| Facing the impending depletion of fossil resources and environmental problems,it is an inevitable trend to produce commodity chemicals,fuels and energy from lignocellulosic biomass.Currently,efficient conversion and utilization of carbohydrate in lignocellulose have been achieved.However,lignin is very difficult to be efficiently conversted because of complex and structure.Annually,over 50 million tons of industrial lignin is produced and mostly as a side stream of biomass separation processes.Hence,utilization of lignin as an alternative for fossil carbon sources in fuel and chemicals is important for high-valued application of biomass.However,the structures of lignin are different by various sources and isolation process,resulting in difference of the distribution and yield of depolymerization product even under the same depolymerization process.Hence,lignin with typical structures is chosen to characterize and analyze original structure of lignin in the plant cell wall and efficient depolymerization of this kind of lignin was proposed.The main research topics and results are as follows:(1)Swollen residual enzyme lignin(SREL)was isolated from Eucalyptus camaldulensis based on mild alkaline preswollen and in-situ enzymatic hydrolysis,and the yield of SREL was high and content of carbohydrates in lignin was low.In this study,SREL was depolymerized in AIC13-catalyzed hydrothermal system to produce phenolic compounds,and lignin and the depolymerization product were comprehensively characterized and investigated.The analysis results were showed that cleavage of almost ?-O-4 linkages,decrease of the molecular weight and increase of free phenolic hydroxyls obviously occurred in AICl3-catalyzed hydrothermal system.In addition,the depolymerization process also resulted in a large amount of volatile fraction,which was composed of phenols,guaiacols,and syringols.Among the volatile fraction,syringaldehyde accounted for about 31.70%of the bio-oil under optimum conditions(at 160? for 1 h).This study showed that in this catalyst system,depolymerization reaction easily occurred under mild conditions(140-160?),while condensation reaction was more likely to occur at high temperature(160-180?).(2)Organosolv lignin(OL)was chosen as the starting feedstock since the structure of OL have some advantages,such as lower content of carbohydrates,typical structures and low molecular weight to understand the structural transformations of lignin during AICl3-catalyzed depolymerization processes.In this work,an efficient base-catalyzed depolymerization and in situ hydrogenolysis process of organosolv lignin depolymerization and char elimination was implemented using the synergic catalyst of NaOH and different hydrogenation catalysts(e.g.,Ru/C,Pt/C and Pd/C).The result showed that Ru/C was the best catalysts in all the catalysts tested in this study based on lignin depolymerization efficiency.Meanwhile,condensation reaction was inhibited and few char formed in the presence of the integrated catalyst NaOH coordinated with Ru/C.In addition,the relatively high content of DL obtained from lignin depolymerisation is possible to be used as excellent flame resistance material.(3)A representative lignin was firstly prepared based on ball-milling and in-situ enzymatic hydrolysis as well as an efficient lignin depolymerization process with highly controllable products was presented using Cs-substituted tungstophosphate(CsTP)cooperated with Raney Ni in the present work.By depolymerization,the molecular weight of the DEL was reduced significantly from 15770 to about 1000 g/mol(for APL)and about 400 g/mol(OPL).Importantly,the yield and selectivity of depolymerization product was high.Meanwhile,there were few chars formed.Besides,it was found that the temperature only affects the yield of the degraded monomers,but don't changes of the distribution of the degraded monomers. |
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