EniChem process

The results obtained with the different catalysts indicate that both Ti02 supported on silica and TS-1 perform well. However, TS-1 was the superior catalyst. The Enichem process for this step in the e-caprolactam process greatly simplifies the current technology (Figure 4.7). 

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

Application To produce low density polyethylene (LDPE) and ethylene vinyl acetate (EVA) by the high-pressure, autoclave or tubular EniChem process. 

The ammoximation of cyclohexanone had been known before the discovery of TS-1, but the performances of conventional catalysts were far below the standards required for development work. In the EniChem process, the reaction is carried out in the liquid phase, at ca. 80°C, using a suspension of TS-1 in aqueous t-butanol, with a slight excess of hydrogen peroxide over the ketone. The substrate and the oxidant undergo total conversion with selectivities close to 98% and 94%, respectively. Inorganic by-products comprise minor amounts of ammonium nitrate and nitrite, N2O, and N2 produced by the oxidation of ammonia, and O2 by the decomposition of the oxidant. 

The truly innovative nature of the EniChem process over earlier ones is apparent. The preparation of hydroxylamine in the latter case necessitates multi-step operation, often ending with major co-production of inorganic salts, as in the Raschig process. The ammoximation of cyclohexanone, with its in situ generation of the intermediate, reduces significantly the investment and operahon costs while improving the environmental compahbility. The new process represents a good example of how to combine profitability and environmental concern. 

Different variations of the Enichem process have been described that may show some improvements in selectivity and efficiency of the catalyst system, but they generally seem to be less attractive from the economic point of view and none of them has been realized until now. For example, since 1986 the Japanese company Daicel especially has applied for numerous patents on modifications of the Enichem process, in which dimethyl carbonate is prepared in the presence of catalyst systems that contain copper and palladium salts and additional modifiers, e. g., quinoid compounds and quatemery phosphonium halides [40-48]. Although Daicel has announced several times the constmction of an industrial plant for the production of dimethyl carbonate, all investment plans now seem to be put aside. The separation of the reaction product from the complicated catalyst system as well as the complete recycling of the palladium compounds, which is a necessary requirement for any economic process design, seem not to be solved sufficiently. 

Extensive efforts to achieve the oxidative carbonylation of methanol in the gas phase using CuCl or Cu(OCH3)Cl complexes supported on active carbon have been undertaken to Dow Chemicals [49, 50], Because of the rapid catalyst deactivation this method has not become an alternative to the Enichem process. 

Scheme 6.6 Reactions involved in the EniChem process for propene epoxidation with in situ generation of HP.

An integrated process has also been reported, but not implemented at a commercial level, by ARCO (now Lyondell) [21]. In this case, the O-donor species is produced by the autoxidation of aryl-substituted secondary alcohols (a-methyl benzyl alcohol) to ketones, and the resulting solution is used to feed the epoxidation reactor. The alcohol is then recovered by hydrogenating the ketone. The main difference with respect to the EniChem process is the higher temperature of the autoxidation process (90-140 instead of 40 °C). 

Several complications in the Enichem process constrain the scale of the reactor volume [12]. The reaction is so exothermic that the reactor needs to be cooled to maintain the optimal 130 °C temperature. Vaporization of the reaction mixture removes only a fraction of the water by-product, and concentration of the water in the reactor hampers the selectivity and rate of the reaction. Therefore, the methanol conversion per run is limited to 20%. The presence of HCl necessitates the use of corrosion-resistant reactors, and either glass linings or high-nickel alloys are used. 

In contrast to these, the Enichem process using TS-I zeolite for the oxidation of phenol by H2O2 leads to a conversion of 20-25%. Even at this high level of conversion, the formation of polyhydroxylated benzene and tars is inhibited by transition-state shape selectivity. 

Phenol hydroxylation using HjOj as Homogeneous catalysts based TS-1 (Enichem) Enichem process allows higher phenol [67 69]... 

Figure 1. Comparison of Current CPL Technology Using Hydroxylamine Derivatives to the New EniChem Process.

In Table IV the byproduction of ammonium sulfate in the ammoximation process is compared to other CPL prtocesses. As shown in Table IV, 3/4 of the ammonium sulfate byproduction is eliminated in the EniChem process compared to the other processes. Finally, the data in Table V show that the ammoximation unit does not produce any consistent quantity of gaseous pollutants. 

A comparison of the current technology and the new EniChem process is shown in Figure L The dramatic simplicity of the ammoximation step is evident. 

The Enichem process for the preparation of propene oxide from propylene involves using H2O2 as the oxidizing agent using titanium silicate catalyst (see Fig. 3.16). 

EniChem through Snamprogetti EniChem process, high pressure, autoclave or tubular reactor. LDPE (density 918-935 kg/m ), MFI = 0.1-400 g/10 min. EVA copolymer (3-40% VA content) for film, injection moulding, profiles, sheets, cable sheetings, crosslinking, and foaming. 

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