Variations in Properties of Coal Macerals Elucidated by Density Gradient Separation

Based on a recently developed separation procedure for coal macerals, closely spaced narrow density fractions of macerals have been examined for petrographic content and ultimate analysis. Each maceral group or maceral type clearly exhibits a range of densities (a density band) and corresponding range of atomic ratios. In general, the H/C and S/C ratios decrease monotonically with density, reflecting changes in the macerals since as density increases the macerals separate in the order: exinite, vitrinite, inertinite. The overall range of H/C values for typical high volatile bituminous coals can vary from as much as 1.2 to 0.4 within the same coal if all three maceral groups are represented. Within each maceral group, less variation is observed. In most bituminous coals, there is 15 to 20% total variation in H/C ratio across the individual maceral bands. The O/C and N/C ratios show different behavior. Relative to the vitrinite O/C and N/C ratios the exinite ratios are very low, but rise steadily as density increases. Within the vitrinite band there is some additional increase before finally leveling off. The inertinite ratios have intermediate values between those of vitrinite and exinite and vary only slightly with density.