Continuous formate-bicarbonate cycle reactor for storing and releasing hydrogen

Abstract

A continuous process for releasing hydrogen using a formate-bicarbonate cycle dehydrogenation reaction, the process comprising: continuously feeding an aqueous solution of formate and a heterogeneous catalyst to a dehydrogenation reactor to form bicarbonate and hydrogen; directing the hydrogen for use as fuel hydrogen; continuously removing a fluid effluent from the dehydrogenation reactor at a rate equal to the feed rate; directing the effluent to a product tank and discharging materials from the product tank; separating the catalyst from the materials; washing and refreshing the catalyst; and returning the fresh catalyst to the dehydrogenation reactor, wherein the bicarbonate is collected in solid form from the product tank.

Description

[Technical Field]

[0001] The present invention relates to a method for storing hydrogen in a chemical carrier in a safe and transportable form, based on a bicarbonate-formate cyclic system, and for releasing hydrogen on demand. [Background technology]

[0002] The bicarbonate-formate cycle consists of two reversible chemical reactions related by an equilibrium constant. On one side of the chemical equilibrium is the hydrogenation reaction of an alkali metal salt of bicarbonate, and on the other side of the chemical reaction are an alkali metal salt of formate and a water molecule: MHCO3 + H2 ⇔ MHCO2 + H2O, for example, KHCO3 + H2 ⇔ KHCO2 + H2O.

[0003] The reaction from left to right is the hydrogenation of bicarbonate to obtain the corresponding formate, thereby storing hydrogen, i.e., the resulting formate is a hydrogen carrier. On demand, the reverse reaction (dehydrogenation) is carried out to release hydrogen: the formate is decomposed to produce bicarbonate and hydrogen, which can be used for any desired purpose, for example as a fuel material.

[0004] Both the hydrogenation and dehydrogenation reactions proceed over a catalyst, which may be the same or different for the two reactions. For reversible hydrogen storage cycles to gain widespread commercial acceptance, the catalyst selected must be highly active, easily separable, and recyclable.

[0005] The higher the concentration of the aqueous formate solution, the greater the amount of hydrogen that can be stored by the solution. However, one of the main challenges of the system arises from the difference in water solubility between formate and bicarbonate. Bicarbonate is significantly less soluble in water than formate. Therefore, during the dehydrogenation process of concentrated formate solutions, a solid precipitate of bicarbonate forms. When a heterogeneous catalyst, such as palladium particles supported on carbon, is used, a slurry consisting of solid bicarbonate and catalyst particles forms, preventing catalyst separation and regeneration.

[0006] Solutions to these problems are presented in U.S. Patent Nos. 10,618,807, 10,207,921, and 10,688,474. These patents demonstrate a reversible hydrogen storage cycle based on the use of a concentrated solution of potassium formate. Using a palladium-carbon catalyst, the concentrated potassium formate solution decomposes to produce hydrogen and a slurry of solid bicarbonate and catalyst particles. The same catalyst is also effective in the reverse reaction, converting the potassium bicarbonate slurry to an aqueous potassium formate solution. The catalyst was successfully regenerated by treating the slurry with an air stream, i.e., without catalyst separation. Therefore, the use of a formate-bicarbonate cycle with occasional catalyst regeneration is of great interest for hydrogen and energy storage.

[0007] U.S. Patent No. 10,944,119 presents a different approach using homogeneous catalysis. The dehydrogenation reaction of aqueous MHCO2 is effectively catalyzed using a metal complex, such as a ruthenium-containing complex, dissolved in a suitable organic solvent. Hydrogen gas is produced while bicarbonate is gradually formed in the aqueous phase, and the organic solvent remains separable from the bicarbonate throughout the reaction. When the catalyst is homogeneous, as in U.S. Patent No. 10,944,119, the differential solubility of bicarbonate / formate in water does not pose a problem, as the solubilized catalyst remains in the organic phase, allowing for catalyst separation due to the immiscibility of the organic solvent in water. However, the introduction of an organic solvent into the process adds other separation and quality control issues to the system.

[0008] Alternatively, a reversible hydrogen storage cycle based on the KHCO3 + H2 ⇔ KHCO2 + H2O reaction can also be operated using two different catalysts. According to this process design, a solid catalyst, such as palladium on carbon, is used to catalyze the hydrogenation of a bicarbonate slurry to form a concentrated aqueous solution of potassium formate. To produce hydrogen, the concentrated formate solution undergoes dehydrogenation as described above in the presence of a catalytic system consisting of a metal-containing complex dissolved in a suitable organic solvent.

[0009] As mentioned above, U.S. Patent Nos. 10,618,807, 10,207,921, and 10,688,474 provide methods for refreshing catalyst in a reactor during processing, including using an aqueous stream containing no organic solvent, which is discharged from the reactor tank after each batch cycle and treated with bicarbonate in air in the reactor. While such an approach is acceptable, it has several unaddressed problems. a. The reactor tank is filled with hydrogen, and the mixture of air and hydrogen is not safe. b. The process is not continuous and therefore the hydrogen flow provided by the system is not steady. c. Scale-up of batch systems is much more limited than that of continuous systems, and the overall production-energy balance tends to be less attractive in batch systems, which is very important for energy storage systems.

[0010] Therefore, there is a need for improved aqueous systems that can be fully continuous, overcome certain characteristics of the formate-bicarbonate cycle system, and still be an attractive system in terms of energy balance. Summary of the Invention

[0011] The inventors have found that the bicarbonate precipitate that gradually forms during the decomposition of formate in aqueous solution consists of surprisingly large particles, e.g., with an average diameter of >200 microns (typically hundreds of microns or even larger). When appropriately small catalyst particles, i.e., less than 100 microns, e.g., less than 50 microns, e.g., less than 40 microns, e.g., less than 10 microns, are used to promote the decomposition of formate, the catalyst can be separated from the solid bicarbonate by size-exclusion techniques. Furthermore, spontaneous separation has been observed to occur during the decomposition of formate and the accompanying hydrogen release. The densities of the formate solution, potassium bicarbonate, and catalyst are each approximately 1.4 g / cm. 3 , about 2.2g / cm 3 and 0.3 g / cm 3 Therefore, potassium bicarbonate crystals precipitated in the solution move downward and settle to the bottom of the reaction vessel, while catalyst particles move upward. Furthermore, hydrogen bubbles produced by the dehydrogenation of formate over a catalyst (e.g., Pd / C) facilitate the upward movement of catalyst particles. The attached photo of the reaction vessel in Figure 9, captured toward the end of a typical formate decomposition reaction carried out over a Pd / C catalyst, shows that the catalyst (black particles) produces hydrogen gas at the top of the solution (bubbles can be seen), while potassium bicarbonate (in the form of a white solid) has already settled to the bottom of the flask. The bulk solution consists of water and unreacted solubilized formate.

[0012] Thus, the present invention primarily relates to a continuous process for releasing hydrogen using a formate-bicarbonate cycle dehydrogenation reaction, comprising continuously feeding an aqueous solution of formate and a heterogeneous catalyst to a dehydrogenation reactor to form bicarbonate and hydrogen, directing the hydrogen for use as fuel hydrogen, continuously removing a fluid effluent from the dehydrogenation reactor, for example at a rate equal to the feed rate, directing the effluent to a product tank, draining the material from the product tank, separating the catalyst from the material, washing and refreshing the catalyst, and returning the refreshed catalyst to the dehydrogenation reactor, wherein bicarbonate is collected in solid form from the product tank.

[0013] The aqueous formate solution undergoing dehydrogenation is preferably potassium formate at a concentration of 7 M or greater, e.g., greater than 8 M, e.g., greater than 10 M, although other options are summarized in Table 1 below. Experimental work reported below shows that the addition of an alkaline agent, e.g., an alkali hydroxide (e.g., KOH) or even better, an alkali carbonate (e.g., K2CO3), to adjust the pH to 9-12 (10-11), e.g., K2CO3 at a concentration greater than 0.5 M, e.g., 0.5-1.0 M, suppresses carbon dioxide evolution and reduces foaming during the dehydrogenation reaction.

[0014] The catalyst consists of a catalytically active transition metal on a solid support particle, where the diameter of the solid support particle is less than 100 μm, e.g., less than 50 microns, e.g., less than 40 microns, e.g., 3 to 40 microns. For example, the catalyst comprises Pd or Pt on a solid support selected from activated carbon, graphite, SiO2, TiO2, or a metal substrate such as Al, Cu, nickel, stainless steel, or any other metal, optionally with a carbon coating.

[0015] A preferred heterogeneous catalyst is Pd-supported carbon (e.g., activated carbon) with carbon particles having a diameter of 4-40 μm. Suitable carbon particles are commercially available or can be prepared by milling.

[0016] A suitable sieve with an appropriate pore size (e.g., 40-150 microns, e.g., 40-80 microns) is attached to the product tank to divide the product tank into a lower section and an upper section, and the flowable effluent from the dehydrogenation reactor is fed to the lower section of the product tank, causing the bicarbonate particles to settle to the bottom of the product tank and the catalyst particles to float and accumulate in the upper section of the product tank. Material is discharged from the upper section of the product tank consisting of a formate solution containing the catalyst particles and fed to a separation and washing unit, where the catalyst particles are separated from the formate solution and washed.

[0017] The separation and washing are preferably carried out off-line, i.e. in batch mode, with the separation and washing unit alternating between a separation mode in which the unit is fed with effluent from the product tank to separate the catalyst particles from the aqueous phase, and a washing mode in which the unit is fed with a washing liquid to wash the catalyst particles.

[0018] The separated catalyst particles are washed with a washing solution selected from the group consisting of water, aqueous acidic solutions, and aqueous oxidizing agents (e.g., hydrogen peroxide). For example, washing with an aqueous acidic stream consisting of a mineral acid (e.g., nitric acid, hydrochloric acid, phosphoric acid, sulfonic acid) or an organic acid (e.g., citric acid, benzoic acid, salicylic acid, acetic acid) at a temperature above 30°C has been shown to be useful, particularly treating the particles with nitric acid, e.g., 5-15 wt. %, 7-13 wt. %, or about 10% HNO3 solution.

[0019] The washed catalyst particles are then refreshed by drying and oxidation, either sequentially or simultaneously. Preferably, the washed catalyst particles are simultaneously dried and oxidized by the action of an air stream to obtain a refreshed catalyst, which is returned to the dehydrogenation reaction.

