Thermochemical conversion of H2O and CO2 into solar fuels via metal oxide based redox reaction

Abstract

This paper reports the thermodynamic analysis of the production of solar syngas (a mixture of H2 and CO with molar ratio equal to 2: 1) via ZnO/Zn based thermochemical H2O and/or CO2 splitting redox reactions. Solar syngas production from CO2 and H2O that 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 and ZnO. The ZnO is recycled to the first, solar step. Syngas is further processed to liquid hydrocarbon fuels via FischereTropsch or other catalytic processes. Second-law thermodynamic analysis is applied to determine the cycle efficiencies attainable with and without heat recuperation for varying the thermal reduction temperature (TR) in the range 1700-1950 K. Furthermore, the effect of various TR on molar flow rate of inert Ar has been presented. Considered is the energy penalty of using Ar dilution in the solar step below 2235 K for shifting the equilibrium to favor Zn production. Thermodynamic analysis has been performed and the analysis shows that solar syngas production via the Zinc Oxide redox cycle is a promising approach for CO2/H2O conversion into alternative fuels.