HYDROGEN STORAGE BASED ON AQUEOUS FORMATE-BICARBONATE (HYDROGEN CARBONATE) EQUILIBRIUM

Abstract

The subject of the invention is a process for the hydrogenation of hydrogen carbonate in an aqueous reaction system, where the process ensures that the hydrogen carbonate, hydrogen and catalyst come into contact with each other while carbon dioxide is present in the gas space. In this phase of the process, formate is produced. The subject of the invention is also a process for the catalytic decomposition of formate in an aqueous reaction system and the hydrogenation of hydrogen carbonate produced in the same reaction system according to the invention, where the reactants and the reaction products are formed in a reversible reaction cycle using the reaction system according to the invention, and this reaction cycle is repeated in the required number of times. In the mentioned formate mg decomposition process, the formate and the catalyst come into contact, so that hydrogen gas and hydrogen carbonate free of COX by-products are produced as the product of the reaction. Further subject of the invention is a hydrogen storage system based on the method according to the invention, preferably a hydrogen accumulator. Further subject of the invention is a hydrogen storage system according to the invention, preferably the use of a hydrogen accumulator for the storage of hydrogen required for the operation of a fuel cell (or other equipment requiring H2) and, where appropriate, for its release in as needed.

Claims

1. A process for the hydrogenation of hydrogen carbonate (HCO.sub.3.sup.?), in an aqueous reaction system, preferably said hydrogen carbonate being selected from sodium hydrogen carbonate (NaHCO.sub.3), lithium hydrogen carbonate (LiHCO.sub.3), cesium hydrogen carbonate (CsHCO.sub.3) and potassium hydrogen carbonate (KHCO.sub.3) and for the production of formate, preferably formate selected from the group of sodium formate (HCOONa), lithium formate (HCOOLi), cesium formate (HCOOCs) and potassium formate (HCOOK), said process comprising bringing said hydrogen carbonate and a catalyst into contact with each other at an elevated temperature, preferably at 60-100? C., more preferably at 80? C., at a pressure of 1-1200 bar, preferably 10-100 bar; where the catalyst is a catalyst with the general formula [Ir(cod)(NHC)P.sub.a]+nP.sub.b, where in the formula Ir is iridium; cod is 1,5-cyclooctadiene; NHC is an N-heterocyclic carbene, preferably 1-R-3-methylimidazol-2-ylidene, where R is C1-C6 alkyl or benzyl; n is an integer from 1 to 4; and P.sub.a and P.sub.b are independently 1,3,5-triaza-7-phosphadamantane (pta), monosulfonated triphenylphosphine (mtppms) or trisulfonated triphenylphosphine (mtppts); characterized in that the hydrogenation of hydrogen carbonate is carried out in such a way that carbon dioxide is present in the gas space.

2. The process according to claim 1, characterized in that the catalyst used is selected from the following: a) a catalyst according to the formula [Ir(emim)(cod)(mtppms]+mtppts, wherein emim is 1-ethyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine; b) a catalyst according to the formula [Ir(bmim)(cod)(mtppms]+mtppts, wherein bmim is 1-butyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine; c) a catalyst according to the formula [Ir(hexmim)(cod)(mtppms]+mtppts, wherein hexmim is 1-hexyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine; d) a catalyst according to the formula [Ir(2mim)(cod)(mtppms]+mtppts, wherein 2mim is 1,3-dimethyl-imidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine; e) a catalyst according to the formula [Ir(Bnmim)(cod)(mtppms]+mtppts, wherein Bnmim is 1-benzyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine; f) a catalyst according to the formula [Ir(emim)(cod)(mtppms]+pta, wherein emim is 1-ethyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and pta is 1,3,5-triaza-7-phosphadamantane; and g) a catalyst according to the formula [Ir(emim)(cod)(mtppms]+mtppms, wherein emim is 1-ethyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine.

