JP3304481B2 - Electrolyzer for hydrogen peroxide production and method for electrolytic production of hydrogen peroxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic cell for producing hydrogen peroxide, which is used as an oxidizing agent in various applications with high efficiency, by electrolytic reduction of oxygen, and a method for producing the hydrogen peroxide.

[0002]

2. Description of the Related Art Hydrogen peroxide is an oxidizing agent used for bleaching pulp and the like. The technology for producing this hydrogen peroxide from an oxygen-containing gas such as oxygen or air using a gas electrode has been conventionally used. Research has been ongoing recently (Electrochemistry 57 , 11, 1073, 1989). The purpose of the gas electrode is to supply a hydrogen gas or an oxygen gas to an oxygen gas or a hydrogen gas normally generated at the anode or the cathode, respectively, to suppress the gas generation, and to suppress power consumption by a voltage associated with the gas generation.

[0003] The gas cathode itself is well known (for example, Japanese Patent Publication No. 2-29757 and Japanese Patent Application Laid-Open No. 59-25179), all of which achieve a voltage drop of about 0.8 to 1 V. The gas electrode is formed by providing a hydrophobic porous layer on one surface and a hydrophilic layer supporting an electrolytic catalyst on the other surface or on the hydrophobic layer, and is mainly manufactured by supporting platinum on a conductive carbon surface.

[0004] However, these electrodes show good performance in the early stage of electrolysis, but the catalyst itself is in direct contact with an electrolytic solution such as an aqueous solution of alkali hydroxide, and the electrochemical reaction takes place therein, so that the resistance of the catalyst is insufficient. In addition, there is a problem that catalyst activity is lost in a short period of time, and it is extremely difficult to produce a large-area gas electrode in which gas and liquid do not leak from each other. No electrodes are present. Furthermore, when air is used as gas in this gas electrode, in order to avoid carbon dioxide in the air reacting with alkali hydroxide in the electrolysis chamber and being converted into sodium carbonate to cause clogging of the membrane and to render the gas electrode unusable. Removal of carbon dioxide from used gas has become a major problem.

[0005] Furthermore although structures with integrated gas electrode and the ion exchange membrane has been proposed (U.S. Pat. No. 3,124,520), H ⁺ from the gas electrode in the structure in the electrolyte chamber (anode) and OH - ^(cathode ), This proposal seems to be advantageous for increasing the size of the gas electrode, but the specific conditions of use and the like are unknown, and have not yet been put to practical use without any suggestion for producing hydrogen peroxide. As for energy savings using gas electrodes for alkaline chloride electrolysis and the like, predictions of practical use have been made to some extent, but specific measures such as means for realizing them and extending the life of gas electrodes are still in place. The fact is that it has not been found. In the above-mentioned electrochemicals 57 , 11, 1073, 1989, an electrolytic cell for producing hydrogen peroxide which is divided into an anode chamber, an intermediate chamber and a cathode chamber by a cation exchange membrane and an anion exchange membrane is described. It has been proposed that a gas cathode be housed therein to perform electrolytic production of hydrogen peroxide.However, since the gas cathode in the cathode chamber does not adhere to the anion exchange membrane, the gas cathode is made of corrosive water. It comes into contact with the catholyte, which is an aqueous solution of potassium oxide, leading to shortening of its life.

[0006]

SUMMARY OF THE INVENTION The present invention relates to an electrolytic cell used for producing hydrogen peroxide by electrolytic reduction of oxygen using a gas cathode, and an electrolytic production method for hydrogen peroxide using the electrolytic cell. An object of the present invention is to provide an electrolytic cell for producing hydrogen peroxide and a method for producing hydrogen peroxide electrolytically, which enable electrolysis on an industrial scale while maintaining good electrode performance for a long period of time.

