(660e) Towards the Development of Clean Combustion Technology: Effects of Sulfur Pollutant on Performance of Bi-Metallic Oxygen Carrier in Chemical-Looping Combustion

We need clean fossil fuel combustion technologies to combat global warming and fulfill growing energy demand. Among the available technologies, one of the cost-effective ones is the chemical looping combustion (CLC) technology. It not only captures nearly 99.99% CO₂ but also has significant potential for other applications such as syngas production, biomass conversion, value-added chemical production, etc. The principle behind CLC is direct reduction-oxidation reactions between a fuel and an oxygen-carrying material rather than air. This material is a solid metal-oxide, either in its active form or supported on inert material. The metal oxide gets reduced by fuel to supply the oxygen required for combustion. The reduced metal oxide is then regenerated in the air to continue further reduction-oxidation cycles.

This technology is still in the research phase with many issues that need further investigation to determine its commercial applicability. One such question is how does sulfur contaminant affect the CLC process? The use of metal oxide complicates the behavior of sulfur pollutants as they can form sulfate or sulfide compounds. Consequently, various problems like low combustion efficiency, particle agglomeration, and chemical degradation can occur. My research goal is to provide an answer applying both experimental and computational chemistry methods.

To begin with, after performing a thorough literature survey, I designed and built a fluidized-bed reactor system from scratch and established a dry impregnation synthesis procedure to produce in-house bi-metallic Cu-Mn oxide batch of 60g/week. I demonstrated the chemical looping combustion of methane, achieving 99% combustion efficiency. To determine how SO₂ affects methane combustion efficiency, I designed and conducted experiments applying the design of experiment (DOE) principle. From the analysis and interpretation of the data, I determined that SO₂ presence lowers the combustion efficiency by about 20-30%. Furthermore, process factors like temperature, metal oxide's degree of reduction, and SO₂ concentration influence the extent of SO₂'s negative effect. From the detailed characterization of Cu-Mn particles via XRD, EDS, XPS, and TPR techniques, I ascertained SO₂ poisons the material by sulfate formation on the surface, thereby lowering the combustion efficiency.

An atomic perspective of SO₂ poisoning is necessary for rational modification of materials. Therefore, I am applying a computational chemistry method called density functional theory to model SO₂ interaction on Cu-Mn oxide surface. I have also employed this method in conjunction with ab initio thermodynamics to model SO₂ poisoning on CuO and achieved about 80% agreement between experimental & computational results.