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2 Fuel 88 (9) 5 55 Contents lists ville t ScienceDirect Fuel journl homepge: Biodiesel synthesis vi homogeneous Lewis cid-ctlyzed trnsesterifiction Nestor U. Sorino Jr., Richrd Venditti, Dimitris S. Argyropoulos * rgnic Chemistry of Wood Components Lortory, College of Nturl Resources, North Crolin Stte University, NC , USA rticle info strct Article history: Received 4 July 7 Received in revised form 25 August 8 Accepted 7 ctoer 8 Aville online 5 Novemer 8 Keywords: Biodiesel Trnsesterifiction Lewis cid Homogeneous ctlysis Lewis cids (AlCl 3 or ZnCl 2 ) were used to ctlyze the trnsesterifiction of cnol oil with methnol in the presence of terhydrofurn (THF) s co-solvent. The conversion of cnol oil into ftty cid methyl esters ws monitored y 1 H NMR. NMR nlysis demonstrted tht AlCl 3 ctlyzes oth the esterifiction of long chin ftty cid nd the trnsesterifiction of vegetle oil with methnol suggesting tht the ctlyst is suitle for the preprtion of iodiesel from vegetle oil contining high mounts of free ftty cids. ptimiztion y sttisticl nlysis showed tht the conversion of triglycerides into ftty cid methyl esters using AlCl 3 s ctlyst ws ffected y rection time, methnol to oil molr rtio, temperture nd the presence of THF s co-solvent. The optimum conditions with AlCl 3 tht chieved 98% conversion were :1 molr rtio t 11 C nd h rection time with THF s co-solvent. The presence of THF minimized the mss trnsfer prolem normlly encountered in heterogeneous systems. ZnCl 2 ws fr less effective s ctlyst compred to AlCl 3, which ws ttriuted to its lesser cidity. Nevertheless, sttisticl nlysis showed tht the conversion with the use of ZnCl 2 differs only with rection time ut not with molr rtio. Ó 8 Elsevier Ltd. All rights reserved. 1. Introduction Biodiesel is n lterntive diesel fuel defined s the mono lkyl esters of long chin ftty cids derived from vegetle oils or niml ft. With the continuous uncertinty nd incresing environmentl impct ssocited with the utiliztion of petroleum-sed diesel fuel, the demnds for iodiesel hd incresed significntly in recent yers. For instnce, the glol production of iodiesel hd incresed from out.5 illion litres in illion litres in 3 [1]. The environmentl, opertionl nd economic enefits ssocited with the utiliztion of iodiesel s n lterntive fuel for diesel engines hve een demonstrted y numerous independent studies nd hve een well ccepted [2 8]. While the se-ctlyzed trnsesterifiction of vegetle oil or niml ft is the most dopted technology for iodiesel commercil production [3,9 1], the process mkes the iodiesel of higher mnufcturing cost compred to petroleum-sed diesel fuel. The process is sensitive to the qulity of the feedstock requiring vegetle oil or niml ft with very low mount of free ftty cid (FFA). The use of refined or high qulity feedstock constitutes 8 88% of the overll production or mnufcturing cost [3,5,11]. Efforts to find lterntive vegetle oil for iodiesel production primrily with the im of lowering the feedstock cost often suggested the utiliztion of wste cooking oil or non-edile vegetle oil contining high * Corresponding uthor. Tel.: +1 (919) ; fx: +1 (919) E-mil ddress: dsrgyro@ncsu.edu (D.S. Argyropoulos). mounts of FFA [ 14]. However, the high mounts of FFA in these oils mke them unsuitle for se-ctlyzed trnsesterifiction. High mounts of FFA resulted in extensive sop formtion s FFA rects with the ctlyst, which is normlly NH or KH, vi sponifiction rection. Sop renders iodiesel purifiction nd ctlyst removl even more chllenging due to the formtion of stle emulsion generting significnt mount of wste wter. The presence of high mounts of FFA in the feedstock therefore eventully