Abatement of perfluorinated compounds using microwave plasmas at atmospheric pressure

Abstract

Microwave plasmas sustained at atmospheric pressure, for instance by electromagnetic surface waves, can be efficiently used to abate greenhouse-effect gases such as perfluorinated compounds. As a working example, we study the destruction and removal efficiency (DRE) of SF6 at concentrations ranging from 0.1% to 2.4% of the total gas flow where N2, utilized as a purge gas, is the carrier gas. O2 is added to the mixture at a fixed ratio of 1.2–1.5 times the concentration of SF6 to ensure full oxidation of the SF6 fragments, providing thereby scrubbable by-products. Fourier-transform infrared spectroscopy has been utilized for identification of the by-products and quantification of the residual concentration of SF6. Optical emission spectroscopy was employed to determine the gas temperature of the nitrogen plasma. In terms of operating parameters, the DRE is found to increase with increasing microwave power and decrease with increasing gas flow rate and discharge tube radius. Increasing the microwave power, in the case of a surface-wave discharge, or decreasing the gas flow rate increases the residence time of the molecules to be processed, hence, the observed DRE increase. In contrast, increasing the tube radius or the gas-flow rate increases the degree of radial contraction of the discharge and, therefore, the plasma-free space close to the tube wall: this comparatively colder region favors the reformation of the fragmented SF6 molecules, and enlarging it lowers the destruction rate. DRE values higher than 95% have been achieved at a microwave power of 6 kW with 2.4% SF6 in N2 flow rates up to 30 standard l/min.

Argon and neon plasma columns in continuous surface wave microwave discharge at atmospheric pressure

“…In our work the surfaguide based microwave plasma torch [3] operated at frequency of 2.45 GHz in both neon and argon at atmospheric pressure was used. Already, the applicator of this kind find applications in a system for post-pump abatement of etch process effluents containing perfluorinated compounds [4]. From the point of view of applications the knowledge about plasma parameters as well as the structure of plasma column is needed.…”

Parametric study of atmospheric pressure microwave-induced Ar∕O2 plasmas and the ambient air effect on the plasma

“…[1][2][3][4][5] From the application point of view, such characteristics are favorable to atomic spectrometry, decomposition of toxic gases like perfluorocarbon gas, and thermally resistible material processing. [5][6][7] In our previous report in which parameters of the plasma produced in a simple single dielectric tube were measured by optical emission methods, 4 the gas flow rate was one of the important conditions along with the microwave power. In this work, we investigated the temperature and density distribution as the flow rate and composition of the supply gas were varied.…”

Microwave plasma for hydrogen production from liquids

“…Such inelastic collisions proceed permanently, with the consequence of also preventing the reformation of the initial molecules. As a result, high pollutant destruction and removal effi ciencies may be attained even at high concentrations [1]. The microwave plasma sources at atmospheric pressure stand out from the other plasma sources as being more effi cient in energy transfer [2].…”