Iron oxide catalyst, dehydrogenation

The Behavior of Titania-Supported Iron Oxide Catalysts in Butene Dehydrogenation... 

The activity of bulk iron oxide catalysts used in non-oxidative dehydrogenations decays under the process conditions imposed. Phase transformations leading to mechanical deterioration of the catalyst bodies, migration of the potassium promoter in the catalyst pellets and through the reactor and carbon deposition, resulting in covering of active sites or pore plugging are possible causes of the observed deactivation [1,2]. 

Description EB is dehydrogenated to styrene over potassium promoted iron-oxide catalyst in the presence of steam. The endothermic reaction is done under vacuum conditions and high temperature. At 1.0 weight ratio of steam to EB feed and a moderate EB conversion, reaction selectivity to styrene is over 97%. Byproducts, benzene and toluene, are recovered via distillation with the benzene fraction being recycled to the EB unit. 

Reactions of Ethylbenzene. Clough and Ramirez (15) have reported that for the dehydrogenation of ethylbenzene over a potassium promoted iron oxide catalyst in the presence of steam the in ortant reactions are ... 

Oxidative dehydrogenation of ethylbenzene with carbon dioxide over ZSM-5-supported iron oxide catalysts... 

Carbon dioxide was proposed as an oxidant in dehydrogenation of ethylbenzene over zeolite-supported iron oxide catalyst, which was highly dispersed in zeolite matrix. The dehydrogenation was mainly proceeded under the oxidative pathway in the presence of carbon dioxide. The presence of carbon dioxide contributed to remarkable enhancement not only in dehydrogenation activity of catedyst but also of its coke resistance. 

Large amounts of styrene are commercially produced by dehydrogenation of ethylbenzene (EB) in the presence of steam using iron oxide-based catalysts. Carbon dioxide, small amounts of which are formed as a by-product in the ethylbenzene dehydrogenation, was known to depress the catalytic activity of commercial catalyst [7,8]. However, it has been recently reported that several examples show the positive effect of carbon dioxide in this catalytic reaction [5,9,10]. In this study, we investigated the effect of carbon dioxide in dehydrogenation of ethylbenzene over ZSM-5 zeolite-supported iron oxide catalyst. 

To examine the effect of iron oxidation state on the dehydrogenation the activity of the iron oxide catalyst was compared as in various pretreatment. As presented in Figure 3, the catalyst pretreated with nitrogen showed rather high activity compared to those pretreated with carbon... 

Ethylbenzene dehydrogenation is generally catalyzed by a potassium-promoted iron oxide catalyst. The most widely used catalysts are composed of iron oxide, potassium carbonate, and various metal oxide promoters. Examples of metal oxide promoters include chromium oxide, cerium oxide, molybdenum oxide, and vanadium oxide. " The potassium component substantially increases catalyst activity relative to an unpromoted iron oxide catalyst. Potassium has been shown to provide other benefits. In particular, it reduces the formation of carbonaceous deposits on the catalyst surface, which prolongs catalyst life. 

Matsui, J. Sodesawa, T. Nozaki, F. Influence of carbon dioxide addition upon decay of activity of a potassium-promoted iron oxide catalyst for dehydrogenation of ethylbenzene. Appl. Catal. 1991, 67, 179-188. 

The catalytic dehydrogenation (DHYD) of ethylbenzene (EB) to styrene (ST) is the major industrial process for the styrene production [1]. The industrial process is usually realized in the temperature regime between 550-620°C with an excess of overheated water vapor mainly over a potassium promoted iron oxide catalyst [1]. Because this process is limited by the thermodynamic equilibrium of the reaction and because it is very energy... 

Mechanism 3 (Scheme 7.15) is accepted to be more thermodynamically favorable [135]. Nederlof [137] and Badstube [299] have investigated the CO2-ODE reaction over iron oxide catalyst supported on activated carbon. Their experimental data correlate with this postulated two-step mechanism, whereby EB dehydrogenation is followed by redox-type RWGS reactions (Fig. 7.7). 

