Intrinsic And Deactivation Kineticses Of Cyclohexanone Ammoximation Over Titanium Silicalite-1

Cyclohexanone oxime, one of the most important precursors of caprolactam for nylon production, was conventionally produced by cyclohexanone-hydrocylamine process, which suffers of several drawbacks such as many reaction steps involved and large amount of byproduct of ammonium salts. A novel process based on the direct ammoximation of cyclohexanone with ammonia and hydrogen peroxide over TS-1 catalyst was developed by Montedipe S.P.A of Italy in the middle of 1980's. This process does not suffer of the disadvantages above and meets the request of"Green Chemical Engineering"with zero emission. The dangerous reagents was not used and ammonium salts did not form in the process and cyclohexanone oxime is easily to separate by extraction. It is an environment-friendly process and is considered to be the most promising way for cyclohexanone oxime production.Notwithstanding the large amount of studies on this system recently, there is not a general agreement about the catalytic reaction mechanism. The deactivation of TS-1 for this reaction is usually considered to be the bottleneck for the industrialization of this process and the mechanism of deactivation is still an ambiguity.In this work, the ammoximation of cyclohexanone with ammonia and hydrogen peroxide over TS-1 catalyst in the liquid phase was investigated. The intrinsic kinetics and deactivation kinetics of ammoximation of cyclohexanone over TS-1 was derived. By analyzing the reaction system, we proposed three kinds of reaction mechanisms. The experimental and simulation results show that the reaction scheme based on the two-mechanisms may be the most possible reaction pathway. The proposed reaction mechanism agrees well with the experimental results.The rate equations for ammoximation of cyclohexanone and decomposition of hydrogen peroxide as well as catalyst deactivation were obtained and the parameters were estimated by Gauss-Newtonian algorithm. The comparison of predicted values from the proposed models with experimental results showed that the absolute average relative error were 9.45% for ammoximation, 6. 21% for decomposition of H2O2 and 6.23% for catalyst deactivation, which showed the reliability of the obtained rate equation and were expected to be used for process design.The structure properties of the catalyst before and after deactivation was analyzed and the results show that some by-products of the reaction covered the surface of the catalyst and blocked the pores in the catalyst, which may be the main reason forcatalyst deactivation. The deactivated titanium silicalite-1 zeolite can be regenerated by heating in air. The activity, the special surface area and also the pore volume of the regenerated catalyst were almost the same as the fresh one, indicating that the structure of the catalyst did not change during deactivation and the deactivation was mainly caused by reversible pore blocking.