Dioxin Control Research Articles

DFT and AIMD insights into heterogeneous dissociation of 2-chlorothiophenol on CuO(111) surface: Impact of H2O and OH

Copper oxides are vital catalysts in facilitating the formation of polychlorinated thianthrenes/dibenzothiophenes (PCTA/DTs) through heterogeneous reactions in high-temperature industrial processes. Chlorothiophenols (CTPs) are the most crucial precursors for PCTA/DT formation. The initial step in this process is the metal-catalyzed production of chlorothiophenoxy radicals (CTPRs) from CTPs via dissociation reactions. This work combines density functional theory (DFT) calculations with ab initio molecular dynamics (AIMD) simulations to explore the formation mechanism of the adsorbed 2-CTPR from 2-CTP, with the assistance of CuO(111). Our study demonstrates that flat adsorption configurations of 2-CTP on the CuO(111) surface are more stable than vertical configurations. The CuO(111) surface acts as a strong catalyst, facilitating the dissociation of 2-CTP into the adsorbed 2-CTPR. Surface oxygen vacancies enhance the adsorption of 2-CTP on the CuO(111) surface, while moderately suppressing the dissociation of 2-CTP. More importantly, water molecules and surface hydroxyl groups actively promote the dissociation of 2-CTP. Specifically, water directly participates in the reaction through “water bridge”, enabling a barrier-free process. This research provides molecular-level insights into the heterogeneous generation of dioxins with the catalysis of metal oxides in fly ash from static and dynamic aspects, providing novel approaches for reducing dioxin emissions and establishing dioxin control strategies.

Formation of Pre-PCTA/DT Intermediates from 2-Chlorothiophenol on Silica Clusters: A Quantum Mechanical Study.

Silica (SiO2), accounting for the main component of fly ash, plays a vital role in the heterogeneous formation of polychlorinated thianthrenes/dibenzothiophenes (PCTA/DTs) in high-temperature industrial processes. Silica clusters, as the basic units of silica, provide reasonable models to understand the general trends of complex surface reactions. Chlorothiophenols (CTPs) are the most crucial precursors for PCTA/DT formation. By employing density functional theory, this study examined the formation of 2-chlorothiophenolate from 2-CTP adsorbed on the dehydrated silica cluster ((SiO2)3) and the hydroxylated silica cluster ((SiO2)3O2H4). Additionally, this study investigated the formation of pre-PCTA/DTs, the crucial intermediates involved in PCTA/DT formation, from the coupling of two adsorbed 2-chlorothiophenolates via the Langmuir-Hinshelwood (L-H) mechanism and the coupling of adsorbed 2-chlorothiophenolate with gas-phase 2-CTP via the Eley-Rideal (E-R) mechanism on silica clusters. Moreover, the rate constants for the main elementary steps were calculated over the temperature range of 600-1200 K. Our study demonstrates that the 2-CTP is more likely to adsorb on the termination of the dehydrated silica cluster, which exhibits more effective catalysis in the formation of 2-chlorothiophenolate compared with the hydroxylated silica cluster. Moreover, the E-R mechanism mainly contributes to the formation of pre-PCTAs, whereas the L-H mechanism is prone to the formation of pre-PCDTs on dehydrated and hydroxylated silica clusters. Silica can act as a relatively mild catalyst in facilitating the heterogeneous formation of pre-PCTA/DTs from 2-CTP. This research provides new insights into the surface-mediated generation of PCTA/DTs, further providing theoretical foundations to reduce dioxin emission and establish dioxin control strategies.

