Process for removing n2o from a gas stream

Abstract

A process for reducing the concentration of N2O in a gas stream and a chemical production unit therefor are provided, the process comprising: (a) providing a gas stream, containing N2O, (b) treating the gas stream with an aqueous washing fluid in an absorption unit operated with a liquid continuous phase, (c) passing the gas stream obtained in step (b) through a droplet separating unit; and (d) contacting the gas stream obtained in step (c) with a N2O decomposition catalyst. The use of a droplet separating unit after an absorption unit enhances the performance of the N2O decomposition catalyst.

Description

[0001] Process for removing N2O from a gas stream

[0002] The present invention relates to a process and a chemical production unit for reducing the concentration of N2O in a gas stream, especially a gas stream derived from an industrial production process, wherein a gas stream containing N2O is provided, followed by treating the gas stream in an absorption unit, passing it through a droplet separating unit and a N2O decomposition unit.

[0003] Background of the invention

[0004] Nitrogen monoxide (NO), nitrogen dioxide (NO2), referred to collectively as NOX, and nitrous oxide (N2O), also known as laughing gas, are known gases which are harmful to the environment, and the related emissions are subject to strict regulations. Thus, efforts have been made to limit the amount of these compounds entering the atmosphere by converting those to environmentally accepted compounds. The gases are usually found in off-gas streams of various industrial processes, for example, in the production of nitric acid, adipic acid, caprolactam or in nitration processes like the production of dinitrotoluene (DNT) as well as in off-gas streams of combustion processes.

[0005] There are already several abatement technologies known for reducing the content of N2O on the one hand and NOXon the other hand.

[0006] Different catalytic and non-catalytic techniques can be used to make nitrous oxide and / or NOXharmless. WO 2012 / 48765 A1 , for example, disclose a process using thermal decomposition of N2O forming N2 and O2. For the catalytic decomposition of N2O into N2 and O2, various catalysts are known, for example, transition metal-containing zeolites, optionally in the presence of a reducing agent (see, for example, WO 2013 / 118064 A1). WO 03 / 084646 A1 discloses a process for reducing the content of NOXand N2O in a process gas or off-gas using an iron- loaded zeolite catalyst and ammonia and methane as reducing agents.

[0007] WO 2011 / 151006 A1 discloses a process for removing N2O and NOXfrom exhaust gases, wherein a NOXdecomposition stage is operated downstream of a N2O decomposition stage at inlet temperatures of < 400°C. Dependent on the water content of the gas to be treated in the N2O decomposition stage and a selected N2O / NOXratio, the operating parameters of the N2O decomposition stage are selected such that a N2O decomposition of 80-98% results, wherein the downstream NOXdecomposition stage may be operated under optimal conditions. The water content of the gas is usually adjusted by suitable measures, if the gas stream does not already contain sufficient water, for example using a saturator or an absorption tower.

[0008] CN 106823793 A discloses a process for removing N2O and NOXfrom an off-gas of an adipic acid production plant, wherein the process comprises a gas-liquid separator to remove water, a step of dilution with air to maintain a N2O content of 8-15 vol%, an integrated (recuperative) heat recovery, a catalytical N2O decomposition unit, an ammonia dosage unit, a unit for catalytic reduction of NOXwith ammonia and a step of steam generation. US 2010 / 0303699 A1 discloses a process for removing N2O from an off-gas by contacting the off-gas with a reducing agent in the presence of an iron-zeolite based catalyst, wherein the steam concentration of the off-gas adjusts the temperature of the off-gas in the catalytic reactor or the amount of the reducing agent to be added.

[0009] CN 110538570 A describes a process for co-processing N2O and VOC, mainly tert-butanol, in an off-gas from a caprolactam production plant using a system comprising a gas storage device for buffering, a spray tower using water for condensing and absorbing most of tert-butanol, wherein a demister is arranged at the top to remove acid mist, a gas dilution device introducing N2, a catalytic reactor using inter alia a Fe-BEA catalyst and a discharging device, when the emission meets the requirements. The catalytic reaction uses the remaining tert-butanol as a reducing agent for N2O to yield N2, CO2 and water. Mass transfer in a spray tower as an absorption unit functions mainly between the dispersed liquid droplets and the continuous gas phase. Thus, a demister is needed due to the presence of a dispersed liquid droplet phase.

[0010] WO 2022 / 152605 A1 discloses a process for working-up IXhO-containing off-gas from an adipic acid production process by catalytically decomposing N2O in a fixed bed reactor, wherein for controlling the N2O decomposition unit a nonlinear model predictive control is used which is based on a reactor model of the fixed bed reactor based on equations of energy transport and species transport for N2, O2 and N2O.

[0011] US 2003 / 0143142 A1 discloses a process for reducing NOXand N2O concentration from residual gas from nitric acid production comprising a first stage of catalytic reduction of NOXand a second stage of catalytic decomposition of N2O, where the molar NOX / N2O ratio prior to entry of the gas into the second stage is in the range from 0.01 to 0.5. The water content of the gas prior to entry into the first or second stage may be of from 0.05 to 1 vol%.

[0012] WO 2024 / 149668 A1 discloses a process for removing NOX, N2O and CO from a gas stream, comprising a first step of removing NOXby adding air, followed by washing the gas stream, a second step of oxidizing CO at least partially and a third step of N2O decomposition, followed by an optionally CO oxidation step.

[0013] Unpublished PCT / EP2024 / 085424 discloses a process for removing NOXand N2O from an exhaust gas stream obtained from a nitration process, wherein the process comprising a step of converting N2O into N2 in the presence of a catalyst and hydrogen cyanide.

[0014] In plant facilities gas streams, especially off-gas streams, may vary in the composition, for example, in the water vapor content. Further, in case a gas stream is washed in an absorption unit, water is usually entrained in the gas stream, when leaving the absorption unit. Thus, the presence of water vapor in IXhO-containing off-gases may have an influence on the performance of a N2O decomposition catalyst, which in turn has an influence on the capability of N2O removal.

[0015] J. Pieterse et al, Applied Catalysis B; Environmental 71 , 2007, 16-22, describe the hydrothermal stability of wet ion-exchanged Fe-ZSM-5 and Fe-BEA catalyst for N2O decomposition in the presence of NO, H2O and O2 at 450°C. The N2O measurements were carried out on a composition typical for a large nitric acid plant: N2O 1500 ppmv (volume-ppm), NO 200 ppmv, H2O 0.5, 5 and 10 vol%, O2 2.5 vol% and balance N2. The N2O conversion is described to remain at a constant level with Fe-H-BEA even in the presence of large amounts of H2O, whereas deactivation was observed with Fe-H-ZSM-5 already in the presence of 0.5 vol% of water.

[0016] Although the lowering of the catalytic activity of such catalysts, for example, of an iron-zeolite based catalyst like Fe-H-BEA, is described not to happen under lab conditions, as described by J. Pieterse et al, this cannot generally be applied to N2O decomposition catalysts used for gas streams derived from industrial off-gases or process gases.

[0017] Thus, there is still a need for providing a process for removing N2O from process gases or offgases wherein the efficiency of a N2O decomposition catalyst, especially a transition metalcontaining catalyst, may be maintained or even improved.

[0018] Therefore, it is an object of the present invention to provide a process for treating a gas stream containing N2O, wherein the performance of a N2O decomposition catalyst may be enhanced.

[0019] Summary of the invention

[0020] It has now been found that a reduced content of water vapor in the gas stream to be treated in a N2O decomposition reaction unit may enhance the performance of a N2O decomposition catalyst, especially with respect to the N2O conversion rate.

[0021] Accordingly, in a first aspect, the invention relates to a process for reducing the concentration of N2O, preferably N2O and NO2, in a gas stream, the process comprising

[0022] (a) providing a gas stream G(1) containing N2O, preferably N2O and NO2;

[0023] (b) treating the gas stream G(1) with an aqueous washing fluid in an absorption unit operated with a liquid continuous phase to obtain a gas stream G(2);

[0024] (c) passing the gas stream G(2) through a droplet separating unit to obtain a gas stream G(3); and

[0025] (d) contacting the gas stream G(3) with a N2O decomposition catalyst to obtain a gas stream G(4).

[0026] In a further aspect, the invention relates to a chemical unit, as defined in any aspect herein, the chemical production unit comprising:

[0027] - an absorption unit operated with an aqueous washing fluid as a continuous liquid phase;

[0028] - a droplet separating unit;

[0029] - a N2O decomposition reaction unit equipped with a N2O decomposition catalyst;

[0030] - means for passing the gas stream G(1) to the absorption unit;

[0031] - means for passing the gas stream G(2) to the droplet separating unit;

[0032] - means for passing the gas stream G(3) to the N2O decomposition reaction unit; and

[0033] - optionally an inlet means for adding a reducing agent upstream of the N2O decomposition reaction unit. Detailed description of the invention

[0034] The term “NOX”, as used herein, designates nitrogen monoxide (NO) and / or nitrogen dioxide (NO2), in particular, a mixture of NO and NO2.

[0035] The term “nitrogen dioxide” or “NO2”, as used herein, is usually in equilibrium with its dimer N2O4, but the amount is calculated in terms of NO2.

[0036] The term “process gas stream”, as used herein, is a gas stream provided during a production process.

[0037] The term “removal of N2O” or “removing N2O” should be understood as at least reducing the concentration of N2O. Likewise, the term “removal of NOXor “removing NOX” should be understood as at least reducing the concentration of NOX. The same applies to the terms “removal of CO”, “removing CO”, “removal of non-methane volatile organic compounds and optionally CO and / or reducing agent “ or “non-methane volatile organic compounds and optionally CO and / or reducing agent”.

[0038] The term “non-methane volatile organic compounds”, as used herein, means a class of hydrocarbons, for example, (cyclo)alkanes, alkenes, alkynes and / or aromatics, carboxylic acids, nitriles, nitro-containing compounds, etc., which might be present as volatile impurities derived from an industrial production process or combustion process of sludge.

[0039] Especially, the term “non-methane volatile organic compounds”, may include at least one compound selected from a C2-Cg-hydrocarbon, a Ci-Cs-carboxylic acid, HCN, Ci-C?-nitro- containing compounds and any mixture thereof. A C2-Cg-hydrocarbon may be ethane, ethylene, pentane, hexane, cyclohexane, benzene, etc., a Ci-Cs-carboxylic acid may be formic acid, acetic acid, oxalic acid, maleic acid, benzoic acid etc., a Ci-C?-nitro-containing compound may be nitromethane, dinitromethane, trinitromethane, etc..

[0040] The pressure in bar, as used herein, means the pressure in bar absolute.

[0041] The term “gas stream G(n) derived from a nitration process”, as used herein, with n = 2 to 4, means that the respective gas stream is originally derived from a nitration process and provided as G(1). Likewise, the term “gas stream G(n) derived from an adipic acid process”, as used herein, with n = 2 to 4, means that the respective gas stream is originally derived from an adipic acid production process and provided as G(1). The same applies to the term “gas stream G(n) derived from a nitric acid production process”.

[0042] As used herein, the indefinite article “a” comprises the singular but also the plural, i.e. , an indefinite article in respect to a component of a composition means that the component is a single compound or a plurality of compounds. If not stated otherwise, the indefinite article “a” and the expression “at least one” are used synonymously. Preferably, the gas stream G(1) provided in step (a) contains nitrous oxide (N2O) and nitrogen dioxide (NO2), which are to be removed, oxygen and nitrogen. Optionally other components to be removed may be present, like nitrogen monoxide (NO), carbon monoxide (CO) and / or nonmethane volatile organic compounds.

[0043] Preferably, the gas stream G(1) provided in step (a) includes N2O and NO2 and optionally NO, generally obtainable by treating a gas stream containing N2O and NO and optionally NO2 by means of oxygen. Thus, the gas stream G(1) preferably contains N2O, NO2 and optionally NO, usually in an residual amount, for example, in case the oxidation is not complete. The gas stream G(1) provided in step (a) is further treated by step (b), step (c) and step (d), which are usually carried out in sequence, optionally comprising further steps upstream and / or downstream of step (d).

[0044] Preferably, the gas stream G(1) is a gas stream derived from an industrial production process or a combustion process of sludge.

[0045] The gas stream G(1), preferably an off-gas stream, may be derived from a combustion process, wherein nitrogenous material is burnt with an oxygen-containing gas, preferably air, for example, a combustion process of sewage sludge containing nitrogeneous material. The combustion process usually uses an excess of oxygen-containing gas, preferably of 5 to 30%, related to the oxygen amount required for converting H- and C-containing components to carbon dioxide and water. Thus, the gas stream from the combustion process usually contains N2O, NO, oxygen and optionally NO2, wherein the oxygen is usually present in an amount sufficient to convert NO to NO2. Thus, a gas stream G(1) derived from a combustion process of sewage sludge and provided in step (a) may be gas stream containing N2O, NO2, oxygen and optionally NO, CO and / or non-methane volatile organic compounds.

[0046] The gas stream G(1) may also be an off-gas stream derived from any industrial production process, like a nitration process or an adipic acid production process.

[0047] Preferably, the gas stream G(1) is a gas stream derived from at least one industrial production process selected from a nitration process P(1), an adipic acid production process P(2) and a nitric acid production process P(3). The gas stream G(1) may also be a mixture of two or more gas streams derived from two or more industrial processes.

[0048] Preferably, the gas stream G(1) is a gas stream derived from an industrial production process, which is a nitration process P(1) of an organic compound.

[0049] A nitration process may be a nitration process P(1) for the production of organic nitro compounds (nitration product), for example, the nitration of benzene, toluene, xylene, phenol, benzoic acid, mono or multiple chlorobenzenes, mono or multiple bromobenzenes, imidazole, 5- ethyl-2-methyl-pyridine. The nitration may be carried out as a mononitration, a dinitration, or a trinitration. Preferably, the gas stream emanates from a mononitration or dinitration, in particular, from the production of mononitrotoluene or dinitrotoluene. Preferably, the gas stream G(1) is a gas stream derived from an industrial production process, which is a nitration process P(1) of an organic compound, the nitration process comprising (P1-a) separating a gas stream containing N2O, NO, CO and optionally NO2 from a nitration product; and

[0050] (P1-b) adding an oxygen-containing gas to obtain a gas stream G(1) provided in step (a).

