KR100598429B1 - Electrode structure for electrodeionization - Google Patents

Abstract

The present invention relates to a non-uniform electrode structure of an electric deionization device, and more particularly, to an electrode applied to an electric deionization device for an electrodeionization (EDI) process, according to an electric deionization module length and height. It relates to a non-uniform electrode structure formed of a structure in which the area gradually decreases along the flow direction of the inflow water flowing into the electrodeionization apparatus to change the current density.

To this end, in the present invention, a desalting chamber filled with an ion exchange material between a cation exchange membrane and an anion exchange membrane and a concentration chamber configured on the outside of the cation and anion exchange membrane are arranged in a stack structure, and an electrode of a cathode and an anode is disposed at the outermost side thereof. In the module structure electrodeionization device having an electrode liquid passage formed therein, the electrode structure of the cathode and anode in the inflow direction of the inflow water in order to change the current density according to the length and height of the electrodeionization module It provides a non-uniform electrode structure of the electrodeionization device, characterized in that formed in a structure that is gradually reduced in area along the outflow direction.

Electrodeionizer, non-uniform electrode structure, current density

Description

Electrode structure for electrodeionization of electrodeionizer

1 is a detailed view of a non-uniform electrode structure applied to the electrodeionization device according to the present invention,

Figure 2 is a schematic diagram showing an electrodeionization device applying a non-uniform electrode according to the present invention,

3 is an equivalent circuit diagram for analyzing impedance measurement results;

4 is a graph measuring the resistance change of the ion exchange resin by electrochemical regeneration according to the height and current density of the ion exchange resin layer based on the equivalent circuit of FIG.

5 is a current vs. voltage curve graph of an electric deionization module to which a conventional general electrode and the non-uniform electrode of the present invention are applied;

6 is a graph showing the performance of the ion removal of the conventional general electrode and the deionization module applying the non-uniform electrode of the present invention,

Figure 7 is a graph of the current efficiency and power consumption of the electric deionization module to which the conventional non-uniform electrode of the general planar electrode and the present invention.

<Explanation of symbols for the main parts of the drawings>

10 cation exchange membrane 12 anion exchange membrane

14 mixed ion exchange resin 16 desalination chamber

18: concentration chamber 20: anode

22: cathode 24: first section

26: second section 28: third section

30 hole 100 non-uniform electrode

The present invention relates to a non-uniform electrode structure of an electric deionization device, and more particularly, to an electrode applied to an electric deionization device for an electrodeionization (EDI) process, according to an electric deionization module length and height. It relates to a non-uniform electrode structure formed of a structure in which the area gradually decreases along the flow direction of the inflow water flowing into the electrodeionization apparatus to change the current density.

In general, when deionization of influent with low ion concentration is performed by electrodialysis, the electrical resistance due to concentration polarization increases simultaneously with the electrical resistance of the influent, thus increasing the membrane area required for power consumption and desalination. As a result, economics are greatly reduced.

In addition, strong concentration polarization is accompanied by additional hydrolysis, which can lead to influent water composition and membrane damage.

Since 1955, Walters, Weiser, Marek et al. Have filled ion exchange resins to promote ion transfer in the desalination chambers of electrodialysis, reducing the electrical resistance and reducing the effects of hydrogen and hydroxide ions generated by concentration polarization. Could be reduced by exchange action.

The process of installing an ion conductive medium such as an ion exchange resin in the desalination chamber of the electrodialysis apparatus is called an electrodeionization process.

The electrodeionization process fills the desalination chamber of the electrodialysis apparatus with ion exchange materials (ion exchange resin or ion exchange fiber, etc.). It is a complex process that can drastically reduce the environmental burden on treatment.

In addition, since the ion exchange material used in the electric deionization device acts only as an ion transfer medium, it can be used continuously without replacement, thereby fundamentally solving the problem of generating the waste ion exchange material.

The electric deionization process was first introduced by Milipore in 1987, and the ionization deionization unit called Ionpure CDI was commercialized for the first time. It uses the principle of alternating dilution and concentration of heavy ions.

In such an electrodeionization module, desalting of ions by the electrochemical facilitation of the ion exchange material in the electric field is mainly performed at the inlet of the inlet wastewater. However, in the vicinity of the module outlet, the ion concentration becomes very thin due to the desalination action at the inlet.

Accordingly, dissociation of water, that is, water splitting phenomena, occurs at the bipolar surface where the anode and the cathode contact with each other due to a rapid decrease in ion concentration by flowing an electric current under an electric field.

