Procedure for the oxidation of ammonia and suitable installation for it

Abstract

A process for the oxidation of ammonia with oxygen in the presence of catalysts containing at least one transition metal oxide, which is not any platinum metal oxide, wherein the ratio of the molar amounts of oxygen to ammonia at the inlet of the gaseous mixture of starting products to the catalyst bed is adjusted to values ​​of 1.25 - 1.75 mol of O2 / mol of NH3 and the temperature at the outlet of the product gas from the catalyst bed is between 700 °C and 950 °C.

Description

Procedure for the oxidation of ammonia and suitable installation for it The invention relates to an improved process for the oxidation of ammonia to prepare nitrogen oxides, which is used in particular in the preparation of nitric acid and caprolactam. The invention also relates to an improved installation for the preparation of ammonia oxidation products. State of the art and problem statement In the technical-scale preparation of nitrogen-containing raw materials for the chemical industry, the catalytic oxidation of ammonia (NH3) to nitrogen oxides (NOx) often involves a basic reaction. Examples of this include the preparation of nitric acid (HNO3) as a starting material for nitrate-containing fertilizers, or the preparation of hydroxylamine or hydroxylammonium salts for the production of caprolactam and, consequently, polyamides. The following embodiments with respect to the state of the art refer by way of example to the preparation of HNO3 by catalytic oxidation of NH3. The preparation of nitric acid is one of the most established procedures in chemical technique, which was developed after the introduction of the Haber-Bosch procedure for the synthesis of NH3 by W. Ostwald based on platinum catalysts for industrial maturation and whose conception still forms the basis of modern HNO3 preparation. Thus, the first technical installation using a platinum catalyst (grooved strips of Pt foil) for the production of 1500 tons per year of ammonium nitrate was built in 1906 in Gerthe, Bochum. Shortly thereafter (1909), the first patents appeared concerning the use of woven platinum networks as catalysts. These were later alloyed with rhodium. Although the catalyst entails high investment costs and is consumed during the oxidation of NH3 (the platinum is released), these catalyst systems are still in use today and, in modified form, represent the state of the art (see Winnacker Küchler, Chemische Technik - Prozesse und Produkte, 5th edition, vol. 3, chapter 3, pp. 248-275, Wiley-VCH Verlag GmbH & Co. KGaA). Recently, platinum metal networks with high proportions of Pd have been increasingly used, since these allow not only a certain reduction in costs, but also cause a reduction of laughing gas (N2O) produced during the unwanted oxidation of NH3, which is a greenhouse gas. The typical dimensions for platinum metal meshes, which are fixed over a wide surface in an ammonia oxidation reactor often referred to as a "burner," are in the range of 0.5–5 m in diameter. The thickness of the mesh packing typically ranges, depending on the number of meshes used, from a few millimeters to approximately two centimeters. A gas mixture, typically consisting of approximately 9-12% by volume of NH3 and air, is circulated through the networks. The temperature in the networks is adjusted to approximately 800-950 °C by means of the exothermic oxidation reaction. In this respect, NH3 is selectively oxidized to give nitric oxide (NO) (see reaction scheme 1 below), which is then further oxidized in the subsequent process to give nitrogen dioxide (NO2) (reaction scheme 2), and finally reacted with water in an absorption tower to give HNO3 (reaction scheme 3). Primary NH3 oxidation - target reaction: NH3 + 5 O2 → 4 NO + 6 H2O (1) NO oxidation: NO + O2 → 2 NO2 (2) Formation of HNO3: NO2 + H2O 2 HNO3 + NO (3) This is the brute reaction resulting from: NH3 + 2 O2 HNO3 + H2O (4) Although, according to this, the O2 content in the combustion air of 21% by volume is just enough to formally guarantee a complete transformation of 10% by volume of NH3 into HNO3, oxygen from additional air (secondary air) is fed into the gas during the technical preparation of HNO3. This procedure is carried out after the catalytic oxidation of NH3 and before the gas enters the absorption tower, to accelerate the oxidation of NO and thus the formation of HNO3 in the absorption tower. Typically, the residual oxygen content of the exhaust gas leaving the absorption tower is approximately 1-5% by volume. According to the usual understanding of the primary oxidation reaction (see Handbook of Heterogeneous Catalysis, 2nd edition, Volume 5, 2008, Chapter 12.2.7.1, p. 2582, WILeY-VCH Verlag GmbH & Co. KGaA, 2008), a high partial pressure of oxygen is necessary in the combustion of NH3 to suppress the formation of nitrogen and laughing gas on the catalyst surface, which are worthless byproducts. This observation corresponds to the stoichiometries of N2 and N2O formation (see reaction schemes 5 and 6 below), which require less oxygen compared to NO formation (reaction scheme 1). Primary oxidation of NH3 - secondary reactions: NH3 + 3 O2 → 2 N2 + 6 H2O (5) NH3 + 4 O2 → 2 N2O + 6 H2O (6) The formation of NO2, which according to reaction scheme (7) would require a high amount of oxygen, does not take place in platinum metal catalysts. NH3 + 7 O2 → 4 NO2 + 6 H2O (7) The formation of byproducts or the selectivity of NOx also depends on the overall operating pressure of the NH3 oxidation. The higher the pressure, the less the NOx yield is reduced. The NOx yields achievable with the current state of the art using different process variations (combustion pressures) are shown in the following table (taken from Winnacker-Küchler, Chemische Technik - Prozesse und Produkte, 5th edition, volume 3, chapter 3, pp. 248-275, Wiley-VCH Verlag GmbH & Co. KGaA). Combustion pressure NH3 content in front of the net NOx performance atmospheric 12.0-12.5% ​​by volume - 98% average pressure (300-600 kPa) 9.5-11.0% by volume - 97% high pressure (700-1400 kPa) 10.0 - 11.0% by volume - 95% One disadvantage of platinum metal lattice catalysts, however, is their stability, which decreases only at the high operating temperature of approximately 900 °C. The catalyst is consumed by the combustion of the noble metal, at a rate of approximately 0.04–0.4 g of Pt / t of HNO3, depending on the combustion pressure. Therefore, the catalyst must be replaced at regular intervals, approximately every 3 to 15 months, depending on the combustion pressure. This leads to significant costs, although some of the burned platinum is recovered through various collection systems (e.g., Pd nets). Due to these drawbacks, repeated efforts were made to develop alternative metal oxide-based catalyst materials, particularly to conserve platinum. A summary of the various efforts regarding the use of oxide catalysts has been provided in Sadykov et al., Appl. Catal. General A: 204 (2000), pp. 59–87. Thus, catalyst systems based on impure iron oxides, often in combination with platinum metal lattices, were used primarily in Eastern Europe, while cobalt oxide-based systems were predominantly used in the Western Hemisphere. All these attempts to establish platinum-free NH3 oxidation catalysts have so far failed to gain traction in the art, since these, compared to highly selective platinum metal catalysts, exhibit lower selectivities for NO formation and the price of the product in modern HNO3 production facilities is determined by the price of NH3 by more than 70%. Transition metal oxide catalysts free of noble metals, which are potentially active under practical conditions, frequently suffer considerable temporary deactivation. This deactivation, in addition to the effects of sintering due to high thermal load, is often caused by a (partial) reduction of the oxides with NH3 to give the corresponding lower-valent oxides, which generally exhibit lower activity and selectivity with respect to NO formation. Examples include the reduction of MnO2 and Mn2O3 to Mn3O4, the reduction of CuO2 to CuO, the reduction of α-Fe2O3 to Fe3O4 and FeO, and, particularly prominently, the reduction of highly active Co3O4 to low-activity CoO. To counteract such deactivation, a technical use of Co3O4 catalysts for the oxidation of In a solid-bed reactor at Incitec Ltd. in Australia, the catalyst bed was periodically rearranged to reoxidize the catalyst, which was reduced with a high concentration of NH3 at the front of the catalyst bed, to the residual oxygen at the rear. This same idea is also supported by the work of Schmidt-Szalowski et al. (see Appl. Catal. A: General 177 (1998) pp. 147-157), who propagate the oxidation of NH3 through Co3O4 catalysts in a fluidized bed. In this case, continuous reoxidation of the CoO4 formed with oxygen is carried out at the bottom of the fluidized bed by means of the turbulence of the catalyst particles. One possibility that has been studied multiple times to suppress the deactivating reduction of the oxides is impurization, that is, the stabilization of the aforementioned binary oxides with other metal oxides that can be reduced with difficulty. However, this is frequently accompanied by a reduction in specific activity, as described by Sadykov et al. in Appl. Catal. General A: 204 (2000) pp. 59-87. The impurization of α-Fe2O3 with A^O3 is mentioned as an example, which formed the basis for the two-stage catalyst systems developed in the 1970s in the USSR for the oxidation of NH3 in combination with a reduced amount of conventional Pt / Rh network catalysts.Transition metal oxides can also be transformed by impurity with other metal oxides into mixed tertiary oxides with different crystal structures, in which the higher oxidation states of the transition metals exhibit a primarily low reducing capacity. In this case, perowskite structures are particularly noteworthy, characterized by high NO activity and high chemical stability. For example, US patent 4,812,300 A claims mixed oxide catalysts of the perowskite type with the general formula ABO3±s for the oxidation of ammonia, where A represents alkali metals, alkaline earth metals, lanthanides, or actinides, and B represents one or more elements from groups IB, IVB to VIIB and VIII. The catalysts must exhibit an equilibrium partial pressure of oxygen greater than 10.13 kPa at 1000 °C, allowing for good oxygen transfer from the lattice to the NH3 molecule without compromising the structural integrity of the perowskite. The catalysts were tested in this case using a temperature-programmed reduction (TPR) apparatus at ambient pressure, with an NH3 concentration of 3.3% by volume and an oxygen content of 6.7% by volume in helium.The particularly preferred perowskite catalysts contain lanthanum and / or strontium as the element in the A position and cobalt, nickel and / or manganese as the element in the B position. WO-99 / 25650 A1 describes a device for the oxidation of NH3, preferably using mixed oxide catalysts formed from rare-earth metals and cobalt. As an example, it describes the oxidation of 10% by volume of NH3 in air at atmospheric pressure with a lanthanum / cerium / cobalt mixed oxide (La:Ce:Co