JPS5939452B2 - Treatment method for cation exchanger - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating a cation exchanger in which a fluorine atom and a cation exchange group are bonded, and an improved fluorine-containing rapid cation exchange method by reaction-treating the cation exchanger. It provides the body.

So-called fluorine-containing rapid ion exchangers, which combine fluorine atoms and ion exchange groups, are considered useful as oxidation-resistant ion exchangers, but as ion exchangers there is a need to further improve performance and develop new functions. be done.

For example, membrane-like rapid cation exchangers containing fluorine are useful as diaphragms for electrolysis of alkali metal salts, but hydroxide ions are unusually easy to permeate through the cation exchange membrane even at high concentrations of alkali metal hydroxides. A very high fixed ion concentration is required to prevent the passage of ions. In addition, there is a demand for a variety of uses for fluorine-containing rapid ion exchangers in various shapes such as film, granules, fine powder, and fibers with new functions. However, rapid ion exchangers containing fluorine may be less reactive than hydrocarbon-based ion exchangers.
It is extremely difficult to improve performance or provide new performance. That is, in the case of hydrocarbon-based granular or membrane cation exchangers, for example, oxidative decomposition results in a porous ion exchanger, or only the surface layer of the anion exchange membrane is oxidized and decomposed to form an anion exchange membrane that is difficult to permeate to sulfate ions. A method of manufacturing has been proposed. However, fluorine-containing ion exchangers are not easily oxidized and decomposed due to their natural property of oxidation resistance. For example, if a hydrocarbon-based cation exchanger has strong oxidizing properties such as a sulfonic acid group, it can be easily decomposed in an oxidizing atmosphere through ion exchange with heavy metal ions such as iron, but fluorine-containing cations It cannot be applied to exchange bodies. The present inventors performed a reaction treatment on a fluorine-containing cation exchanger to simply decompose and remove a specific amount of fluorine atoms or cation exchange groups from the fluorine-containing cation exchanger, thereby improving its performance. The present invention was completed based on the discovery that it is possible to improve the performance or provide new functions.

That is, the present invention uses a polymer having a fluorine atom and a cation exchange group or a functional group that can be easily converted into a cation exchange group, such as aluminum chloride, alkali metal, etc.
Fluorine atoms and/or the cation exchange group in the 5 micron surface layer of the polymer are easily converted into cation exchange groups by treatment with at least one reaction agent selected from naphthalene and alkali metal amide. This is an improved method for treating a cation exchanger, in which 3 to 90% of the functional groups that can be used are removed and, if necessary, the remaining functional groups are converted to cation exchange groups. In the treatment of the cation exchanger of the present invention, it is easy to use a fluorine-containing cation exchanger in which a fluorine atom and a cation exchange group are bonded, or a fluorine atom that is a precursor of the fluorine-containing cation exchanger. It is essential to use as a starting material a polymer in which a functional group that can be converted into a cation exchange group is bonded to the polymer. As the above-mentioned fluorine-containing cation exchanger or its precursor polymer,
There are no particular limitations as long as the fluorine atom and a cation exchange group or a functional group that can be easily converted into a cation exchange group are uniformly bonded. Hereinafter, these will be collectively referred to simply as fluorine-containing cation exchangers. For example, perfluorinated hydrocarbon cation exchangers in which all hydrogen atoms are replaced with fluorine atoms are preferable, but others such as polyvinyl fluoride and polyvinylidene fluoride, in which some fluorine atoms are hydrogen, are preferable. , chlorine, bromine, etc., or a copolymer of a perfluoro vinyl monomer and a hydrocarbon vinyl monomer. In addition, as a cation exchange group, a sulfonic acid group is common, but a carboxylic acid group, a phosphoric acid group, a phosphorous acid group, a sulfuric acid ester group, a phosphoric acid ester group,
Contains at least one or more of phosphite groups, phenolic hydroxyl groups, thiol groups, acid amide groups with dissociable hydrogen atoms, etc., and under the use conditions of cation exchange membranes such as neutral, acidic, and alkaline conditions. There is no restriction at all as long as a functional group capable of becoming negatively charged is chemically and stably bonded. In the present invention, the reaction reagent for treating the above-mentioned fluorine-containing cation exchanger is a defluorinating agent or a reagent that eliminates a cation exchange group or a functional group that can be easily converted into a cation exchange group. The reaction conditions are not particularly limited as long as they are selected from aluminum halides, alkali metal naphthalenes, and alkali metal amides, but the reaction conditions vary depending on the molecular structure, shape, etc. of the fluorine-containing cation exchanger. Not determined.