Dioxin Control in the Co-processing of Waste Printed Circuit Board and Copper Concentrate with an Ausmelt Furnace

Dioxin Control in the Co-processing of Waste Printed Circuit Board and Copper Concentrate with an Ausmelt Furnace

Dioxin emission prediction from a full-scale municipal solid waste incinerator: Deep learning model in time-series input

The immeasurability of real-time dioxin emissions is the principal limitation to controlling and reducing dioxin emissions in municipal solid waste incineration (MSWI). Existing methods for dioxin emissions prediction are based on machine learning with inadequate dioxin datasets. In this study, the deep learning models are trained through larger online dioxin emissions data from a waste incinerator to predict real-time dioxin emissions. First, data are collected and the operating data are preprocessed. Then, the dioxin emission prediction performance of the machine learning and deep learning models, including long short-term memory (LSTM) and convolutional neural networks (CNN), with normal input and time-series input are compared. We evaluate the applicability of each model and find that the performance of the deep learning models (LSTM and CNN) has improved by 36.5% and 30.4%, respectively, in terms of the mean square error (MSE) with the time-series input. Moreover, through feature analysis, we find that temperature, airflow, and time dimension are considerable for dioxin prediction. The results are meaningful for optimizing the control of dioxins from MSWI.

Effect of Water Molecule on the Complete Series Reactions of Chlorothiobenzenes with H/·OH: A Theoretical Study

The chlorothiobenzenes (CTBs) are the principal precursors for the formation of polychlorinated thianthrene/dibenzothiophenes (PCTA/DTs), which have high toxicity and wide distribution in the environment. Under the pyrolysis or combustion conditions, CTBs can react with H/·OH radicals to form the chlorothiobenzyl radicals (CTBRs) through abstraction of the chlorothiobenzyl-hydrogen. The water molecule can play an important role in this process. The coupling of CTBRs is the essential first step in forming PCTA/DTs. In this paper, quantum chemical calculations were carried out to investigate the formation of CTBRs from the complete series reactions of 19 chlorothiobenzene (CTB) congeners with H/·OH radicals in the presence of the water molecule. Using the MPWB1K/6-311 + G(3df,2p)//MPWB1K/6-31 + G(d,p) energy level, schematic energy profiles were constructed with the water molecule and then compared with the non-hydrated case. The present study shows that structural parameters and thermal data, as well as CTBRs formation potential from CTBs, are strongly dominated by the chlorine substitution at the ortho-position of CTBs. Meanwhile, the water molecule can promote the CTBR formation from CTBs abstracted by H/·OH, which has a stronger catalysis effect on the H abstraction from CTBs by OH than from CTBs by H. This study may provide reference parameters for future experimental research, which would enhance measures to reduce dioxin emission and establish dioxin control strategies.

Formation and control of dioxins during thermal desorption remediation of chlorine and non-chlorine organic contaminated soil

Formation and emission of dioxins is a great concern during thermal desorption remediation of organic contaminated soil. The differential formation of dioxins from chlorine organic contaminated soil (COCS) and non-chlorine organic contaminated soil (NCOCS) is still unclear and the control technique for the dioxins generated is an urgent need. In this study, the formation and distribution characteristics of dioxins were investigated in the thermal desorption unit combined with flue gas purification system during COCS and NCOCS treatments. Although organic contaminates were well desorbed, de-novo formation of dioxins was observed for both COCS and NCOCS, as well as synthesis from precursors for NCOCS. The gas-phase dioxin in the flue gas purification system continuously decreased during NCOCS thermal desorption, while the dioxin concentration in the quench tower sharply increased from 0.46 to 2.13 ng/Nm3 through de-novo synthesis during COCS treatment. Furthermore, the emission of dioxins only slightly reduced (for COCS) or even increased (for NCOCS) at 70% operating load. The catalytic adsorption tower within modified activated carbon and V5-Mo5-Ti catalyst after bag filter can reduce the emission of dioxins up to 91.4% at the condition of secondary combustion chamber closure, demonstrating that the catalytic adsorption tower can replace the secondary combustion chamber for controlling dioxin emission. More importantly, the highly toxic low-chlorinated polychlorinated dibenzodioxins and polychlorinated dibenzofurans (PCDD/PCDFs) were selectively removed from flue gas by the catalytic adsorption tower. These results reveal the differential formation characteristics of dioxins during COCS and NCOCS thermal treatments and highlight V5-Mo5-Ti/ modified activated carbon as a promising catalytic adsorption material to control the emission of dioxins from the thermal desorption of organic contaminated soil.

