JPS5857444B2 - Cation exchange membrane for electrolysis - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cation exchange membrane for electrolysis, which has improved electrochemical properties by introducing hydroxam groups.

Currently, most of the chlorine and alkali metal hydroxides produced on an industrial scale are produced in diaphragm electrolysers.

As the diaphragm, a fluid permeable asbestos diaphragm is usually used.

When carrying out alkali chloride electrolysis using this diaphragm, it is possible to obtain relatively high current efficiency, but there are problems with the durability of the diaphragm, and furthermore, the concentration of the caustic alkali produced is 1.
It has a low weight ratio of 1 to 18, and requires a purification and concentration step because it contains a large amount of common salt.

Recently, methods of using cation exchange membranes that are virtually impermeable to hydraulic flow, particularly fluorine-based cation exchange membranes, have been studied for such asbestos diaphragms.

If such a fluorine-based cation exchange membrane is used for alkali chloride electrolysis, it is possible to prevent a large amount of common salt from being mixed into the produced caustic alkali, and it also exhibits considerably excellent properties in terms of chlorine resistance.

As described above, fluorine-based cation exchange membranes have great expectations as an alternative to asbestos diaphragms, but it cannot be denied that their electrochemical properties do not necessarily allow them to be put to practical use.

That is, as the concentration of caustic alkali in the cathode chamber increases, the current efficiency significantly decreases.

The reason for this is thought to be that as the concentration of caustic alkali in the cathode chamber increases, the diffusion of hydroxide ions toward the anode chamber cannot be sufficiently prevented.

As a result of continuing research to improve the electrochemical properties of cation exchange membranes, the present inventors have found that by introducing hydroxamic acid groups into cation exchange membranes, the cation exchange membrane has a selective permeability of cations to anions. succeeded in improving.

That is, the present invention is a cation exchange membrane for electrolysis comprising a polymer into which hydroxamic acid groups are introduced.

Examples of membranes having cation exchange groups used in the present invention include hydrocarbon-based membranes such as divinylbenzene-styrene copolymer, divinylbenzene-acrylic acid copolymer, and polyolefin-hydroxystyrene graft copolymer. However, fluorocarbon-based membranes such as polyvinyl fluorocarbon ether copolymer, polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, etc. are used as the base material, and cation exchange groups are introduced into the membrane to achieve chlorine resistance and heat resistance. It is preferable in terms of properties, etc.

Examples of such cation exchange membranes include Nafion (
(Product name: DuPont) etc. are well known.

As a method for introducing hydroxamic acid groups into these membranes, for example, if the membrane has a carboxyl group as a cation exchange group, it may be directly reacted with hydroxylamine.

If the membrane has a sulfonic acid group, it is converted to sulfonyl chloride and then treated with a compound that has an active group that reacts with sulfonyl chloride and also has a carboxyl group or a group that can be easily converted to a carboxyl group. A carboxyl group may be introduced and this carboxyl group may be reacted with hydroxylamine.

Hydroxamic acid groups can be introduced by treating a cation exchange membrane having carboxyl groups or sulfonic acid groups in this way, but another method is to introduce a polymer having hydroxamic acid groups into a cation exchange membrane. It is also possible to intervene.

Such a polymer has the following general formula (where X = H, halogen, CH3 or its halogen substituted product, Y, Z = H or halogen, CR = styrene, divinylbenzene monomer m, n - each of 2 or more An integer, preferably about m=3 to 5 and n=2 to 4).

In order to interpose this in a cation exchange membrane, for example, a monomer obtained by reacting acrylic acid with N-hydroxysuccinimide, styrene, and a polymerization initiator such as benzoyl peroxide are mixed in a solvent such as benzene. The cation exchange membrane is immersed in the dissolved solution, then pulled up and polymerized by heating or UV irradiation to form a polymer of N-acryloxysuccinimide, which is then treated with hydroxylamine to form the desired hydroxamic acid group. It is possible to produce a cation exchange membrane having the following properties.

The hydroxamic acid group may be introduced either on the surface of the cation exchange membrane or inside the membrane, but the current efficiency is particularly significantly improved when it is introduced only on the cathode surface.

Examples are shown below.

In the examples, all parts are parts by weight.

Example 1 Fluorocarbon-based cation exchange membrane (manufactured by DuPont,
Nafion 315 (trade name, thickness 0.4 mm) was dried in the acid form at 80° C. for 4 hours, then placed in a thionyl chloride solution and refluxed for 48 hours to replace the sulfonic acid groups with sulfonyl chloride.

This membrane was treated in an asymmetrical treatment container with only the cathode side surface treated in ether using an excess amount of ethylenediamine for 40 minutes, and then immersed in an aqueous solution of monochloroethyl acetate for 48 hours at room temperature to remove the carboxylic acid groups from the cation exchange membrane. It was introduced in

Furthermore, this membrane was immersed in hydroxylamine for 12 hours at room temperature to introduce hydroxamic acid groups.

