Critical properties and acentric factors of ionic liquids

Since most ionic liquids (ILs) decompose before reaching their critical state, the experimental measurement of their critical properties are not possible. In this study, the critical temperatures, critical pressures and acentric factors of ten commonly investigated ILs were determined by making an optimum fit of the calculated vapor-liquid equilibrium data of binary mixtures of CO₂+IL to the experimental values found in literature. For this purpose, the Peng-Robinson equation of state (PR EoS) and the differential evolution optimization method were used. The ILs considered were 1-ethyl-3-methylimidazolium hexafluorophosphate ([emim][PF₆]), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([emim][Tf₂N]), 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]), 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([bmim][Tf₂N]), 1-hexyl-3-methylimidazolium tetrafluoroborate ([hmim][BF₄]), 1-hexyl-3-methylimidazolium hexafluorophosphate ([hmim][PF₆]), 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([hmim][Tf₂N]), 1-octyl-3-methylimidazolium tetrafluoroborate ([omim][BF₄]) and 1-octyl-3-methylimidazolium hexafluorophosphate ([omim][PF₆]). To evaluate the ability of the determined parameters in predicting the phase behavior of systems other than the systems that were used for parameter optimization, both sets of parameters obtained in this work and that of Valderrama et al. were used to predict bubble-point pressures of CHF₃+[bmim][PF₆] (by using the PR EoS and the Soave-Redlich-Kwong equation of state. The bubble-point pressures of CO₂+IL systems optimized in this study by the PR EoS were also determined using the Soave-Redlich-Kwong equation of state (SRK EoS). In addition, liquid densities of pure ILs were predicted using a generalized correlation proposed by Valderrama and Abu-Shark. In all cases, the various predicted properties of these ten ILs, were in better agreement with the experimental data, using the critical properties and acentric factor obtained in this study, compared to the values suggested by Valderrama et al.     

Densities and viscosities for ionic liquids [BMIM][BF4] and [BMIM][Cl] and their binary mixtures at various temperatures and atmospheric pressure

The density and viscosity of 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF₄] and 1-butyl-3-methylimidazolium chloride [BMIM][Cl] and their binary mixtures within the temperatures from 303.15 K to 323.15 K and at ambient pressure were determined in this work. The temperature dependences of density and viscosity were satisfactorily described with the linear model and the Vogel-Tammann-Fulcher type equation, respectively. The molar volume and viscosity of binary IL mixtures were predicted through ideal mixing rules showing that almost null deviations for IL mixtures were observed and their mixing was remarkably close to linear ideal behavior in the molar volumes, while comparatively large errors in viscosity occurred. Additionally, the molar volume of the investigated pure ILs and their mixtures could well be predicted by a predictive model presented by Valderrama et al. (Fluid Phase Equilib., 275 (2009) 145).     

A new fragment contribution‐corresponding states method for physicochemical properties prediction of ionic liquids

A new fragment contribution‐corresponding states (FC—CS) method based on the group contribution method and the corresponding states principle is developed to predict critical properties of ionic liquids (ILs). There are 46 fragments specially classified for ILs considering the ionic features of ILs, and the corresponding fragment increments are determined using the experimental density data. The accuracy of the developed method is verified indirectly via predicting density and surface tension of ILs. The results show that the FC—CS method is reasonable with an average absolute relative deviation less than 4%. With the calculated critical properties, corresponding states heat capacity (CSHC) and corresponding states thermal conductivity (CSTC) correlations are proposed to predict heat capacity and thermal conductivity of ILs, respectively. The predicted results agreed well with the experimental data. The proposed FC—CS method and the two corresponding states correlations are important for design, simulation, and analysis of new ionic liquid processes. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1348–1359, 2013     

Prediction of Hydrate Phase Equilibria in Aqueous Solutions of Salt and Organic Inhibitor Using a Combined Equation of State and Activity Coefficient‐Based Model

A thermodynamic model based on combination of the Valderrama modification of the Patel‐Teja equation of state with non‐density dependent mixing rules and a modification of a Debye‐Hückel electrostatic term is extended to systems containing salt and organic inhibitor by correcting the properties of the aqueous phase such as dielectric constant, density and molecular weight. A linear mixing rule is used for determining the dielectric constant of salt‐free mixture by introducing an interaction parameter (in dielectric constant mixing rule), which is tuned using the freezing point data of aqueous solutions containing salt and organic inhibitor. The binary interaction parameter between salt and organic inhibitor is adjusted using water vapour pressure data in the presence of salt and organic inhibitor. The predicted hydrate dissociation conditions are in acceptable agreement with the experimental data, demonstrating the reliability of the model developed in this work.     

