Biodiesel production from rice bran oil fatty acid distillate via supercritical hydrolysis–esterification–transesterification in a microreactor

Abstract

Rice bran oil fatty acid distillate (RBOFAD), a by-product from rice bran oil production, was used as feedstock for the production of biodiesel. The hydrolysis–esterification–transesterification of RBOFAD with ethanol was performed in a microreactor under supercritical conditions. The biodiesel product in the form of fatty acid ethyl ester (FAEE) was obtained. The operating conditions, including the sulfuric acid content (0.2–0.6%), water content (0–7.5%), ethanol-to-oil molar ratio (5:1–16:1), and reaction temperature (260–320 °C), were optimized. The water content could affect the reaction system via both hydrolysis of triglycerides and reverse esterification of fatty acids. Biodiesel with the FAEE content of 93% was obtained at the optimal conditions (sulfuric acid content of 0.4%, water content of 2.5%, ethanol-to-oil molar ratio of 7:1, residence time of 19 min, and reaction temperature of 280 °C). The properties of the biodiesel, including density, viscosity, acidity, oxidation stability, freezing point, and pour point, were compared with standards. The properties such as viscosity, acid value, heating value, and oxidation stability were suitable as biodiesel according to EN14213, except for the contents of ester, monoglyceride, and diglyceride.