Badstube et al. [114] have investigated the CO2-ODE over iron oxide catalyst supported on activated carbon in the presence of CO2. In addition to styrene, benzene, and toluene, they detected CO and H2O. Comparing the experimental data with the postulated mechanisms, they concluded that both the RWGS reaction and the redox cycle mechanism contribute to ethylbenzene dehydrogenation in the... 

Chang JS, ParkSE, Park MS (1997) Beneficial effect of carbon dioxide in dehydrogenation of ethylbenzene to styrene over zeolite-supported iron oxide catalyst. Chem Lett 26 1123-1124... 

It was shown that iron oxide promoted dehydrogenation activity while potash reduced the extent of carbon deposition during operation and also assisted in carbon removal during regeneration. The catalyst gave 85% selectivity at 20% conversion. 

Besides stmctural variety, chemical diversity has also increased. Pure silicon fonns of zeolite ZSM-5 and ZSM-11, designated silicalite-l [19] and silicahte-2 [20], have been synthesised. A number of other pure silicon analogues of zeolites, called porosils, are known [21]. Various chemical elements other than silicon or aluminium have been incoriDorated into zeolite lattice stmctures [22, 23]. Most important among those from an applications point of view are the incoriDoration of titanium, cobalt, and iron for oxidation catalysts, boron for acid strength variation, and gallium for dehydrogenation/aromatization reactions. In some cases it remains questionable, however, whether incoriDoration into the zeolite lattice stmcture has really occurred. 

Two or more soHd catalyst components can be mixed to produce a composite that functions as a supported catalyst. The ingredients may be mixed as wet or dry powders and pressed into tablets, roUed into spheres, or pelletized, and then activated. The promoted potassium ferrite catalysts used to dehydrogenate ethylbenzene in the manufacture of styrene or to dehydrogenate butanes in the manufacture of butenes are examples of catalysts manufactured by pelletization and calcination of physically mixed soHd components. In this case a potassium salt, iron oxide, and other ingredients are mixed, extmded, and calcined to produce the iron oxide-supported potassium ferrite catalyst. 

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. 

The term, metal dusting, was first used about this time to describe the phenomenon associated with hydrocarbon processing. Butane dehydrogenation plant personnel noted how iron oxide and coke radiated outward through catalyst particles from a metal contaminant which acted as a nucleating point. The metal had deteriorated and appeared to have turned to dust. The phenomenon has been called catastrophic carburization and metal deterioration in a high temperature carbonaceous environment, but the term most commonly used today is metal dusting. 

This is an endothermic reaction in which a volume increase accompanies dehydrogenation. The reaction is therefore favoured by operation at reduced pressure. In practice steam is passed through with the ethylbenzene in order to reduce the partial pressure of the latter rather than carrying out a high-temperature reaction under partial vacuum. By the use of selected catalysts such as magnesium oxide and iron oxide a conversion of 35-40% per pass with ultimate yields of 90-92% may be obtained. 

Formaldehyde, produced by dehydrogenation of methanol, is used almost exclusively in die syndiesis of phenolic resins (Fig. 7.2). Iron oxide, molybdenum oxide, or silver catalysts are typically used for preparing formaldehyde. Air is a safe source of oxygen for this oxidation process. 

The results of catalytic activities in the dehydrogenation of ethylbenzene with various iron oxide based catalysts are shown in Fig. l(a-b). The number in the parentheses of the catalyst codes indicates the weight fi-action of metal per gram carbon. On oxidized CNF alone less than 20% conversion of EB is observed after 3 h on stream. The conversion of ethylbenzene... 

Pyruvic acid is the simplest homologue of the a-keto acid, whose established procedures for synthesis are the dehydrative decarboxylation of tartaric acid and the hydrolysis of acetyl cyanide. On the other hand, vapor-phase contact oxidation of alkyl lactates to corresponding alkyl pyruvates using V2C - and MoOa-baseds mixed oxide catalysts has also been known [1-4]. Recently we found that pyruvic acid is obtained directly from a vapor-phase oxidative-dehydrogenation of lactic acid over iron phosphate catalysts with a P/Fe atomic ratio of 1.2 at a temperature around 230°C [5]. 

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