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

本文基于从头算方法，采用B3LYP/6-311+G(2d，p)//B3LYP/6-31G(D)基组和CBS-4M方法，计算了PCDDs/DFS的热化学性质，如热、熵和吉布斯自由能。结果表明，B3LYP/6-311+G(2d，p)//B3LYP/6-31G(D)基组比CBS-4M基组计算卤素的准确度更高。利用PCDDs/DFS计算的热化学性质，从多元体系的多相化学平衡出发，讨论了二恶英生成的调控机理。研究结果较好地解释了垃圾焚烧炉中PCDDs/DFS的排放特征。预测的PCDDs/DFS同系物图谱与实验符合得很好。此外，Hang等人提出的在飞灰表面从头合成PCDDs/DFS的模型。并与电热流动反应器的实验结果进行了比较。结果表明，当飞灰中铜的含量在0.05wt%左右时，该模型能很好地预测PCDDs/DFS的生成量。另一方面，也注意到飞灰中几个百分比的铜强烈地促进了PCDDs/DFS的从头合成。这表明，焚烧粉尘等富铜废物的PCDDs/DFS排放模型必须考虑铜的影响。

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.