Structure and fractal characteristic of micro- and meso-pores in low, middle-rank tectonic deformed coals by CO2 and N-2 adsorption

摘要

The structure and fractal characteristic of micro- (0.32 similar to 2 nm) and meso-pores (2-50 nm) in low, middle rank (maximum vitrinite reflectance, R-o, (max) = 0.65-134%) tectonic deformed coals (TDCs) were revealed by combining low temperature N-2/CO2 adsorption (LPN2/CO(2)GA) 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 similar to 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. (C) 2017 Elsevier Inc. All rights reserved.