JPS6350041B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel method for efficiently and selectively recovering or removing a base from a base-containing solution by diffusion dialysis. Solutions containing bases are now available in large quantities from various industrial, processing, or processing processes. Examples include groundwood pulp processing wastewater containing caustic soda in the viscose silk industry, alkali-containing solutions from metal processing processes, alkali-containing solutions from ion exchange resin regeneration processes, and even alkali-containing solutions obtained by diaphragm electrolysis. Selective recovery of the base in these base-containing solutions and debasing from the solution are sometimes done in order to effectively utilize resources, and sometimes as part of the manufacturing process. As one process,
Furthermore, it is a measure that is absolutely necessary from the standpoint of pollution. As a means for recovering or removing the base from the base-containing solution, the base-containing solution is passed through a cation exchange membrane,
A method has been proposed in which the base is selectively recovered by diffusion dialysis based on the concentration gradient of the base in opposition to water (see Japanese Patent Publication No. 36-19463).
Diffusion dialysis is expected to be widely used in many industrial fields because it can selectively recover bases using a simple device without requiring any special reagents or means such as heating. be done. The present invention has discovered a cation exchange membrane that has extremely superior performance compared to conventional cation exchange membranes when used for diffusion dialysis of such base-containing solutions, and A novel diffusion dialysis method for base-containing solutions is provided. That is, the present invention consists of a copolymer of ethylene and an unsaturated carboxylic acid (meaning acrylic acid or methacrylic acid, hereinafter the same) or a salt thereof, and has an ion exchange capacity of 1.0 to 3.0 milliequivalents/g dry resin. and a cation exchange membrane having a water content of 10 to 30%. In the case of diffusion dialysis of a base-containing solution according to the method of the present invention, the permeability coefficient of the base through the membrane is 6 to 10% higher than that of conventionally known membranes, as shown in the comparative example.
significantly superior. Moreover, in the case of the present invention, even if other substances coexist in the base-containing solution and other anions are present, hydroxyl ions preferentially permeate the membrane, making it possible to recover the base almost selectively. , the value of the recovered base is that much greater, and the range of reuse is also greater. To explain the present invention in more detail below, the copolymer of ethylene and an unsaturated carboxylic acid or a salt thereof used as a cation exchange membrane in the present invention is:
Since it is a substantially linear polymer and does not have a crosslinked structure, there is a fear that the swelling will be extremely large and the resin will be destroyed. When a membrane made of a membrane having a predetermined composition ratio of carboxylic acid or its salt and a predetermined ion exchange capacity is in contact with a base-containing solution, the above-mentioned swelling phenomenon can be significantly suppressed. found. Therefore, the ion exchange capacity of the cation exchange membrane, which is related to the composition of ethylene and unsaturated carboxylic acid or its salt in the copolymer, is important and is 1.0 to 3.0 as described above.
milliequivalents/g dry resin. If it is larger than this range, the water content of the membrane will increase and the separation performance between hydroxide ions and other anions will decrease, and if it is smaller than this range,
This is not preferable because the permeability coefficient of hydroxide ions becomes small. Among them, it has been found that those having an ion exchange capacity of 1.2 to 2.5 milliequivalents/g dry resin are particularly preferred from the above viewpoint. Such ion exchange capacity is achieved by selecting the composition ratio of ethylene and unsaturated carboxylic acid or its salt in the copolymer, as described above. As the unsaturated carboxylic acid or its salt forming the copolymer which is the base material of the cation exchange membrane of the present invention, a carboxylic acid or a carboxylate compound having an unsaturated bond capable of polymerization in the molecule is used,
Preferred examples include acrylic acid, methacrylic acid, itaconic acid, (anhydrous) maleic acid, (anhydrous)
Examples include fumaric acid or a quaternary ammonium salt thereof, an alkali metal salt such as sodium or potassium, or a metal salt of Group 2 of the periodic table such as zinc, calcium or magnesium. Such unsaturated carboxylic acids or salts thereof may be their precursors, such as esters, amides, and nitriles of the above-mentioned acids which give such compounds upon hydrolysis or neutralization. Of course, more than one type of such unsaturated carboxylic acids or salts can be used in forming the copolymer, and if necessary, a third polymerizable compound such as styrene, vinyl chloride, vinylidene chloride, vinyl alcohol, vinyl ether, etc. can be copolymerized. The copolymer of the present invention is produced by any known polymerization method, and its molecular weight is preferably from 5,000 to 500,000, particularly from 15,000 to 500,000, depending on manufacturing needs.
300,000 yen. Among the copolymers of ethylene and unsaturated carboxylic acids or salts thereof of the present invention, from the viewpoint of performance as an ion exchange membrane and availability, copolymers having the following general structural formula are preferred. was found to be particularly preferred. Here, X is hydrogen or a methyl group, Y is hydrogen or a metal atom, and m/(molar ratio) is 0.02
~0.15. Among these, Y is preferably a hydrogen, sodium or zinc atom, and m/ is
Particularly preferred is 0.03 to 0.12. Cation exchange membranes made of these copolymers are
Preferably, it is used at a thickness of 10 to 150μ, particularly 20 to 100μ, in consideration of the permeability coefficient of hydroxide ions and mechanical strength. Further, such a cation exchange membrane can be used by being reinforced with an appropriate thin film support such as a film, cloth, or woven fabric. The material for the support is preferably one having alkali resistance, such as an olefinic polymer or a halogenated vinyl polymer including a fluorine-containing polymer. The shape of the membrane is not limited to a general planar shape, but may also be a hollow fiber shape. On the other hand, the water content of the cation exchange membrane is 30% or less.
Must be maintained at 10% or higher. If it is more than 30%, the separation of hydroxyl ions and other anions is poor, and 15
% or less, the hydroxide ion permeability coefficient is small.
The moisture content is particularly preferably 15 to 25%. As a method to control the moisture content within the above range, PH
The membrane may be immersed in an aqueous solution having a temperature of 3.5 or higher at a temperature of 80°C or lower, preferably for 5 minutes or longer. If a large amount of salt or base that controls pH is present in the treatment solution, it is difficult to keep the water content of the membrane within the above range, so the salt or base present in the treatment solution should be 1N or less. is preferred. Another means of controlling the water content within the above range is to treat the membrane in an aqueous solution containing 50% by weight or less of a polar organic compound. As the polar organic compound for this purpose, methanol, ethanol, acetone, etc. are preferable. Any known means can be employed to perform diffusion dialysis on a base-containing solution using the cation exchange membrane of the present invention. For example, the diffusion dialysis tank may be either a filter press (tightening) type or a unit cell (water tank) type. The base-containing solution is then supplied to the alternating compartments (dialysis chambers) of such a diffusion dialysis tank, while the remaining alternating compartments (diffusion chambers) of the diffusion dialysis tank adjacent to said dialysis compartment are supplied with water or a suitable solution. An aqueous liquid is supplied. The dialysate (base-containing solution) and the diffusion liquid (water) are preferably
Both are preferably dialyzed at 0 to 60°C. Thus, during dialysis, the base in the dialysis chamber is selectively transferred through the membrane to the diffusion chamber, where the base is efficiently recovered. Diffusion dialysis of the present invention can treat any type of base-containing solution, including alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, ammonia, alkylamines, ethanolamines, and ethylenediamines. Examples include base-containing solutions such as. Among these, it is particularly preferable to apply the present invention to a solution in which a base and its salt coexist, since the base and its salt can be selectively separated and recovered. Example 1 A copolymer of ethylene and methacrylic acid, "Surlyn A1707" (trade name of DuPont, USA, part of the carboxylic acid is Na salt, 2.05 milliequivalent/
A membrane with a thickness of 50 µm made of 100% polyester resin (having a dry resin exchange capacity) was treated under the conditions shown in Table 1 to completely remove Na.
It was made into a mold. The water content was determined from the weight W ₁ of the membrane in equilibrium with water at 25°C and the weight W ₂ after drying the membrane at 60°C under reduced pressure of 10 mmHg for 10 hours according to the following formula. Water content = W ₁ − W ₂ / W ₁ × 100 (%) The diffusion constant of caustic soda is 4N NaOH is placed on one side of a cation exchange membrane (effective area Am ² ), water is placed on the other side, and the liquid in both chambers is Dialysis was carried out at a temperature of 25° C. for 2 hours (dialysis time t), and the number of moles of caustic soda transferred to the water side (m) was calculated from the concentration difference ΔC (mol/) between the two chambers using the following formula. U=m/AΔCt Table 1 shows the treatment conditions, water content, and diffusion constant.

