Heterogenization of a homogenous catalyst: synthesis and characterization of imidazolium ionene/OH−@SiO2 as an efficient basic catalyst for biodiesel production†
To develop green and recyclable catalysts for biodiesel production, herein, a reusable, eco-friendly catalyst was designed by immobilizing an oligomeric ionic liquid inside a SiO2 mesoporous matrix. Then, it was used in transesterification of several natural oils with methanol to produce biodiesel. In this study, the effect of an ionic liquid on the reaction rate has been demonstrated and compared with that of KOH as a routine catalyst for this reaction. The catalyst was characterized by FTIR, XRD, BET, FESEM, TEM, and TGA techniques. The effect of different parameters, such as temperature, molar ratio of methanol/oil, and amount of catalyst, was investigated to optimize the reaction conditions. The results showed that after 8 h of reaction at 60 °C with a methanol/oil molar ratio of 8 : 1 and 50 mg of the catalyst, the yield of methyl ester reached 96%. The reaction was also conducted in an autoclave at 200 °C, and the conversion after 1 h was over 97%. More importantly, due the SiO2 coating, the catalyst could be successfully recovered, and the catalyst could be used repeatedly for at least 5 cycles without any significant loss of activity. In particular, we were able to heterogenize a water soluble basic catalyst that was not soluble in methanol and separate it from the reaction mixture very easily.