MXPA99002771A - Preparation of extruids in espine - Google Patents

Abstract

The invention relates to: A process for preparing extrusions in spinales, especially extruded in the form of a honeycomb, which, when dried and calcined, are useful as catalysts. The combustion of hydrocarbons with air as an oxidant of origin, particularly with excess air and at high temperatures, nitrogen aoxide by oxidation of nitrogen present in the air. Examples of these nitrogen oxides are: NO, NO2, NO3, N2O3, N2O4 and N2O5. Being polluting, nitrogen oxides must be removed as completely as possible from the combustion gases to avoid sending this charge to the environment. In view of the fact that the emissions of industrial power plants are being progressively cut by the use of facilities for the treatment of exhaust gases, the abatement of the polluting fraction in the exhaust gases or exhaust of motor vehicles is becoming increasingly important, especially against the background of the increase in the number of vehicles. Multiple solutions have been proposed to reduce NOx emissions from motor vehicle engines. Effective solutions for reducing NOx levels have to comply with a multiplicity of criteria, especially if catalysts are used, for example: high conversion ratio, that is, a substantial NOx elimination, even at high and low temperatures and in the In case of frequent load changes during the operation, avoid the use of ancillary materials such as ammonia or urea, reduce manufacturing and operational costs, long duration in operation, low production of N

Description

PREPARATION OF EXTRUIDS IN SPINELAS This invention relates to a process for preparing extrusions in spinels, especially extruded in the form of a honeycomb structure, which, when dried and calcined, are used as catalysts. The combustion of hydrocarbons with air as an oxidant gives rise particularly to excess air at high temperatures, to nitrogen oxides through the oxidation of nitrogen present in the air. Examples of such nitrogen oxides are NO, O2, NO3, N2O3, N2O4 and N2O5. Being polluting, the nitrogen oxides must be removed as completely as possible from the emission of combustion gases to avoid charging them into the environment. While the emissions of plant dust and industries are progressively reduced through the use of easy treatments of the exhaust gas, reducing the polluting fraction in the exhaust gases or exhaust from automotive vehicles becomes increasingly important, especially against precedent of the increase in the number of motor vehicles. Many solutions have been proposed to reduce NOx emissions from machines for motor vehicles. Effective solutions for decreasing NOx levels have to satisfy a multiplicity of criteria, especially if catalysts are used, for example: high conversion ratio, that is, substantial elimination of N0X, even at high and low temperatures in the event of frequent load changes during operation - avoid the use of auxiliary materials such as ammonia or urea - reduce manufacturing and operating costs - long running time - low N20 production - high mechanical stability of the catalyst. A number of catalysts have been proposed to reduce nitrogen oxides. A trend in the development of suitable catalysts moves in the direction of catalysts in spinels. The use of CUAI2O4 spinels impregnated with copper as an exhaust gas catalyst is described in DE-A-195 46 482. Spinels are used in the form of chips. EP-A-0 779 093 describes corresponding spinel catalysts for reducing nitrogen oxides and for oxidation of hydrocarbons. The spinels are based on zinc, copper and aluminum and are used in the form of chips. EP-A-0 676 232 describes the use of spinels of catalysts for treatment of gas emissions, which lower the levels of nitrogen oxide in gas emissions. These spinels are zinc aluminum that are obtained by precipitation of precursor solutions. Precipitation products can be dried by spray drying or flash evaporation of the solvent and are obtained as powders. It is also possible to mix the catalyst precursors with, for example, urea or glycine and to calcinate the mixture in which case not only spinels are formed but at the same time, also due to the high temperature, a calcination takes place. It is stated that the catalyst may be present in the form of honeycomb structures, but the manufacturing process for honeycomb structures is not described. Spinel catalysts are preferably used in motor vehicles not in the form of chips or granules, but in the form of honeycomb structures consisting of the catalyst material and possessing a number of essentially parallel channels through which the gas that flows to be treated. In a cross-sectional view, such honeycomb structures may correspond to honeycombs, for example. The individual channels can also have a round or rectangular or especially square cut, so that the cross section through the honeycomb structure corresponds to a grid pattern with right angle.

