Preparation and Optimisation of Polyethersulfone-Based Composite Membranes for Air Separation at Low Pressures

Three polymeric solutions with different concentrations (1, 2 and 6% wt) of glassy polymers including ethyl cellulose (EC), poly vinyl alcohol (PVA) and polystyrene (PS) were employed for the preparation of the top layer of composite membranes with 18% wt polyethersulfone (PES) by dip coating. Membrane morphology was characterised using scanning electron microscopy, IR-ATR experiments and gas separation performance. The results indicate that PVA and PS composite membranes improve the selectivity of PES membranes to some extent. EC provides no selectivity. Increasing the PES concentration of the EC composite membrane improves the selectivity considerably. The concentration of EC was increased to 9% wt and the solution was coated on the surface of PES membranes having different concentrations (18, 25 and 37 wt%). Gas permeability and selectivity of EC membranes revealed that a coating solution with an EC concentration of 6% wt is an optimum condition for enhancing the selectivity.