KR20200072288A - Method of reducing scale of cathode for electrolysis of ballast water - Google Patents

Abstract

The present invention relates to a method for reducing the scale of a negative electrode used for electrolysis of ballast water. Specifically, the present invention relates to a method for modifying an electrode surface in order to suppress the generation and electrodeposition of scale generated on the surface of the negative electrode during electrolysis of ballast water. According to an embodiment of the present invention, the method for reducing the scale of a negative electrode for electrolysis of ballast water includes a step of forming a titanium nitride (Ti-N) or carbon nitride titanium (Ti-CN) coating on a surface of a negative electrode made of titanium or a titanium alloy.

Description

Reduction of scale of cathode electrode for ballast water electrolysis {METHOD OF REDUCING SCALE OF CATHODE FOR ELECTROLYSIS OF BALLAST WATER}

The present invention relates to a method for reducing the scale of a cathode electrode used for electrolysis of ballast water. Specifically, it relates to a method of modifying the electrode surface by coating titanium electrode or titanium nitride nitride on the electrode surface to suppress electrodeposition of scale generated on the surface of the cathode electrode during electrolysis of ballast water.

Ballast water refers to the seawater or freshwater in a tank in a ship to balance by lowering the center of gravity of the ship. Ballast water is filled in one port through ballasting and transferred to another port, and discharged into a new port through deballasting. In particular, seawater used as ballast water for international sailing vessels traveling around the world amounts to about 10 billion tons per year, and ecosystem disturbance occurs as about 7,000 marine life included in seawater moves together. .

Accordingly, there is a movement to protect the marine environment. For example, the International Maritime Organization (IMO) created the 2004 Ballast Water Management Convention in order to prevent disturbance of the marine ecosystem due to discharge of ballast water, and the ballast We have published environmental regulations that mandate the installation of water treatment systems.

In order to solve the above-mentioned ecosystem disturbance problem, ballast water must kill marine life. Examples of such ballast water treatment include ozone sterilization treatment, hydrogen peroxide disinfection treatment, and electrolysis treatment.

Among them, the ozone sterilization treatment method has a problem in operating for a long time because the sterilization efficiency is poor in turbid water and the UV lamp required for ozone production is short. In the case of disinfection treatment using hydrogen peroxide, there is an advantage that the sterilizing power is strong and inexpensive, but there is a possibility that residual hydrogen peroxide is discharged, which is difficult for actual use.

On the other hand, the treatment technology of the ballast water electrolysis method is a technique required to sterilize marine organisms by generating a residual oxidant from seawater by applying a constant current to the electrolysis tank when injecting or discharging the ballast water, It has the advantage of being able to control the concentration of residual oxidant required for sterilization in real time.

However, due to the electrodeposition phenomenon of scale (Mg(OH) ₂ , Ca(OH) _2, etc.) generated on the surface of the cathode electrode during the electrolysis reaction of seawater, the reaction resistance between electrodes increases and the residual oxidizer There is a problem that the normal operating life of the electrolysis tank is shortened by increasing the consumption of current to maintain the concentration of.

Particularly, in the case of a titanium cathode electrode used in a conventional electrolysis tank, a rough surface electrode treated with sand blast or the like is used to reduce initial resistance and increase the electrode reaction area during electrolysis. This electrode has a problem in durability of the electrolysis tank system because it does not suppress the electrodeposition of scale generated during electrolysis.

Korean Registered Patent No. 10-0801185 discloses a technique of removing an electrodeposition product generated during an electrolysis treatment process of wastewater by applying a reverse current for a predetermined period and a predetermined time. In addition, the above patent discloses that the seawater electrolytic treatment facility separately installs a pickling process using strong acid or the like to remove scale generated at the cathode, stops the electrolytic treatment process at regular intervals, and pickles the entire electrolytic cell. have.

However, the above methods are required to temporarily suspend the electrolysis treatment, which hinders continuous operation of the process, resulting in a decrease in electrode life and corrosion of the entire facility due to the use of strong acid.

