JPS6125787B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing hydrogen, and more specifically, to a novel method for efficiently producing hydrogen at low voltage, which involves performing water electrolysis in an electrolytic cell with a specific electrode arrangement using a cation exchange membrane. . Reflecting the recent energy situation, hydrogen is attracting attention from many quarters as a new energy source to replace oil. Industrial hydrogen production methods can be roughly divided into water electrolysis methods and coke or petroleum gasification methods. Although the former method uses readily available water as a raw material, it requires a large number of electrolytic equipment, is insufficiently adaptable to excess or insufficient current, and suffers from deterioration due to carbonation of the electrolyte and floor space.
Many issues remain, including equipment costs. On the other hand,
The latter method is generally complicated to operate, requires fairly large equipment, and has problems such as considerable equipment costs. Furthermore, recently, as an improvement to the water electrolysis method, a fluorine-containing cation exchange membrane having a sulfonic acid group as a cation exchange group has been used, and one side of the ion exchange membrane has a cathode using platinum black as a catalyst, and the other side has a cathode using platinum black as a catalyst. A method has been proposed in which an anode using an alloy of reduced oxides of platinum and ruthenium as a catalyst is closely attached to each surface, and water is electrolyzed to efficiently obtain hydrogen (Japanese Unexamined Patent Application Publication No. 1983-1983).
(See Publication No. 78788, etc.) This method uses porous anodes and cathodes that are permeable to gases and liquids, and is susceptible to electrical resistance caused by the electrolyte and generated hydrogen and oxygen gas, which were previously thought to be unavoidable in this type of technology. Because the electrical resistance due to the underlying bubbles is reduced, it is considered a method that can perform electrolysis at a lower voltage than conventional methods. In this method, the anode and cathode are closely bonded to and embedded in the surface of the ion exchange membrane, and the gas generated by electrolysis at the contact interface between the membrane and the electrode easily leaves the electrode. It is made gas and liquid permeable so that the electrolyte can penetrate. However, if the electrode and ion exchange membrane are directly bonded, gas is generated as a result of the electrode reaction, causing phenomena such as swelling in the cation exchange membrane and deteriorating the membrane performance. It was found that this method could not be implemented stably over a period of time. The present inventor continued research into an electrolysis method that does not have the above-mentioned disadvantages and has a cell voltage as low as possible, and found that the surface of the cation exchange membrane has gas and liquid permeability that does not act as an electrode. When water is electrolyzed in an electrolytic cell in which a porous layer is formed and an anode or a cathode is arranged through the porous layer, hydrogen can be obtained at an unexpectedly low voltage, and the above-mentioned disadvantages are also substantially eliminated. It was discovered that it can be done. According to the present invention, the electrode is formed through the gas- and liquid-permeable porous layer that does not function as an electrode,
Preferably, the electrode is placed in contact with the porous layer, but the electrode and the cation exchange membrane are not in direct contact with each other. Therefore, since the electrolysis in the present invention occurs on the electrode separated from the ion exchange membrane by a specific porous layer, the generated gas does not come into direct contact with the ion exchange membrane, and the generated gas does not affect the membrane due to gas generation. It won't cause any trouble. Furthermore, in the case of an electrolytic cell configured in this manner, the cell voltage is unexpectedly low. For example, the cell voltage is lower than that of an electrolytic cell in which a porous electrode is placed in direct contact with the membrane without intervening the specific porous layer. In the present invention, the porous layer formed on the surface of the ion exchange membrane that is permeable to gas and liquid and does not function as an electrode can be either conductive or non-conductive, and its material can also be organic. It may be inorganic or inorganic. When a conductive porous layer is employed, it is formed so that the overvoltage is greater than that of an electrode disposed through the porous layer. In many cases where a conductive material is used, the specific porous layer is formed from a material that itself has a higher overvoltage than the electrode. but,
In some cases, even if the same material as the electrode is used, a porous layer with a higher overvoltage than the electrode can be formed by selecting its shape, and a porous layer that does not function as an electrode can be formed. Further, the specific porous layer is preferably formed from a hydrophilic substance. The material constituting such a specific porous layer varies depending on the type of ion exchange membrane and the type of electrolyte used, but it may be a fluorine-containing material containing a phosphonic acid group, a sulfonic acid group, or a carboxyl group as a cation exchange group. When performing electrolysis using a cation exchange membrane and an alkaline electrolyte, the periodic table -
