Industrial Crops and Products

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Industrial Crops and Products

j ourna l h o m e pa g e : w w w . e l s e v i e r . c o m / l o c a t e / i n d c r o p

Optimization of mechanical oil extraction from Jatropha curcas L.

kernel using response surface method

Erna Subroto

^a

, Robert Manurung

^b

, Hero Jan Heeres

^a

, Antonius Augustinus Broekhuis

^a,∗

aDepartmentofChemicalEngineering,RijksuniversiteitGroningen,Nijenborgh4,9747AGGroningen,TheNetherlands

bSchoolofLifeSciencesandTechnology,InstitutTeknologiBandung,Jl.Ganesha10,Bandung,Indonesia

a r t i c l e i n f o

Articlehistory:

Received28January2014

Receivedinrevisedform13August2014 Accepted14August2014

Availableonline14November2014

Keywords:

JatrophacurcasL.

Oilextraction Hydraulicpress

Face-centeredcompositedesign Responsesurfacemethodology Processoptimization

a b s t r a c t

ExtractionofoilfromJatrophacurcasL.kernelwasinvestigatedusingalab-scalehydraulicpress.Aface centeredcompositedesignofexperimentswasemployedtostudyandoptimizetheeffectofapplied pressure,pressingtemperatureandmoisturecontentonoilrecovery.Aquadraticpolynomialmodelwas generatedtopredictoilrecoveryandwasfoundtocover98%oftherangeforthefactorsstudied,namely 10–20MPaappliedpressure,60–90^◦Cpressingtemperatureand3–5%(w.b.)moisturecontent.Among theprocessparametersstudied,pressingtemperaturehadthemostsignificanteffectontherecovery followedbyappliedpressureandquadraticofmoisturecontent.Modelvalidationexperimentsshow goodcorrespondencebetweenactualandpredictedvalues.Theoptimalextractionconditionforoilyield withintheexperimentalrangeofthevariablesresearchedwasat19MPaappliedpressure,90^◦Cpressing temperature,and3.8%(w.b.)moisturecontent.Atthiscondition,theyieldofoilwaspredictedtobe87.8%.

©2014ElsevierB.V.Allrightsreserved.

1. Introduction

Oneofthemostpromisingrenewableandindependentenergy sourcesinruralareasisJatrophaoil(KumarandSharma, 2008;

Makkar and Becker, 2009).It is non-edible oil, thus it will not impairfoodsecurityissues(Pinzietal.,2009).Asitgrowswellon drymarginalnon-agriculturalland,itwillnotcompetewithland neededforfoodproductionorwithnatureconservation(Achten etal.,2007;MakkarandBecker,2009;Pinzietal.,2009).Jatropha isconsideredamoresustainablefeedstockforenergyproduction thananyotherfood-relatedcropsuchaspalm,rapeseed,soybean orsunflower(Achtenetal.,2007;Pinzietal.,2009).

Theextractionoftheoilfromtheseedisdoneindifferentways.

Methodsusedare:solventextraction,mechanicalextraction,enzy- maticextractionandaqueousextraction.Forapplicationinrural areas,mechanicalextractionisconsideredtobethebestoption.

Inthisextractionhydraulicpressesareusedtoremoveoilfrom theseeds.Thismethodisgenerallypreferredbecauseofitslower initialandoperationalcost,andbecauseitcanbeeasilyoperated bysemi-skilledpersonnel.Itproducesrelativelygoodqualityoilas comparedtothesolventextractionprocessanditallowsforthe

∗Correspondingauthor.Tel.:+31503634918;fax:+31503634479.

E-mailaddress:a.a.broekhuis@rug.nl(A.A.Broekhuis).

useofthecakeresidue(Olajideetal.,2007).However,adisadvan- tageofmechanicalextractionistheloweroilrecoverycompared tosolventextraction.Ithasbeenreportedthatsolventextraction withn-hexanecouldachieveabout70–99%oilrecovery,againsta reportedmaximumof60–80%formechanicalextraction(Achten etal.,2007).

Appliedpressure,pressingtemperature,andpressingtimeare importantprocessparameters,whiletheadjustmentofseedmois- turecontentisshowntobethemostimportantfactoramongst pretreatmentssuchasremovalofhullsorshells,sizereduction orheattreatment.Willemsetal.(2008)reportedhigheroilyield forrapeseed,sesame,linseed,jatrophaseedandjatrophakernel pressedathigherpressuresand/ortemperature.Healsoreported the22%differenceinoilrecoverywhenpressedlinseedatvarious moisturecontentsvariedfrom0to10%.Ourpreviousstudyindeed showsthatappliedpressure,pressingtemperature,andmoisture contentareimportantparametersthatinfluenceoilrecovery.The rateofpressureisfoundtobeoptimumat0.125MPa/s(Subroto etal.,2014).Thisstudyindicatedthattheoptimumoilrecovery iswithintherangeof10–20MPa,60–90^◦Cand3–5%(w.b.).This impliesthatmaximizingtheoilrecoveryislimitedtotheoptimiza- tionoftheseprocessparameters.Thisresearchisaimedtostudy andmodeltheeffectofthesevariablesandtheirinteractiononthe percentageofoilextraction.Themodelwillbeusedtooptimizethe extraction,andtheaccuracyofthemodelwillbetested.

