An apparatus for generating energy through a salinity gradient using a membrane based on cross-linked cellulose fibers

Abstract

The present invention relates to a device for generating electrical energy, comprising: a) a first reservoir A (20A) for receiving an electrolyte solution (22A) having a solute concentration of C A and comprising an electrode (30A) in contact with the electrolyte solution having a concentration of C A ; b) a second reservoir B (20B) for receiving an electrolyte solution (22B) having a concentration of C B of the same solute, C B being lower than C A and comprising an electrode (30B) in contact with the electrolyte solution having a concentration of C B ; c) a membrane (10) separating the two reservoirs, the membrane comprising pores to allow the electrolyte to diffuse from reservoir A to reservoir B through the pores; and d) a device (32) capable of supplying electrical energy generated by a potential difference existing between the two electrodes, characterized in that the membrane comprises at least one layer formed of a cellulose material and comprising a network of crosslinked cellulose nanofibers and / or microfibers.

Description

BACKGROUND OF THE INVENTION

[0001] Generating energy from the salinity gradient is one of the most promising renewable energy sources globally.

[0002] Among the various technologies currently under consideration, the reverse electrodialysis (RED) method is based on the use of membranes whose fundamental property is the selective transport of ions according to the sign of their charge. RED devices typically consist of alternating ion-exchange membranes, with saline and fresh water circulating alternately between the membranes. The alternating circulation of saline and fresh water between these ion-exchange membranes (IEMs) allows the establishment of an ion flow across each IEM of the device. At the end of the stack of membranes, electrodes collect the electric current generated by the overall ion flow.

[0003] One of the problems encountered by devices for generating electrical energy from the salinity gradient (such as current RED devices) is that due to the fact that current membranes generate only a few W / m per unit membrane area (i.e., membrane power), the ability of these devices to generate electricity is very low. 2 membrane electrical power, the ability of these devices to generate electricity is very low.

[0004] In particular, IEMs conduct ionic current weakly, contributing significantly to the resistance of the reverse electrodialysis system. In addition, the preparation of these membranes is very expensive, so a major part of the maintenance investment in the membrane method is used to replace these membranes.

[0005] The international application numbered WO 2014 / 060690 published on April 24, 2014, proposed a method to address this problem. In this method, a nanoporous membrane has been proposed, the inner surface of whose pores is covered with boron nitride, or more generally with a mixture of the elements boron, carbon, and nitrogen. These nanoporous membranes utilize the phenomenon of diffusion osmosis within the pores and generate a membrane power of approximately kW / m 2 of the membrane power. More recently, in the international application numbered WO 2017 / 037213 published on March 9, 2017, a nanoporous membrane has also been proposed, the inner surface of whose pores is covered with titanium oxide, allowing a membrane power of approximately 5 kW / m 2 of the membrane power. However, this method involves the use of membranes based on boron nitride or titanium oxide, and considering the materials required, preparing such membranes on a scale larger than the laboratory scale is complex and extremely expensive. In addition, the materials used in these membranes are potentially hazardous and pose a risk if they are released into the environment.

[0006] Therefore, in view of the above, there is a need for a device that allows the generation of pollution-free and economical electrical energy, and that allows an energy generation of approximately kW / m per square meter of membrane. 2 of energy generation. SUMMARY OF THE INVENTION

[0007] The inventors have discovered a membrane-containing device for generating electrical energy from a salinity gradient, the membrane comprising a layer formed from a network of cellulose nanofibers and / or microfibers, the device allowing an energy generation of approximately kW / m per square meter of membrane 2 of membrane.

[0008] Using such a membrane also allows for the facilitation of the development of larger-scale devices for generating energy from a salinity gradient and for reducing their cost.

[0009] Thus, an object of the present invention is to provide a device for generating energy from a salinity gradient, which is capable of generating a high membrane power and uses an economical and easily preparable membrane, and moreover has a limited environmental risk.

[0010] Device

[0011] A first object of the present invention is a device for generating electrical energy, comprising:

[0012] - A first reservoir A (20A) which is intended to receive an electrolyte solution (22A) having a solute concentration of C A and which comprises an electrode (30A) in contact with the electrolyte solution having a concentration of C A ;

[0013] - A second reservoir B (20B) which is intended to receive an electrolyte solution (22B) having the same solute concentration of C B , C B being lower than C A , and which comprises an electrode (30B) in contact with the electrolyte solution having a concentration of C B ;

[0014] - A membrane (10) separating the two reservoirs, the membrane comprising pores to allow the electrolyte to diffuse from reservoir A to reservoir B through the pores; and

[0015] - A device (32) which allows the provision of electrical energy generated by the potential difference existing between the two electrodes,

[0016] characterized in that the membrane comprises at least one layer formed from a cellulose material and comprising a network of crosslinked cellulose nanofibers and / or microfibers.

[0017] The electrical energy generation device according to the present invention comprises two reservoirs, namely reservoir A (20A) and reservoir B (20B), separated by a membrane 10. Each of the two reservoirs A and B is intended to receive electrolyte solutions having the same solute and concentrations of C A and C BAn electrolyte solution (22A, 22B), in which the electrodes 30A and 30B are immersed. The two electrodes (30A, 30B) are connected to a device that allows the captured electrical energy to be supplied.

[0018] To generate an ion flow through the membrane, the concentration C of the same solute in the electrolyte solutions (22A, 22B) A and C B must necessarily be different.

[0019] In the context of the present invention, C will arbitrarily be considered B to be lower than C A , which causes the solute ions to circulate from reservoir A to reservoir B.

[0020] The membrane (10) separating the two reservoirs A and B contains pores to allow the electrolyte to diffuse through the pores from reservoir A to reservoir B; the diffusion will occur from reservoir A to reservoir B. The pores have a moderate cross-section to allow the circulation of water molecules and solute ions.

[0021] The thickness of the membrane is advantageously between 2 μm and 100 μm, preferably between 2 μm and 75 μm.

