Low-temperature oxidation of free radicals and functional groups in coal during the extraction of coalbed methane

Xu, Qin; Yang, Shengqiang; Hu, Xincheng; Song, Wenli; Cai, Jiawen; Zhou, Baoxue

doi:10.1016/j.fuel.2018.11.060

Cited by 52 publications

(18 citation statements)

References 24 publications

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“…During this process, the old free radical is constantly annihilated, and new free radical are generated. When the free radical continues to accumulate to initiate a chain reaction, the free radical concentration soars, and the reaction with oxygen continues to accelerate to produce a large amount of heat, eventually leading to coal spontaneous combustion 21,22 . According to the experiment, the ESR spectra of coal gangue during heating and oxidation under oxygen concentrations of 0%, 5%, 10%, 15%, and 21% are as shown in Figure 2.…”

Section: Results and Analysismentioning

confidence: 98%

The variations of free radical and index gas CO in spontaneous combustion of coal gangue under different oxygen concentrations

et al. 2021

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Summary In order to study the effect of oxygen concentrations on the change of active groups in the oxidation process of coal gangue, the airflows of different oxygen concentrations were prepared to simulate the oxidation and heating process of coal gangue under oxygen concentrations of 0%, 5%, 10%, 15%, and 21%. During the oxidation and heating process, the free radical parameters were measured at different temperatures in real time. The results show that in the early stage of coal gangue oxidation, the g factor remains at a lower level and do not start to increase until certain temperatures are reached. Besides, the higher the oxygen concentration is, the lower the temperature at which the g factor begins to increase. When the oxygen concentrations are 0%, 5%, 10%, 15%, and 21%, the corresponding temperatures are 225, 200, 150, 150, and 125°C, respectively. Furthermore, with the increase of oxidation temperature, the free radical concentrations experience four stages, namely, the slow increase stage, the rapid increase stage, the stagnant increase stage, and the final increase stage. And the higher the oxygen concentration is, the shorter the free radical stagnant increase stage is. During the oxidation of coal gangue, the line widths decrease slowly before 150°C, and then start to plunge and finally stabilize near the minimum at 350°C. Moreover, the higher the oxygen concentration is, the smaller the minimum values of line widths are. In the oxidation process of coal gangue, the gas product CO amounts are first at a lower level, and then begin to increase rapidly after 150°C. At the same temperature, the increased rates of CO production in coal gangue under the oxygen concentrations of 10%, 15%, and 21% are significantly higher than those under the oxygen concentrations of 0% and 5%. Based on the variation law of free radical parameters in coal gangue under different oxygen concentrations, the actual spontaneous combustion of gangue hills was analyzed and the free radical reaction mechanism of spontaneous combustion of gangue hills was discussed. The research results are of guiding significance for the treatment of spontaneous combustion of coal gangue.

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Section: Results and Analysismentioning

confidence: 98%

The variations of free radical and index gas CO in spontaneous combustion of coal gangue under different oxygen concentrations

et al. 2021

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“…Natural desorption of gases from bituminous coal results in methane release to the atmosphere with smaller amounts of ethane, propane and carbon dioxide 35 – 37 . Extensive studies in this field were performed by Xu et al 38 , 39 and Chen et al 40 . Exposing of coal to air results in parallel processes of coal oxidation and desorption of carbon monoxide and dioxide 41 .…”

Section: Resultsmentioning

confidence: 99%

Improved method of fire hazard assessment taking into account the effect of the primary temperature of a coal seam on the desorption ratio of gas indicators

