Phenolization of hardwood sulfuric acid lignin generated as byproduct in bioethanol production system

In the bioethanol production process via acid saccharification, a large amount of acid hydrolysis lignin is yielded as a byproduct. In this study, the behavior of hardwood sulfuric acid lignin (SAL), which is a typical acid hydrolysis lignin, during phenolization to convert into functional materials is investigated. We compared the product yield, average molecular weight, methoxy content, and reactions of simple model compounds with those of softwood SAL, focusing on the difference between syringyl and guaiacyl units. The beech SAL reacted with phenol more readily than red pine SAL and yielded a greater soluble fraction of phenolized SAL (P-SAL). To investigate the difference in the phenolization activity of the syringyl and guaiacyl units in beech lignin, we prepared syringyl-nucleus-rich sulfuric acid lignin (S-rich-SAL) and guaiacyl-nucleus-rich sulfuric acid lignin (G-rich-SAL) from beech, which were subjected to phenolization. The results suggest that the syringyl unit in SAL had greater phenolization activity and its phenolized products were more soluble in acidic aqueous medium. The study using model compounds also showed that the syringyl unit had higher phenolization reactivity than the guaiacyl unit.