Unraveling the Role of Pore Size in CO ₂ Separation through CANAL Polymer Membranes: A Molecular Dynamics Simulation

Polymer membranes have emerged as competitive materials for the CO2 separation. The pore structure in polymer membranes is one of the key factors in determining the gas separation performance. In this work, three CANAL-Me-DHP membranes (Dense, Flexible, and Swollen membranes) with different pore sizes are constructed. The effect of the pore size on the CO2/CH4 separation performance was investigated using molecular dynamics (MD) simulations. Results show that, in membranes with smaller pores, a strong CO2-membrane affinity governs preferential sorption and permeation of CO2. As pore size increases, CO2/CH4 permselectivity shifts to be codominated by preferential sorption of CO2 and rapid diffusion of CH4. Consequently, the permselectivity of the CO2/CH4 significantly decreases. The Dense membrane exhibited CO2 permeability of 1.44 × 103 barrer and CO2/CH4 permselectivity of 36.00, exceeding the 2018 mixed-gas upper bound. This study explains CO2 separation mechanisms of distinct pore structures within polymer membranes and provides theoretical support for the development of porous polymer membranes.