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ABSTRACT / SUMMARY

The goal of this experiment is to understand the behavior of solubility, mass transfer and

diffusion of the solute from one liquid phase to another liquid phase through

liquid-liquid extraction in a packed column. This experiment are separated into

two parts, which is part A and part B. art A is to determine the distribution

coefficient for the system organic solvent-ropionic acid-water and to show it

dependence on concentration and part B 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. !n the first part, mixture of

organic solvent with de-mineralised water that mixture has been separated to the

organic and aqueous layer. Then "# m$ of the organic and aqueous layer has been

titrated with #." % of &a'( with the addition of different amount of propionic

acid which are " m$ ) m$ and * m$. !n experiment B, *# m$ sample from feed

+", raffinate +"" and extract +" stream are taken. Then "# m$ of feed,

raffinate and extract has been titrated with different amount of &a'(. /hich are

#." % and #.#)* % . After the calculation, the value of mass

transfer coecient is 144561. The experiment is conducted and

completed successfully.

INTRODUCTION

$iquid-liquid extraction can be defined as a separation process that requires the removal

of desired solute component using two immiscible liquids of different density. The feed mixture

contains two components which is the solute and the diluent. 0olute is the component needed to

be extracted and diluent is it1s carrier. As the feed enters, the solute will diffuse into another liquid

known as solvent. $ater, the solvent carrying the solute comes out as an extract. !n the other hand,

the feed without the solute is withdrawn as raffinate. The three ma2or steps involved in this

liquid-liquid extraction process is mixing, phase seperation and withdrawal of phase form the

process unit.

3urthermore, appropriate solvent is required to increase the efficiency of separation

process. 4xamples of two common immiscible solvents are water-ether and water-hexane. /ater


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as a non-polar compound plays a vital role in extraction by not mixing with most of the organic

solvents. 3urthermore, the extracted solute should not be soluble in water but must be soluble in

organic solvent. 3or instance, ben5ene has low solubility in water thus, it it easier to extract it

from water. There are several criterias to be considered before chosing a solvent for liquid-liquid

extraction process. 0olvent needs to have high density differences so that it can be seperated

rapidly by gravity. 0olvents with low viscosity will help to increase overall mass transfer in the

process. !t is also important that the solvent is highly compatible with the solute and carrier. This

is to prevent contamination or any formation of foreign matters, emulsions, and scum layers.

Besides, solvents that are non-toxic, non-flammable and with high flash point promotes a safe

separation system.

$iquid-liquid extraction is widely used in many industries. !n general, this process will be

aided by distillation as the extracted product still contain some amount of solvent. Besides, liquid-

liquid extraction is highly preferred for temperature sensitive products, components with close

boiling point but high solubility differences, seperation based on species type and a5eotrope-

forming mixtures. There are several types of units for this seperation process such as tray column,

packed column, pulsating and agitation. !n addition, some of the application of liquid-liquid

extraction process in industries are uranium recovery in nuclear industry, extraction of bitumen

from water in effluent treatmment, extraction of essential oils in pharmeceutical industry and

copper6iron seperation in mining.

!n liquid-liquid extraction, as in gas absorption and distillation, two phases must be

brought into contact to permit transfer of material and then be separated. 4xtraction equipment

may be operated batchwise or continuous. The extract is the layer of solvent plus extracted solute

and the raffinate is the layer from which solute has been removed. The extract may be lighter or

heavier than the raffinate, and so the extract may be shown coming from top of the equipment in

some cases and from the bottom in others. The operation may of course be repeated if more than

one contact is required, but when the quantities involved are large and several contacts are

needed, continuous flow becomes economical.

!f the components of the original solution distribute differently between the two liquids,

separation will result. The component balances will be essentially identical to those

for leaching , but there are two ma2or differences which are the carrier phase is a liquid, not a

solid, so the physical separation technique will change and two distinct phases develop, so the

simplicity of uniform solution is lost.

http://www.cbu.edu/~rprice/lectures/leach.htmlhttp://www.cbu.edu/~rprice/lectures/leach.htmlhttp://www.cbu.edu/~rprice/lectures/leach.html


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ropionic acid is an important commercial product and extracting it out of aqueous

solution is a growing requirement in fermentation based industries and recovery from waste

streams.


