A method for recovering a catalyst layer from an electrode comprising a conductive substrate and a catalyst layer provided on the conductive substrate.

Abstract

To provide a method for recovering a catalyst layer from an electrode including a conductive substrate and the catalyst layer disposed on the conductive substrate.SOLUTION: A method for recovering a catalyst layer from an electrode including a conductive substrate and the catalyst layer disposed on the conductive substrate includes the step of bringing the electrode including the conductive substrate and the catalyst layer disposed on the conductive substrate into contact with hydrogen chloride gas in an atmosphere of hydrogen chloride gas of 0.1% or more (the step of a hydrogen chloride gas treatment).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for recovering a catalyst layer from an electrode including a conductive substrate and a catalyst layer provided on the conductive substrate.

Background Art

[0002] Currently, electrodes in which a catalyst layer containing a platinum group metal oxide such as iridium oxide or ruthenium oxide is coated on a conductive substrate of an electrode material such as titanium or nickel are widely used in the field of electrochemistry. Since platinum group metals are precious resources, it is important to recover and reuse platinum group metals from used electrodes.

[0003] So far, several methods for recovering platinum group metals from used electrodes have been proposed. For example, there are chemical recovery methods such as hydrogen reduction, and mechanical recovery methods using a grinder or a blasting machine.

[0004] The chemical recovery method by hydrogen reduction is a method of heating at 500°C to 1000°C in a hydrogen gas atmosphere to reduce a platinum group metal oxide such as iridium oxide or ruthenium oxide to a metal and peel it from a conductive substrate such as titanium or nickel. It is a separation and recovery method that utilizes the property that a conductive substrate such as titanium or nickel does not get reduced even when heated and exists as an oxide (see Patent Documents 1 and 2). However, this method does not describe a specific method for separating the catalyst layer from the conductive substrate.

[0005] Further, as a method of chemically peeling, there is a method of acid-dipping and dissolving the substrate coating interface between the conductive substrate and the catalyst layer. However, in the method of peeling by acid dipping, the consumption of the conductive substrate is large and it is difficult to reuse it. In addition, there is a problem that a large amount of acid waste liquid is generated.

[0006] On the other hand, mechanical recovery methods involve physically removing the catalyst layer, which consists of platinum group oxides, by sandblasting the electrode with alumina powder or glass powder on a grinding wheel. However, while this method allows for the complete removal of the catalyst layer from the conductive substrate, the removed platinum group oxides are dispersed in the grinding wheel at low concentrations, resulting in high costs for the purification process and low recovery rates (see Patent Document 3). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2002-194581 [Patent Document 2] Japanese Patent Publication No. 2002-212650 [Patent Document 3] Japanese Patent Application Publication No. 5-212297 [Overview of the project] [Problems that the invention aims to solve]

[0008] As described above, conventional technology has problems such as difficulty in completely detaching the catalyst layer from the conductive substrate and increased costs in the purification process due to malfunctions in collecting platinum group metal oxides. Therefore, the present invention has been made in view of the above problems and aims to provide a method for recovering a catalyst layer from an electrode equipped with a catalyst layer provided on a conductive substrate, which enables easy separation of the catalyst layer and the conductive substrate. [Means for solving the problem]

[0009] Furthermore, in order to achieve the above objective, the present invention provides a method for recovering a catalyst layer from an electrode comprising a catalyst layer provided on a conductive substrate as described below.

[0010] Item 1. A method for recovering a catalyst layer from an electrode comprising a conductive substrate and a catalyst layer provided on the conductive substrate, A method for recovering a catalyst layer from an electrode having a catalyst layer provided on a conductive substrate, comprising a step of bringing the electrode, which has a catalyst layer provided on a conductive substrate, into contact with hydrogen chloride gas under a hydrogen chloride gas atmosphere of 0.1% or more (hydrogen chloride gas treatment step). Item 2. A method for recovering a catalyst layer according to Item 1, further comprising a step of separating the catalyst layer from the conductive substrate (separation step) in an electrode comprising a conductive substrate and a catalyst layer provided on the conductive substrate. Item 3. The method for recovering the catalyst layer according to Item 1 or 2, wherein the conductive substrate is a conductive substrate containing nickel. Item 4. The method for recovering a catalyst layer according to item 1 or 2, wherein the catalyst layer contains a platinum group metal. [Effects of the Invention]

