JPH0948862A - Cation exchange membrane - Google Patents

Abstract

(57) Abstract: 35% to 45% of the pyridine group of poly-4-vinylpyridine having a molecular weight of 2,000 to 5,000 is
Quaternary pyridinium chloride with chloromethylstyrene, the remaining pyridine group, quaternary pyridinium chloride with methyl iodide, quaternized poly-4-vinylpyridine is adsorbed on the surface of the cation exchange membrane, then A cation exchange membrane in which a polymer of the poly-4-vinylpyridine quaternary compound is present on the surface by polymerizing a double bond portion of the poly-4-vinylpyridine quaternary compound. [Effects] This novel cation exchange membrane provides better selective permeation of monovalent ions and its durability than the prior art, and
A low membrane voltage during electrodialysis, which cannot be achieved by the conventional technique, is achieved, and when this cation exchange membrane is used for salt production by electrodialysis, power consumption can be reduced.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention mainly relates to monovalent cations (Na 2) rather than polyvalent cations (Mg ²⁺ , Ca ²⁺ ) when seawater is concentrated by electrodialysis using an ion exchange membrane.
^{The present} invention relates to a novel cation exchange membrane which has a property of selectively permeating ⁺ , K ⁺ ), lasts for a long time, and has an extremely low membrane voltage during electrodialysis.

[0002]

2. Description of the Related Art Conventionally, an anion exchange material is present on the surface of a cation exchange membrane having a property of selectively permeating monovalent ions over polyvalent ions, that is, a monovalent ion selective permeability. Cation exchange membranes are known.
Further, as the cation exchange membrane having the selective permeation of monovalent ions for a long time, a cation exchange membrane in which a polymer of a quaternary ammonium salt group and a vinyl compound having three or more vinylbenzyl groups is present on the surface. Membranes are known (see, for example, Japanese Patent Publication No. 5-85574). This known cation exchange membrane does not show a significant increase in the electric resistance of the membrane as measured by 1000 cycles of alternating current when imparting the monovalent ion selective permeability, and the favorable monovalent ion selective permeability lasts for a long time. . However, there are cases in which the membrane voltage when concentrating seawater by electrodialysis is high, and there is a need for a cation exchange membrane that has good monovalent ion selective permeability for a long time and has a lower membrane voltage during electrodialysis. Has been.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel cation exchange membrane which has good monovalent ion selective permeability for a long time and has an extremely low membrane voltage during electrodialysis. The purpose is.

[0004]

[Means for Solving the Problems] As a result of intensive studies, the present inventors have developed a monovalent ion-selective cation exchange membrane having a low membrane voltage when seawater is concentrated by electrodialysis. By using a mixed quaternary product of poly-4-vinylpyridine with chloromethylstyrene and methyl iodide, the monovalent ion selective permeability, which is better than that of the prior art, is maintained for a long time, and moreover, it can be used during electrodialysis. It was found that a cation exchange membrane having an extremely low membrane voltage can be formed, and the present invention was completed based on this finding. That is, 35 to 45% of the pyridine group of poly-4-vinylpyridine having a molecular weight of 2,000 to 5,000 is quaternary pyridinium chloride with chloromethylstyrene, and the remaining pyridine group is quaternary pyridinium chloride with methyl iodide. The quaternized product of poly-4-vinylpyridine was adsorbed on the surface of the cation exchange membrane, and then the double bond portion of the quaternized product of poly-4-vinylpyridine was polymerized to obtain the poly-4-vinylpyridine. It is a cation exchange membrane having a pyridine quaternary polymer on its surface.

