Contribution of aluminas and aluminosilicates to the formation of PCDD/Fs on fly ashes. (February 2016)

• Record Type: Journal Article
• Authors: Potter, Phillip M.; Dellinger, Barry; Lomnicki, Slawomir M.
• Is Part Of: Chemosphere. Volume 144(2016)
• Page Start: 2421
• Page End: 2426
• Publication Date: 2016-02
• Subjects: PCDD/Fs -- Precursor pathway -- Dioxins -- Aluminosilicate; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2015.11.009
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: Chlorinated aromatics undergo surface-mediated reactions with metal oxides to form Environmentally Persistent Free Radicals (EPFRs) which can further react to produce polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). Previous work using laboratory-made fly ash surrogates composed of transition metal oxides deposited on silica powder has confirmed their ability to mimic fly ash in the production of PCDD/Fs. However, little is known about the propensity of aluminas and aluminosilicates, other components of fly ash, to form PCDD/Fs. A fly ash sample containing both alumina and mullite, an aluminosilicate, was tested for PCDD/F formation ability and compared to PCDD/F yields from the thermal degradation of 2-monochlorophenol (2-MCP) precursor over γ-alumina, α-alumina, and mullite. A packed-bed flow reactor was used to investigate the thermal degradation of 2-MCP over the various catalysts at 200–600 °C. Fly ash gave similar PCDD/F yields to surrogates made with similar transition metal content. γ-alumina, which is thermodynamically unfavorable, was very catalytically active and gave low PCDD/F yields despite a high destruction of 2-MCP. Mullite and α-alumina, the thermodynamically favorable form of alumina, yielded higher concentrations of dioxins and products with a higher degree of chlorine substitution than γ-alumina. The data suggest that certain aluminas and aluminosilicates, commonly found in fly ash, are active catalytic surfaces in the formation of PCDD/Fs in the post-flame cool zones of combustion systems and should be considered as additional catalytic surfaces active in the process. Highlights: Aluminosilicates are catalytically active in the formation PCDD/Fs. Aluminosilicates are particularly active in oxygen rich conditions of the combustors exhaust. Prediction of PCDD/F in combustion sources can be based on the additive catalytic activity of fly-ash components.