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Wang Y, Huang J, Li S, Xu W, Wang H, Xu W, Li X. A mechanistic and kinetic investigation on the oxidative thermal decomposition of decabromodiphenyl ether. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2023; 333:121991. [PMID: 37328125 DOI: 10.1016/j.envpol.2023.121991] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2023] [Revised: 05/30/2023] [Accepted: 06/07/2023] [Indexed: 06/18/2023]
Abstract
The thermal processes of materials containing decabromodiphenyl ether (BDE-209) normally result in the exposure of BDE-209 to high-temperature environments, generating a series of hazardous compounds. However, the evolution mechanisms of BDE-209 during oxidative thermal processes remain unclear. Thus, this paper presents a detailed investigation on the oxidative thermal decomposition mechanism of BDE-209 by utilizing density functional theory methods at the M06/cc-pVDZ theoretical level. The results show that the barrierless fission of the ether linkage dominates the initial degradation of BDE-209 at all temperatures, with branching ratio over 80%. The decomposition of BDE-209 in oxidative thermal processes is mainly along BDE-209 → pentabromophenyl and pentabromophenoxy radicals → pentabromocyclopentadienyl radicals → brominated aliphatic products. Additionally, the study results on the formation mechanisms of several hazardous pollutants indicate that the ortho-phenyl-type radicals created by ortho-C-Br bond fission (branching ratio reached 15.1% at 1600 K) can easily be converted into octabrominated dibenzo-p-dioxin and furan, which require overcoming the energy barriers of 99.0 and 48.2 kJ/mol, respectively. The O/ortho-C coupling of two pentabromophenoxy radicals also acts as a non-negligible pathway for the formation of octabrominated dibenzo-p-dioxin. The synthesis of octabromonaphthalene involves the self-condensation of pentabromocyclopentadienyl radicals, followed by an intricately intramolecular evolution. Results presented in this study can enhance our understanding of the transformation mechanism of BDE-209 in thermal processes, and offer an insight into controlling the emissions of hazardous pollutants.
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Affiliation(s)
- Yao Wang
- School of Physics and Mechatronic Engineering, Guizhou Minzu University, Guiyang, 550025, China
| | - Jinbao Huang
- School of Physics and Mechatronic Engineering, Guizhou Minzu University, Guiyang, 550025, China.
| | - Sijia Li
- School of Physics and Mechatronic Engineering, Guizhou Minzu University, Guiyang, 550025, China
| | - Weifeng Xu
- School of Physics and Mechatronic Engineering, Guizhou Minzu University, Guiyang, 550025, China
| | - Hong Wang
- School of Physics and Mechatronic Engineering, Guizhou Minzu University, Guiyang, 550025, China
| | - Weiwei Xu
- School of Physics and Mechatronic Engineering, Guizhou Minzu University, Guiyang, 550025, China
| | - Xinsheng Li
- School of Resources, Environment and Materials, Guangxi University, Nanning, 530004, China
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Teng Z, Han Y, He S, Hadizadeh MH, Zhang Q, Bai X, Wang X, Sun Y, Xu F. The Homogeneous Gas-Phase Formation Mechanism of PCNs from Cross-Condensation of Phenoxy Radical with 2-CPR and 3-CPR: A Theoretical Mechanistic and Kinetic Study. Int J Mol Sci 2022; 23:ijms23115866. [PMID: 35682547 PMCID: PMC9180072 DOI: 10.3390/ijms23115866] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2022] [Revised: 05/07/2022] [Accepted: 05/11/2022] [Indexed: 12/29/2022] Open
Abstract
Chlorophenols (CPs) and phenol are abundant in thermal and combustion procedures, such as stack gas production, industrial incinerators, metal reclamation, etc., which are key precursors for the formation of polychlorinated naphthalenes (PCNs). CPs and phenol can react with H or OH radicals to form chlorophenoxy radicals (CPRs) and phenoxy radical (PhR). The self-condensation of CPRs or cross-condensation of PhR with CPRs is the initial and most important step for PCN formation. In this work, detailed thermodynamic and kinetic calculations were carried out to investigate the PCN formation mechanisms from PhR with 2-CPR/3-CPR. Several energetically advantageous formation pathways were obtained. The rate constants of key elementary steps were calculated over 600~1200 K using the canonical variational transition-state theory (CVT) with the small curvature tunneling (SCT) contribution method. The mechanisms were compared with the experimental observations and our previous works on the PCN formation from the self-condensation of 2-CPRs/3-CPRs. This study shows that naphthalene and 1-monochlorinated naphthalene (1-MCN) are the main PCN products from the cross-condensation of PhR with 2-CPR, and naphthalene and 2-monochlorinated naphthalene (2-MCN) are the main PCN products from the cross-condensation of PhR with 3-CPR. Pathways terminated with Cl elimination are preferred over those terminated with H elimination. PCN formation from the cross-condensation of PhR with 3-CPR can occur much easier than that from the cross-condensation of PhR with 2-CPR. This study, along with the study of PCN formation from the self-condensation 2-CPRs/3-CPRs, can provide reasonable explanations for the experimental observations that the formation potential of naphthalene is larger than that of 1-MCN using 2-CP as a precursor, and an almost equal yield of 1-MCN and 2-MCN can be produced with 3-CP as a precursor.
