JPH0247254B2 - - Google Patents

Description

[Detailed Description of the Invention] The technology of concentrating or diluting (or desalting) an electrolyte solution by electrodialysis using an ion exchange membrane is generally well known, and has already been used in the process of producing salt from seawater and the desalination of seawater. This method has already been put into practical use in many industrial fields, such as in the production of drinking water, and in the removal and recovery of harmful substances from various types of wastewater.

An electrodialysis device is formed by alternately arranging a large number of cation exchange membranes and anion exchange membranes between electrodes via a chamber frame and tightening them. When desalinating seawater using such an electrodialysis device, conventional devices have a low desalination rate per overflow, that is, during one pass through the desalination chamber, so it is difficult to reach the desired desalination rate. As a means for increasing the desalination, methods have been adopted, such as performing desalination by circulating the electrodialyzer multiple times in a batch method, or arranging a plurality of electrodialyzers in series and sequentially desalting in multiple stages. However, the former batch desalination method requires a circulation pump, circulation tank, and piping between them, and the latter method of arranging them in series also requires multiple dialysis machines, which increases equipment costs. The drawback is that not only does the amount of fuel increase dramatically, but the driving operation is also complicated.

Therefore, we have traditionally tried to simplify equipment, reduce equipment costs,
In order to facilitate operation, it is desired to treat the liquid to be treated in one pass. However, in electrodialysis using an ion-exchange membrane, in order to achieve high desalination or high concentration through one-pass processing, the difference in concentration within the dialysis chamber between adjacent concentration chambers and dilution chambers increases, and electrolytes are transferred through the ion-exchange membrane. Because the diffusion of
The efficiency of desalination or concentration is reduced, and also the so-called current effect is reduced.

The present invention provides a method for efficiently concentrating and desalting an electrolyte solution, particularly a dissolved salt, in one-pass electrodialysis.

That is, the present invention alternately arranges and tightens cation exchange membranes and anion exchange membranes between electrodes via a chamber frame, thereby alternately forming a large number of channels for demineralization chambers and concentration chambers. In a method in which an electrodialysis device is used, an electrolyte solution is supplied to one end of each channel and discharged from the other end, and the electrolyte solution is concentrated or desalted by dialysis during that time, either in the desalination chamber or the concentration chamber. This is an electrodialysis method characterized by reducing the concentration difference between the desalination chamber fluid and the concentration chamber fluid by introducing a new fluid into the middle of the flow path.

The present invention is particularly effective in improving the desalination efficiency by replacing all or part of the concentration chamber liquid midway through the process, but conversely, operations for improving the concentration efficiency may also be effective.

According to the present invention, since the concentration difference between the desalted solution and the concentrated solution can be controlled within a relatively small range, it is possible to prevent a decrease in current efficiency due to diffusion or leakage current to the outside of the current-carrying part.

One of the conventionally known techniques for reducing the concentration difference between the desalted solution and the concentrated solution is to sandwich the desalted solution and the concentrated solution through a membrane and flow them countercurrently. If only the method is carried out, there is a risk that a difference in liquid pressure between the desalted liquid and the concentrated liquid will occur, resulting in a decrease in current efficiency and a decrease in the amount of recovered liquid due to leakage of the liquid. In addition, in the countercurrent method, the differential pressure between the desalted solution and the concentrated solution becomes large, resulting in uneven distribution of the solution to each dialysis room.In rooms where the amount of solution supplied is insufficient, voltage increases due to water splitting and scale precipitation occur. There are some inconveniences such as

Therefore, in the aspect in which the most effect can be expected in the present invention, the direction of the flow in the concentration chamber and the flow in the desalination chamber is
It is to be in the same direction. However, the effects of the present invention can be expected even if the flow is countercurrent.

The present invention will be explained in more detail with reference to the drawings.

FIG. 1 is a diagram showing the positional relationship of a cation exchange membrane, a chamber frame, and an anion exchange membrane in the electrodialysis apparatus used in the present invention.

FIG. 2 is an enlarged view of the chamber frame of the present invention, and is a diagram for explaining the flow within the liquid supply/discharge channel.

FIG. 3 also shows an example of the chamber frame.

For example, when desalting an aqueous solution containing salts, there is a cation exchange membrane between the anode and cathode, a concentration chamber frame, an anion exchange membrane, a desalination chamber frame, and then a cation exchange membrane, which is repeated in this order. This is an electrodialysis apparatus in which chamber frames are arranged to form a concentration chamber and a demineralization chamber, respectively, and FIG. 1 shows a pair of concentration chambers and a demineralization chamber located in the middle thereof. The cation exchange membrane 1, the concentration chamber frame 2, and the anion exchange membrane 3 constitute a concentration chamber, and the anion exchange membrane, the demineralization chamber frame 4, and the cation exchange membrane further constitute a demineralization chamber. ing. In the case of desalination of a liquid to be treated, for example, seawater, the seawater is supplied through the concentration chamber liquid inlet 11 and intermediate inlet 12, and discharged through the intermediate discharge port 13 and outlet 14, respectively. On the other hand, in the case of the demineralization chamber, the liquid to be treated is supplied from the demineralization chamber inlet 15, is desalted as it travels through the channel, and is taken out from the outlet 16.