The quaternary compound of poly-4-vinylpyridine used in the present invention is prepared by polymerizing 4-vinylpyridine by a method capable of controlling the molecular weight, and then using chloromethylstyrene and methyl iodide in appropriate amounts. Quaternary pyridinium is formed. Since the polymerization method of 4-vinylpyridine controls the molecular weight, anionic polymerization using an alkoxide as an initiator is generally preferred. What is important here is that the molecular weight is 2,000 to 5,000. When the molecular weight is less than 2,000, when the quaternary compound of poly-4-vinylpyridine is adsorbed on the surface of the cation exchange membrane, the quaternary compound of poly-4-vinylpyridine reaches the inside of the membrane more than necessary. It diffuses, increases the electrical resistance of the cation exchange membrane, and increases the membrane voltage during electrodialysis. on the other hand,
When the molecular weight is higher than 5,000, the quaternary compound of poly-4-vinylpyridine becomes difficult to be adsorbed on the cation exchange membrane,
Good monovalent ion selective permeability cannot be obtained.

Next, regarding the quaternization of poly-4-vinylpyridine, as a reaction condition, poly-4-vinylpyridine is dissolved in a solvent such as dimethylsulfoxide, chloroform, acetone, methanol, etc. Room temperature to 5
It can be performed at a temperature of 0 ° C. At this time, for example, it is preferable to carry out in the presence of a radical polymerization inhibitor such as t-butylcatechol. The most important point of the present invention is that by using two kinds of quaternizing agents, chloromethylstyrene and methyl iodide, 35 to 45% of pyridine groups of poly-4-vinylpyridine are quaternized with chloromethylstyrene. , The remaining pyridine group is quaternized with methyl iodide. By finding the combination and proportion of this quaternizing agent, it has become possible to obtain a monovalent ion permselective cation exchange membrane having a low membrane voltage during electrodialysis, which has not been obtained by the prior art.
The ratio of the mixed quaternized chloromethylstyrene is 35
If it is less than 40%, the solubility of the poly-4-vinylpyridine quaternary compound in seawater becomes high, so that the durability of the monovalent ion selective permeability of the cation exchange membrane becomes poor, while if it exceeds 45%, the membrane becomes inferior. The resistance increases and the membrane voltage during electrodialysis increases. Furthermore, in this case, since the solubility of the poly-4-vinylpyridine quaternary product in water (seawater) is extremely low, when adsorbing the poly-4-vinylpyridine quaternary product on the cation exchange membrane, It becomes difficult to find a solvent that does not adversely affect other membrane performance such as the permeation concentration. The proportion of the pyridine group quaternized with chloromethylstyrene in the poly-4-vinylpyridine quaternized product was 5.6 to 6.1 ppm derived from the vinylbenzyl group bonded to the pyridine group in its NMR spectrum. The peak that appears,
4.0 to 4. derived from a methyl group bonded to a pyridine group.
It can be determined by comparing each integrated value with the peak appearing at 7 ppm.

In the present invention, a cation exchange membrane is dipped in a solution of the above-mentioned poly-4-vinylpyridine quaternary compound,
After adsorbing 4-vinylpyridine quaternary compound on the surface of the cation exchange membrane, by polymerizing the vinyl group contained in the adsorbed poly-4-vinylpyridine quaternary compound, the membrane voltage during electrodialysis is low. A cation exchange membrane having selective permeation of monovalent ions is obtained.

