Conversion of Cyclohexanone Oxime to Caprolactam

Conversion of the oxime to eaprolactam was achieved by mixing the oxime with an eqnal weight of 20% olenm at a temperature of 120°C. After 15 minntes, the yield of e-eaprolactam was abont 90%. The solution was nentialized with ammonia and the erude lactam separated recovered and purified by distillation. 

In the DSM proeess, ammoninm sulfate formation is redueed from about 5 kg for eaeh kilogram of eaprolactam to 1.8 kg. Boric acid catalysts can be used for the rearrangement of the oxime to the lactam at 330°C in fixed or fluidized beds, but have not been nsed eonnnercially. Strong acid exchange resins have 

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Sticking with nylon production, high-silica pentasil zeolites are used by Sumitomo to overcome environmental issues associated with the conversion of cyclohexanone oxime to caprolactam (Chapter 1, Scheme 1.4). 

The solid state NMR study of the Beckmann rearrangement catalyzed by MFI-type zeolites with different acid catalysts disclose that the conversion of cyclohexanone oxime to caprolactam is catalyzed by SiOH, SiOH[Bl and SiOHAl groups as in silicate-I, zeolites H-[B]ZSM-5 and H-ZSM-5. ... 

However, another approach to find the suitable catalyst for the conversion of cyclohexanone oxime to caprolactam in order to completely eliminate the salt formation has been reported by Sumitomo, of Japan. They reported the use of a solid high-silica zeolite catalyst (ZSM-5) for the gas-phase rearrangement of cyclohexanone oxime at 350 °C. Caprolactam is produced with 95% selectivity at 100% oxime conversion. 

Caprolactam, the monomer from which nylon 6 is synthesized, is prepared from cyclohexanone in two steps. In Step 1, cyclohexanone is treated with hydroxylamine to form cyclohexanone oxime. Treatment of the oxime with concentrated sulfuric acid in Step 2 gives caprolactam by a reaction called a Beckmann rearrangement. Propose a mechanism for the conversion of cyclohexanone oxime to caprolactam. 

Sulfuric acid is used for a variety of other purposes in the chemical industry. For example, it is the usual acid catalyst for the conversion of cyclohexanone oxime to caprolactam, used for making nylon. It is used for making hydrochloric acid from salt via the Mannheim process. Much H2SO4 is used in petroleum refining, for example as a catalyst for the reaction of isobutane with isobutylene to give isooctane, a compound that raises the octane rating of gasoline (petrol). Sulfuric acid is also important in the manufacture of dyestuffs solutions and is the "acid" in lead-acid (car) batteries. 

The caprolactam based Bronsted acidic ionic liquids such as [NHC][BP4], [NHC][CF3C00] and [NHC][N03] have been used to catalyze the rearrangement of cyclohexanone oxime to caprolactam and was found that with a 3 1 mole ratio of ionic liquid oxime, the conversion increased to... 

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... 

Use of mesoporous molecular sieves FSM-16 resulted in high conversion of cyclohexanone oxime but the selectivity for -caprolactam was low [15]. Dai et al. recently discovered that H-MCM-41 and H-FSM-16 have high activity, selectivity and stability for production of e-caprolactam when 1-hexanol was co-fed as diluent [16]. Greater selectivity was obtained with the mesoporous catalyst than with amorphous Si02-Al203. Highly siliceous FSM-16 (Si/Al = 640) was inferior to Al-richer FSM-16 (Si/Al = 40) in terms of both selectivity and catalyst life. 

Conversion of cyclohexanone oxime and. selectivity to caprolactam over a range of solid acids are presented in figures 1 (a) and (b). The corresponding data for cyclopenatanone... 

Figure 1. Conversion of cyclohexanone oxime (a) and selectivity to caprolactam (b) over B203/Al203,300°C [ ], Na/Al203,300°C [ ], HZSM-5, 350°C [ ] and H-Mordenite, 350°C [O],...

Oxime conversion (Xqx) and product selectivities (S), at Xqx SO mol%, in the rearrangement of cyclohexanone oxime to e-caprolactam over AP and APTi catalysts... 

Beckmann Rearrangement. The Beckmann rearrangement of cyclohexanone oxime to s-caprolactam (Scheme 8.15) is an important step in the synthesis of s-caprolactam, the monomer for nylon-6. Traditional reaction conditions involve the use of sulfuric acid as a catalyst for this conversion, and require... 

The conversion of cyclohexanone to cyclohexanone oxime is brought about by the use of hydroxylamine sulphate. The sulphuric acid is neutralised with ammonia to ammonium sulphate and this is separated from the oxime. In the presence of oleum the oxime undergoes the process known as the Beckmann rearrangement to yield the crude caprolactam. After further neutralisation with ammonia the caprolactam and further ammonium sulphate are separated by solvent extraction (Figure 18.7). 