[0051] Preferably, step (P1-b) is carried out without a catalyst.

[0052] Preferably, the reaction conditions of step (P1-b) are such that, if CO is present, CO is not oxidized, when an oxygen-containing gas is added, for example, at a temperature of 5 to 280°C and at a pressure of from 1 to 12 bar. Due to these reaction conditions, CO does not start to react with oxygen in step (P1-b).

[0053] Preferably, the gas stream G(1) derived from a nitration process P(1) contains N2O, oxygen, NO2 and CO and optionally NO and / or non-methane volatile organic compounds.

[0054] Preferably, the gas stream G(1) is a gas stream derived from an industrial production process, which is an adipic acid production process P(2).

[0055] The production process of adipic acid usually includes a step of oxidizing a mixture of cyclohexanone and cyclohexanol to form a liquid reaction mixture in a reaction unit containing adipic acid and NOXand N2O in dissolved form and a gas stream containing NOxand N2O. After separating the liquid reaction mixture, the adipic acid is usually removed from the reaction mixture by crystallization. NOXand N2O in dissolved form are usually removed from the reaction mixture by adding an oxygen-containing gas to the reaction mixture, thereby obtaining a gas stream containing N2O and NO2 and oxygen and optionally residual NO, which is combined with the gas stream containing NOXand N2O withdrawn from the reaction unit. The NO, present in the gas stream withdrawn from the reaction unit, is usually converted to NO2 by means of oxygen contained in the oxygen-containing gas after combining.

[0056] Thus, preferably, a gas stream G(1) derived from an adipic acid production process and provided in step (a) is a gas stream containing N2O, NO2, oxygen and optionally NO, CO and / or non-methane volatile organic compounds.

[0057] Preferably, the gas stream G(1) is a gas stream derived from an adipic acid production process P(2), the adipic acid production process comprising

[0058] (P2-a) oxidizing a mixture of cyclohexanol and cyclohexanone with nitric acid to form a reaction mixture containing adipic acid, N2O, NO and NO2, wherein N2O, NO and NO2 are present in dissolved form and gaseous form;

[0059] (P2-b) separating N2O, NO and NO2 in gaseous form to obtain a gas stream GP2(1);

[0060] (P2-c) separating N2O, NO and NO2 in dissolved form from the reaction mixture by adding an oxygen-containing gas to form a gas stream GP2(2); and

[0061] (P2-d) combining the gas streams GP2(1) and GP2(2) to obtain a gas stream G(1) provided in step (a). Preferably, the reaction conditions of the steps (P2-c) and (P2-d) are such that, if CO is present, CO is not oxidized, when an oxygen-containing gas is added, for example, at a temperature of 5 to 280°C and at a pressure of from 1 to 12 bar. Due to these reaction conditions, CO does not start to react with oxygen in step (P2-c) or (P2-d). Steps (P2-c) and (P2-d) are usually carried out without a catalyst.

[0062] Preferably, the gas stream G(1) is a gas stream derived from an industrial production process, which is a nitric acid production process P(3).

[0063] The gas stream G(1) provided in step (a) may also be a process gas stream from a nitric acid production process P(3). Nitric acid is typically prepared via the Ostwald process by catalytically oxidizing NH3 by means of oxygen, usually air, for example, using a platinum-rhodium catalyst, wherein usually NO and N2O are formed (ammonia combustion). Optionally, N2O may be removed by catalytically thermal decomposition (secondary abatement). The NO formed may be oxidized to NO2 with residual oxygen from the ammonia oxidation and optionally by adding an oxygen-containing gas, preferably air. The NO2 formed is usually absorbed in water to form HNO3. Whether an optional oxygen-containing gas is necessary for the conversion of NO to NO2 is usually dependent on the amount of ammonia in the mixture containing ammonia and oxygen provided in the catalytic oxidation of ammonia.

[0064] Thus, preferably, a (process) gas stream G(1) derived from a nitric acid production process and provided in step (a) may be gas stream containing N2O, NO2, oxygen and optionally NO.

[0065] The gas stream G(1) may be a process gas stream derived from a nitric acid production process P(3), the nitric acid production process comprising

[0066] (P3-a) catalytically oxidizing ammonia by means of oxygen to form a gas stream GPS(1) containing N2O, NO and oxygen;

[0067] (P3-b) optionally a N2O decomposition stage; and

[0068] (P3-c) oxidizing NO of the gas stream GPS(1) to NO2, optionally by adding an oxygen-containing gas, to obtain a gas stream G(1) provided in step (a).

[0069] In the field of a nitric acid production process, the abatement of N2O is termed from primary to quaternary according to the stage of the nitric acid process. Abatement of N2O from the off-gas of the absorption stage and upstream of the off-gas gas expander is termed tertiary abatement. Removal of N2O from the gas after the oxidation of ammonia and before the absorption stage is referred to as secondary abatement, for example by catalytic thermal decomposition using a high temperature-resistant catalyst, like a catalyst based on CuO and ZnO. Measures aimed to avoid N2O formation during the oxidation of ammonia are called primary abatement. Abatement of N2O performed after the expansion (i.e., downstream of the expander) is termed quaternary abatement.

[0070] The gas stream G(1) may also be a mixture of a gas stream derived from the adipic acid production process and a gas stream derived from a nitric acid production process. Preferably, the gas stream derived from a nitric acid production process is mixed as a gas stream GPS(1) to the gas stream derived from an adipic acid production process. The oxygen-containing gas may be oxygen or any gas mixture containing oxygen. Preferably, the oxygen-containing gas is air, oxygen-enriched air or a mixture containing oxygen and inert gases, for example, nitrogen or noble gases, more preferably air or oxygen-enriched air, especially air.

[0071] The pressure of the oxygen-containing gas to be added is usually of from 1 to 10 bar, preferably essentially equal to the pressure of the gas stream, whereto it is added.

[0072] Preferably, the oxygen-containing gas is added in an amount such that the gas stream G(3) contains oxygen in an amount of at least 1 vol%, based on the total volume of the gas stream. This should ensure that the oxidation of NO is essentially complete. The adjusting of the amount of the oxygen-containing gas to be added may be carried out by conventional methods, known in the art. The addition of the oxygen-containing gas may be effected through a suitable inlet unit, for example, a t-junction, wherein optionally a static mixer is arranged downstream of the t- junction.

[0073] The reaction of NO and oxygen to NO2, prior to step (a), is generally carried out at a temperature of from 5 to 280°C, preferably from 8 to 160°C, more preferably from 10 to 50°C, and at a pressure from 1 to 12 bar, preferably from 2 to 10 bar.

[0074] The gas stream G(1) may contain N2O in a wide range of amounts, which is generally dependent on the source of gas stream. The gas stream G(1) may contain N2O in an amount of up to 25 vol%, based on the total volume of the gas stream, more preferably from 0.003 to 25 vol%.

[0075] The gas stream G(1), derived from a nitration process P(1), may contain N2O in an amount of from 0.16 to 3.2 vol%, based on the total volume of the gas stream, preferably from 0.24 to 2 vol%.

[0076] The gas stream G(1), derived from an adipic acid production process P(2), may contain N2O in an amount of from 1.6 to 25 vol%, based on the total volume of the gas stream, preferably from 3.2 to 20 vol%, more preferably from 4 to 14.4 vol%.

[0077] The gas stream G(1), derived from a nitric acid production process P(3), may contain N2O in an amount of from 0.003 to 0.2 vol% (30-2000 ppmv), based on the total volume of the gas stream, preferably 0.05 to 0.2 vol% (500-2000 ppmv) or 0.003 to 0.02 vol% (30-200 ppmv), in case a secondary abatement step (P3-b) is carried out.

[0078] The gas stream G(1), derived from an industrial production process or combustion process of sludge, is usually cooled in one or more stages and optionally compressed to the pressure, usually applied in the absorbing unit of step (b), in one or more stages, wherein the cooling and compressing stages are usually carried out in sequence and terminated with a cooling stage. During cooling, water, if present, preferably in a gas stream derived from a nitric acid production process P(3), may be condensed to form nitric acid of low concentration, for example of from 2 to 5 wt%, due to absorbing NO2. The nitric acid is usually removed prior to step (a).

[0079] Preferably, the temperature of the gas stream G(1) is of from 10 to 50°C, preferably from 20 to 40°C.

[0080] Step (b) includes a step of treating the gas stream G(1) with an aqueous washing fluid in an absorption unit operated with a liquid continuous phase to obtain a gas stream G(2). Mass transfer occurs mainly between the continuous liquid phase and gas bubbles as dispersed phase, contrary to a process with an equipment using a spray unit, for example, a spray tower.

[0081] The absorption unit may be an absorption column containing internals, which is operated with an aqueous washing fluid as continuous liquid phase, preferably in counter current. The aqueous washing fluid usually enters the absorption unit at the upper end, generally above internals, like trays or packings, of the absorption unit, preferably at the top of the absorption unit.

[0082] The gas stream G(1) usually enters the absorption unit at the lower end, generally below the internals, preferably at the bottom of the absorption unit. During said step, NO2 is absorbed in the aqueous washing fluid to form nitric acid and a gas stream G(2) depleted in NOX(NO and NO2). The gas stream G(2) usually contains N2O, oxygen, water vapor, nitrogen and optionally NOX(NO and NO2), CO and / or non-methane volatile organic compounds, thus a gas stream depleted in NOX.

[0083] Preferably, the absorption unit is an absorption column containing trays, a random packing or a structured packing, generally made of metal or ceramics, more preferably an absorption column containing trays.

[0084] The trays are preferably cooled, for example, by providing cooling coils on the trays. For cooling, a cooling medium, particularly water, flows through the cooling coils. The number of trays preferably is of from 5 to 70, more preferably from 5 to 61 , especially from 9 to 51. The trays used for absorbing the NO2 in the aqueous washing fluid may be any trays, for example, sieve trays, perforated trays, valve trays or bubble trays.

[0085] Preferably, step (b) is carried out at a temperature of from 5 to 50°C, more preferably from 5 to 45°C, especially from 5 to 30°C. The absorption unit is usually operated at a pressure of from ambient pressure to 12 bar, preferably from 3 to 11 bar, more preferably from 3 to 10 bar.

[0086] Preferably, the aqueous washing fluid in step (b) is water, preferably demineralized water, or an aqueous HNO3 solution having a concentration of up to 5 wt%, more preferably water.

[0087] Inside the absorption unit, preferably absorption column, NO2 is absorbed in the aqueous washing fluid by formation of nitric acid and NO. The NO reacts with the oxygen in the gas stream by formation of NO2, which again is absorbed in the aqueous washing fluid forming nitric acid and NO. This process repeats along the whole absorption unit so that at the exit of the unit the amounts of NO2 and NO are reduced in the gas stream. Thus, step (b) may also cover the removal of NO formed during the washing step of the gas stream by absorption of NO2 in the aqueous washing fluid and the reaction of NO2 with the water of the aqueous washing fluid.

[0088] Due to the absorption of NO2 in the aqueous washing fluid, besides the gas stream G(2) depleted in NOX(NO and NO2), a solution of nitric acid is formed in step (b), which is removed from the absorption unit at the bottom.

[0089] The concentration of the nitric acid in the solution is of from 20 to 70 wt%, preferably from 40 to 69 wt%. The thus obtained nitric acid, usually after stripping (blowing out) with an oxygencontaining gas like air, may be used in any known manner, for example, in a nitration or oxidation process or for manufacturing fertilizers. The thus obtained nitric acid may be the desired product, in case the gas stream is derived from a nitric acid production process P(3), or a by-product, in case the gas stream is derived from any off-gas, which may be discharged or (re)used, for example, in a nitration process P(1) or oxidation process of P(2).

[0090] The oxygen-containing gas withdrawn after blowing out the nitric acid may be re-used as oxygen-containing gas to be added upstream of step (a), usually as oxidation medium for NO.

[0091] Preferably, the gas stream G(2) contains water vapor in an amount of from 2.5 to 10 vol%, based on the total volume of the gas stream, more preferably from 2.8 to 10 vol%, most preferably from 3 to 10 vol%, especially from 3 to 8 vol%, in particular 4 to 7 vol%.

[0092] Step (c) includes a step of passing the gas stream G(2) through a droplet separating unit to obtain a gas stream G(3). The droplet separating unit may remove washing fluid, especially water, to achieve a reduced water vapor content.

[0093] Preferably, the droplet separating unit is installed in the gas flow after step (b) to obtain a gas stream G(3) and an aqueous phase, which is separated. For example, the droplet separating unit is installed at the top of the absorption unit or downstream of the absorption unit, preferably at the top of the absorption unit. The droplet separating unit usually comprises an inlet means for feeding the gas stream G(2) into said droplet separating unit.

[0094] Preferably, the droplet separating unit is a lamellar droplet separator, a centrifugal droplet separator, a droplet separator containing a fixed bed of particle bulks, a droplet separator containing a structured packing, or a droplet separator containing fabrics made of plastic or metal wires, like woven or knitted fabrics, more preferably knitted fabrics made of plastic or metal wires.

[0095] Preferably, the water vapor content of the gas stream in step (c) is reduced by at least 50%, more preferably by at least 60%, more preferably by at least 70%. The aqueous phase separated in step (c) may be discharged or passed back into the absorption unit of step (b). Preferably, the gas stream G(3), more preferably the gas stream entering step (d), has a water vapor content of < 1.5 vol%, based on the total volume of the gas stream, preferably of from 0.1 to 1.5 vol%, more preferably from 0.1 to 1.2 vol%.

[0096] Depending on the source of gas stream, the gas stream G(3) depleted in NOX, obtained in step (c), usually contains nitrogen as main component, N2O, oxygen, water vapor and optionally residual NOX(NO and / or NO2) and further components.

[0097] The gas stream G(3) obtained in step (c) usually contains nitrogen in an amount of from 50 to 95 vol%, based on the total volume of the gas stream, preferably from 55 to 90 vol%. In case of using air or oxygen-enriched air as the oxygen-containing gas in a step prior to step (a), for example to oxidize NO to NO2, the gas stream G(3) may contain airborne noble gases, mainly argon, and methane. The amount of noble gases, especially argon, in the gas stream G(3) may be of from 0.2 to 0.95 vol%, based on the total volume of the gas stream.

