JP2772899B2 - Method for analyzing nitrogen oxides in sulfuric acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for analyzing trace amounts of nitrogen oxides in sulfuric acid. More specifically, the present invention relates to a method and an apparatus for analyzing the total amount of nitrogen oxides caused by nitric acid, nitrous acid, nitrosyl sulfuric acid and the like contained in sulfuric acid.

[0002]

2. Description of the Related Art Nitrogen oxides (hereinafter sometimes abbreviated as NOx) are contained in sulfuric acid produced from sulfurous acid gas generated in a roasting step of refining non-ferrous metals such as copper, zinc and lead. Contains various impurities such as chlorides and sulfur dioxide. Among these, JIS K 1306: Brucine absorption spectrophotometry, ISO 2363: 2,4-xylenol absorption spectrophotometry, etc. are generally used as a method for analyzing a trace amount of nitrogen oxides in sulfuric acid. Requires highly toxic reagents, complicates the analysis operation, and must rely on manual analysis. Also, it cannot be used as a continuous analysis method. In particular, the amount of NOx in sulfuric acid is 50p
In the case of a low concentration of pm (equivalent to nitrate ion) or less, a technique for accurately analyzing the amount is insufficient, and a method for continuous analysis has not yet been developed.

[0003]

SUMMARY OF THE INVENTION 1 to 50 pp in sulfuric acid
As described above, as a method for analyzing nitrogen oxides contained in about m, there are a brucine absorption spectrophotometry and a 2,4-xylenol absorption spectrophotometry. These methods use highly toxic reagents and also have a lower limit of quantification of 0. It has a drawback that the sensitivity is poor at about 2 ppm, and that it is easily affected by coexisting components. For example, in the case of brucine spectrophotometry, nitrosyl sulfate among nitrogen oxides does not react with brucine, so it cannot be analyzed. Is measured, hydrogen peroxide used as an oxidizing agent reacts with brucine to form a color, which hinders the measurement.

The recently developed ion chromatographic method is described in the 31st Analytical Subcommittee of the Sulfuric Acid Association (March 1, 1992).
2nd) As described in the minutes of the meeting (p-10), it is effective for the analysis of nitrogen oxides contained in high concentrations.
The analysis of trace amounts such as 0 ppm or less is greatly affected by sulfate ions and cannot be used. That is, when the peak area of the nitrate ion is obtained from the chromatogram obtained by using the ion chromatography, the peak of the sulfate ion is too large and overlaps with the peak of the nitrate ion, so that the analysis becomes difficult. Moreover, since all of these methods cannot be used for continuous analysis, they cannot be used when it is necessary to analyze the nitrogen oxide concentration over time.

[0005]

Means for Solving the Problems Accordingly, the present inventors have:
The research was focused on the known fact that nitrate ions and nitrite ions react with ferrous ions in a sulfuric acid solution to form nitrosoferro ions as shown in the formula and the formula. 8FeSO ₄ + 2HNO ₃ + 3H ₂ SO ₄ ─ → 2Fe (NO) SO ₄ + 3Fe ₂ (SO ₄ ) ₃ + 4H ₂ O──4FeSO ₄ + 2HNO ₂ + H ₂ SO ₄ ─ → 2Fe (NO) SO ₄ + Fe ₂ (SO ₄ ) ₃ + 2H ₂ O ── As a result, all the nitrogen oxides contained in the sulfuric acid, ie, the nitrogen oxides caused by nitric acid, nitrous acid, nitrosylsulfuric acid, etc., are once converted into nitrosoferroions, and the nitrosoferroions formed Is heated and decomposed to generate nitric oxide, degassed by passing an inert gas such as nitrogen, and the amount of nitric oxide contained in the degassed gas is determined by a known method. It has been found that NOx in sulfuric acid can be analyzed with extremely high accuracy, and the present invention has been achieved.

