ABSTRACT
Liquid-liquid extraction is a very important separation technology for a wide range of applications in the chemical process industries (CPI). (CPI). Liquid-liquid extraction is the process when the two phases are liquid where a solute or solutes are !eing removed from one liquid phase to another liquid phase. "he o!#ectives of this experiment are to conduct the simple experiments experiments regarding liquid-liquid liquid-liquid extraction extraction to determine determine the distri!uti distri!ution on coefficient coefficient for the system organic solvent-propionic acid water and show its dependence on concentration and to demonstrate how a mass !alance is performed on the extraction column and to measure the mass transf transfer er coeff coeffici icient ent with with the aqueous aqueous phase phase as the contin continuous uous medium medium.. "his "his experi experimen mentt is divided into two parts. $or the first part water and organic solvent is mixed with different volume of propionic acid. "wo layers are formed. %ample from each layers are ta&en and added with phenolphthalein phenolphthalein.. 'fter that it is titrated titrated with a*. $or the second part sample is ta&en from Liquid-liquid extraction unit +P, for feed raffinate and extract. Phenolphthalein is added to the samples. 'fter that it is titrated with different molarity of a*. $or !oth parts the volume of a* needed for the mixture to turns pin&ish-purple colour is recorded for further calculation.
INTRODUCTION
Liquid-liquid extraction is a very important separation technology for a wide range of applications in the chemical process industries (CPI). +nli&e distillation which is !ased on !oiling point differences extraction separates components co mponents !ased on their relative solu!ilities in two immisci!le liquids. xtraction is typically chosen over distillation for separation applications that would not !e cost-effective or even possi!le with distillation. Liquid-liquid extraction is the process when the two phases are liquid where a solute or solute solutess are !eing !eing remove removed d from from one liquid liquid phase phase to anothe anotherr liquid liquid phase. phase. Liquid Liquidli liqui quid d extraction also &nown as solvent extraction and partitioning is a method to separate compounds !ased on their relative solu!ilities solu!ilities in in two different immisci!le liquids usually water and an organic solvent. It is an extraction of a su!stance from one liquid into another liquid phase. Liquidliquid extraction is a !asic technique in chemical la!oratories where it is performed 1
using a variety of apparatus from separatory funnels to countercurrent distri!ution equipment. Liquidliquid extraction (LL) consists in transferring one (or more) solute(s) contained in a feed solution to another immisci!le liquid (solvent). "he solvent that is enriched in solute(s) is called extract. "he feed solution that is depleted in solute(s) is called raffinate. In a liquid-liquid extraction unit a liquid stream (carrier) containing the component(s) to !e recovered (solute) is fed into an extractor where it contacts a solvent. "he two liquids must !e immisci!le or only slightly misci!le/ this allows them to form a dispersion with one liquid dispersed as droplets in the other. 0ass transfer occurs !etween the droplets (dispersed phase) and the surrounding liquid (continuous phase). In order for the two liquids to !e su!sequently separated they must have different densities. "he droplets then accumulate a!ove or !elow the continuous phase depending on the liquids1 relative densities. "he !oundary !etween the continuous phase and the droplet dispersion is referred to as the interface and can !e at the top or !ottom of the extraction column.
Figure 12 Illustrates the general concept of liquid-liquid extraction.
xtraction is typically carried out in continuous staged units which can !e operated in either of two modes2 with co-current mixing or with counter-current mixing. "he co-current
2
mixing mode is generally limited to one theoretical stage per extraction unit whereas countercurrent mixing is amena!le to multiple stages per unit. $or this reason counter-current mixing is usually preferred over co-current mixing. Counter-current extractors can !e arranged in one of two ways ($igure 3) the choice of which depends on the density of the solvent relative to that of the solute carrier. If the solvent is less-dense than the carrier liquid the solvent is fed into the !ottom of the column the solute is carried upward to the top of the extractor and the carrier liquid is removed from the !ottom of the unit ($igure 3 left). If the solvent is more-dense than the carrier liquid the solvent is fed into the top of the column the solute is carried downward to the !ottom of the extractor and the carrier stream is removed from the top ($igure 3 right).
