Formation Of Dioxins Research Articles

Kinetic Properties for the Complete Series Reactions of Chlorophenols with OH Radicals—Relevance for Dioxin Formation

The chlorophenoxy radical (CPR) is a key intermediate species in the formation of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs). In municipal waste incinerators, the reactions of chlorophenols with OH radicals play the most central role in the formation of chlorophenoxy radicals. In this paper, molecular orbital theory calculations have been performed to investigate the formation of chlorophenoxy radicals from the complete series reactions of 19 chlorophenol congeners with OH radicals. The single-point energy calculation was carried out at the MPWB1K/6-311+G(3df,2p) level on the basis of the MPWB1K/6-31+G(d,p) optimized geometries. The kinetic modeling of the PCDD/PCDF (PCDD/F for short) formation demands the knowledge of the rate parameters for the formation of chlorophenoxy radicals from chlorophenols. So, the kinetic properties of the reactions of chlorophenols with OH radicals were deduced over a wide temperature range of 600-1200 K using canonical variational transition-state theory (CVT) with small curvature tunneling contribution (SCT). This study shows that the chlorine substitution at the ortho position in chlorophenol not only has a significant effect on the structures of chlorophenols, prereactive intermediates, the transition states, and chlorophenoxy radicals, but also plays a decisive role in determining the rate parameters.

The Possibilities of Reduction of Polychlorinated Dibenzo-P-Dioxins and Polychlorinated Dibenzofurans Emission

In the study the most important and known polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzo-furans (PCDFs) emission sources are presented and known methods of reduction of dioxin emission to the atmosphere are discussed in detail. It is indicated that the most relevant emission source is a combustion process. The mechanism of dioxin formation in thermal processes is presented in brief. The author characterized primary methods of reduction of PCDDs/PCDFs emission encompassing the interference into the combustion process to minimize their formation and discussed known secondary methods aimed at their removal from the stream of waste gases. It was attempted to make a critical assessment of PCDD/Fs reduction methods described in literature.

Dioxins and organohalogen contaminants in the Asia-Pacific region

This article reviews the outcome of comprehensive investigations conducted in our laboratory at CMES, Ehime University over the past three decades on the distribution, sources, temporal trends and toxic impacts of the persistent and bioaccumulative organohalogen contaminants in Asia-Pacific region with a particular emphasis on developing countries. Results of multi-media monitoring studies were compiled and discussed to provide in-depth understanding on various issues of dioxins and organohalogen contamination in both ambient environment and animals including humans. Prominent contaminations were found in the regions where they have been heavily used. The eastern Asian region is probably a potential source of pollution, particularly by the new contaminants such as polybrominated diphenyls ethers. These groups of contaminants, together with polychlorinated biphenyls, exhibited either decreasing or increasing trends depending on the extent of industrialization in Asian developing region, indicating the necessity for long term monitoring. The open dumping sites for municipal wastes in major cities are significant sources of many toxic chemicals, and these areas are probably one of the challenges for future research due to the long term impacts on the environmental quality and human health. The formation of dioxins and related compounds in such dumping sites and their elevated residues found in breast milk of residents living in and around warrant long term impacts of dioxins upon next generations. Comprehensive and long term monitoring programs are urgently needed with close collaboration and proper capacity building in Asian developing countries in order to mitigate dioxin and organohalogen emission and their risk on ecosystems and human health.

More efficient gas ignition and cooling in large arc smelting furnaces

Thanks to the intensification of steel smelting and the increased fuel component in the energy balance of modern arc smelting furnaces, the quantity of gas formed in the furnace is greater and its composition is changed. This significantly affects the operational efficiency of the system for gas extraction and purification. These changes may call for major reconstruction or replacement of the gas-purification system. As we have been aware for almost two decades, the operation of arc smelting furnaces is associated with a serious environmental problem: the waste gases contain persistent organic pollutants, the most toxic of which are dioxins (polychlorinated dibenzodioxins, PCDD) and furans (polychlorinated dibenzofurans, PCDF). The production and use of such materials was forbidden by the Stockholm convention on persistent organic pollutants, which was signed in 2001 and went into force in 2004. The formation of dioxins and furans by arc smelting furnaces is primarily associated with the use of contaminated metal scrap, which supplies its contaminants to the furnace. These consist of residues of polymer coatings and other materials containing halogens—predominantly chlorine. In shredded automobile scrap, for instance, such pollutants may constitute 2% of the total mass. As an example, we now assess the reduced PCDD/PCDF mass in unorganized emissions when steel scrap is loaded in the arc smelting furnace (per 1 t of scrap, with a maximum

