Department of Chemical Engineering

University of San Carlos –Talamban Campus

Nasipit, Talamban, Cebu City

ChE 512L

Chemical Engineering Laboratory 2

Distillation

(Batch Distillation of Water-Ethanol Mixture)

A laboratory report submitted to:

Engr. Ramelito Agapay

Instructor, ChE 512L

Submitted by:

Campos, Anthony Kevin

Casia, Aljone

August 3, 2012

I. Introduction

Distillation is carried out in two ways: differential distillation and staged distillation. The

difference is what is inside of the distillation column. In differential (simple batch) distillation,

the column contains packing like that used for gas absorption. In small laboratory columns, this

packing is usually random, of raschig rings or even glass beads. Such distillation aims to provide

small amounts of very pure chemicals. The second way to effect these separations is staged

distillation. In staged distillation, the column internals are completely different than those

normally used for gas absorption. Now these internals consist of a series of compartments or

‘‘trays,’’ where liquid and vapor are contacted intimately, in the hope that they will approach

equilibrium. Now, the liquid and vapor concentrations in the column do not vary continuously,

but discretely, jumping to new values on each tray. Staged distillation was an innovation for

commodity chemicals a century ago, and was the standard during the rapid growth of the

chemical industry. [Cussler,2009]

Distillation normally involves three pieces of equipment: a column, a condenser on top of

the column, and a reboiler at the bottom of the column. The reboiler, often a steam-jacketed

kettle, is heated so that much of its contents evaporates and flow upwards through the column.

The vapors passing out of the column are liquefied in the condenser and much of this condensate

is sent back downwards through the column. This countercurrent flow of vapor and condensate is

common to all forms of distillation.

The system we are dealing in the experiment is a separation of a binary mixture of

Ethanol-water solution via differential distillation. The mechanism in which we can concentrate

the ethanol-water mixture to higher ethanol content is their relative volatility. Thus, the driving

force towards separation is their relative volatility. The batch distillation is performing at a

constant reflux ratio of 0.15. It is not possible to neither maintain the bottom concentration nor

increase with respect to time because of the constraint that the operating condition is a batch. The

same is with the distillate concentration. Thus in the separation, decreasing concentration with

respect to time is to be expected for both bottoms and distillate concentrations.

The differential equation is best described by Rayleigh equation (eq1). It assumes that

small amount of dL (differential Liquid) is vaporized, the composition of the liquid changes from

x to x - dx (differential liquid mole fraction) and the amount of liquid from L to L – dL.

∫

The Rayleigh equation is used to calculate for the theoretical average composition yave.

The term ∫

is obtained by graphical integration of the changing bottom liquid mole fraction

with respect to the reciprocal of the difference in the mole fraction of the distillate and bottoms.

Equation 2 is used to determine the average composition.

∫

∫

II. Objectives

1. Determine the average concentration of a specified volume of the distillate that is obtained

from a feed mixture of known composition by operating the distillation unit at constant

reflux.

2. Use experimental data to predict the time required to obtain a particular concentration of

the distillate.

III. Methodology

1. Materials

Graduated cylinder (2L), stopwatch, thermometer, goggles, siphon, pail, wash

bottle, analytical grade EtOH, technical grade EtOH, test tubes, distilled water,

volumetric flask, refractometer, pipet, aspirator

2. Equipment and Apparatus

Analytical balance, weighing scale, refractometer, and distillation set-up.

3. Procedure

a. Preparation of the Standard Calibration Curve

Specific amount of ethanol (analytical grade) with distilled water to make

solutions which corresponds to 20, 40, 60, 80 percent by weight ethanol was prepared. By

using refractometer, the refractive index of each solution was determined. Graph of

percent weight ethanol solution versus refractive index was plotted as the basis for

determining the different concentrations that is obtained from the distillate and bottom

ethanol solution samples.

b. Preparation of Feed

The refractive index of the technical grade ethanol was determined by taking 2mL

sample. From the calibration curve, the corresponding percent weight ethanol was

determined. This data was used as a reference for the preparation of the 27 L ethanol

solution that has 30 wt% EtOH.

