Experimental Liquid Equilibrium Research Articles

COSMO-RS prediction, experimental investigation, and mechanism analysis: A new approach to separating the n-hexane - tert-butanol azeotropic system via liquid-liquid extraction with ionic liquids

n-Hexane and tert-Butanol (TBA) are frequently utilized to refine the conditions for Grignard, Wittig, and Friedel-Crafts alkylation reactions. During the synthesis of loratadine, the formation of azeotropic mixtures n-hexane and TBA, which are challenging to separate through conventional distillation, is inevitable. This study utilizes the COSMO-RS model to identify suitable ionic liquids (ILs) for the separation of the n-hexane - TBA azeotropic system. Based on solvent capacity and selectivity, 1-ethyl-3-methylimidazolium trifluoroacetate ([EMIM][TFA]), 1-butyl-3-methylimidazolium trifluoroacetate ([BMIM][TFA]), and 1-hexyl-3-methylimidazolium trifluoroacetate ([HMIM][TFA]) were selected as extractants. The liquid–liquid equilibrium (LLE) data for the n-hexane - TBA - ILs ternary system were measured at 303.15 K and atmospheric pressure. Distribution coefficients and selectivity were calculated to evaluate the performance of the extractants, with the NRTL model used to correlate the experimental LLE data. The consistency of the NRTL model parameters was corroborated through topological analysis associated with the Gibbs tangent principle. Quantum chemical calculations, including interaction energy, ESP analysis, IGMH analysis, and QTAIM topological analysis, were performed to explore the separation mechanism at the molecular level. The results indicated that the interaction energies between the ILs and TBA were higher than those between the ILs and n-hexane, indicating a stronger attraction of ILs to TBA. Consequently, the ILs effectively separated TBA from the n-hexane - TBA azeotropic system, with extraction capacities ranked as [EMIM][TFA] > [BMIM][TFA] > [HMIM][TFA]. The quantum chemical calculations successfully explained the experimental results, aligning with COSMO-RS model predictions and confirming their reliability. IGMH and QTAIM topological analyses systematically explored the types and strengths of interactions, revealing that hydrogen bonds are predominant between the ILs and TBA, with additional contributions from van der Waals forces. Furthermore, the hydrogen bond strengths between TBA and the anions and cations of the ILs are classified as strong and moderate, respectively. This work provides valuable insights into the separation of azeotropic systems using ILs, elucidating the underlying mechanisms behind this process.

Multiphase Behavior of the Water + 1-Butanol + Deep Eutectic Solvent Systems at 101.3 kPa

The growing demand for more sustainable routes and processes in the mixture separation and purification industry has generated a need to search for innovations, with new solvent alternatives being a possible solution. In this context, a new class of green solvents, known as deep eutectic solvents (DESs), has been gaining prominence in recent years in both academic and industrial spheres. These solvents, when compared to ionic liquids (ILs), are more environmentally friendly, less toxic, low-cost, and easier to synthesize. In addition, they have significantly lower melting points than their precursors, offering a promising option for various applications in this industrial sector. Understanding and studying the thermodynamic behavior of systems composed of these substances in purification and separation processes, such as liquid–liquid extraction and azeotropic distillation, is extremely important. This work aimed to study the phase behavior of liquid–liquid equilibrium (LLE) and vapor–liquid equilibrium (VLE) of water + 1-butanol + DES (choline chloride + glycerol) systems with a molar ratio of 1:2. Experimental LLE data, obtained at 298.15 K and 101.3 kPa, and VLE data, obtained at 101.3 kPa and in the temperature range of 364.05 K–373.85 K, were submitted to the thermodynamic quality/consistency test, proposed by Marcilla et al. and Wisniak, and subsequently modeled using the gamma–gamma approach for the LLE and gamma–phi for the VLE. The non-random two-liquid (NRTL) model was used to calculate the activity coefficient. The results are presented for the VLE in a temperature–composition phase diagram (triangular prism) and triangular phase diagrams showing the binodal curve and tie lines (LLE). The separation and distribution coefficients of LLE were determined to evaluate the extractive potential of the DES. For the VLE, the values of the relative volatility of the system were calculated, considering the entrainer free-basis, to evaluate the presence or absence of azeotropes in the range of collected points. From these data, it was possible to compare DES with ILs as extracting agents, using data from previous studies carried out by the research group. Therefore, the results indicate that the NRTL model is efficient at correlating the fluid behavior of both equilibria. Thus, this study serves as a basis for future studies related to the understanding and design of separation processes.

