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2000 Progress Report: Ferric Oxide/Alkali Metal Oxide Induced Oxidation of CHCs in Polluted Gas Streams
EPA Grant Number: R827719Title: Ferric Oxide/Alkali Metal Oxide Induced Oxidation of CHCs in Polluted Gas Streams
Investigators: Dellinger, Barry , Alderman, Steven , Khachatryan, Lavrent
Current Investigators: Dellinger, Barry , Lomnicki, Slawomir
Institution: Louisiana State University - Baton Rouge
EPA Project Officer: Shapiro, Paul
Project Period: September 1, 1999 through August 31, 2002
Project Period Covered by this Report: September 1, 1999 through August 31, 2000
Project Amount: $358,396
RFA: Exploratory Research - Environmental Engineering (1999)
Research Category: Engineering and Environmental Chemistry
Description:
Objective:The goal of this project is to minimize the formation of polychlorinated dibenzo-p-dioxins and furans (PCDD/PCDF) through modification of conditions in the source. Because it is now well-established that PCDD/PCDF are formed in the post-combustion region, our strategies were focused on techniques that apply to "cool-zone" chemistry.
The mechanism of PCDD/PCDF in combustion sources has been the subject of much controversy. One issue has been the mechanism of the so-called fast de novo pathway in which the presence of a flame upstream of a fly-ash bed results in more rapid formation of PCDD/PCDF than is observed when the fly-ash bed is heated without the presence of flame. The implication of the reported studies is that reactive species generated in the flame react with the carbon in the fly-ash to form PCDD/PCDF. Because of the complexity of the effluent from a flame and the poorly characterized nature of fly-ash, identification of the responsible reactants has been difficult. Consequently, we have chosen to study the reactions of well characterized carbonaceous beds with flame-generated radicals such as OH, Cl.
The formation of acetylene and ethylene at low temperatures (200 to 500?C) under interaction of ArF laser generated OH radicals with the carbon pellets (as replica combustion generated soot and char) represents a partial confirmation of the initial step in extended precursor pathways of PCDD/PCDF formation. The formation of these unsaturated hydrocarbons are significant in that it has been previously shown that these species can be chlorinated by a transition metals and undergo further reaction to form chlorinated aromatic species and PCDD/PCDF.
The rate of formation of acetylene and ethylene increase rapidly above 400?C. Consequently, maintaining post-combustion temperatures below 400?C represents a possible, if not realistic, PCDD/PCDF prevention strategy. An inhibition effect on the gasification of carbon is observed if the carbon is exposed to H2O or N2O for extended periods. Absorption of these gases block active sites, reduce the effective area of surface available for reaction, and consequently reduces the overall rate of gasification.
Upon chlorination of carbon pellets by Cl2 or Cl atoms (generated by N2 laser radiation), carbon tetrachloride is formed as a main chlorinated hydrocarbon (CHC) product. Carbon tetrachloride is catalytically converted by transition metals to C2, C4, and C6 CHCs that are further converted to chlorinated benzenes and phenols, and ultimately converted to PCDD/PCDF. A low temperature zone (200 to 350?C) and a deactivation of the catalyst is needed to prevent the formation of chlorinated hydrocarbons and hence, PCDD/PCDF.
Changing the water concentration and temperature can block the chemisorption of precursors (phenol, halogenated phenols, and benzenes) and chlorinating agents on fly ash surfaces by formation of annealed siloxanes. Other combustion generated species may also block reactive sites. Chlorinated phenols more sensitive to the changing of experimental conditions as they are more readily chemisorbed than chlorobenzene in the temperature region 100 to 500?C.
Using electron paramagnetic resonance spectroscopy (EPR) we have discovered that hydroxy phenols (hydroquinones, resorcinols, and catechols) are stabilized on the surface of fly-ash and fine particulate matter. The discovery of stable radicals of chlorinated hydroxyphenols places an entirely new perspective on the mechanism of formation of PCDD/PCDF and strategies for control. Because our investigation show these radicals might be the principal intermediates in the formation of PCDD/PCDF on surfaces, then the prevention of formation of PCDD/PCDF may take a different track. Radical scavenging and destabilization strategies should now be considered.
Journal Articles on this Report: 1 Displayed | Download in RIS Format
| Other project views: | All 9 publications | 4 publications in selected types | All 4 journal articles |
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Khachatryan L, Dellinger B. The formation of olefins and alkynes from the reaction of hydroxyl radical and carbonaceous material. Journal of the Chemical Society - Perkin Transactions 2 2002;(4):779-783. |
R827719 (2000) R826166 (2000) R826166 (Final) |
not available |
air, atmosphere, adsorption, absorption, exposure, carcinogen, mutagen, chemicals, toxics, particulates, PAHs, Dioxin, nitrogen oxides, pollution prevention, waste reduction, incineration, environmental chemistry, engineering, ecology, industry. , Toxics, Air, Scientific Discipline, RFA, Engineering, Chemistry, & Physics, HAPS, Ecological Risk Assessment, Atmospheric Sciences, Environmental Engineering, particulate matter, Environmental Chemistry, pollution dispersion models, chlorinated hydrocarbons, hydrocarbon, Fourier Transform Infrared measurement, MACT standards, particulates, emission control technologies, cost effective, ferric oxide, chemical transport modeling, toxic contaminants, pollutant transport, catalytic oxidation
Progress and Final Reports:
Original Abstract
2001 Progress Report
Final Report