Liquid-liquid Phase Equilibria Research Articles

Liquid-liquid equilibria and mechanism exploration for the extraction of sulfides from FCC naphtha via organic solvent as extractant

Separation of sulfides from fluid catalytic cracking (FCC) naphtha is of great significance for environmental protection. In this work, the organic solvents N-methyl-2-pyrrolidone (NMP), sulfolane (SUL), and their mixtures were selected to extract sulfides (3-methylthiophene) from model FCC naphtha (n-heptane). Correspondingly, the liquid-liquid phase equilibrium (LLE) data of the systems n-heptane +3-methylthiophene + SUL/NMP/(NMP + SUL) were experimentally obtained at 298.15 K and 101.3 kPa. The distribution coefficient and separation factor were calculated to assess the extraction performance of the solvents. The results showed that mixed solvent (NMP + SUL) could be used as a potential solvent to extract 3-methylthiophene due to its suitable selectivity and solubility. Meanwhile, the density functional theory (DFT) method was applied to explore the extraction mechanism of 3-methylthiophene from n-heptane by NMP or SUL. Electrostatic potential (ESP) analysis, interaction energies, and reduced density gradient (RDG) analysis showed that the main interactions between NMP/SUL and 3-methylthiophene were van der Waals and weak hydrogen bond forces. In addition, the LLE data were correlated by the NRTL and UNIQUAC thermodynamic models with the RMSD values were all <0.30%. Also, the binary interaction parameters were regressed which could be applied for the optimization and design of the separation process.

A comparative study on liquid phase equilibria of aqueous mixtures of two structurally close carboxylic acids with sec-amyl alcohols at 298.2 K

This research reports the results of measurements on liquid-liquid equilibrium (LLE) for the four ternary systems of (water + butyric or 3-methylbutyric acids + sec-amyl alcohol) and (water + butyric or 3-methylbutyric acids + sec-isoamyl alcohol) at 298.2 K and 0.1 MPa. According to the measured solubility and tie-line data, the related phase diagrams for the studied systems were plotted. Due to the strong structural similarity of the studied system's constituents, the influence of the chemical structures of the acids and the solvents on the LLE behavior was comparatively studied. The ternary systems display two forms of LLE phase diagrams. The aqueous systems of butyric acid and the two structural isomers (sec-amyl alcohol and sec-isoamyl alcohol) exhibit type-1 phase behavior of LLE, whereas the type-2 behavior was observed for the systems containing the branched chain carboxylic acid (3-methylbutyric acid). The activity coefficients models of UNIQUAC and NRTL fit the measured tie line-data. According to the measured LLE data, the values of the models' binary interaction parameters were optimized using MATLAB Fminsearch function. Based on the experimental data, the mass distribution coefficients and selectivity were evaluated and systematically compared for the studied systems. Finally, reliability of the obtained NRTL parameters was checked using topological analysis connected to the Gibbs tangent plane test.

Comparative Analysis of Liquid–Liquid Equilibria for Aqueous Systems of Propionic Acid with Structurally Similar Aryl Solvents

Liquid-liquid phase equilibria were comparatively studied for the aqueous mixtures of propionic acid with four structurally similar aryl compounds (2-phenylethanol, 1-phenylpropanol, propiophenone,...

Separation of thiophene from octane/hexadecane with ionic liquids in ternary liquid-liquid phase equilibrium

abstract This work is a continuation of the investigations on desulfurization processes by assessing the applicability of two ionic liquids (ILs), 1-butyl-1-methylpiperidynium dicyanamide, [BMPIP][DCA] and tri-iso-butylmethylphosphonium tosylate, [Pi4,i4,i4,1][TOS], for the separation of thiophene from octane, or hexadecane. The latter two components are used as model substances of the fuel stream. Experimental liquid-liquid phase equilibrium (LLE) data were obtained for four ternary systems {IL + thiophene + octane, or hexadecane} at temperature T = 308.15 K and pressure p = 101 kPa. The DCA-based IL showed better selectivity than the tosylate-based IL in the extraction of thiophene from both alkanes with much lower solute distribution ratio. The selectivity is acceptable in all systems in comparison with currently published data for different ILs. Chromatography analysis showed that the IL was not present in the octane, or hexadecane layer, which simplifies the process of separating the solvent from the hydrocarbon layer. The non-random two liquid (NRTL) model showed satisfactory correlation of the measured phase data.

