(671b) Microwave Assisted Transesterification of Soybean Oil Using Heterogeneous Catalysts

The problem of finding economically viable and environmentally friendly renewable energy sources is a pressing matter. Not only is the world faced with a finite supply of fossil-fuels, but concern is growing over the possibility of climate change caused by greenhouse gas emissions. Biodiesel, a liquid fuel derived from plant or animal oils, represents a renewable energy source that could contribute to the solution of both problems; it can be continually produced as long as we are able to grow plants and it can be made in such a way as to release no net addition of greenhouse gases to the environment [3]. However, technical challenges must be overcome before biodiesel can contribute significantly to the world's energy supply; with current technology biodiesel production is profitable only under special circumstances. One such technical challenge is the problem of finding a way to make the reaction faster and more energy efficient. The research project presented in the following report seeks to address this problem by studying the production of biodiesel using heterogeneous catalysts and microwave reaction systems. Heterogeneous catalysts can make biodiesel more energy efficient, and therefore less expensive, by eliminating the need for expensive purification processes that separate the catalyst from reaction products typical in the use of homogeneous catalysts [4]. Microwave reaction systems both speed up biodiesel production and make it more energy efficient by accelerating the rate of reaction while decreasing energy losses involved in heating the reaction mixture [5].

Several studies have examined the catalytic activity of calcium methoxide [1-3]. Using conventional heating mechanisms for the transesterification reaction, each study found methyl ester yields greater than 90% after about 2.5 hrs of reaction at 65C [1-3]. Wan et al. studied the activity of sodium aluminate in the transesterification of soybean oil using conventional heating; they found yields up to 89.9% after 30 min of reaction at 64C [4].

Materials and Methods

Commercial grade soybean oil was used as the source of triglycerides. Soybean oil and methanol were reacted at 65C for 2 min, 5 min, 10 min, 15 min and 30 min using microwave heating. A CEM MARS Express microwave oven was used with maximum power set to 800 W; the temperature of the reaction mixture was controlled with a fiber optic temperature probe submerged in the reaction mixture. A 250 ml Pyrex round-bottom flask was used for the reaction and magnetic stir bar employed for mixing. Heterogeneous catalysts studied included Al-TUD-1 from Lummus Technology; calcium methoxide and sodium aluminate. The reaction mixture consisted of 41.4 g of soybean oil, 8.93 g of methanol and 1.5 wt% sodium aluminate or 2 wt% calcium methoxide, giving a methanol:oil ratio of 6:1.

Analysis of the reaction products was completed using a Grace EnSight Biodiesel Analyzer employing high performance liquid chromatography. Typically, 10 microlitres of the FAME phase of the reaction products was diluted in 4 ml of ethyl acetate before injection.

Results and Discussion

The yield of the transesterification of soybean oil can be tracked by quantifying the amount of fatty acid methyl ester produced in the reaction. Based on the HPLC analysis described above, calcium methoxide and sodium aluminate give excellent yields for relatively short reaction times under microwave reaction conditions. Calcium methoxide was found to produce methyl ester yields of around 99% after 30 min of reaction time. This represents a huge gain in reaction time compared to the 2.5 hrs found in conventional heating in previous studies. Sodium aluminate was found to give high methyl ester yields for times as short as 10 min, with full conversion being achieved by 30 min at 65C. Again, microwave heating led to an acceleration of the reaction rate.

References

1. Liu, X., Piao, X., Wang, Y., Zhu, S., He, H. (2008) ?Calcium methoxide as a solid base catalyst for the transesterification of soybean oil to biodiesel with methanol.? Fuel. 87, 1076-1082.

2. Gryglewicz, S. (1999). ?Rapeseed oil methyl esters preparation using heterogeneous catalysts.? Bioresource Technology. 70, 249-253.

3. Martyanov, I.N., Sayari, A., (2008). ?Comparative study of triglyceride transesterification in the presence of catalytic amounts of sodium, magnesium, and calcium methoxides.? Applied Catalysis A: General. 339, 45-52.

4. Albuquerque., M.C.G., Jimenez-Urbistondo, I., Santamaria-Gonzales, J., Merida-Robles, J.M., Moreno-Tost, R., Rodriguez-Castellon, E., Jimenez-Lopez, A., Azevedo, D.C.S., Cavalcante Jr., C.L., Maireless-Torres, P. (2008). ?CaO supported on mesoporous silicas as basic catalysts for transesterification reactions.? Applied Catalysis A: General. 334, 35-43.

5. Perin. G., Alvaro G., Westphal, E., Viana, L.H., Jacob, R.G., Lenardao, E.J., D'Oca, M.G.M. (2008) ?Transesterification of castor oil by microwave irradiation.? Fuel. 87, 2838-2841.

6.Wan, T., Yu, P., Wang, S., Luo, Y. (2009). ?Application of Sodium Aluminate As a Heterogeneous Base Catalyst for Biodiesel Production from Soybean Oil.? Energy and Fuels. 23, 1089-1092.