Lab Report Vapor Liquid Equilibrium UITM

8/13/2019 Lab Report Vapor Liquid Equilibrium UITM

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1

TABLE OF CONTENTS

CONTENT PAGE

Abstract / summary 2

Introduction 3

Aims / objectives 4

Theory 5-8

Apparatus 9-11

Experimental procedure 12-16

Result 17-19

Sample calculation 20-26

Discussion 27-28

Conclusion 29

References 30

Recommendation 31

Appendix 32-34



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1.0 ABSTRACT:

Vapor-Liquid Equilibrium (VLE) unit can be used to study about the binary system. The main

purpose of this experiment is to determine the composition of methanol in the vapor phase and liquid

phase. In this experiment, a mixture of methanol and water is initially fed into the evaporator. The

quantity of methanol is added until the volume of methanol added is equal to the volume of water which

is 3.0 litres. The mixture was heated until boiled. The mixture vapor will rise up and will be cooled down

by the condenser at the top of the evaporator. As the vapor starts to condense, the liquid falls back into

the evaporator. When temperature remains constant, the system will stabilize and reached an equilibrium

state. Finally, the samples of vapor and liquid were taken to determine their compositions by using a

digital refractometer.



3

2.0 INTRODUCTION:

One of the most common chemical engineering operations is the separation of two or more

compounds based on the differences of the boiling point. Therefore, this operation is applied in the vapor-

liquid equilibrium (VLE) experiment. In this experiment, vapor-liquid equilibrium unit is suitable for

investigating the relationship between the vapor and liquid at equilibrium state at 1 atm (at atmospheric

pressure) and at high pressure up to 2 bars. The purpose of the experiment using vapor-liquid equilibrium

unit is to construct an equilibrium curve for the methanol and water system at the atmospheric pressure.

The vapor-liquid equilibrium unit actually can be used to study any binary system as well as the

multi component system. For example, in this experiment, the mixture of methanol and water with

unknown composition is fed into an evaporator. When the heater is switched on, the mixture started to

boil. The vapor will rise up and cooled down by the condenser at the top of the evaporator. As the vapor

starts to condense, the liquid will fall back into the evaporator. So, the system will stabilize and finally

reached at equilibrium state when the temperature is constant. Then, the samples of the vapor and liquid

are taken to determine their compositions by using a refractometer to know the refractive index.

This unit must be operated under the supervision of authorized personnel who has been properly

trained to handle this unit. Before attempting to start the experiment and run the unit, make sure that all

operating instructions supplied with this unit carefully and have already been read. Moreover, while

conducting the experiment, the students should always check and identify any leak or make sure that the

level of water is enough to submerge the heater and temperature sensor. All the safety and precautions

should be taken while conducting this experiment. Besides that, the students must be careful while

handling the liquid at high temperature and before draining the samples, the heater must be switched off

in order to cool the liquid in the evaporator.



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3.0 OBJECTIVES:

The objective of this experiment is:

To construct an equilibrium curve for the methanol-water system at atmospheric pressure.

The Vapor-Liquid Equilibrium Unit is a bench top unit designed to investigate the

relationship between vapor and liquid at equilibrium for any binary system as well as for

multi component system. The system may run the unit an elevated pressure.



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4.0 Theory

Vapor liquid equilibrium obeys Roult’s Law which give a definition law that relates the vapor

pressure of an solution was dependent on the mole fraction of a solute added to solution. Roult’s Law

only works for ideal mixture and was commonly used for predicting the vapor-liquid equilibrium for an

ideal solution in equilibrium with an ideal gas mixture from the pure component vapor-pressure data. The

partial vapor pressure of a component in a mixture was equal to the vapor pressure of the pure component

at that temperature multiplied by its mole fraction in the mixture(Clark,2005).Roult’s Law can be

expressed by:

Figure 4.1.1: Schematic diagram of VLE setup

Psolution = XsolventP°solvent (Equation 4.1)

Where

Psolution=vapor pressure of the solution

Xsolvent=mole fraction of the solvent

P°solvent=vapor pressure of the pure solvent



6

In order to reduce VLE calculations by Roult’s Law were the vapor phase was an ideal gas and the

liquid phase was an ideal gas solution.

