Liquid-liquid Equilibrium Experiments Research Articles

Exploring ionic liquids for the extraction separation of aromatic hydrocarbons from diesel via multiple interaction analyses coupled with experimental evaluation

The separation of aromatic hydrocarbons from petroleum fractions is of great significance for both the quality upgrading of products and value-added utilization of aromatic compounds. However, the separation of polycyclic aromatic hydrocarbons (PAHs) and their derivatives from diesel remains challenging because of their lower solubility and selectivity as compared to the monocyclic aromatic compounds. In this work, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TF2N]) was screened from 320 ionic liquid (IL) candidates through solvent capacity predication using COSMO-RS method. Liquid-liquid equilibrium experiments were carried out using a series of tetralin/n-decane mixtures with different tetralin concentrations to evaluate the extraction performance of several solvents. The results indicate that [EMIM][TF2N] has high selectivity up to 95.73 for tetralin over n-decane, which is 4.5 and 3.9 times higher than that of dimethyl sulfoxide and sulfolane. During five regeneration cycles, the [EMIM][TF2N] exhibits consistent extraction performance and nearly complete recovery. Molecular polarity index (MPI) analysis indicates that tetralin has larger dissolving affinity to solvents as compared to n-decane. Combined analyses of interaction energy, energy decomposition, and visualization of weak interaction reveal that the crucial role of weak hydrogen bond in dominating the complex solvent–solute interactions. Compared to n-decane, tetralin shows a stronger interaction with the solvents due to the existence of C-H···π and hydrogen bond interactions. The great difference in interaction energy between {[EMIM]+ + tetralin} and {[EMIM]+ + n-decane}, therefore, endows [EMIM][TF2N] with high selectivity for tetralin. Given the dominant role of cation, a IL, [CN1 = C2SCCS2(CC = C)C1][TF2N] having both high selectivity and high solvent capacity was subsequently explored using the cation generation method based on the SeqVAE model. Furthermore, present study proposes a strategy for the design of ILs for separation and other specific application circumstances.

Sustainable synthesis and extraction of 5-methyl-N-phenyl-2-pyrrolidone produced via reductive amination of levulinic acid

5-methyl-N-substituted-2-pyrrolidones (5MPs) have been proposed as alternatives to N-methyl-2-pyrrolidone, a solvent with industrial and commercial applications which is considered hazardous and undesired by regulators. 5MPs are produced via reductive amination of levulinic acid with a catalyst and a reducing agent like H2. However, the separation of 5MPs from the reaction media is scarcely studied to understand industrial and commercial viability. This work is centered on producing 5-methyl-N-phenyl-2-pyrrolidone from levulinic acid via reductive amination followed by its liquid–liquid extraction using specifically selected extracting solvents. The extraction step considers not only the separation performance but also the environmental, health, and safety (EHS) criteria of the selected solvents. Thus, COSMO-RS, along with EHS guides, were used to screen solvents to extract 5-methyl-N-phenyl-2-pyrrolidone from methanol or water, which are used as reaction solvents. Some promising extracting solvents were studied in ternary liquid–liquid equilibrium experiments based on the partition of 5-methyl-N-phenyl-2-pyrrolidone and the reactants in the extracting solvent + (water or methanol) biphasic system. Subsequently, the solvents were tested for the extraction of the 5-methyl-N-phenyl-2-pyrrolidone from a real reaction mixture, produced by a Pt/TiO2 catalyzed reductive amination at 25 °C and 1.013 bar. Predictions and further validations of the distribution coefficients and selectivities for the solute show that anisole and limonene are favorable solvents for extracting 5-methyl-N-phenyl-2-pyrrolidone from water and methanol media, respectively. Both solvents are attractive alternatives due to their biobased nature, with the former ranked as recommended by EHS guides and the latter having some concerns with environmental criteria. However, both solvents show advantages for a scale-up of the reaction + separation process.