[Table] Example 2 Using membrane No. 3 of Example 1, caustic soda
A solution containing 2.58 mol/1.30 mol/of sodium aluminate is placed on one side of the membrane, and water is placed on the other side.
Diffusion constant of caustic soda was determined in the same manner as in Example 1.
The diffusion constant U _Al of U _NaOH and aluminum was determined. U _NaOH =
8.07, U _Al =0.103. U _NaOH /U _Al is 78, and together with the large U _NaOH , this cation exchange membrane is excellent as a diffusion dialysis membrane. Comparative example: Thickness obtained by applying styrene-butadiene copolymer to polyvinyl chloride cloth and then crosslinking and sulfonating it.
Diffusion dialysis was carried out in the same manner as in Example 2 using a cation exchange membrane of 160μ and water content of 27%. U _NaOH =
0.95, U _Al =0.023. Example 3 Pellets of a copolymer of ethylene and methacrylic acid, "Surlyn A1652" (trade name of DuPont, USA, in which a portion of the carboxylic acid in the copolymer is a Zn salt) and the pellets used in Example 1 were used. “Surlyn A1707”
A membrane with a thickness of 40 μm was produced by extrusion molding the mixture with pellets. The membrane was dissolved in 0.1N KOH at 65%
The membrane was treated at ℃ for 16 hours to obtain a K-type cation exchange membrane. Its thickness is 50μ, exchange capacity is 1.85 meq/g dry resin, moisture content is 23%, and 4N
When KOH was dialyzed, U _KOH was 4.59. Example 4 (including comparative example) A 50 μm thick film made of the same ethylene and methacrylic acid copolymer “Surlyn A1707” used in Example 1
membrane was treated under the conditions shown in Table 2 to completely
It was set as Na type. On one side of the membrane thus obtained (effective area 0.001 m ² ),
Caustic soda 2.58mol/, Sodium aluminate
A solution containing 1.3 mol/ml was placed on the other side, water was placed on the other side, and dialysis was performed for 2 hours (dialysis time t) with the liquid temperature in both chambers set at 25°C. The water content of the membrane and the dialysis constant are as in Example 1.
I asked in the same way. Table 2 shows these results.

