Pretreatment efficacy and lignin solubility of organic solvents on juvenile slash pine chips for lignin value prior to pulping

Abstract

Organic solvent treatment of wood chips can be a key to converting pulp mills into pulp-producing biorefineries. Choosing an optimal solvent requires screening of numerous industrially relevant solvents. This work considers the delignification efficacy of several aqueous organic solvents for juvenile slash pine chips and correlates this efficacy to the lignin solubility. No correlation was shown between the pretreatment efficacy and solubility of ethanol-extracted lignin in organic solvents. At least 10% (v/v) water and 10% (v/v) organic solvent are required for effective delignification, and the different solvent delignification profiles for aqueous mixtures of 1,6 hexamethylene diamine, ethanol, 1-methylimidazole, tetrahydrofuran, and ethylene glycol were determined experimentally. No correlations were found between lignin solubility, Hansen solubility parameters, and delignification. Therefore, solubility measurements should not be a screen for lignin value prior to pulping. However, a 50% (v/v) organic solvent pretreatment at 200 °C for 2 h is a valuable screen to rank the delignification efficacy of organic solvents for further optimization.