That is, the gist of the present invention is to (1) add a ferrous ion solution to sulfuric acid containing nitrogen oxides and heat it, and degas the generated nitrogen monoxide by passing an inert gas through, A method for analyzing nitrogen oxides in sulfuric acid, characterized by quantifying nitrogen monoxide contained in the degassed gas; (2) adding a ferrous ion solution to sulfuric acid containing nitrogen oxides and heating; Nitrogen monoxide generated is degassed by passing an inert gas, and nitrogen monoxide contained in the degassed gas is continuously determined using an infrared spectrophotometer or a chemiluminescence analyzer. (3) Add ferrous ion solution to sulfuric acid containing nitrogen oxides, chlorides and sulfur dioxide and heat to remove the generated nitric oxide with inert gas. Aeration and deaeration, nitric oxide contained in the deaeration gas,
A method for analyzing nitrogen oxides, chlorides, and sulfur dioxide in sulfuric acid, characterized by simultaneously quantifying hydrogen chloride and sulfur dioxide. (4) A ferrous ion solution is added to sulfuric acid containing nitrogen oxides. A gas generator for generating nitrogen monoxide by heating and heating, a means for degassing the generated nitric oxide by passing an inert gas, and a means for quantifying nitrogen monoxide contained in the degassed gas. For analyzing nitrogen oxides in sulfuric acid.

In the analysis method of the present invention, first, NOx
Is put into a container, and a ferrous ion solution, for example, a ferrous sulfate solution is added thereto. The concentration of sulfuric acid is usually preferably 70% or more, and if the concentration of sulfuric acid is lower than 70%, the degassing efficiency of nitric oxide deteriorates. Therefore, when analyzing NOx in sulfuric acid having a sulfuric acid concentration lower than 70%, it is preferable to adjust the concentration to 70% or more using concentrated sulfuric acid with a known NOx concentration. In addition, the ferrous sulfate solution is added so that the concentration of the ferrous ion solution contains 0.005 to 0.5% of ferrous ions in the sulfuric acid solution. If the concentration of ferrous ion is lower than 0.005%, the production of nitrosoferroion is insufficient, and if it is higher than 0.5%, the excess ferrous ion adversely affects the measurement.

By the above operation, NOx contained in sulfuric acid
Is once converted to nitrosoferroion, and then nitrosoferroion is thermally decomposed to generate nitric oxide. In order to convert NOx contained in sulfuric acid into nitrosoferroion, it is preferable to add a ferrous ion solution and bubbling sulfuric acid. For this reason, a container such as a gas generating bottle with a sinter glass is suitably used. The bubbling time of sulfuric acid is usually 10 to 200 seconds. The heating temperature for thermally decomposing the nitrosoferro ion is usually preferably from 60 to 120 ° C. If the heating temperature is lower than 60 ° C., the decomposition of nitrosoferro ions becomes insufficient, which is not preferable. If the heating temperature is higher than 120 ° C., the effect corresponding thereto cannot be obtained. Next, the generated nitric oxide is degassed by passing an inert gas such as nitrogen. At this time, the nitrogen flow rate is 10 to 100 volumes per 1 volume of sulfuric acid. 10
If it is less than 100 parts by volume, the separation of nitric oxide from sulfuric acid will be insufficient, and if it is more than 100 parts by volume, the concentration of nitric oxide will be too low to make the measurement difficult. Thus, the nitric oxide separated together with the degassed gas is once collected in a vacuum vessel to determine the amount of nitric oxide.

The method for quantifying nitric oxide is not particularly limited. For example, nitric oxide in degassed gas is oxidized by an oxidizing agent such as ozone, absorbed into hydrogen peroxide water and converted into nitrate ions. A method of analyzing using an ion chromatograph may be mentioned. Alternatively, it is possible to directly determine the amount of nitric oxide in the degassed gas using an infrared spectrophotometer or a chemiluminescence analyzer. Since these direct analysis methods can be detected and quantified in real time, the concentration of nitric oxide can be measured over time by continuous ventilation. That is, when the above operation is performed continuously, the concentration of nitric oxide in the degassed gas is measured using an infrared spectrophotometer or a chemiluminescence analyzer, and after performing an arithmetic operation, the NOx concentration in sulfuric acid is measured. As ppm.

Next, an apparatus used in the analysis method of the present invention will be described. The analyzer according to the present invention includes a gas generator that generates a nitric oxide by adding a ferrous ion solution to sulfuric acid containing a nitrogen oxide and heats the gas, and removes the generated nitrogen monoxide by passing an inert gas. And means for quantifying nitrogen monoxide contained in the degassed gas. Hereinafter, the apparatus of FIGS. 1 and 2 will be described as an example, but the apparatus of the present invention is not limited thereto.

