Boudouard reaction driven by thermal plasma for efficient CO2 conversion and energy storage

Abstract Conversion of CO2 into CO using plasma processing powered by renewable energy is a promising method to convert intermittent sustainable electricity into storable chemical energy. Despite extensive research efforts worldwide, there is currently no process that achieves economically viable values for both CO2 conversion fraction and energy recovery efficiency simultaneously. Here we demonstrate that a process that utilizes the Boudouard reaction, CO2 + C → 2CO, driven by a thermal plasma allows both 95% CO2 conversion to CO and energy recovery efficiency of 70%, values far higher than seen so far. By comparing the conversion process with and without CO2 excitation by a plasma and by using optical emission spectroscopy we show that the improved performance is due to a novel mode of operation where CO2 is pyrolyzed into an active mixture of CO, O and O2 by an arc discharge which is then introduced into a fixed bed to interact with carbon material. In this way, the free oxygen in the mixture combusts with carbon to form CO, and residual plasma excited CO2 is reduced by carbon. In the overall process, the endothermic Boudouard reaction is partially replaced by an exothermic reaction, and the excess electric energy to produce CO2 plasma is reused in the carbon bed.