JPS59258B2 - Method for producing perfluorocarbon cation exchanger - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a perfluorocarbon cation exchanger, and its object is to provide a perfluorocarbon cation exchanger having chemical resistance, heat resistance, and a high fixed ion concentration. It's about getting a body.

Today, ion exchangers are used as a separation technology without phase change, and are available in various shapes such as ion exchange resins in the form of granules, ion exchange membranes in the form of membranes, ion exchange fibers in the form of fibers, and other tubular objects. It has been proposed and put into practical use.

Ion exchangers of this type compete with each other based on their functions, and the more excellent functions the ion exchanger has, the more it can be used in a wider range of fields. In recent years, in addition to conventional hydrocarbon-based ion exchangers, various ion exchangers to which fluorine atoms are bonded have been studied as ion exchangers having chemical resistance.
For example, there is a perfluoro-based compound having a pendant side chain with an ether bond and a sulfonic acid group bonded to the pendant side chain, and is commercially available under the trade name Naflon. In addition, a linear polymer obtained by polymerizing α, β, β′-trifluorostyrene is treated with chlorosulfonic acid to perform sulfone crosslinking and introduce sulfonic acid groups, and polytrifluoromonochloroethylene is Those treated with phenyllithium to introduce phenyl groups and then treated with chlorosulfonic acid etc. to introduce sulfone groups to become cation exchangers, fluorine-containing polymers with perfluorovinyl ether sulfonyl halide or sulfonic acid , a method of graft polymerizing sulfonates, etc. to form an ion exchanger, perfluorovinyl carboxylic acids, esters,
Various methods have been proposed, including methods for graft polymerizing acid chlorides and the like to form ion exchangers. However, one functional problem with such a fast ion exchanger containing fluorine is that it is not possible to increase the exchange capacity. The reason for this is that the exchange capacity cannot be increased because a special vinyl monomer must be used, and that difunctional crosslinking agents such as divinylbenzene are not used in ordinary hydrocarbon-based ion exchangers. This is because they are insolubilized by hydrophobic bonds or rely on sulfone crosslinks. For ion exchange resins, ion exchange, removal,
Since the purpose is separation, the ion exchange capacity can be increased as long as the ion exchange resin does not become water soluble. However, in the case of an ion exchange membrane that allows ions to permeate, the selective permeability to ions of opposite sign and the resistance when ions permeate, that is, the electrical resistance of the membrane material are extremely important characteristics. In order to obtain an ion exchange membrane with low electrical resistance, the ion exchange capacity is generally increased. In order to increase the selective permeability of ions of the opposite sign, the concentration of fixed ions within the membrane must be increased. Note that the fixed ion concentration is the ion exchange capacity in the membrane divided by the water content. That is, it is necessary to increase the ion exchange capacity and reduce the water content at the same time. However, it is generally not possible to increase the fixed ion concentration because the water content also increases at the same time as the exchange capacity increases. When using an ion exchange membrane for electrodialysis or electrodialysis of dilute salt solutions, dialysis can be performed with relatively high current efficiency even if the fixed ion concentration is low. When the fixed ion concentration is relatively high compared to the fixed ion concentration, or in the case of electrodialysis or electrodialysis of acid solutions or base solutions, high current efficiency in dialysis cannot be obtained unless the fixed ion concentration is significantly increased.

