Method for producing ammonia nitrogen

Abstract

The present invention relates to a method for producing ammonia nitrogen by feeding an electrochemical cell with dinitrogen (N2), said electrochemical cell comprising at least one working electrode immersed in a composition comprising at least one compound (I) containing at least one element from group 13 of the periodic table, and at least one counter electrode; and an electrochemical cell for the reduction of dinitrogen into ammonia nitrogen.

Description

[0001]Method for producing ammoniacal nitrogen The present invention relates to a method for producing ammoniacal nitrogen implementing the supply of dinitrogen (N2) to an electrochemical cell, said electrochemical cell comprising at least one working electrode immersed in a composition comprising at least one compound (I) containing at least one element from group 13 of the periodic table, at least one counter-electrode; as well as an electrochemical cell for the reduction of dinitrogen to ammoniacal nitrogen. Nitrogen (N) plays an essential role in the composition of living matter. In particular, it is one of the major constituents of amino acids, proteins including enzymes, and nucleic acids making up DNA and RNA. It is also a nutrient essential for crop growth.However, even though nitrogen is very abundant on the surface of the globe (there is more nitrogen than carbon, hydrogen and phosphorus combined in the whole constituted by the biosphere, the hydrosphere and the atmosphere), it is present essentially in the form of an extremely stable gas, dinitrogen (N2). Humans can therefore only marginally benefit from such an abundance. Only microorganisms such as Rhizobia involved in the symbiotic fixation of nitrogen by legumes are capable of using this form of nitrogen and transforming it into ammoniacal and then organic nitrogen, which can in turn be used by other living beings and transformed into other forms of reactive nitrogen. Ammonia as a reactive nitrogen constitutes a key molecule with major applications in the agricultural sector, and also has the capacity to store energy (in particular hydrogen).Liquid ammonia can also be used as a fuel that can replace fossil-based liquefied petroleum gas (LPG). Until the 19th. ème century, ammonia was produced by distillation of slurry and manure or by extraction of domestic wastewater. It was then obtained after the second half of the 19th century. ème century as a by-product of the manufactured gas industry (town gas). It was not until the beginning of the 20th century that it was ème century (1909-1913) to see the development of massive industrial production of ammonia via the Haber-Bosch process. Such a process allows the synthesis of ammonia on an industrial scale, from nitrogen and hydrogen (H2) in the presence of a solid catalyst based in particular on iron. The production of ammonia of approximately 200 million tonnes / year by this process has quantitatively exceeded symbiotic fixation since the end of the 20 èmecentury on a global scale and is still in use today. However, this Haber-Bosch process has the following disadvantages: it uses high pressures and temperatures, for example pressures between 100 and 300 bars and temperatures between 300 and 550°C, making this process extremely energy-intensive, requiring centralized and secure production, and involving high operating and transport costs. Furthermore, such a process generates very large quantities of carbon dioxide (around 1.5% of global CO2 production), leading to environmental problems, and its efficiency remains low (20%).In view of the ever-increasing projections of ammonia demand, and the environmental issues associated with its industrial production, other processes have been proposed, notably based on more efficient catalysts to reduce the temperatures and pressures used. In particular, US patent 6,037,459 describes a process comprising a first step of bringing dinitrogen into contact with a compound corresponding to the formula M(NR1R2)3 in which M is a transition metal (e.g. molybdenum), R1 and R2 are chosen from tertiary alkyl groups, phenyl groups and substituted phenyl groups, to form a metal complex with nitride ligands; and a second step of reducing said complex in the presence of a source of hydrogen to form ammonia. This process is carried out under ambient temperature and pressure conditions.In US patent 6,037,459, only the yields of NΞN triple bond scission are described and the formation of ammonia (second step) is not demonstrated. Alternative methods based on biocatalysis, photocatalysis, or electrocatalysis have also been described. In particular, Li et al. [Adv. Mater., 2017, 29, 1700001, 1–6] propose the use of an electrode material comprising amorphous gold nanoparticles supported by graphite oxide and reduced cerium dioxide CeO. x-RGO. The method of Li et al. uses an electrochemical cell continuously supplied with a flow of nitrogen, said cell comprising a saturated Ag / AgCl / KCl reference electrode, a platinum counter electrode, a working electrode made of said electrode material deposited on carbon paper, a pre-treated Nafion 211® membrane, and an electrolyte composed of dilute hydrochloric acid. Said electrode material is used as a cathodic electrocatalyst. It therefore acts as a reducing agent for N2, which then reacts with H protons. +of the electrolyte on the surface of said material to form NH3. Applying an electric potential to said material is a way to reduce the activation barrier of the N2 reduction reaction (NRR). However, yields remain low and raw materials (noble metals such as gold or ruthenium) are rare and extremely expensive. Furthermore, the reduction of dinitrogen competes with the reduction of protons (H +) into dihydrogen H2. The aim of the present invention is therefore to overcome the drawbacks of the prior art and in particular to provide a simple, economical, industrializable process for