Model Optimization and Data Analysis Methods for Low-Temperature CO₂ and N₂ Adsorption Experiments on Carbonaceous Materials

Low-temperature gas adsorption experiments are widely utilized to evaluate the pore structures of porous materials. Understanding the applicability of each model in different types of samples is crucial, as these models can yield diverse interpretations of pore structures from identical experimental data. In this study, low-temperature CO2/N2 isothermal adsorption experiments were conducted on coal, shale, and activated carbon samples to compare and analyze the suitability of each model in different samples and pore size ranges. The key findings are as follows. (1) Low-temperature CO2/N2 adsorption experiments provide insight into pore volume, specific surface area, and pore size distribution ranging from 0.36 to 160 nm in coal, shale, and activated carbon pores. (2) The CO2-DFT model is applicable for analyzing the low-temperature CO2 adsorption experiments in all samples. For the analysis of pores smaller than 35 nm in the low-temperature N2 adsorption experiment, the slit hole nonlocal density functional theory model is recommended for middle-rank coal and the slit/cylindrical Quench Solid Density Functional Theory adsorption branch model for high-rank coal, shale, and activated carbon samples. For pore size larger than 35 nm, the Barrett–Joyner–Halenda model is recommended to analyzing the adsorption branches. (3) For overlapping pore interval of the different model’s analysis results, the CO2-DFT model is recommended for the range of 1.41–1.47 nm, and the N2-DFT model is recommended for the range of 4.14–36.00 nm.