Cyclohexanone ammoximation

TS-1 is a material that perfectly fits the definition of single-site catalyst discussed in the previous Section. It is an active and selective catalyst in a number of low-temperature oxidation reactions with aqueous H2O2 as the oxidant. Such reactions include phenol hydroxylation [9,17], olefin epoxida-tion [9,10,14,17,40], alkane oxidation [11,17,20], oxidation of ammonia to hydroxylamine [14,17,18], cyclohexanone ammoximation [8,17,18,41], conversion of secondary amines to dialkylhydroxylamines [8,17], and conversion of secondary alcohols to ketones [9,17], (see Fig. 1). Few oxidation reactions with ozone and oxygen as oxidants have been investigated. 

The discovery of the new titanium silicates and of their catalytic properties in H2O2 oxidation reactions has had a major impact in catalytic science and its industrial applications. One 10,000 ton/year plant for the production of catechol and hydroquinone has been operating since 1986 with excellent results. Moreover, successful tests conducted on a 12,000-ton/year pilot plant for cyclohexanone ammoximation (Notari, 1993b) could be followed soon by an industrial-size plant that would greatly simplify the synthesis of caprolactam. Both these examples are clear indications of the potentials of the new oxidation chemistry made possible by the new materials. 

Table 4.3 Cyclohexanone ammoximation with different catalysts nh3 + h2o2 —nh2oh + h2o...

Soon after its discovery, TS-1 was recognized as a valuable catalyst for many oxidations by hydrogen peroxide, including alkane oxidation, olefin epoxidation, alcohol oxidation, phenol hydroxylation and cyclohexanone ammoximation (Scheme 13.3) [18]. 

Production of cyclohexanone oxime through cyclohexanone ammoximation... 

Figure 1.20 Process scheme for cyclohexanone ammoximation catalyzed by TS-1. Adapted from Ref (2f), with permission from Enciclopedia italiana.

The reaction in liquid phase, however, appeared the most promising. As an oxidant, preference was given to hydrogen peroxide, a very selective oxidant under mild reaction conditions. An economic estimate shows diat the cost of hydrogen peroxide for captive use makes the cyclohexanone ammoximation process competitive with the conventional processes. 

The results obtained for the cyclohexanone ammoximation by TiS using different solvents are reported in Table n. r-Butanol proved to be the best solvent for the reaction, even if other solvents (toluene, benzene) were used with similar results. 

Peiri, E., Pinelli, D., and Trifiro, F., Silica as Catalyst for Cyclohexanone Ammoximation with Molecular Oxygen A Preliminary Approach to the Kinetic Analysis , Chem. Eng. Sci., 47 (9-11), 2,641(1992). 

Enichem (ENI) Dimethylcarbonate (DMC) Rumene Cyclohexanone ammoximation technology... 

During the last period considerable attention has been given to Ti-silicalite, a zeolite derived from silicalite by partial substitution of framework Si with Ti (refs. 1-3). This zeolite exhibits very valuable catalytic properties for a variety of reactions of industrial interest, in particular for cyclohexanone ammoximation, phenol hydroxilation and olefins epoxidation (refs. 4, 5). Despite that, the stability of Ti-silicalite, as well as fundamental aspects of its characteristics and catalytic behaviour, has not been studied. In this work sorption measurements of small (N ) and large (p- and m-xylene) probe molecules were performed to characterize the porous structure of Ti-silicalite, before and after various thermal treatments. The results, compared to those obtained by spectroscopic and diffractometric techniques, provided information on stability of both zeolite lattice and titanium inserted in the framework. 

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