MXPA99008058A - USE OF Ce/Zr MIXED OXIDE PHASE FOR THE MANUFACTURE OF STYRENE BY DEHYDROGENATION OF ETHYLBENZENE - Google Patents

Abstract

The present invention relates to an improved active support, cerium/zirconium mixed oxides or cerium/zirconium solid solutions, for improved dehydrogenation catalysts useful in converting alkylaromatics to alkenylaromatics, e.g., ethylbenzene to styrene.

Description

USE OF MIXED OXIDES PHASE OF Ce / Zr FOR THE MANUFACTURE OF STYRENE BY DETERMINING ETHYLBENZENE Field Teppi co The present invention concerns an improved active support, mixed cerium / zirconium oxides or solid solutions of cerium / zirconium, for catalysts of dehydrogenation useful for converting alkyl aromatics to alkenyl aromatics, for example ethylbenzene to styrene.

BACKGROUND OF THE INVENTION The most common catalysts used in the industry to make styrene by dehydrogenation of ethylbenzene are based on iron (Fe), potassium (K) and cerium (Ce). The preparation of these catalysts consists in reacting a basic potassium salt, such as potassium carbonate, with an organic iron salt, EDTA for example. A possible active phase for the catalysis of the dehydrogenation of ethylbenzene can be K2Fe05. It has been discovered that cerium oxide has an effect on improving the yield and selectivity of the Fe / K based catalyst system. In the so-called bulk or bulk catalyst, the amount of cerium is generally from about 5 to about 10% by weight. See U.S. Patent 5,171,914, Shell Oil Co., issued August 30, 1991; the North American patent -No. ,023,225, United Catalysis, Inc., issued July 21, 1989; and German Patent DE 3,506,022, BASF A.G., issued February 21, 1985. The cerium source used to make the catalyst can be cerium carbonate which is mixed together with the suspension of iron and potassium salts.

Then, the suspension is calcined at high temperature, up to approximately 800 ° C. This temperature is required to prepare the active phase of iron / potassium and to obtain cerium oxide (Ce02). Like any catalyst, a high surface area and thermal stability are necessary in order to obtain superior activity. However, the calcination of salts does not necessarily lead to high surface area materials. In addition, it was more recently discovered that a higher cerium content compared to bulk catalysts can improve the selectivity and yield of the reaction. See German patent DE 3,521,766, BASF AG, issued June 19, 1985 and U.S. patent 4,758,543, Dow Chem. Co., issued July 19, 1988. As conclusion of these studies, cerium oxide could be used as support for the active phase of Fe / K. However, the standard cerium oxide material has shown very poor thermal stability at high temperature, particularly at temperatures above 800 ° C. Some additional cerium-based compounds have also been used. For example, cerium phosphate and Ce-Zr phosphate were found to be good catalysts for the oxydehydrogenation of alkyl aromatics and alkylpyridines. See U.S. Patent 3,733,327, Dow Chemical Co., issued June 28, 1971. In addition, it has been considered that the oxygen storage capacity (OSC) of ceria is responsible for the activity of the cerium-T oxide. Thus, the materials of higher CSOs can be taken into account for styrene catalysis. One of the effects of ceria is the decoking or decoking of the catalyst that can be poisoned or inactivated after a period of time under reducing conditions. It is an object of the present invention to use stabilized Ce / Zr mixed oxide phases or solid solutions as active supports of a Fe / K based catalyst for the manufacture of styrene by dehydrogenation of ethylbenzene. The mixed oxides of (Ce, Zr) 02 and preferably solid solutions exhibit a very high thermal stability at high temperature as opposed to pure Ce02. They also show an improved OSC compared to ceria. These materials can be obtained by co-precipitation and co-thermolytolysis.

BRIEF DESCRIPTION OF THE INVENTION The present invention is concerned with an improved active support, mixed cerium / zirconium oxides for improved dehydrogenation catalysts useful for converting alkyl aromatics to alkenyl aromatics, for example ethylbenzene to styrene. Unless - stated otherwise, all parts, proportions or percentages are by weight. "Comprising" as used herein means several components that can be used together. Thus, the terms "consists essentially of" and "consisting of" are contained in the term "comprising".

