Ion-selective composite membrane

Abstract

The invention relates to an ion-selective composite membrane, the thickness of which is between 4 pm and 100 pm, and comprising at least one internal layer (2) arranged between two external layers (1, 3), in which: - the external layers (1, 3) are each formed from a first material comprising a network of crosslinked nanofibers and / or microfibers and pores with a diameter of between 10 nm and 10 pm, - the internal layer (2) is formed from a second material comprising nanoparticles functionalized with surface-charged groups and / or groups that become charged in the presence of water, and having pores with a diameter of between 1 nm and 100 nm.

Description

Background Technology

[0001] Ion-selective conductive membranes play an important role in many industrial processes.

[0002] In fact, many of these methods are based on ion-selective conduction between two volumes separated by a membrane, based on the charge sign of the ions, under the influence of stress on both sides of the interface, such as pressure gradient, voltage gradient, or concentration gradient.

[0003] The most commonly used membranes that selectively conduct ions based on their charge sign are called ion exchange membranes (IEMs). Cation exchange membranes (CEMs) and anion exchange membranes (AEMs) are distinct; CEMs allow cation cycling, while AEMs allow anion cycling. These IEMs are prepared from ion exchange resin particles dispersed in an inert polymer binder (homogeneous IEMs) or by directly introducing functional groups into the structure of the polymer constituting the membrane (heterogeneous IEMs).

[0004] IEMs are used, for example, in water treatment to extract unwanted substances from fluids to be treated, such as desalinated saltwater or seawater. In desalination methods, sodium... + Ions and Cl - Extraction is accomplished by the migration of ions through alternating membranes under the influence of an electric field, which allow selective passage of anions (AEM) or cations (CEM). At the end of the treatment, both freshwater and brine are recovered.

[0005] Membranes that selectively conduct ions based on their charge signs are also used in methods for storing electrical energy in the form of electrolyzed hydrogen, or conversely, for using this hydrogen as an electrical energy source (hydrogen fuel cells). These methods involve an electrochemical reaction, namely the electrolysis of water. The electrolysis of water takes place in an electrolyzer, which is a device comprising a set of electrolytic cells placed side-by-side and connected to an electrical energy source via electrodes. Each electrolytic cell is typically formed by contacting two metal plates called electrodes with a solid or liquid electrolytic medium. In the case of a liquid electrolytic medium, the electrolytic cell comprises electrodes immersed in an aqueous solution containing both the water required for the reaction and electrolytes, soluble compounds, and current conductors (e.g., potassium hydroxide (KOH) for alkaline electrolysis or sulfuric acid (H₂SO₄) for acidic electrolysis). The two electrodes are connected to a generator that increases the voltage difference between the two electrodes. When the voltage difference exceeds a certain threshold, current is observed flowing through the circuit, and molecular oxygen (O₂) is formed at the anode (the electrode connected to the positive terminal of the generator) and molecular hydrogen (H₂) is formed at the cathode (the electrode connected to the negative terminal of the generator). For example, under acid hydrolysis, at the anode, water molecules decompose according to the following equation: H₂O ---> 2 H + + 2e- +½ O2, at the cathode, protons are reduced according to the following equation: H + + 1e - ---> ½ H2, generating a flux of hydrated hydrogen ions between the anode and cathode. To prevent H2 and O2 from spontaneously recombining into an explosive gas, it is necessary to place a membrane between the electrodes that allows protons to pass through but not H2 and O2. Recently, in batteries used in proton exchange membrane (PEM) electrolysis, the electrolyte medium is a solid polymer electrolyte in the form of a cation exchange membrane. In these batteries, the porous metal electrode (Ep) is in direct contact with the ECM (M), and both sides of the Ep-M-Ep assembly are in contact with an aqueous solution. In these batteries, the membrane material serves as both the separator and the solid electrolyte.

[0006] However, IEMs typically exhibit weak ion-conducting currents, contributing significantly to the ohmic balance in both electrodialysis and reverse electrodialysis systems. This limits the applicable current density to a few hundred mA·cm² in most cases. -2 This limits the operational scope of IEM technology. Furthermore, the fabrication of these membranes is very expensive, which is why a large portion of the investment in membrane method maintenance is used to replace these membranes.

[0007] IEMs can also be used to produce electricity from electrolyte gradients (especially salinity gradients).

[0008] Therefore, reverse electrodialysis (RED) is based on the use of membranes, whose fundamental property is the selective transport of ions based on their charge sign. RED devices typically consist of alternating AEMs and CEMs separated by spacer membranes to form channels that allow fluid flow. In these cells, the alternating circulation of brine and desalinated water allows an ion flux to be generated at each IEM of the device. At the ends of this membrane stack, electrodes collect the current generated by the entire ion flux.

[0009] One of the problems with devices that generate electricity from salinity gradients (such as current RED devices) is their low electrical productivity, because current IEMs produce only a few W / m of electrical power per unit area of ​​membrane (i.e., membrane power). 2 membrane.

[0010] A method for solving this problem is described in international application No. WO 2014 / 060690, published on April 24, 2014. In this method, nanoporous membranes have been proposed whose pore inner surfaces are coated with boron nitride or more commonly a mixture of boron, carbon, and nitrogen. These nanoporous membranes utilize diffusion-permeation within the pores and generate kW / m². 2High-power membranes. Recently, international application WO 2017 / 037213, published on March 9, 2017, also described nanoporous membranes with titanium oxide coating on the inner surface of their pores, allowing for power outputs of approximately 5 kW / m³. 2 The membrane power is high. However, this method involves using membranes based on boron nitride or titanium oxide, which are complex and extremely expensive to prepare on a larger scale than in a laboratory setting, given the required materials. Furthermore, the materials used in these membranes are environmentally harmful, posing a risk if released into the environment.

[0011] To date, no membrane has been able to selectively conduct ions based on their charge sign, generate high membrane power under the influence of salinity gradients, be simple and economical to prepare, and have limited environmental risks. Summary of the Invention

[0012] Therefore, the object of the present invention is to provide a membrane that selectively conducts ions based on the charge sign of the ions, the membrane being economical and easy to manufacture, and capable of generating high membrane power when integrated into a device that generates electricity from an electrolyte gradient (especially a salinity gradient) or into a reverse device for water purification or desalination.