It is selected from group A, group B, group B, iron group metals, chromium, manganese, etc. alone or alloys, oxides, hydroxides, nitrides, or carbides. In addition, when using a fluorine-containing cation exchange membrane containing sulfonic acid groups or phosphonic acid groups as cation exchange groups and performing electrolysis using a neutral or acidic electrolyte, the periodic table -A group, -B
The metal is selected from simple substances or alloys, oxides, nitrides, carbides, etc. of group metals such as group metals, group B, and iron group metals. In forming the specific porous layer, the above material preferably has a particle size of 0.01 to 300μ, particularly 0.1 to 300μ.
Used in the form of a 100μ powder. At this time, if necessary, binders such as fluorocarbon polymers such as polytetrafluoroethylene and polychlorotrifluoroethylene, celluloses such as carboxymethylcellulose, methylcellulose, and hydroxyethylcellulose, polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, and Thickening agents such as water-soluble substances such as sodium acrylate, polymethylpynylether, casein, polyacrylamide, etc. are used. These binders or thickeners are preferably used in an amount of 0 to 50% by weight, particularly 0.5 to 30% by weight, based on the powder. At this time, if necessary, the formation of a porous layer can be facilitated by adding an appropriate surfactant such as a long-chain hydrocarbon or fluorinated hydrocarbon, as well as a conductive filler such as graphite. can. In any case, the content of particles forming the porous layer in the formed porous layer is 0.05 to 30 mg/
cm ² , particularly 0.1 to 1.5 mg/cm ² . Formation of a specific porous layer from the above materials is described in Japanese Patent Application Laid-open No.
A method similar to that described in Publication No. 54-112398,
Alternatively, after thoroughly mixing the above powder, a binder, a thickener, etc. used as necessary in an appropriate medium, a porous layer cake is obtained on a filter by a filtration method, and the cake is applied to a membrane. It can be attached to the surface of the ion exchange membrane, or the mixture can be made into a paste and applied directly to the surface of the ion exchange membrane by screen printing or the like. The porous layer formed on the ion exchange membrane surface is then preferably molded using a press molding machine.
It is heated and pressed onto the membrane surface at 80 to 220° C. and 1 to 150 kg/cm ² , preferably partially embedded in the membrane surface. Thus, the porous layer formed on the membrane surface preferably has a porosity of 10 to 99%, particularly 25 to 95%, and a thickness of preferably 0.01 to 200%.
A suitable value is μ, particularly 0.1 to 100μ. Further, the average pore diameter is preferably 0.01 to 200μ. In the present invention, any type of electrode can be used as the electrode disposed through the specific porous layer, and for example, a porous electrode such as a porous plate, a mesh, or an expanded metal is used. Porous electrodes with appropriate porosity can be used, and multiple plate-shaped electrodes can be stacked together. However, when using multiple electrodes with different porosity, It is preferable to place smaller ones on the membrane side. Thus, as the anode, platinum group metals, their conductive oxides or their conductive reduced oxides, iron group metals, etc. are usually used, while as the cathodes, platinum group metals, their conductive oxides, iron group metals, etc. is used. In addition, platinum group metals include platinum, rhodium,
Examples include ruthenium, palladium, and iridium, and iron group metals include iron, cobalt, nickel, Raney nickel, stabilized Raney nickel,
Examples include stainless steel, alkali-etched stainless steel (Japanese Patent Publication No. 54-19229), Raney-Nickelmetki cathode (Japanese Patent Application Laid-Open No. 112785-1985), Rodan-Nickelmetki cathode (Japanese Patent Application Laid-open No. 115676-1981). If a porous electrode is used, it can be formed from the material itself forming the anode or cathode. However, when platinum group metals or conductive oxides thereof are used, it is preferable to coat the surface of an expanded valve metal such as titanium or tantalum with these substances. In the present invention, when the above-mentioned anode or cathode is arranged through a porous layer having no electrode activity formed on the membrane surface, the electrode is preferably arranged in contact with the porous layer to reduce the cell voltage. It is effective to make However, these anodes or cathodes do not necessarily need to be placed in contact with the porous layer, and may be placed at appropriate intervals as the case requires. Further, when only one of the anode and the cathode is disposed via a porous layer having no electrode activity according to the present invention, the anode or cathode which is the opposite electrode may be the above-mentioned porous electrode or other known porous layer. The electrode may be placed directly on the anode side or the cathode side of the cation exchange membrane. If it takes these electrodes,
They may be provided in contact with the ion exchange membrane surface, or may be provided at intervals. The ion exchange membrane used in the present invention is made of a polymer containing a cation exchange group such as a carboxyl group, a sulfonic acid group, a phosphonic acid group, or a phenolic hydroxyl group. It is particularly preferable to employ combination. As such a fluorine-containing polymer, for example, a copolymer of a vinyl monomer such as tetrafluoroethylene or chlorotrifluoroethylene and a fluorovinyl monomer containing an ion exchange membrane such as a sulfonic acid, carboxylic acid, or phosphoric acid group is used. Ru. Among these, it is particularly preferable to use monomers that can form the following polymerized units (a) and (b), since hydrogen can be obtained with relatively high current efficiency.