[0098] Preferably, the gas stream G(3) contains oxygen in an amount of at least 1 vol%, based on the total volume of the gas stream, preferably from 2 to 10 vol%, more preferably from 2 to 7 vol%, especially from 2 to 5 vol%.

[0099] Preferably, the gas stream G(3) contains N2O in an amount of up to 30 vol%, based on the total volume of the gas stream, preferably from 0.003 to 30 vol%.

[0100] Preferably, in case the gas stream G(3) is derived from a nitration process P(1), for example, from a production process of DNT, the amount of N2O is of from 0.2 to 4 vol%, based on the total volume of the gas stream, preferably from 0.3 to 2.5 vol%.

[0101] Preferably, in case the gas stream G(3) is derived from an adipic acid production process P(2), the amount of N2O is of from 2 to 30 vol%, based on the total volume of the gas stream, preferably from 4 to 25 vol%, more preferably 5 to 18 vol%.

[0102] Preferably, in case the gas stream G(3) is derived from a nitric acid production process P(3), the amount of N2O is of from 0.003 to 0.2 vol% (30-2000 ppmv), based on the total volume of the gas stream, preferably from 0.05 to 0.2 vol% (500-2000 ppmv) or, in case a secondary abatement process step (P3-b) is carried out, from 0.003 to 0.02 vol% (30-200 ppmv).

[0103] Depending on the source of gas stream, the optional further components present in gas stream G(1) or preferably G(3) to be removed may be CO and / or non-methane volatile organic compounds.

[0104] If present, the amount of CO in the gas stream G(3) may be up to 7 vol%, preferably of from 0.01 to 7 vol%, based on the total volume of the gas stream.

[0105] If present, the amount of (residual) NOXin the gas stream G(3) may be of from 0.004 to 0,5 vol% (40 to 5000 vol-ppm), based on the total volume of the gas stream, preferably from 0.008 to 0.1 vol%. If present, the amount of non-methane volatile organic compounds in the gas stream G(3) may be up to 0.06 vol% (600 ppmv), based on the total volume of the gas stream.

[0106] Further, CO2 may be present in an amount of from 0.1 to 10 vol%, based on the total volume of the gas stream. The lower values for CO and CO2 may be determined by the natural amount of air, when air or oxygen-enriched air is used in a step prior to step (a), for example, to oxidize NO to NO2.

[0107] Preferably, in case the gas stream G(3) is derived from a nitration process P(1 ), for example, from the production of DNT, the optional components to be removed may be NOX, CO and / or non-methane volatile organic compounds. The amount of CO in the gas stream G(3) may be of from 0.5 to 7 vol%, based on the total volume of the gas stream, preferably from 1 to 5 vol%, and the amount of residual NOXmay be of from 0.004 to 0.08 vol% (40 to 800 ppmv), based on the total volume of the gas stream, preferably from 0.008 to 0.04 vol% (80 to 400 ppmv). The amount of non-methane volatile organic compounds in the gas stream obtained in step (c) may be up to 0.06 vol%, preferably from 0.005 to 0.06 vol% (50 to 600 ppmv), based on the total volume of the gas stream, more preferably from 0.01 to 0.05 vol% (100 to 500 ppmv). Further, the amount of CO2 may be of from 2 to 10 vol%, based on the total volume of the gas stream, preferably from 3 to 7 vol%.

[0108] Preferably, in case the gas stream G(3) is derived from an adipic acid production process P(2), the optional components to be removed may be NOX, CO and / or non-methane volatile organic compounds. The amount of CO in the gas stream G(3) may be up to 0.5 vol%, based on the total volume of the gas stream, preferably up to 0.3 vol%, more preferably up to 0.25 vol%. The amount of (residual) NOXmay be of from 0.02 to 0.5 vol% (200 to 5000 ppmv), based on the total volume of the gas stream, preferably from 0.03 to 0.3 vol% (300 to 3000 ppmv), more preferably from 0.05 to 0.1 vol% (500 to 1000 ppmv). The amount of non-methane volatile organic compounds in the gas stream obtained in step (c) may be up to 0.06 vol%, preferably from 0.001 to 0.06 vol% (10 to 600 ppmv), based on the total volume of the gas stream, preferably from 0.001 to 0.03 vol% (10 to 300 ppm). The amount of CO2 may be of from 0.5 to 10 vol%, based on the total volume of the gas stream, preferably from 3 to 8 vol%.

[0109] Preferably, in case the gas stream G(3) is derived from a nitric acid production process P(3), the amount of (residual) NOXmay be of from 0.008 to 0.5 vol%.

[0110] Besides these components, the gas stream may contain further impurities which usually are present in traces, preferably below 0.5 vol%, more preferably below 0.3 vol%, based on the total volume of the gas stream.

[0111] Preferably, the gas stream obtained in step (c) is preheated, usually to a temperature required in the subsequent step, for example step (d). The subsequent step may also be step (e) or another step, as described herein-after. Preheating may be carried out by indirect heat exchange with hot purified gas stream obtained in step (d), which simultaneously is cooled. The temperature to which the gas stream is preheated may be of from 250 to 650°C, preferably dependent on the kind of the N2O decomposition catalyst used in step (d). For this purpose, any suitable heat exchanger may be used, for example, a tube bundle heat exchanger, a ll-tube- bundle heat exchanger, a spiral heat exchanger or a plate heat exchanger. Preferably, a tube bundle heat exchanger is used.

[0112] If preheating the gas stream obtained in step (d) by heat exchange with the purified gas stream is not sufficient, an additional heater may be used, for example, an electric heater or a burner, for example, a gas burner. Preferably, the heater used for additional heating is an electric heater. The additional heater further is used during start-up of the process to heat the gas stream obtained in step (c) to the temperature at which the N2O decomposition stage (d) or any other subsequent step is carried out.

[0113] The gas stream G(3) obtained in step (c) and preheated is usually passed into a N2O decomposition reaction unit of step (d). Step (d) includes a step of contacting the gas stream G(3) in the presence of a N2O decomposition catalyst, thereby generally decomposing N2O into nitrogen and oxygen. The step (d) is also designated as N2O decomposition stage.

[0114] Preferably, the gas stream G(3), more preferably the gas stream entering step (d), has a water vapor content of < 1.5 vol%, preferably < 1.2 vol%, based on the total volume of the gas stream.

[0115] Preferably, the gas stream G(3), more preferably the gas stream entering step (d), has a water vapor content of from 0.1 to 1.5 vol%, preferably 0.2 to 1 .2 vol%, based on the total volume of the gas stream.

[0116] Preferably, the N2O decomposition stage of step (d) is carried out by thermal non-reductive catalytic decomposition (direct decomposition) and / or by reductive catalytic decomposition using a reducing agent (selective catalytic reduction). Preferably, the N2O decomposition stage of step (d) is carried out by thermal non-reductive catalytic decomposition, especially when the amount of N2O in the gas stream to be entered in step (e) is > 2 vol%, based on the total volume of the gas stream.

[0117] The N2O decomposition catalyst used in step (d) may be a transition metal-exchanged zeolitic material C(1) or a catalyst C(2) based on a mixture containing copper oxide (CuO) and zinc oxide (ZnO). The transition metal-exchanged zeolitic material is a transition metal ion- exchanged zeolitic material.

[0118] Preferably, the zeolitic material of catalyst 0(1) may contain Si and Al in its framework structure, wherein the SiO2:AhO3 molar ratio of the zeolite is of from 1 to 50, preferably in the range of from 3 to 20.

[0119] Preferably, the zeolitic material contained in the catalyst in step (d) is obtainable or obtained by an organotemplate-free synthetic process. The term “organotemplate”, as used herein, designates any conceivable organic compound which may act as a structure directing agent in the preparation of a zeolitic material. Preferably, the zeolitic material contained in the catalyst C(1) of step (d) has a framework structure selected from the group consisting of MFI, BEA, FER, MOR, FAU, OFF, ERI, any mixture thereof, and mixed structures of two or more thereof, more preferably MFI, BEA, OFF, ERI, any mixture thereof, and mixed structures of two or more thereof, especially BEA.

[0120] The catalyst C(1) may contain one or more transition metals, usually as a non-framework element. Preferably, the at least one transition metal is selected from the group consisting of Fe, Co, Ni, Cu, Zn, V, Zr, and any mixture thereof, preferably selected from the group consisting of Fe, Co, Cu, Zn and any mixture thereof.

[0121] Preferably, the catalyst C(1) contains the at least one transition metal, calculated as the metal, in an amount of from 0.1 to 10 wt%, based on the total weight of the catalyst, more preferably from 0.5 to 8 wt%, more preferably from 0.5 to 6 wt%.

[0122] Preferably, the catalyst C(1), especially the zeolitic material, contains further at least one alkali metal and / or an earth alkali metal, wherein the at least one alkali metal and / or earth alkali metal is selected from the group consisting of Li, Na, K, Mg and any mixture thereof, more preferably Na, Mg and a mixture thereof, especially Na.

[0123] Preferably, the catalyst C(1) is Fe-BEA, Fe-MFI or Fe / Cu-OFF-ERI, more preferably Fe-BEA.

[0124] Preferably, the catalyst C(1) in step (d) further comprises a binder, more preferably in an amount of from 20 to 50 wt%, based on the total weight of the catalyst, preferably 25 to 40 wt%.

[0125] Alternatively, it is preferred that the catalyst C(1) is substantially free of a binder, for example containing an amount of binder of < 0.1 wt%, more preferably < 0.01 wt%, especially, the catalyst C(1) is free of a binder.

[0126] In case that the catalyst C(1) further comprises a binder or that the catalyst is substantially free of a binder, it is preferred that the binder comprises an inorganic binder. The inorganic binder may be a metal oxide, such as SiC>2, AI2O3, TiC>2, ZrC>2, MgO or any mixture thereof, preferably aluminosilicates or AI2O3 including hydrates thereof, like boehmite or bayerite, more preferably AI2O3.

[0127] An example of a suitable catalyst C(1) is a Fe / Cu-OFF-ERI-zeolite, as described, for example, in CN 113198525 A, as a catalyst of formula (Mgo.o25Ceo.o5Coo.925)Co204-Fei-Cu4-OFF-ERI. Said catalyst is described as a composite of three separate compounds, containing about 20 wt% of (Mgo.o25Ceo.o5Coo.925)Co2C>4 spinel, about 35 wt% of an Fe and Cu exchanged OFF-ERI zeolite and bound by about 45 wt% of Al / Si mixed metal oxide that is presumably also an OFF-ERI zeolite.

[0128] A further example of a suitable catalyst C(1) is a Fe-BEA zeolitic material or a Fe-MFI zeolitic material, preferably a Fe-BEA zeolitic material, as described in WO 2013 / 118064 A1. Preferably, the catalyst C(1) is used in step (d), wherein the gas stream G(1) or G(3), resp., is derived from a nitration process or a nitric acid production process.

[0129] Preferably, the N2O decomposition catalyst is a catalyst 0(2) based on a mixture containing copper oxide (CuO) and zinc oxide (ZnO), more preferably based on a mixture in a weight ratio of CuO to ZnO of from 1 : 1 to 1 .8 : 1. The catalyst may contain a further metal oxide, preferably aluminum oxide and optionally magnesium oxide, usually in an amount of from 50 to 80 wt%, based on the total weight of the catalyst, preferably from 55 to 75 wt%.

[0130] A suitable example of a catalyst C(2) is a catalyst containing a mixture containing, based on the total weight of the catalyst, 14-25 wt% of CuO, 14-20 wt% of ZnO and AI2O3 and optionally 1 to 5 wt% of MgO.

[0131] Preferably, the catalyst C(2) is used in step (d), wherein the gas stream G(1) or G(3), resp., is derived from an adipic acid production process P(2).

[0132] Preferably, the N2O decomposition catalyst used in step (d) is provided as a shaped body of any size and geometry, more preferably as an extrudate.

[0133] The catalyst may be used as a fixed catalyst bed, like randomly packed bed of particles or as a monolithic catalyst, preferably as a randomly packed bed of particles. The catalyst particles used in the catalyst bed are preferably in the shape of solid cylinders, hollow cylinders, multihole cylinders, rings, tablets, crushed pellets, 3D-printed micro extrudates (prepared by 3D micro extrusion), honeycomb structures or strands, more preferably star strands. The strands may have an outer diameter of from 1 .5 to 10 mm, preferably from 2 to 8 mm, and a length of from 2 to 20 mm, preferably from 4 to 10 mm.

[0134] Alternatively, the catalyst, optionally after admixing or coating by a suitable binder, as described herein-before, may be provided on a carrier, via deposition, coating or coextrusion. Typically, the carrier comprises a monolithic unit, especially of honeycomb structure, having a plurality of fine, parallel gas permeable channels extending therethrough. Such carriers are well-known in the art and may be made of any suitable material, for example, of a ceramic material such as cordierite or the like.

[0135] Also, the catalyst particles may either be made of the catalytic active material or may be made of a carrier material, for example, a polymer or a metal, whereto the catalytic active material is applied.

[0136] The parameters used in step (d) may be varied, preferably dependent on the catalyst used.

[0137] Preferably, the N2O decomposition stage of step (d) is carried out at a temperature of from 300 to 800°C, more preferably from 420 to 750°C, especially from 420 to 700°C, and at a pressure of from 800 mbar to 10 bar, more preferably from 900 mbar to 8 bar. Preferably, the N2O decomposition stage of step (d) is carried out at a gas hourly space velocity of from 600 to 30000 standard m3 / (h m3catalyst), more preferably from 1000 to 20000 standard m3 / (h m3catalyst), more preferably from 2000 to 10000 m3 / (h m3catalyst).

[0138] Preferably, in case the catalyst C(1) is used, the N2O decomposition stage of step (d) is carried out at a temperature of from 300 to 600°C, more preferably from 420 to 560°C or from 300 to 400°C, especially 420 to 560°C.

[0139] Preferably, in case the catalyst C(1) is used, and the gas stream G(1) is derived from a nitration process P(1), the N2O decomposition stage of step (d) is carried out at a pressure of from 1000 mbar to 1200 mbar.

[0140] Preferably, in case the catalyst C(2) is used, the N2O decomposition stage of step (d) is carried out without the addition of a reducing agent, at a temperature of from 430 to 800°C, more preferably from 450 to 750°C, especially from 520 to 700°C, and at a pressure of from 1.5 bar to 9 bar, more preferably from 1 .7 bar to 8 bar.

