Device for generating electricity from a salinity gradient with activated carbon cloth

Abstract

The present invention relates to a device for generating electricity, comprising: two electrodes (1); a stack of membranes (9) arranged between the two electrodes, the stack of membranes (9) including alternating membranes (2) selectively permeable to cations and membranes (3) selectively permeable to anions, each membrane being separated from the adjacent membrane by an inter-membrane space in which an activated carbon cloth (4) is positioned; and a device (5) that allows harvesting the electricity generated by the potential difference existing between the two electrodes (1), the stack of membranes (9) being arranged such that the concentration of solute C A Electrolyte solution (7) and the same solute concentration C B and an electrolyte solution (8) of C B is C A The stack (9) contains a device for generating electricity, which is larger than the stack (9) and the solution must alternately circulate within the intermembrane spaces.

Description

[Technical Field]

[0001] The present invention relates to a device for generating electricity from a salinity gradient comprising an activated carbon cloth, as well as a process for using such a device. The present invention also relates to the use of an activated carbon cloth positioned between a cation exchange membrane and an anion exchange membrane in a power generation device. [Background technology]

[0002] Devices involving an ion exchange process between compartments separated by ion exchange membranes can be used to generate electricity by exploiting salinity gradients.

[0003] Electricity generation using salinity gradients is one of the most promising renewable energy sources on a global scale.

[0004] Among the various technologies currently under consideration, the reverse electrodialysis (RED) method is based on converting the energy of the mixture into electrical energy. This technology is based on the use of membranes that are selectively permeable to anions (anion membranes) or cations (cation membranes), whose fundamental property is the selective transport of ions according to the sign of their charge.

[0005] A common type of RED device consists of membranes stacked between a pair of electrodes. The membrane stack includes alternating anionic and cationic membranes between which saltwater and freshwater alternate. The intermembrane space, or the space through which the fluid circulates, is maintained by spacers between the membranes. The alternating circulation of saltwater and freshwater between these membranes—in other words, the establishment of a salinity gradient on either side of each membrane—results in selective ion flow across each membrane. For example, sodium ions flow through the cationic membrane toward the cathode, and chloride ions flow through the anionic membrane toward the anode, creating a difference in electrochemical potential between the two sides of each membrane, commonly referred to as the transmembrane potential. At the ends, an electrode system converts the ionic current into an electric current, and an external electrical circuit transfers electrons from the anode to the cathode. The resulting difference in transmembrane potential generates an electrical current that can be used by devices placed in a circuit connecting the electrodes.

[0006] One of the problems faced by devices for generating electricity from salinity gradients, such as the latest RED devices, is their low power generation capacity.

[0007] This low power generation capacity is mainly due to the fact that current membranes have a power generation capacity of only a few W / m² per unit surface area of ​​the membrane. 2 This is due to the fact that only a small amount of power (i.e., membrane output) is generated.

[0008] The low power generation capacity of this type of RED device is also due to the resistance of various elements of the system to ion flow. This resistance depends primarily on the membrane resistance, the ionic conductivity of the electrolyte solution, especially the solution with the lowest electrolyte concentration, and the inter-membrane distance. In particular, the need to maintain a spacing of several hundred micrometers between membranes using spacers to allow fluid flow within the membrane stack significantly contributes to the overall resistance of the system.

[0009] Spacers also increase the resistance of the device, which can affect the overall performance of the device in terms of output power.

[0010] The spacers conventionally used in such devices are nylon-type fabric spacers.

[0011] To optimize the performance of such spacers, the size of the textile filaments, their arrangement, and spacing are important parameters (Gurreri et al., Journal of membrane science, 497 (2016) 300-317).

[0012] However, RED devices using such spacers still have low output power.

[0013] Another alternative is to use thin spacers, typically on the order of 100 μm or less, which allows the power output to be increased but is not industrially applicable due to the particularly high pressure drop.

[0014] In light of the above, there remains a need to improve the power generated by devices for generating electricity from concentration gradients, in particular by developing spacers that allow for maintaining an intermembrane space of sufficient thickness, but that do not induce excessive resistance. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] International Application No. WO2014 / 0606902017 [Patent Document 2] International Application No. WO2017 / 037213 [Patent Document 3] International Application No. WO2021 / 234296 [Non-patent literature]

[0016] [Non-Patent Document 1] Gurreri et al., Journal of membrane science, 497 (2016), pp. 300-317 Summary of the Invention [Problem to be solved by the invention]

[0017] The object of the present invention is to - two electrodes (1), - a stack of membranes (9) arranged between two electrodes, comprising alternating membranes (2) selectively permeable to cations and membranes (3) selectively permeable to anions, a stack of membranes (9), each membrane being separated from an adjacent membrane by an inter-membrane space in which an activated carbon cloth (4) is positioned; - A device (5) for harvesting the power generated by the potential difference existing between two electrodes (1) Including, The membrane stack (9) is A Electrolyte solution (7) and the same solute concentration C B and an electrolyte solution (8) of C B is C A and the solution must alternately circulate within the inter-membrane spaces of the stack (9), a device for generating electricity.