Examples of this include electrodialytic concentration of acid solutions and electrodialytic concentration of base solutions. Furthermore, there is the ion-exchange membrane method of salt electrolysis, which has recently attracted attention in the salt electrolysis industry from the viewpoint of mercury pollution, and is expected to make significant technical progress. In particular, ion exchange membranes used for the latter purpose must have corrosion resistance in order to withstand the harsh conditions of use. In other words, the above-mentioned ion exchange membrane bonded with fluorine atoms has been developed based on this necessity. A typical example of this type of fluorine-containing ion exchange membrane is a cation exchange membrane in which sulfonic acid groups are introduced by copolymerizing the above-mentioned perfluorovinyl ether sulfonyl fluoride and tetrafluoroethylene and subjecting it to hydrolysis treatment. There is. This membrane is insolubilized in solvents by hydrophobic bonds of tetrafluoroethylene chains, and exhibits different characteristics depending on the treatment conditions before use. For example, one grade of this type of membrane commercially available, NafiOOXR-170, was heated to 100°C to 120°C.
The current efficiency reaches 95% when saturated saline is electrolyzed to obtain 6.0N-NaOH by heating and drying under reduced pressure and used as an electrolytic diaphragm. On the other hand, when this membrane, which has been heated and dried under reduced pressure to improve current efficiency, is boiled in pure water, the current efficiency drops from 95% to 63% at once. This is because the membrane is insolubilized by hydrophobic bonds, and boiling loosens the bonds and increases the water content. This phenomenon clearly corresponds to the measurement of the elasticity of the membrane; the membrane shrinks significantly when drying under reduced pressure and heat, and expands significantly when boiling. Such a change in film properties is a phenomenon that is not observed in films that have been crosslinked through covalent bonding using a crosslinking agent such as divinylbenzene. Styrene-divinylbenzene-based film materials do not require heat-resistant polymer materials as one of the film materials.
Boiling does not significantly reduce membrane performance. From this point of view, the present inventors believe that if a perfluorocarbon ion exchange membrane is formed with a strong covalent crosslinked structure, it will shrink densely and have a low water content, so that the covalent bonds can be formed. The present invention was proposed based on the knowledge that the membrane would exhibit a high fixed ion concentration if a crosslinked structure was formed.

Incidentally, the same can be said of granular, powdery ion exchange resins, and fibrous ion exchange resins. Although the fixed ion concentration of these various forms of ion exchangers does not dominate the characteristics of the ion exchanger to the same extent as with ion exchange membranes, a high fixed ion concentration increases Donnan exclusion and increases the positive ion exchange rate of the ion exchanger. This does not change the fact that the original property of ion exchangers, which is to selectively exchange ions or anions, is further enhanced. Therefore, the method of the present invention significantly improves the characteristics of not only membrane-like ion exchangers but also various shapes of fluorine-containing ion exchangers, and is applicable to all fluorine-containing ion exchangers. This is a universal method for modifying ion exchangers.

In the present invention, an electron beam or radiation is applied to a perfluorocarbon polymer having a cation exchange group or a perfluorocarbon polymer having a functional group that can be easily converted into a cation exchange group at a dose of 0.005 Mrad to 20 Mrad.
The perfluorocarbon vinyl monomer is uniformly grafted and crosslinked to the inside of the polymer by irradiation at a dose in the range of This is a method for producing a perfluorocarbon cation exchanger, which is characterized by converting the perfluorocarbon cation exchanger.

That is, the present invention involves uniformly graft-crosslinking a perfluorocarbon vinyl monomer to the inside of a perfluorocarbon polymer, and, if necessary, introducing a cation exchange group or adding a cation exchange group to the cation exchange group. This is a method for producing a perfluorocarbon-based cation exchanger that performs conversion and has chemical resistance, heat resistance, and a high fixed ion concentration.
In general, fluorine-based polymer compounds have extremely excellent chemical resistance and heat resistance, and are therefore inert to various reaction reagents when attempting to carry out various chemical reactions.

Therefore, it is not easy to form a crosslink through a so-called normal chemical reaction. In the present invention, a perfluorocarbon vinyl monomer is graft-crosslinked onto a perfluorocarbon polymer using an electron beam or radiation. Generally, when a polymer compound is irradiated with radiation or an electron beam, some form a crosslinked structure while others decompose, depending on the degree of irradiation. Perfluorocarbon polymer compounds are considered to be the latter decomposition type polymer compounds. In fact, when irradiated with radiation, the cation exchange membrane, which is a copolymer of perfluorovinyl ether sulfonic acid and tetrafluoroethylene, decomposes as the irradiation time increases. However, decomposition is the generation of radicals in the ion exchanger, and at this time, if a suitable vinyl monomer, especially a perfluorocarbon vinyl monomer, is present, the ion exchanger forms crosslinks. , an increase in water content and a decrease in fixed ion concentration can be prevented. To explain the content of the invention in more detail, the perfluorocarbon polymer for graft crosslinking is an ion exchanger having a C-F bond, and the cation exchange group is a sulfonic acid group, a carboxylic acid group, a phosphonic acid group. groups, phosphonic acid groups, sulfonic acid ester groups, phosphoric acid/phosphite ester groups, thiol groups, phenolic hydroxyl groups, metal chelate compounds that can be negatively charged, acid amide groups with dissociable hydrogen, etc. It is chemically bonded with one or more substances that become negatively charged when dissociated in an aqueous solution, preferably perfluoro-based carboxylic acid or acid or sulfonic acid type cation exchangers.

