Device for generating power by salinity gradient comprising an activated carbon fabric

Abstract

The invention relates to a device for generating power, comprising: - two electrodes (1); - a stack of membranes (9), arranged between the two electrodes, comprising an alternation of membranes selectively permeable to cations (2) and membranes selectively permeable to anions (3), and such that each membrane is separated from an adjacent membrane by an intermembrane space in which an activated carbon fabric (4) is positioned; and - a device (5) making it possible to harvest the electric power generated by a potential differential existing between the two electrodes (1), the stack of membranes (9) being intended to be supplied by an electrolytic solution (7) of concentration CA in a solute and an electrolytic solution (8) of concentration CB in the same solute, CB being greater than CA, the solutions having to circulate alternately in the intermembrane spaces of the stack (9).

Description

[0001] SALINITY GRADIENT ENERGY PRODUCTION DEVICE

[0002] INCLUDING AN ACTIVATED CARBON TEXTILE

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to a salinity gradient energy production device comprising an activated carbon textile, as well as a method implementing such a device.

[0005] The invention also relates to the use of an activated carbon textile positioned between a cation exchange membrane and an anion exchange membrane in an energy production device.

[0006] STATE OF THE ART

[0007] Devices involving ion exchange processes between compartments separated by ion exchange membranes can be used to produce energy by exploiting salinity gradients.

[0008] The production of electrical energy by salinity gradient is one of the renewable energy sources with the greatest potential on a global scale.

[0009] Among the various technologies currently under consideration, the reverse electrodialysis (RED) method is based on the conversion of mixing energy into electrical energy. This technology is based on the use of membranes with selective permeability to anions (anionic membranes) or cations (cationic membranes), whose basic property is the selective transport of ions according to the sign of their charge.

[0010] A common type of RED device consists of membranes stacked between a pair of electrodes. The membrane stack consists of alternating anionic and cationic membranes, between which salt and fresh water are alternately circulated. The intermembrane spaces, i.e., the spaces within which fluids circulate, are maintained by placing spacers between the membranes. The circulation of alternating salt and fresh water between these membranes, in other words the establishment of a salinity gradient on either side of each of these membranes, results in selective ion fluxes across each of these membranes.For example, sodium ion flows through cationic membranes toward the cathode and chlorine ion flows through anionic membranes toward the anode, creating an electrochemical potential difference between the two faces of each membrane, commonly referred to as the membrane potential difference. At the ends, electrode systems convert the ionic current into an electric current, and an external electrical circuit ensures the transfer of electrons from the anode to the cathode. The resultant membrane potential differences therefore produce an electric current that can be used by a device placed on the circuit connecting the electrodes.

[0011] One of the problems with salinity gradient power generation devices, such as current RED devices, is that they have low power generation capacity.

[0012] This low energy production capacity is due in particular to the fact that current membranes develop electrical powers per unit of membrane surface ( / .e. membrane powers) of only a few W / m 2 of membrane.

[0013] The low power generation capacity of these types of RED devices is also due to the resistances that different elements of the system oppose to ionic flows. This resistance depends mainly on the membrane resistance, the ionic conductivity of the electrolyte solution, in particular the solution with the lowest electrolyte concentration, and the intermembrane distance. In particular, maintaining a spacing of several hundred micrometers between the membranes by means of spacers is necessary to allow fluid flow within the membrane stack but contributes significantly to the overall resistance of the system.

[0014] The spacer can also contribute to increasing the resistance of the device and affect the overall performance of the device in terms of power output.

[0015] The spacers conventionally used in such devices are nylon-type fabric spacers.

[0016] The size of the fabric filaments, their arrangement and their spacing are important parameters to optimize the performance of such spacers (Gurreri et al., Journal of membrane science, 497 (2016) 300-317).

[0017] However, RED devices implementing such spacers develop powers that remain low.

[0018] Another alternative is to implement thin spacers, typically of the order of 100 pm or less, which makes it possible to increase the power developed but is not industrially applicable due in particular to high pressure losses.

[0019] In view of the above, there is therefore still a need to improve the electrical power generated by devices for producing electrical energy from a concentration gradient, in particular by developing spacers making it possible to maintain an intermembrane space of sufficient thickness but not inducing excessive resistance.

