Evolution of the Lignin Chemical Structure during the Bioethanol Production Process and Its Inhibition to Enzymatic Hydrolysis
journal contributionposted on 07.05.2020, 14:07 by Chao Zhao, Xianliang Qiao, Qianjun Shao, Muhammad Hassan, Zhongqing Ma
To illuminate the lignin evolution after hydrogen peroxide presoaking prior to ammonia fiber expansion (H-AFEX) pretreatment and enzymatic hydrolysis, ball-milled wood lignins were separated from untreated corn stover, H-AFEX-treated corn stover, and enzymatic hydrolyzed residue, labeled as UN-L, HA-L, and EH-L, respectively. The structural features of EH-L were compared with HA-L and UN-L by elemental analysis, GPC, FT-IR, and NMR. The inhibition deriving from lignin loading and the structure were assessed by adding UN-L/HA-L in enzymatic hydrolysis. The thermogravimetric analysis and thermal degradation kinetics analysis of EH-L were performed to evaluate its industrial utilization. The results showed that a significant decline in molecular weight was observed in EH-L, while the polydispersity index was almost unchanged. The decrease of the G unit and the increase of the S unit were shown in EH-L when comparing to UN-L. The G unit had the strongest inhibition to enzymatic hydrolysis, and the increasing relative proportion of S/G in lignin was beneficial for enzymatic hydrolysis. The resinol structure in lignin was relatively stable after pretreatment and enzymatic hydrolysis. The thermogravimetry analysis indicated that the EH-L exhibited better thermal stability than that of UN-L, offering potential to prepare lignin-based heat-resistant epoxy resin and new flame-resistant materials.