JPS6199849A - Gas detecting element with filter - Google Patents

Abstract

PURPOSE:To prevent the sensitization of a gas detecting element owing to hydrogen sulfide and the false announcement of a gas leak alarm, etc. and to improve the reliability of the element by depositing lead acetate to the gas discriminating filter of the gas detecting element made into the construction in which said element is enclosed by said filter. CONSTITUTION:0.1-5wt% Lead acetate is deposited on the filter constituted of active alumina, active carbon, etc. by a method consisting of immersing the filter in an aq. lead acetate soln. and drying the same or forming the filter material into powder, adding the aq. soln. of lead acetate thereto and drying the mixture after kneading. The resulted filter is so attached as the gas discriminating filter to the gas detecting element as to enclose the element. The hydrogen sulfide which sensitizes the gas detecting element and causes the false announcement is thus adsorbed and fixed by the reaction expressed by the formula, by which the increase in the sensitivity of the gas detecting element is prevented.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a gas detection element with a filter that constitutes a gas detection unit such as a gas leak alarm. [Background Art] CH4, Hz, Cs Ha,
To selectively detect gases such as CaHto,
A filter with a filter for discriminating gases such as activated carbon or activated alumina is attached to the gas detection element, and the filter adsorbs interfering gases, mist, dust, etc., and prevents these interfering gases from reaching the above element. Gas sensing elements have been known for a long time. The purpose of this gas detection element with a filter is to prevent false alarms from gas leak alarms due to ethanol etc. generated during cooking.
It had some effect.

Recently, gas leak alarms installed in the underground dining area have been causing a large number of false alarms, which has become a major problem.

The cause of these false alarms is, of course, the presence of gases that easily react with gas detection elements, such as ethanol and fuel gas, in the atmosphere near the alarm, but what is more important is that By exposing the gas detection element to a harsh atmosphere, the gas detection element itself gradually deteriorates.
This means that the sensitivity to target gases (methane gas, butane gas, hydrogen gas, etc.) is changing. For this reason, even if the above-mentioned ethanol or fuel gas is present at a low concentration, an alarm is issued. Among the substances that cause this change in sensitivity over time (these are called poisonous substances), they particularly make the gas detection element more sensitive (reducing the sensitivity to -1-
) is sulfur dioxide gas (SO2), and 1
Even at low concentrations, less than ppm, the effects are significant.

Therefore, the inventor added barium chloride to the filter.

We have developed a method to prevent sensitization of the gas detection element by supporting one or more of strontium chloride and calcium chloride and adsorbing sulfur dioxide gas on the filter.

However, the same sulfide, hydrogen sulfide (HzS
) has also been found to sensitize gas detection elements at concentrations as low as 1 ppm, and it has become necessary to consider ways to protect gas detection elements from hydrogen sulfide.

[Purpose of the invention]

In view of the above points, it is an object of the present invention to provide a filter sticky gas detection element that does not cause a change in sensitivity of the gas detection element.

[Disclosure of the invention]

In order to achieve the above object, the present invention provides a gas detection element with a filter, which has a structure in which the gas detection element is surrounded by a filter, and the gas detection element with a filter is characterized in that the filter carries lead acetate. do. This invention will be explained in detail below.

Adsorption removal of hydrogen sulfide, which increases the sensitivity of gas detection elements, is possible to some extent with conventional gas discrimination filters (activated alumina, activated carbon, etc.), but cannot be completely removed. To completely remove hydrogen sulfide, add lead acetate (
When P b (CH3Co2)2] is supported, the following reaction occurs, and hydrogen sulfide is chemically adsorbed and fixed on the filter.

]1□S0Pb(CH3COz)2 → pbs+2cH3cOOI (Lead sulfide (PbS) is thermally stable, and acetic acid (CH3COOH) also does not affect the gas detection element. Therefore, gas detection Hydrogen sulfide, which is a substance that makes the element sensitive, becomes a stable and harmless substance that is fixed to the filter material and does not increase the sensitivity of the gas detection element.

As a method for supporting lead acetate on a filter, an aqueous solution containing lead acetate is prepared, the filter is immersed in the aqueous solution, the filter is impregnated with the aqueous solution of lead acetate, and the filter is dried, or the filter material is powdered. There are methods such as adding the lead acetate aqueous solution, kneading and drying.

