Membrane technology for challenging separations: Removal of CO2, SO2 and NOx from flue and waste gases

•Membranes in their various forms, offer an excellent platform for effective gas separation.•The effect of humidity and trace amounts of impurities needs further study.•Stability of achievable permeance with high permeability often undergo physical aging, resulting in a gradual and usually unwanted decrease in permeability.•Membranes with extremely high permeability of unwanted gases have the potential for industrial scale-up.•The preparation of thin-film composite membranes with ultra-high permeability may have a bright future.