Of course, when performing graft crosslinking, it may be any ion exchanger with an ion exchange group bonded to it, or it may have a functional group into which the above-mentioned ion exchange group can be easily introduced or which can be easily converted into an ion exchange group. It may be a polymer. That is, a functional group that can be converted into an ion exchange group may be present, for example in the form of an acid halide group or an acid ester.
Examples of vinyl compound monomers for graft crosslinking include CF2=CF2, CF2=CFCj, CF2=C
F (CF3), perfluoro(alkyl vinyl ether), perfluorobutadiene, hexafluoropropylene, and the like are preferably used as monomers without ion exchange properties.

Monomers that have ion exchange properties or can be easily converted into ion exchange groups include, for example, CF2=CA-CO
X. When graft-crosslinking the perfluorocarbon vinyl monomer to the perfluorocarbon polymer, it is preferable to increase the grafting rate as much as possible and preferably to do it uniformly within the membrane. To this end, it is desirable to use a vinyl monomer that has as good an affinity as possible to the ion exchanger or its parent polymer and penetrates more uniformly. The conditions for graft crosslinking are as follows: Graft crosslinking can be carried out at room temperature or under heating, and the appropriate conditions are selected depending on the type of monomer and polymer. It may be diluted with a solvent, or the vinyl monomer may be dispersed with a dispersant.

In this case, it is preferable to use a solvent that has a high affinity for the polymer, and the above-mentioned polymer made of a copolymer of perfluoro(vinyl alkyl ether sulfonic acid) and tetrafluoroethylene is an oxygen-containing solvent. It is effective to use this type of material because it swells relatively well depending on the solvent of the system. In the case of graft crosslinking to a polymer, active radicals are generated in the polymer in advance, and a vinyl monomer used for graft crosslinking is brought into contact with the activated radicals to perform graft crosslinking, and the polymer and the vinyl used for graft crosslinking are Any of the methods for generating active radicals in a polymer while contacting the monomers is appropriately selected depending on the conditions of the polymer and the monomer to be graft-polymerized.

In addition, as mentioned above, a perfluorocarbon polymer having a cation exchange group or a fluorine-containing polymer that can be easily converted into an ion exchanger is impregnated with a vinyl monomer and polymerized in advance. , A method in which active radicals are generated in this to form a crosslinked structure between the perfluorocarbon polymer and the polymerized polymer by immersion, and a method in which a monomer is made to coexist with this to generate active radicals. A method of graft crosslinking, a method of generating active radicals thereon and causing them to coexist in the monomer, etc. are also effective and are selected as appropriate. Radiation, electron beams, etc. are particularly effective methods for generating these active radicals in polymers.

