JP6438685B2 - Gas detector - Google Patents

Description

  The present invention relates to a gas detector including a gas detection element having a gas sensitive portion that comes into contact with a gas to be detected.

  In Patent Document 1, an adsorption filter using activated carbon, zeolite, silica gel, a plastic gas-selective permeable membrane, or the like is provided to absorb miscellaneous gases such as water vapor, ethanol, or trichrene, and miscellaneous gas detection elements. A gas sensor that can mitigate the effects of gas is disclosed.

  Patent Document 2 discloses a gas sensor in which a disturbing component inflow restricting means is provided between a removing means for removing a disturbing component of a gas to be detected and a gas sensitive part. The interference component inflow restricting means can alleviate the influence when the disturbing component is absorbed and released from the removing means due to a change in atmosphere, and can prevent malfunction of the gas sensor when the atmosphere state changes. Specifically, the disturbance component inflow restricting means is disclosed as an inflow restricting plate provided with a pinhole, and the inflow restricting plate is fixed to the housing by a fixing means between the removing means and the gas sensitive part. Has been.

JP 2003-156463 A JP-A-10-197470

  Anti-condensation sprays and hair sprays used at home may contain siloxane compounds. The siloxane compound is an organic polymer having a “Si—O—Si” siloxane bond in the skeleton.

  When the siloxane compound adheres to the gas detection element, the detection sensitivity of the gas detection element decreases, or the gas detection sensitivity increases with respect to gases other than the gas that should be selectively detected, which may cause malfunction. There was. This is because the siloxane compound contained in the gas to be detected reaches the gas detection element as a disturbing component, and the siloxane compound or a decomposition product thereof adheres to the gas detection element, thereby changing the gas detection characteristics of the gas detection element. It is considered a thing.

  Therefore, for example, in a flammable gas sensor, an adsorption filter using activated carbon as an adsorbent is arranged as in Patent Document 1, so that the siloxane compound is adsorbed by the adsorption filter, and the siloxane compound reaches the surface of the gas detection element. Can be prevented.

  In addition to the siloxane gas (siloxane compound) that affects the gas sensor characteristics, in indoor environments such as kitchens where flammable gas sensors are installed, it has recently been used as an organic gas (VOC) for insect control, disinfection, and disinfection. Increasing cases of large amounts of chlorinated gases such as paradichlorobenzene, sodium hypochlorite, and chlorine dioxide.

  When a combustible gas sensor equipped with the above-described adsorption filter is installed in a room such as a kitchen, the adsorption filter adsorbs interfering components such as a siloxane compound and a chlorine-based gas floating in the room. In particular, the chlorine-based gas preferentially adsorbs or reacts with the noble metal catalyst of the adsorption filter, and as a result, the catalytic activity of the noble metal catalyst may decrease. For this reason, there is a problem that the adsorption capacity of the adsorption filter tends to be lowered early, and the ability to adsorb the interfering component is lowered.

  Also, in order to improve the durability of combustible gas sensors against interfering components such as siloxane compounds, when the amount of adsorbent introduced into the adsorption filter is greatly increased, or when the area of the gas inlet is reduced, While durability against the disturbing component is improved, responsiveness to the gas to be detected is significantly lowered.

  In addition, when the area of the gas inlet is reduced, in a household kitchen where a disturbing component such as a siloxane compound exists, the disturbing component is adsorbed in a large amount by the adsorbent, particularly during the low temperature and low humidity period, and the inside of the combustible gas sensor housing Easy to hold. In such a situation, if the environment becomes a high temperature and high humidity environment, the detached gas that has desorbed from the adsorbent due to the temperature rise of the adsorbent moves to the gas sensing element side, and the desorbed gas does not exist even though there is no gas to be detected. There was a risk of detecting gas.