http://dx.doi.org/10.1016/j.indcrop.2014.08.050 0926-6690/©2014ElsevierB.V.Allrightsreserved.

Table1

PropertiesofJatrophasamplesbeforemoistureconditioning.

Properties JatrophaKalimantan JatrophaSubang Weight(%d.b.)

Seed 100 100

Kernel 63.0 63.4

Shell 37.0 36.6

Oilcontent(%d.b.)

Seed 36.8±0.05 35.1±0.06

Kernel 58.3±0.02 55.3±0.01

Shell 0.1±0.01 0.1±0.01

Moisturecontent(%w.b.)

Seed 8.6±0.18 8.5±0.10

Kernel 7.04±0.13 6.97±0.17

Shell 11.3±0.24 11.1±0.21

2. Materialsandmethods 2.1. Material

Jatropha seeds used in the optimization experiment were obtainedfromPalangkaraya,Central Kalimantan,Indonesia.The maturefruitswereharvestedmanuallyinMarch2011.Theseeds weredriedundersunandstoredinjutebagsinawarehousefacil- ityattemperaturesbetween20and30^◦Candrelativehumidityof 80–90%foronemonth.InadditiontoJatrophafromKalimantan,Jat- rophafromSubangwasusedforoilqualityanalysis.Jatrophaseed fromSubangwasharvestedmanuallyduringJanuary2011,dried undersunandstoredinjutebagsinawarehousefacilityattem- peraturesbetween20and30^◦Candrelativehumidityof70–80%

for3months.AftertransporttotheNetherlandsinApril2011,both seedswerestoredatroomtemperature(withinarangeof18–22^◦C) andrelativehumidityof40–50%.Theseedswerede-shelledman- uallyand boththekernelsandshellswereanalyzedforweight fraction,initialmoistureandtotaloilcontent(seeTable1).Theker- nelswereexposedtomoistureconditioningpretreatmentbefore beingpressed(describedbelow).Thepretreatedkernelswereused directlyinthepressingexperimentstoreducetheinfluenceofstor- agetimeonoilquality.Theoilanalyseswereconducteddirectly afterpressinginMay2011forbothsourcesofJatrophaseeds.

Potassiumhydroxide(pellets,85%,Vetec),oxalicacidanhydrous (≥99%,Sigma–Aldrich),ethanol(95%,Sigma–Aldrich),diethylether (≥99%, Sigma–Aldrich), hexane (≥99, Sigma–Aldrich), Hydranal solvent(Fluka)andHydranaltitrant5(Fluka)wereboughtfrom Sigma–Aldrich(Amsterdam,TheNetherlands).

Foroilrecoverymeasurement,thekernelswereconditionedby ovendrying.Thedryingtemperatureswere35,40and50^◦Cfor desiredmoisturecontentof5,4and3%w.b.,respectively.Afterdry- ing,thekernelwaswrappedtightlyinalowdensitypolyethylene bagof25␮mthicknessandthenputinsideadesiccatorcontain- ingsilicagelforaminimumof1daybeforebeingpressed.Foroil qualityanalysis,thekernelswerestoredinsidethedesiccatorcon- tainingsilicageluntilthedesiredmoisturecontentwasreached, andthenwrappedinthepolyethylenebagforequilibration.

Theinitialmoisturecontentofthesampleswasdeterminedby ovendryingof10gofsampleat105^◦Cfor24h.Duplicatemea- surementswereperformedfor eachsample andaveragevalues weretaken.Moisturecontentafterconditioningwasdetermined bycalculatingtheweightdifferenceofthesampleafterandbefore conditioning.

2.2. Hydraulicpressing

Aschematicrepresentationofthehydraulicpressisshownin Fig.1.Thepressingchamberwasmadefromstainlesssteelwith adiameterof20mmandaheightof70mm.Itisequippedwitha

Table2

Actualandcodedlevelsoftheindependentvariablesintheexperimentaldesign.

Independentvariable Symbol Level

Actual Coded Actual Coded

Appliedpressure (MPa)

P x1 10 −1

15 0

20 1

Heating temperature(^◦C)

T x2 60 −1

75 0

90 1

Moisturecontent (%w.b.)

