Chemical looping processes - particle characterization, ionic diffusion-reaction mechanism and reactor engineering

The chemical looping strategy for fossil energy applications promises to achieve an efficient energy conversion system for electricity, liquid fuels, hydrogen, and/or chemical generation while economically separating CO2 by looping reaction design in the process. Two types of chemical looping technologies have been developed based on two different reactions of chemical looping intermediates. Type I chemical looping systems utilize metal and metal oxide reduction-oxidation properties to perform the looping reactions. Type II chemical looping systems utilize metal oxide and metal carbonate carbonation-calcination properties to perform the looping reactions. The type of metal or metal oxide along with their preparation methods for applications in both types of chemical looping systems plays significant roles in the chemical looping technology performance. Understanding the reaction mechanism associated with looping intermediates in both types of reactions is important to the rate process of reactions, in turn affecting the design of the looping particles. Furthermore, as conversions of gaseous and solid reactants are closely associated with their contact modes, the intricate contact mode plays an important role in determining the reactant conversions and hence the solid reactant flux in the reactors. The purpose of this paper is thus to provide a perspective on the two key aspects of chemical looping technology, which are not well reported in the literature, namely, reaction mechanism and reactor engineering.