[0022] The membrane advantageously contains from 10 g to 20 g of cellulose material per m 2 of membrane, preferably containing from 15 g to 20 g of cellulose material per m 2 of membrane.

[0023] The electrodes (30A, 30B) can be partially or fully immersed in the electrolyte solution (22A, 22B). It can also be provided that the electrodes are in the form of at least a part of the reservoir wall.

[0024] The device (32) allows the captured electrical energy to be supplied that is spontaneously generated by the potential difference existing between the two electrodes (30A) and (30B). It can consist of a simple cable connecting a battery, a light bulb or any other form of electrical device.

[0025] In the device according to the invention, due to the porosity of the membrane material and under the influence of its surface properties (in particular its surface charge), due to the difference in the concentration C A and C B of the same solute in the electrolyte solution, the electrolyte (more particularly the ions generated by the electrolyte) migrates from the most concentrated solution to the less concentrated solution, thereby generating electrical energy.

[0026] The inventors have found, quite unexpectedly, that membranes based on nanofibers and / or cellulose generate a very high membrane power under the action of a salinity gradient, on the order of several hundred W / m 2 of membrane.

[0027] Not wishing to be bound by a particular theory, the inventors believe that this unexpected membrane power is determined by the surface charge of the nanofibers and / or cellulose and the geometry of the network they form, which allows for very good selective ion conduction through the membrane.

[0028] In particular, still according to the inventors, the porosity within the network of cellulose nanofibers and / or microfibers and the charge of the charged surface unexpectedly affect the selective ion passage through the membrane, thereby allowing the membrane to generate an unexpected membrane power.

[0029] The surface charge density of the inner wall of the pores of the membrane is advantageously between 0.001 C / m 2 and 3 C / m 2 and preferably between 0.1 C / m 2 and 1 C / m 2 between.

[0030] The surface charge density of the membrane can be measured by dosimetry.

[0031] Cellulose nanofibers and / or microfibers

[0032] According to the present invention, the term "crosslinked" in relation to cellulose nanofibers and / or microfibers means that the fibers are interconnected to each other by covalent chemical bonds (sometimes called "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.

[0033] The covalent chemical bonds involved in the crosslinking of cellulose nanofibers and / or microfibers can also carry charged groups and / or groups that become charged in the presence of water (for example, in the case where the crosslinking agent used is citrate). In this case, the crosslinking chemical bonds play a role in both the structure and the electrical surface charge of the outer layer (104, 103).

[0034] The network of cellulose nanofibers and / or microfibers advantageously has pores with diameters between 10 nm and 1000 nm.

[0035] According to the present invention, the expression "cellulose nanofibers" refers to three-dimensional objects based on cellulose, where two of the three external dimensions are in the nanoscale (i.e., two of the three dimensions range from 1 nm to 100 nm), and the third external dimension is significantly larger than the other two dimensions and does not have to be in the nanoscale.

[0036] Cellulose nanofibers advantageously have a diameter in the range of 1 nm to 100 nm, preferably in the range of 1 nm to 70 nm, more preferably in the range of 4 nm to 30 nm, especially 4 nm to 20 nm. In addition, their length is advantageously between 0.5 μm and 100 μm, especially between 0.5 μm and 50 μm, such as between 0.5 μm and 10 μm, such as still between 0.5 μm and 2 μm.

[0037] According to the present invention, the expression "cellulose microfiber" refers to a three-dimensional object in which two of the three external dimensions are in the micrometer scale (i.e., two of the three dimensions range from 0.1 μm to 1 μm), and the third external dimension is significantly larger than the other two dimensions.

[0038] Cellulose microfibers advantageously have a diameter in the range of 100 nm to 1000 nm, preferably in the range of 100 nm to 700 nm, more preferably in the range of 100 nm to 200 nm. In addition, their length is advantageously between 0.5 μm and 100 μm, especially between 1 μm and 50 μm, such as between 1 μm and 10 μm, such as still between 1 μm and 5 μm.

[0039] The shape factor of cellulose nanofibers and / or microfibers advantageously is greater than 30, preferably greater than 100.

[0040] Advantageously, relative to the mass of the cellulose material, the cellulose material contains at least 90% by mass of cellulose nanofibers and / or microfibers, at least 95% by mass of cellulose nanofibers and / or microfibers, still more preferably at least 99% of cellulose nanofibers and / or microfibers.

[0041] Cellulose nanofibers and / or microfibers can be obtained by techniques known to those skilled in the art, especially by mechanical, enzymatic or chemical treatment of lignocellulosic materials of natural origin (such as wood).

[0042] In the case of wood, these treatments have the particular effect of separating cellulose from other components of wood (such as lignin and hemicellulose). For this purpose, the natural cellulose fibers are chemically (especially with enzymes) and / or mechanically pretreated or post-treated to initiate deconstruction before mechanical treatment in a homogenizer. It is known that the size (especially the diameter) of the cellulose fibers of the said material can be adjusted according to the treatment carried out on the natural cellulose source.

[0043] Thus, cellulose nanofibers and / or microfibers can be obtained by mechanical treatment of wood fibers, and the mechanical treatment is carried out to provide sufficient mechanical energy to burst the fibers of natural cellulose by breaking at least part of the hydrogen bonds that bind the microfibrils together. There is usually a chemical or enzymatic treatment step before the mechanical treatment. For example, the treatment step can be an oxidation treatment, especially using an oxidizing agent such as TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)oxy). The product thus obtained is usually referred to in the literature as "nanofibrillated cellulose" (abbreviated as "NFC"), "cellulose nanofiber" (abbreviated as "CNF") or "microfibrillated cellulose" (abbreviated as "MFC").

[0044] Generally, MFC materials are prepared by mechanical and / or chemical treatments of lower intensity than those used to obtain NFC, and usually have a fiber diameter greater than that observed in NFC. However, there is no clear definition of MFC and NFC / CNF, so these terms are often used interchangeably in the literature.