3. A process for decomposing a formate, preferably a formate selected from sodium formate (HCOONa), lithium formate (HCOOLi), cesium formate (HCOOCs) and potassium formate (HCOOK) in an aqueous reaction system and for producing hydrogen gas (H.sub.2) free of CO.sub.x by-products, and in the same reaction system, for the hydrogenation of the resulting hydrogen carbonate (HCO.sub.3.sup.?), preferably a hydrogen carbonate selected from the group of sodium hydrogen carbonate (NaHCO.sub.3), lithium hydrogen carbonate (LiHCO.sub.3), cesium hydrogen carbonate (CsHCO.sub.3) and potassium hydrogen carbonate (KHCO.sub.3) in an aqueous reaction system, thus for the production of a formate, preferably a formate selected from the group of sodium formate (HCOONa), lithium formate (HCOOLi), cesium formate (HCOOCs) and potassium formate (HCOOK); where the reactants and the reaction products are formed in a reversible reaction cycle by using the reaction system of the formate decomposition step and the bicarbonate hydrogenation step and by choosing the values of temperature, pressure and pH within the ranges specified below, and this reaction cycle is repeated the required number of times; where the formate decomposition step includes bringing the formate into contact with the catalyst in an aqueous reaction system, at an elevated temperature, preferably at 60-100? C., preferably at 80? C., preferably at a pH greater than 8, preferably at a pH=8.3?0.2, in an Ar gas atmosphere; where the hydrogenation step of the hydrogen carbonate includes bringing the hydrogen carbonate and a catalyst into contact with each other, at an elevated temperature, preferably at 60-100? C., more preferably at 80? C., under pressure of 1-1200 bar, preferably 10-100 bar; where the catalyst is a catalyst with the general formula [Ir(cod)(NHC)P.sub.a]+nP.sub.b, where in the formula Ir is iridium; cod is 1,5-cyclooctadiene; NHC is an N-heterocyclic carbene, preferably 1-R-3-methylimidazol-2-ylidene, where R is C1-C6 alkyl or benzyl; n is an integer from 1 to 4; and P.sub.a and P.sub.b are independently a 1,3,5-triaza-7-phosphadamantane (pta), monosulfonated triphenylphosphine (mtppms) or trisulfonated triphenylphosphine (mtppts); characterized in that the hydrogenation of hydrogen carbonate is carried out in such a way that carbon dioxide is present in the gas space.

4. The process according to claim 3, characterized in that the catalyst used is selected from the following: a) a catalyst according to the general formula [Ir(emim)(cod)(mtppms]+mtppts, where emim is 1-ethyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine; b) a catalyst according to the general formula [Ir(bmim)(cod)(mtppms]+mtppts, where bmim is 1-butyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine; c) a catalyst according to the general formula [Ir(hexmim)(cod)(mtppms]+mtppts, where hexmim is 1-hexyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine; d) a catalyst according to the general formula [Ir(2mim)(cod)(mtppms]+mtppts, where 2mim is 1,3-dimethyl-imidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine; e) a catalyst according to the general formula [Ir(Bnmim)(cod)(mtppms]+mtppts, where Bnmim is 1-benzyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine; f) a catalyst according to the general formula [Ir(emim)(cod)(mtppms]+pta, where emim is 1-ethyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and pta is 1,3,5-triaza-7-phosphadamantane; and g) a catalyst according to the general formula [Ir(emim)(cod)(mtppms]+mtppms, where emim is 1-ethyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine.

5. A method for storing hydrogen comprising the process of claim 3.

6. A method for storing hydrogen comprising the process of claim 4 wherein said storing is for a hydrogen battery.

7. The method of storing hydrogen of claim 5 wherein said storing is for hydrogen required to operate a fuel cell or other equipment requiring H.sub.2 and further optionally comprising releasing of said hydrogen to an extent necessary to operate said fuel cell or other equipment.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] FIG. 1: A catalytic cycle suitable for storing and releasing hydrogen, where the hydrogenation of hydrogen carbonate (HCO.sub.3.sup.?) is carried out in the presence of carbon dioxide (CO.sub.2) in the gas space.

[0043] FIG. 2: The change in pH with increasing CO.sub.2 pressure in 0.1 M NaHCO.sub.3 solution at 80? C.

[0044] FIG. 3: The change of the catalytic cycle number (TurnOver Number, hereinafter: TON) depending on the applied CO.sub.2 pressure using [Ir(emim)(cod)(mtppms]+mtppts catalyst in a batch reactor with a total volume of 100 ml.

[0045] FIG. 4: The change of the catalytic cycle number (TON) values as a function of pH using [Ir(emim)(cod)(mtppms]+mtppts catalyst in a batch reactor with a total volume of 100 ml.

[0046] FIG. 5: The change of the catalytic cycle number (TON) values as a function of the applied CO.sub.2 pressure?using [Ir(emim)(cod)(mtppms]+mtppts catalyst in a batch reactor with a total volume of 600 ml.

[0047] FIG. 6: The change of the catalytic cycle number (TON) values as a function of pH using [Ir(emim)(cod)(mtppms]+mtppts catalyst in a batch reactor with a total volume of 600 ml.

[0048] FIG. 7: Comparison of catalytic cycle number (TON) values obtained in Examples 4-7.

