JPS607223B2 - Oxidizing gaseous substance measuring electrode - Google Patents

Description

[Detailed description of the invention] A continuous coulometry method (continuous coulometric titration method) using potassium bromide and potassium iodide solutions as electrolytes as a method for continuously measuring oxidizing gaseous substances such as chlorine, ozone, and oxidants. A method is known.

The present invention relates to improving the practicality and characteristics of an apparatus for measuring oxidizing gaseous substances using this continuous coulometry method.

First, the basic principle of measurement of oxidizing gaseous substances by continuous coulometry will be explained using the measurement of chlorine gas as an example.

A solution of potassium bromide (potassium iodide is also used, but potassium bromide will be explained here) is interposed between the two platinum electrodes.

A solution of potassium bromide (KBr) dissociates to produce bromide ions (Br-) as follows. Fox Br→Fox Jujuha r
-(M is a monovalent metal) (1) Also, water is slightly dissociated to produce hydrogen ions.

Germany 01 Jugen H- '2} When a suitable DC voltage (usually about 0.2 to 0.3 V) is applied between two platinum electrodes, a current flows at first, but as the current flows, it increases for two days. The reaction proceeds to produce hydrogen (day 2), and a polarization phenomenon occurs between the electrodes, causing current to no longer flow.

If chlorine gas comes into contact with a place under such conditions,
The reaction 10CI2-Br212CI- {4} takes place, and the bromine ion is oxidized to bromine (Br2), which subsequently reacts with the hydrogen produced by the polarization (see glue formula) to form Br20. Day 2 → 2H+2Br- As shown in '51, the hydrogen in the electrode portion (Day 2) becomes hydrogen ions (H+) and is removed, and the polarization phenomenon is canceled (depolarized), so that current begins to flow.

The magnitude of this current is proportional to the amount of chlorine in contact with it, so if the conditions for introducing the sample gas are kept constant, the chlorine concentration can be measured by measuring this current. The above is the principle of measurement of oxidizing gaseous substances by the continuous coulometry method. An example of a conventional measuring device based on this measurement principle is shown in Fig. The cathode 2 is formed by winding the anode 2, and a one-turn anode 3 is provided below it, and a current voltage 4 of about 0.2 to 0.3 V is applied between the two to form a detector, and the electrolyte above the detection part is A potassium bromide (or potassium iodide) solution (electrolyte) 6 from a tank 5 is made to flow as a liquid film over the electrode surface at a very small flow rate, while the sample gas is brought into contact with this liquid film at a constant flow rate. The concentration of oxidizing gaseous substances such as chlorine can be determined by introducing the current flowing between the two electrodes and measuring the current flowing between the two electrodes with an ammeter 7.

In addition, in the official map, "8' is the sample gas inlet, and 9 is the sample gas exhaust pipe. In this measurement system, as can be seen from the chemical reaction equation above, bromine produced by reaction with chlorine etc. ``As the bromine ions return to their original form through an electrochemical reaction, the bromine ions are not consumed, but if measurements are continued without replenishing the potassium bromide solution, water will be lost through evaporation and solidification will occur.'' Therefore, we had to find a way to continuously supply electrolyte to the detection part.Therefore, with such a device,
Periodic preparation and replenishment of the electrolyte was required, making maintenance of the measuring device time-consuming, and the device was large due to the electrolyte storage tank, making it inconvenient to handle. By the way, in order to solve these drawbacks, deliquescent bromides (for example, lithium bromide,
The invention of methods using solutions of calcium bromide, magnesium bromide, etc.) or iodides (e.g. calcium iodide, magnesium iodide, etc.) greatly improved practicality and performance.

