Formic acid production method

Abstract

To provide a method for producing stable formic acid from hydrogen and carbon dioxide. [Solution] A method for producing formic acid from hydrogen and carbon dioxide in the presence of a catalyst, using a reaction medium having a water content of 10% by mass or less, or without using a reaction medium, wherein the catalyst contains an organic iridium complex or the organic ruthenium complex, the partial pressure of the hydrogen is 0.05 MPa or more, and the partial pressure of the carbon dioxide is 0.05 MPa or more.

Description

Technical Field

[0001] The present application relates to a method for producing formic acid from hydrogen and carbon dioxide using a catalyst. The present application claims priority based on Japanese Patent Application No. 2023-010364 filed in Japan on January 26, 2023, the content of which is incorporated herein by reference. Background Art

[0002] Hydrogen has attracted attention as a next-generation fuel. In Japan, various initiatives are being implemented toward the realization of a hydrogen society. In recent years, a method for obtaining hydrogen and carbon dioxide by dehydrogenation of formic acid using an iridium catalyst has been reported (Patent Document 1). Furthermore, it has been reported that the same volume of hydrogen and carbon dioxide can be obtained from formic acid at a pressure of up to 157 MPa without using a compressor (Patent Document 2, Non-Patent Document 1). Overseas, power generation using fuel cells that employ high-pressure gas containing hydrogen and carbon dioxide obtained from formic acid has begun to be put into practical use. However, there are problems in recovering carbon dioxide contained in the high-pressure gas, so the utility value of formic acid as a hydrogen carrier is low in Japan.

[0003] The inventors of the present application have developed a method for easily separating hydrogen and carbon dioxide by utilizing the high-pressure condition of gas obtained from formic acid (Patent Document 1, Patent Document 2, and Non-Patent Document 2). While hydrogen is used as energy, development of effective utilization methods for carbon dioxide is expected. One of the effective utilization methods for carbon dioxide is a technology for regenerating formic acid from hydrogen and carbon dioxide. If formic acid is regenerated from hydrogen obtained from renewable energy such as solar energy and carbon dioxide separated and recovered from high-pressure gas obtained from formic acid, hydrogen can be stored in the form of formic acid without discharging carbon dioxide.

[0004] However, the reaction for obtaining formic acid from hydrogen and carbon dioxide has a high energy barrier. For this reason, the energy barrier is lowered by producing formate from hydrogen and carbon dioxide under alkaline conditions (Non-Patent Document 3). Then, in order to obtain formic acid from the formate produced from hydrogen and carbon dioxide, the formate is neutralized with sulfuric acid or the like and then further distilled (Non-Patent Document 4). In order to eliminate such complicated processes, it is desired to realize a method for stably producing formic acid instead of formate from hydrogen and carbon dioxide.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0006]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

[0007] This application was made in view of these circumstances, and aims to provide a method for producing stable formic acid from hydrogen and carbon dioxide. [Means for solving the problem]

[0008] The inventors of this invention discovered that the aqueous medium used to produce formic acid from hydrogen and carbon dioxide accelerates the decomposition reaction of formic acid back into hydrogen and carbon dioxide. They also found that without the use of an aqueous medium, the decomposition reaction from formic acid to hydrogen and carbon dioxide slows down and does not generate high-pressure gas. Furthermore, they discovered that formic acid is produced when hydrogen and carbon dioxide are mixed under high pressure under anhydrous conditions in the presence of various organometallic complex catalysts or solid catalysts. Therefore, they found that formic acid is efficiently produced when hydrogen and carbon dioxide are reacted under anhydrous conditions—that is, in the absence of an aqueous medium or in a medium containing very little moisture—under high pressure of 0.5 MPa or higher, in the presence of various organometallic complex catalysts or metal-supported solid catalysts. Based on these findings, the inventors further developed and completed the present invention.

[0009] A method for producing formic acid according to one embodiment of the present invention is a method for producing formic acid from hydrogen and carbon dioxide in the presence of a catalyst, using a reaction medium having a water content of 10% by mass or less, or without using a reaction medium, wherein the catalyst contains an organic iridium complex and an organic ruthenium complex, the partial pressure of hydrogen is 0.05 MPa or higher, and the partial pressure of carbon dioxide is 0.05 MPa or higher.

[0010] Another embodiment of the present invention relates to a method for producing formic acid from hydrogen and carbon dioxide in the presence of a catalyst, using a reaction medium having a water content of 10% by mass or less, or without using a reaction medium, wherein the catalyst comprises a support and one or more metals supported on the support: chromium, manganese, iron, cobalt, nickel, copper, zinc, molybdenum, ruthenium, rhodium, palladium, silver, tungsten, rhenium, osmium, iridium, platinum, and gold, and the partial pressure of hydrogen is 0.05 MPa or higher and the partial pressure of carbon dioxide is 0.05 MPa or higher. [Effects of the Invention]

[0011] In this invention, hydrogen and carbon dioxide are reacted at a predetermined pressure or higher using a reaction medium with a water content of 10% by mass or less, or without a reaction medium, in the presence of a predetermined catalyst. Therefore, according to this invention, stable formic acid, rather than a formate salt, can be produced from hydrogen and carbon dioxide. [Brief explanation of the drawing]

