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.
Bibliographical noteFunding Information:
The authors thank Dr. Adam Gladen at the University of Minnesota for the analysis of SEM images to determine fiber geometry and for the reported data on particle surface area and porosity. We gratefully acknowledge the financial support by the National Science Foundation through grant number EFRI-1038307 and through fellowships to Peter Krenzke and Jesse Fosheim from the Graduate Research Fellowship Program. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program. Additional financial support from the University of Minnesota was provided by a Doctoral Dissertation Fellowship to Peter Krenzke.
- Carbon monoxide