Acid functionalized hydrochar as heterogeneous catalysts for solventless synthesis of biofuel precursors

Abstract

Synthesis of biofuel precursors via the hydroxyalkylation alkylation reaction is one of the solutions to the problem of depletion of renewable energy resources. This work examines the preparation of hydrochar via hydrothermal carbonization from low-cost biomass waste. Hydrochar was functionalized with three different Brønsted acidic moieties, namely sulfonic, nitrate and phosphate, to prepare a series of heterogeneous catalysts. All three catalysts have been used for the catalytic reaction between 2-methylfuran and furfural to form C15 fuel precursors under solventless conditions. Detailed optimization reactions varying the catalyst amount, time and temperature have been performed. A best yield of 83% of the product was obtained using sulfonic functionalized hydrochar under mild conditions. The reaction between 2-methylfuran and other carbonyl compounds like acetone and thiophene-2-carboxaldehyde was also performed with the best catalyst and an yield of 68% and 90% of 5,5′-(propane-2,2-diyl)bis(2-methylfuran) and 5,5′-(thiophen-2-ylmethylene)bis(2-methylfuran), respectively were obtained. Temperature programmed desorption studies and green metric calculations were performed to obtain deeper understanding. The insights gained from this comparative study can be beneficial for the design and development of solid acid catalysts for different biomass conversion reactions.