Method for promoting formic acid synthesis reaction, and ionic liquid

Abstract

The present invention provides a method for promoting a formic acid synthesis reaction that enables efficient production of formic acid from carbon dioxide and hydrogen. The method for promoting a formic acid synthesis reaction according to the present invention comprises reacting carbon dioxide with hydrogen in an ionic liquid, and a substituent in a cation of the ionic liquid is at least an amino group or a carboxyl group.

Description

[Technical field]

[0001] The present invention relates to a method for promoting a formic acid synthesis reaction in which formic acid is produced from carbon dioxide and hydrogen, or from hydrogen and carbon dioxide obtained by decomposition of water, and more specifically, to a method for promoting a formic acid synthesis reaction in which formic acid is obtained in an ionic liquid or in an aqueous solution in which an organic compound containing an amino group or a carboxyl group as a functional group is dissolved. [Background technology]

[0002] We continue to live our social lives by converting and utilizing substances that exist on Earth. In particular, the raw materials for organic compounds are mostly fossil fuels, which are converted industrially for use. However, fossil fuels are a finite resource, and there is no guarantee that they can be used forever. Furthermore, the emission of carbon dioxide is unavoidable during the production and utilization process, and this extremely chemically stable carbon dioxide continues to be released. Carbon dioxide, which is stable and has few uses, can also be used as a carbon source if you change your perspective. When organic compounds are burned, energy is released and water and carbon dioxide are produced. Although an energy supply is necessary, it is in principle possible to use natural energy such as sunlight to cause a reverse reaction and produce organic compounds from water and carbon dioxide. In research to date, there has been little success in freely synthesizing organic compounds from water and carbon dioxide, but it is known that there is a possibility of practical synthesis of formic acid, the simplest organic acid. The inventors are betting on this possibility and are aiming for practical application (for example, Patent Documents 1 and 2, Non-Patent Documents 1-3, and cited documents). Meanwhile, conventionally, there has been known a method for industrially producing acetic acid by oxidizing various hydrocarbons contained in butane and naphtha, which are hydrocarbons, in a liquid phase (for example, Non-Patent Document 4 below). Furthermore, Non-Patent Document 4 below describes that in the above-mentioned production of acetic acid, formic acid is obtained as a by-product. Furthermore, Non-Patent Document 4 below describes that formic acid is also obtained as a by-product in the production of pentaerythritol. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Retable 2011 / 093229 [Patent Document 2] Patent No. 7288484 [Non-patent literature] [Non-Patent Document 1] The Journal of Physical Chemistry B 2011,115,14136-14140 and references cited [Non-Patent Document 2] The Journal of Physical Chemistry B 2011,115,9789-9794 and references cited [Non-Patent Document 3] ACS Catalysis 2022,12,11,6770-6780 and citations [Non-Patent Document 4] Takuya Kumamoto, "Industrial synthesis of formic acid and its applications", Chemistry and Education, Chemical Society of Japan, 2012, Vol. 60, No. 8, pp. 358-361, Internet<URL:https: / / www.jstage.jst.go.jp / article / kakyoshi / 60 / 8 / 60_KJ00008195825 / _article / -char / ja / > Non-patent documents 1 to 3 are scientific journals of the American Chemical Society. Summary of the Invention [Problem to be solved by the invention]

[0004] The formic acid is not produced directly from carbon dioxide and water, but from hydrogen and carbon dioxide produced by decomposing water. There is still much room for research into a method for efficiently producing formic acid from hydrogen and carbon dioxide with minimal energy.

[0005] In view of the above problems, an object of the present invention is to provide a method for producing formic acid from hydrogen and carbon dioxide efficiently with minimal energy. [Means for solving the problem]