THE PROBLEM TO BE SOLVED BY THE INVENTION

[0049] The technical problem to be solved with the invention is to provide a reaction system suitable for the reversible storage of hydrogen gas that can be used in fuel cells or other equipment requiring H.sub.2, which enables the production of hydrogen gas (H.sub.2) free of CO.sub.x by-products by breaking down formates in an aqueous reaction system, as well as the hydrogenation of hydrogen carbonates produced in the same reaction system using the same catalyst in such a way, that the activity of the catalyst in the hydrogenation step of hydrogen carbonates is greater than the activity of the catalysts in the previously known hydrogenation process of hydrogen carbonates.

DISCOVERY ACCORDING TO THE INVENTION

[0050] Our invention achieves the mentioned goals with a solution based on the surprising discovery that if the hydrogenation of hydrogen carbonates is carried out in an aqueous reaction system with carbon dioxide present in the gas space, the activity of the catalyst according to the invention will be up to six times higherthe depending on the conditions used (properly chosen pressure and temperature)as in the case of hydrogenation of hydrogen carbonates in an aqueous reaction system with pure hydrogen.

BRIEF DESCRIPTION OF THE INVENTION

[0051] 1. A process for the hydrogenation of hydrogen carbonate (HCO.sub.3.sup.?), in an aqueous reaction system, preferably said hydrogen carbonate being selected from sodium hydrogen carbonate (NaHCO.sub.3), lithium hydrogen carbonate (LiHCO.sub.3), cesium hydrogen carbonate (CsHCO.sub.3) and potassium hydrogen carbonate (KHCO.sub.3) and for the production of formate, preferably formate selected from the group of sodium formate (HCOONa), lithium formate (HCOOLi), cesium formate (HCOOCs) and potassium formate (HCOOK), [0052] said process comprising bringing said hydrogen carbonate and a catalyst into contact with each other at an elevated temperature, preferably at 60-100? C., more preferably at 80? C., at a pressure of 1-1200 bar, preferably 10-100 bar; [0053] where the catalyst is a catalyst with the general formula [Ir(cod)(NHC)P.sub.a]+nP.sub.b, [0054] where in the formula [0055] Ir is iridium; [0056] cod is 1,5-cyclooctadiene; [0057] NHC is an N-heterocyclic carbene, preferably 1-R-3-methylimidazol-2-ylidene, where R is C1-C6 alkyl or benzyl; [0058] n is an integer from 1 to 4; and [0059] P.sub.a and P.sub.b are independently 1,3,5-triaza-7-phosphadamantane (pta), monosulfonated triphenylphosphine (mtppms) or trisulfonated triphenylphosphine (mtppts); [0060] wherein the hydrogenation of hydrogen carbonate is carried out in such a way that carbon dioxide is present in the gas space. [0061] 2. The process according to Point 1, wherein the catalyst used is selected from the following: [0062] a) a catalyst according to the formula [Ir(emim)(cod)(mtppms]+mtppts, wherein emim is 1-ethyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine; [0063] b) a catalyst according to the formula [Ir(bmim)(cod)(mtppms]+mtppts, wherein bmim is 1-butyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine; [0064] c) a catalyst according to the formula [Ir(hexmim)(cod)(mtppms]+mtppts, wherein hexmim is 1-hexyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine; [0065] d) a catalyst according to the formula [Ir(2mim)(cod)(mtppms]+mtppts, wherein 2mim is 1,3-dimethyl-imidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine; [0066] e) a catalyst according to the formula [Ir(Bnmim)(cod)(mtppms]+mtppts, wherein Bnmim is 1-benzyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine; [0067] f) a catalyst according to the formula [Ir(emim)(cod)(mtppms]+pta, wherein emim is 1-ethyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and pta is 1,3,5-triaza-7-phosphadamantane; and [0068] g) a catalyst according to the formula [Ir(emim)(cod)(mtppms]+mtppms, wherein emim is 1-ethyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine. [0069] 3. A process for decomposing a formate, preferably a formate selected from sodium formate (HCOONa), lithium formate (HCOOLi), cesium formate (HCOOCs) and potassium formate (HCOOK) in an aqueous reaction system and for producing hydrogen gas (H.sub.2) free of CO.sub.x by-products, and in the same reaction system, for the hydrogenation of the resulting hydrogen carbonate (HCO.sub.3.sup.?), preferably a hydrogen carbonate selected from the group of sodium hydrogen carbonate (NaHCO.sub.3), lithium hydrogen carbonate (LiHCO.sub.3), cesium hydrogen carbonate (CsHCO.sub.3) and potassium hydrogen carbonate (KHCO.sub.3) in an aqueous reaction system, thus for the production of a formate, preferably a formate selected from the group of sodium formate (HCOONa), lithium formate (HCOOLi), cesium formate (HCOOCs) and potassium formate (HCOOK); [0070] where the reactants and the reaction products are formed in a reversible reaction cycle by using the reaction system of the formate decomposition step and the bicarbonate hydrogenation step and by choosing the values of temperature, pressure and pH within the ranges specified below, and this reaction cycle is repeated the required number of times; [0071] where the formate decomposition step includes bringing the formate into contact with the catalyst in an aqueous reaction system, at an elevated temperature, preferably at 60-100? C., preferably at 80? C., preferably at a pH greater than 8, preferably at a pH=8.3?0.2, in an Ar gas atmosphere; [0072] where the hydrogenation step of the hydrogen carbonate includes bringing the hydrogen carbonate and a catalyst into contact with each other, at an elevated temperature, preferably at 60-100? C., more preferably at 80? C., under pressure of 1-1200 bar, preferably 10-100 bar; [0073] where the catalyst is a catalyst with the general formula [Ir(cod)(NHC)P.sub.a]+nP.sub.b, [0074] where in the formula [0075] Ir is iridium; [0076] cod is 1,5-cyclooctadiene; [0077] NHC is an N-heterocyclic carbene, preferably 1-R-3-methylimidazol-2-ylidene, where R is C1-C6 alkyl or benzyl; [0078] n is an integer from 1 to 4; and [0079] P.sub.a and P.sub.b mean independently a 1,3,5-triaza-7-phosphadamantane (pta), monosulfonated triphenylphosphine (mtppms) or trisulfonated triphenylphosphine (mtppts); [0080] according to which the hydrogenation of hydrogen carbonate is carried out in such a way that carbon dioxide is present in the gas space. [0081] 4. The process according to Point 3, according to which the catalyst used is selected from the following: [0082] a) a catalyst according to the general formula [Ir(emim)(cod)(mtppms]+mtppts, where emim is 1-ethyl-3-methylimidazol-2-ilydene, cod means 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine; [0083] b) a catalyst according to the general formula [Ir(bmim)(cod)(mtppms]+mtppts, where bmim is 1-butyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, .sub.mtppms is monosulfonated triphenylphosphine and .sub.mtppts is trisulfonated triphenylphosphine; [0084] c) a catalyst according to the general formula [Ir(hexmim)(cod)(mtppms]+mtppts, where hexmim is 1-hexyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine; [0085] d) a catalyst according to the general formula [Ir(2mim)(cod)(mtppms]+mtppts, where 2mim is 1,3-dimethyl-imidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine; [0086] e) a catalyst according to the general formula [Ir(Bnmim)(cod)(mtppms]+mtppts, where Bnmim is 1-benzyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine; [0087] f) a catalyst according to the general formula [Ir(emim)(cod)(mtppms]+pta, where emim is 1-ethyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and pta is 1,3,5-triaza-7-phosphadamantane; and [0088] g) a catalyst according to the general formula [Ir(emim)(cod)(mtppms]+mtppms, where emim is 1-ethyl-3-methylimidazol-2-ilydene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine. [0089] 5. Use of the process according to Point 3 for a hydrogen storage system. [0090] 6. The hydrogen storage system according to Point 4, which is a hydrogen battery. [0091] 7. Use of the hydrogen storage system according to Point 5 or 6 for storing the hydrogen required to operate a fuel cell or other equipment requiring H.sub.2, and optionally for releasing thereof to the extent of necessary.

