PLANT DESIGN FOR THE PRODUCTION OF ACETALDEHYDE FROM ACETIC
ACID
A Plant Design Project Report
Presented to the
Department of Chemical Engineering
Faculty of Mechanical and Chemical Engineering
College of Engineering
Kwame Nkrumah University of Science and Technology, Kumasi
By
ANDERSON, KENNETH
ASAMOAH, GILBERT ADU
BOAMAH, NANCY NYANTAKYIWAA
YORKE, ANGELA
In partial Fulfillment of the Requirements
For the Degree of
Bachelor of Science (HONS)
Chemical Engineering
June, 2022
©
ABSTRACT
Our plant will be designed to manufacture 46,048,700 kg/year of acetaldehyde via the
hydrogenation of acetic acid over a 20% wt. palladium on iron oxide catalyst. The acetic acid
will first be produced via the Monsanto process which is the carbonylation of methanol over
a rhodium catalyst. The conversion of acetic acid in the reactor is 46% with a selectivity of
86% to acetaldehyde. Major by-products include ethanol, ethyl acetate, acetone, carbon
dioxide, ethylene, ethane and methane. Acetaldehyde is purified in a series of steps. It is first
absorbed with an acetic-acid rich solvent, then distilled to separate acetaldehyde from heavier
components. Acetaldehyde produced is of 99.6% wt. purity. Unconverted acetic acid is
purified and collected to be used in the reactor to limit the amount of feedstock required.
Ethyl acetate is produced as a by-product in the acetaldehyde distillation column and is
purified and sold. Acetone is also produced and is purified and sold.
i
TABLE OF CONTENTS
ABSTRACT ............................................................................................................................ i
TABLE OF CONTENTS ........................................................................................................ i
LIST OF TABLES ................................................................................................................ iii
LIST OF FIGURES .............................................................................................................. iv
CHAPTER ONE .................................................................................................................... 1
1.0
INTRODUCTION ................................................................................................... 1
1.1 Main Objective ............................................................................................................. 2
1.2 Specific Objectives ....................................................................................................... 2
CHAPTER TWO ................................................................................................................... 4
2.0
LITERATURE REVIEW............................................................................................ 4
2.1 Aldehydes ..................................................................................................................... 4
2.2
Acetaldehyde ........................................................................................................... 4
2.2.1 Definition, Sources and Structure .......................................................................... 4
2.2.2 Uses ........................................................................................................................ 5
2.2.3 Properties ............................................................................................................... 6
2.2.4 Production of Acetaldehyde................................................................................... 7
2.2.5 Alternative Processes and their Disadvantages ..................................................... 7
2.3
Acetic Acid .............................................................................................................. 8
2.3.1 Definition, Sources and Structure .......................................................................... 8
2.3.2 Uses ........................................................................................................................ 8
2.3.3 Properties ............................................................................................................... 9
2.3.4 Production of Acetic Acid ................................................................................... 10
2.3.4.1 The Monsanto Process .................................................................................. 10
2.3.4.2 The Cativa Process ........................................................................................ 12
2.4 Ethyl Acetate – A major by-Product .......................................................................... 12
2.4.1 Uses ...................................................................................................................... 13
2.4.2 Properties ............................................................................................................. 13
CHAPTER THREE.............................................................................................................. 15
3.0 PROCESS SELECTION AND DESCRIPTION ........................................................... 15
3.1 Process Selection ........................................................................................................ 15
i
3.2 Process Description .................................................................................................... 15
3.2.1 Production of Acetic Acid ................................................................................... 15
3.2.2 Reaction Section .................................................................................................. 17
3.2.3 Purification of Acetaldehyde ............................................................................... 18
3.2.4 Separation of Acetic Acid .................................................................................... 19
3.2.5 Ethyl Acetate Separation ..................................................................................... 20
3.2.6 Acetone and Wastewater Removal ...................................................................... 20
CHAPTER FOUR ................................................................................................................ 21
4.0
MATERIAL AND ENERGY BALANCE ............................................................... 21
4.1 Material Balance ......................................................................................................... 21
4.1.1 Reactor 1 (R1) .................................................................................................. 21
4.1.2 Flash Vessel 1 (FV1)........................................................................................ 22
4.1.3 Distillation Column 1 (DC1)............................................................................ 23
4.1.4 Fired Heater 1 (FH1) ........................................................................................ 24
4.1.5 Reactor 2 (R2) .................................................................................................. 25
4.1.6 Acetaldehyde Distillation Column (DC4)........................................................ 26
4.1.7 Splitter .............................................................................................................. 27
4.1.8 Acetic Acid Separation Column (DC5) ........................................................... 28
4.1.9 Decanter (DE1) ................................................................................................ 29
4.1.10 Acetone Distillation Column (DC6) .............................................................. 30
4.1.11 Ethyl Acetate Distillation Column (DC7) ...................................................... 31
CHAPTER FIVE .................................................................................................................. 32
5.0 REFERENCES............................................................................................................... 32
ii
LIST OF TABLES
Table 2.1: Properties of Acetaldehyde ................................................................................... 6
Table 2.2: Properties of Acetic Acid ...................................................................................... 9
Table 3.3: Properties of Ethyl Acetate ................................................................................. 13
iii
LIST OF FIGURES
Figure 1 : Chemical structure of acetaldehyde ....................................................................... 5
iv
CHAPTER ONE
1.0 INTRODUCTION
Acetaldehyde is one of the most important aldehydes, occurring widely in nature and being
produced on large scale in the industry and worldwide. It occurs naturally in coffee, bread
and ripe fruits.
