JPS6362157A - Diaphragm for redox flow battery - Google Patents

Abstract

PURPOSE:To obtain a diaphragm which has small transmissivity of metallic ions and which is high in voltage and coulomb efficiencies, by forming an alkylamine thin film on one of the surfaces of a cation exchange film. CONSTITUTION:A known cation exchange film is used as this film. After one or more kinds of sulfonic halide radicals such as sulfonyl chloride are introduced as amide acceptor radicals into the cation exchange film or its precursor, the surface or the surface vicinity of the film is processed by alkylamine to obtain an acid amide reaction. As regards alkylamine, saturated straight chain aliphatic amine is suitable in point of a speed of its reaction to acid halide radicals or the like, but unsaturated or chain aliphatic amine is available. The number of carbon is 4-30, especially 8-20 for suitable chain length of chain aliphatic amine.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a diaphragm for a redox flow battery. Specifically, a redox membrane having a thin layer of alkylamine on at least 4-4 surfaces of a cation exchange membrane is suitable for increasing voltage efficiency and coulombic efficiency, especially in iron/chromium-based redox flow battery systems. A diaphragm for a flow battery is provided.

(Prior art) Conventionally, an iron chloride/hydrochloric acid solution was circulated as an anolyte and a chromium chloride/hydrochloric acid solution was circulated as a catholyte in a field chamber and a cathode chamber that separated the adjacent electrode from the cathode through a diaphragm, and each metal ion A redox flow battery is known that performs charging and discharging by oxidizing and reducing the valence of 2 and 445. A diaphragm for such a redox flow battery should: ■ be excellent in proton permeability and have low permeation of chromium (Cr) ions and iron (Fe) ions; ■ have excellent hydrochloric acid resistance and strength; and ■ have low membrane resistance in the system in which it is used. It is required to be small and have low electrical resistance during charging and discharging, for example, anion exchange membranes (Japanese Patent Application Laid-open No. 112431/1983) and cation exchange membranes (Nozaki et al., Research Report of Electronic Technology Research Institute). , No. 201, (1
979)) has been proposed. However, in the case of anion exchange membranes, mixing of metal ions in both electrode chambers can be prevented, but due to the movement of chlorine ions (CCC) in the membrane, the membrane resistance in the system used is large, and the voltage during charging and discharging is There is a problem that the drop (IRdrop) becomes large. In addition, in the case of cation exchange membranes, proton ions move through the membrane, which reduces the membrane resistance in the system used, but since metal ions are mixed, it may cause self-discharge, and active materials such as metal salts may There is a problem of decreasing the solubility and concentration of

To solve the above-mentioned problem, recently, for example, a thin anion exchange layer and a thin cation exchange layer have been developed, and AC resistance in hydrochloric acid is 0.
．． A diaphragm having a resistance of 03 to 2Ω・- (JP-A-59-2051<
No. 55), both surface layers are composed of anion exchange thin layers, and at least a cation exchange layer is present as an intermediate layer between them, and the AC resistance in hydrochloric acid is 0.03 to 2Q-1 (Japanese Patent Application Laid-open No. 60-20462), a field ion exchange resin with a high degree of crosslinking, an anion exchange resin with a high degree of crosslinking,
A diaphragm coated with a substance selected from polyamines and hydrophobic polymers (Japanese Unexamined Patent Publication No. 160560/1983) has been proposed and discussed.

(Problem to be Solved by the Invention) However, although the proposed diaphragm as described above satisfies all the required functions, it is difficult to use the diaphragm when used as a diaphragm for an industrial Redovx flow battery. There is a demand for a diaphragm with a small amount of ion permeation and high voltage efficiency and Coulombic efficiency.

(Means for Solving the Problems) As a result of intensive studies in view of the above-mentioned problems, the present inventors have found that a diaphragm in which an alkylamine of a specified chain length is reactively bonded to at least one surface of an adjacent ion-exchange membrane has been developed as described above. The present inventors have discovered that the present invention is suitable as a diaphragm, and have proposed the present invention. That is, the present invention is a diaphragm for a redox flow battery having a thin layer of alkylamine on at least one surface of a cation exchange membrane.

The cation exchange membrane used in the present invention is not particularly limited, and any known cation exchange membrane can be used. In general, a monomer having a cation exchange group or a functional group suitable for introducing a cation exchange group, an aromatic compound having both a halogen-substituted alkyl group and a polymerizable vinyl group.