[0013] Another object of the present invention is to provide a membrane that selectively conducts ions based on the charge sign of the ions, the membrane being prepared from a material that poses virtually no risk to the environment.

[0014] These objectives are achieved through the invention described below.

[0015] Composite membrane

[0016] The first subject of this invention is an ion-selective conductive composite membrane having a thickness between 4 μm and 100 μm and comprising at least one intermediate layer (2) disposed between a first outer layer (1) and a second outer layer (3), wherein:

[0017] - The first outer layer (1) and the second outer layer (3) are respectively formed of a first material, the first material comprising a network of cross-linked nanofibers and / or microfibers and pores with a diameter between 10 nm and 10 µm.

[0018] - The intermediate layer (2) is formed of a second material comprising nanoparticles whose surfaces are functionalized with charged groups and / or become charged groups in the presence of water, and having pores with diameters between 1 nm and 100 nm.

[0019] The inventors unexpectedly discovered that, under the influence of a salinity gradient, the composite membrane of this invention generates very high membrane power, approximately several hundred W / m. 2The membrane is preferably at least 300 W / m 2 More preferably at least 500 W / m 2 .

[0020] Without being bound by any particular theory, the inventors believe that this very high membrane power is determined by the surface charge of the materials used in the layers of the membrane of the present invention, together with the porosity of the first outer layer (1), the second outer layer (3), the intermediate layer (2), and the composite membrane.

[0021] In particular, according to the inventors, this combination of porosity and surface charge endows the composite membrane with nanofluid properties and influences the selective passage of ions through the membrane according to a specific and unexpected mechanism that would not be observed in materials constituting the membrane with greater porosity.

[0022] Structure of composite membrane

[0023] The thickness of the composite membrane is advantageously between 4 μm and 75 μm.

[0024] The thickness of each of the first outer layer (1) and the second outer layer (3) is advantageously between 2 μm and 45 μm, preferably between 2 μm and 30 μm, and more preferably between 2 μm and 25 μm. The outer layers advantageously have the same thickness.

[0025] The thickness of the intermediate layer (2) is preferably between 10 nm and 10 μm, more advantageously between 10 nm and 2 μm, preferably between 10 nm and 1 μm, preferably between 10 nm and 800 nm, preferably between 10 nm and 400 nm, and more preferably between 200 nm and 500 nm.

[0026] Preferably, the thickness of each of the first outer layer (1) and the second outer layer (3) is advantageously between 2 μm and 45 μm, and the thickness of the intermediate layer (2) is between 10 nm and 10 μm.

[0027] According to the inventors, the very small thickness of the intermediate layer allows for excellent permeability while achieving highly selective ion conduction.

[0028] In this invention, the thickness of the composite film and the thickness of different layers are measured by scanning electron microscopy of the cross-section of the dry film.

[0029] The composite membrane preferably includes a second material that is less than 10% by weight relative to the weight of the first material, more preferably a second material that is between 2% and 8% by weight relative to the weight of the first material, and more preferably a second material that is between 3% and 5% by weight relative to the weight of the first material.

[0030] The surface charge density on the inner wall of the composite membrane pores is advantageously 0.001 C / m. 2 Up to 3 C / m 2 Between, preferably 0.1C / m 2 Up to 1 C / m 2 between.

[0031] The surface charge density of the composite membrane was measured by dosimetry.

[0032] Intermediate layer (2)

[0033] Second material

[0034] According to the present invention, the term "nanoparticle" refers to a three-dimensional object in which at least one outer dimension is at the nanometer scale (i.e., at least one dimension is in the range of 1 nm to 100 nm).

[0035] The second material advantageously comprises nanoparticles in the form of individual nanoparticles, i.e., nanoparticles that are not aggregated or, in other words, not covalently bonded together.

[0036] The second material advantageously comprises at least 50% by mass of nanoparticles, at least 95% by mass of nanoparticles, and more preferably at least 99% by mass of nanoparticles, relative to the mass of the second material.

[0037] Advantageously, nanoparticles are not in the form of nanotubes.

[0038] The nanoparticles are preferably layered nanoparticles.

[0039] According to the present invention, the term "layered nanoparticle" refers to nanoparticles comprising atoms in the form of a single atomic monolayer (bound together by covalent bonds). Layered nanoparticles may consist of a single atomic monolayer (two-dimensional material) or a stack of 2 to 5 atomic monolayers (bound together by weak bonds, such as van der Waals forces).

[0040] In other words, layered nanoparticles are three-dimensional objects, with the first outer dimension being at the nanometer level, and the other two dimensions being significantly larger than the first dimension, particularly varying between the nanometer and micrometer levels.

[0041] The layered nanoparticles preferably have a median size between 5 μm and 50 μm, more preferably between 10 μm and 20 μm, and even more preferably 15 μm (also referred to as "D50").

[0042] D50 means that 50% by weight of the particles have a smaller size.

[0043] According to the present invention, the terms "monolayer," "bilayer," and "multilayer" in relation to layered nanoparticles refer to layered nanoparticles composed of one atomic monolayer, two atomic monolayers, and three to five atomic monolayers, respectively. Bilayer and multilayer layered nanoparticles are typically stabilized by weak interactions between atomic monolayers (e.g., van der Waals interactions).

[0044] The layered nanoparticles are preferably layered nanoparticles of metal oxides (especially SnO2 or TiO2), layered nanoparticles of transition metal dichalcogenides (e.g., molybdenum disulfide MoS2), layered nanoparticles of carbon, or mixtures thereof.

[0045] Layered carbon nanoparticles are advantageously layered carbon nanoparticles of monolayer graphene, layered carbon nanoparticles of bilayer graphene, layered carbon nanoparticles of multilayer graphene, or mixtures thereof.

[0046] According to the present invention, the term "monolayer graphene" refers to a two-dimensional crystalline material composed of carbon, exhibiting a specific allotropic form, which can be represented as a planar honeycomb structure. More specifically, monolayer graphene is composed of individual sp... 2 A thin sheet composed of planes of hybrid carbon atoms. Therefore, it can be described as a monolayer.

[0047] According to the present invention, the term "bilayer graphene" (or BLG) refers to a material composed of two graphene monolayers stacked together (stabilized by van der Waals interactions between the two graphene monolayers). BLG can be obtained by exfoliation of graphite or by chemical vapor deposition (CVD).

