The Performance in a Fixed Bed Reactor of Copper-Based Oxides on Titania as Oxygen Carriers for Chemical Looping Combustion of Methane

Chemical looping combustion (CLC) of methane has been proposed in the past decade as an efficient method for CO₂ capture without important cost penalties. The combustion is carried out in a two-step process using, in the first one, the lattice oxygen of a reducible inorganic oxide for methane combustion and, in the second one, air for further carrier regeneration. An additional advantage of the CLC is the improbable generation of thermal NO_x because the operating temperature used for carrier regeneration is relatively low. Copper-based oxygen carriers with different copper contents have been prepared by successive wet impregnations on porous titania, used as support, with an aqueous solution of copper nitrate. The prepared oxygen carriers have been subsequently studied in five-cycle reduction−regeneration tests in a fixed bed reactor at atmospheric pressure with the aim of carrier characterization, analysis of the components in the outlet gas, and the study of the effect of some of the main parameters influencing the problem, including copper content and operating temperature. A further 20-cycle performance test has also been carried out with the oxygen carrier with the highest copper loading. The study reveals that copper does not interact with titania as support, which remains unaltered as rutile along all the two steps involved in the process. However, it is redistributed on the support because the melting points of some of the involved copper phases are close to the operating temperature. Neither carbonaceous deposits on the carrier in the reduction step nor subsidiary chemical reactions, especially those involving CO formation, takes place. The copper-based oxygen carriers exhibited a good performance in 20-cycle tests in a fixed bed reactor showing high reactivity and no substantial decay in efficiency with the number of cycles.