[0012] [Figure 1] This graph shows the relationship between the partial pressure of carbon dioxide and TOF in Example 4. [Figure 2] This graph shows the relationship between reaction time and TON in Example 5. [Figure 3] This graph shows the relationship between the partial pressures of hydrogen and carbon dioxide and TON in Example 7. [Figure 4] This graph shows the relationship between reaction time and TON in Example 7. [Modes for carrying out the invention]

[0013] The embodiment of the present invention provides a method for producing formic acid from hydrogen and carbon dioxide in the presence of a predetermined catalyst and using a reaction medium having a water content of 10% by mass or less, or without using a reaction medium. The formic acid produced is not a formate salt and is stable. "Not a formate salt" means that it is HCO2H and HCO2 - Na + This means that it is not a salt of such as. Stable formic acid is defined as formic acid in which the decrease in concentration is 1% by mass or less even after 72 hours at atmospheric pressure and 25°C in a glass or resin container under conditions without a catalyst. This specified catalyst may contain an organic iridium complex or an organic ruthenium complex. Furthermore, this specified catalyst may comprise a carrier and a specified metal supported on the carrier. This specified metal is one or more of the following: chromium, manganese, iron, cobalt, nickel, copper, zinc, molybdenum, ruthenium, rhodium, palladium, silver, tungsten, rhenium, osmium, iridium, platinum, and gold. Note that this specified metal may be an alloy.

[0014] These catalysts are preferably uniformly dissolved or dispersed in a reaction medium that contains little to no water, i.e., a reaction medium with a water content of 10% by mass or less. Here, water content refers to the ratio of the mass of water to the total mass of the reaction medium. Note that "a reaction medium that contains little to no water" includes a reaction medium with a water content of 0% by mass, i.e., a reaction medium that contains no water. In order to suppress the re-decomposition of the formic acid produced in the presence of the catalyst to generate hydrogen and carbon dioxide, the water content (content ratio) of the total mass of the reaction medium is preferably 0% by mass or more and 5% by mass or less, more preferably 0% by mass or more and 1% by mass or less, and even more preferably 0% by mass or more and 0.5% by mass or less. In addition, organic compound liquids, subcritical fluids, and supercritical fluids can be used as reaction mediums.

[0015] Furthermore, these catalysts may be dispersed or in contact with a reaction medium that contains little or no water, as solids or gels in which organoiridium complexes and organoruthenium complexes are supported on polymer compounds, or as solids in various forms such as powders, wires, or films. These catalysts may also be used in combination. When formic acid is produced without a reaction medium, hydrogen and carbon dioxide should be brought into contact with these catalysts. The origin and purity of the hydrogen and carbon dioxide used are not particularly limited. In addition, when formic acid is produced without a reaction medium, depending on the partial pressure of carbon dioxide, it may become a subcritical or supercritical fluid, and this carbon dioxide fluid may function as a reaction medium.

[0016] Examples of organoiridium and organoruthenium complexes are those represented by the following general formula (1), where M is iridium or ruthenium. A and B are ligands that independently contain nitrogen, carbon, oxygen, or sulfur as coordinating atoms to M. A and B may be the same or different. A⌒B is a bidentate ligand that coordinates to M. L is an aromatic anionic ligand or an aromatic ligand. The aromatic ring of this aromatic anionic ligand or aromatic ligand may have one or more substituents. Z is any ligand or is absent. [C] n- It is a counterion when n≠0, and does not exist when n=0. m and n are integers.

[0017] [ka]

[0018] [C] is an anion. n- For example, hexafluoride phosphate ion (PF6 - ), difluorophosphate ion (F2PO2 - ), tetrafluoroborate ion (BF4 - ), bis(fluorosulfonyl)imide ion, bis(trifluorosomethansulfonyl)imide ion, hydroxide ion (OH -), acetate ion, carbonate ion, phosphate ion, sulfate ion, nitrate ion, fluoride ion, chloride ion, bromide ion, iodide ion and other halide ions, hypofluorite ion, hypochlorite ion, hypobromite ion, hypoiodite ion and other hypohalite ions, fluorite ion, chlorite ion, bromite ion, iodite ion and other halite ions, fluorate ion, chlorate ion, bromate ion, iodate ion and other halate ions, perfluorate ion, perchlorate ion, perbromate ion, periodate ion and other perhalate ions, trifluoromethanesulfonate ion (OSO2CF3 - ), tetrakis(pentafluorophenyl)borate ion [B(C6F5)4 - , and combinations of two or more of these.

[0019] Examples of [C], which is a cation, n- include lithium ion, magnesium ion, sodium ion, potassium ion, calcium ion, barium ion, strontium ion, yttrium ion, scandium ion, lanthanoid ions and other various metal ions, hydrogen ion, and combinations of two or more of these.

[0020] Examples of substituents substituting an aromatic ring of L which is an aromatic anionic ligand or an aromatic ligand include a hydroxy group (-OH), a nitro group (-NO2), a halogen group (-X), a carboxyl group (-COOH), a sulfonic group (-SO3H), an alkyl group which may have one or more substituents, an alkoxy group (-OR), an alkylthio group (-SR), an amino group (-NRR'), an alkylamino group, an amide group (-CONRR'), an ester group (-COOR), and a phenyl group. When a plurality of substituents substituting the aromatic ring of L are present, these substituents may be the same or different.

[0021] The organic iridium complex or organic ruthenium complex represented by general formula (1) is preferably represented by any of the following general formulas (2) to (6) and general formulas (2') to (6'). In the organic iridium complex or organic ruthenium complex represented by any of the following general formulas (2) to (6) and general formulas (2') to (6'), [C] n- The C represents a counterion, while the other C, i.e., the C coordinated to M, represents carbon. Also, the N and O coordinated to M represent nitrogen and oxygen, respectively.

