MXPA98010165A - Catalytic carrier - Google Patents

Abstract

A process for the production of an alumina-based catalyst carrier in which a carrier body baked with a source of titania is impregnated in a liquid medium that upon titania produces heating and then calcined to generate titania uniformly dispersed in the carrier in an amount of up to 10% in pe

Description

CATALYST CARRIER FIELD OF THE INVENTION This invention relates to catalyst carriers specifically to catalyst carriers based on ceramic components, such as alumina, which can be used as supports for metal catalyst and metal oxide components, useful in a variety of chemical reactions.

BACKGROUND OF THE INVENTION The use of ceramic-based carriers and specifically carriers of alumina-based catalysts has been previously described in several patents including U.S. Patent Nos. 5,100,859; 5,055,442; 5,037,704; and 4,874,739. Such carriers have a wide variety of possible applications in the catalytic field and are especially useful where the alumina base is alpha-alumina. The catalyst support needs to have, in combination, at least a minimum surface area on which the catalyst component can be deposited, high water absorption and crushing resistance. The problem is that usually the increase of one property can mean the reduction of another. In this way, the high crushing resistance can mean low porosity. Often, equilibrium is achieved by trial and error making the technique of catalyst carriers even more unpredictable than another technique of chemical procedures. Carriers based on alpha-alumina have an excellent balance of crushing strength, abrasion resistance, porosity and catalytic performance which makes them ideal for a variety of catalytic applications. It has been found that physical properties can be improved by incorporating a titania component into the baked mixture to produce the carrier. Although it has been found that such modification with titania greatly improves physical properties, such as crushing strength and abrasion resistance, it has been found that it does tend to affect the dosage of the carrier structure and this can result in unacceptable properties. . This problem grows with the increasing concentration of added titania. There is therefore a considerable advantage in the provision of a process for the incorporation of a highly beneficial titania component without causing such densification.

