VOLUME 23
JANUARY 2009 Copyright 2009 by the American Chemical Society
Articles Comparison of Novozym 435 and Amberlyst 15 as Heterogeneous Catalyst for Production of Biodiesel from Palm Fatty Acid Distillate M. M. Rahman Talukder,* J. C. Wu, S. K. Lau, L. C. Cui, G. Shimin, and A. Lim Institute of Chemical and Engineering Sciences, 1 Pesek Road, Jurong Island, Singapore 627833, Singapore ReceiVed July 31, 2008. ReVised Manuscript ReceiVed October 10, 2008
Palm fatty acid distillate (PFAD), a byproduct from the palm oil refinery process, has recently been utilized as an alternative feedstock for biodiesel (BD) production via homogeneous acid-catalyzed esterification. This process suffers from catalyst recovery, wastewater treatment, and BD purification. To minimize the problem, heterogeneous catalysts, Novozym 435 (immobilized Candida antarctica lipase B) and Amberlyst 15 (acidic styrene-divinylbenzene sulfonated ion-exchange resin), are tested and their catalytic activities under various reaction conditions are compared. Novozym 435 acts fast and its optimal specific activity (g BD/h/g catalyst) is 50-fold higher than that of Amberlyst 15. The maximum BD yields obtained using Novozym 435 and Amberlyst 15 are 95 and 97%, respectively. Both catalysts are recycled more than 15 cycles without losing their activities. The results suggest that both Novozym 435 and Amberlyst 15 can be effectively used for BD production from PFAD.
Introduction Biodiesel [fatty acid methyl ester (FAME)] is industrially produced from natural triglyceride, typically vegetable oils. Many biodiesel industries are currently stopped due to the shortage of feedstock, vegetable oils, the price of which accounts for 75-85% of biodiesel’s cost. Among vegetable oils, palm oil ranks among the best in terms of availability and cost. The price of palm oil has significantly increased due to the tremendous growth of biodiesel (FAME) industries. Therefore, there is a need to explore alternative feedstock for biodiesel (BD) production. Palm fatty acid distillate (PFAD), a byproduct from the palm oil refinery process, with a free fatty acid (FFA) content of more than 93 wt %, has recently been reported as an alternative and relatively cheaper feedstock for BD production via homogeneous acid (H2SO4) catalyzed esterification.1 This process suffered from the difficulties in BD purification, catalyst recovery, and * To whom correspondence should be addressed. Fax: +65-63166182. E-mail:
[email protected]. (1) Chongkhong, S.; Tongurai, C.; Chetpattananondh, P.; Bunyakan, C. Biomass Bioenergy 2007, 31, 563–568.
wastewater treatment, thereby increasing BD production cost. Although homogeneous base catalysts are currently used for production of biodiesel from vegetable oil, they are not suitable for PFAD due to the formation of soap, hindering biodiesel purification and glycerol recovery. In contrast, heterogeneous catalysts can be easily recovered and provide clean technology with a simplified downstream process. Heterogeneous catalysts such as solid acids2,3 and immobilized lipases4-6 have been reported for biodiesel production from vegetable oil. However, there is no report on the use of such catalysts for production of biodiesel from PFAD. Here, we report the application of Novozym 435 (immobilized Candida antarctica lipase B) and Amberlyst 15 (acidic styrenedivinylbenzene sulfonated ion-exchange resin) as heterogeneous (2) Ni, J.; Meunier, F. C. Appl. Catal. A 2007, 333, 122–130. (3) Jitputti, J.; Kitiyanan, B.; Rangsunvigit, P.; Bunyakiat, K.; Attanatho, L.; Jenvantipanjakul, P. Chem. Eng. J. 2006, 116, 61–66. (4) Du, W.; Xu, Y.; Liu, D.; Zeng, J. J. Mol. Catal. B 2004, 30, 125– 129. (5) Talukder, M. M. R.; Puah, S. M.; Wu, J. C.; Choi, W. J.; Chow, Y. Biocat. Biotrans. 2006, 24, 257–262. (6) Talukder, M. M. R.; Beatrice, K. L. M.; Song, O. P.; Puah, S.; Wu, J. C.; Won, J. C.; Chow, Y. Energy Fuel 2008, 22, 141–144.
