Tie-line Compositions Research Articles

Novel Green Aqueous Two-Phase Systems (ATPSs) based on choline salts and application to the removal of pharmaceutical pollutants from water

Aqueous Two-Phase Systems (ATPSs) constitute extractive media with applicability for the removal of a wide range of solutes, such as antioxidants or pharmaceuticals, and can be designed in a non-toxic and environmentally friendly manner. Nevertheless, prior to their general use at large scale, their liquid-liquid equilibria (solubility curves and tie-line compositions) need to be thoroughly determined.In this work, 6 solubility curves were obtained for novel aqueous ternary systems containing choline salts (choline chloride, choline bicarbonate, choline (2R,3R)-bitartrate and choline di-hydrogen citrate) and either ethyl lactate (EL) or polyethylene glycol (PEG), at 298.15 K and 0.1 MPa. Moreover, 3 tie-line compositions were successfully determined for the system {ethyl lactate (1) + choline (2R,3R)-bitartrate (2) + water (3)}. Then, this novel ATPS was applied in the removal of three common pharmaceutical pollutants from aqueous media (acetaminophen, amoxicillin and salicylic acid). In these partition studies, salicylic acid and acetaminophen were effectively extracted to the top phase, with the highest partition coefficients (K=9±2) being obtained for salicylic acid in the longest tie-line (length of 0.8816). Acetaminophen achieved the most promising results (K=2.2±0.1) in the shortest tie-line (length of 0.6192).

Cryo-EM images of phase-separated lipid bilayer vesicles analyzed with a machine-learning approach

Lateral lipid heterogeneity (i.e., raft formation) in biomembranes plays a functional role in living cells. Three-component mixtures of low- and high-melting lipids plus cholesterol offer a simplified experimental model for raft domains in which a liquid-disordered (Ld) phase coexists with a liquid-ordered (Lo) phase. Using such models, we recently showed that cryogenic electron microscopy (cryo-EM) can detect phase separation in lipid vesicles based on differences in bilayer thickness. However, the considerable noise within cryo-EM data poses a significant challenge for accurately determining the membrane phase state at high spatial resolution. To this end, we have developed an image-processing pipeline that utilizes machine learning (ML) to predict the bilayer phase in projection images of lipid vesicles. Importantly, the ML method exploits differences in both the thickness and molecular density of Lo compared to Ld, which leads to improved phase identification. To assess accuracy, we used artificial images of phase-separated lipid vesicles generated from all-atom molecular dynamics simulations of Lo and Ld phases. Synthetic ground-truth data sets mimicking a series of compositions along a tieline of Ld + Lo coexistence were created and then analyzed with various ML models. For all tieline compositions, we find that the ML approach can correctly identify the bilayer phase with >90% accuracy, thus providing a means to isolate the intensity profiles of coexisting Ld and Lo phases, as well as accurately determine domain-size distributions, number of domains, and phase-area fractions. The method described here provides a framework for characterizing nanoscopic lateral heterogeneities in membranes and paves the way for a more detailed understanding of raft properties in biological contexts.

Harnessing the power of natural deep eutectic solvents (choline chloride/sucrose) and polypropylene glycol in the formation of aqueous biphasic systems and the application of these systems in drug extraction.

In recent times, there has been considerable interest in utilizing aqueous biphasic systems (ABSs) containing natural deep eutectic solvents (NADESs) for the extraction of various substances. In this study, we focused on investigating the phase behavior of ABSs composed of poly(propylene) glycol 400 and NADESs (specifically, choline chloride/sucrose with molar ratios of 2 : 1 and 1 : 1). By analyzing the compositions of tie-lines, it was observed that these ABSs, which consist of four components, exhibit characteristics similar to ternary systems. To examine the influence of molar ratios on phase separation, the binodal model was applied to the obtained binodal data. The NRTL and UNIQUAC models were employed to establish correlations for the tie-lines. Moreover, we examined the extraction capabilities of the aforementioned ABSs for three commonly used drugs: diclofenac potassium, acetaminophen, and salicylic acid. To assess the efficiency of extraction, partition coefficients and extraction efficiencies were calculated for each drug. The results revealed that the extraction efficiency of these drugs into the polymer-rich top phase is dependent on their hydrophobicity. Furthermore, we employed the Diamond-Hsu equation, along with its modified version, to establish correlations between the experimental partition coefficients of the drugs and NADES overall concentrations.

