WO2012104819A1

WO2012104819A1 - Electrolyser and assembly comprising same, in particular for the production of h2 and o2

Info

Publication number: WO2012104819A1
Application number: PCT/IB2012/050508
Authority: WO
Inventors: Arash Mofakhami
Original assignee: Ceram Hyd
Priority date: 2011-02-03
Filing date: 2012-02-03
Publication date: 2012-08-09
Also published as: EP2670889A1; CA2826002A1; JP2014504680A; FR2971262B1; AU2012213033A1; US20140202875A1; FR2971262A1

Abstract

The present invention relates to an electrolyser for the production of at least one chemical substance, such as hydrogen, oxygen, chlorine or hypochlorous acid, or sodium hydroxide, by electrolysis of pure water or of water containing at least one salt, base and/or acid such as NaCl, H₂SO₄, KOH or NaOH, comprising a stack of at least a first and a second consecutive electrolytic cells, each electrolytic cell (10) comprising: - an anode, - a cathode, - an ion exchange membrane (11) positioned between the anode and the cathode, the ion exchange membranes (11) of the first electrolytic cell and of the second electrolytic cell being separated by a bipolar electrode (15) constituting, on the one hand, the anode of the first electrolytic cell and, on the other hand, the cathode of the second electrolytic cell.

Description

Electrolyser and assembly comprising it, in particular for the production of H? and O

The present invention relates to the production of chemical substances such as dihydrogen, dioxygen, chlorine, hypochlorous acid or sodium hydroxide, by electrolysis of pure water or of water containing salts, bases and / or acids such as NaCl, H ₂ SO ₄ , KOH, NaOH, by means of an electrolyzer comprising a plurality of electrolytic cells each equipped with at least one ion exchange membrane disposed between an anode and a cathode.

The invention aims to improve the electrolysers, so as to facilitate the production of the targeted substance (s) and to lower the cost thereof.

The subject of the invention is thus an electrolyzer for producing dihydrogen and dioxygen or other chemical substances, comprising a stack (also called stack) of at least a first and a second consecutive electrolytic cell, each electrolytic cell comprising:

an anode,

a cathode,

at least one ion exchange membrane disposed between the anode and the cathode,

the exchange membranes of the first and second electrolytic cells being separated by a bipolar electrode constituting on the one hand the anode of the first electrolytic cell and, on the other hand, the cathode of the second electrolytic cell.

The electrolyser according to the invention is of an easier assembly compared to known electrolysers in which the anodes and cathodes of the different cells are separated from each other.

In addition, the electrical circulation in the electrolyzer, especially in a cell and / or between the different electrolytic cells, can be improved.

The electrolyser can be configured for the production of dihydrogen, oxygen, chlorine, hypochlorous acid, sodium hydroxide, by electrolysis of pure water or water containing at least one salt, an acid and / or a base such as Nacl, H ₂ SO ₄ , KOH or NaOH.

The bipolar electrode may comprise a bipolar plate in one piece, the bipolar plate being associated where appropriate with at least one gate and at least one porous plate, in particular with one or two grids and with one or two porous plates, a grid and a porous plate being able to be arranged on both sides of the bipolar plate. Throughout the application, the term "plate" should be broadly understood as synonymous with wall and not limited to a flat part, even if the flat shape is preferred. A grid may at least partially define the anode chamber of the first cell, and another grid the cathode chamber of the second cell. Each anode or cathode chamber may be delimited on the one hand by the bipolar plate and on the other by a porous plate. The porous plate provides proper support for the adjacent ion exchange membrane. The porous plate also serves to act as a diffuser to the flow of electrolyte and gas, so as to promote the electro-chemical reaction. The gas and electrolyte tightness of the chambers and the circulations in each of the anode and cathode chambers independently and sealed between them are also obtained thanks to the same seal assembled with an axial rotation of 180 °.

The bipolar electrode can be made entirely in one piece, the bipolar plate, the grids and the porous plates being in this case integral with each other before mounting in the electrolyzer.

The bipolar electrode, or at least the bipolar plate, may comprise at least one of the following materials: nickel, iridium, ruthenium, palladium, cadmium, molybdenum, platinum, stainless steel, titanium, tantalum, iron alloy, alloy nickel, lead alloy and / or a thin film of tantalum oxide, iridium oxide, ruthenium oxide, lead oxide, ferric oxide, platinum, platinum carbon, palladium, nickel, cadmium, and / or molybdenum.

The at least one porous plate may comprise at least one of the following materials: nickel, iridium, ruthenium, palladium, cadmium, molybdenum, platinum, stainless steel, titanium, tantalum, iron alloy, nickel alloy, lead alloy and / or a thin layer of tantalum oxide, iridium oxide, ruthenium oxide, lead oxide, ferric oxide, platinum, platinum carbon, palladium, nickel, cadmium, and / or molybdenum.

The at least one porous plate may for example comprise titanium coated with a layer of one of the above materials on the face adjacent to the ion exchange membrane. The anode may comprise at least one of the following materials: titanium, tantalum, iridium, iron alloy, lead alloy, and / or a thin layer of tantalum oxide, iridium oxide, oxide ruthenium, lead oxide, and / or ferric oxide. The thin layer may in particular be placed on the face of the anode adjacent to the ion exchange membrane.

