Pretreatment of waste biomass in deep eutectic solvents: Conductive heating versus microwave heating

[Display omitted] •Deep eutectic solvents (DES) can deconstruct rice hulls at low temperature & pressure.•Enzymatically hydrolyzed DES pretreated rice hulls give 100X more glucose yield.•Microwave pretreatment is faster & requires less energy than conductive pretreatment.•The DES (FA:CC 2:1 mol ratio) was able to delignify rice hulls. Deep Eutectic Solvents (DESs) have recently emerged as an environmentally-friendly way to separate lignin from cellulose and hemicellulose in recalcitrant biomass prior to enzymatic hydrolysis to enhance glucose yields. Rice hulls, a widely-available secondary agricultural residue was pretreated with FA: CC (formic acid and choline chloride in a 2:1 mol ratio) using conductive heating and microwave heating. Pretreated biomass using either heating technique gave glucose titers 100 times higher than raw rice hulls after enzymatic hydrolysis. FTIR analysis shows similar findings for both heating techniques. For biomass pretreatment using DESs, microwave heating requires less than half of the energy (0.10 kW-h) compared to conductive heating (0.31 kW-h). Conductive heating requires more residence time of biomass for the pretreatment process. Thus, this work shows the potential benefits of a microwave heating technique for deconstruction of biomass using DESs.