Cobalt and nickel separation in aqueous two-phase systems with polyethylene glycol 20,000 and sodium electrolytes

The separation of Co(II) and Ni(II) in aqueous two-phase systems (ATPSs) formed by the polymer polyethylene glycol 20,000 and several sodium electrolytes, coupled with the organic extractant 1-nitroso-2-naphthol was studied. First, the liquid-liquid equilibrium experiments were carried out to describe the phase diagrams of the ATPS. Then, the metal separation efficiency was evaluated considering several factors. It was observed that pH had a great influence on the selective metal chelation. When lowering the pH to 2 and 1 in the system with sodium sulfate, it was possible to suppress the Ni extraction under 5%. These results showed that the differences in the metal chelate stabilities could displace the equilibrium reaction with Ni(II) for selective extraction. In addition, experimental results showed that the interactions between metal cations and the salt anions also determined the separation efficiency. For the system with sodium sulfate (Na2SO4), Ni(II) extraction was suppressed at pH 2, but when sodium citrate (Na3C6H5O7) was used, the suppression occurred at pH lower than 0.5, while sodium tartrate (Na2C4H4O6) and sodium hydrogen phosphate (Na2HPO4) were not suitable for selective extraction. High separation factors of 11,080, 1136, and 3300 were obtained for the aqueous systems with Na2SO4 at pH 2, and pH 1, and Na3C6H5O7 at pH 0.5, respectively. Finally, the extraction at higher metal ion concentrations was tested. When the concentration of 1N2N was 1000 mg/kg, the maximum amount of extracted Co reached about 85 mg/kg within 15 min, which corresponds to complete extraction considering a metal:1N2N ratio of 1:4.

Comparative study on ionic liquids and deep eutectic solvents in the separation of fuel additive isopropyl alcohol and ethyl acetate by the experimental study and molecular simulation

Due to their excellent properties, ionic liquids (ILs) and deep eutectic solvents (DESs) have become the two most widely studied extractants. In this work, the separation process of EAC and IPA was systematically investigated, the suitable ILs/DESs were preliminarily screened using the COSMO model. Then, the combination mechanism of ILs/DES-IPA was elucidated through the ESP and the electron density difference analysis. The mutual penetration distances, IGMH and AIM analysis were used to analyze the extraction mechanism. The results showed that [EMim][AC] had the best extraction capacity. Subsequently, Liquid-liquid equilibrium experiments were carried out on two selected ILs and two DESs, the order of the extraction capacity was [EMim][AC] > [EMim][H2PO4] > (ChCl-EG) > (ChCl-Gly), which was consistent with the result of theoretical analysis. Moreover, the experimental data were regressed by the NRTL model, with the RMSD were all below 0.012, indicating that the NRTL model could well predict the phase behavior of the system. In addition to providing data support for the separation design of the EAC-IPA system, this work provides a basis for the selection of extractants for the low-carbon alcohol ester system.

Extraction desulfurization with mixed solvents of organic solvent + organic solvent or deep eutectic solvent as extractants: Liquid-liquid equilibrium experiments and molecular dynamics simulations

To meet the stringent requirements for sulfur content in gasoline, fuel oil desulfurization has become an indispensable process in petrochemical production. This study aimed to extract thiophene from heptane using a novel mixed solvent. In this work, the performance of single solvent N, N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and sulfolane (SULF) was investigated for the separation of thiophene and heptane at 298.15 K or 308.15 K, respectively. Ternary liquid-liquid equilibrium (LLE) data (heptane + thiophene + DMF, heptane + thiophene + DMSO and heptane + thiophene + SULF) shows that DMF has the highest distribution coefficient and DMSO has the highest selectivity. Subsequently, compared to a single solvent, the mixed solvent composed of the molar ratio of 1:7 tetrabutylammonium bromide-SULF (DES1) and DMSO has the highest selectivity and applicable distribution coefficient. The conclusion can be obtained from the quaternary LLE data (heptane + thiophene + DMF/DMSO, heptane + thiophene + DES1/DMSO and heptane + thiophene + DES1/DMF). And the NRTL and UNIQUAC models were used to correlate the LLE data. The mechanism of thiophene extraction from thiophene/heptane was elucidated by molecular dynamics (MD) simulations. The analysis of non-bonded interaction energies shows that the electrostatic force plays a major role in the separation of thiophene/heptane for the mixed solvent, and radial distribution functions demonstrates that the oxygen atom of DMSO, nitrogen atom atom of DMF and bromide ion of DES1 have strong interaction with hydrogen atom of thiophene. Therefore, this study provides theoretical guidance for the application of mixed solvents in the desulfurization of fuel oil process.

