Investigation of the Elementary Reaction Mechanisms of Fly-Ash Mediated Formation of PCDD/F

EPA Grant Number: R826166
Title: Investigation of the Elementary Reaction Mechanisms of Fly-Ash Mediated Formation of PCDD/F
Investigators: Dellinger, Barry
Current Investigators: Dellinger, Barry , Alderman, Steven , Khachatryan, Lavrent
Institution: Louisiana State University - Baton Rouge
EPA Project Officer: Shapiro, Paul
Project Period: October 1, 1997 through September 30, 2000
Project Amount: $202,976
RFA: Exploratory Research - Environmental Engineering (1997) RFA Text |  Recipients Lists
Research Category: Engineering and Environmental Chemistry , Land and Waste Management


Combustion and thermal processes are generally recognized as the major source of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) in the environment. The US-EPA has targeted their emissions for stringent new regulation that generally involve the installation of costly new control devices that only transfer the PCDD/F to different media. The goal of this project is to prevent the formation of PCDD/F through modification of conditions in the source. Since it is now well-established that PCDD/F are formed in the post-combustion region, our strategies focus on techniques that apply to "cool-zone" chemistry.

We have developed a unified pathway of formation that incorporates most of the known observations and theories of PCDD/F formation. This pathways suggests the following hypothesized control strategies that we will test in this project:

  1. Control through prevention of de novo formation of small-molecule, PCDD/F precursors that are formed from gas-solid reactions of combustion-generated radicals with combustion generated soot and char.
  2. Control of chemisorption of large-molecule precursors (formed from gas-phase molecular growth involving the de novo precursors) on fly-ash surfaces.
  3. Control of surface catalyzed chlorination by transition metal chlorides.


We will use model fly-ashes and model soots/chars to test each step in our unified pathway and determine: 1) the rate controlling step, 2) the rate controlling reagents, and 3) the range of conditions under which each step occurs. A packed-bed flow reactor will be used to study chemisorption and chlorination of chemical probes. Surface analysis of the model fly-ashes (i.e. doped silica and alumina foams) will be performed to determine the chemical nature of their surfaces and will be used to correlate their structure with observed yields of PCDD/F. A laser photolysis/photoionization mass spectrometer system will be used to study the products of reactions of Cl, H, O, OH, and HO2 with various soots in a wall-coated reactor. The data from each type of experiment will be incorporated into a unified reaction kinetic model.

Expected Results:

The goal of this project is to manage risk from exposure to combustion-generated PCDD/F. We will develop specific methods for prevention of formation of PCDD/F that can be subjected to field evaluation. We will also develop a unified model of formation that will suggest general prevention strategies for further development. Successful implementation of these techniques will speed the reduction in PCDD/F emissions as well as reduce the cost of control.

Publications and Presentations:

Publications have been submitted on this project: View all 11 publications for this project

Journal Articles:

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

Supplemental Keywords:

PCDD/F, dioxins, incineration, green chemistry, sustainable development, environmental chemistry., RFA, Scientific Discipline, Toxics, Waste, Environmental Chemistry, pesticides, Incineration/Combustion, Environmental Engineering, reaction mechanisms, combustion generated radicals, sustainable development, fly ash, metal chlorides, emission controls, furans, dioxins, kinetc models, green chemistry

Progress and Final Reports:

  • 1998
  • 1999
  • Final Report