Thermal energy storage via sorption of water using an intercalated lamellar uraniferous material

Abstract

The invention relates to the use of a lamellar uraniferous material that is intercalated with molecules of an organic compound and that, by virtue of this intercalation, is capable of reversibly and sustainably sorbing water molecules over time, with high sorption / desorption kinetics and a high energy density, making it a material of choice for thermal energy storage via sorption of water. The invention also relates to a method for storing thermal energy using this material, to a thermal energy storage device for implementing this method, and to a novel intercalated lamellar uraniferous material. The invention is applicable to any field in which thermal management is to be optimized, including buildings, industrial structures, and urban heat networks, through recovery of thermal energy produced at a site and subsequent redistribution thereof, as required, to that site or to another site.

Description

[0001] Thermal energy storage by water sorption using an intercalated uranium-bearing lamellar material

[0002] technical field

[0003] The invention relates to the field of thermal energy storage - also called heat storage - by thermochemical means, more specifically by sorption of water at low temperature (i.e. below 150 °C).

[0004] More specifically, the invention relates to the use, for thermal energy storage by water sorption, of a uranium-bearing lamellar material which is intercalated by molecules of an organic compound and which, thanks to this intercalation, is capable of sorbing water molecules in a reversible and durable manner over time, with high sorption / desorption kinetics and high energy density, making it a material of choice for thermal energy storage by water sorption.

[0005] It also relates to a process of thermal energy storage by water sorption in which this material is used, as well as to a thermal energy storage device enabling the implementation of this process.

[0006] It also relates to a new intercalated uranium-bearing lamellar material.

[0007] The invention is likely to be used in all areas where thermal management needs to be optimized, whether in buildings, industrial structures or urban heat networks, by recovering the thermal energy produced on a site and its subsequent redistribution, according to needs, on that site or any other site.

[0008] Prior art

[0009] In the context of the energy transition, which aims to reduce the environmental impact of energy production, distribution, and consumption, particularly by reducing fossil fuel consumption in favor of renewable energies (solar, wind, geothermal, biomass, etc.), the development of thermal energy storage systems is receiving considerable attention. Three techniques have emerged in the field of thermal energy storage: sensible heat storage, latent heat storage, and sorption storage.

[0010] Thermal energy storage by sorption relies on the reversible nature of a physico-chemical reaction, this reaction being endothermic in one direction, which allows the system to store heat (charging stage), and exothermic in the other direction, which allows the system to release heat according to energy needs (discharging stage).

[0011] One of the key advantages of sorption storage is that heat is stored in the form of chemical potential. As a result, there is no heat loss during the charging, storage, and discharging phases, unlike sensible and latent heat storage, which require effective thermal insulation and inevitably lead to a loss of stored heat over time.

[0012] Among sorption storage systems, those based on water sorption—that is, on a reversible dehydration / hydration reaction of a material—are currently the most studied. These systems have the advantage of being able to harness both solar thermal energy and waste industrial heat.

[0013] However, to efficiently store heat by water sorption, a material must meet three criteria, namely:

[0014] - high resistance to cycling, meaning the ability to maintain its performance after numerous charge and discharge cycles, or in other words, after numerous cycles of water sorption / desorption, so as to retain its full efficiency over the long term,

[0015] - short charging and discharging times, or in other words, high sorption / desorption kinetics so that heat can be rapidly stored and then released by the material, and

[0016] - a high energy density, that is to say a capacity to store and, therefore, to release a significant amount of energy (per unit volume or mass).

[0017] However, the materials proposed so far for heat storage by water sorption do not meet these three criteria. Furthermore, the fuels used in most nuclear reactors currently operating worldwide are prepared from enriched uranium produced by enrichment plants.

[0018] Uranium enrichment generates so-called depleted uranium because its uranium-235 isotopic ratio is lower than that of natural or reprocessed uranium that has undergone enrichment.

[0019] As a general rule, the isotopic ratio in 235 The U content of depleted uranium is less than 0.5% and, more specifically, between 0.2% and 0.4%.

[0020] Uranium enrichment facilities have been in operation for more than half a century and their operation has led to the accumulation of large stocks of depleted uranium which, depending on the enrichment facility, is stored in different forms.

[0021] While depleted uranium is notably used in the manufacture of MOX type nuclear fuels (mixture of uranium and plutonium oxides), this use is limited and it would be desirable to find other ways of utilizing depleted uranium in order to reduce the volumes of depleted uranium already accumulated and those yet to come.

[0022] In view of the above, the inventors set themselves the objective of providing a material that meets the criteria of cycle life, short charge / discharge times and high energy density required for use as a water sorption heat storage material and that can, if necessary, be synthesized from depleted uranium.

[0023] They also set themselves the objective of ensuring that this material has a low charging temperature in order to:

[0024] - on the one hand, to be able to use, for its fuel, the residual heat from industrial processes (because 60% to 70% of wasted energy dissipates as heat between 100°C and 200°C) or so-called "low temperature" energy sources such as solar or geothermal energy, and

[0025] - On the other hand, to reduce operational safety risks when used in a thermal energy storage system. They also set themselves the goal that this material could be prepared by a process that is simple to implement and whose cost is compatible with industrial-scale operation.