Więckowski

Howaniec

Smoliński

2022

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The methods of fire risk assessment in its early phase employed so far used to take into account only the temperature of the heating of coal. The research works reported so far in this field have been conducted at ambient temperatures, without considering the rock mass primary temperature occurring in a particular coal seam and neglecting the depth of coal seams. The method for the determination of the composition of gases emitted from coal samples, employed in the study presented here, takes into account the effect of rock mass pressure, and therefore the depth of the coal seam, as well as the temperature typical for the rock mass in a particular coal mine. In the paper the results of the experimental research on the effects of the primary temperature of a coal seam on the content of gases emitted from coal, performed with the use of a specially designed experimental stand are presented. The method may be useful in developing fire hazard predictions for longwalls with residual coal in goafs. The relations between the self-ignition characteristics as well as selected physical properties of coal samples and carbon monoxide emission were also given. The research results proved that the accurate fire hazard assessment requires considering other than just self-heating of coal causes of carbon monoxide emission, including the rock mass primary temperature, which is expected to improve the existing methods of fire risk assessment in coal mines and post-mining areas.

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“…This implied that -COOH had a high reaction activity and was the main reaction group during the low temperature oxidation process. 23 When the temperature was below 200°C, the carboxyl group's change range in the air atmosphere was similar to its change range in the argon atmosphere. This means then, that it could be inferred that oxygen was not directly involved in the change of the -COOH content at this stage.…”

Section: The Change In -Coohmentioning

confidence: 93%

“…However, under air atmosphere, the amount of C-O-C at 500°C was 3.6 times more than that at 30°C. This demonstrated that C-O-C was a stable structure, and that the participation of oxygen hindered the formation of C-O-C. 23 It was therefore difficult for C-O-C to participate in the coal oxidation reaction, but it could stably exist at a high temperature.…”

Section: The Change In C-o-cmentioning

confidence: 99%

“…Tang and Wang 22 studied the secondary oxidation characteristics of two lignites and found that the aliphatic hydrocarbons were oxidized and that the new oxygen-containing functional groups were formed during the first oxidation process, which thus increased the risk of spontaneous combustion in preoxidized coal. Xu et al 23 found that -CH 2 -and -CH 3 were the main reaction groups, -C-O was the main reaction product, and that methane inhibited the oxidation reaction of functional groups. Cai et al 24 found that the contents of -CH 2 -and -CH 3 gradually decreased as the oxidation temperature increased, and that their changes were closely related to the formation of carbon monoxide.…”

Section: Introductionmentioning

confidence: 99%

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The evolution law of functional groups during the heating of coal in oxygen and oxygen‐free atmospheres

et al. 2021

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There is a change in both the quantity and type of functional groups due to the fact that they become oxidized and pyrolyzed during the spontaneous coal combustion process. In order to study the oxidation and pyrolysis mechanisms that are at play during the evolution of these functional groups, in situ Fourier transform infrared (FTIR) spectroscopy was employed to test the real-time evolution of these functional groups in both air and argon atmospheres. The differences found between functional groups when under an oxygen oxygen-free environment were analyzed. The results show that when the temperature exceeds 200°C, the changes in functional groups steadily increase and that regardless of whether the atmosphere is made up of argon or air, the oxygen-containing functional groups change significantly. In this situation, −OH, −CH 3 , and −CH 2 -are important reactants in the whole heating process; −COOH and −C=O are reactants during the low temperature oxidation stage, but when reaching the high temperature stage, they become the products; C-O-C and C=C is a stable reaction product. During the coal spontaneous combustion process, oxidation and pyrolysis work as two coupling reactions: The heat released by the oxidation reaction pyrolyzes the macromolecular structure and coal-oxygen complexes, while a large number of active groups are produced during pyrolysis, which then provides the reactants for the oxidation reaction. These results reveal the changes that functional groups go through during the process of oxidation and pyrolysis, and provide a theoretical basis for the development of efficient fire-fighting materials.

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Low-temperature oxidation of free radicals and functional groups in coal during the extraction of coalbed methane

Cited by 52 publications

References 24 publications

The variations of free radical and index gas CO in spontaneous combustion of coal gangue under different oxygen concentrations

The variations of free radical and index gas CO in spontaneous combustion of coal gangue under different oxygen concentrations

Improved method of fire hazard assessment taking into account the effect of the primary temperature of a coal seam on the desorption ratio of gas indicators

The evolution law of functional groups during the heating of coal in oxygen and oxygen‐free atmospheres

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