JPS6340871B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing hydrogen by electrolyzing water;
More specifically, by electrolyzing water by diaphragm electrolysis using a specific cation exchange resin membrane,
This invention relates to a method for efficiently producing hydrogen.

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.

In the water electrolysis method, a diaphragm is used to separate the cathode and anode of the electrolytic cell, and water is usually supplied to the cathode chamber and electrolyzed to produce hydrogen in the cathode chamber, the so-called two-chamber method. The diaphragm electrolysis method is known. Conventionally, asbestos diaphragms have been most commonly used as diaphragms in this field, but in the case of asbestos diaphragms, the asbestos itself is corroded by electrolyte, so it cannot withstand long-term use and has a short lifespan. In addition to the major drawback of being small, in this case, the diaphragm is microporous and allows the electrolyte and generated gas to pass through, resulting in the disadvantage that the resulting hydrogen is contaminated with oxygen, reducing its purity. .

The inventor of the present invention has conducted intensive research in order to produce hydrogen with high purity and efficiency by electrolyzing water using a cation exchange resin membrane as a diaphragm. It has been found that this object can be advantageously achieved by using a fluorine-containing ion exchange resin membrane having an exchange group so as to have a specific ion exchange capacity as a diaphragm.

That is, in the present invention, in producing hydrogen by electrolyzing water by diaphragm electrolysis using a cation exchange resin membrane as a diaphragm, -(CF ₂ X) (CF ₂
X and X' are hydrogen atoms, chlorine atoms, fluorine atoms, or fluoroalkyl groups) as an ion exchange group, and a fluorine-containing cation having an exchange capacity of 0.1 to 4 milliequivalents/gram dry resin. It is characterized by the use of an exchange resin membrane.

In the case of the present invention, not only the hydrogen obtained is of high purity, but even when the electrolyte is alkaline, there is no problem of corrosion as seen in asbestos diaphragms, and stable operation can be performed for a long period of time. It is.

The present invention will be described in more detail below. The diaphragm used in the present invention is one that substantially does not allow the electrolyte solution or generated gas to pass through, and furthermore, contains specific hydroxyl groups to have a specific ion exchange capacity. Must be a fluorine-containing cation exchange resin membrane. It is an essential property of the ion exchange resin membrane of the present invention that generated gases such as oxygen are not substantially permeable, and if it does not have this property, the purity of the obtained hydrogen will decrease, and the above-mentioned present invention purpose is not achieved at all. Therefore, the ion exchange resin membrane of the present invention must be non-porous and dense.
For example, water permeability is an effective measure for determining non-porosity, and in the present invention, when the water permeability is 1 m of water column pressure (60°C, PH10 in 4N NaCl), 100
It needs to be ml/hour/m ² or less; if it is more than this, the purity will be greatly reduced due to the permeation of the electrolyte and the generated gas. Among these, the water permeation rate is particularly preferably 10 ml/hour/m ² or less.

As described above, the ion exchange group used in the present invention is a hydroxyl group having the general formula -C( _CF2X )( _CF2X ')-OH. Here, X and X' are the same as above, but the fluoroalkyl group has 1 to 10 carbon atoms, and a perfluoroalkyl group is particularly preferred. It is especially preferable that X and X' are both fluorine atoms. Further, as mentioned above, the ion exchange capacity needs to be 0.1 to 4 milliequivalents/gram dry resin, and if it is smaller than this range, the electrical resistance of the membrane becomes high and the electrolytic voltage increases. On the other hand, if it exceeds this range, the water content of the membrane increases and the current efficiency decreases, which is unsuitable. Within this range, those having an ion exchange capacity of 0.5 to 2 milliequivalents/gram dry resin, particularly 0.8 to 1.8 milliequivalents/gram dry resin are particularly preferred in terms of performance.

The fluorine-containing cation exchange resin membrane having the specific hydroxyl group of the present invention can have various structures, and among them, the membrane containing the following two structures (a) and (b) is used. Preference is given to using polymers.

Here, Y is a hydrogen atom, a chlorine atom, a fluorine atom, or _-CF3 , and Y' and Y'' are selected from the same group as Y or are a perfluoroalkyl group having 1 to 10 carbon atoms or It is a perfluoroalkoxy group, Z and Z' are each selected from the same group as Y and Y', 1 is 0 or 1, and m and n are both integers of 1 to 6. X′ is the same as defined above.

