TAILORING MIXED MATRIX COMPOSITE MEMBRANES FOR GAS SEPARATIONS

Polymeric gas separation membrane materials have improved significantl y over the past two decades due to systematic optimization in backbone structure. Recent evidence suggests, however, that advantages of a pu rely polymer-based approach are reaching diminishing returns for impor tant separations such as O-2 and N-2. Zeolites, carbon molecular sieve s (CMS), and rigid rod polymers offer attractive transport properties but are difficult and expensive to process. Mixed matrix composite (MM C) membranes, incorporating molecular sieving materials within polymer ic substrates, may provide economical, high performance gas separation membranes if defects at the molecular sieve/polymer interface can be eliminated. In addition, careful matching of the intrinsic permeabilit y and selectivity of the support matrix and the molecular sieve domain s is necessary. Theoretical O-2 permeability and O-2/N-2 selectivity p redictions are presented for such optimized membranes of zeolite 4A an d CMS in Ultem(R) and Udel(R) matrices using two idealized expressions based on classical and more recent results. Positive and desirable de viations from these idealized results can be anticipated if a continuo us molecular sieving phase is formed, but this special case is not req uired if a proper selection of the polymer matrix is made. (C) 1997 El sevier Science B.V.