[0007]

The electrolytic cell for producing hydrogen peroxide according to the present invention is divided by a cation exchange membrane into an anode chamber containing an anode and a cathode chamber containing a gas cathode.
Further, the cathode chamber is divided into a solution chamber in contact with the anode chamber and a gas chamber containing the gas cathode by an anion exchange membrane in close contact with the gas cathode. In the method of the present invention, electrolysis is performed while supplying water or an alkali hydroxide aqueous solution to the anode chamber and the solution chamber of the electrolytic cell having such a configuration, and supplying an oxygen-containing gas to the gas chamber. An electrolytic production method for hydrogen peroxide, which comprises producing hydrogen oxide. Hereinafter, the present invention will be described in detail.

As described above, in the conventional electrolytic production of hydrogen peroxide using a gas cathode, the gas cathode, which is not sufficiently corrosion-resistant, comes into direct contact with a catholyte, which is usually corrosive, and the chemical corrosion of the catholyte causes It is considered that the catalyst layer of the gas cathode is consumed and this is one of the causes of shortening the life of the gas cathode in the electrolytic production of hydrogen peroxide. However, the present inventors have recognized that the role of the cathode in the electrolytic production of hydrogen peroxide is to supply hydrogen peroxide ions to the cathode chamber, and have tried to eliminate other functions as much as possible. In other words, in the electrolytic cell and the electrolytic method of the present invention, the electrolytic cell is partitioned into an anode chamber and a cathode chamber containing a gas cathode by a cation exchange membrane, and the cathode chamber is further partitioned by an anion exchange membrane in close contact with the gas cathode. By partitioning into a solution chamber and a gas chamber, in addition to the fact that the electrolyte does not exist in the gas chamber where the gas cathode is present and does not inherently come into contact with corrosive substances, the presence of the anion exchange membrane causes gas It is intended to prevent the cathode from coming into direct contact with a corrosive electrolytic solution and to extend the life of the gas cathode.

When the cation exchange membrane, the anion exchange membrane and the gas cathode are arranged as described above, water or a diluted alkali hydroxide aqueous solution is supplied to the anode chamber and the solution chamber, and an oxygen-containing gas such as oxygen or air is supplied to the gas chamber. The oxygen in the oxygen-containing gas is reduced on the gas cathode to form OH ^- ions and HO ₂ ^- ions, which penetrate the anion exchange membrane and reach the solution chamber, where hydrogen ions (H ⁺ ) Or reacts with alkali ions to produce hydrogen peroxide or alkali hydrogen peroxide and alkali hydroxide. In this electrolysis flow, permeation of sodium ions and the like in the alkali hydroxide supplied into the solution chamber toward the gas chamber is prevented by the anion exchange membrane, and HO ₂ ^- ions generated on the gas cathode surface are prevented. Is prevented from penetrating the anion exchange membrane by the charge and moving toward the solution chamber and coming into contact with the cathode again, and the movement of the ions further reliably prevents the sodium ions from coming into contact with the gas cathode. In addition, the gas cathode does not come into contact with ions in the corrosive electrolytic solution, and the life of the gas cathode can be extended.

Further, in comparison with a system in which the cathode chamber is divided into a solution chamber and a gas chamber by the porous gas cathode itself, the electrolytic cell and the electrolysis method according to the present invention separate the two chambers from the gas cathode and the gas chamber. Since it uses an anion exchange membrane that is much more dense than the cathode and has excellent liquid impermeability, gas-liquid leakage, especially the corrosive catholyte in the solution chamber, is reliably prevented from penetrating into the gas chamber, and Since the deterioration and the decrease in current efficiency can be suppressed, it can also be used for electrolysis on an industrial scale that requires operation at a high current density. However, since the contact area between the catalyst and the gas decreases with the progress of the electrolytic reaction or the movement of the generated ions is slightly restricted, the desired performance is not obtained as in the case of a small electrolytic cell such as a fuel cell. This is not always realized, and especially at high current densities, the overvoltage tends to increase, and in practice, it is desirable to operate at a current density of 5 KA / m ² or less.

