A Study On Depolymerization Of Lignin To Phenolic Compounds

The lignin structure often changes along with biomass pretreatment. In this study, different lignin depolymerization methods for phenolic compounds production based on lignin structure were designed and investigated.The potential of lignin-first refinery to phenols was first investigated from the aspects of feedstock selection, noble metal reduction, catalyst recovery, and process improvement. The results showed that lignin-first biorefinery can be operated under lower Ru/Biomass ratio, generally a 0.003 ratio of Ru input is sufficient for biomass depolymerization. Addition of 0.5 wt.% Nickel into Ru/C catalyst resulted in a magnetic separable catalyst for biomass catalytic depolymerization. Catalytic conversion of nutshell in methanol with Ru/C catalysts at 250? resulted in fractional conversion to stable bio-oil and methane rich gas products, while wood samples rich in extractables resulted in lignin monomers with terpene groups. The lignin-first biorefinery could be operated under mild conditions (?120?) through integration of acid pretreatment with in-situ hydrogenation. The results also indicated that lignin derived oil, though produced under reductive atmosphere, suffered from structure change during storage as revealed by the HSQC and GC/MS investigation. Timely upgrading of the resulting oil was thus necessary.The hydro-cracking of extracted lignin with certain catalysts and hydrogen donor solvents was then studied by a direct coal liquefaction (DCL)-like process, which was performed at an initial hydrogen pressure of 8 MPa. The lignin conversion and phenols yield, both of which increased with a rise in temperature, were maximized at 89.0 wt.% and 30.2 wt.% of dry feedstock mass, respectively using in-situ dispersed FeOOH and tetralin as hydrogen donor at 440?. The lignin to phenols conversion mechanism and process challenge was investigated by detailed characterization of the products. It was found that the mechanistic reason on the hindrance of lignin to phenols conversion is the presence of large amounts of strong Caryl-C bonds in lignin structure. The hydrogen donor solvent favors the breaking of Caryl-C bonds through the co-reaction of solvent and lignin.The research work reported in the thesis will provide important fundamental insights and technical solution for lignin application.