Study of the Formation of the First Aromatic Rings in the Pyrolysis of Cyclopentene

The
thermal decomposition of cyclopentene was studied in a jet-stirred
reactor operated at constant pressure and temperature to provide new
experimental information about the formation of the first aromatic
rings from cyclic C5 species. Experiments were carried
out at a residence time of 1 s, a pressure of 106.7 kPa, temperatures
ranging from 773 to 1073 K and under diluted conditions (cyclopentene
inlet mole fraction of 0.04). Species were quantified using three
analytical methods: gas chromatography, synchrotron vacuum ultraviolet
photoionization mass spectrometry (SVUV-PIMS), and single photon laser
ionization mass spectrometry (SPI-MS). Several species could be quantified
using both methods allowing comparison of experimental data obtained
with the three apparatuses. Discrepancies observed in mole fraction
profiles of some large aromatics suggest that the direct sampling
in the gas phase (with a molecular beam or a capillary tube) provide
more reliable results. The main reaction products are 1,3-cyclopentadiene
and hydrogen. The formation of many unsaturated C2–C6 olefins, diolefins and alkynes was also observed but in smaller
amounts. Benzene, toluene, styrene, indene, and naphthalene were detected
from 923 K. SVUV-PIMS data allowed the identification of another C6H6 isomer which is 1,5-hexadien-3-yne rather than
fulvene. The quantification of the cyclopentadienyl radical was obtained
from SVUV-PIMS and SPI-MS data with some uncertainty induced by the
possible contribution to the signal for m/z 65 of a fragment from the decomposition of a larger ion.
This is the first time that a radical is quantified in a jet-stirred
reactor using non-optical techniques. SPI-MS analyses allowed the
detection of species likely being combination products of allyl and
cyclopentadienyl radicals. A model was developed for the pyrolysis
of cyclopentene. This model includes routes of formation of aromatics
from the cyclopentadienyl radical. The comparison of experimental
and computed data is overall satisfactory for primary reaction products
whereas discrepancies are still observed for aromatics.

本研究在恒压恒温的射流搅拌反应器（jet-stirred reactor）中开展环戊烯热分解实验，旨在获取环状C5物种生成首个芳香环的新型实验数据。
实验采用1 s的停留时间、106.7 kPa的压力，反应温度区间为773~1073 K，且处于稀释条件下（环戊烯入口摩尔分数为0.04）。
采用三种分析方法对产物物种进行定量：气相色谱法、同步辐射真空紫外光电离质谱（SVUV-PIMS）以及单光子激光电离质谱（SPI-MS）。其中多种物种可通过两种及以上方法实现定量，由此可对比三套实验装置获取的实测数据。
部分大分子芳烃的摩尔分数分布存在差异，这表明采用分子束或毛细管的气相直接采样方式可获得更可靠的实验结果。
主要反应产物为1,3-环戊二烯与氢气。研究同时检测到多种C2~C6不饱和烯烃、二烯烃与炔烃，但含量相对较低。
在923 K及以上温度可检测到苯、甲苯、苯乙烯、茚与萘。
通过SVUV-PIMS数据还鉴定出一种C6H6异构体，经确认其为1,5-己二烯-3-炔而非富烯。
环戊二烯基自由基的定量结果基于SVUV-PIMS与SPI-MS数据得到，但由于质荷比m/z 65的信号可能受到更大离子分解产生碎片的干扰，该定量结果存在一定不确定性。
本研究首次在射流搅拌反应器中采用非光学技术实现自由基的定量检测。
通过SPI-MS分析，研究人员检测到可能为烯丙基与环戊二烯基自由基结合产物的物种。
本研究构建了环戊烯热解反应模型，该模型涵盖了由环戊二烯基自由基生成芳烃的反应路径。
整体而言，实验数据与模型计算结果在初级反应产物上吻合较好，但芳烃类产物仍存在一定偏差。