JPS6026144B2 - Improved fluorine-containing cation exchange resin membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved fluorine-containing cation exchange resin membrane, more specifically, it has high electrolytic performance, chlorine resistance, and mechanical performance as a diaphragm in diaphragm electrolysis of aqueous alkali chloride solutions. The present invention relates to a fluorine-containing cation exchange resin membrane that has excellent properties and can be used effectively and stably over a long period of time.

An electrolysis method using a so-called diaphragm method is known, in which a diaphragm is used to partition the electrolytic cell from the cathode, and an alkali chloride aqueous solution is supplied to the anode chamber and electrolyzed to produce alkali hydroxide in the cathode chamber.

In recent years, a highly pure alkali hydroxide aqueous solution containing no alkali chloride has been produced by using an intestinal ion-exchanged sardine resin membrane as a diaphragm that does not substantially allow electrolytes to pass through, but selectively allows only alkali metal ions to pass through. It is proposed to do so. Among them, fluorine-containing intestinal ion exchange resin membranes are
Because it has chlorine resistance and alkali resistance, it is excellent as the above-mentioned diaphragm.Among these, fluorine-containing ion exchange resin membranes whose ion exchange groups are carboxylic acid groups or functional groups that can be converted to carboxylic acid groups are particularly suitable for use in high-concentration water. High current efficiency can be maintained even when producing alkali oxide, so
It has been reported to be particularly excellent. (Tokusei Sho 5
1-130495, 51-140899, etc.) However, fluorine-containing cation exchange resin membranes with carboxylic acid groups as exchange groups that have such high electrical performance also have poor tensile strength, bending strength, etc. However, there are still insufficient mechanical properties, and therefore there is a need for improvement in durability.

The present inventor has conducted intensive research into improving the mechanical properties of the fluorine-containing cationic exchange resin membrane without impairing its excellent mechanical properties using such a carboxylic acid group as an exchange group. Continuing, we used a carboxylic acid group or a functional group that can be converted to this group as an ion exchange group, and blended at least two types of fluoropolymers with different ion exchange capacities, and calculated the ion exchange capacity (milliequivalent/g dry resin), 1
．． It has been found that the objective can be advantageously achieved by setting the ratio to 0 to 2.0. Even though the ion exchange resin membrane has the same ion exchange capacity, it is not composed of a fluorine-containing polymer having only one kind of exchange capacity, but according to the present invention, it is possible to use a cation exchanger membrane by blending at least two or more kinds of fluorine-containing polymers having an exchange capacity. It is an industrially extremely advantageous fact that the present inventor has found and found that when a resin film made of F is constructed, the respective disadvantages of both are eliminated and the performance of only the respective advantages is exhibited.

According to the present invention, a carboxylic acid group or a functional group convertible to the carboxylic acid group is used as an ion exchange group, and at least two or more types of fluoropolymers having different ion exchange capacities are blended to have an ion exchange capacity of 1.0 to 2. 0.0, the ion exchange capacity of at least one of the fluorine-containing polymers is preferably 0.9 or less, particularly preferably 0.8 or less, and The content of the fluoropolymer constituting the intestinal ion exchange resin membrane is preferably 5% by weight or less of the total amount of the fluoropolymer constituting the cation exchange membrane,
In particular, it is preferable that the amount is 3% by weight or less.

It is not preferable to use an excessive amount of the fluoropolymer having a low exchange capacity because it impairs the electrical performance of the intestinal ion exchange resin membrane. The content of the low exchange capacity fluoropolymer is preferably 1% by weight, particularly preferably 3% by weight or more. On the other hand, by blending the fluoropolymer with a high ion exchange capacity to be blended with the fluoropolymer with a low exchange capacity, the exchange capacity of the intestinal ion exchange ≠ the exchange capacity of the heated fat membrane falls within the above-targeted range. As such, its exchange capacity and quantity are chosen.

However, if the ion exchange capacity is too high, the mechanical properties of the cation exchange membrane will be impaired, so the upper limit is preferably 3.
．． It is preferable to make it 0, especially 2.5 or less. Thus, by blending the above-mentioned at least two types of fluoropolymers, the number of customers exchanged after blending can be increased to 1.0 to 2.0 as described above, but especially 1.2.
It is preferable to make it 1.6. The fluorine-containing polymer and wrinkles used to produce the fluorine-containing cation exchange resin membrane in the present invention are a polymer polymer having a fluorinated olefin monomer and a carboxylic acid or a functional group convertible to the group. Copolymers with monomers are used. As the copolymer, it is particularly preferable to use monomers that can form the following polymerized units of {i} and 'rho, respectively. {A) KuCF2
-CXX1), where × is fluorine, chlorine, hydrogen or -CF3,
XI is X or CF3(CF2)m-, where m is 1 to
5, and Y is selected from the following:

(CF2)pA,-. -(CF2.) pA, (CF2)
p (C ratio) qAp, q, n are both 1 to 10,
Z and Rt are groups selected from 1F or a fluorine-containing alkyl group having 1 to 10 carbon atoms, and A is 1CN, 1COF,
-COOR, -COOM, -CONR, R2, etc. indicate a functional group that can be converted into -COO or -CO by a hydrolysis or neutralization reaction. R, is an alkyl group having 1 to 10 carbon atoms, M
is an alkali metal or quaternary ammonium group, R2
, R3 represents hydrogen or an alkyl group having 1 to 10 carbon atoms.
In the case of a copolymer consisting of the above polymerized units of river and [o-],
The proportions of the above {i} and 'o- are such that the polymerized units of [〇} in the copolymer are appropriately selected so as to provide the desired exchange capacity.

In producing the fluorine-containing copolymer, the above (i, [
One or more monomers constituting the polymerized unit of 〇' can be used, and in addition to these monomers, other components such as CF2=CFRf (Rf is a carbon number of 1 to 1
0 fluorine-containing alkyl group), CF2=CF-CF=CF
2. Crosslinking a copolymer obtained by using one or more types of divinyl monomers such as CF2=CF0 (CF2) and ~40CF=CF2 to improve the mechanical strength of the membrane in some cases. I can do it.

The fluorine-containing polymer of the present invention may be a graft copolymer or a block copolymer, but a copolymer obtained by directly copolymerizing monomers such as the above-mentioned It is particularly preferred in terms of dispersibility.

The molecular weight of the fluoropolymer is related to the film formability of the resulting film, so the molecular weight of each fluoropolymer should be selected so that the blend of at least two types of fluoropolymers has a predetermined volumetric flow rate. is preferred. That is, the temperature (T) at which the volumetric flow rate of such a blend is 8/sec is 1.
Those having a high molecular weight having a molecular weight in the range of 60 to 300% are preferred. When two types of fluoropolymers having different exchange capacities thus obtained are blended, a conventional method can be used. That is, it is preferable to use an appropriate roller or Banbury mixer, at a temperature preferably from 7 pi○ or more to the melting point of the polymer, with a deep shear stress of preferably 1 and d/c or more, and a zIJ speed Q.
Mixing or kneading is carried out under the conditions of usually 1 minute to 1 hour while applying a voltage of 1/sec or more.

In such cases, polyethylene, polyp if necessary.

Olefin polymers such as pyrene, as well as fluorine-containing polymers such as polytetrafluoroethylene and copolymers of ethylene and tetrafluoroethylene, can be blended, and fabrics, nets, etc. made of these polymers can also be blended. The membrane can be reinforced by supporting the copolymer with a support consisting of a woven fabric, non-woven fabric or porous film. Note that the weight of the resin forming the blend or support that does not have such an ion exchange group is not included in the value of the ion exchange capacity. Furthermore, following or together with the blending of the fluoropolymer, the fluoropolymer is formed into a film.

The film forming method may be any known method, such as press forming, roll forming, extrusion forming, solution casting, dispersion forming, or powder forming. The film is formed in this way, but as an ion exchange resin membrane, it is non-porous due to the inherent need to allow only specific ions to pass through selectively, without substantially allowing the electrolyte to pass through, for example during dissolution. It is necessary to form a film into a delicate film, and in this sense, the water permeability of the film is less than 100 ships/hour/in water column 1 (60°C, NaCI in PHIO state), especially 1
It is preferable to keep it below 0w'/hour/time. The film thickness is preferably 20 to 1000 microns, more preferably 50 to 1000 microns.
Preferably it is 500 microns. Before and after the production process of such a fluoropolymer, preferably after purification,
When the polymer is not a carboxylic acid group itself but a functional group that can be converted into the carboxylic acid group, these functional groups are converted to the carboxylic acid group by appropriate treatment.

