Study On Pore Effect And Coke Deposition Behavior In Cyclohexylamine To Cyclohexanone Oxime By Metal-free Silica Catalysts

Cyclohexanone oxime is an important intermediate for the production of ?-caprolactam,and it is used to produce polyamide fiber and resin.Currently,three industrialized synthetic methods for producing cyclohexanone oxime have been developed:cyclohexanone-NH2OH route,UV-photo-nitrosation of cyclohexane route and toluene route.Unfortunately,three process has too many steps,complex equipment and process control is difficult.More importantly,it give rise to many problems concerning the handing,health,safety,corrosion,and waste disposal of the by-product.With cyclohexanone oxime demand increasing,as well as responsible care and sustainable development have become trend of industrial production,the simplified process routes of the production of cyclohexanone oxime has become the important research subject of attention.The influence of pore architecture on the catalytic activity and selectivity of metal-free silica catalysts for the selective cyclohexylamine oxidation has been investigated in this article,and the effects of the pore structure on their coke deposition behavior in the cyclohexylamine-to-cyclohexanone oxime reaction were studied according to the different topologies of SBA-15,SBA-16,MCM-41 and HMS.Meanwhile,the evolution and inactivation of coke deposition on SBA-15 were also explored.The main research contents are as follows:(1)Preparation of four types of metal-free silica mesoporous molecular materials with different pore sizes:2D wormhole pore(HMS),2D hexagonal arrangement of uniform cylindrical pore(SBA-15 and MCM-41),3D cagelike pore(SBA-16 and KIT-6)and intraparticle mespore(hollow-structured Silicalite-1).At the same time,2D hexagonal arrangement of uniform cylindrical pore MCM-41 was also modified to prepare MCM-41 with different pore sizes.The pore architecture and chemical composition of obtained silicas are characterized by N2 physisorption analysis,XRD,HRTEM,as well as FT-IR,Raman and ED AX spectra.(2)Four types of metal-free silica mesoporous molecular materials with different pore sizes and modified MCM-41 were used in the gas-phase selective oxidation of cyclohexamine,and the effects of pore structure types on cyclohexanone oxime prepared by cyclohexamine were investigated.SBA-15 with a uniform cylindrical pore channel exhibits the best catalytic activity among the investigated metal-free silica catalysts,the cyclohexanone oxime selectivity reaches 86.16%at an cyclohexamine conversion of 14.62%.The sizes of the reactant and product molecules was calculated by the computational chemistry and compared with the pore structure of the mesoporous molecular material with different framework structures,explained different mesoporous molecular sieve material structure with different catalytic properties,and further puts forward the characteristics of the catalyst should have suitable the reaction.(3)Four metal-free silica mesoporous molecular with different pore structure were used in the gas-phase selective oxidation of cyclohexylamine.The effects of different pore structures on the coke deposition behavior were investigated.The amount of coke deposits on the SBA-15 was found to increase with the increase of reaction time.The coke deposits is composed of the by-products of the reaction,including"soft" carbon and "hard" carbon.Inactivation of SBA-15 was caused by the plugging of the pore structure by coke deposits.At the same time,according to the research contents of this paper,the characteristics of the catalyst that has the best catalytic activity and can minimize coke deposition should be proposed.