WO2024100197A1

WO2024100197A1 - Hydrogen production method

Info

Publication number: WO2024100197A1
Application number: PCT/EP2023/081314
Authority: WO
Inventors: Soundarrajan CHANDRASEKARAN; Volodymyr Lysenko; Olivier Tillement
Original assignee: Oui Hydrogen
Priority date: 2022-11-10
Filing date: 2023-11-09
Publication date: 2024-05-16
Also published as: FR3141933A1

Abstract

The invention relates to a method for producing hydrogen by means of hydrolysis on the basis of solid forms of metals of which the standard electrode potential (E°) with respect to the standard hydrogen electrode is less than -0.4 volt, in particular magnesium, aluminum, or zinc, in which method these solid forms are brought into contact with an aqueous medium containing a water-soluble chelating agent which is an organic acid AO and a non-water-soluble chelating agent AC, whereby hydrogen and heat are produced as well as metal ions which are chelated by the chelating agent AC. The invention also relates to a method for producing thermal energy via combustion of the hydrogen that is produced. The invention also relates to a method for producing electricity by supplying a fuel cell with the hydrogen that is produced.

Description

TITLE: Hydrogen production process

The present invention relates to a process for producing hydrogen by hydrolysis reaction from a mixture of water and a product containing metals, preferably magnesium.

Magnesium reacts with water when it is in the form of nanopowder or nanoparticles. However, the formation of surface hydroxide on the nanoparticles blocks the hydrogen production reaction. Other disadvantages are linked to the cost of producing nanoparticles, due to the energy expenditure required, the need to store the nanoparticles in an inert atmosphere to avoid oxidation, the tendency of these nanoparticles to agglomerate, etc. The formation of hydroxide can be avoided or controlled using additives such as strong acids, carbonaceous materials, transition metals, however with the disadvantage of making the reuse of magnesium difficult.

Magnesium chips can also be used, but this requires the use of organic acid, for example citric acid. However, an excess of organic acid is necessary to avoid neutralization of the organic acid - Mg conjugate base during hydrolysis, which can result in an increase in pH, unstable hydrogen production and heat production. In addition, magnesium is found in aqueous solution, for example in the form of magnesium citrate, which is difficult to manage and water consumption is excessive. CN1 11003688 and WO201 1136147 thus describe the use of citric acid.

EP 2 583 937 describes a hydrogen generation system, which contains a hydrogen generating agent, a metal ion sequestering agent, and a pH adjusting agent. Preferably and in all examples, a single agent having these two functions is used. It does not disclose the combination of two chelating agents having successive effects, namely an initial and temporary chelation for the first, and a final chelation for the second, under conditions allowing continuous regeneration of the first, avoiding saturation of the system.

The objective of the present invention is to propose a new method of producing hydrogen making it possible to overcome the disadvantages of the prior art.

Another objective of the invention is to provide a method making it possible to avoid blocking the reaction by acid-base neutralization.

Yet another objective of the invention is to provide a method making it possible to continually maintain an acidic pH until the magnesium, or other metal, dissolvable in the acidified aqueous medium is exhausted. Yet another objective of the invention is to provide a method making it possible to obtain a solid residue of metal, in particular magnesium, which can be easily recovered and reprocessed.

Another objective of the invention is to provide a method making it possible to use the thermal energy produced following the hydrolysis reaction, which is an exothermic reaction.

Another objective of the invention is to carry out the hydrolysis and chelation reactions in a closed reactor or a cartridge, making it possible to control the hydrolysis reaction and the production of hydrogen and/or heat. The invention therefore also aims to provide such a reactor or cartridge.

These objectives, as well as others which will become apparent in the light of the description, are achieved by a method of producing hydrogen from solid forms of metals.

The invention particularly targets metals whose standard electrode potential (E°) relative to the standard hydrogen electrode is less than approximately -0.4 volts. These solid forms can be any form of solid particles of metal, or containing metal, as will be detailed below. The preferred metal is magnesium, for example in the form of magnesium particles or containing magnesium. Said solid forms or solid particles are brought into contact with, for example dispersed in, an aqueous medium containing two chelating agents for the metal cation (for example Mg ²⁺ ), (i) a water-soluble or solubilized organic acid (designated chelating agent or organic acid AO in the following) and (ii) a chelating agent not soluble in water (designated AC in the following). This results in hydrolysis reactions, the generation of hydrogen, the production of heat, and the stable chelation of the metal ion, for example Mg ²⁺ , by the chelating agent AC. The method includes in particular the recovery of the hydrogen produced, advantageously the continuous regeneration of the organic acid AO, and, possibly, the regeneration of the chelating agent AC for its reuse.