producing ammoniacal nitrogen, using abundant raw materials, preferably capable of being recycled, which makes it possible to reduce carbon emissions and which implements relatively mild reaction conditions. The first subject of the invention is a process for producing ammoniacal nitrogen, characterized in that it comprises at least the following steps: i) a step of supplying an electrochemical cell with dinitrogen (N2), said electrochemical cell comprising at least one working electrode immersed in a composition maintained under stirring, and at least one counter-electrode, said composition comprising at least one electrolyte solution and at least one compound corresponding to a formula (I) below: R 1 R 2MY (I), in which: - M is an element from group 13 of the periodic table, preferably chosen from boron, aluminum, and one of their mixtures, - R 1 and R 2 , identical or different, are chosen from an alkyl group, an aryl group, an aryl-alkyl group, a -OR group, and an -SR group, R being an alkyl group, an aryl group, or an aryl-alkyl group, and - Y is a group chosen from a halogen -X, a -OR group 3 , a -SR group 3 , a triflate group, a mesylate group, and a triflimidate group, R 3being an alkyl group, an aryl group, or an aryl-alkyl group, ii) a step of applying a potential difference between the working electrode and the counter-electrode, or of applying a potential or a current intensity to the working electrode, and iii) a step of acid hydrolysis of the composition. The process of the invention is simple, easy to implement, economical, and allows the production of ammoniacal nitrogen under relatively mild reaction conditions. In particular, the use of a compound of formula (I) as defined above in a reducing medium (i.e. thanks to the contribution of electrons from the working electrode) allows the activation of the triple bond of the dinitrogen and the formation of intermediate species which then lead by hydrolysis to ammoniacal nitrogen. Finally, the process is industrializable, uses abundant raw materials, possibly able to be recycled, and allows the environmental impact to be reduced.Step i) The compound of formula (I) R. 1 R 2 MY According to the invention, boron is particularly preferred as element M. The groups R 1 and R 2 The compound of formula (I) R 1 R 2 MY is not a radical compound. In the compound of formula (I), R 1 forms a single covalent bond with the element M and R 2 forms a single covalent bond with the element M. R 1 and R 2 , identical or different, are selected from an alkyl group, an aryl group, an aryl-alkyl group, an -OR group, and an -SR group, R being an alkyl group, an aryl group, or an aryl-alkyl group. An alkyl group as the R group 1 and / or R 2may be linear or branched, cyclic or non-cyclic. The alkyl group may comprise from 1 to 14 carbon atoms, and preferably from 2 to 10 carbon atoms. An alkyl group is preferably selected from ethyl, propyl, isopropyl, cyclohexyl, bicyclo[2.2.1]-2-heptyl, and isopinocampheyl. Of such groups, any of cyclohexyl, bicyclo[2.2.1]-2-heptyl, or isopinocampheyl is most preferred. The alkyl group as the group R 1 and / or R 2 may comprise one or more heteroatoms, such as an oxygen atom, or a sulfur atom, provided that a carbon atom of the alkyl group is directly bonded to the element M of formula (I) and that none of the heteroatom(s) present in the alkyl group is directly covalently bonded to another heteroatom. An aryl group as the R group 1 and / or R 2may be substituted or unsubstituted. The aryl group may comprise from 6 to 30 carbon atoms, and preferably from 6 to 18 carbon atoms. An aryl group is preferably selected from a phenyl group, a -C6F5 group, a 2,4,6-(Me)3-C6H2 group, and a 2,4,6-(iPr)3-C6H2 group. Among such groups, any of the 2,4,6-(Me)3-C6H2 or 2,4,6-(iPr)3-C6H2 groups is most preferred. The aryl group as the R group 1 and / or R 2 may comprise one or more heteroatoms, in particular when the aryl group is substituted (i.e. in the substituents of said aryl group), such as an oxygen atom or a nitrogen atom, it being understood that a carbon atom of the aryl group is directly linked to the element M of formula (I). An aryl-alkyl group as group R 1 and / or R 2is a group comprising at least one alkyl group and at least one aryl group which are linked directly by a carbon (of the aryl group)-carbon (of the alkyl group) covalent bond, or via an oxygen atom or a nitrogen atom, the aryl and alkyl groups being as defined previously for the R groups 1 and R 2. The alkyl-aryl group may be directly linked to element M of formula (I) by a carbon atom of the aryl group or by a carbon atom of the alkyl group. An alkyl group R of the group -OR or -SR may be linear or branched, cyclic or non-cyclic. The alkyl group R may comprise from 1 to 10 carbon atoms, and preferably from 1 to 4 carbon atoms. An aryl group R of the group -OR or -SR may be substituted or unsubstituted. The aryl group R may comprise from 6 to 30 carbon atoms, and preferably from 6 to 18 carbon atoms. An aryl group R is preferably selected from a phenyl group, a naphthyl group, an anthracenyl group, or a pyrenyl group.An aryl-alkyl group R of the group -OR or -SR is a group comprising at least one alkyl group and at least one aryl group which are linked directly by a carbon (of the aryl group)-carbon (of the alkyl group) covalent bond or via an oxygen atom, or a sulfur atom, the aryl and alkyl groups being as previously defined for the group R. The groups R. 1 and R 2 may be covalently linked, in particular via a carbon-carbon bond, to form together a divalent group, said R groups 1 and R 2 being as defined above. In this embodiment, the divalent group does not form a planar ring with the element M. For example, the divalent group may be an alkyl group (i.e. R 1 and R 2 are alkyl groups), and preferably a 9-bicyclo[3.3.1]nonane group. According to one embodiment of the invention, R 1 and R 2, identical or different, are chosen