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.

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.

In the prolific literature about asphaltenes, the effects of temperature and pressure on their stability are subjects of discussion. A new high-pressure cell, requiring a very small amount of sample and with wide working conditions, has been built in order to study the asphaltene phase behavior after injection of various gases and precipitants. A filtration technique is used to conclude on the effects of temperature, pressure, and composition. The precipitant used in this work is CO 2 . Two crude oils (from South America and the Middle East) were studied up to 383 K and 60 MPa. It was found for both oils that asphaltenes were more soluble when temperature was decreased and pressure was increased in the presence of a gas component. These effects were discussed with simple principles of thermodynamics.

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.

We present molecular dynamics simulations (MDS) for interpreting the molecular aggregation of four different asphaltene molecular models. These simulations are based on recent small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) experiments from Eyssautier and co-workers [

Multiscale characterization of asphaltenes and their extrography fractions titrated with n-heptane was performed. Chemical characterization via FT-ICR MS and GPC ICP HR-MS, stability monitoring via QCR, and AFM images of deposits indicate that "island"-enriched samples tend to form fewer, well-organized deposit aggregates, whereas samples with abundant "archipelago"-like molecules produce larger aggregates and less well-organized deposits. The combination of QCR and AFM leads to the conclusion that "island"-enriched samples lead to smaller deposits compared to "archipelago"-like molecules.

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An experimental method is proposed for determining the asphaltene instability envelope of a crude oil or crude oil + antisolvent system under reservoir conditions by using a thickness shear mode acoustic wave sensor fully immersed in oil under pressure. The technique allows determining the upper asphaltene instability pressure by carrying out constant mass expansion experiments, whereas the lower asphaltene instability pressure can be determined during constant mass compression tests. The basis of the technique is presented, and measurements have been carried out in a bottomhole oil + CO 2 system with various CO 2 contents at reservoir temperature. Finally, the effect of temperature on the asphaltene instability envelope was studied on two systems with 45 and 55 mol % CO 2 .