An example of the structure is shown in Fig. 2, where 1' is an electrode support body with a non-conductive liquid retaining material such as glass cloth on its outer surface.
A sheet of gauze, sponge, etc. or felt 10 is impregnated with a deliquescent bromide or iodide solution, and a platinum wire (
The cathode 2 and the anode 3 are made by winding silk (silk) and forming the cathode 2 and the anode 3.
．． The structure is such that a DC voltage 4 of 3V is applied and the current flowing between the two electrodes is measured by an ammeter 7. When an oxidizing gas such as chlorine gas comes into contact with this detection part, a current flows and the chlorine gas can be measured, which is the same as with conventional devices, but because a solution of a deliquescent substance is used as the electrolyte, In addition, the electrolyte always remains in a liquid state in equilibrium with the moisture in the air and does not evaporate to dryness. It became possible to perform continuous measurements. As a result, the trouble of periodic preparation and replenishment of electrolyte solution has been eliminated, resulting in a major advance in terms of equipment maintenance.In addition, an electrolyte storage tank has been eliminated, making the equipment configuration compact and convenient to carry. , many advantages were obtained. Great progress was made by using a deliquescent bromide solution as an electrolyte, but as a result of a detailed study of the characteristics of the electrode with the structure shown in Figure 2, it was found that It was found that there were some problems.'1
1. Being affected by wind speed.

When this detector is installed in the air and used to detect chlorine gas in the air, the output current changes as the wind speed changes even if the chlorine concentration remains unchanged.

(2' It takes a long time to return to zero after detecting chlorine gas. If the electrode is in contact with chlorine gas of about 3 pm for about 3 minutes, the response speed of return when the chlorine gas concentration becomes zero from then on is very slow, about 2 hours with 90% response.

{3} Poor reproducibility of electrode output current.

The electrodes shown in Fig. 2 are configured in the experimental apparatus shown in Fig. 3, and approximately 4 p.m.
When we investigated the reproducibility of the output current by alternately introducing pm chlorine gas and gas with zero chlorine concentration at a constant flow rate, we obtained the results shown in Figure 4, and each time we repeated the introduction of chlorine gas, There is a phenomenon in which the output current increases.

In addition, in Fig. 3, 11 is a chlorine standard gas cylinder;
2 is a pure nitrogen gas cylinder, 13 is a switching cock, 14 is an electrode, and 15 is a container for introducing chlorine standard gas or pure nitrogen gas, to which the electrode 14 is attached. 4 is a power source for applying a DC voltage to the electrodes, and 7 is an ammeter for measuring the electrode output current.

■ The electrode output current for a constant gas concentration is not constant.

Figure 5 shows the electrode output current when a gas with a constant concentration of about 0.3 ppm is passed for a long time using the apparatus shown in Figure 3.
The output current was not constant and showed a tendency to continue to rise little by little.

This means that when this electrode is used as a concentration alarm, even if a harmlessly low concentration of gas is present, it will eventually issue an alarm. {5' If the electrode gets wet with water, the detection ability will be lost.

As can be seen from the structural diagram in Figure 2, when exposed to water, the electrolyte is washed away and the characteristics are lost.The above phenomenon also occurred with other oxidizing gases other than chlorine gas.

In other words, an electrode using deliquescent bromide with the structure shown in Figure 2 requires almost no maintenance as long as it is used as a leak detector for chlorine gas, etc., when the concentration is completely zero under normal conditions. Although it is very useful due to its features, it has been found that it has drawbacks that prevent it from being used for the purpose of measuring concentration.

The present invention relates to an electrode of a new structure that has all the advantages of the above-mentioned electrodes, such as maintenance-free, compact size, and eliminates all the disadvantages of the above-mentioned detectors.

An example of the electrode structure according to the present invention is shown in FIG. 6, where 1 is an electrode support tube, 16 is a gas permeable diaphragm adhered to the tip of the electrode support tube 1, 2 is a cathode, and 17 is a lead wire from the cathode. , 3 is the anode, 18 is the leader line from the anode,
19 is an internal solution (electrolytic solution, a solution whose main component is deliquescent bromide or iodide), and 4 is 0.2 between the cathode and anode.
A power supply provides a DC voltage of ~0.3V, and 7 is an ammeter for measuring the current flowing between the cathode and the anode.

FIG. 7a shows another example of the electrode structure according to the present invention,
1 is an electrode support tube, 19 is an internal solution (a solution whose main component is deliquescent bromide or iodide), 2 is a cathode, IT is a lead wire from the cathode, 3 is an anode, 18 is a lead wire from the anode, 16 is a lead wire from the anode. The diaphragm is attached to two diaphragm supports. 21 is a diaphragm support fixture, and an O-ring 22 is used to airtightly attach the corneal diaphragm support 20 to the electrode support tube as shown in the figure.

