We have analyzed eight heavy vacuum gas oil (HVGO) distillation fractions, initial boiling point (IBP)−343, 343−375, 375−400, 400−425, 425−450, 450−475, 475−500, and 500−525 °C, of an Athabasca bitumen by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Acidic, basic, and nonpolar components were detected by negative-ion and positive-ion electrospray ionization (ESI) and automated liquid injection field desorption ionization (LIFDI) positive-ion FT-ICR MS. Ultrahigh mass resolving power (m/Δm 50% ≈ 350 000) and high mass accuracy (<500 ppb) facilitate the assignment of a unique elemental composition to each peak in the mass spectrum. Thus, each distillate was characterized by mass, heteroatom class, type (number of rings and double bonds), and carbon number distribution to correlate compositional changes with increased boiling point. Negative-ion ESI FT-ICR MS identifies high relative abundance nonaromatic O2 species that span the entire distillation range. All ionization methods reveal an increase in double-bond equivalents (DBE, the number of rings plus double bonds) and carbon number with increased distillation temperature. In addition, some structural information can be inferred from increases in DBE value with increased distillation temperature. Summed data for individual distillation cuts yield class specific isoabundance contours similar to that for the feed HVGO, suggesting that class-specific carbon number and DBE distributions for individual distillation cuts could be estimated from the high-resolution feed HVGO mass spectrum.

Molecular weight and specific gravity distribution data are required for characterizing oils containing complex mixtures, and this characterization information is very essential for the computation of thermodynamic properties and phase equilibria. The accuracy of these computations will be enhanced if molecular weight and specific gravity data of fractions containing similar groups/structures or common solubility properties are used. This is because the critical properties normally correlate better for a single fraction than for the whole oil. Data in this work is relevant to the phase equilibrium calculations and predictions of asphaltene precipitation from representative Canadian bitumens. Athabasca and Cold Lake bitumen samples were used and divided into asphaltene and deasphalted oil fractions by adding 40 volumes of n-heptane. The deasphalted oils were divided into saturate, aromatic, and resin fractions using a modified ASTM D2007 procedure. The average molecular weights of these SARA fractions were measured using vapor pressure osmometry (VPO), and the molecular weight distributions of the SARA fractions were measured using gel permeation chromatography (GPC) calibrated with polystyrene standards. Results were verified using VPO measurements, and the correction factors for the GPC distributions were calculated. The specific gravities of saturate and aromatic fractions were measured using an Anton-Paar densitometer, and resin fraction values were obtained using a water pycnometer and those of asphaltenes using a helium pycnometer. Specific gravity distributions were computed using the measured data and the correlation reported in the literature.

Because acids in petroleum materials are known to corrode processing equipment, highly acidic oils are sold at a discount [on the basis of their total acid number (TAN)]. Here, we identify the acidic species in raw Canadian bitumen (Athabasca oil sands) and its distilled heavy vacuum gas oil (HVGO) as well as acid-only and acid-free fractions isolated by use of an ion-exchange resin (acid-IER) and negative-ion electrospray ionization Fourier transform ion cyclotron resonance (ESI FT-ICR MS) mass spectrometry. The ultrahigh mass resolving power (m/∆m 50% > 400 000) and high mass accuracy (better than 500 ppb) of FT-ICR MS, along with Kendrick mass sorting, enable the assignment of a unique elemental composition to each peak in the mass spectrum. Acidic species are characterized by class (N n O o S s heteroatom content), type [number of rings plus double bonds to carbon or double-bond equivalent (DBE)], and carbon number distribution. We conclude that the analytical capability of FT-ICR MS and the selectivity of the ESI process eliminate the need for acid fractionation to characterize naphthenic acids in bitumen. However, because the acid-free fraction (not retained on the acid-IER) contains S x O y heteroatomic classes not observed in the parent bitumen, acid-IER fractionation does help to identify such low-abundance species. Further, we observe that a subset of the acids identified in the parent bitumen distill into the HVGO fraction. Variations in the carbon number and aromaticity of the classes are discussed in detail.