10.1021/ef8006245 CCC: $40.75 2009 American Chemical Society Published on Web 12/09/2008
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catalyst for production of biodiesel from PFAD. Novozym 435 and Amberlyst 15 are among the best commercial heterogeneous biocatalyst and acid catalyst, respectively. The performances of these two catalysts are compared. Experimental Section Materials. Novozym 435, Amberlyst 15, and standard methyl esters were purchased from Sigma. PFAD was purchased from Wawasan Tebrau SDN BHD, Johor, Malaysia. It consists of 97 wt % FFA and the rest is triglycerides, diglycerides, monoglycerides, and traces of impurities. The methanol and organic solvents were bought from J.T. Baker. All chemicals were analytical grade and were used as received. Esterification of PFAD. The esterification of PFAD was carried out in 100 mL screw-capped bottles. PFAD in the presence or absence of solvent was first preheated to reaction temperature. Novozym 435 or Amberlyst 15 was mixed with preheated PFAD and the reaction was initiated by adding methanol. Operating parameters such as reaction temperature in the range of 50-60 °C, methanol content in range of 5-25 wt % of PFAD, Novozym 435 in the range of 0.5-6 wt % of PFAD, and Amberlyst 15 in the range of 10-60% of PFAD were investigated. Recycling of Novozym 435 and Amberlyst 15. Novozym 435 and Amberlyst 15 in isooctane-mediated system were filtered after reaction, washed respectively with tert-butyl alcohol and methanol, and freeze-dried. The reaction time for each cycle was kept constant at 2 and 7 h for Novozym 435 and Amberlyst 15, respectively. Analysis. The sample after specified reaction time was diluted with hexane (40 mL) and filtered to separate Novozym 435 and Amberlyst 15. The filtrate was then centrifuged at 5000 rpm to obtain the upper layer. The methyl esters (biodiesel) content in the upper layer was analyzed by HPLC with a UV detector at 210 nm.7,8 A Prevail-C18 5 µm column (4.6 × 250 mm, Altech Inc.) was employed. The mobile phase consisted of three different components: hexane, 2-propanol, and methanol. Reservoir A contained methanol and reservoir B contained a mixture of 2-propanol and hexane (5:4, v/v). The gradient went from 100% A to 50% A + 50% B linearly over 30 min. The flow rate of the mobile phase was 1 mL/min and the sample injection volume was 10 µL. The yield of BD was calculated as grams of BD produced per gram of PFAD. The acid content in the sample before and after reaction was analyzed by the standard titration method. For this, sample (0.5 g) was dissolved in 50 mL of acetone-ethanol (50/50, v/v) and then titrated against 0.2 N NaOH using phenolphthalein indicator.
Figure 1. Biodiesel yield at different methanol concentration. Reaction conditions for Novozym 435 catalytic system: PFAD, 5 g; Novozym 435, 0.2 g; temperature, 60 °C; agitation speed, 250 rpm; reaction time, 2 h. Reaction condition for Amberlyst 15: PFAD, 5 g; Amberlyst 15, 1.5 g; temperature, 60 °C; agitation speed, 250 rpm; reaction time, 7 h.
Figure 2. Effect of catalyst load. Reaction conditions are the same as those in Figure 1, except the methanol content for Novozym 435 and Amberlyst 15 catalytic system are 13 and 20 wt % of PFAD, respectively.
Results and Discussion Methanol Poisoning of Novozym 435 and Amberlyst 15. Figure 1 shows that BD yield in the Novozym 435 catalytic system drops at a methanol content of more than 13 wt % of PFAD, while the yield in Amberlyst 15 catalytic system remains the same at higher methanol content, indicating that Amberlyst 15 is more methanol tolerant than Novozym 435. Methanol has been reported as a poison9 for Novozym 435, therefore, the yield at higher methanol content decreases. In subsequent studies, methanol contents for Novozym 435 and Amberlyst 15 are kept constant at 13 and 20 wt %, respectively. Effect of Novozym 435 and Amberlyst 15 Amount. To optimize catalyst amount, reaction times for Novozym 435 and Amberlyst 15 are kept constant at 2 and 7 h, respectively. Figure 2 shows that the minimum amount of Novozym 435 (1 wt % of PFAD) required for obtaining maximum BD yield is much (7) Holcapek, M.; Jandera, P.; Fischer, J.; Prokes, B. J. Chromatogr. 1999, 858, 13–31. (8) Chen, J. W.; Wu, W. T. J. Biosci. Bioeng. 2003, 95, 466–469. (9) Shimada, Y.; Watanabe, Y.; Sugihara, A.; Tominaga, Y. J. Mol. Catal. B 2002, 76, 133–142.
Figure 3. Biodiesel yield with reaction time at different reaction temperatures. Reaction conditions are the same as those in Figure 2.
lower than that of Amberlyst 15 (30 wt % of PFAD). The results indicate that Novozym 435 is more active than Amberlyst 15. BD formation with time is found to be linear within the reaction time 0.25 and 1.0 h for Novozym 435 and Amberlyst 15, respectively (Figure 3), and the specific activity (grams of BD per hour per gram of catalyst) of Novozym 435 is 50-fold higher than that of Amberlyst 15. Time Course Methyl Esterification of PFAD. Since PFAD melting point and methanol boiling point are respectively about
Biodiesel from Palm Fatty Acid Distillate
Energy & Fuels, Vol. 23, 2009 3 Table 1. Effect of Organic Solventa on Esterification of PFAD biodiesel yield (%)
Figure 4. Effect of added water on Novozym 435 and Amberlyst 15 activities. Reaction conditions are the same as those in Figure 2, except the reaction temperature for the Novozym 435 catalytic system is 50 °C.
50 and 65 °C, the time course of methyl esterification was examined at temperatures of 50 and 60 °C (Figure 3). Novozym 435 activities at both 50 and 60 °C are the same and BD yield reaches 90% at reaction time of 2 h, after which it remains the same. In contrast, Amberlyst 15 is more active at 60 °C and the BD yield reaches a maximum (97%) at a time range of 6-8 h. Effect of Water Content. Water usually inhibits esterification and accelerates hydrolysis. To know the inhibition effect of water on esterification of PFAD, different amounts of water were added into the reaction mixture and BD yield was analyzed. Figure 4 shows that water inhibits the activity of Amberlyst 15 more considerably than that of Novozym 435. For example, in presence of water equivalent to 4 wt % PFAD, BD yield in Amberlyst 15 catalytic system drops from 97 to 80%, while in the case of Novozym 435, it drops from 90 to 86%. Novozym 435 is most active for esterification and least active for hydrolysis; therefore the effect of water on the esterification activity of Novozym 435 is not significant. Amberlyst 15 is very hygroscopic and may adsorb water on its surface, inhibiting the access of hydrophobic substrate, PFAD. Hence, the activity dropped. Esterification of PFAD in Organic Solvent. Organic solvents are often used in a reaction to improve mixing efficiency between reactants, ease recovery of catalyst, and shift the reaction equilibrium forward. From this viewpoint, several organic solvents of log P values between -1.3 and 4.5 are tested (Table 1). It is found that nonpolar solvent, such as isooctane or hexane, improves BD yield in Novozym 435 catalytic system from 90 to 95%, while their effect on the yield in Amberlyst 15 catalytic system is negligible. Polar solvent is generally more toxic to Novozym 435 than nonpolar solvent. It was found that Novozym 435 exhibited only 5% of its initial activity after 24 h incubation with dimethyl sulfoxide (DMSO), while the same enzyme keeps its 90% activity when incubated with isooctane. The inactivation of Novozym 435 by polar solvent such as DMSO and dimethylformamide (DMF) has previously been reported.10,11 Both Novozym 435 and Amberlyst 15 adsorb polar solvent, inhibiting the access of nonpolar PFAD to their active site, causing a decrease in BD yield. Nonpolar solvent facilitates the separation of water (byproduct) from the oil phase, shifting the reaction equilibrium forward. (10) Plou, F. J.; Cruces, M. A.; Ferrer, M.; Fuentes, G.; Pastor, E.; Bernabe, M.; Christensen, M.; Comelles, F.; Parra, J. L.; Ballesteros, A. J. Biotechnol. 2002, 96, 55–66.
solvent (log P)
Novozym 435 catalytic system
Amberlyst 15 catalytic system
no solvent isooctane (4.5) hexane (3.5) acetonitrile (-0.33) tetrahydrofuran (0.49) acetone (-0.23) tert-butanol (0.8) dimethylsulfoxide (-1.3)
90.2 95.2 94.5 91.3 79.5 82.1 73.3 7.0
97.4 96.8 97.0 80.2 77.5 72.5 44.2 16.6
a log P values of solvents are obtained from the literature.12,13 Reaction conditions for Novozym 435 catalytic system: solvent to PFAD ratio, 1.0 (v/v); PFAD, 5g; Novozym 435, 0.2 g; temperature, 50°C; agitation speed, 250 rpm; methanol content, 13 wt % of PFAD; reaction time, 2 h. Reaction condition for Amberlyst 15: solvent to PFAD ratio, 1.0 (v/v); PFAD, 5g; Amberlyst 15, 1.5g; temperature, 60°C; agitation speed, 250 rpm; methanol content, 20 wt % of PFAD; reaction time, 7 h.
