WO2016063302A2

WO2016063302A2 - Process for combustion of nitrogen for fertilizer production

Info

Publication number: WO2016063302A2
Application number: PCT/IN2015/050141
Authority: WO
Inventors: Garudadri LAKSHMI PRASANNA KUMAR
Original assignee: Swasa Agro Solutions Private Limited
Priority date: 2014-10-24
Filing date: 2015-10-21
Publication date: 2016-04-28
Also published as: WO2016063302A3

Abstract

The present invention relates to materials, methods, and system that can be used for fixation of elemental nitrogen for fertilizer production. This invention is to provide a new simple and energy efficient process for the preparation of nitrogen compounds that can be assimilated by plants. Since, elemental nitrogen in the atmosphere cannot be used directly by either plants or animals, and it must be converted to a reduced (or 'fixed') state in order to be useful for higher plants and animals. The present invention is related to the Nitrogen fixation, i.e., the conversion of nitrogen gas into nitrogen compounds that can be assimilated by plants.

Description

Process for Combustion of Nitrogen for Fertilizer Production Field of Invention

The present invention relates to materials, methods, and system that can be used for fixation of elemental nitrogen for fertilizer production. Since, elemental nitrogen in the atmosphere cannot be used directly by either plants or animals, and it must be converted to a reduced (or 'fixed') state in order to be useful for higher plants and animals. The present invention is related to the Nitrogen fixation, i.e., the conversion of nitrogen gas into nitrogen compounds that can be assimilated by plants.

Background of Invention Elemental nitrogen in the atmosphere cannot be used directly by either plants or animals, and must convert to a reduced (or 'fixed') state in order to be useful for higher plants and animals. Nitrogen fixation is the conversion of nitrogen gas into nitrogen compounds that can be assimilated by plants. Biological fixation is the most common, but fixation can also occur by lightning and through industrial processes: Biological: Nitrogen gas→ Organic Nitrogen

Lightning: Nitrogen gas→ Nitrate

Industrial: Nitrogen gas→ Nitrate and Ammonia/Ammonium ion

Of the total nitrogen fixation, 65% is contributed by biological nitrogen fixation and industrially produced nitrogen fertilizers, primarily produced by the Haber-Bosch process, accounts for 25% of the total annual nitrogen fixation.

Nitric acid is produced industrially by the Ostwaldt process by catalyzed combustion of ammonia with air. The yield of this exothermic reaction is strongly affected by rapid quenching of the reaction gases.

The preparation of nitrogen oxides by reaction of nitrogen with oxygen under plasma conditions is already known for a long time. The reaction conditions described in the state of the art can be divided into high temperature plasma reactions and low temperature plasma reactions, with the temperature of the product gases leaving the reaction space not being a suitable distinctive feature. For the application of high temperature plasma reactions the rapid cooling of the reaction products is of particular importance, because the thermal formation of NO from N₂ and O₂ requires very high temperatures, while on the other hand the reaction product decomposes rapidly at high temperatures. The endo-thermal compound NO is only meta-stable even at temperatures below 700 K. For low temperature plasma reactions the decomposition problem is smaller, because the average gas temperature remains comparatively low even inside the plasma zone, while the high electron energy within the plasma induces the required molecular excitations and dissociations. Another discriminating feature is the use of catalysts in addition to the plasma for supporting the nitric oxide formation inside a reactor. The main purposes of the processes and devices described in the prior art are on one hand the production of nitric acid solutions from the generated nitrogen oxides and on the other hand the exhaust gas purification in connection to combustion engines, for which in a first step nitrogen oxides are generated in a controlled manner, which are subsequently converted to NH₃, which is admixed to the combustion exhaust gas.

For example CH 645 321 A5 describes a method and a device for the generation of nitrogen oxides from a nitrogen and oxygen containing gas by plasma reaction inside a reactor and in presence of WO₃ or M0O₃ as catalyst. The plasma is generated by a plasma torch and is characterized by an electron temperature of 1 to 5 eV, vibrational temperature of 5000 - 12000 K, and rotation-translation temperature of 1000 - 8000 K. The wall temperature is 440-1550 K. A magnetic coil may be installed to influence the plasma zone. The method is performed in a pressure range of 10-760 mmHg and with a 40 MHz alternating current power supply. The method may include recycling of the N₂/O₂ mixture to the plasma reactor. For an O₂ : N₂ ratio of about 1 : 1 a 5-10% content of NO₂ in the product gas is achieved, up to 19% nitrogen fixation for energy input 100 kcal/L N₂ are achieved with the method.