[0006] [Summary of knowledge on formic acid synthesis reaction] The basis for promoting a chemical reaction is to have a large number of reactive substrates present in the reaction field, to have them meet and collide with each other to transition the energy state of the reactive substrates to a higher state, and to have them proceed to an activated complex (called a transition state or an activated state, hereinafter these terms are synonymous). Carbon dioxide and hydrogen are gases at room temperature and pressure, and if the reaction field is in a different state, such as a liquid, the reaction will not proceed unless the reactive substrate is taken into the reaction field. Therefore, the present inventors have intensively studied and found that by making at least an amino group or a carboxyl group as the substituent in the cation of the ionic liquid, at least one of the reactive substrates, carbon dioxide, is easily taken into the substituent, and the reaction is promoted. As a result, it has been found that the reaction between carbon dioxide and hydrogen is promoted in the ionic liquid, and formic acid is efficiently synthesized. In addition, the substituents in the cations of the ionic liquid or the organic compound contain at least an amino group or a carboxyl group, and a method for efficiently synthesizing formic acid has been found by reacting carbon dioxide and hydrogen in water in which the ionic liquid or the organic compound is present, leading to the invention. Furthermore, in an ionic liquid used as a field for synthesizing formic acid by reacting carbon dioxide and hydrogen, it has been found that by making the substituents in some or all of the cations of the ionic liquid at least an amino group or a carboxyl group, carbon dioxide and / or hydrogen are easily incorporated into the ionic liquid, which is the reaction field, and further, that these reaction substrates are easily transferred to an activated state, and it has been found that the ionic liquid is a reaction field and reaction medium that can efficiently synthesize formic acid. In addition, the reaction proceeds by incorporating the reaction substrate into the solvent and transferring it to an activated state, and it has been found through intensive research that the activated state is close to carbonic acid and has a structure close to formate anion, which promotes the progress of the reaction. In other words, the reaction is promoted by creating a reaction environment that promotes the activation of these. It is desirable that the substituents are arranged so that they can adsorb or bond to at least the oxygen atom in the carbon dioxide molecule. Furthermore, although the carbon dioxide molecule is a linear molecule, it is preferable that the molecule has a twisted structure.In addition, it is desirable that the substituents are arranged so that they can also adsorb or bond with hydrogen molecules, and it is desirable that the substituents are arranged so that the hydrogen of a nonpolar molecule has a polar structure within the molecule.

[0007] In the method for producing formic acid according to the present invention, the anion of the ionic liquid is preferably a formate anion.

[0008] According to this configuration, an activated state is created, creating an environment that is favorable for the formation of an activated complex, making it easier to obtain formic acid. In other words, formic acid can be efficiently produced from carbon dioxide and water.

[0009] The cation of the ionic liquid preferably contains an imidazolium salt.

[0010] According to this configuration, formic acid can be produced efficiently.

[0011] In addition, the method for producing formic acid preferably further includes a hydrogen production step of electrolyzing water using renewable energy to produce the hydrogen.

[0012] According to this configuration, it is possible to obtain the hydrogen used in the formic acid production step while suppressing an increase in the burden on the global environment. Effect of the Invention

[0013] As described above, according to the present invention, a method for promoting a formic acid synthesis reaction that can efficiently produce formic acid from carbon dioxide and hydrogen can be provided. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram showing a method for promoting a formic acid synthesis reaction according to one embodiment of the present invention. [Diagram 2] 1 is a schematic cross-sectional view of an apparatus used in a method for promoting a formic acid synthesis reaction according to one embodiment of the present invention. [Diagram 3]An example of the chemical structure of an ionic liquid. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] In a method for promoting a formic acid synthesis reaction according to one embodiment of the present invention, a substituent in a cation of an ionic liquid has at least an amino group or a carboxyl group. The anion of the ionic liquid has a formate anion. Furthermore, the cation of the ionic liquid is an imidazolium salt.

[0016] Alternatively, in a method for promoting a formic acid synthesis reaction in which carbon dioxide and hydrogen are reacted in water containing an organic compound including an ionic liquid (including a dissolved aqueous solution, or a state in which an organic compound and an aqueous solution exist at a concentration equal to or higher than the saturation concentration; these are referred to as the second medium. On the other hand, the ionic liquid is referred to as the first medium), to synthesize formic acid, a substituent in a cation of the organic compound is at least an amino group or a carboxyl group.

[0017] Alternatively, the ionic liquid is used as a site for synthesizing formic acid by reacting carbon dioxide with hydrogen, and the substituents in some or all of the cations in the ionic liquid are at least an amino group or a carboxyl group.

[0018] The hydrogen is supplied from water and obtained by electrolysis of water. Alternatively, hydrogen may be obtained by reacting CO with water and via the water-gas shift reaction (CO+H2O→HCOOH→H2+CO2). Needless to say, hydrogen generated in various chemical reaction processes can also be used. Hereinafter, "according to one embodiment of the present invention" will be simply referred to as "according to the present embodiment."

[0019] The method for promoting a formic acid synthesis reaction according to this embodiment is carried out, for example, under the concept shown in FIG.

