Characterization of Crude Oils through Alkyl Chain-Based Separation by Gel Permeation Chromatography and Mass Spectrometry

Abstract

The complexity of petroleum crude oils necessitates a combination of analytical techniques to gain the in-depth compositional knowledge needed to enhance oil production or develop optimal refining strategies. This study focuses on the fractionation of four Arabian crude oils through gel permeation chromatography (GPC) to obtain chemically well-defined fractions, which are then characterized in detail using atmospheric pressure photoionization Fourier transform-ion cyclotron resonance mass spectrometry, and field desorption time-of-flight mass spectrometry. GPC is found to be a valuable tool because the described methodology produces petroleum fractions with nonpolar components reproducibly separated by total alkyl chain length. While the early-eluting fractions contained large saturated compounds and small aromatic systems with extensive alkyl chains, as well as potential asphaltene material, the later-eluting GPC fractions contained molecules with a wide range of aromatic rings but very limited alkyl chains. The molecular size contribution of aromatic rings did not change the elution time of the studied petroleum components as it appears counterbalanced by non-size effects. Preliminary tandem mass spectrometry experiments revealed the presence of noncondensed aromatic rings alongside species with up to nine fused aromatic rings in the late-eluting GPC fractions, as demonstrated for S2 class species. Finally, the GPC separation was also tested on a South American crude oil sample and found to fractionate it by the same molecular criterion, i.e., total alkyl chain length, independent of the crude oil API gravity, total sulfur and nitrogen contents, or geographical origin.

Saturated Compounds in Heavy Petroleum Fractions

“…The resulting mass spectra and identified hydrocarbon formulas in the form of carbon number versus double bond equivalent (DBE) values are shown in Figure (top to bottom) for the lightest (#14), middle (#20), and heaviest (#26) vacuum-boiling fractions and for the vacuum residue (#27). In agreement with prior analyses of saturates fractions using similar experimental parameters, molecular ions were obtained with limited fragmentation. , The mass spectra of cuts #20 and #27 contain signals attributed to the Agilent APPI tune mix ( m / z = 322, 366, 922, and 1521) initially used for verifying the mass calibration. Mass spectra for all six characterized samples are provided in Figure S3.…”

Chemical Characterization Using Different Analytical Techniques to Understand Processes: The Case of the Paraffinic Base Oil Production Line

“…As can be seen in Figure 5, there is a relationship between the quantity of tailing after the main peak and the log of viscosity. These results, coupled with the amount of polyaromatics given by HPLC3, suggest that the aromatic compounds have a later elution time, as was already suggested by Panda et al [10] and by Alawani et al [5]. This result means that retention time, asymmetry of the curve, the percentage of aromatics, and viscosity are linked.…”

Compositional Trends for Total Vanadium Content and Vanadyl Porphyrins in Gel Permeation Chromatography Fractions Reveal Correlations between Asphaltene Aggregation and Ion Production Efficiency in Atmospheric Pressure Photoionization

“…These results are consistent with the idea that London forces between alkyl side chains drive the self-assembly of asphaltene nanoaggregates to produce more massive clusters, widely reported by Rogel, 64 Carbognani, 65 and Stachowiak et al 66 It is critical to point out that there is not a clear correlation between asphaltene aggregation in industrial applications (e.g., fouling in production facilities) and GPC elution trends. For example, Muller et al 67,68 fractionated geologically diverse crude oils by GPC and used off-line FT-ICR MS for molecular characterization. The earlier-eluting fractions revealed abundant small aromatic cores (1−3 fused rings) with extensive alkyl substitution, whereas the later-eluting compounds were alkyl-depleted/sizable aromatic structures (5−9 fused rings).…”

“…, fouling in production facilities) and GPC elution trends. For example, Muller et al , fractionated geologically diverse crude oils by GPC and used off-line FT-ICR MS for molecular characterization. The earlier-eluting fractions revealed abundant small aromatic cores (1–3 fused rings) with extensive alkyl substitution, whereas the later-eluting compounds were alkyl-depleted/sizable aromatic structures (5–9 fused rings).…”