Capture by Condensation
Richard M. Kelly - Praxair Inc. (SESHA Journal Volume 15 Number 2 - Summer 2001 pp. 19 - 24 )
A technical solution for condensation of mixed PFCs from semiconductor exhaust streams is described. The method exhibits a high PFC removal efficiency and produces a high concentration, liquid PFC product. The problem of PFC freezing is mitigated both by condenser configuration and operation at elevated pressure, but more uniquely, by the re-circulation of carbon tetrafluoride (CF4), to act as a solvent for the heavier PFCs. Technical feasibility studies were carried out a Praxair's Technology Center laboratories. Experiments were run using a synthetic exhaust gas, comprising nitrogen with added PFCs. The synthetic exhaust gas was processed at flow rates of up to 50 scfh. A wide range of PFCs were examined, with concentrations in the approximate range 0.5 to 1%. All PFCs were removed from the carrier gas at efficiencies of greater than 99%. A rudimentary mass balance indicated that the PFC concentrate comprised > 90% PFCs in all cases.