| Transport during mixture pervaporation through zeolite membranes was investigated. Organic/H2O separation factors for pervaporation of 5 wt% C1–C4 organic feeds through a hydrophobic Ge-substituted ZSM-5 zeolite membrane at 303 and 333 K increased, in general, with organic feed fugacity. Organic heats of adsorption and sizes also affected the separations, but to a lesser extent than fugacities did. These separations and other separations with hydrophobic and hydrophilic zeolite membranes reported in the literature suggest that competitive adsorption coverages on zeolites depend on feed fugacity ratios.; Diffusion rates of H2O, methanol, ethanol, 2-propanol, and acetone in unary and binary feeds permeating through a Ge-ZSM-5 membrane were measured with isotopic-transient pervaporation. Labeled molecules were added to the feed during steady-state pervaporation, and their transient responses in the permeate were measured. Coadsorbed molecules in the membrane are directly shown to slow or speed up the diffusion rates of each other at high coverages. For ethanol/methanol mixtures, ethanol diffused faster and methanol slower than the corresponding pure material. For an acetone/methanol mixture, however, both molecules diffused slower than pure acetone, which is the slower diffusing molecule. This inhibition is attributed to molecules with dissimilar sizes being more constrained than pure acetone in the pores.; Pervaporation through B-substituted ZSM-5 zeolite membranes on multi-channel monolith supports and small-pore (0.38-nm diameter) SSZ-13 zeolite membranes was also investigated. The monolith membranes, which had larger surface to volume ratios than tubes, effectively removed C1–C3 alcohols and acetone from 5 wt% organic/H2O binary feeds between 303 and 333 K. The separation factors for C2 and C 3 alcohols and acetone were higher than those reported for a B-ZSM-5 tubular membrane. Methanol and ethanol fluxes were also comparable to the tubular membrane fluxes. The SSZ-13 membranes selectively removed H2 O from HNO3/H2O liquid mixtures to break the azeotrope at 69.5 wt% HNO3, and exhibited stability in the low-pH conditions for up to 13 days. These SSZ-13 membranes also separated light-gas mixtures with selectivities higher than the Knudsen selectivities. |
