Phase-Changing Absorbents for CO2 Capture

A process to capture CO₂ from flue gas using a liquid material that reacts rapidly with CO₂ to form a solid offers many advantages over conventional liquid-only CO₂ capture methods. The net CO₂ capacity of the system will be increased, the overall system size will be decreased, and the energy required for desorption will be decreased due to the absence of a co-solvent. However, this process also poses significant process design challenges. The material needs to form a solid in the presence of all components of the flue gas, including water. A method for transporting the solids into a pressurized desorber needs to be developed, and the properties of the particles formed in the absorption unit needs to be optimized for maximum absorption and maximum capture of solids from the gas stream as well as for the method of solids transport selected and for the heat transfer into the solids during desorption. Several materials have been developed and have been demonstrated to rapidly form a powdery solid upon reaction with CO₂ in a laboratory-scale spray dryer under various conditions. The physical properties of these materials including the heat of absorption of CO₂, vapor pressure, CO₂ absorption and desorption isotherms, heat capacity, and viscosity have been measured and are used in a process model to predict the impact of this process on the cost of electricity. The design of the process, the materials developed, and the impact on cost of electricity will be discussed.