Ternary Liquid–Liquid Equilibrium Data for the N-Formylmorpholine + Toluene + {n-Nonane or n-Decane} Systems at (303.2, 323.2, and 343.2) K and 101.3 kPa

The design and operation of the process to extract aromatics from petroleum intermediates via solvent extraction can be enhanced in terms of efficiency by access to liquid–liquid equilibrium (LLE) data. This study serves to contribute LLE data for a heavy alkane, aromatic, and solvent mixture, which is of limited availability in the open literature. Ternary LLE phase compositions were experimentally measured and thermodynamically modeled for the systems N-formylmorpholine (NFM) + toluene + (n-nonane or n-decane) at 303.2, 323.2, and 343.2 K and 101.3 kPa. The direct analytical method was used to obtain the LLE data using a double-walled glass cell. The phase equilibrium samples were quantitatively analyzed using gas chromatography. The ternary systems were successfully correlated using the non-random two-liquid and universal quasichemical thermodynamic models. The effectiveness of using NFM as an alternative solvent to extract toluene from a mixture containing n-nonane or n-decane was evaluated by determi...

Liquid-liquid phase equilibrium and interaction exploration for separation of azeotrope (2,2,3,3-tetrafluoro-1-propanol + water) with two imidazolium-based ionic liquids

For separating azeotropic mixture 2,2,3,3-tetrafluoro-1-propanol (TFP) and water, two kinds of imidazolium-based ionic liquids 1-hexyl-3-methylimidazolium trifluoromethanesulfonate ([HMIM][OTf]) and 1-octyl-3-methylimidazolium trifluoromethanesulfonate ([OMIM][OTf]) were adopted to separate TFP and water. The liquid-liquid equilibrium behavior for the mixtures (water + TFP + [HMIM][OTf]) and (water + TFP + [OMIM][OTf]) were measured at temperature of 298.15 K and pressure of 101.3 kPa. The extraction ability of [HMIM][OTf] and [OMIM][OTf] was explored with partition ratio and selectivity. In the meantime, the hydrogen bond lengths, total electron density, interaction energies and deformation electron density were calculated to analyze the interactions between the [HMIM][OTf]/[OMIM][OTf] and (TFP/water). Also, the liquid-liquid equilibrium data was fitted by the NRTL model.

Revisiting the Liquid-Liquid Phase Behavior of n-Alkanes and Ethanol.

Mixtures of alkanes and ethanol are important in many areas, for example, as fuel blends. This paper describes new experimental data obtained for the liquid-liquid equilibrium phase behavior of normal alkanes (n-alkanes; CnH2n+2; 9 ≤ n ≤ 24) with ethanol. The results were obtained by applying the cloud point method in a temperature range of T = 230-423 K at ambient pressure. All systems are partially miscible with an upper critical solution point. The two phase regions of the phase diagrams show no indication of any obvious optical irregularities, like birefringence, coloring, formation of schlieren, or remarkable turbidity, except critical opalescence. With increasing length of the molecular chain of the n-alkanes, the (liquid-liquid) critical point is shifted to higher temperatures and higher ethanol content. The data are analyzed numerically implying Ising criticality. The nonsymmetric shape of the phase body is considered in different approaches for describing the diameter by presuming (a) the validity of the rectilinear diameter rule, (b) a nonlinear diameter predicted in the theory of complete scaling, and (c) combining both concepts. The numerical analysis yields the critical temperature, the critical composition, the width, and the diameter of the phase diagrams. The results are compared with literature data sets from similar mixtures; these data are also evaluated in terms of the models applied here. Phase diagrams of 13 different sets of mixtures are measured and analyzed to extract general aspects of the behavior of the normal alkane-ethanol mixtures. A simple Flory-Huggins-like approach allows a semiquantitative description of the experimental results of the critical temperatures. Therefore, it confirms the picture of molecular ordering within the solutions.