Note that the amount of lead acetate supported on the filter is preferably 0.1 to 5 wt% with respect to the filter.

The following will explain based on Examples and Comparative Examples (Examples) Commercially available activated alumina (manufactured by Shayu Aluminum Scouring ■)
Processed into a cylindrical shape with an outer diameter of 22+u+, an inner diameter of 15 mm, and a height of 20 mm, a 25 wt% lead acetate aqueous solution (temperature 40°C) was prepared.
It was soaked in water for 1 hour to impregnate it with the aqueous solution.

Thereafter, this was dried at 100° C. for 2 hours. From weight measurements of the activated alumina before dipping and after drying, it was found that the amount of supported lead acetate was 2 wt % based on the activated alumina. As shown in Figure 1, this cylinder made of activated alumina supporting lead acetate is used as a filter l, the upper end of this cylinder is closed with Pyrex glass 2, and the lower end is sealed with epoxy adhesive to prevent gas detection. It was adhered to element 3.

(Comparative Example) A commercially available activated Narumina (manufactured by Sumitomo Aluminum Refining Co., Ltd.) was processed in the same manner as in the example, without supporting lead acetate, and shaped as shown in FIG. 1 in the same manner as in the example.

In order to evaluate the performance of the above two gas detection elements with filters, the following tests were conducted. These gas detection elements with filters are energized in a test tank in which hydrogen sulfide is continuously generated so that the hydrogen sulfide concentration is 10 ppm, and taken out periodically to detect methane (CH4) gas and hydrogen (H2) gas. Changes in sensitivity were measured. The measurement of sensitivity is d, P
, (de-w point, dew point) element resistance value (Ra) in purified air at 13°C, element resistance value (Rm) at 500 ppm, 1500 ppm, and 4500 ppm of methane gas, and 500 ppm of hydrogen gas, respectively.
This was done by measuring the element resistance value (Rh) at ppm, 1500 ppm, and 4500 ppm. The test results of the filter-equipped gas detection element of the example are shown in FIG. 2, and the test results of the filter-equipped gas detection element of the comparative example are shown in FIG. In addition, in these figures, the values of Rm and Rh are 3 each because the concentrations of methane gas and hydrogen gas are 5 and 5, respectively, starting from the top.
00,150Q, shows the value at 4500ppm, R
The reason why h is shifted from Rm is to make it easier to express.

From the comparison between Figures 2 and 3, the filtered gas detection element made of activated alumina supporting lead acetate has a higher element resistance value Rm and Rh for methane gas and hydrogen gas than the filtered gas detection element made only of activated alumina. Since there is no decrease in sensitivity, that is, no sensitization occurs, and the sensitivity characteristics are stable, it can be said that the element is not poisoned by hydrogen sulfide.

In the above embodiment, activated alumina was used as the filter material, but activated carbon may also be used as the filter material.

(Effects of the Invention) As seen above, the filter-equipped gas detection element of the present invention has lead acetate supported on the gas discrimination filter, which improves the hydrogen sulfide adsorption effect. , the filter-equipped gas detection element according to the present invention is
Since it is not poisoned by hydrogen sulfide and does not cause an increase in sensitivity, using it will prevent false alarms or false alarms from gas leak alarms, etc., and improve reliability.

[Brief explanation of the drawing]

Fig. 1 is a partial cross-sectional perspective view showing the shape of an element using an activated alumina cylinder as a filter, Fig. 2 is a graph showing sensitivity changes of a gas detection element with a filter made of activated alumina carrying lead acetate, and Fig. 3 The figure is a graph showing the sensitivity change of a gas detection element with a filter made only of activated alumina. 1...Cylindrical filter made of activated alumina 2...Glass 3...Gas detection element agent Patent attorney Takehiko Matsumoto
Mysterious Jr.
Rh R171r-4-.

Claims (4)

[Claims] (1) A gas detection element with a filter having a structure in which the gas detection element is surrounded by a filter, wherein the filter carries lead acetate. (2) A gas detection element with a filter according to claim 1, wherein the filter material is activated alumina. (3) A gas detection element with a filter according to claim 1, wherein the filter material is activated carbon. (4) The filter-equipped gas detection element according to any one of claims 1 to 3, wherein the amount of lead acetate supported on the filter is 0.1 to 5 wt% relative to the filter.