Liquid Equilibrium Research Articles

Isobaric Vapor–Liquid Equilibrium of the Binary Mixtures Toluene + Styrene and Styrene + α-Methylstyrene

Isobaric vapor–liquid equilibria of the binary mixtures toluene + styrene at 30 and 40 kPa and styrene + α-methylstyrene at 20 and 25 kPa were measured applying a recirculation still. The measured vapor–liquid equilibrium data were modeled adopting the non-random two-liquid (NRTL) excess Gibbs energy model with the RK (Redlich–Kwong) equation of state. The NRTL binary interaction parameter optimization was carried out employing own measured data and literature data for the toluene + styrene system. The applied model correlates well with the experimental data at the pressure range of 101–30 kPa. Moreover, the NRTL binary parameter regression was performed applying own measured data and literature data separately for the styrene + α-methylstyrene system. The model fitted with the parameters obtained from own measured data described the multiphase behavior of the system better than the parameters obtained from literature data. Additionally, the binary systems showed ideal behavior over the whole range of investigation as the calculated activity coefficients approached unity and no azeotropes were observed.

Determination and Correlation of Vapor–Liquid Equilibria for the Nitric Acid + Water, Nitric Acid + Water + Phosphoric Acid, and Nitric Acid + Water + Phosphoric Acid + Sulfuric Acid System

The wet-process production of phosphoric acid by the nitric acid method is considered as a promising technology with great development prospects due to no production of the byproduct phosphogypsum. However, the traditional nitro-phosphate fertilizer producing process cannot separate nitrogen and phosphorus thoroughly, which limits its applications. The key to solving this problem is to remove nitric acid from the crude phosphoric acid product obtained in the nitric acid wet process by evaporation. Therefore, it is important to measure the vapor–liquid equilibrium (VLE) data of the nitric acid + water + phosphoric acid + sulfuric acid quaternary system under different pressures and concentrations. In this study, the VLE data of the following systems were measured at 10, 20, 40, 60, 80, and 97.4 kPa by the quasi-static ebulliometric method: (1) nitric acid + water; (2) nitric acid + water + phosphoric acid; and (3) nitric acid + water + phosphoric acid + sulfuric acid. The electrolyte non-random two-liquid parameters for the following pairs were correlated with the VLE data by using Aspen Plus as a tool: HNO3-H2O, H3PO4-H2O, HNO3-H3PO4, HNO3-H2SO4, H3PO4-H2SO4, H+[H2PO4]−-H+[NO3]−, H+[NO3]−-H+[HSO4]−, and H+[H2PO4]−-H+[HSO4]−. The obtained VLE data and interaction parameters can provide the basis for the nitric acid method of mother liquor denitrification in the subsequent industry.

The Effect of Sulfate Electrolytes on the Liquid–Liquid Equilibrium of 2-MTHF/Water/5-HMF: Experimental Study and Thermodynamic Modeling

We investigate the influence of sulfate salts and sulfuric acid on the equilibrium behavior of 2-methyltetrahydrofuran (2-MTHF)/H2O/5-hydroxymethylfurfural (5-HMF). Liquid–liquid equilibrium measurements are performed at atmospheric pressure and in a temperature range of T = (293–333) K. The compositions of the aqueous and organic phases, together with the dissociation state of the sulfate species, are determined with infrared spectroscopy and Indirect Hard Modeling. We show that the addition of the salts Na2SO4 and Li2SO4 results in salting out of 2-MTHF and 5-HMF from the aqueous phase. With increasing temperature, this effect gets less pronounced. In contrast, the addition of H2SO4 does not result in any salting-out behavior. The investigation of the dissociation states shows that H2SO4 dissociates to HSO4– while Na2SO4 and Li2SO4 dissociate completely to SO42–. Parameter regression is performed to model the liquid–liquid equilibrium with the electrolyte perturbed-chain statistical associating fluid theory (ePC-SAFT) equation of state. For the analyzed salts, Na2SO4 and Li2SO4, the performed parameter regression accurately predicts the measurement results. Still, we observe slight deviations between measured values and modeling when predicting the liquid–liquid equilibrium and the liquid density in the presence of sulfuric acid.

