(117c) Non-Equilibrium Kinetic Model for the Reversible Adsorption of Carbon Dioxide on a K-Promoted Htlc
A non-equilibrium kinetic model was developed to describe the reversible adsorption and desorption behavior of CO2 on K-promoted hydrotalcite like compound (HTlc). The model consisted of a reaction pathway involving three reactive and reversible processes and four phases. Two of the reactions were of the Langmuir-Hinshelwood type representing slow and intermediate kinetic processes, and one was a mass transfer limited chemisorption process representing very fast kinetics. The nine inherently unique parameters in the model (three for each process) were determined by calibrating the model to a dynamic non-equilibrium experiment carried out with CO2 on K-promoted HTlc and consisting of a single long duration adsorption and desorption cycle with a 700 min half cycle time that approached but did not attain equilibrium at the end of each step. The parameters that fitted this long duration cycle where then used to successfully predict the dynamic behavior of far shorter duration adsorption and desorption cycles carried out at 15, 30, 45, 60 and 75 min half cycle times. Numerous, more conventional approaches, such as non-isothermal diffusion models with multiple mass transfer mechanisms and even combined with a single reaction were explored but could not predict the dynamic behavior nearly as well as the kinetic model over both the long and short duration cycles. With the kinetic model capturing the adsorption and desorption kinetics of the fast mass transfer limited processes, with it reaching periodic behavior right after the first adsorption step, and with it showing independence between the working capacity of the sample and the activation time of the sample, it revealed for the first time that the adsorption and desorption behavior of CO2 on K-promoted HTlc is a associated with a combination of completely reversible adsorption, diffusion and reaction phenomena.