M x3 3 −1

4 0

5 1

perforatedplate(diameterof1mm)coveredwithfinewiremesh (100mesh).Thiswasplacedatthebottomofthepressingchamber actingasfilterduringextraction.Anelectrical-resistanceheating ringattachedaroundthepressingchamberisusedtopreheatthe pressing chamberduringoperationwithina temperaturerange of60–90^◦C.Pressuresupto20MPawereappliedbyahydraulic plunger. Thepressis completedwithathermocouple(±2.5^◦C), pressuremeasurement(±1MPa),andalevelindicator(±0.01mm), whichmeasuresthedistancetheplungertraveled.

Approximately7gofkernelswasplacedinthepressingcham- ber.Afterwards,theplungerisputontopofthekernels.Thesample ispreheatedfor5minwithoutapplyingmechanicalpressure.Sub- sequently, themechanical pressure wasincreased linearlyat a pressingrateof0.125MPa/suntilthedesiredpressureisreached.

Totalpressingtimewas10min.Forvalidationexperiment,three replicatemeasurementswereperformedforeachsampleandaver- agevaluesweretaken.

2.3. Statisticalanalysis

Levelsfortheindependentvariables,i.e.appliedpressure,X₁, pressingtemperature,X₂,andmoisturecontent,X₃,werebasedon resultsobtainedinapreviousstudy(Subrotoetal.,2014).Athree- factor-three-levelfacecenteredcentralcompositedesign(CCRD) wasappliedwherethevaluesoftheindependentvariablesXwere codedasthevariables,xintherangeof−1and+1level(shown inTable2).Themathematicaltransformationofanyactuallevelof appliedpressure,temperature,andmoisturecontentintothecoded levelcanbeobtained,respectively,fromthefollowingequations:

x=(X−XM) XD

(1)

XM= (Xmax+Xmin)

2 (2)

XD=(Xmax−XM) (3)

x1=(X1−15)

5 , x2=(X2−75)

15 , x3=X3−4 (4)

whereXM,XD,Xmax,andX_ministhemeanvalue,intervalofvariation, maximumandminimumvalueofX,respectively.While,x₁,x₂and x₃arethecodedvaluesandX₁,X₂andX₃aretheactualvaluesfor appliedpressure,temperatureandmoisturecontent.

Theexperimentalplanwasdesignedandtheresultsobtained wereanalyzedusingDesignExpertversion8.0.0software(State- EaseInc.,StatisticsMadeEasy,Minneapolis,MN,USA)tobuildand evaluatemodelsandtoplotthethree-dimensionalresponsesur- facecurves.Theexperimentaldatawereanalyzedfortheresponse.

Twentyexperimentswereperformedwhichconsistedofeight factorialpoints,sixextrapoints(starpoints)andsixreplicatesfor thecenterpoint.Thesixreplicatesforthecenterpointwereusedto estimatetheexperimentalerror.Ananalysisofvariance(ANOVA)

Fig.1.Schematicrepresentationofthehydraulicpress.

andR²(coefficientofdetermination)statisticwereusedtocheck theadequacyofthedevelopedmodel.UsinganF-test,itwaspossi- bletotestthevariationofthedataaroundthefittedmodel(lackof fit).Thesignificancelevelwasstatedat95%,withp-value0.05.Con- firmatoryexperimentswerecarriedouttovalidatetheequations usingthecombinationsofindependentvariables.Thesewerenot partoftheoriginalexperimentaldesign,butwithintheexperimen- talregion.TheoptimalconditionsfortheJatrophaoilrecoverywere obtainedusingthesoftware’snumericaloptimizationfunction.

2.4. Totaloilcontentandoilrecovery

Totaloilcontentofthekernelswasdeterminedbytheweight ofsubstancesthatareextractedbyn-hexaneaccordingtostan- dardSoxhletextractionmethod.Thekernelsweredriedovernight inanovenat105^◦C.Thedriedkernelsweregrindedusingacof- feegrinder(Princess242195,PrincessHouseholdAppliancesB.V., TheNetherlands)andapproximately10gweretransferredintoa celluloseextractionthimble(Whatman,I.D.×H18×55mm,GE).

Thiswasextractedwithhexaneatitsboilingpointfor24h.The hexane–oilmixturewasevaporatedinarotaryvacuumevaporator whilethecakewasdriedintheovenat80^◦Covernight.Duplicate measurementswereperformedandaveragevaluesweretaken.The totaloilcontentwasdefinedasweightofoilextractedoverthedry weightofthesampletaken.Theoilrecoverywasdefinedasthe ratiooftheamountofoilexpressedduringmechanicalpressingto thetotaloilcontentofthesampleatdryweightbasis.

