ABSTRACT

We know that liquid liquid extraction is crucial in our industry, where it is used in

washing acid, in extraction for valuable products from fermentation broth, purification in heat

sensitive materials and others. This Liquid-liquid Extraction experiment is divided into two parts.

The objective of the first experiment is to determine the distribution coefficient for the system

orgnic solvent-propionic acid – water and to show its dependence on concentration. The

objective of the second experiment is to demonstrate how a mass balance is performed on the

extraction column and to measure the mass transfer coefficient with the aqueous phase as the

continuous medium. In the first experiment, we are required to titrate NaOH to two different

layers which are aqueous and organic layer with different volume of propionic acid required. The

first trial is with 5ml of propionic acid and then followed by 3ml and 1ml of propionic acid. The

results are then recorded and as the value of distribution coefficient, K for 5ml, 3ml and 1ml of

Propionic Acid are 0.70, 0.41, and 0.74 respectively. In the second experiment, liquid liquid

extraction column is used in order to collect feed, raffinate, and extract which all these 3 will be

titrated with 0.1M and 0.025M of NaOH solution. The data of how much of NaOH in mL needed

the solution to turn light pink is recorded. The value of the mass transfer coefficient calculated is

0.3556 kg/min for 0.1 M NaOH, while 0.044 kg/min for concentration of 0.025 M of NaOH. The

experiment is considered succeed.

1

INTRODUCTION

Liquid-liquid extraction can be defined as transferring one or more solute(s) contained in

a feed solution to another immiscible liquid (solvent). The solvent that is enriched in solute(s) is

called extract. The feed solution that is depleted in solute(s) is called raffinate. This experiment

is about to extract substance from liquid phase into another liquid phase performed using a

separator funnel.

In order to separate a substance from a mixture, we dissolve the substance in a suitable

solvent. By dissolving the substance, we can separate the soluble compound from an insoluble

compound.

As we know, the title of this experiment is liquid liquid extraction, thus the main process

involved is extraction. Extraction involves the contacting of a solution with another solvent that

is immiscible with the original. Due to different densities, two phases are formed after the

addition of the solvent. Mass transfer will occur when the solute in the solution has more affinity

towards the added solvent.

Figure 1: Liquid liquid extraction unit

There are two types of streams exist in general extraction column which are input stream

and output stream. The solvent metering pump is calibrated in percentage of maximum flow

which varies slightly from pump to pump. Initially, the pump should be calibrated by setting F2

2

to 100%, setting valve V8 to the calibrate position and measuring the flow from the pump, using

a measuring cylinder and stopwatch. We need to calculate the flow rate produced settings of 10%

intervals (mL per minute), then plot a graph of mL per minute against percentage of metering

pump stroke to obtain any selected flow using the graph.

OBJECTIVES

The objectives of this experiment are:

To conduct the experiments regarding liquid-liquid extraction.

To determine the distribution coefficient for the system of organic solvent-propionic

acid-water and show its dependence on concentration.

Demonstrate how a mass balance is performed on the extraction column and to measure

the mass transfer coefficient with the aqueous phase as the continuous medium.

3

THEORY

Liquid-liquid extraction is a useful method to separate components or compounds of a mixture.

The extraction is based on the transfer of a solute substance from a liquid phase into another

liquid phase according to the solubility.

At an equilibrium, in a dilute solution, the concentration of the solute in the two phases are called

the distribution coefficient or distribution constant, K and describes in the following formula:

K = Y/X

Y: is the concentration of the solute in the extract phase

X: is the concentration of the solute in raffinate phase

The distribution coefficient can also be described as the weight fraction of the solute in the two

phases in equilibrium constant:

K= y’/x

y’: is the weight fraction of the solute in the extract

x: is the weight fraction of the solute in the raffinate

The rate at which a soluble component is transferred from one solvent to another will be

dependent, including on the interface between the two immiscible liquids. Thus, the situation is

an advantage for an interface between two immiscible liquids.