Model framework to quantify the effectiveness of garbage classification in reducing dioxin emissions

Although waste incineration is a promising disposal method, it produces unwanted combustion by-products, such as toxic dioxins, that can be unintentionally emitted. Kitchen scraps can result in incomplete combustion of waste, which accelerates the formation of dioxins, especially for the small-sized incinerators without identical operating temperature. Consequently, garbage classification before waste incineration is critical for dioxin control in the small-sized waste incineration industries. To date, the influence of garbage classification on dioxin emissions has not been quantified. In this study, a model framework integrating the grey prediction model and autoregressive prediction model was established and used to predict future dioxin emissions from small-sized waste incineration. If garbage classification is ideally strictly implemented, annual dioxin emissions could be reduced by up to 1697 g TEQ over the next 10 years. Garbage classification reduced emissions by about 30.7% compared with incineration of mixed municipal solid waste without classification (5534 g TEQ over the next 10 years). The established model framework can effectively assess the influence of garbage classification on dioxin emissions from waste incineration, which could facilitate the widespread adoption of garbage classification.

Dioxins control as co-processing water-washed municipal solid waste incineration fly ash in iron ore sintering process

Co-processing water-washed municipal solid waste incineration fly ash (WM-FA) in iron ore sintering process is of great prospect. In this paper, the emission characteristics of dioxins during sintering process combined with WM-FA were studied, and the control method for dioxins was proposed. The results showed that adding WM-FA in the form of pellets with diameter 5–8 mm slightly influenced sinter quality. Increasing the diameter of WM-FA from 5–8 mm to 10–12 mm helped to reduce the concentration of PCDD/Fs from 1.0425 ng I-TEQ/N m3 to 0.7720 ng I-TEQ/N m3. However, compared with no WM-FA adding case, adding WM-FA pellets caused the increase of PCDD/Fs concentration in the sintering flue gas. A novel method for dioxin control was proposed through preparing WM-FA into 5–8 mm pellets and coated with CaO-containing additive with its function to adsorb and fix HCl and Cl2, which were the key components to synthesize dioxin. Due to the inhibiting effect of CaO to the chlorination reaction, the emission concentration of PCDD/Fs was decreased to 0.6240 ng I-TEQ/N m3, which was lower than that of no WM-FA adding case. The research findings lay a foundation for the resource utilization of WM-FA and the harmonious development of city and steel plant.

Global status of dioxin emission and China’s role in reducing the emission

The global status of dioxin emissions across 150 countries/regions were compiled in this study. China, the major emitter of dioxin and the largest developing country, was chosen as an example to illustrate its emission reductions. The global dioxin emissions were about 97.0 kg TEQ/year, Asia and Africa emitted the most dioxins among the continents. Globally, open burning processes were the most important sources of dioxins. Dioxin emissions in developed countries have remained at low and stable level, while those in developing countries have remained at relatively high level or have continued to increase in recent years. It can be speculated that the global dioxin emissions will increase first and then decrease in the future. Chinese dioxin emissions were stable around 9 kg toxic equivalent (TEQ) in recent years, while 17 subcategories are the key sources of dioxin control in the future. Moreover, according to analysis toward China’s dioxin emission trend and sources, there is a large space for dioxins reduction in industries such as metal production, waste incineration and disposal. The results indicated that there is at least 30–70% of reduction scope in China based on three scenarios, and this will reduce the world's annual dioxin emissions by 2.7–6.8%.

Formation, Measurement, and Control of Dioxins from the Incineration of Municipal Solid Wastes: Recent Advances and Perspectives

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) consist of 210 kinds of pollutants, 17 of which are highly toxic to humans. PCDD/F is mainly produced during comb...

