Caprolactam Conventional processes

The yield of caprolactam in the conventional process is approximately 70% of theoretical based on cyclohexane. The process makes about 0.94 pounds of caprolactam per pound of cyclohexane consumed. The yield is approximately 92% of theoretical based on phenol and yields about 1.11 pounds of caprolactam per pound of phenol consumed266. 

Another case in point pertains to the manufacture of the bulk chemical, caprolactam, the raw material for Nylon 6. The conventional process (Fig. 1.9) in-... 

The conventional process (Figure 2.32a) involves the reaction of cyclohexanone tvith hydroxylamine sulfate (or another salt), producing cyclohexanone oxime that is subjected to the Beckmann rearrangement in the presence of stoichiometric amounts of sulfuric acid or oleum. The overall process generates about 4.5 kg of ammonium sulfate per kg of caprolactam, divided roughly equally over the two steps. The Sumitomo process (Figure 2.32b) instead produces virtually no waste and allows caprolactam to be obtained in >98% yield (based on cyclohexanone 93% based on FI2O2). 

In conventional processes, hvdroxylamine preparation, oximation and the Beckmann rearrangement produce a total of up to 4.41 of ammonium sulfate per ton of caprolactam. The molar yield of lactam is around 70 per cent of theory in relation to cyclohexane, and 91 per cent in relation to phenol. With the BASF technology, only 2.61 of ammonium sulfate is produced per ton of caprolactam, and the molar yield in relation to cyclohexane is 70 per cent of theory. The use of the HPO process reduces the production of ammonium sulfate to 1.8 t per ton of caprolactam, and the molar yield is 61 per cent in relation to cyclohexane, and 93 per cent in relation to phenoL... 

This proces uses the same steps as the conventional process for manufacturing caprolactam from cyclohexane oxidation, oximation of cydododecanone, Beckmann rearrangement... 

There are seven commercial processes for producing caprolactam the Ras-hig (conventional) process, CAPROPOL process, BASF process, DSM-HPO process. Allied process, Toray PNC process, and the SNIA Viscosa process. Two of these, the CAPROPOL and BASF processes, utilize pure oxygen and are described in Chapter 5. Hydrogen is used to produce cyclohexane for all but the SNIA Viscosa process which uses toluene as a feedstock. The hydrogenation of benzene to cyclohexane has been described earlier in this chapter. The CAPROPOL, BASF, DSM-HPO, and SNIA Viscosa processes all involve hydrogenation in downstream steps. The hydrogenations are discussed here. 

Selective oxidation of cyclohexane to cyclohexanol and cyclohexanon is a very important reaction for the industrial production of adipic acid and caprolactam, which are the main raw materials for the manufacture of nylon. The conventional process is based on a homogeneous catalytic oxidation with cobaltdil) acetate as a catalyst. During this process, many unwanted coproducts are formed such as allqrl acetates other ketenes, or alkyl chlorides. Moreover, most industrial processes of the adipic acid production involve the nitric acid oxidation of cyclohexanol. Taking into account that the worldwide adipic acid production is more than 2 million metric tons per year (359), it has been evident that despite the... 

The formation of oxime and rearrangement to caprolactam are conventional. The rearrangement produces 1.5 kg of the total 2.4 kg by-product ammonium sulfate per kilogram of caprolactam. Purification is accompHshed by vacuum distillation. A similar caprolactam process is offered by Inventa (11). 

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 ... 

Snia Viscosa. Catalytic air oxidation of toluene gives benzoic acid (qv) in ca 90% yield. The benzoic acid is hydrogenated over a palladium catalyst to cyclohexanecarboxyhc acid [98-89-5]. This is converted directiy to cmde caprolactam by nitrosation with nitrosylsulfuric acid, which is produced by conventional absorption of NO in oleum. Normally, the reaction mass is neutralized with ammonia to form 4 kg ammonium sulfate per kilogram of caprolactam (16). In a no-sulfate version of the process, the reaction mass is diluted with water and is extracted with an alkylphenol solvent. The aqueous phase is decomposed by thermal means for recovery of sulfur dioxide, which is recycled (17). The basic process chemistry is as follows ... 

