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CL 251: Chemical Engineering Lab I Lab Report-04 Vapor-Liquid Equilibrium
Sagar Chawla 12110081
Abstract:-
The purpose of this experiment is to determine the liquid-vapor equili equ ilibrium brium data for a given binary system of benzene and acetone by construct equilibrium between vapor and liquid. Data for binary system was ca lculated by measuring the boiling te mperature of solution. Composition of liquid and vapor vapor is measured by refractometery. Boiling point of binary mixture is depending on t heir compositions in the mixture. Boiling po int of mixture will change as composition co mposition of mixture mixture change. cha nge. Boiling point of mixture is decreases as composition of acetone is increases in mixture because acetone is more volatile component than benzene. Composition of benzene and acetone in liquid and vapor phase changes as boiling point of mixture changes. Error in data is probably due to human error and there were some leaks in apparatus.
Introduction:-
Separation of two or more compound based on their different composition in mixture is one of the most common operations in Chemical engineering. There is no changes occur in the macroscopic properties of a s ystem with time in Equilibrium condition. Vapor liquid Equilibrium is a condition where the rat e of evaporation is equal to the t he rate of condensation. Boiling point temperature te mperature of mixture is depends upon the co mposition of acetone and benzene in the mixture. Boiling point temperature of mixture is Intermediate temperature between the two pure compound boiling points. Relative vo latility latility is a measure of comparing the vapor pressures of components in a liquid mixture. When the volatilities of both liquids are same, then separation would be impossible. The vaporliquid equilibrium data gives the basic information information of o f the system that is required for t he design of the equilib equ ilibrium rium stages of o f vapor liquid separation equipment like distillation. Equilibrium data represent the composition of the mixture in vapor phase p hase and liquid phase. Equilibrium compositions are function of temperature and pressure. Separation at Industry level is done in isobaric condition. There is a relation between refractive index o f the solution and mole fraction and Composition of a component in a solution can be measured by knowing the refractive index (R.I) of the solution for acetone the R.I and mole fraction (XA) relation is given as: R.I = -0.1397*X A + 1.4995
(1)
Relation between partial pressure and temperature is given by Antoine equation:
= −
(2)
Where: 0
T- Saturation temperature ( C)
– Saturated partial pressure. A, B and C are constants which vary for different components. For acetone: A= 14.31, B=2765.22, C=228.06. For benzene: A= 13.78, B=2726.81,C=217.57
= + = Total Pressure = ∗ = ∗ At equilibrium, the relationship between the compositions of species i in the vapor and liquid phases is often defined by a K-value, or equilibrium ratio:
= = =
Where: YA= Mole fraction of acetone (A) in vapour YB = Mole fraction of benzene (B) in vapour XA= Mole fraction of acetone (A) in liquid XB = Mole fraction of benzene (B) in liquid The relation between reaction coefficient (ϒ X ) and mole mole fractions can be given as: YA = (PA / PT) *
A 500ml solution of benzene and 100ml solution of acetone was taken in a beaker. The mixture solution was injected into still vaporizer. Power was switched on and the t he temperature of the heater was set to 100 degree Celsius and heated the mixture. Mixture started to boil after sometime. The vapor goes up into the condenser co ndenser and is collected co llected in the collector. The condensed vapor was then again poured back into the vaporizer and
again system was left left to attain equilibrium. equilibrium. After equilib equ ilibrium rium was attained, att ained, temperature becomes constant but a slight variation in temperature was observed and the value of temperature was noted down. Refractive index of both condensed vapor and liquid in vaporizer was measured by refractometer. The T he mixture from still was drained out and same procedure was repeated repeat ed for solutions of composition: 250ml benzene + 250ml acetone and 200ml benzene + 300ml acetone. And then using R.I values, values of XA and YA was determined
Result:
Table 1.Data of Properties for Benzene and Acetone
Component
0
Density at 20 C
Molecular
Boiling Point
0
R.I at 20 C
Weight (Kg/lit)
0
(g/mol)
( C)
(nD)
Benzene
0.87
78.11
80.1
1.50
Acetone
0.79
58.08
56.0
1.35
Table 2.Boiling point for different compositions calculated was as follows: Acetone volume
Benzene volume
Temperature
(ml)
(ml)
( C)
100
400
69
250
250
60.9
300
200
58.3
0
Table 3 Data of. Refractive Index of Liquid and Vapor phase at boiling points for different compositions.
Temperature
69
60.9
58.3
66.4
58.7
57.1
1.4725
1.3773
1.3973
1.4407
1.4190
1.3968
(Liquid) 0
C
Temperature ( Vapour) 0
C
R.I (Liquid) nD R.I (Vapour) nD
Table 4.Data of mole fractions of Aceto ne and Benzene at different boiling points in liquid and vapor phase
Temperature
69
60.9
58.3
XA
0.1932
0.8747
0.7316
XB
0.8067
0.1253
0.2684
YA
0.4209
0.5762
0.7351
YB
0.5791
0.4238
0.2649
(Liquid) 0
C
Table 5.Calculatting the Van Laar constants a and b and other data.
Temperature
69
60.9
58.3
ϒA
3.6133
1.0902
1.6616
ϒB
1.8068
8.5475
2.4964
0
(Liquid) C
Ln(ϒA/ ϒB)
0.6930
-0.8943
-0.1768
K A
2.1778
0.6588
1.0049
K B
0.7178
3.3829
0.9867
A
7.3719
0.05613
1.4729
B
0.4889
28.0169
1.05718
Ln(ϒ A / ϒ B ) Vs XA 0.8 0.6 0.4 0.2 0 0-0.2 .193271296
0.874731568
0.731567645
log vs xa
-0.4 -0.6 -0.8 -1
Graph 1.Difference in area about X-axis for Ln(ϒA/ ϒB) Vs XA plot.
2.5
2
1.5 LnϒA Vs XA
1 LnϒB Vs XA
0.5
0 0
0.2
0.4
0.6
0.8
1
Graph 2. Interrelation between Ln(ϒA) and Ln(ϒB) Vs XA plots.
Discussion & Conclusion:-
It can be seen that boiling point of mixture decreases and co mposition of more volatile compound in vapor phase is increases as quantity of more volatile compound is increases. This difference in composition between the vapor and liquid phases becomes the basis for separating the compounds. Whole process was done at constant pressure, if pressure is vary throughout the process then some variation is occur in properties of compounds because that properties are function of pressure and temperature. Acetone is more volatile because it has week van der Waal’s forces than benzene. Data of vapor-liquid equilibrium is useful to design setup for different industrial separation process.
Appendix:
Sample calculation: 0
For 100ml of acetone and 400ml of benzene boiling temperature: 69 C. R.I(vapour) = 1.4725 nD R.I (liquid) = 1.4407 nD Thus from equation (1) XA = ( R.I -1.4995)/ (-0.1397) XA = (1.4407 (1.4407 -1.4995)/ -1.4995)/ (-0.1397) XA = 0.193271 Thus XB = 1- XA XB = 0.8067
