Solid-liquid contact characteristics and microscopic wetting mechanism between coal and water in gas atmosphere

Abstract

In order to reveal the coal-water contact characteristics under the gas atmosphere, the change rule of coal-water wetting angle under different CH4 and He pressures was investigated experimentally, combining with the proximate analysis, 13C NMR and FTIR, the coal macromolecular model was constructed to simulate coal-water adsorption under the condition of pre-adsorbed gas. Results showed that the coal-water wetting angle gradually increases with the rising ambient pressure under CH4 and He conditions. The increase trend is more obvious under CH4 condition, and the wetting angle increases from 77.43° to 111.33°. The molecular dynamics simulation results showed that the energy of the coal macromolecular system under CH4 condition is lower and thus the interface is more stable, the adsorption energy of coal for a single H2O molecule gradually increased with the growing of CH4 and He pressures, the wettability of coal is weakened, and the weakening degree is more obvious in the adsorptive gas environment. Finally, based on the gas-liquid adsorption energy, adsorption amount and adsorption site, the microscopic wetting mechanism of coal containing gas was further analyzed. The research results are of great significance for improving the wettability of coal seam water injection.