Iron Oxide Catalysts For Dehydrogenation Research Articles

Waste-free life cycle of iron oxide catalysts for dehydrogenation of olefins and alkylaromatic hydrocarbons

For the processes of obtaining isoprene, styrene, divinylbenzene by dehydrogenation methods, iron oxide catalysts are used, the synthesis method of which is close to a waste-free technology. Waste is catalyst dust and chips formed during the screening stage of commercial products, flue gases formed during the activation of the catalyst. In the article, the authors consider the problems associated with waste in the production and operation of iron oxide catalysts for the dehydrogenation of olefins and alkylaromatic hydrocarbons. A method is proposed for the use of catalyst dust formed at the stage of catalyst preparation and utilization of spent iron oxide catalyst for the dehydrogenation of olefins and alkylaromatic hydrocarbons. The possibility of utilization of an ironcontaining spent catalyst for the production of iron oxide pigment and its further use in the production of building materials is shown. A number of decorative concrete samples have been prepared to study the effect of pigment as an additive on the properties of the building material. The dependence of the color gamut of the samples on the amount of pigment applied was studied, strength characteristics were studied in accordance with the regulatory requirements for strength, heat resistance and frost resistance.

Formation of a ceramic structure of promoted iron oxide catalyst

The paper concerns with the mechanism of the promoters influence on the ceramic structure of the iron oxide catalyst for the dehydrogenation of olefin and alkylaromatic hydrocarbons. The research shows the dynamics of changes in the porous structure of alloyed and unalloyed catalysts as a result of heat treatment in air at several temperatures significantly exceeding the operating temperature. Moreover, the paper presents data on the mechanical strength of alloyed and unalloyed model catalysts. Indeed, the particles are sintered to each other at the contact points of the globules forming a mechanically strong and thermally stable framework. However, the particles are sintered to each other at the contact points of the globules forming. Supposedly, potassium performs the function of a kind of flux. It lowers the temperature of the melting phase formation, which ensures a strong sintering of the ceramic material (catalyst) particles to each other. Hereby, there is a formation of a stable framework without a noticeable reduction of the catalyst working surface. The addition of zirconium oxide as an alloying agent provides an increase in the depth and degree of annealing of imperfections during the restructuring of the catalyst structure. Additionally, it provides the redistribution of the released energy. This assumption is confirmed by increasing of the alloyed catalyst granules mechanical strength. The results of research can be used for development and modification of iron-oxide catalysts for dehydrogenation of olefinic and alkylaromatic hydrocarbons.

Salient features of deactivation of an iron oxide catalyst for dehydrogenation of methylbutenes to isoprene in industrial adiabatic reactors

The problems of deactivation of iron oxide catalysts in the process of industrial dehydrogenation of methylbutenes to isoprene have been considered. The dependence of deactivation of the catalyst fixed bed on the time on-stream of different sections of the catalyst along the reactor height has been examined. The cause of poor performance of a part of the catalyst bed has been revealed and substantiated. Based of the results of the study, the authors propose an approach to predicting the catalyst performance during a long time on-stream.

Distribution of alkaline promoters within the structure of iron oxide catalyst for dehydrogenation

Along with potassium, cesium is an efficient promoter of catalytic activity of iron oxide catalysts for dehydrogenation of olefins and alkylaromatic hydrocarbons. In the reaction medium, a catalyst is a ferrite system consisting of potassium β″-polyferrite, potassium and cesium monoferrites, and magnetite. The character of the distribution of alkaline promoters within the catalyst structure is studied to provide the theoretically substantiated calculation of the optimal composition of this type of catalysts. The preferred location of cesium ions is shown to be the structure of β″-polyferrite of K2 − zCszFe2+Fe103+O17 composition. The catalytic activity of this system with different contents of cesium in the dehydrogenation of ethylbenzene to styrene (flow-type reactor; 0.1 MPa; 600°C; hourly space velocity of ethylbenzene, 1 h−1; ethylbenzene : steam weight ratio, 1 : 3) was tested. The maximum specific rate of styrene formation is attained at a Cs : Fe ratio in the interval 0.023–0.027, corresponding to the coefficient z = 0.26–0.30. It is impractical to introduce more cesium. Theoretical propositions for targeted transporting of a promoting agent to a given phase of a catalytically active ferrite system are developed. The content of expensive cesium compounds in iron oxide catalyst is optimized.

