Effect of replacing methane by high pressure nitrogen on coal matrix pore

In order to study the effect of high-pressure gas adsorption and desorption on the development scale and the structure of coal matrix pore, the experiment of isothermal adsorption-desorption of replacing methane by injecting high-pressure nitrogen was carried out on coal samples collected from No.6 coal mine of Hebi. The curves of low-temperature nitrogen adsorption and desorption of coal samples before and after methane replacement were measured by low-temperature liquid nitrogen adsorption method. The changes of pore structure characteristics and distribution of coal matrix were compared and analyzed by using three analytical models of BET, BJH and QSDFT. The analysis results show that the pore volume, the specific surface area and pore structure of coal samples have changed in the process of high-pressure gas replacement, the BET specific surface area of the pore was reduced from 12.746 0 m²/g to 7.227 0 m²/g, the total pore volume was reduced from 0.009 0 cm³/g to 0.006 6 cm³/g. The pore development scale and distribution were obviously changed, but the pore morphology was basically unchanged, and the variation of pore distribution was mainly manifested in the reduction of micropore volume and specific surface area, while the volume of mesopores and micropores kept basically unchanged.