Microscopic mechanism of methane adsorption in shale: Experimental data analysis and interaction potential simulation

Dong, Yintao; Ju, Binshan; Zhang, Suian; Tian, Yapeng; Ma, Shuai; Liu, Nannan; Lu, G.

doi:10.1016/j.petrol.2019.106544

Cited by 7 publications

(10 citation statements)

References 24 publications

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“…The potential well in the interaction potential distribution curve is where CO 2 /CH 4 may be adsorbed, and the peak in the density profile indicates that CO 2 /CH 4 may form an adsorption layer . Based on these findings, the interaction potential distribution curves and the density profiles of CO 2 /CH 4 in the micropore structures were compared, as shown in Figure .…”

Section: Results and Discussionmentioning

confidence: 99%

“…62−65 The potential well in the interaction potential distribution curve is where CO 2 /CH 4 may be adsorbed, and the peak in the density profile indicates that CO 2 /CH 4 may form an adsorption layer. 35 Based on these findings, the interaction potential distribution curves and the density profiles of CO 2 / CH 4 in the micropore structures were compared, as shown in Figure 10. With increasing pore diameters, the depth of the potential well and the main density peak both decrease, implying that the interaction of the wall with CO 2 /CH 4 decreases and confirming that CO 2 /CH 4 is mainly adsorbed in pores with diameters <2 nm.…”

Section: Resultsmentioning

confidence: 99%

“…When the spacing is less than 0.61 nm, the methane molecule cannot enter the adsorption site, so the methane molecules cannot be adsorbed. 35 Hence, pores of different diameters (0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, and 2.4 nm) from the macromolecular models were selected to eliminate the influence of anisotropy and heterogeneity in the coal. Pores with different configurations at each diameter were selected, and the final result calculation used average values.…”

Section: Simulation Detailsmentioning

confidence: 99%

“…Micropores are the main site of adsorption. When the spacing is less than 0.61 nm, the methane molecule cannot enter the adsorption site, so the methane molecules cannot be adsorbed . Hence, pores of different diameters (0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, and 2.4 nm) from the macromolecular models were selected to eliminate the influence of anisotropy and heterogeneity in the coal.…”

Section: Simulation Detailsmentioning

confidence: 99%

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Effects of Pore Parameters and Functional Groups in Coal on CO₂/CH₄ Adsorption

Dong

Zhai²,

Guo

2021

ACS Omega

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The mechanisms of CO 2 /CH 4 adsorption in coal are the theoretical foundation for CO 2 sequestration in coal seams targeted for enhanced coalbed methane recovery. Herein, by changing the model (low rank coal: WMC, middle rank coal: XM and high rank coal: CZ) with plenty of side aliphatic chains and functional groups established in the literature, the influence and mechanism of pore parameters and functional groups(−CH 3 , − OH, −C 2 O, −C=O) on the adsorption of CO 2 and CH 4 in different rank coals are systematically studied. Using the Connolly surface algorithm to calculate the pore volume (V F ) and the specific surface area (S SA ) of coal with different functional groups, it can be seen that the influence of the functional group change on the pore structure is related to the coal rank. Changing the various functional groups in the original coal structure to a unified functional group (−CH 3 , −OH, −C 2 O, or −CO) will increase the accessible pore volume (V F ) and the specific surface area (S SA ), except in low-rank and middle-rank coal, where the ordered arrangement of −CO will decrease V F and S SA . The adsorption capacities of different pore parameters and functional groups were calculated by Grand Canonical Monte Carlo simulation and density functional theory. On pure adsorption, the pore parameters exert greater influence than the functional groups. By comparing the adsorption energy of the original pore structure containing functional groups and that of modified pores without functional groups, the contributions of the pore structure and original functional groups on CO 2 /CH 4 adsorption are 71 and 29% and 83 and 17%, respectively. Small-diameter pores and −C 2 O have a strong adsorption capacity. In terms of competitive adsorption, the −C O functional groups and pore diameters ranging from 1.0 to 2.0 nm can significantly enhance the selectivity of CO 2 over CH 4 . The CH 4 and CO 2 adsorption does not occur via rigorous monolayer adsorption; multilayer adsorption can occur for CH 4 and CO 2 with pore diameters of 1.0−2.0 and 1.0−2.2 nm, respectively, thus causing micropore filling. These quantitative results establish a foundation for the development of adsorption theory for CO 2 /CH 4 in coal.

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Section: Results and Discussionmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Simulation Detailsmentioning

confidence: 99%

Section: Simulation Detailsmentioning

confidence: 99%

See 2 more Smart Citations

Effects of Pore Parameters and Functional Groups in Coal on CO₂/CH₄ Adsorption

Dong

Zhai²,

Guo

2021

ACS Omega

View full text Add to dashboard Cite

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“…When the pore size is large, that is, the distance between the pore walls is large, the molecule has a small adsorption potential and two peaks appear, and the molecules are less attracted by gravity. As the pore size decreases, the distance between the walls of the pores decreases, and the adsorption potential gradually increases until there is only one peak [43]. Besides, the curvature of the solid surface has a positive correlation with the strength of the force field.…”

Section: Pore Structurementioning

confidence: 99%

Methane Adsorption Interpreting with Adsorption Potential and Its Controlling Factors in Various Rank Coals

et al. 2020

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Water content, metamorphism (coal rank) particle size, and especially pore structure, strongly influence the adsorption capacity of coal to methane. To understand the mechanism of methane adsorption in different rank coals, and its controlling factors, isothermal adsorption experiments with different coal ranks, moisture contents and particle sizes at the temperature of 303.15 K were conducted. In addition, the pore structures of coals were investigated through N2 adsorption/desorption experiments at the low-temperature of 77 K for selected coals from the Junggar Basin of NW China, Qinshui Basin and Ordos Basin of north China. Moreover, the adsorption potential of methane on the surface of the coal matrix was calculated, the controlling factors of which were discussed. The obtained methane isothermal adsorption result shows that the Langmuir volume (VL) of coal is independent of the particle size, and decreases with the increase of moisture content, which decreases first and then increases when the coal rank increases. Combined with the pore structure by the N2 adsorption at 77 K, VL increases with the increase of pore surface area and pore volume of coal pores. Besides, the adsorption potential of all selected coals decreased with the increase of the methane adsorption volume, showing a negative relationship. The interesting phenomena was found that the surface adsorption potential of the coal matrix decreases with the increase of moisture content, and increases with the decrease of particle size at the same pressure. With the same adsorption amount, the adsorption potential on the surface of coal matrix decreases first, and then increases with the increase of coal rank, reaching a minimum at Ro,m of 1.38%, and enlarging with the increase of pore surface area and the pore volume of coal pores. These findings may have significant implications for discovering CBM accumulation areas and enhancing CBM recovery.

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