statistically significant increase in the incidence of lung cancer has been reported in several
studies of chronically exposed workers. However, some of these studies contain deficiencies
such as lack of exposure information, short follow up, and confounding factors.
In several studies, an increased incidence of tumors has been observed in rats exposed by
inhalation, drinking water, and gavage. Astrocytomas in the brain and spinal cord and tumors of
the Zymbal gland (in the ear canal) have been most frequently reported, as well as tumors of the
stomach, tongue, small intestine in males and females, and mammary gland in females.
EPA has classified acrylonitrile as a Group B1, probable human carcinogen (cancer-causing
agent).
EPA uses mathematical models, based on human and animal studies, to estimate the probability
of a person developing cancer from breathing air containing a specified concentration of a
chemical. EPA calculated an inhalation unit risk estimate of 6.8 × 10-5 (µg/m3)-1. EPA
estimates that, if an individual were to continuously breathe air containing acrylonitrile at an
average of 0.01 µg/m3 (1 x 10-5 mg/m3), over his or her entire lifetime, that person would
theoretically have no more than a one-in-a-million increased chance of developing cancer as a
direct result of breathing air containing this chemical. Similarly, EPA estimates that breathing
5 | Acrylonitrile by Propene Ammoxidation

air containing 0.1 µg/m3 (1 x 10-4mg/m3) would result in not greater than a one-in-a-hundred
thousand increased chance of developing cancer, and air containing 1.0 µg/m3 (1 x 103 mg/m3) would result in not greater than a one-in-ten thousand increased chance of
developing cancer. For a detailed discussion of confidence in the potency estimates, please see
IRIS.
EPA has calculated an oral cancer slope factor of 0.54 (mg/kg/d)-1.
Hence, In conclusion the effects of acrylonitrile on human health and the environment depend on how
much acrylonitrile is present and the length and frequency of exposure. Effects also depend on the health
of a person or the condition of the environment when exposure occurs. Breathing acrylonitrile for short
periods of time adversely affects the nervous system, the blood, the kidneys, and the liver. These effects
subside when exposure stops. Nervous system effects of AN range from headaches and dizziness to
irritability, rapid heartbeat, and death. Symptoms of acrylonitrile poisoning may occur quickly after
exposure or after levels of breakdown products like cyanide build up in the body. Direct contact with
acrylonitrile liquid severely damages the skin. Acrylonitrile liquid or vapor irritates the eyes, the nose,
and the throat. These effects are not likely to occur at levels of acrylonitrile that are normally found in the
environment.
There are several health effects case studies of acrylonitrile workers. The methods used in these studies
limit conclusions that can be made from the results. These studies show that workers repeatedly
breathing small amounts of acrylonitrile over long periods of time may develop cancer. Cancer occurs
primarily in the respiratory tract. Laboratory studies show that repeated exposure to acrylonitrile in air
or in drinking water over a lifetime also causes cancer in animals. Studies also show that repeated
exposure to acrylonitrile adversely affects the respiratory and central nervous systems and causes
developmental toxicity in laboratory animals.
Acrylonitrile has moderate toxicity to aquatic life. By itself it is not likely to cause environmental harm at
levels normally found in the environment. Acrylonitrile can contribute to the formation of photochemical
smog when it reacts with other volatile substances in air.
FIGURE 4: Health Data from Inhalation Exposure
6 | Acrylonitrile by Propene Ammoxidation
ACGIH TLV--American Conference of Governmental and Industrial Hygienists' threshold limit value
expressed as a time-weighted average; the concentration of a substance to which most workers can be
exposed without adverse effect.
AIHA ERPG--American Industrial Hygiene Association's emergency response planning guidelines. ERPG 1
is the maximum airborne concentration below which it is believed nearly all individuals could be exposed
up to one hour without experiencing other than mild transient adverse health effects or perceiving a
clearly defined objectionable odour; ERPG 2 is the maximum airborne concentration below which it is
believed nearly all individuals could be exposed up to one hour without experiencing or developing
irreversible or other serious health effects that could impair their abilities to take protective action.
LC50 (Lethal Concentration50)--A calculated concentration of a chemical in air to which exposure for a
specific length of time is expected to cause death in 50% of a defined experimental animal population.
LOAEL--Lowest-observed-adverse-effect level.
NIOSH IDLH--National Institute of Occupational Safety and Health's immediately dangerous to life or
health limit; NIOSH recommended exposure limit to ensure that a worker can escape from an exposure
condition that is likely to cause death or immediate or delayed permanent adverse health effects or
prevent escape from the environment.
NIOSH REL--NIOSH's recommended exposure limit; NIOSH-recommended exposure limit for an 8- or 10h time-weighted-average exposure and/or ceiling.
OSHA PEL--Occupational Safety and Health Administration's permissible exposure limit expressed as a
time-weighted average; the concentration of a substance to which most workers can be exposed without
adverse effect averaged over a normal 8-h workday or a 40-h workweek.
The health and regulatory values cited in this factsheet were obtained in December 1999.
a. Health numbers are toxicological numbers from animal testing or risk assessment values developed by
EPA.
b. Regulatory numbers are values that have been incorporated in Government regulations, while advisory
numbers are non-regulatory values provided by the Government or other groups as advice. OSHA
numbers are regulatory, whereas NIOSH, ACGIH, and AIHA numbers are advisory.
c. The LOAEL is from the critical study used as the basis for the EPA RfC.
4 Sohio Process
It is the most famous method used by industries in order to produce Acrylonitrile by Propylene.
Propylene and ammonia are reacted in the presence of air at almost stoichiometric quantities at 30 psia
and a temperature of 662°F - 1112°F. The catalysts used in the process are mostly based on mixed metal
oxides such as bismuth-molybdenum oxide, iron-antimony oxide, uranium-antimony oxide, tellurium molybdenum oxide etc. The reactor product is cooled by quenching with water and is neutralized using
sulphuric acid to remove unconverted ammonia. Acrylonitrile is removed by extractive distillation, while
crude acetonitrile and hydrogen cyanide are separated from the bottom products. Hydrogen cyanide is
then removed by distillation.
Some of the wastes that are generated from the process are processed as follows:
7 | Acrylonitrile by Propene Ammoxidation


Ammonium sulphate that is produced as the bottoms product from the neutralizer can be used as
a fertilizer.
Unconverted ammonia is vented to the atmosphere. Aqueous wastes containing cyanides,
sulphates etc., are disposed of either incinerated, deep well injection or by biological treatment.
Reactor
The reactor is a large-diameter cylindrical vessel provided with a gas -distribution grid for supporting the
fluid bed, as well as with injection devices for feeding the gaseous reactants. The optimal catalyst particles
size is in the range 40 to 100 μ m, in which the presence of a certain amount of fines is necessary for
ensuring homogeneous fluidization. The gas velocity is slightly above the minimum, in general between
0.4 to 0.5 m/s. Trays or screens, usually between 5 and 15, can be placed transversally in order to reduce
the negative effect of back mixing. This modification gives much better performance in term of
acrylonitrile yield. Because of the highly exothermal reaction cooling coils are immersed in the fluid bed.
Since the temperature of reaction is around 420 – 450 ° C high – pressure steam of 30 to 40 bar can be
raised.
