Remarkable Fractionation of the Hydrogen Isotope (delta D) of Hydrocarbon during the Fast Aromatization Process: Insights from the Pyrolysis Experiments of n-Butylcyclohexane
Remarkable Fractionation of the Hydrogen Isotope (delta D) of Hydrocarbon during the Fast Aromatization Process: Insights from the Pyrolysis Experiments of n-Butylcyclohexane
复制标题
快速芳构化过程中烃类氢同位素 (delta D) 的显着分馏：正丁基环己烷热解实验的见解
DOI：
10.1021/acsearthspacechem.8b00111
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发表时间：
2018
影响因子：
3.4
通讯作者：
Liao Zewen
中科院分区：
文献类型：
--
作者：
Cheng Bin;Liang Yungan;Xu Jianbing;Deng Qian;Wei Zhiwei;Faboya Oluwabamise L.;Liao Zewen
烃芳构化涉及多个C-H键的断裂和脂肪族环的脱氢，从而在芳烃和它们的对应物前体之间分馏稳定的氢。尽管如此，对于芳烃化合物氢同位素（δD）分馏以及烃类芳构化过程中δD分馏特征的研究仍然很少。以正丁基环己烷（BCH）为原料，在封闭的金管体系中进行不同时间的热裂解，研究了BCH的芳构化过程。通过对BCH裂解产物中甲苯（Tol）和甲基环己烷（MCH）的δD变化的研究，探讨了BCH裂解产物中脂肪环上C-H键的断裂行为。24 h BCH热解产物的结果表明，甲苯强烈富集2 H，而MCH严重贫化，ΔδDTol-MCH（δDTol- δDMCH）为162.3‰ [维也纳标准平均海水（VSMOW）]。与BCH的初始氢同位素相比，Δδ DMCH-BCH和Δδ DTol-BCH分别为−46.5和115.8‰。随着热解时间的延长，Tol和MCH之间的δD分馏程度逐渐减轻。推测在烃类芳构化反应初期，脂肪环的脱氢反应是以C-1H键裂解和C-2 H保留在芳环上的可能性较大为起点，导致芳烃的δD分馏作用较强。这一观察结果是非常有指导意义的，因为烃的快速芳构化引起了显着的氢同位素分馏，这可能在快速和高温热事件（如陨石穿过大气时）产生的芳烃的强烈2 H富集中起重要作用。
Hydrocarbon aromatization involves the cleavage of multiple C–H bonds and the dehydrogenation of aliphatic rings, with a resultant fractionation of stable hydrogen between aromatic hydrocarbons and their counterpart precursors. Despite this understanding, there is still the paucity of studies on the hydrogen isotope (δD) fractionation of aromatic compounds and the δD fractionation characteristics during the aromatization process of hydrocarbons. In the present study,n-butylcyclohexane (BCH) was thermally pyrolyzed in a closed gold tube system at different time intervals to investigate the aromatization process of the monoaliphatic ring hydrocarbon. The δD evolutions of toluene (Tol) and methylcyclohexane (MCH) from the BCH pyrolysates were also examined, with the aim of studying the cleavage behavior of the C–H bond at the aliphatic ring. The results of the 24 h BCH pyrolysates showed that toluene was strongly enriched with2H, whereas MCH was heavily depleted, with ΔδDTol–MCH(δDTol– δDMCH) being 162.3‰ [Vienna Standard Mean Ocean Water (VSMOW)]. In comparison to the initial hydrogen isotope of BCH, ΔδDMCH–BCHand ΔδDTol–BCHwere −46.5 and 115.8‰, respectively. With an increasing pyrolysis time, the degree of δD fractionation between Tol and MCH gradually mitigated. It is speculated that the dehydrogenation of the aliphatic ring started with more possibility of cracking the C–1H bond and then having more C–2H being retained in the aromatic ring at the initial stage of hydrocarbon aromatization, leading to the strong δD fractionation of the aromatic hydrocarbon. This observation is quite instructive, in that fast aromatization of the hydrocarbon caused a remarkable hydrogen isotope fractionation, which may play a significant role in the strong2H enrichment of aromatic hydrocarbons generated from a fast and high-temperature thermal event, such as a meteorite when passes through the atmosphere.