atomic ratio = 8:2:10). US patent 3,888,792 A describes the use of rare-earth metal-doped Co3O4 for the oxidation of NH3, which is expected to exhibit high selectivity and long-term stability compared to pure Co3O4. Tests on selected samples were conducted with an NH3 / air volume ratio of 1:10 under atmospheric pressure. In a long-term test exceeding 900 h with Ce-doped Co3O4, which also included a temporary pressure increase to 700 kPa, the NOx yield consistently exceeded 90%. WO 2009 / 028949 A1 claims mixed oxide catalysts for the preparation of NO by reacting a gas mixture consisting of NH3 and O2, conforming to the general formula A3-xBxOg-y. A and B are selected for this purpose from metals of the Mn, Cr, Co, Fe, and Al group. The catalysts were tested at atmospheric pressure with a gas mixture composed of 10% by volume NH3 in air or 10% by volume NH3, 18% by volume O2, and 72% by volume argon. The maximum NOx selectivity of 96% was achieved with a mixed oxide of the composition Mn1, 5Co-i, 5O4. As another example, US patent 3,962,138 A is mentioned. This patent claims catalysts for the oxidation of NH3, consisting of 60-95% Co3O4, 5-15% A₂O₃, and 0-25% of a thorium, cerium, zinc, or cadmium oxide. The molded catalysts were tested in a reactor with a 10 cm diameter at a pressure of 400-500 kPa with a gas mixture consisting of 10% NH3 by volume in air. With the best catalysts, each containing approximately 10% ThO₂, a NOx yield of approximately 93-95% was achieved after an operating time of 400 h. The addition of A₂O₃ and ThO₂ resulted in a significant improvement in NOx yield and reduced the catalyst exposure time. Document DE 10 2012 000 419 A1 discloses a low-temperature oxidation of ammonia in the preparation of nitric acid by passing a gas stream containing ammonia and oxygen through a support layer of LaSrCo oxide catalyst particles heated to below 500 °C, followed by cooling of the nitrogen oxide-containing gas stream. As an example, this reaction is described by the conversion of a gas stream containing 5% by volume carbon dioxide, 5% by volume water, 10% by volume oxygen, 200 ppm ammonia, and nitrogen as the remainder. Document WO 2006 / 010904 A1 describes oxidation procedures, which are carried out in catalysts of selected perowskite. The catalysts contain bismuth and / or lanthanides, with the exception of lanthanum. The oxidation of ammonia in air is described as the model reaction. Document DE 199 03 616 A1 describes a process for preparing low-oxidation nitrogen oxides by catalytic oxidation of ammonia in a mixture with air and steam in an oxidation catalyst. It mentions catalysts containing noble metals or catalysts containing metal oxides. WO 01 / 49603 A1 discloses a cerium oxide and manganese oxide, as well as a catalyst containing magnesium, aluminum, zinc, or calcium oxide and an activator, for the selective oxidation of ammonia with oxygen to give dinitrogen oxide (N2O). The reaction is carried out at relatively low temperatures of 250 °C or lower. Document DE 2 148 707 A describes a catalyst for the oxidation of ammonia to give nitrogen oxides. It is composed mainly of cobalt oxide and is characterized by a specific surface area of ​​0.1-7 m² / g and a volume / weight porosity of 1-15%. US patent 5,849,257 describes a process for preparing nitrogen oxides, in which ammonia is reacted with oxygen in the presence of water vapor over a copper / manganese oxide catalyst. The catalyst is characterized by a special X-ray spectrum. Document EP 0 384 563 B1 describes a procedure for the oxidation of ammonia in the presence of a cobalt oxide catalyst, which has been doped with lithium. US patent 2013 / 0039828 A1 discloses a catalyst structure suitable for an ammonia oxidation process, characterized by a flexible arrangement of catalyst units. The catalysts may contain platinum metals or other metals. In a scientific publication [J. Catal. 276 (2010) 306-313], Biausque and Schuurmann describe the high-temperature oxidation mechanism of NH3 to NO using a LaCoO3 catalyst. This involves, among other things, various tests with varying O2 and NH3 content. In one series of tests—starting from an NH3 concentration of 3% by volume—the oxygen content was varied between 10% and 40% by volume, and in another series of tests—starting from an oxygen content of 20% by volume—the NH3 content was varied between 1% and 5% by volume. In this regard, they found that the NOx yield obtained showed a negative dependence on the partial pressure of O2 and a positive dependence on the partial pressure of NH3.That is, with increasing partial pressure of O2 and decreasing partial pressure of NH3, an increase in the formation of N2 and N2O was observed, which contrasts with the known behavior of platinum catalysts for the oxidation of NH3. In Catal. Lett. (2011) 141: 1215-8 they describe Tianfeng Hou et al. the catalytic oxidation of ammonia to give nitrogen monoxide in the presence of perowskite catalysts of the LaMnO3 and LaVO4 type. In many of the cases cited above in the state of the art, the oxidation of NH3 in air is studied, as is usual in the classic Ostwald procedure, or a corresponding volume ratio of O2 / NH3 of at least 1.9 is adjusted in the practical examples. The studies or the published data are almost always limited to atmospheric conditions, which provide clearly higher selectivities for NO formation than would be expected for high pressures. However, the large-scale NOx yields achieved with Pt / Rh network catalysts are not attainable. This is particularly true even with high NH3 yields, i.e., with a high inlet concentration of 10% by volume and high operating pressure, which are advantageous and common for practical applications due to the small size of the equipment and optimal tuning for subsequent NO / NO2 absorption. Thus, the NOx yield is typically reduced with high concentrations or high (partial) pressures of ammonia. This is especially the case for catalysts based on known oxides such as Co3O4 (see, for example, Andrew, SPS; Chinchen, GC, "The loss in selectivity of a cobalt oxide ammonia oxidation catalyst" in "Studies in surface science and catalysis"; 6 (1980), p. 1).141-148, (Catalyst deactivation: proceedings of an international symposium, Antwerp, October 13-15, 1980), which exhibit significantly lower activity compared to metallic platinum-based catalysts. A high partial pressure of ammonia requires, to a greater extent, undesirable secondary and subsequent reactions, leading to the formation of N2 or N2O. In industrial applications, transition metal oxide catalysts play no role in the oxidation of NH3, with the exception of the occasionally mentioned combination of iron oxide-based catalysts with noble metal networks, despite multiple efforts. Now, as before, Pt / Rh network catalysts are used in this case almost without exception. As mentioned previously, differences can be made in this respect depending on the operating pressure of the NH3 combustion (atmospheric pressure / medium pressure / high pressure) and the prevailing pressure level of NOx absorption in the absorption tower, between different process or installation variants. (see also Winnacker-Küchler, Chemische Technik - Prozesse und Produkte, 5th edition, volume 3, chapter 3, p. 248275, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, 2005; Thiemann, M., Scheibler, E., Wiegand, KW Nitric Acid, Nitrous Acid, and Nitrogen Oxides, Wiley-VCH Verlag GmbH & Co. KGaA, 2000). Of particular importance in this regard are the so-called single-pressure or monopressure process, which uses medium or high pressure for both NH3 combustion and NOx absorption, and the so-called dual-pressure process, which uses medium-pressure NH3 combustion and high-pressure NOx absorption. Previously common systems that used atmospheric pressure combustion and medium-pressure absorption have now been largely replaced by more economical single-pressure or dual-pressure processes with greater capacities. Figure 1 shows a simplified flow diagram of a typical medium single-pressure installation. Thus, the facilities for the preparation of HNO3 normally contain an NH3 evaporator for the facilitation of gaseous NH3, an air compactor for the combustion air, an NH3 oxidation reactor for the accommodation of the Pt network catalysts with an integrated process gas cooler, various heat exchangers or coolers and condensers for the further cooling of the process gas or for heating the waste gas leaving the absorption tower, an absorption tower for the absorption of NOx and formation of HNO3, a reactor for the (catalytic) separation of NOx and possibly residual N2O contained in the waste gas, as well as a waste gas turbine for energy recovery by releasing the waste gas into the atmosphere.In two-pressure installations, there is an additional compression stage located between the NH3 oxidation reactor and the absorption tower for compacting the process gas to the desired absorption pressure. Documents US 2012 / 0183467 A1 and WO 01 / 49603 A1 and EP 0 799 792 A1 and WO 2006 / 010904 A1 describe other devices and procedures for oxidation, in particular also catalysts especially for the oxidation of ammonia. Aim The objective of the present invention is to provide, based on transition metal oxide catalysts, an improved process and a suitable installation for the oxidation of NH3, characterized by high NOx yields compared to those achieved to date with these catalysts. Furthermore, the process is characterized by long catalyst exposure times and low catalyst costs. Description of the invention This objective is achieved by facilitating an ammonia oxidation process with oxygen in the presence of catalysts containing at least one transition metal oxide, which is not a platinum metal oxide, in which the ratio of the molar amounts of O2 and NH3 in the reaction gas fed to the catalyst at the inlet of the gaseous mixture of starting products in the catalyst bed is adjusted to a value clearly below the conventional ratio of 1.9 mol / mol, so that a high NOx yield is achieved, and in which catalysts other than the commercially available platinum metal network catalysts used so far are used. We have surprisingly found that when using non-platinum metal catalysts, specifically selected transition metal oxide catalysts such as LaCoO3 or LaMnO3, the yield of the NOx product can be significantly increased when the oxygen content or the O2 / NH3 ratio in the gaseous starting product mixture is adjusted so that almost all the oxygen reacts with ammonia according to the primary oxidation reactions (reaction schemes 1, 5, 6, and 7), leaving little or no residual oxygen in the resulting product gas. A large excess of oxygen, as is usually the case otherwise, has a negative effect in this instance. It has turned out that by reducing the oxygen content or the molar ratio of oxygen to ammonia before the entry of the gaseous mixture of starting products into the catalyst bed, the NOx yield can be increased even with high partial pressure of NH3, i.e., high total pressure or high concentration of NH3, to values ​​that, on the contrary, can only be achieved with platinum metal catalysts (Pt / Rh networks). The present invention relates to a process for the oxidation of ammonia