Gas sorption in polymers, molecular sieves, and mixed matrix membranes

Gas sorption has been an underutilized technique for characterizing organic-inorganic hybrid (mixed matrix) membranes. Sorption in these membranes, which are composed of rigid inorganic domains, such as zeolites, dispersed in a polymer matrix, should be approximately additive. Sorption in the neat polymers and zeolites were first measured to demonstrate that sorption in mixed matrix membranes is approximately additive in the absence of other effects. Sorption in mixed matrix membranes was demonstrated to be additive. This extends to cases where sorption in one or both phases of the mixed matrix membrane is affected by an outside contaminant. For example, zeolite 4A is extremely hydrophilic and easily affected by contaminants from processing or from the test gases. Zeolite 4A encapsulated within a polymer matrix can still be affected by these same components, and this causes sorption lower than predicted based on that in unaffected polymers and sieves. This sorption analysis has proven to be very important in understanding the permeabilities and selectivities of mixed matrix membranes. (C) 2007 Wiley Periodicals, Inc.