JPH0625746B2 - Electrochemical acid gas detector - Google Patents

Description

TECHNICAL FIELD The present invention relates to a detector for electrochemically measuring an acid gas such as hydrogen fluoride gas.

(Prior Art) Acidic gas such as hydrogen chloride or hydrogen sulfide is detected by an electrochemical gas in which a working electrode and a counter electrode are arranged in a container sealed with a gas permeable membrane to contain dilute sulfuric acid as an electrolytic solution. This is performed by using a detector and measuring the oxidation current and the relational current of the test gas dissolved in the electrolytic solution from the gas permeable membrane.

By the way, if hydrogen fluoride gas, which is a kind of acidic gas, is to be detected by this electrochemical type detector, it causes oxidation of hydrogen fluoride gas at the working electrode, that is, a reaction of 2HF → F ₂ ⁻ + 2H ⁺ 2e. , The working station requires an electrode potential of 3.06 V (hydrogen reference electrode potential) or more (FIG. 5).

However, this electrode potential of 3.06 V is much higher than the electrode potential of 1.23 V (hydrogen reference electrode potential) for electrolyzing the water that constitutes the electrolytic solution on the other hand, so that the electrolysis current of water is fluorinated. There is a problem that it is added to the oxidation current of hydrogen gas, and it becomes impossible to measure the oxidation current of hydrogen fluoride gas to be detected.

(Purpose) In view of such problems, the present invention provides an electrochemical acid gas detector capable of detecting various kinds of acid gases including hydrogen fluoride gas without causing electrolysis in an electrolytic solution. The purpose is to do.

(Structure) Therefore, details of the present invention will be described below based on illustrated embodiments.

FIG. 1 shows an embodiment of the present invention. In the figure, reference numeral 1 denotes an electrolyte solution 7 to be described later by providing openings at both ends to provide an acid gas permeable film 2 and an oxygen permeable film 3. In the container for housing the oxygen gas permeable membrane 2, the working electrode 4 is provided, and the oxygen permeable membrane 3 is provided with a third electrode including an oxygen reference electrode 5 such as platinum black. A counter electrode 6 is disposed between the reference electrode 5 and the reference electrode 5 to form a cell. Reference numeral 7 denotes the above-mentioned electrolytic solution, which dissolves potassium iodate KIO ₃ and potassium iodide KI in distilled water to generate a halogenate ion composed of iodate ion IO ₃ ⁻ and a halogen ion composed of iodine ion I ^−. Has been prepared. Between the working electrode 4 and the oxygen reference electrode 5 of the cell thus formed, a DC voltage power source 8 of about -0.73 V is connected with the working electrode 4 side serving as a positive electrode, and the working electrode 4 and the counter electrode 6 are connected to each other. It is connected by a load resistor 9. In the figure, reference numeral 10 is an amplifier for separating the working electrode 4 and oxygen reference electrode 5, and 11 is a preamplifier for amplifying the reducing current flowing through the load resistor 9.

In this embodiment, the hydrogen fluoride gas that has passed through the acid gas permeable membrane 2 is dissolved into the electrolytic solution 7 and is liberated into fluorine ion F ⁻ and hydrogen ion H ⁺ , and the hydrogen ion H ⁺ is iodine in the electrolytic solution 7. 3 molecules of iodine I ₂ are produced by the reaction of 6H ⁺ + IO ₃ ⁻ + 5I ⁻ → 3I ₂ + 3H ₂ O used for the acid ion IO ₃ ⁻ and iodine ion I ⁻ . On the other hand, the working electrode 4 receives a potential of about 0.5 V (potential to the hydrogen reference electrode) from the oxygen reference electrode 5 and the DC voltage power supply 8, and iodine released by acid gas without causing electrolysis of water. I ₂ is caused to generate 2 I ^{− −} by a reaction of I ₂ + 2e → 2 I ₋ , and iodine I ₂ generated in proportion to the hydrogen fluoride gas dissolved in the electrolytic solution 7 is reduced to iodine ion. Needless to say, the reduction current flowing between the working electrode 4 and the counter electrode 6 when reducing the free iodine I ₂ to ions, that is, the load resistor 9, is proportional to the concentration of hydrogen fluoride gas that has passed through the acid gas permeable membrane 2. From
By measuring the terminal voltage of the load resistor 9, the concentration of hydrogen fluoride gas can be obtained.