with oxygen in the presence of catalysts containing at least one transition metal oxide, which is not a platinum metal oxide, wherein the molar ratio of oxygen to ammonia in the inlet of the gaseous mixture of starting products to the catalyst bed is adjusted to values ​​of 1.25 - 1.75 mol of O2 / mol of NH3 and the temperature at the outlet of the product gas from the catalyst bed is between 700 °C and 950 °C. In particular, the molar ratio is found to be adjusted according to the invention of oxygen with respect to ammonia in the range of 1.30 - 1.75 mol of O2 / mol of NH3, preferably a ratio of 1.35 - 1.60 mol of O2 / mol of NH3 is adjusted and very preferably a ratio of 1.35-1.50 mol of O2 / mol of NH3 is adjusted. In the case of carrying out a preferred variant of the procedure according to the invention, the ratio of the molar amounts of oxygen to ammonia of the gaseous mixture of starting products at the inlet to the catalyst bed is selected so that it is in the range between 0.1 mol of O2 / mol of NH3 below and 0.4 mol of O2 / mol of NH3 above an optimum molar ratio, the optimum molar ratio being that ratio of the molar amounts of oxygen to ammonia at the inlet of the gaseous mixture of starting products to the catalyst bed, with which a maximum of the NOx yield is achieved. The ratio of molar amounts of oxygen to ammonia at the catalyst bed inlet is particularly preferential between 0.05 mol of O2 / mol of NH3 below and 0.3 mol of O2 / mol of NH3 above the optimum ratio, and especially advantageously between 0.025 mol of O2 / mol of NH3 below and 0.25 mol of O2 / mol of NH3 above the optimum ratio. The determination of the optimum molar ratio of O2 / NH3 or the optimum oxygen content can be carried out by means of a series of corresponding tests under the desired procedural conditions in a specific way, i.e. with a selected catalyst in a defined installation, with a defined space velocity and flow rate, with a defined outlet or inlet temperature, a defined pressure and a defined reaction medium containing oxygen and a defined amount of ammonia.In this respect, the oxygen concentration at the catalyst bed inlet is selected with a constant NH3 concentration so that the corresponding molar O2 / NH3 ratio lies between a minimum O2 / NH3 ratio, for example, 1.25 mol / mol, and a maximum O2 / NH3 ratio, for example, 1.75 mol / mol. This ratio is preferably varied by a selected increment, for example, less than or equal to 0.1 mol O2 / mol NH3, and the NOx yield achieved in each case is determined. The molar ratio of oxygen to ammonia that, under otherwise identical reaction conditions, provides the maximum NOx yield is then the optimum oxygen-to-ammonia ratio. In another preferred variant of the process according to the invention, the ratio of the molar quantities of oxygen to ammonia in the inlet of the gaseous mixture of starting products in the catalyst bed is adjusted to values ​​less than or equal to 1.75 mol of O2 / mol of NH3, preferably to values ​​less than or equal to 1.60 mol of O2 / mol of NH3 and especially preferably to values ​​less than or equal to 1.50 mol of O2 / mol of NH3, increasing the oxygen content in the product gas at the outlet of the catalyst bed to at least 0.3% by volume, preferably to at least 0.4% by volume and particularly preferably to at least 0.5% by volume. In a preferred embodiment of this preferred variant of the process according to the invention, a suitable molar ratio according to the invention of O2 / NH3 less than or equal to 1.75 mol O2 / mol NH3, or a suitable oxygen content according to the invention, of the gaseous mixture of starting products at the inlet of the catalyst bed is established by the oxygen content of the product gas at the outlet of the catalyst bed. A suitable molar ratio according to the invention of O2 / NH3, or—with a predetermined inlet concentration of NH3—a suitable oxygen content according to the invention, is selected at the inlet of the catalyst bed such that the oxygen content in the product gas at the outlet of the catalyst bed is between 0.3% by volume and 10.0% by volume, preferably between 0.4% by volume and 6.0% by volume, and especially preferably between 0.5 and 4.0% by volume, especially to between 0.3% by volume and 2.0% by volume, particularly to between 0.4% by volume and 2.0% by volume, and most preferably to between 0.5% by volume and 1.5% by volume. The practical adjustment of the appropriate O2 / NH3 ratio according to the invention can be carried out for certain process conditions, i.e., with a selected catalyst in a defined installation, with a defined space velocity and flow rate, with a defined inlet or outlet temperature, a defined pressure, and a defined reaction medium containing oxygen and ammonia, for example, so that under these process conditions, starting from a predetermined O2 / NH3 ratio, for example, starting from a conventional O2 / NH3 ratio of 1.9 mol / mol or in particular starting from an O2 / NH3 ratio of 1.75 mol / mol, with a fixed amount of ammonia, the oxygen content at the inlet of the catalyst bed is reduced until the aforementioned low oxygen contents are present or detected in the product gas at the outlet of the catalyst bed. The determination of NOx and O2 content at the catalyst bed outlet can be performed using procedures familiar to the expert. For example, NOx content can be measured using IR / UV analyzers with heated gas measuring cells. Suitable analyzers include multi-component FT-IR systems or single-component systems with multiple IR or UV channels. Alternatively, NOx content can also be measured using a chemiluminescence analyzer with a pre-connected converter for the reduction of NO2 to NO. Oxygen content can be measured, among other things. advantageously with a heated analyzer for paramagnetism measurement or a zirconium probe. The oxygen content of the product gas at the catalyst bed outlet can also be determined computationally as the difference between the oxygen content of the gaseous mixture of starting products at the catalyst bed inlet and the oxygen consumption in the catalyst bed. The oxygen consumption in the catalyst bed is thus derived from the outlet concentrations of the components N2, NO, NO2, and N2O, or from the product selectivities derived from the inlet concentration of NH3 and the corresponding stoichiometric ratios of O2 / NH3 according to equations (1), (5), (6), and (7). The procedure according to the invention is preferably operated with pressures from 100 kPa abs. to 1000 kPa abs., especially preferably with pressures from 150 kPa abs. to 600 kPa abs., and most especially preferably with pressures from 200 kPa abs. to 5 kPa abs. The concentration of NH3 at the inlet to the oxidation reactor in the process according to the invention preferably ranges from 1-17% by volume, most preferably from 4-15% by volume, and in particular from 7-14% by volume. The upper limit of the NH3 content is advantageously determined in this respect by the lower explosion limit of the NH3-oxygen mixture, which also depends on other possible gas components, such as water vapor. For each volume percentage of ammonia in the gas mixture that reacts chemically with the catalysts, a specific amount of heat is released. In the case of a starting mixture of NH3 in air, this corresponds to a temperature increase of approximately 68 K between the starting mixture and the product mixture under adiabatic conditions. The temperature of the process gas at the outlet of the oxidation catalyst is predetermined by the ammonia concentration in the gas mixture at the catalyst inlet, which is determined by the installation of the inlet mixture containing ammonia and oxygen. The catalyst used according to the invention develops its maximum power preferably within a lower temperature range than platinum-based metal catalysts. The temperature at the outlet of the catalyst bed, for example, of the molded catalyst body arrangement, can preferably be adjusted according to the invention between 750 °C and 850 °C (measured at the outlet of the gas mixture from the catalyst bed, or, in the case of multiple catalyst beds, at the outlet of the last catalyst bed). This can be achieved by adjusting the inlet temperature of the starting gas mixture and / or the ammonia concentration in the starting gas mixture. Furthermore, the larger spatial extent of the molded catalyst body arrangement used according to the invention, compared to platinum-based metallic catalyst networks, enables polytropic operation through the evacuation or partial discharge of the heat of reaction. This can be achieved, for example, by cooling the reactor walls or by incorporating cooling devices into the catalyst arrangement. As already mentioned, the high activity of the molded catalyst bodies allows for a low start-up temperature or low blow-out temperature, and thus a low inlet temperature of the gaseous mixture of starting materials containing NH3 and oxygen into the (first) catalyst bed, for example, in an arrangement of molded catalyst bodies. This inlet temperature can range from 20 °C to 300 °C, preferably from 50 °C to 200 °C, and most preferably from 50 °C to 150 °C. Catalysts For the process according to the invention, basically all catalysts are suitable, which contain as an active component at least one transition metal oxide, which is not any oxide of a platinum metal. A platinum metal in this respect, in the context of this description, is an element of the 5th and 6th period of groups 8 to 10 of the periodic table of elements, that is, an element of the group of Ru, Rh, Pd, Os, Ir and Pt. The catalysts used according to the invention show, under the operating conditions of the process according to the invention, i.e., with an NH3 / O2 ratio adjusted according to the invention in the range between 0.1 mol O2 / mol NH3 below and 0.4 mol O2 / mol NH3 above the optimum molar ratio, surprisingly high NOx yields, compared to the NOx yields under the operating conditions of conventional processes for ammonia oxidation, where the ratio of the molar amounts of oxygen and ammonia in the inlet of the gaseous mixture of starting products to the catalyst is at least 1.9 mol O2 / mol NH3. Therefore, the catalysts used according to the invention under the operating conditions of the process according to the invention allow NOx yields that can be comparable to or even better than the NOx yields in the Ostwald process using metal lattice catalysts of commercially available platinum. In particular, suitable catalysts are those containing transition metal oxides, which are not platinum metal oxides and, under the condition mentioned above, do not allow any irreversible reduction to give actively lower valence oxides. Therefore, in this respect, catalysts containing stabilized, i.e., impured, transition metal oxides can be used, which are not platinum metal oxides or contain mixed oxides of these transition metal oxides. Examples of impured transition metal oxides are, for instance, iron oxides impured with bismuth oxide, chromium oxide, or manganese oxide. The mixed oxides that can be used preferentially have a spinel, delaphosite structure or, more preferably, a perowskite or brownmillerite structure. The perowskites used