Cyclohexanone oxime zeolites

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). 

Beckmann rearrangement of oxime is an acid catalysed reaction. The environmental problems associated with the use of sulphuric acid instigated interest to use number of solid acid catalysts [1], There are only scanty references about Lewis acid ion-exchanged MeAlPOs. Beyer et al. [2], Mihalyi et al. [3] and Mavrodinova et al. [4] already suggested the presence of Lewis acid metal ions as MO+ species in zeolites. The present study focussed the synthesis and characterisation of Fe3+, La3+ and Ce3+ ion-exchanged MAPO-36. The catalytic results of Beckmann rearrangement of cyclohexanone oxime over ion-exchanged catalysts are delineated in this article. 

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... 

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 ". 

It has been described the reaction of cyclohexanone oxime with solids of different nature, as zeolites (refs. 4 and 5) and aluminum phosphates (ref. 6), giving rise to the Beckmann rearrangement product, E-caprolactame when the reactions are carried out in the gas phase at relatively high temperatures (>300°C). 

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 ... 

Strong acid zeolites with 12-MR pores do not seem suitable candidates for the Beckmann rearrangement therefore. However, provided a diluting alcohol such as 1-hexanol is fed together with cyclohexanone oxime, long catalyst lifetimes and high selectivities can be observed, even for H-Beta and H-USY. Clearly, the 1-... 

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. 

Similarly, for the vapor phase Beckman rearrangement of, e.g., cyclohexanone oxime into caprolactam (Scheme 12) the zeolite structure was initially thought to be the most decisive factor for selectivity. Small pore zeolite HA (pore size 4A) produced caprolactam with only... 

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... 

A second approach to isolating redox metal ions in stable inorganic matrices, thereby creating oxidation catalysts with interesting activities and selectivities, is to incorporate them in a zeolite lattice framework. The first example of such a redox zeolite was the synthetic titanium(IV) zeolite, titanium siliealite (TS-1), developed by Enichem [30-32]. TS-1 was shown to catalyze a variety of synthetically useful oxidations with 30% H202, such as olefin epoxidation, oxidation of primary alcohols to aldehydes, aromatic hydroxylation, and ammoxi-mation of cyclohexanone to cyclohexanone oxime (see Fig. 9). 

Hydrogenation is selective for size and shape.200 Cyclohexene, but not cyclododecene, was reduced by hydrogen with a rhodium in NaY zeolite. The Beckmann rearrangement of cyclohexanone oxime to caprolactam (6.37) (for... 

Table 2.5 Beckmann rearrangement of cyclohexanone oxime over zeolites...

Yashima et al. compared the catalytic performance of H-ZSM-5, H-FER, H-MOR, Ca-A, H-B-MFI, and H-SAPO-5 in the Beckmann rearrangement of cyclohexanone oxime [28]. H-B-MFI was calcined at 603 K only and tetra-n-propylammo-nium remained in the pore. The conversions obtained with Ca-A (molecular sieve 5 A, 8MR) and H-B-MFI were low. As shown in Figure 3, however, the selectivity for e-caprolactam was higher over Ca-A, H-FER (10 MR) and H-B-MFI and lower over H-SAPO-5 (12-MR), H-ZSM-5, and H-MOR (12-MR), which could accommodate cyelohexanone oxime in their pores. It was concluded that the selective formation of e-caprolactam proceeded on the active sites on the external surface of zeolite crystallites rather than in the narrow space of the zeolite pore [28]. They even deduced that at higher reaction temperature cyclohexanone oxime would enter the pore, producing undesirable products such as cyclohexanone and 1-cyanopentene, which are smaller than e-caprolactam, because of the size effect. On the other hand, Curtin and Hodnett reported that caprolactam selectivity was lower over the zeolites with smaller pore diameters [29]. 

Figure 5. Change in cyclohexanone oxime conversion and lactam selectivity with time on stream in the vapor phase Beckmann rearrangement over 12-MR zeolites. Diluent (a) methanol, (b) 1-hexanol. (X) H-BEA, (A) H-LTL, (V) H-OFF-ERI, ( ) H-USY (Si02/Al203 = 62), (O) H-MOR, (O) H-MTW 623 K, oxime/diluent/N, molar ratio of 1/9/5.9 and W/F of 80 g cat h mol oxime [41].

Burguet et al. investigated the catalyst decay accompanying the reaction of cyclohexanone oxime over ultrastable H-Y zeolite [58]. The basic compounds present during the reaction i. e. oxime, -caprolactam, methylpyridine, 5-cyano-pent-l-ene, hydroxylamine, and aniline were considered to be the catalyst poisons. Hydroxylamine is more basic than the other products and might be more poisonous. Hydroxylamine selectivity decreased with temperature, which could explain qualitatively the apparent decrease in the deactivation constant (k with increasing temperature. 

The rearrangement of oximes over solid acids has been studied for some time although the total number of studies has remained low. Zeolite and alumina based solid acids have been mostly studied and the substrate most often used has been cyclohexanone oxime, with a view to its transformation into caprolactam [1-15). A major problem associated with this reaction is coke formation and it appears with all catalyst types studied to date. The origin of coke formation have not been established, although there is a tendency to assume that it arises via a similar set of conditions to those which are responsible for coke formation in, for example, toluene disproportionation. 

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 effect of various organic additives on the catalj ic performance of zeolites and Al-containing MCM-41 in the liquid phase Beckmann rearrangement of cyclohexanone oxime 5 was investigated at 130 °C. Over USY zeolite with a large amount of EFAL, the lactam yield was improved by adding ethanol, dimethyl sulfoxide, ammonia, diethylamine or pyridine to the... 

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. ... 

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