(292a) Diffusion mechanism of CO2 in zeolite 5A pellets

In this work we present collective effort from the Adsorption Group at the University of Edinburgh to understand the CO­₂ transport mechanism in commercial 5A zeolite pellets. The study is based on a rigorous approach which includes the experimental determination of CO­₂ kinetics through different experimental techniques and the direct use of all measurable parameters for the modelling of some relevant carbon capture processes.

Kinetic and equilibrium experiments were carried out using the Zero Length Column (ZLC) technique on a single 5A pellet. Following the recommendations described in our recent review on the use of the technique [1], we carried out a systematic assessment of the adsorption performance of the system at different temperature and partial pressures of CO₂. ZLC experiments with different carrier gases provided unequivocal proof of macropore diffusion control for CO₂ in 5A. The ZLC experimental study offers a practical example of the application of the best practices suggested in our review paper.

Kinetic results were also cross-checked using a newly designed Adsorption Differential Volumetric Apparatus (ADVA). The system is specifically designed for kinetic tests and relies on the use of two absolute and a small-range differential pressure transducers, allowing to measure accurately very fast kinetics using very small volumes of sample.

Kinetic, equilibrium and structural properties experimentally measured in our laboratory are then used for the simulation of relevant carbon capture processes, including membrane separation, direct air capture and CO₂ capture processes at higher concentrations. The study aims to highlight how accurate process predictions rely not only on the quality of the adsorption data but also (and sometimes more importantly) on the correct interpretation of the data.

[1] Brandani, S., Mangano, E. The zero length column technique to measure adsorption equilibrium and kinetics: lessons learnt from 30 years of experience. Adsorption 27, 319–351 (2021). https://doi.org/10.1007/s10450-020-00273-w