Design and fabrication of high performance membrane for carbon dioxide separation via blending poly(ethylene oxide-b-amid 6) with dense, glassy and highly CO2-philic amidoximated polymers

Blend membranes based on the poly(ethylene oxide-b-amid 6) (Pebax 1657) block copolymer and carbon dioxide (CO2)-philic glassy polymers including polyacrylonitrile (PAN), acrylonitrile/ vinylimidazole copolymer (P(ANco-VIm)) or corresponding amidoximated derivatives, i.e. P(AO-AN) and P(AO-AN-co-VIm), as additive were prepared using solution casting method. To increase CO2-philic groups, acrylonitrile- based polymers were amidoximated via reacting with hydroxyl ammonium chloride (NH2OH.HCl) reagent where amidoximation process was evaluated by FTIR and 1H NMR. Compatibility and morphology of components in the blend membranes and blend density were examined by ATR-IR and DSC, FE-SEM and densitometry tests, respectively. Shifting of the peaks in the ATR-IR spectra showed that the Pebax 1657 chains establish a hydrogen bonding with the homo- or copolymer chains. The crystallinity and melting temperature (Tm) of polyamide (PA) domains in the Pebax 1657 decreased by increasing the amount of acrylonitrile- based polymers and their amidoximated derivatives. Also, the glass transition temperature (Tg) of the polyethylene oxide (PEO) domains increased due to the glassy nature of the additives. FE-SEM results indicated that all membranes are dense and there is a good interaction between the Pebax and the additives. The dense structure and free volume reduction in the membranes were confirmed by increasing membrane density resulting from increase in the amount of acrylonitrilebased polymer and amidoximated derivatives. The permeability of CO2, nitrogen (N2) and methane (CH4) gases from pure and blend membranes was measured by constant pressure/ variable volume method at 3 bar and ambient temperature. By increasing the amount of acrylonitrile- based polymers, i.e. PAN and P(AN-co-VIm), up to 20 wt%, the permeability of CH4, N2 and CO2 increased and then decreased with further increasing of the additive content. In blend membranes containing amidoximated polymers, i.e. (P(AO-AN) and P(AO-AN-coVIm)), CO2 permeability and of CO2/N2 and CO2/CH4 selectivity showed an increased trend up to 60%wt additive due to increased number and type of nitrogen atoms in the membrane structure. Compared to the pure Pebax 1657, CO2 permeability and CO2/N2 and CO2/CH4 selectivity in blend membrane containing 40 wt% of P (AO-AN-co-VIm) copolymer increased by 193%, 497% and 495%, respectively.

Automated summary

The study focused on improving the CO2 affinity of blend membranes based on poly(ethylene oxide-b-amid 6) by adding acrylonitrile-based polymers and their amidoximated derivatives. The glassy nature of the additives increased the glass transition temperature of the polyethylene oxide domains, while decreasing the crystallinity and melting temperature of the polyamide domains. By optimizing the amount of additives, the permeability and selectivity of the membranes were enhanced, but excessive addition resulted in performance deterioration.