Electrochemical device using a porous polymer spacer having charged functional groups and forming a continuous three-dimensional network

Abstract

The invention relates to an electrochemical device comprising: - two electrodes (1); - a stack of membranes (9), placed between the two electrodes (1), comprising alternating membranes selectively permeable to cations (2) and membranes selectively permeable to anions (3), and such that each membrane (2, 3) is separated from a neighboring membrane (2, 3) by an intermembrane space, a spacer (4) being positioned in at least one of the intermembrane spaces thus defined, said spacer (4) consisting of a porous polymer material forming a continuous three-dimensional network, having a porosity greater than 70%, preferentially greater than 80%, the pores of which are interconnected, and having charged surface functional groups; - an aqueous electrolyte solution (7, 8) comprising a solute in the form of a dissolved salt, having a pH ranging from 6 to 9 and impregnating the pores of said spacer; - and a device (5) for harvesting the electrical energy generated by a potential differential existing between the 2 electrodes (1) or for applying a potential difference between the 2 electrodes (1).

Description

[0001] DESCRIPTION

[0002] DEVICE USING A POROUS POLYMERIC SEPARATOR HAVING CHARGED FUNCTIONAL GROUPS AND FORMING A CONTINUOUS THREE-DIMENSIONAL NETWORK

[0003] FIELD OF INVENTION

[0004] The present invention relates to electrochemical devices for implementing ion transfer processes within electrolytic solutions using a porous polymeric material having charged functional groups and forming a continuous three-dimensional network as a spacer, as well as methods implementing such devices.

[0005] The invention also relates to the use of such materials as a spacer within a power generation or deionization device.

[0006] STATE OF THE ART

[0007] Electricity generation by salinity gradient is one of the renewable energy sources with the greatest potential on a global scale.

[0008] Among the various technologies currently under consideration, reverse electrodialysis (RED) relies on converting mixing energy into electrical energy. This technology uses membranes with selective permeability to anions (anionic membranes) or cations (cationic membranes), whose fundamental property is the selective transport of ions according to their charge.

[0009] A common type of RED device consists of membranes stacked between a pair of electrodes. The membrane stack comprises alternating anionic and cationic membranes between which salt water and fresh water are alternately circulated. The intermembrane spaces, that is, the spaces within which the fluids flow, are maintained by placing spacers between the membranes. The circulation of alternating salt water and fresh water between these membranes, in other words, the establishment of a salinity gradient across each membrane, results in selective ion fluxes across each membrane.For example, sodium ions flow through cationic membranes toward the cathode, and chloride ions flow 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 electrical current, and an external electrical circuit ensures the transfer of electrons from the anode to the cathode. The resulting membrane potential difference thus produces an electrical current that can be used by a device placed in the circuit connecting the electrodes.

[0010] One of the problems encountered by devices for generating electricity from a salinity gradient, such as current RED devices, is that they exhibit a low electricity production capacity.

[0011] This low energy production capacity is mainly due to the fact that current membranes develop electrical power per unit membrane surface area (i.e., membrane power) of only a few W / m². 2 of membrane.

[0012] The low energy production capacity of these types of RED devices is also due to the resistance that various system components present to ionic flow. This resistance depends primarily on membrane resistance, the ionic conductivity of the electrolyte solution (particularly the least concentrated electrolyte solution), and the intermembrane spacing. Specifically, maintaining a spacing of several tens or hundreds of micrometers between the membranes using spacers is necessary to allow fluid flow within the membrane stack but also significantly contributes to the overall system resistance.

[0013] 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.

[0014] Electrodialysis deionization devices operate in the opposite way. Electrodialysis is an electrochemical separation process that uses direct current to move ions across selective ion-exchange membranes. By applying a voltage between the electrodes, ionic fluxes are generated, allowing a saline solution to be converted into a more concentrated salt solution and a salt-depleted solution.

[0015] As with RED devices, membrane resistance and intermembrane distance, as well as the presence of the spacer, can hinder ionic fluxes and affect desalination efficiency.

[0016] The spacers typically used in such devices are nylon fabric spacers.

[0017] The size of the tissue filaments, their arrangement and their spacing are important parameters for optimizing the performance of such spacers (Gurreri et al, Journal of membrane science, 497 (2016) 300-317).

[0018] However, RED devices implementing such spacers develop power levels that remain low. EP2405994 describes spacers made of ion-exchange materials. Advantageously, the spacer comprises a portion made of a material selectively permeable to cations, positioned opposite a membrane selectively permeable to cations, and a second portion made of a material selectively permeable to anions, positioned opposite a membrane selectively permeable to anions.

[0019] The power outputs of RED devices using 300pm spacers are on the order of W / m 2 .

[0020] Application WO2019126773 describes nylon spacers whose surface is coated with a polymeric material of the ion exchange resin type having properties of exchanging cations and another polymeric material of the ion exchange resin type having properties of exchanging anions.

[0021] Spacers are used in a desalination process and help to reduce the resistance of the device.

[0022] These spacers are made of several materials, particularly ion-exchange resins, and are complex to manufacture. Furthermore, their performance remains unsatisfactory.

[0023] As discussed above, another alternative is to implement very thin spacers, typically on the order of 50 pm or less, which allows for increased power output but is not industrially applicable due to high pressure losses.

[0024] In these devices, the spacer can also be the source of resistance that impairs its performance.

[0025] In light of the above, there remains a need to improve the performance of such electrochemical devices, particularly by developing spacers that maintain a sufficiently thick intermembrane space without inducing excessive resistance, or even facilitate ion movement within the device. This would increase the electrical power generated or the separation or deionization efficiency, depending on the type of device. SUMMARY OF THE INVENTION

[0026] The invention relates to an electrochemical device comprising:

[0027] - two electrodes;

[0028] - a stack of membranes, arranged between the two electrodes, comprising an alternation of membranes selectively permeable to cations and membranes selectively permeable to anions,

[0029] and such that each membrane is separated from a neighboring membrane by an intermembrane space, a spacer being positioned in at least one of the intermembrane spaces thus defined,

[0030] said spacer being made of a porous polymer material forming a continuous three-dimensional network, having a porosity greater than 70%, preferably greater than 80%, whose pores are interconnected, and possessing charged surface functional groups;

[0031] - an aqueous electrolytic solution comprising a solute in the form of a dissolved salt, having a pH ranging from 6 to 9 and impregnating the pores of said spacer;

[0032] - and a device D for harvesting the electrical energy generated by a potential difference existing between the 2 electrodes or for applying a potential difference between the 2 electrodes.

