DIFFUSION OF LIGHT ALKANES IN SILICALITE STUDIED BY THE ZERO LENGTH COLUMN METHOD

Micropore diffusion coefficients for propane, n-butane, and isobutane in three samples of silicalite crystals were measured by the zero length column (ZLC) method. Experiments were analyzed by the traditional long-time approach and by a new short-time method. For isobutane, micropore diffusion coefficients obtained from all three samples by both analysis methods agreed well with previously reported chromatographic and membrane measurements. For the linear alkanes, the rate of micropore diffusion, even in the largest crystals (350 x 100 mum), was too fast for reliable measurement and the form of the ZLC response curves was consistent with equilibrium control. Taken as a lower limit, the apparent diffusion coefficients obtained for propane and n-butane are consistent with the results of microscopic experiments and recent chromatographic and frequency response studies.