Study on high efficiency separation of low condensation lignin and its dissolution mechanism by 1, 4 butanediol combined with p-toluene sulfonic acid pretreatment system

Separating low condensed lignin from lignocellulosic biomass is of great importance for achieving its full component conversion. This study proposed a new efficient and environmentally friendly alcohol/acid pretreatment system using 1,4-butanediol (1,4-BDO) as a solvent, combined with p-toluene sulfonic acid (p-TsOH) to efficiently separate low condensed lignin. The results showed that the system could remove 85.55 % of hemicellulose and 84.78 % of lignin in a short time, with a high retention rate of cellulose. Based on the phenomenon of 1,4-BDO molecule protecting lignin structure, the recovered low-condensed lignin structure contains the main aliphatic hydroxyl structure, and the remaining solid surface lignin condensation grains were fewer, and the fiber crystallinity was high, which was beneficial for the preparation of high-value products. In addition, the lignin dissolution kinetics revealed that the p-TsOH/1,4-BDO pretreatment had a lower reaction activation energy, clarifying the solvation effect of 1,4-BDO on efficient lignin dissolution. Finally, combining density functional theory (DFT) from the molecular level clarified that the hydrogen bonding and conjugated effect between 1,4-BDO and lignin structure could effectively reduce the self-condensation reaction of lignin molecules. This study achieved effective separation of lignocellulosic biomass, providing a theoretical basis for the application of 1,4-BDO in biomass component separation, and promoting the development of green and efficient component separation technologies.