2.5. Oilqualityanalysis

Hydraulicpressedoilswhichstillcontainedsomefineparticles werecentrifugedat2000×gfor10min.Theclearoilswererecov- eredandusedforoilanalysis.Chemicalandphysicalanalysesofthe sampleswerecarriedoutaccordingtothestandardtestmethods:

DINEN14111,DINEN14104,DINENISO12937,DINEN14112, DINEN14107andDINEN14538foriodinevalue,acidvalue,water content,oxidativestability,phosphoruscontent,andcalciumand magnesium(Ca+Mg)content,respectively.Densityanalysiswas

carriedoutbymeasuringthemassofthesampleswithrespect totheirvolumeusinga 10mLpycnometer.Thedensityat15^◦C wasobtainedbyextrapolationofdatacollectedfrom30to100^◦C, in10^◦Cincrements.Dynamicviscosityanalysiswascarriedout byusingacone-and-plateviscometerAR1000-N(40mm2^◦alu- minumcone)at40^◦Cwithashearrateof40/sfor10min.Kinematic viscositywascalculatedfromthecorrespondingdynamicviscos- ityanddensityatcorrespondingtemperature.Theflashpointof thesampleswasmeasuredaccordingtothemethodsdescribedin ASTMD6450usingaMINIFLASHFLP/H/L.Cloudpoint(CP)andpour point(PP)weremeasuredusingaTanakaScientificLimitedType MPC-102LaccordingtomethodsdescribedinASTMD6749and ASTMD2500,respectively.

AccordingtotheGermanfuelstandard DIN51605: 2010-10 forpureplantoil,theacidvalue,phosphoruscontent,andwater contentshouldnotexceed2mgKOH/goil, 3ppm,and750ppm respectively,andoxidative stabilityshouldbeatleast6h.Most chemicalpropertyanalysesontheplantoilswereconductedin ourlaboratorywiththeexceptionofphosphoruscontent,which wasconductedbyASGAnalytik-ServiceGmBH,Germany.Dupli- catemeasurementswereperformedoneachsampleandaverage valuesweretaken.

3. Resultsanddiscussions

3.1. Fittingthemodelandanalysisofvariance(ANOVA)

In order todetermine theoptimum process parameters, i.e.

appliedpressure,pressingtemperatureandmoisturecontentfor maximumoilrecovery,theexperimentsweredesigned accord- ingtoafacecenteredcentralcompositedesigninthreevariables followingtheResponseSurfaceMethodology(RSM). Theexper- imental set-up and corresponding experimental responses are shown inTable3.Theoilrecovery fromthesamplesexhibited anincreasewithincreasingtemperatureandpressure.Thelow- estvalueof68.9%wasobtainedat10MPapressure,60^◦Cand3%

(w.b.)moisture;thehighestvalueof86.4%wasobtainedat20MPa, 90^◦Cand3%(w.b.)moisture.

Table3

Experimentallayoutoffacecenteredcentralcompositedesignanditscorrespondingobservedvaluesofoilrecovery.

Run Variableproperties

Pressure(MPa) Temperature(^◦C) Moisturecontent(%w.b.) Oilrecovery(%d.b.)

1 10 60 3 69.6

2 20 60 3 78.6

3 10 90 3 79.1

4 20 90 3 86.4

5 10 60 5 73.7

6 20 60 5 78.6

7 10 90 5 79.0

8 20 90 5 82.3

9 10 75 4 78.2

10 20 75 4 84.6

11 15 60 4 79.8

12 15 90 4 86.1

13 15 75 3 80.5

14 15 75 5 79.3

15 15 75 4 83.3

16 15 75 4 84.2

17 15 75 4 83.2

18 15 75 4 83.7

19 15 75 4 84.7

20 15 75 4 82.6

Fitting of the data to various models (linear, two factorial, quadratic and cubic) and their subsequentanalysis of variance showsthatthehydraulicpressingofJatrophakernelismostprop- erlydescribedwithaquadraticpolynomialmodel.TheAdjusted R²ofthequadraticmodel(0.9752)washigherthanthatoflinear (0.5431)andtwofactorial(0.5186)models.Thecubicmodelwas foundtobealiased.Thesecond-orderpolynomialmodelsusedto expresstheoilrecovery(Y)asafunctionofindependentvariables (Eqs.(5)and(6))areshownbelow(intermsofcodedandactual levels):

Oilrecovery(coded)=83.41+3.09x1+3.26x2+0.13x3

−0.41x1x2−1.01x1x3−1.04x2x3

−1.71x²₁−0.16x₂²−3.21x²₃ (5)

OilRecovery(actual)=51.43+3.89X1+0.68X2+33.77X3

−0.005X1X2−0.20X1X3−0.07X2X3

−0.06X₁²−0.001X₂²−3.21X₃² (6)

