(178b) Lessons Learnt from over 30 Years of the Zero Length Column Experiment

The Zero Length Column (ZLC) technique was introduced in 1988 by Eic and Ruthven [1] with the aim to develop a new experimental method for the measurement of diffusivity of hydrocarbon molecules in zeolite crystals. The idea behind the new methodology was to overcome the limitations of conventional chromatographic methods by decoupling and minimising the secondary effect unavoidably present when measuring transport kinetics (heat effects, mass transport resistance, axial dispersion). Experimentally, this is achieved by shrinking the length of the adsorption column to a monolayer of crystals, making the system effectively a well-mixed cell. This greatly simplifies the model and the analysis of the data.

Over the years the technique has been widely used and adapted to a broader range of materials and experimental conditions, and an overview will be presented. While the ZLC has been successfully used for the determination of the kinetics of systems dominated by micro- and macropore diffusion as well as surface resistance it still is not available as a commercial unit. As a result new users have to develop their system. The second part of the talk will therefore discuss the basic design of a ZLC system for both kinetic and equilibrium measurements. This is often influenced by the models used to interpret the results. While for equilibrium measurements a stable system provides accurate results, kinetic experiments can be interpreted incorrectly if a minimum set of tests are not performed. We will conclude providing recommendations on what kinetic experiments should be carried to avoid potential pitfalls.

[1] M. Eic and D. M. Ruthven. A new experimental technique for measurement of intracrystalline diffusivity. Zeolites, 8(1), 40–45, 1988.