Intensification of the reverse water–gas shift process using a countercurrent chemical looping regenerative reactor

Abstract

Chemical reactions have thermodynamic limits on species conversion which can negatively impact process design. Unconverted feedstock often needs to be separated and recycled, increasing energy demand, process complexity and cost. Just as is the case for heat exchangers, countercurrent reactor systems can improve the thermodynamic limits on species exchange and conversion. This work describes and demonstrates a countercurrent redox reactor system, which can be realised in a packed-bed chemical-looping reactor by storing the favourable oxygen chemical potential inclines using the unique properties of non-stoichiometric oxides. The concept is analogous to a regenerative heat exchanger, but for oxygen exchange and storage, and so we use the term regenerative reactor. We apply this approach to the reverse water–gas shift reaction, which is a critical step in the processing of synthetic e-fuels. The concept is modelled and experimentally validated via a lab-scale demonstration performed with CeO2 at 1073 K, which resulted in a CO2-to-CO molar conversion of 88 %, compared to a thermodynamic limit of 58 % for the conventional process at the same conditions. The modelling results indicate that the ideal thermodynamic conversion can be approximately doubled via this method. Furthermore, the CO is formed separately from the H2 flow, allowing for the syngas composition to be finely tuned for downstream processing.