No abstract

The recent growing interest in biofuels is due to the continuous increase in crude oil prices, limited resources of fossil energies, and environmental concerns. In what concerns road transportation, biodiesel is being considered a good alternative to conventional diesels. It consists of a blend of fatty acid esters, and its production and formulation needs to be optimized to ensure that the fuel quality complies with the legal standards. Although in various aspects biodiesel is superior to conventional diesel, it also poses some problems such as its poor behavior at low temperatures and higher hygroscopicity than conventional diesel. Up to now, little information is available about the water solubility in fatty acid methyl and ethyl esters and commercial biodiesels. To overcome this lack of data, water solubility measurements were carried out for 11 pure esters and 6 biodiesels in the temperature range 288.15-323.15 K. This new experimental data was successfully modeled with the cubic-plus-association (CPA) equation of state with global average deviations inferior to 7% for the ester systems, and predictions with deviations of 16% for commercial biodiesels were achieved.

The understanding of the specific interactions between salt ions and ionic liquids (ILs) in aqueous solutions is relevant in multiple applications. The influence of a series of anions on the solubility of 1-butyl-3-methylimidazolium tricyanomethane in aqueous environment was here studied. This study aims at gathering further information to evaluate the recently proposed 1,2 mechanisms of salting-in-and salting-out-inducing ions in aqueous solutions of ILs and to provide insights at the molecular-level on the phenomena occurring in these systems. The observed effect of the inorganic species on the aqueous solubility of the ionic liquid qualitatively follows the Hofmeister series, and it is dependent on the nature and concentration of the anions. The liquid-liquid equilibrium data and 1 H NMR results here reported support a model according to which salting-in-and salting-out-inducing ions operate by essentially different mechanisms. While salting-out is an entropically driven effect resulting from the formation of hydration complexes and the increase of the surface tension of cavity formation, the salting-in phenomena is a consequence of the direct binding of the ions to the hydrophobic moieties of the IL. Further evidence here obtained suggests that the interactions of the inorganic ions are not only established with the cation of the IL, but also with the anion, with the observed solubility effect the result of a balance between those two types of interactions.