The chemical CO₂ capture by carbonation-decarbonation cycles

The abatement of CO₂ emitted from combustion is a hot research topic. Current CO₂ capture techniques of adsorption, absorption, membrane separation and cryogenics involve high investment and operation costs. For moderate and high temperature exhaust gas, carbonation/decarbonation cycles offer an attractive alternative. An objective assessment method (screening index) was applied to select the most appropriate chemical reactions, with MgO and Mg(OH)₂ being screened as having the highest potential. Macro-thermogravimetric experiments determined a CO₂ capture yield between 60 and 70% for Mg(OH)₂ at temperatures between 260 and 330 °C, and from 85 to 98% for MgO at temperatures of 400-440 °C. Reaction rates were measured for both MgO-CO₂ and Mg(OH)₂-CO₂. The reaction kinetics are best fitted by the Jander 3D-diffusion approach. The Arrhenius equation is applied to the reaction rate constant, and both its activation energy and pre-exponential factor are determined. Integrating the Jander expression in the reaction rate equation enables to predict the CO₂-capture conversion for any selected temperature and/or contact time.