Figure 22 Counter-current extraction units can !e set up in one of two ways. Left2 4hen the solvent is lighter than the carrier liquid the solvent is introduced at the !ottom of the column and the solute is carried up toward the top of the extractor. 5ight2 4hen the solvent is heavier than the carrier the solvent is introduced at the top of the column and the solute is carried downward !y the solvent toward
3
OBJECTIVES
"he o!#ectives of this experiment2 6) "o conduct the simple experiments regarding liquid-liquid extraction. 3) "o determine the distri!ution coefficient for the system organic solvent-propionic acid water and show its dependence on concentration. 7) 8emonstrate how a mass !alance is performed on the extraction column and to measure the mass transfer coefficient with the aqueous phase as the con tinuous medium.
THEORY
' mixture was !rought into contact with another phase in order to separate one or more of the components in the mixture. Liquid-liquid extraction was considered as one of the separation method. 9y ta&ing advantage of a solu!ility differential of the su!stance in different solvents liquid-liquid extraction technique was used to purify impure su!stances. "wo different solvent were mixed together with the impure sample and one of them was referred to as the extracting solvent. "here would !e partition !etween the solvents since the sample was solu!le in !oth solvent. "he final ratio of the concentrations of the sample in the two solvents was determined !y its distri!ution (or partition) coefficient :. ' quantitative measure of the how an organic compound would !e distri!uted !etween aqueous and organic phases was called the distri!ution coefficient or distri!ution constant : descri!ed as2
K =
Y X
where ; was the concentration of the solute in the extract phase (extracting solvent) whereas < was the concentration of the solute in raffinate phase (original solvent). "he greater the concentration of sample in the extracting solvent the higher the distri!ution coefficient would !e that lead to more efficient of extraction. "he molecules would naturally distri!ute themselves in 4
the solvent where they were more solu!le once the system reached equili!rium. Inorganic and water solu!le materials would stay in the water layer and more organic molecules would remain in the organic layer. 's for trichloroethylene-propionic acid-water system using the liquid-liquid extraction unit +P, their mass !alances were as followed2 Propionic acid extracted from organic phase (raffinate) = >?(<6 <3) Propionic acid extracted !y aqueous phase (extract) = >w(;6 ?) "heoretically
>?(<6 <3) = >w(;6 ?)
where >w2 water flow rate L@s >?2 trichloroethylene flow rate L@s <2 propionic acid concentration in the organic phase &g@L ;2 propionic acid concentration in the aqueous phase &g@L and the su!script 6 for top of column while 3 for !ottom of column.
0ass transfer coefficient2
MTC =
Rate of acidtransfer volumeof packing× mean drivingforce
where log mean driving force
∆ x 1 2 driving force at top of column = (< - ?) 3 ∆ x2
¿
2 driving force at !ottom of column = (<6 <6A)
∆ x 1− ∆ x 2 ∆ x1 ¿( ) ∆ x2
5
<6A and <3A were the concentrations in the organic phase that would !e in equili!rium with concentrations ;6 and ;3 in the aqueous phase.
APPARATUS AND MATERIAL
6. 3,? mL conical flas&
3. ,? mL measuring cylinder 7. 6? mL measuring cylinder
B. 3,? mL separating funnel
6
,. ,? mL !urette
. Liquid-liquid extraction unit +P,
D. "richloroethylene E. %odium *ydroxide solution ( ?.6 0 and ?.?3, 0) F. Phenolphthalein 6?. Propionic acid 66. 4ater
7
PROCEDURE
xperiment Part ' 6. 3. 7. B. ,.
,? mL of trichloroethylene and ,? mL of water were added and mixed in a conical flas&. , mL of propionic acid was then added to the mixture. ' stopper was placed and the mixture was sha&e for , minutes. "he mixture was then poured into a separating funnel and was let to form layer of liquid. ach of the !ottom and upper samples were titrated against ?.6 0 a* using three
drops of phenolphthalein as the indicator. . 5ecord the value of titration needed to change the colour of mixture to light pin&. D. %teps 6 to were repeated for 7 mL and 6 mL of propionic acid added into the mixture. xperiment Part 9 6. 6?? mL of propionic acid was added to 6? L of trichloroethylene. "he mixture was then filled into the organic phase tan& (!ottom tan&). 3. "he level control was switched to the !ottom of the column !y &eeping the !ottom electrodes on (%3 valve was switched on). 7. "he water feed tan& was filled with 6, L of clean demineraliGed water (>67 valve was open). "he water feed pump was started (valve %7) and the flow rate of water was regulated to the maximum !y opening valve C6. B. "he flow rate was reduced to ?., L@min as the water reached the top pac&ing. ,. "he metering pump (%B) was started. . ' steady condition was achieved !y running the set up for 6,-3? minutes. "he flow rate was monitored during the period to ensure that it remain constant. D. "wo or three !atches of 7? mL sample were ta&en from the feed raffinate and extract stream (valve >6). E. 6? mL of each sample was titrated against ?.?3, 0 a* using phenolphthalein as the indicator (to titrate the feed and raffinate continuous stirring using magnetic stirrer would !e needed).
