Magnesium oxide prepared via metal–chitosan complexation method : application as catalyst for transesterification of soybean oil and catalyst deactivation studies.

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ContentslistsavailableatScienceDirect

Journal

of

Power

Sources

j ou rn a 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 / j p o w s o u r

Magnesium

oxide

prepared

via

metal–chitosan

complexation

method:

Application

as

catalyst

for

transesteriﬁcation

of

soybean

oil

and

catalyst

deactivation

studies

Gizelle

I. Almerindo

a

_,

_Luiz

_F.D.

_Probst

a

_,

_Carlos

_E.M.

_Campos

b

_,

_Rusiene

_M.

_de

_Almeida

c,∗

_,

Simoni

M.P.

Meneghetti

c

_{, Mario}

_R.

_Meneghetti

c

_,

_Jean-Marc

_Clacens

d

_,

_Humberto

_V.

_Fajardo

e a_Departamento_de_Química,_Universidade_Federal_de_Santa_Catarina,_88040-900,_{Florianópolis}_–_SC,_Brazil

b_Departamento_de_Física,_Universidade_Federal_de_Santa_Catarina,_88040-900,_{Florianópolis}_–_SC,_Brazil c_Instituto_de_Química_e_{Biotecnologia,}_Universidade_Federal_de_Alagoas,_5702-970,_Maceió_–_AL,_Brazil

d_Laboratoire_de_Catalyse_en_Chimie_Organique_(LACCO),_Université_de_Poitiers,_UMR_CNRS_6503,₄₀_Avenue_du_Recteur_Pineau,₈₆₀₂₂_Poitiers_Cedex,_France e_Departamento_de_Química,_Universidade_Federal_de_Ouro_Preto,_35400-000,_Ouro_Preto_–_MG,_Brazil

a

r

t

i

c

l

e

i

n

f

o

Articlehistory: Received17March2011

Receivedinrevisedform5May2011 Accepted12May2011

Available online 19 May 2011 Keywords: Magnesiumoxide Chitosan Ethanol Biodiesel

a

b

s

t

r

a

c

t

Asimplemethodtopreparemagnesiumoxidecatalystsforbiodieselproductionbytransesteriﬁcation

reactionofsoybeanoilwithethanolisproposed.Themethodwasdevelopedusingametal–chitosan

complex.Comparedtothecommercialoxide,theproposedcatalystsdisplayedhighersurfaceareaand

basicityvalues,leadingtohigheryieldintermsoffattyacidethylesters(biodiesel).Thedeactivationof

thecatalystduetocontactwithCO2andH2Opresentintheambientairwasveriﬁed.Itwasconﬁrmed

thattheactivecatalyticsiteisahydrogenocarbonateadsorptionsite.

1. Introduction

Magnesium oxide (MgO) is a potential catalyst for various reactions due to the unique basic character of its surface, as demonstrated by an isoelectric point of around 12 [1–7]. For thisreasonMgOcancatalyzethetransesteriﬁcationreactionsof vegetableoilstobiodieselwithshort-chainalcohols.Beinga het-erogeneouscatalyst,MgOcouldimprovethesynthesismethods byeliminatingtheadditionalcostsassociatedwithconventionally usedhomogeneouscatalysts[8–12].Inthisregard,the heteroge-neouscatalystsareeconomicallyandecologicallyimportantwhen comparedwithhomogeneouscatalystsbecausetheyare environ-mentallybenign,mucheasiertoseparatefromliquidproducts,they facilitatethepuriﬁcationstages,canbereused,arenon-corrosive, havehighthermalstabilityandpresentfewerdisposalproblems

[11].

Manytypesof heterogeneouscatalystsfor theproductionof biodieselcanbefoundintheliterature,forexample,alkalineearth oxidesandseveralalkalinemetalcompoundssupportedon alu-minaorzeolite[11].Manyofthesecatalystshavehighefﬁciency

∗ Correspondingauthor.Tel.:+558232141773;fax:+558232141384. E-mailaddress:rusiene@hotmail.com(R.M.deAlmeida).

andactivityinthetransesteriﬁcationreaction,however,under con-ditionsofhightemperatureandpressure,andwithlongreaction times.

