1

1.0 SUMMARY

The main objectives of this experiment are to operate vapor – liquid separation

process using a Bubble Cap Column Distillation Unit, and also to analyze the sample for the

top and bottom product by refractometer to obtain the refractive index. Other objective is to

calculate the number of stages by using McCabe Thiele method. In distillation process, the

purities of distillate are depending on some factors such as the operating time, temperature,

reflux factor and chemical properties. The unit operation distillation is a method used to

separate the components of a liquid solution, which depends upon the distribution of these

various components between a vapor and a liquid phase. On this experiment the component

that use is ethanol and water with the ratio of 3:27 which is 3 liters of ethanol and 27 liters of

water. At the bottoms contain mixture of ethanol and water heated around 70°C and 90°C

where is in the range of ethanol boiling point. The top product is contains of mostly pure

ethanol which is obtained from the condensation process. The purities of distillate

composition are determined by reflection index measurement. The data taken in every 5

minutes and recorded.For the first set of reflux ratio which is at 1.0, the top product gives the

value of 1.360 of refractive index. While at bottom product the refractive index is 1.332.

While the second experiment is 2.0 reflux ratio, the result shows that the top product

refractive index is 1.356 and for the bottom product refractive index is 1.331. It can be say

that, the distillation process already separate the ethanol and reach its initial purity. The reflux

ratio is important because it give influence on the number of tray required.

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2.0 OBJECTIVES

To operate vapor – liquid separation process using a Bubble Cap Distillation Unit.

To analyze the sample for the Top and Bottom Product by Refractometer to obtain the

Refractive Index in order to determine their respective composition.

To calculate the number of stages by using McCabe Thiele method.

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3.0 INTRODUCTION AND THEORY

` Distillation is a process of separating the liquid into a different product by difference

of purity nor temperature through conversion of a liquid into vapor that is subsequently

condensed back into liquid. Distillation is widely used for separating mixtures or product in

industries.

Distillation is used to separate liquids from nonvolatile solids, as in the separation of

alcoholic liquors from fermented materials, or in the separation of two or more liquids having

different boiling points, as in the separation of gasoline, kerosene, and lubricating oil from

crude oil. Other industrial applications include the processing of such chemical products as

formaldehyde and phenol and the desalination of seawater. The distillation process appears to

have been utilized by the earliest experimentalists. Aristotle (384–322 bc) mentioned that

pure water is made by the evaporation of seawater. Pliny the Elder (ad 23–79) described a

primitive method of condensation in which the oil obtained by heating rosin is collected on

wool placed in the upper part of an apparatus known as a still.

The main purpose of distillation is to separate a mixture by taking advantage of

different substances’ readiness to become a vapor. If the difference in boiling points between

two substances is great, complete separation may be easily accomplished by a single-stage

distillation. If the boiling points differ only slightly, many re distillations may be required. If

a water and alcohol distillate is returned from the condenser and made to drip down through a

long column onto a series of plates, and if the vapor, as it rises to the condenser, is made to

bubble through this liquid at each plate, the vapor and liquid will interact so that some of the

water in the vapor condenses and some of the alcohol in the liquid vaporizes.

4

The feed tray divides the column into a top (enriching or rectification) section and a

bottom (stripping) section. The feed flows down the column where it is collected at the

bottom in the re boiler. Heat is supplied to the re boiler to generate vapor. The source of heat

input can be any suitable fluid, although in most chemical plants this is normally steam. In

refineries, the heating source may be the output streams of other columns. The vapor raised in

the re boiler is re-introduced into the unit at the bottom of the column. The liquid removed

from the re boiler is known as the bottoms product or simply, the bottoms. The vapor travels

up the column, and as it exits the top of the unit, it is cooled by a condenser. The condensed

liquid is stored in a holding vessel known as the reflux drum. Some of this liquid is recycled

back to the top of the column and this is called the reflux. The condensed liquid that is

removed from the system is known as the distillate or top product.

