Formic acid recovery method

Abstract

To provide a formic acid recovery method that possible to recover formic acid in a solution as a solid formate without requiring significant energy consumption, including heat.SOLUTION: A formic acid recovery method includes a recovery step for mixing a solution containing formic acid and an alkyl amine represented by the formula (1) with an organic solvent containing a base to recover a solid formate. R1R2R3 N (1) (in formula (1), at least two of R1-R3 independently represent an alkyl group with a carbon number of 6 or more and 12 or less, the remainder being a hydrogen atom).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for recovering formic acid. [Background technology]

[0002] In addition to its use as a chemical product such as a preservative, antibacterial agent, and antifreeze, formic acid is expected to be used as a hydrogen carrier in recent years. Formic acid is produced, for example, by a method using an enzyme or a method of electrochemically or catalytically synthesizing it from carbon dioxide. In general, formic acid produced by the above-mentioned method is often obtained as a dilute aqueous solution with a low concentration, for example, about 0.001 mol / L to 0.025 mol / L. In consideration of its use as a material or hydrogen carrier, a technology is required to recover and concentrate formic acid from a dilute aqueous solution of formic acid without consuming a large amount of energy.

[0003] Patent Document 1 discloses a method for concentrating a basic solution containing formate ions using a cation exchange resin. Patent Document 2 discloses a method for isolating formic acid by distillation from a liquid phase composed of formic acid and an amine obtained by phase separation. Patent Document 3 discloses a method for reacting an organic acid salt with a polyacid to produce an organic acid, and then separating the organic acid using a nanofiltration membrane.

[0004] However, it is difficult to concentrate formic acid to a high concentration by separating the formic acid using an ion exchange resin or a nanofiltration membrane as used in Patent Document 1 and Patent Document 3. In addition, considering that the boiling point of formic acid is 101° C., the recovery of formic acid by distillation as used in Patent Document 2 requires energy for heating. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2020-015684 A [Patent Document 2] Special Publication No. 2012-530747 [Patent Document 3] JP 2012-193120 A Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a method for recovering formic acid, which can easily recover formic acid in a solution as a solid formate salt without consuming a large amount of energy for heating or the like. [Means for solving the problem]

[0007] The present invention relates to a method for recovering formic acid, comprising a recovery step of mixing a solution containing formic acid and an alkylamine represented by the following formula (1) with an organic solvent containing a base to recover a solid formate salt. R 1 R 2 R 3 N (1) (In formula (1), R 1 ~R 3 At least two of the groups are independently alkyl groups having 6 to 12 carbon atoms, and the remaining groups are hydrogen atoms.

[0008] The formic acid recovery method further includes an extraction step of extracting the formic acid from an aqueous solution containing formic acid using the alkylamine and an organic solvent into an organic solvent layer containing the alkylamine and the organic solvent, and a distillation step of distilling the organic solvent from the organic solvent layer under reduced pressure or normal pressure to obtain a solution containing the formic acid and the alkylamine, and it is preferable that the solution containing the formic acid and the alkylamine obtained by the distillation step is used as the solution containing the formic acid and the alkylamine in the recovery step.

[0009] In the method for recovering formic acid, the base is preferably a Bronsted base stronger than the alkylamine.

[0010] In the method for recovering formic acid, the base is preferably ammonia.

[0011] In the method for recovering formic acid, the organic solvent used in the recovery step preferably contains at least one of ethanol and 2-propanol.

[0012] In the method for recovering formic acid, the aqueous solution containing formic acid is preferably an aqueous solution containing formic acid produced from an electrochemical cell (including those driven by solar cells).

[0013] In the method for recovering formic acid, 1 ~R 3 are preferably all independently an alkyl group having 6 to 12 carbon atoms.

[0014] In the method for recovering formic acid, 1 ~R 3 The total number of carbon atoms is preferably 12 or more.