DESCRIPTION OF THE INVENTION The present invention provides an improvement over the description in the application Serial No. 08 / 118,487 in the sense that teaches about the advantages of the addition of the titania component by an impregnation of the baked porous carrier before the deposition of a catalyst over the carrier. More specifically, the invention provides a process for the production of an alpha-alumina catalyst carrier comprising: a) forming a mixture comprising alumina components, ceramic binder, a lighted medium and optionally, organic combustion materials, optional forming materials and lubricants; b) forming the mixture as carrier bodies; c) drying and baking the bodies at a temperature of 1200 to 1500 ° C to form porous carrier bodies; d) impregnating the porous carrier bodies with a titania generator in a liquid medium; and then e) baking the impregnated bodies at a temperature sufficient to remove volatile substances and generate titania. In the discussion that follows, the invention will be discussed in terms of added "titania" because, after the baking operation, it is assumed, for the purposes of this application, that the titanium remaining in the carrier will be in the form of oxide. Since titania is not soluble in water, it must be introduced into the pores of the baked porous carrier, in the form of solution or sol. It should be understood, therefore, that any suitable soluble titanium salt can be used, provided that it decomposes to the oxide and leaves no residue or does not develop components that could interfere with the activity or performance of the catalyst deposited on the carrier. In this way, titanyl oxalate, bis (ammonium lactate) titanium (IV) dihydroxide or similar organic salts are suitable. In addition, the titania sols or the waterborne mixtures of typically decomposable titanium compounds are usable, provided they are sufficiently fluid to penetrate the pores of the carrier. It is also possible to use a titanium alkoxide or other organometallic compound in a suitable liquid carrier. In the context of this specification, it is understood that the term "titania generator" encompasses all such options, water mixtures and suitable salt sols which, under the conditions in which the carrier is produced, form titania. Generally, the use of a titanyl salt is preferred as the titania generator and the oxalate or the dihydroxy bis-lactate are the titanium salts plus the preferred ones because they are very soluble and because they decompose at relatively low temperatures of about 200 °. C-320 ° C. With decomposition, an amorphous titania base is formed, which generally has a very high surface area for optimal results. It is preferred to calcinate the impregnated carrier at a temperature equal to or greater than about 450 ° C-500 ° C at which the anatase form is generated. Heating to higher temperatures higher than about 773 ° C generates the rutile form. None of these consequences is disastrous, especially if a greater amount of titania is used towards the upper end of the preferred range, but it should be noted that prolonged exposure to higher temperatures can result in the completion of titania and crystal formation. bigger. This, in general, is not to be desired. Therefore, it is desirable to calcinate the impregnated carrier at a temperature of about 450 ° to 700 ° C, and more preferably from 500 to 600 ° C for a time of 15 to 20 ° C and preferably about 30 to 60 minutes. It is often considered advantageous to add the titania generator of an amount representing from about 0.05 to about 10%, and more preferably from about 0.1 to about 2.0% of the weight of the baked carrier (calculated as TIO2) • Generally, it gives little advantage of selectivity as a result of incorporating more than about 0.5% titania. The impregnation is preferably performed by immersing the carrier particles in a titania generator which is then decomposed to titania with absorbing the carrier particles. The baking of the impregnated carrier is carried out under conditions adapted to generate titania. In the presence of alumina, baking may result in the formation of aluminum titanate and this is generally less preferred than titania. Certain forms of alumina and binder material may contain titania as impurities or components. The contribution of such forms of titania in the amounts specified above is not included. The carrier is heated to a temperature that is high enough to concretize the alumina particles and produce a structure with adequate physical properties to withstand the environment in which it is expected to operate. In practice, temperatures of 1200-1500 ° C, particularly of 1300-1500 ° C, are used to carry out the concretion (lower temperatures usually require longer times to achieve the same degree of concretion as higher temperatures). ). The preferred catalyst carrier of the invention may comprise various alpha-alumina components chosen to contribute to the desired physical properties, including porosity, pore volume, crushing resistance and the like. A combination of two different alpha-aluminas is often preferred, having a component of larger particles mixed with a second component having smaller particles, with weight ratios of 10:90 to 90:10. The goal of this is to finish with the surface area (in that document, it is understood that a reference to "surface area" means the BET surface area which is measured using nitrogen or krypton as absorbed gas), in the finished product from 0.4 m / g to 5 m2 / g. The surface area in the finished carrier is slightly less than for the alumina-free particles. In this manner, a convenient mixture may comprise, for example, two types of alpha-alumina particles, the first having a surface area of about 1 m2 / g and the second measuring a surface area of 3 m / g to 5 m2 / g. . One can form part of the alpha-alumina in situ from a precursor which is preferably boehmite. Good results are also obtained if the precursor comprises a mixture of boehmite with an aluminum trihydrate, such as gibbsite or bayerite. When such a mixture is used, it is often preferred to use a weight ratio of the monohydrate (boehmite), to the trihydrate from 1:10 to 1: 3 and more preferably from 1: 8 to 1: 4. It is often preferred that, when a sol is formed from the precursor or the addition of water, a seed material with a submicron particle size is also added. These have the effect of reducing the temperature at which the transition to alpha-alumina occurs and reducing the crystal size of the alpha-alumina produced with the transformation. The seed used can be any material that is effective to produce the nucleation sites in the precursor, in order to reduce the transition temperature at which the transition alumina is converted to alpha-alumina. Seeds that meet this goal generally have the same type of crystal lattice as the alpha-alumina itself and network dimensions that do not differ much from those of alpha-alumina. Clearly, the most suitable seed is alpha-alumina itself and submicron-sized particles are the preferred seed. However, it is possible to use other seeds, such as alpha-ferric oxide and chromium oxide. The alpha-alumina formed from the preferred seed precursor, when the destroyed mixture is baked, generally has a much finer crystal size than the alpha-alumina particles with which the precursor is mixed with seed unless, During baking, keep it at high temperature for a prolonged period. As it is produced, the sol-gel material with seed has a submicron crystal structure, but it is maintained at temperatures of over 1400 ° C for prolonged periods.