Extractive distillation using salt-based deep eutectic solvent as entrainer for separating acetonitrile-water mixture

Salt-based deep eutectic solvents (DESs) have been proposed in this work for the separation of the azeotrope of acetonitrile and water (H2O). The vapor–liquid equilibrium experiments indicated that (ChCl:U:CaCl2)1:2:0.36 exhibits an higher selectivity among all of the entrainers investigated and eliminates the azeotropic point of acetonitrile and water mixture. Moreover, the calculated values by NRTL model coincide well with the experimental data for the systems (acetonitrile + H2O + (ChCl:U:CaCl2)1:2:0.36). Based on the thermodynamic study, the conceptual process design was established to evaluate the competitiveness of the suggested entrainers for the separation of acetonitrile and water. It was determined that the thermodynamic efficiency (η) in the extractive distillation (ED) process utilizing the new salt-based DESs entrainers increases 60.31 % compared with the benchmark entrainer ethylene glycol (EG). Conversely, the ED process using (ChCl:U:CaCl2)1:2:0.36) entrainer can reduce the total annual cost (TAC) by about 7.81 % and the CO2 emissions (ECO2) by 14.74 %. The ED process using (ChCl:U:CaCl2)1:2:0.36) as entrainer shows the high energy efficiency, low economy cost and low CO2 emissions with a great industrial application prospect when compared to the bench marked process.

Solute structure effect on polycyclic aromatics separation from fuel oil: Molecular mechanism and experimental insights

AbstractIonic liquids (ILs) are promising solvents for separating aromatics from fuel oils. However, studies for separate polycyclic aromatics with ILs are rare and insufficient, and the impact of solute structure on extraction performance still needs to be determined. In this work, we use 1‐ethyl‐3‐methylimidazolium bis([trifluoromethyl]sulfonyl)imide ([EMIM][NTF2]) as an extractant to separate 1‐methylnaphthalene, quinoline, and benzothiophene from dodecane mixtures. Liquid–liquid equilibrium experiments identified the optimal operating conditions. Nine solute molecules, including five alkanes and four aromatic hydrocarbons, were used to study the relationship between extraction performance and solute structure. Molecular dynamics simulation and quantum chemistry calculations gave a deep insight and reasonable interpretation of the structure‐performance relationship at the molecular level. An industrial‐scale extraction process was proposed. The IL can be easily regenerated using heptane as a back‐extractive solvent. A high‐purity fuel oil with aromatic content below 0.5 wt% is obtained after 8‐stage extraction.

Efficient separation of alcohol ester via extractive distillation and pressure swing distillation based on molecular interaction mechanism analysis

N-amyl alcohol, n-amyl formate, n-propanol and n-propyl formate are all organic solvents with important industrial application value. In industrial production, related alcohol ester azeotropic systems are often generated. Therefore, it is necessary to study the refining process of these substances. The work designed purification processes for two different azeotropic systems of alcohol esters via extractive distillation and pressure swing distillation methods. The required binary interaction parameters were obtained through vapor–liquid equilibrium experiments. Based on experimental data, a suitable entrainer was determined through different methods of analysis. The processes were optimized with the economic cost as the objective. In addition, it evaluated and analyzed different processes from multiple perspectives. This work explores the purification process of alcohol ester systems, providing theoretical guidance for achieving efficient separation of alcohol ester systems.

