JPS6335286B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION The present invention relates to an improved clamp type electrodialysis device.

More specifically, it is a tightening type electrodialysis device that is constructed by combining a large number of cation exchange membranes, anion exchange membranes, gaskets, and spacers in an alternating manner, and by reducing the thickness of the gasket for the dilution chamber. The present invention provides an excellent electrodialysis device that reduces the voltage required during dialysis, but does not cause liquid leakage, a decrease in limiting current, or other deterioration in performance.

``Industrial Application Fields'' Electrodialysis equipment is used for concentrating and desalinating seawater, desalinating underground brine, etc. In particular, the method of using an electrodialysis device is widely used to obtain concentrated brine by concentrating seawater.

``Prior Art'' There are various characteristics required of such an electrodialysis device, and measures for improving the characteristics have been proposed from various angles in recent years.

For example, in Japanese Patent Publication No. 49-43188, the liquid pressure in the concentration chamber is made larger than the liquid pressure in the dilution chamber, or a filler is inserted into the concentration chamber so that the ion exchange membrane facing the concentration chamber is directed toward the dilution chamber. It has been shown that the limiting current density increases by the method of dialysis while pressing, and in Japanese Patent Publication No. 17316/1983, the thickness of the current-carrying part spacer is made 2 to 18% thicker than the thickness of the gasket, thereby improving the operation of the dialysis tank. A clamping type electrodialysis device is disclosed that maintains a low polarization potential in the dialysis device.
In addition, in Japanese Patent Publication No. 55-33362, the section perpendicular to the flow direction of the liquid in the tidal channel part has a substantially wavy shape, and the amplitude of the waveform is at least equal to the thickness of the frame (gasket). It is disclosed that the presence of a corrugated plate allows the hydraulic pressure loss to be kept small and also to improve liquid dispersion in the compartment. Furthermore, Japanese Patent Application Laid-open No. 171404/1983 discloses that by improving the tidal channel portion, uniform supply of liquid and prevention of liquid leakage can be achieved.
In particular, the test report (No. 10) of the Japan Monopoly Public Corporation Odawara Laboratory states that when the gasket thickness is 1 mm and the gasket thicknesses in the concentration chamber and dilution chamber are different,
Inserting a spacer that differs from the gasket thickness is disclosed.

"Problems to be Solved by the Invention" The present inventors have attempted to improve electrodialysis equipment from a completely different perspective from these conventionally implemented or proposed methods, and as a result of intensive studies, the present invention has been developed. I was able to accomplish this. The present invention provides an electrodialysis device with low voltage, no reduction in limiting current, and little leakage of liquid, but it is simply a matter of reducing the difficulty of manufacturing technology by making the gasket and spacer thinner. It is something to avoid. In particular, for gaskets with a thickness of less than 1 mm, the thinner the gasket, the more difficult it becomes to manufacture it with high precision, leading to an increase in manufacturing costs, or in extreme cases, making it impractical.

``Structure of the Invention'' The present invention provides a clamping type electrodialysis device that is constructed by alternately combining a large number of cation exchange membranes and anion exchange membranes via gaskets and spacers, in which the thickness of the gasket for the dilution chamber is as low as 100 mm. The same or thinner than the dilution chamber current carrying part spacer, and the thickness of the concentration gasket is thinner than the concentration chamber current carrying part spacer, and the total thickness of the dilution chamber current carrying part spacer and the concentration current carrying part spacer. is greater than the sum of the thickness of the concentration gasket and the dilution chamber gasket.

"Means for Solving the Problem" FIG. 1 is a sectional view taken along the line A-B in FIG. 2, showing the features of the electrodialysis apparatus of the present invention. Figure 2 shows the configuration of a general electrodialysis device, which includes a cation exchange membrane 1, a gasket 2 for the concentration chamber, a tidal channel 3 for the concentration chamber, a spacer 4 for the concentration chamber energization section, and a communication hole for the concentrated liquid. 5, anion exchange membrane 6,
A large number of dilution chamber gaskets 7, dilution chamber tide paths 8, dilution chamber energizing part spacers 9, and dilution chamber communication holes 10 are alternately combined and stacked, and a tightening frame (not shown) and a supply are provided on both sides. A drain frame (not shown) is further provided with an anode (not shown) and a cathode (not shown) on both sides thereof.

