Method of manufacturing ammonia comprising a coated material

Abstract

Method for manufacturing ammonia comprising a coated material The invention relates to a method for manufacturing ammonia in which an element present in the reactive medium is coated with a protective coating of tantalum nitride TaN of hexagonal crystallographic structure or doped tantalum nitride TaN of hexagonal crystallographic structure. Figure for abstract: Fig. 1.

Description

Title of the invention: Method for manufacturing ammonia comprising a coated material Technical field

[0001] The present disclosure relates to materials useful in ammonia manufacturing processes and more specifically to protective coatings to be applied to metallic elements in contact with ammonia. Prior art

[0002] Ammonia synthesis processes require the use of specific materials.

[0003] Indeed, ammonia synthesis processes use very aggressive environments which can be a source of nitriding, electrochemical reduction or even corrosion of the materials which are placed in contact with the reagents of such a process and in particular ammonia.

[0004] These different degradation mechanisms, which can also be complementary, quickly lead to losses in the mechanical strength of the materials. This is why ammonia synthesis processes require the use of specific alloys, for example Inconel 625.

[0005] It remains, however, useful for those skilled in the art to develop new materials for the application stated above. Statement of the invention

[0006] The invention aims precisely to meet this need and thus proposes a method for manufacturing ammonia from a reactive medium in which an element present in the reactive medium is coated with a protective coating of tantalum nitride TaN of hexagonal crystallographic structure or doped tantalum nitride TaN of hexagonal crystallographic structure.

[0007] Indeed, the inventors have determined that tantalum nitride TaN with hexagonal crystallographic structure or doped tantalum nitride TaN with hexagonal crystallographic structure has excellent resistance capabilities to oxidation, corrosion and nitriding, particularly with respect to molten salts and ammonia.

[0008] The hexagonal crystallographic structure of the coating is responsible for the improved resistance of the tantalum nitride coating.

[0009] For the purposes of the invention, it will be understood that a process for manufacturing ammonia is a process which allows a reaction between at least a first reactant comprising hydrogen H and a second reactant comprising nitrogen N in order to form ammonia NH3 and possibly one or more by-products.

[0010] The reactive medium comprises these reagents, the ammonia formed and any by-products or intermediate products.

[0011] The element present in the reactive medium being coated, it must be understood that it is the coating of this element which is in contact with the reactive medium.

[0012] In one embodiment, the protective coating of tantalum nitride TaN of hexagonal crystallographic structure or doped tantalum nitride TaN of hexagonal crystallographic structure is in contact with ammonia and / or at least the first or second reagent.

[0013] For example, the protective coating may be in contact with ammonia only, ammonia and the first reactant, ammonia and the second reactant, ammonia and both reactants, or in contact with the first reactant only, the second reactant only, or both reactants only.

[0014] In one embodiment, the method may be a so-called “Haber-Bosch” method in which the first reactant is dihydrogen H2 and the second reactant is dinitrogen N2.

[0015] In one embodiment, the method may be plasmacatalytic, wherein the first reactant is dihydrogen H2 and the second reactant is dinitrogen N2, the plasmacatalytic method relying on the formation of a plasma comprising the reactants in the presence of a catalyst, for example iron Fe, cobalt Co, tungsten W or ruthenium Ru.

[0016] In one embodiment, the process may be photocatalytic, wherein the first reactant is water H2O and the second reactant is nitrogen N2. The photocatalytic process is characterized by supplying energy to the system in the form of light to enable the formation of ammonia. Furthermore, in such a process, the electrolyte must enable the exchange of protons to ensure the formation of ammonia.

[0017] In one embodiment, the process may be an electrocatalytic process, wherein the first reactant is hydrogen H2 or water H2O and the second reactant is nitrogen N2. In an electrocatalytic process, electrons are supplied to the system to force the reaction.

[0018] More precisely, the electrocatalytic process proposes an oxidation of water H2O or dihydrogen H2 at the anode of an electrochemical system to form protons H+ and a reduction of dinitrogen N2 at the cathode to allow the production of ammonia NH3, a proton transfer taking place between the anode and the cathode.

[0019] Preferably, the ammonia manufacturing process is an electrocatalytic process. Indeed, this process offers the best compromise in terms of costs, yield and safety.

[0020] The inventors found that the tantalum nitride TaN coating of structure hexagonal crystallographic or doped tantalum nitride TaN with hexagonal crystallographic structure not only achieves excellent oxidation, nitriding and corrosion resistance properties, but also excellent electric current conduction properties.

