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The objective of this work was to investigate the mechanism of the inhibition of aggregation of petroleum asphaltenes using new ionic liquids (IL). The ionic liquids conjugate a good solubility in nonpolar environment with strong electron donor-acceptor properties. In this study, 1-propyl boronic acid-3-alkylimidazolium bromides and 1-propenyl-3-alkylimidazolium bromides were tested. A lateral chain containing either the boronic acid or the propenyl moiety was substituted for the classical 1-methyl-3-alkylimidazolium bromide. The boronic acid is a weak acid but a very efficient Lewis acid. It was demonstrated that the presence of the boronic acid moiety enhances interactions between asphaltenes and ionic liquids and limits considerably asphaltene aggregation. The length of the side alkyl chain of the ionic liquid is an important parameter also. The minimum length of eight carbons was necessary to obtain sterical stabilization of IL-asphaltene complexes.

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The interactions between asphaltenes and short- to medium-chain n-alkanes were studied using titration microcalorimetry and inverse chromatography. The exothermic heat effects observed upon mixing of asphaltenes and n-alkanes were interpreted in terms of assembling of the two types of compounds into mixed structures. We show that the energy of the interactions between n-alkanes and the asphaltene hydrocarbon chains is close to the energy of the interactions between the asphaltene chains. We propose that the latter interactions are responsible for the formation of the asphaltene aggregates and are the driving force of the aggregate assembly into higher structures.

Results obtained with flocculation threshold experiments and with inverse gas chromatography were used to validate the use of the solubility parameter approach to asphaltene flocculation phenomena. It was found that values of solubility parameters obtained with both methods are in good agreement. The global solubility parameter of the crude oils was factorized in terms of Linear Solvation Energy Relationship (LSER) coefficients corresponding to a given fluid. Results confirm the validity of the three-dimensional solubility parameter proposed by Hansen to deal with petroleum fluids.

Activity coefficients at infinite dilution, gammainfinity, of organic compounds in two new room-temperature ionic liquids (n-methacryloyloxyhexyl-N-methylimidazolium bromide (C10H17O2MIM)(Br) at 313.15 and 323.15 K and n-acryloyloxypropyl-N-methylimidazolium bromide(C6H11O2MIM)(Br)) were determined using inverse gas chromatography. Phase loading studies of the net retention volume per gram of packing as a function of the percent phase loading were used to estimate the influence of concurrent retention mechanisms on the accuracy of activity coefficients at infinite dilution of solutes in both ionic liquids. It was found that most of the solutes were retained largely by partition with a small contribution from adsorption and that n-alkanes were retained predominantly by interfacial adsorption on ionic liquids studied in this work. The solvation characteristics of the two ionic liquids were evaluated using the Abraham solvation parameter model.