Asymmetric membranes of modified poly(ether ether ketone) with an ultra-thin skin for gas and vapour separations

A series of high flux asymmetric membranes of PEEKWC, a modified poly(ether ether ketone), was prepared by the dry–wet phase inversion method. The polymer concentration in the casting solution, the type of external nonsolvent, the type and concentration of internal nonsolvent and the casting conditions (temperature and evaporation time) were optimized in order to obtain a very thin dense skin. The membrane performance was tested in terms of gas permeance and permselectivity for N2, O2, CH4, He and CO2. In the case of pinhole defects, membranes were coated with dilute silicone solution. Thus, membranes were prepared with a thickness of the skin layer down to about 35 nm and permselectivity even slightly better than the typical selectivity of comparable thick dense PEEKWC membranes. The best membrane exhibits CO2 permeance of 0.187 m3/(m2 h bar) (69 GPU), and O2 permeance 0.038 m3/(m2 h bar) (14 GPU), with a CO2/CH4 and O2/N2 selectivity of 32 and 6.4, respectively, and may compete with presently available commercial membranes. Preliminary data on water and ethanol vapour permeance have also been determined in view of possible use of the membranes in gas/vapour separation and pervaporation applications.