Kinetic and Mechanistic Studies of the Reactions of Hydroxyl Radical with the Chloroethenes over an Extended Temperature Range

EPA Grant Number: R826169
Title: Kinetic and Mechanistic Studies of the Reactions of Hydroxyl Radical with the Chloroethenes over an Extended Temperature Range
Investigators: Taylor, Philip H. , Dellinger, Barry
Current Investigators: Taylor, Philip H.
Institution: University of Dayton
EPA Project Officer: Shapiro, Paul
Project Period: November 24, 1997 through November 23, 2000
Project Amount: $356,702
RFA: Exploratory Research - Environmental Engineering (1997) RFA Text |  Recipients Lists
Research Category: Engineering and Environmental Chemistry , Land and Waste Management

Description:

The chloroethenes are widely used toxic organic chemicals and frequently observed products of incomplete combustion of chlorinated hydrocarbons. High-temperature incineration is currently considered the best available technology for the safe disposal of these toxic compounds. Experimental and modeling studies have repeatedly shown that OH radical reactions are among the most important elementary steps in the high-temperature oxidation of hydrocarbon species under near-stoichiometric conditions. Hence, information regarding the reaction rates of OH with chloroethenes is also of major importance to the study of the high-temperature oxidation of these compounds. With the exception of CH2=CHCl, there is a lack of reliable OH rate data for the chloroethenes at temperatures approaching those in the flame and post-flame environment, since the temperature ranges of previous experimental studies that focused on atmospheric reactivity extended only to ~400 K.

Approach:

We propose to study the high-temperature reaction kinetics of OH radicals with the chloroethenes using a modified laser photolysis/laser-induced fluorescence technique. Our experimental approach is well established through previous EPA grants. 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. Diagnostic experiments will include studies of the effect of pressure on observed rate coefficients and studies of deuterium isotope effects. The diagnostic experiments will be used to interpret quantum RRK modeling of the various reactions. Ab initio calculations will be used to provide accurate high pressure limit rate parameters for the QRRK modeling.

Expected Results:

The overall goal of this research is to determine the rates and mechanisms of OH reactions with chloroethenes over an extended temperature range. The specific rate coefficients can be used to improve the design of hazardous waste incinerators with respect to these thermally stable products of incomplete combustion. Thermochemical data will also be determined under conditions when the rate of reverse dissociation is comparable with that of direct addition process and the chemically activated Cl elimination channel is negligibly slow. Specific goals of this research include: 1) The first absolute rate measurements of the reaction of OH with CH2=CCl2, cis-CHCl=CHCl, trans-CHCl=CHCl, CHCl=CCl2, and CCl2=CCl2 over an extended temperature range with determination of accurate Arrhenius or modified Arrhenius parameters; 2) determination of the relative importance of Cl elimination versus H atom abstraction at elevated temperatures; and 3) determination of the relative importance of Cl elimination versus adduct stabilization at lower temperatures.

Publications and Presentations:

Publications have been submitted on this project: View all 6 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 2 journal articles for this project

Supplemental Keywords:

Hydroxyl radical, CHCs, incineration, environmental engineering, laser-induced fluorescence, exposure, air., RFA, Scientific Discipline, Waste, Environmental Chemistry, Incineration/Combustion, Environmental Engineering, high temperature reaction kinetics, hazardous waste incinerators, laser induced flourescence, hydroxyl radicals, mechanistic study, toxic organic chemicals, detailed chemical kinetics, combustion contaminants

Relevant Websites:

http://www.udri.udayton.edu/enviroscience

Progress and Final Reports:

  • 1998
  • 1999 Progress Report
  • Final Report