vapor liquid equilibrium( ethanol+water)

Course Number: ChE-302

Course Title: Chemical Engineering Laboratory-II

Experiment Number: 03

Name of the Experiment: Vapor-Liquid Equilibrium

Submitted by:

Mahe Rukh

Student Number: 1202036

Section: A2 Group Number: 02

Department of Chemical Engineering

Partners’ Student Numbers: 1202037

1202038

1202039

1202040

Date of Performance:

03/10/15

Date of Submission:

10/10/15

Submitted to:

Dr. Syeda Sultana Razia

Professor

Department of chemical engineering

BUET

Vapor-Liquid Equilibrium

1.0 Summary

The aim of this experiment is to produce vapor-liquid equilibrium at atmospheric pressure and to

determine equilibrium composition and temperature. This experiment helps one to inspect the

relationship between vapor and liquid phases and to understand the concept of VLE

comprehensively. A binary system e.g. ethanol-water system was used in this experiment. The

mixture was fed into an evaporator and the evaporated vapor was cooled down using condenser.

The condensed liquid falls back into round bottom flask. This cycle continues until the

temperature becomes constant. Samples from both round bottle flask and distillate collector were

collected to measure refractive indices. At equilibrium point refractive indices of vapor and

liquid achieve constant values. Using refractive index vs. composition diagram equilibrium

composition was measured. The experimental values of equilibrium compositions with ‘Txy’

diagram and ‘X-Y’ diagram are then compared with the theoretical values. The equilibrium

temperature of the vapor liquid equilibrium system was found to be 820C. The mole fraction of

ethanol in liquid phase was .10 and that in vapor phase was .54, while the corresponding

theoretical values are 0.29 and 0.57 correspondingly.

2.0 IntroductionEquilibrium can be referred to as a static condition in which there is no change in macroscopic

properties of a system with time. According to Vapor-liquid equilibrium(VLE) the rate of

condensation of vapor is equal to the rate of vaporization without any net interconversion

between liquid and vapor phase. In this experiment our goal was to create vapor liquid

equilibrium at atmospheric pressure and to determine equilibrium temperature and composition

for a binary system. Undoubtedly the concept of vapor liquid equilibrium is the heart of many

chemical processes and has immense importance in chemical and environmental engineering as

various processes like drying, distillation and evaporation depend greatly on VLE. According to

theory it needs forever to reach equilibrium but in real practice it can be reached in a closed

space if vapor and liquid phases are in contact with each other for long period without any

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interference. For multicomponent system equilibrium condition can be defined by following

equations

;

; and

Where P and T are pressure and temperature of different phases and G is Gibb’s free energy also called as chemical potential.

Temperature-composition curve (T-x,y diagram), composition of liquid phase vs. composition of

vapour phase (y-x diagram) are the most common graphical representation of binary vapor liquid

equilibrium system. And these diagrams were used to obtain result. This experiment also gives

us insight on distillation process.

3.0 Experimental work

3.1 Apparatus

Refractometer

Thermometer

Round bottom flask

Sample collector

SOLTEQ® Vapor Liquid Equilibrium Unit

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3.1 Experimental setup

Figure-01: Experimental setup for vapor-liquid equilibrium

3.2 Procedure

At first the refractive index of the feed solution was determined at room temperature.

Then 200 ml of ethanol water feed solution of composition 24% ethanol (by weight) was

poured to the equilibrium still through thermometer point and no gas leakage must be

ensured

As Temperature should not exceed 80-degree Celsius cooling water flow was started to

condenser.

Then the mixture was heated by electric heater. The heater needed to be adjusted in such

a way that the mixture of vapor and liquid was raised through the narrow neck above the

flask.

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After 30 minutes when temperature reached a constant value samples were collected from

both round bottom flux and distillate collector in small sample bottles. And their

corresponding refractive indices were recorded after they cool down.

Step 5 was repeated until a constant refractive index was obtained and the system was

assumed to reach equilibrium.

The temperature was recorded with thermometer which was the equilibrium temperature.

Samples from both round bottom flux and distillate collector ware collected and

refractive indices were measured with refractometer.

At last refractive index-composition curve was used to obtain the equilibrium conditions.