[0018] Advantageously, the activated carbon cloth has a thickness ranging from 100 μm to 1000 μm, preferably from 200 μm to 600 μm.

[0019] Advantageously, the activated carbon cloth has a thickness of 200 to 3000 m 2 / g, preferably 1000 to 2000m 2 Specific surface area S in the range of / g BET It has.

[0020] Another object of the invention is a process for generating electricity using a device such as described above, comprising: i) The concentration of solute in the membrane stack (9) C AElectrolyte solution (7) and the same solute concentration C B and supplying an electrolyte solution (8) of C B is C A and the solution is alternately circulated within the inter-membrane spaces of the stack (10). ii) Concentration C B The electrolyte in the intermembrane space is supplied by the electrolyte solution (7) at a concentration of C A allowing the electrolyte solution (8) to diffuse towards the adjacent inter-membrane space, which is supplied by the electrolyte solution (8); iii) using a device (5) to capture the power generated by the potential difference existing between the two electrodes (1).

[0021] Advantageously, the concentration ratio C B / C A is in the range of 2 to 100, preferably 5 to 50.

[0022] Advantageously, the electrolyte solutions (7) and (8) are aqueous solutions containing a solute selected from alkali or alkaline earth metal halides, preferably selected from NaCl, KCl, CaCl2 and MgCl2, more preferably NaCl.

[0023] Another object of the present invention is the use of an activated carbon cloth positioned between a membrane selectively permeable to cations and a membrane selectively permeable to anions in a device intended to carry out a process for generating electricity. [Means for solving the problem]

[0024] Other aspects of the invention are described below and in the claims. [Brief explanation of the drawings]

[0025] [Figure 1]FIG. 1 is an exploded view showing two electrodes (1) and five membranes positioned between the two electrodes, according to a device of the present invention, comprising a membrane stack (9) of alternating membranes (2) selectively permeable to cations and membranes (3) selectively permeable to anions, with activated carbon cloth (4) positioned in the inter-membrane space between two adjacent membranes. [Figure 2] 1 is a schematic cross-sectional view of a reverse electrodialysis (RED) device used in Example 1, comprising: two electrodes (1); a stack of seven membranes arranged between the two electrodes, each membrane comprising alternating membranes (2) selectively permeable to cations and (3) selectively permeable to anions, each membrane being separated from an adjacent membrane by an intermembrane space in which an activated carbon cloth (4) is positioned; and a device (5) for harvesting the power generated by the potential difference existing between the two electrodes, wherein a redox solution (6) circulates between the electrodes (1), and the membrane stack is supplied with an electrolyte solution (7) of a solute with a concentration CA and an electrolyte solution (8) of the same solute with a concentration CB, where CB is greater than CA, and the solutions circulate alternately in the intermembrane spaces of the stack. DETAILED DESCRIPTION OF THE INVENTION

[0026] The object of the present invention is to provide a device using spacers which overcomes the drawbacks of the prior art, is simple to implement, can be manufactured inexpensively and allows for improved performance.

[0027] Another object of the present invention is to provide a process for generating electricity using the claimed device.

[0028] These objectives are achieved by the invention described below.

[0029] device The first object of the present invention is to - two electrodes (1), - a membrane stack (9) arranged between two electrodes (1) comprising alternating membranes (2) selectively permeable to cations and membranes (3) selectively permeable to anions, a stack of membranes (9), each membrane being separated from an adjacent membrane by an inter-membrane space in which an activated carbon cloth (4), i.e., a spacer, is positioned; - and a device (5) for harvesting the power generated by the potential difference existing between two electrodes (1) Including, The membrane stack (9) is A Electrolyte solution (7) and the same solute concentration C B and an electrolyte solution (8) of C B is C A and the solution must alternately circulate within the inter-membrane spaces of the stack (9), a device for generating electricity.

[0030] In this embodiment, the concentration of the same solute, C A and C B The difference between these two causes the electrolyte to move from the more concentrated solution to the less concentrated solution.