The cathode may comprise at least one of the following materials: nickel, iridium, palladium, cadmium, molybdenum, platinum, titanium, tantalum, iron alloy, lead alloy, nickel alloy and / or a thin layer of platinum, platinum carbon, palladium, nickel, cadmium, and / or molybdenum. The thin layer may in particular be disposed on the face of the cathode adjacent to the ion exchange membrane.

The bipolar electrode may in particular be entirely made of the same material, for example titanium. More specifically, the bipolar plate may be entirely made of the same material, for example titanium. The grid or grids may be entirely made of the same material, for example titanium. The porous plate or plates may be entirely made of the same material, for example titanium.

Frames and seals may be interposed between the electrodes. The flow of electrolytes between the cells can be done through holes made in the frames and joints and to the circulation ducts formed in the joints.

The bipolar electrode, in particular the bipolar plate, may alternatively comprise a coating of a material, for example tantalum. The coating may have a thickness between 10 and 100 μιη, for example of the order of 50 μιη.

The ion exchange membrane preferably comprises boron nitride and more preferably activated boron nitride.

By "activation" of boron nitride, it is sought to promote ionic conduction in boron nitride. In activated boron nitride, the activated [BN] crystallite generates on its surface -OH, -H, -SO ₃ H or -SO ₄ H bonds that will create NH ₂ ⁺ , B-OH ₂ ⁺ , B groups. -SOxH ₂ ⁺ or N-SOxH ₂ ⁺ . The conduction of the ions can also be carried out by means of doublets available on oxygen atoms inserted in nitrogen vacancies of the boron nitride. Such nitrogen gaps containing oxygen atoms may be especially present when the boron nitride was obtained from B ₂ 0 ₃ or H ₃ B0 ₃ . The boron nitride used may comprise at least one, for example one or more substituent element (s), of the following list: boron oxide, calcium borate, boric acid, sulfuric acid. The presence of such elements can promote activation, especially when present in a mass proportion of between 1 and 20%. The presence of boric acid, for example present in the pores of boron nitride or in amorphous form, may make it possible to promote the creation of B-OH and NH bonds.

In order to proceed with the activation, the boron nitride, or the membrane which contains it, may be exposed to a fluid which makes it possible to provide H ₃ 0 ⁺ or S0 ₄ ^{2 -} ions and to form B bonds in the boron nitride. OH and / or B-SO ₄ H, B-SO ₃ H, N-SO ₄ H, N-SO ₃ H and / or NH bonds The fluid may for example be an acid solution containing H ₃ O ₃ ions. ^+, for example strong acids such as HC1, H2SO4, H ₃ P0 _4, H2S2O7, or weak acids, or not to be an acidic solution, but for example a basic solution containing OH ions ^", for example a solution soda or potash. The concentration of the solution can have an influence on the speed and the level of activation obtained, ie on the level of ionic conductivity obtained, but not on the appearance of the activation itself. The acid concentration is for example between 1 and 18 mol / L and the concentration of the sodium hydroxide may be between 0.5 and 1 mol / L.

In order to promote the creation of bonds of crystallite [BN] with -OH, -SO ₄ H, -SO ₃ H, -SO ₄ H, -SO ₃ H and / or -H, the boron nitride or the membrane containing boron nitride at an electric field, for example an electric field between 15 and 40,000 V / m in the presence of a 1 M H ₂ SO ₄ acid solution for example.

The electric field can be delivered by an external generator. The applied voltage is for example between 1.5 V and 50 V, for example of the order of 30 V. The voltage source may be constant, or, alternatively, non-constant. It can be configured to detect the end of the activation automatically, for example when the current density in the material increases sharply. The intensity of the current flowing during activation in the boron nitride can be of the order of 10 mA / cm ² at 1000 mA / cm ² .

Activation by a fluid can be carried out at a temperature between 0 and 90 ° C, for example of the order of 60 ° C, or at room temperature. After being exposed to the solution, the boron nitride can be rinsed and optionally dried before being used to make the electrolyser. The fluid can be removed so that its residual content is less than 2%.

The fluid exposure step may have a duration of less than 50 hours. In one exemplary embodiment of the invention, the activation of the boron nitride is obtained by mixing boron nitride, for example in powder form, with acid, for example concentrated sulfuric acid, for example 3M during a predetermined time, then by rinsing it, before using the activated boron nitride to manufacture the ion exchange membrane, for example by mixing the activated boron nitride powder with a polymer matrix.

The ion exchange membrane may comprise a polymeric matrix. The polymer matrix may comprise at least one polymer from the following list: polyvinyl alcohol (PVA), vinylcaprolactam, PTFE (Teflon ^®), sulfonated polyether sulfone, this list not being limiting .... The polymer matrix may for example include the PTFE DuPont, known under the trade name Teflon ^®, PTFE or another company. Ion conduction with PTFE can be as good as with other polymers, up to 0.2 S / cm.

The proportion by weight of boron nitride in the membrane may be greater than 50% better than or equal to 95%, especially in the case of association with PTFE. It is for example in some embodiments of the order of 70%, and 90% in other embodiments.

The mechanical strength of the ion exchange membrane (Mechanical Strength at 300μιη) can be satisfactory for a small amount of PTFE, for example of the order of 4 MPa (Young's modulus) to 5% by weight of PTFE at 25 ° C. and increases significantly with a larger amount of PTFE, for example on the order of 6 MPa to 15%.

The temperature range of use of the ion exchange membrane can be wide enough, up to 180 ° C.