[0011] According to the present invention's method for recovering a catalyst layer from an electrode equipped with a catalyst layer on a conductive substrate, the catalyst layer can be easily separated and recovered from the conductive substrate by bringing the electrode equipped with the catalyst layer on the conductive substrate into contact with hydrogen chloride gas in a hydrogen chloride gas atmosphere of a certain concentration (subjecting it to a hydrogen chloride gas treatment step). Furthermore, since there is little consumption of the conductive substrate, it is possible to reuse the conductive substrate for valuable purposes. The present invention has the effect of easily separating the catalyst layer and the conductive substrate without using special reagents or equipment. [Brief explanation of the drawing]

[0012] [Figure 1] An example of the experimental apparatus used in the embodiments of the present invention is shown. [Best Mode for Carrying Out the Invention]

[0013] The present invention will be described in detail below.

[0014] The present invention relates to a method for recovering a catalyst layer from an electrode comprising a conductive substrate and a catalyst layer provided on the conductive substrate, This method for recovering a catalyst layer from an electrode equipped with a catalyst layer on a conductive substrate includes a step of bringing the electrode, equipped with a conductive substrate and a catalyst layer provided on the conductive substrate, into contact with hydrogen chloride gas under a hydrogen chloride gas atmosphere of 0.1% or more (hydrogen chloride gas treatment step).

[0015] The recovery method of the present invention includes a step (hydrogen chloride gas treatment step) of bringing a conductive substrate and an electrode equipped with a catalyst layer provided on the conductive substrate into contact under a hydrogen chloride gas atmosphere of 0.1% or more. By bringing the conductive substrate and the electrode equipped with a catalyst layer provided on the conductive substrate into contact with hydrogen chloride gas under a hydrogen chloride gas atmosphere, a corrosion reaction at the interface between the conductive substrate and the catalyst layer proceeds, making it possible to easily separate the conductive substrate and the catalyst layer.

[0016] The hydrogen chloride gas treatment process of the present invention involves bringing a conductive substrate and an electrode comprising a catalyst layer provided on the conductive substrate into contact in a hydrogen chloride gas atmosphere of a predetermined concentration. The concentration of hydrogen chloride gas should be 0.1% or more, preferably 0.3% or more, more preferably 0.5% or more, and particularly preferably 1.0% or more. There is no particular upper limit to the hydrogen chloride gas concentration, but for example, it should be 20% or less, preferably 15% or less, and more preferably 10% or less. Within the above range, the corrosion reaction at the contact interface between the conductive substrate and the catalyst layer proceeds without problems, and the conductive substrate and the catalyst layer can be easily separated. The hydrogen chloride gas concentration in the hydrogen chloride gas atmosphere can be measured by commonly used methods. For example, it can be measured with a gas detection tube.

[0017] In the hydrogen chloride gas treatment step, the hydrogen chloride gas atmosphere of a predetermined concentration may be a mode in which after blowing hydrogen chloride gas of a target concentration and then sealing in a closed container or reaction tank, an electrode including a conductive substrate and a catalyst layer provided on the conductive substrate is brought into contact, or a mode in which while blowing hydrogen chloride gas of a target concentration into a container or reaction tank, an electrode including a conductive substrate and a catalyst layer provided on the conductive substrate is brought into contact in the container or reaction tank. Further, it may be a mode in which a hydrochloric acid aqueous solution of a predetermined concentration is added and an electrode including a conductive substrate and a catalyst layer provided on the conductive substrate is brought into contact with vaporized hydrogen chloride gas in a closed container or reaction tank.