[0045] The cellulose nanofibers and / or microfibers are preferably nanocellulose nanofibers and / or microfibers.

[0046] The cellulose material can particularly contain up to 5% by mass of hemicellulose, more preferably up to 3% by mass of hemicellulose, or up to 1% by mass of hemicellulose.

[0047] The cellulose material can particularly contain up to 5% by mass of lignin, more preferably up to 3% by mass of lignin, or up to 1% by mass of lignin.

[0048] Due to the fact that cellulose monomers naturally carry alcohol groups at their C2, C3 or C6 carbon atoms, the cellulose nanofibers and / or microfibers of the present invention inherently carry a negative surface charge.

[0049] 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 inner layer (102) and / or the groups that become 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 film of the present invention.

[0050] The charged groups carried by the microfibers and / or nanofibers and / or the groups that become charged in the presence of water are advantageously covalently bonded to the surface of the cellulose microfibers and / or nanofibers.

[0051] Any charged group known to those skilled in the art that allows increasing the charge density of the microfibers and / or cellulose nanofibers of the present invention and / or a group that becomes charged in the presence of water can be used within the scope of the present invention.

[0052] Advantageously, the negatively charged groups and / or groups that become charged in the presence of water carried by the cellulose nanofibers and / or microfibers are selected from sulfonate groups -SO3 - , carboxylate groups -CO2 - , carboxyalkyl R-CO2 - (where R is a C1-C4 alkyl group, preferably a C1 alkyl group), aminodiacetate groups -N(CH2CO2 - )2, phosphonate groups PO3 2- , amine oxime groups -C(=NH2)(NOH), aminophosphonate groups -CH2-NH-CH2-PO3 2- , thiol groups -SH, and mixtures thereof.

[0053] Preferably carboxylate groups -CO2 - and carboxyalkyl R-CO2 - (where R is a C1-C4 alkyl group, preferably a C1 alkyl group).

[0054] Thus, cellulose nanofibers and / or microfibers carrying -CO2 - carboxylate groups (i.e., oxidized cellulose nanofibers and / or microfibers) can be obtained, for example, by oxidation of the nanofibers and / or microfibers of cellulose (such as TEMPO oxidation). The oxidation preferably occurs on the primary alcohol group carried by the C6 carbon atom of the monomer of the cellulose nanofibers and / or microfibers.

[0055] Cellulose nanofibers and / or microfibers carrying carboxyalkyl R-CO2 - can be obtained, for example, by etherification of the cellulose nanofibers and / or microfibers. The etherification preferably occurs on the alcohol groups carried by the C2, C3, or C6 carbon atoms of the monomer of the cellulose nanofibers and / or microfibers.

[0056] 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 a positively charged group and / or a group that becomes charged in the presence of water.

[0057] This embodiment is preferred when the charged group and / or the group that becomes charged in the presence of water of the functionalized nanoparticles in the inner layer (102) has a positive sign.

[0058] Any charged group known to those skilled in the art that allows for imparting a positive surface charge to cellulose nanofibers and / or microfibers and / or a group that becomes charged in the presence of water can be used in the context of the present invention.

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

[0060] Preferably a quaternary ammonium group.

[0061] Single-layer film

[0062] In a first embodiment, the present invention relates to a device according to the present invention, the film of which comprises a single layer (101) formed of a cellulose material as defined above.

[0063] The inventors have shown that, surprisingly, compared to the films of the prior art, films comprising a single layer (101) formed of a crosslinked cellulose nanofiber and / or microfiber network allow for the generation of surprisingly high film power and are compatible with industrial development.

[0064] The thickness of the film comprising the single layer (101) is advantageously between 2 μm and 50 μm, preferably between 5 μm and 20 μm, more preferably between 10 μm and 20 μm.

[0065] In the present invention, the thickness of the film and different layers is measured by measuring dry film sections by scanning electron microscopy.

[0066] Method for preparing a monolayer film

[0067] A film comprising a single layer can be easily prepared by a method comprising the following steps:

[0068] i) Filtering a solution comprising cellulose nanofibers and / or microfibers on a filtering support to form a layer comprising nanofibers and / or microfibers;

[0069] ii) Filtering a crosslinking solution capable of crosslinking the cellulose nanofibers and / or microfibers of the layer obtained in step i);

[0070] iii) Drying the product of step ii), preferably drying in an oven;

[0071] iv) Removing the filtering support to obtain a film comprising the layer.

[0072] The method is simple, easy to implement and economical, and allows the thickness of each layer of the composite film to be controlled.

[0073] The cellulose nanofibers and / or microfibers used in the method are as defined in the first object of the present invention.

[0074] The filtration in steps i) and ii) is advantageously carried out with a vacuum pump, preferably under a vacuum of 1 bar.

[0075] The solution of cellulose nanofibers and / or microfibers contains 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.

[0076] The nanofibers and / or microfibers of the solution in step i) can be functionalized as detailed in the first object of the present invention.

[0077] The crosslinking solution implemented in step ii) advantageously contains 0.005M to 0.02M of one or more crosslinking agents, preferably 0.008M to 0.012M of one or more crosslinking agents.

[0078] As detailed above, the crosslinking agent preferably carries charged groups and / or groups that become charged in the presence of water.

[0079] Any other techniques known to those skilled in the art can be considered, whether discontinuous (i.e., batch) or continuous, such as by a technique called "roll-to-roll processing", where the film is continuously produced and then stored in the form of a roll.

[0080] Composite film

[0081] In a second embodiment, the device comprises a composite film, which comprises two outer layers (104, 103), each outer layer being formed of a cellulose material as defined above, between which an inner layer (102) formed of a second material is provided, the second material comprising nanoparticles functionalized with charged groups and / or groups that become charged in the presence of water.

[0082] The second material advantageously has pores with a diameter between 10 nm and 100 nm.

[0083] The inventors have found, unexpectedly, that such a composite film produces a significantly higher membrane power than a film comprising a single layer (101) as defined above.