The feeding strategy of reactants should take into account the reaction mechanism. Usually, the oxygen
(air) is introduced below the bottom grid, with the mixed propylene and ammonia through “spiders”
positioned above the grid. The catalyst plays an important role in preserving the safety as scavenger for
oxygen radicals. No explosion was ever encountered over decades of operation.
Figure 5: Sketch of the fluid - bed reactor for acrylonitrile synthesis.
The operating pressure should be as low as possible to prevent the formation of by-products. On the
other side higher pressure would be preferable for quenching and scrubbing of gases. Overpressures of
0.5 to 2 bar are preferable. Almost complete conversion of propylene may be seen and selectivity around
80% in acrylonitrile can be obtained. The data are representative for modern catalysts.
The residence time in the reactor is between 2 and 20 s, with an optimal range from 5 to 10 s. longer
residence time gives more by-products. A more sophisticated design of the fluid - bed reactor requires
advanced modelling and simulation capabilities.
The main reactions and the side reactions of the process occur in reactor as follows:
CH2=CH-CH3 + NH3 + 3/2 02
Propylene
Ammonia
Oxygen
C3H3N +
Acrylonitrile
3 H 20
Water
Apart from the above main reaction there are the following side reactions:
CH2=CH-CH3 + O2
CH2=CH-CHO + H20
Acrolein
Water
8 | Acrylonitrile by Propene Ammoxidation
CH3=CH-CH3 + NH3 + 9/4 O2
CH3-CN + 1/2 C02 + 1/2 CO + H20
Acetonitrile
CH2=CH-CHO + NH3 + 1/2 02
CH3-CN +
3/2 02
CH2=CH-CN + 2H2O
CO2 + HCN +H2O
Kinetic data for the above reactions are given in Table 1 (Hopper, 1992).
TABLE 4.2
KINETIC DATA FOR THE ACRYLONITRILE PROCESS
Reaction Number
Activation Energy, Ei
(cal/mol)
Rate Constant, ki(sec-1)
At 662 F
1
2
3
4
5
19000
19000
7000
7000
7000
0.40556
0.00973
0.01744
6.81341
0.073
The rate equations for the acrylonitrile process are:
(-r1)=k1CC3H6
(-r2)=k2CC3H6
(-r3)=k3CC3H6
(-r4)=k4CCH2CHCHO
(-r5)=k5CCH3CN
The rate constants, expressed in kj's, are expressed in the Arrhenius form as
ki,T1=ki,T2 * exp [-(E/R){(1/T1)-(1/T2)}]
Where:
k = Rate constant,
E =Activation energy,
T1 and T2 = Temperatures.
R = Gas constant.
On conversion of the above parameters (as shown in Appendix), the equations become:
(-r1)=1.57089 * 105 * exp(-19000/RT)
(-r2)=3.768 * 103 * exp(-19000/RT)
(-r3)=1.99 * exp(-7000/RT)
(-r4)=780.07 * exp(-7000/RT)
(-r5)=8.357 * exp(-7000/RT)
Effect of different variables on Conversion
1. Effect of Residence Time: The residence time of the inlet particles in the reactor is related to the
volume of the reactor as per equation
9 | Acrylonitrile by Propene Ammoxidation
ɼ=
Where
ɼ is the residence time.
V is the volume of reactor
Q is the flow rate of feed
Therefore, varying the reactor volume effectively varied the residence time.
Figure 6: Effect of residence time on conversion
2.
Effect of Reaction Temperature
The conversion of the key inlet component in the PFR and the CSTR schemes increases as the
temperature increases. The conversion increases from 11 % to 63% for CSTR for a temperature range of
700°F to 1000°F. The conversion increases from 12% to 71 % when the reactor used is a PFR for the
same temperature range.
Figure 7: Effect of Reaction Temperature on Conversion.
3.
Effect of Reaction Pressure
The conversion in a PFR scheme varies from 14% to 53%. The conversion increases for a CSTR too
within the same pressure range from 13.5% to 43 .8%. It can also be seen from the trend in figure
given below that the conversion increases at a much higher rate for the PFR rather than a CSTR.
10 | Acrylonitrile by Propene Ammoxidation
Figure 8: Effect of reaction pressure on conversion.
4.
Effect of Catalyst
The catalysts used in the process are mostly based on mixed metal oxides such as bismuth-molybdenum
oxide, iron-antimony oxide, uranium-antimony oxide, tellurium - molybdenum oxide etc. Conversion of
Propylene various with different composition of metals in catalyst.
Mechanism proposed is appended below:
11 | Acrylonitrile by Propene Ammoxidation
I) Reactor 2) Neutralizer 3) Absorber 4) Recovery 5) HCN Column 6) Extractive Distillation Column 7)
Acetonitrile Purification Column 8) Acrylonitrile Purification Columns
Figure 9: Process flow diagram of the Acrylonitrile Process
5 Aspen Simulation
Reactor


Industrially Fluidized Catalytic Cracker is used as a reactor and since most of the reaction
(nearly 80%) occurs in the riser of FCC unit so we can approximate that with PFR (Plug
flow reactor) which is available there in Aspen Plus.
Property Method used in simulation: NRTL
1
B1
2
12 | Acrylonitrile by Propene Ammoxidation
React or Design
Stream ID
1
T emperature
K
Pressure
atm
Vapor Frac
2
623.1
685.1
2.20
2.20
1.000
1.000
4008.000
4123.149
kg/hr
114854.402
114854.402
Volume Flow
l/min
1.55259E+6 1.75611E+6
Ent halpy
MM Btu/hr
Mole Flow
kmol/hr
Mole Flow
kmol/hr
Mass Flow
26.062
-77.890
AMMONIA
408.000
177.703
O2
646.000
295.512
30.000
725.933
340.000
104.662
H2O
PROP Y-01
ACRYL-01
230.296
ACROL-01
5.041
CO2
0.001
CO
0.001
ACET O-01
0.001
HYDRO-01
Conversion
N2
2584.000
2584.000
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
0.5
1
1.5
2
2.5
Along the length of the reactor, m
Quencher
It is used to remove ammonia from the reactor effluent and low down its temperature using
sulphuric acid. It produces ammonium sulphate salt ((NH 4)2SO4) at bottom which is used as a
fertilizer and the top effluent is sent to absorber.
Simulation of quencher is done using RadFrac model.
Property Method used : UNIQUAC
No. of Stages : 10
Sulphuric acid: 30% concentrated H2SO4
13 | Acrylonitrile by Propene Ammoxidation
Que ncher Design
Strea m ID
3
Temperature
K
Pressure
atm
Vapor Frac
4
5
6
513.0
601.1
308.7
1.00
2.00
4.00
405.7
3.00
0.932
1.000
0.000
1.000
Mole Flow
kmol/hr
300.000
4123.149
980.761
3264.685
Ma ss Flow
kg/hr
12610.362
114854.402
33917.221
93547.543
Volum e Flow
l/m in
196081.905
1.69469E+6
739.243
603747.856
Enthalpy
MMBtu/hr
-108.716
-90.515
-171.056
-28.174
Mole Flow
kmol/hr
PROPY-01
104.662
8.658
96.004
OXYGEN
295.512
0.560
294.952
AMMONIA
177.703
trac e
trac e
0.001
< 0.001
0.001
ACRYL-01
230.296
163.867
66.429
ACROL-01
5.041
2.546
2.495
CARBO-01
HYDRO-01
ACETO-01
WATER
SULFU-01
210.000
0.001
0.001
< 0.001
725.933
712.387
223.546
0.187
0.961
90.000
AMMON-01
88.851
trac e
CO
0.001
trac e
0.001
N2
2584.000
3.703
2580.297
Bottom stream coming out of quencher mainly consists of ammonium sulphate. This stream is
further passed into Crystallizer where crystals of ammonium sulphate are produced which is
used as fertilizer.