In an electrode having such a structure, attachment and detachment of the diaphragm 16 is performed using the diaphragm support 2.
Since the diaphragm is replaced every 0 minutes, it is extremely easy to attach and remove the diaphragm when replacing the internal fluid, etc., and care must be taken to avoid wrinkles and leakage of the internal fluid when attaching the diaphragm. The electrode with this structure has the feature that these requirements can be achieved extremely easily without requiring any skill.Furthermore, with this diaphragm attachment method, the attachment state can always be reproduced in a constant state, so it is easy to replace the diaphragm. However, the change in electrode output is slight.
An exploded state of the electrode having the structure shown in FIG. 7b is shown in FIG.

Next, as an example of the present invention, an electrode having the structure shown in Fig. 7 (hereinafter referred to as a diaphragm type electrode) was used, and its characteristics were investigated using chlorine gas as the oxidizing gas, and the following results were found. The results were obtained.

As for the internal liquid, about 50 g of lithium bromide is mixed with about 1 g of water.
Approximately 50% of the solution was used, and platinum plates of approximately 50% x 1mm were used for the cathode and anode. Next, the results obtained are described.

1. Not affected by wind speed.

This electrode was attached to the experimental apparatus shown in Fig. 3 ~ approx.

As a result of passing 5 ppm gas at various flow rates and examining the relationship between flow rate and electrode output, we obtained the relationship shown in Figure 8.If the flow rate (wind speed) is 0.03/sec or more, the electrode output is It was found to be almost constant.

Meteorologically, wind speed is often expressed in terms of wind power, and a state where smoke is rising straight up is called zero wind power, but zero wind power is defined as a wind speed of 0 to 0.2 skin/sand. According to the experimental results shown in FIG. 8, it is clear that the electrode output is constant as long as the wind speed is equal to or higher than the upper limit wind speed of about 1/7 of the wind speed of 0. Therefore, it was possible to significantly improve the performance compared to the electrode with the conventional structure shown in FIG. 2 (hereinafter referred to as an exposed electrode). ■ Fast response speed and quick return to zero.

Using the experimental apparatus shown in FIG. 3, chlorine gas of about 100 pm was introduced, followed by 100 ml of chlorine gas.

FIG. 9 shows the recording results of the output of the diaphragm electrode when gas was introduced. When the electrode came into contact with chlorine gas, the response speed of the electrode output was extremely slow at 90% response, about 12 seconds, and when switching to zero gas, the response time for the electrode output was extremely fast, at about 14 seconds for 90% response. Furthermore, in order to compare with conventional exposed-type electrodes, we investigated the return response speed of the electrode output when switching to zero gas after continuously introducing chlorine of about 1 pm for about 6 hours. Even after passing through chlorine for an extremely long period of time, the 90% return to zero response is approximately 1 minute, which is significantly faster than the 90% response of conventional exposed electrodes, where the 90% response to zero is measured in hours. It is clear that progress has been made.鐐 The reproducibility of the electrode output is extremely good.

Figure 10 shows the recording results of the electrode output when approximately pm chlorine gas and zero gas were alternately repeated using the apparatus shown in Figure 3, but the characteristics of the exposed electrode (Figure 4) and It can be seen that the reproduction accuracy has been significantly improved.

{4} The electrode output for a constant concentration of chlorine gas is stable.

FIG. 11 shows the recording results of the electrode output when approximately pm of chlorine was continuously introduced for about 3 hours, and the electrode output was extremely stable.

It is shown that significant progress has been made in terms of stability compared to the exposed electrode, where the output of the electrode relative to chlorine gas always continued to rise slightly and never stabilized.

{5) Even if the electrode gets wet with water, the detection ability will not be lost.

The electrolyte (internal solution) is covered with a diaphragm along with the cathode and anode, and is held airtight by an O-ring.
Unlike exposed electrodes, they do not lose their sensing ability even when exposed to water or after being immersed in water. '6) Maintains detection ability for a long time without any maintenance.

As the electrolyte (internal solution), as in the case of exposed electrodes,
Since a solution of a deliquescent substance is used, the electrolyte does not evaporate to dryness and can be used continuously for a long time without losing detection ability without replenishing the electrolyte.As described above, the diaphragm type according to the present invention The electrode overcomes all of the drawbacks of exposed electrodes.

