JPS6045275B2 - How to install an ion exchange membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for installing an ion exchange membrane, particularly a method for installing a fluorine-containing cation exchange membrane containing carbonic acid groups in a monopolar cell using conventional asbestos as a diaphragm instead of asbestos. This is related to.

As a method for obtaining caustic alkali by electrolyzing alkali chloride, the diaphragm method is becoming mainstream in place of the mercury method from the viewpoint of pollution prevention.

As for the diaphragm method, a method using a filter diaphragm made of asbestos or the like is currently used industrially.

As an electrolytic cell using asbestos as a diaphragm, for example, a can body having a large number of upright anodes fixed to the bottom of the tank and a large number of finger-like cathodes whose surfaces are coated with asbestos is used. A monopolar tank that is inserted and covered is used as a so-called diamond jam lock tank or hooker tank. However, the caustic alkali obtained by these asbestos methods has a low concentration and contains alkali chloride as an impurity, so it is usually difficult to use it as is for various uses such as industrial chemicals.

In response to this, various methods have been proposed in which an ion exchange membrane is used in place of the asbestos diaphragm as a means for obtaining higher purity and higher concentration caustic alkali through electrolysis.

As such an ion exchange membrane, a fluorine-containing cation exchange membrane is preferable from the viewpoint of alkali resistance and chlorine resistance, and as the cation exchange group, carboxylic acid is preferable because caustic alkali can be obtained at high concentration and high current efficiency. The group is said to be preferred.

If you have an electrolytic cell that uses asbestos,
If an ion exchange membrane like the one described above is attached to this,
Not only is equipment cost substantially unnecessary, but it is also possible to obtain highly purified and highly concentrated caustic alkali.

When a fluorine-containing cation exchange membrane having a carboxylic acid group as an ion exchange group is used for electrolysis of alkali chloride,
Usually, the terminal end of the carboxylic acid group is used in the form of an alkali metal of the same kind as the alkali metal of the resulting caustic alkali, such as sodium.

However, according to the inventor's study, when attaching such an alkali metal-type carboxylic acid group-containing fluororesin film to the electrode surface, especially in a bag-like manner, the film's It has been found that it has poor flexibility and is extremely difficult to work with, and that if you try to force it to attach, there is a high risk that the membrane will be damaged or torn by the corners or edges of the electrode. Ta.

Such a risk is caused by the fact that the carboxylic acid group of the membrane has the general formula -(COO). ．． X (X is an alkali metal or -NR
R'', R and R'' are hydrogen or a lower alkyl group, and m is the valence of X).

On the other hand, according to studies conducted by the present inventors, the form of the carboxylic acid group has the general formula -COOL (L is hydrogen or has 1 to 2 carbon atoms).
When the membrane is formed in the form of an alkyl group (0 alkyl group), the membrane exhibits sufficient flexibility, making it extremely easy to cover the electrode, especially attaching it in a bag-like manner to surround the electrode, and there is no risk of damage. It has been found that the objective can be achieved without any substantial deterioration in electrolytic performance.

The fluorine-containing cation exchange membrane containing a carboxylic acid group used in the present invention is one in which the carboxylic acid group has the general formula -(COO)N,X (M, X are the same as above) under electrolysis of alkali chloride. It is.

Preferably, X is the same alkali metal as the alkali chloride that is the electrolyte. The ion exchange capacity of the carboxylic acid group is important as it relates to the performance of the membrane in electrolysis, and although it varies slightly depending on the type of fluorine-containing polymer forming the membrane, it is preferably 0.5 to 4. 0 milliequivalent/y
A dry resin, particularly a 0.8 to 2.0 meq/y dry resin, is preferred in view of the electrochemical and mechanical properties of the membrane. The above-mentioned fluorine-containing cation exchange membrane is subjected to the above-mentioned -(
COO). The following (a) having a functional group that can become NX
It is preferable to use a polymer having the following structures.

where X is F, Cl, H or -CF3, X'' is x or CF3 (CF2)..., m is 1 to 5, and Y is selected from It is preferable that A has a structure in which A is bonded to carbon containing fluorine.

A is a group selected from the above (COO
Indicates a functional group that can be converted to +MX.

In the case of a polymer consisting of the polymerized units of (a) and (1) above, in order for the membrane to achieve the above ion exchange capacity, the polymerized units of (1) are preferably 1 to 40 mol%, particularly 3 to 25% by mole. Preferably, the mole percent is ζ. Furthermore, the molecular weight of the polymer constituting the fluorine-containing cation exchange membrane used in the present invention is important as it is related to the electrochemical properties and mechanical properties of the membrane obtained, and the molecular weight is 100,000 to 20Cg5, Particularly preferred is 150,000 to 41 million.