At a current density of 1 KA / m ² , which is a practical current density for the electrolytic production of hydrogen peroxide, oxygen depends on the performance of the anion exchange membrane, but oxygen is supplied to the cathode chamber as compared with the conventional hydrogen generating cathode. When the electrolysis is performed while supplying the air, the electrolysis voltage is reduced by about 0.9 V, and when the electrolysis is performed while the air is supplied, the electrolysis voltage is reduced by about 0.8 V. In addition, carbon dioxide in the above-described supply gas may cause clogging of the membrane, which is not an exception in the present invention. However, by passing an oxygen-containing gas through lime water before supply, the clogging of the membrane can be substantially reduced. Can be prevented. This is presumed to be because the gas and the liquid do not associate directly in the hydrophilic layer as in the conventional case. The electrolytic cell of the present invention is desirably configured as a conventional filter press type electrolytic cell. Also, on-site assembly and operation can be easily performed.

The anion exchange membrane used in the present invention may come into contact with a high concentration of about 10% by weight of a high-temperature aqueous alkali hydroxide solution. For this reason, it is preferable to use a fluorine-based ion-exchange membrane with high alkali resistance as used in conventional cation-exchange membranes. This is because the anion exchange membrane surface is protected by the migration of anions from the cathode side and the accompanying water, which are the characteristic actions of the gas cathode, and there is no bubble stirring effect due to gas generation. It is presumed. However, in the case of continuous operation for one year or more, the above-mentioned fluororesin-based ion exchange membrane should be used. The anion exchange membrane that can be used in the present invention is Neosepta ACL, trade name of Tokuyama Soda Co., Ltd.
E-5P and Tosflex IE-SF34 (trade name, which is a fluorine-based anion exchange membrane manufactured by Tosoh Corporation). The anion exchange membrane may be formed from a granular anion exchange resin.

The anion exchange membrane prevents the gas cathode from directly contacting the corrosive catholyte and also prevents the catholyte in the solution chamber from penetrating the anion exchange membrane and coming into contact with the gas cathode. . Therefore, the anion exchange membrane must be securely fastened at its periphery with a chamber frame of the electrolytic cell or the like to prevent liquid leakage.

The gas cathode installed on the gas chamber side of the anion exchange membrane has a function of generating hydrogen peroxide ions by a reaction of H ₂ O + O ₂ + 2e ⁻ → HO ₂ ⁻ + OH ⁻ , The generated ions are transferred to the solution chamber by the electric field through the anion exchange membrane. The gas cathode is arranged in the gas chamber so as not to come into contact with the liquid. Therefore, since no association occurs in the liquid phase, a conventional electrode composed of two layers, a hydrophobic layer and a hydrophilic layer, or an electrode in which a catalyst is embedded in the hydrophobic layer may be used. The gas cathode is formed by mixing a carbon powder or graphite powder carrying a catalyst such as platinum or silver with a dispersant of a water-repellent resin such as polytetrafluoroethylene (hereinafter referred to as PTFE) and processing the mixture into a sheet. And a carbon cloth or a metal mesh can also be used as the core material. As a current collector for supplying power to the gas electrode, for example, a porous body (expanded mesh, punch plate, etc.) or a porous sintered body of platinum or silver-plated stainless steel, nickel, copper, or the like is used. Power is supplied by pressing against the cathode.

The anode accommodated in the anode compartment separated from the solution compartment by the cation exchange membrane is a dimensionally stable anode (D
It is preferable to use an electrode which carries a catalyst layer mainly composed of a noble metal oxide on a valve metal substrate such as titanium known as SA). As the cation exchange membrane, it is preferable to use a fluorine-based ion exchange membrane used for ordinary ion exchange membrane method alkali chloride electrolysis. As these ion exchange membranes, for example, trade name Nafion of Asahi Glass Co. There are Flemion, a trade name of a company, and Aciplex F, a trade name of Asahi Kasei Corporation.