Figure 1: Basic Operation of Distillation

Most methods of distillation used by industry and in laboratory research are variations

of simple distillation. But still there are a few method of distillation such as fractional

distillation, vacuum distillation and Azeotropic distillation. Each method of distillation have

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their own benefits to the process. But each distillation column will used different type of

packing. Examples of common packing that were used in industries are packed column and

bubble cap. There were other type of pack or tray such as pro-pak,heli-

pak,ceramicsaddles,wire mesh and specialized structured packing.

Bubble-cap tray is device or packing that was mounted in a rectifying column that

concentrates the alcohol. Vapor from the still pot rises into the column and enters a pipe on

the bottom of the tray. The cap forces the vapor into the liquid sitting on top of the tray.

Some of the vapor condenses overflows the weir on the tray and falls down the column.

Some of the alcohol in the liquid vaporizes creating a higher concentration of alcohol and

rises further in the column where the process is repeated at the net bubble cap tray. The caps

have slots to break up and reduce bubble size.

Figure 2: Bubble-cap trays in Distillation column

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4.0 DATA AND RESULT

4.1 RESULT OF CALIBRATION DISTILLATION

Test

tube

Volume of

Ethanol(ml)

Volume of Deionized-

Water(ml)

Refractive

Index(RI)

Mole fraction

A1 0 20 1.331 0

A2 1 19 1.333 0.015955475

A3 2 18 1.334 0.033097026

A4 3 17 1.336 0.051562012

A5 4 16 1.339 0.071509854

A6 5 15 1.342 0.093126648

A7 6 14 1.344 0.116630989

A8 7 13 1.346 0.142281191

A9 8 12 1.348 0.170385834

A10 9 11 1.350 0.201314185

A11 10 10 1.353 0.235514577

A12 11 9 1.357 0.273535252

A13 12 8 1.355 0.316054182

A14 13 7 1.356 0.363919846

A15 14 6 1.358 0.418208435

A16 15 5 1.357 0.480305729

A17 16 4 1.358 0.552027053

A18 17 3 1.358 0.635797691

A19 18 2 1.357 0.734932554

A20 19 1 1.358 0.854085295

A21 20 0 1.360 1

Table 1: Data recorded to obtain references graph of mixture of ethanol and water

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4.2 GRAPH FOR REFERENCE

Graph Of Refractive Index VS Mole Fraction

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4.3 CALCULATION FOR FEED LINE MOLAR FRACTION XF

9

4.4 DATA AND RESULT FOR BUBBLE CAP DISTILLATION WITH

REFLUX RATIO: 1.0

Rotameter reading R1 (L/hr) = ________ 3______

Rotameter reading R2 (L/hr) = _________ 3_______

Temperature T4 (oC) = __________92______

Temperature T2 (oC) = __________82______

Table 2: Data obtain from bubble cap distillation of mixture ethanol and water by using the

value of reflux ratio: 1.0

Time, t

(min)

TOP PRODUCT BOTTOM PRODUCT

Refractive

index (RI)

Mole fraction Refractive

index (RI)

Mole fraction

0 1.358 0.535 1.334 0.025

5 1.359 0.62 1.332 0.02

10 1.360 1.00 1.332 0.02

15 1.360 1.00 1.332 0.02

20 1.360 1.00 1.332 0.02

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4.4.1 MATERIAL BALANCE (REFLUX RATIO: 1.0)

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GRAPH 2 : MOLE FRACTION OF ETHANOL IN VAPOR (Y) VS MOLE FRACTION OF

ETHANOL IN LIQUID (X) FOR REFLUX RATIO: 1.0

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4.5 REFLUX RATIO= 2.0

Rotameter reading R1 (L/hr) = _________1.4_________

Rotameter reading R2 (L/hr) = _________2.8_________

Temperature T4 (oC) = ________ 94 ________

Temperature T2 (oC) = _________95_________

Time, t

(min)

TOP PRODUCT BOTTOM PRODUCT

Refractive index

(RI)

Mole fraction Refractive index

(RI)

Mole fraction

0 1.359 0.620 1.332 0.02

5 1.359 0.620 1.332 0.02

10 1.358 0.535 1.332 0.02

15 1.357 0.470 1.331 0.00

20 1.356 0.410 1.331 0.00

Table 3: Data obtain from packed column distillation of mixture ethanol and water by using

the value of reflux ratio: 2.0

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4.5.1 MATERIAL BALANCE (REFLUX RATIO: 2.0)