c. Pre-start up Operation

All vents were opened. Prior to closing the reboiler steam inlet valve, all of the drain

valves, steam supply valve, steam regulating valve, reflux control valve, recycle valve,

and the valve that connects the two receiver valve were closed. The seal of the cylindrical

still was opened by a wrench wherein the prepared 27 L EtOH was poured using siphon

until the flask is about 2/3 full. Soft water was allowed to flow through the pipeline. The

soft water inlet valve was opened slowly as soon as steady flow is obtained. This is to

ensure that no air bubbles are trapped in the pipelines. Two thermometer were provided

to the thermometer pockets.

d. Start-up Operation

The by-pass valve was opened to allow the stem to surge through the drain and

release incondensable gases. The by-pass valve was closed and the steam supply valve

was slowly opened. The steam supply pressure gauge was ensured that it indicates a

value greater than 20 psig. Then the regulating valve was slowly adjusted to regulated

steam pressure wherein the pressure was set to 10 psig.

e. Experiment Proper

When the liquid mixture in the still started to boil, total reflux is operated for 20

minutes. Then the reflux control valve was opened to give a total offtake of products. The

time to fill the upper product receiver from the lower to upper mark was noted.

The recycle valve was opened to drain the product back to the reboiler. After it

was drained, the recycle valve was closed again and noted that it will not be opened again

in the duration of the experiment. Once again, total reflux was operated for a few

minutes. The reflux control valve was adjusted to approximately 1/6th

open. the time

required to fill the product receiver was noted to the same mark as before. The distillate

was withdrawn simultaneously at regular interval of about 5 minutes. The sample was

mixed properly by shaking and 10mL sample was collected every 5 min for the

determination of its refractive index. I that time interval, the temperatures of the bottoms

and distillate was also recorded. The sampling was allowed to distill until 3L of the

distillate was collected.

f. Shutdown Operation

The reflux control valve was set to total reflux and the steam regulating valve was

closed. The residual steam in the reboiler was carefully vented through the by-pass valve.

The condenser cooling water was turned off when the boiling has stopped. The ethanol

solution in the bottoms was allowed to cool. Lastly, the solution was drained to a suitable

receiver.

IV. Results and Discussion

1. Objective 1

There are three ways to determine the average mole fraction of the distillate yave, one is

the theoretical method using Rayleigh Equation (Table 1), second is experimental data in

which the 3 L distillate was mixed thoroughly and sample was collected to determine its yave

(Table 2), the third one is the determination of the yave using the contribution of the different

volume fraction of the distillate (Table 3).

Table 1 Determination of yDave using Rayleigh equation*

time(min) xD xB 1/(yD-xB) ln(Lo/Lt) Lo/Lt yD,ave

0 0.6833 0.1452 1.8582 0.01545

1.0795 0.6713

5 0.7057 0.1366 1.7571 0.01885

10 0.6602 0.1262 1.8728 0.01317

15 0.6638 0.1191 1.8358 -0.00923

20 0.6708 0.1242 1.8293 0.01133

25 0.6443 0.1181 1.9005 0.00366

30 0.6646 0.1161 1.8232 0.02498

35 0.6558 0.1023 1.8069 -0.00709

40 0.65669 0.10626 1.8168 0.00532

45 0.64647 0.10335 1.8412

*a thorough presentation of the data is found in the appendices A.3

Table 2 Determination of yDave using

average mole fraction of the total

distillate collected

Refractive

index

Weight

Percent YDave

1.3632 82.97 0.6558

Table 3 Determination of yDave by volume fraction

time(min) Volume(mL)* Volume

fraction** yD yD(contribution)

a

0 970 0.304 0.6833 0.2080

0-5 358 0.112 0.7057 0.0793

5-10. 245 0.077 0.6602 0.0508

10-15. 250 0.078 0.6638 0.0521

15-20. 243 0.076 0.6708 0.0512

20-25. 240 0.075 0.6443 0.0485

25-30. 225 0.071 0.6646 0.0469

30-35. 225 0.071 0.6558 0.0463

35-40. 210 0.066 0.65669 0.0433

40-45. 220 0.069 0.64647 0.0446

Sum: 3186 1 yDave*** 0.6711

*Volume of the distillate collected per time interval

**Volume of distillate collected per time interval

divided by the total volume of distillate at 45th min.