[0084] Not wishing to be bound by a particular theory, the inventors believe that this improvement in the membrane power is due to a synergistic effect between on the one hand the properties of the cellulose nanofiber and / or microfiber network and on the other hand the properties of the layer of nanoparticles functionalized with charged groups. The thickness of the composite membrane is advantageously preferably between 4 μm and 100 μm, more preferably between 4 μm and 75 μm.

[0085] The thickness of each outer layer (104, 103) is advantageously between 2 μm and 45 μm, preferably between 2 μm and 30 μm. The outer layers advantageously have the same thickness. The thickness of the inner layer (102) is correspondingly advantageously between 10 nm and 2 μm, between 10 nm and 1 μm, between 10 nm and 800 nm, preferably between 10 nm and 400 nm, preferably between 200 nm and 500 nm.

[0086] Preferably, the thickness of each outer layer (104, 103) is advantageously between 2 μm and 25 μm, and the thickness of the inner layer (102) is between 10 nm and 2 μm.

[0087] According to the inventors, the very small thickness of the inner layer (102) allows for excellent permeability while significantly increasing the selective conduction of ions.

[0088] Preferably, the membrane contains less than 10% by weight of a second material relative to the weight of the cellulose material, preferably between 2% and 8% by weight of a second material relative to the weight of the cellulose material, more preferably between 3% and 5% by weight of a second material relative to the weight of the first material.

[0089] In this embodiment, the cellulose material of the outer layers (104, 103) ensures the integrity of the inner layer (102), especially during its use, where the inner layer is subjected to stresses (such as pressure gradients) on both sides of the membrane.

[0090] Preferably, the nanofibers and / or microfibers of the outer layers (104, 103) carry charged groups or groups that become charged in the presence of water, and these groups advantageously have the same charge as the charged groups of the functionalized nanoparticles of the inner layer (102) or the groups that become charged in the presence of water.

[0091] This has the advantage of increasing the surface charge of the entire membrane.

[0092] According to the inventors, the presence of these charged groups with the same sign or groups that become charged in the presence of water in the inner layer (102) and the outer layers (104, 103) of the membrane allows for a synergistic effect, namely an unexpectedly improved selective conduction of ions through the membrane.

[0093] Thus, in this embodiment, the cellulose material plays a role in the structure of the membrane and its ability to ensure ion-selective conduction.

[0094] In addition, the covalent chemical bonds involved in the crosslinking of the nanofibers and / or microfibers can also carry charged groups and / or groups that become charged in the presence of water (for example, when the crosslinking agent used is citrate). In this case, the crosslinking chemical bonds play a role in both the structure and the electrical surface charge of the outer layer (104, 103).

[0095] Functionalized nanoparticles

[0096] According to the present invention, the term "nanoparticle" refers to a three-dimensional object in which at least one external dimension is in the nanoscale (i.e., the range of at least one dimension is between 1 nm and 100 nm).

[0097] The second material advantageously comprises nanoparticles in the form of individual nanoparticles, i.e., non-aggregated nanoparticles, or in other words, nanoparticles covalently bonded to each other.

[0098] Relative to the mass of the second material, the second material advantageously comprises at least 50% by mass of nanoparticles, at least 95% by mass of nanoparticles, more preferably at least 99% of nanoparticles.

[0099] Advantageously, the nanoparticles are not in the form of nanotubes.

[0100] The nanoparticles are preferably layered nanoparticles.

[0101] According to the present invention, the term "layered nanoparticle" refers to a nanoparticle comprising atoms in the form of a single layer of atoms bonded together by covalent bonds. The layered nanoparticle can consist of a single atomic monolayer (2D material), or a stack of 2 to 5 atomic monolayers bonded together by weak bonds such as van der Waals forces.

[0102] In other words, the layered nanoparticle is a three-dimensional object in which the first external dimension is in the nanoscale, and the other two dimensions are significantly larger than the first dimension, and particularly vary between the nanoscale and the microscale.

[0103] The layered nanoparticles preferably have a median size (also referred to by the acronym "D50") between 5 μm and 50 μm, preferably between 10 μm and 20 μm, and more preferably 15 μm.

[0104] According to the present invention, the terms "monolayer", "bilayer", "few-layer" in relation to layered nanoparticles respectively denote layered nanoparticles composed of a single atomic monolayer, two atomic monolayers, and 3 to 5 atomic monolayers. The bilayer and few-layer layered nanoparticles are generally stabilized by weak interactions (such as van der Waals interactions) between the atomic monolayers.

[0105] The layered nanoparticles are preferably layered nanoparticles of metal oxides (especially SnO2 or TiO2), layered nanoparticles of transition metal chalcogenides (such as molybdenum disulfide MoS2), layered nanoparticles of carbon, or mixtures thereof.

[0106] The layered carbon nanoparticles are advantageously layered nanoparticles of single-layer graphene, bilayer graphene, few-layer graphene, or mixtures thereof.

[0107] Single-layer graphene nanoparticles are preferred.

[0108] According to the present invention, single-layer graphene is a two-dimensional crystalline material composed of carbon of a specific allotrope (which can be represented as a planar honeycomb). More specifically, single-layer graphene is a sheet composed of a single plane of sp 2 hybridized carbon atoms. Thus, it can be described as a single layer.

[0109] According to the present invention, bilayer graphene (or BLG) is a material composed of a stack of 2 graphene monolayers, stabilized by van der Waals-type interactions between the 2 graphene monolayers. BLG can be obtained by exfoliation of graphite or chemical vapor deposition (CVD).

[0110] According to the present invention, few-layer graphene (or FLG) is a material composed of a stack of 3 to 5 graphene sheets, stabilized by van der Waals-type interactions between different graphene planes.

[0111] The layered carbon nanoparticles are advantageously layered nanoparticles of single-layer molybdenum disulfide, bilayer molybdenum disulfide, few-layer molybdenum disulfide, or mixtures thereof.

