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CHEMICAL ENGINEERING LABORATORY
CHE 465
VAPOR-LIQUID EQUILIBRIUM UNIT
EXPERIMENT
NAME MATRIX NO.AHMAD IFWAT AHMAD KAMAL 2011144359NUR SYAHIDAH MOHD SUBARI 2011785691MUHAMMAD SHAMIL AZHA IBRAHIM 2011195429
LECTURER : MISS ADIEB
DATE OF SUBMISSION : 22ND OCTOBER 20121
2
ABSTRACT
The experiment was carried out to investigate the relationship between vapour and liquid at
equilibrium and at atmospheric pressure. The experiment was also conducted to 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 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. 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 graphs,
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.
3
INTRODUCTION
Vapour-liquid equilibrium data are the basic information of the system required for the design of
equilibrium stages of vapour-liquid separation equipment like distillation. The unit can be used to study any
binary system as well as multi component system.
Vapour-liquid equilibrium unit is a condition where liquid and its vapour (gas phase) are
in equilibrium with each other, a condition or state where the rate of evaporation (liquid changing to vapour)
equals the rate of condensation (vapour changing to liquid).
Several kinds of equilibria are important in mass transfer. In all situations, two phases are involved,
and all combinations are found except two gas phases or two solid phases. The controlling variables are
temperature, pressure and concentrations. To classify equilibria and to establish the number of independent
variables, phase rule is used.
Equation 1
∅=number of degreesof freedom
C=number of components
P=numberof phases
In this case, for VLE (Vapour Liquid Equilibrium) unit, two components are used and found in both
phases. Thus, its degree of freedom is:
∅=2−2+2=2
When the pressure is fixed (isobaric), only one variable can be change independently such as the
liquid-phase concentration and both temperature and vapour phase concentration then follow.
4
∅=C−P+2
OBJECTIVES
The objectives of the experiment are:
1. To investigate the relationship between vapour and liquid at equilibrium and at atmospheric pressure.
2. To construct the equilibrium curves at atmospheric pressure for binary system namely methanol and
water.
5
THEORY
Vapour-liquid equilibrium unit is suitable for investigating the relationship between vapour and
liquid at equilibrium at normal pressure and at high pressure up to 20.0 bars. Equilibrium data represent the
composition of the mixture in the vapour phase (Y) and that in the corresponding equilibrium liquid phase
(X) at equilibrium. In order to separate a binary mixture using distillation process, there must be differences
in volatilities of the components. The greater the difference, the easier it is to do so. Volatility is the measure
of an element to evaporate easily by means element with lower boiling point.
A vapour-liquid equilibrium unit is carried out by manipulating its mixture composition such as the
volume of methanol and water. It is more convenient to express compositions using mole fraction. Mole
fraction is the number of moles of one component to the total number of moles in the mixture.
The compositions are presented in mole fractions of the more volatile component. Equilibrium
compositions are functions of temperature and pressure. Therefore the data are reported under isothermal or
isobaric conditions.
In order to be able to predict the phase behaviour of a mixture, limits of phase changes are to be determined.
The limits in the case of gas-liquid phase changes are called the bubble point and the dew point.
The bubble point is the point at which the first drop of a liquid mixture begins to vaporize.
The dew point is the point at which the first drop of a gaseous mixture begins to condense.
Plotting both the bubble and the dew points on the same graph could come up with what is called a P-xy or
a T-xy diagram, depending on whether it is graphed at constant temperature or constant pressure. The "xy"
implies that the curve is able to provide information on both liquid and vapour compositions.
o Example: Binary system of benzene-toluene mixture.
6
mole fraction= molesof componenttotalnumber of moles
Isochoric condition (constant temperature)
Graph of pressure versus benzene composition
P-xy diagram
Benzenecomposition (mole fraction)
7
Isobaric conditions (constant temperature)
Graph of temperature versus benzene composition
T-xy diagram
Benzenecomposition (mole fraction)
8
Temperature(¿0C)¿
Graph of benzene composition in vapour (Y) and liquid (X) phase.
