SiW ₁₂O ₄₀-based ionic liquid catalysts: Catalytic esterification of oleic acid for biodiesel production

Heteropoly acid (SiW ₁₂O ₄₀)-based ionic liquid (SWIL) and silica supported SiW ₁₂O ₄₀-based ionic liquid (SWIL/SiO ₂) catalysts with different contents of SWIL were designed and prepared. The structures of the catalysts were experimentally characterized and theoretically analyzed, and catalytic activities and reusability of the catalysts were evaluated through an esterification reaction between oleic acid and methanol. The results showed that SWIL had excellent activity and good reusability. SWIL dissolved in the reaction mixture during the reaction process and could be precipitated and separated from products at room temperature after methanol and water were removed. The fresh SWIL/SiO ₂ had high catalytic activity close to that of SWIL and could be easily separated from the reaction system just through simple filtration. However, the leaching of SWIL in the esterification reaction caused the deactivation of SWIL/SiO ₂. SWIL contents of SWIL/SiO ₂ played an important role on the catalytic activity and reusability of SWIL/SiO ₂.