Calculation of the Total Sulfur Content in Crude Oils by Positive-Ion Atmospheric Pressure Photoionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Herein, a method to calculate the total sulfur concentration in petroleum samples from the chemometric modeling of data obtained by positive-ion atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry [(+) APPI FT-ICR MS] is described. Analysis by FT-ICR MS provides both a measurement of the total sulfur concentration and detailed molecular-level speciation of sulfur-containing compounds. A total of 30 crude oil samples ranging from 0.2 to 4.6 wt % sulfur were employed to train the sulfur prediction model. The ratios of the percent relative abundance (%RA) between the sulfur classes (S_<i>x</i>) and the hydrocarbon (HC) class were employed as variables for principal component analysis (PCA). The PCA results reveal a highly linear trend along the principal component with the highest explained variance (PC1). Analysis of the loadings plot reveals that the S₁/HC ratio governs the trend in PC1. Values for PC2 are governed by S₁/HC, S₂/HC, and S₃/HC ratios and provide the ability to distinguish between oils with higher total sulfur contents (greater relative abundance of S₂- and S₃-containing compounds for sulfur of >1 wt %). Thus, these results indicate that the sulfur concentration of crude oils can be modeled by a linear combination of variables based on S_<i>x</i>/HC ratio(s). The model successfully predicted sulfur concentrations for 11 test samples within 0.36% standard deviation, as compared to sulfur concentrations obtained from bulk elemental analysis

Calculation of the Total Sulfur Content in Crude Oils by Positive-Ion Atmospheric Pressure Photoionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Herein, a method to calculate the total sulfur concentration in petroleum samples from the chemometric modeling of data obtained by positive-ion atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry [(+) APPI FT-ICR MS] is described. Analysis by FT-ICR MS provides both a measurement of the total sulfur concentration and detailed molecular-level speciation of sulfur-containing compounds. A total of 30 crude oil samples ranging from 0.2 to 4.6 wt % sulfur were employed to train the sulfur prediction model. The ratios of the percent relative abundance (%RA) between the sulfur classes (S_<i>x</i>) and the hydrocarbon (HC) class were employed as variables for principal component analysis (PCA). The PCA results reveal a highly linear trend along the principal component with the highest explained variance (PC1). Analysis of the loadings plot reveals that the S₁/HC ratio governs the trend in PC1. Values for PC2 are governed by S₁/HC, S₂/HC, and S₃/HC ratios and provide the ability to distinguish between oils with higher total sulfur contents (greater relative abundance of S₂- and S₃-containing compounds for sulfur of >1 wt %). Thus, these results indicate that the sulfur concentration of crude oils can be modeled by a linear combination of variables based on S_<i>x</i>/HC ratio(s). The model successfully predicted sulfur concentrations for 11 test samples within 0.36% standard deviation, as compared to sulfur concentrations obtained from bulk elemental analysis

Advances in Asphaltene Petroleomics. Part 1: Asphaltenes Are Composed of Abundant Island and Archipelago Structural Motifs

For decades, discussion of asphaltene structure focused primarily on molecular weight. Now that it is widely accepted that asphaltene monomers are between ∼250 and 1200 g/mol, disagreement has turned to asphaltene architecture. The classic island model depicts asphaltenes as single core aromatic molecules with peripheral alkyl side chains, whereas the less widely accepted archipelago model, includes multiple aromatic cores that are alkyl-bridged with multiple polar functionalities. Here, we analyze asphaltene samples by positive-ion atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry and perform infrared multiphoton dissociation to identify their aromatic core structures to shed light on the abundance of island and archipelago structural motifs. Our results indicate that island and archipelago motifs coexist in petroleum asphaltenes, and unlike readily accessible island motifs, asphaltene purification is required to detect and characterize archipelago species by mass spectrometry. Moreover, we demonstrate that mass spectrometry analysis of asphaltenic samples is biased toward the preferential ionization/detection of island structural motifs and that this bias explains the overwhelming mass spectral support of the island model. We demonstrate that the asphaltene structure is a continuum of island and archipelago motifs and hypothesize that the dominant structure (island or archipelago) depends upon the asphaltene sample

Advances in Asphaltene Petroleomics. Part 2: Selective Separation Method That Reveals Fractions Enriched in Island and Archipelago Structural Motifs by Mass Spectrometry

Advances in high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) enable molecular-level characterization of ultracomplex asphaltene samples. Such analyses most often reveal compounds that are highly aromatic but alkyl-deficient in nature and, thus, support the classical “island” model of asphaltene architecture. However, recent works that combine chromatographic separations with mass spectrometry for the analysis of crude oils have shown that differences in ionization may greatly affect the analysis of complex mixtures (known as the matrix effect). Simply, compounds that ionize with greater efficiency are preferentially observed and mask the detection of poorly ionized compounds. Asphaltenes are not immune to this phenomenon. In the first of this series (10.1021/acs.energyfuels.7b02873), it was demonstrated that asphaltenes generated by different precipitants showed greatly varied monomer ion yields (ionization efficiencies). This work focuses on the development of an extrography fractionation method that selectively targets the removal of asphaltene species that exhibit high monomer ion yields and, thus, restrict mass spectral characterization of less efficiently ionized species. Silica gel was used as the stationary phase, and a unique solvent series separated asphaltenes based on their interaction with the silica surface, which was later determined to depend heavily upon the structure as well as monomer ion yield. The first two solvents (acetone and acetonitrile) isolated compounds that most efficiently produce monomeric asphaltene ions and, thus, cause bias in mass spectrometric analyses of whole asphaltenes. A solvent polarity gradient was then used, with <i>n</i>-heptane, toluene, tetrahydrofuran, and methanol, to separate remnant asphaltene compounds on the basis of polarity and structure. Our results demonstrate that mass spectrometry of whole asphaltenes does not reveal the complete molecular composition but rather preferentially exposes highly aromatic, alkyl-deficient, island-type structures. Early eluting fractions are shown to resemble the composition of the whole asphaltene and are enriched in island structures, whereas the analysis of later-eluting fractions reveals archipelago structural motifs as well as species with atypical asphaltene molecular compositions. We also demonstrate that, as molecular weight increases, the asphaltenes exhibit increased contributions of archipelago structural motifs. Higher mass ions (<i>m</i>/<i>z</i> > 550), even from asphaltene fractions enriched in island structures, exhibit fragmentation pathways that originate from archipelago structures. Thus, positive-ion atmospheric pressure photoionization (APPI) FT-ICR MS provides molecular-level data that suggest that the island model is not the dominant structure of asphaltenes. It coexists with abundant archipelago structures, and the ratios of each are sample-dependent

