SPEEK membranes by incorporation of NaY zeolite for CO2/N2 separation

Mixed-matrix membranes (MMMs) have aroused great attention for CO2 capture due to high gas separation properties and good processability. However, besides high cost, poor interfacial compatibility and inorganic particles aggregation in MMMs hinder their further development. Herein, we chose microporous sodium zeoliteY (NaY) as a filler, which was added into sulfonated poly (ether ether ketone) (SPEEK) to engineer the MMMs for CO2/N2 separation. We deeply studied the influence of NaY incorporation on microstructure and separation properties of the membrane. It is obvious that NaY particles were evenly distributed in the SPEEK matrix due to strong interfacial interaction by hydrogen bonding, which was verified by ATR-FTIR and SEM results, and the string-like nanochannels were formed from the SAXS observation. MMM incorporated with 20 wt% NaY exhibited the separation properties (CO2 permeability of 765 Barrer; CO2/N2 selectivity of 63) at 1 bar under the pure gas conditions, which were superior to the pristine SPEEK membrane as well as the MMMs incorporated with other zeolites, transcending the 2008 Robeson's upper bound. The enhancement in separation properties is due to the fact that CO2 molecules preferentially pass through the string-like nanochannels faster than N2 molecules under elevated relative humidity owing to selective surface flow effect. Moreover, an increase in total water of MMMs loaded with NaY also contributed to enhanced CO2 permeability, while improved CO2/N2 selectivity resulted from high bound water. More importantly, stability studies reveal that the MMM (with 20 wt % NaY loading) held outstanding CO2 separation properties for over 360 h, demonstrating outstanding stability under a gas mixture testing condition.