Iron oxide catalyst, dehydrogenation ethylbenzene

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. 

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... 

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... 

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. 

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. 

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... 

Styrene. All commercial processes use the catalytic dehydrogenation of ethylbenzene for the manufacture of styrene.189 A mixture of steam and ethylbenzene is reacted on a catalyst at about 600°C and usually below atmospheric pressure. These operating conditions are chosen to prevent cracking processes. Side reactions are further suppressed by running the reaction at relatively low conversion levels (50-70%) to obtain styrene yields about 90%. The preferred catalyst is iron oxide and chromia promoted with KzO, the so-called Shell 015 catalyst.190... 

Styrene (phenyl ethylene, vinyl benzene freezing point -30.6°C, boiling point 145°C, density 0.9059, flash point 31.4°C) is made from ethylbenzene by dehydrogenation at high temperature (630°C) with various metal oxides as catalysts, including zinc, chromium, iron, or magnesium oxides coated on activated carbon, alumina, or bauxite (Fig. 1). Iron oxide on potassium carbonate is also used. 

In particular, the dehydrogenation of ethylbenzene to styrene, a large-scale process, is performed with iron oxide-containing catalysts in the... 

Relevant to this issue is dehydrogenation of ethylbenzene for the manufacture of styrene which uses alumina supported iron oxide as the preferred catalyst in most cases. Therefore, when an alumina membrane is used in conjunction with stainless steel piping or vessels as the membrane reactor, caution should be exercised. An estimate of the effects of their exposure to the reaction mixuire at the application temperature of 600 to 640 C is desirable. Wu et al. [1990b] estimated that the alumina membrane contributes to less than 5% conversion of ethylbenzene and the stainless steel tubing or piping could account for as much as 20% conversion. The high activity of the stainless steel is attributed to iron and chromium oxide layers that may form on the wetted surface. 

Therefore, it can be concluded that carbon dioxide was utilized as an oxidant on dehydrogenation of ethylbenzene to improve its activity and that an active phase of iron oxide in the catalyst is considered to be rather reduced iron oxide, like Fc304, dispersed in zeolite matrix. 

Dehydrogenation of ethylbenzene over iron oxide-based catalyst in the presence of carbon dioxide... 

The iron oxide-based catalysts were prepared by Figure 1. Pathways of dehy-a coprecipitation method. In a typical experiment, drogenation of ethylben-1.4 g of catalyst (0.18-0.30mm) was set in a quartz tube reactor. Ethylbenzene was fed through a vaporizer, and was mixed with CO2. The flow rate was 130 ml/min. The dehydrogenation was conducted at 550 °C under atmospheric pressure. The product was analyzed by GC. ... 

The dehydrogenation reaction proceeds over an iron or an iron-chromium catalyst that usually also contains potassium in the form of potassium carbonate, so that at elevated temperatures various complex mixed carbonates and oxides are formed, e.g., KFe02. Temperatures are elevated, in the order of 630° C, and pressures are usually subatmospheric for improved per-pass conversions. Steam dilution is performed to further lower the partial pressure of the reactants. Because the reaction is strongly endothermic, various reaction stages with interheat (and interstage addition of superheated steam) are normally employed. Fig. 18 illustrates a typical process scheme for the dehydrogenation of ethylbenzene to styrene. 

---