FIG. 2 shows a second embodiment of the present invention, in which an opening is formed at one end to provide the acidic gas permeable membrane 2 and the above-mentioned electrolytic solution 7 is formed.
The working electrode 4 is disposed on the side of the acidic gas permeable membrane 2 of the container 12 in which is stored, and the counter electrode 13 made of platinum also serving as a reference electrode is disposed facing the working electrode 4, and the side of the working electrode 4 is used as a load. A DC voltage power supply 14 of about 0.3 V (with respect to the hydrogen reference electrode potential) is connected, and the working electrode 4 and the counter electrode 13 are connected by a load resistor 15.

According to this embodiment, the working electrode 4 has a constant potential of 0.8 which is determined by the concentration of atmospheric saturated oxygen dissolved in the electrolytic solution 7.
I ₂ + 2e → 2I ⁻ without receiving electrolysis of the electrolytic solution 7 by receiving a constant potential in which the voltage (reference electrode potential for hydrogen) is lowered to a potential of about 0.5 V by the DC voltage power supply 14. By the reaction, iodine I ₂ liberated in proportion to the hydrogen fluoride gas dissolved in the electrolytic solution 7 is reduced to iodine ions.

FIG. 3 shows a third embodiment of the present invention,
A silver is placed in a container 12 which has an opening at one end and is sealed with an acid gas permeable membrane 2 to contain the above-mentioned electrolyte solution 7 and a working electrode 4 is disposed on the acid gas permeable membrane 2 side. / A counter electrode 16 made of silver iodide is provided.

According to this embodiment, the working electrode 4 receives a potential of about −0.15 V (reference electrode potential for hydrogen) generated by the counter electrode 16 formed of silver / silver iodide and the electrolytic solution 7. Without causing electrolysis of water, the reaction I ₂ + 2e → 2I ⁻ reduces iodine I ₂ liberated in proportion to the hydrogen fluoride gas dissolved in the electrolytic solution 7 to iodine ion 2I ⁻ , Acidic gas can be detected accurately without the need for an external DC voltage power supply.

FIG. 4 shows a fourth embodiment of the present invention, in which an opening formed at one end is sealed with an acidic gas permeable membrane 2 and the acidic gas permeation of the container 12 containing the electrolytic solution 7 described above. In the cell having the working electrode 4 on the side of the membrane 2 and the counter electrode 16 made of silver / silver iodide, the potential of the working electrode 4 can be reduced by free halogen and oxygen can be reduced. The potential which is not allowed, that is, the electrode potential which is lower than the oxidation potential of free halogen and higher than the reduction potential of oxygen, for example, 0.3 to 0.5.
DC voltage power supply 1 that gives a potential that can be held in volts
7 is connected.

According to this embodiment, the hydrogen fluoride gas that has passed through the gas permeable membrane 4 dissolves in the electrolytic solution 5 and is liberated into fluorine ions F ⁻ and hydrogen ions H ⁺ , and the hydrogen ions H ⁺ are iodine in the electrolytic solution 5. It acts on the acid ion IO ₃ ⁻ and the iodine ion I ⁻ to cause a reaction of 6H ⁺ + IO ⁻ + 5I ⁻ → 3I ₂ + 3H ₂ O to generate 3 molecules of iodine I ₂ . On the other hand, the working electrode 4 is maintained at an electrode potential below the oxidation potential of free halogen and above the reduction potential of oxygen by the DC voltage power supply 17 connected between both electrodes.
The iodine molecule I ₂ is reduced to the iodine ion 2I ⁻ by selectively causing only the reaction of I ₂ + 2e → 2I ⁻ without reducing the oxygen dissolved therein. Thereby, the acid gas concentration can be accurately detected regardless of the amount of dissolved oxygen in the electrolytic solution 7.