[0015] In the method for recovering formic acid, the concentration of the formic acid in the solution containing the formic acid and the alkylamine is preferably 0.30 mol / L or more. Effect of the Invention

[0016] According to the present invention, there is provided a method for recovering formic acid, which is capable of recovering formic acid in a solution as a solid formate salt in a simple manner without consuming a large amount of energy for heating or the like. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present invention. The embodiment is merely an example of implementing the present invention, and the present invention is not limited to the embodiment.

[0018] The method for recovering formic acid according to the present embodiment includes a recovery step of mixing a solution containing formic acid and an alkylamine represented by the following formula (1) (hereinafter, may be simply referred to as an alkylamine) with an organic solvent containing a base to recover a solid formate salt. R 1 R 2 R 3N (1) (In formula (1), R 1 ~R 3 At least two of the groups are independently alkyl groups having 6 to 12 carbon atoms, and the remaining groups are hydrogen atoms.

[0019] In the recovery step, a solution containing formic acid and an alkylamine is mixed with an organic solvent containing a base in a container, whereby the base contained in the organic solvent reacts with formic acid to generate a formate. When mixing the solutions, for example, the solution in the container is adjusted to a temperature of 5°C or higher and 35°C or lower, and stirred for 1 minute to 10 minutes. Since the formate obtained is solid, for example, the suspension containing the generated formate can be separated by a filtration process or other separation process to easily recover the solid formate. Therefore, the formic acid in the solution can be recovered as a formate easily without consuming a large amount of energy for heating or the like.

[0020] The base contained in the organic solvent used in the recovery step is preferably a Bronsted base as strong as the alkylamine, and more preferably a Bronsted base stronger than the alkylamine. When the base is a strong Bronsted base, it becomes easier to recover formic acid in the solution as a salt different from the salt of the alkylamine. The strength of the Bronsted base is determined by pka, and the higher the pKa value, the stronger the Bronsted base. Examples of the base include hydroxides of Group 1 such as sodium hydroxide, potassium hydroxide, and lithium hydroxide, salts of Group 2 such as magnesium hydroxide and calcium hydroxide, and ammonia (ammonium). These may be used alone or in combination of two or more. Among these, ammonia (ammonium) is preferred in that the base remaining in the separation liquid can be easily distilled off, considering that, for example, after the formate is recovered, the alkylamine contained in the separation liquid (for example, the filtrate) from which the formate is separated is extracted and reused. The extracted alkylamine is reused, for example, as the alkylamine used in the extraction step described below.

[0021] The organic solvent used in the recovery step of this embodiment is preferably a good solvent for alkylamines and a poor solvent for formates, in that it can isolate and recover formates with high purity. Examples of organic solvents include ethers such as diethyl ether, tetrahydrofuran, and 1,4-dioxane, alcohols such as methanol, ethanol, and 2-propanol, hydrocarbons such as pentane and hexane, ketones such as acetone and 2-butane, and esters such as ethyl acetate. These may be used alone or in combination of two or more.

[0022] In the organic solvent containing a base, it is preferable that the base is dissolved in the organic solvent in order to improve the recovery amount of the solid formate, and it is preferable that the solubility of the base in the organic solvent is large. In addition, in order to improve the recovery amount of the formate, for example, ammonia is preferable as the base, and methanol, ethanol, 2-propanol, tetrahydrofuran, and 1,4-dioxane are preferable as the organic solvent, and ethanol and 2-propanol are more preferable. In consideration of extracting and reusing the alkylamine contained in the separation liquid (e.g., filtrate) from which the formate is separated after recovery of the formate, ethanol having a lower boiling point is more preferable.

[0023] The equivalent of the base contained in the organic solvent is preferably equal to or greater than the equivalent of formic acid in the solution containing formic acid and alkylamine, from the viewpoint of improving the recovery amount of the solid formate. The upper limit of the equivalent of the base may be, for example, 1.5 or less per equivalent of formic acid in the solution containing formic acid and alkylamine, taking into consideration the effort of distilling off the remaining base.

[0024] As a method for separating and recovering the solid formate from the suspension containing the generated formate, for example, reduced pressure or normal pressure filtration is preferred. When filtering, it is preferred to cool the solution containing the formate in order to improve the recovery amount of the solid formate. In addition, after filtering, an organic solvent is used as a washing liquid to remove the alkylamine remaining in the residue, thereby increasing the purity of the formate in the residue.

