batch distillation.docx

1.0: OBJECTIVES

Experiment 9: Batch distillation (structure packing) at total reflux

- To study the effect of liquid and vapor loading on the height equivalent theoretical

plates (HETP).

- To determine HETP at total reflux in batch distillation column.

Experiment 10: Batch distillation (structure packing) at constant reflux

- Students are required to study the change of top and bottom composition sample over

time in batch distillation at constant reflux.

- To determine height equivalent theoretical plates (HETP) in constant reflux batch

distillation column.

2.0: INTRODUCTION

Batch distillation is one of distillation process types. In batch distillation a fixed

amount of charge is added to the still to separate into its component and then repeated. This is

in contrast with continuous distillation; the other type of distillation where it is an ongoing

separation in which a mixture is continuously fed into the process and separated fractions are

removed without interruption as output streams.

Top product composition varies with time. It depends on bottom product composition,

number of trays and reflux ratio. There is no steady state as long as compositions are

changing with time. At start, top product; distillate (D) is rich in more volatile component

since it is easier to vaporize and going up the column. After a few time, more volatile

component become lesser at distillate (D). A batch column is like the top half of a continuous

column where it has a rectifying section only.

Batch distillation is preferred method for separation when feed quantities are small

and composition varies widely with time. It is hard to observe when the process is handling

through continuous distillation since its product withdrawn continuously as the feedstock.

Others, batch distillation is used while high purity streams are required for curtain product

such in the pharmaceutical industry and in wastewater treatment units, and when the process

requires frequent cleaning which would interrupt continuous processing.

1

http://en.wikipedia.org/wiki/Continuous_distillation

The simplest and most frequently used batch distillation configuration is the batch

rectifier, including the alembic and pot still. The batch rectifier consists of reboiler, rectifying

column, a condenser, some means of splitting off a portion of the condensed vapor (distillate

product); reflux drum, and receivers.

The reboiler is filled initially with liquid mixture and heated to vaporize the solution.

The fast-moving atom will escape as vapour and flows upwards in the rectifying column and

condenses at the condenser. After passing through the condenser, some of the condensate

either is forcing back to the column as reflux or flows down as top product (distillate) and

collected at its receivers. Returning back the portion of condensate will provide intimate

contact between vapour and liquid to improve the separation process. As the supply of the

material is limited and lighter components are removed, the relative fraction of heavier

components will increase and the refractive index will decrease as the distillation progresses.

Figure 2.1: Diagram of Batch Rectifier

2

http://en.wikipedia.org/wiki/Reflux

http://en.wikipedia.org/wiki/Condensation

http://en.wikipedia.org/wiki/Condenser_(heat_transfer)

http://en.wikipedia.org/wiki/Reboiler

http://en.wikipedia.org/wiki/Pot_still

http://en.wikipedia.org/wiki/Alembic

The other simple batch distillation configuration is the batch stripper. The batch

stripper has same parts as the batch rectifier but only the charge pot is located above the

column. During operation (after charging the pot and starting up the system) the high boiling

constituents are primarily separated from the charge mixture. The liquid in the pot is depleted

in the high boiling constituents, and enriched in low boiling ones. The high boiling product is

drawn into the bottom product receivers. The residual low boiling product is withdrawn from

the charge pot. However, batch stripping process seldom practiced in industry.

Figure 2.2: Diagram of Batch stripper

Reflux is the liquid condensed from the rising vapor which returns to the pot flask.

The Reflux ratio is the ratio between the boil up rate and the take-off rate. Or in other words,

it is the ratio between the amount of reflux that goes back down the distillation column and

the amount of reflux that is collected in the receiver (distillate). If 5 parts of the reflux go

back down the distillation column and 1 part is collected as distillate then the reflux ratio is

5:1. In the case where all the reflux is collected as distillate the reflux ratio would be 0:1. If

no distillate is collected then a reflux ratio is not assigned. Instead we call this "total reflux"

or equilibration.

3

The higher the reflux ratio, the more vapor and liquid contact can occur in the

distillation column. So higher reflux ratios usually mean higher purity of the distillate. It

also means that the collection rate for the distillate will be slower. Reflux ratio is dependent

for the overall efficiency of batch distillation column. An increase in the reflux ratio will

cause the overall efficiency to drop. A better overall efficiency is obtained thus the number of

stages will increase if reflux ratio is smaller. Furthermore, different reflux ratio will give a

different operating line in graphical method.