Y i P = X i P i sat (eq 4.2) ∑

P =∑ (eq 4.3)

P= (eq 4.4)∑

P =

∑

(Equation 4.5)

When we discussed the phase behavior of pure fluids, we found that the temperature and pressure

were constant when the two phases were in equilibrium. Thus, the saturated liquid and vapor points were

both at the same temperature. When the liquid is heated it will boil at the same temperature as that at

which the vapor will condense when it is cooled. Another way of saying the same thing is that the bubble

point (boiling point) and dew point are the same for a pure fluid.

When we have two components in both the vapor and liquid phases, the bubble point and dew points no

longer coincide. There is a difference in composition between the liquid and vapor phases that are in

equilibrium at the same T and P .It means that when you raise the temperature of a mixture until it boils,

more of the more-volatile component ends up in the vapor phase. The liquid phase is left enriched in the

less-volatile component. Thus, you can achieve a partial separation in the mixture. This is the principle

behind distillation that accounts for most of the separation done in the chemical industry(Rowley,Vapor

Liquid Equilibrium).By using the partial pressure calculation of Roult’s Law,value of compositions vapor

and liquid can be findalso its boiling point.The graph from figure 4.1.1 below can be plotted when all the

values were get while figure 4.1.2 was for composition of two different component when its equilibrium

state achieved.



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Figure 4.1.2 : Boiling Point Diagram



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Figure 4.1.3: Equilibrium Diagram

In other hand,Vapor Liquid Equilibrium also can be determine by other law which was Dalton’s

Law.Dalton’s Law states that the total pressure exerted by the mixture of non -reactive gases is equal to

the sum of the partial pressure of gases itself(Dalton’s Law,2013).Mathematically,the pressure of a

mixture of gases can be defined as the summation,

∑ (Equation 4.6)

Or

Ptotal=p1+p2+ p3+...+pn

Where pn is partial pressure for each component.



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5.0 Apparatus

Vapor Liquid Equilibrium Unit

Refractometer

Distilled water

Measurement cylinder

Dropper

Power supply

Suck pump

Mask

Gloves

Methanol Beaker



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5.0 Apparatus

Figure 5.19:V9

Figure 5.6:V3

Figure 5.7:Heater

Figure 5.8:

Eva orator

Figure 5.12: V4

Figure 5.13:V5

Figure 5.14: V1

Figure 5.16: TI 02

Figure 5.21: Pressure

Gau e

Figure 5.20: Safety

Valve

Figure 5.15: Control

Panel

Figure 5.11:V6

Figure 5.10 Cooling

Water

Figure 5.9: V10

Figure 5.5: V7

Figure 5.1:V2

Figure 5.2: V13

Figure 5.18:V8 Figure 5.17: V14

Figure 5.4:V12 Figure 5.3: V11

Figure 5.0 :- Model BP16 Vapor Liquid Equilibrium Unit



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Figure 5.22 :- REFRACTOMETER

Figure 5.23 :- Control Panel of Model BP16 VLE

Figure 5.28:PT 1

Figure 5.27:

MAIN SWITCH

Figure 5.26:

SUIZ HEATER

Figure 5.25:TI 02

Figure 5.24: TIC

01



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6.0 Procedures

6.1 General start-up procedures

1. The equilibrium data for the binary system were obtain to studied from lecture.

2. A calibration curve of refractive index vs. composition plot was prepared for the particular

binary system.

3. The evaporator and condenser were checked to ensure it empty with liquid.

4. All the valves were ensuring initially closed and the heater power was switched off.

5. The main power at the control panel was switched on. All sensors and indicators were checked

to make sure it well functioning.

6.2 General Experiment Procedures

1. The liquid mixture of 3 to 6L at the desired composition were prepared and was poured into the

evaporator through valve 1 and closed it.

2. The valve V13 and V14 were opened at the level sight tube. The liquid level has been sure that

it above the safety line on the level sight tube. The valves V13 and V14 were closed back.

3. The valve V8 was opened for operation at atmospheric pressure.

4. Turn on the compressed air supply and set the desired pressure at the regulator for operation at

elevated pressure. The valve V9 was opened to start pressurizing the unit, Then the valve V9 was

closed when the pressure has been reached.

5. The valve V10 was opened and adjusted to allow about 5 to 10 L/min of cooling water to flow

through the condenser.

