Reduction of perfluorinated compound emissions using atmospheric pressure microwave plasmas: Mechanisms and energy efficiency

Abstract

The abatement of perfluorinated compound (PFC) gases is investigated using atmospheric pressure microwave-surface-wave plasmas. These PFCs are diluted in nitrogen gas with concentration ranging from 5000 to 10 000 ppmv. The abatement mechanisms of SF6 and CF4 are examined, and conversion schemes are presented in the case where oxygen is added to the gas mixture. The PFC fragments are oxidized, forming acid-like by-products that are finally trapped irreversibly using a humidified soda lime scrubber. Gas-phase analysis was performed using Fourier transform infrared (FTIR) spectroscopy. The abatement efficiency is found to increase with increasing absorbed microwave power and gas residence time. The energy efficiency of the abatement process is shown to increase, with PFC concentrations in the gas mixture up to 10 000 ppmv. A complete conversion of SF6 is achieved for energy densities ranging from 700 to 1200 J/cm3 for concentrations ranging from 5000 to 10 000 ppmv. Lowering the microwave excitation frequency and using swirling flow are shown to reduce the energy cost per abated molecule.