High selective delignification using oxidative ionic liquid pretreatment at mild conditions for efficient enzymatic hydrolysis of lignocellulose

• Oxidative ionic liquid treatment can selectively extract lignin from lignocellulose.
• Depolymerization and solvation by ionic liquid contributed to extraction of lignin.
• Enzymatic hydrolysis after oxidative ionic liquid pretreatment was enhanced.
• Oxidative ionic liquid treatment mainly extract the amorphous portion of biomass.

Herein, the oxidative ionic liquid (IL) pretreatment for overcoming recalcitrance of lignocellulose with selective delignification was investigated, and the subsequent enzymatic hydrolysis was evaluated. IL pretreatment incorporating oxygen delignification could enhance lignin extraction with high selectivity at low carbohydrate loss. The dual-action of oxidative decomposition and dissolution by 1-butyl-3-methlimidazolium chloride (BmimCl) on biomass were synergistically acted, accounting for efficient recalcitrance removal. In addition, the mild oxidative IL treatment only slightly converted crystalline cellulose into amorphous structure, and the extensive extraction of the amorphous lignin and carbohydrate resulted to the expose of cellulose with high susceptibility. Correspondingly, the enzymatic hydrolysis of the pretreated lignocellulose was greatly enhanced. The oxidative IL treatment at mild conditions, collaborating BmimCl treatment with oxygen delignification is a promising and effective system for overcoming the robust structure of lignocellulose.