[0031] Spacer Surprisingly and unexpectedly, the inventors have discovered that activated carbon cloth, by enhancing ionic conduction, makes it possible to improve the performance of power generating devices in terms of generated power compared to spacers conventionally used in such devices.

[0032] The spacer according to the present invention is an activated carbon cloth (4).

[0033] For purposes of this invention, "activated carbon fabric" means a woven, knitted, or nonwoven sheet of fabric comprising activated carbon fibers.

[0034] The activated carbon fabric can be a sheet of woven fabric comprising yarns based on activated carbon fibers, or a sheet of knitted fabric comprising at least one yarn based on activated carbon fibers, or a sheet of nonwoven fabric comprising activated carbon fibers.

[0035] A nonwoven fabric is a substantially planar fibrous assembly with a nominal level of structural integrity imparted by physical and / or chemical processes, excluding weaving, knitting, or papermaking. In this sense, the nonwoven fabric of the present invention meets the definition of a nonwoven fabric according to ISO Standard 9092 of April 2019. Thus, a fibrous assembly refers to an assembly of fibrous materials, such as fibers, continuous filaments, or cut yarns, of any length or cross-sectional area. The nonwoven fabric may contain yarns derived from activated carbon fibers.

[0036] A woven fabric is an essentially planar assembly of mutually parallel threads, known as warp threads, through which threads, known as weft threads, pass, said threads preferably intermingling by weaving.

[0037] A yarn based on activated carbon fibers means that the yarn comprises activated carbon fibers.

[0038] The activated carbon nonwoven fabric may be made of activated carbon fibers.

[0039] The activated carbon nonwoven fabric may be a composite nonwoven fabric containing activated carbon fibers and fibers of one or more materials other than activated carbon.

[0040] The activated carbon nonwoven fabric may be a composite nonwoven fabric made of activated carbon fibers and fibers of one or more materials other than activated carbon.

[0041] The woven or nonwoven activated carbon fabric may be made of yarns containing activated carbon fibers.

[0042] The yarn of the woven or nonwoven activated carbon fabric may be a composite yarn comprising activated carbon fibers and fibers of one or more materials other than activated carbon.

[0043] The yarn of the woven or nonwoven activated carbon fabric may be a composite yarn made of activated carbon fibers and fibers of one or more materials other than activated carbon.

[0044] The yarn of the woven or nonwoven activated carbon fabric may be a yarn comprising, on the one hand, activated carbon fibers and, on the other hand, fibers of one or more materials other than activated carbon.

[0045] The threads of the woven or nonwoven activated carbon fabric may, on the one hand, be threads made of activated carbon fibers and, on the other hand, threads comprising fibers of one or more materials other than activated carbon.

[0046] The yarns of the activated carbon woven or nonwoven fabric may be, on the one hand, yarns containing activated carbon fibers and, on the other hand, yarns made from fibers of one or more materials other than activated carbon.

[0047] The threads of the woven or nonwoven activated carbon fabric may, on the one hand, be threads made of activated carbon fibers and, on the other hand, threads made of fibers of one or more materials other than activated carbon.

[0048] Advantageously, the woven or nonwoven activated carbon fabric consists of threads made of activated carbon fibers.

[0049] The activated carbon nonwoven fabric can be, for example, an activated carbon felt. In a particular embodiment, the activated carbon felt is obtained by needling fibers.

[0050] At least one yarn derived from activated carbon fibers of the activated carbon knitted fabric is as described above.

[0051] When the activated carbon cloth includes fibers of one or more materials other than activated carbon, the fibers of one or more materials other than activated carbon may make it possible to change the mechanical properties of the activated carbon cloth, for example by increasing its stiffness.

[0052] The activated carbon cloth can be formed by combining activated carbon fibers together.

[0053] Activated carbon fabric may be formed by combining and binding together activated carbon fibers with fibers of one or more materials other than activated carbon.

[0054] Activated carbon fabrics may be formed from fabrics containing fibers of activated carbon precursors, which are then subjected to subsequent treatments to form the activated carbon fabrics. The treatments for obtaining activated carbon films are well known to those skilled in the art. In particular, these are thermochemical treatments carried out at temperatures between 200°C and 3000°C.

[0055] In this embodiment, when the fabric comprises fibers of one or more other materials other than the activated carbon precursor, the one or more materials other than the activated carbon are advantageously heat-resistant materials, preferably silica or glass.

[0056] Advantageously, the mass of activated carbon fibers of the activated carbon cloth is equal to at least 50% of the total mass of the activated carbon cloth.

