Initial case for splitting carbon dioxide to carbon monoxide and oxygen.

Abstract

The United States presently imports almost ⅔ of the more than 20 million barrels of petroleum that it consumes daily. The largest fraction of this consumption, again about ⅔, is for transportation. Unfortunately, much of the non-domestic oil extraction, which we both directly and indirectly rely on, is from fields in unstable parts of the world. The national security and economic implications of our dependence upon foreign oil as well as the dangers of climate change resulting from green house gas emissions prompts a search for alternative sources of liquid fuels. Independence from problematic oil producers can be achieved to a great degree by applying decades-old synfuel technologies to convert non-conventional resources such as coal, oil-shale and tar-sands into liquid fuels. Unfortunately tapping into and converting these resources into liquid fuels only exacerbates green house gas emissions as they are carbon rich, but hydrogen deficient. Additionally, deploying these technologies requires large investments in time and capital.The "hydrogen economy" is a newer alternative, but it poses significant infrastructure and technological challenges. However, if we adopt revolutionary thinking about energy and fuels, it may be possible to the meet the future fuel challenges while maintaining our traditional hydrocarbon fuel framework. We must recognize that hydrocarbon fuels are energy carriers, not energy sources. The energy stored in a hydrocarbon is released for utilization by oxidation to form CO 2 and H 2 O. Furthermore, just as H 2 O can be "reenergized" by applying energy to split water back into H 2 and O 2 , hydrocarbons can be recycled by capturing CO 2 (and H 2 O) and "re-energizing" them back into hydrocarbon form. That is, there is a hydrocarbon analogy to the envisioned hydrogen economy that realizes the benefits of hydrogen while capitalizing on much of the existing liquid fuel infrastructure. Of course, the only credible pathway for implementing this vision is through the application of persistent energy sources (e.g. solar or nuclear). In this document, the concept of applying high temperature thermochemical cycles to split CO 2 into CO and O 2 as a starting point for synthetic fuel production is introduced and potential advantages of this approach are discussed. 4 5

A review on solar thermal syngas production via redox pair-based water/carbon dioxide splitting thermochemical cycles

“…Above 1200 K ceria was found to react more efficiently with H 2 O and CO 2 as the dopant concentration is increased. Results from studies of SNL addressing comparatively the thermodynamics of the WS and CDS processes considering CeO 2 as a redox material [18] indicated that at any temperature below $ 1800 K, reduction of CO 2 to CO by Ce 2 O 3 -the reduced form of CeO 2 according to reaction (7) -is thermodynamically favored. Furthermore, at temperatures greater than 1100 K, CO 2 reduction is more favored than H 2 O reduction.…”

“…Such chemical reactions are natural gas steam reforming [12][13][14], gasification of solid carbonaceous materials like coal or biomass [15][16][17], or Water Splitting (WS) to hydrogen and oxygen. This last reaction can then be followed either by reaction of H 2 with CO 2 via the Reverse WaterGas Shift (RWGS) reaction or by reaction of H 2 with CO coming from Carbon Dioxide Splitting (CDS) to CO and O 2 , to produce syngas [18,19]. In addition, CSP systems can be employed alternatively to photovoltaics for syngas synthesis indirectly, e.g.…”

Hydrogen production via thermochemical water splitting

“…Results from studies of Sandia National Laboratories in the United States that compared the thermodynamics of the WS and CDS processes and considered CeO 2 to be a redox material (Miller, 2007) indicated that at any temperature below about 1800 K, reduction of CO 2 to CO by Ce 2 O 3 (the reduced form of CeO 2 according to reaction (11.7)) is thermodynamically favored, and furthermore, at temperatures greater than 1100 K, CO 2 reduction is more favored than H 2 O reduction. Similar efforts were extended to ferrites (Miller et al, 2009).…”

Summary report : direct approaches for recycling carbon dioxide into synthetic fuel.

“…Specifically the project focused on the creation of a direct and efficient CO 2 splitting (2CO 2 → 2CO + O 2 ) process that can be efficiently driven by nuclear or solar sources of thermal energy. Part of our rationale for CO 2 splitting (CDS) being a foundation for synfuel production has been outlined in an earlier report arising from this project [20]. [21].…”

“…This aspect of the project was not continued into the second year for several reasons. First, water splitting is more thermodynamically favorable than CDS at temperatures below about 800 °C [20]. Second, basic thermodynamic considerations indicate that the thermochemical approach to this chemistry may well require ultra-high temperatures if the cycle is to be limited to two steps involving metal oxides [62].…”