In addition, in Korean Patent Publication No. 2011-0078158, a metal component that forms a scale on an electrode is removed in advance by sequentially performing a reverse osmosis process (RO) and a capacitive deionization process (CDI) before introducing seawater into the electrolytic cell. Thus, a technique for preventing scale formation at the electrode is disclosed. However, this method has low economic efficiency in that the seawater must undergo a pretreatment step before the electric tank is introduced.

Therefore, in order to develop a ballast water electrolysis tank having a long life, it is required to modify the surface of a titanium electrode capable of suppressing scale electrodeposition of the cathode electrode of the electrolysis tank.

The present invention is to solve the problem of increasing the electrode resistance and decreases the life of the electrolysis tank by depositing scale on the surface of the electrode during electrolysis of ballast water.

To this end, the present invention aims to provide a method for reducing the scale of an existing commercial titanium-based negative electrode by coating titanium nitride (Ti-N) or titanium nitride (Ti-CN) on the surface of a titanium electrode.

The above-mentioned subject includes the step of coating titanium nitride (Ti-N) or titanium nitride (Ti-CN) on the surface of a cathode electrode made of titanium or a titanium alloy, reducing the scale of the cathode electrode for electrolysis of ballast water It is achieved by the method.

Preferably, the titanium nitride (Ti-N) coating purge nitrogen gas, ammonia gas, or a mixed gas thereof in a vacuum chamber and evaporate the titanium target using plasma at a temperature of 200 to 400° C. to the cathode surface. It can be formed by depositing titanium nitride.

Also preferably, the titanium nitride (Ti-CN) coating purge nitrogen gas and methane gas in the same volume ratio in a vacuum chamber, and evaporate the titanium target using plasma at a temperature of 200 to 400°C to the cathode surface. It can be formed by depositing titanium nitride.

Also, preferably, the cathode electrode may be a general plate material, a positive hole network, a membrane hole network, an expanded wire mesh type, or a mesh type.

According to the method of the present invention, in the electrolysis of ballast water, scale is electrodeposited continuously on the electrode surface, thereby increasing the electrode resistance and increasing the voltage under the same current, resulting in energy efficiency and production efficiency of residual oxidant (TRO) required for sterilization of marine organisms. It can solve the problem of lowering. In addition, according to the method of the present invention, titanium nitride (Ti-N) or titanium nitride (Ti-CN) coated on the surface of the cathode electrode is used for the generation of OH-ions and residual oxidants (TRO), which are the cause of scale formation. By suppressing the reduction, it is possible to significantly extend the operating life of the ballast water electrolyzer.

1 is a photographic image of a Ti-N coated titanium electrode surface in Example 1 of the present invention.
FIG. 2 is a photographic image of a Ti-CN coated titanium electrode surface in Example 2 of the present invention.
3 is a photographic image of a conventional commercial titanium electrode.
4 is a photographic image of an electrode obtained by polishing an existing commercial titanium electrode using an abrasive.
5 is a graph showing the voltage change in a continuous seawater electrolysis experiment (current density, 0.05A/cm ² ) conducted for 23 hours by applying a TiN-coated titanium electrode according to Example 1 of the present invention.
6 is a graph showing the voltage change in a continuous seawater electrolysis experiment (current density, 0.05A/cm ² ) performed for 23 hours by applying a TiCN coated titanium electrode according to Example 2 of the present invention.
7 is a graph showing a voltage change in a continuous seawater electrolysis experiment (current density, 0.05A/cm ² ) performed for 23 hours by applying an existing commercial titanium electrode as Comparative Example 1 of the present invention.
8 is a comparative example 2 of the present invention showing a voltage change in a continuous seawater electrolysis experiment (current density, 0.05A/cm ² ) conducted for 23 hours with an electrode polished with an existing commercial titanium electrode using an abrasive. It is a graph.
Figure 9 shows the results of corrosion resistance test using 30% hydrochloric acid for the electrodes prepared in Comparative Example 1, Example 1 and Example 2.
10 is a continuous seawater electrolysis experiment (current density, 0.05A/cm) for 23 hours by applying the titanium electrodes of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 of the present invention as the cathode of a seawater electrolysis tank. ² ) is the data analyzing the voltage change.

