Direct fractionation of wood chips by deep eutectic solvent facilitated pulping technology and application for enzyme hydrolysis

Abstract In the practical application of deep eutectic solvents (DESs) for fractionation of lignocelluloses, the rigorous requirements for the size of starting materials and the long duration of the treatment (even required 12 h) have impeded industrial applications of DES. Herein, the energy-efficient pulping technology was proposed for direct fractionation of wood chips by applying DES (choline chloride: lactic acid) as a cooking solvent. The combination of the pulping technology and DES treatment process enables direct fractionation of wood chips (by bypassing the excessive powderization step) and substantially reduces the pretreatment time owing to the synergistic effect of elevated temperature and pressure. The DES pulping technology can selectively dissolve lignin by cleavage of the lignin-carbohydrate complex (LCC) and β-O-4 linkages, the wood chips can be converted into DES-Pulp at a cooking temperature of 130 °C and preservation time of 1 h, which is an efficient pretreatment method for the enzymatic hydrolysis of wood chips. The enzymatic saccharification ratios of the DES-Pulps are between 35.4% and 88.2% at different DES cooking temperatures. The DES pulping process at a cooking temperature of 140 °C and cooking preservation time of 1 h exhibited the highest cellulose saccharification ratio of 88.2%. For DES-Pulp prepared from low cooking temperature, mechanical treatment can improve their saccharification efficiency, for example, the enzymatic hydrolysis efficiency of the DES-Pulp combined with PFI refining (10 min) was improved from 71.4% to 85.4% at a cooking temperature of 130 °C.