Modification of Poly(ether-b-amide) Membrane Properties Using Glycerol for CO2/N2 Gas Separation

Carbon dioxide (CO2) separation from flue gases as a green-house gas produced from the combustion of fossil fuels is one of the main concerns in controlling the green-house gas emissions. Among the various technologies employed for gas separation, membrane technology due to its many advantages has attracted more attentions. A new blend membranes were prepared by solution casting/solvent evaporation method from poly(ether-b-amide) (Pebax) – as a backbone structure – and glycerol as an additive in the membrane matrix. CO2 and N2 permeability rates were measured at pressures of 2-10 bar and temperature of 25 °C. Afterwards, the CO2/N2 gas permeation properties were determined. Moreover, the effect of different glycerol loadings (0-25 wt%) in the membrane matrix and also the effect of feed pressure on CO2 permeability and CO2/N2 selectivity were investigated. Morphological characteristics of the prepared membranes were determined by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) analyses. The achieved results showed that by addition of glycerol to Pebax matrix, CO2 permeability was decreased somewhat but the CO2/N2 selectivity was considerably increased. At pressure of 10 bar, CO2/N2 selectivity of the blend membrane with 15 wt% glycerol was 172% higher than that of pure Pebax, while the CO2 permeability declined only by about 23%. Therefore, the blend membrane containing 15 wt% glycerol with a good CO2 permeability and a high CO2/N2 selectivity was selected as the optimum membrane. The FE-SEM observations revealed the compatibility and homogeneity of glycerol in the Pebax matrix. The XRD analysis determined that the addition of glycerol decreases the membrane crystallinity and the d-spacing between the polymer chains. The DSC results revealed that the insertion of glycerol in the membrane structure decreased the glass transition temperature. The FTIR spectra showed no new absorption band except for those for the constituent species, which suggests a physical interaction between Pebax and glycerol.