Therefore,itisofinteresttoinvestigatethepossibilityof replac-ing the homogeneous base catalysts by solid base catalysts in transesteriﬁcationreactionsassociatedwithlowertemperatures andshorterreactiontimesthanthosenormallyfoundinthe lit-eratureforheterogeneouscatalysts.Intheliterature,highmethyl esteryieldswiththeuseofheterogeneouscatalystsarealso associ-atedwiththereactionoccurringathightemperatures(170–250◦C) andwithlongerreactiontimes,inacontinuousorbatchreactor

[8].However,publishedstudyshowedthatnanocrystallineMgO catalystscanbeusedeffectivelyasheterogeneouscatalystsinthe methylictransesteriﬁcationofvegetableoilsatlowtemperatures

[1].

Anotherimportantfactoristhepossibilitytostorethecatalysts andguaranteetheircatalyticactivityforimmediateuse.However, basecatalystscanlosetheiractivityoncontactwithambientairdue totheadsorptionofCO2andH2Oatthesurfaceofthesolidas

car-bonatesandhydroxylgroups[13].Granadosetal.[14]investigated theeffectofCO2 inairontheactivityofCaOinthe

transesteriﬁ-cationofsunﬂoweroil.ThisCaOcatalystgraduallylostitsactivity becauseitssurfacesiteswerepoisonedbycontactwithCO2and

H2Oinair.However,theeffectsofH2OandCO2onthecatalytic

Open access under the Elsevier OA license.

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propertiesofbasecatalystsandthedeactivationmechanismhave notbeenfullyinvestigated[15].

Morespeciﬁcally,shortchainalcohols(methanolorethanol)are normallyusedintheproductionofbiodiesel,however,few stud-iesinvolvingheterogeneouscatalysisintheproductionofethylic biodieselarefoundintheliterature[16].Ethanolhasseveral advan-tagescomparedtomethanol,whichisgenerallyobtainedfromraw materialsoffossilorigin,withlowtoxicity, producingbiodiesel witha greatercetaneindex and withgreater lubricity,but the mostimportantis probablyitsrenewable origin[17–19]. How-ever,ethanol is less reactive,requiring a greater excess of this alcoholtoobtainyieldssimilartothoseobtainedwithmethanol. Furthermore,longerreactiontimesarerequired,higher temper-atures,anhydridealcohol,andoilwithlowwatercontentforthe separationofglycerol[20].

TheobjectiveofthisstudywastoprepareMgOcatalystsforthe transesterificationreactionofsoybeanoilwithethanolforthe pro-ductionofbiodiesel.InthispaperweverifiedthepotentialofMgO asatransesterificationcatalyst,preparedusingametal–chitosan complexationmethod,andcomparedittothatofacommercial magnesiumoxide.Thedeactivationofthecatalystpreparedusing themethodhereproposedduetocontactwiththeCO2andH2O

presentinambientairwasalsoveriﬁed.

2. Experimental

2.1. Samplepreparationandcharacterization

FortheMgOextrudatepreparation,15.3gofchitosan(Aldrich) weredissolved in 300mLof CH3COOH solution (10%,v/v) and

31.8gofMg(NO3)2·6H2O(Vetec)weredissolvedindistilledwater.

Anaqueoussolutionofmagnesiumsalt(Mg)wasthenaddedto thepolymersolutionunderstirring.ThechitosanmonomertoMg molarratiowas1.5–2.0.TheMg–chitosansolutionwasaddedto aNH4OHsolution(50%,v/v)undervigorousstirring,intheform

ofextrudates,withaperistalticpump.Thegelextrudatesformed wereremovedfromtheNH4OHsolutionanddriedatambient

tem-peraturefor120h.TheMgOsamplewasobtainedbycalciningthe driedsamplesat550◦Cinairﬂowfor4hwithaheatingrateof 5◦Cmin−1.

Inthiscontext,theMgOpreparedasdescribedabovewas com-paredwithcommercialMgOobtainedfromRiedel-deHaën(99.9% purity).Theseweredesignatedasfreshcatalysts,sincethecatalytic testwascarriedoutimmediatelyaftercalcination.Inorderto ver-ifytheeffectofstorageonthedeactivationofthecatalystobtained usingthemethoddescribedabove,itwasexposedforaperiodof 180daysinambientairtoextendthecarbonationandhydration processes.ThiscatalystwascalledMgO(stored).

