CO2 adsorption on a fine activated carbon in a sound assisted fluidized bed: Thermodynamics and kinetics

Abstract

Combustion of fossil fuels is one of the major sources of CO2, it is therefore necessary to develop technologies that will allow to utilize fossil fuels while reducing CO2 emissions to the atmosphere. Removal of CO2 from flue gases has become an effective way to mitigate CO2 emissions and adsorption is considered to be one of the methods. In particular, adsorption on fine and ultra-fine sorbents in a sound assisted fluidized bed has been proved to be a promising alternative, being able to maximize CO2 adsorption capacity and kinetics. However, before the design of an adsorption equipment, investigation of equilibrium and kinetics plays a decisive role.In this work, the previous research was furthered into the investigation of the mechanism (isotherm), nature/strength (thermodynamics) and rate (kinetics) of CO2 adsorption on a commercial activated carbon in a sound assisted fluidized bed. Langmuir and Freundlich equations were used to model the CO2 adsorption isotherm in the low pressure region (i.e. typical of a combustion flue gas). The results revealed that Freundlich equation was more accurate for predicting the adsorbed amount than the Langmuir one, which indicates a heterogeneous surface binding. Then, adsorption behavior was elucidated by energy function such as standard Gibbs free energy, enthalpy and entropy, suggesting the spontaneity and feasibility of adsorption of CO2 by activated carbon, and its exothermic and physical nature. The isosteric heat of adsorption was also evaluated; its decrease with surface loading further indicated the heterogeneity of adsorption sites and also variation in adsorbate–adsorbent interactions. Finally, this study also presented a kinetic analysis of CO2 adsorption, from which CO2 binding on activated carbon was deduced to follow pseudo-first order kinetic.