[0020] [Conceptual diagram of the method for promoting the formic acid synthesis reaction] In order to promote the reaction, it is important to bring the reactive substrates, carbon dioxide and hydrogen, together, change their structure to one that facilitates the reaction, and transition to an active complex. At room temperature and pressure, carbon dioxide and hydrogen are gases that freely translate, vibrate, and rotate, forming a stable structure on average. Both are linear molecules, which is their stable structure.

[0021] FIG. 1 shows a conceptual diagram of this reaction. In order to facilitate the meeting of the freely moving carbon dioxide and hydrogen, it is necessary to capture each of them with a solvent or the like. In the case of a solution, they are taken in by the solvent, that is, solvated. In addition to solvation, a structure in which there is a space between the solvent molecules into which carbon dioxide and hydrogen can enter and which can trap them is also acceptable. For a structure that can solvate or trap, it is sufficient that the amount of at least one of carbon dioxide and hydrogen is large. In order to promote the uptake of each molecule, it is necessary to provide a structure or functional group on the solvent side that can easily take in each molecule. As a result of the inventors' earnest studies, as described above, it was found that the substituent in the cation of the ionic liquid is preferably a structure having at least an amino group or a carboxyl group. Alternatively, it was found that it is preferable to use an ionic liquid in water in which an organic compound containing the ionic liquid exists (including a dissolved aqueous solution, or a state in which an organic compound and an aqueous solution exist at a concentration above saturation). It was also found that an ionic liquid having a substituent in the cation as described above is more likely to activate (promote) the reaction. As mentioned above, the reaction proceeds by incorporating the reaction substrate into the solvent and transitioning to an activated state, but it has been found through intensive research that the activated state is preferably close to carbonic acid and has a structure close to formate anion, and that this promotes the progress of the reaction. In other words, the point is to promote the reaction by creating a reaction environment that promotes the activation of these states and transition to this state. Furthermore, it has been found that when the anion of the ionic liquid has a formate anion, it transitions to an activated state and is prone to structural change to an active complex. Furthermore, the cation of the ionic liquid is an imidazolium salt. In other words, it has been found that these measures make it easy for carbon dioxide and hydrogen to be incorporated into the solvent, and furthermore, the incorporated carbon dioxide and hydrogen have a structure that is prone to react, which further promotes the structural change to an active complex, resulting in a situation in which formic acid is likely to be produced. Furthermore, as mentioned above, it is desirable that the substituent is arranged so that at least the oxygen atom in the carbon dioxide molecule can be adsorbed or bonded. Furthermore, although the carbon dioxide molecule is a linear molecule, a structure that is twisted into a twisted shape is preferable.In addition, the substituents are preferably arranged so that hydrogen molecules can be adsorbed or bonded, and the hydrogen of a non-polar molecule is preferably arranged so that the substituents have a structure that has polarity within the molecule. Using these findings, a specific method for promoting the formic acid synthesis reaction is disclosed.

[0022] [Formic acid synthesis reaction accelerator] The method for promoting a formic acid synthesis reaction according to this embodiment is similar to that described in Japanese Patent No. 7288484, and is carried out, for example, in an apparatus as shown in FIG. The device 1 for carrying out the method for promoting a formic acid synthesis reaction according to this embodiment is a batch reaction device having a storage space S capable of storing an ionic liquid (first medium) or water containing an organic compound containing an ionic liquid (including a dissolved aqueous solution, or a state in which an organic compound and an aqueous solution exist at a concentration equal to or higher than the saturation concentration: second medium). Here, a batch reaction device is taken as an example for explanation, but a flow reaction device may also be used. Specifically, the apparatus 1 for carrying out the method for promoting a formic acid synthesis reaction according to this embodiment includes a reaction tank 10 formed in a cylindrical shape and having a storage space S therein capable of storing a first medium or a second medium, a jacket 20 covering the outer surface and bottom surface of the reaction tank 10, and a reaction medium storage tank 30 for storing a reaction medium containing the first medium or the second medium. In addition, the apparatus 1 for carrying out the method for promoting a formic acid synthesis reaction in this embodiment is equipped with a pipe L for connecting the reaction tank 10 and the reaction medium storage tank 30, and a valve V for adjusting the open / closed state of the pipe L. Furthermore, the apparatus 1 for carrying out the method for promoting a formic acid synthesis reaction according to this embodiment preferably includes an inert gas storage tank (not shown) in which an inert gas such as nitrogen gas, helium gas, or argon gas is stored, a pipe connecting the inert gas storage tank to the reaction tank 10, and a valve for adjusting the open / closed state of the pipe.

