High Selectivity Gas Separation by Interfacial Diffusion Membranes

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. Interfacial diffusion membranes formed from a polyetherimide layer on a macroporous α‐Al2O3 support offer very high CO2/N2 and H2/N2 permselectivities of >2200 and >4000 that are made for the first time. A nanopore confinement effect on polymer crystallization and ordering leads to a N2 gas tight membrane barrier while permissive for CO2 and H2 gas diffusion.