[0020] SUMMARY OF THE INVENTION

[0021] The subject of the invention is a device for the production of energy comprising:

[0022] - two electrodes (1),

[0023] - a stack of membranes (9), arranged between the two electrodes, comprising an alternation of membranes selectively permeable to cations (2) and membranes selectively permeable to anions (3), and such that each membrane is separated from a neighboring membrane by an intermembrane space in which an activated carbon textile (4) is positioned

[0024] - a device (5) for harvesting the electrical energy generated by a potential differential existing between the 2 electrodes (1), the stack of membranes (9) being intended to be supplied by an electrolytic solution (7) of concentration CA in a solute and an electrolytic solution (8) of concentration CB in the same solute, CB being greater than CA, said solutions having to circulate alternately in the intermembrane spaces of said stack (9).

[0025] Advantageously, the activated carbon textile has a thickness ranging from 100 μm to 1,000 μm, preferably from 200 μm to 600 μm.

[0026] Advantageously, the activated carbon textile has a specific surface area SBET ranging from 200 to 3,000 m 2 / g, preferably 1,000 to 2,000 m 2 / g.

[0027] The invention also relates to a method for producing electrical energy using a device as described above comprising the following steps: i) supplying the stack (9) of membranes with an electrolytic solution (7) of concentration CA in a solute and an electrolytic solution (8) of concentration CB in the same solute, CB being greater than CA, so that said solutions circulate alternately in the intermembrane spaces of said stack (10); ii) allowing the electrolytes to diffuse from the intermembrane spaces supplied by the electrolytic solution (7) of concentration CB to the adjacent intermembrane spaces supplied by the electrolytic solution (8) of concentration CA; ll) capturing the electrical energy generated by the potential differential existing between the two electrodes (1), using the device (5). Advantageously, the concentration ratio CB / CA ranges from 2 to 100, preferably from 5 to 50.

[0028] Advantageously, the electrolytic solutions (7) and (8) are aqueous solutions comprising a solute chosen from alkali metal halides or alkaline earth metal halides, preferably chosen from NaCl, KG, CaCh and MgCh, more preferably NaCl.

[0029] Another subject matter relates to the use of an activated carbon textile positioned between a membrane selectively permeable to cations and a membrane selectively permeable to anions in a device intended for the implementation of an energy production process.

[0030] Other aspects of the invention are as described below and in the claims.

[0031] DESCRIPTION OF FIGURES

[0032] [Fig. 1]: shows in exploded view the 2 electrodes (1) and 5 membranes positioned between the two electrodes with a stack of membranes (9) comprising an alternation of membranes selectively permeable to cations (2) and membranes selectively permeable to anions (3), with an activated carbon textile (4) positioned in the intermembrane space between 2 neighboring membranes according to the device of the invention.

[0033] [Fig. 2]: schematically represents in section the reverse electrodialysis device (RED) used in example 1 comprising:

[0034] - two electrodes (1),

[0035] - a stack of 7 membranes, arranged between the two electrodes, comprising an alternation of membranes selectively permeable to cations (2) and membranes selectively permeable to anions (3), and such that each membrane is separated from a neighboring membrane by an intermembrane space in which an activated carbon textile (4) is positioned

[0036] - a device (5) for harvesting the electrical energy generated by a potential differential existing between the 2 electrodes.

[0037] A redox solution (6) circulates between the electrodes (1). The stack of membranes is supplied with an electrolytic solution (7) of concentration CA in a solute and an electrolytic solution (8) of concentration CB in the same solute, CB being greater than CA, said solutions circulating alternately in the intermembrane spaces of the stack. DETAILED DESCRIPTION OF THE INVENTION

[0038] The aim of the present invention is to overcome the drawbacks of the prior art and to provide a device using a spacer which is simple to implement, inexpensive to manufacture and makes it possible to obtain improved performance.

[0039] Another object of the invention is to provide a method for producing electrical energy using the device of the invention.

[0040] These aims are achieved by the invention which will be described below.

[0041] DEVICE

[0042] The first subject of the invention is a device for the production of energy comprising:

[0043] - two electrodes (1);

[0044] - a stack of membranes (9), arranged between the two electrodes (1), comprising an alternation of membranes selectively permeable to cations (2) and membranes selectively permeable to anions (3), and such that each membrane is separated from a neighboring membrane by an intermembrane space in which an activated carbon textile (4) is positioned, i.e. a spacer;

[0045] - and a device (5) for harvesting the electrical energy generated by a potential differential existing between the 2 electrodes (1), the stack of membranes (9) being intended to be supplied by an electrolytic solution (7) of concentration CA in a solute and an electrolytic solution (8) of concentration CB in the same solute, CB being greater than CA, said solutions having to circulate alternately in the intermembrane spaces of said stack (9).

[0046] In this embodiment, the difference in CA and CB concentrations in the same solute causes the mobility of electrolytes from the more concentrated solution to the less concentrated solution.