XY diagram
9
APPARATUS / MATERIALS
Beaker
Thermometer
Refractometer
Water
Methanol
Tissue paper
Goggles
Gloves
Measuring Cylinder
Sample bottles
VLE Equipment
10
PROCEDURE
General Start-up procedures
1. A quick operation was prepared to ensure that the unit was in proper operating condition.
2. The unit was connected to the nearest power supply.
3. The valves were opened at the feed port and the level sight tube ( V1, V2, and V3)
4. The boiler was filled with distilled water through the feed port and make sure that the water level is
at about half of the boiler’s height. Then, the valves, V1 and V2 and the level sight tube were closed.
5. The power supply switch was turned on.
6. The experiment was then carried out.
General Shut-down procedures
1. The heater was switched off and the boiler temperature was allowed to drop.
Note: The valve at the water inlet port was made sure not to be opened as it is highly pressurized at
high temperature.
2. The main switch and the main power supply was switched off.
3. The water next use was retained.
4. The upper part of the level sight tube, V3 was opened to drain off the water. V1 and V2 was then
opened to drain off the water.
Sampling procedures
1. Vapour sampling from the condenser.
i) Vent valve V6 was ensured to be opened and drain valve V7 was closed.
ii) Valve V5 was slowly opened to allow some condensed vapour from the condenser to flow
into the top sample collector. Valve V5 is closed.
iii) Valve V7 was opened to collect the sample in a sampling vial.
iv) The cap on the vial was immediately closed and the sample was immersed in cold water.
v) The sample is used on different litres of water and methanol as shown on result.
11
2. Liquid sampling from the evaporator
i) Valve V4 was ensured to be opened and drain valve V3 is 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 was closed back.
iv) Valve V3 was opened to let the sample in a sampling vial to be collected.
v) The cap on the vial was immediately closed and the sample was immersed in cold water.
vi) The sample is used on different water and methanol as shown on results.
12
RESULTS
Volume of Water
(L)
Volume of Methanol
(L)
Temperature(¿0C)¿
Vapour Liquid
Refractive Index
Vapour Liquid
3.0 0.1 89.4 97.9 1.3386 1.3328
3.0 0.3 86.4 94.7 1.3381 1.3327
3.0 0.5 84.6 91.7 1.3389 1.3329
3.0 1.0 81.1 86.3 1.3401 1.3357
3.0 2.0 76.2 80.2 1.3404 1.3373
3.0 3.0 73.9 77.3 1.3393 1.3398
Table 1
Volume of Water
(L)
Volume of Methanol
(L)
Temperature(¿0C)¿
Vapour Liquid
Refractive Index
Vapour Liquid
1.0 2.0 70.6 73.2 1.3360 1.3386
1.0 3.0 69.0 71.6 1.3403 1.3407
1.0 5.0 67.1 69.3 1.3350 1.3388
Table 2
13
CALCULATIONS
