Utilization of fuel synthesis by-products as reducing agents in solar thermochemical syngas production

Solar thermochemical redox cycles followed by a synthesis process are a potentially carbon-neutral way to produce versatile carbonaceous products. The required high temperature of the redox cycle, however is correlated to high heat losses and limits the process efficiency. Use of natural gas as a reductant can lower the temperature, but this approach depends on a fossil carbon source and is not carbon neutral. We propose a novel concept in which short chained hydrocarbons, which are a by-product of the synthesis process are recycled and used as a reductant in the solar redox cycle. In the present study we investigate the use of C 1 –C 4 alkanes, which are by-products of high or low temperature Fischer-Tropsch synthesis as reductants in a ceria-based redox cycle. Thermodynamic simulation results imply that both higher degrees of reduction and lower reduction temperatures are feasible and that the energy demand for the reduction step can be decreased by 61% or 24% for high or low temperature Fischer-Tropsch synthesis, respectively. • A two-step solar ceria redox cycle coupled to Fischer-Tropsch synthesis is investigated. • Gaseous by-products from Fischer-Tropsch synthesis are recycled and used as reductant in the redox cycle. • Using the reductant, part of the ceria can be reduced at energetically beneficial conditions. • Recycling allows downscaling of the redox cycle. • Energy savings in the reduction and product quality are evaluated.