Japan’s waste management policies for dioxins and polychlorinated biphenyls

We summarize the measures taken by the Japanese government to prevent the emission of dioxins and polychlorinated biphenyls (PCBs) into the environment. Because incineration is the main method of waste management in Japan, reducing the amount of dioxins emitted from waste incinerators is an essential aspect of proper waste treatment. Intensive measures to prevent the formation of dioxins at the source have been implemented, with a focus on waste treatment methods and improving comprehensive management. The efforts have been very successful, with a 95% reduction in the amount of dioxins emitted between 1997 and 2003. The toxicity of PCBs has been monitored with keen interest since the Yusho incident. Unfortunately, treatment facilities for PCB wastes were not built until long after PCBs had been removed from use, and PCB wastes remained in storage in an untreated state. The Japanese government has promoted the construction of facilities for treating PCB wastes, and five such facilities have commenced operations. To more completely eradicate dioxins, a future challenge will be to reduce the amount of PCB-derived dioxins, which are persistent in the environment and have a long exposure pathway from the environment media to the organism and the human body.

Possible Role for Cu(II) Compounds in the Oxidation of Malonyl Dichloride and HCl at Cu(110) Surfaces

The pathway for the chlorination of Cu(110) surfaces by malonyl dichloride and HCl is changed in the presence of oxygen with STM results suggesting the formation of a surface CuCl2 state at room temperature that may have implications for mechanistic models of the Deacon process and of dioxin formation at aerosol particle surfaces.

Pyrolysis of permethrin and formation of precursors of polychlorinated dibenzo- p-dioxins and dibenzofurans (PCDD/F) under non-oxidative conditions

This article reports the computational and experimental results of the thermal decomposition of permethrin, a potential source of dibenzo- p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF). We have performed a quantum chemical analysis by applying density functional theory to obtain the decomposition pathways of permethrin and the formation mechanism of dibenzofuran. We have conducted the pyrolysis experiments in a tubular reactor and identified the pyrolysis products to demonstrate the agreement between the experimental measurements and quantum chemical calculations. The initiation of the decomposition of permethrin involves principally the aromatisation of permethrin into 3-phenoxyphenylacetic acid, 2-methylphenyl ester (J) and concomitant loss of 2HCl. This rearrangement is followed by the rupture of the O–CH 2 linkage in J, with a rate constant derived from the quantum chemical results of 1 × 10 15 exp(−68 kcal/mol/ RT) s −1 for temperatures between 700 and 1300 K. This is confirmed by finding that the rate constant for unimolecular rearrangement of permethrin into J is 1.2 × 10 12 exp(−53 kcal/mol/ RT) s −1 over the same range of temperatures and exceeds the direct fission rate constant at all temperatures up to 850 ± 120 °C as well as by the experimental detection of J prior to the detection of the initial products incorporating diphenyl ether, 1-methyl-3-phenoxybenzene, 3-phenoxybenzaldehyde and 1-chloromethyl-3-phenoxybenzene. As the temperature increases, we observe a rise in secondary products formed directly or indirectly (via phenol/phenoxy) including aromatics (naphthalene), biphenyls (biphenyl, 4-methyl-1,1′-biphenyl) and dibenzofuran (DF). In particular, we discover by means of quantum chemistry a direct route from 2-phenoxyphenoxy to naphthalene. We detect no polychlorinated dibenzo- p-dioxins and dibenzofurans. Unlike the case of oxidative pyrolysis [Tame, N.W., Dlugogorski, B.Z., Kennedy, E.M., 2007b. Formation of dioxins in fires of arsenic-free treated wood: Role of organic preservatives. Environ. Sci. Technol. 41, 6425–6432] where significant yields of both PCDD and PCDF were obtained, under non-oxidative conditions the thermal decomposition of permethrin does not form appreciable amounts of PCDD or PCDF and the presence of oxygen (and/or a sizable radical pool) appears necessary for the formation of dibenzo- p-dioxin itself or PCDD/F from phenol/phenoxy.

