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PEI-silica for direct air capture using fluidised bed reactor

https://doi.org/10.1016/j.ces.2014.05.018

“The results of the air capture tests for the two batches of PEI–silica adsorbent are summarized in Table S1 (Supplementary information) and illustrated in Fig. 5Fig. 6. For the first three runs of partially degraded PEI-A batch which lasted for 4, 5 and 6 days, almost all the CO2 that had been passing through the bed materials was captured, indicating a nearly 100% of capture efficiency. This implies that within a short gas–solid contact time of only 7.5 s, the adsorbent was capable of adsorbing almost all CO2 contained in the ambient air. When the test time was longer than 6 days, however, the capture rate (α) decreased due to the fact that the loaded mass of PEI–silica adsorbent had achieved CO2 saturation after around 6 days of adsorption. No more CO2 could be captured beyond this point and the CO2 contained in the air would escape from the top of the BFB. For the fresh PEI-B batch, CO2 began to break through the adsorbent bed from around 7–8 days and the CO2 saturation of the adsorbent was estimated to take place at around 10 days.”

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Fig. 5. Total CO2 volume passing through the bed during adsorption, the amount released during desorption and the CO2 capture rate (α) (a) for runs of A-1 to A-5, (b) for runs of B-1 to B-4 (CO2 volume is at the condition of 1 atm and 20 °C).”

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Fig. 6. The ratio of adsorbed CO2 mass to the mass of bed materials (a) for runs of A-1 to A-5, (b) for runs of B-1 to B-4.”

“The saturation time is obviously dependant on the loaded bed mass and the adsorption capacity. After the adsorbent becomes saturated, qad represents the equilibrium adsorption capacity. As shown in Fig. 6(a) for PEI-A batch, this equilibrium adsorption capacity is found to be around 5.2 wt% over three runs (A-3 to A-5), comparing to 7.2 wt% for flue gas containing 15% CO2 capture tests performed previously using the same adsorbent and in the same BFB reactor. For PEI-B batch in Fig. 6(b), the equilibrium adsorption capacity has decreased from 11.1 wt% for the flue gas (15% CO2) capture case to around 7.3 wt% for air capture case. The capacity of 10.1 wt% of PEI-B for capturing a lower concentration of CO2 (5%) from the simulated flue gas is also included in Fig. 6(b) for comparison.

No obvious reduction in CO2 air capture capacity has been found with 5 cycles of PEI-A and 4 cycles of PEI-B (Fig. 6), indicating good cyclic regenerability of the PEI–silica adsorbent. However, more cycles of identical running time are needed to verify the long-term regenerability and stability of the PEI–silica adsorbent.”

 

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