DEPARTMENT OF CHEMICAL ENGINEERING

MANIPAL UNIVERSITY JAIPUR

CE 1705 PROSS PLANT DESIGN

B. Tech. IV Year 7th Semester, 2019

PRODUCTION OF ACRYLIC ACID VIA CATALYTIC PARTIAL

OXIDATION OF PROPYLENE

Instructor:
Ir. Nandana Chakinala

Submitted By:

TANIMA SHARMA (169102024)

NEHA KUMARI (169102016)
MANAS AGARWAL (169102014)
Table of Contents

ABSTRACT ...............................................................................................................................5
INTRODUCTION ......................................................................................................................6
PHYSICAL PROPERTIES......................................................................................................6
CHEMICAL PROPERTIES ....................................................................................................7
ENVIRONMENTAL EFFECTS ..............................................................................................7
APPLICATIONS.....................................................................................................................7
REACTIONS INVOLVED [7] ................................................................................................8
PROCESS FLOW SHEET ..........................................................................................................9
PROCESS DESCRIPTION ....................................................................................................... 10
FEED STREAMS .................................................................................................................. 10
COMPRESSOR .................................................................................................................... 10
MIX-1 ................................................................................................................................... 11
HEATER ............................................................................................................................... 11
REACTOR ............................................................................................................................ 12
COOLER............................................................................................................................... 14
VAPOUR- LIQUID SEPARATOR ....................................................................................... 14
ABSORBER .......................................................................................................................... 15
MIX-2 ................................................................................................................................... 17
EXTRACTOR – COMPONENT SPLITTER......................................................................... 17
DISTILLATION COLUMN .................................................................................................. 18
Case Study 2: Distillation .................................................................................................. 19
ENERGY ANALYSIS .............................................................................................................. 20
MAXIMUM ENERGY RECOVERY .................................................................................... 21
ECONOMIC ANALYSIS ......................................................................................................... 21
REFRENCES ............................................................................................................................ 25
APPENDIX .............................................................................................................................. 25
LIST OF TABLES
Table 1: Feed Conditions and Flowrates .................................................................................... 10
Table 2: Composition of Air Feed ............................................................................................. 10
Table 3: Material balance and stream properties across the compressor ..................................... 10
Table 4: Duty requirement by the compressor ........................................................................... 11
Table 5: Material balance and stream properties across the mixer unit ....................................... 11
Table 6: Compositions of outlet stream from mixer (mix).......................................................... 11
Table 7: Heater parameters ........................................................................................................ 11
Table 8: Material balance and stream properties across heater ................................................... 12
Table 9: Dimensions of the Reactor. .......................................................................................... 13
Table 10: Material Balances and stream conditions across the reactor. ...................................... 13
Table 11: Heat extracted from the reactor .................................................................................. 13
Table 12: Composition of the stream entering the reactor and product stream leaving the reactor.
................................................................................................................................................. 13
Table 13: Material balance and stream conditions across the cooler ........................................... 14
Table 14: Cooler parameters...................................................................................................... 14
Table 15: Dimensions of the V-L separator. .............................................................................. 14
Table 16: Material balance and stream compositions across the V-L separator .......................... 15
Table 17: Component material balance across the V-L separator ............................................... 15
Table 18: Dimensions of the Absorber. ..................................................................................... 15
Table 19: Material balance and stream conditions across the absorber unit ................................ 16
Table 20: Component material balance across the absorber unit ................................................ 16
Table 21: Material balance and stream conditions across the mix-2 ........................................... 17
Table 22: Component Material Balance across mix-2 ................................................................ 17
Table 23: Material balance and stream conditions across the mix-2 ........................................... 17
Table 24: Component material balance across the extractor ....................................................... 18
Table 25: Set parameters for the Distillation Column ................................................................ 19
Table 26: Material balance and stream conditions across the distillation column. ...................... 19
Table 27: Condenser and Reboiler duties for Distillation column .............................................. 19
Table 28: Component balance across the distillation column ..................................................... 19
Table 29: Energy Analysis Results ............................................................................................ 21
Table 30: Cost of Various Equipment ........................................................................................ 22
Table 31: Estimation of Total Capital Investment ...................................................................... 23
Table 32: Raw material cost evaluation ..................................................................................... 23
Table 33: Utility cost evaluation ................................................................................................ 24
Table 34: Total production cost evaluation ................................................................................ 24
Table 35: Gross profit in $/year ................................................................................................. 24
Table 36: Material Balances and stream conditions (1). ............................................................. 25
Table 37: Material Balances and stream conditions (2) .............................................................. 25
Table 38: Compositions of streams (1). ..................................................................................... 26
Table 39: Compositions of streams (2). ..................................................................................... 26
Table 40: Energy Streams ......................................................................................................... 26
LIST OF FIGURES
Figure 1: Molecular Structure of Acrylic Acid [3]. ......................................................................6
Figure 2: Process Flow Diagram of the Simulated Plant for production of Acrylic Acid. .............9
Figure 3: Case Study 1- Reactor Volume vs. Propylene Conversion .......................................... 12
Figure 4: Composition change with the tray number in the absorber. ......................................... 16
Figure 5: Composition at different trays in the Distillation column. ........................................... 18
Figure 6: Fraction of water removed in extractor vs. minimum reflux and actual trays in distillation
column ...................................................................................................................................... 20
Figure 7: MER generated by Aspen Energy Analyzer................................................................ 21
ABSTRACT
In the following study, the simulation of the acrylic acid production via catalytic partial oxidation
process is carried out using the simulator ASPEN Hysys. NRTL-ideal was used as the fluid
package. The production rate of acrylic acid was 16680 tone/year, assuming 8000 working hours
per year. A continuous stirred tank reactor with a volume of 37.64 m3 was simulated to get a
propylene conversion of 90%. The separation system consists of a vapor-liquid separator, a vapor
recovery system (absorber) and a liquid recovery system (Extractor-dummy and Distillation).Two
sensitivity studies were carried out: 1) influence of the volume of reactor on the propylene
conversion; 2) influence of the water removal from extraction column on the number of trays and
minimum reflux ratio of distillation column. At the distillation column a liquid bottom stream
containing Acrylic acid with 99.24 % purity is obtained. Energy and Economic analysis was
performed and it was determined that the plant had a total capital investment of 23 million dollars
and a gross yearly income of 8.6 million dollars.
INTRODUCTION
Acrylic acid is the simplest unsaturated carboxylic acid and is a building block for thousands of
consumer products. It is a commodity chemical with a current market demand of nearly 13 billion
pounds worth $14 billion. Acrylic acid (2-propenoic acid) is a highly reactive carboxylic acid that
can react with itself to form poly-acrylic acid, which is used as an absorbent in hygiene products.
It also can react with alcohols to form acrylates (esters) that are used in a wide range of polymers.
However, polymers commonly called acrylic (Plexiglas, textiles, etc.) contain acrylate monomers
but are often produced from chemicals other than acrylic acid [1]. The majority of the market
growth is projected to occur in China and India as these countries produce increasing amounts of
products using acrylic acid as intermediates with application including detergents, coatings,
adhesives, sealants, as well as personal care items. Currently, the US accounts for 25% of global
production [2].