  In order to prevent such erroneous detection, the gas sensor described in Patent Document 2 is provided with a disturbing component inflow restricting means (an inflow restricting plate provided with a pinhole) so that the disturbing component moves toward the gas detecting element. Was preventing. The inflow restricting plate is fixed to the housing by a fixing means. If there is a gap between the periphery of the inflow restricting plate and the housing, the disturbing component easily moves to the gas detection element side from the gap. There was a risk of moving. In this case, in order to eliminate the gap between the periphery of the inflow restricting plate and the housing, it is conceivable to seal the periphery of the inflow restricting plate with an adhesive or the like. However, in such a method, the production efficiency of the gas sensor is reduced. There is a problem that the cost is reduced and the cost is increased.

  Accordingly, an object of the present invention is to provide a gas detector that is not easily affected by various disturbing components and has excellent response of the gas to be detected.

In order to achieve the above object, a gas detector according to the present invention is a gas detector including a gas detection element having a gas sensitive portion that comes into contact with a gas to be detected. A double housing for housing the element, and the outer housing on the outside of the double housing includes a gas introduction port for introducing the gas to be detected, and a first oxidation catalyst unit for reacting and adsorbing the interference component. The inner casing of the double casing includes a second dioxide catalyst portion that reacts and adsorbs the interfering component, and the first oxidation catalyst portion is an oxidation catalyst having a carrier supported on a noble metal. A second catalyst means comprising a first catalyst means, wherein the second dioxide catalyst portion is an oxidation catalyst in which a noble metal is supported on a carrier different from the carrier in the first catalyst means and the first catalyst means; From the direction of gas to be detected It lies in the fact that with the.

According to this configuration, the introduced gas introduced into the outer casing from the gas inlet first passes through the first oxidation catalyst unit. At this time, if the introduced gas contains a disturbing component, the disturbing component reacts with the first oxidation catalyst portion and is decomposed and adsorbed.
If all of the disturbing components are not processed by the first oxidation catalyst part, the remaining disturbing components reach the second dioxide catalyst part in the inner housing. At this time, the disturbing component introduced into the first dioxide catalyst portion reacts with the second dioxide catalyst portion and is decomposed and adsorbed.

  By passing through the first oxidation catalyst portion of the outer housing and the second dioxide catalyst portion of the inner housing in this manner, the disturbing components react and are decomposed and adsorbed in each, and thus reach the gas detection element. There are very few disturbing components. Therefore, in the gas detector of the present invention, by providing the oxidation catalyst part (the first oxidation catalyst part and the second dioxide catalyst part) in both the outer casing and the inner casing, various kinds of siloxane compounds and chlorine-based gases can be used. Even when used in a kitchen where disturbing components coexist, it can be made more difficult to be affected by various disturbing components, and in particular, durability against siloxane compounds can be improved.

  Further, as a result of examining the gas responsiveness in Examples described later, it is recognized that the gas detector of the present invention has an excellent gas responsiveness.

  Therefore, the gas detector of the present invention is not easily affected by various disturbing components and has excellent response of the gas to be detected.

In this configuration, the first oxidation catalyst portion includes a first catalyst means that is an oxidation catalyst in which a noble metal is supported on a carrier, and the second dioxide catalyst portion includes the first catalyst means and the first catalyst means. obtain Bei the second catalyst means is an oxidation catalyst supported a noble metal on different carriers, in this order from the direction of introduction of the gas to be detected from the carrier in.

  According to this configuration, by providing a plurality of different types of catalyst means particularly in the second dioxide catalyst part, it becomes possible to react with various interference components and decompose and adsorb them, thereby efficiently processing the interference components. It can be carried out.

The second characteristic configuration of the gas detector according to the present invention is that the second dioxide catalyst section includes the second catalyst means on the upstream side of the first catalyst means.

  According to this configuration, since the upstream second catalyst means can decompose and adsorb the interfering component via the first oxidation catalyst portion, it is introduced into the first catalyst means disposed downstream of the second catalyst means. The amount of disturbing components that are produced can be greatly reduced.

The third characteristic configuration of the gas detector according to the present invention is that the carrier in the first catalyst means is made of a carbon-based material.

  If the first catalyst means having the component of this configuration is used, the interfering component can be reacted and adsorbed.

A fourth characteristic configuration of the gas detector according to the present invention is that the carrier of the first catalyst means in the first oxidation catalyst portion is fibrous activated carbon, and the carrier of the first catalyst means in the first dioxide catalyst portion is powdery. The point is activated carbon.

  Since the fibrous activated carbon has a large specific surface area and a small pressure loss (the response to the introduced gas becomes faster), the adsorption performance and the response to the introduced gas can be improved in the first oxidation catalyst portion. In addition, since the powdered activated carbon has a large specific surface area and a large pressure loss, the reactivity with the introduced gas can be improved in the second dioxide catalyst portion.

A fifth characteristic configuration of the gas detector according to the present invention is that the carrier of the first catalyst means in the first oxidation catalyst portion is granular activated carbon, and the carrier of the first catalyst means in the second dioxide catalyst portion is powdered activated carbon. It is in the point.

  According to this configuration, the average particle diameter of the granular activated carbon of the first catalyst means in the first oxidation catalyst portion is larger than the average particle diameter of the powdered activated carbon of the first catalyst means in the second dioxide catalyst portion. The pressure loss in the first oxidation catalyst portion is smaller than that in the carbon dioxide catalyst portion, and the response to the introduced gas in the first oxidation catalyst portion can be accelerated.

The sixth characteristic configuration of the gas detector according to the present invention is that the carrier in the second catalyst means is a solid acid catalyst.

  If it is the 2nd catalyst means which has the component of this structure, an interference component can be reacted and adsorbed.

It is the schematic which shows a gas detection element. It is the schematic of a bridge circuit. It is the schematic of the gas detector of the example of this invention (invention example 1 and 5). It is the schematic of the gas detector of another embodiment (invention example 2-4). It is the schematic of the gas detector of a comparison sensor (comparative examples 1-8). It is the graph which showed the result of Example 1 (siloxane compound durability).

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
As shown in FIGS. 1 to 3, the gas detector X of the present invention includes a gas detection element 10 having a gas sensitive portion 12 that comes into contact with a gas to be detected. The gas detection element 10 is accommodated in double casings 51 and 52, and the outer casing 51 outside the dual casings 51 and 52 includes a gas inlet 20 for introducing a gas to be detected, A first oxidation catalyst unit 31 for reacting and adsorbing the interference component is provided.
The inner housing 52 inside the double housings 51 and 52 includes the second dioxide catalyst portion 32 that reacts and adsorbs the disturbing components.

  The first oxidation catalyst unit 31 includes a first catalyst means 30A that is an oxidation catalyst in which a noble metal is supported on a carrier. Further, the second dioxide catalyst section 32 is configured to convert the first catalyst means 30A and the second catalyst means 30B, which is an oxidation catalyst in which a noble metal is supported on a carrier different from the carrier in the first catalyst means 30A, into the gas to be detected. Prepare in this order from the direction of introduction.

  In the present embodiment, a hot-wire semiconductor gas detection element is illustrated as the gas detection element 10, but is not limited thereto. Other gas detection elements include conventionally known gas detection elements such as catalytic combustion type gas detection elements, substrate type semiconductor type gas detection elements, solid electrolyte type gas detection elements, and gas detection elements using MEMS technology.

  The hot wire type semiconductor gas detection element 10 has a gas sensitive part 12 whose main component is a metal oxide which is covered with a coiled noble metal wire 11 and sintered. The noble metal wire 11 has the same material, wire diameter, coil diameter, number of coil turns, and the like as those used in a conventional hot-wire semiconductor gas detection element, and is not particularly limited. As the material of the noble metal wire 11, platinum or the like can be applied.

  The gas sensitive part 12 can use a metal oxide semiconductor. As the metal oxide semiconductor, for example, tin oxide, indium oxide, zinc oxide and the like can be used, but are not particularly limited.

  As shown in FIG. 2, the gas detector X according to the present embodiment includes a hot-wire semiconductor gas detection element 10 that detects a gas to be detected (flammable gas such as LPG, methane, hydrogen, or carbon monoxide), a fixed The load resistor R0 and the fixed opposite side resistors R1 and R2 are incorporated in the bridge circuit. The bridge circuit constantly supplies a voltage from the power source E, and holds the hot-wire semiconductor gas detection element 10 at a temperature at which the gas to be detected reacts.