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OBJECTIVES

!n experiment art A, the ob2ectives are to determine the distribution coefficient for

the system organic solvent 7 propionic acid 7 water as well as to its dependence on

concentration. %eanwhile, the ob2ectives of experiment art B are todemonstrate 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.

THEORY

!n dilute solution at equilibrium, the concentrations of the solute in the two phases are called

the distribution coefficient or distribution constant 8, as describe in the followings9

K = Y/X ..............(1)

where : is the concentration of the solute in the extract phase whereas ; is the concentration of

the solute in raffinate phase. The distribution coefficient can also be expressed as

the weight fraction of the solute in the two phases in equilibrium contact9

K = y’/x ................(2)

where y1 is the weight fraction of the solute in the extract and x is the weight fraction of the solute

in the raffinate.


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Th !h"#y $"# !h %y%!& T#'h"#"!hy*+,#"-'"*' '+0!# '% % $""%

$et>

w 9 /ater flow rate, $6s

o 9 Trichloroethylene flow rate, $6s

; 9 ropionic acid concentration in the organic phase, kg6$

: 9 ropionic acid concentration in the aqueous phase, kg6$

0ubscripts 9 " 9 Top of column

9 ) 9 Bottom of column

M%% B*

ropionic acid extracted from the organic phase +raffinate.

?o+;"@;) .................+

ropionic acid extracted by the aqueous phase +extract

?w+:"@# ..................+

Therefore theoretically,

o+;"@;) ? w+:"@# ...................+*

M%% !#*%$# "$$''*!

MTC ? ......................+ ,,.+,,,+

force g meandrivin packing of vol

transfer acid of Rate

×


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where $og mean driving force 9 +C;"-C;) 6 ln +C;"6C;)

C;" 9 Driving force at the top of the column ? +;) - #

C;) 9 Driving force at the bottom of the column ? +;"-;"E

where ;"E and ;)

E are the concentrations in the organic phase which would be in equilibrium with

concentrations :" and :) + ? #.# in the aqueous phase, respectively. The

equilibrium values can be found using the distribution coefficient for the chemicals

used +Assume that : ? 8 ; relation holds at equilibrium for a constant 8. Fate of

acid transfer may be calculated using 4quation + or + based on raffinate or

extract phases, respectively.


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,ROCEDURE

4xperiment art A

". *# ml of trichloroethylene was mixed with *#ml water in conical flask. Then )ml of

propionic acid was added to the mixture.

). A stopper is placed and the mixture is shaken for * minutes.

. The mixture is then separated using the separation funnel.

. 4ach of the bottom and upper samples is titrated against #."% &a'( using different amount

of phenolphthalein as the indicator. +* m$, m$, " m$

4xperiment art B

Extraction

Product

Control panel

eed


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". "##m$ of propionic acid was added to "# litres of trichloroethylene. The mixture is then

filled into the organic phase tank +bottom tank.

). The level control is switched to the bottom of the column by keeping the bottom electrodes

on +the 0) valve is switched on.

. The water feed tank was filled with "* litres of clean demineralised water +the " valve

was open. The water feed pump was started +valve 0 and the flow rate of water was

regulated to the maximum by opening valve G".

. The flow rate is reduced to #.* litre6min as soon as the water reaches the top packing.

*. The metering pump +0 is started.

. 0teady conditions must be achieved by running the set up for "*-)# minutes. The flow rate is

monitored during the period to ensure that they remain constant.

H. Two or three batches of # ml sample are taken from the feed, raffinate and extract streams

+valve ".

I. "# ml of each sample is titrated against #.#)*% &a'( using phenolphthalein as the indicator

+to titrate the feed and raffinate continuous stirring using magnetic stirrer may be needed.

RE3ERENCE

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