[0057] When activated carbon fabric is obtained from a fabric containing fibers of activated carbon precursor, which fabric is then sent to a subsequent treatment to obtain the activated carbon fabric, the mass of activated carbon fibers relative to the total mass of the activated carbon fabric can be calculated from the mass ratio of the various fibers or yarns used to produce the fabric and the mass of the fabric before and after treatment. When the fabric contains, for example, silica or glass fibers, their mass remains unchanged after the treatment. The effect of treatment on the mass of each type of fiber or yarn in the fabric can also be evaluated separately.

[0058] Advantageously, the activated carbon cloth has a thickness ranging from 100 μm to 1000 μm, preferably from 200 μm to 600 μm.

[0059] When the thickness of the activated carbon cloth is less than 100 μm, the flow of the electrolyte solution in the inter-membrane space may be hindered, resulting in a pressure drop phenomenon and a significant increase in the power required to circulate the electrolyte solution.

[0060] When the thickness of the activated carbon cloth is greater than 1000 μm, the electrical resistance linked to the thickness of the intermembrane compartment becomes too large, affecting the efficiency of the device.

[0061] In the present invention, the specific surface area of ​​a fabric is measured using the BET (Brunauer, Emmett, and Teller) method according to the standard ISO 9277 of September 2010.

[0062] Activated carbon cloth is 1m 2 / g to 3000m 2 / g specific surface area.

[0063] Advantageously, the activated carbon cloth is 200 m 2 / g to 3000m 2 / g, preferably 1000m 2 / g to 2000m 2 / g specific surface area.

[0064] Activated carbon cloth is 1m 2 / g to 10m 2 / g or 1m 2 / g to 5m 2 / g specific surface area.

[0065] The activated carbon cloth of the present invention is a material having a void volume that allows the electrolyte solution to circulate. It can have a void volume percentage of at least about 50%, preferably at least about 60%. In the present invention, the void volume percentage is calculated based on the total void volume V of the sample. interstitial and the total volume occupied by the sample, V E Ratio to P=V interstitial / V E The total void volume is determined indirectly by the weight difference between the impregnated sample and the unimpregnated sample with a wetting liquid of known density, such as alcohol. More precisely, V interstitial Here's the next method a) Mass m E Providing samples of b) impregnating the sample from step a) with a liquid of density ρL; c) mass m of the impregnated sample from step b) Ei and determining d) Formula V interstitial =(m Ei -m E ) / ρL according to V interstitial and calculating

[0066] Volume V E can be determined as the product of the surface area of ​​the sample and its thickness.

[0067] In one embodiment of the present invention, the activated carbon cloth has a density of 0.05 to 0.20 g / cm 3 In the present invention, the density of the activated carbon cloth is determined by the mass m of the sample. E and volume V E The ratio of d=m E / V E is defined as:

[0068] In the present invention, the term "activated carbon fibers" refers to fibers obtained from carbon-containing precursors using processes well known to those skilled in the art, in particular thermochemical processes carried out at temperatures between 200°C and 3000°C.

[0069] Advantageously, the carbon-containing precursor is a polymer or macromolecule, preferably chosen from one of the following: phenol-aldehyde resin, polyacrylonitrile (PAN), rayon, lignin, or mixtures thereof.

[0070] Phenol-aldehyde resin, polyacrylonitrile (PAN), rayon, and mixtures thereof are preferred.

[0071] The processes used to obtain activated carbon fibers from carbon-containing precursors include, by way of example: - optionally a step of oxidative pretreatment of the carbon-containing precursor, - a calcination or carbonization step, - includes processes that include a step of physical activation consisting of calcination in the presence of a gas such as carbon dioxide, water or oxygen, or chemical activation using an activating agent, for example an acid such as phosphoric acid, or a base such as potassium hydroxide.

[0072] According to one variant of this process, the precursor can be activated directly before the calcination step.

[0073] Advantageously, the activated carbon fibers consist essentially of carbon, i.e., 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.

[0074] Advantageously, the activated carbon fibers contain 80 to 100% by weight of carbon, 0 to 10% by weight of nitrogen, 0 to 10% by weight of oxygen, and 0 to 5% by weight of hydrogen.

[0075] The activated carbon fibers of the fabric advantageously have a diameter of less than 50 μm, preferably less than 20 μm, particularly preferably less than 10 μm. The fibers of the activated carbon fabric advantageously have a diameter of more than 0.1 μm, preferably more than 1 μm. The activated carbon fibers can have a diameter in the range of 0.1 μm to 50 μm, preferably 1 to 20 μm, particularly preferably 1 to 10 μm.