[0021] More particularly, the hexagonal crystallographic structure of tantalum nitride or doped tantalum nitride offers electrical conduction nearly 10 times greater than that of the cubic form of tantalum nitride.

[0022] In one embodiment, the ammonia manufacturing process may be an electrocatalytic process and the protective coating may be in contact with a molten salt electrolyte.

[0023] Indeed, such a coating has resistance properties compatible with such an application.

[0024] For example, molten salt electrolyte can be used to enable the transfer of protons between the anode and the cathode.

[0025] In one embodiment, the coated element is in contact with ammonia. Indeed, the resistance to corrosion and nitriding of the tantalum nitride coating is sufficient to ensure excellent resistance of the coated element.

[0026] In one embodiment, the ammonia manufacturing process may be an electrocatalytic process and the coated element may be selected from an end plate, an interconnect plate, an electrode or a bipolar plate of an electrocatalytic cell.

[0027] Preferably, the coated element is an electrode.

[0028] Indeed, the electrodes are currently the elements limiting the industrial applicability of the processes for manufacturing ammonia by electrocatalysis, and it is to the credit of the inventors to have succeeded in obtaining a functional electrode for such a process, which also has resistance and conduction properties superior to those of the prior art while allowing use in aggressive environments.

[0029] In one embodiment, the coating is undoped tantalum nitride TaN with a hexagonal crystallographic structure.

[0030] In one embodiment, the coating is made of doped tantalum nitride with a hexagonal crystallographic structure.

[0031] Regardless of the dopant and dopant content, it is important that the doped tantalum nitride remains of hexagonal crystallographic structure.

[0032] On the other hand, the invention is not limited either by the nature of the dopant, or by the quantity of the latter provided that the doped tantalum nitride TaN remains of hexagonal crystallographic structure.

[0033] In one embodiment, the coating is doped tantalum nitride TaN of hexagonal crystallographic structure, and the coating comprises a total content in doping less than or equal to 5 atomic %, the dopant being chosen from alkali metals, alkaline earth metals and / or transition metals or a mixture of two or more of these elements. In other words, the coating is made of TabxAxN doped tantalum nitride of hexagonal crystallographic structure with A designating a dopant corresponding to one or more elements chosen from alkali metals, alkaline earth metals and / or transition metals with x strictly positive and less than 0.05.

[0034] The clarification that x is strictly positive in the preceding definition is in no way intended to exclude from the invention an undoped tantalum nitride TaN coating, but rather aims to avoid redundancy with this embodiment described separately.

[0035] In one embodiment, the dopant may be one or more elements selected from alkali metals, alkaline earth metals and / or transition metals.

[0036] Such a dopant may be chosen to further functionalize the coating, for example by increasing its corrosion resistance or by improving the stability of the crystalline phase.

[0037] In one embodiment, the dopant is a single dopant selected from alkali metals, alkaline earth metals and / or transition metals.

[0038] In one embodiment, the dopant may be chosen from potassium K, sodium Na, calcium Ca, magnesium Mg, yttrium Y, vanadium V, titanium Ti and a mixture of one or more of these elements.

[0039] In one embodiment, the dopant is unique and chosen from potassium K, sodium Na, calcium Ca, magnesium Mg, yttrium Y, vanadium V and titanium Ti.

[0040] In one embodiment, the dopant content is less than or equal to 5 atomic % or less than or equal to 1.0%.

[0041] In one embodiment, the dopant content is greater than or equal to 0.01 atomic % or even greater than or equal to 0.05 atomic %.

[0042] For example, the dopant content may be between 0.01% and 5.0 atomic %, or even between 0.05% and 5.0 atomic %, or even between 0.1 and 1.0 atomic %.

[0043] Indeed, this dopant content is a sufficient, but not necessary, condition to ensure that the structure of tantalum nitride remains hexagonal despite the presence of a dopant.

[0044] In one embodiment, the tantalum nitride coating may be written TabxAx N with A selected from potassium K, sodium Na, calcium Ca, magnesium Mg, yttrium Y, vanadium V, and titanium Ti, and x between 0 exclusive and 0.05 inclusive.

[0045] In one embodiment, the coated element is metallic.

[0046] This is particularly advantageous in the case where the coated element must ensure a electrical conduction function, for example when the coated element is an electrode.

[0047] In one embodiment, the coated element may be made of an iron-based alloy, for example stainless steel, or a nickel-based alloy or a titanium-based alloy.

[0048] Indeed, an advantage of the coating of tantalum nitride of hexagonal crystallographic structure or of doped tantalum nitride of hexagonal crystallographic structure is that it confers sufficient resistance to the underlying substrate to allow the use of an inexpensive substrate.