Several processes have been proposed to prepare honeycomb structures in spinels. DE-C-36 19 337 describes a process for the preparation of TiO2-SiO2 oxide compounds which can also contain zirconium dioxide. An aqueous solution that contains the active ingredients such as vanadium and copper, or a powder of the active constituents in the form of oxide is added together with an auxiliary for molding to a titanium-containing oxide, such as TiO2, TiO2-SiO2 and Ti2-Si2-Zr2. The constituents are mixed and kneaded while adding an adequate amount of water. The mixture is then molded in an extrusion molding apparatus. The molded product is dried and calcined. DE-A-44 19 974 refers to the process for preparing molded catalysts based on titanium oxide and its use. The catalyst can be in the form of a honeycomb structure. It is also prepared by calcining a mass of titanium dioxide powder in a mixture with water, ammonium metatungstate solution, polyethylene glycol as plasticizer assistant, monoethanolamine and glass fibers. This homogeneously kneaded material is molded in a honeycomb extruder and the honeycomb catalyst is subsequently dried and calcined. US 5,219,816 relates to catalysts for dehydrogenation and processes for their preparation. To prepare the support which is based on a spinel, aluminum oxide material is mixed with magnesium nitrate and extruded in a suitable mold. After drying, the calcination is carried out at temperatures from 600 to 700 ° C. The preparation of honeycomb structures, especially copper-aluminum spinels, by existing processes has a number of disadvantages. The extrusion of molded material in honeycomb structures requires a large feeding time, which corresponds to a low feed rate. Frequently only feed speeds of 5 to 10 c / min are achieved. The drying time of the extruded honeycomb structures is very long. And this is frequently at least a month at room temperature. As they dry out and in the course of subsequent calcination, the honeycomb structures are generally prone to distortions, eg, parallelogram distortion and pincushion distortion, and develop longitudinal and transverse cracks. Even prolonging the drying time does not lead to better results. Such honeycomb structures are mechanically unstable due to fissures and deformations, and conduct a non-uniform gas flow through the catalyst, so much so that it is difficult or even impossible for constant reaction conditions to stabilize the entire catalyst. Furthermore, for example in motor vehicle catalysts, the honeycomb structures are fitted in a liner [sic]. When the parallelogram and pincushion distortions occur, the honeycomb structures no longer end up at the same level of the coating, so that the exhaust gas can bypass the catalyst, greatly reducing the function of the catalyst as a whole. In this case, the catalyst considered as a whole in this way exhibits decreased activity. It is an object of the present invention to provide a process for preparing extruded spinels, especially spinels with honeycomb structure, which avoids the disadvantage of the existing processes and leads to a uniform, undistorted honeycomb structure which are free of cracks, which They have high mechanical stability and sustained use force and are impermeable to temperature change. These should quickly adjust in dedicated components, for example in coatings, so that the maximum activity in operation is achieved. In addition, manufacturing processes will be accelerated compared to existing processes. We have found that this object is carried out according to the invention by a process for the preparation of extruding molding compositions comprising spinel powder with or without extrusion aids, stabilizers, shrinkage reducers, pore formers, peptizing aids or mixtures of them, subsequent drying and calcination of the extrudates, wherein the molding composition also contains aluminum oxides or hydrates of aluminum oxides and metal nitrates. Preferred are metal nitrates that give an acid reaction in aqueous solution. Particular preference is given to copper nitrate. Instead of the preferred Cu (NU3) 2 * 3H2O it is also possible to use hydrates containing less or more moles of water of crystallization. further, the use of other metal nitrates is also possible as long as their cations are spinel-forming and the presence of the resulting metal oxides is desirable in the catalyst. The molding material is preferably extruded into honeycomb structures, as described at the beginning. Typical honeycomb structures have channels from 1 to 5 mm in diameter and from 0.2 to 