Isobutene ammoxidation

Isobutene ammoxidation Isobutene, air, ammonia, H2SO4 Catal3ftic ammoxidation to methacrylonitrile. Asahi Kasei... 

The literature on ammoxidation is very wide. The majority of papers and patents published in this field deal with propene and propane ammoxidation to acrylonitrile, of isobutane and isobutene ammoxidation to methacrylonitrile and methyl-aromatics and methylpyridines (picoUne) ammoxidation to the corresponding cyano-containing compounds, as discussed in the previous sections. A small amount of literature deals with the ammoxidation of the following molecules ... 

Compared with propene, the oxidation of isobutene is more rapid but less selective, yet selectivities of over 75% appear feasible. Combustion is the main side reaction. One would expect that some considerable attention would be shown in the literature to isobutene oxidation as a route to the industrially important methacrylic acid, but this is not the case. Nor is it with the production of methacrylonitrile, analogous to the propene ammoxidation. Only in the patent literature is a high activity noticeable. 

The ammoxidation of isobutene has not received much attention. The only contribution in this field is by Onsan and Trimm [2.44] for a rather unusual catalyst, a mixture of the oxides of Sn, V and P (ratio 1/9/3) supported on silica. At 520 C, a maximum selectivity to methacrylonitrile + methacrolein of 80% was reached with a Sn—V—P oxide catalyst (ratio 1/9/3), an isobutene/ammonia/oxygen ratio of 1/1.2/2.5 and a contact time of 120 g sec l ]. The kinetics are very similar to those for the pro-pene ammoxidation. Again, the data are initially analysed by means of (parallel) power rate equations, for which the parameters were calculated, while a more detailed analysis proves that a Langmuir—Hinshelwood model with surface reaction as the rate-controlling step provides the best fit with regard to the two main products. At 520° C, the equation which applies for the production of methacrolein plus methacrylonitrile is... 

Other applications of the ammoxidation include the reactions of isobutene (—> a-methacrylonitrile), a-methylstyrene (- atropanitrile), y5-picoline nicotine nitrile and nicotinamide), toluene benzonitrile), and xylenes (—> phthalo-nitrile, terephthalonitrile, and isophthalonitrile on the way to fiber- grade diamines). 

It is well known that the catalysts used for oxidation reactions such as those of propylene to acrolein, isobutene to methacrolein, or for ammoxidations (propylene to acrylonitrile, methyl-substituted benzenic rings to the corresponding aromatic nitriles) contain many components. This complexity in elemental composition is reflected by a complexity in phase composition. 

Important classes of reactions not included in the above list, because they are not yet used on a commercial scale, are (i) the oxidative dehydrogenation of C2-C5 alkanes, (ii) the selective oxidation of alkanes, such as the synthesis of maleic and phthalic anhydride from n-pentane and methacrolein or methacrylic acid from isobutene, and (iii) propane ammoxidation to acrylonitrile [317-319]. 

In other examples, extensively studied by Delmon et al., SbaOa was used with M0O3 for isobutene oxidation to methacrolein [29, 30], and for the dehydration of N-ethyl formamide [46,47]. Antimony is one of the elements frequently found in selective oxidation catalysts, as in the pionneering work on uranium antimony oxides for ammoxidation of propene [48], and more recently in ammoxidation of propane on V-Sb-Al system [49]. 

Alkene ammoxidation technology also encompasses several other allylic alkenes, most notably isobutene. When isobutene is the reactant, the selective nitrile product is methacrylonitrile. 

---