Method and plant for storing and releasing hydrogen

Abstract

A method for storing and releasing hydrogen (H2). The method comprises a hydrogenation phase, which comprises introducing hydrogen (H2) and an aqueous mixture of material adapted to bind with hydrogen in a reactor (2), creating two countercurrent streams (91, 92), to then store the hydrogen-bound material in one or more tanks (52). The method also comprises a dehydrogenation phase, which comprises obtaining an aqueous solution of hydrogen-bound material and introducing it in the reactor (2) so that at least part of the hydrogen is unbound from the material, creating two concordant streams (91, 92), a hydrogen stream (91) and an aqueous mixture stream (92), which flow toward the top (22) of the reactor (2), and making at least part of the hydrogen (H2) exit from the reactor (2); both phases are provided in the same reactor (2) and the transition from the hydrogenation phase to the dehydrogenation phase is provided by reversing the flow of the aqueous solution (92). The present invention also relates to a plant for providing the method.

Description

[0001] METHOD AND PLANT FOR STORING AND RELEASING HYDROGEN

[0002] The present invention relates to a plant and a method for storing and releasing hydrogen.

[0003] More specifically, the method and plant according to the invention fall within the field of chemical systems for hydrogen storage based on materials, in particular formates and / or bicarbonates.

[0004] As is known, hydrogen is a particularly promising energy carrier and fuel within a sustainable energy economy, and there is therefore a growing need for technologies that can ensure the storage of hydrogen in industrial quantities in a simple and safe manner.

[0005] Two main types of hydrogen storage techniques are known: the first is so-called “physically-based” storage, and the second is so-called “materials-based” storage.

[0006] Currently, physically-based hydrogen storage comprises three main technologies: compressed hydrogen, liquid hydrogen, and cryogenically compressed hydrogen. As is known, these technologies have significant problems, especially in terms of safety.

[0007] The second type of hydrogen storage technology mentioned above, to which the present invention relates, is based on the use of specific “materials” / substances capable of storing hydrogen, typically through chemisorption, physisorption, or Kubas interaction.

[0008] In adsorption, hydrogen is stored in a material, typically MOFs and hydrides, through the reversible formation of a chemical bond or by complexation. These technologies have the advantage of avoiding the need for high storage pressures and allowing greater management flexibility.

[0009] A first technology based on “materials” or solid media provides for the use of MOFs (Metal-Organic Frameworks), highly porous crystalline materials constituted by metal clusters coordinated by organic linkers. These materials can adsorb large amounts of hydrogen.today. One limitation of this technology is the low energy density of formate and bicarbonate solutions, which limits the amount of hydrogen that can be stored per unit volume. To increase energy density, more concentrated solutions can be used.

[0010] Disadvantageously, currently known storage methods using formates / bicarbonates in aqueous solution are rather complex and typically require the use of two different types of reactor: one for the hydrogenation phase (therefore for storage) and one for the dehydrogenation phase (therefore for release).

[0011] These known reactors, in particular the hydrogenation ones, are particularly complex and therefore expensive to provide and operate.

[0012] CN119633691 describes a reactor with tubes containing a fixed bed of catalyst for the hydrogenation / dehydrogenation of aromatic LOHCs (DBT / MBT), with thermal oil heat exchangers.

[0013] WO2024 / 105675 describes continuous bicarbonate / formate reaction systems comprising multiple reactors, separation systems, and mechanical screens.

[0014] US10,944,119 describes a dehydrogenation system with a homogeneous catalyst in organic solvents.

[0015] US 10,207,921 describes a batch bicarbonate-formate cycle, in which the catalyst is regenerated by oxidation in air.

[0016] There is therefore the need for a process that meets the requirements from the various energy, economics, and safety viewpoints that constitute prerequisites for the industrialization and widespread adoption of hydrogen technologies.

[0017] Consequently, the need is currently felt to identify innovative systems and technologies for hydrogen storage that have a low risk profile combined with low operating costs and acceptable ease of provision.

[0018] The aim of the present invention is therefore to provide a method and a related system for hydrogenation and dehydrogenation, i.e., for the storageand release of H2, that combine a high safety profile with high yields.