from an alkyl group, an aryl group, and an aryl-alkyl group. According to a preferred embodiment of the invention, at least one of the groups R 1 and R 2 is an alkyl group, and more preferably, the two R groups 1 and R 2 are alkyl groups. According to a particularly preferred embodiment of the invention, R 1 and R 2 are identical. The R groups 1 and R 2 of compound (I) are non-stabilizing groups. In other words, their function is not to stabilize the radical R 1 R 2 M° generated during the process, and therefore make it more reactive towards dinitrogen N2. The YY group is a group chosen from a halogen -X, a -OR group 3 , a -SR group 3 , a triflate group (-OSO2CF3), a mesylate group (-OSO2CH3), and a triflimidate group (NTf2or N(SO2CF3)2), R3 being an alkyl, aryl, or aryl-alkyl group. X is preferably a chlorine atom or a bromine atom, and particularly preferably a chlorine atom. A group R 3 alkyl can be linear or branched, cyclic or non-cyclic. The R group 3 alkyl may comprise from 1 to 10 carbon atoms, and preferably from 1 to 4 carbon atoms. A group R 3 aryl may be substituted or unsubstituted. The R group 3 aryl may comprise from 6 to 30 carbon atoms, and preferably from 6 to 18 carbon atoms. A group R 3 aryl is preferably selected from phenyl, 2,4,6-(Me)3-C6H2, 2,4,6-(iPr)3-C6H2 and naphthyl groups. A group R 3aryl-alkyl is a group comprising at least one alkyl group and at least one aryl group which are linked directly by a carbon (of the aryl group)-carbon (of the alkyl group) covalent bond or via an oxygen atom, or a sulfur atom, the aryl and alkyl groups being as previously defined for the group R 3 . Y is preferably a halogen X. The Y group of compound (I) is a group having nucleofugal properties. In other words, its function is to facilitate the formation of the radical R 1 R 2M°. According to a particularly preferred embodiment of the invention, the compound of formula (I) is chosen from dialkylchloroboranes, dialkylbromoboranes, dialkylchloroaluminium compounds, and dialkylbromoaluminium compounds, such as the halides of diisopinocampheylborane, dicyclohexylborane, or bis(bicyclo[2.2.1]-2-heptyl)borane, or haloboranes based on 9-borabicyclo[3.3.1]nonane. The compound of formula (I) has the advantages of being readily commercially available or of being readily accessible synthetically. The compound of formula (I) has the characteristics of a Lewis acid, namely a chemical entity one of the atoms of which constitutes it has an electronic vacancy. The working electrode The working electrode preferably comprises (or is preferably made of) at least one inert electrically conductive material.The inert electrically conductive material may be chosen from carbon, platinum, stainless steel, and metal oxides. The carbon may be vitreous carbon, pyrolytic carbon, or diamond doped, for example with boron or sulfur. The electrically conductive material is preferably in the form of a porous material such as a foam (e.g., carbon foam), a felt, a grid, or a fabric. When the electrically conductive material is a metal oxide, it may be transparent. Among the metal oxides that can be used as an electrically conductive material, mention may be made of indium-tin oxide. In the invention, the expression "inert electrically conductive material" means that the electrically conductive material does not react chemically with the various elements present in the electrochemical cell.Preferably, the inert electrically conductive material of the working electrode has a specific surface area, measured by the BET method, of at least 0.1 m. 2 / g, and particularly preferably at least 100 m 2 / g. This thus makes it possible to optimize the contact surface between the working electrode and the composition, and in particular between the working electrode and the compound of formula (I). During step i), the working electrode is immersed in whole or in part in the composition. This thus makes it possible to promote contact between the working electrode and the compound of formula (I), and thus to obtain a large exchange surface. The counter-electrode The counter-electrode preferably comprises (or is preferably made of) at least one inert electrically conductive material. The inert electrically conductive material may be chosen from carbon, platinum, stainless steel, and metal oxides. The carbon may be graphite, pyrolytic carbon, or diamond doped, for example with boron or sulfur. The electrically conductive material may be in the form of a porous material such as a foam (e.g. carbon foam), a felt, a grid, or a fabric.When the electrically conductive material is a metal oxide, it may be transparent. Among the metal oxides that can be used as an electrically conductive material, mention may be made of indium-tin oxide. Preferably, the inert electrically conductive material of the counter-electrode has a specific surface area, measured by the BET method, of at least 0.1 m. 2 / g, and particularly preferably at least 100 m 2 / g. This thus makes it possible to optimize the exchange surface between the counter-electrode and the electrolyte solution (several compartments) or the composition (1 single compartment). The counter-electrode is preferably immersed in whole or in part in an electrolyte solution. The electrolyte solution may be that of the composition. In this embodiment, during step i), the counter-electrode is then immersed in whole or in part in the composition. This thus makes it possible to promote contact between the counter-electrode and the composition, and thus to obtain a large exchange surface. The electrolyte solution of the composition The electrolyte solution allows the transport of current within the electrochemical cell. The electrolyte solution may comprise (or be made up of) the combination of an organic solvent and a salt; or an ionic liquid. An ionic liquid is well known to those skilled in the art and may be considered as a molten salt at room temperature (eg18-25°C). The ionic liquid has an organic cationic part and acts as a solvent in the present invention, in the same way as a conventional organic solvent. In the invention, the term organic solvent means a conventional organic solvent, i.e. free of salt or which is not in the form of a salt. The organic solvent is preferably chosen from aprotic organic solvents, and in particular chosen from ethers, carbonates, nitriles, amides and phosphoramides, such as THF (tetrahydrofuran), methyl-THF, N,N'-dimethylformamide, acetonitrile, benzonitrile, hexamethylphosphoramide, or propylene carbonate. The salt is soluble in the organic solvent, preferably at concentrations of at least about 0.1 mol / l, for example at concentrations ranging from about 0.1 to 0.5 mol / l. The salt is preferably an inert salt.In the invention, the expression "inert salt" means that the salt does not react in a chemical reaction with the various elements present in the electrochemical cell, and in particular, it is not reduced at the working electrode in the operating potential range of the electrochemical cell. The salt may be chosen from alkali metal salts and quaternary ammonium salts, and preferably from quaternary ammonium salts. Examples of alkali metal salts include lithium salts, such as LiTFSI, LiPF6, or LiClO4. Examples of quaternary ammonium salts include tetraalkylammonium salts such as tetra-n-butylammonium bis(trifluoromethanesulfonyl)imidate (TBATFSI), tetra-n-ethylammonium perchlorate, tetra-n-butylammonium hexafluorophosphate, or tetra-n-propylammonium tetrafluoroborate.The ionic liquid may be selected from ammonium salts, imidazolium salts, phosphonium salts, pyrrolidinium salts, and piperidinium salts, and preferably from alkylammonium salts, alkylimidazolium salts, alkylphosphonium salts, alkylpyrrolidinium salts, and alkylpiperidinium salts. The ionic liquid preferably comprises an anionic portion of the bis(trifluoromethanesulfonyl)imidate type.Examples of ionic liquids include triethylbutylammonium bis(trifluoromethanesulfonyl)imidate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imidate, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imidate, trimethylbutylammonium bis(trifluoromethanesulfonyl)imidate, 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imidate, N-propyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imidate, or 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imidate. The ionic liquid is preferably immiscible in water. This facilitates subsequent purifications. The reference electrode The electrochemical cell may further comprise a reference electrode. This can be used to control the potential of the working electrode and limit ohmic drops.The reference electrode may be selected from a saturated silver nitrate electrode Ag / AgNO3, a saturated calomel electrode (SCE), or a silver chloride electrode Ag / AgCl. The reference electrode is preferably fully or partially immersed in an electrolyte solution. The electrolyte solution may be that of the composition. In this embodiment, during step i), the counter electrode is then fully or partially immersed in the composition. During step i), the composition comprising the compound of formula (I) and the electrolyte solution is brought into contact with nitrogen (N2). During step i), the electrochemical cell is supplied with nitrogen, preferably in a continuous flow. The electrochemical cell is preferably supplied with nitrogen via bubbling nitrogen into the composition of the electrochemical cell. Step i) is preferably carried out in a dry or anhydrous medium.In other words, step i) is preferably carried out in a glove box or in a suitable device to avoid contact of the composition with air and / or moisture. Indeed, contact with moisture and / or air leads to the formation of secondary products such as H2, and / or R. 1 R 2 MOMR 1 R 2The nitrogen supplied to the electrochemical cell is preferably dry nitrogen. In order to protect the reaction medium from moisture and / or air, the electrochemical cell is preferably airtight. Step i) may last from approximately 0.5 h to 20 h, and preferably from approximately 2 h to 12 h. Step i) is preferably carried out at a temperature ranging from approximately -80°C to 60°C, and particularly preferably from approximately 0°C to 30°C. During step i), the composition is kept stirring, for example using a mechanical or magnetic stirrer; or using a flow or circulation electrochemical cell; or using only the bubbling of nitrogen into the composition of the electrochemical cell. Stirring makes it possible to promote contact of the composition with the nitrogen and with the electrodes, and thus to promote the reaction during step ii).Step i) may be carried out at a pressure ranging from about 1 bar to 200 bar, and preferably from 1 bar to 100 bar. A pressure of 1 bar is advantageous from an industrial point of view. Step i) is preferably carried out at atmospheric pressure. The compound of formula (I) may have a molar concentration in the composition ranging from 10. -5 mol / l at 10 -1 mol / l approximately, and preferably 10 -3 mol / l at 10 -2 mol / l approximately. Step ii) Step ii) consists of applying a potential or current to the working electrode or a potential difference between the working electrode and the counter electrode. The potential, potential difference, or current applied must be sufficient to allow the reduction of compound (I) to the radical R 1 R 2 M°. The range of values ​​of the potential or current can vary depending on the type of working electrode used, the temperature, the nature of R 1 and / or R 2, electrolyte solution, etc. The potential difference applied between the working electrode and the counter electrode may range from approximately 2V to 50V, and preferably from approximately 3V to 20V. This embodiment of applying a potential difference between the working electrode and the counter electrode is particularly suitable in