Figure 1: Molecular Structure of Acrylic Acid [3].

Acrylic acid is an important polymer as raw material for many industrial and consumer products.
It can numerous to apply for surface coatings, textiles, adhesives, paper treatment, baby diapers,
feminine hygiene products detergents and super absorbent polymers as known. Currently, most
acrylic acid is obtained from the catalytic partial oxidation of propene which is a by-product of
ethylene and gasoline production. In this two-step oxidation reaction via acrolein is usually
preferred, achieving about 90 % overall yield. However, this conventional process affects global
CO2 emissions: 175 kg of CO2 is released in converting propene to one ton of acrylic acid and
petrochemical carbons sources are limited and not renewable [4].
PHYSICAL PROPERTIES
 Acrylic acid is a colorless liquid with a distinctive acrid odor.
 Flash point 130°F.
 Boiling point 286°F.
 Freezing point 53°F.
 Corrosive to metals and tissue.
 Prolonged exposure to fire or heat can cause polymerization. If polymerization takes place
in a closed container, violent rupture may occur. The inhibitor (usually hydroquinone)
greatly reduces the tendency to polymerize.
CHEMICAL PROPERTIES
 It is miscible with water, alcohol, ether, benzene, chloroform, and acetone. It polymerizes
readily in the presence of oxygen. Exothermic polymerization at room temperature may
cause acrylic acid to become explosive if confined. It is sensitive to heat and sunlight.
 It is normally supplied as the inhibited monomer, but because of its relatively high freezing
point it often partly solidifies and the solid phase (and the vapour) will then be free of the
inhibitor which remains in the liquid phase.
 Even the un-inhibited form may be stored safely below the melting point, but such material
will polymerize exothermically at ambient temperature and may accelerate to a violent or
explosive state if confined. It is also a fire hazard when exposed to heat or flame.
 Acrylic acid is incompatible with strong oxidizers, strong bases, strong alkalies and pure
nitrogen. It may polymerize (sometimes explosively) on contact with amines, ammonia,
oleum and chlorosulfonic acid, iron salts and peroxides. It may corrode iron and steel [5].

ENVIRONMENTAL EFFECTS
 Due to the breakdown of acrylic acid in the environment and its moderate acute toxicity,
the chemical would not be expected to be toxic to aquatic or terrestrial animals at levels
normally found in the environment. As a volatile organic compound, acrylic acid can
contribute to the formation of photo-chemical smog in the presence of other precursors [5].
 Acute toxic effects may include the death of animals, birds, or fish, and death or low growth
rate in plants. Acute (short term) effects are seen two to four days after animals or plants
come in contact with a toxic chemical substance. Acrylic acid has slight acute toxicity to
aquatic life and high toxicity to birds. Insufficient data are available to evaluate or predict
the short-term effects of acrylic acid to plants or land animals [6].
 Chronic toxic (long term) effects may include shortened lifespan, reproductive problems,
lower fertility, and changes in appearance or behaviour. Chronic effects can be seen long
after first exposure(s) to a toxic chemical [6].

