On the influence of some inorganic salts on the partitioning of citric acid between water and organic solutions of tri-n-octylamine: Part I: Methyl isobutyl ketone as organic solvent

Reactive extraction is a commonly applied process to recover carboxylic acids from aqueous solutions. Such processes are nowadays designed using process simulation software. However, the essential prerequisite for such a simulation is the availability of a reliable thermodynamic model for the encountered phase equilibrium. Industrial experience revealed that even very small amounts of a strong electrolyte (e.g., sodium chloride) can considerably reduce the amount of carboxylic acid extracted from the aqueous into the organic phase. This contribution presents new experimental results for the influence of sodium nitrate, sodium chloride, sodium sulfate, sodium citrate and hydrochloric acid on the partitioning of citric acid to the coexisting aqueous/organic liquid phases of the system water + methyl isobutyl ketone (organic solvent) + tri-n-octylamine (chemical extractant) at 25 °C. A detailed discussion of the experimental results reveals that the dramatic decrease of the partition coefficient of carboxylic acid is caused by the chemical loading of the extractant by the inorganic acid, i.e. both acids (the weak carboxylic acid as well as the strong inorganic acid) compete for the sodium ions (in the aqueous phase) and for the amine (in the organic phase). In phase equilibrium the amine is predominantly loaded with the inorganic acid while the sodium salt of the carboxylic acid remains in the aqueous phase. That behavior is described by a thermodynamic framework that is able to predict the complex liquid–liquid equilibrium from information determined exclusively from investigations on subsystems.     

On the influence of some strong electrolytes on the partitioning of acetic acid to aqueous/organic two-phase systems in the presence of tri-n-octylamine: Part II: Toluene as organic solvent

Water-insoluble amines (dissolved in an organic solvent/organic solvent mixture) are often used for the extractive recovery of carboxylic acids from aqueous phases. The basic design of the extraction process requires a thermodynamic framework that should be able to describe the liquid–liquid phase equilibrium not only in the phase forming systems (water + carboxylic acid + organic solvent + reactive extractant), but also when the aqueous feed phase contains additionally small amounts of strong electrolytes. Even small amounts of strong electrolytes might considerably reduce the recovery rate. In part I of this series such a model was presented and discussed for methyl isobutyl ketone as organic solvent and tri-n-octylamine (TnOA) as the chemical extractant. The present part II is to demonstrate that the procedures/methods described for methyl isobutyl ketone as organic solvent can be applied also for other organic solvents. By way of example, here toluene is that organic solvent. New experimental results are reported for the influence of sodium chloride, sodium nitrate, sodium sulfate, sodium acetate and hydrochloric acid on the partitioning of acetic acid to coexisting aqueous/organic liquid phases of the system (water + toluene + tri-n-octylamine) at 25 °C. An extension/adaptation of the previously published thermodynamic framework is successfully applied to describe/predict the new experimental liquid–liquid phase equilibrium data.     

Phase equilibria for liquid mixtures of (benzonitrile + a carboxylic acid + water) atT = 298.15 K

(Liquid  +  liquid) equilibrium data are presented for mixtures of {benzonitrile(1)  +  acetic acid or propanoic acid or butanoic acid or 2-methylpropanoic acid or pentanoic acid or 3-methylbutanoic acid(2)  +  water(3)} atT =  298.15 K. The relative mutual solubility of each of the carboxylic acids is higher in the benzonitrile layer than in the aqueous layer. The influence of 3-methylbutanoic acid, pentanoic acid, 2-methylpropanoic acid, and butanoic acid on the solubility of the hydrocarbons in benzonitrile is greater than that of the acetic and propanoic acids. Three three-parameter equations have been fitted to the binodal curve data. These equations are compared and discussed in terms of statistical consistency. The NRTL and UNIQUAC models were used to correlate the experimental tie lines and to calculate the phase compositions of the ternary systems. The NRTL equation fitted the experimental data far better than the UNIQUAC equation. Selectivity values for solvent separation efficiency were derived from the tie line data.     

