International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 12 (2016) pp 7767-7771
© Research India Publications. http://www.ripublication.com
Three column configuration for the separation of IPA-water using by
heteroazeotropic distillation
Manish Pokhrel, Daniel Owusu Asante and Jung Ho Cho*
Department of Chemical Engineering, Kongju National University, 592, Shindangdong,
Cheonan, Chungnam 331-280, South Korea.
Department of Chemical Engineering, Kongju National University, Buiding No 9, Room 1017,
Cheonan-si, Chungnam, 31080, South Korea.
mainly focuses on the minimization of energy consumption
for the separation process varying the IPA at the concentrator
top.
Abstract
Modeling and optimization study for the distillation of almost
pure 2-propanol (IPA) from dilute mixture of IPA with water
has been made by the use of three-column configurations.
PRO/II 9.2 has been used for the process simulation. For the
thermodynamic model, NRTL liquid activity coefficient
model has been used. The IPA at the concentrator top was
varied to optimize the re-boiler heat duty.
105
Experimental
Estimated
Temperature (oC)
100
INTRODUCTION:
2-Propanol (Isopropyl alcohol, IPA) is widely used in semiconductor industry as a cleaning agent, thus the recovery of
IPA from waste solvent stream is an important issue worthy of
detail study (1). IPA-water forms a homogeneous minimumboiling azeotrope at 87.4–87.7 mass% (67.5-68.1 mole %) and
80.3–80.4oC (2) as shown in figrures 1 and 2. Therefore, a
high-purity IPA product over its azeotropic composition
cannot be obtained through conventional distillation because
an infinite number of trays are required to reach to the
azeotropic point (3). Many separation methods can be used to
separate the azeotropic mixture like extractive distillation,
pressure swing distillation or azeotropic distillation. Here, we
focus on the azeotropic distillation which makes uses of a
decanter coupled with one or more distillation columns, which
exploits both vapor-liquid and liquid-liquid equilibrium
driving forces (4). In azeotropic distillation a third component
E is added to the feed. A or B components become either a
stable or unstable node on the residue curve in the relevant
distillation region, thus being removable as product by either
an indirect or a direct split, respectively (5). In Azeotropic
distillation process parametric sensitivity, multiple steady
states, long transient, and nonlinear dynamics were found by
many authors using theoretical models and computer
simulation (6). In this research, modeling and optimization
were performed to obtain ultra-pure IPA from the mixture of
IPA and water using cyclohexane (CH) as entrainer. By adding
cyclohexane to the IPA-water mixture, forms a ternary
heterogeneous azeotrope of IPA-water-CH which is lower
than any other binary azeotropic temperatures thereby
obtaining nearly pure IPA as a bottom product of the
azeotropic distillation column. Three-column configurations
were used for the exploratory study. The three-column
sequence contains a pre-concentrator column, an azeotropic
column, and an entrainer recovery column.
The function of pre-concentrator column is to reduce the
amount of water that exists in the fresh feed. This study
95
90
85
80
75
0.0
0.2
0.4
0.6
0.8
1.0
Composition,Mole Fraction of IPA, (P=1atm)
Figure 1: Composition of IPA Vs. temperature
Vapor Composition, Mole Fraction IPA
1.0
Estimated
Experimental
0.8
0.6
0.4
0.2
0.0
0.0
0.2
0.4
0.6
0.8
1.0
Liquid Composition,Mole Fraction IPA
Figure 2: Liquid composition Vs. vapor composition of IPA..
Steady state design of the overall process:
This study takes the design specifications adopted from Arifin
and Chien (1). An equimolar composition of IPA and water
with feed rate of 100kmol/hr has been taken at 25oC. The IPA
purity from the IPA product stream is set to 99.999 mol% and
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 12 (2016) pp 7767-7771
© Research India Publications. http://www.ripublication.com
99.9 mol% water from the wastewater stream. The decanter is
operated at 40oC.
The number of trays were varied from 10-30. The operating
pressure was set to 1.1 atm with no pressure drop. For the
simulation PRO/II with PROVISION 9.2, a commercial
process simulator was used. Finally, the minimum re-boiler
heat duty was calculated by varying the IPA composition at
the concentrator top.
is almost pure water and the top stream is recycled back to the
2nd column. The azeotropic column is taken without a decanter.
The condenser used in the 1st and 3rd columns is partial
condenser. The re-boiler used is kettle conventional.
D2
Make-up
Vapor
S7
Thermodynamic model used in simulation
For the following study, NRTL liquid activity coefficient
model have been used to estimate vapor-liquid and liquidliquid equilibria for azeotropic distillation unit modeling.
Liquid activity coefficient for component ‘i’ in mixture is
expressed as:
G x 
k x τ G 
 j τ jiG jix j
ji j 
k kj kj 
lnγ 

τ 
ij
i

k G x
k G ki x k
j  k G kjx k 
kj k 
(1)
Where τij and Gji in Eq. (1) are the optimum binary interaction
parameters that minimize deviations from experimental data.
