JPS5927219B2 - Method for producing a composition that converts nitrogen dioxide into nitric oxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a composition that converts nitrogen dioxide into nitrogen monoxide, and particularly provides an advantageous method for producing a composition that has a high conversion rate. .

Conventionally, a composition that converts nitrogen dioxide into nitrogen monoxide has been indispensable as a nitrogen dioxide converter for a nitrogen monoxide analyzer using a chemiluminescence method.

However, since there are problems in terms of conversion rate and operating temperature range, there is a demand for the development of a product that is satisfactory in terms of performance and an advantageous manufacturing method.

Therefore, the present invention has been made in view of the above points, and includes a method for producing a composition for converting nitrogen dioxide into nitrogen monoxide, which has a substrate and a carbide layer on the surface of the substrate, and specifically specifies the components of the substrate. The present invention also provides a manufacturing method that facilitates the formation of a carbide layer.

An example of the method for producing a composition for converting nitrogen dioxide into nitrogen monoxide of the present invention will be described below.

The substrate is made of one or more selected from chromium, molybdenum, tungsten, vanadium, titanium, tantalum, silicon, and boron, and its surface is composed of a carbide layer.

In this case, the carbide layer has a thickness of 1
μm or more is required, and the shape of the starting material is preferably one with a large specific surface area.

Items with a large specific surface area include, in addition to net shapes, linear shapes, granular shapes, block shapes, plate shapes, rod shapes, pipe shapes, whisker shapes,
Examples include fibrous and cloth-like materials.

In addition to the conversion rate, the components of the substrate also depend on the reaction temperature range (usually 1
A temperature of 00 to 350°C is suitable.

) were selected by considering their safety, performance deterioration, etc.

Further, when the base body is made of an alloy of the metal group mentioned above, it is sufficient that the main component is a component of the metal group.

Formation of the carbide layer includes an oxidation step and a carbonization step.

This oxidation step takes into account the smooth carbonization step, and is obtained by oxidizing the surface of the substrate with chemicals or heating it in an oxidized carbon atmosphere.

Moreover, the carbonization step is to solid-phase carbonize or gas-phase carbonize the oxide film generated in the oxidation step.

Next, the content of the present invention will be explained more specifically and in detail by showing experimental examples, but the present invention is not limited to these experimental examples.

Experimental Example 1 As a starting material, a 100-mesh net made from titanium wire with a thickness of 0.5 mm was selected, and then the surface of this net was heated in air at 650°C for 30 minutes to form an oxide film. .

Thereafter, this oxide film was carbonized in a gas phase under the following conditions.

Reaction gas composition: methane 35 vo7'%, hydrogen 65
vo7 Temperature: 1450°C Time: 3 hours In this case, the carbide layer was determined by X-ray diffraction after carbonization.TiC2
It was confirmed that all of them had changed to TiC.

Note that the thickness of the carbide layer was 18 μm.

The composition produced through these steps was filled into a reaction tube, and the flow rate was 100 mt/min, and the nitrogen dioxide concentration was 0.
The reaction was carried out in nitrogen under the conditions of 8, and the conversion rate of -pm nitrogen oxide was measured.

As a result, a conversion rate of 90% at 100°C and 99% or higher at 250°C was obtained.

Experimental Example 2 A 100-mesh net made from a tungsten wire with a thickness of 0.5 m + nφ was selected as a starting material, and the surface of this net was heated in air at 600° C. for 30 minutes to form an oxide film.

Following this oxidation step, carbonization was performed under the same conditions as in Experimental Example 1,
A 75 μm carbide layer was produced.

After carbonization, X-ray diffraction was performed and it was confirmed that all WOs had changed to WC.

Then, the substrate on which the carbide layer was formed was filled into a reaction tube and reacted in nitrogen at a flow rate of 200 m, /, /ml ns and a carbon dioxide concentration of 100 ppm, and the conversion rate of nitrogen monoxide was measured.

As a result, a conversion rate of 96% at 100°C and 99% or higher at 200°C was obtained.

Furthermore, vanadium, tantalum, silicon, and boron were selected as the composition of the substrate, and the surfaces of these substrates were oxidized and then carbonized to produce a composition.

The conversion rates of nitric oxide were similarly measured for these compositions, and conversion rates of 90 factors or higher were obtained in all cases.

