Ritter and co-workers [1] recently showed that an initially fast adsorption or desorption phenomenon was followed by a state of extremely slow uptake or release of CO2 in K-promoted HTlc that requires hours perhaps days to reach equilibrium. The CO2 loadings at such an equilibrium state were also considerably different than those attained during the initial stages of adsorption or desorption. Then, they developed a model to describe this behavior in terms of a Langmuir-Hinshelwood type of kinetic mechanism [2].

That model was a based on a non-equilibrium kinetic approach that describes the reversible adsorption and desorption behavior of CO2 on a K-promoted HTlc. It combined adsorption, diffusion and reaction together with a Langmuir-Hinshelwood mechanism to describe the uptake and release processes of CO2 on a K-promoted HTlc. The results from that work convincingly revealed that the adsorption and desorption behavior of CO2 on a K-promoted HTlc is associated with complex, highly coupled, completely reversible adsorption, diffusion and reaction phenomena. It also revealed that a true equilibrium state might never be achieved in this material or that it might take an inordinate amount of time to achieve, with the claimed equilibrium states reported in the literature perhaps only being associated with the initial fast stages of adsorption or desorption observed by Ritter and co-workers [1,2].

The objective here is to report on the development of a temperature and pressure dependent form of the non-equilibrium kinetic model that describes the reversible adsorption and desorption behavior of CO2 on a K-promoted HTlc not only as a function of temperature but also as a function of pressure. This model combines adsorption, diffusion and reaction together with a Langmuir-Hinshelwood approach to describe the uptake and release processes of CO2 on a K-promoted HTlc but now over broad ranges of temperature and pressure. Experimental results and corresponding model predictions will be presented in terms of the CO2 loadings in a K-promoted HTlc during repeated CO2 adsorption and desorption cycles.

References

1. A. D. Ebner, S. P. Reynolds and J. A. Ritter, “Understanding the Adsorption and Desorption Behavior of CO2 on a K-Promoted HTlc through Non-Equilibrium Dynamic Isotherms,” Ind. Eng. Chem. Res., 45, 6387-6392 (2006).

2. A. D. Ebner, S. P. Reynolds and J. A. Ritter, “Non-Eqilibrium Kinetic Model that Describes the Reversible Adsorption and Desorption Behavior of CO2 in a K-Promoted HTlc,” Ind. Eng. Chem. Res., 46, 1737-1744 (2007).