Amide solvents for extraction and separation of 1-hexene from n-heptane: Effect of the amount of methyl groups

In this work, the influence mechanism of methyl group in the structure of amide solvent on the extraction and separation of alkene (1-hexene or 1-octene) from n-heptane has been studied by a combination of liquid–liquid equilibrium (LLE) experiments and quantum chemical calculations. For LLE experiments, as the number of methyl groups in the extractant structure increases, its selectivity for alkene (1-hexene or 1-octene) gradually decreases, and the distribution coefficients of alkene (1-hexene or 1-octene) and n-heptane gradually increase. In the interaction between 1-hexene and extractant, the amount and intensity of C-H⋯O interactions, as well as the presence or absence of N/C-H⋯π interactions and their intensities, are all affected by the amount (0,1,2,3) of methyl group introduced into the amide solvent. The existence of the C-H⋯O and N-H⋯π interactions were verified by the infrared spectroscopy. With increasing methyl group amounts in the extractant structure, the dispersion interaction strengthens, while the contribution percentage of electrostatic interaction and ΔEelst/ΔE declines, leading to the increase of distribution coefficient and decrease of selectivity for alkene (1-hexene or 1-octene) respectively.

Kinetic modeling of dual-stage oxidative extractive denitrogenation of model fuel

The petroleum fraction of crude oil is laden with notorious nitrogen compounds, whose removal facilitates fuel oil transport and enhances the longevity of hydrodesulfurization catalysts. Petroleum refining operation thus demands the adoption of unconventional techniques, such as coupled oxidative–extractive denitrogenation. Kinetic models can provide insights into the reaction mechanism and the design and performance of reactors. In this work, nine different kinetic models were developed by applying the Langmuir–Hinshelwood and Eley–Rideal approaches to various reaction pathways. The screening of the kinetic models was done based on the values of the rate law parameters and corresponding R 2 and adjusted R 2 values calculated through a multi-parametric, non-linear regression based on the Levenberg–Marquardt algorithm. Out of all the models, the Eley–Rideal model corresponding to the rate expression rs9 was found to be the best fit, reflecting that hydrogen peroxide remained in bulk while pyridine alone was adsorbed on the catalyst. The selection of suitable extractants for the extractive removal of oxidation products was made based on their extraction efficiency and partition coefficients. The ternary liquid–liquid equilibrium (LLE) data for the (acidulated water-pyridine-isooctane) and (acidulated water-pyridine N-oxide-isooctane) systems were plotted, and Othmer–Tobias, Hand, and Bachman correlations explained the consistency of the experimental LLE data.

Study of quaternary liquid-liquid equilibria for systems (water/ methanol/ cyclohexanol+ toluene): Experimental and modelling

The experimental liquid-liquid equilibrium (LLE) data for the extraction of methanol from aqueous solution using mixed solvents (toluene + cyclohexanol) at 291.15 K and atmospheric pressure at the ratios (0, 0.25, 0.4, 0.6, 0.8, 1) was studied. The values of the solvent ratio 0 and 1 led us to study the liquid-liquid equilibrium of the ternary systems (water/methanol/cyclohexanol) and (water/methanol/toluene). The compositions of the coexisting phases were determined by the cloud point method. The tie line data for ternary and quaternary systems were correlated by NRTL model. The Othmer-Tobias and Hand correlations were also tested, to verify the reliability of the experimental tie lines data. The separation factor and the distribution coefficient were calculated from the experimental data to evaluate the effect of using mixed solvents. It was found that the ratio M = 0.4 is the best suited for the liquid-liquid extraction of methanol from water.

