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J. of Supercritical Fluids 79 (2013) 73–75

Contents lists available at SciVerse ScienceDirect

The Journal of Supercritical Fluids

journa l homepage: www.e lsev ier .com/ locate /supf lu

nfluence of impurities on biodiesel production from Jatropha curcas L. byupercritical methyl acetate process

oorzalila Muhammad Nizaa, Kok Tat Tanb, Keat Teong Leec,∗, Zainal Ahmadc

Faculty of Chemical Engineering, UiTM Pulau Pinang, 13500 Permatang Pauh, Pulau Pinang, MalaysiaDepartment of Petrochemical Engineering, Faculty of Engineering and Green Technology, Universiti Tunku Abdul Rahman, Jalan Universiti, Bandar Barat, 31900 Kampar, Perak,alaysia

School of Chemical Engineering, Universiti Sains Malaysia, Engineering Campus, Seri Ampangan, 14300 Nibong Tebal, Pulau Pinang, Malaysia

r t i c l e i n f o

rticle history:eceived 29 June 2012eceived in revised form 21 February 2013ccepted 24 February 2013

eywords:iodieselupercritical methyl acetate

a b s t r a c t

Generally, water and free fatty acid (FFA) content in oils could cause a serious problem during conven-tional transesterification such as saponification. Thus, without any pre-treatment, vegetable oil, especiallywith high FFA content, will be affected. In this study, a non-catalytic supercritical methyl acetate (SCMA)process was utilized to produce biodiesel from Jatropha curcas L. oil. The effects of water and FFA contenton the yield of biodiesel were investigated. The results obtained for the effects of water on the yield ofbiodiesel were compared with the supercritical methanol (SCM) process and conventional catalytic reac-tion. Results revealed that the catalytic reaction suffers from low yield with the presence of high water

upercritical methanolater

ree fatty acidsatropha oil

content in oil. Meanwhile, the yield of both the SCM and SCMA reactions were found to increase slightlywith the increment of water content in the mixture. On the other hand, the results for the effect of FFAon the yield of biodiesel were compared with the SCM reaction. It was found that the presence of FFA hasa negligible effect in both the SCMA and SCM reactions. These findings demonstrate that pre-treatmentprocedures are not necessary in the SCMA process for Jatropha oil which normally contains a high FFAcontent.

. Introduction

Biodiesel is one of the alternative fuels comprised of mono-lkyl esters of long-chain fatty acids derived from vegetable oilsr animal fat. This fuel is obtained by a transesterification reac-ion with an alcohol, with or without the presence of a catalyst, toroduce glycerol as a co-product [1]. The use of biodiesel in dieselngines is advantageous for its environmental friendliness overetrol–diesel such as reducing carbon dioxide emissions, providing

ubricity improvement [2,3], and having better properties in termsf biodegradability, free sulphur content, viscosity, density andash point [4,5]. In addition, the feedstock for biodiesel productionan be derived from renewable sources such as edible/non-edibleils and waste animals fats, which are abundantly available andnexhaustible [6]. Therefore, production of biodiesel could ensurehe sustainability of human development and an energy source inhe future.

The common method to produce biodiesel is by conventionalransesterification using alkaline catalyst. Normally, conventionalransesterification reactions will be accompanied by side reactions

∗ Corresponding author. Tel.: +60 4 5996467; fax: +60 4 5941013.E-mail address: chktlee@eng.usm.my (K.T. Lee).

896-8446/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.supflu.2013.02.021

© 2013 Elsevier B.V. All rights reserved.

such as saponification and hydrolysis if low quality feedstock isemployed due to the presence of impurities such as free fatty acids(FFA) and water, respectively. For instance, as shown in Eq. (1),excessive FFA content in the base catalyzed reaction could leadto the formation of soap and water. Therefore, high FFA contentpresent in vegetable oil must be neutralized with excess base. Thiscould complicate the production process, and the yield obtainedwill be reduced since the FFA has been neutralized and not con-verted to biodiesel esters.

On the other hand, the presence of water could consume thecatalyst and reduces catalyst efficiency [7]. As shown in Eq. (2),water induces the hydrolysis reaction of biodiesel esters to FFA andalcohol. The FFA can subsequently react with base-catalyst and willresult in the formation of more soap and water until the catalyst isfinally consumed and deactivated.