[0022] [ka]

[0023] The organoiridium complex and organoruthenium complex represented by general formula (1) are more preferably represented by any of the following general formulas (7) and (8), and general formulas (7') and (8'). That is, L is more preferably a pentamethylcyclopentadienyl ligand or a p-cymene ligand. Q is nitrogen (N), oxygen (O), or carbon (C).

[0024] [ka]

[0025] [ka]

[0026] In organoiridium and organoruthenium complexes represented by any of general formulas (1) to (8), general formula (7'), and general formula (8'), examples of ligand Z include water molecules, hydride ions, alkoxide ions, hydroxide ions, halide ions, carbonate ions, trifluoromethanesulfonate ions, sulfate ions, nitrate ions, formate ions, and acetate ions. Examples of alkoxide ions include alkoxide ions derived from methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, isobutyl alcohol, and tert-butyl alcohol.

[0027] The organic iridium complex represented by general formula (7) and the organic ruthenium complex represented by general formula (7') are preferably represented by any of the following general formulas (9) to (12) and general formulas (9') to (12'). However, X7~X 21 and X 22 ~X 25 These are, independently of each other, nitrogen, carbon, oxygen, or sulfur. Note that X h (h is an integer between 7 and 21) or X i When (i is an integer between 22 and 25) is oxygen or sulfur, X h or X i R that joins j (j is an integer between 1 and 21) and R k (where k is an integer between 22 and 25) does not exist. Y1~Y6, Y 7 , and Y 8 These are, independently of each other, nitrogen or carbon.

[0028] R1~R 21 and R 22 ~R 26These are, independently of each other, a hydrogen atom, a hydroxyl group, a nitro group, a halogen group, a carboxyl group, or a sulfone group, or an alkyl group, alkoxy group, alkylthio group, amino group, alkylamino group, amide group, ester group, or phenyl group which may have one or more substituents. These substituents are a hydroxyl group or an oxyanion group (-O - ) is preferable. Adjacent R1~R 21 and R 22 ~R 26 They may form rings with each other. The bonds between the ligand-forming elements are single or double bonds. The heterocycle may be aromatic or non-aromatic. In general formulas (12) and (12'), Q is oxygen, sulfur, or selenium.

[0029] [ka]

[0030] [ka]

[0031] In formulas (9) to (12) and (9') to (12'), the ring containing N is preferably an aromatic heterocycle. R1 to R 21 and R 22 ~R 25 These groups are preferably electron-donating groups, and more preferably are hydrogen atoms, hydroxyl groups, amino groups, monoalkylamino groups having 1 to 6 carbon atoms, dialkylamino groups having 2 to 12 carbon atoms, nitrogen-containing saturated heterocyclic groups having 3 to 6 carbon atoms (e.g., azilidinyl group, azetidinyl group, pyrrolidinyl group, piperidyl group, etc.), and alkoxy groups having 1 to 3 carbon atoms. 26 The group is preferably an electron-donating group, more preferably an aromatic hydrocarbon group having 6 to 10 carbon atoms, and even more preferably a phenyl group or a naphthyl group. Counter-ion [C] n-Preferred anions include sulfate anions, chloride anions, hexafluorophosphate anions, nitrate anions, tetrafluoroborate anions, and bis(trifluoromethanesulfonate)imide anions. In formulas (9) and (9'), X8 is preferably a nitrogen atom, and X 11 It is preferable that it is a nitrogen atom. In equations (10) and (10'), X 14 It is preferable that X is a nitrogen atom. 16 ~X 19 It is preferable that it is a carbon atom. In equations (11) and (11'), X 14 ~X 16 It is preferably a carbon atom, X 17 X is preferably a carbon atom or a nitrogen atom. 18 X is preferably a carbon atom or a nitrogen atom. 19 ~X 21 It is preferable that it is a carbon atom. In equations (12) and (12'), X 22 ~X 25 It is preferable that it is a carbon atom.

[0032] The organic iridium complex and the organic ruthenium complex may be supported on a polymer compound by covalent or ionic bonds (hereinafter sometimes referred to as the "immobilized catalyst"). Examples of polymer compounds include polystyrene, polyethylene, polyethyleneimine, polyacrylic acid, polymethyl methacrylate, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, polyester, polyamide, polylactic acid, and polylysine. Among these, the polymer compound is preferably one or more of polyethyleneimine, polyacrylic acid, polymethyl polyacrylate, polyvinyl alcohol, polyvinylpyrrolidone, and polylysine. In the immobilized catalyst, the organic iridium complex and the organic ruthenium complex are preferably bonded to the side chains of these polymer compounds. Furthermore, in the immobilized catalyst, the organic iridium complex and the organic ruthenium complex may form a crosslinking structure that crosslinks these polymer compounds. When the polymer compound is polyethyleneimine, the organic iridium complex and the organic ruthenium complex are preferably those represented by formula (11), where R 14 ~R 17 At least one of them is bonded to the secondary amino group of the polyethyleneimine molecule via a monoaminoalkylene group having 1 to 10 carbon atoms, and R 18 ~R 21 It is more preferable that at least one of these is bonded to the carboxyl group of the other polyethyleneimine molecule via a monoaminoalkylene group having 1 to 10 carbon atoms. When the polymer compound is polyacrylic acid, the organic iridium complex and organic ruthenium complex are preferably those represented by formulas (11) and (11'), where R 14 ~R 17 At least one of them is bonded to the carboxyl group of the polyacrylic acid molecule via a diaminoalkylene group having 1 to 10 carbon atoms, and R 18 ~R 21It is more preferable that at least one of these is bonded to the carboxyl group of another polyacrylic acid molecule via a diaminoalkylene group having 1 to 10 carbon atoms. These polymers may also have crosslinking structures other than those derived from organic iridium complexes or organic ruthenium complexes. Examples of crosslinking agents that form such crosslinking structures include methylenebisacrylamide. The mass of iridium (as atomic weight 192.2) is preferably 0.001 to 30% by mass, more preferably 0.01 to 20% by mass, and most preferably 0.05 to 10% by mass, relative to the total mass of the immobilized catalyst. When the mass percentage of iridium in the constituent units having the organic iridium complex is within the above range, a reaction field for producing formic acid can be provided. The mass of ruthenium (as atomic weight 101.1) is preferably 0.001 to 30% by mass, more preferably 0.01 to 20% by mass, and most preferably 0.05 to 10% by mass, relative to the total mass of the immobilized catalyst. If the mass percentage of ruthenium in the constituent units having an organic ruthenium complex is within the above range, a reaction field for producing formic acid can be provided.