5 mm in thickness in the separation walls. The process of the invention makes it possible to prepare spinels of honeycomb structures that are free of distortions and fractures. The extrusion of the molding materials into honeycomb structures can take place at feed rates of up to 80 cm / min. The drying time at room temperature is, in general, only about 1 week. The obtained honeycomb structures are very stable mechanically and with respect to temperature fluctuations. A multiplicity of spinel powders can be used in accordance with the present invention. Suitable spinel powders are described, for example, in EP-A-0 676 232, EP-A-0 779 093, DE-A-195 46 482 and also in DE A-196 53 200, which was not published to date. of priority. Spinels are described, for example in C.W. Correns, Einführung in die Mineralogie, Springer Verlag 1949, pages 77 to 80. Further descriptions can be found in H. Remy, Lehrbuch der anorganischen Chemie, Akademische Verlagsgesellschaft Geest & Portig K.-G. Leipzig 1950, pages 308 to 311 and also in Roe pp, Chemielexikon, 9th edition 1995, page 4245. Spinels are formally derived from MgAl2? 4. Magnesium can be replaced by other divalent ions such as zinc, copper, iron. Aluminum can be replaced by other trivalent ions, such as iron or bromine. In the reticle of the spinel the oxygen atoms form a compact cubic structure corresponding to a centered face grid. Half of the octahedron vacancies are occupied by aluminum, the other half of the vacancies are empty. One eighth of the tetrahedral vacancies are occupied by magnesium. Preference is given to using a copper-aluminum spinel powder which may be 0-10% by weight replaced by Zr02, Ce? 2, Sn02, W03, M0O3, Ti02, V05, Nb203, La203 or mixtures thereof and additionally doped with noble metals. Spinel powders preferably have an average particle size of 0.1 to 50 μm, particularly preferably of about 1 to 30 μm, especially from 2 to 10 μm. They are obtained by several processes as exemplified in the references cited above. Spinel powders can be prepared by, for example, mixing the oxide powders of the metals present in the spinel, pressing the mixture of oxides and calcination. The calcination temperature is preferably not less than 700 ° C. Examples of suitable oxides are Zr? 2, SiO2, AI2O3, Ti02, Ce02, Sn02, 03, M0O3, Nb2? 3, La? 3 and V2O5. The preparation can also take the form of mixing with solutions of metal salts of the metals present in the spinel, the subsequent precipitation, drying and calcination. Instead of a solution it is also possible to use a suspension of metal salts. Preference is given to using the salts with inorganic acids, such as nitrates, sulfates, carbonates or halides, depending on the solubility. It is also possible to use salts of organic acids. Examples are formats, acetates, propionates, oxalates or citrates. The precipitation can be caused by the addition of precipitants such as ammonia, alkali metal carbonates, carbonates or basic alkali metal hydroxides [sic]. In addition, the solutions can be dried and sprayed by spray drying or flash evaporation. The drying may be followed by a calcination step to preferably not less than 600 ° C. In addition, the compounds of the spinel precursor metals can be mixed with a source of carbon and nitrogen to form a mixture that is then burned. In combustion, the resulting high temperatures form the spinels. Examples of suitable carbon and nitrogen sources are organic compounds such as urea or glycine. Other suitable manufacturing processes are described in, for example, DE-A-42 24 881. For example, metal oxides such as AlOOH (boehmite), CuO, ZnO and optionally other suitable metal oxides can be kneaded with water in the presence of a binder, extruded, dried and calcined, in which case the extrudate obtained can be pulverized. Instead of metal oxides it is possible to use the corresponding hydroxides, hydrates, oxides, carbonates, salts of organic acids, nitrates, chlorides, sulfates or phosphates as described above. To prepare bimodal or polymodal catalysts, AlOOH can be replaced by a mixture of AlOOH and AI2O3, preferably? - or d-l2? 