τij and Gji can be expressed as:
bij cij
τ ji  a 

 d lnT  e T  f TlnT
ij T
ij
ij
ij
T2
Decanter
D1
OR
AO
Feed
T2
T1
S2
T3
IPA
Water
Figure 3: Flow-sheet diagram for the three-column azeotropic
distillation
(2)
G jiji  exp(  jiji jiji )
(3)
In Eq. (2) T refers to the absolute temperature.
The VLE experimental data for IPA-water (7), IPA-CH (8)
and LLE data for water-CH (9) have been regressed and
optimized to obtain a new set of binary interaction parameters.
The fitting of these experimental data for IPA-water have been
shown in figures (1) and (2). The new set of binary interaction
parameters have been listed in table (1)
Table 1: NRTL binary interaction parameters for IPA-water,
IPA-CH and Water-CH Binaries
Ci
Cj
aij
bij
aji
bji
cij
IPA
Water
10.770
-3837.6
-9.5916
4328.4
0.3
IPA
CH
0
110.96
0.00000
674.88
0.3
Water
CH
32.864
-8459.6
-4.6904
2575.3
0.2
Figure 4: Ternary map diagram for IPA-water-CH from
PRO/II
Table 2: Material balance around the decanter
Components
IPA
Water
Cyclohexane
Figure (4) shows ternary LLE diagram for the IPA-water-CH
system at 40oC along with the streams of the second column
and the decanter. Fig (3) shows he process flow diagram for
the three-column. The fresh feed is fed to the pre-concentrator
column in which the top product is close to the azeotropic
composition of IPA and water and the bottom product is
almost pure water. The top product (concentrated IPA) is sent
to the azeotropic column (2nd column) which is dealt together
with the decanter. The top of the 2nd column has IPA-waterCH whose composition is close to the ternary azeotrope which
has the lowest boiling point than any other binaries. The
bottom stream consists of ultra-pure IPA. The top product is
then again fed to the 3rd column from which the bottom stream
Top tray
0.254
0.203
0.543
Left phase
0.54
0.20
0.26
Right phase
0.157
0.015
0.828
RESULT AND DISCUSSION:
The three-column simulation for the separation of IPA and
water was successfully performed using Cyclohexane as an
entrainer. The design specifications have been met. The
entrainer Cyclohexane is thus a successful candidate for the
separation of IPA-water system. The purpose of the study is to
minimize the total re-boiler heat duty by optimizing the
various parameters. The number of stages for the 1st column
was set at 9 while that for 2nd and 3rd columns were fixed at 20
and 10 respectively.
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 12 (2016) pp 7767-7771
© Research India Publications. http://www.ripublication.com
The feed tray location for the 1st, 2nd and 3rd column was
varied to obtain the optimum tray location. The optimum feed
tray location for the 1st column was found out at 3 while that
for 2nd and third columns were at 2 and 5 respectively. Since
the 2nd column is without a condenser the organic reflux from
the decanter is fed to the top of the 2nd column and the
aqueous outlet from the decanter is fed to the solvent recovery
column (3rd column). The top product of the 3rd column is
recycled back to the azeotropic column as shown is fig 3.
In fig 6, it is shown the liquid fraction of IPA, water and CH
distribution among the trays. The liquid fraction of IPA
increases as starting from tray 1 and finally reaches to unity at
tray 20 whereas the liquid fraction of CH tends to zero at tray
20. The liquid fraction of water stays more or less constant
throughout the trays with almost zero liquid fractions.
A case study for the minimum IPA concentration on the preconcentrator varying the re-boiler heat duty was performed.
Fig 7 shows that the heat duty of azeotropic column increases
slowly with increase in the concentration of IPA at the
concentrator top whereas the heat duty of concentrator column
slowly decreases initilaay and increases abruptly when the
concentration of IPA is near to the azeotropic point with water.
Fig 8 shows the overall heat duty against the IPA
concentration on the concentrator top. It is seen that the heat
duty decreases upto some concentration of IPA and rises
sharply as IPA-water compostion tends to reach the azeotropic
point suggesting that it is safer for the concentrator column to
be operated below its optimum ethanol concentration.
Because changes in the feed composition, temperature, and
flow rate, or errors in the stage efficiency, can affect the reflux
ratio of concentration required to obtain given separation
specifications with a fixed number of stages, it is best to
design an ethanol concentration somewhat below the
economically optimum point (10). 59.80 mol% of IPA at the
concentrator top gave the optimum overall heat duty of 3.0259
M*Kcal/hr. The heat duties of each column are shown in table
4.
