JPS6363243B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an anion exchange membrane for stable operation of a clamp type electrodialysis device over a long period of time, and a clamp type electrodialysis device incorporating the anion exchange membrane in a specific location. Regarding electrodialysis equipment.

Conventionally, it is widely known that electrodialysis equipment using ion exchange membranes is used to desalinate or concentrate seawater or electrodialyze acids, and clamp-type electrodialysis is one form of dialysis equipment used for these purposes. There is a device.

Tightening type electrodialysis equipment generally consists of a large number of cation exchange membranes and anion exchange membranes arranged alternately through gaskets and spacers, or a large number of ion exchange membranes attached to gaskets via gaskets. A dialysis device of the type that is arranged to form multiple chambers (dilution chamber and concentration chamber), with a cathode chamber and an anode chamber placed at both ends, and is tightened, for supplying and discharging each solution to the dilution chamber and concentration chamber. This dialysis device is equipped with communication holes and distribution grooves.

These clamp-type electrodialysis devices are becoming larger every year, but since assembly and disassembly are extremely difficult, the membrane group is usually divided into several stacks for ease of handling. There is. Each stack consists of 50 to 400 pairs of membranes, which are tightened with bolts or the like by tightening frames at both ends. In this case, the clamping frame serves not only to form and hold the stack but also to serve as a liquid supply frame, and each stack is provided with a header for supplying and draining desalinated liquid or concentrated liquid.

When desalting or concentrating an electrolyte solution for a long period of time using a clamp-type electrodialysis device, a part of the anion exchange membrane, that is, a energized part near the part that forms the distribution groove for supplying and draining the concentrated solution, The membrane changes color and becomes less brittle over time when electricity is applied, and if the operation continues, poorly soluble salts such as slag, calcium carbonate, and magnesium hydroxide will form on the membrane surface of the anion exchange membrane on the concentration chamber side, eventually damaging the membrane. It turned out that the car was no longer drivable.

FIG. 1 is a schematic diagram showing the deteriorated and damaged parts of the anion exchange membrane. In the figure, 1 is an anion exchange membrane, and the area 2 surrounded by the dotted line corresponds to the current-carrying area. The deterioration and damage location 3 occurs in an energized portion (also simply referred to as a portion near the distribution groove) near a portion 4 forming a distribution groove for supplying and discharging the concentrated liquid.

Deterioration, damage, etc. of the anion exchange membrane near the distribution grooves as described above occur regardless of the size of the device, but they tend to become more severe as the device becomes larger.

When such adverse effects occur, it is necessary to stop electrodialysis, dismantle the equipment, and replace the anion exchange membrane, which requires a great deal of time and labor and causes a decrease in operating efficiency. There are some drawbacks.

The present inventors investigated the deterioration, damage, and scale formation in the vicinity of the distribution grooves of the anion exchange membrane, and as a result, it became clear that the cause of the deterioration and damage was due to leakage current. In other words, when electricity is started and electrodialysis is performed, a difference occurs in the concentration of the desalted solution and the concentrated solution, and when comparing the resistance of the two liquids, the resistance of the concentrated solution is small, so a part of the current applied to the current-carrying part is transferred to the concentrated solution. A so-called leakage current occurs, which is a phenomenon in which the current flows into the communication hole through the distribution groove. As a result, the current flowing through the current-carrying parts near the distribution grooves becomes locally excessive, causing water decomposition on the ion exchange membrane surface and deteriorating the ion exchange membrane, but this particularly affects the anion exchange membrane. turned out to be large. As a countermeasure for the deterioration and damage of the anion exchange membrane caused by this leakage current, various studies were conducted and the above-mentioned problems were resolved by insulating the area near the distribution groove of the anion exchange membrane to increase the electrical resistance. They discovered that electrodialysis can be performed stably over a long period of time, and completed the present invention.

The present invention relates to an anion exchange membrane characterized in that, when incorporated into a clamp-type electrodialysis device, an energized portion near the distribution groove (portion near the distribution groove) through which concentrated liquid is supplied and discharged is insulated. be.

In the present invention, the insulation treatment in the vicinity of the anion exchange membrane distribution groove is performed in order to increase electrical resistance against leakage current. In general, the electrical resistance may be set to 5 to 10 times the electrical resistance of the anion exchange membrane itself. For example, the following method may be used.

(1) Covering method with insulating film An insulating film made of polypropylene, polyethylene, tetron, etc. that does not dissolve in the electrolyte solution is adhered or heat-sealed to the area near the distribution groove using an adhesive.

(2) A method of applying a solution that forms an insulating film.

A polymer substance capable of forming a film, such as natural rubber, chloroprene, or nitrile rubber, is dissolved in a volatile organic solvent and applied to the area near the distribution groove using a brush or brush.

(3) A method of adsorbing or applying ionic substances.