[0019] An object of the invention is to provide a plant and a method for hydrogen storage using materials that are, with respect to the background art, easier to provide and / or more economical.

[0020] Another object of the invention is to provide a plant and a method for hydrogen storage using materials that are advantageous from the energy standpoint with respect to the background art.

[0021] Another object of the invention is to provide a plant and a method for hydrogen storage using materials that are versatile and adaptable for large-scale use.

[0022] This aim, as well as these and other objects that will become better apparent hereinafter, are achieved by a method according to claim 1, optionally provided with the characteristics recited by one or more of the dependent claims.

[0023] This aim and these and other objects are also achieved by a plant according to claim 12, optionally provided with the characteristics recited by one or more of the dependent claims.

[0024] Further characteristics and advantages will become better apparent from the description of preferred, but not exclusive, embodiments of a plant for the storage and release of hydrogen and of the method provided therein, illustrated by way of non-limiting example with the aid of the accompanying drawings, wherein:

[0025] Figure 1 A is an operating diagram of a first embodiment of the plant, according to the invention, in a hydrogenation configuration;

[0026] Figure IB is an operating diagram of the first embodiment of the plant, according to the invention, in a dehydrogenation configuration;

[0027] Figure 2 is an operating diagram of a second embodiment of the plant, according to the invention, in a hydrogenation configuration;

[0028] Figure 3 is a schematic sectional view, taken along a vertical plane, of a reactor of the plant, in a hydrogenation configuration;Preferably, this material comprises or consists of one or more salts which are dehydrogenated and become hydrogenated (by binding with hydrogen) during the hydrogenation phase and vice versa during the dehydrogenation phase (therefore, an aqueous mixture of dehydrogenated salts is provided at the beginning of the hydrogenation phase).

[0029] In the preferred embodiments, said material comprises a bicarbonate (preferably of sodium and / or potassium) that becomes formate (of sodium and / or potassium) during the hydrogenation phase and vice versa during the dehydrogenation phase. In a further embodiment, the material comprises ammonium bicarbonate (NH4HCO3) which becomes ammonium formate (NH4HCO2) in the hydrogenation phase and vice versa in the dehydrogenation phase.

[0030] It is also possible that in some embodiments the aqueous mixture of material, which is fed into a reactor 2 for the hydrogenation phase, comprises both bicarbonate (reacting part) and formate (not reacting with hydrogen); this facilitates any crystallization of the formate (particularly useful in case of transport toward other sites).

[0031] Optionally, the aqueous mixture of material also comprises a catalyst C, preferably a catalyst based on a precious metal, even more preferably based on a Pd / Ag bimetallic alloy. According to a particularly advantageous optimal solution, the catalyst based on a Pd / Ag bimetallic alloy is photodeposited onto a suitable photoactive semiconductor medium (preferably TiO2and / or WO3).

[0032] To provide the hydrogenation phase, gaseous hydrogen H2must be supplied.

[0033] To provide the hydrogenation phase, the gaseous hydrogen H2and the aqueous mixture of material (designated by the letter M in Figures 3-5) are introduced in a vertically extended reactor 2 that has a bottom 21 and a top 22, so as to create two countercurrent streams 91, 92: a hydrogen stream 91 flowing toward the top 22 of reactor 2 and an aqueous mixture stream 92flowing toward the bottom 21 of said reactor 2; in this way, when the streams 91, 92 cross, at least part of the hydrogen H2binds by chemical reaction with at least part of the material contained in the aqueous mixture.

[0034] The hydrogenation phase is shown in Figure 3. In practice, the two countercurrent streams 91, 92 are provided by feeding the aqueous mixture M from an upper region of the reactor (from a height closer to the top 22 of the reactor 2 than to the bottom 21) and the gaseous hydrogen H2from a lower region of reactor 2 (from a height closer to the bottom 21 of the reactor 2 than to the top 22). In greater detail, the aqueous mixture M is introduced in the reactor 2 through a first upper supply duct 32 that leads into the reactor 2 proximally with respect to its top 22 (i.e., in a region closer to the top 22 than to the bottom 21). The aqueous mixture M is discharged through a lower supply / discharge duct 33 that leads into the reactor 2 at the bottom 21 of said reactor 2 or proximally thereto (i.e., in a region closer to the bottom 21 than to the top 22).