The remainder of the report provides detailed analysis of the Theory and Working

Equations for the experiment. The experimental procedure is outlined in Material and

Methods section. Presentation of the findings and detailed discussion of the results can be

found in Results and Discussion section. Finally, summary of the report and

recommendations are included in Conclusion and Recommendation section.

4

3.0: THEORY AND WORKING EQUATIONS

Distillation is a common process in engineering, basically used to separate various

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

between a vapour phase and a liquid phase, as stated by Christie John Geankoplis, in his

book, “Transport Process and Separation Process Principles”. He also stated that, all

components must be present in both phases, and the vapour phase is created from the liquid

phase by vaporization at the boiling point.

Taking the principles from the stated book, the author also stated that, the basic

requirements for the separation of components by distillation is that the composition of the

vapour be different from the composition of the liquid with which it is in equilibrium at the

boiling point of the liquid. It is concerned with solutions where all components are

appreciably volatile- such as ethanol-water solutions.

Advancement in technology has created many types of distillation process, but in this

experiment, the method used is batch distillation. Two types of batch distillation tested are

batch distillation with total reflux, and batch distillation with constant reflux. First of all, in

batch distillation, solutions are heated in the fractionating tower until the boiling point is

reached, then the evaporating vapour will be condensed and the product is collected as the

distillate. So, theoretically the distillate should contain more of the more volatile component,

which is Ethanol, where the bottom product will contain more of the less volatile component,

which is water.

In the book, Geankoplis wrote that in actual practice, total reflux can be defined or

realized by returning all the overhead condensed vapour from the top of the tower back to the

tower as reflux. Also, the liquid in the bottom is reboiled. This means, all the products

distillate and bottoms are reduced to zero flows, as is the fresh feed to the tower. In the

constant reflux case, a reflux ratio of the distillation process is chosen, which actually mirrors

the ratio of which the vaporised liquid is recycled back into the tower and flows into the

distillate. Technically, reflux ratio of 3 means that for 30 seconds of vaporised liquid flows

back into the tower, 10 seconds of it goes into the distillate. Stage distillation with reflux is

also known as rectification.

In tray towers, a theoretical tray is defined as tray in which equilibrium is attained

between the gas or vapour leaving and the liquid leaving the tray. HETP in m (ft) is defined

as the height of the packed column necessary to a give a separation equal to one theoretical

plate. The design of mass transfer towers requires evaluation of the number of theoretical

5

stages or transfer units. Hence, the height of packing H in m (ft) required to perform a given

separation is;

Height of packing, H = 1m

HETP= Height of packing , Hnumber of theoretical platesneeded , N t

The equation of the operating line for enriching section:Reflux ratio = 3At t=0,

yn+1=R

R+1xn+

xD

R+1

The Rayleigh Equation is useful in the analysis of simple distillation, as it shows how the

concentration and quantity are related. As the process is unsteady state in nature, the

derivation is based on a differential approach to changes in concentration with time. The

equation to be derived (known as the Rayleigh Equation) shows the relationship between

total moles remaining in the still and the mole fraction of the more volatile component in

the still. (Source: http://www.separationprocesses.com/Distillation/DT_Chp02a.htm)

Rayleigh equation: ∫L2

L1

dLL

=lnL1

L2

=∫x2

x1

dxy−x

In L1-In L2 =∫x2

x1

dxy−x

L1 = initial moles of liquid originally in still

L2 = final moles of liquid remained in still

x1 = initial liquid composition in still (mole fraction of ethanol)

x2 = final liquid composition in still (mole fraction of ethanol)

y= initial composition of ethanol in the vapour

6

4.0: MATERIALS & METHODS

Experiment 9:

1. A set of water-ethanol mixture within a specific range (0% to 100%) is prepared. 6

readings of refractive index (RI) were obtained from 6 different concentration of

water-ethanol mixture. A graph is generated based on the data.

2. The initial volume and refractive index of the liquid mixture in the reboiler is

recorded and heater power is set to 1.5kW.

3. The temperature of reboiler is set at 85oC. The reflux control is ensured at total reflux

positioned.

4. When the readings reached were stable, the top column temperature is recorded. The

sample distillate and bottom product is collected.

