JP2006250569A - Filter for gas sensor, and catalytic combustion type city gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure long-term reliability of a catalytic combustion type city gas sensor, by improving greatly the adsorption removal rate of a poisoning component in the atmosphere lowering detection sensitivity of a gas detection element. <P>SOLUTION: In the catalytic combustion type city gas sensor wherein a filter 6 for the gas sensor having activated carbon filled therein is mounted on the periphery of the gas detection element 1 for detecting combustible gas in the atmosphere, fibrous activated carbon having a peak of a distribution of a pore diameter of the activated carbon in a domain over 1.2 nm is filled as the filter 6 for the gas sensor. Preferably, the fibrous activated carbon having the peak of the distribution of the pore diameter of the activated carbon in the domain over 1.2 nm and subjected to activation treatment advanced until having a specific surface area over 1,500 (m<SP>2</SP>/g) is filled as the filter 6 for the gas sensor. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a flammable gas sensor used for a gas leak alarm installed in a general household kitchen or a commercial kitchen.

  Furthermore, the present invention relates to a gas sensor filter filled with activated carbon that is mounted so as to cover the periphery of a gas detection element in order to prevent erroneous reporting due to ethyl alcohol-based steam used during cooking.

  Examples of combustible gas sensors used in gas leak alarms include semiconductor gas sensors and catalytic combustion gas sensors. The semiconductor gas sensor uses tin oxide, which is a metal oxide semiconductor, as a gas sensitive body, and changes the resistance when oxygen adsorbed on the heated sensor surface reacts with combustible gas and desorbs adsorbed oxygen. It is something to detect.

  The catalytic combustion type gas sensor has a gas detection element in which a platinum wire having a large resistance temperature coefficient is coiled, and an oxidation catalyst is formed in a bead shape so as to embed the coil, and the detection principle is about 300 to 400. The flammable gas undergoes an oxidation reaction with oxygen in the atmosphere on the surface of the gas detection element heated to ℃, and the temperature of the gas detection element rises due to the heat generated at that time. It is amplified and detected by a bridge circuit.

  Here, in a gas sensor for a gas leak alarm, a filter cap filled with activated carbon may be put around the gas detection element. This type of filter prevents the so-called false alarm that the gas detection element is sensitive to the vapor (ethyl alcohol) evaporating from the miso or porridge used during cooking, and an alarm is issued even if it is not a gas leak. Objective. That is, even if alcohol vapor is present in the environment, the activated carbon in the filter section adsorbs and removes it to prevent false alarms.

  On the other hand, there are various types of activated carbon used for the gas sensor filter, in which granular activated carbon having a size of about 0.2 to 1 mm is filled in the gas introduction path so as to have a certain thickness. In general, in addition to this, granular activated carbon is molded with a binder to form a disk, or sponge or fibrous activated carbon may be used.

  Here, the integrated activated carbon obtained by molding or the like has advantages such as good workability at the time of filling and gas blow-out due to the deviation of the activated carbon layer due to vibration.

  As an example, JP-A-8-159999 and JP-A-9-5275 describe a filter in which activated carbon is filled in a cylindrical shape as a filter of a catalytic combustion type gas sensor.

  In this cylindrical activated carbon, gas flows in from the outer peripheral surface of the cylinder. Therefore, in the case of disk-shaped activated carbon, the gas inflow direction is limited to the upper surface (end surface) of the disk. The transmission area can be increased several times.

  In the above-mentioned catalytic combustion type gas sensor, the gas to be detected is constantly burned and consumed on the surface of the gas detection element. Therefore, the gas permeability when the detection gas passes through the filter and is supplied to the vicinity of the gas detection element is gas. Significantly affects sensitivity. That is, compared with a disk-shaped activated carbon layer, the use of cylindrical activated carbon can suppress a decrease in gas sensitivity.

  As the material for this cylindrical activated carbon, it is considered that the most practical use is one in which fibrous activated carbon is integrated into a cylindrical shape. The reason for this is that in order to uniformly fill spherical or granular activated carbon into a cylindrical shape, a net-like container is required to keep the granular activated carbon, and the filling operation becomes extremely complicated. Because it ends up.

  On the other hand, if the activated carbon is a fibrous material, it can be easily formed into a sheet shape or integrally formed into a cylindrical shape using a binder, and the activated carbon is retained as in the case of granular activated carbon. A net-like structure is not required.