leds to decresed iodiesel conversion nd yield. In fct, studies hve demonstrted tht the mount of FFA in the feedstock for iodiesel production should not e higher thn.5% in order to fford product tht psses the ASTM iodiesel stndrd [14]. Acid-ctlyzed trnsesterifiction is more suitle for wste or unrefined oil. The process hs not gined s much ttention s the se-ctlyzed trnsesterifiction ecuse of the slower rection rte nd the very high methnol to oil molr rtio requirements. The two-step iodiesel process ddressed this issue y using n cid ctlyst followed y norml se-ctlyzed trnsesterifiction. The first step involved the esterifiction rection etween the methnol nd FFA to produce the corresponding ftty cid methyl ester (FAME) using H 2 S 4,H 3 P 4 or recently, Fe 2 (S 4 ) 3 [,15] s ctlyst. Severl reserch efforts hve lso een performed on the use of Lewis or Bronsted cids s ctlysts to convert vegetle oil into FAME in oth homogeneous nd heterogeneous systems. Heterogeneous Lewis cid ctlyzed-trnsesterifiction ws chieved using Fe Zn doule metl cynide for the preprtion of iodiesel 1-231/$ - see front mtter Ó 8 Elsevier Ltd. All rights reserved. doi:1.11/j.fuel

3 N.U. Sorino et l. / Fuel 88 (9) nd ioluricnt from vegetle oil contining reltively high mount of FFA nd wter [1]. Sn, P nd Zn complexes in the form M(3-hydroxy-2-methyl-4-pyrone) 2 (H 2 ) 2 hve een demonstrted to e effective in homogeneous Lewis cid ctlyzedtrnsesterifiction of vegetle oil vi the formtion of four-memered ring trnsition stte [17]. Another recent study used croxylic slts of Cd, Mn, P nd Zn s ctlysts for iodiesel synthesis from vegetle oil contining high mount of free ftty cids [13]. This study presents the use of common Lewis cids, AlCl 3 nd ZnCl 2, in iodiesel synthesis primrily to demonstrte n lterntive ctlyst for the simultneous esterifiction of long chin ftty cid nd trnsesterifiction of vegetle oil. ptimiztion of rection conditions ws performed nd supported y sttisticl nlysis. 2. Mterils nd methods 2.1. Trnsesterifiction of cnol oil Typicl iodiesel preprtion ws performed y recting 2. g of commercil cnol oil with known mount of methnol, THF nd AlCl 3 or ZnCl 2 s ctlyst t different rection time nd temperture. In ll the runs, the mount of ctlyst nd THF were 5% (y weight sed on oil) nd 1:1 with respect to methnol (y weight), respectively. The rection ws conducted in round ottom flsk sumerged in n oil th ttched to reflux condenser, temperture controller nd mgnetic stirrer. After the rection, the excess methnol nd THF were removed y vcuum distilltion followed y extrction with petroleum ether or hexnes nd filtrtion to remove the ctlyst. The finl product ws otined y removing the solvent y vcuum distilltion Esterifiction of steric cid Steric cid ws trnsesterified following the procedure descried ove using AlCl 3 s ctlyst t 11 C with molr rtio of methnol to steric cid of nd rection time of h Effect of THF Since ZnCl 2 did not result in stisfctory conversion, the effect of THF ws investigted only with AlCl 3. The effect of THF ws investigted using 5% AlCl 3 (y weight sed on oil), h rection time with different vlues of methnol to oil molr rtio (,,, nd ). The trnsesterifiction ws conducted following the procedure descried ove except tht THF ws not dded in the system NMR nlysis All purified products were nlyzed y 1 H NMR to determine the % conversion. Aout 3 mg of the smple ws dissolved in CDCl 3 for the nlysis. Spectr were recorded using Bruker Avnce 3 MHz NMR Spectrometer Sttisticl nlysis The effect of molr rtio nd temperture on the conversion of cnol oil to FAME were nlyzed y univrite nlysis of vrince (ANVA) to determine the optimum conditions for the rection. Three different sets of experiments