Separation of n-hexane-ethanol azeotropic mixture using choline chloride +1,4-butanediol deep eutectic solvents

For an environmentally friendly and economical separation process of ethanol from n-hexane which is hard to handle due to the azeotrope, the liquid-liquid extraction was carried out by using choline chloride (ChCl) based deep eutectic solvents (DESs) in different molar ratios with 1,4-butanediol: DES1 (ChCl:1,4-butanediol=1:3), DES2 (ChCl:1,4-butanediol=1:4), and DES3 (ChCl:1,4-butanediol=1:5). The liquid-liquid phase equilibrium was performed on the n-Hexane (1) + Ethanol (2) + DES (3) systems at 298.15 K and atmospheric pressure. The binodal curve is determined by using the turbidity method. The various physico-chemical properties such as refractive index, viscosity, and density were measured for compositions in the binodal point. The equilibrium compositions of liquid-liquid phase equilibrium were determined from the refractive index value at the binodal points, and were predicted by COSMO-SAC model. The miscibility area predicted by COSMO-SAC model became larger as the molar ratio of 1,4-butanediol in DES increased, that is, DES3 shows the most miscible area. While in the experimental results, the miscibility depending on DES-type does not show a large difference. The experimental values for PI shows the order of DES2 (ChCl:1,4-butanediol=1:4)> DES1 (ChCl:1,4-butanediol=1:3)> DES3 (ChCl:1,4-butanediol=1:5) at less 3 wt% concentration of ethanol, but at higher concentration range (>3 wt%) DES3 shows the best value. Both of DES2 and DES3 are profitable to adopt in the extraction process of ethanol from n-hexane owing to the high performance index, high distribution coefficient, and high selectivity. The experimental results show the possibility of DESs as an alternative to ionic liquids in the separation of azeotropic mixtures, taking into account the properties of DES such as low price, uncomplicated manufacturing methods, environmentally friendly, and low toxicity.

Liquid–Liquid Equilibrium for Ternary Systems 2,2,2-Trifluoroethanol + Water + (Ethyl Acetate/Isopropyl Acetate/Isobutyl Acetate) at 308.15 K under 101.3 kPa

2,2,2-Trifluoroethanol (C2H3F3O, TFE) is a useful fluorine-containing alcohol. During the synthesis and application of TFE, TFE, and water can form an azeotropic mixture. To recover TFE from the mixture of TFE and water by liquid–liquid extraction (LLET), in the current work, three organic solvents, isobutyl acetate (C6H12O2), isopropyl acetate (C5H10O2), and ethyl acetate (C4H8O2), were chosen as the extractants. The liquid–liquid equilibrium (LLE) behavior for the three mixtures (water + TFE + ethyl acetate/isopropyl acetate/isobutyl acetate) was investigated at 101.3 kPa and 308.15 K. Selectivity (S) and distribution constant (D) were calculated as indexes to evaluate the extraction capacity of the three extractants. The results indicated that isobutyl acetate has better extraction ability in extracting TFE from its aqueous solution of TFE compared to the esters. The NRTL model was used to regress the determined tie-line data. The coherence of the fitted parameters of the NRTL model with the experimental data was checked by topological analysis.

Simultaneous Predictions of Chemical and Phase Equilibria in Systems with an Esterification Reaction Using PC-SAFT

The study of chemical reactions in multiple liquid phase systems is becoming more and more relevant in industry and academia. The ability to predict combined chemical and phase equilibria is interesting from a scientific point of view but is also crucial to design innovative separation processes. In this work, an algorithm to perform the combined chemical and liquid-liquid phase equilibrium calculation was implemented in the PC-SAFT framework in order to predict the thermodynamic equilibrium behavior of two multicomponent esterification systems. Esterification reactions involve hydrophobic reacting agents and water, which might cause liquid-liquid phase separation along the reaction coordinate, especially if long-chain alcoholic reactants are used. As test systems, the two quaternary esterification systems starting from the reactants acetic acid + 1-pentanol and from the reactants acetic acid + 1-hexanol were chosen. It is known that both quaternary systems exhibit composition regions of overlapped chemical and liquid-liquid equilibrium. To the best of our knowledge, this is the first time that PC-SAFT was used to calculate simultaneous chemical and liquid-liquid equilibria. All the binary subsystems were studied prior to evaluating the predictive capability of PC-SAFT toward the simultaneous chemical equilibria and phase equilibria. Overall, PC-SAFT proved its excellent capabilities toward predicting chemical equilibrium composition in the homogeneous composition range of the investigated systems as well as liquid-liquid phase behavior. This study highlights the potential of a physical sound model to perform thermodynamic-based modeling of chemical reacting systems undergoing liquid-liquid phase separation.

