JPS62147352A - Combustible gas sensor - Google Patents

Abstract

PURPOSE:To make it possible to prevent the wrong information of a sensor due to alcohol, by supporting 0.01-0.20wt% of a platinum catalyst by the temp. compensation element of a catalytic combustion type combustible gas sensor. CONSTITUTION:The gas detection element 3 and temp. compensation element 4 of a catalytic combustion type combustible gas sensor is covered with the carrier with a catalyst of a coil 1 formed by spirally winding a metal wire. At this time, 0.01-0.20wt% of a platinum catalyst is supported by the compensation element 4. By this method, only alcohol is selectively burnt even by the compensation element 4 and the combustion part of alcohol in the side of the detection element 3 is cancelled. By this constitution, the sensitivity of the sensor to alcohol is reduced and erroneous operation due to alcohol can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a catalytic combustion Omachi combustible gas sensor, and more specifically to a combustible gas sensor that prevents malfunction due to alcohol.

C. Prior Art and its Problems] In recent years, catalytic combustion type combustible gas sensors have begun to be widely used in general households as an extremely effective means of preventing gas leak accidents. However, if the alcohol vaporizes during cooking or warming sake, and coexists in the air as relatively high concentration alcohol vapor, the gas sensor may malfunction due to its operating principle and issue an alarm, so it may not operate on the safe side. However, improvements were desired.

As shown in Fig. 1, the gas detection element used in a catalytic combustion type combustible gas sensor consists of a hot wire made of a wire made of a material with a high temperature coefficient of resistance, such as platinum, into a coil shape, and a support 2 made of activated alumina or the like. It has a structure in which a catalyst with excellent oxidizing activity against combustible gas components such as proby and methane is attached to this. On the other hand, the temperature compensation element generally has a similar shape to the gas detection element, except that it is inert to combustible gases, and the actual sensor consists of the gas detection element 3 and the gas detection element 3, as shown in Figure 2. The i-variant compensation element 4 is set at a position in contact with the bridge circuit. The gas detection element 3 and the temperature compensation element 4 are usually used by heating the catalyst to a temperature necessary for oxidizing the combustible gas by passing a current through a coil.

If alcohol vapor comes into contact with the cell in such a state, the alcohol will burn on the catalyst on the gas sensing element side, and the resistance of the coil on the gas sensing element side will change, causing the bridge to become unbalanced. The same result as when the sensor comes into contact with the detected gas components, such as propane or methane, is produced, and the Senna gives a false alarm.

As a solution to the above problems, 1) A catalyst capable of selectively oxidizing gases such as propane and methane is used on the gas detection element side.

2) A catalyst capable of selectively oxidizing alcohol is used on the temperature compensation element side, so that the amount of alcohol burned on the gas detection element side can be canceled.

There are two methods.

In method 1), it is necessary to find a catalyst that burns relatively flame-resistant propane, methane, etc., but does not burn easily flammable alcohol, but this is technically difficult. Not realistic. Method 2) only requires finding a catalyst that has a selectivity completely opposite to ①, and is more likely than method 1) from the perspective of the order of oxidation speed of each gas.

Based on this idea, the inventors conducted experiments on various catalysts, and by supporting a small amount of platinum catalyst on the temperature compensation element side, most of the detected gases such as propane and methane were combusted on the temperature compensation element side. We discovered that it is possible to create a catalytic combustion type combustible gas sensor that is able to selectively burn most alcohols without having to burn alcohol, significantly reducing the alcohol sensitivity of the gas sensor, and making malfunctions less likely to occur due to alcohol. Ta.

[Purpose of the invention]

An object of the present invention is to provide a catalytic combustion type combustible gas sensor that prevents malfunctions caused by alcohol.

[Key points of the invention]

The main point of this invention is to selectively burn only alcohol in the temperature compensation element by supporting a small amount of platinum catalyst on the temperature compensation element side, and to cancel the combustion and oxidation of alcohol on the gas detection element side. , which aims to reduce the sensor's sensitivity to alcohol and prevent malfunctions caused by alcohol.

[Example of actual employment of invention]

The content of the present invention will be explained in detail below using examples.

Example 1 Outside the coil (l O, 25
ms.

Coil outer length 0.45++ll+1. A coil with 7 turns was prepared.

Next, activated alumina powder with an average particle size of 5 μm and alumina sol were combined so that the weight ratio of activated alumina to alumina in the alumina sol was 20:1, and an appropriate amount of pure water was added to this. It was made into a paste.

This paste was applied to a platinum coil using a thin wire to form an element carrier in which the coil 1 was covered with a coating layer 2 mainly composed of activated alumina in a substantially spherical shape as shown in FIG. Thereafter, the device carrier with a diameter of 0.50 m to 0.55 mm was dried at room temperature for 3 hours, dried overnight at 110°C, and fired in an electric furnace at 800°C for 3 hours. It was processed and used as a gas detection element or temperature compensation element.

b) Creation of gas detection Hisako The carrier was immersed in a hydrochloric acid solution of chloroplatinic acid and palladium chloride at a concentration of 1:1 and a total of 10 layers of platinum and palladium. After soaking at room temperature for 1 hour, it was taken out and dried at room temperature for 3 hours, at 110°C overnight, and then at 400°C in hydrogen.

