Fe–Zn double-metal cyanide complexes catalyzed biodiesel production from high-acid-value oil

A kind of solid catalyst of Fe(Ⅱ)–Zn double-metal cyanide (DMC) complexes was prepared through co-reaction of potassium ferrocyanide, zinc chloride and complexing agent of tert-butanol. This catalyst was characterized by using several techniques such as XRD, TG/FT-IR, EA, BET and SEM. And it proved to be highly active for the simultaneous transesterification of triglycerides and esterification of free fatty acids (FFAs). Results show that the catalyst has a hybrid-structure comprised of both crystal and amorphous species. Its good water-resistance depends on the amorphous state, which has surface hydrophobicity. Zn2+ may be the active site of catalysis. The effect of various factors on the reaction was also studied, including different co-complexing agents, DMC concentration, reaction temperature, methanol/oil molar ratio, reaction time, water and fatty acid content and so on. The yield rate reached 98% under the optimum conditions, and the recovery rate maintained more than 90% after 10 batches.