For example DE 101 24 548 Al describes a method for cleaning exhaust gases by means of NH₃. In a first step nitrogen oxides are formed by exposing a fat combustion exhaust gas to thermal plasma, e.g. an arc discharge or a dielectric barrier discharge. The combustion exhaust gas besides oxygen and nitrogen also contains carbon oxides as well as not combusted or only partially converted fuel. The method is performed in a micro reactor which allows good quenching conditions and in a pressure range of 0.1 to 10 m bar. The electrode gap in the micro reactor is 0.01 - 10 mm. The plasma is excited by an alternating current of 10 Hz-30 GHz, preferably 50-250 MHz. About 10-20 eV per NO molecule are supplied by the voltage in the range of 10 Vp-100 kVp, preferably 500 Vp - 1.5 kVp. Pulsed voltage may also be applied. Optional pellets inside the reactor lead to accelerated quenching as well as sliding spark discharges. The pellets also may contain a catalyst. The electrodes may be plate electrodes or arranged coaxial and in either case may exhibit a structured surface for field enhancement. DE 103 53 313 Al reveals a similar exhaust gas purification system, where the generation of nitrogen oxides is facilitated by a corona stabilized spark discharge. The electrodes are opposing each other at the short walls of a reaction chamber. The individual discharge period is some microseconds. The electrodes exhibit sharp tips for field enhancement. The reaction chamber has a wall length ratio of at least about 5: 1 to allow a high volume flow rate and a large relative plasma volume in the reaction chamber. The plasma reactor preferably exhibits a plurality of reaction areas, which may be arranged in a star shaped manner. The repetition frequency of the spark discharge is at least 5 kHz. The gas temperature inside the reaction area is between 3300 K and 3700 K. DE 10 2006 043 096 Al describes a microwave excited plasma reactor as component of an exhaust gas purification system. In comparison to thermal plasmas induced by current discharges the larger difference between electron and gas temperatures provides better synthesis conditions for nitrogen oxides and therefore an improved energy efficiency of the process. The reactor can be shaped as a coaxial conductor and the plasma zone can be exposed to a magnetic field. The microwave frequency is preferably 2.4 - 2.5 GHz, which allows application of commercial magnetrons with 2.45 GHz working frequency. The plasma is generated at atmospheric pressure. The reactor is supplied with air or combustion exhaust gas. By constructive means the gas movement inside the reactor can be modified, so that the pressure inside the reaction zone is reduced and/or wall contact of the plasma is prevented. The input power is 400 - 2000 kJ per m³ of input gas. The amount of formed nitrogen oxide can be influenced by controlling the microwave power, the gas flow rate or by switching the microwave generator on and off. The reactor can contain separate means for plasma ignition. The concentration of nitrogen oxides in the reactor exhaust gas is about 2%.

EP 1 630 133 A1 reveals the production of nitrogen oxides, in particular N₂Os, with a device inside which a gas containing oxygen and nitrogen is exposed to a dielectric barrier discharge or silent discharge, which is generated by high voltage direct current. The preparation of nitrogen oxides takes place inside a modified ozonizer. The nitrogen oxides are condensed from the product gas mixture at low temperature or are absorbed by a liquid. The residual gas can be recycled to the production process. Preferably the ratio N₂:0₂ is adjusted within the range of 80 : 20 to 25 : 75 and pre-dried gas with maximal 10 ppm water content is used to prevent the formation of nitric acid. Application of a gas mixture without hydrocarbon content is advantageous to prevent water formation during the plasma reaction. Hydrocarbon contents of maximal 15 ppm are preferred. The reactor is operated at a pressure of at least 2 bar. The energy density of the barrier discharge is 2-6 kW/m². The amount of N₂O₅ isolated from the product gas equals up to 10% of the simultaneously generated ozone amount and at least 1% of the total product gas amount consists of nitrogen oxides. Optimized nitrogen oxide yields are obtained by operating the plasma reactor in a temperature range of +3°C to 100°C. If the exhaust gas of the nitrogen oxide separation is not recycled into the plasma process, an additional scrubber system has to be installed to neutralize ozone contained in the exhaust gas. If the product gas mixture is scrubbed with water instead of condensing the nitrogen oxides, pure nitric acid can be obtained. The N₂O5 yield can be increased by admixing other nitrogen oxides like NO₂ to the gas mixture introduced into the plasma reactor. Aim of the process is to achieve maximized yields of N₂O5 in the product gas mixture in comparison to other nitrogen oxides by generating simultaneously ozone and nitrogen oxides inside the same reactor.