The present invention therefore relates to a method of producing hydrogen by hydrolysis from solid forms of metals whose standard electrode potential (E°) relative to the standard hydrogen electrode is less than approximately -0.4 volt, method in which said solid forms are brought into contact with an aqueous medium containing two chelating agents, (i) a water-soluble chelating agent which is an organic acid AO and (ii) a non-water-soluble chelating agent AC. The metal is hydrolyzed, hydrogen is produced, and the metal ions are chelated by the chelating agent AC or are bound to the chelating agent AC in solid form. The hydrogen produced is recovered, preferably the recovery is carried out continuously. In particular, the metal can be magnesium, aluminum or zinc. Without wishing to be bound by theory, to take the preferred example of magnesium, it is estimated that the organic acid AO causes the solubilization and temporary chelation of magnesium in the form of Mg ²⁺ , and the production of Hp. This chelation is temporary because the AC chelating agent competes for the Mg ²⁺ ion once it is generated, and the nature of the two chelants is chosen to promote the capture or chelation of the Mg ²⁺ ion by the AC chelating agent. In other words, the organic acid AO is continuously regenerated in situ by the capture of the cation by the chelating agent AC present in a relative quantity (compared to the quantity of Mg ²⁺ and organic acid AO) sufficient to ensure this effect. In the case of citric acid, for example, magnesium citrate is formed each time the cation is captured by citric acid, but is dissolved immediately or quickly by the effect of the chelating agent AC. Provided there are sufficient quantities of the different species, this sequence of reactions allows complete hydrolysis of magnesium, and production of hydrogen which is not stopped by the saturation of the organic acid molecules AO. Furthermore, the AC chelating agent can be easily regenerated because its solid form easily allows its separation.

The present invention preferably relates to a method for producing hydrogen by hydrolysis from solid forms or solid particles of magnesium, or containing magnesium, in which said solid forms or particles are brought into contact with, for example dispersed in, an aqueous medium containing two Mg ²⁺ chelating agents, (i) a solubilized organic acid which is an organic acid AO and (ii) a non-water soluble chelating agent AC, whereby hydrogen is produced as well as Mg ²⁺ ions which are chelated by the chelating agent AC. The hydrogen produced is recovered, preferably the recovery is carried out continuously.

The particles may be formed from pure magnesium or may contain magnesium and one or more other components. By “containing magnesium”, we mean particles containing magnesium as the only metal (monometal) or containing several metals (e.g. alloy, hydrides). It goes without saying that a high magnesium content is preferred in order to make the method economically interesting. Generally, it is preferred to use particles having a magnesium content greater than or equal to approximately 20%, preferably greater than or equal to approximately 50%, better still greater than or equal to 70, 80, 90, or 95% by weight relative to the weight. total of a particle.

Solid forms of magnesium include nanometric or micrometric forms, or larger shapes of any geometry, such as pencils, bars, cubes or parallelepipeds, chips, fragments. All these forms or particles of magnesium or containing magnesium can therefore have variable dimensions, typically between approximately 0.5 mm and approximately 200 mm, in particular between 0.5 and 50 mm. As for the MgHs hydride form, this is generally in the form of nanopowder or nanoparticles.

If a metal other than magnesium is used, such as aluminum or zinc, the solid forms or particles may be formed of that pure metal or may contain that metal and one or more other components. By “containing this metal”, we mean particles containing it as the only metal (monometal) or containing several metals (e.g. alloy, hydrides). It goes without saying that a high metal content is preferred in order to make the method economically interesting. Generally, it is preferred to use particles having a metal content greater than or equal to approximately 20%, preferably greater than or equal to approximately 50%, better still greater than or equal to 70, 80, 90, or 95% by weight relative to the weight. total of a particle. The solid forms are of the same type as described for magnesium.

The AC chelating agent may in particular be what is commonly called an acid cation exchanger or a cation exchange resin.

This may be a strong cation exchange resin or a strongly acidic cation exchanger. Such a resin comprises a polymer matrix, preferably a polystyrene matrix (or styrene polymer) or a styrene-divinylbenzene copolymer, and one or more sulfonate groups. These are therefore sulfonated resins, polymers or copolymers. These sulfonate groups are protonated, ie charged with H ⁺ ions. It is possible in particular to use these strongly acidic cation exchangers obtained by sulfonation of styrene polymers or styrene-divinylbenzene copolymers using sulfuric acid, as described for example in US 6,384,092, to which those skilled in the art may refer. We can cite the following commercial resins: Amberlite® IRC120, “hydrogen form”, Dowex® G26 “hydrogen form”; Amberlyst® 15 “hydrogen form”; Lewatit® Monoplus S100 “hydrogen form”.