Molecular insights into azeotrope separation in the methyl tert-butyl ether production process using ChCl-based deep eutectic solvents

Deep eutectic solvents (DESs) were first applied in the azeotrope separation process for the production of methyl tert-butyl ether (MTBE). Quantum chemistry and molecular dynamics simulations were used to explore the interaction mechanism of ChCl-based DESs in the liquid–liquid extraction of the MTBE–methanol (MeOH) system. The results showed that the extraction of MeOH by DESs mainly depended on the Van der Waals interactions between Cl atoms in ChCl and H atoms in the MeOH hydroxyl group. Hydrogen bond donors also enhanced the extraction effect to a certain extent. Liquid-liquid equilibrium experiments were carried out for the three selected DESs, and the ideal separation effect was obtained. The complete separation process of the MTBE-MeOH system was developed based on experimental data. This work demonstrates the application of DESs in the MTBE-MEOH system and provides guidance for the selecting and analysis of other DES extractants for the separation of low-carbon alcohol systems.

Tf2N]-based ionic liquids for the selective liquid-liquid extraction of levulinic acid/formic acid: COSMO-RS screening and ternary LLE experimental data

The separation of Levulinic (LA) acid and Formic acid (FA) from aqueous streams represents an important and challenging separation in biorefineries, where ionic liquids (ILs) provide a sustainable environment for liquid-liquid extractions of these acids. In this work, a COSMO-RS screening of bis (trifluoromethylsulfonil)imide [Tf2N]− based IL was first conducted and then followed by experimental validation to search for the most suitable cation for this separation. After the screening, ternary liquid-liquid equilibrium experiments at 298.15K and the subsequent data correlation using the Non-Random Two Liquid model (NRTL) were performed for future industrial implementation. Results indicated that the phosphonium cations, especially the trihexylthetradecyl phosphonium cation [P66614]+, produced the highest selectivity rates among all the experimentally measured ILs.

Co-production of volatile fatty acids and biogas from an anaerobic digestion system using in situ extraction

Trioctylamine (TOA) and tributyl phosphate (TBP) along with three diluents (canola oil, lamp oil, and oleyl alcohol) were identified as potentially suitable solvents for direct comparison for the application of in situ volatile fatty acid (VFA) extraction from anaerobic digestion (AD) systems. The highest degree of extraction at pH 5.0 was observed for TOA/oleyl alcohol (50.5 ± 0.1%) in liquid-liquid equilibrium experiments. Biochemical methane potential (BMP) tests were conducted for solvent toxicity on the biogas producing consortium, using the three best solvents. From these experiments, the samples extracted using TOA/canola oil and TBP/lamp oil performed better than the control in total gas production (168 mL ± 26 mL and 146 ± 5 mL) and methane percentage (12.6 ± 2.8% and 14.7 ± 6.7% respectively). The control produced 115 ± 39 mL of gas (9.7 ± 1.3% of methane). Over a 28 day digestion period, 2.40 ± 0.30 g/L and 5.84 ± 0.36 g/L of VFAs from 10 mL of solvent were successfully recovered from TBP/lamp oil and TOA/ oleyl alcohol, respectively, in these BMPs. To demonstrate applicability at a larger scale, a novel 17 L AD-bioreactor was modified by placing an in situ extraction tube inside the reactor, connected to a circulator and back-extraction unit. 0.078 g of total VFAs were extracted out with TOA/oleyl alcohol using a pH-swing back-extraction unit. Additionally, the AD bioreactor produced 6.71 L of biogas with a methane percentage of 43% over a 22 day digestion period. This implies that in situ LLE extraction may be industrially applicable as a potential co-production process for biogas and VFAs, significantly building from previous VFA extraction work.

