Two-step biodiesel production using supercritical methanol and ethanol

Current industrial biodiesel production utilizes an alkali catalyst that can participate in saponification side reactions. The side reactions are reduced by using highly refined vegetable oil feedstocks. Also, the catalyst must be extracted from the final product in a washing step. A catalyst-free alternative for the production of biodiesel was developed. It involves two reaction steps: 1) triglyceride hydrolysis (fat splitting) at subcritical conditions to separate glycerol from fatty acids, and 2) fatty acid esterification in supercritical alcohol to form fatty acid alkyl esters. The catalyst-free process can potentially be used with a variety of low-cost vegetable and animal fats without undesired side reactions. The focus of this project was on the esterification reaction. Experiments were carried out with methanol and ethanol in a batch reaction system at supercritical conditions. High conversions could be attained at short reaction times. It was determined that the reaction followed second-order reversible kinetics. In addition, a novel Raman spectroscopic method was developed for the analysis of esterification reaction products.