As a result of repeated experiments under various conditions, a cation exchanger obtained by removing the fluorine atom or cation exchange group from a fluorine-containing cation exchanger was found to have a surface layer of 5 microns with fluorescent X-rays. By removing 3% to 90%, preferably 5% to 85% of the fluorine atoms and/or cation exchange groups in the fluorine-containing cation exchanger, compared to the untreated fluorine-containing cation exchanger. As a result, significant performance improvements or new functional effects can be realized. For example, the fluorine-containing cation exchanger obtained by the reaction treatment of the present invention has a much higher fixed ion concentration than the untreated fluorine-containing cation exchanger, and the above-mentioned alkali It is extremely useful as a diaphragm for electrolysis of metal salts, and it is possible to maintain and obtain a high concentration of alkali metal hydroxide with high current efficiency. This is because by removing the cation exchange groups of the fluorine-containing cation exchange membrane, a hydrophobic atmosphere is formed, the water content is reduced, and the fixed ion concentration within the membrane is improved. It is also believed that by removing the fluorine atoms from the fluorine-containing cation exchange membrane, the hydrophobic bonding portion is decomposed, the ion exchange capacity per unit weight increases, and the fixed ion concentration within the membrane also increases. In this case, if the hydrophobic atmosphere is too strong, the electrical resistance of the membrane will generally increase dramatically, so it is important not to decompose the cation exchange groups, but to remove the fluorine atoms and decompose the hydrophobic bond parts. It is. Therefore, in the present invention, when manufacturing a cation exchange membrane suitable for use as a diaphragm for electrolysis of alkali metal salts, it is necessary to consider the fixed ion concentration and electrical resistance in consideration of the balance between ion exchange capacity and water content. It is necessary to decompose and remove the fluorine atom or the cation exchange group, or both, in the fluorine-based cation exchange. In addition, when the cation exchange groups on the surface of a granular or film-like fluorine-containing cation exchanger are selectively decomposed and removed, inorganic ions can be selectively removed from a salt solution containing large organic ions. Ion-exchange removal does not cause irreversible changes in the properties of the ion-exchange resin, and electrodialysis of a salt solution containing giant organic ions causes little increase in the electrical resistance of the membrane over time. Furthermore, in this case, when a salt solution containing two types of ions with different charges is subjected to electrodialysis or ion exchange treatment, an effect of selectively permeating or ion-exchanging ions with a lower charge is also exhibited. A method for removing cation exchange groups or fluorine atoms by treating the fluorine-containing cation exchanger of the present invention will be described below, but the method is not limited thereto. Examples of methods for treating a fluorine-containing cation exchanger with a reaction reagent to decompose and remove cation exchange groups (or functional groups that can be easily converted into cation exchange groups) include anhydrous aluminum trichloride,
A method of heating and melting aluminum halides such as anhydrous aluminum tribromide, or a method of liquefying and sublimating these compounds and bringing this vapor into contact with an ion exchanger is especially effective for decomposing and removing ion exchange groups. It is effective for In addition, using the above reaction reagent, carbon, fluorine, cation exchange groups and other elements,
For example, when hydrogen, chlorine, oxygen, nitrogen, sulfur, etc. are bonded in a polymer chain, it is also an effective method to selectively decompose the bonded sites. For example, a cation exchanger obtained by hydrolyzing a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether sulfonyl chloride has ether bonds, which can be selectively cleaved with anhydrous aluminum halide. In these cases, depending on the bonding form of the above elements and the way they exist in the polymer chain, they promote the generation of a hydrophobic binding atmosphere or increase the exchange capacity. In addition, in order to decompose and remove the fluorine atom of a fluorine-containing cation exchanger, a reagent with a fluorine-deflating action, which is generally used to improve the adhesion of conventional fluorine-containing cation exchangers, especially polytetrafluoroethylene, is used. For example, an alkali metal amide such as NaNH2, an alkali metal naphthalene such as sodium-naphthalene-THF, etc. are preferably used.
Next, the method for treating a fluorine-containing cation exchanger according to the present invention will be explained in more detail, but the method is not limited thereto.

