CN1228535A

CN1228535A - Ethylene sensor for fire alarm of coal mine

Info

Publication number: CN1228535A
Application number: CN 98113813
Authority: CN
Inventors: 董永来; 李文钊; 于春英; 江义
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 1998-03-05
Filing date: 1998-03-05
Publication date: 1999-09-15

Abstract

The olefiant gas sensor for fire alarm of coal mine consists of air-pervious film, working electrode, electrolytic liquor, opposite electrode and oxygen-pervious film, in which the air-pervious film and oxygen-pervious film are overlapped in the shell body, a constant-pressure source is added between the working electrode and opposite electrode, a carbon monoxide filter is placed in the front of the air-pervious film, and its adopted carbon monoxide purification catalyst uses CuO2, TiO2, SnO2 or MnO2 as carrier, and uses noble metals of Pt and/or Pd as active component, noble metal contents respectively are 0.01-5.0% wt; in which the electrode is made up by using noble metal Pt black catalyst, mixing it with polytetrafluoroethylene and applying their mixture on the teflon air-pervious film, and its noble metal content is 40-95%.

Description

Ethylene sensor for coal mine fire alarm

The invention relates to an ethylene sensor for detecting trace (0.5-100 ppm) ethylene from underground coal mine or air, in particular to an ethylene sensor for detecting trace (0.5-100 ppm) ethylene, which is characterized in that air or gas containing trace ethylene firstly diffuses through a purification catalyst in the first step to purify carbon monoxide gas which can cause influence; and secondly, diffusing the ethylene to enter an ethylene sensor for electrochemical oxidation reaction to obtain a current signal so as to obtain the concentration of trace ethylene.

Ethylene is one of the marking gases of coal mine fire, and is another gas which appears immediately after a coal bed spontaneously releases a large amount of carbon monoxide, so that the occurrence of coal mine underground fire can be forecasted by detecting trace ethylene. Although there is a sensor capable of detecting carbon monoxide (see technical identification certificate of KG3021 type carbon monoxide sensor, 506LC carbon monoxide sensor issued by general coal mine headquarters in china, 1991, and institute of chemico-physical research in college of science in china), if a sensor capable of effectively detecting ethylene is matched with a carbon monoxide sensor, the accuracy of fire prediction can be improved. At present, methods for detecting trace ethylene comprise an infrared absorption method and a chromatographic hydrogen flame analysis method, but cannot be directly used for underground analysis of coal mines due to the safety requirement of the coal mines.

The invention aims to provide an economical ethylene sensor which is suitable for large-scale underground coal mine and contains trace (ppm) ethylene in air or gas.

The invention provides an ethylene sensor for coal mine fire alarm, which is formed by superposing a breathable film (2), a working electrode (3), an electrolyte (4), an opposite electrode (5) and an oxygen permeable film (6) of the breathable film (2) in a shell, wherein a constant voltage source A is added between the working electrode (3) and the opposite electrode (5), and the ethylene sensor is characterized in that:

a carbon monoxide filter (1) is arranged in front of the permeable membrane (2), and the carbon monoxide purifying catalyst adopted by the carbon monoxide filter is CuO₂、TiO₂、SnO₂Or MnO₂As a carrier, Pt and/or Pd noble metals are used as active ingredients, and the content of the noble metals is 0.01-5.0 wt% respectively;

wherein the electrodes (3) and (5) are formed by mixing a noble metal Pt black catalyst and coating polytetrafluoroethylene on a polytetrafluoroethylene breathable film, and the content of the noble metal is 40-95%.

Further, the gas permeable film (2) used in the present invention is a polytetrafluoroethylene gas permeable film; the oxygen permeable membrane (6) is a fluoroethylene fluoropropene copolymer; the electrolyte is phosphoric acid or sulfuric acid solution, and the concentration is 0.1-5.0M.

