Ferric Oxide Mediated Formation of PCDD/Fs from 2-Monochlorophenol

Abstract

The copper oxide, surface-mediated formation of polychlorinated dibenzop-dioxins and dibenzofurans (PCDD/F) from precursors such as chlorinated phenols is considered to be a major source of PCDD/F emissions from combustion sources. In spite of being present at 2–50x higher concentrations than copper oxide, virtually no studies of the iron oxide-mediated formation of PCDD/F have been reported in the literature. We have performed packed bed, flow reactor studies of the reaction of 50 ppm gas phase 2-monochlorophenol (2-MCP) over a surface of 5% iron oxide on silica over a temperature range of 200–500 °C. Dibenzo-p-dioxin (DD), 1-monochlorodibenzo-p-dioxin (1-MCDD), 4,6-dichlorodibenzofuran (4,6-DCDF), and dibenzofuran (DF) were formed in maximum yields of 0.1, 0.2, 0.3, and 0.4 %, respectively. The yield of PCDD/F over iron oxide peaked at temperatures 50–100 °C higher in temperature than over copper oxide. The maximum yields of DD, 1-MCDD and 4,6-DCDF were 2x and 5x higher over iron oxide, respectively, than over copper oxide, while DF was not observed at all for copper oxide. The resulting PCDD/PCDF ratio was 0.39 versus 1.2 observed for iron oxide and copper oxide, respectively, which is in agreement with PCDD to PCDF ratios in full-scale combustors that are typically ≪1. The combination of 2–50x higher concentrations of iron oxide than copper oxide in most full-scale combustors and 2.5x higher yields of PCDD/F observed in the laboratory, suggest that iron oxide may contribute as much as 5–125x more than copper oxide to the emissions of PCDD/F from full-scale combustors.

An Overview of PCDD/F Inventories and Emission Factors from Stationary and Mobile Sources: What We Know and What is Missing

“…The reaction involves the attachment of the precursor on the surface of the catalytic matrix on the fly ash (Briois et al, 2007). The catalyzers are typically the transition metals such as Cu and Fe, which are present in fly ash and APCDs (Lomnicki and Dellinger, 2003;Nganai et al, 2008). Transitional-metals, especially copper, have been shown to enhance the formation of PCDD/Fs (Luijk et al, 1994;Ryu et al, 2005;Liao et al, 2016).…”

Iron and copper catalysis of PCDD/F formation

“…Iron chlorides and oxides stimulated the formation of chlorinated organic compounds in several model systems (Hoffman et al 1990;Nganai et al 2009;Ryan and Altwicker 2004). Moreover, Fe 2 O 3 catalyses the dimerisation of gas-phase precursors adsorbed onto the surface of a carbon matrix (Nganai et al 2009;Gullett et al 1990). …”

Identification the Content of the Windbox Dust Related to the Formation of PCDD/Fs during the Iron Ore Sintering Process

“…In principle, high Al, Fe, K, Pb and Ca concentrations found in the WB dust samples might be because: 1. fluxes, iron ore fines and coke breeze used in the iron ore sintering process could contain a variety of impurities, including Al 2 O 3 , and K 2 O (Cieplik et al, 2003;Nakano et al, 2005;Sammut et al, 2010); 2. the use of limestone (CaCO 3 ) and dolomite (CaMg(CO 3 )) as fluxes in the sintering process (Cieplik et al, 2003); and 3. the return fine used in the sintering process usually contains Pb compounds (Sammut et al, 2010). Among these five metal contents, several studies have shown that the existence of Fe and K might lead to the increase in PCDD/Fs formation (Hinton and Lane, 1991;Nganai et al, 2009;Fujimori et al, 2009). To the contrary, the existence of Pb (chloride and oxide) and Ca (oxide) might inhibit the formation of PCDD/Fs (Qian et al, 2005;Fujimori et al, 2009).…”