The boron nitride present in the ion exchange membrane may be in the form of a powder composed of grains having a greater transverse dimension of between 0.5 and 15 μιη, being for example centered on 5 μιη. According to an operating hypothesis, the ionic conduction in the boron nitride takes place on the surface of the activated boron nitride crystallites constituting the grains.

In an alternative embodiment, the boron nitride is composed of a nanoparticle powder, that is to say grains comprising a single nano-sized crystal, for example between 10 and 500 nanometers.

The ion exchange membrane may have a thickness of between 50 and 500 μιη, for example of the order of 200 μιη to 300 μιη approximately. A relatively small thickness makes it possible to improve the ionic conduction. Nevertheless, the thickness of the ion exchange membrane is sufficient to allow the membrane to withstand high pressures in the electrolyser, if necessary. This pressure can for example reach 30 bars in an exemplary embodiment of the invention.

The term "permeability of a material" means an intrinsic quantity to the latter which measures its ability to pass a fluid or a liquid loaded with a gas and which is independent of the porosity of the material. Dihydrogen or dioxygen dissolved in water can pass through the ion exchange membrane. This phenomenon causes the presence of dihydrogen in the dioxygen and dioxygen in the dihydrogen collected.

The presence of dihydrogen in dioxygen can be a hazard. The lower explosive limit (LEL) corresponds to a presence of approximately 4% of dihydrogen in air or in oxygen. Thus, a LEL scale is defined, 100% LEL corresponding to 4% of the presence of dihydrogen in oxygen.

The permeability of dihydrogen and dioxygen through the ion exchange membrane is preferably sufficiently low to allow the dihydrogen content in oxygen to be less than 70% LEL at 30 bar and at 90 ° C. The electrolyser may include an alarm that triggers if this limit is exceeded. The assembly may comprise one or more sensors arranged at the outlet of the electrolyzer to control the levels of dihydrogen in dioxygen and dioxygen in dihydrogen, which can ensure a sufficient degree of purity of dihydrogen. In case of insufficient purity, the operation can be stopped.

Porosity means all the interstices connected or not of a material that may contain fluids, liquids or gases. Porosity is a numerical value that characterizes these interstices, corresponding to the ratio of the void volume of the material divided by the total volume. The ion exchange membrane is preferably non-porous in operation, so that it is gas tight under operating conditions. In contrast, the dry ion exchange membrane may not be non-porous. It may not be gas tight.

Each electrolytic cell may consume water, the reaction taking place in an electrolytic cell being for example the following: ₂ 0 - »H ₂ + ~ 0 ₂ . This reaction can take place in acidic medium, which facilitates the circulation of ions ¾0 ⁺ or H ⁺ protons from the anode to the cathode through the ion exchange membrane.

The electrolyte can thus comprise water and acid. The acid may be chosen from the following list, which is not limiting: sulfuric acid, phosphoric acid, carboxylic acid. The acid may have a concentration in the range of 5 to 20% by weight, for example.

This reaction can also take place in a basic medium, which makes it possible to facilitate the circulation of the OH ^" ions from the cathode to the anode through the ion exchange membrane.

The electrolyte can thus comprise water and a base. The base can be chosen from the following list, which is not limiting: potash KOH and sodium hydroxide NaOH. The base may have a concentration in the range of 5 to 30% by weight, for example.

Depending on the substance or substances that one seeks to produce, one may not have to add acid or base during use, but only water for example.

In operation, a voltage across each of the electrolytic cells is for example between 1.24 and 5 V, being for example of the order of 1.48 V or more. The current flowing in the electrolytic cells may be between 200 and 1000 A operating in operation, being for example of the order of 500 A for an active surface area of 500 cm ² .

In an alternative embodiment, at least one cell of the stack may comprise a single ion exchange membrane between the anode and the cathode. The cell may comprise two chambers, an anode chamber being defined between the anode and the membrane and a cathode chamber between the cathode and the membrane. In this configuration, the electrolyser can allow the production of H ₂ and 0 ₂ , Cl ₂ and NaOH or Cl ₂ and H ₂ .

In an alternative embodiment, at least one cell of the stack may comprise two ion exchange membranes, preferably two membranes forming between them an intermediate chamber. The cell can have three chambers. In this configuration, the electrolyser can allow the production of HCIO and NaOH or the desalination of salt water and thus the production of pure water.

At least one cell may comprise a non-selective ion exchange membrane such as a membrane comprising boron nitride, and a selective exchange membrane such as a membrane based on Nafion.

By "non-selective exchange membrane" is meant a membrane having the ability to drive both anions and cations.

Means may make it possible to establish an electrolyte circulation in the intermediate chamber, in particular to take a substance produced during operation of the electrolyzer therein.

The subject of the invention is also an electrolytic assembly comprising:

an electrolyser as defined above,

a reservoir associated with cathodic production, for example dihydrogen, to deliver the dihydrogen obtained at a given pressure, and

a reservoir associated with the anodic production, for example of oxygen, for delivering the oxygen obtained at a given pressure.

The electrolyte can be stored in each of the two tanks.

The assembly may comprise fluid communication between the two tanks, in particular at their base. The assembly may include an electrolyte level tester in each of the tanks. The fluid communication can be controlled by means of a transfer valve, as will be described later, depending on the electrolyte levels in each of the tanks.

