Biochar-based catalyst for simultaneous reactions of esterification and transesterification

Biochar, a by-product of fast pyrolysis of woody biomass, was developed as a renewable catalyst for simultaneous transesterification and esterification of canola oil and fatty acid (oleic acid) mixture at 150 degrees C under 1.52 MPa. Surface area and porosity of biochar were increased significantly from negligible to 990 m(2)/g, and 0.9 cm(3)/g through chemical activation method with KOH. The resultant biochar was sulfonated with fuming sulfuric acid to produce the biochar-based catalyst with high surface area and porosity (949 m(2)/g and 0.85 cm(3)/g). The ester formation yield was investigated based on the molar ratios of alcohol to canola oil (A:O), alcohol to oleic acid (A:FFA), or at constant mass ratio of alcohol to the mixture of oil and oleic acid. Increasing the FFA concentration from 15, 30 to 50 wt.% (at constant A: O molar ratio) resulted in slight increase of reaction yields from 27.9, 35.1, to 36.7%, respectively. Results also revealed a continuous increase in reaction yield from 38.0 to 48.1% as increasing A: FFA molar ratio (from 10: 1 to 30: 1) at constant A: O. However, increasing A: O ratio (from 10: 1 to 30: 1) at constant A: FFA resulted in an unexpected decrease in the reaction yield from 48.1 to 28.8%. The biochar based catalyst showed promising catalytic activity (48% yield in 3 h) for the combination of transesterification and esterification reactions in a mixture of canola oil and oleic acid for biodiesel production. Reaction yield decreased by similar to 8% upon reusing the catalyst. (C) 2012 Elsevier B. V. All rights reserved.