[0020] The separability of the catalyst particles from the bicarbonate particles based on the difference in particle size can also be utilized to carry out the hydrogenation reaction (i.e., the reaction of the bicarbonate slurry with hydrogen under heterogeneous catalysis) in a continuous mode with in-line catalyst separation (i.e., after completion of the reaction and before transferring the formate product to the product tank). Thus, the present invention provides a continuous process for storing hydrogen using a formate-bicarbonate cycle hydrogenation reaction, comprising: continuously feeding an aqueous slurry of bicarbonate, hydrogen, and a heterogeneous catalyst into a hydrogenation reactor having a sieve attached adjacent to the reactor outlet to prevent bicarbonate particles from exiting the reactor; continuously removing an effluent from the hydrogenation reactor outlet, e.g., at a rate equal to the feed rate, into a separator, where the effluent is in the form of a suspension containing dissolved formate and suspended catalyst particles, and possibly residual solubilized bicarbonate; separating the effluent into an aqueous formic acid solution and solid catalyst, the separation being downstream of the hydrogenation reactor and upstream of a product tank; directing the aqueous formate to the product tank; washing and refreshing the catalyst in a washing unit; and continuously returning the refreshed catalyst to the hydrogenation reactor. Washing and refreshing of the catalyst particles is achieved using the same washing liquid and air streams as described for the dehydrogenation reaction.

[0021] The hydrogenation and dehydrogenation reactions may be carried out separately, at different locations, or may be implemented to obtain a complete cycle for energy storage and release. That is, the present invention provides a process comprising a continuous hydrogenation reaction to produce a concentrated aqueous formate solution from bicarbonate and hydrogen in the presence of a heterogeneous catalyst, and a continuous dehydrogenation reaction to decompose said concentrated aqueous formic acid solution into a bicarbonate slurry and hydrogen gas in the presence of a heterogeneous catalyst, wherein the reactions are carried out periodically with separation and refreshment of the catalyst.

[0022] More specifically, the present invention provides a process for storing and releasing hydrogen using a formate-bicarbonate cycle, the process comprising: A) a hydrogenation reaction of bicarbonate and hydrogen in the presence of the heterogeneous catalyst to produce an aqueous solution of formate; B) a dehydrogenation reaction in which the aqueous formate solution of A) is decomposed in the presence of a heterogeneous catalyst as described above to form bicarbonate and hydrogen gas, and the bicarbonate is fed to the hydrogenation reaction of step A), These reactions are carried out in a cyclical manner with separation and refreshing of the catalyst.

[0023] The present invention further provides an apparatus for continuously producing hydrogen by dehydrogenation of an aqueous formate solution, the apparatus comprising: a first storage tank (71) in which an aqueous formate solution is held, the first storage tank being connected to the dehydrogenation reactor (72) by a feed line, with a heat exchanger optionally located along the feed line; a catalyst feeder (83 / 83) for feeding the dry granular or powdered material to the dehydrogenation reactor (e.g., a screw conveyor hopper); a dehydrogenation reactor (72) having a first outlet with a gas discharge line (77) for removing hydrogen gas generated in the reactor and delivering the hydrogen to a pressure cylinder or a fuel cell, and a second outlet with a liquid discharge line for directing a fluid effluent from the dehydrogenation reactor to a product tank (73); a product tank (73) divided by a sieve into a lower section (73A) and an upper section (73B), wherein a liquid discharge line (87) from the dehydrogenation reactor enters the lower section of the product tank (73A); a separation and washing unit (74) which is alternately fed from the product tank (73) by suitable arrangement of valves, the upper section of the product tank (73B) being connected by a discharge line (88) to the separation and washing unit (74) or from a washing liquid supply line (75), thereby alternating between a separation mode fed by effluent pumped from the product tank through the discharge line and a washing mode fed by washing liquid, The separation and washing unit includes a return line (86) for conducting the liquid phase consisting of the formate solution collected during the separation to the dehydrogenation reactor, and a catalyst recycle line (89) connected to the dry oxidation unit (79) for supplying refreshed catalyst to the catalyst feeder (82 / 83) or used catalyst to the storage tank (81). The drying and oxidation unit (79) is fed by an air line, i.e., an air stream is used to dry and oxidize the catalyst particles and force them into the catalyst feeder (82 / 83). The dehydrogenation apparatus is further equipped with a nitrogen line.

[0024] The present invention further provides an apparatus for the continuous storage of hydrogen by reacting an aqueous bicarbonate slurry with hydrogen to form formate, the apparatus comprising: a first storage tank (41) in which the bicarbonate slurry is held and which is connected to a mixing unit (43) by a supply line; a catalyst feeder (52 / 58) for feeding dry granular or powdered material into a mixing unit (43), e.g., a screw conveyor hopper; a mixing unit (43) equipped with an agitator to produce an aqueous slurry of bicarbonate and catalyst particles and a discharge line (59) to feed the suspension to a first hydrogenation reactor (44); a first hydrogenation reactor (44) and optionally a second hydrogenation reactor (45) arranged in series, wherein the discharge line (59) of the mixing unit (43) is connected to the inlet of the first hydrogenation reactor (44), each hydrogenation reactor having a gas inlet connected to a hydrogen supply line (55) for introducing hydrogen gas into each hydrogenation reactor, the first hydrogenation reactor (44) or the second hydrogenation reactor (45) optionally discharging to a solid / liquid separation unit (46), the first hydrogenation reactor (44) having a sieve mounted adjacent to the reactor outlet to prevent bicarbonate particles from exiting the reactor; a product tank (47) connected to the solid / liquid separation unit (46) for receiving therefrom a liquid stream comprising an aqueous formate solution; and a washing tank (49) connected to the solid / liquid separation unit (46) for receiving the solid catalyst particles collected in the solid / liquid separation unit (46), the washing tank being connected to the drying and oxidation unit (50) by a catalyst recycle line (60) for supplying refreshed catalyst to the catalyst feeder (52 / 58) or used catalyst to the recycle tank (51). The drying and oxidation unit (50) is fed by an air line, i.e., an air flow is used to dry and oxidize the catalyst particles and force them into the catalyst feeder (52 / 53). The hydrogenation apparatus is further equipped with a nitrogen line.

[0025] Thus, the present invention demonstrates a new method for storing and releasing hydrogen using the formate-bicarbonate cycle. The system is continuous for both the reaction and the catalyst refresh process. The advantages of the present approach are that it stabilizes the hydrogen production rate, is scalable, and does not involve mixing hydrogen with air, which can lead to explosions, making it a much safer approach.

[0026] This forms the basis of yet another aspect of the present invention, which is a method for distributing hydrogen on demand from a production site to a customer, the method comprising: a hydrogenation reaction to produce an aqueous formate solution from bicarbonate and hydrogen in the presence of a heterogeneous catalyst, the hydrogenation reaction being carried out in a continuous operation mode with online catalyst refresh and recycle; transporting formate salt to a hydrogen distribution site in either aqueous or dry form; a dehydrogenation reaction in which an aqueous formate solution is decomposed in the presence of a heterogeneous catalyst to form bicarbonate and hydrogen gas on demand, wherein the hydrogenation reaction is carried out in a continuous operation mode, for example with offline catalyst refresh and recycle.

[0027] The catalyst can be a Pd or Pt-based catalyst, but other transition metal catalysts, such as silver, nickel, ruthenium, or molybdenum catalysts, or combinations thereof with platinum or palladium catalysts, have also been found to be effective. The catalyst may be distributed on any substrate; a typical substrate for the catalyst is activated carbon. Other options include SiO2, TiO2, or metal substrates such as Al, Cu, or any other metal. In other embodiments of the present invention, woven carbon fibers can be used as the catalyst substrate, or a polymer matrix can be used for the same purpose. In other embodiments of the present invention, activated carbon, carbon black, or graphene oxide, in reduced or non-reduced form, can be used as the catalyst substrate. A preferred form of catalyst consists of a metal (e.g., Pd) supported on fine particles, e.g., particles having a size range of 4 to 40 microns, e.g., carbon particles (having the carbon types described above) with a catalyst metal concentration of 0.5 to 10% by weight, e.g., 1 to 2% by weight.

[0028] The dehydrogenation of the aqueous formate solution is carried out at a temperature in the range of 30 to 90 degrees Celsius, although operation at room temperature is also acceptable in some cases. The temperature of the hydrogenation reaction is preferably in the range of 20 to 40 degrees Celsius.

[0029] The hydrogenation reaction is carried out under pressure, i.e. above atmospheric pressure. Typical values ​​of hydrogen pressure are 10-20 atmospheres. In other cases, the hydrogen pressure is 20-50 atmospheres or 50-200 atmospheres.

[0030] Formate and bicarbonate salts other than potassium salts can be used (e.g., cesium and ammonium salts). Table 1 shows the change in energy concentration of the formate-bicarbonate cycle as the counterion in the process changes. The solubility of the corresponding formate and bicarbonate salts changes, as does the concentration at which separation between the salts is possible. [Table 1]

[0031] In some embodiments of the invention, the hydrogenation process is carried out using a slurry having a bicarbonate content equivalent to 10-14 moles / liter. According to other embodiments of the invention, the amount of bicarbonate is 3-10 moles, and in other embodiments, very large amounts of bicarbonate are used above (>14M), and with the addition of water in situ, even water-free solid bicarbonate can be used for process initialization.

[0032] In some embodiments of the present invention, the hydrogenation reaction separation process is carried out in-line immediately after completion of the reaction and before transferring the product of the reaction to the product tank. In other embodiments of the present invention, the catalyst is separated from the formate off-line by an additional process on the product tank (similar to the process discussed for the dehydrogenation reaction process).

[0033] In some embodiments of the invention, the dehydrogenation process is carried out at high molar concentrations, typically between 10 and 14 M formate, in other embodiments of the invention the formate concentration is between 5 and 10 M, and in other embodiments very high concentrations of formate, greater than 14 M, are used; even solid formate can be used for process initialization with the addition of water in situ.

[0034] In some embodiments of the present invention, the dehydrogenation process is carried out at 50-90°C, in other embodiments of the present invention, the reaction temperature is from room temperature to as low as 50°C.

[0035] In some embodiments of the present invention, the hydrogenation process begins with a reactant tank filled with potassium bicarbonate salt in slurry form. The slurry flows through a mixing unit into a reactor to produce formate. After the reaction, the product and catalyst are separated, the liquid is transferred to a potassium formate tank, and the catalyst is washed and refreshed and returned to the reaction through the mixing unit.

[0036] In some embodiments of the present invention, in the hydrogenation process, a pump or another mixing unit is added to the reactant tank to prevent the slurry from clogging the pipes. In other embodiments of the present invention, the slurry is lifted by a screw to distribute the solids in solution in the reactant tank for the same purpose.

