(144a) Uptake Kinetics of Non-Isothermal Systems: Definition of the Ruthven Number.

Amongst the many contributions made by Doug Ruthven to the fields of adsorption fundamentals and adsorption engineering, probably one of the most important ones has to be the critical analysis of uptake experiments carried out in the late 1970s and early 1980s [1-3]. This was the result in part of his collaboration with Jörg Kärger that led to the first comprehensive comparison of macroscopic and microscopic measurements of diffusion in zeolites [4] and the realization that in many instances early uptake rate measurements did not take into account the intrusion of heat and bed effects. Here the focus is on the challenges associated with heat effects.

While the problem of combined heat and mass transfer in zeolites is complex and dependent on several dimensionless groups, Ruthven showed that a single combined dimensionless group could be used to identify when isothermal conditions were valid in gravimetric experiments (perfect step change in external concentration). For the first time it became apparent that even reducing the pressure step of the experiment could not lead to isothermal conditions, something that was often assumed, originally even by Ruthven himself.

In a recent review of common practices in uptake rate experiments [5] it has become apparent that many of the things learnt in the early 1980s have been retained only by few and in particular the importance of establishing isothermal conditions in uptake experiments. It is therefore timely to highlight the importance of the key dimensionless group idenfied by Ruthven and it is proposed that it should be named after him.

The talk will conclude with the extension of the use of the dimensionless group to volumetric (constant volume, variable pressure) and zero length column experiments and an analysis of the implications for micropore and macropore diffusion for Langmuir type isotherms.

[1] Lee L.K. and Ruthven D.M., Analysis of thermal effects in adsorption rate measurements. J. Chem. Soc., Faraday Trans. 1, 1979, 75, 2406-2422. https://doi.org/10.1039/F19797502406

[2] Ruthven D.M., Lee L.K. and Yucel H. Kinetics of non-isothermal sorption in molecular sieve crystals. AIChE J. 1980, 26, 16-23. https://doi.org/10.1002/aic.690260104

[3] Ruthven D.M. and Lee L.K. Kinetics of nonisothermal sorption: Systems with bed diffusion control. AIChE J. 1981, 27, 654-663. https://doi.org/10.1002/aic.690270418

[4] Kärger J. and Ruthven D.M., Diffusion in zeolites. Comparison of sorption and nuclear magnetic resonance diffusivities. J. Chem. Soc., Faraday Trans. 1, 1981, 77, 1485-1496. https://doi.org/10.1039/F19817701485

[5] Wang J., Mangano E., Brandani S. and Ruthven D.M. A review of common practices in gravimetric and volumetric adsorption kinetic experiments. Adsorption, 2021, 27, 95–318 https://doi.org/10.1007/s10450-020-00276-7