Energy Fuels 2009, 23, 4651–4658 Published on Web 08/11/2009
: DOI:10.1021/ef900474e
Effect of Mass Transfer and Enzyme Loading on the Biodiesel Yield and Reaction Rate in the Enzymatic Transesterification of Crude Palm Oil Jia Huey Sim, Azlina Harun @ Kamaruddin,* and Subhash Bhatia School of Chemical Engineering, Engineering Campus, Universiti Sains Malaysia, Seri Ampangan, Nibong Tebal, 14300 Penang Received May 18, 2009. Revised Manuscript Received July 22, 2009
Efforts in minimizing mass transfer effects in enzymatic transesterification of crude palm oil in a biphasic system have always been the compromise between enzyme loading and agitation speed. Therefore, effect of enzyme loading and agitation speed on fatty acid methyl ester (FAME) productivity in terms of intrinsic and external mass transfer limitations and the effective reaction time were determined using factorial design. FAME yield response was significantly affected by agitation speed, enzyme loading and reaction time, whereas initial reaction rate was solely dependent on the enzyme loading. Graphical plots of experimental results revealed that the mass transfer effect for the transport of reactant from bulk liquid to immobilized lipase and within the intraparticle of immobilized lipase were absent at 150 rpm and 6.65% enzyme loading. Optimization conditions for a kinetically controlled domain proposed by the response surface methodology established 100% FAME yield in 4 h reaction time at initial reaction rate of 2.77% FAME yield per min.
Table 1. Designated Candidate Points for Process Variables with Corresponding Studied Ranges
Introduction Transesterification is the reaction of a fat or oil with an alcohol to form esters and glycerol. Enzymatic transesterification for fatty acid methyl ester (FAME) production with mild operating conditions and high specificity in product synthesis circumvents several difficulties arising during chemical processing. There are two principal considerations in the economics of biodiesel production: (a) the costs of feed (oil and acyl alcohol) and (b) the process operation cost.1-5 Expenses on the feed are attributed to 60-75% of transesterification production cost.6-8 Malaysia is known as the largest palm oil producers with 27.2 million tons of crude palm oil (CPO) production. Thus it becomes a great incentive to promote the development of biodiesel production from CPO.13 The cost for
factorial design: four levels - three factors dependent variables FAME yield initial reaction rate
1
2
3
4
A: agitation speed (rpm): 150 175 200 225 B: enzyme loading (%): 2.5a 5.0a 7.5a 10.0a C: reaction time (h): 0.00 2.00 4.00 6.00
a The percentage of enzyme quantities used in weight per unit weight of CPO.
CPO resulted from palm oil extraction is relatively low compared to refined vegetable oil that undergoes process degumming, bleaching, deoderization, and hydrogenation. Besides, CPO contains high triglycerides, that is, over 96%, and low free fatty acid is also another added advantage. Hexane, petroleum ether, acetone, and other organic solvent have been adopted to dissolve hydrophobic vegetable oil into methanol for homogeneous reaction mixture in addition to removing byproduct glycerol periodically. Consequently, lipase inactivation caused by insoluble methanol and byproduct glycerol can be omitted. However, these hydrophobic organic solvents were unable to completely dilute both methanol and glycerol. Thus, lipase still exhibits poor stability in such reaction media. The use of moderate polarity tert-butanol (log P = 0.35) dissolves completely the hydrophilic methanol and glycerol together with the hydrophobic vegetable oil when all components are present in equilibrium state. Thus, both the negative effects caused by excessive methanol and byproduct glycerol could be totally eliminated.14 The application of tert-butanol as reaction medium have resulted in high biodiesel yield of 95% catalyzed by the combined Lipozyme TL IM and Novozym 435, and
*To whom correspondence should be addressed. Telephone: þ604599 6417. Fax: þ604-594 1013. E-mail:
