(602ai) A Comparative Study of Biodiesel Synthesis From Soybean Oil Via Transesterification Reaction Using Calcium Methoxide in the Absence and Presence of Ultrasound

Biodiesel is produced by the reaction of lipid feedstocks with an alcohol such as methanol in the presence of a catalyst (NaOH, KOH or their methoxides) to yield methyl esters (biodiesel) and byproduct glycerol [1,2]. However removal of the base after reaction is a major problem since aqueous quenching results in the formation of stable emulsions and saponification (i.e., soap formation), making separation of the methyl ester difficult and resulting increased production costs. Also, this reaction does not tolerate the presence of water or fatty acids and the use of acids such as H₂SO₄, H₃PO₄, and HCl pose environmental and corrosion problems [3]. On the other hand, use of solid base catalyst offers several process advantages. It can be easily separated from the reaction products and the much more simplified product separation steps result in high yields of methyl esters. Glycerol is also directly produced with high purity (at least 98 %) and is free from any contaminations, thus increasing the profitability of the process. It also gives the opportunity to operate in a continuous process increasing the production capacities and further lowering the production costs. The use of alkaline earth metal oxides as solid base catalysts for transesterification of vegetable oils has been reported in the literature [4]. The basic strength of alkaline earth metal oxides and hydroxides was observed to increase in the order of Mg < Ca < Sr < Ba. From the economical and ecological point of view, calcium derived bases were found to be the most promising as they are inexpensive, exhibit low methanol solubility, and are the least toxic of all. In the present study a commercially available calcium methoxide catalysts has been used in the transesterification of soybean oil to produce biodiesel in a cylindrical jacked glass reactor stirred by mechanical agitation and a 20 kHz ultrasonic, and a novel low-intensity, multi-frequency ultrasonic reactor operated at 611 kHz. In this presentation, the effects of various process parameters such as catalyst concentration, methanol to oil molar ratio and the temperature of the reaction systems on the kinetics of the reaction and the optimization of the process will be discussed. The characterization of the catalytic material (fresh and used) by nitrogen adsorption–desorption (BET) and thermogravimetric and differential scanning calorimetry (TGA-DSC), and the effect of storage time on the activity of the catalyst will also be discussed.

References

1. Mahamuni, N.N.; Adewuyi, Y.G.  Optimization of the Synthesis of Biodiesel via Ultrasound-Enhanced Base-Catalyzed Transesterification of Soybean Oil Using a Multifrequency Ultrasonic Reactor”. Energy & Fuels. 2009, 23, 2757-2766.

2. Mahamuni, N.N.; Adewuyi, Y.G. Application of Taguchi Method to Investigate the Effects of Process Parameters on the Transesterfication of Soybean Oil Using High Frequency Ultrasound. Energy & Fuels, 2010, 24, 2120-2126.

3. Deshmane, V.G., Gogate, P., Pandit, A. Ultrasound-assisted Synthesis of Biodiesel from Palm Fatty Acid Distillate. Industrial Engineering Chemistry Research. 2008, 48 (17), 7923-7927

4. Watkins, R.S, Lee A.F et al. Li-CaO Catalyzed Triglyceride Transesterification for Biodiesel Application. Green Chemistry. 2004, 6(7), 335-340.