Transcription of SOLVENT EXTRACTION
1 SOLVENT EXTRACTIONC ontent Introduction Principle of SOLVENT EXTRACTION Distribution coefficient Distribution ratio Relation between Distribution coefficient and distribution ratio Factors affecting SOLVENT EXTRACTION , separation factor Batch EXTRACTION Countercurrent EXTRACTION Application of SOLVENT EXTRACTION Numerical problems Solventextraction,alsocalledliquid-liqui dextraction(LLE)andpartitioning Solventextractionistheprocessinwhichacom poundtransfersfromonesolventtoanotherowi ngtothedifferenceinsolubilityordistribut ioncoefficientbetweenthesetwoimmiscible( orslightlysoluble)solvents. Itisamethodofquantitativeseparationofcom pounds. Whenextractingsolventisstirredwithsoluti oncontainingsolutethensolutefromoriginal solventgetstransferredintoanextractingso lvent.
2 Whenstirringisstoppedextractingsolventfo rmseparatelayerandnowitcontainssoluteofi nterest. Comparedwithotherseparationmethods,itgiv esabetterseparationeffectthanchemicalpre cipitation,andahigherdegreeofselectivity andfastermasstransferthantheionexchangem ethod. Comparedwithdistillation,solventextracti onhasadvantagessuchaslowenergyconsumptio n,largeproductioncapacity,fastaction, used solvents ethyl acetate( %), diethyl ether ( %), dichloromethane ( %) and chloroform( %) dissolved up to 10 % in water. Water also dissolves in organic solvents: ethyl acetate(3 %), diethyl ether ( %), dichloromethane ( %) chloroform( %).Uses of SOLVENT EXTRACTION process Solventextractionisusedintheprocessingof perfumes,vegetableoil,orbiodiesel.
3 Itisalsousedtorecoverplutoniumfromirradi atednuclearfuel,aprocesswhichisusuallyca llednuclearreprocessing. (wellbelowthemeltingpointofthesolute) to be considered Thesolventshouldbeabletodissolveatleasto necomponenttoalargeextentthantherestofth ecomponentsinthemixture. Thecompoundformedafterthereactionshouldb eeasilyseparatedfromtheextractedcompound sothatitcanbereused. Thedensityofthecompoundshouldbedifferent fromtherequiredcomponenttohelptheseparat ionreadily. Itshouldbeinexpensiveandcost-effective. Thesolventshouldnotbetoxicorcorrosiveasi tcanharmtheextractioninstruments. Otherfactorsimportantduringsolventselect ionareviscosity,boilingpoint,flammabilit y, coefficient Whenasolutionisplacedinaseparatoryfunnel andshakenwithanimmisciblesolvent,solutes oftendissolveinpartintobothlayers.
4 Thecomponentsaresaidto"partition"between thetwolayers,or"distributethemselves"bet weenthetwolayers. Whenequilibriumhasestablished,theratioof concentrationofsoluteineachlayerisconsta ntforeachsystem,andthiscanberepresentedb yavalueK Kiscalledthepartitioncoefficientordistri butioncoefficient. KD=Molarityinorganicphase/Molarityinaque ousphaseDistribution coefficient Whenacompoundisplacedincontactwithtwoimm iscibleliquidsthenthecompounditselfgetdi stributedinthesetwoliquids. Thisisanequilibriumprocess(dissolutioneq uilibrium)governedbytemperatureofthesyst em. SupposecompoundAistobeextractedfromaqueo ussolutionintoorganicliquid,thenforcompo undA,dissolutionequilibriumcanberepresen tedbytheequation A (aq) A (org)Distribution coefficient Underdissolutionequilibriumconcentration ofcompoundAinaqueousphaseandinorganicpha seisdefinite.
