JPS589372B2 - Nitric oxide quantitative generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for quantitatively generating nitric oxide, and more particularly to a device for quantitatively generating nitric oxide using a gas-permeable permeation tube.

Nitric oxide gas (standard gas) with a known concentration is indispensable, for example, for calibrating the scale of a continuous measurement device for nitrogen oxides in environmental gas analysis, and is generally a gas with a known concentration filled in a cylinder. is used.

However, when a cylinder is filled with a dilute gas on the order of ppm or less, there are problems with the stability of the concentration, such as concentration distribution within the cylinder and changes over time.

Furthermore, when using diluted nitrogen monoxide with a concentration of several ppm, a large amount of diluting gas is required, resulting in disadvantages such as an increase in the size of the apparatus.

Therefore, in recent years, many attempts have been made to generate a dilute nitrogen monoxide standard gas of several ppm or less by chemical or physical methods.

For example, a method of flowing nitrogen gas over a nitrite aqueous solution to decompose and generate nitrogen oxides from the aqueous solution to obtain dilute nitrogen oxide-containing nitrogen gas (Shigeru Tanaka et al., Analytical Chemistry Vol. 26, No. 5, No. 285 Page, 1977) and a constant concentration of nitrogen monoxide standard gas diffused through a Teflon membrane with a pressure difference.
A method for obtaining a dilute standard gas by mixing the released nitrogen monoxide with a diluent gas (Ibusuki et al., Proceedings of the 36th Spring Annual Conference of the Chemical Society of Japan 1H36, p. 75, 1977
) are known.

However, in the former method, nitrogen dioxide and water vapor are generated in addition to nitrogen monoxide, and a dilute gas containing only nitrogen monoxide cannot be obtained.

In addition, in the latter method, the standard gas is further diffused through the membrane due to the pressure difference, so there are many factors that determine the concentration, and it cannot be said to be practical.

On the other hand, as a method for preparing a dilute standard gas of nitrogen dioxide,
The so-called permeation tube method involves filling liquefied nitrogen dioxide into a nitrogen dioxide-permeable container, placing it in a diluent gas stream at a constant temperature, and determining the concentration from the weight loss of the container and the diluent gas flow rate. This method has been put into practical use along with a similar standard gas preparation method for sulfur dioxide.

Although this method can be applied to the preparation of a standard gas of nitrogen monoxide, since it requires liquefied nitrogen monoxide, it has drawbacks such as safety and troublesome handling.

An object of the present invention is to eliminate the drawbacks of the prior art described above, and to easily prepare a standard gas containing only nitrogen monoxide using a gas generating source containing nitrogen monoxide, particularly an aqueous nitrogen monoxide solution that is easy to obtain and handle. An object of the present invention is to provide a device for quantitatively generating nitric oxide.

In order to achieve the above object, the present invention provides a nitric oxide generator comprising a permeation tube having a gas-permeable membrane and in which a nitric oxide generating source is enclosed.
The gas permeable membrane is characterized in that it has a two-layer structure, and a desiccant layer and an acidic gas absorbent layer are provided between these layers.

That is, the present invention allows gas generated from a nitrogen monoxide source containing water to permeate the permeation membrane of the permeation tube configured as described above, and prevents water that is about to evaporate from the tube by the desiccant held between the permeation membranes. It also captures nitrogen oxides in a highly oxidized state of dinitrogen trioxide or higher using an acidic gas absorbent, effectively limiting the gas released outside the container to only nitrogen monoxide. .

As the nitric oxide generating source used in the present invention, nitrite nitrogen, that is, an aqueous solution of nitrous acid and its salts, is most preferably used, but activated carbon adsorbed with nitric oxide and iron nitrosyl complex solutions are also suitable. This can be a source of serious problems.

However, among these preparation methods, the method using a nitrite aqueous solution is the easiest and cheapest, and still generates a large amount of nitrogen monoxide.

The permeation tube used in the present invention consists of a closed container having an opening covered with a gas permeable membrane.

