Kinetics of DBU-catalyzed transesterification for biodiesel in the DBU–ethanol switchable-polarity solvent

The production of biodiesel from soybean oil and ethanol was investigated in switchable-polarity solvent (SPS) media of DBU and ethanol. The highest biodiesel yield catalyzed by DBU could reach 97.9% under optimized conditions, i.e. ethanol–oil molar ratio: 12 : 1, DBU–oil molar ratio: 2 : 1, reaction temperature: 70 °C, reaction time: 2 h. According to the kinetic analysis, the reaction order of oil was estimated to be 0.7, the apparent activation energy was 16.763 kJ mol−1, the pre-exponential factor was 561.31 mol0.3 mL−0.3 min−1 using the Arrhenius equation for the first time, which explains the high efficiency of the DBU catalyst. The DBU-catalyzed transesterification in the DBU–ethanol switchable-polarity solvent offered an interesting alternative, which would be used to simplify the transesterification and separation to a single step.