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

Nganai, Shadrack; Lomnicki, Slawo

doi:10.1504/ijep.2017.10008687

Cited by 4 publications

(4 citation statements)

References 43 publications

(52 reference statements)

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“…The system for thermal diagnostic studies (STDS) is a continuous flow reactor system using an in-line GCMS at the head of the GC column at − 60 °C. It is a well-tested technique for the analysis of a broad range of organic materials, including amino acids Nganai et al [17]. The experimental details for STDS are reported elsewhere [18].…”

Section: Materials and Experimental Proceduresmentioning

confidence: 99%

Dioxin and dibenzofuran like molecular analogues from the pyrolysis of biomass materials—the emerging challenge in bio-oil production

et al. 2021

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Introduction The aggressive search for renewable energy resources and essential pyrosynthetic compounds has marked an exponential rise in the thermal degradation of biomass materials. Consequently, clean and sustainable transport fuels are increasingly desirable in a highly industrialized economy, for energy security and environmental protection. For this reason, biomass materials have been identified as promising alternatives to fossil fuels despite the challenges resulting from the possible formation of toxic nitrogen-based molecules during biomass degradation. In order to understand the free radical characteristic challenges facing the use of bio-oil, a brief review of the effects of free radicals in bio-oil is presented. Methodology Pyrolysis was conducted in a tubular flow quartz reactor at a residence time of 2 s at 1 atm. pressure, for a total pyrolysis time of 5 min. The thermal degradation of biomass components was investigated over the temperature range of 200 to 700 °C typically in 50 °C increments under two reaction conditions; pyrolysis in N2 and oxidative pyrolysis in 5% O2 in N2. The pyrolysate effluent was analysed using a Gas chromatograph hyphenated to a mass selective detector (MSD). Results The yield of levoglucosan in the pyrolysis of cellulose in the entire pyrolysis temperature range was 68.2 wt % under inert conditions and 28.8 wt % under oxidative conditions. On the other hand, formaldehyde from pyrolysis of cellulose yielded 4 wt % while that from oxidative pyrolysis was 7 wt % translating to ⁓ 1.8 times higher than the yield from pyrolysis. Accordingly, we present for the first time dioxin-like and dibenzofuran-like nitrogenated analogues from an equimassic pyrolysis of cellulose and tyrosine. Levoglucosan and formaldehyde were completely inhibited during the equimassic pyrolysis of cellulose and tyrosine. Conclusion Clearly, any small amounts of N-biomass components such as amino acids in cellulosic biomass materials can inhibit the formation of levoglucosan–a major constituent of bio-oil. Overall, a judicious balance between the production of bio-oil and side products resulting from amino acids present in plant matter should be taken into account to minimize economic losses and mitigate against negative public health concerns.

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Section: Materials and Experimental Proceduresmentioning

confidence: 99%

Dioxin and dibenzofuran like molecular analogues from the pyrolysis of biomass materials—the emerging challenge in bio-oil production

et al. 2021

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“…Precursors are chemicals that initiate a reaction for instance in the formation of dioxins, furans and their associated analogues and include chlorophenols (CP), chlorobenzenes (CBz), and polyaromatic hydrocarbons (PAHs) in addition to oxygenated compounds that are structurally similar to dioxins [76,105]. These precursor compounds form dioxins through chlorination, condensation and oxidation processes [106].…”

Section: The Precursor Synthesis Of Dioxins and Furansmentioning

confidence: 99%

“…Review Paper SN Applied Sciences (2020) 2:1729 | https://doi.org/10.1007/s42452-020-03551-y interestingly show that the release of PCDD/Fs is directly proportional to the rate of consumption of carbon [54]. The formation of PCDDs is believed to be a sequential multistep reaction that proceeds by coupling of chlorophenol-often a surface catalysed mechanism involving ring closure which proceeds via a catalytic process by an electron donor oxidant whose role is to enable the coupling of two benzene rings as shown in Scheme 2 [76,105]. This mechanism also proposes the formation of polychlorodibenzofurans (PCDFs) from the combustion chamber from where chlorine is released in form of HCl which ultimately reacts with products formed from incomplete combustion to generate dioxin precursor compounds (Scheme 3), notably chlorinated phenols and benzenes at a temperature of about 450 °C [131].…”