APPLICATIONS
 Acrylic acid is an important commercial chemical. It is used to make plastics, molding
powders, construction units, paint, leather chemicals and paper coatings. Acrylic acid is
used in some automotive products. It is used in textiles coatings, specialty inks, adhesives,
disposable diapers and detergents. It is also used in medicine and in dentistry for plates,
artificial teeth and orthopedic cement [5].
 Most acrylic acid is consumed in the form of the polymer. The dominant share of acrylic
acid is converted to esters. Today growth is in the demand for superabsorbents (SAPs) for
use in diapers and hygienic products. Acrylic acid accounts for 80-85% of raw materials
used in the manufacture of SAPs [2].
 Another major use for acrylic acid is the manufacture of polyacrylates which are used as
thickeners, dispersants and rheology controllers. Acrylic acid is also employed as a
comonomer with acrylamide in anionic polyacrylamide and to produce hydroxyacrylates
for use in industrial coating formulations [2].
REACTIONS INVOLVED [7]

These reactions are industrially carried out in a fluidized bed reactor at a temperature of 310˚C
and pressure of 4.3 bars [7]. The operating temperature rang is very narrow as above 320˚C
the catalyst coking begins and below 300˚C the kinetics does not support the production of
acrylic acid. Therefore, the temperature has to be maintained the reactor.
 PROCESS FLOW SHEET

Figure 2: Process Flow Diagram of the Simulated Plant for production of Acrylic Acid.
PROCESS DESCRIPTION
The process described in this report produces 16,680 tons/year of 99.24 mol% pure acrylic acid
per year (assuming 8000 working hours/year). It was simulated using Aspen Hysys. NRTL- ideal
was used as a fluid package. Various components of the process along with the material and energy
balances are shown below. A more elaborate material and energy balance sheet obtained from the
simulation is shown in the Appendix.

FEED STREAMS
The raw materials for the production of acrylic acid are propylene, air and steam. Steam is added
to provide thermal ballast or the exothermic heat of reaction. Its presence also helps to avoid coking
of the catalyst in the reactor. The air is present as a source of oxygen for oxidation of propylene to
acrylic acid.

Table 1: Feed Condit ions and Flowrates

Unit Air feed Steam feed Propylene feed
Vapour Fraction 1.00 1.00 1.00
Temperature C 25.00 159.00 25.00
Pressure bar 1.00 6.02 11.50
Molar Flow kgmole/h 541.95 394.60 50.50
Mass Flow tonne/h 15.59 7.11 2.13

Table 2: Composit ion of Air Feed

Air feed
Comp Mole Frac (Oxygen) 0.189
Comp Mole Frac (Nitrogen) 0.811

COMPRESSOR
Air feed is compressed to increase the pressure to the required pressure of the reactor. It is a
stainless steel centrifugal compressor with a motor. The required duty of the compressor is 898.1
KW, which is very high, so this can be split up in a series of compressors.

Table 3: Material balance and stream properties across the compressor

Unit Inlet- Air feed Outlet -Compressed air
Vapor Fraction 1.00 1.00
Temperature C 25.00 225.46
Pressure bar 1.00 4.30
Molar Flow kgmole/h 541.95 541.95
Table 4: Dut y requirement by the compressor
Unit Q1
Energy kJ/h 3.23E+06

MIX-1
All the feed streams are mixed together using a mixer which is a tee in this case and then sent to
the reactor.

Table 5: Material balance and stream properties across the mixer unit
Parameters Unit In-Compressed In-Steam In-Propylene Out-
air feed feed Mix
Vapour Fraction 1.00 1.00 1.00
Temperature C 1.00 159.00 25.00 168.22
Pressure bar 225.46 6.02 11.50 4.30
Molar Flow kgmole/h 4.30 394.60 50.50 987.05
Mass Flow tonne/h 541.95 7.11 2.13 24.82
Liquid Volume Flow m3/h 15.59 7.12 4.08 29.35

Table 6: Composit ions of outlet stream from mixer (mix).

Compositions mix
Comp Mole Frac (Propene) 0.051
Comp Mole Frac (H2O) 0.400
Comp Mole Frac (Oxygen) 0.104
Comp Mole Frac (Nitrogen) 0.445

HEATER
After being mixed, the feed is allowed to enter a heater which in this case is a heat exchanger,
where it is pre-heated to a certain temperature in order to reduce the heat load of the reactor. High
Pressure stream was used as utility in this heat exchanger. The heat duty of the heater was 212.1
KW. After performing energy analysis, the area of the heater was calculated as 143.1 m2.

Table 7: Heater parameters

Unit
Heat Load kJ/h 7.6E+05
Area 𝑚2 143.1
Number of shells - 1
LMTD ℃ 69.87
Overall U kJ/h-𝑚2 -℃ 76.4
Table 8: Material balance and stream properties across heater
Unit In-mix Out-to reactor
Vapour Fraction 1.00 1.00
Temperature ℃ 168.22 190.00
Pressure bar 4.30 4.30
Molar Flow kgmole/h 987.05 987.05
Mass Flow tonne/h 24.82 24.82
Liquid Volume Flow m3/h 29.35 29.35

REACTOR
The reactor we are using here is stainless steel continuous stir tank rector (CSTR). The production
of acrylic acid takes place in fluidized bed reactor as discussed in the introduction. In industries
commonly the catalyst for this process include Mn2O3, V2O5, and MoO3 ground together and then
calcinated at high temperatures. We are aware that the behavior of fluidized bed lies between that
of plug flow reactor (PFR) and continuous stir tank reactor (CSTR). Initially a PFR was used but
very low conversion of propylene (0.5) and selectivity of acrylic acid (0.02) was obtained. Further
a back mixing stream was introduced in the PFR to make it behave closer to a fluidized bed but
still not much conversion was obtained. The back mixing stream fraction had to be greatly
increased (0.7) to get good conversion (0.8) but at such high flowrates, the size of reactor was very
high. Finally a CSTR was used and the desired conversion and selectivity was obtained.