[0047] Spacer

[0048] Surprisingly and unexpectedly, the inventors discovered that an activated carbon textile, by increasing ionic conduction, makes it possible to improve the performance of energy production devices in terms of electrical power generated, compared to the spacers conventionally used in such devices. The spacer according to the invention is an activated carbon textile (4).

[0049] For the purposes of the present invention, the term "activated carbon textile" means a sheet of a woven, knitted or non-woven textile comprising activated carbon fibers.

[0050] The activated carbon textile may be a sheet of a woven textile comprising yarns based on activated carbon fibers, or a sheet of a knitted textile comprising at least one yarn based on activated carbon fibers, or a sheet of a non-woven textile comprising activated carbon fibers.

[0051] A nonwoven textile is an essentially planar fibrous assembly, having a nominal level of structural integrity imparted by means of physical and / or chemical processes, excluding weaving, knitting or papermaking. In this sense, the nonwoven textile of the invention meets the definition according to ISO 9092 of April 2019 of a nonwoven textile. By fibrous assembly, it is thus understood the assembly of fibrous materials such as fibers, continuous filaments or chopped yarns of any length or section. The nonwoven textile may include yarns obtained from activated carbon fibers.

[0052] A woven textile is an essentially flat assembly of threads parallel to each other, called warp threads, crossed by threads called weft threads, said threads preferably being intermingled by weaving.

[0053] By activated carbon fiber yarn, it is meant that the yarn includes activated carbon fibers.

[0054] Activated carbon non-woven fabric can be made of activated carbon fibers.

[0055] The activated carbon nonwoven fabric may be a composite nonwoven fabric comprising activated carbon fibers and fibers of one or more materials other than activated carbon.

[0056] The activated carbon nonwoven fabric may be a composite nonwoven fabric consisting of activated carbon fibers and fibers of one or more materials other than activated carbon.

[0057] The activated carbon woven or non-woven fabric may be made of yarns comprising activated carbon fibers. The yarns of the activated carbon woven or non-woven fabric may be composite yarns comprising activated carbon fibers and fibers of one or more materials other than activated carbon.

[0058] The yarns of the woven or non-woven activated carbon textile may be composite yarns made of activated carbon fibers and fibers of one or more materials other than activated carbon.

[0059] The yarns of the woven or non-woven activated carbon textile may be yarns comprising activated carbon fibers on the one hand and yarns comprising fibers of one or more materials other than activated carbon on the other hand.

[0060] The yarns of the woven or non-woven activated carbon textile may be yarns made of activated carbon fibers on the one hand and yarns comprising fibers of one or more materials other than activated carbon on the other hand.

[0061] The yarns of the woven or non-woven activated carbon textile may be yarns comprising activated carbon fibers on the one hand and yarns made of fibers of one or more materials other than activated carbon on the other hand.

[0062] The yarns of the woven or non-woven activated carbon textile may be yarns made of activated carbon fibers on the one hand and yarns made of fibers of one or more materials other than activated carbon on the other hand.

[0063] Advantageously, the woven or non-woven activated carbon textile is made of threads made of activated carbon fibers.

[0064] The non-woven activated carbon textile may, for example, be an activated carbon felt. In a particular embodiment, the activated carbon felt is obtained by needling fibers.

[0065] The at least one yarn obtained from activated carbon fibers of the activated carbon knitted textile is as described above.

[0066] When the activated carbon textile comprises fibers of one or more materials other than activated carbon, the fibers of the material(s) other than activated carbon can make it possible to modify the mechanical properties of the activated carbon textile by increasing, for example, its rigidity.

[0067] Activated carbon textile can be obtained by assembling activated carbon fibers.

[0068] Activated carbon textile can be obtained by assembling activated carbon fibers and fibers of one or more materials other than activated carbon.

[0069] The activated carbon textile can also be obtained from a textile comprising fibers of an activated carbon precursor, said textile being subjected to a subsequent treatment to obtain said activated carbon textile. The treatments for obtaining said activated carbon film are well known to those skilled in the art. These are in particular thermochemical processes carried out at temperatures between 200°C and 3000°C.

[0070] In this embodiment, when the textile comprises fibers of one or more other materials different from the activated carbon precursor, the material(s) different from the activated carbon are advantageously temperature-resistant materials, preferably silica or glass.

[0071] Advantageously, the mass of the activated carbon fibers of the activated carbon textile is equal to at least 50% of the total mass of the activated carbon textile.