It is the main product produced in this process. Acetaldehyde was chosen as the main product
because of its profitability of its scale and its wide use in the industry. Worldwide,
acetaldehyde production has increased over the past years due to tremendous increase in
acetaldehyde consumption. China is the largest consumer of acetaldehyde in the world,
accounting for almost half of global consumption in 2012. Western European is the secondlargest consumer of acetaldehyde worldwide, accounting for 20% of world consumption in
2012.
Major use of acetaldehyde has been the production of acetic acid. It is also used in the
industry as a chemical intermediate, principally for the production of pyridine and pyridine
bases, glycol chloral and peracetic acid. Acetaldehyde has been used in the manufacture of
aniline dyes and synthetic rubber and to harden gelatin fibers. In 1976, approximately 19,000
lb of acetaldehyde were used as food additives, primarily as food and fish preservatives and
as a synthetic flavoring agent to impart orange, apple and butter flavors.
The global market for acetaldehyde is declining due to the use of more economically starting
materials for principal derivatives and a lower demand for some acetal derivatives. However,
in recent times, there is a vast potential for the profitability in manufacturing acetaldehyde
due to a decline in the number of suppliers and an increase in potential.
1
Traditionally, acetaldehyde was mainly used as a precursor to acetic acid. This application
has declined because acetic acid is produced more efficiently from methanol by the Monsanto
and Cativa processes. Acetic acid is inexpensive and can be generated more efficiently from
methanol by Monsanto and Cativa processes. Due to the possible legislation of MTBE out of
gasoline, there may be a worldwide of excess methanol, so any chemical that use methanol
may become economically attractive. That is the reason for using acetic acid as our starting
material. About 75% of acetic acid made for use in the industry is made by carbonylation of
methanol.
Production of acetaldehyde from acetic acid has received great interest due to the high
selectivity of up to 86% at a 46% acetic acid conversion. 20% Palladium on iron oxide is
used as a catalyst. This catalyst gives the selectivity of 86% to the desired reaction at 46%
acetic acid conversion. Acetic acid that has been produced by the Monsanto process reacts
with hydrogen and gives acetaldehyde as the main product and ethanol, ethyl acetate,
acetone, water and light hydrocarbons as the by-products. Ethyl acetate is chosen as the main
by-product. This project gives the full techno-economic assessment, including economic and
cash flow analysis. (daRosa et al., 2002)
1.1 Main Objective
•
To design a plant for the production of acetaldehyde from acetic acid
1.2 Specific Objectives
•
To design a process flow diagram for the production of acetaldehyde from acetic
acid
•
To know the various units involved in the production of acetaldehyde from acetic
acid
2
•
To design selected equipment for the unit operations in the plant
•
To perform material and energy balances for the process selected
•
To determine where best the plant should be situated
•
To select necessary instrumentation and process controls for the plant
•
To discuss the safety and pollution aspects of the plant as well as propose means
of control
•
To evaluate economic viability of the plant based on costs, cash flow, profits and
return on investments
3
CHAPTER TWO
2.0 LITERATURE REVIEW
2.1 Aldehydes
Aldehydes are classes of organic compounds in which a carbon atom shares a double bond
with an oxygen atom, a single bond with a hydrogen atom, and a single bond with another
atom or group of atoms. The double bond between carbon and oxygen is characteristic of all
aldehydes and is known as the carbonyl group. Aldehydes are important starting materials
and intermediates in organic synthesis, because they undergo a wide variety of reactions and
are readily available by many synthetic methods. The reactivity of these compounds arises
largely through two features of their structures: the polarity of the carbonyl group and the
acidity of any α-hydrogen that is present.
2.2 Acetaldehyde
2.2.1 Definition, Sources and Structure
Acetaldehyde is an organic chemical compound with the formula CH3CHO or C2H4O,
sometimes abbreviated by chemists as MeCHO (Me = methyl). The acetaldehyde has the
usual functional group of an aldehyde bound to a methyl group. Its systematic IUPAC name
is called ethanal. Other names include acetic aldehyde or ethyl aldehyde. It is one of the most
important aldehydes, occurring widely in nature and being produced on a large scale in
industry. Acetaldehyde occurs naturally in coffee, bread and ripe fruits and is produced by
plants. It is also produced by the partial oxidation of ethanol by the liver enzyme alcohol
dehydrogenase and is a contributing cause of hangover after alcohol consumption. Pathways
of exposure include air, water, land, or groundwater, as well as drink and smoke.
