Caprolactam catalysts, Beckmann

Zeolites have also been described as efficient catalysts for acylation,11 for the preparation of acetals,12 and proved to be useful for acetal hydrolysis13 or intramolecular lactonization of hydroxyalkanoic acids,14 to name a few examples of their application. A number of isomerizations and skeletal rearrangements promoted by these porous materials have also been reported. From these, we can underline two important industrial processes such as the isomerization of xylenes,2 and the Beckmann rearrangement of cyclohexanone oxime to e-caprolactam,15 which is an intermediate for polyamide manufacture. Other applications include the conversion of n-butane to isobutane,16 Fries rearrangement of phenyl esters,17 or the rearrangement of epoxides to carbonyl compounds.18... 

The transformation of oximes to lactams (the Beckmann rearrangement) was one of the earliest such acid-catalyzed reactions to be reported with TS-1 (138) and TS-2 (247) catalysts. The rearrangement of cyclohexanone oxime to e-caprolactam proceeds with high selectivity in the presence of TS-1, with high catalyst stability (138,247). 

It can be obtained from cyclohexane. Cyclohexane is air oxidised to yield a mixture of cyclohexanol and cyclohexanone. Cyclohexanol is dehydrogenated to cyclohexanone over copper catalyst. Cyclohexanone when treated with hydroxylamine sulphate at 20°-95°C gives an oxime. The oxime when treated with concentrated sulphuric acid undergoes Beckmann rearrangement to yield caprolactam. 

The common name caprolactam comes from the original name for the Ce carboxylic acid, caproic acid. Caprolactam is the cyclic amide (lactam) of 6-aminocaproic acid. Its manufacture is from cyclohexanone, made usually from cyclohexane (58%), but also available from phenol (42%). Some of the cyclohexanol in cyclohexanone/cyclohexanol mixtures can be converted to cyclohexanone by a ZnO catalyst at 400°C. Then the cyclohexanone is converted into the oxime with hydroxylamine. The oxime undergoes a very famous acid-catalyzed reaction called the Beckmann rearrangement to give caprolactam. Sulfuric acid at 100-120°C is common but phosphoric acid is also used, since after treatment with ammonia the by-product becomes... 

The industrial e-caprolactam processes with cyclohexanone oxime as intermediate product were recently reviewed . The catalytic gas-phase Beckmann rearrangement has great industrial interest. Since the process proposed by DuPont in 1938 the investigation on catalytic gas-phase Beckmann rearrangement has been investigated, and a large variety of catalysts have been tested for the reaction. 

The deactivation and regeneration of the catalyst are also important processes in the industrial production of the caprolactam by the Beckmann rearrangement and have been... 

Recently, the Sumitomo Chemical Co., Ltd. developed the vapour-phase Beckmann rearrangement process for the production of 8-caprolactam. In the process, cyclohexanone oxime is rearranged to e-caprolactam by using a zeolite as a catalyst instead of sulfuric acid. EniChem in Italy developed the ammoximation process that involves the direct production of cyclohexanone oxime without producing any ammonium sulfate. The Sumitomo Chemical Co., Ltd. commercialized the combined process of vapour-phase Beckmann rearrangement and ammoximation in 2003 ". 

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). 

The rearrangement of cyclohexanone oxime to caprolactam is still an important step in nylon production, and the heterogeneously catalyzed Beckmann rearrangement has been extremely well investigated (4, 16-19). In order to obtain catalysts that couple a high lactam selectivity to long lifespan, careful tuning of the zeolite properties is required. Some important factors are ... 

The TS-1 catalyzed hydroxylation of phenol to a 1 1 mixture of catechol and hydroquinone has already been commercialized by Enichem. Another reaction of considerable commercial importance is the ammoximation of cyclohexanone to cyclohexanone oxime, an intermediate in the manufacture of caprolactam. It could form an attractive alternative to the established process that involves a circuitous route via oxidation of ammonia to nitric acid followed by reduction of the latter to hydroxylamine (see Fig. 10). The ammoximation route employs a more expensive oxidant (H202) but is shorter and produces considerably less salt. However, we note that is does not provide a complete solution to the salt problem as substantial amounts are also produced in the subsequent Beckmann rearrangement of the oxime. The answer to this problem is probably also in the deployment of an efficient solid catalyst. 

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. 

Cyclohexanone, 2-cyclohexen-l-one, 5-hexenenitrile, and hexanenitrile are commonly observed by-products in the Beckmann rearrangement of cyclohexanone oxime. Aniline and 2-methylpyridine are also occasionally formed. An outline of the reaction scheme is shown in Figure 7. From the selectivity change with time with AIPO4 as catalyst, it was found that e-caprolactam, cyclohexanone, and... 

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,... 

E-Caprolactam is an important starting material for the production of nylon-6. It is synthesized by the Beckmann rearrangement reaction of cyclohexanone oxime catalyzed by a solid acid catalyst. Many solid acid catalysts, such as mixed boron oxide [1-3], Si02-Al203 [4,5], metal phosphates [6-8] and moclified zeolites [3,9-12], are reported to catalyze the cycdohexanone oxime rearrangement. The acid function of the catalyst is essential to effect the rearrangement reaction. 

The Beckmann rearrangement of cyclohexanone-oxime into e-caprolactam is commercially important for the production of synthetic fibers. Sato et al. [121] reported the Beckmann rearrangement of cyclohexanone-oxime in the absence of acid catalysts in scHaO and its interesting reactivity in the near-critical region of pure water. 

The Beckmann rearrangement of cyclohexanone oxime in the gas phase has been investigated over siliceous MCM-41- and MCM-48-type materials. At 275°C complete conversion occurs for several hours with selectivities for s-caprolactam up to 65 %, until the catalysts deactivate rapidly. The deactivation of the mesoporous catalysts is considerably reduced as compared to that obtained over an amorphous silica gel. MCM-48 exhibits the highest catalyst lifetime which, for MCM-41-type materials, is longer with larger pore diameter. With an aluminum-containing H-MCM-41 catalyst an increased e-caprolactam selectivity is achieved. 

Recent Developments in the Catalyst Regeneration for the Beckmann Rearrangement of Cyclohexanone Oxime to E-Caprolactam... 

The regeneration of B-MFI as the heterogeneous catalyst for the gas phase Beckmann-rearrangement of cyclohexanone oxime to e-caprolactam in a continuous fluidised bed was investigated. 

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