6. The temperature controller TIC-01 was set to slightly above the expected boiling point of theliquid mixture.

7. The heater was switched on.

8. The temperature rise in TCI-01 was observed. When the temperature at TCI-02 started to

increased sharply, the liquid in the evaporator has begun to boil. The pressure at PI-01.All the

temperature and pressure were waited to stabilize at a steady state value.

9.The evaporator pressure and the liquid, vapor temperatures recorded.



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10.A vapor and liquid sample were collected from the unit as described in section 3.4.

6.3 General Shut-Down Procedures

1. The heater was switched off.

2. The valve V10 was opened to allow cooling water flow rate through the condenser.

3. The valve V11 was opened to allow cooling water to flow through the cooling coil in the

evaporator.

4. When the unit has been pressurized, valve V8 was slowly opened to depressurize the unit.

5. Temperature was waited at the unit until it drops to below 50°C.

6. Valves V2 and V3 opened to drain all liquid from the evaporator.

7. Valves V5 and V7 opened to drain all liquid accumulated at the condenser.

8. All valves were closed and the main power at the control panel was switched off.



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6.4 Sampling Procedures

Both vapor and liquid samples can be taken from the unit for analysis.

1. Vapor sampling from the condenser.

i. The vent valve V6 was ensured opened and drain valve V7 was closed.

ii. Valve V5 was slowly opened to allow some condensed vapor from the condenser to

flow into the top sample collector. Valve V5 closed.

iii. Valve V7 was opened to collect the sample in a sampling vial.

iv. The cap on the vial was immediately closed and was immersed in cold water.

2. Liquid sampling from the evaporator

i. Vent valve V4 was ensure that it opened and drain valve V3 was closed.

ii. Valve V12 was opened to allow cooling water to flow through the bottom sample

collector.

iii. Then, valve V2 was slowly opened to allow some liquid from the evaporator to flow

into the sample collector. Valve V2 closed.

iv. Valve V3 was opened to collect the sample in a sampling vial.

v. The cap on the vial was immediately closed and was immersed in the cold water.



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6.5 Experiment 1: Equilibrium Curve at Atmospheric Pressure

Objective:

To construct an equilibrium curve for the methanol-water system at atmospheric pressure.

1. The general start-up procedures as described in section 6.1 were performing.

2. 12-L of pure methanol and 5-L of deionized water were prepared.

3. Valve V8 was opened.

4. 0.1-L methanol and 3-L water were poured into the evaporator through valve V1.Then, V1

was closed.

5. Valves V13 and V14 were opened at the level sight tube. The liquid level was ensuring it was

above the safety line on the level sight tube.V13 and V14 were closed back.

6. Valve V10 was opened and adjusted to allow about 5 L/min of cooling water to flow through

the condenser.

7. The temperature controller TIC-01was set to about 100°C.The heater was switched on.

8. The temperature rose in TIC-01 was observed. When the temperature at TI-02 starts to

increase sharply, the liquid in the evaporator has begun to boil. The pressure at PI-01 was

observed. Waited until temperatures and pressure stabilized at a steady state value.

9. The evaporator pressure and the liquid, vapor temperatures value were recorded.

10. A liquid and vapor sample were collected from the unit as described in section 6.4.The

samples were analyzed to determine their compositions.

11. The heater was switched off and valve V11 opened to allow cooling water to flow through the

cooling coil in the evaporator.

12. The temperature at TI-02 was waited to drop significantly to signify that boiling has stopped.

Valve V11 closed.

13. Additional 0.2-L methanol was poured into the evaporator through V1.Valve V1 closed. There

was now about 0.3-L methanol and 3-L water in the evaporator. Steps 5 to 12 were above

repeated.

14. An additional 0.2-L methanol was poured into the evaporator through valve V1.Valve V1 was

closed. There was now about 0.5-L methanol and 3-L water in the evaporator .Steps 5 to 12

above were repeated.



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15. An additional 0.5-L methanol was poured into the evaporator through valve V1.Valve V1 was

closed. There was now about 1-L methanol and 3-L water in the evaporator .Steps 5 to 12


16. An additional 1-L methanol was poured into the evaporator through valve V1.Valve V1 was






18. Valve V2 and V3 were opened to drain all liquid from the evaporator.

19. 2-L methanol and 1-L water were poured into the evaporator through V1.Valve V1 was closed.

