The zero-length column technique was extended here to the case where the decay of the adsorbed phase concentration was observed directly using nuclear magnetic resonance. An adsorption–desorption apparatus compatible with a 400MHz NMR spectrometer was developed. It operated with nitrogen or helium as the inert purge gas. The column of adsorbent material was placed in the sensitive region of the superconducting magnet and the radio-frequency coil of the NMR spectrometer. The time-scales of the adsorption and desorption processes depended upon concentration, temperature and crystal shape and were found to be in the range of 1 to 10min. From the desorption branch, the non-equilibrium ZLC-NMR measurements indicated intracrystalline diffusion coefficients in the range of 10−13 to 10−11m2/s for various alkanes in silicalite-1. These values were found always to be smaller than the values measured using pulsed field gradient NMR under equilibrium condition (table 36); indicating that there must have existed additional transport resistance at the external surface of the silicalite-1 crystals.

Combining Macroscopic and Microscopic Diffusion Studies in Zeolites using NMR Techniques. K.Banas, F.Brandani, D.M.Ruthven, F.Stallmach, J.Kärger: Magnetic Resonance Imaging, 2005, 23[2], 227-32

Table 37

Apparent Activation Energy for

Alkane Diffusion in Silicalite