Research On Depolymerization Of Lignin With Mo-Based Catalyst In Supercritical Ethanol

Lignin is the most abundant natural amorphous polymer,which is made from coniferous alcohol,myrosinol and p-coumarol by enzymatic dehydrogenation polymerization.It is an important renewable resource for the preparation of phenolic monomers and liquid fuels.Catalytic conversion of lignin into liquid fuels,phenolic compounds and other high value-added aromatic compounds by solid catalysts is a research hotspot in the field of high value utilization of lignin.Due to the complex chemical bond connection between lignin structural units and the easy reintegration of intermediates in the depolymerization process,lignin depolymerization process generally has some key technical problems,such as easy coking and poor selectivity of target products.In view of the above problems,this topic adopted the green and economical clay material sepiolite(SEP)with good hydrothermal stability supported Mo active metal to prepare a stable and efficient Mo/SEP catalyst,and realized the efficient depolymerization of lignin under the condition of supercritical ethanol.The reaction mechanism of Mo/SEP-400 catalyzing the depolymerization of lignin in supercritical ethanol was revealed.The concrete results achieved are as follows:(1)The physical and chemical properties of Mo-based catalysts with different supports were analyzed by a variety of modern analytical methods,and the influence of supports on the depolymerization of lignin was studied.Supports have significant effects on the pore structure,surface acidity and the content of Mo species on the surface of Mo-based catalysts.Among the catalysts supported by natural mineral materials,Mo-based sepiolite(SEP)catalyst shows the best activity for the depolymerization of lignin.(2)According to the results of the selection of support,sepiolite was used as the support to prepare a series of Mo based catalysts at different calcination temperatures,and the effects of calcination temperature on the structure and properties of Mo/SEP catalysts were studied.The results show that the calcination temperature can affect the surface Mo species and acidity of Mo/SEP.Mo-based catalyst(Mo/SEP-400)calcined at 400? contains the most surface Mo5+ species,while the acidity of Mo/SEP-400 increases with temperature.In addition,Mo/SEP-400 showed the best depolymerization activity of lignin,and the calcination temperature affected the content of monomer components in lignin oil.The highest yield of monomer phenolic compounds in lignin oil was obtained on Mo/SEP-600 catalyst,which reached 112.0 mg/g lignin.(3)Reaction temperature and time have significant effects on the results of lignin depolymerization.When Mo/SEP-400 was used as catalyst for depolymerization of lignin,the best effect could be achieved at 310? for 4 h,and the lignin oil yield reached 80.3%.The depolymerization mechanism of lignin on Mo/SEP-400 in supercritical ethanol was proposed.Lignin is first cracked into fragments under the condition of supercritical ethanol,and then the lignin fragments interact with the Mo5+of the catalyst to form phenol and ethoxy.The ethoxy group interacts with the B acid site to form the active ethoxy species.The active ethoxy group leads to intramolecular or intermolecular C-alkylation,eventually forming alkylated phenolic monomers.Figure[24]Table[12]Reference[111]...