Alcohol and water adsorption and capillary condensation in MFI zeolite membranes

A boron-substituted MFI membrane was selective for 2-propanol/water separations during pervaporation in part because 2-propanol expanded the MFI crystals and thus shrank the size of the membrane defects. Permporosimetry measurements show that adsorption of 2-propanol, 1-butanol, and ethanol decreased helium flow through the defects, apparently because these alcohols swell MFI crystals. In contrast, neither methanol nor water adsorption appeared to change the defect size. Helium flow through membrane defects was also blocked by capillary condensation, but this was only observed when the pressure drop across the membrane was less than about 20 kPa. Thus defect blockage by crystal expansion was observed without capillary condensation by carrying out permporosimetry with a pressure drop of 89 kPa. The defect sizes were estimated from capillary condensation to be approximately 2 nm.