High efficiency solar chemical-looping methane reforming with ceria in a fixed-bed reactor

High efficiency solar chemical-looping methane reforming is demonstrated in a prototype reactor operated in a high-flux solar simulator. The reactor includes six tube assemblies, which each comprise a fixed-bed of ceria particles and a gas-phase heat recuperator. The cycle was accomplished by alternating the flow to one tube assembly between CH₄ and CO₂. In the initial series of experiments, temperature, CH₄ concentration, reduction flow rate, and cycle duration were varied to minimize carbon accumulation and maximize efficiency. In the second set of tests, the reactor was operated at optimized conditions for ten cycles at 1228 and 1274 K. Higher temperature favors better performance. At 1274 K, CH₄ conversion is 0.36, H₂ selectivity is 0.90, CO selectivity is 0.82, CO₂ conversion is 0.69, and the energetic upgrade factor is 1.10. Heat recovery effectiveness is over 95%. Solar-to-fuel efficiency is 7% and the thermal efficiency is 25%. Projected solar-to-fuel and thermal efficiencies are 31 and 67% for the full-scale reactor and 56 and 85% for a commercial reactor with lower thermal losses. The demonstrated efficiencies are the highest reported to-date for this process. The projected scaled-up efficiencies suggest solar chemical-looping methane reforming could be a competitive approach for production of solar fuels.