4.0 Observed data

Refractive index of feed solution= 1.357

Initial composition of feed solution= 24 mole% ethanol

Table 01: Data for refractive index of ethanol water system in liquid and vapor phase

No. of

observation

Temperature

(oC)

Refractive index

liquid phase

(average values)

Refractive index vapor phase

(average values)

1 82 1.355 1.361

2 82 1.348 1.3622

3 82 1.352 1.3625

4 82 1.3485 1.362

5 82 1.34875 1.362

6 82 1.348 1.362

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5.0 Calculated data

Table 02: Data for composition of ethanol water system in liquid and vapor phase

No. of

observation

Temperature

(oC)

Refractive index liquid phase (average values)

Mole fraction, x (mole %)

Refractive index vapor phase

(average values)

Mole fraction, y (mole %)

1 82 1.355 20 1.361 41

2 82 1.348 12 1.36225 60

3 82 1.352 10 1.3625 60

4 82 1.3485 11 1.362 54

5 82 1.34875 11 1.362 54

6 82 1.348 10 1.362 54

6.0 Sample Calculation

Equilibrium temperature= 82oC

From experiment

Composition of ethanol in mole percent

In vapor phase= 54%

In liquid phase= 10%

Literature values of composition of ethanol in mole percent from Txy diagram

Liquid phase = 29%

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Vapor phase = 57 %

From the x-y diagram

Vapor phase = 44 (mole %) ethanol for the composition of liquid phase = 10 (mole %) ethanol.

Liquid phase = 24 (mole %) ethanol for the composition of vapor phase = 54 (mole %) ethanol.

7.0 Graphical representation

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 170

75

80

85

90

95

100

105

liquid

vapor

Mole fraction of liquid (x) and vapor (y) of Ethanol

Tem

par

atu

re (

C

)

(0.1,82) (0.29, 82) (0.54,82)

(0.57, 82)

Figure 02: Temperature vs. molar composition of liquid(x) and vapor(y) phase

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Molar composition of Ethanol in Liquid (x)Mol

ar c

omp

osit

ion

of

Eth

anol

in v

apor

(y)

(0.24, 0.54)

(0.1, 0.44)

Figure 03: Molar composition of Ethanol in liquid vs. molar composition of Ethanol in vapor

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8.0 Results

Equilibrium temperature= 82oC

Equilibrium composition of ethanol in liquid phase= 10%(mole)

Equilibrium composition of ethanol in vapor phase= 54%(mole)

9.0 Discussions

The experiment was carried out successfully by following the procedures. The values we

obtained experimentally showed deviations from literature values due to errors introduced in the

experiment. At 82-degree Celsius the equilibrium composition of Ethanol in liquid and vapor

phase should be 29% and 57% respectively. Whereas we achieved 10 mole% ethanol

composition in liquid phase and 54mole% in vapor phase. From the data it is evident that

deviation is significant. Moreover, from X-Y diagram we can observe experimentally obtained

equilibrium composition lay below the theoretically obtained equilibrium values. However, the

compositions obtained experimentally should have lied on equilibrium curves as the

compositions are equilibrium compositions. The probable causes for such deviations are

explained below-

The provided graph of refractive index vs. composition graph was for 30o C. but the

temperature of the day of performance was above 30oC which may have influenced the

result.

ethanol is highly volatile and transfer of ethanol from one vessel to another vessel

provided room for ethanol loss. As a result, measurement of refractive index was not

accurate.

Our system was not properly insulated and there was temperature difference between top

and bottom part of the equilibrium still. Hence, the temperature values that were recorded

were not the actual temperature values of the mixture. Therefore, lack of proper

insulation is responsible for deviation in results.

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Narrow pipes were used in the apparatus which increased pressure above the liquid. As a

result, vapor could not pass freely and pressure was not constant everywhere. But this

process should be isobaric and constancy of pressure is a prime requirement of this

experiment.

After measuring refractive index of a sample the sampling bottle was not cleaned

properly. Any drop of liquid from previous sample can change concentration of new

sample and manipulate results.

10.0 References

Wankat, Phillip.C. (2012). Separations process engineering,3rd edition, Upper Saddle River, New Jersey: Prentice Hall.

Introduction to Chemical Engineering Processes/Vapor-Liquid equilibrium, Wikibooks,

retrieved from

https://en.wikibooks.org/wiki/Introduction_to_Chemical_Engineering_Processes/Vapor-

Liquid_equilibrium

Vapor–liquid equilibrium, Wikipedia, retrieved from

https://en.wikipedia.org/wiki/Vapor%E2%80%93liquid_equilibrium

VLE, Academia, retrieved from

https://www.academia.edu/11843101/VLE_Lab_Report_2015_

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Marking Scheme: Normal Report

Name: Mahe Rukh

Student number: 1202036

Section and marks allocated Marks

Summary(1)

Introduction (1)

Experimental Work (1.5)

Observed Data (1)

Calculated Data (1)

Sample Calculation (1)

Graphs (1)

Results and Discussion (1)

References and Nomenclature (0.5)

Writing Quality and Style (1)

Total (10)

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vapor liquid equilibrium( ethanol+water)

Documents

vaporliquid equilibriumvle

equilibrium temperature

vapor phase

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composition of liquid

condensed liquid

evaporated vapor

refractive indices of