Advances in high carbon dioxide separation performance of poly (ethylene oxide)-based membranes

Poly (ethylene-oxide) (PEO)-based membranes have attracted much attention recently for CO2 separation because CO2 is highly soluble into PEO and shows high selectivity over other gases such as CH4 and N2. Unfortunately, those membranes are not strong enough mechanically and highly crystalline, which hinders their broader applications for separation membranes. In this review discussions are made, as much in detail as possible, on the strategies to improve gas separation performance of PEO-based membranes. Some of techniques such as synthesis of graft copolymers that contain PEO, cross-linking of polymers and blending with long chains polymers contributed significantly to improvement of membrane. Incorporation of ionic liquids/nanoparticles has also been found effective. However, surface modification of nanoparticles has been done chemically or physically to enhance their compatibility with polymer matrix. As a result of all such efforts, an excellent performance, i.e., CO2 permeability up to 200 Barrer, CO2/N2 selectivity up to 200 and CO2/CH4 selectivity up to 70, could be achieved. Another method is to introduce functional groups into PEO-based polymers which boosted CO2 permeability up to 200 Barrer with CO2/CH4 selectivity between 40 and 50. The CO2 permeability of PEO-based membranes increases, without much change in selectivity, when the length of ethylene oxide is increased.