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.

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.

We examine solution-phase aggregation for a whole crude oil, whole bitumen, and bitumen distillate fractions by negative-ion electrospray ionization [(-) ESI] detected by both high-resolution [Fourier transform ion cyclotron resonance (FT-ICR)] and low-resolution [linear quadrupole ion trap (LTQ)] mass spectrometry (MS). Aggregate formation for both crude oil and bitumens is concentration-dependent. At high concentrations (i.e., >1 mg/mL), the disruption of noncovalent interactions between heteromultimers by low-energy collisionactivated dissociation (CAD) yields LTQ dissociation mass spectra with molecular-weight distributions identical to those observed by FT-ICR MS analysis at lower concentrations for purely monomeric species. These materials can exist as aggregates in solution even at high dilution (less than 0.1 mg/mL). We demonstrate the concentration and boiling point dependence for multimerization of polar acidic species in the Athabasca bitumen and bitumen distillates. Interestingly, the lowest boiling distillation cut (375-400 °C) displays the highest aggregation tendency, with dimers at concentrations as low as 0.05 mg/mL. Higher boiling point distillation cuts display a decreased aggregation tendency with an increasing cut point. High-resolution negative-ESI FT-ICR MS of the bitumen distillation fractions reveals the elemental composition, and thus the class, type, and carbon number of the multimeric species. Acidic heteroatomic classes for the distillation cut multimers include O