report vle.docx

8/14/2019 report VLE.docx

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Abstract

This experiment is carried out to demonstrate and understand the principle of vapour-liquid

equilibrium. Besides, the experiment is also performed to construct an equilibrium curve for the

methanol-water system at atmospheric pressure. With every different volume of methanol and

water, the refractive index for the composition of the mixture is determined. Moreover, graph of

refractive index (RI) against composition of methanol-water is plotted. Mol fraction of water and

methanol are obtained through the RI value based on the graph. The T-xy diagram and xy

equilibrium diagram are plotted. The experiment can be said to be successfully done.

Introduction

This experiment is carried out using water and methanol. In order to obtain the equilibrium

stages of vapour-liquid separation experiment like distillation, vapour-liquid equilibrium data are

used. Generally the vapour-liquid equilibrium unit is applied to any binary system and also multi

component systems comprised of non-reacting substances. A liquid mixture of methanol-water

with a known composition is fed into a vessel equipped with means of measuring pressure and

temperature. Next, when approaching equilibrium state, samples of the vapour and liquid are

taken to determine its refractive index. The equilibrium state is said to be reached when vapour

rises from the evaporator into the condenser as the liquid boils and as the vapour starts to

condense, the liquid will flow back into the evaporator. The data are recorded. Equilibrium data

represent the composition of mixture of vapour phase (Y) in corresponding equilibrium liquid

phase (X) at equilibrium. Moreover, calibration curve of refractive index against composition of

methanol-water is prepared and thus the value of mole fraction for each component is

determined. Based on the calibration curve, vapour and liquid compositions against the vapour

temperature and equilibrium curve diagram are plotted.


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Objectives

1. To demonstrate and understand the principle of vapour-liquid equilibrium.2. To construct an equilibrium curve for the methanol-water system at atmospheric pressure.

Theory

Vapour-liquid equilibrium (VLE) data can be used to determine the sizes, particularly the

height, of distillation columns for the mixtures. This is because distillation columns are designed

based on the boiling point properties of the components in the mixtures being separated. Besides,

the vapour-liquid equilibrium unit is applied to any binary system and also multi component

systems. The amount, the volume, the pressure, the temperature and the density of both liquid

and gas will all remain constant with time. When this happens to a system, it is said to be in an

equilibrium state or to have attained equilibrium. It is a state where the rate of evaporation equals

the rate of condensation on a molecular level. For example, a mixture of methanol-water is

initially fed into fed into a vessel equipped with means of measuring pressure and temperature.

When samples of the vapour and liquid are taken to be analysed, water and methanol will start to

allocate themselves between liquid and vapour phases as the equilibrium state is reached

provided that the temperature, pressure, liquid mol fractions and vapour mol fractions are

remained constant. Furthermore, phase rule justifies the condition needed to obtain equilibrium

state. It states that in any two phase system, when any of its intensive properties are specified

although quantities of the phase and extensive properties are diverged. On the macroscopic level,

evaporation appears to stop once the vapor pressure has been attained in a closed container. On

the other hand, the microscopic level, though, molecules are still escaping from the liquid surface

into the vapor above, as shown in the figure below.


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Figure 1: Molecular interpretation of vapor pressure.

The vapour pressure remains constant because every molecule which escapes (like A) is

immediately replaced by another molecule reentering from the vapour (like B). Any given

molecule spends some of its time in the vapour and some in the liquid.

Moreover, equilibrium data which is represented in mole fractions of more volatile

component (A) shows the composition of the mixture of vapour phase (Y) corresponds to

equilibrium liquid phase (X) at equilibrium. The data reported are under isothermal or isobaric

because of the equilibrium composition is in the function of temperature and pressure.


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i. The vapour-liquid equilibrium data are represented as equilibrium composition:

ii. Relative volatility:

iii. The Gibbs-Duhem equation for the binary system for checking thermodynamicconsistency of the data by integral test :

iv. The Van Laar equation are:

[ ]


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Figure 2: Schematic diagram of VLE setup

Other than that, constant pressure VLE data is obtained from boiling point

diagrams. VLE data of binary mixtures is often presented as a plot, as shown in the figure

below. The bubble-point and the dew-point of a binary mixture at constant pressure are

collected from the VLE plot. The curved line describes the compositions of the liquid and

vapour in equilibrium at some fixed pressure, which is known as the equilibrium line.

The deviation the curve line from the diagonal line indicates of how wide the lines are, or

the amount of separation that will take place.


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Figure 3: Vapour (Y) against liquid (X) at fixed pressure.

