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 alpha-Al2O3 scaffold as a 3.9 mu m amorphous layer, and inside the near-surface area of the scaffold over approximate to 130 nm, is partly crystallized. Combinations of extremely high gas selectivities are found of >2200 for CO2/N-2 and >4000 for H-2/N-2, combined with CO2 and H-2 permeances of 2.2 x 10(-10) and 4.0 x 10(-10) [mol (m(2) Pa s)(-1)], respectively. For CO2 (5-50%) and N-2 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 degrees 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.