| Lignin is the most abundant natural polymer on the planet and it has been widely accepted as an excellent renewable starting material for bulk chemicals production because of its useful functional groups such as hydroxyl,benzene,aldehyde etc.To date,lots of efforts have been devoted to the efficient utilization of this sustainable aromatic polymer,including pyrolysis,hydrothermal depolymerization,hydrogenolysis and oxidation.However,these techniques need to be improved in terms of product yield and selectivity.Furthermore,the products from current lignin depolymerization technologies are generally high viscosity,high acidity and low volatility,thus,labor-intensive post-separation and condition-rigid upgradation is inevitable to get high quality biochemical and biofuel.Moreover,the serious char generation from the phenolic oligomer recondensation is a big challenge in lignin utilization as well.Therefore,in this perspective,catalytic depolymerization of lignin with high product selectivity and less char formation is significative and essential.In this thesis,we propose a novel and effective catalytic approach for lignin hydrogenolysis over the zirconium phosphate supported metallic(Ni/Zr P)using isopropanol as solvent and hydrogen transfer promoter.The results demonstrate that,under the synergistic effect between acidic Zr P and hydrogenation active center of metallic Ni,p-hydroxyl phenyl structural unit of lignin(H-lignin)can be selectively converted to para ethyl phenol,an important,versatile and bulk chemical from petrochemical industry currently.The main contents are summarized as follow:(1)A series of Ni/Zr P catalysts had been prepared by wetness impregnation method and used in the lignin selective hydrogenolysis.It is found that,with the optimized catalyst of 15%Ni/Zr P-2.0,87.3% lignin conversion could be obtained with less than 5.2 wt% char formation at mild condition of 260 °C for 4 h.Product analysis demonstrates that 15.1 wt% phenolic monomer yield is given at the relative low hydrogen pressure of 2.0 MPa.Especially,6.1 wt% of these volatile products is identified to be para ethyl phenol.Furthermore,co MParative characterizations on the original and regenerated lignin,and the phenolic oligomer using various technologies(HSQC,NMR,FT-IR,GPC,and elemental analysis)demonstrate that the effective cleavage of p CA8 linkage of H lignin is responsible for this high para ethyl phenol yield.(2)In order to further improve the product selectivity of lignin hydrogenolysis and reduce the solid residue,we further constructed a Ni-Fe bimetallic catalytic system.The results show that the addition of Fe can significantly increase the catalytic activity of Ni/Zr P on the lignin selective hydrogenolysis reaction and char elemination.Under the optimal reaction conditions,a 19.5 wt% mono-phenol yield can be achieved,wherein the yield of 4-ethylphenol increases to 8.20 wt%,and the solid residue sharply dropped to 1.76 wt%.Catalyst characterization results show that the introducing of Fe contributed to the formation of Ni-Fe alloy structure,which effectively promotes the hydrogenolysis process of lignin... |
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