14 | Acrylonitrile by Propene Ammoxidation
Absorber
Function of Absorber is to remove the residual gases, containing unconverted propylene, CO2
and other VOC.
Simulation is done using RateFrac model
Property method used: UNIQUAC
Random Packing: 5 segments of Raschig rings made up of ceramic, diameter=0.375in
Height of each packing segment=10ft
Column Diameter=5ft
Columns with random packing are best suited for liquid flows at high velocity.
For feeding liquid into the absorber, orifice type distributor is used. Since the depth of
packing>20ft, a distributor is needed for liquid.
15 | Acrylonitrile by Propene Ammoxidation
Absorber Des ign
Stream ID
7
Temperature
K
P res sure
atm
Vapor Frac
Mole Flow
kmol/hr
Mass Flow
kg/hr
Volume Flow
l/min
Enthalpy
MMBtu/hr
Mole Flow
kmol/hr
8
9
10
303.1
278.1
278.7
2.00
1.00
2.00
2.20
0.950
0.000
1.000
0.000
3264.685
10122.870
2940.477
10447.079
93547.543 182366.337
643255.296
-44.938
288.2
84437.083 191476.797
3001.633 560282.200
3219.146
-2754.141
-2.686
-2796.394
P RO P Y-01
96.004
65.706
30.298
O XYGEN
294.952
292.418
2.533
A MMON IA
trace
CA RBO-01
0.001
0.001
< 0.001
A CRYL-01
66.429
3.970
62.459
A CROL-01
2.495
0.151
2.344
A CETO -01
< 0.001
trace
< 0.001
12.932
10333.484
trace
0.961
H YDRO -01
WA TER
223.546
SULFU-01
0.961
A MMON -01
ACN Recovery
10122.870
trace
CO
0.001
0.001
trace
N2
2580.297
2565.298
14.999
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
20
16 | Acrylonitrile by Propene Ammoxidation
40
60
80
Feed Temp (°C)
100
120
ACN Recovery
1
0.995
0.99
0.985
0.98
0.975
0.97
0.965
0.96
0.955
0.95
0.2
0.3
0.4
0.5
0.6
Packing diameter (in)
0.7
Recovery Unit (Re-boiled Stripper)
Idea is to recover the useful components from the aqueous solution like ACN, AN etc.
Simulation is done using Radfrac packed stripper column
Property method used: UNIQUAC
No. of stages: 10
Boil up ratio: 1
Random Packing: Saddles made up of ceramic, diameter=0.5in
Total tower height=40ft
Column diameter=5ft
Air cooled heat exchanger: Forced daft, Aluminium fins, 0.5in fin height, 7 fins/linear
inch, axial flow fans
Decanter: Plate contactor
17 | Acrylonitrile by Propene Ammoxidation
Recovery column Des ign
Stream ID
10
Temperature
K
P res sure
atm
15
288.2
13
287.9
16
300.0
378.4
2.20
1.20
1.20
1.20
0.000
0.000
0.000
0.000
10447.079
7334.782
114.226
10332.857
Vapor Frac
Mole Flow
kmol/hr
Mass Flow
kg/hr
Volume Flow
l/min
3219.146
2194.977
134.460
3401.570
Enthalpy
MMBtu/hr
-2796.394
-1990.986
8.414
-2739.310
Mole Flow
kmol/hr
30.298
30.298
trace
2.533
2.533
trace
< 0.001
< 0.001
trace
A CRYL-01
62.459
62.459
trace
A CROL-01
2.344
2.344
trace
A CETO -01
< 0.001
< 0.001
trace
191476.814 132138.154
P RO P Y-01
O XYGEN
5250.614 186226.267
A MMON IA
CA RBO-01
H YDRO -01
WA TER
10333.485
1.593
10331.895
0.961
< 0.001
0.961
CO
trace
trace
trace
N2
14.999
14.999
trace
SULFU-01
7334.782
A MMON -01
1
0.998
AN Recovery
0.996
0.994
0.992
0.99
0.988
0.986
0.984
0.982
0.98
0.2
1.2
18 | Acrylonitrile by Propene Ammoxidation
2.2
3.2
4.2
Boil up ratio
5.2
6.2
1
B1
B2
3
4
B7
5
6
B4
7
8
B5
9
10
B3
11
16
15
B6
12
B9
14
B8
13
Overall
19 | Acrylonitrile by Propene Ammoxidation
Overall Design
Stream ID
1
Temperature
K
Pressure
atm
Vapor Frac
3
5
8
9
13
16
623.1
513.0
308.7
278.1
278.7
300.0
378.4
2.20
1.00
4.00
1.00
2.00
1.20
1.20
1.000
0.932
0.000
0.000
1.000
0.000
0.000
4008.000
300.000
980.760
10122.870
2940.477
114.226
10332.857
12610.362
33917.204 182366.337
84437.082
Mole Flow
kmol/hr
Mass Flow
kg/hr
114854.402
Volume Flow
l/min
1.55259E+6 196081.905
Enthalpy
MMBtu/hr
Mole Flow
kmol/hr
26.062
-108.716
739.243
3001.633 560282.193
-171.056
-2754.141
5250.614 186226.267
134.460
3401.570
-2.686
8.414
-2739.310
PROPY-01
340.000
8.658
65.706
30.298
trace
OXYGEN
646.000
0.560
292.418
2.533
trace
AMMONIA
408.000
< 0.001
0.001
< 0.001
trace
ACRYL-01
163.867
3.970
62.459
trace
ACROL-01
2.546
0.151
2.344
trace
ACETO-01
0.001
trace
< 0.001
trace
12.932
1.593
10331.895
trace
< 0.001
0.961
trace
0.001
trace
trace
3.703
2565.298
14.999
trace
CARBO-01
HYDRO-01
WATER
30.000
SULFU-01
210.000
712.387
90.000
0.187
AMMON-01
88.851
CO
N2
10122.870
2584.000
20 | Acrylonitrile by Propene Ammoxidation
6 Plant Wide Control System Design
Pressure Driven Overall Flow Sheet
In order to put controllers in plant, first, whole plant is made pressure driven using pumps,
compressors and valves etc. Pressure driven overall flow sheet is appended below:
21 | Acrylonitrile by Propene Ammoxidation
Dynamic Stripper:
17
B18
20
B15
PC1
19
B19
18
B14
L C2
16
15
21
22
B17
Dynamic Absorber and Stripper:
PC1
B18
25
B21
33
32
B15
PC3
B11
13
18
30
20
B13
B16
21
29
B19
L C4
L C2
B14
28
34
31
22
B20
B17
35
22 | Acrylonitrile by Propene Ammoxidation
7 Liquid Separation Scheme
Materials to be recovered
The raw acrylonitrile stream contains approximately 85% acrylonitrile and 5% water, the rest being
organic impurities, namely HCN, Acrolein and acetonitrile. This section will handle the treatment of the
raw acrylonitrile stream recovered by absorption-stripping as described previously. The dissolved gases
from stripping column are neglected. Also, for the purposes of simulation, heavies present in raw
acrylonitrile product are neglected. In practice they are separated as bottom streams along with cyanoacrolein, which is produced in HCN separation column.