FIG. 1 shows that NOx contained in sulfuric acid is separated as nitric oxide using a gas generator, oxidized by adding ozone, absorbed in hydrogen peroxide solution, converted into nitrate ions, and then ion chromatographed. It is the schematic which shows an example of the apparatus for analyzing using a graph. In FIG. 1, 1 is a gas generating bottle with a sinter glass for bubbling sulfuric acid,
2 is a syringe for adding ferrous ions, 3 is a mist separator for removing sulfuric acid mist, 4 is a vacuum bottle for collecting generated nitric oxide, and 5 is an inert gas such as nitrogen. A Tedlar bag 6 for supplying is a constant temperature water tank for heating the gas generating bottle 1.

More specifically, after sulfuric acid was put into the gas generating bottle 1 and heated, the ferrous ion solution was added using the syringe 2 and then sufficiently depressurized using a vacuum pump in advance. The cock of the vacuum bottle 4 is opened, and the gas generating bottle 1 is bubbled with the inert gas in the Tedlar bag 5. Through this series of operations, NOx in the sulfuric acid reacts with ferrous ions to once become nitrosoferroion, which is immediately decomposed to produce nitric oxide, degassed from the sulfuric acid with an inert gas, and Collected in 4. Ozone is added to the vacuum bottle to oxidize nitric oxide to nitrous oxide, then absorbed in aqueous hydrogen peroxide to convert it to nitrate ions, and analyzed using an ion chromatograph.

The method of the present invention can also be applied as a continuous analysis method. FIG. 2 is a schematic diagram showing an example of an apparatus for continuous analysis. 11 is a metering pump for supplying sulfuric acid, 12
Is a metering pump for supplying ferrous ions, 13 is a mass flow controller for introducing inert gas, 14 is a gas generating bottle with sinter glass, 15 is a thermocontroller,
6 is a NO meter, 17 is a heater for heating the gas generating bottle, and 18 is an overflow pipe. The sulfuric acid and ferrous ion solution are sent to the gas generating bottle 14 using the metering pumps 11 and 12, and then heated by the heat of dilution and the heater.
Bubble with an inert gas such as nitrogen gas introduced through 3. The excess sulfuric acid solution flows out to the waste liquid tank through the overflow pipe 18, and the ventilation gas is guided from above the gas generating bottle 14 to the NO meter 16 such as an infrared spectrophotometer or a chemiluminescence analyzer. Further, the temperature of the sulfuric acid solution is kept constant by the thermocontroller 15.

When a continuous analysis is performed using such an apparatus, the relationship expressed by the following equation (1) is established between NO in the degassed gas and NOx in the sulfuric acid. For example, sulfuric acid having a nitrogen oxide concentration of 0.1 ppm (in terms of nitrate ion) is converted to 0.02
When the nitrogen gas is supplied at a rate of 0.2 liter (20 ° C., 1 atm) / min and the nitrogen gas is supplied at a rate of 0.2 liter / min, the degassed gas obtained by the calculation according to the equation (1) is about 7
ppm of nitric oxide.

[0015]

(Equation 1)

Accordingly, the N contained in the degassed gas is measured using a commercially available infrared spectrophotometer or chemiluminescence analyzer.
When analyzing O, set the lower limit of quantification of the NO meter to 0.2 p.
pm, the lower limit of quantification of NOx in sulfuric acid is 0.00
It corresponds to 3 ppm. Thus, by using the method of the present invention, it is possible to analyze trace amounts of nitrogen oxides in sulfuric acid of 0.01 ppm or less.

According to the present invention, the obtained nitrogen monoxide gas contains very little nitrogen dioxide gas.
According to the result of analysis using the Salzman absorption solution, the molar ratio of nitrogen dioxide / nitrogen monoxide was 1/2000 or less. Therefore, there is no need to consider the effects of nitrogen dioxide when selecting a continuous analyzer for nitrogen oxide analysis.
The analyzer can be greatly simplified.