FR 2 549 459 Al describes the production of nitrogen oxides for the preparation of nitric acid inside a microwave plasma reactor in a pressure range of 10 mbar to 130 mbar, preferably 25 to 75 mbar. The microwaves applied have a wave length of 1 to 50 cm, preferably 3 to 25 cm. The reaction is supported by the presence of catalysts, which preferably consist of tungsten oxides or molybdenum oxides. These oxides can be generated inside the plasma reactor itself by combustion of the metals in the plasma discharge. It is described that with an irradiation frequency of 2.45 GHz and a power of 1500 W into a parallelepiped shaped cavity the formation of a plasma is possible in the pressure range of 1 mbar to 1100 mbar. The process gas is a mixture of oxygen and nitrogen, in particular air. Air can be enriched with oxygen, a ratio N₂:0₂ of 65% : 35% is mentioned. It is also possible to introduce oxygen into the process gas flow after it has already passed the plasma zone. The plasma excitation generates nitrogen molecules with a vibrational temperature of about 3500 K. A gas flow of 18 L/h N₂ and 4 L/h O₂ through a quartz glass tube with 15 mm diameter is irradiated inside a microwave cavity with a wavelength of 12.4 cm and with 10 Watts power. The pressure is 65 mbar and M0O₃ is used as catalyst. The product gas mixture contains 6% nitrogen oxides and an energy consumption of 28 MJ/kg NO is calculated. Without catalyst the nitrogen oxide content of the product gas mixture is only 4%, which equals to an energy consumption of 43 MJ/kg NO.

GB 116,503 describes a plasma system yielding an NO concentration of 2.5% in the reaction exhaust gas. Air is passed through an electric arc with a water-cooled exhaust pipe installed near to the arc. The exhaust pipe does not serve as electrode and has dimensions suitable to achieve high gas velocities. The reaction exhaust gases are rapidly cooled to a temperature of 1200° to 1500°, which prevents back reaction of the NO formed in the arc discharge. GB 855,084 describes a device which can be used for the conversion of air or of air enriched with oxygen to nitrogen oxides. Preferably an arc discharge between electrodes is generated by high voltage DC power, but also AC can be applied. The process gas is introduced with a pressure of up to 5 bar. The product mixture is rapidly removed from the reaction zone, preferably through an outlet nozzle inside one of the electrodes. The minimum gas velocity is not substantially below the speed of sound. The oxidation of NO with oxygen contained in the product gas mixture to higher oxides can take place inside an additional reaction space at 30 - 120°C. Ν¾ concentrations of 5-10 vol% could be achieved with this device. The electrode gap in the experimental setup is between 0.8 and 1.3 cm. High NO₂ concentrations are achieved particularly at standard pressure, with voltages of 400 - 500 V, for currents of 0.5 - 0.6 A and with oxygen concentrations of at least 50 mol% in the introduced gas. The energy consumption for high nitrogen oxide concentrations (about 10 %) amounts to about 6 kWh/m³ introduced gas.

GB 873,090 describes a similar device, which is operated with high frequency power of 10-200 MHz. The reaction space is formed as resonance chamber. Starting from air as process gas and at about standard pressure inside the reaction chamber, concentrations of up to 6.4 mol% NO₂ are achieved. The power input into the reactor is about 16 kWh/m³ input air.