All technical terms used in the present invention, unless defined otherwise, have the following definitions and conform to the meaning as commonly understood by those skilled in the art in the relevant field of the present invention. In addition, although a preferred method or sample is described herein, similar or equivalent ones are included in the scope of the present invention.

The term "about" refers to 30, 25, 20, 15, 10, 9, 8, 7, 6, 5, for reference amount, level, value, number, frequency, percent, dimension, size, amount, weight or length It means an amount, level, value, number, frequency, percentage, dimension, size, amount, weight or length that varies by 4, 3, 2 or 1%.

Throughout this specification, the terms “comprises” and “comprising”, unless the context requires otherwise, include the steps or components presented, or groups of steps or components, but any other steps or components, or It should be understood that it implies that a group of steps or components is not excluded.

The present invention relates to a method for reducing scale of a cathode electrode for ballast water electrolysis. Specifically, the method of the present invention includes the step of coating titanium nitride (Ti-N) or titanium nitride (Ti-CN) on the surface of a cathode electrode made of titanium or titanium alloy. The method of the present invention inhibits the generation of OH-ions at the cathode generated during the electrolysis of ballast water and the reduction of residual oxidant (TRO), thereby reducing the scale (Mg(OH) ₂ , Ca(OH) _2, etc. on the electrode surface. ) Can be effectively prevented from being reduced.

Ballast water in the present invention may be seawater or freshwater as water stored therein to balance the ship, and more preferably seawater.

)을 갖는 전극이며 기계식 연마 방식을 통해 처리된 전극(표면 거칠기 값은 약 0.8㎛ 내지 6.3㎛ 이하 (

)일 수 있다. In the above, the cathode electrode may preferably include titanium metal or titanium alloy having a purity of 100%. The cathode electrode may be a general plate material, a positive hole network, a membrane hole network, an expanded wire mesh type, or a mesh type. In addition, the negative electrode is a rough surface treated with a conventional commercial electrode, such as sand blast (sand blast) (surface roughness is about 6.3 to 25 μm or less (

) And an electrode processed through a mechanical polishing method (surface roughness is about 0.8 μm to 6.3 μm or less (

).

Hereinafter, the scale reduction method of the cathode electrode of the present invention will be described in more detail.

However, the following examples and the accompanying drawings are only examples used to show the state after coating of the present invention, and the electrode coating range of the present invention is not limited by the drawings.

When the ballast water is seawater, the reaction that occurs during electrolysis of seawater can be explained by the following equation.

[Scheme 1]

Anode (+ ^{pole): 2Cl - → Cl 2 ↑} + 2e - ( main reaction)

_{Cl 2 + H 2 O → HClO} + H + + Cl - ( side reaction)

[Scheme 2]

Cathode (- ^{_{pole): 2H 2 O + 2e -}} → H 2 ↑ + 2OH - ( main reaction)

Na ^{+ +} OH ^- → NaOH (side reaction)

^{Mg +2 + Ca +2 + 4OH -} → Mg (OH) 2 + Ca (OH) 2 ( side reaction)

