Studies On High-solid Lignocellulose Pretreatment And Novel Aminated Lignins

The entire utilization of renewable lignocellulosic biomass is crucial for achieving sustainable development of biorefinery and moving away from dependence on fossil fuels.However,there still remain many challenges that limit scale-up and commercialization of biorefinery,to name a few,low bioconversion efficiency of biomass and difficulties on lignin valorization.This study mainly improves biomass biodegradability and obtains lignin feedstock which is easily valorized from the two aspects:pretreatment process innovation and novel lignin preparation.In order to address the problem that the efficiency of lignin removal and enzymatic hydrolysis is not performed well in high-solid biomass pretreatment,a novel ionic liquid-ethylenediamine synergistic pretreatment under mild conditions was developed in this study.The results suggest that the 90:10 ionic liquid-ethylenediamine ratio was recommended to avoid xylan loss at higher ethylenediamine addition ratios,while simultaneously maximizing fermentable sugar yields.Compared to separate ionic liquid pretreatment,the lignin removal showed more than a 2-fold improvement in synergistic pretreatments at high solid loadings(36 wt%),and the glucose yield was increased from 77%to 94%.The initial continuous and complete ultrastructure of corn stover was destroyed more efficiently,which would provide easier paths for ionic liquids to disrupt the hydrogen-bond network in native cellulose,thus reducing its real crystallinity from 1.43 to 0.8-1.0.Also,there were more nativeβ-O-4 structures preserved in treated lignin after this synergistic pretreatment.Poor solubility and recalcitrant condensed structures of lignin have emerged as the main obstacle for effective valorization of lignin.Here,a solid-state pretreatment using ethylenediamine was developed to fractionate new lignins streams with extraordinary aqueous solubility and minimal condensed structure from corn stover.Substantial hydrophilic amine and amide groups were introduced into lignin structures in ethylenediamine pretreatments by ammonolysis,nucleophilic attack and Schiff base reactions,which endows aminolignin with extraordinary aqueous solubility(≥86 wt%)over a wide range of p H.In addition,extremely high solid loadings(1:0.8,g/m L)limited the mobility and accessibility of reactive lignin intermediates owing to pretreatment system keeping in the solid state,physically obstructing the lignin condensation.Chemically,theα-amination of lignin decreased condensation as well,because of a larger steric hindrance at theα-carbon and the blocking of active sites.The suppressed lignin condensation enables the extensively depolymerization of native lignin to stable low molecular weight products(M_w=1200-1400 Da)in the ethylenediamine system.Taken these together,this study provides mild and effective solid-state pretreatment technologies,which are of great significance for the development of high-solid pretreatments in lignocellulosic bioethanol and lignin valorization.Additionally,in-depth analysis of pretreatment mechanism and lignin structure and nature changes provides the basic theory for downstream conversion of lignin.