Development of Separation Sequence
30
35
40
Temperature C
45 50 55 60
65
70
75
80
T-xy for ACRYL-01/HYDRO-01
25
T-x 1.0133 bar
T-y 1.0133 bar
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1
Liquid/Vapor Molefrac ACRYL-01
From the binary distillation curve of AN and HCN, it is evident that both streams can be obtained as pure
species. However, since the composition of stream is far from equimolar, therefore in a single column
with reasonable number of trays and condenser duty, large amount of AN also goes into the top stream.
Therefore, a second column at lower pressure is used to recover AN from the top stream. Net AN
Recovery is close to 99.9%, however, some of HCN is lost due to reaction with Acrolein. This reaction is
important for removal of Acrolein in the form of heavies.
CH = CH
CH = CH
CH
HC
→
C
CH
CH
CH
C
HC
→
C
CH
CH
C
HCN and Acrolein are both toxic. Also, HCN is most easily separated component. By using heuristics for
design, these 2 components are removed first.
23 | Acrylonitrile by Propene Ammoxidation
81.5
T-xy for ACRYL-01/ACETO-01
T-y 1.0133 bar
78
78.5
Temperature C
79
79.5
80
80.5
81
T-x 1.0133 bar
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1
Liquid/Vapor Molefrac ACRYL-01
After removing HCN, AN and ACN are valuable components that can be recovered from bottom streams.
However, the binary distillation curve for AN-ACN mixture suggests that separation by ordinary
distillation is extremely difficult. In such a scenario, changing column pressure may be considered. It is
observed that changing the pressure does not have a great effect on relative volatilities. Therefore this
option is ruled out. Addition of another component to change the relative volatilities is considered next.
An ideal extracting fluid must:
 Sufficiently change relative volatility
 Be easily separated from two components
Water is used as an extracting fluid because it is readily available and non-toxic. Residue curve of waterAN-ACN system shows that a large amount of water is required to ensure efficient separation. Water to
feed ratio for extractive distillation is 10:1. AN is obtained as a top product whereas ACN is obtained as a
side stream. The bottom product consists of heavies (such as cyano-acrolein and is sent to wastewater
treatment section).
24 | Acrylonitrile by Propene Ammoxidation
0 .3
0 .2
AC
ET
O01
0 .4
0 .5
0 .1
0 .9
0 .2
0 .8
0 .3
0 .7
0 .4
0 .6
0 .5
ER
AT
0 .6
W
fra
c
c
fra
0 .7
le
Mo
0 .8
Mo
le
0 .9
0 .1
Residue curve for ACRYL-01/WATER/ACETO-01
0.1
0.2
0.3
0.4 0.5 0.6 0.7
Molefrac ACRYL-01
0.8
0.9
Extractive distillation step leads to 2 product streams with water present in them. From the binary
distillation curves of AN-water and ACN-water, following features of the separation scheme are
immediate:

T-xy for ACRYL-01/WATER
T-x 1.0133 bar
T-y 1.0133 bar
65
70
Temperature C
75
80
85
90
95
100
105

Acylonitrile may be obtained as a pure component if AN conc. in the input stream is high. This can
be achieved if less water is entrained in the top stream of extractive distillation. This achieved by
using a decantor for phase separation.
Side stream contains large amount of water, whereas the amount of valuable ACN is very small.
From the binary distillation curve it is evident that at best the azeotropic point can be reached.
However, this should be good enough a concentration because amount of ACN is anyway small (5
moles for 100 moles of raw-AN). Therefore a small amount of water can be separated by
advanced drying techniques.
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1
Liquid/Vapor Molefrac ACRYL-01
25 | Acrylonitrile by Propene Ammoxidation
Extractive distillation is defined as distillation in the presence of a miscible, high boiling, relatively nonvolatile component, the solvent, that forms no azeotrope with the other components in the mixture. The
method is used for mixtures having a low value of relative volatility, nearing unity. Such mixtures cannot
be separated by simple distillation, because the volatility of the two components in the mixture is nearly
the same, causing them to evaporate at nearly the same temperature at a similar rate, making normal
distillation impractical. The solvent interacts differently with the components of the mixture thereby
causing their relative volatilities to change. This enables the new three-part mixture to be separated by
normal distillation.
85
T-xy for ACE TO-01/WATE R
T-x 0.5 bar
60
Temperature C
65
70
75
80
T-y 0.5 bar
0
0.2
0.4
0.6
Liquid/Vapor Molefrac ACETO-01
0.8
1
Simplifying Assumptions
 Gases present in raw acrylonitrile are neglected and therefore not accounted for in simulation
steps. In practice, they are vented out in phase separators.
 In case of distillation columns, equilibrium separations are assumed for the base case design.
Simulation of Separation Steps and Equipment Sizing
The simulated process flow sheet is shown below. It consists of 5 fractionation columns and 2 decanters.
LS1
LS2
LS4
LS7
LS8
LS5
LS9
Column to separate HCN from Raw acrylonitrile
Column to recover AN and ACN from vapor stream of HCN
Extractive Distillation of AN and ACN using water
Separate the side stream from extractive distillation to remove water from
acetonitrile
Separate top stream from extractive distillation to obtain pure acrylonitrile
Decanter to separate and recycle water from the top stream of extractive distillation
Decanter to phase separate water and acrylonitrile to further purify product stream
A steady state simulation is carried out to fit the flow sheet, so as to obtain following design parameters.
Reasonable initial guesses are taken considering typical industrial columns used for similar separation
factors. The design parameters are thereby optimized to obtain maximum product recovery as well as
minimum or negligible side products in the final product stream.
