Effects of polyol-based deep eutectic solvents on the efficiency of rice straw enzymatic hydrolysis

• DES deposited on the treated solid surface inhibits hydrolytic enzyme access. • Sodium carbonate wash efficiently removes residual DES on treated solids. • Removal of residual DES increases cellulose accessibility to cellulose. • Enhanced cellulose accessibility to cellulase produces high glucose release. Deep eutectic solvent treatment to overcome lignocellulose resistance to deconstruction has great potential for the production of biofuels and bioproducts. Most investigations have been focused on optimizing the sugar yield from specific feedstocks. However, little is known about the interaction between deep eutectic solvent and cellulose during pretreatment, post-treatment cellulose accessibility to enzymes, and lignin fractionation. We evaluated four deep eutectic solvents that consisted of choline chloride and biomass-derived polyols (ethylene glycol, glycerol, xylitol, and sorbitol). Choline chloride-glycerol (ChCl-Gly) pretreatment retained >90 % glucan from rice straw, even at high pretreatment severity (>4.2 severity factor). In addition, ChCl-Gly pretreatment fractionated 74 wt.% lignin and completely removed acetyl groups from xylan, which enhanced glucan digestibility from 21 % to 87 %. However, the ChCl-Gly deep eutectic solvent became deposited on the solids and limited cellulose accessibility to cellulase enzymes. A sodium carbonate wash was highly effective in removing the deposited ChCl-Gly from the pretreated solids and enhancing cellulase accessibility to cellulose. The simple production and biodegradability without interfering with glucan make ChCl-Gly a promising lignocellulose pretreatment agent. In addition, the ability to fractionate both lignin and sugars enables biorefineries to use the lignin as a co-product.