CO2 splitting in an aerosol flow reactor via the two-step Zn/ZnO solar thermochemical cycle

Using concentrated solar energy as the source of high-temperature process heat, a two-step CO2 splitting thermochemical cycle based on Zn/ZnO redox reactions is applied to produce renewable fuels. The solar thermochemical cycle consists of (1) the solar endothermic dissociation of ZnO to Zn and O2; (2) the non-solar exothermic reduction of CO2 with Zn to CO and ZnO; the latter is recycled to the 1st solar step. The second step of the cycle is experimentally investigated in a hot-wall quartz aerosol flow reactor, designed for quenching of Zn(g), formation of Zn nanoparticles, and in-situ oxidation with CO2. The effects of varying the reactants stoichiometry, reaction temperatures, and inlet flow temperatures for radial and annular flows were investigated. Chemical conversions of Zn to ZnO of up to 88% were obtained for a residence time of 3 s. For all of the experiments, the reactions primarily occurred heterogeneously on the reaction zone surfaces, outside the aerosol jet flow.