DETAILED DESCRIPTION OF THE INVENTION

[0092] In the course of our work, we developed a process for the hydrogenation of hydrogen carbonate (HCO.sub.3.sup.?) in an aqueous reaction system in the presence of a catalyst, where the process includes bringing the aforementioned hydrogen carbonate, hydrogen and catalyst into contact with each other in such a way that carbon dioxide is present in the gas space, thus formate (HCOO.sup.?) is produced.

[0093] In the course of our work, we came to the surprising discovery that if the hydrogenation of hydrogen carbonate in an aqueous reaction system is carried out in such a way that carbon dioxide is present in the gas space, then the activity of the catalyst according to the invention will be up to six times higherdepending on the applied pressure and temperature , than in the case of hydrogenation of hydrogen carbonate in an aqueous reaction system with pure hydrogen.

[0094] Based on the above, the first aspect of our invention is to provide a process for the hydrogenation of a hydrogen carbonate (HCO.sub.3.sup.?), preferably sodium hydrogencarbonate (NaHCO.sub.3), lithium hydrogencarbonate (LiHCO.sub.3), cesium hydrogencarbonate (CsHCO.sub.3) or potassium hydrogencarbonate (KHCO.sub.3) in an aqueous reaction system in the presence of carbon dioxide in the gas space, and for the production of a formate, preferably sodium formate (HCOONa), lithium formate (HCOOLi), cesium formate (HCOOCs) or potassium formate (HCOOK), where the hydrogen carbonate and the catalyst are brought into contact with each other at an elevated temperature, preferably at 60-100? C., more preferably at 80? C., at a pressure of 1-1200 bar, preferably 10-100 bar.