The molecule has a planar-trigonal together with tetrahedral geometry. (daRosa et al. 2002)
4
Figure 1 : Chemical structure of acetaldehyde
2.2.2 Uses
The predominant use of acetaldehyde is as an intermediate in the synthesis of other
chemicals. Acetaldehyde is primarily used for the production of pyridine and pyridine bases,
peracetic acid, pentaerithritol, butylene glycol and chloral. It is used in the production of
esters, particularly ethyl acetate and isobutyl acetate. It is also used in the synthesis of
crotonaldehyde as well as flavor and fragrance acetals, acetaldehyde 1,1 dimethylhydrazone,
acetaldehyde cyanohydrin, acetaldehyde oxime and various acetic esters, paraldehyde
halogenated derivatives. Acetaldehyde has been used in the manufacture of aniline dyes and
synthetic rubber, to silver mirrors and to harden gelatin fibers. It has been used in the
production of polyvinyl acetal resins, in fuel compositions and to inhibit mold growth on
leather. Acetaldehyde is also used in the manufacture of disinfectants, drugs, perfumes,
explosives, lacquers and varnishes, photographic chemicals, phenolic and urea resins, rubber
accelerators and antioxidants, and room air deodorizers; acetaldehyde is a pesticide
intermediate. Acetaldehyde, an alcohol denaturant, is generally recognized as a safe
compound for the intended use as a flavoring agent. It is an important component of food
flavorings added to milk products, baked goods, fruit juices, candy, desserts, and soft drinks.
5
In 1976, approximately 19,000 lb of acetaldehyde were used as food additives, primarily as
fruit and fish preservatives and as a synthetic flavoring agent to impart orange, apple and
butter flavors. (Depew et al., 2000)
2.2.3 Properties
Table 2.1: Properties of Acetaldehyde
PROPERTY
VALUE
Molecular weight
44.053 g/mol
Density
0.784 g/cm3
Boiling point
293.3 K
Melting point
149.78 K
Color
Colorless
Odor
Ethereal
Viscosity
0.21 mPa s at 293 K
Refractive index
1.3316
Dipole moment
2.7 D
Solubility in water
Miscible
Vapor pressure
740 mmHg at 293 K
Acidity (pKa)
13.57
Heat capacity
89 J/mol K
Standard molar entropy
160.2 J/mol K
Standard enthalpy of formation
-192.2 kJ/mol
6
2.2.4 Production of Acetaldehyde
A method of producing acetaldehyde hydrogenates acetic acid in the presence of an iron
oxide catalyst containing 20% wt. Palladium. The catalyst has a specific surface area of less
than 150 m2/g. The hydrogenation is performed at a temperature of about 280°C to 325°C.
The hydrogenation of acetic acid produces a partially gaseous product, from which
acetaldehyde is absorbed from with a solvent containing acetic acid. The gas remaining after
the absorption step contains hydrogen, and this gas is recycled for the hydrogenati3on of
acetic acid. In addition to acetaldehyde, ethyl acetate is produced as a main by-product and
is purified and sold. Other major by-products are ethanol, acetone, carbon dioxide, and the
light hydrocarbons methane, ethane and ethylene. Though this process can also be effectively
catalyzed by mercury compounds, the toxic nature of mercury makes it unfeasible. (daRosa
et al. 2002)
2.2.5 Alternative Processes and their Disadvantages
Acetaldehyde can be made commercially via the Wacker process, the partial oxidation of
ethylene. The major disadvantage of that process is that it is very corrosive requiring very
expensive materials of construction. Another major disadvantage is that the reaction is prone
to over-oxidation of the reactant, the products of which are thermodynamically more stable
than acetaldehyde which is the partial oxidation product. This over-oxidation of the reactant
reduces the yield of acetaldehyde produced and converts expensive ethylene into carbon
oxides.
Acetaldehyde is also manufactured by oxidizing ethanol using air. A mixture of air and
ethanol vapor is fed into a multi-tubular reactor. Temperature is maintained between 400°C
and 500°C and the pressure at 29.4 psi. The catalyst used is chromium activated copper.
Vapor coming out of the reactor is passed through a scrubber and unreacted ethanol is
7
separated and recycled. However, this process gives a relatively poor yield of acetaldehyde.
(daRosa et al. 2002)
2.3 Acetic Acid
2.3.1 Definition, Sources and Structure
Acetic acid, systematically named ethanoic acid, is an acidic, colorless liquid and organic
compound with the chemical formula CH3COOH. Acetic acid is the second simplest
carboxylic acid consisting of a methyl group that is attached to a carboxyl functional group.
Acetic acid is classified as a weak monobasic acid (-CO2H) but the three hydrogen atoms
linked to the carbon atom (CH3) are not replaceable by metals. Acetic acid is produced and
excreted by acetic acid bacteria, notably the genus Acetobacter and Clostridium
acetobutylicum. These bacteria are found universally in foodstuffs, water and soil and acetic
acid is produced naturally as fruits and other foods spoil. The global demand for acetic acid
is about 6.5 million metric per year (Mt/a), of which approximately 1.5Mt/a is met by
recycling; the remainder is manufactured from methanol. This growing demand for acetic
acid is a major driving force to find a better catalyst to produce acetic acid more efficiently.
About 75% of acetic acid made for use in the industry is made by carbonylation of methanol.