were tested individully: the use of AlCl 3 t 75 C, AlCl 3 t 11 C nd ZnCl 2 t 11 C. 3. Results nd discussion H NMR nlysis The trnsesterifiction of cnol oil with methnol using AlCl 3 or ZnCl 2 s ctlyst ws monitored y 1 H NMR. Fig. 1 shows the 1 H NMR spectr of cnol oil nd incompletely trnsesterified cnol oil. The methylene glyceridic protons of the triglycerides resonted t round ppm s two doulets while the glyceridic methine protons resonted t round 5.25 ppm (Fig. 1) [ ]. Percent conversion ws clculted sed on the integrtion vlues of the methylene glyceridic protons nd methyl protons of the FAME, which resonted t 3.7 ppm (Fig. 1). Note tht the glyceridic protons of the intermedite products, mono- nd diglycerides, lso resonted t the sme region s the methylene protons of the strting triglycerides. The glyceridic methine protons were not included in the clcultion since the pek overlps with the lkelinic protons of the unsturted ftty cids of the triglycerides. AlCl 3 ws lso used to esterify steric cid with methnol. Fig. 2 shows the spectr of steric cid nd the purified product otined from the esterifiction rection. Agin, the methyl protons of methyl sterte, which were sent in the 1 H NMR spectr of steric cid, resonted t 3.7 ppm. The use of AlCl 3 to ctlyze the esterifiction of steric cid to methyl sterte resulted in 9% conversion. The ctlyst therefore is suitle for simultneous esterifiction of free ftty cid nd trnsesterifiction of triglycerides. Using AlCl 3, the competing sponifiction rection of free ftty cid could e eliminted giving higher FAME yield nd purity even with the use of strting vegetle oil with high levels of free ftty cids ptimiztion of rection conditions AlCl 3. s ctlyst: effect of rection time, molr rtio nd temperture In trnsesterifiction rection of vegetle oil, three moles of methnol re required to rect stoichiometriclly for every mole of triglyceride molecule to give three moles of the corresponding FAME nd mole of glycerol. Since this rection is reversile, methnol is usully dded in excess of its stoichiometric mount to drive the rection forwrd. In se ctlyzed-trnsesterifiction, molr rtio of is enough to produce 9 98% conversion of vegetle oil with.5 1.% (y weight sed on oil) of ctlyst for 2 h rection. Acid ctlyzed-trnsesterifiction of vegetle oil proceeds severl times slower thn its se ctlyzed counterprt. This could e explined y the different mechnisms y which these two rections occur. In se ctlyzed-trnsesterifiction, strong nucleophile methoxide ion is generted from the rection of the se ctlyst with methnol. The methoxide once produced esily ttcks the cronyl cron to form tetrhedrl trnsition stte tht would eventully led to the formtion of the product. n the other hnd in cid-ctlyzed trnsesterifiction, the cronyl group needs to e ctivted prior to the nucleophilic ttck of methnol, which is reltively weker nucleophile. Hence, while it only tkes out 2 h to fford 95 98% conversion of triglycerides to FAME under sic ctlyst [21], cid ctlyzed-trnsesterifiction normlly requires 48 h rection time to otin comprle conversion. The vrile prmeters employed were rection time (,, h), methnol to oil molr rtio (,,, nd ), rection temperture (75, 11 C), presence of THF s co-solvent (1:1 methnol to THF y weight in runs with THF), nd type of ctlyst (AlCl 3 or ZnCl 2 ). In ll the runs, the ctlyst mount ws kept t 5% sed on the weight of oil. For cid-ctlyzed trnsesterifiction of wste cooking oil using H 2 S 4 s ctlyst, Zheng nd co-workers

