Wikström Evalena, Ryan Shawn, Touati Abderrahmane, Gullet Brian K
U.S. Environmental Protection Agency, National Risk Management Research Laboratory, Air Pollution Prevention and Control Division, Air Pollution Technology Branch, Research Triangle Park, North Carolina 27711, USA.
Environ Sci Technol. 2003 May 1;37(9):1962-70. doi: 10.1021/es026240r.
De novo formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs and PCDFs) was investigated in an Entrained Flow Reactor (EFR) to simulate combustion conditions. The parameters investigated were carbon content and nature in fly ash; type of gas-phase environment (oxidative versus reducing conditions) influence of combustion gases such as water, carbon monoxide, and carbon dioxide; amount of gas-phase chlorine; reaction temperature (250-600 degrees C); and reaction time (minutes vs hours). The comprehensive data set was further evaluated with principal component analysis (PCA) to statistically determine the role and importance of each parameter for de novo formation of PCDDs and PCDFs. Results revealed that an initial fast de novo formation occurs within the first minutes with a formation rate in the orders of hundreds of pmol per minutes; however, the reactivity of the ash was found to decline with time. An average formation rate as low as 3 pmol/min was measured after 6 h. The slower de novo formation of PCDDs and PCDFs was found to be through different reaction mechanisms and, thus, controlled by different parameters. The amount of Cl2 in the gas phase was observed to be an important parameter for PCDFs formation; meanwhile the levels of O2 were not found to be a PCDF rate controlling parameter. The formation rate of PCDDs was significantly lower than the PCDFs, and two mechanisms appear to be controlling the formation, one depending on the amount of O2 and one on the amount of Cl2 present in the gas phase. Overall the most significant parameter for the rate of formation for both PCDDs and PCDFs was revealed to be the reaction temperature. A maximum rate of formation was observed between 300-400 degrees C for the PCDDs and 400-500 degrees C for the PCDFs.
在一台携带流反应器（EFR）中研究了多氯二苯并对二噁英和二苯并呋喃（PCDDs和PCDFs）的从头形成，以模拟燃烧条件。所研究的参数包括飞灰中的碳含量和性质；气相环境类型（氧化与还原条件）、燃烧气体如H₂O、CO和CO₂的影响；气相氯的含量；反应温度（250 - 600℃）；以及反应时间（分钟与小时）。利用主成分分析（PCA）对综合数据集进行了进一步评估，以统计确定每个参数对PCDDs和PCDFs从头形成的作用和重要性。结果表明，在最初几分钟内会发生快速的从头形成，形成速率为每分钟数百皮摩尔；然而，发现灰的反应性会随时间下降。6小时后测得的平均形成速率低至3皮摩尔/分钟。发现PCDDs和PCDFs较慢的从头形成是通过不同的反应机制，因此受不同参数控制。观察到气相中Cl₂的含量是PCDFs形成的一个重要参数；同时未发现O₂水平是PCDFs速率控制参数。PCDDs的形成速率明显低于PCDFs，似乎有两种机制控制其形成，一种取决于O₂的含量，另一种取决于气相中Cl₂的含量。总体而言，PCDDs和PCDFs形成速率的最显著参数是反应温度。PCDDs在300 - 400℃之间观察到最大形成速率，PCDFs在400 - 500℃之间观察到最大形成速率。
