Valorization of humin as a glucose derivative to fabricate a porous carbon catalyst for esterification and hydroxyalkylation/alkylation

A challenge of today's industry is to transform low-value side products into more value-added materials. The acid-catalyzed conversion of hemi(cellulose) to platform chemicals in green chemical/fuel production and biorefinery yields large formation of insoluble byproduct called humin. Herein, humin obtained from dehydration of glucose was transformed into a novel class of effective carbonaceous solid acid catalyst for the first time via low-temperature pyrolysis followed by sulfonation. A range of preparation conditions were investigated, and the structure-function relationships of the resulting catalysts were also discussed based on the analysis of structure and composition. Comparing with the glucose-derived carbon catalyst, the humin-derived catalyst has substantially larger surface area and higher SO₃H density, which enable it to display higher catalytic activity and efficiency not only in esterification of levulinic acid and n-butanol (yield = 95.0%, 373 K), but also in hydroxyalkylation/alkylation of 2-methylfuran and furfural (yield = 64.2%, 323 K). Additionally, the catalyst could be repeatedly employed for at least four cycles without obvious deactivation, exhibiting good reusability. This work provides a green method to convert humin byproduct into economic and eco-friendly solid acid catalyst and may contribute to a holistic approach for biomass utilization.