Brush with ionic organic substances such as humic acid, surfactant, and sodium dodecylbenzenesulfonate.
Apply it to the area near the distribution groove with a brush, etc. The coating substance exchange-adsorbs onto the anion exchange membrane, causing the membrane to lose its exchange ability and increase its electrical resistance.

(4) Method of reducing membrane exchange capacity Treat the area near the distribution groove with oxidizing agents such as hydrogen peroxide, chlorine, and sodium hypochlorite, alkali metals such as sodium metal, and reducing agents such as hydrogen and hydrogen sulfide. and reduce exchange capacity. Thermal decomposition also reduces the exchange capacity. Furthermore, a method of impregnating a monomer such as styrene, vinyl acetate, divinylbenzene, etc. and then polymerizing these is also employed.

In the present invention, since the insulation treatment is performed on the current-carrying portion of the anion exchange membrane, it goes without saying that the area should be as narrow as possible from the viewpoint of current efficiency. Therefore, when insulating the area near the distribution groove, it is preferable to determine the area by taking into account experience, electrodialysis conditions, etc. Generally, as shown in FIG. 1, it is desirable to insulate the membrane in a triangular shape, with the base facing the distribution groove and the apex pointing toward the center of the membrane.

If the above-mentioned insulated anion exchange membrane is incorporated into a clamp-type electrodialysis device, long-term operation is possible without causing various problems caused by leakage current.

However, it is not necessary to replace all anion exchange membranes with insulated anion exchange membranes. The present inventors have discovered that adverse effects such as damage to the anion exchange membrane due to leakage current are initially observed in the anion exchange membrane near the clamping frame, and gradually move to the center between the clamping frames as the operating time elapses; It has also been found that the above disadvantages can be overcome by replacing and incorporating an appropriate number of insulated anion exchange membranes of the present invention closer to the clamping frame.

The second invention is a clamping type electrical appliance in which a plurality of anion exchange membranes with insulating treatment in the vicinity of the distribution grooves are incorporated in each of the clamping frames between the clamping frames, and ordinary anion exchange membranes are incorporated in the remaining parts. Provides dialysis equipment.
When using such a device, not only is there no negative effect due to leakage current, but it also has the advantage of higher current efficiency and lower cost than when all anion exchange membranes are replaced with insulated anion exchange membranes. be.

In this device, generally 1 of the logarithm between the tightening frames is used.
~20% of the anion exchanger is insulated, and it is preferable that these are separated and incorporated closer to the tightening frame.

The device is preferably used in large electrodialysis machines consisting of several stacks, each stack generally consisting of 50 to 400 membrane pairs and clamped by clamping frames at both ends. in this case,
It is sufficient that 10 to 20% of the logarithm in the stack constituted by the clamping frame is an insulated anion exchange membrane, and that they are installed separately toward the clamping frame.

Examples will be described below, but the present invention is not limited thereto.

Comparative Example 1 Frame-shaped gasket with a notch in the center (external dimensions
400×1000mm, current-carrying part dimensions 320×775mm, current-carrying area
^2dm2 , thickness 0.75mm) through cation exchange membrane,
Neocepta C-66-5T (manufactured by Tokuyama Soda Co., Ltd.), an anion exchange membrane, and Neocepta AFN (manufactured by Tokuyama Soda Co., Ltd.) are placed between a PVC clamping frame and liquid supply frame, with 100 concentration chambers and dilution chambers. The stack was configured so that there were 101 rooms. The thickness of each desalination chamber and concentration chamber corresponds to the membrane spacing.
A diagonal mesh spacer made of polyethylene whose size corresponded to that of the current-carrying surface was inserted. Four such stacks were assembled, set between an anode and a cathode, and tightened from both ends with a press to form an electrodialyzer. Batch desalination experiments were conducted in this electrodialysis tank to obtain desalinated water (TDS below 500 ppm) using seawater (temperature approximately 23°C) as the raw material. An amount of seawater equivalent to 6 cm/sec was flowed into the desalination chamber and the concentration chamber at an intermembrane flow rate. In addition, the operating current is 7 A/dm ² at the start of desalination, 0.6 A/dm ² at the end of desalination, and during the period of desalination, a current ~ conductivity tracking method is used to control the current according to the conductivity of the desalting solution. The average current density for one batch is approximately
It was 4A/ ^dm2 . One batch takes approximately 11 minutes.
The production amount per batch was 400 in 30 seconds.
Operation was continued for 15 days under the above operating conditions, and the electrodialysis tank was dismantled. As a result of the disassembly, in all stacks, an equilateral triangle with sides of 5 to 6 cm was installed in the current-carrying part near the distribution part that supplies and drains concentrated liquid from the 5 to 20 anion exchange membranes adjacent to the clamping frame. The shape changes from yellowish-white to reddish-orange, and some parts of the membrane become hard and brittle.
Precipitation of CaCO ₃ scale was observed. but,
No other abnormality was observed in the central current-carrying portion of the anion exchange membrane. Further, regarding the cation exchange membrane, the phenomenon observed in the anion exchange membrane described above was not observed.