[0035] Figures 3 and 4 show that in the preferred embodiment the lower supply / discharge duct 33 is located exactly at the bottom 21 of the reactor 2. Advantageously, a surface 121 for guiding toward the lower supply / discharge duct 33 is provided on the bottom 21 of the reactor using an inert material.

[0036] The gaseous hydrogen H2is introduced in the reactor 2 through an intake duct 42 that leads into the reactor 2 proximate to the bottom 21 (preferably above the lower supply / discharge duct 33, as in the illustrated embodiment, and in any case below the first upper supply duct 32) and is made to exit through a discharge duct 43 that leads into the reactor 2 at, or at least proximate to, the top 22 (preferably above the first supply / discharge duct 32).

[0037] During the hydrogenation phase, the upper discharge duct 29, which will be described hereinafter, is conveniently closed (for example, by virtue of closure means 129 such as a valve).any unreacted gaseous hydrogen, designated by the reference numeral 4 IB, and the compressor will serve solely to recover the load losses of the distribution unit 23 and the head of the hydraulic column of the reactor 2.

[0038] Moreover, to minimize the flow rate of recycled gas and consequently maximize H2conversion without increasing the size of the reactors 2, one or both of the following optional solutions may be implemented:

[0039] i. Providing, inside the reactor 2, flow breaking elements 25 that slow the rise of the hydrogen stream 91 (i.e., the bubbles 99) and / or break the bubbles, reducing their size, and prevent local accumulations of solids and / or catalyst C.

[0040] ii. Increasing the velocity of the stream of the aqueous solution (in countercurrent to the gas) by means of one or more recirculations which are external to the reactor 2, so that the net rise rate of the bubbles 99 is lower than in the case without liquid recirculation. Under the operating conditions provided for in the preferred embodiments, the catalyzed reaction is not affected by the presence of reaction products, and this allows high recirculation ratios of the liquid, which also aids in a homogeneous redistribution of the catalyst C in the liquid phase.

[0041] During the hydrogenation phase, the aqueous solution M (preferably of bicarbonates) can be introduced in the reactor 2 at a variable concentration, even exceeding the solubility threshold. In this case, the solution that is present in the reactor 2 will be predominantly saturated with reacting salts.

[0042] As shown in Figure 7, in this embodiment, which provides for the possibility of recirculating the aqueous solution M (with a recycle stream 38), the reaction rate is a function of the concentration of material (bicarbonate in the preferred embodiments) and the concentration profile along the reactor can be optimized by acting on the recycle ratio with the goal of maximizing its kinetics.

[0043] During the hydrogenation phase, the operating temperature insideTo provide the dehydrogenation phase, an aqueous solution M’ of hydrogen-bound material (formate in the preferred embodiments) is provided by mixing the hydrogen-bound material that was stored during the hydrogenation phase with water, for example by using a mixing device (mixer) 35.

[0044] The aqueous solution M’ thus obtained is fed into the reactor 2 so that at least part of the hydrogen unbinds from said material, creating in the reactor 2 two concordant streams 91, 92 (i.e., in equicurrent), a hydrogen stream 91 and an aqueous mixture stream 92, both of which flow toward the top 22 of the reactor 2, as shown in Figure 4.

[0045] In greater detail, during the dehydrogenation phase, the aqueous mixture M’ is fed into the reactor 2 through the lower supply / discharge duct 33 and is made to exit through an upper discharge duct 29, in practice reversing the aqueous solution stream 92 with respect to the hydrogenation phase. In this phase, the first upper supply duct 32 is conveniently closed (for example, by virtue of closure means 132, such as a valve). Gaseous hydrogen H2is always discharged through the discharge duct 43 at the top 22 of the reactor 2.

[0046] This (having the two liquid and gas flows in the same direction) allows faster discharge of the gaseous phase.

