Figure 2 illustates that CO 2 is switched off after 120 minutes, followed by a 10-minute purge phase. After this, the temperature is increased to 105°C, resulting in a sharp peak of CO 2 release during the temperature ramp (see Figure 3 ). The colour code indicates PEI concentration in the sample in wt%. The sample with 0% is
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Figure 2 CO 2 breakthrough curves
a reactor filled with 2 mL corundum. While the capacity increases with rising PEI content up to 20%, a dramatic decrease in storage capacity is found when PEI is further increased to 30%. Initially, CO 2 uptake proceeded rapidly, as observed by a concentration drop absent for the inert corundum reference. Thereafter, a gradual, asymptotic rise towards the inlet concentration persisted for the full two-hour capture time set in this experiment. This is a clear indication that readily accessible surface sites became occupied
quickly and subsequent adsorption became diffusion‑limited. The question remains open as to whether prolonged exposure in this slow‑uptake regime contributes meaningfully to an energy‑efficient DAC process. Screening samples with respect to shorter adsorption/desorption cycles could be more reasonable than comparing total storage capacities after several hours of exposure when the overall space-time-yield of CO 2 separation needs to be maximised. According to current
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Figure 3 CO 2 signal plotted as function of temperature
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