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

Abstract

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.