Cyclohexanone oxime titanium silicalite

Cyclohexanone is thus converted to cyclohexanone oxime, an intermediate in the manufacture of Nylon-6. The catalyst is titanium silicalite-2. Commercialized by Enichem who built a 12,000 ton/year plant in Porta Marghera in 1994. 

In classical processes cyclohexanone is converted to the corresponding oxime by reaction with hydroxylamine (see Fig. 2.27). The oxime subsequently affords caprolactam via the Beckmann rearrangement with sulphuric or phosphoric acid. Alternatively, in a more recent development, not yet commercialized, a mixture of cyclohexanone, ammonia and hydrogen peroxide is directly converted to cyclohexanone oxime over a titanium(IV)-silicalite (TS-1) catalyst. This route is more direct than the classical route and reduces the amount of salt formation but it involves the use of a more expensive oxidant (H2O2 rather than O2). 

Titanium (TS-1), niobium (NbS-1), and tantalum silicalite-1 (TaS-1) with MFI structure were synthesized by microwave heating of the TPAOH impregnated xerogels which were prepared by sol-gel process. Highly crystalline products were obtained in 30 min to 2 h with yields over 90%. The metallosilicates showed high catalytic performances in Beckmann recirrangement of cyclohexanone oxime to caprolactam. 

It is known that cyclohexanone oxime can be formed from the ketone, ammonia, H2O2 and tungstate [192]. However, it has been found recently that titanium silicalite, TS-1, also catalyses this reaction [193]. As a heterogeneous system, this is of great interest for improving manufacture, and a pilot plant has been announced [194]. It is also disclosed that, in the absence of ketone, hydroxylamine is formed from H2O2 and ammonia... 

An alternative route to cyclohexanone oxime developed in Italy by Enichem is shown in the following reaction. Cyclohexanone oxime is produced by the ammoxidation of cyclohexanone with ammonia and aqueous hydrogen peroxide in the presence of a solid, recyclable catalyst, titanium silicalite (TS-1). This reaction step eliminates approximately one-third of total salt formation. However, the oxime is still converted to caprolactam through the conventional route (Beckmann rearrangement), catalyzed by stoichiometric amounts of sulfuric acid, and produces ammonium sulfate salt. Therefore, this alternative process still leaves something to be desired. 

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