[0076] The diameter of the activated carbon fibers in the fabric can be determined using a scanning electron microscope (SEM).

[0077] Advantageously, the surface charge density of the activated carbon is between 0.1 mmol / g and 3 mmol / g.

[0078] The surface charge density is measured by dosimetry.

[0079] Advantageously, the surface charge density of the activated carbon is 10 -5 meq / m 2 From 10 -2 meq / m 2 It is between.

[0080] When the charged groups in the activated carbon are monovalent ionic groups, 1 meq of surface charge corresponds to 1 mmol of surface charge, i.e., 1 mmol of charged groups. In this case, the surface charge density of the activated carbon is advantageously 10 -5 mmol / m 2 From 10 -2 mmol / m 2 It is between.

[0081] In the device according to the invention, each membrane is separated from the adjacent membrane by an inter-membrane space in which the activated carbon cloth (4) described above is positioned.

[0082] The activated carbon cloth according to the present invention is simple and inexpensive to manufacture and allows for improved performance of power generating devices compared to spacers conventionally used in such devices.

[0083] The thickness of the intermembrane space between the two membranes can be controlled using a gasket or other system that allows the thickness of the intermembrane space to be controlled, thereby ensuring that it remains waterproof while allowing the electrolyte solution to circulate and the activated carbon fabric to be positioned in accordance with the present invention.

[0084] film For purposes of this invention, a "membrane" means a material in sheet form that is permeable to at least a portion of the ions in an electrolyte solution. The phrase "selectively permeable to anions or cations" means that the membrane allows the majority of anions or cations to pass through while preventing or significantly retarding the passage of ions of the opposite charge.

[0085] Advantageously, the membrane is also permeable to the solvent of the electrolyte solution, preferably water.

[0086] Any type of membrane (3) that is selectively permeable to anions or any type of membrane (2) that is selectively permeable to cations is compatible with the present invention.

[0087] The membrane (3) selectively permeable to anions or the membrane (2) selectively permeable to cations may be in the form of a homogeneous layer of one material or a stack of several layers of different materials.

[0088] Advantageously, the anion-selectively permeable membrane (3) or cation-selectively permeable membrane (2) of the present invention is an ion-exchange membrane, i.e., a membrane made of at least one inorganic or organic material bearing ionizable groups, also called ion-exchange groups, which give the membrane the property of selective permeability to ions. For the purposes of the present invention, an ionizable group is a chemical group that, when placed in a liquid, has the ability to release an ion, called a counterion, and fix an ion of the same charge contained in this liquid.

[0089] In one embodiment, the membrane comprises an organic polymer bearing ionizable groups, commonly referred to as an “ion exchange resin.” Thus, the membranes of the present invention can be formed from a matrix of insoluble polymer that has contained an ion exchange resin or from a matrix of insoluble polymer that has ionizable groups grafted onto it.

[0090] In one embodiment, the insoluble polymer is typically a hydrocarbon matrix advantageously selected from a polysaccharide matrix such as a cellulose or dextran matrix, a polystyrene matrix, a polytetrafluoroethylene matrix, or a copolymer matrix such as a styrene and divinylbenzene copolymer.

[0091] In one embodiment, the membrane (2) selectively permeable to cations is selected from the group consisting of epoxide groups, hydroxyl groups, carbonyl groups, carboxyl groups, sulfonic acid groups -SO3 - R is a carboxyalkylate group R—CO2, where R is a C1 to C4 alkyl, preferably a C1 alkyl. - , aminodiacetate group -N(CH2CO2 - )2, phosphonic acid group PO3 2-, amidoxine group -C(=NH2)(NOH), aminophosphonic acid group -CH2-NH-CH2-PO3 2- , thiol groups -SH, and mixtures thereof.

[0092] In one embodiment, the membrane (3) selectively permeable to anions contains a quaternary ammonium group -N(R) where R is a C1-C4 alkyl. 3+ a tertiary ammonium group —N(H)R, where R is C1-C4 alkyl, preferably C1 alkyl 2+ , dimethylhydroxyethylammonium group -N(C2H4OH)CH3) 2+ and mixtures thereof. Advantageously, the membrane has a thickness of between 10 μm and 200 μm, preferably between 10 μm and 100 μm, more preferably between 10 μm and 75 μm.

[0093] Advantageously, the membrane comprises channels connecting the two faces of the membrane, which may pass from one side of the membrane to the other or form a network of channels to ensure the circulation of ions and / or solvents between the two sides of the membrane.