Farther growth of the polymeric chain proceeds in the nsnal manner. Compared to the polymeric materials obtained by conventional methods, the mechanochemically synthesized polyacryl and polymethacrylamides have lower molecular weights (Simonescu et al. 1983). Acrylonitrile, styrene, e-caprolactam, and isoprene as well as aryl and methacrylamides have special optimal duration of the polymerization on grinding (Oprea and Popa 1980). In the case of the aryl and methacrylamides, the polymerization proceeds slowly, usually between 24 and 72 h. After that, some acceleration takes place and the process is completed in 96 h (in total). 

The use of solar energy in chemical processing has also been investigated. Studies describe, for example, the cycloaddition reaction of a carbonyl compound to an olefin carried out in a solar furnace reactor (91) or oxidation of 4-chlorophenol in a solar-powered liber-optic cable reactor (92). The concept of using solar light for the synthesis of e-caprolactam was evaluated, and it was shown that the return on investment was better than for the conventional technology (93). Solar reactors can also be used advantageously in water treatment plants (94). 

Some convention is employed in the sources of AS, mainly for the benefit of statisticians, who try to follow developments in the AS business. AS that is obtained from caprolactam or acrylonitrile manufacture is normally referred to as co-product. On the other hand, AS that is produced from coke ovens, flue gas desulphurization, smelter tail gas, sewage treatment, gypsum, waste acid from methyl methacrylate and from other chemical processes is usually termed byproduct241. 

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. 

Comparing the structure of the monomer with that of the polymer as shown in Table I, we see that the polymerization of the / -carboxy-methyl caprolactam must involve isomerization of the monomer ring system. This isomerization may be described by several possible processes, all of which are characterized by reaction between the amide and acid group of the / -carboxymethyl caprolactam. Based upon the results of our studies on the structure of this polymer (5) we may eliminate confidently those processes according to which the formation of the glutarimide moiety results either by intrachain cyclization or by trans-cyclization of certain intermediate polymer structures. The former would involve a polymer formed by a conventional ring opening polymerization ... 

Figure 4.7 Comparison of conventional and Enichem processes for the production of e-caprolactam.

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. 

A process based on the ammoximation of cyclohexanone and on the catalyzed rearrangement of the oxime went on stream in Japan in 2003 it allows the salt-free production of s-caprolactam, at lower investment and operating costs than by conventional routes. 

Following the successful application of zeolites in the major oil refining processes, zeolites entered the field of bulk chemicals synthesis, e.g. ethylbenzene, cumene and recently caprolactam. Their applications in the areas of fine chemicals arc also growing. An important factor is that zeolites, compared to conventional Brocnsted and Lewis acid catalysts, are low-waste catalysts and are regarded as green . After the early review on zeolite-catalyzed organic reactions by Venuto and Landis [ 1J the field has been reviewed several times [2-11],... 

Since its discovery some 55 years ago, the synthesis of caprolactam has been the subject of intense research and development. Interest in alternative routes continues today and current activities receiving a lot of attention are carbon monoxide-based routes under development by DSM, EniChem and DuPont [32]. Numerous routes using a variety of feedstocks have been patented and many have been piloted, however, only seven have actually been commercialized. The first was the process developed by I. G. Farben based on Schlack s chemistry known today as the Rashig or conventional route. Other commercial routes are the CAPROPOL process, the BASF process, the DSM-HPO process, the Allied process, the Toray PNC process, and the SNIA Viscosa process. 

The economics of the oxygen-based NO reduction process is difficult to compare because different caprolactam processes vary so widely. Nevertheless, an early study by Stanford Research Institute (SRI) found that the capital investment for the NO reduction process was about one-half that for the conventional Rashig process. The basis of this comparison included both the hydroxylamine unit as well as the oximation step. Operating costs were not reported, but the conclusion by SRI was that the NO Reduction process offered a decided advantage over the conventional Rashig process [31]. 

A typical system for polymerization casting of caprolactam thus uses as a catalyst 0.1—1 mol% N-acetyl caprolactam and 0.15-0.50 mol% of the sodium salt of caprolactam. The reaction temperature is initially about 150°C, but during polymerization it rises to about 200°C. The technique is especially applicable to the production of large, complex shapes that could not be made by the more conventional plastics processing techniques. 

Reimschuessel reviewed the water-initiated, ring-opening polymerization of caprolactam in detail [27]. In an attempt to analyze the process from its kinetic and mechanistic aspects, the equilibrium reactions 2.11, 2.12, and 2.13 are conventionally presented as follows ... 

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