[0025] The recovered formate is preferably dried by heating, reducing pressure, or both for storage. Ammonium formate can be recovered by using ammonia as the base in the organic solvent used in the recovery step, and this ammonium formate is chemically stable and can also be used as a hydrogen source.

[0026] In addition, the formic acid recovery method according to the present embodiment further includes, prior to the recovery step, an extraction step of extracting the formic acid from an aqueous solution containing formic acid using an alkylamine represented by the above formula (1) and an organic solvent into an organic solvent layer containing the alkylamine and the organic solvent, and a distillation step of distilling the organic solvent from the organic solvent layer under reduced pressure or normal pressure to obtain a solution containing the formic acid and the alkylamine, and the solution containing the formic acid and the alkylamine obtained in the distillation step may be used as the solution containing the formic acid and the alkylamine in the recovery step described above.

[0027] In the extraction step, for example, an aqueous solution containing formic acid, an alkylamine, and an organic solvent are mixed in a container and left to stand for a predetermined time. As a result, formic acid is extracted into an organic solvent layer containing an alkylamine and an organic solvent that is phase-separated from water. When mixing the solutions, for example, the temperature of the solution in the container is adjusted to 5°C or higher and 35°C or lower, and the solution is stirred for 1 minute to 10 minutes. The time for leaving the mixed solution to stand is, for example, 5 minutes or longer.

[0028] In the above alkylamine, R 1 ~R 3 At least two of the above are independently alkyl groups having 6 to 12 carbon atoms. The alkyl groups having 6 to 12 carbon atoms may be linear, branched, or cyclic alkyl groups, but among these, linear alkyl groups are preferred. The alkyl groups are preferably alkyl groups having 6 to 10 carbon atoms, more preferably alkyl groups having 8 carbon atoms, in that the alkylamine is easily separated from water and formic acid is easily extracted into the organic solvent layer.

[0029] The alkylamine is R 1 ~R3 two of R are independently an alkyl group having 6 to 12 carbon atoms, and the remaining one is a secondary amine having a hydrogen atom; 1 ~R 3 may be a tertiary amine in which all of R are independently an alkyl group having 6 to 12 carbon atoms. The alkylamine is easily separated from water, and formic acid is easily extracted into the organic solvent layer. 1 ~R 3 It is more preferable that all of are independently an alkyl group having 6 to 12 carbon atoms.

[0030] R 1 ~R 3 may all be different alkyl groups, or R 1 ~R 3 Two of the alkyl groups may be the same, or all of the alkyl groups may be the same. From the viewpoint of the cost of the alkylamine, R 1 ~R 3 are preferably all the same alkyl group.

[0031] R 1 ~R 3 The total number of carbon atoms in R is preferably 12 or more, and more preferably 16 or more. 1 ~R 3 If the total number of carbon atoms in R is 11 or less, the solubility of the salt of formic acid and alkylamine in water increases, and the amount of formate recovered may decrease. In addition, from the viewpoint of operability, it is preferable that the salt is a liquid at room temperature and normal pressure. 1 ~R 3 The total number of carbon atoms is preferably 36 or less.

[0032] Among the alkylamines satisfying the above conditions, one kind may be used alone, or a plurality of kinds may be used in combination.

[0033] The equivalent amount of the alkylamine is preferably in the range of 0.5 equivalents or more and 10 equivalents or less relative to the amount of formic acid in the aqueous solution containing formic acid.

[0034] The organic solvent used in the extraction step is preferably a solvent with low solubility in water in order to separate the solvent from water. Also, a solvent with a low boiling point is preferred so that the solvent can be distilled off without consuming a large amount of energy. Considering the fractional distillation with formic acid, which has a boiling point of 101°C, the boiling point of the organic solvent is preferably 80°C or lower, more preferably 60°C or lower. Since it is desirable for the organic solvent to be liquid at room temperature, the lower limit of the boiling point of the organic solvent is preferably 25°C or higher, more preferably 35°C or higher. Also, it is desirable for the organic solvent used in the extraction step to dissolve the alkylamine used together and to dissolve formic acid.

