A combined liquid chromatography coupled to a mass spectrometer with an ICP detector (μSEC-HR ICP MS; μSEC ICP for brevity) technique was used to analyze the metals in four asphaltenes and their corresponding A1 (toluene insoluble), A2 (toluene soluble), and trapped compound (TC, heptane soluble) fractions. For three of the asphaltene samples, the normalized μSEC ICP profiles for both nickel and sulfur were very similar, showing that nickel porphyrins were distributed in almost all types of asphaltene aggregates. Extensive overlapping with sulfur profiles was observed for all vanadium and nickel profiles at retention times below the maximum bands. This suggests that large amounts of nickel and other organometallic or metal-porphyrin-type (MP) compounds are interlocked with asphaltene molecules, forming aggregates in solution. The separation of MP compounds using common separation techniques is very difficult as extraction would require dissociation into several molecules. The presence of TCs (e.g., compounds other than asphaltenes that are soluble in n-heptane) in asphaltene aggregates was related to the fractal structure of asphaltene aggregates in which voids are filled with components coming from the surrounding media. Apparently, complete trapping of TCs is achieved by performing aggregate rearrangement after penetration, leading to an aggregate structure in which the TCs remain trapped. A similar trapping mechanism is proposed herein for the MP compounds. Accordingly, no covalent bonds or specific interactions appear to be required to account for the presence of MPs within asphaltene aggregates.

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The coupling of size exclusion chromatography (SEC) and normal phase (NP) HPLC using entirely organic mobile phases (tetrahydrofuran, xylene) with inductively coupled plasma mass spectrometry (ICP MS) were developed and investigated for the molecular distribution of nickel and vanadium in crude oils. The metal species were fractionated by SEC using three columns in series with the increasing porosity (100, 1000 and 100000 A) covering the molecular mass range (in eq. polystyrene) between 300 and 2 Â 10 6 Da. The resolution achieved allowed the discrimination of at least three classes of Ni and V species with varying proportions of the metals as a function of the origin of crude oil, crude oil fraction (asphaltene, maltene) and dilution factor. Normal phase HPLC-ICP MS allowed the separation of the porphyrin-type fraction as well as separation of the remaining species into three distinct fractions. The metal species in the SEC fractions were found to be sufficiently stable to be collected and preconcentrated to allow the development of a bidimensional chromatography SEC-NP-HPLC-ICPMS for the probing of the metal distribution in crude oils in terms of molecular weight and polarity.

The size distribution of sulfur, vanadium, and nickel was determined for four crude oils and their distillation cuts using gel permeation chromatography (GPC) coupled to inductively coupled plasma high-resolution mass spectrometry (ICP HR MS). The results show a trimodal distribution of vanadium and nickel compounds in the crude oils, the atmospheric residues, and the vacuum residues and, for sulfur compounds, either a mono- or bimodal distribution depending upon the distillation cut considered. A correlation exists between the sulfur fraction retention times and the temperature cuts of the distillation for a temperature below 560 °C and also between the viscosity of the crude oils and the proportion of trapped sulfur compounds in a higher boiling temperature fraction. The thermic treatment applied for the distillation increases the aggregation of low- and medium-molecular-weight compounds of vanadium and nickel into higher molecular weight aggregates between the crude oil on the one hand and the atmospheric residue and vacuum residue on the other hand, especially when the crude oil has a high total sulfur content.

In this paper the aggregation of asphaltenes is studied for two asphaltene molecule families, namely PA3 and CA22 analogues, based on the work of Schuler et al. (JACS, 2015, 137, 31, 9870). The chemical characteristics of these molecules were screened by changing the heteroatoms on the backbone and the lateral chain-ends. These molecules were mixed together with different relative concentrations and for the first time the aggregation of different asphaltenes was determined using molecular dynamics simulations (MDS). The results show that the interaction energies vary for different heteroatom arrangement within a given structure and depend on the type of asphaltene. Moreover, we showed that the chain-ends have a crucial role on this phenomenon.

Trapping of compounds by asphaltenes in guest-host complexes (GHC) is an important phenomenon relevant to many properties of the system, such as asphaltene structure, swelling and solvent trapping, geochemical impact, as well as the trapping of metalloporphyrins, free radicals, resins, and other crude oil components, such as, e.g., paraffin. Several trapping mechanisms, such as adsorption and occlusion, during asphaltene separation from crude oil can be considered, but most interest is attracted to GHC, in which the guest is firmly bound and cannot be completely liberated from the host by solvent extraction. An example of such trapping is presented, with the guest being paraffinic and other resin-like compounds hereafter called trapped compounds (TCs). TCs were isolated from asphaltenes by the partition of the asphaltene sample in fractions A1 (toluene insoluble) and A2 (toluene soluble). A small quantity (about 8%) of a heptane-soluble TC fraction was isolated along with the A2 fraction. The presence of TCs in asphaltenes and their absence in fractions A1 and A2 were detected by means of laser desorption ionization-time of flight mass spectrometry (LDI-TOF MS) in the 450-600 molecular-mass range. These finding suggests that the TC sample is probably trapped in a network formed by both A1 and A2 fractions.

The size distributions of sulfur (S), vanadium (V), and nickel (Ni) compounds in four crude oils, two residues, and their saturate, aromatic, resin, and asphaltene (SARA) fractions were determined using gel permeation chromatography (GPC) coupled to inductively coupled plasma high-resolution mass spectrometry (ICP HR MS). The results show trimodal distributions of V, Ni, and S compounds in the crude oils and residues. V and Ni compounds are present in both resins and asphaltenes. Trimodal distributions are clearly apparent in the resins but not apparent in the asphaltenes. In the latter, the predominant compounds have a high molecular weight (HMW), even when the solution of asphaltenes is diluted by 40000-fold. In the resins, compounds with a medium molecular weight (MMW) were expected; however, HMW compounds were observed, indicating that nanoaggregates or large molecules exist in both the asphaltenes and resins. Low-molecular-weight (LMW) compounds are predominantly present in the resins and do not represent more than 22% of V and Ni present in crude oil. These compounds appear to have molecular weights similar to simple metalloporphyrins.