Solubility, Correlation, Dissolution Properties, and Molecular Simulations of an Explosive Intermediate in Twelve Pure Solvents

The solubility and thermodynamic properties of N-nitropyrazole (N-NP) in different pure solvents are crucial for crystallization, purification, and further theoretical research. The solid–liquid equilibrium solubility of N-NP in the range of 293.15–323.15 K was determined in 12 pure solvents of water, mesitylene, n-hexane, cyclohexane, ethanol, chlorobenzene, benzonitrile, propylene glycol, anisole, dimethyl sulfoxide, N,N-dimethylformamide, and o-dichlorobenzene by the laser dynamic method at an atmospheric pressure of 0.1 MPa. In the temperature range of 293.15–323.15 K, the solubility of N-NP in water, mesitylene, n-hexane, cyclohexane, ethanol, chlorobenzene, benzonitrile, propylene glycol, anisole, dimethyl sulfoxide, N,N-dimethylformamide, and o-dichlorobenzene displayed the mole fraction solubility of 0.001271–0.003540, 0.033858–0.139782, 0.001966–0.009268, 0.002621–0.013898, 0.013601–0.058669, 0.097849–0.310726, 0.170722–0.387823, 0.017647–0.065427, 0.069507–0.379656, 0.225911–0.457260, 0.210072–0.415353, and 0.017651–0.172345, respectively. The measured solubility data of N-NP had a good correlation with the modified Apelblat equation, the NRTL equation, the Wilson equation, as well as the λh equation. Through the comparison of the minor average of the root-mean-square deviation (103RMSD) and the coefficient of determination (R2), the Wilson equation yielded a more satisfactory correlation result. Thermodynamic parameters of mixing enthalpy (ΔmixH), mixing entropy (ΔmixS), and mixing Gibbs energy (ΔmixG) were calculated and analyzed based on the experimental data. The positive ΔmixH and ΔmixS implied that the dissolution process of N-NP in the selected solvents was endothermic and entropy-driven. The relative contributions of enthalpy and entropy demonstrated that enthalpy was the main contributor to the Gibbs free energy in the dissolution process. In addition, the solute–solvent interaction was calculated to elaborate the solubility of N-NP in selected solvents deeply. In addition, the solid–liquid surface tension and the surface entropy factor of N-NP were discussed on the basis of the experimental solubility data.

LLE, VLE and dynamic viscosity for the furfural + nonane mixture at low pressure: Measurements and modeling

This work reports new experimental data for the furfural + nonane mixture for the temperature range between 303.25 K and 441.55 K at low pressure. Vapor-liquid equilibria (VLE), liquid–liquid equilibria (LLE), and dynamic viscosity (µ) are reported and modeled under isobaric condition. Experimental data measurement is done using the same validated equipment applied in authors previous work. The expanded uncertainties for boiling temperature, viscosity- temperature, liquid–liquid temperature and dynamic viscosity are around 0.21 K, 0.12 K, 0.42 K and 0.0881 mPa∙s (0.95 level of confidence). After data is collected, phase equilibria are modeled using a modified Peng-Robinson equation of state coupled with the Huron Vidal and NRTL mixing rules. Also, dynamic viscosity is modeled using a generalized logistic function type in order to describe all the composition domains. The average absolute relative deviation using the models LLE, VLE, and viscosity is around of 0.01 %, 2.39 %, and 2.93 %. The results indicate that the new data can be modeled using the selected models.

