JPH0677006B2 - How to measure total nitrogen content - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for measuring total nitrogen content, and more particularly to a method for measuring total nitrogen content in water.

[Conventional technology]

Nitrogen compounds present in water are divided into nitrate nitrogen and ammonia nitrogen. There is a water quality test method that measures the total amount of these nitrogen compounds. FIG. 2 is a conceptual diagram of a conventional oxidizer of a device for measuring total nitrogen content in water. An oxidation catalyst layer 3 is formed under the vertical reaction tube 1 arranged in the heating furnace 4,
Oxygen gas is supplied to the upper part of the reaction tube 1 through a pipe 6. A heat-resistant filler 8 such as quartz wool is placed on the upper and lower ends of the catalyst layer 3 to fix the catalyst. The lower end opening of the reaction tube 1 is connected to a nitric oxide detector. Then, after heating to a predetermined temperature in the heating furnace 4, the sample is introduced into the oxygen gas by the sample introducing device 7 to convert all the nitrogen compounds in the sample into nitric oxide, and the monoxide outside the system shown in FIG. It is transferred to the nitrogen detector.

Conventionally, the method of integrally heating the reaction tube as shown in FIG. 2 has been adopted, so that it is not possible to convert all the nitrogen compounds in the sample into nitric oxide, which causes a measurement error. It was

The inventors of the present invention have conducted extensive studies on the oxidation reaction conditions of the catalyst. We have found conditions that suppress side reactions that generate nitrogen oxides.

[Problems to be solved by the invention]

The present invention overcomes the drawbacks of conventional methods for measuring total nitrogen content,
It is an object of the present invention to provide a method for measuring the total nitrogen content that enables highly accurate analysis by surely converting all nitrogen compounds including sulfate nitrogen and ammonia nitrogen into nitric oxide while suppressing side reactions. To do.

[Means for solving problems]

The present invention forms an oxidation catalyst layer in the lower part of a vertical reaction tube arranged in a heating furnace, and introduces a nitrogen compound-containing sample into an oxygen-containing gas supplied from above the reaction tube so that all nitrogen compound In the method for measuring the total nitrogen content, which is measured by converting nitrogen into nitric oxide, 1/3 to 1/2 from the upper end of the catalyst layer.
The method for measuring the total nitrogen content is characterized in that the lower part is heated to 750 to 950 ° C, and at least the lower part of the space of the reaction tube is heated to 500 to 700 ° C.

The catalyst used here is a commonly used oxidation catalyst,
For example, Cu, Ni, Pt based catalysts, or those obtained by supporting these catalysts on a carrier such as alumina. Further, the oxygen-containing gas supplied to the reaction tube can be diluted with an inert gas as needed before use.

FIG. 1 is a conceptual diagram of an oxidation device for carrying out the present invention. The difference from the conventional apparatus of FIG. 2 lies in the heating furnace that forms a heating region in the reaction tube 1. That is, 2 through the spacer 9.
By installing two heating furnaces 4 and 5, two temperature regions and a temperature gradient region between them are formed.

FIG. 3 is a diagram showing an example of the positional relationship between the temperature distribution in the reaction tube and the catalyst layer. The horizontal axis represents the temperature inside the reaction tube, and the vertical axis represents the height position of the reaction tube based on the lower end of the catalyst layer. On the left side, the range a or a'occupied by the catalyst layer in the reaction tube is indicated by diagonal lines. The upper part of the catalyst layer where a temperature gradient of 100 to 300 ° C is provided is b or b '. In the graph on the right side, the solid line shows the temperature distribution by the two-stage heating method when the catalyst layer height is a in the left figure. The dotted line shows the temperature distribution by the two-stage heating method when the catalyst layer height is a ', and each is an example of the present invention. On the other hand, the one-dot chain line shows the temperature distribution by the conventional one-step heating method. In this case, the inside of the catalyst layer is kept at the same temperature. In the temperature setting of the present invention, the lower part c of the catalyst layer is 750 to 950 ° C, preferably 800 to 900 ° C.
And 500-700 ° C at least below the space of the reaction tube,
It is preferably 550 to 650 ° C. And, the catalyst layer upper part b or b'is 100 to 300 ° C., preferably 100 to 1 ° C.
Set a temperature gradient of 50 ° C and set the ratio of the upper part of the catalyst layer to b / a or Was set to 1/3 to 1/2. By setting such a temperature, not only nitrate nitrogen but also ammonia nitrogen can be surely converted to nitric oxide, and it is possible to prevent the production of other nitrogen oxides. This ensures that the ammonia nitrogen is converted into nitric oxide in the relatively low temperature region above the catalyst layer, and the relatively high temperature region below the catalyst layer is made to have an appropriate length to prevent the above side reaction. It is thought that it was possible to do it.