[email protected]. (1) Kose, O.; Tuter, M.; Aksoy, H. A. Bioresour. Technol. 2002, 83, 125–129. (2) Shah, S.; Sharma, S.; Gupta, M. N. Indian J. Biochem. Biophys. 2003, 40, 392–399. (3) Kaieda, M.; Samukawa, T.; Matsumoto, T.; Ban, K.; Kondo, A.; Shimada, Y.; Noda, H.; Nomoto, F.; Ohtsuka, K.; Izumoto, E.; Fukuda, H. J. Biosci. Bioeng. 1999, 88, 627–631. (4) Watanabe, Y.; Shimada, Y.; Sugihara, A.; Noda, H.; Fukuda, H.; Tominaga, Y. J. Am. Oil Chem. Soc. 2000, 77, 355–360. (5) Watanabe, Y.; Shimada, Y.; Sugihara, A.; Tominaga, Y. J. Am. Oil Chem. Soc. 2001, 78, 703–707. (6) Jeong, G. T.; Yang, H. S.; Park, D. H. Bioresour. Technol. 2009, 100, 25–30. (7) Ma, F.; Hanna, M. A. Bioresour. Technol. 1999, 70, 1–15. (8) Krawczyk, T. Inform 1996, 7, 801–829. (9) Samukawa, T.; Kaieda, M.; Matsumoto, T.; Ban, K.; Kondo, A.; Shimada, Y.; Noda, H.; Fukuda, H. J. Biosci. Bioeng. 2000, 90, 180–183. (10) Xu, Y.; Du, W.; Liu, D. J. Mol. Catal., B 2005, 32, 241–245. (11) Noureddini, H.; Gao, X.; Philkana, R. S. Bioresour. Technol. 2005, 96, 769–777. (12) Thoenes, P. Biofuels and commodity markets - Palm oil focus. http://www.fao.org/es/ESC/common/ecg/110542_en_full_paper_English.pdf (July 31st, 2008), (13) Crabbe, E.; Nolasco-Hipolito, C.; Kobayashi, G.; Sonomoto, K.; Ishizaki, A. Process Biochem. 2001, 37, 65–71. r 2009 American Chemical Society
independent variables
study levels
(14) Nie, K.; Xie, F.; Wang, F.; Tan, T. J. Mol. Catal., B 2006, 43, 142–147.
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Energy Fuels 2009, 23, 4651–4658
: DOI:10.1021/ef900474e
Sim et al.
Table 2. Sample of Experimental Design Spreadsheet at 150 rpm for Process Optimization experimental runs
independent variables
dependent responses
agitation speed, A (rpm)
enzyme loading, B (wt %)
reaction time, C (hrs)
initial reaction rate (%FAME yield/min)
FAME yield (%FAME yield)
1 2 3 4
150 150 150 150
2.5 2.5 2.5 2.5
0 2 4 6
0 1.02 1.02 1.02
0 40.93 71.01 75.12
5 6 7 8
150 150 150 150
5.0 5.0 5.0 5.0
0 2 4 6
0 1.74 1.74 1.74
0 68.30 100 100
9 10 11 12
150 150 150 150
7.5 7.5 7.5 7.5
0 2 4 6
0 2.47 2.47 2.47
0 88.53 100 100
13 14 15 16
150 150 150 150
10.0 10.0 10.0 10.0
0 2 4 6
0 3.28 3.28 3.28
0 89.54 98.82 99
No.
Table 3. Summary of ANOVA on the Significance of FAME Yield Model and Initial Reaction Rate Model
there was no obvious loss in lipase activity even after being used for 200 cycles. Immobilized Candida antarctica lipase (Novozym 435) is well-known as an excellent transesterification biocatalyst that effectively catalyze the methanolysis of vegetable oil. However, the expensive production cost of Novozym 435 becomes a major obstacle for the implementation of enzymatic transesterification technology. Lipozyme TL IM (an immobilized lipase from Thermomyces lanuginosus) with market price at USD 125.91 kg-1 is considerably cheaper than Novozym 435 at USD 125.91 kg-1. From lipases screening in a preliminary study, FAME yield achieved in transesterification reaction mediated by Lipozyme TL IM was comparable with Novozym 435. In this research, the possibility of using Lipozyme TL IM for catalyzing unrefined CPO to biodiesel was explored. The aim of the study is to determine the effect of critical process parameters on CPO transesterification process in terms of mass transfer limitations and FAME productivity and eventually to process optimization. Factorial design combined with RSM is used to develop a system in favor of kinetically controlled reaction as well as a correlating relationship between process variables: agitation speed, enzyme loading, and reaction time with dependent responses: FAME yield and initial reaction rate. Response surface methodology in statistical analysis examined significant levels for each parameter on FAME production prior to determining the optimum operating conditions for enzymatic transesterification.
source
coefficient estimate
F value
prob>F
model A B C B2 C2 BC
FAME Yield Response 88.84 -0.05 4.44 18.34 252.48 22.70 179.07 -0.88 57.41 -1.47 14.54 -0.80 25.09