As in Reaction Scheme 2, during electrolysis of seawater, scale is generated by Mg(OH) ₂ and Ca(OH) ₂ generated in the cathode reaction. In the present invention, the ship is balanced by replacing the titanium oxide (Ti-O) layer formed on the surface of a commercial titanium electrode with titanium nitride (Ti-N) or titanium carbon nitride (Ti-CN) having high hardness, wear resistance and conductivity. The production of OH- ions generated at the titanium cathode during water electrolysis can be suppressed. The OH-ions produced at the cathode coated with titanium nitride (Ti-N) and titanium carbon nitride (Ti-CN) help to form perchloric acid (HClO) necessary for sterilization of marine organisms on the anode surface, and residual oxidizer (TRO) It prevents the reduction of and suppresses the generation of scales (Mg(OH) ₂ , Ca(OH) _2, etc.) generated by side reaction with OH- ions. In addition, since the electrodeposition of the scale of the cathode electrode is suppressed due to the high hardness, releasability, and excellent sliding property of titanium nitride (Ti-N) and titanium carbon nitride (Ti-CN), the efficiency of the seawater electrolysis process is reduced. Can be prevented.

According to one embodiment of the present invention, the scale reduction method of the cathode electrode of the present invention uses a surface coating method.

Titanium nitride (Ti-N) and titanium nitride (Ti-CN) coatings use high-hardness titanium nitride and titanium carbon nitride by using a plasma method that can be deposited in a short time in a temperature range where there is little deformation of titanium. Can be coated.

In addition, the coating of the present invention can be applied to a surface of a commercial titanium electrode having a rough surface or a surface of a titanium electrode subjected to general polishing or electropolishing.

The titanium nitride (Ti-N) or titanium carbon nitride (Ti-CN) coating may be formed according to the methods of Examples 1 and 2 below, respectively, and Ti-N or Ti- on a commercial titanium-based electrode surface. By forming the CN coating, it is possible to replace the titanium oxide (Ti-O) layer of an existing commercial electrode.

The coating is characterized by coating on the surface using plasma at a low temperature at which deformation of titanium does not occur. Preferably, the temperature may be 200°C to 400°C, more preferably 300°C. Conventionally, gas nitriding treatment is performed at a high temperature of about 800° C. or higher, but in this case, there is a problem in that the metal is deformed or the surface hardness is weak. The present invention does not deform the shape and properties of the metal by performing a surface coating at a low temperature of 200 to 400°C, and has a higher hardness value than a normal heat treated surface.

The coating of titanium nitride (Ti-N) according to an embodiment of the present invention uses a high purity titanium target of 99.99% and nitrogen (N ₂ ) gas, ammonia (NH ₃ ) gas, or a mixed gas thereof to form Ti on the electrode surface. -N Form a film. The reaction for forming a Ti-N film with the mixed gas can be described by Reaction Scheme 3 below.

[Scheme 3]

4Ti + N ₂ + 2NH ₃ → 4TiN + 3H ₂ ↑

The titanium nitride (Ti-CN) according to an embodiment of the present invention is the same as the coating method used in Example 2 below and purged with nitrogen (N ₂ ) gas and methane gas (CH ₄ ) in a 1:1 volume ratio. By depositing, a Ti-CN film is formed on the surface of the titanium electrode. The reaction for forming Ti-CN with the mixed gas can be described by Reaction Scheme 4 below.

[Reaction Scheme 4]

2Ti + N ₂ + 2CH ₄ → 2TiCN + 4H ₂ ↑

When the cathode electrode prepared according to the method of the present invention is used in a ballast water electrolytic facility, the generation of scale is reduced and the electrodeposition of the scale is reduced by suppressing the generation of OH- ions on the electrode surface and the reduction of residual oxidant (TRO). Since it is prevented, even in a continuous electrolysis reaction in which ballast water is introduced or discharged, it can be used for a long time without reducing energy efficiency and efficiency of generating residual oxidant (TRO).

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to the following Examples.