[0112] Depending on the sign of its charge, when the composite film is placed in the presence of water, charged groups or groups that become charged in the presence of water impart a negative or positive surface charge on the inner layer (102) of the composite film.

[0113] Any charged group known to those skilled in the art that allows increasing the surface charge of graphene particles or a group that becomes charged in the presence of water can be used in the context of the present invention.

[0114] In one embodiment, the surface of the nanoparticles is functionalized with a negatively charged group and / or a group that becomes negatively charged in the presence of water.

[0115] The negatively charged group and / or the group that becomes negatively charged in the presence of water are advantageously selected from epoxy groups, hydroxyl groups, carbonyl groups, carboxyl groups, sulfonate groups -SO3 - 、carboxyalkyl R-CO2 -(wherein R is a C1-C4 alkyl group, preferably a C1 alkyl group), amino diacetate group -N(CH2CO2 - )2, phosphonate group PO3 2- , amidoxime group -C(=NH2)(NOH), aminophosphonate group -CH2-NH-CH2-PO3 2- , thiol group -SH, and mixtures thereof.

[0116] Preferably, the nanoparticles functionalized on the surface with a negatively charged group or a group that becomes negatively charged in the presence of water are layered nanoparticles of graphene oxide (or GO).

[0117] The layered graphene oxide nanoparticles have a negatively charged group or a group that becomes negatively charged in the presence of water, preferably selected from epoxy groups, hydroxyl groups, carbonyl groups, carboxyl groups, and mixtures thereof.

[0118] In one embodiment, the surface of the nanoparticles is functionalized with a positively charged group and / or a group that becomes positively charged in the presence of water.

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

[0120] Method for preparing a composite film

[0121] The composite membrane according to the second embodiment can be prepared by a method comprising the following steps:

[0122] i) Filtering a solution containing cellulose nanofibers and / or microfibers on a filter medium to form a first outer layer (104) containing cellulose nanofibers and / or microfibers;

[0123] ii) Filtering a solution of functionalized nanoparticles on the outer layer (104) obtained at the end of step i) to form an inner layer (102) on the first outer layer (104);

[0124] iii) Filtering a solution of cellulose nanofibers and / or microfibers to form a second outer layer (103) containing nanofibers and / or microfibers on the inner layer (102) obtained at the end of step ii);

[0125] iv) Filtering a crosslinking solution capable of crosslinking the cellulose nanofibers and / or microfibers of the outer layers (104, 103);

[0126] v) Dry the product of step iv) in an oven;

[0127] vi) Remove the filtration support to obtain the composite membrane.

[0128] Cellulose nanofibers and / or microfibers and nanoparticles functionalized on the surface with charged groups and / or groups that become charged in the presence of water are as defined in the first object of the present invention.

[0129] The method is simple, easy to implement and economical, and allows controlling the thickness of each layer of the composite membrane.

[0130] The filtration in steps i), ii), iii) and iv) is advantageously carried out with a vacuum pump, preferably at a vacuum of 1 bar.

[0131] Step i1) can be optionally carried out after the filtration of step i), including filtering the crosslinking solution on the outer layer obtained at the end of step i).

[0132] Step ii1) can be optionally carried out after the filtration of step ii), including filtering the crosslinking solution on the inner layer (102) obtained at the end of step ii).

[0133] The solution of nanofibers and / or microfibers implemented in steps i) and iii) contains 0.1 wt% to 1 wt% of cellulose nanofibers and / or microfibers, preferably 0.3 wt% to 0.6 wt% of cellulose nanofibers and / or microfibers.

[0134] The nanofibers and / or microfibers of the solution in steps i) and iii) can be functionalized as detailed in the first object of the present invention.

[0135] The solution of functionalized nanoparticles implemented in step ii) contains 0.001 wt% to 0.01 wt% of nanoparticles, preferably 0.003 wt% to 0.006 wt% of functionalized nanoparticles.

[0136] The crosslinking solution implemented in step iv) advantageously contains 0.005 M to 0.02 M of one or more crosslinking agents, preferably 0.008 M to 0.012 M of one or more crosslinking agents.

[0137] The drying in step v) is advantageously carried out at a temperature allowing the crosslinking reaction to occur, and the temperature is lower than the temperature that damages the fibers and / or nanofibers. Preferably, the drying temperature is between 80 °C and 150 °C, especially between 80 °C and 120 °C, more preferably still between 80 °C and 100 °C.

[0138] As described in detail above, the crosslinking agent preferably carries a charged group and / or a group that becomes charged in the presence of water.

[0139] Any other technique known to those skilled in the art can be considered, whether discontinuous (i.e., batch) or continuous, such as by a technique called "roll-to-roll processing", in which the film is continuously produced and then stored in the form of a roll.

[0140] Other components of the device

[0141] The reservoirs A and B of the device according to the invention each contain electrolyte solutions (22A, 22B) having the same solute with concentrations of C A and C B respectively, and C B is lower than C A .

[0142] Each of the reservoirs A and B can be any device or natural environment, which is open or closed and capable of containing a liquid.

[0143] By placing electrolyte solutions with different concentrations in the two reservoirs A and B, an osmotic flow is generated between the two reservoirs, preferably by diffusion osmosis, i.e., without any osmotic pressure occurring. In another embodiment, by varying the solubility of the salt with temperature, a concentration gradient can also be obtained through the temperature gradient between the two reservoirs.

[0144] In the context of the present invention, the concentration ratio Rc (Rc is equal to the ratio of the concentration of the highest concentration solution / the concentration of the lowest concentration solution) can be between 1 and 10 9 Preferably, the concentration ratio of C A / C B is greater than 1 and less than or equal to 10 9 , advantageously greater than 10 and less than or equal to 10 5 .