APPARATUS AND MATERIALS

- Methanol- Distilled water- Refractometer- SOLTEC Vapour Liquid Equilibrium Unit (MODEL: BP16)- Sample collector- Dropper- 500 ml measuring cylinder- 50 ml measuring cylinder- 500 ml measuring beaker


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PROCEDURES

1. The general start-up procedures are performed as described in Section 6.1.2. About 12-L of pure methanol and 5-L deionized water are 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. Valve V13 and V14 are opened at the level sight tube. The liquid level is made sureabove the safety line on the level sight tube. Valve V13 and V14 are closed back.

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

7. The temperature controller TIC-01 is set about 100C. The heater is switched on.8. Temperature rise in TIC-01 is 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 is observed.

All temperature 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 samples from the unit are collected as described in Section 6.4.11.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 at TI-02 is waited to drop significantly to signify that boiling hasstopped. Valve V11 is closed.

13.An additional 0.2-L methanol is poured into the evaporator through valve V1. Valve V1is closed. There is now about 0.3-L methanol and 3-L water in the evaporator. Steps 5 to

12 above are repeated.

14.An additional 0.2-L methanol is poured into the evaporator through valve V1. Valve V1is closed. There is now about 0.5-L methanol and 3-L water in the evaporator. Steps 5 to

12 above are repeated.

15. An additional 0.5-L methanol is poured into the evaporator through valve V1. Valve V1is closed. There is now about 1-L methanol and 3-L water in the evaporator. Steps 5 to 12

above are repeated.


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16.An additional 1-L methanol is poured into the evaporator through valve V1. Valve V1 isclosed. There is now about 2-L methanol and 3-L water in the evaporator. Steps 5 to 12

above are repeated.


above are repeated.

18.Valve V2 and V3 are opened to drain all liquid from the evaporator.19.2-L methanol and 1-L water are poured into the evaporator through valve V1. Valve V1

is closed. Steps 5 to 12 above are repeated.


above are repeated.


are repeated.

22.The general shut-down procedures are performed as described in Section 6.3.

RECOMMENDATION

- The general start up and shut down need to perform before and after the experiment iscarried out.

- The heater need to switch off for every time the additional methanol is poured into theevaporator and the temperature need to be lower than 50C to make sure the liquid is

cooling down.

- The temperature of the liquid and vapour samples need to be cooling down to the roomtemperature before the refractive index is taken from refractometer.

- The water should be added to the SOLTEC Vapour Liquid Equilibrium Unit first beforethe methanol to prevent the methanol to expand due to high temperature inside the

evaporator.


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REFERENCES

- http://lorien.ncl.ac.uk/ming/distil/distilvle.htmhttp://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Vapor-Liquid-

Equilibrium-843.html
http://lorien.ncl.ac.uk/ming/distil/distilvle.htmhttp://lorien.ncl.ac.uk/ming/distil/distilvle.htmhttp://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Vapor-Liquid-Equilibrium-843.htmlhttp://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Vapor-Liquid-Equilibrium-843.htmlhttp://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Vapor-Liquid-Equilibrium-843.htmlhttp://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Vapor-Liquid-Equilibrium-843.htmlhttp://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Vapor-Liquid-Equilibrium-843.htmlhttp://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Vapor-Liquid-Equilibrium-843.htmlhttp://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Vapor-Liquid-Equilibrium-843.htmlhttp://lorien.ncl.ac.uk/ming/distil/distilvle.htm


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UNIVERSITI TEKNOLOGI MARA

FAKULTI KEJURUTERAAN KIMIA

PROCESS ENGINEERING LAB 1

(CPE 453)

NAME (STUDENT ID) : 1) HANANI BINTI MOHAMAD HUSAIN SAH (2012847858)

2) MOHAMAD KHIR ZAHARI BIN HARIP (2012615808)

3) MUHAMAD ASYRAF BIN MD ZAMRI (2012636808)

4) SUDINI BINTI ABDUL KAHAR (2012484556)

GROUP : 4

EXPERIMENT : VAPOUR LIQUID EQUILIBRIUM

DATE PERFORMED : 9 OCTOBER 2013

SEMESTER : 3

PROGRAMME/CODE : EH221 3B

SUBMIT TO : PUAN NOR SHARLIZA MOHD SAFAAI

No. Title Allocated Marks (%) Marks

1 Abstract/Summary 5

2 Introduction 10

3 Aims / Objectives 54 Theory 10

5 Apparatus 5

6 Methodology/Procedure 10

7 Results 10

8 Calculations 10

9 Discussion 20

10 Conclusion 5

11 Recommendations 5

12 Reference / Appendix 5

TOTAL MARKS 100

Remarks:

Checked by :

---------------------------

Date :

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