The Study Of Cyclohexanone Ammoximation On TAPO-5

Cyclohexanone oxime is a crucial intermediate for the synthesis of ?-caprolactam which is a major organic chemical material of Nylon-6 and other polyamide engineering plastics.The industrial production method for cyclohexanone oxime is cyclohexanone-hydroxylamine which is less desirable owing to its complex technology,low atom economy,equipment corrosion,and serious environmental problems and so on.To improve the economic and environmental benefits of industrial production,people have being committing to the development of new synthesis routes.The liquid ammoximation of cyclohexanone to cyclohexanone oxime is a new green synthesis process.However,there are some defects in the using catalyst of TS-1,such as high cost,fast activity decline and difficult recovery etc,limit the promotion of this process.Hence,the design and preparation of high efficient catalysts to displace TS-1 are still the focus of the researcher.The incorporation of Ti atom into aluminophosphate sieves?TAPO-5?has the advantages of uniform constitute,regular structure,Lewis acid sites and the active centre to catalyze the ammoximation of cyclohexanone,which to been the most promising catalysts.Based on the above analysis,a series of TAPO-5 molecular sieves were prepared by hydrothermal synthesis.In this paper,we have carefully investigated the effects of titanium contents,crystallization time,and calcinationatmosphere on the physico-chemical properties of TAPO-5 molecular sieves.XRD,XRF,nitrogen adsorption-desorption,diffuse reflectance UV-Visible spectra,Raman,and Py-FTIR spectra were used to characterize the crystal structure,specific surface area,acid quantity,the content of titanium and different titanium species.The catalytic activity and main effect factors on cyclohexanone ammoximation were studied.The main conclusions are as follows:?1?Ti as the active center of the reaction,the catalytic ammoximation results demonstrated that TAPO-5 with highest content of Ti had highest yield,but the exceeded Ti could cause the decline of crystallinity and the decrease of the micro-mesoporous structure.?2?TAPO-5 zeolites with different Ti species: the isolated tetrahedral Ti,highly dispersed extra-framework Ti,and anatase TiO₂,respectively.The Py-FTIR spectra showed that extra-framework Ti species could generate a kind of Lewis acid sites which can improve the catalytic activity.?3?The carbon-modified TAPO-5 sieves were prepared by template,and the materials were calcined in the N₂-H₂ mixed atmosphere.The catalytic results of ammoximation showed that cyclohexanone oxime selectivity over TAPO-5 were increased with the high calcination temperature.It gives the 91.7% selectivity to cyclohexanone oxime under the optimum conditions.