UNIFAC Model for Liquid-Liquid Phase Equilibrium of Penicillin G and 6-APA System

This study investigated the effect of pH and type of solvent on liquid-liquid phase equilibrium in the system of pure penicillin G and mixed penicillin G with 6-APA. Penicillin G extraction was carried out in a pH range of 2.0–5.0 at 4 oC using several types of solvents. The liquid-liquid phase equilibrium mathematical model is prepared assuming that a single stage of thermodynamic equilibrium occurs in a batch process of liquid-liquid extraction. The coefficient of activity was calculated by the UNIFAC method. From the experiment, it was found that the extraction process of penicillin G was strongly influenced by pH of the solution. The highest yield of extraction was achieved with different solvents in the two types of solution. For pure penicillin G system, the highest yields was obtained in n-butyl acetate solvent (95.51%) while for penicillin G mixture with 6-APA, it was obtained in methyl iso-butyl ketone solvent (92.6%). The UNIFAC model have been tested against five three-component liquid-liquid phase equilibrium systems at pH 2.0 and 2.5. It was able to estimate the concentration of penicillin G in the organic phase with a relatively average error between experiment and calculation of 8.32%

Phase Diagrams of n-Type Low Bandgap Naphthalenediimide-Bithiophene Copolymer Solutions and Blends.

Phase diagrams of n-type low bandgap poly{(N,N′-bis(2-octyldodecyl)naphthalene -1,4,5,8-bis(dicarboximide)-2,6-diyl)-alt-5,5′,-(2,2′-bithiophene)} (P(NDI2OD-T2)) solutions and blends were constructed. To this end, we employed the Flory–Huggins (FH) lattice theory for qualitatively understanding the phase behavior of P(NDI2OD-T2) solutions as a function of solvent, chlorobenzene, chloroform, and p-xylene. Herein, the polymer–solvent interaction parameter (χ) was obtained from a water contact angle measurement, leading to the solubility parameter. The phase behavior of these P(NDI2OD-T2) solutions showed both liquid–liquid (L–L) and liquid–solid (L–S) phase transitions. However, depending on the solvent, the relative position of the liquid–liquid phase equilibria (LLE) and solid–liquid phase equilibria (SLE) (i.e., two-phase co-existence curves) could be changed drastically, i.e., LLE > SLE, LLE ≈ SLE, and SLE > LLE. Finally, we studied the phase behavior of the polymer–polymer mixture composed of P(NDI2OD-T2) and regioregular poly(3-hexylthiophene-2,5-dyil) (r-reg P3HT), in which the melting transition curve was compared with the theory of melting point depression combined with the FH model. The FH theory describes excellently the melting temperature of the r-reg P3HT/P(NDI2OD-T2) mixture when the entropic contribution to the polymer–polymer interaction parameter (χ = 116.8 K/T − 0.185, dimensionless) was properly accounted for, indicating an increase of entropy by forming a new contact between two different polymer segments. Understanding the phase behavior of the polymer solutions and blends affecting morphologies plays an integral role towards developing polymer optoelectronic devices.

Physico-chemical properties of ionic liquids: Density, viscosity, density at high pressure, surface tension, octan-1-ol/water partition coefficients and thermodynamic models

Ionic liquids (ILs) are an important new media and one of the most attractive solvents used in extraction and separation processes. This work presents some important physico-chemical properties and topics related to ILs, which were found by us as good extractive solvents for the desulfurization of fuels and for the separation of water/biobutan-1-ol. It consists of the most important series of experimental measurements of density and viscosity of pure ILs and in binary systems with thiophene and butan-1-ol: (N-hydroxyethylpyridinium tricyanomethanide, [C2OHPy][TCM] + thiophene), or (N-hydroxypropylpyridinium tricyanomethanide, [C3OHPy][TCM] + thiophene) or (N-benzyl-N-dodecyl-N,N-dimethylammonium bis(trifluoromethyl-sulfonyl)imide, [N1,1,12,Bz][NTf2] + butan-1-ol). These systems exhibit mainly negative molar excess volumes, VE in systems with thiophene and slightly positive and negative in the system with butan-1-ol. The Redlich – Kister equation was used for correlation of the liquid density, excess molar volumes and dynamic viscosity deviations as a function of temperature and composition, whereas Vogel-Fulcher-Tammann, VFT was used for describing the temperature dependence of dynamic viscosities. Very often, the high pressure is proposed for new technologies of separation and that is why we present the influence of pressure on the density of [C2OHPy][TCM], [C3OHPy][TCM] and [N1,1,12,Bz][NTf2] in a wide range of temperature from T = (298.15–348.15) K and pressure from p = (0.1–40) MPa. The Tait equation was used for the correlation of density as a function of mole fraction, temperature, and pressure. The influence of pressure for ILs, is as usual, not significant. The thermal expansion coefficient α and isothermal compressibility coefficient κ as a function of temperature T, and pressure p are presented. Herein, surface tension of new ILs was measured for the collection of physico-chemical properties of the ILs used in this work. Also, the octan-1-ol/water, Kow partition coefficients in ternary liquid-liquid phase equilibrium were determined for the systems {[C2OHPy][TCM], or [C3OHPy][TCM] (1) + octan-1-ol (2) + water (3)} at temperature T = 298.15 K and the discussion of the biocompatibility of the used ILs is presented.

