Sikes Travis, Banyon Colin, Schwind Rachel A, Lynch Patrick T, Comandini Andrea, Sivaramakrishnan Raghu, Tranter Robert S
Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 South Cass Ave., Lemont, IL 60439, USA.
Phys Chem Chem Phys. 2021 Sep 14;23(34):18432-18448. doi: 10.1039/d1cp02437j. Epub 2021 Aug 23.
The thermal decomposition of styrene was investigated in a combined experimental, theory and modeling study with particular emphasis placed on the initial dissociation reactions. Two sets of shock tube/time-of-flight mass spectrometry (TOF-MS) experiments were performed to identify reaction products and their order of appearance. One set of experiments was conducted with a miniature high repetition rate shock tube at the Advanced Light Source at Lawrence Berkeley National Laboratory using synchrotron vacuum ultraviolet photoionization. The other set of experiments was performed in a diaphragmless shock tube (DFST) using electron impact ionization. The datasets span 1660-2260 K and 0.5-12 atm. The results show a marked transition from aromatic products at low temperatures to polyacetylenes, up to CH, at high temperatures. The TOF-MS experiments were complemented by DFST/LS (laser schlieren densitometry) experiments covering 1800-2250 K and 60-240 Torr. These were particularly sensitive to the initial dissociation reactions. These reactions were investigated theoretically and revealed the dissociation of styrene to be a complex multichannel process with strong pressure and temperature dependencies that were evaluated with multi-well master equation simulations. Simulations of the LS data with a mechanism developed in this work are in excellent agreement with the experimental data. From these simulations, rate coefficients for the dissociation of styrene were obtained that are in good agreement with the theoretical predictions. The simulation results also provide fair predictions of the temperature and pressure dependencies of the products observed in the TOF-MS studies. Prior experimental studies of styrene pyrolysis concluded that the main products were benzene and acetylene. In contrast, this study finds that the majority of styrene dissociates to create five styryl radical isomers. Of these, α-styryl accounts for about 50% with the other isomers consuming approximately 20%. It was also found that C-C bond scission to phenyl and vinyl radicals consumes up to 25% of styrene. Finally the dissociation of styrene to benzene and vinylidene accounts for roughly 5% of styrene consumption. Comments are made on the apparent differences between the results of this work and prior literature.
在一项结合实验、理论和建模的研究中，对苯乙烯的热分解进行了研究，特别强调了初始解离反应。进行了两组激波管/飞行时间质谱（TOF-MS）实验，以确定反应产物及其出现顺序。一组实验是在劳伦斯伯克利国家实验室的先进光源处，使用同步加速器真空紫外光电离，在微型高重复率激波管中进行的。另一组实验是在无膜激波管（DFST）中使用电子轰击电离进行的。数据集涵盖1660 - 2260 K和0.5 - 12 atm。结果表明，在低温下从芳香族产物到高温下的聚乙炔，直至CH，有明显的转变。TOF-MS实验由覆盖1800 - 2250 K和60 - 240 Torr的DFST/激光纹影密度测量（LS）实验进行补充。这些实验对初始解离反应特别敏感。对这些反应进行了理论研究，结果表明苯乙烯的解离是一个复杂的多通道过程，具有强烈的压力和温度依赖性，并通过多阱主方程模拟进行了评估。用本研究中开发的机理对LS数据进行的模拟与实验数据非常吻合。通过这些模拟，获得了与理论预测吻合良好的苯乙烯解离速率系数。模拟结果还对TOF-MS研究中观察到的产物的温度和压力依赖性提供了合理的预测。先前对苯乙烯热解的实验研究得出结论，主要产物是苯和乙炔。相比之下，本研究发现，大多数苯乙烯解离生成五种苯乙烯基自由基异构体。其中，α-苯乙烯基约占50%，其他异构体约占20%。还发现，C-C键断裂生成苯基和乙烯基自由基消耗了高达25%的苯乙烯。最后，苯乙烯解离生成苯和亚乙烯基约占苯乙烯消耗的5%。对本研究结果与先前文献结果之间的明显差异进行了评论。
