Revealing the structure and distribution changes of corn stalk lignin during the Organosolv Pretreatment

Abstract

During the pretreatment of biomass, the research on the migration process of lignin in the cell wall and the change of chemical structure is very important for improving pretreatment and subsequent lignin upgrading. Hence, corn stalk lignin was extracted by 1, 4-dioxane organosolv system under mild conditions with varying pretreatment time and 0.1 M hydrochloric acid as catalyst. The heterogeneity of lignin removal in the different morphological areas of the cell wall was revealed by advanced imaging techniques. Results indicated that during the pretreatment with dioxane organosolv, the removal of lignin started from the secondary wall of the cell wall, and gradually developed outward to the compound middle lamella. Meanwhile, the resulting lignin obtained through different pretreatment times was characterized by two-dimensional heteronuclear single quantum coherence spectroscopy (2D-HSQC) and gel permeation chromatography (GPC). These characterization results indicated that there were more syringyl (S) units in the lignin that were removed first, and the proportion of guaiacyl (G) units was increased as the pretreatment continued. All the evidence supports the idea that the main reason for the significant differences in lignin structures at various periods of the lignin removal process is that the lignin come from different cell wall regions.