[0048] According to the present invention, the term "multilayer graphene" (or FLG) refers to a material consisting of 3 to 5 graphene sheets stacked together (stabilized by van der Waals interactions between different graphene planes).

[0049] The preferred material is single-layer graphene layered nanoparticles.

[0050] According to a preferred embodiment, the second material advantageously comprises at least 50% by mass of monolayer graphene, more preferably at least 95% by mass of monolayer graphene. The layered monolayer graphene nanoparticles preferably have a median size (also referred to as "D50") between 5 μm and 50 μm, more preferably between 10 μm and 20 μm, and more preferably 15 μm.

[0051] The layered nanoparticles of molybdenum disulfide are advantageously monolayered, bilayered, multilayered, or mixtures thereof.

[0052] According to the charge sign, when the composite membrane is placed in the presence of water, the charged groups or groups that become charged in the presence of water impart negative or positive surface charge to the intermediate layer (2) of the composite membrane.

[0053] Any charged group known to those skilled in the art that allows for the increase of surface charge on graphene particles, or that becomes charged in the presence of water, can be used in the context of this invention.

[0054] In one embodiment, the surface of the nanoparticles is functionalized with negatively charged groups and / or becomes negatively charged groups in the presence of water.

[0055] The negatively charged group and / or the group that becomes negatively charged in the presence of water is advantageously selected from epoxide groups, hydroxyl groups, carbonyl groups, carboxyl groups, sulfonate groups, and SO3 groups. - Carboxyl alkyl group R-CO2 - R is a C1-C4 alkyl group, preferably a C1 alkyl group, and the aminodiacetic acid ester group is -N(CH2CO2). - )2, Phosphate group PO3 2- amidoxine group -C(=NH2)(NOH), aminophosphonate group -CH2-NH-CH2-PO3 2- , thiol groups -SH, and mixtures thereof.

[0056] Preferably, the nanoparticles functionalized with negatively charged groups on their surface or transformed into negatively charged groups in the presence of water are layered nanoparticles of graphene oxide (or GO).

[0057] The layered graphene oxide nanoparticles have negatively charged groups or become negatively charged groups in the presence of water, and are advantageously selected from epoxide groups, hydroxyl groups, carbonyl groups, carboxyl groups, and mixtures thereof.

[0058] In one embodiment, the surface of the nanoparticles is functionalized with positively charged groups and / or becomes positively charged groups in the presence of water.

[0059] Advantageously, the positively charged group and / or the group that becomes positively charged in the presence of water is selected from quaternary ammonium groups -N(R)3. + R is a C1-C4 alkyl group, and the tertiary ammonium group is -N(H)(R)2 + R is a C1-C4 alkyl group, preferably a C1 alkyl group, and the dimethylhydroxyethylammonium group is -N(C2H4OH)(CH3)2. + , and their mixtures.

[0060] First outer layer (1) and second outer layer (3)

[0061] First Material

[0062] According to the present invention, the term "nanofiber" refers to a three-dimensional object based on cellulose, wherein two of the three external dimensions are nanoscale (i.e., the range of two of the three dimensions is 1 nm to 100 nm), and the third external dimension is significantly larger than the other two dimensions, but is not necessarily nanoscale.

[0063] Therefore, the diameter of the nanofibers ranges from 1 nm to 100 nm, preferably from 1 nm to 70 nm, more preferably from 4 nm to 30 nm, and particularly from 4 nm to 20 nm. Furthermore, the length of the nanofibers is advantageously between 0.5 μm and 100 μm, particularly between 0.5 μm and 50 μm, for example between 0.5 μm and 10 μm, and also for example between 0.5 μm and 2 μm.

[0064] According to the present invention, the term "microfiber" refers to a three-dimensional object in which two of the three external dimensions are at the micrometer level (i.e., the range of two of the three dimensions is 0.1 μm to 10 μm), and the third external dimension is significantly larger than the other two dimensions.

[0065] Therefore, the microfibers have a diameter ranging from 0.1 μm to 10 μm, advantageously from 0.1 μm to 5 μm, further advantageously from 0.1 μm to 2 μm, particularly from 0.1 μm to 1 μm, 0.1 μm to 7 μm, or 0.1 μm to 0.2 μm.

[0066] Furthermore, the length of the microfibers is advantageously between 0.5 μm and 100 μm, particularly between 1 μm and 50 μm, for example between 1 μm and 10 μm, and also for example between 1 μm and 5 μm.

[0067] Advantageously, the nanofibers and / or microfibers have a shape factor that is advantageously greater than 10, preferably greater than 100.

[0068] According to the present invention, the term "shape factor" in relation to nanofibers and / or microfibers refers to the ratio of their length L to their diameter d (L / d).

[0069] The diameter of nanofibers and / or microfibers can be measured by TEM or SEM.

[0070] According to the present invention, the term "crosslinking" in relation to nanofibers and / or microfibers means that the fibers are linked together by covalent chemical bonds (sometimes referred to as "bridges") to form a three-dimensional network. In other words, they are not simply aggregated or self-assembled by weak bonds.

[0071] The first material plays a structural role in the composite membrane, and in particular, it allows the aforementioned functionalized nanoparticles to be retained in the form of an intermediate layer (2) placed between the first outer layer (1) and the second outer layer (3).

[0072] Furthermore, the first material of the first outer layer (1) and the second outer layer (3) ensures the integrity of the intermediate layer (2), especially during use, when the intermediate layer (2) is subjected to stress, such as the pressure gradient across the membrane.

[0073] Nanofibers and / or microfibers advantageously carry charged groups or become charged groups in the presence of water.

[0074] In the first embodiment, the charged groups of the first outer layer (1) and / or the groups that become charged in the presence of water have opposite signs to the charged groups of the second outer layer (3) and / or the groups that become charged in the presence of water. In this embodiment, the composite membrane is a bipolar composite membrane.

[0075] In the second embodiment, the charged groups of the two first outer layers (1) and the second outer layer (3) and / or the groups that become charged in the presence of water have the same symbols, which are advantageously the same as the charged groups of the functionalized nanoparticles or the groups that become charged in the presence of water.

[0076] This has the advantage of increasing the surface charge of the entire composite film of the present invention.