That is, the cation exchange groups may be decomposed only in the surface layer of the fluorine-containing cation exchanger, or may be decomposed uniformly into the interior. In particular, in the case of membrane-like fluorine-containing cation exchangers, decomposition occurs only on one membrane surface, decomposition occurs in a gradient from the surface of the membrane toward the back surface, and decomposition occurs in a layered manner only on one membrane surface. Decomposition, decomposition into layers on both sides, decomposition in a gradient from both sides of the membrane-like object toward the inside, one membrane surface is decomposed uniformly, and the other membrane surface is not decomposed at all, and two sheets of the membrane-like object are glued together. Alternatively, any state regarding the cross section of the film-like material may be used, such as a method of fusion bonding. The same applies to the width direction and length direction of the film-like material.
For example, when used as a membrane, the concentration of the electrolyte in contact differs along the length of the membrane, and when it is necessary to show the same transfer number, the part of the membrane that comes into contact with a concentrated electrolyte solution has fixed ions. The concentration is high, and it is necessary to keep the fixed ion concentration low in the part of the membrane that is in contact with the dilute electrolyte solution. Furthermore, in the decomposition treatment of the fluorine-containing cation exchanger, for example, a reagent that selectively removes fluorine atoms and a reagent that selectively decomposes cation exchange groups may be used in combination.

That is, after reacting with a fluorine atom removal reagent, it is treated with a cation exchange group decomposition reagent, or conversely, after being treated with a cation exchange group decomposition reagent, it is treated with a fluorine atom removal reagent. In the case of a membrane-like material, the treatment method includes reacting a fluorine atom removing reagent from one membrane surface and reacting a cation exchange group decomposing reagent from the other membrane surface. Incidentally, in the fluorine-containing cation exchanger subjected to such decomposition treatment, active sites remain in the polymer chain from which the chain has been cut or the fluorine atom has been extracted. That is, even if the intended performance of the fluorine-containing cation exchanger is temporarily achieved through decomposition, it may further decompose from its active parts. Therefore, in order to prevent this, it is also desirable to carry out decomposition prevention treatment after the decomposition treatment to prevent further decomposition of the disassembled portion. This can be carried out in the same way as normal polymerization, condensation, etc. of polymers or stabilization of condensed terminals. For example, if the decomposed terminal has an active halogen atom, a reagent that reacts with it, such as an amine, may be used. All you have to do is react with Some more detailed examples are shown below.
A perfluoro-based polymer film obtained from a copolymer of tetrafluoroethylene and perfluoro(3,6-dioxa4-methyl-J-octensulfonyl fluoride) is placed in an autoclave, and an anhydrous solution is placed at the bottom of the autoclave. As a result of adding aluminum chloride and heating it to 200℃ to generate steam, and exposing the above perfluoro membrane to this steam, the amount of sulfonic acid groups in the surface layer was significantly reduced, and the amount of fluorine was significantly increased. No decrease observed. This is thought to be caused by decomposition into, for example, etc., but some of these terminal groups are unstable, and it is also possible to treat them with ammonia, primary, or secondary amines in order to stabilize the decomposed terminals. It may be valid.

This treatment reduces the amount of sulfonyl fluoride groups on the surface layer of the membrane-like fluorine-containing cation exchanger, and when it is hydrolyzed to form a sulfonate, the amount of ion exchange groups on the membrane surface decreases. Since hydrophobic binding is emphasized, the water content is further reduced, the fixed ion concentration in the surface layer of the ion exchange membrane is increased, and the performance of the membrane is improved. In addition, the above-mentioned perfluoro-based polymer film having a sulfonyl fluoride group was immersed in potassium hydroxide to make it into a potassium ion form, and then the film made into an acid form with nitric acid was immersed in an ammonia solution of Na-NH2. When immersed, a phenomenon is observed in which the fluorine atoms of the film are removed and there is almost no decrease in the sulfonic acid groups.