[0033] The invention relates to a method for producing electrical energy using such a device comprising the following steps

[0034] (i) supply the membrane stack with an electrolytic solution of concentration CA in a solute and an electrolytic solution 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

[0035] ii) allow the electrolytes to diffuse from the intermembrane spaces supplied by the electrolytic solution of concentration CB to the adjacent intermembrane spaces supplied by the electrolytic solution of concentration CA; iii) capture the electrical energy generated by the potential difference existing between the two electrodes, using device D.

[0036] The invention also relates to a deionization process using such a device comprising the following steps:

[0037] (i) supply the membrane stack with an electrolytic solution of concentration C in a solute such that said solution circulates in the intermembrane spaces of said stack

[0038] ii) apply a potential difference between the anode and the cathode iii) recover at the stack output an electrolytic solution of concentration C1 in this same solute greater than the concentration C and an electrolytic solution of concentration C2 in this same solute less than the concentration C.

[0039] Another object of the invention relates to the use of a porous polymer material forming a continuous three-dimensional network, having a porosity greater than 70%, preferably greater than 80%, whose pores are interconnected, and having charged surface functional groups, as a spacer positioned between a membrane selectively permeable to cations and a membrane selectively permeable to anions in a power generation or deionization device supplied by at least one aqueous electrolytic solution comprising a solute in the form of a dissolved salt and having a pH of 6 to 9.

[0040] The invention is also as described below.

[0041] DESCRIPTION OF THE FIGURES

[0042] [Fig. 1]: represents a scanning electron microscope view of a spacer according to the invention.

[0043] [Fig. 2]: shows in exploded view the 2 two 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 a spacer (4) positioned in the intermembrane space between 2 neighboring membranes according to a reverse electrodialysis (RED) device.

[0044] [Fig. 3]: schematically illustrates in cross-section the reverse electrodialysis (RED) device used in the examples including:

[0045] - two electrodes (1),

[0046] - a stack of membranes, arranged between the two electrodes, comprising an alternation of membranes selectively permeable to cations (2) and membranes selectively permeable to anions (3),

[0047] and such that each membrane is separated from a neighboring membrane by an intermembrane space in which a spacer (4) is positioned,

[0048] - a device (5) for harvesting the electrical energy generated by a potential difference existing between the 2 electrodes.

[0049] A redox solution (6) circulates between the electrodes (1). The membrane stack is 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 circulating alternately in the intermembrane spaces of the stack.

[0050] DETAILED DESCRIPTION OF THE INVENTION

[0051] The object of the present invention is to overcome the drawbacks of the prior art and to provide a device for generating power or deionizing energy using a simple, inexpensive-to-manufacture spacer that offers improved performance. Another object of the invention is to provide a method for generating electrical energy or deionizing energy using the device of the invention.

[0052] These goals are achieved by the invention which will be described below.

[0053] The invention advantageously relates to an energy production device using the salinity gradient existing between a seawater solution and a freshwater solution or in a seawater desalination device.

[0054] DEVICE

[0055] The invention primarily relates to an electrochemical device comprising:

[0056] - two electrodes;

[0057] - a stack of membranes, arranged between the two electrodes, comprising an alternation of membranes selectively permeable to cations and membranes selectively permeable to anions,

[0058] and such that each membrane is separated from a neighboring membrane by an intermembrane space, a spacer being positioned in at least one of the intermembrane spaces thus defined,

[0059] said spacer being made of a porous polymer material forming a continuous three-dimensional network, having a porosity greater than 70%, preferably greater than 80%, whose pores are interconnected, and possessing charged surface functional groups;

[0060] - an aqueous electrolytic solution comprising a solute in the form of a dissolved salt, having a pH ranging from 6 to 9 and impregnating the pores of said spacer;

[0061] - and a device D for harvesting the electrical energy generated by a potential difference existing between the 2 electrodes or for applying a potential difference between the 2 electrodes.

[0062] Spacer: A spacer is defined as a porous solid element impregnated with an electrolytic solution within the device according to the invention. The spacer allows the free flow of the electrolytic solution within the device. Thus, the porosity of the spacer allows the electrolytic solution to flow through said spacer.

[0063] In the device according to the invention, the spacer separates 2 ion exchange membranes, a cationic membrane and an anionic membrane, the spacer being positioned in the intermembrane space present between these 2 membranes.

[0064] The terms spacers or separators can be used interchangeably.

[0065] Surprisingly and unexpectedly, the inventors discovered that a spacer made of a porous polymer material forming a continuous three-dimensional network, having a porosity greater than 70%, preferably greater than 80%, whose pores are interconnected, and possessing charged functional groups, makes it possible to improve the performance of electrochemical energy production or deionization devices compared to the spacers classically used in such devices.

[0066] The three-dimensional network formed by the polymer material is a continuous network, meaning it is not made up of an assembly of fibers, filaments, or threads of the polymer material. It is not a textile, whether woven, non-woven, or knitted.

[0067] Thus, the spacer according to the invention is not a nonwoven textile, that is to say, it is not an essentially flat fibrous assembly possessing a nominal level of structural integrity conferred by means of physical and / or chemical processes, excluding weaving, knitting, or papermaking. In this sense, the spacer according to the invention does not meet the definition of a nonwoven textile according to ISO 9092 of April 2019.

[0068] The spacer according to the invention is not a woven textile, that is to say, it is not an essentially flat assembly of parallel threads called warp threads crossed by threads called weft threads, said threads being preferably interwoven by weaving.