[0145] The electrolyte solution is an aqueous solution containing an electrolyte. The electrolyte can be of any chemical nature as long as they are dissolved in the solution in the form of charged ions. Preferably, these ions will come from dissolved salts such as NaCl, KCl, CaCl2, and MgCl2. The electrolyte solution can be:

[0146] - A synthetic solution;

[0147] - A natural solution, such as fresh water from lakes or rivers, groundwater, brackish water, seawater;

[0148] - Industrial production water, oil production water, or biological solutions.

[0149] Preferably, the electrolyte solution is an aqueous solution containing a solute selected from alkali metal halides or alkaline earth metal halides, preferably selected from NaCl, KCl, CaCl2, and MgCl2, and more preferably the solute is NaCl.

[0150] To improve the osmotic flow generated on both sides of the membrane according to the present invention, the pH of the solution can be adjusted according to the isoelectric point of the material constituting the membrane.

[0151] In the context of the present invention, pH iso refers to the pH of the isoelectric point of the material constituting the membrane. The pH is measured by methods known to those skilled in the art, in particular by acid / base potentiometric titration. iso .

[0152] More advantageously, to increase the asymmetry of the device and expand the amount of electrical energy generated by the device, a pH gradient can also be established between the two reservoirs, and the pH difference between the two solutions will be greater than 1, preferably greater than 2.

[0153] The reservoirs A and B of the device according to the present invention each further comprise electrodes (30A, 30B) arranged to contact the electrolyte solutions (22A, 22B).

[0154] Different types of electrodes can be used to recover the potential or current generated between the two reservoirs.

[0155] All types of electrodes capable of collecting Na + or Cl - ion flows can be used, preferably electrodes composed of: silver and silver chloride (Ag / AgCl), carbon and platinum (C / Pt-), carbon (C-), graphite, or [Fe(CN)6] 4– / [Fe(CN)6] 3– type iron complexes.

[0156] The electrodes can be partially or completely immersed in the electrolyte solution. It can also be provided that the electrodes take the form of at least a part of the reservoir wall.

[0157] The electrodes can be in particular flow-through electrodes ("redox flow"). The principle of these electrodes is based on oxidation and reduction reactions at each electrode.

[0158] The electrodes are preferably capacitive electrodes or supercapacitor electrodes. The principle of these electrodes is based on the interaction between the electrode and the electrolyte, which results in the spontaneous appearance of charge accumulation at the interface.

[0159] These electrodes are connected to a device (32) that allows the capture and then supply of the electrical energy spontaneously generated by the potential difference existing between the electrodes. These electrodes can be connected, in particular, by a simple cable connecting a battery, a light bulb, or any other form of electrical device.

[0160] The device described in this way allows the collection of electrical energy generated by an ionic current of charged ions passing through a nanofluidic membrane.

[0161] In a specific embodiment of the present invention, the device may comprise N reservoirs (20) and N - 1 membranes (10), where N is an integer, particularly between 3 and 100, and more particularly between 3 and 50.

[0162] In this device, the reservoirs and membranes are as defined above. Thus, the assembly will consist of alternating reservoirs, which alternately contain a high - concentration electrolyte solution and a low - concentration electrolyte solution, separated from each other by the membranes.

[0163] Electricity production method

[0164] A second object of the present invention is a method for generating electrical energy using the device as described in the first object of the present invention, which comprises the following steps:

[0165] i) Supplying an electrolyte solution (22A) having a solute and a concentration of C A in reservoir A (20A) such that the electrode (30A) provided in the reservoir A is in contact with the solution (22A),

[0166] ii) Supplying an electrolyte solution (22B) having the same solute and a concentration of C B in reservoir B (20B), where C B is lower than C A such that the electrode (30B) provided in the reservoir B is in contact with the solution (22B),

[0167] iii) Allowing the electrolyte to diffuse from reservoir A to reservoir B through the membrane (10),

[0168] iv) Capturing the electrical energy generated by the potential difference existing between the two electrodes using the device (32).

[0169] Preferably, steps i) and ii) are implemented by providing the electrolyte solution having a concentration of C A and the electrolyte solution having a concentration of C B in the form of a continuous flow.

[0170] More generally, those skilled in the art will easily perform these different steps using their common general knowledge. Description of the Drawings

[0171] Figure 1Schematically shows an example of an electric energy generating device according to the present invention, which includes two reservoirs 20A and 20B, namely reservoir A and reservoir B respectively, separated by a membrane 10. Each of the two reservoirs contains electrolyte solutions 22A and 22B with the same solute having concentrations of C A and C B respectively, and electrodes 30A and 30B are immersed in the electrolyte solutions. The two electrodes 30A and 30B are connected to a device that allows the captured electric energy to be supplied. Each of reservoir A and B can be any device or natural environment, which is open or closed and capable of containing a liquid. In order to generate an ion flow through the membrane, the concentrations C A and C B of the same solute in the electrolyte solutions 22A and 22B must be different. In the context of the present invention, it is arbitrarily considered that C B is lower than C A , which causes the ions of the solute to cycle from reservoir A to reservoir B. The membrane 10 separating the two reservoirs A and B contains pores to allow the electrolyte to diffuse from reservoir A to reservoir B through the pores. The diffusion will occur from reservoir A to reservoir B. The pores have a moderate cross-section to allow water molecules and solute ions to cycle. The electrodes 30A and 30B can be partially or fully immersed in the solutions 22A and 22B. It can also be stipulated that the electrodes are in the form of at least a part of the reservoir wall. The device (32) allows the captured electric energy to be supplied, which is spontaneously generated by the potential difference existing between the two electrodes 30A and 30B. It can consist of a simple cable connecting a battery, a light bulb or any other form of electrical equipment.

[0172] Figure 2 Schematically shows a cross-section of an example of a membrane (10) according to the present invention, which includes a single layer (101), and the single layer is formed of a cellulose material containing cross-linked cellulose nanofibers and / or microfibers.

