Mechanisms for formation of inorganic byproducts in plasma chemical processing of hazardous air pollutants

Abstract

Plasma chemical behavior of hazardous air pollutants (HAPs) (Cl/sub 2/C=CCl/sub 2/, Cl/sub 2/C=CHCl, Cl/sub 3/C-CH/sub 3/, Cl/sub 2/CH-CH/sub 2/Cl, CH/sub 3/Cl, CH/sub 3/Br and benzene), their molecular probes (CH/sub 4/, CH/sub 3/-CH/sub 3/, and CH/sub 2/=CH/sub 2/), and carbon oxides (CO/sub x/) was investigated with a ferroelectric packed-bed plasma reactor to obtain information on the formation of CO/sub x/ and N/sub 2/O. It has been shown that the oxidation of CO to CO/sub 2/ is a slow reaction in plasma, and that CO and CO/sub 2/ mainly result from different precursors. Simultaneous achievement of complete oxidative decomposition of HAPs in plasma and recovery of CO as a chemical feedstock could be favorable. The process of N/sub 2/O formation is affected by HAP structures and oxygen concentration. In the decomposition of olefinic HAPs, such as Cl/sub 2/C=CCl/sub 2/ and Cl/sub 2/C=CHCl, high-power short-residence-time operations are effective in suppressing N/sub 2/O formation. In the cases of CH/sub 3/Cl and CH/sub 3/Br, low specific energy density operations could be necessary to reduce N/sub 2/O concentrations. The yields and selectivities of CO, CO/sub 2/ and N/sub 2/O change drastically by adding only 2% of oxygen to N/sub 2/, and oxygen concentration is not a good factor to control these inorganic oxides.