Catalytic transesterification to biodiesel at room temperature over several solid bases

The transesterification activity of several solid base catalysts in biodiesel production was systematically studied and evaluated at room temperature. Commercialized calcined silicates showed stronger transesterification ability than other commonly-used oxides, and provided considerable biodiesel yields. Biodiesel yield of > 96% was obtained for Na2SiO3 catalyst (calcined at 400 degrees C) at 28 degrees C within 12 h with methanol/oil molar ratio of 12/1 and catalyst dosage of 5 wt%, and for CaSiO3 catalyst (calcined at 550 degrees C) at 28 degrees C within 24 h with methanol/oil molar ratio of 27/1 and catalyst dosage of 23 wt%. The high activity of Na2SiO3 came from low activation energy of 104.6 kJ/mol and considerable higher pre-exponential factor of 3.73 x 10(15) min(-1), which produced high turnover frequency of 0.234 min(-1) at 28 degrees C. The introduction of CA-O-Si structure in CaSiO3 resulted in high surface basicity of 0.70 mmol/g and high pre-exponential factor of 3.79 x 10(19) min(-1) but high activation energy of 136.4 kJ/mol. The loss of catalyst activity was mainly due to the variation of surface silicate structure during transesterification.