Computational and experimental insights into variable temperature propylene (C3H6), propane (C3H8), and hydrogen sulfide (H2S) sorption in ultra-high permselectivity CANAL ladder polymers

Abstract

Membranes are a promising technology for energy-efficient separations of high-value gaseous chemical streams (e.g., hydrogen sulfide from methane or propane from propylene). Among the classes of emerging microporous polymers, CANAL polymers have attracted significant interest because of their selectivities and plasticization resistance for acid gas separations. In this work, a computational atomistic system is developed for CANAL-Me-Me₂F, an archetypal CANAL polymer. Computed properties (free volume distribution, wide-angle X-ray scattering, and thermal expansion coefficients) align with experimental results. High-pressure sorption isotherms of H₂, N₂, O₂, CH₄, CO₂, H₂S, C₃H₆, and C₃H₈ were computed via grand canonical Monte Carlo and iterated Monte Carlo–molecular dynamics simulations, demonstrating good agreement with experimental isotherms at 35 °C. H₂S, C₃H₆, and C₃H₈ isotherms were further computed between temperatures of 55–190 °C, followed by extraction of dual-mode sorption (DMS) parameters. Sorption energetics showed less exothermic Langmuir affinity for the more polarizable gases (H₂S and C₃H₆) in CANAL-Me-Me₂F relative to PIM-1, which is ascribed to the lack of heteroatoms in CANAL-Me-Me₂F, and supported by simulations of a hypothetical nitrile-functionalized CANAL-Me-Me₂F. This study develops a computational approach that can probe the unique nanoscale behavior of CANAL polymers and applies it to studying the thermodynamics of condensable gas sorption within CANAL-Me-Me₂F.