WO2014037918A1

WO2014037918A1 - Process for fixation of elemental nitrogen

Info

Publication number: WO2014037918A1
Application number: PCT/IB2013/058398
Authority: WO
Inventors: Dirk ZABEL; Christian Bauch; Mullandram Nateshan BHASKARAN; Banibrata Pandey
Original assignee: SPAWNT RESEARCH GmbH; NAGARJUNA Corp Ltd
Current assignee: SPAWNT RESEARCH GmbH; NAGARJUNA Corp Ltd
Priority date: 2012-09-09
Filing date: 2013-09-09
Publication date: 2014-03-13
Anticipated expiration: 2015-03-09

Description

"PROCESS FOR FIXATION OF ELEMENTAL NITROGEN"

FIELD OF INVENTION

The present invention relates to materials, methods, and system that can be used for fixation of elemental nitrogen.

BACKGROUND

Elemental nitrogen in the atmosphere cannot be used directly by either plants or animals, and must be converted 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% contributes 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.

Ammonia is produced industrially by the Haber-Bosch process by an iron catalyzed reaction of nitrogen with hydrogen. The yield of this exothermic reaction is strongly affected by the temperature and the pressure of the reaction gases.

The reaction of nitrogen and hydrogen to ammonia is performed at 500°C at a pressure of approximately 200 bar. The high temperatures are required for a sufficient activation of the iron catalyst and the high pressure for increasing the yield of ammonia. The yield of ammonia is about 11 percent so the gas mixture is guided back to the reactor to get an economic synthesis after removal of the formed ammonia.

The Haber-Bosch process has a requirement of high energy, nonrenewable hydrocarbon and high operational cost. There are conventional methods to manufacture various precursor materials for manufacturing ammonia and urea. One such process is production of calcium cyanamide. The educts for the synthesis of calcium cyanamide according to established processes are calcium carbide and nitrogen. The reaction is performed in a furnace at a temperature of approximately 900°C. The disadvantages of this process are the use of calcium carbide whose production from calcium oxide and carbon in an electric arc furnace requires high temperatures about 2000-3000°C. With generation of these high temperatures high costs for electricity and special materials for the production plant are associated. Furthermore the formed product contains carbon as impurity. Thus, the removal of this impurity is necessary and possible by combustion by addition of oxygen into the reaction zone of the furnace of the calcium cyanamide production. An avoidance of use of calcium carbide for synthesis of calcium cyanamide enables a process of synthesis of calcium cyanamide from the educts calcium oxide, carbon and nitrogen at about 1500°C that is characterized in that the carbon is generated in presence of calcium oxide in a fluidized bed reactor by incomplete combustion of hydrocarbons (DE000001229053B). By this procedure, the calcium oxide is heated up to 1200 to 1400°C and the mixture of calcium oxide and formed carbon reacts with nitrogen to calcium cyanamide. JP55080718 discloses the process of producing calcium cyanamide in one-step reaction by counter currently contacting a mixed gas formed by subliming urea or cyanic acid and a carrier gas to solid raw material in a non-oxidizing atmosphere. US2180382 disclose the process of preparing calcium cyanamide in a revolving furnace at various degrees of dilution. Another process described in US 2052920 discloses process of producing calcium cyanamide from calcium phosphate or phosphate rock between temperature 900- 1600°C to drive of the phosphate in presence of a carbonaceous compound followed by heating the second furnace zone to temperature between 1600-1900°C to form calcium carbide. DE 3439367 Al discloses the production of calcium cyanamide in a rotary kiln by nitrification of calcium carbide at a temperature range 900-5000°C. Also it is known to produce calcium cyanamide from urea by reacting urea with an oxygenous calcium compound at temperatures of between 120 - 900°C (WO1995024358A1). The first step of synthesis of urea starting from calcium cyanamide is the hydrolysis of calcium cyanamide in presences of carbon dioxide. The cyanamide formed in this step can be reacted with water to urea. Because of the highest stability of cyanamide in aqueous solutions at pH = 5 the last reaction is performed in acidic solutions (pH < 2) or in alkaline solutions (pH > 12) respectively.

