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10.1016/j.indcrop.2013.02.034
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To cite this version:
Evon, Philippe and Kartika, Ika Amalia and Cerny,
Muriel and Rigal, Luc Extraction of oil from jatropha seeds using a
twin-screw extruder: Feasibility study. (2013) Industrial Crops and Products,
vol. 47 . pp. 33-42. ISSN 0926-6690
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Extraction
of
oil
from
jatropha
seeds
using
a
twin-screw
extruder:
Feasibility
study
Ph.
Evon
a,b,∗,
I.
Amalia
Kartika
c,
M.
Cerny
a,b,
L.
Rigal
a,baUniversitédeToulouse,INP,LaboratoiredeChimieAgro-industrielle,ENSIACET,4AlléeEmileMonso,BP44362,31030ToulouseCedex4,France bINRA,LaboratoiredeChimieAgro-industrielle,31030ToulouseCedex4,France
cDepartmentofAgroindustrialTechnology,FATETA-IPB,DarmagaCampus,P.O.Box220,Bogor16002,Indonesia
Keywords: Twin-screwextruder Jatropha Oilextraction Oilquality
a
b
s
t
r
a
c
t
Theobjectiveofthisstudywastoevaluatethefeasibilityofmechanicalpressingtoextractoilfrom jat-rophaseedsusingatwin-screwextruder.Experimentswereconductedusingaco-rotating(ClextralBC 21,France)twin-screwextruder.Theinfluenceofoperatingconditionsonoilyield,specific mechani-calenergyandoilqualitywasexamined.Operatingconditionsincludedscrewconfiguration,pressing temperatureandscrewrotationspeed.
Generally,itwasthescrewconfiguration,orprofile,thatmostaffectedoilextractionefficiency.The bestoilyields,aminimum57.5%,wereobtainedwithatriturationzonecomposedof10monolobeand 10bilobepaddles,andapressingzonecomposedof50mmlong,reversepitchscrewswitha−33mm pitch.Inaddition,oilextractionyieldincreasedwithdecreasingtemperatureandscrewrotationspeed. Highestoilextractionyield(70.6%)withgoodpresscakequality(residualoilcontentlowerthan8%)was obtainedunderoperatingconditionsof153rpmscrewrotationspeed,5.16kg/hinletflowrateofjatropha seeds,and80◦Cpressingtemperature.Thecorrespondingexpressedoilwasinexpensivetoproduce
(71Wh/kgseedprocessedor314Wh/kgexpressedoilforspecificmechanicalenergy)comparedwith anothercontinuoustechnique,i.e.thesingleexpellerpress,commonlyusedformechanicalextraction ofjatrophaoil.Itsqualitywasalsosatisfactoryforbiodieselproduction.Theacidvalue,thedensityand thekinematicviscositywere5.4mgofKOH/gofoil,915kg/m3and36.7×10−6m2/s,respectively.
1. Introduction
Jatrophacurcasisadrought-resistantshrubortreebelongingto thefamilyEuphorbiaceae,whichiscultivatedinCentralandSouth America,South-EastAsia,IndiaandAfrica(Gubizetal.,1999).It isa plantwithmanyattributes,multipleusesandconsiderable potential(Openshaw,2000;Achtenetal.,2008;KumarandSharma, 2008).In Indonesia, theland areaunder jatropha is increasing becausethisplantcanbeusedtoreclaimland,preventand/or con-trolerosion,plusitprovidesanewagriculturaldevelopmentmode withnocompetitionbetweenfoodandnon-fooduses.Theseedis thepartofthejatrophaplantwiththehighestpotentialfor uti-lization.Itcontainsbetween40and60%oil,andbetween20and 30%proteins.Thejatrophaseedisgenerallytoxictohumansand animals,withphorbolesterandcurcinidentifiedasthemaintoxic agents(Gubizetal.,1999;HaasandMittelbach,2000).
∗ Correspondingauthorat:UniversitédeToulouse,INP,LaboratoiredeChimie Agro-industrielle,ENSIACET,4AlléeEmileMonso,BP44362,31030ToulouseCedex 4,France.Tel.:+33562446080;fax:+33562446082.
E-mailaddress:Philippe.Evon@ensiacet.fr(Ph.Evon).
J. curcas oil is regarded as a potential alternative to diesel fuel,andvegetableoilshavenumerousadvantagesinthisrespect becausetheyarenontoxic,andsafetostoreandhandlebecause oftheirhighflashpoints.Thefactthatjatrophaoilcannotbeused fornutritionalpurposeswithoutdetoxification,makesitsuseas anenergysourceforfuelproductionvery attractive.Theuseof biodieselfromjatrophaoilisapromisingalternativetofossilfuel becauseitisrenewable,andenvironmentallyfriendly,andcanalso beproducedlocally.
Conventionalindustrialtechnologyforthesynthesisofbiodiesel fromvegetable oils,involvesisolation of theoil fromtheseed, refining,andthentransesterification.Industrialoilextractionfrom oilseeds, is usually carried out by mechanical pressing with a hydraulicorsingleexpellerpress,followedbysolventextraction withn-hexane.Thehydraulicpressishighlyeffectiveforindustrial extractionofoilfromoilseedsbymechanicalpressing,butitisa dis-continuousprocess.However,thelasttwentyyearshasseenmuch, focusedresearchconcerningcontinuousoilextractionusing extru-siontechnology(Isobeetal.,1992;Croweetal.,2001;Wangand Johnson,2001;Singhetal.,2002;Zhengetal.,2003).Thisprocess inasingle-screwpress,iswidelyusedforoilseeds,witha single-screwofvariablepitchandchanneldepth,slowlyrotatinginacage
typebarrel(Isobeetal.,1992).However,transportofmaterialin thistypeofpress,dependsmainlyonfrictionbetweenthematerial andthebarrel’sinnersurfaceandscrewsurfaceduringscrew rota-tion.Thusasolid,corecomponentisoftennecessarytoproduce thisfriction,causingoverheating,highenergyconsumption,and oildeterioration.Furthermore,single-screwpressesprovide insuf-ficientcrushingandmixingiftheyarenotequippedwithbreaker bars,orotherspecialequipment.
Atwin-screw oilpress canbeexpectedtosolvethese prob-lemsbecauseofthehighertransportationforce,similartoagear pump,andbettermixingandcrushingatthetwin-screw inter-face,improvingmechanicallysisofthecells.Inaddition,energy consumption of the twin-screw press is more efficient (Isobe et al., 1992; Bouvier and Guyomard, 1997). Thus increasingly, twin-screw extrusion technologyhasbeen usedsuccessfully to undertakemechanical pressingof various oilseeds(Isobeet al., 1992; Guyomard, 1994; Bouvier and Guyomard, 1997; Lacaze-Dufaureetal.,1999;AmaliaKartikaetal.,2005,2006;Evonetal., 2007,2009;Faye,2010;Sritietal.,2012).
