JPH06242060A - Hydrocarbon sensor - Google Patents

Abstract

PURPOSE:To provide a hydrocarbon sensor for detecting gas concentration without requiring any external power supply for measuring the resistance of sensor element regardless of the drift of sensor resistance by measuring the concentration of hydrocarbon gas through the use of electromotive force generated spontaneously from the sensor itself. CONSTITUTION:A pair of porous electrodes 2, 3 touch a proton conductive solid electrolyte 1 at a position where the solid electrolyte 1 is sandwiched. One of the pair of porous electrodes 2, 3 is composed of an electrode catalyst which is inactive to combustion of hydrocarbon gas to be measured whereas the other electrode is composed of an active electrode catalyst. The active electrode 2 of hydrocarbon sensor is employed as a catalyste and concentration of hydrocarbon is measured through the use of electromotive force induced in the sensor by the difference between the partial pressure of steam above the inactive electrode 3 and the partial pressure of steam produced at the time of combustion of hydrocarbon gas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrocarbon sensor for measuring the concentration of hydrocarbon gas in gas.

[0002]

2. Description of the Related Art Many hydrocarbon gas sensors such as semiconductor type sensors and catalytic combustion type combustible gas sensors have been reported so far, and many of them have been put into practical use. In the case of a contact combustion type sensor, the temperature of the sensor element rises due to the combustion of combustible gas, and the resistance of the sensor element changes with this temperature rise. This is a method of measuring the hydrocarbon concentration by passing a current for measurement and obtaining the resistance value of the sensor element from the voltage change at that time. In the case of a semiconductor type sensor, for example, when an element supporting various combustion catalysts on SnO ₂ is kept at a high temperature and the sensor element is exposed to a hydrocarbon gas, when the hydrocarbon gas burns, it is adsorbed on the semiconductor element surface. The gas concentration is measured by utilizing the resistance change of the sensor element caused by the consumption of the oxygen. In these sensors, various combustion catalysts are carried on the surface of the sensor element based on tin oxide, and the difference in the activity of the catalysts is used to change the amount of oxygen adsorbed by the sensor element during combustion of hydrocarbon gas. The gas concentration is detected from the change in resistance of the sensor element due to the change.

[0003]

However, in the above-mentioned prior art, since a current is applied to the sensor element and the resistance value of the sensor element is obtained from the voltage value at that time, a power source for resistance measurement is required, and the sensor There is a problem that the circuit of becomes complicated. Further, the resistance value of the sensor element varies considerably depending on the method of manufacturing the sensor, and thus the completed sensor element needs to be individually calibrated. Further, there is a problem that the resistance value of the sensor needs to be aged in order to prevent drift in the initial state.

The present invention has been made in view of the above problems, and the resistance of the sensor element as in the prior art is measured by measuring the hydrocarbon gas concentration by utilizing the electromotive force spontaneously generated by the sensor itself. An object of the present invention is to provide a hydrocarbon sensor and a method for measuring a hydrocarbon concentration, which can detect a gas concentration without requiring an external power source for measurement and being affected by a temporal change in sensor resistance.

[0005]

A hydrocarbon sensor according to the present invention has a proton conductive solid electrolyte and a pair of porous electrodes which are in contact with the solid electrolyte at positions sandwiching the solid electrolyte. One of the quality electrodes is composed of an electrocatalyst which is inactive in combustion of the hydrocarbon gas to be measured, and the other is composed of an active electrode catalyst.

[0006]

The inventors of the present application repeated various experimental studies in order to develop a sensor that can detect the hydrocarbon gas concentration regardless of the change in the sensor resistance by utilizing the electromotive force generated by the sensor itself. As a result, by using a proton conductive solid electrolyte and by using a conductive catalyst having different activities for combustion of hydrocarbon gas as an electrode material for the electrolyte, when the hydrocarbon gas burns on the solid electrolyte, It was found that the hydrocarbon gas concentration can be measured by using the electromotive force generated by the difference in the partial pressure of water vapor generated in.

That is, since the activities of the conductive catalysts contacting both surfaces of the solid electrolyte are different, complete combustion occurs on the active catalyst side and incomplete combustion occurs on the inert catalyst side. For this reason, since the amounts of water vapor generated on both electrodes are different from each other, a water vapor partial pressure difference occurs, and an electromotive force is generated between both electrodes due to this water vapor partial pressure difference. Since this electromotive force is proportional to the concentration of the hydrocarbon gas, the hydrocarbon gas concentration can be obtained.

[0008]

Embodiments of the present invention will now be described with reference to the accompanying drawings. FIG. 1 is a sectional view showing a sensor probe according to an embodiment of the present invention. An active electrode 2 is formed by baking on one plane of a disk-shaped perovskite-type proton conductive solid electrolyte 1, and an inactive electrode 3 is also formed by baking on the other plane. These proton-conductive solid electrolytes 1 are, for example, CaZr _0.9 I
n _0.1 O ₃ -α and the active electrode 2 is La _0.6 Ba _0.4 C.
It consists oO _3, inert electrode 3 is made of Ag. A lead wire 4 made of, for example, a Pt wire is attached to each of the active electrode 2 and the inactive electrode 3.

