Cellulose-derived superparamagnetic carbonaceous solid acid catalyst for cellulose hydrolysis in an ionic liquid or aqueous reaction system

Abstract

A cellulose-derived carbonaceous solid acid catalyst that has superparamagnetism was synthesized by incomplete hydrothermal carbonization of cellulose followed by Fe₃O₄ grafting and –SO₃H group functionalization. The as-prepared superparamagnetic carbon catalyst contained –SO₃H, –COOH, and phenolic –OH groups and exhibited good catalytic activity for the hydrolysis of cellulose in either an ionic liquid phase or aqueous phase. A total reducing sugar (TRS) yield of 68.9% was obtained with ionic liquid 1-butyl-3-methyl imidazolium chloride ([BMIM][Cl]) at 130 °C for a 3 h reaction time. A TRS yield of 51% was obtained with water at 180 °C for a 9 h reaction time. The catalyst was applied to rice straw for which a TRS yield of 35.5%, based on the total mass of loaded rice straw, was obtained in [BMIM][Cl] at 150 °C in 2 h. The superparamagnetic carbonaceous solid acid catalyst was easily separated from the reaction products with an external magnetic field and used for subsequent recycling experiments. The activity of the recycled catalyst decreased with a recycle number that is attributed to some loss of the catalyst and adsorption of humin products on the active catalyst sites.