GB 890,414 also describes a device, in which the reaction products are removed from the discharge zone by a nozzle and accelerated to high velocity. In this case the product gas is directed into a separate a reaction chamber, inside which additional reactants are admixed to the primary product gas. For the production of nitrogen oxides pure nitrogen is passed through the electric arc at about 1- 4 bar and oxygen admixed to the product gas only in the reaction chamber. For an electrical current of 0.9 A at 150-200 V in the discharge zone and an oxygen admixture equal to a ratio N₂:0₂ of 32 : 68, 10 L NO per kWh electrical energy could be prepared. GB 955,702 describes a special electrode and discharge chamber construction for the same purpose.

GB 241,413 claims the direct generation of nitric acid inside a reactor, which besides electrodes for the generation of an electric arc also contains means for gas scrubbing with oxygen and hydrogen releasing liquids. The scrubbing liquid can also be transported directly into the discharge gap by conduits inside the electrodes and decomposed. The released hydrogen stabilizes the electric arc while oxygen supports the oxidation of the nitrogen oxides to higher oxidation stages. Additionally the presence of the scrubbing liquid supports the rapid cooling of the gases containing nitrogen oxides, so that the back reaction of the formed nitric acid is prevented. Nitric acid is collected inside the reactor and removed by a discharge tube. Electrodes made from copper or copper alloys support the formation of nitric acid, in particular electrodes made from 20% cadmium and 80% copper. Reaction conditions and yields are not given. GB 296,064 passes air first through an ozonizer and then through an electric arc to generate nitrogen oxides. The device is operated with alternating current of 12500 V and a frequency of at least 350 Hz. A multiphase rotary current is preferred to establish a larger and more homogeneous discharge zone between several electrodes. The presence of ozone during the electric arc reaction improves the yield of nitrogen oxides in comparison to pure air. A complete conversion to NO is mentioned, but it is not clear which species is completely converted and experimental proof is missing.

GB 886, 156 describes an apparatus in which a mixture of oxygen and nitrogen is introduced through a nozzle into a reaction chamber, within which a set of DC electrodes induces a glow discharge inside the formed gas jet. After separation of the reaction products the exhaust gas can be recycled into the feed gas. Inert gases can be admixed. The voltage between the electrodes is 100 - 2000 V. The DC may be pulsed or shaped in some cases also AC may be applied. The reacting components do not both need to enter the reaction chamber through the gas jet, an additional supply port into the reaction chamber is possible. Separate opposing gas jets for each reaction component may be installed. The gas discharge can be influenced by an additional magnetic field. Experiments with air yielded conversions of up to 67.9 % of the initially contained oxygen and power consumptions, which equaled 7 kWh/kg HNO₃ in the best case (without power consumption of the vacuum pump). Pressure values mentioned in the application are between 3 and 50 mmHg inside the plasma chamber. Chemical analyses showed that Ν₂0_¾ was the only detectable nitrogen oxide in the process exhaust gas. Therefore the production of nitric acid is simplified in comparison to the absorption of other nitrogen oxides by water, because no additional oxidation reactions occur inside the absorption unit.

GB 915,771 generates a dielectric barrier discharge via radio frequency power, which is ignited at low pressure and stabilized during slow pressure increase. The discharge zone is distinguished from a conventional glow discharge by its high temperature. Finally air or a mixture of oxygen and nitrogen is passed through the device at normal pressure. Frequencies mentioned in the application text are 10-200 Mhz or even higher, such as 3000 MHz. Contact of the plasma to the reactor walls can be prevented by directed gas introduction of by application of magnetic fields, so that the reactor walls do not overheat. The reactor walls may be cooled by suitable means in addition. Concentrations of up to 5% NO in the process exhaust gas are detected, which is about 20 kWh/kg HNO₃ in the best case. Gas reactions at pressures of more than 400 mmHg are claimed. Not all reaction partners have to pass the discharge zone, at least one reaction partner may be introduced into the reactor outside the plasma zone.

