Title page for ETD etd-08262004-112107


Type of Document Dissertation
Author Evans, Catherine Spearing
Author's Email Address cevans2@lsu.edu
URN etd-08262004-112107
Title Comparison Studies of the Mechanistic Formation of Polyhalogentaed Dibenzo-P-Dioxins and Furans from the Thermal Degradation of 2-Bromophenol and 2-Chlorophenol
Degree Doctor of Philosophy (Ph.D.)
Department Chemistry
Advisory Committee
Advisor Name Title
Barry Dellinger Committee Chair
Brian Hales Committee Member
Robert Strongin Committee Member
William Crowe Committee Member
Elizabeth J. Podlaha-Murphy Dean's Representative
Keywords
  • brominated hydrocarbons
  • combustion
  • dioxins
Date of Defense 2004-07-19
Availability unrestricted
Abstract
Emissions of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) and polybrominated dibenzo-p-dioxins and furans (PBDD/Fs) from hazardous waste incinerators, and many other sources for combustion have been considered environmentally hazardous and a major health threat. Recently, a growing number of materials containing brominated hydrocarbons, commonly used flame retardants, have been disposed in municipal and hazardous waste incinerators. This results in the increased potential for formation of PBDD/Fs and other hazardous combustion by-products. In contrast to chlorinated hydrocarbons, the reactions of brominated hydrocarbons have been studied only minimally. In fact, studies have shown that brominated phenols form higher yields of PBDD/Fs than the analogous chlorinated phenols form PCDD/Fs. For this study, the individual homogeneous, gas-phase oxidative and pyrolytic thermal degradations of 2-bromophenol and 2-chlorophenol were studied in a 1 cm i.d., fused silica flow reactor at a concentration of 88 ppm, with a reaction time of 2.0 s, and over a temperature range of 300 to 1000C. In addition, 50:50 mixture of 2-chlorophenol and 2-bromophenol with a combined concentration of 88 ppm was studied under similar conditions. Also in order to compare previous work with 2-chlorophenol, the surface catalyzed gas-phase reactions for 2-bromophenol to form PBDD/Fs are described over a temperature range from 250 to 550C. The results are compared and contrasted with each other in order to understand the roles oxygen, chlorine and bromine play in the formation of PCDD/Fs and PBDD/Fs. Reaction pathways to PCDD/F and PBDD/F products as well as all other products detected are proposed that are consistent with the experimental data for each condition. The presence of oxygen increases the formation of PBDFs and PCDFs. Presence of bromine increases the concentration of Cl radicals which in turn increases chlorination and formation of 4,6-dichlorodibenzofuran (4,6-DCDF). However the yields of the PCDFs and PBDFs are considerably less with the presence of both bromine and oxygen. The pool of OH and concentration of the chlorine atoms is reduced and thus prevents these furans from becoming major products.
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