The gas detection element 10 is accommodated in the housing 50. The gas detector X of the present invention has a double casing structure, and the casing 50 includes an outer casing 51 on the outside and an inner casing 52 covered with the outer casing 51.
At one end of the outer casing 51, a gas inlet 20 that is an opening for introducing a gas to be detected is formed. A first oxidation catalyst unit 31 is disposed on the gas inlet 20 side in the outer casing 51. An explosion-proof wire mesh 21 is disposed between the gas inlet 20 and the first oxidation catalyst unit 31.

  The first oxidation catalyst unit 31 accommodates a first catalyst means 30A that reacts and adsorbs various interfering components such as organic silicone gas, siloxane compound, chlorine-based gas, alcohol, and toluene floating in the room. The first catalyst means 30A is an oxidation catalyst in which a noble metal is supported on a carrier. As the carrier, for example, a carbon-based material can be used, and as the carbon-based material, activated carbon, carbon black, or the like can be used, but is not limited thereto. As the noble metal, Pt, Pd, Ru, Ag or the like can be used, and the noble metal to be used may be 1 to 10% by weight. The shape of the first catalyst means 30A is not particularly limited, and for example, a powder shape, a fiber shape, a spherical shape, a granular shape, or the like can be applied.

  In the present embodiment, a case will be described in which the carrier of the first catalyst means 30A in the first oxidation catalyst section 31 is fibrous activated carbon, and the carrier of the first catalyst means 30A in the second dioxide catalyst section 32 is powdered activated carbon. Since the fibrous activated carbon has a large specific surface area and a small pressure loss (the response to the introduced gas becomes faster), the adsorption performance and the responsiveness to the introduced gas can be improved in the first oxidation catalyst portion 31. In addition, since the powdered activated carbon has a large specific surface area and a large pressure loss, the reactivity with the introduced gas can be improved in the second dioxide catalyst portion 32.

The basis weight of the fibrous activated carbon (the first catalyst means 30A in the first oxidation catalyst section 31) is preferably about 500 to 850 g / m ² , and the powdered activated carbon (the first catalyst means 30A in the second dioxide catalyst section 32) is good. ) Is preferably about 5 to 90 μm.

  The inner casing 52 is provided with the second dioxide catalyst portion 32. The first dioxide catalyst portion 32 accommodates a first catalyst means 30A and a second catalyst means 30B that react and adsorb the above-described disturbing components. The second catalyst means 30B is an oxidation catalyst in which a noble metal is supported on a carrier different from the carrier in the first catalyst means 30A. Thus, by providing a plurality of different types of catalyst means in the second dioxide catalyst section 32, it becomes possible to react and decompose and adsorb various kinds of interference components, and to efficiently perform the processing for the interference components. it can.

  As the carrier used in the second catalyst means 30B, for example, a solid acid catalyst can be used. For example, silica alumina is preferably used as the solid acid catalyst in view of cost. Acid salts (cesium salts of phosphotungstic acid, barium salts, rubidium salts, etc.), sulfated zirconia, zirconia tungstate, sulfonated activated carbon, sulfonated carbon, sulfonated ion exchange resin, Y-type high silica zeolite, Al-containing mesoporous silica Etc. can also be used. Since the heteropolyacid salt is a solid superacid, it has a smaller capacity than silica alumina and can provide adsorption performance equivalent to that of silica alumina, which is suitable for downsizing the housing.

  As the noble metal used in the second catalyst means 30B, the noble metal used in the first catalyst means 30A can be used. The shape of the 2nd catalyst means 30B is not specifically limited, For example, shapes, such as a powder form, spherical shape, and a granular form, are applicable. For example, when the 2nd catalyst means 30B is made into a powder form, the average particle diameter is good to set it as 5-90 micrometers.

  In the present embodiment, porous sheets 41 and 42 having air permeability are disposed on the upper side of the first catalyst means 30A and the lower side of the second catalyst means 30B in order to stabilize the shape thereof. When the shape of the first catalyst means 30A and the second catalyst means 30B is highly stable, the upper and lower porous sheets 41 and 42 may be omitted, and an explosion-proof wire mesh is formed on the lower surface of the lower porous sheet 42. 43 is arranged. Further, a stop member 44 that can be positioned in a state where the first catalyst means 30A, the second catalyst means 30B, the porous sheets 41 and 42, and the explosion-proof wire mesh 43 are laminated is disposed on the lower surface of the explosion-proof wire mesh 43. It is.

  In the present embodiment, the restricted vent 40 is disposed between the first catalyst means 30A and the second catalyst means 30B. The opening area of the restricted vent 40 is set smaller than the opening area of the gas inlet 20. In the present embodiment, the opening area of the restricted vent 40 is 11% with respect to the opening area of the gas inlet 20, but is not limited to such an aspect.

  As described above, when the opening area of the restricted vent 40 is set smaller than the opening area of the gas inlet 20, the detached gas released from the adsorbent due to the temperature increase of the first oxidation catalyst unit 31 is a gas having a large opening area. It becomes easy to move to the outside of the housing 50 through the introduction port 20. Therefore, it is possible to prevent the separation gas from being detected even though the gas to be detected does not exist.

  In the present embodiment, the case where one restricted vent 40 is provided has been described, but the number of the restricted vents 40 is preferably one. If a plurality of restricted vents 40 are formed at one end of the inner housing 52, the effect of reducing the inflow of disturbing components by one restricted vent 40 will be reduced.

  In the gas detector X of the present invention, the housing 50 that houses the gas detector X has a double housing structure. Therefore, when assembling the gas detector X, a space for accommodating the first catalyst means 30A and the second catalyst means 30B can be easily formed simply by assembling the outer casing 51 and the inner casing 52.

  In the present embodiment, the introduced gas introduced into the outer casing 51 from the gas inlet 20 first passes through the first oxidation catalyst unit 31. At this time, if the introduced gas contains an obstructing component, the obstructing component reacts with the first catalyst means 30A accommodated in the first oxidation catalyst unit 31 and is decomposed and adsorbed. That is, when, for example, a siloxane compound or a chlorine-based gas is included as an interference component, the siloxane compound and the chlorine-based gas react with the first catalyst means 30A and are decomposed and adsorbed.

  When all of the disturbing components are not processed by the first oxidation catalyst unit 31, the remaining disturbing components reach the second dioxide catalyst unit 32 in the inner housing 52 via the restricted vent 40. At this time, since the opening area of the restricted vent 40 is set to be smaller than the opening area of the gas inlet 20, the amount of disturbing components introduced into the second dioxide catalyst portion 32 can be greatly reduced. The disturbing component introduced into the second dioxide catalyst portion 32 reacts with the first catalyst means 30A and is decomposed and adsorbed. If all of the interfering components are not treated by the first catalyst means 30A, the remaining interfering components reach the second catalyst means 30B, react with the second catalyst means 30B, and are decomposed and adsorbed.

  In this way, since the interference component reacts and is decomposed and adsorbed by passing through the first catalyst means 30A and the second catalyst means 30B in the outer casing 51 and the inner casing 52, the gas sensing element 10 Very few disturbing components are reached. Therefore, the gas detector X of the present invention includes the first oxidation catalyst unit 31 and the second dioxide catalyst unit 32, so that even if used in a kitchen where various interference components such as siloxane compounds and chlorine-based gas coexist. Thus, it is possible to make it more difficult to be affected by various interference components.

  If the oxidation catalyst is not accommodated in the upstream first oxidation catalyst part 31, the disturbing components are reacted and adsorbed only by the oxidation catalyst accommodated in the downstream second dioxide catalyst part 32. In this case, there is a possibility that the catalytic activity of the oxidation catalyst in the second dioxide catalyst portion 32 may be lowered early. However, as in the present invention, if the upstream first oxidation catalyst unit 31 is also configured to accommodate the oxidation catalyst, the ability to decompose and adsorb the disturbing components in the upstream first oxidation catalyst unit 31 can be improved. In the upstream first oxidation catalyst section 31, the disturbing components can be decomposed and adsorbed preferentially. Thereby, the catalytic activity of the oxidation catalyst in the second dioxide catalyst portion 32 on the downstream side close to the gas detection element 10 is less likely to be lowered at an early stage, and the gas detection element 10 becomes even more difficult to be affected by various interference components.

[Another embodiment 1]
In the embodiment described above, the case where the second dioxide catalyst unit 32 is provided with the second catalyst unit 30B downstream of the first catalyst unit 30A is not limited to such a mode, but the upstream side of the first catalyst unit 30A. The second catalyst means 30B may also be provided on the side.

  In this configuration, the second catalyst means 30B on the upstream side can react and adsorb disturbing components that have passed through the first oxidation catalyst section 31, and therefore the first catalyst means 30B disposed downstream of the second catalyst means 30B. The amount of interfering components introduced into the catalyst means 30A can be greatly reduced.

[Another embodiment 2]
In the embodiment described above, the case where the carrier of the first catalyst unit 30A in the first oxidation catalyst unit 31 is fibrous activated carbon and the carrier of the first catalyst unit 30A in the second dioxide catalyst unit 32 is powdered activated carbon has been described. However, the present invention is not limited to this, and the carrier of the first catalyst means 30A in the first oxidation catalyst portion 31 may be granular activated carbon, and the carrier of the first catalyst means 30A in the second dioxide catalyst portion 32 may be powdered activated carbon. .

  In this case, the average particle diameter of the granular activated carbon (first catalyst means 30A in the first oxidation catalyst portion 31) is preferably about 200 to 800 μm. The average particle diameter of the powdered activated carbon (the first catalyst means 30A in the second dioxide catalyst portion 32) is preferably the same as that in the above-described embodiment (about 5 to 90 μm). That is, in this embodiment, the average particle diameter of the granular activated carbon of the first catalyst means 30A in the first oxidation catalyst section 31 is larger than the average particle diameter of the powdered activated carbon of the first catalyst means 30A in the second dioxide catalyst section 32. Therefore, the pressure loss in the first oxidation catalyst unit 31 is smaller than that in the first dioxide catalyst unit 32, and the response to the introduced gas in the first oxidation catalyst unit 31 can be accelerated.

[Example 1]
Assuming the environment used in the kitchen, the performance (siloxane compound durability) of the hot-wire semiconductor gas detector X of the present invention (Invention Examples 1 to 5) was examined. The gas to be introduced was a mixed gas having 125 ppm of toluene + 125 ppm of paradichlorobenzene + 5 ppm of OMCTS (siloxane gas). A similar test was performed for the comparative sensor (Comparative Examples 1 to 8).
The sensor drive was pulsed drive (heating the sensor element to around 500 ° C. for 0.1 seconds every 30-second period to detect methane gas), and the methane alarm set concentration was 3000 ppm.

  Details of each example of the present invention are shown in Table 1.

That is, in Invention Examples 1 to 5, fibrous activated carbon (70 mg: 650 g / m ² ) was used as the carrier of the first catalyst means 30A in the first oxidation catalyst part 31. As the noble metal supported on the carrier, Pt was used in Examples 1 and 2, Pd was used in Example 3, and Ag was used in Examples 4 and 5. In Examples 1 to 5 of the present invention, Pt-supported powdered activated carbon (25 mg: average particle size of 30 μm) was used as the first catalyst means 30A in the second dioxide catalyst portion 32.

The amount of the precious metal supported on the fibrous activated carbon in the first oxidation catalyst portion 31 is preferably 1 to 10% by weight, and in this example, 3% by weight.
The amount of Pt supported by the Pt-supported powdered activated carbon in the second dioxide catalyst portion 32 is preferably 5 to 15% by weight, and in this example, 10% by weight.
The precious metal loading (% by weight) is preferably larger for powdered activated carbon than for fibrous activated carbon (or granular).
The amount of Pt supported on the Pt-supported silica alumina is preferably 2 to 15% by weight, and in this example, 3% by weight.

