Post-plasma quenching to improve conversion and energy efficiency in a CO2 microwave plasma

Transforming CO2 into value-added chemicals is crucial to realizing a carbon-neutral economy, and plasmabased conversion, a Power-2-X technology, offers a promising route to realizing an efficient and scalable process. This paper investigates the effects of post-plasma placement of a converging-diverging nozzle in a vortexstabilized 2.45 GHz CO2 microwave plasma reactor to increase energy efficiency and conversion. The CDN leads to a 21 % relative increase in energy efficiency (31 %) and CO2 conversion (13 %) at high flow rates and nearatmospheric conditions. The most significant performance improvement was seen at low flow rates and subatmospheric pressure (300 mbar), where energy efficiency was 23 % and conversion was 28 %, a 71 % relative increase over conditions without the CDN. Using CFD simulations, we found that the CDN produces a change in the flow geometry, leading to a confined temperature profile at the height of the plasma, and forced extraction of CO to the post-CDN region.