Re-boiler heat duty (M*Kcal/hr)
3.075
3.070
3.065
3.060
3.055
3.050
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Feed tray location
Figure 5(b): Feed tray location and the recycle stream tray
location for the 2nd column
Re-boiler heat duty (M*Kcal/hr)
3.0470
3.0468
3.0466
3.0464
3.0462
3.0460
1
2
3
4
5
6
7
Feed tray location
Figure 5(c): Feed tray location Vs re-boiler heat duty for the
3rd column
3.14
3.12
0.8
3.10
0.6
Liquid fraction
Re-boiler heat duty (M*Kcal/hr)
1.0
3.08
IPA
Water
CH
0.4
0.2
3.06
0.0
3.04
1
2
3
4
5
6
7
0
Feed tray location
5
10
15
20
Tray number
Figure 5(a): Feed tray location Vs re-boiler heat duty for the
1st column
Figure 6: Liquid fraction Vs tray number for 2nd column
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 12 (2016) pp 7767-7771
© Research India Publications. http://www.ripublication.com
Table 4: Condenser and Re-boiler heat duties of 1st, 2nd and 3
columns
Re-boiler heat duty (M*Kcal/hr)
1.6
Concentrator heat duty
Azeo tower heat duty
stripper heat duty
1.5
1.4
Column Name
T1
T2
T3
Condenser Duty M*KCAL/HR -0.0004
_
-0.0219
Reboiler Duty
M*KCAL/HR 0.9852 1.1557 0.885
1.3
1.2
1.1
CONCLUSION
The azeotropic mixture of IPA-water can be separated using
Cyclohexane as entrainer. The simulation has been performed
using three columns. The simulation has been optimized by
regressing the binary interaction parameters and case studies
have been performed to find the minimum re-boiler heat duty.
For the minimization of re-boiler heat duty it was found that
the feed tray location for the 1st column was at 3, for the 2nd
column at 2 and for the third column at 5. 59.80mol% of IPA
at the concentrator top gave the minimum re-boiler heat duty
of 3.0259 M*Kcal/hr.
1.0
0.9
0.8
54
56
58
60
62
64
IPA mol% at concentrator top
Figure 7
Re-boiler heat duty (M*Kcal/hr)
3.7
3.6
NOTATIONS:
IPA-Isopropyl alcohol
CH-Cyclohexane
1st column-Concentrator column
2nd column-Azeotropic column
3rd column-Stripper column
AO-Aqueous outlet
OR-Organic reflux
3.5
3.4
3.3
3.2
3.1
3.0
54
56
58
60
62
REFERENCES:
64
IPA mol% at concentrator top
[1]
Figure 8
Table 3: Stream property table (material balance)
Stream
Units
FEE D1
Name
D
Stream Description
Phase
Liqu Vap
id or
Temperat
C
25.0 82.8
ure
0
1
Pressure
ATM
1.00 1.10
Flowrate
KG100. 83.6
MOL/HR 00 0
Composit
ion
IPA
0.50 0.60
WATER
0.50 0.40
CH
0.00 0.00
S2
S7
Liqu
id
102.
36
1.10
16.4
0
Vap
or
82.7
3
1.10
158.
71
VAP IPA A0
OR
OR D2 H20 MAKE
UP
Vapor Liqu
id
65.73 84.8
3
1.10 1.10
295.0 49.9
7
8
Liqu
id
40.0
0
1.00
186.
34
Liqu
id
40.0
0
1.00
108.
74
Vap
or
82.6
3
1.10
75.1
1
[2]
Liqu Liquid
id
102. 25.00
36
1.10 1.00
33.6 0.00
2
[3]
[4]
0.00 0.58 0.25 1.00 0.39 0.17 0.57 0.00 0.00001
1.00 0.41 0.23 0.00 0.60 0.01 0.42 1.00 0.00
0.00 0.01 0.52 0.00 0.01 0.81 0.02 0.00 1.00
[5]
From table 3 it is seen that the design specifications have been
met and the recovery of IPA is more than 99.9% with IPA
purity more than 99.99%. A small amount of make-up stream
is added to compensate the loss of entrainer. The top vapor is
condensed using cooling water entering at 32oC and leaving at
40oC.
[6]
7770
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 12 (2016) pp 7767-7771
© Research India Publications. http://www.ripublication.com
[7]
[8]
[9]
[10]
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Properties of Mixtures of Isopropyl Alcohol and
Water
Storonkin, A. V.; Morachevskii, A. G. Zh. Fiz. Khim.,
1956, 30, 1297 Liquid-vapor equilibrium in the
benzene+cyclohexane +isopropyl alcohol system
nopoulos, C.; Wilson, G. M. AIChE J., 1983, 29, 990
Cho, J., Park, J., & Jeon, J. (2006). comparison 3-2column config in EtOH dehyd using Azeo
distillation_Cho et al_2005.pdf. Journal of Industrial
Engineering and Chemistry.
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