If the liquid to be treated (also called stock solution) initially supplied to the concentration chamber and the desalination chamber is the same, the salt concentration in the solution in the flow path of both chambers is approximately the same near each inlet, but the solution continues through the flow path. As time passes, ion movement progresses through the ion exchange membrane, and the desalinated indoor salt concentration decreases.
The salt concentration in the concentration chamber increases at approximately the same rate as this, and the concentration difference between the two chambers increases rapidly. Therefore, in the middle of the flow path, in the case of FIG. By supplying the solution through the intermediate inlet 12, the concentration of the solution in the concentrating chamber channel can be lowered, and the difference in concentration between the solution and the solution in the desalting chamber channel can be reduced. In this way, in addition to simply reducing the diffusion loss due to concentration differences, by bringing the concentration of the liquid in contact with both sides of the ion exchange membrane closer together, the stress on the ion exchange membrane is reduced, preventing the occurrence of distortion and wrinkles in the membrane.
Liquid leakage etc. can be prevented.

FIG. 2 is an enlarged view of the dialysis chamber (concentration chamber or desalination chamber) frame on the side where liquid is exchanged in the middle of the flow path in the present invention. The liquid supply and discharge system will be explained with reference to this figure. That is, the most common method is to supply the stock solution from a,
This is a method of discharging from b, separately supplying from c, and discharging from d, but another preferable embodiment is to supply the stock solution from c and discharge from d, and use this d discharged liquid as it is or with an adsorbent. This is a method in which a necessary chemical treatment or other solution is mixed by contact, and the solution is supplied from a and discharged from b. In yet another preferred embodiment, the stock solution is supplied from a, at least a part of it is discharged from b, and the remainder is allowed to flow into the upper channel through the flow hole 17 (provided as necessary).
A portion of the dialysis product solution is supplied from c. That is, when performing electrodialysis with the intention of desalting, for example, a structure as shown in FIG. 2 is used for the concentration chamber frame, and the stock solution is supplied from a and the desalted dialysis product is supplied from c. Of course, when the concentrate is used as an electrodialysis product, the same means as described above may be applied to the dilution chamber frame. In another embodiment, as shown in Example 2 below, the stock solution a can be supplied, the solution can be discharged from b, the solution can be separately supplied from d, and the solution can be discharged from c.

In the present invention, the point is that demineralized water or concentrated aqueous solution to be obtained by electrodialysis is continuously passed through a channel as long as possible, and the end of the channel is connected to the dilution chamber or concentration chamber. The purpose is to supply the liquid from at least two locations selected from the partial inlet and the intermediate inlet.

FIG. 3 shows an example of the actual use of a chamber frame for supplying liquid from the middle of the flow path. As shown in this example, the stock solution and the like are supplied from the tide channel 20, which is normally used for supplying the stock solution, through the inlet 11 with a spacer such as a net interposed therebetween. Generally, it is in the latter half of the flow path that an extreme concentration difference occurs between the liquids in both chambers, so it is preferable to supply the intermediate supply liquid to the latter half of the flow path. and intermediate inlet 1
2 is in the rear half and communicates with tideways 21 and 23, respectively. Note that 24 and 25 are tideways that communicate with the adjacent dialysis room. Examples are shown below.

Example 1 The chamber frame has a structure in which the flow path of the liquid to be treated is bent as shown in Fig. 3, that is, the thickness is 0.75 mm, the width is 1000 mm, the length is 2200 mm, and the frame has a width of 210 mm and a length of 8000 mm. A cation exchange membrane [trade name "Neocepter"
CL-25T” (manufactured by Tokuyama Soda Co., Ltd.) Strongly acidic membrane with sulfonic acid as an exchange group] and anion exchange membrane Basic membranes] are arranged alternately and tightened between the electrodes to form the concentration chamber 301.
An electrodialysis device consisting of 300 demineralization chambers and desalination chambers was assembled. As for the electrodes, the cathode was a stainless steel plate and the anode was a platinum-plated titanium plate.