Evaluation and Screening of Dioxin Control Technology in Waste Incineration Flue Gas

To determine the best control technology for dioxin in waste incineration flue gas, a three-level comprehensive evaluation index system with environment, economy, and technology as the first-level indexes was constructed. The fuzzy comprehensive evaluation method and the analytic hierarchy process (AHP) were used to evaluate ten dioxin pollution control technologies or technology groups including "double bag activated carbon adsorption technology," "sulfur and sulfide inhibition technology," and "sulfur and sulfide inhibition technology+activated carbon fixed bed reactor technology". The "sulfur and sulfur compound inhibition technology+activated carbon fixed bed technology" scored the highest, and thus is currently the best control technology for dioxin pollution in waste incineration exhaust gas. This technology is suitable for small rural waste incinerators to ensure that dioxin emissions meet the standards. Depending on the local economic development level, enterprise scale, furnace profile, and technological process, waste incineration enterprises in various regions of China can adopt this index evaluation system and method to evaluate the dioxin control technologies and select the best one suitable for the enterprise so that dioxin emissions in the waste incineration flue gas can be effectively controlled.

Influence of gas atmosphere on synergistic control of mercury and dioxin by non-thermal plasma

In this paper, narrow-pulse power discharge is used to study the synergistic control of mercury and dioxins, in which 1,2,4-trichlorobenzene (TCB) was used as a dioxin analog, by using a self-designed experimental system. The competitive effects of NO, SO2 and HCl on the TCB removal by non-thermal plasma are discussed. The influence of acid gas on TCB degradation is reflected in the competitive effect. NO has the greatest influence on TCB degradation efficiency. The oxidation efficiency of Hg0 decreased by about 10% in all three acidic gas atmospheres, and the effect of each gas component on Hg0 oxidation is complex. In the flue gas atmosphere of ‘acid gas + Hg0 + TCB’, the mechanism of the synergistic control of Hg0 and TCB by the non-thermal plasma is different, which has competition and promotion relationship between each other. The contribution of various flue gas components to the results was complicated, but the overall experimental results show that the synergistic control effect of the system can continue to improve. According to the generated product backstepping, ·OH plays an important role in the synergistic control of the degradation of Hg0 and TCB. Through this study, we hope to provide basic research data for the collaborative control of flue gas in the incineration industry.

Detoxification of municipal solid waste incinerator (MSWI) fly ash by single-mode microwave (MW) irradiation: Addition of urea on the degradation of Dioxin and mechanism.

The detoxification of municipal solid waste incinerator (MSWI) fly ash dioxins urgently requires an effective treatment technology. In this study, we adopted a single-mode microwave (MW)-based pyrolysis to treat MSWI fly ash under N2 atmosphere and further elucidated the main influencing factors, including the chemical inhibitor, for dioxin control. The results show that (1) the detoxification process was optimized with a mass ratio of fly ash to SiC of 1:9, 23.1% (wt%) urea addition and pyrolysis temperature of ˜ 480 °C; (2) the total polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) destruction efficiency and the bioassay-derived 2,3,7,8-TCDD toxic equivalent (Bio-TEQ) removal efficiency reached 98.5% and 97.9%, respectively, accompanied with ˜ 1.3% of the total amount of dioxin being submitted to exhaust gas; (3) the MW-based pyrolysis of urea (133˜300 °C) was favourable for the generation of hot spots as well as the PCDD/F rapid destruction in fly ash. In addition, the leaching toxicity of heavy metals was also partially reduced after MW pyrolysis reactions. To the best of our knowledge, this is the first report adopting a MW-based pyrolysis to eliminate dioxin in MSWI fly ash with the addition of urea, which is a promising alternative to current methods.

Experimental study on dioxin formation in an MSW gasification-combustion process: An attempt for the simultaneous control of dioxins and nitrogen oxides