according to the invention preferably have the structure ABO3-5, in which A represents mono-, di- or trivalent cations and B represents tri-, tetra- or pentavalent cations, the ionic radius of A is greater than the ionic radius of B and 8 is a number between 0.001 and 1.5, preferably between 0.01 and 0.9 and especially preferably between 0.01 and 0.5. In the perowskites used according to the invention, mixtures of different A cations and / or B cations may also be found. The brownmillerites used according to the invention normally have the structure A2B2O5-5, in which A, B, and 8 have the meanings defined above. Mixtures of different A cations and / or B cations may also be found in the brownmillerites used according to the invention. B cations can appear within a compound in various oxidation states. Some or all of the B cations can also be trivalent or higher-valent cations with a constant oxidation state. The use of perowskites of the general molecular formula ABO3±8 and / or brownmillerites of the general molecular formula A2B2O5±8, in which the A position is occupied by more than 50%, preferably more than 80%, and most preferably more than 95%, by one or more elements selected from the rare-earth and alkaline-earth metal groups, and in which the B position is occupied by more than 50%, preferably more than 80%, and most preferably more than 95%, by one or more elements selected from the Cr, Mn, Fe, Co, Ni group, is particularly advantageous in this respect. Co is particularly preferred. A particularly suitable perowskite compound is LaCoO3±8 with 8 between 0.01 and 0.5. Like other impurity agents, transition metals are particularly suitable, whose oxides exist preferably in the tetravalent state, such as Ce or Mn. Naturally, small quantities of platinum metals or platinum metal oxides, for example up to 10% by weight, and in particular up to 5% by weight, relative to the active catalyst component(s), may be added to the catalysts used according to the invention. The presence of other metal (oxides), commonly used as additional impurities, is also possible. Examples of such impurities are alkali metals and / or alkaline earth metals. These impurities, if present, are also found only in small quantities, for example up to 10% by weight, and in particular up to 5% by weight, relative to the active catalyst component(s). The preparation of the catalytically active components or transition metal oxides used in the process according to the invention, as well as their formulation, will be addressed here only as an example, since those skilled in the art are familiar with various preparation methods suitable for this purpose. The prior art technologies that can be used for the preparation of the catalytically active components will be described below. The catalytically active components used in the process according to the invention can be prepared by reaction of solids. For this purpose, mixtures of oxides, binary oxides, or oxide-forming agents, such as carbonates, are commonly used as starting materials. The starting materials are thoroughly mixed into a composition adapted to the target phase and then calcined. Under calcination conditions, the catalytically active phases are formed in the form of crystallites. To increase the homogeneity of the starting mixture, intensive grinding of the starting materials is often carried out, sometimes with the addition of processing aids such as water. To increase the conversion of the desired crystalline phase, several stages of grinding and calcination can be performed alternately. After establishing a sufficient degree of crystallinity of the target phase, the particle size is adjusted, for example by dry grinding, to a size suitable for further shaping processes for generating molded catalyst bodies, such as extrusion or pressing. Another suitable preparation method involves the precipitation technique, in which the starting materials are obtained by precipitation in solutions. As precursors of metal oxides, they can be used for This includes, for example, metal hydroxides or complexed metal cations, such as citrates or oxalates, which can be precipitated in metal salt solutions. These solutions may contain only the primary component or both the primary and secondary components, and precipitation reagents can be used. Suitable precipitation reagents include, for example, alkalis such as ammonia or ammonium carbonate. Furthermore, the hydrolysis of alkoxides can be used to prepare precursors of metal oxides. A special technique that can be employed is the so-called sol-gel synthesis, in which stable colloidal systems are used instead of solutions. For alkoxides, hydrolysis agents such as water or various alcohols can be used. The stoichiometry of the metal oxide phases to be prepared is predetermined by carefully selecting the ratios of the starting compounds, such as metal salts or alkoxides. The metal oxide precursors thus prepared are processed by filtration, washing, and drying. In the subsequent calcination stage, the metal oxide phases are formed, which can then be homogenized by alternating milling and calcination stages. Further powder processing stages follow, notably milling and fractionation, to make the resulting powders available for shaping by, for example, extrusion or compression. Catalytically active components can also be prepared by pyrolysis reactions. This involves reacting metal-containing starting materials, such as metal salts, organometallic compounds, or precipitation products, in a strongly exothermic reaction at high temperatures, for example, up to 1000 °C. Oxidizing agents, such as ammonium nitrate, and organic fuels like urea, citric acid, or glycine can be added to the starting materials in this type of preparation. The pyrolysis reaction can be initiated from solutions, suspensions, or solids. The stoichiometry of the target phase can be adjusted by carefully arranging the starting compounds. The resulting powders are high-purity phases with high to very high specific surface area. For the formation of the prepared transition metal oxide powder, these and other active components or co-components can be introduced or embedded in a discretionary matrix, preferably ceramic, or they can be applied on a discretionary support, preferably ceramic. Ceramic material based on oxides, carbides or nitrides of selected elements from the Si, Al, Mg, Zr and B group is preferred; in particular, ceramic materials such as cordierite, mullite, magnesium oxide or especially silicon carbide, which is characterized by high chemical and mechanical strength and excellent thermal conductivity, are preferred. Furthermore, the use of complete catalysts, i.e., molded bodies consisting essentially of catalytically active material, is particularly suitable and preferred within the meaning of the invention. Thus, the molded catalyst bodies must be composed of more than 70%, preferably more than 80%, and most preferably more than 85% of the total weight of the molded body of catalytically active material. The molded catalyst body can be of any size and geometry, preferably with a high surface area to volume ratio and a low pressure drop in the flow. Molded bodies with a surface area to volume ratio of 0.5 to 10 mm⁻¹ are preferred, particularly those with a ratio of 1 to 5 mm⁻¹. All geometries commonly used in catalysis are typical, such as cylinders, hollow cylinders, multi-hole cylinders, rings, granules, trilobes, or honeycomb structures. Honeycomb monoliths or so-called miniliths (very small molded honeycomb bodies) are especially preferred and are generally used as bulk material.Molded bodies can be prepared by forming procedures known in ceramic processing, such as dry pressing, granulation or extrusion. The arrangement of the molded catalyst bodies can be done, for example, as a stacking without a rule or as an ordered packing. Reactor The ammonia oxidation reactor used according to the invention can be configured as a conventional ammonia oxidation reactor or "burner." This is particularly advantageous when retrofitting existing installations, as no or only minor mechanical modifications are required. Pt / Rh networks are frequently found on a loose stack of ceramic rings. In the process according to the invention, the molded catalyst body can then be incorporated in place of the Pt / Rh networks and ceramic rings, as previously mentioned, either as a stack or as an orderly packing, for example, of honeycomb-like bodies within the reactor. Special precautions must generally be taken at the reactor edge to prevent any of the ammonia / oxygen-containing gaseous starting product mixture from flowing past the catalyst.Such precautions may include, for example, metal strips impermeable to gases stable at high temperatures, which are attached to the wall of the 5. reactor and on which the catalyst stack or the outer elements of the ordered catalyst packing are partially supported. In the case of new installations, it can be highly advantageous to use alternative construction methods to the classic ammonia oxidation reactor design, which is characterized by a large diameter and very low height in the direction of the catalyst packing flow. Reducing the cross-section of the inlet flow can mitigate potential difficulties with the uniform distribution of the incoming gas mixture. A rapid flow of the catalyst bed with short residence times is particularly preferred, as this suppresses undesirable secondary reactions, such as the catalytic decomposition of the NO formed, and also allows for a compact, space-saving design of the ammonia oxidation reactor.For other possible configurations of the ammonia oxidation reactor, equipped with the catalyst used according to the invention, refer to document WO 2008 / 148487A1. The process according to the invention is preferably operated at space velocities of 50,000 h⁻¹ to 500,000 h⁻¹, and most preferably between 100,000 h⁻¹ and 300,000 h⁻¹. In this context, the term "space velocity" refers to the ratio of the volume proportions of gas mixture (measured at 273.15 K and 101.325 kPa) per hour to a volume proportion of catalyst, i.e., the stacking or packing volume. The space velocity can therefore be adjusted by adjusting the volumetric flow rate of the gas and / or the volume or quantity of the catalyst. Regardless of the preferred construction method for the respective application, the ammonia oxidation reactor of the process according to the invention is preferably equipped with a device for igniting the reaction on the catalyst. For example, a hydrogen flame directed onto the gas inlet side of the molded catalyst body of a movable lance can be used for this purpose. Performing the procedure The molar ratio according to the invention of O2 / NH3 in the gas flow at the inlet to the oxidation catalyst can be technically achieved in a different way. More simply, a quantity of this type of gaseous NH3 can be added to an air stream to achieve the desired O2 / NH3 molar ratio. A ratio of 1.25–1.75 mol O2 / mol NH3 corresponds in this case to an NH3 content of 14.4% by volume–10.7% by volume, a ratio of 1.3–1.75 mol O2 / mol NH3 corresponds to an NH3 content of 13.9% by volume–10.7% by volume, and a ratio of 1.35–1.6 mol O2 / mol