Infrared spectrawere obtainedfrom 400to 4000cm−1; the samples (2mg dried chitosan and Mg–chitosan samples) were mechanicallyblendedwith200mgofKBr.Thedatawererecorded usinganFTPerkin-Elmer16PCinfraredspectrophotometer.

The thermogravimetric analysis (TGA) was performed with a Shimadzu TGA-50 thermobalance using 11mg of sample (Mg–chitosan)withaheatingrateof10◦Cmin−1 andairﬂowof 50mLmin−1.

Samples were characterized by N2 adsorption/desorption

isothermsobtainedat thetemperatureof liquid nitrogenusing an automated physisorption instrument (Autosorb-1C, Quan-tachromeInstruments).Priortothemeasurements,thesamples wereoutgassedinavacuumat200◦Cfor2h.Speciﬁcsurfaceareas werecalculatedaccordingtotheBrunauer–Emmett–Teller(BET) method,andtheporesizedistributionswereobtainedaccording totheBarret–Joyner–Halenda(BJH)methodfromtheadsorption data.

Temperatureprogrammeddesorption(TPD)ofCO2

measure-mentswereperformedusingaQuantachromeChemBET3000. The crystalline structure of the dried powder sample was determinedbyX-raydiffraction(XRD)withaPanAnalytical diffrac-tometer (Xpert PRO model) using Cu K␣ (=1.5418 ˚A) as the incidentradiation,operatingat40kVand30mA.Tobetterdeﬁne thestructuralparametersobtainedfromtheXRDpatternaRietveld analysisprocedurewasperformedusingtheGSASsoftware pro-gram and a starting model based on information given onthe ICSDcardnumber52026[21–23].Theaveragecrystallitesizeand microstrainwerecalculatedbysubtractingtheinstrumentalline broadeningcontributionusingtheyttriumoxidestandardandthe formalismpresentedbyLarsonandVonDreele[21].

Thesample morphology wasobserved onscanning electron micrographs,obtainedwithaPhilipsXL30scanningelectron micro-scopeoperatingatanacceleratingvoltageof20kV.

Thermogravimetricanalysiscoupledwithmassspectrometry (TG-MS)wereperformedonaSDTQ600apparatusfromTA Insru-mentscoupledbyaheatedcapillarycolumnwithaPrismaQMS200 massspectrometerfromBalzers.TomeasuretheamountofCO2

(m/z=44)andH2O(m/z=18)formed,thesampleswereheatedto

900◦C(heatingrate:10◦Cmin−1)underadriedair(100mLmin−1).

2.2. Catalytictest–transesteriﬁcationexperiments

Alltransesteriﬁcation reactionswerecarriedoutin a250mL closedbatchreactorequippedwithatemperature-controlledbath, reﬂuxcondenser and amagnetic stirreroperating at 1000rpm. Thereactionswerenormallyperformedat150◦Cduring3hwith ethanol:oil:catalystmolarratioof600:100:5.Soybeanoil (com-mercialgrade)wassuppliedbyBungeAlimentosS.Aandwasused asreceived.Afterofreaction,thereactionmixturewaswashed threetimeswithdistilledwaterandcentrifugedat5000rpmfor 10min.

Inordertoquantitativelyevaluatetheleachingofsolidbase catalystunderthereactingcondition,fattyacidethylesters frac-tionwassentforelementalanalysisviaﬂameatomicabsorption analysis(FLLA).

2.3. Analyticalprocedures

Thefattyacidethylesters(FAEEs)obtainedfromthe transester-ificationreactionweredeterminedbygaschromatographyusinga Varian3400CXinstrument,equippedwithacapillaryinjection sys-temoperatingat240◦C,withasplitratioof100:1andsamplesize of1␮L.AnapolarcapillarycolumnVF-1ms(FactorFour),with2.2m length,0.32mminternaldiameterand0.1mmfilmthickness,was employedandthecolumntemperatureprogramwas:initial tem-peratureof50◦C(1min),15◦Cmin−1to180◦C,7◦Cmin−1to230◦C and30◦Cmin−1to245◦C.Thedetectionsystemwasequippedwith aflameionizationdetector(FID)operatingat250◦C.Thecarriergas washighpurityhydrogen.