In the sensor probe constructed as described above, since the conductive catalyst electrodes 2 and 3 contacting both surfaces of the solid electrolyte 1 have different activities with respect to the hydrocarbon gas, the active catalyst electrode 2 side is not affected by the hydrocarbon gas. Complete combustion occurs,
Incomplete combustion occurs on the inert catalyst electrode 3 side. Therefore, the amount of water vapor generated on both electrodes is different from each other,
A difference in water vapor partial pressure occurs on both electrodes, and an electromotive force is generated between both electrodes due to the difference in water vapor partial pressure. Since this electromotive force is proportional to the concentration of the hydrocarbon gas or has a correlation with both of them, if the relation between the electromotive force and the hydrocarbon gas concentration is obtained in advance, this relation is measured as the calibration data. The hydrocarbon gas concentration can be calculated based on the electromotive force.

Next, the result of the characteristic test of the hydrocarbon sensor of this embodiment will be described. A hydrocarbon sensor having the structure shown in FIG. 1 was manufactured. First, the manufacturing method will be described. La _0.6 Ba _0.4 was formed on one side of a disk-shaped sample of CaZr _0.9 In _0.1 O ₃ -α (diameter: 7.8 mm, thickness: 7.9 mm), which is a perovskite-type proton conductive solid electrolyte 1.
CoO ₃ powder paste is applied and 1000 ℃ in air 1
This was heat-treated for a period of time to be baked to form an active electrode 2 as a catalyst which is active with respect to hydrocarbon gas.
After that, apply Ag paste on the other side and apply 750
It was heat-treated in air at 1 ° C. for 1 hour and baked to form an inert electrode 3 which was inert to hydrocarbon gas. A Pt wire was attached as a lead wire 4 to the electrodes 2 and 3 of the sensor element thus manufactured. Then, the voltmeter 5 shown in FIG. 5 was connected to the lead wire 4 and the electromotive force of the sensor at room temperature was measured.

Next, this sensor element was set in the electric furnace 6 at 770 ° C. An alumina tube 7 is inserted in the electric furnace 6, and the sensor element is inserted in the alumina tube 7.
It was placed in the center of the electric furnace 6. Then, after mixing the hydrocarbon gas (measurement gas) from the cylinder 9 with the air from the cylinder 10 by the mixer 8 at a predetermined ratio, it is introduced into the alumina pipe 7 through the pipe 11 and inside the alumina pipe 7. It was supplied to the sensor element. The measurement gas from the cylinder 9 was introduced into the electric furnace at a flow rate of 260 ml / min. Then, the composition of the outlet gas was calibrated by a gas chromatograph (not shown).

FIG. 3 shows an example of measurement of the sensor electromotive force when the measurement gas from the cylinder 9 is methane gas, and FIG. 4 shows an example of measurement of the sensor electromotive force when propane gas is used. In each figure, the horizontal axis represents time and the vertical axis represents sensor electromotive force. The sensor probe according to this example exhibited stable electromotive force with respect to changes in the concentration of hydrocarbon gas, and had good reproducibility. Also, the time required to respond is
The response speed was quite rapid when the gas replacement of the experimental equipment was taken into account within 2 minutes.

FIG. 5 shows the relationship between the sensor electromotive force and the hydrocarbon gas concentration, with the horizontal axis representing the hydrocarbon gas (propane and methane gas) concentration and the vertical axis representing the sensor electromotive force. In the concentration measurement of propane gas and methane gas, a good one-to-one correspondence was found between the gas concentration and the sensor electromotive force.

As the electrode catalyst provided in the sensor element, the sensitivity can be changed by combining two kinds of conductive catalysts having different catalytic activities with respect to the combustion of the hydrocarbon gas to be measured. Further, the type of gas to be measured can be selected by setting the type of catalyst to an appropriate one.

[0015]

As described above, according to the present invention,
As a probe for a hydrocarbon gas sensor, a proton conductive solid electrolyte is used for the sensor element, an electrode catalyst active for combustion of hydrocarbon gas is arranged on one side, and an electrode inert for combustion of hydrocarbon gas on the other side. By arranging the catalyst, the hydrocarbon concentration is measured by using the electromotive force generated by the difference in the amount of water vapor generated on both electrodes when the hydrocarbon gas reaches the sensor electrode and burns. The hydrogen concentration can be measured continuously and stably and easily.

[Brief description of drawings]

FIG. 1 is a sectional view of a sensor probe according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a measuring method using the present sensor probe.

FIG. 3 is a graph showing an electromotive force characteristic of a sensor probe when measuring a methane gas concentration.

FIG. 4 is a graph showing an electromotive force characteristic of a sensor probe when measuring a propane gas concentration.

FIG. 5 is a graph showing the electromotive force characteristics of the sensor element with respect to the hydrocarbon gas concentration.

[Explanation of symbols]

 1; Solid Electrolyte 2; Active Electrode 3; Inert Electrode 4; Platinum Wire 5; Voltmeter 6; Electric Furnace 7; Alumina Tube 8; Gas Mixer 9; Hydrocarbon Gas Cylinder 10; Air Cylinder 11; Gas Inlet Tube

Front Page Continuation (72) Inventor Ho Yashima Mitake 2192-345 Mitake Town, Kani District, Gifu Prefecture

Claims (2)

[Claims] 1. A proton-conductive solid electrolyte, and a pair of porous electrodes that come into contact with the solid electrolyte at positions sandwiching the solid electrolyte, one of the porous electrodes being one of the hydrocarbon gas to be measured. Composed of a combustion-inert electrocatalyst,
A hydrocarbon sensor characterized in that the other is composed of an active electrode catalyst. 2. The hydrocarbon concentration is measured using a sensor electromotive force generated by the difference between the partial pressure of water vapor generated when the hydrocarbon gas is burned on the active electrode catalyst and the partial pressure of water vapor on the inert electrode catalyst. The hydrocarbon sensor according to claim 1, wherein: