Gas adsorption characteristics changes in shale after supercritical CO2-water exposure at different pressures and temperatures

Tectonic coal is a kind of soft coal that is generated during tectonic movement. Gas outbursts usually occur in seams containing both virgin coal and tectonic coal. To reveal the adsorption characteristics of this type of coal seam (containing both virgin coal and tectonic coal), both tectonic coal and virgin coal were collected from the same longwall face and a series of laboratory tests were conducted, including coal sorption tests and pore specific surface measurements. Both the tectonic coal and virgin coal were crushed into coal powder (0.18–0.25 mm) for the coal sorption tests. In these laboratory tests, different mass ratios between tectonic coal and virgin coal were tested. We found that with the increase of the percentage of tectonic coal, the adsorption volume showed a rising trend, reached its maximum value, and then decreased. The specific surface areas of the mixed coal samples had the same evolution trends as those of the adsorption volume. From the laboratory tests, we found that when the mass ratio of virgin coal to tectonic coal was 1:1, both the adsorption volume and the specific surface areas reached their maximum values. Due to the percentage variation of the tectonic coal in the panel with the advancement of the longwall face, when the tectonic coal accounted for 50% of the total coal, the gas content would rise. Thus, proper measures should be adopted for outburst hazards control. The mathematical model between the change of specific surface area and the stress and strain of pore expansion before and after gas adsorption was established, and the relationship between the change of pore structure and gas emission before and after gas adsorption was obtained. It provides a theoretical basis for further research on coal and gas outburst mechanisms.

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Study on the Effect of Soft and Hard Coal Pore Structure on Gas Adsorption Characteristics

Advances in Civil Engineering ◽

10.1155/2021/1425227 ◽

2021 ◽

Vol 2021 ◽

pp. 1-10

Author(s):

Xun Zhao ◽

Tao Feng ◽

Ping Wang ◽

Ze Liao

Keyword(s):

Pore Structure ◽

Adsorption Capacity ◽

Residence Time ◽

Coalbed Methane ◽

Gas Adsorption ◽

Nitrogen Adsorption ◽

Hard Coal ◽

Research Results ◽

Adsorption Characteristics ◽

Soft Coal

In order to grasp the effect of soft and hard coal pore structure on gas adsorption characteristics, based on fractal geometry theory, low-temperature nitrogen adsorption and constant temperature adsorption test methods are used to test the pore structure characteristics of soft coal and its influence on gas adsorption characteristics. We used box dimension algorithm to measure the fractal dimension and distribution of coal sample microstructure. The research results show that the initial nitrogen adsorption capacity of soft coal is greater than that of hard coal, and the adsorption hysteresis loop of soft coal is more obvious than that of hard coal. And the adsorption curve rises faster in the high relative pressure section. The specific surface area and pore volume of soft coal are larger than those of hard coal. The number of pores is much larger than that of hard coal. In particular, the superposition of the adsorption force field in the micropores and the diffusion in the mesopores enhance the adsorption potential of soft coal. Introducing the concept of adsorption residence time, it is concluded that more adsorption sites on the surface of soft coal make the adsorption and residence time of gas on the surface of soft coal longer. Fractal characteristics of the soft coal surface are more obvious. The saturated adsorption capacity of soft coal and the rate of reaching saturation adsorption are both greater than those of hard coal. The research results of this manuscript will provide a theoretical basis for in-depth analysis of the adsorption/desorption mechanism of coalbed methane in soft coal seams and the formulation of practical coalbed methane control measures.

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Molecular simulation of gas adsorption characteristics and diffusion in micropores of lignite

Fuel ◽

10.1016/j.fuel.2020.117443 ◽

2020 ◽

Vol 269 ◽

pp. 117443 ◽

Cited By ~ 7

Author(s):

Dameng Gao ◽

Lin Hong ◽

Jiren Wang ◽

Dan Zheng

Keyword(s):

Molecular Simulation ◽

Gas Adsorption ◽

Adsorption Characteristics ◽

And Diffusion

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First-Principles Exploration of Hazardous Gas Molecule Adsorption on Pure and Modified Al60N60 Nanoclusters

Nanomaterials ◽

10.3390/nano10112156 ◽

2020 ◽

Vol 10 (11) ◽

pp. 2156 ◽

Cited By ~ 1

Author(s):

Qi Liang ◽

Xi Nie ◽

Wenzheng Du ◽

Pengju Zhang ◽

Lin Wan ◽

...

Keyword(s):

First Principles ◽

Gas Adsorption ◽

Energy Gap ◽

Theoretical Work ◽

Change Rate ◽

Adsorption Characteristics ◽

Gas Molecule ◽

Hazardous Gases ◽

Gas Molecules ◽

Hazardous Gas

In this work, we use the first-principles method to study in details the characteristics of the adsorption of hazardous NO2, NO, CO2, CO and SO2 gas molecules by pure and heteroatom (Ti, Si, Mn) modified Al60N60 nanoclusters. It is found that the pure Al60N60 cluster is not sensitive to CO. When NO2, NO, CO2, CO and SO2 are adsorbed on Al60N60 cluster’stop.b, edge.ap, edge.ah, edge.ap andedge.ah sites respectively, the obtained configuration is the most stable for each gas. Ti, Si and Mn atoms prefer to stay on the top sites of Al60N60 cluster when these heteroatoms are used to modify the pure clusters. The adsorption characteristics of above hazardous gas molecules on these hetero-atom modified nanoclusters are also revealed. It is found that when Ti-Al60N60 cluster adsorbs CO and SO2, the energy gap decreases sharply and the change rate of gap is 62% and 50%, respectively. The Ti-modified Al60N60 improves the adsorption sensitivity of the cluster to CO and SO2. This theoretical work is proposed to predict and understand the basic adsorption characteristics of AlN-based nanoclusters for hazardous gases, which will help and guide researchers to design better nanomaterials for gas adsorption or detection.

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