Structure and fractal characteristic of micro- and meso-pores in low, middle-rank tectonic deformed coals by CO2 and N2 adsorption

5 years ago

Structure and fractal characteristic of micro- and meso-pores in low, middle-rank tectonic deformed coals by CO2 and N2 adsorption

$Structure and fractal characteristic of micro- and meso-pores in low, middle-rank tectonic deformed coals by CO2 and N2 adsorption$

The structure and fractal characteristic of micro- (0.32∼2 nm) and meso-pores (2–50 nm) in low, middle-rank (maximum vitrinite reflectance, R o, max = 0.65–1.34%) tectonic deformed coals (TDCs) were revealed by combining low temperature N2/CO2 adsorption (LPN2/CO2GA) and fractal theory. The main conclusions are as follows: 1) The evolution of pore shapes in TDC sequence manifests as the stable existence of Type II pores (<3.3 nm) of bad connectivity, gradually increasing of the fine bottleneck pores of 3.3∼4 nm, and gradually decreasing of open plate pores of <10 nm 2) The total specific surface area (SSA, determined by Brunauer-Emmett-Teller (BET) model) and pore volume (PV, determined by Barrett-Joyner-Halenda (BJH) model) of meso-pores increase with the enhancement of tectonic deformation, especially for the ductile deformation. The meso-pores’ SSA are mainly provided by meso-pores of 2–10 nm and 10–20 nm in TDCs, however both the SSA proportion of 2–10 nm and of 10–20 nm increase with the increasing tectonic intensity, indicating that the tectonic deformation especially the ductile deformation can promote the migration of meso-pores’ SSA to small aperture directions. The micro-pore SSA and PV (determined by Density-Function-Theory (DFT) model) are mainly provided by the micro-pores of 0.4–0.7 nm and 0.8–1.0 nm, respectively. 3) The volume heterogeneity are characterized by D V1 (8–50 nm, Frenkel-Halsey-Hill (FHH) model), D V2 (2–8 nm, FHH model), and D V3 (0.32–2.0 nm, Sierpinski model). The D 2V increases both with the brittle and ductile deformation. D 1V only increase significantly with the ductile deformation. The significant increase of D V3 with the ductile deformation indicates that the ductile deformation process has a significant promoting effect for the micro-pores’ volume heterogeneity. 4) The surface heterogeneity can be characterized by D S1 (0.32–0.62 nm), D S2 (0.62–2.0 nm), D S3 (2–25 nm), and D S4 (25–50 nm), all of which increase with the enhancement of the tectonic deformation, demonstrating that the tectonic deformation has a more significant transformation effect for the surface heterogeneity than the volume heterogeneity. However, D S2 increases more sharply than D S1 and also D S4 increases more sharply than D S3, demonstrating that the transformation effect of tectonic deformation on the surface heterogeneity gradually weakened with the decreasing of the pore scale.

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DOI: S138718111730481X