It can also be a weak cation exchange resin. Such a resin comprises a polymer matrix, preferably an acrylic polymer or a copolymer of acrylonitrile and a crosslinking aliphatic monomer, and one or more carboxylic groups. As is known per se, it may in particular be a resin produced from an acrylic polymer or copolymer, which is subjected to hydrolysis with sulfuric acid to generate carboxylic acid functional groups. Those skilled in the art may refer to DK162651. The following commercial resins can be cited: AmberLite® MAC-3 H; Lewatit® CNP80; Amberlite® HPR8300 H.

The organic acid AO is preferably a water-soluble carboxylic acid comprising from 1 to 4 carboxylic groups, which may in particular be chosen from the acid acetic acid, citric acid, tartaric acid, malonic acid, malic acid, maleic acid, nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA) and/or modified EDTA of preferably with magnesium or methyl ester, which improves solubility in water. More particularly, this acid is polycarboxylic and it contains 2 to 4 carboxylic groups, better still 2 or 3 carboxylic groups. This is preferably citric acid.

The organic acid AO initiates the hydrolysis and release of the magnesium cation. It also has a chelating power of this magnesium cation. In the case of acetic acid, this chelating power is shared between two acetic acid molecules. For other AOs, the presence of at least two carboxylic acid groups allows a single molecule to chelate the magnesium ion, but we do not exclude the cooperation of two molecules to carry out this chelation. In all cases, the chelating force of the AO acid is lower than that of the chelating agent AC under the conditions of the invention. The chelating agent AC, for example, has a stronger chelated complex formation constant than the organic acid AO.

The pKa is a characteristic of the acids or reactive groups used in the invention. The lower the pKa, the higher the strength of the acid or acid group. Sulphonic acids and sulfonate groups provide strong chelating capacity. Chelating agents are chosen with a pKa lower than that of the soluble organic acid used.

For 1 mole of metal, in particular magnesium, it is possible to use at least 0.5, or better still at least 1 mole of organic acid AO (for example range from approximately 0.5 to approximately 1 or approximately 1.5) and/ or at least 1 mole, or better still at least 2 moles of AC chelating agent (for example range from approximately 1 to approximately 3, in particular from approximately 1.5 or approximately 2 to approximately 3). Preferably, an excess of AC is used relative to the quantity of metal; typically, by excess, we mean a quantity of moles of AC multiplied by at least 1.5 or 2 (for example x 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2 .5, 3, etc.) relative to the quantity of metal in moles. Also preferably, an excess of AC compared to the AO is used; typically, by excess, we mean a quantity of moles of AC multiplied by at least 1.5 or 2 or 3 (for example x 1.5, 1.6, 1.7, 1.8, 1.9, 2 , 2.5, 3, etc.) relative to the quantity of moles of AO. In the case of citric acid, for 1 mole of metal, in particular Mg, it is possible to use at least 0.5 to 1 mole of citric acid and at least 1 or 1.5 to 2 moles, preferably 2 moles of cation exchange resin. The quantity of water can be 250 to 750 ml of water for 1 mole of metal, in particular Mg. The hydrogen production time can be between 30 and 60 minutes for this condition. We can control the speed of the reaction and therefore the duration of hydrogen production. Indeed, the greater the acid concentration, the faster the reaction. Likewise, the higher the strength of the acid, the faster the reaction also occurs. And these parameters are linked to the capacity of the fuel cell.

The heat produced by the hydrolysis reaction can advantageously be recovered and used, for example to power a heating circuit. The first tests carried out showed that the water from the hydrolysis reaction could reach a temperature of between 45 and 80°C.

Another object of the invention is therefore a process for producing heat or thermal energy. This process includes the implementation of the hydrogen production method disclosed herein. This process further comprises supplying the hydrogen produced to a combustion system or a hydrogen engine, which will use the oxidation of dihydrogen by dioxygen to produce energy and water.

Another object of the invention is therefore a method of producing hydrogen and/or heat or thermal energy, by hydrolysis from solid forms of metals whose standard electrode potential (E°) relative to the standard hydrogen electrode is less than about -0.4 volt, method in which said solid forms are brought into contact with an aqueous medium containing two chelating agents, (i) a water-soluble chelating agent which is an organic acid AO and (ii) a non-water soluble chelating agent AC. The metal is hydrolyzed, hydrogen and heat are produced, and the metal ions are chelated by the AC chelating agent or become bound to the AC chelating agent in solid form. The heat is recovered and can power a heating circuit. The hydrogen produced is also advantageously recovered, preferably the recovery is carried out continuously. The hydrogen can then be used in a fuel cell, or burned to supply the heating circuit with heat. In particular, the metal can be magnesium, aluminum or zinc. The characteristics stated above regarding the hydrogen production method apply to this other method.

