Modelling of equilibrium working capacity of PSA, TSA and TVSA processes for CO2 adsorption under direct air capture conditions

In this study, direct air capture performance of polymeric adsorbent was studied by determining CO2-isotherms in very dilute conditions (CO2 partial pressure up to 5 mbar). The effect of cold conditions (0 degrees C and-10 degrees C) and humidity on the CO2 capacity was also studied. The experimental isotherms were used in temperature-dependent equilibrium modelling to simulate equilibrium CO2 working capacities in pressure-swing adsorption (PSA), temperature-swing adsorption (TSA) and temperature-vacuum swing adsorption (TVSA). Experimental adsorption capacities of 0.80 mmol(CO2)/g(sorbent) and 0.89 mmol(CO2)/g(sorbent) were obtained from 400 ppmv CO2 in dry cold conditions and at 25 degrees C in humid conditions, respectively. The highest experimental capacity gained from 400 ppmv CO2 was 1.06 mmol(CO2)/g(sorbent) in humid cold conditions. In terms of the working capacity, PSA was found not to be a viable process option. Humidity promoted TSA working capacity up to by 0.36 mmol(CO2)/g(sorbent) (78%). TSA could produce larger than 0.5 mmol(CO2)/g(sorbent) working capacity levels even with very low regeneration temperatures (50-60 degrees C) when adsorbing either in dry cold conditions or humid warm conditions. Such EWC levels with dry TVSA could only be achieved using 90 degrees C regeneration temperature with adsorption in either cold conditions or from compressed air. Based on these results, TVSA should only be considered in PtX applications requiring high-purity CO2.