[0141] The N2O decomposition stage of step (d) may be carried out by thermal non-reductive catalytic decomposition and / or by reductive catalytic decomposition using a reducing agent. The reducing agent may already be present in the gas stream or may be added prior to the step (d). For example, in case CO is present in the gas stream, CO may act as a reducing agent.

[0142] The reducing agent may be one or a mixture of at least two reducing agents. Suitable examples are hydrocarbons, like Ci-Cs-alkanes, CO, hydrogen or ammonia. Examples of a Ci-Cs-alkane may be, for example, methane and / or propane and / or butane, preferably methane, for example, natural gas.

[0143] The reductive catalytic N2O decomposition with methane usually provides nitrogen, CO2 and water (3 N2O + CH4 3 N2O + CO2 + 2 H2O). The reductive catalytic N2O decomposition with ammonia or hydrogen usually provides nitrogen and water.

[0144] The reducing agent is usually added prior to step (d) in an amount sufficient to enable an essentially complete decomposition of N2O. The molar ratio of reducing agent(s) to N2O in the gas stream G(3) may be varied on a wide range, for example, of from 0.1 to 2.5, preferably of from 0.15 to 2, dependent on the kind of the reducing agent. The amount of reducing agent to be added may be determined by methods known to one skilled in the art, for example by onlineanalysis.

[0145] Preferably, the molar ratio of a Ci-Cs-alkane as reducing agent, especially methane, to N2O is of from 0.1 to 0.5, more preferably 0.15 to 0.45.

[0146] Preferably, the molar ratio of hydrogen as reducing agent to N2O is of from 0.5 to 1.1 , more preferably from 0.7 to 1.0. Preferably, the molar ratio of NH3 as reducing agent to N2O is of from 1.2 :1 , more preferably from 1.1 to 1.0. Usually, the upper limit of dosing NH3 is adjusted such that an ammonia slip complies with national regulations.

[0147] Preferably, in case step (d) is carried out in the presence of a reducing agent, the temperature of step (d) may be of from 300 to 600°C, preferably from 330 to 520°C.

[0148] Dependent on the temperature used in step (d), the thermal non-reductive catalytic decomposition and the reductive catalytic decomposition using a reducing agent may occur simultaneously. Thus, the amount of reducing agent is preferably less than the required stoichiometric amount.

[0149] The addition of the reducing agent may be effected through a suitable inlet unit, for example, a t-junction, a suitable dosing lance or through appropriately configured nozzles. Preferably, a mixer may be provided downstream of the inlet unit in the line for the gas stream and promote the mixing of the gas stream with the reducing agent supplied. Sufficient mixing may be achieved by using a static mixer or by sufficient mixing length. In the case of using different reducing agents, supply and adding into the gas stream may be separate or together.

[0150] Preferably, step (d) is carried out without adding a reducing agent, like a hydrocarbon, ammonia or hydrogen, especially in case the catalyst C(2) is used as a N2O decomposition catalyst.

[0151] In case the gas stream G(1) contains CO, preferably in case the gas stream G(1) is derived from a nitration process P(1), more preferably from a production process of DNT, CO may act as a reducing agent, thereby forming nitrogen and CO2. Depending on the amounts of CO and N2O in the gas stream and the reaction conditions, particularly the GHSV, either all of CO comprised in this gas stream reacts with N2O or only a part of CO reacts with N2O.

[0152] Typically, in case the gas stream G(1) derives from a nitration process P(1), more preferably from a production process of DNT, the gas stream contains CO in molar excess to N2O.

[0153] Both reactions, the thermal non-reductive catalytic decomposition of N2O forming nitrogen and the reductive catalytic decomposition with CO forming CO2 and nitrogen are usually carried out simultaneously at the same conditions. Therefore, if the gas stream contains CO in the reaction of step (d), a part of N2O reacts with CO forming CO2 and nitrogen and, simultaneously, N2O is decomposed into nitrogen and oxygen.

[0154] Optionally, the process may include further steps, usually dependent on the source of the gas stream, preferably dependent on the kind of components to be removed or added during the process like a (residual) reducing agent, and the amounts thereof.

[0155] In case the gas stream G(3) contains residual NOX, CO and / or non-methane volatile organic compounds or the gas stream G(4) obtained in step (d) contains residual reducing agent, the instant process may comprise further suitable steps in order to reduce the concentration thereof. Further, in case the concentration of the N2O in the gas stream G(3) obtained in step (c) is > 3 vol%, based on the total volume of the gas stream, an additional step may be carried out to reduce the N2O concentration.

[0156] Preferably, the process may comprise one or more further steps selected from the following steps:

[0157] (c-1) removing partially N2O from the gas stream G(3) by a two-stage absorption I desorption process using an absorption unit operated with a liquid continuous phase;

[0158] (e) removing (residual) NOX, if present in the gas stream G(3), in the presence of a NOXdecomposition catalyst 0(3) and optionally in the presence of a reducing agent;

[0159] (f) removing CO, if present in the gas stream G(3), in the presence of a catalyst C(4); or

[0160] (g) removing non-methane volatile organic compounds and optionally CO and / or reducing agent, if present in the gas stream G(3), in the presence of a catalyst 0(5).

[0161] Preferably, step (c-1) is carried out after step (c) and prior to step (d) or any of steps (e) to (g).

[0162] Preferably, step (c-1) is carried out, when the gas stream G(3) contains N2O in an amount of > 3 vol%, based on the total volume of the gas stream, more preferably with a gas stream, derived from an adipic acid production process P(2) or a mixture of said gas stream with a gas stream derived from a nitric acid production process P(3), especially with a gas stream derived from an adipic acid production process P(2).

[0163] Preferably, the gas stream G(3) is fed at least partially, preferably completely, into a N2O isolation stage (c-1), wherein N2O is concentrated from at least a part of the gas stream by a two-stage absorption / desorption process with water. Preferably, the absorption and desorption steps (c-1) are carried out by different pressures.

[0164] Preferably, in the first stage of the two-stage absorption / desorption process, N2O is absorbed in water in a first absorption unit, preferably a first absorption column. The first absorption unit is usually operated at a pressure of from 15 to 30 bar, more preferred from 17 to 28 bar, especially from 19 to 26 bar, and at a temperature of from 10 to 45°C, preferably from 20 to 42°C, more preferably from 30 to 35°C. Following the first absorption stage, N2O is usually desorbed from the water in a first desorbtion unit, which is operated at a pressure of from 1 to 1.5 bar, preferably from 1 .05 to 1 .3 bar, more preferably from 1.1 to 1.2 bar and at a temperature of from 10 to 45°C, preferably from 20 to 42°C, more preferably from 30 to 35°C. After being desorbed from the water, the resulting gas stream is fed into a second absorption unit, preferably an absorption column, which is operated at a pressure of from 15 to 30 bar, preferably from 17 to 25 bar, more preferably from 19 to 23 bar and at a temperature of from 10 to 45°C, preferably from 15 to 30°C, more preferably from 20 to 35°C. In a second desorbtion unit, which is usually operated at a pressure of from 1 to 1.5 bar, preferably from 1.05 to 1.3 bar, more preferably from 1.1 to 1.2 bar, concentrated N2O is obtained. The concentrated N2O may be used in various processes, for example, as an oxidizing agent, for example, in a process for producing cyclododecanone or cyclopentanone.

[0165] The absorption units of step (c-1) are generally absorption units operated with a liquid continuous phase, as described for step (b), preferably absorption columns containing a random packing or a structured packing, generally made of metal or ceramics, more preferably absorption columns containing a random packing.

[0166] Preferably, the first and the second absorption unit of step (c-1) contain a further droplet separating unit in the gas flow after step (c-1), preferably at the top of each absorption unit or downstream of each absorption unit, preferably at the top of each absorption unit. The droplet separating units may be of the same type as described for step (c).

[0167] Only a part of the N2O of the gas stream G(3) is generally removed by step (c-1) to form a gas stream Gc-i(3), which is withdrawn from the first absorption unit and / or the second absorption unit of step (c-1).

[0168] Preferably, step (c-1) removes 0.5 to 5 vol% N2O, based on the total volume of the gas stream G(3), from the gas stream G(3). The gas stream Gc-i(3), obtained in step (c-1), may still contain 2.5 to 25 vol% of N2O, based on the total weight of the gas stream, especially gas stream G(3).

[0169] The gas stream G(3) may be a gas stream Gc-i(3), in case step (c-1) is carried out with the complete gas stream G(3) or may be combined with Gc-i(3), in case the gas stream G(3) is fed partially to step (c-1).

[0170] Any of step (e), step (f) or step (g) may be carried out upstream and / or downstream of step (d). Step (e) and step (f) may be carried out simultaneously. Step (g) and step (d) may be carried out simultaneously.

[0171] Step (e) includes a step of decomposing (residual) NOXin the gas stream G(3) in the presence of a NOx decomposition catalyst C(3) with or without a reducing agent. The amount of (residual) NOx in the gas stream G(3) may be of from 0.004 to 0.5 vol% (40 to 5000 vol-ppm), based on the total volume of the gas stream, preferably from 0.008 to 0.1 vol%.

[0172] Preferably, step (e) is carried out with a reducing agent, more preferably, the reducing agent contains ammonia. The reducing agent is preferably added prior to step (e). The molar ratio of ammonia to NOXmay be of from 1 .01 to 1 .5, preferably from 1 .05 to 1 .4, more preferably from 1.1 to 1.3. Usually, the upper limit of dosing NH3 is adjusted such that an ammonia slip complies with national regulations. The amount of ammonia to be added may be determined by suitable methods known to one skilled in the art. In case step (e) and step (d) are carried out with ammonia as a reducing agent, the addition of ammonia may preferably only once, prior to the first performed step of step (e) or step (d). The amount of ammonia to be added is adjusted accordingly.

[0173] A suitable catalyst C(3) may be any conventional NOXdecomposition catalyst (SCR catalyst), especially a catalyst containing a transition metal and / or a transition metal oxide, for example, an oxide of iron, nickel, copper, cobalt, manganese, rhodium, rhenium, vanadium or titanium, or metallic platinum, gold or palladium, or else mixtures of two or more of these compounds I metals. Preferably, the catalyst C(3) is based on V2Os-TiO2 or a zeolite-based catalyst, for example the catalyst C(1) used in step (d), especially a Fe-BEA catalyst. Step (e) may be carried out at a temperature of from 200 to 500°C, preferably from 230 to 420°C, more preferably from 230 to 350°C.

[0174] Step (e) may be carried out at a pressure of from 800 mbar to 10 bar.

[0175] In case the gas stream G(1) or G(3), resp., is derived from a nitration process P(1 ) , step (e) may be carried out at a pressure of from 900 mbar to 8 bar, preferably from 1000 to 1200 mbar. In case the gas stream G(1) or G(3), resp., is derived from an adipic acid production process P(2) or a nitric acid production process P(3), step (e) may be carried out at a pressure of from 5 to 10 bar.

[0176] The gas hourly space velocity (GHSV) in step (e) may be of from 600 to 40000 standard m3 / (m3catalyst ■ h), preferably from 1000 to 35000 standard m3 / (m3catalyst ■ h) and more preferably from 2500 to 30000 standard m3 / (m3catalyst ■ h).

[0177] Preferably step (e) is carried out in the presence of ammonia as reducing agent, in case the gas stream G(3) contains CO in an amount of < 0.1 vol%, based on the total volume of the gas stream.

[0178] Preferably, step (e) is carried out upstream of step (d), especially in case the gas stream G(1) or G(3), resp., is derived from a nitric acid production process P(3) or a nitration process P(1), in particular a production process for DNT.

[0179] Preferably, step (e) is carried out downstream of step (d), more preferably with ammonia as reducing agent, especially in case the gas stream G(1) or G(3), resp., is derived from an adipic acid production process.

[0180] Preferably, the gas stream contains CO in an amount of > 0.5 vol%, based on the total volume of the gas stream G(3), more preferably 0.5 to 1.5 vol%, especially derived from a nitration process P(1). Preferably, step (f) is carried out at an amount of CO in the gas stream G(3) of > 0.5 vol%.

[0181] Step (f) includes a step of removing CO, if present in the gas stream G(3), in the presence of a catalyst C(4), wherein CO2 is usually formed. Any process known to a skilled person may be used for oxidizing CO to CO2 in step (f). The oxygen needed for oxidizing is usually present in the gas stream to be treated.

[0182] Step (f) is usually carried out in a reaction unit in the presence of a CO oxidizing catalyst C(4). The reaction unit, for example, may be a vessel with a catalyst bed or a monolithic shaped body containing the catalyst C(4). Preferably, a reaction unit is used which contains at least one monolithic shaped body. The monolithic shaped body preferably is designed as a straight prism with a round base or a 4- or 6-sided base, e.g., cylinders or cuboids. The monolithic shaped body may be made of the catalytic active material or may be made of a ceramic or metal body which is coated with the catalytic active material. The monolithic shaped body containing the catalytic active material may be mounted in direct contact into the vessel forming the reaction unit or may be incorporated into a supporting framework.

[0183] The catalyst C(4) used in step (f) preferably is a 3-way catalyst C(4a) as used for the treatment of exhaust gases for simultaneous destruction of CO, hydrocarbons and NOXfrom engine combustion. Thus, residual traces of NOX, which still may be contained may be reduced at least partially during the oxidation of CO. A 3-way catalyst C(4a) contains usually a ceramic monolithic unit of a honeycomb structure, which is coated with a metal oxide-containing wash coat, wherein particles of at least one noble metal, like platinum, palladium, ruthenium or rhodium, are finely dispersed. The wash coat contains at least one metal oxide selected from the group consisting of AI2O3, TiO2, SiO2, CeO2, ZrO2 and any mixture thereof.

[0184] Alternatively, but less preferred the catalyst C(4) may be a 2-way catalyst C(4b) or a so-called VOC catalyst for the conversion of hydrocarbons and CO to CO2 and water by reaction with oxygen. A 2-way catalyst C(4b) may be based on mixed oxides like oxides of aluminum, silicon, copper and / or magnesium containing a noble metal like platinum, rhodium, ruthenium, palladium or any mixture thereof, more preferably containing platinum.