[0077] According to the inventors, the presence of charged groups with the same sign or groups that become charged in the presence of water within the intermediate layer (2) and the first outer layer (1) and the second outer layer (3) of the composite membrane allows for a synergistic effect, i.e., an unexpected improvement in the selective conduction of ions through the composite membrane.

[0078] Therefore, in this embodiment, the first material plays a role in the structure of the composite membrane and in ensuring the ability to selectively conduct ions.

[0079] Furthermore, the covalent bonds involved in the crosslinking of nanofibers and / or microfibers can also contain charged groups and / or become charged groups in the presence of water, for example, when the crosslinking agent used is a citrate. In this case, the crosslinked chemical bonds play a role in both the structure and the surface charge of the nanoporous material.

[0080] In one embodiment, the nanofibers and / or microfibers are composed of conductive materials, such as activated carbon as described below.

[0081] In this embodiment, the first outer layer (1) and the second outer layer (3) can conduct electrons, so when the composite membrane is used in membrane electrolysis or reverse electrolysis methods, preferably in electrodialysis or reverse electrodialysis methods, the first outer layer (1) and the second outer layer (3) can be used as capacitive electrodes. In other words, the outer layers conduct the current required for the electrolysis reaction or to carry out electrodialysis, or collect the current generated by the electrolysis reaction or the reverse electrodialysis reaction.

[0082] According to this embodiment, when the composite membrane is used in the reverse electrodialysis method, the fluid can flow in the pores of the first outer layer (1) and the second outer layer (3), and the electrical energy generated by the reverse electrodialysis is directly collected by the nanofibers and / or microfibers of the first outer layer (1) and the second outer layer (3).

[0083] Therefore, the composite membrane according to this embodiment allows for the manufacture of reverse electrodialysis equipment where it is not necessary to use spacers to form channels that allow fluid to flow between the membranes (as in the case of the RED type equipment described above).

[0084] This has the advantage of greatly reducing the resistance associated with the spacing between the membranes (“bulk”), often referred to as bulk resistance, thus enabling systems that generate higher membrane power.

[0085] organic materials

[0086] The first material of the first outer layer (1) and the second outer layer (3) advantageously includes nanofibers and / or microfibers of organic materials.

[0087] According to the present invention, organic materials are materials that essentially consist of carbon, oxygen and hydrogen.

[0088] Organic materials essentially consist of carbon, oxygen, and hydrogen, meaning that organic materials contain at least 90 mol% of carbon, oxygen, and hydrogen, preferably at least 95 mol% of carbon, oxygen, and hydrogen, and more preferably at least 97 mol% of carbon, oxygen, and hydrogen.

[0089] According to a preferred embodiment, the organic material comprises 70 mol% to 100 mol% carbon, 0 to 30 mol% hydrogen, and 0 to 15 mol% oxygen.

[0090] In addition, organic materials are advantageously free of fluorine, an element commonly found in ion exchange membranes (IEMs).

[0091] Organic materials are advantageously selected from cellulose, activated carbon, or mixtures thereof.

[0092] Cellulose matrix

[0093] In one embodiment, the first material is a cellulose matrix comprising cross-linked cellulose nanofibers and / or microfibers.

[0094] According to the present invention, the term "crosslinking" in relation to cellulose nanofibers and / or microfibers means that the fibers are interconnected by covalent chemical bonds (sometimes referred to as "bridges") to form a three-dimensional network in the form of a cellulose matrix. In other words, they are not simply aggregated or self-assembled by weak bonds.

[0095] The cellulose nanofiber and / or microfiber network advantageously has pores with diameters between 10 nm and 1000 nm.

[0096] Advantageously, the cellulose nanofibers have a diameter ranging from 1 nm to 100 nm, preferably from 1 nm to 70 nm, more preferably from 4 nm to 30 nm, and particularly from 4 nm to 20 nm. Furthermore, the length of the cellulose nanofibers is advantageously between 0.5 μm and 100 μm, particularly between 0.5 μm and 50 μm, for example between 0.5 μm and 10 μm, and also for example between 0.5 μm and 2 μm.

[0097] Advantageously, the diameter of the cellulose microfibers ranges from 100 nm to 1000 nm, preferably from 100 nm to 700 nm, and more preferably from 100 nm to 200 nm. Furthermore, the length of the cellulose microfibers is advantageously between 0.5 μm and 100 μm, particularly between 1 μm and 50 μm, for example between 1 μm and 10 μm, and also for example between 1 μm and 5 μm.

[0098] Advantageously, the cellulose nanofibers and / or microfibers have a shape factor that is advantageously greater than 30, preferably greater than 100.

[0099] Advantageously, the cellulose matrix comprises at least 90% by mass of cellulose nanofibers and / or microfibers, at least 95% by mass of cellulose nanofibers and / or microfibers, and more preferably at least 99% by mass of cellulose nanofibers and / or microfibers, relative to the mass of the cellulose matrix.

[0100] Cellulose nanofibers and / or microfibers can be obtained by techniques known to those skilled in the art, particularly by mechanical, enzymatic or chemical treatment of naturally derived lignocellulosic materials (e.g., wood).

[0101] In the case of wood, these treatments have the particular effect of separating cellulose from other components of the wood, such as lignin and hemicellulose. For this purpose, natural cellulose fibers undergo chemical pretreatment or post-treatment, particularly enzymatic treatment, and / or mechanical treatment, to induce deconstruction prior to mechanical processing in a homogenizer. It is known that the size (particularly the diameter) of the cellulose fibers in the material can be adjusted according to the treatments undergone by the natural cellulose source.

[0102] Therefore, cellulose nanofibers and / or microfibers can be obtained by mechanically treating lignocellulose fibers to provide sufficient mechanical energy to break the hydrogen bonds that hold the microfibers together. Mechanical treatment typically follows a chemical or enzymatic treatment step. For example, this treatment step can be an oxidative treatment, particularly using an oxidizing agent such as TEMPO (2,2,6,6-tetramethylpiperidin-1-yl oxide). The resulting product is commonly referred to in the literature as “nanofibrillar cellulose” (abbreviated as “NFC”), “cellulose nanofibers” (abbreviated as “CNF”), or “microfiber cellulose” (abbreviated as “MFC”).