The cation exchange membrane used in the present invention is not particularly limited, and known cation exchange membranes can be used, but in order to fully exhibit the feature of low membrane voltage during electrodialysis, For example, it is preferable to use a cation exchange membrane having a low membrane resistance using a polyvinyl chloride core material. In the present invention, as a condition for adsorbing the poly-4-vinylpyridine quaternary compound on the surface of the cation exchange membrane, water as a solvent, an aqueous solution of an inorganic salt or dimethylsulfoxide with these,
A mixed solvent with an organic solvent such as acetone or methanol can be used. The concentration of the poly-4-vinylpyridine quaternary compound is generally several thousands ppm. However, the poly-4-vinylpyridine quaternary compound used in the present invention has a low solubility in water, and in order to allow the poly-4-vinylpyridine quaternary compound to be uniformly adsorbed on the film surface, the poly-4-vinylpyridine quaternary compound is used at the adsorption temperature. Since it is preferable that the vinylpyridine quaternary compound is completely dissolved, it is preferable to use a mixed solvent of an aqueous solution of an inorganic salt and an organic solvent. At this time, the concentrations of the inorganic salt and the organic solvent may be selected from the range that does not adversely affect the performance of the cation exchange membrane used, but the inorganic salt concentration is about 0.1 to 0.5 N, and the organic solvent concentration is several%. Degree is general. The temperature and time of adsorption differ depending on the cation exchange membrane used, but generally the temperature may be 30 to 50 ° C. and adsorption may be performed for several hours to several tens of hours. Here, the amount of the poly-4-vinylpyridine quaternary compound to be adsorbed on the surface of the cation exchange membrane varies depending on the type of the cation exchange membrane, but it ensures good monovalent ion permeation and also during electrodialysis. In order to keep the membrane voltage low, generally about 1 to 3 meq / m ² is preferable.

Poly-adsorbed on the surface of the cation exchange membrane
The polymerization of the vinyl group contained in the 4-vinylpyridine quaternary compound can be carried out by bringing the cation exchange membrane having the poly-4-vinylpyridine quaternary compound adsorbed therein into contact with a solution containing a polymerization initiator. . At this time, as the initiator,
For example, a radical polymerization initiator such as 2,2′-azobis (2-amidinopropane) dihydrochloride or a redox initiator such as potassium persulfate-sodium sulfite is preferably used. As the solvent, water, an aqueous solution of an inorganic salt, or a mixed solvent of these and an organic solvent such as dimethyl sulfoxide, acetone, or methanol can be used, but the adsorbed poly-4-vinylpyridine quaternary product is removed from the film. 1.0 as a solvent that prevents
A ~ 3.0 N saline solution is preferred. The polymerization temperature and time vary depending on the type of the initiator, but in general, room temperature to 5
It is selected from 0 ° C. and a range of several hours to several tens of hours.

The molecular weight obtained as described above is 2,0.
35% to 45% of the pyridine group of poly-4-vinylpyridine of 00-5,000 is quaternary pyridinium chloride with chloromethylstyrene, and the remaining pyridine group is quaternary pyridinium chloride with methyl iodide, poly-4- The quaternary product of vinyl pyridine is adsorbed on the surface of the cation exchange membrane, and then the double bond portion of the poly-4-vinyl pyridine quaternary product is polymerized to give the poly-4-vinyl pyridine quaternary product. In the cation exchange membrane where the polymer was present on the surface, part of the poly-4-vinylpyridine quaternary compound penetrates to the inside of the cation exchange membrane, and at the remaining portion, anions are exchanged on the cation exchange membrane surface. It forms a thin layer of properties. Surface analysis by SIMS (Secondary Ion Mass Spectroscopy) reveals about 100-50 inside the film.
An infiltrated layer of 0 nm poly-4-vinylpyridine quaternary and an anion exchange layer was detected at the membrane surface of 10 to 50 nm. The thickness of these layers is necessary and sufficient for maintaining a low membrane voltage during electrodialysis and maintaining good monovalent ion selective permeability for a long time. If the permeation into the membrane is thinner than the above, the durability of the monovalent ion selective permeability becomes poor, and if the anion exchangeable layer is thinner than the above, the monovalent ion selective permeability itself becomes poor. If both thicknesses are thicker than the above,
The membrane voltage during electrodialysis becomes high. One of the reasons why the membrane voltage during electrodialysis was high in the prior art is that the above layers were thicker than necessary.

[0011]

Now, the present invention will be described in further detail with reference to Examples and Comparative Examples. The symbols used in the examples have the following meanings. (1) F ₂ : Shows the relative selective permeability of divalent cations to monovalent cations in a cation exchange membrane in seawater concentration, the lower the value, the higher the monovalent cation selective permeability, ( It is given by the equation (1).

