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

本研究利用B3LYP/6-311 + G(2d,p)// B3LYP/6-31G(d)基集和cb - 4m，基于从头算量子化学计算了pcdd / df的焓、熵和吉布自由能等热化学性质。结果表明，B3LYP/6-311 + G(2d,p)// B3LYP/6-31 G(d)基集对卤化物的测定比CBS-4M更准确。利用计算得到的pcdd / df的热化学性质，基于多元素体系的多相化学平衡，讨论了二恶英生成的调控机制。研究结果很好地解释了城市生活垃圾焚烧炉中pcdd /DFs的排放特征。本文还指出，对pcdd / df的同族谱图的预测与实验结果吻合较好。此外，将Hang等人提出的在粉煤灰表面重新合成pcdd / df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，该模型能较好地预测粉煤灰中Cu含量在0.05 wt%左右时pcdd /DFs的生成量。另一方面，粉煤灰中含有的几个百分点的Cu对pcdd /DFs的重新合成有很强的促进作用。这表明，在对诸如碎纸机粉尘等富铜垃圾焚烧产生的pcdd /DFs排放进行建模时，必须考虑到Cu效应。

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.