DETAILED DESCRIPTION OF THE INVENTION The thermal stability of inorganic compounds can be defined as the stability of the surface area when the material is aged at a high temperature. For many applications, particularly catalysis, a high surface area and highly stable materials are required by end users. According to the present invention, "mixed oxides of cerium and zirconium and solid solutions having good thermal stability are produced." The present invention is concerned with an improved active support, mixed cerium / chloroconium oxides or solid solutions of cerium / zirconium, for improved dehydrogenation catalysts useful for converting alkyl aromatics to aromatic alkenyl, preferably ethylbenzene to styrene The phases of mixed oxides of stabilized Ce / Zr or solid solutions are preferably used as active supports for a catalyst based on Fe / K for the preparation of styrene by dehydrogenation of ethylbenzene. The mixed oxides of (Ce, Zr) 02 and preferably solid solutions exhibit a very high temperature thermal stability at high temperature as opposed to pure Ce02. They also demonstrate an improved CSO with respect to ceria. These materials can be obtained by co-precipitation and co-thermohydrolysis. The mixed oxides of (Ce, Zr) 02 and solid solutions are formed by conventional processes such as co-thermohydrolysis or co-precipitation. Each of these processes is described generally separately later herein.

Co-thermohydrolysis The first step of the co-thermohydrolysis process involves the preparation of a mixture in aqueous medium of at least one soluble cerium compound, preferably a salt and at least one soluble zirconium compound, preferably a salt. The mixture can be obtained either from solid compounds which are dissolved in water or directly from aqueous solutions of these compounds, followed by mixing in any order of the defined solutions. "Of the water-soluble cerium compounds, one example is the Ce IV salts, such as nitrates in which ceric ammonium nitrate is included, which are suitable for the present invention. Preferably a cerium nitrate is used. The saline solution of Ce IV may contain some Ce III. However, it is preferred that the salt contain at least about 85% Ce IV. An aqueous solution of cerium nitrate which is obtained by the action of nitric acid on a ceric hydrated oxide, prepared by a standard reaction of the Ce III saline solution, carbonate prepared for example in a conventional manner, for example by the action of nitric acid on the waxy carbonate and addition of a solution of ammonia in the presence of an oxidizing agent, preferably hydrogen peroxide. It is also possible to use ceric nitrate solutions obtained by the electrolytic oxidation of a waxy nitrate. The aqueous solution of Ce I ¥ salt may have some free acid, for example of a normality ranging from about 0.1 to about 4 US. In the present invention, it is possible to use either a solution containing some free acid or a preneutralized solution by addition of a base, such as an aqueous solution of ammonia or alkali hydroxides, for example sodium, potassium, etc. Preferably, an ammonia solution is used to reduce free acidity. In this case, it is possible to define the neutralization speed (r) of the initial solution by means of the following equation: r = (n3 - n2) / n where neither represents the total number of moles of Ce IV present in the solution after neutralization, n2 represents the number of OH ions "effectively used to neutralize the initial free acidity of the aqueous solution of Ce IV and n3 represents the number total moles of OH ions "of the added base. When a neutralization step is used, excess base can be used in order to ensure complete precipitation of the Ce (0H) 4 species. Preferably, r is less than about 1, more preferably about 0.5. The soluble zirconium salts used in the invention can be, for example, zirconium sulfate, zirconyl nitrate or zirconyl chloride. The amount of cerium and zirconium contained in the mixture corresponds substantially to the stoichiometric ratio required to obtain the final desired composition. Once - that the mixture is obtained it is then heated. This heat treatment called te-ppohydrolysis is carried out at a preferred temperature of between about 80 ° C and the critical temperature of the reaction medium, usually between about 80 and about 350 ° C, more preferably between about 90 and about 200 ° C. The heating step can be carried out under an atmosphere of air or under an inert gas such as nitrogen. Any suitable reaction time can be used, usually between about 2 and about 24 hours. The heat treatment may be carried out under atmospheric pressure or under any higher pressure, such as saturated vapor pressure. When the temperature is higher than the reflux temperature of the reaction medium (usually greater than about 100 ° C), for example between about 150 and about 350 ° C, the reaction is carried out in a closed reactor or autoclave. The pressure can be equal to the autogenous pressure and can be correlated with the chosen temperature.It is also possible to increase the pressure in the reactor.If required, some additional base can be added directly after the heating stage to the reaction medium for the purpose of improving the reaction yield After the heating step, a solid precipitate is recovered from the reactor and separated from the mother liquor by any known process, for example filtration, settling or centrifugation. in another embodiment the precipitate is then dried, under air conditions for example at a fluctuating temperature of about 80 at about 30 ° C; preferably from about 100 to about 150 ° C. The drying step is preferably carried out until substantially no weight loss is observed. After the optional drying step, the recovered precipitate is then calcined. This allows the formation of a crystalline phase. Usually, the calcination is carried out at temperatures ranging from about 200 to about 1000 ° C. The calcination temperature is usually greater than about 300 ° C and preferably ranges from about 400 to about 800 ° C.