US 4,167,463 uses focused pulsed laser beams for the generation of high gas temperatures and rapid cooling rates in reactions to nitrogen oxides in mixtures of nitrogen and oxygen. Performing the method at elevated, but not defined pressures is mentioned.

US 4,287,040 reveals the generation of nitrogen oxides from air in an electric discharge and with admixing small amounts of nitrogen oxides to the input gas. The nitrogen oxide traces lead to a significant increase of the nitrogen oxide amounts isolated from the process exhaust gas in comparison to pure air. The process may be performed with glow discharges of with arc discharges. A multitude of discharge zones may be arranged in parallel or in series for performing the process.

US 4,705,670 describes a reactor for the production of nitric acid. A solution of the reaction products flows through the reactor and serves as liquid electrode. A discharge is generated above the liquid electrode by an alternating current of at least about 6000 V to 20000 V. The second electrode is attached on the outside to the upper reactor wall, which serves as dielectric. Oxygen, nitrogen, and water are converted to NO, ozone, and H₂O₂ as primary products. These products are absorbed by the liquid electrode and react to nitric acid in the solution. The acid discharged from the reactor may be cooled and recycled to the reactor to achieve higher acid concentrations. Frequency and/or energy density of the plasma discharge may be changed periodically to increase and decrease the formation of specific products periodically. A plurality of discharge zones with different energy densities and/or frequencies may be arranged in one reactor. It is intended to accelerate the oxidation of NO to higher oxides and therefore the formation of nitric acid by the presence of more efficient oxidation agents. The liquid electrode contributes to the cooling of the reaction products. Regarding frequency ranges, 60 - 600 Hz for the generation of ozone and H₂O₂ and 1 kHz to 300 kHz for the generation of elevated NO concentrations are mentioned. US 2005/0079112 Al deals with a device for the production of nitrogen oxides in a system for exhaust gas purification. A reactor for the generation of a non-thermal surface discharge is described. The reactor contains a staple of dielectric plates, which are equipped with electrodes on both sides. Between the plates the process gas flows in parallel to the plate surfaces. By suitable electrical connection of the electrodes surface discharges between the plates are generated. The electrode pattern allows influence on the surface discharge and thus also on the nitrogen oxide concentration of the reactor exhaust gas.

US 2012/0297673 Al generates NO from a gas containing oxygen and nitrogen by means of a corona discharge. This plasma may be induced by microwave irradiation or by RF alternating current, but also by direct current. NO reacts with oxygen to Ν¾ outside the corona chamber and the gas then is injected into a liquid to give nitric acid and finally nitrate. Nitrate is also formed when only nitrogen passes the corona discharge and the product is injected into water. A plurality of corona chambers, reaction chambers and absorption units may be arranged in parallel or in series to perform the process. Suitable frequencies mentioned are 2.45 GHz, 30000-60000 Hz, 20-50 kHz.

WO 95/07610 Al generates a gas mixture containing NO from an N₂ and O₂ containing gas mixture by exposure to a glow discharge. Maximum pressure for the process is 5 bar, preferably 3 bar. The glow discharge is generated between two electrodes inside the reactor by direct current or high frequency alternating current. Experimentally at 40 mA, 800 V and with an air flow of 10 L/min 500 ppm NO and less than 10 ppm NO₂ are obtained in the product gas. NO concentrations of 10 ppm to 10000 ppm in the product gas may be obtained by the process. The operating voltage is 100 - 1000 V. The reactor is operated with currents which do not lead to electric arcing. The reactor may contain additional means for igniting the glow discharge. An a different embodiment the electrodes may be attached to the outside of the reaction chamber opposing each other and induce the glow discharge by high frequency power of at least 1 MHz. The operating pressure of the reactor is between 0.01 and 3 bar. Advantage of the device is the low concentration of byproducts like Ν¾ or ozone, because the system is mainly designed for medical applications. WO 2012/150865 Al describes a reactor for the production of NO, inside which an electric arc is moved through a flow of air or air enriched with oxygen. A magnetic field is applied for moving the arc. The arc may be generated by alternating or by direct current. The temperature inside the arc is adjusted to 3000 - 5000 K. Additional measures like spraying water droplets into the gas flow in front or directly behind the plasma zone, excess air, or admixing bypass air stabilize the temperature of the NO containing plasma at less than 2000 K. The pressure inside the reactor is 0.1 - 1 bar, pre-warming of input gas and cooling of exhaust gas may be performed in a heat exchanger. A retention time of 0.1 s leads to 8 vol% NO, 0.001 s retention time yield 12 vol% NO. A power consumption of 30 GJ/t N or less is calculated. All numbers are based on simulation, no experimental results are given.

