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b-cyclodextrin (CD) was deposited in defects of MFI membranes in an effort to increase separations selectivity, but single gas permeation measurements, permporometry, pervaporation with i-octane, and temperature-programmed oxidation (TPO) showed instead that CD prevented the MFI crystals from swelling as much when some molecules adsorbed in the MFI pores. The CD acted as a molecular-sized wedge in defects without completely filling membrane defects, and thus some defect area remained open to flow. For membranes without CD, the flux through defects, as measured by the flux of i-octane (because it is too large to adsorb in MFI pores), decreased several orders of magnitude in the presence of n-hexane.  With CD deposited in the defects, however, the flux through the defects, with n-hexane adsorbed in the MFI pores, was two orders of magnitude higher. Because crystal swelling was inhibited, the flux of some molecules (SF₆, i-butane) was higher after CD deposition. Competing effects of inhibited crystal swelling (which increased flux through defects) and blockage of defect area by CD (which decreased flux through defects) meant that fluxes of some molecules decreased and others increased after CD deposition, depending on the amount of CD. These results explain previous behavior reported in the literature and also demonstrate that many methods used to characterize MFI membranes do not yield a good indication of membrane quality. The ratios of single gas fluxes for small and large molecules are not good indications of the amount of flux through defects.  The CD was only partially removed by calcination at 675 K, and TPO demonstrated that higher temperatures were required to remove CD and its decomposition products.

Another approach to block flow through defects in MFI membranes used disposition of  Na₂SO₄ , which decreased the flux dramatically. To understand the behavior, salt was deposited from aqueous solution in alumina supports with 5-nm pores, which are slightly larger than the membrane defects. The salt deposition did not increase ideal selectivities above Knudsen selectivities, but interesting flow behavior resulted. Whereas permeance was independent of pressure drop for the support, as expected for Knudsen diffusion, permeance increased exponentially with pressure drop for supports containing salt. The flux also decreased exponentially as the temperature increased, whereas flux through the support without salt decreased only slightly. The pressure exerted during salt crystallization appeared to crack the alumina supports, however, and increase pore size dramatically.

Attempts to tune zeolite membrane selectivity were carried out on LTA and MFI membranes. Because the zeolite crystals swell when certain molecules adsorb in their pores, intercrystalline defects shrank and flux flow through defects decreased. In some cases, membrane flux was reduced by more than three orders of magnitude. It was hypothesized that varying the amount of adsorbate could control defect size so that defects could be used for separations. Defect size distributions and the presence of a few larger defects appeared to make such separations difficult to achieve however.