[0185] Preferably, step (f) is carried out at a temperature of from 230 to 600°C, preferably from 250 to 540°C. The pressure applied in step (f) may be of from 800 mbar to 10 bar, preferably of from 900 mbar to 8 bar, especially from 1 to 1 .5 bar (e.g., at an excess pressure of from 5 to 300 mbar relative to the atmospheric pressure).

[0186] Preferably, step (f) is carried out at a gas hourly space velocity (GHSV) of from 4000 to 200000 standard m3 / (m3catalyst ■ h), more preferably from 8000 to 150000 standard m3 / (m3catalyst ■ h).

[0187] Step (f) is usually carried out upstream of step (d). In case that CO is still present in the gas stream G(4), for example, when CO functions as a reducing agent, a second step (f) may be carried out downstream of step (d). The residual oxygen present in the gas stream G(4) is usually sufficient for oxidizing CO to CO2, so that no additional oxygen-containing gas needs to be added.

[0188] Preferably, step (e) and step (f) are carried out simultaneously upstream of step (d), morepreferably using a 3-way catalyst C(4a) and without adding a reducing agent, more preferably with a gas stream G(1) or G(3), resp., derived from a nitration process P(1). The oxygen needed for oxidizing is usually present in the gas stream to be treated. The conditions usually correspond to those, as described for step (f).

[0189] Preferably, step (g) includes a step of removing non-methane volatile organic compounds and optionally CO and / or (residual) reducing agent(s), especially methane, if present in the gas stream G(3), in the presence of a catalyst C(5), wherein usually CO2 and water are formed. Preferably, step (g) is carried out downstream of step (d). The operating conditions of step (g) are similar to those of step (d), preferably in case the gas stream G(1), or G(4), resp., is derived from a nitration process P(1).

[0190] Step (g) and step (d) may be carried out simultaneously, preferably in case the gas stream G(1), or G(3), resp., is derived from a nitration process P(1) or an adipic acid production process P(2).

[0191] The catalyst 0(5) may be a 2-way catalyst or a so-called VOC catalyst, for example a 2-way catalyst C(4b), as described for step (f), or a N2O decomposition catalyst in case step (d) and step (g) are carried out simultaneously.

[0192] Step (g) may be carried out at a temperature of from 300 to 600°C, more preferably from 420 to 560°C, and at a pressure of from 800 mbar to 10 bar, more preferably from 900 mbar to 8 bar, most preferably from 1000 to 1200 mbar.

[0193] Preferably, step (g) is carried out at a gas hourly space velocity of from 600 to 30000 standard m3 / (h m3catalyst), more preferably from 1000 to 20000 standard m3 / (h m3catalyst), more preferably from 2000 to 10000 m3 / (h m3catalyst).

[0194] Preferably, step (g) and step (d) may be carried out in different reaction units or the same reaction unit using different catalyst beds.

[0195] The N2O decomposition catalyst of step (d) may also remove CO and / or non-methane volatile organic compounds and / or reducing agent like methane. Thus, step (d) and step (g) may be carried out simultaneously, using the N2O decomposition catalyst and the conditions, as described for step (d).

[0196] Preferably, the N2O decomposition catalyst C(1) of step (d) may remove CO and / or nonmethane volatile organic compounds and / or reducing agent like methane from a gas stream G(3), preferably derived from a nitration process P(1). Thus, step (d) and step (g) may be carried out simultaneously, using the N2O decomposition catalyst C(1) and the conditions, as described for step (d).

[0197] Preferably, step (g) and step (d) are carried out simultaneously using a N2O decomposition catalyst C(1), in case the gas stream G(1), or G(3), resp., is derived from a nitration process P(1), more preferably derived from a production process of DNT.

[0198] Preferably, the N2O decomposition catalyst C(2) of step (d) removes CO and / or non-methane volatile organic compounds from a gas stream G(3), preferably derived from an adipic acid production process P(2) or a mixture of a gas stream derived from an adipic acid production process P(2) and a gas stream derived from a nitric acid production process P(3), more preferably derived from an adipic acid production process P(2). Thus, step (d) and step (g) may be carried out simultaneously, using the N2O decomposition catalyst C(2) and the conditions, as described for step (d). Preferably, step (g) and step (d) are carried out simultaneously using a N2O decomposition catalyst C(2), in case the gas stream G(1), or G(3), resp., is derived from an adipic acid production process.

[0199] Preferably, the instant process includes the steps (a) to (d) using a catalyst 0(1) and optionally step (e) and step (f), carried out simultaneously upstream of step (d) using a 3-way catalyst C(4a) without adding a reducing agent, optionally step (g), in case the gas stream G(1) is derived from a nitration process P(1), more preferably from a production process of DNT.

[0200] Preferably, the instant process includes the steps (a) to (d) using a catalyst 0(2) and optionally step (c-1), step (e) and step (g), wherein step (g) is carried out simultaneously with step (d), wherein the gas stream G(1) is derived from an adipic acid production process P(2) or a mixture of a gas stream derived from an adipic acid production process P(2) and a gas stream derived from a nitric acid production process P(3), more preferably derived from an adipic acid production process P(2), wherein step (e) is preferably carried out downstream of step (d).

[0201] Preferably, the instant process includes the steps (a) to (d) using a catalyst 0(1) and optionally step (e), in case the gas stream G(1) is derived from a nitric acid production process P(3), wherein step (e) is preferably carried out upstream of step (d)

[0202] The purified gas stream, as obtained in the final step, especially step (d), step (g) or step (e), is cooled, preferably by indirect heat exchange with the cooled gas stream obtained in the preheating step, carried out after step (c), which simultaneously is heated. The cooled gas stream may be expanded, for example in a turbine expander, and released into the atmosphere.

[0203] The design of the reaction units, required for step (e), optional step (f), optional step (g) and optional step (h), is not critical and is known in the art.

[0204] Preferably, the reaction unit used in step (d) is a reaction unit containing a fixed bed reaction unit.

[0205] The design for the catalyst bed may be configured variously in a reaction unit, for example, in a tubular reaction unit with axial flow, in a radial reaction unit containing a radial basket with radial flow or in a reaction unit with lateral flow. One or more catalyst beds may be present, which may be arranged in serious within a reaction unit.

[0206] Preferably, the step (d) and the one or more optional steps (e), (f) and (g) are carried out in separate reaction units.

[0207] Preferably, two steps may be carried in one reaction unit containing different catalyst beds.

[0208] Preferably, step (d) and step (g) may be carried out in one reaction unit containing at least one catalyst bed for N2O decomposition and at least one catalyst bed containing a catalyst 0(5). The reaction unit for step (d) and subsequent step (g) is preferably a tubular reaction unit with axial flow.

[0209] Preferably, step (d) and step (e) may be carried out in separate reaction units or may be carried out in one reaction unit containing at least one catalyst bed for N2O decomposition and at least one catalyst bed for NOXdecomposition. The reaction unit for step (e) and subsequent step (d) and subsequent step (g) is preferably a tubular reaction unit with axial flow.

[0210] In case subsequent steps are carried at a different temperature or pressure, the conditions will be adjusted between the steps, for example, by cooling or heating means, preferably by indirect heat exchange and / or electrically, as well as by adapting the pressure accordingly.

[0211] For starting the process, firstly, the N2O decomposition catalyst and optionally the catalysts for the optional steps (e), (f) and (g) have to be brought to operating temperature. This may be achieved by passing a gaseous medium like air, nitrogen or exhaust gas through a heater and then passing the gaseous medium over the catalyst(s). The gaseous medium used for heating may either be pressurized by a blower so that it flows through the heater and the catalysts, or it may be taken, for example, from the plants operating network. For heating the gaseous medium, for example, an electric heater may be used. Alternatively, the gaseous medium may be heated by direct or indirect heat exchange with exhaust gases from natural gas combustion or by a regenerative heat exchanger, which is operated with the hot exhaust gas from the catalysts. Preferably, a combination of electric heating and regenerative heating is used, the heating may also be carried out in several stages simultaneously, e.g., regenerative and electrical heating at the same time.

[0212] The heating of the catalyst(s) may be carried out in a straight pass or in a cycle. If the heating is carried out in a cycle, the gaseous medium after having passed the catalysts to be heated is passed again to the input side of the heater by using a suitable blower.

[0213] The purified gas stream obtained in (d) or any optional step of (e), step (f) or step (g), which is carried out downstream of step (d), contains NOXand N2O and CO, if present, in an amount to fulfill national regulations, for example, the First Ordinance on the Implementation of the Federal Immission Control Act (Bundes-lmmissionsschutzverordnung).

[0214] The purified gas stream obtained in (d) or any optional step of (e), step (f) or step (g), which is carried out downstream of step (d), contains usually less than 2000 ppmv of N2O, based on the total volume of the gas stream, preferably less than 1000 ppmv, more preferably less than 500 ppmv, especially less than 100 ppmv.

[0215] The purified gas stream obtained in (d) or any optional step of (e), step (f) or step (g), which is carried out downstream of step (d), contains usually less than 400 mg of NOXper m3dry gas at normalized conditions, preferably less than 200 mg of NOXper m3dry gas at normalized conditions, more preferably less than 100 mg of NOXper m3dry gas at normalized condition, where NOXis assumed as NO2. In case, CO is present in the gas stream to be purified, the purified gas stream obtained in (d) or any optional step of (e), step (f) or step (g), which is carried out downstream of step (d), contains less than 400 weight-ppm of CO, based on the total weight of the dry gas stream, preferably less than 100 weight-ppm.

[0216] In a further aspect, the invention relates to a chemical production unit for carrying out the process, as defined in any aspect herein, the chemical production unit comprising:

[0217] - an absorption unit operated with an aqueous washing fluid as a continuous liquid phase;

[0218] - a droplet separating unit;

[0219] - a N2O decomposition reaction unit equipped with a N2O decomposition catalyst;

[0220] - means for passing the gas stream G(1) to the absorption unit;

[0221] - means for passing the gas stream G(2) to the droplet separating unit;

[0222] - means for passing the gas stream G(3) to the N2O decomposition reaction unit; and

[0223] - optionally an inlet means for adding a reducing agent upstream of the N2O decomposition reaction unit.

[0224] Preferably, the chemical production unit comprises further at least one of the following units:

[0225] - a N2O isolation unit containing two absorption units operated with a continuous liquid phase;

[0226] - a NOx decomposition reaction unit equipped with a NOXdecomposition catalyst C(3);

[0227] - a reaction unit equipped with a CO oxidizing catalyst C(4); or

[0228] - a reaction unit equipped with a catalyst C(5) for removing non-methane volatile organic compounds and optionally CO and / or residual reducing agent.

[0229] The instant process of treating gas streams enables a higher conversion rate of the N2O decomposition step when a droplet separating unit is installed in an absorption unit upstream of said step, to reduce the water vapor content of the gas stream. This allows for a lower amount of catalyst in step (d) and / or longer catalyst lifetime and, thus, lower investment costs and operating costs, as the catalyst has to be less replaced.

[0230] The present invention is further illustrated by the following set of embodiments and combinations of embodiments resulting from the dependencies and back-references as indicated. In particular, it is noted that in each instance where a range of embodiments is mentioned, for example, in the context of a term such as "The process of any one of embodiments 1 to 4", every embodiment in this range is meant to be explicitly disclosed for the skilled person, i.e. the wording of this term is to be understood by the skilled person as being synonymous to "The process of any one of embodiments 1, 2, 3 and 4". Further, it is explicitly noted that the following set of embodiments represents a suitably structured part of the general description directed to preferred aspects of the present invention, and, thus, suitably supports, but does not represent the claims of the present invention.

[0231] 1. A process for reducing the concentration of N2O, preferably N2O and NO2, in a gas stream, the process comprising

[0232] (a) providing a gas stream G(1) containing N2O, preferably N2O and NO2;

[0233] (b) treating the gas stream G(1) with an aqueous washing fluid in an absorption unit operated with a liquid continuous phase to obtain a gas stream G(2); (c) passing the gas stream G(2) through a droplet separating unit to obtain a gas stream G(3); and

[0234] (d) contacting the gas stream G(3) with a N2O decomposition catalyst to obtain a gas stream G(4).

[0235] 2. A process according to embodiment 1, wherein the gas stream G(1) contains further NO2 and oxygen.

[0236] 3. A process according to embodiment 1, wherein the gas stream G(1) contains further NO2, oxygen and optionally NO, CO and / or non-methane volatile organic compounds.

[0237] 4. The process according to embodiment 1 , 2 or 3, wherein the gas stream G(1) is a gas stream derived from an industrial production process or a combustion process of sludge.

[0238] 5. The process according to any one of embodiments 1 to 4, wherein the gas stream G(1) is a gas stream derived from at least one industrial production process selected from a nitration process P(1 ) , an adipic acid production process P(2) and a nitric acid production process P(3).

[0239] 6. The process according to any one of embodiments 1 to 5, wherein the gas stream G(1) is a gas stream derived from an industrial production process, which is a nitration process P(1) of an organic compound.

[0240] 7. The process according to any one of embodiments 1 to 6, wherein the gas stream G(1) is a gas stream derived from an industrial production process, which is a nitration process P(1) of an organic compound, the nitration process comprising

[0241] (P1-a) separating a gas stream containing N2O, NO, CO and optionally NO2 from a nitration product; and

[0242] (P1-b) adding an oxygen-containing gas to obtain a gas stream G(1) provided in step (a).

[0243] 8. The process according to embodiment 7, wherein step (P1-b) is carried out without a catalyst.

[0244] 9. The process according to any one of embodiments 1 to 8, wherein the nitration process P(1) is a nitration process of benzene, toluene, xylene, phenol, benzoic acid, mono or multiple chlorobenzene, mono or multiple bromobenzene, imidazole or 5-ethyl-2-methyl pyridine, preferably a nitration process for producing mono- or dinitrotoluene, more preferably dinitrotoluene (DNT).

