JPS5846324B2 - Inion Koukan Makuno Saiseisenjiyouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for regenerating anion exchange membranes that have suffered from so-called organic contamination.

More specifically, the present invention relates to a method for regenerating an anion exchange membrane contaminated with organic anions by bringing it into contact with an inorganic salt solution.

In the conventional ion exchange membrane electrodialysis method, when electrodialysis is performed by arranging cation exchange membranes and anion exchange membranes alternately and applying a DC voltage, molecular weight substances such as humic acid and alkylbenzenesulfonic acid are present in the treated water. If large organic anions are contained, the anion exchange membrane will be subject to organic contamination.
The electrical resistance of the anion exchange membrane increases significantly, resulting in
It is well known that the disadvantage is that the dialysis voltage increases, making continuous operation of electrodialysis impossible.

On the other hand, if a neutral diaphragm without ion exchange groups is used instead of an anion exchange membrane, organic contamination will be eliminated and stable operation will be possible even when the processing liquid contains organic anions with large molecular weights. is known to be possible.

To address this problem, an electrodialysis method (Japanese Patent Application No. 91371/1983) has been proposed that combines (1) a porous anion exchange membrane containing imidazole groups with a normal cation exchange membrane; The present inventors have invented (2) an electrodialysis method that combines a weakly basic anion exchange membrane and a normal cation exchange membrane.

However, although the anion exchange membranes used in methods (1) and (2) exhibit much better resistance to organic contamination than ordinary anion exchange membranes, they have the following drawbacks.

(A) (The anion exchange membrane obtained in step 11 has a low current efficiency because the concentration diffusion through the membrane is large.

The anion exchange membrane obtained in (2) has a small transport number and therefore has a low current efficiency.

(B) Over the long term, there is a tendency for organic pollution to occur.

That is, organic pollution progresses in the following order.

■ First, the divalent ion selective permeability of the anion exchange membrane begins to decrease.

■ The divalent ion permselectivity of the anion exchange membrane decreases to a minimum value.

From this stage, the voltage of the electrodialyzer begins to rise.

■ Membrane resistance rises rapidly and dialysis becomes impossible.

The methods that have been proposed so far are methods in which the stage ① of the deterioration process is prolonged, and it is thought that after long-term operation, the process progresses to stages ① and ②.

Furthermore, when the selective permselectivity of divalent ions of the anion exchange membrane decreases, the ratio of divalent ions such as sulfate ions in the diluent flow increases, liquid resistance increases, and the limiting current density also decreases.

Therefore, this tendency of decreasing selective permselectivity for divalent ions not only leads to serious organic contamination, but also reduces the limiting current density and increases the size of the electrodialysis tank, which is not desirable.

Therefore, it has been desired to establish a method for restoring this divalent ion permselectivity from the viewpoint of making it possible to more safely impart organic contamination resistance to the electrodialysis tank.

On the other hand, in recent years, when desalting a salt solution, there has been a tendency to emphasize not only the reduction of the total salt concentration but also the balance of each ion in the produced desalted water.

In order to meet these demands and perform electrodialysis economically, it is desirable that the ion exchange membrane have an appropriate ion selective permeability and that the value does not change.

From this point of view as well, it is not preferable that the selective permselectivity of divalent ions of the anion exchange membrane gradually decreases over a long period of time.

The present inventors have conducted intensive research on these points and have finally developed the method of the present invention.