Extraction of ethanol from mixtures with n-hexane by deep eutectic solvents of choline chloride + levulinic acid, + ethylene glycol, or + malonic acid

The separation of azeotropic mixtures is a great challenge for concentrating a desired chemical compound because it cannot be attained by a simple distillation process. Liquid-liquid extraction can be an alternative process to resolve the separation problem if an appropriate solvent is selected to effectively partition the mixture. In this work, the feasibilities of three different deep eutectic solvents (DESs) for breaking azeotropes of n-hexane and ethanol mixture were examined by means of liquid-liquid extraction. Choline chloride (ChCl) was chosen as a base compound and three hydrogen bond donors (HBDs) of levulinic acid, ethylene glycol, and malonic acid were added at their eutectic ratio to form DESs. Liquid-liquid equilibrium experiments for an azeotropic n-hexane + ethanol system were carried out to determine binodal compositions and, then, evaluate the compositions at both liquid phases at 298.2 K and atmospheric pressure by employing the prepared DESs. Refractive index, density, and viscosity at the binodal compositions were measured to provide properties required for extraction process establishment. The measured tie-lines were compared with the predicted results calculated by COSMO-SAC model. Moreover, the ability for extracting ethanol was evaluated with distribution coefficient and selectivity. It was found that the distribution coefficient and selectivity values are high enough to support a scaling-up process by a liquid–liquid extraction.

Olefin separation from FCC naphtha by dimethyl sulfoxide: Effect of structure on the separation and correlation of thermodynamic models

The performance of dimethyl sulfoxide (DMSO) solvent in separating olefins from aromatics and thiophene sulfides was evaluated through a series of ternary liquid-liquid equilibrium (LLE) experiments at 101.325 kPa and 303.15 K. The influences of the structures of olefins, aromatics, and thiophene sulfides on the separation efficiency were analyzed. Normal 1-hexene and isomer 2,4,4-trimethyl-1-pentene were easily separated from aromatics or thiophene sulfides, which only contain aromatic ring structures, such as benzene and thiophene. The reason is that the induced dipole on the aromatic ring structure introduced by the DMSO solvent significantly improved the polarity of aromatics and thiophene sulfide molecules, thereby enhancing the interaction with the ring structure. In addition, olefins were easier to separate from thiophene sulfides than from aromatics. The olefin separation factor of separating 2,4,4-trimethyl-1-pentene from thiophene was three times greater than that of separating the same olefin from benzene. The binary parameters between DMSO and olefins, aromatics, and thiophene sulfides for NRTL and UNIQUAC models were obtained through ternary LLE experiments. The maximum value of the root-mean-square deviation of the simulated compositions of phases compared with experimental data was 0.0052 in the two adopted models. Hence, the regressed binary parameters could efficiently describe the experimental LLE process. On the basis of the obtained binary parameters, the NRTL and UNIQUAC models are suitable for predicting the performance of olefin separation from fluid catalytic cracking naphtha. However, the NRTL model is more precise than the UNIQUAC model.

Effect of water addition on extraction ability of eutectic solvent choline chloride+ 1,2-propanediol for separation of hexane/heptane+ethanol systems

The ability of binary deep eutectic solvent choline chloride+1,2-propanediol (DES1; 1 : 3 mole ratio) and ternary deep eutectic solvent choline chloride+1,2-propanediol+water (DES2; 1 : 3 : 3 mole ratio) for breaking the azeotropes hexane/heptane+ethanol by means of liquid-liquid extraction was evaluated. Liquid-liquid equilibrium experiments were performed at 298.15 K, at atmospheric pressure, and data were correlated by NRTL and UNIQUAC models. Thermodynamic properties (density, viscosity, refractive index and speed of sound) of DES1 and DES2 were determined in temperature range from 288.15 K to 333.15 K and at atmospheric pressure. Extraction ability of the investigated eutectics yielded promising results in comparison with conventional solvents. Besides a high selectivity towards ethanol, an advantage of DES2 is its lower viscosity and higher distribution ratio values, which is an important aspect for a potential industrial application. Another advantage of both investigated eutectics is their easy and high recoverability from the extract layer based on their negligible vapor pressure.