The growth of the crystals begins and the size differentiation may become less evident. The carrier of the invention preferably has a porosity of at least 50% and more conveniently from about 60 to about 75%. The porosity is related to the surface area which is preferably 0.4 to 5 and more preferably 0.6 to 1.2 m / g. Porosity can be obtained by the addition of organic combustion material, such as crushed walnut shells or solid particles of a combustible hydrocarbon. Porosity can also be obtained without the use of combustion material by choosing particle sizes of the concreted ceramic components from each other to form the carrier. It is usually preferred to add to the mixture, in which the carrier is to be made, from 1 to 3% by weight based on the alumina components, expressed as alumina from a ceramic binder material to give added strength to the baked carrier. Conventional ceramic binder materials can be used and after baking these typically contain components (expressed as oxides), such as silica, alumina, alkaline earth metal oxides, alkali metal oxides, iron oxide and titanium oxide, the first two being the dominant components. Binder materials containing significant amounts of alkali metals, ie up to about 5% and more preferably 2% to 4%, are considered particularly suitable. Particularly suitable binding materials include calcium silicate and magnesium silicate, either added as such or formed in situ.

DESCRIPTION OF THE PREFERRED MODALITIES The invention is described in more detail with reference to the following examples which are for purposes of illustration only and are not intended to imply any necessary limitations on the essential scope of the invention.

EXAMPLE 1 This example details the preparation of the carriers that are made using the formulations described in the following examples. The ceramic components are mixed with a combustion material (nut shell flour) and boric acid for about 1 minute. Water and a component with alpha-alumina seed are added, the water being in an amount that is necessary to make the mixture extrudable. Generally, this is approximately 30% by weight. The mixture is stirred for about 4.5 minutes and then approximately 5% by weight, based on the weight of the ceramic components, of petrolatum is added as an extrusion auxiliary material. The mixture is then stirred for another 3.5 minutes before being extruded into hollow cylinders and dried to remove essentially all of the bound water. These were then baked in a tunnel oven at a maximum temperature of about 1460 ° C-1490 ° C for about 5 hours. The mixed ingredients were as follows: Alpha-alumina component ceramics (Type # 1) 46.7% Alpha-alumina (Type # 2) 27.4% Alpha-alumina seed (Type # 3) 2.2% Gibsite 18.3% Bohemite dispersible 4.1% Ceramic bond 1.3% Other components expressed as a percentage of the total ceramic components: Organic combustion (crushed walnut shells) 20% Oil ointment lubricant 5% Boric acid 0.15% Water, enough to be extruded approximately 30% Alumina Type # 1 Type # 2 Type # 3 Gibsita Med size of part. 3.0-3.4μ 4.0-8.0μ < 1. Oμ 4.0-20μ Crystallite size 1.6-2.2μ 3.0-4.0μ Na20 content (%) 0.02-0.06 0.1-0.3 - 0.1-0.3 Surface area - - 10-135 m2 / g The ceramic binder has (in% by weight) a typical composition of: SÍO2 I2O3 Fß2? 3 TiO2 CaO MgO N 2? K20 61.3 28.6 0.85 0.68 2.92 1.79 1.15 2.67 Impregnation of the carrier The baked catalyst was divided in two and a portion was then impregnated with a material that generates titania in an amount sufficient to give a final titanium content in the carrier dried and finished in the desired amount. The other portion was not given any treatment with titania at all. The impregnation was carried out by removing by weight the appropriate source of titanium in an amount necessary to give the desired level in the final carrier. Example 1, this was in the form of a water-soluble titanium salt (bis (ammonium-lactate) titanium dihydroxide IV), commercially available as "TYZOR LA". The total volume of solution used was in each case equivalent to the total pore volume of the carrier. The carrier is impregnated by slow addition to the carrier in the form of pellets with agitation. When the addition is complete, the impregnated carrier is allowed to stand for 30 minutes and then dry overnight at 120 ° C. It was then calcined at 500 ° C for 6 hours, except where otherwise specified.

