title: Mechanistic studies on the role of PAHs and related compounds in PCDD/F formation on model fly ashes.
abstract: Model fly ashes containing Florisil, CuCl2.2H2O and PAHs with structures similar to dibenzo-p-dioxin or dibenzofuran were heated at 250 degrees C in He/O2 with regard to a supposed intramolecular reaction mechanism for oxygen incorporation. Highest reactivities in PCDF formation could be found for model compounds containing a biphenyl structure, while condensed pi-systems lead to a decrease in reactivity for such compounds. Biphenyl is almost completely converted to dibenzofuran. PCDD formation from six-membered rings like xanthene/9,10-dihydroanthracene is of minor importance. 18O-labeling of gaseous oxygen reveals no common reaction step for oxygen incorporation using 9-fluorenone, xanthene, diphenyl ether and diphenyl-2-carboxylic acid as model compounds. Pre-existing oxygen in reactants is a major source for ether groups in PCDD and PCDF. Determination of labeled and unlabeled CO and CO2 besides He/O2 reflects higher reactivities towards oxidation for model compounds containing ether groups than for compounds with carbonyl groups.
authors.affiliation: ITC-CPV, Forschungszentrum Karlsruhe GmbH, Germany. joerg.wilhelm@itc-cpv.fzk.de
authors.forename: J
authors.initials: J
authors.lastname: Wilhelm
authors.forename: L
authors.initials: L
authors.lastname: Stieglitz
authors.forename: E
authors.initials: E
authors.lastname: Dinjus
authors.forename: R
authors.initials: R
authors.lastname: Will