Poly(ethylene glycol) diacrylate as a novel chaotropic compound for design of aqueous biphasic systems

In this work novel solvent, poly(ethylene glycol) diacrylate (PEGDA) of average number molecular weight 700, is proposed for design of aqueous biphasic systems with salting-out agents: K3PO4/Na3C6H5O7/K2CO3/MnSO4/Li2SO4/ZnSO4. Ternary liquid-liquid equilibrium experiments were conducted at constant temperature 298.15K and 0.1MPa, where binodal curves and tie-lines were determined. The consistency of equilibrium data were checked and confirmed using Othmer-Tobias and Bancroft equations. Density ρ, viscosity η and refractive index nD have been experimentally measured for PEGDA 700+water system over the temperature range T=(293.15 to 323.15) K with temperature step 5K and at atmospheric pressure. Excess molar volumes VE, viscosity deviations Δη, deviations in refractive index ΔnD, excess Gibbs free energy of activation of viscous flow ∆G⁎E, partial molar volumes V¯i, excess partial molar volumes V¯iE and it's values at infinite dilutions V¯iE,∞ were calculated from experimental data and used to analyze non-ideal behavior of polymer aqueous solution. Fourier-transform infrared analysis (FT-IR) of PEGDA+water mixture and corresponding pure components was performed at T=298.15K in order to gain insight into the molecular structure of the mixture. FT-IR analysis indicates the absence of hydrogen bonding between PEGDA 700 and water. This leads to the conclusion that non-ideal behavior of mixture is contributed to geometrical packing or van der Waals forces of different species.

Efficient Determination of Liquid–Liquid Equilibria Using Microfluidics and Raman Microspectroscopy

Experimental liquid–liquid equilibrium (LLE) data are indispensable for many applications ranging from extraction column design to water partitioning of organics in the environment. However, conventional LLE experiments are time-consuming and need large sample volumes. Therefore, a measurement setup is presented for the time and material efficient determination of LLE data. The measurement setup combines the advantages of microfluidics and Raman microspectroscopy: The small dimensions of the used H-cell microchannel lead to rapid equilibration and small sample consumption; Raman microspectroscopy allows for rapid in situ quantification of all components. The measurement setup has successfully been validated by measuring the LLE of the ternary system cyclohexane–methanol–toluene. Excellent agreement with the literature data has been achieved. Thus, the developed setup allows for the efficient determination of liquid–liquid equilibria in multicomponent mixtures.

Evaluation of Deep Eutectic Solvent for the selective extraction of toluene and quinoline at T = 308.15 K and p = 1 bar

The current work reports the selective separation of aromatic and poly aromatic hydrocarbon (PAH) with Deep Eutectic Solvents (DES). The low cost DES are based on a mixture of a hydrogen bond donor and organic salt. The organic salt namely Methyltriphenylphosphonium bromide(MTBP) along with the hydrogen bond donor (HBD) were taken in a ratio of 1:4 to synthesize potential DES. DES were then varied based on the selection of two hydrogen bond donor namely ethylene glycol(DES1) and glycerol(DES2). In order to study their effectiveness, Liquid-liquid Equilibrium experiments were performed for the removal of toluene and quinoline respectively. LLE data corresponding to the ternary systems:[DES1(1) + Toluene(2) + Heptane(3)],[DES2(1) + Toluene(2) + Heptane(3)], [DES1(1) + Quinoline(2) + Heptane(3)] and [DES2(1) + Quinoline(2) + Heptane(3)] were generated at 308.15 K and atmospheric pressure. 1H NMR analysis were then used for the quantification of both extract and raffinate phases. Distribution coefficient (β) and selectivity (S) were subsequently obtained and it was found that toluene had a poor selectivity than quinoline. The cross contamination of DES and heptane across either phases were found to be nearly zero. Further the Non-random two liquid (NRTL) and UNiversal QUAsi Chemical (UNIQUAC) thermodynamic model were used to compare the experimental tie line data. This gave an excellent fit with a root mean square deviation (RMSD) values for both models ranging from (0.28–0.31%) and (0.22–0.73%) respectively. DES1, namely Methyltriphenylphosphonium bromide + ethylene glycol was thus recommended as a potential solvent for the separation of aromatic and PAH component.

