Toward the Development of a Detailed Mechanism of Transition Metal Catalyzed Formation of PCDD/F from Combustion Generated Hydrocarbons

EPA Grant Number: R828191
Title: Toward the Development of a Detailed Mechanism of Transition Metal Catalyzed Formation of PCDD/F from Combustion Generated Hydrocarbons
Investigators: Dellinger, Barry
Current Investigators: Dellinger, Barry , Lomnicki, Slawomir
Institution: Louisiana State University - Baton Rouge
EPA Project Officer: Shapiro, Paul
Project Period: July 1, 2000 through June 30, 2003
Project Amount: $345,000
RFA: Combustion Emissions (1999) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Air

Description:

The formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F or "diox:ns" for short) in combustion sources is one of our most pressing environmental issues. Field studies strongly suggest that they are formed in the post-combustion, cool-zone of combustors by surface-mediated/catalyzed pathways. Laboratory studies have demonstrated that some transition metals, incorporated into silica-based fly ash, can catalyze dioxin formation in the 250 to 500 C range. However, the exact mechanism has not been determined. We propose to investigate the following hypothesized (and partially demonstrated) mechanism: 1) metal-catalyzed chlorination of C-olefins; 2) metal-catalyzed molecular growth and aromatization of the resulting chlorocarbons; and 3) surface mediated condensation of chlorinated benzenes to form PCDD/F. We have previously demonstrated that chlorination and aromatization occur on silica-Cu (II) surfaces, that chlorobenzenes chemisorb on silica surfaces, and that PCDD/F congener distributions are formed that are consistent with those observed for full-scale incinerators. We now propose to investigate the applicability of our theorized mechanism of aromatization of CHCs to other surfaces and determine the additional surface mediated reactions that occur in their conversion to PCDD/F.

Approach:

We will examine the previously observed products of metal catalyzed chlorination of acetylene: trichloroethylene, tetrachloroethylene, and dichloroacetylene. We will investigate their reactions on Fe (111) and Cu (II) doped silica and alumina surfaces. The study will be performed using a gas-solid reactor, coupled to a GC-MS, that permits controlled study of the heterogeneous reactions of these compounds on various surfaces at temperatures from 150 to 600 C. We will utilize isotopically-labeled chlorine compounds to attempt to verify our proposed mechanism that involves carbon-to-transition metal chlorine transfer in key steps. Surface adsorbed products, including PCDD/F and chlorinated phenols, will be analyzed using conventional soxhlet extraction and clean-up procedures followed by GC-MS analysis. Advanced surface analysis techniques including XANES, EXAFS, XPS, IR and Raman will be used to characterize valence state and chemical species of the iron and copper. Homogeneous reaction studies of model compounds for the proposed organo-silicon and organo-copper intermediates will be performed to further elucidate the mechanism of dioxin formation.

Expected Results:

If successful, we will have, for the first time, demonstrated a detailed mechanism of formation of PCDD/F from ubiquitous, combustion generated hydrocarbons. It appears that mechanisms similar to those responsible for dioxin formation are also responsible for combustion emissions of other halogenated hydrocarbons (HHCs) and endocrine disrupting chemicals (EDCs). The development of a unified mechanism and understanding of formation of halogenated combustion by-products will greatly facilitate the development of improved risk management and assessment strategies.

Publications and Presentations:

Publications have been submitted on this project: View all 8 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 3 journal articles for this project

Supplemental Keywords:

Dioxin-like compounds, incineration., RFA, Health, Scientific Discipline, Toxics, Waste, Health Risk Assessment, Environmental Chemistry, pesticides, Endocrine Disruptors - Environmental Exposure & Risk, HAPS, endocrine disruptors, Analytical Chemistry, Atmospheric Sciences, Incineration/Combustion, Endocrine Disruptors - Human Health, 33/50, combustion byproducts, dioxin, surface mediated reactions, hydrocarbon, fly ash, metal chlorides, endocrine disrupting chemicals, Tetrachloroethylene, air pollution, chemical mixtures, Trichloroethylene, complex combustion effluents, hydrocarbons, dioxins, chlorinated phenols, incineration, homogenous reaction studies

Progress and Final Reports:

  • 2001
  • 2002
  • Final Report