Preparation of the catalyst The carriers described above were used to prepare an ethylene oxide catalyst. The method of preparation was generally as described in U.S. Patent No. 5,380,697. Each of the carrier samples described above was given an identical treatment.

The procedure The following describes the test conditions and normal procedures of the microreactor catalyst that were used to test the catalysts for the production of ethylene oxide from ethylene and oxygen. 3 to 5g of the crushed catalyst is introduced (Mali 14-20) to a U-shaped stainless steel tube with an internal diameter of 5.33 mm. The U-tube is immersed in a bath of molten metal (heating medium) and the ends are connected to a gas flow system. It is adjusted for the weight of the catalyst used and the flow velocity of the inlet gas to achieve a space velocity per gas area of 6800 ml of gas per ml of catalyst per hour. The inlet gas pressure is 2041 KN / m2. This gas mixture passed through the catalyst bed (in a one-time operation) during the entire test cycle (including start) consists of 25% ethylene, 7.0% oxygen, 7% dioxide carbon, 61% nitrogen and 2.5 to 10 ppmv ethyl chloride as moderator.

The reactor temperature (heat medium) is increased by 180 ° C for a period of half an hour and then to 190 ° C and then 200 ° C in successive half-hour periods. After that, it was raised to 10 ° C per hour for the next two hours followed by an additional hour to reach the operating temperature of 225 ° C. The temperature is then adjusted so that a constant level of ethylene oxide is achieved in the product stream of 1.5% (T ^ s). The moderator level is maintained at 10 ppb for 6.5 hours and after that for 2. Due to the slight differences in the composition of the feed gas, the gas flow velocities and the calibration of the analytical instruments used to determine the Feeding gas and product compositions, the selectivity of the measured activity of a given catalyst may vary slightly from one test cycle to the next. To allow for a significant comparison of the performance of the catalysts tested at different times, the catalysts described in this illustrative (ie in parallel) mode were simultaneously tested. The results revealed: with the titania, the values of Si.5 and i.5 were 83.3% and 227 ° C. If the treatment with titania, the corresponding values were 82.5% and 235 ° C. That indicates that impregnation is a very effective way to ensure the benefits of incorporating titania into the carrier.

EXAMPLE 2 An additional carrier according to the invention was produced together with a comparison carrier and treated with a catalyst exactly as described in example 1. The carrier differed however in the composition which was as follows: Alpha-alumina component ceramics (Type # 4) 74.5% Alpha-alumina (Type # 5) 24.5% Ceramic bond 1.0% Other components expressed as a percentage of the total ceramic components: Organic combustion (crushed walnut shells) 25% Oil ointment lubricant 5% Boric acid 0.1% Water, enough to be extruded approximately 30% Alumina Type # 4 Type # 5 Size med. of part. 3.0-4.0μ 2.5-3.7μ Crystalline size 3.0-3.2μ 2.0-2.5μ Na20 content (%) 0.02-0.03 0.08-0.10 The ceramic bond has (in% by weight) a typical composition of: Si02 A1203 Fe203 thio2 CaO MgO Na20? 2o 58. 76 36.55 1.22 1.51 0.90 0.26 0.11 0.57 The baked catalyst was halved and a portion was then treated with an aqueous solution of titanyl oxalate in the manner described above in an amount sufficient to give a final titanium content in the dried and finished 500 ppm carrier. The other portion was not treated with titania at all. To allow significant comparison of performance, the catalysts described in this illustrative mode (ie in parallel) were simultaneously tested. The results revealed: with the titania, the values of Si.5 and Ti.5 form 82.5% and 232 ° C. Without treatment with titania, the corresponding values were 81.7% and 235 ° C.

EXAMPLE 3 In this example, the effect of baking constraints that are used to generate the titania in the carrier on the selectivity of the resulting catalyst was evaluated. In each case, the carrier was produced in the same way and the catalyst deposited on it was the same. The evaluation of the selectivity was carried out in the manner described in example 1. The carrier was produced in particles with a diameter of either 6 mm or 8 mm and the amount of titanium added amounted to 0.05% by weight in each case .