[0026] Description of the invention

[0027] The invention aims precisely to propose, firstly, the use of an intercalated uranium-bearing lamellar material for the storage of thermal energy by water sorption, in which:

[0028] - the material comprises a hydrated uranyl compound which is formed from a stack of sheets, each comprising a plurality of uranium atoms bonded to oxygen atoms, for example by iono-covalent bonds, two successive sheets of the stack delimiting an inter-sheet space in which water molecules exist, and

[0029] - the material further comprises molecules of an organic compound which are intercalated between two successive sheets of the hydrated uranyl compound, the organic compound comprising at least a first and a second terminal functional group linked to each other by a spacer arm, the first terminal functional group being capable of forming hydrogen bonds with one or more oxygen atoms of one of the two successive sheets and, optionally, one or more water molecules, and the second terminal functional group being capable of forming hydrogen bonds with one or more oxygen atoms of the other of the two successive sheets and, optionally, one or more water molecules.

[0030] Thus, according to the invention, the uranium-bearing lamellar material, which is used for thermal energy storage by water sorption, is characterized by being intercalated by molecules of an organic compound, this intercalation having the following effect:

[0031] - on the one hand, to enlarge the interlayer spaces of the material and, by the same token, to increase its capacity to sorb water molecules, that is to say to accommodate water molecules between two successive layers; and - on the other hand, to ensure that the sorption of water by the material is totally reversible and to guarantee that this reversibility does not affect the integrity of the structure of this material (whether by phase transition, agglomeration or amorphization).

[0032] According to the invention, the spacer arm of the organic compound is advantageously a hydrocarbon chain which can be interrupted by one or more functional groups capable of forming hydrogen bonds with one or more water molecules and / or of which one or more carbon atoms can bear a pendant functional group, capable of forming hydrogen bonds with one or more water molecules.

[0033] The choice of the first and second terminal functional groups of the organic compound, which may be identical or different, is not particularly limited, provided that these functional groups can form hydrogen bonds with one or more oxygen atoms present in the leaflets and possibly one or more water molecules. Similarly, the choice of the functional group(s) optionally present in the hydrocarbon chain of the spacer arm (in other words, functional group(s) interrupting the hydrocarbon chain, as mentioned above) and / or attached to this hydrocarbon chain (in other words, pendant functional group, as mentioned above) is also not particularly limited, provided that these functional groups can form hydrogen bonds with one or more water molecules.

[0034] These functional groups, and in particular the first and second terminal functional groups of the organic compound, may include primary, secondary or tertiary amine groups, primary, secondary (or imide) or tertiary amide groups, hydroxyl groups, carboxylic acid groups, imine groups, oxime groups and / or sulfonic acid groups.

[0035] So :

[0036] - when the functional groups are terminal or carried by the hydrocarbon chain of the spacer arm, the functional groups may include -NH2, -NHR, -NRR', -CONH2, -CONHR, -CONRR', -CONHCOR, -CONRCOR', -N(COR)2, -CON(COR)2, -OH, -COOH, -CH=NH, -CH-NR, -CR=NH, -CR=NR', -N=CH2, -N=CHR, -N=CRR', -CH=NOH, -CR=NOH and / or -SO3H, in which R and R', if present, independently represent an alkyl group, preferably in C1 to C2, while

[0037] - when functional groups are present in the hydrocarbon chain of the spacer group, they can in particular be groups -NH-, -NR-, -CONH-, -CONR-, -CONHCO-, -CONRCO-, -CH=N-, -CR=N-, -N=CH- - -N=CR-, and / or -C(=NOH)- in which R, if present, represents an alkyl group, preferably in Ci to Ce.

[0038] Among these groups, preference is given to primary or secondary amine groups and hydroxyl groups.

[0039] Preferably, the first and second terminal functional groups of the organic compound are identical to each other.

[0040] Preferably, the spacer arm of the organic compound also consists of an alkyl or alkylene chain, linear or branched, comprising 2 to 20 carbon atoms and, even better, 4 to 8 carbon atoms.

[0041] Organic compounds that meet all these preferences are primary alkyldiamines, linear or branched, and linear or branched alkyldiols in C2 to C20 and, preferentially, in C4 to C8.

[0042] Among these, preference is given to linear primary alkyldiamines.

[0043] According to the invention, the uranium-bearing lamellar material can, a priori, be any compound of hydrated uranyl.

[0044] Thus, it can be chosen from among the following:

[0045] - compounds with a fourmarierite-type structure, such as schoepite with the structural formula [(11O2)5O2(O1-1)12]. I2H2O, metaschoepite with the structural formula [(UO2)4O(OH)6].5H2O, fourmarierite with the structural formula Pb[(UO2)4O3(OH)4]. H2O, leesite with the structural formula K(H2O)2[(UO2)4O2(OH)s].3H2O or bobfinchite with the structural formula Na[(UO2)8O3(OH)n].10H2O;

[0046] - compounds with a protasite-type structure, such as protasite with the structural formula Ba[(UO2)3O3(OH)2].3H2O or a compound with the general structural formula [A + 2(i+ X ) or B 2+ (i+ X )][(UO2)6O(4+2x)(OH)(6-2x)].nH2O in which A + is Na + K + or Cs + , B 2+ is that 2+ , Sr 2+ Ba 2+ or P 2+ , x = 0 or 1), such as billietite with structural formula Ba(UO2)6O4(OH)6.4H2O or compreignacite with structural formula