A case study was performed to study the effect of CSTR volume on the conversion of propylene
as shown in Figure 3 below. For the desired conversion of 90%, the reactor volume was found out
as 37.64 m3.

Reactor Volume vs. Conversion

94

92

90 37.64
Propylene Convesion

88

86

84

82

80

78
0 10 20 30 40 50 60
Reactor Volume m3

Figure 3: Case Study 1- Reactor Volume vs. Propylene Conversion

Table 9: Dimensions of the Reactor.
Volume(𝑚3 ) 37.64
Diameter (m) 3.173
Height (m) 4.760

In order to keep the temperature of the reactor constant at 310˚C, the outlet temperature was fixed.
Since it is a CSTR, the outlet temperature is equal the temperature inside the reactor. Since the
reactions occurring in the reactor are exothermic, some heat needed to be removed from the reactor
in order to maintain the temperature. This heat was equal to 10.25 MW which was taken up to
generate HP steam which was used in the heater discussed before.

Table 10: Material Balances and stream condit ions across the reactor.
Unit In - to reactor Out - product
Vapour Fraction 1.00 1.00
Temperature C 190.00 310.00
Pressure bar 4.30 4.30
Molar Flow kgmole/h 987.05 971.61
Mass Flow tonne/h 24.82 24.82
Liquid Volume Flow m3/h 29.35 28.12

Table 11: Heat extracted from the reactor

Unit Q-2
energy kJ/h -3.69E+07

Table 12: Composit ion of the stream entering the reactor and product stream
leaving the reactor.
To reactor Product
Comp Mole Frac (Propene) 0.051 0.005
Comp Mole Frac (AcrylicAcid) 0.000 0.030
Comp Mole Frac (AceticAcid) 0.000 0.009
Comp Mole Frac (H2O) 0.400 0.468
Comp Mole Frac (CO2) 0.000 0.032
Comp Mole Frac (Oxygen) 0.104 0.003
Comp Mole Frac (Nitrogen) 0.445 0.452
COOLER
The reactor effluent enters the cooler which in this case is a heat exchanger with air as the cooling
utility. Here the temperature is reduced in a way that the acetic acid, and acrylic acid condenses so
that it can separated in a vapor- liquid separation system. The duty of the cooler was 7445 KW,
which is a very huge amount and hence requires a large area. After performing energy analysis,
the area of the cooler was calculated as 1261 m2.

Table 13: Material balance and stream condit ions across the cooler
Unit In - Product Out - To V-L separator
Vapour Fraction 1.00 0.55
Temperature C 310.00 70.00
Pressure bar 4.30 3.00
Molar Flow kgmole/h 971.61 971.61
Mass Flow tonne/h 24.82 24.82
Liquid Volume Flow m3/h 28.12 28.12

Table 14: Cooler parameters

Unit
Heat Load –Q4 kJ/h 2.68E+07
Area 𝑚2 1261
Number of shells - 4
LMTD ℃ 121.9
Overall U kJ/h-𝑚2 -℃ 286.2

VAPOUR- LIQUID SEPARATOR

After being cooled the reactor effluent are sent to V-L separator where the phase separation takes
place. The liquid phase products are separated from vapor phase products. The vapor liquid
separator in this case is a simple stainless steel tank of the dimensions specified in Table 9 below.
In the V-L separator, the unreacted propylene and oxygen, the inert nitrogen, the carbon dioxide
formed as by product and some amount of water go to the vapor phase and the acrylic acid, acetic
acid and water remain in the liquid phase. Further the vapors are sent to the vapor recovery system.

Table 15: Dimensions of the V-L separator.

Volume(𝑚3 ) 7.098
Diameter(m) 1.372
Height (m) 4.801
Table 16: Material balance and stream composit ions across the V-L separator
Unit In- to V-L separator In- to absorber Out - L2
Vapour Fraction 0.55 1.00 0.00
Temperature C 70.00 70.00 70.00
Pressure bar 3.00 3.00 3.00
Molar Flow kgmole/h 971.61 533.32 438.28
Mass Flow tonne/h 24.82 15.13 9.70
Liquid Volume Flow m3/h 28.12 18.53 9.60

Table 17: Component material balance across the V-L separator

Molar flows(Kgmol/hr) to V-L separator to absorber L2
Propene 5.05 4.62 0.43
Acrylic Acid 29.26 2.24 27.02
Acetic Acid 8.91 1.1 7.81
H2O 454.61 51.64 402.97
CO2 30.75 30.72 0.03
Oxygen 3.38 3.38 0.00
Nitrogen 439.65 439.63 0.02

ABSORBER
The absorber is a stainless steel sieve tray column which is used for vapor recovery. It is operating
under counter current conditions, where deionized water is used as the solvent for absorbing the
small amount of acrylic acid that got separated into the vapor phase in the V-L separator. The
vapor product from the V-L separator was fed from the bottom and water was fed from the top.
During this absorption operation, certain gaseous compounds, such as nitrogen, carbon dioxide,
oxygen and propylene that were not absorbed by the solvent, are removed at the top and vented to
the atmosphere. Acrylic acid and acetic acid got completely absorbed in water and came out as
liquid stream L1. The composition change with the trays of the column was studied as shown in
Figure 4. The top tray is number 1 tray and the bottom tray is number 10. We can see that at the
top the mole fraction of acrylic acid becomes zero. This suggests that all the acrylic acid is obtained
at the bottom with the solvent and none leaves with the gas at the top. Also, if the number of trays
was decreased from 10, some acrylic acid was leaving with the gas and hence 10 is the optimum
number of trays required.

