Application of plasma catalysis system for C₄F₈ removal

Octafluorocyclobutane (C₄F₈) with a GWP₁₀₀ (global warming potential) of 10,000 times of CO₂ is listed as potent greenhouse gas. Therefore, development of effective control technologies for reducing C₄F₈ emissions has become an emerging issue to be addressed. In this study, decomposition of C₄F₈ was investigated via three systems including catalytic hydrolysis, non-thermal plasma, and plasma catalysis, respectively. Decomposition of C₄F₈ achieved with catalytic hydrolysis reaches the highest efficiency of 20.1%, being obtained with γ-Al₂O₃ as catalyst in the presence of 10% H₂O_(g) and operating temperature of 800 °C. For plasma-based system, the highest C₄F₈ conversion obtained with non-thermal plasma is 62% at a voltage of 23 kV. As for the plasma catalysis system, 100% C₄F₈ conversion efficiency can be achieved at an applied voltage of 22–23 kV. The effects of various parameters such as gas flow rate and C₄F₈ concentration on plasma-based system show that the plasma catalysis also has better resistivity for the high gas flow rate. The highest energy efficiency of 0.75 g/kWh is obtained for the gas flow rate of 500 mL/min, with the C₄F₈ conversion of 41%. The highest conversion 89% was achieved with the O₂ content of 0.5%. Addition of Ar improves the performance of plasma-based system. When Ar is controlled at 20%, C₄F₈ conversions obtained with plasma catalysis reach 100% at applied voltage of 22–23 kV even in the presence of 5% O₂. The main products of the C₄F₈ conversion include CO₂, NO_x, and COF₂ when O₂ is added into the system. As water vapor is added, HF is also formed. This study has confirmed that combined non-thermal plasma with catalyst system to convert C₄F₈ is indeed feasible and has good potential for further development.