Density of water (H ¿¿2O)=1g /cm3 ¿
Density of methanol (CH 3OH ¿=0.7918 g /cm3
Molecular weight H 2O=18g /mol
Molecular weight CH 3OH=32 g/mol
Number of moles= Mass of substanceMolecularweight of substance
Therefore,
i) Number of moles of H 2O
Volume H 2O=3 L
Mass of H 2O=1g H 2O
cm3H 2O×
106 cm3
1000 L×3 LH 2O=3000 g H 2O
Molesof H2O=3000 g H 2O×1mol H 2O
18 g H 2O=166.667mol
Volume H 2O=1L
Mass of H 2O=1g H 2O
cm3H 2O×
106 cm3
1000 L×1L H 2O=1000g H 2O
Molesof H2O=1000 gH 2O×1mol H 2O
18 g H 2O=55.556mol
14
ii) Number of moles CH 3OH
Volume CH 3OH=0.1 L
Mass of CH 3OH=0.7918gCH 3OH
1cm3CH3OH×
106cm3
1000 L×0.1 LCH 3OH=79.18 gCH 3OH
Molesof CH 3OH=79.18 gCH 3OH×1molCH 3OH
32gCH 3OH=2.4744molCH3OH
Volume CH 3OH=0.3 L
Mass of CH 3OH=0.7918gCH 3OH
1cm3CH3OH×
106cm3
1000 L×0.3 LCH 3OH=237.54 gCH3OH
Molesof CH 3OH=237.54 gCH 3OH×1molCH3OH
32gCH 3OH=7.4231molCH 3OH
Volume CH 3OH=0.5 L
Mass of CH 3OH=0.7918gCH 3OH
1cm3CH3OH×
106cm3
1000 L×0.5 LCH 3OH=395.9gCH 3OH
Molesof CH 3OH=3.95 .9 gCH3OH×1molCH 3OH
32gCH 3OH=12.3719molCH 3OH
Volume CH 3OH=1.0 L
Mass of CH 3OH=0.7918gCH 3OH
1cm3CH3OH×
106cm3
1000 L×1.0 LCH 3OH=791.8 gCH 3OH
15
Molesof CH 3OH=791.8 gCH 3OH×1molCH 3OH
32gCH 3OH=24.7438molCH 3OH
Volume CH 3OH=2.0 L
Mass of CH 3OH=0.7918gCH 3OH
1cm3CH3OH×
106cm3
1000 L×2.0 LCH 3OH=1583.6 gCH 3OH
Molesof CH 3OH=1583.6 gCH 3OH ×1molCH 3OH
32 gCH3OH=49.4875molCH 3OH
Volume CH 3OH=3.0 L
Mass of CH 3OH=0.7918gCH 3OH
1cm3CH3OH×
106cm3
1000 L×3.0 LCH 3OH=2375.4 gCH 3OH
Molesof CH 3OH=2375.4 gCH 3OH×1molCH3OH
32gCH 3OH=74.2313molCH3OH
Volume CH 3OH=2 L
Mass of CH 3OH=0.7918gCH 3OH
1cm3CH3OH×
106cm3
1000 L×2LCH 3OH=1583.6 gCH 3OH
Molesof CH 3OH=1583.6 gCH 3OH ×1molCH 3OH
32 gCH3OH=49.4875molCH 3OH
Volume CH 3OH=3 L
Mass of CH 3OH=0.7918gCH 3OH
1cm3CH3OH×
106cm3
1000 L×3 LCH 3OH=2375.4 gCH 3OH
16
Molesof CH 3OH=2375.4 gCH 3OH×1molCH3OH
32gCH 3OH=74.2313molCH3OH
Volume CH 3OH=5 L
Mass of CH 3OH=0.7918gCH 3OH
1cm3CH3OH×
106cm3
1000 L×5 LCH 3OH=3959 gCH 3OH
Molesof CH 3OH=3.959 gCH 3OH×1molCH 3OH
32gCH 3OH=123.7188molCH 3OH
17
Volume
H 2 0 used
(L)
Volume
CH 3OH
used (L)
Mole
H 2 0
(mol)
Mole
CH 3OH
(mol)
Moltotal
mol (H 20+CH 3OH )
Mole
fraction
H 2 0
(mol H 2 0
mol total )
Mole fraction
CH 3OH
(molCH 3OH
mol total )
3.0 0.1 166.667 2.4744 169.1414 0.99 0.01
3.0 0.3 166.667 7.4231 174.0901 0.96 0.04
3.0 0.5 166.667 12.3719 179.0389 0.93 0.07
3.0 1.0 166.667 24.7438 191.4108 0.87 0.13
3.0 2.0 166.667 49.4875 216.1545 0.77 0.23
3.0 3.0 166.667 74.2313 240.8983 0.69 0.31
1.0 2.0 55.556 49.4875 105.0435 0.53 0.47
1.0 3.0 55.556 74.2313 129.7873 0.42 0.58
1.0 5.0 55.556 123.7188 179.2748 0.31 0.69
Mole fraction of Methanol (CH 3OH ).
