CHEMICAL ENGINEERING LABORATORY CHE 465 VAPOR-LIQUID EQUILIBRIUM UNIT EXPERIMENT
NAME
MATRIX NO.
AHMAD IFWAT AHMAD KAMAL
2011144359
NUR SYAHIDAH MOHD SUBARI
2011785691
MUHAMMAD SHAMIL AZHA IBRAHIM
2011195429
LECTURER : MISS ADIEB DATE OF SUBMISSION : 22
ND
OCTOBER 2012
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.
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
In this case, for VLE (Vapour Liquid Equilibrium) unit, two components are used and found in both phases. Thus, its degree of freedom is:
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.
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.
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 l iquid and vapour compositions. o
Example: Binary system of benzene-toluene mixture.
Isochoric condition (constant temperature) Graph of pressure versus benzene composition
P-xy diagram
Isobaric conditions (constant temperature) Graph of temperature versus benzene composition T-xy diagram
0
Graph of benzene composition in vapour (Y) and liquid (X) phase.
XY diagram
APPARATUS / MATERIALS
Beaker
Thermometer
Refractometer
Water
Methanol
Tissue paper
Goggles
Gloves
Measuring Cylinder
Sample bottles
VLE Equipment
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.
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.
RESULTS
0
Volume of Water
Volume of Methanol
Refractive Index
(L)
(L)
Vapour
Liquid
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
0
Volume of Water
Volume of Methanol
(L)
(L)
Vapour
Liquid
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
Refractive Index
CALCULATIONS
Density of methanol ( Molecular weight Molecular weight Density of water
Therefore, i)
Number of moles of
Volume
Volume
ii)
Number of moles
Volume
Volume
Volume
Volume
Volume
Volume
Volume
Volume
Mole fraction of Methanol (
Volume
).
Volume
Mole
Mole
used
(mol)
(mol)
(L)
used (L)
3.0
0.1
3.0
0.3
3.0
0.5
3.0
1.0
3.0
2.0
3.0
3.0
1.0
2.0
1.0
3.0
1.0
5.0
Mole fraction
Mole fraction
( ) ( )
2.4744 7.4231 12.3719 24.7438 49.4875 74.2313
169.1414
0.99
0.01
174.0901
0.96
0.04
179.0389
0.93
0.07
191.4108
0.87
0.13
216.1545
0.77
0.23
240.8983
0.69
0.31
105.0435
0.53
0.47
129.7873
0.42
0.58
179.2748
0.31
0.69
Table 3
18
Composition of Methanol (
Vapour
Liquid
) in mole fraction
Mole fraction
Refractive Index, RI
) (
) (
Vapour
Liquid
Mole fraction
(vapour)
(liquid)
Y
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
Temperature and mole fraction of Methanol (
) 19
0
Mole fraction
Y
X
Y
X
(Vapour)
(Liquid)
(Vapour)
(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)
T-xy diagram 120
120
100
100
) 80 C ( e r u t a 60 r e p m e T 40
80
20
20
0
0
60
liquid vapour
40
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Composition of methanol (mole fraction)
21
Graph of mole fraction in liquid versus mole fraction in vapour
XY diagram 1.2
1.2
e s a h 1 p d i u q i l n0.8 i l o n a h t e 0.6 m f o n o i t c 0.4 a r f e l o m =0.2 X
1
0.8
0.6
0.4
0.2
0
0 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
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.
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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-LiquidEquilibrium-843.html RETRIEVED 21 OCTOBER 2012 3. http://en.wikipedia.org/wiki/Methanol_(data_page) RETRIEVED 21 OCTOBER 2012
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