CHE144 - Lab Report : VLE Lab Report (2015)

VAPOUR LIQUID EQUILIBRIUM LAB REPORT Page 1

TABLE OF CONTENT

No Title Page

1 Abstract………………………………. 2

2 Introduction………………………….. 3

3 Objectives…………………………….. 4

4 Theory………………………………... 5 – 6

5 Material And Apparatus……………… 7 – 9

6 Methodology…………………………. 10 – 14

7 Data and Results……………………… 15 – 16

8 Calculations…………………………... 17 – 27

9 Discussion……………………………. 28 – 31

10 Conclusion……………………………. 32

11 Recommendations……………………. 33

12 Reference……………………………... 34

13 Appendix……………………………... 35 – 37


1.0 ABSTRACT

The experiment are carried out to study the relationship between vapour and liquid at

equilibrium and at atmospheric pressure. The experiment was also conducted to build or

construct the equilibrium curves at atmospheric pressure for binary system namely methanol and

water. The experiment was carried out using the Vapour Liquid Equilibrium (VLE) unit. A

mixture of methanol-water with known composition is initially fed into the evaporator. When the

heater is switched on, the mixture will start to boil. The mixture vapour will rise up and will be

cool down by the condenser at the top of the evaporator. The system will stabilize and finally

reach an equilibrium state when temperature remains constant. Samples of vapour and liquid are

taken to determine their compositions.

At the end of the experiment, a graph of mole fraction of vapour against mole fraction of

liquid and a graph of temperature against mole fraction of liquid and vapour were plotted. This

equilibrium curves at atmospheric pressure for binary system namely methanol and water clearly

shows the relationship between vapour and liquid at equilibrium and at atmospheric pressure. It

can be said that from the graph that we had plotted, the relationship between vapour and liquid at

equilibrium and at atmospheric pressure is that they exist in linear. The experiment was

considered a success as all the objectives were achieved as we want.


2.0 INTRODUCTION

Vapour-Liquid Equilibrium (VLE) can be defined as a condition where liquid and vapour

are in equilibrium to each other. Rate of liquid evaporated to vapour s is the same as rate of

vapour condensed into liquid. It is called equilibrium state when there is no net rate difference,

this vapour-liquid interconvertions is zero. For pure Substance, it is implies at the boiling point.

The purpose of this experiment using Vapour-Liquid Equilibrium is to construct an

equilibrium curve for methanol and water system at atmosphere pressure. The mixture of

methanol and water is fed into the evaporator. After the heater is on, the mixture is left to boil.

The evaporated vapour then rise and cooled down by the condenser. The condensed liquid will

fall back into the evaporator. This cycle continues until it reach the equilibrium state, when the

temperature become constant.

The sample of the liquid and the vapour are taken for test. By using the Refractometer,

we can determine the composition of the mixture or the Refractive Index (RI). Refractive Index

is define as the ratio of velocity of light in a vacuum to its velocity in a specified medium. An

example for the application of Vapour-Liquid Equilibrium (VLE) in an equipment is the

Distillation Column. In the equipment, the VLE concept are used. The reboiler in the column is

used to boil the necessary mixture and the condenser is used to cool down the vapour.


3.0 OBJECTIVE

1. To investigate the relationship between the vapour and liquid at different temperature.

2. To construct the equilibrium curve for methanol-water system at atmospheric pressure, 1

atm.

3. To understand the concept of Vapour-Liquid Equilibrium (VLE) thoroughly.

4. To find out the application for the Vapour-Liquid Equilibrium (VLE).

5. To differentiate the plotted graph between Refractive Index (RI) and range of

composition mixtures based on the experimental data obtained.


4.0 THEORY

Vapor–liquid equilibrium (VLE) is a condition in which a liquid and its vapor (gas phase) are

in equilibrium with each other, a condition or state where the rate of evaporation(liquid changing

to vapor) equals the rate of condensation (vapor changing to liquid) on a molecular level such

that there is no net (overall) vapor–liquid inter conversion. A substance at vapor–liquid

equilibrium is generally referred to as a saturated fluid. For a pure chemical substance, this

implies that it is at its boiling point. The notion of "saturated fluid" includes saturated liquid

(about to vaporize), saturated liquid–vapor mixture, and saturated vapor (about to condense).

