Double exponential model (DEM) for K2CO3 based carbon capture

https://doi.org/10.1016/j.ccst.2021.100011

“Loading K₂CO₃ on porous supports can enhance its overall CO₂ sorption kinetics. Nasiman et al. proved that CO₂ sorption over K₂CO₃-carbon composite proceeded about 1.5 or 2 fold faster than that over bulk K₂CO₃, and the fast carbonation kinetics were associated with the formation of nanostructure in the carbon composite support (Nasiman and Kanoh, 2020). For supported K₂CO₃ adsorbents, their CO₂ sorption processes could be more complicated, which involved both the carbonation of K₂CO₃ and the physical adsorption of porous supports. Modified kinetic models had been constructed to describe the CO₂ sorption kinetics of supported K₂CO₃ adsorbents. Assuming that K₂CO₃ remained stable as solid phase and the introduced H₂O would not result in the dissolution of K₂CO₃, a double exponential model (DEM) was established to reveal the carbonation kinetic characteristics of K₂CO₃-impregnated mesoporous silica adsorbents (Eq. 12).”

“where M is the weight gain after carbonation, A and B are the pre-exponential factors of the H₂O diffusion-hydration reaction stage and the CO₂ diffusion-carbonation reaction stage, k1 and k2 are the reaction rate constants of the two stages, and C is the constant.”

“In DEM, the carbonation process of potassium-based adsorbents was divided into two stages as the H₂O diffusion-hydration reaction stage and the CO₂ diffusion-carbonation reaction stage (Fig. 9b). It required a higher activation energy for the proceeding of H₂O diffusion-hydration than CO₂ diffusion-carbonation, and the kinetic rate constant for H₂O diffusion-hydration was 1 order of magnitude lower than that for CO₂ diffusion-carbonation, indicating that the former was the rate limiting step in the whole carbonation process (Guo et al., 2015d).”