[0095] In one embodiment of the invention, the amount of CO.sub.2 present in the gas space during the contact between said hydrogen carbonate and the catalyst is: p(CO.sub.2)>0 bar and p(CO.sub.2)?50 bar.

[0096] The mentioned catalyst is a catalyst of the general formula [Ir(cod)(NHC)P.sub.a]+nP.sub.b, which is suitable for the decomposition of formates in an aqueous reaction system and the production of hydrogen gas (H.sub.2) free of CO.sub.x by-products, or for the hydrogenation of hydrogen carbonates (HCO.sub.3.sup.?), where in the formula Ir is iridium, cod is 1,5-cyclooctadiene and NHC is an N-heterocyclic carbene, preferably 1-R-3-methylimidazol-2-ylidene, where R is C1-C6 alkyl or benzyl, P.sub.a and P.sub.b independently of each other are 1,3,5-triaza-7-phosphadamantane (pta), monosulfonated triphenylphosphine (mtppms) or trisulfonated triphenylphosphine (mtppts), and n is an integer from 1 to 4.

[0097] If the catalytic hydrogenation of bicarbonate into formate according to the invention and the catalytic decomposition of formate into bicarbonate are combined in such a way that the mentioned steps are carried out in the same reaction system, in an aqueous medium, in the presence of a water-soluble catalyst, i.e. the reactants and reaction products are formed in a reversible reaction cycle, then we can create a hydrogen storage system.

[0098] Based on the above, a further aspect of our invention is to provide a process for the decomposition of formate, preferably sodium formate (HCOONa), lithium formate (HCOOLi), cesium formate (HCOOCs) or potassium formate (HCOOK) in an aqueous reaction system and for the production of hydrogen gas (H.sub.2) free of CO.sub.x by-products, and for the hydrogenation of a hydrogen carbonate (HCO.sub.3.sup.?), preferably sodium hydrogen carbonate (NaHCO.sub.3), lithium hydrogen carbonate (LiHCO.sub.3), cesium hydrogen carbonate (CsHCO.sub.3) or potassium hydrogen carbonate (KHCO.sub.3), produced in the same reaction system, in an aqueous reaction system in the presence of carbon dioxide in the gas space to produce formate, preferably sodium formate (HCOONa), lithium formate (HCOOLi), cesium formate (HCOOCs) or potassium formate (HCOOK), where using the reaction system of the process for decomposing of formate and for hydrogenating hydrogen carbonate according to the invention, and by choosing the reaction conditions, such as temperature, pressure and pH, within the ranges given below, the reactants and reaction products are formed in a reversible reaction cycle, and this reaction cycle is repeated in the required number of times.

[0099] In the mentioned process, the formate decomposition step is carried out by bringing the formate, preferably sodium formate (HCOONa), lithium formate (HCOOLi), cesium formate (HCOOCs) or potassium formate (HCOOK) into contact with the catalyst in an aqueous reaction system at an elevated temperature, preferably at 60-100? C., preferably at 80? C., preferably at a pH greater than 8, preferably at a pH=8.3?0.2, in an Ar gas atmosphere.

[0100] A further aspect of our invention is a hydrogen storage system that includes the components described above in the invention. The hydrogen storage system according to the invention is preferably a hydrogen accumulator.

[0101] Another aspect of the invention is the use of the hydrogen storage system according to the invention to store the hydrogen required for the operation of a fuel cell (or other equipment requiring H.sub.2) and, where applicable, to release it as needed.

[0102] In the following, our invention is illustrated with examples for a better understanding, which, however, we do not intend to interpret as a limitation of the invention.

EXAMPLES

Example 1: Examining the Change in pH in NaHCO.SUB.3 .Solution as a Function of CO.SUB.2 .Pressure

[0103] We investigated the change of pH in a 0.1 M NaHCO.sub.3 solution at a temperature of 80? C. as a function of the applied CO.sub.2 pressure (Xiaolu Li, Cheng Peng, John P. Crawshaw, Geoffrey C. Maitland, J. P. Martin Trusler, Fluid Phase Equilibria, 2018, 458, 253-263).

[0104] The change in pH as a function of the CO.sub.2 pressure can be seen in FIG. 2, from which it can be clearly read that the pH of the solution shifts in an acidic direction as the CO.sub.2 pressure increases, however, the change is not lineareven a small amount of carbon dioxide causes a significant degree of acidification. It can be concluded that by using the highest CO.sub.2 pressure (50 bar) that we used, the pH practically drops from 8.2 to 5.7.