Table4summarizestheANOVA(F-test)andp-valuethatare usedtoestimatethecoefficientsofthemodel,tocheckthesignif- icanceofeachparameter,andtoindicatetheinteractionstrength ofeachparameter.ItwasobservedfromtheANOVAanalysisthat theconfidencelevelwasgreaterthan95%whilethep-valueofthe modelwaslessthan0.0001.Themodelwiththep-valuebelow0.05 wasstatisticallysignificant,whichimpliedthatthemodelwassuit- ableforthisexperiment.Meanwhile,the“lackoffit”ofthismodel wasinsignificantwiththep-valuebeing0.76.Themaineffects,i.e.

X1 andX2,andinterationeffects,i.e.X₁²,X₃²,X1X3,X2X3,aresig- nificantbasedonthecalculatedp-values.Theeffectofmoisture contentonoilrecoveryexhibitedap-valueof0.54.Thisexceedsa p-valuelevelof0.05andindicatesthattheeffectisnotsignificant.

Thecoefficientofdetermination(R²)andadjustedcoefficient ofdetermination(R²_adj)were0.987and0.975,respectivelywhich indicatedthattheestimatedmodelfitstheexperimentaldatasat- isfactorily.Leeetal.(2010)suggestedthatforagoodfitofamodel, R²shouldbeatleast0.80.TheR²fortheseresponsevariableswas higherthan0.80,indicatingthattheregressionmodelsexplained themechanismwell.

Fig.2ashowstheexperimentalversuspredictedoilrecovery obtainedfromEq.(6).Alineardistributionisobservedwhichis indicativeofawell-fittingmodel.ThevaluespredictedfromEq.(6) wereclosetotheobservedvaluesofoilrecoveryfromJatropha kernel. Thenormalprobability plotisalsopresented inFig.2b.

Theplotindicatesthat theresiduals(difference betweenactual andpredictedvalues)follow anormaldistributionand forman approximatelystraightline.

3.2. Modelvalidation

The adequacy of the model equations to predict optimum responsevalueswastestedusingtheconditionsshowninTable5.

Theprocessing conditionsfor maximumrecoverywereused to experimentallyvalidateandpredictthevalues oftheresponses usingthemodelequation.Closeagreementexistsbetweenvalues calculatedusingthemodelequationandtheexperimentalvalues oftheresponsevariablesatthepointofinterest.TheX²goodness- of-fittestwasusedtoexaminethevalidityofthemodel(Table5) (MooneyandSwift,1999).Thetestshowsthatthereisnotasignif- icantdifferencebetweenthepredictedandactualvaluessincethe X²value(0.02)ismuchsmallerthanthecut-offvalueofX²for95%

confidencelevelfor3degreesoffreedom(7.81).Thisindicatesthat thegeneratedmodelisvalidat95%confidencelevel.

Fromtheestablishedequation,themaximumoilrecoverypre- dicted is 87.8% at process parameters equal to19MPa applied pressure,90^◦Cpressingtemperatureand3.8%(w.b.)moisturecon- tent.Theactualoilrecoveryobtainedis87.4±0.5%.

3.3. Effectofindependentprocessingparameters

Theeffectofthefourindependentvariablesontheoilrecovery ofJatrophaisshowninFig.3.Oilrecoveryimprovedwithincreas- ingpressureasshowninFig.3a;inparticularwhentheapplied pressurewasincreasedfrom10to15MPa.However,uponincreas- ingtheappliedpressurefrom15to20MPa,oilrecoveryseemedto leveloff.Forexample,forJatrophakernelcontaining4%(w.b.)mois- tureandpressedat75^◦Ctheoilrecoveryincreasedby5pointsfrom 78.6to83.4%byraisingtheappliedpressurefrom10to15MPa.The oilrecoveryonlyincreasedby1pointto84.8%whenthepressure wasraisedto20MPa.Athigherpressures,theinter-kernelvoidis muchsmallerthanatlowpressures,whichrestrictstheflowofoil.

Theseresultsindicatethatexcessivepressuredidnotnecessarily

Table4

ANOVAforresponsesurfacequadraticmodel.

