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 °C under 1.52 MPa. Surface area and porosity of biochar were increased significantly from negligible to 990 m2/g, and 0.9 cm3/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 m2/g and 0.85 cm3/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 ∼8% upon reusing the catalyst.

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► Biochar developed as a low-cost, novel, and renewable solid acid catalyst precursor.
► Simultaneous transesterification/esterification of oil and oleic acid (FFA) tested.
► Highest reaction yield was 48.1% at 150 °C/1.52 MPa after 3 h of reaction time.
► Increasing FFA concentration (15–50%) resulted in slight reaction yield increase.
► Increasing alcohol amount at ∼25% FFA concentration showed optimum reaction yield.