Enhancement of ethanol production from spruce wood chips by ionic liquid pretreatment

► Spruce chips and powder were pretreated by solvents: two ionic liquids and NMMO. ► The efficiency of pretreatment was examined by enzymatic hydrolysis and fermentation. ► 1-Ethyl-3-methylimidazolium acetate was the most efficient solvent. ► Ethanol yield of wood powder was improved from 9.7% to 81.5% of theoretical yield. ► Ethanol yield of wood chips was improved from 2.7% to 66.8% of theoretical yield.