[0012]

[Equation 1]

Measurement method: A cation exchange membrane was used together with an anion exchange membrane A-172 manufactured by Asahi Kasei Kogyo Co., Ltd., an electrodialyzer SV-7 manufactured by Asahi Kasei Kogyo Co., Ltd. (effective energization area 0.5d).
m ² ), seawater is used as the diluent, and the seawater flow rate is 4
Electrodialysis is performed at cm / sec, a temperature of 25 ° C., and a current density of 3 A / dm ² , and each concentration is measured and calculated using the above formula. (2) V / P: Cell voltage per cell during electrodialysis If the conditions other than the cation exchange membrane are kept constant, the membrane voltage during electrodialysis of the cation exchange membrane will be higher or lower than this value. Can be evaluated by

Measurement method: A cation exchange membrane was used together with an anion exchange membrane A-172 manufactured by Asahi Kasei Kogyo Co., Ltd., an electrodialyzer SV-7 manufactured by Asahi Kasei Kogyo Co., Ltd. (effective energization area 0.5d).
m ² ), and using seawater whose Cl ^- concentration was kept constant at 0.4 N as a diluting solution, the seawater flow rate was 4 cm /
sec, temperature 25 ° C., current density 3 A / dm ² , electrodialysis was performed, 10 pairs of cell voltages were measured, and the value was divided by 10 to obtain the value.

On the other hand, the following method was used as a method for evaluating durability of monovalent ion selective permeability. The diluted surface of the film whose F ₂ and V / P had been measured was applied with a load of 2 kg to 20 cm /
Rubbing with a sponge 10 times at a speed of sec to physically damage the anion exchange layer on the membrane surface,
F ₂ was measured again and durability was evaluated by using the change of F ₂ as a scale. This rubbing 10 times is one cycle and the maximum is 10
The durability was evaluated by rubbing the cycle.

[0016]

Example 1 Production of cation exchange membrane: 89 parts by weight of styrene, purity of 56
% Divinylbenzene, 15 parts by weight of dimethyl phthalate, 6 parts by weight of nitrile butadiene rubber, 15 parts by weight of polyvinyl chloride powder, and 2 parts by weight of benzoyl peroxide were mixed to obtain a paste-like mixture made of polyvinyl chloride. The cloth was coated, sandwiched between polyethylene terephthalate films, and polymerized at 90 ° C. for 12 hours.
This film polymer was treated with 99.5% sulfuric acid at 40 ° C. for 2 hours.
Sulfonation was carried out for 4 hours to obtain a cation exchange membrane.

Production of adsorption treatment liquid: On the other hand, 880 parts by weight of dimethyl sulfoxide were mixed with 130 parts by weight of 4-vinylpyridine and 4 parts by weight of 30% potassium methoxide methanol solution in a nitrogen atmosphere, and anionic polymerization was carried out at 25 ° C. for 8 hours. Then, a solution of poly-4-vinylpyridine having a molecular weight of 3,000 in dimethyl sulfoxide was obtained. To this solution, 76 parts by weight of chloromethylstyrene, 105 parts by weight of methyl iodide, t
-Butylcatechol (1 part by weight) was added, and a quaternary pyridinium-forming reaction was carried out at 40 ° C for 24 hours. 40% of the pyridine group of poly-4-vinylpyridine was a vinylbenzyl group, and the rest was a quaternary pyridinium group. A 24 wt% solution of poly-4-vinylpyridine quaternary product was obtained. 16 parts by weight of this poly-4-vinylpyridine quaternary solution was added to 1.0
It was dissolved in 00 parts by weight of 0.3N saline at 40 ° C. to obtain an adsorption treatment liquid.

