Formation of Chlorinated PAHs in the Combustion and Thermal Processing of Chlorine Containing MaterialsEPA Grant Number: R826167
Title: Formation of Chlorinated PAHs in the Combustion and Thermal Processing of Chlorine Containing Materials
Investigators: Taylor, Philip H. , Dellinger, Barry
Current Investigators: Taylor, Philip H.
Institution: University of Dayton
EPA Project Officer: Hahn, Intaek
Project Period: November 24, 1997 through November 23, 2000
Project Amount: $360,366
RFA: Exploratory Research - Environmental Engineering (1997) RFA Text | Recipients Lists
Research Category: Safer Chemicals , Land and Waste Management
Description:Impending strict regulations of all combustion and thermal sources under the CAAA, RCRA, and EPA's Combustion Strategy will be based on calculated risk and the ability of the source to minimize emissions of harmful air pollutants. Research indicates that emissions of a potentially complex array of planar, chlorinated polynuclear aromatic hydrocarbons (ClPAHs) are major carcinogenic and/or endocrine disrupting products formed from thermal processing of chlorine containing materials. However there is insufficient information on the nature and origin of pollutant emissions with which to make scientifically defensible regulatory decisions. It is the origin and pathways of formation of these chemicals that we propose to study.
We have identified three research objectives for our proposed study: 1) determine the types of ClPAHs that can be formed, 2) determine their mechanism and rate of formation, and 3) develop reaction kinetic models of their formation. Previous research on molecular growth of chlorinated hydrocarbons (CHCs) indicates that C2 olefinic and acetylenic radical-molecule Cl-displacement reactions may proceed more rapidly than the corresponding H-displacement reactions. This finding, along with the resistance of CHCs to oxidation, suggests that PAH formation may be more facile in chlorine containing systems than purely hydrocarbon systems. Thus the central hypothesis that we will test is that CHCs are more prone to formation of PAH than hydrocarbon species.
Approach:We will study the reactions of the basic building blocks of all ClPAH and PAH, i.e. C2 olefinic and acetylenic molecules and radicals. Most CHCs will initially decompose to these relatively stable species or they will be formed by the reaction of inorganic chlorine and other organics. A laser photolysis/photo-ionization mass spectrometry (LP/PIMS) technique will be used to follow the course of these reactions. Unsaturated C2 radical precursors in the presence of reactive C2 substrates will be introduced into a high-temperature flow cell. Radiation from an excimer laser will photolyze the precursor to form the radical of interest which will then react with the substrate in the flow-cell. The PIMS will be used to follow the consumption of reactants and formation of products. A range of ionization sources and the design of the system will allow us to study a key reactions over temperatures of 295 to 1200 K and for pressures of 20 to 600 torr.
Varying the chlorination pattern of the reactants will allow us to determine the effect of chlorine on the rates of molecular growth reactions which are expected to be of the chemically-activated, addition/elimination type. We will use the Master Equation and RRKM chemical activation reaction formalism to analyze and extrapolate the experimental data.