Permeation of carbon dioxide and methane gases through novel silver-incorporated thin film composite Pebax membranes

The selectivity of a membrane for CO2/CH4 separation is critical for purification of natural gas, landfill gas, and biogas since CO2 is the major impurity present in gas mixtures while CH4 is the major hydrocarbon constituent. The performance of poly(ether-block-amide) (Pebax 2533) membrane and its silver-incorporated form were investigated with respect to their permeation properties for these two gases. Thin-film composite (TFC) membranes of Pebax were prepared by dissolving 20 g of the polymer in 80 mL of 3:7 volumetric ratio of m-cresol/isopropanol solvent mixture, followed by casting on polyvinylidene fluoride (PVDF) ultrafiltration substrate. Silver incorporation was carried out by loading silver tetrafluoroborate (AgBF4) at 36% of the Pebax polymer weight in the same dope solution. Membranes were characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) to study inter-molecular interactions, crystalline nature, and surface and cross-sectional morphologies, respectively. At a feed pressure of 1 MPa, Pebax gave a CO2 permeance of 32.8 GPU at a CO2/CH4 selectivity of 15.3, whereas Ag-Pebax exhibited an enhanced selectivity of 36.2, even though its permeance was reduced to 12.1 GPU. The Ag-Pebax membrane was further upscaled as a spiral-wound module of 0.20 m(2) effective area to test its commercial feasibility.