MXPA97001681A

MXPA97001681A - Catalysts for the dehydrogenation of ethylbenzene to stretch

Info

Publication number: MXPA97001681A
Application number: MXPA/A/1997/001681A
Authority: MX
Inventors: Cavalli Luigi; Rubini Carlo; Conca Esterino
Original assignee: Montecatini Tecnologie Srl
Priority date: 1996-03-08
Filing date: 1997-03-05
Publication date: 1998-04-01

Abstract

The present invention relates to catalysts in the form of cylindrical granules, suitable for the dehydrogenation of ethylbenzene to styrene and comprising, as a ferric oxide active component and promoters which are selected from the group consisting of alkali metal or alkaline earth metal oxides, oxides of elements of the series of chromium, tungsten and molybdenum lanthanides, characterized by the absence of macroporosities with a radius greater than 50,000 A and / or by the mechanical characteristics of resistance to axial breakage and abrasion.

Description

CATALYSTS FOR THE DEHYDROGENATION OF ETHYLBENZENE TO STYRENE DESCRIPTION OF THE INVENTION The present invention relates to catalysts which have a specific physical form and which are suitable for the hydrogenation of aluminum and styrene. and currently pending applicant, describes catalysts that have a complex geometric shape, by t-jempl «;« a hollow cylindrical shape with a circular cross section or muí ti lobulada, with perforations in the various lobes, obtained by compression molding of "tableting" powders, using a lubricant applied to the walls of the mold cane and to the punches or punches of the mold for protection The resulting catalysts are characterized by constant size parameters, high characteristics of abrasion and resistance to breakage and a very narrow pore radius distribution, by virtue of the aforementioned type of porosity and> ie the high ratio between the geometric area and the volum in the particles. I03 catalysts allow to considerably reduce the pressure drop that occurs REF: 24210 in a fixed bed reactor and significantly improve the catalyst activity and selectivity. In the patent literature with respect to the catalytic dehydrogenation of ethylbenzene to styrene. the interest has almost always been directed towards improving and optimizing the chemical composition, in order to achieve even more satisfactory yields. The improvements are generally obtained by varying the composition with respect to the main components or using different promoters. To date, limited attention has been paid to the geometry of the catalyst. The importance of the shape can be correlated directly with the pressure used in the process. Since the dehydrogenation reaction is accompanied by an increase in the equilibrium, a reduction in pressure facilitates the change of equilibrium towards the products (styrene and hydrogen), with a consequent improvement in transfusion. Therefore, it is desirable to modify the shape of the catalyst to allow a lower pressure operation (thus also reducing the pressure drop in the catalyst bed). In addition, the dehydrogenation reaction is carried out in the presence of steam to reduce the partial pressure of the styrene. to change the balance towards the styrene formation. In order to solve this problem, two modifications have been adopted with respect to the form: 1) The diameter of the null has been increased (up to 5 mm) without altering its length. This has solved the problem only to a very limited extent, since in fact a decrease in the pressure drop is obtained, due to the reduced bulk density (and therefore due to an increase in the empty fraction), but At the same time, the geometric surface exposed to catalysis has decreased. The result of these two contrasting effects has been a reduction in performance. 2) A trilobal or pentalobulated geometric shape has been introduced. • A slight improvement was achieved in this case. Nevertheless. 3e should bear in mind that the lobed shape has the disadvantage that powder is more easily formed, since the lobes are weak fracture points with respect to the solid cylindrical shape. At an industrial level, the process used to give shape to the catalysts is extrusion molding. It should be noted that this technologically simple process has a very important limitation: specifically, it does not allow to obtain complex geometrical shapes, particularly hollow shapes. With respect to the composition, the catalysts for the dehydrogenation of ethylbenzene to styrene comprise iron oxide, alkali metal or alkaline earth metal oxides and other oxides which are selected from the group consisting of cerium oxides. of molybdenum, tungsten and chromium. The life of the catalysts can be improved by adding chromium oxide as a stabilizer. U.S. Patent No. 3,360,597 describes catalysts containing 0.5 to 5 * of Cr70_. besides 80 to 90% of Fe-, 0 ^ and of 9 to 18 * of K-CO.,. The catalyst is prepared in accordance with a process that includes mixing, in water. of yellow iron oxide, chromium oxide and potassium carbonate to obtain a paste, from which the catalyst is obtained in the form of cylindrical granules by extrusion, drying and calcination. U.S. Patent No. 5,023,225 describes a catalyst for the dehydrogenation of ethylbenzene to styrene which is based on iron oxide, alkali metal or alkaline earth metal oxides, and cerium, molybdenum or tungsten oxide, characterized in that the iron oxide Yellow is mixed with small amounts of chromium oxide before molding the catalyst. The molding process is characterized by the iron oxide The mixture mixed with the xi or chromium is heated to a temperature of 300 1000 * 0 to be transformed into a red oxide before mixing the components in the form of a paste. The molding is done by extrusion. i. -3 dehydrogenation catalysts of the present invention have a hollow geometrical shape (with one or more perforations) obtained by compression moideadv (tableting), with a method in which the lubricant to be used does not it is dispersed in the DOIVO to be compressed (bulk lubrication), but it is applied to the walls of the molding chamber and to the punches or punches of the mold (external lubrication). The resulting catalysts have, C «J? with respect to those prepared by bulk lubrication, a greater porosity, a narrower pore radius distribution and a reduction in macroporosity. The porosity for 3 is generally between 0.15 and 0.35 cm / g (determined by mercury absorption). The surface area is usually between 1 and 6 rn ~ / g (determined by the method BET). The pore distribution curve does not include macroporosidadea with a greater average pore radius than 50,000 A. More than 0% of the porosity has an average radius greater than 600 A. More preferably, the average radius is between 800 and 1800 A.