***average distillate is obtained by summing up the yD(contribution) aobtained by multiplying volume fraction to yD

Table 4 Summary of the yDave

Method yDave %differenced

1a 0.6713 0

2b 0.6558 2.34

3c 0.6711 0.03

abased from yDave of Table 1

bbased from yDave of Table 2

cbased from yDave of Table 3

ddata is realative to method 1

The data presented in Table 4 is a summary of the yDave wherein the percent difference of

method 1 and 3 are apparently similar these method of obtaining yDave are the determination

using Rayleigh equation and the method of volume fraction. It showed that the confirmation

from experimental data is best correlated by the Rayleigh equation. Method 2 did not fit the 0.67

range because probably the mixing of all the distillate is not enough and that we did not really

got representation of the average distillate concentration. Another speculation is the dissipation

of ethanol solution towards the atmosphere upon mixing. We mixed the distillate solution in the

pale wherein it is susceptible to volatilization causing the solution to decrease its concentration

of about 0.02 based from 0.67. The value 0.67 is a valid assumption of the correct yDave if we

look at to how these data are obtained. It is the when we collected sample of the distillate and

assured that the collected sample was sealed tightly compared to method 2 wherein the sample

obtained has been exposed to air for some time.

Fig. 1 Graph of mole fraction EtOH versus time (Distillate).

Figure 1 is confirmation of the obtained yDave that the obtained yDave is within the range of

the decreasing mole fraction with respect to time. The expected decrease in mole fraction with

respect to time for a batch distillation is confirmed in Fig 1 and 2 as discussed in the

introduction.

0.6400

0.6500

0.6600

0.6700

0.6800

0.6900

0.7000

0.7100

0 5 10 15 20 25 30 35 40 45Mole

Fra

ctio

n o

f et

OH

solu

tion

Time [mins]

Fig. 2 Graph of mole fraction EtOH versus time (Bottoms).

2. Objective 2

Table 5 Data for

determining time

of maximum

concentration

time(min) yD,ave

0 0.6833

0-5 0.6941

0-10 0.6877

0-15 0.6807

0-20 0.6838

0-25 0.6779

0-30 0.6763

0-35 0.6713

0-40 0.6727

0-45 0.6713

Table 5 shows the yDave when it reaches maximum average concentration of the distillate

obtained. The data shows that at the 5th

minute, the average concentration of the distillate is at its

0.1000

0.1050

0.1100

0.1150

0.1200

0.1250

0.1300

0.1350

0.1400

0.1450

0.1500

0.1550

0 5 10 15 20 25 30 35 40 45

Mo

l Fra

ctio

n E

tOH

,xB

Time, t (min)

Fig. 4 Time vs. Mol Fraction EtOH at Bottoms

maximum, It can also be explain in Fig. 1 wherein the peak is also at its 5th

minute. The

supporting data for this can be seen in the appendices (from A.2-1 to A.2-9)

V. Conclusion

The average mole fractions of the distillates are 0.6713, 0.6558 and 0.6711.

The time required to obtain a maximum average concentration of the distillate is 5

minutes.

VI. References

Geankoplis, C.J. (2009). Transport Processes and Unit Operations, 4th

Edition, Prentice

Hall,New Jersey.

