Pebax/PEG Grafted CNT Hybrid Membranes for Enhanced CO₂/N₂ Separation

In the present study, poly(ethylene glycol) (PEG) functionalized carbon nanotubes (CNT-PEG) were used as nanoadditives to fabricate hybrid membranes for enhanced CO₂ separation in Pebax 1657 matrix. The resultant membranes were characterized using various techniques. It is found that grafting PEG onto CNT fibers greatly improves the CNT dispersion. No noticeable aggregation can be found in the hybrid membranes with CNT-PEG content of up to 20 wt %. X-ray diffraction results denote that the CNT-PEG in the Pebax matrix increases the amorphous phase content, which is beneficial for CO₂ permeation. Gas permeation properties were investigated using mixed gas permeation tests at different relative humidity conditions. It is found that CO₂ permeability first increases and then decreases with increasing CNT-PEG content at the dry state. The water vapor in the gas stream further improves the CO₂ permeability. At 100% relative humidity, CO₂ permeability of 369.1 barrer with CO₂/N₂ selectivity of 110.8 was obtained for a hybrid membrane containing 3 wt % CNT-PEG, which overcomes the Robeson upper bound. The combination of high permeability and selectivity makes the Pebax/CNT-PEG hybrid membranes promising for industrial CO₂ separation applications.