Effective Removal of CF4 by Combining Nonthermal Plasma with γ-Al2O3

Abstract

Conversion of CF4 was experimentally evaluated with three systems including catalytic hydrolysis, NTP-alone and plasma catalysis. Firstly, activity of γ-Al2O3 for CF4 conversion was tested via catalytic hydrolysis. Experimental results indicate that the highest CF4 conversion (72%) could be achieved with γ-Al2O3 in the presence of 45% H2O(g) with the operating temperature of 900 °C and the apparent activation energy is calculated as 85 kJ/mol using power rate law model. For plasma-based systems, results indicate that CF4 conversions achieved with plasma catalysis remain 100% with the applied voltage ranging from 12 to 23 kV, while the highest CF4 conversion achieved with NTP-alone is 86%. For the effects of various parameters on plasma-based systems, the results indicate that plasma catalysis also has better resistivity for higher total flow rate, CF4 concentration and O2 contents. Especially, CF4 conversion could maintain at 100% with the operating applied of 23 kV as CF4 concentration is increased to 10,000 ppm. On the other hand, CF4 conversion achieved with NTP-alone is 18% at the same conditions. In addition, negative effect of O2 on plasma catalysis could be reduced by the addition of Ar due to its good discharge properties and high excitation threshold energy (13 eV). The kinetics of plasma catalysis is investigated for CF4 conversion by a simplified model, and the results indicate that overall energy constant achieved with plasma catalysis reaches 0.015 mg J−1. Overall, plasma catalysis is demonstrated with good potential for the reduction of CF4 emission.