A study was made to determine the solubility behavior of 17 ionic liquids (ILs) with asphaltenes and a quantum-chemical density functional theory approximation using a def-TVZP basis set and the Perdew−Burke−Ernzerhof functional. The conductor-like model from COSMO-RS was used within the real solvent approximation to determine the density, molar volume, viscosity, and heat capacity with a statistical thermodynamic treatment of the interacting surface charges of the individual molecules. The solubility parameter of ILs and asphaltenes was determined using the relationship of the density and solubility parameters proposed by Panuganti et al. (Ind. Eng. Chem. Res. 2013, 52, 8009−8020). The results of the thermodynamic and solubility parameters were compared with the experimental data, and a close agreement was verified. The relative solubility of the asphaltenes with respect to ILs was determined using the δ values and Hansen's method, i.e., spheres approximation. The structure and size of the cation (including the cationic ring head and the alkyl chain length) of ILs have an influence on their ability for dispersing asphaltenes according to the molecular interactions that govern the miscibility behavior of ILs and asphaltenes, i.e., van der Waals, π−π, cation−π, and hydrophobic interactions.

The electrochemical oxidation in DMSO of four new derivatives of caffeic acid (CA), two dimeric amides and two dimeric esters, is reported in this article. Although all of them contain two caffeoyl electroactive moieties in their structures, small differences in the connectors result in interesting changes in the electrochemical behaviour of this type of compound. Voltammograms of both esters do not show appreciable differences between them; however, an electrografting process occurs during the electrochemical oxidation of one of them, which suggests that the identity of the connector has an influence on the ability of the diesters to interact with the electrode surface. On the other hand, voltammograms of dimeric amides were more complex than those corresponding to dimeric esters. Electronic effects of diamine connectors seem to be related to the fact that caffeoyl moieties suffer from separate oxidation processes in both compounds. In contrast to their ferulic acid (FA) analogues, which have been studied by our group before, CA dimeric amides do not interact in an appreciable way with the electrode surface. In addition, a relationship between the oxidation potential and the inhibition percentage of the DPPH (2,2'-diphenyl-1-picrylhydrazyl) radical was not observed for the symmetrical CA derivatives studied here. However, the molecular flexibility seems to play a very important role in the Free Radical Scavenging Activity (FRSA) of this type of compound.

Two series of imidazolium-based ionic liquids (ILs) were tested as rheological modifiers of heavy crude oils. ILs with the 1-butyl-3-alkylimidazolium cation optimize the effect on viscosity at low concentrations, whereas those with the 1-benzyl-3-alkylimidazolium cation are similarly effective only at higher concentrations, which is due to a stronger IL–IL interaction with respect to the IL–asphaltene interaction. The most effective ILs were [C6bim][PF6], [phetbim][PF6], and [C9bim][NTf2], with viscosity falling in the order of 44.0%, 38.2%, and 32.9%, respectively. An analysis of structural features suggests that the type of anion and the strength of the ion pair interaction play an important role in the capacity of the salts to interact with the crude oil components. In addition, computational methodologies, such as atoms in molecules and non-covalent interactions, were used to analyze the main intermolecular interactions between the most effective [C6bim][PF6] and two different substructures of an asphaltene model. According to these results, hydrogen bonding (F⋯H–C, F⋯H–N, and O⋯H–C), C–H–π, and van der Waals interactions contribute to the breaking up of the π–π stacking interactions between the complexes resulting from the self-association of the aromatic compounds; as a consequence, the crude oil viscosity decreases.