As a result, there is no change in the ion exchange capacity of the membrane, but the water content increases and the electrical resistance of the membrane decreases.
Further, the fine powder of the above-mentioned perfluoro-based polymer having a sulfonyl fluoride group is uniformly mixed with the fine powder of polyethylene trifluoromonochloride, and a low polymer of ethylene trifluoromonochloride is added as a plasticizer. (oil) is mixed uniformly and heat-fused to form a polymer film, and when this is immersed in molten aluminum chloride, only the part of the polymer having perfluorinated sulfonyl fluoride groups is removed. is decomposed, and a microporous membrane of polyethylene trifluoride monochloride can be obtained.

Example 1 After molding a copolymer of tetrafluoroethylene and perfluoro(3,6-dioxa-4-methyl-J-m[octensulfonyl fluoride) into a 0.2 mm sheet,
This was immersed in 6.0N-KOH at 80°C, then washed with water, and then immersed in 5N-HNO3 to convert it into a sulfonic acid group.

Its exchange capacity was 0.91 meq/g dry membrane (Type H). This cation exchange membrane was sufficiently dried in a vacuum dryer at 110° C., then wrapped around a stainless steel cylinder, the back side of the membrane was completely sealed, and then placed in an autoclave. The inside of the autoclave was divided into two stages, a stainless steel wire mesh was placed in the center, anhydrous aluminum trichloride crystals were placed under the wire mesh, and the above-mentioned cation exchange membrane wrapped around the stainless steel cylinder was placed on top of the wire mesh. Ta. This autoclave was completely sealed and immersed in an oil bath at 200° C. for the predetermined time shown in Table 1. Thereafter, the membrane was taken out and thoroughly washed with 2N hydrochloric acid, and the sealed membrane surface and the membrane surface exposed to aluminum chloride vapor were examined using fluorescent X-rays to measure the amounts of S and F. F. shown in Table 1. The S value is the ratio of the membrane surface exposed to aluminum chloride vapor to the sealed membrane surface, and it can be seen that S is selectively decomposed and removed. The analysis error of F using fluorescent X-rays is ±0.
The analysis error of 01, S is ±0.005. The same applies to the following examples. Next, electrolysis of saturated saline solution was carried out using each membrane shown in Table 1.

A titanium wire mesh coated with titanium oxide and ruthenium oxide was used as the anode, and a mild steel wire mesh was used as the cathode. Effective current carrying area is 1 dm゛, current density is 30
Saturated saline was supplied to the anode chamber by A/Drrl, and the concentration of the saline at the outlet was 3.5N. Further, pure water was supplied into the cathode chamber so that 6.0N-NaOH was constantly obtained from the cathode chamber. Table 1 shows the results of current efficiency and voltage.

Example 2 Exchange capacity when a copolymer of tetrafluoroethylene and perfluoro(3-6-dioxa-4-methyl-J-octensulfonyl fluoride) is hydrolyzed to form a sulfonic acid type cation exchange membrane is 0.66 meq/g dry membrane (H type) and has a thickness of 2 mm,
A 4 mm thick sheet of the same 0.91 meq/g dry membrane (H type) was heat-fused with a plain woven polytetrafluoroethylene cloth in between to form a polymer membrane. did.

This sulfonyl fluoride type polymer film was placed in a stainless steel autoclave, the membrane surface with high exchange capacity was completely sealed, and aluminum bromide anhydride crystals were placed in the autoclave at 120°C. After heating to generate vapor of aluminum bromide 5 and exposing the membrane surface with a small exchange capacity to this vapor for the treatment time shown in Table 2, it was washed with water and further immersed in 6.0N-KOH at 80°C. The sulfonyl fluoride inside the membrane was hydrolyzed and converted to sulfonic acid potassium salt. After thoroughly washing this cation exchange membrane with pure water and drying it, it was exposed to F and S using fluorescent X-rays.
The amount of was measured. Using each membrane shown in Table 2, electrolysis of a saturated KCl solution was carried out under the same conditions using the same apparatus as in Example 1, and 6.0 NKOH was constantly generated from the cathode chamber.
obtained.

The results are shown in Table 2. Example 3 The same tetrafluoroethylene and perfluoro(3
・A film-like polymer consisting of a copolymer of 6-dioxa-4-methyl-J-octensulfonyl fluoride was mixed with 1.5 parts of metallic sodium and 38 parts of naphthalene in 500 parts of tetrahydrofuran with the sulfonyl fluoride group intact. After being immersed in the dissolved solution for each of the predetermined times shown in Table 3, it was thoroughly washed with methanol.

