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 ® MH 1657). With this aim, three different concentrations of Pebax ® MH 1657 in the casting solution (1, 3 and 5 wt%) were used to prepare dense membranes with a thickness of 40 µm. 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 ® 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 CO 2 separation, gas separation tests were conducted with the gas mixture CO 2 /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°C and under a feed pressure of 3 bar, a CO 2 permeability of 110 Barrer and a CO 2 /N 2 selectivity of 36.

Poly(ether-block-amide) (PEBA, commercialized as Pebax) copolymer membranes show a highly promising platform for preparing high-performance membranes for CO 2 capture from process streams containing CH 4 and N 2 . Pebax combines high CO 2 affinity with the desired mechanical strength for polymeric membranes thanks to its flexible polyether segment and hard polyamide block, respectively. Furthermore, researchers have been improving the performance of these membranes by preparing a thin Pebax selective layer on top of porous supports and by incorporating inorganic and organic nanofillers into the Pebax matrix to overcome the permeance-selectivity limit. The chemical and structural characteristics of Pebax membranes according to the different fabrication techniques and parameters are discussed first. Then, the recent developments in terms of both Pebax-based thin film composite and mixed matrix membranes are summarized. Finally, thermal and water stabilities of these membranes are addressed.

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