[0047] K2(UO2)6O4(OH)6.8H2O;

[0048] - compounds with a uranophane-type structure, such as kasolite with the structural formula [Pb(UO2)(SiO4)].H2O or a compound with the general structural formula A(UO2) x (SiO3OH) x .nH2O in which A is K + , N / A + , That 2+ , Mg 2+ Cu 2+ , Cs + or P 2+, x = 1 or 2, such as uranophane with structural formula Ca(UO2)2(SiO3OH)2.5H2O, boltwoodite with structural formula (K,Na)(UO2)(SiO3OH).l,5H2O, cuprosklodowskite with structural formula Cu(UO2)2(SiO3OH)2.6H2O, sklodowskite with structural formula Mg(UO2)2(SiO3OH)2.5H2O;

[0049] - compounds with a P-U3O8 type structure, such as anthnite with structural formula U 4+ 2(UO2)4Oe(OH)4.9H2O or spriggite with structural formula Pb3(UO2)6O8(OH)2.3H2O;

[0050] - compounds with iriginite-type structure, such as iriginite with structural formula (UO2)Mo2O7.3H2O;

[0051] - compounds with sayrite-type structure, such as sayrite with structural formula Pb2(UO2)5O6(OH)2.4H2O;

[0052] - compounds with zippeite-type structure, such as marecottite with structural formula Mg3(UO2)8(SO4)4O6(OH)2.28H2O or a compound with the general structural formula A(H2O) x [(UO2) 2y(SO4)yO2+z(OH) z ] such as zippeite in which A = K3, x= 3, y = 2 and z = 1, Na-zippeite in which A = Nas ; x = 12, y = 4 and z = 3, Mg-zippeite in which A = Mg, x = 3.5, y = 1 and z = 0, Zn-zippeite in which A = Zn, x = 3.5, y = 1 and z = 0, and Co-zippeite in which A = Co, x = 3.5, y = 1 and z = 0;

[0053] - compounds with a phosphuranylite-type structure, such as larisaite with the structural formula Na(H3O)(UO2)3(SeO3)O2.4H2O or a compound with the general structural formula A 2+ 2(UO2)3O2(XO4)2.nH2O in which

[0054] - compounds with an autunite-type structure, such as abernathyite with the structural formula K(UO2)(AsO4).3H2O or a compound with the general structural formula A 2+(UO2)2(XO4)2.nH2O in which X = As or P, such as autunite with structural formula Ca(UO2)2(PO4)2.10-12H2O, zeunerite with structural formula Cu(UO2)2(AsO4)2.12H2O or saléeite with structural formula Mg(UO2)2(PO4)2.10H2O; and

[0055] - compounds with francevillite-type structure, such as francevillite with structural formula Bao,96Pbo,o4[(UO2)2( 20s)](H2O)5, curienite with structural formula Pb[(UO2)2(V2O8)](H2O)5, sengirite with structural formula Cu2[(UO2)2( 2Os)](OH)2(H2O)6 and / or a magnesium uranyl chromate with structural formula Mg2[(UO2)2(Cr2O8)](H2O)4.

[0056] Preferably, the hydrated uranyl compound is a compound whose sheets comprise uranyl oxides, i.e., UO2 cations 2+ linked to one or more oxygen atoms, and / or uranyl hydroxides, i.e. UO2 cations 2+ linked to one or more hydroxyl groups.

[0057] Better still, we prefer that this compound be a uranyl oxyhydroxide, that is to say a compound in which the UO2 cations 2+ are linked to both one or more oxygen atoms and one or more hydroxyl groups, which is, for example, the case of the fourmarierite-type, protasite-type, P-U3O8-type and zippeite-type compounds mentioned previously.

[0058] Preferably of all, the hydrated uranyl compound is metaschoepite, with the structural formula [(UO2)4O(OH)6].5H2O, more simply written in the literature as UO3.2H2O.

[0059] According to a particularly preferred embodiment of the invention, the material is a metaschoepite intercalated by molecules of a linear primary alkyldiamine, preferably at C2 to C20 and, even better at Ce (i.e., by molecules of 1,6-diaminohexane).

[0060] According to the invention, the hydrated uranyl compound is advantageously synthesized from a depleted uranium source, for example depleted uranyl nitrate.

[0061] Thus, for example, and as is known in itself, metaschoepite can be synthesized from studtite, with the structural formula [(UO2(O2)(H2O)2].2H2O, which can itself be precipitated from a uranyl nitrate solution obtained by dissolving depleted UsOs with nitric acid. Furthermore, the intercalation of molecules of the organic compound between the layers of the hydrated uranyl compound can be achieved by any intercalation technique known to allow the intercalation of molecules of an organic compound within a host compound.

[0062] In particular, it can be achieved by the wet intercalation technique, which is based on immersing the host compound, at a controlled temperature, in an aqueous solution containing the molecules of the organic compound, or by the gaseous intercalation technique, isothermal or vapor transport, which is based on bringing the host material into contact with the molecules of the organic compound in gaseous form.