Modelling phase behavior of triglycerides, diglycerides and monoglycerides related to biodiesel transesterification in mixtures of alcohols and CO2 using a polar version of PC-SAFT

Soh et al. [1] showed that one can achieve high conversion (98%) of triglycerides to fatty acid methyl esters at 95 °C when carbon dioxide (CO2) is used as a co-solvent to enhance mixing of the immiscible alcohol and triglyceride. Soh's results demonstrated the benefits of using CO2 as a co-solvent yet did not provide information on the evolution of the phase behavior during the reaction. The PC-SAFT equation of state has been employed to understand and predict the phase behavior of the various biodiesel components versus temperature and pressure in the presence of CO2. In previous work [2] the interaction between alkyl-esters and low molecular weight alcohols, glycerol, and CO2 were investigated. Polar PC-SAFT and the Group Contribution PPC-SAFT EoS were used to model phase equilibria amongst the various multicomponent systems. The same approach is extended here, specifically applied to mixtures containing tri-, di- and monoglycerides plus low molecular weight alcohols and CO2.Data for different types of glycerides are scarce and in general the phase boundary curves in CO2-based mixtures are only weakly dependent on CO2 concentration, creating curves with very high slopes in P-T space that accumulate larger prediction errors compared to the previously investigated alkyl-ester systems. Nonetheless, it was found that one could generate a general correlation for binary interaction coefficient that depends only on carbon chain length and degree of unsaturation for description of triglyceride-CO2 mixtures. Binary interaction parameters as low as 12% were obtained for all glyceride-methanol systems and binary interaction coefficient below 3.5% are sufficient to correctly capture CO2 – glyceride vapor-liquid and liquid-liquid phase equilibria.

New phase equilibrium data at ambient and high pressure for strongly asymmetric mixtures containing menthol

New data on phase equilibria in binary and ternary mixtures containing (−)-menthol, n-decane, 1-decanol and water are presented and discussed. In particular, experimental liquid-liquid equilibrium phase diagrams in ternary systems {(−)-menthol + (n-decane, or 1-decanol) + water} are reported along with the predictions by means of leading thermodynamic models, namely, perturbed-chain statistical associating fluid theory (PC-SAFT) and conductor-like screening model for real solvents (COSMO-RS). Freezing pressure data for binary systems {(−)-menthol + (n-decane, or 1-decanol)} are reported and the corresponding high-pressure solid-liquid equilibrium phase diagrams are discussed and analyzed by using the Yang equation. The measured data are referred to ambient-pressure phase diagrams published previously.

Prediction of phase equilibrium and interfacial properties in the quaternary system water + 1-hexanol + hexylacetate + acetic acid

The knowledge of the liquid-liquid phase equilibrium and the corresponding interfacial properties of quaternary liquid mixtures can be used for the optimization of extraction processes relevant for industrial application. The purpose of this work is the theoretical prediction of the above mentioned interfacial properties for the quaternary mixtures water + 1-hexanol + hexylacetate + acetic acid using the incompressible version of the density gradient theory in combination with the NRTL activity coefficient model. The prediction is based on phase equilibria data including vapor-liquid and liquid-liquid equilibria of the corresponding binary and ternary subsystems and binary experimental interfacial tension data of the two binary subsystems water + 1-hexanol and water + hexylacetate forming a miscibility gap. The predicted interfacial tensions of the quaternary were verified by new measurements utilizing the spinning drop method and an excellent agreement was achieved. Additionally, for the first time, the simultaneous enrichment of two different components inside the liquid-liquid interfacial layer could be observed.