8
RESULT AND CALCULATION EXPERIMENT A
Concentration of
>olume of propionic
a* (0) Concentration of um!ers acid (mL) a*?.6 (0)
of titration 6 3 7 Average 6 3 7 Average
?.?3,
?.6
,.? 7.? 6.?
$eed E., E. F.? !" 7., 3., 7.? #!$
>olume of a* titrated (mL) >olume of a* titrated (mL) +pper 9ottom E? B3., xtract 5affinate ,? 36 7 7.B , 6?.F 7.? 66., 7., 6?. #!# 11!$ ?. ,. ?.E ,.B ?.D B., $!" %!1"
EXPERIMENT B
CALCULATIONS
$ormula2 $inding distri!ution coefficient2 : = ;@< 4here ;2 concentration of solute in extract phase 9
<2 concentration of solute in raffinate phase $inding mass transfer coefficient2 6
3 7 B ,
06>6 = 03>3 4here/ 06 concentration of a* 03 concentration of propionic acid >6 volume of a* >3 volume of propionic acid 5ate of acid transfer = >4 (;6 - ?) >? (<6 - <3) = >4 (;6 - ?) : = ;6 @
= r 3L = 3.7 J 6?-7m7 = 3.7L
D
0ass transfer coefficient =
5ate of acid transfer (>olume of pac&ing J mean driving force)
$inding the distri!ution coefficient2 $or ?.60 of a* 6
6.? ml of propionic acid +pper (;)2 06>6 = 03>3 (?.6)(?.?7) = 03 (?.??6) 03 = 7. 0
9ottom (<)2 06>6 = 03>3 (?.6)(?.?,) = 03 (?.??6) 03 = ., 0
: = ;@< = 7. 0 @ ., 0 = ?.,, 3
7.? ml of propionic acid +pper (;)2 06>6 = 03>3
9ottom (<)2 06>6 = 03>3 10
(?.6)(?.?,) = 03 (?.??7) 03 = 6.D 0
(?.6)(?.?36) = 03 (?.??7) 03 = ?.D 0
: = ;@< = 6.D 0 @ ?.D 0 = 3.7E 7
,.? ml of propionic acid +pper (;)2 06>6 = 03>3 (?.6)(?.?E) = 03 (?.??,) 03 = 6. 0
9ottom (<)2 06>6 = 03>3 (?.6)(?.?B3,) = 03 (?.??,) 03 = ?.E, 0
: = ;@< = 6. 0 @ ?.E, 0 = 6.EE
11
$inding the mass transfer coefficient2 $or ?.60 of a* 5affinate2 06>6 = 03>3 (?.6)(?.??,6D) = 03 (?.?6) 03 = ?.?,6D 0 of propionic acid KKK. (< 6) $eed2 06>6 = 03>3 (?.6)(?.??7) = 03 (?.?6) 03 = ?.?7 0 of propionic acid xtract2 06>6 = 03>3 (?.6)(?.???D) = 03 (?.?6) 03 = ?.??D 0 of propionic acid KKK. (;6)
5ate of acid transfer = >4 (;6 - ?) = ?.3 L@min (?.??D mol@L) = ?.??6B mol@min
>? (<6 - <3) = >4 (;6 - ?) ?.3 L@min (?.?,6D mol@min <3) = ?.??6B mol@min <3 = ?.?BBD 0
12
Log mean drive force = (H<6 - H<3) @ ln (H<6 @ H<3) H<6 = (<3 ?) = ?.?BBD 0 : = ;6 @
at equili!rium assume 5 = 6.BD (from experiment ')
5ate of acid transfer (>olume of pac&ing J mean driving force) =
?.??6B mol@min 3.7 L J ?.?B6F
= ?.?6B [email protected] = ?.?6B 0@min = ?.?6B &g@min
13
DISCUSSION
Liquid-liquid extraction is process which is used to separate chemicals in liquid mixture !y adding immisci!le solvent. "he aim of this experiment is to determine the distri!ution coefficient and the mass transfer coefficient. In the first experiment the mixture of trichloroethylene propionic acid-water is separated !y using separator funnel. 0ost extractions will involve water !ecause it is highly polar and immisci!le with most organic solvent. "he chemicals is sha&e for , minutes to ma&e sure the two solutions is in contact which each other to allow solute to !e extracted into the second layer. 