JP-A-8-159999 JP-A-9-5275

  As described above, the main purpose of installing the activated carbon filter is to prevent false alarms by adsorbing alcohol-based vapor generated in the kitchen, but the other important function is to increase the detection sensitivity of the gas detection element. It is possible to adsorb and remove poisoning components in the atmosphere that lower the temperature and to ensure long-term reliability of the gas sensor.

Components that lower the detection sensitivity of gas detection elements include organic components containing chlorine and sulfur-containing compounds such as sulfurous acid gas and hydrogen sulfide. Among them, organosilicon compounds are sensitive to gas detection elements. It is said to be a so-called permanent poisoning substance that irreversibly lowers. The component of the organosilicone compound decomposes on the heated catalyst element and becomes thermally stable silicon oxide (SiO ₂ ), which covers the active sites of the catalyst and reduces detection sensitivity. .

  Usually, the generation source of the organosilicone vapor contained in the atmosphere of a general household includes tile caulking agents, floor wax, furniture polish, hair spray, and the like, which are composed of the components described later.

  On the other hand, activated carbon has the property of physically adsorbing high-boiling organic gases with a relatively large molecular weight in the pores, and ethanol vapor is similar in nature to organic gases, so it is easy to physically adsorb to activated carbon. Organosilicone compounds also have a relatively high boiling point and are more easily adsorbed on activated carbon than ethanol vapor.

  That is, the activated carbon filter used in the gas sensor that detects flammable gas in the atmosphere has a function of adsorbing and removing organosilicon compounds contained in a minute amount in the atmosphere and maintaining the gas sensitivity of the gas sensor for a long period of time. Note that methane, which is a main component of city gas, has a low molecular weight and a low boiling point, and therefore is hardly adsorbed on activated carbon. Therefore, it is not an obstacle to use an activated carbon filter for a city gas sensor that detects methane.

Therefore, the present inventor attaches a filter made of standard fibrous activated carbon (specific surface area: about 1000 m ² / g) into a cylindrical shape to a catalytic combustion type city gas sensor, and performs the catalytic combustion type city gas by the following method. The poisoning resistance performance of the gas sensor was investigated.

  The following three types of compounds are selected as indicator substances for silicone-based poisoning components, and one of the three types of silicone-based components is specified in a sealed container that holds a catalytic combustion type city gas sensor in an energized state. After injecting to a concentration and holding in that state for 15 hours, electricity was passed in clean air for 1 hour, and the gas sensitivity to methane before and after poisoning was measured.

Silicone (1): Hexamethyldisiloxane (C ₃ H ₁₈ OSi ₂ )
(Formula weight: 162, boiling point: 101 ° C., a chain molecule having one Si—O—Si bond in the molecule)
Silicone (2): Octamethylcyclotetrasiloxane (C ₈ H ₂₄ O ₄ Si ₄ )
(Formula weight: 297, boiling point: 175 ° C., cyclic molecule having 4 Si—O—Si bonds in the molecule)
Silicone (3): Decamethylcyclopentasiloxane (C ₁₀ H ₃₀ O ₅ Si ₅ )
(Formula weight: 371, boiling point: 210 ° C., cyclic molecule having 5 Si—O—Si bonds in the molecule)

  Here, the above-described silicone (1) is a typical index component that is generally used in the test standards of alarm devices when evaluating the influence of silicone vapor on the gas sensor. Silicone (2) and silicone (3) described above are also representative components of the silicone-based vapor contained in a general household atmosphere, as with silicone (1). Among these, silicone (2) and silicone (3) Is said to have a relatively high content in the atmosphere of ordinary households.

FIG. 2 is a diagram showing the results of poisoning tests using silicone (1), silicone (2), and silicone (3). As shown in FIG. 2, the contact combustion type city gas sensor equipped with a cylindrical filter made of standard fibrous activated carbon (specific surface area: about 1000 m ² / g) is highly poisonous to silicone (1). Although performance was shown, the silicone (2) and silicone (3) were inferior in terms of poisoning resistance compared to silicone (1).

That is, the standard fibrous activated carbon (specific surface area: about 1000 m ² / g) used in this test has excellent adsorption performance for the silicone (1) that has been used for the poisoning test so far. Although it has it, it turned out that the adsorption | suction performance is low with respect to silicone (2) and silicone (3) which are comparatively abundant in an actual environment.