[0063] Preferably, the material is in powder form. However, it can also be in the form of agglomerates, such as beads, extrudates or pellets, obtained from a powder using agglomeration techniques known to those skilled in the art.

[0064] The invention also relates to a method for storing thermal energy by water sorption, which includes at least the steps of: a) dehydration by heating of an intercalated uranium lamellar material as previously defined, thereby storing thermal energy by the material; b) keeping the dehydrated material protected from moisture; c) rehydration of the dehydrated material, thereby releasing the thermal energy stored in step a); and d) recovery of the thermal energy released in step c).

[0065] According to the invention, step a) is preferably carried out until total or almost total dehydration of the material is obtained.

[0066] Typically, such dehydration is achieved by heating the material to a temperature of no more than 150 °C, and preferably no more than 100 °C, for a period ranging from 15 minutes to 25 hours, and preferably from 30 minutes to 5 hours, depending in particular on the quantity of material to be dehydrated and its form. Heating the material for dehydration can be carried out using any energy source, although preference is given to heating by a decarbonized or "low-carbon" energy source, such as nuclear or renewable energy (solar, wind, hydroelectric, biomass, etc.), and / or by a waste industrial energy source (such as that produced by furnaces, boilers, incinerators, etc.).

[0067] This heating can notably consist of bringing the material into contact with a flow of hot air, preferably dried or dehumidified.

[0068] Rehydration of the dehydrated material (step c)) can be carried out by bringing this material into contact with liquid water, water vapor, or humidified air, for example, air with 90% or even 95% relative humidity. It can also be carried out at ambient temperature, that is, at a temperature typically between 20°C and 25°C.

[0069] According to the invention, the storage process can operate on a cyclic model of alternation between a charging phase (corresponding to step a)) and a discharging phase (corresponding to step c)), the charging and discharging phases being separated by a phase of storage stricto sensu of thermal energy (corresponding to step b)), each cycle making it possible to recover and store thermal energy when it is available in excess and to release it as soon as there is a demand for energy.

[0070] Thanks to the use of a material as defined above, the process of the invention offers numerous advantages, including:

[0071] - high energy density storage, for example at least 0.7 GJ / m³ 3 ;

[0072] - storage of theoretically unlimited duration;

[0073] - the ability to operate within a limited temperature range (20°C - 150°C) and, therefore, perfectly compatible with the use, for charging phases, of so-called "low temperature" energy sources such as solar or geothermal energy; and

[0074] - a valorization of depleted uranium stocks. The invention also relates to a device for implementing a thermal energy storage process by water sorption as previously defined, which comprises at least:

[0075] - a reactor comprising at least one bed containing an intercalated uranium-bearing lamellar material as previously defined;

[0076] - means of heating the bed containing the material to dehydrate the material and store thermal energy;

[0077] - means of removing the water produced by the dehydration of the material and of preserving the dehydrated material away from moisture;

[0078] - means of supplying water to the bed containing the material to rehydrate the material and release the stored thermal energy; and

[0079] - means of recovering the released thermal energy.

[0080] This device can easily be designed to be transportable from a site where thermal energy can be recovered to a site where there is a need for thermal energy.

[0081] As previously mentioned, the material contained in the bed can be in the form of powder, beads, extrudates or pellets.

[0082] When the compound is in powder form, the bed is preferably a fluid bed. When the compound is in the form of beads, extrudates, or pellets, the bed is preferably a fixed bed.

[0083] The invention further relates to a uranium-bearing lamellar material comprising a hydrated uranyl compound formed from a stack of sheets, each comprising uranyl oxides and / or uranyl hydroxides, in which two successive sheets delimit an inter-sheet space where water molecules exist, and which is characterized in that molecules of an organic compound comprising at least a first and a second terminal functional group linked to each other by a spacer arm are intercalated between two successive sheets of the hydrated uranyl compound, the first terminal functional group being capable of forming hydrogen bonds with one or more oxygen atoms of one of the two successive sheets and optionally one or more water molecules.and the second terminal functional group being capable of forming hydrogen bonds with one or more oxygen atoms from the other of the two successive sheets and possibly one or more water molecules.

[0084] According to the invention, this material is intercalated by an organic compound which preferably has the characteristics previously stated in the context of the use of a uranium-bearing lamellar material for the storage of thermal energy by water sorption.

[0085] Furthermore, it is preferred that the hydrated uranyl compound it comprises be a uranyl oxyhydroxide, which can therefore be chosen in particular from the fourmarierite-type, protasite-type, P-U3O8-type or zippeite-type compounds previously mentioned.

[0086] Preferably of all, the hydrated uranyl compound is metaschoepite, with the structural formula [(UO2)4O(OH)6].5H2O, more simply written in the literature as UO3.2H2O.

[0087] According to a particularly preferred embodiment of the invention, the material is a metaschoepite intercalated by molecules of a linear primary alkyldiamine, preferably at C2 to C20 and, even better at Ce.

[0088] Other features and advantages of the invention will become apparent from the following detailed description, which is given by way of illustration and not limitation, with reference to the attached figures 1 to 14.