Sourceofvariation Degreeoffreedom Sumofsquares Meansquare F-value p-Valueprobability

Model 9 323.92 35.99 83.85 <0.0001^a

Pressure,P 1 95.48 95.48 222.44 <0.0001^a

Temperature,T 1 106.28 106.28 247.58 <0.0001^a

Moisture,M 1 0.17 0.17 0.39 0.5444^b

PT 1 1.36 1.36 3.17 0.1053^b

PM 1 8.20 8.20 19.11 0.0014^a

TM 1 8.61 8.61 20.06 0.0012^a

P² 1 8.03 8.03 18.71 0.0015^a

T² 1 0.07 0.07 0.16 0.6957^b

M² 1 28.32 28.32 65.98 <0.0001^a

Residual 10 4.29 0.43

Lackoffit 5 1.46 0.29 0.52 0.7563^b

Pureerror 5 2.83 0.57

Correctiontotal 19 328.22

R² 0.987

Adj.R² 0.975

Valuesof‘p-value’<0.0500indicatemodeltermsaresignificant.

aSignificant.

b Notsignificant.

haveapositiveinfluenceonoilrecovery.Asimilarobservationwas observedbyWillemsetal.(2008)whilepressingJatrophaseedand kernelfrom20to70MPa.

Pressingtemperaturesignificantlyraisedoilrecoveryasshown inFig.3b.Thiswasobservedfor Jatrophakernel with4%(w.b.) moisturecontentwhen pressed under15MPa, theoilrecovery increasedfrom80.0to86.5%byincreasingthetemperaturefrom60 to90^◦C.Increasingthetemperaturecoagulatestheprotein,soften- ingthesolidstructureanddecreasestheoilviscosity.Kabuteyetal.

(2012)mentionedpre-heatingtemperaturesofthejatrophaseeds decreasedseedhardness(N/mm),contrary,seeddeformation(mm) increasedin relationto theeffect of pre-heating temperatures.

Burubaietal. (2007)reportedthat seeddeformationof African nutmegincreasedwithincreasingtemperatures.Increaseindefor- mationrelatedtothevolumeofoilreleasesfromcompressedcake.

Tambunanetal.(2012)foundthatincreasingpressingtemperature from50to80^◦Cincreaseoilrecoveryfrom70to80.9%inpressing ofJatrophaseed.

TheeffectofmoisturecontentonoilrecoveryisshowninFig.3c.

Ata pressing temperature of 75^◦C and an applied pressure of 15MPa,oilrecoveryincreasedfrom80.3to83.4%withanincrease inmoisture contentfrom3 to 4%(w.b.) butthen decreased to 80.1%whenthemoisturecontentwasraisedto5%(w.b.).Moisture contentaffectsthehardnessandcompactnessofthekernel.Sam- plewithlowermoisturecontenthashigherhardness(Karajand Müller,2010)whileathighermoisturecontentsplasticizationpro- motescakecompactionandrestrictstheflowofoil.Asreported byKabuteyet al.(2011)increasing moisturecontent from1to 10%reducesthedeformation.Theresultshowsthatthevalueof 4%(w.b.)wasfoundtobetheoptimummoisturecontentforJat- rophakernel.Achehebetal.(2012)alsofound3.95%astheoptimum moisturecontentforpistachionut.

3.4. Effectsofinteractivefactors

Theeffectofinteractionbetweenfactors,i.e.appliedpressure, temperatureand moisturecontentisshown in Figs.4–6.Fig.4 depictstheeffectofappliedpressureandpressingtemperatureon thepressingofJatrophakernelwithmoisturecontentof4%.The effectoftemperatureismoresignificantatlowerappliedpressure.

Forexampleat10and20MPa,theoilrecoveryincreasefrom74.8to 82.1%andfrom81.8to87.5%,respectively.Thiseffectwasobserved byMpagalileandClarke(2005)whenpressingcoconut.Theinter- actionbetweenappliedpressureandpressingtemperatureonoil recoverywasexplainedbyBargaleetal.(1999).Theeffectmaybe attributedtotheinteractionoftemperatureandpressurewhichat higherlevelstendtobecomecounteractive:increasingthetemper- aturedecreasestheviscosityoftheoiltherebyincreasingitsfluidity throughthecompressedmediumwhereasanincreaseinpressure makesthecakeharderwhichrestrictstheflowofoil.

Acomparativestudyoftheresultsshowedthattheoilrecovery atanypressurewasaffectedbythemoisturecontentofthesample.

Theeffectofappliedpressureandmoisturecontentonoilrecovery isshowninFig.5.Anincreaseinoilrecoveryisobservedwhenthe appliedpressurewasincreasedfrom10to15MPa.However,the oilrecoverytendstoleveloffathigherpressurelevelsfrom15to 20MPa.Thiseffectwasobservedforalllevelsofmoisturecontent usedinthisstudy.Forexample,whenJatrophakernelwith3%(w.b.) moisturecontentispressedat75^◦C,theoilrecoveryincreasedfrom 74.5to80.3%uponincreasingpressurefrom10to15MPaandthen slightlyincreasedto82.7%whenthepressureisraisedto20MPa.

