Vapor-phase Beckmann rearrangement cyclohexanone oxime

There is, as is well known, a close similarity between the crystalline and porous structures of silicalite-1 and silicalite-2. The same similarity therefore exists between TS-1 and TS-2, and it appears logical that they should have very similar catalytic properties. TS-2 has been evaluated as a catalyst for many different reactions, such as Beckmann rearrangement of cyclohexanone oxime with vapor-phase reactants H202 oxidation of phenol, anisole, benzene, toluene, n-hexane, and cyclohexane and ammoximation of cyclohexanone. As described in detail in Section V.C.3, differences that had been claimed between the catalytic properties of TS-1 and those of TS-2 have not been substantiated. Later investigations have shown that, when all the relevant parameters are identical, the catalytic activities of TS-1 and TS-2 are also identical. The small differences in the crystalline structure between the two materials have no influence on their catalytic properties (Tuel et al., 1993a). 

As already discussed in Chapter 1, the commercialization, by Sumitomo [GO-64], of a vapor phase Beckmann rearrangement of cyclohexanone oxime to caprolactam over a high-silica MFI (ZSM-5 type) zeolite (Fig. 2.21) is another benchmark in zeolite catalysis. The process, which currently operates on a 90000 tpa scale, replaces a conventional one employing stoichiometric quantities of sulfuric acid and producing ca. 2 kg of ammonium sulfate per kg of caprolactam. 

Most of the catalytic activity of zeolites has been concerned with their ability to act as shape selective solid acids. The vapor phase Beckmann rearrangement of cyclohexanone oxime over HY zeolite at 300°C gave caprolactam in 80% selectivity at 82% conversion (Eqn. 10.22). 5... 

Allied Chemical recently proposed a simplified technique, producing caprolactam from cyclohexanone, ammonia and oxygen in a single step, in the vapor phase, on a sffica or alumina-based catalyst However, the drawback of this process resides in the fact that only half of the oxime is converted in situ to caprolactam. This makes it necessary to resort to the Beckmann rearrangement For a 50 per cent conversion of cyclohexanone, the molar selectivity of oxime and caprolactam is 68 per cent Although this method considerably reduces the production of ammonium sulfate, the yields are still too low for it to appear to be more economical than the foregoing routes. 

Figure 5. Change in cyclohexanone oxime conversion and lactam selectivity with time on stream in the vapor phase Beckmann rearrangement over 12-MR zeolites. Diluent (a) methanol, (b) 1-hexanol. (X) H-BEA, (A) H-LTL, (V) H-OFF-ERI, ( ) H-USY (Si02/Al203 = 62), (O) H-MOR, (O) H-MTW 623 K, oxime/diluent/N, molar ratio of 1/9/5.9 and W/F of 80 g cat h mol oxime [41].

The control of selectivity in the vapor phase Beckmann rearrangement seems to be difficult this can be ascribed to the drastic experimental conditions required. Liquid-phase reactions over heterogeneous catalysts have been investigated. The Beckmann rearrangement of cyclohexanone oxime in the liquid phase was performed under reflux conditions in a variety of solvents [44]. When chlorobenzene was used solvent conversion and selectivity increased with temperature up to 405 K. From plots of conversion against time it was concluded that catalyst deactivation under liquid-phase conditions is small, in contrast with the rapid deactivation observed when the reaction was conducted in the vapor phase. 

AlP04-Ti02 catalysts. V. Vapor-phase Beckmann rearrangement of cyclohexanone oxime... 

Vapor-phase Beckmann rearrangement of cyclohexanone oxime over AIPO4 (AP) and AlP04-Ti02 (APTi, 25-75 wt%) catalysts was investigated. Apparent rate constants and activation parameters were calculated in terms of the kinetic model of Bassett and Habgood for first order reaction processes. In all cases the selectivity to e-caprolactam increased with reaction temperature and,... 

Shouro, D., Moriya, Y, Nakajima, T., and Mishima, S. 2000. Mesoporous silica ESM-16 catalysts modified with various oxides for the vapor-phase Beckmann rearrangement of cyclohexanone oxime. App/. Catal. A.- Gen. 198 275-282. 

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