[0047] Optionally, an additional recirculation of the aqueous mixture is also provided in which, through a recirculation duct 38 (visible in the plant diagram of Figure IB), at least part of the aqueous mixture M’ exiting from the reactor 2 is reintroduced in the reactor 2 itself, again proximate to the bottom 21, in order to increase the velocity of the H2bubbles generated by the reacting liquid solution.

[0048] At least part of the hydrogen H2therefore exits from the reactor 2 and, through at least one suitable discharge path 46 (such as a pipe or duct), can be discharged from the plant 1, 1’ to be utilized or stored in a known manner. In this phase, the hydrogen H2can be compressed from the pressureat the output of the reactor 2 to the pressure required by the end user (for example, 10 bar).

[0049] Preferably, during the dehydrogenation phase the temperature inside the reactor 2 is comprised between 65 °C and 120 °C and the pressure inside the reactor 2 is comprised between 1 and 20 bar absolute.

[0050] A device for controlling the pressure inside the reactor 2 can be provided in a known manner.

[0051] The change in pressure (decrease from the hydrogenation phase to the dehydrogenation phase) and possibly temperature (typically an increase from the hydrogenation phase to the dehydrogenation phase, in the preferred embodiments in which bicarbonate / formate is used), together with the reversal of the stream of the aqueous solution 92, is sufficient to provide dehydrogenation, i.e., to transition from the hydrogenation phase to the dehydrogenation phase.

[0052] Therefore, according to the invention, the hydrogenation phase and the dehydrogenation phase can be provided in the same reactor 2.

[0053] Transition from the hydrogenation phase to the dehydrogenation phase is provided simply by reversing the flow of the aqueous solution 92 in the reactor 2 and conveniently adjusting the pressure and (if necessary) temperature conditions in the reactor. In practice, transition from one phase to the other is achieved by means of a simple switch that can be provided by arranging in the plant 1, 1’ a suitable hydraulic system 3 for the aqueous solution, which comprises a hydraulic circuit 30 in which the reactor 2 is inserted, configured to reverse the flow of the aqueous solution on command. The variation in pressure and temperature can be controlled using known control devices.

[0054] In other words, the method is provided in a single reversible reactor 2 that operates in alternating phases of hydrogenation and dehydrogenation.

[0055] Thus far, the method has been described with reference to a single reactor 2; however, it is advantageously possible to perform both thehydrogenation phase and the dehydrogenation phase in parallel in a plurality of reactors 2 connected in parallel along the hydraulic circuit 30, as in the plant 1 of Figures 1A and IB.

[0056] Alternatively, it is also possible to perform both the hydrogenation phase and the dehydrogenation phase in series in a plurality of reactors 2 connected in series along the hydraulic circuit 30, as in the plant 1’ of Figure 2.

[0057] Embodiments with multiple reactors 2 are useful to achieve the desired reaction times and can be chosen as a function of the hydrogen flowrates to be processed.

[0058] A plant 1, 1’ comprising a plurality of reactors 2 can be configured to use a single reactor 2 or a number of reactors 2 chosen in each instance according to the requirements.

[0059] Preferably, the aqueous mixture that exits from the reactor 2 is depressurized (preferably to substantially atmospheric pressure) and then treated to recover the catalyst (when present), and then the remaining liquid part is stored for later reuse. This depressurization takes place in a separator device 53 and may release small quantities of gas (H2), which is conveniently recycled and / or utilized.

[0060] The catalyst C is recovered using known techniques - for example, centrifugation, sedimentation, filtration, or a combination thereof - provided in a dedicated separator device 51.

[0061] Optionally, after the catalyst recovery process in which the catalyst C is separated from the aqueous solution that has exited the reactor 2, the catalyst undergoes a regeneration treatment (so as to restore the temporarily deactivated active sites) in a dedicated regeneration apparatus 6 (for example, a suitable regeneration reactor), obtaining a regenerated catalyst.

[0062] The catalyst C thus regenerated is added to the aqueous mixture directed toward the reactor 2 during the hydrogenation phase.