Example 2: Investigation of the Effect of CO.SUB.2 .on the Activity of the [Ir(Emim)(Cod)(Mtppms]+Mtppts Catalyst

[0105] The general formula of the tested catalyst is [Ir(emim)(cod)(mtppms]+mtppts, where emim is 1-ethyl-3-methylimidazol-2-ylidene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is triple sulfonated triphenylphosphine.

[0106] Reaction mixture: in a 100.0 mL constant temperature batch reactor (100 mL Series 5500 HP Compact Reactor manufactured by Parr Instruments): [0107] 20.0 ml solution volume, [0108] 80? C., [0109] [Ir]=0,0005 mol/dm.sup.3, [0110] [mtppms]=[Ir], [0111] [mtppts]=0,001 mol/dm.sup.3, [0112] [HCO.sub.3Na]=0.1 mol/dm.sup.3, [0113] p(H.sub.2)=50 bar, [0114] p(CO.sub.2)=varied in the range of 0-50 bar, [0115] reaction time=1 hour.

[0116] In summary, we found that by varying the CO.sub.2 pressure between 0 and 50 bar (under the reaction conditions used), the achieved TON value increases from 121 to 213, which means an almost two-fold increase in reaction rate. The formate concentration in the solution obtained after a reaction time of 1 hour without the use of CO.sub.2 is [HCO.sub.2.sup.?].sub.0=60.5 mM, and in a 50 bar CO.sub.2 atmosphere [HCO.sub.2.sup.?].sub.50=106.5 mM. From this, a total of 2.13 mmol HCO.sub.2 was formed in an atmosphere of 50 bar CO.sub.2, which is only 6.5% more than the originally measured amount of bicarbonate (2 mmol). The obtained measurement results are shown in FIG. 3.

[0117] From the data in FIG. 3, we determined the change in the catalytic cycle number as a function of pH using the data in FIG. 2 presented in Example 1 (change in pH with increasing CO2 pressure). The obtained results are shown in FIG. 4.

Example 3: Investigation of the Effect of CO.SUB.2 .on the Activity of the [Ir(Emim)(Cod)(Mtppms]+Mtppts Catalyst

[0118] Reaction mixture: in a 600.0 ml constant temperature batch reactor (600 ml Series 5500 HP Compact Reactor manufactured by Parr Instruments): [0119] 200.0 ml solution volume, [0120] 80? C., [0121] [Ir]=0,00005 mol/dm.sup.3, [0122] [mtppms]=[Ir], [0123] [mtppts]=0,0001 mol/dm.sup.3, [0124] [HCO.sub.3Na]=0.1 mol/dm.sup.3 [0125] p(H.sub.2)=50 bar, [0126] p(CO.sub.2)=varied in the range of 0-50 bar, [0127] reaction time=1 hour.

[0128] In summary, we found that by varying the CO.sub.2 pressure between 0 and 50 bar (under the reaction conditions used), the achieved TON value increases from 260 to 576, which means a more than two-fold increase in speed. The formate concentration in the solution obtained after a reaction time of 1 hour without the use of CO.sub.2 is HCO.sub.2.sup.?].sub.0=13.0 mM, and in a 50 bar CO.sub.2 atmosphere [HCO.sub.2].sub.50=28.8 mM. In other words, the resulting formate concentration does not approach the measured bicarbonate concentration (100.0 mM) in any case, the maximum degree of bicarbonate conversion (conversion) is 28.8%. The obtained measurement results are shown in FIG. 5.

[0129] From the data in FIG. 5, we determined the change in the catalytic cycle number as a function of pH by using the data in FIG. 2 mentioned in Example 1 (change in pH with increasing CO.sub.2 pressure). The obtained results are shown in FIG. 6.

Example 4: Investigation of the Effect of CO.SUB.2 .on the Activity of the Catalyst [Ir(Bmim)(Cod)(Mtppms]+Mtppts

[0130] The general formula of the tested catalyst is [[Ir(bmim)(cod)(mtppms]+mtppts, where bmim is 1-butyl-3-methylimidazol-2-ylidene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine.

[0131] Reaction mixture: in a 100.0 and 600.0 ml constant temperature batch reactor (100 and 600 ml Series 5500 HP Compact Reactor manufactured by Parr Instruments): [0132] 20.0 and 200.0 ml solution volume, [0133] 80? C., [0134] [Ir]=0,0005 mol/dm.sup.3 and 0,00005 mol/dm.sup.3, [0135] [mtppms]=[Ir], [0136] [mtppts]=0,001 mol/dm.sup.3 and 0,0001 mol/dm.sup.3, [0137] [HCO.sub.3Na]=0.1 mol/dm.sup.3 [0138] p(H.sub.2)=50 bar, [0139] p(CO.sub.2)=0 or 50 bar [0140] reaction time=1 hour.

