JPS5918661B2 - gas analysis method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas analysis method using electrolysis, and more particularly to a gas analysis method for fractionating and quantifying gases containing nitrogen oxides, sulfur dioxide, etc. by electrolytic reduction.

As a gas analysis method using an iron complex, a method using a solution of ferrous aminocarboate complex (Japanese Patent Application No. 102861/1988) or ferrous oxycarboate complex (Japanese Patent Application No. 15701/1989) as an absorbent. It has been known.

Using these absorption liquids has the following advantages in gas analysis. (1) In particular, when using an aminocarboatoferrous complex, it is possible to completely absorb both nitrogen oxides and sulfur dioxide, making it possible to eliminate the need for standard gases used to calibrate general gas analyzers. .

That is, it has become easy to adjust the standard solution by adding sodium nitrite and sodium sulfite to calibrate the analyzer. (2) Absorption rate for nitrogen oxides and formation constant of trosyl complex = [Fe(No)
L]/([Fe(■)L]・PNo), however, Fe(N
o) L is a nitrosyl complex, F(■)L is a ferrous complex, P
Since NO has a high partial pressure of nitrogen monoxide, the concentration of the substance to be measured in the solution increases, making it possible to increase the sensitivity of gas analysis.

In addition, compared to gas analysis using conventional potentiostatic electrolysis method (can measure both sulfur dioxide and nitrogen oxides), it has extremely high selectivity, and one detector can measure the highest Ξ components (oxidizing substances, Although it has advantages such as being able to measure sulfur dioxide and nitrogen oxides, it has the following disadvantages. (1) When used as an automatic analyzer, it is preferable to use the solution after rinsing it.

<When using Kugaeshi, substances generated when sulfur dioxide and nitrogen oxides are absorbed into the solution (sulfur dioxide and nitrosyl complex)
It is necessary to reduce the concentration of the product in the liquid by providing a process for treating it, and as one method, an electrolytic treatment process has been provided. Another possible method is to take time to sample until the solubility equilibrium of each component is achieved, but this is not preferable as it requires a long time. In addition, when reducing and eliminating sulfur dioxide and nitrosyl complexes in this electrolytic process, problems such as the generation of free sulfur occur during reduction, and depending on the electrode reaction rate, this electrolytic elimination takes time. I had a problem with it. (2) In the case of the reaction between ferrous iron complexes and oxygen, very radical chemical species (such as 0H radicals) are generated as one of the intermediate products during the reduction of oxygen, which attacks the ligands of the iron chain. , there is a problem of degrading the ligand.

If the concentration of the ligand decreases, the concentration of the ferrous complex, Fe()L1, will also decrease, which in turn will reduce the concentration of the nitrosyl complex in the solution, even if the concentration of nitrogen oxides in the gas remains constant. Therefore, in order to obtain stable measured values, it is necessary to add new ligands in accordance with the amount of ligands that are deteriorating. An object of the present invention is to eliminate the drawbacks (1) and (2) above and to provide a gas analysis method using electrolysis that enables stable automatic analysis.

The present invention provides an aqueous solution containing a ferrous compound and having a hydrogen ion concentration of 1 or less by adding an inorganic acid.
Contact with a gas containing at least one of nitrogen oxides, sulfur dioxide, and an oxidizing component capable of oxidizing the ferrous compound in the solution, and electrolyze the chemical species generated in the solution by the contact. quantification, thereby measuring the concentration of at least one component among the three components in the gas.

As the absorption liquid in the present invention, an aqueous solution of an acidic ferrous compound made of an inorganic acid is used.

Ferrous iron generates a nitrosyl complex from nitrogen monoxide and nitrogen dioxide, and reacts with oxidizing components to become ferric iron. As long as the rate at which these reactions occur is constant, both components b1 can be quantified with high accuracy. In addition, sulfur dioxide quickly creates a solubility equilibrium with this acidic solution b1 and
It is possible to measure this dissolved sulfur dioxide with high accuracy. When the acidity of the solution decreases, the solubility equilibrium of sulfur dioxide increases, and the amount of dissolved sulfur dioxide relative to the nitrosyl complex becomes large in excess, which interferes with the detection and quantification of the nitrosyl complex. In the absorption liquid of the present invention, the solubility equilibrium of nitrogen oxides is extremely small compared to conventional absorption liquids using iron citrate, etc. Therefore, regarding nitrogen oxides, the maximum amount of nitrosyl It is necessary to form a complex in a liquid to make the detection and quantification of nitrosyl complexes as easy as possible. Also, as long as the acid concentration is constant, b1 nitrogen oxides,
Measurements of sulfur dioxide are more accurate when carried out under dissolution equilibrium conditions. For this reason, it is desirable to increase the acidity of the solution, especially for sulfur dioxide, in order to shorten the time until dissolution equilibrium as much as possible and increase the response speed. It is desirable to use mercury for the detection electrode in the present invention except for the detection of oxidizing components. Mercury has a large hydrogen overvoltage and can completely eliminate interfering reactions such as hydrogen generation reactions. The detection and quantification of the oxidizing component is carried out at the most noble electrode potential of the three components, and here, even with other electrode materials, interference due to hydrogen generation is not a problem. The reaction between oxidizing components such as oxygen and ferrous iron is irreversible, and one reaction product, ferric iron, accumulates in the liquid, so it must be constantly reduced.