[0063] As can be seen from the diagrams of the plant 1, 1’ of Figures 1A-2,regeneration occurs in the opposite direction with respect to the base process. The catalyst is regenerated via the opposite reaction with respect to the one taking place in the reactor 2; for example, if the hydrogenation reaction occurs in the reactor 2, the dehydrogenation reaction occurs in the regenerator 6, and vice versa. The volumes to be managed are very small, and therefore regeneration does not penalize the process. The concentrated solution of regenerated catalyst is then pumped to supply the reactors 2, for example via a channel 61 connected to the mixer 35. Water is recovered both during the decompression of the mixture exiting from the reactor 2 and during the dehydration of the material, and can be recycled to supply the reactors 2 or directly to the storage tanks to maintain a constant salt concentration.

[0064] With particular reference now to the plant 1, 1’ for the storage and release of hydrogen H2, which allows to provide the method that has just been described, said plant is adapted to carry out both the hydrogenation phase and the dehydrogenation phase.

[0065] In its essential features, the plant 1, 1’ comprises:

[0066] - at least one reactor 2 of the type previously described;

[0067] - a hydraulic system 3 (i.e., a system of ducts 32, 33, 36, 37, pumps 31A-31B, valves, and any electronic control thereof, etc.) configured to convey the aqueous solution into the reactor(s) 2 and from there toward at least one storage apparatus 5;

[0068] - a pneumatic system 4 (i.e., a system of ducts 45, 46, compressors 41A-41B, valves, etc.) configured to convey hydrogen H2into the reactor(s) 2 so as to create within said reactor(s) 2 the hydrogen stream 91 that flows toward the top 22 of the reactor 2, and from the reactor 2 at least toward one or more recirculation ducts 47 and / or toward the outlet 88 of the plant 1, 1’.

[0069] As already mentioned, the plant 1, 1’ can be configured in at least two configurations: in a hydrogenation configuration, to provide the hydrogenation phase, and in a dehydrogenation configuration, to provide thedehydrogenation phase.

[0070] In the hydrogenation configuration, the hydraulic system 3 generates in the reactor 2 a stream of the aqueous solution 92 that flows toward the bottom 21 of the reactor 2.

[0071] In the dehydrogenation configuration, the hydraulic system 3 generates in the reactor 2 a stream of the aqueous solution 92 that flows toward the top 22 of the reactor 2.

[0072] In this way, both of said phases are provided within the same reactor 2.

[0073] In greater detail, the hydraulic system 3 comprises a hydraulic circuit 30 in which at least one closed path is provided from the reactor 2 to the storage apparatus 5 and from there to the reactor 2.

[0074] The hydraulic system 3 furthermore comprises one or more pumping devices 31 A, 3 IB for generating the stream of aqueous solution 92.

[0075] The hydraulic circuit 30 comprises at least the already described first upper supply duct 32, which leads into the reactor 2 proximally to the top 22, and at least the second lower supply / discharge duct 33, which leads into the reactor 2 proximally to the bottom 21.

[0076] In the preferred and illustrated embodiments there are multiple reactors 2 (the number may vary depending on the requirements), each connected to a respective first upper supply duct 32, a lower supply / discharge duct 33, and an upper discharge duct 29.

[0077] In the embodiment of Figure 1A, the reactors 2 are connected in parallel along the hydraulic circuit 30, which comprises an upper branch 36, from which all the first upper supply ducts 32 branch off, and a lower branch 37, to which all the lower supply / discharge ducts 33 lead.

[0078] In the embodiment of Figure 2, the reactors 2 are connected in series along the hydraulic circuit 30, so that the lower supply / discharge duct 33 of the first reactor becomes the first upper supply duct of the second reactor 2 (entering proximally at the top 22 thereof) and so on.Preferably, along the hydrogen circuit 40, downstream of the reactors 2, there is a water recovery device 49 adapted to separate water when present in the hydrogen circuit (in practice, a full dehydrator / water absorber). The water recovery device 49 is connected to a water recovery recycle duct 39 that conveys the water into the hydraulic circuit 30 upstream of the reactor(s) 2 when the plant 1, 1’ is in the hydrogenation configuration.

[0079] Along the hydraulic circuit 30, upstream of the reactors 2 (in the hydrogenation condition), there is the mixing device 35 for mixing water with the material adapted to bind with hydrogen and the catalyst (when present) to form the aqueous solution.