The thickness of the dilution chamber gasket used in the present invention is:
Less than 0.4-1.0mm. In particular, preferably 0.5~
It is 0.8mm. If it is thinner than 0.4mm, the strength of the gasket will be weakened, manufacturing accuracy will be reduced, and the function of the gasket will be easily impaired. On the other hand, if the thickness is 1 mm or more, the voltage will be high and it cannot be said to be an excellent electrodialysis device.

The thickness of the insert in the dilution chamber gasket tidal section is as follows:
The thickness of the gasket for the dilution chamber should be 0 to 0.25 mm, preferably 0.05 to 0.15 mm. If it is thinner than the thickness of the gasket for the dilution chamber, internal leakage of liquid is likely to occur, and conversely, the concentrated liquid may leak into the diluted liquid. Also, the resistance to liquid flow increases,
This is disadvantageous because a large pressure difference between the dilution chamber and the concentration chamber must be maintained. Furthermore, when seawater is used as the diluent, it is disadvantageous because the period until the tidal channel is blocked by the adhesion of the contained suspended matter is shortened. If it is larger than 0.25 mm, the ion exchange membrane is likely to be damaged at the contact portion between the ion exchange membrane and the spacer, which is not a good idea. The insert for the tidal channel is preferably a spacer alone or a spacer with polyester, polypropylene, etc. superimposed on both sides or one side of the spacer.

The thickness of the current carrying part spacer for the dilution chamber is preferably 0.15 to 0.3 mm thinner than the gasket for the dilution chamber. When the thickness difference is less than 0.15 mm, the voltage drop is small, and when it is larger than 0.3 mm, the ion exchange membrane is greatly deformed, making it difficult to obtain stable performance over a long period of time. Gaskets for concentration chambers are usually 0.4 to 0.6
It is between mm. Of course, even if it deviates from this range, it does not impair the effect of the present invention, but if it is thin, it will be difficult to manufacture and operate, and if it is thick, it will be necessary to increase the voltage or disperse the liquid in the concentration chamber. In order to improve this, a higher liquid flow rate is required, which increases the required power. The thickness of the spacer used in the energizing part of the concentration chamber is 0.35 times smaller than the thickness of the gasket for the concentration chamber.
~0.2mm thick ones are used. That is, it is desirable that the spacer for the current-carrying part for the dilution chamber is slightly larger than the thickness of the gasket for the dilution chamber, and that the spacer for the current-carrying part for the concentration chamber is thicker than the thickness of the gasket for the concentration chamber.

The present invention is completed in that the total thickness of the spacer for the concentration chamber current-carrying part and the spacer thickness for the dilution chamber current-carrying part is 0.02 to 0.1 mm larger than the sum of the thickness of the gasket for the concentration chamber and the gasket for the dilution chamber.
Beyond these ranges, if the total spacer thickness is larger than the total gasket thickness, the contact between the ion exchange membrane and the spacer will be abnormally strong, inhibiting the flow of liquid near the ion exchange membrane and reducing the limiting current. easy to invite. On the other hand, if it is too small, a gap is likely to be formed between the ion exchange membrane and the spacer, causing the flow of the liquid to become laminar, which may lead to a decrease in the limiting current.

The material of the gasket of the present invention is not particularly limited, but it is generally mass-produced synthetic resins such as vinyl chloride, polypropylene, vinyl acetate-polyvinyl alcohol copolymer, natural rubber, and synthetic rubber, with various additives added as necessary. It is molded and processed. The material for the spacer is preferably polyethylene or polypropylene because they are readily available. In particular, the shape of the spacer is preferably a diagonal mesh.

"Function" The electrodialysis apparatus of the present invention is an excellent electrodialysis apparatus with low voltage, little leakage of liquid, and no other adverse effects, and therefore enables more efficient electrodialysis than conventional electrodialysis apparatuses.

The present invention will be explained in more detail below by way of Examples, but the present invention is not limited thereto.

Example 1 A cation exchange membrane (Aciplex K-172) with a current carrying area of ² dm2, a gasket for the concentration chamber (made of natural rubber)
0.5mm), energizing part spacer for concentration chamber (polyethylene diagonal mesh, thickness 0.8mm), anion exchange membrane (Aciplex A-172), gasket for dilution chamber (0.75mm made of natural rubber), energizing part for dilution chamber 20 pairs of spacers (polyethylene diagonal net, thickness 0.5 mm) and dilution chamber tidal channel spacer (polypropylene diagonal net, thickness 0.8 mm) are stacked, and a tightening frame is placed on both sides. were arranged to form a stack. Furthermore, a frame for supplying and draining liquid and an anode are installed on both sides.
Attached the cathode.