The principle of the present invention (fig. 1) is to remove carbon monoxide and the like in a gas by using a selective carbon monoxide purification catalyst,while a trace amount of ethylene in the air or gas diffuses through the purification catalyst and the polytetrafluoroethylene gas-permeable membrane (air permeability: 22.7 ml/atm.sec.cm)²) Reaches the catalyst layer of the working electrode to catalyzeUnder the action of the agent, the agent and water in sulfuric acid or phosphoric acid electrolyte are subjected to oxidation reaction to generate carbon dioxide and release electric charges; on the opposite electrode, oxygen diffuses through the oxygen permeable membrane (air permeability: 2.8X 10)^-5Ml/atmosphere second cm²) And the breathable film (with the same air permeability as the working electrode) reaches the catalyst layer of the opposite electrode, and under the action of the catalyst, the breathable film and hydrogen protons in the electrolyte are reduced into water and absorb charges. When an external circuit is turned on, current flows through the reactor, and the flowing current is proportional to the ethylene concentration, and the whole reaction formula can be represented by the following formula: (1) (2) (3)

so-called oxygen permeable membranes, which are practically not selective for gases, even 21% of the oxygen in the air, due to their low permeability

The amount of permeation is small, so that the amount of permeation of ppm level ethylene concentration is negligible.

(3) The reaction of formula (I) cannot be carried out spontaneously, an external potential is required to be maintained, the magnitude of the potential has a great influence on the oxidation of ethylene, and the reaction can be carried out smoothly only when the potential of the working electrode is maintained at a proper potential, so that a part for maintaining the potential of the working electrode constant is also arranged in an external circuit, which is defined as "constant potential". The ethylene sensor can be used under the conditions of room temperature and relative humidity less than or equal to 98 percent, the detection use range is 0-100 ppm, and carbon monoxide gas less than 1000ppm can not interfere with the ethylene sensor.

The technique of the invention is further illustrated by the following examples:

example 1: 1.0% Pt + 1.0% Pd/MnO₂Clean-up catalyst preparation

Weighing10 g MnO₂Weighing 0.025 g/ml chloroplatinic acid and 4.0 ml palladium chloride solution respectively, uniformly mixing the three, adding a proper amount of water to prepare paste, extruding the paste into particles with phi 2 multiplied by 2, putting the particles into a tubular furnace, drying the particles for 2 hours at 100 ℃ in a nitrogen atmosphere, introducing mixed gas of nitrogen and hydrogen (10-30 percent hydrogen) to reduce the particles for 2 hours, cooling the particles to room temperature, passivating the particles for 2 days, and taking the particles out. The removed sample was washed with deionized water for chloride ion, pH =7, and dried at 100 ℃ for 2 hours.

Example 2: electrode preparation and installation

Weighing Pt black 0.15 g, weighing 60% (weight ratio) polytetrafluoroethylene emulsion 0.09 ml, mixing, adding appropriate amount of distilled water, concocting into paste, and coating two pieces with area of 2 cm²A polytetrafluoroethylene air-permeable film with a thickness of 0.2 mm (air permeability: 22.7 ml/atm.sec.cm)²) And drying the prepared electrode in a tube furnace at 100 ℃ for 2 hours, and sintering the electrode at 260 ℃ for 5 minutes to form the electrode, wherein the electrode is arranged in a shell made of polyvinyl chloride material.

Example 3: ethylene sensor Performance 1

Since ethylene in coal mines is a gas that appears after a large amount of carbon monoxide appears, and detection of a trace amount of ethylene is a weight-off for a coal mine fire alarm, the ethylene sensor must have a very high sensitivity, and table 1 shows a sensitivity test when the ethylene sensor is subjected to 0.5ppm ethylene. The experiment was carried out in a 2.6 litre closed vessel, the amount of ethylene to be injected being calculated by volume. As can be seen from Table 1, the ethylene sensor is fully capable of detecting 0.5ppm of ethylene, but the response time is relatively long, and may be related to the ethylene concentration, since the response time is only 1.5 minutes for 10ppm of ethylene.