For example, one CN, one COF, one COOR, -CO
OM, CONR2R3 (M, R, ~R3 are the same as above)
In this case, it can be converted into a carboxylic acid group by hydrolysis or neutralization with an acid or alkali alcohol solution. The intestinal ion exchange membrane made of the fluoropolymer of the present invention has excellent performance in both electrical and mechanical properties, as described above.

For example, its mechanical properties are dramatically improved in tear strength and bending strength, and when the electrical properties are kept the same, the former is improved by about 2 to 3 times, and the latter by about 40 to 7 pings. It will be done. For this reason, it can be widely adopted in various fields. For example, it is advantageously used as a diaphragm in electrolytic reduction, fuel cells, or diffusion dialysis, especially in fields where corrosion resistance is required. In particular, when used as a diaphragm for two-chamber diaphragm electrolysis of alkali chloride as described above, it can exhibit high performance that cannot be obtained with conventional fluorine-containing cation exchange membranes. Fluorine-containing intestinal ion exchanger f of the present invention
As a means for producing alkali hydroxide by electrolyzing alkali chloride using a sword resin membrane, any known diaphragm electrolysis method can be employed.

For example, the electrolysis voltage and current density are preferably 2.3 to 5.5 volts and 5 to 10 peaks A/d. As the anode used for electrolysis, for example, a dimensionally stable, corrosion-resistant electrode having a graphite or titanium base coated with a platinum group metal, or coated with an oxide of a platinum group metal can be appropriately used. Further, any method such as an electrolytic cell or a bipolar cell can be adopted. Thus, for example, with the cation exchange resin membrane of the present invention, an anode and a cathode are separated to form an anode chamber and a cathode chamber, an aqueous alkali chloride solution is supplied to the anode chamber for electrolysis, and hydroxide is removed from the cathode chamber. Even in the case of a so-called two-chamber type tank for obtaining alkali IJ, an aqueous sodium chloride solution with a concentration of 2N or more is used as a raw material, and the temperature is 40 to 100°C, preferably 50 to 9,000°C.
By electrolyzing at a current density of 5 to 50 A/d, 4
Sodium hydroxide with a high concentration of 0% or more can be produced stably over a long period of time at a low electrolytic voltage of 4 volts or less and with a high current efficiency of 90% or more without causing any significant deterioration.

Examples are given below to more specifically illustrate the present invention, but it goes without saying that the present invention is not limited to the above description and the following examples.

In addition, the exchange capacity of the fluorine-containing cation exchange resin membrane in the following examples was determined as follows. That is, the H-type intestinal ion exchange≠period lipid membrane was treated with 6000,5
The mixture was allowed to stand for a period of time to completely convert to the H type, and was thoroughly washed with water so that no HCI remained. Thereafter, the H-type 0.59 membrane was immersed in a solution prepared by adding 0.1N NaOH25 to completely convert it to the Na+ type. The membrane was then taken out and the amount of NaOH in the solution was determined by back titration with 0.1N hydrochloric acid. The volumetric flow rate is the amount of polymer flowing out of an orifice with a diameter of 1 side and a length of 2 at a constant temperature under a pressure of 30 kg/ground in units of side 3/second.

In addition, the tensile strength of the membrane is indicated by the tensile propagation velocity, and JI
The bending strength was measured using the SZ1702 (1962) method, and the bending strength was measured using a Toyo Seiki bending strength tester according to JISP811.
5, a sample with a width of 1.5 mm, a thickness of 300 mm, and a length of 14 mm was measured under the conditions of a load of 1.5 kg, an angle of 1350 mm, and 10 mm, and the number of bending failures was expressed. Ta.
Example 1 Tetrafluor.

Ethylene and CF2=CF0(CF2)3COOCH3 were copolymerized in bulk using azobisisobutyronitrile as a catalyst to obtain a copolymer with an ion exchange capacity of 1.6 meq/dry resin and a TQ of 230°C.

