Decomposition of CO₂in a solar-gliding arc plasma reactor: Effects of water, nitrogen, methane, and process optimization

The decomposition of carbon dioxide (CO2) is a primary step towards its utilization in chemical synthesis processes that can help mitigate atmospheric CO2 emissions and fulfill the need for fuels and chemicals. The synergistic utilization of solar and electrical energy is investigated in a solar-gliding arc (glidarc) plasma system for the decomposition of CO2. The approach exploits the highly reactive species and radicals present in gliding-arc plasmas (a form of nonequilibrium electrical discharge) and the absorption of solar energy by the plasma towards enhancing reaction kinetics involved in gas-phase atmospheric pressure CO2 decomposition. Solar-glidarc plasma processing is investigated using undiluted CO2 and mixtures of CO2 with water vapor (CO2 saturated with water vapor), nitrogen, and methane. A two-phase Design Of Experiments (DOE) approach is followed to guide the investigation and analyze experimental results: phase 1 to identify the significance of the main parameters of the solar-glidarc reactor operation, and phase 2 to evaluate the optimal operating conditions towards maximizing CO2 decomposition. The results reveal that the CO2:CH4 (7:1) mixture yielded the maximum CO2 conversion of 49%, followed by 44% by the CO2-N2 (1:7) gas mixture. In contrast, the undiluted CO2 and CO2-H2O experiments show maximum CO2 conversions of 5% and 3%, respectively, and energy efficiencies of 15% and 12%, respectively. The optimal performance of the solar-glidarc reactor is attained with the CO2-N2 gas mixture, reaching a maximum energy efficiency of 70% and CO2 conversion of 44%.