This work is a continuation of our researches on the study of thermodynamic properties of organic compound mixtures and made up of two sections: an experimental section and a theoretical section. The experimental solid–liquid equilibrium diagrams of binary systems: piperidine + benzene and piperidine + n-octane, measured at atmospheric pressure, have been obtained by means of an apparatus derived from that of Smit. The advantage of this apparatus compared to that of Rossini and that of Jacob is the higher measurement accuracy and the low amount of product used. In the theoretical section, in addition to the calculation of the liquidus curves in the ideal case, the DISQUAC model and the Dortmund-UNIFAC method were applied to the two mixtures to predict the liquidus curves and make a comparison.

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.

The phase transition leading to the petroleum asphaltene flocculation is considered as either a liquid-solid or liquid-liquid transition. Despite the fact that asphaltenes obtained by the usual procedure are amorphous solids, numerous arguments support the second hypothesis. In this work, we present studies of asphaltene flocculation kinetics and compare the results with the kinetics of coalescence of flocculated asphaltenes that have been redispersed mechanically in the solvent. Redispersion of flocculated asphaltenes was realized using an ultrasound bath. Kinetic measurements were performed using a dynamic light scattering technique. The Malvern 4800 apparatus used in this study makes it possible for us to observe the growth of aggregates in the range of 2-5000 nm. It was found that kinetic curves for redispersed asphaltenes are very similar to those of the initial flocculation induced by an antisolvent. This finding confirms the liquid-like behavior of flocculated asphaltenes. Moreover, the energy of cohesion of asphaltene aggregates is very low, and consequently, the amount of energy needed for redispersion is also low. The aging of the flocculated sample accelerates the aggregation kinetics, which points to very slow reorganization of the asphaltene structure, leading to more compact, solid-like flocs.