[0049] The use of an inexpensive substrate thus makes it possible to reduce the overall cost of the process described. Brief description of the drawings

[0050] [Fig. 1] [Fig. 1] is a structure for carrying out a method in one embodiment of the invention.

[0051] [Fig.2] [Fig.2] represents electrical conductivity results as a function of the temperature obtained for a tantalum nitride coating with a cubic crystallographic structure.

[0052] [Fig.3] [Fig.3] represents electrical conductivity results as a function of the temperature obtained for a tantalum nitride coating with hexagonal crystallographic structure.

[0053] [Fig.4] [Fig.4] represents real and theoretical diffractograms for a re tantalum nitride garment. Description of the embodiments

[0054] The invention is now described by means of figures, present for descriptive purposes to illustrate certain embodiments of the invention and which should not be interpreted as limiting the latter.

[0055] [Fig.l] illustrates an arrangement for an electrocatalytic structure 100 allowing the realization of a method described above.

[0056] Such a structure has numerous parts present in the reactive medium and in contact with ammonia, at least one of them being coated with a coating comprising tantalum nitride TaN of hexagonal crystallographic structure or doped tantalum nitride TaN of hexagonal crystallographic structure.

[0057] For example, [Fig.l] shows an anode 201 and a cathode 202 separated by an electrolytic medium 203 allowing the H+ protons to be conducted, a circuit 204 allowing the anode to be electrically connected to the cathode, the circuit 204 comprising an electrical generator 205. The generator 205 allows the circulation of electrons from the anode to the cathode.

[0058] In the cell presented, ammonia NH3 is obtained from dihydrogen H2 and dinitrogen N2.

[0059] Dihydrogen H2 is oxidized at the anode 201 to form protons and electrons according to the following redox reaction: H2 = 2H+ + 2e.

[0060] The protons pass through the medium 203 to reach the cathode, while the electrons pass through the circuit 204.

[0061] In one embodiment, the medium 203 is a molten salt electrolyte.

[0062] For example, the medium 203 can be chosen from lithium chloride LiCl, potassium chloride KC1, cesium chloride CsCl, calcium chloride CaCl2, barium chloride BaCl2, sodium chloride NaCl, strontium chloride SrCl2, or a combination of two or more of these molten salts.

[0063] Dinitrogen N2 is reduced at cathode 202 to form ammonia NH3 according to the following redox reaction: N2 + 6H++ 6e = 2NH3.

[0064] In the example shown, the cathode 202 comprises an element 202a, for example metallic, covered with a coating 202b of tantalum nitride TaN of hexagonal crystallographic structure.

[0065] Thus, in the example shown, the coating 202b is in contact with the second reagent N2, the ammonia NH3 and the electrolytic medium 203.

[0066] This embodiment is only an example and it could be the same for the anode 201 or the elements 204, 205 or only some of these elements.

[0067] The example proposed in [Fig. 1] illustrates an embodiment but is not limiting of the ammonia production processes that the invention intends to cover.

[0068] Indeed, the invention proposes to take advantage of the properties of resistance to corrosion, oxidation and nitriding of a coating comprising tantalum nitride TaN of hexagonal crystallographic structure or doped tantalum nitride TaN of hexagonal crystallographic structure.

[0069] Furthermore, it is possible to take advantage of the excellent electrical conduction properties of these coatings.

[0070] In one embodiment, the metal element may be the anode 201, the cathode 202 and / or one or more circuit elements 204, 205.

[0071] In one embodiment, the manufacturing method may comprise a plurality of interconnected cells, for example, a plurality of electrocatalytic cells, operating analogously to cell 100 described in [Fig.l].

[0072] In such an embodiment, the coated element may be an end plate, an interconnection plate, an electrode or a bipolar plate of a cell of an electrocatalytic process.

[0073] In one embodiment, the tantalum nitride TaN coating of structure hexagonal crystallographic structure or doped tantalum nitride TaN with hexagonal crystallographic structure can be obtained by a high-power pulsed magnetron sputtering method (referred to by the acronym "HiPIMS" in the English literature for "High-Power Impulse Magnetron Sputtering").

[0074] In such a method, a tantalum or doped tantalum target is used and the coating of the element is carried out under an atmosphere containing nitrogen, the polarization of the target being controlled during the coating by imposing on it the superposition of a continuous polarization at a potential between -199 V and -100 V and a pulsed polarization whose pulses are at a potential between -900 V and -701 V.

[0075] Such parameters for high power pulsed magnetron sputtering ensure that the resulting coating of doped or undoped tantalum nitride has a hexagonal crystallographic structure.