TABLE 1 sensitivity test of ethylene sensor at 0.5ppm ethylene concentration

Response time (min) shows concentration (ppm)

0- 0

5 0.2

10 0.2

30 0.3

60 0.4

90 0.5

Standard before ethylene feeding

Example 4: ethylene sensor Performance 2

Ethylene sensors were assembled from the purified catalyst prepared in example 1 and the electrode prepared in example 2 and tested at various ethylene concentrations, the results of which are shown in table 2. The potentiostat used in the experiment was manufactured by beidou electrical corporation of japan, and the output current of the sensor was recorded by an X-Y recorder (shanghai automated instrument co., ltd.) at room temperature. As can be seen from Table 2, the linear range of ethylene detection by the ethylene sensor is 0 to 100 ppm.

TABLE 2 ethylene concentration vs. sensor output current

Ethylene concentration (ppm) Current output (μ A)

10 1.0

20 1.9

50 4.8

100 9.5

150 11.5

200 12.5

Example 5: ethylene sensor Performance 3

Because the ethylene sensor can detect trace ethylene and carbon monoxide, the purification catalyst in the ethylene sensor must purify carbon monoxide completely to eliminate the interference of carbon monoxide on the ethylene sensor, so as to achieve the purpose of accurately detecting ethylene, the purification experiment results of four purification catalysts at different carbon monoxide concentrations are listed in table 3, the experiment is carried out at room temperature, and the experiment conditions are the same as those in example 3. As can be seen from table 3, the output current was large when the sensor was not equipped with a purification catalyst, indicating that the carbon monoxide gas interfered with the ethylene sensor very much. However, in the presence of the purification catalyst, even if the carbon monoxide concentration reached 1000ppm, the ethylene sensor did not detect carbon monoxide, indicating that carbon monoxide was completely purified by diffusion into the purification catalyst.

TABLE 3 purification of carbon monoxide by clean-up catalyst Experimental results carbon monoxide concentration No clean-up catalyst Pt. Pd/MnO₂Pt·Pd/TiO₂Pt·Pd/CuO₂Pt·Pd/SnO₂(ppm) Current output (μ A)

100 19 0 0 0 0

200 38 0 0 0 0

300 56 0 0 0 0

400 75 0 0 0 0

600 110 0 0 0 0

1000 180 0 0 0 0

Example 6: ethylene sensor Performance 4

Because air or gas contains water vapor, especially the coal mine underground contains saturated water vapor, the water vapor resistance of the purification catalyst in the ethylene sensor is a detection instrument for indicating whether the ethylene sensor has practical value, and the water vapor resistance of the purification catalyst is listed in table 4. The experiment is that the purification catalyst is placed in a closed container containing saturated water vapor (the relative humidity is 95-98%), and after 7 days, the experiment of purifying carbon monoxide by the ethylene sensor is carried out, and the experiment is repeated. As can be seen from Table 4, the purification catalyst was still excellent in purification effect even when it was left in saturated water vapor for 50 days.

TABLE 4 Water vapor resistance of the clean-up catalyst

Carbon monoxide concentration (ppm) sensor output current (μ A)

100 0

200 0

400 0

600 0

1000 0

Claims

1. The utility model provides an ethylene sensor for colliery fire alarm, constitutes in the casing by ventilated membrane (2), working electrode (3), electrolyte (4), opposite electrode (5), oxygen permeation membrane (2) ventilated membrane (6) coincide, and it has constant voltage source A, its characterized in that to add between working electrode (3) and opposite electrode (5):

a carbon monoxide filter (1) is arranged in front of the permeable membrane (2), and the carbon monoxide purifying catalyst adopted by the carbon monoxide filter is CuO₂、TiO₂、SnO₂Or MnO₂As a carrier, Pt and/or Pd noble metals are used as active ingredients, and the content of gold is 0.01-5.0 wt% respectively;

2. The ethylene sensor for coal mine fire alarm of claim 1 wherein: the used breathable film (2) is a polytetrafluoroethylene breathable film.

3. The ethylene sensor for coal mine fire alarm of claim 1 wherein: the oxygen permeable membrane (6) is a fluoroethylene fluoropropene copolymer.

4. The ethylene sensor for coal mine fire alarm of claim 1 wherein: the electrolyte is phosphoric acid or sulfuric acid solution, and the concentration is 0.1-5.0M.