As shown in FIG. 3, in Invention Examples 1 and 5, in the second dioxide catalyst portion 32, the upstream second catalyst means 30B is not provided, and the downstream second catalyst means 30B is Pt-supported powdery silica alumina ( 15 mg) was used.
As shown in FIG. 4, in Examples 2 to 4 of the present invention, Pt-supported powdery silica alumina (7.5 mg) was used for the upstream and downstream second catalyst means 30B in the second dioxide catalyst portion 32, respectively. .

  In Comparative Examples 1 to 8, the first casing 33 is replaced with the first oxidation catalyst section 31 in the outer casing 51, the second comparator section 34 is replaced with the second dioxide catalyst section 32 in the inner casing 52, respectively. The arranged one was used (FIG. 5).

  Details of each comparative example are shown in Table 2.

That is, in the first comparison unit 33, Comparative Examples 1 to 3 used fibrous activated carbon (70 mg), and Comparative Examples 4 to 8 used Pt-supported fibrous activated carbon (70 mg).
In the second comparison section 34, Comparative Examples 1 and 3-7 have a three-layer structure (in order of powdered silica alumina, powdered activated carbon, and powdered silica alumina), and Comparative Example 2 has a single layer structure (powdered activated carbon). Comparative Example 8 had a two-layer structure (in order of powdered silica alumina and powdered activated carbon). In addition, in the case where noble metal was supported in the second comparison unit 34, Pt was supported in all cases.

The results are shown in FIG.
In Comparative Example 1, since neither the first comparison unit 33 nor the second comparison unit 34 (three-layer structure) carries noble metal, the lower limit value of the alarm concentration (1/3 of the methane alarm set concentration) is reached in about 330 days. (1000 ppm)).
In Comparative Example 2, noble metal was supported in the second comparison part 34 (single-layer structure), but no noble metal was supported in the first comparison part 33, and the lower limit of the alarm concentration was reached in about 390 days.
In Comparative Example 3, noble metal was supported in the second comparison unit 34 (three-layer structure), but no precious metal was supported in the first comparison unit 33, and the lower limit of the alarm concentration was reached in about 630 days.
In Comparative Example 4, noble metal was supported in the first comparison part 33, but no noble metal was supported in the second comparison part 34 (three-layer structure), and the lower limit value of the alarm concentration fell below about 360 days.
In Comparative Example 5, noble metal was supported in the first comparison unit 33 and noble metal was supported in the intermediate layer in the second comparison unit 34 (three-layer structure), but the lower limit of the alarm concentration was reached in about 570 days.
In Comparative Example 6, noble metal was supported in the first comparison unit 33 and noble metal was supported in the upper layer and the intermediate layer in the second comparison unit 34 (three-layer structure), but the lower limit of the alarm concentration was reached in about 660 days. It was.
In Comparative Example 7, the noble metal was supported in the first comparison unit 33 and the noble metal was supported in the intermediate layer and the lower layer in the second comparison unit 34 (three-layer structure), but the alarm concentration fell below the lower limit value in about 690 days. It was.
In Comparative Example 8, noble metal was supported in the first comparison part 33 and noble metal was supported in the second comparison part 34 (two-layer structure), but the lower limit value of the alarm concentration was lowered in about 710 days.

On the other hand, as in Invention Examples 1 and 5, the first catalyst means 30A in the first oxidation catalyst portion 31 is made of noble metal-supported fibrous activated carbon, and the second dioxide catalyst portion 32 is made of Pt-supported powdered activated carbon or Pt-supported powder. By adopting a two-layer structure in the order of silica-alumina, the methane alarm set concentration was kept above the lower limit value (Invention Example 1: 1500 ppm, Invention Example 5: 1200 ppm) even at about 720 days.
Further, as in Invention Examples 2 to 4, the first catalyst means 30A in the first oxidation catalyst part 31 is made of noble metal-supported fibrous activated carbon, and the second dioxide catalyst part 32 is Pt-supported powdery silica alumina, Pt-supported powder. By forming a three-layer structure in the order of glassy activated carbon and Pt-supported powdered silica-alumina, the methane alarm set concentration is not less than the lower limit value even in about 720 days. Example 4: 1700 ppm) was maintained. In particular, the highest siloxane durability was exhibited by supporting Pt in both the first oxidation catalyst portion 31 and the second dioxide catalyst portion 32.

