Effective Pore Distribution and Mechanism of CO2/CH4 Dynamic Separation by Carbon Molecular Sieves

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Addressing the pressing demand for biogas and landfill-gas upgrading within the global energy transition, this work strategically combines thermodynamic and kinetic separation principles to identify, from a cooperative-separation perspective, the effective pore-size range that governs carbon molecular sieve (CMS) performance. Thirty anthracite-derived CMS samples with distinct pore structures were synthesized and employed as a statistical set to link pore architecture with dynamic adsorption performance. The results clarify the effective pore-size range and mechanism for enhanced CMS selectivity: CH4 uptake depends exclusively on ultramicropores (<10 Å), with a negligible contribution from mesopores (>20 Å), whereas CO2 uptake is less sensitive to pore-size distribution. CO2/CH4 separation performance improves linearly with the volume fraction of mesopores >20 Å, defining a 20–60 Å mesopore window as optimal for cooperative CMS. Mechanistic studies show that a high mesopore fraction significantly slows CH4 adsorption while maintaining a fast CO2 uptake, thereby amplifying their intrinsic adsorption-rate difference. This work breaks from the conventional purely thermodynamic or kinetic sieving paradigm and offers new design criteria for CMS tailored to on-site biogas and landfill-gas purification.