Regeneration of Na2Q in an Electrochemical CO2 Capture System

The CO2 capture system based on the electrochemical desorption at room temperature and atmospheric pressure may solve the high regeneration energy consumption problem of the amine-based postcombustion CO2 capture technology. In our former work, 0.7 M Na2Q was used to absorb CO2, and the pH mediator, tiron (QH2), was used to adjust the pH of the solution during the redox process to desorb CO2 and regenerate the absorbent. However, the absorbent does not completely regenerate due to the poor reduction of Q. In this work, the regeneration of 0.05–0.7 M Na2Q and the modification of graphite felt (GF) electrodes were further investigated. The results show that the reproducibility and the cyclicality of the Na2Q solution with a lower concentration (0.1 M) are better than those of 0.7 M Na2Q under the same conditions. The GF electrodes after acid treatment, heat treatment, phosphorus-doped, or MnO2-modified improve their electrochemical activities under acidic and weakly alkaline conditions. Phosphorus-doped or MnO2-modified GF electrodes also significantly improve the redox reaction under strongly alkaline conditions. The process of CO2 capture combining the Na2Q regeneration with the CO2 absorption is proposed to improve the reducibility of Q. In addition, a possible electrochemical reaction process of the Na2Q system is proposed. QH2 is oxidized to produce Q, in which a 1,4-Michael reaction to produce sodium 1,2,4-trihydroxybenzene-3,5-disulfonate occurs. The byproduct tiron-o-quinone is also produced, which could further polymerize to form oligomers. During the reduction of high-concentration Na2Q, the oligomers precipitate out of the solution, resulting in inhibition of the reduction.