5 KD=Concentration in organic phase / Concentration in aqueous phaseAmount remain extracted Fromequilibriumcoefficientitisclearthats omequantityofacompoundwillremainunextrac tedinaqueousphase. Insingleextraction,quantitativeseparatio nofacompoundfromaqueousphaseintoorganicp haseisnotpossible. Thusforquantitativeextractionofacompound fromaqueousphaseintoorganicphase, Xa[ ]Where, volumeofaqueousphasetakenforextractionV0 Volumeoforganicphaseusedforextractionata timeinmultipleextractionVaqKDV0+ VaqEfficiency of EXTRACTION Percentextractionisanothertermusedinsolv entextractiontoexpressefficiencyofextrac tion. Percentextractionorefficiencyofextractio n(%E)canbecalculatedas %E= 100 x m mol extracted Total m mol in aqueous phaseSeparation factor Ifthesolutiontobeextractedconsistsoftwos olutesAandB,andwehavetoseparateAfromB,th enwewilluseextractingsolventwhichwilldis solvemorequantityofAandverylessquantityo fB.
6 Underthiscondition,effectivenessofsepara tionisexpressedintermsofseparationcoeffi cientorseparationfactor. Itistheratioofdistributioncoefficientsof twosolutesAandBanddenotedby-=shouldbever yhightoseparatetwosolutesbysolventextrac tion, ratio Manysubstancesundergodissociationinaqueo usphaselikeweakcarboxylicacidsuchasbenzo icacid,phenol,etc. NowconsidertheweakacidHAwhichwilldissoci ateinaqueousphaseasfollows HA A-+ H+ Thesubstanceswhichundergobyaccountingdis sociationinaqueouslayerthedistributionco efficientinmodifiedformcanbedefinedasdis tributionratio(D) D=[HA ] org[A-]aq+ [HA] aqFactors affecting SOLVENT EXTRACTION Maskingagent thesearechemicalspecieswhichdonotallowto extractunwantedmetalionwithmetalionofint erest.
7 Modifiers thesearethesubstanceswhenaddedintoaqueou sphase, Oxidationstate bycarryingoutredoxreactionwithsuitablere agent, affecting SOLVENT EXTRACTION pH Saltingeffect Synergicagents , EXTRACTION methods of Metal ions Chelateformation Ion-Association method Solvation Synergic extractionSolvent EXTRACTION techniquesChelateformation Metalformsstableandneutralcomplexeswithc helatingagents. Suchchelatesareusuallywatersoluble Thechelatingagentsareusuallybidentateorm ultidentateorganicligandswhichprovidehyd rophobicpockettothemetalion. association method Itistheprocessinwhichmetaliongetssolvate dbysolventmoleculeandtrappedinsidethesol ventcage. Thesolventusedforsolvationissolubleinorg anicphase,hencemetaliongetsextractedfrom aqueousphaseintoorganicphase.
8 Carboxylicacids,ternaryamines, EXTRACTION Thesearethereagentswhichwhenaddedtoorgan icphaseincreasetheefficiencyofextraction Theygetassociatedwithmetalcomplex, EXTRACTION techniques Batch EXTRACTION Continuous EXTRACTION Countercurrent extractionBatch EXTRACTION Batchextraction,thesimplestandmostcommon lyusedmethod,consistsofextractingthesolu tefromoneimmisciblelayerintootherbyshaki ngthetwolayersuntilequilibriumisattained ,afterwhichthelayersareallowedtosettlebe foresampling. Thisiscommonlyusedonthesmallscaleinchemi callaboratories. Themostcommonlyemployedapparatusforperfo rmingabatchextractionisaseparatoryfunnel . Thebatchextractionsmayalsobeusedwithadva ntagewhenthedistributionratioislargeCoun tercurrent EXTRACTION Extractionbycontinuouscountercurrentdist ributionisthethirdgeneraltypeandisusedpr imarilyforfractionationpurposes.
9 Theseparationthroughcontinuouscountercur rentmethodisachievedbyvirtueofthedensity differencebetweenthefluidsincontact. Inverticalcolumns,thedenserphaseentersat thetopandflowsdownwardswhilethelessdense phaseentersfromthebottomandflowsupwards. Thechoiceofmethodtobeemployedwilldependp rimarilyuponthevalueofthedistributionrat ioofthesoluteofinterest, essential for an extractant1) ) ) ) ) ) ) ) )ThereisnoemulsionformationApplications of SOLVENT EXTRACTION Determinationofiron Determinationofleadintheblood Determinationofcopperinthealloyssuchasst eel Determinationofuranium SeparationandPurificationoforganiccompou ndsbyorganicchemists Usedindrugindustrybyanalyticalchemists,b io-chemists,pharmachemists.
