Structural Comparison of Asphaltenes of Different Origins Using Multi-stage Tandem Mass Spectrometry

Abstract

In this work, six petroleum asphaltene samples of different geographical origins were studied using atmospheric pressure chemical ionization (APCI) in positive ion mode in a linear quadrupole ion trap mass spectrometer (LQIT). APCI doped with carbon disulfide reagent was selected as the ionization method as it has been previously demonstrated to generate stable molecular ions with no fragmentation for asphaltene molecules. The mass spectra measured using this approach revealed the apparent molecular weights (MWs) of the molecules in the asphaltene samples. The results show that petroleum asphaltenes from the American continent, Europe and China have similar apparent molecular weight distributions, ranging from 200 up to 1450 Da, with slightly different apparent average MWs ranging from 570 to 700 Da. Further, molecular ions with eight randomly selected mass-to-charge ratios (m/z) ranging from m/z 500 up to m/z 808 were isolated for each asphaltene sample and subjected to collisionally activated dissociation (CAD) at the same collision energy to examine their structures. The CAD mass spectra (MS 2 experiment) provided information on the maximum total number of carbons in the alkyl chains and the smallest possible size of the aromatic cores in the ionized molecules. Additionally, MS 3 experiments were performed to investigate the fragmentation patterns of the fragment ions generated in the MS 2 experiments. The results obtained support the island structural model for these asphaltenes. Moreover, molecules of greater MWs are shown to have more carbons in alkyl chains (ranging from 17 to 41) but the minimum core size is fairly constant.

Investigation of Island/Single-Core- and Archipelago/Multicore-Enriched Asphaltenes and Their Solubility Fractions by Thermal Analysis Coupled with High-Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

“…Similar results were observed for model compounds as well as asphaltenes by using mass spectrometry with collision-induced dissociation (CID) fragmentation, which results in an average number of 3-8 fused rings with up to 20 carbon atoms in alkyl-side chains. [19,[28][29][30] Nonetheless, although the island model serves to describe some asphaltene properties, such as reservoir geodynamics, it is incongruent with asphaltene behavior in several scenarios, e.g., products observed after thermal upgrading or pyrolytic degradation. After thermal cracking, the newly formed maltene fraction has been found to consist of alkylated 1-5-ring aromatics, alkanes, and alkenes, as well as naphthenes.…”

A Geological Model for the Origin of Fluid Compositional Gradients in a Large Saudi Arabian Oilfield: An Investigation by Two-Dimensional Gas Chromatography (GC × GC) and Asphaltene Chemistry

“…2 with a single polycyclic aromatic hydrocarbon (PAH) per molecule previously proposed by time resolved fluorescence polarization studies [24][25] has been confirmed by laser desorption, laser ionization mass spectrometry (L 2 MS). [26][27] Further evidence for 1.5 nm asphaltene structures has been observed in tandem mass spectrometry coupled with collisional activation decomposition, 28 in interfacial studies at an oil-water interface, [29][30][31] and in sum-frequency generation experiments. 32 2.0 nm nanoaggregates of about seven molecules have also been confirmed by SALDI-MS. 26,33 These weakly bound nanoaggregates are readily disrupted.…”

Asphaltene Molecular Representation: Impact on Aggregation Evaluation

“…Figure 1 depicts the asphaltene molecular representations obtained from the stochastic algorithm, with their corresponding molecular weights and the fraction they have in the mixture. These representations were generated from the experimental data of Maya crude oil [20], [21]. It is worth noting that all four molecules, as individuals, as well as the pondered average of the set, are within the accepted criteria for the asphaltene structural description [22].…”