This electrodialysis device was used to desalinate seawater with a total dissolved salt (TDS) of 34,000 ppm. Raw seawater is supplied to the desalination room at a flow rate of 6.0 cm/sec to 8000 mm.
After being desalted while passing through the channel, it was discharged from the end of the channel. On the other hand, raw seawater was supplied to the concentration chamber at a flow rate of 5.0cm/sec, but from the inlet.
It was discharged at a depth of 6000mm, and new raw seawater was introduced in its place at a flow rate of 2.5cm/sec. to this device
When a current of 582A was applied, from the desalination chamber
8.9 m ³ of desalted solution with TDS of 380 ppm was obtained per hour. On the other hand, from the 6000mm flow path of the concentration chamber,
Concentrated liquid with TDS62800ppm was discharged. 6000 again
The TDS of the liquid supplied through the mm channel and discharged from the end of the concentration chamber was 46,100 ppm. The voltage at this time was 245V. Moreover, the current efficiency was 92%.

Comparative Example 1 In Example 1, the concentrated liquid was discharged at the end of the channel without being discharged from the middle of the channel. That is, both the desalinated liquid and the concentrated liquid were supplied from the inlet, and the raw seawater was desalted or concentrated while passing through the respective channels toward the outlet, and was discharged from the outlet. When seawater was desalinated in the same manner as in Example 1, when the applied current value was 582 A, the concentration of the desalted solution discharged from the desalination chamber was TDS 950 ppm.
The concentration of the concentrate was TDS 69000 ppm. The current efficiency at this time was 90% and the voltage was 240V. In addition, in order to lower the concentration of the desalted solution discharged, the current value was increased, and when the current value was 592A, the concentration of the desalted solution discharged was TSD400ppm,
The current efficiency at this time was 90% and the voltage was 260V. Compared to Example 1, both the current and voltage were larger in order to reach the same desalted solution concentration, and the dialysis power required to obtain a unit volume of desalted solution was increased.

Example 2 The concentrated liquid was discharged at the 6000 mm point in the same way as in Example 1, but fresh seawater was supplied from the end of the channel instead of the 6000 mm point. It was discharged from somewhere. When seawater was desalinated in the same manner as in Example 1, the concentration of the desalinated solution discharged when the applied current value was 578 A was TDS 370 ppm, and the current efficiency was 92
%, the voltage was 243V.

Example 3 In Example 1, the concentrated liquid was discharged 6000 mm in the middle of the flow path, but the liquid to be newly introduced into the concentration chamber was discharged 6000 mm into the desalination liquid flow path.
A solution obtained by extracting 10% of the desalted solution was used. Seawater was otherwise desalinated in the same manner as in Example 1. When the applied current value was 575A, the concentration of the desalination solution discharged was TDS 380ppm, the current efficiency was 93%, and the voltage was 241V.

Example 4 In Example 1, raw seawater was supplied at a flow rate of 5.0 cm/sec at a point 6000 mm in the middle of the flow path of the concentration chamber, and was discharged at the end of the flow path, and the discharged liquid was introduced into the inlet of the flow path. It was supplied again and passed through to the 6000 mm channel, and then discharged. Others are Example 1
When desalinating seawater in the same manner as above, the concentration of the desalinated solution discharged when the applied current value is 582A is
At a TDS of 400ppm, the current efficiency was 92% and the voltage was 246V.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating a part of a dialysis chamber of an electrodialysis apparatus. FIG. 2 is a diagram illustrating how the liquid flows within the dialysis chamber frame. FIG. 3 is a drawing showing another form of a dialysis room frame used in the present invention. In the figure, 1 is a cation exchange membrane, 2 is a concentration chamber (or dilution chamber) frame, 3 is an anion exchange membrane, and 4 is a dilution chamber (or concentration chamber) frame.

Claims (1)

[Claims] 1. By alternately arranging and tightening cation exchange membranes and anion exchange membranes between electrodes via chamber frames, a large number of channels for demineralization chambers and concentration chambers are alternately formed. In a method of supplying an electrolyte solution to one end of each flow path and discharging it from the other end using an electrodialysis device, the electrolyte solution is concentrated or desalted by dialysis during that time. An electrodialysis method characterized by reducing the concentration difference between a desalination chamber fluid and a concentration chamber fluid by introducing a new fluid into one of the channels. 2. The method according to claim 1, wherein the newly introduced liquid is the same as the initially introduced liquid. 3. The method according to claim 1, wherein the newly introduced liquid is a dialysis product liquid produced by the same electrodialyzer. 4. The method according to claim 1, wherein a part of the desalination chamber fluid of the same electrodialysis apparatus is introduced into the concentration chamber. 5 An electrodialysis device having a demineralization chamber and a concentration chamber each forming a curved flow path in a plane orthogonal to the current direction, and having a solution extraction and inlet port in the portion of the concentration chamber flow path after the midpoint. A method according to claim 1 using the apparatus provided. 6. Introducing the stock solution to be supplied to one of the concentration chamber and dilution chamber in the middle of the flow path of the chamber, and circulating at least a portion of the liquid discharged from the chamber to the first entrance of the flow path of the chamber. A method according to claim 1. 7. The method according to claim 1, in which at least a part of the liquid in the flow path is discharged when a new liquid is introduced in the flow path.