Theadvantagesoftwin-screwextrudersstemfromtheir capac-ity to carry out various functions and processes. According to
Dziezak(1989),theseinclude(i)anabilitytoprovidebetterprocess controlandversatility,especiallyinpumpingefficiency,controlof residencetimedistribution,anduniformityofprocessing,(ii)an abilitytoprocessspecialtyformulations,whichthesingle-screw extrudercannothandleand(iii)machinesetupflexibility,allowing self-cleaningmechanismsandrapidchangeoverofscrew configu-rationswithoutdisassemblingtheextruder.
Co-penetratingand co-rotatingtwin-screwextrudersarethe mostcommon(Dziezak,1989),andaverywidechoiceofscrew elementsisavailable.Thelatteraffectdifferentfunctionssuchas conveying,heating,cooling,shearing,crushing,mixing,chemical reactions,liquid/solidextraction,liquid/solidseparation,and dry-ing(Rigal, 1996).The screwprofiledefines thearrangement of screwelementswithdifferentcharacteristics(pitch,staggerangle, andlength)indifferentpositionsandwithdifferentspacing.Itis themainfactorinfluencingperformance(producttransformation, residencetimedistribution,andmechanicalenergyinput)during extrusionprocessing(Gogoietal.,1996;Choudhuryetal.,1998; GautamandChoudhury,1999a,b).
Theforwardpitchscrewsmainlyensureconveyingaction.The monolobepaddles exertradialcompressionand shearingaction onthematter buthave limited mixingability. The bilobe pad-dles,incombinationwithforwardpitchscrews,exertsignificant mixing,shearing,conveying,andaxialcompressionactionsonthe matter.Thebilobepaddlesfavortheintimatemixingrequiredfor theliquid/solidextractionofsolublecomponentsinthecell struc-ture.Finally,thereversepitchscrewsproduceintensiveshearing andconsiderablemixingofthematter,andexertastrongaxial compressionincombinationwiththeforwardpitchscrews(Rigal, 1996).Thereversepitchscrewsarefrequentlyusedtoputpressure onthematter,whichisessentialforthesubsequentseparationof liquidandsolidphasesbyfiltration.
When oleic sunflower oil is expressed using a twin-screw extruder,alongerreversepitchscrewimprovesoilyield,whichcan attain80%underoptimizedoperatingconditions(Lacaze-Dufaure etal.,1999).Whentworeverse pitchscrewsareused,oil yield increasesasthedistancebetweenthemincreases,andalsowith adecreaseinthescrewpitch(AmaliaKartikaetal.,2005).The opti-mumoilyieldobtainedwithsuchascrewconfigurationiscloseto 70%buttheintroductionofasecondfiltrationzoneimprovesthisto 85%(AmaliaKartikaetal.,2005).Thecorrespondingpresscake con-tainslessthan13%residualoilandthequalityoftheoilproduced issimilartothatobtainedusingtraditionalindustrialextraction.
For jatropha seeds, no previous study has dealt with the use of twin-screw extrusion technology for oil extraction by
mechanical pressing. However, the use of such a technology appearspromising,eveniftheequipmentandmaintenancecosts must be carefully considered. For the moment, mechanical oil extraction from jatropha seedsis generally carried out using a hydraulicpress(Tambunanetal.,2012)orasingleexpellerpress (KarajandMüller,2011;Pradhanetal.,2011;Ofori-Boatengetal., 2012).Similarly,oilextractionefficiencyisquitepromisingusing a KometD85-1G (Germany)mechanical screwpress(Karajand Müller,2011).Yieldinthiscaseattains89.3%(m/m)underoptimum operatingconditions(16mmforsinglescrewpitch,1.5mmmesh sizefor presscylinder,8mm fornozzle restrictorsize,220rpm forscrewrotationspeed,and4.0kg/hforthroughputofjatropha seeds), leading to a specific energy input of 462Wh/kg seed processed,orabout1.6kWh/kgexpressedoil.Residualoilcontent inthecorrespondingpresscakeisonly5.6%.
Thisstudyaimstoshowthataco-rotatingtwin-screwextruder can be used for the extraction of oil from jatropha seeds by mechanicalpressing.Itproposestoevaluatetheeffectsofscrew configuration,pressingtemperatureandscrewrotationspeedon oilextractionefficiency.Theextractionperformance characteriza-tionisassessedbydeterminingextractionyield,mechanicalenergy inputandoilquality.
2. Materialsandmethods 2.1. Materials
Alltrialswerecarriedoutusingasinglebatchofjatrophaseeds (IP2Lampungvariety)suppliedbytheIndonesianSpicesand Indus-trialCropsResearchInstitute(Sukabumi,Indonesia).Theharvested fruitswerefirstdriedatambienttemperature.Thecapsuleswere thenremovedmanuallytoobtaintheseeds,whichwere17–18mm long(x-axis),10–11mmwide(y-axis)and8–9mmthick(z-axis). Andinordertofacilitatetheirintroductionintothetwin-screw extruder,theywerecrushedbeforethestudyusingauniversal cut-tingmill(FritschPulverisette19,Germany)withnosieveinsert fitted.Aftermilling,mostofthekernelswereseparatedfromthe shellsinthegroundmaterial.Thesolidparticlesfromthekernels were10–13mmlong(x-axis),6–8mmwide(y-axis)and3–4mm thick (z-axis). The moisture content was 5.49±0.10% (French standardNFV03-903).Allsolventsandchemicalswereanalytical gradeandwereobtainedfromMerck(Germany),Macherey-Nagel (Germany),Sigma–Aldrich(USA)andProlabo(France).
2.2. Twin-screwextruder
Experiments wereconductedwith a ClextralBC21 (France) co-rotatingandco-penetratingtwin-screwextruder.Thisconsists oftwo identical,co-rotating andintermeshingscrews. The two shaftsturninthesame directionand thevariouspaired(twin) screwsetups,oppositeeachotherinthedifferentmodules,thus co-rotateandintermesh(co-penetrate).Ithadseven,100mmlong modularbarrels,anddifferenttwin-screwsmadeupof segmen-talscrewelements,25and50mminlength(Fig.1).Modules2,3, 4,5and7weretemperaturecontrolled(electricallyheated,and watercooled).Crushedjatrophaseedswerefedintotheextruder inletportusingavolumetricscrewfeeder(K-TronSoderKCL-KT20, Switzerland).Theyenteredasequenceofthreeoperations: convey-ing(forwardpitchscrews)inmodule1,trituration(asuccessionof 10monolobepaddlesandoneortwoseriesof10bilobepaddles)in modules2–4or5andpressing(reversepitchscrews)inmodule7. Afiltersectionconsistingoffourhemisphericaldisheswith500mm diameterperforationswaspositionedonmodule6toenablethe fil-trate(oilcontainingthe‘foot’,i.e.thesolidparticlesforcedthrough thefilter)tobecollected separatelyfromthepresscake.Screw
Fig.1.SchematicmodularbarreloftheClextralBC21twin-screwextruderusedforextractionofoilfromjatrophaseeds. rotationspeed(SS),seedfeedrate(QS),andbarreltemperature(c)
weremonitoredfromacontrolpanel.