Phase equilibrium in systems with ionic liquids: An example for the downstream process of the Biphasic Acid Scavenging utilizing Ionic Liquids (BASIL) process. Part I: Experimental data

Experimental results are presented for the (liquid + liquid), (solid + liquid) and (solid + liquid + liquid) equilibria occurring in the downstream process of a typical example for the Biphasic Acid Scavenging Utilizing Ionic Liquids (BASIL)-processes. In a BASIL process an organic base is used to catalyze a chemical reaction and, at the same time, to scavenge an acid that is an undesired side product of that reaction. The particular example of a BASIL process treated here is the reaction of 1-butanol and acetylchloride to butylacetate and hydrochloric acid, where the acid is scavenged by the organic base 1-methyl imidazole (1-MIM) resulting in the ionic liquid 1-methyl imidazolium chloride. The reaction results in a two-phase system as butylacetate and the ionic liquid reveal a large liquid–liquid miscibility gap. The organic base has to be recovered. This is commonly achieved by treating the ionic liquid–rich liquid phase with an aqueous solution of sodium hydroxide (i.e., converting the ionic liquid to the organic base) and extracting the organic base by an appropriate organic solvent (e.g., 1-propanol). The work presented here deals in experimental work with the (liquid + liquid), (solid + liquid) and (solid + liquid + liquid) phase equilibria that are encountered in such extraction processes. Experimental results are reported for temperatures between about 298 K and 333 K: for the solubility of NaCl in several solvents (1-propanol, 1-MIM), (water + 1-MIM), (1-propanol + 1-MIM), (water + 1-propanol), and (water + 1-propanol + 1-MIM) and for the (liquid + liquid) equilibrium as well as for the (solid + liquid + liquid) equilibrium of the ternary system (NaCl + water + 1-propanol) and of the quaternary system (NaCl + water + 1-propanol + 1-MIM).     

Solubility of fragrance raw materials in water: Experimental study,correlations, and Mod. UNIFAC (Do) predictions

The (liquid + liquid) and (solid + liquid) phase equilibria of nine binary mixtures containing fragrance raw materials (FRM) such as aliphatic ketones and compounds based on cyclohexane with water were investigated. The systems {2-heptanone, or 2-nonanone, or 2-undecanone, or 2-tridecanone, or cyclohexyl carboxylic acid (CCA), or cyclohexyl acetic acid (CAA), or 2-cyclohexyl ethanol (2CE) or cyclohexyl acetate (CA), or 2-cyclohexyl ethyl acetate (2CEA) + water (2)} have been measured by a dynamic method in wide range of temperatures from (290 to 360) K and ambient pressure. For all systems immiscibility in the liquid phase was detected. The experimental data was correlated by means of the NRTL equation, utilizing parameters derived from the (liquid + liquid) equilibrium. Additionally, the binary mixtures were predicted with the Mod. UNIFAC (Do) model, with known from literature parameters, with very good results.     

The impact of uni-univalent electrolytes on (water + acetic acid + toluene) equilibria: Representation with electrolyte-NRTL model

The presence of salts can significantly alter the (liquid + liquid) equilibrium and extraction process. In this work, a study was conducted on the (liquid + liquid) equilibria of (water + acetic acid + toluene + sodium chloride or potassium chloride) at temperatures (288.2, 298.2 and 313.2) K. This chemical system, irrespective of salt, is frequently used in (liquid + liquid) extraction investigations. The selected salt concentrations in initial aqueous solutions were (0.9 and 1.7) mol · L⁻¹. The results show that salting-out effect of the salts was significant, so that an enhancement in the acetic acid distribution coefficient was achieved within (15.6 to 66.8)% with NaCl and within (2.5 to 37.6)% with KCl. Meantime, high separation factors were found at low temperatures and low solute concentrations. The electrolyte-NRTL model was satisfactorily used to correlate the phase equilibria. In this regard for each salt, the temperature dependent binary interaction parameters between components were calculated. The predicted tie-line mole fractions give root-mean square deviation (RMSD) values of only 0.0038 and 0.0045 for the systems containing NaCl and KCl, respectively.     