In addition, catalysts have values of constant size raremeters. This constancy of the amaft • procedures can not be obtained with the milling process «:« which uses the internal lubrication, because they are ordered "• '-« riisiuerables microfractures in a part or all of the catalyst particle, causing fragility and L subsequent deformation of the same.Decid to these deformations, the process of compression molding that uses lubrication- in bulk, has never been used in the industrial practice for the production of hollow granular catalysts In addition, it has been found that the catchers according to the present invention are characterized by mechanical properties, particularly by a maximum axial tensile strength (in the direction of the axis of the perforations). considerably greater than that of the corresponding catalysts obtained by buit lubrication.The maximum tensile strength is greater than 15 N / particle and is preferably between 20 and 80 N / particle.The resistance to abrasion is also high. The percentage of dust is usually less than 3%. In the catalysts obtained by extrusion. The abrasion resistance is usually between 4 and Q% by weight. The catalysts according to the present invention, by virtue of the fact that they are hollow, allow to achieve a greater transformation, for the same weight, with respect to the catalysts in a solid form (ie without gaps or perfructions). In addition, the greater presence of voids provided by these catalysts allows operation. for an equal feed flow rate, at process pressures lower than those required when using solid form catalysts. The greater presence of voids allows operating with higher vapor / ethene ratios than those used with catalysts that have a solid form. thus obtaining a greater transformation for an equal process pressure. The weight ratio of steam / ethylene ibene used with the catalysts of the present invention is greater than 1.5 and may be up to 2.5 or more. The presence of perforations allows to work with a wall thickness smaller than that of the catalysts in a solid form and, therefore, to use the catalytic mass better. The minimum wall thickness that can be achieved with these catalysts is between 0.6 and 0.8 mm. For the same weight, the catalytic mass that can be used with the catalysts according to the present invention is at least 1.5 times greater than that of the solid form catalysts having an iameti or minimum J nim, which is compatible with l mechanical performance for use in practice. The pressure drop observed with ios The trilobulated form of taper in accordance with the present invention is at least 1.3 times less than i 'of the catalysts in a solid form for a surface of the surface. m tri exposed equal. The lubricants that can be used to prepare the catalysts according to the present invention include solids and liquids capable of reducing the coefficient of friction between the powder to be tableted and the parts of the tableting machine that make contact with said unit. Examples of suitable lubricants are stearic acid and palmitic acid; salts of alkali metals and alkaline earthquakes of these acids, such as magnesium stearate and potassium stearate: carbon black, talc, monoglycerides and tungsten glycerol such as glycerol monostearate and glycerol monooleate. paraffin oil and perf luoropol ethers. Liquid lubricants can be used in the form of solutions or in the form of systems dispersed in dispersing agents. The amount of liquid lubricant is usually between 0.Q25 and 25 mg per granule.

