Design of electrochemical system for simultaneous removal and utilization of $CO_2$ and $SO_2$ in flue gas

Abstract

Sulfur dioxide ($SO_2$) emissions, primarily from coal-fired power plant, should be and has been regulated due to adverse effects on humans and environment. Among flue gas desulfurization (FGD), scrubbing with sodium hydroxide (NaOH) is often used, but it requires the adjustment of pH from 4 to 5.5 to avoid carbon dioxide ($CO_2$) absorption into the form of bicarbonate ion, which slows down the kinetics of $SO_2$ absorption. In this study, NaOH-based absorbent with high pH, in which $SO_2$ and $CO_2$ were simultaneously absorbed, was incorporated into a functional electrochemical system, which contributes to: (1) purifying $CO_2$ up to the concentration of 90 %

(2) mineralizing $SO_2$ into the form of $Na_2$$SO_4$

(3) and finally producing hydrogen, which is a potential energy carrier. As a result, using graphite electrodes, demonstration of expected reaction at both anode and cathode been made. When voltages applied, pH, sulfate concentration, TIC increased and decreased as expected. At 3V, sulfite oxidation would be concluded within 3 hours, and its faraday efficiency is close to 100%. In reality, high purity of $CO_2$ and $H_2$ gas would be generated. Graphite electrode, however, proved to be an unsuitable electrode for this cell by result of TIC and gas volume. Among precious metal catalysts, platinum turned out to be the best catalyst for sulfite oxidation from LSV and CV results.