Influence of coal rank on CPSD in low-temperature N2 adsorption

doi:10.16265/j.cnki.issn1003-3033.2022.04.008

Abstract

Abstract:

In order to study coal adsorption theory and adsorption mechanism of coalbed methane, six coal samples of different ranks were selected for low-temperature N₂ adsorption experiments to explore CPSD of filled N₂ molecules in coals. Then, experimental isotherm characteristics were analyzed through density functional theory (DFT) and theory of volume filling of micropore (TVFM), and critical filling pressure (CFP) and CPSD for micropore fillings were obtained. Finally, relative pressure segmentation method was used to verify the results by fitting of Langmuir equation-Dubinin-Astakhov (D-A) equation-Brunauer-Emmet-Teller (BET) equation. The results show that N₂ adsorption/desorption isotherm of coal samples, from low to high rank, transitions from type II to type I. And proportion of N₂ molecules present in forms of micropore filling and monolayer adsorption in low-rank coals is greater than that of high-rank ones. CPSD decreases first and then increases as coal rank goes from low to high. The higher the rank is, the smaller CPSD range of 6 coal samples will be, which is between 1.61-2.19 nm.

Key words: coal rank, low-temperature N₂, adsorption experiment, critical filling pore size distribution (CPSD), micropore filling, pore structure

HONG Lin, WANG Wenjing, GAO Dameng, GUO Yingchao, MA Honghai. Influence of coal rank on CPSD in low-temperature N₂ adsorption[J]. China Safety Science Journal, 2022, 32(4): 51-58.

Figures/Tables 10

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References 23

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煤样	煤矿	分类	水分	灰分	挥发分	固定碳
S₁	蒲河	褐煤	16.84	11.59	34.72	36.86
S₂	准格尔	长焰煤	5.21	14.20	24.93	55.67
S₃	小凌河	气煤	2.14	26.06	29.63	42.17
S₄	鹤岗	1/3焦煤	1.62	6.78	33.08	58.52
S₅	常村	贫煤	1.25	9.17	13.24	76.34
S₆	余吾	无烟煤	1.46	9.78	10.55	78.21

煤样	等温线类型	滞后环类型	孔隙形状	P/P₀ (B点)	Q_B占总吸附量比例/%
S₁	Ⅱb	H2	墨水瓶孔	0.098 86	31.24
S₂		H3	非均匀狭缝孔	0.060 05	13.70
S₃			非均匀狭缝孔	0.043 09	13.34
S₄			0.062 26		11.77
S₅	Ⅰb	H4	均匀且狭窄的狭缝孔	0.110 94	19.57
S₆	Ⅰb	H4	均匀且狭窄的狭缝孔	0.160 89	11.52

煤样	CFP(P/P₀)	CPSD/nm	D-A指数
S₁	8.0×10^-4~0.033 9	1.73~2.19	1.362 0
S₂	5.5×10^-4~0.030 2	1.70~2.17	1.534 3
S₃	2.4×10^-4~0.010 0	1.64~1.99	1.532 4
S₄	1.4×10^-4~0.010 4	1.61~2.00	1.833 0
S₅	5.0×10^-4~0.010 6	1.69~2.00	2.544 4
S₆	8.4×10^-4~0.010 7	1.73~2.01	2.437 5

煤样	P/P₀	R²		P/P₀	R²
煤样	P/P₀	D-A	Langmuir	P/P₀	D-A	Langmuir	BET
S₁	8.0×10^-4~0.033 9	0.999 21	0.994 2	0.033 9~0.302 1	0.967 46	0.985 22	0.999 76
S₂	5.5×10^-4~0.030 2	0.999 45	0.994 02	0.030 2~0.302 35	0.951 76	0.985 47	0.999 54
S₃	2.4×10^-4~0.010 0	0.999 80	0.996 19	0.010 0~0.321 4	0.890 9	0.970 82	0.999 72
S₄	1.4×10^-4~0.010 4	0.998 83	0.995 03	0.010 4~0.300 2	0.874 45	0.982 49	0.999 56
S₅	5.0×10^-4~0.010 2	0.999 28	0.998 65	0.010 2~0.321 2	0.984 32	0.999 87	0.990 27
S₆	8.4×10^-4~0.010 7	0.998 63	0.997 72	0.010 7~0.321 5	0.934 71	0.998 55	0.984 62

Influence of coal rank on CPSD in low-temperature N₂ adsorption

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