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Affiliation(s)
- Zhuochao Teng
- Environment Research Institute, Shandong University, Qingdao 266237, China; (Z.T.); (Y.H.); (M.H.H.); (Q.Z.); (X.B.); (X.W.)
| | - Yanan Han
- Environment Research Institute, Shandong University, Qingdao 266237, China; (Z.T.); (Y.H.); (M.H.H.); (Q.Z.); (X.B.); (X.W.)
| | - Shuming He
- School of Environment, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou 310024, China;
| | - Mohammad Hassan Hadizadeh
- Environment Research Institute, Shandong University, Qingdao 266237, China; (Z.T.); (Y.H.); (M.H.H.); (Q.Z.); (X.B.); (X.W.)
| | - Qi Zhang
- Environment Research Institute, Shandong University, Qingdao 266237, China; (Z.T.); (Y.H.); (M.H.H.); (Q.Z.); (X.B.); (X.W.)
| | - Xurong Bai
- Environment Research Institute, Shandong University, Qingdao 266237, China; (Z.T.); (Y.H.); (M.H.H.); (Q.Z.); (X.B.); (X.W.)
| | - Xiaotong Wang
- Environment Research Institute, Shandong University, Qingdao 266237, China; (Z.T.); (Y.H.); (M.H.H.); (Q.Z.); (X.B.); (X.W.)
| | - Yanhui Sun
- College of Environment and Safety Engineering, Qingdao University of Science & Technology, Qingdao 266042, China;
| | - Fei Xu
- Environment Research Institute, Shandong University, Qingdao 266237, China; (Z.T.); (Y.H.); (M.H.H.); (Q.Z.); (X.B.); (X.W.)
- Correspondence: ; Tel.: +86-532-58631992
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Altarawneh M. Temperature-dependent profiles of dioxin-like toxicants from combustion of brominated flame retardants. JOURNAL OF HAZARDOUS MATERIALS 2022; 422:126879. [PMID: 34411962 DOI: 10.1016/j.jhazmat.2021.126879] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2021] [Revised: 07/22/2021] [Accepted: 08/09/2021] [Indexed: 06/13/2023]
Abstract
Literature provides detailed mechanisms underpinning the formation of a wide array of bromine (Br)-containing molecules with a prime focus on dioxin-like compounds. However, from a more applied point of view, the practical deployment of attained thermo-kinetic parameters remains inadequate in the absence of a robust kinetic model that connects bromine transformation at the molecular level with pertinent experimental observations. Herein and to fill in this gap, this study constructs a chemical kinetic model to account for the "homogenous gas phase" emission of Br-aromatic pollutants from the oxidative thermal decomposition of a monobromobenzene molecule (MBZ). The latter serves as a model compound for brominated flame retardants (BFRs) present in e-waste. The model consists of sub-mechanisms (that include reaction rate constants and thermochemical T-dependent functions) for HBr oxidation, combustion mechanism of C1-C6 species, bromine transformation, and synthesis of Br dioxin-like compounds. Reaction rate parameters were obtained for a large array of reactions that constitute the core of the model. For instance, the obtained activation energies for the initial pathways in the formation of brominated biphenyls reside in the range of ~15-45 kJ/mol. Considering oxidation of 5000 ppm MBZ in a plug flow reactor, the model reasonably predicts the temperature-dependent profiles (between 500 and 1200 °C at atmospheric pressure) of a few PBDD/Fs (i.e., polybrominated dibenzo-p-dioxins) isomers in reference to limited corresponding experimental measurements. Most Br dioxin-like compounds appear in the narrow temperature window of 600-1000 °C and achieve their highest abundance at molar yields in the range of 1.0-15 mmol/mol MBZ. A high load (100-120 mmol/mol MBZ) of brominated environmentally persistent free radicals (Br-EPFR) emerges and shifts from bromophenoxy radicals to bromocyclopentadienyl radicals around 700 °C. Oxidation of a 2-bromophenol molecule results in the formation of higher yields of Br-toxicants when compared with that of MBZ. The assembled model provides an informed hazards assessment into the potential emission inventories of Br-compounds in the gas phase at conditions encountered in real scenarios, such as open burning and primitive treatment of e-waste. Via an atomic-base understanding of the complex bromine chemistry and speciation, the model allows the underlying operational conditions that reduce the emission of Br-notorious pollutants to be surveyed and fine-tuned.
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Affiliation(s)
- Mohammednoor Altarawneh
- United Arab Emirates University, Department of Chemical and Petroleum Engineering, Sheikh Khalifa bin Zayed Street, Al-Ain 15551, United Arab Emirates.