The thus obtained gas sensing element, which was reduced for 3 hours and had a mixed catalyst of platinum and palladium supported on the element carrier, was commonly used as a pair of all the temperature compensation elements described below.

(1) Creation of temperature compensation element After immersing the element carrier in a IIk degree chloroplatinic acid aqueous solution containing 0.2 wt. After drying overnight, it was sucked in hydrogen at 400° C. for 3 hours to allow platinum to be supported on the element carrier. When the amount of platinum supported on the element carrier was investigated by chemical analysis, it was found to be 0.07 weight percent of platinum.

A bare sample of the gas sensing layer and temperature compensating element manufactured in this way was used as a sensor C to measure performance.

Since the gas detection element in the following actual example is the same as the gas sensing element produced in Actual Example 1, only the details of the preparation of the temperature compensation element will be described.

Example 2 A single carrier of platinum was immersed in an aqueous solution of 4e chloroplatinic acid with a weight of 1.0% at room temperature for 1 hour, and then the same operation as in Example 1) was carried out to produce a temperature compensating element. . Chemical analysis of the device thus produced was performed in the same manner as in Example 1, and it was found that a pair using a temperature compensating element and a gas detection element supported by 0.45% platinum was called sensor E. do.

Example 3 After immersing an element carrier of platinum in a chloroplatinic acid aqueous solution having a concentration of 4% at room temperature for 1 hour, the same operation as in Example 1) was carried out to prepare a temperature compensating element. When the element thus produced was subjected to chemical analysis in the same manner as in Example 1, it was found that 0.17% by weight of platinum was supported.

A pair using this temperature compensation element and gas detection element is referred to as sensor D.

Example 4 After immersing the device carrier in a chloroplatinic acid aqueous solution having a concentration of 0.05% by weight of platinum at room temperature for 1 hour,
A temperature compensation element was prototyped by performing the same operation as above. When the device thus prototyped was actually chemically analyzed in the same manner as in Example 1, it was found that 0.02% by weight of platinum was supported.

A pair using this temperature compensation element and gas detection element is referred to as sensor B. To compare the performance of these pairs,
As a pair commonly used in the past, a group element carrier before catalyst is supported is used for the temperature compensation element, and a gas detection element commonly used in Examples 1 to 4 is used for the gas detection element.
This was designated as sensor A.

Incorporate sensors A-E into a bridge circuit as shown in Figure 2, change the bridge voltage (Ya) from 1.5v to 2.5V, Q, 4vo 1% ethyl alcohol/air, 0.2
The outputs for vol. 1% isobutane/air and 0.4 vol. 1% methane/air were investigated, and the results shown in FIGS. 3 to 5 were obtained, respectively. Note that isobutane is a gas species with properties similar to propane 7 and fl, and is used as an evaluation gas in place of propane. In the curve diagrams of FIGS. 3 to 5, the output car bridge' pressure curves of sensors A to E are as follows. Each song is shown in order as @A-E. From FIG. 3, it can be seen that sensor A (song @A), in which the temperature compensating element does not carry a catalyst, has a significantly high output, that is, sensitivity to alcohol. My father created a sensor B-E (song @ B-4) with a trace amount of platinum catalyst supported on the temperature compensation element.
It can be seen that the output for alcohol of :) is significantly lower than that of sensor A (curve A) K in which no platinum catalyst is supported, and the alcohol sensitivity is reduced. This tendency becomes more pronounced as the bridge voltage increases and as the amount of platinum supported on the temperature compensation element increases (amount of platinum supported: sensor E>D)C)B)
A=0) Significant. This is because as the amount of platinum supported increases, the number of oxidation active sites in the temperature compensation element increases, and as the bridge voltage increases, the element temperature rises, promoting the combustion reaction of alcohol on the catalyst of the temperature compensation element. This is for the purpose of

However, as can be seen from FIG. 4, a significant increase in the amount of platinum supported is not very desirable because it results in a decrease in the output with respect to isobutane, which is the detection gas.

This tendency is particularly noticeable when the bridge voltage is high, and the output for isobutane of sensor E (curve E), which has the largest amount of platinum supported, and senna A (curve A), which does not support platinum in the temperature compensation element, is 2. When compared with 5V bridge pressure, it can be seen that it is reduced to about 1/3. This is clearly due to the fact that isobutane, which is the detection gas, is partially burned on the temperature compensation element side. That is, an increase in the amount of platinum supported is not preferable because it lowers the oxidation selectivity in the temperature compensation element.

As can be seen from FIG. 5, this tendency is not observed at all for flame-retardant methane.

The lower limit of the bridge voltage that generally operates the senna.

