No abstract

No abstract

Innate sulfur components in high boiling petroleum samples were used as an internal standard for the estimation of the sample's composition through atmospheric pressure photo ionization (APPI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The first step was recording a representative mass spectrum for the aromatic components through the use of a time-of-flight mass spectrometer (TOF MS) to tune the FT-ICR MS parameters. The molecular weight and number of sulfur atoms per species identified in the high-resolution measurement, their mass spectrometric abundance, and the total sulfur content were combined to calculate the mass fraction of each (and by sum all) aromatic sulfur species present. Aromatic hydrocarbon (HC) compound quantification was based on an equimolar response compared to the aromatic sulfur species. Nitrogen species were treated analogously to the sulfur compounds by distributing the total nitrogen content. The mass balance of all aromatic compounds yields the mass fraction of saturated compounds (saturates), which is not directly accessible through the APPI process. The validity and biases of this approach were evaluated on a series of vacuum distilled fractions with narrow boiling ranges using comprehensive two-dimensional gas chromatography (GCxGC) as a reference technique. There are clear biases of the presented mass spectrometric approach compared to the GCxGC analysis, especially the underestimation of monoaromatic compounds and the overestimation of diaromatic sulfur compounds (benzothiophenes); however, the results agree surprisingly well for saturated compounds and, overall, for the aromatic hydrocarbon-and sulfur-containing compound families. The saturates fraction results also matched reasonably with gravimetrically determined saturates contents, and the isolated fractions were further characterized using field desorption/field ionization TOF MS. The inclusion of saturated compound carbon number distribution, in combination with FT-ICR MS data, yields a more complete compositional description of the studied vacuum gas oil samples. The method was also applied to two typical boiling range vacuum gas oil samples (derived from a Norwegian and an Arabian crude oil) to provide an insight into the usefulness and limitations of high-resolution mass spectrometry in a semiquantitative context, which is deemed important for many oil and gas industry applications.

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.

No abstract