Comparative study of the effectiveness of protic and aprotic ionic liquids in microwave-irradiated catalytic conversion of lignocellulosic June grass to biofuel precursors

Abstract

This work compares the effectiveness of protic (PIL) and aprotic (APIL) ionic liquids in microwave-irradiated transition metal-catalysed one-pot conversion of a cellulose-rich non-edible lignocellulose, namely, June grass – composed of cellulose (82.3%), hemicelluloses (1.3%), with crystallinity index of 54% – to biofuel precursors such as glucose, hydroxymethylfurfural (HMF), levulinic (LA) and formic (FA) acids. Reaction parameters such as catalyst-substrate loading, IL-substrate loading, water concentration, temperature, and time are optimized to target specific biofuel precursor molecules and regulate the product distribution. The APIL ([BMIM]Cl) gives a maximum glucose yield of 88.2% at 180 °C and 40% water concentration, while the PIL ([Et3NH][HSO4]) produces a maximum HMF yield of 34.8% at 180 °C with no added water, and maximum LA and FA yields of 19.2% and 7.6%, respectively, at 200 °C. The PIL-based conversion targeting HMF as the biofuel precursor molecule, with glucose, LA, and FA as co-products, gives a product: reactant cost ratio 194.