Diffusion of linear and branched C6 alkanes in silicalite-1 studied by the tapered element oscillating microbalance

The kinetic patterns of adsorption and desorption have been studied for linear and branched C-6 alkanes in silicalite-1 of uniform shape and size by a novel technique - the tapered element oscillating microbalance (TEOM). Unlike the conventional gravimetric method, the TEOM technique minimizes external mass and heat transfer limitations in transient experiments due to a high flow rate of the carrier gas through the sample bed without affecting measurements. Model equations, in which the thermodynamic factor for intracrystalline diffusivities has been taken into account, enable the determination of diffusivities from adsorption and desorption patterns operated in the non-linear adsorption range and bypass simplifying assumptions for analytic solutions. The determined diffusivities at zero coverage for the studied adsorptives, which cover three orders of magnitude (10(-12)-10(-15) m(2)/s), are in good agreement with those available by zero-length column and chromatography methods so far. It is shown that the TEOM technique can be easily used not only for steady state and equilibrium measurements, but also for transient uptake and desorption experiments. (C) 2001 Elsevier Science B.V. All rights reserved.