26 | Acrylonitrile by Propene Ammoxidation
27 | Acrylonitrile by Propene Ammoxidation
Distillation Columns
Column
Stages
Pressure (bar)
Reflux ratio
Boilup ratio
Distillate to feed ratio
Top Temp (oC)
Bottom Temp (oC)
Condenser type
Q cond (MW)
Q reboiler (MW)
Tray type
Tray Spacing (m)
LS1
40
F=10
LS2
30
F=10
1.1
2
1
5.35
3
0.18
61.83
80.04
Total
0.4915
0.5198
Sieve
0.5
30.40
71.00
Total
0.1719
0.1726
Sieve
0.6
0.648
LS7
20
F=5
LS9
30
F=15
R=15
0.5
8.5
0.1
0.006
56.37
80.97
Total
1.4898
1.0524
Sieve
0.8
1.1
0.2
1
85.22
105.40
Total
2.2250
Ceramic
Raschig ring
0.5
0.73
1.95
2.035
Packing type
Packed HETP (m)
Packing void fraction
Packing surface area (cm2/cm3)
Column diameter (m)
LS4
40
F=20
ExtW=1
R=20
1.22
0.340
1.167
73.59
74.81
Total
0.8740
0.9164
Sieve
0.6
0.7684
Overall Process Balance
Input
Streams
Temperature
RAW-AN
Product Streams
EXTW
T-LS2
B-LS8
Wastewater
T-LS7
B-LS4
B-LS7
D-LS9
65
75
30.4
74.8
56.4
105.4
81
60
1.1
1.22
1
1.1
0.5
1.22
0.5
1.1
0
0
0
0
0
0
0
0
100
946.5
5.35
98.866
5.447
23.236
902.393
10.708
4948.376
17051.46
158.679
4718.7
193.088
424.317
16299.78
205.28
6.703
18.065
0.227
6.513
0.267
0.466
17.407
0.223
2.972
-63.767
0.123
2.115
-0.05
-1.547
-60.62
-0.687
85
0
0.616
83.677
0.355
0
0
0.352
HCN
5
0
4.498
0
0.002
0
0
0
ACN
4.5
0
0.008
0.211
3.581
0
0.698
0.002
Acrolein
0.5
0
0
0
0
0
0
0
Water
5
946.5
0.228
14.978
1.509
23.149
901.283
10.354
Heavies
0
0
0
0.088
0.412
0
oC
Pressure
bar
Vapor Frac
Mole Flow
kmol/hr
Mass Flow
kg/hr
Volume Flow
m3/hr
Enthalpy
MMkcal/hr
Mole Flow kmol/hr
AN
Product
Recovery (%)
0
HCN
0
AN
ACN
89.96
98.43
79.58
Mol frac.
0.8407
0.8464
0.6574
Wt frac.
0.7654
0.9397
0.7607
It can be seen that the process gives reasonable recoveries for all the products. The main product of this
process, acrylonitrile is recovered up to 98.43%. However, the purity of product streams is not very high.
28 | Acrylonitrile by Propene Ammoxidation
Most of them contain entrained water and therefore additional separation steps may be required to
remove water depending on the application.
Water Recovery
For extractive distillation, large amount of water is required. Therefore the process results in large
amount of wastewater. This mostly consists of heavies and small amount AN and ACN that could not be
recovered. It is therefore desirable to separate pure water from this stream, so that it can be recycled for
extractive distillation. Also, the remaining effluent can be further treated to recover remaining valuable
products depending on product and operating costs. Pure water is recovered from wastewater in WT1.
The process leads to recovery of 98.73% recovery of water used for extractive distillation and can be
recycled to reduce the overall water requirement for the process.
29 | Acrylonitrile by Propene Ammoxidation
8 Pollutants And Their Control
Air Pollution
Absorber Vent Gas. The absorber vent gas stream contains nitrogen, oxygen, unreacted propylene ,
hydrocarbon impurities from the propylene feed stream, CO, CO 2, water vapour, and small quantities of
ACN, acetonitrile, and hydrogen cyanide. Two control methods are used to treat this stream: thermal
incineration and catalytic oxidation.
The thermal incineration units have demonstrated VOC destruction efficiencies of 99.9% or greater, while
most catalytic units can achieve destruction efficiencies only in the 95-97% range. Destruction efficiencies
in the 99% and greater range can be achieved with catalytic oxidizers, but these are not achieved on a
long-term basis because of deactivation of the catalyst by a number of causes. The advantage of catalytic
oxidation is low fuel usage, but emissions of NOx formed in the reactors and not destroyed across the
catalyst can pose problems.
Column Waste Purge Gas. Waste gas releases from the recovery column, light-ends column, product
column, and the acetonitrile column are frequently tied together and vented to a flare. The estimated VOC
destruction efficiency of the flare is 98-99% for all streams with a heat content of 300 Btu/scf or greater.
The use of a flare is ideally suited for streams that are intermittent and having heating values of 300
Btu/scf.
Fugitive emissions. Fugitive emissions from piping, valves, pumps, and compressors are controlled by
periodic monitoring by leak checking with a VOC detector and a directed maintenance program.
Incinerator Stack Gas. Staged combustion and ammonia injection are used to control the emissions of NOx
from the incinerator that treats the absorber off-gas vent, the crude acetonitrile waste gas stream, and the
by-product liquid HCN stream. Staged combustion suppresses the formation of NOx by operating under
fuel-rich conditions in the flame zone where most of the NOx is formed and oxygen-rich conditions
downstream at lower temperatures where NOx is not appreciably formed.
Ammonia injection reduces NOx by selectively reacting ammonia with NOx. The reaction occurs at
temperatures in the range of 870-980°C (1600-1800°F) and, as such, the ammonia must be injected in the
postflame zone of the combustion chamber. Residence times of 0.5-1.0 second are required for NOx
destruction efficiencies in the range of 80%, which is compatible with the residence time required for
VOC destruction.
Deep Well/Pond Emissions. Emissions of acrolein and other odorous components in vents from
wastewater treatment steps are controlled with water scrubbers. In some cases, pond emissions are
controlled by adding a layer of a low-vapor-pressure oil on the surface of the pond to limit volatilization.
Storage Tank Emissions. Product storage tank emissions are controlled with double-seal floating roofs or,
in some cases, water scrubbers. Field experience indicates that a removal efficiency of 99% can be
achieved with water scrubbing.
Product Transport Loading. Emissions from product transport loading vents are gathered and sent to a
flare or incinerator for VOC control. Destruction efficiencies of 98-99% are achieved using the flare and
greater than 99% using incineration.
Solid/Liquid Waste
Wastes include salts of hydrogen cyanide, metal cyanide complexes, and organic cyanides (cyanohydrins)
as solutions or solids. The wastewater from the wastewater column contains ammonium sulphate and
heavy hydrocarbons, while the wastewater from the acetonitrile column mainly contains heavy bottoms.
The wastewater from both these columns is typically dis-charged to a deep well pond. Other methods of
waste treatment include alkaline chlorination in a recycle lagoon system, and incineration.
30 | Acrylonitrile by Propene Ammoxidation
9 Modifications to Design
Quench Column (Acidic)
Quench column is used to cool the reactor outlet to 30oC, as well as remove ammonia as sulphate. The
feed gas is quenched with 30-40% sulphuric acid. Recycled water is added to compensate for
vaporization losses.
Equipment:
The quenching is carried out in a packed column in order to increase the heat transfer area as well as area
for dissolution of ammonia. Since sulphuric acid is highly corrosive, ceramic packing in the form Raschig
rings are used. Random packing is used due to high flow rates. (Similar packing is used in manufacture of
sulphuric acid, in SO3 absorption to form oleum.) In order to prevent corrosion of column walls, it is lined
with glass. The ring diameter in packing is large (1in) in order to prevent clogging due to tiny catalyst
particles.
Associated Problem:
Modelling a quench column is particularly difficult because of 5 main processes that take place in a single
transfer unit:
 Transfer of NH3 into the liquid phase
 Reaction b/w NH3 and H2SO4 in the bulk liquid phase
 Vaporization of water from liquid phase
 Heat transfer
 Clogging of catalyst particles into packing
To simplify the problem, clogging can be ignored. However, on simulation in aspen, the model failed to
give a satisfactory result.