Nonelectrolyte NRTL-NRF model to study thermodynamics of strong and weak electrolyte solutions

An electrolyte activity coefficient model is proposed by combining non-electrolyte NRTL-NRF local composition model and Pitzer–Debye–Hückel equation as short-range and long-range contributions, respectively. With two adjustable parameters per each electrolyte, the present model is applied to correlation of the mean activity coefficients of more than 150 strong aqueous electrolyte solutions at 298.15 K. Also the results of the present model are compared with the other local composition models such as electrolyte-NRTL, electrolyte-NRTL-NRF and electrolyte-Wilson-NRF models. Moreover, the present model is used for prediction of the osmotic coefficient of several aqueous binary electrolytes systems at 298.15 K. Also the present activity coefficient model is adopted for representation of nonideality of the acid gases, as weak gas electrolytes, soluble in alkanolamine solutions. The model is applied for calculation of solubility and heat of absorption (enthalpy of solution) of acid gas in the two {(H₂O + MDEA + CO₂) and (H₂O + MDEA + H₂S)} systems at different conditions. The results demonstrate that the present model can be successfully applied to study thermodynamic properties of both strong and weak electrolyte solutions.     

(Liquid + liquid) equilibria in ternary aqueous mixtures of phosphoric acid with organic solvents at T = 298.2 K

(Liquid + liquid) equilibrium (LLE) data for the ternary mixtures of {water (1) + phosphoric acid (2) + organic solvents (3)} were determined at T = 298.2 K and atmospheric pressure. The organic solvents were cyclohexane, 2-methyl-2-butanol (tert-amyl alcohol), and isobutyl acetate. All the investigated systems exhibit Type-1 behaviour of LLE. The immiscibility region was found to be larger for the (water + phosphoric acid + cyclohexane) ternary system. The experimental LLE results were correlated with the NRTL model, and the binary interaction parameters were obtained. The reliability of the experimental tie-line results was tested through the Othmer–Tobias and Bachman correlation equations. Distribution coefficients and separation factors were evaluated over the immiscibility regions and a comparison of the extracting capabilities of the solvents was made with respect to these factors. The experimental results indicate the superiority of cyclohexane as the preferred solvent for the extraction of phosphoric acid from its aqueous solutions.     

Solubility of sodium 4-nitrotoluene-2-sulfonate in (propanol + water) and (ethylene glycol + water) systems

The solubility data of sodium 4-nitrotoluene-2-sulfonate (NTSNa) in aqueous organic solutions (propanol + water) and (ethylene glycol + water) were measured at temperatures ranging from (290 to 351) K using a dynamic method. The mole fraction of water in solvent mixtures ranged from 0 to 0.8. The solubility values are correlated with the electrolyte non-random two-liquid (E-NRTL) model. From the results obtained, the E-NRTL model provides a satisfactory mathematical representation of the experimental results for the (NTSNa + propanol + water) system and an unsatisfactory result for the (NTSNa + ethylene glycol + water) system. Thus, the modified Apelblat model is applied to describe the (NTSNa + ethylene glycol + water) system also. The calculated (solid + liquid) equilibrium temperatures with the modified Apelblat model are in good agreement with the experimental results. The root-mean-square deviations of solubility temperature varied from (0.08 to 0.94) K for two models. The effect of different aqueous organic solutions on the reaction of oxidation 4-nitrotoluene-2-sulfonic acid (NTS) to 4,4′-dinitrostilbene-2,2′-disulfonic acid (DNS) was discussed.     

