Coupling of hydrothermal and ionic liquid pretreatments for sequential biorefinery of Tamarix austromongolica

Abstract

Fractional pretreatment of lignocellulose is compelling to synergistically enhance its carbohydrate and lignin outputs for the extension of renewable energy sources. A two-stage approach using hydrothermal and ionic liquid (1-butyl-3-methylimidazoliumacesulfamate, [bmim]Ace) pretreatments was evaluated for hierarchically extracting hemicelluloses and lignin from Tamarix austromongolica, while providing a cellulose-rich fraction that could be readily hydrolyzed by cellulase for the recovery of fermentable glucose and residual lignin. Autohydrolysate-derived xylooligosaccharides (XOS), high-quality lignin, and accessible cellulose were successively acquired at the end of the process. The molecular weights, structural characteristics, functional groups and transitional fate of hemicelluloses and lignin were thoroughly explored towards a waste-free concept. This integrated biorefinery removed the amorphous portions, disrupted the rigid structure and altered cellulose I to II, thereby improving the enzymatic digestibility from 11.6 to 90.2%. Results confirmed that 60.98 mg/g XOS (DP 2–6), 352 mg/g glucose and 178.2 mg/g lignin were harvested via this coupled process. In-depth HSQC and 31P NMR techniques signified that the lignins contained large amounts of β-aryl ether units and hydroxyl groups, rendering them essentially suitable for depolymerizing into aromatic chemicals from biomass to energy. It was reasonable to diversify the energy-oriented product portfolio as a function of this sequential process, such as high-purity XOS, fermentable glucose and lignin, which can remarkably boost the feasibility of bioenergy.