[0094] The channels of the membrane of the invention advantageously have an average diameter of from 1 to 500 nm, preferably from 1 to 100 nm, more preferably from 2 to 100 nm, more preferably from 10 to 100 nm.

[0095] In certain embodiments of the invention, the membrane is 2 10 per 5 Larger than the channel, preferably 1 cm of membrane 2 10 per 8 The density of channels per unit area of ​​the membrane is greater than the density of channels per unit area of ​​the membrane.

[0096] The channels of the membranes of the present invention can have any type of morphology, for example, a tubular morphology, a conical asymmetric morphology, or a bottleneck morphology.

[0097] In one particular embodiment, at least a portion of the interior surface of the membrane channel is coated with boron nitride, a compound based on carbon, boron and nitrogen, or an oxide of titanium, preferably titanium dioxide.

[0098] The effect of these coatings, as detailed in International Applications WO2014 / 0606902017 and WO2017 / 037213, is to increase the surface charge on the internal surfaces of the channels, significantly improving the power generated by devices containing such nanofluidic membranes with high surface charge densities. In this embodiment, the membrane advantageously has channels with an average diameter between 2 and 100 nm. In one embodiment, the membrane of the present invention is a free-standing membrane. For purposes of the present invention, "free-standing membrane" means a membrane that does not need to be supported by one or more rigid (e.g., a sheet of porous solid material) or deformable (e.g., a sheet of polymeric material) supports to ensure its mechanical integrity.

[0099] In another embodiment, the membrane comprises at least one layer formed from a cellulose material comprising a network of crosslinked cellulose nanofibers and / or cellulose microfibers, as detailed in International Application No. WO2021 / 234296.

[0100] The device according to the invention comprises a stack of membranes (9) arranged between two electrodes (1), comprising alternating membranes (2) selectively permeable to cations and membranes (3) selectively permeable to anions, Each membrane comprises a stack of membranes (9) separated from adjacent membranes by inter-membrane spaces in which activated carbon cloth as described above is positioned.

[0101] A stack of membranes according to the invention means an arrangement of membranes as illustrated in Figures 1 and 2, i.e. the membrane is arranged between two electrodes (1) positioned opposite each other and in different parallel planes.

[0102] In a particular embodiment of the invention, the device comprises N+1 membranes and N intermembrane spaces, where N is an even integer, in particular a number between 2 and 1000, preferably between 2 and 250, for example between 2 and 100.

[0103] The device can also be described in terms of membrane pairs, where the number of membrane pairs is equal to N / 2.

[0104] Other components of the device Electrodes (1) and devices (5) The device according to the invention comprises a pair of electrodes (1) and a device (5) for harvesting the power generated by the potential difference existing between the two electrodes (1).

[0105] Various types of electrodes can be used in the device.

[0106] When the electrolyte solution is aqueous NaCl, any type of electrode capable of collecting Na+ or Cl- ion flux, preferably silver and silver chloride (Ag / AgCl), carbon and platinum (C / Pt-), carbon (C-), graphite or [Fe(CN)6] 4- / [Fe(CN)6] 3- An electrode made of an iron complex of the type may be used.

[0107] The electrodes can be redox flow electrodes, as shown in Figure 2. The principle of these electrodes is based on an oxidation and reduction reaction at each of the electrodes.

[0108] Various possible RedOx pairs include FeCl3 / FeCl2, K3Fe(CN)6 / K4Fe(CN)6, Fe(III)-EDTA / Fe(II)-EDTA, Na3Fe(CN)6 / Na4Fe(CN)6, etc.

[0109] In addition to the RedOx couple, the recirculating solution (6) contains A +C B ) / 2 solute solution.

[0110] The electrode can also be a capacitive flow electrode, which contains a dispersion of conductive particles, called a slurry, in a medium containing a solute. The conductive particles can be activated carbon particles, carbon nanotubes, or any other conductive agent.

[0111] Each electrode may be in contact with a membrane selectively permeable to ions of the same sign, i.e., each electrode may be in contact with a membrane selectively permeable to cations, or each electrode may be in contact with a membrane selectively permeable to anions.

[0112] The electrodes (1) are connected together to a device (5) for collecting, i.e. circulating and capturing, the electrical power spontaneously generated by the potential difference existing between them, which advantageously forms an external electrical circuit including a current collector and an electrical cable, a battery, a light bulb, or any other form of electrical consuming device.

[0113] electrolyte solution Solute concentration C A of electrolyte solution and the same solute concentration C B An electrolyte solution of C B C A An electrolyte solution, which is greater than 0.01, is circulated in the intermembrane space of the membrane stack (9). This solution alternates between circulating in the stack (9), i.e., the concentration of solute C A An electrolyte solution of circulates in the intermembrane space between the two membranes, with the same solute concentration C B The electrolyte solution circulates within one or more adjacent intermembrane spaces.