For the system Trichloroethylene-Propionic Acid-Water is described as follows:

Mass Balance:

Propionic acid extracted from the organic phase in raffinate,

¿V o(X1−X2)

4

Propionic acid extracted by the aqueous in the extractor,

¿V w (Y 1−0)

Thus, the theoretically,

V o (X1−X2 )=V w(Y 1−0)

Mass transfer coefficient,

¿ Rateof acid transferVolumeof packing xMeandriving force

Let

V w : Water flow rate, L/s

V o : Trichloroethylene flow rater, L/s

X : Propionic acid concentration in the organic phase, kg/L

Y : Propionic acid concentration in the aqueous phase, kg/L

Subscripts : 1: Top column

2: Bottom column

Log mean driving force is given as, ∆ X1−∆ X2

ln (X1−∆ X2)

∆ X1: Driving force at the top of the column = (X 2−0)

∆ X2: Driving force at the bottom of the column = (X 1−X1¿)

X1¿ is the concentration in the organic phase which would be in equilibrium with concentration

Y 1 in the aqueous phase. The equilibrium values can be found using the distribution coefficient

found in the first experiment.

5

APPARATUS

250 ml conical flask stoppered flask

250 ml measuring cylinder

250 ml separating funnel

Pipette with rubber bulb

Burette

Sodium Hydroxide solution (0.1M)

Phenolphthalein

Propionic acid

6

PROCEDURE

Experiment A:

1. A mixture of 50 ml organic solvent and 50 ml of demineralised are made up in a conical

flask.

2. 5 ml of propionic acid is added. 5ml can be pipette into the flask using a pipette with a

rubber bulb.

3. A stopper is placed into a flask and it is shaken for a minimum of 5 minutes.

4. It is then poured into a separating funnel and it is left for 5 minutes. Later, the lower

aqueous later is removed.

5. A 10 ml of sample of the layer is taken and titrated against 0.1M sodium hydroxide

solution using phenolphthalein as indicator.

6. The experiment is repeated for two further concentration of propionic acid. For example,

for initial additions of 3 ml and 1 ml of propionic acid.

Experiment B:

1. 100 ml of propionic acid is added to 10 litres of organic phase. The mixture is mixed well

to ensure an even concentration then the organic phase feed tank (bottom tank) is filled

with the mixture.

2. The level control is switched to the bottom of the column (electrode switch S2)

3. The water feed tank is filled with 15 litres of clean demineralised water, the water feed

pump is started and the column is filled with water at a high flow rate.

4. As soon as the water is above the top of the packing, the flow rate is reduced to 0.21 litre

per minute.

5. The metering pump is started and a flow rate is set to 0.2 litre per minute.

6. The unit is ran for 15 to 20 minutes until steady conditions are achieved, the flow rates

are monitored during this period to ensure that they remain constant.

7. 15ml of sample from the feed, raffinate and extract streams are taken. It is ensured to not

use the calibration valve V8 for taking feed samples.

8. 10 ml of each sample is titrated against 0.1M NaOH using phenolphthalein as the

indicator.

7

Note: To titrate the feed and raffinate they need continuous stirring using magnetic stirrer. As an

alternative, 0.025 M NaOH may be used which lead to phase inversion of raffinate and feed

streams so that the aqueous is the continuous phase.

