Non-linear high Tg polyimide-based membranes for separating CO2/CH4 gas mixtures

A novel series membranes based on non-linear all-aromatic polyimides (PIs) was investigated with the aim to understand how PI backbone geometry and local electrostatics govern gas transport ability separate CO2/CH4 mixtures. Non-linear 3-ring aromatic diamines, exocyclic bond angles varying between 120 134°, enable design of high Tg (>276 °C) PIs. polar 1,3,4-oxadiazole diamine (ODD) (μ = 3D) monomer a non-polar m-terphenyl (TPD) reference were synthesized coupled 3 dianhydrides, i.e. ODPA, ODDA, 6FDA. In 6FDA-based CO2 permeabilities (PCO2) are highest series. The 6FDA-ODD membrane shows excellent performance PCO2 values at all feed pressures. Up 12 bar (6 CO2) none reached their plasticization pressure. promotes permeability, whereas presence an electrostatic dipole moment associated heterocycle governs separation selectivity.