[0033] The iridium-containing moiety constituting the aforementioned organic iridium complex is preferably represented by any of the following general formulas (13) to (19). The ruthenium-containing moiety constituting the aforementioned organic ruthenium complex is preferably represented by one of the following general formulas (13') to (19').

[0034] [ka]

[0035] [ka]

[0036] R, R 1 , and R 2These are, independently of each other, a hydrogen atom, a hydroxyl group, a nitro group, a halogen group, a carboxyl group, or a sulfone group, or an alkyl group, alkoxy group, alkylthio group, amino group, alkylamino group, amide group, ester group, or phenyl group which may have one or more substituents. Adjacent R, R 1 , and R 2 They may form a ring with each other.

[0037] The catalyst may comprise a support and a predetermined metal supported on the support (hereinafter also referred to as "solid catalyst"). This predetermined metal is one or more selected from the group consisting of chromium, manganese, iron, cobalt, nickel, copper, zinc, molybdenum, ruthenium, rhodium, palladium, silver, tungsten, rhenium, osmium, iridium, platinum, and gold. This predetermined metal may be an alloy. Examples of specific metal and support combinations include Pd / C, Pd-Au / C, Pd-Ag / C; Pd / rGO, Pd-Au / rGO, Pd-Ag / rGO; Pd / PDA / rGO, Pd-Au / PDA / rGO, Pd-Ag / PDA / rGO, etc. Here, Pd / C is a carbon support on which palladium is supported, Pd-Au / C is a carbon support on which an alloy of palladium and gold is supported, and Pd-Ag / C is a carbon support on which an alloy of palladium and silver is supported. Pd / rGO is a graphene oxide support on which palladium is supported, Pd-Au / rGO is a graphene oxide support on which an alloy of palladium and gold is supported, and Pd-Ag / rGO is a graphene oxide support on which an alloy of palladium and silver is supported. Pd / PDA / rGO is a material in which palladium is supported on a support made of graphene oxide and paradiaminobenzene. Pd-Au / PDA / rGO is a material in which a palladium-gold alloy is supported on a support made of graphene oxide and paradiaminobenzene. Pd-Ag / PDA / rGO is a material in which a palladium-silver alloy is supported on a support made of graphene oxide and paradiaminobenzene. In the palladium-gold alloy, the mass ratio expressed as palladium:gold is preferably 1:4 to 4:1, more preferably 2:3 to 3:2, and even more preferably 1:1. In the palladium-silver alloy, the mass ratio expressed as palladium:silver is preferably 2:3 to 3:2, and even more preferably 1:1. The mass ratio expressed as [metal or alloy]:[total support] is preferably 1:99 to 10:90, more preferably 3:97 to 7:93, and even more preferably 5:95.

[0038] When producing formic acid using a catalyst comprising a carrier and a predetermined metal supported on the carrier, the predetermined metal is preferably one or more of gold, silver, and platinum. Examples of carriers include carbon materials such as carbon and carbon resin, alumina, silica, zeolite, mesoporous silica, titania, zirconia, magnesia, and one or more of ceria. Among these, the carrier is preferably one or more of carbon materials, alumina, and silica. The particle size of the supported metal is preferably 1 nm to 1 μm, and more preferably 5 nm to 500 μm.

[0039] The reaction media used when producing formic acid by reacting hydrogen and carbon dioxide include pentane, hexane, heptane, octane, nonane, decane, toluene, styrene, xylene, mesitylene, methanol, ethanol, trifluoroethanol, pentafluoroethanol, propanol, isopropyl alcohol, hexafluoroisopropanol, butanol, isobutyl alcohol, pentanol, isopentyl alcohol, hexanol, cyclohexanol, 1,4-dioxane, tetrahydrofuran, methyltetrahydrofuran, diethyl ether, ethylene glycol, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, acetic acid, trifluoroacetic acid, and acetic acid. Examples include isobutyl, isopropyl acetate, isopentyl acetate, ethyl acetate, butyl acetate, propyl acetate, acetone, methyl ethyl ketone, cyclohexanone, dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, N,N-diethylacetamide, tetramethylurea, tetraethylurea, dimethyl sulfoxide, dichloromethane, chloroform, dichloroethane, tetrachloroethane, chlorobenzene, dichlorobenzene, trichlorobenzene, phenol, dimethyl sulfoxide, and combinations of two or more of these. Among these, a reaction medium that dissolves the organic iridium complex and organic ruthenium complex is preferred in order to better exhibit the catalytic function of the organic iridium complex and organic ruthenium complex. The water content of these organic solvents is preferably 10% by mass.

