SOLAR SYNGAS PRODUCTION FROM H_2O AND CO_2 VIA TWO STEP THERMOCHEMICAL CYCLES BASED ON FeO/Fe_3O_4 REDOX REACTIONS: KINETIC ANALYSIS

摘要

Syngas production via a two-step H_2O/CO_2-splitting thermochemical cycle based on FeO/Fe_3O_4 redox reactions is considered using highly concentrated solar process heat. The closed cycle consists of: 1) the solar-driven endothermic dissociation of Fe_3O_4 to FeO; 2) the non-solar exothermic simultaneous reduction of CO_2 and H_2O with FeO to CO and H_2 and the initial metal oxide; the latter is recycled to the first step. The second step was experimentally investigated by thermogravimetry for reactions with FeO in the range 973 -1273 K and CO_2/H_2O concentrations of 15-75%. The reaction mechanism was characterized by an initial fast interface-controlled regime followed by a slower diffusion-controlled regime. A rate law of Langmuir-Hinshelwood type was formulated to describe the competitiveness of the reaction based on atomic oxygen exchange on active sites, and the corresponding Arrhenius kinetic parameters were determined by applying a shrinking core model.