Identifier

etd-09182010-105119

Degree

Doctor of Philosophy (PhD)

Department

Chemistry

Document Type

Dissertation

Abstract

Formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) which occurs inexorably from most thermal and combustion processes constitutes a major toxic component of environmental pollutants. Generally, it is well established that transition metal-mediated reactions account for the majority of PCDD/F emissions from combustion sources. Specifically, both copper and iron ions, which occur abundantly in combustion generated particulate matter, are considered probably the most active in promoting PCDD/F formation typically in the low temperature post-combustion zone and flue gas pollution control devices. It has also been demonstrated that chlorinated phenols are key intermediates in essentially all pathways of PCDD/F formation. Chlorinated benzenes have been presumed to be potent precursors that form PCDD/Fs and are among the most abundant aromatic compounds in incinerator exhaust. Notably, numerous studies have been reported in regard to surface-mediated processes of PCDD/F formation via de novo synthesis and transition metal-mediated processes from reactions of chlorinated phenols. However, few experimental studies have been conducted on chlorinated benzenes. In addition, even though iron oxide is present at 2-50 times higher concentrations than copper oxide, virtually no studies of the iron oxide mediated formation of PCDD/Fs have been reported in the literature. For this study, PCDD/F formation over iron oxide and copper oxide surfaces were investigated using the reactants 2-MCP and 1,2-DCBz in pure and mixture form. The surface-mediated reactions were studied under pyrolytic and oxidative conditions over a temperature range of 200 to 550 oC. For the entire study, simplified model surfaces of 5% copper (II) oxide on silica and 5% iron (III) oxide on silica were used in order to facilitate comparison with previous data from similar experiments performed with pure samples of 2-MCP and 1,2-DCBz. Precursor 2-MCP is useful as a model chlorinated phenol, while 1,2-DCBz was selected because it has been found to be present in high concentration in relation to other congeners of polychlorinated benzenes in combustion exhaust and is nearly isoeletronic with 2-MCP, that provides a basis for comparison of product distributions and yields. Reaction pathways of PCDD/F products as well as the intermediates involved are comprehensively analyzed and discussed.

Date

2010

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Dellinger, Barry

Included in

Chemistry Commons

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