Semi Quantitative Analysis using CFD in Comsol Multiphysics
Balance for a Differential element:
AL : Acid (liquid phase)
NL and NG : Ammonia in liquid and gas phase respectively
WL and WG : Water in liquid and gas (vapour) phase respectively
31 | Acrylonitrile by Propene Ammoxidation
SL : Ammonium sulphate dissolved in liquid phase
BG : Gases that are sparingly soluble and hence ignored in mass transfer (ACN, HCN, AN, propylene etc)
dN : Transfer of ammonia from gas to liquid
dW : Vaporization of water
r : Rate of reaction for dissolution of ammonia in sulphuric acid
a : Effective area
Use of CFD
In order to obtain a better insight into the problem, CFD simulations are carried out using COMSOL
Multiphysics. The motivation is to model a smallest repeated transfer unit of the column for all the above
factors. The following assumptions are made for developing a basic model:
1. Radial variations in the column are neglected unless there is a different stream. That is, both
liquid and gas streams are radially uniform and vary only along the length of the column.
2. The channelled flow through the packing can be assumed to be a flow through a cylinder of
radius same as the Raschig ring.
3. The gas is assumed to bubble through the liquid inside the flow domain. Further, concentration of
NH3 inside a single bubble is uniform.
4. The dissolution of NH3 follows first order kinetics. This is a fair assumption since sulphuric acid
is in a large amount (for cooling requirements).
The assumptions stated above lead to the following geometry.
Methodology:
Initially fluid flow in the geometry is used as a base model. Later transport of diluted species (with
reaction) and heat transfer are added and coupled with the initial physics. To keep the model simple,
vaporization is ignored for the time being.
Simulation results in velocity profiles, concentration profiles and heat transfer. In 2D axisymmetric
domain, the line integral of concentration along the radius multiplied with velocity gives the total species
transfer. Such units can be taken as an array to build the entire column.
Simulation Results:
Velocity
Concentration (NH3)
32 | Acrylonitrile by Propene Ammoxidation
Temperature
With a steady state model in place, it has to be used now for actual equipment design. For this purpose
another simplifying assumption is made. For each Raschig ring, we assume pseudo steady state. Which
means, a single Raschig ring can be analysed for steady state model. However, two different rings may be
at different steady states. With steady state simulation as a base model, time dependent steady is carried
out.
The actual process of quenching operates at steady state. The time dependent analysis actually
simulates the spatial motion of a gas bubble across the column through different rings. For
example t=0, is the state when gas enters the column and t=tR is the state when gas leaves the
column. Therefore the final result of this analysis would provide the required residence time.
Since sulphuric acid is used in excess for cooling the gas and ammonia reacts to form salt in liquid phase,
the concentration of ammonia is neglect at each ring inlet.
Initial concentration of NH3 (assuming ideal gas mixture) is 0.0347 mol/m3. Final product should have
atleast 99% of ammonia removed. By transient analysis we plot the volume averaged concentration in gas
bubble vs time.
At about t=15s, the conc decreases below required value. Hence, the required residence time for the
reactor considering ammonia absorption is 15s.
However, for considering heat transfer, more careful analysis is needed because the ring inlet
temperature of liquid also changes across the length of column. The approach followed here is to use the
residence time obtained by mass transfer considerations and find the temperature change for various
33 | Acrylonitrile by Propene Ammoxidation
values of ring inlet temperature ( ). Since the operation is like a counter current heat exchanger,
temperature of gas is taken as
. The transient temperature profile is normalized with .
It is observed that tR = 15s is sufficient for heat transfer operations also. Hence, this is the required
residence time.
34 | Acrylonitrile by Propene Ammoxidation
Economy Optimization: Economy ptimization is simulated in “Haskell”. Code is appended below:
data Unit = Unit { pid :: String,
inp :: [Stream],
otp :: [Stream],
util :: [Utility]
} deriving (Show)
data Stream = Stream { sid :: String,
comp :: [(String, Double)],
flow :: Double
} deriving (Show)
data Utility = Utility { uid :: String,
val :: Double
} deriving (Show)
type CostTable = [(String, Double)]
lookUp :: CostTable -> String -> Double
lookUp [] x = 0
lookUp ((a,b) : ls ) x | (a==x) = b
| otherwise = lookUp ls x
costStr :: CostTable -> Stream -> Double
costStr cT a = (flow a) * sum (map (mult cT) (comp a))
mult :: CostTable -> (String, Double) -> Double
mult cT x = snd(x) * lookUp cT (fst x)
costUtil :: CostTable -> Utility -> Double
costUtil cT a = val a * lookUp cT (uid a)
margin :: CostTable -> Unit -> Double
margin cT a = sum (map (costStr cT) (otp a)) +
sum (map (costUtil cT) (util a)) sum (map (costStr cT) (inp a))
costTab :: CostTable
costTab = [("HCN", 100),
("AN", 500),
("ACN", 200),
("lp-steam", 15),
("mp-steam", 20),
("hp-steam", 40),
("C3H6", 70),
("air", 0),
("Cool-water", 5)
]
35 | Acrylonitrile by Propene Ammoxidation
10 Plant Location
Naturally to obtain the plant location we had to look at a number of aspects primarily
 Availability of raw materials
 Industrialized Hub
 Market Demand for the Products
 Transportation and Port Access

Skilled Workforce
Ammonia :
Taking a closer look at these aspects for Ammonia we found the major producing regions of Ammonia
being :
1. GSFC (Baroda) 1350
2. Nagarjuna Fertilizers (Kakinada) 900
3. Tata Chemicals Ltd. 1350
4. IFFCO (Kalol) 1160
5. GNFC (Bharuch) 1350
6. Shriram Fertilizers (Kota) 600
7. KRIBHCO (Hazira) 2600
8. National Fertilizers (Panipat) 900
The numbers indicate production.
Fig 1: Ammonia Price
Ref:http://www.agr.gc.ca/pol/maddam/index_e.php?s1=pubs&s2=rmar&s3=php&page=rmar_01_0
3_2009-07-10
Most of the ammonia plants set up in India until 1968 were on a turnkey basis. In 1966, the Government
of India decided to set up a series of single stream 600 TPD ammonia plants. Ammonia plants at
Durgapur, Barauni and Cochin were set up through foreign aid which also included supply of
equipment.Some of these plants have not performed well due to improper equipmentselection. Over a
period of time, the performance got worse and some of theseplants have been shut down. Subsequently,
Indian fertilizer companies selected reliable technology andproper equipment on the basis of competitive
bidding. With the discovery oflarge reserves of offshore gas, a number of 1350 TPD ammonia plants
arebeing installed based on technology supplied by Haldor Topsoe and M. W.
The 36% to 94% for naphtha based plants, 56% to 81 %for fuel oil-based plants, 44% to 92% for gas
based plants and only 20% to 42% for coal based plants. Specific energy consumption also showed wide
36 | Acrylonitrile by Propene Ammoxidation
deviations with reference to the process, the feedstock and the year ofinstallation. The best performance
was recorded by the gas-based plant of 1FFCO, Kalol with 8.98 Kcal/tonne of ammonia. The source of
hydrogen was then changed over to fuel oil and finally to natural gas and naphtha. Natural gasis an ideal
feedstock, which is cheap, easily transportable by pipelines and relatively pure.capacity utilisation
(averaged over last five years) of the ammonia plantsvaried from plant to plant.