Perry, R.H. et.al. Eds. (2008) Perry’s Chemical Engineer’s Handbook, 8th

Edition,

McGraw-Hill, Inc., New York

Cussler, E.L. (2007) Diffusion Mass Transfer in Fluid System, 3rd

Edition, Cambridge

University Press, New York

VII. Appendices

A.1-1 Determination of the reflux

ratio

Filling Time

[s] Reflux

Ratio Fully

Open 1/6 Open

266 306 0.1504

A.1-2 Experimental yDave

Refractive

Index, nD

Dilution

Factor

Experimental

YAVE

1.3632 2.1667 0.8447

A.1-3 Graphical Integration involving Rayleigh’s Distillation

A.2-1

time(min) mD mB xD xB 1/(yD-xB) ln(Lo/Lt) Lo/Lt yD,ave

0 0.847 0.303 0.6833 0.1452 1.8582 0.0155 1.0156 0.6941

5 0.860 0.288 0.7057 0.1366 1.7571

A.2-2

time(min) mD mB xD xB 1/(yD-xB) ln(Lo/Lt) Lo/Lt yD,ave

0 0.847 0.3027 0.6833 0.1452 1.8582

0.0343 1.0349 0.6877 5 0.860 0.288 0.7057 0.1366 1.7571

10 0.832 0.270 0.6602 0.1262 1.8728

A.2-3

time(min) mD mB xD xB 1/(yD-xB) ln(Lo/Lt) Lo/Lt yD,ave

0 0.847 0.3027 0.6833 0.1452 1.8582

0.0475 1.0486 0.6807 5 0.860 0.2880 0.7057 0.1366 1.7571

10 0.832 0.2697 0.6602 0.1262 1.8728

15 0.835 0.2569 0.6638 0.1191 1.8358

1.74

1.76

1.78

1.80

1.82

1.84

1.86

1.88

1.90

1.92

0.1010 0.1110 0.1210 0.1310 0.1410

1/(

YD-X

B)