Purification and Fractionation of Lignin via ALPHA: Liquid-Liquid Equilibrium for the Lignin-Acetic Acid-Water System.

In order to effectively practice the Aqueous Lignin Purification with Hot Agents (ALPHA) process for lignin purification and fractionation, the temperatures and feed compositions where regions of liquid-liquid equilibrium (LLE) exist must be identified. To this end, pseudo-ternary phase diagrams for the lignin-acetic acid-water system were mapped out at 45-95 °C and various solvent: feed lignin mass ratios (S:F). For a given temperature, the accompanying SL (solid-liquid), SLL (solid-liquid-liquid), and one-phase regions were also located. For the first time, ALPHA using acetic acid (AcOH)-water solutions was applied to a lignin recovered via the commercial LignoBoost process. In addition to determining tie-line compositions for the two regions of LLE that were discovered, the distribution of lignin and key impurities (the latter can negatively impact lignin performance for materials applications) between the two liquid phases wasalso measured. As a representative example, lignin isolated in thelignin-rich phase was reduced 7x in metals and 4x in polysaccharides by using ALPHA with a feed solvent composition of 50-55% AcOH and an S:F of 6:1, with said lignin being obtained at a yield of 50-70% of the feed lignin and having a molecular weight triple that of the feed.

Measurements, correlations and thermodynamic modeling of aqueous two-phase systems of polyvinylpyrrolidone (PVP) + sulfate/citrate salts

Aqueous two-phase systems (ATPS) can be described as an alternative to traditional liquid-liquid extraction systems, typically consisting of a polymer and a salt solution. An alternative polymer called polyvinylpyrrolidone (PVP) has emerged as a viable option for ATPS due to its low cost, stability, and potential. This study aimed to investigate the effect of the molecular weight of poly (vinylpyrrolidone) (PVP) (K17, K25, and K30) and the temperature (298.15, 303.15, and 308.15 K) in the system ATPSs composed of PVPs and sodium sulfate/potassium sulfate/tri sodium citrate. The tie-line data were determined by measuring the density (ρ) and refractive index (nD). Moreover, the phase compositions and plait point are investigated for different PVPs molecular weight, temperature, and salt type. In addition, the effect of these parameters on the binodal curve, tie-line length (TLL), and slope of tie line (STL) are analyzed in detail by comparing them with the literature data. The impact of the parameters on the binodal curves was investigated by utilizing the values of the effective excluded volume parameter (EEV) that were calculated from the LLE data. Furthermore, the binodal curves and the tie-line compositions were well-fitted by using some semi-empirical equations. The phase separation ability is enhanced with temperature and PVPs molecular weight. The modified UNIFAC-NRF is used to correlate the liquid-liquid equilibrium data of the studied systems and the optimized binary group interaction parameters were determined.

Experimental and theoretical assessment of phenomena linked with separation and purification of biodiesel from Ricinus communis seed oil