Used lubricants can be applied by sprinkling the formation chamber and the punches or punches; is d ^. 'go. f '- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - • - - The molding chamber and the drums can be manufactured from. or can be coated with. self-absorbing materials. such as p i i etraf luoroet i leño or cemiic material. This allows to avoid or reduce the use 0 of lubricants. The catalysts according to the present invention preferably have a hollow cylindrical shape with one or more perforations. In the case of catalysts with two or more perforations, the axes are substantially parallel to one another and to the axis of the granule and are substantially mutually equidistant. Preferably, the perforations have a circular cross section. In the case of catalysts with three perforations, the axes form, in relation to the cross section of the particle, the corners of a substantially equilateral triangle; said corners are oriented towards the points where the transversal section makes contact with the circumscribed circumference. The lobes of preference are cylindrical and circular, identical to each other and coaxial to the perforations. The granules can also have a substantially triangular cross section with rounded corners. The relationship between the placement of the perforations (ie, the distance between their respective is) and the diameter of said perforations. preferably it is between 1.15 and 1.5 and more preferably between 1.3 and 1.4. The relationship between the height of the particle and the placement of the perforations is preferably between 1.5 and 2.5 and more preferably between 1.7 and 2.3. In the case of catalysts having a circular cross section. the relationship between the radius of curvature of each lobe and the placement of the perforations, preferably between 0.6 and 0.9. more preferably between 0.7 and 0.8. The relationship between the radius of curvature of the lobes and the radius of the perforations is preferably between 1.3 and 2.7. more preferably between 1.8 and 2.10. The ratio between the radius of the circle circumscribed in the cross section and the radius of curvature of the circular lobes is preferably between 1.6 and 2. more preferably between 1.7 and 1.85. The surface to volume ratio of each granule in the multi-lobed version is preferably greater than 2.0 and more preferably greater than 2.2. In the case of catalysts having a triangular cross section, the ratio between the radius of curvature of each rounded corner and the placement of the perforations is preferably between 0.6 and 0.9 and more preferably < = 'ntre 0.7 and 0.8. The relationship between the radius of the circle circumscribed to the cross section and the radius of curvature of each rounded corner, preferably it is between 1.6 and 2, more preferably between 1.7 and 1.85. The relationship d? surface with respect to volume of each granule, in the version having a triangular cross section, preferably is greater than 2.0, more preferably greater than 2.2. In preparing the catalysts according to the present invention, the powder containing the precursors and / or the active components of the catalyst is mixed dry or mixed with the addition of a small amount of water, to obtain a mixture containing the uniformly distributed components. The resulting mixture is subjected to desiccation and / or to a calcination cycle at temperatures between 120 and 1000 * C for a time that is sufficient to remove water and volatile decomposition products.

