Toward Extensive Utilization of Pulping Liquor from Chemical-Mechanical Pulping Process of Wheat Straw in Biorefinery View

Extensive utilization of renewable biomass is crucial for the progress of carbon neutral and carbon peak implementation. Wheat straw, as an important by-product of crops, is hardly ever efficiently utilized by conventional processes. Here, we proposed a mild acid-coupled-with-enzymatic-treatment process to realize the utilization of lignin and hemicelluloses from pulping liquor on the basis of the chemical-mechanical pulping process. The pulping liquor was treated with acid first to precipitate lignin, and it was further hydrolyzed with xylanase to obtain XOSs. The recovered lignin was characterized by FT-IR, 2D-HSQC, GPC, etc. It was found that lignin undergoes depolymerization and condensation during acid treatment. Also, saccharide loss enhanced with the decrease in pH due to the presence of the LCC structure. As a result, an optimized pH of 4 for the acid treatment ensured that the removal rate of lignin and loss rate of polysaccharides achieved 77.15% and 6.13%, respectively. Moreover, further xylanase treatment of the pulping liquor attained a recovery rate of 51.87% for XOSs. The study presents a new insight for the efficient utilization of lignin and hemicellulose products from non-woody materials in the prevailing biorefinery concept.