AsimilartrendwasobservedforJatrophakernelwith5%(w.b.) moisturecontent:theoilrecoveryincreasedfrom76.3to80.1%

byincreasingpressurefrom10to15MPaandthenleveledoffto 80.4%towardsapressureof20MPa.Thislevelingoftheoilrecovery

Table5

Validationofmodelequation.

Run Variableproperties Oilrecovery(%)

P T M Experimental(E) Predicted(P)

1 19 90 3.8 87.4±0.5 87.8

2 15 60 3 75.1±1.1 75.9

3 15 60 5 77.7±1.7 77.7

4 10 60 4 75.3±0.6 74.8

5 20 60 4 81.2±1.1 81.8

X²=

_(E−P)²

P =0.02.

Fig.2. Correlationofactualconversionsandvaluespredictedbythemodel(a)and normalprobabilityofresiduals(b).

wasappreciablynoticeableinsampleswithhighermoisturecon- tent,whichshowsthatundersuchconditionshighpressureisnot effectiveinincreasingtheoilrecovery.Thiseffectwasobservedby MpagalileandClarke(2005)whenpressingcoconut.

Moisturecontentaffectsthehardnessandcompactnessofthe kernel.Atlowermoisturecontents,evaporationcausesthesur- faceofthesampletoharden,thusrequiringahigherpressureto beusedtoovercomethehardenedsampleduringpressing.Thus increasingpressureincreasestheoilrecovery.Athighermoisture contents,thepresenceofwaterwillactsasplasticizerbetweenthe protein-richcakeandoilwhichformspaste-likeplastizedmate- rial.Thispromotescakecompactionandrestrictstheflowofoil.

Thusincreasingpressureathighermoisturecontentgavehardly noticeablechangesorevensomereductioninoilrecovery.

Theeffectoftemperatureandmoisturecontentonoilrecovery isshowninFig.6.ThiswasobservedforJatrophakernelwith3%

(w.b.)moisturecontentwhenpressedat15MPa:theoilrecovery increasedfrom75.9to84.5%byincreasingthetemperaturefrom60

Fig.3. Effectofvariousindividualparameters:appliedpressure(a),temperature (b),andmoisturecontent(c),onthepressingofJatrophakernel.Oneparameteris variedwhiletheothersarekeptconstantattheircenterpoints.

Fig.4.Responsesurface(a)andcontourplots(b)ofoilrecoveryasfunctionof appliedpressureandtemperatureatmoisturecontentof4%(w.b.).

to90^◦C.AsimilartrendwasobservedforJatrophakernelcontain- ing5%(w.b.)moisturecontent:oilrecoveryincreasedfrom77.7to 82.1%byincreasingpressingtemperaturefrom60to90^◦C.Increas- ingtemperatureatlowmoisturecontentgaveamorenoticeable effectonoilrecoverythanathighermoisturecontent.

Theinteractiveeffectbetweenpressingtemperatureandmois- ture content can be explained as: increasing the temperature reduces the viscosity of the oil thereby increasing its fluidity throughthecompressedmedium.Anincreaseinmoisturecontent makesthecakelesscompressibleandrestrictstheoilflow.Thus increasingpressingtemperatureathighermoisturecontentgave lessnoticeablechangesinoilrecoveryincrement.

Manipulatingmoisturecontentenabledhighoilexpressioneffi- cienciesto be attained even at relatively low pressure or low temperature.Lowmoisturecontentsamplesneedlowertemper- atureorappliedpressuretogetthesameoilrecoverycompared tohighermoisturecontent.Forexample,oilrecoveryof83.4%was attainedatapressureof15MPaandatemperatureof75^◦Cforker- nelswith4%moisturecontent,whileanoilrecoveryof82%was obtainedatapressureof20MPaandtemperatureof90^◦Cforker- nelswith5%moisturecontent.Similarresultswereobtainedby MpagalileandClarke(2005)andEbeweleetal.(2010)inthestudy ontheeffectofmoisturecontent,appliedpressureandpressing temperatureoncoconutgratingandrubberseedexpression.

Fig.5.Responsesurface(a)andcontourplots(b)ofoilrecoveryasfunctionof appliedpressureandmoisturecontentatpressingtemperatureof75^◦C.