The Vapor-Liquid Equilibrium is used to determine the equilibrium in binary phase by

vaporization and diffusion. Binary mixtures are mixtures of two component and two phase

system. These mixtures are said to be in equilibrium when their internal properties reaches the

same reading. The four internal properties are the reading of temperature, pressure, liquid mol

fractions and vapor mol fractions. According to the phase rule, the condition of two phase

system, when two intensive properties are specified, the extensive properties may be differed.

But, in equilibrium, the intensive properties will be counted.

In this experiment, we use water and methanol which both are in pure substance and in binary

mixtures. Water and methanol are ideal mixtures so it obeys Raoult’s Law.

For Raoult’s Law being applied in this experiment, for ideal gas vapor mixture in equilibrium

ideal solution, equation becomes:

PA = XAPA0

Where,

PA = partial pressure of component A in a solution

PA0

= vapor pressure of pure A

XA = mole fraction of component A in a solution

Gives the mole fraction of component A in the gas phase as

yA = XAPAA0

P

http://en.wikipedia.org/wiki/Liquid

http://en.wikipedia.org/wiki/Vapor

http://en.wikipedia.org/wiki/Chemical_equilibrium

http://en.wikipedia.org/wiki/Evaporation

http://en.wikipedia.org/wiki/Condensation

http://en.wikipedia.org/wiki/Boiling_point

http://en.wikipedia.org/wiki/Saturated_vapor


Extend to the binary system, Raoult’s Law and Dalton Law equation:

P = pA + pB = XAPA + (1- XA)Pb = XA(PA – PB) + PB

OR

XA = P - PB

PA - PB

The equations is used to find XA for ideal binary mixtures at selected temperatures between the

boiling temperatures of two pure components at given pressure.

The distribution coefficient or have just K-value for the component i,

yA = Kixi

Raoult’s and Dalton’s Law gives the reasonable estimates and the value of mole fraction, partial

pressure can be determined by using these laws at equilibrium state.

To find the composition of water and methanol, this equation was used


5.0 MATERIAL AND APPARATUS

Material :-

1. Methanol

2. Distilled Water

Apparatus:-

1. SOLTEQ® Vapour Liquid Equilibrium Unit (Model : BP 16)

2. Dropper

3. Sample Collector

4. Refractometer

5. 2-L measuring cylinder

6. 500-ml measuring cylinder

7. 500-ml measuring beaker

8. Goggles

9. Gloves


Figure 1 Unit Construction for Vapour Liquid Equilibrium Unit (Model : BP16)

1. Condenser 6. Pressure Relief Valve

2. Evaporator 7. Control Panel

3. Bottom Sample Collector 10. Top Sample Collector

4. Cooling Water Supply 11. Rotameter

5. Cooling Water Drain 12. Heater


Figure 2 Process Flow Diagram for the Vapour-Liquid Equilibrium Unit


6.0 METHODOLOGY

6.1) General Start-up Procedures

1. The equilibrium data for the binary system to be studied is obtained from

literature.

2. A calibration curve of refractive index vs. composition plot fo the particular

binary system is prepared by referring at calibration table for methanol-water.

3. The evaporator and condenser are checked to make sure they are empty of liquid.

4. Ensuring that all the valves are initially closed and the heater power switch is

turned off.

5. The main power is switch on at the control panel. All sensors and indicators are

checked to make sure they are functioning properly.

6.2) General Experiment Procedures

1. About 3 to 6-L of liquid mixture at the desired composition is prepared and

poured into the evaporator through valve V1. The valve V1 is closed.

2. Valves V13 and V14 at the level sight tube is opened. The liquid level is

determined to be above the safety line on the level sight tube. The valves, V13

and V14 are closed back.

3. Valve V8 is opened to make sure the operation is at atmospheric pressure.

4. Valve V10 is opened and adjusted to allow about 5 to 10-L/min of cooling water

to flow through the condenser.

