Production of ethyl levulinate fuel bioadditive from 5-hydroxymethylfurfural over sulfonic acid functionalized biochar catalysts

Abstract In this work, a series of novel -SO3H functionalized biochar materials were prepared and investigated for the first time as catalysts for the production of fuel additive ethyl levulinate (EL) from biomass-derived 5-hydroxymethylfurfural (HMF). The employed biochar was directly produced from vineyard pruning wastes by a simple hydrothermal treatment using water in subcritical conditions followed by 3 different one-step sulfonation processes. The effects of sulfonating agent, reaction temperature, reaction time and alcohol solvent were examined. Full HMF conversion together with outstanding EL yields (over 84%) were achieved at 130 °C and after 6 h over the biochar functionalized with the organosilane 2-(4-chlorosulphonylphenyl)ethyltrimetoxysilane (BioC-S3). Catalyst characterization suggested that the high acid strength (0.983 mmol H+·g−1) derived from the anchoring of arylsulfonic groups were responsible for the promotion of acid-driven etherification and ethanolysis steps. The BioC-S3 catalyst can be recycled without a significant loss of catalytic activity, indicating the stability of – SO3H organosilane group structure in the porous biochar. The obtained results offer a competitive alternative for the production of fuel additives, such as alkyl levulinates, using low-cost and easy-to-prepare biochar-based catalysts, all from lignocellulose resources, as an example to support a future exploitation of a potential biorefinery.