不同温度压力下丙酮－环己烷体系液体密度的测定和推算

使用ＤＭＡ５５型精密密度计和ＤＭＡ５１２型高压外测量池，测定了丙酮－环己烷体系在温度范围为２８８．１５Ｋ至３１８．１５Ｋ和压力从常压至１９．５１ＭＰａ下的液体密度；建立了一个新的液体混合物密度模型，推算了该体系在不同温度压力下的混合物密度，取得令人满意的结果。     

不同温度压力下乙醇－乙酸乙酯体系液体密度的测定和预测

使用ＤＭＡ５５型精密密度计和ＤＭＡ５１２型高压外测量池，测定了乙醇－乙酸乙酯体系在温度范围为２８８．１５Ｋ至３１８．１５Ｋ和压力从常压至１９．５ＭＰａ下的液体密度．应用三重随机局部组成密度模型，预测了该体系在不同温度、压力下的密度，取得令人满意的结果．     

DENSITY ESTIMATION OF AMMONIUM-BASED IONIC LIQUIDS

Density is an important property of ionic liquids (ILs) that is required for process and product design. A recent article by Gardas and Coutinho (2008) reports the extended density correlation of ILs in wide ranges of temperature and pressure. However, they validated the density correlation only for ILs based on the following cations: imidazolium, pyridinium, pyrrolidinium, and phosphonium. The objective of this study is to validate the density correlation for ammonium-based ILs. The density model was tested against experimental densities available in the literature of ammonium-based ILs at a wide range of temperatures (273.15–393.15 K) and at 1 atm (0.1 MPa) of pressure. The results show that the predicted densities are in good agreement with available experimental literature values. The average absolute relative deviation (AARD) is 1.57%.     

Compressibility of polyethylene melts at low pressures

Branched polyethylene has quite different rheological and physical properties from its linear homologue. Despite their many different properties, the densities of linear and branched polyethylene melts at atmospheric pressure have been reported to be identical at all temperatures. However, it was not known whether their melt densities at a given temperature would also be identical at all pressures. In this investigation, the compressibilities of one linear and two branched polyethylene melts at 160°C, 190°C, and 220°C were studied, and it was found that they had an identical compressibility over the present experimental pressure range of ca. 0–455 psi (0–31 atm). Both the specific volume and the density at each temperature could be very accurately expressed as linear functions of pressure for this pressure range. Time-dependent compressive property was not observed within the present low pressure range.     

Densities and surface tensions of ionic liquids/sulfuric acid binary mixtures

The densities and surface tensions of [Bmim][TFO]/H_2SO_4, [Hmim][TFO]/H_2SO_4 and [Omim][TFO]/H_2SO_4 binary mixtures were measured by pycnometer and Wilhelmy plate method respectively. The results show that densities and surface tensions of the mixtures decreased monotonously with increasing temperatures and increasing ionic liquid(IL) molar fraction. IL with longer alkyl side-chain length brings a lower density and a smaller surface tension to the ILs/H_2SO_4 binary mixtures. The densities and surface tensions of the mixtures are fitted well by Jouyban–Acree(JAM) model and LWW model respectively. Redlich-Kister(R–K) equation and modified Redlich-Kister(R–K) equation describe the excess molar volumes and excess surface tensions of the mixtures well respectively. Adding a small amount of ILs(xILb 0.1) into sulfuric acid brings an obvious decrease to the density and the surface tension. The results imply that the densities and surface tensions of ILs/H_2SO_4 binary mixtures can be modulated by changing the IL dosage or tailoring the IL structure.     

Ion-based SAFT2 to represent aqueous multiple-salt solutions at ambient and elevated temperatures and pressures

Ion-based SAFT2 is extended to the properties of aqueous multiple-salt solutions at ambient and elevated temperatures and pressures. The short-range interactions between two different cations are allowed to obtain better representations of the solution properties. The adjustable parameter used in the mixing rule for the segment energy is fitted to the experimental osmotic coefficients of two-salt solutions containing one common anion at various temperatures and low pressures. The predictions of the osmotic coefficients, densities, and activity coefficients of multiple-salt solutions including brine/seawater are found to agree with experimental data.     