[0018] This shows an example of the contact mode in the hydrogen chloride gas treatment step of the present invention. As shown in FIG. 1, a predetermined amount of hydrochloric acid aqueous solution 7 is added into a separable flask 3, a pedestal 6 for installing an electrode is arranged, and an electrode is installed on the pedestal. A lid 3 provided with a thermometer 1 passing through rubber 2 is fixed with a clamp 4, and the electrode 5 is brought into contact in a hydrogen chloride gas atmosphere.

[0019] The hydrogen chloride gas used in the hydrogen chloride gas treatment step in the recovery method of the present invention may be directly used hydrogen chloride gas or hydrogen chloride gas generated from a hydrochloric acid aqueous solution.

[0020] When using a hydrochloric acid aqueous solution, the concentration of the hydrochloric acid aqueous solution is not particularly limited, and it can be used without problems as long as it can be set to a concentration of a predetermined hydrogen chloride gas. For example, a 1 to 50% hydrochloric acid aqueous solution is acceptable, a 5 to 45% hydrochloric acid aqueous solution is preferable, a 10 to 40% hydrochloric acid aqueous solution is more preferable, and a 15 to 38% hydrochloric acid aqueous solution is even more preferable. With a hydrochloric acid aqueous solution having the above concentration, it can be adjusted to a predetermined hydrogen chloride gas concentration without problems.

[0021] In the hydrogen chloride gas treatment step of the recovery method of the present invention, the contact time between the hydrogen chloride gas, the conductive substrate, and the electrode comprising a catalyst layer provided on the conductive substrate is not particularly limited and is acceptable as long as it is sufficient time for the corrosion reaction at the contact interface between the conductive substrate and the catalyst layer to proceed. For example, it is in the range of 1 minute to 500 hours, preferably in the range of 30 minutes to 300 hours, and more preferably in the range of 60 minutes to 200 hours.

[0022] In the hydrogen chloride gas treatment step of the recovery method of the present invention, the temperature of the hydrogen chloride gas atmosphere is not particularly limited, but for example, it may be from 0°C to 80°C, preferably from 15°C to 70°C, and more preferably from room temperature to 60°C.

[0023] In a hydrogen chloride gas treatment process, an electrode comprising a catalyst layer provided on a conductive substrate that has been brought into contact with hydrogen chloride gas can be separated from the conductive substrate and the catalyst layer by a commonly used physical method (separation process).

[0024] In the separation process of the present invention, for example, the conductive substrate and catalyst layer may be separated by spraying high-pressure water at a pressure of about 5 to 100 megapascals onto the electrode surface; the conductive substrate and catalyst layer may be separated by polishing (brushing) the electrode surface using a brush or the like; the conductive substrate and catalyst layer may be separated by sandblasting the electrode surface using alumina powder or glass powder on an abrasive wheel; or the conductive substrate and catalyst layer may be separated by ultrasonic cleaning. An electrode having a catalyst layer provided on a conductive substrate that has undergone a hydrogen chloride gas treatment process can be easily separated from the conductive substrate and catalyst layer by subjecting it to a separation process.

[0025] The catalyst layer separated from the conductive substrate can be recovered under normal conditions. For example, the platinum group metals in the catalyst layer can be reduced by hydrogen reduction and metallized. If it is ruthenium, it can be volatilized as RuO4 by heating and oxidizing it in hypochlorous acid and then recovered as ruthenic chloride by trapping it in hydrochloric acid. If it is iridium, it can be converted to iridium chloride salt by passing it through chlorine gas with alkali chloride, and then the alkali can be separated to recover iridium chloride or iridium chloride. Alternatively, it can be recovered by dissolving it in aqua regia. Of course, it can also be recovered electrolytically. In this case, titanium oxide and tantalum oxide contained in the same catalyst layer are not reduced by hydrogen, so they are not chlorinated or dissolved and can be completely separated from the platinum group metals. Some of the catalyst layer may dissolve in acid, but this can be almost completely recovered by neutralizing the used acid with ammonia, precipitating it as ammonium salts of platinum group metals, and then separating them by filtration.