Then, it was immersed in 6.0N-KOH to hydrolyze the sulfonyl fluoride groups and convert them into potassium sulfonate. The amount of fluorine atoms in the surface layer of this cation exchange membrane was examined using fluorescent X-rays. Separately, a membrane immersed in 6.0NKOH without the above metal sodium-naphthalene treatment was also investigated. Using each of the above membranes, electrolysis of saturated saline water was carried out in the same electrolytic cell as in Example 1 under the same conditions.

The results are shown in Table W.3. Example 4 The potassium perfluorosulfonate type cation exchange membrane used in Example 1 was mixed with each of the potassium perfluorosulfonate type cation exchange membranes shown in Table 4 in a solution containing 5 parts of sodium metal in 100 parts of liquid ammonia cooled with dry ice-methanol. It was immersed for a predetermined time.

The surface layer of each film obtained was analyzed using fluorescent X-rays to determine the amount of F. At the same time, similar measurements were made on untreated membranes. Next, the same electrolysis of saturated saline solution as in Example 3 was carried out using each of the above membranes.

The results are shown in Table 4. Note that the current efficiency is data obtained on the third day after starting electrolysis of saturated saline.

The electrical resistance of the film is 5.0N-NaOH and 5.0N-N.
The membrane was sandwiched between aCl and the measurement was performed at 80° C. for 1000 cycles of alternating current. Example 5 A linear polymer obtained by polymerizing α, β, β1-trifluorostyrene by a conventional method is treated with chlorosulfonic acid (purity 90% or more) at 70°C to undergo chlorsulfonation treatment to obtain chlorsulfone. introduced a group.

This was heated to form sulfone crosslinks with the chlorsulfone groups, resulting in a finely powdered ion exchange resin having a three-dimensional structure. Next, this fine powder was mixed with a fine powder of polytrifluoromonochloroethylene in a ratio of 1:1 by weight, and then a low molecular weight polytrifluoromonoethylene ethylene (manufactured by Daikin Industries, Ltd.,
Add 0.2 of type roll #3) to 1 part of the polymer mixture and heat and pressure mold it to a thickness of 0.2 m! It was made into a polymer film. This polymer film-like material was diluted with 4.0N-NaOH.
The sulfonyl chloride groups in the film were converted to sodium sulfonate by immersion in the solution. The obtained cation exchange membrane was then immersed for 12 hours in a solution of 5 parts of sodium metal and 40 parts of naphthalene in 500 parts of tetrahydrofuran. As a result of measuring the exchange capacity, it was found that the cation exchange membrane before treatment had a capacity of 1.2 meq/g dry membrane (H
0.1 milliequivalent/g dry film (H
type) below. Furthermore, as a result of applying water pressure to this treatment membrane and examining the water permeability of pure water, the cation exchange membrane had almost no water permeability, but the cation exchange membrane had almost no water permeability, but the water permeability of 120CC/[Hr-Cri.
(K9/Cd)]. Therefore, when the pore diameter was determined by measuring the amount of water permeation while varying the pressure, it was found to be a microporous membrane with a micropore diameter of approximately 0.2 microns. On the other hand, the same polymer film as described above was made into an iron ion type, which was then immersed in a hydrogen peroxide solution.

Note that 30% hydrogen peroxide solution was used and left for 48 hours, but the exchange capacity of the cation exchange membrane was 1.0 milliequivalent/
It had decreased only to a gram dry film (H type). In addition, there was almost no water permeation through the membrane. Example 6 A granular polymer compound obtained by copolymerizing tetrafluoroethylene and perfluoro(3,6-dioxa-4-methyl-J-octensulfonyl fluoride) was 6.0N-KO
When immersed in H at 80°C, its exchange capacity was 0.91 meq/g dry resin (H form).

