Experimental comparison of regeneration methods for CO 2 concentration from air using amine-based adsorbent

Comparison of different regeneration options for direct air capture (DAC) has usually been limited to only consider pure CO2 production, limiting the process options to e.g. temperature-vacuum swing adsorption (TVSA) or steam-stripping. In this work, detailed experimental comparison is conducted of temperature swing adsorption (TSA/TCSA) and TVSA for DAC. Particularly, TVSA is assessed with air or inert gas purge flow (TVCSA) and without purge flow. The working capacity, regeneration specific energy requirement (SER) and adsorbent regenerability of these processes was compared. For all other studied regeneration options except TVSA without purge flow, over 85% regeneration was obtained already at 60 degrees C. Isobaric TSA at 60 degrees C had the lowest regeneration SER of 4.2 MJ/kgCO2. Coupling TSA with mild vacuum improved desorption rate and increased working capacity from 0.47 to 0.51 mmolCO2/gsorbent, requiring 7.5 MJ/kgCO2 for regeneration. Without purge flow, TVSA resulted in only 0.39 mmolCO2/gsorbent with the SER of 8.6 MJ/kgCO2 at 100 degrees C. Due to lower allowable regeneration temperature of 60 degrees C, mild vacuum TVSA with air flow also had a lower cyclic capacity decrease rate of 0.26%/cycle compared to 0.38%/cycle with TVSA without purge flow at 100 degrees C. However, using 100 degrees C with air flow in the TVSA process lead to a significant capacity decrease of 0.6%/ cycle. Therefore, using either air or inert purge flow below 100 degrees C coupled with mild vacuum has benefits over the TVSA process with no inflow in terms of CO2 productivity, specific energy requirement and adsorbent regenerability. For utilization purposes that require low-concentration CO2, TVSA with purge flow should thus be considered as a viable regeneration option for direct air capture along with isobaric TSA. Superscript/Subscript Available

Automated summary

Comparison of regeneration options for direct air capture shows that using TVSA with air or inert gas purge flow leads to better regeneration efficiency. Lower temperatures result in better regeneration performance, with TVSA coupled with mild vacuum showing lower cyclic capacity decrease rate.