JPH0534623B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for measuring the concentration of a solute in an aqueous solution.

BACKGROUND ART Conventionally, chemical analysis methods or instrumental analysis methods such as atomic absorption spectrometry and ion chromatography have been used to measure the concentration of solutes in aqueous solutions. Furthermore, as a simpler method, for example, a float type hydrometer may be used.

Problems to be Solved by the Invention However, the above-mentioned chemical analysis methods and instrumental analysis methods are generally time-consuming and have problems such as requiring large-scale equipment. There are problems such as consuming the aqueous solution and changing its concentration. Further, even when using a float type hydrometer, there are problems such as its operation is complicated and it is unsuitable when attempting to continuously measure the concentration of solute.

Means for Solving the Problems The present invention provides an electrical appliance in which a bonded body or pressure-bonded body formed by integrally bonding or press-bonding a cathode on one side of an ion exchange resin membrane and an anode on the other side is covered with a water-repellent plastic membrane. When a chemical cell is immersed in the aqueous solution to be measured and a constant DC voltage is applied between the anode and cathode,
The concentration of solutes in an aqueous solution can be determined by utilizing the relationship that the current flowing as a result of electrolysis of water absorbed by the ion exchange resin membrane is substantially directly proportional to the water vapor pressure corresponding to the concentration of solute in the aqueous solution to be measured. It measures the concentration, and at this time, the hydrogen and oxygen generated during the electrolysis of the water are mixed and returned to water using the catalyst medium of the electrode, thereby consuming the aqueous solution. The present invention provides a method that allows continuous measurement without changing the concentration.

Action When water is absorbed into the ion exchange resin membrane of an electrochemical cell in which a cathode and an anode are integrally bonded or pressure-bonded to an ion exchange resin membrane, and a direct current is passed between the anode and anode electrodes, the ion exchange resin membrane acts as an electrolyte, and the water in the ion exchange resin membrane is electrolyzed. When a cation exchange membrane as a hydrogen ion conductor is used as the ion exchange resin membrane, the following reaction occurs.

Cathode: 2H ⁺ +2e→H ₂ ...(1) Anode: H ₂ O→1/2O ₂ +2H ⁺ +2e ...(2) Total reaction: H ₂ O→H ₂ +1/2O ₂ ...(3 ) Furthermore, when an anion exchange membrane as a hydroxide ion conductor is used as the ion exchange resin membrane, the following reaction occurs.

Cathode: 2H ₂ O + 2e → H ₂ + 2OH ^- ... (1') Anode: 2OH ^- →1/2O ₂ +H ₂ O ... (2') Total reaction: H ₂ O → H ₂ + 1/2O ₂ ... ...(3') When such an electrochemical cell coated with a water-repellent plastic membrane is immersed in an aqueous solution, only the water in the aqueous solution turns into steam and passes through the water-repellent plastic membrane, forming an ion-exchange resin membrane. Absorbed. Therefore, when a direct current is passed between the anode and anode electrodes of this electrochemical cell, electrolysis of the water absorbed in the ion exchange resin membrane also occurs. Furthermore, when a constant DC voltage is applied between the anode and anode electrodes, the current flowing between the anode and anode electrodes is approximately directly proportional to the water vapor pressure of the aqueous solution. Therefore, the concentration of an aqueous solution can be measured using this relationship.

However, in measuring the solute concentration of the target aqueous solution, the aqueous solution is consumed as the water is electrolyzed, and the solute concentration increases with the passage of measurement time. Furthermore, hydrogen is generated from the cathode and oxygen is generated from the anode, which is very dangerous, and when measuring in a closed container, there are problems such as an increase in the internal pressure of the container.

In the present invention, a space or passage is provided in advance so that hydrogen and oxygen generated by water electrolysis can be mixed, and then the hydrogen and oxygen generated by water electrolysis are placed between the electrodes at either the cathode or the anode, or on the surface of both electrodes. The method uses the catalytic action of water to turn it back into water.

In this case, the above-mentioned overall reactions (3) and (3') are as follows, and the produced water is returned to the aqueous solution through the water-repellent plastic membrane, so the above problems are solved and the target aqueous solution is consume or
Continuous measurement is possible without changing the concentration.