[0114] Osmotic flow occurs between two adjacent intermembrane spaces preferably by diffusion osmotic pressure, ie, without the appearance of osmotic pressure.

[0115] In certain embodiments, a concentration gradient can be obtained and / or regulated via a temperature gradient between two electrolyte solutions, which affects the solubility of the electrolyte as a function of temperature.

[0116] In the context of the present invention, the concentration ratio Rc is the ratio of the concentration of the more concentrated solution to the concentration of the less concentrated solution, i.e., the ratio C B / C A Shows.

[0117] Preferably, the concentration ratio C B / C A is in the range of 2 to 100, preferably 5 to 50.

[0118] An electrolyte solution is an aqueous solution containing electrolytes. The electrolytes can be of any chemical nature as long as they are dissolved in the solution in the form of ions. Preferably, these ions come from dissolved salts such as NaCl, KCl, CaCl2 and MgCl2. An electrolyte solution is: - synthetic solutions, - Natural solutions, such as fresh water from lakes or rivers, groundwater, brackish water, or seawater; or - Industrially produced water, petroleum produced water, or biological fluids It may be.

[0119] Particularly advantageously, the electrolyte is NaCl.

[0120] Advantageously, solution C B is a seawater solution, and solution C A is a freshwater solution.

[0121] Advantageously, the device is A and C B a means for switching the flow of an electrolyte solution of solute concentration C A An electrolyte solution of circulates in the intermembrane space between the two membranes, with the same solute concentration C A Mode (1), in which an electrolyte solution of circulates through one or more adjacent intermembrane spaces, and solution C A and C B The circulation is reversed in mode (2).

[0122] To improve the osmotic flow that occurs on either side of a membrane according to the invention, the pH of the solution can be adjusted as a function of the isoelectric point of one or more of the materials that make up the membrane.

[0123] For the purposes of the present invention, pHiso means the pH at the isoelectric point of the material or materials comprising the membrane. pHiso is measured by methods known to those skilled in the art, in particular by potentiometric acid / base titration.

[0124] More preferably, to increase the asymmetry of the device and amplify the amount of power generated by the device, a pH gradient may be set up between the two reservoirs, with the pH difference between the two solutions being greater than 1, preferably greater than 2.

[0125] Process for generating electricity A second object of the present invention is a process for generating electricity using a device as described above, comprising: i) The concentration of solute in the membrane stack (9) C A Electrolyte solution (7) and the same solute concentration C B and supplying an electrolyte solution (8) of C B is C A and the solution circulates alternately within the inter-membrane spaces of the stack (9). ii) Concentration C B The electrolyte in the intermembrane space is supplied by the electrolyte solution (7) at a concentration of C A allowing the electrolyte solution (8) to diffuse towards the adjacent inter-membrane space, which is supplied by the electrolyte solution (8); iii) using a device (5) to capture the power generated by the potential difference existing between the two electrodes (1).

[0126] Steps i) and ii) are preferably carried out at a concentration C A Electrolyte solution and concentration C B This is accomplished by supplying the electrolyte solution in the form of a continuous flow.

[0127] The flow rates of the electrolyte solutions (7) and (8) are adjusted to optimize the salt concentration gradient of the device by adjusting the residence time of the electrolyte solutions within the device.

[0128] Advantageously, the electrolyte solutions (7) and (8) are at a temperature between 10°C and 40°C, preferably between 15°C and 25°C.

[0129] Advantageously, the process according to the invention is a power generation process that exploits the difference in salinity between seawater and freshwater solutions.

[0130] Using Spacers Another object of the present invention relates to the use of an activated carbon cloth as described above positioned between a cation exchange membrane and an anion exchange membrane in an electricity generating device.

[0131] Advantageously, activated carbon cloth is used as the spacer.

[0132] The power generating device is as described above.

[0133] (Example) The invention will be understood more clearly on reading the following examples, which illustrate the invention without limiting it.

[0134] The illustrated devices and processes are for generating electrical power by reverse electrodialysis power generation.

[0135] device: The device used is illustrated in FIG.

[0136] The device contains seven cation membranes (2) and anion membranes (3), each 1 cm 2 has a surface area of

[0137] The electrode (1) is connected to an external electrical circuit that includes a voltmeter.

[0138] The materials used in the examples are listed below.

[0139] film: - a cation exchange membrane marketed by the company Fumasep under the name FKS30 (2), - an anion exchange membrane marketed by the company Fumasep under the name FAS (3).

[0140] Spacer: - nylons sold by SEFAR under the name SEFAR NITEX 06-335 / 48 for nylons with a thickness of 300 μm or SEFAR NITEX 06-1140 / 66 for nylons with a thickness of 500 μm; - Activated carbon felt (4) obtained from a polyacrylonitrile precursor with a thickness of 300 μm or 500 μm.

[0141] There are six spacers.

[0142] Salt solution to supply the device Seawater solution with a NaCl concentration of 35 g / l (concentration C B solution) and a solution with a NaCl concentration of 1117 g / l (concentration C A Solutions) are used (corresponding to solutions 8 and 7, respectively, in Figure 2).

[0143] The temperature of the salt water is 25°C.

[0144] The saline flow rate is 1 ml / min.

[0145] Redox Solution The electrode rinse solution (6) consisted of 0.25 M Na3Fe(CN)6, 0.25 M Na4Fe(CN)6, and (C B +C A ) / 2.

[0146] The temperature of the rinse solution is 25°C.

[0147] The flow rate of the solution is 0.25 ml / min.

[0148] Example 1 Preparation of devices D1 and D2 according to the invention and comparison with comparative devices C1 and C2 not according to the invention.

[0149] These results are shown in Table 1.

[0150] [Table 1]

[0151] however, - ΔV is the potential measured by the voltmeter when the external circuit is open, - I the current measured by the ammeter when the external circuit is closed, - R is the surface resistance of the device calculated by Ohm's law: R s =U / IS, - Pmax=V 2 / 4R

[0152] Table 1 shows that by using a 500 μm activated carbon felt spacer according to the present invention instead of a nylon spacer of the same thickness as conventionally used in a power generating device, the power per unit area is more than four times greater.

[0153] When the spacer thickness is 300 μm, the power gain obtained with the activated carbon spacer according to the present invention is 2.5. [Explanation of symbols]

[0154] 1 electrode 2. A membrane that selectively allows cations to pass through 3. Membranes that are selectively permeable to anions 4 activated carbon cloth 5 Devices 6 Redox Solutions 7 Electrolyte solution 8 Electrolyte solution 9. Membrane stacking

Claims

1. 1. A device for generating electricity, comprising: - two electrodes (1), - a stack of membranes (9) arranged between the two electrodes, comprising alternating membranes (2) selectively permeable to cations and membranes (3) selectively permeable to anions, a stack of membranes (9), each membrane being separated from an adjacent membrane by an inter-membrane space in which an activated carbon cloth (4) is positioned; - a device (5) for harvesting the power generated by the potential difference existing between the two electrodes (1); Including, The stack of membranes (9) is A Electrolyte solution (7) and the same solute concentration C B and an electrolyte solution (8) of C B is C A and said solution must alternately circulate within the inter-membrane spaces of said stack (9).

2. 2. The device according to claim 1, characterized in that the activated carbon cloth has a thickness ranging from 100 μm to 1000 μm, preferably from 200 μm to 600 μm.

3. The activated carbon cloth has a thickness of 200 to 3000 m 2 / g, preferably 1000 to 2000m 2 Specific surface area S in the range of / g BET 3. The device according to claim 1 or 2, characterized in that it comprises:

4. A process for generating electrical power using a device as claimed in any one of claims 1 to 3, comprising: i) adding a concentration C of solute to said stack of membranes (9) A Electrolyte solution (7) and the same solute concentration C B and supplying an electrolyte solution (8) of C B is C A and the solution circulates alternately within the intermembrane spaces of the stack (9). ii) Concentration C B The electrolyte in the intermembrane space is supplied by the electrolyte solution (7) at a concentration of C A allowing the electrolyte solution (8) to diffuse towards the adjacent inter-membrane space, iii) using said device (5) to capture said power generated by said potential difference existing between said two electrodes (1); The process includes:

5. Concentration ratio C B / C A 5. The process according to claim 4, characterized in that is in the range of 2 to 100, preferably 5 to 50.

6. The electrolyte solutions (7) and (8) are selected from alkali or alkaline earth metal halides, preferably NaCl, KCl, CaCl 2 and MgCl 2 6. The process according to claim 4 or claim 5, characterized in that the solution is an aqueous solution containing a solute selected from the group consisting of NaCl and NaCl.

7. 1. Use of an activated carbon fabric positioned between a membrane selectively permeable to cations and a membrane selectively permeable to anions in a device intended to carry out a process for generating electrical power.

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