[0037] In some embodiments of the present invention, the slurry in the hydrogenation process is mixed with the catalyst on the way to the first reactor in a mixing tank. The mixing tank can be replaced with other methods for mixing solids into liquids, such as a vortex pipe or screw.

[0038] In some embodiments of the present invention, the catalyst loading in the reactor is constant. In other embodiments of the present invention, the catalyst loading is adjusted to control a constant product flow out of the reactor in both the hydrogenation and dehydrogenation processes.

[0039] In some embodiments of the present invention, the ratio of catalyst in the reactor to catalyst during the refresh cycle is constant. Typical values ​​are 1:1 to 1:2 for catalyst inside:outside the reactor. However, better and faster refresh cycles can reduce the ratio to 1:0.1 to 1:0.3, or even 1:0.3 to 1:1, lowering the overall cost of the system.

[0040] In some embodiments of the present invention, the slurry is forced into the first reactor against pressure during the hydrogenation process. The pressure is the pressure of the hydrogen gas reactant in the hydrogenation reaction, and must be high enough to ensure sufficient conversion to prevent spontaneous reverse dehydrogenation of formate back to bicarbonate. A typical pressure is 10 bar, but pressures of 10-20 bar or 20-50 bar can also be used, with pressures of 50-200 bar also being used in some embodiments of the present invention.

[0041] In some embodiments of the present invention, a heat exchanger is used to maintain the same temperature within the reaction tank. Typical temperatures for hydrogenation reactions are 25-35 degrees Celsius. In other embodiments of the present invention, lower temperatures are used to reduce the reverse reaction, and in yet other embodiments of the present invention, temperatures between 35-70 degrees Celsius are used to increase the reaction rate.

[0042] In some embodiments of the present invention, the reaction tank is monitored using several sensors. The most important parameters that need to be monitored are the temperature, pressure, and amount of material in the reactor. For example, the amount of material in the tank is monitored by a wet point sensor or a height sensor.

[0043] In some embodiments of the present invention, the feed stream to the hydrogenation reactor comprises a solid catalyst and a bicarbonate slurry. A sieve (i.e., size filter) is placed near the exit point of the reactor to prevent the solid bicarbonate from exiting the first reactor and allow the catalyst to be transferred to the next reactor, so that the solid bicarbonate fraction is consumed by the reaction and only the liquid portion can proceed to the next reactor.

[0044] In some embodiments of the invention, additional reactors are used after the first reactor. In some embodiments of the invention, the second or more reactors may be CSTR reactors. However, because the reaction is liquid-phase only, other reactor options are possible for that portion of the process. Examples are PFR reactors at low temperatures or static mixer or auger reactors.

[0045] In some embodiments of the present invention, the pressure in the second or more reactors is higher than the pressure in the first reactor to achieve higher conversion and eliminate the need for filtration.

[0046] In some embodiments of the present invention, the output stream of the reactor in the hydrogenation process is fed to a liquid-solid separator. In other embodiments of the present invention, it can be fed directly to a product tank.

[0047] In some embodiments of the present invention, the separator is process-matched and therefore continuously transfers the product as an output stream to a product tank. A filter collects the solid portion of the catalyst, and a stream of inert gas is used to push the catalyst cake into a washing tank, segment by segment.

[0048] In some embodiments of the present invention, the separator is a CONTIBAC filter or similar separator manufactured by DrM that is capable of continuously and efficiently separating the formate liquid and catalyst.

[0049] In some embodiments of the invention, the product tank is a vessel of similar size to the reactant tanks and the product is used directly for supply to the consumer, while in other embodiments of the invention the product is dried and shipped to the consumer as a solid.

[0050] The catalyst leaving the separator is pumped to a washing tank. In some embodiments of the present invention, a refresh cycle is performed by washing the catalyst from traces of format and bicarbonate to prevent the production of hydrogen during the refresh cycle.

[0051] In some embodiments of the present invention, purified water is used to wash the catalyst, which can be reused for the next wash cycle or for flowing to wastewater.

[0052] In some embodiments of the present invention, further washing of the catalyst with an acid or optional further washing with a liquid material is performed.

[0053] In some embodiments of the invention, the water or acid wash is performed at room temperature. In some embodiments of the invention, higher temperatures are used. Typical wash temperatures are 30-50 degrees Celsius, while other treatments can be performed at 50-80 degrees Celsius, although higher temperatures can also be used.

[0054] In some embodiments of the present invention, the catalyst is transferred from the wash tank to the dryer as a wet cake.

[0055] In some embodiments of the present invention, the dryer may be a conveyor equipped with heating elements or IR lamps. In other embodiments of the present invention, the dryer is a screw with airflow of any speed and temperature. In yet other embodiments of the present invention, other oxidizing agents, such as chemical vapors or UV heating or electrostatic charging, are used to reactivate the catalyst.

[0056] In yet another embodiment of the present invention, plasma treatment or other oxidizing agents such as ozone flow are used to reactivate the catalyst.

[0057] In some embodiments of the present invention, the catalyst is promoted into a hopper and returned to the mixing tank by a feed screw, while in other embodiments of the present invention, the catalyst is forced by a pump.

[0058] In some embodiments of the present invention, the catalyst activity becomes so low that it is necessary to completely recycle the catalyst, at which point the used catalyst is fed to a recycle tank and fresh catalyst is added directly to the hoop.

[0059] In some embodiments of the present invention, the reactant tank in the dehydrogenation process is potassium formate, which is fed directly to the reactor and mixed therein with fresh or refreshed catalyst. After reaction, the product and catalyst flow to a product tank, where the product is separated off-line from the catalyst by a continuous flow of product exiting the product tank and flowing to a separator. From the separator, the liquid is returned to the product tank, where the catalyst is washed, refreshed, and returned directly to the reactor by a mixing unit.

[0060] In some embodiments of the present invention, the separator is in-line and the catalyst is removed from the product stream before it enters the product tank.

[0061] In some embodiments of the present invention, the dehydrogenation process begins with a high concentration of potassium formate, typically greater than 7 M, e.g., 7-10 M, and in other cases, 11-15 M salt concentration. However, this concentration is still below the solubility limit, and therefore the formate is fully solubilized.

[0062] In some embodiments of the present invention, the formate salt is provided as a solid and premixed with water before being fed to the reactor.

[0063] In yet another embodiment of the invention, the formate concentration is greater than 15.7M and some or most of the salt in the tank is in a solid state, providing an additional mechanism to prevent clogging.

[0064] In some embodiments of the present invention, the catalyst is mixed with formate at the inlet to the reactor, and the dosage of refreshed catalyst and formate solution is controlled to maintain the same catalyst concentration and conditions during the reaction.

[0065] In some embodiments of the present invention, the catalyst feed is from a closed unit where a flow of inert gas displaces air to maintain a safe process flow.

[0066] In some embodiments of the present invention, the catalyst ratio between the catalyst in the reactor and the catalyst during the refresh cycle is constant. Typical values ​​are 1:1 to 1:2 for catalyst inside:outside the reactor. However, better and faster refresh cycles can reduce the ratio to 1:0.1 to 1:0.3, or even 1:0.3 to 1:1, lowering the overall cost of the system.

[0067] In some embodiments of the invention, a heat exchanger controls the temperature of the reaction between the catalyst and the formate. Typical temperatures are 50-70 degrees Celsius or 70-90 degrees Celsius. In other embodiments of the invention, lower temperatures are used.

[0068] In some embodiments of the present invention, the dehydrogenation tank is monitored by several sensors. The most important parameters that need to be monitored are the reactor temperature, pressure and amount of material in the reactor.

[0069] In some embodiments of the present invention, the dehydrogenation reactor can be a CSTR reactor to thoroughly mix the materials. However, a low-temperature auger reactor equipped with a static mixer or screw can also be a good choice, as heating can be more efficient in these types of reactors. These reactors also allow the temperature to increase with propagation within the reaction, which is a major advantage in increasing reaction conversion. By controlling the residence time and reaction temperature, optimal conversion can be achieved.

[0070] In some embodiments of the present invention, an additional stream may be added to the dehydrogenation reactor to extract solid bicarbonate that forms and settles within the reactor.

[0071] In some embodiments of the present invention, a return stream from the separator is added to compensate for the amount of extract or to increase the conversion.

[0072] In some embodiments of the present invention, the hydrogen gas stream is used by a consumer.

[0073] In some embodiments of the invention, the separator is not in-line with the process and can therefore function in batch cycles to separate the catalyst from the formate solution and alternately wash the catalyst. During the separation cycle, the formate can be returned directly to the product tank or, better, to the reactor for a second pass to increase conversion.

[0074] In some embodiments of the present invention, the solid catalyst is periodically collected on a separator filter and the catalyst is forced into a dryer unit using an inert gas flow (to prevent explosion).

[0075] In some embodiments of the present invention, the separator for the dehydrogenation process is a CONTIBAC filter or similar separator manufactured by DrM, which is capable of continuously and efficiently separating the formate liquid and catalyst.

[0076] In some embodiments of the invention, the product tank is a vessel of similar size to the reactant tanks and the product is used directly for supply to the consumer, while in other embodiments of the invention the product is dried and shipped to the consumer as a solid.

[0077] In some embodiments of the present invention, the catalyst exiting the separator is forced into a washing tank.

[0078] In some embodiments of the present invention, the refresh cycle is performed by washing the catalyst from traces of formate and bicarbonate to prevent hydrogen production during the refresh cycle.

[0079] In some embodiments of the present invention, purified water is used to wash the catalyst, which can be reused for the next wash cycle or for flowing to wastewater.

[0080] In some embodiments of the present invention, further washing of the catalyst with an acid or optional further washing with a liquid material is performed.

[0081] In some embodiments of the invention, the water or acid wash is performed at room temperature. In some embodiments of the invention, higher temperatures are used. Typical wash temperatures are 30-50 degrees Celsius, while other treatments can be performed at 50-80 degrees Celsius, although higher temperatures can also be used.

[0082] In some embodiments of the present invention, the catalyst is transferred from the wash tank to the dryer as a wet cake.

[0083] In some embodiments of the present invention, the dryer may be a conveyor equipped with heating elements or IR lamps. In other embodiments of the present invention, the dryer is a screw with airflow of any speed and temperature. In other embodiments of the present invention, other oxidation means such as chemical vapor or UV heating or electrostatic charging are used to reactivate the catalyst.

[0084] In some embodiments of the present invention, the catalyst is promoted into a hopper and returned to the mixing tank by a feed screw, while in other embodiments of the present invention, the catalyst is forced by a pump.

[0085] In some embodiments of the present invention, the catalyst activity becomes so low that it is necessary to completely recycle the catalyst, at which point the used catalyst is fed to a recycle tank and fresh catalyst is added directly to the hoop.

