Impacts of Adsorbed N ₂ on the Diffusion of CO ₂ and H ₂ O in CALF-20 Assessed via a Frequency Response Method

The diffusion of CO2 and H2O in CALF-20 was examined at various concentrations in both N2 and He carrier gases, with N2 having a measurable impact on the diffusion of CO2 and H2O in the pores of CALF-20. The results highlight the importance of considering N2 adsorption in CO2 capture materials. Because multiple diffusion data points were required as a function of concentration, concentration swing frequency response (CSFR) was used to examine the system, and to increase the throughput of this device, a methodology was developed based on the Fourier transform of the response of an adsorbent bed to a square wave perturbation of the inlet concentration. The results show that CSFR can distinguish between thermal, diffusion, and mixed-gas control, with only the appropriate model fitting the data. FT-CSFR allowed multiple data points to be obtained with a single experiment and generally produced results 3× faster than sine wave-only frequency response data collection.