5. The temperature controller TIC-01 is set to slightly above the expected boiling

point of the liquid mixture.

6. The heater is switched on.

7. The temperature rise in TIC-01 is observed. When the temperature at TI-02

started to increase sharply, the liquid in the evaporator is determined to begin

boiling. The pressure at PI-01 is observed. Temperature and pressure are waited to

stabilize at a steady state value.

8. The evaporator pressure and the liquid and vapour temperatures are recorded.

9. A vapour and liquid sample from the unit is collected as described in Sampling

Procedure.


6.3) General Shut-down Procedures

1. The heater is switched off.

2. Valve V10 is opened to increase the cooling water flow rate through the

condenser.

3. Valve V11 is opened to allow the cooling water to flow through the cooling coil

in the evaporator.

4. The temperature at the unit is waited to drop to below 50⁰C.

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

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

7. All the valves are closed and the main power is switched off at the control panel.

6.4) Sampling Procedure

Both vapour and liquid samples from the unit are taken out for analysis.

The sample volume that is taken is minimum, less than 25ml. This is to avoid any effect

on the volume remained in the evaporator.

1. Vapour sampling from the condenser

i. Ensuring that the vent valve V6 is opened and drained valve V7 is closed.

ii. Valve V5 is opened slowly to allow some condensed vapour from the

condenser to flow into the top sample collector. Valve V5 is closed.

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

iv. The cap on the vial is immediately closed and immersed the sample in

cold water.

2. Liquid sampling from the evaporator

i. Ensuring that the vent V4 is opened and drain valve V3 is closed.

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

sample collector.

iii. Valve V2 is opened slowly to allow some liquid from the evaporator to

flow into the sample collector. The valve V2 is closed.

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

v. The cap on the vial is immediately closed and immersed the sample in

cold water.


6.5) Experiment 1 : Equilibrium Curve at Atmospheric Pressure

1. The general start-up procedures as described in Section 6.1 is performed.

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

3. Valve V8 is opened.

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

Valve V1 is closed.

5. Valves V13 and V14 at the level sight tube is opened. The liquid level is

determined to be above the safety line on the level sight tube. The valves V13 and

V14 is closed back.

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

through the condenser.

7. The temperature controller TIC-01 is set to about 100⁰C. The heater is switched

on.

8. The temperature rise in TIC-01 is observed. When the temperature at TI-02

started to increase sharply, the liquid in the evaporator is determined to began

boiling. The pressure at PI-01 is observed. All the temperatures and pressure are

waited to stabilize at a steady state value.

9. The evaporator pressure and the liquid and vapour temperatures are recorded.

10. A liquid and vapour sample from the unit is collected as described in Section 6.4.

The samples are analyzed to determine their compositions.

11. The heater is switched off and valve V11 is opened to allow cooling water to flow

through the cooling coil in the evaporator.

12. The temperature drop at TI-02 is observed and waited to drop significantly which

signify that boiling has stopped. Valve V11 is closed.

13. All the liquid from the condenser is collected by opening valve V5 and V7 and

the liquid is poured back into the evaporator through valve V1. Valves V5 and V7

are closed.

14. All the liquid from the bottom sample collector is collected by opening valve V3

while closing valve V2 and the liquid is poured back into the evaporator through

valve V1. The valves V3 and V1 is closed.

15. An additional 0.2-L methanol is poured into the evaporator through valve V1.

Valve V1 is closed. Now, there is about 0.3-L methanol and 3-L water in the

evaporator. Steps 5 to 14 above is repeated.


Valve V1 is closed. Now, there is about 0.5-L methanol and 3-L water in the



Valve V1 is closed. Now, there is about 1-L methanol and 3-L water in the


18. An additional 1-L methanol is poured into the evaporator through valve V1.







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

21. 2-L methanol and 1-L water are poured into the evaporator through valve V1.

Valve V1 is closed.







24. The general shut-down procedures is performed as described in Section 6.3.


6.6) Safety Precautions :-

1. The unit is operated under the supervision of an authorized staff who has been

properly trained to handle the unit.

