ZEOLITE MEMBRANES FOR GAS SEPARATIONS

POROUS INORGANIC MEMBRANES CAN BE USED AT HIGH TEMPERATURES, AND HAVE HIGH FLUXES, MECHANICAL STRENGTH, AND CHEMICAL STABILITY. HOWEVER, COMMERCIALLY AVAILABLE INORGANIC MEMBRANES HAVE LARGE PORES (>40A), AND A WIDE PORE SIZE DISTRIBUTION. WHILE SUCH MEMBRNES ARE IDEALLY SUITED FOR REMOVING HIGH MOLECULAR WEIGHT COMPONENTS FROM A LIQUID STREAM (ULTRAFILTRATION), THEIR ABILITY TO SEPARATE GASES IS LIMITED. BECAUSE THESE MEMBRANES OPERATE ON KNUDSEN DIFFUSION, THEIR SEPARATION COEFFICIENTS ARE FAR TOO LOW FOR USE IN GAS SEPARATIONS. ON THE OTHER HAND, ZEOLITE MEMBRANES HAVE MUCH SMALLER PORES, AND A WELL DEFINED PORE SIZE DISTRIBUTION. SINCE THEY SEPARATE MOLECULES BY MOLECULAR SIEVING, THEY OFFER VERY HIGH SELECTIVITY. UNFORTUNATELY, WHILE THE POTENTIAL OF ZEOLITE MEMBRANES HAS LONG BEEN RECOGNIZED, THERE IS STILL NO SUITABLE PROCESSING METHOD BY WHICH EITHER SELF-SUPPORTED ZEOLITE MEMBRANES OR COMPOSITE MEMBRANES (A ZEOLITE FILM ON A POROUS SUPPORT) CAN BE MADE. IN PHASE I, ZSM-5 ZEOLITE FILMS WILL BE PREPARED ON AL OR SI SUBSTRATES USING A NOVEL SYNTHETIC METHOD, AND THEN THE CHEMICAL COMPOSITION, MORPHOLOGY, THERMAL STABILITY, AND ION-EXCHANGE ABILITY OF THE RESULTING FILMS WILL BE CHARACTERIZED. PHASE II WILL FURTHER REFINE THE PREPARATION PROCESS, OPTIMIZE THE FILM CHARACTERISTICS, AND MEASURE THE PERMEABIITY FACTOR OF SUPPORTED ZEOLITE GAS SEPARATION MEMBRANES.'