Research On The Electrochemical Process Of Emission Reduction Of Carbon Dioxide And Sulfur Dioxide

In this thesis, various products in the oxygen cathodic reduction such as H2O2、OH-and H+are made good use to build two pollutant treatment processes by an electrochemical drive method. The two processes includes:carbon dioxide (CO2) capture and recovery in an energy-saving approach and sulfur dioxide (SO2) conversion from flue gas in a green way. They can solve the problem of second pollution and high energy which is caused by water electrolysis side reaction, achieving the emission reduction of carbon dioxide in the atmosphere and sulfur dioxide from flue gas.A process for the capture and recovery of carbon dioxide was designed basing on the products of H+in anodic chamber and OH-in cathodic chamber. During cathodic oxygen reduction reaction and cathodic water reduction reaction, cell voltage and energy consumption of the process at different current densities were investigated as well as content of the captured carbon dioxide from air. Under O2or air atmosphere (with and without including CO2and H2O). cell voltage and energy consumption of the process at the current density were also investigated as well as content of the captured carbon dioxide from air. The results showed that cathodic water reduction reaction was approximately regarded as not to occur when the cell voltage of a reaction was2.2V. At the same current densities of0.250and0.500mA cm-2, energy consumption of cathodic oxygen reduction reaction was lower than that of cathodic water reduction reaction. But the content of the captured carbon dioxide from air was nearly the same in both reactions. Moreover, cell voltages of cathodic oxygen reduction reaction were inferior to2.2V. At current density of0.500mA cm-2under O2or air atmosphere (with and without including CO2and H2O), all the cell voltages were2.1V and energy consumption were all30.24J. In addition, the content of the captured carbon dioxide from air was nearly the same. Consequently, a process for the capture and recovery of carbon dioxide from air atmosphere could be effectively carried out when the cell voltage of the reaction was2.1V.A process for sulfur dioxide (SO2) conversion from flue gas in a green way was designed basing on the products of H+in anodic chamber and OH-and H2O2in cathodic chamber. Electrochemical supply of OH-and H+ions, O2function in the flue gas, pH variation behavior during the flue gas absorption process, the application of current density, the selected initial pH of solution and CO2effect were investigated in the process. Experiments demonstrated that cathodic reaction product OH-would make for the scavenging of the SO2absorption-and oxidation-released H+as well as the CO2absorption-released H+. In addition, the accumulation of H2O2and oxygen from flue gas could accelerate the SO2oxidation, and anodic reaction product H+would be employed to prepare NaHSO4. During the absorption process of simulated flue gas in the aqueous solution, pH variation in the cathodic chamber went through two stages with constant current application:the transient (0-20min) with two peaks and the steady (20-60min). Moreover, CO2almost did not pose an effect on the flue gas desulfurization process at a pH range of5.0-6.0. The absorption efficiency of SO2could achieve more than98.4%in the aqueous solution with initial pH6.0. When the initial pH in the solution was6.0and absorption efficiency of SO2reached98.4%, the content of obtained Na2SO4and NaHSO4was5.62mM and0.837mM, respectively. Therefore, it could realize continuous and highly effective absorption and quick oxidation of SO2from flue gas in the aqueous solution in the process. Moreover, SO2from flue gas was transformed to Na2SO4and NaHSO4with high added economic value, which realized green conversion of SO2from flue gas.