Imparting monovalent ion selective permeability to the cation exchange membrane: The cation exchange membrane previously prepared in this treatment liquid
Immerse at 40 ° C. for 24 hours, and put on a cation exchange membrane with poly-4-
Vinyl pyridine quaternary was adsorbed. After that, poly-
The cation exchange membrane on which 4-vinylpyridine quaternary compound was adsorbed was taken out from the adsorption treatment liquid, and 1,000 parts by weight of 1.
Immerse for 1 minute in an initiator solution prepared by dissolving 1 part by weight of potassium persulfate and sodium sulfite in 0N saline, then take out, put in a polyethylene bag and seal at 40 ° C.
It was placed in a constant temperature bath for 8 hours to polymerize the vinyl group in the poly-4-vinylpyridine quaternary product. Then, the membrane was taken out, washed with 0.5N saline solution three times, and poly-
A cation exchange membrane in which a polymer of 4-vinylpyridine quaternary compound was present was obtained.

The F ₂ and V / P of this cation exchange membrane are shown in Table 1. On the other hand, the results of durability evaluation of the monovalent ion selective permeability of this cation exchange membrane are shown in FIG.

[0020]

Comparative Example 1 57 parts by weight of chloromethylstyrene, 123 parts by weight of methyl iodide and t-butyl were added to a solution of poly-4-vinylpyridine having a molecular weight of 3,000 and obtained in the same manner as in Example 1 in dimethylsulfoxide. 1 part by weight of catechol was added, and a quaternary pyridinium-forming reaction was carried out at 40 ° C. for 24 hours to give 30% of the pyridine group of poly-4-vinylpyridine.
As a result, a 24 wt% solution of a poly-4-vinylpyridine quaternary product was obtained in which a quaternary pyridinium compound was used as a quaternary pyridinium compound with a vinylbenzyl group (%) and a residual methyl group. 16 parts by weight of this poly-4-vinylpyridine quaternary solution was added to 1,000 parts by weight of 0.3N.
It was dissolved in saline at 40 ° C. to obtain an adsorption treatment liquid.

Using this adsorption treatment liquid, the cation exchange membrane before being provided with the same monovalent ion selective permeability prepared in Example 1 was subjected to adsorption treatment under the same conditions as in Example 1. . Thereafter, the cation exchange membrane having the poly-4-vinylpyridine quaternary compound adsorbed was treated in the same manner as in Example 1,
The vinyl group in the poly-4-vinylpyridine quaternary product was polymerized to obtain a cation exchange membrane having a polymer of the poly-4-vinylpyridine quaternary product on the surface.

The F ₂ and V / P of this cation exchange membrane are also shown in Table 1. On the other hand, the results of the durability evaluation of the monovalent ion selective permeability of this cation exchange membrane are also shown in FIG. In the case of Comparative Example 1, since the proportion of quaternization of poly-4-vinylpyridine quaternized product with chloromethylstyrene is as low as 30%, the monovalent ion selective permeability is poor and its durability is low.

[0023]

Comparative Example 2 A solution of poly-4-vinylpyridine having a molecular weight of 3,000 and obtained in the same manner as in Example 1 was dissolved in dimethylsulfoxide, and 95 parts by weight of chloromethylstyrene, 88 parts by weight of methyl iodide and t-butyl were added. 1 part by weight of catechol was added, and a quaternary pyridinium-formation reaction was carried out at 40 ° C. for 24 hours, and 50% of the pyridine group of poly-4-vinylpyridine was a vinylbenzyl group, and the remainder was a quaternary pyridinium-formation polymethyl group. -24-of 4-vinylpyridine quaternary compound
A wt% solution was obtained. When 16 parts by weight of this poly-4-vinylpyridine quaternary solution was added to 1,000 parts by weight of 0.3N saline solution at 40 ° C. to try to dissolve it, it was not completely dissolved and was a suspension. However, we decided to use this as the adsorption treatment liquid.

