Structured catalysts based on Mg–Al hydrotalcite for the synthesis of biodiesel

Abstract

The performance of metallic (Fecralloy®) monoliths based on Mg–Al hydrotalcite for the synthesis of biodiesel through the methanolysis of sunflower oil is reported for the first time. A Mg–Al hydrotalcite was synthesized and the oxides obtained after calcination at 500°C were employed for preparing the slurries used for washcoating the monoliths. Using methanol as the solvent and sepiolite as binder allowed to reach 96% adherence after sonication. The positive effect of sepiolite on adherence seems to be related with its fibrous nature and ability for crosslinking with the hydrotalcite particles. However, catalytic tests have shown a negative effect of sepiolite on the methanolysis activity that can be attributed to the partial neutralization of the basic sites and/or masking of the hydrotalcite particles. The performance of the structured catalysts has been investigated in a monolithic stirrer reactor under very mild conditions (60°C and 1atm). Using 2wt.% of catalyst allowed reaching 62–77% oil conversion after 10h. However, the poor adherence of the coating in the reaction mixture prevented the effective reutilization of the catalysts. Further work is required concerning the formulation of the coating slurries to improve adherence in the chemically aggressive medium involved in the synthesis of biodiesel.