After that, it was immersed in 4N caustic soda solution at 60°C for 24 hours.
The remaining sulfonyl chloride groups were converted to sodium sulfonate.

The thus treated cation exchange membrane was used to separate the anode and cathode to form a two-chamber electrolytic cell.

A platinum-plated titanium electrode was used as the anode, and a stainless steel electrode was used as the cathode. The distance between the two electrodes was 0.4 cm, and the effective area of the diaphragm was 56.25 ffl. Saturated saline water was electrolyzed under the following conditions. .

180cc/hour of saturated saline in the anode chamber and 2 cc/hour in the cathode chamber.
5 parts by weight of caustic soda solution was charged, and electrolysis was performed for 120 hours at a current density of 20 A/dm'' while supplying pure water whose flow rate was adjusted so as to obtain a solution of the same concentration.

The caustic soda solution discharged from the cathode chamber was collected and the current efficiency was determined from the generated caustic soda.

For comparison, electrolysis was performed under the same conditions using a Nafion 315 membrane that was not subjected to the above treatment.

The results are shown in Table 1. Example 2 The same cation exchange membrane as in Example 1 was placed in an asymmetrical treatment container, and only the cathode side was treated with 80 parts of N-acryloxycono monophosphate imide.
After being immersed in a solution consisting of 30 parts of styrene, 180 parts of benzene, and 0.2 parts of benzoyl peroxide, it was taken out and kept in a dryer at 60° C. for 24 hours in a nitrogen atmosphere.

A copolymer of N-acryloxysuccinimide and styrene is formed on the surface of this film.

This membrane was immersed in hydroxylamine and left at room temperature for 12 hours to introduce hydroxamic acid groups onto the cathode surface.

Using this membrane, electrolysis of saturated saline solution was carried out under the same conditions as in Example 1, except that the concentration of the produced caustic soda solution was adjusted to 27% by weight.

The results are shown in Table 2. Example 3 220 parts of styrene, 15 parts of divinylbenzene with a purity of about 50% by weight, 30 parts of dioctyl phthalate, 100 parts of polyethylene fine powder, and 5 parts of benzoyl peroxide were mixed to form a uniform paste.

This was applied to a polyethylene cloth and polymerized by heating to obtain a polymer film.

This membrane was reacted with 98% sulfuric acid at a temperature of 70° C. for 10 hours to obtain a cation exchange membrane having sulfonic acid groups.

On the other hand, the membrane was refluxed in a thionyl chloride solution for 48 hours to replace the sulfonic acid groups with sulfonyl chloride.

Only the surface on the cathode side of this membrane was treated with an excess amount of ethyleneamine in ether for 40 minutes, and then immersed in an aqueous solution of monochloroethyl acetate for 48 hours at room temperature to introduce carboxylic acid groups into cation exchange groups.

Furthermore, this membrane was immersed in hydroxylamine for 12 hours at room temperature to introduce hydroxamic groups.

Thereafter, it was immersed in a 4N caustic soda solution and left at 60° C. for 24 hours to convert the remaining sulfonyl chloride groups to sodium sulfonate.

Saturated saline solution was electrolyzed under the same conditions as in Example 1, except that the concentration of the produced caustic soda solution was adjusted to 18% by weight using the above two types of membranes.

The results are shown in Table 3. Example 4 Tetrafluoroethylene and CF=CFOCFCFOCF2CF2C00H2 were copolymerized to produce a carboxylic acid type cation exchange membrane (exchange capacity 0.90 meq/g polymer, thickness 50μ).

On the other hand, only the cathode side surface of this carboxylic acid type cation exchange membrane was treated with hydroxylamine at room temperature for 6 hours to introduce hydroxamic acid groups.

Saturated saline solution was electrolyzed under the same conditions as in Example 1 using the above two types of membranes.

Claims (1)

[Scope of Claims] 1. A cation exchange membrane for electrolysis comprising a polymer into which hydroxamic acid groups are introduced. 2. The cation exchange membrane according to claim 1, wherein the base material of the cation exchange membrane is a hydrocarbon-based or fluorocarbon-based polymer. 3. The cation exchange membrane according to claim 1 or 2, wherein a hydroxamic acid group is introduced by replacing the carboxyl group of the cation exchange membrane. 4 General formula (provided that X2I-(, zsDgen, CH3 or its) 1
0-gen substitution product, Y, Z=H or halogen, CR=styrene, monomer of divinylbenzene, m. Claim 1 or 2, in which a hydroxam group is introduced by interposing a polymer represented by n = an integer of 2 or more)
The cation exchange membrane described in Section 1. 5. The cation exchange membrane according to any one of claims 1 to 4, wherein a polymer into which a hydroxam group is introduced is interposed only on the cathode surface of the cation exchange membrane.