[0035] Considering the above, examples of the organic solvent to be used include cyclohexane (boiling point 81°C), benzene (81°C), carbon tetrachloride (77°C), diethyl ether (35°C), chloroform (62°C), ethyl acetate (77°C), dichloromethane (40°C), petroleum ether (30 to 60°C), hexane (69°C), pentane (69°C), methyl ethyl ketone (80°C), carbon disulfide (47°C), etc. Among these, dichloromethane and diethyl ether, which easily separate from water and have low boiling points, are preferred.

[0036] The organic solvent used in the extraction step may be one of the above, or a combination of two or more of the above. It is preferable to use one of the above because it is easy to set the conditions for distilling off the organic solvent in the distillation step.

[0037] The amount of the organic solvent used in the extraction step is preferably adjusted so that the concentration of the alkylamine is in the range of 1 to 100 times the concentration of formic acid in the aqueous solution containing formic acid.

[0038] The amount of formic acid in the aqueous solution containing formic acid is not particularly limited, but is preferably in the range of, for example, 1 mmol / L to 20 mol / L. The aqueous solution containing formic acid may or may not contain an inorganic salt.

[0039] The aqueous solution containing formic acid is not particularly limited, and examples thereof include an aqueous solution containing formic acid generated from an electrochemical reactor, a photoelectrochemical reactor (including one driven by a solar cell), or a photocatalytic reactor (including one driven by a solar cell), an aqueous solution containing formic acid obtained from an enzyme reaction, etc. The pH of the aqueous solution containing formic acid is preferably 7 or less, for example, from the viewpoint of increasing the extraction rate of formic acid into the organic solvent layer.

[0040] In the distillation step, for example, the organic solvent layer obtained in the extraction step is separated, and the organic solvent in the organic solvent layer is distilled off under reduced pressure or normal pressure. The method for distilling off the organic solvent from the organic solvent layer may be, for example, a normal distillation method or evaporation method. When the boiling point of the organic solvent is high, it is preferable to distill off the organic solvent under reduced pressure. The concentration of formic acid in the solution containing formic acid and alkylamine obtained in the distillation step (i.e., the solution containing formic acid and alkylamine used in the recovery step) is, for example, preferably 0.30 mol / L or more, more preferably 1.0 mol / L or more. EXAMPLES

[0041] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0042] <Example 1> (1) Formic acid (Fujifilm Wako Pure Chemical Industries, Ltd., 0.152 mL, 4 mmol) was added to TOA (Tokyo Chemical Industry Co., Ltd., tri-n-octylamine, 4.00 mL) to prepare a TOA solution containing formic acid (1.0 mol / L). (2) To the TOA solution containing formic acid (1), an ethanol solution containing ammonia (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 2.00 mol / L, 2 mL) was added, and the resulting white solid was filtered under reduced pressure. The obtained white solid weighed 207 mg. (3) Take a portion of the white solid into an NMR sample tube. 1 Using a H-NMR measurement device (JNM-ECX400P, manufactured by JEOL Ltd.), 1As a result of H-NMR measurement, a peak derived from ammonium formate was confirmed, but no peaks derived from TOA or ethanol were confirmed, and therefore the white solid obtained in (3) was confirmed to be ammonium formate (yield 82%, 3.27 mmol).

[0043] <Example 2> (1) Formic acid (0.152 mL, 4 mmol) was added to TOA (4.00 mL) to prepare a TOA solution containing formic acid (1.0 mol / L). (2) (1) Ammonia-containing 2-propanol solution (Fujifilm Wako Pure Chemical Industries, Ltd., 2.00 mol / L, 2 mL) was added to the TOA solution containing formic acid, and the resulting white solid was filtered under reduced pressure. The obtained white solid was 207 mg (yield 82%, 3.27 mmol).

