Technical description of dry potassium-based adsorbents for CO2 capture

“In a typical temperature swing adsorption (TSA) process using twin fluidized-bed reactors, flue gas stream containing 8-15%CO2 and 5-12%H2O is purged to the carbonator packed with potassium-based adsorbents, and CO2 reacts with K2CO3 at 60-100°C under a moist condition through the carbonation reaction (Eq. 1Fig. 2) (Zhao, C. et al., 2013). The spent potassium-based adsorbents are transported to the regenerator, in which KHCO3 is regenerated in a moderate temperature range of 120-200°C upon steam stripping (backward reaction of Eq. 1). The regenerated potassium-based adsorbents are recycled to the carbonator for cyclic CO2 capture, and the released CO2/H2O mixtures are facilely separated by condensing the steam to obtain high-purity CO2 ready for sequestration (Zhao, C. et al., 2013). The theoretical CO2 adsorption capacity of pure K2CO3 is as high as 7.25 mmol CO2/g K2CO3. However, its carbonation conversion reported in literatures only attains 45%, which is far from expectation (Zhao et al., 2009cZhao et al., 2009d). In addition, its CO2 adsorption rate is limited by the intrinsically poor textural properties. As the carbonation process goes on, the formed KHCO3 product layer grows thicker, which will impede the diffusion of CO2 and H2O, and the reaction kinetics will thus be limited (Zhao et al., 2012a). Moreover, the trace impurities such as SOx, NOx, HCl and H2S present in flue gas stream will cause the deactivation of adsorbent (Kim et al., 2012Wu et al., 2011a). Besides, the participation of moisture in the carbonation process has made it rather difficult to clearly identify the complicated reaction pathways.”




Fig. 2. Schematic diagram of dry potassium-based adsorbents for CO2 capture in a typical temperature swing adsorption (TSA) process.”

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