3.5. Oilquality

OilexpressionexperimentswerecarriedoutwithJatrophaker- nels from different plantations. The best processing conditions showedtobe:19MPaappliedpressure,90^◦Cpressingtemperature and3.8%(w.b.)moisturecontent.Dataontheoilsaresummarized in Table6.The qualityof theobtainedoilmettheDIN 51605:

2010-10standardforplantoilbasedfuelexceptonphosphorus contentandgroupIImetals.Acidvalueisameasurementofthe hydrolyticdegradationofoilduringstorageorprocessing,i.e.the hydrolysisofester bondsin lipidsbyenzymeaction orbyheat andmoisture,resultsintheliberationofFFAs.Theoxidativestabil- ityindexisassociatedwiththeoxidativedegradationofoilwhich resultsindevelopmentofrancidity.AhigherOxidativeStability Index(OSI)expressedinhoursInductionPeriod(IP)meansmore resistancetooxidation.Phosphoruscontentindicatesthepresence ofphosphor-derivedcomponentsinoilsuchasphospholipidsand phytates.Theiodinevalueisameasureofthedegreeofunsatura- tionoftheoil(thehighertheiodinevalue,thegreaterthedegree ofunsaturation).JatrophaoilfromKalimantanhasahigherphos- phoruscontentcomparedtoJatrophaoilsfromSubangasisshown inTable6.Soilnutritionorfertilizerisconsideredasacausefor thisresultwithJatrophafromKalimantangrownonmorenutri- tiouslandthanthatfromSubang.AccordingtoLickfettetal.(1999), phosphoruscontentinseedisaffectedbythelevelofphosphorus

Table6

PhysicalandchemicalcharacteristicsofJatrophacurcasL.oil.

Parameters Testmethods Units DIN51605:2010-10 Value

Flashpoint ASTMD6450 ^◦C 101(min) 200^b–204^a

Coldpoint ASTMD6749 ^◦C (−1)^b–(−2)^a

Pourpoint ASTMD2500 ^◦C (−3)^b–(−4)^a

Iodinevalue DINEN14111 g/100g 125(max) 108^a–113^b

Density(15^◦C) Pycnometer kg/m³ 910–925 923^a–925^b

Kinematicviscosity(40^◦C) Viscometer mPas 36(max) 35.8^a–37.2^b

Oxidativestability(110^◦C) EN14112 hours 6(min) 9.49^a–13.99^b

Acidvalue DINEN14104 mgKOH/g 2(min) 0.25^b–0.6^a

Phosphorus DINEN14107 ppm 3(max) 2.8^a–25.9^b

Group2metal(Ca+Mg) DIN51627-6 ppm 2(max) 3.8^a–31.2^b

Moisturecontent DINENISO12937 ppm 750(max) 697^a–747^b

Note:JatrophasampleusedforanalysisarefromSubang(a)andKalimantan(b).

Fig.6.Responsesurface(a)andcontourplots(b)ofoilrecoveryasfunctionof temperatureandmoisturecontentatappliedpressureof15MPa.

fertilizersupplyorphosphoruscontentinsoil.Thehigheroxida- tivestabilityofJatrophaoilfromKalimantanisattributedtothe presenceofphospholipids,phytatesandothernaturalantioxidants.

Phospholipidisknownforitsantioxidantpropertiesandcanwork togetherwithnaturalantioxidantssuchastocopherols(Choeand Min,2006).

4. Conclusions

A face centered central composite RSMdesign was usedto determinetheoptimumconditionsfortheprocessingparameters

appliedintheextractionofoilfromJatrophacurcasL.kernelby hydraulic pressing. It is found that applied pressure, pressing temperature,andthequadraticsofappliedpressureandmoisture content, as well as interaction between applied pressure and moisturecontentandbetweenpressingtemperatureandmoisture contentaresignificantfactorsaffectingtheoilrecovery.Thesecond orderpolynomialequationdevelopedinthisstudyshowsahigh correlationbetweenobservedandpredicatedoilrecoveryvalues.

Responsesurfaceanalysiswasfoundtobeagoodapproachforvisu- alizingprocess-parameterinteraction.Themodelsdevelopedby RSMshallbeusefulforpredictingtheoptimumprocessingcondi- tiontoachievemaximumoilrecoveryofJ.curcasL.kernelpressing.

Oilextractionexecutedatanappliedpressureof19MPa,apressing temperatureof90^◦Candakernelmoisturecontentof3.8%(w.b.) gaveanactualoilrecoveryof87.4±0.5%whichcloselymatchesthe predictedvalueof87.8%.Theoilqualitysatisfiestherequirements setbytheDIN51605:2010-10normforplantoilbasedfuels.

Conflictofinterest

Theauthorshavedeclarednoconflictofinterestonfinancialand orcommercialapplicationofthisstudy.

Acknowledgements

The authors are grateful to the Koninklijke Nederlandse AkademievanWetenschappen,ScientificProgrammeIndonesia– Netherlands(SPIN-KNAW),TheNetherlandsforthefinancialsup- port. We also would like toacknowledge AnnaApeldoorn and JanvanderVeldefortechnicalandanalyticalsupport.Finally,the authorsthankBoyA.Fachri,YusufAbduhandallcolleaguesatthe UniversityofGroningen,DepartmentofChemicalEngineering,for allsupportandvaluablesuggestions.

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