Isobutene heterogeneous oxidation

More recent studies by Irvine and Knox [50] on the competitive oxidation of isobutane with ethane and propane at 300 °C have also led them to conclude that at low rates of reaction of isobutane a heterogeneous component leading to isobutene does indeed occur in parallel, but independently of the homogeneous reaction under most experimental conditions used in slow oxidation studies. They have suggested, however, in agreement with Semenov, that the reaction responsible probably involves the direct reaction of oxygen with isobutane adsorbed on the surface of the reactor (see p. 263), viz. 

Baldwin and Walker [99] have pointed out that, from kinetic considerations, surface reactions of alkylperoxy radicals cannot play a significant role except at very low overall rates of reaction and conclude that it is more likely that surface destruction of relatively stable intermediates such as the alkyl hydroperoxides or hydrogen peroxide are the main cause of surface effects in hydrocarbon oxidation. Luckett and Pollard [68, 134] have provided evidence, which suggests that the surface destruction of tert-butylhydroperoxide is indeed important during the oxidation of isobutane below ca. 320 °C. Since isobutene and acetone are known products of the decomposition of tert-butylhydroperoxide, it is clear that many of the foregoing results can be explained in these terms, but if this is the predominant heterogeneous reaction the yield of acetone would be... 

A typical example for the oxidative dehydrodimerization of alkenes by heterogeneous catalysis is the conversion of isobutene to 2,5-dimethyl-1,5-hexadiene (DMH) catalyzed by metal oxides. The overall reaction scheme is ... 

Membranes based on the above poly(phenylene oxide) binder and the hypercrosslinked particulate derived from finear polystyrene exhibit even higher selectivity, 540, in H2/isobutene separation, most likely due to size exclusion effect [396]. This experimental finding indicates that such type of heterogeneous membranes may successfully be used for effective separation... 

The propionaldehyde that forms can be subjected to an aldol reaction with formaldehyde to produce methacrolein, as claimed by BASF [20]. Hydroformylation and aldol condensation can also be performed as a tandem reaction in an aqueous two-phase system [21]. Both approaches to methacrolein are interesting alternatives to the partial oxidation of isobutene on heterogeneous catalysts [22]. 

Cavani, R, Comuzzi, C., Dolcetti, G., Etienne, E., Finke, R.G., SeUeri, G., Trifiro, F., and TrovareUi, A. Oxidative dehydrogenation of isobutane to isobutene Dawson-type heteropolyoxoanions as stable and selective heterogeneous catalysts./. Catal 1996,160, 317. 

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