Solar syngas production from CO2 and H2O in a two-step thermochemical cycle via Zn/ZnO redox reactions: Thermodynamic cycle analysis

Solar syngas production from CO₂ and H₂O is considered in a two-step thermochemical cycle via Zn/ZnO redox reactions, encompassing: 1) the ZnO thermolysis to Zn and O₂ using concentrated solar radiation as the source of process heat, and 2) Zn reacting with mixtures of H₂O and CO₂ yielding high-quality syngas (mainly H₂ and CO) and ZnO; the ZnO is recycled to the first, solar step, resulting in net reaction βCO₂ + (1 − β)H₂O → βCO + (1 − β)H₂. Syngas is further processed to liquid hydrocarbon fuels via Fischer-Tropsch or other catalytic processes. Second-law thermodynamic analysis is applied to determine the cycle efficiencies attainable with and without heat recuperation for varying molar fractions of CO₂:H₂O and solar reactor temperatures in the range 1900-2300 K. Considered is the energy penalty of using Ar dilution in the solar step below 2235 K for shifting the equilibrium to favor Zn production.