Chlorination Mechanism of Carbon during Dioxins Formation by Using Cl-K Near Edge X-Ray Absorption Fine Structure

環境有機化学物質の多くは塩素が存在している．そのため，炭素の塩素化機構を知る必要がある．都市ごみ焼却プロセスの一次燃焼後に捕集される飛灰中には，大量のダイオキシン類が生成する．本研究は，塩素のCl-K X線吸収端近傍構造（NEXAFS）の測定を実飛灰及び重金属塩化物1種を混合した模擬飛灰に対して行い，飛灰での炭素の塩素化機構を解明することを目的とした．その結果，Cl-K NEXAFSにより塩素の形態が有機物なのか無機物なのかをピークにより簡便に分類でき，重金属の種に依存せず横断的な分析を容易にできることが明らかになった．スペクトル解析の結果，実飛灰中でのダイオキシン類の生成に大きく関与すると考えられる，塩化銅（II）の300℃ での還元，塩化鉄（III）の400℃ での酸化を模擬飛灰のCl-K NEXAFSにより示すことができた．

305 アルミニウムスクラップ溶解炉からのPOPs排出抑制のためのバグフィルター運転条件の探索(大気環境保全・改善技術(2))

Research on operationg conditions of fabric filters to minimize an emission of unintentionally produced POPs from aluminum alloy smelting plants was conducted. A small experimental fabric filter installed in a tentative flue gas line from a recycled aluminum smelting furnace was used instead of the actual operating filter. The results shows that more than 90 % removal efficiency of dioxins by using the fabric filter requires as low as 75C of the temperature of filter surface for the aluminum smelting plants. It means dioxin formation in the fabric filter could not be ignored below 100 C although it is known to be negligible less than 200 C in the case of waste incinerators flue gas. Injection of NaOH solution in an upper stream of the filter is quite effective for dioxin reduction and not so far for PCBs and HCBz. However, injection of activated carbon is effective enough in reduction of PCBs and HCB and not so far of dioxins. The reason of same operation exerts different effects on reduction of PCBs and HCB by fabric filters from dioxins, is attributed to the difference of their formation mechanisms.

De-novo formation of dioxins and furans and the memory effect in waste incineration flue gases

The formation of dioxin (polychlorinated-rho-dibenzodioxins - PCDD) and furan (polychlorinated dibenzofurans - PCDF) in waste incineration flyash in relation to temperature has been investigated in a bench scale reactor. The PCDD/PCDF released into the exhaust gases of the reactor and trapped in a condensation and vapour phase adsorption system were also determined. The concentrations of PCDD/PCDF in the flyash were analysed in detail for all congeners and isomers including the mono-, di- and tri-PCDD/PCDF. De-novo synthesis of PCDD/PCDF was clearly seen in the flyash with large changes in concentrations of PCDD/PCDF with only small changes in temperature. Exhaust gas PCDD/PCDF were detected at all temperatures, with the maximum emission occurring at a flyash temperature of 350 degrees C, where the equivalent of over 42 times the total dioxin/furan concentration of the original flyash was lost to the vapour phase per unit mass of initial flyash. Although the desorbed species were mainly the lower mono- to tri-congener group of dioxins and furans, the desorbed dioxin/furans had a considerable toxic equivalent value.

Thermogravimetric desorption and de novo tests I: Method development and validation

Thermogravimetric analysis (TGA) has been combined with evolved gas analysis (EGA) with the purpose of simulating the thermal behaviour of filter dust samples under inert (desorption) and de novo test oxidising conditions. Emphasis is on studying de novo formation of dioxins, surrogates and precursors arising from filter dust derived from thermal processes, such as municipal solid waste incineration and metallurgy. A new method is tested for sampling and analysing dioxin surrogates and precursors in the TGA effluent, which are collected on sampling tubes; the adsorbed compounds are eventually desorbed and quantified by TD-GC–MS. The major sources of error and losses are considered, including potential sorbent artefacts, possible breakthrough of volatiles through sampling tubes, or eventual losses of semi-volatiles due to their incomplete desorption or re-condensation inside the TG Analyser. The method is optimised and validated for di- to hexa-chlorinated benzenes in a range of 10–1000 ppb with average recovery exceeding 85%. The results are compared with data obtained in similar studies, performed by other research groups. As a result, the method provides the means for simulating de novo synthesis of dioxins in fly-ash and facilitates reliable and easy estimation of de novo activity, comparable with results of other studies, in combination with wide flexibility of testing conditions.

