National Conference, CHEMCON 2010, 27-29 Dec 2010
VAPOR LIQUID EQUILIBRIUM AND RESIDUE CURVE MAP
FOR ACETIC ACID-WATER-ETHYL
ACETATE TERNARY
SYSTEM
Desai
Sunita. S. ,Sinhgad
College
of Engineering,
Gadekar
Shamla V.
Pune, P.L.V.N. Saichandra, Sinhgad College of Engineering,
,BVDUCOE,
ABSTRACT
Azeotropic
behavior
is relatively
a common
phenomenon,
one of the most
efficient methods of treating an azeotrope is the introduction of an entrainer (mass
separation)
through
the process of heterogeneous
distillation.
For the design of such a process the need of vapor liquid equilibrium
(VLE) data remains of the fundamental
azeotropic
and/or extractive
importance. The number of ternary and
quaternary VLE data available in the literature is very scarce in comparison with
homogeneous
binary VLE data. So the attempt is made to find experimental
data for the ternary system acetic acid-water-ethyl
using modified form of Othmer's
VLE
acetate at 301 K and 1 atm, by
still apparatus and analyzed by refractive index
method. The system becomes heteroazeotropic
due to addition of ethyl acetate
which acts as an entrainer. The obtained experimental
VLE data was used to plot
the residue curve map (RCM) which is a triangular diagram often used to describe
the equilibrium
effective
relationships
for ternary mixtures. Ternary diagrams
tool for the heuristic
synthesis
and shortcut
design
makes an
to separation
processes. The RCM analysis is also used to estimate distillation parameters such
as feed location, distillations regions etc.
KEYWORDS:
Experimental
data; VLE;
Ternary; Residue Curve Map
National Conference, CHEMCON 2010, 27-29 Dee 2010
INTRODUCTION
Azeotropic
behavior
is relatively
a common
phenomenon,
one of the most
efficient methods of treating an azeotrope is the introduction of an entrainer (mass
separation)
through
the process of heterogeneous
distillation.
For the design of such a process the need of vapor liquid equilibrium
(VLE) data remains of the fundamental
azeotropic
and/or extractive
importance. The number of ternary and
quaternary VLE data available in the literature is very scarce in comparison with
homogeneous
binary VLE data. So the attempt is made to find experimental
data for the ternary system acetic acid-water-ethyl
of Othmer's
becomes
VLE
acetate by using modified form
still apparatus and analyzed by refractive index method. The system
heteroazeotropic
due to addition
entrainer This type of ternary system
of their wide application
of ethyl acetate
which acts as an
have been investigated extensively
because
in industrial processes such as purified terphthalic
acid
and acetic acid recovery. The phase behavior of the mixtures of this type plays an
important role in the research of critical phenomenon and wetting transitions. The
obtained VLE data for the acetic acid- water - ethyl acetate was used to plot the
residue curve map (RCM) , which is a triangular diagram often used to describe
'he equilibrium relationships
for ternary mixture[I,2].
XPERIMENTAL
Chemical
An Iytical grade chemicals and a laboratory source of distilled water were used.
The solvents and the acid were tested for purity by density as well as refractive
index determination.
The properties of chemicals at 30°C are given below [3].
Substai ce
nD
p (gm/crrr')
B.P.oC
Acetic a ~id
1.3680
1.0392
118.50
Water
1.3320
0.9957
100.00
E~yl acetate
l.3700
0.8939
77.10
I
"
National Conference, CHEMCON 2010, 27-29 Dec 2010
Experimental apparatus, procedure and analysis
Equilibrium
apparatus
used for measuring
vapor-liquid
equilibrium
data was
developed by Othmer. The still is classed as a circulating still. Circulation method
was used to find VLE data for acetic acid -water-ethyl
of the still are boiling chamber/
acetate. The main features
section, condensation
section, reflux section,
heating media.
Heating coils are provided inside the boiling section. The schematic diagram of
the apparatus assembly is shown in figurel.
The feed mixture consisting of three components
acetate
were
equilibrium
receiver
fed to the boiling
heated
continuously
until thermal
was attained. The vapors will start to rise and are condensed
and
temperature
section,
i.e. acetic acid, water and ethyl
again
recirculated.
After
thermal
equilibrium
in the
i.e. when
the
of vapor and liquid were same, sample of vapor and liquid were
withdrawn from the respective ports and analyzed
by using refractometer
[4].
Calibration chart
The most
important
and first part of the experiment
is preparation
of the
calibration chart. The LLE data for the system Acetic acid - Water - Ethyl acetate
in reported DECHEMA
series is as shown in table 1 & 2. [5,6]. Binodal curve and
feed points are shown in figure 2.
RE UL T AND DISCUSSION
From obtained experimental
results as in table 3 and VLE plot as shown in figure
3 fo lowing points are discussed.
Nodes and Saddle points
We find that there are two nodes present in the system. The highest boiling acetic
acid (l18 0c) becomes a stable node and the minimum boiling azeotrope between
water and ethyl acetate (70.38 0c) becomes unstable node. Ethyl acetate and water
acts as saddle points. The continuous
distillation
line or distillation
dark line shown in figure 4 is called as
boundary line. Due to presence of distillation
line
ternary p .ot is divided in two separate regions i.e. region I and region II as shown
National Conference, CHEMCON 2010, 27-29 Dec 2010
in figure 4. Each distillation
region must contain one stable node, one unstable
node and at least one saddle [8-10].
