Sumitomo caprolactam

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). 

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 ". 

Another pertinent example is provided by the manufacture of caprolactam [135]. Current processes are based on toluene or benzene as feedstock, which can be converted to cyclohexanone via cyclohexane or phenol. More recently, Asahi Chemical [136] developed a new process via ruthenium-catalysed selective hydrogenation to cyclohexene, followed by zeolite-catalysed hydration to cyclo-hexanol and dehydrogenation (Fig. 1.49). The cyclohexanone is then converted to caprolactam via ammoximation with NH3/H202 and zeolite-catalysed Beckmann rearrangement as developed by Sumitomo (see earlier). 

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. 

Figure 24 Synthesis of E-caprolactam by the EniChem-Sumitomo process.

The first commercial applicahon, made possible by an agreement between EniChem and Sumitomo, went on-stream in 2003 in Japan, within the context of an integrated process for the produchon of e-caprolactam by a new salt-free technology (ca GOOOOta ). Actually, besides the ammoximation step, no major byproduct is produced even in the gas-phase rearrangement carried out on silicalite-1 as the catalyst. On the whole, the ammonium sulfate is no longer a burden and the gaseous emissions too are drashcally reduced. 

Not only strong acid sites but also relatively weak acid sites could be utilized in the development of improved industrial processes. One of the most significative examples is the new Sumitomo process for caprolactam manufacture, which combines a first step of ammoximation (originally developed by the Eni group [241-243]) with a second step of Beckmann rearrangement based on the use of silicalite-1 (Eigure 2.32). 

Figure 2.32 Commercial (a) versus Sumitomo (b) process for caprolactam manufacture.

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). 

Note that in all textbooks of green chemistry the new Sumitomo process of caprolactam synthesis is given as an example, because it eliminates ammonium sulfate generation, while, usually, the DSM route is not considered. In reality, ammonium sulfate generation is only one aspect of the impact on the environment. 

Recycling Sumitomo Chemical demonstrates a positive approach to recycling as a means of reducing environmental impact. In 1991 it set up a Committee for Plastics Recycling , which is working both to develop easy-to-recycle plastics, and to mould regenerated plastics. Examples of other initiatives include the recovery of sodium ion and sulphur from wastewater and the use of reverse osmosis for recovering caprolactam. 

FIGURE 9.23. Sumitomo process combined ammoximation and vapor phase Beckmann rearrangement for caprolactam synthesis. 

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. 

The rearrangement step is most efficiently performed by the original solid catalyst based on Si/Al zeolite and coded as ZSM-5, discovered by the research team of Sumitomo Co. (Scheme 1.20c) [17, 18]. It catalyzes the rearrangement to caprolactame with 95 % selectivity and 100 % yield, without side products. 

An integrated process, which combines catalytic EniChem TS-1, catalyzed direct ammoximation of cyclohexanone and Sumitomo Chemical vapour-phase Beckmann rearrangement, both exploiting MFI based zeolite-like materials, is now industrially used for greener caprolactam production from cyclohexanone without co-producing any ammonium sulfate (Fig. 15.2). ... 

Exploiting this combined process, in April 2003 Sumitomo began commercial operation of a new caprolactam prodnction line in Ehime, Japan, enhancing the existing capacity of 93,000 t/y to 160,000. By this new integrated process, low-valne anunoninm sulfate is no longer co-produced, NOx and SOx emissions are gready reduced or eliminated, and water is the only co-product. Also, the plant is much simpler and, consequently much cheaper. 

Kitamura, M., Ichihashi, H. andTojima, H. (1992). Process for Producing -Caprolactam and Activating Solid Catalysts Thereof, European Patent EP0494535. Sumitomo Chemical CO Assignee. 

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