[0086] The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings, in which: [Brief explanation of the drawings]

[0087] [Figure 1] A conceptual illustration of the formate-bicarbonate reaction cycle for energy and hydrogen storage.

[0088] [Figure 2] 1 shows a schematic of the concept of a continuous hydrogenation reactor.

[0089] [Figure 3] 1 shows a schematic of the continuous dehydrogenation reactor concept.

[0090] [Figure 4a] A block diagram of a continuous hydrogenation reactor is shown on two levels. [Figure 4b] A block diagram of a continuous hydrogenation reactor is shown on two levels.

[0091] [Figure 5a] A block diagram of a continuous dehydrogenation reactor is shown in two levels. [Figure 5b] A block diagram of a continuous dehydrogenation reactor is shown in two levels.

[0092] [Figure 6] Figure 1 shows the turnover number (TON), i.e., the amount of hydrogen released, over time by a catalyst exposed to a 4 M formate solution. The graph compares the used catalyst with a catalyst reactivated by air.

[0093] [Figure 7] Figure 1 shows the TON reached over time for a catalyst exposed to a 4 M formate solution. This graph compares different catalyst reactivation processes.

[0094] [Figure 8a] The graph shows the TON reached over time for a catalyst exposed to a 4 M formate solution. The graph compares different catalyst reactivation processes with two different acids. [Figure 8b] The graph shows the TON reached over time for a catalyst exposed to a 4 M formate solution. The graph compares different catalyst reactivation processes with two different acids.

[0095] [Figure 9] 1 is a photograph showing a reaction vessel for a dehydrogenation step.

[0096] [Figure 10a] The current hydrogen-on-demand system and the newly proposed system are conceptually shown. [Figure 10b] The current hydrogen-on-demand system and the newly proposed system are conceptually shown.

[0097] [Figure 11] 1 shows the effect of adding an alkaline agent on the dehydrogenation reaction. DETAILED DESCRIPTION OF THE INVENTION

[0098] Hydrogen storage is one of the most important challenges in the energy industry today. The effective and reproducible storage and release of hydrogen is a key point in our ability to efficiently produce clean energy at a reasonable cost.

[0099] Figure 1 shows the formate-bicarbonate cycle for storing hydrogen and energy. On the left side of the diagram, an alkali metal salt of bicarbonate is hydrogenated with hydrogen to produce water and formate 11, and on the right side of the diagram, water reacts with an alkali metal salt of formate to produce bicarbonate and hydrogen 10. Both sides of the cycle have low reaction energies, making it easy to complete the entire cycle without significant side reactions.

[0100] The formate dehydrogenation process 11 occurs in the presence of a catalyst. The catalyst can be a Pd or Pt-based catalyst, although other transition metal catalysts have been used and found to be effective. The catalyst can be distributed on any substrate; a typical substrate for the catalyst is activated carbon. Other options include SiO2, TiO2, or even metal substrates such as Al, Cu, or any other metal, either neat or with a coating made of activated carbon supported on these metals.

[0101] For efficient dehydrogenation of formate 11 and water, low reaction temperatures are required, with typical values ​​of 30–90 °C having been used previously. Lower temperatures result in slower reaction rates, while higher temperatures result in a significant increase in side reactions.

[0102] The parameters of the hydrogenation process reaction 10 are almost as mild as those of the dehydrogenation process. The reaction temperature of the hydrogenation process can be controlled in the range of 20 to 40 degrees Celsius.

[0103] Because this is an equilibrium reaction, as the forward reaction proceeds, the reverse reaction also increases, limiting the conversion. Therefore, increasing the hydrogen pressure reduces the reverse reaction and increases the overall conversion of the hydrogenation process. Typical values ​​for hydrogen pressure for the process are 10-20 atmospheres, which is a relatively low pressure for that type of process.

[0104] To make this cycle as environmentally friendly as possible, it is best to use water and no other solvents, but both reactions can proceed in other solvents as long as water is present as a reactant in the dehydrogenation reaction 10.

[0105] In aqueous solutions, the key parameter for the reaction is the solubility of the salt. Both formate and bicarbonate salts are highly soluble in water. However, the solubility of formate is much higher than that of bicarbonate. At room temperature, aqueous solutions containing formate can be soluble up to 15.7 M as bicarbonate solutions under the same conditions, and are soluble up to and beyond 3.4 M, at which point bicarbonate precipitation begins.

[0106] The solubility difference poses a significant challenge at high formate molar concentrations, as bicarbonate precipitation begins and the reaction is no longer a liquid-liquid reaction. Because the heterogeneous catalyst is also a solid, a good separation procedure between the solid bicarbonate and the catalyst is crucial for scale-up of the system.

[0107] A key parameter for system scale-up is the catalyst refresh and recycle system. As explained, a major issue overlooked by previous publications, the present invention focuses on the ability to refresh and recycle formate-bicarbonate catalysts in a reproducible and scalable manner.

[0108] 2 and 3 are block diagrams of a system that takes into account all the specific features of the formate-bicarbonate energy cycle system.

[0109] Figure 2 shows a block diagram of the hydrogenation of bicarbonate to formate. This side of the equation is referred to herein as "storage" because in that side of the reaction, hydrogen is stored inside the formate for later use.

[0110] The storage process characteristics of the system at high molar concentrations (10-14 M) are as follows: a. Reactant 12, bicarbonate, exceeds its solubility in water, thus resulting in a two-phase reaction between solid pure bicarbonate salt and a 3.4 M aqueous solution of bicarbonate (at room temperature, solubility increases with increasing temperature). b. The product 15 is an aqueous formate solution (the solubility of formate in water is much higher than the solubility of bicarbonate, as explained above), and therefore the reaction is a slurry-to-liquid reaction. c. The storage reactor 13 is pressurized with hydrogen gas. Therefore, it is useful to mix the catalyst with the bicarbonate downstream of the hydrogenation reactor. Mixing 16 is also necessary to introduce additional catalyst into the reaction. d. The separation process at the end of reaction 14 is a liquid-solid separation, where the liquid is formate which is transferred to product tank 15 and the solid is the catalyst which needs to be refreshed 17 after each cycle. e. The refresh and recycle section is an important feature of the system because catalyst cost is the major cost of the system and continuous refreshing extends the life of the catalyst, increasing the economic justification of the system. f. Active catalysts are refreshed on-site to reduce costs17, while inactive catalysts are recycled at the plant18.

[0111] The separation process can be carried out inline between the reaction and the product, as shown in Figure 2. However, another valid possibility is to separate the catalyst from the formate offline. In this case, the product tank 15 is located immediately downstream of the reactor 13, and the separation and washing 14 is downstream of the product tank, returning the liquid portion to the product tank and the catalyst to the refresh 17.

[0112] Figure 3 shows a block diagram of the dehydrogenation of formate to bicarbonate. This side of the equation is referred to herein as "release" because in that side of the reaction, hydrogen is released from the formate and used as energy at the same site.

[0113] The release process characteristics at high molar concentrations (10-14 M) of the system are as follows: g. Reactant 20, formate salt, has less than its maximum solubility in water and is therefore a liquid reactant (i.e., an aqueous solution). h. Product 24 is bicarbonate above its solubility limit in water and is therefore a two-phase product of solid pure bicarbonate and a 3.4 M aqueous solution of bicarbonate. i. The discharge reactor 21 is heated to 50-90°C to increase the reaction rate, but the formate and catalyst cannot be mixed before entering the reactor because they react at lower temperatures. Mixing occurs inside the reactor. j. The final separation process in reaction 26 is a liquid-solid-solid separation where the liquid is the formate which is returned to product tank 24 and the solid is both the catalyst and the bicarbonate which must be separated. The solid carbonate should stay in the product tank and the catalyst needs to be refreshed 22 after each cycle. k. The refresh and recycle section is an important feature of the system because catalyst cost is the major cost of the system and continuous refreshing extends the life of the catalyst, increasing the economic justification of the system. l. Active catalysts are refreshed on-site to reduce costs22, and catalysts that are no longer active are recycled at the plant23.

[0114] Figures 4a and 4b show an example of a continuous storage system that produces formate from bicarbonate and continuously refreshes the catalyst to increase the productivity of the system. The major units / operations are outlined in dashed lines in Figure 4A.

[0115] The reactant tank is a potassium bicarbonate tank 31 which flows through a mixing unit 33 to the reactor 32. After the reaction, the product and catalyst are separated 34 and the liquid goes to a potassium formate tank 33, where the catalyst is washed and refreshed 35 and returned to the reaction by the mixing unit 33.

[0116] An example of a storage system's features is shown in schematic detail in Figure 4b. The reactant tank 41 is a high-concentration potassium bicarbonate tank. Typically, the salt concentration is 7-10M, and in other cases 11-15M. As a result, most of the salt in the tank is in solid form, necessitating a mechanism to prevent clogging. The pump 42 below the reactant tank keeps the slurry circulating during the reaction, creating a uniform supply of slurry to the reactor, and is an example of a method to prevent the slurry from clogging the pipes. Other options for mixing the slurry for the same purpose could be a lifting screw to distribute the solids in solution, or adding a mixing device within the reactant tank.

[0117] The slurry is mixed with catalyst on the way to the first reactor in a mixing tank 43. The mixing tank can be replaced by other methods for mixing solids into liquids, such as a vortex pipe or screw.

[0118] The purpose of the mixer is two-fold: first, it allows the catalyst to be continuously fed into the reactor even though the reactor is pressurized; and second, it allows the bicarbonate to be mixed with the catalyst prior to the reactor.

[0119] The catalyst enables the reaction, but when its activity declines, a refresh cycle is required to restore the catalyst to its optimum performance. To make this possible, a fraction of the catalyst is removed from the reactor during each time segment, and a similar amount of catalyst must be added to the reactor in the same time segment to keep the reaction rate constant. The purpose of the mixer tank is to add the catalyst at the correct rate after the refresh.

[0120] The amount of catalyst in the reactor is assumed to remain constant throughout the reaction, and the catalyst conditions are also assumed to remain constant. To enable this, catalyst refreshment should continue during the reaction, i.e., additional catalyst should be removed from the reactor during the refresh cycle. The ratio of catalyst amount in the reactor to catalyst in the refresh cycle depends on the residence time in the reactor and the residence time for refreshing the catalyst. Typical values ​​are 1:1 to 1:2 for catalyst inside the reactor:outside the reactor. However, better and faster refresh cycles can reduce the ratio to 1:0.1 to 1:0.3, lowering the overall cost of the system.

