Sulfonated porous biomass-derived carbon with superior recyclability for synthesizing ethyl levulinate biofuel

The synthesis of ethyl levulinate (EL) via esterification of levulinic acid (LA) with ethanol, which can be derived from biomass, has become an attractive topic since EL can be applied in many fields, such as fuel additives for petroleum and biodiesel, food additives and fragrance. Herein, the sulfonated porous carbon catalysts derived from the rinds of corn stalk biomass wastes were prepared by using sulfuric acid and phosphoric acid as the sulfonating agent and activator, respectively. The preparation parameters were optimized based on the catalytic activity for LA esterification with ethanol and the acid density of the corresponding catalysts. Also, various reaction factors were optimized to improve the catalytic efficiency over the optimal sulfonated corn stalk-derived carbon (s-CSC). Under the conditions of reaction temperature 80 °C, catalyst dosage 5 wt%, ethanol-to-LA molar ratio 5.0:1 and reaction time 8 h, the LA conversion reached 94% and 93% catalyzed by s-CSC and the optimal porous catalyst (s-p-CSC), respectively. Noticeably, benefitting from the hierarchical porous structure with large surface area, s-p-CSC exhibited much better recyclability than s-CSC. This work offers a highly effective solid acid catalyst for the synthesis of biofuel.