[0069] Figure 1 illustrates a polymeric material forming a continuous three-dimensional network according to the invention.

[0070] The three-dimensional network formed by the polymer material is a continuous network. Unlike a material composed of an assembly of fibers, filaments, or wires, it does not exhibit discontinuities corresponding to the junctions between distinct fibers, filaments, or wires in contact with each other, as is the case in such a material. Without wishing to be bound by any particular theory, the applicant believes that such discontinuities or nodes in a spacer resulting from the assembly of fibers, filaments, or wires are the cause of an increase in the non-ohmic component of the resistance associated with the spacer, interpreted as contact resistances between the discontinuous components of such a spacer.With a polymer material forming a continuous three-dimensional network according to the invention, the non-ohmic resistance linked to the spacer is minimized, which makes it possible to reduce the total resistance (ohmic and non-ohmic resistance) and thus optimize the performance of the device by facilitating the transfer of ions within the device.

[0071] Advantageously, the spacer is made of a porous polymer material having a porosity greater than 90%, preferably greater than 95%, and even more preferably greater than 97%. Particularly advantageously, its porosity is greater than 99% or 99.5%.

[0072] The spacer's porosity, exceeding 70%, combined with interconnected pores, allows for pore impregnation and the flow of the electrolyte solution. This reduces pressure drop phenomena.

[0073] Advantageously, the maximum porosity of the spacer is less than 99.9%. Thus, advantageously, the spacer is made of a porous polymer material having a porosity ranging from 90% to 99.9%, preferably from 95% to 99.9%, and even more preferably from 97% to 99.9%. Particularly advantageously, its porosity ranges from 99% to 99.9% or from 99.5% to 99.9%.

[0074] The pores, or alveoli, of the spacer are interconnected, that is to say that the spacer does not have a closed porosity with pores isolated from each other in the matrix of the material and not communicating with each other.

[0075] The pores of the spacer according to the invention communicate with each other. This is also referred to as open porosity.

[0076] In the present invention, porosity is defined as the ratio between the pore volume Vpores of a sample and the total volume occupied by the sample VE: P = V pOres / E. The pore 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, V pO res can be measured according to the following method: a) provide a sample of mass IÏIE; b) impregnate the sample from step a) with a liquid of density pL;

[0077] c) determine the mass of the sample impregnated in step b);

[0078] d) Calculate V pO res according to formula V pO res=(mEi- mE) / pL.

[0079] The volume VE can be determined as the product of the sample surface area and its thickness.

[0080] Advantageously, the spacer has a density of less than 30 kg / m³ 3 , preferably ranging from 11 kg / m 3 at 3 kg / m 3 .

[0081] In the invention, the density of the spacer is defined as the ratio between the mass of a sample mE and its volume E: d = rriE / VE.

[0082] According to some embodiments, the pores of the spacer have an average diameter between 10 pm and 200 pm.

[0083] According to other embodiments, the pores of the spacer have an average diameter between 20 pm and 1000 pm.

[0084] Advantageously, the pores of the spacer have an average diameter between 10 pm and 100 pm, preferably between 20 pm and 80 pm.

[0085] The average diameter of the pores or alveoli can be determined using scanning electron microscopy (SEM). This can be determined by image analysis of one or more sections of the spacer obtained with SEM. In the analyzed section(s), the surface area of ​​each pore is approximated as a disk of diameter D, and the average diameter corresponds to the mean of the diameters D.

[0086] Advantageously, the spacer has a thickness ranging from 50 pm to 2000 pm.

[0087] When the spacer is too thick, the resistance it creates affects the effectiveness of the device.

[0088] The thickness of the spacer also depends on the type of device used.

[0089] In the case of devices according to the invention where one or more electrolytic solutions must flow through the spacer, as is the case for RED energy production devices or electrodialysis deionization devices which are described in more detail below, the thickness of the spacer must not be too small to allow the flow of electrolytic solutions.

[0090] Thus, when the thickness of the spacer is less than 50 pm, the flow of electrolytic solutions in the intermembrane spaces may be hindered, pressure loss phenomena may occur and the power required to circulate the electrolytic solutions may be greatly increased.

[0091] Thus, in the case where the electrochemical device is a RED type device, the spacer advantageously has a thickness ranging from 50 pm to 1000 pm, even more preferably from 50 pm to 600 pm.

[0092] In the case where the electrochemical device is an electrodialysis device, the spacer advantageously has a thickness ranging from 100 pm to 2000 pm, preferably from 200 pm to 1000 pm, even more preferably from 200 pm to 600 pm.

[0093] Advantageously, the spacer does not exhibit a porosity gradient. Advantageously, the spacer is homogeneous or uniform, meaning that its porosity is essentially the same regardless of the volume of spacer analyzed and / or the average pore diameter is essentially identical regardless of the cross-section of the spacer analyzed.

[0094] Any polymer capable of forming a continuous three-dimensional polymeric network, having a porosity greater than 70%, preferably greater than 80%, whose pores are interconnected, and bearing charged functional groups may be used.

[0095] It is understood that these surface functional groups are charged when the polymer material is in contact with the electrolytic solution in the device according to the invention, i.e. at a pH ranging from 6 to 9.

[0096] The polymer material can have negatively charged surface functional groups in the pH range of 6 to 9.

[0097] The polymer material can have positively charged surface functional groups in the pH range of 6 to 9.

[0098] According to embodiments, the charged surface groups of the polymer material can be positively charged groups and / or negatively charged groups, the overall charge of the material being able to be positive or negative depending on the relative proportion of positively and negatively charged functional groups.

[0099] The polymer material can exhibit an overall positive or negative charge when in contact with an aqueous electrolytic solution having a pH ranging from 6 to 9. The functional groups can be present throughout the network of the porous polymer material, i.e. they are not groups present only on the surface of the porous polymer material introduced for example by grafting or complexation.

[0100] In this case, the polymer material is obtained by polymerization of one or more monomers carrying the functional groups.