[0040] The pressures of hydrogen and carbon dioxide in the production of formic acid are not particularly limited, but for efficiency, the hydrogen pressure, i.e., the partial pressure of hydrogen, is 0.05 MPa or higher, the carbon dioxide pressure, i.e., the partial pressure of carbon dioxide, is 0.05 MPa or higher, and the total pressure is 0.1 MPa or higher. Preferably, the partial pressure of hydrogen is 0.5 MPa or higher and the partial pressure of carbon dioxide is 0.4 MPa or higher. More preferably, the partial pressure of hydrogen is 0.5 MPa or higher, the partial pressure of carbon dioxide is 1 MPa or higher, and the total pressure is 1.5 MPa or higher. Even more preferably, the partial pressure of hydrogen is 0.5 MPa or higher and the partial pressure of carbon dioxide is 3 MPa or higher. Most preferably, the partial pressure of hydrogen is 0.5 MPa or higher, the partial pressure of carbon dioxide is 7.2 MPa or higher, and the total pressure is 8 MPa or higher. The partial pressure of hydrogen, the partial pressure of carbon dioxide, and the upper limit of the total pressure depend on the pressure resistance of the reaction vessel, etc. For example, the total pressure can be adapted to 200 MPa or higher, but if the pressure is too high, it can be adapted to 160 MPa or higher, more preferably 80 MPa or higher, even more preferably 50 MPa or higher, and most preferably 35 MPa or higher. Specifically, the partial pressure of hydrogen is preferably 0.05 MPa to 100 MPa, preferably 0.05 MPa to 80 MPa, preferably 0.05 MPa to 40 MPa, even more preferably 0.05 MPa to 34.95 MPa, more preferably 0.5 MPa to 34.5 MPa, even more preferably 0.5 MPa to 34.0 MPa, particularly preferably 0.5 MPa to 32.0 MPa, and most preferably 0.5 MPa to 27.8 MPa. The partial pressure of carbon dioxide is preferably 0.05 MPa to 100 MPa, more preferably 0.4 MPa to 120 MPa, even more preferably 1 MPa to 160 MPa, particularly preferably 3 MPa to 165.05 MPa, and most preferably 7.2 MPa to 165.5 MPa. The total pressure is preferably 0.1 MPa to 200 MPa, more preferably 1.5 MPa to 200 MPa, even more preferably 6 MPa to 200 MPa, even more preferably 8 MPa to 200 MPa, particularly preferably 10 MPa to 200 MPa, and most preferably 12 MPa to 200 MPa.

[0041] When producing formic acid by reacting hydrogen and carbon dioxide, the reaction temperature is not particularly limited as long as formic acid is produced, because the boiling and melting points of formic acid change depending on the reaction pressure. However, in order to suppress the self-decomposition of formic acid, when the reaction is carried out at a total reaction pressure of about 0.1 MPa, it is preferable to carry out the reaction at a temperature of 120°C or lower. At 0.1 MPa, the boiling point of formic acid is 101°C or lower, so it is preferable to have a temperature of 101°C or lower, and even more preferably below the boiling point of formic acid when carried out under other pressure conditions. Furthermore, in order to improve the efficiency of formic acid production, when the reaction is carried out at a total reaction pressure of 0.1 MPa, it is preferable that the reaction temperature is 8.4°C or higher, which is the melting point of formic acid, and even more preferably above the melting point of formic acid when carried out under other conditions. As a result, it is more preferable that the temperature is between 8.4°C and 120°C, between 8.4°C and 101°C, between 10°C and 101°C, or between 32°C and 101°C.

[0042] The manufacturing method for formic acid may be a batch method, a semi-batch method, or a distribution method.

[0043] The time (reaction time) for maintaining the above total pressure within a predetermined range is not particularly limited, but it can be suitably carried out without specifying a time as long as it is 10 minutes or more. However, it is preferable to ensure a sufficient time for the formic acid to reach equilibrium. For example, 10 minutes to 100 hours is preferred, 30 minutes to 100 hours is preferred, 1 hour to 100 hours is more preferred, and 2 hours to 100 hours is even more preferred.

[0044] The temperature (reaction temperature) to be maintained within a predetermined range during the above reaction time is preferably 120°C or lower, more preferably 110°C or lower, even more preferably 30°C to 100°C, and particularly preferably 40°C to 90°C.

[0045] The TOF value is not particularly limited, but the catalytic rotation speed (TOF value) calculated by the formula described in the examples [h -1 ] is 0h -1 Over 150 hours -1 Preferably less than 0h -1 Over 140 hours -1The following is more preferable, 0h -1 More than 120h -1 The following is more preferable, 0h -1 Over 100 hours -1 The following are particularly preferable. [Examples]

[0046] Example 1: Organoiridium complex catalyst and organoruthenium complex A 30 mL stainless steel autoclave equipped with a pressure sensor and a temperature sensor was filled with 10 mL of each reaction medium shown in Tables 1 and 2 below, and the reaction medium was degassed by bubbling with nitrogen. After degassing, 40 μL of 5 mM solutions of each organoiridium complex was added to the autoclave. Next, the autoclave was pressurized with carbon dioxide to 2 MPa, stirred at 1200 rpm at room temperature for 90 minutes, and then the carbon dioxide pressure was reduced to 0.5 MPa. Then, the autoclave was pressurized with hydrogen at 0.5 MPa to a total pressure of 1.0 MPa, and the mixture was heated to 50°C to allow the hydrogen and carbon dioxide to react.