Hydrogen ions and hydroxide ions formed by water decomposition as described above should be replaced by an ion exchange resin to be absorbed to prevent a decrease in current efficiency.

Excessive increase in ion exchange resin content may occur in order to prevent rapid water decomposition in the electrochemical regeneration zone at the module outlet, while limited ion exchange resin content for the purpose of preventing water decomposition. Reducing the current density within the ion reduction performance is reduced.

In consideration of this phenomenon, the impedance obtained by applying alternating current of various frequencies and magnitudes to the electrodeionization module through impedance spectroscopy, and measuring the voltage thereof is applied to the physical and electrochemical structures of the system using various schematic methods. Can be analyzed.

As the current density changes with the height of the electric deionization module, it was measured that the current commercial electric deionization system shows high power consumption with low current efficiency due to excessive current density.

In order to overcome this problem of power consumption, two methods are being considered.

The first is to supply different current density according to the module height. However, the first method is economical because it requires several expensive power supplies.

The second method is to control the current density according to the module height, and to control the electrode area non-uniformly. The present invention has been invented based on the impedance spectroscopy method based on this principle.

On the other hand, Korean Patent Publication 1984-0000995 discloses a gas biporous electrode for an electrolytic cell, which is a typical use to generate electricity such as a gas electrode fuel cell or to act as a cathode depressed as in a chloro alkali battery. It can be used for battery decomposition.

The volume of the maximized electrode can be known by the effective surface area where three-phase contact is made. In order to achieve a higher current density in a given device, the gas electrode is porous.

The above patented technology is used as an electric generator for fuel cells in terms of its application, and the electric deionization reactor can be divided into a desalination zone and an electrochemical regeneration zone, and to date, a device considering current distribution in two areas There is no development.

The present invention has been researched and developed to improve the disadvantages of the electrode used in the conventional electrodeionization process, the electrode area is changed to change the current density according to the length and height of the electrodeionization module based on the impedance spectroscopy measurement In order to provide a non-uniform electrode structure to be made, it can provide the following advantages.

First, it is not a porous structure for maximizing electrode reaction and effectively removing the generated water like fuel cells, and is different in its purpose or application,

Second, through the electrochemical impedance study, the electrochemical regeneration area is measured according to the module length and height in the electrodeionization device, and the distribution of current density is controlled by the electrode area to reduce power consumption and the amount of platinum coated on the electrode. To reduce operating costs and equipment installation costs,

Third, the present invention considering the distribution of current density for the reactor operation of the electrodeionization system is effective in the electrochemical conditions to which the reactor operation is applied, unlike the existing technology,

Fourth, unlike conventional technologies, which are characteristic of power generation in terms of use, and three-dimensional porous materials such as carbon electrodes are considered as porous electrode materials, a reactor operation in which desalination zone and electrochemical regeneration zone are considered according to module height and length is considered. It is useful for water treatment to be applied, and in particular, it is formed in a planar structure rather than a porous shape such as a carbon electrode, and thus the electrode area is applied to different modules.

Fifth, the use of platinum in the anode in the case of the existing electrode caused an increase in the equipment installation cost, the present invention can improve the economics by reducing the platinum requirement required by the electrode by adjusting the area of the electrode,

Sixth, it is excellent in both performance and economy by showing high current efficiency with lower power consumption than conventional electrodes such as general planar electrode even in electric deionization performance.

Seventh, the present invention was invented in the process of identifying the principle for the electric deionization system, there are advantages that can improve both performance and economics by adjusting the electrode area in the existing equipment.

The present invention for achieving the above object is a desalting chamber filled with an ion exchange material between the cation exchange membrane and the anion exchange membrane and the concentration chamber configured on the outside of the cation and anion exchange membrane is arranged in a stack structure, the outermost negative electrode In the electric deionization apparatus of the modular structure in which the electrodes of the positive electrode and the positive electrode are arranged, and an electrode liquid passage is formed therein,

In order to change the current density according to the length and height of the electric deionization module of the electrode structure of the cathode and the anode is formed in a structure that is gradually reduced in the area along the outflow direction in the inflow direction of the inlet water It provides a non-uniform electrode structure.

In a preferred embodiment, the electrode is a plate structure in which the area is divided into a three-layer structure along the vertical direction, wherein the first section, which is a section coinciding with the inlet of the inflow of the desalination chamber, has a maximum current density (100%). The hole is formed to have an electrode area of 50 to 80% based on the first section, and the outlet section through which the inflow of the desalination chamber flows out. The third section, which is a section corresponding to the first section, has a hole formed to have an electrode area of 30 to 60% based on the first section.

