The chemical CO_2 capture by carbonation-decarbonation cycles

摘要

The abatement of CO_2 emitted from combustion is a hot research topic. Current CO_2 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 CO_2 capture yield between 60 and 70% for Mg(OH)_2 at temperatures between 260 and 330 ℃, and from 85 to 98% for MgO at temperatures of 400-440 ℃. Reaction rates were measured for both MgO-CO_2 and Mg(OH)_2-CO_2- 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 CO_2-capture conversion for any selected temperature and/or contact time.