  In order to solve the above-described problems, the present inventor has conducted various investigations as to why there is a difference in adsorption performance depending on the difference in the silicone component. As a result, the inventors have found that the following relationship exists between the pore structure of the fibrous activated carbon and the silicone component that is the adsorbing species. FIG. 3 is a graph showing the relationship between the pore radius (nm) and the pore volume (ml / g) of fibrous activated carbon.

(1) A standard fibrous activated carbon (specific surface area: about 1000 m ² / g) has a pore structure having a very sharp distribution with a pore radius of about 1 nm as shown by curve 10 (grade 10) in FIG. have.

(2) Since the above-mentioned silicone (1) is a chain molecule and has a low molecular weight, the molecular size is on the order of 1 nm or less, and it can be sufficiently adsorbed to pores having a pore radius of about 1 nm. It is.

(3) On the other hand, since the silicone (2) and silicone (3) described above are cyclic molecules having 4 to 5 Si—O—Si bonds in the molecule, the molecular size thereof is silicone (1 ) Several times larger than Therefore, silicone (2) and silicone (3) are fibrous carbons whose specific molecular size is too large and whose pore radius is about 1 nm (dominant surface area: about 1000 m ² / g). Is hardly absorbed.

  The reason why the pore size distribution of the fibrous activated carbon has a sharp peak in a specific range is as follows.

  In general, activated carbon uses natural carbon materials such as coconut shells and coal as raw materials, and reacts them at high temperatures in gases such as water vapor, carbon dioxide, and air to produce fine pores by partial reaction of carbonaceous matter. Carbon. This treatment for generating micropores is called activation treatment. The pores have a diameter of 1 to 20 nm, the inner walls of the pores have a large surface area, and various substances are adsorbed on the surface. Since natural carbonaceous materials such as coconut shells and coal have a relatively heterogeneous structure, the diameter of micropores generated by activation is relatively broadly distributed from so-called macropores to micropores.

  On the other hand, fibrous activated carbon is made from a carbonaceous material spun with a synthetic resin such as a phenol resin, and has a high regularity in the arrangement of carbon. Therefore, the pores after carbon is removed by activation are more likely to be pores having a relatively uniform diameter than activated carbon made from coconut shell charcoal.

Compared to standard fibrous activated carbon (specific surface area: about 1000 m ² / g) for adsorbing silicone components having a relatively large molecular size such as silicone (2) and silicone (3) described above, The present inventor estimated that it would be necessary to use activated carbon having a large pore size.

  Therefore, by further advancing the activation treatment of the fibrous activated carbon, the activated carbon having a larger surface area and a larger pore diameter, and a catalytic combustion type gas sensor equipped with a cylindrical activated carbon using this activated carbon, Evaluation of poisoning resistance similar to that described above was performed.

  As a result, if a fibrous activated carbon having a pore radius of 1.2 nm or more is used, excellent adsorption performance for relatively large molecular components such as silicone (2) and silicone (3) described above. Was found to be obtained. Furthermore, activated carbon having pores with a pore radius of 1.6 nm or more, preferably about 2.2 nm, showed the most excellent adsorption performance.

  In addition, in the fibrous activated carbon obtained on a commercial basis, those having a pore radius of about 2.2 nm are the largest. The reason for this is that if it is attempted to obtain a material having a pore radius larger than this, it is necessary to lengthen the time required for activation, which is economically disadvantageous. This is because there is a problem in physical properties that the strength is lowered and the fiber is easily broken.

  As described above, the present invention provides a gas sensor filter capable of greatly improving the adsorption removal rate of poisonous components in the atmosphere that lowers the detection sensitivity of the gas sensor, and the gas sensor filter is a gas detection element. An object of the present invention is to provide a contact combustion type city gas sensor mounted around the vehicle.

  According to the first aspect of the present invention, there is provided a gas sensor filter filled with activated carbon that is mounted around a gas detection unit that detects flammable gas in the atmosphere. A filter for a gas sensor is provided, which is filled with fibrous activated carbon having a peak distribution of pore radii.

  According to invention of Claim 2, it is a cylindrical molded object, The fibrous activated carbon into which gas is allowed to flow in from the side wall part of the cylinder was filled, The gas sensor of Claim 1 characterized by the above-mentioned. A filter is provided.