the case where the electrochemical cell does not include a reference electrode. The potential applied to the working electrode may range from approximately -4V to -1V, and preferably from approximately -3V to -2V, preferably relative to a reference electrode of saturated silver nitrate Ag / AgNO3. This embodiment of applying a potential to the working electrode is particularly suitable in the case where the electrochemical cell includes a reference electrode. The intensity of the current applied to the working electrode may range from approximately 0.01A to 10A, and preferably from approximately 0.5A to 1A.The working electrode and the counter electrode are electrically connected to a voltage or current source. During step ii), the working electrode acts as an electron provider. The electrons go directly into solution upon contact with the compound (I). The working electrode then reduces the compound (I), which then reacts with the nitrogen to form one or more species based on nitrogen and the element M, in particular of the following formula (II): N(MR. 1 R 2 ) 3-x H x, x being an integer ranging from 0 to 3. The working electrode therefore does not participate in the chemical process of reduction of dinitrogen as such. The formation of one or more species based on nitrogen and the element M as defined above is explained in particular by the conduct of a radical chain reaction involving at least one or more radicals based on the element M which are sufficiently unstable to react with the nitrogen of the dinitrogen. Compound (I) by its formula (I) and thus the definition of Y, M, R 1 and R 2 , has the ability to activate the triple bond of dinitrogen in a reducing medium, and to minimize, or even avoid, the dimerization of the radical R 1 R 2M°. Consequently, step ii) implements the electrochemical reduction of the compound (I), which is completely different from the electrochemical processes of the prior art which implement surface processes where the working electrode plays the role of electron provider but also of catalyst. Step ii) can be carried out in potentiostatic or galvanostatic mode. According to a particularly preferred embodiment of the invention, steps i) and ii) are concomitant. In other words, a potential, a potential difference, or a current is applied while the electrochemical cell is supplied with nitrogen. The electrochemical cell implemented in step i) can comprise a single compartment containing the composition as defined in the invention, the electrodes, and the nitrogen; can comprise two compartments C1 and C2, in particular so as to isolate the counter-electrode from the working electrode.This thus makes it possible to avoid diffusion phenomena between the two electrodes; or may comprise three compartments C1, C2 and C3, to ensure electrical contact between compartments C1 and C2, while isolating the counter-electrode from the working electrode. An electrochemical cell with two compartments C1 and C2 preferably comprises: - a compartment C1 containing the composition as defined in the invention, the working electrode immersed (in whole or in part) in said composition, and the reference electrode immersed (in whole or in part) in said composition if the reference electrode exists, - a compartment C2 containing the counter-electrode immersed (in whole or in part) in an electrolyte solution, and - a membrane separating the two compartments C1 and C2. The membrane may be a sintered glass, an ion exchange membrane such as a cationic membrane (eg Nafion®), or a polymer material such as a fluorinated organic polymer material.The electrolyte solution of compartment C2 may comprise (or consist of) the combination of an organic solvent and a salt; or an ionic liquid. The organic solvent is preferably chosen from aprotic organic solvents, in particular chosen from ethers, carbonates, nitriles, amides and phosphoramides, such as THF (tetrahydrofuran), methyl-THF, N,N'-dimethylformamide, acetonitrile, benzonitrile, hexamethylphosphoramide, or propylene carbonate. The electrolyte solution of compartment C2 may further comprise an oxidizable species which in particular makes it possible to prevent the oxidation of the organic solvent of compartment C1. The oxidizable species may advantageously be chosen from ferrocene, tetrathiafulvalene, or one of the derivatives of tetrathiafulvalene.The salt is soluble in the organic solvent, preferably at concentrations of at least about 0.1 mol / l, for example at concentrations ranging from about 0.1 to 0.5 mol / l. The salt is preferably an inert salt. The salt may be selected from alkali metal salts and quaternary ammonium salts, and preferably from quaternary ammonium salts. Examples of alkali metal salts include lithium salts, such as LiTFSI, LiPF6, or LiClO4. Examples of quaternary ammonium salts include tetraalkylammonium salts such as TBATFSI, tetra-n-ethylammonium perchlorate, tetra-n-butylammonium hexafluorophosphate, or tetra-n-propylammonium tetrafluoroborate.The ionic liquid may be selected from ammonium salts, imidazolium salts, phosphonium salts, pyrrolidinium salts, and piperidinium salts, and preferably from alkylammonium salts, alkylimidazolium salts, alkylphosphonium salts, alkylpyrrolidinium salts, and alkylpiperidinium salts. The ionic liquid preferably comprises an anionic portion of the bis(trifluoromethanesulfonyl)imidate type. Examples of ionic liquids include triethylbutylammonium bis(trifluoromethanesulfonyl)imidate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imidate, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imidate, trimethylbutylammonium bis(trifluoromethanesulfonyl)imidate, 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imidate, N-propyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imidate, or. 