3, AI2O3 with different pore size distribution can be used for this purpose. Drying preferably takes place at from 10 to 200 ° C, particularly preferably from 20 to 150 ° C, especially from 30 to 120 ° C. Freeze drying is also possible (for example from -40 to 0 ° C, from 0.05 to 0.8 bar). Freeze drying is particularly mild, but it also consumes more time. The geometric shape is sufficiently well preserved. The calcination preferably takes place from 600 to 900 ° C. As described above, there are processes to extrude spinel powders, or a mixture of the precursor salts, into a honeycomb structure. This invention in contrast, incorporates the spinel powder - optionally next to extrusion aids, stabilizers, shrinkage reducers, pore formers, peptizing auxiliaries or mixtures thereof - in addition to aluminum oxides or aluminum oxide hydrates and nitrates metallic Preference is given to using aluminum oxide hydrate and, for example, copper nitrate in a Cu: Al molar ratio of from about 0.3 to 0.7, particularly preferably from 0.4 to 0.6. The aluminum oxide hydrate used is preferably aluminum oxide hydroxide, aluminum trioxide or mixtures thereof. The metal salts can be used in the form of their hydrates. The amount of aluminum oxide hydrate and metal nitrate is preferably within the range of 15 to 55% by weight, based on the amount of spinel powder. The spinel powder is kneaded with the additional constituents in a plastic material, which is then extruded into extruded, especially honeycomb structures. The extrudate is preferably dried from 10 to 200 ° C, particularly preferably from 20 to 150 ° C, especially from 30 to 120 ° C, and calcined from 500 to 900 ° C. The addition of aluminum oxide hydrate and metal nitrate makes it possible to obtain the honeycomb structures of the invention free of distortions and fissures. To date it is not known exactly what this effect is attributable to. The ratio of the mixing of aluminum oxide hydrate to metal nitrate (copper nitrate) is preferably chosen such that it corresponds to the mixing ratio present in a spinel. Based on the present spinelass powder, preference is given to the addition of from 5 to 25% by weight of AlOOH and from 10 to 30% by weight of metallic nitrate (for example, Cu (N? 3) z '3H20). The molar ratio of metal oxide to I2O3 in this spinel precursor should not be significantly substoichiometric. The molar ratio should preferably be within the range from 0.6 to 1.4. In place of AlOOH (boehmite) it is also possible to use Al (OH) 3 (bayerite or hydrargillite) or other aluminum oxide hydrates and mixtures thereof. For a description of a large number of suitable aluminum oxide hydrates, see, Hollemaniberg, Lehrbuch der anorganischen Chemie, Walter D. Gruyter Berlin, New York, 1985. Preference is given to using copper boemite and nitrate having a water content of 2 to 6 mol. The spinel powder used can be prepared in several ways. Examples are: - the coprecipitation of hydroxides with subsequent calcination, - the mixture of oxides and subsequent calcination, - the use of old recycled combs, - the use of waste and production residues, - the mixture of salts, spray drying and subsequent calcination. . Spinelass powder and extrudates obtained in this way, especially honeycomb structures, can be impurified with other oxides, such as Zr 2, Ce 2, Sn 2, WO3, M0O3, TiO2, V2O5, Nb2? 3, La2? 3 and / or noble metals such as Pt, Pd, Ru, Ag, Au. The doping preferably takes place in amounts of about 0 to 10% by weight, based on the calcined honeycomb structure. The extrusion of the molding material in honeycomb structures preferably takes place at a feed rate of up to 80 cm / min, according to the invention. The drying time at room temperature is preferably about one week, according to the invention. The honeycomb structures of the invention are used as catalysts or catalyst support for the catalytic cleaning of emissions of gases containing nitrogen oxides. This is consequently understood especially for the purification of emissions of combustion gases, preferably emissions of diesel gases. However, it is also useful for the purification of other emissions of NOx-containing gases, for example plants fed by waste energy, which burn coal, which burn oil. Proper doping can make honeycomb structures also useful for cleaning emissions of industrial gases containing 2O. Similarly, decomposition of dioxin is also possible given adequate doping with TIO2, V2O5 and O3 and dioxin decomposition processes can take place simultaneously with or immediately after debugging. The decomposition of dioxin may preferably take place under oxidizing conditions on a TiO2 / V2O5 / WO3 catalyst as described, for example, in EP-A-0 447 537. Other emissions of gases containing polyhalogenated compounds can also be cleaned. Particular preference is given to using honeycomb structures - after doping with noble metal, especially - as the storage capacity of a hydrocarbon supports a catalyst in 3 forms. The following examples illustrate the invention.

