Coupling System Of H₂ Production From Aqueous-phase Reforming And Selective Hydrogenolysis Of Lignin Catalyzed By Ru/C

Recently,the efficient utilization of the renewable resource has attracted increasing attention,in order to optimize the energy structure and to reduce the dependence on fossil energy.In the field of renewable energy,scientists have found that biomass resource as the only renewable resource with fixed carbon.As one of the important components of biomass,lignin is not only an aromatic polymer from a wide range of sources in nature,but also contains phenolic hydroxyl group,aldehyde group and other functional groups,which can be depolymerized and utilized to obtain a variety of high value-added chemicals.However,the traditional hydrogenolysis of lignin requires the use of additional hydrogen,and the depolymerization conditions are severe.Moreover,there are technical problems such as low lignin conversion rate,poor selectivity of products.In response to these issues,the coupling system of hydrogen production from solvent and hydrogenolysis of lignin in aqueous phase reforming was constructed based on the study of hydrogen production from phase reforming system and realize the selectively catalytic depolymerization of lignin without additional hydrogenation source.Moreover,the depolymerization mechanism of lignin were clarified by lignin model compounds.The main contents of this study are summarized as follows:(1)Methanol and water were used as reactants to study the performance of hydrogen production from aqueous phase reforming.Gas composition was detected by GC-TCD,and gas products were quantitatively analyzed by RK equation and internal standard method.The catalytic activities of different catalysts in aqueous phase reforming were investigated.The results showed that the hydrogen production activities of the reforming catalysts were in the following order:Pt/C>Ru/C>Cu/C>Pd/C>Ni/C>Co/C.The results shows that catalysts could catalyze aqueous phase reforming for hydrogen production effectively.(2)The coupling system of CH₃OH/H₂O for hydrogen production from aqueous phase reforming of solvent and lignin hydrogenation was constructed to selectively depolymerize lignin.Then the coupling performance of reforming catalysts in the aqueous phase reforming and selective hydrogenolysis of lignin was investigated.Under the optimal reaction conditions,(250?,4h,1.0 MPa Ar,the solvent volume ratio was methanol:water=4:1),89.3%of the lignin could be converted over Ru/C,affording 22.3 wt.%yield of volatile products and 8.7 wt.%yield of 4-ethylphenol,Ru/C showed excellent performance.Comparative analysis of lignin and re-lignin explained that the transformation of H structure unit and the fracture of p CA₈ bond were the important reasons for the high yield of 4-ethyl phenol.At the same time,the change of reaction conditions can affect the hydrogen production of the system,which promotes the conversion of unsaturated products to saturated products,thereby achieving high yield and selectivity of products.(3)The ?-O-4 lignin model compound(4-methoxy-?-[(2-methoxyphenoxy)methyl]-benzenemethanol)was used as reaction substrate,Ru/C catalyst is performed to explore activation and cleavage of specific chemical bonds of lignin.Under the optimized conditions(1.0 MPa Ar,4 h,210?),4-ethylanisole,guaiacol with 85.5%and 98.2%yields were obtained by depolymerization of 0.1 mmol?-O-4 lignin model compound respectively.Through the analysis of the transformation of the products,we suggest that the lignin model compound breaks the C-O bond preferentially,and the hydroxyl group on the side chain is eliminated,then the addition reaction of double bond takes place to get the saturated product.