Vapor Liquid Equilibrium

Topics: Gas, Vapor pressure, Vapor-liquid equilibrium Pages: 12 (1867 words) Published: April 17, 2014
TITLE
Vapour Liquid Equilibrium
OBJECTIVE
To find the Vapour-Liquid Equilibrium (VLE) relationship for binary mixture and to plot the equilibrium curve. INTRODUCTION
The term equilibrium is referred to as when a system is in a static condition and there is absolutely no changes that occur as time goes by. Vapour-liquid equilibrium is a condition where a liquid and its vapor are in equilibrium with each other, a condition or state where the rate of evaporation is equal to the rate of condensation on a molecular level such that there is no overall vapour liquid inter-conversion (Smallwood, I. M ,1993).In theory equilibrium takes forever to reach, such an equilibrium is practically reached in a relatively closed location if a liquid and its vapour are allowed to stand in contact with each other long enough with no interference or only gradual interference from the outside (Smith, C. L ,2012).In this experiment, two liquid which have different volatilities are boiled to several temperature. The liquid which has higher volatility are then collected from liquid and vapour sampling ports to determine its refractive index respectively in order to obtain its compositions.Relative volatility ( α ) is a measure comparing the vapor pressures of the components in a liquid mixture of chemicals (Seader, J. D., Henley, E. J. & Roper, D. K., 2011). When the relative volatilities of both key components are equal, = 1 and separation would be impossible under the given conditions because the compositions of the liquid and the vapor phase are the same (azeotrope).As the value of increases above 1, separation becomes progressively easier.

MATERIALS AND EQUIPMENT
Vapour –liquid equilibrium apparatus
Beaker
Dripper
Refractometer
3.2L of isopropyl-water mixture
Distilled water

Vapour – Liquid Equilibrium Apparatus

RESULT AND CALCULATION

Calibration Curve
Concentration of isopropanol
(%)
1st reading
(%)
2nd reading
(%)
3rd reading
(%)
Average
(%)
Refractive Index
20
7.0
7.0
7.0
7.00
1.34325
40
17.2
17.2
17.0
17.13
1.35912
60
22.3
22.4
22.3
22.33
1.36776
80
25.5
25.5
26.0
25.67
1.37349
100
26.6
26.6
26.8
26.67
1.37524
Table 1Calibration curve data.
Vapour
Temperature
(°C)
Pressure
(bar)
1st reading
(%)
2nd reading
(%)
3rd reading
(%)
Average
(%)
Refractive Index
75
4.744
12
12
11.8
11.93
1.35082
80
4.620
15.4
15.4
15.1
15.30
1.35616
85
4.599
14.7
14.8
14.3
14.60
1.35504
90
4.539
14.2
13.7
14.2
14.03
1.35413
95
4.554
13.2
13.0
13.1
13.10
1.35266
Table 2Vapour sample data tabulation.
Liquid
Temperature
(°C)
Pressure
(bar)
1st reading
(%)
2nd reading
(%)
3rd reading
(%)
Average
(%)
Refractive Index
75
4.744
2.3
2.3
2.3
2.30
1.33630
80
4.620
2.1
2.1
2.1
2.10
1.33601
85
4.599
2.0
2.0
2.0
2.00
1.33586
90
4.539
1.7
1.7
1.7
1.70
1.33543
95
4.554
1.1
1.1
1.2
1.13
1.33460
Table 3Liquid sample data tabulation.
Sample calculation for the interpolation of Brix value (%) to refractive index: 40 % composition of isopropanol which having 17.13% Brix taken as example. Brix(%)
Refractive Index
17.00
1.35891
17.13

18.00
1.36054
Table 4Example of conversion of Brix value (%) to reflective index.

A calibration curve was plotted to relate composition of isopropanol with refractive index.

Figure 1
From calibration curve, obtain the relationship between isopropanol’s composition and refractive index given as y = 0.0004x + 1.3403 where y is refractive index and x is composition. Taking refractive index of vapour sample at 75 °C (i.e. 1.35082) as sample calculation 1.35082= 0.0004x+1.3403

x=
x= 26.3 (The composition of isopropanol is 26.3 % in vapour at 75 °C) The composition of isopropanol for vapour and liquid were calculated using correlation above and tabulated as below. Temperature

(°C)
Pressure
(bar)
Vapour
Liquid

Refractive Index
Composition
(%)...
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