Research on the evolution of microstructurale damage of high-rank coal under supercritical CO2 pulsating action

To characterize the microcomponents and pore structure of high-rank coals under supercritical CO ₂ pulsation, the effects of supercritical CO ₂ pulsation on the mineral composition, organic functional groups, pore structure and pore fractal characteristics of high-rank coals were investigated on the basis of a combination of X-ray diffraction (XRD), Fourier transform infrared (FTIR), high-pressure mercuric pressure, low-temperature liquid nitrogen, and low-field nuclear magnetic resonance experiments. The results showed that after supercritical CO ₂ pulsation, the mineral compositions and organic functional group contents of the coals changed to different degrees, among which the contents of calcite, ilmenite and illite decreased, the contents of ferro-dolomite and kaolinite increased, and the characteristic peaks of oxygen-containing, benzene-ring-five-substituted H, and aliphatic functional groups decreased. The pore and fractal structure of the coals after supercritical CO ₂ pulsation was significantly altered, the total pore volume of the coal body increased by 188%, the percentage of seepage pore volume increased by 13 times, and the porosity increased by 8.272%. The fractal dimensions of the coal samples after supercritical CO ₂ pulsation all showed a decreasing trend, and the complexity of their pore structure and surface roughness decreased.