Low viscosity lactam-based ionic liquids with carboxylate anions: Application in the separation of systems toluene/heptane, cyclohexene/cyclohexane, and phenol/water

• Published in: Journal of molecular liquids Vol. 346; p. 117720
• Main Authors: Bessa, Aline M.M., Pinheiro, Regiane S., Feitosa, Filipe X., de Sant'Ana, Hosiberto B., de Santiago-Aguiar, Rílvia S.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15-01-2022
• Subjects: Aromatic; Ionic liquid; Liquid-liquid equilibrium; Low viscosity lactam; Olefins; Phenol; Liquid-liquid equilibrium; Phenol; Low viscosity lactam; Aromatic; Olefins; Ionic liquid
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2021.117720

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•Five different LLE systems including lactam based ILs were correlated by NRTL model.•FTIR spectra were used for verified decomposition of ILs containing hexanoate anion.•ILs containing hexanoic acid cannot be used in water-containing separation systems.
Low viscosity lactam-based ionic liquids (ILs) were evaluated as extractor solvents in organic components separation. Experimental data for liquid–liquid equilibrium (LLE) were obtained from the toluene + heptane + IL, cyclohexene + cyclohexane + IL and phenol + water + IL systems at 298.15 K and atmospheric pressure. The reliability of experimental data has been verified by the Othmer-Tobias, Bachman and Hand equations. ILs γ-butyrolactam acetate (BTA), γ-butyrolactam butyrate (BTB), and γ-butyrolactam hexanoate (BTH); and ε-caprolactam acetate (CPA) and ε-caprolactam hexanoate (CPH) were used. It has been observed that anion structures influence on all miscibility of ternary mixtures, while cation structures influence on cyclohexene + cyclohexane + IL. Ionic liquids containing lower chain anions (BTA, BTB and CPA) formed two phases with heptane and toluene mixture. However, ILs containing higher chain anions (BTH and CPH) formed heterogeneous systems only with the water + phenol mixture. Only BTA showed partial miscibility in the cyclohexene + cyclohexane system. ILs containing acetate anion presented selectivity higher than 1 in aromatic and aliphatic separation. This also happened on lower concentrations of cyclohexene in olefin and paraffin separation. CPA presented selectivity higher than BTA in liquid–liquid extraction of toluene from heptane. In this system, BTA and CPA can be reused for three times without changes in the chemical structure of ILs and with a small reduction in selectivity (5.4 to 3.8 for BTA and 17.2 to 11.8 for CPA). The thermodynamic model NRTL was used to obtain binary interaction parameters and to correlate LLE experimental data for toluene + heptane + IL system. A comparison between experimental and calculated data indicates a good representation of data. ILs containing hexanoate anion presented degradation in water, the hexanoic acid remained in organic-phase, while γ-butyrolactam was transferred to water-phase. Therefore, it was not possible to determine LLE data.