Example 1 -Titanium nitride (Ti-N) coating

A mesh-type titanium-based electrode was prepared, and impurities on the electrode surface were primarily removed using alcohol and acetone. The primary treated electrode was placed in a vacuum chamber where a high vacuum of about 1x10 ^-6 Torr was maintained, and a titanium target was prepared. After purging the vacuum chamber with nitrogen (N ₂ ) gas, a voltage of 10 kV to 150 kV was applied to the electrode, and the titanium target was evaporated using plasma by raising the temperature to about 300°C. At this time, the titanium target used was a high purity titanium target of 99.99%, and the titanium evaporated due to the plasma is in an ionized state, and is combined with nitrogen (N ₂ ), a gas filled in the chamber on the surface of the titanium electrode to which voltage is applied. It is deposited on the surface of the electrode. 1 shows a photograph of an electrode having a titanium nitride (Ti-N) coating on the surface prepared above. Referring to FIG. 1, the manufactured electrode has a golden color.

In addition, the titanium electrode prepared as above was used as a negative electrode, and as a positive electrode, a titanium electrode of the same material was synthesized through pyrolysis by combining ruthenium and a palladium used as a cocatalyst, followed by pyrolysis, followed by continuous for 23 hours. The change in voltage is shown in FIG. 5 by conducting a seawater electrolysis experiment (current density, 0.05A/cm ² ).

Example 2 -Titanium carbon nitride (Ti-CN) coating

A mesh-type titanium-based electrode was prepared, and impurities on the electrode surface were primarily removed using alcohol and acetone. The primary treated electrode was placed in a vacuum chamber where a high vacuum of about 1x10 ^-6 Torr was maintained, and a titanium target was prepared. After purging the vacuum chamber with nitrogen (N ₂ ) gas and methane (CH ₄ ) gas at a 1:1 (volume ratio), apply a voltage of 10 kV to 150 kV to the electrode and raise the temperature to about 300° C. and plasma the titanium target ( plasma). In this case, the titanium material used was a high purity titanium target of 99.99%, and the titanium evaporated due to the plasma was in an ionized state, and nitrogen (N ₂ ) and methane (CH), which were gases filled in the chamber on the surface of the titanium electrode to which voltage was applied, were applied. ₄ ) It is deposited by bonding with gas carbon. An electrode photograph having titanium nitride (Ti-CN) coating on the surface prepared above is shown in FIG. 2. 2, the electrode has a dark gray color.

In addition, the titanium electrode prepared above was used as a negative electrode, and as a positive electrode, a titanium electrode, which is the same material, was synthesized through pyrolysis by synthesizing ruthenium and a palladium used as a cocatalyst, followed by pyrolysis, and then continuously for 23 hours. A change in voltage is shown in FIG. 6 by conducting a typical seawater electrolysis experiment (current density, 0.05 A/cm ² ).

Comparative Example 1- Conventional commercial titanium electrode

(약 6.3㎛ - 25㎛)이다. The electrode of Comparative Example 1 is a conventional commercially available titanium electrode having a surface roughened by sandblasting the titanium electrode, and a photo is shown in FIG. 3. The surface roughness value of the electrode is

(About 6.3 µm-25 µm).

In addition, the titanium electrode prepared as above was used as a negative electrode, and as a positive electrode, a titanium electrode of the same material was synthesized through pyrolysis by combining ruthenium and a palladium used as a cocatalyst, followed by pyrolysis, followed by continuous for 23 hours. The seawater electrolysis experiment (current density, 0.05A/cm ² ) was performed to show the change in voltage in FIG. 7.

Comparative Example 2- Conventional commercial titanium electrode polished with abrasive

(약 0.8㎛ - 6.3㎛)이다. Polish both sides of the existing commercial titanium electrode using abrasives for 5 minutes on a metal grinder that can be polished on both sides at the same time, and then apply a solid light baekbaek bag (chromium oxide/about 400-500 rooms) or chungbong (chromium oxide/about 800-1000 rooms). The primary and secondary polishing operations were performed. The photograph of the prepared electrode is shown in FIG. 4. The surface roughness value of the electrode is

(About 0.8㎛-6.3㎛).

In addition, the titanium electrode prepared above was used as a negative electrode, and as a positive electrode, a titanium electrode of the same material was synthesized through pyrolysis by combining ruthenium and a palladium used as a cocatalyst, and then produced through thermal decomposition, followed by continuous for 23 hours. The seawater electrolysis experiment (current density, 0.05 A/cm ² ) was performed to show the voltage change in FIG. 8.