Incidentally, in the above-mentioned embodiment, the explanation has been made by taking the hydrogen fluoride gas, which cannot be detected conventionally, as an example, but other acidic gas such as chloride, which is liberated when dissolved in water, produces hydrogen ions. It is obvious that it can be applied to the detection of hydrogen gas, chlorine gas, carbon dioxide gas, and the like.

Further, in the above-mentioned examples, an aqueous solution of potassium iodate and potassium iodide is used as the electrolytic solution, but the electrode is subjected to reduction by an electrode potential whose reduction voltage is lower than the electrolysis voltage of water. 6H ⁺ + ClO ₃ A halogenate ion such as ⁻ + 5Cl ⁻ → 3Cl ₂ 3H ₂ O 6H ⁺ + BrO ₃ ⁻ + 5Br ⁻ → 3Br ² + 3H ₂ O and a reaction between a halogen ion and a hydrogen ion can be used. Needless to say, in this case, the working electrode 16 in the embodiment shown in FIGS. 3 and 4 is obviously formed of silver / silver chloride or silver / silver bromide, respectively. Furthermore, in the above-described embodiment, the working electrode 4 and the counter electrodes 6 and 16 are connected by the load resistor 9, but the electrodes 11 are connected by using the input impedance P of the amplifier 11 that amplifies the reducing current. The load resistance of can be omitted.

Incidentally, in this embodiment, the explanation has heretofore been made by taking an undetectable hydrogen fluoride gas as an example, but an acidic gas which liberates hydrogen ions when dissolved in water, for example, hydrogen chloride gas, chlorine gas It is obvious that it can be applied to the detection of carbon dioxide gas and the like.

(Effect) As described above, according to the present invention, since the halogenate ion and the aqueous solution in which the halogen ion is dissolved are used as the electrolytic solution, the low reduction voltage of the halogen molecule can be utilized, and the electrolysis of water can be performed. Acid gas can be electrochemically measured with high accuracy without causing

Also, since an aqueous solution in which halogen ions and halogen ions are dissolved is used as the electrolytic solution, and the counter electrode is formed of silver and silver halide, an external DC voltage power supply is unnecessary, and a potential sufficient to reduce halogen molecules is provided. Acidic gas can be electrochemically measured with high accuracy without being applied to the working electrode to cause electrolysis of water.

Further, an aqueous solution in which halogen ions and halogen ions are dissolved is used as an electrolytic solution, and a counter electrode is formed of silver and silver halide, and the potential thereof is set to 0.3 to 0.
Since the voltage is maintained at 5 V, not only the reduction voltage of halogen molecules can be used to prevent the electrolysis of water and the reduction of oxygen in the air that dissolves in the electrolytic solution to improve the measurement accuracy. It is possible to prevent unnecessary consumption of halogen ions due to the dissolution of oxygen and extend the life of the counter electrode formed of silver / silver iodide.

[Brief description of drawings]

1 to 4 are configuration diagrams of an apparatus showing an embodiment of the present invention, and FIG. 5 is an explanatory diagram showing an oxidation-reduction state. 2 ... Acidic gas permeable membrane 4 ... Working electrode, 5 ... Oxygen reference electrode 6, 13 ... Counter electrode, 7 ... Electrolyte solution 8, 14 ... DC voltage power supply, 16 ... Counter electrode 17 ... DC voltage power supply

Claims (3)

[Claims] 1. A container sealed with a gas permeable membrane, a counter electrode, a working electrode in the vicinity of the gas permeable membrane, an electrolytic solution containing halogenate ions and halogen ions, and a working electrode. An electrochemical acid gas detection device, wherein a potential higher than the reduction potential of oxygen and lower than the oxidation potential of free halogen is applied. 2. The electrochemical acid gas detector according to claim 1, wherein the counter electrode is composed of silver / silver halide. 3. The electrochemical acid gas detection device according to claim 1, wherein the potential is 0.3 to 0.5 volt.