[0047] Two hours after the start of the reaction, the autoclave was cooled with ice water to stop the reaction, and then the inside of the autoclave was slowly returned to atmospheric pressure. The amount of formic acid produced in the solution remaining in the autoclave was measured by high-performance liquid chromatography (HPLC) (the same applies below). By normalizing the amount of catalyst added (0.2 μmol) and the amount of formic acid produced (mol / 10 mL) by the reaction time, the catalytic turnover rate (TOF value) [h] was calculated using the following formula. -1 The following values ​​were calculated (the same applies below). The results are shown in Tables 1 and 2. TOF value [h -1 ] = Amount of formic acid produced (mol / 10mL) / (Catalyst amount 0.2 μmol × 2 hours)

[0048] The chemical structure of the organoiridium complex used in Example 1 is shown below.

[0049] [ka]

[0050]

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[0051]

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[0052]

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[0053]

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[0054]

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[0055]

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[0056]

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[0057]

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[0058]

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[0059]

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[0060]

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[0061] [ka]

[0062] Compounds 1a to 1e, 2a to 2e, 3a to 3d, 4a to 4d, 5a to 5d, 6a and 6b, 7a and 7b, 8a and 8b, 9a and 9b, and 10a to 10e were synthesized according to the description in Inorganic Chemistry, 2020, 59, 7, 4191-4199. Compounds 1f to 1i were prepared by dissolving compound 1a in a mixture of water and methanol, and then adding an equivalent amount of silver hexafluorophosphate (compound 1f), silver nitrate (compound 1g), silver tetrafluoroborate (compound 1h), or bis(trifluoromethanesulfonamide) silver (compound 1i), respectively, and allowing anion exchange to occur.

[0063] [Table 1]

[0064] [Table 2]

[0065] As shown in Table 1, the TOF (Time of Fuel) was highest when water was used as the reaction medium. However, once the autoclave returned to atmospheric pressure, the catalyst initiated dehydrogenation of the generated formic acid, and after 2 hours, most of the formic acid decomposed into hydrogen and carbon dioxide. In other words, the formic acid obtained by the method using water as the reaction medium was unstable and impractical. To suppress this decomposition of formic acid, it is necessary to remove the catalyst or the generated formic acid from the autoclave. However, this removal process complicates the formic acid production process or equipment. On the other hand, as shown in Table 2, formic acid was obtained at a good rate even when the iridium ligand in the catalyst was changed. Furthermore, formic acid was obtained at a good rate even when the counteranion or the anion coordinating to iridium in the catalyst was changed.

[0066] The chemical structure of the organoiridium complex used in Example 1 is shown below.

[0067] [ka]

[0068] [ka]

[0069] [ka]

[0070] [ka]

[0071] [ka]

[0072] [ka]

[0073] Compounds 13a to 13c, 14a to 14e, 15, 17a to 17d, and 18 were synthesized based on the description in Inorganic Chemistry, 2020, 59, 7, 4191-4199. Compounds 16a to 16e were synthesized by first synthesizing the ligands based on the description in Tetrahedron Letters, 2005, 46, 2197-2199, and then synthesizing the complexes based on the description in Inorganic Chemistry, 2020, 59, 7, 4191-4199.

[0074] The chemical structure of the organoruthenium complex used in Example 1 is shown below.

[0075] [ka]

[0076] Compound 19 was synthesized based on the description in the International Journal of Hydrogen Energy, 2019, 44 (53), 28507-28513.

[0077] [Table 3]

[0078] As shown in Table 3, formic acid was obtained at a good rate even when the ligand of iridium in the catalyst was changed. Furthermore, formic acid was obtained at a good rate even when the counteranion or the anion coordinating to iridium in the catalyst was changed. Furthermore, even when the metal in the catalyst was changed from iridium to ruthenium, formic acid was obtained at a good rate.

[0079] Example 2: Immobilized catalyst Except for replacing the organoiridium complex catalyst with either the immobilized catalyst 10a or 10b described below, formic acid was produced from hydrogen and carbon dioxide in the same manner as in Example 1, using hexafluoroisopropanol as the reaction medium. The results are shown in Table 3 below. Immobilized catalyst 10a or 10b was obtained by supporting the organoiridium complex used in Example 1 on branched polyethyleneimine with a molecular weight of 10,000 or more.

[0080] Specifically, branched polyethyleneimine (Sigma-Aldrich, branched polyethyleneimine, molecular weight 10,000) and the ligand 4,4'-dichloro-2,2'-bipyridine were reacted in an autoclave to obtain a solid polymer with the ligand immobilized. Subsequently, an organoiridium complex [Cp * Ir(H2O)3](SO4)(Cp * The reaction was carried out by adding a pentamethylcyclopentadienyl group (hereinafter the same) to obtain an immobilized catalyst 10a or immobilized catalyst 10b in which compound 1a or compound 1b was immobilized on polyethyleneimine. In the chemical formulas representing immobilized catalyst 10a or immobilized catalyst 10b, m, m', n, n', n'', and n''' are natural numbers.

