Cascade fractionation of poplar into xylose, glucan oligomers and less-condensed lignin via synergistic formic acid–LiBr molten salt hydrate pretreatment

Lignocellulose as an appealing renewable carbon resource holds great potential to produce high-value-added products. The implementation of an integrated pretreatment process that enables effective fractionation and targeted valorization is crucial for ensuring the feasibility of future biorefinery scenarios. In this study, a stepwise approach using formic acid (FA)–LiBr molten salt hydrate (LiBr MSH) pretreatment was successfully developed for producing high yields of xylose, glucose, glucan oligomers, and less-condensed lignin from poplar. Results showed that FA pretreatment removed the most hemicellulose, releasing a high yield (71.63%) of xylose at 160 °C for 1 h. Subsequent acidified LiBr MSH pretreatment at 100 °C for 0.5 h resulted in a remarkably high cellulose degradation rate of 84.55%, yielding 41.87% glucose and 42.68% glucan oligomers. Meanwhile, 95.57% purity of lignin with abundant uncondensed moieties (i.e., β-O-4 bonds, Hibbert’s ketones) was obtained. The proposed integrated FA–LiBr MSH pretreatment exhibited great potential as an efficient deconstruction strategy in the current biorefinery scenario.