In addition, various methods can be used to produce the above polymer, but for example, when producing by copolymerizing the monomers forming the units (a) and (g), By using one or more monomers and also copolymerizing a third monomer,
It is also possible to modify the resulting membrane.

Thus, for example, CF2=CFORf(R, is C1~1
By using a perfluoroalkyl group (0 perfluoroalkyl group),
It imparts flexibility to the resulting film, and also CF2=CF-C
F=CF2, CF2=CFO(CF2)1~, COF=
By using a divinyl monomer such as CF2 in combination, the resulting copolymer can be crosslinked and mechanical strength can be imparted to the membrane.

The copolymerization of the fluorinated olefin monomer and a polymerizable monomer having a carboxylic acid group or a functional group convertible to the carboxylic acid group, as well as a third monomer, can be carried out by any known method. obtain.

That is, if necessary, polymerization can be carried out by catalytic polymerization, thermal polymerization, radiation polymerization, etc. using a solvent such as a halogenated hydrocarbon. Further, methods for forming an ion exchange membrane from a copolymer include known methods such as press molding, roll molding, and extrusion. This can be carried out by molding, solution casting, dispersion molding, powder molding, or the like.

Also, the film thickness is 20 to 600μ, preferably 50 to 400p.
It is appropriate to make it so. The fluorine-containing cation exchange membrane used in the present invention is a blend of olefin polymers such as polyethylene and polypropylene, and fluorine-containing polymers such as polytetrafluoroethylene and copolymers of ethylene and tetrafluoroethylene, as necessary. It can also be molded.

The membrane can also be reinforced by supporting the copolymer on a cloth, a woven fabric such as a net, a nonwoven fabric, or a porous film made of these polymers. Note that the weight of the resin forming the blend or support is not included in the above ion exchange capacity value. The ion exchange membrane coated on the electrode has a carboxylic acid group of the produced membrane having the general formula -COOL
(L is the same as above), it can be immediately coated on the electrode, but the carboxylic acid group of the film to be coated is -(COO). When it is an NX group, it can be set to one αxl (L is the same as above).

For such conversion of the ion exchange group, an appropriate means is selected depending on the type of the above-mentioned X.

For example, when L is H, the conversion to -COOH is carried out by contacting the membrane with an aqueous solution of an inorganic or organic acid, preferably in the presence of a polar organic compound.

Further, as the inorganic acid used, mineral acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid are preferable, and as the organic acid, acetic acid, propionic acid, perfluoroacetic acid, P-toluenesulfonic acid, etc. are preferable. These acids are preferably used as a 0.5-9% aqueous solution.

Moreover, as the polar organic compound used as necessary, methanol, ethanol, butanol, ethylene glycol, dimethyl sulfoxide, acetic acid, phenol, etc. are preferable. These polar organic compounds are preferably 0.
It is added to the above aqueous solution in an amount of 5 to 9% by weight.

The contact treatment between the membrane and the acid aqueous solution is preferably performed at a concentration of 10 to 120
It is appropriate to carry out the reaction at a temperature of 30 minutes to an additional time at ℃. In addition, when converting the above L into an alkyl group having 1 to 20 carbon atoms,
After converting it into an acid form as described above, it is reacted with the corresponding alcohol, or the acid form is converted into an acid halide by reaction with phosphorus trichloride, phosphorus oxychloride, etc., and this and the alcohol are combined. This is carried out by reacting or converting the acid form into an acid anhydride by reacting with acetic anhydride, perfluoroacetic anhydride, etc., and then reacting this with an alcohol.

In addition, in some cases, the above membrane may be mixed with a chloride such as thionyl chloride, phosphorus trichloride, phosphorus oxychloride, etc., preferably 1 to 12 (substituted).
By contacting for about 25 hours, -(COO).
．． This can also be achieved by directly converting X to an acid anhydride and reacting this with an alcohol.

Also, -(COO). ．． It is also possible to directly convert the X-type film into the -COOL-type film in the coexistence of alcohol and a small amount of organic acid or inorganic acid.

The alcohol used to esterify the acid, acid halide or acid anhydride is preferably an alcohol having 1 to 20 carbon atoms, such as methanol, ethanol, propanol. Alcohol, butanol, dodecyl alcohol, sebacyl alcohol, etc. are used. Esterification is preferably carried out using the above-mentioned (COO). ．． This is carried out by immersing X in an aqueous solution of the same or different inorganic or organic acid as used in converting it into the acid form.