TABLE-US-00002 TABLE 1 The obtained catalytic cycle number (TON) values TON 50 bar H.sub.2 50 bar H.sub.2 + 50 bar CO.sub.2 100 ml reactor 144 212 600 ml reactor 368 808

[0141] In summary, we found that by changing the pressure of CO.sub.2 from 0 to 50 bar (under the reaction conditions used), the achieved TON value increases from 144 to 212 and from 368 to 808, which also in this case is due to the effect of CO.sub.2 means a significant increase in reaction rate.

Example 5: Investigation of the Effect of CO.SUB.2 .on the Activity of the [Ir(Hexmim)(Cod)(Mtppms]+Mtppts Catalyst

[0142] The general formula of the investigated catalyst is [Ir(hexmim)(cod)(mtppms]+mtppts, where hexmim is 1-hexyl-3-methylimidazol-2-ylidene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine.

[0143] Reaction mixture: in a 100.0 and 600.0 ml constant temperature batch reactor (100 and 600 ml Series 5500 HP Compact Reactor manufactured by Parr Instruments): [0144] 20.0 and 200.0 ml solution volume, [0145] 80? C., [0146] [Ir]=0,0005 mol/dm.sup.3 and 0,00005 mol/dm.sup.3, [0147] [mtppms]=[Ir], [0148] [mtppts]=0,001 mol/dm.sup.3 and 0,0001 mol/dm.sup.3, [0149] [HCO.sub.3Na]=0.1 mol/dm.sup.3 [0150] p(H.sub.2)=50 bar, [0151] p(CO.sub.2)=0 or 50 bar [0152] reaction time=1 hour.

TABLE-US-00003 TABLE 2 The obtained catalytic cycle number (TON) values TON 50 bar H.sub.2 50 bar H.sub.2 + 50 bar CO.sub.2 100 ml reactor 134 204 600 ml reactor 285 522

[0153] In summary, we found that by changing the CO.sub.2 pressure from 0 to 50 bar (under the reaction conditions used), the achieved TON value increases from 134 to 204 and from 285 to 522, which in this case is also due to the effect of CO.sub.2 means a significant increase in reaction rate.

Example 6: Investigation of the Effect of CO.SUB.2 .on the Activity of the Catalyst [Ir(2Mim)(Cod)(Mtppms]+Mtppts

[0154] The general formula of the tested catalyst is [Ir(2mim)(cod)(mtppms]+mtppts, where 2mim is 1,3-dimethylimidazol-2-ylidene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine.

[0155] Reaction mixture: in a 100.0 and 600.0 ml constant temperature batch reactor (100 and 600 ml Series 5500 HP Compact Reactor manufactured by Parr Instruments): [0156] 20.0 and 200.0 ml solution volume, [0157] 80? C., [0158] [Ir]=0,0005 mol/dm.sup.3 and 0,00005 mol/dm.sup.3, [0159] [mtppms]=[Ir], [0160] [mtppts]=0,001 mol/dm.sup.3 and 0,0001 mol/dm.sup.3, [0161] [HCO.sub.3Na]=0.1 mol/dm.sup.3 [0162] p(H.sub.2)=50 bar, [0163] p(CO.sub.2)=0 or 50 bar [0164] reaction time=1 hour.

TABLE-US-00004 TABLE 3 The obtained catalytic cycle number (TON) values TON 50 bar H.sub.2 50 bar H.sub.2 + 50 bar CO.sub.2 100 ml reactor 158 256 600 ml reactor 228 786

[0165] In summary, we found that by changing the CO.sub.2 pressure from 0 to 50 bar (under the reaction conditions used), the achieved TON value increases from 158 to 256 and from 228 to 786, which is also in this case the effect of CO.sub.2 means a significant increase in reaction rate.

Example 7: Investigation of the Effect of CO.SUB.2 .on the Activity of the Catalyst [Ir(Bnmim)(Cod)(Mtppms]+Mtppts

[0166] The general formula of the tested catalyst is [Ir(Bnmim)(cod)(mtppms]+mtppts, where Bnmim is 1-benzyl-3-methylimidazol-2-ylidene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and mtppts is trisulfonated triphenylphosphine.

[0167] Reaction mixture: in a 100.0 and 600.0 ml constant temperature batch reactor (100 and 600 ml Series 5500 HP Compact Reactor manufactured by Parr Instruments): [0168] 20.0 and 200.0 ml solution volume, [0169] 80? C., [0170] [Ir]=0,0005 mol/dm.sup.3 and 0,00005 mol/dm.sup.3, [0171] [mtppms]=[Ir], [0172] [mtppts]=0,001 mol/dm.sup.3 and 0,0001 mol/dm.sup.3, [0173] [HCO.sub.3Na]=0.1 mol/dm.sup.3 [0174] p(H.sub.2)=50 bar, [0175] p(CO.sub.2)=0 or 50 bar [0176] reaction time=1 hour.

