CO production from CO₂ and H₂ via the rWGS reaction by thermochemical redox cycling in interconnected fluidized beds

The reverse water gas shift (rWGS) reaction represents an attractive route for CO2 activation with H-2 to generate CO that can be used as an intermediate in the production of fuels and chemicals. Here, we investigate the implementation of the rWGS reaction via thermochemical redox cycling, in which the overall rWGS reaction is split up into two half reactions of reduction and oxidation of a metal/metal oxide solid material. This can be practically implemented by spatially separating the two half-reactions in a two-reactor circulating fluidized bed in which metal/metal oxide particles are continuously circulated between the two reactors and thus provide a net oxygen transport from one reactor to the other. In this context, we aim to answer the question whether it is more beneficial to exploit crystalline phase changes or oxygen non-stoichiometry in the material to transport oxygen, by process analysis based on thermodynamic data. We find that phase change materials offer a better potential process efficiency, however at the expense of an inflexible CO product purity. For all materials, a tradeoff exists between process efficiency and CO product purity, and we identify a number of promising phase change materials that populate this trade-off and appear suitable to produce a high enough CO concentration for industrial methanol synthesis without any further gas purification.