Total reaction: H ₂ O → (H ₂ +1/2O ₂ →) H ₂ O ……(4) The reason why the electrochemical cell is covered with a water-repellent plastic membrane is because the aqueous solution to be measured is an ion exchange resin. When in direct contact with the membrane, a nearly constant current flows, regardless of the concentration of the aqueous solution;
This is because, depending on the solute, electrolysis of the solute itself occurs instead of electrolysis of water, making it impossible to measure the concentration of the aqueous solution.

As the ion exchange resin membrane used in the present invention, a cation exchange membrane having a perfluorocarbon resin skeleton and a sulfonic acid group as an ion exchange group is most suitable, but an anion exchange membrane having a hydroxyl group may also be used. Furthermore, a hydrocarbon type material such as styrene-divinylbenzene copolymer may be used as the resin skeleton of the ion exchange resin membrane.
Further, the electrode may be integrally joined to the ion exchange resin membrane, or a mesh-like or porous electrode may be pressed into contact with the ion exchange resin membrane. Further, the electrodes may be arranged on both sides of the ion exchange resin membrane, or only on one side.

As a method for joining the electrode to the ion exchange resin membrane, a so-called electroless plating method or a hot pressing method in which a mixture of catalyst powder and a binder is hot pressed can be applied. Platinum group metals and the like can be used as electrode materials. Further, as the material for the water-repellent plastic film covering the electrochemical cell, fluororesin is the best material, but polyvinyl chloride, polypropylene, polyethylene, etc. can also be used. Although it is desirable that the water-repellent plastic membrane be porous, it may also be non-porous.

The measuring method of the present invention is particularly effective in measuring the concentration of sulfuric acid in lead-acid batteries, the salt content in urine, and the like.

Examples Some examples of the present invention will be described in detail below.

[Example 1] Platinum (4 mg/
cm ² ) were joined by electroless plating method, with an outer diameter of 10 mm,
Current collectors made of expanded titanium (outer diameter 10 mm, inner diameter 5 mm) with titanium lead wires coated with polytetrafluoroethylene are placed on both sides of the donut-shaped ion exchange resin membrane-catalyst electrode assembly with an inner diameter of 5 mm. The whole was then covered with a porous polytetrafluoroethylene membrane.

In the electrochemical cell (concentration sensor) thus obtained, a space is provided in the center of the electrode so that oxygen and hydrogen generated by water electrolysis can mix. A cross-sectional structural diagram is shown in Fig. 1.

[Example 2] Similar to Example 1, a 10 mm x 10 mm ionic resin membrane-catalyst was prepared by bonding platinum (4 mg/cm ² ) to both sides of a perfluorocarbon sulfonic acid resin membrane (DuPont Nafion 117) by electroless plating. Expanded titanium (10 mm x 10 mm) with titanium lead wires, with nine holes of 2 mm in diameter made in the electrode assembly and coated on both sides with polytetrafluoroethylene.
A current collector consisting of the following materials was disposed, and the entirety thereof was covered with a porous polytetrafluoroethylene film.

In the electrochemical cell (concentration sensor) obtained in this way, the evenly distributed perforations in the ion exchange resin membrane-catalyst electrode assembly allow the oxygen and hydrogen generated by water electrolysis to mix extremely smoothly. do. A cross-sectional structural diagram is shown in Fig. 2.

[Example 3] Similar to Example 1, platinum (4 mg/cm ² ) was bonded to both sides of a perfluorocarbon sulfonic acid resin membrane (Nafion 117, manufactured by Dupont) by electroless plating to create an ion exchange resin membrane-catalyst with a diameter of 3 mm. A current collector made of expanded titanium (diameter 3 mmφ) with titanium lead wires coated with polytetrafluoroethylene is arranged on both sides of the electrode assembly, and the entire body is made of porous polytetrafluoroethylene, leaving a space leading to both electrodes. Covered with ethylene membrane. In the electrochemical cell (concentration sensor) obtained in this way, oxygen and hydrogen generated by water electrolysis are mixed in the space between the ion exchange resin membrane-catalyst electrode assembly and the porous polytetrafluoroethylene membrane. It will fit. A cross-sectional structural diagram is shown in Fig. 2.

In these figures, 1, 1a, 1b, 1c,
1d is an ion exchange resin membrane made of perfluorocarbon sulfonic acid resin, 2, 2a, 2b, 2c,
3d is a cathode made of platinum, 3, 3a, 3b, 3
c, 3d are anodes made of platinum, 4, 4a, 4b,
4c and 4d are cathode current collectors made of expanded titanium, 5, 5a, and 5b are anode current collectors made of expanded titanium, 6 is a water-repellent plastic film made of porous polytetrafluoroethylene film, and 7 is a water-repellent plastic film made of porous polytetrafluoroethylene film. A space or hole for mixing oxygen and hydrogen.