TABLE-US-00005 TABLE 4 The obtained catalytic cycle number (TON) values TON 50 bar H.sub.2 50 bar H.sub.2 + 50 bar CO.sub.2 100 ml reactor 121 262 600 ml reactor 361 1119

[0177] In summary, we found that by changing the CO.sub.2 pressure from 0 to 50 bar (under the reaction conditions used), the achieved TON value increases from 121 to 262 and from 361 to 1119, which is also in this case the effect of CO.sub.2 means a significant increase in reaction rate.

Example 8: Investigation of the Effect of CO.SUB.2 .on the Activity of the [Ir(Emim)(Cod)(Mtppms]+Pta Catalyst

[0178] The general formula of the tested catalyst is [Ir(emim)(cod)(mtppms]+pta, where emim is 1-ethyl-3-methylimidazol-2-ylidene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine and pta is 1,3,5-triaza-7-phosphadamantane.

[0179] Reaction mixture: in a 100.0 and 600.0 ml constant temperature batch reactor (100 and 600 ml Series 5500 HP Compact Reactor manufactured by Parr Instruments): [0180] 20.0 and 200.0 ml solution volume, [0181] 80? C., [0182] [Ir]=0,0005 mol/dm.sup.3 and 0,00005 mol/dm.sup.3, [0183] [mtppms]=[Ir], [0184] [pta]=0,001 mol/dm.sup.3 and 0,0001 mol/dm.sup.3, [0185] [HCO.sub.3Na]=0.1 mol/dm.sup.3 [0186] p(H.sub.2)=50 bar, [0187] p(CO.sub.2)=0 or 50 bar reaction time=1 hour.

TABLE-US-00006 TABLE 5 The obtained catalytic cycle number (TON) values TON 50 bar H.sub.2 50 bar H.sub.2 + 50 bar CO.sub.2 100 ml reactor 67 108 600 ml reactor 260 1084

[0188] In summary, we found that by changing the CO.sub.2 pressure from 0 to 50 bar (under the reaction conditions used), the achieved TON value increases from 67 to 108 and from 260 to 1084, which in this case is also due to the effect of CO.sub.2 means a significant increase in reaction 25 rate.

Example 9: Investigation of the Effect of CO.SUB.2 .on the Activity of the [Ir(Emim)(Cod)(Mtppms]+Mtppms Catalyst

[0189] The general formula of the tested catalyst is [Ir(emim)(cod)(mtppms]+mtppms, where emim is 1-ethyl-3-methylimidazol-2-ylidene, cod is 1,5-cyclooctadiene, mtppms is monosulfonated triphenylphosphine. [0190] Reaction mixture: in a 100.0 and 600.0 ml constant temperature batch reactor (100 and 600 ml Series 5500 HP Compact Reactor manufactured by Parr Instruments): [0191] 20.0 and 200.0 ml solution volume, [0192] 80? C., [0193] [Ir]=0,0005 mol/dm.sup.3 and 0,00005 mol/dm.sup.3, [0194] [mtppms]=0.0015 mol/dm.sup.3 and 0,00015 mol/dm.sup.3, [0195] [HCO.sub.3Na]=0.1 mol/dm.sup.3 [0196] p(H.sub.2)=50 bar, [0197] p(CO.sub.2)=0 or 50 bar reaction time=1 hour.

TABLE-US-00007 TABLE 6 The obtained catalytic cycle number (TON) values TON 50 bar H.sub.2 50 bar H.sub.2 + 50 bar CO.sub.2 100 ml reactor 263 320 600 ml reactor 325 2050

[0198] In summary, we found that by changing the CO.sub.2 pressure from 0 to 50 bar (under the applied reaction conditions), the achieved TON value increases from 263 to 320 and from 325 to 2050, which in this case is also due to the effect of CO.sub.2 means a significant increase in speed.

[0199] FIG. 7 provides a visual presentation of the results presented in Examples 4-9. The results clearly prove that both in the case of changing the carbene ligand and the phosphine ligand, it can be proven that in the presence of CO.sub.2 (under the given conditions) the rate of hydrogenation of bicarbonate increases several times (2-6 times).

INDUSTRIAL APPLICABILITY

[0200] The process for the hydrogenation of hydrogen carbonate, which is the subject of our invention, provides an opportunity to provide a renewable energy source, the basis of which is a process for the catalytic decomposition of formate in an aqueous reaction system and the production of hydrogen gas free of CO.sub.x by-products, and for the catalytic hydrogenation of hydrogen carbonate produced in the same reaction system in an aqueous reaction system in the presence of carbon dioxide in the gas space, and thus to produce the corresponding formate.