Struct Bond (2020) 184: 121–144
https://doi.org/10.1007/430_2020_65
# Springer Nature Switzerland AG 2020
Published online: 9 August 2020
Measurement of Diffusion in Small Pore
Zeolites to Improve Selectivity in Separation
Processes
Enzo Mangano and Stefano Brandani
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
2 The ZLC Technique: Description of the Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
3 The ZLC Technique: Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
4 Measurement of CO 2 Diffusivities in Zeolite Rho . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
Abstract The determination of mass transport coefficients is essential for the design
of adsorption separation processes, especially for those driven by kinetic selectivity.
In this chapter, a specific focus is given to the experimental measurements of
adsorption kinetics in nanoporous zeolites. A selection of zero length column
(ZLC) experiments on a series of zeolite Rho samples is presented to demonstrate
the use of the ZLC technique to determine accurately the time constant of an
adsorption process. The examples chosen examine the kinetic behaviour of complex
materials characterised by severe hindering effect resulting in highly selective but
very slow materials. In addition, the kinetic characterisation is complicated by the
specific nature of Rho zeolites, which undergo structural change during the adsorption process. The discussion of the experimental methodology and the analysis of the
results offer the opportunity to highlight some of the challenges related to the
experimental determination of adsorption kinetics and discuss some of the best
experimental practices. The contribution emphasises the importance of designing
experimental methods addressing the needs of the inventors of novel materials: rapid
and reliable measurements, small amount of sample required, rapid assessment of
the performance and feedback for continuous improvement of the synthesis process
and material development.
E. Mangano and S. Brandani (*)
School of Engineering, The University of Edinburgh, Edinburgh, UK
e-mail: s.brandani@ed.ac.uk
https://doi.org/10.1007/430_2020_65
# Springer Nature Switzerland AG 2020
Published online: 9 August 2020
Measurement of Diffusion in Small Pore
Zeolites to Improve Selectivity in Separation
Processes
Enzo Mangano and Stefano Brandani
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
2 The ZLC Technique: Description of the Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
3 The ZLC Technique: Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
4 Measurement of CO 2 Diffusivities in Zeolite Rho . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
Abstract The determination of mass transport coefficients is essential for the design
of adsorption separation processes, especially for those driven by kinetic selectivity.
In this chapter, a specific focus is given to the experimental measurements of
adsorption kinetics in nanoporous zeolites. A selection of zero length column
(ZLC) experiments on a series of zeolite Rho samples is presented to demonstrate
the use of the ZLC technique to determine accurately the time constant of an
adsorption process. The examples chosen examine the kinetic behaviour of complex
materials characterised by severe hindering effect resulting in highly selective but
very slow materials. In addition, the kinetic characterisation is complicated by the
specific nature of Rho zeolites, which undergo structural change during the adsorption process. The discussion of the experimental methodology and the analysis of the
results offer the opportunity to highlight some of the challenges related to the
experimental determination of adsorption kinetics and discuss some of the best
experimental practices. The contribution emphasises the importance of designing
experimental methods addressing the needs of the inventors of novel materials: rapid
and reliable measurements, small amount of sample required, rapid assessment of
the performance and feedback for continuous improvement of the synthesis process
and material development.
E. Mangano and S. Brandani (*)
School of Engineering, The University of Edinburgh, Edinburgh, UK
e-mail: s.brandani@ed.ac.uk