Advances in Asphaltene Petroleomics. Part 3. Dominance of Island or Archipelago Structural Motif Is Sample Dependent
Advances in Asphaltene Petroleomics. Part 3. Dominance of Island or Archipelago Structural Motif Is Sample Dependent
复制标题
DOI：
10.1021/acs.energyfuels.8b01765
复制
发表时间：
2018-09-01
期刊：
影响因子：
5.3
通讯作者：
Rodgers, Ryan P.
中科院分区：
文献类型：
--
作者：
Chacon-Patino, Martha L.;Rowland, Steven M.;Rodgers, Ryan P.
沥青质结构是石油化学中最有争议的话题之一。争议集中在沥青质分子内的芳族核的组织（单芳族核、岛和多芳族核、群岛），特别是岛模型与沥青质热解/热裂解产物组成之间的不一致。这些产物与岛状和群岛状沥青质结构基序的共存是一致的。然而，群岛模型仍然缺乏石油界的广泛接受，部分原因是质谱结果支持岛屿模型。在本系列的第一和第二部分中，我们证明了岛物种的超高大气压光电离（APPI）电离效率（单体离子产率）是由于大芳族核在甲苯中不广泛聚集的弱纳米聚集，而更多的群岛占主导地位的馏分被证明具有低单体离子产率，由于更大的聚集倾向。这种差异导致偏向岛化合物的选择性电离，因此错误的质谱支持岛结构模型的优势。基于聚集趋势的分离方法以及因此单体离子产生的效率对于进入群岛结构至关重要。在本文提出的工作中，我们证明了岛屿或群岛结构基序的优势是样本依赖的。采用正离子APPI傅里叶变换离子回旋共振质谱（FT-ICR MS）对怀俄明州存款（岛屿为主）和阿萨巴斯卡沥青（群岛为主）的C-7沥青质和沥青质抽提物组分进行了表征。怀俄明州存款沥青质类似于“经典”岛型沥青质结构：它们表现出高浓度的高度芳族/烷基缺乏的物种与组成空间接近多环芳烃（PAH）的限制。红外多光子解离（IRMPD）的裂解结果证实，岛是怀俄明州存款C-7沥青质的主要结构基序;所有extrography馏分的主要裂解途径包括损失的CH 2单位（或脱烷基化），没有显着的芳香性损失。相反，阿萨巴斯卡沥青C-7沥青质表现出“非典型”分子组成。超过40wt%的样品被提取在最新的extrography馏分，这是由难以分离的物种，其中一部分表现出低的双键当量（DBE = 5-12）和扩展的同源系列与碳数高达60。所有阿萨巴斯卡沥青衍生馏分的碎片化行为表现出的主要贡献的群岛图案。我们的研究结果表明，沥青质的Yen-Mullins分子定义不能用来描述所有的沥青质样品。岛屿和群岛结构图案共存，和extrography分离揭示了一个结构连续体，是丰富的群岛图案作为增加分子量和极性的函数。岛/群岛的比例是样品依赖性的，其准确的量化应显着提高富含沥青质的原料的经济价值，通过预测的产率和最佳条件的升级过程。
Asphaltene structure is one of the most controversial topics in petroleum chemistry. The controversy is centered on the organization of aromatic cores within asphaltene molecules (single aromatic core, island and multiple aromatic core, archipelago) and specifically the inconsistency between the island model and the composition of the products derived from asphaltene pyrolysis/thermal cracking. Such products are consistent with the coexistence of island and archipelago asphaltene structural motifs. However, the archipelago model continues to lack the widespread acceptance of the petroleum community, in part due to mass spectrometry results in support of the island model. In the first and second part of this series, we demonstrated that the disproportionally high atmospheric pressure photoionization (APPI) ionization efficiency (monomer ion yield) of island species is due to weak nanoaggregation of large aromatic cores which do not extensively aggregate in toluene, whereas more archipelago-dominant fractions were shown to have low monomer ion yield due to a greater propensity for aggregation. The discrepancy leads to bias toward the selective ionization of island compounds and thus the erroneous mass spectrometry support of the predominance of the island structural model. A separation method based on aggregation trends and therefore the efficiency of monomeric ion production is critical to access archipelago structures. In the work presented herein, we demonstrate that dominance of island or archipelago structural motif is sample dependent. We present the positive-ion APPI Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) characterization of asphaltenes and asphaltene extrography fractions derived from Wyoming Deposit (island dominant) and Athabasca Bitumen (archipelago dominant) C-7 asphaltenes. Wyoming Deposit asphaltenes resemble the "classical" island-type asphaltene structure: they exhibit a high concentration of highly aromatic/alkyl-deficient species with a compositional space close to the polycyclic aromatic hydrocarbon (PAH) limit. Fragmentation results from infrared multiphoton dissociation (IRMPD) confirm that island is the dominant structural motif in Wyoming Deposit C-7 asphaltenes; the predominant fragmentation pathway for all extrography fractions consists of loss of CH2 units (or dealkylation), without significant loss of aromaticity. Conversely, Athabasca Bitumen C-7 asphaltenes exhibit an "atypical" molecular composition. More than 40 wt % of the sample is extracted in the latest extrography fractions, which are composed of difficult-to-ionize species, a fraction of which exhibit atypically low double bond equivalent (DBE = 5-12) and extended homologous series with carbon numbers up to 60. The fragmentation behavior of all Athabasca Bitumen-derived fractions demonstrates a predominant contribution of archipelago motifs. Our results suggest that the Yen-Mullins molecular definition of asphaltenes cannot be used to describe all asphaltene samples. Island and archipelago structural motifs coexist, and extrography separation reveals a structural continuum that is enriched with archipelago motifs as a function of increasing molecular weight and polarity. The ratio island/archipelago is sample dependent, and its accurate quantification should significantly improve the economic value of asphaltene-enriched feedstocks by prediction of yields and optimal conditions for upgrading processes.