Sustainable recycling of phenol-assisted deep eutectic solvent for efficient lignocellulose fractionation and enzymatic hydrolysis

Pretreatment centers on facilitating the efficient removal of lignin for enhancing enzymatic saccharification but difficulty avoids the formation of the condensed lignin. However, the specific effects of the condensed lignin on cellulose properties are still not clear. Herein, a recyclable lignin-derived phenol-assisted ternary eutectic solvent (DES), with the ability to make lignin's proclivity towards condensation, is proposed for enhancing lignocellulose fractionation and enzymatic hydrolysis. The effect of the DES types, molar ratio, temperature, and time on lignocellulosic fractionation and cellulose structure was explored comprehensively. Under the optimum conditions (choline chloride/phenol/formic acid DES with a molar ratio of 1:0.05:2, 120 °C, 6 h), the DES pretreatment promoted the removal of lignin (76.36 %) and hemicelluloses (85.09 %). Meanwhile, the glucose and xylose yield of the cellulose-rich residue by enzymatic hydrolysis dramatically enhanced to 99.51 % and 76.72 %, which was 4 times and 12 times higher than that of the raw material, respectively. The increased efficiency was due to the introduction of phenol to efficiently promote lignin dissolution, enhancing the accessibility, surface area, and crystallinity of cellulose. After five recycling processes, the recycled DES still preserved an ultrahigh efficiency in lignocellulosic fractionation and enzymatic saccharification. This green phenols-assisted DES pretreatment opens a novel avenue for efficient lignocellulosic fractionation and cellulose enzymatic hydrolysis.