Thefourscrewprofiles(1–4)testedinthisstudywerebasedon thoseusedinAmaliaKartikaetal.(2005,2006)forsunfloweroil extraction.Thedifferencesbetweenthemconcernedtheir tritura-tionzones,situatedinmodules2–4or5,andtheirpressingzones, situatedinmodule7.Thetriturationzonewascomposedofa suc-cessionof10monolobepaddlesandtwoseriesof10bilobepaddles forprofiles1and2.But,itwasshorterforprofiles3and4with10 monolobepaddlesandonlyoneseriesof10bilobepaddles.Forthe pressingzone,thereversepitchscrewsusedinprofiles1–3were 25mmlong,withapitchof−16mm.Theywerepositioned imme-diatelyafterthefiltrationmoduleforprofiles1and3,and25mm fromtheendofmodule6forprofile2.Thereversepitchscrewsused inprofile4werelonger(50mminsteadof25mm),theirpitchwas greater(−33mminsteadof−16mm),andtheywerepositioned immediatelyafterthefiltrationmodule.
2.3. Experimental
Thirteenexperimentswereconductedfortheexpressionofoil fromjatrophaseedsinthetwin-screwextruder(Table1). Differ-entoperatingconditionsweretestedincludingscrewprofile,screw rotationspeedandtemperatureinthepressingzone.Thefeedflow ofjatrophaseedswasaround5kg/hforalltheexperiments, mean-ingthatthedevice’sfillingcoefficientdependeddirectlyonthe screwrotationspeed.Foreachscrewprofiletested,thisspeedhad toremainabovea limitvaluetoavoid thetwin-screw extruder becomingclogged:55–60rpmforprofiles1and2,around65rpm forprofile3,andaround140rpmforprofile4,respectively.
Foreachexperiment,theextruderwaslefttofunctionfor30min beforeanysampling,toensurestabilizationoftheoperating con-ditions(seedfeedflow,temperature,andmotortorque).Afterthis, thefiltrateandthepresscakewereimmediatelycollected fora periodlongenough(30min),tominimizeanyvariationintheoutlet flowrates.Samplecollection,timedusingastopwatch,wascarried outonceforeachtrial,meaningthatthethirteenexperimentswere notreplicated.Thefiltrateandthepresscakewereweighed,andthe filtratewasthencentrifuged(8000×g,15min,20◦C)toeliminate thefoot.
Theoilyieldswerecalculatedfromthefollowingformulae: RL=QQF×TL
S×LS×100, (1)
whereRListheoilyieldrelativetothetotaloilthattheseedcontains
(%),QStheinletflowrateofjatrophaseeds(kg/h),QFtheflowrate
ofthefiltrate(kg/h),TLthemasscontentoftheexpressedoilinthe
filtrate(%),andLSthetotaloilcontentinthejatrophaseeds(%).
RC= (QS×LS)−(QC×LC)
QS×LS ×100, (2)
whereRCistheoilyieldbasedontheresidualoilcontentofthe
presscake(%),QCtheflowrateofthepresscake(kg/h),andLCthe
oilcontentinthepresscake(%).
AlthoughRLandRCareexpressedintermsoftheoilintheseed,
RC isalwayshigherthanRL becauseitincludesalltheoil inthe
filtrate(expressedoilplusoilinthefoot).
Theenergyconsumedbythemotorwasdeterminedfromthe followingformulae:
P=PM× SS
Smax×
T
Tmax×cos ϕ, (3)
wherePistheelectricalpowersuppliedbythemotor(W),PMthe
motor’spowerrating (PM=8300W), Tand Tmaxthetest torque
andmaximumtorque(100%)oftheextrudermotor(%),cosϕits theoreticalyield(cosϕ=0.90),andSSandSmaxthetestspeedand
maximumspeed(682rpm)oftherotatingscrews(rpm), respec-tively.
SME= P
QS, (4)
where SMEis thespecific mechanical energyconsumed bythe motorperunitweightofjatrophaseeds(Wh/kg).
SME′= P
QF×TL, (5)
where SME′ isthespecificmechanical energyconsumedbythe
motorperunitweightofexpressedoil(Wh/kg).
Fortrial13,theextruderwasstoppedimmediatelyafter sam-plecollection,andopenedinordertoobservethematterinside. Thiswascollectedintensuccessivezonesalongtheprofile(profile 4).Eachsamplecollectedwasweighed,anddriedovernightina ventilatedoven(105◦C)todetermineitsmoisturecontent.Then,
thesamplescollectedinzones1,4,6,and10wereobservedwitha NachetFranceZ45P(France)×15binocularmagnifier,andfive dif-ferentphotographsweretakenofeachsample,andanalyzedusing theArchimed4.0(France)software.Particlesizedistributionwas determinedbymanuallymeasuringthediameterofalltheparticles onthefivephotographs,usingtheImageJ(USA)software. 2.4. Analyticalmethods
Thevariousconstituentsweredeterminedaccordingtothe fol-lowingFrenchstandards:moisturecontentNFV03-903;mineral
Table 1 Results of the expression experiments conducted with the Clextral BC 21 twin-screw extruder. Trial number 1 2 3 4 5 6 7 8 9 10 11 12 13 Operating conditions Screw profile 1 2 2 2 3 3 3 4 4 4 4 4 4 SS (rpm) 65 66 79 93 76 73 73 153 170 191 212 150 150 QS (kg/h) 5.05 5.03 5.03 5.03 5.18 4.97 4.98 5.16 4.96 5.10 4.94 5.06 4.91 CF (g/h rpm) 77.7 76.5 63.7 54.1 68.4 68.0 68.3 33.8 29.2 26.7 23.3 33.7 32.8 c7 ( ◦C) 80 80 80 80 80 100 120 80 80 80 80 100 120 Filtrate Q F (kg/h) 1.96 1.36 1.21 0.84 1.90 1.52 1.62 1.72 1.61 1.64 1.57 1.59 1.55 TL (%) 43.9 34.9 0.0 0.0 48.9 43.2 45.5 67.7 68.6 64.7 57.6 64.2 61.2 TF (%) 56.1 65.1 100.0 100.0 51.1 56.8 54.5 32.3 31.4 35.3 42.4 35.8 38.8 HF (%) 4.13 ± 0.03 d 4.57 ± 0.04 a n.d. A n.d. A 4.15 ± 0.10 d 3.98 ± 0.03 e 4.15 ± 0.05 d 4.32 ± 0.08 bc 4.21 ± 0.06 cd 4.20 ± 0.10 cd 4.36 ± 0.04 b 4.38 ± 0.03 b 4.10 ± 0.02 de MF (% of dry matter) 5.25 ± 0.12 c 5.27 ± 0.08 c n.d. A n.d. A 5.56 ± 0.03 a 4.94 ± 0.02 d 5.42 ± 0.02 abc 5.04 ± 0.17 d 5.51 ± 0.03 a 5.54 ± 0.10 a 5.32 ± 0.06 bc 5.44 ± 0.03 ab 5.32 ± 0.02 bc Press cake QC (kg/h) 3.02 3.61 3.77 4.14 3.19 3.31 3.22 3.32 3.24 3.34 3.26 3.26 3.13 HC (%) 5.34 ± 0.07 a 4.80 ± 0.02 c 4.11 ± 0.00 e 4.11 ± 0.05 e 4.94 ± 0.14 b 3.15 ± 0.07 f 2.83 ± 0.08 g 4.16 ± 0.05 e 4.41 ± 0.00 d 4.15 ± 0.01 e 4.13 ± 0.08 e 1.59 ± 0.04 h 0.59 ± 0.00 i LC (% of dry matter) 5.88 ± 0.01 m 19.10 ± 0.05 c 25.54 ± 0.11 b 28.03 ± 0.01 a 6.76 ± 0.01 l 13.90 ± 0.00 d 13.28 ± 0.02 e 7.74 ± 0.01 k 7.98 ± 0.03 j 8.62 ± 0.08 g 8.96 ± 0.06 f 8.12 ± 0.02 i 8.28 ± 0.01 h MC (% of dry matter) 5.67 ± 0.14 bc 4.90 ± 0.03 f 4.42 ± 0.02 g 4.52 ± 0.14 g 5.58 ± 0.01 cd 5.35 ± 0.01 e 5.47 ± 0.01 d 5.92 ± 0.02 a 5.74 ± 0.00 b 5.75 ± 0.01 b 5.57 ± 0.02 cd 5.68 ± 0.00 bc 5.64 ± 0.01 bc PC (% of dry matter) 21.27 ± 0.02 fg 18.89 ± 0.19 i 17.73 ± 0.05 j 17.67 ± 0.07 j 21.46 ± 0.11 f 20.76 ± 0.12 h 21.12 ± 0.22 g 23.82 ± 0.14 a 23.11 ± 0.06 b 22.65 ± 0.03 c 21.94 ± 0.03 e 22.36 ± 0.16 d 22.32 ± 0.19 d Oil yields (%) RL 53.6 29.6 0.0 0.0 56.1 41.5 46.3 70.6 70.0 65.3 57.5 63.5 60.7 RC 89.6 59.1 42.4 30.6 87.6 71.8 73.8 85.0 84.4 83.0 82.2 83.8 83.5 Energy consumed T (%) 23.8 37.1 10.7 6.8 21.1 11.0 3.7 21.8 19.8 15.8 13.0 15.0 13.9 P (W) 169.1 267.6 92.3 68.8 175.2 88.0 29.3 365.0 368.7 331.2 301.9 246.4 229.1 SME (W h/kg seed processed) 33.5 53.2 18.3 13.7 33.8 17.7 5.9 70.8 74.3 64.9 61.1 48.7 46.6 SME ′ (W h/kg expressed oil) 196.1 563.2 – – 189.2 133.9 39.9 314.4 332.9 312.0 333.4 240.9 241.1 CF is the device’s filling coefficient (g/h rpm); it is defined as the ratio of the inlet flow rate of jatropha seeds (QS ) to the screw rotation speed (SS ). c7 is the barrel temperature at the level of module 7 ( ◦C). Modules 2–5 were heated to 80 ◦C for all trials. TF is the mass content of the foot in the filtrate (%). HF is the moisture content in the foot of the filtrate (%). MF is the mineral content in the foot of the filtrate (%). HC is the moisture content in the press cake (%). MC is the mineral content in the press cake (%). PC is the protein content in the press cake (%). Means in the same line with the same letter (a–m) are not significantly different at P < 0.05. A Non determined.
contentsNFV03-322;oilcontentsNFV03-908;proteincontents NFV18-100.Fortheoilcontentdetermination,jatrophaoilwas extracted fromtheinitialmaterial (seedsor press cakes)using theSoxhletextractionapparatusandn-hexaneasextracting sol-vent.Oilextractionwascarriedoutintwosuccessivestepseach of 5hduration, in orderto avoid underestimating theoil con-tent.Betweenthesetwosteps,thematerialwasregroundusing aFossCyclotec1093(Denmark)millfittedwitha300mmscreen. Alldeterminationswerecarriedoutinduplicate.
2.5. Oilqualityanalysis
The following quality parameters were calculated for the expressedoils;(i)theacidvalueandtheacidity(basedonoleic acid),expressedinmgofKOH/gofoilandin%,respectively(French standard NFT60-204),whichareanindicationoftheoil’sfree fattyacidcontent,(ii)theiodinevalue,expressedasthenumber ofcentigramsofiodineabsorbedpergramofoil(Frenchstandard NFT60-203),whichis ameasureofthedegreeofunsaturation oftheoil(thehighertheiodinevalue,thegreaterthedegreeof unsaturation),and(iii)thephosphoruscontent,expressedinmg ofphosphorusperkgofoil(FrenchstandardNFT60-227),which determinesphosphorusortheequivalentphosphatidecontentby ashingtheoilinthepresenceofmagnesiumoxide,followedby thespectrophotometricmeasurementofphosphorusasayellow phosphovanadomolybdiccomplex.Totalphospholipidcontentwas determinedbymultiplyingthephosphoruscontentby26,as sug-gestedintheFrenchstandardNFT60-227concerningvegetable oilsingeneral.Alldeterminationswerecarriedoutinduplicate.
Inaddition,thedensityofexpressedoils,inkg/m3,was
deter-minedat 25◦C usinga methoddescribed bytheAssociation of
OfficialAnalyticalChemists(AOAC,2006).Thedynamicviscosityof expressedoils,inmPas,wasmeasuredat40◦CusingaCarri-med
CSL100(USA)controlledstressrheometerequippedwitha cone-plategeometry(40mmdiameter,3◦59angle),andtheshearstress
appliedwas30N/m2.Thekinematicviscosityat40◦C,expressed
in10−6m2/s,wascalculatedastheratioofthedynamicviscosity
tothedensityof theoil. Alldeterminationswerecarriedoutin duplicate.
2.6. FattyacidcompositionofSoxhletextractedoil,andexpressed oilsfromjatrophaseeds
ThefattyacidcompositionofSoxhletextractedoil(i.e.theoil extractedfromjatrophaseedsusingtheSoxhletextraction appa-ratusandn-hexaneasextractingsolvent),andexpressedoils,was determinedbygaschromatography(GC).Thesampleanalyzedwas dilutedintert-butylmethylether(TBME)withaconcentrationof around20mg/mL.A100mLaliquotofthepreparedsamplewas thenconvertedtomethylestersaccordingtotheFrenchstandard NFISO5508using50mLof0.5mol/Ltrimethylsulfoniumhydroxide (TMSH)inmethanol.
