With a decrease in world oil reserves and a higher demand for petroleum and its derived products, the effective exploitation of oil reservoirs has become increasingly important. Enhanced oil recovery (EOR) assisted by surfactants is an effective method for recovering the oil from reservoirs that have lost their drive after the application of primary and secondary recovery methods. This research is aimed at showing the suitability of several ionic liquids as effective replacements for conventional surfactants in EOR. The reservoir fluid has been modelled as a ternary system of water (pure water or aqueous solution of NaCl) plus the ionic liquid trihexyl(tetradecyl)phosphonium chloride plus dodecane. Determination of its liquid-liquid phase equilibrium indicates the formation of a Winsor type III system, with a triphasic region and adjacent biphasic regions. The interfacial tensions in the system corroborate the ability of the ionic liquid to act as a surface active agent, as desirable for its use in an EOR process. A relevant transport property such as viscosity, in addition to density, has been experimentally measured for the equilibrium phases.

Citrus essential oils have numerous applications in multiple sectors, including food, drink and personal care industries. Although mainly constituted by terpenes, the appealing characteristics of citrus essential oils are due to oxyterpenes and other derived oxygenated compounds. In fact, the presence of terpenes in the essential oil may lead to instability or loss of quality. Therefore, concentration of the oil in its oxyterpene compounds by removal of terpenes is desirable. The techniques currently in use for deterpenation of essential oils present a series of issues. In the search for better deterpenation processes, here the use of ionic liquids as solvents in liquid-liquid extraction is explored. In particular, the ionic liquids 1-ethyl-3-methylimidazolium acetate and 1-butyl-3-methylimidazolium acetate are investigated for their extraction of oxyterpene from a modelled citrus essential oil composed of limonene (terpene) and linalool (oxyterpene). The choice of the ionic liquids, in addition to other complementary characteristics, was based on a rationale of potential interactions that can be created preferentially with the linalool. The results show a great performance of these acetate-based ionic liquids, as compared to any other ionic or molecular solvent tested to date, for the concentration in oxyterpenes of the citrus essential oil.

The enhanced oil recovery (EOR) through microemulsion flooding implies the formulation of a complex aqueous mixture containing surfactants, co-surfactants, cosolvents, or viscosity-increasing polymers, among other additives. The optimal formulation is associated with a three-phase behavior, in which the interfacial tension becomes significantly low. One parameter that greatly affects this formulation is the temperature. In this work, it has been shown that the three-phase system generated when adding trihexyl(tetradecyl)phosphonium chloride ionic liquid to a water−oil mixture remains stable in a wide range of temperatures and in the presence of salt. In contrast to conventional systems, no co-surfactant is required. This thermal stability is an interesting feature from the EOR point of view. The use of higher temperatures implies that a slightly minor quantity of ionic liquid is needed to solubilize the water and oil mixtures. Moreover, when the temperature is increased, there is an important decrease of the microemulsion−water/brine interfacial tension and a mild decrease in the case of the microemulsion−oil. The trihexyl(tetradecyl)phosphonium chloride ionic liquid was proven to be an effective surface-active agent to recover oil.

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Three 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ionic liquids, namely, those with ethyl-, hexyl-, or decyl- as the alkyl substituent chain, were evaluated as potential solvents for the deterpenation of citrus essential oil by liquid−liquid extraction. The citrus essential oil was simulated as a mixture of the terpene limonene and the oxyterpene linalool. The liquid−liquid equilibrium data for the ternary systems formed by limonene, linalool, and each of the ionic liquids selected were experimentally determined at 298.15 K. The suitability of the ionic liquids as solvents for the proposed process was evaluated by means of solute distribution ratio and selectivity values. The influence of the alkyl side chain in the imidazolium cation of the ionic liquids on the liquid−liquid equilibrium data was analyzed. By comparison with data previously reported in the literature for analogous systems, the influence of the ionic liquid anion on the proposed separation was also analyzed. The experimental data were satisfactorily correlated by means of both the nonrandom two-liquid (NRTL) and the universal quasichemical activity coefficient (UNIQUAC) thermodynamic models.

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The ionic liquids 1-methylpyridinium methylsulfate and 1-ethylpyridinium ethylsulfate were tested as solvents for the deterpenation by liquid-liquid extraction of citrus essential oil, simulated as a mixture of limonene and linalool. Liquid-liquid equilibrium data for the ternary systems limonene þ linalool þ 1-alkylpyridinium alkylsulfate (with the alkyl chain being methyl or ethyl) were determined at 298.15 K and atmospheric pressure, and suitably correlated with the UNIQUAC thermodynamic model. A comparison was established between the performance of these ionic liquids, as well as with others previously reported in the literature, to evaluate the influence of different structural features of the ionic liquids on their deterpenation ability.