The Study Of Catalytic Degradation Of Lignin And Its Conversion Into Liquid Fuels

The interest in lignin valorisation has been growing steadily in recent years, due to its special chemical structure and intrinsic value. Lignin is one of the three major components in biomass, and consists mainly of phenylpropane units. Because of its unique structure, lignin can be converted into phenolic compounds first, and then further converted to hydrocarbons and alcohols, which is a promising way for the large-scale lignin valorisation. In this work, depolymerization of lignin was studied to increase the yield and selectivity; then the obtained liquid products-lignin phenols were used as feedstock for selective production of value-added hydrocarbon fuels by aqueous-phase catalytic hydrogenation. Finally, nickel-based hydrogenation catalysts were prepared and tested. The purpose is to find a cheap and efficient catalytst suitable for applications in aqueous-phase environment, thus reducing the production cost of fuels from lignin.Depolymerization tests were first performed on lignin from corn stalk using isopropanol as solvent and Ru/C as catalyst. The optimized reaction condition was determined using orthogonal array experimental design, which is:Ru/C catalyst amount0.20g, temperature280℃, pressure2.5MPa, reaction time8h. Under this condition, the yield of bio-oil could reach74%; and a combined selectivity of60%for phenolics, cyclic alcohols, cyclic ketones and hydrocarbons (HCs) were also achieved. The elemental analysis for lignin feedstock and bio-oil products indicated that deoxygenation happened concurrently with the depolymerization; The Fourier infrared spectrum (FT-IR) study and GC-MS analysis further indicated that the cleavage of β-O-4ether bonds and decarbonylation were happened in the process of degradation, with the formation of new functional groups such as phenolic hydroxyl and alkyl.Four solvent systems were chosen to explore the lignin depolymerization, which include ethanol aqueous solution, acidic aqueous solution, alkaline aqueous solution, and aqueous solution, The obtained liquid products were then catalytically hydrogenated to convert to hydrocarbons, and a selectivity of97%for HCs was achieved (for the case of using NaOH aqueous solution as reaction medium). It was found that alkaline solution could help the demethylation and demethoxylation for phenolic compounds, thus reducing the amount of methoxyl group in the products. And the optimum reaction conditions for depolymerization of lignin in alkaline solution were found to be:temperature260℃, reaction time1h, and alkaline amount lg-Finally, catalysts like Ni/SiO2, Ni/ZrO2, Ni/SiO2-ZrO2(the molar ration of Si/Zr were1,3,5,7) were prepared via sol-gel method, and were used in aqueous phase catalytic hydrogenation of phenol and lignin phenols. It was found that Ni/ZrO2(Ni30wt%) showed good performance in aqueous catalytic hydrogenation of phenol, with the selectivity for hydrocarbons,,alcohols (including ketones), and phenols43.28%、55.32%and1.40%respectively; Ni/SiO2(Ni20wt%) and Ni/SiO2-ZrO2(Ni30wt%) exhibted good performance for selective production of alcohols&ketones with the selectivity of97.90%and99.78%respectively; Ni/SiO2-ZrO2(Ni20wt%Si/Zr=3) indicated good performance in aqueous catalytic hydrogenation of lignin phenols, and the selectivity of hydrocarbons, alcohols&ketones, and phenol was47.48%、24.77%and8.20%respectively. What’s more, it was found that the performance for hydrogenation of lignin phenols would be getting even better when either SiO2or SiO2-ZrO2used as the support alone, which indicated that SiO2has unique advantages of serving as the support for hydrogenation catalysts.