[0101] The functional groups that are charged when the polymer material is in contact with the electrolytic solution in the device according to the invention, i.e. at a pH ranging from 6 to 9, are the surface functional groups of the polymer material.

[0102] The polymer material may have an isoelectric point of less than 5, less than 4 or less than 3.

[0103] Thus, at a pH above the isoelectric point, the polymer is negatively charged, that is to say, it has an overall negative charge.

[0104] In the pH range of 6 to 9 of the electrolytic solutions implemented in the device according to the invention, the polymer is then negatively charged when it is in contact with said electrolytic solutions.

[0105] The polymer material can have an isoelectric point greater than 10.

[0106] Thus, at a pH below the isolelectric point, the polymer is positively charged, that is to say, it has an overall positive charge.

[0107] In the pH range of 6 to 9 of the electrolytic solutions implemented in the device according to the invention, the polymer is then positively charged when it is in contact with said electrolytic solutions.

[0108] The isoelectric point is determined by measuring the zeta potential as a function of pH. The isoelectric point corresponds to the pH at which the zeta potential is zero.

[0109] The polymer material may possess positively charged groups by protonation of a functional group present throughout the network of the polymer material in the pH range of 6 to 9, it being understood that only the surface functional groups of said material are then charged.

[0110] The polymer material may possess negatively charged groups through deprotonation of a functional group present throughout the polymer material's network in the pH range of 6 to 9, provided that only the surface functional groups of said material are then charged. The functional group may be an -NH- group.

[0111] Polymers that can be used include polyurethanes (PU) and formaldehyde-melamine resins.

[0112] Advantageously, the polymer is a formaldehyde-melamine resin.

[0113] The polymer material can be a polymer foam or polymeric foam.

[0114] Foam, according to the IUPAC definition, is a dispersion in which a significant amount of gas is dispersed in a solid material (source: PAC, 1972, 31, 577. (Manual of Symbols and Terminology for Physicochemical Quantities and Units, Appendix II: Definitions, Terminology and Symbols in Colloid and Surface Chemistry) - page 606).

[0115] Polyurethane (PU) foams can be obtained by a polyaddition reaction between a monomer containing two or more hydroxyl groups (-OH), called polyols, and another monomer containing two or more isocyanate groups (-NCO). A urethane bond (-NHC(O)O-) can thus be formed.

[0116] The ratio between polyol and isocyanate, the concentration of catalysts, surfactants, blowing agents and additives allow control of the properties of the foam obtained.

[0117] Similarly, melamine foams can be formed by a reaction between formaldehyde and melamine to form a precondensate which, in the presence of a porogenous agent, will expand with hot air, water vapor or microwave irradiation and then undergo a curing step.

[0118] Advantageously, the polymer is a melamine foam. Melamine foam has -NH- groups present throughout the polymer network, which can deprotonate in the pH range of 6 to 9.

[0119] Surprisingly, the implementation of spacers as described above improves the performance of the devices according to the invention compared to spacers conventionally used in the prior art, in particular polyester spacers.

[0120] In other embodiments, the porous polymer material as described above comprises surface groups including functional groups bearing positive and / or negative charges. These functional groups bearing positive and / or negative surface charges can be introduced onto the surface of the porous polymer material by grafting or by complexation.

[0121] According to some embodiments, the charged surface functional groups of the polymer material carry negative charges.

[0122] Advantageously, the functional groups are chosen from the sulfonate group -SO3; the carboxylate group -CO2; the aminodiacetate group -N(CH2CC>2')2, the phosphonate group PC>2 3 ' ; the amidoximate group -C(=NH2)(NO'), the aminophosphonate group -CH2-NH-CH2-PO3 2 ', the thiolate group -S and their mixtures.

[0123] It is understood that each charged functional group can be present on the polymer chains as a side chain or be linked to the polymer chains via an intermediate -X- group, which is called a linker or spacer. In the latter case, the side chain group is the charged -X- functional group, and the charged functional group is the terminal group.

[0124] The spacer -X- is a divalent hydrocarbon linking group that may optionally contain one or more heteroatoms. For the purposes of this invention, "divalent hydrocarbon linking group" means a spacer group that bridges the polymer chains and the terminal functional group. Advantageously, this spacer group X is a saturated or unsaturated, linear or branched hydrocarbon chain that may optionally contain one or more heteroatoms, such as, for example, nitrogen, oxygen, and sulfur. This hydrocarbon chain may optionally include a cyclic group, such as a phenyl group.

[0125] The X group may be a phenyl group.

[0126] The functional group may be a sulfonate group.

[0127] The pendant group may have a sulfonate group as its terminal functional group. The pendant group may be a phenyl group bearing a sulfonate group.

[0128] According to some embodiments, the surface functional groups of the polymer material carry positive charges.

[0129] Advantageously, the functional groups are chosen from the quaternary ammonium group -N(R)s + with R an alkyl group in C1-C4, the tertiary ammonium group -N(H)R)2 + with R an alkyl in C1-C4, preferably an alkyl in C1, the dimethylhydroxyethylammonium group -N(C2H4OH)CH3)2 + , and their mixtures.

[0130] It is understood that each functional group can be present on the polymer chains as a side group or be linked to the polymer chains via an intermediate -X- group, which is called a linker or spacer. In the latter case, the side group is the charged -X- functional group, and the charged functional group is the terminal group.

[0131] The spacer -X- is a divalent hydrocarbon linking group that may optionally contain one or more heteroatoms. For the purposes of this invention, "divalent hydrocarbon linking group" means a spacer group that bridges the polymer chains and the terminal functional group. Advantageously, this spacer group X is a saturated or unsaturated, linear or branched hydrocarbon chain that may optionally contain one or more heteroatoms, such as, for example, nitrogen, oxygen, and sulfur. This hydrocarbon chain may optionally include a cyclic group, such as a phenyl group.

[0132] Advantageously, the X group is a -phenyl-alkyl chain- group, of the type phenyl-(CH2)n- with n between 1 and 10, whose alkyl chain is possibly substituted.

