Biodiesel fuel production from waste animal fats using alternative solid catalysts

Biodiesel fuel (BDF) has attracted attention as an alternative fossil fuel. BDF comprises fatty acid methyl esters (FAME) produced generally from triacylglycerols (TG) in vegetable oils treated with methanol. In Europe, BDF is manufactured from virgin vegetable oils grown on vast farmlands, while in Japan, where cultivation areas are small, it is manufactured from used cooking oils. Used cooking oils in Japan partly come from animal fats, which produce free fatty acids (FFAs) upon degradation. FFAs react with an alkali hydroxide used as the catalyst, and the produced soap brings about decrease a BDF yield. Since a massive amount of waste water due to homogeneous alkali catalysis of alkali hydroxide dissolved in methanol is discharged from the producing process, the post-processing is required. Due to these limitations, the applicability of the anion exchange resins as alternatives to the alkali catalyst was examined. It was clarified that the anion exchange resin was activated by binding with methoxide ions, which are regenerated during transesterif ication, allowing for their reuse. Compared to the hydroxide-type resins that are deactivated by adsorption of FFAs generated during the reaction, the methoxide-type resins maintain their activity, as no FFA is generated. Such deactivation could be controlled by esterifying FFAs with cation exchange resins before transesterification.