CHEMICAL LOOPING

Chemical-looping combustion: development of oxygen carrier materials and hydrogen production process

             Chemical-looping combustion (CL) relies on using separate reactors to conduct the reduction and oxidation reactions of metal oxides, to obtain products like hydrogen, carbon dioxide, and nitrogen from separate compartments, all while simultaneously recovering heat. A CL system consists of a reduction reactor and an oxidation reactor, within which the following chemical reactions occur:
 
(Reduction reactor) CmHn + (2m+1/2n) MO + heat → 2m M + H2O + CO2
(Oxidation reactor）M + 1/2 O2 → MO + heat
 
             In CL, lattice oxygen atoms within the metal oxide are used as the oxygen source. Low grade heat is used for the reduction reaction, while high grade heat is produced via the oxidation reaction. This results in an energy conversion system that can undergo both fuel combustion and heat recovery by coupling exothermic and endothermic reactions. Moreover, by introducing water vapor into the reduction reactor, hydrogen can also be produced. These versatile applications have led to CL gathering interest in recent years as a route towards environmentally friendly energy systems.
             Our lab is working on developing metal oxide particles that can exhibit high activity and high stability during continuous redox cycles, given that these parameters are critical in determining the efficiencies and lifetimes of CL systems. Alongside fundamental research on particle synthesis and characterization, we are also conducting CL reaction experiments using a fluidized bed. The synthesized carrier particles are fluidized within the reactor and evaluated under various conditions based on the outlet gas composition and kinetic analysis, to determine the reaction mechanisms and develop high efficiency systems.

 
             We are also working on hydrogen evolution via the thermal decomposition of methane, and on alternative carrier particles that would enable carbon dioxide utilization. We are investigating a system that performs both hydrogen evolution via methane decomposition, and carbon monoxide synthesis by reacting the carbon remaining on the particle surfaces after methane decomposition with carbon dioxide, in two separate reactors.
 

Relevant equipment
Chemical looping evaluation equipment

             In addition to developing carrier particles and evaluating their characteristics, we conduct chemical looping reaction experiments using a fluidized bed. 

Fluidized bed containing carrier particles

             Natural minerals like ilmenite (FeTiO₃) are commonly used as the metal oxide particles for CL. While natural minerals can be considered beneficial for their low cost, they demonstrate low reactivity due to their small surface areas. To artificially develop high performance particles, research efforts have been directed towards composite particles consisting of metal oxides particles and support particles. Below is a SEM image of an Al2O3 supported Fe2O3 artificial particle.