Theyield(%FAEEs)wasquantiﬁedinthepresenceoftricaprylin as the internal standard. Approximately0.15g of the products obtainedusingthetransesteriﬁcationproceduredescribedin Sec-tion2 wasweighedin a vial.Anamountof1mLof tricaprylin solution (0.01g/100mL hexane) was added. This solution was injectedintothechromatographicapparatusandthepeakareas ofthecompoundswereintegrated.

Each experiment was run twiceand thevalue obtained for eachsamplewastheaverageoftwoinjections.Thebiodieselyield (%FAEEs)wascalculatedasintheEq.(1).

%FAEEs= mtricaprylin_A ABftricaprylin

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where,mtricaprylinistheweightoftheinternalstandard,ABthepeak

areaofFAEEs,ftricaprylintheresponsefactor,Atricaprylinthepeakarea

oftheinternalstandard,andmsthesampleweight.

Thefreefattyacidsfoundinthesoybeanoil(characterizedas oleicacid,inthepercentagesgivenintheAOCSofﬁcialmethodCa 5a-40)totaled0.1%.

3. Resultsanddiscussion

3.1. Samplecharacterization

Theinfrared spectraforchitosan (Cht)and theMg–chitosan composite(Mg–Cht)takenbeforethecalcinationprocess(Fig.1) wereanalysed inorder toobtaininformation onthefunctional groupsthatparticipateinthebindingorinteractionwithMgin theintermediatestageoftheporousMgOextrudatepreparation.

Inpolymericassociationshydroxylgroupsabsorbintheformof abroadbandataround3400cm−1[24].Thebandsintheregion of3440cm−1 in thetwo spectraareassociated withstretching of the OH groups overlapped with N–H stretching of the chi-tosanbiopolymer.Therewasnodisplacementinrelationtothe wavenumberindicating thattheintermolecular interactions,by way of thebiopolymer hydrogen bonds,were maintained. The decreaseintheintensityofthebandin3440cm−1 onthe spec-trumforthecompound(Mg–chitosan)isdue totheinteraction ofMgwiththeoxygenatomsofthehydroxylgroupsaswellas of theaminegroups of thebiopolymer boundtothe glycoside ring.Inaddition,bandsat 1650and 1600cm−1 onthechitosan spectrumwere,respectively,associatedwiththeC Ostretching vibrationofsecondaryamidegroupsfromthepartially deacety-latedchitinresiduesandwiththeN–Hdeformationvibrationsof theprimaryaminesofchitosan[25].Thereductionofthesebands oftheMg–chitosancomplexisrelatedtotheinteractionofMgwith carbonylgroupsfromthepartiallydeacetylatedchitinresiduesas wellastheinteractionofthemanganeseionwithaminegroups. Duetotheincompletedeacetylationofchitosan(90%)mentioned previouslythebandat1380cm−1,whichisattributedtotheC–H deformationoftheCH3group,isassociatedwiththefew

remain-ingacetamidegroupspresentinthepolymericchain[25].Itcan thus benoted that theamine groups of chitosan are themain effectivebondingsitesforthemetallicions,resultingincomplexes stabilizedbycoordination.Nitrogenelectronspresentintheamine

500 1000 1500 2000 2500 3000 3500 4000 0 20 40 60 80 100 Cht-Mg Cht Transmittance (%) Wavenumber (cm-1)

Fig.1.Infraredspectraofchitosan(Cht)andchitosan–Mg(Mg–Cht)composite beforeheat-treatmentprocess.Inset:chemicalstructureofchitosan.

800 600 400 200 0 0 50 100 Cht-Mg Cht Mass (%) Temperature (ºC) 1000 800 600 400 200 0 -0,020 -0,015 -0,010 -0,005 0,000 Mg-Cht Cht DTG Temperature (ºC)

a

b

Fig.2. Thermogravimetricanalysisofchitosan(Cht)andchitosan–Mg(Cht–Mg).

andN-acetylaminegroupscanestablishcoordinatecovalentbonds withmetalionsandsomehydroxylgroupspresentinchitosancan actasdonors[26].Theinfraredspectra(IR)conﬁrmthe modiﬁ-cationofcertaincharacteristicregionsofthefunctionalgroupsof thebiopolymer,mainlythosewhicharesusceptibletointeraction withtheMgsalt,withoutmodifyingthesemicrystallinechitosan structure.