[0081] [ka]

[0082] Furthermore, formic acid was produced from hydrogen and carbon dioxide in the same manner as in Example 1, using hexafluoroisopropanol as the reaction medium, except that the organoiridium complex catalyst was replaced with the immobilized catalyst 11a described below. The results are shown in Table 3 below. Immobilized catalyst 11a was prepared based on the description in R. Kanega, MZ Erterm, N. Onishi, DJ Szalda, E. Fujita, Y. Himeda, Organometallics, 2020, 39, 1519-1531. In the chemical formula representing immobilized catalyst 11a, m' and n' are natural numbers.

[0083] [ka]

[0084] Furthermore, formic acid was produced from hydrogen and carbon dioxide in the same manner as in Example 1, using hexafluoroisopropanol as the reaction medium, except that the organoiridium complex catalyst was replaced with the immobilized catalyst 12 described below. The results are shown in Table 3 below. The immobilized catalyst 12 was synthesized by the following method. Specifically, polyacrylic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., molecular weight 250,000) and the ligand 4,4'-dichloro-2,2'-bipyridine were reacted in an autoclave to obtain a solid polymer with the ligand immobilized. Subsequently, the organoiridium complex [Cp * The reaction was carried out by adding Ir(H2O)3](SO4) to obtain an immobilized catalyst 12 in which compound 1a was immobilized on polyacrylic acid. In the chemical formula representing the immobilized catalyst 12, m, m', n, n', n'', and n''' are natural numbers.

[0085] [ka]

[0086] [Table 4]

[0087] As shown in Table 4, formic acid was obtained at a good rate even when an immobilized catalyst consisting of an organoiridium complex supported on a polymer compound was used.

[0088] [ka]

[0089] [ka]

[0090] The immobilized catalyst 19 was synthesized according to K. Sawahara, S. Takana, T. Kodaira, R. Kanega, H. Kawanami, ChemSusChem, 2024, 17, e202301282.

[0091] The immobilized catalyst 20a was synthesized by the following method. Acrylic acid, methylenebisacrylamide as a crosslinking agent, and sodium dodecyl sulfate as a surfactant were dissolved in a methanol / water = 1:1 solution. Then, azobisisobutyronitrile was added and the mixture was heated at 80°C for 10 minutes to precipitate the polymer. The precipitated polymer was filtered, washed three times with a methanol / water = 1:1 solution, and dried. The dried polymer was dispersed in dichloromethane, and N 1 ,N 1 '-([2,2'-bipyridine]-4,4'-diyl)bis(hexane-1,6-diamine) was added, followed by 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide as a dehydrating agent, and the reaction was carried out at room temperature for 12 hours. The resulting solid was dispersed in water, and the organoiridium complex [pentamethylcyclopentadienyliridium(H2O)3] sulfate was added and the reaction was carried out to obtain immobilized catalyst 20a. Immobilized catalyst 20b was obtained in the same manner as immobilized catalyst 20a, except that acrylic acid was replaced with methacrylic acid.

[0092] [ka]

[0093] [Table 5]

[0094] As shown in Table 5, formic acid was obtained at a good rate even when an immobilized catalyst consisting of an organoiridium complex supported on a polymer compound was used.

[0095] Example 3: Solid Catalyst Except for changing the organoiridium complex catalyst to the solid catalyst shown in Table 4 below, formic acid was produced from hydrogen and carbon dioxide in the same manner as in Example 1, using hexafluoroisopropanol as the reaction medium. The results are shown in Table 4. Pd / C (Pd / C, STD type (Pd 5%) (water-containing) manufactured by N.E. Chemcat) is a solid catalyst in which palladium is supported on carbon at a loading rate of 5% by mass. The water content is 10% by mass or less. The loading rate (%) of the catalytic metal is calculated as mass of supported catalytic metal / mass of support × 100.

[0096] Pd-Au / C is a solid catalyst in which an alloy containing palladium and gold in equal mass (1:1) is supported on carbon at a loading rate of 5% by mass. Pd-Ag / C is a solid catalyst in which an alloy containing palladium and silver in equal mass (1:1) is supported on carbon at a loading rate of 5% by mass. Pd / rGO is a solid catalyst in which palladium is supported on a support material obtained by converting a carbon material (VULCAN XC72 Carbon Black (hereinafter the same)) to graphene oxide at a loading rate of 5% by mass. Pd / PDA / rGO is a solid catalyst in which paradiaminobenzene is supported on a support material obtained by converting a carbon material to graphene oxide, and then palladium is further supported on it at a loading rate of 5% by mass. In all cases, the water content is 10% by mass or less.

[0097] Pd-Au / PDA / rGO is a solid catalyst that uses a support material obtained by converting a carbon material to graphene oxide, on which paradiaminobenzene is supported, and then an alloy containing palladium and gold in equal mass (1:1) is further supported at a loading rate of 5% by mass. The water content is 10% by mass or less. Pd-Au / C, Pd-Ag / C, Pd / rGO, Pd / PDA / rGO, and Pd-Au / PDA / rGO were manufactured based on the description in Heng Zhong, Masayuki Iguchi, Fu-Zhang Song, Maya Chatterjee, Takayuki Ishizaka, Ikuhiro Nagao, Qiang Xu, Hajime Kawanami, Sustainable Energy & Fuels, 1, 1049, 2017.