NH3 corresponds to an NH3 content of 13.5% by volume–11.6% by volume. Another possible step for adjusting the molar ratio according to the invention of O2 / NH3 consists in the combustion of NH3 together with air or instead feeding, for example, a gas flow containing less than 20% by volume, preferably less than 10% by volume, and most preferably less than 5% by volume of oxygen. When the process according to the invention for the oxidation of NH3 is integrated into a process for the preparation of nitric acid or caprolactam, the NH3 combustion can be fed along with air or, preferably, with a certain proportion of the low-oxygen waste gas, for example, extracted from a waste gas purification reactor for the reduction of N2O and NOx. This is illustrated in Figure 2 for a two-pressure HNO3 plant. In this case, the purified waste gas flow (210) is depressurized before being fed into the NH3 combustion, again by means of a turbine (11), to the corresponding NH3 combustion pressure level. The purified, recycled waste gas must have an oxygen content of < 5% by volume, in particular < 3% by volume, and especially < 2% by volume. The residual NOx content must be < 20 ppmv, preferably < 10 ppmv, and most preferably < 5 ppmv. The air flow supplied to the NH3 combustion can also be divided, for example, by pressure swing adsorption, cryogenic decomposition, or membranes (e.g., a ceramic membrane that conducts oxygen anions), into a partial flow with reduced O2 content and a flow enriched in O2. One such embodiment is shown in Figure 3 as an example. The partial flow with reduced O2 content, for example, 13% O2 ​​by volume, is then fed with the NH3 to be burned (e.g., 10% by volume), while the partial flow enriched in O2 is fed to the process gas after the primary NH3 oxidation. Furthermore, the O2 / NH3 ratio according to the invention can be adjusted before the NH3 feed and contact with the NH3 oxidation catalyst by diluting the O2-containing gas stream with steam. The steam can then be condensed again after NH3 combustion by cooling the process gas stream before it enters the absorption tower, resulting in the formation of a weak acid. It is also conceivable to add other inert gas components to dilute the gas flow containing O2. The possibilities mentioned above for adjusting the molar ratio according to the invention of O2 / NH3 do not represent any conclusive list and may also be used in discretionary combination. Facilities The invention also relates to an installation for the oxidation of ammonia comprising A) a reactor (3) for the oxidation of ammonia equipped with at least one feed line for a gaseous mixture of starting products with at least one discharge line for a process gas, B) a catalyst (3a) inside the reactor (3), containing at least a transition metal oxide, which is not an oxide of a platinum metal, and C) a device for adjusting a molar ratio of oxygen to ammonia less than or equal to 1.75 mol / mol in the gaseous mixture of starting products by mixing an oxygen-containing gas stream with an O2 content <20% by volume with a selected amount of ammonia, wherein the oxygen-containing gas stream is generated c1) by means of a device for diluting an air stream with a gas stream containing less than 20% by volume, preferably less than 10% by volume, and especially preferably less than 5% by volume of oxygen or c2) by means of a device for oxygen depletion of a gas mixture containing oxygen, preferably from air or c3) by a combination of measures c1 and c2. The installation according to the invention can be operated at high pressure. In this variant, the installation includes at least one compactor (1) by means of which a gas flow containing oxygen, for example air, is compressed and fed to a reactor (3) for ammonia oxidation. The ammonia is fed to the reactor (3) by introducing the ammonia into the compressed oxygen-containing gas flow. The depressurization of process gases from the reactor (3) or from parts of the installation connected downstream to the reactor (3) to ambient pressure is carried out downstream after leaving the reactor (3) or the parts of the installation connected downstream to the reactor (3) by suitable means known to the expert. If the installation according to the invention is used, for example, for the generation of nitric acid, then the nitrogen oxide generated in the reactor (3) is mixed with secondary gas containing oxygen, for example, with secondary air, oxidized to give NO2, and introduced into an absorption tower (8), where the reaction of NO2 with water to give nitric acid takes place.The waste gas containing nitrogen oxides from the absorption tower (8) leaves it, is fed to a waste gas purification unit (9), leaves it as purified waste gas, is then fed to a waste gas turbine (10), where it is de-stressed with energy production and is discharged into the environment. The installation according to the invention preferably contains at least a second compactor for compacting the secondary gas flow containing oxygen before entering an absorption tower (8), in which the generated nitrogen oxide is treated with water. In a special embodiment, the air flow is diluted according to c1) with water vapor and / or nitrogen with an O2 content of <5% by volume. In another special embodiment, oxygen depletion according to c2) is carried out from a gas mixture containing oxygen, preferably air, by pressure change adsorption, cryogenic decomposition or by means of membranes. The invention also relates to an installation for the oxidation of ammonia and subsequent absorption of NOx comprising A) a reactor (3) for the oxidation of ammonia equipped with at least one feed line for a gaseous starting product mixture and at least one discharge line for a process gas, B) a catalyst (3a) inside the reactor (3), containing at least one transition metal oxide, which is not an oxide of a platinum metal, C) a device for adjusting a molar ratio of oxygen to ammonia less than or equal to 1.75 mol / mol in the gaseous starting product mixture by mixing an oxygen-containing gas stream with an O2 content of <20% by volume with a selected amount of ammonia, wherein the oxygen-containing gas stream is generated c1) by means of a device for diluting an air stream with a gas stream containing less than 20% by volume, preferably less than 10% by volume, especially preferably less of 5% by volume of oxygen or c2) by means of a device for oxygen depletion of a gas mixture containing oxygen, preferably from air, or c3) by a combination of measures c1 and c2, D) an absorption tower (8) for the absorption of NOx and formation of HNO3, HNO2 or nitrate or nitrite solutions and E) a device arranged between the reactor (3) for ammonia oxidation and the absorption tower (8) for combining the process gas flow containing NOx with a gas flow containing oxygen, containing more than 25% by volume, preferably more than 30% by volume, and especially preferably more than 40% by volume of oxygen. In a special embodiment, the air flow according to c1) is diluted with water vapor or with a nitrogen flow containing less than 20% by volume, preferably less than 10% by volume, and most preferably less than 5% by volume of oxygen. A nitrogen flow with an O2 content of <5% by volume, drawn from the waste gas pipeline downstream of the absorption tower, is particularly preferred. In another special embodiment, oxygen depletion according to c2) is carried out from a gas mixture containing oxygen, preferably air, by pressure change adsorption, cryogenic decomposition or by means of membranes. Preferably, the generation of the oxygen-containing gas flow is carried out, which is combined according to E) with the NOx-containing process gas flow, by oxygen enrichment of the air by pressure change adsorption, cryogenic decomposition or by means of membranes. Furthermore, preferably at the top of the absorption tower (8), a peroxide-containing stream is added. This may be a liquid stream containing a dissolved peroxide. Examples include solutions containing an inorganic peroxide compound, such as hydrogen peroxide or perborate, or solutions containing an organic peroxy compound, such as an organic peroxide, an organic hydroperoxide, or an organic percarboxylic acid or their esters. Preferably, the aforementioned facilities for the oxidation of ammonia are integrated into a facility for the preparation of nitric acid or caprolactam. Figures 1-3 illustrate, using the example of a nitric acid preparation plant, the prior art (Figure 1) and, by way of example, various versions of a plant according to the invention (Figures 2-3). They show: Figure 1: A simplified schematic representation of a conventional medium-pressure single-stage plant for the production of nitric acid. Figures 2 to 3: Schematic representations of variants of the procedure according to the invention / of the installation according to the invention integrated into a two-pressure installation for the production of nitric acid. Figures 4, 5 and 6: the dependence of the NOx yield on the oxygen content in the gaseous mixture of starting products or on the molar ratio of oxygen to ammonia in the gaseous mixture of starting products for three variants of the process according to the invention. Figure 1 shows a simplified flow diagram of a conventional medium-pressure single-stage reactor. In an air compactor (1), an air stream fed through pipe 100 is compressed and fed to the reactor (3) for ammonia oxidation via pipe 120. Before entering the reactor (3), the compressed air in pipe 120 is mixed with gaseous ammonia, which was previously fed in liquid form through pipe 110 to an ammonia evaporator (2). A portion of the compressed air from pipe 120 is also separated and fed through pipe 130 as so-called secondary air to the process gas before entering the absorption tower (8). In the reactor (3), where platinum metal lattices (3a) are fixed as catalysts over a wide surface, the oxidation of ammonia takes place, predominantly to NO and H₂O.The resulting product gas releases a first portion of the heat of reaction in the heating section of the reactor (3) to a heat exchanger (3b). It then leaves the reactor (3) and, with continuous oxidation of the NO formed using oxygen from the waste air or supplied via pipe 130, passes through another heat exchanger (4) for further cooling of the process gas before being fed to the absorption tower (8). At least one heat exchanger is configured as a condenser (5) for this purpose, in which a portion of the NOx and H2O formed is separated as acid condensate, which is then fed via pipe 150 using a pump (6) to the absorption tower (8). The remaining gas mixture, containing the still predominant portion of the NOx, is introduced, after combination with secondary air from pipe 130, via pipe 140 into the absorption tower (8).The additional air fed to the process gas serves for the subsequent oxidation of the NO contained in the gas. Procedure for producing NO2. In the absorption tower (8), the reaction of NOx with water to produce nitric acid takes place, which leaves the absorption tower (8) through pipe 160. The necessary water is fed to the absorption tower (8) through pipe 170. The waste gas containing nitrogen oxides from the absorption tower (8) leaves it through pipe 180, passes, among other things, through the heat exchanger (4), where it is heated, and is then fed to the waste gas purification unit (9). There, in modern installations, with the addition of gaseous ammonia (feed pipe 230), a catalytic degradation of the N2O contained in the waste gas and of the nitrogen oxides (NOx) into nitrogen and oxygen, or into nitrogen and water, is carried out.The purified waste gas leaving the waste gas purification (9), which is predominantly made up of nitrogen and in lower parts of water and oxygen and eventually traces of remaining nitrogen oxides, is then fed through pipeline 190 to a waste gas turbine (10), where it is de-stressed with energy production, leaves through pipeline 200 and is discharged into the environment. The flow diagram of a typical two-pressure installation for the preparation of HNO3 differs from the medium single-pressure installation depicted in Figure 1 by an additional compression stage, which is arranged in pipeline 140 after the feed of the secondary air flow 130 and before the entrance to the absorption tower (8). Similarly, a functional unit for bleaching the product acid with the secondary air flow is not shown in Figure 1. This unit may be integrated into the bottom of the absorption column or may also be implemented as a separate column, arranged in a two-pressure installation before the secondary air flow 130 is fed into the process gas flow line 140 downstream of the compression stage mentioned above for the process gas. Figure 2 reproduces as an example a flow diagram of one or more variants of the procedure according to the invention as well as one or more variants of an installation according to the invention using the example of a two-pressure nitric acid installation. The air compactor (1), the ammonia evaporator (2), the reactor (3), the heat exchanger (3b, 4), the condenser (5), the pump (6), the absorption tower (8), the waste gas purification (9) and the waste gas turbine (10) as well as the pipelines 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200 and 230 correspond in function and connection to the elements represented in Figure 1. Since this is a two-pressure installation, unlike Figure 1, it additionally shows a compactor (7), with which the process gas from pipeline 140 is compacted before its entry into the absorption tower (8). Furthermore, unlike Figure 1, the catalyst (3c) is not a platinum metal network, but is made as a packing or stacking of molded catalyst bodies, which contain a transition metal oxide, which is not an oxide of a platinum metal. Additionally, the installation shown in Figure 2 includes a conduit 220, through which a dilution medium in the form of a gas with an oxygen content of <20% by volume, such as oxygen-depleted air or water vapor, can be fed into the gaseous mixture of starting products before it enters the reactor (3). Furthermore, it is possible to feed a portion of the purified waste gas from the purification (9) of the waste gas (which contains predominantly nitrogen) before it enters the waste gas turbine (10) to an expander (11) and de-pressure it sufficiently so that it can be fed to the compressed air in conduit 120. With these measures (feeding a dilution medium with an oxygen content of <20% by volume through feed line 220 or partially recirculating the purified waste gas through line 210), individually or in combination, the desired oxygen-to-ammonia ratio according to the invention in the gaseous mixture of starting products can be adjusted in a controlled manner. Furthermore, with the installation shown in Figure 2, with or without the use of feed lines 210 and 220, the desired oxygen-to-ammonia ratio according to the invention in the gaseous mixture of starting products can be adjusted by means of a reduced primary air flow 120 compared to conventional HNO3 processes and a high secondary air flow 130. Figure 3 describes other variants of the procedure according to the invention as well as an installation according to the invention using the example of a two-pressure nitric acid installation. The air compactor (1), the ammonia evaporator (2), the reactor (3), the catalyst bed (3c), the heat exchanger (3b, 4), the condenser (5), the pump (6), the process gas compactor (7), the absorption tower (8), the waste gas purification (9) and the waste gas turbine (10), as well as the pipelines 100, 110, 140, 150, 160, 170, 180, 190, 200 and 230, correspond in function and connection mainly to the elements represented in Figure 2. Additionally, a device (12) for air decomposition is provided in the installation of Figure 3, into which the air from the air compactor (1) and compressed air is introduced.In device (12), a (partial) separation of air is carried out into a proportion with reduced oxygen content and a proportion with high oxygen content. The gas mixture with high nitrogen content is fed into line 120 and fed to reactor (3). The gas mixture with high oxygen content is fed into... Pipe 130 is fed to the gas mixture coming from the condenser (5), which contains predominantly NOx in pipe 140. With these measures, a desired oxygen-to-ammonia ratio in the gas mixture of starting products can also be adjusted in a controlled manner. Figure 3 also shows a conduit 240 through which a liquid flow containing peroxide can be directed to the absorption tower (8). This feed provides an alternative supply of the oxygen required for NO oxidation in the absorption tower. This measure can be used as an alternative to, or in combination with, measure E mentioned above, a device arranged between the reactor (3) for ammonia oxidation and the absorption tower (8) for combining the NOx-containing process gas flow with an oxygen-containing gas flow. Figures 4 to 6 show, using selected transition metal oxide catalyst examples (Figure 4 and 5: active component LaCoOa; Figure 6: active component LaMnOa), how increased NOx yields can be achieved with the oxidation of NHa for different variants of the process according to the invention on a laboratory scale by reducing the oxygen content in a gas mixture containing ammonia and oxygen, i.e., by adjusting the ratio according to the invention of the molar amounts of oxygen and ammonia in the inlet of the gas mixture of starting products to the catalyst bed. For this purpose, honeycomb catalysts 1 cm long, approximately 18 mm in diameter, and with a cell density of either 200 cpsi or 400 cpsi were used in a quartz glass tubular reactor with an inner diameter of 20 mm. A synthetic gas mixture of ammonia, oxygen, and nitrogen was flowed through these catalysts. The gas flow rates were controlled using thermal mass flow meters (FMFs), with the ammonia concentrations adjusted to 5% by volume (Figure 4) or 10% by volume (Figures 5 and 6). The oxygen concentration was varied between 20% and 6% by volume (Figure 4), between 19% and 12% by volume (Figure 5), or between 19% and 11% by volume (Figure 6). The space velocity in each case was 100,000 h⁻¹. By regulating the pressure at the reactor outlet, an operating pressure of 450 kPa (Figures 4 and 6) or 200 kPa (Figure 5) was set.The individual conditions of the examples reproduced in figures 4-6 are set out in the following table. Conditions Figure 4 Figure 5 Figure 6 Active component LaCoOa LaCoOa LaMnOa Honeycomb length cm cm cm Honeycomb diameter mm mm mm Cell density 200 cpsi 400 cpsi 200 cpsi Space velocity 100,000 h-1 100,000 h-1 100,000 h-1 Pressure 450 kPa 200 kPa 450 kPa Outlet temperature 750 °C 825 °C 900 °C NHa inlet concentration 4.5-4.8% by volume 9.1-9.a % by volume 9.1 - 9.2% by volume Oxygen inlet concentration 6. 20% by volume -19% in volume 11. 19% by volume To compensate for heat losses, the reaction tube was encased in a metal jacket and passed through two tubular furnaces arranged one above the other. The resulting reaction temperature was measured with a thermal element approximately 1 mm below the honeycomb (Toutlet). This outlet temperature reached approximately 750 °C for an ammonia inlet concentration of 5% by volume (Figure 4) and 825 °C (Figure 5) or approximately 900 °C (Figure 6) for a 10% by volume concentration. Test gas analyses were performed by alternately switching between the reactor inlet and outlet to an analyzer. An FT-IR analyzer (Thermo-Nicolet model "6700 Advanced Gold"), equipped with a 15 cm long heated cuvette, was used to determine the volume concentrations of ammonia, nitrogen monoxide (NO), nitrogen dioxide (NO2), and water.The determination of the O2 concentration was carried out using the OXYMAT 6 apparatus, heated version of the Siemens company. The indicated volume concentration corresponds, to a first approximation, to the molar concentrations of the individual components. For each adjustment of a new oxygen inlet concentration, a steady-state operating point was expected based on the analytical result of the gas at the reactor outlet. Figures 4 to 6 show the calculated yields of the total parameter NOx (= NO + NO2) with respect to the ammonia inlet concentrations depending on the oxygen inlet concentration, considering for the calculation of NOx yield from molar concentrations the volume modifications linked with the individual primary reactions (schemes 1, 5, 6 and 7). In each case, a prominent maximum in NOx performance can be clearly distinguished, corresponding to the density of the measurement points located in Figure 4 with an O2 content of 7% by volume, corresponding to a ratio of molar O2 and NH3 inlet concentrations of 1.4 mol / mol, in Figure 5 with an O2 content of 13% by volume, corresponding to a ratio of molar O2 and NH3 inlet concentrations of 1.3 mol / mol, and in Figure 6 with an O2 content of 12% by volume, corresponding to a ratio of molar O2 and NH3 inlet concentrations of 1.2 mol / mol. Furthermore, it can be clearly distinguished that with a non-in-accordance ratio of the molar O2 and NH3 inlet concentrations of 1.9 mol / mol, as normally used in conventional technical processes for the oxidation of ammonia (10% by volume of NH3 in air), a clearly lower NOx yield is achieved than in the selected range in accordance with the invention of the optimum molar ratio of oxygen to ammonia. A decrease in the range mentioned above leads to a clearly reduced NOx yield, as is evident in Figure 4 with an O2 content of 6% by volume corresponding to a molar O2 and NH3 inlet concentration ratio of 1.2 mol / mol, in Figure 5 with an O2 content of 12% by volume corresponding to a molar O2 and NH3 inlet concentration ratio of 1.2 mol / mol, and in Figure 6 with an O2 content of 11% by volume corresponding to a molar O2 and NH3 inlet concentration ratio of 1.1 mol / mol. The honeycomb bodies were manufactured by extruding LaMnO3 or LaCoO3 powders, processed accordingly with the addition of appropriate binders and plasticizing adjuvants, followed by drying and calcination. The starting powders for the catalysts under test were prepared by alkaline precipitation of stoichiometrically prepared solutions of the corresponding metal salts, followed by filtration, washing, and final calcination of the resulting precipitates. Phase formation and the purity of the respective perowskite phases were tested using XRD (X-ray diffraction).