The radiation dose varies depending on the polymer and the type of vinyl compound to be graft-crosslinked, but the radiation dose is 0.005 Mrad to 20 Mrad.
Usually done in rad. Homopolymers may be produced from the polymer after graft cross-linking, preferably without participating in graft cross-linking, and unpolymerized monomers may also be present, so these should be extracted or washed. . Of course, if there is no particular problem even if the homopolymer is present in the polymer, removal operations such as extraction may not be necessary. Furthermore, when a polymer having a functional group that can be easily converted into an ion exchange group is used as a starting material for graft crosslinking, the polymer may be converted into an ion exchange group after graft crosslinking. In addition, if the vinyl compound used for graft crosslinking is a monomer that has a functional group such as an acid halide that can be easily converted into an ion exchange group, the ion exchange group may be added depending on the purpose of use and if necessary. There is no harm in converting it to . Such an ion exchanger obtained by graft-crosslinking a perfluorocarbon ion exchanger with a vinyl compound can be used for various conventionally known ion exchangers, and at the same time, it can be used under more severe conditions. Especially excellent. That is, its performance is exhibited in an oxidizing atmosphere, a high temperature atmosphere, and an atmosphere containing an organic solvent. For example, a cation exchange membrane, which is a film-like material, has a transportability, especially in electrodialysis of concentrated electrolyte solutions, and also in alkali hydroxide when obtaining chlorine, hydrogen, oxygen, and alkali hydroxides by electrolysis of aqueous alkali metal salt solutions. The current efficiency of product production is significantly improved. However, at the same time, it is unavoidable to some extent that the electrical resistance of the film increases. Even if the electric power consumption rate is reduced by increasing the current efficiency, if the electrical resistance of the membrane increases significantly, its industrial usefulness will be reduced. Therefore, by the graft crosslinking method of the present invention, the electrical resistance can be increased by 0.5 at 25°C.
It is desirable that the electrical resistance of the film measured in 5N-NaOH does not exceed 10 times that of the untreated film, and the amount of monomer to be graft-crosslinked may be appropriately determined in consideration of the electrical resistance. . Although the cation exchanger of the present invention will be specifically explained in the following examples, the present invention is not limited to the following examples.

In the examples, the electrical resistance of the film was measured in 0.5N-NaC' at room temperature by 1000 cycles of alternating current. The fixed ion concentration is the number of equivalents of NaOH required to neutralize the H-type ion exchanger 19, and the exchange capacity is determined, and then this membrane is 0.5N-NaC/! Immerse it in the water for equilibrium and take it out to determine the water content. This is the value obtained by dividing the exchange capacity found earlier by the moisture content found at this time. Example 1 A potassium sulfonate type cation exchange membrane obtained by hydrolyzing a polymer membrane obtained from a copolymer with tetrafluoroethylene was exposed to γ rays from a CO6O source at room temperature in a nitrogen atmosphere for 0. After 3 Mrad irradiation, the sample was immersed in liquid tetrafluoroethylene for 8 hours, taken out, and dried under reduced pressure until it reached a constant weight.

The weight increase was 23%. The electrical resistance of this film is 74Ω
It was -d. The electrical resistance of the untreated membrane without the above tetrafluoroethylene graft crosslinking treatment is 4.
．． It was 8Ω-d. Further, when the fixed ion concentration was measured, it was 10.2N in the sample treated with the graft crosslinking and polymerization of tetrafluoroethylene, but 6.3N in the untreated sample. Example 2 The perfluorinated potassium sulfonate type cation exchange membrane used in Example 1 was immersed in a monomer consisting of CF2 = 90 parts of ethyl alcohol for 24 hours, and then immersed in CO6O.
γ for 24 hours at a dose rate of 0.1 Mrad/hour from a source of
The line was irradiated.

After irradiation, this membrane was thoroughly extracted with benzene, methanol, and water, and the performance of this membrane was measured. As a result, the electrical resistance is 4
．． The 5Ω-d1 fixed ion concentration was 9.2N.

In addition, the electrical resistance of the untreated membrane without graft crosslinking is 4
．． The fixed ion concentration was 6.3N at 8Ω-d. Example 3 A film-like polymer consisting of a copolymer of perfluoro(3-6-dioxa-4-methyl-J-octensulfonyl fluoride) and tetrafluoroethylene was prepared as CF2=CFOCF.
After immersion in a mixture of 2CF2COOC2H5 and C2F4 for 24 hours, γ from a CO6O source at a rate of 0.02 Mrad/hour in a nitrogen atmosphere under pressure
Graft crosslinking was carried out by irradiation with radiation.

Claims (1)

[Claims] 1. Electron beam or radiation is applied to a perfluorocarbon polymer having a cation exchange group or a perfluorocarbon polymer having a functional group that can be easily converted into a cation exchange group at a dose in the range of 0.005 Mrad to 20 Mrad. irradiation to uniformly graft-crosslink the perfluorocarbon vinyl monomer to the inside of the polymer, and convert functional groups that can be converted into cation exchange groups into cation exchange groups as necessary. A method for producing a featured perfluorocarbon cation exchanger.