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imidate. The ionic liquid is preferably immiscible in water. This facilitates subsequent purifications. Compartment C2 does not comprise compound (I). The electrolyte solution (respectively the salt) of compartment C2 may be identical to the electrolyte solution (respectively the salt) of compartment C1. Step iii) At the end of step ii), species based on nitrogen and element M are present in the composition, and are then hydrolyzed in an acid medium during step iii), to form ammoniacal nitrogen. In the invention, ammoniacal nitrogen includes the two most reduced forms of nitrogen: ammonium (NH4 + ) and ammonia (NH3). Ammoniacal nitrogen is therefore chosen from ammonium (NH4 +), ammonia (NH3), and their mixture. Generally speaking, depending on the conditions of step iii), and in particular the quantity of acid, we will obtain ammonium (excess acid) or ammonia (stoichiometric quantities relative to N(MR 1 R 2 ) 3-x H x). Step iii) of hydrolysis in an acid medium can be carried out by bringing a crude reaction product obtained in the preceding step ii) into contact with an acid solution or with a gaseous acid (in the form of a gas). The acid solution can comprise an aqueous solvent (e.g. water) and at least one acid such as hydrochloric acid, hydrobromide, sulfuric acid, or nitric acid, or an aprotic organic solvent and at least one acid such as hydrochloric acid, hydrobromide, sulfuric acid, or nitric acid. The aprotic organic solvent can be chosen from ethers such as diethyl ether or dioxane, and alkanes such as hexane or heptane. The gaseous acid can be gaseous hydrochloric acid. Step iii) advantageously leads to ammonium, in particular when the acid is used in excess relative to the compound of formula (I). The aqueous solvent is preferably water.The acid solution may have a pH ranging from approximately 0 to 6. Step iii) may last from approximately 1 min to 30 min, and preferably from approximately 2 min to 10 min. Step iii) is a very rapid, almost instantaneous step. Step iii) is preferably carried out at a temperature ranging from approximately -20°C to 40°C, and particularly preferably from approximately 0°C to 20°C. Step iii) is preferably carried out with stirring. Step iii) is preferably carried out at atmospheric pressure. Step iii) makes it possible to produce ammonia NH3 and / or ammonium NH4. +. In step iii), contacting a reaction crude obtained in the preceding step ii) with an acid solution can be carried out by adding the acid solution to the composition. Other steps of the process The process can further comprise, after step ii) and before step iii), a step ii-1) during which the current or potential applied to the working electrode or the potential difference applied between the working electrode and the counter-electrode is stopped. The process can also comprise, after step ii), or ii-1) and before step iii), a purification step ii-2). This step ii-2) makes it possible to remove at least a portion of the secondary products (e.g. salts) possibly formed during step ii). In other words, step ii-2) makes it possible to separate the nitrogen-based species and the element M formed in step ii), from the salts.Step ii-2) may be carried out by extraction of a reaction mixture formed in step ii), or ii-1), in particular using an apolar organic solvent. The species based on nitrogen and the element M formed in step ii) or ii-1) are soluble in said apolar organic solvent and may be separated from the salts by filtration. The apolar organic solvent may be chosen from alkanes such as hexane, pentane, or heptane. The preferred apolar organic solvent is pentane. The process may further comprise, before step i), a step i-0) of preparing the compound of formula (I). The compound of formula (I) may be prepared according to a double hydroboration or hydroalumination protocol as described in the following articles: H.C. Brown, N. Ravindran, J. Am. Chem. Soc.1976, 98, 1798–1806 and H.C. Brown, N. Ravindran, J. Am. Chem. Soc.1976, 98, 1785–1798; or by the reaction of two equivalents of alkene with one equivalent of a monohaloborane (e.g. corresponding to the formula YBH2in which Y is as defined in the invention) in THF or diethyl ether, at room temperature. Generally, one equivalent of the compound MH2Y reacts with two equivalents of an alkene R'CH=CH2to form the compound (R'CH2CH2)2MY. The process of the invention preferably does not use gaseous species other than dinitrogen (N2) as starting reagent. The process may further comprise a step iv) of recycling the compound (I). In this embodiment, step iii) preceding step iv) is preferably carried out by contacting under an inert atmosphere the crude reaction product obtained in step ii), ii-1), or ii-2) above with an acid solution comprising an aprotic organic solvent and at least one acid, or a gaseous acid, said acid solution and said gaseous acid being as defined above, so as to preferably form ammonia NH3, then step iv) can be carried out by distillation of the ammonia NH3.The remaining liquid composition comprises the compound (I) in the electrolyte solution and can be reused in another reaction. The second subject of the invention is an electrochemical cell for the reduction of dinitrogen to ammoniacal nitrogen, characterized in that it comprises: * a composition comprising at least one electrolyte solution and at least one compound corresponding to the following formula (I): R. 1 R 2 MY (I), in which: - M is an element from group 13 of the periodic table, preferably chosen from boron, aluminum, and one of their mixtures, - R 1 and R 2 , identical or different, are chosen from an alkyl group, an aryl group, an aryl-alkyl group, a -OR group, and an -SR group, R being an alkyl group, an aryl group, or an aryl-alkyl group, and - Y is a group chosen from a halogen -X, a -OR group 3 , a -SR group 3, a triflate group, a mesylate group, and a triflimidate group, R 3being an alkyl group, an aryl group, or an aryl-alkyl group, * a working electrode immersed (in whole or in part) in said composition, and * a