Steps 5 to 12 above were repeated.

20. An additional 1-L methanol was poured into the evaporator through valve V1.Valve V1 wasclosed. There was now about 5-L methanol and 1-L water in the evaporator .Steps 5 to 12





22. The general shut-down procedures as described in section 6.3 were performed.



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7.0 RESULT

Vapor liquid equilibrium data

Water (L) Methanol

(L)

Temperature (oC) Refractive Index (nD)

Vapor Liquid Vapor Liquid

3.0 0.1 93.0 89.3 1.34074 1.33367

3.0 0.3 89.3 86.6 1.33895 1.33385

3.0 0.5 87.5 83.6 1.33899 1.33384

3.0 1.0 83.3 81.5 1.33832 1.33384

3.0 2.0 79.9 76.5 1.33830 1.33394

3.0 3.0 77.8 73.6 1.33798 1.34040

Table 7.1

Water (L) Methanol

(L)

Temperature (oC) Refractive Index (nD)

Vapor Liquid Vapor Liquid

1.0 2.0 72.7 71.6 1.34187 1.34246

1.0 3.0 71.0 70.1 1.33969 1.34230

1.0 5.0 70.1 68.6 1.33812 1.34162

Table 7.2

Methanol Water

Density (g/m ) 0.79 1

Molecular weight (g/ mol) 32.04 18

Table 7.3



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Temperature and mole fraction of Methanol ()

Mole fraction

Y

(Vapor)

X

(Liquid)

Y

(Vapor)

X

(Liquid)

93.0 89.3 0.01341 0.01333

89.3 86.6 0.05356 0.05335

87.5 83.6 0.09373 0.09337

83.3 81.5 0.1740 0.1734

79.9 76.5 0.3078 0.3068

77.8 73.6 0.4148 0.4155

72.7 71.6 0.6307 0.6340

71.0 70.1 0.7770 0.7785

70.1 68.6 0.9233 0.9257



19

0

10

20

30

40

50

60

70

80

90

100

0 0.2 0.4 0.6 0.8 1

t e m p e r a t u r e ( ° C )

Vapor/Liquid Mole Fraction (x/y)

T-xy diagram for methanol-water system

Temperature Vapor (C)

Temperature Liquid (C)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

V a p o r m o l f r a c t i o n

Liquid mol fraction

X-Y Equilibrium Graph



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8.0 CALCULATIONS

i) Number of moles of

VOLUME OF WATER (L) MOLES OF WATER (MOL)

3 166.667

1 55.556

Volume

Volume

Density of water

Density of methanol (79

Molecular weight Molecular weight 2

ℎ





22

Volume

79

99

99 2

Volume

79

79

79 2

Volume 2

79

2

2

Volume

79

27

27 2



23

Volume 2

79

2

2

Volume

79

27

27 2

Volume

79 99

99 2



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Mole fraction of Methanol ().

Table 8.2

Volume used (L) Volume used (L) Mole

(mol)

Mole

(mol)

(

)

Mole fraction

(

)

Mole fraction

3.0 0.1 7 2.4744 169.1414 0.99 0.01

3.0 0.3 7 7.4231 174.0901 0.96 0.04

3.0 0.5 7 12.3719 179.0389 0.93 0.07

3.0 1.0 7 24.7438 191.4108 0.87 0.13

3.0 2.0 7 49.4875 216.1545 0.77 0.23

3.0 3.0 7 74.2313 240.8983 0.69 0.31

1.0 2.0 97 105.0435 0.53 0.47

1.0 3.0 72 129.7873 0.42 0.58

1.0 5.0 27 179.2748 0.31 0.69



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Composition of Methanol () in mole fraction

Mole fraction Refractive Index, RI Mole fraction

Vapor Vapor

( )

(

)

Vapor Liquid

(vapor)

Y

(liquid)

X

93.0 89.3 0.99 0.01 1.34074 1.33367 0.01341 0.01333

89.3 86.6 0.96 0.04 1.33895 1.33385 0.05356 0.05335

87.5 83.6 0.93 0.07 1.33899 1.33384 0.09373 0.09337

83.3 81.5 0.87 0.13 1.33832 1.33384 0.1740 0.1734

79.9 76.5 0.77 0.23 1.33830 1.33394 0.3078 0.3068

77.8 73.6 0.69 0.31 1.33798 1.34040 0.4148 0.4155

72.7 71.6 0.53 0.47 1.34187 1.34246 0.6307 0.6340

71.0 70.1 0.42 0.58 1.33969 1.34230 0.7770 0.7785

70.1 68.6 0.31 0.69 1.33812 1.34162 0.9233 0.9257

Table 8.3



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Temperature and mole fraction of Methanol ()