Thethermogravimetric(TGA/DTG)profilesareshowinFig.2a andb.Itcanbeseenthattheeliminationofresidualmaterialis dependentonthesamplecomposition(chitosanorMg–chitosan composite).Thepresenceofmagnesiumleadstotheremovalof carbonaceous materialsat lowertemperatures. TheTGA profile suggestsatemperatureof550◦Cforthetotaleliminationofthe residualmaterialoftheMg–chitosancompoundand580◦Cforthe purechitosan.TheTGAandIRresultsconfirmtheformationofa novelmaterial.

AssummarizedinTable1,thepreparationmethodledtoa sam-plewithbettertexturalproperties,suchasspeciﬁcsurfacearea and pore volume,than thecommercialsample(MgO(C)). Thus, thebiopolymermustbeusedwiththeprecursormaterial,which iseliminatedduringthethermaltreatmentgeneratingthepores (215 ˚A)thatcontributetotheobservedincreaseinsurfacearea[27]. Thesurfaceareaandporevolumeareconsideredtobeimportant parametersaffectingtheoverallperformanceofacatalyst.

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Table1

TextureparameterscalculatedfromN2adsorptionisothermsandcatalytic perfor-mancesatethanol:oil:catalystmolarratioof600:100:5,at150◦C/3h.

Catalyst SBET(m2g−1) VBJH(cm3g−1) %FAEEs

MgO* _54.4 _0.292 ₇₅

MgO(C)* _14.2 _0.024 ₃₀

MgO(stored) 40 0.250 14

SBET=speciﬁc surface area; VBHJ=pore volume; MgO(C)=commercial oxide; %FAEEs=biodieselyield.

* _Fresh_catalysts.

TheXRDpatternofthefreshMgOpowder(Fig.3)showsvery strong,slightlybroadenedpeaks,consistentwithnanometric-sized fcc MgO crystals (space group Fm-3m) with lattice parameters (4.22203 ˚A).TheaveragesizeandmicrostrainoftheMgO crystal-liteswere150 ˚Aand1.4%,respectively.

Scanningelectronmicroscopy(SEM)wascarriedoutinorder toobservethemorphologiesofthesamplesobtained(MgOfresh). TheSEMimageshowninFig.4revealsthatthesampleprepared usingthemethodheredevelopedhasaporousaspect,consistent withthehighervaluesforspeciﬁcsurfaceareaandporevolume obtainedfromthephysicalmeasurementofN2.Duringthe

calci-120 100 80 60 40 20 0 8 16 Intensity (x 10 3 cts) 2 θ (degrees)

Fig.3.XRD:experimental(noisyline)andcalculated(thickline)XRDpatternsof freshMgOsampleproducedbymetal–chitosancomplexationmethod.Greyline representsthedifferencebetweenexperimentalandcalculatedpatterns.

Fig.4. Scanningelectronmicroscopy(SEM)imageofMgO.

Fig.5.Scanningelectronmicroscopy(SEM)imagefortheMgO(stored).

nationsteptheeliminationofvolatilematerialsoccurs,andcavities areproducedasaresultoftheirremoval.Atthesametime,asolid rearrangementtakesplace,formingthecrystallinematrix. How-ever,thesamplestoredforaperiodof180daysinambientairdoes notshowthesameaspect,asshowninFig.5,possiblyduetothe chemisorptionofCO2andH2Oatthesurfacesitesas

hydrogeno-carbonatespecies.