[0103] Typically, MFC materials are prepared with fewer mechanical and / or chemical treatments compared to those used to obtain NFC, and therefore MFCs usually have fibers with larger diameters than those observed in NFC. However, there are no clear definitions for MFC and NFC / CNF, so these terms are often used interchangeably in the literature.

[0104] Cellulose nanofibers and / or microfibers are preferably nanocellulose nanofibers and / or microfibers.

[0105] Cellulose nanofibers and / or microfibers may include impurities from their preparation methods. These impurities may in particular be hemicellulose or lignin.

[0106] Therefore, the cellulose matrix may specifically include up to 5% by mass of hemicellulose, more preferably up to 3% by mass of hemicellulose, or up to 1% by mass of hemicellulose.

[0107] The cellulose matrix may specifically include up to 5% by mass of lignin, more preferably up to 3% by mass of lignin, or up to 1% by mass of lignin.

[0108] Since cellulose monomers naturally have alcohol groups on their C2, C3 or C6 carbon atoms, the cellulose nanofibers and / or microfibers of the present invention inherently carry a negative surface charge.

[0109] In one embodiment, the inherent negative surface charge of the cellulose nanofibers and / or microfibers of the present invention can be increased by functionalizing them with negatively charged groups and / or groups that become negatively charged in the presence of water. This embodiment is particularly advantageous when the charged groups of the functionalized nanoparticles of the intermediate layer (2) and / or the groups that become negatively charged in the presence of water have a negative sign. In fact, this has the advantage of increasing the surface charge of the entire composite membrane of the present invention.

[0110] The charged groups carried by the microfibers and / or nanofibers and / or groups that become charged in the presence of water are advantageously covalently chemically bonded to the surface of the cellulose microfibers and / or nanofibers.

[0111] Any charged group known to those skilled in the art and capable of increasing the charge density of the microfibers and / or cellulose nanofibers of the present invention, and / or groups that become charged in the presence of water, may be used within the scope of the present invention.

[0112] Advantageously, the negatively charged groups on cellulose nanofibers and / or microfibers and / or groups that become negatively charged in the presence of water are selected from sulfonate groups -SO3. - Carboxylic acid ester group -CO2 - Carboxyl alkyl group R-CO2 - (where R is a C1-C4 alkyl group, preferably a C1 alkyl group), aminodiacetic acid ester group -N(CH2CO2) - 2. Phosphate group PO3 2- amidoxine group -C(=NH2)(NOH), aminophosphonate group -CH2-NH-CH2-PO3 2- , thiol groups -SH, and mixtures thereof.

[0113] Preferably, the carboxylic acid ester group -CO2 - and carboxyl alkyl group R-CO2 - (Where R is a C1-C4 alkyl group, preferably a C1 alkyl group).

[0114] Therefore, with -CO2 - Cellulose nanofibers and / or microfibers with carboxylic acid ester groups (i.e., oxidized cellulose nanofibers and / or microfibers) can be obtained, for example, by oxidation of cellulose nanofibers and / or microfibers (e.g., by TEMPO oxidation). Oxidation preferably occurs on the primary alcohol group attached to the C6 carbon atom of the monomer of the cellulose nanofibers and / or microfibers.

[0115] R-CO2 with carboxyl alkyl group -Cellulose nanofibers and / or microfibers (i.e., carboxylated cellulose nanofibers and / or microfibers) can be obtained, for example, by etherification of cellulose nanofibers and / or microfibers. Etherification preferably occurs on the alcohol group attached to the C2, C3, or C6 carbon atom of the monomer of the cellulose nanofibers and / or microfibers.

[0116] In another embodiment, the inherent negative surface charge of the cellulose nanofibers and / or microfibers of the present invention can be reversed by functionalizing them with positively charged groups and / or groups that become charged in the presence of water.

[0117] The embodiment is preferred when the charged groups of the functionalized nanoparticles in the intermediate layer (2) and / or the charged groups in the presence of water are positive.

[0118] Any charged group known to those skilled in the art that allows for the imparting of a positive surface charge to cellulose nanofibers and / or microfibers, or that becomes charged in the presence of water, can be used in the context of this invention.

[0119] Advantageously, the positively charged group and / or the group that becomes positively charged in the presence of negatively charged water is selected from quaternary ammonium groups -N(R)3. + R is a C1-C4 alkyl group, and the tertiary ammonium group is -N(H)(R)2 + R is a C1-C4 alkyl group, preferably a C1 alkyl group, and the dimethylhydroxyethylammonium group is -N(C2H4OH)(CH3)2. + , and their mixtures.

[0120] Preferably, it contains quaternary ammonium groups.

[0121] In a particular embodiment, the nanofibers and / or microfibers of the first outer layer (1) and the second outer layer (3) advantageously carry charged groups or become charged groups in the presence of water, and the charged groups of the first outer layer (1) or become charged groups in the presence of water have opposite signs to the charged groups of the second outer layer (3). In this embodiment, the composite membrane is a bipolar composite membrane.

[0122] Activated carbon materials

[0123] In one embodiment, the first material is an activated carbon felt comprising cross-linked activated carbon nanofibers and / or microfibers.

[0124] According to the present invention, the term "crosslinking" in relation to nanofibers and / or microfibers of activated carbon means that the fibers are interconnected by covalent chemical bonds (sometimes referred to as "bridges") to form a three-dimensional network in the form of activated carbon felt. In other words, they are not simply aggregated or self-assembled by weak bonds.

[0125] The thickness of the activated carbon felt is advantageously between 5 μm and 60 μm, preferably between 5 μm and 50 μm, and more preferably between 5 μm and 45 μm.

[0126] The pores of activated carbon felt have an advantageous diameter between 1 μm and 10 μm.

[0127] Advantageously, the activated carbon microfibers have a diameter ranging from 0.1 μm to 10 μm, preferably from 1 μm to 10 μm, and more preferably from 2 μm to 10 μm. Furthermore, the length of the activated carbon microfibers is advantageously between 10 μm and 500 μm, particularly between 20 μm and 400 μm, for example between 20 μm and 300 μm, and also, for example, between 1 μm and 200 μm.

[0128] The activated carbon felt preferably includes activated carbon microfibers.

[0129] Advantageously, the activated carbon nanofibers and / or microfibers have a shape factor that is advantageously greater than 10, preferably greater than 50.

