Heavy Petroleum Composition. 5. Compositional and Structural Continuum of Petroleum Revealed

Abstract

Twenty-five years ago, Boduszynski et al. conducted a comprehensive study of heavy oil composition and concluded that crude oil composition increases gradually and continuously with regard to aromaticity, molecular weight, and heteroatom content from the light distillates to non-distillables (the Boduszynski continuum model). Previous exhaustive characterization of heavy vacuum gas oil by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) provided compositional data that strongly supports the continuum model. However, when the molecular formulas obtained by FT-ICR MS for the distillates and asphaltenes from the same parent crude oil are plotted as double bond equivalents (DBE) versus carbon number, a gap appears between the compositional space of "asphaltenes" and "maltenes", in contradiction to the Boduszynski−Altgelt model. Here, a heavy distillate cut (atmospheric equivalent boiling point of 523−593 °C) is fractionated according to the number of aromatic rings by HPLC-2. The C7-deasphalted whole oil (C7-DAO), its pentane soluble/insoluble fractions, and each of their ring number fractions are comprehensively characterized by atmospheric pressure photoionization (APPI) FT-ICR MS and tandem mass spectrometry (MS/MS). The HPLC-2 fractions from both the C5-soluble and C5insoluble C7-DAO represent a gradual and continuous progression that fills the compositional "gap" in carbon number and aromaticity between asphaltenes and maltenes as a function of the increasing aromatic ring number, as predicted by Boduszynski. MS/MS results indicate that each ring number fraction comprises both island and archipelago structural motifs. FT-ICR MS reveals a continuum in carbon number and aromaticity. The C5-insoluble C7-DAO components have a similar structure but with higher-order fused ring core structures and are composed of a higher proportion of archipelago structures than the C5-soluble C7-DAO components. Thus, fractionation by the aromatic ring number of "maltenic" and "asphaltenic" species from the C7solubles from a high boiling distillate validates the compositional continuum of petroleum components, and MS/MS exposes the aromatic building blocks of "maltenic" and "asphaltenic" species (structural continuum) that comprise island and archipelago structural motifs.

Characterizing aliphatic moieties in hydrocarbons with atomic force microscopy

“…The model molecules introduced here are consistent with asphaltene molecular properties regarding molecular weight, boiling point, H/C ratio and double bond equivalent as reported previously. 30–32 …”

Recent developments in atmospheric pressure photoionization‐mass spectrometry

“…Rather than targeted analysis, the aim in petroleomics is often to characterize different compound classes and their proportions. The characterization is typically done based on exact masses from ultra‐high resolution FTICR‐MS, which can derive double‐bond equivalences, and identities and numbers of heteroatoms (McKenna et al, 2010a, b, 2013a; Kekäläinen et al, ; McKenna, Marshall, & Rodgers, ; Podgorski et al, ). Promising results for structural elucidation of crude‐oil components have also been achieved with ion‐mobility spectrometry (IMS) and theoretical collision cross‐section calculations (Ahmed et al, ).…”

Asphaltenes: Separations, structural analysis and applications

“…Laser desorption laser ionization (L 2 DIMS) MS [36] and surfaceassisted laser desorption/ionization (SALDI) MS [35] also supported for the island geometry and could give unbiased information of all asphaltene components without aggregation. Meanwhile, the archipelago structure has been supported by NMR, FT-ICR MS/MS [37] and thermal cracking methods [10] . A continuum between island and archipelago structures was recently proved by a series results of FT-ICR MS and the ratios of island and archipelago structures were depended on the asphaltene sample [38] .…”