AIR SEPARATION PROPERTIES AND STABILITIES OF BLEND MEMBRANES OF LIQUID-CRYSTALS WITH ETHYL CELLULOSE

Air separation properties and stabilities of four blend membranes, 1-30-mu m thick, prepared from ethyl cellulose (EC) with a small amount of nematic and cholesteric liquid crystals, such as p-heptyl-p'-cyanobiphenyl (7CB), p-pentylphenol-p'-methoxybenzoate (5PMB), benzoate-containing liquid crystal mixture (DYC), and cholesteryl oleyl carbonate (COC), were investigated by the variable volume method. To provide more significant information guiding membrane-based air separation, air was directly used as the test gas. The membranes showed both higher oxygen permeability, P-O2, and oxygen over nitrogen separation factor, P-O2/P-N2, in the temperature range of the liquid crystalline phase. Oxygen-enriched air (OEA) flux, Q(OEA), and oxygen concentration, Y-O2, increased simultaneously with increasing transmembrane pressure difference. Stability studies revealed that the efficiencies of concentrating oxygen using 1-7-mu m thick DYC/EC (9/91) membranes laminated to porous polyethersulfone membranes were almost constant for a 120-510-hour operating time. The membrane possessed a Q(OEA) of 9.0 x 10(-4) cm(3)(STP)/s . cm(2) and Y-O2 of 40% at 30 degrees C and 0.41 MPa for a single-stage process. The results suggest that the membranes could be used effectively in enriching oxygen from air.