[0089] Brief description of the figures

[0090] Figure 1 illustrates the X diffractograms obtained for samples of metaschoepite intercalated by linear primary alkyldiamine molecules, as a function of the number of carbon atoms in the alkyl chain of these alkyldiamines and, for comparison, the diffractogram obtained for a sample of non-intercalated metaschoepite; in this figure, the peaks corresponding to the (200) diffraction planes of the inter-sheet spaces of the metaschoepite samples are indicated and the inter-sheet distances are shown.

[0091] Figure 2 illustrates the evolution of the interlayer distance, denoted dooz and expressed in angstroms, of the samples of intercalated metaschoepite whose X diffractograms are shown in Figure 1, as a function of the number of carbon atoms, denoted Cx, that comprise the alkyl chain of the intercalating alkyldiamines.

[0092] Figure 3 illustrates the evolution of water uptake, noted H2O / U, as determined by dynamic vapor sorption (DVS) for the samples of intercalated metaschoepite whose X diffractograms are shown in Figure 1, as a function of time, noted t and expressed in minutes.

[0093] Figure 4 illustrates the calorimetric profiles as obtained by wet-air scanning differential scanning calorimetry (DSC), under isothermal conditions (22 °C), for the intercalated metaschoepite samples whose X diffractograms are shown in Figure 1; in this figure, the ordinate axis corresponds to the heat flux, denoted O and expressed in mW, while the abscissa axis corresponds to time, denoted t and expressed in minutes.

[0094] Figure 5 illustrates the evolution of the hydration enthalpy, denoted AHhydr and expressed in J / g, of the samples of intercalated metaschoepite whose calorimetric profiles are illustrated in Figure 4, as a function of the number of carbon atoms, denoted Cx, that comprise the alkyl chain of the intercalating alkyldiamines.

[0095] Figure 6 illustrates the water sorption isotherm (curve S) and water desorption isotherm (curve D) as obtained for a sample of metaschoepite intercalated by 1,6-diaminohexane molecules, as a function of the relative humidity, noted HR and expressed in %, to which this sample was subjected.

[0096] Figure 7, given for comparison, is a figure analogous to Figure 6 but relating to a sample of non-intercalated metaschoepite.

[0097] Figure 8 illustrates the evolution of the heat flux, denoted O and expressed in mW, as observed by DSC, under isothermal conditions (22 °C), for a sample of metaschoepite intercalated by 1,6-diaminohexane molecules, during an in situ cycling of 20 cycles alternating dry and humid air.

[0098] Figure 9 illustrates the enthalpy values, denoted AH and expressed in J / g, as obtained by integrating the peaks shown in Figure 8; in this figure, the solid circles correspond to the hydration enthalpy values, while the empty squares correspond to the dehydration enthalpy values. Figure 10 illustrates the variation in water content, denoted H₂O / U, as observed by DVS, for a sample of metaschoepite intercalated with 1,6-diaminohexane molecules, during an in situ cycling of 50 cycles at 60 °C.

[0099] Figure 11 illustrates the X diffractograms presented by a sample of metaschoepite intercalated with 1,6-diaminohexane molecules before (curve A) and after (curve B) an in situ cycling of 50 cycles at temperature (60 °C).

[0100] Figure 12 is a scanning electron microscope (SEM) image, at a magnification of x2000, of a sample of metaschoepite intercalated by 1,6-diaminohexane molecules that have not undergone cycling.

[0101] Figure 13 is an image analogous to Figure 12 but relating to a sample of metaschoepite intercalated by 1,6-diaminohexane molecules that have undergone in situ cycling of 100 cycles at temperature (60 °C).

[0102] Figure 14, given for comparison, illustrates the variation in water content, noted H2O / U, as observed by DVS, for a sample of metaschoepite intercalated by molecules of a linear primary alkylamine, during an in situ cycling of 15 cycles under isothermal conditions (22 °C).

[0103] Detailed description of specific implementation methods

[0104] I - Preparation of the metaschoepite:

[0105] Metaschoepite, which is used in what follows, is prepared from studtite, of structural formula [(UO2(O2)(H2O)2].2H2O, which is itself prepared from a uranyl nitrate solution.

[0106] To obtain studtite, a 30% aqueous solution of hydrogen peroxide (H₂O₂) is added dropwise to an aqueous solution containing 0.5 mol / L uranyl nitrate to achieve a final H₂O₂ / U molar ratio of 2. The resulting solution is stirred for 3 minutes. The pale yellow precipitate is collected by centrifugation (5,000 rpm), after which it is washed several times with distilled water and then with a 50:50 v / v hydroethanolic solution to remove residual nitrates. The resulting powder is dried overnight in an oven at 30 °C, yielding the studtite. To obtain metaschoepite, studtite is first converted into amorphous uranium trioxide, UOsam, by grinding and then calcination under argon flow, at 300 °C for 2 hours, with a heating rate of 5 °C / min.Then, amorphous uranium trioxide is converted into metaschoepite by hydration for 35 hours, in a chamber maintained at room temperature (22 °C) and under an airflow with a relative humidity of 95%. The color change of the powder, from orange to yellow, indicates the formation of metaschoepite, with the structural formula [(UO2)4O(OH)6].5H2O, more simply written in the literature as UO3.2H2O.