Co-precipitation The first step of the co-precipitation process is the preparation of a mixture in an aqueous medium of at least one soluble cerium compound, preferably a salt and at least one soluble zirconium compound, preferably a salt or both. The mixture can be obtained either from solid compounds that are dissolved in water or directly from aqueous solutions of these compounds, followed by mixing in any order of the defined solutions. The cerium salt solution used can be any aqueous cerium salt solution, in the wax and ceric state which is soluble under the preparation conditions, in particular a waxy chloride or cerium nitrate solution in the wax or ceric state or a mixture of the -isms. The zirconium salt solution used can be any aqueous zirconium salt solution which is soluble under the conditions of preparation. Suitable water-soluble cerium compounds include Ce III salts, such as nitrates or halides such as chlorides for example. The soluble zirconium salts used in the invention may be nitrates, sulfates or halides, for example, zirconium sulfate, zirconyl nitrate or zirconyl chloride. Zr - (IV) salts can be used. The amount of cerium and zirconium contained in the mixture corresponds to the stoichiometric ratio required to obtain the desired final composition. It is preferable to use a cerium or zirconium salt with a high degree of purity, more preferably greater than about 99%. Optionally an oxidizing agent can be used.

Among the oxidizing agents that are suitable are the solutions of sodium, potassium or perchlorate of ammonium, chlorate, hypochlorite or persulfate, hydrogen peroxide or air, oxygen or ozone. An oxidizing agent, preferably hydrogen peroxide can be added to the cerium / zirconium mixture or to the cerium or zirconium salt before mixing. The amount of the oxidizing agent relative to the salts to be oxidized can vary within wide limits. In general, it is greater than the stoichiometric amount and preferably corresponds to an excess. The precipitation can be carried out by reaction of the solution or saline solutions and a basic solution. The basic solution can be added to the cerium and / or zirconium salt solution to precipitate the hydroxides or saline solutions can be added to the base solution. The base can be a solution of ammonia or alkaline hydroxide solution, for example sodium, potassium, etc. The base solution used can be in particular an acid solution of ammonia or sodium or potassium hydroxide. Preferably an ammonia solution is used. The normality of the base solution is not a critical factor according to the invention; It can vary within wide limits. The precipitation is carried out in batches or on a continuous basis. In the case of continuous precipitation, the pH of the reaction is maintained at a value between about 7 and about 11, preferably between about 7.5 and about 9.5. The residence time of the material in the reactor is normally at least about 15 minutes, preferably at least minutes. The reaction can be carried out at any appropriate temperature such as room temperature. In the case of batch precipitation, the amount of base added is preferably at least the amount required to precipitate Ce (OH) 4 and Zr (OH). After the reaction step, a solid precipitate is recovered from the reactor and separated from the mother liquor by any known process, for example filtration, «Settlement or centrifugation. The precipitate can be separated by conventional solid / liquid separation techniques such as decanting, drying, filtration and / or centrifugation. The precipitate obtained can then be optionally washed. The next stage of the process is the calcination of the material, either with or without an intermediate drying stage. This allows the formation of a crystalline solid solution phase. Usually, the calcination is carried out at temperatures ranging from about 200 to about 1000 ° C. Calcining temperatures greater than about -300 ° C are suitable, preferably ranging from about 350 to about 800 ° C. Usually, the mixed oxides of Ce / Zr and solid solutions are fine powders with a particle size of less than about 10 microns. They can be granulated or extruded by any of the known processes for preparing an active support. The dehydrogenation catalyst compositions of the present invention comprise the mixed cerium / zirconium oxide or solid solution as an active support, a catalytic iron component and a potassium catalytic promoter. In general, the catalyst compositions of the present invention comprise, by weight, from about 5% to about 30% of an iron catalyst component; from about 40% to about 60% of a potassium catalytic promoter and from about 10% to about 60% of the active support. The improved catalysts of the present invention are generally prepared by mixing the active support component, the catalytic iron component and the catalytic promoter (potassium compound) and any optional component followed by drying and calcination of the resulting mixture, preferably a a temperature of about 750 ° C or higher. In general, the calcination temperatures "fluctuate from approximately 500 ° C to approximately 800 ° C. The catalytic composition of the present invention can be prepared in various ways known in the art. One method comprises grinding in a ball mill a mixture of the desired compounds, adding a small amount of water and extruding the compound to produce pellets or small pellets which are then dried and calcined. Another method is to mix the components together with water, dry them to form a powder and form tablets. Another method involves mixing the components together with an excess of water, partially drying and then subsequently extruding, drying and calcining the resulting pellets. The dehydrogenation catalyst compositions of the present invention contain iron as an essential catalyst component. An iron salt such as iron citrate is a suitable catalyst component of iron. Many forms of iron oxide are used in the preparation of dehydrogenation catalysts and are suitable as catalytic components of iron. While various forms of the iron oxide may be employed in the compositions of the present invention, the preferred form employed in the catalytic compositions of the present invention is red iron oxide or a mixture of red iron oxide (Fe203) and oxide of yellow iron (Fe203.H20). The dehydrogenation catalytic compositions of the present invention may also contain one or more potassium compounds as the catalytic promoter. The potassium promoter material can be added to the catalyst in several ways. For example, it can be added as oxide or as other compounds that are convertible, at least in part, under roasting conditions to the oxide. Hydroxides, carbonates, bicarbonates and the like are suitable. The potassium compound is preferably present in the "catalyst as potassium carbonate (K2C03) or as a mixture thereof with potassium oxide." The catalytic iron and potassium promoter form oxides of catalytically active Fe / K.