The method of the present invention is based on the knowledge that by bringing an anion exchange membrane contaminated with organic anions into contact with an aqueous inorganic salt solution, the membrane resistance and divalent ion permselectivity coefficient can be restored to the initial (1) state. In particular, if the water to be treated such as brine that undergoes electrodialysis treatment contains organic anions that contaminate the membrane, such as dodecylbenzenesulfonate ions, the contaminating organic ions may cause divalent anions to be removed. Although the permselectivity of the membrane decreases, as long as the decrease is within the range, the permselectivity can be easily restored by bringing the organically contaminated membrane into contact with an aqueous inorganic salt solution. It is based on

The method of the present invention addresses the drawbacks of conventionally proposed methods, namely, its application to desalination by electrodialysis of aqueous salt solutions containing organic contaminating anions such as humic acid, dodecylbenzenesulfonic acid, and sodium naphthalene trisulfonate. It improves the disadvantages of the anion exchange membrane, such as a large salt diffusion coefficient or a small anion transfer number, and furthermore prevents the long-term tendency of the divalent ion selectivity coefficient to decrease, and eliminates such organic contaminating anions. This enables stable desalination of ion-containing liquids by electrodialysis.

The anion exchange membrane to be used in the method of the present invention may basically be any type of anion exchange membrane that has been proposed in the past.

However, in order to further enhance the effects of the present invention, it is preferable to use a material having a large anion transport number and a small salt diffusion coefficient.

In carrying out the method of the present invention, the electrodialysis tank may be disassembled and the anion exchange membrane taken out and immersed in a salt solution, or the electrodialysis tank may be placed in the dilution stream without being disassembled. Washing may be carried out by circulating a saline solution.

The inorganic salts for cleaning used in the present invention may be any water-soluble inorganic salts, or may be a mixture of two or more inorganic salts.

The concentration of the aqueous salt solution is preferably close to the concentration of the diluting solution from the viewpoint of not causing a change in the elongation rate of the membrane, but this is not particularly limiting.

However, there is a close relationship between salt concentration and the time required for regeneration, and the higher the concentration, the shorter the regeneration time.

Therefore, from a practical standpoint, it is more than 0.05 standard.

The regeneration interval varies depending on the concentration of organic contaminating anions in the liquid to be treated, but the following sulfate ion selective permeability is measured during electrodialysis, and when this value decreases, regeneration is stopped. Bye.

Sulfate ion selective permselectivity: The above-mentioned permselectivity at the beginning of use of the membrane is indicated by 0 (Fo14)B. .

Example 1 A cation exchange membrane (manufactured by Mukasei Kogyo -101) and an anion exchange membrane (manufactured by Mukasei Kogyo CA-1) with an effective current carrying area of 1 dm
) 10 pairs constitute an electrodialyzer.

11,000 ppm of brine containing chloride and sulfate ions, including 0.5 ppm of sodium dotecylbenzenesulfonate, was supplied to this dialysis tank, desalted at a current density of 0.35 A/am, and TDS (total Dissolved salts) 200
The operation was carried out under conditions to obtain demineralized water of ppm.

At this time, the time-dependent change in the sulfate ion permselectivity coefficient FSO4 was as follows.

1 After 500 hours of slow operation, 3.0N saline was circulated to the dilution side of the dialysis tank for 30 minutes, and then again Example 2 Using the same dialysis tank as used in Example 1, as raw water. TDS 1100 ppm treated municipal sewage water containing 1.0 ppm sodium dodecylbenzenesulfonate was supplied, desalted at a current density of 0.35 A/dm, and then diluted with TDS.
The operation was carried out under the condition that demineralized water with a DS of 200 ppm was obtained.

At this time, the time-dependent change in the sulfate ion permselectivity coefficient FSO4 was as follows.

After 13,000 hours, operation was stopped, and after circulating a 1.0N sodium sulfate solution to the dilution side of the dialysis tank for 2 hours, desalination was started again, and the FSO4 value showed I 0.95.

Claims (1)

[Claims] 1. In electrodialysis of brine containing contaminant organic anions, the sulfate ion selective permeability (F S
In the process of decreasing O4, the membrane should be reduced to at least 0 before the residual I permselectivity of the membrane decreases to 0.4 or less as a ratio to the permselectivity at the initial stage of use.
．． 1. A method for regenerating an anion exchange membrane, the method comprising bringing it into contact with an aqueous solution of an inorganic salt according to the 05 standard.