Biodiesel production from rapeseed oil by various supercritical carboxylate esters

Biodiesel is commonly produced from triglycerides and methanol, with glycerol as the by-product. This process has caused the overproduction of glycerol, which leads to its price devaluation and its likelihood to become a new type of waste. In this research, therefore, we explored the potential of converting rapeseed oil into fatty acid alkyl esters (FAAEs) and triacins, instead of glycerol, by using supercritical carboxylate ester treatments in a batch-reaction system. As a result, it was found out that at reaction temperature of 350 °C and pressures up to 17.8 MPa, interesterifications of triglycerides with various carboxylate esters have occurred without using any catalysts under supercritical condition, producing FAAE and triacins. Among all supercritical carboxylate esters, supercritical methyl acetate showed the highest product yield, i.e., 97.7 wt%, when both FAAE and triacin were considered as the product. Additionally, the mixture of FAAE and triacin in 3:1 molar ratio exhibited no detrimental effects on biodiesel quality.