As the gas permeable membrane, a membrane made of a polyolefin resin such as polyethylene or polypropylene, a fluororesin such as tetrafluoroethylene resin, a silicone resin, or the like is used.

The film thickness is not particularly limited, and any thickness from a thin film to a plate-like film can be selected as long as the desired permeability can be obtained.

The above-mentioned permeable membrane in the present invention has a two-layer structure separated by an interval, one of the permeable membranes is joined so as to cover the opening of the tube, and a desiccant layer is further provided between the two layers of permeable membranes. It is provided with an acidic gas absorbent layer.

It is preferable that the desiccant layer and the acidic gas absorbent are arranged in this order from the one closest to the opening of the permeation tube.

Further, a filling material such as glass coolant may be filled between the gas permeable membrane and the desiccant, between the desiccant and the acidic gas absorbent, and between the absorbent and the gas permeable membrane, respectively, as required.

The desiccant mentioned above is for preventing the dissipation of water vapor, and although general desiccant agents can be used, strong desiccant agents such as phosphorus pentoxide and magnesium perchlorate are particularly preferably used.

The acidic gas absorbent removes acidic gases such as nitrogen dioxide, and uses sodium hydroxide, potassium hydroxide, soda lime, etc., for example.

It is also possible to use a substance that has the properties of both a desiccant and a gas absorbent (for example, an alkaline desiccant such as magnesium oxide), but in this case, only one type of chemical needs to be filled between the permeable membranes. .

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

That is, the accompanying drawing is a schematic sectional view showing an example of a permeation tube used in the present invention.

This tube includes a glass container 1 having an upper opening, a gas permeable membrane 2A provided to cover the upper opening of the glass container, and abutting against the periphery of the opening of the container 1 with the gas permeable membrane 2A sandwiched therebetween. The cylindrical part 3, the glass wool layer 4A, the desiccant layer 5, the glass wool layer 4B, the acidic gas absorbent 6 and the glass wool layer 4C filled in order on the gas permeable membrane 2A in contact with the cylindrical part, It mainly consists of a gas permeable membrane 2B provided to cover the upper part of the glass wool layer 4C, and grooves are provided at the joint ends of the container 1 and the cylindrical part 3 to prevent gas leakage. Furthermore, a gas-impermeable synthetic resin cylinder 8 molded to match the groove is provided on the outside of the cylinder, and the ends of the gas-permeable membranes 2A and 2B are inserted between these cylinders, and the ends of the gas-permeable membranes 2A and 2B are inserted from the outside. It is configured so that it can be tightened.

The glass container 1 and the cylindrical portion 3 are made of a gas-impermeable synthetic resin pipe 8 (for example, a thick-walled polytetrafluoroethylene resin pipe) as described above.
However, as another method, direct bonding using an epoxy adhesive is also possible.

However, the glass container 1 and the cylindrical portion 3 may be welded together without using a bonding agent.

Still glass wool layers 4A, 4B and 4c are coated with desiccant 5
It is provided to hold the gas absorbent 6, and is not necessarily required in the present invention if the desiccant etc. are self-holding.

Also, other retention means such as foam can be used in place of the glass wool layer.

The above-mentioned permeation tube is placed in an airflow of diluent gas, and a certain amount of nitrogen monoxide gas is diffused from the tube to the outside of the permeable membrane, thereby making it possible to obtain a predetermined low concentration gas.

Examples of the present invention will be shown below.

Example 1 The permeation tube shown in the drawing was prototyped, and nitrogen dilution gas for nitric oxide was prepared using this tube.

This gas concentration is determined from the weight loss of the tube and the gas flow rate, and this value was compared with the nitrogen monoxide analysis value obtained using a nitrogen oxide analyzer using a chemiluminescence method.

A liquid containing 1 mol/l sodium nitrite and 1N sulfuric acid mixed in a ratio of 1:2 is introduced as an internal liquid 9 into a glass container 1 in the drawing.

Polyethylene films are used as the gas permeable membranes 2A and 2B.

The glass container 1 and the cylindrical portion 3 were joined by applying an adhesive to the joint, and then covering the joint with a thick polytetrafluoroethylene resin cylinder 7.

