石油沥青质中杂原子化合物的高分辨质谱分析

使用傅里叶变换离子回旋共振质谱研究沥青质及其亚组分的分子组成。结果表明,重质油及其沥青质中杂原子化合物分子组成十分复杂,负离子电喷雾结合高分辨傅里叶变换离子回旋共振质谱(FT-ICR MS)鉴定出了N1、N1O1、N1O1S1、N1O2、N1S1、O2、O2S1、O2S2、O2S3、O3、O3S1、O4等多种杂原子类型,含氧化合物和分子中存在多个杂原子的化合物在沥青质中相对富集。加拿大油砂沥青减压渣油(VTB)C7沥青质较C5沥青质中化合物缩合度更高;不同原油沥青质组成差异很大,VTB沥青质中杂原子类型多,分子缩合程度较高,而苏丹VR沥青质中含氧化物丰度较高。分子缩合度的微小变化也能对沥青质的溶解度产生较大影响,通过对不同极性亚组分分析,从分子层次证明了高缩度和多杂原子化合物最容易在低极性或非极性溶剂中沉淀出来。通过对非碱性氮化合物和酸性化合物的分子组成分析,获得了沥青质分子组成的重要信息,尽管在实验选用的仪器条件下仅能对沥青质中部分化合物进行分析,但是可以确定沥青质中存在很多小分子化合物。

Compositional analysis of petroleum asphaltenes by negative ion electrospray high resolution FT-ICR mass spectrometry

Molecular composition of petroleum asphaltenes has been a major research challenge for petroleum chemistry community both in upstream and downstream of petroleum industry. Heavy petroleum asphaltenes and their subfractions were characterized by using negative ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry (MS). The composition of heteroatoms in heavy petroleum samples and asphaltenes is rather complex. Class species such as N₁, N₁O₁, N₁O₁S₁, N₁O₂, N₁S₁, O₂, O₂S₁, O₂S₂, O₂S₃, O₃, O₃S₁, O_4are identified with high resolution FT-ICR MS. Oxygen and multi-heteroatom containing species tend to precipitate into asphalenes. Heptane derived asphaltenes have higher molecular condensation degree than pentane derived asphaltenes. Molecular composition of asphaltenes from various crude oil is very different. Asphaltenes derived from Canada vacuum topped bitumen(VTB) have more heteroatom classes and higher molecular condensation degree than that of Sudan heavy oil asphaltenes. Sulfur species are absent from Sudan heavy oil asphaltenes in which oxygen class species show a very high relative abundance. Minimal variations in molecular condensation degree can lead to significant changes in asphaltene solubility in solvents. The research results provide evidence at molecular level that compounds with high molecular condensation degree and/or multi heteroatoms tend to precipitate from solvent with non or weak polarity. The characterization on neutral nitrogen and acidic oxygen compounds reveals the compositional complexity of asphaltenes. Under current conditions only limited amount of asphaltene moieties are revealed in negative ion ESI analysis, however a significant amount of small molecules are highly likely to present in petroleum asphaltenes.