Alkali-Assisted Deep Eutectic Solvent Studies on the Separation of Total Cellulose, Lignin, and Crude Tall Oil from Larch Residue

Abstract

Converting Larix olgensis Henry residue into biochemicals and biofuels can bring both economic value and ecological benefits. However, due to the relatively single composition units of the three major components of lignocellulose in larch residue, coupled with its high lignin content and abundant lipids, its conversion process is challenging. This study applied a pretreatment method combining alkali-assisted DES (Deep Eutectic Solvent) pretreatment with crude tall oil production. Larch was used as the raw material, and the pretreatment conditions were optimized by adjusting the pretreatment time and temperature to achieve lignin and crude tall oil isolation while retaining the maximum amount of cellulose. Under optimal pretreatment conditions (120 °C for 5 h), 41.7% of lignin was removed, while 89% of cellulose and 51% of hemicellulose were retained. Furthermore, the separation efficiencies of the main components in the isolated crude tall oil—linoleic acid, isopimaric acid, and dehydroabietic acid—were 49%, 14.9%, and 10.4%, respectively. The lignin obtained under these conditions was rich in β-O-4 bonds, and although some fragments were degraded, the pretreatment did not result in the recombination of lignin fragments. This characteristic not only facilitates subsequent degradation but also presents the potential for efficient depolymerization at high rates in future applications. Additionally, the single structural unit provides a high degree of selectivity for the production of specific depolymerization products. Overall, this study provides a comprehensive analysis of the effective deconstruction of larch residues, paving the way for future industrial applications.

Keywords: Tall oil, Deep eutectic solvent (DES), Alkali-assisted, Fractionation, Lignocellulosic material