Selective Catalytic Hydrogenation And Depolymerization Of Lignin With Ni/MgO

Currently,global environmental problems and energy crisis have become increasingly serious.China has thereby accelerated the transformation of its energy structure and gradually reduced its reliance on traditional fossil resources and focused on the development of clean energy.Among the exploited clean energy sources,biomass,as the only renewable green energy source,is considered as the most potential alternative for fossil raw materials for large-scale industrial chemical production.Moreover,the use of high-valued biomass energy is of great significance for ensuring China's sustainable development and low-carbon economy.As one of the important components of biomass,lignin is the most abundant natural aromatic polymers in the nature.It contains a large number of functional groups in the molecule,and can be converted to phenolic monomers and other high added-value chemicals through depolymerization.Therefore,lignin valorization is an important way for efficient biomass utilization.However,there are many technical issues with complex products and poor selectivity during the current lignin conversion process,for example,low phenlic monomer yield and serious char formation.In response to these problems,a highly efficient reaction system for catalyzing the depolymerization of lignin was constructed in this paper.Through the design of catalyst and catalytic system,a highly selective process was achieved for lignin conversion.The detailed study contents are as follows:(1)Various Ni/MgO catalysts were prepared,and their catalytic activities on hydrogenation and depolymerization of bagasse lignin was investigated by optimizing the reaction conditions.The experimental results showed that,under the optimal reaction conditions,the conversion of lignin reached 93.40 %,the yield of aromatics was 14.97 %,and especially the yield of 4-ethylphenol product was up to 6.33 %.In order to understand the structure evolution of lignin in this process,we performed a series of characterizations on the lignin before and after reaction using HSQC,NMR,FT-IR,GPC,ANO and elemental analysis.As a result,we found that in the building blocks(H,G and S)of lignin,H-lignin is the most active and easily depolymerized,which contributed to the production of the 4-ethylphenol.Thus,this study indicated that the selective depolymerization of lignin is feasible.In addition,we proposed a possible route for the depolymerization of lignin.(2)In order to further improve product selectivity and reduce the residual,we constructed a Cu-Ni bimetallic catalyst system.The results indicated that the addition of Cu reduced the amount of catalyst by 50 % while the activity of the catalyst was promoted.Under the optimal conditions,15.66 % aromatics products were obtained,in which the yield of 4-ethylphenol increased to 6.85 % and the residue was decreased to 13.41 %.Through series of characterization of the catalyst,we found that the introduction of Cu weakened the interaction between Ni and the support,making more NiO exposed to the surface,which in turn increases the active sites on the catalyst surface and improves the catalytic performance,thus promoting the hydrogenation and depolymerization of lignin.