Characterizing non-zeolitic pore volume in zeolite membranes by temperature-programmed desorption

Temperature-programmed desorption is shown to be an effective method to measure the volume of non-zeolitic pores in a MFI membrane. A molecule that was too large to adsorb into the MFI pores at room temperature and the experimental time scale, 2,2-dimethylbutane, was adsorbed in the non-zeolitic pores, and its liquid density was used to estimate their pore volume. When n-hexane or n-octane adsorbed in the MFI pores, the non-zeolitic pore volume decreased by 55%, whereas benzene adsorbed in the MFI pores had no effect. The non-zeolitic pore volume decreased because n-hexane and n-octane swell the MFI crystals of the membrane and decrease the non-zeolitic pore size (the space between the MFI crystals), but benzene does not.