RCOOHFFA

+ NaOHBase catalyst

↔ RCOONa+Soap

+ H2OWater

(1)

RCOOR′Alkyl ester

+ H2OWater

Base catalyst←→ RCOOHFFA

+ R′OHAlcohol

(2)

In our previous work, we have produced biodiesel from non-catalytic supercritical methyl acetate (SCMA), employing Jatrophaoil as feedstock [8]. In SCMA, triacetin is produced as side productrather than glycerol. In addition, triacetin is a valuable compound

7 rcritical Fluids 79 (2013) 73–75

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4 N.M. Niza et al. / J. of Supe

nd could be utilized as a fuel additive. In the previous work, theptimum conditions were reported to be at a reaction temperaturef 400 ◦C, 32 min for reaction time, and 50 mol/mol molar ratiof methyl acetate to oil. Nonetheless, the Jatropha oil used in thistudy has high FFA content with a value of 10.5% (w/w). Hence, inhe present work, the feasibility of supercritical methyl acetate foriodiesel production from Jatropha oil was investigated further byocusing on the influence of impurities such as water and FFA con-ent on biodiesel yield. The effect of water on the yield of biodieselas also compared with that from conventional transesterification.

. Materials and methods

.1. Raw materials and chemicals

The raw material which is Jatropha curcas L. oil was purchasedrom Bionas Sdn. Bhd. For the transesterification reaction, thehemicals used are methyl acetate (≥99) and methanol (99.8), pur-hased from Merck. For the effect of FFA content, pure oleic acidas used in the reaction. The internal standard which is methyleptadecanoate (≥99.5) and reference standards such as methylalmitate, methyl stearate, methyl oleate and methyl linoleateere purchased from Fluka Chemie and utilized for gas chromatog-

aphy analysis.

.2. Apparatus

The transesterification by SCMA process was carried out usingsupercritical reactor system, which can sustain the high temper-ture and pressure needed in supercritical treatment. The systemainly consists of a reaction tube of 12 mL made from stainless

teel 316, a furnace and a chilled water bath. A pressure gaugend temperature controller were utilized to monitor the reactionemperature and pressure, respectively.

.3. Procedures

To simulate the effects of water on biodiesel yield, the waterontent was varied with 5, 7, 10, 15 and 20 wt% of oil. The reactionas carried out at optimum conditions of 400 ◦C reaction temper-

ture, 32 min of reaction time and at 50:1 molar ratio of methylcetate to oil as obtained from our previous study [8]. Initially, are-determined amount of reactants were charged into the reac-ion tube. A pressure gauge was connected onto the tube, and theube was then inserted in a furnace which was heated to a pre-etermined temperature. After the desired reaction period waseached, the reaction was stopped immediately by transferring theube into the chilled water bath. Subsequently, the product was col-ected, and excess methyl acetate was removed by evaporation. Theample was then analyzed using gas chromatography to determinehe fatty acid methyl esters (FAME) content. The effect of waterontent was also investigated in the supercritical methanol reac-ion at optimum conditions of SCM; 358 ◦C, molar ratio of methanolo oil at 44:1 and 27 min of reaction time [8]. Since Jatropha oil con-ists of high FFA content, experimental results were also obtainedrom reaction with the conventional acid-catalyzed method using

ethanol to assess the effect and behavior of water content oniodiesel yield through conventional transesterification at a tem-erature of 65 ◦C with a molar ratio of methanol to oil of 6:1 andwt% of sulphuric acid [9].

Oleic acid, the highest FFA percentage in Jatropha oil, was choseno investigate the effect of free fatty acids content on biodiesel. The

leic acid content was varied from 5 to 20 wt% of oil. The reactionas carried out at optimum conditions as obtained from the opti-ization of SCMA study [8]. For comparison, experiments were also

arried out in the SCM reaction at optimum conditions of 358 ◦C,

Fig. 1. Effect of water addition in the SCM, SCMA and acid catalyzed reaction.

44 mol/mol of methanol to oil molar ratio and 27 min of reactionperiod [8].

2.4. Analytical procedure

The FAME samples were first diluted with an internal standard.Then 1 �L of each sample was injected into a gas chromatograph(PerkinElmer, Clarus 500) equipped with a NukolTM capillary col-umn (15 m×0.53 mm; 0.5 �m film) and a flame ionization detector(FID). n-Hexane was used as the solvent while helium gas was usedas the carrier gas. The oven temperature was set at 110 ◦C and thenincreased to 220 ◦C at a rate of 10 ◦C/min. The temperature of thedetector and injector were set at 250 ◦C and 220 ◦C, respectively.The yield of FAME was calculated using the areas obtained in thegas chromatographic analysis with the following Eq. (3).

