氯酚前驱物形成二恶英机理的理论研究

发布时间：2018-05-04 19:04

本文选题：二恶英 + 密度泛函理论　；参考：《山东大学》2015年硕士论文

【摘要】：二恶英是一类典型的持久性有机污染物(POPs),由于其剧毒性对环境和人类产生严重危害,已被列入《斯德哥尔摩公约》中的POPs名单。二恶英是伴随人类生产活动形成的一种副产物,通过研究二恶英的生成机理及其影响因素,找到减少和避免二恶英的生成和排放的方法,从而减少其对人类健康的危害。垃圾焚烧过程中二恶英的生成机理是十分复杂的,也是最受人们关注并且研究最多的,虽然目前对此过程二恶英的生成机理还存在一些争议,但是通常认为二恶英是通过从头合成和前驱物合成两种途径生成的。本文主要围绕垃圾焚烧过程中二恶英前驱物生成机理,通过量子化学计算开展了一系列的研究工作,在深入研究二恶英的前驱物生成机理过程中,提出了酚氧自由基、苯自由基和苯氧双自由基形成二恶英的理论模型,并设计了一系列自由基的自耦合与交叉耦合反应,运用变分过渡态理论计算了它们的热力学和动力学性质；我们还对氯酚前驱物的表面催化机理进行了详细的研究,设计了氯酚在氧化铜和二氧化硅表面的反应路径,并和分子耦合反应作比较来分析氧化铜和二氧化硅在二恶英生成过程的催化机理和催化效果。论文的主要研究内容和成果如下：一、氯酚气相生成二恶英新机理。氯酚是公认的形成二恶英的最重要的前驱物,但人们对其转化成二恶英分子机理的认识仍不十分清晰。我们选择2-氯酚为模型化合物,通过密度泛函理论计算,研究了一系列二恶英的形成机制,发现酚氧自由基、苯自由基和苯氧双自由基均是形成二恶英的重要中间体,对二恶英的形成有重要贡献。本文设计了一系列自由基的自耦合与交叉耦合反应,运用变分过渡态理论计算了它们的热力学和动力学性质,研究结果改进了人们对二恶英形成机理的认识,也为相关的实验研究提供了一定的理论指导。二、氯酚在氧化铜,二氧化硅表面反应生成二恶英的机理。前驱物分子主要通过高温气相反应和低温表面催化反应形成二恶英,其中70%以上的二恶英是通过表面催化机理生成的。研究表明,垃圾焚烧过程的飞灰中含有过渡金属氧化物、金属氯化物和大量二氧化硅,这些被认为是生成二恶英的重要催化剂,但具体作用机制还不清楚。本论文分别研究了2,4,5-TCP在氧化铜和二氧化硅表面的吸附及反应机理,并和分子耦合反应作比较。研究结果表明,氯酚分子极易吸附在二氧化硅表面形成稳定的氯酚盐,但后续反应过程中由于硅氧键难以断裂而对形成二恶英没有明显催化效果,而氧化铜对氯酚反应形成二恶英有催化作用,研究结果为理解二恶英表面形成机理提供了一定的理论依据。
[Abstract]:Dioxin, a typical persistent organic pollutant, has been listed in the POPs list of Stockholm Convention because of its high toxicity to the environment and human beings. Dioxin is a by-product formed with human production. By studying the formation mechanism of dioxin and its influencing factors, we can find a way to reduce and avoid the formation and emission of dioxin, so as to reduce its harm to human health. The formation mechanism of dioxin in MSW incineration process is very complex, and it is the most concerned and studied, although there are still some controversies on the formation mechanism of dioxin in MSW incineration process. However, it is generally believed that dioxins are produced by both ab initio synthesis and precursor synthesis. Based on the mechanism of dioxin precursor formation during MSW incineration, a series of research work was carried out by quantum chemical calculation. In the process of studying the formation mechanism of dioxin precursor, phenolic oxygen free radical was proposed. A theoretical model for the formation of dioxins from benzene radical and benzoxy double radical is proposed. A series of self-coupling and cross-coupling reactions are designed and their thermodynamic and kinetic properties are calculated by the variational transition state theory. We also studied the surface catalytic mechanism of chlorophenol precursor in detail and designed the reaction path of chlorophenol on the surface of copper oxide and silica. The catalytic mechanism and catalytic effect of copper oxide and silicon dioxide in the formation of dioxin were analyzed by comparison with the molecular coupling reaction. The main research contents and achievements are as follows: 1. New mechanism of gas phase formation of dioxins from chlorophenols. Chlorophenol is recognized as the most important precursor for dioxin formation, but the mechanism of its conversion to dioxin is still unclear. We selected 2-chlorophenol as model compound and studied the formation mechanism of a series of dioxins by density functional theory (DFT). It was found that phenolic radical, benzene radical and benzoxy bisradical are important intermediates for dioxin formation. It has an important contribution to the formation of dioxins. In this paper, a series of self-coupling and cross-coupling reactions of free radicals are designed, and their thermodynamic and kinetic properties are calculated by using variational transition state theory. The results improve the understanding of the formation mechanism of dioxins. It also provides some theoretical guidance for related experimental research. Second, the reaction mechanism of chlorophenol on the surface of copper oxide and silica. The precursor molecules form dioxins mainly through high temperature gas phase reaction and low temperature surface catalytic reaction, in which more than 70% of the dioxins are generated by surface catalytic mechanism. The results show that the fly ash of MSW incineration process contains transition metal oxide, metal chloride and a large amount of silica, which are considered as important catalysts for the formation of dioxins, but the mechanism of action is not clear. In this paper, the adsorption and reaction mechanism of 2H4 + 5-TCP on the surface of copper oxide and silica were studied, and the results were compared with those of molecular coupling reaction. The results show that chlorophenol molecules are easy to adsorb on the surface of silica to form stable chlorophenol salts. However, in the subsequent reaction process, due to the difficulty of breaking the bond between silicon and oxygen, there is no obvious catalytic effect on the formation of dioxins. Copper oxide can catalyze the formation of dioxins in chlorophenol reaction. The results provide a theoretical basis for understanding the surface formation mechanism of dioxins.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X705;X50

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