This work is focused on the study of two methylimidazolium-based ionic liquids (IL) as more sustainable solvents not only in deterpenation processes, but also in petrochemical processes, including separating aromatic from aliphatic hydrocarbons and the removal of impurities in fossil fuels. In fact, IL can act as alternative separation agents to traditional organic solvents in different liquid-liquid extraction processes.
For this purpose, the activity coefficients at infinite dilution, 𝛾∞, of 52 solutes (water, alkanes, cycloalkanes, ketones, ethers, cyclic ethers, aromatic hydrocarbons, esters, alcohols, terpenes and terpenoids) in 1-butyl-3-methylimidazolium hexafluorophosphate [C4mim][PF6] and in the equimolar IL mixture of [C4mim][PF6] and 1-butyl-3-methylimidazolium chloride [C4mim][Cl] were measured by inverse gas chromatography technique over the temperature range of (333.2-453.2) K. Similar data in pure [C4mim][Cl] was already available in the literature. From the 𝛾∞ values, some thermodynamic parameters (such as excess partial molar properties, selectivities, capacities, gas-liquid partition coefficients, and solvent performance indexes) can be estimated in order to evaluate the ionic liquid performance.
The majority of the studied solutes showed higher 𝛾∞ values in the equimolar IL mixture than in pure [C4mim][PF6]. Poor interaction (𝛾∞ >> 1) was observed between both IL studied and the less polar solutes (alkanes and cycloalkanes). On the other hand, alcohols and water showed high interaction with the equimolar IL mixture (𝛾∞ < 1). Hydrocarbon terpenes, ether, and ketone terpenoids have higher interaction with pure [C4mim][PF6], and alcohol terpenoids have more favorable interactions with the equimolar IL mixture. With regard to separation factors, the IL studied showed, in general, poor selectivities and capacities for terpenes/terpenoids mixtures being the best result obtained for the carvacrol/-terpinene mixture. On the other hand, promising results were obtained for the separation of several model mixtures (octane/benzene, cyclohexane/benzene, octane/thiophene, and octane/pyridine) of the fuel industries. The studied solvents were among the IL having the best performance indexes which provided important insights on the use of alternative solvents for the removal of aromatics from aliphatic hydrocarbons and the removal of contaminants from fuels.
