Decomposition of SF6–R134a effluents by RF plasma

The efficiency of recovery achieved by open or closed loop extraction of RPC exhaust gases is in the range of 90–95% under optimum conditions. For a large detector setup operating on one volume change per day basis, a 5% loss amounts to discharging 50 kg of R134a and 0.5 kg of SF6 into atmosphere every day. The emissions are equivalent to create nearly 50 000 m3 of carbon dioxide daily. The gas emissions need to be completely converted to safer compounds.The gases such as R134a and SF6 are stable compounds. In order to decompose these, the mixture is first activated by adding of 50% oxygen and 2% argon and under typical RF plasma conditions of 13.56 MHz, 1 Torr pressure and 0.2 W/cm2 power density. The chemical reaction takes place on the surface of a silicon electrode. The product of the reaction is mainly SiF4 (gas), which is further hydrolyzed to form HF solution and silicon hydroxide sludge. More than 90% of the effluent gas mixture can be effectively removed by this method.