Amino acids to reduce the escape of organic amines in the CO2 capture process

Carbon neutrality and carbon peaking are important strategic policies for our country. Carbon dioxide capture technology is the bottom of the realization of this strategy, in which amine escape is an important issue for the development of this technology. Herein, the proposal to utilize amino acids for reducing volatilization of organic amines was introduced for the first time. Diethylaminoethanol (DEEA), widely applied and highly volatile, was selected as the primary target for volatility reduction, while hydroxyethyl ethylenediamine (AEEA) and piperazine (PZ) were chosen as the main absorbents for absorption and desorption processes. The effects of DEEA addition on the main absorbent, different types of amino acid additives on volatility, and amino acids on absorption and desorption performance were investigated, respectively. Glutamine (Tyr) demonstrated significant potential in reducing the volatilization of organic amines; when 2% Tyr was added during gas–liquid equilibrium experiments, it resulted in a 74.5% decrease in DEEA volatilization within the absorbent system. Simulated gas–liquid entrainment escape showed that CO2 loading reduced volatilization by 42.31%, with a further reduction of 53.93% achieved when loaded with 0.5 molCO2/mol amine; this loading also had a promotional effect on absorption and desorption processes. Moreover, Tyr exhibited excellent stability without generating any degradation products, thereby prolonging absorber lifespan and minimizing economic cost losses.

Systematic screening ionic liquid as extractant for benzene-cyclohexane separation

In the separation of aromatic-alkane systems, ionic liquids (ILs) demonstrate superior performance over organic solvents. In this work, a rational screening strategy is proposed for tailoring ILs for the benzene-cyclohexane extraction. The reliability of COSMO-RS and UNIFAC-IL for this system are first assessed by comparing experimentally reported and model-predicted ternary liquid–liquid equilibria. The key thermodynamic evaluations of ILs are predicted by COSMO-RS and UNIFAC-IL separately while their important physical properties and commercial availability are estimated by a deep learning model and prepared python program. The screened promising IL [EPY][Tf2N] is tested by liquid–liquid equilibrium experiments and the NRTL parameters are regressed. The process simulation with the chosen IL is conducted using Aspen Plus and then compared with that of a benchmark IL, affirming the exceptional efficacy of the identified [EPY][Tf2N] as a prospective solvent for the benzene-cyclohexane separation. This study can be a crucial reference for guiding screening of ILs for various separation applications.

Surrogates for Liquid-Liquid Extraction.

Fuel surrogates are mixtures that mimic the properties of real fuels with only a small number of components, simplifying the calculation and simulation of fuel-related processes. This work extends a previously published surrogate optimization algorithm toward the generation of fuel surrogates with a focus on liquid-liquid extraction characteristics. For this purpose, experimental liquid-liquid equilibrium data from batch extraction experiments are incorporated into the calculation procedure as an additional constraint. The use of the method is demonstrated by optimizing a surrogate for the catalytic reformate. Application of the surrogate to an extraction process and comparison with experimental data demonstrate that the resulting surrogate accurately depicts the properties of the real mixture with regard to liquid-liquid extraction performance. This demonstrates that the use of such surrogates is of particular interest for mixtures used as extracting agents for biofuels.

Enhancing aromatics extraction by double salt ionic liquids: Rational screening‐validation and mechanistic insights

AbstractDespite offering remarkable advantages as solvents, double salt ionic liquids (DSILs) have been scarcely studied for extractive dearomatization from hydrocarbons as well as many other applications, thus urging a theoretical guidance method. In this work, a systematic framework combining the rational screening validation and mechanistic analysis is proposed for tailoring DSILs for the o‐xylene/n‐octane separation. From an initial pool of commercially available ionic liquids (ILs), key thermodynamic properties of paired DSILs are predicted by COSMO‐RS while their important physical properties are estimated from those of corresponding parent ILs (retrieved from experimental database or predicted by a deep learning model). Promising DSILs are tested by liquid–liquid equilibrium experiments, wherein the effect of ion ratio is also evaluated. The mechanism underlying the tunability of DSIL thermodynamic properties is disclosed by quantum chemistry calculation and molecular dynamics simulation. This work can be a valuable reference for guiding the design of DSILs for diverse applications.