WO 2013/052548 A2 describes an apparatus for the generation of NO, which contains a reaction chamber with two electrodes. Inside a gas flow containing oxygen and nitrogen discharges are induced by a control unit, which are adjusted in terms of frequency and duration. The current during each discharge period is substantially constant. The gas flow is controlled. Direct current is applied in a pulsed manner with a frequency of 0.1 - 100 Hz and 20 Ds - 500 ms pulse duration. The current is 20 - 3000 mA. A magnetic field around discharge zone can be established, which increases the NO yield and therefore also the energy efficieny. The NO concentration in exhaust gas can be adjusted to between 1 and 1000 ppm NO. A predetermined NO concentration with little byproducts shall be achieved, because the system is mainly designed for medical use.

Prior art has further focused on solving the material and temperature challenges, has not been able to improve the yield and energy efficiency significantly from the first proven technology. Thus there is a need address the deficiencies and design a process for fixing Nitrogen molecule without damaging the other materials present in the system.

Summary of Invention

The primary object of this invention is to eliminate the problems and inefficiencies of the prior art by providing a new process for the combustion of nitrogen with oxygen. A further object of this invention is to provide a new simple and energy efficient process for the preparation of nitrogen compounds that can be assimilated by plants.

A further object of the present disclosure is to provide a nitrogen fixation system, which includes a nitrogen source, such as air, air with enhanced nitrogen or oxygen content.

A further object of this invention is to utilize microwave assisted reactions for nitrogen fixation especially for the synthesis nitrogen oxides. Here, the fixation of elemental nitrogen is through the process of cold plasma generated through the microwave. The present invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings and listed out in appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention. Brief Description of the Drawings

Fig 1 Cold Plasma Generated Through Microwave Irradiation Detail Description of Invention

Unless otherwise explained, all the scientific and technical terms used herein have the same meaning as commonly understood by the person skilled in the similar art. Generally the present disclosure provides a method for production of nitrogen oxides from nitrogen containing gases. In working example 1 product formation is effected by the presence of a cold plasma generated through microwave irradiation.

Plan of the experimental setup (dimensions in mm): la: Magnetron Head MH 2000S- 215BB connected to lb: microwave power supply MX4000D-110KL, 2: wave guide with stub tuner (45*90*515), 3: reaction chamber in form of a copper tube (high: 100, length: 290, diameter: 35), 4: right-angled wave guide (45*90* 145), 5: adjustable short (45*90*210), 6: quartz tube with NS 29 adapters at the ends connected to the 7: nitrogen supply and 8: service vacuum (length 490, diameter: 28). Experimental Setup:

The used microwave components Magnetron Head MH 2000S-215BB and Microwave Power Supply MX4000D-110KL were manufactured by MUEGGE. The magnetron head is connected to the power supply and to a microwave guide with an adjustable short at the end of the wave guide and the reaction chamber in form of a horizontal copper tube mounted right-angled to the wave guide. The cross point of wave guide and copper tube is the reaction zone in the microwave set up. A quartz tube with a diameter of 25 millimetres is positioned in the reaction chamber and filled with the solid educts. The quartz tube was connected to the cooling trap and vacuum pump on the left side and on the right side to the gas supply using a three-way stop cock for adjusting the gas flow. Liquid nitrogen was used to freeze the formed products in the cooling trap during the experiments.

