JPS6070336A - Method for yielding gas having constant concentration - Google Patents

Abstract

PURPOSE:To supply vapor of a pure material having a constant concentration, by passing a balance gas through a porous carrier, in which liquid or solid pure material is impregnated, at a constant temperature and at a constant speed, and diluting the yielded gas by a diluting gas. CONSTITUTION:A saturated vapor yielding cell 5 is filled with a porous carrier 20, in which a pure material is impregnated. The temperature of the cell is kept at a constant temperature lower than a room temperature. A balance gas is adjusted to a constant flow rate by mass flow rate adjusting devices 2 and 3 through an introducing port 1, a line 15, and lines 16 and 17. Then the gas is sent to a mixing valve 18 through lines 8 and 9. The gas is also introduced into the cell 5 through an introducing pipe 10. In the cell 5, the saturated vapor of the pure material is yielded and sent to the mixing valve 18 through a discharge port 11 and a line 12. The vapor is mixed with the balance gas from the line 8 and diluted. The mixture is outputted through a line 13, a gas mixing pipe 7, and a line 14.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for continuously generating vapor of a pure substance at a constant concentration, and particularly relates to a method for continuously generating vapor of a pure substance that is liquid or solid at room temperature at an arbitrary constant concentration below the saturation concentration. This relates to a method for generating

Continuous generation of pure substance vapor at a constant concentration is extremely important for the purpose of generating standard gas for calibration in instrumental analysis of various gas concentrations. For example, it is necessary to supply standard gases for gas analysis in a wide range of fields, such as measurement of the absolute concentration of water vapor in the air, analysis of air pollution gases, analysis of harmful gases in working environments, analysis of odors, and analysis of indoor living environments. . Continuous supply of gas at a constant concentration is also required in fields other than analytical purposes, such as standard gas for biological tests for evaluating the toxicity of gases.

Conventionally, for substances that are gaseous at room temperature, a standard gas is continuously generated by using a gas filled in a container prepared to a known concentration, or by mixing pure gas with a diluent gas at a constant flow rate. However, the above method cannot be applied to vapors of substances that are liquid or solid at room temperature.

Conventionally, gas permeation methods and gas diffusion methods have been put into practical use as methods for continuously generating vapor of a liquid or solid substance at a constant concentration at room temperature. In the gas infiltration method, a liquid or solid pure substance is generally sealed in a gas infiltration tube, and the gas generated from the pure substance permeates the wall of the infiltration tube and diffuses out of the tube at a constant rate. Taking advantage of this fact, constant concentration gas is continuously generated. On the other hand, in the gas diffusion method, when the gas generated from a pure substance placed in a gas diffusion tube is diluted by diffusion through the space inside the diffusion tube, the diffusion rate is constant at a constant temperature. occurs continuously. However, in the constant concentration gas generation method using the gas permeation method and gas diffusion method described above, even if the gas permeation rate and gas diffusion rate are constant, the amount of gas generated or the gas concentration is determined by the length of the permeation tube, the film thickness, and the material. The exact concentration value of the generated gas needs to be determined experimentally because it varies depending on the geometrical state of the diffusion tube and other factors. In addition, in any of the above methods, it takes a long time for gas permeation or gas diffusion to reach an equilibrium state, especially for substances with low vapor pressure, and the concentration generated is limited to a low concentration range. .

The inventors of the present invention solved the problems seen in conventional constant concentration gas generation, and as a result of intensive research on a method to continuously generate vapor of a substance at an arbitrary concentration below its saturated concentration, we found that this method differs from the conventional method. A method for continuously generating constant concentration gas based on the principle was discovered, and the present invention was completed. The method of the present invention is based on the fact that the vapor pressure of a liquid or solid substance at a constant temperature and pressure is unique and constant depending on the substance, and continuously generates a saturated gas of the substance at a constant temperature. The principle is to dilute at a fixed rate as necessary.

That is, according to the present invention, a porous carrier impregnated with a liquid or solid pure substance is maintained at a constant temperature, and a balance gas that does not interact with the pure substance is passed over the surface of the carrier at a constant flow rate. Accordingly, a method for generating a constant concentration gas is provided, which is characterized in that a gas with a saturated concentration of the pure substance is continuously generated, and the generated gas is diluted to an arbitrary concentration using a diluent gas having an arbitrary flow rate ratio. .

Next, the present invention will be explained with reference to the drawings. In Fig. 1, 5 is a saturated steam generation cell, and the inside of the cell is filled with a porous carrier impregnated with a pure substance, or a thin film material 2o with a large surface area. be done. The porous support or thin film material is maintained at a constant temperature below room temperature.

