Experimental Study On The Filling Characteristics Of N₂/CO₂ Micropores In Coals

In view of the complex pore structure of coal,a special form of adsorption will occur in the micropores in coals—Micropores Filling,resulting in different N2/CO2 occurrence forms in coals,which in turn affects the coal’s ability to adsorb N₂/CO₂.Using a combination of theoretical analysis,laboratory experiments,and fitting verification,an experimental study on the N2/CO2 micropore filling characteristics of coals is carried out,and the boundary points of different N2/CO2 occurrence forms（filled and adsorbed）in coals are distinguished.It is of great significance to promote the related research on the main occurrence forms of CH4 in coals.The main research results are as follows:Through the study of the pore structure characteristics of carbon nanotubes,it is concluded that the best analysis scheme for coal pore structure test experiment is that CO2 is suitable for micropore stage analysis in coals,especially ultra-micropore（≤1nm）,N2 is suitable for non-micropore stage analysis,and NLDFT model has the best applicability and accuracy,and the method to accurately characterize the pore structure of coal body is LPGA-N2-CO2 combined characterization method.Through the study of the low-pressure N2 adsorption experiment（LPGA-N2）and the low-pressure CO2 adsorption experiment（LPGA-CO2）of coals,it is concluded that the isotherms of the coals LPGA-N2 experiment are all the composite of type I（a）and type II standard isotherms curve.The dominant adsorption interval in the low pressure region is P/P0≈10^-6～10^-2（LPGA-N₂）and P/P₀≈10^-3～0.02（LPGA-CO₂）,which corresponds to the N2/CO2 micropore filling stage in coals.Through the research on the N2/CO2 adsorption performance of coals with different metamorphic degrees,it is concluded that with the increase of coal metamorphism,the adsorption capacity of N2 decreases,and the adsorption capacity for CO2 first decreases and then increases.The CO2 adsorption capacity of the same coal is higher than that of N2 adsorption.The amount is 2 to 20 times.Through the analysis of the N2/CO2 micropore filling characteristics in the coals,it is concluded that the critical filling pressure of N2/CO2 micropore filling in coals is between P/P0≈10^-4～0.03 and P/P₀≈10^-3～0.028,the critical filling pore size is between 1.7～2.2nm and1.4～1.6nm respectively,that is:2.2nm and 1.6nm are the boundary points of different occurrence forms（filling state and adsorption state）of N2 and CO2 in coals,respectively.The primary filling and secondary filling stages are divided according to the critical filling pore.The experimental research on the N2/CO2 micropore filling characteristics of coals is of great significance for exploring the main occurrence forms of CH4 in coals,the microscopic mechanism of coal and gas outburst,preventing coal and gas outburst disasters,and implementing carbon sequestration efficiently.