Impact of dilute acid treatment on improving the selectivity of lignin and hemicellulose removals from pre-hydrolysis liquor

Pre-hydrolysis liquor (PHL) of the dissolved pulp production process contains sugar and lignin is paper-making wastewater. Although sugar has the potential for value-added applications, the presence of lignin is problematic for the utilization of PHL. To improve the removal of lignin and maintain a high concentration of sugars in PHL, a novel process was introduced that included a dilute acid treatment, activated carbon (AC), and resin treatment of PHL, respectively. The results confirmed that most of the colloidal lignin and part of dissolved lignin were removed by dilute acid post-hydrolysis and the bonds of lignin-carbohydrate complexes were broken, and the adsorption efficiency of AC and resin was improved. In addition, the research found that high temperature can improve the adsorption efficiency of lignin on AC. In the case of without using PAC, the dilute acid treatment can reduce the dosage of AC from 25 g/L to 12.5 g/L and improve the flow rate of PHL through the resin from 0.1 mL/s to 0.8 mL/s in removing lignin to 90 %, while maintaining sugars in PHL. Also, the particle size of the PHL was significantly reduced by dilute acid-post hydrolysis which is probably because of the broken of beta-O-4 aryl ether bond of lignin in PHL indicated by the analysis of 2D-HSQC. This work provides a practical technical process for industrial application of PHL and production of sugar solutions (mainly xylose) with high purity.