Characterization of lignin derived from water-only flowthrough pretreatment of Miscanthus

The structural characterization of lignin improves the understanding of the complex lignocellulosic biomass pretreatment which is vital for the economic success of biofuels production. In this study, water-only flowthrough pretreatment is employed to Miscanthus at 160 degrees C for various reaction times to derive the mode of depolymerization process of Miscanthus lignin. Thus, after aqueous phase depolymerization, lignin-derived entities in the pretreated biomass and hydroIyzates were chemically characterized with the aid of various advanced analytical techniques, such as 1D and 2D NMR, FTIR, Py-GC/MS and GC/MS. Both FTIR and Py-GC/MS analysis of pretreated solid residues revealed progressive reduction in H, G and S lignin during flowthrough pretreatment. There was over 60% reduction of S/G ratio, indicative of lignin monomeric compositional change through water-only flowthrough reaction. In agreement with compositional analysis, the FTIR and NMR (1D and 2D) analysis of pretreated hydrolyzate strongly suggested for selective removal and degradation of S-lignin over H and G-lignin. In addition, low content of monomeric and dimeric lignin derivatives were detected by GC-MS analysis of the liquid hydrolyzate, indicating the possibility for existence of soluble oligomeric lignin-derived entities in the hydrolyzates. Our results suggested that under water-only flowthrough pretreatment conditions with Miscanthus samples, lignin depolymerization reactions were associated with selective hydrolysis of 8-O-4' sub-structures along with cleavage of cinnamic and/or coumarylate ester linkages followed by oxidative cleavage at C alpha-C beta position, in conjunction with the preferential removal of S-lignin during the delignification process. (C) 2013 Elsevier B.V. All rights reserved.