counter-electrode immersed (in whole or in part) in said composition or in an electrolyte solution. The electrochemical cell may also comprise a reference electrode immersed (in whole or in part) in said composition or in an electrolyte solution. The electrochemical cell, the electrolyte solution, the composition, the compound corresponding to a formula (I), the working electrode, the counter-electrode, and the reference electrode are as defined in the first subject of the invention. Brief description of the drawings The accompanying drawings illustrate the invention. Figure 1 represents an example of an electrochemical cell according to the invention or implemented according to the method of the invention.Figure 2 represents another example of an electrochemical cell according to the invention or implemented according to the method of the invention. Other characteristics and advantages of the present invention will appear in the light of the description of non-limiting examples of the method and the electrochemical cell according to the invention. Examples Figure 1 represents an electrochemical cell 1 for the reduction of dinitrogen to ammoniacal nitrogen comprising a composition 2 comprising at least one electrolyte solution and at least one compound corresponding to a formula (I), a working electrode 3 immersed in said composition, and a counter-electrode 4 immersed in said composition. The electrochemical cell 1 may further comprise a reference electrode 5, as well as a system 6 (eg tube) for introducing the dinitrogen into the electrochemical cell via an inlet 7.The system 6 is positioned such that the nitrogen 8 can be incorporated or released into the composition 2 near the working electrode 3. The electrochemical cell 1 may further comprise inlets and outlets (not shown in FIG. 1) for circulating the composition in flow within the electrochemical cell 1, for example with a pumping system. The electrochemical cell 1 may further comprise an outlet (not shown in FIG. 1) to allow the nitrogen to exit, and thus circulate it in flow within the electrochemical cell 1.Figure 2 represents an electrochemical cell 10 for the reduction of nitrogen to ammoniacal nitrogen comprising: - a first compartment C111 containing a composition 21 comprising at least one electrolyte solution and at least one compound corresponding to a formula (I), a working electrode 30 immersed in said composition, and, optionally, a reference electrode 50; and - a second compartment C212 containing a counter-electrode 40 immersed in an electrolyte solution 22. The two compartments are separated by a membrane 90. Compartment C1 further comprises a system 60 (eg tube) for introducing nitrogen into the electrochemical cell via an inlet 70. System 60 is positioned such that nitrogen 80 can be incorporated or released into composition 21 near working electrode 30.Example 1: Process for producing ammoniacal nitrogen from dinitrogen using an electrochemical cell comprising a composition containing dicyclohexylchloroborane as a compound of formula (I) An electrochemical cell comprising three compartments C1, C2 and C3 was used in the process of the invention and comprises: - a compartment C1 containing: * a composition maintained under stirring comprising 3 ml of anhydrous THF, 6x10. - 4 moles of tetra-n-butylammonium bis-trifluoromethanesulfonimidate (TBATFSI) [TBATFSI concentration of 0.2 mol / l], and 9x10 -5moles of dicyclohexylchloroborane [concentration of compound (I) of 0.03 mol / l]; * a working electrode consisting of a glassy carbon rod planted in a glassy carbon foam (10 mm x 5 mm x 7 mm), said working electrode being immersed in said composition; and * a reference electrode consisting of a silver wire immersed in an acetonitrile solution comprising 10 -2mol / l of silver nitrate and 0.2 mol / l of TBATFSI, - a compartment C2 containing a counter-electrode consisting of a glassy carbon (or graphite) rod planted in a piece of carbon felt (10 mm x 10 mm x 100 mm), said counter-electrode being immersed in an electrolyte solution comprising DMF and TBATFSI [TBATFSI concentration of 0.2 mol / l], - a compartment C3 containing an electrolyte solution comprising anhydrous tetrahydrofuran (THF) and TBATFSI [TBATFSI concentration of 0.2 mol / l], - a membrane separating compartments C1 and C3, consisting of a sintered glass disc, and - a membrane separating compartments C3 and C2, consisting of a sintered glass disc. Compartment C3 ensures electrical contact between compartments C1 and C2 while limiting the diffusion of constituents between the working electrode and the counter-electrode.The body of the reference electrode is brought into contact with the composition of compartment C1 via a glass extension containing an electrolyte solution comprising anhydrous THF and TBATFSI [TBATFSI concentration of 0.2 mol / l]. Said reference electrode is thus immersed in said composition. The electrochemical cell as described above is supplied with nitrogen (N2), the electrochemical cell being placed in a glove box under a nitrogen atmosphere (step i)). Then, a potential of -2.7 V is applied to the working electrode for 4 hours (step ii)). The progress of the reaction is monitored by coulometry. After stopping the electrolysis, the quantity of ammonium produced is estimated from a sample of 0.5 ml of the electrolyzed solution. This sample is treated by adding excess HCl (in solution in ether) (step iii)), then evaporating all the volatile species under reduced pressure.The amount of ammonium formed is estimated via an analysis of the residue by 1H NMR spectroscopy recorded in DMSO-d6 in the presence of trimethoxybenzene, used as an internal reference. Example 2: control methods (not part of the invention) The control method consists of reproducing the experiment described above in the absence of the compound of formula (I) or in the absence of application of a potential. No formation of ammonium was observed.

