Quantum chemical and kinetic study on dioxin formation from the 2,4,6-TCP and 2,4-DCP precursors.
Quantum chemical and kinetic study on dioxin formation from the 2,4,6-TCP and 2,4-DCP precursors.
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DOI：
10.1021/es1004285
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发表时间：
2010-04
影响因子：
11.4
通讯作者：
Qingzhu Zhang;Wanni Yu;Ruixue Zhang;Qin Zhou;R. Gao;Wen-xing Wang
中科院分区：
文献类型：
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作者：
Qingzhu Zhang;Wanni Yu;Ruixue Zhang;Qin Zhou;R. Gao;Wen-xing Wang
本研究主要研究了2,4,6-三氯苯酚（2,4,6- tcp）和2,4-二氯苯酚（2,4- dcp）前体在城市垃圾焚烧炉（MWIs）气相和飞灰样品中作为主要氯酚同属物存在的多氯二苯并对二恶英（pcdd）和二苯并呋喃（pcdf）的均相气相生成。对其形成机理进行了分子轨道理论计算。在MPWB1K水平上，以6-31+G（d,p）基集计算各驻点的几何参数和振动频率。在MPWB1K/6-311+G（3df,2p）理论能级下进行单点能量计算。采用具有小曲率隧穿（SCT）贡献的典型变分过渡态（CVT）理论，预测了在感兴趣的温度范围（600-1200 K）内关键基本步骤的速率常数。首次拟合了速率-温度公式。报道了反应的指前因子、活化能和反应速率常数。本研究表明，氯酚缩合形成pcdd至少需要一个邻位氯取代基。本文的研究结果将有助于阐明和详细阐述氯酚前体在实际废物燃烧中产生PCDD/ pcdf（简称PCDD/Fs）的机理。
This study focuses on the homogeneous gas-phase formation of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) from the 2,4,6-trichlorophenol (2,4,6-TCP) and 2,4-dichlorophenol (2,4-DCP) precursors, which were found both in the gas phase and in the fly ash samples as the dominating chlorophenol congeners in municipal waste incinerators (MWIs). Molecular orbital theory calculations have been performed for the formation mechanism. The geometrical parameters and vibrational frequencies of all the stationary points were calculated at the MPWB1K level with the 6-31+G(d,p) basis set. Single-point energy calculations were carried out at the MPWB1K/6-311+G(3df,2p) level of theory. Canonical variational transition-state (CVT) theory with small curvature tunneling (SCT) contribution was used to predict the rate constants of crucial elementary steps over the temperature range of interest (600-1200 K). The rate-temperature formulas were fitted for the first time. The pre-exponential factor, the activation energy, and the rate constants are reported. This study shows that at least one chlorine substituent in the ortho position is needed for the formation of PCDDs from the condensation of chlorophenols. The results presented here should help to clarify and detail the formation mechanism of PCDD/PCDFs (PCDD/Fs for short) from chlorophenol precursors in real waste combustion.