Solar syngas production from CO 2 and H 2O in a two-step thermochemical cycle via Zn/ZnO redox reactions: Thermodynamic cycle analysis

Abstract

Solar syngas production from CO 2 and H 2O is considered in a two-step thermochemical cycle via Zn/ZnO redox reactions, encompassing: 1) the ZnO thermolysis to Zn and O 2 using concentrated solar radiation as the source of process heat, and 2) Zn reacting with mixtures of H 2O and CO 2 yielding high-quality syngas (mainly H 2 and CO) and ZnO; the ZnO is recycled to the first, solar step, resulting in net reaction βCO 2 + (1 − β)H 2O → βCO + (1 − β)H 2. 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 CO 2:H 2O 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.