Enhanced CO(2)/CH(4) Separation Performance of a Mixed Matrix Membrane Based on Tailored MOF‐Polymer Formulations

Membrane‐based separations offer great potential for more sustainable and economical natural gas upgrading. Systematic studies of CO(2)/CH(4) separation over a wide range of temperatures from 65 °C (338 K) to as low as −40 °C (233 K) reveals a favorable separation mechanism toward CO(2) by incorporating Y‐fum‐fcu‐MOF as a filler in a 6FDA‐DAM polyimide membrane. Notably, the decrease of the temperature from 308 K down to 233 K affords an extremely high CO(2)/CH(4) selectivity (≈130) for the hybrid Y‐fum‐fcu‐MOF/6FDA‐DAM membrane, about four‐fold enhancement, with an associated CO(2) permeability above 1000 barrers. At subambient temperatures, the pronounced CO(2)/CH(4) diffusion selectivity dominates the high permeation selectivity, and the enhanced CO(2) solubility promotes high CO(2) permeability. The differences in adsorption enthalpy and activation enthalpy for diffusion between CO(2) and CH(4) produce the observed favorable CO(2) permeation versus CH(4). Insights into opportunities for using mixed‐matrix membrane‐based natural gas separations at extreme conditions are provided.