Study on competitive adsorption of O2/CH4 mixed gas by coal from molecular perspective

doi:10.16265/j.cnki.issn1003-3033.2025.01.0485

Abstract

Abstract:

To deeply understand the competitive adsorption characteristics of O₂/CH₄ gas mixtures on the coal surface, the pore distribution and chemical structure of the coal surface were analyzed using the Grand Canonical Monte Carlo(GCMC) method. Molecular simulation was used to investigate adsorption capacity and heat variations during the competitive adsorption of O₂/CH₄ gas mixtures under varying concentrations, pressures, and temperatures. Moreover, the competitive adsorption mechanism of O₂/CH₄ gas mixtures on the coal surface was revealed by adsorption selectivity. The results indicated that the isothermal adsorption curves were identical when the concentration ratio of O₂ to CH₄ was 7/3. The integrated adsorption heat under different conditions was approximately 19.5-20.0 J/g for O₂ and 24.0-24.8 J/g for CH₄. When the concentration ratio of O₂ to CH₄ ranged between 7/3 and 2/8, the integrated adsorption heat of O₂ was higher than that of CH₄. The increased temperature decreased the adsorption capacity of both gases but increased the adsorption selectivity of O₂ to CH₄. Moreover, the effect of gas pressure on competitive adsorption weakened with pressure increase. CH₄ adsorbed faster than O₂under low gas pressures, and CH₄ reached saturation adsorption earlier than O₂when the total pressure increased. When the O₂ concentration in the gas mixtures increased, the adsorption selectivity of O₂ for CH₄ decreased. However, CH₄ consistently showed higher adsorption competitiveness than O₂.

Key words: coal, O₂/CH₄ gas mixtures, competitive adsorption, adsorption heat, molecular simulation

CLC Number:

X936

HE Shujing, PENG Chengyang, KANG Jianhong, ZHANG Gengxian. Study on competitive adsorption of O₂/CH₄ mixed gas by coal from molecular perspective[J]. China Safety Science Journal, 2025, 35(1): 137-145.

Figures/Tables 11

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Table 1

Fitting parameters of Langmuir model for competitive adsorption of O2/CH4 gas mixtures

$φ O 2$	p/MPa	$n O 2$ / (mmol·g^-1)	$n C H 4$ / (mmol·g^-1)	$b O 2$ / MPa	$b C H 4$ / MPa	$ε O 2$ / (J·g^-1)	$ε C H 4$ / (J·g^-1)	R²
0.1	0~10	0.155 47	1.614 21	0.275 07	0.798 56	19.690 3	24.778 8	0.999 68
0.2	0~10	0.232 28	1.477 19	0.191 59	0.804 22	19.785 3	24.098 4	0.999 74
0.3	0~10	0.353 45	1.452 39	0.185 14	0.827 03	19.908 1	24.254 2	0.999 87
0.4	0~10	0.486 36	1.308 22	0.122 18	0.843 09	19.989 7	24.087 6	0.999 36
0.5	0~10	0.564 87	1.239 57	0.099 36	0.877 93	19.983 7	24.459 8	0.999 33
0.6	0~10	0.663 54	1.060 65	0.089 94	0.935 41	19.605 0	24.370 0	0.999 94
0.7	0~10	0.978 43	0.966 40	0.071 59	0.984 22	19.877 3	24.404 6	0.999 89
0.8	0~10	1.222 20	0.595 67	0.068 76	0.997 85	19.909 8	24.039 7	0.999 87
0.9	0~10	1.399 78	0.398 41	0.023 58	1.122 94	19.756 7	24.778 6	0.999 51

Table 1

Fig.9

Fig.10

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Study on competitive adsorption of O₂/CH₄ mixed gas by coal from molecular perspective

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