Solubility of perfumery and fragrance raw materials based on cyclohexane in 1-octanol under ambient and high pressures up to 900 MPa

The (solid + liquid) phase equilibria (SLE) of binary mixtures containing 1-octanol and fragrance raw materials based on cyclohexane were investigated. The systems {1-octanol (1) + cyclohexyl carboxylic acid (CCA), or cyclohexyl acetic acid (CAA), or cyclohexyl acetate (CA), or 2-cyclohexyl ethyl acetate (2CEA), or 2-cyclohexyl ethanol (2CE)(2)} have been measured by a dynamic method in wide range of temperatures from (220 to 320) K and ambient pressure. For all systems SLE diagrams were detected as eutectic mixtures with complete miscibility in the liquid phase. The experimental data were correlated by means of the Wilson and NRTL equations, utilizing parameters derived from the (solid + liquid) equilibrium. The root-mean-square deviations of the solubility temperatures for all calculated data are dependent upon the particular system and the particular equation used.Additionally, the SLE in binary mixture that contain {1-octanol (1) + CCA (2)} has been measured under very high pressures up to about 900 MPa at the temperature range from T = (303.15 to 353.15) K. The thermostatted apparatus for the measurements of transition pressures from the (liquid + solid) state was used. The freezing and melting temperatures at a constant composition increase monotonously with pressure. The high pressure experimental results obtained at isothermal conditions (p–x) were interpolated to more convenient T–x diagram. Data of the (pressure + temperature) composition relation at the high pressure (solid + liquid) phase equilibria was correlated by the polynomial based on the Yang model.The basic thermodynamic properties of pure substances viz. the melting point, enthalpy of fusion, enthalpy of solid–solid phase transition, and glass transition, have been determined by the differential scanning calorimetry (DSC).     

Experimental observations on the competing effect of tetrahydrofuran and an electrolyte and the strength of hydrate inhibition among metal halides in mixed CO2 hydrate equilibria

In the present work, experimental data on the equilibrium conditions of mixed CO₂ and THF hydrates in aqueous electrolyte solutions are reported. Seven different electrolytes (metal halides) were used in this work namely sodium chloride (NaCl), calcium chloride (CaCl₂), magnesium chloride (MgCl₂), potassium bromide (KBr), sodium fluoride (NaF), potassium chloride (KCl), and sodium bromide (NaBr). All equilibrium data were measured by using Cailletet apparatus. Throughout this work, the overall concentration of CO₂ and THF were kept constant at (0.04 and 0.05) mol fraction, respectively, while the concentration of electrolytes were varied. The experimental temperature ranged from (275 to 305) K and pressure up 7.10 MPa had been applied. From the experimental results, it is concluded that THF, which is soluble in water is able to suppress the salt inhibiting effect in the range studied. In all quaternary systems studied, a four-phase hydrate equilibrium line was observed where hydrate (H), liquid water (L_W), liquid organic (L_V), and vapour (V) exist simultaneously at specific pressure and temperature. The formation of this four-phase equilibrium line is mainly due to a liquid–liquid phase split of (water + THF) mixture when pressurized with CO₂ and the split is enhanced by the salting-out effect of the electrolytes in the quaternary system. The strength of hydrate inhibition effect among the electrolytes was compared. The results shows the hydrate inhibiting effect of the metal halides is increasing in the order NaF < KBr < NaCl < NaBr < CaCl₂ < MgCl₂. Among the cations studied, the strength of hydrate inhibition increases in the following order: K⁺ < Na⁺ < Ca²⁺ < Mg²⁺. Meanwhile, the strength of hydrate inhibition among the halogen anion studied decreases in the following order: Br^? > Cl^? > F^?. Based on the results, it is suggested that the probability of formation and the strength of ionic–hydrogen bond between an ion and water molecule and the effects of this bond on the ambient water network are the major factors that contribute to hydrate inhibition by electrolytes.     

The buffering-out effect and phase separation in aqueous solutions of EPPS buffer with 1-propanol, 2-propanol,or 2-methyl-2-propanol at T = 298.15 K

