Energy Fuels 2010, 24, 746–751 Published on Web 10/19/2009
: DOI:10.1021/ef900854h
Transesterification of Camelina Sativa Oil using Supercritical and Subcritical Methanol with Cosolvents Prafulla D. Patil, Veera Gnaneswar Gude, and Shuguang Deng* Chemical Engineering Department New Mexico State University Las Cruces, New Mexico 88003 U.S.A. Received August 5, 2009. Revised Manuscript Received September 29, 2009
Transesterification of camelina oil using supercritical methanol with hexane as a cosolvent and subcritical methanol along with potassium hydroxide as a cosolvent/catalyst was investigated to study the methyl ester conversion process. It was found that cosolvents play a vital role in reducing the severity of critical operational parameters and maximize the biodiesel yield. The experimental results from the process parametric evaluation studies show that supercritical methanol with hexane as a cosolvent could produce maximum methyl esters using the following conditions: reaction temperature of 290 °C, methanol to oil ratio of 45, and reaction time of 40 min. For subcritical methanol condition with 0.3 wt % potassium hydroxide as a cosolvent, methyl ester yields of þ90% are obtained using the following conditions: reaction temperature of 180 °C, methanol to oil molar ratio of 30, and a reaction time of 20 min. Process variables critical to the methyl ester conversion are determined to be cosolvent ratio, molar ratio of alcohol to oil, and reaction time. Fuel properties of the biodiesel produced are comparable to those of regular diesel and conform to the ASTM standards.
Biodiesel production by transesterification reaction can be catalyzed with alkali, acid, or enzyme catalysts. Alkali and acid transesterification processes require shorter reaction time and lower costs as compared to the enzyme catalyst process.7,8 The alkali process gives high purity and yield of biodiesel in a shorter reaction time.2 However, this process is not suitable for feedstocks with high free fatty acid (FFA) content. As a result, a two-step transesterification process (acid esterification followed by alkali transesterification) was developed to reduce high free fatty acid content and improve the biodiesel yield.9 Longer reaction time and lower recovery of catalyst were the drawbacks of the two-step process. To overcome these disadvantages of the two-step acid catalyzed process, a process using both homogeneous Lewis acid catalyst and heterogeneous metal oxide catalyst was implemented.10,11 However, for this process, the reaction temperature was high and catalyst activity was weak, which resulted in low methyl ester yield. In order to solve these problems, Saka and Demirbas have proposed that biodiesel can be prepared from vegetable oil through a noncatalytic transesterification via supercritical alcohol method.12-14 The basic premise of supercritical treatment is to exploit the effect of pressure and temperature upon thermophysical properties of the solvent, such as dielectric constant, viscosity, specific weight, and polarity.15 Table 1 compares the physiochemical
1. Introduction Biodiesel is a nontoxic, biodegradable, renewable fuel that can be produced from a range of organic feedstock including fresh or waste vegetable oils, animal fats, and oilseed plants. Biodiesel has significantly lower emissions than petroleum-based diesel when it is burned, whether used in its pure form or blended with petroleum diesel. It does not contribute to a net rise in the level of carbon dioxide in the atmosphere and alleviates the intensity of the greenhouse effect.1,2 In addition, biodiesel is better than diesel fuel in terms of sulfur content, flash point, aromatic content, and biodegradability.3 Vegetable oils are becoming a promising alternative to diesel fuel because they are renewable in nature, environmentalfriendly and can be produced locally. Camelina sativa is an underexploited crop species of great economical potential. Camelina sativa oil is rich in omega-3 fatty acids and yields an average of 1200-1400 pounds per acre.4 The production cost for Camelina sativa oil is substantially lower than many other oil crops such as rapeseed, corn, and soybean, which makes camelina an attractive potential crop for biodiesel and many other industrial applications.5 Camelina sativa has positive energy balance for the production of biodiesel ester (net energy ratio=1.47).6 *To whom correspondence should be addressed. Telephone: þ1-575646-4346. Fax: þ1-575-646-7706. E-mail:
[email protected]. (1) Vicente, G.; Martinez, M.; Aracil, J. Bioresour. Technol. 2004, 92, 297–305. (2) Antolin, G.; Tinaut, F. V.; Briceno, Y.; Castano, V.; Perez, C.; Ramirez, A. Bioresour. Technol. 2002, 83, 111–114. (3) Martini, N.; Schell, S. Proceedings of the Synopsis; Springer: Portdam, Germany, Berlin, 1998; p 6. (4) Leonard, C. INFORM 1998, 9, 830–838. (5) Putnam, D. H.; Budin, J. T.; Field, L. A.; Breene, W. M. In New Crops; Simon, J. E., Ed.; Wiley: New York, 1993. (6) Sahapatsombut, U.; Suppapitnarm, A. International Conference on Green and Sustainable Innovations, 2006. r 2009 American Chemical Society
(7) Muniyappa, P. R.; Brammer, S. C.; Noureddini, H. Biores. Technol. 1996, 56, 19–24. (8) Dorado, M. P.; Ballesteros, E.; Lopez, F. J.; Mittelbach, M. Energy &Fuels 2004, 18, 77–83. (9) Patil, P. D.; Deng, S. Fuel 2009, 88, 1302–1306. (10) Peng, X. C.; Peng, Q. J.; Ouyang, Y. Z. Mod. Chem. Ind. 1999, 19, 26–27. (11) Patil, P. D.; Deng, S. Energy & Fuels 2009, 23, 4619-4624. (12) Demirbas, A. Energy Convers. Manage. 2002, 43, 2349–2356. (13) Demirbas, A. Energy Sources 2002, 24, 835–841. (14) Saka, S.; Kusdiana, D. Fuel 2001, 80, 225–231. (15) Saka, S.; Kusdiana, D.; Minami, E. J. Sci. Ind. Res. 2006, 65, 420–425.
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pubs.acs.org/EF
Energy Fuels 2010, 24, 746–751
: DOI:10.1021/ef900854h
Patil et al.
In this study, transesterification of camelina oil using supercritical methanol with hexane as a cosolvent and subcritical methanol with potassium hydroxide (KOH) as a cosolvent/catalyst are investigated. Effects of different reaction parameters on the biodiesel yield are presented.
Table 1. Physicochemical Properties of Methanol at Ordinary and Supercritical Conditions
properties specific gravity, kg/l ionic product, log Kw dielectric constant viscosity, Pa-s hydrogen bonding No. solubility parameter (MPa)1/2
ordinary condition (25 °C, 1 bar)
supercritical condition (250 °C, 20 MPa)
0.7915 -0.77 32.6 5.4 10-4 1.93 7.1
0.272 not available 7.2 0.58 10-4