[0133] The functional group can be a quaternary ammonium group -N(R)a + with R an alkyl in C1-C4.

[0134] The pendant group may have a quaternary ammonium group -N(R)a as its terminal functional group + with R an alkyl in C1-C4.

[0135] The pendant group can be a phenyl-(CH2)n- group with n between 1 and 10, whose alkyl chain is possibly substituted and which bears a terminal quaternary ammonium functional group -N(R)a + with R an alkyl in C1-C4.

[0136] When charged functional groups are introduced by grafting, the polymer is modified by chemical reaction between reactive groups present on the polymer chains and reactive groups present on the graft, said graft further comprising said charged functional groups.

[0137] Charged functional groups can be introduced by complexation. In this case, a complex can form between the polymer, which itself carries charges, and a chemical entity carrying charges of the opposite sign.

[0138] If the polymer constituting the three-dimensional network is negatively charged, a complex can, for example, form with another positively charged polymer, and vice versa.

[0139] Surprisingly, the presence of these surface groups on the polymer material enhances the performance of the device according to the invention. Advantageously, the polymer is a melamine foam comprising surface functional groups carrying positive or negative charges as described above.

[0140] In this case, melamine foam can be obtained through chemical modification. Before chemical modification, melamine foam may contain amine functional groups as well as residual methylol groups. These groups can be used to chemically modify the foam. Thus, functional groups carrying positive or negative charges, as described above, can be introduced onto the polymer material.

[0141] Advantageously, the spacer can be compressed without losing its mechanical integrity; that is, without the three-dimensional network, given its very high porosity, collapsing. The spacer can be compressed by at least 50%, advantageously by at least 60%, and even more advantageously by at least 70%.

[0142] By spacer can be compressed by at least 50% means a spacer in the form of a parallelepiped which is compressed perpendicular to one of its faces so that its thickness, in the direction of compression, is reduced by 50%.

[0143] Without wishing to be bound by any particular theory, the applicant believes that the presence of charged functional groups on the polymer material facilitates ion transport across the spacer surface. The spacer thus possesses unique surface ion conduction properties. The applicant believes that the charged surface functional groups introduced onto the porous polymer material further enhance ion transport across the spacer surface.

[0144] The applicant also believes that it is the combination of the unique properties of the spacer according to the invention (very high porosity, continuous nature of the three-dimensional network, presence of charges) which makes it possible to obtain optimized properties with regard to the transport of ions within the device.

[0145] With increased ionic conduction on the surface of the spacer, the device is more efficient.

[0146] It is understood that the spacer as described above corresponds to the portion of the spacer within the device where ion transport takes place. The spacer may, of course, include other materials, for example, around its periphery to ensure sealing in areas where ion transport does not occur.

[0147] Nature of the device The electrochemical device further comprises a stack of membranes, arranged between the two electrodes, comprising an alternation of membranes selectively permeable to cations and membranes selectively permeable to anions, and such that each membrane is separated from a neighboring membrane by an intermembrane space, a spacer as described above being positioned in at least one of the intermembrane spaces thus defined.

[0148] The membrane stack can be designed to be supplied with an aqueous electrolytic solution of concentration CA in a solute and an aqueous electrolytic solution of concentration CB in the same solute, CB being greater than CA. These solutions are to circulate alternately in the intermembrane spaces of the stack. A spacer is then positioned in the intermembrane spaces through which the electrolytic solution Ca is to circulate. Device D allows the electrical energy generated by the potential difference between the two electrodes to be harvested.

[0149] According to some embodiments, a spacer is positioned in each intermembrane space.

[0150] The difference in concentrations CA and CB in the same solute causes the mobility of electrolytes from the more concentrated solution to the less concentrated solution.

[0151] In this case, the device is a reverse electrodialysis or RED device.

[0152] The membrane stack can be supplied with an aqueous electrolytic solution of concentration C containing a solute that must circulate in the intermembrane spaces of the stack, with a spacer positioned in each intermembrane space. Device D allows a potential difference to be applied between the two electrodes in this case.

[0153] In this case, applying the voltage causes the electrolyte cations to migrate towards the cathode and the electrolyte anions in the opposite direction towards the anode. A solute-enriched solution and a solute-depleted solution are collected at the device outlet.

[0154] In this case, the device is an electrodialysis deionization device.

[0155] Membranes

[0156] For the purposes of this invention, "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 mostly anions or cations to pass through, and strongly inhibits or delays the passage of ions of the opposite charge.

[0157] Advantageously, the membrane is also permeable to water.

[0158] Any type of membrane that is selectively permeable to anions or cations is compatible with the invention.

[0159] The membrane, which is selectively permeable to anions or cations, can be in the form of a homogeneous layer of one material or a stack of several layers made of different materials.

[0160] Advantageously, the membrane selectively permeable to anions or cations of the invention is an ion-exchange membrane, that is, a membrane formed of at least one mineral or organic material bearing ionogenic groups, also called ion-exchange groups, which confer to 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 bind an ion of the same charge contained in that liquid.

[0161] In one embodiment, the membrane comprises an organic polymer bearing 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.

[0162] 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 copolymer matrix such as a styrene-divinylbenzene copolymer.

[0163] The membrane may also be as defined in the following applications, some of which were filed by the applicant. The membrane may be a nanofluidic membrane with a high surface charge density, as detailed in international applications WO 2014 / 0606902017 and WO 2017 / 037213. In another embodiment, as detailed in international application WO2021 / 234296, the membrane comprises at least one layer formed of a cellulosic material comprising a network of nanofibers and / or cross-linked cellulose microfibers.In another embodiment, as detailed in international application WO2021 / 234294, the membrane comprises at least one inner layer disposed between two outer layers, in which the outer layers are each formed of a first material comprising a network of nanofibers and / or cross-linked microfibers and the inner layer is formed of a second material comprising nanoparticles functionalized on the surface by charged groups and / or which become charged in the presence of water.