Next, these electrochemical cells (concentration sensors) are immersed in sulfuric acid aqueous solutions adjusted to various concentrations, and cathodes 2, 2a, 2b, 2c, 2d and anodes 3, 3a, 3
As a result of measuring the current that flows when a constant DC voltage of 3V is applied between terminals b, 3c, and 3d, the relationship between the water vapor pressure and current of the sulfuric acid solution shown in Figure 4 and the concentration of the sulfuric acid solution shown in Figure 5 are obtained. The relationship between the current and the current was obtained.

In addition, 20 of these electrochemical cells (concentration sensors)
ml of 20% sulfuric acid aqueous solution in a container with an internal volume of 30 ml, and when a DC voltage of 3 V was applied between the cathodes 2, 2a, 2b, 2c, 2d and the anodes 3, 3a, 3b, 3c, 3d. Figure 6 A and B show the changes over time in the flowing current, the internal pressure of the sealed container, and the concentration of sulfuric acid.

It can be seen from FIG. 4 that the current of the electrochemical cell (concentration sensor) is directly proportional to the water vapor pressure, and from FIG. 5 it is possible to know the concentration of the sulfuric acid aqueous solution from the current of the electrochemical cell (concentration sensor).

As can be seen from FIG. 6, there was no change in the concentration of the aqueous solution as the measurement time elapsed, and there was no change in the pressure inside the closed container, so it was confirmed that there was no gas generation associated with the measurement. Furthermore, after the measurement, the amount of water in the aqueous solution was measured and it was confirmed that there was no change, indicating that the aqueous solution was not consumed during the measurement.

In addition, the response speed of the electrochemical cell (concentration sensor) when changing the concentration of the sulfuric acid aqueous solution is as fast as approximately 1 minute, and the concentration of sulfuric acid can be continuously measured using this electrochemical cell (concentration sensor). It turns out that it is possible.

Effects of the Invention As described above, according to the present invention, a target aqueous solution can be consumed with a simple operation of applying a constant DC voltage to an extremely small electrochemical cell (concentration sensor) and measuring the current. Since the method does not change the concentration or generate gas, it is possible to safely and continuously measure the concentration of the solute in an aqueous solution even in a closed container. Therefore, it is highly effective in measuring the sulfuric acid concentration in sealed lead-acid batteries, for example.
Its industrial value is extremely high.

[Brief explanation of the drawing]

1 to 3 are cross-sectional structural diagrams showing some examples of electrochemical cells to which the method of the present invention is applied; FIG. 4 is a diagram showing the relationship between the water vapor pressure of an aqueous sulfuric acid solution and the current flowing through the electrochemical cell; Figure 5 is a diagram showing the relationship between the concentration of sulfuric acid aqueous solution and the current flowing through the electrochemical cell, Figure 6 A and B are the current flowing through the electrochemical cell,
FIG. 3 is a diagram showing changes over time in the concentration of an aqueous solution and the internal pressure of a closed container. 1, 1a, 1b, 1c, 1d... ion exchange resin membrane, 2, 2a, 2b, 2c, 2d... cathode,
3, 3a, 3b, 3c, 3d... Anode, 6... Water repellent plastic film.

Claims (1)

[Claims] 1. An electrochemical cell consisting of a bonded body or pressure-bonded body formed by integrally bonding or press-bonding a cathode and an anode to an ion-exchange resin membrane and covering the body with a water-repellent plastic membrane is immersed in an aqueous solution to be measured, and the contact between the cathode and the anode is When a constant DC voltage is applied between them, the current flowing as a result of electrolysis of the water absorbed in the ion exchange resin membrane is substantially directly proportional to the water vapor pressure corresponding to the concentration of the solute in the aqueous solution. In the method of measuring the concentration of solutes in an aqueous solution, hydrogen and oxygen generated during the electrolysis of water are mixed, and an anionic and
A method for measuring the concentration of a solute in an aqueous solution, which is characterized in that the concentration of a solute in an aqueous solution is returned to water using the catalytic action of the electrode on the surface of one or both of the anodes.