PDMS Coated Polyethersulphone Composite Membranes for Separation of Propylene and Nitrogen Gas Mixtures

Aseries of rubber-like composite membranes were prepared for separation of gases such as propylene and nitrogen. The support layer was fabricated from different concentrations of polyethersulphone (20, 22 and 24% PES) and the coating layer was prepared from different concentrations of polydimethylsiloxane (3, 5, 7 and 9% PDMS). Permeances and selectivities of the prepared membranes for propylene and nitrogen gases and their mixtures were measured under transmembrane pressure of 1-10 bar. The influence of various parameters, such as PES concentration in support layer and PDMS concentration in coating layer at different pressures, on membrane performance were evaluated. It was shown that the membrane selectivity was increased with an increment in the feed pressure. At constant pressure for similar supports the propylene permeance and membrane selectivity were enhanced by increasing PDMS of the coating layer. For membranes with equivalent PDMS content in the coating layer, the performance of membrane was increased with PES decline in support layer. The permeability ratio of propylene over nitrogen in gas mixture (real selectivity) was low compared to the permeability ratio for pure gases passing through the membrane (ideal selectivity) at comparable operating pressure for similar membranes. At 5 bar pressure real selectivity of 3.6 was obtained while the ideal selectivity was 20.2.