Destruction of freons by the use of high-voltage glow plasmas

The decomposition of two different Freon species, Freon 21 (CHFCl2) and Fre on 142-B (CF2ClCH3), was carried out using a high-voltage glow discharge pl asma. The plasma is produced in a tubular reactor consisting of an inner ir on electrode and an outer electrode being either aluminum or copper, a glas s tube between the electrodes serves as a dielectric. The reaction gases, 0 .5% Freon in helium and 5% oxygen in helium (moisture added), are mixed bn line. The conversion measured by a gas chromatograph as the disappearance o f the Freon species is very high for both species. For Freon 21, the conver sion ranges from 75% up to 100% in the input voltage regime between 1.60 an d 5.44 kV depending on the mixture. In the case of Freon 142 B, higher volt ages are needed to achieve similar conversions. The input voltage of 3.50 k V yields 70% conversion, 3.88 kV yields 77% conversion, and 5.44 kV gives 1 00%, The conversion of Freon 21 drops with increasing flow rate and decreas es from 88% at 15 mL/min to 78% at 40 mL/min and to 47% at 100 mL/min. A mo re drastic decrease is seen with respect to CO2 production, which decreases by 30% when the flow rate is changed from 20 to 40 mL/min and by 42% if ch anged to 60 mL/min. Oxygen increases CO2 production via breakdown of Freon by 90%. Further addition of water increases CO2 production by another 25% c ompared to the reaction with oxygen. Carbon dioxide is the main carbon oxid e produced at a CO/CO2 ratio of 0.05 to 0.07. Further reaction products are hydrogen fluoride and chlorine. Furthermore, mass spectroscopic and optica l emission studies were carried out to obtain insight on the reaction mecha nism.