In one embodiment, the methods of the invention ensuring the reactions of hydrolysis, hydrogen production, heat production, and chelation of metal ions or metal, are carried out in a closed reactor or in a cartridge closed. Depending on one method, the reactor or the cartridge are intended to constitute portable devices, for example with an internal volume of between approximately 0.5 and approximately 5 liters, in particular between approximately 1 and approximately 2 liters.

Hydrolysis reactions can be carried out in a closed reactor or cartridge. In an interesting embodiment, the production of hydrogen (and heat) can be controlled. This particularity can be obtained by using a reactor or cartridge, which is also an object of the invention, comprising, within its volume, a moving part arranged so as to be able to support the solid form of metal to be hydrolyzed, and controllable means for moving the moving part from a position in which said part is located near the bottom of the volume, to another position in which the moving part is in the upper or upper part of the volume. The volume of the reactor or cartridge is also suitable and intended to receive the aqueous medium, in a quantity which frees up free space in the upper or upper part of the volume. The reaction is controlled as follows: the moving part and the solid form of the metal are in the position near the bottom of the volume, and therefore immersed in the aqueous medium, the hydrolysis reactions occur; the moving part and the solid form of metal are moved to the upper or upper part, in the space without an aqueous medium, which stops the hydrolysis reactions. Control allows you to move from one position to another, to produce hydrogen or stop this production. The moving part may in particular have the shape of a piston, moving inside the volume. In other words, the hydrolysis reaction can be carried out in a closed reactor or cartridge comprising a movable part between a position in which the solid form of metal is immersed in the aqueous medium, and is subjected to hydrolysis, and a position in which it is outside this aqueous environment, and is not subject to hydrolysis.

Another object of the invention is a process for producing electricity. This process includes the implementation of the hydrogen production method disclosed herein. This process further comprises supplying a fuel cell with the hydrogen produced, this cell comprising at least one anode (allowing the dissociation of hydrogen into protons and electrons) and at least one cathode (making it possible to reduce oxygen by protons and electrons to form water), making it possible to drive the reaction of producing an electric current and producing water. In one embodiment, the process comprises a hydrogen storage phase, particularly of short duration, between the production of hydrogen and the supply of the fuel cell. In particular, this storage phase lasts until magnesium is depleted. In another embodiment, hydrogen is continuously introduced into the fuel cell as it is produced.

Another object of the invention is a process for producing thermal energy from the hydrogen produced. This process comprises the implementation of the hydrogen production method disclosed here, then the combustion of all or part of the hydrogen produced. This process includes in particular supplying the hydrogen produced to a combustion system or a hydrogen engine, which will use the oxidation of dihydrogen by dioxygen to produce energy and water. [Fig 1] Figure 1 shows a bar graph showing, over time, the proportion of undissolved magnesium from magnesium-containing solid particles, and the production of hydrogen, for various conditions.

In all examples, magnesium shavings (“magnesium scrap”) are used, namely magnesium sold by Sigma Aldrich “Mg turnings” at 98% Mg purity.

Comparative example 1:

24.3 mg of magnesium shavings are placed in 0.5 ml of water. No reaction or production of hydrogen is observed. See Figure 1, A.

Comparative example 2:

24.3 mg of magnesium chips are placed in 0.5 ml of water containing 312 mg (approximately 1 mmol) of a strong cation exchange resin, namely Amberlite® IR 120 form H. The resin was washed at distilled water before use. No reaction or production of hydrogen is observed. See Figure 1, B.

Comparative example 3:

24.3 mg of magnesium shavings are placed in 0.5 ml of water containing 0.5 mmol of citric acid. A hydrolysis reaction is observed, but this stops after approximately 60 minutes due to acid-base neutralization (the pH increased from 2 to 7 in this time interval). About 8.4 mg of magnesium did not dissolve and about 13 ml of hydrogen was produced. See Figure 1, C.

Example 4:

24.3 mg of magnesium chips (1 mmol) are placed in 0.5 ml of water containing 0.5 mmol of citric acid and 312 mg (approximately 1 mmol) of a strong cation exchange resin, namely Amberlite® IR 120 form H. The hydrolysis reaction has occurred. However, the conditions are not optimal, since a slowdown in the reaction has been observed. After 60 minutes, approximately 2 mg of magnesium had not dissolved and approximately 20 ml of hydrogen had been produced. See Figure 1, D.