The molecular weight of the polymer containing structures (a) and (b) is preferably about 3,000 to 300,000, particularly 10,000 to 10,000 in view of its performance as an ion exchange membrane and the necessity for film formation. Ten thousand things are good. Further, in order for the polymer to achieve the above-mentioned ion exchange capacity, it is preferable that the structure (b) is contained in the polymer in an amount of 1 to 40 mol%, particularly 3 to 20 mol%.

In order to produce the polymer having the structures (a) and (b) above, for example, the following method is employed.

1. Respective monomer compounds capable of providing the structures (a) and (b), such as fluorinated olefin, and CF ₂ =
Direct copolymerization with a hydroxyl group-containing monomer such as CF-C( _CF3 ) ₂ -OH or _CH2 =CH- _CH2 -C( _CF3 ) ₂ -OH.

2. A hydroxyl group-containing monomer as described above is graft-polymerized onto a polymer or copolymer such as a fluorinated olefin such as tetrafluoroethylene or hexafluoropropylene.

3. A polymer or copolymer such as the above-mentioned fluorinated olefin in the presence of a radical generator,
(CF ₂ X) (CF ₂ X') React with a compound such as C=O.

In producing the polymer for producing the fluorine-containing cation exchange resin membrane of the present invention, for example, the following monomers can be used in combination to modify the resulting polymer. That is, for example, by using CF ₂ =CFOR _f (R _f is a perfluoroalkyl group having 1 to 10 carbon atoms) in combination, flexibility can be imparted to the film, or CF ₂ =CF−CF=CF ₂ ,
By using a divinyl monomer such as CF ₂ =CFO(CF ₂ ) _1-3 CF = CF ₂ in combination, the resulting polymer can be crosslinked and mechanical strength can be imparted to the membrane.

The means for forming an ion exchange resin membrane from the thus obtained polymer can be carried out by known methods such as press molding, roll molding, extrusion molding, solution casting, dispersion molding, or powder molding.
Thus, the film thickness is preferably between 20 and 500 microns,
Furthermore, an ion exchange membrane with a thickness of 50 to 300 microns is preferably used.

The cation exchange resin membrane of the present invention may be formed using an olefin polymer such as polyethylene or polypropylene, preferably a fluorine-containing polymer such as polytetrafluoroethylene or a copolymer of ethylene and tetrafluoroethylene, if necessary. It is possible to improve the mechanical strength of the membrane by molding the copolymer as a blend, or by supporting the copolymer with a support made of cloth, net, or other woven fabric, nonwoven fabric, or porous film made of these polymers. can. Note that when such blends or supports are used, the weight of these resins is not included in the ion exchange capacity described above.

As a means for electrolyzing water and producing hydrogen using the above-mentioned cation exchange resin membrane, any known or well-known diaphragm electrolysis method can be employed. For example, in the present invention, any type of electrode can be used as the electrode used for water electrolysis, such as a porous electrode such as a perforated plate, a mesh, or an expanded metal. Porous electrodes with appropriate porosity can be used, and multiple plate-shaped electrodes can be stacked together, but when using multiple electrodes with different porosity, It is preferable to arrange a material with low porosity 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,
Ruthenium, palladium, and iridium are exemplified, and iron group metals include iron, cobalt, Raney cobalt, nickel, Raney nickel, stabilized Raney nickel, stainless steel, alkali-etched stainless steel (Japanese Patent Publication No. 1982-19229), and Raney nickel metal cathode. (Japanese Unexamined Patent Publication No. 112785/1985),
Examples include the Rodan-Nitzkelmecki cathode (Japanese Patent Application Laid-open No. 115676/1983).

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. Furthermore, the electrolytic cell may be of any type, such as a monopolar cell or a bipolar cell.

Thus, for example, an anode and a cathode are separated using the cation exchange resin membrane of the present invention, an anode chamber and a cathode chamber are configured in an electrolytic cell, water is supplied to the cathode chamber for electrolysis, and hydrogen is removed from the cathode chamber. Even in the case of a so-called two-chamber type tank that produces hydrogen, high-purity hydrogen can be efficiently and stably produced over a long period of time by electrolyzing at an appropriate electrolytic voltage and current density using an alkaline aqueous solution as described below as a raw material. can.