This study investigated the phenomena associated with the separation and purification of biodiesel produced from Ricinus communis oil seeds using experimental and theoretical approaches. The alkaline transesterification technique was used to produce the biodiesel from the Ricinus communis oil seeds which were later compared with standards based on EN and ASTM. Experimental investigation of the components in the mixture for separation and purification was conducted using the standard turbidimetric method for binodal solubility and tie-line compositions. The gas chromatographic technique was used to determine the composition of the homogeneous mixture. Novel components separation and purification of the Ricinus communis seed oil biodiesel was achieved using ternary diagrams highlighting the constituent components of the biodiesel at different temperatures for enhanced separation and purification. At the coexisting extract and raffinate phases, the orientation angle of the component compositions increases as the methanol concentration increases and temperature increases. The analysis of seed oil in terms of its physicochemical properties showed density, refractive index, acid value, and free fatty acid values of 905 kg/m3, 1.486, 0.79 mg KOH/g, and 0.390 mg KOH/g respectively. The fatty acid composition of the seed oil and biodiesel revealed that the major characteristics of the oil and biodiesel were defined by the presence of linoleic acid (C18:2) and a ricinoleic acid hydroxyl group (C18:1, OH) with compositions of approximately 30% and 20% respectively. Fourier Transform Infra-Red (FTIR) spectrometry analysis of the oil and biodiesel showed that the absorption spectrum in terms of the wave number (cm−1) ranged from 1000 to 4000 cm−1 with esters as the main functional group providing the main structural backbone. The presence of different fatty acids leads to lateral homogeneity of the biodiesel molecules which can serve to organize the molecules into discrete domains with different properties for enhanced separation and purification at the investigated temperatures. Optimal separation and purification were achieved at the different temperatures showing the castor oil biodiesel, glycerol, and methanol components system at the prevailing composition, time, and temperatures from the tie-lines and binodal solubility compositions. This approach provides a means for the design of a more efficient separation process for optimal biodiesel purification after production with knowledge of how the components are distributed in the ternary mixture after the transesterification reaction. This, leads to greater efficiency of the process, reducing material and operational costs and eliminating environmental issues linked with the biodiesel production process as the volume of wastewater generated would be hugely eradicated. The findings of this study will be useful in the setting up of a small-to-medium-size biodiesel production facility with improvement in the efficiency of product separation and purification.

Binodal Curves and Tie-Line Compositions for a Poly(ethylene glycol) 6000 + Lithium Citrate + Water Aqueous Two-Phase System and the Partitioning of Salbutamol Drug at T = 288.15–318.15 K

The partitioning of salbutamol drug in a poly(ethylene glycol) 6000 + lithium citrate + water system was investigated at T = 288.15, 298.15, 308.15, and 318.15 K. The binodal curves and tie-line compositions were determined at different temperatures, and the studied aqueous two-phase system (ATPS) was used to study the partitioning of salbutamol drug. The results showed that the ability of the system for two-phase formation increases at higher temperatures. The good performance of the empirical Merchuk equation was obtained to model the binodal curves. The tie-line compositions were also fitted using the Setschenow-type equation and electrolyte Wilson models. Furthermore, the ability of the studied ATPSs for the extraction of salbutamol is shown based on the obtained partitioning parameters, and the partitioning coefficient was increased from the value of ∼0.48 at T = 288.15 K to ∼1.7 at T = 318.15 K. Overall, the studied ATPS can be employed to extract salbutamol from aqueous medium in a range of biological temperatures.

Separation of methanol and ethanol from azeotropic MTBE mixtures using choline chloride-based deep eutectic solvents

In this study, the performance of five different choline chloride – based deep eutectic solvents (DESs), including ChCl – urea, ChCl – ethylene glycol, ChCl – glycerol, ChCl – 1,2- propanediol, and ChCl – glucose, has been experimentally and computationally investigated for the purpose of liquid – liquid extraction at 298.15 K and 1 atm. In this regard, the effect of them on the extraction efficiency to separate methanol and ethanol from azeotropic systems, methyl tert-butyl ether (MTBE) + ethanol and MTBE + methanol, is studied. To synthesize these DESs, chlorine chloride as a hydrogen bond acceptor (HBA) is blended with urea, ethylene glycol, glycerol, 1,2- propanediol, and glucose as hydrogen bond donors (HBDs). Through the investigation, it is revealed that all the studied DESs deliver a distribution coefficient, β, that is higher than unity (β > 1). Similarly, the measured selectivities for these DESs have presented values that are far greater than unity (S ≫ 1). This is advantageous as it demonstrates their industrial applications. Furthermore, to have a better view of how effective they are in terms of the extraction capacity, the experimental data have been compared to the performance of ionic liquids used for the liquid – liquid extraction of MTBE + methanol. The reliability of the tie-line compositions was checked by applying the Othmer–Tobias equation. Additionally, to show the consistency, UNIQUAC Functional-group Activity Coefficients (UNIFAC) as a thermodynamic model has been employed to predict the equilibrium tie-lines. The predicted data is compared with the experimentally measured data through the calculation of the root-mean-square deviation (RMSD), showing that both predicted and experimental data are in a good agreement together.