Examples Inventive example 1) Starting material 3000 g of a copper-aluminum spinel powder which is stoichiometric in relation to Cu is taken. Its loss at ignition is 6%, so much that the actual mass of spinel is 2820 g. The powder is formally composed of 20% = 564 g = 7.09 mol of CuO and 80% = 2256 g = 22.1 mol of AI2O3. In this way it contains 0.32 mol of CuO per mol AI2O3, that is, it is strongly substoichiometric. Spinel powder can be virgin material or be recycled material, for example from the continuous process. The virgin spinel powder was prepared in the line of the method described in Example 2 of EP-A-0 676 232, namely by mixing copper nitrate and AlOOH in the presence of water, spray drying in a conventional manner and calcining at room temperature. 800 ° C.

Mixing of AlOOH + Cu (NO3) 2 '3H20 3000 g of the minced spinel powder was mixed with a mixture of 402.8 gd Wet Pural® (in mineralogical terms boemit = AlOOH, formally it contains 73.74% of A1203 = 297.0 g = 2.9 mol of A1203) and 703 g of copper nitrate trihydrate (= 232 g = 2.9 mol (formally) of CuO). The mixture had an equimolar composition, that is, according to the formula CUAI2O4.

Pre-mixing The mixture of spinelass powder and pre-mix formally comprises 796 g = 10.0 mol of CuO and 2553 g = 25.0 mol of AI2O3. The molar ratio of CuO to AI2O3 in this way is 0.4: 1.

Preparation of plastically deformable material 3000 g of spinel powder and 1352 g of the pre-mix were intimately mixed for 5 minutes. Then 246.4 g of carbon fibers, 41 g of Walocel® (hydroxymethylcellulose), 41 g of polyethylene oxide and 2000 g of demineralized water were added, and the material is kneaded for 6 hours. Then 41 g of monoethanolamine are added, and the kneading is continued for 7 hours. During the kneading, 350 g of vaporized water were replaced. The carbon fibers were 3 mm long and 5 micrometers in diameter.

Preparation of honeycomb structures Honeycomb structures are extruded in custom extruders, dried and calcined under the following conditions: Extrusion speed: 50 cm / min Drying time: 8 days Appearance of the calcined honeycomb satisfactory Mechanical stability: Hardness at bursting 181 N / cm2 Stability at very good temperature changes: Catalytic activity: very good, stable at 100% Example 2 (comparative) In situ preparation of copper nitrate trihydrate and beomite. 4841 g of Cu (N03) 2 * 3H20, 9482 g of AlOOH, 522 g of carbon fibers, 128 g of monoethanolamine, 128 g of lactic acid, 96 g of carboxymethylcellulose and 5020 g of water are mixed, kneaded similarly to the example 1. The kneaded material is used to produce honeycombs having 160 2 cells / square inch (25 cells / cm).

Extrusion speed: 10 cm / min Drying time: 28 days Bursting hardness: 50 N / cm Catalytic activity: 80% of example 1 Appearance: many longitudinal cracks, severe distortion Stability at the change of additional cracks appear temperature: Example 3 (inventive) Similar to example 1 of the invention, except with cordierite, but without compression aids and pore formers. The spinel powder and AlOOH and also Cu (N? 3) 2"3H20 are mixed as described in Example 1, added with 12% cordierite and 30% water and processed into honeycombs of 160 cells per square inch.