Observing copper chloride during dioxin formation using dispersive XAFS

AbstractThe incineration of municipal solid waste generates dioxins. To control dioxins, it is necessary to determine the mechanism of their formation. Because copper chloride (CuCl2) is one of the strongest catalysts of dioxin formation in fly ash, it is important to study the chemical changes of this compound. To determine the chemical changes of copper, Cu‐K x‐ray absorption near edge structure (XANES) spectra were examined during the heating of model fly ash using a time‐resolved dispersive x‐ray absorption fine structure (DXAFS) technique. The change in the absorption edge of the Cu‐K XANES spectrum revealed a change in the valence of copper and the temperature dependence of the reduction and oxidation of CuCl2. From room temperature to 270 °C, CuCl2 was reduced, and from > 270 to 300 °C, copper was reoxidized in the presence of 10% oxygen. At a constant temperature of 210 or 300 °C, copper was dynamically reduced and oxidized. In experiments using different gas streams, HCl gas had no effect on the reaction of copper, while oxygen gas was essential for the reoxidation of copper. Our results suggest that dioxin formation in fly ash occurs via the chlorination of carbon with the reduction of CuCl2 and carbon gasification catalyzed by copper oxides. Copyright © 2008 John Wiley & Sons, Ltd.

Verification of dioxin formation in a catalytic oxidizer

Emissions and inlet concentrations of polychlorinated dibenzo- p-dioxins and dibenzofurans (PCDD/PCDF) have been measured from a catalytic oxidizer and a thermal oxidizer. The catalyst inlet temperature was 427 °C. The thermal oxidizer operating temperature was 791 °C. Data of the toxic dioxin and furan congeners are reported. Important results of this field study are: (1) the catalytic oxidizer in this study produced an increase in PCDD/PCDF congener concentration of almost 10-fold from the inlet to the outlet (stack), thus verifying results of a previous study that evaluated only PCDD/PCDF emissions. All congeners increased from inlet to the stack. (2) The thermal oxidizer had little effect on PCDD/PCDF levels. There was a decrease in four of the congeners and an increase in 13 congeners. (3) Ambient air was the main source of PCDD/PCDFs in the stack emissions of the thermal oxidizer in this study. Laboratory investigations are needed to understand how PCDD/PCDFs are formed (and emitted) under conditions of this study.

Reduction in Dioxin Emissions by the Addition of Urea as Aqueous Solution to High-temperature Combustion Gas

In order to study the effect of urea addition to the waste gas on the dioxin formation, a series of experiments is carried out using the fly ashes sampled from two different types of solid waste incinerators. A remarkable suppression effect is obtained for the dioxin formation, while no clear change is observed for the obtained organic chlorine. Considering these results, the method of urea addition to the water splayed into the cooling tower of waste gas is proposed as an effective measure to suppress the dioxin formation at the cooling stage of the combustion gases. A verification test is carried out using an actual solid waste incinerator. When the concentration of urea in the splayed water is set to 0.1%, the toxicity concentration of the dioxins in the waste gas is reduced to approximately half that in the case without the addition. Further, the addition of urea does not significantly affect the concentration of NOx in the waste gas.