This cation exchange resin was placed in an autoclave containing anhydrous aluminum chloride so that the resin did not come into contact with the anhydrous aluminum chloride crystals. It was then heated to 180° C. for 30 minutes to ensure uniform contact of the anhydrous aluminum chloride vapor with the resin. This resin was sandwiched between hot plates heated to 240'C and pressed to form a sheet. When we determined the amount of S and F on this sheet using fluorescent X-rays, we found that
Compared to the one not treated with anhydrous aluminum chloride (S and F of untreated resin are 1.0), S is 0.82 and F is 0.
It was 95. A surfactant (laurylpyridinium chloride) adsorption experiment was conducted on the resin treated with this anhydrous aluminum chloride vapor and the untreated resin. That is, the ion exchange resin treated with anhydrous aluminum chloride and the untreated resin were placed separately in 100 cc of pure water containing 200 ppm of lauryl pyridinium chloride, and the ion exchange or adsorption of lauryl pyridinium chloride onto the ion exchange resin was carried out. I asked for the quantity. Immersion of ion exchange resin (amount of each used is 2≦y) into the solution at 25.0°C
The adsorption amount was calculated by determining the amount of decrease in laurylpiwazinium chloride in the solution using an ultraviolet absorption spectrum. As a result, the amount of adsorption on the surface treated with anhydrous aluminum chloride was 3.5 x 10-4 meq/7 dry H+ type resin, and on the untreated resin was 1.2 x 1
It was 0-1 meq/y dry H+ type resin. Example
7 A polymer compound having the following structural formula is formed into a film (P,.s
is O or an integer from 1 to 3, Q. r,. t is a positive integer,
The ratio of q and t and R. q,. The exchange capacity of the membrane-like material after hydrolysis of t is 1.47 meq/7・dry membrane, and the ratio of sulfonic acid groups is 0.12 meq/f・dry membrane). (With a plain woven tetrafluoroethylene cloth in between) 8.0N-
It was immersed in KOH and hydrolyzed to obtain a cation exchange membrane having sulfonic acid groups and carboxylic acid groups.

Its total exchange capacity is 1.47 meq/g dry membrane (H
The sulfonic acid groups were 0.12 meq/g dry film (Form H). This cation exchange membrane was placed in the K-type in an autoclave containing anhydrous aluminum chloride crystals, and the membrane was treated so as not to come into contact with the anhydrous aluminum chloride crystals. In other words, autoclave. 170℃
The membrane was placed in an oil bath and heated for 30 minutes, and one side of the membrane was exposed to the vapor of anhydrous aluminum chloride. In this case, the back side of the membrane was completely sealed to prevent contact with anhydrous aluminum chloride vapor. The treated membrane was taken out, washed with water, and conditioned with 1N-HNO3 and 1N-KOH.
Equilibrated with 6.0N-KOH. This membrane was exposed to anhydrous aluminum chloride vapor, and F, S, and K fluorescent X-rays were measured on the front and back sides of the membrane. Using this membrane, electrolysis of saturated saline solution was carried out using the same electrolytic cell and electrolysis method as in Example 1. The results are shown in Table 5. Note that the electrical resistance of the film was measured in the same manner as in Example 4.

Claims (1)

[Scope of Claims] 1. A polymer that combines a fluorine atom and a cation exchange group or a functional group that can be easily converted into a cation exchange group,
Treatment with at least one reaction agent selected from aluminum halide, alkali metal naphthalene, and alkali metal amide to remove fluorine atoms and/or the cation exchange group or 3 to 9 functional groups that can be easily converted into cation exchange groups
A method for treating a cation exchanger, the method comprising removing 0% of the functional group and converting the remaining functional group into a cation exchange group, if necessary. 2. The cation according to claim 1, wherein the polymer is a copolymer of tetrafluoroethylene and perfluoro(3,6-dioxa-4-methyl-octensulfonyl fluoride) or a hydrolyzate thereof. How to handle exchangers. 3. The method for treating a cation exchanger according to claim 1, which is a diaphragm for electrolysis of an alkali metal salt. 4. The method for treating a cation exchanger according to claim 1, which is a cation exchange resin for desalting an aqueous salt solution containing giant organic ions. 5. The method for treating a cation exchanger according to claim 1, which is a cation exchange membrane for electrodialysis of an aqueous salt solution containing giant organic ions. 6. A method for treating a cation exchanger according to claim 1, which is a cation exchange membrane for electrodialysis that selectively permeates cations with a small charge from a mixed salt solution containing cations with different charges. .