ThefattyacidmethylesterswerethenanalyzedbyGCusing aVarian3800(USA)gaschromatograph,equippedwithaflame ionizationdetector.Thecarriergaswasheliumwithaflowrateof 1.2mL/min.MethylesterswereseparatedinaCPSelectCB (Var-ian,USA)fusedsilicacapillarycolumn(50m,0.25mmi.d.,0.25mm filmthickness).Theinitialoventemperaturewasheldat185◦Cfor
40min,increasedatarateof15◦C/minto250◦Candthenheldthere
for10min.Theinjectoranddetectortemperatureswere250◦C.All
determinationswerecarriedoutinduplicate. 2.7. Statisticalanalyses
Alldeterminationswereconductedinduplicateanddataare expressedasmeans±SD.Themeanswerecomparedbyusingthe
single-factoranalysisofvariance(ANOVA)followedbyDuncan’s multiplerange tests.Thedifferences betweenindividual means werefixedtobesignificantatP<0.05.Allanalyseswereperformed byusingtheSASdataanalysissoftware.
3. Resultsanddiscussion
3.1. Chemicalcompositionofthejatrophaseeds
The oil content of the jatropha seeds used in this study was 33.73±0.34% of the dry matter, and this agrees with the 22–48% results reported by some researchers (Achten et al., 2008; Becker and Makkar, 2008). Mineral and protein contents were4.81±0.08%of thedrymatterand 15.64±0.19% of the dry matter, respectively. The fatty acid composi-tion of the oil extracted from the jatropha seeds using the Soxhletextractionapparatusandn-hexaneasextractingsolvent wasmyristic(0.12±0.01%),palmitic (14.12±0.17%),palmitoleic (0.81±0.02%),stearic(7.14±0.29%),oleic(43.49±0.79%),linoleic (32.90±0.80%),linolenic (0.17±0.01%),arachidic (0.22±0.01%), gadoleic(0.33±0.02%),andbehenic(0.71±0.02%).Thus, theoil expressedinthisstudywasrichinoleicandlinoleicfattyacids,like otherjatrophaoilsdescribedintheliterature(Foidletal.,1996; Gubizetal.,1999;HaasandMittelbach,2000;Openshaw,2000; Achtenetal.,2008;BeckerandMakkar,2008;KumarandSharma, 2008),andcontained1.8±0.0%offreefattyacids.
3.2. Influenceoftheoperatingconditionsonoilextraction efficiency
Asobservedinpreviousstudiesdealingwiththeextractionof sunfloweroil (Lacaze-Dufaureetal.,1999;AmaliaKartikaetal., 2005,2006;Evonetal.,2007,2009), theextruderwaseffective becauseofitscapacitytocrushthejatrophaseedswhilst press-ing.Thetriturationzone(monolobeandbilobepaddles)reduced thesize ofthesolid particles significantly,and this mechanical actionledtothereleaseofpartoftheoil, andthecompressing actionbythereversepitchscrewswasessentialforliquid/solid separation. Positioned at the beginning of module 7, the CF2C reversepitchscrewspushedpartofthemixtureupstreamagainst thegeneralmovementintheextruder,andthiscounterpressure ensuredtheefficiencyoftheliquid/solidseparationabovethemetal filter.
Foralltheexperiments,filtratesamplesandpresscakesamples werealwayscollectedseparately.Theoilcontentinthepresscake waslowerthaninthejatrophaseedsanditvariedfrom28.0to5.9% ofthedrymatter(Table1)dependingontheoperatingconditions used.Thisledtoanoilyield(RC),basedontheresidualoilcontent
ofthepresscake,ofbetween30.6and89.6%(Table1).Logically, thehighertheoilyield(RC)thelowertheoilcontentinthepress
cake,andthisrelationwasindeedlinear.Theproteincontentinthe presscakewashigherthanintheactualjatrophaseedsduetothe oilexpression,anditvariedfrom17.7to23.8%ofthedrymatter (Table1).Inaddition,forallthescrewprofilestested,thelowerthe oilcontentinthepresscake,thehigheritsproteincontent.Theoil yield(RL),definedastheratiooftheexpressedoiltothetotaloil
thattheseedcontained,variedfrom0.0to70.6%(Table1).Itwas alwayslowerthantheoilyield(RC)duetotheoilcontainedinthe
filtratefoot(Fig.2),andthedifferencebetweenthesetwooilyields tendedtoincreasewithincreasingfiltratefootcontent.
Moreover,themasscontentofthefootinthefiltratewasat least31%,whichseemshighcomparedtovaluesgenerallyobtained withsingle-screwpresses(usuallylessthan5%).Theuseofafilter section with smallerperforations (less than 500mm in diame-ter),wouldprobablyreducetheamountofsolidparticlesforced
Fig.2.Variationinoilextractionyieldsfortrials1–13.
through,withoutpreventingtheoilfromdraining.However,sucha filtrationmodulecouldnotbetestedinthisstudy.Becausethefoot iscommonlyrecycledintothepressduringcommercialoperations, loweringthefiltratefootcontentwouldalsoreducetheamountof materialforrecycling,thusminimizingtheimpactonthroughput. Inthefirstscrewprofiletested(profile1),thetriturationzone wascomposedofasuccessionof10monolobepaddlesandtwo seriesof10bilobepaddles.Theobjectofsuchaconfigurationwas toobtainefficientmechanicallysisofthecellsandthereforegood releaseofoil.Thisgavethelowestpresscakeoilcontent,andthe highestoilyield(RC)ofthestudy(trial1):5.9%ofthedrymatter
and89.6%,respectively(Table1).However,thereductioninthesize ofthesolidparticleswassogreatthatthequantitydriventhrough thefilterwasveryhigh(56.1%forthemasscontentofthefootin thefiltrate).Consequently,theoilyield(RL)wasonly53.6%witha
ratherlowspecificmechanicalenergy(33.5Wh/kgseedprocessed or196.1Wh/kgexpressedoil).
Inthesecondscrewprofiletested(profile2),thereversescrew elementswereplaced25mmfromtheendofthefiltrationmodule inanattempttolowerthefootcontentinthefiltrate.However,the oppositewasobserved.Infact,thisexperiment(trial2),conducted atthesamescrewrotationspeedasthepreviousone(66rpm),gave ahighervalueforthefootmasscontentinthefiltrate:65.1%against 56.1%(Table1).Inaddition,theoilcontentinthepresscakewas muchhigher(19.1%ofthedrymatter),leadingtoadecreaseinboth oilyields(RCandRL):59.1and29.6%,respectively.Anincreasein
thefootcontentinthefiltrateleadingtohigherresidualoilcontent inthepresscake,isalsoobservedwithsingle-screwpressing.