Selecting the conditions of molding iron oxide catalysts for dehydrogenation

The effect of the conditions for molding iron oxide catalysts for dehydrogenation of isoamylenes to iso� prene on their operation characteristics was studied. The investigation of laboratory samples allowed us to deter� mine the optimum molding pressure (200-250 MPa) under which high mechanical strength (strength factor KG = 33.4-37.3 N/mm), the stability of the kinetic characteristics in the dehydrogenation reaction, and the formation of 15-50 nm pores, ensuring the occurrence of the process in the kinetic region, were attained. we propose using the extrudate density as an indirect criterion for estimating the molding pressure under industrial conditions of extrusion. It was shown that in order to develop high strength properties (KG ~ 29.1 N/mm) of the catalysts upon their production under industrial conditions and to ensure the occurrence of the reaction in the kinetic region, the extrudate density must be 2.40-2.46 g/cm 3 . The obtained results were verified via paste molding on various indus� trial extruders, thereby enabling us to recommend the type of molding extrusion equipment.

Effects of cracking and coke formation on the selectivity of iron oxide catalysts in the dehydrogenation of methylbutenes to isoprene

The contributions of cracking and coke formation reactions to a decrease in the selectivity of domestic and imported catalysts for the dehydrogenation of methylbutenes (isopentanes and isoamylenes) into isoprene have been determined. It has been found that hydrothermal treatment in industrial reactors favorably affected an increase in the catalytic characteristics of a domestic iron oxide catalyst for dehydrogenation. The conditions for catalyst activation have been optimized with respect to the temperature and duration of hydrothermal treatment.

Transformation of the phase structure of an iron oxide catalyst for dehydrogenation of methyl butenes under industrial exploitation conditions

X-ray phase, differential-thermal, and elemental analyses were used to study the transformation of the phase structure of an iron oxide catalyst for dehydrogenation of methyl butenes after exploitation.

A study of the action of magnesium on iron oxide catalysts for dehydrogenation of ethylbenzene to styrene

Mossbauer study of the action of magnesium on iron oxide catalysts for the dehydrogenation of ethylbenzene to styrene has been carried out systematically. The presence of opportune amount of Mg enhances the stability and dispersivity of catalysts. Therefore Mg is one kind of useful structure promoter.

The effect of cerium on iron oxide catalysts for dehydrogenation of ethylbenzene

In situ Mössbauer study of ethylbenzene dehydrogenation on potassium-promoted iron oxide containing different contents of cerium oxide has been investigated. The results show that the addition of cerium to the FeK systems decreased the hyperfine magnetic fields for Fe 3+ ions, due to the near neighbor and next near neighbor of Fe 3+ ions to be partially occupied by cerium ions. In addition, the presence of cerium enhanced the stability of the FeK phase and reducibility of Fe oxide to Fe 3O 4 at the reaction condition.

Influence of carbon dioxide addition upon decay of activity of a potassium-promoted iron oxide catalyst for dehydrogenation of ethylbenzene

In the catalytic dehydrogenation of ethylbenzene to styrene, the detailed influence of the addition of carbon dioxide upon the decay of activity of commercial potassium-promoted iron oxide catalyst has been investigated in the presence of steam. In addition, the rates of potassium component losses from the catalyst bed were experimentally determined by measuring potassium concentration in the layer of condensed water from the effluent during the catalytic reaction. The close correlation between the rate of potassium loss and decay of catalytic activity suggested that catalyst deactivation is mainly due to a decrease in the amount of potassium ferrite (K 2Fe 2O 4) which plays an important role, providing active sites for the catalytic reaction of ethylbenzene dehydrogenation. Furthermore, the addition of small amounts of carbon dioxide to reactant feed gas (in concentrations ranging from 0.1 to 0.5 mol-% of CO 2/total mol of feed) resulted in a slight decrease in the rate of styrene formation; however, it was found to be effective to a certain extent for depression of the decay of the catalyst's activity.