[Table] Example 5 (comparative synthesis example) A copolymer of ethylene and acrylic acid was
Obtained according to the method described in 23494. The acrylic acid content of the obtained copolymer was 14.8% by weight.
(ion exchange capacity 2.05 meq/g). The thus obtained copolymer was heated and compression molded into a 100μ thick film, and then in the same manner as in Example 4.
The moisture content and diffusion constant were determined and shown in Table 3.

【table】

Claims (1)

[Scope of Claims] 1. Consisting of a copolymer of ethylene and acrylic acid or methacrylic acid or a salt thereof, having an ion exchange capacity of 1.0 to 3.0 milliequivalents/g dry resin, and a water content of 10 to 30%. A method for diffusion dialysis of a base-containing solution, which comprises performing diffusion dialysis on a base-containing solution using a cation exchange membrane having a cation exchange membrane. 2 A copolymer of ethylene and acrylic acid or methacrylic acid or a salt thereof has the general structural formula (Here, X is hydrogen or a methyl group, Y is hydrogen or a metal atom, and m/(molar ratio) is 0.02
~0.15. ). 3. The method according to claim 2, wherein the metal atom is a sodium or zinc atom. 4. The method according to claim 1 or 2, wherein the cation exchange membrane has a thickness of 10 to 150μ. 5. The method of claim 1, wherein the base-containing solution is an aqueous solution of an alkali metal hydroxide. 6. The method according to claim 1 or 5, wherein the base-containing solution has a concentration of 0.5N to 14N. 7. The method according to claim 1, wherein diffusion dialysis is performed at a temperature of 5 to 60°C.