Increasingthescrewrotationspeedfrom66to93rpm(trials 3and4)didnotimprovetheoilextraction.Indeed,itresultedin adecreaseinthemeanresidencetimeofthematterinthe twin-screwextruderandinadecreaseinthedevice’sfillingcoefficient from76.5to54.1g/hrpm(Table1),plusthecompressionofthe mixtureinthereversescrewelementswaslessefficient.Because theliquid/solidseparation wasmoredifficult,theoilcontentin thepress cakeincreasedfrom 19.1 to28.0% ofthedry matter, andtheoilyield(RC)decreased from59.1to30.6%.Inaddition,
thecentrifugationappliedtothefiltratesfromtrials3and4did notmanagetoseparateanyexpressedoilfromthefoot,andthus theoilyield(RL)was0%forboth.Whenthescrewrotationspeed
wasatleast79rpm,themechanicalactioninthetriturationzone wasprobablytoointenseandthesolidparticlessosmall,thatthey weredriventhroughthefilterveryeasily.Theuseofafiltersection
withsmallerperforationscouldreducethisphenomenon.But,as mentionedabove,suchasolutioncouldnotbeconsideredforthis study.
Profile3consistedofreducingthelengthofthetriturationzone (10monolobepaddlesandonlyoneseriesof10bilobepaddles), withthesamepressingzoneasforprofile1.Afirstattempt(trial5) wasconductedwithascrewrotationspeedof76rpmtoavoid clog-gingthemachine,andwiththesamepressingtemperatureasfor theprevioustrials(80◦C).Thereductionofthemechanicalaction
inthetriturationzoneledtoaslightdecreaseinthefootmass con-tentinthefiltrate:51.1%insteadof56.1%fortrial1(Table1).But, suchadifferencehadnosignificanteffectontheoilcontentinthe presscake,ontheoilyields(RCandRL),oronthespecific
mechani-calenergy:6.8%ofthedrymatterinsteadof5.9%ofthedrymatter fortrial1,87.6%insteadof89.6%fortrial1,56.1%insteadof53.6% fortrial1,and189.2Wh/kgexpressedoilinsteadof196.1Wh/kg expressedoilfortrial1,respectively.
Twoother experiments were conducted withprofile 3. The screwrotationspeedwasverysimilar(73rpm),buttwodifferent pressingtemperatureswereused:100◦Cfortrial6and120◦Cfor
trial7.Theflowofmaterialacrossthereversepitchscrewsbecame lessviscouswiththeincreaseinpressingtemperature,andthisled toalessefficientliquid/solidseparation.Consequently,theoil con-tentinthepresscakewasatleast13.3%ofthedrymatter(trial 7)insteadof6.8%ofthedrymatterat80◦C,andtheoilyield(RC)
decreasedfrom87.6to71.8%and73.8%(trials5,6and7), respec-tively(Table1).Moreover,bothfiltrateshadaslightlyhigherfoot contentthanfor trial5:56.8 and54.5%, respectively.However, thesetwovalueswerestilltoohigh,and theoil yield(RL)
logi-callydecreasedfrom56.1%at80◦Cto41.5%at100◦Cand46.3%at
120◦C.
Afourthscrewprofilewasalsotested(profile4).Itconsisted ofusing anothertypeof reversescrewelementin thepressing zone,withlongerCF2Cscrews(50mminsteadof25mm),andwith ahigher i.e.lessrestrictive pitch(−33mm insteadof −16mm). However,thetriturationzoneremainedthesameasforprofile3, i.e.10monolobepaddlesand10bilobepaddles.Sixexperiments wereconductedwiththisprofile(trials8–13).BecausetheCF2C screwswerelonger,thedevice’s fillingcoefficientneededtobe lowerwiththisprofile(4)thanwiththethreeothers,toavoid clog-gingthetwin-screwextruder:nohigherthan33.8g/hrpminstead of54.1–77.7g/hrpmfortrials1–7(Table1).Trials8–11evaluated theinfluenceofscrewrotationspeed(from153to212rpm)on
oilextractionefficiency,usingapressingtemperatureof80◦C.The
effectofthelatterwasmeasuredintrials8,12and13whereitwas 80–120◦Cwithascrewrotationspeedofbetween150and153rpm.
Themasscontentofthefootinthefiltratewasnevermorethan 42.4%fortrials8–13,comparedtoatleast51.1%foralltheother trials,meaningthatthereversescrewelementsusedinprofile4, loweredthefiltrate’sfootcontentsignificantly.
For trials 8–11, the decrease in screw rotation speed from 212rpm(trial11)to153(trial8)directlyaffectedthedevice’s fill-ingcoefficient,increasingitfrom23.3to33.8g/hrpm(Table1). Thus,thedegreeoffilloftheCF2Cscrewsincreasedasscrew rota-tionspeeddecreased,andthisledtoabetterpressingactiononthe matterandsotoamoreefficientliquid/solidseparation.Thiswas demonstratedbytheincreasein themotor’storquefrom13.0% (trial11)to21.8%(trial8)andbythecorrespondingdecreasein thepresscakeoilcontentfrom9.0to7.7%ofthedrymatter. Conse-quently,theoilyield(RC)increasedslightlywithdecreasingscrew
rotationspeed:from82.2%(trial11)to85.0%(trial8).Becausethe masscontentofthefootinthefiltratedecreasedatthesametime (from42.4to32.3%),theoilyield(RL)alsoincreased,butmore
sig-nificantly:from57.5%(trial11)to70.6%(trial8).Thesametendency hasbeenpreviouslyobservedforsunfloweroilexpression(Amalia Kartikaetal.,2005,2006).However,theoilextractionefficiency wasnotreallydifferentforthetwolowestvaluesofscrewrotation speed:70.0%fortheoilyield(RL)at170rpm(trial9)and70.6%
at153rpm(trial 8),respectively.Moreover,evenifthemotor’s torqueincreasedwithadecreaseinscrewrotationspeed,the spe-cificmechanicalenergyperunitweightofexpressedoilwaslargely independentofthedevice’sfilling:between312and333Wh/kg.
Fortheoptimalscrewrotationspeed(around150rpm), increas-ingthepressingtemperaturefrom80to120◦C(trials8,12and
13)didnotimproveoilextractionefficiency(Table1),asalready mentionedintheliterature,forsunflowerseeds(AmaliaKartika etal.,2005,2006).Indeed,theinfluenceofpressingtemperature ontheresidencetimeandenergyinputissignificantlycorrelated withmaterialviscosityanddegreeoffill(GautamandChoudhury,
1999a).The highest degreeof fill wasobtained whenthe flow of materialacrosstheCF2C screws wasmore viscous,thusthe residencetime and theenergyinput decreasedwithincreasing pressingtemperature.Thisledtoadecreaseinthemotor’storque (from21.8to13.9%),toanincreaseinthepresscakeoilcontent (from7.7to8.3%ofthedrymatter),toanincreaseinthefiltrate’s footcontent(from32.3to38.8%),toaslightdecreaseintheoilyield (RC)(from85.0to83.5%),andaboveall,toasignificantdecreasein
theoilyield(RL)(from70.6to60.7%).
