Mechanistic Studies of the Transformation of Polychlorinated Dibenzo-p-Dioxins via Hydroxyl Radical Attack

EPA Grant Number: R828189
Title: Mechanistic Studies of the Transformation of Polychlorinated Dibenzo-p-Dioxins via Hydroxyl Radical Attack
Investigators: Taylor, Philip H.
Institution: University of Dayton
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 2000 through September 30, 2003
Project Amount: $320,000
RFA: Combustion Emissions (1999) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Air

Description:

Polychlorinated dibenzo-p-dioxins (PCDD) are considered among the most toxic organic chemicals associated with our industrial society. The gas-phase transformation of these chemicals under high-temperature incineration (destruction) conditions is not well understood. Experimental and modeling studies have repeatedly shown that OH radical reactions are among the most important elementary steps under these reaction conditions. A review of the literature demonstrates that knowledge of the rate of reaction of OH with dibenzo-p-dioxin and PCDD is limited to three low temperature experimental studies, or inferred by estimates of room temperature reactivity. The mechanism of reaction is completely uncharacterized.

Approach:

We propose to study the high-temperature reaction kinetics of OH radicals with dibenzo-p-dioxin (DD) and selected chlorinated dioxins using a modified laser photolysis/laserinduced fluorescence technique. This technique will be used in conjunction with a specially fabricated high-temperature fused silica test cell operated under atmospheric pressure, slow flow, single reaction conditions. In the absence of reactant thermal decomposition, accurate rate constant measurements with this apparatus can span a temperature range of 295 to ~1000 K. This extended range encompasses temperatures in the incinerator post-flame zone and allows for more precise extrapolation of rate constants to higher temperature combustion environments. Mechanistic experiments will include studies of the effect of pressure on observed rate coefficients, and product analysis using a highly sensitive Saturn 2000 ion trap GC-MS-MS analytical system. The mechanistic studies will be used to guide and interpret quantum RRK modeling of the various reactions.

Expected Results:

This study will identify key gas-phase pathways for the transformation of PCDD at elevated temperatures. These pathways. with formation pathways being studied in complementary research programs by the P1 and other investigators, are important inputs in the development of a comprehensive gas-phase model of the transformation of PCDD for a wide range of conditions. This model can be used to manage risk by preventing and controlling formation and emission. The fundamental data and models developed in this study will contribute to the infrastructure of knowledge of reactions of chlorinated hydrocarbons and their impact on the environment.

Publications and Presentations:

Publications have been submitted on this project: View all 9 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 1 journal articles for this project

Supplemental Keywords:

RFA, Scientific Discipline, Toxics, Waste, Chemical Engineering, Environmental Chemistry, Chemistry, pesticides, Incineration/Combustion, Environmental Engineering, dioxin, industrial waste, gas-phase transformation, chemical contaminants, analytical chemistry, hydrocarbons, mechanistic study, toxic organic chemicals, incineration, fused silica test cell, combustion contaminants, laser photolysis

Progress and Final Reports:

  • 2001 Progress Report
  • 2002 Progress Report
  • Final Report