2. All operating instructions supplied with the unit is carefully read and understood

before attempting to operate the unit.

3. Always make sure that there is enough liquid all the time to fully submerge the

heater and temperature sensor.

4. Be extremely careful when handling liquid at high temperature.

5. Always switch off the heater and allow the liquid to cool down before draining.

6. Do not touch the hot components of the unit.

7. Feed stock which severely affect stainless steel 304 and polypropylene (PP) are

not to be used.

8. The system should not be subjected to shock, sudden impact, vibration, or

additional load.

9. Restore the system to operating conditions after any repair job.

10. Always check and rectify any leak.

11. Do not exceed the maximum cooling water pressure of 2 bar(g) for the condenser.

12. Be extremely careful when handling hazardous, flammable or polluting materials.

13. Do not stretch the Viton O-rings during servicing.

14. Make sure the system is sufficiently ventilated at all times during operation,

maintenance and storage.

15. Only properly trained staff shall be allowed to carry out any servicing or repair

job. Manufacturer's manual must always be observed.


7.0 DATA AND RESULTS

Table 1 : Calibration Table For Methanol-Water

Volume of

Methanol

(mL)

Volume of

Water

(mL)

Mol fraction wt% Refractive index

(RI)

0 10 0.0000 0.00 1.332

1 9 0.0470 8.07 1.336

2 8 0.1000 16.49 1.338

3 7 0.1598 25.29 1.340

4 6 0.2283 34.50 1.342

5 5 0.3074 44.13 1.343

6 4 0.3997 54.23 1.343

7 3 0.5087 64.83 1.343

8 2 0.6390 75.96 1.334

9 1 0.7996 87.67 1.330

10 0 1.000 100.00 1.332

Table 2 : Methanol and Water properties

Methanol

(99.7%)

Water

(

) 0.79 1

(

) 32.04 18


Table 3 : The Methanol-Water system

Pressure Volume

Methanol

Volume

Water

Temperature (⁰C) RI

Liquid Vapour Liquid Vapour

1 atm 0.1 3 98.0 92.5 1.338 1.339

0.3 3 94.9 89.4 1.332 1.337

0.5 3 92.4 87.4 1.333 1.338

1 3 87.5 83.0 1.332 1.338

2 3 82.2 78.8 1.333 1.336

3 3 79.8 76.8 1.333 1.337

2 1 74.9 72.3 1.334 1.336

3 1 73.7 71.1 1.336 1.332

5 1 70.9 69.4 1.336 1.331

Composition Experiment Composition Literature % error

Liquid Vapour Liquid Vapour Liquid Vapour

0.0195 0.0195 0.0150 0.2655 -30.00 92.66

0.0566 0.0568 0.0336 0.3727 -68.45 84.76

0.0918 0.0922 0.0512 0.4268 -79.30 78.40

0.1717 0.1724 0.1006 0.5470 -70.68 68.48

0.3044 0.3050 0.1871 0.6534 -62.69 53.32

0.4098 0.4110 0.2494 0.6969 -64.31 41.02

0.6273 0.6282 0.4209 0.8053 -49.04 21.99

0.7630 0.7607 0.4780 0.8308 -59.62 8.44

0.9210 0.9175 0.6240 0.8721 -47.60 -5.21


8.0 CALCULATIONS

Calculation for mole fraction of methanol of the calibration table:-

Volume of Methanol Volume of Water

0mL 10mL

No of mol of solute

No of mol of solvent

( )


1mL 9mL

No of mol of solute


( )



2mL 8mL

No of mol of solute


( )


3mL 7mL

No of mol of solute


( )



4mL 6mL

No of mol of solute


( )


5mL 5mL

No of mol of solute


( )



6mL 4mL

No of mol of solute


( )


7mL 3mL

No of mol of solute


( )



8mL 2mL

No of mol of solute


( )


9mL 1mL

No of mol of solute


( )



10mL 0mL

No of mol of solute


( )