Magnesium perchlorate was used as the desiccant 5, and potassium hydroxide powder was used as the acidic gas absorbent 6.

The order in which these materials are filled in the cylindrical portion 3 is as follows: glass wool, magnesium perchlorate, glass wool, potassium hydroxide, and glass wool are placed on the polyethylene film of the glass container 1, and the top is further covered with a polyethylene film. Ta.

The tube was placed in a nitrogen stream at 21° C. and a flow rate of 500 ml/min, and the concentration of nitrogen monoxide in the gas was measured.

As a result of the measurement over 238 minutes, the weight loss of the tube was 0.0397 g, or 1.32 mmol, while the amount of nitrogen monoxide generated from the gas analysis value was 1.35.
mmol, and both values were almost the same.

In addition, the concentration of nitric oxide at this time ranges from 350 ppm to 1
It showed a linear decrease up to 50 ppr and no nitrogen dioxide was detected.

Next, measurements were carried out over 315 minutes under the same conditions using a tube of the same construction with a larger amount of magnesium chlorate and potassium chloride and a thicker polyethylene film.

During this time, the concentration of nitrogen monoxide in the released gas was maintained at about 27 ppm.

The amount of nitric oxide generated from this measured value was 0. 168
On the other hand, the amount of nitrogen monoxide generated determined from the weight loss of the tube was 0.160 mmIJ mole.

Again, no nitrogen dioxide was detected.

Comparative Example 1 A similar tube was made in Example 1 but filled only with sodium hydroxide as an absorbent without using a desiccant, and 6
Gas was diffused in a nitrogen stream of 500 ml/min at 10°C.

The amount of nitric oxide measured by the analyzer during 1.14 hours was only 0.763 μmol, but when the weight loss of the tube was calculated as the amount of nitric oxide released, it was 11.
The amount reached 5 μmol, and the two values did not match at all.

When this experiment was conducted for 6.10 hours at a temperature of 33°C, the reading on the analyzer remained constant at 0.72 ppm.
The calculated value of the nitric oxide concentration based on the amount of tube weight loss was 54 ppm, and the two values were also significantly different in this case.

Note that nitrogen dioxide was not measured in this comparative example either.

Example 2 In Comparative Example 1, magnesium oxide was used instead of sodium hydroxide, and the temperature was 33°C under the same conditions as Comparative Example 2.
．． The gas was allowed to evolve over a period of 5 hours.

The nitrogen dioxide analyzer value of this gas stabilized at 6.2 ppm, and the total amount of nitrogen monoxide generated was 0.127 mmol, which was calculated based on the amount of tube weight loss, which was 0.
．． It was almost the same as 135 mmol.

This seems to be because magnesium oxide has the properties of both an acid gas absorbent and a desiccant.

As described above, according to the present invention, by providing the desiccant layer and the acidic gas absorbent layer in the permeation tube, only nitrogen monoxide can be diffused out of the tube from the generated nitrogen monoxide-containing gas.

Therefore, an aqueous solution of nitrite nitrogen, which is easy to obtain and handle, can be used as a nitrogen monoxide generation source, and excellent effects such as the amount of nitrogen monoxide released are stable over time can be obtained.

[Brief explanation of drawings]

The drawing is a schematic sectional view showing an example of a permeation tube used in the present invention. 1... Glass container, 2A, 2B... Gas permeable membrane, 3
...Glass tube, 4A, 4B, 4C... Glass wool, 5... Desiccant, 6... Acidic gas absorbent, 7...
Synthetic resin tube.

Claims (1)

[Scope of Claims] 1. A nitrogen monoxide generator comprising a permeation tube having a gas permeable membrane and a nitrogen dioxide generation source sealed inside, the gas permeable membrane having a two-layer structure, A quantitative generation device for nitrogen dioxide, characterized in that a desiccant layer and an acid gas absorbent layer are provided between the layers. 2. The quantitative generation device for nitrogen monoxide according to claim 1, wherein the nitrogen monoxide generation source is an aqueous nitrite nitrogen solution.