[0245] 10. The process according to any one of embodiments 1 to 5, wherein the gas stream G(1) is a gas stream derived from an industrial production process, which is an adipic acid production process P(2). 11. The process according to any one of embodiments 1 to 5 and 10, wherein the gas stream G(1) is a gas stream derived from an adipic acid production process P(2), the adipic acid production process comprising

[0246] (P2-a) oxidizing a mixture of cyclohexanol and cyclohexanone with nitric acid to form a reaction mixture containing adipic acid, N2O, NO and NO2, wherein N2O, NO and NO2 are present in dissolved form and gaseous form;

[0247] (P2-b) separating N2O, NO and NO2 in gaseous form to obtain a gas stream GP2(1 );

[0248] (P2-c) separating N2O, NO and NO2 in dissolved form from the reaction mixture by adding an oxygen-containing gas to form a gas stream GP2(2); and

[0249] (P2-d) combining the gas streams GP2(1 ) and GP2(2) to obtain a gas stream G(1) provided in step (a).

[0250] 12. The process according to any one of embodiments 1 to 5, wherein the gas stream G(1) is a gas stream derived from an industrial production process, which is a nitric acid production process P(3).

[0251] 13. The process according to any one of embodiments 1 to 5 and 12, wherein gas stream G(1) is a gas stream derived from a nitric acid production process P(3), the nitric acid production process comprising

[0252] (P3-a) catalytically oxidizing ammonia by means of oxygen to form a gas stream GPS(1) containing N2O, NO and oxygen;

[0253] (P3-b) optionally decomposing N2O; and

[0254] (P3-c) oxidizing NO of the gas stream GPS(1 ) to NO2, optionally by adding an oxygencontaining gas, to obtain a gas stream G(1) provided in step (a).

[0255] 14. The process according to any one of embodiments 1-5 and 10-13, wherein the gas stream G(1) is a mixture of a gas stream derived from the adipic acid production process P(2) and a gas stream derived from a nitric acid production process P(3), wherein preferably the gas stream derived from a nitric acid production process P(3) is mixed as gas stream GP3(1) to the gas stream derived from an adipic acid process P(2).

[0256] 15. The process according to any of embodiments 1 to 4, wherein the gas stream G(1) is a gas stream derived from a combustion process of sewage sludge containing nitrogenous material using an oxygen-containing gas.

[0257] 16. The process according to any one of embodiments 7 to 9, 11 and 13 to 15, wherein the oxygen-containing gas is air, oxygen-enriched air or a mixture containing oxygen and an inert gas, preferably air or oxygen-enriched air, more preferably air.

[0258] 17. The process according to any one of embodiments 7 to 9, 11 and 13 to 16, wherein the oxygen-containing gas is added in an amount such that the gas stream G(3) contains oxygen in an amount of at least 1 vol%, based on the total volume of the gas stream. 18. The process according to any one of embodiments 1 to 17, wherein the gas stream G(1) contains N2O in an amount of up to 25 vol%, based on the total volume of the gas stream, more preferably from 0.003 to 25 vol%.

[0259] 19. The process according to any one of embodiments 1 to 18, wherein the temperature of the gas stream G(1) is of from 10 to 50°C, preferably from 20 to 40°C.

[0260] 20. The process according to any one of embodiments 1 to 19, wherein NO2 of the gas stream G(1) is absorbed in the aqueous washing fluid to form nitric acid and a gas stream G(2) depleted in NOX(NO and NO2).

[0261] 21. The process according to any one of embodiments 1 to 20, wherein the absorption unit operated with a liquid continuous phase is an absorption column containing trays, a random packing or a structured packing, preferably an absorption column containing trays.

[0262] 22. The process according to embodiment 21 , wherein the number of trays is of from 5 to 70, preferably from 5 to 61, more preferably from 9 to 51.

[0263] 23. The process according to any one of embodiments 1 to 22, wherein the temperature in the absorption unit is of from 5 to 50°C, preferably from 5 to 45°C, more preferably from 5 to 30°C.

[0264] 24. The process according to any one of embodiments 1 to 23, wherein the absorption unit operates at a pressure of from ambient pressure to 12 bar, preferably from 3 to 11 bar, more preferably from 3 to 10 bar.

[0265] 25. The process according to any one of embodiments 1 to 24, wherein the aqueous washing fluid in step (b) is water or an aqueous HNO3 solution having a concentration of up to 5 wt%, preferably water.

[0266] 26. The process according to any of embodiments 1 to 25, wherein step (b) includes removal of NO obtained during the formation of HNO3 in step (b) by means of oxygen present in the gas stream of the absorption unit.

[0267] 27. The process according to any one of embodiments 20 to 26, wherein the nitric acid formed in step (b) is separated at the bottom of the absorption unit.

[0268] 28. The process according to any one of embodiments 20 to 27, wherein the nitric acid formed in step (b) has a concentration of from 20 to 70 wt%, preferably from 40 to 69 wt%.

[0269] 29. The process according to any one of embodiments 20 to 28, wherein the nitric acid formed in step (b) and separated is purified by blowing out the nitric acid with an oxygencontaining gas, preferably air. 30. The process according to embodiment 29, wherein the oxygen-containing gas withdrawn after blowing out the nitric acid is re-used as oxygen-containing gas, preferably added upstream of step (a).

[0270] 31. The process according to any one of embodiments 20 to 30, wherein the nitric acid formed in step (b) and optionally further treated is the desired product of a nitric acid production process P(3) or a by-product, which is re-used in an industrial production process.

[0271] 32. The process according to any one of embodiments 1 to 31, wherein the gas stream G(2) contains water vapor in an amount of from 2.5 to 10 vol%, based on the total volume of the gas stream, preferably from 2.8 to 10 vol%, more preferably from 3 to 10 vol%, especially from 3 to 8 vol%, in particular 4 to 7 vol%.

[0272] 33. The process according to any one of embodiments 1 to 32, wherein the droplet separating unit in step (c) is installed in the gas flow after step (b) to obtain a gas stream G(3) and an aqueous phase, which is separated.

[0273] 34. The process according to any one of embodiments 1 to 33, wherein the droplet separating unit in step (c) is installed in the gas flow after step (b), preferably at the top of the absorption unit or downstream of the absorption unit, preferably at the top of the absorption unit.

[0274] 35. The process according to any one of embodiments 1 to 34, wherein the droplet separating unit is selected from the group consisting of a lamellar droplet separator, a centrifugal droplet separator, a droplet separator containing a fixed bed of particle bulks, a droplet separator containing a structured packing and a droplet separator containing a fabric made of plastic or metal wires, preferably selected from the group consisting of a droplet separator containing a fixed bed of particle bulks, a droplet separator containing a structured packing or a droplet separator containing a fabric made of plastic or metal wires, more preferably a droplet separator containing a fabric made of plastic or metal wires.

[0275] 36. The process according to embodiment 35, wherein the droplet separator containing a fabric made of plastic or metal wires is selected from the group consisting of a knitted fabric or a woven fabric, preferably a knitted fabric made of metal wires.

[0276] 37. The process according to any one of embodiments 1 to 36, wherein the gas stream G(3) contains water vapor in an amount of < 1.5 vol%, based on the total volume of the gas stream, preferably < 1.2 vol%.

[0277] 38. The process according to any one of embodiments 1 to 37, wherein the gas stream G(3) contains water vapor in an amount of from 0.1 to 1.5 vol%, based on the total volume of the gas stream more preferably from 0.1 to 1.2 vol%. 39. The process according to any one of embodiments 1 to 38, wherein the gas stream entering step (d) contains water vapor in an amount of < 1.5 vol%, based on the total volume of the gas stream, preferably of from 0.1 to 1.5 vol%, more preferably from 0.1 to 1.2 vol%.

[0278] 40. The process according to any one of embodiments 1 to 39, wherein the water vapor amount in step (c) is reduced by at least 50%, preferably by at least 60%, more preferably by at least 70 vol%.

[0279] 41. The process according to embodiment 33, wherein the aqueous phase separated in step (c) is discharged or passed back into the absorption unit of step (b).

[0280] 42. The process according to any one of embodiments 1 to 41 , wherein the gas stream G(3) contains N2O in an amount of up to 30 vol%, based on the total volume of the gas stream, preferably from 0.003 to 30 vol%.

[0281] 43. The process according to any one of embodiments 1 to 42, wherein the gas stream G(3) contains oxygen in an amount of at least 1 vol%, based on the total volume of the gas stream.

[0282] 44. The process according to any one of embodiments 1 to 43, wherein the gas stream G(3) contains NOXin an amount of from 0.004 to 0.5 vol%, based on the total volume of the gas stream, preferably from 0.008 to 0.1 vol%.

[0283] 45. The process according to any one of embodiments 1 to 44, wherein the gas stream G(3) contains nitrogen in an amount of from 50 to 95 vol%, based on the total weight of the gas stream, preferably 55 to 90 vol%.

[0284] 46. The process according to any one of embodiments 3 to 45, wherein the gas stream G(3) contains CO in an amount of up to 7 vol%, preferably of from 0.01 to 7 vol%, based on the total volume of the gas stream.

[0285] 47. The process according to any one of embodiments 3 to 46, wherein the gas stream G(3) contains non-methane volatile organic compounds in an amount of up to 0.06 vol%, based on the total volume of the gas stream.

[0286] 48. The process according to any one of embodiments 5 to 9 and 16 to 47, wherein the gas stream G(3) derived from a nitration process P(1) contains N2O, NOX, CO and nonmethane volatile organic compounds.

[0287] 49. The process according to any one of embodiments 5 to 9 and 16 to 48, wherein the gas stream G(3) derived from a nitration process P(1) contains N2O in an amount of from 0.2 to 4 vol%, based on the total volume of the gas stream, preferably 0.3 to 2.5 vol%.

[0288] 50. The process according to any one of embodiments 5 to 9 and 16 to 49, wherein the gas stream G(3) derived from a nitration process P(1) contains, based on the total volume of the gas stream, CO in an amount of from 0.5 to 7 vol%, preferably from 1 to 5 vol%, NOXin an amount of from 0.004 to 0.08 vol%, preferably from 0.008 to 0.04 vol%, and nonmethane volatile organic compounds in an amount of from 0.005 to 0.06 vol%, preferably from 0.01 to 0.05 vol%.

[0289] 51. The process according to any one of embodiments 5, 10, 11 , 14 and 16 to 47, wherein the gas stream G(3) derived from an adipic acid production process P(2) contains N2O and optionally NOX, CO and non-methane volatile organic compounds.

[0290] 52. The process according to any one of embodiments 5, 10, 11 , 14, 16 to 47 and 51 , wherein the gas stream G(3) derived from an adipic acid process P(2) contains N2O in an amount of from 2 to 30 vol%, based on the total volume of the gas stream, preferably from 4 to 25 vol%, more preferably 6 to 18 vol%.

[0291] 53. The process according to any one of embodiments 5, 10, 11 , 14, 16 to 47, 51 and 52, wherein the gas stream G(3) derived from an adipic acid process P(2) contains, based on the total volume of the gas stream, CO in an amount of up to 0.5 vol%, preferably up to 0.3 vol%, more preferably up to 0.25 vol%, NOXin an amount of from 0.02 to 0.5 vol%, preferably from 0.03 to 0.3 vol%, more preferably from 0.05 to 0.1 vol%, and non-methane volatile organic compounds in an amount up to 0.06 vol%, preferably from 0.001 to 0.06 vol%, more preferably 0.001 to 0.03 vol%.

[0292] 54. The process according to any one of embodiments 5, 12 to 14 and 16 to 45, wherein the gas stream G(3) derived from a nitric acid production process P(3) contains N2O and NOX.

[0293] 55. The process according to any one of embodiments 5, 12 to 14, 16 to 45 and 54, wherein the gas stream G(3) derived from a nitric acid production process P(3) contains N2O in an amount of from 0.003 to 0.2 vol%, based on the total volume of the gas stream, preferably 0.05 to 0.2 vol% or, in case a step (P3-b) is carried out, 0.003 to 0.02 vol%.

[0294] 56. The process according to any one of embodiments 5, 12 to 14, 16 to 45, 54 and 55, wherein the gas stream G(3) derived from a nitric acid production process P(3) contains NOXin an amount of from 0.008 to 0.5 vol%, based on the total volume of the gas stream.

[0295] 57. The process according to any one of embodiments 1 to 56, wherein the gas stream G(3) is preheated, preferably by indirect heat exchange with a gas stream obtained in step (d), which simultaneously is cooled.

[0296] 58. The process according to any one of embodiments 1 to 57, wherein the gas stream G(3) is preheated to a temperature of from 250 to 650°C.

[0297] 59. The process according to any one of embodiments 1 to 58, wherein step (d) is carried out by thermal non-reductive catalytic decomposition and / or by reductive catalytic decomposition using a reducing agent. 60. The process according to any one of embodiments 1 to 59, wherein step (d) is carried out by thermal non-reductive catalytic decomposition at an amount of N2O present in gas stream G(3) of > 2 vol%, based on the total volume of the gas stream.

[0298] 61. The process according to any one of embodiments 1 to 60, wherein the N2O decomposition catalyst is a catalyst C(1) containing a transition metal-exchanged zeolitic material or a catalyst C(2) based on a mixture containing copper oxide (CuO) and zinc oxide (ZnO).

[0299] 62. The process according to embodiment 61 , wherein the zeolitic material of catalyst 0(1) contains Si and Al in its framework structure, wherein the SiO2:AhO3 molar ratio of the zeolitic material is of from 1 to 50, preferably from 3 to 20.

[0300] 63. The process according to embodiment 61 or 62, wherein the zeolitic material contained in the catalyst 0(1) is obtainable or obtained by an organotemplate-free synthetic process.

[0301] 64. The process according to any one of embodiments 61 to 63, wherein the zeolitic material contained in the catalyst 0(1) has a framework structure selected from the group consisting of MFI, BEA, FER, MOR, FAU, OFF, ERI, any mixture thereof, and mixed structures of two or more thereof, preferably MFI, BEA, OFF, ERI, any mixture thereof, and mixed structures of two or more thereof, more preferably BEA.

[0302] 65. The process according to any one of embodiments 61 to 64, wherein the transition metal of catalyst 0(1) is at least one transition metal selected from the group consisting of Fe, Co, Ni, Cu, Zn, V, Zr and any mixture thereof, preferably Fe, Co, Cu, Zn and any mixture thereof, more preferably Fe.

[0303] 66. The process according to any one of embodiments 61 to 65, wherein the catalyst C(1) contains the at least one transition metal, calculated as the metal, in an amount of from 0.1 to 10 wt%, based on the total weight of the catalyst, preferably from 0.5 to 8 wt%, more preferably from 0.5 to 6 wt%.