[0044] <Example 3> (1) Formic acid (0.152 mL, 4 mmol) was added to DOA (Tokyo Chemical Industry Co., Ltd., di-n-octylamine, 4.00 mL) to prepare a DOA solution containing formic acid (1.0 mol / L). (2) To the DOA solution containing formic acid (1), an ethanol solution containing ammonia (2.00 mol / L, 2 mL) was added, and the resulting white solid was filtered under reduced pressure. The obtained white solid was 67 mg (yield 27%, 1.08 mmol).

[0045] <Example 4> (1) Formic acid (0.152 mL, 4 mmol) was added to DOA (4.00 mL) to prepare a DOA solution containing formic acid (1.0 mol / L). (2) (1) To the DOA solution containing formic acid, a 2-propanol solution containing ammonia (2.00 mol / L, 2 mL) was added, and the resulting white solid was filtered off under reduced pressure. The obtained white solid was 96 mg (yield 38%, 1.52 mmol).

[0046] <Example 5> (1) Formic acid (0.152 mL, 4 mmol) was added to TOA (4.00 mL) to prepare a TOA solution containing formic acid (1.0 mol / L). (2) To the TOA solution containing formic acid (1), a methanol solution containing ammonia (Merck, 7.00 mol / L, 0.6 mL) was added, and the resulting white solid was filtered under reduced pressure. The obtained white solid was 151 mg (yield 60%, 2.40 mmol).

[0047] <Example 6> (1) Formic acid (0.152 mL, 4 mmol) was added to TOA (4.00 mL) to prepare a TOA solution containing formic acid (1.0 mol / L). (2) To the TOA solution containing formic acid (1), ammonia-containing methanol solution (7.00 mol / L, 0.6 mL) and 1.4 mL of hexane were added, and the resulting white solid was filtered under reduced pressure. The obtained white solid was 143 mg (yield 57%, 2.28 mmol).

[0048] <Example 7> (1) Formic acid (0.046 mL, 1.2 mmol) was added to TOA (4.00 mL) to prepare a TOA solution containing formic acid (0.3 mol / L). (2) To the TOA solution containing formic acid (1), an ethanol solution containing ammonia (2.00 mol / L, 0.6 mL) was added, and the resulting white solid was filtered under reduced pressure. The obtained white solid was 60 mg (yield 79%, 0.95 mmol).

[0049] <Example 8> (1) Formic acid (0.046 mL, 1.2 mmol) was added to TOA (4.00 mL) to prepare a TOA solution containing formic acid (0.3 mol / L). (2) (1) To the TOA solution containing formic acid, a 2-propanol solution containing ammonia (2.00 mol / L, 0.6 mL) was added, and the resulting white solid was filtered off under reduced pressure. The obtained white solid was 44 mg (yield 59%, 0.71 mmol).

[0050] <Example 9> (1) Formic acid (0.046 mL, 1.2 mmol) was added to TOA (4.00 mL) to prepare a TOA solution containing formic acid (0.3 mol / L). (2) To the TOA solution containing formic acid (1), a methanol solution containing ammonia (7.00 mol / L, 0.18 mL) was added, and the resulting white solid was filtered under reduced pressure. The obtained white solid was 60 mg (yield 79%, 0.95 mmol).

[0051] <Example 10> (1) Formic acid (0.046 mL, 1.2 mmol) was added to TOA (4.00 mL) to prepare a TOA solution containing formic acid (0.3 mol / L). (2) (1) A tetrahydrofuran solution containing ammonia (Merck, 2.00 mol / L, 0.60 mL) was added to the TOA solution containing formic acid, and the resulting white solid was filtered under reduced pressure. The obtained white solid was 15 mg (yield 20%, 0.24 mmol).

[0052] The yields of ammonium formate isolated in Examples 1 to 10 are summarized in Table 1.

[0053] [Table 1]

[0054] According to the methods of the Examples, formic acid in a solution can be easily recovered as a formate salt without consuming a large amount of energy for heating, etc. Among Examples 1 to 10, Examples 1 and 2, which used an ethanol solution containing ammonia or a 2-propanol solution containing ammonia as an organic solvent containing a base, showed high yields of ammonium formate.