Table 18: Dimensions of the Absorber.

Diameter(m) 1.5
Tray/packed space (m) 0.5
Tray/packed volume(𝑚3 ) 0.88
 Tray No. vs Composition - Absorber
0.035 1
0.995
0.03
A.A, AcrA, Gases mole fraction

0.99
0.025

Water mole fraction

0.985
0.98
0.02
0.975
0.015
0.97

0.01 0.965
0.96
0.005
0.955
0 0.95
1 2 3 4 5 6 7 8 9 10
Tray Number

Propylene and other gases Acrylic Acid Acetic Acid Water

Figure 4: Composition change with the tray number in the absorber.

Table 19: Material balance and stream condit ions across the absorber unit
Unit to absorber Solvent -DIW off gases L1
Vapour Fraction 1.00 0.00 1.00 0.00
Temperature C 70.00 25.00 47.57 61.81
Pressure bar 3.00 1.00 1.00 2.00
Molar Flow kgmole/h 533.32 73.00 537.07 69.25
Mass Flow tonne/h 15.13 1.32 15.03 1.41

Table 20: Component material balance across the absorber unit

Molar flows(Kgmol/hr) to absorber Solvent -DIW off gases L1
Propene 4.62 0 4.57 0.05
Acrylic Acid 2.24 0 0.02 2.22
Acetic Acid 1.1 0 0.17 0.93
H2O 51.63 73 58.58 66.05
CO2 30.72 0 30.72 0
Oxygen 3.38 0 3.38 0
Nitrogen 439.63 0 439.63 0
MIX-2
The liquid product streams from the V-L separator and the absorber were mixed before being sent
to the liquid recovery system. This was done using a mixer which in this case was a tee.

Table 21: Material balance and stream condit ions across the mix -2
UnitL1 L2 To extractor
Vapour Fraction 0.00 0.00 0.00
Temperature C 61.81 70.00 68.93
Pressure bar 2.00 3.00 2.00
Molar Flow kgmole/h 69.25 438.28 507.54
Mass Flow tonne/h 1.41 9.70 11.10
Liquid Volume Flow m3/h 1.40 9.60 11.00

Table 22: Component Material Balance across mix -2

Molar flows(Kgmol/hr) L1 L2 to extractor
Propene 0.05 0.43 0.48
Acrylic Acid 2.22 27.02 29.24
Acetic Acid 0.93 7.81 8.74
H2O 66.05 402.97 469.02
CO2 0 0.03 0.03
Oxygen 0 0 0
Nitrogen 0 0.02 0.02

EXTRACTOR – COMPONENT SPLITTER

The mixed stream is then sent to extractor which in this case is a component splitter column.
Initially the liquid-liquid extractor was used with di-isopropyl ether (DIE) as the solvent but due
to very large amount of water present, it did not give the required separation at any conditions so
we used dummy component splitter where the small amount of propylene and a fraction of water
was separated from the acrylic acid and acetic acid. The propylene would get separated in the V-
L system itself at real conditions, but in the simulator there are some interaction parameters due to
which some propylene was left. The fraction of water separated was decided based on further
separation in a distillation column and will be discussed later as Case study 2 in the Distillation
Column section.

Table 23: Material balance and stream condit ions across the mix -2
Unit to extractor to waste water treatment to distillation
Vapour Fraction 0.00 1.00 0.00
Temperature C 68.93 105.00 50.00
Pressure bar 2.00 1.00 1.01
Molar Flow kgmole/h 507.54 375.75 131.79
Table 24: Component material balance across the extractor
Molar flows(Kgmol/hr) to extractor to waste water treatment to distillation
Propene 0.48 0.48 0
Acrylic Acid 29.24 0 29.24
Acetic Acid 8.74 0 8.74
H2O 469.02 375.23 93.79
CO2 0.03 0.03 0
Oxygen 0 0 0
Nitrogen 0.02 0.02 0

DISTILLATION COLUMN
Final purification occurs in distillation column, where 99.2 mole% of acrylic acid is produced as
the bottom product, and 8.3 mole% acetic acid is produced as the top product with rest water. For
evaluating the minimum reflux ratio and number of stages, a short cut distillation column was
used. In the short cut distillation column a recovery of 99.5 % of acrylic acid in the bottoms and
99.5% acetic acid in distillate was set. For these recoveries, an Rmin of 0.9 and 30 number of stages
was obtained. Using these specifications a distillation column was set up but the required amount
of separation was not achieved. The reflux ratio had to be increased to 3 in order to achieve 99%
recovery and a product stream with 99.24 % purity. The composition change at different trays was
also studied as shown in Figure 5 below. We can see that for reflux ratio of 3, the mole fraction of
acrylic acid reaches around 0.99 after the 30th tray and then becomes contant. Also, we can see
that mole fraction of acetic acid initially increases till 21st tray and then reduces. Therefore, we can
conclude that 30 trays are optimum for this separation.

