A Systematic Hierarchical Thermodynamic Analysis of Hydrogen Producing Iron-Chlorine Reaction Clusters

Here, we apply our systematic methodology for thermochemical cycle evaluation to the well-studied Fe-Cl system. Using an integer linear program, thermochemical cycles are identified from species consisting of Fe, Cl, H, and O atoms and a corresponding nonlinear (in temperature) thermodynamic database. Using Aspen Plus simulation software and heat pinch analysis, maximum attainable cycle efficiencies of up to 51% are calculated, exceeding our base-level target of 35%. The most promising of these cycles is evaluated in more detail considering thermodynamic yields. A higher-level evaluation results in a significant reduction in cycle efficiency due to increased thermal requirements resulting from low-yield reactions and competing by-products. Results of this higher-level analysis and the base-level analysis are consistent with literature findings on Fe-Cl thermochemical cycles.