Perovskite oxygen carrier with chemical memory under reversible chemical looping conditions with and without SO2 during reduction

Abstract

Oxygen carrier materials (OCM) are usually exposed to sulfur-contained gases in the fuel reactor for chemical looping combustion. This work provides both experimental and model work to understand the SO2 effect on the heterogeneous redox kinetics of a CaMn0.375Ti0.5Fe0.125O3-δ-based perovskite oxygen carrier. The cycle reactivity and redox kinetics under reducing conditions were conducted with and without SO2 in a micro-fluidized bed thermogravimetric analysis technology (MFB-TGA). The redox kinetic behaviors were simulated by a bubbling fluidized bed reactor model coupled with a two-stage kinetic model. The SO2 can react with the perovskite to increase the oxygen transfer capacity from 4 wt% to 5 wt%. When the temperature is higher than 1173 K, SO2 has almost no effect on the H2 reduction reactivity, while the oxidation reactivity decreases by 50%, but the oxidation is still fast enough to achieve 4 wt% capacity within 8 s. When the temperature is lower than 1173 K, there is a significant sulfur-poisoning effect during oxidation and reduction. The analyses of XRD, SEM-EDS, and in-situ DRIFTS indicated that most of the absorbed sulfur mainly existed in the sulfate/sulfide shell on the particle surface. The chemical kinetics and physical structure of CaMn0.375Ti0.5Fe0.125O3-δ perovskite can be completely recovered in the absence of SO2, and this perovskite oxygen carrier is chemically memorable and reversible in its solid structure. The fundamental understanding of the sulfur effect on the redox kinetics and solid structure of the perovskite oxygen carrier provides a new insight to the material development and corresponding reaction mechanisms.