[0072] When the activated carbon textile is obtained from a textile comprising fibres of an activated carbon precursor, said textile then being subjected to further treatment to obtain said activated carbon textile, the mass of the activated carbon fibres relative to the total mass of the activated carbon textile can be calculated from the mass ratio of the different fibres or yarns used to manufacture the textile and the mass of the textile before and after treatment. Indeed, when the textile comprises silica or glass fibres for example, their mass remains unchanged after said treatment. The impact of the treatment on the mass of each type of fibre or yarn of the textile can also be evaluated separately.

[0073] Advantageously, the activated carbon textile has a thickness ranging from 100 μm to 1,000 μm, preferably from 200 μm to 600 μm.

[0074] When the thickness of the activated carbon textile is less than 100 μm, the flow of electrolytic solutions in the intermembrane spaces may be hindered, pressure drop phenomena may occur and the power required to circulate the electrolytic solutions may be greatly increased. When the thickness of the activated carbon textile is greater than 1000 μm, the electrical resistance related to the thickness of the intermembrane compartment is too high and affects the efficiency of the device.

[0075] In the present invention, the specific surface area of ​​the textile is measured by the BET (Brunauer, Emmett and Teller) method according to the ISO 9277 standard of September 2010.

[0076] Activated carbon textile can have a specific surface area of ​​1 m 2 / g at 3,000 m 2 / g.

[0077] Advantageously, the activated carbon textile has a specific surface area of ​​200 m 2 / g at 3,000 m2 / g, preferably 1000 m 2 / g at 2000 m 2 / g.

[0078] Activated carbon textile can have a specific surface area of ​​1 m 2 / g at 10 m 2 / g or 1 m 2 / g at 5 m 2 / g.

[0079] The activated carbon textile of the invention is a material having interstitial volumes allowing the circulation of electrolytic solutions. It may have a percentage of interstitial volume of at least about 50% and preferably at least about 60%. In the present invention, the percentage of interstitial volume is defined as the ratio between the total interstitial volume Vinterstitiei of a sample and the total volume occupied by the sample VE: P= Vinterstitiei / VE- The total interstitial volume is determined indirectly by differential weighing of a sample impregnated and a sample not impregnated with a wetting liquid of known density, such as an alcohol. More precisely, nterstitiei can be measured according to the following method: a) providing a sample of mass rriE; b) impregnating the sample of step a) with a liquid of density pL; c) determine the mass rriEi of the impregnated sample from step b); d) calculate V interstitiei according to formula V in terstitiei=(mEi - m E ) / pL.

[0080] The volume VE can be determined as the product of the sample surface area and its thickness.

[0081] In one embodiment of the present invention, the activated carbon textile has a density ranging from 0.05 to 0.20 g / cm 3 . In the invention, the density of the activated carbon textile is defined as the ratio between the mass of a sample mE and its volume VE: d =ITIE / VE. In the invention, the term "activated carbon fibers" refers to fibers obtained from a carbon precursor according to methods well known to those skilled in the art, in particular thermochemical methods carried out at temperatures between 200°C and 3000°C.

[0082] Advantageously, the carbon precursor is of the polymer or macromolecule type, preferably a carbon precursor chosen from phenol-aldehyde resins, polyacrylonitrile (PAN), rayon, lignin, or one of their mixtures.

[0083] Phenol-aldehyde resins, polyacrylonitrile (PAN), and rayon and their blends are preferred.

[0084] Among the processes implemented to obtain activated carbon fibers from carbon precursor, let us cite by way of illustration the process comprising the following steps: optionally a step of pre-oxidation of the carbon precursor, calcination or carbonization, physical activation which may consist of calcination in the presence of gas such as carbon dioxide, water or oxygen, or chemical activation by means of an activating agent, such as an acid like phosphoric acid or a base like potassium hydroxide.

[0085] According to a variant of this process, the precursor can be directly activated before a calcination step.

[0086] Advantageously, the activated carbon fibers consist essentially of carbon, that is to say they preferably consist of at least 80 mol% carbon, preferably at least 90 mol% carbon, more preferably at least 95 mol% carbon, the remainder being elements such as oxygen, nitrogen and hydrogen. Advantageously, the activated carbon fibers comprise from 80 to 100% by weight of carbon, from 0 to 10% by weight of nitrogen, from 0 to 10% oxygen and from 0 to 5% by weight of hydrogen.

[0087] The activated carbon fibers of the textile advantageously have a diameter of less than 50 pm, preferably less than 20 pm, particularly preferably less than 10 pm. The fibers of the activated carbon textile advantageously have a diameter greater than 0.1 pm, preferably greater than 1 pm. The activated carbon fibers may have a diameter ranging from 0.1 pm to 50 pm, preferably ranging from 1 to 20 pm, particularly preferably ranging from 1 to 10 pm.

