Influence of nonthermal plasma reactor type on CF₄ and SF₆ Abatements

Dielectric barrier discharge (DBD) and packed-bed reactor (PBR) are two of the commonly used nonthermal-plasma (NTP) reactors. In this paper, these two reactors are applied to remove two perfluorocompounds (PFCs), i.e., CF₄ and SF₆, which are extensively used in semiconductor- and liquid-crystal-display-manufacturing industries. Experimental results indicated that PBR constructed by packing dielectric pellets (chemical compositions: CuO 64%, ZnO 24%, Al₂O₃ 10%, and MgO 2% by weight) inside the DBD reactor achieved a higher CF₄ removal efficiency and a lower SF₆ removal efficiency than that of the DBD reactor. In other words, different behavior between CF₄ and SF₆ removal efficiencies achieved with two different types of NTP reactors was found in this paper. To elucidate this interesting finding, the influences of the discharge power, the reactor temperature, the catalytic effect, the nature of pollutants, and the plasma characteristics of DBD and PBR were investigated. It is found that the last two factors are mainly responsible for the interesting finding. At the same discharge gap, it is well known that PBR possesses higher mean electron energy than nonpacked plasma reactor (like DBD). Nevertheless, the dissociative attachment reaction of SF₆SF₆ + e → SF₅^- + F plays an important role for SF₆ removal at low-electron-energy region. Therefore, a nonpacked plasma reactor is more suitable for SF₆ removal; on the contrary, a PBR with higher mean electron energy is favorable for CF₄ abatement. The finding provides useful information on selecting an appropriate NTP reactor for removing a specific PFC.