Alternatively, and depending on the possibilities, this fluidic communication can be free and allow to ensure a balance of the electrolyte level in the two tanks. In this way, when the electrolysis produces dihydrogen and dioxygen, the ratio of the relative volumes available for the gases obtained in each of the tanks is always constant, thus respecting the stoichiometry of the reaction and thus the pressure balance. in the tanks. The interest of a connection between the tanks and to ensure the balance of liquid levels in each of the tanks.

The assembly may include a water supply. This can be done in one embodiment by the oxygen tank, in case of production of this gas. Alternatively, it can be carried out by the dihydrogen reservoir.

The electrolyte may contain, in addition to water, the following ions: hydroxyl and sulfate.

On the anode side, sulfate ions in the presence of electrical voltage transform water into gaseous oxygen and hydroxyl ions. Oxygen is recovered and the hydroxyl ions pass through the membrane to the cathode. It follows therefore a consumption of water. On the cathode side, the hydroxyl ions in the presence of the electrical voltage are transformed into hydrogen and water. The presence of sulfate ions maintains the level of the hydroxyl ion concentration.

In an exemplary embodiment of the invention, the electrolyser comprises seven successive electrolytic cells with an active surface of 500 cm ² per cell. Such an electrolyzer can consume in operation a power of 7 kW with a yield of 70%.

In another embodiment of the invention, the electrolyser comprises 70 successive electrolytic cells. Such an electrolyzer can consume in operation a power of 70 kW with a yield of 70%.

Each ion exchange membrane may have a total surface area of the order of 1050 cm ² , being for example of dimensions 30 cm × 35 cm, ie an active area of 500 cm ² .

The electrolyser may include a front flange and a rear flask that line the consecutive electrolytic cells. The front and rear flaps may include stainless steel, for example 316L stainless steel.

In the presence of gas releases not released into the atmosphere, the assembly comprises a stabilization device for stabilizing the pressure in the tanks, for example at a value between 10 and 30 bar. It is also possible to work at atmospheric pressure. The stabilization device may comprise an overflow device for each reservoir for regulating the pressure in the corresponding reservoir, and to obtain an identical pressure in each of the reservoirs, which can to avoid damaging the electrolytic cells and in particular the ion exchange membranes.

Each of the tanks can also be equipped with a control pressure sensor, as well as a degassing outlet equipped with a safety valve controlled in case of emergency.

Each of the tanks may further comprise an outlet valve allowing the user to recover the gas produced. The gases produced can be recovered for direct use or to be compressed, for example to a value of 300 bar, for example to be transported.

In the case of production of dihydrogen and oxygen, the outlet of the dihydrogen reservoir can be equipped with a device containing a catalyst making it possible to burn the residual oxygen which may be present in the dihydrogen reservoir, so as to obtain pure dihydrogen. It is also possible to use a dryer for removing residual water, which could for example be obtained by combustion of dihydrogen with the residual oxygen. The flow rate of dihydrogen obtained can then be measured as well as having a sensor to check the purity of the gas obtained.

The assembly may furthermore comprise an electrolyte temperature sensor in each of the reservoirs on the one hand, and in the electrolytic cells themselves, on the other hand, so as to control the temperature of the electrolyte and maintain a operating temperature substantially constant, for example at a value between 0 ° C and 120 ° C, or between 70 ° C and 120 ° C. It may for example be of the order of 70 ° C. Maintaining a sufficiently high operating temperature makes it possible to promote the electrochemical reaction, independently of the choice of pressure. On the other hand, it is necessary not to exceed a limit temperature beyond which the whole is likely to deteriorate. If necessary, the assembly may also include at least one or two devices for cooling the electrolyte before entering the electrolyser, optionally equipped with a temperature sensor for controlling the cooling efficiency.

The assembly may further comprise a heating device, for example useful in cold environments, depending on the temperature difference between the operating temperature and the outside temperature. The heating device may for example comprise resistors arranged in the electrolyte, for example in the electrolyte reservoirs or near the stack of cells. Alternatively, the voltage can be increased at the beginning of operation to obtain ohmic losses to heat the assembly, then return to the operating voltage.

The assembly may also include thermal insulation with the outside.

Stabilizing the temperature at an operating temperature improves the efficiency and life of the electrolyser.

The solenoid valves can be made at least partially of PVDF.

The power supply of the electrolyser is preferably housed in an electrical cabinet comprising an industrial computer for controlling the intensity and / or the voltage of the current supplied to the stack of electrolytic cells from the intensity and the network voltage.

The control cabinet can also be equipped with a remote connection allowing remote maintenance of the assembly.

The operating time of the assembly can be of the order of 10000 hours at least.

It is also possible to equip the assembly with an electrolyte retention tank.

The assembly may comprise an acidity sensor or on the contrary be devoid of it.

The invention further relates to a process for producing hypochlorous acid, using an intermediate chamber electrolyser. The anode chamber of a cell may contain water, the cathode chamber of the water and the intermediate chamber of the brine.

The invention further relates to an electrolyzer cell, comprising:

an anode,

a cathode,

two exchange membranes, in particular:

a selective exchange membrane and a non-selective exchange membrane disposed between the anode and the cathode, preferably a non-selective membrane based on activated boron nitride and preferably a selective membrane based on Nafion, the non-selective membrane; preferably protecting the selective membrane from a basic or acidic environment.

The invention will be better understood on reading the detailed description which follows, examples of embodiment and the examination of the attached drawing, in which:

FIG. 1 is a perspective view of a stack of electrolytic cells according to the invention,

FIG. 2 is an exploded view of the stack of electrolytic cells of FIG. 1;

FIG. 3 is an exploded view of an electrolytic cell,

FIGS. 4a to 41 are top views of each of the parts constituting the stack of FIGS. 1 and 2,

FIGS. 5 and 6 are diagrammatic and partial cross-sectional views of the electrolytic cell of FIG. 3,

FIGS. 7a to 7c are perspective views of assemblies according to the invention,

FIG. 8 schematically illustrates the operation of the assembly according to the invention,

FIGS. 9a and 9b illustrate the control of the temperature of the electrolyte,

FIGS. 10, 11a and 11b, and 12a to 12c schematically illustrate the management of the electrolyte flows in the assembly according to the invention,

FIG. 13 schematically represents a variant of electrolyser according to the invention,

FIG. 14 illustrates the flow of electrolyte in a stack of cells according to an alternative embodiment of the invention, and

- Figure 15 illustrates the use of holes in the various elements to define the circulation in the different rooms.

FIGS. 1 and 2 illustrate a stack 1 of electrolytic cells according to the invention. This stack comprises in the example described seven electrolytic cells 10 separated by six bipolar electrodes 4 and at the ends two end electrodes 4a.

Each of the cells comprises, as illustrated in FIGS. 3, 4a to 41, at least one ion exchange membrane 11, on each side of which are arranged porous plates 12 each surrounded by a frame 13. The two porous plates 12 may be of different sizes, as shown in Figures 4e and 4g, one may be larger than the other so as to bear against the frame surrounding the other porous plate during assembly of the stack, so as to ensure good mechanical protection of the ion exchange membrane avoiding any shear phenomenon, as shown in Figure 6. The frames 13 having a shape corresponding to the associated porous plate, they therefore each have a different shape, as shown in Figures 4d and 4h. The largest porous plate may be on the cathode side or the anode side, indifferently. Each frame 13 makes it possible to position the corresponding porous plate. It provides mechanical protection. Frames 13 may be made of titanium, plastic, for example nylon, Teflon, PFA, HDPE, or epoxy.

On both sides of the porous plates are arranged grids 14, which can be of identical size and shape, as in the example described. Each grid makes it possible to define at least partially on the one hand the anionic chamber and on the other hand the cathode chamber. The grids 14 may be made of titanium.

Each gate 14 is surrounded by a seal 15. The same seal is used for each cathode and anode chamber but arranged in an inverted direction, in order to avoid the mixing of the electrolytes circulating in the anode chamber and circulating in the cathode chamber. In the example described, the seal 15 is serrated in order to favor its crushing, which can make it possible to absorb the manufacturing differences on the thickness of the stack, deviations which are due to the manufacturing tolerance of each piece of stacking.

The grids 14 may each comprise lugs 14a configured to penetrate into the circulation ducts 15a formed in the seal 15. These lugs 14a allow support on the ion exchange membrane during clamping of the stack and make it possible to improve the sealing at this level, which avoids the mixing of gases produced.

Finally, a bipolar plate 4 closes the anode chamber of a first electrolytic cell and the cathode chamber of a second adjacent electrolytic cell. It can be made of titanium. The bipolar plate defines, with the grids 14 and the porous plates, a bipolar electrode 15 constituting on the one hand the anode of the first electrolytic cell and, on the other hand, the cathode of the second electrolytic cell, and separates the ion exchange membrane of the first electrolytic cell from that of the second electrolytic cell.

The bipolar electrode 15, in other words the two grids, the two porous plates and the bipolar piece, constitute a set of five pieces as illustrated in FIG. 5, and may be made in one piece, for example in titanium, by diffusion bonding. To do this, the five pieces are placed in a mold, pressed to keep them in position, and then heated to a high temperature, for example of the order of 1500 ° C. Then appear points of welding on the titanium, so that one can obtain a bipolar electrode in one piece.

Examples of values for the different thicknesses of an electrolytic cell will be given in the following:

porous plate and frame: 0.5 to 0.6 mm,

grid: 1.25 mm, which makes it possible to promote the circulation of the electrolyte and to avoid hydraulic head losses,

- joint: 1.5 mm, to be achieved during crushing 1.25 mm, bipolar plate: 0.5 to 0.6 mm.

ion exchange membrane: 0.2 to 0.5 mm

This gives a total cell thickness of, for example, between 4.2 and 4.8 mm.

The surface of the ion exchange membrane may be of the order of

1000 cm ² in total. The active part, that is to say the part allowing the electrochemical reaction, may be only of the order of half, for example 500 cm ² . Part of the surface of the membrane may be used as a seal, being the size of the frames associated with the porous plates.

The electrolyser comprises catalysts of the electrochemical reaction. These catalysts are preferentially arranged between the ion exchange membrane and the porous plates. The catalysts are preferably deposited on the ion exchange membrane rather than on the porous plates.

In an alternative embodiment, the catalysts comprise on the one hand a catalyst deposited on the ion exchange membrane, and on the other hand a thin layer deposited on the porous plates forming the anode and / or the cathode, as described below. above. In this case, the porous plates comprise a thin layer of a catalyst material on their side adjacent to the ion exchange membrane.

The ion exchange membrane may comprise two catalyst layers, one on each side, in the case where the cell comprises a single ion exchange membrane.

In an alternative embodiment, each ion exchange membrane comprises a single catalyst layer, in the case where the cell comprises two ion exchange membranes.