Mole fraction

Y

(Vapor)

X

(Liquid)

Y

(Vapor)

X

(Liquid)

93.0 89.3 0.01341 0.01333

89.3 86.6 0.05356 0.0533587.5 83.6 0.09373 0.09337

83.3 81.5 0.1740 0.1734

79.9 76.5 0.3078 0.3068

77.8 73.6 0.4148 0.4155

72.7 71.6 0.6307 0.6340

71.0 70.1 0.7770 0.7785

70.1 68.6 0.9233 0.9257

Table 8.4





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1.34246 to 1.34162. The refractive index for vapor methanol is also decrease from 1.34187 to

1.33812. The mole fraction of the liquid methanol is increase from 0.6340 to 0.9257. The

mole fraction of the vapor methanol is also increase from 0.6307 to 0.9233.

Through the X-Y equilibrium graph, when the mole fraction of liquid methanol

increase the mole fraction of vapor methanol is also increase. The mole fraction that had been

used in the graph is calculated using the mole fraction formula.

Methanol is a volatile liquid. During the experiment, putting the methanol in the

beaker without closing the beaker can cause the half of the methanol is vaporize slowly. The

methanol is added before the temperature heater is lower than 50°C. All this action can cause

the error for this experiment and it can give not accurate reading. The eyes are not

perpendicular when the reading of methanol in the cylinder is recorded.



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10.0 CONCLUSION

As the conclusion, this experiment was successful carried out. The relationship between the

vapor and liquid at the normal pressure was successfully determined. The maximum mole

fraction of methanol is 1. The objective of this experiment is to construct an equilibrium

curve for the methanol-water system at atmospheric pressure. From the data of this

experiment, the composition of methanol in vapor is higher than the liquid. The composition

of methanol in vapor and liquid is increase when the volume of methanol is also increase.

When the objective of this experiment was achieved, it can be concluded that this experiment

is successfully done.



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11.0 RECOMMENDATION

Make sure that the evaporator, condenser and tubing’s are cleaned properly. Flush the

system with the de-ionized water.

Always make sure that there is enough liquid all the time to fully submerged the

heater and temperature sensor.

Be extremely careful when handling the liquid at high temperature.

Always switch of the heater and allow the liquid to cool before draining.

Make sure that the eyes is perpendicular during the reading the methanol in the

cylinder is recorded.



31

12.0 Reference

1. http://www.fpharm.uniba.sk/fileadmin/user_upload/english/Physical_Chemistry/3-

Liquid-vapour_equilibrium.pdf , Retrieved 25 November 2013

2. http://www.chemguide.co.uk/physical/phaseeqia/idealpd.html Retrieved 25

November 2013

3. http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Vapor-Liquid-

Equilibrium-843.html Retrieved 25 November 2013

4. Manual Lab Report CPE 451

5. http://lorien.ncl.ac.uk/ming/distil/distilvle.htm Retrieved 25 November 2013

6. http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Vapor-Liquid-

Equilibrium-843.html Retrieved 25 November 2013

http://www.fpharm.uniba.sk/fileadmin/user_upload/english/Physical_Chemistry/3-Liquid-vapour_equilibrium.pdf




http://www.chemguide.co.uk/physical/phaseeqia/idealpd.html

http://lorien.ncl.ac.uk/ming/distil/distilvle.htm

http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Vapor-Liquid-Equilibrium-843.html






http://lorien.ncl.ac.uk/ming/distil/distilvle.htm

http://www.chemguide.co.uk/physical/phaseeqia/idealpd.html





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13.0 Appendix

Figure 13.1 :-Distilled Water Figure 13.2 :-Measurement Cylinder

Figure 13.3 :-Dropper Figure 13.4 :-Power Supply





Figure 13.9 :- Model BP16 Vapor Liquid Equilibrium Unit

Documents

Lab Report Vapor Liquid Equilibrium UITM