Extrusion speed: 45 cm / minute Drying time: 10 days Bursting hardness: 150 N / cm2 Catalytic activity: 95% of example 1 Appearance: slight longitudinal cracks, the honeycombs are dimensionally stable Stability to the change of DUer? To temperature: Example 4 (inventive) Similar to example 1 of the invention, but with cordierite. Unlike Example 3 of the invention, compression aids and pore formers are present. The quantities of the initial materials are shown in table 1.

Extrusion speed: 50 cm / min Drying time: 10 days Bursting hardness: 283 N / cm Catalytic activity: 100% of example 1 Appearance: satisfactory Stability to temperature changes: good Table 1 20 1 together they produce spinel powder 2 carbon fibers: regular length 3 mm and 5 micrometers diameter 3 hydroxymethyl cellulose: sizing for alocel® carpet ... [sic] 4 carboxymethyl cellulose: Kikkolate® NB-L from Nichirin Chemical Co. Ltd. Japan 5 polyethylene oxide: Alkox® E 160 from Meisei Chemical Industries Co. Ltd., Japan

Claims (1)

1. CLAIMS The process for preparation of spinel extrusions by extrusion of molding compositions containing spinel powders with or without extrusion aids, stabilizers, shrinkage reducers, pore formers or mixtures thereof, subsequently drying and calcination of the extrudates, where The molding composition also contains aluminum oxides or hydrated aluminum oxides and metal nitrates. The process of claim 1, wherein the molding composition is extruded into honeycomb structures. The process of claim 1 or 2, wherein the spinel powder used is a powder of copper-aluminum spinels which may be 0-10% by weight replaced by Zr02, Ce02, Sn02 W03, M0O3, Ti02, V205, Nb203 , La320 or mixtures thereof and additionally doped with noble metals. The process of any of claims 1 to 3, wherein the hydrous aluminum oxide and copper nitrate is used in a Cu: l molar ratio of 0.3 to 0.7. The process of any of claims 1 to 4, wherein the hydrous aluminum oxide used is aluminum oxide hydroxide, aluminum trihydroxide or mixtures thereof. The process of any of claims 1 to 5, wherein the amount of hydrated aluminum oxide and copper nitrate, calculated as AlOOH and Cu (N03) 2 * 3H20, is within the range of 15 to 55% by weight, with based on the amount of spinel powder. The process of claim 6, wherein copper boemite and nitrate are used having a water content of about 2 to 6 mol. The honeycomb structures obtainable by a process as claimed in any of claims 1 to 7, wherein the extrudate is dried at 10-200 ° C or freeze-dried at -40 to 0 ° C under a pressure of 0.05 to 0.8 bar and calcined at 500-900 ° C. A method for using the honeycomb structures as mentioned in claim 8 as a catalyst or catalyst support for the catalytic cleaning of emissions of gases containing nitrogen oxides and for the catalytic cleaning of emissions of gases containing polyhalogenated organic compounds SUMMARY OF THE INVENTION The invention relates to a process for preparing extrusions in spinels, especially extruded in the form of a honeycomb, which, when dried and calcined, are useful as catalysts. The combustion of hydrocarbons with air as an oxidant gives rise, particularly with excess air and at elevated temperatures, to nitrogen oxide by oxidation of the nitrogen present in the air. Examples of these nitrogen oxides are: NO, N02, N0, N2? 3, N2? 4 and N2Os. Being polluting, the nitrogen oxides must be eliminated as completely as possible from the combustion gases to avoid sending this charge to the environment. In view of the fact that emissions from industrial power plants are being progressively reduced by the use of facilities for the treatment of exhaust gases, the abatement of the pollutant fraction in the exhaust gases or exhaust of motor vehicles is increasingly being important, especially against the antecedent of the increase in the number of vehicles. Multiple solutions have been proposed to reduce N0X emissions from motor vehicle engines. Effective solutions for reducing N0X levels have to comply with a multiplicity of criteria, especially if catalysts are used, for example: - high conversion ratio, that is, a substantial elimination of N0X, even at high and low temperatures and in the case of frequent load changes during the operation - avoid the use of auxiliary materials such as ammonia or urea - reduce manufacturing and operational costs - long duration in operation - low production of N20.