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

## TL;DR

This study identifies the optimal pore structure in carbon molecular sieves for efficiently separating CO2 and CH4 in biogas and landfill-gas upgrading.

## Contribution

The work introduces a cooperative-separation mechanism combining thermodynamic and kinetic principles to optimize CMS pore architecture for gas separation.

## Key findings

- CH4 uptake is controlled solely by ultramicropores (<10 Å), with no contribution from mesopores.
- CO2/CH4 separation improves linearly with mesopore volume fraction in the 20–60 Å range.
- High mesopore fractions slow CH4 adsorption but maintain fast CO2 uptake, enhancing separation efficiency.

## Abstract

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.