The pressure imposed by the generators is less than 15 kg / cm "and can reach 1000 kg / cpr or more, and has been found, and this constitutes an additional aspect of the present invention. that the catalytic testers with the mechanical characteristics, for the maximum resistance to axial traction. that fall within those catchers that can be obtained by molding with external lubrication, can also be achieved by shaping using lump lubrication, as long as the powder, before :: conformed is subjected to thermal treatments capable of ensuring that the decomposition reactions will occur with the weight loss that occurs before the moiding stage. In this case, the internal lubricant 1. 5 uses on an amount that is less than 5% by weight. The resulting powder is suitable for preparing granules of the desired shape and size, using the compression molding method. After molding, the granules are calcined at a temperature of 600-900"C. Promoters and stabilizers, such as calcium, magnesium, chromium, molybdenum, and tungsten oxide, can be distributed in the mass of the null graph or on its surface, it is possible to use several methods to provide the surface deposition of the desired components. For example, the component or components can be sprayed onto the granules during tabletting, after the external lubrication step. It is also possible to use a lubricant which acts as a precursor of the desired component, for example alkali metal and alkaline earth metal stearates. These compounds, after calcination, are transformed into the corresponding mixed oxides or oxides or salts. It is possible to use other mixtures of lubricants and oxides or other catalytically active compounds and spray a thin layer on the surface of the granules during molding. As an alternative it is possible to coat the catalyst granules with a thin layer, carrying out a step separately from the tabletting and afterwards. According to a preferred method, the catalyst granules at the exit of the calcination stage are treated, while being heated to a temperature of 80-200'C. with a solution or dispersion of the promoter and stabilizing oxides or metal salts, by means of a nebulizer. The concentration of the dispersion, the contact time and the temperature at which the deposition is made can be changed in such a way as to ensure rapid and complete evaporation of water and other dispersing liquids. in order to form a surface layer having a desired thickness, generally between 0.1 and 100 microns. In terms of weight of the final composition, expressed as oxides. the catalysts comprise 50-92 * ferric oxide, 5-20% alkali metal oxide, 0.5-14% alkaline earth metal oxide. of 2-10% oxide of elements of the lanthanide series, of 0.5-6% oxide of a metal of group six of the periodic table of the elements. Potassium oxide is preferred among the alkali metal oxides, while magnesium oxide and calcium oxide are preferred among the atherous earth metals. Cerium oxide is preferred among the oxides of the lanthanide series and the molybdenum and tungsten oxides are preferred among the oxides of group six of the periodic table of the elements. It is possible to use, for example, ferric hydroxide, ferric nitrate or ferric carbonate, potassium hydroxide or carbonate, cerium carbonate or ammonium molybdate as precursors of the active components. A representative composition but not limiting. is the following, expressed as oxide in percent by weight: Fe_03 = 78%; K, 0-12%; CeOn = 5%; Mg = 2%: W0_ = 0.9%; Mo03 = 2.1% Another representative composition. again expressed as a percentage of oxides by weight, it is as follows: Fe 0_ = 74%; K-0-6%; CeG -10%; MgO-4%; WO-6% Catalysts having a non-uniform composition, obtained by surface deposition of the promoter and the stabilizing components on the granules, contain 40-95% iron oxide, 5-30% alkali metal oxide, 0.05-4% alkaline metal oxide, 0.1-10% oxide of an element of the lanthanide series, 0.05-4% chromium oxide, molybdenum oxide or tungsten oxide. In particular, potassium oxide, calcium oxide, magnesium oxide, cerium oxide and chromium, molybdenum and tungsten oxides are preferred after iron oxide. Following are preferred, but not limiting, examples of compositions. The asterisk indicates that the component can be deposited on the surface.