4 52 N.U. Sorino et l. / Fuel 88 (9) 5 55 CH 2 CR 1 G2 CHCR 2 CH 2 CR 3 G1 CH 3 H 3 CH 3 CR + glycerol M G2 G1 M ppm Fig H NMR spectr of cnol oil () nd incompletely trnsesterified cnol oil () ppm ppm Fig H NMR spectrum of steric cid () nd trnsesterified steric cid () with 9% conversion. [22] hd identified tht methnol:oil:ctlyst molr rtios nd rection temperture were the most significnt fctors ffecting the FAME yield. In the cse of se-ctlyzed trnsesterifiction, the yield nd purity of the product is most ffected y the initil concentrtion of the ctlyst [23] nd methnol to oil molr rtio []. The optimum conditions for the conversion of cnol oil to FAME using AlCl 3 or ZnCl 2 were determined y univrite nlysis of vrince. Fig. 3 shows the effect of rection time (Fig. 3) nd methnol to oil molr rtio (Fig. 3) on the conversion of cnol oil to FAME using AlCl 3 s ctlyst t 75 C. With methnol to oil

5 N.U. Sorino et l. / Fuel 88 (9) rection time (hrs) Fctor:Time TIME N 1 2 Duncn, Mens for groups in homogeneous susets re disp The error term is Men Squre(Error) Uses Hrmonic Men Smple Size The group sizes re unequl. The hrmonic me of the group sizes is used. Type I error levels not gurnteed. c. Alph.5. 8 molr rtio (MeH to oil) Fctor: Molr rtio MLE RATI N 1 2 Duncn, Mens for groups in homogeneous susets re disply The error term is Men Squre(Error) Uses Hrmonic Men Smple Size 3... Alph.5. Fig. 3. Effect of rection time () nd molr rtio () on the conversion of cnol oil to FAME using 5% AlCl 3 s ctlyst (y wt sed on oil) t 75 C nd THF s co-solvent (1:1 methnol to THF y weight). In (), different molr rtios were,,,, nd. In (), different rection time were,, nd h. The tles show the results of sttisticl nlysis using ANVA. molr rtio of, the rection proceeds slowly ffording only out % conversion fter h rection. With molr rtios of to, the rection rtes were lmost the sme from to h. At 95% confidence level, the % conversion t h differs significntly from nd h. Incresing rection time from to h did not provide significnt increse in the conversion. At shorter rection time ( h), incresing the methnol to oil molr rtios did not result in significnt increse in the conversion giving only % mximum conversion even t higher molr rtios. n the other hnd with nd h rection time, significnt increses in the conversion were oserved from to molr rtios nd remin lmost unchnged from to molr rtios. Sttisticl nlysis showed tht the conversion otined from molr rtio ws significntly different from the conversion otined from to molr rtios regrdless of rection time. While the optimum conditions with the use of 5% AlCl 3 (sed on weight of oil) ws estlished t n h rection time nd methnol to oil molr rtio of, the mximum conversion otined ws only in the rnge of 84 8%. Since reltively lower conversions were otined with the use of AlCl 3 t 75 C, the trnsesterifiction t higher temperture ws then conducted. Fig. 4 shows the effect of rection time (Fig. 4) nd methnol to oil molr rtio (Fig. 4) on the conversion of cnol oil to FAME using AlCl 3 s ctlyst t 11 C s well s the results otined from sttisticl nlysis. The rection time ffects the conversion depending on the methnol to oil molr rtio. At lower molr rtio of, the conversion otined from to h ws only out 7% with mximum conversion of 25% t h rection time. The rtes of rection from to h for molr rtios of, were similr nd low. Under these conditions, the conversion rnges only from 81% to 98% suggesting tht the commonly oserved higher rection rtes t the eginning of trnsesterifiction rection hd occurred within the first h of the rection. The plot of % conversion vs rection time with molr rtio of nd ws typicl for trnsesterifiction. At h rection time, the% conversion from higher molr rtios ( nd ) ws even lower thn tht otined from lower molr rtios of nd. The effect of methnol to oil molr rtio is clerly depicted in Fig. 4. For oth 75 nd 11 C, while the conversion hd incresed with incresing