[0164] By membrane stacking, we mean an arrangement of membranes as illustrated in Fig. 2, i.e., the membranes are arranged between the 2 electrodes positioned opposite each other.

[0165] In a particular embodiment of the invention, the device may comprise N+1 membrane and N intermembrane spaces, N being an even integer, in particular between 2 and 1000, preferably between 2 and 250, for example between 2 and 100.

[0166] We can also talk about membrane pairs in the device. In this case, the number of membrane pairs is equal to N / 2.

[0167] Other components of the device

[0168] Electrodes and device D

[0169] The device according to the invention comprises a pair of electrodes and a device D for harvesting the electrical energy generated by the potential difference existing between the 2 electrodes or for applying a potential difference between the 2 electrodes.

[0170] The type of electrodes depends on the type of device according to the invention. Any type of electrode commonly used in devices according to the invention and well known to those skilled in the art may be used.

[0171] Different types of electrodes can be used in a device comprising an electrode stack, whether it is a power generation device or a separation device.

[0172] 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 Iron complexes of the type [Fe(CN)e] 4 “ / [Fe(CN)6] 3 -.

[0173] The electrodes can be, in particular, redox-flow electrodes, as illustrated in Figure 2. The principle of these electrodes is based on an oxidation reaction and a reduction reaction at each electrode. Among the various possible redox couples are FeCh / FeCh, K3Fe(CN)6 / K4Fe(CN)6, Fe(III)-EDTA / Fe(II)-EDTA, and Na3Fe(CN)β / Na4Fe(CN)6.

[0174] In addition to the RedOx couple, the recirculating solution may include a solute solution of concentration (CA+CB) / 2.

[0175] The recirculating solution can be an aqueous saline solution, for example seawater, where the redox function is ensured by the dissociation of the water molecule, producing dihydrogen. The dihydrogen produced can be recovered and stored.

[0176] The electrodes are preferably capacitive or supercapacitive. The principle of these electrodes is based on an interaction between the electrodes and the electrolyte which leads to the spontaneous accumulation of charges at the interfaces.

[0177] Each electrode can be in contact with a membrane that is selectively permeable to ions of the same sign, that is, each electrode can be in contact with a membrane that is selectively permeable to cations or each electrode can be in contact with a membrane that is selectively permeable to anions.

[0178] In one embodiment, the electrodes are connected together to a device D that collects, that is, circulates and captures, the electrical energy spontaneously generated by the potential difference existing between them. This device forms an external electrical circuit advantageously comprising an electrical cable, a battery, a light bulb, or any other type of electrical load.

[0179] According to another embodiment, the electrodes are connected together to a device D allowing a voltage to be applied between the 2 electrodes.

[0180] Electrolyte solutions

[0181] Electrolytic solutions are aqueous solutions comprising a solute in the form of a dissolved salt and having a pH ranging from 6 to 9.

[0182] Advantageously, the pH of electrolytic solutions ranges from 7 to 8.

[0183] The solutes can be of any chemical nature as long as they dissolve in the solution in the form of ions.

[0184] Advantageously, the solute is chosen from alkali metals or alkaline earth halides, preferably from NaCl, KCl, CaCh, and MgCh, and preferably NaCl again. Electrolyte solutions can be:

[0185] - synthetic solutions;

[0186] - natural solutions, such as fresh water from lakes or rivers, groundwater, brackish water, seawater;

[0187] - industrial production water, petroleum production water or biological solutions.

[0188] Electrolytic solutions are advantageously natural solutions, such as fresh water from lakes or rivers, groundwater, brackish water, seawater with a pH of 6 to 9.

[0189] METHOD FOR PRODUCING ELECTRICAL ENERGY OR DEIONIZING IN A DEVICE COMPRISING A STACK OF MEMBRANE

[0190] Another object of the invention relates to a method for producing electrical energy using such a device and comprising the following steps:

[0191] (i) supply the membrane stack with an aqueous electrolytic solution of concentration CA in a solute and an aqueous electrolytic solution 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

[0192] ii) allow the electrolytes to diffuse from the intermembrane spaces supplied by the electrolytic solution of concentration CB to the adjacent intermembrane spaces supplied by the electrolytic solution of concentration CA;

[0193] iii) capture the electrical energy generated by the potential difference existing between the two electrodes, using device D.

[0194] In one embodiment, an electrolytic solution of concentration CA in a solute and an electrolytic solution of concentration CB in the same solute, CB being greater than CA, are circulated in the intermembrane spaces of the stack of membranes. The solutions circulate alternately in the stack, meaning that the electrolytic solution of concentration CA in a solute circulates in the intermembrane space between two membranes and the electrolytic solution of concentration CA in the same solute circulates in the adjacent intermembrane space(s).

[0195] An osmotic flow is generated between two adjacent intermembrane spaces, preferably by diffusio-osmosis, i.e., without any osmotic pressure arising. Steps i) and ii) are preferably implemented by supplying the electrolytic solution of concentration CA and the electrolytic solution of concentration CB as a continuous flow.

[0196] The flow rate of the electrolytic solutions is adjusted to optimize the salinity gradient of the device by playing on the residence time of the electrolytic solutions within the device.

[0197] Advantageously, electrolytic solutions of concentration CA and CB are at a temperature between 10°C and 40°C, preferably at a temperature between 15°C and 35°C.

[0198] Advantageously, the process according to the invention is an energy production process exploiting the difference in salinity between a seawater solution and a freshwater solution.

[0199] Indeed, the pH of these solutions is usually in the range of 6 to 9. Advantageously, solution CB is a seawater solution and solution CA is a freshwater solution.

[0200] 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.

[0201] In the context of the present invention, the concentration ratio Rc denotes the ratio of the concentration of the most concentrated solution to the concentration of the least concentrated solution, i.e. the ratio CB / CA.

[0202] Preferably, the CB / CA concentration ratio is from 2 to 100, preferably from 5 to 50.