CaO + 3 C ^ CaC₂ + CO (1) CaC₂ + N₂ £aCN₂ + C (2)

CaCN₂ + 3H₂0 ^► 2NH₃ + CaC0₃ -— (3)

CaCN₂ + H₂0 + C0₂ W₂NCN + CaC0₃ -— (4)

The technical production of cyanogen is carried out by oxidation of hydrocyanic acid with oxygen in presence of a silver catalyst or by oxidation with chlorine or nitrogen dioxide. The oxidation of cyanide with copper (II) is a useful method for the synthesis of cyanogen in laboratory scale. Nitrogen monoxide is produced industrially by Pt/Pt-Rh catalyzed combustion of ammonia at 820-950°C (Ostwald process) and can be easily oxidized with oxygen to nitrogen dioxide

There is a need to develop a process of producing calcium cyanamide, which does not require extensive energy. Accordingly, the present invention is to generate calcium cyanamide in a single step reaction instead of conventional 2 step reaction.

In one embodiment, the present disclosure provides a nitrogen fixation system. The system includes a nitrogen source, such as air, air with enhanced nitrogen content or the pure nitrogen source. In a specific example, the system includes a feed of stream of nitrogen concentrator. In another embodiment, the carbon used in the process is pulverized activated charcoal and/or gaseous carbon compounds. Still another embodiment is the use of atmospheric or near atmospheric plasma which may be of vacuum and/or combination of vacuum and fluidized bed plasma process.

The system of the present invention utilizes the microwave assisted reactions for nitrogen fixation especially for the synthesis of ammonia. The fixation of elemental nitrogen is through the process of cold plasma generated through the microwave. The reaction temperatures of the solid educts are in the range of 200°C to 1300°C, preferably 400°C to 1100°C, especially preferred 600°C to 1000°C. In case of fluidized bed reactions the temperature of the solid educts can be lower especially in the temperature range of 100°C to 1300°C, preferably 150°C to 900°C, especially preferred 200°C to 400°C. The excitation of the educts is performed via a non-isothermic plasma reaction, i.e., the gas temperature is much lower than the temperature of the electrons in the plasma (cold plasma). In order to obtain the desired product composition an important fact regarding reaction conditions is that the reaction is performed in a low pressure range. That means that the mean free path length in the plasma is much higher compared to other plasma reactions at higher pressures like arc-, corona- and silent-discharges (e.g. ozone generator). Because of the lower pressure needed for the process thermal losses are comparably small which results in a good energy efficiency. Thus, referred to the volume of the reaction zone (diameter 23 millimeters, length 50 millimeters) the power densities are relatively low in the range of 0,5 to 15 W/cm³. In case of the synthesis of ammonia and cyanogen they are for instance at 3,6 W/cm³ and in case of the synthesis of nitrogen oxides they are at about 7,2 W/cm³. In case of the synthesis of nitrogen oxides is the required energy approximately 16 kJ/mol if it is assumed that the main component of the reaction product is nitrogen dioxide.

DETAIL DESCRIPTION

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 ammonia and or urea or cyanamide or nitrogen oxide or cyanogen or a combination thereof by fixation of elemental nitrogen using activated carbon or other carbon sources in an atmosphere of nitrogen or nitrogen containing gases in presence of cold plasma generated through microwave irradiation.

The carbon used is in the form of activated pulverized carbon and/or gaseous carbon containing compounds and the formation of ammonia is determined by Nessler's reagent. The cyanide formation in any of the reactions is detected as Prussian blue after reaction with iron ions.

Fig 1: 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 sup'ply 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. Methods

Detection of cyanide as Prussian Blue

The reaction of iron (II) in presence cyanide to the complex compound hexacyanoferrate(ll) [Fe(CN)₆]^4" in alkaline solutions is a suitable reaction for the detection of cyanide in aqueous solutions:

6 CN^" [Fe (CN) ₆]⁴

After addition of hydrochloric acid the hexacyanoferrate forms with an excess of iron ions a blue precipitate, Prussian Blue Fe₄ [Fe (CN) ₆]₃ according to the following reaction equation:

4 Fe³⁺ + 3 [Fe (CN) ₆Γ Fe₄ [Fe (CN) ₆f (6)

The Prussian blue contains various amounts of hydrate water which depends on the conditions of formation. Thus, the composition of Prussian Blue is given by the formula Fe₄ [Fe (CN) ₆]₃ * 14-16 H₂0.