molr rtios from to, further increse with molr rtio of or hd decresed the conversion especilly with h rection time. The presence of high excess of methnol could hve dectivted the ctlyst t this temperture. Another possiility for the decrese in conversion could e ttriuted to the recomintion of FAME with glycerol considering tht trnsesterifiction is reversile rection. In the presence of high mount of methnol, seprtion of glycerol nd FAME into two lyers is less fvorle ecuse of the higher soluility of glycerol in the system fvoring the ckwrd rection []. Sttisticl nlysis showed tht the use of AlCl 3 t 11 C hs optimum conditions of molr rtios conducted t h rection time to give mximum conversion of 98%. At ny given rection time nd methnol to oil molr rtio, the conversion of cnol oil to FAME hd incresed with incresing rection temperture from 75 to 11 C. While the optimum conversions t 75 nd 11 C differ y %, they were oth otinle with the use of methnol to oil molr rtio of nd with rection time of h ZnCl 2 s ctlyst: effect of rection time nd molr rtio ZnCl 2 ws less effective in ctlyzing the trnsesterifiction of cnol oil into FAME, which is ttriuted to its weker cidity. Except with molr rtio of, incresing the rection time did not result in significnt increse in the conversion, which rnged only from 3% to 22%. Nevertheless, sttisticl nlysis showed tht the conversions otined from nd h rection times were not significntly different thn the conversions from nd h rection times. Moreover, the sence of plteu in Fig. 5 suggests tht the conversion would still increse if the rections were to extend more thn h. Sttisticl nlysis lso showed tht the conversion does

6 54 N.U. Sorino et l. / Fuel 88 (9) time (hrs) Fctor:Time TIME N 1 2 Duncn, Mens for groups in homogeneous susets re disp l The error term is Men Squre(Error) Uses Hrmonic Men Smple Size 5... Alph.5. 8 molr rtio Fctor: Molr rtio MLE RATI N Duncn, Mens for groups in homogeneous susets re displyed. The error term is Men Squre(Error) Uses Hrmonic Men Smple Size 3... Alph.5. Fig. 4. Effect of rection time () nd molr rtio () on the conversion of cnol oil to FAME using 5% AlCl3 s ctlyst (y wt sed on oil) t 11 C nd THF s co-solvent (1:1 methnol to THF y weight). In (), different molr rtios were,,,, nd. In (), different rection time were,, nd h. The tles show the results of sttisticl nlysis using ANVA rection time (hrs) Fctor: Time TIME N 1 2 Duncn, Mens for groups in homogeneous susets re disp The error term is Men Squre(Error) Uses Hrmonic Men Smple Size 5... Alph.5. 8 molr rtio Fctor: Molr rtio MLE RATI Duncn, N Mens for groups in homogeneous susets re dis The error term is Men Squre(Error) Uses Hrmonic Men Smple Size 3... Alph.5. Fig. 5. Effect of rection time () nd molr rtio () on the conversion of cnol oil to FAME using 5% ZnCl2 s ctlyst (y wt sed on oil) t 11 C nd THF s co-solvent (1:1 methnol to THF y weight). In (), different molr rtios were,,,, nd. In (), different rection time were,, nd h. The tles show the results of sttisticl nlysis using ANVA. not vry significntly with incresing molr rtio. This is especilly true when the rection time ws only h, where the conversion rnged only from 3% to % with molr rtio rnging from to. With the use of ZnCl 2, the mximum conversion chieved ws only 48%, otinle with molr rtio of nd rection time of h. This conversion is comprle with the use of AlCl 3 with molr rtio ut with rection time of only h nd even much lower compred to the conversion otined with AlCl 3 with molr rtio of nd rection time of h tht resulted in 83% conversion. It is very cler therefore tht ZnCl 2 owing to its lesser cidity is fr less effective thn AlCl 3 in ctlyzing the trnsesterifiction of vegetle oil.