[0173] Figure 3 Schematically shows a cross-section of an example of a membrane (10) according to the present invention, wherein the membrane is a composite membrane including two outer layers (104, 103), each outer layer is formed of a cellulose material containing cross-linked cellulose nanofibers and / or microfibers, and an inner layer (102) is provided therebetween. The inner layer is formed of a material containing nanoparticles, and the nanoparticles are functionalized on the surface with charged groups and / or groups that become charged in the presence of water. Detailed implementation

[0174] Examples

[0175] The present invention will be better understood after reading the following embodiments, which illustrate the present invention but do not limit the present invention.

[0176] Example 1: Preparation of Single - layer Membrane and Membrane Power Measurement

[0177] Equipment and Raw Materials

[0178] The materials used are listed as follows:

[0179] - Buchner filter

[0180] - 1 bar vacuum pump

[0181] - 0.1μm PVDF filter paper

[0182] - Oven

[0183] The raw materials used in this example are listed as follows:

[0184] - Negatively charged cellulose nanofibers obtained by carboxymethylation or TEMPO oxidation;

[0185] - Citric acid, 99 vol%.

[0186] Preparation of Single - layer Membrane

[0187] The preparation method used is as follows:

[0188] · Filter 3.5 ml of nanofiber solution on a Buchner filter with PVDF filter paper.

[0189] Set the vacuum pump to 1 bar vacuum;

[0190] ● After filtering all the solution, then filter 10 ml of citric acid solution (which acts as a cross - linker between nanofibers) on it;

[0191] ● After filtering all the citric acid solution and stopping the pump, open the Buchner device and take out the filter paper and its filtrate.

[0192] Then place the filter paper - filtrate assembly in a research oven at 85 °C for 15 minutes (for drying and cross - linking reaction).

[0193] Finally, separate the membrane from its filtering medium. To make the operation easier, it can be immersed in isopropyl alcohol solution beforehand.

[0194] The membrane thus obtained consists of 17.5 g / m 2 of nanofibrillated cellulose.

[0195] These membranes have an inner layer of graphene oxide with a thickness of about 100 nm and an outer cellulose layer with a thickness of about 10 μm respectively.

[0196] Membrane Power of Single - layer Membrane

[0197] Testing was carried out using a device made of two independent reservoirs, each containing a sodium chloride (NaCl) solution. 1 M sodium chloride was dissolved in the concentrated solution, and then 0.1 M, 0.01 M, and 0.001 M were dissolved in the dilute solution to allow for Rc gradients of 10, 100, and 1000 to be set between the two reservoirs.

[0198] The two reservoirs were separated by a composite membrane obtained as detailed in Example 1 according to the present invention.

[0199] Silver grid Ag / AgCl electrodes were immersed in each reservoir on both sides of the membrane to measure the current generated through the membrane.

[0200] The results are shown in Table 1.

[0201] Table 1

[0202]

[0203] Where:

[0204] - U Osmo is the potential related to the membrane, from which the Nernst potential (U Nernst) of the electrode is derived

[0205] - I Osmo is the current related to the membrane, which is calculated by measuring the resistance of the membrane and according to Ohm's law I = U / R

[0206] - P Osmo Max is calculated by the formula Pmax = (U × I) / 4

[0207] The membrane power is expressed in W / m 2 and the value obtained on a 1 cm 2 membrane is multiplied by 10000.

[0208] Example 2: Preparation of the composite membrane and measurement of membrane power

[0209] Equipment and raw materials

[0210] The materials used were the same as those detailed in Example 1.

[0211] The raw materials used in this example are listed as follows:

[0212] - Cellulose nanofibers negatively charged by carboxymethylation or TEMPO oxidation;

[0213] - Citric acid, 99 vol%;

[0214] - Graphene oxide, sold by Sigma Aldrich, reference number 777676.

[0215] Preparation of the composite membrane

[0216] The preparation method implemented in this embodiment is described in detail as follows:

[0217] ● Filter 1.75 ml of nanocellulose solution through PVD filter paper on a Buchner filter.

[0218] Set the vacuum pump to 1 bar vacuum;

[0219] ● After filtering all the solutions, filter 5 ml of citric acid solution (which will serve as a cross-linking agent between the nanofibers) on it;

[0220] ● After filtering the citric acid, filter 7 ml of graphene oxide solution;

[0221] ● After filtering the graphene oxide solution, filter 1.75 ml of nanocellulose solution again;

[0222] ● After filtering all the solutions, filter 5 ml of citric acid solution (which will serve as a cross-linking agent between the nanofibers) on it;

[0223] ● After filtering all the citric acid solution and stopping the pump, open the Buchner device and remove the filter paper and its filtrate.

[0224] Then place the filter paper assembly with the filtrate in a research oven at 85 °C for 15 minutes (drying and cross-linking reaction).

[0225] Finally, separate the membrane from its filtration medium. To make the operation easier, it can be immersed in isopropyl alcohol solution beforehand.

[0226] The membrane thus obtained consists of 17.5 g / m 2 of nanocellulose and 0.34 g / m 2 of graphene oxide (2 wt%).

[0227] The nanocellulose content and the mass content of graphene oxide were changed. A nanocellulose content below 10 mg / m 2 does not allow for obtaining a membrane with sufficient mechanical strength.

[0228] For reasons of mechanical strength and ionic resistance, a value of 17 g / m 2 of cellulose and 4 wt% of graphene oxide seems to be optimal.

[0229] The membrane power of the composite membrane

[0230] Testing was carried out using a device made of two independent reservoirs, each containing a sodium chloride (NaCl) solution. The concentrated solution had 1 M sodium chloride dissolved in it, and then the dilute solutions had 0.1 M, 0.01 M, and 0.001 M dissolved in them to allow for Rc gradients of 10, 100, and 1000 to be set between the two reservoirs.

[0231] The two reservoirs were separated by a composite membrane obtained as detailed in Example 1 according to the present invention.

[0232] Silver grid Ag / AgCl electrodes were immersed in each of the reservoirs on both sides of the membrane to measure the current generated through the membrane.