TG-MScouplinganalysesof MgOand MgO(C)are presented in Figs. 6–8. Fig. 6 representsthe catalysts weight loss, while

Figs.7and8representthethermalevolutionofCO2(m/z=44)and

H2O(m/z=18)respectively.Fig.6showstwomajorweightloss,

oneat120◦Ccorrespondingtohydrationwaterlossasconﬁrmed inFig.8;andanotherbetween300◦Cand400◦C.Thislastweight losswasbetterunderstoodthankstoMSanalyses.ConsideringCO2,

weobservedadesorptionat380◦CforMgO(C)andMgO(Fig.7).We alsoobservedH2Odesorptionpeaksatthesametemperaturethat

forCO2forallthesolids(Fig.8).ThisdesorptionofbothCO2and

H2Oatthesametemperatureprovesthatthenatureofthebasic

sitesarehydrogenocarbonates.ThebiggerH2Odesorptionpeak

ofMgOcorrespondstohydroxyl groups.Athighertemperature, MgO(C)exhibitstwo otherCO2 desorptionpeaks;oneat450◦C

correspondingtomoderatebasicsiteandanotherathigher tem-perature(600◦C)correspondingtostrongbasicsites.Thesetwolast CO2desorptionsoccurswithoutlossofwater,indicatingthatthe

natureoftheadsorbedsitesiscarbonates.Noneofthese“chitosan MgO”exhibitcarbonatetypeadsorptionsites,butonly hydrogeno-carbonateones,whichis reallyunusualforMgO type catalysts. These“chitosanMgO”aretheninterestingtoperformreactionsthat needmoderatebasicityasthetransesteriﬁcationreaction. More-over,theabsenceof strongbasicsites couldpreventsomeside reactionsandthentheformationofby-products.

3.2. Catalytictesting

The preliminaries results obtained from the catalytic tests (%FAEEs)areshowninTable1.Itcanbeobservedthatthematerials areactive,formingFAEEswithpercentagesof30–75%forthefresh catalysts,at3hofreaction.

Thecatalyticactivityexhibitedbythistypeofoxideisrelatedto thepresenceofbasicBrøsntedsitesinthesurfaceofthematerial

[28,29].Thesesitesonthemagnesiumoxidearestrongenough,pKa isaround16,togeneratealcohoxideswhicharetheactivespecies ontransesteriﬁcationunderbasicreactionconditions[30,31].

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-0.2 -0.1 0.0 0.1 Temperature Difference (°C/mg) 60 70 80 90 100 Weight (%) 800 600 400 200 0 Temperature (°C) MgO––––––– MgO (c)– – – –

Fig.6. TG-DTAanalysisofMgOandMgO(C).

Thisstudyrevealedgoodcorrelationsbetweenthepresenceof basicsitesinthecatalysts,asshowninFig.7,withtheexception oftheMgO(stored)sampleusedtoverifytheeffectofstoragein ambientair.ThecatalystMgO(stored)wasstoredinambientairfor aperiodof180dayswhichledtoadecreaseinthecatalystactivity

Fig.7. m/z=44(CO2)TG-MSanalysisofMgOandMgO(C).

Fig.8.m/z=18(H2O)TG-MSanalysisofMgOandMgO(C).

becauseofthepoisoningofthesamplebycarbonation/hydration oftheactivesites[15].TheyieldofFAEEsdecreasedfrom75%to 14%forthefreshandstoredcatalysts,respectively.

AstudyonthespeciﬁcadsorptionofCO2,CO2+H2Oas

per-formedtobetterunderstandthenatureofthepoisoningof the catalyticsites(Figs.9and10).WhenafreshlycalcinedMgOwas analysedbyTG-MS,nodesorptionofH2OorCO2 wereobserved,

exceptalowphysisorbedwaterpeakunder100◦Cwhichisdue toexperimentalartifact(refreshmentoftheovenbyundriedair). Whena freshlycalcined MgO wasexposedtoCO2 during 15h,