Example 1 - synthesis of ammonia

The solid educts were reacted with the gaseous nitrogen under plasma conditions generated by microwave irradiation at low pressure. For this a mixture of calcium oxide (11.7 g) and carbon in form of pulverized activated charcoal (25 g) was placed in a quartz tube. The high of filling is approximately 5 millimetres at a length of 5 centimetres. Two plugs of quartz wool on every side of the solid educts are stabilizing the filling against influences of the nitrogen flow. The filling in the quartz tube was positioned in the reaction zone of the microwave oven. The tube was evacuated and the pressure of nitrogen was adjusted to 10 hPa. The power of microwave irradiation was set to 300 W. Pink N₂ plasma was ignited in the gas phase above the solid educt mixture and the radiated microwave radiation was absorbed completely. After a reaction time of 60 minutes the reaction was stopped and the ammonia condensed in the cooling trap was detected as Millon^'s base using Nessler^'s reagent and by its typical odor. Furthermore it was possible to detect cyanide in the solid products. The cyanide was doubtlessly detected as Prussian Blue after reaction with iron ions.

Example 2 - synthesis of ammonia

The solid educts were reacted with the gaseous nitrogen under plasma conditions generated by microwave irradiation at low pressure. For this a mixture of calcium hydroxide (6.6 g) and carbon in form of pulverized activated charcoal (2.1 g) was placed in a quartz tube. The high of filling is approximately 5 millimetres at a length of 5 centimetres. Two plugs of quartz wool on every side of the solid educts are stabilizing the filling against influences of the nitrogen flow. The filling in the quartz tube was positioned in the reaction zone of the microwave oven. The tube was evacuated and the pressure of nitrogen was adjusted to 10 hPa. The power of microwave irradiation was set to 300 W. Pink N₂ plasma was ignited and the radiated microwave radiation was absorbed completely. After a reaction time of 60 minutes the reaction was stopped and the ammonia condensed in the cooling trap was detected as Millon^'s base using Nessler^'s reagent and by its typical odor. Furthermore it was possible to detect less amounts of cyanide in the material deposited in the cooling trap. The cyanide was doubtless detected as Prussian Blue after reaction with iron ions. Example 3 - synthesis of cyanogen

Carbon in form of dried activated charcoal reacted with the gaseous nitrogen under plasma conditions generated by microwave irradiation at low pressure under formation of cyanogen (CN) ₂. For this a carbon (ca. 0.5 g) was placed in a quartz tube at a length of 5 centimetres. Two plugs of quartz wool on every side of the solid educts are stabilizing the filling against influences of the nitrogen flow. The filling in the quartz tube was positioned in the reaction zone of the microwave oven. The tube was evacuated and the pressure of nitrogen was adjusted to 10 hPa. The power of microwave irradiation was set to 300 W. Pink N₂ plasma was ignited and the radiated microwave radiation was absorbed completely. After a reaction time of 60 minutes the reaction was stopped and a colourless solid material was condensed in the cooling trap. The physical properties like melting and boiling point of this material are in agreement with in literature described physical properties of cyanogen. Furthermore after hydrolysis of this material with potassium hydroxide solution cyanide was detected as Prussian Blue by reaction with iron ions.

Example 4 - 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 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 byproducts 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.

Example 5 - synthesis of calcium cyanamide

The solid educts were reacted with the gaseous nitrogen under plasma conditions generated by microwave irradiation at low pressure. For this a mixture of calcium oxide and carbon in form of pulverized activated charcoal was placed in a quartz tube. Two plugs of quartz wool on every side of the solid educts are stabilizing the filling against influences of the nitrogen flow. The filling in the quartz tube was positioned in the reaction zone of the microwave oven. The tube was evacuated and nitrogen was guided through the tube. After a reaction time of 60 minutes the reaction was stopped and calcium cyanamide could be detected in the solid products of the reaction.

Example 6 - synthesis of urea from calcium cyanamide

The calcium cyanamide synthesized according to the described process was pulverized and hydrolyzed in hot water (60-70°C) under alkaline conditions and vigorous stirring. The alkaline hydrolysis of calcium cyanamide leads to the formation of the intermediate cyanamide which reacts in a second step to the required product urea. The formed urea was qualitatively determined via the biuret reaction with copper (II) ions after heating of the evaporated urea solution and dissolving in diluted sodium hydroxide solution. Upon addition of copper sulfate solution a violet colour indicates the presence of biuret, which was formed by condensation of urea.