Refining of Diesel and Ship Fuels by Extraction and Combined Methods. Part 1. Use of Ionic Liquids as Extractants

Modern and perspective environmental requirements to the quality of diesel and ship fuels are considered. Data on the selectivity and solvency of ionic liquids with respect to aromatic hydrocarbons and heterocyclic sulfur- and nitrogen-containing compounds, obtained using gas-chromatographic data on the limiting activity coefficients of model mixture components in ionic liquids, are discussed. Experimental data on the liquid-liquid phase equilibrium in model systems consisting of a saturated hydrocarbon, an aromatic sulfur- or nitrogen-containing compound, and an ionic liquid and on the component distribution ratios and separation factors are presented. The advantages and drawbacks of ionic liquids as extractants in selective refining of diesel fractions and vacuum gasoils to obtain raffinates meeting perspective environmental requirements to diesel and ship fuels are considered.

Ternary liquid-liquid phase equilibria of {ionic liquid + thiophene + (octane/hexadecane)}

In this work we studied the applicability of two ionic liquids (ILs) for the separation of thiophene from octane, or hexadecane, as a model of the diesel stream. Experimental liquid-liquid phase equilibrium (LLE) data were obtained for four ternary systems {IL + thiophene + octane, or hexadecane} at T = 308.15 K and pressure p = 101 kPa. The ILs 1,3-dihydroxyimidazolium bis{(trifluoromethyl)sulfonyl}imide, [OHOHIM][NTf2] and 1-butyl-3-methylimidazolium trifluoromethanesulfonate, ([BMIM][CF3SO3]), [BMIM][OTf] were used to assess the desulfurization process. [BMIM][OTf] showed better selectivity than [OHOHIM][NTf2] in the extraction of thiophene from both, octane and hexadecane. The distribution ratio in all systems is acceptable in comparison with currently published data for different ILs. Chromatography analysis showed that the IL was not present in the octane, or hexadecane layer. This simplifies the process separating the solvent from the hydrocarbon layer. The data obtained have been correlated with the non-random two liquid (NRTL) model.

Separation of water/butan-1-ol with ionic liquids in ternary liquid-liquid phase equilibrium

In this work ionic liquids (ILs) as a novel popular solvents are proposed for removing butan-1-ol from the aqueous fermentation media. Ternary liquid-liquid phase equilibrium data are presented for mixtures of {ionic liquid (1) + butan-1-ol (2) + water (3)} at T = 328.15 K and ambient pressure. The ILs with long alkane chains such as hexadecyltrimethylammonium bis{(trifluomethyl)sulfonyl}imide, [N16,1,1,1][NTf2], 1,3-didecyl-2-methylimidazolium dicyanamide, [D2MIM][DCA] and tetrabutylphosphonium bis{(trifluomethyl)sulfonyl}imide, [P4,4,4,4][NTf2] have been tested. The results are discussed in terms of the selectivity and solute distribution ratio of separation of related systems. The complete miscibility in the binary liquid systems of butan-1-ol with three used ILs was observed. The ammonium-based IL in comparison with phosphonium-based IL shows lower selectivity and solute distribution ratio. The non-random two liquid NRTL model was used successfully to correlate the experimental tie-lines and to calculate the phase composition error in mole fraction in the ternary systems.

Ethanol and methanol Unifac subgroup parameter estimation in the prediction of the liquid-liquid equilibrium of biodiesel systems

The biodiesel conventional production method is based on the homogeneous transesterification reaction, in which the quality and quantity of the raw materials used have considerable effect on the separation of phases of the generated products. The presence of glycerol in biodiesel, for example, has a maximum permissible value of only 0.02% (EM 14214). On the other hand, high purity glycerol needs to be marketed separately. In this way, a better understanding of the phase equilibrium becomes fundamental for the proper design, operation and optimization of the process. In the literature, the thermodynamic modeling focuses on the UNIQUAC and NRTL models. Such models can predict phase equilibrium for each system separately, and the interaction parameters are distinct and unique. However, the use of several types of vegetable or residual oils has been reported for biodiesel production. On the other hand, group-contribution thermodynamic models, such as UNIFAC, could be used to predict the phase equilibrium behavior of reactional biodiesel systems formed from these different types of oils. This work contributes to this subject, providing generalized UNIFAC interaction parameters for the already specified subgroup methanol (CH3OH) and a new specific subgroup, ethanol (CH3CH2OH). The UNIFAC-LL database parameters were used, except for methanol and ethanol subgroups proposed here, for calculations with ten vegetable oils, for which experimental data are available. The mean square error (0.92%, methanol; 1.20%, ethanol) was considerably lower when compared to the available UNIFAC-LL data (10.58%, methanol; 8.89%, ethanol) and work of the literature (2.21%, methanol; 3.92%, ethanol) that uses a greater number of adjustable parameters. The results show that the methodology employed is consistent and can be useful in predicting liquid-liquid phase equilibrium for both reactive methyl and ethyl biodiesel systems considered.

