Tailored bamboo fractionation with ternary deep eutectic solvent system to maximize biorefinery toward enzymatic saccharification and lignin recovery

Six different ternary deep eutectic solvent (DES) of tetraethylammonium chloride (TEAC)/oxalic acid (OA)polyols were synthesized to improve the production of fermentable sugars and lignin by-products. The bamboo fractionation and bioconversion of cellulose residues can be enhanced by the ternary DES pretreatment, and its increasing efficiency was positively related to the alkyl carbon chain length and hydroxyl number of polyols in the hydrogen bond donor. The 1,4-butanediol (BDO)-assisted DES pretreatment showed excellent performance in achieving high xylan removal (86.7 %) and delignification (91.98 %). The pretreated bamboo was used for enzymatic hydrolysis and ethanol fermentation, with glucose yield and ethanol production of 76.13 % and 16.17 g/L, which was significantly improved by 30 % and 48 % compared to bamboo treated with corresponding binary TEAC/OA. The characterization of trinary pretreated bamboo revealed that the addition of polyols helped to protect the beta-O-4 substructure of lignin, reduce the recondensation of lignin fragments, and thus enhance enzyme digestibility. Furthermore, 37.9% of lignin with high purity and highly active hydroxyl substructures was recovered. The proposed novel TEAC/OA-BDO DES mixture has great potential as an effective pretreatment solvent for future bamboo biorefinery.