[0080] In the preferred and illustrated embodiments, the water recycle duct 39 and the channel 61 for the catalyst arriving from the regeneration apparatus 6 converge in the mixing device 35.

[0081] Along the hydraulic circuit 30 there is at least one pump 31 A, 3 IB to generate the stream of aqueous solution. Preferably, there are at least two pumps 31 A, 3 IB, positioned one downstream and one upstream of the reactors 2. In the illustrated examples, one pump 31A is positioned upstream of the mixing device 35.

[0082] With reference now to the storage apparatus 5, comprised in the plant 1, 1’ downstream of the reactors 2, it may comprise, positioned along the hydraulic circuit 30, at least one device 51, 53 for separating the hydrogencontaining material (and possibly, if present, the catalyst) contained in the aqueous solution originating from the at least one reactor 2.

[0083] Preferably, at least one separating device 51, 53 consists of a separator device 51 , such as a centrifuge or the like, adapted to separate the catalyst from the mixture (when present).

[0084] In the storage apparatus 5, or upstream of it, there is preferably a depressurization device for reducing the pressure of the aqueous mixture originating from the reactors 2.

[0085] The storage apparatus 5 comprises one or more tanks 52 for storingthe hydrogen-containing material. When the separator device 51 and / or the depressurization device is present, the tanks 52 are located downstream of these, being connected thereto.

[0086] Conveniently, the tanks 52 are insulated so as to ensure thermal insulation for heat retention and energy efficiency. Advantageously, in the preferred embodiments, the tanks 52 can be manufactured with easily available and economical materials, since the salts are neither corrosive nor toxic and therefore no special precautions are required during the salt storage phase.

[0087] A respective pump 31C, 3 ID for extracting the material from the tanks is preferably associated with each tank 52.

[0088] It should be noted that the catalyst regeneration apparatus 6 is positioned downstream of the separation unit 51 (considering the flow of the solution in the hydrogenation configuration), between the latter and the mixer 35.

[0089] In both of the illustrated embodiments, the pneumatic system 4 is substantially the same and comprises a hydrogen circuit 40 that forms at least one closed path for hydrogen, in which the at least one reactor 2 is inserted along with one or more pressure generators 41 A, 4 IB (compressors) configured to generate the hydrogen stream 91.

[0090] In the preferred and illustrated embodiments, the hydrogen circuit 40 comprises a common delivery branch 48 from which the hydrogen intake ducts 42 branch off and lead into the reactors 2. A flow control valve is conveniently arranged along each of said intake ducts 42.

[0091] Also in these embodiments, the discharge ducts 43 from which any unreacted hydrogen exits from the reactors lead into a common discharge branch 46 that serves as a discharge path for the hydrogen and conveys the hydrogen H2toward the water recovery device 49 (when present).

[0092] Other constructive details can be easily inferred from the plant diagrams of Figures 1A, IB, and 2, which use the common symbols used inthe hydraulic systems sector and are known to the person skilled in the art; for example, note the check valves positioned downstream of the mixer 35 and downstream of the compressors 41 A, 4 IB along the delivery branch 48.

[0093] The operation of the plant 1, 1’ is clear and evident from what has been described.

[0094] In particular, in the preferred and illustrated embodiments, the transition from the hydrogenation configuration to the dehydrogenation configuration is achieved by reversing the flow, for example by transitioning from the configuration of Figure 1A to the one of Figure IB and by varying the operating conditions (temperature and pressure) as described (in any case, determining the temperature and pressure suitable for the chemical reactions expected in the reactor is within the scope of the person skilled in the art).

[0095] Advantageously, this “switch” allows to optimize the fluid dynamics underlying the expected kinetic and thermodynamic performance, improving its yield.

[0096] In particular, it is possible to maximize kinetics and thermodynamic equilibrium depending on whether the reactor is operated in hydrogenation or dehydrogenation by adjusting the fluid dynamics of the reactors.

[0097] Moreover, the part of the reactors 2 is simplified with respect to the background art, thereby achieving a less costly industrial application.