Cross-linking agent 9 After polymerization with a suitable combination of a polymerization catalyst, other monomers copolymerizable with the above monomers, a plasticizer, or if necessary a finely powdered thermoplastic polymer substance as a reinforcing material, a base material, etc., cross-linking treatment is performed. And, if necessary, a membrane obtained by introducing an ion exchange group is used.

Examples of monomers having a cation exchange group or a functional group suitable for introduction of a cation exchange group include styrene, vinyltoluene, styrene sulfonic acid derivatives, and vinyl sulfonic acid derivatives.

Acrylic acid ester, maleic anhydride, etc. are used. Divinyl compounds such as divinylbenzene are generally used as crosslinking agents.

Examples of the aromatic compound having both a halogen-substituted alkyl group and a polymerizable vinyl group include chloromethylstyrene, chloromethylvinylnaphthalene, bromomethylstyrene, and bromomethylvinylnaphthalene. Examples of the polymerization catalyst include benzoyl peroxide, azobisin butyronitrile, and dicumyl peroxide.

Examples of other copolymerizable monomers include acrylonitrile, maleic anhydride, acrylic esters, and methacrylic esters. Examples of fine powder thermoplastic polymer substances include polyethylene, polypropylene, polyvinyl chloride, acrylonitrile-vinyl chloride copolymer, vinyl chloride-vinylidene chloride copolymer,
It is a known soluble and dispersible polymer compound such as NBR, SBR, and polybutadiene. Furthermore, the base material may be inorganic or organic, such as glass fiber.

Vinylon, Kanelon, Tehiron*7) ”:/
Saran, nylon, Bonnell C or higher, product name).

A known cloth or net-like material such as polyethylene or polypropylene may be used.

In the present invention, the method for forming a thin layer of alkylamine on at least one surface of the cation exchange membrane is not particularly limited, but it is generally recommended to bond the alkylamine by acid amidation (bonding). That is, cation exchange membranes or their precursors may have sulfonic acid halide groups, such as sulfonyl chloride, sulfonyl bromide, sulfonyl iodide, as well as carboxylic acid halide groups or sulfonic anhydride groups, as amidation acceptor groups.

After introducing one or more carboxylic anhydride groups.

A method in which the acid amidation reaction is carried out by treating the surface or the vicinity of the surface with an alkylamine is preferable.As the Ao alkylamine, from the viewpoint of reaction rate with the above-mentioned acid halide group, saturated linear aliphatic Amines are preferred, but unsaturated or branched aliphatic amines are also effective.

The chain length of the chain aliphatic amine is 4 to 30 carbon atoms, especially 8 to 2 carbon atoms.
0 is preferable, and when an amine with a chain length shorter than 4 is used, the amount of metal ions permeated through the obtained diaphragm is large, and when an amine with a chain length longer than 30 is used, the membrane resistance is Preferred chain aliphatic alkylamines such as butylamine, octylamine, hexamethylene diamine, laurylamine, and stearylamine are preferable because of their large size.

Dioctylamine, cyamylamine, ethylenediamine, di(2ethylhexyl)amine, N-methylhexylamine, N-methylpropylamine, diallylamine, didecylamine, etc. are used. Further, as an aromatic alkylamine, for example, benzylamine.

Dibenzylamine, 1,3-4-piperidylpropane, dicyclohexylamine, 4-pipecoline, etc. are used.

In the present invention, the conditions for reacting the alkylamine on the surface of the field ion exchange membrane or its precursor are as follows: under reduced pressure, normal pressure, or increased pressure, the temperature is from -20°C to a temperature below which decomposition and deterioration of the polymer compound does not occur. Although there is no particular restriction, when only the surface layer of the layer is reacted, it is preferable to react in a relatively short time so that the reaction proceeds depending on the reaction rate of the amine. After the reaction, excess unreacted alkylamine may be washed away with a solvent that dissolves the alkylamine, and the remaining unreacted acid halide groups or acid anhydride groups may be converted into cation exchange groups. As a means for converting into an ion exchange group, conventionally known hydrolysis reactions can be used without any limitations. For example, aqueous solutions of alkali metals, alkaline earth metals, and hydroxide ion type organic amines.

It is possible to hydrolyze a polymer compound by immersing it in a water-organic solvent mixture at room temperature or under heating. (most commonly hydroxide) Aqueous or alcoholic solutions of IJum, potassium hydroxide, etc.