Further, when the apparatus of the present invention is used, chloride contained in sulfuric acid is easily converted into hydrogen chloride under sulfuric acidity, so that it can be separated together with nitric oxide. In addition, dissolved sulfur dioxide can be separated easily because it can be easily degassed by passing an inert gas. Therefore, for example, when using the apparatus shown in FIG.
By adding ozone and hydrogen peroxide solution to the vacuum bottle, it is possible to quickly and simultaneously analyze nitrate ions, chloride ions and sulfate ions using an ion chromatograph.

When the continuous analysis shown in FIG. 2 is performed, the detectors for hydrogen chloride and sulfur dioxide are installed in series or in parallel with the NO meter, so that nitrogen oxides, chlorides and sulfur dioxide in sulfuric acid can be obtained. Can be analyzed continuously and simultaneously.

[0020]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, but the present invention is not limited to these Examples and the like.

Example 1 The temperature of a thermostatic water bath 6 was adjusted to 80 ° C. by using an analyzer shown in FIG. 1 in which the volume of a gas generating bottle 1 with a sinter glass was 50 ml and the volume of a vacuum bottle 4 was 1000 ml. The experiment was performed using a nitrogen gas supply device (Tedlar bag 5) as an active gas. Nitrate standard solution was added to sulfuric acid for precision analysis, and the nitrate ion concentration was 0.108 pp each.
m, sulfuric acid adjusted to 1.08 ppm, 10.8 ppm
After adding a ferrous sulfate solution to 0 ml from the syringe 2 so that the ferrous sulfate ion concentration becomes 0.05%, the cock of the vacuum bottle 4 is opened and nitrogen gas is ventilated to reduce NOx in the sulfuric acid. It was collected in a vacuum bottle 4 as nitric oxide. After adding 50 ml of oxygen containing 1% of ozone and 20 ml of 0.1% hydrogen peroxide solution to the vacuum bottle 4 to make nitrate ions, an ion chromatograph equipped with an electric conductivity type detector (Yokogawa Analytical Systems Co., Ltd.) ), IC7000 type), the analysis results shown in Table 1 were obtained. From Table 1, it is clear that most of the nitrate ions added in advance were collected as nitric oxide.

[0022]

[Table 1]

Example 2 Using the same analyzer as in Example 1, an experiment was conducted on sulfuric acid containing a known concentration of chloride ion and sulfur dioxide in the same manner as nitrate ion under the same experimental conditions. Table 2 shows the results of analysis using ion chromatography.
As shown in Table 2, all three components could be quantified with high accuracy.

[0024]

[Table 2]

EXAMPLE 3 In FIG. 2, a sulfuric acid for precision analysis containing a known amount of nitrate ion was measured using a continuous analyzer designed so that the gas generating bottle 14 with a sinter glass had an inner diameter of 25 mm and a liquid depth of 100 mm. NOx in was quantified. Using a metering pump 11 for supplying sulfuric acid, the nitrate ion concentration was 20.0 ppm,
Sulfuric acid adjusted to 5.0 ppm and 1.0 ppm
Liter / min, 0.002 liter / min of 5% ferrous sulfate solution using a metering pump 12 for supplying ferrous ion (corresponding to 0.05% ferrous sulfate ion concentration)
, And nitrogen gas was passed from the mass flow controller 13 for introducing an inert gas at a rate of 0.4 L / min (20 ° C.). Liquid temperature 80 ℃
The degassed gas was introduced into a chemiluminescence analyzer (manufactured by HORIBA, Ltd., Model CLA-510) while adjusting the pressure, and the reading of the NO meter was read. The indicated value of the NO meter was almost constant over 10 minutes as shown in Table 3. When the NOx concentration in the sulfuric acid was converted from the concentration of nitric oxide in the degassed gas using the equation (2), it could be determined with good accuracy as shown in Table 3.