[0107] II - Intercalation of alkyldiamine molecules of formula H2N(CH2) X NH2 in samples of metaschoepite:

[0108] From the metaschoepite obtained in point I above, a series of different samples of intercalated metaschoepite are prepared, designated respectively below as MSCPIC2, ​​MSCPIC3, MSCPiC4, MSCPiC6, MSCPiC8, MSCPiC10 and MSCPiC12, using, as intercalating molecules, molecules of:

[0109] - 1,2-diaminoethane for MSCPiC2,

[0110] - 1,3-diaminopropane for MSCPiC3,

[0111] - 1,4-diaminobutane for MSCPiC4,

[0112] - 1,6-diaminohexane for MSCPiC6,

[0113] - 1,8-diaminooctane for MSCPiC8,

[0114] - 1,10-diaminodecane for MSCPiCIO, and

[0115] - 1,12-diaminododecane for MSCPiC12.

[0116] For each intercalation, a mass mi of the intercalating alkyldiamine is dissolved in a volume of distilled water, and then a mass m2 of metaschoepite is added to the resulting aqueous solution. The masses ml and m2 and the volume of water are chosen such that the molar ratio of U / alkyldiamine is 1 / 5 and the molar ratio of U / H2O is 1 / 300. The mixture is then stirred (600 rpm) at room temperature for 6 hours and then centrifuged (5000 rpm). The centrifuged pellet is collected and washed three times with distilled water before being dried by freeze-drying. For the sake of simplicity, the expression "intercalated metaschoepite(s)" is used in the following text instead of "intercalated metaschoepite sample(s)".

[0117] III - Characterization of metaschoepites intercalated by alkyldiamine molecules:

[0118] 111.1 - Influence of intercalation on the interlayer space of the metaschoepite:

[0119] The intercalated metaschoepites prepared in point II above are subjected to analysis by powder X-ray diffraction.

[0120] This analysis is performed using a BRUKER D8 ADVANCE diffractometer, with a 0-0 Bragg-Brentano geometry, equipped with a LynxEye detector. The wavelength used is that of copper (Kot: X = 1.54056 Å).

[0121] The X diffractograms thus obtained are illustrated in Figure 1. For comparison, the X diffractogram obtained for a sample of non-intercalated metaschoepite is also illustrated in this figure.

[0122] Figure 1 shows that the intercalation of alkyldiamine molecules in metaschoepite leads to an increase in the interlayer distance from 7.34 Å for non-intercalated metaschoepite to 22.9 Å for MSCPiC12 metaschoepite, intercalated by 1,12-diaminododecane.

[0123] Moreover, as seen in Figure 2, which illustrates the evolution of the inter-sheet distance as a function of the number of carbon atoms in the alkyl chain of the intercalating alkyldiamines, this evolution is linear and allows, by linear regression, to establish the equation according to which the inter-sheet distance, dooz, of an intercalated metaschoepite is equal to 1.44Cx + 4.32, Cx being the number of carbon atoms in the alkyl chain of the alkyldiamine used for its intercalation.

[0124] 111.2 - Influence of intercalation on the hydration behavior of metaschoepite:

[0125] - Water sorption capacity of intercalated metaschoepites: In order to assess their water sorption capacity, the intercalated metaschoepites prepared in point II above are subjected to dynamic vapor sorption (DVS) analyses, this analytical technique allowing measurement of the mass variation of a material as a function of the water vapor pressure applied to it.

[0126] These analyses are performed using a TA Instruments QA-5000 SA DVS device.

[0127] Prior to analysis, the intercalated metaschoepites are dehydrated by heating at 60 °C under dry air for 1 hour. They are then swept by a stream of humid air (relative humidity: 95%) at a flow rate of 0.2 L / min. Water sorption by a metaschoepite is considered maximal when the mass change of that sample is less than 0.01% over 15 minutes.

[0128] The evolution over time of the water uptake of intercalated metaschoepites, expressed as the ratio of the number of water molecules per uranium atom, noted H2O / U, presented by these metaschoepites, is illustrated in Figure 3.

[0129] As this figure shows, the greater the interlayer distance of an intercalated metaschoepite, the greater the capacity of that metaschoepite to absorb water.

[0130] Thus, a minimum of 0.47 HzO molecules per uranium atom was sorbed by the MSCPiC2 metaschoepite while a maximum of 3.11 HzO molecules per uranium atom was sorbed by the MSCPiC12 metaschoepite.

[0131] - Hydration energies of intercalated metaschoepites

[0132] In order to quantify the hydration energies involved during the sorption of water by the intercalated metaschoepites, these metaschoepites are subjected, after being dried, to analyses by differential scanning calorimetry (or DSC from the English Differential Scanning Calorimetry) under humid air (relative humidity: 90%).

[0133] These analyses are performed using a SETARAM DSC 131 differential scanning calorimeter coupled to a BRONKHORST CEM W-101A humidifier-evaporator. To enable coupling, a polylactic acid (PLA) printed component is placed at the humidifier outlet and inserted into the calorimeter chamber. This component is designed to create a compartment that allows for the homogeneous exposure of the sample to be analyzed and the reference crucible to the humid air scan. The analyses are carried out at 22°C with a constant humid air flow rate of 1 L / min, ensuring a rapid system response and stable humidity levels from the first few minutes of sample hydration.

[0134] The results of these analyses are illustrated in Figures 4 and 5, which show, respectively, the exothermic peaks observed for the different intercalated metaschoepites and, respectively, the values ​​of the hydration enthalpies, AHhydr, taken from the integration of these peaks.