[0023] The reaction tank 10 includes a cylindrical side wall portion 10a, a bottom wall portion 10b that closes the bottom side of the cylindrical side wall portion 10a, and a top wall portion 10c that closes the top side of the cylindrical side wall portion 10a. In the reaction tank 10, as described above, the cylindrical side wall portion 10a is closed by the bottom wall portion 10b and the top wall portion 10c, thereby making the accommodation space S an enclosed space. The first medium or the second medium is accommodated in the accommodation space S of the reaction tank 10 from the reaction medium storage tank 30 via a pipe L. The reaction medium may be accommodated in the accommodation space S after reducing the pressure in the accommodation space S using a vacuum pump (not shown), or may be accommodated under atmospheric pressure (1.01325×105 Pa (0.101325 MPa)) without reducing the pressure in the accommodation space S. The reaction medium is preferably accommodated in the accommodation space S under atmospheric pressure conditions without reducing the pressure in the accommodation space S. In the reaction tank 10, after the reaction medium is accommodated in the accommodation space S, the inert gas stored in the inert gas storage tank is sealed in the accommodation space S, and at least a part of the air contained in the gas phase part of the accommodation space S may be replaced with the inert gas, or all of the air contained in the gas phase part of the accommodation space S may be replaced with the inert gas. Replacement with an inert gas is the best mode, but is not essential. In this state, carbon dioxide and hydrogen are sealed in the storage space S. A predetermined amount of each gas is sealed in at a pressure higher than the pressure in the storage space S. The specific configuration of the device and the method of sealing are the same as those for inert gas. The reaction vessel 10 may be provided with a stirring device (not shown) for stirring the reaction medium contained in the containing space S. By providing the reaction tank 10 with the stirring device, the reaction can be carried out while stirring the reaction medium contained in the storage space S with the stirring device. This makes it possible to carry out the synthesis reaction of formic acid contained in the reaction medium more efficiently.

[0024] As described above, the apparatus 1 for carrying out the method for promoting a formic acid synthesis reaction according to this embodiment is a batch reaction apparatus, and therefore the reaction tank 10 is a batch vessel. The batch vessel means one that can contain the reaction medium and reaction substrates used in a single treatment in a sealable manner. Since the reaction vessel 10 has an inner wall surface that comes into contact with the reaction medium contained therein and the reaction substrate, it is preferable that the inner wall surface be made of a non-metallic material. Preferred materials for forming the inner wall surface include resin, glass, ceramic, diamond-like carbon, and the like.

[0025] The resin may be, for example, a plastic such as polyimide (PI), polyamide (PA), polyamideimide (PAI), polyethersulfone (PES), polyetherimide (PEI), polyetheretherketone (PEEK), aromatic polyester (PET, PEN, etc.), polyarylene sulfide (PAS), or a general rubber. In this embodiment, from the viewpoint of stability against hydrothermal reactions, the resin is preferably a silicone resin, a silicone rubber, a fluororesin, a fluororubber, an epoxy resin, or the like. Among these resins, the resin is preferably a fluororesin. Examples of the fluororesin include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene-ethylene copolymer (ETFE), and polyvinylidene fluoride (PVdF). The resin may be used as a constituent material for the inner wall surface either alone or as a mixture of two or more kinds.

[0026] Examples of the glass include soda glass, borosilicate glass, quartz glass, and crystal glass.

[0027] Examples of the ceramic include alumina (Al2O3), zirconia (ZrO2), titania (TiO2), silica (SiO2), silicon carbide (SiC), silicon nitride (Si3N4), zircon (ZrO2·SiO2), aluminosilicate (Al2O3·SiO2), barium titanate (BaTiO3), aluminum nitride (AlN), steatite (MgO·SiO2), forsterite (2MgO·SiO2), mullite (3Al2O3·2SiO2), cordierite (2MgO·2Al2O3·5SiO2), and the like. The ceramic may be used as a constituent material for the inner wall surface either alone or as a mixture of two or more kinds.

[0028] The entire wall defining the storage space S of the reaction vessel 10 may be made of the above material, or only the surface layer (the surface layer forming the inner wall surface of the reaction vessel 10) may be made of the above material. The material may be formed into multiple layers. The reaction vessel 10 may have, for example, a metal main body, and a glass layer and a resin layer are laminated on the inner wall surface of the main body.