[0098] In practice it has been found that the method and plant according to the present invention achieve the intended aim and objects, since they allow to combine a high safety profile and a high yield.

[0099] Another advantage of the method and plant according to the invention resides in that they are easier to provide and also more economical than the background art, as well as advantageous from an energy standpoint.

[0100] A further advantage of the method and plant according to the invention, is that they are versatile and adaptable on a large scale.

[0101] Another particular advantage of the method and plant is that theysimplify the recovery of waste heat (e.g., exhaust gases at 90-100 °C) and / or the implementation of heat pumps for high energy efficiency of the plant, thanks to the low temperatures required for the catalytic reactions of the salts, in particular in the embodiments in which the PdAg / TiCh catalyst is used.

[0102] A further advantage of the method and plant resides in that they can be provided so that the transition from the hydrogenation phase / configuration to the dehydrogenation phase / configuration can occur while keeping the temperature in the reactor unchanged and changing only the pressure, since the temperature could remain within the same range during the two reactions, so as to avoid thermal inertia and minimize transient phases.

[0103] Another advantage provided by the present invention is the high volumetric and gravimetric density achieved with crystallization units for the storage / transport of both the hydrogenated material (sodium and / or potassium formate) and the dehydrogenated material (sodium and / or potassium bicarbonate).

[0104] The method and plant thus conceived are susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept.

[0105] All the details may furthermore be replaced with other technically equivalent elements.

[0106] The disclosures in Italian Patent Application No. 102025000008646, from which this application claims priority, are incorporated herein by reference.

[0107] Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

CLAIMS1. A method for storing and releasing hydrogen (H2), comprising a hydrogenation phase intended to store hydrogen (H2) and a dehydrogenation phase intended to release hydrogen (H2);wherein said hydrogenation phase comprises the steps of:a. supplying an aqueous mixture (M) of material adapted to bind with hydrogen (H2);b. supplying hydrogen (H2) in gaseous form;c. introducing said hydrogen (H2) and said aqueous mixture (M) of material in a reactor (2) having a bottom (21) and a top (22), creating two countercurrent streams (91, 92), a hydrogen stream (91) flowing towards the top (22) and an aqueous mixture stream (92) flowing towards the bottom (21) of the reactor, so that at least part of the hydrogen (H2) binds with at least part of said material;d. storing said hydrogen-bound material;and wherein said dehydrogenation phase comprises the steps of: e. supplying an aqueous mixture of said hydrogen-bound material stored in step d. mixed with water;f. introducing the aqueous solution of hydrogen-bound material in said reactor (2) so that at least part of the hydrogen is unbound from said material, creating two concordant streams (91, 92), a hydrogen stream (91) and an aqueous mixture stream (92), both of which flow toward the top (22) of the reactor (2);g. making at least part of the hydrogen (H2) exit from the reactor (2); said steps c. and f. being provided in the same reactor (2);the transition from said hydrogenation phase to said dehydrogenation phase being provided by reversing the flow of the aqueous solution (92) and varying the temperature and / or pressure in the reactor (2).

2. The method according to claim 1, wherein said material comprisesone or more salts which are dehydrogenated and become hydrogenated in said step c. and vice versa in said step f.

3. The method according to claim 1 or 2, wherein said material comprises sodium bicarbonate and / or potassium bicarbonate which becomes sodium formate and / or potassium formate in said step c. and vice versa in said step f.

4. The method according to one or more of the preceding claims, wherein said aqueous mixture of material introduced in the reactor (2) also comprises a catalyst, preferably a catalyst based on a bimetallic alloy.

5. The method according to the preceding claim, wherein a catalyst recovery step is provided in which the catalyst is separated from the aqueous solution that has left the reactor (2) following step c. or f., and said catalyst is then subjected to a regeneration treatment, obtaining a regenerated catalyst; said regenerated catalyst is added to the aqueous mixture directed toward the reactor (2) before step c. or f.

6. The method according to one or more of the preceding claims, wherein in the hydrogenation phase, in said step c., the temperature inside the reactor is comprised between 60°C and 80°C.