As described above, a characteristic deterioration phenomenon or the occurrence of scale is observed in a specific part of the anion exchange membrane adjacent to the clamping frame of the stack. When these phenomena occur, there arises the inconvenience that the operation of electrodialysis must be stopped and the membrane must be replaced with a new one, even though a portion of the membrane has deteriorated.

Example 1 When performing electrodialysis in the same manner as in Comparative Example 1 using gaskets and ion exchange membranes with the same specifications as Comparative Example 1, an anion exchange membrane with insulation treatment applied to each of 10 anion exchange membranes adjacent to both ends of the stack clamping frame was used. An ion exchange membrane was used. Insulation treatment was carried out by gluing Tetron film with a thickness of 0.04/m from the dilution chamber side using a nitrile rubber adhesive to the area corresponding to the area where the deterioration phenomenon occurred in Comparative Example 1 so that the area was about 10cm square. Ivy. Assemble 4 stacks in the same way as Comparative Example 1 to configure an electrodialyzer and convert seawater to desalinated water (TDS 500ppm).
We conducted an experiment to obtain the following.

After a 15-day desalination experiment, the stack was dismantled and the inside was inspected. No phenomena such as discoloration or deterioration that occurred in Comparative Example 1 were found in the anion exchange membrane used. Furthermore, no abnormal phenomena were observed in other parts, indicating that the insulation treatment was effective.

Example 2 Rubber glue made by dissolving natural rubber in methyl ethyl ketone was applied to the location corresponding to the location where the anion exchange membrane deterioration phenomenon occurred in Comparative Example 1, and dried to form a natural rubber film for insulation treatment. It was used as an anion exchange membrane. An experiment was conducted to obtain desalinated water from seawater under the same conditions as in Comparative Example 1, using the insulated anion exchange membranes for each of 10 anion exchange membranes adjacent to both ends of the stack clamping frame.

After the 15-day desalination experiment, the stack was disassembled and inspected, and no abnormality was found in the anion exchange membrane, and satisfactory results almost the same as in Example 1 were obtained.

Example 3 A 1% aqueous solution of sodium dodecylbenzenesulfonate was applied to a location corresponding to the location where the anion exchange membrane deteriorated in Comparative Example 1 to obtain an insulated anion exchange membrane. The resistance of the treated part is approximately
It had increased to ^1000Ωcm3 . In addition, before treatment, it is 1.5Ωcm ³
It was hot. Using such an insulated anion exchange membrane, it was incorporated into a stack in the same manner as in Example 1, and
In the same way, we conducted an experiment to obtain desalinated water from seawater.

After the 15-day desalination experiment, the stack was disassembled and inspected, and no abnormalities were found in the anion exchange membrane or other parts, and satisfactory results almost the same as in Example 1 were obtained.

Example 4 A 0.5N potassium ferricyanide solution was thoroughly soaked into the area corresponding to the area where the anion exchange membrane deteriorated in Comparative Example 1, and then 3% hydrogen peroxide was soaked and left for 5 hours. It was made into an insulated anion exchange membrane. The exchange capacity of the processing part is
It had decreased to 0.4 meg/g・Cl type dry film.

Note that the dry membrane was 2.1 meq/g·Cl type before treatment. Using the anion exchange membrane thus insulated, it was assembled into a stack in the same manner as in Example 1, and an experiment was conducted to obtain desalinated water from seawater in the same manner.

After a 15-day desalination experiment, the stack was disassembled and inspected, and no abnormalities were found in the anion exchange membrane or other parts, and satisfactory results were obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the deteriorated and damaged parts of the anion exchange membrane. In the diagram, 1... anion exchange membrane, 2... energized parts, 3... deterioration, damaged parts, 4
...Represents the portions forming the distribution grooves.

Claims (1)

[Scope of Claims] 1. An anion exchange membrane characterized in that, when incorporated into a clamp-type electrodialysis device, a current-carrying portion near a distribution groove for supplying and discharging a concentrated solution is insulated. 2. The anion exchange membrane according to claim 1, wherein the insulation treatment is performed by adhering or heat-sealing an insulating film to the corresponding location. 3. The anion exchange membrane according to claim 1, wherein the relevant portions are insulated so that the electrical resistance is 5 to 10 times the electrical resistance of the anion exchange membrane itself. 4 When installed in a clamping type electrodialysis device, install multiple anion exchange membranes, each of which has an insulated electrically conductive part near the distribution groove for supplying and discharging concentrated liquid, between the clamping frames. A tightening type electrodialysis device with one built-in and a normal anion exchange membrane built into the rest. 5. The clamping type electricity set forth in claim 4, in which 10 to 20% of the logarithms between the clamping frames are insulated anion exchange membranes, and these are divided and incorporated closer to the clamping frame. Dialysis machine.