CO2 capturing methods: Chemical looping combustion (CLC) as a promising technique.

This reports recent advances on CO2 capturing methods, focusing on chemical looping combustion (CLC) as a promising technology to achieve this goal. Generally, there are three main methods to capture CO2 resulting from fossil fuel combustion: post-combustion, oxy-combustion, and pre-combustion. In CLC, which is either classified as a pre-combustion method or as the fourth capturing method, the solid oxygen carrier provides the oxygen needed for combustion. This technique helps to avoid diluting the combustion effluent stream with the N2 released from air and therefore, minimizes the requirement of CO2 separation, a major cost of CO2 capture. In addition, it minimizes the formation of NOx that results when N2 comes in contact with oxygen and fuels at high temperatures. The desired properties of oxygen carrier candidates for CLC are high reduction and re-oxidation rates, high oxygen capacity, good stability and fludiziability at high temperatures, friendly to the environment, and low cost. Transition metal oxides are common candidates for CLC. Most investigations in this field have examined the reactivity and stability of oxygen carriers but few investigations have focused on their reduction and re-oxidation reaction mechanisms. Researchers have proposed two mechanisms for these reactions, the nucleation-nuclei growth and unreacted shrinking core models. Despite numerous investigations of CLC, there is still a lack of knowledge in some of its aspects such as the underlying surface chemistry and the economic impact. This work critically reviewed all capturing methods of CO2 with focusing on CLC process as a promising technology due to its ability to concentrate the resulted CO2 and minimizes the separation cost. This work provides essential insight information into CLC technology and highlights its status and needs.