noCO2 adsorptionwasdetectedwhilewhenbothCO2 andH2O

were simultaneouslyputin contact with thesame freshly cal-cinedMgO duringonly3h,both ofthem wereadsorbed.Ifthe MgOstaysunderambientairmorethan2monthafterits calci-nation,thesameadsorptionis observedwithmoreintensity.It provesthatthepoisoningofthecatalystisduetotheformation ofhydrogenocarbonatesonthebasiccatalyticsitesofMgO.Only thebasicsitescorrespondingtohydrogenocarbonatesadsorption aretheninvolvedinthecatalytictranseterificationofsoybeanoil byethanol.Wecanthussuggestthatthestorageofthecatalyst underdryaircouldbesufficienttoavoiditspoisoning.Theseresults areconsistentwiththecharacteristicsoftheMgOcatalyst,which hasbasicssites,thisbeingarequirementforthereaction.Inthis regard,Henriquesandco-workers[8]alsoshowedthatMgO,as wellasmixedoxides,areefficientcatalystsforthe transesterifi-cationofvegetableoils,usingmethanolasanalcoholysisagent. Theyreportedafattyacidmethylesteryieldofover60%at130◦C for7hreactiontime.Theuseoftheconventionalmicrocrystalline MgOcatalystinthemethylic transesterificationofsunfloweroil reportedlyledtoaconversionof80%at220◦C[1].

It isimportanttoremarkthatthecatalyticactivityishigher forMgO,sinceCO2 poisoningissloweroverMgOincomparison

withMgO(C).IntheMgO(C)strongbasicLewissitesarepresented and theatmosphericCO2 reactsvery quicklytoformless

reac-tivecarbonatedspecies.InthecaseofMgO,theatmosphericCO2

reactsslowlywithmoderateBrönstedsitespresented,to gener-atehydrogenocarbonatesinthepresenceofwatertraces.Thisis conﬁrmedbythestoragestudy,discussedabove.

Itisworthnotingthatalongwiththeethylicalcoholusedinthe reactionbeingofrenewableorigin,thecatalystwassynthesized fromchitosan,whichisabiomaterial.

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Fig.9.m/z=18(H2O)TG-MSanalysisof“chitosanMgO”.(a)Directlyaftercalcinationsoftheprecursor,(b)directlyaftercalcinationsoftheprecursorthenadsorptionof CO2during15hat30◦C,(c)directlyaftercalcinationsoftheprecursorthenadsorptionofbothCO2andH2Oduring3hat30◦C,(d)2monthofstorageaftercalcinations (MgO(stored)).

Fig.10. m/z=44(CO2)TG-MSanalysisof“chitosanMgO”.(a)Directlyaftercalcinationsoftheprecursor,(b)directlyaftercalcinationsoftheprecursorthenadsorptionof CO2during15hat30◦C,(c)directlyaftercalcinationsoftheprecursorthenadsorptionofbothCO2andH2Oduring3hat30◦C,(d)2monthofstorageaftercalcinations (MgO(stored)).

4. Conclusions

ThemethoddescribedhereinforthepreparationoftheMgO cat-alystsviametal–chitosancomplexation,ledtoasigniﬁcantincrease intheirsurfaceareaandthebasicity.Thesecharacteristicsprovide arelativelyhigherconversiontofattyacidethylesterswhen com-paredwithacommercialoxide.However,solidbasecatalystsare susceptibletobepoisonedbysomecomponentsinairsuchasCO2

andH2Oastheycaninteractwithbasesitesanddecreasecatalyst

activity.

Inthisstudy,higherconversionsforthefreshcatalystswere associated withlowertemperaturesand shorter reaction times thanthosenormallyfoundintheliterature.Thisindicatesthegreat potentialforthedevelopmentofheterogeneouscatalystsforthe productionofethylicbiodiesel,allowingconversionsequivalentto thoseobtainedwithhomogeneouscatalyststobeachievedunder viablereactionconditionsfromacommercialpointofview.

WealsoprovedthatbothCO2andH2Oarenecessarytopoison

thecatalyst.Therefore,catalystactivationorproperstorageis

nec-essarytomaintaincatalystactivityandsuchstudiesareunderway inourresearchgroup.Thisstudyopensanewapproach,employing heterogeneousbaseMgOcatalystsforbiodieselproductionusing ethanolasthealcoholysisagent.

Whenmagnesiumoxideisemployedfortransesteriﬁcaionof vegetable oil withethanol, it is possible that leaching of solid basecatalystoccurs.Theamountofleachedmagnesiumcoming fromthecatalystpreparedusingthemetal–chitosancomplexation methodreached0.18%duringthebiodieselformation.

Acknowledgements

The authors gratefully acknowledge CNPq and FAPEMIG for ﬁnancialsupport.

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