[0121] From the mixer, the slurry is forced against pressure into the first reactor 44. The pressure is that of the hydrogen gas 55, the reactant in the hydrogenation reaction, and must be high enough to convert the formate back to bicarbonate without causing spontaneous reverse dehydrogenation. A typical pressure is 10 bar; pressures of 10-20 bar or 20-30 bar are better, but they are also more energy-intensive. 10 bar is a good compromise between cost and performance.

[0122] The reaction produces heat, and for control reasons, a heat exchanger 57 is used to maintain the same temperature in the reaction tank. Typical temperatures are between 25 and 35 degrees Celsius. Lower temperatures are preferred to reduce back reactions.

[0123] The reaction tank can be monitored by several sensors. The most important parameters that need to be monitored are the reactor temperature, pressure and the amount of material in the reactor. To monitor the last, a height sensor or a wet point sensor can be used.

[0124] The feed stream to the reactor contains a solid catalyst and a bicarbonate slurry. The solid portion of the bicarbonate slurry should remain in the reactor until consumed by the reaction; only the liquid portion should continue to the next stage. To this end, a size filter is placed near the reactor's exit point to prevent solid bicarbonate from leaving the first reactor and allow the catalyst to be transferred to the next reactor. The conditions in the first reactant tank 44 are determined by the residence time and hydrogen pressure. The filter sets the effluent concentration to a maximum of 3.4 M bicarbonate; for a typical reaction with an input stream of 10 M bicarbonate, the minimum conversion is approximately 66%.

[0125] The filter also forces the output stream of the reactor into a liquid so that the input stream to the next reactor 45 is no longer a slurry but a liquid containing catalyst.

[0126] The second reactor 45 can be a CSTR reactor similar to the first reactor. However, because the reaction is liquid phase only, other reactor options are possible for that part of the process. Examples are a PFR reactor at low temperature or a static mixer or auger reactor.

[0127] To achieve higher conversion and eliminate the need for filtration, the pressure in the second reactor must be higher than the pressure in the first reactor.

[0128] From the second reactor 45, an output stream is fed to a liquid-solid separator 46. The separator is in series with the process and therefore continuously transfers the product as an output stream to a product tank 47. However, a filter collects the solid portion of the catalyst, which in segments pushes the catalyst cake into a wash tank 49 using a nitrogen stream 53 (to prevent explosion). The separator may be, for example, a CONTIBAC filter manufactured by DrM.

[0129] The product tank 47 is a liquid container of similar size to the reactant tanks, and product liquid is available through an outlet pipe 56 .

[0130] The catalyst leaving the separator 46 is forced into a washing tank 49. It is extracted from the reaction process and transferred to a refreshing process.

[0131] The refresh procedure is explained in detail in the following figures, however, here we will focus on the process parameters of the refresh cycle.

[0132] The first step of the refresh cycle is to wash the catalyst from traces of formate and bicarbonate, thereby preventing the production of hydrogen during the refresh cycle. For this purpose, water 54 is purified in column 48 and fed to wash tank 49. Additional water can be reused for the next wash cycle or can be passed to wastewater.

[0133] After the initial water wash, the catalyst can be further washed with an acid. Figure 4b is only one example of a process, and therefore does not show an acid wash, but an acid wash can be introduced at the same process point and by the same means as the water wash. Therefore, the water wash should be considered an example of any additional wash with a liquid material.

[0134] Another point is the processing temperature. Water or acid can be used at temperatures higher than room temperature. Typical cleaning temperatures are 30-50 degrees Celsius, while other processes can be carried out at 50-80 degrees Celsius, and higher temperatures can be used.

[0135] From the wash tank 49, the catalyst is transferred as a wet cake to a dryer. The dryer can be a conveyor with heated elements or IR lamps, but a simpler approach is a screw with airflow. The purpose of the air is both to dry the catalyst and to oxidize it. Therefore, simple air can be very useful, although other oxidizers such as chemical vapors or UV heating or electrostatic charging are also effective here.

[0136] The catalyst is sent to hoop 52 and fed back to mixing tank 43 by feed screw 58. This completes the refresh cycle and feeds the catalyst back into the reaction cycle.

[0137] After an extended period of catalyst cycling and refresh cycles, the catalyst activity may become too low and require complete recycling, at which point the used catalyst is fed to a recycle tank 51 and fresh catalyst is added directly to the hoop 52.

[0138] Figures 5a and 5b show an example of a continuous release system that releases hydrogen from formate and continuously refreshes the catalyst, increasing the productivity of the system. The major units / operations are outlined in dashed lines in Figure 5A.

[0139] The reactant tank is a potassium formate tank 61 that flows directly to the reactor 63 where it mixes with fresh catalyst 62. After reaction, the product and catalyst flow to a product tank 64. In this example, the product is separated from the catalyst by a continuous flow of product exiting the product tank 64 and flowing to a separator 65. From the separator, the liquid returns to the product tank, and the catalyst is washed and refreshed 66 and returned directly to the reactor 63 by a mixing unit 62.

[0140] An example of the features of a release system is shown in schematic detail in Figure 4b. Reactant tank 71 is a high-concentration potassium formate tank. Typically, it has a salt concentration of 7-10 M, and in other cases 10-15 M. However, this concentration is still below the precipitation concentration, and therefore the formate is still entirely in the liquid phase.

[0141] Another possibility, not shown in the examples, is to use a concentration greater than 15.7 M, in which some or most of the salt in the tank is in solid form and a mechanism to prevent clogging is added. For example, a pump could be added below the reactant tank to prevent the slurry from clogging the pipes and to keep the slurry circulating during the reaction, ensuring a uniform slurry supply to the reactors. Other options for the same purpose of mixing the slurry could be a lifting screw to distribute the solids in solution or adding a mixing device within the reactant tank. In this case, the reaction between the formate and the catalyst begins immediately under non-pressurized conditions, so the slurry is mixed with the catalyst en route to the first reactor in a special mixing unit.

[0142] The catalyst enables the reaction, but when its activity decreases, a refresh cycle is required to restore the catalyst to its optimum performance. To enable this, a fraction of the catalyst is removed from the reactor during each time segment, and a similar amount of catalyst must be added to the reactor in the same time segment to keep the reaction rate constant.

[0143] The mixing process at the inlet to the reactor 72 controls the correct dosage of refresh catalyst and formate solution to maintain the same catalyst concentration and conditions during the reaction.

[0144] The catalyst feed to the reactor 72 should be from a closed unit where a flow of nitrogen 80 or other inert gas displaces air to maintain a safe process flow.

[0145] During the reaction, the amount of catalyst in the reactor is assumed to be constant, and the catalyst conditions are also assumed to be constant. To allow catalyst refreshment to continue during the reaction, i.e., during the reaction to refresh cycles, additional amounts of catalyst must be removed from the reactor. The ratio of the amount of catalyst in the reactor to the catalyst in the refresh cycle depends on the residence time in the reactor and the residence time for refreshing the catalyst. Typical values ​​are 1:1 to 1:2 for catalyst inside:outside the reactor. However, better and faster refresh cycles can reduce the ratio to 1:0.1 to 1:0.3, lowering the overall cost of the system.

[0146] The reaction between the catalyst and formate consumes heat, so a heat exchanger 84 is used to control the temperature in the reaction tank. Typical temperatures are 50-70°C, and can be 70-90°C. If the temperature is too low, the reaction will be too slow, and as the temperature increases, side reactions may occur.

[0147] The reaction tank can be monitored by several sensors. The most important parameters that need to be monitored are the temperature of the reactor, the pressure and the amount of material in the reactor.

[0148] The reactor 72 may be a CSTR reactor to ensure sufficient mixing of the materials. However, a low-temperature auger reactor with a static mixer or screw may be a better choice as the discharge reactor because heating may be more efficient in this type of reactor. These reactors also allow the temperature to increase with propagation within the reaction, which is a major advantage in increasing reaction conversion. Controlling the residence time and reaction temperature can achieve optimal conversion.

[0149] During the reaction, solid bicarbonate is formed in the reactor. The solid portion of the bicarbonate settles during the reaction and can be extracted from the reactor, increasing the reaction conversion to the theoretical limit of 100%. To that end, an additional stream 85 is shown to extract material from the reactor. Another stream 86 is added to compensate for the extraction by the return stream from separator 74.

[0150] From the reactor 72, a liquid output stream is fed to a product tank 73 from which another gaseous stream of hydrogen is taken as it is sent to use 77.

[0151] Inside the product tank 73 there is a mixture of solid bicarbonate, solid catalyst, and a liquid mixture of formate and some bicarbonate (depending on the conversion). To provide sufficient separation between the catalyst and the solid bicarbonate, a filter is added to the product tank to settle the solid bicarbonate (73A) and keep the catalyst inside the solution (73B) and feed it to separator 74.

[0152] The separator is not in-line with the process and therefore can function in a batch cycle to separate the catalyst from the formate solution and alternately wash the catalyst. During the separation cycle, the formate can flow directly to product tank 73 or more fully back to reactor 72 for a second pass via stream 86 as shown in the figure.

[0153] Inside the separator 74, a filter is fitted to collect the solid part of the catalyst, and segment by segment the catalyst is pushed using a nitrogen flow 80 (to prevent explosion) to a dryer unit 79. The separator may be, for example, a CONTIBAC filter manufactured by DrM.

[0154] The product tank 73 is a liquid container of similar size to the reactant tanks and product, and allows potassium bicarbonate slurry to be made available through an outlet pipe 76.

[0155] The first step of the refresh cycle is to wash the catalyst from traces of formate and bicarbonate, thereby preventing the production of hydrogen during the refresh cycle. For this purpose, water is purified in column 75 and fed to separator 74 during the wash cycle in the separator. Additional water can be reused for the next wash cycle or can flow to wastewater.

[0156] After the initial water wash, the catalyst can be further washed with water or acid. Figure 4b is only one example of a process, and therefore does not show an acid wash, but an acid wash can be introduced at the same process point and by the same means as the water wash. Therefore, the water wash should be considered an example of any additional wash with a liquid material.

[0157] Another point is the processing temperature. Water or acid can be used at temperatures higher than room temperature. Typical cleaning temperatures are 30-50 degrees Celsius, while other processes can be carried out at 50-80 degrees Celsius, and higher temperatures can be used.

[0158] From separator 74, the catalyst is transferred as a wet cake via 89 to dryer 79. The dryer may be a conveyor with heated elements or IR lamps, but a simpler approach may be a screw with airflow 78. The purpose of the air is both to dry the catalyst and to oxidize it. Thus, a simple airflow can be very useful, although other oxidizers such as chemical vapors or UV heating or electrostatic charging would also be effective here.