Tray vs Mole Fractions

1.0
0.9
0.8
0.7
Mole fractions

0.6
0.5
Reflux Ratio = 3
0.4
0.3
0.2
0.1
0.0
1

17

25
2
3
4
5
6
7
8

10
11
12
13
14
15
16

18
19
20
21
22
23
24

26
27
28
29
30
Condenser

Reboiler

Trays
Acrylic Acid Acetic Acid Water

Figure 5: Composition at different trays in the Distillation column.

Table 25: Set parameters for the Dist illat ion Column
Number of stages 30
Diameter(m) 1.5
Tray/packed space (m) 0.55
Tray/packed volume(𝑚3 ) 0.97
Reflux ratio 3
Distillate rate 102.6

Table 26: Material balance and stream condit ions across the dist illat ion column.
Unit to distillation Acetic acid Product-Acrylic Acid
Vapour Fraction 0.00 0.00 0.00
Temperature C 50.00 99.70 140.88
Pressure bar 1.01 1.01 1.01
Molar Flow kgmole/h 131.79 102.60 29.19
Mass Flow tonne/h 4.32 2.22 2.10
Liquid Volume Flow m3/h 4.18 2.20 1.98

Table 27: Condenser and Reboiler dut ies for Dist illat ion column
Unit Q-reb Q-cond
energy kJ/h 1.70E+07 1.61E+07

Table 28: Component balance across the distillat ion column

Molar flows(Kgmol/hr) to distillation Acetic acid Product-Acrylic Acid
Propene 0 0 0
Acrylic Acid 29.24 0.27 28.97
Acetic Acid 8.74 8.52 0.22
H2O 93.79 93.79 0
CO2 0 0 0
Oxygen 0 0 0
Nitrogen 0 0 0

Case Study 2: Distillation

The distillation performed above is very difficult because of the complexity of the system of acrylic
acid, acetic acid and water. Water and acrylic acid forms a minimum boiling azeotrope together,
so they can’t be separated using normal distillation but acetic acid breaks that azeotrope. Also,
acetic acid and acrylic acid separation is almost impossible but it has been found that acetic
acid can readily be separated from acrylic acid by distillation when an entrainer capable of forming
an azeotropic mixture with acrylic acid is present [8]. Therefore, it is important that all three
components i.e. water, acrylic acid, and acetic acid are present for distillation to occur. It was
noticed that if the amount of water present in the distillation feed was too low, the number of trays
and reflux ratio was also too high. Also, it was noticed that higher the mole fractions of water
present in the distillation feed, lower was the recovery and purity of acrylic acid in the distillate
and the separation became more difficult. Therefore, a certain amount of water had to be removed
in the extractor or the component splitter. For determining the fraction of water to be removed, a
case study was made as shown in Figure 6 below. According to this case study, the actual trays
and minimum reflux ratio were minimum for a maximum possible water removal of 0.8. therefore
in the component splitter 0.8 fraction of water was removed and 0.2 fraction was sent along with
the acrylic acid and acetic acid to the distillation column.

extractor- water removed vs minimum reflux and actual trays

0 0.2 0.4 0.6 0.8 1 1.2

4.5 80
4 70
3.5 60
minimum reflux

actual trays
50
2.5
40
2
30
1.5
1 20

0.5 10

0 0
0 0.2 0.4 0.6 0.8 1 1.2
extractor- water removed
minimum reflux ratio actual trays

Figure 6: Fraction of water removed in extractor vs. minimum reflux and actual trays in
distillation column

ENERGY ANALYSIS
The energy analysis performed by the aspen simulator showed that 4 heat exchanger were required.
Their heat loads are as shown in Table 29 below. We can see that there are two hot process streams
namely product-to V-L separator and Q2 (Reactor heat) and two cold process streams namely Mix
–to reactor and to reboiler. For these streams four different utility streams were present. The
product to V-L separator hot stream was cooled using air as the utility in the cooler. The Q2 stream
from the reactor was used to generate HP steam which was then used to heat the mix - to reactor
stream in the heater. Another utility stream i.e. MP steam was used in the reboiler. Using this data
an MER was generated as shown in Figure 7 below.
 Table 29: Energy Analysis Results
Heat Load Hot stream Hot Hot Cold stream cold cold
exchanger (kJ/h) 𝑻𝒊𝒏 𝑻𝒐𝒖𝒕 𝑻𝒊𝒏 𝑻𝒐𝒖𝒕
(℃) (℃) (℃) (℃)
Heater 7.6E+05 HP steam 250 249 Mix-to reactor 168.2 190
(utility stream) (process stream)
Cooler 2.7E+07 Product-to V-L separator 310 70 Air 30 35
(process stream) (utility stream)
Q2 3.7E+07 Q2 310 309. HP steam generation 249 250
(process stream) 5 (utility stream)
Reboiler 1.7E+07 MP steam 175 174 To reboiler 140.5 140.9
(utility stream) (process stream)