7. The method according to one or more of the preceding claims, wherein in the hydrogenation phase, in said step c., the hydrogen is compressed at a pressure comprised between 30 and 150 bar.

8. The method according to one or more of the preceding claims, wherein in the hydrogenation phase, in said step c., the stream of hydrogen (91) in the reactor is at least partially slowed down, and / or the bubbles contained in said hydrogen stream are at least partially broken, by means of flow breaking elements (25) positioned inside the reactor (2).

9. The method according to one or more of the preceding claims, wherein in the hydrogenation or dehydrogenation phase, simultaneously with said step c. or f., a recycle stream of the aqueous solution is created outside the reactor (2) so as to increase the speed of the stream of theaqueous mixture (92) in the reactor (2).

10. The method according to one or more of the preceding claims, wherein in the dehydrogenation phase, in said step f., the temperature inside the reactor (2) is comprised between 65 °C and 120°C and the pressure inside the reactor is comprised between 1 and 20 bar absolute.

11. The method according to one or more of the preceding claims, wherein said storage step d. comprises concentrating the hydrogen-bound material by subjecting it to a crystallization or drying process.

12. A plant (1; T) for the storage and release of hydrogen (H2), adapted to provide a hydrogenation phase intended to store hydrogen (H2) and a dehydrogenation phase intended to release hydrogen (H2), comprising:- at least one vertically extended reactor (2) provided with a bottom (21) and atop (22);- a hydraulic system (3) configured to convey an aqueous solution into the reactor (2) and from there to at least one storage apparatus (5);- a pneumatic system (4) configured to convey hydrogen (H2) into the reactor (2) so as to create in the reactor (2) a stream of hydrogen (91) which flows towards the top (22) of the reactor (2), and from the reactor (2) at least towards one or more recirculation ducts and / or towards an outlet (88) of the plant (1);said plant (1; T) being configurable:- in a hydrogenation configuration, to provide the hydrogenation phase, in which the hydraulic system (3) generates in the reactor (2) a stream of the aqueous solution (92) which flows towards the bottom (21) of the reactor (2), and- in a dehydrogenation configuration, to provide the dehydrogenation phase, in which the hydraulic system (3) generates in the reactor (2) a stream of the aqueous solution (92) which flows towards the top (22) of the reactor (2);so that both of said phases are provided within the same reactor (2).

13. The plant according to the preceding claim, wherein said hydraulic system (3) comprises:- a hydraulic circuit (30) in which at least one closed path is provided from the reactor (2) to the storage apparatus (5) and from there to the reactor (2), and- one or more pumping devices (31 A, 3 IB) for generating the stream of aqueous solution (92);said hydraulic circuit (30) comprising at least one first upper supply duct (32) which leads into the reactor (2) proximally to the top (22) of the reactor (2), and at least one lower supply / discharge duct (33) which leads into the reactor (2) proximally to the bottom (21) of the reactor (2).

14. The plant according to claim 12 or 13, comprising a plurality of reactors (2) connected in series along said hydraulic circuit (30), each of said reactors (2) being connected to a respective first upper supply duct (32) which leads out proximally to the top (22) of the reactor (2), and to at least one respective lower supply / discharge duct (33) which leads into the reactor (2) proximally to the bottom (21) of the reactor (2).

15. The plant according to claim 12 or 13, comprising a plurality of reactors (2) connected in parallel along said hydraulic circuit (30), each of said reactors (2) being connected to a respective first upper supply duct (32) which leads proximally to the top (22) of the reactor (2), and to at least one respective lower supply / discharge duct (33) which leads into the reactor (2) proximally to the bottom (21) of the reactor (2).

16. The plant according to any of claims 12 to 15, wherein said storage apparatus (5) comprises, positioned along said hydraulic circuit (30), a separator device (51) for separating a catalyst contained in the aqueous solution originating from the at least one reactor (2); said separator device (51) being connected to one or more tanks (52) for storing said hydrogencontaining material.

17. The plant according to any of claims 12 to 16, comprising, alongsaid hydraulic circuit (30), a catalyst regeneration apparatus (6) configured to regenerate one or more catalysts when present in said aqueous solution exiting from the at least one reactor (2).

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