A -Butylpyridinium tetrafluoroborate, containing dissolved phosphorus pentachloride, allows catalytic Beckmann rearrangement of cyclohexanone oxime giving e-caprolactam with good conversion and selectivity <2001TL403>. The same ionic liquid containing dissolved ytterbium(m) trifluoromethanesulfonate was used to perform Friedel-Crafts acylation of furan and thiophene <2005JIG398>. 

About 90% of the caprolactam is produced by the conventional cyclohexanone process. Cyclohexanone is obtained by catalytic oxidation of cyclohexane with air, or by hydrogenation of phenol and dehydrogenation of the cyclohexanol byproduct. The conversion of cyclohexanone to cyclohexanone oxime followed by Beckmann rearrangement gives caprolactam. About 10% of caprolactam is produced by photonitrosation of cyclohexane or by nitrosation of cyclohexanecarboxylic acid in the presence of sulfuric acid264. 

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. 

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. 

Another reaction commercialized by EniChem is the ammoximation of ketones, particularly the conversion of cyclohexanone to cyclohexanone oxime (47). This latter compound is an intermediate in the manufacturing of caprolactam, the monomer for Nylon 6. This reaction, outlined in Figure 10.13, proceeds with both high conversion and selectivity for the oxime product. Again, TS-1 is uniquely active for this reaction compared to other catalysts, and TS-1 can catalyze this reaction on a variety of substrates. It is believed that in all cases the hydroxylamine is first formed, followed by reaction with the ketone. TS-1 is currently used commercially by EniChem to produce 12,000 ton per year of cyclohexanone oxime. 

The second TS-1 based process which is likely to go into commercial production is the synthesis of cyclohexanone oxime from cyclohexanone, ammonia, and hydrogen peroxide (Roiiia et al., 1990) (reaction 6.13), which is the first step in the preparation of e-caprolactam (Montedipe, pilot plant). Oxime selectivity is >98% at a conversion of 99.9%. 

E-Caprolactam (CL) is a very important monomer for the production of nylon-6, and about 4.2 million tons of CL were manufactured worldwide in 1998 [126]. Most current methods of CL production involve the conversion of cyclohexanone with hydroxylamine sulfate into cyclohexanone oxime followed by Beckmaim rearrangement by the action of oleum and then treatment with ammonia, giving CL. A serious drawback ofthis process is the co-production of a large amount of ammonium sulfate waste [126, 127]. Raja and Thomas reported a method for one-step production of cyclohexanone oxime and CL by the reaction of cyclohexanone with ammonia under high-pressure air (34.5 atm) in the presence of a bifunctional molecular sieve catalyst [128]. Hydrogen peroxide oxidation of cyclohexanone in the presence of NH3 catalyzed by titanium silicate is reported to produce CL [129]. In patent work, on the other hand, the transformation of l,l -peroxydicyclohexylamine (PDHA) to a 1 1 mixture of CL and cyclohexanone by LiBr has been reported [130]. 

The preparation of s-caprolactam via the Beckman rearrangement of cyclohexanone oxime was first described by Wallach in 1900. In the I.G. Faiben process, phenol was hydrogenated to cyclohexanol, at 140°-160°C and 15 bar, with a nickel oxide/silica catalyst. The cyclohexanol was del drogenated to cyclohexanone using a zinc/iron catalyst at 400°C, and the cyclohexanone oxime was formed by reaction with hydroxylamine monosidfonate. Conversion to cyclohexanone oxime was maximized at pH 7 by neutralizing the solution with ammonia. The organic layer of cmde oxime was crystallized and then isomerized to s-caprolactam with 20% oleum at 120°C. e-Caprolactam was purified and the ammonium sulfate recovered. 

Toray. The photonitrosation of cyclohexane or PNC process results in the direct conversion of cyclohexane to cyclohexanone oxime hydrochloride by reaction with nitrosyl chloride in the presence of uv light (15) (see Photochemical technology). Beckmann rearrangement of the cyclohexanone oxime hydrochloride in oleum results in the evolution of HCl, which is recycled to form NOCl by reaction with nitrosylsulfuric acid. The latter is produced by conventional absorption of NO from ammonia oxidation in oleum. Neutralization of the rearrangement mass with ammonia yields 1.7 kg ammonium sulfate per kilogram of caprolactam. Purification is by vacuum distillation. The novel chemistry is as follows ... 

In conclusion, decrease in cyclohexanone oxime yield and caprolactam selectivity with time on stream is a major factor in the use of boria on alumina catalyst in the rearrangement reaction. Coke deposition and basic by-product adsorption have been suggested as a means of deactivation. In addition the conversion of water soluble boron, which is selective to lactam formation, to an amorphous water insoluble boron species is another factor that can account for the catalyst deactivation. 

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