[0026] The electrodes used in the recovery method of the present invention can be either anodes or cathodes, as long as they are electrodes used in electrolysis. Preferably, they are electrodes for electrolysis of sodium chloride.

[0027] The conductive substrate for the electrode is not particularly limited, as long as it is conductive and functions as an electrode substrate; any conductive substrate used in known electrodes can be used.

[0028] The conductive substrate preferably contains a metal, and more preferably is composed of a metal. Preferred metals include nickel, stainless steel, iron, copper, steel, and titanium, with nickel being the most preferred among these. Suitable conductive substrates containing nickel include those composed of nickel, as well as, for example, stainless steel coated with nickel. The conductive substrate should contain 20% by mass or more of nickel, preferably 50% by mass or more. It is more preferably 75% by mass or more, and particularly preferably 90% by mass or more.

[0029] Furthermore, there are no particular limitations on the shape of the conductive substrate, and examples include plate-shaped, rod-shaped, and porous (expanded metal, perforated metal, blind-shaped, plain weave, micromesh, etc.). From the viewpoint of increasing the surface area of ​​the coating provided on the conductive substrate, a porous shape is preferred.

[0030] The size of the conductive substrate is not particularly limited and can be set appropriately according to the size of the electrolytic cell, the size of the electrodes, etc., but for example, the length is about 300 mm to 2,500 mm, the width is about 200 mm to 1,500 mm, and the thickness is about 0.1 mm to 6 mm.

[0031] The surface of the conductive substrate may be roughened to improve the adhesion of the catalyst layer, etc. The surface roughness Ra of the conductive substrate can be set to, for example, about 1 to 10 μm. Methods for roughening the surface of the conductive substrate include blasting.

[0032] Furthermore, the surface of the conductive substrate may be etched to improve the adhesion of the catalyst layer, etc. Examples of etching methods include immersing the conductive substrate in an acid such as hydrochloric acid. After etching, it is preferable to wash the surface of the conductive substrate with water until it becomes neutral and then dry it.

[0033] The catalyst layer of the electrode used in the recovery method of the present invention is formed on a conductive substrate. More specifically, it is preferable that the catalyst layer is formed on the surface of the conductive substrate.

[0034] The material used in the catalyst layer can be appropriately selected from elemental metals or metal oxides, and is generally selected from transition metals. Furthermore, it is preferable that it contains at least platinum group metals from the viewpoint of reducing overpotential during electrolysis. Examples of metals that can be used in the catalyst layer include platinum, palladium oxides, ruthenium oxides, and iridium oxides. The catalyst layer may contain only one type of metal or a combination of multiple metals. When using a combination of multiple metals, the ratio can be adjusted as appropriate.

[0035] The state of the metal in the catalyst layer is not particularly limited. For example, platinum is preferably included in the form of platinum metal, and may also include platinum oxide, platinum hydroxide, etc. Palladium is preferably included in the form of palladium oxide, and may further include palladium metal, palladium hydroxide, etc. Ruthenium is preferably included in the form of ruthenium oxide, and may further include ruthenium metal, ruthenium hydroxide, etc. Nickel is preferably included in the form of nickel oxide, and may further include nickel metal, nickel hydroxide, etc. Iridium is also preferably included in the form of iridium oxide, and may further include iridium metal, iridium hydroxide, etc. Furthermore, the metals may be in the form of alloys or amorphous metals of the above-mentioned metals.

[0036] Furthermore, from the viewpoint of reducing the hydrogen generation potential during electrolysis while effectively suppressing the decrease in the effective surface area of ​​platinum group metals caused by the reverse current when electrolysis is stopped, the content of platinum group metals in the catalyst layer (i.e., the amount of platinum group metals supported) is preferably 2 g / m². 2 Above, a comfortable 3g / m 2 More preferably 4 g / m² 2 The above points are important. The more platinum group metals that are loaded, the more effective they are, but from an economic standpoint, the upper limit for the amount of platinum group metals loaded is, for example, 20 g / m³. 2 These are some examples.