Comparative Evaluation of Liquid–Liquid Phase Equilibria for Aqueous Mixtures of Acetic Acid with Structurally Related Aryl Carbonyl Compounds at 298.2 and 308.2 K

Experimental solubility curves and tie-line compositions were comparatively investigated for the aqueous mixtures of acetic acid with three structurally similar aryl carbonyl compounds (propiophenone, acetophenone, and methyl benzoate) at (298.2 and 308.2) K and 101 kPa. The studied ternary mixtures display type-1 phase behavior. The correlation of the measured tie lines was performed by the NRTL and UNIQUAC models. The model binary interaction parameters were obtained by measured tie-line values and minimizing an objective function. The consistency of the NRTL parameters was validated through topological analysis connected to the Gibbs tangent principle and stability test. Evaluation of the capacity of each solvent was performed using the calculation of distribution coefficients and separation factors. Distribution coefficient (constant) and selectivity (separation factor) values were evaluated over the immiscibility region using the experimental equilibrium data. The influence of extraction temperature on the immiscibility region was found to be minor.

Thermodynamic insights into phase behavior a new aqueous two-phase system at different temperatures: Experimental equilibria, data correlation and modeling

In the current research, a novel aqueous ternary-two-phase system (ATPS) containing a deep eutectic solvent (DES formed by mixing choline chloride with polyethylene glycol 400) and the non-ionic surfactant Triton X-100 was designed. The phase behavior of this system including phase diagrams (binodal curves) and tie-line compositions was thermodynamically investigated at the temperature range of 298.15 to 316.15 K under atmospheric pressure. This system presented a DES-rich top phase and a surfactant-rich bottom phase. The plait point of binodal diagrams together with the tie-lines length (TLL) and the slope of tie-lines (STL) were determined at each of the operational temperatures. The influence of temperature on the binodal curves and the tie-lines was analyzed from which it was found that an increase in the temperature expands the two-phase region in the binodal curve as well as increases the length of the tie-lines. Moreover, the binodal curves data and the tie-line compositions were successfully correlated using a series of semi-empirical models with satisfactory results. Finally, the molar Gibbs energy, molar enthalpy and molar entropy of the cloud points of binodal curve were calculated and the results showed that the formation of the two-phase system is spontaneous and endothermic as well as the entropy is its driving force.

Phase diagrams of PEG1000,1500,2000,4000,6000 + lithium citrate + water ATPSs, and the partitioning of salbutamol at T = 298.15 K

Salbutamol is a drug used to treat the pulmonary diseases by ameliorate the medium and large airways in the lungs. Partitioning of salbutamol drug on the aqueous two-phase systems (ATPSs) of PEG1000,1500,2000,4000,6000 + trilithium citrate + water was determined at T = 298.15 K. The effect of molecular mass of polymer (MMP) on the binodal and tie-line compositions were studied. Results showed that the biphasic area was extended as the MMP was increased. The salting-out ability were quantified using the Setschenow model, and the binodal curves were modeled by a nonlinear 3-parameter equation. Furthermore, electrolyte Wilson along with the osmotic virial models have adequately been implemented to fit the tie-line compositions. Also, the studied ATPSs were implemented to study the partitioning of salbutamol drug on the salt-affluent and polymer-affluent phases. It is observed that, ATPSs of PEG1000 is premium to extract the salbutamol to the polymer-affluent phase, where, the ATPSs of PEG6000 is more favorable to extract the drug to the salt-affluent phase.