Other known catalytic additives may be included in the catalysts of the invention but are not essential. Thus, an optional component of the catalytic composition of the invention is a chromium copolyate which serves as a stabilizer for the active catalyst components. Chromium compounds have usually been added to alkali-promoted iron oxide catalysts to extend or prolong their life. Chromium, as used in the compositions of this invention, may be added to the catalyst in the form of a chromium oxide or in the form of chromium compounds which decompose after calcination to chromium oxides, such as, for example, nitrates of chrome, hydroxides, acetates and the like. If potassium chromates are used, such materials can also contribute of course to the required concentration of potassium essentially present in the dehydrogenation catalyst compositions as discussed hereinabove. A second optional component, used to improve the selectivity of the catalyst is molybdenum which can be added as its oxide or as molybdate. The strength or physical strength, activity and selectivity of the catalytic compositions of the present invention can be improved by the addition of certain binding agents. Binders may include for example calcium aluminate or Portland cement. These cements can be added individually or in combination. The density of the catalyst compositions herein can also be modified by the addition of various fillers, for example, combustible materials such as graphite and methyl cellulose. Such materials may be added to the compositions during the preparation but are burned after the pellets or catalytic pellets have been formed during the calcination step. These auxiliaries that promote porosity can also facilitate the extrusion of the catalytic pellets. The catalysts of the present invention are especially effective in promoting the dehydrogenation of ethylbenzene to produce styrene. Such a dehydrogenation reaction is usually carried out at reaction temperatures of about 500 ° C to about 700 ° C. However, higher or lower temperatures may be used, as is known to those skilled in the art. The use of subatmospheric, atmospheric or super-atmospheric pressures is also appropriate. However, since it is preferable to operate at a pressure as low as possible, atmospheric or subatmospheric pressure is preferred. The process is preferably carried out as a continuous operation. It is preferred to use a fixed bed which may consist of a single "stage" or of a series of stages of the same catalyst in one or more reactors, steam / water may also be added to the hydrocarbon reagent feed to assist in the separation of the carbonaceous residues of the catalyst The contact time of the gas containing reagent with the catalyst is expressed in volume of liquid hydrocarbon reagent per volume of catalyst per hour The determination of the range of LHSV to effect the desired degree of conversion for the particular feed it is within the knowledge of the skilled in the art, any known method for the production of styrene can be used, U.S. Patent No. 3,733,327 issued to Vrieland et al., May 15, 1973, U.S. Patent No. 4,758,543. issued to Sherrod et al., July 19, 1988 and U.S. Patent No. 5,023,225 issued to Williams et al., e. June 11, 1991 contain descriptions of processes for the production of styrene and extension are incorporated herein by reference. The use of the active supports of the present invention or catalysts obtained from these materials after mixing or reaction with Fe and a K salt and / or after the treatment of these materials at high temperature and / or after the granulation or extrusion of these materials for the dehydrogenation of ethylbenzene to styrene obtains significant benefits that they are illustrated in the following examples. The following examples are provided to better describe the present invention. They are for illustrative purposes and it will be noted that changes and variations can be made with respect to these compositions that are not shown below. Such changes or variations that do not materially alter the compositions, formulation, process or function are still considered in the spirit and scope of the invention as cited by the following claims.