The results are shown in table 1 below TABLE 1 8 mm 6 mm calcination Temperature Temperature of (mi.) Calcination (° C) calcination (° C) 250 300 400 500 500 550 600 fifteen - . 15 - 8.18 82.2 - - - - 30 - - 82.6 82.8 - 82.6 82.9 Four. Five - . 45 - - - - 82.7 82.9 82.8 60 -. 60 - - - 82.9 82.5 83.0 82.8 360 58.4 83.0 82.9 83.3 83.3 _ _ The ceramic binder has (in% by weight) a typical composition of: Si02 A1203 Fe203 Ti02 CaO MgO Na2o? 2o 61.3 28.6 0.85 0.68 2.92 1.79 1.15 2.67 As will be apparent from the above data, the baking should preferably be at a temperature of about 300 ° C or higher or for a time which is at least 15 minutes and up to about 360 minutes or more, allowing higher temperatures shorter times.

EXAMPLE 4 The following example examines the effect of the baking conditions on the selectivity in the manner described in Example 1, except that the selectivity was assessed with the adjusted conditions, such that the conversion to ethylene oxide at 40% and the Feed composition was as follows: Oxygen 8.5% by volume Ethylene 30.0% by volume Carbon dioxide 5.0% by volume Nitrogen 54.0% by volume Ethyl chloride 2.5 ppmv and a flow velocity of 3300 GHSV was maintained at a pressure of 1448 kJSr / m2). The figures cited are therefore the values of S40 and T40. Impregnation was carried out using the titanyl oxalate salt. Content of CALCINATION TEMPERATURE (° C) Titanium (% by weight) 250 500 750 1000 1250 1350 0. 00 81.8 - 82.1 - 231 - 229 - - - 0.05 80.9 82.4 82.0 81.8 81.6 - 231 218 219 222 233 - 0.50 - 81.2 82.4 81.7 82.4 - - 226 222 220 221 - 1.00 - 76.4 79.1 82.1 82.6 82.5 - 227 219 218 219 225 2. 00 - 73.1 81.8 82.1 82.5 82.6 _ 230 219 220 219 220 The titania content can be obtained from the titanium content figures cited above by multiplying by 1.67. The above data suggest that baking at too high a temperature can be detrimental and that longer baking times at temperatures above about 500 ° C does not improve the selectivity.

Claims (6)

NOVELTY OF THE INVENTION CLAIMS

1. - A process for producing an alpha-alumina catalyst carrier comprising: a) forming a mixture comprising alumina components, ceramic binder, a liquid medium and optionally, organic combustion materials, optional forming materials and lubricants; b) forming the mixture as carrier bodies; c) drying and baking the bodies at a temperature of 1200 to 1500 ° C to form porous carrier bodies; d) impregnating the porous carrier bodies with titania generator in a liquid medium; and then e) baking the impregnated bodies at a temperature sufficient to remove volatile substances and generate titania.

2. - A method according to claim 1, further characterized in that the body of baked or dried carrier is impregnated using a titania generator selected from the group consisting of titania sol and an aqueous solution of a titanium compound containing ligands that make combustion with volatile products.

3. A process for the production of a catalyst carrier according to claim 1, further characterized in that at least 80% by weight of the ceramic components is provided by the alpha-alumina.

4. - A method according to claim 1, further characterized in that the titania generator is added by impregnation in an amount of volume equal to the previous volume of the carrier and sufficient to provide 0.05 to 10% by weight of the weight of the finished carrier .

5. - A method according to claim 1, further characterized in that the impregnated carrier is calcined at a temperature between 450 and 700 ° C.

6. - A method according to claim 1, further characterized in that a ceramic binder material comprising silica, alumina and an alkali metal is added to the extrudable mixture in an amount which is from 1 to 3% by weight of the components of alumina, expressed as alpha-alumina, in the mixture.