(73f) Effect of SO2 on CuMn2O4 Oxygen Carrier’s Reactivity for Chemical Looping with Oxygen Uncoupling (CLOU)

In the United States, roughly 1.8 million tons CO₂ per year is released from the electric power sector with coal being the largest CO₂ emission source¹. To stabilize the amount of CO₂ concentration in the atmosphere, carbon capture and storage (CCS) is being considered a promising technology where CO₂ is captured from large point sources like power plants and stored in suitable geological formations. Recently, among the various CCS technologies, chemical looping combustion (CLC) has gained positive interest because of its high CO₂ capture efficiency. A variant of CLC is chemical looping with oxygen uncoupling (CLOU) that is most suitable for solid fuel combustion. In CLOU, the fuel reacts with gas-phase oxygen released by the decomposition of a metal oxide (oxygen carrier) at suitable temperatures and oxygen partial pressures, unlike the CLC where the fuel reacts with the solid metal oxide to access the lattice oxygen. Since solid fuel oxidation with gas phase oxygen is kinetically favorable compared to oxidation on a solid metal oxide, CLOU is considered more effective than CLC for coal combustion. As an oxygen carrier CuMn₂O₄ has received much attention for the CLOU process because of its significant oxygen release capacity and high fuel conversion efficiency. However, the effect of impurities in coal, such as sulfur, on the reactivity of oxygen carriers is not well understood.

The purpose of this study is to investigate the effect of sulfur dioxide (SO₂) on CuMn₂O₄ particles’ oxygen release capacity and reactivity with CH₄. CuMn₂O₄ particles are tested in a batch fluidized bed reactor in a CH₄-SO₂-CO₂ (reducing gas) environment. The reduced particles are then oxidized in 5% O₂-balance N₂ mixture to regenerate. The oxygen carrier particles are exposed to the reducing gas mixture for various durations to determine the effect of SO₂ exposure time on CH₄ conversion and CO₂ yield. The outlet gas species, namely CO, CO₂, unreacted CH₄ and released O₂ are measured with a gas chromatograph (GC) equipped with a TCD detector. Additionally, SO₂ concentration is varied for a fixed reduction period to examine the effect of SO₂ concentration on CO₂ yield. The oxygen carrier particles before and after SO₂ exposure at various conditions are characterized by XRD, SEM-EDX and XPS to observe any possible sulfate phase formation or sulfur accumulation on the surface. Preliminary results have shown that addition of SO₂ has a slight negative effect on overall CH₄ conversion, which becomes more pronounced with increasing SO₂ exposure time.

1.U.S. Energy Information Administration (2016)