Efficient extraction of S-heterocyclic aromatics from fuel oil with oxalic acid-based deep eutectic solvent

The presence of thiophenes in fuel oil not only affects the quality of oil products, but also causes serious environmental problems. The efficient extraction of S-heterocyclic aromatics from fuel oil by π-electron donor-based (i.e., oxalic acid) deep eutectic solvents (DESs) is proposed for the first time. The distribution coefficient and separation factor of n-heptane + 2-methylthiophene/3-methylthiophene/thiophene in 100 DESs were predicted by COSMO-RS model, and the optimal DESs (i.e., Tetraethylammonium chloride-oxalic acid / Tetraethylammonium bromide-oxalic acid) was selected as the potential extractants. The selectivity and extraction capacity of the two DESs were measured and compared by liquid–liquid equilibrium experiments. The thermodynamic consistency of the experimental data was tested by Othmer-Tobias and Hand equations, which show that R2 is>0.95, and the experimental results have high reliability. The interaction mechanism between the extractant and the target systems was analyzed by molecular dynamics simulation and quantum chemical calculation. The results of the mean square displacement and fraction free volume show that thiophene has higher displacement and diffusion in DES2 (i.e., tetraethylammonium bromide and oxalic acid) compared to 2-methylthiophene and 3-methylthiophene molecules. Moreover, the interaction analysis show that electrostatic energy is the main effect between molecules. Finally, the weak interaction between different molecular pairs was identified by the molecular surface electrostatic potential and the independent gradient model. This work provides insight into the design and screening of novel DESs for the extraction and separation of S-heterocyclic aromatics.

Separation of furfuryl alcohol from water using hydrophobic deep eutectic solvents

Furfuryl alcohol (FA) is an important organic chemical feedstock that must be separated from water to upgrade it into high-value-added products. Since FA forms an azeotrope with water, liquid-liquid extraction is a suitable option for separating both compounds. This work evaluates the separation of FA from water using hydrophobic deep eutectic solvents (DES). Three DES were prepared using menthol, thymol, and octanoic acid by combining them in molar ratio as follows: thymol + octanoic acid (1:2), menthol + octanoic acid (1:2), and thymol + menthol (1:1). Experimental liquid-liquid equilibria (LLE) of ternary systems water + FA + DES measured at 313.15 K and 101.13 kPa were used to determine the distribution coefficient and selectivity values for FA when using each DES. The experimental results were compared with molecular dynamics (MD) using Martini 3 force field and modeled using Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) without any adjustable binary parameters. According to the results, selectivities and distribution coefficients using hydrophobic DES have comparable values to traditional volatile organic compounds (VOCs) used to separate FA from water. In general, DES shows better distribution coefficients compared with typical organic solvents. According to the results, a good alternative would be menthol + octanoic acid (1:2) or thymol + menthol (1:1) to replace typical VOCs. MD and PC-SAFT provide accurate estimations for ternary LLE in the range of examined thermodynamic conditions, which confirms the predictive consistency of both approaches. Microscopic properties computed with MD simulations evidence a surface activity or absolute adsorption of FA in the interfacial region, which is correlated with favorable distribution coefficients and selectivities.

Extraction of C6 α-olefin against n-paraffin in coker naphtha with deep eutectic solvents: Quantum chemical calculations and experimental investigation

Extraction technology is often employed to separate olefin/paraffin mixtures due to the advantages of mature process, flexible operation, and large processing capacity. This work aims to investigate the effectiveness of novel deep eutectic solvents (DESs) for the extraction of 1-hexene/n-hexane model coker naphtha using a combination of simulations and experiments. The results showed that the aliphatic or aromatic groups in the hydrogen bond acceptors or hydrogen bond donors have a strong affinity for 1-hexene, and the components containing hydroxyl or aromatic groups possess the ability to provide protons, which is beneficial to dissolve 1-hexene. Combining the results of the melting point predicted by the group and group-interaction contribution model, three DESs, namely ethanolamine-sulfolane 1:5 (DES1), tetrabutylammonium bromide-bis[2-(2-hydroxyethoxy)ethyl] ether 1:4 (DES2), and methyltriphenylphosphonium bromide-Triethylene glycol 1:4 (DES3), were finally prepared. Then, quantum chemical calculations were used to investigate the separation mechanism between the DESs and 1-hexene/n-hexane, demonstrating single-center and multi-center hybrid weak hydrogen bonds dominated by the dispersion attraction between DESs and 1-hexene. Finally, liquid–liquid equilibrium experiments were used to examine the effects of DESs type, composition, and temperature on the separation performance, and the results showed that the DES1 has both high distribution coefficient of 1-hexene and selectivity of 1-hexene/n-hexane, as well as good recycle stability. This work demonstrates that new DESs can be used as alternative solvents to traditional organic solvents and ionic liquids, and provides ideas for the separation of olefins and paraffins in coker naphtha.