Therefore, in the present invention, an electrode for ferric reduction is required, but since the electrolytic current at this electrode can be compared with the concentration of oxidizing components, the electrolytic current or quantity of electricity can be used as an index to reduce the oxidizing components. It becomes possible to measure the concentration of When measuring the concentration of the above gases, an absorption liquid is placed in an electrolytic cell having a mercury electrode and an electrode made of mercury or other material as working electrodes, the above gas is introduced, and the mercury electrode in the electrolytic cell is used to measure the concentration of the above gas. , the concentration of at least one component among nitrogen oxides, sulfur dioxide, and oxidizing components is measured, and the other electrode is used to reduce ferric iron to ferrous iron, and this reduction current value or quantity of electricity is measured. By detecting this, the concentration of oxidizing components in the gas is measured.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Using the detector shown in Figure 1, nitrogen monoxide, sulfur dioxide,
Using a mixed gas of oxygen and nitrogen as a sample, we examined the quantitative performance of the detector by varying the concentrations of each gas.

As the absorption liquid, a (1+4) phosphoric acid acidic 0.2 mO1-3 ferrous sulfate aqueous solution was used. (1+4) phosphoric acid was used as the counter electrode solution, and both solutions were separated using an anion exchange membrane. The cathode 4 for reducing ferric iron in the absorption liquid 1 was a platinum wire mesh electrode, and sulfur dioxide and nitrosyl complexes were detected and measured by a DC electrolysis method using a rotating mercury electrode 7 by an AC polarographic method. Here, what is AC polarographic method?
It sweeps a DC voltage with alternating current superimposed on the detection electrode.
As shown in FIG. 3, a change in conductivity is observed as an output. The detection electrode 7 is a rotating mercury electrode of a thin film supporting type, in which the lower end of a glass tube having an inner diameter of 6 mm is closed with a porous membrane, and the membrane holds mercury. The electrode potential of the platinum cathode 4 was maintained at -0.2 vs. SCE at the reference electrode 9.

Mixed gas 100dTI1J with known concentration of each component
n-1 was passed through the gas introduction tube 10 into the catholyte 1 of the detector, and the measured values of each electrode after 10 minutes were recorded. nitric oxide,
Correlation curves between the concentrations of sulfur dioxide and oxygen in the gas and the measurement results are shown in FIGS. 3 and 4. In the figure, A is a calibration curve for sulfur dioxide, B is a calibration curve for nitrogen monoxide, and C is a calibration curve for oxygen. As is clear from the figure, good calibration curves were obtained in all cases, and the method of the present invention has sufficient performance for measuring nitric oxide and sulfur dioxide at the pus level and oxygen at the percent level. That is clear. Next, using the above-mentioned mixed gas containing no oxygen, the circuit of the cathode 4 was opened and similar measurements were carried out, and as in the case of FIG. 3, a good calibration curve was obtained.

Comparative Example 1 Using the detector shown in Figure 1, except for the absorption liquid composition, Example 1 was used.
Measurements were carried out in the same manner.

As absorption liquid 1, a 1 m0 I-Dm-3 monosodium dihydrogen phosphate aqueous solution containing 0.01 m01-h-3 iron ethylenediaminetetraacetate was used. In this case, after introducing the gas,
Even after 0 minutes, stable measured values like those in Example 1 were not obtained. Therefore, the potential of the platinum cathode 4 is set to -0
．． When the voltage was set at 85 V vs. SCE, a stable measured value was obtained about 25 minutes after the gas was introduced. As described above, the absorption liquid of this comparative example required a long time for response. Next, when a phosphoric acid acidic sodium phosphate aqueous solution (adjusted to PH3) containing 0.01 m01-Dm-3 iron citrate was used as absorption liquid 1, under the conditions of Example 1, 30 minutes had passed after gas introduction. However, as in Example 1, stable measured values could not be obtained.

Therefore, the potential of the platinum cathode 4 was set to -0.85 V vs. SCE, and a stable measured value was obtained about 20 minutes after the gas introduction. In this case too, a long time was required for response. In measurements using these absorption liquids, measurement tests were conducted with the gas composition being a mixture of nitrogen monoxide, sulfur dioxide, and nitrogen, and with the same conditions except for the exclusion of oxygen, an oxidizing component. At a potential of -0.3 V vs. SCE, no steady measured value was obtained even after 30 minutes had passed after gas introduction, which was different from the case of Example 1.

However, when the platinum electrode potential was set to -0.85 V vs. SCE, stable measured values could be obtained approximately 20 minutes after gas introduction. This is carried out for approximately 20 minutes until the amount of the electrolyte absorbed in the absorption liquid 1 and generated undergoes electrolysis at an electrode with a potential of -0.85 vs. SCE and the amount newly generated become approximately constant. This is thought to be because it takes several minutes. However, when the platinum electrode potential is -0.3 vs. SCE, the products in the absorption liquid derived from nitrogen monoxide and sulfur dioxide do not undergo electrolytic reduction, so in order for the product concentration in the liquid to be constant,
One must wait until absorption equilibrium is achieved, which may take an hour or more. Example 2 Using the detector shown in Figure 2, nitrogen monoxide, sulfur dioxide,
Using a mixed gas of oxygen and nitrogen as a sample, we examined the quantitative performance of the detector by varying the concentrations of each gas.