Claims

1. A process for the oxidation of ammonia with oxygen in the presence of catalysts containing at least one transition metal oxide, which is not any platinum metal oxide, wherein the ratio of the molar amounts of oxygen to ammonia at the inlet of the gaseous starting product mixture to the catalyst bed is adjusted to values ​​of 1.25 - 1.75 mol O2 / mol NH3 and the temperature at the outlet of the product gas from the catalyst bed is between 700 °C and 950 °C.

2. A process according to claim 1, characterized in that the molar ratio of O2 to NH3 in the gaseous mixture of starting products at the inlet to the catalyst bed is 1.30–1.75 mol O2 / mol NH3, particularly advantageously 1.35–1.60 mol O2 / mol NH3, and most advantageously 1.35–1.50 mol O2 / mol NH3.

3. A process according to any one of claims 1 or 2,characterized in that the ratio of the molar amounts of O2 to NH3 in the gaseous mixture of starting products at the inlet to the catalyst bed is selected so that it is in the range between 0.1 mol of O2 / mol of NH3 below and 0.4 mol of O2 / mol of NH3 above an optimum molar ratio, wherein the optimum molar ratio is that ratio of oxygen to ammonia at the inlet of the gaseous mixture of starting products to the catalyst bed, with which a maximum NOx yield is achieved.

