Characterization and performance in a multicycle test in a fixed-bed reactor of silica-supported copper oxide as oxygen carrier for chemical-looping combustion of methane

Abstract

Chemical-looping combustion of carbonaceous compounds is a proposed two-step process for complete CO2 capture and substantial reduction of NOx emissions. In the first stage, the reduction stage, the framework oxygen of a reducible inorganic oxide is used for the combustion of the carbonaceous material. In the second stage, the regeneration stage, the carrier in a reduced state is regenerated with air to recover the properties of the fresh carrier, ready to reinitiate a new cycle. This article provides results for the performance of a copper oxide silica-supported oxygen carrier in a 20-cycle test of chemical-looping of methane in a fixed-bed reactor at 800 °C and atmospheric pressure. The mesoporous nature of silica provided a good dispersion of the active phase imparting a high mechanical strength to the overall carrier. Additionally, silica is stable under highly reducing agents and inert in the two involved processes. The respective CH4, CO2, and CO breakthrough curves in the reduction stage show that the reduction reaction rate is fast and highly selective to CO2 formation. CO emissions are very low, only yielded at the end of the reduction stage, when the reduction stage should be stopped to initiate a regeneration stage. Characterization studies using different techniques, such as TPR, SEMEDX, and powder XRD, reveal that CuO might decompose into Cu2O at the operating conditions used in the reduction stage, but fortunately, the decomposition rate is so low that it has no effect on the oxygen amount initially available for chemical-looping combustion. Copper does not promote the thermal decomposition of methane, and deposited carbon, consequently, could not be detected in the reduced carrier. In a 20-cycle test neither performance decay nor mechanical degradation of the oxygen carrier has been observed.