Activity decay of potassium-promoted iron oxide catalyst for dehydrogenation of ethylbenzene

The decay of activity of a commercial potassium-promoted iron oxide catalyst for ethylbenzene dehydrogenation was examined continuously over a period of about 1000 h at 630, 640 and 650°C in the presence of steam using a differential reactor. Initially, the activity of the catalyst decreased slowly and the deactivation rate was gradually increased. On the basis of information obtained from physico-chemical analysis of the used catalyst samples, it is speculated that the gradual loss and migration of potassium promoter from the surface of the catalyst pellet is the major cause of the decay in catalytic activity. A deactivation kinetic model is presented which is based on a decrease in the potassium promoter with process time. This kinetic model was in fair agreement with the experimental data relating to catalyst deactivation.

Roles of potassium in potassium-promoted iron oxide catalyst for dehydrogenation of ethylbenzene

Experimental kinetic data on the dehydrogenation of ethylbenzene over potassium-promoted iron oxide catalysts containing various amounts of potassium were obtained in the temperature range 550–620 °C. Unimolecular reactions for the formations of styrene, benzene and toluene on the different sites, where potassium reduced the activation energies, were considered on the basis of Langmuir-Hinshelwood type mechanism. Using a method of in situ catalyst deactivation with CO 2, potassium ferrite formed in the surface of the catalyst under reaction was suspected to take part in the formation of the active sites.

Active phase in potassium-promoted iron oxide catalyst for dehydrogenation of ethylbenzene

Effects of steam and CO 2 treatments of the potassium-promoted iron oxide on the dehydrogenation activity and the crystal structure were examined at 620 °C. The steam treatment remarkably increased the activity for the formations of styrene, benzene and toluene, while the CO 2 treatment decreased the activity. The crystal structure and surface state of the catalyst were investigated by using XRD and XPS. Potassium ferrite of cristobalite type structure formed on the surface of iron oxide was presumed as an active phase for the reactions.

Iron Oxide Catalysts for Dehydrogenation of Ethylbenzene in the Presence of Steam

Abstract Catalyst research for ethylbenzene (EB) dehydrogenation has been interest to many chemical manufacturers because styrene monomer is such a large-volume chemical and a steady growth of styrene markets is predicted. EB is relatively easy to dehydrogenate and the reaction may be effected by a simple thermal gas-phase process as observed by Berthelot in 1869 [l]. However, a much higher selectivity to styrene is obtained by contact catalysts. The historical evolution of EB dehydrogenation processes has been summarized by Kearby [21 and others [3].

Effect of Potassium Promoter on Iron Oxide Catalysts for Dehydrogenation of Ethylbenzene to Styrene

Abstract The catalytic activity and the sintering property of iron oxide catalysts with and without potassium additives have been studied. The potassium oxide acts as a promoter and is effective under given conditions in increasing the activity of the catalyst from four to ten times. The effects of the promoter can be classified thus: (1) Structural promoter: The increase in the apparent bulk density and the shrinkage of the catalyst tablet upon calcination during the preparation of the catalyst are prevented by potassium additives. The differences in the specific surface area and in the pore volume of the catalyst between with and without potassium promoter are slight. These effects on iron oxide appear to be caused largely by the formation of K2Fe22O34. (2) Synergetic promoter: The potassium promoter changes the apparent energy of activation of the dehydrogenation reaction from 28 to 43 kcal/mol. The increase in the catalytic activity is due to the increase in the pre-exponential factor. The increase in the factor can be explained in terms of the higher concentration of the active center produced by the interaction of the potassium promoter with iron oxide. (3) Selectivity promoter: The formation of benzene by a side reaction is retarded by potassium additives.

Effect of matrix promoters in iron oxide catalysts for dehydrogenation of ethylbenzene

Effect of matrix promoters in iron oxide catalysts for dehydrogenation of ethylbenzene