[0029] The material forming the inner wall surface preferably has a elution amount of metal ions by formic acid at room temperature (23±2° C.) of 1000 ppm or less. The amount of eluted metal ions can be measured by an ICP method or the like.

[0030] As described above, by forming the inner wall surface of the reaction vessel 10 from a non-metallic material, the inner wall surface of the reaction vessel 10 becomes acid-resistant. Furthermore, when the inner wall surface is made of a metal such as stainless steel, there is a concern that the carboxyl group (COOH) contained in formic acid (HCOOH) may form an ionic bond with the metal. However, when the inner wall surface is made of a non-metal, the formation of the ionic bond as described above can be suppressed. That is, the formic acid forms an ionic bond with the inner wall surface via a carboxyl group, thereby making it possible to prevent the formic acid from being adsorbed onto the inner wall surface. This makes it possible to produce formic acid from the carbon dioxide and hydrogen more efficiently.

[0031] The jacket 20 is equipped with a heating device (not shown) such as a heater. The jacket 20 heats the reaction vessel 10 by a heating device such as a heater.

[0032] The reaction medium storage tank 30 may be any tank having an internal storage space S for storing the reaction medium. On the other hand, since the reaction medium storage tank 30 has an inner wall surface that comes into contact with the stored reaction medium, it is preferable that the inner wall surface be made of a non-metallic material. Preferred materials for forming the inner wall surface include resin, glass, ceramic, diamond-like carbon, and the like. The resin, glass, and ceramic may be the same as those described above. EXAMPLES

[0033] The present invention will be described in more detail below with reference to examples. The following examples are intended to further explain the present invention, and are not intended to limit the scope of the present invention. In the examples, a part of the promotion method using the findings described in the above [Summary of findings on formic acid synthesis reaction] and [Conceptual diagram regarding the promotion method of formic acid synthesis reaction] is disclosed. Although it depends on the position and number of the substituents, it is promoted if the requirements for realizing the findings described in the above [Summary of findings on formic acid synthesis reaction] and [Conceptual diagram regarding the promotion method of formic acid synthesis reaction] are met. Therefore, in the following examples, the position and number are not mentioned in detail because there are countless combinations, but it is the arrangement of the substituents that meets the above requirements, or the number of the substituents.

[0034] [Ionic liquid] In the present invention, an ionic liquid is defined as an organic compound salt having a melting point of 100° C. or less. Examples of ionic liquids include imidazolium salt-based ionic liquids represented by the general formula (Chemical Formula 1) in FIG. 3 and phosphonium salt-based ionic liquids represented by the general formula (Chemical Formula 2) below, as well as pyridinium salt-based ionic liquids, pyrrolidinium salt-based ionic liquids, and tetraalkylammonium salt-based ionic liquids.

[0035] [In Chemical Formula 1, R1 and R2 are the same or different and each represents an alkyl group in which at least a portion of the hydrogen atoms may be substituted with a fluorine atom, or an aryl group in which at least a portion of the hydrogen atoms may be substituted with a fluorine atom. X1, X2, and X3 are the same or different and each represents an alkyl group in which at least a portion of the hydrogen atoms may be substituted with a fluorine atom, an aryl group in which at least a portion of the hydrogen atoms may be substituted with a fluorine atom, a hydrogen atom, or a fluorine atom. Y- represents a counter anion for the imidazolium cation.]

[0036] [In Chemical Formula 2, R1, R2, R3, and R4 are the same or different and each represents an alkyl group in which at least a portion of the hydrogen atoms may be substituted with a fluorine atom, or an aryl group in which at least a portion of the hydrogen atoms may be substituted with a fluorine atom. Z- represents a counter anion for the phosphonium cation.]

[0037] In the imidazolium salt-based ionic liquid represented by the above general formula (Chemical Formula 1) and the phosphonium salt-based ionic liquid represented by the above general formula (Chemical Formula 2), examples of the alkyl group in which at least a portion of the hydrogen atoms in R1, R2, R3, R4, X1, X2, and X3 may be substituted with fluorine atoms include linear or branched alkyl groups and perfluoroalkyl groups having 1 to 18 carbon atoms, and specific examples include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, an n-hexyl group, an n-octyl group, an n-decyl group, an n-dodecyl group, an n-tetradecyl group, an n-octadecyl group, a trifluoromethyl group, a pentafluoroethyl group, a heptafluoro n-propyl group, a heptafluoro isopropyl group, and a nonafluoro n-butyl group. Examples of the aryl group in which at least a portion of the hydrogen atoms may be substituted with fluorine atoms include a phenyl group and a pentafluorophenyl group.