Ammonium ionic liquids in separation of water/butan-1-ol using liquid-liquid equilibrium diagrams in ternary systems

In this work ionic liquids (ILs) as a novel popular solvents are proposed for removing butan-1-ol from the aqueous phase. Ternary liquid-liquid phase equilibrium data are presented for mixtures of {ionic liquid, IL (1) + butan-1-ol (2) + water (3)} at T = 328.15 K and pressure 101.3 kPa. The new synthesized by us ammonium-based ILs with long alkane chains, such as dimethyldodecylphenoxyethylammonium bis{(trifluoromethyl)sulfonyl}imide, [N1,1,12,2OPh][NTf2], dimethyldodecylphenoxyethylammonium dicyanamide, [N1,1,12,2OPh][DCA], benzyldimethyldodecylammonium bis{(trifluoromethyl)sulfonyl}imide, [N1,1,12,Bz][NTf2] and benzyldimethyldodecylammonium dicyanamide, [N1,1,12,Bz][DCA] have been tested. The selectivity and the solute distribution ratio of separation water/butan-1-ol were calculated and compared to the literature data. The complete solubility of butan-1-ol in the proposed ILs was observed at T = 328.15 K and pressure 101.3 kPa. The [N1,1,12,Bz][NTf2] is picked out as the most potential candidate as an extractant of butan-1-ol from water. The [N1,1,12,Bz][NTf2] shows only slightly lower selectivity than that observed in few phosphonium-based IL. The experimental tie-lines were successfully correlated with non-random two liquid NRTL model.

Liquid-liquid equilibrium of alcohol–ester systems with deep eutectic solvent on the base of choline chloride

The liquid-liquid equilibrium (LLE) for the mixtures of ethanol – ethyl propionate, n-propanol – n-propyl propionate and n-butanol – n-butyl propionate with deep eutectic solvents (DES) was studied. DES was used on the basis of choline chloride with malonic acid in a mole ratioof 1:1. The studies were carried out at two temperatures, 293.15 K and 313.15 K and atmospheric pressure. The compositions of the coexisting organic and DES phases were determined. On the basis of experimental data, alcohol distribution coefficient and selectivity were calculated and analysed. The effect of the temperature and length of the alcohol alkyl chain on the alcohol distribution coefficient and selectivity were established. Using the non-random two liquids model (NRTL), a thermodynamic simulation of obtained experimental data on the liquid-liquid phase equilibrium was carried out.

Separation of m-cresol from aromatic hydrocarbon and alkane using ionic liquids via hydrogen bond interaction

Abstract Low temperature coal tar contained a large amount of phenols, aromatic hydrocarbons and alkanes; the separation of phenols from coal tar has a great significance to the deep processing of coal tar. In this work, the separation of m-cresol from cumene and n-heptane by liquid–liquid extraction using ionic liquids (ILs) as extractants was studied. The suitable ILs were screened by conductor-like screening model for real solvents (COSMO-RS) model and the liquid–liquid phase equilibrium (LLE) experiments were to verify the accuracy of the screening results. The extraction conditions such as extraction time, extraction temperature and mass ratio of ILs to model oils were evaluated. An internal mechanism of the m-cresol extract by ILs was revealed by COSMO-RS calculation and FT-IR. The results showed that the selected ILs can extract m-cresol effectively from cumene and n-heptane, 1-ethyl-3-methylimidazolium acetate (emimCH3COO) was the best extraction solvent. A hydrogen bond between anion of ILs and phenolic hydroxyl groups was observed. M-cresol in model oils could be extracted with extraction efficiencies up to 98.85% at an emimCH3COO: model oils mass ratio of 0.5 and 298.15 K, emimCH3COO could be regenerated and reused for 4 cycles without obvious decreases in extraction efficiency and extractant mass.