[0098] [Table 6]

[0099] As shown in Table 6, formic acid was obtained at a good rate even when a solid catalyst with a catalytic metal supported on a carrier was used.

[0100] Example 4: Reaction pressure change Formic acid was produced from hydrogen and carbon dioxide in the same manner as in Experiment No. 6 of Example 1, except that the partial pressure of carbon dioxide in the autoclave was varied from 1 MPa to 15 MPa. The results are shown in Figure 1. As shown in Figure 1, the rate of formic acid production (TOF = 320 h) was observed when the reaction pressure (total pressure) was from 1 MPa to 3 MPa. -1 The largest value was found at 6 MPa, 7 MPa, and 8 MPa in the subcritical region. Furthermore, the rate of formic acid production decreased in the subcritical region. Also, as shown in Figure 1, the rate of formic acid production increased even at reaction pressures (total pressure) from 8 MPa to 13 MPa, which are above the critical pressure of carbon dioxide, with a maximum TOF of 370 h. -1 The largest yield was obtained. Therefore, by using the catalyst of this invention to react hydrogen with carbon dioxide in a subcritical or supercritical state, formic acid can be efficiently produced.

[0101] Example 5: Reaction time change Formic acid was produced from hydrogen and carbon dioxide in the same manner as in Experiment No. 6 of Example 1, except that the partial pressure of hydrogen in the autoclave was set to 0.5 MPa, the partial pressure of carbon dioxide to 12 MPa, and the total pressure was set to 12.5 MPa, and the reaction time was varied from 1 hour to 100 hours. The turnover number of catalysts (TON value) was calculated using the following formula with compound 1b (0.2 μmol) and the amount of formic acid produced (mol). The results are shown in Figure 2. As shown in Figure 2, the reaction reached near equilibrium after about 48 hours, the amount of formic acid produced became constant, and the TON value was approximately 2000 or less. TON value = Amount of formic acid produced (mol / 10mL) / Amount of catalyst 0.2 μmol

[0102] Example 6: Reaction temperature change Formic acid was produced from hydrogen and carbon dioxide in the same manner as in Example 5, except that the reaction time was set to 2 hours and the reaction temperature was varied from 30°C to 120°C. The time of fluctuating temperatures (TOF) at 30°C, 40°C, 50°C, 80°C, 100°C, and 120°C were 184h, respectively. -1 , 202h -1 , 368h -1 , 454h -1 , 575h -1 , and 575h -1 The reaction temperature was higher, which increased the rate of formic acid production. However, above 100°C, the TOF value remained constant, and no improvement in the rate of formic acid production was observed.

[0103] Example 7: Investigation of the optimal hydrogen-to-carbon dioxide ratio and total pressure Under the same conditions as in Example 5, the total pressure was set to 12.5 MPa, and the hydrogen pressure was varied from 0.5 MPa to 7 MPa, while the carbon dioxide pressure was simultaneously varied from 12 MPa to 5.5 MPa to produce formic acid. The results are shown in Figure 3. As a result, good TON values ​​were observed in the range from approximately 3 MPa for hydrogen and 9.5 MPa for carbon dioxide to 7 MPa for hydrogen and 5.5 MPa for carbon dioxide. In particular, the rate and amount of formic acid produced increased most significantly when the hydrogen and carbon dioxide pressures were approximately the same. Furthermore, the conditions were investigated from 1 MPa to 15 MPa under a hydrogen to carbon dioxide pressure ratio of 1:1. The results are shown in Figure 4. It was found that the rate and amount of formic acid produced increased with increasing pressure, and further increases were achieved with even higher pressures. When the reaction time was extended to 96 hours, the TON value rose to its maximum value of 6182.

Claims

1. A method for producing formic acid from hydrogen and carbon dioxide, using a reaction medium having a water content of 10% by mass or less in the presence of a catalyst, or without using a reaction medium, The catalyst contains an organic iridium complex or an organic ruthenium complex, The partial pressure of hydrogen is 0.05 MPa or higher, and the partial pressure of carbon dioxide is 0.05 MPa or higher. A method for producing formic acid, wherein the organoiridium complex and the organoruthenium complex include at least one selected from the group consisting of compounds 1a to 1i, 2a to 2e, 3a to 3d, 4a to 4d, 5a to 5d, 6a to 6b, 7b, 8a to 8b, 9b, 10a to 10e, 13a to 13c, 14a, 14c to 14e, 15, 16a to 16e, 17a to 17d, 18, and 21, represented by the following formula. 【Chemistry 1】 【Chemistry 2】 【Transformation 3】 【Chemistry 4】 【Transformation 5】 【Transformation 6】 【Transformation 7】 【Transformation 8】 【Chemistry 9】 【Chemistry 10】 【Chemistry 11】 【Chemistry 12】 【Chemistry 13】 【Chemistry 14】 【Chemistry 15】 【Chemistry 16】 【Chemistry 17】 【Chemistry 18】 【Chemistry 19】 【Chemistry 20】

2. In claim 1, A method for producing formic acid, wherein the organic iridium complex or the organic ruthenium complex is supported on a polymer compound.

3. In claim 1, A method for producing formic acid, wherein the partial pressure of carbon dioxide is 1 MPa or more and 6 MPa or less, or 8 MPa or more and 13 MPa or less.

4. In claim 3, A method for producing formic acid from hydrogen and carbon dioxide at a reaction temperature of 30°C to 100°C.

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