Buffering-out is a new liquid–liquid phase separation phenomenon observed in mixtures containing a buffer as a mass separating agent. The (liquid + liquid) equilibrium (LLE) and (solid + liquid + liquid) equilibrium (SLLE) data were measured for the ternary systems {3-[4-(2-hydroxyethyl)piperazin-1-yl]propanesulfonic acid (EPPS) buffer + 1-propanol, 2-propanol, or 2-methyl-2-propanol + water} at T = 298.15 K under atmospheric pressure. The phase boundary data were fitted to an empirical equation relating to the concentrations of organic solvent and buffer. The effective excluded volume (EEV) values of EPPS were obtained from the phase boundary data. The phase-separation abilities of the investigated aliphatic alcohols were discussed. The reliability of the experimental tie-lines was satisfactorily confirmed by the Othmer–Tobias correlation. The experimental tie-lines data for the ternary systems have been correlated using the NRTL activity coefficient model. The separation of these aliphatic alcohols from their azeotropic aqueous mixtures is of particular interest to industrial process. The addition of the EPPS as an auxiliary agent breaks the (1-propanol + water) and (2-methyl-2-propanol + water) azeotropes. The possibility of using the new phase separation systems in the extraction process is demonstrated by using different dyestuffs.     

Thermodynamic evaluation and optimization of the (Ca + C + O + S) system

A critical evaluation of all available thermodynamic and (solid + liquid) phase equilibrium data for the (Ca + C + O + S) system has been performed. The liquid phase was modelled using the Modified Quasichemical Model in the pair approximation. The present database reproduces the (solid + liquid) equilibria of the experimentally studied subsystems of the (Ca + C + O + S) system within the experimental error limits. Estimations of the phase equilibria of systems lacking experimental data were made. The database of thermodynamic data for all phases can be used, along with other databases and Gibbs free energy minimization software, to calculate the phase equilibria and all thermodynamic properties of (Ca + C + O + S) mixtures, which are of great importance for several industrially relevant processes.     

Molecular dynamics simulation of surfactant effects on ion transport through a liquid–liquid interface between partially miscible liquids

Molecular dynamics (MD) simulations of water + 1-hexanol + NaCl mixtures with and without a surfactant (methanol) were performed to analyze the surfactant's effect on the transport of a sodium ion through the liquid–liquid interface. Without surfactant, the 1-hexanol forms a bilayer at the interface with OH groups directed outward toward the aqueous phase. Addition of the surfactant produces higher concentrations of the surfactant on the aqueous side of the interface without altering the organic bilayer structure. An electrical double-layer is created in both cases as chloride ion concentration is enhanced near the interface and sodium ion concentration is enhanced toward the center of the water phase. A potential of mean force (PMF) was calculated for the transfer of a sodium ion through the interface. Although the surfactant reduced the interfacial tension, the total work required for the ion transfer increased with the addition of the surfactant.     

Cation effect on the (PEG 8000 + sodium sulfate) and (PEG 8000 + magnesium sulfate) aqueous two-phase system: Relative hydrophobicity of the equilibrium phases

The partitioning of four dinitrophenylated (DNP-) amino acids in aqueous two-phase systems of (polyethylene glycol (PEG)-8000 + sodium sulfate) and (polyethylene glycol (PEG)-8000 + magnesium sulfate) in five different tie-lines was experimentally determined at T = 298.15 K. The Gibbs energy of transfer of a methylene group between the two phases was calculated from the measured partition coefficients. This characterizes the relative hydrophobicity of the equilibrium phases. Values of ΔG¹(CH₂) were in range from (−0.674 to −1.012) kJ · mol⁻¹. A comparison of both systems was carried out. The results show that the cation type has a strong influence on the amino acids partitioning process. The largest relative hydrophobicity was noted for the ATPS system formed by sodium sulfate. This showed to be a better system for the separation.     

Application of hollow fiber liquid phase microextraction for pinic acid and pinonic acid analysis from organic aerosols

A method based on hollow fiber liquid phase microextraction (HF-LPME) for analysis of pinic acid and pinonic acid was developed and for the first time successfully applied to ambient aerosol samples. In this method, the aerosol samples were dissolved in 0.05 M H₂SO₄ and the solution was extracted using three-phase HF-LPME where donor phase was 0.1 M (NH₄)₂CO₃. Different parameters like type of organic solvent for membrane phase, extraction time and stirring speed etc. were optimized. Optimum extraction time was 4.5 h and optimum-stirring speed was found to be 900 rpm. We used 6-undecanone as organic phase along with tri-n-octylphosphine oxide (optimum TOPO contents was 15% w/v), which gave an enormous enrichment for both pinic and pinonic acid. Enrichment factors of 28,050 and 27,400 times were obtained for pinonic acid and pinic acid, respectively, that are the highest ever published. The extraction efficiency for pinic acid and pinonic acid were 68.5% and 70.1%, respectively. Very low limits of detection were obtained. Values of 1.0 ng L^?1 and 0.5 ng L^?1 in aqueous solutions, corresponding to 24 pg m^?3 and 12 pg m^?3 in aerosol samples were the limits of detections for pinonic acid and pinic acid, respectively. Both pinonic acid and pinic acid were found in all aerosol samples analyzed.     

