Study On Bi₂O₃/Bi₂WO₆ Selective Breaking Bonds Of Lignin Models In Deep Eutectic Solvents Under Visible Light

The use of biomass energy can effectively reduce the consumption of primary energy and slow down the global warming,which is an effective way to solve the increasingly serious global energy crisis.Lignin,which accounts for nearly one-third of the biomass,is mostly discarded without proper utilization in practical application.The lignin contains a large number of aromatic ring structures.If lignin can be effectively degraded into small molecular substances,its added value can be greatly improved and the pollution problems caused by its treatment process can be reduced.In order to study the depolymerization conditions of lignin,this thesis first starts with the dimer model substance,which was the basis of lignin,to conduct synthesis and depolymerization,then explores and analyzes the depolymerization conditions of lignin of spruce wood.The specific research content is as follows:(1)Lignin dimer model substance of 2-(2-methoxyphenoxy)-1-(4methoxyphenyl)ethanone containing ?-O-4 bond and 3-methoxy-4-benzyloxy vanillyl ethyl ketone containing?-O-4 bond were synthesized.Fourier transform infrared spectroscopy,nuclear magnetic resonance and elemental analysis were conducted to evidence the successful synthesis of target product.The optimal synthesis conditions of the model objects were explored.(2)A series of eutectic solvents with different proportions and different water contents were prepared.The Bi2O3/Bi2WO6 photocatalysts with different molar ratios were synthesized and characterized by infrared,photocurrent,impedance,etc.The Bi2O3/Bi2WO6 photocatalyst with a molar ratio of 1:1 was selected for further study.under visible light irradiation.The optimal depolymerization rate of 2-(2-Methoxyphenoxy)-1-(4methoxyphenyl)ethanone(80.15%)was obtained when betaine and citric acid at a ratio of 1.2:1 were dissolved in a solution containing 60%water with 2 mg catalyst under a light intensity of 238 W for 8 hours.The optimal depolymerization rate of 3-methoxy-4-benzoxy vanillin ethyl ketone(69.58%)was obtained when choline chloride and 1,2-propanediol at a ratio of 1.6:1 were dissolved in a solvent containing 40%water with 2 mg catalyst under a light intensity of 238 W for 8 hours.(3)Klason lignin,dioxane lignin and alkali lignin were extracted from spruce tree.Under the optimal conditions for the depolymerization of the dimer,the three lignins were treated separately,and the product components in the solution after the reaction were detected.The HPLC-MS results showed that under the corresponding photocatalytic conditions,the spruce lignin could produce a small amount of p-hydroxybenzaldehyde,p-coumaric acid,guaiacol,p-hydroxybenzoic acid,4-n-propylphenol,etc.