Vinegar is mostly dilute acetic acid produced by fermentation and subsequent oxidation of
ethanol. (Jones, 2000)
2.3.2 Uses
Acetic acid is an important chemical reagent and industrial chemical, used in the production
of cellulose acetate for photographic film, polyvinyl acetate for wood glue, and synthetic
fibers and fabrics. In households, diluted acetic acid is often used in descaling agents. It is
frequently used as a solvent for reactions involving carbocations or as a solvent for
recrystallization to purify organic compounds. Vinegar, which is typically no less than 4%
8
acetic acid by mass, is used directly as a condiment and in the pickling of vegetables and
other foods. (Jones, 2000)
2.3.3 Properties
Table 2.2: Properties of Acetic Acid
PROPERTY
VALUE
Molar mass
60.052 g/mol
Appearance
Colorless liquid
Odor
Heavily vinegar-like
Density
1.049 g/cm3 (liquid)
1.27 g/cm3 (solid)
Melting point
289 K
Boiling point
391 K
Solubility in water
Miscible
Vapor pressure
11.6 mmHg at 293 K
Acidity (pKa)
4.756
Magnetic susceptibility
-31.54 * 10-6 cm3/mol
Refractive index
1.371
Viscosity
1.22 mPa s
Dipole moment
1.74 D
Heat capacity
123.1 J/mol K
Standard molar entropy
158 J/mol K
9
Standard enthalpy of formation
-483.88 kJ/mol
Standard enthalpy of combustion
-875.5 kJ/mol
Sourced from: (Jones, 2000)
2.3.4 Production of Acetic Acid
In 1960, the Monsanto process for carbonylation methanol to produce acetic acid was
invented, which uses a rhodium catalyst. This was the leading technology until 1996 when
the Cativa Process, which involves an iridium catalyst, was invented. (Jones, 2000)
2.3.4.1 The Monsanto Process
The Monsanto Process is an industrial method for the manufacture of acetic acid by catalytic
carbonylation of methanol. This process operates at a pressure of 30-60 atm and temperature
of 150-2000C and gives a selectivity greater than 99%. It was developed in 1960 by the
German chemical company, BASF, (largest chemical company). Over 1-million-pound
acetic acid is being produced annually by this process. Monsanto process is a homogenously
catalyzed conversion of methanol into acetic acid or carbonylation of methanol.
Carbonylation refers to reactions that introduce carbon monoxide into organic and inorganic
substrates. Carbon monoxide is abundantly available and conveniently reactive, so it is
widely used as a reactant in industrial chemistry.
The first stage of the process involves the injection of the raw materials namely methanol,
carbon monoxide and water into the reactor to initiate the methanol carbonylation process.
The carbonylation reaction is carried out in a stirred tank reactor on a continuous basis.
Liquid is then removed from the reactor through a pressure reduction valve. This then enters
the flash tank, where light component of methyl acetate, methyl iodide, some water and
product acid are removed as vapor through the top of the vessel. The gases are fed forward
10
to the distillation train for further purification whilst the remaining the remaining liquid in
the flash tank, containing the dissolved catalyst is recycled to the reactor.
Liquid from the reactor enters the lower half of a multiple-tray distillation column operating
at conditions above atmospheric conditions. Hydrogen iodide present in the feed stream is
concentrated in the acetic acid solution in the bottom of the column. This stream is recycled
back to the reactor. Carbon monoxide, water, methyl iodide and some entrained hydrogen
iodide comprise the overhead stream from the column which passes through a condenser and
phase separator where uncondensed gas is directed towards the scrubber. The condensate
separates into two phases: a water phase consisting of some organic compounds and an
organic phase (methyl iodide) containing some water. The organic phase is recycled to the
reactor whilst part of the water phase is used as reflux in the distillation column and excess
is recycled to the reactor.
Solution of acetic acid in water containing some iodide, catalyst and by-products is
withdrawn from the bottom and introduced into a second multiple-tray distillation column
operating at conditions above atmospheric conditions. In this column, water and remaining
inert is withdrawn overhead and directed towards to the scrubber. A portion of the condensate
is returned as reflux to the column and excess is recycled to the reactor. To avoid
accumulation of water in the system, a portion of the water separated in the column is
discarded.
Residual hydrogen iodide in the feed stream to the column concentrates at a location near the
middle of the distillation column. By continually withdrawing the solution containing
hydrogen iodide from the middle of the distillation column, virtually all of the hydrogen
iodide is removed from the column. This solution can be recycled directly to the reactor or
11
alternatively to the lower half of the previous distillation column, where it is concentrated
and removed with the bottoms stream of that column.
Acetic acid is withdrawn from the drying column without further processing; acetic acid
vapor is withdrawn from the top of the column and passes through a condenser from which
it is pumped to storage. Liquid acetic acid containing residual catalyst is periodically
withdrawn from the top of the column and recycled to the reactor. (Jones, 2000)
2.3.4.2 The Cativa Process
The Cativa process is similar to the Monsanto process in that, they all produce acetic acid
via the carbonylation of methanol. The Monsanto and Cativa processes are sufficiently
similar that they can use the same chemical plant. However, the Cativa process employs the
use of Iridium catalyst. Initial studies by Monsanto had shown Iridium to be less active than
Rhodium for carbonylation of methanol unless the Iridium is promoted with Ruthenium
(Jones, 2000).