【formula】

[Formula] Here, X is F, C1, H or -CF ₃ ,
X' is X or CF ₃ (CF ₂ )m, m is 1 to 5, and Y is selected from the following:

【formula】

【formula】

【formula】

【formula】

x, y, z are all 0 to 10, and Z, Rf are -
F or a perfluoroalkyl group having 1 to 10 carbon atoms. A also represents -SO ₃ M, -OOM or - which can be converted into these groups by hydrolysis.
_SO2F : -CN, -COF or -COOR, M represents hydrogen or an alkali metal, and R represents an alkyl group having 1 to 10 carbon atoms. The cation exchange membrane used in the present invention preferably has an ion exchange capacity of 0.5 to 4.0 milliequivalents/
Preferred is gram dry resin, especially 0.8 to 2.0 meq/gram dry resin. In order to provide such an ion exchange capacity, in the case of an ion exchange resin made of a copolymer consisting of the polymerized units of (a) and (b) above,
Preferably, the amount of polymerized units (b) is preferably 1 to 40 mol%, particularly 3 to 25 mol%. The cation exchange membrane used in the present invention does not necessarily need to be formed from one type of polymer, nor does it need to have only one type of ion exchange group. For example, there are laminated membranes of two types of polymers with smaller ion exchange capacity on the cathode side, and ion exchange membranes with weakly acidic exchange groups such as carboxylic acid groups on the cathode side and strong acidic exchange groups such as sulfonic acid groups on the anode side. Can be used. These ion exchange membranes are manufactured by various conventionally known methods, and if necessary, these ion exchange membranes are preferably made of fabrics such as cloth or net made of a fluorine-containing polymer such as polytetrafluoroethylene,
It can be reinforced with non-woven fabric, metal mesh, porous material, etc. Further, the thickness of the ion exchange membrane of the present invention is preferably 20 to 500μ, preferably 50μ
It is forced to ~400μ. The porous layers on the anode and cathode side, which are preferably bonded to and formed on the surface of these ion exchange membranes, are formed in an appropriate form of ion exchange groups so as not to cause decomposition of the ion exchange groups possessed by the ion exchange membrane. For example, in the case of a carboxylic acid group, it is bonded in its ester form, and in the case of a sulfonic acid group, it is bonded in its -SO ₂ F type by the action of pressure and heat. Next, the present invention will be explained in more detail using examples. Example 1 Modified polytetrafluoroethylene with a particle size of 1 μm or less (the polytetrafluoroethylene surface was mixed with tetrafluoroethylene and CF ₂ =CFOCF ₂
Particles coated with a copolymer of COOCH ₃ , hereafter modified
2.5 parts of an aqueous dispersion containing 7.0% by weight of PTFE (hereinafter referred to as PTFE) and 5 parts of titanium oxide powder with a particle size of 25μ or less are mixed together, and after thorough mixing in advance, 2 parts of isopropyl alcohol and 1 part of cyclohexanol are added,
A paste was obtained by kneading again. The paste was applied to a printing substrate with an ion exchange capacity of 1.70meq using a printing plate with a mesh count of 200, a 60μ thick stainless steel screen with an 8μ thick screen mask underneath, and a polyurethane squeegee. /g dry resin, polytetrafluoroethylene with thickness 210μ and CF ₂ =CFO
