Non-catalytic and glycerol-free biodiesel production from rice bran oil fatty acid distillate in a microreactor

Abstract

Obtained from rice bran oil refining process, rice bran oil fatty acid distillate (RBOFAD) is a low-value, non-edible, and unwanted by-product, which can be used as a promising alternative raw material for biodiesel production. However, the conventional biodiesel process cannot handle this material due to the high content of free fatty acid (FFA). A novel supercritical process for biodiesel synthesis using dimethyl carbonate (DMC) as acyl acceptor in a microreactor was proposed in this work for the raw material with high FFA. High quality of biodiesel and value-added by-product (glyoxal) were obtained in our process. In this process, the biodiesel content of 80.9% was achieved for the case of RBOFAD as feedstock, compared to only 43.6% for the case of refined rice bran oil as feedstock. The influence of operating conditions on biodiesel and glyoxal content including reaction temperature, residence time, and DMC-to-RBOFAD molar ratio was investigated and optimized via response surface methodology. The biodiesel content of 97.1% was achieved at the optimal conditions (reaction temperature of 360 °C, residence time of 35 min, and RBOFAD-to-oil molar ratio of 11:1). The required pressure and the amount of DMC were significantly reduced compared to other processes. Most of the biodiesel properties met the international standards except for some impurities (mono- and diglycerides). These results provided the new insight for the development of biodiesel production from low-grade feedstocks.