The immersion treatment is preferably carried out at 30 to 120°C for about 3 to 40 hours.

There are no particular restrictions on the shape or type of the electrolytic cell to which such a fluorine-containing cation exchange membrane containing a carboxylic acid group is attached, but cage-shaped electrodes such as the diamond shamlock cell or Hooker cell as described above may be used. It is particularly suitable for the case where the electrode of a monopolar cell is provided in a bag-like manner.

There are no particular restrictions on the actual attachment method; it is possible to form the membrane into a bag shape in advance using known means and cover the electrode with it, or to use a sheet-like membrane to cover the electrode surface. It is also possible to cover it and join the membrane there to form a bag.

When joining membranes in this way, if the ion exchange group of the membrane is of the 1αx type, the decomposition temperature of the polymer (increased at a rate of 10'C/min in a nitrogen atmosphere) The temperature at which the weight of the polymer decreases by 5% when heated is 350-3
Since the temperature is as high as 70°C, it is possible to easily and firmly heat-seal the film. Heat fusion is generally 100-
Heating to 330°C, preferably about 130 to 300°C,
This can be easily carried out under pressure of ~300k9/Crl. In this way, the fluorine-containing cation exchange membrane coated on the electrode and having a single αx type ion exchange group must be hydrolyzed in order to be used for electrolysis of alkali chloride, which is the same kind of alkali chloride as the electrolyte. Contains alkali ions.

This can be carried out by, for example, introducing caustic alkali into the cathode chamber and introducing an aqueous alkali chloride solution into the anode chamber, while supplying electricity in the same manner as in the usual electrolytic operation. This is carried out by bringing a membrane having a COOL type ion exchange group into contact with an aqueous caustic solution.

Such treatment usually uses a caustic alkali aqueous solution with a weight of 10 to 3%, and the aqueous solution is heated at 50 to 100'C for 2 to 30 minutes.
It is appropriate to allow the contact to be approximately 2 feet apart.

Next, the present invention will be explained by examples. Polytetrafluoroethylene and CF2 =
Ion exchange capacity 1.45 rneq/f dry resin made of copolymer of CFO(CF2)3C00CH3, thickness 22
A 0μ ion exchange membrane was attached.

5. First, the ion exchange membrane was bonded to a length of 7cm: 89× by heat fusion method.
It is formed into a cylindrical shape with an approximately rectangular cross section of 6 cm and open at both ends, and then a flare with a width of 11 d and an opening of 89 x 6 d in the center is placed at both open ends just above the lid or bottom. It was attached using the heat fusion method. The obtained flared membrane is placed in the gap between the cathodes of the cathode box, which has a space in which the anode is fitted during assembly.
Flares on the upper and lower sides of the cylindrical membrane are taken out on the upper and lower end surfaces of the cathode fingers, respectively. By this method, the flared ion exchange membrane was fitted into two voids separated by the cathode fingers of the cathode box.

The phosphorus-contacting flares were then heat-sealed to each other, so that the entire cathode was covered with an ion exchange membrane. The cathode box was placed in a caustic soda aqueous solution at 90'C with a concentration of 25% by weight.
The ion exchange membrane was immersed for a period of time to perform hydrolysis.

Next, an anode was fitted inside the cylindrical membrane after the hydrolysis, and an electrolytic cell was assembled according to a conventional method.

When assembling the tank, in order to prevent damage to the ion exchange membrane, which has become less flexible due to hydrolysis, a synthetic resin spacer net was placed over the anode in advance to prevent the metal part of the anode from coming into direct contact with the membrane. Considered. Then, an FRP lid for retaining salt water was attached, and the assembly was completed.

After attaching the membrane and assembling the tank using this method,
There was no leakage, and the AC resistance of the membrane that was attached and hydrolyzed in this way was 1850Ω・d.
18 A small piece of the membrane was treated separately under the same conditions.
It was found that it was almost the same as 90Ω·d, and that it did not cause any trouble to the electrolytic operation.

Claims (1)

[Claims] 1. The ion exchange group is used with the formula -(COO)_mX (X represents an alkali metal or -NRR', R, R' are hydrogen or a lower alkyl group, and m is the valence of X) In coating the electrode with a fluorine-containing cation exchange membrane, the ion exchange group of the membrane is coated in a state of the formula -COOL (L represents hydrogen or an alkyl group having 1 to 20 carbon atoms). How to install an ion exchange membrane.