In fact, when applying a water electric field, it is preferable to add an alkali together with water to the anode chamber for the purpose of lowering the electrical resistance during electrolysis.

When using an alkali, part or all of the caustic alkali generated in the cathode chamber by water electrolysis can be added to the anode chamber, and the caustic alkali can be recycled. The concentration of caustic alkali in the anode chamber is preferably about 5 to 45% by weight. As the caustic alkali to be used, alkali metal hydroxides are suitable.

During electrolysis, it is appropriate to adopt a current density of 10 to 150 A/dm ² , preferably 20 to 100 A/dm ² .

Further, by adopting a temperature of 80 to 150°C, preferably 80 to 120°C during electrolysis of the anolyte, the voltage surface, electrical resistance, etc. can be brought into the most favorable state.

Of course, in the present invention, not only such a two-chamber type tank but also a plurality of the above-mentioned cation exchange resin membranes,
Alternatively, the so-called cation exchange resin membrane and a plurality of other cation exchange resin membranes or diaphragms are used to partition an anode and a cathode to form an intermediate chamber in addition to an anode chamber and a cathode chamber. It can also be carried out in a three-chamber type or more multi-chamber type electrolytic cell.

Examples are given below to more specifically illustrate the present invention, but it goes without saying that the present invention is not limited to the above description and the following examples.

Example 1 60 g of polytetrafluoroethylene fine powder (trade name: Polymist, manufactured by Allied Chemical Company, USA) was
1,1-bis-(trifluoromethyl)-2,3,
After being added to 3-trifluoro-2-propen-1-ol and heated at reflux temperature for 2 hours, the polymer powder was filtered. This monomer-impregnated powder has a dose rate of
After 8 hours of irradiation with CO ⁶⁰ gamma rays at a rate of 0.01 megarats/hour, the sample was sufficiently dried in a vacuum dryer at 80° C. until there was no change in weight. The obtained graft polymer powder was hot pressed to produce a cation exchange resin membrane with a thickness of 200 μm and a size of 8 cm×8 cm. The ion exchange capacity of this membrane was 1.23 meq/g dry resin, and the water permeability was 4.9 ml/hr/m ² at 1 m of water column pressure (60° C. in 4N NaCl, pH 10).

Using such a cation exchange resin membrane, a two-chamber electrolyte layer partitioned into an anode chamber and a cathode chamber was formed. A nickel electrode was used as the anode, and stainless steel was used as the cathode, the distance between the two electrodes was 2.2 cm, the effective area of the diaphragm was 25 cm ² , and a caustic potassium aqueous solution was electrolyzed under the following conditions.

The anode chamber is filled with a 30% KOH aqueous solution, the cathode chamber is also filled with a 30% KOH aqueous solution, and the anode chamber is filled with a 30% KOH aqueous solution.
A KOH aqueous solution was electrolyzed at 100°C while water was supplied to the cathode chamber to maintain the KOH concentration in both electrode chambers at 20%, and the following results were obtained.

Current density (A/dm ² ) Cell voltage (V) 40 4.2 60 5.0 Example 2 A FEP film (a copolymer film of tetrafluoroethylene and hexafluoropropylene) with a thickness of 125 μm and a size of 20 cm x 20 cm was 1-bis-
After immersion in (trifluoromethyl)-2,3,3-trifluoro-2-propen-1-ol and heating at reflux temperature for 10 hours, the monomer-impregnated film was exposed to CO ⁶⁰ at a dose rate of 0.01 Mrad/h. gamma rays
After irradiation for 15 hours, it was sufficiently dried in a vacuum dryer at 100°C until there was no change in weight. The film was sandwiched between aluminum foils and lightly pressed at 150°C, resulting in a film of 8 cm.
An ion exchange membrane of 8cm x 8cm was set in a battery container.
The ion exchange capacity of the membrane was 1.13 meq/gram dry resin.

When electrolysis was carried out under the same conditions as in Example 1, the following results were obtained.

40A/ ^dm2 : 4.8V 60A/ ^dm2 : 5.7V

Claims (1)

[Claims] 1 When producing hydrogen by electrolyzing water by diaphragm electrolysis using a cation exchange resin membrane as a diaphragm, -C
A hydroxyl group consisting of (CF ₂ X) (CF ₂ A method for producing hydrogen, comprising using a fluorine-containing cation exchange resin membrane having a dry resin of 0.1 to 4.0 milliequivalents/gram.