A gasification-combustion conversion process has been proposed for MSW disposal, and the positive effect of “homogeneous conversion” and “staged combustion” on the stabilization of Cl atoms and the rupture of CCl has been proved previously in fundamental experiments. To verify and evaluate their inhibition effect on dioxin generation, a bench-scale experimental system of the proposed process was established in the present work and an experimental study on the formation of dioxins in the process was carried out. Since both dioxins and nitrogen oxides should be strictly controlled while applied in industry, the simultaneous control of nitrogen oxides was also considered. Results indicated that “homogeneous conversion” has a clear inhibition effect on dioxins in both the syngas from gasification and the flue gas from combustion, which is a very important process in the stabilization of Cl atoms and the control of dioxins. During the “staged combustion” of the syngas, the increase of SR1, the rise of temperature and the extension of residence time all have a clear inhibition effect on dioxins in the flue gas. The extension of residence time seems to be more efficient, and while increasing SR1 and temperature, the regeneration of active chlorine species and the increase of NO need to be concerned. By the combination of “homogeneous conversion” with a temperature of 700 °C and “staged combustion” with a SR1/SR2 ratio of 0.7/0.4, a temperature of 900 °C, a residence time of 241 ms, a satisfactory simultaneous control of both dioxins and nitrogen oxides was obtained in the experiments of the present work.

Application status and comparison of dioxin removal technologies for iron ore sintering process

The emission of dioxins from the iron ore sintering process is the largest emission source of dioxins, and the reduction in dioxin emission from the iron ore sintering process to the environment is increasingly important. Three approaches to control the emission of dioxins were reviewed: source control, process control, and terminal control. Among them, two terminal control technologies, activated carbon adsorption and selective reduction technology, were discussed in detail. Following a comparison of the reduction technologies, the terminal control method was indicated as the key technology to achieve good control of dioxins during the sintering process. For the technical characteristics of the sintering process and flue gas, multiple methods should be collectively considered, and the most suitable method may be addition of inhibitors + ultra-clean dust collection (electrostatic precipitation/bag filter) + desulphurization + selective catalytic reduction to sufficiently remove multiple pollutants, which provides a direction for the cooperative disposal of flue gas pollutants in future.

Catalytic decomposition of dioxins and other unintentional POPs in flue gas from a municipal waste incinerator (MWI) in China: a pilot testing.

Unintentionally produced persistent organic pollutants (UPOPs) include polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), dioxin-like polychlorinated biphenyls (dl-PCBs), pentachlorobenzene (PeCBz), and hexachlorobenzene (HxCBz). With the booming of municipal waste incinerators (MWIs) in China, the emission of UPOPs has generated great concern. As an alternative technology of dioxin control, catalytic decomposition has not been used in China, mainly due to the absence of national demonstration projects. Also, the simultaneous removal of various UPOPs has not been well investigated.In this study, a pilot-scale selective catalytic oxidative (SCO) system using a self-developed honeycomb catalyst was built and tested in a typical municipal waste incinerator (MWI) of China. The original concentration of PCDD/Fs in flue gas after the treatment of activated carbon injection (ACI) still exceeded the national emission standard (0.1ng I-TEQ/Nm3), while the concentrations of PeCBz and HxCBz were one order of magnitude higher than that of PCDD/Fs. For the testing temperature varying from 300 to 200°C, the removal efficiency of PCDD/Fs range from 39 to 95%, followed by dl-PCBs with the range of 56-89%. PeCBz and HxCBz were also removed, though their removal efficiencies were lower than those of PCDD/Fs and dl-PCBs. Both temperature and degree of chlorination influence the removal efficiencies.

Determination of optimum dose of adsorbent for PCDD/F removal in the flue gas of a medical waste incineration plant

In this study, congener profile and gas/particle partitioning of PCDD/F compounds was investigated and the optimum adsorbent (activated lignite) injection dose for the control of dioxins and furans was determined in a medical waste incineration plant.99% of the congeners was found to be in particle phase in the flue gas. Especially, congeners with higher chlorine substitution were dominant. Samples were taken at two different points, one in the upstream of activated lignite injection and the other is in the stack. At the first sampling point, particle phase concentration was found to be between 29 and 282ngNm−3 (1–21ng I-TEQNm−3) and gas phase concentration ranged between 0.3 and 4ngNm−3 (0.1–0.2ng I-TEQNm−3). Emission limit of 0.1ng I-TEQNm−3 was not exceeded at the stack where concentrations ranged from 2.5 to 5.52ngNm−3 (0.0 to 0.2ng I-TEQNm−3) and 0.03 to 0.2ngNm−3 (0–0ng I-TEQNm−3) for particle and gas phases, respectively.Optimum activated lignite dosage was determined to be 0.5kgh−1. Adsorption on activated lignite is considered as removal mechanisms of gas phase PCDD/Fs in flue gas. In addition to as 99% of these compounds are present in particle phase, they are captured by the bag filter.

