Production of Fatty Acid Methyl Esters via the In Situ Transesterification of Soybean Oil in Carbon Dioxide-Expanded Methanol

The production of fatty acid methyl esters (FAME) by direct alkali- and acid-catalyzed in situ transesterification of soybean flakes in CO(2)-expanded methanol was examined at various temperatures and pressures. Attempts to synthesize FAME from soy flakes via alkaline catalysis, using sodium methoxide as a catalyst, in gas-expanded methanol were unsuccessful. However, performing the reactions in 54 mL of a 1.2 N sulfuric acid-methanol mixture containing 50% mole fraction CO(2) resulted in an 88.3 (+/- 1.5)% conversion of the triacylglycerol (TAG) in 22.5 g soy flakes to FAME within 10 h. Decreasing the total volume of the liquid phase by one-third from 54 mL to 36 mL, while keeping the mmol of acid and all other variables constant, resulted in an 88.2(+/- 5.0)% conversion of triglyceride to FAME. Quantitative HPLC analysis showed that 99.8 and 92.3% of the total mass balance for FAME, TAG, and free fatty acid (FFA) could be accounted for in the reactions performed at the liquid-phase volumes of 54 and 36 mL, respectively. The overall results show that the introduction of CO(2) into the system increases the rate of reaction by as much as 2.5 fold in comparison to control reactions without CO(2). Additionally, we observed a direct correlation between FAME yield and the concentration of acid catalyst. We also determined by nitrogen analysis that at least 82.9% of protein is retained in the lipid-free soy flakes after acid-catalyzed in situ transesterification in CO(2)-expanded methanol.