2.4 Ethyl Acetate – A major by-Product
In addition to acetaldehyde, ethyl acetate and other products including acetone, ethanol and
lighter hydrocarbons are produced as by-products in the production of acetaldehyde. Ethyl
acetate was chosen as a major by-product because of it uses in industry.
Ethyl acetate, systematically called ethyl ethanoate, is an organic compound with the formula
C4H8O2. Ethyl acetate is the ester of ethanol and acetic acid through an esterification reaction.
Ethyl acetate is synthesized in the industry mainly via the classic Fischer esterification
reaction of ethanol and acetic acid. (Pattanaik & Mandalia, 2011)
12
2.4.1 Uses
Ethyl acetate is used primarily as a solvent and diluents, being favored because of its low
cost, low toxicity and agreeable odor. It is commonly used to clean circuit boards and in some
nail varnish removers. Coffee beans and tea leaves are decaffeinated with this solvent when
supercritical CO2 extraction is not possible. It is also used in paints as an activator or hardener.
Ethyl acetate is present in confectionery, perfumes and fruits. In perfumes, it evaporates
quickly, leaving the scent of the perfume on the skin. (daRosa et al. 2002)
2.4.2 Properties
Table 3.3: Properties of Ethyl Acetate
PROPERTY
VALUE
Molar mass
88.106 g/mol
Appearance
Colorless liquid
Odor
Ether-like, fruity
Density
0.902 g/cm3
Melting point
189.6 K
Boiling point
350.2 K
Solubility in water
8.3 g/100 mL
Vapor pressure
73 mmHg at 293 K
Refractive index
1.3720
Viscosity
0.426 cP
Dipole moment
1.78 D
Acidity (pKa)
25
13
Magnetic susceptibility
-54.10 * 10-6 cm3/mol
Sourced from: (Pattanaik & Mandalia, 2011)
14
CHAPTER THREE
3.0 PROCESS SELECTION AND DESCRIPTION
3.1 Process Selection
Acetaldehyde will be produced via the hydrogenation of acetic acid in the presence of a
palladium catalyst. Acetaldehyde could be produced via the partial oxidation of ethylene
and oxidation of ethanol but they both produce poor yields of acetaldehyde. Conversion of
acetic acid in the reactor is 46% with a selectivity of 86% to acetaldehyde. Acetic acid will
be produced via the Monsanto process which is the carbonylation of methanol in the
presence of a rhodium catalyst. Acetic acid could be produced via the Cativa process but
the catalyst used is less active compared with the rhodium catalyst. The first section of our
plant manufactures acetic acid whiles the last section focuses on the production of
acetaldehyde followed by a series of purification steps in order to get an acetaldehyde
product of 99.6% wt. purity.
3.2 Process Description
3.2.1 Production of Acetic Acid
The feedstocks for the reaction of interest are methanol, carbon monoxide, and water and it
utilizes a rhodium catalyst. The raw materials namely carbon monoxide as gas at room
temperature, methanol and water at about 20℃ are fed to reactor R1 through streams S1,
S2 and S3 from tanks TK1, TK2 and TK3 respectively. The operating pressure of the
reactor is 1 bar. The reaction is carried out in a continuous stirred tank reactor. The gaseous
by products such as CO2 and H2 are taken off from the top through stream S10 and directed
towards a gas holder GH1. The liquid products are then taken off the bottom through
stream S4 which is passed through a pressure reduction valve V1 to a flash vessel FV1
15
operating at a pressure of 1.1 bar and temperature of 115℃ where light components
consisting of methyl acetate, methyl iodide, some water, and product acid are removed as
vapor through the top of the vessel through stream S6. The gases are fed forward to a series
of distillation columns for further purification whilst the remaining liquid in the flash vessel
containing the dissolved catalyst comes from the bottom as stream S49 which is pumped
back to the reactor through stream S51.
The light components which predominantly contains acetic acid enters a multiple-tray
distillation column DC1 operating at a pressure of 1.2 bar and temperature of 112℃.
Hydrogen iodide present in the feed stream is concentrated in the acetic acid solution in the
bottom of the column. This stream S13 is recycled back to the reactor. Carbon monoxide,
water, methyl iodide and some entrained hydrogen iodide comprise the overhead stream.
Solution of acetic acid in water containing some catalyst and by- products is withdrawn
from the bottom through stream S7 and introduced into a second multiple-tray distillation
column DC2 operating at a pressure of 1.2 bar and temperature of 120℃. In this column,
water and remaining inert is withdrawn as the overhead through stream S38 and joins with
stream S29. The combined stream S48 is recycled to the reactor R1.
Acetic acid is withdrawn from the drying column through stream ST19 into a third
multiple-tray distillation column DC3. This column is designed to separate the unwanted
propionic acid produced as part of the process from the desired acetic acid produced to
obtain a purity of greater than 99.9%. The operating conditions of distillation column DC3
are 125℃ and 1 bar. Acetic acid at 125℃ comes out as the overhead product and passes
through a condenser from which it is pumped to storage tank STK1 through stream S9. The
major liquid by product of the reaction is propionic acid which comes out as the bottom
product from DC3 and is fed to tank TK5 through stream S11.