In a more preferred embodiment, the area of the second section of the electrode based on the first section is characterized by consisting of an area ratio of 70 ± 5%.

In addition, the area of the third section of the electrode based on the first section is characterized by consisting of an area ratio of 50 ± 5%.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is a side view illustrating a non-uniform electrode structure applied to an electrodeionization device according to the present invention, and FIG. 2 is a schematic view of the electrodeionization device to which the non-uniform electrode according to the present invention is applied.

Referring to the configuration of a conventional electric deionization apparatus with reference to the accompanying Figure 2, the deionization chamber 16 is filled with a mixed ion exchange resin 14 in the space between the cation exchange membrane 10 and the inner ion exchange membrane 12 ) And the concentration chamber 18 arranged in the outer space of the cation exchange membrane 10 and the anion exchange membrane 12 are composed of one module.

In addition, the above-described one module is composed of a plurality of stacked structure in the left and right direction, the non-uniform anode 20 and the non-uniform cathode 22 having the electrode structure according to the present invention is disposed at the outermost position, the electrical The electric deionization device including the deionization module is completed.

Here, the electrode structure of the present invention applied to the above-described electrodeionization device in detail as follows.

In order to change the current density according to the length and height of the electrodeionization module, the electrode structure including the anode 20 and the anode 22 is composed of a non-uniform electrode 100, the non-uniform electrode 100 Is formed in a structure in which the area gradually decreases along the outflow direction in the inflow direction of the inflow water.

That is, the non-uniform electrode 100 according to the present invention is an integral plate body structure whose area is divided into a three-layer structure along the vertical direction (inflow direction from inflow direction of inflow water).

In general, electrode materials used in electrochemical wastewater treatment equipment such as electrodialysis and electrodeionization are platinum coated electrodes, iridium electrodes, nickel electrodes, etc. for the anode, and stainless steel (SUS316) for the cathode. ), Electrodes coated with platinum on titanium, iridium electrodes, nickel electrodes and the like are typical.

Preferably, the first section of the non-uniform electrode 100 (the section corresponding to the inlet of the inflow of the desalination chamber) is formed as a flat section without holes in order to maximize the current density (100%). do.

In addition, a plurality of holes 30 are formed in the second section 26, which is a central section of the non-uniform electrode 100, to have an electrode area of 50 to 80% based on the area of the first section 24. In the third section of the non-uniform electrode 100 (the section corresponding to the outlet portion in which the inflow water from the desalination chamber flows out), an electrode area of 30 to 60% based on the area of the first section 24 is obtained. More holes 30 are formed to penetrate.

More specifically, the area of the second section 26 of the non-uniform electrode 100 based on the area of the first section 24 of the non-uniform electrode 100 is composed of an area ratio of 70 ± 5%. Preferably, the area of the third section 28 of the non-uniform electrode 100 based on the area of the first section 24 is preferably composed of an area ratio of 50 ± 5%.

The area ratio is a function of the concentration of the influent, and as the concentration of the influent flowing into the desalination chamber 16 increases, the area of the first section 24 of the nonuniform electrode 100 increases, which is nonuniform. The number of second and third sections (holes) of the electrode 100 is also reduced.

On the other hand, the lower the concentration of influent water flowing into the desalination chamber 16, the smaller the area ratio of the first section 24 of the non-uniform electrode 100, and the second section to reduce the current density toward the outlet. And the electrode area also decreases continuously with the increase of the third section number (hole number).

On the other hand, forming the area ratio of the electrode in the form having a net or mesh structure has the same effect, but in the formation method, it is formed by drilling holes because the electrode having a network structure of three or more stages must be connected separately. It is more economical in terms of production cost. Therefore, it is economically preferable to apply the nonuniform electrode structure of the present invention.

Hereinafter, the present invention will be described in more detail with reference to Examples. It will be apparent to those skilled in the art that the scope of the present invention is not limited by these examples.

Comparative example

The module configuration used for the impedance spectroscopy experiments was carried out using a 1 cell pair 3 cell structured electrodeionizer filled with a cation exchange resin (Amberlite IR120).

A CMX cation exchange membrane and an AMX anion exchange membrane were used, Na ₂ SO ₄ 1000 ppm as the electrode solution, H ₂ SO ₄ 0.01M as the concentrate, 10 ppm Co (NO ₃ ) ₂ was used as the influent.

