(548n) DES Pretreatment Leading to Highly Concentrated Sugar Hydrolysate and Valorizable Lignin

This study investigated high-solid loading deep eutectic solvent (DES) pretreatment and resultant valorizable lignin and concentrated sugar hydrolysate. Switchgrass was pretreated using acidified choline chloride:ethylene glycol (ChCl:EG) at high solid loadings of 20-27%. Highly concentrated sugar hydrolysate was obtained from the pretreated switchgrass via 20% solid loading enzymatic hydrolysis after only 48 h, which contained 164 g/L glucose with a glucose yield of 85%. ChCl:EG was highly recyclable, showing good performance when it was reused for new pretreatment cycles. 2D HSQC NMR revealed that ether bonds in switchgrass lignin were cleaved and guaiacyl lignin degraded during the pretreatment. The degree of bond cleavage and lignin subunit degradation depended on the solid loading for pretreatment. The lignin derived from a higher solid loading pretreatment preserved the original structure of natural lignin better, thus producing increased amounts of phenolic monomers upon pyrolysis. This study demonstrated that highly efficient high-solid loading DES pretreatment can not only solubilize lignin and hemicellulose but also enable the production of valorizable lignin and sugar hydrolysate with high concentration.