Kinetics of component reactions in calcium looping appeared during the multistep thermal decomposition of Portland cement under various atmospheric conditions

Calcium looping (CaL) reactions in a Ca(OH)2-CaCO3-CaO system for energy storage and CO2 absorption occur during the thermal decomposition of cement and concrete materials. Herein, we report the kinetic behavior of the reactions in a cement matrix as the necessary information for establishing a CaL cycle supported by cement/concrete materials. The thermal decomposition of Portland cement samples, characterized by different Ca(OH)2/CaCO3 ratios, under different atmospheric water vapor and CO2 conditions were investigated to reveal the kinetic behavior of the component reactions and the changes with atmospheric conditions. The multistep thermal decomposition, characteristic of each sample and atmospheric condition, were separated into individual reaction steps through a kinetic deconvolution analysis. Using the extracted kinetic curves for the reactions of Ca(OH)2 and CaCO3, retardation effects of atmospheric water vapor and CO2 on the thermal decompositions of Ca(OH)2 and CaCO3, respectively, were kinetically described by introducing different accommodation functions (AF) comprised of the partial pressures of the gases and their equilibrium pressure. In addition, the kinetic description of the catalytic effect of water vapor on the thermal decomposition of CaCO3 was achieved by introducing alternative AF of water vapor pressure. The thermally induced carbonation of Ca(OH)2, which occurred in the presence of atmospheric CO2, was characterized kinetically as physico-geometrically regulated consecutive reactions of thermal decomposition of Ca(OH)2 and subsequent carbonation of the as-produced CaO. Kinetic information concerning the reactions of Ca(OH)2 and CaCO3 in the cement materials is reported in details.