Abstract: A solid base catalyst (K₂SiO₃/C) capable of microwave absorption was used for the transesterification of soybean oil under microwave radiation. The K₂SiO₃/C catalyst was prepared by an impregnation method that loaded K₂SiO₃ on carbon particles (1–3.5 mm diameter) followed by drying at 120 °C. The catalysts were characterized by X-ray diffraction, scanning electron microscopy- energy dispersive spectrometry, and the Hammett indicator method. K₂SiO₃ was well distributed on the support. The effects of reaction variables such as catalyst loading, molar ratio of methanol to oil, and reaction time (under microwave radiation and conventional heating) were studied. When the conventionally heated reaction was carried out at 65 °C with a methanol/oil molar ratio of 30:1 and a catalyst concentration of 24 wt%, the biodiesel conversion was 96.5% after 2.5 h reaction time. The same reaction reached equilibrium after 1.5 h under microwave radiation, and the conversion of biodiesel was 96.7%.

Key words: biodiesel, solid catalyst, potash water glass, carbon particle, microwave absorption