[0135] As seen in Figure 5, the highest hydration enthalpy (155 J / g) is obtained for metaschoepite MSCPiC6, intercalated by 1,6-diaminohexane molecules.

[0136] Since the metaschoepite MSCPiC6 appears to be the one that presents the most interest for heat storage, the following experiments were therefore focused on this metaschoepite.

[0137] - Water sorption / desorption isotherm of metaschoepite MSCPIC6

[0138] The affinity for water of metaschoepite MSCPiC6 is assessed by comparing its water sorption / desorption isotherm, shown in Figure 6, with that of non-intercalated metaschoepite, shown in Figure 7.

[0139] These isotherms, which represent the variation in water content of metaschoepites as a function of the relative humidity of the equilibrium medium at a given temperature, are established by DVS. To do this, a crucible is filled with a 10 mg powdered sample of the metaschoepite to be analyzed and then sealed with a lid using a press. The crucible is then drilled and placed in a sample chamber. The sample is then dried at 60 °C and 0% relative humidity for 60 minutes or until the selected equilibrium criteria are met (stability of 0.01% by mass for 15 minutes) to ensure complete drying of the sample before analysis.

[0140] The analysis is performed by varying the relative humidity from 0% to 95% in 5% increments according to a sorption / desorption cycle. The sample mass is measured every 5 seconds, and equilibrium conditions are defined such that the mass change is less than 0.01% for 15 minutes and the recording time per increment remains less than 24 hours to limit the total recording time. The mass of the dried sample is used as a reference to translate the sample's mass gain into a number of water molecules per uranium atom (H₂O / U ratio). In all cases, mass stability is reached before 24 hours (the maximum time per programmed increment), thus validating the sorption experiments.

[0141] As seen in Figure 6, the quasi-closed isotherm obtained for metaschoepite MSCPiC6 indicates that the intercalation of this metaschoepite by 1,6-diaminohexane molecules allows a reversible hydration reaction by alternating dry and humid air, which is not the case for non-intercalated metaschoepite (see Figure 7).

[0142] - Behavior during the cycling of the metaschoepite MSCPiCô

[0143] The cyclability of the MSCPiC6 metaschoepite is evaluated by monitoring the reversibility of water sorption / desorption by this metaschoepite over a large number of cycles.

[0144] Initially, the thermal behavior of metaschoepite MSCPiC6 during a 20-cycle cycle was analyzed by DSC under isothermal conditions (22°C), with alternating dry and humid air (relative humidity: 90%). The objective was to monitor the energy exchanged during water sorption / desorption through simple alternation of dry and humid air. The apparatus used was the same as that described in section III.2 above.

[0145] The results of this analysis are presented in Figures 8 and 9, Figure 8 showing the evolution of the heat flux, O, observed during the 20 cycles while Figure 9 shows the enthalpy values, AH, of hydration (empty squares) and dehydration (solid circles) respectively obtained by integrating the peaks shown in Figure 8.

[0146] As shown in Figure 9, the average enthalpy of hydration over 20 cycles is 149 J / g. The cycles appear to be repeatable as no significant variation in enthalpy values ​​is observed.

[0147] Secondly, the influence of dehydration by heating at 60 °C on the cyclability of metaschoepite MSCPiC6 was evaluated over 50 cycles by DVS (using the same apparatus as that mentioned in section III.2 above), and the crystallographic structures exhibited by this metaschoepite, before and after the 50 cycles, were analyzed by powder X-ray diffraction (using the same apparatus as that mentioned in section II.1 above). The results of these analyses are presented in Figures 10 and 11, Figure 10 showing the variation in water content, H2O / U, while Figure 11 shows the crystallographic structures before (curve A) and after (curve B) the 50 cycles.

[0148] As shown in Figure 10, the amount of water absorbed by the MSCPiC6 metaschoepite remains very stable as the number of cycles increases, while, as shown in Figure 11, the crystallographic structures of this metaschoepite, before and after the 50 cycles, are substantially similar, thus proving its stability to low-temperature (60°C) cycling.

[0149] Furthermore, as seen in Figures 12 and 13, an analysis carried out on a FLEXSEM 1000 type scanning electron microscope (SEM) of the MSCPiC6 metaschoepite, before and after an in situ cycling of 100 cycles at temperature (60 °C), does not reveal any additional agglomeration, which would be due to cycling, of the powder constituting this metaschoepite.

[0150] IV - Comparative example: Intercalation of n-propylamine molecules in a metaschoepite sample:

[0151] From the metaschoepite obtained in point 1 above, a sample of metaschoepite intercalated with molecules of a linear-chain alkyl compound comprising only one primary amine functional group, namely n-propylamine, is prepared.

[0152] To do this, a mass m of metaschoepite is brought into contact with a diluted aqueous solution of n-propylamine whose pH has been previously adjusted to 11 by adding HCl (10%).

[0153] The mixture is placed in an ultrasonic bath for 1 hour to ensure particle dispersion, then stirred (600 rpm) for 6 hours at room temperature. Afterward, the resulting suspension is filtered, and the retentate is washed with a water / ethanol mixture, air-dried, and then ground.

