A quantum mechanical study on the formation of PCDD/Fs from 2-chlorophenol as precursor.
A quantum mechanical study on the formation of PCDD/Fs from 2-chlorophenol as precursor.
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DOI：
10.1021/es801599n
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发表时间：
2008-09
影响因子：
11.4
通讯作者：
Qingzhu Zhang;Shanqing Li;X. Qu;Xiangyang Shi;Wen-xing Wang
中科院分区：
文献类型：
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作者：
Qingzhu Zhang;Shanqing Li;X. Qu;Xiangyang Shi;Wen-xing Wang
在燃烧和热处理过程中形成多氯二苯并对二恶英和多氯二苯并呋喃的最直接途径是氯代苯酚等化学前体的气相反应。深入了解二恶英的形成机理和动力学特性是理解二恶英形成的前提。本文采用分子轨道理论对2-氯苯酚（2-CP）气相均相生成二恶英（PCDD）/呋喃（Fs）的过程进行了计算。构造了势能面的轮廓，并讨论了可能的形成途径。在MPWB 1 K/ 6-311+G（3f，2 p）水平上进行了单点能量计算。几个积极有利的形成途径被首次揭示。采用正则变分过渡态理论（CVT）和小曲率隧穿贡献（SCT），在600 ~ 1200 K的宽温度范围内推导了关键基元步骤的速率常数.拟合了速率-温度关系式。反应温度和氯苯氧自由基（CPRs）浓度对PCDD和PCDF的生成比例有很大的影响。
The most direct route to the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in combustion and thermal processes is the gas-phase reaction of chemical precursors such as chlorinated phenols. Detailed insight into the mechanism and kinetics properties is a prerequisite for understanding the formation of PCDD/Fs. In this paper, we carried out molecular orbital theory calculations for the homogeneous gas-phase formation of PCDD/Fs from 2-chlorophenol (2-CP). The profiles of the potential energy surface were constructed, and the possible formation pathways are discussed. The single-point energy calculation was carried out at the MPWB1K/ 6-311+G(3f,2p) level. Several energetically favorable formation pathways were revealed for the first time. The rate constants of crucial elementary steps were deduced over a wide temperature range of 600 approximately 1200 K using canonical variational transition-state theory (CVT) with small curvature tunneling contribution (SCT). The rate-temperature formulas were fitted. The ratio of PCDD to PCDF formed shows strong dependency on the reaction temperature and chlorophenoxy radicals (CPRs) concentration.