EXAMPLES A catalyst is prepared by mixing ceria (Ce02) with potassium carbonate and iron oxide (Fe203) to obtain the following composition: Fe203: 2.5% K20: 2.5% Ce02: 95% Another catalyst is prepared as previously described, but instead of ceria, a solid solution of (Ce, Zr) 02 containing 80% of Ce02 and 20% of Zr02 obtained by co-thermohydrolysis is used. The final composition is: Fe203: 2.5% K20: 2.5% Ce02: 76% Zr02: 19% ~ After grinding in ball mill, the mixed powders are calcined at a temperature of about 750 ° C for about 2 hours. The dehydrogenation of ethylbenzene is carried out in a 240 mm long 316L stainless steel tube with an inlet for the compounds to be hydrogenated and gases and an outlet for the compounds that reacted. The catalytic test is equipped with two chromatographs. The first has an FID detector (column filled with silicocel + 10% FFAP) and the second has a katharometer (column filled with Hayesep A). The reactor is heated with a fluidized sand bath. The catalyst is diluted in the reactor with glass beads.

Example 1: The reactor is charged with approximately 27.2 g of ceria-based catalyst (20 cm3). The temperature is adjusted to a temperature of about 550 ° C and a mixture of about 27.2 ml of water and about 15.63 ml of ethylbenzene per minute is sprayed into the reactor. The carrier gas is nitrogen with a flow rate of approximately 3.28 l / h. The pressure is slightly higher than atmospheric. The conversion and selectivity are measured after a 2 hour test run. The results are as follows: conversion: 60% selectivity of styrene 85.1%.

Example 2: The experiment of Example 1 is repeated with the catalyst based on (Ce, Zr) 02. The results are as follows: Conversion: 77.5% styrene selectivity: 90.0"" These results demonstrate the improvement due to (Ce, Zr) 02.

Claims (12)

1. Claims 1. A dehydrogenation catalyst characterized in that it comprises: an active support selected from the group consisting of: mixed cerium / zirconium oxides, solid cerium / zirconium solutions and mixtures thereof.
2. 2. A dehydrogenation catalyst prepared by a method characterized in that it comprises the steps of: a) mixing: i) an active support selected from the group consisting of mixed cerium / zirconium oxides, solid cerium / zirconium solutions and mixtures of the same; ii) a catalytic component of iron and iii) a catalytic potassium promoter.
3. 3. The method of compliance with the claim 2, characterized in that it further comprises the step of calcining the mixture at a temperature of approximately 750 ° C for about 2 hours.
4. 4. The method of compliance with the claim 3, characterized in that it also comprises the step of extruding the mixture.
5. 5. The method according to claim 3, characterized in that it also comprises the step of granulating the mixture.
6. 6. A method for preparing styrene characterized in that it comprises the step of converting ethylbenzene to styrene using a dehydrogenation catalyst comprising: an active support selected from the group consisting of: mixed cerium / zirconium oxides, solid solutions of cerium / zirconium and mixtures thereof.
7. 7. A method in accordance with the claim 6, characterized in that the reaction temperature fluctuates from about 500 ° C to about 700 ° C.
8. 8. A process for the preparation of styrene by the non-oxidizing dehydrogenation of ethylbenzene, characterized in that it comprises the steps of: contacting ethylbenzene and steam at a temperature ranging from about 500 ° C to about 700 ° C with a dehydrogenation catalyst comprising an active support selected from the group consisting of mixed cerium / zirconium oxides, solid cerium / zirconium solutions and mixtures thereof.
9. 9. The process according to claim 8, characterized in that the dehydrogenation catalyst further comprises a catalytic iron component and a potassium catalytic promoter.
10. 10. The process according to claim 9, characterized in that the iron catalyst component is a salt of iron or iron oxide and the catalytic promoter of "potassium is K2C03
11. 11. The process according to claim 9, characterized in that the catalyst of dehydrogenation is prepared by a process comprising the steps of: mixing the active support, a catalytic component of iron and catalytic potassium promoter and calcination of the mixture
12. 12. The process according to claim 11, characterized in that the mixture is calcined at a temperature of about 750 ° C for about 2 hours.