Abstract
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 CO2 separation, gas separation tests were conducted with the gas mixture CO2/N2. 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 CO2 permeability of 110 Barrer and a CO2/N2 selectivity of 36.
Highlights
Carbon dioxide is a final combustion product of carbon-containing fuels
Dense membranes with no defects usually follow the solution-diffusion model. This model assumes that no pores exist in the membrane, and species are separated based on their solubility and diffusivity through the membrane, instead of molecular sieving [14]
For the three casting solution concentrations, the Scanning electron microscopy (SEM) images confirm the defect-free morphology of the PEBA membranes, without the existence of porosity or pinholes, which suggests that gases are transported following the solution-diffusion mechanism
Summary
Carbon dioxide is a final combustion product of carbon-containing fuels It is generated in big quantities and emitted in the gaseous form in the case of industrial and energy production sites, transportation, building heating, etc. PEBA block copolymers are synthesized from polyoxyalkylene glycols (PEG or PTMG) and dicarboxylic acid terminated aliphatic polyamides (such as nylon-6 or nylon-12) [3]. Such block copolymers consist of soft (rubbery) and hard (glassy) segments that provide high gas permeability without the loss of selectivity and mechanical stability [5,6]. In spite of its good properties, many efforts are still being made to improve even more its CO2 separation performance, the majority of them concern the incorporation of nanoparticles into the polymeric matrix or the synthesis of a composite membrane [7,8,9,10]
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