8

RESULT AND CALCULATIONS

EXPERIMENT A

DETERMINATION OF DISTRIBUTION COEFFICIENT OF SOLUTION WITH WATER AND ITS DEPENDENCE ON CONCENTRATION

PROPANOIC ACID ADDED (Ml)

AQUEOUS LAYER ORGANIC LAYER K=Y/X

TITRE OF M/10 NaOH(mL)

PROPIIONIC CONCENTRATION(Y)

TITRE OF M/10 NaOH(mL)

PROPIIONIC CONCENTRATION(X)

5 50 1.00 71 1.43 0.70

3 15 0.50 36.8 1.23 0.41

1 13 1.30 17.5 1.75 0.74

9

EXPERIMENT B :

DEMONSTRATING A MASS BALANCE IN THE EXTRACTION COLUMN AND MEASURING THE MASS COEFFICIENT, K, WITH AUQEOUS PHASE AS THE CONTINOUS MEDIUM

FLOW RATE OF AQUEOUS PHASE

(L/ min)

0.2

FLOW RATE OF ORGANIC PHASE

(L/ min)

0.2

SODIUM HYDROXIDE

CONCENTRATION (M)

0.1 M 0.025 M CONCENTRATION OF PROPIONIC ACID (M)

0.1 M 0.025 M

FEED (mL) 17.0 54.1 0.17 0.14RAFFINATE (mL) 10.0 15.0 0.10 0.04EXTRACT (mL) 6.0 23.2 0.06 0.06

PROPIONIC ACID EXTRACTED FROM THE

ORGANIC PHASE (mol/min)

0.04 0.03PACKING DIMENSIONS :

LENGTH: 1.2 mDIAMETER : 50 mm

PROPIONIC ACID EXTRACTED FROM THE

AQUEOUS PHASE (mol/min)

0.012 0.0025

MASS TRANSFER COEFFICIENT

(kg/min )

0.3556 0.044

10

SAMPLE CALCULATIONS:

Exper iment A

1) Ca l cu l a t i on o f concen t r a t i on (Aqueous )

( 5ml P rop ion i c Ac id )

Fo rmu la : M1V1 = M2V2

M1 = Concen t r a t i on o f NaOH (mo le s )

V1 = Vo lume o f NaOH (ml )

M2 = Concen t r a t i on o f P rop ion i c a c id (mo le s )

V2 = Vo lume o f P rop ion i c a c id (m l )

(0 .1 ) (50 ml ) = M2(5ml )

M1 = 1 .00 M

(3ml P rop ion i c Ac id )

( 0 .1 ) (15 ml ) = M2(3ml )

M2 = 0 .50 M

(1ml P rop ion i c Ac id )

( 0 .1 ) (13 ml ) = M2(1ml )

M2 = 1 .3 M

Ca lcu l a t i on o f concen t r a t i on (0 rgan i c )

( 5ml P rop ion i c Ac id )

( 0 .1 ) (71 ml ) = M2(5ml )

M1 = 1 .42 M

11

( 3ml P rop ion i c Ac id )

( 0 .1 ) (36 .8 ml ) = M2(3ml )

M2 = 1 .23 M

(1ml P rop ion i c Ac id )

( 0 .1 ) (17 .5 ml ) = M2(1ml )

M1 = 1 .75 M

2) Ca l cu l a t i on o f D i s t r i bu t i on Coe f f i c i en t , K :

D i s t r i bu t i on coe f f i c i en t ( 5ml P rop ion i c Ac id )

Fo rmu la : K = Concen t r a t i on o f t he so lu t e i n t he ex t r ac t phase , Y

Concen t r a t i on o f t he so lu t e i n t he r a f f i na t e phase , X

K = 1 .00 M

1 . 43M

K = 0 .70

D i s t r i bu t i on coe f f i c i en t ( 3 m l P rop ion i c Ac id )

K = 0 .50 M

1 . 23 M

K = 0 .41

Di s t r i bu t i on coe f f i c i en t ( 1 m l P rop ion i c Ac id )

12

K = 1 .30 M

1 . 75 M

K = 0 .74

Expe r imen t B

1) Concen t r a t i on o f P rop ion i c Ac id a t f e ed :

Fo rmu la : M1V1 = M2V2

(0 .1 ) (17 .0 ml ) = M2(10ml )

M 2 = 0 .17M

Concen t r a t i on o f P rop ion i c Ac id a t Ra f f i na t e (X1)