[0130] Advantageously, relative to the mass of the activated carbon felt, the activated carbon felt comprises at least 90% by mass of activated carbon nanofibers and / or microfibers, at least 95% by mass of activated carbon nanofibers and / or microfibers, and more preferably at least 99% activated carbon nanofibers and / or microfibers.

[0131] Activated carbon nanofibers and / or microfibers can be obtained by techniques known to those skilled in the art, particularly by partial combustion and thermal decomposition of fibrous carbon precursors.

[0132] They are typically obtained by carbonizing fibers of resins containing organic (wood, fruit pits, nut shells) or mineral (peat, coal, lignite) carbon precursors, and then activating them with an activator. The carbon atoms then appear in the form of planar aromatic rings, which are randomly combined in a geometry similar to crepe paper.

[0133] Activated carbon nanofibers and / or microfibers are essentially composed of carbon, i.e., they include at least 60 mol% carbon, preferably at least 70 mol% carbon, more preferably at least 80 mol% carbon, with the remainder including elements such as oxygen and hydrogen.

[0134] According to a preferred embodiment, the activated carbon nanofibers and / or microfibers comprise 60 mol% to 100 mol% carbon, 0 to 30 mol% hydrogen, and 0 to 15 mol% oxygen.

[0135] Furthermore, since the ends of the polyaromatic units that make up activated carbon are oxygen and hydrogen atoms in the form of hydroxyl, carboxylic acid, lactone, phenol, chromene and pyranone, activated carbon nanofibers and / or microfibers inherently carry a negative surface charge.

[0136] Activated carbon nanofibers and / or microfibers conduct electricity.

[0137] method

[0138] The second subject of the present invention is a method for manufacturing a composite membrane according to the first objective of the present invention, characterized in that the method comprises the following steps:

[0139] i) Filtering a solution comprising nanofibers and / or microfibers onto a filter support to form a first outer layer comprising nanofibers and / or microfibers (1).

[0140] ii) A particle solution of nanoparticles whose surfaces are functionalized with charged groups and / or in the presence of water on the first outer layer (1) obtained at the end of step i) is formed on the first outer layer (1), thereby forming an intermediate layer (2).

[0141] iii) Filter the solution of nanofibers and / or microfibers to form a second outer layer (3) comprising nanofibers and / or microfibers on the intermediate layer (2) obtained at the end of step ii).

[0142] iv) Filtering a cross-linked solution that enables the nanofibers and / or microfibers of the first outer layer (1) and the second outer layer (3) to cross-link;

[0143] v) Dry the product from step iv), preferably in an oven;

[0144] vi) Remove the filter support to obtain a composite membrane.

[0145] Nanofibers and / or microfibers, as well as functionalized nanoparticles, are as defined in the first objective of this invention.

[0146] This method is simple, easy to implement, economical, and allows for control over the thickness of each layer of the composite membrane.

[0147] The filtration in steps i), ii), iii) and iv) is advantageously carried out using a vacuum pump, preferably under a vacuum of 1 bar.

[0148] After filtration in step i), step i1) may optionally be performed, including filtering the crosslinked solution onto the first outer layer (1) obtained at the end of step i).

[0149] After the filtration in step ii), step ii1) may optionally be performed, including filtering the crosslinked solution onto the intermediate layer obtained at the end of step ii).

[0150] The solution of nanofibers and / or microfibers used in steps i) and iii) comprises 0.1% to 1% by weight of cellulose nanofibers and / or microfibers, preferably 0.3% to 0.6% by weight of cellulose nanofibers and / or microfibers.

[0151] The nanofibers and / or microfibers of the solution in steps i) and iv) can be functionalized, as detailed in the first objective of this invention.

[0152] The particle solution of functionalized nanoparticles used in step ii) comprises 0.001 wt% to 0.01 wt% of functionalized nanoparticles, preferably 0.003 wt% to 0.006 wt% of functionalized nanoparticles.

[0153] The crosslinking solution used in step v) advantageously comprises one or more crosslinking agents of 0.005M to 0.02M, preferably one or more crosslinking agents of 0.008M to 0.012M.

[0154] The drying in step v) is advantageously carried out at a temperature that allows the crosslinking reaction to occur, and below the temperature that would damage the fibers and / or nanofibers. Preferably, the drying is carried out at a temperature between 80°C and 150°C, particularly between 80°C and 120°C, and even more preferably between 80°C and 100°C.

[0155] As described above, the crosslinking agent preferably has charged groups and / or becomes charged groups in the presence of water.

[0156] Citrate is preferred.

[0157] At the end of step vi), the composite membrane is in a state of dry material.

[0158] The method may further include step vii), which involves applying a pressure of 3 to 4 bar to the composite membrane obtained at the end of step vii) at a temperature ranging from 60°C to 95°C, preferably from 80°C to 90°C, for at least 5 minutes, thereby mechanically strengthening the ion-selective conductive membrane.

[0159] The pressure applied in step vii) can be performed using a press, particularly a hot press.

[0160] Any other techniques known to those skilled in the art may be considered, whether discontinuous (i.e., batch-based) or continuous, such as by a technique known as “roll-to-roll processing,” in which the film is produced continuously and then stored in rolls.

[0161] use

[0162] A third object of the present invention is to use the composite membrane according to the first object of the present invention or the composite membrane prepared by the method defined in the second object of the present invention as an ion-selective membrane.

[0163] This conduction is advantageously achieved by applying stress to both sides of the composite membrane, preferably under the influence of a voltage gradient or a concentration gradient.

[0164] The fourth object of the present invention is to use the composite membrane according to the first object of the present invention or the composite membrane prepared by the method defined in the second object of the present invention for the extraction of ionic or ionizable substances from water to be treated, for the extraction of organic compounds from water to be treated, for carrying out electrolysis or reverse electrodialysis, and particularly for the production of electricity, especially for the production of electricity from salinity gradients.

[0165] Composite membranes can be used to extract ionic or ionizable substances from water to be treated. They are particularly useful in methods for extracting ionic or ionizable substances from water to be treated, such as desalination and deionization. For example, it may involve treating water contaminated with elements selected from ionized forms of manganese and iron, and / or with substances such as nitrate ions, ammonium ions, carbonate ions, or organic compounds in ionized form.