LD y-e n% K O S? eu% Maü% CaO * Cr_ Cu% MoO -,% W0 2 ¡0.0 * ¡/ /: 2.1 «0.9 14 0.1 '2' 0.9 '4.5 4.0! / - 5.8 7 I? • 2 j 0.1 * / H ¡0.1 * ^ 0.9 U 2.3 0.1 *; 0.1 * Ü 78 4.6 0.1 0.1 '0.1' 0.1 The reaction for the dehydrogenation of ethylbenzene to styrene. it is usually carried out at a temperature of 540 to 650 * C, at pressures that are greater, less or equal to the atmospheric pressure. Low pressures are preferred for thermodynamic reasons, since these allow higher conversions for an equal temperature. The following examples are presented to illustrate and not limit the present invention. Analytical determinations The maximum axial tensile strength was determined in accordance with ASTM D 4179/82; 3ß determined id apparent density (with aseptañepto per blow) in accordance with i ASTM D 164 / '32. Comparison Example 1 A slurry was prepared by mixing ferrous oxide. cerium carbonate, magnesium carbonate and o, of tungsten with an aqueous solution of otasium hydroxide. to obtain a fine catalytic product having the following composition ^ expressed in% by weight of xides). i or oxides% Faith., 0. 76.1 K2 ° 14.0 15 CeO. i, 6.5 MgO 2.5 WO, 0.9 The paste was extruded from granules with a length of 5 mm and a diameter of 3.5 mm. The 20 extruded granules were dried at 150 ° C for 16 hours and then calcined at 400 ° C for 2 hours. Some of the granules were calcined at 700 ° C for 2 hours.These granules are the catalyst 1.

EXAMPLE 1 A second part of the granules prepared according to comparison example 1 was milled and the powder subjected to tabletting, using stearic acid as external lubricant. The puncher and cylindrical chamber of the tableting machine were coated with a thin layer of stearic acid, applied continuously by a current of air. Cylinders of 4 mm in length were punched with a perforation of 2 mm in diameter. The pressure used was 500 kg / cm. The cylindrical granules were calcined at 700 * C for 2 hours. This is the number 2 catalyst. The maximum axial tensile strength of this catalyst was 13.4 N / particle. Example 2 A second part of the granules prepared according to Comparison Example 1. was milled and subjected to tabletting (with external lubrication using stearic acid) in a trilobal form with three parallel perforations having an internal diameter of i.3 mm. with all 3 ios wall thicknesses of 0.8 mm, a radius of circumference of 2.5 mm and a height of 5 mm. The perforations were located in the corners of an equilateral triangle. The tablets were calcined at 700 * C for 2 hours. This is the number 3 catalyst. The maximum axial tensile strength of this catalyst was 20.9 N / particle. Example 3 A catalyst with the following composition by weight, expressed as oxides, was prepared by the method of Comparison Example 1: Fe2C > 3 »74.5%; K20-6.1%: CeO * 9.ó%; MgO-4.0%; W03 = 5.8% Fe ^ O, in the red spheroidal form as Fe.O, was used. The K20 was introduced in the form of KOH. The calcination was carried out at 800 ° C for 4 hours. This is the catalyst number 4. Example 4 Part of the grains prepared according to Example 3. were milled and tabletted according to the method of Example 2, to obtain trilobal granules with three perforations, having the characteristics specified in Example 2. Magnesium stearate was used instead of stearic acid as an external lubricant.

The maximum axial tensile strength of this catalyst was 32 N / particle; 38% of the volume was comprised by pores with a radius of 600 to 800 A, 11% by pores with a radius of 800 to 1000 A, 12% by pores that have a radius of 1000 to 2000 A, and 6 % by pores with a radius of 2000 to 4000 A. There were no macroporosities with a radius greater than 50000 A. The surface area of the catalyst was 4.9 m / g; the porosity was 0.17 ml / g. This is the catalyst number 5. Example 5 The catalysts number 1, 2. 3, 4 and 5 were tested in a steel reactor with an internal diameter of 35 mm. In each test, 200 cm of the catalyst was placed in the reactor, held in a steel grid. Tests were carried out at 570 ', 590 * and 610 * C for each catalyst; in these tests, water vapor and ethylbenzene, preheated to the above temperatures, were passed through the catalytic bed with a water / ethylbenzene ratio of 2.4 by weight; the exit pressure was 1.05 atmospheres and the space velocity per hour of the eti ibenzene was 0.5. Samples of the reaction products were collected more than 2 hours after the system had stabilized for at least 20 hours for each condition. The percentages of transformation and molar selectivity are listed in the table below.