[0055] [Note] (1) A method for recovering formic acid, comprising a recovery step of mixing a solution containing formic acid and an alkylamine represented by the following formula (1) with an organic solvent containing a base to recover a solid formate salt: R 1 R 2 R3 N (1) (In formula (1), R 1 ~R 3 At least two of the groups are independently alkyl groups having 6 to 12 carbon atoms, and the remaining groups are hydrogen atoms. (2) an extraction step of extracting the formic acid from an aqueous solution containing the formic acid using the alkylamine and an organic solvent into an organic solvent layer containing the alkylamine and the organic solvent; and a distillation step of distilling off the organic solvent from the organic solvent layer under reduced pressure or normal pressure to obtain a solution containing the formic acid and the alkylamine, The method for recovering formic acid according to (1) above, characterized in that the solution containing the formic acid and the alkylamine obtained by the distillation step is used as the solution containing the formic acid and the alkylamine in the recovery step. (3) The method for recovering formic acid according to the above (1) or (2), wherein the base is a Bronsted base stronger than the alkylamine. (4) The method for recovering formic acid according to (3) above, wherein the base is ammonia. (5) The method for recovering formic acid according to any one of the above (1) to (4), wherein the organic solvent used in the recovery step includes at least one of ethanol and 2-propanol. (6) The method for recovering formic acid according to (2) above, characterized in that the aqueous solution containing formic acid is an aqueous solution containing formic acid generated in an electrochemical reactor, a photoelectrochemical reactor (including one driven by a solar cell), or a photocatalytic reactor (including one driven by a solar cell). (7) R 1 ~R 3 The method for recovering formic acid according to any one of the above (1) to (6), wherein each of the formulas is independently an alkyl group having 6 to 12 carbon atoms. (8) R 1 ~R 3The method for recovering formic acid according to any one of the above (1) to (7), wherein the total number of carbon atoms is 12 or more. (9) The method for recovering formic acid according to any one of (1) to (8) above, wherein a concentration of the formic acid in the solution containing the formic acid and the alkylamine is 0.30 mol / L or more.

Claims

1. A method for recovering formic acid, comprising the step of mixing a solution containing formic acid and an alkylamine represented by the following formula (1) with an organic solvent containing a base to recover a solid formate salt: R １ R ２ R ３ N (1) (In formula (1), R １ ~R ３ At least two of the groups are independently an alkyl group having 6 to 12 carbon atoms, and the remaining groups are hydrogen atoms.

2. an extraction step of extracting the formic acid from an aqueous solution containing the formic acid using the alkylamine and an organic solvent into an organic solvent layer containing the alkylamine and the organic solvent; and a distillation step of distilling off the organic solvent from the organic solvent layer under reduced pressure or normal pressure to obtain a solution containing the formic acid and the alkylamine, 2. The method for recovering formic acid according to claim 1, wherein the solution containing the formic acid and the alkylamine obtained in the distillation step is used as the solution containing the formic acid and the alkylamine in the recovery step.

3. 3. The method for recovering formic acid according to claim 1, wherein the base is a Bronsted base stronger than the alkylamine.

4. 4. The method for recovering formic acid according to claim 3, wherein the base is ammonia.

5. 3. The method for recovering formic acid according to claim 1, wherein the organic solvent used in the recovery step includes at least one of ethanol and 2-propanol.

6. 3. The method for recovering formic acid according to claim 2, wherein the aqueous solution containing formic acid is an aqueous solution containing formic acid produced in an electrochemical reactor, a photoelectrochemical reactor (including one driven by a solar cell), or a photocatalytic reactor (including one driven by a solar cell).

7. R １ ~R ３ The method for recovering formic acid according to claim 1 or 2, characterized in that each of the is independently an alkyl group having 6 to 12 carbon atoms.

8. R １ ~R ３ 3. The method for recovering formic acid according to claim 1, wherein the total number of carbon atoms is 12 or more.

9. 3. The method for recovering formic acid according to claim 1, wherein a concentration of the formic acid in the solution containing the formic acid and the alkylamine is 0.30 mol / L or more.

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