Abstract
This work presents some important issues and topics related to chemical thermodynamics of ionic liquids (ILs). It consist of a series of experimental measurements in binary and ternary phase equilibrium systems connected with possible extraction of 2-phenylethanol (PEA) from aqueous phase “in situ” during the bioproduction. New experimental (solid + liquid) phase equilibrium (SLE) data for two binary systems {IL (1) + PEA (2)} and few (liquid + liquid) phase equilibrium (LLE) in binary systems {IL (1) + H2O (2)}, as well as LLE in five ternary systems of {IL (1) + PEA (2) + water (3)} at temperature T = 308.15 K and ambient pressure are reported. The systems are composed of the ILs: N-butyl-N-trimethylammonium bis{(trifluoromethyl)sulfonyl}imide, [N1114][NTf2], (2-hydroxyethyl)-N-trimethylammonium bis{(trifluoromethyl)sulfonyl}imide, [N1112OH][NTf2], N-N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis{(trifluoromethyl)sulfonyl}imide, [N2212OCH3][NTf2], N-methyl-N-trioctylammonium bis{(trifluoromethyl)sulfonyl}imide, [N1888][NTf2], and N-triethyl-N-octylammonium bis{(trifluoromethyl)sulfonyl}imide, [N2228][NTf2], with PEA or water. The miscibility of some of these ILs with water was known from the literature. A differential scanning calorimetry (DSC) was used to determine the melting point and the enthalpy of melting, solid-solid phase transition temperature and enthalpy, as well as glass transition of the ILs. The [N1114][NTf2] and [N1112OH][NTf2] showed complete miscibility in the liquid phase in a binary system with PEA at temperatures higher than the solubility curve. The latest ILs as [N2212OCH3][NTf2], [N1888][NTf2], and [N2228][NTf2] showed complete miscibility with PEA at temperature T = 308.15 K. The solubility of the ILs in PEA decreases in the order [N1114][NTf2] > [N1112OH][NTf2]. All systems revealed immiscibility gap with water (literature and our data). The solubility of water in the ILs increases in the order [N1888][NTf2] < [N2228][NTf2] < [N2212OCH3][NTf2] < [N1114][NTf2] < [N1112OH][NTf2]. The average selectivity of the extraction of PEA from water increases in the following order: [N1112OH][NTf2] (Sav = 130) < [N1114][NTf2] (Sav = 294) < [N2212OCH3][NTf2] (Sav = 319) < [N2228][NTf2] (Sav = 711) < [N1888][NTf2] (Sav = 806). The correlation of the solubility curves in binary systems, and tie-lines in ternary systems was undertaken with the NRTL excess Gibbs energy equation. The model correlates the solubility of the ternary systems with an acceptable average root mean square deviation (σx = 0.0039). Our results of ternary LLE may be used to design future alternative technological processes of the extraction of PEA from the fermentation broth with [N1888][NTf2] or [N2228][NTf2].
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