Calculation for the composition experiment :-


0.1L 3L

No of mol of solute


For Liquid ,

( )

For Vapour ,

( )



0.3L 3L

No of mol of solute


For Liquid ,

( )

For Vapour ,

( )


0.5L 3L

No of mol of solute


For Liquid ,

( )

For Vapour ,

( )



1L 3L

No of mol of solute


For Liquid ,

( )

For Vapour ,

( )


2L 3L

No of mol of solute


For Liquid ,

( )

For Vapour ,

( )



3L 3L

No of mol of solute


For Liquid ,

( )

For Vapour ,

( )


2L 1L

No of mol of solute


For Liquid ,

( )

For Vapour ,

( )



3L 1L

No of mol of solute


For Liquid ,

( )

For Vapour ,

( )


5L 1L

No of mol of solute


For Liquid ,

( )

For Vapour ,

( )


Table 4 : Mol Fraction of methanol and water

Volume

Methanol

(L)

Volume

Water

(L)

Moles of

CH3OH

(mol)

Moles of

H2O

(mol)

Moltotal

CH3OH + H2O

(mol)

Mol fraction

CH3OH

(

)

Mol fraction

H2O

(

)

0.1 3 2.4657 166.6667 169.1327 0.0146 0.9854

0.3 3 7.3970 166.6667 174.0640 0.0425 0.9575

0.5 3 12.3283 166.6667 178.9953 0.0689 0.9311

1 3 24.6567 166.6667 191.3237 0.1289 0.8711

2 3 49.3134 166.6667 251.9804 0.1957 0.6614

3 3 73.9700 166.6667 240.6370 0.3074 0.6926

2 1 49.3134 55.5556 104.8694 0.4702 0.5298

3 1 73.9700 55.5556 129.5260 0.5711 0.4289

5 1 123.283 55.5556 178.8390 0.6894 0.3106

Table 5 : Composition of methanol in Mol fraction

Mol fraction

CH3OH

(

)

Refractive Index Mole fraction


0.0146 1.338 1.339 0.0195 0.0195

0.0425 1.332 1.337 0.0566 0.0568

0.0689 1.333 1.338 0.0918 0.0922

0.1289 1.332 1.338 0.1717 0.1724

0.1957 1.333 1.336 0.3044 0.3050

0.3074 1.333 1.337 0.4098 0.4110

0.4702 1.334 1.336 0.6273 0.6282

0.5711 1.336 1.332 0.7630 0.7607

0.6894 1.336 1.331 0.9210 0.9175


9.0 DISCUSSION

Table 6 : Temperature and mol fraction of Methanol

Temperature (⁰C) Mole fraction of Methanol


98.0 92.5 0.0195 0.0195

94.9 89.4 0.0566 0.0568

92.4 87.4 0.0918 0.0922

87.5 83.0 0.1717 0.1724

82.2 78.8 0.3044 0.3050

79.8 76.8 0.4098 0.4110

74.9 72.3 0.6273 0.6282

73.7 71.1 0.7630 0.7607

70.9 69.4 0.9210 0.9175

0

20

40

60

80

100

120

1 2 3 4 5 6 7 8 9

Tem

pe

ratu

re (

⁰C)

Vapour/Liquid Mole Fraction (x/y)

T-xy Diagram for Methanol-Water System

Liquid

Vapour

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9


0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1 1.2

Vap

ou

r m

ol f

ract

ion

Liquid mol fraction

X-Y Equilibrium Diagram for Methanol-Water System at 1atm

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

Vap

ou

r M

ol F

ract

ion

Liquid Mol Fraction

X-Y Equilibrium Graph


Table 7: Refractive Index and Mol Fraction of methanol from calibration table

Volume of Methanol

(mL)

Mol fraction Refractive index (RI)

0 0.0000 1.332

1 0.0470 1.336

2 0.1000 1.338

3 0.1598 1.340

4 0.2283 1.342

5 0.3074 1.343

6 0.3997 1.343

7 0.5087 1.343

8 0.6390 1.334

9 0.7996 1.330

10 1.000 1.332

1.328

1.33

1.332

1.334

1.336

1.338

1.34

1.342

1.344

1.346

0 0.2 0.4 0.6 0.8 1 1.2

Re

frac

tive

Ind

ex

Mol fraction

Refractive index (RI)


This experiment is carried out to investigate the relationship between vapour and liquid

of binary mixture (methanol and water) at equilibrium at 1 atm. The equilibrium curve at 1 atm

(atmospheric pressure) for methanol and water can be construct. The Vapour-Liquid Equilibrium

(VLE) unit are used to carried out the experiment.