The upper limit is determined as follows.

a) It is used in a region where the combustion reaction of the detected gas in the sensor is controlled by gas diffusion, that is, in a region where the sensor output with respect to voltage is saturated.

b) The device is heated to a temperature at which deterioration of device performance due to moisture adsorption under high humidity does not occur, that is, the bridge voltage is increased.

C) Use at an element temperature at which the catalyst and carrier constituting the sensor do not undergo thermal deterioration over a long period of time, that is, below the bridge voltage.

d) Use a bridge voltage that will not cause the platinum coil that makes up the sensor to break even after long-term use.

Considering the above constraints, the lower limit of the bridge voltage of this sensor is approximately 2. OV, the upper limit is 2.5v. By the way, the temperature of the element is determined by the bridge voltage being 2. Approximately 270℃ at Ov, 2
．． 5 V-1' was about 390°C.

Next, the lower the sensitivity of senna to alcohol, the better, but as is clear from Figure 4, when the platinum loading is set to 0.45 wt%, the sensitivity of inbutane also decreases, which is not desirable. . Generally, it is said that if the alcohol sensitivity is equal to or less than the sensitivity of methane and inbutane, that is, the senna output is made to be about the same or less, malfunctions of senna due to alcohol will not occur under normal usage conditions.

Considering the above, comparing FIGS. 3 to 5 in black, it can be seen that the amount of platinum supported on the temperature compensating element is preferably about 0.01 to about 2% by weight. FIG. 6 is a curve diagram in which the voltage dependence of the output with respect to methane, inbutane, and alcohol was investigated when a platinum catalyst of 0.01% by weight and 0.20% by weight was supported on the temperature compensating element. In FIG. 6, curves A22B and C are curves showing the voltage dependence of output for methane, isobutane, and alcohol when using a temperature compensating element supporting 0.01% platinum catalyst. two.

E and H are methane and isobutane in the case of 0.2x tX.

FIG. 3 is a curve diagram showing voltage dependence of output with respect to alcohol. As can be seen from this curve diagram, by supporting 0.01 to 0.20% by weight of platinum catalyst on the temperature compensating element, it has almost no effect on the sensitivity to methane or isobutane, and only the sensitivity to alcohol. It has become clear that it is possible to significantly reduce

From the above explanation, by supporting a trace amount of platinum catalyst of 0.01 to 0.20% by weight on the temperature compensation element, only the alcohol sensitivity can be significantly increased without reducing the sensitivity of detection gases such as propane and methane. It is clear that it can be lowered. Note that for combustible gases including hydrogen gas, it is preferable to make the sensitivities of methane and hydrogen gas almost the same;
, 4y water; J/sensor A-E for raw air (curve A-E
) As can be seen from the curve diagram in Fig. 7 showing the bridge voltage dependence of the output of It is possible to almost satisfy the conditions, and of course it can be applied to such uses.

〔Effect of the invention〕

0.0 for the temperature compensation element of the contact heat/Akatsuki combustible gas sensor
By supporting a fine platinum catalyst with a concentration of 1 to 0.20, it is possible to selectively burn only alcohol in the temperature compensation element and cancel most of the alcohol combustion on the gas detection element side. As a result of using eggs, a flammable gas sensor can be obtained in which the alcohol taste of the sensor is greatly reduced, and false alarms caused by alcohol can be practically prevented.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of the element of a catalytic combustion type combustible gas sensor.
Figure 2 is a bridge circuit diagram used in a catalytic combustion type combustible gas sensor, Figure 3 is a curve diagram showing the dependence of the sensor output bridge pressure on 0.4 vol% ethyl alcohol/air, and Figure 4 is a 0.4 vol% ethyl alcohol/air curve diagram. A curve diagram showing the dependence of sensor output and bridge voltage on 2VO 1% isobutane/air, Figure 5 is a curve diagram showing the dependency of sensor output on bridge voltage for 0.4volS% methane/air, and Figure 6 is a curve diagram showing the dependence of sensor output on bridge voltage for 0.4volS% methane/air. .Curve diagram showing sensor output-bridge voltage dependence for 4 vol% ethyl alcohol/air, 0.2% isobutane/air, 0.4 vol +X methane/air,
FIG. 7 is a curve diagram showing the dependence of senna output on bridge voltage for 0.4 vol% hydrogen/air. DESCRIPTION OF SYMBOLS 1... Coil, 2... Covering layer, 3... Gas detection element, 4... Temperature compensation element. ] - Fig. 1 Fridge voltage (V) Fig. 7' Ritsu voltage (7) Fig. 4. Fig. 5" Sodge Electric J King (V) Fig. 5 Buzon ° Electric rF,, (J) )) 6 Fig. 7" Zo, 7 Di° Voltage (V) Fig. 7

Claims (1)

[Claims] In a catalytic combustion type combustible gas sensor having a gas detection element and a temperature compensation element, each of which is a spirally wound coil of metal wire coated with a catalyst-carrying carrier, the temperature compensation element has a temperature of 0.01.
A flammable gas sensor characterized by supporting ~0.20% by weight of a platinum catalyst.