16
3.2.2 Reaction Section
Acetic acid and hydrogen serve as the reaction’s feedstock. We assumed both starting
materials to be at 25℃. Acetic acid is available as a liquid and the hydrogen gas is
available at 13.8 bar. The pure hydrogen feed is mixed with the hydrogen recycle stream
S24, and this combined stream is compressed from 14.7 bar to 18.1 bar in the compressor
C1.
The acetic acid and hydrogen streams, S39 and S20 respectively, are both heated in the
fired heater which raises their temperature to 315℃. The off gases collected which are rich
in hydrogen and hydrocarbons are burned and used as a source of fuel in the fired heater.
The reactor R2 is a cylindrical vessel containing a packed bed of 20% wt. Pd- Fe2O3
catalyst pellets. The operating conditions of the reactor are 315℃ temperature and pressure
17.4 bar. The hydrogen and acetic acid are fed in a 5:1 molar ratio to ensure that the right
oxidation state for the desired conversion is achieved. Conversion of acetic acid is only
46%, which will enhance the selectivity to acetaldehyde, which is 86% at the given
conditions. Ethanol, acetone, carbon dioxide and light hydrocarbons are the by-products
formed in the reactor. The reactor effluent S15 is at 12.8℃ and contains 11% hydrogen,
21% acetaldehyde and 38% acetic acid by mass.
The following are the reaction mechanisms that occur in the reactor R2;
CH3COOH + H2
CH3CHO + H2O
CH3COOH + 2H2
CH3CH2OH + H2O
2CH3COOH
CH3COCH3 + CO2+ H2O
3CH3COOH + 9H2
2CH4 + C2H6 + C2H4+ 6H2O
17
CH3COOH + CH3CH2OH
CH3COOCH2CH3 + H2O
3.2.3 Purification of Acetaldehyde
The reactor effluent S15 must be cooled in the heat exchanger HX1 in order to achieve high
recovery in the absorption column. Cooling water from TK8 is used to cool the stream to
45℃ in HX1. This partially condenses the stream and the cool effluent S16 is fed to the
flash vessel FV2 to separate the liquid and vapor phases. Only the vapor stream S17 exiting
the flash vessel is sent to the absorber AB1, which it enters at the bottom stage. The solvent
fed to the top of the absorber is the pure acetic acid mixed with the acetic acid-rich bottoms
product from DC4. This solvent selectively absorbs acetaldehyde under high pressure (the
top stage operates at 16.1 bar).
The recovery of acetaldehyde rises as the recycle amount increases. The selected solvent
recycle allows recovery of 95% of acetaldehyde, while also leaving a feasible separation
and relatively low column costs. The pressure of the absorber is also high as possible in
order to improve acetaldehyde recovery. Hydrogen gas exiting AB1 is recycled to the gas
holder TK9. The bottoms product from the absorber, S23 is combined with S22. The
combined stream S26 passes through a valve to reduce the pressure to 3 bar before being
fed to the acetaldehyde distillation column DC4.
The main goal of the DC4 is to obtain a pure stream of acetaldehyde with 99.6% wt. purity.
This column is operated at 25℃ temperature and pressure 1 bar. Acetaldehyde and the light
hydrocarbons vaporize at this temperature. Vapor acetaldehyde is condensed and collected
via stream S28 into STK2. Some of the acetaldehyde is lost to the stream offgas.
Esterification reaction occurs at the bottom of DC4. It is the reaction between the ethanol
and some unreacted acetic acid, which forms ethyl acetate and water. Equilibrium for this
18
reaction is achieved wherever acetic acid and ethanol are present together but for the
purpose of this design, it was assumed this reaction occurs only at bottom stage of DC4,
where the high temperature and the presence of acetic acid and ethanol favor this reaction.
The presence of ethyl acetate is very important in the acetic acid separation section of this
process, where ethyl acetate forms an azeotrope with water, easing the separation of water
from acetic acid. The bottoms products S42 from the acetaldehyde distillation column DC4
is spilt by a splitter with S43 proceeding to the acetic acid separation section. The
remainder S44 is cooled by the cooling water in the heat exchanger HX2 and then recycled
to the top stage of the absorber AB1 where it acts as the solvent to absorb the acetaldehyde
in the absorption column.
3.2.4 Separation of Acetic Acid
The main goal of the acetic acid separation column DC5 is to obtain a pure stream of
acetic acid, which can be recycled to the reactor feed. The reasons for this are twofold.
The primary reason is that the high cost of acetic acid makes it economically feasible for
us to reuse the unreacted acetic acid rather than dispose of it. This is particularly relevant
because of the low conversion in the reactor, which results in a significant amount of
unreacted acetic acid in the system. The second reason is that acetic acid is an impurity in
water and its substantial presence in the wastewater stream will increase costs of
wastewater treatment.