The absorption liquid is (1+1) phosphoric acid acidic 0.05m01-Dm-
An aqueous solution of ferrous sulfate was used. For the counter electrode (1+1)
Phosphoric acid was used, and both liquids were separated using a porous ethylene fluoride resin membrane. The cathode 5 for reducing ferric iron is a mercury pool electrode, the hanging drop mercury electrode 8 is a detection electrode for sulfur dioxide and nitrosyl complexes, and the mercury pool electrode potential is -0.2.
As V, while electrolyzing with ferric iron using a direct current method, sulfur dioxide and a nitrosyl complex were measured using an AC polarographic method using a hanging mercury electrode, and the height of the observed waves was measured.
The wave height 10 minutes after gas introduction and the concentration of each gas show a good linear relationship in the concentration range studied, and especially in the case of nitrogen monoxide and sulfur dioxide, a calibration curve passing through the origin can be obtained. The concentration range of each gas is nitric oxide 0 to 446,
Sulfur dioxide is 0-662 pus, oxygen is 0-2170. Next, oxygen was measured by directly reading the electrolytic current value of the mercury pool electrode 5, without using the hanging mercury electrode.

In this case as well, a good calibration curve could be obtained for oxygen concentrations of 0 to 21%. Furthermore, the detector with this absorption liquid composition operated very stably even after a total operating time of more than 10 hours and a standing time of more than 20 days.

Comparative Example 2 Using the detector shown in FIG. 1, measurements were carried out under the same conditions as in Example 2 except for the absorption liquid.

The absorption liquid used was a phosphoric acid aqueous sodium phosphate solution (adjusted to PH3) containing 0.01 mO1-3 iron citrate, and the mercury pool electrode potential was -0.85 V vs. SCE. When the iron citrate concentration in the absorption liquid was measured after measuring oxygen concentrations ranging from 0 to 21% for about 10 hours, it was found to be 0.0.
It had decreased to 06m01-Dm-3. Also, during this measurement, the sensitivity of this detector to nitrogen monoxide and sulfur dioxide gradually decreased. Comparative Example 3 Using the detector shown in FIG. 2, measurements were carried out under the same conditions as in Example 2 except for the absorption liquid.

(1+1) phosphoric acid was used as the absorption liquid, the detection electrode 8 was a dropping mercury electrode, and the potential of the mercury pool electrode 5 was set to -0.2 V vs. SCE. In this case, the same results as in Example 2 were obtained regarding sulfur dioxide. Regarding oxygen,
Dissolved oxygen in the absorption liquid 1 could be measured satisfactorily by the AC polarographic method. However, with regard to nitric oxide, there is no ferrous iron, and it is present in the absorption liquid as a nitrosyl complex.
It was impossible to measure in the concentration range of 0 to 446 PP1. The experiment in Example 2 was conducted under exactly the same conditions except that a 2N sulfuric acid acidic 0.1 m01-Dm-3 ferrous sulfate aqueous solution was used as the absorption liquid 1.

As a result, good calibration curves were obtained for nitrogen monoxide, sulfur dioxide, and oxygen. As described above, according to the present invention, it is possible to stably measure nitrogen oxides and sulfur dioxide at a high level, and oxidizing components from a percent level to a low level over a long period of time. Comparing the method of Japanese Patent Application No. 53-15701, in addition to these advantages, it has the advantage that automatic measurement is extremely easy and stable sensitivity can be obtained even for long-term measurements.

Therefore, it is extremely effective for automatically measuring nitrogen oxides, sulfur dioxide, and oxidizing components in combustion exhaust gas.

[Brief explanation of the drawing]

1 and 2 are schematic sectional views showing an embodiment of the gas analysis detector used in the present invention, and FIGS. 3 and 4 are
FIG. 3 is a diagram showing a calibration curve in an example of the present invention. 1... Absorption liquid (catholyte) containing a ferrous compound,
2...Counter electrode (anolyte), 3...Diaphragm, 4...Cathode (platinum), 5...Cathode (
mercury), 6... Counter electrode (anode), 7...
Rotating mercury electrode, 8... Hanging mercury drop electrode or dropping mercury electrode, 9... Reference electrode, 10...
・Gas introduction pipe, 11...Mercury, 12...
・Lead wire, 13... Rotating rod for stirring.

Claims (1)

[Claims] 1. An oxidizing component capable of oxidizing nitrogen oxides, sulfur dioxide, and the ferrous compounds in the solution, which contains an aqueous solution containing a ferrous compound and having a hydrogen ion concentration of 1 or less by adding an inorganic acid. The solution is brought into contact with a gas containing at least one of the three components, and the chemical species generated in the solution due to the contact is electrolytically quantified, thereby measuring the concentration of at least one of the three components in the gas. A gas analysis method characterized by: