Study On Depolymerization Of Lignin In Hydrogen Donor Solvent System

Lignin is considered to be the most important and only renewable source of aromatic chemicals on the planet and has great economic value.The catalytic hydrogenolysis of lignin is currently the most efficient conversion method,which can convert lignin into high-value monophenolic compounds and has good prospects for industrial applications.However,due to the complexity of lignin catalytic hydrolyzing process,there are still many key scientific problems to be solved,such as low product yield due to insufficient lignin depolymerization,low selectivity of target products due to unclear catalyst bond breaking mechanism,uneconomical and environmentally friendly transformation process,and easy condensation of depolymerized products,etc.In order to solve the above problems,the catalytic depolymerization of lignin was searched through quantum model calculation,and the efficient,green,and sustainable hydrogen donor solvent system was screened,and the theoretical method of lignin depolymerization in hydrogen donor solvent system was established.The main research contents and conclusions are as follows:Based on the density functional theory(DFT),the optimal adsorption configuration of the lignin dimer model compound on the metal surface was obtained and the influence of different metals on the structure of the lignin dimer model compound was investigated.The results showed that for the lignin model compound containing?-1 bond,the adsorption on the surface of Ni,Cu and Fe after hydrogen pre-adsorption can promote the rupture of the C_?-C_?bond in the lignin model compound.For lignin model compounds containing?-O-4 bonds,the adsorption on the surface of Ni,Cu,W,and Fe after hydrogen pre-adsorption can promote the breaking of C_?-O bonds in the lignin model compounds.The hydrogenolysis of lignin in hydrogen donor solvents without catalysts was studied to find out the best mixed solvent(ethanol/isopropanol)and the hydrogenolysis of lignin in the mixed solvent was explored.The results showed that the yield of monomer products(4-propenyl eugenol and isoeugenol)produced by the hydrogenolysis of lignin(OPL)in ethanol/isopropanol mixed solvent could reach 33wt%.After depolymerization,the lignin(OPL)contained only 14 linkages per 100 basic structural units,including 4?-O-4,9?-?and 2?-5 linkages.Most of the?-O-4 linkage was broken.The acid or ion introduced during the lignin extraction process acts as a catalyst in the depolymerization process in ethanol/isopropanol mixed solvent.Coupling ethanol/isopropanol mixed solvent and catalysts,the non-precious metal catalysts were investigated to break the bonds of the lignin dimer model compounds containing?-O-4,?-O-4 and C-C linkages.The results showed that Ni/C and Ni Cu/C catalysts had good catalytic capability for the bond breaking of lignin model compounds containing?-O-4 linkage and Ni/C,Ni Cu/C and Ni W/C catalysts had better catalytic capability for the bond breaking of lignin model compounds containing?-O-4 linkage.The ethanol/isopropanol mixed solvent and non-precious metal catalysts are applied to the hydrogenolysis of real lignin.The results showed that the Ni Cu/C catalyst exhibited the best catalytic capability and obtained the highest monomer yield(63.4wt%).The dehydrogenation of isopropanol to acetone was the main source of hydrogen(in the form of hydrogen radicals)in the reaction.The introduction of Cu promoted the hydrogen donation efficiency of ethanol/isopropanol solvent and reduced the consumption of ethanol/isopropanol solvent.Cu greatly promoted the dimer pinoresinol(?-?type)structure in lignin to break.The Ni₁₀Cu₅/C catalyst coupled with ethanol/isopropanol mixed solvent is also very efficient for depolymerizing industrial lignin into high-value monophenolic products.In the above studies,the depolymerization of lignin in ethanol/isopropanol mixed hydrogen donor solvent system provides a new way to produce high-value monophenol chemicals,and lays a theoretical and technical foundation for the comprehensive utilization of lignin.