The promotional effect of MoO3 doped V2O5/TiO2 for chlorobenzene oxidation

A series of V2O5–MoO3/TiO2 catalysts prepared by an impregnation method was investigated on their catalytic performance of chlorobenzene oxidation. This study demonstrated that MoO3 is a dopant, which can improve catalyst redox properties and enhance chlorobenzene oxidation catalytic activity at low temperature. Compared to V2O5–TiO2 and V2O5–WO3/TiO2 catalysts, V2O5–MoO3/TiO2 catalysts showed outstanding activity on chlorobenzene oxidation, which is due to the promoting influence of MoO3. For excellent catalytic performance and good N2 selectivity with water, the V2O5–MoO3/TiO2 catalysts may have promising commercial potential for the synergetic control of dioxins and NOx emitted from stationary sources.

Study on Emission Control of Dioxins by Thermal Decomposition

In this paper, we present the data regarding the thermal decomposition of PCDD/Fs during the manufacturing process of ceramisite from MSWI fly ash, and the efficiency of bag filter with activated carbon injection technology to reduce the gas emission of PCDD/Fs. The distribution of seventeen 2,3,7,8-chlorinated dioxins and furans in MSWI fly ash, ceramisite product, bag filter ash and emission gases were analyzed, and the international toxic equivalents (I-TEQ as 2,3,7,8-tetraCDD) values were calculated by using international-toxicity equivalency factor (I-TEF). The total I-TEQ value of PCDD/Fs in MSWI fly ash reached up to 904.944 ng/kg. After high temperature calcining, only 1.250 ng I-TEQ/kg of PCDD/Fs is left in the ceramisite product. The concentrations of PCDD/Fs in two kinds of bag filter ashes, with activated carbon injection (AC) and without activated carbon injection (NAC), were 324.723 ng I-TEQ/kg and 217.066 ng I-TEQ/kg, respectively. The distribution patterns of seventeen 2,3,7,8-chlorinated dioxins and furans in MSWI fly ash, ceramisite product and bag filter ashes are alike, which suggested that the secondary formation of PCDD/Fs did not significantly occur during the thermal process of manufacturing ceramisite from MSWI fly ash. When no activated carbon was injected, the gas emission of PCDD/Fs was 0.373 ng I-TEQ/Nm3, but 100 mg/Nm3 of activated carbon injection, the gas emission of PCDD/Fs was declined to 0.081 ng I-TEQ/Nm3, which is lower than the gas emission limit established by the European Union Directive of 0.1 ng I-TEQ/Nm3. Therefor, we can recommend that the manufacturing ceramisite from MSWI fly ash using the developed rotary kiln system is an effective measure to safely dispose the MSWI fly ash on the aspect of dioxin emission control.

Multiple testing of food contact materials: A predictive algorithm for assessing the global migration from silicone moulds

For reasons of food safety, packaging and food contact materials must be submitted to migration tests. Testing of silicone moulds is often very laborious, since three replicate tests are required to decide about their compliancy. This paper presents a general modelling framework to predict the sample's compliance or non-compliance using results of the first two migration tests. It compares the outcomes of models with multiple continuous predictors with a class of models involving latent and dummy variables. The model's prediction ability was tested using cross and external validations, i.e. model revalidation each time a new measurement set became available. At the overall migration limit of 10mgdm−², the relative uncertainty on a prediction was estimated to be ∼10%. Taking the default values for α and β equal to 0.05, the maximum value that can be predicted for sample compliance was therefore 7mgdm−2. Beyond this limit the risk for false compliant results increases significantly, and a third migration test should be performed. The result of this latter test defines the sample's compliance or non-compliance. Propositions for compliancy control inspired by the current dioxin control strategy are discussed.