(22j) Synthesis and Kinetics of Biodiesel Formation Via Calcium Methoxide Base-Catalyzed Transesterification Reaction in the Absence and Presence of Ultrasound

Biodiesel also called fatty acid methyl ester (FAME) is a clean-burning, renewable fuel produced from vegetable oils, animal fats and recycled cooking oil and greases etc. It is not only biodegradable and non toxic but also free of sulfur making it a cleaner burning fuel than petroleum diesel with reduced emission of smoke, unburnt hydrocarbons and particulate matter, sulfur oxides (SO_x), and carbon monoxide (CO). Generally, biodiesel is produced via transesterification reactions where triglycerides react with alcohol in the presence of acid catalysts, base catalysts or enzymes in homogeneous catalystic systems. Many types of heterogeneous basic catalysts, such as zeolites and modified zeolites, alkaline earth metal oxides, supported alkaline earth metal oxides, supported alkali metals, alkali and alkaline earth mixed hydrotalcites/layered double hydroxides, rare earth/lanthanide based, ion exchange resin, zirconia based and various other compounds showing active basic sites have been proposed or studied in the literature. Biodiesel synthesis by using most of these catalysts have shown promising results with good-to-high yields, but the majority of these methods suffer at least from one of several disadvantages. These include low activity, use of solvents, need for high temperature, long reaction time, high methanol-to-oil ratio, high catalyst loading, high cost and catalyst toxicity. Alkaline earth metal oxides are the most studied solid-base catalysts for transesterification of vegetable oils in the literature. The existence of basic sites on the alkali earth oxides have been attributed to the presence of M²⁺-O^2-ion pairs in different coordination environments. 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 solubilities, and are the least toxic of most of the catalysts studied to date.

Ultrasound has proven to be a very useful tool in enhancing the reaction rates in a variety of reacting systems due to its ability to improve mixing and mass transfer especially in biphasic systems and allow operation at mild conditions of temperature and pressure. The enhancement of biodiesel synthesis resulting from ultrasonic cavitation in homogeneous catalytic systems has been reported by several prior investigators. However, studies in heterogeneous catalysis involving ultrasound are still limited. In the present study, high surface area calcium methoxide catalysts are used for the transesterification of soybean oil in a cylindrical jacked glass reactor. A detailed parametric experimental study was performed to select the best parameters (or conditions) for the specified purpose of this investigation. The effect of storage time on the activity of the catalyst was also evaluated by carrying out the transesterification reaction with fresh catalyst as well as the catalyst stored for 160 days.  Transesterification in the presence of ultrasound at both low (20 kHz) and high (611 kHz) frequencies were also studied. Finally, the kinetics of this calcium methoxide base-catalyzed transesterification of soybean oil with and without ultrasound was evaluated for the first time using a previously reported kinetic and mass transfer model for heterogeneous systems. Also, a new novel ultrasonic reactor designed for scale-up studies and future extension of this work will be outlined.

References

Deshmane, V.G.; Adewuyi, Y.G. Synthesis and Kinetics of Biodiesel Formation via Calcium Methoxide Base-Catalyzed Transesterification Reaction in the Absence and Presence of Ultrasound. Fuel, 2013, 107, 474-482 http://dx.doi.org/10.1016/j.fuel.2012.12.080

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. http://pubs.acs.org/doi/abs/10.1021/ie060844c

Mahamuni, N.N.; Adewuyi, Y.G. Fourier Transform Infrared Spectroscopy (FTIR) Method to Monitor Soy Biodiesel and Soybean Oil in Transesterification Reactions, Petrodiesel-Biodiesel and Blend Adulteration with Soy Oil”, Energy & Fuels. 2009, 23, 3773-3782. http://dx.doi.org/10.1021/ef900130m

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. http://dx.doi.org/10.1021/ef900047j