Seawater after two-stage sand filtration was flowed into the dilution chamber so that the linear velocity of the liquid in the current-carrying section was 6 cm/sec. Initially, the concentration chamber was filled with seawater and circulated through a concentrated liquid supply tank.

A direct current of 7 amperes was applied to this, and electrodialysis was started. After 5 hours, both the concentrate concentration and the stack voltage reached equilibrium. At that time, the concentration of the concentrated solution was 3.7 standard in terms of chloride ion concentration, and the stack voltage was:
It was 6 volts. In addition, when we measured the differential pressure between the diluted liquid inlet and diluted liquid outlet of the liquid supply/drainage frame, we found that
It increased over time. The rate of rise was 45 cm of water column over 10 days.

Meanwhile, in other stacks, the concentration chamber remains empty.
The dilution chamber was filled with seawater under a static pressure of 2cm of water, and the seawater was circulated for 3 hours. When we measured the amount of seawater leaking into the concentration chamber, it was 2 ml per hour. After that, seawater was flowed into both the concentration chamber and the dilution chamber at a linear velocity of 4 cm/sec, and a direct current of 5 cm was applied to both chambers.
The voltage was measured gradually increasing from amperes. The limiting current was around 15 amperes.

Comparative Example 1 In Example 1, the cation exchange membrane, anion exchange membrane, gasket for the concentration chamber, and gasket for the dilution chamber were kept as they were, the current carrying part spacer for the concentration chamber was made 0.5 mm thick, and the tidal path for the dilution chamber was changed. Part spacer thickness
Replaced with 0.75mm.

Operating under the same conditions as Example 1, the stack voltage was
At 6.6 volts, the differential pressure rise rate was 45 cm of water column. The leakage rate was 10 ml/hour, and the limiting current was 14 amperes. Next, determine the thickness of the current-carrying part spacer for the concentration chamber.
0.75mm, dilution chamber current-carrying part spacer thickness 0.5mm
I drove instead. Stack voltage is 6.1 volts,
The differential pressure increase rate was 50 cm water column. The leakage rate was 5 ml/hour, and the limiting current was 10 amperes.

Example 2 In Example 1, the concentration chamber gasket thickness was 0.5
A stack was created in which the thickness of the spacer for the current-carrying part of the concentration chamber was 0.75 mm, the thickness of the gasket of the dilution chamber was 0.5 mm, the thickness of the spacer of the current-carrying part of the dilution chamber was 0.3 mm, and the spacer thickness of the dilution chamber tidal passage part was 0.6 mm. The linear velocity of the diluent in the current-carrying section of the dilution chamber was 4 cm/sec. The stack voltage was 5.4 volts and the differential pressure rise rate was 60 cm of water. The leakage rate was 3 ml/hour, and the limiting current was 13 amperes.

Comparative Example 2 In Example 1, the stack was operated under the same conditions as in Example 1, except that the thickness of the spacer for the current-carrying part of the concentration chamber was 0.5 mm, the spacer of the current-carrying part of the dilution chamber was 0.5 mm, and the spacer of the dilution chamber tidal passage was 0.5 mm thick. The stack voltage is 6 volts, the differential pressure rise rate is 60 cm water column, and the leakage rate is 12 ml/hour.
The limiting current was 10 amperes.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view taken along the line AB in FIG. 2, and is a schematic diagram for clearly showing the features of the present invention. Figure 2 shows
This shows the stack, which is the main component of a typical electrodialysis machine.

Claims (1)

[Claims] 1. In a tightening type electrodialysis device configured by combining a large number of cation exchange membranes and anion exchange membranes alternately via gaskets and spacers, the thickness of the gasket for the dilution chamber is the same as that of the tidal channel insert for the dilution chamber. The gasket for the concentration chamber is thinner than the current-carrying part spacer for the dilution chamber, and the thickness of the gasket for the concentration chamber is thinner than that of the current-carrying part spacer for the concentration chamber. An electrodialysis device characterized in that the thickness of the gasket for the chamber and the thickness of the gasket for the concentration chamber are larger by 0.02 to 0.1 mm.