349839 Production of Biodiesel from Free Fatty Acids and Triglycerides By Reaction with High Temperature Methanol

Monday, November 4, 2013
Grand Ballroom B (Hilton)
Supriya Thote, Chemical Engineering, University of Arkansas, Fayetteville, AR

Natural oils like vegetable oil, algae oil and tall oil can be used as feedstock for the production of biodiesel. The free fatty acids (FFAs) present in natural oils react with methanol by esterification whereas the fatty acids present in triglycerides (TGs) react by transesterification to produce fatty acid methyl esters (FAMEs), the main component of biodiesel and glycerol, a byproduct that is commonly used in the production of soap.  Traditional methods of production of biodiesel involve either an acid or an alkali based catalyzed process. Both acid-catalyzed and base-catalyzed processes have limitations. An acid neutralization step is required in this acid-catalyzed process and alkali-catalyzed processes have high sensitivity to the presence of water. However, recent research has revealed a new catalyst-free process for making biodiesel - the reaction of oil with methanol at high temperature to improve the miscibility of the two liquids. New research has further indicated that that the process of conversion TGs to FAMEs might be benefit from the presence of water. Previous research done at the University of Arkansas on the reaction of tall oil with methanol yielded surprisingly positive results for a novel subcritical, catalyst-free process. This study first reproduced the results described in the research paper Production of biodiesel fuel from tall oil fatty acids via high temperature methanol reaction by White et al published in the journal Fuel in 2011. In addition to reproducing the previous results, this research also documented the effect of changing the methanol to oil molar ratio and residence time on the production of different FAMEs form FFAs present in tall oil. A 8 mL continuous tubular reactor was used for the experiments. The reactor tube was coiled to allow better mixing of reactants. Methanol and oil are pumped from their respective reservoirs through separate pumps into a single, coiled tubular reactor. The products formed in the reactor then flowed through a double pipe heat exchanger to cool down the reaction mixture and prevent further reaction. Reactor temperature and pressure were continuously monitored at the inlet and outlet of the reactor. The subcritical experiments yielded similar results as in the previous study; in fact, the conversions obtained were slightly higher that indicated by the model developed in White et al. In the second part of this research, new experiments to convert fatty acids present in soybean oil into FAMEs in the presence of water were performed. Soybean oil was chosen for study because it is the most popular vegetable oil in use, and hence is the most likely candidate for conversion to vegetable oil. These reactions were carried on in a setup similar to the one described for tall oil. Additionally, a 60 mL coiled reactor was used to allow for a wider range of residence times. The water used in the reaction was mixed with the methanol. Mainly, the effects of temperature, water content, residence times and methanol to oil molecular ratio were observed. Although vegetable oil is composed mostly of triglycerides (TAGs), these can be converted into free fatty acids (FFAs) through hydrolysis and then further converted to FAMEs.  The hydrolysis of triglycerides was carried out in conjunction with transesterification for the conversion FFAs into FAMEs for a catalyst-free reaction. The experiments yielded interesting results. The presence of small amounts water did result in a better conversion of TGs to FAMEs, excess water seemed to inhibit the esterification reaction. This study hence establishes that hydrolysis and esterification can be carried out in the same reactor and while shedding light on the relationship of temperature and water to methanol ratio with the conversion of TGs present in soybean oil to FAMEs.

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