Upgrading CO2 with methane

The use of carbon dioxide as a reactant could help to mitigate its impact on climate, but it is difficult to activate as an oxidant. Buelens et al. combined methane in a high-temperature “super-dry” reforming process that generates reactive carbon monoxide. Both molecules were fed into a reactor containing a nickel methane-reforming catalyst, an iron oxide solid oxygen carrier, and calcium oxide as a CO₂ sorbent. The adsorbed CO₂ was treated with an inert gas purge that shifted the equilibrium, releasing mainly CO. This isothermal process avoids carbon buildup and can be used with biogas methane that contains substantial levels of CO₂.

Abstract

Efficient CO₂ transformation from a waste product to a carbon source for chemicals and fuels will require reaction conditions that effect its reduction. We developed a “super-dry” CH₄ reforming reaction for enhanced CO production from CH₄ and CO₂. We used Ni/MgAl₂O₄ as a CH₄-reforming catalyst, Fe₂O₃/MgAl₂O₄ as a solid oxygen carrier, and CaO/Al₃O₂ as a CO₂ sorbent. The isothermal coupling of these three different processes resulted in higher CO production as compared with that of conventional dry reforming, by avoiding back reactions with water. The reduction of iron oxide was intensified through CH₄ conversion to syngas over Ni and CO₂ extraction and storage as CaCO₃. CO₂ is then used for iron reoxidation and CO production, exploiting equilibrium shifts effected with inert gas sweeping (Le Chatelier’s principle). Super-dry reforming uses up to three CO₂ molecules per CH₄ and offers a high CO space-time yield of 7.5 millimole CO per second per kilogram of iron at 1023 kelvin.

Science 28 Oct 2016:
Vol. 354, Issue 6311, pp. 449-452
DOI: 10.1126/science.aah7161

http://science.sciencemag.org/content/354/6311/449