Table 2. Reusability of Novozym 435 and Amberlyst 15 in Isooctane-Mediated Systemsa BD yield (%)
a
cycle no.
Novozym 435 catalytic system
Amberlyst 15 catalytic system
1 3 5 7 9 11 13 15
95.1 95.3 94.9 94.6 95.6 95.3 94.7 94.9
97.4 98.0 97.8 97.1 97.2 97.5 97.3 97.0
Reaction conditions are the same as those mentioned in Table 1.
Figure 5. Effect of isooctane to PFAD ratio (v/v) on esterification of PFAD. Reaction conditions for Novozym 435 catalytic system: PFAD, 5 g; Novozym 435, 0.2 g; temperature, 50 °C; methanol content, 13 wt % of PFAD; agitation speed, 250 rpm; reaction time, 2 h. Reaction condition for Amberlyst 15: PFAD, 5 g; Amberlyst 15, 1.5 g; methanol content, 20 wt % of PFAD; temperature, 60 °C; agitation speed, 250 rpm; reaction time, 7 h.
Figure 5 shows the effect of isooctane content on BD yield. The maximum BD in Novozym 435 catalytic system is observed at an isooctane to PFAD ratio of 0.75-1 (v/v) and dropped at a ratio of 2. However, the effect of isooctane content on BD yield in Amberlyst 15 catalytic system is negligible. The time course of the esterification of PFAD in the presence of isooctane is shown in Figure 6. In Novozym 435 catalytic system, the presence of isooctane slightly reduces the reaction (11) Carrea, G.; Riva, S.; Secundo, F.; Danieli, B. J. Chem. Soc., Perkin Trans. 1989, 1, 1057–1061.
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washing but with drying, and (3) with washing but without drying. It was found that removing water that is adsorbed onto catalysts is a crucial point in catalyst recycling, and solvent washing alone is not enough to completely remove the water; therefore, drying is essential. Without washing but with drying, Amberlyst 15 and Novozym 435 kept their 95 and 90% activity at 10 cycles, indicating that not only water but other minor compounds such as carotene and vitamin E present in PFAD might be adsorbed onto catalysts, and the solvent washing is, therefore, necessary for prolong use of the catalyst. Conclusions
Figure 6. Biodiesel yield with time in isooctane-mediated systems. Reaction conditions are the same as those in Figure 5, except the isooctane to PFAD ratio is kept constant at 0.75 (v/v).
rate, but the ultimate BD yield increases. In the case of Amberlyst 15 catalytic system, the reaction rate increases, but the ultimate BD yield remains the same. Since, BD yield in Amberlyst 15 catalytic system without isooctane is already high (97%), further improvement in the yield seams difficult. Since isooctane is to some extent toxic to Novozym 435, the reaction rate decreased. The presence of isooctane enhanced mass transfer by reducing the viscosity of PFAD distillate, thereby increasing the rate of reaction catalyzed by Amberlyst 15. The amount of free fatty acid in PFAD at the end of esterification is reduced from 97 wt % to 1 and 3 wt % for Amberlyst 15 and Novozym 435 catalytic system, respectively. Table 2 shows that both Amberlyst 15 and Novozym 435 could be reused more than 15 cycles without losing their activities. The present method of catalyst recycling (solvent washing followed by drying) was developed after testing different methods: (1) without washing and drying, (2) without
Novozym 435- and Amberlyst 15-catalyzed esterification of PFAD in the presence and absence of organic solvents are investigated. Novozym 435 is found to be poisoned at methanol content of higher than 13 wt % of PFAD. In contrast, no methanol poisoning to Amberlyst 15 is observed, even at methanol content of 25 wt %. Both catalyst activities are reduced by the presence of water, but Amberlyst 15 is more negatively influenced than Novozym 435. Different organic solvents are tested and nonpolar solvents such as isooctane and hexane improve BD yield in Novozym 435 catalytic system, but their effect on the yield in Amberlyst 15 catalytic system is negligible. Polar solvents such as DMSO inactivate both catalysts. Although, Novozym 435 is relatively more active, Amberlyst 15 could be better choice because of higher BD yield and low catalyst cost. Acknowledgment. Financial support from the Agency of Science Technology and Research (ASTAR) of Singapore is gratefully acknowledged. EF8006245 (12) Laane, C.; Boeren, S.; Vos, K.; Veeger, C. Biotechnol. Bioeng. 1987, 30, 81–87. (13) Degn, P.; Zimmermann, W. Biotechnol. Bioeng. 2001, 74, 483– 491.