[0233] The results of these measurements are shown in Table 2.

[0234] Table 2

[0235]

[0236] Where:

[0237] - U Osmo is the potential of the membrane from which the Nernst potential (U Nernst) of the electrode is derived

[0238] - I Osmo is the current associated with the membrane, which is calculated by measuring the resistance of the membrane and according to Ohm's law I = U / R

[0239] - P Osmo Max is calculated by the formula Pmax = (U × I) / 4

[0240] The membrane power is expressed in W / m 2 and the value obtained on a 1 cm 2 membrane is multiplied by 10000.

[0241] It was also observed that during heating at 85 °C, by applying a pressure of 3 to 4 bar to the membrane between two metal plates, the mechanical stability of the membrane was improved by 10% to 20%.

Claims

1. An apparatus for generating electrical energy, comprising: a) A first reservoir A (20A) which is intended to receive an electrolyte solution (22A) having a solute concentration of C A and which comprises an electrode (30A) in contact with the electrolyte solution having a concentration of C A ; b) A second reservoir B (20B) intended to receive an electrolyte solution (22B) having the same solute at a concentration C B which is lower than C B and which includes an electrode (30B) in contact with the electrolyte solution at a concentration C A ; B ​ c) a membrane (10) separating two reservoirs, said membrane comprising pores to allow an electrolyte to diffuse through said pores from reservoir A to reservoir B; and d) A device (32) that allows the provision of electrical energy generated by the potential difference existing between two electrodes, characterized in that, The membrane comprises at least one layer formed of a cellulose material and comprising a network of cross-linked cellulose nanofibers and / or microfibers.

2. The apparatus according to claim 1, wherein the thickness of the membrane is between 2 μm and 100 μm.

3. The apparatus according to claim 1 or 2, wherein the thickness of the membrane is between 2 μm and 75 μm.

4. The device according to claim 1 or 2, wherein the membrane comprises 10 g to 20 g of cellulose material per m 2 of the membrane.

5. The apparatus according to claim 4, wherein the membrane comprises from 15 g to 20 g of cellulose material per m 2 of membrane.

6. The apparatus according to claim 1 or 2, wherein the cross-linked cellulose nanofibers and / or microfibers are functionalized with negatively charged groups and / or groups that become negatively charged in the presence of water.

7. The device according to claim 6, wherein the crosslinked cellulose nanofibers and / or microfibers are functionalized with a group selected from: sulfonate group -SO3 - , carboxylate group -CO2 - , aminodiacetate group -N(CH2CO2 - )2, phosphonate group PO2 3- , amidoxime group -C(=NH2)(NOH), aminophosphonate group -CH2-NH-CH2-PO3 2- , thiol group -SH, and mixtures thereof.

8. The apparatus according to claim 1 or 2, wherein the cross-linked cellulose nanofibers and / or microfibers are functionalized with positively charged groups and / or groups that become positively charged in the presence of water.

9. The device according to claim 8, wherein the crosslinked cellulose nanofibers and / or microfibers are functionalized with a group selected from: quaternary ammonium group -N(R)3 + wherein R is a C1-C4 alkyl group, tertiary ammonium group -N(H)R)2 + wherein R is a C1-C4 alkyl group, dimethylhydroxyethylammonium group -N(C2H4OH)CH3)2 + , and mixtures thereof.

10. The apparatus according to claim 9, wherein R is a C1 alkyl group.

11. The apparatus according to claim 1 or 2, wherein the membrane comprises a single layer (101) formed of a cellulose material and comprising a network of cross-linked cellulose nanofibers and / or microfibers.

12. The apparatus according to claim 1 or 2, wherein the membrane is a composite membrane comprising two outer layers (104, 103), each outer layer formed of a cellulose material and comprising a network of cross-linked cellulose nanofibers and / or microfibers, with an inner layer (102) disposed between the two outer layers (104, 103), said inner layer being formed of a second material comprising nanoparticles, said nanoparticles being functionalized with charged groups and / or groups that become charged in the presence of water.

13. The apparatus according to claim 12, wherein the thickness of each outer layer (104, 103) is between 2 μm and 25 μm, and the thickness of the inner layer (102) is between 10 nm and 2 μm.

14. The apparatus according to claim 12, wherein the nanoparticles are layered nanoparticles.

15. The apparatus according to claim 14, wherein the layered nanoparticles are layered nanoparticles of metal oxides, transition metal chalcogenides, carbon, or mixtures thereof.

16. The apparatus according to claim 14, wherein the layered nanoparticles are graphene oxide layered nanoparticles functionalized on the surface with negatively charged groups or groups that become negatively charged in the presence of water.

17. The apparatus according to claim 15, wherein the layered nanoparticles of transition metal chalcogenides are layered nanoparticles of molybdenum disulfide.

18. A method of generating electrical energy using the apparatus according to claim 1 or claim 2, comprising the steps of: i) An electrolyte solution (22A) having a solute and a concentration of C is supplied in a reservoir A (20A) such that an electrode (30A) provided in the reservoir A is in contact with the solution (22A). A ​ ii) An electrolyte solution (22B) having the same solute and a concentration of C is supplied in the reservoir B (20B), B where C B is lower than C A such that the electrode (30B) provided in the reservoir B is in contact with the solution (22B). iii) allowing an electrolyte to diffuse through the membrane (10) from reservoir A to reservoir B, iv) using a device (32) to capture the electrical energy generated by the potential difference present between two electrodes.

19. The method according to claim 18, characterized in that, The electrolyte solution is an aqueous solution containing a solute selected from alkali metal halides or alkaline earth metal halides.

20. The method according to claim 19, wherein the solute is selected from NaCl, KCl, CaCl2, and MgCl2.

21. The method according to claim 18, wherein C A / C B The concentration ratio of is greater than 1 and less than or equal to 10 9 .

22. The method according to claim 21, wherein the concentration ratio of C A / C B is greater than 1 and less than or equal to 10 5 .

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