Measurements and prediction of ternary liquid–liquid equilibria for mixtures of IL + sulfur compound + hexadecane

For the practical application of ionic liquids as possible solvents for the removal of thiophenic compounds in the diesel fuel, the liquid–liquid equilibrium (LLE) data of such systems is necessary for the design and optimization of process equipment. In this work, LLE experiments were carried out on four ternary systems consisting of one of two pyrrolidinium or phosphonium-based ionic liquids (IL), one of two sulfur compounds and hexadecane as a representative for diesel fuel. For benzothiophene, the system consisting of the [HMPyrr][TFSI] IL as a solvent possesses the highest solute distribution coefficient (2.754) while a solute distribution coefficient of 3.722 was recorded for dibenzothiophene using the [P4444][MeSO3] as an extraction solvent. The LLE data were fairly correlated with the NRTL model especially at the region of low mole fraction of the sulfur compounds. The data presented in this work can therefore be integrated into process simulators and can be used for preliminary techno-economic evaluation of an ionic liquid-based deep extractive desulfurization of diesel fuel.

Phase Equilibria upon Denitrification of Liquid Fuels Using Imidazolium-Based Ionic Liquids: Experiment and Quantum Chemical Calculations

The interaction between pyrrole and pyridine with 1-ethyl-3-methylimidazolium ethyl sulfate ([EMIM][EtSO4]) was investigated using quantum chemical calculations, the conductor-like screening model for real solvent (COSMO-RS) approach, and experimental ternary liquid–liquid equilibrium (LLE) data. Geometry optimization was performed usign density functional theory (DFT) with B3LYP functional and 6-311+G* basis set for individual species and complexes of [EMIM][EtSO4] with pyrrole/pyridine. The amount of charge transfer in [EMIM][EtSO4] + pyrrole was found to be ∼20% greater than that in [EMIM][EtSO4] + pyridine, indicating that CH−π interaction was stronger with pyrrole. The more negative interaction energy for the complex [EMIM][EtSO4] + pyrrole implies that [EMIM][EtSO4] has a more favorable interaction with pyrrole than with pyridine. σ-profile analysis using COSMO-RS confirmed the pivotal role of the CH-π interaction between [EMIM][EtSO4] and pyrrole or pyridine. Ternary LLE experiments were performed ...

Application of mutually immiscible ionic liquids to the separation of aromatic and aliphatic hydrocarbons by liquid extraction: a preliminary approach

The recently discovered class of ionic liquids--mutually immiscible ionic liquids--are explored in this work for their first practical application: the separation of aromatic and aliphatic hydrocarbons by solvent extraction. For this preliminary approach, benzene and hexane were chosen as representatives of each group of hydrocarbons; the ionic liquids 1-ethyl-3-methylimidazolium bis( (trifluoromethyl)sulfonyl)amide and trihexyl(tetradecyl)phosphonium bis( (trifluoromethyl)sulfonyl)amide, which are both liquid at room temperature and hydrophobic, were selected as potential solvents. Liquid-liquid equilibrium experiments were carried out at 25 degrees C for the quaternary system formed by the two hydrocarbons and the two ionic liquids. Typical extraction parameters were calculated and analysed in order to evaluate the possibilities of the mutual immiscible ionic liquids in accomplishing the separation target. A comparison with the case of using just one of the ionic liquids was made.