Unveiling the thermodynamic and molecular mechanisms for the separation of diethoxymethane and ethanol azeotrope by deep eutectic solvents

The selection of efficient and environmental extractants is essential for the sustainable development of extraction processes. Based on the conductor-like screening model for the segment activity coefficient (COSMO-SAC), three deep eutectic solvents (DESs) were screened from 1000 DESs for the separation of diethoxymethane (DEM) and ethanol (EA). Subsequently, the liquid–liquid equilibrium behavior of the DEM + EA + DES system at different temperatures was measured. The results show that benzyltrimethylammonium chloride/glycerol (BTACl/GLY) has the highest selectivity and benzyltrimethylammonium chloride/ethylene glycol (BTACl/EG) and tetraethylammonium chloride/ethylene glycol (TEACl/EG) have similar extraction performance. More importantly, the extraction performance of DESs reported in this work is stronger than that of the solvents already reported. Additionally, analysis of the separation mechanism by various quantum chemical methods revealed that the purification of DEM and EA mixtures is mainly ascribed to the difference in electrostatic forces between the solvent and DEM/EA. The result confirmed that solvents with small molecular structures and strong nucleophilic sites are more competitive in separating the mixtures.

Absorption of ethylene dichloride with imidazolium-based ionic liquids

A series of imidazolium-based ionic liquids (ILs) with good thermal stability, consisting of [Bmim][BF4], [Bmim][OAc], [Bmim][SCN], [Bmim][DCA], [Emim][DCA], and [Hmim][DCA], were synthesized as absorbents for the absorption of ethylene dichloride (EDC). Among them, the ILs with the anion of [DCA]- possess the best absorption performance of EDC, and [Bmim][DCA] has the EDC absorption capacity of 0.3700 g EDC/g IL (313.15 K, atmospheric pressure) for the given inlet EDC concentration, higher than that of the other Bmim-based ILs. It was demonstrated that the absorption of EDC by [Bmim][DCA] is physical absorption, and the chemical structures of [Bmim][DCA] were consistent after five absorption–desorption cycles as well as no obvious decay in absorption capacity. It was demonstrated that anions of ILs play a more significant role in EDC absorption compared with cations through the analysis of interaction energy and weak interaction obtained by quantum chemical calculation, which also confirms the anions and cations act synergistically on EDC by H-bond and van der Waals (vdW) interaction. Besides, the vapor–liquid equilibrium (VLE) data for [Bmim][DCA]-EDC binary system with different compositions were determined at 303.15–353.15 K and compared with the predicted vapor pressure by the UNIFAC-Lei model. The predicted results show a good agreement with the experimental data, with an average relative deviation (ARD) of 3.98 %, indicating the reliability of the UNIFAC-Lei model.

Assessing the quality of SAFT equations for the vapor-liquid equilibrium of pure water

The family of eight representative (and most commonly used) SAFT equations of state for water and the cubic-plus-association equation are examined with respect to their ability to predict accurately the vapor–liquid equilibrium (VLE) of water. The problem originates from the fact that all these equations use only the experimental equilibrium liquid densities and pressures for the parameter evaluation. Consequently, when reproducing the VLE calculations once the parameters are evaluated, the equilibrium properties cannot be then determined accurately by the equations, in principle, because the computation involves also the omitted vapor density. In this contribution, the errors of the predicted equilibrium densities, orthobaric pressures, and related properties are determined and discussed. It turns out that even the properties used in the equations’ parametrizations (pressure and liquid density) are not always reproduced with acceptable accuracy, with average errors being around two percent and errors of the individual data points exceeding in many cases even ten percent. Properties not included in the parametrization are then predicted with larger average errors, in general.

Equilibrium solubility of 6-propyl-2-thiouracil in nine pure solvents: Determination, correlation, Hansen solubility parameter and thermodynamic properties

Investigation upon the solid–liquid equilibrium on solubility data of 6-propyl-2-thiouracil (PLT) in pure organic solvents is essential for separation and purifying in industry process. In this work, PLT solubility in nine neat solvents was experimentally determined at 278.15 K–323.15 K under P = 0.1 MPa. These selected solvents were tetrahydrofuran(THF), acetone, acetonitrile,1-butanol,1-pentanol, 2-butanol, methyl acetate, ethyl acetate,1-propyl acetate, respectively. Experiment results showed that solubility was consistent with temperature and decreased according to the order: THF > acetone>1-butanol≈1-pentanol> 2-butanol > methyl acetate > ethyl acetate>1-propyl acetate > acetonitrile. Solvent effect and Hansen solubility parameter (HSP) were incited to explain dissolution rule on solute. Four thermodynamic models (modified Apelblat model, Van't model, λh model and NRTL model) were adopted to correlate PLT solubility and provide good correlations on basis of RD, ARD and RMSD. In addition, thermodynamic properties (ΔH°, ΔS° and ΔG°) of PLT dissolution process in pure solvents were discussed and proved to be endothermic, entropically driven and non-spontaneous process.