Inconclusion,thehighestoilyield(RL)forthisstudywas70.6%,
obtainedunderthefollowingoperatingconditions:profile4screw configuration,153rpmscrewrotationspeed,5.16kg/hinletflow rateofjatropha seeds,and80◦C pressingtemperature.In
addi-tion,thecorrespondingpresscakequalitywassatisfactory(only 7.7%residualoilcontentofthedrymatter).Moreover,thespecific mechanicalenergywas71Wh/kgseedprocessedor314Wh/kg expressedoil,whichismuchlowerthantheenergyinputneeded withamechanicalscrewpressofasimilarscale(462Wh/kgseed processedorabout1.6kWh/kgexpressedoil)(KarajandMüller, 2011).However,thesevaluesneedtobeconfirmedwhenthe jat-rophaoilisextractedwithtwin-screwextrudersofhighercapacity. Theamountoffootinthefiltratewasstillhighundertheseoptimal conditions(32.3%).Thecorrespondingthroughputwas0.55kg/h, and itrepresented 11%oftheinlet flow rateofjatropha seeds. Andonceagain,reducingthediameterofperforationsinthefilter sectionshoulddiminishthefiltratefootcontent.
Theshutdownandopeningofthetwin-screwextruderatthe endoftrial13madeitpossibletoobservethelocationofthematter inside,alongtheoptimizedscrewprofile(profile4).Themonolobe paddles(DM)andespecially thebilobe paddles(BB)werefilled morethantheconveyingelementssituatedinmodules1–3(Fig.3). Theircrushingabilitywasconfirmedbythereductioninthesize ofthesolidparticlesobservedaftereachofthesetworestrictions (Fig.4):553mmand377mmfortheaverageparticlesize, respec-tively,compared to1094mmattheinlet.Because oftheirhigh pressingactiononthematter,leadingtotheliquid/solid
separa-Fig.3.Drysolidmassresultsforthecontentsofthetwin-screwextruder:drysolidmass( )andmoisturecontent()ofthematterinside,collectedintenzonesalong profile4followingshutdownandopeningofthetwin-screwextruderattheendoftrial13.Foreachzone,thedrysolidmassindicatedcorrespondstothemasscollected overa50mmzonelength.T2F,trapezoidaldouble-threadscrew;C2F,conveyingdouble-threadscrew;DM,monolobepaddle-screw;BB,bilobepaddle-screw;CF2C,reverse screw.ThenumbersfollowingthetypeofscrewindicatethepitchofT2F,C2F,andCF2CscrewsandthelengthoftheDMandBBscrews.
Fig.4. Cumulativenumberofparticlesasafunctionofparticlesizeforthematterinside,collectedattheendoftrial13,inzones1,4,6,and10alongprofile4.
tion,theCF2Cscrews(zone9)werelogicallytheelementsofthe screwprofilewhichweremostfilled(Fig.3).Theintensiveshearing appliedtothematteralsocontributedtoanadditionalreductionin thesizeofsolidparticles(Fig.4):only274mmfortheaveragesize inthepresscake.
3.3. Influenceofoperatingconditionsonoilquality
Theaverageacidvaluesofexpressedoils(Table2)compared favorablywiththoseobtainedfromtheliterature(Akintayo,2004; Meheretal.,2009;Pradhan etal.,2011).Theacidvaluewasat least5.6mgofKOH/g ofoil fortheexpressedoilsfromprofiles 1–3,andthetwohighestacidvalueswereobtainedfortrials1and 2:9.2mgofKOH/gofoiland6.6mgofKOH/gofoil,respectively. And thesetwo trials wereassociated with thehighest motor’s torquevalues:23.8and37.1%,respectively(Table1).Consequently, greatermechanicalactiononthemattercouldperhapscontribute toanincreaseinthehydrolysisofthetriglycerides.Thelowestacid valueswereobtainedfortheexpressedoilsproducedusingthe optimalscrewprofile(profile4):from5.0to5.4mgofKOH/gof oil,orfrom2.5to2.7%fortheacidity(Table2).Thesevaluesare quiteacceptableforsubsequentsynthesisofbiodiesel.Indeed,the acidvaluehassignificanteffectsonthetransesterificationof trigly-cerideswithalcohol,usingacatalyst(Goodrum,2002).Inalkaline transesterification,thefreefattyacidsquicklyreactwiththe cata-lysttoproducesoapsthatareexceedinglydifficulttoseparate,and thismayreducethequantityofcatalystavailablefor transesterifi-cation,loweringtheyieldofbiodieselproduct.Thesoapsproduced, cancauseanincreaseinviscosityandtheappearanceofgels,and alsomaketheseparationofglyceroldifficult(Qianetal.,2008).Low, freefattyacidcontentintheoil(lessthan3%),isthereforerequired foralkali-catalyzedtransesterification(CanakciandGerpen,2001). Theiodinevalueisameasureofthelevelofunsaturatedfatsand oils.Ahigheriodinevalueindicatesahigherlevelofunsaturated fatsandoils(KyriakidisandKatsiloulis,2000;Knothe,2002).For thisstudy,theaverageiodinevaluesforexpressedoilswerequite stable(from73.0to79.6gofiodine/100gofoil)evenifmostofthe lowestiodinevalueswereobtainedfortheexpressedoilsproduced usingtheoptimalscrewprofile(profile4):from73.1to75.5gof iodine/100gofoil.Thiswasconfirmedbythefattyacid composi-tionofexpressedoilsthatwaslargelyindependentoftheoperating conditionsusedwiththetwin-screwextruder.Asfortheoil con-tainedinthejatrophaseeds,alltheexpressedoilswererichinoleic andlinoleicfattyacids:42.9–44.0%and33.0–34.9%,respectively. Andatthesametime,thecontentsofpalmitic,palmitoleic and stearicfattyacidswere:14.1–14.9%,0.7–0.8%and6.9–7.3%, respec-tively.However,theiodinevalueswerelowerthansomereported
in theliterature (92.5–107.0gof iodine/100gof oil) (Akintayo, 2004;Meheretal.,2009;Pradhanetal.,2011),indicatingthatthe expressedoilsproducedinthisstudywerecomposedofglycerides withlessunsaturatedfattyacids.