[0088] The diameter of the activated carbon fibers in the textile can be determined using a scanning electron microscope (SEM).

[0089] Advantageously, the surface charge density of activated carbon is between 0.1 mmol / g and 3 mmol / g. The surface charge density is measured by dosimetry.

[0090] Advantageously, the surface charge density of the activated carbon is between 10' 5 meq / m 2 and 10' 2meq / m 2 .

[0091] When the charged groups of the activated carbon are monovalent ionic groups, 1 meq of surface charge corresponds to 1 mmol of surface charge, or 1 mmol of charged group. In this case, the surface charge density of the activated carbon is thus advantageously between 10' 5 mmol / m 2 and 10' 2 mmol / m 2 .

[0092] In the device according to the invention, each membrane is separated from a neighboring membrane by an intermembrane space in which an activated carbon textile (4) is positioned as described above.

[0093] The activated carbon textile according to the invention is simple, inexpensive to manufacture and makes it possible to improve the performance of energy production devices compared to the spacers conventionally used in such devices.

[0094] The thickness of the intermembrane space between 2 membranes can be controlled by means of a seal or any other system making it possible to control the thickness of the intermembrane space, to ensure its sealing while allowing the circulation of electrolytic solutions and to position the activated carbon textile according to the invention.

[0095] Membrane

[0096] For the purposes of the present invention, the term "membrane" means a material in the form of a sheet permeable to at least some of the ions in the electrolytic solution. The expression "selective permeability to anions or cations" means that the membrane allows the majority of anions or cations to pass through it, and inhibits or strongly delays the passage of ions of opposite charge.

[0097] Advantageously, the membrane is also permeable to the solvent of the electrolytic solution, preferably water.

[0098] Any type of membrane selectively permeable to anions (3) or cations (2) is compatible with the invention.

[0099] The membrane selectively permeable to anions (3) or cations (2) may be in the form of a homogeneous layer of a material or a stack of several layers formed of different materials. Advantageously, the membrane selectively permeable to anions (3) or cations (2) of the invention is an ion exchange membrane, that is to say a membrane formed of at least one mineral or organic material carrying ionogenic groups, also called ion exchange groups, which give the membrane its property of selective permeability to ions. For the purposes of the invention, an ionogenic group is a chemical group which, when placed in a liquid, has the ability to release an ion, called a counter-ion, and to fix an ion of the same charge contained in this liquid.

[0100] In one embodiment, the membrane comprises an organic polymer carrying ionogenic groups, commonly referred to as an "ion exchange resin". The membrane of the invention can thus be formed from a matrix of an insoluble polymer in which an ion exchange resin has been included, or from a matrix of an insoluble polymer onto which ionogenic groups have been grafted.

[0101] In one embodiment, the insoluble polymer is typically a hydrocarbon matrix advantageously chosen from a polysaccharide matrix such as a cellulose or dextran matrix, a polystyrene matrix, a polytetrafluoroethylene matrix, or a matrix of a copolymer such as a copolymer of styrene and divinylbenzene.

[0102] In one embodiment, the cation-selectively permeable membrane (2) comprises cation exchange groups advantageously chosen from the epoxide group, the hydroxyl group, the carbonyl group, the carboxyl group, the sulfonate group -SO , the carboxyalkylate group R-CC with R a C1-C4 and preferably C1 alkyl, the aminodiacetate group -N(CH2CO2')2, the phosphonate group PO3 2 ' ; the amidoxin group -C(=NH2)(NOH), the aminophosphonate group -CFk-NH-CFk-POs 2 ' , the thiol group -SH, and mixtures thereof.

[0103] In one embodiment, the anion-selectively permeable membrane (3) comprises anion exchange groups advantageously chosen from the quaternary ammonium group -N(R)3 + with R a C1-C4 alkyl, the tertiary ammonium group -N(H)R)2 + with R a C1-C4 alkyl, preferably a C1 alkyl, the dimethylhydroxyethylammonium group -N(C2H4OH)CH3)2 +, and mixtures thereof. Advantageously, the thickness of the membrane is between 10 pm and 200 pm, preferably between 10 and 100 pm, preferably between 10 pm and 75 pm.