Aromatic volatile organic compounds absorption with phenyl‐based deep eutectic solvents: A molecular thermodynamics and dynamics study

AbstractThe suitability of phenyl‐based deep eutectic solvents (DESs) as absorbents for toluene absorption was investigated by means of thermodynamic modeling and molecular dynamics (MD). The thermodynamic models perturbed‐chain statistical associating fluid theory (PC‐SAFT) and conductor‐like screening model for real solvents (COSMO‐RS) were used to predict the vapor–liquid equilibrium of DES–toluene systems. PC‐SAFT yielded quantitative results even without using any binary fitting parameters. Among the five DESs studied in this work, [TEBAC][PhOH] consisting of triethyl benzyl ammonium chloride (TEBAC) and phenol (PhOH), was considered as the most suitable absorbent. Systems with [TEBAC][PhOH] had lowest equilibrium pressures of the considered DES–toluene mixtures, the best thermodynamic characteristics (i.e., Henry's law constant, excess enthalpy, Gibbs free energy of solvation of toluene), and the highest self‐diffusion coefficient of toluene. The molecular‐level mechanism was explored by MD simulations, indicating that [TEBAC][PhOH] has the strongest interaction of DES–toluene compared to the other DESs under study. This work provides guidance to rationally design novel DESs for efficient aromatic volatile organic compounds absorption.

Group Contribution Based Graph Convolution Network: Predicting Vapor–Liquid Equilibrium with COSMO-SAC-ML

Group Contribution Based Graph Convolution Network: Predicting Vapor–Liquid Equilibrium with COSMO-SAC-ML

Solvent-catalyst optimization of ionic liquid-based CO2 conversion to propylene carbonate: Laboratory validation and techno-economic analysis

Ionic liquids (ILs) have been widely suggested as efficient catalysts to produce propylene carbonate (PC) from CO2 and propylene oxide (PO). Recently, the use of liquid-liquid extraction (LLE) has been proposed to efficiently separate ILs from PC since it reduces energy consumption, with fatty alcohols when selecting hydrophobic ILs. However, the study of this reaction-separation system at experimental level is scarce. In addition, the solvent-catalyst system design to improve the global process performance is a current challenge. This work develops an integrated experimental-computational multiscale approach to improve the PC production process by CO2 cycloaddition to PO using the IL [P66614][Br] as catalyst. Reaction yield and liquid-liquid equilibrium measurements were carried out for the experimental validation of the proposed catalytic/separation systems using different solvents (fatty alcohol and water). Process modelling and techno-economic analysis were performed using Aspen Plus for solvent-catalyst optimization, proceeding with an integrated iterative experimental-computational approach to decrease energy requirements and operating costs. It was found that the presence of solvents in the reaction affects conversion and selectivity of the reaction, with fatty alcohols increasing PC yield and enabling IL/PC separation, while water reduces PC selectivity. On the other hand, the presence of water in the process allows reducing electricity demands as well as vacuum requirements. It was possible to modulate fatty alcohol and water dosages to minimize energy consumption, vacuum requirements and utility costs. Optimal configurations have an energy consumption of approximately 0.6 kWh/kgPC and utility costs of 6.6 $/tPC.