[0166] This treatment can be carried out under the influence of concentration gradient (filtration) or voltage (electrodialysis) on both sides of the composite membrane.

[0167] In other words, under the influence of voltage across the composite membrane, the composite membrane can be used in any type of ion separation method in an aqueous medium.

[0168] Electrodesalination (commonly referred to as "desalination") is an electrodialysis technique designed to extract ions, particularly sodium and chloride ions, from seawater. Electrodialysis aims to remove all types of ions from solutions with relatively high ion concentrations, especially industrial wastewater. Electrodeionization is an electrodialysis technique used to extract solutions with lower ion concentrations, often solutions that have already undergone reverse osmosis treatment, and is particularly useful for obtaining ultrapure water. Electrodeionization is especially used in the pharmaceutical industry.

[0169] When the composite membrane is bipolar, it can be used in bipolar electrolysis methods, advantageously bipolar electrodialysis. The composite membrane can also be used to extract one or more organic compounds, preferably alcohols or alkanes, advantageously C1-C12, such as methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, glycerol, methane, ethane, propane, butane, and mixtures thereof, from water to be treated.

[0170] Composite membranes can also be used to perform electrolysis reactions. In this case, under the influence of a voltage gradient, ions migrate through the composite membrane, increasing oxidation and reduction reactions at the electrodes. For example, this could be a water electrolysis reaction, where hydrogen is produced under the influence of a voltage across the composite membrane.

[0171] Composite membranes can also be used to implement reverse electrolysis reactions, particularly for electricity production.

[0172] The composite membrane is preferably used in the manufacture of equipment designed to generate current through reverse electrodialysis under the action of an electrolyte concentration gradient (preferably a salinity gradient) acting on both sides of the composite membrane. Attached Figure Description

[0173] Figure 1 The schematic cross-sectional view of the membrane according to the present invention is shown, wherein the first outer layer (1) and the second outer layer (3) are formed of a cellulose matrix including cross-linked cellulose nanofibers and / or microfibers, and the intermediate layer (2) is formed of a material including nanoparticles functionalized with charged groups on the surface and / or charged groups in the presence of water. Detailed Implementation

[0174] Example

[0175] The invention will be better understood after reading the following non-limiting description of embodiments of the invention.

[0176] Example 1: Preparation of the composite membrane according to the present invention

[0177] Equipment and raw materials

[0178] The materials used in this embodiment are listed below:

[0179] - Buchner funnel

[0180] - 1 bar vacuum pump

[0181] - 0.1 µm PVDF filter paper

[0182] - Test Oven

[0183] The raw materials used in this embodiment are listed below:

[0184] - Cellulose nanofibers that are made negatively charged by carboxymethylation or TEMPO oxidation;

[0185] - Citric acid, 99% by volume;

[0186] - Graphene oxide sold by Sigma Aldrich under reference number 777676.

[0187] Preparation of composite membranes

[0188] The preparation method used in this embodiment is described in detail below:

[0189] Filter 1.75 ml of nanocellulose solution through a Buchner funnel equipped with a PVD filter. Set the vacuum pump to 1 bar.

[0190] After filtering all the solutions, filter 5 ml of citric acid solution onto them (which will be used as a cross-linking agent between the nanofibers).

[0191] After filtering out citric acid, filter out 7 ml of graphene oxide solution.

[0192] After filtering the graphene oxide solution, 1.75 ml of nanocellulose solution was filtered.

[0193] After filtering all the solutions, filter 5 ml of citric acid solution onto them (which will be used as a cross-linking agent between the nanofibers).

[0194] After all the filtered citric acid solution has been used to stop the pump, open the Buchner apparatus and remove the filter paper and filtrate.

[0195] The filter paper / filtrate assembly was then placed in an 85°C research oven for 15 minutes (drying and cross-linking reaction).

[0196] Finally, separate the membrane from its filter medium. To make things easier, it can be soaked in an isopropanol solution beforehand.

[0197] The resulting membrane has a density of 17.5 g / m³. 2 Nanocellulose.

[0198] The content of nanocellulose and the mass content of graphene oxide are different. The nanocellulose content is around 10 mg / m³. 2 The following methods cannot obtain membranes with sufficient mechanical strength.

[0199] For reasons of mechanical strength and resistance to ions, 17 g / m 2 These values ​​for cellulose and 4% by weight of graphene oxide appear to be optimal.

[0200] These membranes have a graphene oxide interlayer with a thickness of about 100 nm and a cellulose outer layer with a thickness of about 10 µm.

[0201] Membrane power measurement

[0202] The tests were conducted using a device comprising two independent reservoirs, each containing a concentrated solution of sodium chloride (NaCl) with a solubility of 1 M, followed by diluted solutions of 0.1 M, 0.01 M, and 0.001 M, thus establishing Rc gradients of 10, 100, and 1000 between the two reservoirs.

[0203] The two reservoirs are separated by a composite membrane according to the invention, obtained as detailed in Example 1.

[0204] The silver lattice Ag / AgCl electrode was immersed in each reservoir on both sides of the membrane to measure the current generated through the membrane.

[0205] The results of these measurements are shown in Table 1.

[0206] Table 1

[0207]

[0208] in:

[0209] UOsmo is the membrane voltage, from which the Nernst voltage (UNernst) of the electrode is derived.

[0210] IOsmo is the current associated with the membrane, calculated by measuring the membrane's resistance according to Ohm's law, I = U / R.

[0211] P Osmo Max is calculated using the formula Pmax = (U x I) / 4.

[0212] Membrane power in W / m 2 This means that 1 cm 2 The value obtained on the composite membrane is multiplied by 10,000.

[0213] It was also observed that by applying a pressure of 3 to 4 bar to the membrane between the two metal plates during heating at 85°C, the mechanical stability of the membrane was improved by 10% to 20%.

[0214] Comparative Example 2: Membranes not conforming to the present invention that do not include graphene oxide

[0215] Preparation of films excluding graphene oxide that do not conform to the present invention

[0216] The materials used are those detailed in Example 1.

[0217] The preparation method used in this comparative example is as follows:

[0218] Filter 3.5 mL of nanocellulose solution through a Buchner funnel equipped with a PVDF filter. Set the vacuum pump to 1 bar.

