High permeability hydrogel membranes of chitosan/poly ether-block-amide blends for CO2 separation

• Hydrogel membranes were prepared by physical blending of chitosan and Pebax.
• Fractional free volume of membranes increased with increment of Pebax content.
• More CO2 transport channels were formed and higher water content was obtained.
• Membranes displayed high CO2 permeability and good operation stability.

A series of hydrogel membranes from chitosan (CS)/poly ether-block-amide (Pebax) blends were prepared and utilized for CO2 separation. The membranes were characterized by field emission scanning electron microscope (FESEM), Fourier transform infrared spectra (FT-IR), differential scanning calorimeter (DSC), X-ray diffraction (XRD), positron annihilation lifetime spectroscopy (PALS), dynamic mechanical analyzer (DMA) and tensile machine. The membranes exhibited high CO2 permeabilities along with good operation stabilities. When the mass ratio of CS to Pebax was 1:1, the membrane showed the highest CO2 permeability (2884 barrer) and a moderate separation factor (23.2 for CO2/CH4 and 65.3 for CO2/N2) at 85 °C. The high separation performance of these membranes was primarily arisen from the incorporation of Pebax. On one hand, when blending Pebax into CS, the increased fractional free volume led to more gas transport channels generated in polymer network, which directly increased CO2 permeability. On the other hand, the increased fractional free volume also led to higher water content in membranes, which further increased CO2 permeability. The effects of feed pressure and operating temperature on membranes properties were systematically investigated to further understand the transport mechanism in these membranes.