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

Abstract In this work, CO 2 adsorption on a novel composite material, CB-FM, obtained coating a low-cost carbon black (CB) with magnetite fine particles (FM), has been characterized from the thermodynamic point of view. In particular, the mechanism (isotherm), nature/strength (thermodynamics) of CO 2 adsorption has been investigated by performing dynamic breakthrough experiments in a lab-scale fixed bed reactor. The effect of both temperature (18–150 °C) and CO 2 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 CO 2 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.