MAXIMUM ENERGY RECOVERY

35 C

TO REBOILER

Figure 7: MER generated by Aspen Energy Analyzer

ECONOMIC ANALYSIS
There were some technical problems in our Aspen economic analyzer, therefore the economic
analysis was done manually. The purchased equipment costs were taken from a web source [9] at
Jan 2002 and it was corrected to Sep 2018 using Chemical Engineering Plant Cost Index (CEPCI).
Also, the capacity for a few equipment had to be corrected which was done using the six-tenths
rule. After evaluating the purchased equipment cost, the other costs were evaluated using the cost
estimation ratio factors given in Peter’s and Timmerhaus [10]. Table 30 gives the costs of various
equipment. Table 317 below shows the calculation for Total Capital Investment.
Table 30: Cost of Various Equipment
Compressor
Centrifugal-motor 898.1 KW Stainless Steel
CEPCI index Cost$
Jan-02 390.4 1341374
Sep-18 1030.7 3541379
Heater
143.1 m2 212.1 KW Stainless Steel
CEPCI Index Cost$
Jan-02 390.4 26595
Sep-18 671.1 45717
Reactor
300 psi 37.64 m3 Stainless Steel
CEPCI Index Capacity (m3) Cost
Jan-02 390.4 1 38793
Sep-18 753.3 37.64 660087
Cooler
1261 m2 7445 KW Stainless Steel
CEPCI Index Area (m2) Cost
Jan-02 390.4 50 11952
Sep-18 671.1 1261 142484
V-L Separator
7.093 m3 Stainless Steel
CEPCI Index Cost$
Jan-02 390.4 63909
Sep-18 671.1 109860
Absorber
Diameter = 1.5 m Spacing = 0.5 m Stainless Steel
CEPCI Index Cost$
Jan-02 390.4 33192
Sep-18 671.1 57057
Distillation
Diameter = 1.5 m Spacing = 0.5 m Stainless Steel
Index Cost$
Jan-02 390.4 36532
Sep-18 753.3 70491
Table 31: Est imat ion of Total Capital Investment
Cost ($)
Purchased Equipment (Delivered)-E 4627074
Purchased Equipment Installation - 39% E 1804559
Instrumentation 28% E 1295581
Piping 31% E 1434393
Electrical 10% E 462707
Building 22% E 1017956
Yard Improvements 10% E 462707
Service Facilities 55% E 2544891
Land 6% E 277624
Total Direct Cost, D 13927493
Engineering and Supervision 32% E 1480664
Construction 34% E 1573205
Total Direct and Indirect Cost (D+I) 16981362
Contractor's Fee 5%(D+I) 849068
Contingency 10%(D+I) 1698136
Fixed Capital Investment 19528567
Working Capital Investment (15% of Total Capital Investment) 3446218
Total Capital Investment 22974784
Cost ($/year)
Annualized Capital Investment (n=10 yrs, I=10%) 3739040

Further, the raw material and utility costs were evaluated. The cost data was taken from Chemical
Market Reporter [6]. Table 32 and 33 shows the raw material and utility costs respectively. Other
operating costs and yearly expenses were evaluated using the cost estimation ratio factors given in
Peter’s and Timmerhaus [10]. Table 34 below shows the calculations for Total production cost in
$/year.

Table 32: Raw material cost evaluat ion

Raw Material Cost
Raw Materials Cost $/kg Flow (Kg/hr) Cost ($/hr)
Propylene 0.7 2125.07 1487.55
Steam 0.0009 7108.76 6.40
Air 0.0007 15589.54 10.91
1504.86
Working hours 8000hr/year
Cost ($/yr) 12038878
 Table 33: Ut ilit y cost evaluat ion
Utility Cost
Utility Duty (KJ/hr) Delta T C Cp (KJ/kg C) Requirement (Kg/hr) Cost ($/KJ) Cost ($/hr)
Air 26801777.5 5 1 5360355.5 1.0E-09 0.03
HP steam 36112758.3 1 1703 21205.4 2.5E-06 90.28
MP steam 16965269.1 1 1981 8564.0 2.2E-06 37.32
127.63
Working Hours 8000 hr/year
Cost ($/year) 1021058

Table 34: Total production cost evaluat ion

0 $/year
Raw Materials 12038878
Operating Labour (10% of Total Product Cost) 4178088
Direct Supervisory (10 % of operating labour) 417809
Utilities 1021058
Maintanance and Repairs (4% of Fixed Capital) 781143
Operating Supplies (10% of Maintanence and Repairs) 78114
Laboratory Charges (10% of Operating Labor) 417809
Patents and Royalties (1% of Total Product Cost) 417809
Direct Production Cost 19350708
Depreciation of Fixed Capital (SLM) (n=10 yrs, Salvage =10% of Fixed Capital) 1757571
Local Taxes (1% of Fixed Capital) 175757
Insurance (0.5% of Fixed Capital) 87879
Fixed Charges 2021207
Plant Overhead (5% of Total Product Cost) 2089044
Manufacturing Cost 23460959
Administrative Cost (15% of Operating Labour, Maintainance, Supervision) 806556
Distribution and Selling Cost (5% of Total Product Cost) 2089044
Research and Development (5% of Total Product Cost) 2089044
Financing (3% of Total Capital Investment) 689244
General Expenses 5673888
Total Production Cost = Manufacturing+General Expenses 29134847

Table 35: Gross profit in $/year

Selling Price ($/Kg) Production Rate (Kg/year) Income ($/year)