Carboxylic and sulfonic N-substituted naphthalene diimide salts as highly stable non-polymeric organic electrodes for lithium batteries

Two N-substituted naphthalene tetracarboxylic diimide (NTCDI) ionic compounds, carboxylic and sulfonic sodium salts, were prepared and used as positive electrode active materials in lithium-half cells. The aim of this investigation was to assess the solubility-suppressing effect of two different negatively charged substituent groups on a redox-active organic backbone using a carbonate-based liquid electrolyte. NTCDI derivatives were obtained in high yields from reaction of naphthalene tetracarboxylic dianhydride with neutralized glycine or with neutralized taurine. They were mixed with carbon black and cycled in galvanostatic mode against lithium metal using 1 M LiPF₆ EC/DMC liquid electrolyte. These two NTCDI derivatives exhibit a quite stable electrochemical activity upon cycling at an average potential of 2.3 V vs. Li⁺/Li⁰ giving rise to specific capacity values of 147 mAh·g^− 1 and 113 mAh·g^− 1 for the dicarboxylate and the disulfonate derivative, respectively. This study clearly supports the useful effect of such grafted permanent charges as a general rule on the electrochemical stability of crystallized organic materials based on the assembly of small redox-active units.     

Thermodynamic optimization of the (Na2O + SiO2 + NaF + SiF4) reciprocal system using the Modified Quasichemical Model in the Quadruplet Approximation

All available thermodynamic and phase diagram data for the condensed phases of the ternary reciprocal system (NaF + SiF₄ + Na₂O + SiO₂) have been critically assessed. Model parameters for the unary (SiF₄), the binary systems and the ternary reciprocal system have been found, which permit to reproduce the most reliable experimental data. The Modified Quasichemical Model in the Quadruplet Approximation was used for the oxyfluoride liquid solution, which exhibits strong first-nearest-neighbor and second-nearest-neighbor short-range ordering. This thermodynamic model takes into account both types of short-range ordering as well as the coupling between them. Model parameters have been estimated for the hypothetical high-temperature liquid SiF₄.     

(Liquid + liquid), (solid + liquid), and (solid + liquid + liquid) equilibria of systems containing cyclic ether (tetrahydrofuran or 1,3-dioxolane), water,and a biological buffer MOPS

Two liquid phases were formed as the addition of a certain amount of biological buffer 3-(N-morpholino)propane sulfonic acid (MOPS) in the aqueous solutions of tetrahydrofuran (THF) or 1,3-dioxolane. To evaluate the feasibility of recovering the cyclic ethers from their aqueous solutions with the aid of MOPS, we determined experimentally the phase diagrams of the ternary systems of {cyclic ether (THF or 1,3-dioxolane) + water + MOPS} at T = 298.15 K under atmospheric pressure. In this study, the solubility data of MOPS in water and in the mixed solvents of water/cyclic ethers were obtained from the results of a series of density measurements, while the (liquid + liquid) and the (solid + liquid + liquid) phase boundaries were determined by visually inspection. Additionally, the tie-line results for (liquid + liquid) equilibrium (LLE) and for (solid + liquid + liquid) equilibrium (SLLE) were measured using an analytical method. The reliability of the experimental LLE tie-line results data was validated by using the Othmer–Tobias correlation. These LLE tie-line values were correlated well with the NRTL model. The phase diagrams obtained from this study reveal that MOPS is a feasible green auxiliary agent to recover the cyclic ethers from their aqueous solutions, especially for 1,3-dioxolane.