Modeling of PCDDs/DFs Formation During Municipal Solid Waste Incineration Processes

本文采用从头算量子化学方法，在B3 LYP/6-311 + G（2d，p）//B3 LYP/6- 31 G（d）基组和CBS-4 M基组下，计算了PCDDs/DFs的焓、熵和吉布斯自由能等热化学性质。结果表明，B3 LYP/6-311 + G（2d，p）//B3 LYP/6-31 G（d）基组比CBS-4 M基组对卤化物的计算精度更高.利用计算得到的PCDDs/DFs的热化学性质，从多元素体系的多相化学平衡出发，探讨了二恶英生成的控制机制。结果较好地解释了垃圾焚烧炉中PCDDs/DFs的排放特性。此外，还将Hang等人提出的飞灰表面从头合成PCDDs/DFs的模型与电加热流动反应器的实验结果进行了比较。结果表明，所采用的模型以及预测的PCDDs/DFs的生成量，如果飞灰中含有相对少量的铜约0.05重量%。另一方面，值得注意的是，飞灰中含有几个百分点的铜强烈促进从头合成的多氯二苯并对二恶英/DF。这表明，PCDDs/DFs排放的建模从富铜废物，如粉碎机粉尘焚烧考虑铜的影响。

In this study, thermo-chemical properties such as enthalpy, entropy and Gibb's free energies of PCDDs/DFs have been calculated based on ab initio quantum chemistry using B3LYP/6-311 + G(2d,p)// B3LYP/6-31G(d) basis set and CBS-4M. Results show that B3LYP/6-311 + G(2d,p)// B3LYP/6-31 G(d) basis set gives more accurate value than CBS-4M for the halogenide. Using the computed thermo-chemical properties of PCDDs/DFs, the governing mechanisms of dioxin generation have been discussed based on multi-phase chemical equilibrium in regard to a multi-element system. The result well explains the characteristic of PCDDs/DFs emission in municipal solid waste incinerator. It is also pointed out that he temperature dependence of predicted congener patterns for PCDDs/DFs well coincide with those of experiments.Furthermore, the model for de novo synthesis of PCDDs/DFs on the fly ash surface proposed by Hang et al. has been compared with the experimental results obtained by using the electrically heated flow reactor. It is revealed that the employed model well predicts the amount of PCDDs/DFs generation if the fly ash contains relatively small amount of Cu around 0.05 wt%. On the other hand, it is noted that several percent of Cu contained in fly ash strongly promoted de novo synthesis of PCDDs/DFs. This suggests that the modeling of PCDDs/DFs emission form the incineration of Cu rich waste such as shredder dust has to take Cu effect into account.