[0026]

(Equation 2)

[0027]

[Table 3]

Example 4 20 ppm of nitrate ion and chlorine ion 18 ppm, sulfur dioxide 15 ppm under the same experimental conditions as in Example 3.
An experiment was conducted on sulfuric acid for precision analysis containing Degassed gas is used for chemiluminescence spectrometer (HLA, CLA-510)
And an HC1 automatic analyzer (Model 15 manufactured by Nippon Thermo Electron Co., Ltd.) and an infrared spectrophotometer (model VIA # 510 manufactured by Horiba, Ltd.) to chemiluminescence the nitric oxide contained in the degassed gas. Analyzer, hydrogen chloride to HC
1 An automatic analyzer and sulfur dioxide were analyzed using an infrared spectrophotometer. The values obtained by converting the results into NOx, Cl ⁻ , and SO ₂ in sulfuric acid using the formulas (2), (3), and (4) are as shown in Table 4, and can be quantified with good accuracy. done.

[0029]

(Equation 3)

[0030]

[Table 4]

Comparative Example 1 Sulfuric acid containing 50 ppm of nitrate ions was directly analyzed using an ion chromatograph. 100 ml of sulfuric acid 1 ml with pure water
and analyzed using an ion chromatograph set to the same analysis conditions as in Example 1. As a result, it was difficult to quantify nitrate ions because the peak of sulfate ions was too large.

[0032]

According to the analysis method of the present invention, N in sulfuric acid
Ox can be analyzed down to a trace amount of 0.01 ppm or less. Further, NOx in sulfuric acid can be continuously analyzed by introducing the generated nitric oxide into a continuous analyzer such as an infrared spectrophotometer or a chemiluminescence analyzer.
As a result, the behavior of NOx in the sulfuric acid facility can be easily clarified, and the quality of the sulfuric acid product can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of an analyzer according to the present invention.

FIG. 2 is a schematic view showing an example of the analyzer of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas generating bottle with sinter glass 2 Syringe cylinder 3 Mist separator 4 Vacuum bottle 5 Tedlar bag 6 Constant temperature water tank 11 Metering pump for supplying sulfuric acid 12 Metering pump for supplying ferrous iron 13 Mass flow controller 14 Gas generating bottle with sinter glass 15 Thermo Controller 16 NO meter 17 Heater 18 Overflow piping

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shoji Yokoyama 346, Miyanishi, Harima-cho, Kako-gun, Hyogo Prefecture Inside the Beppu Plant of the Sumitomo Seika Co., Ltd. (56) References JP-A-56-86339 (JP, A) JP-A-55-67649 (JP, A) JP-A-53-142299 (JP, A) JP-A-61-21966 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01N 31/00

Claims (7)

(57) [Claims] 1. A ferrous ion solution is added to sulfuric acid containing nitrogen oxides and heated, and the generated nitric oxide is degassed by passing an inert gas therethrough, and the monoxide contained in the degassed gas is degassed. A method for analyzing nitrogen oxides in sulfuric acid, characterized by quantifying nitrogen. 2. A ferrous ion solution is added to sulfuric acid containing nitrogen oxides and heated, and the generated nitric oxide is degassed by passing an inert gas through, and the monoxide contained in the degassed gas is degassed. A method for analyzing nitrogen oxides in sulfuric acid, wherein nitrogen is continuously determined using an infrared spectrophotometer or a chemiluminescence analyzer. 3. A ferrous ion solution is added to sulfuric acid containing nitrogen oxides, chlorides, and sulfur dioxide, and heated, and the generated nitric oxide is degassed by passing an inert gas therethrough. A method for analyzing nitrogen oxides, chlorides, and sulfur dioxide in sulfuric acid, comprising simultaneously quantifying nitrogen monoxide, hydrogen chloride, and sulfur dioxide contained in a gas. 4. The ferrous sulfate solution according to claim 1, wherein the ferrous sulfate solution has a concentration of 0.005 to 0.5% as a ferrous ion concentration in the sulfuric acid solution. The described method. 5. The method according to claim 1, wherein the concentration of sulfuric acid is 70% or more, and the heating temperature is 60 to 120 ° C. 6. A gas generator for generating nitric oxide by adding a ferrous ion solution to sulfuric acid containing nitrogen oxides and heating, and degassing generated nitrogen monoxide by passing an inert gas. An apparatus for analyzing nitrogen oxides in sulfuric acid, comprising: means for quantifying nitric oxide contained in degassed gas. 7. The apparatus according to claim 6, wherein the means for quantifying nitric oxide contained in the degassed gas can be continuously quantified using an infrared spectrophotometer or a chemiluminescence analyzer.