In one embodiment of the invention, the catalysts comprise on the one hand platinum on the (or one of) ion exchange membrane (s) on the hydrogen production and hydrogenation side. secondly de l ') ₂ of the (any of) membrane (s) exchange (s) ion (s) on the side of the production of oxygen.

In one exemplary embodiment of the invention, the catalysts comprise platinum on one side (or one of) ion exchange membrane (s) on the cathode side and secondly lr0 ₂ on the (or the other) ion exchange membrane (s) on the side of the anode.

An example of a process for depositing catalysts on the ion exchange membrane will now be described.

Porous plate size caches are used which are arranged on the ion exchange membrane to deposit catalyst only on that portion of the ion exchange membrane to be covered by the porous plate.

The lr0 _{2 is} deposited by mixing the latter in the form of a powder with ethanol and a liquid proton conductor used as an adhesive, such as Nafion® or activated boron nitride mixed with PTFE. The resulting liquid can be placed in a sonotrode to break the granules and is sprayed onto one side of the membrane. The membrane can be heated immediately after the projection or during the projection at a temperature of the order of 50 ° C to allow easy evaporation of the ethanol present in the mixture.

The same can be done with platinum by adding active charcoal to the mixture. In an alternative embodiment, catalysts deposited on the porous plates are used. In an exemplary embodiment, 1 mg / cm ² of platinum and 2 mg / cm ² of iridium oxide are deposited.

In the example considered, the cells are further assembled together and kept clamped between end flanges 2a and 2b by spring washers 5. These washers are in a non-flat example of embodiment, forming a spring, to adjust the pressure to which the stack of electrolytic cells is subjected so as to ensure a substantially constant resultant pressure. This pressure may be for example of the order of 100 bars. A stack of washers can be used to increase the stiffness constant. The stack of electrolytic cells can be clamped in a controlled manner by calculating the appropriate tightening torque.

The stack may comprise bipolar plates 4 all identical. The bipolar plates can in particular be all flat.

Alternatively, the stack may comprise flat bipolar plates 4 arranged between the ion exchange membranes and two bipolar plates 4a of different shape at each end, otherwise called anode collector and cathode collector. These can be configured to contact each with a copper piece 7 having a sleeve 8 for penetrating into a central orifice of the end flange 2a, 2b corresponding, to allow power supply of the stack. The copper part 7 can be insulated from the flange by an unillustrated seal and be surrounded by a seal 9 to ensure sealing and distribution of forces. The sleeve 8 may be surrounded by a Teflon® insert to protect the power supply.

The electrolyser further comprises hydraulic connectors defining two inputs and two outputs, more specifically an input 3a and an output 3b for a cathode-end chamber and an input 3c and an output 3d for an anode end chamber, the cathode and anode chambers between two successive cells communicating with each other. Each hydraulic connector may comprise an intermediate insert, for example made of titanium.

The front flange 2a, also represented in FIG. 4k, houses the electrolyte inputs and outputs, namely more precisely the electrolyte inlet 3a on the side of the production of oxygen, the exit of the charged electrolyte with oxygen 3b, as well as the entrance electrolyte on the side of the production of dihydrogen 3c, and finally the electrolyte outlet loaded with dihydrogen 3d.

The electrolyte flows in the electrolyser between the electrolytic cells according to the shape of the seals 15 arranged around the grids.

A electrolytic assembly 20 comprising the electrolyzer described above, as well as a reservoir 21 of dihydrogen to deliver the dihydrogen obtained, and a reservoir 22 of oxygen to deliver the oxygen obtained are now described with reference to FIGS. 7a, 7b and 8. In the example considered, the cross section of the hydrogen reservoir is twice the cross section of the oxygen tank, but it could be otherwise.

The circulation of the electrolyte is controlled by solenoid valves Vi, V ₂ , V ₃ , and V ₄ and the circulation provided by pumps Pi and P ₂ , for example in "all or nothing".

The electrolyte used in an exemplary embodiment can be demineralized water with 10% by weight of H ₂ SO ₄ .

The electrolyte is stored in each of the two reservoirs of dihydrogen and oxygen, the assembly comprising fluid communication between the two tanks, at their base, controlled by a transfer valve EVi, to maintain a level of equilibrium. electrolyte level and acid level in both tanks.

In view of the production reactions of dihydrogen and oxygen, there is a flow of H ₃ O ⁺ ions through the membrane. In addition, given the ability of the membrane to conduct both anions and cations, there is an inverse flow of sulfate ions across the membrane. In this way, the concentration of sulphate ions decreases on the side of the production of dihydrogen and increases on the side of the production of dioxygen. Indeed, the ion exchange membrane containing boron nitride is a non-selective ionic membrane, unlike a membrane comprising Nafion®. It thus allows the circulation of sulfate ions through the membrane, so that the concentration of these can vary in the chambers on either side of the membrane. It is therefore desirable to regulate this concentration. For this purpose, the assembly comprises a transfer valve EVi, a water supply pump P _{3 as} well as weirs DEV1 and DEV2 respectively on the side of the exit of hydrogen and the side of the exit of oxygen. The level of electrolyte in the oxygen and dihydrogen reservoirs is maintained in normal operation between a high level and a low level. As long as the electrolyte level is thus maintained between these high and low levels, the feed pump P ₃ and the transfer valve EVi remain inactive, as illustrated in FIG.

When the electrolyte level in the dihydrogen reservoir exceeds the high level due to the natural transfer of water through the membranes in normal operation of the electrolyser, the opening of the transfer solenoid valve EVi and a pressure control DEV1 by the DEV1 hydrogen gas outlet allows the levels to be rebalanced to reach either the high level of the oxygen tank, as shown in Figure 11a, or the low level of the hydrogen tank, as shown in Figure 1b. , depending on the amount of electrolyte remaining in the assembly.

When the electrolyte levels in the two reservoirs are low because of the consumption of all available water, the feed pump P ₃ starts to fill the oxygen tank with water, as shown in FIG. FIG. 12a, from a demineralized water reservoir 23.

It should be noted that during normal operation of the electrolyser, an imbalance of acid concentration between the two reservoirs of dihydrogen and oxygen is induced by the actual operation of the membranes. The anionic oxygen reservoir recovers the majority of SO ₄ ^{2 "} sulphate ions and the hydrogen reservoir is depleted of SO ₄ ^2" sulphate ions. After the filling of the oxygen tank, a transfer back and forth between the two reservoirs makes it possible to rebalance the concentrations of sulphate ion SO ₄ ^{2 "} between the two reservoirs, as illustrated in Figures 12b and 12c, thus the cycle depends on the amount of water consumed between the high and low levels The same regulation can be applied when the electrolyte used is low, except that an inversion of the transfers is applied.

The assembly may also include two condensers 24 for recovering substantially water vapors and possibly electrolyte that can escape the tanks.

The pressure at the outlet of the tanks 21, 22 can be controlled by means of the DEVi and DEV ₂ dischargers. The pressures can be adjusted to have a maximum pressure on the side of the production of dihydrogen, the pressure differential can be positive and reach up to 10 bar on the side of the production of dihydrogen. For this purpose, it is possible to use a porous plate of larger size on the side of the production of oxygen and of smaller size on the other side, taking into account the difference of the pressures. This can advantageously make it possible to obtain a purer hydrogen for a longer period.

Of course, it is not beyond the scope of the present invention if the size of the porous plates is reversed.

The user can choose the operating pressure. The pressure in the tanks can be controlled by a loop consisting of two pressure sensors PH ₂ and P0 ₂ and the two outlets DEVi and DEV ₂ . The control loop regulates the flow of gas to adjust the pressure in the tanks.

Each of the tanks 21, 22 may further comprise a safety valve 25 and an opening 26 for the initial filling of the tanks.

The outlet of the tanks 21, 22 is also equipped with a dryer 27 for removing the residual water, which could for example be obtained by combustion of dihydrogen with the residual oxygen.

The flow rates of dihydrogen and of oxygen obtained can then be measured at 28, and sensors at 29 can be measured to verify the purity of the gases obtained.

The assembly may furthermore comprise sensors for the temperatures of the electrolyte in each of the reservoirs on the one hand, and in the electrolytic cells themselves, on the other hand, so as to control the temperature of the electrolyte and of the electrolyte. maintain a substantially constant operating temperature, for example at a value between 70 and 120 ° C. Maintaining a sufficiently high operating temperature makes it possible to promote the electrochemical reaction, independently of the choice of pressure. On the other hand, it is necessary not to exceed a limit temperature beyond which the whole is likely to deteriorate. If necessary, the assembly may also include at least one or two devices for cooling the electrolyte before entering the electrolyser, optionally equipped with a temperature sensor for controlling the cooling efficiency.

The assembly comprises in the example described two cooling devices 50, each for cooling the electrolyte from the hydrogen and dioxygen tanks. Each cooling device 50 comprises in the example describes three elements: cooling pump 51, liquid-liquid heat exchanger 52 receiving hot electrolyte tanks and air-liquid heat exchanger 53, as shown in Figure 9a.

The cooling device can thus comprise two operating levels, as illustrated in FIG. 9b. In a first level 55, it is cooled by activating the cooling pump only, to circulate the electrolyte in the air-liquid exchanger before returning cooled to the stack of cells. In a second level 56, it is possible to activate both the cooling pump and the fan of the air-liquid exchanger. Finally, if this is not enough, the system is configured to automatically decrease the current. The temperature thresholds determining the levels used can be appropriately determined depending on the desired operating temperature for the assembly. The thresholds indicated in FIG. 9b are in particular only indicative.

Finally, the power supply of the electrolyser is housed in an electrical cabinet 40 comprising an industrial computer for controlling the intensity and the voltage of the current supplied to the stack of electrolytic cells from the intensity and voltage network.

The control cabinet can also be equipped with a remote connection 41 enabling remote maintenance of the assembly.

In the example just described, the power used to produce the dihydrogen and the oxygen is 5kW. Of course, it is not beyond the scope of the present invention when the power consumed is other, and the assembly is larger or smaller. By way of example, FIG. 7c illustrates an assembly configured to consume a power of 1 kW.

The invention is not limited to the production of dihydrogen and dioxygen.

The invention applies to the production of other substances and in particular of hypochlorous acid.

The invention is not limited to the presence of an exchange membrane per cell.

Thus, according to one aspect of the invention, the cell comprises at least two exchange membranes 11 between the anode and the cathode, defining an intermediate chamber I. An example of such a cell is shown in Figure 13.

In such a cell, two membranes 11 are disposed between the anode and the cathode of the cell, which may furthermore comprise all the elements described above.

Thus the cell may comprise the stack illustrated in FIG. 3, with the difference that two membranes 11 are used instead of the single membrane 11 and are separated by a frame so as to define the intermediate chamber I. In addition, Additional fluidic communications may be provided.

For example, an inlet 3g and an outlet 3f are added to allow circulating the electrolyte in the intermediate chamber I as illustrated in FIGS. 14 and 15.

The electrolyser can thus have three inputs and three outputs in the mode of replacement of the single membrane per cell by two membranes defining an additional circulation chamber I. In this case, a third tank not shown can be provided to accommodate the electrolyte .

The circulation of the electrolyte in the anode chambers A, cathode C and intermediate I can be done as illustrated in FIG. 14.

In the case of production of hypochlorous acid, water is circulated for example in the anode chamber or chambers, in the cathode chamber or chambers, for example water, in the intermediate chamber (s), for example brine (for example water / NaCl) and the hypochlorous acid is recovered in the intermediate chamber (s) and the soda in the cathode chamber (s).

Claims

1. Electrolyser for the production of at least one chemical substance, such as dihydrogen, dioxygen, chlorine or hypochlorous acid, or sodium hydroxide, by electrolysis of pure water or water containing at least one salt, base and / or acid such as NaCl, H ₂ SO ₄ , KOH or NaOH, comprising a stack of at least a first and a second consecutive electrolytic cell, each electrolytic cell (10) comprising:

an anode,

a cathode,

at least one ion exchange membrane disposed between the anode and the cathode,

the ion exchange membranes (11) of the first and second electrolytic cells being separated by a bipolar electrode (15) constituting on the one hand the anode of the first electrolytic cell and on the other hand the cathode of the second electrolytic cell .

2. Electrolyser according to the preceding claim, wherein the bipolar electrode (15) comprises a bipolar plate (4) in one piece, the bipolar plate being associated where appropriate with at least one gate (14) and at least a porous plate (12).

3. Electrolyser according to one of the preceding claims, wherein the bipolar electrode (15) is entirely integral, the bipolar plate (4), the grids (14) and the porous plates (12) being integral with each other before mounting in the electrolyzer.

4. Electrolyser according to any one of the preceding claims, wherein the bipolar electrode (15) comprises at least one of the following materials: nickel, iridium, ruthenium, palladium, cadmium, molybdenum, platinum, stainless steel, titanium, tantalum , iron alloy, nickel alloy, lead alloy, and / or a thin layer of tantalum oxide, iridium oxide, ruthenium oxide, lead oxide, ferric oxide, platinum, platinum carbon, palladium, nickel, cadmium, and / or molybdenum.

An electrolyzer according to any one of the preceding claims, wherein the anode comprises at least one of the following materials: titanium, tantalum, iridium, iron alloy, lead alloy, and / or a thin layer of oxide tantalum, iridium oxide, ruthenium oxide, lead oxide, and / or ferric oxide.

6. Electrolyser according to any one of the preceding claims, wherein the cathode comprises at least one of the following materials: nickel, iridium, palladium, cadmium, molybdenum, platinum, titanium, tantalum, iron alloy, lead alloy, nickel alloy and / or a thin layer of platinum, carbon platinum, palladium, nickel, cadmium, and / or molybdenum.

7. Electrolyser according to any one of the preceding claims, wherein the ion exchange membrane (11) comprises boron nitride, especially activated boron nitride.

8. Electrolyser according to any one of the preceding claims, wherein the ion exchange membrane (11) comprises a polymeric matrix, in particular based on PTFE.

9. Electrolyser according to any one of the preceding claims, wherein the ion exchange membrane (11) has a thickness of between 100 and 500 μιη.

10. Electrolyzer according to the preceding claim, the electrolyte comprising water and acid, water and a base or water and a salt.

11. Electrolyser according to any one of the preceding claims, a cell having a single ion exchange membrane between the anode and the cathode.

12. Electrolyser according to any one of claims 1 to 8, at least one cell of the stack comprising two ion exchange membranes (11), preferably two membranes between them an intermediate chamber (I).

13. Electrolyzer according to any one of claims 1 to 8, at least one cell comprising a non-selective ion exchange membrane such as a membrane comprising boron nitride, and a selective exchange membrane such as a Nafion-based membrane. .

14. Electrolyser according to claim 12, comprising means for establishing a flow of electrolyte in the intermediate chamber (I), in particular for the purpose of removing a substance produced during operation of the electrolyzer therein.

15. Electrolytic assembly comprising:

an electrolyser (1) according to any one of the preceding claims, a reservoir, in particular of dihydrogen (21) for storing the dihydrogen obtained, and

a reservoir, in particular of oxygen (22) for storing the oxygen obtained.

16. Assembly according to the preceding claim, wherein the electrolyte is stored in each of the two tanks.

17. An assembly according to the preceding claim, comprising a fluid communication between the two tanks, preferably at their base, preferably further controlled by a transfer valve (EVi), to allow the maintenance of a balance of the electrolyte level in the two tanks.

18. A method for producing hypochlorous acid, using an electrolyzer according to claim 12, wherein the anode chamber of a cell preferably contains water, the cathode chamber of water and the chamber. intermediate brine.

19. Electrolyser cell, comprising:

an anode,

a cathode,

two exchange membranes (11), in particular:

a selective exchange membrane and a non-selective exchange membrane (11), disposed between the anode and the cathode, preferably a non-selective membrane based on activated boron nitride and preferably a selective membrane based on Nafion; the non-selective membrane preferably protecting the selective membrane from a basic or acidic environment.