Investigation of Ionic Liquids as Extraction Solvents for Separating Bicyclic Aromatic S/N-Compounds from FCC Diesel

To improve the quality of fluid catalytic cracking (FCC) diesel, ionic liquids (ILs) were used as promising neoteric solvents to extract bicyclic S/N-compounds (quinoline and 1-benzothiophene) from FCC model oil. In addition to the thermodynamic properties, including solvent capacity and selectivity, physical properties such as viscosity and thermal stability are also considered as important factors in the IL screening process. 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2MIM][NTF2]) was selected as the most suitable extraction solvent by the COSMO-RS model, and the accuracy of this model was verified based on the collected experimental data. Liquid–liquid equilibrium experiments were performed to study the effects of the initial quinoline and 1-benzothiophene concentrations, mass solvent ratio, extraction stages, and the presence of other aromatics on the extraction efficiency. Then, the extraction mechanism and the differences in the extraction effects for the quinoline and 1-benzothiophene systems were explored by quantum chemical calculation and molecular dynamics simulation. The consistency between experiments and theoretical calculation indicates that the electrostatic interaction is the main reason for the difference in the extraction efficiency between the quinoline and 1-benzothiophene systems.

Liquid–Liquid Equilibrium Measurement for the Separation of n-Propanol + n-Propyl Acetate Using Imidazolium-Based Ionic Liquids with Different Anions at T = 303.15 K

Separating the mixture of the target product n-propyl acetate (NPAC) and the unreacted reactant n-propanol (NPA) is necessary during the production of NPAC. NPA and NPAC cannot be separated by simple distillation because the two could form an azeotrope under atmospheric pressure. Liquid–liquid extraction is an energy-saving and environment-friendly method for separating azeotropic mixtures. Ionic liquids (ILs) are promising alternatives to conventional extractants for separating azeotropes due to the advantages of designability and negligible vapor pressure. In this study, the liquid–liquid equilibrium (LLE) data for the ternary systems of NPAC + NPA + 1-butyl-3-methylimidazolium dihydrogen phosphate ([BMIM][H2PO4]) or 1-butyl-3-methylimidazolium thiocyanate ([BMIM][SCN]) or 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) were determined at 303.15 K and 101.3 kPa. The accuracy of the experimental LLE data was checked by the Bachman, Hand, and Othmer–Tobias equations. The selectivity and partition coefficient were calculated to evaluate the extraction capability of the selected extractants. The experimental LLE data were correlated with the nonrandom two-liquid model, and the binary interaction parameters were regressed. Finally, the separation mechanism of the three ILs was explored through σ-profile analysis.

Liquid-liquid equilibria of the ternary systems water + C1 – C3 alcohols + dimethyl adipate at 298.15 K and atmospheric pressure: Experimental data and modeling