5. The refractive index is measured and the value is recorded into table. (Note : the

sample should not be discarded as it is used to perform material balance at the end of

the experiment). Step 4 and 5 is repeated to different heating power such as 2.0, 2.5,

3.0 and 3.5 KW.

6. The theoretical number of plates for each sampling time is determined by using

McCabe-Thiele method and HETP is calculated. The graph of HETP versus heating

power and distillate flow rate versus heating power is plotted and the relationship is

observed.

Experiment 10:

1. A set of water-ethanol mixture within a specific range (0% to 100%) is prepared. 6

readings of refractive index (RI) were obtained from 6 different concentrations of

water-ethanol mixture. A graph is generated based on the data.

2. The initial volume and refractive index of the liquid mixture in the reboiler is

recorded and heater power is set to 3.5kW.

3. The reflux ratio is 3 ( reflux timer is set to 30 second for set 1 and 10 second for set 2)

and the reflux control is set to timer controller reflux.

4. When steady state is reached, the top column temperature is recorded. The sample

distillate and bottom product is collected.

5. The refractive index is measured and the value is recorded into table. (Note : the

sample should not be discarded as it is used to perform material balance at the end of

the experiment). Step 4 and 5 is repeated for 60 minutes.

7

6. The theoretical number of plates for each sampling time is determined using

McCabe-Thiele method and HETP is calculated. The amount of ethanol left in the

evaporator is calculated and plotted against time using the Rayleigh equation.

8

5.0: RESULT AND DISCUSSIONExperiment 9: Batch Distillation (Structure Packing) At Total Reflux

Volume of ethanol (ml)

Volume of water (ml)

ethanol mol fraction

refractive index, RI

0 10 0.0000 1.344182 8 0.0717 1.352374 6 0.1709 1.363176 4 0.3168 1.368188 2 0.5528 1.3698910 0 1.0000 1.36718

Table 5.1: Data for refractive index and ethanol mol fraction for a set of mixtures containing ethanol and water

In experiment 9, we are required to study the effect of liquid and vapor loading on the

height equivalent theoretical plates (HETP) and to determine HETP at total reflux in batch

distillation column. Total reflux is a condition which exists when the reflux valve is totally

closed and all the condensed liquid is being returned down the column. First of all, the

refractive index of 6 samples with different volume of ethanol and water is taken to

determine the compositions of distillate product, XD and bottom product, Xw.

0.0000 0.1000 0.2000 0.3000 0.4000 0.5000 0.6000 0.7000 0.8000 0.9000 1.00001.33

1.335

1.34

1.345

1.35

1.355

1.36

1.365

1.37

1.375

Graph Of Refractive Index (RI) Vs Ethanol Mol Fraction

Ethanol mol fraction

refr

activ

e in

dex

(RI)

Figure 5.1: Graph of refractive index (RI) verses ethanol mol fraction for a set of mixtures containing ethanol and water

9

Heating

Power (kW)

Distillate product Bottom product

HETP

Temperature (oC)

Refractive Index

(RI)

Mole fraction

of ethanol

(xD)

Flow Rate

(ml/min)

Temperature (oC)

Refractive Index

(RI)

Mole fractio

n of ethanol

(xW)1.5 75.3 1.36498 0.200 17.43 90.1 1.35453 0.088 1.5182.0 87.3 1.36679 0.206 53.17 90.5 1.35324 0.076 1.3922.5 87.6 1.36788 0.248 75.00 91.3 1.35213 0.065 1.1373.0 87.7 1.36818 0.303 85.71 91.7 1.35220 0.063 1.0753.5 93.5 1.36934 0.381 101.41 91.9 1.34910 0.040 0.767

Table 5.2: Data for distillate and bottom product for the selection of different set of heater power

5 sets of heating power (1.5kW, 2.0kW, 2.5kW, 3.0kW, and 3.5kw) are used in this

experiment and data obtained is tabulated in Table 5.2. Graph of refractive index (RI) versus

ethanol mole fraction is plotted as above as Figure 5.1. The compositions of distillate

product, XD and bottom product, XW can be calculated from this graph by using molecular

weight and density. Figure 5.1 shows that when the composition of ethanol in the mixture

increases, the refractive index increases. This is caused by the density of the mixture. Since

the refractive index is inversely proportional to the overall density of the mixture, when the

composition of ethanol increases, the overall density of the ethanol decreases and thus the

refractive index increases.

