Valorization of de-oiled microalgal biomass as a carbon-based heterogeneous catalyst for a sustainable biodiesel production.

[Display omitted] • Valorization of de-oiled microalgal biomass as heterogeneous acid catalyst. • Hydrophobic carbon acts as potential support for sulfonated carbon catalysts. • The catalyst exhibited high catalytic activity and stability. • High FAME yield was obtained with improved fatty acid composition. • FAME yield >90% was obtained after four successive reuse cycles. In this study, a novel carbon-based solid acid catalyst was synthesized by carbonization of de-oiled microalgal biomass followed by sulfonation. The effect of catalyst synthesis conditions such as carbonization temperature, sulfonation time, and H 2 SO 4 concentration on the surface acidity of the catalyst and free fatty acid conversion was determined. The de-oiled microalgal biomass-based solid acid (DMB) catalyst was predominantly composed of carboxylic, phenolic, and sulfonic groups as indicated by the FTIR analysis and supported by the XPS analysis. The catalyst was further characterized by various methods to determine its physiochemical properties. A maximum fatty acid methyl ester (FAME) yield of 94.23% for microalgal oil (AO) and 96.25% for waste cooking oil (WCO) was obtained under optimized transesterification conditions. The catalyst exhibited high catalytic activity (FAME yield >90%) until the fourth cycle. Most of the biodiesel properties were within the permissible limit of EN 14,212 and ASTM D6751 standards. [ABSTRACT FROM AUTHOR]