DISTRIBUTION OF AMMONIA CAPACITY:
Amongst the operating plants, maximum ammonia capacity exists in Gujarat (21.9% of total installed
capacity), followed by Maharashtra (15.6%). Maximum operating capacity exists in the public sector
(56%) followed by the the private sector (27%) and the co-operative sector (17%). However,
amongplants under implementation, 60% of the capacity lies in the private sector,resulting in public
sector's share as 49% followed by the private sector with 35% and the co-operaive sector with 16%.
Fig 2: Ammonia Feedstocks
Ref : http://www.dsir.gov.in/reports/techreps/tsr019.pdf
37 | Acrylonitrile by Propene Ammoxidation
Fig 3 : Current and Propoed Gas Pipelines in India
Refhttp://www.tribuneindia.com/2004/20040304/science.htm
Propylene
In India total ethylene capacity is expected to reach 4987 KTA by 2016-17 and Reliance Industries Ltd has
planned capacity expansion to2898 KTA by 2016-17 followed by IOC at 565 KTA, HMEL at 450, HPL
Halida at 345 KTA, ONGC OPAL at 340 KTA, and BPCL at 170 KTA.
Meanwhile, Propylene prices have increasingly become volatile from 500 $/tonne (Spot CFR NE Asia) in
April 2002 it has touched close to 1500 $/tonne in recently in March 2012 and currently at 1150 $/tonne
in June 2012. (Source ICIS)
38 | Acrylonitrile by Propene Ammoxidation
Fig : Current and Future Share of Major Propylene Producers
Ref : http://cpmaindia.com/propylene_about.php
Table : Projected and Current Propylene Production in India
Actual
Projected
2011-12
2012-13
2013-14
2014-15
2015-16
2016-17
RIL Group
2778
2728
2728
2728
2898
2898
GAIL, Auraiya
35
35
70
70
70
70
HPL, Haldia
345
345
345
345
345
345
HPCL Vizag
54
54
54
54
54
54
HMEL, Bhatinda
225
450
450
450
450
450
BPCL
130
170
230
230
230
230
IOC
565
565
565
565
565
565
340
340
340
Capacity (kt)
OPAL
Others
75
35
35
35
35
35
Total
4117
4382
4477
4817
4987
4987
39 | Acrylonitrile by Propene Ammoxidation
Propylene Derivatives
2010-11
2011-12
% Share
Growth Rate
2011-12 (%)
PP
3004
3796
95%
26%
2-EH/Oxo-Alcohol
73
74
2%
1%
Phenol
40
40
1%
0%
Acrylonitriile
42
44
1%
5%
Propylene Oxide
23
23
1%
0%
IPA
0
0
0%
Epichlorohydrin
7
7
0%
0%
n-Butanol
15
15
0%
0%
EPDM
0
0
0%
Total
3203
3999
40 | Acrylonitrile by Propene Ammoxidation
Gujarat is India’s ‘Petro Capital’ State with 30% of Petrochemicals, 50% Chemicals and Pharmaceuticals
business. Ranking on top in Marine Production, Fisheries and Ports, the state has manufacturing India’s
90% soda ash, 70% salt and 20% caustic soda. Petroleum and chemicals and Petroleum Investment
Region (PCPIR) is being set up at Dahej which may further add to strengthen the sector base.
Gujarat has the distinction of being the first state to enact the Special Economic Zone (SEZ) Act, 2004.
Special Economic Zones (SEZs) are growth engines that can boost manufacturing, augment exports and
generate employment. The Government has introduced the scheme of SEZs in order to provide a hassle
free operational regime and encompassing state of the art infrastructure and support services.
Special Economic Zone (SEZ) is a specifically delineated duty free enclave and shall be deemed to be
41 | Acrylonitrile by Propene Ammoxidation
foreign territory for the purpose of trade and operations and duty and tariffs. SEZ units may be set up for
manufacture of goods and for rendering of services – public, private or joint sector or by the State
Government.
SEZs, cover industrial and labour aspects, including flexible labour laws and exit options. The Gujarat SEZ
Act, 2004 has made key provisions with respect to the appointment and termination of labour for units
established in SEZs.
he concept of ‘Fixed erm Employment’ introduced by the SEZ Act has helped in accounting for the least
manpower days lost due to labour strife, among comparable industrial states.
SEZs in Gujarat approved by the MoCI, New Delhi as on 30/09/2008
Formal approval to SEZs
Land recommendation by
GOG for SEZs (in hectare)
Total
506.54
03
*Notified and Functional *
9808.62
07
Notified SEZs
6114.17
15
Formal approval to SEZs
7733.09
24
In-principle approval to SEZs
5231.41
11
29423.83
60
Functional SEZs before enactment of Act
Total
Gujarat, the state which pioneered the concept of the Special Investment Region (SIR), will establish 12
new industrial hubs in the next 5-6 years and expects the private sector to play a leading role in
facilitating the process.Gujarat passed an act for the SIRs and set up the first such hub -- Petroleum
Chemical and Petrochemical Investment Region (PCPIR) spread across 4.53 lakh square hectare-- in
Bharuch recently.The state government now plans to set up the SIRs to act as industrial hubs for various
sectors
including
auto
ancillaries,
chemicals,
healthcare,
electronics
and
so
on.
Investment worth over Rs 70,000 crore has already gone into PCPIR and the official said similar
expenditure is likely to be incurred in other SIRs as well.
From the point of view of investement , Pro Industry Policies and other factors aforesaid BHARUCH ,
GUJARAT would be an ideal location for the plant based on our preliminary research.
42 | Acrylonitrile by Propene Ammoxidation
11 References
1.
Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological Profile for
Acrylonitrile. Public Health Service, U.S. Department of Health and Human Services, Atlanta, GA.
1990.
2. International Agency for Research on Cancer (IARC). IARC Monographs on the Evaluation of the
Carcinogenic Risk of Chemicals to Humans: Some Monomers, Plastics and Synthetic Elastomers,
and Acrolein. Volume 19. World Health Organization, Lyon. 1979.
3. U.S. Environmental Protection Agency. Health Assessment Document for Acrylonitrile (Revised
Draft). EPA/600/8-82-007. Environmental Criteria and Assessment Office, Office of Health and
Environmental Assessment, Office of Research and Development, Research Triangle Park, NC.
1982.
4. U.S. Environmental Protection Agency. Integrated Risk Information System (IRIS) on
Acrylonitrile, National Center for Environmental Assessment, Office of Research and
Development, Washington, D.C. 1999.
5. U.S. Department of Health and Human Services. Registry of Toxic Effects of Chemical Substances
(RTECS, online database). National Toxicology Information Program, National Library of
Medicine, Bethesda, MD. 1993.
6. U.S. Environmental Protection Agency. Health Effects Assessment for Acrylonitrile. EPA/600/888/014. Environmental Criteria and Assessment Office, Office of Health and Environmental
Assessment, Office of Research and Development, Cincinnati, OH. 1988.
7. U.S. Environmental Protection Agency. Health Effects Assessment Summary Tables. FY 1997
Update. Solid Waste and Emergency Response, Office of Emergency and Remedial
Response, Cincinnati, OH. EPA/540/R-97-036. 1997.
8. U.S. Environmental Protection Agency. Health and Environmental Effects Profile for
Acrylonitrile. EPA/600/x-85/372. Environmental Criteria and Assessment Office, Office of
Health and Environmental Assessment, Office of Research and Development, Cincinnati, OH.