Next, the method of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic longitudinal sectional view showing an example of an electrolytic cell for producing hydrogen peroxide according to the present invention. The electrolytic cell main body 1 is divided into an anode chamber 3 and a cathode chamber 4 by a cation exchange membrane 2.
An anode 5 such as SE is provided. The cathode chamber 4 is further provided with a solution chamber 7 on the side of the anode chamber 3 by the anion exchange membrane 6, a gas cathode 8 in close contact with the anion exchange membrane 6, and a mesh-shaped current collector 9 for supplying power to the gas cathode 8. And a gas chamber 10 in which is stored. A diluted alkali hydroxide aqueous solution supply port 11 and a diluted alkali hydroxide aqueous solution outlet 12 are provided at the lower and upper portions of the side wall of the anode chamber 3, respectively. A supply port 13 and an outlet 14 for hydrogen peroxide and a concentrated aqueous solution of concentrated alkali hydroxide are provided, and an oxygen-containing gas supply port 15 is provided at the upper and lower portions of the side wall of the gas chamber 10, respectively.
And an oxygen-containing gas outlet 16 is provided.

The anode chamber 3 and the solution chamber 7 of the electrolytic cell body 1
When a dilute alkaline hydroxide aqueous solution is supplied to both electrodes while supplying an oxygen-containing gas to the gas chamber 10, hydrogen peroxide ions and hydroxide ions generated on the surface of the gas cathode 8 penetrate the anion exchange membrane 6. In the solution chamber 7, hydrogen peroxide and alkali hydroxide are generated. The oxygen gas generated in the anode chamber is desirably circulated to the gas chamber and used as an oxygen-containing gas supply source. In the electrolytic production of hydrogen peroxide, the gas cathode in the gas chamber is substantially free of corrosive substances in the gas chamber, and the aqueous solution of alkali hydroxide, which is the catholyte present in the solution chamber, is assured by the anion exchange membrane. The gas cathode 8 is separated from the gas cathode to prevent leakage of the catholyte, thereby extending the life of the gas cathode 8. Also, unlike the case of a normal gas electrode, the solution chamber and the gas chamber are separated by an ion exchange membrane, and the leak of the alkali hydroxide aqueous solution is reliably prevented, and it can be used even in a large electrolytic cell. It can also be applied to electrolysis on a scale.

[0018]

EXAMPLES Next, examples illustrating the electrolytic production of hydrogen peroxide according to the present invention will be described, but the present invention is not limited to these examples.

Example 1 Graphite powder having an average particle size of 7 μm (TGP-7,
Tokai Carbon Co., Ltd.) and Polytetrafluoroethylene Dispersion 30J (Mitsui Fluorochemicals Co., Ltd.) were mixed at a weight ratio of 2: 1, and the solvent was volatilized at room temperature. The sheet was developed, processed into a sheet by being sandwiched between two upper and lower titanium plates, and rolled. The sheet was fired in air at 350 ° C. for 10 minutes to obtain a gas electrode. A nickel expanded mesh (long diameter 4 mm, short diameter 2 mm, plate thickness 0.2 mm) is provided on one side of this gas electrode.
Was disposed as a current collector, and an anion exchange membrane (ACLE-5P manufactured by Tokuyama Soda Co., Ltd.) was disposed on the other surface to be integrated to obtain a gas electrode structure. The structure is incorporated into a cathode chamber of an acrylic resin electrolytic cell partitioned into an anode chamber and a cathode chamber by a cation exchange membrane of Nafion 117 (manufactured by DuPont, USA). The chamber was divided into a solution chamber on the chamber side and a gas chamber having the gas electrode and the current collector. A nickel oxygen-generating anode (long diameter: 8 mm, short diameter: 3.7 mm, plate thickness: 1 mm) was placed in the anode chamber so as to be in contact with the cation exchange membrane, and 10% hydroxylation was applied to the anode chamber and the solution chamber. Filled with aqueous sodium solution. Oxygen generated at the anode was supplied to the gas chamber through a pipe, and an excess oxygen gas corresponding to 10% of the generated amount was supplied to the gas chamber. When electrolysis was performed at room temperature with a current density of 10 A / dm ^2, the cell voltage was 1.6 V, and 2%
Of hydrogen peroxide was generated, and the current efficiency at this time was 80%.

Comparative Example 1 An electrolytic cell was assembled in the same manner as in Example 1 except that the anion exchange membrane was not used, and electrolysis was performed under the same conditions as in Example 1. The cell voltage was as low as 1.2 V. However, 10 minutes after the start of electrolysis, the aqueous sodium hydroxide solution began to leak from the solution chamber to the gas chamber.

[0024]

According to the present invention, the cation exchange membrane is divided into an anode chamber accommodating an anode and a cathode chamber accommodating a gas cathode, and the cathode chamber is further provided with an anion exchange membrane in close contact with the gas cathode. An electrolytic cell for producing hydrogen peroxide, characterized by being divided into a solution chamber in contact with an anode chamber and a gas chamber containing the gas cathode.

In the present invention, the solution chamber in which the corrosive catholyte is present and the gas chamber in which the gas cathode is present are partitioned by a dense anion exchange membrane, and the gas chamber in which the gas cathode is present is inherently corrosive. The absence of the substance avoids direct contact of the poorly resistant gas cathode with the corrosive substance, thus achieving a longer life of the gas cathode. Moreover, since the solution chamber and the gas chamber are reliably separated by the anion exchange membrane, the leakage of the catholyte to the gas chamber is prevented,
Therefore, the gas cathode is prevented from indirectly coming into contact with the catholyte, and a longer life can be achieved.

As the size of the electrolytic cell is increased, it becomes difficult to prevent the catholyte in the solution chamber from leaking into the gas chamber. However, the electrolytic cell of the present invention can almost completely prevent the leak as described above. The present invention also allows for larger electrolyzers and thereby industrial scale operation. Similarly, in the case of the electrolysis method according to the present invention, the use of the anion-exchange membrane can extend the life of the gas cathode and contribute to the enlargement of the electrolytic cell.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view showing an example of an electrolytic cell for producing hydrogen peroxide according to the present invention.

[Explanation of symbols]

1 ・ ・ ・ Electrolyzer main body 2 ・ ・ ・ Cation exchange membrane 3 ・ ・
・ Anode chamber 4 ・ ・ ・ Cathode chamber 5 ・ ・ ・ Anode 6 ・ ・ ・ Anion exchange membrane 7 ・ ・ ・ Solution chamber 8 ・ ・ ・ Gas cathode 9
・ ・ ・ Current collector 10 ・ ・ ・ Gas chamber

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-54-132498 (JP, A) JP-A-56-47578 (JP, A) JP-A-56-69384 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C25B 1/00-15/08

Claims (3)

(57) [Claims] 1. A cation exchange membrane divided into an anode chamber for housing an anode and a cathode chamber for housing a gas cathode, and the cathode chamber is in contact with the anode chamber through an anion exchange membrane closely contacting the gas cathode. An electrolytic cell for producing hydrogen peroxide, wherein the electrolytic cell is partitioned into a solution chamber and a gas chamber containing the gas cathode. 2. A cation exchange membrane divided into an anode chamber containing an anode and a cathode chamber containing a gas cathode, and the cathode chamber comes into contact with the anode chamber by an anion exchange membrane closely contacting the gas cathode. Electrolysis is performed while supplying an oxygen-containing gas to the gas chamber of the electrolytic cell for producing hydrogen peroxide partitioned into a solution chamber and a gas chamber containing the gas cathode, and the hydrogen peroxide is supplied to the anode chamber in the solution chamber. A method for producing hydrogen peroxide, wherein oxygen is generated in each step. 3. The method according to claim 2, wherein the oxygen generated in the anode chamber is circulated to the gas chamber to produce hydrogen peroxide.