[0159] The catalyst is sent to hoop 82 and fed back to reactor 72 by feed screw 83. This completes the refresh cycle and feeds the catalyst back into the reaction cycle.

[0160] After an extended period of catalyst cycling and refresh cycles, the catalyst activity may become too low and require complete recycling, at which point the used catalyst is fed to a recycle tank 81 and fresh catalyst is added directly to the hoop 82.

[0161] The key to this invention is the catalyst refresh cycle. This process flow allows for extended catalyst operating cycles and is designed to mitigate a major concern in the system: premature catalyst degradation.

[0162] Different catalyst refresh procedures can be used to extend the catalyst life cycle, and Figures 6-8 show different example processes for replicating the initial conditions of the catalyst.

[0163] The catalyst reactivation process can be tested by pre-treatment and post-treatment activation. A simple way to describe activation is to use the catalyst turnover number (TON) and turnover frequency (TOF) at each time segment during the reaction. Both parameters indicate different characteristics of catalyst activity, therefore, TON and activity will be used synonymously in the following.

[0164] TON represents the average number of active sites undergoing a complete reaction cycle per gram of catalytic metal present in the catalyst. In the first stage of the process, all sites are new and able to undergo a complete reaction cycle, thus increasing the TON. However, over time, some sites become inactive (deactivated), and therefore the TON increases at a slower rate. After a while, most sites cease their activity, and the TON remains fairly stable. This is mostly because some of the activity is maintained for a very long period of time. This behavior can be seen very clearly in Figures 6-8, where the TON saturates over time, regardless of the treatment used to reactivate it.

[0165] The derivative of all graphs over time is the TOF of the catalyst, which is an important parameter in the design of the refresh cycle. The best performance of the catalyst is in the first stage of the reaction, where the TON increases rapidly. Therefore, for the design of this process, it is important to continuously add new or refreshed catalyst to the reactor, as suggested by the present invention, so that the catalyst performance is optimal not only in the first stage but throughout the entire reaction. At the same time, by continuously refreshing the catalyst, the hydrogen production rate remains constant, which is an important issue for energy consumers.

[0166] Figure 6 shows the most basic process for treating a catalyst: washing in water and drying with airflow. The washing water should be deionized to keep the catalyst intact, and the water can be at room temperature. However, higher water temperatures are better for the process because they precipitate traces of potassium salts on the catalyst and the solubility constants of both salts increase with temperature. Typical washing water temperatures are 30-50 degrees Celsius; washing at 50-80 degrees Celsius or even higher temperatures in pressurized tanks is also possible.

[0167] The reactivated catalyst 90 shown in Figure 6 was reactivated by washing with water and drying with a stream of air. The graph clearly shows that the reactivated catalyst performance was superior to another used catalyst 91 that was not reactivated.

[0168] The reactivation process can be carried out by other means as well as air and water. Figures 7 and 8 show other examples of catalyst reactivation processes.

[0169] Figure 7 shows a comparison between several different refresh procedures. The large deviation in TON after 1 hour of reaction between different treatments indicates that the refresh procedure is important for the success of the continuous refresh process.

[0170] Untreated used catalyst shows the lowest activity 97, water washing at 50°C shows better activity 96, but better activity is achieved with acids 92-95. Organic acids such as citric acid 95 show lower reactivation ability than inorganic acids, while hydrochloric acid 93 and nitric acid 94 are better than phosphoric acid 95.

[0171] FIG. 8 also shows the acid concentration effect in two different acids: nitric acid (FIG. 8a) and hydrochloric acid (FIG. 8b).

[0172] In the case of nitric acid, a comparison of untreated catalyst 100 with catalyst washed with nitric acid up to a 2% concentration 101 showed no effect on overall catalyst reactivation. However, at a concentration of 10%, nitric acid significantly increased catalyst activity 102. This graph shows that higher concentrations are optimal for reactivation with nitric acid, as the effect of refreshing on catalyst activity was reduced.

[0173] In the case of hydrochloric acid, even small concentrations of acid had a strong effect on catalytic activity 104 , and at higher concentrations, hydrochloric acid had only a small additional effect on catalytic activity 105 .

[0174] A typical hydrogenation process requires 50-100m 3 , preferably 70m 3The tank is filled with a 4-14M, preferably 10M, potassium bicarbonate salt slurry, which is pumped into a mixing tank at a rate of 50-150 L / min, preferably 120 L / min. Simultaneously, 2-5 kg / min, preferably 3.2 kg / min, of catalyst is forced into the same mixing tank by a feed screw under nitrogen. The mixed slurry is then pumped from the mixing tank into a 500-1500 L, preferably 1000 L, CSTR reactor under hydrogen gas pressure of 5-20 bar, preferably 10 bar. The slurry is mixed for a residence time of 3-10 minutes, preferably 6 minutes, filling the tank to a volume of 300-700 L, preferably 620 L. The tank is then stabilized at the same volume, with 50-150 L / min, preferably 130 L / min, of slurry entering the reactor and 50-150 L / min, preferably 130 L / min, of liquid leaving the reactor. The liquid, 50-70% formate and 30-50% bicarbonate, enters the second reactor at a pressure of 10-50 bar, preferably 20 bar, for another 5-15 minutes, preferably 10 minutes, to increase the conversion rate to 90%. The final product enters the separator at a rate of 50-150 L / min, preferably 130 L / min, and the liquid portion continuously flows into the product tank at a rate of 50-150 L / min, preferably 120 L / min. In the separator, the catalyst is filtered and periodically forced into a washing tank at a rate of 5-15 L / min, preferably 10 L / min, of wet catalyst. The catalyst is washed in the washing tank with 10-30 L, preferably 20 L, of distilled water at a temperature of 30-60°C, preferably 50°C, and then fed to a dryer. The air stream dries the water from the catalyst for 10 to 25 minutes, preferably 20 minutes, while the screw continuously pushes the catalyst through the hoop. The catalyst is fed from the hoop into the mixing reactor at a rate of 2 to 5 kg / min, preferably 3.2 kg / min, completing the refresh cycle.

[0175] A typical dehydrogenation process requires 50-100 m 3 , preferably 70m 3The tank is filled with a 4-14M, preferably 10M, potassium formate slurry, which is pumped into the reactor at a rate of 50-150 L / min, preferably 120 L / min. Simultaneously, 2-5 kg / min, preferably 3.2 kg / min, of catalyst is forced into the same reactor via a feed screw under nitrogen. The liquid flows into a 1000-3000 L, preferably 2000 L, low-temperature auger reactor at a temperature of 30-60°C, preferably 70°C. The slurry is mixed for 5-20 minutes, preferably 10 minutes, and the reactor is filled to capacity by 500-2000 L, preferably 1200 L, and allowed to stabilize at the same volume. Here, 50-150 L / min, preferably 120 L / min, of formate and 2-5 kg / min, preferably 3.2 kg / min, of catalyst enter the reactor, and 50-150 L / min, preferably 130 L / min, of slurry exits the reactor. The slurry is 70-90% bicarbonate and 10-30% formate, including the catalyst. 50-150 L / min, preferably 130 L / min, of the final product flows to the product tank, where it is separated. The separator operates offline at a rate of 100-300 L / min, preferably 260 L / min, and performs two tasks: first, it separates the catalyst from the solution in the tank and returns the liquid to the product tank at a rate of 100-300 L / min, preferably 260 L / min; second, the catalyst is washed with distilled water at a rate of 10-30 L / min, preferably 20 L / min, at a temperature of 30-60°C, preferably 50°C. The separator changes its function every 0.5 to 5 minutes, preferably every 1 minute. The catalyst is filtered in the separator and then pushed into a dryer every 0.5 to 5 minutes, preferably every 1 minute. An air stream dries the water from the catalyst, and a screw pushes the catalyst into a hoop. The catalyst is fed from the hoop into the mixing reactor at a rate of 2 to 5 kg / min, preferably 3.2 kg / min, completing the refresh cycle.

[0175] Figure 10a conceptually illustrates the current hydrogen-on-demand system.

[0176] In the current process, hydrogen is produced on-site in several remotely located large factories 101 or small electrolyzers 112. While remote production is safer and cheaper, the complexity and high cost of transporting the hydrogen presents economic and environmental disadvantages.

[0177] Hydrogen can be transported from the production site to the fueling station by truck 102 or pipe 111. Transportation by truck 102 must be done at high pressure to efficiently move large amounts of hydrogen to the fueling station. However, high-pressure tanks are expensive, and there is a limit to the amount of hydrogen that can be transported at one time for safety reasons. Therefore, the pressure of the designed truck is 200 to 500 bar, and it is expected to carry about a 20-meter cube of hydrogen.

[0178] The price per kg of hydrogen for an average 50 km journey in such a truck is $1.4 / kg of hydrogen with current truck technology, which can be reduced to $0.6 / kg of hydrogen with significant efforts. For trucks, the high transportation costs significantly increase the price of hydrogen for customers, reducing the propensity to adopt hydrogen energy solutions.

[0179] Another method of transporting hydrogen is by pipe 111. The use of hydrogen in pipes over long distances can pose even more significant safety hazards; damage to the pipes, either over time or due to an accident, can create an explosion hazard. The use of pipes also reduces the allowable pressure of the hydrogen to 20 bar, incurring the additional cost of pressurizing the hydrogen gas to a higher pressure on-site.

[0180] Hydrogen arriving at the fueling station by truck 102, pipe 111, or produced on-site by electrolyzer 112 must be unloaded, stored, and released as needed. To enable this, two different compressor options can be used. The first option is a high-pressure compressor that holds the hydrogen gas at 950 bar on-site 103, and the second option is a medium-pressure compressor that holds the hydrogen gas at 500 bar 108. The difference between these two options is that in the first option, the hydrogen is already ready to be dispensed but is held in very expensive containers, and in the second option, the container costs are lower, but the hydrogen is not ready to be dispensed and must be compressed to 950 bar before being dispensed on demand in a smaller booster compressor.

[0181] The first option uses tanks of 4 to 7 cubic meters to store hydrogen at 950 bar104, while the second option uses tanks of 6 to 10 cubic meters to store hydrogen at 500 bar109.

[0182] The estimated costs of the compressors and all other components of the system are shown in Table 2. The costs of both the high-pressure and intermediate-pressure vessels are in the $1 million to $1.5 million range, with the intermediate-pressure compressor at the lower end of the range and the high-pressure compressor at the higher end. The same applies to the cost of storing hydrogen; a suitably sized low-pressure vessel is expected to be at the lower end of the range, while a similarly sized high-pressure vessel is expected to cost approximately $500,000. The cost of the booster compressor 110 is insignificant compared to the costs above; its estimated cost is included in the general costs associated with the amount of hydrogen being compressed, estimated at approximately $0.04 / kg of hydrogen. [Table 2]

[0183] In both cases, before distribution, the hydrogen passes through a heat exchanger to pre-cool the gas to -40 degrees Celsius 105. After cooling, the hydrogen gas stream goes to a fuel station 106 and from there to the customer.