4. A process according to at least one of claims 1 to 3, characterized in that the ratio of the molar amounts of oxygen and ammonia at the inlet to the catalyst bed is between 0.05 mol O2 / mol NH3 below and 0.3 mol O2 / mol NH3 above the optimum molar ratio, particularly advantageously between 0.025 mol O2 / mol NH3 below and 0.25 mol of O2 / mol of NH3 above the optimum molar ratio.

5. A method according to at least one of claims 1 to 4, characterized in that the optimum molar ratio of oxygen to ammonia is determined by performing a series of tests under given procedural conditions with a selected catalyst in a defined installation, with defined space velocity and flow rate, with defined inlet or outlet temperature, defined pressure, and a defined reaction medium containing oxygen and a defined amount of ammonia, wherein the oxygen concentration at the inlet to the catalyst bed is selected such that the corresponding molar O2 / NH3 ratio varies between a minimum molar O2 / NH3 ratio, preferably a minimum molar O2 / NH3 ratio of 1.25 mol / mol, and a maximum molar O2 / NH3 ratio, preferably a maximum molar O2 / NH3 ratio of 1.75 mol / mol.The NOx yield achieved in each case is determined, and then the molar ratio of oxygen to ammonia that, under otherwise identical reaction conditions, provides the maximum NOx yield is determined.

6. A process according to at least one of claims 1 to 5, characterized in that the ratio of the molar amounts of oxygen to ammonia in the inlet of the gaseous mixture of starting products to the catalyst bed is adjusted to values ​​less than or equal to 1.75 mol O2 / mol NH3, preferably to values ​​less than or equal to 1.60 mol O2 / mol NH3, and particularly preferably to values ​​less than or equal to 1.50 mol O2 / mol NH3, and wherein the oxygen content in the product gas at the outlet of the catalyst bed is at least 0.3% by volume, preferably at least 0.4% by volume, and particularly preferably at least 0.5% by volume.

7. A process according to claim 6, characterized in that the ratio of the molar amounts of oxygen to ammonia in the inlet of the gaseous mixture of starting products to the catalyst bed is selected such that the oxygen content in the product gas at the outlet of the catalyst bed is between 0.3% by volume and 10.0% by volume, preferably between 0.4% by volume and 6.0% by volume, and particularly preferably between 0.5% and 4.0% by volume.

8. A process according to claim 7, characterized in that the ratio of the molar amounts of oxygen to ammonia in the inlet of the gaseous mixture of starting products to the catalyst bed is selected such that the oxygen content in the product gas at the outlet of the catalyst bed is between 0.3% by volume and 2.0% by volume, preferably between 0.4% by volume and 2.0% by volume.0% by volume, particularly preferably between 0.5% and 1.5% by volume.

9. A process according to at least one of claims 1 to 8, characterized in that the NH3 concentration at the inlet of the oxidation reactor is between 1-17% by volume, especially preferably between 4-15% by volume, and in particular between 7-14% by volume.

10. A process according to at least one of claims 1 to 9, characterized in that the temperature at the outlet of the product gas from the catalyst bed is between 750°C and 850°C.

11. A process according to at least one of claims 1 to 10, characterized in that the heat of reaction is partially discharged, in particular by cooling the reactor walls and / or by placing cooling devices integrated into the catalyst arrangement.

12. A process according to at least one of claims 1 to 11,characterized in that the inlet temperature of the gaseous mixture of starting products containing NH3 and oxygen into the catalyst bed is between 20 °C and 300 °C, preferably between 50 °C and 200 °C and especially preferably between 50 °C and 150 °C.

13. Process according to at least one of claims 1 to 12, characterized in that the volumetric flow rate of the gaseous mixture of starting products and / or the volume of catalyst are adjusted so as to result in a space velocity of 50,000 h-1 to 500,000 h-1, preferably between 100,000 h-1 and 300,000 h-1.

14. A process according to at least one of claims 1 to 13, characterized in that the catalyst contains doped transition metal oxides, which are not platinum metal oxides and / or mixed oxides of these transition metal oxides.

15. A process according to claim 14, characterized in that the mixed oxides have a spinel, delaphosite, structure.perowskite or brownmillerite.

16. A process according to claim 15, characterized in that the mixed oxide with a perowskite structure has the general molecular formula ABO3±s and / or in that the mixed oxide with a brownmillerite structure has the general molecular formula A2B2O5±5, wherein 8 takes a value between 0.01 and 0.5, A represents mono-, di-, or trivalent cations, and B represents tri-, tetra-, or pentavalent cations, and the ionic radius of A is greater than the ionic radius of B.

17. A process according to claim 16, characterized in that position A of the perowskite and / or the brownmillerite is occupied by more than 50%, preferably more than 80%, and especially more preferably more than 95%, by one or more elements selected from the rare-earth metal and alkaline-earth metal groups, especially preferably by La, and position B of the perowskite and / or the brownmillerite is occupied by more than 50%preferably more than 80%, especially preferably more than 95%, by one or more elements selected from the Cr, Mn, Fe, Co, Ni group, especially preferably by Co and Mn, particularly preferably by Co.

18. Process according to claim 17, characterized in that the perowskiite has the composition LaCoO3±s.

19. Process according to at least one of claims 1 to 18, characterized in that the catalyst contains introduced or embedded transition metal oxides, which are not platinum metal oxides, and optionally other active components and / or co-components in a matrix, preferably a ceramic matrix, or contains transition metal oxides, which are not platinum metal oxides, and optionally other active components and / or co-components applied on a support.

20. Process according to at least one of claims 1 to 19,characterized in that the catalyst is a complete catalyst, i.e., a molded body, which is essentially made of catalytically active material.

21. A process according to at least one of claims 1 to 20, characterized in that the molar ratio of O2 / NH3 in the gaseous mixture of starting products at the inlet to the catalyst bed is adjusted by adding gaseous ammonia to an air flow.

22. A process according to at least one of claims 1 to 20, characterized in that the molar ratio of O2 / NH3 in the gaseous mixture of starting products at the inlet to the catalyst bed is adjusted by adding gaseous ammonia and adding a gas having an oxygen content of less than 20%, preferably less than 10%, and most preferably less than 5%.to an airflow.

23. Installation for the oxidation of ammonia comprising: A) reactor (3) for the oxidation of ammonia equipped with at least one feed line for a gaseous mixture of starting products and with at least one discharge line for a process gas, B) catalyst (3c) inside the reactor (3), containing at least one transition metal oxide, which is not an oxide of a platinum metal, C) device for adjusting a molar ratio of oxygen to ammonia in the gaseous mixture of starting products less than or equal to 1.75 mol / mol, a gas stream containing oxygen with an O2 content <20% by volume being mixed with a selected amount of ammonia, wherein the gas stream containing oxygen c1) is generated by a device for diluting an air stream with a gas stream containing less than 20% by volume, preferably less than 10% by volume,24. Installation for the oxidation of ammonia according to claim 23 with subsequent absorption of NOx comprising elements A), B) and C) of claim 23 as well as D) an absorption tower (8) for the absorption of NOx and the formation of HNO3, HNO2 or nitrate or nitrite solutions, and E) a device arranged between the reactor (3) for the oxidation of ammonia and the absorption tower (8) for combining the process gas stream containing NOx with a gas stream containing oxygen, containing more than 25%, preferably more than 30%, and most preferably more than 40% oxygen,and / or a conduit (240) leading to the absorption tower (8) for the introduction of a peroxide-containing flow.

25. Installation for the oxidation of ammonia according to claim 23, characterized in that it is integrated into an installation for the preparation of nitric acid or caprolactam.

26. Installation according to at least one of claims 23 to 25, characterized in that the air flow according to c1) is diluted with water vapor or with a nitrogen flow, containing less than 20% by volume, preferably less than 10% by volume, and especially preferably less than 5% by volume of oxygen.

27. Installation according to at least one of claims 23 to 26, characterized in that the dilution of the air flow according to c1) is carried out with a gas flow extracted from the waste gas downstream of the absorption tower (8).

28. Installation according to at least one of claims 23 to 27,characterized in that the oxygen depletion of an oxygen-containing gas mixture, preferably air according to c2), is achieved by pressure swing adsorption, cryogenic decomposition, or by means of membranes.

29. Installation according to at least one of claims 24 to 28, characterized in that the oxygen-containing gas flow according to E) is achieved by oxygen enrichment of air by pressure swing adsorption, cryogenic decomposition, or by means of membranes.

30. Installation according to at least one of claims 23 to 29, characterized in that it comprises at least one compactor (1), by means of which an oxygen-containing gas flow is compressed and fed to the reactor (3) for ammonia oxidation.

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