A mechanistic link between coal pore development and molecular structure evolution

The primary factor influencing the adsorption-desorption properties of gases in coal is its porosity. However, the control mechanism of coal pore structure remains unclear. To address this issue, this study employed Fourier transform infrared (FTIR), carbon-13 nuclear magnetic resonance (
13
C-NMR), low-temperature gas adsorption, and scanning electron microscopy (SEM), combined with Materials Studio molecular simulations and fractal theory, to construct and qualitatively/quantitatively characterize the pore structures of three coal samples with varying ranks. Results indicate that micropores dominate the specific surface area and pore volume in coal samples of varying ranks, followed by mesopores. With increasing coal rank, both the aromatic carbon content and the degree of molecular ordering exhibit a progressive enhancement The formation of micropores (<2 nm) is primarily associated with aromatic structures, suggesting that micropore connectivity is controlled by these structural motifs. Structural parameter analysis indicates that aromatic bridge carbon content significantly promotes micropore development. Conversely, methyl carbon content enhances mesopore formation. This study aims to elucidate the controlling influence of various molecular structures on pore genesis, thereby providing a theoretical foundation for understanding pore structure evolution in coal reservoirs.