Review on biodiesel production by two-step catalytic conversion

Abstract

Abstract Many researchers have done intensive efforts to enhance the biodiesel yield through two-step reaction in the production process. These processes have been applied under various conditions; including the type of feedstock oil, alcohol, catalyst, heating mode and reaction time. Chemical property of feedstock oil is the most important factor related to the selection of the best suitable two-step reaction technology. This review discusses two double-step reaction technologies; the first step esterification followed by the second step transesterification (called E + T technology), and two-step transesterification (denominated T1+T2 technology). The purpose of the two-step reaction is to optimize the operating cost of the production process such as lowering alcohol ratio, reducing reaction time, and minimizing yield loss. If free fatty acid content is more than 2 wt% then the first step esterification will be followed by the second step transesterification (E + T technology). The target of the first step esterification is to decrease the free fatty acid content in feedstock oils as much as possible in order to reduce the soap formation in the second step transesterification. Soap formation prevents the separation of biodiesel and glycerol phase and also needs higher amount of water for washing. It is the main reason of biodiesel loss because of turning ester to soap. The T1+T2 technology should be applied to low free fatty acid content feedstock oils (