Example 1 - Synthesis of Nitrogen Oxides

For microwave assisted synthesis of nitrogen oxides air was guided through the quartz tube of the experimental set up and irradiated with microwave radiation. The irradiated power was adjusted to 600 W and a pink coloured plasma could be ignited. The irradiated power was almost complete absorbed, the reflected power was approximately 8 percent. The pressure was adjusted so that the plasma state was stable (approximately 10 hPa). During the reaction nitrogen oxides were deposited in the frozen cooling traps. After a reaction time of 120 minutes the reaction was stopped and the cooling traps were heated up carefully to -10°C to melt the produced mixture of nitrogen oxides which contains as main product nitrogen dioxide and as by products nitrogen monoxide and the corresponding dimers dinitrogen trioxide and dinitrogen tetroxide. The resulting amount of nitrogen oxides was 12g. Nitrogen oxides were characterized via their typical colors. Dinitrogen trioxide is collected as a deep blue liquid which evaporates slowly under formation of typical brown vapours of nitrogen dioxide with its characteristic odour.

While there has been disclosed what is considered to be the preferred embodiment of the present invention, it is understood that various changes in the detailed description may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.

Claims

Claims:

1. The process for combustion of elemental nitrogen for fertilizer production, comprising combustion of nitrogen and/or nitrogen containing mixtures with oxygen and/or oxygen containing mixtures in a cold plasma process.

2. Process as claimed in Claim 1 in which NO is formed as the primary product.

3. Process as claimed in Claim 1 in which at least one nitrogen oxide is added to the reaction mixture in order to improve the formation of NO, preferably chosen from the group NO₂, NO, N₂O4, N₂0, wherein said nitrogen oxide is preferably formed during said process.

4. Process as claimed in Claim 3 in which the reacted gas mixture is at least partially recycled back through the reaction zone.

5. Process as claimed in Claim 1 in which nitrogen is reacted in a cold plasma reaction.

6. Process as claimed in Claim 1 in which plasma is effected via an electrodeless gas discharge.

7. Process as claimed in Claim 1 in which plasma is effected with electrodes that are covered with a dielectric material, preferably chosen from the group quartz glass, glass, aluminium oxide, silicon dioxide.

8. Process as claimed in Claim 1 in which plasma is effected with electrodes where at least one of the electrodes is an dielectric, preferably water or an aqueous solution.

9. Process as claimed in Claim 1 in which more than one reaction zone is present separated by rest zones, preferably designed as cooling zones, where reactants in the excited state are allowed to react with each other and/or to cool down.

10. Process as claimed in Claim 1 in which the gas temperature is maintained below 800°C, preferably below 600°C, especially preferred below 400°C, notably below 200°C.

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11. Process as claimed in Claim 10 in which the gas temperature in the cooling zones is reduced to below 400°C, preferably below 200°C, especially preferred below 100°C, notably below 50°C.

12. Process as claimed in Claim 1 in which the gas temperature before entering the reaction zone is increased to more than 200°C, preferably more than 400°C, especially preferred more than 600°C, notably more than 800°C.

13. Process as claimed in Claim 1 in which the molar ratio of N₂ and O₂ is adjusted to a higher value or to a lower value compared to the respective ratio in air, preferred close to a 1 to 1 value.

14. Process as claimed in Claim 1 in which the reacted gas mixture is recycled by sending it partially or completely through the reactor again for two or multiple times in order to combust a higher portion of the nitrogen.

15. Process as claimed in Claim 1 in which the reacted gas mixture is refreshed with nitrogen and/or oxygen and recycled partially or completely by sending them through the reaction zone again in order to consume a larger portion of the supplied nitrogen, preferably most of the nitrogen, especially preferred near to all of the nitrogen.

16. Process as claimed in Claim 1 in which the off-gases are reduced significantly via refreshing the reacted gas mixture with oxygen and nitrogen in a near to 1 to 1 ratio and recycling through the reaction zone multiple times.

17. Process as claimed in Claim 16 in which reduction of the off-gases via recycling is performed, wherein reduction of the off-gases is only limited by accumulation of trace gases, comprising argon, carbon dioxide and other noble gases, in the reaction mixture leading to reduced efficiency of the process.

18. Process as claimed in Claim 17 in which accumulation of trace gases, comprising argon, carbon dioxide and other noble gases, in the reaction mixture to undesired values is encountered by discharging of off-gas continuously or discontinuously.

