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https://doi.org/10.29013/AJT-19-9.10-49-51
Eshkabilova Mavjuda Ergashboyevna, Doctor of Philosophy in Chemistry (PhD), teacher of Samarkand Construction Institute of Samarkand city, Uzbekistan Sidikova Xulkar Gulomovna, applicant of the Jazzakh State Institut of Jizzakh city, Uzbekistan Abduraxmanov Ergashboy, Doctor of Chemical Sciences, professor, Head of the Department of Analytical Chemistry Samarkand State University of Samarkand city, Uzbekistan E-mail: ergash50@yandex.ru
SELECTIVE THERMOCATALYTIC SENSOR FOR NATURAL GAS MONITORING
Abstract. In the scientific literature and practice, it was traditionally believed that the widely used thermochemical sensors do not provide the selectivity for determining the individual components of a gas mixture. In this work, we developed a sensor for the selective determination of natural gas in the presence of carbon monoxide and hydrogen.
The selectivity of the sensor is ensured using thermosensitive elements with different activity to the components of the gas mixture, differences, the activity of which is ensured by the selection of the composition of the catalyst. In this case, the output signal of the measuring sensor element of the sensor is proportional to the total concentration of the mixture of substances (H2, CO and CH4), and the output signal of the comparative sensitive element is proportional to the concentration of the mixture of substances (H2 and CO) - except for the detected component (CH4), and the signal difference is the first and second elements is proportional to the concentration of the determined component (CH4) in the mixture.
Keywords: thermocatalytic sensor, selectivity, sensitivity, silver oxide, iron oxide, nickel oxide, carbon monoxide, sol-gel technology, natural gas.
Introduction. Natural gas is one of the most important resources that are actively used in industry and in everyday life. It is almost non-toxic. However, in combination with air at a concentration of from 5.3 to 14.9% they form an explosive mixture [1]. In this regard, the development of sensors for the rapid determination of natural gas is one of the relevant tasks.
The aim of this work is to develop a sensor providing selective determination of natural gas in the presence of CO and H2.
It is known that the widely used thermocatalytic sensors (TCS) do not provide selectivity for determining a gas mixture [2]. One of the possible methods for ensuring the selectivity of TCS of combusti-
Section 5. Chemistry
ble gases is the use of heat-sensitive elements (HSE), which have different sensitivity to the components of the gas mixture [3,4]. In this regard, the main task in the development of selective TCS for natural gas detection is the selection of catalytic systems of HSE.
Results and discussion. In the temperature range of 100-250 °C the selectivity of In2O3, Ag2O, Fe3O4 and Ni2O3 mixture during the oxidation of combustible gases was studied. As a result of these experiments, it was found that the most optimal for the sensing element of the thermocatalytic sensor of natural gas are the catalyst 0.75In2O3-0.25Ag2O. It is advisable to use 0.50Fe3O4-0.50Ni2O3 as a catalyst for the comparative element. Taking into account the specifics of the problem being solved and using the above catalysts, sensors were made for the selective
determination of natural gas in the presence of CO and H2. The sensitive elements of the sensor have the form of a miniature ball of 7-oxide aluminum inside which there is a spiral of platinum wire (Fig. 1), which simultaneously serves as a heating element and a resistance thermometer. Given this, the output signal of the measuring sensor element of the sensor is proportional to the total concentration of the mixture of substances (H2, CO and CH4), and the output signal of the comparative sensitive element is proportional to the concentration of the mixture of substances (H2 and CO) - except for the detected component (CH4), and the signal difference is the first and second elements is proportional to the concentration of the determined component (CH4) in the mixture.
Figure 1. Selective thermocatalytic sensor of natural gas
Tests of the developed sensors included special selection of the optimal supply voltage, it follows that
experiments related to the selection of the supply the maximum value of the TCS signal with a catalyst
voltage value, the establishment of calibration char- 0.75In203-0.25 Ag2O and 0.50Fe304-0.50Ni203
acteristics of the sensor, as well as the identification when determining natural gas is observed in the
of its degree of selectivity. From the results on the range of 2.8-3.0 V.
Table 1.- Sensor signal connection to supply voltage (n = 5, P = 0.95)
No. Sensor supply voltage, V Sensor Signal, mV
x ±AX S Sr • 102
1. 2.5 20.6 ± 0.1 0.09 1.2
2. 2.8 27.0 ± 0.8 0.15 1.7
3. 3.0 28.1 ± 0.4 0.11 1.4
4. 3.5 25.9 ± 0.4 0.11 1.4
The developed sensor has a response start time (t0of 3-4 s, a time constant (t063) of no more than 9 s, and a readout time (t ) of13 s. The dependence of the TCS signal on the concentration of natural gas in the gas mixture in the studied range (from 0.1 to 5.0% vol.) ofthe gas concentration in the air is straight.
The effect of H2 and CO content on the determined value of the sensor output signal was studied. As follows from the obtained data, TCS with a measuring and compensation element catalyst are characterized by natural gas selectivities in the presence of H and CO.
Table 2.- Natural gas sensor selectivity results (n=5, P=0.95)
No. Gas mixture composition,%vol. Natural gas found, vol%
x ± Ax S Sr • 102
1. Natural gas (0.50) + air(res) 0.48 ± 0.06 0.05 1.2
2. Natural gas (0.50) + С0(1.00) + air(res) 0.52 ± 0.03 0.03 1.6
3. Natural gas (0.50) + H2(1.00) + air(res) 0.51 ± 0.03 0.04 1.7
The error of the sensors due to unmeasured com- detect natural gas from a mixture of combustible
ponents in gas mixtures does not exceed 2.0%. substances. The developed sensor is used to mea-
Conclusion. In summary, a highly sensitive sen- sure pre-explosive concentrations of natural gas in
sor has been developed which allows to selectively atmospheric air.
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Абдурахманов Э., Рузиев Э. А. Селективные термокаталитические сенсоры в экоаналитическом мониторинге газообразных выбросов // Химическая промышленность,- С-Пб., 2003.- Т. 80.-№ 9.- С. 19-25.
Эшкобилов Ш. А., Эшкобилова М. Э. Абдурахманов Э. Катализатор для селективного термокаталитического сенсора природного газа // Журнал «Химическая промышленность» Россия. 2015.- 5 c.
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