[0104] The membrane advantageously comprises channels which connect the two faces of the membrane. The channels can pass right through the membrane or form a network of channels allowing the circulation of ions and / or solvent between the two faces of the membrane. The channels of the membrane of the invention advantageously have an average diameter of between 1 and 500 nm, preferably between 1 and 100 nm, more preferably between 2 and 100 nm, more preferably between 10 and 100 nm.

[0105] In a particular embodiment of the invention, the membrane has a density of channels per unit of membrane surface area greater than 10 5 channels per cm 2 membrane, preferably greater than 10 8 channels per cm 2 of membrane.

[0106] The channels of the membrane of the invention may have any type of morphology, for example a tubular, asymmetrical conical type, or neck-shaped morphology.

[0107] In a particular embodiment, at least a portion of the inner surface of the membrane channels is coated with boron nitride, a compound based on carbon, boron and nitrogen, or a titanium oxide, preferably titanium dioxide. These coatings have the effect of increasing the surface charge of the inner surface of the channels and significantly improving the electrical power generated by the devices comprising such nanofluidic membranes with a high surface charge density, as detailed in international applications WO 2014 / 0606902017 and WO 2017 / 037213. In this embodiment, the membranes advantageously have channels having an average diameter of between 2 and 100 nm. In one embodiment, the membrane of the invention is self-supporting.For the purposes of the present invention, the term "self-supporting membrane" means a membrane which does not need to be supported by one or more rigid supports (for example sheets of a porous solid material) or deformable supports (for example sheets of a polymer material) to ensure its mechanical integrity.

[0108] In another embodiment, as detailed in international application WO2021 / 234296, the membrane comprises at least one layer formed from a cellulosic material comprising a network of nanofibers and / or crosslinked cellulose microfibers.

[0109] The device according to the invention comprises a stack of membranes (9), arranged between the two electrodes (1), comprising an alternation of membranes selectively permeable to cations (2) and membranes selectively permeable to anions (3) as described above, and such that each membrane is separated from a neighboring membrane by an intermembrane space in which an activated carbon textile is positioned as described above.

[0110] By stacking of membranes according to the invention, we mean an arrangement of the membranes as illustrated in Figures 1 and 2, that is to say that the membranes are arranged between the 2 electrodes (1) positioned opposite each other and are in different parallel planes.

[0111] In a particular embodiment of the invention, the device may comprise N+1 membrane and N intermembrane spaces, N being an even whole number, in particular between 2 and 1000, preferably between 2 and 250, for example between 2 and 100.

[0112] We can also talk about pairs of membranes of the device. In this case, the number of pairs of membranes is equal to N / 2.

[0113] The device according to the invention comprises a pair of electrodes (1) and a device (5) for harvesting the electrical energy generated by the potential differential existing between the 2 electrodes (1).

[0114] Different types of electrodes can be used in the device.

[0115] In the case where the electrolytic solutions are NaCl solutions, any type of electrode capable of collecting the flow of Na+ or Cl- ions can be used, and preferably electrodes composed of Silver and Silver Chloride (Ag / AgCl), Carbon and Platinum (C / Pt-), Carbon (C-), Graphite or even Iron complexes of the type [Fe(CN)e] 4_ / [Fe(CN)6] 3 -.

[0116] The electrodes can in particular be circulation electrodes (in English "redox-flow") as illustrated in Figure 2. The principle of these electrodes is based on an oxidation reaction and a reduction reaction at each of the electrodes.

[0117] Among the different possible RedOx couples, let us mention the couples FeCb / FeCb, K3Fe(CN)6 / K4Fe(CN)6 , Fe(III)-EDTA / Fe(II)-EDTA and Na3Fe(CN)6 / Na4Fe(CN)6.

[0118] In addition to the RedOx couple, the recirculating solution (6) can include a solute solution of concentration (CA+CB) / 2.

[0119] The electrodes can also be capacitive flow electrodes comprising a dispersion of conductive particles called "slurry" in the medium comprising the solute. The conductive particles can be activated carbon particles, carbon nanotubes or any other conductive agent.

[0120] Each electrode can be in contact with a membrane selectively permeable to ions of the same sign, that is, each electrode can be in contact with a membrane selectively permeable to cations or each electrode can be in contact with a membrane selectively permeable to anions.

[0121] The electrodes (1) are connected together to a device (5) for collecting, that is to say for circulating and capturing the electrical energy spontaneously generated by the potential differential existing between them. This device forms an external electrical circuit advantageously comprising a current collector and an electrical cable, a battery, a bulb or any other form of electrical consumer.

[0122] An electrolytic solution of concentration CA in a solute and an electrolytic solution of concentration CB in this same solute, CB being greater than CA, are circulated in the intermembrane spaces of the membrane stack (9). The solutions circulate alternately in the stack (9), which means that the electrolytic solution of concentration CA in a solute circulates in the intermembrane space between 2 membranes and that the electrolytic solution of concentration CB in this same solute circulates in the adjacent intermembrane space(s).

[0123] An osmotic flow is generated between two adjacent intermembrane spaces, preferably by diffusio-osmosis, i.e. without any osmotic pressure appearing.

[0124] In a particular embodiment, the concentration gradient can be obtained and / or modulated via a temperature gradient between the two electrolytic solutions, which influences the solubility of the electrolyte as a function of temperature.

[0125] In the context of the present invention, the concentration ratio Rc designates the ratio of the concentration of the most concentrated solution to the concentration of the least concentrated solution, i.e. the CB / CA ratio.

[0126] Preferably, the CB / CA concentration ratio ranges from 2 to 100, preferably from 5 to 50. Electrolytic solutions are aqueous solutions comprising electrolytes. The electrolytes may be of any chemical nature as long as they dissolve in the solution in the form of ions. Preferably, these ions come from dissolved salts such as NaCl, KG, CaCh and MgCh. Electrolytic solutions may be:

[0127] - synthetic solutions;

[0128] - natural solutions, such as fresh water from lakes or rivers, groundwater, brackish water, seawater;

[0129] - industrial production water, oil production water or biological solutions.

[0130] Particularly advantageously, the electrolyte is NaCl.

[0131] Advantageously, the CB solution is a seawater solution and the CA solution is a freshwater solution.

[0132] Advantageously, the device comprises means for switching the flow of the electrolytic solutions of concentration CA and CB, which are produced according to a mode (1) in which the electrolytic solution of concentration CA in a solute circulates in the intermembrane space between 2 membranes and the electrolytic solution of concentration CA in this same solute circulates in the adjacent intermembrane space(s) and a mode (2) in which the circulation of the solutions CA and CB is reversed.

[0133] To improve the osmotic flow generated on either side of the membrane according to the invention, the pH of the solutions can be adjusted according to the isoelectric point of the material(s) constituting the membrane.

[0134] In the context of the present invention, pHiso means the pH of the isoelectric point of the material(s) constituting the membrane. pHiso is measured by methods known to those skilled in the art, in particular by the acid / base potentiometric titration method.

[0135] Even more favorably, to increase the asymmetry of the device and amplify the quantity of electrical energy produced by the device, a pH gradient can also be established between the two reservoirs, the pH difference between the two solutions will be greater than 1, preferably greater than 2.

[0136] PROCESS FOR PRODUCING ELECTRICAL ENERGY

[0137] A second subject of the invention relates to a method for producing energy using a device as described above comprising the following steps i) supplying the stack of membranes (9) with an electrolytic solution (7) of concentration CA in a solute and an electrolytic solution (8) of concentration CB in the same solute, CB being greater than CA, so that said solutions circulate alternately in the intermembrane spaces of said stack (9); ii) allowing the electrolytes to diffuse from the intermembrane spaces supplied by the electrolytic solution (7) of concentration CB to the adjacent intermembrane spaces supplied by the electrolytic solution (8) of concentration CA; ll) capturing the electrical energy generated by the potential differential existing between the two electrodes (1), using the device (5).

[0138] Steps i) and ii) are preferably implemented by supplying the electrolytic solution of concentration CA and the electrolytic solution of concentration CB in the form of a continuous flow.

[0139] The flow rate of the electrolytic solutions (7) and (8) is adjusted to optimize the salinity gradient of the device by adjusting the residence time of the electrolytic solutions within the device.

[0140] Advantageously, the electrolytic solutions (7) and (8) are at a temperature between 10°C and 40°C, preferably at a temperature between 15°C and 25°C.

[0141] Advantageously, the method according to the invention is an energy production method exploiting the difference in salinity between a seawater solution and a freshwater solution.

[0142] USING THE SPACER

[0143] Another object of the invention relates to the use of an activated carbon textile as described above, positioned between a cation exchange membrane and an anion exchange membrane in an energy production device.

[0144] Advantageously, activated carbon textile is used as a spacer.

[0145] The power generation device is as described above.

[0146] EXAMPLES

[0147] The present invention will be better understood by reading the following examples which illustrate the invention without limitation. The device and method illustrated are a device and method for producing energy by reverse electrodialysis.

[0148] The device used is illustrated in Figure 2.

[0149] The device comprises 7 cationic (2) and anionic (3) membranes each having a surface area of ​​1 cm 2 .