On the other hand, both of the above monomers were subjected to solution polymerization using azobisisobutyronitrile as a catalyst and trichlorotrifluoroethane as a solvent to obtain a copolymer having an ion exchange capacity of 0.70 milliequivalents/dry resin and To of 230oo. Next, 8 parts of the former copolymer and 2 parts of the latter copolymer were blended using a roll, and further press-molded at 230 qo to obtain a film with a thickness of 250 mounds. By hydrolyzing the film, an ion exchange membrane having an ion exchange capacity of 1.42 milliequivalents/ta dry resin was obtained. The ion exchange membrane was used to partition an anode and a cathode to form a two-chamber electrolytic cell. A rhodium-coated titanium electrode was used for the anode, and stainless steel was used for the cathode.
The effective area of the diaphragm was set to 25, and sodium chloride electrolysis was carried out under the following conditions.

A small aqueous sodium chloride solution is supplied to the anode chamber, and sodium hydroxide from Su is supplied to the cathode, a small aqueous sodium chloride solution is supplied to the anode chamber at 150 cc/hour, and 0.1N sodium hydroxide is supplied to the cathode chamber. At the same time, the current density is 20A
/d, electrolysis was carried out at a liquid overflow of 920 and pH of the anolyte at 3. The sodium hydroxide solution overflowing the sodium chloride solution from the anode chamber was collected, and the current efficiency was determined from the produced sodium hydroxide. As a result, one state of sodium hydroxide was obtained with a current efficiency of 93% and a voltage of 3.8 volts. As for the improved mechanical properties of the ion exchange membrane, tear propagation strength and bending strength were measured, and each was 6k.
A value of 2000 g/enemy was obtained. On the other hand, tetrafluoroethylene and CF2=CF0(CF2)3COOC
An ion exchange membrane with an ion exchange capacity of 1.44 milliequivalents/dry resin obtained by copolymerizing with H3 shows the same electrolytic performance as the above blend, but the tear propagation strength is 2 kg/g in mechanical properties. The bending strength was rated 5. Example 2 Tetrafluoroethylene and were copolymerized in the same manner as in Example 1, and the ion exchange capacity and To were 1.40 meq.
A copolymer of 200 qC was obtained at 72 meq/ta dry resin.

Next, 75 parts of the former copolymer and 25 parts of the latter copolymer were added.
The mixture was blended using a roll and then press-molded at 21mm to obtain a film with a thickness of 250mm.

The film was hydrolyzed to obtain an ion exchange membrane having an ion exchange capacity of 1.23 milliequivalents/ta dry resin. The ion exchange membrane provided one state of caustic soda with a current efficiency of 91%. Regarding mechanical properties, the tear propagation strength was 7K9/2, and the bending strength was 250. On the other hand, an ion exchange membrane obtained from a copolymer of To200oC with an ion exchange capacity of 1.25 meq. dry resin copolymerized with tetrafluoroethylene exhibits the same electrolytic performance as the above blend membrane. In terms of properties, the tear propagation strength was 3 kg/m, and the bending strength was 80 times.

Example 3 Tetrafluoroethylene and CF2=CF0(CF2)3
The COOC ratio was subjected to bulk polymerization using azobisisoptyronitrile as a catalyst to obtain a copolymer with a To of 230 qo using an ion exchange capacity of 1.60 milliequivalent dry resin.

Claims (1)

[Scope of Claims] 1. Ion exchange capacity (which is obtained by blending at least two or more types of fluorine-containing polymers with different ion exchange capacities, in which a carboxylic acid group or a functional group convertible to the carboxylic acid group is an ion exchange group) Milliequivalents/gram dry resin) is 1.0 to 2.0
A fluorine-containing cation exchange resin membrane. 2. The fluorine-containing cation exchange resin membrane according to claim 1, wherein the ion exchange capacity (milliequivalent/gram dry resin) of at least one of the fluorine-containing polymers is 0.9 or less. 3 Ion exchange capacity (milliequivalents/gram dry resin) is 0
．． 3. The fluorine-containing cation exchange resin membrane according to claim 1 or 2, wherein the content of the fluorine-containing polymer having a molecular weight of 9 or less is 50% by weight or less of the total amount of the fluorine-containing polymer. 4. The fluorine-containing cation exchange resin membrane according to claim 1, 2, or 3, wherein the functional group that can be converted into a carboxylic acid group is a functional group that is added to the carboxylic acid group by hydrolysis or neutralization reaction.