[0038] In R1, R2, R3, R4, X1, X2, and X3, some or all of the hydrogen atoms in these structures are substituted with amino or carboxyl groups. Examples of Y-, which is the counter anion for the imidazolium cation, and Z-, which is the counter anion for the phosphonium cation, include halide ions such as chloride ion (Cl-), bromide ion (Br-), and iodide ion (I-), as well as methanesulfonate anion (CH3SO3-), trifluoromethanesulfonate anion (CF3SO3-), bis(trifluoromethanesulfonyl)imide anion ((CF3SO2)2N-), and formate anion (HCO2-).

[0039] Suitable ionic liquids include ionic liquids whose counter anion is formate anion (i.e., formate salts), which are excellent in reaction selectivity (high purity of the formic acid produced) and reaction rate as a medium for producing formic acid from carbon dioxide and hydrogen as raw materials. Ionic liquids whose counter anion is formate anion can be synthesized from ionic liquids whose counter anion is an anion other than formate anion, such as bromide ion, by an anion exchange method using a strong base ion exchange resin (Biomacromolecules, vol. 7, pp. 3295-3297, 2006). Various ionic liquids whose counter anion is other than formate anion are commercially available, but non-commercially available ionic liquids can be synthesized according to the method described in, for example, Ionic Liquids in Synthesis I, Wiley-VCH, 2007.

[0040] Example 1: In the reaction vessel 10 shown in FIG. 2, 1,3-dini-n-propyl-2-methylimidazolium chloride salt (an ionic liquid with a water content of 1.5% by weight and with some hydrogen of the methyl group substituted with a carboxyl group) was placed at a filling rate of 50%. After degassing with a vacuum pump, carbon dioxide was injected so that the pressure in the reaction vessel was 15.0 bar, and hydrogen was further introduced so that the pressure in the reaction vessel was 30.0 bar. After closing the connection valve to seal the reaction vessel, the reaction vessel 10 was heated to 60°C. 0.2% by weight of dichlorotetrakis(triphenylphosphine)ruthenium may be added as a metal catalyst as appropriate. After 50 hours, the amount of formic acid produced was quantified using 1H-NMR measurement or the like. For example, in the case of 1H-NMR measurement, the amount of formic acid produced was confirmed by integrating the formic acid peak near 8 ppm.

[0041] Example 2: Carbon dioxide and hydrogen were reacted under the same conditions as in Example 1, except that an ionic liquid in which one hydrogen of one methyl group was substituted with an amino group was used as the ionic liquid 1,3-di-n-propyl-2-methylimidazolium chloride salt.

[0042] The results of Example 1 and Example 2 are compared. The results of Example 2 are compared based on the results of Example 1. The amount of carbon dioxide produced in Example 2 was about twice as much as that produced in Example 1. This is because the amount of carbon dioxide taken up into the ionic liquid was greater in Example 2 than in Example 1.

[0043] Example 3: Carbon dioxide and hydrogen were reacted under the same conditions as in Example 1, except that an ionic liquid in which one hydrogen of one methyl group was substituted with an amino group was used for 1,3-di-n-propyl-2-methylimidazolium formate, which is an ionic liquid. The production amount in Example 2 was about 2.3 times that in Example 1.

[0044] Example 4: Carbon dioxide and hydrogen were reacted under the same conditions as in Example 1, except that an ionic liquid in which one hydrogen of one methyl group was substituted with an amino group was used as the ionic liquid 1,3-di-n-propyl-2-methylimidazolium chloride salt. The production amount in Example 2 was about 2.3 times larger than that in Example 1.

[0045] Example 5: Carbon dioxide and hydrogen were reacted under the same conditions as in Example 1, except that an ionic liquid in which one hydrogen of one methyl group was substituted with a carboxyl group was used as the ionic liquid 1,3-di-n-propyl-2-methylimidazolium chloride salt. The production amount in Example 2 was about 2.1 times larger than that in Example 1.