[0304] 67. The process according to any one of embodiments 61 to 66, wherein the zeolitic material contained in the catalyst of step (e) contains further at least one alkali metal and / or an earth alkali metal, wherein the at least one alkali metal and / or earth alkali metal is selected from the group consisting of Li, Na, K, Mg and any mixture thereof, preferably Na, Mg and a mixture thereof, more preferably Na.

[0305] 68. The process according to any one of embodiments 61 to 67, wherein the catalyst C(1) in step (d) is Fe-BEA, Fe-MFI or Fe / Cu-OFF-ERI, preferably Fe-BEA.

[0306] 69. The process according to any one of embodiments 61 to 68, wherein the catalyst C(1) further contains a binder. 70. The process according to any one of embodiments 61 to 69, wherein the catalyst C(1) is substantially free of a binder, preferably wherein the catalyst C(1) consists of 0.1 wt% or less of binder, based on the total weight of the catalyst, more preferably 0.01 wt% or less, most preferably wherein the catalyst is free of a binder.

[0307] 71. The process according to embodiment 69 or 70, wherein the binder contains an inorganic binder, preferably a metal oxide, more preferably selected from the group consisting of SiC>2, AI2O3, TiC>2, ZrC>2, MgO and any mixtures thereof, most preferably selected from the group consisting of AI2O3, MgO and a mixture thereof.

[0308] 72. The process according to embodiment 69 or 71 , wherein the catalyst C(1) contains the binder in an amount of from 20 to 50 wt%, based on the total weight of the catalyst, preferably 25 to 40 wt%.

[0309] 73. The process according to any of embodiments 61 to 72, wherein the catalyst C(1) is used in step (d) and the gas stream G(1) is derived from a nitration process or a nitric acid production process.

[0310] 74. The process according to any one of embodiments 61 , wherein the N2O decomposition catalyst is a catalyst C(2) based on a mixture containing CuO and ZnO, preferably in a weight ratio of CuO to ZnO of from 1 :1 to 1.8 : 1.

[0311] 75. The process according to embodiment 61 or 74, wherein the catalyst C(2) contains a further metal oxide, preferably selected from the group consisting of AI2O3, MgO and a mixture thereof.

[0312] 76. The process according to any one of embodiments 75, wherein the catalyst C(2) contains the further metal oxide in an amount of from 50 to 80 wt%, based on the total weight of the catalyst, preferably from 55 to 75 wt%.

[0313] 77. The process according to any one of embodiments 61 and 74 to 76, wherein the catalyst C(2) is used in step (d) and the gas stream G(1) is derived from an adipic acid production process P(2).

[0314] 78. The process according to any one of embodiments 1 to 77, wherein the N2O decomposition catalyst in step (d) is provided as a shaped body, preferably as an extrudate.

[0315] 79. The process according to any one of embodiments 1 to 78, wherein step (d) is carried out at a temperature of from 300 to 800°C, preferably from 420 to 740°C, especially from 420 to 700°C.

[0316] 80. The process according to any one of embodiments 1 to 79, wherein step (d) is carried out at a pressure of from 800 mbar to 10 bar, preferably from 900 mbar to 8 bar. 81. The process according to any one of embodiments 1 to 80, wherein step (d) is carried out at a gas hourly space velocity of from 600 to 30000 standard m3 / (h m3catalyst), preferably from 1000 to 20000 standard m3 / (h m3catalyst), more preferably from 2000 to 10000 m3 / (h m3catalyst).

[0317] 82. The process according to any one of embodiments 61 to 73 and 78 to 81 , wherein step (d) is carried out at a temperature of from 300 to 600°C, preferably from 420 to 560°C, and by using the catalyst C(1).

[0318] 83. The process according to any one of embodiments 61 to 73 and 78 to 82, wherein step (d) is carried out at a pressure of from 1000 to 1200 mbar, by using the catalyst C(1) and the gas stream G(1) is derived from a nitration process P(1).

[0319] 84 The process according to any one of embodiments 61 to 73 and 78 to 82, wherein step (d) is carried out at a pressure of from 4 to 10 bar, by using the catalyst C(1) and the gas stream G(1) is derived from a nitric acid production process P(3).

[0320] 85. The process according to any one of embodiments 61 and 74 to 77, wherein step (d) is carried out by using the catalyst C(2) and at a temperature of from 430 to 800°C, preferably from 450 to 750°C, more preferably from 520 to 700°C.

[0321] 86. The process according to any one of embodiments 61 , 74 to 77 and 85, wherein step (d) is carried out by using the catalyst (C2) and at a pressure of from 1 .5 to 9 bar, more preferably from 1.7 to 8 bar.

[0322] 87. The process according to embodiment 60, wherein step (d) is carried out in the presence of a reducing agent and the reducing agent is added prior to step (d) or is already present in the gas stream.

[0323] 88. The process according to any one of embodiments 59, 61 to 73, 78 to 84 and 87, wherein step (d) is carried out in the presence of a reducing agent and the N2O decomposition catalyst is the catalyst C(1).

[0324] 89. The process according to embodiment 59, 87 or 88, wherein the reducing agent is selected from the group consisting of an Ci-Cs-alkane, CO, hydrogen, ammonia and any mixture thereof, preferably methane, CO, hydrogen, ammonia and any mixture thereof.

[0325] 90. The process according to any one of embodiments 59 and 87 to 89, wherein the molar ratio of the reducing agent to N2O in the gas stream G(3) is of from 0.1 to 2.5, preferably of from 0.15 to 2.

[0326] 91. The process according to any one of embodiments 59 and 87 to 90, wherein the reducing agent is a Ci-Cs-alkane, preferably methane, and the molar ratio of the Ci-Cs-alkane to N2O in the gas stream G(3) is of from 0.1 to 0.5, more preferably 0.15 to 0.45. 92. The process according to any one of embodiments 59 and 87 to 90, wherein the reducing agent is hydrogen and the molar ratio of hydrogen to N2O in the gas stream G(3) is of from 0.5 to 1.1 , more preferably from 0.7 to 1.0.

[0327] 93. The process according to any one of embodiments 59 and 87 to 90, wherein the reducing agent is ammonia and the molar ratio of NH3 to N2O in the gas stream G(3) is of from 1.2 :1, more preferably from 1.1 to 1.0.

[0328] 94. The process according to any one of embodiments 59 and 87 to 93, wherein step (d) is carried out in the presence of a reducing agent, the temperature of step (d) is of from 300 to 600°C, preferably from 330 to 520°C.

[0329] 95. The process according to embodiment 59 or 60, wherein step (d) is carried out without adding a reducing agent.

[0330] 96 The process according to any one of embodiments 59 to 73 and 95, wherein step (d) is carried out without adding a reducing agent and the N2O decomposition catalyst is the catalyst C(1).

[0331] 97. The process according to embodiment 59 to 61 and 74 to 77, wherein step (d) is carried out without adding a reducing agent and the N2O decomposition catalyst is the catalyst C(2).

[0332] 98. The process according to any one of embodiments 3, 59, 61 to 73, 78 to 83, 87 to 89, 95 and 96, wherein CO is present in the gas stream G(3), preferably derived from a nitration process P(1 ) , and acts as a reducing agent in step (d).

[0333] 99. The process according to any one of embodiments 3, 59, 61 to 73, 78 to 83, 87 to 89, 95, 96 and 98, wherein the gas stream G(3) contains CO in a molar excess to N2O.

[0334] 100. The process according to any one of embodiments 3, 59 to 73, 78 to 83, 87 to 89, 95, 96, 98 and 99, wherein the gas stream G(3) contains CO and step (d) is carried out by thermal non-reductive catalytic decomposition and by reductive catalytic decomposition using CO as a reducing agent.

[0335] 101. The process according to any one of embodiments 3, 59 to 73, 78 to 83, 87 to 89, 95, 96 and 98 to 100, wherein a part of N2O reacts with CO forming CO2 and nitrogen and, simultaneously, a part of N2O is decomposed into nitrogen and oxygen.

[0336] 102. The process according to any of embodiments 1 to 101, the process further comprising at least one step of:

[0337] (c-1) removing partially N2O from the gas stream G(3) by a two-stage absorption I desorption process using two absorption units operated with a liquid continuous phase;

[0338] (e) removing (residual) NOX, if present in the gas stream G(3), in the presence of a NOXdecomposition catalyst C(3) and optionally in the presence of a reducing agent; (f) removing CO, if present in the gas stream G(3), in the presence of a catalyst C(4); or

[0339] (g) removing non-methane volatile organic compounds and optionally CO and / or reducing agent, if present in the gas stream G(3), in the presence of a catalyst C(5).

[0340] 103. The process according to embodiment 102, wherein step (c-1) is carried out after step (c) and prior to step (d) or any of steps (e), (f) and (g) to form a gas stream Gc-i(3).

[0341] 104. The process according to embodiment 102 or 103, wherein step (c-1) is carried out, when the gas stream G(3) contains N2O in an amount of > 3 vol%, based on the total volume of the gas stream.

[0342] 105. The process according to any one of embodiments 102 to 104, wherein step (c-1) is carried out and the gas stream G(1) is derived from an adipic acid production process P(1).

[0343] 106. The process according to any one of embodiments 102 to 105, wherein the gas stream G(3) is fed at least partially, preferably completely, into step (c-1).

[0344] 107. The process according to any one of embodiments 102 to 106, wherein the absorption units of step (c-1) are absorption columns containing a random packing or a structured packing, preferably a random packing.

[0345] 108. The process according to any of embodiments 102 to 107, wherein the absorption units of step (c-1) comprise a droplet separating unit in the gas flow, preferably at the top of the absorption unit or downstream of the absorption unit, preferably at the top of the absorption unit.

[0346] 109. The process according to embodiment 108, wherein the droplet separating unit is selected from the group consisting of a lamellar droplet separator, a centrifugal droplet separator, a droplet separator containing a fixed bed of particle bulks, a droplet separator containing a structured packing and a droplet separator containing a fabric made of plastic or metal wires, preferably selected from the group consisting of a droplet separator containing a fixed bed of particle bulks, a droplet separator containing a structured packing or a droplet separator containing a fabric made of plastic or metal wires, more preferably a droplet separator containing a fabric made of plastic or metal wires.

[0347] 110. The process according to embodiment 109, wherein the droplet separator containing a fabric made of plastic or metal wires is selected from the group consisting of a knitted fabric or a woven fabric, preferably a knitted fabric made of metal wires.

[0348] 111. The process according to any of embodiments 102 to 110, wherein step (c-1) removes 0.5 to 5 vol% N2O, based on the total volume of the gas stream G(3), from the gas stream G(3). 112. The process according to embodiment 102, wherein any of steps (e) to (g) are carried out upstream and / or downstream of step (d).

[0349] 113. The process according to embodiment 102 or 112, wherein step (e) is carried out upstream of step (d).

[0350] 114. The process according to embodiment 102 or 112, wherein step (e) is carried out downstream of step (d).

[0351] 115. The process according to embodiment 102 and 112 to 114, wherein step (e) is carried out in the presence of ammonia as a reducing agent, which is preferably added prior to step (e).

[0352] 116. The process according to embodiment 114, wherein the molar ratio of ammonia to NOXof from 0.8 to 1.5, preferably from 0.9 to 1.4, more preferably from 1.0 to 1.2.

[0353] 117. The process according to any one of embodiments 102 and 112 to 116, wherein the catalyst C(3) of step (e) is a SCR catalysts containing a transition metal and / or a transition metal oxide, wherein preferably the transition metal is selected from the group consisting of Pt, Au, Pd and any mixture thereof, and the transition metal oxide is selected from the group consisting of an oxide of Fe, Ni, Cu, Co, Mn, Rh, Re, V, Ti and any mixture thereof.

[0354] 118. The process according to any one of embodiments 102 and 112 to 117, wherein the catalyst C(3) of step (e) is a catalyst based on X^Os-TiCh or a transition metal-containing zeolitic material, more preferably a Fe-BEA catalyst.

[0355] 119. The process according to any one of embodiments 102 and 112 to 118 wherein step (e) is carried out at a temperature of from 200 to 500°C, preferably from 230 to 420°C, more preferably from 230 to 350°C.

[0356] 120. The process according to any one of embodiments 102 and 112 to 119, wherein step (e) is carried out at a pressure of from 800 mbar to 10 bar.

[0357] 121 . The process according to any one of embodiments 102 and 112 to 120, wherein the gas stream G(1) is derived from a nitration process P(1) and step (e) is carried out at a pressure of from 800 mbar to 8 bar, preferably from 1000 mbar to 1200 mbar.

[0358] 122. The process according to any one of embodiments 102 and 112 to 120, wherein the gas stream G(1) is derived from a nitric acid production process P(3) or adipic acid production process P(2) and step (e) is carried out at a pressure of from 5 to 10 bar.

[0359] 123. The process according to any one of embodiments 102 and 112 to 122, wherein step (e) is carried out at a gas hourly space velocity (GHSV) of from 600 to 30000 standard m3 / (m3catalyst ■ h), preferably from 1000 to 20000 standard m3 / (m3catalyst ■ h) and more preferably from 2000 to 10000 standard m3 / (m3catalyst ■ h). 124. The process according to any one of embodiments 102, 112, 113 and 115 to 123, wherein step (e) is carried out upstream of step (d) and the gas stream G(1) is derived from a nitric acid production plant P(3) or a nitration process P(1 ) , in particular a production process for DNT.

[0360] 125. The process according to any one of embodiments 102, 112, 114 to 120, 122 and 123, wherein step (e) is carried out downstream of step (d) and the gas stream G(1) is derived from an adipic acid production plant.

[0361] 126. The process according to any of embodiments 102 and 112 to 125, wherein step (e) is carried out in the presence of ammonia as a reducing agent, in case the gas stream G(3) contains CO in an amount of < 0.1 vol%, based on the total volume of the gas stream.

[0362] 127. The process according to embodiment 102 or 112, wherein step (f) is carried out upstream of step (d), optionally in addition downstream of step (d).

