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‐Al 2 O 3 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 CO 2 /N 2 and >4000 for H 2 /N 2 , combined with CO 2 and H 2 permeances of 2.2 × 10 −10 and 4.0 × 10 −10 [mol (m 2 Pa s) −1 ], respectively. For CO 2 (5–50%) and N 2 dry and water‐saturated gas mixtures, only CO 2 permeance is detected. The presence of water appears to affect CO 2 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.