According to invention of Claim 3, it is the filter for gas sensors with which the activated carbon with which the surroundings of the gas detection means which detects the combustible gas in air | atmosphere was filled was filled, Comprising: Ratio of 1500 (m < ² > / g) or more A filter for a gas sensor is provided, which is filled with fibrous activated carbon having a surface area.

  According to the fourth aspect of the present invention, there is provided a gas sensor filter filled with activated carbon mounted around a gas detection means for detecting flammable gas in the atmosphere, wherein the activated carbon is narrowed to a region of 1.2 nm or more. A filter for a gas sensor is provided, which is filled with fibrous activated carbon that has been activated until it has a peak in the distribution of pore radii.

  According to the fifth aspect of the present invention, there is provided a contact combustion type city gas sensor in which the gas sensor filter according to any one of the first to fourth aspects is mounted around the gas detection means.

  In the gas sensor filter according to claim 1, fibrous activated carbon having a peak of pore radius distribution of activated carbon is filled in a region of 1.2 nm or more. Therefore, compared with the case where standard fibrous activated carbon having a peak of the pore radius distribution of the activated carbon is packed in the region of about 0.9 nm, the amount of gas in the atmosphere is reduced. The adsorption / removal rate of poisonous components can be greatly improved. Thereby, long-term reliability of the gas sensor can be ensured.

  The filter for a gas sensor according to claim 2 is filled with fibrous activated carbon that is a cylindrical molded body and into which gas can flow from a side wall portion of the cylinder. That is, the gas sensor filter according to claim 2 is filled with fibrous activated carbon formed into a cylindrical shape so that gas can flow in from the outer peripheral surface. Therefore, the substantial permeation area of the gas can be made larger than when the activated carbon is formed in a disc shape so that the gas can flow from the end face.

The filter for gas sensor according to claim 3 is filled with fibrous activated carbon having a specific surface area of 1500 (m ² / g) or more. Therefore, adsorption removal of poisonous components in the atmosphere that lowers the detection sensitivity of the gas detection means compared to the case where standard fibrous activated carbon having a specific surface area of about 1000 (m ² / g) is packed. The rate can be greatly improved. Thereby, long-term reliability of the gas sensor can be ensured.

  The filter for a gas sensor according to claim 4 is filled with fibrous activated carbon that has been activated until the pore radius distribution peak of the activated carbon has a peak in a region of 1.2 nm or more. Therefore, compared with the case where standard fibrous activated carbon that has not been activated until it has a peak of the pore radius distribution of the activated carbon in a region of 1.2 nm or more is filled, the detection sensitivity of the gas detection means is improved. It is possible to greatly improve the adsorption / removal rate of the poisoning components in the atmosphere that are reduced. Thereby, long-term reliability of the gas sensor can be ensured.

  In the catalytic combustion type city gas sensor according to claim 5, it is possible to reduce the possibility that the detection sensitivity of the gas detection means is lowered due to the poisoned component in the atmosphere. Thereby, long-term reliability can be ensured.

  Specifically, a filter using fibrous activated carbon having a sharp pore distribution peak at a specific radius of a pore radius of 1.2 nm or more with respect to a gas detection means for detecting a combustible gas in the atmosphere. By mounting, it becomes possible to adsorb and trap cyclic organosilicone vapor contained in a relatively large amount in the actual environment in the pores with high efficiency.

  In particular, by attaching an integrated filter made of this fibrous activated carbon into a cylindrical shape to a contact combustion type city gas sensor, it has high gas sensitivity and can be poisoned by cyclic silicone vapor present in the actual environment. A highly reliable catalytic combustion type city gas sensor that maintains stable sensitivity and alarm performance for a long period of time and a city gas alarm having the same can be obtained.

  Hereinafter, a first embodiment of a catalytic combustion type city gas sensor of the present invention will be described. FIG. 1 is a cross-sectional view of the catalytic combustion type city gas sensor of the first embodiment. As shown in FIG. 1, in the contact combustion type city gas sensor of the first embodiment, the gas detection element 1 for detecting the combustible gas in the atmosphere and the temperature compensation element 2 block their thermal influence. Are held by the two metal pins 5 on the same sensor base 4 via the heat shielding plate 3. The gas detection element 1 is an oxidation catalyst element in which palladium is supported on gamma alumina. A platinum coil is embedded therein, and the gas detection element 1 is heated and held at about 400 ° C. by a current flowing through the coil. In the gas detection element 1, when methane is present in the atmosphere, the methane is oxidized on the surface of the element, and the temperature rises according to the combustion heat. As a result, the resistance value of the platinum coil is increased. .