Vacuum distillation and ab initio molecular dynamic simulation of Al–Li alloys

Al–Li alloys, which offer excellent properties, are widely used in aviation, high-speed railway and other fields. The amount of scrap produced will increase as the alloy content increases. Therefore, it is important to study the recovery of Al and Li from Al–Li alloys. In this study, the theories of saturated vapor pressure and vapor–liquid equilibrium composition are adopted to determine the possibility of separating Al from Li, and the results show that Al–Li alloys decomposition by vacuum distillation is feasible. In addition, it is determined that Li and Al can be recycled in the gas and liquid phases, respectively. The separation of Al-7.87 wt% Li alloy by vacuum distillation was studied. The results indicated that, at a pressure of 10 Pa, a distillation temperature of 1223 K, and a soaking time of 60 min, the volatilization and recovery rates of Li were 99.77 wt% and 80.65 wt%, respectively. The lithium content in the condensate was 99.72 wt%, while that of Al was 99.98 wt%. Using AIMD to analyze the Al-7.87 wt% Li alloy melt over a range of 700–1473 K, the simulation results were found to be consistent with the experimental results and thus could be applied to the planning of vacuum distillation.

Thermodynamic Properties of Solutions in the H2O–Na2SO4–Al2(SO4)3 System

The vapor pressure in the H2O–Na2SO4–Al2(SO4)3 system at 15, 25, and 35°C was measured by a static method. The vapor pressure in the H2O–Al2(SO4)3 and H2O–Na2SO4–Al2(SO4)3 systems at 25 and 50°C was measured by the dew point method. A set of parameters of the Pitzer–Simonson–Clegg (PSC) model was determined to describe adequately vapor– liquid equilibria in the H2O–Al2(SO4)3 and H2O–Na2SO4–Al2(SO4)3 systems in the temperature range from 15 to 50°С.

Atomistic modeling of liquid-liquid phase equilibrium explains dependence of critical temperature on G-crystallin sequences.

Atomistic modeling of liquid-liquid phase equilibrium explains dependence of critical temperature on G-crystallin sequences.

Stirred, ultrasound-assisted and microwave-assisted extraction process of β-carotene from Rhodotorula glutinis in biorefinery downstream

Due to the general population awareness about the specific health hazards of synthetic chemical dyes, natural colorant materials have been gaining attention in the past several years. Among them, β-carotene is widely used as a soluble orange–red pigment in food industry, while also presenting medical care benefits. Thus, considerable efforts have been dedicated to the development of an efficient serial, cost effective and sustainable extraction process for its recovery. Herein, solid–liquid (SLE), ultrasound-assisted (UAE) and microwave-assisted (MAE) equilibrium separation were carried out using 4 organic solvents for β-carotene isolation of from Rhodotorula glutinis yeast. Results suggested that technique-wise, UAE performed similarly to SLE, whereas MAE was not as optimal. According to the solvent applied, the colorant followed the increasing trend: dichloromethane < diethyl ether < dimethyl carbonate < ethyl acetate. The latter resulted in 45 ± 3 μg g−1, 42 ± 2 μg g−1 and 41 ± 3 μg g−1, while being extracted with UAE, SLE and MAE, respectively. These operation findings show the positive relationship effect of the greener solvent during the SLE, UAE and MAE activity for the optimisation of high-added value molecular compound, pro-vitamin A, from fungi. Additionally, a diffusion-based model system was implemented for the first time to determine mass transfer phenomena. When correlated with experiments, good measurement accuracy was validated; hence, showing promising results as a predictive model in future research studies, especially mechanistic.

Isobaric Vapor–Liquid Equilibrium Experiment of N-Propanol and N-Propyl Acetate at 101.3 kPa

N-Propanol (NPA) and n-propyl acetate (NPAC) can form an azeotrope under normal pressure, so their separation cannot be carried out by conventional distillation. Therefore, 1-butyl-3-methylimidazole acetate ([BMIM][OAC]) and ethylene glycol (EG) were selected as entrainers for extractive distillation of the two substances. Isobaric vapor–liquid equilibrium data were obtained by experiments of NPA + NPAC, NPA + NPAC + [BMIM][OAC], and NPA + NPAC + EG at normal pressure; the experimental results showed that the separation effect of [BMIM][OAC] is significantly better than that of EG. Finally, the data were fitted and correlated with the NRTL model. The ARD (average relative deviation) of NPA + NPAC, NPA + NPAC + [BMIM][OAC], and NPA + NPAC + EG is less than 5%, indicating that the NRTL model has good applicability to the vapor–liquid system.