[0184] If the customer is a high pressure hydrogen gas vehicle 107, hydrogen is supplied at 950 bar and the hydrogen motor vehicle tank is maintained at 700 bar.

[0185] Figure 10b conceptually illustrates the proposed hydrogen-on-demand system.

[0186] In the proposed hydrogen-on-demand system, hydrogen is produced at a remote location 120 to avoid safety issues in transportation and storage. The produced hydrogen is stored at the production site in the form of formate by the hydrogen storage system disclosed above in Figures 2 and 4 121. Because the storage system is at the production site, its size can be made very large, thereby enabling distribution of hydrogen to a significant number of fueling stations. A system of this size significantly reduces the cost of storing hydrogen, making it an attractive alternative to hydrogen energy.

[0187] The formate produced at the production site is a non-hazardous material and can be distributed to fuel stations by ordinary water trucks 122 without size or safety restrictions. Even in the event of an accident, no damage can occur from the formate, and no explosions or environmental problems are expected.

[0188] Another way to transport formate from the production site to the fuel station is by pipe 123. Again, there are no safety issues.

[0189] To unload the truck, a very simple pump 124 is required, and both the unloading and storage of the formate solution do not involve large costs. 300 kg of hydrogen can be stored in a 15 cubic meter tank without any particular safety issues. The tank can be a simple plastic tank 125, and the only significant additional cost at the fuel station is the small hydrogen release system 126 described above in Figures 3 and 5.

[0190] The expected cost of the hydrogen storage and release system used at the production site and fueling station is expected to be in the range of $200,000-$400,000, with an additional cost of $0.50 / Kg of hydrogen. Transportation costs are known and are estimated to be $0.10 / Kg of hydrogen in addition to other common commodity transportation costs. On-site storage costs are expected to be very low.

[0191] As with the current solution, a booster compressor 127 is required to compress the vented hydrogen gas to 950 bar. The cost is insignificant compared to the costs mentioned above, and the estimated cost is included in the general costs associated with the amount of hydrogen being compressed, estimated at approximately $0.04 / Kg of hydrogen.

[0192] In the proposed process, before distribution, the hydrogen passes through a heat exchanger to pre-cool the gas to -40 degrees Celsius 128. After cooling, the hydrogen gas stream goes to a fuel station 129 and from there to the customer.

[0193] If the customer is a high pressure hydrogen gas vehicle 130, hydrogen is supplied at 950 bar and the hydrogen motor vehicle tank is maintained at 700 bar.

[0194] The estimated costs of the proposed system are shown in Table 3 below. [Table 3]

[0195] The table shows the significant cost savings of the proposed solution. It is also clear that the proposed solution is significantly safer and therefore allows for the realization of a hydrogen energy solution without significant industrial changes.

[0196] example Example 1 - Refreshing Treatment: 100 g of purified water was placed in a container containing 10 g of hydrochloric acid and heated to 50°C. 10 g of Pd / C catalyst (5%) was added to the container and the mixture was stirred for 5 minutes. After 5 minutes, the catalyst was transferred to another container through filter paper and collected on the filter paper. The catalyst was transferred to another container, and an additional 200 ml of purified water was added at a temperature of 50°C, and the slurry was mixed for an additional 5 minutes. The slurry was again filtered, collected on filter paper, and then transferred to a container, where the catalyst was dried for 10 minutes by passing air through it at a rate of 10,000 mL / min.

[0197] Example 2 - Refreshing Treatment: 100g of purified water was placed in a container containing 10g of nitric acid and heated to 50°C. 10g of used catalyst was added to the container and the mixture was stirred for 5 minutes. After 5 minutes, the catalyst was transferred to another container through filter paper and collected on the filter paper. The catalyst was transferred to another container, and an additional 200ml of purified water was added at a temperature of 50°C, and the slurry was mixed for another 5 minutes. The slurry was again filtered and collected on filter paper, then transferred to a container and dried for 10 minutes by airflow at a rate of 10,000mL / min.

[0198] Example 3 - Refreshing Treatment: 500 g of purified water was placed in a glass beaker and heated to 70°C. The used catalyst was placed in a plastic net bag in the water for 1 hour. After 1 hour, the used catalyst was removed from the beaker and dried with heated air at a temperature of 80°C at a rate of 5 L / min for 30 minutes.

[0199] Example 4 - Refreshing Treatment: 27 ml of 37% hydrochloric acid was added to a beaker of purified water to a total volume of 1 liter. 100 g of the solution was poured into another beaker, and the used catalyst was placed in a plastic net bag in the solution for 1 hour. After 1 hour, the used catalyst was washed with purified water until a neutral pH was observed. The used catalyst was then removed from the beaker and dried with heated air at a temperature of 80°C at a rate of 5 l / min for 30 minutes.

[0200] Example 5 - Refreshing treatment: 500 g of purified water was placed in a glass beaker and heated to 70°C. The used catalyst was placed in a plastic net bag in the water for 15 minutes. After that, the used catalyst was removed from the beaker and dried with heated air at a temperature of 80°C at a rate of 5 L / min for 15 minutes.

[0201] Example 6 - Refreshing Treatment: 27 ml of 37% hydrochloric acid was added to a beaker of purified water to a total volume of 1 liter. 100 g of the solution was poured into another beaker, and the used catalyst was placed in a plastic net bag in the solution for 15 minutes. After 1 hour, the used catalyst was washed with purified water until a neutral pH was observed. The used catalyst was then removed from the beaker and dried with heated air at a temperature of 80°C at a rate of 5 l / min for 15 minutes.

[0202] Example 7 - Refreshing Treatment: 30 g of catalyst was placed in a 500 ml reactor in a sealed cup. A formate solution was pumped into the reactor, where it reacted to produce hydrogen from the formate and aqueous solution. The hydrogen generation rate was constantly monitored, and if the hydrogen rate was lower than the set target point, the system control stopped the reaction. The reactor was then removed from the formate, and water was fed into the reactor until it was filled with water. The water was heated to 70°C on its way to the reactor by a heat exchanger and allowed to remain in the reactor for 10 minutes. The water was then drained from the reactor, and a second cleaning cycle was initiated. After three cleaning cycles, the water was drained, and air was allowed to flow through the reactor at a rate of 1000 ml / min for 10 minutes.

[0203] Example 8 - Refreshing Treatment: 30 g of catalyst was placed in a 500 ml reactor in a sealed cup. A formate solution was pumped into the reactor, where it reacted to produce hydrogen from the formate and aqueous solution. The hydrogen generation rate was constantly monitored, and if the hydrogen rate was lower than the set target point, the system control stopped the reaction. The reactor was then drained from the formate, and water was fed into the reactor until it was filled with hydrochloric acid solution. The hydrochloric acid solution concentration was 1% by weight (27 ml of 37% hydrochloric acid was added to a beaker of purified water to a total volume of 1 liter) and remained in the reactor for 10 minutes. It was then drained to allow it to flow out, and the reactor was filled with purified water. On its way to the reactor, the water flowed through a heat exchanger, heated to 70 °C, and remained in the reactor for another 10 minutes. The water was then drained from the reactor, the pH of the water was measured, and if the pH was not neutral, a further cleaning cycle was initiated. After several washing cycles, the water was completely neutralized and air was allowed to flow through the reactor at a rate of 1000 ml / min for 10 minutes.

[0204] Example 9—Evacuation Procedure: 70 grams of potassium formate was added to 50 ml of water and stirred to obtain a clear solution. 2.12 g of Pd / C (2%) catalyst was added to this solution, and the solution was placed in a 100 ml beaker. An alkaline agent (0.025 M KOH or 0.75 M potassium carbonate) was added to achieve a pH of 11. The beaker was heated to 70°C. The hydrogen gas generated from the reaction and collected as an output stream was directed into a chamber and measured by gas chromatography to determine the composition of the gas stream. After the reaction was complete, the chamber was again flushed with nitrogen, and the solution was filtered to separate the liquid from the catalyst and bicarbonate. Figure 11 shows bar graphs showing the % CO2 in the collected gas for the following reactions: 10 M potassium formate (center bar), 10 M potassium formate + 0.75 M KOH (left bar), and 10 M potassium formate + 0.025 M KOH (right bar). The results demonstrate the effectiveness achieved by adding alkaline agents in minimizing CO2 evolution, with K2CO3 showing to be a particularly useful alkaline agent for this purpose. Preparation 1~6 The following series of examples describes the preparation of several Pd / C catalysts useful in this invention. The catalysts were produced by a sequential procedure involving two or three major steps, starting from commercially available (or crushed) activated carbon particles having diameters in the range of 4 to 40 microns. Preparation 1 Step 1 - Carbon activation: 10 grams of carbon was placed in a 250 ml beaker, and 10% HNO3 (100 ml) was gently added to the beaker. The mixture was stirred at 125 °C for 24 hours. After the reaction, the mixture was added to 1000 ml of water, and the solid was filtered and washed to a neutral pH condition. Step 2 - Preparation of catalyst: 100 mg of palladium nitrate was added to a beaker. 600 ml of water was gently added, followed by 1 g of activated carbon from step 1. Mixing was continued for 60 minutes. To a second beaker, 100 ml of water was added along with 1 gram of potassium formate. The second solution was decanted into the first solution. This solution was stirred for an additional 24 hours. The product was filtered, washed, and then dried in an oven at 80°C under nitrogen. Preparation 2 Step 1 - Carbon activation: 10 grams of carbon was placed in a 250 ml beaker, and 10% HNO3 (100 ml) was gently added to the beaker. The mixture was stirred at 125 °C for 24 hours. After the reaction, the mixture was added to 1000 ml of water, and the solid was filtered and washed to a neutral pH condition. Step 2 - Catalyst Preparation: 100 mg of palladium nitrate was added to a beaker. 600 ml of water was gently added. In a second beaker, 1 g of potassium formate and 1 g of activated carbon from Step 1 were added to 100 ml of water. The second solution was filtered, and the soaked carbon was gently added to the first solution, followed by mixing for 60 minutes. The mixture was allowed to continue stirring for an additional 24 hours. The product was filtered, washed, and dried in an oven at 80°C under normal air conditions. Preparation 3 Step 1 - Carbon activation: 10 grams of commercially available carbon was placed in a 250 ml beaker, and 100 ml of 10% NaCl solution was gently added to the beaker. The mixture was stirred at a temperature of 125°C for 24 hours. After the reaction, the mixture was added to 1000 ml of water. The solid was separated by filtration and washed to a neutral pH condition. Step 2 - Preparation of catalyst: 100 mg of palladium nitrate was added to a beaker. 600 ml of water was gently added, followed by 1 g of activated carbon from step 1. The mixture was stirred for 60 minutes. To a second beaker, 100 ml of water was added along with 1 g of potassium formate. The second solution was then gently added to the first solution. Stirring was maintained for an additional 24 hours. The product was filtered, washed, and dried in an oven at 80°C under air. Preparation 4 Step 1 - Carbon activation: 10 grams of commercial carbon was placed in a 250 ml beaker, and 100 ml of 10% HNO3 was gently added to the beaker. The mixture was stirred at a temperature of 125°C for 24 hours. After the reaction, the mixture was added to 1000 ml of water. The solid was filtered and washed to a neutral pH condition. Step 2 - Heat treatment: The carbon particles were heated to 400°C before use. Step 3 - Preparation of catalyst: 100 mg of palladium nitrate was added to a beaker. 600 ml of water was gently added, followed by 1 g of activated carbon from step 2. The mixture was stirred for 60 minutes. To a second beaker, 100 ml of water was added along with 1 g of potassium formate. The second solution was then gently added to the first solution. Stirring was continued for an additional 24 hours. The product was filtered, washed, and dried in an oven at 80°C under air. Preparation 5 Before use, the carbon particles were heated to 400°C. The other conditions were the same as those described in Preparation 1. Preparation 6 Preparation 1 was repeated, with a refreshment treatment (containing 1 wt % hydrochloric acid) before the first catalyst use.