[0150] The electrodes (1) are connected by an external electrical circuit comprising a voltmeter.

[0151] The raw materials used in the examples are listed below:

[0152] Membranes:

[0153] - Cation exchange membrane (2) marketed by Fumasep under the reference FKS 30;

[0154] - Anion exchange membrane (3) marketed by Fumasep under the reference FAS. Spacers:

[0155] - Nylon marketed by the company SEFAR under the reference SEFAR NITEX 06-335 / 48 for nylon with a thickness of 300pm or SEFAR NITEX 06-1140 / 66 for nylon with a thickness of 500pm;

[0156] - Activated carbon felt (4) obtained from a polyacrylonitrile precursor with a thickness of 300pm or 500pm.

[0157] There are 6 spacers.

[0158] Saline solutions for feeding the device

[0159] A seawater solution with a NaCI concentration of 35g / l (CB concentration solution) and a NaCI concentration solution of 1.17g / l (CA concentration solution) are used (corresponding respectively to solutions 8 and 7 in Figure 2).

[0160] The temperature of saline solutions is 25°C.

[0161] The flow rate of saline solutions is 1 ml / min.

[0162] Redox Solution

[0163] The aqueous solution for rinsing the electrode (6) comprises 0.25 M Na3Fe(CN)e, 0.25 M Na4Fe(CN)6 and (CB + CA) / 2 in NaCI.

[0164] The temperature of the rinse solution is 25°C.

[0165] The flow rate of the solution is 0.25 ml / min.

[0166] Example 1: Preparation of devices D1 and D2 in accordance with the invention and comparison with comparative devices C1 and C2 not in accordance with the invention. The results are presented in Table 1.

[0167] [Table 1] with: - AV the potential measured by a voltmeter when the external circuit is open;

[0168] - 1 the current measured by an ammeter when the external circuit is closed;

[0169] - R the surface resistance of the device calculated by Ohm's law: R s = U / IS ;

[0170] - Pmax = V 2 / 4R Table 1 shows that by using a 500 pm activated carbon felt spacer according to the invention instead of a nylon spacer of the same thickness conventionally used in power generation devices, the power developed per unit area is multiplied by a factor greater than 4.

[0171] When the thickness of the spacer is 300 pm, the power gain obtained with the activated carbon spacer according to the invention is 2.5.

Claims

CLAIMS 1. Device for the production of energy comprising: - two electrodes (1), - a stack of membranes (9), arranged between the two electrodes, comprising an alternation of membranes selectively permeable to cations (2) and membranes selectively permeable to anions (3), and such that each membrane is separated from a neighboring membrane by an intermembrane space in which an activated carbon textile (4) is positioned - a device (5) for harvesting the electrical energy generated by a potential differential existing between the 2 electrodes (1), the stack of membranes (9) being intended to be supplied by an electrolytic solution (7) of concentration CA in a solute and an electrolytic solution (8) of concentration CB in the same solute, CB being greater than CA, said solutions having to circulate alternately in the intermembrane spaces of said stack (9).

2. Device according to claim 1 characterized in that the activated carbon textile has a thickness ranging from 100 pm to 1000 pm, preferably from 200 pm to 600 pm.

3. Device according to any one of the preceding claims, characterized in that the activated carbon textile has a specific surface area SBET ranging from 200 to 3,000 m 2 / g, preferably 1,000 to 2,000 m 2 / g.

4. Method for producing electrical energy using a device as described in any one of the preceding claims comprising the following steps: i) supplying the stack of membranes (9) with an electrolytic solution (7) of concentration CA in a solute and an electrolytic solution (8) of concentration CB in the same solute, CB being greater than CA, so that said solutions circulate alternately in the intermembrane spaces of said stack (9) ii) allowing the electrolytes to diffuse from the intermembrane spaces supplied by the electrolytic solution (7) of concentration CB to the adjacent intermembrane spaces supplied by the electrolytic solution (8) of concentration CA; iii) capturing the electrical energy generated by the potential differential existing between the two electrodes (1), using the device (5).

5. Method according to claim 4, characterized in that the CB / CA concentration ratio ranges from 2 to 100, preferably from 5 to 50.

6. Method according to claim 4 or claim 5, characterized in that the electrolytic solutions (7) and (8) are aqueous solutions comprising a solute chosen from alkali metal halides or alkaline earth metal halides, preferably chosen from NaCl, KG, CaCh and MgCh, more preferably NaCl.

7. Use of an activated carbon textile positioned between a membrane selectively permeable to cations and a membrane selectively permeable to anions in a device intended for implementing an energy production process.

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