Although an alcoholic aqueous solution or the like is used, a solvent that can swell the polymer chain may be appropriately selected depending on the type of polymer compound.

To give a more specific example of the S-type sulfonic acid, for example, a resin substrate with a three-dimensional structure obtained by polymerizing a heptamer mixture of chlorosulfonic acid or carbon tetrachloride, tetrachloride, etc. Immersion in a chlorosulfonic acid solution diluted with a solvent such as chloroethane at room temperature or lower than room temperature, or SO2 and C2
After photochemically chlorosulfonating the substrate by irradiating it with ultraviolet rays in a gas of Z, the sulfonyl chloride group on the surface of the substrate is reacted with the amino group by applying an alkylamine or a solution thereof or by immersing it in the solution. The resin substrate having the sulfonic acid amide on the surface obtained by smelting is then immersed in an alkaline solution to convert the remaining sulfonyl chloride groups into sulfonate. Similarly, examples of carboxylic acid amide types include maleic anhydride, styrene, and divinylbenzene.

The surface of a resin base made of a copolymer of haloalkylstyrene is treated with an alkylamine solution to form an acid amide bond, and the remaining carboxylic acid anhydride is then hydrolyzed to form the redox flow battery diaphragm of the present invention. can be obtained.

In the present invention, the thickness of the alkylamine layer on the surface of the cation exchange membrane is selected depending on the fence of the cation exchange membrane, the ion exchange capacity, etc., but the reaction amount of the alkylamine is important and the electrical resistance of the membrane is large. Become. Therefore, the diaphragm of the present invention has an electrical resistance measured in IN-HCl of 1.5 compared to a field ion exchange membrane to which no alkylamine is bonded.
It is desirable that the range does not exceed twice that. For this purpose, it is necessary to apply a film with a thickness of 2ooX or more and a thickness of 1A or less on only one side of the film.
It is effective to react in a range of 1 to 50% of the total ion exchange groups. Note that if the amount is too small, the amount of metal ions permeated will be large and the Coulombic efficiency will be reduced, and if it is too large, the IR drop during discharge will be large, and in either case, the purpose of the present invention is not achieved. Not achieved on the feet.

(Functions and Effects) As described above, according to the redox flow battery diaphragm of the present invention in which a thin layer of alkylamine is formed on the surface of the cation exchange membrane, the %lC iron/chromium based redox flow battery system It is possible to increase the voltage efficiency and coulomb efficiency.

Although the detailed mechanism by which the diaphragm of the present invention exhibits such excellent performance is not clear, it is presumed to be due to the synergistic effect of the bond between the acid amide group and the alkyl group.

(Examples) Hereinafter, the present invention will be described in detail based on Examples, but the present invention is not particularly limited to the following Examples.

Example 1 and Comparative Example 1 10 parts by weight of methicine, 2 parts by weight of chloromethylstyrene, 2 parts by weight of acrylonitrile, 1 part by weight of dioctyl phthalate
Add 0 parts by weight of benzoyl peroxide to a monomer mixture solution prepared by heating and mixing 1 part by weight of finely powdered polyvinyl chloride.
．． After adding 2 parts by weight and applying it to a polyvinyl chloride cloth,
A polymer membrane matrix (thick film) was obtained by heating and polymerizing. The obtained thick film was placed in a solution of sulfuric acid-chlorosulfonic acid (1:1),
It was treated at 40°C for 1 hour. Next, the membrane was immersed in a 5% dioctylamine (inpropyl ether) solution for 16 hours, and then in a 2N aqueous sodium hydroxide solution for 2 hours to obtain a diaphragm of the present invention.

On the other hand, for comparison, the chlorosulfonated membrane was immersed in a 2N aqueous solution of caustic soda for 2 hours without being treated with dioctylamine to obtain a cation exchange membrane.

Each of the above-mentioned membranes was assembled into a liquid flow type unit cell having an electrode area of 10 J and having a carbon cloth minode at each of the anode and cathode.
A 4N hydrochloric acid aqueous solution containing M iron at a temperature of 40°C and 1!
Charging and discharging experiments were conducted at a flow density of AQmA/4.

The results are shown in Table 1.