Region I
The points in region I are in direction towards stable node acetic acid
via ethyl acetate as a saddle point. There are three vertices in this region I1. Highest boiling point stable node, acetic acid.
2.
Saddle point, ethyl acetate.
3. The point S unstable node, minimum boiling azeotrope on water ethyl
acetate edge.
The residue curve emerges
from the unstable node and goes via saddle point
towards the stable node. From figure 4 points 4,5,6,7,9,10
lie in this region, the
residue curves for these points tends towards stable node acetic acid.
Region II
The points in this region II are also directing towards stable node
acetic acid. There are three vertices in this region II 1. Highest boiling point stable node, acetic acid
2.
Saddle point, ethyl acetate.
3. The point S unstable node, minimum boiling azeotrope on water ethyl
acetate edge. It has lowest boiling point.
From figure 4 the residue curves for points 8,12,11,3,2 in region IIemerges from
the unstable node and goes towards stable node acetic acid via saddle point water.
From figure 4 i) B.P. of point 4 is 74.50C and B.P. of point 6 is 71°C
ii) B.P. of point 10 is 84°C and B.P. of point 9 is 73°C
iii) B.P. of point 14 is 97°C and B.P. of point 10 is 96°C
which
shows that temperature
increases
along the residue
curve.
Thus one
important property of residue curve "The temperature must always increase along
the residue curve", is verified from above points.
National Conference, CHEMCON 2010, 27-29 Dec 2010
CONCLUSION
The separation of non ideal mixtures are complex, the product purity can not be
achieved due to presence of azeotropes in the system, residue curve map is found
to be effective tool for such system. Vapor liquid equilibrium
the ternary system acetic acid-water-ethyl
data is obtained for
acetate by experimentation
and with
this data residue curve map is plotted.
The residue curve map gives correct visualization of physical and thermodynamic
limits of the system which
is used for proper design of distillation
Distillation region I and II found to be the correct to operate the column
Note"
111-4
All
Teflon
d,men$k)rls
stopcccs..
in
Bmm
mm
..
"'
Counler
)
Figure 1: Vapor liquid equilibrium apparatus
column.
National Conference, CHEMCON 2010, 27-29 Dec 2010
Acetic Acid (118°C)
(Stable node)
o " 100
FIG.2
BINODAL CURVE & fEED POINTS
Figure 2: Binodal curve and feed points
(Experimental
tie lines in mole% at temperature
=
40.00q
Acetic Acid(IIBOC)
(Stable node)
Wiler
-\."II
••••
CI>•••••
b_
•. v__ c_,..."oo.
Figure 3: VLE for acetic acid-water-ethyl
system at 301 K and 1 atm.
acetate ternary
National Conference, CHEMCON 2010,27-29
Dec 2010
Acetic Acid (1 J 8"C)
(Stable node)
o .
100
Figure 4: Residue curve map for acetic acid-water-ethyl
acetate ternary system.
Table 1: Reported LLE data in mole% for acetic acid-water-ethyl
Left phase
Sr.No.
[ 1]
Right phase
[2]
[ 1]
[2]
1
18.547
3.091
97.329
0.899
2
22.391
5.892
96.236
1.762
3
26.777
8.368
94.975
2.666
4
31.5 I3
10.504
93.791
3.490
5
34.457
12.332
92.804
4.294
[ 1] Water
[ 2 ] Acetic ACId
Table 2: Calibration chart for acetic acid - water - ethyl acetate
Sr.No.
Mole%
Mole%
Refractive
[water]
[acetic
Index
acetate
National Conference, CHEMCON 2010, 27-29 Dec 2010
acid]
I
97.329
0.899
1.3395
2
92.804
4.294
1.3380
3
80.0
9.5
1.3570
4
17.5
12.5
1.3670
5
25.5
14.5
1.3685
6
80
0
1.3690
7
36
14
1.3700
8
30
15
1.3705
9
56
10
1.3710
10
34.46
12.33
1.3725
Table 3: Experimental
vapor liquid equilibrium data for acetic acid-water-ethyl
acetate ternary system
Point
Liquid
Liquid
Vapor
Temperature
Composition
Composition
Mole%
Mole%
°c
No
[water]
[ acetic
[water]
[ acetic
acid]
acid]
1
77
21.66
15.24
15.12
10.0
2
76
45.94
21.86
78.46
2.197
3
84
41.53
23.61
58.76
5.56
4
74.5
11.00
29.14
24.13
26.93
5
73
17.70
13.70
60
0
6
71
10.95
17.33
38.06
6.29
National Conference, CHEMCON 2010, 27-29 Dec 2010
7
75
25.96
18.54
61.83
0.63
8
71
34.43
12.31
38.67
7.62
9
73
2.77
13.51
70
0
10
84
1.43
14.93
5.41
8.93
11
83
37.98
13.78
31.71
9.88
12
69
34.68
11.69
80
0
13
96
90.23
1.08
42.71
0.726
14
97
80.70
18.18
37.97
9.28
ABBREVIATION & SYMBOLS
VLE
vapor liquid equilibrium
LLE
liquid liquid equilibrium
RCM
residue curve map
B.P.
boiling point
nD
refractive index
p
density
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(1999).
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National Conference, CHEMCON 2010, 27-29 Dec 2010
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