There is one stream entering the acetic acid distillation column. The feed stream, S30 is
from the bottoms of the acetaldehyde separation column. It primarily consists of the
unreacted acetic acid and the products of side reactions such as water, ethyl acetate,
acetone and ethanol. The bottoms stream S54 of DC 5 consists of purified acetic acid that
is collected in TK14 for reuse.
19
The feed S30 pumped to 6.9 bar before entering the column. The column is operated at a
temperature of 100℃ and a pressure of 6.6 bar. The condenser is operated at 6.6 bar
because as pressure increases, the water-ethyl acetate azeotrope becomes more water-rich,
easing the separation from acetic acid. This significantly increases the purity of acetic acid
that is collected at the bottoms. A total condenser is used because the distillate must be
fed to the decanter DE1 as a liquid. The exit stream from this DC 5 is fed to the decanter
DE1, which is used to separate the water from the ethyl acetate in the feed stream.
3.2.5 Ethyl Acetate Separation
Ethyl acetate is produced at the bottom of DC4 through an esterification reaction between
the by-product ethanol and unreacted acetic acid. In DC5, ethyl acetate forms an azeotrope
with water to aid in the acetic acid separation. S31 leaving DC5 contains the low-boiling
azeotrope of ethyl acetate and water, some acetic acid and acetone. The stream enters the
decanter DE1 and by the principle of buoyancy separates it into two streams. Stream S34
enters DC7 and it contains ethyl acetate and acetic acid. The temperature in this column is
90℃ and the pressure is 2 bar. Ethyl acetate is collected as the distillate via stream S35 into
TK10 whiles acetic acid is collected as the bottoms product via stream S55 into TK14.
3.2.6 Acetone and Wastewater Removal
Stream S32 enters DC6 and it contains acetone and water. This column operates at a
temperature of 70℃ and a pressure of 1.7 bar. Acetone is collected as the distillate via stream
S33 into TK12. The wastewater is also collected into tank TK16 via stream S56 to be further
treated before it will be disposed of.
20
CHAPTER FOUR
4.0 MATERIAL AND ENERGY BALANCE
4.1 Material Balance
4.1.1 Reactor 1 (R1)
OUTPUT
INPUT
Component Mass, kg
Mass %
H2O
1000
0.812
CO
64000
51.981
CH3OH
58120
47.206
Total
123120
100
Component Mass, kg
Mass %
H2
111.11
4.348
CO2
2444.44
95.652
Total
2555.55
100
R1
OUTPUT
Component
Mass, kg
Mass %
CH3COOH
120000
20.193
HI
129292.8
21.756
CO
3111
0.523
C3H6O2
153602.86
25.847
CH3COOCH3 7475.4
1.258
CH3I
143434.2
24.136
H2O
37363.2
6.287
Total
594279.46
100
21
4.1.2 Flash Vessel 1 (FV1)
OUTPUT
INPUT
Component
Mass, kg
Mass %
CH3COOH
120000
20.193
HI
129292.8
21.756
CO
3111
0.523
C3H6O2
153602.86 25.847
CH3COOCH3 7475.4
1.258
CH3I
143434.2
24.136
H2O
37363.2
6.287
Total
594279.46 100
Component
Mass, kg
Mass %
CH3COOH
60000
20.193
HI
64646.4
21.756
CO
1555.5
0.523
C3H6O2
76801.42
25.847
CH3COOCH3
3737.37
1.258
CH3I
71717.1
24.136
H2O
18681.6
6.287
Total
297139.73
100
FV1
OUTPUT
Component
Mass, kg
Mass %
CH3COOH
60000
20.193
HI
64646.4
21.756
CO
1555.5
0.523
C3H6O2
76801.42
25.847
CH3COOCH3 3737.37
1.258
CH3I
71717.1
24.136
H2O
18681.6
6.287
Total
297139.73
100
22
4.1.3 Distillation Column 1 (DC1)
OUTPUT
Component
INPUT
Mass, kg
Mass %
CH3COOCH3 3737.37
4.424
CO
1555.5
1.841
Component
Mass, kg
Mass %
H2O
7472.64
8.845
CH3COOH
60000
20.193
CH3I
71717.1
84.890
HI
64646.4
21.756
Total
84482.61 100
CO
1555.5
0.523
C3H6O2
76801.42
25.847
CH3COOCH3 3737.37
1.258
CH3I
71717.1
24.136
H2O
18681.6
6.287
Total
297139.73
100
DC1
OUTPUT
Component
Mass, kg
Mass %
CH3COOH 60000
28.214
C3H6O2
76801.42
36.115
H2O
11208.96
5.271
HI
64646.4
30.399
Total
212656.78 100
23
