High Selectively C2H4/C2H2 Separation by cyano-functionalized alkadiyne-pyrene conjugated frameworks membrane

Abstract

The effective separation of gas molecules is of significant importance and presents a considerable challenge in industrial processes, particularly for species with similar kinetic diameters such as ethylene and acetylene. Here, we demonstrate that incorporating cyano (CN) groups into the poly (1,3,6,8-tetraethynylpyrene) (PTEP) conjugated frameworks membrane not only narrows the pore size of the membrane, but also introduces C-H···N hydrogen bonding interactions and the resulting orientational matching with ethylene(C2H4), thereby facilitating its selective and efficient permeation. In contrast, acetylene molecules, which cannot form such interactions, are effectively hindered, enabling highly efficient separation of C2H4/C2H2 mixtures. Density functional theory (DFT) calculation reveal a diffusion barrier of only 0.87 kcal/mol for C2H4 through the CN-functionalized membrane, compared to 6.87 kcal/mol for C2H2, resulting in an ideal selectivity of approximately 1×104 at 298 K. Molecular dynamics (MD) simulations further demonstrate a dynamic selectivity of 46.7 ± 4.1 at room temperature, about 47 times higher than that of the pristine PTEP membrane, surpassing most reported covalent organic framework (COF) membranes. The corresponding permeance was measured as 2419 ± 145 GPU for C2H4 and 84.7 ± 18.8 GPU for C2H2. This work proposes a versatile strategy for precise regulation of both membrane pore size and chemical functionality to achieve advanced gas separation performance, providing valuable insights for the rational design of next-generation separation membranes.