The aim of this study was to examine the possibility of using a green organic solvent, dimethyl adipate (DMA), as a separation agent in the extraction of different alcohols from aqueous solutions. For that purpose, the liquid–liquid equilibria (LLE) of four ternary systems were analytically determined at 298.15 K and atmospheric pressure using stirred and thermo-regulated cells: {water + methanol + dimethyl adipate (DMA)}, {water + ethanol + DMA}, {water + 1-propanol + DMA}, {water + 2-propanol + DMA}. Phase diagrams for these four ternary systems were obtained by determining a binodal curve and tie-lines data using a visual cloud-point method, but also gas chromatography. Distribution coefficients and separation factors were calculated for the immiscibility region. Hand and Othmer-Tobias correlations were used to examine the reliability of the tie-line data. In addition, the experimental ternary LLE data were correlated with the UNIversal QUAsiChemical (UNIQUAC) activity coefficient models. The obtained results showed that DMA is a suitable candidate for the extraction of methanol, ethanol, 1-propanol, and 2-propanol from water. With some alcohols, this potential is more noticeable than with others. The potential of DMA as a separation agent is increasing in the following sequence: methanol < ethanol < 2-propanol < 1-propanol, and that also could be noticed from the selectivity values that also increase in this sequence. The UNIQUAC model proved as successful in correlating the LLE data.

Structure-activity relationship and experimental study of organic solvents and deep eutectic solvents in separation of cyclohexane-ethyl acetate

Selecting the appropriate extractant is of great significance for solving the problems of high energy consumption and difficult separation in the extractive distillation process. In this study, four deep eutectic solvents (DESs) were designed by combining menthol hydrogen bond acceptors with lauric acid and capric acid hydrogen bond donors and tetrabutylammonium bromide hydrogen bond acceptors with levulinic acid and ethylene glycol hydrogen bond donors. The interaction mechanism and structure–activity relationship between azeotropic system, hydrogen bond donor, hydrogen bond acceptor and deep eutectic solvent were studied. σ-profile, interaction energy, reduced density gradient, electrostatic potential, and natural bond orbital were used to study the microscopic mechanism and structure–activity relationship of azeotropes separated by DESs. On this basis, the vapor–liquid equilibrium experiments of separating ethyl acetate-cyclohexane azeotrope by DESs were carried out. The results showed that separating ethyl acetate-cyclohexane by using DESs is feasible and that the DES synthesized by using levulinic acid and tetrabutylammonium bromide is preferable for separation. Studying the relationship between DES structures and the azeotrope provides a theoretical basis for the screening and design of DES extractants for the separation of alkane-ester azeotropes using extractive distillation.

Biological Buffer Effect on Liquid–Liquid Equilibria of Systems Containing n-Butanol + Methyl Isobutyl Ketone + Water

Biofuel, that is, n-butanol, production from plant-based biomass represents a renewable energy resource that can be a substitute for fossil fuel. Thus, it is important to study the separation of n-butanol from its aqueous solution to obtain a high-purity product. Liquid–liquid extraction is a beneficial process in alcohol production to recover alcohol from the aqueous medium. Liquid–liquid equilibrium (LLE) data are needed for rational design and optimal separation operation, such as biological separation and extraction processes. The objective of this study is to determine LLE data for quaternary systems of n-butanol, methyl isobutyl ketone (MIBK), water, and a biological buffer at 303.15 K and atmospheric pressure (P = 0.1 MPa). The effect of biological buffer addition into aqueous solution was also studied. Three different biological buffers, 4-(2-hydroxyethyl)-1-piperazine propanesulfonic acid (EPPS), 4-morpholinepropanesulfonic acid (MOPS), and 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid (HEPES), were applied in this study for the comparison. The separation factor and distribution coefficient were evaluated in this study to interpret the extraction performance of n-butanol. According to the experimental results, the extraction performance was in the order of HEPES > EPPS > MOPS, describing the strength of buffering-out as well. Furthermore, it was found that the aid of a biological buffer in the LLE systems consisting of n-butanol, MIBK, and water resulted in better extraction performance than that of the LLE systems in the absence of a biological buffer. The reliability of the experimental LLE tie-line data was satisfactorily ascertained by the Hand correlation. The non-random two-liquid and universal quasi-chemical thermodynamics models correlated well the experimental LLE tie-line data with the root mean square deviation of less than 1%. The binary interaction parameters of both models were also obtained in this study.