Thermodynamic Modeling of Liquid-Liquid Equilibrium in Ternary Systems with Biodiesel and Isolated Ester (Methyl Palmitate)

Liquid-liquid equilibrium data were measured and analyzed for two ternary systems (biodiesel + methanol + glycerol and methyl palmitate + methanol + glycerol). Biodiesel, produced by the conventional chemical route at 60 °C for 60 min, using methanol and soybean oil at a molar rate of 10:1 and potassium hydroxide concentration (KOH) of 1 wt% exhibited thermal decomposition at temperatures between 100 and 250 ºC, reaching mass loss of approximately 98.8%, confirming soybean oil conversion into biodiesel by gas chromatography and thermogravimetry. Tie line composition quality was verified using Othmer-Tobias and Hand correlation equations. The distribution and selectivity coefficients were calculated for the immiscibility regions. The experimental tie line data exhibited good correlation in the UNIQUAC and NRTL thermodynamic models. The biodiesel system displayed deviations of 0.66 and 0.53% for the UNIQUAC and NRTL models, respectively. In addition, the methyl palmitate system showed a 1.23 and 0.48% deviation for the UNIQUAC and NRTL model, respectively. The individual behavior of the main biodiesel esters , based on the UNIQUAC model parameters, demonstrated that the type of fatty acid does not interfere in model correlation, likely due to the similarity between their composition and properties.

Phase Equilibria of the Ternary System of Lithium Sulfate + Polyethylene Glycol (PEG3000) + Water at Different pH: Experiment Determination, Correlation, and Thermodynamic Modeling

The phase equilibrium data for the ternary systems [lithium sulfate (Li2SO4) + polyethylene glycol (PEG3000) + water] were measured at 298.15 K and at various pH values (2.94, 4.90, and 6.80). The solid–liquid equilibrium data including the solubility, density, and refractive index were determined using the isothermal dissolution equilibrium method. The liquid–liquid equilibrium (LLE) data for the aqueous two-phase system were obtained experimentally by measuring the biphasic physical properties, including the density and refractive index at 298.15 K. Subsequently, the binodal curves were correlated by using the Pirdashti and Merchuk equations, the effective excluded volumes were calculated from the binodal curve data, and the tie-line compositions were adjusted to the Othmer–Tobias and Bancroft equations, respectively. Results show that the solubility of Li2SO4 in the aqueous polymeric solution mitigates as the content of PEG increases, eventually. It was found that the more acidic solution induces the salting-out effect, and the LLE formed easily at the lower pH of studied systems. Finally, the extended UNIQUAC, the modified UNIQUAC-FV, and the modified UNIFAC-NRF models were selected to correlate the LLE data of the studied systems, and the modified UNIQUAC-FV model gives a better correlation for tie-lines data.

Calculated Elasticity of Al-Bearing Phase D

Using first-principles calculations, this study evaluates the structure, equation of state, and elasticity of three compositions of phase D up to 75 GPa: (1) the magnesium endmember [MgSi2O4(OH)2], (2) the aluminum endmember [Al2SiO4(OH)2], and (3) phase D with 50% Al-substitution [AlMg0.5Si1.5O4(OH)2]. We find that the Mg-endmember undergoes hydrogen-bond symmetrization and that this symmetrization is linked to a 22% increase in the bulk modulus of phase D, in agreement with previous studies. Al2SiO4(OH)2 also undergoes hydrogen-bond symmetrization, but the concomitant increase in bulk modulus is only 13%—a significant departure from the 22% increase of the Mg-endmember. Additionally, Al-endmember phase D is denser (2%–6%), less compressible (6%–25%), and has faster compressional (6%–12%) and shear velocities (12%–15%) relative to its Mg-endmember counterpart. Finally, we investigated the properties of phase D with 50% Al-substitution [AlMg0.5Si1.5O4(OH)2], and found that the hydrogen-bond symmetrization, equation of state parameters, and elastic constants of this tie-line composition cannot be accurately modeled by interpolating the properties of the Mg- and Al-endmembers.