[0076] In order to qualify the hexagonal crystallographic structure, one can, for example, obtain a small-angle X-ray diffraction spectrum to verify that it includes the characteristic lines of the hexagonal crystallographic structure.

[0077] Alternatively, the target used may be a doped tantalum target, comprising a dopant level ensuring the deposition of the desired quantity of dopant.

[0078] Alternatively, one can use a pure tantalum target, and one or more secondary target(s) consisting of the dopant(s).

[0079] Details of the high-power pulsed magnetron sputtering method can be found in patent application PCT / FR2020 / 050801. Examples

[0080] Figures 2 and 3 illustrate the improvement of using an undoped tantalum nitride coating of hexagonal structure over a tantalum nitride coating of cubic structure.

[0081] The measurements are given for a 0.5 μm coating made on the surface of 316L steel by a so-called 4-point measurement.

[0082] [Fig.2] shows the electrical conductivity results o (in Q '.cm *) obtained as a function of temperature (in °C) for a coating of tantalum nitride TaN with a cubic structure.

[0083] Curves 21, 22, 23, 24 respectively represent results obtained under argon 21, under argon with 5% dihydrogen H222, under air 23 and under dioxygen O2 24.

[0084] [Fig.3] shows the electrical conductivity results (in Q '.cm ') obtained as a function of temperature (in °C) for a hexagonal structure tantalum nitride TaN coating.

[0085] Curves 31, 32, 33, 34 respectively represent results obtained under argon 21, under argon with 5% dihydrogen H222, under air 23 and under dioxygen O2 24.

[0086] Figures 2 and 3 illustrate on the one hand that the conduction properties are at least 10 times better for the hexagonal structure coating than for the cubic structure coating.

[0087] Furthermore, Figures 2 and 3 show that the conduction properties of hexagonal structure tantalum nitride remain excellent at temperature, and whatever the temperature.

[0088] Furthermore, it could be observed that even after 1 hour in a hot phosphoric acid bath, a 316L steel part coated with tantalum nitride of hexagonal structure with a thickness of 0.5 μm, deposited by a high-power pulsed magnetron sputtering method, showed no signs of corrosion.

[0089] [Fig.4] shows a small angle X-ray diffraction spectrum obtained for the hexagonal structure tantalum nitride coating of the example.

[0090] [Fig.4] shows the theoretical lines of the diffractogram of non-tantalum nitride doped with hexagonal structure 41a to 41h, as well as the actual diffractogram obtained 51 for the sample described above.

[0091] We find on the latter the characteristic line 51a of tantalum nitride with hexagonal structure, as well as the characteristic lines of a 316L steel 51b and 51c.

Claims

Claims

1. A method of manufacturing ammonia from a reactive medium in which an element present in the reactive medium (202a) is coated with a protective coating (202b) of tantalum nitride TaN of hexagonal crystallographic structure or doped tantalum nitride TaN of hexagonal crystallographic structure.

2. The method of manufacturing ammonia according to claim 1, wherein the method of manufacturing ammonia is an electrocatalytic method.

3. A method of manufacturing ammonia according to claim 2, wherein the protective coating (202b) is in contact with a molten salt electrolyte.

4. A method of manufacturing ammonia according to any one of claims 1 to 3, wherein the protective coating (202b) is in contact with ammonia.

5. A method of manufacturing ammonia according to claim 2, 3 or 4 attached to claim 2 or 3, wherein the coated element (202a) is selected from an end plate, an interconnection plate, an electrode (202) or a bipolar plate of an electrocatalytic cell.

6. A method of manufacturing ammonia according to claim 5, wherein the coated member is an electrode (202).

7. A method of manufacturing ammonia according to any one of claims 1 to 6, wherein the coating (202b) is made of doped tantalum nitride of hexagonal crystallographic structure, the coating comprising a total dopant content of less than or equal to 5 atomic % and the dopant being selected from alkali metals, alkaline earth metals and / or transition metals or a mixture of two or more of these elements.

8. A method of manufacturing ammonia according to claim 7, wherein the dopant is selected from potassium K, sodium Na, calcium Ca, magnesium Mg, yttrium Y, vanadium V, titanium Ti and a mixture of one or more of these elements.

9. A method of manufacturing ammonia according to claim 7 or 8, wherein the dopant content is between 0.01% and 5.0 atomic%.

10. A method of manufacturing ammonia according to claim 1 to 9, wherein the coated member (202a) is a metallic member.

11. A method of manufacturing ammonia according to claim 10, wherein the coated member is made of stainless steel or a base alloy. nickel or titanium-based alloy.

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