4.1.4 Fired Heater 1 (FH1)
INPUT
Component Mass, kg
INPUT
Mass %
CH3COOH
51205.8548 100
Total
51205.8548 100
Component Mass, kg
Mass %
H2
8534.3091
100
Total
8534.3091
100
FH1
OUTPUT
Component
Mass, kg
Mass %
CH3COOH
51205.8548
85.714
H2
8534.3091
14.286
Total
59740.164
100
24
4.1.5 Reactor 2 (R2)
INPUT
Component
Mass, kg
Mass %
CH3COOH
51205.8548
85.714
H2
8534.3091
14.286
Total
59740.164
100
R2
OUTPUT
Component
Mass, kg
Mass %
CO2
94.0236
0.238
H2
0.1805
0.0005
CH4
20.2711
0.051
C2H4
20.2711
0.051
C2H6
22.4276
0.057
C2H4O
5256.701
13.299
CH3COOH
27651.1616
69.953
C2H5OH
354.0984
0.896
H2O
5633.4521
14.252
Acetone
475.7254
1.204
Total
39528.3124
100
25
4.1.6 Acetaldehyde Distillation Column (DC4)
INPUT
Component
Mass, kg
Mass %
CO2
94.0236
0.218
H2
0.0129
0.00003
CH4
20.2711
0.047
C2H4
20.2711
0.047
C2H6
22.4276
0.052
H2
0.0129
0.008
C2H4O
5256.701
12.187
CH4
20.2711
12.911
CH3COOH
27651.1616 64.106
C2H4
20.2711
12.911
C2H5OH
354.0984
0.821
C2H6
22.4276
14.285
H2O
8107.1717
18.795
CO2
94.0236
59.885
Acetone
475.7254
1.103
Total
157.0063
100
EthAc
1131.7347
2.624
Total
43133.5994 100
OUTPUT
Component
Mass, kg
Mass %
DC4
OUTPUT
Component
Mass, kg
Mass %
Acetone
475.7254
1.261
EthAc
1809.1402
4.796
H2O
8245.7319
21.860
CH3COOH
27189.2941
72.082
Total
37719.8916
100
OUTPUT
Component
Mass, kg
Mass %
C2H4O
5256.701
100
Total
5256.701
100
26
4.1.7 Splitter
Mass, kg
Mass %
Acetone
142.7176
1.261
EthAc
542.7421
4.796
H2O
2473.7196
21.860
CH3COOH
8156.7882
72.082
Total
11315.9675
100
Component
INPUT
Component
Mass, kg
Mass %
Acetone
475.7254
1.261
EthAc
1809.1402
4.796
H2O
8245.7319
21.860
CH3COOH
27189.2941
72.082
Total
37719.8916
100
SPLITTER
OUTPUT
Component
Mass, kg
Mass %
Acetone
333.0078
1.261
EthAc
1266.3981
4.796
H2O
5772.0123
21.860
CH3COOH
19032.5059
72.082
Total
26403.9241
100
27
4.1.8 Acetic Acid Separation Column (DC5)
INPUT
Component
Mass, kg
Mass %
Acetone
333.0078
1.261
Component Mass, kg
EthAc
1266.3981
4.796
CH3COOH
17129.2553 100
H2O
5772.0123
21.860
Total
17129.2553 100
CH3COOH
19032.5059
72.082
Total
26403.9241
100
OUTPUT
Mass %
DC5
OUTPUT
Component
Mass, kg
Mass %
Acetone
333.0078
3.591
EthAc
1266.3981
13.654
H2O
5772.0123
62.234
CH3COOH
1903.2506
20.521
Total
9274.6688
100
28
4.1.9 Decanter (DE1)
OUTPUT
Component
Mass, kg
Mass %
CH3COOH
1903.2506
60.046
EthAc
1266.3981
39.954
Total
3169.6487
100
INPUT
Component
Mass, kg
Mass %
Acetone
333.0078
3.591
EthAc
1266.3981
13.654
H2O
5772.0123
62.234
CH3COOH
1903.2506
20.521
Total
9274.6688
100
DE1
OUTPUT
Component
Mass, kg
Mass %
H2O
5772.0123
94.545
Acetone
333.0078
5.455
Total
6105.0201
100
29
4.1.10 Acetone Distillation Column (DC6)
INPUT
Component
Mass, kg
Mass %
OUTPUT
H2O
5772.0123
94.545
Component
Mass, kg
Mass %
Acetone
333.0078
5.455
Acetone
333.0078
100
Total
6105.0201
100
Total
333.0078
100
DC6
OUTPUT
Component
Mass, kg
Mass %
H2O
5772.0123
100
Total
5772.0123
100
30
4.1.11 Ethyl Acetate Distillation Column (DC7)
OUTPUT
INPUT
Component
Mass, kg
Mass %
Component
Mass, kg
Mass %
CH3COOH
1903.2506
60.046
EthAc
1266.3981
100
EthAc
1266.3981
39.954
Total
1266.3981
100
Total
3169.6487
100
DC7
OUTPUT
Component
Mass, kg
Mass %
CH3COOH
1903.2506
100
Total
1903.2506
100
31
CHAPTER FIVE
5.0 REFERENCES
Depew, L. S., Collins, N. A., Lee, P. E. C., & Matthew, W. (2000). United States Patent CSE.
Jones, J. H. (2000). The CativaTM Process for the Manufacture of Acetic Acid: Iridium
catalyst improves productivity in an established industrial process. Platinum Metals
Review, 44(3), 94–105.
Pattanaik, B. N., & Mandalia, H. C. (2011). Ethyl Acetate: Properties, Production Processes
and Applications - A Review. International Journal of Current Research and Review,
3(12), 23–40.
32