A mixture of methanol-water with known composition is initially fed into the evaporator.

When the heater is switched on, the mixture will start to boil. The mixture vapour will rise up

and will be cooled down by the condenser at the top of the evaporator. As the vapour starts to

condense, the liquid falls back into the evaporator. The system will stabilize and finally reach an

equilibrium state when temperature remains constant. Samples of vapour and liquid are taken to

determine their compositions. The reading is observe and recorded. The graph x-y diagram is

construct as Vapour at axis X and Liquid at axis Y. The VLE diagram will show the Bubble

Point, first drop of liquid mixture begins to vaporize, and the Dew Point, the first point gaseous

start to condense into liquid form.

Based on the data recorded, the point can be plot and eventually a line can be obtained. The

relationship of vapour and liquid at equilibrium and at 1 tm or atmospheric pressure is shown to

exist in linear. Then, the graph of T-xy can be plotted. This graph represents data for 2

component (Binary) system. The system are Temperature against Mole fraction of vapour and

Temperature against Mole fraction of liquid. After the Refractive Index (RI) for vapour and

liquid are recorded, the graph for RI can be plotted and the bell-like shape graph is obtained.

By using the calculation of density for each compound , the Mole fraction of vapour and

liquid can be find out. The density of methanol is 0.79 g/cm whereas the density of water is 1

g/cm. By using the density and the volume of methanol and water that we used , we can figure

out the mass of the water and the methanol.


10.0 CONCLUSION

In a conclusion, the experiment was carried out successfully by following the correct

procedures. The objective by doing this experiment is to determine the vapor-liquid equilibrium

conditions for the binary methanol-water system and correlate the results for use in the analysis

of the distillation column. Explore the conditions for which Dalton’s and Raoult’s laws are

adequate to describe the vapor-liquid equilibrium. Moreover by doing this experiment, we were

able to construct and plot the graph of temperature versus vapor/ liquid mole fraction and vapor

mol fraction versus liquid mol fraction graph. In a meantime, by doing calculation and obtaining

data, we can get the graph that are mention above. Thus, the relationship between the vapor and

liquid at 1 atm was successfully determined. The maximum mole fraction of methanol is 1. The

objective of this experiment also to construct an equilibrium curve for methanol- water

system at atmospheric pressure. From the data that we obtain, 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 was successfully done.


11.0 RECOMMENDATION

To improve the experiment and obtaining the best result, the experiment should have

been repeated three times in order to get the average readings and to get the reading more

accurately. This will reduce the deviation from theoretical result and reduce the error of reading.

Besides, the experiment itself took more than four hours to be done once, however due to

limitation of time, the experiment could only be done once. Therefore, to get better results, the

experiment should have been repeated twice.

In addition, we also can compare our result to the other group or we can make a group

discussion with the other group to make sure that our results are accurate or not. We should also

increase our knowledge on how to handle the experiment better.


12.0 REFERENCE

1. Yunus A. Cengal & Michael A. Boles, “Thermodynamics – An Engineering Approach”,

3rd

Edition, 4th

Edition, McGraw Hill, 2002.

2. T. M. Duncan and J. A. Reimer, “Chemical Engineering Design and Analysis : An

Introduction”, Cambridge University Press, 1998.

3. Gmehling, J. and Onken, U, “Vapor-Liquid Equilibrium Data Collection”, Dechema,

Frankfurt, Germany, Vol. 1, Page 60, 1977.



13.0 APPENDIX


Documents

CHE144 - Lab Report : VLE Lab Report (2015)