Equilibrium Studies of Biodiesel Ethyl Esters Prepared with a Potassium Glyceroxide Catalyst

Abstract

Biodiesel fuel is produced by the transesterification of triacylglycerides to alkyl esters using short chain alcohols, whereby ethanol represents a safe, sustainable substitute for methanol. Due to the inherent solubility of the resulting fatty acid ethyl esters (FAEE) in residual ethanol solvent, efficient phase separation of the postreaction mixture requires near anhydrous initial conditions. A recyclable catalytic system of 1:1 potassium glyceroxide:glycerol allowed for direct comparison of liquid–liquid phase equilibria between ethanol and methanol transesterification reaction experiments with increasing water content. A maximum water tolerance of 1.06 mol water:1 mol catalyst was observed for the ethanolysis reactions, representing a minimum of 4.6-fold greater anhydrous stringency as compared to methanolysis reactions. These results are supported by equilibrium calculations comparing methoxide, ethoxide, and glyceroxide concentrations at 0%, 80%, and 99% reaction completion. The catalyst system was applied to virgin soybean and recycled canola oils, and mass balances, including distilled product yields, are presented. Additionally, life cycle assessment revealed that biodiesel made from biobased ethanol and potassium glyceroxide resulted in approximately 20% reduction of greenhouse gases as compared to soybean methyl esters produced from sodium methoxide.