TIME-LAG MEASUREMENTS FOR DIFFUSION OF AROMATICS THROUGH A SILICALITE MEMBRANE

Intracrystalline diffusivities of benzene, toluene, and the three xylene isomers in silicalite were determined by the membrane technique. A zeolite membrane was fabricated by embedding a large silicalite crystal in an epoxy resin and mounted in a permeability cell. The membrane was subjected to a known pressure gradient and the rate of transport and, hence, the intracrystalline diffusivity through the zeolite membrane was determined from the rate of pressure increase on the outflow side. The measured diffusivities of aromatics ranged from 5 x 10(-14) to 10(-13) m(2)/s. The technique offers a reasonable alternative to other macroscopic methods such as gravimetric and chromatographic methods for measuring intracrystalline diffusivities. However, the limitations of the technique are that (1) it measures integral diffusivity rather than differential diffusivity and (2) the fabrication of a zeolite membrane represents a formidable task.