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 CO 2 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 CO 2 /CH 4 separation performance was investigated using molecular dynamics (MD) simulations. Results show that, in membranes with smaller pores, a strong CO 2 -membrane affinity governs preferential sorption and permeation of CO 2 . As pore size increases, CO 2 /CH 4 permselectivity shifts to be codominated by preferential sorption of CO 2 and rapid diffusion of CH 4 . Consequently, the permselectivity of the CO 2 /CH 4 significantly decreases. The Dense membrane exhibited CO 2 permeability of 1.44 × 10 3 barrer and CO 2 /CH 4 permselectivity of 36.00, exceeding the 2018 mixed-gas upper bound. This study explains CO 2 separation mechanisms of distinct pore structures within polymer membranes and provides theoretical support for the development of porous polymer membranes.