  The temperature compensation element 2 is made of only gamma alumina that is inactive to methane oxidation, and is heated to about 400 ° C. like the gas detection element 1. On the temperature compensation element 2, methane does not substantially oxidize. Therefore, if methane is present, a difference is generated between the coil resistance value of the gas detection element 1. The difference between the resistance values is taken out as an output by a bridge circuit configured in substantially the same manner as the bridge circuit described in, for example, JP-A-8-159999.

  As described in detail in Japanese Patent Application Laid-Open No. Hei 8-159999, the gas detection element 1 and the temperature compensation element 2 are each made of two metals standing on the sensor base 4 at both ends of each platinum wire. The pin 5 is held by welding.

  Around the gas detection element 1 and the temperature compensation element 2, an integral and cylindrical activated carbon 6 made of fibrous activated carbon is mounted as a gas sensor filter, and the zenith portion of the activated carbon 6 prevents gas from entering. The metal cap 7 is covered. Furthermore, the activated carbon 6 and the cap 7 are covered with a double net 8 made of stainless steel. The stainless steel double net 8 is provided in order to satisfy the standard of the explosion-proof structure stipulated in the law as the inspection rule for the gas leak alarm. The skirt of the net 8 is fixed to the sensor base 4 by a ring-shaped caulking metal fitting 9.

  The gas sensor filter is integrally formed into a cylindrical shape using fibrous activated carbon 6 as described in detail in Japanese Patent Application Laid-Open No. Hei 8-159999. Specifically, first, a fibrous activated carbon filler is dispersed in water together with a small amount of binder, and an end-sealed metal tube having a large number of micropores on the wall surface is immersed in this state. Then, suction is performed from the opening of the tube on the water surface, and an activated carbon fiber filler is laminated on the outer wall surface of the tube. Next, it is pulled up from the liquid and dried, and the tube is pulled out to obtain an earth-like tubular molded body, which is cut into a predetermined length. As a result, the fibrous activated carbon 6 as the gas sensor filter shown in FIG. 1 is obtained.

  In the contact combustion type city gas sensor of the first embodiment, the fibrous activated carbon 6 is formed so that gas flows in from the side wall portion of the fibrous activated carbon 6 formed into a cylindrical shape, that is, from the outer peripheral surface of the fibrous activated carbon 6. Has been placed.

  Furthermore, in the contact combustion type city gas sensor of the first embodiment, as a gas sensor filter, there is a peak of the pore radius distribution of the activated carbon in the region of 1.2 nm or more as shown by the curve 15 (grade 15) in FIG. Fibrous activated carbon 6 is filled.

In other words, in the catalytic combustion type city gas sensor of the first embodiment, fibrous activated carbon 6 having a specific surface area of 1500 (m ² / g) or more is filled as a gas sensor filter.

Specifically, in the contact combustion type city gas sensor of the first embodiment, the filter for the gas sensor has a peak of the pore radius distribution of the activated carbon in a region of 1.2 nm or more, and 1500 (m ² / g ) Fibrous activated carbon 6 that has been activated until it has the above specific surface area is filled.

  The contact combustion type city gas sensor of 2nd Embodiment is comprised similarly to the contact combustion type city gas sensor of 1st Embodiment mentioned above except the point mentioned later.

Specifically, in the contact combustion type city gas sensor of the second embodiment, as a gas sensor filter, the pore radius distribution of the activated carbon in the region of 1.6 nm or more as shown by the curve 20 (grade 20) in FIG. A fibrous activated carbon 6 having a peak is filled. In other words, in the catalytic combustion type city gas sensor of the second embodiment, fibrous activated carbon 6 having a specific surface area of 2000 (m ² / g) or more is filled as a gas sensor filter. In detail, in the contact combustion type city gas sensor of 2nd Embodiment, it has a peak of distribution of the pore radius of activated carbon in a 1.6 nm or more area | region as a filter for gas sensors, and is 2000 (m < ² > / g). ) Fibrous activated carbon 6 that has been activated until it has the above specific surface area is filled.

  The catalytic combustion type city gas sensor of the third embodiment is configured in the same manner as the catalytic combustion type city gas sensor of the first embodiment described above, except for the points described below.