Table 3
18
Composition of Methanol (CH 3OH ) in mole fraction
Temperature(¿oC )¿ Mole fraction Refractive Index, RI Mole fraction
Vapour Liquid H 2 0
(Mol H 20
Moltotal )
CH 3OH
(MolCH3OH
Moltotal )
Vapour Liquid CH 3OH
(vapour)
Y
CH 3OH
(liquid)
X
89.4 97.9 0.99 0.01 1.3386 1.3328 0.0134 0.0133
86.4 94.7 0.96 0.04 1.3381 1.3327 0.0535 0.0533
84.6 91.7 0.93 0.07 1.3389 1.3329 0.0937 0.0933
81.1 86.3 0.87 0.13 1.3401 1.3357 0.1742 0.1736
76.2 80.2 0.77 0.23 1.3404 1.3373 0.3083 0.3076
73.9 77.3 0.69 0.31 1.3393 1.3398 0.4152 0.4153
70.6 73.2 0.53 0.47 1.3360 1.3386 0.6279 0.6291
69.0 71.6 0.42 0.58 1.3403 1.3407 0.7774 0.7776
67.1 69.3 0.31 0.69 1.3350 1.3388 0.9212 0.9238
Table 4
19
Temperature and mole fraction of Methanol (CH 3OH )
Temperature(¿0C)¿ Mole fraction
Y
(Vapour)
X
(Liquid)
Y
(Vapour)
X
(Liquid)
96.8 94.7 0.0134 0.0133
93.4 90.7 0.0535 0.0533
91.9 87.6 0.0937 0.0933
88.7 84.9 0.1742 0.1736
85.1 79.3 0.3083 0.3076
80 76.8 0.4152 0.4153
77.4 73.1 0.6297 0.6291
73.2 70.4 0.7774 0.7776
69.6 66 0.9212 0.9238
Table 5
20
Graph of Temperature versus mole fraction (x,y)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
20
40
60
80
100
120
0
20
40
60
80
100
120
T-xy diagram
liquidvapour
Composition of methanol (mole fraction)
Tem
pera
ture
(C
)⁰
21
Graph of mole fraction in liquid versus mole fraction in vapour
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
0.2
0.4
0.6
0.8
1
1.2
0
0.2
0.4
0.6
0.8
1
1.2
XY diagram
X =
mol
e fr
acti
on o
f m
etha
nol i
n liq
uid
phas
e
Y = mole fraction of methanol in vapour phase
22
DISCUSSION
The experiment was carried out to investigate the relationship between vapour and liquid
at equilibrium and at atmospheric pressure. The experiment was also conducted to 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 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. 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 graphs, the relationship between vapour and liquid at
equilibrium and at atmospheric pressure is that they exist in linear.
23
CONCLUSION
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 graphs, 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.
24
RECOMMENDATION
To improve the experiment and obtain best results, the experiment should be repeated
three times in order to get average readings. This will reduce the deviation from theoretical
results. The experiment itself took a mere four hours to be done once, so with insufficient time,
the experiment could only be done once. To get better results, the experiment should have been
repeated twice.
Besides that, the sample bottles should be cleaned and washed thoroughly so that there
are no impurities inside the bottle. Any impurities in the sample bottles would effect the results
of the experiment.
Next, readings taken from the measuring cylinder should be taken at eye level to avoid
parallax error. Also, while pouring methanol into the measuring cylinder, goggles should be
worn to avoid the methanol from splashing into the eyes. If this accident does occur, wash
thoroughly with water.
25
REFERENCES
1. http://en.wikipedia.org/wiki/Vapor%E2%80%93liquid_equilibrium RETRIEVED 21
OCTOBER 2012
2. http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Vapor-Liquid-
Equilibrium-843.html RETRIEVED 21 OCTOBER 2012
3. http://en.wikipedia.org/wiki/Methanol_(data_page) RETRIEVED 21 OCTOBER 2012
26