Fractal dimension of coal particles and their CH4 adsorption

We describe the fractal analysis of three differently sized coal samples (0.350–0.833 mm, 0.245–0.350 mm, and 0.198–0.245 mm). The influence of fractal dimension on CH4 adsorption capacity is investigated. The physical parameters of the samples were determined via the Brunauer–Emmett–Teller (BET) theory. A CH4 adsorption study over the pressures range from 0 to 5 MPa was carried out with a new volumetric measurement system. The CH4 adsorption was measured using the differently sized coal. Two fractal dimensions, D1 and D2 were determined over the pressure ranges from 0 to 0.5 MPa and from 0.5 to 1 MPa, using the Frenkel-Halsey-Hill (FHH) method. We conclude that the two fractal dimensions correlate with the CH4 adsorption capacity of the coal: increasing CH4 adsorption capacity occurs with a corresponding increase in fractal dimension. Furthermore, D1 and D2 are positively correlated with surface area, pore volume, and samples size. The size distribution of the samples has fractal characteristics.