Thephosphoruscontentofoilextractedfromjatrophaseeds usingtheSoxhletextractionapparatusandn-hexaneas extract-ing solvent, was 178.1±12.7mg/kg of oil, corresponding to 4631±330mg of phospholipids/kg of oil. This appeared to be higherthansomeliteraturevalues:110–150mgofphosphorus/kg ofoilinthecaseofjatrophaoilsextractedunderthesame condi-tions(Nareshetal.,2012).Generally,thephosphoruscontentin theexpressedoilswaslowerthanintheSoxhletextractedoilfrom jatrophaseeds(Table2),givingreadingsfortrials2–9thatwere withintheliteraturevalues.Theexpressedoilrichestin phospho-lipids,wasproducedwithprofile1(178.3mgofphosphorus/kgof oilor 4635mg ofphospholipids/kgofoil), andwaspairedwith thepresscakepoorestinlipids(only5.9%ofthedrymatterfor itsoilcontent)(Table1).Thisindicatesthathere,jatrophaseeds weresubjecttointensecrushing,leadingtomoreefficient rup-turingofcellwallsandsotoahigherco-extractionofmembrane phospholipids.Conversely,theexpressedoilfromprofile2was thepoorestinphospholipids(104.1mgofphosphorus/kgofoilor 2708mgofphospholipids/kgofoil),andthecorrespondingpress cake had a highoil content(19.1% of the dry matter). For the expressedoilsfromtheoptimalscrewprofile(profile4),ahigh screwspeedfavoredco-extractionofthephospholipidsduetothe increaseinshearingaction.Indeed,thephosphoruscontentwas around130mg/kgofoilwithascrewspeedbelow170rpm (tri-als8and9),anditreached170mg/kgofoilwithascrewspeed ofatleast191rpm(trials10and11).Similarly,itincreasedfrom 130.1to174.2mg/kgofoil whenthepressingtemperaturewas increasedfrom80to120◦C(trials8,12and13).Thisfacilitated
moreeffectivedryingoftheseeds,thusmoreefficientcrushing, duetotheirreducedelasticity,attheleveloftheCF2Cscrews.And thisintensecrushing,rupturedthecellwallsandledtoamore effi-cientco-extractionofthemembranephospholipids,aspreviously reportedbyLacaze-Dufaureetal.(1999)andAmaliaKartikaetal. (2005,2006)forsunfloweroilextractioninatwin-screwextruder. Thesamephenomenonwasalsoobservedfortheexpressedoils fromprofile3,wherethehighestphosphoruscontent(144.9mg/kg ofoil)correspondedtothe120◦Cpressingtemperature(trial7).
However,ifnecessary, phospholipidscan beremovedfromthe expressedoilsusingadegummingprocess.Arecentstudyshowed that the phosphoruscontent of an oil extracted from jatropha seeds by mechanical pressing, decreased from 46 to approxi-mately2.3mg/kg of oil aftercombining water degumming and
Table 2 Quality of expressed oils. Trial number 1 2 5 6 7 8 9 10 11 12 13 Acid value (mg of KOH/g of oil) 9.16 ± 0.00 a 6.57 ± 0.03 b 6.26 ± 0.02 c 6.19 ± 0.04 d 5.55 ± 0.01 e 5.39 ± 0.00 f 5.14 ± 0.00 g 5.00 ± 0.01 i 5.01 ± 0.00 i 5.00 ± 0.01 i 5.03 ± 0.02 h Acidity (%) 4.54 ± 0.00 a 3.25 ± 0.01 b 3.10 ± 0.01 c 3.07 ± 0.02 d 2.75 ± 0.01 e 2.67 ± 0.00 f 2.55 ± 0.00 g 2.48 ± 0.00 h 2.48 ± 0.00 h 2.48 ± 0.00 h 2.49 ± 0.01 h Phosphorus content (mg/kg of oil) 178.3 ± 12.3 a 104.1 ± 6.7 d 128.1 ± 4.9 bc 115.2 ± 6.1 cd 144.9 ± 8.9 b 130.1 ± 7.8 bc 127.6 ± 6.8 bc 172.5 ± 9.2 a 169.2 ± 4.9 a 168.4 ± 5.4 a 174.2 ± 9.3 a Phospholipids content (mg/kg of oil) 4635 ± 321 a 2708 ± 175 d 3330 ± 128 bc 2996 ± 159 cd 3768 ± 232 b 3382 ± 202 bc 3317 ± 177 bc 4486 ± 239 a 4399 ± 128 a 4378 ± 141 a 4528 ± 241 a Means in the same line with the same letter (a–i) are not significantly different at P < 0.05.
aciddegumming steps,andit waslessthan1mg/kgofoilafter membranefiltration(Liuetal.,2012).
The density of the expressed oils was between 915.0 and 917.8kg/m3, meaningthat it wasrelatively independentofthe
twin-screw extrusionconditions,aspreviouslyobservedforthe iodinevalue.Atthesametime,thedynamicviscositywasbetween 30.2and34.5mPasandthekinematicviscositybetween32.9and 37.7×10−6m2/s,whichareclosetotheacceptablevaluesquoted
intheliteratureforjatrophaoil(Akintayo,2004;Meheretal.,2009; Pradhanetal.,2011).
3.4. Potentialusesofthepresscakes
In this study, theoil content in thepress cakewas atleast 5.9%ofthedrymatter(Table1).Althoughthiscouldbea disad-vantage fordirect utilizationof thecake,it couldbeconverted intousableenergybycombustion,gasificationorpyrolysis(Yorgun etal.,2001;Gerc¸el,2002).Asamixtureofproteinsand lignocellu-losicfiberscomingmainlyfromtheshellsbutalsofromthekernel breakdownprocess,thepresscakecanalsobeconsideredasa nat-uralcomposite.Thus,itcouldbetransformedintobiodegradable and value-addedagromaterialsbythermo-pressing(Evon etal., 2010a,b,2012),byinjection molding(Rouillyetal.,2006)orby usingacastingtechnique(Gueguenetal.,1998).Finally,thepress cakecouldactasreinforcingfillerforabiodegradablepolymer,i.e. polycaprolactone(PCL),andhavepotentialusesinbiocomposite applications(Diebeletal.,2012).
4. Conclusion
Theextractionofoilfromjatrophaseedsbymechanical press-ingwascarriedoutusingthetwin-screwextrusiontechnology.The operatingconditions(screw configuration,screwrotationspeed and pressing temperature) had an important influence on the oil yield, thespecificmechanical energy and thequality ofthe expressedoil.Thelowestfootcontentsforthefiltrate(31–42%), wereobtainedwith10monolobepaddlesand10bilobepaddles in thetrituration zone,and with−33mmreversepitch screws, 50mminlength,inthepressingzone.Theoilyieldwasatleast57% withsuchascrewprofile,anditsystematicallyincreasedasthe screwrotationspeed andpressingtemperatureweredecreased. Thehighestoil yieldof71%wasobtainedunderoperating con-ditionsof153rpmand80◦C(5.16kg/hfortheinletflowrateof
jatrophaseeds).But,themasscontentofthefootinthefiltratewas high(32%)undertheseconditions.Thequalityofthe correspond-ingpresscakewasreasonable,witharesidualoilcontentofless than8%ofthedrymatter.Moreover,theextrusionprocessusing theoptimaloperatingconditions,producedanoilofgoodquality forbiodieselproduction,andatamoderatecost.
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