Thermodynamic study of ATPS involving ethyl lactate and different inorganic salts

• Novel ethyl lactate-based Aqueous Two-Phase Systems were studied. • Pitzer-Debye-Hückel + UNIQUAC thermodynamic modelling of experimental ATPS data was carried out. • The experimental binodal data and tie-lines compositions were successfully fitted using several empirical equations. In this work, three Aqueous Two-Phase Systems (ATPS) involving ethyl lactate and the inorganic salts (NH 4 ) 2 SO 4 , K 2 HPO 4 and NaH 2 PO 4 have been studied. To analyse the separation process, binodal curves and tie lines were experimentally determined at T = 298.15 K and atmospheric pressure. The experimental binodal data were successfully fitted using several empirical equations: Merchuk et al. , Hu et al. , Han et al. and Jayapal et al. , and the degree of consistency of the tie line compositions was evaluated using Othmer-Tobias and Brancoft equations. The liquid–liquid equilibria were fitted using the Pitzer-Debye-Hückel + UNIQUAC and the UNIQUAC thermodynamic models. For all systems, the modelled tie lines were very similar to the experimental ones, but the first model presented somewhat smaller deviations, which allows to conclude that long-range forces present in these systems with strong salts should be considered.

Experimental study and thermodynamic modeling of phase equilibria of systems containing cyclohexane, alcohols (C4 and C5), and deep eutectic solvents

Liquid-liquid equilibrium (LLE) data were measured and comparatively analyzed for six ternary mixtures of (cyclohexane + alcohols + deep eutectic solvents) at T = 298.2 K and p = 101 kPa. In this work, three choline chloride-based deep eutectic solvents (ChCl-DESs) were prepared for the extraction of the two structurally similar primary alcohols (1-butanol and 3-methyl-1-butanol) from a hydrocarbon (cyclohexane). The chosen DESs were DES1 (ChCl-propylene glycol with molar ratio = 1:3), DES2 (ChCl-ethylene glycol with molar ratio = 1:2), and DES3 (ChCl-glycerol with molar ratio = 1:2). The quality of the tie-line compositions was checked using the Othmer-Tobias correlation equation. The NRTL model was successfully applied to fit the experimental equilibrium data. The model binary interaction parameters were optimized by the Particle Swarm Optimization (PSO) algorithm. The model validation confirms that all the calculated parameters are consistent with the experimental data. Evaluation of the capacities of the deep eutectic solvent was carried out via the calculation of solute distribution coefficients and selectivity from the LLE data. The influence of the chemical structure of the alcohol on the phase equilibria was investigated. The extraction ability of the studied deep eutectic solvents displays promising results. The highest solute distribution coefficients were determined for (cyclohexane + 1-butanol + DES1).

Aqueous two-phase system formed by alkanolammonium-based Protic Ionic Liquids and acetone: Experimental data, thermodynamic modeling, and Kraft lignin partition

Aqueous two-phase systems (ATPS) formed by Protic Ionic Liquids (PILs) are a potential alternative to recovery PILs after their use in pretreatment step and valorization of lignocellulosic biomass. Besides, ATPS based on PILs may be applied to Kraft lignin fractionation toward a more sustainable environment. In this study, nine alkanolammonium-based PILs were synthesized using organic acids (formic, acetic, propionic, lactic, and glycolic) as precursors. These PILs were combined with acetone to form ATPS at low temperatures, and the partition of Kraft lignin was tested using these same systems. The presence of an extra hydroxyl group in the PILs’ anionic part increased their ability to form ATPS, due to the increase in their acidity. Also, increasing the alkyl chain length of the PILs’ anionic part impairs the formation of ATPS. In contrast, the behavior was observed for the cationic part, due to the increase in the PILs’ hydrophobicity nature. Regarding the partition of Kraft lignin applying 2-hydroxyethylammonium-based PILs, the increase in the alkyl chain length of the PILs’ anionic part leads to stronger PILs-lignin interactions, which favored the lignin’s migration to the bottom phase (PILs-rich phase), and lower partition coefficient values, as follows: formate < acetate < propionate anions. The presence of an extra hydroxyl group in the PILs’ anionic part (lactate and glycolate-based PILs) impaired PILs-lignin interactions, and consequently, increased the partition coefficient, compared to propionate and acetate-based PILs. Finally, the increase in the PILs’ cationic part leads to the improvement in PILs-lignin interactions, and lower partition coefficient values were observed, following the sequence for lactate-based PILs: tris(2-hydroxyethyl)ammonium < bis(2-hydroxyethyl)ammonium < 2-hydroxyethylammonium; and the following sequence for propionate-based PILs: tris(2-hydroxyethyl)ammonium ≈ bis(2-hydroxyethyl)ammonium < 2-hydroxyethylammonium. The glycolate-based PIL showed the highest partition coefficient value, which is related to its small alkyl chain length and the presence of an extra hydroxyl group, making PIL-lignin interactions weaker. The results showed that acetone emerges as a phase-forming agent to remove, at least partially, the lignin dissolved in PILs aqueous solutions, allowing their recycle and reuse after the pretreatment step, for example. Finally, the NRTL activity coefficient model was used to correlate tie-line compositions, and the interaction parameters were estimated for each system determined.

