(717c) Performance of Bi-Metallic Cu-Mn Oxygen Carrier for Chemical Looping Combustion with Oxygen Uncoupling in Presence of so2

Chemical looping with oxygen uncoupling (CLOU) is a variant of chemical looping combustion (CLC), which is one of the promising carbon capture and storage technologies. In CLOU, the fuel reacts with gaseous O₂ released by a metal oxide (oxygen carrier) at suitable temperatures and oxygen partial pressures, unlike the CLC, where only the lattice oxygen reacts with the fuel. The kinetically favored gas-solid reaction makes CLOU more effective than CLC for solid fuels like coal and biomass. As a CLOU oxygen carrier, bi-metallic Cu-Mn has demonstrated high fuel combustion efficiency for both solid and gaseous fuels. However, there has been no study to show how fuel sulfur or its combustion product SO₂ affects its performance.

The purpose of this study is to investigate how SO₂ affects the performance of a bi-metallic Cu-Mn oxide with CH₄. The oxygen carrier was reduced via CH₄-N₂ gas mixture with and without SO₂. A parametric study was conducted with various SO₂ concentrations (1000, 3000, 5000 ppm), temperatures (850, 900, and 950°C) and reducing gas compositions (3, 6, and 9% CH₄). The results indicate that increasing the SO₂ concentration beyond 1000 ppm adversely affects CH₄ conversion. Presence of SO₂ reduces CO₂ conversion while increasing CO and unreacted CH₄ fraction in the flue gas. However, the drop in CH₄ reactivity is minimized as temperature increases. When CH₄ composition is reduced to 3%, effect of SO₂ on CH₄ conversion is small. To determine the possibility of sulfur compounds formation, the particles were characterized via XRD and XPS before and after SO₂ exposure. XRD analysis of the particles exposed to 5000 ppm SO₂ shows no sulfate or sulfide crystal structures, while the XPS analysis reveals the SO₄^2- presence. Formation of SO₄^2- on the oxygen carrier surface might be contributing to the decreased reactivity of CH₄ with the oxygen carrier.