(116d) The Reaction Mechanism and Kinetics of Magnesium Oxide for CO2 Immobilization

The CO₂ immobilization is significant for the sustainable energy and chemistry industries. And the magnesium oxide is a clean and economic agent using for the CO₂ immobilization. Therefore, the reaction of CO₂ with magnesium oxide suspended in water was investigated, the mechanism proposed, and the kinetics regressed as well. The CO₂ pressures from 1 to 5 (MPa), as well as ratios of solid to liquid, stirring speeds and temperatures, significantly influenced the dissolution of magnesium oxide. And as high as 26.63 g/L MgO was dissolved in the solution under the condition of CO₂ pressure 5 MPa at 50 °C.

In the process, the magnesium oxide became magnesium hydroxide through hydration reaction, and then the hydroxide dissolved by carbonated water. In the carried out reaction of CO₂ with magnesium hydroxide suspension, no solid product was found covering the solid Mg(OH)₂. Therefore, a reaction mechanism based on the hydration of Mg²⁺ was proposed, where the concept of ‘progressive liquid film’ was introduced to the reaction system. And the derived kinetic model for the dissolution was fitted the experiment data well. The pressurized magnesium hydroxide dissolution was found to be rate-controlled by the diffusion in the progressive liquid film around the solid material. The apparent activation energy, obtained from 17.1 to 25.4 (kJ/mol) in the experiments, indicated also that the dissolution inclined to be diffusion rate controlled. Moreover, the apparent diffusion coefficients of H⁺ in the liquid film were calculated and an empirical expression was obtained for the first time. The kinetic model might be applicable to other dissolution reactions similarly with just soluble product.