[0154] Preliminary temperature cycling experiments, with alternating dry air at 100 °C and humid air (relative humidity: 95%) at 22 °C, showed that this cycling led to a decrease in the number of n-propylamine molecules per uranium atom with each cycle, due to the decomposition of this alkylamine and, consequently, of the metaschoepite structure. Therefore, the metaschoepite was subjected to 15 cycles under isothermal conditions (22 °C) with alternating dry and humid air (relative humidity: 95%). Figure 14 shows the variation in water content, denoted H₂O / U, of the metaschoepite intercalated by n-propylamine molecules, as observed by DVS during this cycling.

[0155] As can be seen in this figure, the sorption capacity of the metaschoepite intercalated by n-propylamine molecules decreases with each cycle of dehydration / hydration to which it is subjected, which seems to indicate that, even when cycling is carried out under isothermal conditions (22 °C), it leads to a decomposition of the n-propylamine and, consequently, of the structure of the intercalated metaschoepite.

[0156] Conversely, and as shown in Figure 10, the water sorption capacity of a metaschoepite intercalated by molecules of an alkyldiamine, such as the metaschoepite MSCPiC6, remains very stable when this metaschoepite is subjected to prolonged cycling (50 cycles), even when this cycling is carried out at temperature (60 °C).

Claims

Demands 1. Use of an intercalated uranium-bearing lamellar material for thermal energy storage by water sorption, wherein: - the material comprises a hydrated uranyl compound formed from a stack of sheets, each comprising a plurality of uranium atoms bonded to oxygen atoms, two successive sheets of the stack delimiting an inter-sheet space in which water molecules exist, said hydrated uranyl compound being a uranyl oxyhydroxide, and - the material further comprises molecules of an organic compound which are intercalated between two successive sheets of the hydrated uranyl compound, the organic compound comprising at least a first and a second terminal functional group linked to each other by a spacer arm, the first terminal functional group being capable of forming hydrogen bonds with one or more oxygen atoms of one of the two successive sheets and, optionally, one or more water molecules, and the second terminal functional group being capable of forming hydrogen bonds with one or more oxygen atoms of the other of the two successive sheets and, optionally, one or more water molecules, said organic compound being a primary alkyldiamine, linear or branched.

2. Use according to claim 1, wherein the spacer arm of the organic compound consists of a linear or branched alkyl or alkylene chain comprising from 2 to 20 carbon atoms and, preferably, from 4 to 8 carbon atoms.

3. Use according to claim 1 or claim 2, wherein the hydrated uranyl compound is metaschoepite of structural formula [(UO2)4O(OH)e].5H2O.

4. Use according to claim 3, wherein the metaschoepite is intercalated by molecules of a linear primary alkyldiamine, preferably in C4 to Cs and, even better in Ce.

5. A method for storing thermal energy by water sorption, comprising the successive steps of: a) dehydration by heating of an intercalated uranium-bearing lamellar material as defined in claims 1 to 4, thereby storing thermal energy by the material; b) keeping the dehydrated material protected from moisture; c) rehydration of the dehydrated material, thereby releasing the thermal energy stored in step a); and d) recovery of the thermal energy released in step c).

6. A method according to claim 5, wherein step a) is carried out at a temperature not exceeding 150 °C, preferably not exceeding 100 °C.

7. A method according to claim 5 or claim 6, wherein step c) comprises bringing the dehydrated material into contact with water vapor or humidified air.

8. Device for implementing a thermal energy storage process by water sorption according to any one of claims 5 to 7, comprising: - a reactor comprising at least one bed containing an intercalated uranium-bearing lamellar material as defined in any one of claims 1 to 4; - means of heating the bed containing the material to dehydrate the material and store thermal energy; - means of removing the water produced by the dehydration of the material and of preserving the dehydrated material away from moisture; - means of supplying water to the bed containing the material to rehydrate the material and release the stored thermal energy; and - means of recovering the released thermal energy.

9. Intercalated uranium-bearing lamellar material, comprising a hydrated uranyl compound formed from a stack of sheets, each comprising uranyl oxides and / or uranyl hydroxides, and in which two successive sheets delimit an inter-sheet space where water molecules are present, characterized in that molecules of an organic compound are intercalated between two successive sheets of the hydrated uranyl compound, which comprises at least a first and a second terminal functional group linked to each other by a spacer arm, the first terminal functional group being capable of forming hydrogen bonds with one or more oxygen atoms of one of the two successive sheets and optionally one or more water molecules, and the second terminal functional group being capable of forming hydrogen bonds with one or more oxygen atoms of the other of the two successive sheets and optionally one or more water molecules,said hydrated uranyl compound being a uranyl oxyhydroxide, and said organic compound being a primary alkyldiamine, linear or branched.

10. Material according to claim 9, wherein the spacer arm of the organic compound is made up of a linear or branched alkyl or alkylene chain comprising from 2 to 20 carbon atoms and, better still, from 4 to 8 carbon atoms.

11. Material according to claim 9 or claim 10, wherein the hydrated uranyl compound is metaschoepite of structural formula [(UO2)4O(OH)6].5H2O.

12. Material according to claim 11, which is a metaschoepite intercalated by molecules of a linear primary alkyldiamine, preferably at C4 to Cs and, even better at C6.

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