Center for Combustion and Environmental Research, Department of Mechanical Engineering, University of Colorado at Boulder, Boulder, Colorado 80309-0427, USA.
J Chem Phys. 2013 Sep 28;139(12):124305. doi: 10.1063/1.4821600.
A silicon carbide microtubular reactor has been used to measure branching ratios in the thermal decomposition of furan, C4H4O. The pyrolysis experiments are carried out by passing a dilute mixture of furan (approximately 0.01%) entrained in a stream of helium through the heated reactor. The SiC reactor (0.66 mm i.d., 2 mm o.d., 2.5 cm long) operates with continuous flow. Experiments were performed with a reactor inlet pressure of 100-300 Torr and a wall temperature between 1200 and 1600 K; characteristic residence times in the reactor are 60-150 μs. The unimolecular decomposition pathway of furan is confirmed to be: furan (+ M) ⇌ α-carbene or β-carbene. The α-carbene fragments to CH2=C=O + HC≡CH while the β-carbene isomerizes to CH2=C=CHCHO. The formyl allene can isomerize to CO + CH3C≡CH or it can fragment to H + CO + HCCCH2. Tunable synchrotron radiation photoionization mass spectrometry is used to monitor the products and to measure the branching ratio of the two carbenes as well as the ratio of [HCCCH2]/[CH3C≡CH]. The results of these pyrolysis experiments demonstrate a preference for 80%-90% of furan decomposition to occur via the β-carbene. For reactor temperatures of 1200-1400 K, no propargyl radicals are formed. As the temperature rises to 1500-1600 K, at most 10% of the decomposition of CH2=C=CHCHO produces H + CO + HCCCH2 radicals. Thermodynamic conditions in the reactor have been modeled by computational fluid dynamics and the experimental results are compared to the predictions of three furan pyrolysis mechanisms. Uncertainty in the pressure-dependency of the initiation reaction rates is a possible a source of discrepancy between experimental results and theoretical predictions.
一种碳化硅微tubular 反应器已被用于测量呋喃热分解的分支比，C4H4O。通过将包含在氦气流中的呋喃（约 0.01%）稀混合物通过加热的反应器来进行热解实验。SiC 反应器（0.66 毫米内径，2 毫米外径，2.5 厘米长）以连续流操作。在 100-300 托的反应器入口压力和 1200-1600 K 之间的壁温度下进行实验；在反应器中的特征停留时间为 60-150 μs。呋喃的单分子分解途径被确认为：呋喃（+ M） ⇌α-卡宾或β-卡宾。α-卡宾片段为 CH2=C=O + HC≡CH，而β-卡宾异构化为 CH2=C=CHCHO。甲酰基烯丙基可以异构化为 CO + CH3C≡CH 或分解为 H + CO + HCCCH2。可调谐同步辐射光致电离质谱用于监测产物，并测量两个卡宾的分支比以及[HCCCH2]/[CH3C≡CH]的比值。这些热解实验的结果表明，80%-90%的呋喃分解通过β-卡宾发生。对于 1200-1400 K 的反应器温度，不会形成丙炔基自由基。当温度升高到 1500-1600 K 时，CH2=C=CHCHO 的分解最多产生 10%的 H + CO + HCCCH2 自由基。通过计算流体动力学对反应器中的热力学条件进行建模，并将实验结果与三种呋喃热解机制的预测进行比较。引发反应速率对压力的依赖性的不确定性可能是实验结果与理论预测之间存在差异的一个来源。