The electrode having a Ti-N coating on the surface of the titanium electrode of Example 1 (FIG. 1) is excellent in corrosion resistance of titanium, and generally has a lifetime that is three times higher than that of an existing titanium electrode. In addition, as a result of measuring the hardness (HV) for the electrode of Example 1 and the electrode of Example 2, it was measured as Ti-N (2300), Ti-CN (3500), respectively.

In addition, corrosion resistance was tested using 30% hydrochloric acid for the electrodes of Examples 1 and 2 and the electrodes of Comparative Example 1. The results are shown in Fig. 9. Referring to FIG. 9, surface corrosion proceeds as the conventional electrode, Comparative Example 1, changes rapidly after about 2 minutes, but Example 1 increases only about 0.1 V for 25 minutes, and Example 2 maintains the initial voltage. . Through this, it can be seen that the electrode whose surface was modified according to the method of the present invention exhibited excellent corrosion resistance effect on the surface.

Example 1 Referring to FIGS. 5 and 10, which are the results of a seawater electrolysis experiment over 23 hours for an electrode, there is an increase in resistance due to the generation of scale (Mg(OH) ₂ , Ca(OH) _2, etc.) and electrodeposition phenomenon. It was confirmed that it maintains an operating voltage of 4 V or less (resistance is about 80 Ω or less).

The titanium electrode coated with Ti-CN of Example 2 (FIG. 2) has characteristics similar to Ti-N. 6 and 10, which are the results of the 23 hour seawater electrolysis experiment, the terminal voltage was about 4.1 V and the resistance value was high, about 82 Ω, but Ti compared with the electrode polished with abrasive (Comparative Example 2, FIG. 8). -The effect of inhibiting the electrodeposition of the scale of the titanium electrode coated with CN was confirmed.

On the other hand, in the case of the conventional commercial titanium electrode of Comparative Example 1 (FIG. 3), as shown in FIGS. 7 and 10, the voltage increases, that is, the resistance increases as the electrolysis time increases in a continuous seawater electrolysis experiment. It can be seen and confirmed that the voltage rises to about 4.7 V (resistance is about 94 Ω). In the case of Comparative Example 1, compared to Example 1, Example 2, and Comparative Example 2, it took the most resistance, and it can be seen that the resistance value increased due to the increase in the inactive area of the electrochemical reaction due to scale electrodeposition due to the rough surface characteristics.

Since the specific parts of the present invention have been described in detail above, it is clear that for those skilled in the art, this specific technology is only a preferred embodiment, and the scope of the present invention is not limited thereto. Accordingly, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

Claims (4)

A method of reducing scale of a cathode electrode for electrolysis of ballast water, comprising coating titanium nitride (Ti-N) or titanium carbon nitride (Ti-CN) on the surface of a cathode electrode made of titanium or a titanium alloy. The cathode of claim 1, wherein the titanium nitride (Ti-N) coating purges nitrogen gas, ammonia gas, or a mixed gas thereof in a vacuum chamber, and evaporates the titanium target using plasma at a temperature of 200 to 400°C. Formed by depositing titanium nitride on the surface, a method for reducing the scale of a cathode electrode for ballast water electrolysis. The cathode surface of claim 1, wherein the titanium nitride (Ti-CN) coating purges nitrogen gas and methane gas in an equal volume ratio in a vacuum chamber, and evaporates the titanium target using plasma at a temperature of 200 to 400°C. It is formed by depositing titanium nitride on, a method for reducing the scale of the cathode electrode for ballast water electrolysis. The method of claim 1, wherein the cathode electrode is a general plate material, a positive hole network, a membrane hole network, an expanded wire mesh type, or a mesh type, and the scale of the cathode electrode for ballast water electrolysis is reduced.

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