(300c) Solar Syngas Production from H2o and CO2 Applicable for Methanol or Fischer-Tropsch Synthesis

We report on the experimental demonstration of the solar production of syngas – a specific mixture of CO and H₂ − from CO₂ and H₂O using a modular solar concentrator-reactor system. This system delivers concentrated solar process heat to drive the simultaneous co-splitting of CO₂ and H₂O via a ceria-based thermochemical redox cycle. We present representative on-sun runs with fully-automated consecutive redox cycles and show experimental parameter analysis for control strategies optimising syngas quality, yield, efficiency and conversion. We further present a dynamic grey-box model of the system that allows additional insights to the system’s performance.

The solar reactor for effecting this redox cycle consists of a cavity-receiver containing a reticulated porous ceramic (RPC) foam structure made of pure CeO₂. Two identical solar reactors are mounted side-by-side on the focus of a solar dish concentrator that enables the operation of both solar reactors simultaneously by alternating the solar radiative input between them. Thus, while one solar reactor is performing the endothermic reduction step on sun, the second solar reactor is performing the exothermic oxidation step off sun. During the reduction step, the solar reactor is heated with concentrated sunlight up to 1500 °C and the total pressure is lowered to 4 mbar by a vacuum pump to evolve a pure stream of O₂ from CeO₂. During the oxidation step, CO₂ and H₂O are co-injected into the reactor’s cavity, react with the reduced ceria, and are transformed into syngas - a specific desired mixture of CO and H₂.

The syngas composition can be tailored by changing H₂O:CO₂ feed ratios as well as choosing adequate oxidation start/end conditions to meet the desired quality and stoichiometry suitable for Fischer-Tropsch or methanol synthesis. Thus, the need for additional downstream refining of the syngas, e.g. via the energy intensive reverse water-gas shift reaction, is eliminated.

The entire system is controlled to perform fully automated consecutive redox cycles while continuously updating cycle parameters based on real time analysis and feedback loops. Changing process parameters such as reduction/oxidation temperatures, gas flow rates, or oxidation start/end conditions allows optimising the cycles towards maximising either efficiency, quality, yield or conversion. Full day on-sun consecutive cycles demonstrate the stability and robustness of the system.

A dynamic model of the reactor system allows further parameter analysis and offers additional insight to the system performance. The grey-box model is based on energy and mass balances and is using a lumped-parameter approach where parameter identification and validation is achieved through comparing numerically simulated results to experimental data collected over multiple characteristic cycles.