Chromatographic Enrichment and Subsequent Separation of Nickel and Vanadyl Porphyrins from Natural Seeps and Molecular Characterization by Positive Electrospray Ionization FT-ICR Mass Spectrometry

We report a novel chromatographic method to enrich and separate nickel and vanadyl porphyrins from a natural seep sample and combine molecular level characterization by positive-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Vanadyl and nickel porphyrin model compound elution from primary secondary amine (PSA) stationary phase combined with UV-vis spectroscopy confirms enrichment and subsequent fractionation of nickel and vanadyl porphyrins into polarity-based subfractions. A more than 100-fold increase in signal-to-noise ratio for nickel porphyrins enables unequivocal elemental composition assignment confirmed by isotopic fine structure for all isotopes >1% relative abundance, and the first mass spectral identification of ⁶¹Ni porphyrin isotopologues derived from natural seeps. Oxygen-containing vanadyl porphyrins and sulfur-containing vanadyl porphyrins are isolated in the same fraction simultaneously from the same sample. We provide the first chromatographic evidence of carboxylic acid functionalities peripheral to the porphyrin core, in agreement with previous studies

Chromatographic Enrichment and Subsequent Separation of Nickel and Vanadyl Porphyrins from Natural Seeps and Molecular Characterization by Positive Electrospray Ionization FT-ICR Mass Spectrometry

We report a novel chromatographic method to enrich and separate nickel and vanadyl porphyrins from a natural seep sample and combine molecular level characterization by positive-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Vanadyl and nickel porphyrin model compound elution from primary secondary amine (PSA) stationary phase combined with UV-vis spectroscopy confirms enrichment and subsequent fractionation of nickel and vanadyl porphyrins into polarity-based subfractions. A more than 100-fold increase in signal-to-noise ratio for nickel porphyrins enables unequivocal elemental composition assignment confirmed by isotopic fine structure for all isotopes >1% relative abundance, and the first mass spectral identification of ⁶¹Ni porphyrin isotopologues derived from natural seeps. Oxygen-containing vanadyl porphyrins and sulfur-containing vanadyl porphyrins are isolated in the same fraction simultaneously from the same sample. We provide the first chromatographic evidence of carboxylic acid functionalities peripheral to the porphyrin core, in agreement with previous studies

Advanced Chemical Characterization of Pyrolysis Oils from Landfill Waste, Recycled Plastics, and Forestry Residue

Waste material pyrolysis has proven useful for the production of pyrolysis oils; however, the physical properties and chemical composition of pyrolysis oils are greatly influenced by the feedstock. It is well established that lignin- and cellulose-rich material produces pyrolysis oils high in aromatic oxygen-containing compounds, whereas pyrolysis oils produced from other sources such as plastics and household wastes are far less characterized. Here, three fast pyrolysis oils produced from landfill waste, recycled plastics, and pine forestry residue are compared by elemental analysis, Fourier transform infrared spectroscopy (FT-IR), comprehensive 2D gas chromatography (GC×GC), Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), and liquid chromatography. GC×GC, FT-ICR MS, and liquid chromatography provide insight into the chemical composition of pyrolysis oils, whereas FT-IR analysis identifies functional groups. Landfill and plastic pyrolysis oils were found to contain higher hydrocarbon content that resulted from little or no cellulosic material in their feedstock. In contrast, pine pyrolysis oil is more aromatic and contains a higher abundance of polar species due to the number of oxygen functionalities. The hydrocarbons in plastic pyrolysis oil are more saturated than in landfill and pine pyrolysis oils. Due to their lower oxygen content, landfill and plastic pyrolysis oils are more attractive than pine pyrolysis oil as potential fuel candidates

Dual-Column Aromatic Ring Class Separation with Improved Universal Detection across Mobile-Phase Gradients via Eluate Dilution

The herein described High Performance Liquid Chromatography (HPLC) platform (termed HPLC-3) combines a complex solvent gradient with two electron acceptor columns to provide aromatic ring class (ARC) separation for heavy oils. The separation yields seven major fractions: saturates, monoaromatics (1 ring), diaromatics (2 rings), triaromatics (3 rings), tetra-aromatics (4 rings), polyaromatics and polars (5+ polars), and aliphatic sulfides. The system utilizes a photodiode array detector (PDA) for online measurements of aromaticity in series with an evaporative light scattering detector (ELSD) to provide improved quantitative mass determination across the entire solvent gradient. A new postcolumn dilution strategy was successfully utilized to compensate for solvent effects on the ELSD signal. The method allows for calibration across the entire HPLC-3 solvent gradient and simultaneously diverts ∼90% of the sample effluent for fraction collection and further characterization. In addition to the major ARC fractions, the retention characteristics of various heteroatomic functional groups were studied to demonstrate the HPLC-3 system’s ability to further separate polar compounds on the basis of hydrogen bonding