Example 5:

24.3 mg of magnesium chips (1 mmol) are placed in 0.5 ml of water containing 0.5 mmol of citric acid and 624 mg (approximately 2 mmol) of a strong cation exchange resin, namely Amberlite® IR 120 form H. The hydrolysis reaction was complete with the hydrolysis of 24.3 mg of magnesium in 30 minutes, with approximately 22 ml of hydrogen produced (> 98%). The pH of the final solution was 2. See Figure 1, E.

Note that the rate of hydrogen produced was measured by the water displacement method in all examples. Greater accuracy can be achieved using gas chromatography. An ICP analysis would show that all of the magnesium has been chelated by the resin, and that there is no residual solubilized magnesium.

The resin, which is solid, can then be easily recovered and treated with an acid such as hydrochloric acid (HCl) or sulfuric acid (H2SO4) to release the magnesium. The resin is thus regenerated for reuse.

Magnesium chloride, like magnesium sulfate, depending on the acid used in the previous step, can then be transformed into magnesium oxides by heating above approximately 100°C. Magnesium oxides can then be converted to metallic magnesium by conventional carbothermal, metallothermal or electrolytic techniques.

The temperature of the solution was measured at several times during the hydrolysis reaction. Temperatures between 45 and 80°C were measured.

Example 6:

A fuel cell producing 1 kWh of electricity (considering an efficiency of around 40% of the cell) requires producing around 950 liters (85 g) of hydrogen. To do this, we use 1 kg of Mg + 20 I of water + 4 kg of citric acid + 26 kg of strong cation exchange resin, namely Amberlite® IR 120 form H.

The resulting Mg-resin product can be easily recovered, for example by filtration, the resin is then regenerated and can be reused. Likewise, citric acid can be reused many times.

The resin can be regenerated, and the magnesium recovered, as described in the example

5.

Claims

1. Method of producing hydrogen by hydrolysis from solid forms of metals whose standard electrode potential (E°) with respect to the standard hydrogen electrode is less than -0.4 volt, method in which said solid forms are placed in contact with an aqueous medium containing two chelating agents, (i) a water-soluble chelating agent which is an organic acid AO and (ii) a non-water-soluble chelating agent AC, the chelating agent AC having a chelated complex formation constant stronger than the organic acid AO and/or the chelating agent AC having a pKa lower than that of the organic acid AO, whereby hydrogen is produced as well as metal ions which are chelated by the chelating agent AC.

2. Method according to claim 1, in which the metal is magnesium, aluminum or zinc, preferably magnesium.

3. Method according to claim 1 or 2, in which the chelating agent AC is a strong cation exchange resin, comprising a polymeric matrix, preferably a polystyrene matrix or a styrene-divinylbenzene copolymer, and one or more protonated sulfonate groups; or the chelating agent AC is a weak cation exchange resin, comprising a polymeric matrix, preferably an acrylic polymer or a copolymer of acrylonitrile and a crosslinking aliphatic monomer, and one or more carboxylic groups.

4. Method according to any one of claims 1 to 3, in which the chelating agent AO is a carboxylic acid soluble in water, comprising from 1 to 4 carboxylic groups, preferably chosen from acetic acid, citric acid, tartaric acid, malonic acid, malic acid, maleic acid, nitrilotriacetic acid (NTA), and ethylenediaminetetraacetic acid (EDTA), optionally modified with magnesium or ester methyl, preferably this acid has from 2 to 4 carboxylic groups, better still 2 or 3 carboxylic groups, preferably it is citric acid.

5. Method according to any one of claims 1 to 4, in which the chelating agent AC is in excess relative to the organic acid AO.

6. Method according to any one of claims 1 to 5, in which the respective quantities are, for 1 mole of metal, at least 1 mole of organic acid AO and at least 1 mole of chelating agent, preferably AO and AC are in excess compared to the quantity of metal.

7. Method according to any one of claims 1 to 6, in which the thermal energy produced by the hydrolysis reactions is recovered.

8. Method according to any one of claims 1 to 7, in which the hydrolysis reaction is carried out in a closed reactor or cartridge comprising a movable part between a position in which the solid form of metal is immersed in the aqueous medium, and is subject to hydrolysis, and a position in which it is outside this aqueous medium, and is not subject to hydrolysis.

9. Method for producing thermal energy, comprising production of hydrogen according to any one of the preceding claims, then combustion of all or part of the hydrogen produced.

10. Method of producing electricity, comprising producing hydrogen according to any one of claims 1 to 8, then supplying a fuel cell with the hydrogen produced.