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Liu X, Yang L, Liu G, Zheng M. Formation of Environmentally Persistent Free Radicals during Thermochemical Processes and their Correlations with Unintentional Persistent Organic Pollutants. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2021; 55:6529-6541. [PMID: 33956443 DOI: 10.1021/acs.est.0c08762] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Attention is increasingly being paid to environmentally persistent free radicals (EPFRs), which are organic pollutants with the activities of free radicals and stabilities of organic pollutants. EPFRs readily form during thermal processes through the decomposition of organic precursors such as phenols, halogenated phenols, and quinone-type molecules, which are also important precursors of toxic unintentionally produced persistent organic pollutants (UPOPs). We have found that EPFRs are important intermediates for UPOP formation during thermal-related processes. However, interest in EPFRs is currently mostly focused on the toxicities and formation mechanisms of EPFRs themselves. Little information is available on the important roles EPFRs play in toxic UPOP formation during thermal processes. Here, we review the mechanisms involved in EPFR formation and transformation into UPOPs during thermal processes. The review is focused on typical EPFRs, including cyclopentadiene, phenoxy, and semiquinone radicals. The reaction temperature, metal species present, and oxygen concentration strongly affect EPFR and UPOP formation during thermal-related processes. Gaps in current knowledge and future directions for research into EPFR and UPOP formation, transformation, and control are presented. Understanding the relationships between EPFRs and UPOPs will allow synergistic control strategies to be developed for thermal-related industrial sources of EPFRs and UPOPs.
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Affiliation(s)
- Xiaoyun Liu
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Science, Chinese Academy of Sciences, Beijing 100085, China
- College of Resource and Environment, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Lili Yang
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Science, Chinese Academy of Sciences, Beijing 100085, China
| | - Guorui Liu
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Science, Chinese Academy of Sciences, Beijing 100085, China
- College of Resource and Environment, University of Chinese Academy of Sciences, Beijing 100049, China
- School of Environment, Hangzhou Institute for Advanced Study, UCAS, Hangzhou 310000, China
| | - Minghui Zheng
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Science, Chinese Academy of Sciences, Beijing 100085, China
- College of Resource and Environment, University of Chinese Academy of Sciences, Beijing 100049, China
- School of Environment, Hangzhou Institute for Advanced Study, UCAS, Hangzhou 310000, China
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Liu G, Zhan J, Zhao Y, Li L, Jiang X, Fu J, Li C, Zheng M. Distributions, profiles and formation mechanisms of polychlorinated naphthalenes in cement kilns co-processing municipal waste incinerator fly ash. CHEMOSPHERE 2016; 155:348-357. [PMID: 27135696 DOI: 10.1016/j.chemosphere.2016.04.069] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2016] [Revised: 03/29/2016] [Accepted: 04/19/2016] [Indexed: 06/05/2023]
Abstract
Co-processing municipal solid waste incinerator (MSWI) fly ash in cement kilns is challenging because the unintentional production of persistent organic pollutants (POPs) during the process is not well understood. The distributions, profiles and formation mechanisms of polychlorinated naphthalenes (PCNs) as new POPs covered under Stockholm Convention in two cement kilns co-processing MSWI fly ash were studied. The average concentrations of PCNs in stack gas samples were 710 ng m(-3). The PCN concentration in particle samples collected from different process stages in the cement kilns ranged from 1.1 to 84.7 ng g(-1). Three process sites including suspension pre-heater boiler, humidifier tower, and the kiln back-end bag filter were identified to be the major formation sites of PCNs in cement kilns co-processing MSWI fly ash. The PCN distribution patterns were similar to that of polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/Fs), which indicates the possibility for simultaneous control of PCNs and PCDD/Fs in cement kilns co-processing fly ash. Chlorination was suggested to be an important formation mechanism of PCNs, and chlorination pathways of PCN congeners are proposed based on the congener profiles. Thermodynamic calculations, including relative thermal energies (ΔE) and standard free energy of formation (ΔG), and the charge densities of the carbon atoms in PCN supported the proposed chlorination mechanisms for PCN formation. The results presented in this study might provide helpful information for developing techniques and strategies to control PCN emissions during cement kilns co-processing MSWI fly ash.
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Affiliation(s)
- Guorui Liu
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, P.O. Box 2871, Beijing 100085, China
| | - Jiayu Zhan
- State Key Laboratory of Solid Waste Reuse for Building Materials, Beijing Building Materials Academy of Sciences Research, Beijing 100041, China
| | - Yuyang Zhao
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, P.O. Box 2871, Beijing 100085, China
| | - Li Li
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, P.O. Box 2871, Beijing 100085, China
| | - Xiaoxu Jiang
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, P.O. Box 2871, Beijing 100085, China
| | - Jianjie Fu
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, P.O. Box 2871, Beijing 100085, China
| | - Chunping Li
- State Key Laboratory of Solid Waste Reuse for Building Materials, Beijing Building Materials Academy of Sciences Research, Beijing 100041, China
| | - Minghui Zheng
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, P.O. Box 2871, Beijing 100085, China; Institute of Environment and Health, Jianghan University, Wuhan 430056, China
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