Effects of equilibrium time and adsorption models on the characterization of coal pore structures based on statistical analysis of adsorption equilibrium and disequilibrium data

Low-pressure CO2 adsorption is an important tool for quantitatively characterizing the micropore characteristics of porous materials. While only adsorption data obtained at adsorption equilibrium will ensure the accuracy of the method. In this paper, 82 sets of CO2 adsorption equilibrium and disequilibrium data of coal samples with different particle sizes were investigated, and the influence of equilibrium criterion and data analysis methods on the adsorption data and calculation of pore characteristics was studied by statistical analysis method. Furthermore, to explore methods to distinguish between low-pressure CO2 adsorption equilibrium and disequilibrium data, the correlation between different analysis methods and the adsorption equilibrium and disequilibrium data were then analyzed. The results suggest: for the coal samples with complex micropore structures, the linearly increasing CO2 adsorption isotherm is most likely caused by the disequilibrium adsorption; the analysis on adsorption disequilibrium data often leads to underestimation of the pore structures in small pore size range, and moreover the Dubinin-Astakhow method (D-A) is particularly sensitive to adsorption disequilibrium data, which would lead to great errors for the calculation of pore characteristics; the more developed the micropore structures, the higher the demarcation point between the correlation coefficient of the Dubinin-Radushkevich method (D-R) and adsorption equilibrium and disequilibrium data, where the fitting errors obtained by using the Monte-Carlo method (M-C) to fit the adsorption equilibrium data were mostly less than 0.2. This study could provide some guidance for more accurate use of gas physisorption methodology, especially for porous solid materials with complex micropore structures like coal.