The two-stage heating method of the present invention only needs to form the above temperature distribution, and the number of heaters is not particularly problematic.

(Example) From the bottom of a heat-resistant glass reaction tube having a diameter of 25 mm and a total length of 430 mm
Quartz wool is laid at a thickness of 10 mm at 100 mm, and various catalysts shown in Table 1 are filled on it at a height of 110 mm.
Further, quartz wool was placed on it. A heating furnace that heats the lower part of the catalyst layer is placed at a position 100 to 180 mm from the bottom of the reaction tube, and a 20 mm thick spacer is placed above it to raise the height to 19 mm.
A heating furnace for heating the space of 0 mm mainly in the reaction tube was arranged. The temperature of the catalyst layer is measured at a height of 30 mm from the bottom,
The temperature of the space was measured at a height of 75 mm above the upper surface of the catalyst layer. Then, the temperatures of the catalyst layer and the reaction tube space were heated to the values shown in Table 1.

On the other hand, an aqueous solution sample containing 10 ppm each of (NH ₄ ) ₂ SO ₄ , NaNO ₃ and NaNo ₂ was prepared. Oxygen gas was flown into the reaction tube at a flow rate of 0.2 / min, and 30 μl of the sample was injected into the reaction tube with an auto sample injector for analysis. A decompression type chemiluminescence detector (MCI-TN-05, NO detector (manufactured by Mitsubishi Kasei Co., Ltd.) was used as a detector of nitric oxide.

The analysis results are shown in Table 1. The values in the table are conversion rates of other nitrogen compounds with the conversion rate of NaNO ₃ being 100.

The results of the same analysis with the temperature of the lower part of the catalyst layer and the temperature of the space of the reaction tube made equal are shown in Table 1 as a comparative example.

As is clear from this table, the conversion to nitric oxide is more reliably promoted in the examples than in the comparative examples, regardless of the type of catalyst. The difference in conversion rate between the two is several%
However, there is a significant difference in the accuracy of this type of analysis.

〔The invention's effect〕

The present invention, by adopting the above configuration, can reliably convert various nitrogen compounds to nitric oxide without being affected by the type of catalyst, and can accurately measure the total nitrogen content. It was

[Brief description of drawings]

FIG. 1 is a conceptual diagram of an apparatus for carrying out the present invention, FIG. 2 is a conceptual diagram of a conventional apparatus, and FIG. 3 is a diagram showing a positional relationship between a temperature distribution in a reaction tube and a catalyst layer.

Claims (2)

[Claims] 1. An oxidation catalyst layer is formed below a vertical reaction tube arranged in a heating furnace, and a nitrogen compound-containing sample is introduced into an oxygen-containing gas supplied from above the reaction tube. In the method for measuring the total nitrogen content by converting a nitrogen compound into nitric oxide, 1/3 from the upper end of the catalyst layer is measured.
A method for measuring the total nitrogen content, characterized in that the temperature below ½ is heated to 750 to 950 ° C, and at least the space below the reaction tube is heated to 500 to 700 ° C. 2. The method according to claim 1, wherein a temperature gradient of 100 to 300 ° C. is provided in the upper 1/3 to 1/2 of the catalyst layer.