Screen printing was performed on one side of an ion exchange membrane made of a copolymer of (CF ₂ ) ₃ COOCH ₃ to a size of 20 cm x 25 cm. The printed layer obtained on one side of the ion exchange membrane was dried in air to solidify the paste. On the other hand, titanium oxide having a particle size of 25 μm or less was screen printed on the other side of the ion exchange membrane in exactly the same manner.
Thereafter, the printed layer was pressed onto the ion membrane at a temperature of 140°C and a molding pressure of 30 kg/cm ² , and then immersed in a 25% by weight aqueous potassium hydroxide solution at 90°C to hydrolyze the ion membrane and elute methylcellulose. The titanium oxide layer obtained on the ion exchange membrane has a thickness of 20μ and a porosity of 70%, with a titanium oxide layer of 1.5
Contained mg/ ^cm2 . Next, on the anode side of the ion membrane, use nickel expanded metal (breadth diameter 2.5 mm, long axis 5 mm), and on the cathode side, use SUS304 expanded metal (breadth diameter 2.5 mm).
mm, major axis 5.0 mm) in a 52% caustic soda aqueous solution.
The cathode, which has been etched at 150°C for 52 hours to have a low hydrogen overpotential, is brought into pressure contact with the ion membrane at a pressure of 0.01 Kg/ ^cm2 , and a 30% caustic potassium aqueous solution is placed in the anode chamber and water is placed in the cathode chamber. While supplying the anode chamber,
Electrolysis was carried out at 100℃ while maintaining the caustic potassium concentration in the cathode chamber at 20%, and the following results were obtained. Current density (A/dm ² ) Cell voltage (V) 40 1.71 60 1.88 Example 2 In Example 1, as an ion exchange membrane, CF ₂ =
CF ₂ and CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ SO ₂ F
Example 1 except that a cation exchange membrane (ion exchange capacity 0.87meq/g dry resin, membrane thickness 125μ) consisting of a copolymer of Electrolysis was carried out in exactly the same manner and the following results were obtained. Current density (A/dm ² ) Cell voltage (V) 40 1.74 60 1.95 Example 3 Using the cation exchange membrane to which the tantalum pentoxide used in Example 2 was attached, tantalum was replaced with Pt-Ir as the electrode. Electrolysis was carried out in the same manner as in Example 1, except that electrolysis was carried out using a coated 20-mesh wire mesh while supplying 3% dilute sulfuric acid, and the following results were obtained. Current density (A/dm ² ) Cell voltage (V) 40 1.51 60 1.65 Comparative example Electrolysis was carried out in the same manner as in Example 1 except that the porous layer was not attached to the cation exchange membrane in Example 1. The results were obtained. Current density (A/dm ² ) Cell voltage (V) 40 2.12 60 2.25

Claims (1)

[Scope of Claims] 1. A hydrogen production method comprising supplying water to a cathode chamber of an electrolytic cell in which an anode and a cathode are partitioned by a cation exchange membrane for electrolysis, wherein at least one of the anode and the cathode is an anode. A method for producing hydrogen, characterized in that the membrane is disposed through a gas- and liquid-permeable porous layer that does not function as an electrode and is formed on the surface of an ion-exchange membrane. 2 The porous layer that does not act as an electrode has a porosity of 10
99% and a thickness of 0.01 to 200μ. 3. The manufacturing method according to claims 1 and 2, wherein the cation exchange membrane is made of a fluorine-containing polymer having a sulfonic acid group, a carboxylic acid group, or a phosphoric acid group.