Separation of lignin from industrial prehydrolysis liquor using a solid acid catalyst

The concept of a biorefinery has been introduced in the pulp and paper industry in order to improve the industry’s profitability and competitiveness by generating new revenues from new products. Prehydrolysis liquor (PHL) produced from the Kraft based dissolving pulp production process contain monomeric sugars and oligomeric sugars, acids, degraded lignin, furfurals, and other dissolved low molecular weight extractable substances. Fractionation of dissolved organic compounds from the prehydrolysis liquor is of great economic significance, as the organic compounds are platform chemicals that can be used for the production of bio-based chemicals, materials, and products. The aim of the study was to separate acid soluble lignin from the prehydrolysis liquor during hydrolysis of oligomers using microwave-assisted solid acid catalyst treatment. HZSM-5 was used as a solid catalyst and microwave irradiation power, catalyst loading and reaction time were investigated as manipulated variables to determine the effect on lignin removal and monomeric sugar yield. Lignin characterization and quantification were done using UV, FTIR, and NMR analysis. HPLC was used to identify and quantify components in the PHL and reaction products. Approximately 90% of acid-soluble lignin, 70% of organic acid and 100% furfural could be removed from the PHL with relatively low sugar losses (< 2 wt. %). The results show that solid acid catalyst treatment was effective for not only removing lignin from the PHL but also most known fermentation inhibitors. Combining inhibitor removal, hydrolysis of residual oligomer fractions to fermentable sugars and recovery of platform chemicals in a single treatment step could not only significantly reduce the cost of second-generation ethanol production but also greatly improve the economic viability of forest-based bio-refineries such as paper and pulp mill