Thermochemical pretreatments of maize stem for sugar recovery: Comparative evaluation of microwave and conventional heating.

• Microwave thermochemical pretreatments efficiently decomposed hemicellulose. • Microwave thermochemical pretreatments produced high yields of monosaccharides. • Microwave thermochemical pretreatments removed 96.1 % lignin content from biomass. • Efficient microwave thermochemical pretreatment was completed within 5 min. • Microwave heating consumed 25–34 folds less energy than conventional heating. Microwave (MW) heating is attracting great attention in biorefinery processes, because of its special dipole rotation heating mechanism. In the current study, MW and conventional heating methods were employed to assist the thermochemical pretreatments (H 2 O, H 2 SO 4 or NaOH) of maize stem biomass. Their influences on sugar release and biomass compositions during pretreatments were comparably evaluated. Compared to conventional heating pretreatment, MW thermochemical pretreatments are highly efficient in sugar recovery, contributing to 4.3 times higher amount of sugar release (1.25 vs 0.30 μmol/mg biomass) with reaction time 8 times shorter (5 vs 40 min) and selectively producing glucose as the major constituent (0.75 μmol/mg biomass) using 0.2 M H 2 SO 4 as pretreatment media. MW thermochemical pretreatment also effectively removed lignin (up to 91.6 %) within 5 min, which was significantly higher than conventional heating pretreatment (51.2 %). Conventional heating pretreatment successfully removed hemicellulose and converted the crystalline cellulose into amorphous cellulose, which is probably due to its longer heating time. Rapid MW thermochemical pretreatments efficiently fractionated hemicellulose and removed lignin content while keeping the crystalline cellulose structure. MW and conventional heating pretreatments led to similar digestibility of biomass solid residues. Overall, MW thermochemical pretreatment represents an energy efficient alternative strategy, as it consumed 25–34 folds less energy than conventional heating pretreatment for effective biomass fractionation and value-added chemical production. [ABSTRACT FROM AUTHOR]