Specifically, in the catalytic combustion type city gas sensor of the third embodiment, as a gas sensor filter, the pore radius distribution of the activated carbon in the region of 2.2 nm or more as shown by the curve 25 (grade 25) in FIG. A fibrous activated carbon 6 having a peak is filled. In other words, in the catalytic combustion type city gas sensor of the third embodiment, fibrous activated carbon 6 having a specific surface area of 2500 (m ² / g) or more is filled as a gas sensor filter. In detail, in the contact combustion type city gas sensor of 3rd Embodiment, it has a peak of distribution of the pore radius of activated carbon in the area | region of 2.2 nm or more as a filter for gas sensors, and 2500 (m < ² > / g). ) Fibrous activated carbon 6 that has been activated until it has the above specific surface area is filled.

[Comparative Example]
The contact combustion type city gas sensor of the comparative example is configured in the same manner as the contact combustion type city gas sensor of the first embodiment described above, except for the points described below.

  Table 1 shows the fibrous activated carbon used as a filter in the catalytic combustion type city gas sensor of the comparative example. The activated carbon raw materials shown in Table 1 are standard products that are generally commercially available as fibrous activated carbon. That is, in the catalytic combustion type city gas sensor of the comparative example, a fibrous activated carbon as a standard product was used as a filter.

  Table 2 shows the poisoning conditions in the poisoning test of the catalytic combustion type city gas sensor of the comparative example. In the poisoning test of the contact combustion type city gas sensor of the comparative example, the contact combustion type city gas sensor was exposed to silicone vapor under the conditions shown in Table 2, and the methane gas sensitivity before and after exposure was measured by the contact combustion type city gas sensor. In addition, the density | concentration of the silicone type vapor | steam in a real environment is 0.1 ppm or less at most, and it can be said that the poisoning conditions of Table 2 are extremely severe conditions compared with a real environment.

  The result of the poisoning test of the catalytic combustion type city gas sensor of the comparative example is included in FIG. 2 described above. The sensitivity remaining rate on the vertical axis in FIG. 2 indicates how much methane sensitivity after exposure remains with respect to the methane sensitivity before exposure, as shown in the following formula. It shows that it is excellent in poisoning resistance.

Methane sensitivity remaining rate (%) = ((sensitivity to 0.4% methane after exposure) / (sensitivity to 0.4% methane before exposure)) × 100

  For comparison, the broken line in FIG. 2 shows the sensitivity remaining rate of the contact combustion type city gas sensor not equipped with the activated carbon filter.

  As shown in FIG. 2, when the activated carbon filter is not attached, the sensitivity decreases to about 20% or less before poisoning, whereas when grade 10 activated carbon is used as a filter, silicone (1 ) Was removed with high efficiency. However, this grade 10 activated carbon filter was found to have poorer adsorption performance for silicone (2) and silicone (3) than silicone (1).

[Example 1]
Grade 10 activated carbon, which is a standard product used in the comparative example, has a larger pore size than the standard product because of its low adsorption performance for silicone (2) and silicone (3) having a cyclic molecular shape and a relatively large molecular size. Fibrous activated carbon material was used as a filter to evaluate its poisoning resistance.

  Table 3 shows the fibrous activated carbon used as a filter in the catalytic combustion type city gas sensor of the example. The same poisoning test as in the comparative example was performed on three types of fibrous activated carbon raw materials as shown in Table 3 in which the activation treatment was further advanced than the standard products shown in Table 1 to increase the pore diameter.

  FIG. 3 shows the pore distribution of grade 10 fibrous activated carbon used in the comparative example, and the pore distribution of grade 15, grade 20 and grade 25 fibrous activated carbon shown in Table 3 used in the examples. Show. The horizontal axis in FIG. 3 indicates the pore radius (nm) of the fibrous activated carbon, and the vertical axis indicates the pore volume (ml / g). The pore volume indicates a cumulative value of pore volume accumulated from the narrower pore diameter. That is, FIG. 3 shows that there is the most frequent pore diameter in the region where the pore volume increases sharply. That is, the numerical values shown in the rightmost column of Table 3 indicate the pore diameters that are present most frequently.

  FIG. 4 is a view showing the poisoning test results of the catalytic combustion type city gas sensor using the activated carbon shown in Tables 1 and 3. As shown in FIG. 4, when a grade 15 fibrous activated carbon having a pore radius distribution peak at 1.2 nm is used, the comparative grade having a pore radius distribution peak at 0.9 nm is used. It was found that the anti-poisoning performance was greatly improved as compared with the case of using 10 fibrous activated carbon.

