Ethylbenzene heterogeneous oxidation

Dehydrogenation, Ammoxidation, and Other Heterogeneous Catalysts. Cerium has minor uses in other commercial catalysts (41) where the element s role is probably related to Ce(III)/Ce(IV) chemistry. Styrene is made from ethylbenzene by an alkah-promoted iron oxide-based catalyst. The addition of a few percent of cerium oxide improves this catalyst s activity for styrene formation presumably because of a beneficial interaction between the Fe(II)/Fe(III) and Ce(III)/Ce(IV) redox couples. The ammoxidation of propjiene to produce acrylonitrile is carried out over catalyticaHy active complex molybdates. Cerium, a component of several patented compositions (42), functions as an oxygen and electron transfer through its redox couple. 

In contrast, a similarly doped Co(salen) aerogel (Figure 5.10) was slow in catalysing the oxidation of ethylbenzene to acetophenone despite showing quantitative conversion of ethylbenzene, a yield not possible with a similar heterogenized system obtained by conventional impregnation when a drastic reduction in activity is observed after 50% conversion.21... 

The greatest advantage of the above catalytic system was the elimination of the unweleome induetion period which otherwise occurs commonly for cobalt(II)-based oxidation catalysts. This has been possible because through direct use of a eobalt(III)-based heterogeneous system it has been possible to eliminate the time required to ehange Co(II) to Co(III). The isolated yield of acetophenone was found to be 70% at 94% seleetivity during aerobie oxidation of ethylbenzene under atmospheric liquid phase eonditions. 

In the C4 coproduct route isobutane is oxidized with oxygen at 130-160°C and under pressure to tert-BuOOH, which is then used in epoxidation. In the styrene coproduct process ethylbenzene hydroperoxide is produced at 100-130°C and at lower pressure (a few atmospheres) and is then applied in isobutane oxidation. Epoxidations are carried out in high excess of propylene at about 100°C under high pressure (20-70 atm) in the presence of molybdenum naphthenate catalyst. About 95% epoxide selectivity can be achieved at near complete hydroperoxide and 10-15% propylene conversions. Shell developed an alternative, heterogeneous catalytic system (T1O2 on SiOi), which is employed in a styrene coproduct process.913 914... 

In heterogeneous catalysis the applicability of this method has been demonstrated. The method is explained below for the acid-catalyzed oxidative dehydrogenation of ethylbenzene as used by Kito ct al. [37-41] aiming at maximizing the selectivity to styrene by promoting SnOi with various inorganic compounds. 

Commodity organic chemicals (Chapter 1) largely produced by heterogeneously catalyzed routes include acrylic acid (Section 2.8), acrylonitrile (Section 2.10), adipic acid (Section 2.2.2), cumene (Section 5.2.3) ethylbenzene (Section 5.2.1) methanol (Section 4.7.1) styrene (Section 3.9) terephthalates (Section 2.3) ethylene oxide (Section 2.4) vinyl acetate (Section 2.15.7), and many others in a word, heterogeneous catalysis is huge. 

Two variants of the Oxirane process are used (Figure 1) for the commercial production of propene oxide (PO) [29]. They differ in the hydrocarbon (isobutane or ethylbenzene (EB)) that is the precursor of the hydroperoxide, and, hence, in the alcohol co-product. ARCO operates both processes using a homogeneous molybdenum catalyst. Shell, in contrast, operates only the EB variant and uses a heterogeneous Ti /Si02 catalyst. 

Matienko, L. L Mosolova, L. A. The mechanism of selective ethylbenzene oxidation with molecular O, catalyzed by complexes of nickel (II), cobalt (II) and iron (III) with macrocychc polyethers. In Uspekhi v Oblasti Geterogennogo Kataliza i Geterotsiklov (Progress in Heterogeneous Catalysis and Heterocycles), Rakhmankulov, D. L., Ed. Khimiya Moscow, 2006 p. 235. 

High-valent early transition metals like titanium(IV) and vanadium(V) have been shown to efficiently catalyze the epoxidation of alkenes. The preferred oxidants using these catalysts are various alkyl hydroperoxides, typically tert-butyl hydroperoxide (TBHP) or ethylbenzene hydroperoxide (EBH P). One of the routes for the industrial production of propylene oxide is based on a heterogeneous Ti ySi02 catalyst, which employs EBHP as the terminal oxidant [6]. 

The epoxide is used as a monomer for polymer production. The byproduct ethylbenzene alcohol can be dehydrated to styrene, also a monomer for the production of polymers. If isobutane is used, iso-butylhydroperoxide replaces ethylbenzene-hydroperoxide as the oxidant. The byproduct tert-butanol can be converted with methanol to an ether that is an important additive in new environmental friendly gasolines. Complexes of Mo, V, or Ti are used in homogeneous epoxidation catalysis, while heterogeneous Ti02/Si02 catalysts can be used also. The active sites consist of a titanium ion with a fourfold coordination of oxygen in a tetrahedral geometry. Titanium acts essentially as a Lewis acid to activate the 0-0 bond in the hydroperoxide. 

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