Electrochemical Redox Flow Devices for the Electrically Driven Scrubbing of Acid Gases

The concept, thermodynamic analysis, and preliminary experimental results are presented for an electrochemical redox flow system capable of scrubbing acid gases from either dilute streams (such as air) to more concentrated industrial flue gases.  The ability to electrically scrub acid gas offers significant advantages over existing thermal and pressure swing techniques.  Thermal scrubbing is an ineffective strategy when not coupled with a Rankine cycle due to the narrow temperature range and resulting poor Carnot efficiency.  Pressure swing systems, in contrast, are able to operate through electrical energy, but suffer from the inability to separate gas sorbates from dilute streams due to the weak binding enthalpies inherent to physical sorption processes.

An electrochemical scrubbing process offers the possibility of a truly “drop-in” solution for powerplants that requires no reconfiguration of their internal turbine systems.  Additionally, electrochemical scrubbers can be installed anywhere with access to electricity in order to supply new markets for CO₂ such as photosynthetic biofuels or electrofuels that will have large CO₂ demands but may not want to be located near an existing powerplant.

The system consists of an electrochemical flow cell (which closely resembles a redox flow battery) in tandem with a traditional gas absorber unit. A theoretical framework for evaluating redox-responsive sorbents for redox flow separations based on their kinetic and thermodynamic properties is presented.  Experimental results of the sorbents have been analyzed with this framework to demonstrate the feasibility of the electrochemical redox flow scrubbing process.