Promotion of lignin depolymerization and cellulose utilization via the coupling effects of DDQ pre-oxidation and HCOOH extraction

The full utilization of biomass plays an important role in the environment and energy. In this study, the coupling pretreatment of DDQ pre-oxidation and HCOOH extraction was employed to realize the separation and modification of three components of sugarcane bagasse for full utilization. Especially, the modified lignin was depolymerized to obtain aromatic monomers, and cellulose-rich residue was used to prepare lignocellulose straws. Furthermore, the coupling effects between DDQ pre-oxidation and HCOOH extraction on chemical and physical properties of modified lignin and lignocellulose straws were studied. In addition, the mechanism of lignin depolymerization and lignocellulose straw synthesis were explored as well as the mass balance of the biorefinery process. The results showed that the total yield of aromatic monomers increased by nearly 2 times and the conversion of lignin was 95.1 % after DDQ pre-oxidation. The mechanism showed that DDQ selectively oxidized Cα-OH bond of lignin to Cα = O bond, which not only avoided the formation of carbocation, but also reduced the bond dissociation energy of β-O-4 bond. Moreover, the tensile strength of hydrophobic lignocellulose straw increased by nearly 2 times and its flexural strength was 10.36 MPa. Modified lignin and modified cellulose were connected via hydrogen bonds, which enhanced the intermolecular crosslinking of molecules, thus improving the mechanical properties of lignocellulose straws. Besides, the maximum xylose relative content and concentration of xylose were 61.16 % and 17.57 g/L, respectively. This study provides a method for high-value and green utilization of sugarcane bagasse.