ダイオキシン生成抑制技術

ダイオキシン生成抑制技術

ENVIRONMENTAL FRIENDLY CONSUMPTION OF SCRAP TIRES IN EAF'S TO SAVE POWER & CARBON

World wastes nearly 1.3 billions of tire/year, while Iran wastes 8 millions pieces of tire annually. This study and investigation shows that waste tires can be a substitute for coal & coke in EAF as environmental friendly. In this study Esfahan Steel Company (ESCo) consumed waste tires with 6 Mg capacity EAF. Thirteen grades of steel including Iow, medium & high C content as well as Iow & high alloys were produced during 73 heats. The result was very successful & coke consumption rate reduced from 18 to 0 kg/Mg of steel. Electricity consumption decreased from 448 to 388 kWh/Mg. Stack gas analysis & measuring was done and the achieved results indicate the polluted gases content such as CO, NOX and SO2 is much less than the limited range. Industrial tests continued in Iran Alloy Steel Co. where 20 heats were made in 40 Mg capacity EAF with 30 MVA transformer capacities. The results are as follows: waste tires can be substitute for C in EAF steelmaking & the costs lowered by 5 €/Mg; the use of waste tires for additional chemical energy can further decrease electric energy consumption up to by 10-25%. The average S% in steel products was lower than 0.026; the environment is improved by consumption of waste tires in EAF instead of burying them in landfills. The process is reliable, economic & ecological. The large sized scrap tires like these of graders, mining earth movers, trucks & farm tires can be charged in EAF as whole used tires. Dioxin formation peaks at 200°C and decreases unsymmetrically with increasing temperature. Tires have virtually no Hg.

Improvement of Gas Utilization Ratio in the Gaseous Reduction of Iron Oxide and Suppression of Dioxins Formation in Combustion Processes by the Enhancement of Carbon Deposition

Improvement of Gas Utilization Ratio in the Gaseous Reduction of Iron Oxide and Suppression of Dioxins Formation in Combustion Processes by the Enhancement of Carbon Deposition

Dioxin levels in fly ash coming from the combustion of bagasse

Levels of dioxins (PCDD/Fs) were determined in fly ash samples collected from a power plant burning bagasse for production of electricity. The concentrations ranged from 2.2 pgWHO-TEQ/g to 190 pg WHO-TEQ/g with samples collected after ESP containing significantly much higher (more than 12 times on average) levels than samples collected before ESP. Our results seem to indicate that both the de novo and the precursor mechanisms are significantly involved in the formation of dioxins the fly ash during combustion of bagasse.

Dioxin/furan formation and release in the cement industry

Cement kilns firing hazardous waste are explicitly mentioned in the Stockholm Convention as an “industrial source having the potential for comparatively high formation and release of these chemicals to the environment”. The substitution of fossil fuels with alternative waste derived fuels is a well-developed practice in a number of countries. In the European cement industry about 6 million tonnes are used which corresponds to a thermal substitution rate of 17%. The current study evaluates around 2200 dioxin/furan stack emission measurements collected from various sources. It is demonstrated that most cement kilns can meet an emission level of 0.1 ng TEQ/Nm 3 if primary measures, i.e. process-integrated measures, are applied. Reducing the temperature to a level lower than 200 °C at the inlet of the air pollution control device is the key factor which has shown to limit dioxin formation and emissions at all types of cement kilns, independent of waste feeding.

Ecotoxicological characterization of photoelectrocatalytic process for degradation of pentachlorophenol on titania nanotubes electrode

Luminescence bioassay using Vibrio fischeri and in vitro ethoxyresorufin- O-deethylase (EROD) induction bioassay using H4-IIE rat hepatoma cell were employed to test toxicity changes during the photoelectrocatalysis process for the degradation of pentachlorophenol (PCP) on TiO 2 nanotubes electrode. Acute toxicity of the reaction solution reduced by 83% after 120 min of irradiation. Bioassay-derived 2,3,7,8-TCDD equivalents (TEQ bio) increased from 0.72 to 6.72 ng l −1 during the former reaction stage, decreasing rapidly to 1.25 ng l −1 during the latter reaction stage. HRGC/HRMS analysis detected polychlorinated dibenzo- p-dioxins/dibenzofurans (PCDD/Fs) congeners in the reaction mixtures. TEQ bio and chemical-derived 2,3,7,8-TCDD equivalents (TEQ cal) were about of the same order of magnitude. Both results illustrated the formation of dioxins and their removal by photoelectrocatalysis. Moreover, photoelectrocatalysis showed a significant priority over direct photolysis and photocatalysis depending on the reaction conditions, not only for PCP removal but also for reduction in toxicity.