Section: The Precursor Synthesis Of Dioxins and Furansmentioning

confidence: 99%

“…This process is characterized by the following steps (a) creation of fly ash and incomplete combustion products (b) formation of surface-active molecular precursors (c) complex organic radical reactions and (d) partial desorption of products [127]. Chlorinated phenols such as 2-monochlorophenol (2-MCP) and benzenoids (benzenes) at a temperature window of 200-450 °C then undergo both condensation and de-chlorination reaction processes which are catalytically induced [76,114]. Polychlorinated benzenes are suggested to form by either radical mechanisms or by the combination of chlorine and chlorobenzyl radicals [127].…”

Section: The Precursor Synthesis Of Dioxins and Furansmentioning

confidence: 99%

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A review of persistent organic pollutants: dioxins, furans, and their associated nitrogenated analogues

et al. 2020

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Dioxins and furans are no doubt the most notorious class of organochlorine toxicants in the environmental system whose adverse effects are detrimental to public health with extreme negative economic impacts. Polychlorinated dibenzop-dioxin and dibenzofurans and dioxin-like compounds such as the polychlorinated biphenyls, carbazoles are in the class of persistent organic pollutants-prioritized under the Stockholm convention as the "dirty dozens", besides being listed as group 1 human carcinogens by the International Agency for Research on Cancer. Because of their recalcitrant nature in the environment, bioaccumulation in lipids of cells of animals and their general toxicities, this family of compounds has received increased scientific interest in pollution and toxicology research. Accumulation of these toxicants in lipids of animals, and human exposure has been traced to animal products such as meat, eggs, milk and fish. Combustion events, industrial and municipal waste incineration practices, open fires and some industrial activities especially those dealing with metallurgy are well-established sources of these environmental contaminants. The critical aspects of dioxins, furans and their analogues; notably their sources their mechanistic formation by precursor initiation, de novo pathways, how they manifest their toxicity by activation of aryl hydrocarbon receptor, detoxification of these chemicals from the environment and the analytical methods used to quantify and detect from environmental sample matrices has been explored in this work. This review also provides an in-depth examination of the toxic characteristic behaviour of dioxins and furans, polycyclic aromatic hydrocarbons as well as the emerging nitrogenated analogues of dioxins such as polychlorinated carbazole, and carbazole itself.

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Role of Fe2O3 in fly ash surrogate on PCDD/Fs formation from 2-monochlorophenol

et al. 2019

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The correlation between the content and morphology of Fe 2 O 3 and the yields of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) was studied in this work. Three fly ash surrogates containing 1%, 2.5%, and 4% of Fe 2 O 3 were prepared and their effects on PCDD/Fs formation were investigated and compared to our previously studied 5% iron oxide sample using 2-monochlorophenol precursor model. As the intermediate of PCCD/Fs, environmentally persistent free radical formation propensity was correlated with the PCDD/Fs formation yields for different iron oxide samples. PCDD/Fs yield increases exponentially with the increasing iron content under pyrolytic conditions. On the contrary, low iron oxide content promotes oxidation and lowers yields of PCDD/Fs. Changing iron oxide clusters morphology (crystallinity and cluster size) affects the mechanism of PCDD/Fs formation-on larger crystallites, a bidentate chemisorption of precursor is preferred leading to lower chlorinated congeners, while smaller clusters promote formation of PCDFs through mixed monodentatebidentate surface species, resulting in formation of congeners with 1 chlorine more. This studies further confirm the propensity of iron oxide to predominantly form PCDFs. The iron content also defines PCDDs:PCDFs ratio.

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

Cited by 4 publications

References 43 publications

Dioxin and dibenzofuran like molecular analogues from the pyrolysis of biomass materials—the emerging challenge in bio-oil production

Dioxin and dibenzofuran like molecular analogues from the pyrolysis of biomass materials—the emerging challenge in bio-oil production

A review of persistent organic pollutants: dioxins, furans, and their associated nitrogenated analogues

Role of Fe2O3 in fly ash surrogate on PCDD/Fs formation from 2-monochlorophenol

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