Example 2 and Comparative Example 2 10 parts by weight of styrene, 1 part of divinylbenzene with a purity of 55%
parts by weight, 1 part by weight of dibutyl phthalate, 5 parts by weight of fine polyvinyl chloride powder, and 0.2 parts by weight of benzoyl peroxide.
A paste-like mixture obtained by mixing heavy titanium was applied to a polyvinyl chloride cloth, deaerated, one side covered with polyester film, and heated and polymerized at 70°C for 3 hours and 80°C for 4 hours. A polymer membrane with a length of about 0.13 m was obtained. This is mixed with 98% concentrated sulfuric acid and chlorosulfonic acid with a purity of over 90%.
1 for 45 minutes at 40° C. to introduce sulfonyl chloride groups and sulfonic acid groups. The ratio of sulfonyl chloride groups to sulfonic acid was 60:40. Next, the water on the surface of this membrane was wiped off and air-dried, and it was immersed in a 5% butylamine (hexane) solution for 8 hours at room temperature, then immersed in a 2N aqueous solution of caustic soda for 1 hour, and The diaphragm of the present invention was obtained by immersing it in specified hydrochloric acid.

On the other hand, for comparison, the membranes were subjected to the same chlorosulfonation treatment, and then immersed in t2 normal caustic soda solution and then immersed in 1 N hydrochloric acid to obtain a cation exchange membrane.

Table 1 below shows the results of charging and discharging experiments conducted in the same manner as in Example 1.

Example 3 and Comparative Example 6 10 parts by weight of styrene, 55% pure divinylbenzene szz parts, 3 parts by weight of bromomethylstyrene, 4 parts by weight of maleic anhydride, 71 parts of dioxane and 2 parts by weight of azoinbutyronitrile. Add and mix evenly, then add 2
It was poured into a polypropylene cloth sandwiched between two parallel glass plates. It was heated under pressure in an autoclave at 60° C. for 4 hours and at 70° C. for 7 hours, and after cooling, the glass plate was removed and the polymer membrane reinforced with cloth was taken out. Then,
This was immersed in N-methylhexylamine at 25°C for 2 hours. Furthermore, this was mixed with methanol of 2N caustic soda.
The @ membrane of the present invention was obtained by immersing it in a 1:1 mixed solution of water to hydrolyze the acid anhydride group and convert the carboxylate to Na salt.

On the other hand, for comparison, a cation exchange membrane was obtained by directly hydrolyzing the polymer membrane synthesized above without reacting it with N-methylhexylamine.

The results of charging and discharging experiments conducted in the same manner as in Example 1 are also listed in Table 1 below.

Example 4 and Comparative Example 4 A copolymer film of tetrafluoroethylene and perfluoro(3,6-thioxer-4-methyl-7-octensulfonyl fluoride) was mixed with 600 parts of water, 400 parts of dimethyl sulfoxide, and 15 parts of potassium hydroxide. A potassium sulfonate type cation exchange membrane was obtained by immersing the membrane in a bath consisting of 300 ml of water and hydrolyzing it. Next, this film was immersed in 3N nitric acid at 60°C to completely convert it to the acid form, and then phosphorus pentachloride crystals were uniformly dispersed on both film surfaces, and this was placed between a hot plate kept at 150°C. The crystals of phosphorus pentachloride were sublimed and left for 1 hour.

Next, this membrane was mixed with 400 parts of hexamethylene diamine and 1 part of water.
After immersing the sample in a bath consisting of 0.00 parts at room temperature for 24 hours, it was immersed as it was in a hydrolysis tower consisting of a water-dimethylsulfoxy toker solution to hydrolyze unreacted sulfonyl chloride groups. The diaphragm of the present invention was obtained by thoroughly washing and immersing this membrane in 1N hydrochloric acid.

On the other hand, for comparison, the above membrane was hydrolyzed without being treated with hexamethylene diamine to obtain a cation exchange membrane.

The results of charging and discharging experiments conducted in the same manner as in Example 1 are also listed in Table 1 below.

Claims (1)

[Claims] 1) A diaphragm for a redox flow battery having a thin layer of alkylamine on at least one surface of the cation exchange membrane.2) A patent claim in which the alkylamine is a chain aliphatic amine having 4 to 30 carbon atoms. 3) The diaphragm according to claim 1, wherein the alkylamine is at least one selected from dioctylamine, butylamine, N-methylhexylamine, and hexamethylene diamine 4) Cation 5) A diaphragm according to claim 1, wherein the alkylamine forms a thin layer on the surface of the exchange membrane through chemical bonding.
The diaphragm according to claim 1, which is 0%