Acrylic Acid (Product) 2.47 16807071.68 41513467.05
Gross Earning ($/year) = Income- (Total Production cost + Total capital Investment) 8639580
 REFRENCES
[1] Chien, I., Yu, B., & Lee, H. (2017). Process Simulation and Design of Acrylic Acid Production.
Epigenetic Biomarkers and Diagnostics. Elsevier Inc. https://doi.org/10.1016/B978-0-12-803782-
9.00013-3
[2] Puwar, A., & Jalan, K. (2018). Production of Acrylic Acid, 7(8), 403–417.https://doi.org/
10.21275/ ART2019294
[3]https://www.acs.org/content/acs/en/molecule-of-the-week/archive/a/acrylic-acid.html
[accessed on :23rd November 2019]
[4] https://www.sciencedirect.com/topics/chemistry/acrylic-acid [accessed on:23rd Nov 2019]
[5] http://www.npi.gov.au/resource/acrylic-acid [accessed on :23rd November 2019]
[6]https://www.icis.com/explore/resources/news/2007/11/01/9074870/acrylic-acid-uses-and-
market-data/ [accessed on :23rd November 2019]
[7] Javier, E., Sánchez, P., María, R., & Silva, S. (2019). Simulation of the acrylic acid production
process through catalytic oxidation of gaseous propylene using ChemCAD ® simulator
Simulación del proceso de producción del ácido cítrico a través de la oxidación, 27, 142–150.
[8] Y., Akira (1969) Separation And Purification Of Acrylic Acid From Acetic Acid By Solvent
Extraction And Azeotropic Distillation With A Two Component Solvent-Entrainer System,
3,433,831.
[9] http://www.mhhe.com/engcs/chemical/peters/data/ce.html [accessed on: 24th November 2019]
[10] Peters, M. S., & Timmerhaus, K. D. (1980). Plant design and economics for chemical
engineers. New York: McGraw-Hill.

APPENDIX

Table 36: Material Balances and stream condit ions (1).

Unit propylene feed air feed steam feed mix compressed air to V-L separator product to reactor
Vapour Fraction 1.0 1.0 1.0 1.0 1.0 0.5 1.0 1.0
Temperature C 25.0 25.0 159.0 168.2 225.5 70.0 310.0 190.0
Pressure bar 11.5 1.0 6.0 4.3 4.3 3.0 4.3 4.3
Molar Flow kgmole/h 50.5 542.0 394.6 987.0 542.0 971.6 971.6 987.0
Mass Flow tonne/h 2.1 15.6 7.1 24.8 15.6 24.8 24.8 24.8
Liquid Volume Flow m3/h 4.1 18.2 7.1 29.4 18.2 28.1 28.1 29.4

Table 37: Material Balances and stream condit ions (2)

Unit to absorber L2 Solvent -DIW off gases L1 to extractor to distillation to waste water treatment Acetic acid Product-Acrylic Acid
Vapour Fraction 1.0 0.0 0.0 1.0 0.0 0.0 0.0 1.0 0.0 0.0
Temperature C 70.0 70.0 25.0 47.6 61.8 68.9 50.0 105.0 99.7 140.9
Pressure bar 3.0 3.0 1.0 1.0 2.0 2.0 1.0 1.0 1.0 1.0
Molar Flow kgmole/h 533.3 438.3 73.0 537.1 69.3 507.5 131.8 375.7 102.6 29.2
Mass Flow tonne/h 15.1 9.7 1.3 15.0 1.4 11.1 4.3 6.8 2.2 2.1
Liquid Volume Flow m3/h 18.5 9.6 1.3 18.4 1.4 11.0 4.2 6.8 2.2 2.0
 Table 38: Composit ions of streams (1).
propylene feed air feed steam feed mix compressed air to V-L separator product to reactor
Comp Mole Frac (Propene) 1.00 0.00 0.00 0.05 0.00 0.01 0.01 0.05
Comp Mole Frac (AcrylicAcid) 0.00 0.00 0.00 0.00 0.00 0.03 0.03 0.00
Comp Mole Frac (AceticAcid) 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.00
Comp Mole Frac (H2O) 0.00 0.00 1.00 0.40 0.00 0.47 0.47 0.40
Comp Mole Frac (CO2) 0.00 0.00 0.00 0.00 0.00 0.03 0.03 0.00
Comp Mole Frac (Oxygen) 0.00 0.19 0.00 0.10 0.19 0.00 0.00 0.10
Comp Mole Frac (Nitrogen) 0.00 0.81 0.00 0.45 0.81 0.45 0.45 0.45

Table 39: Composit ions of streams (2).

to absorber L2 Solvent -DIW off gases L1 to extractor to distillation to waste water treatment Acetic acid Product-Acrylic Acid
Comp Mole Frac (Propene) 0.01 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00
Comp Mole Frac (AcrylicAcid) 0.00 0.06 0.00 0.00 0.03 0.06 0.22 0.00 0.00 0.99
Comp Mole Frac (AceticAcid) 0.00 0.02 0.00 0.00 0.01 0.02 0.07 0.00 0.08 0.01
Comp Mole Frac (H2O) 0.10 0.92 1.00 0.11 0.95 0.92 0.71 1.00 0.91 0.00
Comp Mole Frac (CO2) 0.06 0.00 0.00 0.06 0.00 0.00 0.00 0.00 0.00 0.00
Comp Mole Frac (Oxygen) 0.01 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00
Comp Mole Frac (Nitrogen) 0.82 0.00 0.00 0.82 0.00 0.00 0.00 0.00 0.00 0.00

Table 40: Energy Streams

Unit Q1 Q4 Q5 Q-reb Q-2 Q-100 Q-cond
Heat Flow kJ/h 3.23E+06 2.68E+07 1.60E+07 1.70E+07 -3.69E+07 7.64E+05 1.61E+07