Process optimization of a fixed bed reactor system for direct air capture

The extraction of CO₂ directly from the atmosphere (Direct Air Capture) is commonly employed using supported-amine sorbents. This adsorption technology is under rapid development with novel sorbent materials emerging and with processes being demonstrated on increasingly larger scale. Optimization of such processes requires accurate knowledge on sorbent characteristics and knowledge on how operational variables affect process performance. This study primarily focuses on the latter, where we aim to quantify the influence of operational parameters on the energy duty and CO₂ productivity. In addition, we examine the influence of weather conditions on the adsorption rate. For this, we develop a dynamic model of the complete temperature-vacuum swing adsorption cycle (TVSA). This model was validated by experimental results on a kg-scale direct air capture system. The impact of selected operational variables was assessed by two-dimensional sensitivity analyses. We show that desorption temperature is preferably high, limited by the chemical stability of the sorbent material in this particular case. In addition, the sorbent working capacity should be high when opting for an optimization towards energy duty, whereas it reaches a clear optimum in terms of CO₂ productivity. Finally, we conclude that weather conditions and diurnal variations can significantly affect the performance of a direct air capture process and should certainly be considered during design and operation. With these insights and the developed model, this study provides a sound basis for further process development and optimization of direct air capture using fixed bed technology combined with solid amine sorbents.