19. Process as claimed in Claim 1 in which a mixture comprising nitrogen and oxygen, preferably nearly exclusively nitrogen and oxygen, especially preferred

2 nearly exclusively nitrogen and oxygen in a near to 1 to 1 ratio or air is used as feed gas for the reaction.

20. Process as claimed in Claim 19 in which one or more trace gases, comprising moisture, carbon dioxide, noble gases, are removed from the feed gas before the reaction is performed.

21. Process as claimed in Claim 1 in which the reaction is performed in a pressure range from 0, lhPa to 2000hPa, preferred lhPa to 1200hPa, especially preferred 3hPa to HOOhPa,

22. Process as claimed in Claim 21 in which the reaction is performed in a pressure range from 0,5hPa to lOOhPa, preferred 2hPa to 50hPa, especially preferred 3hPa to 20hPa, notably 4hPa to lOhPa.

23. Process as claimed in Claim 21 in which the reaction is performed in a pressure range from lOOhPa to 1500hPa, preferred 200hPa to 1400hPa, especially preferred 300hPa to 1300hPa, notably 5 OOhPa to HOOhPa.

24. Process as claimed in Claim 1 in which the reaction is performed in a temperature range of 0°C to 400°C, preferred 10°C to 200°C, especially preferred 15°C to 100°C, notably 20°C to 50°C.

25. Process as claimed in Claim 1 in which the reaction is performed in a temperature range of 400°C to 10000°C, preferred 800°C to 5000°C, especially preferred 1200°C to 3000°C, notably 1600°C to 2500°C.

26. Process as claimed in Claim 1 in which the reaction is performed via a microwave sustained gas discharge.

27. Process as claimed in Claim 1 in which the reaction is performed via a high voltage sustained gas discharge.

28. Process as claimed in Claim 27 in which the reaction is performed at more than 5kV, preferably more than 8kV, especially preferred more than lOkV.

29. Process as claimed in Claim 27 in which the reaction is performed at more than 30kV, preferably more than 50kV, especially preferred more than 80kV.

30. Process as claimed in Claim 27 in which the reaction is performed with an ac gas discharge at a frequency of more than 40Hz, preferred more than 4kHz, especially preferred more than 50kHz, notably more than lOOkHz.

31. Process as claimed in Claim 27 in which the voltage is applied in pulsed form.

32. Process as claimed in Claim 27 in which the reaction is performed with exitation of the reaction gas mixture in a spark gap, preferred in a rotating spark gap and/or a rotating spark.

33. Process as claimed in Claim 32 in which the rotation of the spark is induced by exposure to a magnetic field.

34. Process as claimed in Claim 5 in which the plasma is exposed to a magnetic field.

35. Process as claimed in Claim 34 in which the magnetic field is variable with respect to strength and/or direction and/or shape.

36. Process as claimed in Claim 27 in which the reaction is performed with excitation of the reaction gas mixture in a plasma torch.

37. Process as claimed in Claim 1 in which nitrogen oxides and ozone are produced simultaneously or alternately.

38. Process as claimed in Claim 5 in which the reaction is effected by an inductively coupled plasma.

39. Process as claimed in Claim 5 in which the reaction is effected by an capacitively coupled plasma.

40. Process as claimed in Claim 5 in which the plasma is stabilized by supporting measures chosen from a group comprising electron injection, glow-discharge, spark discharge, corona discharge, admixture of noble gases.

41. Process as claimed in Claim 1 in which nitrogen is reacted in the presence of water, preferably water vapour.

42. Process as claimed in Claim 41 in which said water is applied as a falling film, leading to formation of water vapour as well as cooling of reaction gases.

43. Process as claimed in Claim 41 in which nitrogen is bubbled through liquid water and the ratio of nitrogen to water vapour is adjusted via its vapour pressure by setting the water temperature to the desired value.

44. Process as claimed in Claim 1 in which plasma is formed in a glass reactor preferably in a quart glass reactor.

45. Process as claimed in Claim 1 in which at least one additional reaction step is performed in order to yield products, which can be used for the preparation of fertilizers, preferably an oxidation and/or a hydrolysis step.

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