Temperature "C% Transformation,% Selectivity Ca. 1 570 50.31 93.30 BD = 1.08 '590 62.47' 91.34 610 74.62 | 88.05 Cat. 2 570 54.66 93.34 BD - 1.01 590 64.85 91.52 j_ Cat. 3 570 55.12 93.53) BD = 0.857 590 65.43 91.70 610 76.17 89.08 1 Cat. 4, 1 570 60 i 88 BD - 1.42 i, 1 Cat 570 60 90.5! BD «1.08 BD «bulk density in g / ml. It is noted that in relation to this date. The best method known by the applicant to carry out the aforementioned invention is that which is clear from the present description of the invention. Having described the invention as an antecedent, what is contained in the following is claimed as property.

Claims

CLAIMS i. Catalysts in the form of granules that have a defined cylindrical shape. r view with one or more perforations. which are useful in the dehydrogenation of ethenebenzene to styrene. characterized because < -: > ? nr end n as active components. ferric oxide and promoters which are selected from the group consisting of alkaline and alkaline earth metal oxides, lanthanide oxides and chromium, tungsten and molybdenum oxides. obtained by compression molding of powders of the precursors and / or of the 3 active components, using for lubrication a lubricant that is applied to the walls of the chamber of moiaeado and to the punches or punches of the mold.
2. Catalysts in the form of granules having a defined cylindrical shape, provided with one or more perforations, which are useful in the dehydrogenation of ethylbenzene to styrene, characterized in that they comprise, as active components, ferric oxide and promoters selected from the group which consists of oxides of alkaline and alkaline earth metals, oxides of Ine3 of lanthanides and oxides of chromium, tungsten or molybdenum, which have a porosity between 0.15 and 0.35 crrT / g and where, in the distribution curve of the radius of pores, more than 50% of the pores have a radius greater than 600 A and where there are no macroporosities with a radius greater than 50,000 A.
3. Catalysts according to any < ie claims 1 and 2. characterized because they are in the form of cylindrical granules with one or more "-rf": "clusters that are parallel to one another and to the axis of the crane.
4. Conflict catalysts with any of claims 1 and 2. characterized in that they have the form of lobe-filled granules, with lobes that are coaxial with the perforations.
5. Catchers in accordance with the indication 4. provided with three perforations, characterized in that the relationship between the placement of the perforations and the diameter thereof is between 1.15 and 1.5 and the relationship between the height of the granules and the placement of the perforations is between 1.5 and 2.5.
6. Cylinders in the form of granules having a defined cylindrical shape, provided with one or more perforations, which are useful in the dehydrogenation of ethylbenzene to styrene and which comprise as active components, ferric oxide and promoters which are selected from the group consists of alkali and alkaline earth metal oxides, oxides of the lanthanide series and chromium, tungsten and molybdenum oxides. characterized because they have a maximum resistance to the axial traction (in the direction of the e of the e ..- c? < .nß) greater than 15 N part ícuia.
7. Cat. S in accordance with claim 6. characterized in that the maximum tensile strength is between 20 and 80 N / particle.
8. Catalysts according to any of claims 7 and 7, characterized in that they are in the form of lobe-shaped granules, with lobes that are coaxial with the axis of the perforations and wherein the relationship between the placement of the perforations and the diameter of the perforations. they are between 1.15 and 1.5 and the relationship between the height of the granules and the placement of the perforations is between 1.5 and 2.5.
9. A process for the dehydrogenation of ethylbenzene to styrene, characterized in that catalysts are used which are selected from those according to any of the preceding claims 1 to 8.
10. A process according to claim 9 »characterized in that the weight ratio of steam / ethylene benzene used in the dehydrogenation of ethyl benzene is greater than 1.5.