14

GRAPH 3 : MOLE FRACTION OF ETHANOL IN VAPOR (Y) VS MOLE FRACTION OF ETHANOL IN

LIQUID (X) FOR REFLUX RATIO: 2.0

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5.0 DISCUSSION & ANALYSIS

In this experiment, we were operating bubble cap distillation equipment. The purpose

of distillation process is to identify how to operate vapor-liquid separation. In bubble cap,

each stage consist of a tray designed to contact raising vapor with descending liquid, which

increases the vapor composition of the more volatile component. Data of the top and bottom

product which is the refractive index value were collected and analyzed, the efficiency of

distillation operation were calculated by using McCabe Thiele method.

There were three graph obtained. First, there is a reference graph where the data were

collected from a sample of series of measured ethanol and water mixture. It was used to

obtain the molar fraction of mixture of ethanol and water distillate in bubble cap distillation.

Moreover, there were two different reflux ratio value being experimented. Reflux

ratio is the ratio of reflux flow to distillate flow and is a measure of how much of the material

going up the top of the column is returned back to the column as reflux. As we compare the

results obtained, it shows that the refractive index of reflux ratio 1.0 is increasing with time

while for reflux ratio 2.0 the refractive index is decreasing as time increases. Based on the

observation, we found that the more liquid that is rich in the more volatile components are

being recycled back into the column.

From graph 2 and 3, McCabe Thiele method was applied in order to determine the

number of stages. Based on graph 2, which is for reflux ratio 1.0, the value of XD is 1.00, XF

is 0.26, and XB is 0.02. By constructing the graph with the value obtained, the number of

stages cannot be identify and therefore we could not get to know how much the plates

available. However, for graph 3, number stages is 1 and no plates require. The value for XD

for third graph is 0.41, XF is 0.26, and XB is 0.00.

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There are very high different in the value of distillate when comparing the result in

graph 2 and graph 3. The experiment by using reflux ratio more higher give out a lover mole

fraction of ethanol in liquid phase. Normally, less reflux ratio, the more stages needed to

reach the desired composition plus if the reflux ratio decreases, then its arriving at a condition

where rectifying, stripping and the feed line intersect at the equilibrium line. However, the

results are differ from the theory, the main error caused by the reflux ratio setting. During the

process, the reflux ratio is not constantly stable and it need to be monitored well.

Distillation process is consist of binary mixture that needed to be purified by the help

of stages and plates. The error of this experiment especially on the first one may due to the

fact that the concentration of the binary mixture was taken as an approximation. The

temperature kept fluctuating from time to time and therefore we could not get a steady state

of temperature when taking stage readings for both top and bottom products.

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6.0 CONCLUSION & RECOMMENDATION

In conclusion, from distillation by using reflux ratio with value of 2 gets no plates but

only consist of 1 stage. However distillation by using reflux ratio equal to 1:1 does not give

any clear reading of stages because we get total 100% of ethanol in distillate top product.

Vapour-liquid separation through distillation was studied using bubble cap distillation

process unit. In trays and bubble cap distillation tower the holes in each tray are covered with

caps called bubble caps. The slots in these bubble caps disperse the raising vapor through the

liquid on the tray. Each bubble cap has many slots and each tray has many bubble caps to

spread up the vapor. This ensures maximum contact between vapor and liquid and ensures

the maximum of mass transfer between liquid and vapour. Based on the data obtained, the

refractive index for top and bottom product was analysed thus, the top product was Ethanol

while the bottom product was water. The time obtained for the vapour – liquid separation is

nearly finish was 30 minute. It can be concluded that this method used for the separation of

Ethanol-water mixture can be considered a reasonably reliable method. This experiment can

be improved by taking the data more than once. Other than that, the condition of machine

should be checked thoroughly so that no damages or leakages occur in this experiment in

order to achieve more accurate result. Besides that, lab manual also should be read properly

before entering the laboratory to avoid any misunderstanding, misconception in order to run

the experiment smoothly.