7 N.U. Sorino et l. / Fuel 88 (9) Effect of THF Trnsesterifiction of vegetle oil with methnol is twophse process due to the huge differences in polrities of methnol nd oil. THF, dded t the level of 1.25 volume per volume of methnol, my ct s co-solvent in the trnsesterifiction of vegetle oil with methnol [1]. The ddition of THF led to the formtion of homogeneous oil-rich trnsesterifiction process resulting to fster rection rtes. In our cse however, dding 1:1 THF to methnol y weight resulted in cler homogeneous system when the methnol to oil molr rtio ws or greter. With methnol to oil molr rtio of, the resulting mixture ws it cloudy due to the low soluility of the ctlyst in the system. Formtion of two lyers were oserved when the methnol to oil molr rtio ws only even in the presence of THF. The oiling point of THF is only 2 degrees higher thn methnol nd hence ws recovered together with methnol y distilltion. Fig. shows the effect of dding THF s co-solvent in the trnsesterifiction of cnol oil with methnol using AlCl 3 t 11 C, h rection time nd vrying methnol to oil molr rtios ( ). The ddition of THF decresed the conversion y 1% when methnol to oil molr rtio ws only. As mentioned ove t this molr rtio, the mount of THF (since the mount of THF ws sed on the mount of methnol used) dded ws not enough to fvor the formtion of single-phse system. Since AlCl 3 is more solule in polr solvents, the methnol-thf phse ws enriched with the ctlyst. For se-ctlyzed trnsesterifiction, ctlyst-rich methnol phse is not much of prolem since the very first rection involved in this process is the genertion of methoxide ion from the rection of the sic ctlyst (usully NH or KH) with methnol. n the other hnd with the AlCl 3 in the methnol-thf phse, ctivtion of the cronyl cron of the triglyceride molecules ws minimized since this occurs vi the electrophilic ttck of AlCl 3 with the cronyl oxygen tht eventully leds to lower conversion. At higher molr rtios, the ddition of THF resulted in significntly higher conversions s result of the formtion of onephse system. In the presence of THF, the mss trnsfer prolem normlly encountered in heterogenous system ws eliminted. Moreover, with AlCl 3 nd triglyceride in the sme phse, ctivtion of cronyl cron is more fvorle eventully leding to higher conversion. 4. Summry nd conclusions with THF without THF molr rtio (MeH to oil) Fig.. Effect of dded THF s co-solvent in the conversion of cnol oil to FAME using 5% AlCl3 s ctlyst t 11 C nd h rection time with incresing methnol to oil molr rtio. The use of AlCl 3 nd ZnCl 2 s ctlyst for iodiesel synthesis ws reported. AlCl 3, eing stronger Lewis cid thn ZnCl 2, ctlyzed the trnsesterifiction of cnol oil fr more effectively thn ZnCl 2. It ws lso demonstrted tht AlCl 3 could ctlyze the esterifiction of steric cid suggesting tht it is potentil lterntive ctlyst for iodiesel preprtion using cheper vegetle oil contining high mount of FFA. Sttisticl nlysis showed tht the optimum conditions to fford 98% conversion of cnol oil to FAME is with the use of methnol to oil molr rtio nd rection time of h t 1 C in the presence of 5% AlCl 3 s ctlyst nd THF s co-solvent. The dded THF minimized the mss trnsfer prolems normlly encountered in heterogeneous systems resulting in n increse in conversion. Regrdless of molr rtio nd rection time, conversions using AlCl 3 hd incresed with increse in rection temperture. While sttisticl nlysis showed tht the conversion differed significntly with molr rtio nd rection time with the use of AlCl 3, conversion using ZnCl 2 differed only with rection time nd not with molr rtio. References [1] Demirs MF, Blt M. Recent dvnces on the production nd utiliztion trends of io-fuels: glol perspective. Energy Convers Mnge ;47: [2] M F, Hnn MA. Biodiesel production: review. Bioresour Technol 1999;7:1 5. [3] Zhng Y, Due MA, McLen DD, Ktes M. Biodiesel production from wste cooking oil: 2. Economic ssessment nd sensitivity nlysis. Bioresour Technol 3;9:229. [4] Knothe G, Shrp CA, Ryn TW. Exhust emissions of iodiesel, petrodiesel. Net methyl esters, nd lknes in new technology engine. Energy Fuels ;:3 8. [5] Demirs A. Importnce of iodiesel s trnsporttion fuel. Energy Policy 7;35:41 7. [] Murillo S, Miguez JL, Porteiro J, Grnd E, Morn JC. 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