( 0 .1 ) (10 .0 ml ) = M2(10ml )

M2 = 0 .1M

Concen t r a t i on o f P rop ion i c Ac id a t Ex t r ac t (Y1)

( 0 . 1 ) (6 .0 m l ) = M2(10ml )

M2 = 0 .06 M

2) The f l ow r a t e o f aqueous and o rgan i c phase = 0 .2 L /min

3 ) Ra t e o f a c id t r ans f e r = Vw (Y1 - 0 )

= 0 .2 (0 .06 - 0 )

= 0 .012 mo l /min

0 .012 kg / s = Vo (X1 - X2)

= 0 .2 (0 .1 – X2)

X2 = 0 .04 mo l /min = 0 .04 M

13

4) Log mean d r i v ing fo r ce =

ΔX1 - ΔX2

lnΔX1

ΔX2

To ca l cu l a t e t he X 1* , c a l cu l a t e t he ave rage d i s t r i bu t i on coe f f i c i en t f r om

expe r imen t A

K = 0 .70 +0 .41+0 .74

3

K = 0 .62

Y1 = 0 .06 M

K = Y1 X1

*

X 1* = 0 .097M

∆ X 1 = ( X2-0 )= 0 .04 M

∆ X 2 = ( X1-X 1* )= 0 .1 -0 .097=0 .003

Log mean d r i v ing fo r ce =

ΔX1 - ΔX2

lnΔX1

ΔX2

= (0 .04 ) - (0 .003 )

ln ( 0.040.003)

= 0 .0143

5) Mass t r ans f e r coe f f i c i en t ( ba sed on t he r a f f i na t e phase )

14

=

Rate of Acid TransferVolume of Packing × Mean Driving Force

= 0 . 012

2 . 36 x0 .0143

= 0 .3556 kg /min

*us ing t he s ame way ca l cu l a t e fo r 0 .025 M NaOH

15

DISCUSSION

The experiment liquid-liquid extraction was conducted in the purpose of determining the

coefficient distribution, K as well as the mass transfer coefficient. For that, the experiment was

divided into two parts with each carrying a different objective. The extraction method that was

used is based on the relative principle of solubility where a solution can be separated and

extracted into its individual component.

For first part of the experiment, which is to determine the distribution of coefficient,

titration method is carried out between a solution against 0.1M Sodium Hydroxide (NaOH). The

solution is made up of 50 mL organic solvent and another 50 mL de-mineralized water that is

also added with 5 mL of propionic acid. The mixture was then shaken for 5 minutes in a stopper-

enclosed beaker. This step is repeated with an addition of 3 mL and 1 mL of propionic acid. Due

to the immiscibility of both liquids, a two-layer solution was formed and titration was carried out

for both layers. The bottom part is known the aqueous layer whereas the upper is called as the

organic layer. Titration was carried out until the colour changed from colourless to light pink

where the amount of NaOH used was recorded.

Based on the results, it is shown that with the addition of 5 mL propionic acid, it took 50

mL and 71 mL of NaOH for the aqueous and organic layer to change colour respectively. Based

on these, the distribution coefficient, K was calculated to be 0.70. Next, for the addition of 3 mL

propanoic acid, it took 15 mL and 36.8 mL of NaOH for the aqueous and organic layer

respectively with the K calculated to be 0.41. Finally, with 1 mL addition of propionic acid, the

amount of NaOH that was needed was 13 mL and 17.5 mL for aqueous and organic layer

respectively. The mass transfer coefficient for this trial is 0.74.

Based on the calculations done for the distribution coefficients, it can be seen that as the

volume of propionic acid added increases, the value of K decreases. However, for the case of 1

mL propionic acid addition, the value of K had been gotten as 0.74, which is higher than the

other two values. This is possibly due an error that had occurred during the titration process

when the amount of NaOH titrated was not stopped when the solution turned pink. This is

because the colour change was a sudden process and to get the exact amount on that point was

16

quite difficult to achieve. Theoretically, the distribution coefficient K should be inversely

proportional to the volume of the propionic acid whereby the addition of propionic acid will

decrease the value of K.

