TIME-LAG MEASUREMENTS FOR DIFFUSION OF AROMATICS THROUGH A SILICALITEMEMBRANE

Intracrystalline diffusivities of benzene, toluene, and the three xyle ne isomers in silicalite were determined by the membrane technique. A zeolite membrane was fabricated by embedding a large silicalite crysta l in an epoxy resin and mounted in a permeability cell. The membrane w as subjected to a known pressure gradient and the rate of transport an d, hence, the intracrystalline diffusivity through the zeolite membran e was determined from the rate of pressure increase on the outflow sid e. 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 f or 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 mem brane represents a formidable task.