Impacts of Adsorbed N2 on the Diffusion of CO2 and H2O in CALF-20 Assessed via a Frequency Response Method

The diffusion of CO2 and H2O in CALF-20 was examined at various concentrations and in N2 and He carrier gases. The data show that N2 has 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 and the effect that co-adsorbed N2 can have on CO2 and H2O diffusion mechanisms. Because multiple diffusion data points were required as a function of concentration, concentration swing frequency response (CSFR) was used to examine the system. CSFR typically involves perturbing the inlet concentration sinusoidally at a single frequency while monitoring the concentration response at the effluent. 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. FT-CSFR allows multiple data points to be obtained with a single experiment and generally produces results 3x faster than sinewave-only frequency response data collection.