  From this result, in the presence of a chlorine-based gas such as paradichlorobenzene, the chlorine-based gas coats the noble metal catalyst particles or reacts with the noble metal catalyst, the catalytic activity decreases, and the siloxane durability decreases. An oxidation catalyst portion is disposed on both of the inner casings 52, and at least two layers of catalyst means are disposed on the inner casing 52, and a noble metal-supported solid acid catalyst (Pt-supported powdered silica is disposed downstream of the catalyst means. It was recognized that the configuration of (alumina) was good. With this configuration, the ability to decompose the interference component (organic gas) by the noble metal catalyst is improved upstream of the inner casing, and the chlorine-based gas is preferentially adsorbed or reacted to the noble metal catalyst. The amount of disturbing components flowing into the body 52 can be significantly reduced. Furthermore, by forming a plurality of catalyst means in the inner casing 52 and efficiently treating the disturbing components, it is considered that high siloxane durability can be maintained for a long time even in an environment where chlorine-based gas coexists. .

[Example 2]
The gas response to the detected gas (methane gas) was investigated.
In the sensors of Invention Examples 1 to 5 and Comparative Examples 1 to 4 described above, the time required for response was measured with respect to 12,500 ppm of methane gas. Sensor driving was performed under the same conditions as in Example 1. The results are shown in Table 3.

As a result, Examples 1 to 5 of the present invention required a response time of 24 to 25 seconds, and were found to have a response equal to or higher than that of Comparative Examples 1 to 4. Therefore, it was recognized that the gas detector X of the present invention can be made more difficult to be affected by various disturbing components while having excellent gas responsiveness.
The remarkably low response of Comparative Example 2 is due to the specific surface area of the Pt-supported activated carbon. In Examples 1-5 of the present invention, in addition to Pt-supported activated carbon, silica alumina belonging to a solid acid catalyst having a smaller specific surface area than Pt-supported activated carbon is used, in addition to excellent adsorptivity and durability, and high responsiveness. Realized.

  INDUSTRIAL APPLICABILITY The present invention can be used for a gas detector provided with a gas detection element having a gas sensitive part that comes into contact with a gas to be detected.

X gas detector 10 gas detection element 12 gas sensitive part 20 gas inlet 31 first oxidation catalyst part 32 second dioxide catalyst part 51 outer casing 52 inner casing

Claims (6)

A gas detector including a gas detection element having a gas sensitive portion that comes into contact with a gas to be detected,
A double housing for accommodating the gas sensing element;
The outer outer casing of the double casing includes a gas introduction port for introducing the gas to be detected, and a first oxidation catalyst unit for reacting and adsorbing a disturbing component,
The inner case inside the double case includes a second dioxide catalyst part that reacts and adsorbs the interfering component ,
The first oxidation catalyst portion includes a first catalyst means that is an oxidation catalyst in which a noble metal is supported on a carrier,
From the introduction direction of the gas to be detected, the second dioxide catalyst portion is a first catalyst means, and a second catalyst means that is an oxidation catalyst in which a noble metal is supported on a carrier different from the carrier in the first catalyst means. Gas detector provided in this order . 2. The gas detector according to claim 1 , wherein the second dioxide catalyst section includes the second catalyst means on the upstream side of the first catalyst means. The gas detector according to claim 1 or 2 , wherein the carrier in the first catalyst means is a carbon-based material. The gas detector according to claim 3 , wherein the carrier of the first catalyst means in the first oxidation catalyst part is fibrous activated carbon, and the carrier of the first catalyst means in the second dioxide catalyst part is powdered activated carbon. The gas detector according to claim 3 , wherein the carrier of the first catalyst means in the first oxidation catalyst part is granular activated carbon, and the carrier of the first catalyst means in the second dioxide catalyst part is powdered activated carbon. The gas detector according to any one of claims 1 to 5 , wherein the carrier in the second catalyst means is a solid acid catalyst.

Images