(380r) Multiscale Modeling of Group D Iron Oxide Particles in Chemical Looping Systems: From Atomisitc Scale to Continuum Scale

Chemical looping (CL) technology, which utilizes solid oxygen carriers to enable full or partial oxidation of fossil fuel, is one of the most promising CO₂ capture platform in the field of clean energy due to its capability in simplified inherent CO₂ capture and value-added chemical production. Process modeling with Aspen Plus has been conducted on a specific coal-based CL power production process. The results show a better energy and exergy efficiency of CL process compared to conventional power production process with CO₂ capture. Reactivity of oxygen carriers is crucial for CL processes. In the CL technology developed at The Ohio State University (OSU), iron oxide is employed as the active oxygen carriers due to their abundance and low cost. In addition to process simulations that are based on thermodynamics, kinetics modeling for the gas-solid reaction of iron oxide with hydrogen (H₂), carbon monoxide (CO), methane (CH₄) and oxygen (O₂) in both atomistic and continuum scales were developed. In the atomistic scale, Ab initio density functional theory (DFT) simulations were employed to unravel the reaction pathways of CO and CH₄ oxidation with Fe₂O₃. The first-principles simulations provide a detailed insight of the reaction mechanisms and the rate-limiting steps (RLS), and hence the rational for material modifications. Results from DFT simulations were further validated by temperature programmed reduction experiments (TPR). Copper was identified as the most efficient dopant among 1^st-row transition metals as it loweres the reduction initiation temperature with CO and CH₄ by 50 and 150 °C, respectively. In continuum scale, the development of kinetics model is essential for the optimum design of operating conditions and reactor configurations. In this work, reduction/oxidation kinetics models that can tackle multi-step reactions (i.e., Fe³⁺->Fe²⁺->Fe) without presuming any rate-controlled mechanism for the gas-solid reactions of group D iron-titanium composite particles were established. The obtained kinetics models were verified in a thermogravimetric analyzer (TGA) under common operating temperatures and gas compositions in CL processes. The proposed models and insights gained from the simulations under different scales could be valuable in the development of future CL technology.