[0037] From a similar viewpoint, the thickness of the catalyst layer is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. The thicker the catalyst layer, the more effective it is, but from an economic standpoint, the upper limit of the catalyst layer thickness is, for example, 20 μm.

[0038] In the recovery method of the present invention, the catalyst layer can be easily separated from an electrode comprising a conductive substrate and a catalyst layer provided on the conductive substrate. [Examples]

[0039] Next, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

[0040] (Examples) Electrode sections cut to 25cm x 25cm from MD-C50 (manufactured by Daiso Engineering Co., Ltd.; conductive substrate: nickel, substrate shape: expanded metal, catalyst layer: platinum), which had been used for 8 years in sodium chloride electrolysis, were used in the test. 500ml of hydrochloric acid aqueous solution of predetermined concentrations (Example 1: 36 wt%, Example 2: 30 wt%, Example 3 and Comparative Example 1: 20 wt%) was added to a 2L separable flask, and a base was placed in contact with it. The 25cm x 25cm electrode sections were placed on the base. A lid equipped with a thermometer was secured with a clamp, and the 25cm x 25cm electrode sections were brought into contact with hydrogen chloride gas vaporized from the hydrochloric acid aqueous solution. The contact time was 60 minutes, and the temperature was 25°C (Examples 1 and 2) and 50°C (Example 3 and Comparative Example 1).

[0041] Catalyst layer separation test Electrode fragments that had come into contact with hydrogen chloride gas were removed, and the electrode surface was brushed with a brush to visually confirm the separation state of the conductive substrate and the catalyst layer. A circle (○) indicated that the catalyst layer was separated from the conductive substrate, while a cross (×) indicated that the catalyst layer was not separated. Table 1 shows the separation state of the catalyst layer from the conductive substrate at various hydrogen chloride gas concentrations.

[0042] Method for measuring hydrogen chloride gas concentration The concentration of hydrogen chloride gas in a hydrogen chloride gas atmosphere was calculated from the table of partial pressures of hydrogen chloride gas in hydrochloric acid.

[0043] JPEG0007859003000001.jpg2075

[0044] As shown in Table 1, electrodes brought into contact with hydrogen chloride gas in an atmosphere with a concentration ranging from 0.32% to 10.5% (Examples 1 to 3) showed easy separation of the conductive substrate and the catalyst layer. On the other hand, electrodes brought into contact with a 0.04% hydrogen chloride gas atmosphere (Comparative Example 1) did not show separation of the conductive substrate and the catalyst layer. In other words, a method for easily separating the catalyst layer from the conductive substrate involves bringing an electrode, which comprises a conductive substrate and a catalyst layer provided on the conductive substrate, into contact with hydrogen chloride gas at a concentration of 0.1% or more. [Explanation of Symbols]

[0045] 1 thermometer 2. Rubber stopper 3 Separable Flasks 4 clamps 5 electrode pieces 6 bases 7. Hydrochloric acid solution

Claims

1. A method for recovering a catalyst layer from an electrode comprising a conductive substrate and a catalyst layer provided on the conductive substrate. In, A method for recovering a catalyst layer from an electrode having a catalyst layer provided on a conductive substrate, comprising a step of bringing an electrode, which includes a conductive substrate and a catalyst layer provided on the conductive substrate, into contact with hydrogen chloride gas (hydrogen chloride gas treatment step) in a hydrogen chloride gas atmosphere of 0.1% or more, wherein the temperature of the hydrogen chloride gas atmosphere is from 0°C to 80°C.

2. Furthermore, in an electrode comprising a conductive substrate and a catalyst layer provided on the conductive substrate, A method for recovering a catalyst layer according to claim 1, comprising a step of separating the catalyst layer from a substrate (separation step).

3. The catalyst according to claim 1 or 2, wherein the conductive substrate is a conductive substrate containing nickel. Method for recovering layers.

4. Recovery of the catalyst layer according to claim 1 or 2, wherein the catalyst layer contains platinum group metals. method.

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