Study for CO2 separation with poly(ethylene oxide terephthalate)-poly(butylene terephthalate) multiblock copolymer membranes: Approaching a greener solvent preparation

Green solvent alternatives for the multiblock copolymer Polyactive™ were selected to test their effectiveness in membrane fabrication for gas separation. Solubility tests were conducted to assess the solvent-polymer compatibility, followed by membrane fabrication using a drop casting-solution method. Ethyl lactate was identified as a potential greener solvent, compared to more commonly used solvents like chloroform and tetrahydrofuran, as it maintained the membrane conformation, thermal and chemical stability, and thermal degradation characteristics as demonstrated by membrane characterization using SEM, FTIR, TG and DSC. Single gas transport parameters (permeability, diffusivity and solubility) for N 2 , H 2 , CH 4 , He and CO 2 were obtained via the time-lag method for the prepared membranes. A temperature dependence study was conducted in the 25-70 ºC range, calculating activation energies for gas transport properties and ideal selectivities. Mixed gas measurements were also performed, comparing separation selectivities to those (ideal selectivities) obtained in single gas, indicating a potential competitive adsorption effect between less permeable species, leading to more selective separation in gas mixture. Membranes prepared with different polymer concentrations (1, 2 and 5 wt%) in ethyl lactate achieve a CO 2 /N 2 ideal selectivity of up to 50.4 at a CO 2 permeability of 179 Barrer. This enhanced performance was attributed to ethyl lactate higher boiling point, resulting in a more densely packed polymer structure as reflected by the higher crystallinity and lower fractional free volume measured through XRD, DSC and pycnometry analyses. • Ethyl lactate enables greener Polyactive™ membrane fabrication with high performance. • Membranes prepared with ethyl lactate showed enhanced crystallinity and selectivity. • Thermal stability and gas separation properties were maintained with the green solvent. • CO₂/N₂ separation improved due to competitive adsorption and increased crystallinity.