TY - JOUR
T1 - Characterization of Ultramicropores and Analysis of Their Evolution in Tectonically Deformed Coals by Low-Pressure CO2Adsorption, XRD, and HRTEM Techniques
AU - Li, Yunbo
AU - Song, Dangyu
AU - Liu, Shimin
AU - Pan, Jienan
N1 - Funding Information:
This research was supported by the National Natural Science Foundation of China (no. 41602175), the China Postdoctoral Science Foundation (no. 2015M572104), the Henan Province basic and frontier technology research projects (no. 152300410099), State Key Laboratory Cultivation Base for Gas Geology and Gas Control (Henan Polytechnic University) (WS2019A07) and the Coal Seam Gas Joint Foundation of Shanxi (no. 2016012001). We appreciate the helpful comments of three anonymous reviewers on an earlier version of this manuscript.
Publisher Copyright:
Copyright © 2020 American Chemical Society.
PY - 2020/8/20
Y1 - 2020/8/20
N2 - Porosity in coal is the main space and migration channel for coalbed methane, and more than 90% of the specific surface area of coal comes from ultramicropores (<1.1 nm), which are expected to be affected by metamorphic and deformation processes in tectonically deformed coal (TDC). It is important to know how ultramicropores occur and evolve for safe mining and coalbed methane development. In this work, we employ low-pressure CO2 adsorption at 273 K (LPCO2), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM) techniques to investigate ultramicropores in one undeformed coal and seven TDCs from the Huaibei coalfield in Northern China. The results show that the pore volume (PV) and specific surface area (SSA) of ultramicropores ranged from 0.00839 to 0.02009 cm3/g and from 27.44 to 76.432 m2/g, respectively. As the deformation intensity increases, the PV and SSA of TDCs decrease in the brittle deformed stage and then increase in the ductile deformed stage. The results suggest that brittle deformation has a limited effect on the molecular structure of coal and only compacts the intermolecular space due to stress. However, ductile deformation can alter the molecular structure of coal to increase the PV and SSA of ultramicropores. fS and fL calculated by HRTEM images in different deformed tectonic coals have the same evolution law as do d002 and Lc obtained from XRD. The increase of La and Lc in ductile coal (73.4% and 47.6%) is much greater than that of brittle deformed coal (4.05% and 14.4%). SSA and d002 are negatively correlated in the brittle deformed coal and are positively correlated in the ductile deformed coal. The rotation, folding, and recombination of the aromatic layer during the ductile deformation process by mechanochemical action is the main reason.
AB - Porosity in coal is the main space and migration channel for coalbed methane, and more than 90% of the specific surface area of coal comes from ultramicropores (<1.1 nm), which are expected to be affected by metamorphic and deformation processes in tectonically deformed coal (TDC). It is important to know how ultramicropores occur and evolve for safe mining and coalbed methane development. In this work, we employ low-pressure CO2 adsorption at 273 K (LPCO2), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM) techniques to investigate ultramicropores in one undeformed coal and seven TDCs from the Huaibei coalfield in Northern China. The results show that the pore volume (PV) and specific surface area (SSA) of ultramicropores ranged from 0.00839 to 0.02009 cm3/g and from 27.44 to 76.432 m2/g, respectively. As the deformation intensity increases, the PV and SSA of TDCs decrease in the brittle deformed stage and then increase in the ductile deformed stage. The results suggest that brittle deformation has a limited effect on the molecular structure of coal and only compacts the intermolecular space due to stress. However, ductile deformation can alter the molecular structure of coal to increase the PV and SSA of ultramicropores. fS and fL calculated by HRTEM images in different deformed tectonic coals have the same evolution law as do d002 and Lc obtained from XRD. The increase of La and Lc in ductile coal (73.4% and 47.6%) is much greater than that of brittle deformed coal (4.05% and 14.4%). SSA and d002 are negatively correlated in the brittle deformed coal and are positively correlated in the ductile deformed coal. The rotation, folding, and recombination of the aromatic layer during the ductile deformation process by mechanochemical action is the main reason.
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U2 - 10.1021/acs.energyfuels.0c01403
DO - 10.1021/acs.energyfuels.0c01403
M3 - Article
AN - SCOPUS:85091877243
SN - 0887-0624
VL - 34
SP - 9436
EP - 9449
JO - Energy and Fuels
JF - Energy and Fuels
IS - 8
ER -