[0219] After filtering all the solutions, filter 10 ml of citric acid solution (used as a crosslinking agent between nanofibers) on top.

[0220] After all the filtered citric acid solution has been used to stop the pump, open the Buchner apparatus and remove the filter paper and filtrate.

[0221] The filtrate filter paper assembly was then placed in an 85°C research oven for 15 minutes (drying and cross-linking reaction).

[0222] Finally, separate the membrane from its filter medium. To make things easier, it can be soaked in an isopropanol solution beforehand.

[0223] The resulting membrane has a density of 17.5 g / m³. 2 Nanocellulose.

[0224] Membrane power of membranes that do not conform to the present invention

[0225] Except that the membrane in this comparative embodiment does not include graphene oxide, the apparatus used is similar in all respects to the apparatus detailed in Example 1.

[0226] The results of these measurements are shown in Table 2.

[0227] Table 2

[0228]

[0229] in:

[0230] UOsmo is the voltage associated with the membrane, from which the Nernst voltage (UNernst) of the electrode is derived.

[0231] IOsmo is the current associated with the membrane, calculated by measuring the membrane's resistance according to Ohm's law, I = U / R.

[0232] P Osmo Max is calculated using the formula Pmax = (U x I) / 4.

[0233] Membrane power in W / m 2 This means that 1 cm 2 The value obtained on the membrane is multiplied by 10,000.

Claims

1. An ion-selective conductive composite membrane having a thickness between 4 µm and 100 µm and comprising at least one intermediate layer (2), said intermediate layer (2) being disposed between a first outer layer (1) and a second outer layer (3), wherein: - The first outer layer (1) and the second outer layer (3) are respectively formed of a first material, the first material comprising a network of cross-linked nanofibers and / or microfibers and pores with a diameter between 10 nm and 10 µm. - The intermediate layer (2) is formed of a second material comprising nanoparticles whose surfaces are functionalized with charged groups and / or become charged groups in the presence of water, and having pores with diameters between 1 nm and 100 nm.

2. The membrane according to claim 1, wherein, The thickness of each of the first outer layer (1) and the second outer layer (3) is between 2 µm and 45 µm, and the thickness of the intermediate layer (2) is between 10 nm and 10 µm.

3. The membrane according to claim 1 or 2, wherein, The nanoparticles are layered nanoparticles.

4. The membrane according to claim 3, wherein, The layered nanoparticles are layered nanoparticles of metal oxides, layered nanoparticles of transition metal dichalcogenides, layered nanoparticles of carbon, or mixtures thereof.

5. The membrane according to claim 3, wherein, The layered nanoparticles are layered nanoparticles of graphene oxide.

6. The membrane according to claim 4, wherein, The layered nanoparticles of the transition metal dichalcogenide are layered nanoparticles of molybdenum disulfide.

7. The membrane according to claim 1 or 2, wherein, Ionized groups, charged groups, and / or groups that become charged in the presence of water have a negative charge.

8. The membrane according to claim 7, wherein, The group is selected from epoxide groups, hydroxyl groups, carbonyl groups, carboxyl groups, sulfonate groups, and SO3 groups. - Carboxyl alkyl group R-CO2 - R is a C1-C4 alkyl group, and the aminodiacetic acid ester group is -N(CH2CO2). - )2, Phosphate group PO3 2- ; Amine oxime group -C(=NH2)(NOH), aminophosphonate group -CH2-NH-CH2-PO3 2- , thiol groups -SH, and mixtures thereof.

9. The membrane according to claim 8, wherein, The carboxyl alkyl group is R-CO2 - , where R is a C1 alkyl group.

10. The membrane according to claim 1 or 2, wherein, Charged groups and / or groups that become charged in the presence of water have a positive charge.

11. The membrane according to claim 10, wherein, The group is selected from quaternary ammonium groups -N(R)3 + R is a C1-C4 alkyl group, and the tertiary ammonium group is -N(H)(R)2 + R is a C1-C4 alkyl group, dimethylhydroxyethylammonium group -N(C2H4OH)(CH3)2 + , and their mixtures.

12. The membrane according to claim 11, wherein, The tertiary ammonium group is -N(H)(R)2 + , where R is a C1 alkyl group.

13. The membrane according to claim 1 or 2, wherein, Cross-linked nanofibers and / or microfibers are nanofibers and / or microfibers of organic materials.

14. The membrane according to claim 13, wherein, The organic material is cellulose or activated carbon.

15. The membrane according to claim 1 or 2, wherein, Cross-linked nanofibers and / or microfibers have charged groups on their surface and / or become charged groups in the presence of water.

16. The membrane according to claim 15, wherein, The groups have the same charge sign as the charged groups of the functionalized nanoparticles in the intermediate layer (2) and / or the groups that become charged in the presence of water.

17. A method for manufacturing the composite membrane according to claim 1, the method comprising the following steps: i) Filtering a solution comprising nanofibers and / or microfibers onto a filter support to form a first outer layer comprising nanofibers and / or microfibers (1). ii) A particle solution of nanoparticles whose surfaces are functionalized with charged groups and / or in the presence of water on the first outer layer (1) obtained at the end of step i) is formed on the first outer layer (1), thereby forming an intermediate layer (2). iii) Filter the solution of nanofibers and / or microfibers to form a second outer layer (3) comprising nanofibers and / or microfibers on the intermediate layer (2) obtained at the end of step ii). iv) Filtering a cross-linked solution that enables the nanofibers and / or microfibers of the first outer layer (1) and the second outer layer (3) to cross-link; v) Dry the product from step iv); vi) Remove the filter support to obtain a composite membrane.

18. The membrane according to claim 17, wherein, Step v) is performed in an oven.

19. Use of the composite membrane as defined in claim 1 or 2, or the composite membrane prepared by the method defined in claim 17, as an ion-selective conductive membrane.

20. The composite membrane as defined in claim 1 or 2, or the composite membrane prepared by the method as defined in claim 17, is used for extracting ionic or ionizable substances from water to be treated, for extracting organic compounds from water to be treated, for carrying out electrolysis reactions, or for carrying out reverse electrodialysis reactions.

21. The use according to claim 20, wherein it is used for producing electricity.

22. The use according to claim 21, for producing electricity from a salinity gradient.

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