Use of Benzyl Alcohol as a Solvent for Kraft Lignin

Abstract

Lignin, an abundant and complex aromatic biopolymer, holds significant potential for producing value-added chemicals and materials. However, its utilization is limited by its solubility in common organic solvents. In this study, we investigated the solubility of softwood Kraft lignin in benzyl alcohol and compared it to other traditionally studied solvents. Methanol achieved a lignin solubility yield of 59%, while ethanol (18%) and acetone (34%), due to their longer alkyl chains and lower polarity, were less effective in solubilizing larger lignin fragments. Benzyl alcohol, on the other hand, exhibited a complete dissolution of lignin, thereby exceeding by far the capability of the standard solvents. Furthermore, benzyl alcohol resulted in a moderate molecular weight of 3621 g/mol for the lignin fragments and a narrow polydispersity index of 1.54. The complete solubility of lignin in benzyl alcohol suggests significant potential for high yield lignin fractionation and subsequent chemical modifications, which are essential for valorization. Despite the high boiling point of benzyl alcohol, the enhanced solubility could facilitate the production of homogeneous lignin fractions with increased reactive sites, thereby broadening the scope of lignin applications in coatings and industrial materials.