Using this adsorption treatment liquid, the cation exchange membrane before being provided with the same monovalent ion selective permeability prepared in Example 1 was subjected to adsorption treatment under the same conditions as in Example 1. . Thereafter, the cation exchange membrane having the poly-4-vinylpyridine quaternary compound adsorbed was treated in the same manner as in Example 1,
The vinyl group in the poly-4-vinylpyridine quaternary product was polymerized to obtain a cation exchange membrane having a polymer of the poly-4-vinylpyridine quaternary product on the surface.

The F ₂ and V / P of this cation exchange membrane are also shown in Table 1. On the other hand, the results of the durability evaluation of the monovalent ion selective permeability of this cation exchange membrane are also shown in FIG. In the case of Comparative Example 2, since the proportion of the quaternization of the poly-4-vinylpyridine quaternary product with chloromethylstyrene was as high as 50%, V
/ P is high, that is, the membrane voltage during electrodialysis of this membrane is high.

[0026]

Comparative Example 3 793 parts by weight of dimethylsulfoxide was added to N,
20 parts by weight of N, N ′, N ′, N ″ -pentamethyliminobispropylamine, 46 parts by weight of chloromethylstyrene and 0.8 parts by weight of t-butylcatechol were mixed and reacted at room temperature for 48 hours, A 7.7% solution of a compound in which three amines of N, N ′, N ′, N ″ -pentamethyliminobispropylamine were quaternized ammonium with chloromethylstyrene was obtained. 13 parts by weight of this solution was dissolved in 1,000 parts by weight of 1.0 N saline to prepare an adsorption treatment liquid.

The cation exchange membrane before the same monovalent ion selective permeability as that prepared in Example 1 was imparted to this adsorption treatment liquid at 40 ° C. for 2 hours, and the cation exchange membrane was subjected to N, N
A quaternary ammonium compound of N, N ', N', N "-pentamethyliminobispropylamine was adsorbed. Then, a quaternary ammonium compound of N, N, N ', N', N" -pentamethyliminobispropylamine was adsorbed. A cation exchange membrane having a quaternary ammonium compound adsorbed was treated in the same manner as in Example 1 to give N,
The vinyl group in the quaternary ammonium compound of N, N ', N', N "-pentamethyliminobispropylamine is polymerized to form N, N, N ', N', N" -pentamethyliminobispropyl on the surface. A cation exchange membrane in which a polymer of a quaternary ammonium compound of amine was present was obtained.

Table 1 also shows F ₂ and V / P of this cation exchange membrane. On the other hand, the result of durability evaluation of the monovalent ion selective permeability of this cation exchange membrane is shown in FIG. In the prior art as in Comparative Example 3, the monovalent ion selective permeability and its durability are excellent, but the V / P is high, that is, the membrane voltage of this membrane during electrodialysis is high.

[0029]

[Table 1]

[0030]

EFFECTS OF THE INVENTION The cation exchange membrane of the present invention provides a monovalent ion permeation that is equal to or better than that of the prior art and its durability, and has a low membrane voltage during electrodialysis, which cannot be achieved by the prior art. When the cation exchange membrane of the present invention is used for salt production by electrodialysis, the power consumption can be reduced.

[Brief description of drawings]

FIG. 1 shows the films of Example 1 and Comparative Examples 1 to 3 in Examples,
It is a figure showing the durability of monovalent ion selective permeability evaluated by the method described in the examples.

Claims (1)

[Claims] 1. 35% to 45% of the pyridine group of poly-4-vinylpyridine having a molecular weight of 2,000 to 5,000,
Quaternary pyridinium chloride with chloromethylstyrene, the remaining pyridine group, quaternary pyridinium chloride with methyl iodide, quaternized poly-4-vinylpyridine is adsorbed on the surface of the cation exchange membrane, then A cation exchange membrane in which a polymer of the poly-4-vinylpyridine quaternary compound is present on the surface by polymerizing a double bond portion of the poly-4-vinylpyridine quaternary compound.