(622c) N2 Mass Transport in Commercial Lilsx Beads Using the Adsorption Differential Volumetric Apparatus

In the production of O₂ from air LiLSX is the state-of-the-art material in industrial applications. As the systems are optimized for productivity, thus rapid cycles, it becomes essential to have an accurate estimate of the mass transport kinetic parameters. The process is limited by the desorption of N₂, making the effective macropore diffusivity of N₂ a key performance parameter [1]. Testing commercial samples using gram-scale quantities poses significant limitations as heat effects can become dominant in this fast system. Here we present a methodology for the simultaneous determination of both the correct effective diffusivity and the underlying thermal parameters using a purposely designed Adsorption Differential Volumetric Apparatus (ADVA).

To try and limit the intrusion of heat effects special purpose-made copper sample holders were used to isolate each individual bead and increase the thermal mass of the sample+holder assembly. However, for this fast diffusing systems, non-isothermal effects are inevitable even for close-to-vacuum pressures and small pressure steps. This is the case even when using only 4 clearly isolated beads with a sample mass of less than 30 mg.

Measurements were carried out from below 0.25 kPa to 55 kPa [2] on two commercial LiLSX binderless Zeochem beads. Following the recommended experimental protocol [3] over a temperature range of -10 to 30ËšC, a consistent set of effective diffusion time and thermal parameters was extracted unequivocally for each formed adsorbent. These measurements can be used to compare the materials quantitatively and provide accurate kinetic information for the design of vacuum-swing adsorption processes.

One of the important conclusions that can be inferred from the results is that above 40 kPa the system is completely heat limited, even with small pressure steps. The use of larger sample sizes and larger pressure or concentration steps will therefore inevitably have significant heat effects, complicating the interpretation of the results and possibly indicating limited or no differences between materials. Combining the experimental accuracy of the ADVA system and the linear non-isothermal model overcomes the significant challenges posed by the N₂-LiLSX system and work is in progress to extend the methodology to small beads used in medical O₂ applications.

References

[1] S. Brandani, F. Brandani, E. Mangano, P. Pullumbi, Microporous and Mesoporous Materials. 2020, 304, 109277. https://doi.org/10.1016/j.micromeso.2019.01.015.

[2] J.-Y. Wang, E. Mangano, S. Brandani, F. Brandani, P. Pullumbi, Separation and Purification Technology. 2022, 283, 120210. https://doi.org/10.1016/J.SEPPUR.2021.120210.

[3] J.-Y. Wang, E. Mangano, S. Brandani, D. M. Ruthven, Adsorption. 2021, 27 (3), 295–318 https://doi.org/10.1007/s10450-020-00276-7