'fter the mixing is done the mixture will !e pour into separator funnel and split into two layers. "he densities of the solvent will predict which solvent is the upper or lower layer (Lewis 3??D). %ince water is denser than propionic acid it forms two la yers which the upper layer contains propionic acid meanwhile the !ottom layer contains water. $rom the experiment the value of upper layer concentration when ,.? ml and 7.? ml of propionic acid is added is larger than the value of lower layer concentration except for 6.? ml of propionic acid. "he distri!ution coefficient : is calculated !y divided the concentration solute in extract phase with concentration solute in raffinate phase. "he concentration of sodium hydroxide used to titrate the upper and lower layer is ?.60. "he distri!ution coefficient when ,.? ml 7? ml and 6.?ml of propionic acid is added is 6.EE 3.7E and ?.,, respectively. It can !e said that the distri!ution coefficient from ,.? ml to 6.? ml of propionic acid is not consistent/ it increased at 7.? ml of propionic acid and then decreased. 't equili!rium the molecules naturally distri!ute themselves in the solvent where they are more solu!le. Inorganic and water solu!le materials will stay in the water layer and more organic molecules will remain in the organic layer (Lewis 3??D). 4hich in this experiment from the calculated distri!ution coefficient and for volume of propionic acid of ,.? ml and 7.? ml the solute is mostly in organic solvent meanwhile for volume of 6.? ml the solute is mostly in water. In experiment 9 the feed extract and raffinate are o!tained from liquid-liquid extraction column. $rom this information we can calculate the mass transfer coefficient. "he sample then is titrated with ?.6 0 and ?.?3,0 a*. "he mass transfer coefficient value when titrated with ?.60 is ?.?6B&g@min meanwhile for ?.?3, 0 a* the value cannot !e calculated as the distri!ution coefficient for ?.?3,0 cannot !e o!tained !ecause experiment ' is not repeat using ?.?3,0 of a*. 14
CONCLUSION
$rom the experiment ' the distri!ution coefficient calculated from the concentration solute in extract and raffinate for each different value of propionic acid/ ,.? ml 7.?ml and 6.? ml is 6.EE 3.7E and ?.,, respectively. "he solute is mostly in organic solvent for value of propionic acid/ ,.? ml 7.?ml meanwhile for volume of 6.? ml the solute is mostly in water. "he mass transfer coefficient for ?.60 is ?.?6B&g@min. "he mass transfer coefficient will differ according to the concentration of a* used. In conclusion the main o!#ective of this experiment to determine the distri!ution coefficient and mass transfer coefficient are achieved successfully. RECOMMENDATION&
6
0a&e sure the colour change after the titration should approximately a!out the same
3
colour on each other. 0a&e sure the eyes are perpendicular with the meniscus of the !urrete when ta&ing
7 B ,
reading. 0a&e sure to rinse all the apparatus !efore used it repeatly with another su!stance. 0a&e sure to use the correct concentration of sodium hydroxide when titrate. 5epeat the experiment at least 7 times to get an accurate value. 0a&e sure to wear appropriate personal protective equipment (PP) when conducting the experiment.
REFERENCES 15
Lewis 5. . (3??D). Liquid-liquid xtraction. PreLab D7F3. doi26?.6??3@FDE?BD?66BD7,.hawley?FEFF 'nonymous (3?63). Liquid/ Liquid Extraction Unit (UOP5). 5etrieved 'pril 3 3?6 from https2@@eng.na#ah.edu@apparatus@37E6 8esign
principles
of
liquid-liquid
extractions.
5etrieved
'pril
3E
3?6
from
http2@@www.aiche.org@resources@pu!lications@cep@3?6,@novem!er@design-principles-liquid-liquidextraction. Mean&oplis C.. (3?6B). "ransport Processes N %eparation Process Principle (includes unit operations). Pearson ducation Limited.
APPENDIX 16
17
