Biochar based solid acid catalyst for biodiesel production

Abstract

A promising catalyst based on a biomass pyrolysis by-product, biochar, has been developed for the production of biodiesel. Two carbon-based solid acid catalysts were prepared by sulfonating pyrolysis char with concentrated or fuming sulfuric acids. Prepared catalysts were studied for their ability to catalyze transesterification of vegetable oils and esterification of free fatty acids. The catalyst sulfonated with the concentrated sulfuric acid demonstrated considerable conversion in free fatty acid esterification, while indicating limited transesterification activity. Using the stronger sulfonating reagent, fuming sulfuric acid, resulted in much higher transesterification activity. Further investigation of the latter catalyst was conducted to determine the effect of sulfonation time (5 and 15 h) and surface area on the transesterification reaction. The surface area of the biochar was increased by chemical treatment using 10 M potassium hydroxide through porosity development. The resulting four catalysts were compared for their catalytic activity. Results showed the catalyst with the highest surface area and acid density to have the highest catalytic activity for the production of biodiesel from canola oil in the presence of methanol as the reagent. Furthermore, the catalyst with the higher surface area indicated higher transesterification activity among the catalyst with similar acid densities. The effects of alcohol to oil (A:O) molar ratio, reaction time and catalyst loading on the esterification reaction catalyzed by the sulfonated biochar were also investigated. Free fatty acid (FFA) conversion increased with increasing A:O molar ratio, reaction time and catalyst loading. The catalyst has a tremendous potential to be used in a process converting a high FFA feedstock to biodiesel.