In the second part of the experiment, which is to determine the mass transfer coefficient,

the liquid-liquid extraction column is used to obtain the feed, raffinate and extract solution. The

flow rate used for the whole experiment is 0.2 L/min. 15 mL of feed, raffinate and extract

solution is obtained from the liquid extraction column after 15 to 20 minutes the system is at the

steady condition. The samples used in the titration process are 0.1 M and 0.025M of Sodium

Hydroxide, NaOH solution. Calculations where then done based on the data collected to obtain

the mass transfer coefficient. For the sample of 0.1 M NaOH, the propionic acid extracted from

organic phase is 0.04 mol/min and the aqueous phase is 0.012 mol/min. On the other hand, for

the sample of 0.025 M of NaOH, the propionic acid extracted from organic phase and aqueous

phase are 0.03 mol/min and 0.025 mol/min respectively. Finally, the mass transfer by titration of

0.1M NaOH is calculated to be 0.3556 kg/min meanwhile for the 0.025M NaOH is 0.044

kg/min.

17

CONCLUSION

The objective of this experiments are to conduct the experiments regarding liquid-liquid

extraction and to determine the distribution coefficient for the system of organic solvent-

propionic acid-water and show its dependence on concentration. Besides, we are also

demonstrated how a mass balance is performed on the extraction column and to measure the

mass transfer coefficient with the aqueous phase as the continuous medium. Based on the

experiment 1, the distribution coefficient for the system recorded is 0.74. It can be seen that as the

volume of propionic acid added increases, the value of K decreases. However, the results does not follow

theoretically which is the distribution coefficient K should be inversely proportional to the volume of the

propionic acid whereby the addition of propionic acid will decrease the value of K. For the second

experiment, the mass transfer by titration of 0.1M NaOH is calculated to be 0.3556 kg/min meanwhile for

the 0.025M NaOH is 0.044 kg/min. In conclusion, both experiments were conducted safely and

successfully except for the some errors during the experiments.

18

RECOMMENDATION

From the experiment that we have conducted, there are several recommendations that can

be taken to obtain more accurate results which do not differ much from the theoretical values and

observations. Before starting the experiment, we need to make sure that we have our safety attire

such as lab coat, safety helmet, and fully covered shoes to handle the experiment. We also need

to make sure the unit is checked properly where it is in a good conditions and follow the

procedures properly. If needed, use the medical gloves to avoid any solution in contact with our

hands. During titration, it needs to be made in the fume chamber to avoid us inhaling any toxic

gases and so the gaseous produced is sucked immediately when there is a gas released in a

chemical reaction. Also during titration, make sure the titration is stopped until a light pink

solution is formed to get the accurate result. When taking the reading of the volume of sodium

hydroxide titrated, avoid parallax error by making sure that eyes level is perpendicular with the

scale of the burette.

19

REFERENCES

1. Thermopedia. (2011). Extraction, Liquid-liquid. Retrieved 7 November 2014, from

http://www.thermopedia.com/content/752/

2. M. Lovric. (2000). Liquid-liquid extraction. Retrieved 7 November 2014, from

http://en.wikipedia.org/wiki/Liquid%E2%80%93liquid_extraction

3. Chemwiki (2001). Liquid liquid extraction. Retrieved 7 November 2014, from

http://chemwiki.ucdavis.edu/Reference/Lab_Techniques/Liquid-Liquid_Extraction

4. Organic Chemistry. (2014). Extraction. Retrieved 7 November 2014, from

http://orgchem.colorado.edu/Technique/Procedures/Extraction/Extraction.html

5. Liquid-Liquid Extraction Theory, Julie Lawson, 2007, Department of Chemical

Engineering Units.

20

APPENDIX

21