Claims

1. 1. A continuous process for releasing hydrogen using a formate-bicarbonate cycle dehydrogenation reaction, the process comprising: continuously feeding an aqueous solution of formate and a heterogeneous catalyst to a dehydrogenation reactor to form bicarbonate and hydrogen; directing the hydrogen for use as fuel hydrogen; continuously removing a fluid effluent from the dehydrogenation reactor and directing the effluent to a product tank; discharging materials from the product tank and separating the catalyst from the materials; washing and refreshing the catalyst; and returning the refreshed catalyst to the dehydrogenation reactor, wherein bicarbonate is collected in solid form from the product tank.

2. 10. The process of claim 1, wherein the catalyst consists of a catalytically active transition metal on solid support particles, wherein the solid support particles have a diameter of less than 100 μm.

3. 3. The process of claim 2, wherein the heterogeneous catalyst is Pd or Pt on carbon and the carbon particles have a diameter of 4 to 40 μm.

4. 4. The process of claim 1 or 3, wherein a sieve is attached to the product tank dividing the product tank into a lower section and an upper section, and the flowable effluent from the dehydrogenation reactor is fed to the lower section of the product tank, causing bicarbonate particles to settle to the bottom of the product tank and catalyst particles to float and accumulate in the upper section of the product tank.

5. 5. The process of claim 4, wherein the material discharged from the upper section of the product tank consists of a formate solution containing catalyst particles and is fed to a separation and washing unit where the catalyst particles are separated from the formate solution and washed.

6. 6. The process of claim 5, wherein the separation and washing are performed offline in a batch mode.

7. 7. The process according to claim 5 or 6, wherein the separated catalyst particles are washed in the separation and washing unit with a washing liquid selected from the group consisting of water, an aqueous acidic solution and an aqueous oxidizing solution.

8. The process of any one of claims 1 to 7, wherein the catalyst is washed with an acidic aqueous stream at a temperature above 30°C.

9. 10. A process according to any one of the preceding claims, wherein the washed catalyst particles are refreshed by drying and oxidation, performed sequentially or simultaneously.

10. 10. The process of claim 9, wherein the washed catalyst particles are simultaneously dried and oxidized by the action of an air stream to obtain refreshed catalyst, which is returned to the dehydrogenation reaction.

11. 11. The process of any one of claims 1 to 10, wherein the aqueous formate solution comprises potassium formate at a concentration of 7M or greater.

12. 12. The process of any one of claims 1 to 11, wherein the dehydrogenation reaction is carried out in the presence of an alkaline agent selected from the group consisting of alkali hydroxides and alkali carbonates.

13. 13. The process of claim 12, wherein the dehydrogenation reaction is carried out using an aqueous solution of potassium formate at a concentration of 7 M or greater in the presence of potassium carbonate at a concentration of 0.5 M or greater.

14. 1. A continuous process for storing hydrogen using the dehydrogenation reaction of the formate-bicarbonate cycle, comprising: continuously feeding an aqueous slurry of bicarbonate, hydrogen, and a heterogeneous catalyst to a hydrogenation reactor having a sieve attached proximate to the reactor outlet to prevent bicarbonate particles from exiting the reactor; continuously removing an effluent from the outlet of the hydrogenation reactor and directing it to a separator, the effluent being in the form of a suspension comprising dissolved formate and suspended catalyst particles and residual solubilized bicarbonate; separating the effluent into an aqueous formic acid solution and a solid catalyst, the separation being downstream of the hydrogenation reactor and upstream of a product tank; directing the aqueous formate to the product tank; washing and refreshing the catalyst in a wash tank; and continuously returning the refreshed catalyst to the hydrogenation reactor.

15. 10. The process of any one of the preceding claims, wherein the hydrogen storage or release rate is controlled by adjusting the amount of catalyst fed to the hydrogenation or dehydrogenation reactor, respectively.

16. 1. A process for storing and releasing hydrogen using the formic acid-bicarbonate cycle, the process comprising: A) a hydrogenation reaction of bicarbonate and hydrogen in the presence of the heterogeneous catalyst of claim 14 to produce an aqueous solution of formate; B) a dehydrogenation reaction in the presence of a heterogeneous catalyst according to any one of claims 1 to 13, wherein the aqueous formate solution of A) is decomposed to form bicarbonate and hydrogen gas; and providing the bicarbonate to the hydrogenation reaction of step A), A process wherein the reaction is carried out in a cyclical manner with separation and refreshing of the catalyst.

17. 1. An apparatus for the continuous production of hydrogen by dehydrogenation of an aqueous formate solution, said apparatus comprising: a first storage tank (71) in which an aqueous formate solution is held, the first storage tank being connected to the dehydrogenation reactor (72) by a feed line, with a heat exchanger optionally positioned along said feed line; a catalyst feeder (83 / 83) for feeding dry granular or powdered material to the dehydrogenation reactor (e.g., a screw conveyor hopper); a dehydrogenation reactor (72) having a first outlet with a gas discharge line (77) for removing hydrogen gas generated in the reactor and delivering the hydrogen to a pressure cylinder or a fuel cell, and a second outlet with a liquid discharge line for directing a fluid effluent from the dehydrogenation reactor to a product tank (73); a product tank (73) divided by a sieve into a lower section (73A) and an upper section (73B), wherein the liquid discharge line (87) from the dehydrogenation reactor enters the lower section of the product tank (73A); a separation and scrubbing unit (74) which is alternately fed from the product tank (73) by appropriately arranging valves, the upper section of the product tank (73B) being connected to the separation and scrubbing unit (74) by a discharge line (88) or from a scrubbing liquid supply line (75), thereby alternating between a separation mode fed by effluent pumped from the product tank through the discharge line and a scrubbing mode fed by the scrubbing liquid, the separation and scrubbing unit (74) comprising a return line (86) for conducting a liquid phase consisting of a formate solution collected during separation to the dehydrogenation reactor, and a catalyst recycle line (89) connected to a dry oxidation unit (79) for feeding the refreshed catalyst to the catalyst feeder (82 / 83) or the used catalyst to a storage tank (81).

18. 18. The apparatus of claim 17, wherein the drying and oxidation unit (79) is fed by an air line to dry, oxidize and force the catalyst particles into the catalyst feeder (82 / 83).

19. 19. The apparatus of claim 17 or 18, further comprising a nitrogen line.

20. 1. An apparatus for the continuous storage of hydrogen by reacting an aqueous bicarbonate slurry with hydrogen to form formate, said apparatus comprising: a first storage tank (41) in which the bicarbonate slurry is held and which is connected to a mixing unit (43) by a supply line; a catalyst feeder (52 / 58) for feeding dry granular or powdered material into said mixing unit (43), e.g., a screw conveyor hopper; a mixing unit (43) comprising an agitator for producing an aqueous slurry of bicarbonate and catalyst particles and a discharge line (59) for feeding said suspension to a first hydrogenation reaction; a first hydrogenation reactor (44) and optionally a second hydrogenation reactor (45) arranged in series, wherein the discharge line (59) of the mixing unit (43) is connected to the inlet of the first hydrogenation reactor (44), each hydrogenation reactor having a gas inlet connected to a hydrogen supply line (55) for introducing hydrogen gas into each hydrogenation reactor, optionally discharging to a solid / liquid separation unit (46), the first hydrogenation reactor (44) or the second hydrogenation reactor (45) having a sieve mounted adjacent to the reactor outlet to prevent bicarbonate particles from exiting the reactor; a product tank (47) connected to said solid / liquid separation unit (46) for receiving therefrom a liquid stream comprising aqueous formate salt; a washing tank (49) connected to the solid / liquid separation unit (46) to receive the solid catalyst particles collected in the solid / liquid separation unit (46), the washing tank being connected to a drying and oxidation unit (50) by a catalyst recycle line (60) to supply refreshed catalyst to the catalyst feeder (52 / 58) or used catalyst to a recycle tank (51).

21. 21. The apparatus of claim 20, wherein the drying and oxidation unit (50) is fed by an air line to dry, oxidize and force the catalyst particles into the catalyst feeder (52 / 53).

22. 22. The apparatus of claim 20 or 21, further comprising a nitrogen line for supplying a stream of nitrogen to the washing tank.

23. 1. A method for distributing hydrogen on demand from a production site to a customer, comprising: a hydrogenation reaction to produce an aqueous formate solution from bicarbonate and hydrogen in the presence of a heterogeneous catalyst, the hydrogenation reaction being carried out in a continuous operation mode with online catalyst refresh and recycle; transporting the formate salt to a hydrogen distribution site in either aqueous or dry form; a dehydrogenation reaction in which an aqueous formate solution is decomposed in the presence of a heterogeneous catalyst to form bicarbonate and hydrogen gas on demand, wherein the hydrogenation reaction is carried out in a continuous operation mode with offline catalyst refresh and recycle.

Images