High Selectivity Gas Separation by Interfacial Diffusion Membranes

Abstract A new generation of inorganic/organic polymeric interfacial diffusion membranes is presented that have unprecedented combinations of high selectivity and flux. The membranes consist of an inorganic scaffold, with pores that are filled with a thermoplastic polymer that crystallizes in the pore space while a nm thin interfacial area remains amorphous. The polyetherimide, present on top of the α‐Al₂O₃ scaffold as a 3.9 µm amorphous layer, and inside the near‐surface area of the scaffold over ≈130 nm, is partly crystallized. Combinations of extremely high gas selectivities are found of >2200 for CO₂/N₂ and >4000 for H₂/N₂, combined with CO₂ and H₂ permeances of 2.2 × 10⁻¹⁰ and 4.0 × 10⁻¹⁰ [mol (m² Pa s)⁻¹], respectively. For CO₂ (5–50%) and N₂ dry and water‐saturated gas mixtures, only CO₂ permeance is detected. The presence of water appears to affect CO₂ permeances very little at both 22 and 57 °C. Selective molecular transport is blocked in the crystalline areas and takes place exclusively in the amorphous interfacial area. It is governed by a combination of affinity, mobility, and size‐exclusion. Conservative estimates of the membrane permeability indicate that their properties by far exceed the Robeson boundary.