  It has also been found that by using grade 20 or grade 25 fibrous activated carbon having a larger pore radius, further excellent poisoning resistance can be obtained.

[Example 2]
A city where a catalytic combustion type city gas sensor equipped with two types of filters prepared with the grade 10 activated carbon of the comparative example and the grade 25 activated carbon of the example 1 is mounted on the city gas alarm and the city using the grade 10 activated carbon. A gas alarm and a city gas alarm using activated carbon of grade 25 were paired and installed in 20 kitchens for about five years, and removed every year to monitor the transition of methane alarm concentration. .

  FIG. 5 is a diagram showing the monitoring result of the transition of the methane alarm concentration. The vertical axis in FIG. 5 indicates the methane gas concentration at which a gas leak alarm is issued, and the initial setting is such that an alarm is given at a methane concentration of about 0.35%. As the value of the alarm concentration increases, the detection sensitivity of the gas detection element 1 (see FIG. 1) with respect to methane decreases. In addition, the plot in FIG. 5 has shown the maximum value and the minimum value of the alarm density | concentration of the city gas alarm device which attached two types of filters, the grade 10 activated carbon filter and the grade 25 activated carbon filter, respectively.

  As shown in Fig. 5, in the catalytic combustion type city gas sensor using grade 10 fibrous activated carbon as a filter, the alarm concentration of methane has shifted to a high concentration side over time, and its variation range has increased. In the case of the catalytic combustion type city gas sensor of the present invention using grade 25 fibrous activated carbon as a filter, the fluctuation of the alarm concentration toward the high concentration side was suppressed to be extremely small even after 5 years of use.

  In addition, as shown in FIG. 5, the reason why the degree of desensitization of the methane alarm concentration of the catalytic combustion type city gas sensor using grade 10 fibrous activated carbon as a filter greatly varies between max and min is Therefore, it is interpreted that the type, concentration, frequency of occurrence, etc. of silicone-based steam differ depending on the installation location of the catalytic combustion type city gas sensor.

  On the other hand, as shown in FIG. 5, the degree of change over time of the methane alarm concentration of a contact combustion type city gas sensor using grade 25 fibrous activated carbon as a filter does not vary much between max and min, and the contact combustion type The reason why the alarm performance of the city gas sensor is stably maintained for a long period of time is because the adsorption performance of the grade 25 fibrous activated carbon with respect to the cyclic silicone-based steam present in the actual environment is excellent. This is interpreted as being hardly affected by variations in environmental conditions such as concentration and frequency of occurrence.

It is sectional drawing of the contact combustion type city gas sensor of 1st Embodiment. It is the figure which showed the result of the poisoning test using silicone (1), silicone (2), and silicone (3). It is the figure which showed the relationship between the pore radius (nm) and pore volume (ml / g) of fibrous activated carbon. It is the figure which showed the poisoning test result of the contact combustion type city gas sensor using the activated carbon shown in Table 1. It is the figure which showed the monitoring result of transition of a methane warning density | concentration.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas detection element 2 Temperature compensation element 3 Heat shielding board 4 Sensor base 5 Metal pin 6 Activated carbon (gas sensor filter)
7 Cap 8 Net 9 Caulking bracket

Claims (5)

  A filter for a gas sensor filled with activated carbon mounted around a gas detection means for detecting a combustible gas in the atmosphere, and a fibrous activated carbon having a peak of pore radius distribution of activated carbon in a region of 1.2 nm or more A filter for a gas sensor, wherein   The filter for a gas sensor according to claim 1, wherein the filter is a cylindrical molded body and is filled with fibrous activated carbon into which gas is allowed to flow from a side wall portion of the cylinder. A filter for a gas sensor filled with activated carbon mounted around a gas detection means for detecting a combustible gas in the atmosphere, and filled with fibrous activated carbon having a specific surface area of 1500 (m ² / g) or more. Characteristic filter for gas sensor.   A gas sensor filter filled with activated carbon that is mounted around a gas detection means for detecting a combustible gas in the atmosphere, and activated until a pore radius distribution peak of activated carbon is present in a region of 1.2 nm or more. A filter for a gas sensor, which is filled with fibrous activated carbon that has been advanced.   A catalytic combustion type city gas sensor, wherein the gas sensor filter according to any one of claims 1 to 4 is mounted around the gas detection means.

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