In addition, as a chlorine detection electrode using a diaphragm, the 12th
An electrode with the structure shown in the figure has been published, but although it uses a diaphragm, unlike the diaphragm-type electrode according to the present invention, it has several problems.

First, the structure will be explained. 23 is a gas permeable diaphragm;
24 is a ring for holding a diaphragm, 25 is a working electrode, 26 is a counter electrode, 27 is a counter electrode cover, 28 is an electrolytic solution tank, 29 is an electrolytic solution tank, and 30' is an electrode protection cover.

By the way, with this electrode structure, the flat sheet-shaped corneal membrane is placed over the tip of the cylindrical electrode as shown in the figure, and the circumference is secured with a ○ ring, so wrinkles occur at the 0-ring part. This may cause the electrolyte inside to leak out. Furthermore, wrinkles are likely to occur in the portion of the electrode tip that comes into contact with the working electrode 25.

By the way, since it is impossible to always reproduce wrinkles in the same state every time the diaphragm is replaced, there is a possibility that the electrode output of the electrode with this structure changes greatly every time the diaphragm is replaced. Next, in this electrode, since the electrolyte used as the internal solution is not a deliquescent liquid solution, water becomes water vapor and evaporates through the diaphragm, gradually reducing the electrolyte. It is necessary to store the electrode, and therefore, as shown in FIG. 12, the electrode must be quite large, which is inconvenient for use.

Furthermore, despite this, it is necessary to replenish the electrolyte approximately once every three months, which is troublesome in terms of maintenance. There is also concern about changes in properties during that time as the
In contrast, the diaphragm-type electrode according to the present invention uses a solution of a deliquescent substance as the electrolyte, so it does not evaporate to dryness and maintains a solution state while maintaining equilibrium with the humidity in the air. Therefore, there is no need to replenish the electrolyte, and the concentration of the electrolyte changes only slightly due to changes in the humidity in the air, and the electrode characteristics are stable.As detailed above, The diaphragm-type electrode according to the present invention not only has many superior properties not found in the conventional diaphragm-type electrodes, but also has many excellent properties that are not found in conventional diaphragm-type electrodes. ``Figure 2 is an example diagram including the electrode structure of the conventional measuring device, Figure 3 is a diagram of the experimental equipment used to measure the electrode characteristics of the conventional and present invention shown in Figure 2, and Figure 4. , Fig. 5 is the output current characteristic diagram of the conventional electrode in the experimental apparatus shown in Fig. 3, Fig. 6 and Fig. 7 a.
are electrode structure diagrams according to embodiments of the present invention, and FIG. 7b, respectively.
8 and 9 are exploded views of an electrode according to an embodiment of the present invention.
10 and 11 are electrode characteristic diagrams obtained when an experiment was carried out by combining the electrode according to an embodiment of the present invention as shown in FIG. 7 with the experimental apparatus shown in FIG. 3, and FIG. FIG. 2 is a cross-sectional view of a diaphragm type electrode.

1... Electrode support tube, 2... Cathode, 3...
・Anode, 4...Power supply, 7...Ammeter, 16
...Gas permeable diaphragm, 17...Leader line from the cathode, 18...Leader line from the anode,
19...Internal solution (electrolyte), 20...
Diaphragm support, 21... Diaphragm support fixture, 22
・…”○ ring.

Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12

Claims (1)

[Scope of Claims] 1. In an electrode support tube whose lower opening is closed with a gas-permeable diaphragm, a cathode to which a current-carrying lead wire is connected is disposed close to the gas-permeable diaphragm, and an appropriate connection is made between the cathode and the electrode support tube. Arrange anodes connected to energizing lead wires at intervals,
A solution mainly composed of a deliquescent substance consisting of bromide or iodide of lithium, calcium, and magnesium, or a mixture thereof is contained as an internal liquid so as to immerse the cathode and anode in the electrode support tube. An oxidizing gaseous substance measuring electrode characterized by: 2 A gas-permeable diaphragm adhered to a diaphragm support,
The oxidizing gaseous substance measuring electrode according to claim 1, wherein the opening at the bottom of the electrode support tube is closed via an O-ring.