Analysis On The Catalytic Reaction Of Cyclohexanone Ammoximation Over Titanium Silicalite-1(TS-1)

Cyclohexanone oxime, as a key intermediate, is primarily used in the production ofε-caprolactam. Almost all of the present commercial processes for oxime synthesis employ the cyclohexanone-hydroxylamine route, which is environment-unfriendly because of the production of large amount and lower value by-product of ammonium sulphate, and facing the problems for disposal and purification. Titanium Silicalite-1 (TS-1) catalytic cyclohexanone ammoximation process developed by Enichem Co. is advantageous from the environmental point of view and meets the requirement of"Green Chemical Engineering"with zero-emission. It is considered to be a new approach for cyclohexanone oxime production. Notwithstanding several studies on this process, there is not a general agreement about the catalytic reaction pathway, and the theoretical bases for existing kinetic models are also absent. Furthermore, the evolution of catalytic activity, the main reason for deactivation and the regeneration method of deactivated catalyst are importmant in industrialization.In this paper, the mechanism of catalytic ammoximation of cyclohexanone to cyclohexanone oxime with H2O2 over TS-1 catalyst was investigated by monitoring the reaction intermediates using in-situ diffuse reflectance inferred Fourier transform spectroscopy (in situ DRIFTS). The results show that two types of active sites exist on the catalyst, and two kinds of active precursors are formed in the ammoximation process simultaneously, one is cyclohexylamine, which is produced from the reaction of adsorbed ammonia with adsorbed cyclohexanone on the silanol groups of TS-1; another is hydroxylamine that is from the reaction of adsorbed ammonia with the Ti peroxides, which is generated by the interation of H2O2 and TS-1.Under the hypothesis that the formation of hydroxylamine and the adsorption of cyclohexanone were the rate control steps, an intrinsic kinetic equation of cyclohexanone ammoximation over TS-1 was derived based on a double mechanism model. Meanwhile, a power function type of kinetic equation used to described H2O2 decomposition was also built up. The kinetic parameters were estimated by nonlinear least square method, and the reaction tendency was predicted using the two kinetic equations.The results of consecutive experiments demonstrate that the activity of TS-1 keeps stable within 60 h and afterwards decreases rapidly. The results of comparative experiments and characterization of deactivated catalysts show that coking is the main...