From Table 5.2, it is shown that when the heating power increases, the distillate

product, XD increases while the bottom product, XW decreases. Besides, the value of distillate

product is always greater than the bottom product disregard of the heating power. Since

ethanol is a volatile component, the concentration of ethanol is increased in the vapor from

each stage going upward but increased in the liquid from each stage going downward.

HETP is defined as the height of the packed column necessary to give a separation equal to

one theoretical plate. The ethanol equilibrium data is plotted as in Figure B-1, B-2, B-3,

B-4 and B-5 in appendix A. Then, the theoretical plates can be determined from the graph by

using the Mc-Cabe Thiele method. From the graph, the number of theoretical plates for

different heating power is 0.6588 (at 1.5kW), 0.7182 (at 2.0kW), 0.8798 (at 2.5kW), 0.9302

(at 3.0kW), and 1.303 (at 3.5kW). Thus it can be said that the number of theoretical plates

10

increases with greater value of heating power. Finally, the value of HETP can be calculated

from the number of theoretical plates as in appendix A.

1.0 1.5 2.0 2.5 3.0 3.5 4.00

0.20.40.60.8

11.21.41.6

Graph Of HETP Vs Heating Power

heating power(kW)

HETP

(m)

Figure 5.2: Graph of HETP vs heating power

1.5 1.7 1.9 2.1 2.3 2.5 2.7 2.9 3.1 3.3 3.50.00

20.00

40.00

60.00

80.00

100.00

120.00

Graph Of Distillate Flow Rate Vs Heating Power

Heating power (kW)

Disti

llate

flow

rate

(ml/

min

)

Figure 5.3: Graph of distillate flow rate vs heating power

From the graph of HETP versus heating power, it is shown that the value of HETP is

decreases when the heating power increases. The value of HETP at heating power of 1.5kW,

2.0kW, 2.5kW, 3.0kW and 3.5 kW is found as 1.518, 1.392, 1.137, 1.075 and 0.767

respectively. While for the graph of Distillate Flow rate (mL/min) versus Heating power

(kW), the distillate flow rate is directly proportional to the heating power. When the heating

power increases, the distillate flow rate also increases.

11

Experiment 10: Batch Distillation (Structure Packing) At Constant Reflux

The second experiment that we have conducted is experiment 10. In this experiment,

we are required to study the change of top and bottom composition sample over time in batch

distillation at constant reflux (reflux ratio = 3) and to determine the height equivalent

theoretical plates (HETP). Before conducting the batch distillation process, the refractive

indices of a series ethanol-water mixture of different composition were measured by

refractometer.

Time(min)


HETP

Temperature (oC)

Refractive Index

(RI)

Mole fractio

n of ethanol

Temperature (oC)

Refractive Index

(RI)

Mole fraction

of ethanol

5.0 97.6 1.36263 0.159 92.1 1.35226 0.0658 1.48110.0 97.7 1.36317 0.165 92.2 1.35214 0.0647 1.44620.0 98 1.36527 0.224 92.2 1.35213 0.0646 1.27430.0 98.1 1.36657 0.248 92.2 1.35209 0.0640 1.18540.0 98.1 1.36731 0.256 92.2 1.35208 0.0639 1.12450.0 98.1 1.36825 0.303 92.2 1.35206 0.0638 1.09960.0 98.1 1.36827 0.305 92.2 1.35199 0.0629 1.053

Table 5.3: Data for distillate and bottom product for each sampling time

The refractive index of distillate product and the bottom product can be read from

Table 5.3. The sample is collected at every 10 minutes of a 60 minute operation process. For

each mixture, their respective compositions of distillate and bottom product are calculated by

using their molecular weight and density. All the details are listed in Table5.3 as time passed

by, it can be seen that the top product become richer in ethanol while the bottom product has

leaner ethanol. This is due to the lower boiling point of ethanol (78.3° C) than water (100°C).

Therefore, at each time interval, the mole fraction of ethanol is higher in the distillate product

rather than in the bottom product. For example at time= 10min, the mole fraction of ethanol

in the distillate product is 0.165 but only 0.0647 mole fraction of ethanol found in the bottom

product.