Claims

Claims 1. A process for producing ammoniacal nitrogen, the ammoniacal nitrogen being selected from ammonium (NH4 + ), ammonia (NH3), and their mixture, characterized in that it comprises at least the following steps: i) a step of supplying an electrochemical cell with dinitrogen (N2), said electrochemical cell comprising at least one working electrode immersed in a composition maintained under stirring, and at least one counter electrode, said composition comprising at least one electrolyte solution and at least one compound corresponding to the following formula (I): R 1 R 2 MY (I), in which: - M is an element of group 13 of the periodic table, - R 1 and R 2-Y, identical or different, are chosen from an alkyl group, an aryl group, an aryl-alkyl group, an -OR group, and an -SR group, R being an alkyl group, an aryl group, or an aryl-alkyl group, and -Y is a group chosen from a halogen -X, an -OR group 3 , a group -SR 3 , a triflate group, a mesylate group, and a triflimate group, R 3 being an alkyl group, an aryl group, or an aryl-alkyl group, ii) a step of applying a potential difference between the working electrode and the counter electrode, or of applying a potential or current intensity to the working electrode, and iii) a step of acid hydrolysis of the composition.

2. A process according to claim 1, characterized in that the element M is selected from boron, aluminum, and a mixture thereof.

3. A process according to claim 1 or 2, characterized in that the two groups R 1 and R 2are alkyl groups.

4. A method according to any one of the preceding claims, characterized in that Y is a halogen X.

5. A method according to any one of the preceding claims, characterized in that the working electrode comprises at least one inert electrically conductive material selected from carbon, platinum, stainless steel, and metal oxides.

6. A method according to any one of the preceding claims, characterized in that the counter electrode comprises at least one inert electrically conductive material selected from carbon, platinum, stainless steel, and metal oxides.

7. A method according to any one of the preceding claims, characterized in that the electrolyte solution comprises a combination of an organic solvent and a salt; or an ionic liquid.

8. A method according to any one of the preceding claims, characterized in that the electrochemical cell further comprises a reference electrode.

9. A method according to any one of the preceding claims, characterized in that the compound of formula (I) has a molar concentration in the composition ranging from 10 -5 mol / l at 10 -1mol / l.

10. A process according to any one of the preceding claims, characterized in that step ii) is carried out under potentiostatic or galvanostatic conditions.

11. A process according to any one of the preceding claims, characterized in that steps i) and ii) are concurrent.

12. A process according to any one of the preceding claims, characterized in that step iii) of hydrolysis in acidic medium is carried out by contacting a crude reaction product obtained in the preceding step ii) with an acidic solution or with a gaseous acid.

13. A process according to claim 12, characterized in that the acidic solution has a pH ranging from 0 to 6. 14.A method according to any one of the preceding claims, characterized in that the electrochemical cell comprises: - a compartment C1 containing the composition, the working electrode immersed in said composition; and the reference electrode immersed in said composition if the reference electrode exists, - a compartment C2 containing the counter electrode immersed in an electrolyte solution, and - a membrane separating the two compartments C1 and C2.

15. Electrochemical cell for the reduction of dinitrogen to ammoniacal nitrogen, characterized in that it comprises: * a composition comprising at least one electrolyte solution and at least one compound corresponding to the following formula (I): R 1 R 2 MY (I), in which: - M is an element of group 13 of the periodic table, - R 1 and R 2-Y, identical or different, are chosen from an alkyl group, an aryl group, an aryl-alkyl group, an -OR group, and an -SR group, R being an alkyl group, an aryl group, or an aryl-alkyl group, and -Y is a group chosen from a halogen -X, an -OR group 3 , a group -SR 3 , a triflate group, a mesylate group, and a triflimate group, R 3 being an alkyl group, an aryl group, or an aryl-alkyl group, * a working electrode immersed in said composition, and * a counter electrode immersed in said composition or in an electrolyte solution.

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