During the process operation, the influent water introduced into the desalting chamber filled with the cation exchange resin was flowed at a flow rate of 2 ml / min, and the concentrate and the electrode solution were circulated at a flow rate of 2 ml / min and 10 ml / min, respectively.

The power supply was carried out using Agilent Co., USA, model: 6613C for 8 hours constant current experiment under 1.3, 2.5, 5.6, 7.78 A / m ² .

In order to observe the change caused by the electrical regeneration of the ion exchange resin layer before and after the process operation, impedance measurement was performed by the 4-terminal method.

A flat platinum electrode was used as an electrode for current supply, and a platinum wire having a diameter of 0.25 mm was used as an electrode for voltage measurement.

At this time, the frequency band was used at 1 Hz and 0.1 Hz and the amplitude was set to 0.2 V.

In addition, platinum wires were inserted into the ion exchange resin layers 1, 3, 5, 7, 9 cm from the inlet to confirm the change of the electrical regeneration effect of the ion exchange resin layer according to the height.

On the other hand, for the analysis of the impedance measurement results, an equivalent circuit as shown in FIG. 3 is constructed, and the resistance when moving the inside of the ion exchange resin is Rb, and the resistance when moving the interface between the resin is Ri, at the interface. The current flow was represented by the capacitance of Ci, and the following impedance equation was derived through this equivalent circuit.

Based on the equivalent circuit and the impedance equation, the change of the resistance (Rb) of the ion exchange resin by electrochemical regeneration according to the height and current density of the ion exchange resin layer was measured. The results are shown in FIG. same.

4 is a graph showing the resistance measurement value of the ion exchange resin according to the current density and the stack module height (the height of the ion exchange resin layer) using impedance spectroscopy.

As a result of ion analysis, it was determined that electrochemical regeneration takes place at the point where complete removal of cobalt ions occurs at 2.55 A / m ² , indicating a 15 mΩ electrical resistance. Therefore, it was found that the stack module height and current density operation beyond the point where the power consumption shows more 15 mΩ electrical resistance should be avoided.

That is, the ion exchange resin has a different resistance due to the difference in mobility according to the type of the substituted ions. Since the mobility of hydrogen ions is greater than that of cobalt ions, when the ion exchange resin is electrically regenerated, hydrogen ions in the cobalt ion The lower the resistance value, the higher the current density and the higher the stack, the greater the degree of electrochemical regeneration, and the lower the resistance value of the ion exchange resin.

Desalination occurs at the inlet of the electrodesorption stack module (desalting chamber filled with ion exchange resin), and if the current density required is also applied to the outlet, electrochemical regeneration is accelerated and thus reduced as the current efficiency is accelerated. . Such a decrease in current efficiency causes an increase in operating cost and an increase in power consumption, while at the same time increasing power consumption.

As a result, as shown in Figure 4 it can be seen that the reduction in the current density is required when the module height is reduced, the supply of a different current density according to the height of the stack module can be prevented from reducing the current efficiency.

Therefore, the use of several different power supplies according to the stack module height to supply different current densities is an uneconomical method. Therefore, the method of controlling the electrode area to reduce the current density according to the stack module height has proved effective. .

Here, it can be seen that the method of controlling the electrode area to reduce the current density according to the stack module height according to the following embodiment is effective.

Example

Based on the result of the comparative example using a general planar platinum electrode, the nonuniform electrode which concerns on this invention was installed in the electrodeionization apparatus. In addition, the removal rate and the current efficiency were measured in comparison with the general electrode of the comparative example, in which the electrode area was not controlled.

The electrodeionization apparatus used in the experiments of the examples was performed in 50 cm 2 per cell, 1 cell pairs, the flow rate of the dilution chamber and the concentration chamber is 10 ml / min.

In addition, the influent used was 10 ppm KCl, the concentrate was 500 mW / cm Na ₂ SO ₄ , and the electrode rinse solution was 2000 mmW / cm Na ₂ SO ₄ .

The ion exchange resin (25 ml) filled in the dilution chamber was composed of IR120 cation exchange resin (Rohm & Haas Co., USA) and IRA 402 anion exchange resin (Rohm & Haas Co., USA). Exchange membranes (Tokuyama Corp., Japan) and AMX anion exchange membranes (Tokuyama Corp., Japan) were used.

Therefore, a constant current experiment was performed for 4 hours at a current density of 1.6 A / m ² using a power supply, and the results are shown in the graphs of FIGS. 5 to 7.

