Comportamento redox de transportadores de oxigênio do sistema Fe2O3/ZrO2 em ciclos térmicos para possível aplicação em CLC

Abstract

Chemical Looping Combustion (CLC) is a technique that has been utilized as an energetically efficient method for CO2 capture and storage by the combustion of gaseous fuels. This technique involves the use of an oxygen carrier that transfers the oxygen obtained from air to the fuel, without direct contact between them. The oxygen carrier is a metal oxide (in example of Fe, Cu, Mn, Ni or Co) that acts as an active phase and is generally supported by an inert phase (in example Al2O3, TiO2, ZrO2). Recent works on the literature indicate that the primary mechanism of charge mobility in a ceramic lattice, and consequently transport of oxygen, during combustion, is more related to ionic diffusivity on the material rather than intraparticle gaseous diffusion. Considering that it’s well known that stabilized zirconias have a high degree of oxygen vacancy, which leads to high charge mobility, and that there are very few studies in the literature about the Fe2O3/ZrO2 system with stabilized ZrO2, the present work aims to present the preparation of oxygen carriers in this system, their characterization and application in oxidation-reduction thermal cycles. The preparation of oxygen carriers was done using the incipient wetness impregnation method, with samples varying from 20%, 35% to 50%mol Fe, followed by high energy ball milling for zirconia stabilization. In some samples, almost all the iron was incorporated into the zirconia structure. The samples were analyzed using XRF, XRD, SEM-FEG, TGA and Mossbauer Spectroscopy. For the thermal cycles at 900ºC, synthetic air was used as oxidating gas, a mixture of 15%CH4/20%H2O/N2 was used as reducing gas and N2 as a flush gas between the oxidation-reduction steps. The results were satisfactory for use in CLC systems, with oxygen transport capacities reaching values as high as about 200%, indicating multiple reductions of the active phase.