Carbocation scavenger assisted full fractionation of poplar for production of xylo-oligosaccharides (XOSs), lignin and high-titer bioethanol

Pretreatment leads to significant structural changes of lignocellulose that affects biomass fractionation and valorization. This work proposed carbocation scavengers assisted benzoic acid (BA) and deep eutectic solvent (DES) pretreatments, in which 2-naphthol (2N) addition in BA pretreatment facilitated production of highly active xylo-oligosaccharide (XOSs yield of 42.46 %, with X2-X3 percentage of 68.06 %), and 2-naphthol-7-sulphonate (NS) addition in DES post-treatment facilitated lignin removal (∼94.53 %), providing a cellulose-enriched and readily-hydrolyzed solid. Besides, high-titer ethanol (57.88 g/L) was produced through high-solid-loading pre-hydrolysis simultaneous saccharification and fermentation (PSSF) process on this BA2N-DES/NS pretreated solid, with ethanol yield of 85.21 %. Moreover, various analysis (GPC, 31 P NMR and 2D HSQC NMR) revealed that, this cascade fractionation process allowed recovery of high-purity and less-condensed lignin while preserving abundant β-O-4 linkages, which could be readily assembled into regular sphere-shape lignin nanoparticles with average size of 188.2 nm. Results presented great potential of the carbocation scavengers assisted combinational pretreatment as a first step for lignocellulosic biorefinery to co-produce xylo-oligosaccharides (XOSs), lignin and high-titer bioethanol.