Synthesis gas production via the solar partial oxidation of methane-ceria redox cycle: Conversion, selectivity, and efficiency

• The solar partial oxidation of methane-ceria redox cycle is evaluated.
• A first-law analysis is formulated in terms of conversions and selectivities.
• Experiments identify conditions enabling high conversion and selectivity.
• Methane conversion reaches 60% and oxidizer conversion reaches 93%.
• Projected efficiencies reach 27% for measured performance.

The importance of methane conversion, syngas selectivity, and oxidizer conversion for efficient syngas production by the partial oxidation of methane using a metal oxide redox cycle is quantified. The operating conditions which enable high conversion of methane to syngas over cerium oxide and conversion of carbon dioxide to carbon monoxide in the subsequent oxidation reaction are identified experimentally. The parametric study considers operating temperatures of 900 and 1000 °C and methane flow rates from 1 to 15 mL min−1 g−1 in a fixed bed of porous ceria particles. The reduced ceria is reoxidized in a flow of 10 mL min−1 g−1 CO2 to produce CO. A trade-off of achieving high methane conversion is observed. For example, at 1000 °C, the cycle-averaged methane conversion increases from 13% for reduction in 15 mL min−1 g−1 to 60% in 1 mL min−1 g−1. For the same change in methane flow rate, the cycle-averaged selectivities decrease from 78% to 39% (CO) and 77% to 40% (H2) and the oxidizer conversion decreases from 93% to 48%. The maximum projected solar-to-fuel thermal efficiency is 27% for cycling at 1000 °C with reduction in 5 mL min−1 g−1 methane.