[0046] Example 6: Carbon dioxide and hydrogen were reacted under the same conditions as in Example 1, except that a tetraalkylphosphonium cation with a methyl group as the alkyl group was used as the cation of the ionic liquid and an ionic liquid in which one hydrogen of one methyl group was substituted with an amino group for a salt with a chloride anion was used. The amount produced in Example 2 was about 1.5 times that of Example 1.

[0047] Example 7: Carbon dioxide and hydrogen were reacted under the same conditions as in Example 1, except that the reaction was carried out in a solution of 1,3-di-n-propyl-2-methylimidazolium chloride, an ionic liquid in which one hydrogen of one methyl group was substituted with an amino group, dissolved in water. The amount of production in Example 2 was about 1.3 times that in Example 1.

[0048] Example 8: For 1,3-di-n-propyl-2-methylimidazolium chloride salt, which is an ionic liquid, one hydrogen of one methyl group was substituted with an amino group, and the ionic liquid was dissolved in water to prepare a medium in which the solution was supersaturated, and carbon dioxide and hydrogen were reacted under the same conditions as in Example 1, except that the amount of production in Example 2 was about 1.7 times larger than that in Example 1.

[0049] Comparative Example: Carbon dioxide and hydrogen were reacted under the same conditions as in Example 1, except that an ionic liquid in which one hydrogen atom in one methyl group of 1,3-di-n-propyl-2-methylimidazolium chloride salt was used, and one hydrogen atom in one methyl group was not substituted with a carboxyl group or an amino group but remained as hydrogen (unsubstituted), was used. The amount of production in the comparative example was about 0.5 times less than that in Example 1.

[0050] The above-mentioned embodiment is merely an example, and the present invention is not limited thereto. In the above-mentioned embodiment and embodiment, the method of inserting electrodes into the reaction vessel 10 and not passing electricity therethrough has been described, but the present invention is not limited thereto, and the reaction may be promoted by passing electricity therethrough. The reaction may also be promoted by introducing a substance that exhibits catalytic action, such as a metal catalyst. Furthermore, the reaction temperature may be increased to increase the energy state of the reaction substrate by the Arrhenius effect, thereby promoting the reaction. [Explanation of symbols]

[0051] 1: carbon monoxide production apparatus, 10: reaction tank, 20: jacket, 30: formic acid aqueous solution storage tank, 10a: Side wall part, 10b: Bottom wall part, 10c: Top wall part, L: piping, S: storage space, V: valve.

Claims

1. A medium for promoting the occurrence of a transition state and promoting the reaction, comprising an ionic liquid, and used as a site for synthesizing formic acid by reacting carbon dioxide with hydrogen, the medium comprising: A medium characterized in that the substituents in some or all of the cations of the ionic liquid are at least amino groups or carboxyl groups, and are arranged so as to be capable of adsorbing or bonding to oxygen atoms in carbon dioxide molecules and to form a transition state structure.

2. A method for promoting a formic acid synthesis reaction, comprising reacting carbon dioxide and hydrogen in an ionic liquid to promote the development of a transition state and promoting the reaction to synthesize formic acid, comprising: The method for promoting a formic acid synthesis reaction is characterized in that the substituent in the cation of the ionic liquid is at least an amino group or a carboxyl group, and is arranged so as to be capable of adsorbing or bonding to an oxygen atom in a carbon dioxide molecule and to form a transition state structure.

3. The anion of the ionic liquid is a formate anion. The method for promoting a formic acid synthesis reaction according to claim 2.

4. The cation of the ionic liquid is an imidazolium salt. A method for promoting a formic acid synthesis reaction according to claim 2 or 3.

5. A method for promoting a formic acid synthesis reaction, comprising reacting carbon dioxide and hydrogen in water in the presence of an organic salt containing an ionic liquid to promote the development of a transition state and synthesizing formic acid by promoting the reaction, comprising the steps of: The method for promoting a formic acid synthesis reaction is characterized in that the substituent in the cation of the organic salt is at least an amino group or a carboxyl group, and is arranged so as to be capable of adsorbing or bonding to an oxygen atom in a carbon dioxide molecule and to form a transition state structure.

6. 6. The method for promoting a formic acid synthesis reaction according to claim 5, wherein the water in which the organic salt containing the ionic liquid is present is water in which a salt is present at a saturation concentration or higher.

7. The method for promoting a formic acid synthesis reaction according to claim 2, claim 3, claim 5, or claim 6, further comprising a hydrogen production step of electrolyzing water using renewable energy to produce the hydrogen.

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