In appendix B, Figure B-6 to Figure B-12 shows the equilibrium diagram for system

ethanol-water at different time interval for a 60 minute operating system. The number of

theoretical plates is calculated by using McCabe-Thiele method. In order to use this method,

one assumption is made which is there must be equimolar overflow through the tower

between the feed inlet and the top tray and the feed inlet and the bottom tray. From the

experiment result, it is shown that the number of theoretical plates increases with time. For

12

t=5 minutes to 60 minutes, the number of theoretical plates obtained is as following: 0.6754,

0.6917, 0.7852, 0.8440, 0.8893, 0.9095, and 0.9495 respectively.

0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.00

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Graph Of HETP Against Time

Time(min)

HETP

(m)

Figure 5.4: Graph of HETP against time

Figure 5.4 shows the HETP against time. The calculation of the value of HETP can be

found in appendix B. Theoretically, the HETP is inversely proportional to the number of

theoretical plates. The higher the number of theoretical plates results in lower value of HETP.

From the graph, the HETP decreases when time passed by. This obeys the theory which

mentions that when the total bed height considered constant, the higher the number of

theoretical plates, the lower the value of HETP in order to fulfill the high number of

theoretical plates needed. From this experiment, the highest value of HETP is 1.484m, which

is at t= 5 min.

Time(min) Amount of ethanol left(litre)5.0 3.697210.0 3.686120.0 3.685130.0 3.679140.0 3.678150.0 3.677160.0 3.6680

Table 5.4: Data for amount of ethanol left for each sampling time

13

0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.03.65003.65503.66003.66503.67003.67503.68003.68503.69003.69503.7000

Graph Of Amount Of Ethanol Left In The Evaporator Against Time

Time(min)

Amou

nt o

f eth

anol

left

(litr

e)

Figure 5.5: Graph of amount of ethanol left in the evaporator against time

Figure 5.5 shows the amount of ethanol left in the evaporator against time. It can be

seen that when time passed by, the amount of ethanol left in the evaporator decreases. The

final volume of the ethanol is less than the initial volume of ethanol left in the evaporator.

This is true since more ethanol is used as time goes by.

In both experiment, the liquid-vapor is assumed to be in equilibrium state when

leaving tray in ideal conditions. However, there is always insufficient time for the liquid and

vapor to contact and mix. Therefore in actual condition, the equilibrium state for liquid-vapor

always cannot be achieved. This results in reducing of actual mass transfer.

14

6.0 : CONCLUSION AND RECOMMENDATION

For experiment 9, the number of theoretical plates obtained for different heating

power is 0.6588 (at 1.5kW), 0.7182 (at 2.0kW), 0.8798 (at 2.5kW), 0.9302 (at 3.0kW), and

1.303 (at 3.5kW). The higher the heating power, the higher the number of theoretical plates is

needed to distil off ethanol. Besides, the value of HETP for heating power of 1.5kW, 2.0kW,

2.5kW, 3.0kW and 3.5 kW is found as 1.518, 1.392, 1.137, 1.075 and 0.767 respectively.

This shows that when the heating power increases, the number of theoretical stages increases

but the value of HETP will decrease. The distillate flow rate is directly proportional to

heating power, which means that as heating power increases the distillate flow rate also

increases.

For experiment 10, the number of theoretical plates obtained for different time

interval (each 10 minutes for a 60 minutes operating process) is 0.6754, 0.6917, 0.7852,

0.8440, 0.8893, 0.9095 and 0.9495 respectively. The number of theoretical plates obtained is

very small, which is not more than 1 stage. Since the actual number of stages must be greater

than 1 stage, this result deviates from the actual result. As time goes by, the value of HETP

obtained is decreasing from 1.481m to 1.053m.

There is some precaution steps are recommended for result improvement of the

experiment. First of all, the start-up operation should be taken with care before the

experiment begins. The drain valve and the sample taking valves should be closed before the

stable condition of the operating condition is achieved. Besides, we should only start the

experiment when the operating condition has reached 85°C to ensure the ethanol boils and the

mixture is at equilibrium condition. We should also be extra careful when the sample of

bottom product is taken since the liquid is hot. Apart from that, human errors should also be

avoided when the sample reading is taken. For example, the reading of the refractive index

should be repeated at least three times to get the average reading in order to get a more

accurate result.

15

7.0: REFERENCES

1. Perry, R. H., and D. Green, Perry’s Chemical Engineers’ Handbook, 6th edition,

McGraw-Hill, 1988.