1985.
9. Occupational Safety and Health Administration (OSHA). Occupational Safety and Health
Standards, Toxic and Hazardous Substances. Code of Federal Regulations. 29 CFR 1910.1045.
1998.
10. American Conference of Governmental Industrial Hygienists (ACGIH). 1999 TLVs and BEIs.
Threshold Limit Values for Chemical Substances and Physical Agents, Biological Exposure
Indices. Cincinnati, OH. 1999.
11. National Institute for Occupational Safety and Health (NIOSH). Pocket Guide to Chemical
Hazards. U.S. Department of Health and Human Services, Public Health Service, Centers for
Disease Control and Prevention. Cincinnati, OH. 1997.
12. American Industrial Hygiene Association (AIHA). The AIHA1998 Emergency Response Planning
Guidelines and Workplace Environmental Exposure Level Guides Handbook. 1998.
43 | Acrylonitrile by Propene Ammoxidation
12 Appendix
Pinch Analysis:
Pinch analysis is a procedure that evolved during the energy crisis of 1970, from a necessity to increase
the energy savings, especially when using heat exchanger networks which resulted in optimization of
heat integration.
Significance of Pinch:
1. No heat is transferred across the pinch at minimum utilities.
2. Two heat exchanger networks are designed on either side of the pinch.
3. Energy is added on one side of the pinch and removed on the other side.
4. At the pinch all the hot streams are hotter than cold streams by min .
Methodology for pinch Analysis
a) Development of Composite Curves: The entire process is represented on a temperature enthalpy
diagram by composite curves which represent the cumulative heat sources and sinks within the
process. These composite curves are arrived at from stream data derived from a process heat and
material balance. These allow prediction of hot and cold targets ahead of design.
b) Grid Diagram Development: This is a diagram which helps in developing heat recovery
networking. The hot streams run from left to right while cold streams run counter-current at the
bottom.
c) Pinch Identification: A grand composite curve is drawn which is composed of the composite
curves for all the streams and the equipment are "appropriately placed". Appropriate placement
can be done for equipment that can be represented in terms of heat sources and sinks. This
implies that this can be used for heat pumps, distillation columns, evaporators, heat engines, etc.
From this grand composite curve, the pinch temperature can be determined.
Stream
C1
C2
C3
C4
C5
C6
H1
H2
H3
H4
H5
H6
T1(C)
25
111.7
82.7
111.3
128.3
81.9
420
104.5
38.9
87.1
56.5
70.6
T2(C)
210
117.8
82.8
111.4
128.4
82
120
70
38.8
87
56.4
70.5
mCp
0.0384
4.3
25.4
130
21
30.2
0.039
0.635
26.9
53
17
27.4
Q
7.1
26.3
2.54
13
2.1
3.02
11.8
22.1
2.69
5.3
1.7
2.74
Temperature Interval Method
Streams
C1
T1
25
C2
111.7
C3
82.7
C4
111.3
C5
128.3
C6
81.9
T2
210
117.8
82.8
111.4
128.4
44 | Acrylonitrile by Propene Ammoxidation
Adjusted Temperatures
1’
2’
25
210
111.7
117.8
82.7
82.8
111.3
111.4
128.3
128.4
81.9
Symbol
T23
T1
T5
T4
T11
T10
T7
T6
T3
T2
T13
82
H1
420
H2
104.8
H3
38.9
H4
87.1
H5
56.5
H6
70.6
82
410
120
110
94.8
70
60
28.9
38.8
28.8
77.1
87
77
46.5
56.4
46.4
60.6
70.5
Interval
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Ti-1-Ti
410-210
210-128.4
128.4-128.3
128.3-117.8
117.8-111.7
111.7-111.4
111.4-111.3
111.3-110
110-94.8
94.8-82.8
82.8-82.7
82.7-82
82-81.9
81.9-77.1
77.1-77
77-60.6
60.6-60.5
60.5-60
60-46.5
46.5-46.4
46.4-28.9
28.9-28.8
28.8-25
45 | Acrylonitrile by Propene Ammoxidation
60.5
ΣCh-ΣCC
0.039
0.0006
-20.9994
0.0006
-4.2994
0.0006
-129.999
0.0006
-0.0384
0.5966
-24.8034
0.5966
-29.6034
0.5966
53.5966
0.5966
27.9966
0.5966
-0.0384
16.9616
-0.0384
26.8616
-0.0384
T12
T0
T8
T9
T18
T21
T22
T14
T15
T19
T20
T16
T17
H
7.8
0.04896
-2.09994
0.0063
-26.2263
0.00018
-12.9999
0.00078
-0.58368
7.1592
-2.48034
0.41762
-2.96034
2.86368
5.35966
9.78424
2.79966
0.2983
-0.5184
1.69616
-0.672
2.68616
-0.14592
Qsteam
To=410
To=410
7.8
T1=210
To=410
0.04896
T2=128.
4
-2.09994
To=410
T3=128.3
0.0063
To=410
T4=117.8
-26.2263
To=410
T5=111.7
0.00018
To=410
T6=111.4
-12.9999
To=410
T7=111.3
0.00078
To=410
T8=110
-0.58368
To=410
T9=94.8
7.1592
To=410
T10=82.8
-2.48034
To=410
7.8
7.84896
5.74902
5.75532
-20.471
-20.4708
-33.4708
-33.47
-34.0537
-26.8945
-29.3748
-28.9572
-31.9175
-29.0539
-23.6942
-13.91
-11.1103
-10.812
-11.3304
-9.63424
-10.3062
-7.62008
-7.766
41.8537
41.90266
39.80272
39.80902
13.58268
13.58286
0.58292
0.5837
0
7.15922
4.67888
5.0965
2.13616
4.99984
10.3595
20.14374
22.9434
23.2417
22.7233
24.41946
23.74746
26.43362
26.2877
T11=82.7
0.41762
T12=82
-2.96034
T13=81.9
2.86368
To=410
T14=77.1
To=410
5.35966
T15=77
9.78424
T16=60.6
2.79966
T17=60.5
0.2983
To=410
T18=60
-0.5184
To=410
T19=46.5
To=410
1.69616
T20=46.4
-0.672
To=410
T21=28.9
2.68616
To=410
T22=28.8
-0.14592
To=410
T23=25
To=410
QCW
46 | Acrylonitrile by Propene Ammoxidation
Pinch = 94.8 C (Cold)
104.8 C (Hot)
Qsteam = 41.85
QCW = 26.2877
Evaluation of Rate Equations:
47 | Acrylonitrile by Propene Ammoxidation
( )(
We know that ki,t1 = ki,t0
)
R = 1.987 ca1/mole K
to =470°C = 743°K
Using data from table 4.2,
k1 = 0.40556
(
= 0.40556
(
)(
.
)
)
.
(
(
=1.57498E+05
)
)
Similarly,
(
k2 = 0.00973
(
=3.778E+03
(
k3 = 0.00973
= 1.99
(
(
(
= 780.82
= 8.3658
.
)
)
)(
)
)(
)
)
k4 = 6.81341
k5 = 0.073
)(
.
(
.
(
.
)
)(
)
)
48 | Acrylonitrile by Propene Ammoxidation