Experimental Example 3 As a starting material, chromium-molybdenum (20wt%Cr-80wt%Mo) granules with an average diameter of 3fML were selected, and the surface thereof was heated in air at 650°C for 1 hour, and carbonized under the following conditions. , a 50 μm carbide layer was formed.

Carrier gas: Hydrogen Temperature: 1150°C Time: 2 hours After carbonization, microscopic observation revealed that the thickness of the carbide layer was:
It was 28 μm.

The composition produced in this manner was filled into a reaction tube and reacted in nitrogen at a flow rate of somt/min and a carbon dioxide concentration of 0.6 ppm, and the conversion rate of nitrogen monoxide was measured.

As a result, a conversion rate of 94% at 100°C and 99% or more at 200°C was obtained.

Furthermore, regarding the composition of the substrate, an alloy other than the chromium-molybdenum alloy selected from the metal group mentioned above was selected, the surface of which was oxidized, and then a carbide layer was formed.The conversion rate was similarly measured for the sample.

As a result, a conversion rate of 90 coefficient or higher was obtained in all cases at 100°C.

Experimental Example 4 A sponge-like silicon block having an average diameter of 3rIan was carbonized in a gas phase under the following conditions.

Reaction gas composition: methane 35 vo,/,%, hydrogen 65 v
o7% Temperature: 1250°C Time: 2 hours After carbonization, X-ray diffraction was performed and it was confirmed that the surface layer was silicon carbide.

Furthermore, as a result of microscopic observation, the average thickness of the carbide layer was 15 μm.
Met.

A reaction tube was filled with the sponge-like silicon whose surface layer was made of silicon carbide, and the flow rate was set at 200 mt.
The reaction was carried out in nitrogen under the following conditions: /mlns NO2 concentration 0.8 ppm, and the N02→NO conversion rate was measured.

As a result, an exchange rate of O8 or more was obtained at 250°C.

Similarly, a sponge-like vanadium ring and a boron lump were carbonized in the vapor phase under the above conditions.

Regarding sponge-like vanadium having an average thickness of 15 μm, under the same conditions as above, the NO2→NO exchange rate showed measured values of 82% at 100°C and 98% at 200°C.

Furthermore, for the sponge-like phosphatide having an average thickness of 15 μm, an exchange rate of O8 coefficient or higher was obtained at 200°C.

Furthermore, the composition obtained by the production method of the present invention was found to have the following points from the above-mentioned experimental examples and other experimental examples.

(2) Although the reaction with nitrogen dioxide in the reaction gas proceeds even at room temperature, a temperature range of 100 to 350°C is usually appropriate.

■ Space velocity of reaction gas (GH8V) is 10000~3
No effect was observed in the experimental range of 0,000 gas volume/carbide volume/hour.

■ If used at temperatures below 400°C, particularly below 350°C, consumption of carbide by oxygen should not occur.

This is because the reaction with oxygen begins for the first time at temperatures above 400°C and becomes rapid at around 450°C.

■ Ammonia, a coexisting component, has almost no effect at temperatures below 250°C.

■ Photochemical reaction products such as peroxyacetyl nitrate and alkyl nitrate should not be affected.

This is because this can be avoided by using a reaction temperature of 100-120°C.

Therefore, the method for producing a composition for converting nitrogen dioxide into nitrogen monoxide according to the present invention can advantageously produce a composition particularly for a nitrogen dioxide converter, and the conversion rate can be maintained over a long period of time.

Further, the composition is capable of selectively and quantitatively converting nitrogen dioxide into nitrogen monoxide when analyzing nitrogen oxides in the ambient air and source exhaust gas.

Furthermore, the manufacturing method of the present invention does not require special equipment and can be easily and reliably obtained, making it suitable for mass production and capable of stable supply.

Claims (1)

[Claims] 1. A method for producing a composition for converting nitrogen dioxide into nitrogen monoxide, which has a substrate and a carbide layer on the surface of the substrate, wherein the substrate is made of chromium, molybdenum, tungsten, vanadium, titanium, silicon, or A metal or alloy containing one or more types of boron as a main component is selected, and the formation of the carbide layer is a process in which an oxide film is formed on the surface of the substrate, and then this oxide film is formed in a solid phase or a gas phase. 1. A method for producing a composition for converting nitrogen dioxide into nitrogen monoxide, comprising a step of carbonizing the composition.