Great interest in studies of the adsorptive removal of CO2

The breakthrough analyzer mixSorb continues to experience great international interest for practical adsorption studies of gas mixtures. One field of application is the active removal of CO2 from the air or exhaust gases in terms of climate protection. Corresponding adsorption studies should take place under realistic conditions – these can be dry or humid gas streams. A mixSorb with evaporator option allows such comparative studies. Currently, breakthrough curves with respect to CO2 sorption from gas mixtures have been determined. The following figure illustrates the behavior of three adsorbents in a dry gas mixture.

Breakthrough curves of 2,000 ppm CO₂ of dry nitrogen in zeolite 4A, 5A and Lewatit VP OC 1065

Breakthrough curves of 2,000 ppm CO₂ of dry nitrogen in zeolite 4A, 5A and Lewatit VP OC 1065 at 313 K, 1 bar, 5,000 cm3·min-1

The two zeolites adsorb water so strongly that they are hardly suitable for CO2 separation from moist gas streams, as would be the case in direct air capturing applications. For the purification of dry gas streams, however, they show advantages due to better kinetics. For the polymer levatite, a sorption loading of 0.819 mmol·g-1 was obtained from the breakthrough curve in the following figure. This adsorbent is the most suitable of the selected materials to adsorb CO2 in the range of low concentrations in the presence of moisture, and is thus predestined for the Direct Air Capturing application. All obtained loadings are summarized in the table.

Breakthrough curves of 2,000 ppm CO₂ from a wet nitrogen flow in zeolite 4A, 5A and Lewatit VP OC 1065

Breakthrough curves of 2,000 ppm CO₂ from a wet nitrogen flow in zeolite 4A, 5A and Lewatit VP OC 1065 at 313 K, 50 % relative humidity, 1 bar and 5,000 cm3·min¹

Loadings from breakthrough tests of 2,000 ppm CO₂ from dry and wet (50 % RH) nitrogen at 313 K, 1 bar, volume flow 5,000 cm³·min-1

Sample CO2 load of dry N2 CO2load of moist N2
Zeolite 4A 0.768 mmol·g-1 < 0.010 mmol·g-1
Zeolite 5A 0.341 mmol·g-1 < 0.010 mmol·g-1
Lewatit VP OC 1065 0.605 mmol·g-1 0.819 mmol·g-1

On the basis of preliminary experiments, Lewatit can be recommended for direct air capturing applications. For material development, the experiments showed the valuable indication that an improvement of the sorption kinetics of the polymer appears desirable.

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