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7.0 REFERENCES

1) http://www.che.ufl.edu/unit-ops-lab/experiments/Distillation/CD-Operating-

Instructions.pdf

2) Christie John Geankoplis, Transport Processes and Separation Process Principles,

Pearson Education International, 2003, USA, Page 706

3) Azyyati Binti Johari, Mass Transfer Chapter 2 Power Point Slide Note, UNIKL

MICET, 2014, Page 95

4) Braz. J. Chem. Eng. vol.26 no.3 São Paulo July/Sept. 2009

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8.0 APPENDIX

8.1 DATA OF PROPERTIES (ETHANOL & WATER)

Test Tube Volume of Ethanol

(m3)

Volume of Water(m3) Mass of

Ethanol(kg)

Mass of

Water(kg)

Mol of

Ethanol(mol)

Mol of

Water(mol)

A0 0 0.000020 0 0.02 0 1.11111111

A1 0.000001 0.000019 0.000789 0.019 0.017114967 1.0555555556

A2 0.000002 0.000018 0.001578 0.018 0.034229935 1

A3 0.000003 0.000017 0.002367 0.017 0.051344902 0.9444444444

A4 0.000004 0.000016 0.003156 0.016 0.068459872 0.8888888889

A5 0.000005 0.000015 0.003645 0.015 0.085574832 0.8333333333

A6 0.000006 0.000014 0.004734 0.014 0.102689805 0.7777777778

A7 0.000007 0.000013 0.005523 0.013 0.119804772 0.7222222222

A8 0.000008 0.000012 0.006312 0.012 0.136919743 0.6666666667

A9 0.000009 0.000011 0.007101 0.011 0.154034707 0.6111111111

A10 0.000010 0.000010 0.007890 0.01 0.171149675 0.5555555555

A11 0.000011 0.000009 0.008679 0.009 0.188264642 0.5

A12 0.000012 0.000008 0.009468 0.008 0.205379513 0.4444444444

A13 0.000013 0.000007 0.010257 0.007 0.222464577 0.3888888889

A14 0.000014 0.000006 0.011046 0.006 0.239609544 0.3333333333

A15 0.000015 0.000005 0.011835 0.005 0.256724512 0.2777777778

A16 0.000016 0.000004 0.012624 0.004 0.273839479 0.2222222222

A17 0.000017 0.000003 0.013413 0.003 0.290954447 0.1666666667

A18 0.000018 0.000002 0.014202 0.002 0.308069414 0.1111111111

A19 0.000019 0.000001 0.014992 0.001 0.325184382 0.0555555556

A20 0.000020 0 0.015780 0 0.342299349 0

20

TEST TUBE TOTAL MOLE OF ETHANOL

AND WATER

MOLE FRACTION OF

ETHANOL

REFRACTIVE INDEX

A0 1.111111111 0 1.331

A1 1.072670523 0.015955475 1.333

A2 1.034229935 0.033097026 1.334

A3 0.995729347 0.051562012 1.336

A4 0.957348759 0.071509854 1.339

A5 0.918908171 0.093126648 1.342

A6 0.880467583 0.116630989 1.344

A7 0.842025994 0.142281191 1.346

A8 0.803586406 0.170385834 1.348

A9 0.765345818 0.201314185 1.350

A10 0.726705234 0.235514577 1.353

A11 0.688264642 0.273535252 1.357

A12 0.640824054 0.316054182 1.355

A13 0.611383466 0.363919846 1.356

A14 0.572942878 0.418208435 1.358

A15 0.534502291 0.480305729 1.357

A16 0.496061702 0.552027053 1.358

A17 0.457621114 0.635797691 1.358

A18 0.419180525 0.734932554 1.357

A19 0.380139937 0.854085295 1.358

A20 0.342299349 1 1.360

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8.2DATA FOR EQUILIBRIUM LINE

Equilibrium Data for Ethanol-Water Mixtures

Mole fraction of ethanol in liquid, x Mole fraction of ethanol in vapor, y

0.00 0.00

0.05 0.38

0.10 0.53

0.40 0.75

0.60 0.79

0.80 0.86

0.94 0.94

0.90 0.91

0.94 0.94

0.96 0.96

0.98 0.99