XB

Rayleigh's Distillation

A.2-4

time(min) mD mB xD xB 1/(yD-xB) ln(Lo/Lt) Lo/Lt yD,ave

0 0.847 0.3027 0.6833 0.1452 1.8582

0.0382 1.0390 0.6838

5 0.860 0.2880 0.7057 0.1366 1.7571

10 0.832 0.2697 0.6602 0.1262 1.8728

15 0.835 0.2569 0.6638 0.1191 1.8358

20 0.839 0.2660 0.6708 0.1242 1.8293

A.2-5

time(min) mD mB xD xB 1/(yD-xB) ln(Lo/Lt) Lo/Lt yD,ave

0 0.8465 0.3027 0.6833 0.1452 1.8582

0.0496 1.0508 0.6779

5 0.8598 0.2880 0.7057 0.1366 1.7571

10 0.8324 0.2697 0.6602 0.1262 1.8728

15 0.8347 0.2569 0.6638 0.1191 1.8358

20 0.8390 0.2660 0.6708 0.1242 1.8293

25 0.8224 0.2550 0.6443 0.1181 1.9005

A.2-6

time(min) mD mB xD xB 1/(yD-xB) ln(Lo/Lt) Lo/Lt yD,ave

0 0.8465 0.3027 0.6833 0.1452 1.8582

0.0532 1.0547 0.6763

5 0.8598 0.2880 0.7057 0.1366 1.7571

10 0.8324 0.2697 0.6602 0.1262 1.8728

15 0.8347 0.2569 0.6638 0.1191 1.8358

20 0.8390 0.2660 0.6708 0.1242 1.8293

25 0.8224 0.2550 0.6443 0.1181 1.9005

30 0.8351 0.2514 0.6646 0.1161 1.8232

A.2-7

time(min) mD mB xD xB 1/(yD-xB) ln(Lo/Lt) Lo/Lt yD,ave

0 0.847 0.3027 0.6833 0.1452 1.8582

0.0782 1.0814 0.6713

5 0.860 0.2880 0.7057 0.1366 1.7571

10 0.832 0.2697 0.6602 0.1262 1.8728

15 0.835 0.2569 0.6638 0.1191 1.8358

20 0.839 0.2660 0.6708 0.1242 1.8293

25 0.822 0.2550 0.6443 0.1181 1.9005

30 0.835 0.2514 0.6646 0.1161 1.8232

35 0.830 0.2257 0.6558 0.1023 1.8069

A.2-8

time(min) mD mB xD xB 1/(yD-xB) ln(Lo/Lt) Lo/Lt yD,ave

0 0.847 0.3027 0.6833 0.1452 1.8582

0.0711 1.0737 0.6727

5 0.860 0.2880 0.7057 0.1366 1.7571

10 0.832 0.2697 0.6602 0.1262 1.8728

15 0.835 0.2569 0.6638 0.1191 1.8358

20 0.839 0.2660 0.6708 0.1242 1.8293

25 0.822 0.2550 0.6443 0.1181 1.9005

30 0.835 0.2514 0.6646 0.1161 1.8232

35 0.830 0.2257 0.6558 0.1023 1.8069

40 0.83023 0.2331 0.65669 0.10626 1.8168

A.2-9

time(min) mD mB xD xB 1/(yD-xB) ln(Lo/Lt) Lo/Lt yD,ave

0 0.847 0.3027 0.6833 0.1452 1.8582

0.0765 1.0795 0.6713

5 0.860 0.2880 0.7057 0.1366 1.7571

10 0.832 0.2697 0.6602 0.1262 1.8728

15 0.835 0.2569 0.6638 0.1191 1.8358

20 0.839 0.2660 0.6708 0.1242 1.8293

25 0.822 0.2550 0.6443 0.1181 1.9005

30 0.835 0.2514 0.6646 0.1161 1.8232

35 0.830 0.2257 0.6558 0.1023 1.8069

40 0.83023 0.2331 0.65669 0.10626 1.8168

45 0.82379 0.2276 0.64647 0.10335 1.8412

A.3 Data in determining the mole fraction of the bottoms and distillate

time Distillate

Volume

Temperature

[°C]

Refractive Index, nD V1 V2 Dilution

Factor

Weight percent etOH Mole fraction 1

(YD-

XB) Bottoms Distillate

Bottoms Distillate

[min] [mL] Bottoms Distillate Original Diluted [mL] [mL] Diluted Corrected Bottoms Distillate

0 970 82.0 76.0 1.3511 1.3634 1.3573 5.00 10.1625 2.0325 0.30 0.42 0.85 0.1452 0.6833 1.86

5 358 82.0 79.0 1.3503 1.3632 1.3568 5.00 10.4850 2.0970 0.29 0.41 0.86 0.1366 0.7057 1.76

10 245 84.0 78.5 1.3493 1.3631 1.3562 5.00 10.5075 2.1015 0.27 0.40 0.83 0.1262 0.6602 1.87

15 250 85.5 79.5 1.3486 1.3631 1.3559 5.00 10.7065 2.1413 0.26 0.39 0.83 0.1191 0.6638 1.84

20 243 87.0 80.0 1.3491 1.3631 1.3561 5.00 10.6875 2.1375 0.27 0.39 0.84 0.1242 0.6708 1.83

25 240 87.0 80.5 1.3485 1.3631 1.3558 5.00 10.8925 2.1785 0.26 0.38 0.82 0.1181 0.6443 1.90

30 225 86.0 80.0 1.3483 1.3631 1.3557 5.00 10.9025 2.1805 0.25 0.38 0.84 0.1161 0.6646 1.82

35 225 86.5 80.0 1.3469 1.3632 1.3551 5.00 11.1815 2.2363 0.23 0.37 0.83 0.1023 0.6558 1.81

40 210 86.0 80.5 1.3473 1.3630 1.3552 5.00 11.1440 2.2288 0.23 0.37 0.83 0.1063 0.6567 1.82

45 220 86.5 80.5 1.3470 1.3630 1.3550 5.00 11.1625 2.2325 0.23 0.37 0.82 0.1033 0.6465 1.84

A.4 Calibration Curve

0

10

20

30

40

50

60

70

80

90

100

1.33 1.332 1.334 1.336 1.338 1.34 1.342 1.344 1.346 1.348 1.35 1.352 1.354 1.356 1.358 1.36 1.362 1.364 1.366

Pe

rce

nt

We

igh

t Et

OH

Refractive Index