2. Christie John Geankoplis. Unit Operations: Transport Processes and Separation

Process Principles, Fourth Edition, Pearson Education International, 2003.

3. Jaime Benitez. Principles and Modern Applications of Mass Transfer Operations,

Second Edition, John Wiley & Sons Inc.

4. Sharma. Principles of Mass Transfer, PHI Learning Pvt. Ltd., 2007.

5. http://lorien.ncl.ac.uk/ming/distil/distil0.htm

6. http://academic.evergreen.edu/curricular/whatscookin

7. http://www.fpharm.uniba.sk/fileadmin/user_upload/english/Fyzika/

Refractive_index.pdf

8. http://www.solvent--recycling.com/reflux.html

9. http://www.separationprocesses.com/Distillation/DT_Chp02a.htm

16

Appendix AExperiment 9: Batch distillation (structure packing) at total reflux

Volume of ethanol (ml)

Volume of water (ml)

Mole of ethanol, ne

Mole of water, nw

Ethanol mol fraction

Refractive index, RI

0 10 0.0000 0.5541 0.0000 1.344182 8 0.0343 0.4433 0.0717 1.352374 6 0.0685 0.3324 0.1709 1.363176 4 0.1028 0.2216 0.3168 1.368188 2 0.1370 0.1108 0.5528 1.3698910 0 0.1713 0.0000 1.0000 1.36718

Table A-1: Data for refractive index and ethanol mol fraction for a set of mixtures containing ethanol and water

Mol fraction of ethanol in liquid, x Mol fraction of ethanol in vapor, y0.0000 0.00000.0190 0.17000.0721 0.38910.0966 0.43750.1238 0.47040.1661 0.50890.2337 0.54450.2608 0.55800.3273 0.58260.3965 0.61220.5079 0.65640.5198 0.65990.5732 0.68410.6763 0.73850.7472 0.78150.8943 0.89431.0000 1.0000

Table A-2: Ethanol- water equilibrium data (Perry, R H.)

17

Heating

Power (kW)


HETP

Temperature (oC)

Refractive Index

(RI)

Mole fraction

of ethanol

(xD)

Flow Rate

(ml/min)Temperatur

e (oC)

Refractive Index (RI)

Mole fractio

n of ethanol

(xW)1.5 75.3 1.36498 0.200 17.43 90.1 1.35453 0.088 1.5182.0 87.3 1.36679 0.206 53.17 90.5 1.35324 0.076 1.3922.5 87.6 1.36788 0.248 75.00 91.3 1.35213 0.065 1.1373.0 87.7 1.36818 0.303 85.71 91.7 1.35220 0.063 1.0753.5 93.5 1.36934 0.381 101.41 91.9 1.34910 0.040 0.767

Table A-3: Data for distillate and bottom product for the selection of different set of heater power


Time(min)


HETP

Temperature (oC)

Refractive Index

(RI)

Mole fractio

n of ethanol

Temperature (oC)

Refractive Index

(RI)

Mole fraction

of ethanol

5.0 97.6 1.36263 0.159 92.1 1.35226 0.0658 1.48110.0 97.7 1.36317 0.165 92.2 1.35214 0.0647 1.44620.0 98 1.36527 0.224 92.2 1.35213 0.0646 1.27430.0 98.1 1.36657 0.248 92.2 1.35209 0.0640 1.18540.0 98.1 1.36731 0.256 92.2 1.35208 0.0639 1.12450.0 98.1 1.36825 0.303 92.2 1.35206 0.0638 1.09960.0 98.1 1.36827 0.305 92.2 1.35199 0.0629 1.053

Table A-4: Data for distillate and bottom product for each sampling time

Time(min) Mole fraction of ethanol,x2 In L2 L2 Amount of ethanol left(litre)

5.0 0.06584.1481

9 63.3194 3.6972

10.0 0.06474.1451

8 63.1288 3.686120.0 0.0646 4.1449 63.1115 3.6851

30.0 0.06404.1432

6 63.008 3.6791

40.0 0.06394.1429

9 62.9908 3.6781

50.0 0.06384.1427

2 62.9736 3.677160.0 0.0629 4.1402 62.8192 3.6680

18

6

Table A-5: Data for amount of ethanol left in the evaporator for each sampling time