[0203] Advantageously, the device includes means for switching the flow of electrolytic solutions of concentrations CA and CB, which are implemented according to a mode (1) in which the electrolytic solution of concentration CA in a solute flows in the intermembrane space between two membranes and the electrolytic solution of concentration CA in the same solute flows in the adjacent intermembrane space(s), and a mode (2) in which the flow of solutions CA and CB is reversed. Even more favorably, to increase the asymmetry of the device and amplify the amount 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 being greater than 1, preferably greater than 2.

[0204] Another object of the invention relates to a deionization process using a device as described above comprising a membrane stack, said process comprising the following steps:

[0205] (i) supply the membrane stack with an aqueous electrolytic solution of concentration C in a solute such that said solution circulates in the intermembrane spaces of said stack

[0206] ii) apply a potential difference between the anode and the cathode

[0207] iii) recover at the output of stacking an electrolytic solution of concentration C1 in this same solute greater than the concentration C and an electrolytic solution of concentration C2 in this same solute less than the concentration C.

[0208] Steps i) and ii) are preferably implemented by supplying the electrolytic solution of concentration C in the form of a continuous flow.

[0209] The flow rate of the electrolytic solution of concentration C is adjusted to optimize the transfer of ions from one intermembrane space to a neighboring intermembrane space as a function of the applied voltage.

[0210] Advantageously, the process according to the invention is a seawater desalination process.

[0211] In this embodiment, the application of a voltage between the 2 electrodes causes the cations of the electrolyte to migrate towards the cathode and the anions of the electrolyte in the opposite direction towards the anode.

[0212] USING THE SEPARATOR

[0213] Another object of the invention relates to the use of a porous polymer material forming a continuous three-dimensional network, having a porosity greater than 70%, preferably greater than 80%, whose pores are interconnected, and having charged surface functional groups, as a spacer positioned between a membrane selectively permeable to cations and a membrane selectively permeable to anions in a power generation or deionization device supplied by at least one aqueous electrolytic solution comprising a solute in the form of a dissolved salt and having a pH of 6 to 9.

[0214] The spacer, membranes, electrolytic solution(s) and energy production or deionization device are as described above.

[0215] EXAMPLES

[0216] The present invention will be better understood by reading the following examples which illustrate the invention in a non-limiting way.

[0217] The device and process illustrated are a device and process for producing energy by reverse electrodialysis.

[0218] 1. Materials Characterization

[0219]

[0220] The polymer materials used are characterized by implementing the characterization techniques described in the description.

[0221] Measurement of the isoelectric point of the polymer material:

[0222] Zeta potential values ​​are measured using a Zetasizer-type instrument (Nano ZS90, Malvern Panalytical, UK). Polymer material samples are ground into a fine powder and then dispersed in solutions at different pH values ​​(2-10) for zeta potential measurements.

[0223]

[0224] The device used is similar to that shown in Figure 3 except for the number of cationic (2) and anionic (3) membranes and spacers.

[0225] The device used comprises 21 membranes, including 11 cationic membranes (2) and 10 anionic membranes (3) (compared to 4 and 3 respectively for the device in Figure 3), each having a surface area of ​​9 cm² 2 .

[0226] A spacer (4) is positioned between 2 adjacent membranes. The device used therefore has 20 spacers.

[0227] The electrodes (1) are connected by an external electrical circuit comprising a voltmeter and an ammeter. The raw materials used in the examples are listed below:

[0228] Membranes:

[0229] - Cation exchange membrane (noted Mb+) marketed by Fumasep under the reference FKS 30;

[0230] - Anion exchange membrane (noted Mb-) marketed by Fumasep under reference FAS30.

[0231]

[0232] - Woven nylon canvas marketed by the company SEFAR under the reference SEFAR NITEX 03-200 / 47 with a thickness of 150pm and an openness rate of 47%;

[0233] - SINOYQX YQX-ll melamine foam compressed to 125 pm thickness having a porosity of 99.8% and a pore size of 50 pm;

[0234] - negatively charged melamine foam obtained from the previous commercial melamine foam (the method of preparation of which is described below).

[0235] Saline solutions for feeding the device

[0236] An aqueous NaCl solution at 35 g / L (solution with concentration Cb) and an aqueous NaCl solution at 1.17 g / L (solution with concentration Ca) are used (corresponding to solutions (7) and (8) in Figure 3, respectively). The pH of these two solutions is 7.5. The temperature of the saline solutions is 25°C.

[0237] The flow rate of the saline solutions is 1.5 cm / s.

[0238] Redox Solution

[0239] The electrode system is a redox-flow system with a circulating electrolyte composed of a 0.5M NaCl solution and 0.25M 50 / 50 potassium ferri / ferrocyanide. The collectors are made of carbon felt and graphite.

[0240] The temperature of the rinsing solution is 25°C.

[0241] The flow rate of the solution is 3 cm / s.

[0242] 3. Preparation of melamine foams carrying negative surface charges introduced by grafting onto the melamine foam

[0243] The single-step grafting process involves grafting sodium sulfanilate (SSA) (0.1 M) onto melamine foam (MM) using a radical grafting technique catalyzed by iron powder (2 g / g SSA) in the presence of hydrochloric acid (0.5 M) and sodium nitrite (0.1 M). The grafting process involves reacting the amine groups of SSA with the amine groups of melamine foam. To achieve this, the melamine foam is immersed in an excess of the reagent solution for 1.5 hours at room temperature.

[0244] The foam is then removed from the solution and rinsed successively in a 0.5 M HCl solution, then a 0.5 M NaCl solution, and finally with distilled water.

[0245] The grafted melamine foam is then dried.

[0246] Sulfonate groups give melamine foam a negative surface charge.

[0247] 4. Results

[0248] Preparation of the devices:

[0249] Devices D1 and D2 according to the invention (using raw, ungrafted melamine foam and melamine foam with negative surface charges as spacers, respectively) and comparative device C1 not according to the invention (using nylon fabric as a spacer) - the electrolytic solutions are pH 7.5 for all 3 devices

[0250] and a C2 device not in accordance with the invention (using raw melamine foam - not grafted as a spacer) - the electrolytic solutions are of pH 5. The results are presented in Table 1.

