PCDD/PCDF Ratio in the Precursor Formation Model over CuO Surface

Abstract

The discrepancies between polychlorinated dibenzo-p-dioxin to polychlorinated dibenzofuran (PCDD to PCDF) ratios in laboratory and field studies in the exhaust of combustion sources are not fully explained by available formation models. In this paper we present the results of experimental studies of the surface mediated formation of PCDD/F at the conditions mimicking the combustion cool zone from a mixture of 1,2-dichlorobenzene (1,2-DCBz) and 2-monochlorophenol (2-MCP) over a model surface consisting of 5% CuO/Silica. The PCDD to PCDF ratio was found to be strongly dependent on the ratio of chlorinated benzenes to chlorinated phenols and oxygen content. The higher the 1,2-DCBz to 2-MCP ratio, the lower the PCDD to PCDF ratio. PCDFs are formed predominantly from chlorinated benzenes, while chlorinated phenols are responsible for majority of PCDDs. These laboratory results are in general agreement with full-scale measurement and can be used to improve predictive models of PCDD/F formation.

Surface catalysed PCDD/F formation from precursors - high PCDF yield does not indicate de novo mechanism!

“…The same proportions of CBz, CPh and PCDD/F were detected during experiments using 1,2-DCBz as a precursor over copper and iron oxide systems (Nganai et al, 2014, 2012). This leads to the following assumption: is it possible that de novo formation as described in Figure 6 pays no contribution to the overall PCDD/F emission?…”

“…Figure 5 presents the integrated average yields of PCDD/F for the mixtures of 2-MCP and 1,2-DCBz and, for comparison, data published before for PCDD/F formation over CuO surfaces, determined at the same experimental conditions (Nganai et al, 2014). Based on Figure 5, it is apparent that with decreasing 2-MCP content in the feed stream, the PCDF formation yield is increasing and the plateau at the level of ~0.4% for pyrolytic and ~0.6% for oxidative conditions.…”

“…This stems from the fact that most experimental studies involving precursors perceived PCDD/PCDF-ratios bigger than one. However, recent studies have indicated that the type of the PCDD/F precursor and/or the speciation of the active metal are a critical factor in determining the PCDD/PCDF-ratio (Nganai et al, 2014, 2012, 2011). In fact, chlorinated benzenes (CBz) have been suggested to be precursors of (mostly) PCDF and the PCDD/PCDF-ratio observed in the exhaust of thermal sources is dependent on the relative concentration of chlorinated benzenes vs. chlorinated phenols (CPh) in the gas phase.…”

Fast indirect measurement of PCDD/F TEQ emission from municipal solid waste incineration: a review

“…The emission limit and measurement method for PCDD/F emissions from MSW incineration has been established in many countries with developed environmental monitoring programs [22][23][24][25][26][27][28][29][30][31]. As can be seen in Table 1, most of the regulation standards just require measurements of PCDD/F emissions one or two times per year, e.g., at least once a year in China [24] and Japan [28].…”

“…Since Öberg et al reported the correlations of hexachlorobenzene with TeCDD, PeCDD and PeCDF [37] and stated that PCDD/Fs could be predicted from chlorinated benzenes and phenols [38], PCDD/F indicators have been an active research topic [22,35,[39][40][41][42][43][44][45][46][47][48]. Prior indicators studied can be divided into 6 categories: CO, THC (total hydrocarbons), specific PCDD/F congeners, PAHs (polycyclic aromatic hydrocarbons), chlorophenols and chlorobenzenes.…”