Pore structure characterization of low volatile bituminous coals with different particle size and tectonic deformation using low pressure gas adsorption

Abstract

Low pressure N2 and CO2 adsorption experiments were performed on two low volatile bituminous coals to gain insights into mesopore and micropore characteristics and the effects of particle size, composition (mineral matter and maceral) and tectonic deformation on them. Original coal and tectonized coal were sieved into five particle size fractions, i.e., 18–35 mesh (0.50–1.00mm), 35–60 mesh (0.25–0.50mm), 60–120 mesh (0.125–0.250mm), 120–230 mesh (0.063–0.125mm) and 230–450 mesh (0.032–0.063mm). Low pressure gas adsorption analysis, proximate analysis and maceral analysis were conducted on each particle size fraction. Specific surface area of mesopore varies from 0.22m2/g to 3.06m2/g and from 1.00m2/g to 2.07m2/g in original coal and tectonized coal, and that of micropore is from 123.7m2/g to 164.6m2/g and from 100.7m2/g to 106.7m2/g, respectively. The vast majority of total specific surface area is within micropores. Mesopore specific surface area and volume are dependent on particle size. Decreasing particle size makes some inaccessible mesopores become accessible to N2 molecules, increasing mesopore specific surface area and volume. In contrast to mesopore characteristics, micropore characteristics are independent of particle size. Mineral matter contributes minimally to micropore specific surface area and volume. There is no consistent relationship between mineral matter and mesopore characteristics. Maceral composition, which is represented by the ratio of vitrinite to inertinite, has a uniformly negative correlation with mesopore characteristics, but plays a different role in micropore characteristics. The heterogeneity in composition resulting from sieving is reduced, so the effect of particle size on pore characteristics is weakened in the tectonized coal. Tectonic deformation enhances mesopore specific surface area and volume by removing constricted pore openings and increasing accessible mesopores. Moreover, tectonic deformation is likely to cause micropores collapse, which results in a significant decrease in micropore specific surface area and volume.