[0251] [Table 1]

[0252]

[0253] with :

[0254] - V membrane = AV the potential measured by the voltmeter when the external circuit is open;

[0255] - 1 the current is measured by an ammeter at the closing of the external circuit; - R, the surface resistance of the device is calculated by Ohm's law: R = V / IS;

[0256] - Pmax = Vmembrane * J / 4

[0257] Similar results are obtained for the nylon fabric spacer using electrolytic solutions of pH 5.

[0258] Table 1 shows that the performance of a device with a raw melamine foam spacer or a nylon canvas spacer is similar when the pH of the electrolytic solutions is 5.

[0259] Table 1 shows that by using a raw melamine foam spacer instead of a nylon canvas spacer, the power developed per unit area is multiplied by a factor of 2 when the pH of the electrolytic solutions is 7.5.

[0260] Table 1 also shows that by using a melamine foam spacer carrying negative surface charges instead of a nylon canvas spacer, the power developed per unit area is multiplied by a factor greater than 3 when the pH of the electrolytic solutions is 7.5.

[0261] The table also shows that by using a melamine foam spacer carrying negative surface charges instead of a raw melamine foam spacer, the power developed per unit area is increased by about 60% when the pH of the electrolytic solutions is 7.5.

[0262] The applicant believes that the difference in effectiveness between the device and the raw melamine spacer, depending on pH, is related to the charge of the melamine's functional groups. At pH 7.5, melamine has a higher overall negative charge than at pH 5, which promotes ion transfer within the device. Surface charge grafting further increases the device's effectiveness.

Claims

Tl DEMANDS 1. Electrochemical device comprising: - two electrodes; - a stack of membranes, arranged between the two electrodes, comprising an alternation of membranes selectively permeable to cations and membranes selectively permeable to anions, and such that each membrane is separated from a neighboring membrane by an intermembrane space, a spacer being positioned in at least one of the intermembrane spaces thus defined, said spacer being made of a porous polymer material forming a continuous three-dimensional network, having a porosity greater than 95%, whose pores are interconnected, and possessing charged surface functional groups; - an aqueous electrolytic solution comprising a solute in the form of a dissolved salt, having a pH ranging from 6 to 9 and impregnating the pores of said spacer; - and a device D for harvesting the electrical energy generated by a potential difference existing between the 2 electrodes or for applying a potential difference between the 2 electrodes.

2. Device according to claim 1 in which the pores of the spacer have a diameter between 10 pm and 100 pm, preferably between 20 pm and 80 pm.

3. A device according to any one of the preceding claims, wherein the polymer material has negatively charged surface functional groups selected from the following: the sulfonate group -SO3; the carboxylate group -CO2; the aminodiacetate group -N(CH2CC>2')2; the phosphonate group PC>2 3 ' ; the amidoximate group -C(=NH2)(NO'), the aminophosphonate group -CH2-NH-CH2-PO3 2 ', the thiolate group -S and their mixtures.

4. A device according to any one of claims 1 to 2, wherein the polymer material has positively charged surface functional groups selected from the quaternary ammonium group -N(R)s + with R an alkyl group in C1-C4, the tertiary ammonium group -N(H)R)2 + with R an alkyl in C1-C4, preferably an alkyl in C1, the dimethylhydroxyethylammonium group -N(C2H4OH)CH3)2 + , and their mixtures.

5. A device according to any one of the preceding claims, characterized in that the stack of membranes is intended to be supplied with an aqueous solution electrolytic solution of concentration CA in a solute and an aqueous electrolytic solution of concentration CB in the same solute, CB being greater than CA, said solutions circulating alternately in the intermembrane spaces of said stack, a spacer being positioned in the intermembrane spaces through which the electrolytic solution of concentration CA must circulate, and in that device D allows the electrical energy to be collected from the potential difference existing between the 2 electrodes.

6. Device according to claim 5, characterized in that a spacer is positioned in each intermembrane space.

7. Device according to any one of claims 1 to 4 characterized in that the stack of membranes is intended to be supplied with an electrolytic solution of concentration C in a solute to circulate in the intermembrane spaces of said stack, a spacer being positioned in each intermembrane space, and in that the device D allows a potential difference to be applied between the 2 electrodes.

8. A method for producing electrical energy using a device as described in claim 5 or claim 6 comprising the following steps: i) supplying the membrane stack with an electrolytic solution of concentration CA in a solute and an electrolytic solution of concentration CB in the same solute, CB being greater than CA, such that said solutions circulate alternately in the intermembrane spaces of said stack ii) allow the electrolytes to diffuse from the intermembrane spaces supplied by the electrolytic solution of concentration CB to the adjacent intermembrane spaces supplied by the electrolytic solution of concentration CA; iii) capture the electrical energy generated by the potential difference existing between the two electrodes, using device D.

9. A process according to claim 8, characterized in that the CB / CA concentration ratio ranges from 2 to 100, preferably from 5 to 50.

10. A deionization process using a device as described in claim 7 comprising the following steps: (i) supply the membrane stack with an electrolytic solution of concentration C in a solute such that said solution circulates in the intermembrane spaces of said stack ii) apply a potential difference between the anode and the cathode iii) recover at the output of stacking an electrolytic solution of concentration C1 in this same solute greater than the concentration C and an electrolytic solution of concentration C2 in this same solute less than the concentration C.

11. A process according to any one of claims 8 to 10, characterized in that the electrolytic solution(s) are aqueous solutions comprising a solute selected from alkali halides or alkaline earth halides, preferably selected from NaCl, KCl, CaCh and MgCh, preferably NaCl.

12. Use of a porous polymer material forming a continuous three-dimensional network, having a porosity greater than 95%, whose pores are interconnected, and having charged surface functional groups, as a spacer positioned between a membrane selectively permeable to cations and a membrane selectively permeable to anions in a power generation or deionization device powered by at least one aqueous electrolytic solution comprising a solute in the form of a dissolved salt and having a pH of 6 to 9.

Images