Example 7 - synthesis of ammonia

The solid educts was reacted with gaseous humidified nitrogen and C0₂ under plasma conditions generated by microwave irradiation at low pressure. For this calcium carbonate (30.7 g) in pulverized form was placed in a quartz tube. The high of filling is approximately 5 millimetres at a length of 5 centimetres. Two plugs of quartz wool on every side of the solid educts are stabilizing the filling against influences of the nitrogen flow. The filling in the quartz tube was positioned in the reaction zone of the microwave oven. The nitrogen/C0₂ mixture was passed through a washing bottle with water at room temperature for humidification. The tube was evacuated and the pressure of the humid nitrogen/C0₂ mixture was adjusted to 10 hPa. The power of microwave irradiation was set to 300 W. Pink N₂ plasma was ignited in the gas phase above the solid and the radiated microwave radiation was absorbed completely. After a reaction time of 60 minutes the reaction was stopped and the ammonia condensed in the cooling trap was detected as Millon^'s base using Nessler^'s reagent and by its typical odor.

Claims

The Claims:

Process for fixation of elemental nitrogen, in which the fixation of nitrogen takes place upon reaction of nitrogen and/or nitrogen containing mixtures in a cold plasma reaction in the presence of carbon or a carbon containing material.

Process as claimed in Claim 1 in which nitrogen is reacted in the presence of carbon and/or at least one metal salt.

Process as claimed in Claim 1 in which nitrogen is reacted in the presence of at least one carbon containing material and/or at least one metal salt

Process as claimed in Claim 2 or 3 in which the at least one metal salt is chosen from a group of compounds which comprises oxides, hydroxides and carbonates of the elements of the main groups I or II of the periodic system, preferably sodium, potassium, magnesium, calcium and barium, especially preferred calcium or mixtures thereof respectively.

Process as claimed in Claim 4 in which nitrogen is reacted with carbon or a gaseous carbon containing material and/or a metal salt in a fluidized bed reactor.

Process as claimed in Claim 5 in which nitrogen is reacted with carbon or a gaseous carbon containing material and/or a metal salt in a fixed bed reactor and /or fluidized bed reactor.

Process as claimed in Claim 6 in which nitrogen is reacted with carbon containing material of either solid or gaseous and/or a metal salt in a packed bed reactor.

8. As claimed in any of the preceding claims that carbon containing gaseous material is oxide of carbon

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

10. Process as claimed in Claim 9 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.

11. Process as claimed in Claim 1 in which the carbon or carbon containing material is chosen from a group of compounds which comprises charcoal, activated charcoal, graphite, mineral coal, lignite, coke, high-temperature coke, anthracite and carbon black preferably charcoal, activated charcoal, lignite and coke, especially preferred charcoal and coke or mixtures , gaseous carbon containing compound thereof respectively.

12. Process as claimed in Claim 1 in which the carbon or carbon containing material is obtained from biomass preferably via pyrolysis of biomass and/or from air.

13. Process as claimed in Claim 1 in which said nitrogen or nitrogen containing mixture is obtained from liquefied air and/or from steam-reforming processes.

14. Process as claimed in Claim 1 in which nitrogen is reacted in the presence of oxygen, preferably in the form of air.

15. Process as claimed in Claim 3 or 4 in which the solid educts have a temperature of 200°C to 1300°C, preferably 400°C to 1100^eC, especially preferred 600°C to 1000°C. 16. Process as claimed in Claim 1 in which plasma is formed by applying an alternating current and/or electromagnetic radiation to the plasma zone preferably via a high- frequency plasma discharge, especially preferred via microwave radiation discharge.

17. Process as claimed in Claim 1 in which plasma is formed in a glass reactor preferably in a quartz glass reactor.

18. Process as claimed in Claim 1 in which the cold plasma reaction is conducted within a pressure range of 0,01hPa to lOOOhPa, preferably 0,lhPa to lOOhPa, especially preferably lhPa to 50hPa in particular 5hPa to 30hPa.

19. Process as claimed in Claim 1 in which the cold plasma reaction is a heterogeneous reaction, i.e. a solid/gas plasma reaction.

20. Process as claimed in Claim 1 in which at least one additional reaction step is performed in order to yield said products preferably a hydrolysis step.

21. Products from a process for fixation of elemental nitrogen as claimed in Claim 1 comprising urea, cyanamides, dicyandiamide, melamine, ammonia, amides, cyanides, cyanogen, nitrogen oxides, nitrides, preferably cyanamides, ammonia, cyanides, cyanogen, nitrogen oxides especially preferred cyanamides, ammonia, or mixtures thereof respectively.

22. Products from a process for fixation of elemental nitrogen as claimed in Claim 1 comprising urea, cyanamides, dicyandiamide, melamine, amides, cyanides, nitrides, preferably cyanamides, cyanides, urea, melamine especially preferred cyanamides or mixtures thereof respectively.