FAME yield (%) =∑

Weight of fatty acid methyl estersWeight of Jatropha oil used (g)

× 100 (3)

3. Results and discussion

3.1. Effect of water content on FAME yield

Fig. 1 shows a direct comparison of the yield of FAME obtainedfrom the three methods; SCMA, SCM and conventional acid-catalyzed reaction. In the conventional acid-catalyzed reaction, theaddition of water in the reaction led to a significant reduction of theyield of FAME. The yield of FAME was reduced to 15% when only 5%of water was added. The reduction in yield of biodiesel observedat high water content was attributed to equilibrium being reachedin the reaction. At this point, the increased water concentrationcauses the reverse reaction, thus hydrolysing the triglycerides intoFFA as shown in Eq. (4). Furthermore, formation of water in themethyl esterification of FFA with methanol in the acid catalyzedmethod could reduce the catalyst activity in the transesterification[7]. Consequently, the efficiency of sulphuric acid is significantlyaffected. Therefore, the conventional acid-catalyzed method maynot be suitable for Jatropha oil with high FFA content as more FFAwill be produced in the reaction resulting in a low yield of FAME.

On the other hand, the addition of water in the SCMA reactiondid not have any significant change on the yield of FAME. Similar tothe acid-catalyzed reaction, the presence of water in the reactionmixture induces hydrolysis of triglycerides, which will produce FFAand glycerol as shown in Eq. (4) [10]. Subsequently, the FFA willbe esterified with methyl acetate to produce FAME and acetic acid

as shown in Eq. (5) [11]. The glycerol formed in the reaction willthen react with acetic acid to produce triacetin and water (Eq. (6)).Hence, with the presence of water in the SCMA reaction, there is no

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Fig. 2. Effect of addition of free fatty acid in the SCM and SCMA reactions.

dverse effect on the yield of FAME compared to the conventionalcid-catalyzed method.

riglyceride + Water � Freefattyacid + Glycerol (4)

reefattyacid + Methylacetate � Biodiesel + Aceticacid (5)

lycerol + Aceticacid � Triacetin + Water (6)

Meanwhile, in the SCM reaction, the amount of water addednto the reaction system also did not have any significant effect onhe yield of FAME. Similarly in the SCMA reaction, the presence ofater could induce the hydrolysis of triglycerides, which subse-

uently produces free fatty acids and glycerol. The free fatty acidill then react with methanol to produce FAME and water. Kusdi-

na and Saka also have reported that the presence of water in theCM method could presumably act as an acid catalyst [7].

In comparing between the SCM and SCMA methods, the SCMreatment has been shown to have higher tolerance toward waterontent compared to the SCMA reaction. This observation is due tohe fact that the reaction rate of methanol in the water added forCM treatment is higher than in SCMA. Water has the capability ofissolving both non-polar and polar solutes since its dielectric con-tant can be adjusted from a room temperature value of 80–5 at itsritical point [12]. Therefore, water can solubilize most non-polarrganic compounds including most hydrocarbons at temperaturebove 250 ◦C. In addition, water at temperatures between 280 ◦Cnd 350 ◦C is rich with ionic products. Hence, when it is mixed witholar methanol, the mixture will have both strong hydrophilic andydrophobic properties [7].

.2. Effect of FFA content on FAME yield

Fig. 2 shows the results of the influence of FFA on FAME yieldor SCMA and SCM. The results revealed that FFA contained in oilsoes not affect the yield of FAME substantially in SCM and SCMAeactions. Instead, the presence of FFA may slightly increase theonversion of biodiesel as the oleic acid content was increased inatropha oil. In the SCM reaction, the addition of FFA can be ester-

fied with methanol to produce FAME. This esterification reactionlso produces water as a side product which could help in hydroly-is process of triglycerides and subsequently increase the reactionield [6].

[

al Fluids 79 (2013) 73–75 75

On the other hand, the addition of FFA content in SCMA alsoslightly increase the yield of FAME. As reported by Saka andIsayama, this may be due to the starting material of oleic acidand/or the acetic acid produced that plays the role of acid catalysiswhich could improve biodiesel production [13]. Although this reac-tion produced acetic acid as the side product, this can be removedfrom the reaction by employing vacuum evaporation due to thedifference in boiling points. Hence, the performance of the SCMAmethod in high FFA content oils is comparable with the establishedsupercritical methanol (SCM) method.

4. Conclusion

Overall, the performance of SCMA and SCM in producing FAMEwith the presence of impurities such as FFA and water is compara-ble. Both processes show a high tolerance toward the presence ofimpurities in the reaction medium with consistent high yield. How-ever, SCMA has the advantage compared to SCM since the SCMAprocess could produce a valuable compound, triacetin, as a sideproduct, instead of the unwanted glycerol. On the other hand, theacid-catalyzed reaction suffered a substantial reduction in FAMEyield even with a low percentage of water (5%).

Acknowledgments

The authors would like to acknowledge Ministry of HigherEducation, Malaysia (FRGS Grant No.: 6071233) for the financialsupport given.

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