Innate Sulfur Compounds as an Internal Standard for Determining Vacuum Gas Oil Compositions by APPI FT-ICR MS

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.

Saturated Compounds in Heavy Petroleum Fractions

“…Briefly, the saturated components were determined to be the mass balance after all aromatic compounds have been determined through the use of innate sulfur compounds as internal standard for atmospheric pressure photoionization (APPI) Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). The prior reported determination of saturates by comprehensive 2-dimensional gas chromatography with flame ionization detection (GCxGC-FID) is extended here to the heavier VGO fractions . The error bars in Figure represent the relative standard deviation as follows: for the saturates (SATs) a repeated analysis of cut #20, for the GCxGC-FID data an arbitrary 15%, and for the APPI FT-ICR MS data obtained for three repeat analyses.…”

“…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.…”

“…In agreement with prior analyses of saturates fractions using similar experimental parameters, molecular ions were obtained with limited fragmentation. 25,28 The mass spectra of cuts #20 and #27 contain signals 24 In the modeling part of this work we address the deconvolution of the two distributions to exclude the lighter boiling contamination from the data. Despite a varying ion abundance for repeated FD TOF MS measurements, the mass spectrometric identifications are reproducible.…”

A three-dimensional semi-quantitative method to monitor the evolution of polycyclic aromatic hydrocarbons from vacuum gas oil feedstocks to lighter products

“…Finally CPC×SFC/HRMS analysis allowed a more accurate characterisation than an analysis by SFC/HRMS. As shown previously [20], a strong ionisation suppression can occur during VGO analysis by SFC/HRMS due to ionisation competition of analytes entering simultaneously in the ionisation source [29]. By calculating the weighted average nC based on the intensity of ions detected in SFC/HRMS, it appeared that the average nC for a given DBE was higher than the one calculated using data from CPC×SFC/HRMS analysis.…”

“…Although analytical devices become more and more powerful, petroleomics is still a challenge for chemical analysis [18]. Ultra high-resolution mass spectrometry such as Fouriertransform ion cyclotron resonance mass spectrometry (FT-ICR-MS) plays an important role in this research field by identifying several thousands of oil components and globally improving knowledge about HCK reactions [19][20][21][22]. Nevertheless, mass spectrometry alone cannot resolve the complexity of petroleum due to ionisation competition leading to qualitative data and the inability to differentiate isomeric species [23].…”