Isotherms and thermodynamics of CO2 adsorption on a novel carbon-magnetite composite sorbent

In this work, CO2 adsorption on a novel composite material, CB-FM, obtained coating a low-cost carbon black (CB) with magnetite fine particles (FM), has been character- ized from the thermodynamic point of view. In particular, the mechanism (isotherm), nature/strength (thermodynamics) of CO2 adsorption has been investigated by performing dynamic breakthrough experiments in a lab-scale fixed bed reactor. The effect of both tem- perature (18-150 oC) and CO2 partial pressure (0.5-20% vol.) has been investigated. Then, five adsorption models, i.e. Langmuir, Freundlich, Sips, Toth and Dubinin-Radushkevich (D-R) isotherms, were applied to evaluate the feasibility of adsorbate-adsorbent interaction and to describe the CO2 adsorption isotherm in the low pressure region typical of a combustion flue gas. Besides that, the most important thermodynamic properties, i.e. the standard Gibbs free energy, standard enthalpy change and entropy change and isosteric heat of adsorption as a function of surface coverage, were evaluated using van't Hoff and Clausius-Clapeyron equations.