Poly(ether-block-amide) copolymer membrane for CO2/N2 separation: the influence of the casting solution concentration on its morphology, thermal properties and gas separation performance

The present work is focused on the study of the effect that the casting solution concentration has on the morphology and gas separation performance of poly(ether-block-amide) copolymer membranes (Pebax (R) MH 1657). With this aim, three different concentrations of Pebax (R) MH 1657 in the casting solution (1, 3 and 5 wt%) were used to prepare dense membranes with a thickness of 40 mu m. The morphology and thermal stability of all membranes were characterized by scanning electron microscopy, X-ray diffraction, differential scanning calorimetry, rotational viscometry and thermogravimetric analyses. An increase in crystallinity was notable when the amount of solvent in the Pebax (R) MH 1657 solution was higher, mainly related to the polymer chains arrangement and the solvent evaporation time. Such characteristic seemed to play a key role in the thermal degradation of the membranes, confirming that the most crystalline materials tend to be thermally more stable than those with lower crystallinity. To study the influence of their morphology and operating temperature on the CO2 separation, gas separation tests were conducted with the gas mixture CO2/N-2. Results indicated that a compromise must be found between the amount of solvent used to prepare the membranes and the crystallinity, in order to reach the best gas separation performance. In this study, the best performance was achieved with the membrane prepared from a 3 wt% casting solution, reaching at 35 degrees C and under a feed pressure of 3 bar, a CO2 permeability of 110 Barrer and a CO2/N-2 selectivity of 36.