19

Appendix B

Experiment 9: Batch Distillation (Structure Packing) At Total Reflux

Sample Calculation

At 20oC,

Density of water, ρwater=0.99823 g/cm3

Density of ethanol, ρethanol=0.789 g/cm3

Relative molecular mass of water = 18.016 g/mol

Relative molecular mass of ethanol = 46.07 g/mol

To find the mol fraction of ethanol:

ne=mmr

= ρ vmr

n = no. of mol of ethanol

ρ = density of ethanol

v = volume of ethanol used

mr= relative molecular mass of ethanol

nw=mmr

= ρvmr

n = no. of mol of water

ρ = density of water

v = volume of water used

mr= relative molecular mass of water

mol fraction of ethanol =ne

ne+nw

For example, volume of ethanol used = 2 ml and volume of water used is 8 ml

ne=ρvmr

=0.789× 246.07

=0.03425 mol

nw=ρvmr

=0.99823 ×818.016

=0.44326 mol

Mol fraction of ethanol =ne

ne+nw

=0.07173 mol

20

To find the HETP,

1. Find the theoretical number of plates in the distillation unit using McCabe-Thiele

method.

2. Calculate the HETP.

Height of packing, H = 1m

HETP= Height of packing , Hnumber of theoretical platesneeded , N t

When heating power is 1.5kW,

Figure B-1: Equilibrium diagram for system ethanol-water when heating power is 1.5kW

Number of theoretical plates = 0.6588

HETP = 1

0.6588

HETP= 1.518

21




HETP = 1

0.7182 =1.392




HETP = 1

0.8798

HETP= 1.137

22




HETP = 1

0.9302

HETP= 1.075




HETP = 1

1.303

HETP= 0.767

23


The equation of the operating line for enriching section:

Reflux ratio = 3

At t=0,

yn+1=R

R+1xn+

xD

R+1

yn+1=3

3+1xn+

0.1593+1

∴ yn+1=0.75 xn+0.03975

When time is 5 min,

Figure B-6: Equilibrium diagram for system ethanol-water when time = 5 min


HETP = 1

0.6754

HETP= 1.481

24

When time is 10 min,



HETP = 1

0.6917 =1.446




HETP = 1

0.7852

HETP=1.2735

25




HETP = 1

0.8440

HETP=1.185




HETP = 1

0.8893 = 1.124

26

When time= 50min,



HETP = 1

0.9095

HETP= 1.099

When time= 60min,


Number of theoretical plates = 0. 9494

HETP = 1

0.9494

27

HETP= 1.053

The amount of the ethanol left:

The initial volume of ethanol in still, Vethanol = 4 Litres

The initial volume of water in still, Vwater = 12 Litres

The original number of moles of ethanol:

ne=ρvmr

=0.789× 400046.07

=68.504 mol

The original number of moles of water:

nw=ρvmr

=0.99823 ×1200018.016

=664.90 mol

Mol fraction of ethanol =ne

ne+nw

=0.0934

Rayleigh equation: ∫L2

L1

dLL

=lnL1

L2

=∫x2

x1

dxy−x

In L1-In L2 =∫x2

x1

dxy−x

L1 = initial moles of liquid originally in still

L2 = final moles of liquid remained in still

x1 = initial liquid composition in still (mole fraction of ethanol)

x2 = final liquid composition in still (mole fraction of ethanol)

y= initial composition of ethanol in the vapour

The feed composition of ethanol, x1 = 0.0934

The final composition of ethanol, x2 = 0.0629

From the equilibrium diagram of ethanol water mixture, the initial mole fraction of ethanol in

vapor, y = 0.43

ln 68.5−ln L2= ∫0.0629

0.0934dx

y−x

ln L2=ln ( y−0.0934 )−ln ( y−0.0629 )+4.227

ln L2=ln (0.43−0.0934 )−ln ( 0.43−0.0629 )+4.227

28

ln L2=4.140

L2=62.819 moles

The amount of the ethanol left in the evaporator =

46.07g

mol×62.819 moles

0.789g

cm3

= 3.668 litres

The same method of calculation is repeated to calculate the amount of ethanol left in the still

for different interval of time.

29

Appendix C

Figure C-1: The flow diagram of batch distillation unit (structured packing)

Figure C-2: Batch Packed Distillation Column (Model: BP81-SP)

30

batch distillation.docx

Documents

batch column

continuous distillation

batch stripper

type of distillation

distillation progresses

diagram of batch rectifier

distillation process

continuous column