5 shows a current versus voltage curve of an electric deionization module to which a conventional general planar electrode and a non-uniform electrode of the present invention are applied.

When comparing the common flat electrode and the nonuniform electrode, the current density in which water dissociation accelerates under the electric field is 0.6 A / m 2 for the normal flat electrode and 1.6 A / m 2 for the nonuniform electrode.

In the case of the general planar electrode, since it should be operated under a lower current density than the non-uniform electrode of the present invention, the performance can be expected to decrease, and in order to exhibit the same performance, the initial equipment cost must be increased to increase the effective area of the module.

On the other hand, the performance of the electrodialysis tank is proportional to the current density, and the effective area of the required electrodeionization module is inversely proportional to the current density. Therefore, since the equipment cost, the depreciation angle ratio, etc. of the electric deionization device decrease in inverse proportion to the current density, the non-uniform electrode of the present invention was found to be effective even when comparing the current versus voltage curves.

6 is a graph showing the performance of the ion removal of the conventional general electrode and the deionization module of the non-uniform electrode of the present invention.

The non-uniform electrode of the present invention was found to be effective in terms of performance by exhibiting a higher removal rate of more than 99% compared to the general planar electrode.

FIG. 7 is a graph showing the current efficiency and power consumption of the conventional depolarization module and the non-uniform electrode of the present invention.

When comparing the current efficiency, as shown in Figure 7, the non-uniform electrode of the present invention having an electrode area of 70% of the general planar electrode is better, and the operating cost can be reduced by showing a difference of 5 mWh even in power consumption It proved better in economics. This means that when applied to the site, the power consumption is increased by more than 13 Wh when processing 1 ton of raw water, and the difference is more than 1 kWh for 100 tons, which is very economically advantageous.

As seen above, the non-uniform electrode structure of the battery deionization device according to the present invention provides the following advantages.

1) Based on the results of electrochemical impedance studies, the electrochemical regeneration zone changes according to the module length and height in the electrodeionization device to control the distribution of current density in all areas to reduce power consumption and platinum coated on the electrode. Reduced requirements can reduce operating costs and equipment installation costs.

2) In terms of electric deionization performance, it shows higher current efficiency with lower power consumption than conventional electrodes such as general planar electrode, which has advantages in both performance and economy.

3) Electrodeionization device with non-uniform electrode is for next generation clean separation process to replace the existing ion exchange resin tower process, removal of harmful ions from water and sewage, desalination from plating wastewater and food wastewater, nuclear power It can be widely used for primary coolant purification and make-up water production in power plants.

4) It is possible to manufacture 70% of area compared to the general flat electrode, which saves the platinum and other electrode materials required for titanium and reduces the initial equipment cost and is very effective in ion removal, current efficiency and power consumption. Therefore, the non-uniform electrode of the present invention, which can be applied to more applications of the electrodeionization process and facilitates the application of the clean technology of the electrodeionization process in the situation of tightening regulations on environmental pollution, is ion exchanged. It can clearly provide economic profit generation in industrial sites where the balance law has been applied.

Claims (4)

A desalting chamber filled with an ion exchange material between the cation exchange membrane and the anion exchange membrane and a concentration chamber constituted on the outside of the cation and anion exchange membrane are arranged in a stack structure, and the cathode and anode electrodes are arranged at the outermost side, respectively, and at the same time. In the electrodeionization device of the modular structure in which the electrode liquid passage is formed, In order to change the current density according to the length and height of the electric deionization module of the electrode structure of the cathode and the anode is formed in a structure that is gradually reduced in the area along the outflow direction in the inflow direction of the inlet water Non-uniform electrode structure. The method according to claim 1, wherein the electrode is a plate structure in which the area is divided into a three-layer structure in the vertical direction, the first section, which is a section corresponding to the inlet of the inflow of the desalination chamber is the maximum current density (100%) Formed into a flat plate without holes; The second section, which is the central section, has a plurality of holes formed therethrough so as to have an electrode area of 50 to 80% based on the first section; The third section, which is a section coinciding with the outlet portion from which the inflow water of the desalination chamber flows out, has more holes formed therein so as to have an electrode area of 30 to 60% based on the first section. Non-uniform electrode structure. The non-uniform electrode structure according to claim 1 or 2, wherein an area of the second section of the electrode is composed of an area ratio of 70 ± 5% based on the first section. The non-uniform electrode structure according to claim 1 or 2, wherein an area of the third section of the electrode is composed of an area ratio of 50 ± 5% based on the first section.

Images