Phase behavior for 1-butyl-3-methylimidazolium tetrafluoroborate with sodium oxalate/succinate/formate aqueous two-phase systems at 298.15 and 308.15 K

The liquid––liquid equilibrium (LLE) data and phase composition of the aqueous 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) + sodium oxalate (Na2C2O4), [Bmim]BF4 + sodium succinate (Na2C4H4O4) and [Bmim]BF4 + sodium formate (NaHCOO) mixtures have been measured at 298.15 and 308.15 K. The effect of salts and temperature on binodal curves were studied in this work and a significant relationship has been observed between the salting-out ability and the Gibbs energy of hydration of the ions. The binodal data obtained were correlated by the Pirdashti and Merchuk equations and the tie-line compositions were well-fitted by the Othmer-Tobias and Bancroft equations and the experimental tie-line data were well correlated with extended UNIQUAC model. Additionally, the effective excluded volume values were also determined to analyze the salting-out abilities of the three salts which follow the order of Na2C2O4 > Na2C4H4O4 > NaHCOO.

Liquid–Liquid Equilibrium of Imidazolium Ionic Liquids + Phosphate + Water Aqueous Two-Phase Systems and Correlation

Binodal curves of the aqueous 1-butyl-3-methylimidazolium tetrafluoroborate([C4mim]BF4) + kosmotropic salt (Na3PO4,(NH4)3PO4) + water aqueous two-phase systems were determined experimentally at 288.15, 298.15, 308.15 and 318.15 K. Three empirical equations were used to correlate the binodal data. All three empirical equations reproduce the data with a high degree of precision. The effect of temperature on the binodal curves was studied. Corresponding to two different salts, the two-phase area decreases with increasing temperature. From the binodal model for these systems, the effective excluded volumes (EEV) were obtained. The binodal curves and EEV both indicate that the salting-out abilities are in the order: Na3PO4 > (NH4)3PO4. And, the reliability of the tie-line compositions was proved by the empirical correlation with the Othmer–Tobias and Bancroft equations. The results show that the salting-out strength is greater at lower temperatures. Additionally, a relatively simple two-parameter equation was used for the correlation of the tie-line data.

Measurements and thermodynamic modelling of liquid–liquid equilibrium of PEG 6000–phosphate affinity aqueous two-phase systems at various ligand concentrations and pH

ABSTRACT The equilibrium behaviours of affinity two-phase liquid−liquid systems composed of polyethylene glycol (PEG) 6000 + phosphate salt + water were experimentally investigated at various pH values (4.5, 6, 7.5 and 8.4) and phosphate ligand mass fractions (PEG–PO4) (0%, 25%, 50%, 75%, 100%). The binodal curves were fitted to an empirical equation and the coefficients for the different pH and ligand concentration were estimated. The experimental tie-line compositions were estimated and correlated using the Othmer–Tobias and Bancroft equations, and the parameters were evaluated. The effects of the medium pH and the ligand amount on the phase behaviour were studied. It is found that the pH increasing and ligand concentration decreasing cause an expansion of the biphasic region. The liquid–liquid equilibrium experimental data obtained were well correlated to the activity coefficients of the non-random two-liquid (NRTL) model, and the mean deviations less than 0.68% between experimental and calculated mass fractions show that the NRTL activity model has a good ability to correlate the equilibrium compositions of the present system.