1 is the introduction port for balance gas (dilution gas);
The balance gas introduced from the line passes through line 5,
The flow is divided into two parts, and one of the flows passes through line 16 and mass flow regulators 2 and 3, is adjusted to a constant flow rate, and is then sent to mixing valve 18 through line 8. The other flow passes through line 17, passes through mass flow rate controllers 2 and 3, and is regulated to a constant flow rate, and then is introduced into saturated steam generation cell 5 from line 9 through balance gas introduction pipe 10. be done.

In the steam generation cell 5, pure saturated steam is generated, which is sent through the outlet 11 and the line 12 to the mixing valve 1B, where it is mixed and diluted with the balance gas that has passed through the line 8. This diluted pure substance vapor is introduced through line 13 into gas mixing tube 7 and from there is led out through line 14. 4 is a constant temperature bath and 6 is a temperature detector.

The invention also applies to the generation of multiple gas mixtures, the apparatus for which is shown in FIG. In FIG. 2, the same symbols as those shown in FIG. 1 have the same meanings. In this device, saturated steam of separate pure substances is generated in the saturated steam generation cells 5-1, 5-2 and 5-3, and these steams are introduced into the gas mixing pipe 7 and mixed there, line 1
4.

In the present invention, when the pure substance serving as the steam generation source is in liquid form, the pure substance is placed at the bottom of the saturated steam generation cell and impregnated into the porous carrier by capillary action, so that the carrier is constantly filled with the pure substance. Wet and evaporate from the support surface. Furthermore, when the pure substance is a solid, it can be used by dissolving it in a solvent in advance, impregnating it into a carrier, and then removing the solvent. The support in the saturated vapor generation cell is used to promote evaporation by increasing the evaporation area of the pure substance, and to quickly reach vapor pressure equilibrium.If it is a porous material that has no chemical interaction with the pure substance, Any of these can be used, but preferred are cellulose fiber materials, glass fiber materials, mineral particles such as diatomaceous earth, granular polymer materials, and more preferably net-like or woven cellulose fibers, and honeycomb-structured materials. The filter used is one in which cellulose filter paper and cotton gauze are laminated, and a piece of gauze is bonded to the bottom of the laminated cotton gauze for soaking in liquid and absorbing the liquid. As the balance (dilution) gas introduced into the saturated steam generation cell, any gas that does not interact with pure substances, such as air, nitrogen, helium, and argon, can be selected depending on the purpose.

According to the present invention, vapor pressure equilibrium is quickly established between the pure substance and the passing gas in the saturated steam generation cell, and the saturated concentration gas of the pure substance at that temperature is continuously sent out from the cell outlet. It will be done. The equilibrium vapor pressure of a substance under constant temperature and constant pressure belongs to the physical properties inherent to the substance, and as long as gas-liquid equilibrium or gas-solid equilibrium is established within the cell, the concentration of the gas produced will depend on the physical state of the structure of the device. is constant regardless. Further, the saturated vapor concentration of these pure substances can be easily determined from known data as the vapor pressure at a predetermined temperature. Further, when adjusting the gas concentration below the saturation concentration, it is easy to dilute the generated saturation concentration gas to an arbitrary concentration with a diluent gas at a predetermined flow rate ratio and continuously supply the diluted gas.

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

Example After injecting 20 mn of organic solvent as a pure substance shown in the table into the inner bottom of a saturated steam generation cell made of cylindrical glass with an inner diameter of 15 mm and a height of 200 mm, a circular cotton gauze laminate with a diameter of about 15 mm was placed in the lower layer. Insert it so that it is immersed in an organic solvent. The height of the laminate is set to 30 to 50 mm, and after the organic solvent has permeated to the upper layer of the laminate, the saturated steam generating cell is placed in a constant temperature water layer and purified air is passed through the gas inlet at a flow rate of 20 mQ/min. Gas chromatography analysis of the generated gas every 30 minutes after ventilation showed a constant concentration over 48 hours with a relative standard deviation of less than 2%.

The table also shows the analytical values of saturated gases generated from various organic solvents at 0°C and 10°C using the above-mentioned apparatus, and the vapor pressure values obtained from literature.

[Brief explanation of drawings]

Figures 1 and 2 show examples of apparatuses for implementing the present invention. Figure 1 shows a constant concentration gas generator containing a single pure substance, and Figure 2 shows a constant concentration gas generator containing a plurality of pure substances. The generator is shown. 1... Balance gas inlet, 2, 3... Mass flow controller, 4... Constant temperature chamber, 5.5-1.5-2.5-3...
- Saturated steam generation cell, 6... temperature detector, 20...
Porous carrier, liquid pure substance.

Claims (1)

[Claims] (1) A porous carrier impregnated with a liquid or solid pure substance is kept at a constant temperature, and a balance gas that does not interact with the pure substance is passed through the surface of the carrier at a constant flow rate to produce the pure substance. Continuously generates gas with a saturated concentration of
A constant concentration gas generation method characterized by diluting the generated gas to an arbitrary concentration using a diluent gas having an arbitrary flow rate ratio.