[0363] 128. The process according to embodiment 102, 112 or 127, wherein step (f) is carried out at an amount of CO in the gas stream G(3) of > 0.5 vol%, based on the total volume of the gas stream G(3), preferably from 0.5 to 1.5 vol%, and the gas stream G(1) is derived from a nitration process P(1).

[0364] 129. The process according to any one of embodiments 102, 112, 127 and 128, wherein the catalyst C(4) used in step (f) is a 3-way catalyst C(4a) or a 2-way catalyst C(4b), preferably a 3-way catalyst C(4a).

[0365] 130. The process according to any one of embodiments 102, 112 and 127 to 129, wherein the 3-way catalyst C(4a) used in step (f) contains a ceramic monolithic unit of a honeycomb structure, coated with a metal oxide-containing wash coat containing particles of at least one noble metal.

[0366] 131 . The process according to embodiment 130, wherein the wash coat of the 3-way catalyst C(4a) contains at least one metal oxide selected from the group containing of AI2O3, TiO2, SiO2, CeO2, ZrO2 and any mixture thereof, and particles of at least one noble metal selected from the group consisting of Pt, Pd, Ru, Rh and mixture thereof.

[0367] 132. The process according to any one of embodiments 102, 112 and 127 to 131 , wherein step (f) is carried out at a temperature of from 230 to 600°C, preferably from 250 to 540°C.

[0368] 133. The process according to any one of embodiments 102, 112 and 127 to 132, wherein step (f) is carried out at a pressure of from 800 mbar to 10 bar, preferably of from 900 mbar to 8 bar, more preferably from 1 to 1 .5 bar. 134. The process according to any one of embodiments 102, 112 and 127 to 133, wherein step

[0369] (f) is carried out at a gas hourly space velocity (GHSV) of from 4000 to 200000 standard m3 / (m3catalyst ■ h), preferably from 8000 to 150000 standard m3 / (m3catalyst ■ h).

[0370] 135. The process according to embodiment 102, 112, 113 and 127 to 134, wherein step (e) and step (f) are carried out simultaneously upstream of step (d), preferably without adding a reducing agent, and the gas stream G(1) is derived from a nitration process.

[0371] 136. The process according to any one of embodiments 102, 112, 113 and 127 to 135, wherein step (e) and step (f) are carried out simultaneously using the 3-way catalyst C(4a).

[0372] 137. The process according to any one of embodiments 102, 112, 113 and 127 to 136, wherein step (e) and step (f) are carried out simultaneously using a 3-way catalyst C(4a) at a temperature of from 230 to 600°C, preferably from 250 to 540°C, at a at a pressure of from 800 mbar to 10 bar, preferably of from 900 mbar to 8 bar, more preferably from 1 to 1.5 bar, and at a gas hourly space velocity (GHSV) of from 4000 to 200000 standard m3 / (m3catalyst ■ h), preferably from 8000 to 150000 standard m3 / (m3catalyst ■ h).

[0373] 138. The process according to embodiment 102 or 112, wherein the catalyst C(5) used in step

[0374] (g) is a 2-way catalyst C(4b) containing a noble metal or a N2O decomposition catalyst, preferably in case step (g) and step (d) are carried out simultaneously.

[0375] 139. The process according to embodiment 102, 112 or 138, wherein step (g) is carried out downstream of step (d), preferably in case the gas stream G(1) is derived from a nitration process P(1).

[0376] 140. The process according to any one of embodiments 102, 112, 138 and 139, wherein step (g) is carried out at a temperature of from 300 to 600°C, preferably from 420 to 560°C, and at a pressure of from 800 mbar to 10 bar, preferably from 900 mbar to 8 bar, more preferably from 1000 mbar to 1200 mbar.

[0377] 141. The process according to any one of embodiments 102, 112 and 138 to 140, wherein step (g) is carried out at a gas hourly space velocity of from 600 to 30000 standard m3 / (h m3catalyst), preferably from 1000 to 20000 standard m3 / (h m3catalyst), more preferably from 2000 to 10000 m3 / (h m3catalyst).

[0378] 142. The process according to any one of embodiments 102, 138, 140 and 141 , wherein step (g) and step (d) are carried out simultaneously using the N2O decomposition catalyst C(1) and the gas stream G(1) is derived from a nitration process P(1).

[0379] 143. The process according to any one of embodiments 102, 138, 140 and 141 , wherein step (g) and step (d) are carried out simultaneously using the N2O decomposition catalyst C(2) and the gas stream G(1) is derived from an adipic acid production process P(2) or a mixture of a gas stream derived from an adipic acid production process P(2) and a gas stream derived from a nitric acid production process P(3), preferably derived from an adipic acid production process P(2). The process according to any one of embodiments 1 to 9, 16 to 50, 57 to 73, 78 to 83, 87 to 96, 98 to 102, 112, 113, 121 , 124 and 127 to 142, the process comprising the steps (a) to (d) using a catalyst C(1) and optionally step (e) and step (f), carried out simultaneously upstream of step (d) using a 3-way catalyst C(4a) without adding a reducing agent, optionally step (g), wherein the gas stream G(1) is derived from a nitration process P(1), preferably derived from a production process of DNT. The process according to any one of embodiments 1 to 5, 10, 11 , 14, 16 to 47, 51 to 53, 57 to 61 , 74 to 81 , 85 to 87, 97, 98, 100 to 102, 112 to 120, 122, 123, 125, 126, 138, 143, the process comprising the steps (a) to (d) using a catalyst C(2) and optionally step (c-1), step (e) and step (g), wherein step (g) is carried out simultaneously with step (d), and wherein the gas stream G(1) is derived from an adipic acid production process P(2) or a mixture of a gas stream derived from an adipic acid production process P(2) and a gas stream derived from a nitric acid production process P(3), more preferably derived from an adipic acid production process P(2), wherein step (e) is preferably carried out downstream of step (d). The process according to any one of embodiments 1 to 5, 12 to 14, 16 to 45, 54 to 73, 78 to 82, 84, 87 to 96, 102, 112 to 120, 123, 124 and 126, the process comprising the steps (a) to (d) using a catalyst C(1) and optionally step (e), in case the gas stream G(1) is derived from a nitric acid production process P(3), wherein step (e) is preferably carried out upstream of step (d). A chemical production unit for carrying out the process, as defined in any one of embodiments 1 to 146, the chemical production unit comprising:

[0380] - an absorption unit operated with an aqueous washing fluid as a continuous liquid phase;

[0381] - a droplet separating unit;

[0382] - a N2O decomposition reaction unit equipped with a N2O decomposition catalyst;

[0383] - means for passing the gas stream G(1) to the absorption unit;

[0384] - means for passing the gas stream G(2) to the droplet separating unit;

[0385] - means for passing the gas stream G(3) to the N2O decomposition reaction unit; and

[0386] - optionally an inlet means for adding a reducing agent upstream of the N2O decomposition reaction unit. The chemical production unit according to embodiment 147, the chemical production unit comprises further at least one of the following units:

[0387] - a N2O isolation unit containing two absorption units operated with a continuous liquid phase;

[0388] - a NOx decomposition reaction unit equipped with a NOXdecomposition catalyst C(3);

[0389] - a reaction unit equipped with a CO oxidizing catalyst C(4); or

[0390] - a reaction unit equipped with a catalyst C(5) for removing non-methane volatile organic compounds and optionally CO and / or residual reducing agent. All cited documents are incorporated herein by reference.

[0391] The following examples shall further illustrate the present invention without restricting the scope of this invention.

[0392] Examples

[0393] N2O conversion rates were analyzed by a FT- 1 R (Advance Optima A02000)

[0394] Example 1

[0395] Non-reductive, thermal decomposition of N2O using a N2O decomposition catalyst C(2) (mixture containing, based on the total weight of the catalyst, 20 wt% of CuO, 20 wt% of ZnO and AI2O3)

[0396] A gas flow containing N2O, H2O and N2 (balance) was passed through a catalyst for step (d) at a pressure of 5 bar and at a temperature of 500°C with a GHSV of 4000 standard m3 / (m3catalyst ■ h). Only the H2O vapor content in the gas flow fed to the catalyst system has been varied and replaced by N2. The achieved N2O conversion rates depending on the water vapor content are shown in Table 1 :

[0397] Table 1

[0398] It was shown that the N2O conversion rate could be significantly improved with a reduced water vapor content < 1.5 vol% in the gas flow, compared to a gas flow having a water vapor of > 2.5 vol%.

[0399] Example 2

[0400] Non-reductive, thermal decomposition of N2O using a N2O decomposition catalyst C(1) (Fe-BEA zeolite, prepared in analogy to Example 5 of WO 2013 / 118064 A1)

[0401] A gas flow containing N2O (1.8 vol%), NO (72 ppmv), H2O vapor and N2 (balance) was passed through a catalyst for step (d) at a pressure of 0.12 barg and at a temperature, as indicated in Table 2, with a GHSV of 30000 standard m3 / (m3catalyst ■ h). The achieved N2O conversion rates depending on the water vapor content are shown in Table 2: Table 2

[0402] It was shown that the N2O conversion rate could be significantly improved with a reduced water vapor content < 1.5 vol% in the gas flow, compared to a gas flow having a water vapor of > 2.5 vol%.

[0403] Example 3

[0404] Reductive, thermal decomposition of N2O using a N2O decomposition catalyst C(1) (Fe-BEA zeolite, prepared in analogy to Example 5 of WO 2013 / 118064 A1) a) Reducing agent: CH4(300 ppmv) b) Reducing agent: NH3 (1000 ppmv)

[0405] A gas flow containing N2O (0.1 vol%), O2(5 vol%), reducing agent, H2O vapor and N2(balance) was passed through a catalyst for step (d) at a pressure of 0.1 barg and at a temperature, as indicated in Table 3, with a GHSV of 10000 standard m3 / (m3catalyst ■ h). The achieved N2O conversion rates depending on the water vapor content are shown in Table 3:

[0406] Table 3

[0407] Although water is formed during the reductive, catalytical decomposition reaction, it was shown that the N2O conversion rate could be significantly improved with a reduced water vapor content 1 vol% in the gas flow, compared to a gas flow having a water vapor content of 5 vol%.

Claims

1. Claims1. A process for reducing the concentration of N2O in a gas stream, the process comprising(a) providing a gas stream G(1) containing N2O;(b) treating the gas stream G(1) with an aqueous washing fluid in an absorption unit operated with a liquid continuous phase to obtain a gas stream G(2);(c) passing the gas stream G(2) through a droplet separating unit to obtain a gas stream G(3); and(d) contacting the gas stream G(3) with a N2O decomposition catalyst to obtain a gas stream G(4).

2. A process according to claim 1 , wherein the gas stream G(1) contains further NO2, oxygen and optionally NO, CO and / or non-methane volatile organic compounds.

3. The process according to claim 1 or 2, wherein the gas stream G(1) is a gas stream derived from an industrial production process or a combustion process of sludge.

4. The process according to claim 1, 2 or 3, wherein the gas stream G(1) is a gas stream derived from at least one industrial production process selected from a nitration process P(1 ) , an adipic acid production process P(2) and a nitric acid production process P(3).

5. The process according to any one of the preceding claims, wherein the absorption unit operated with a liquid continuous phase is an absorption column containing trays, a random packing or a structured packing, preferably an absorption column containing trays.

6. The process according to any one of the preceding claims, wherein the gas stream G(2) contains water vapor in an amount of from 2.5 to 10 vol%, based on the total volume of the gas stream, preferably from 2.8 to 10 vol%, more preferably from 3 to 10 vol%, especially from 3 to 8 vol%.

7. The process according to any one of the preceding claims, wherein step (d) is carried out by thermal non-reductive catalytic decomposition and / or by reductive catalytic decomposition using a reducing agent.

8. The process according to any one of the preceding claims, wherein the N2O decomposition catalyst is a catalyst C(1) containing a transition metal-exchanged zeolitic material or a catalyst C(2) based on a mixture containing copper oxide (CuO) and zinc oxide (ZnO).

9. The process according to claim 8, wherein the zeolitic material contained in the catalyst C(1) has a framework structure selected from the group consisting of MFI, BEA, FER, MOR, FAU, OFF, ERI, any mixture thereof, and mixed structures of two or more thereof, preferably MFI, BEA, OFF, ERI, any mixture thereof, and mixed structures of two or more thereof, more preferably BEA; andthe transition metal of catalyst C(1) is at least one transition metal selected from the group consisting of Fe, Co, Ni, Cu, Zn, V, Zr and any mixture thereof, preferably Fe, Co, Cu, Zn and any mixture thereof, more preferably Fe.

10. The process according to claim 8 or 9, wherein the catalyst C(1) in step (d) is Fe-BEA, Fe- MFI or Fe / Cu-OFF-ERI, preferably Fe-BEA.

11. The process according to any one of the preceding claims, wherein the gas stream entering step (d) contains water vapor in an amount of < 1.5 vol%, based on the total volume of the gas stream, preferably of from 0.1 to 1.5 vol%, more preferably from 0.1 to 1.2 vol%.

12. The process according to any of claims 1 to 11 , the process further comprising at least one step of:(c-1) removing partially N2O from the gas stream G(3) by a two-stage absorption I desorption process using two absorption units operated with a liquid continuous phase;(e) removing NOX, if present in the gas stream G(3), in the presence of a NOXdecomposition catalyst C(3) and optionally in the presence of a reducing agent;(f) removing CO, if present in the gas stream G(3), in the presence of a catalyst C(4); or(g) removing non-methane volatile organic compounds and optionally CO and / or reducing agent, if present in the gas stream G(3), in the presence of a catalyst C(5).

13. The process according to claim 12, wherein step (e) is carried out upstream of step (d).

14. The process according to claim 12 or 13, wherein step (e) and step (f) are carried out simultaneously upstream of step (d), preferably without adding a reducing agent.

15. A chemical production unit for carrying out the process, as defined in any one of claims 1 to 14, the chemical production unit comprising:- an absorption unit operated with an aqueous washing fluid as a continuous liquid phase;- a droplet separating unit;- a N2O decomposition reaction unit equipped with a N2O decomposition catalyst;- means for passing the gas stream G(1) to the absorption unit;- means for passing the gas stream G(2) to the droplet separating unit;- means for passing the gas stream G(3) to the N2O decomposition reaction unit; and- optionally an inlet means for adding a reducing agent upstream of the N2O decomposition reaction unit.

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