Volumetric properties of ionic liquids from cubic equation of state: Application to pure and mixture

In this work, we developed a cubic equation of state (CEOS) for modeling the volumetric properties of various ionic liquids (ILs). Two temperature-dependent parameters presented in the CEOS, have been determined from two sets of corresponding states correlations which are based on the critical point data or the surface tension of ILs. The predicted densities of pure ILs were compared with the experimental data over a broad pressure range from 1 to 100 MPa. The total average absolute deviations (AADs) of the calculated densities of 948 data points from the experimental data are 1.82% using the critical property and 0.96% using the surface tension and liquid density as scaling parameters. Furthermore, the proposed CEOS was successfully extended to mixtures including IL + IL and IL + solvent systems. 1282 literature data points for mixtures were taken to check the reliability of the mixture version of the proposed CEOS. The AAD of the calculated densities of the mixtures using the surface tension and liquid density as scaling parameter is 0.37%. Furthermore, the excess molar volumes (V^E) of the studied binary mixtures have been successfully computed by the use of the proposed CEOS.     

方阱流体汽液共存性质的Monte Carlo模拟

本文应用Ｇｉｂｂｓ系综ＭｏｎｔｅＣａｒｌｏ方法，对纯方阱流体的汽液共存性质进行了模拟计算。得到汽液两相的饱和密度，并根据模拟数据外推以估测临界点。由此得到的对比临界温度和密度分别为Ｔｃ＝ＲＴｃ／ε＝１．２７，ρｃ＝ρｃσ３＝０．３１，与Ａｌｄｅｒ等人的分子动力学模拟结果吻合。此外，还计算了六个温度下两相的构型能、压力和径向分布函数。     

离子液体热物理性质与相行为预测的基团贡献法

离子液体（ILs）由于其优越的性能目前已成为多个领域的研究热点,但热力学基础数据的缺乏是其应用的障碍之一,除实验测定外,基团贡献法也为设计和筛选ILs提供了重要的性质预测方法。概述了预测纯ILs的熔点、黏度、密度、热容、电导率、声速、生态毒性、界面性质、临界性质、传递性质等一系列热物理性质的基团贡献方法,同时对含有ILs混合体系相行为的基团贡献估算模型进行了评述,展望了基团贡献法今后需进一步努力的方向。     

高温高压下甲烷在碳酸氢钠溶液中溶解度测定及模型计算

用新建立的一套测定高温和高压下气体溶解度的实验装置，测定了在不同温度、压力和浓度下，甲烷在碳酸氢钠溶液中的溶解度。用改进的适用于电解质体系的ＰＴ方程对甲烷在碳酸钠溶液中的溶解度进行了计算。     

Zum Stand der Extraktion mit komprimierten Gasen

The state of the art of extraction with compressed gases . Gases under high pressure have the properties of solvents. Their utilization has led to the development of novel methods of separation, extending materials separation process engineering by a new group of process techniques. Catalysts can be dissolved in high-density gas phases and thus effect favourable reaction conditions. In the neighbourhood of the critical temperature, liquid-like densities of the compressed gas are already achieved at relatively moderate pressures in the range from 50 to about 300 bar. A comparatively high solvent power of the gaseous phase ensues. This property of a compressed gas can be varied within wide limits by a change of pressure and temperature. With decreasing density it approaches the behaviour of a normal gas, with increasing density that of a liquid. Thus, there is the possibility of separating out the dissolved material again. The working temperature of such a process is largely determined by the critical temperature of the gas employed. Since a number of readily available gases have critical temperatures in the region up to 50°C, the first separations to be examined during the development of this process were those of temperature-sensitive and low-volatile mixtures. Polar materials having substantially higher critical temperatures such as ammonia, methanol and water promise a further series of possible applications.     

Ionic Liquids for Propene‐Propane Separation

This paper presents an extensive study on the feasibility of ionic liquids (IL) for the extractive distillation of propene‐propane mixtures. A new experimental method for express screening of non‐volatile entrainers was elaborated. A series of ILs and their mixtures were screened at ambient temperature and low pressures. The screening results show that every tested IL turns a low boiler propene into a high boiler and the alkene‐to‐alkane separation factor can be as low as 0.28. The solubility and separation efficiency can be tuned by adjusting the chemical structures of the ions forming the IL. It was found that shortening of the alkyl substituents of the imidazolium ions leads to a decrease in capacity and to an increase in the separation factor. Interestingly, ILs containing nitrile functionalities in either the cation or the anion showed, in our experiments, enhanced separation ability combined with still good capacities. From our thermodynamic measurements, [EMIM][[B(CN)₄] was proved to be the most promising candidate. Binary mixtures of ILs were also tested and resulted in separation factors and capacities between the values for the individual ILs. For the most promising candidates, also autoclave measurements at elevated temperatures and pressures were carried out. These experiments indicate that the separation ability decreases with growing temperature and loading. In general, our study definitely proves the high potential of ILs to act as entrainers in the extractive distillation of propene‐propane mixtures or for the separation of any other low‐boiling alkene‐alkane mixture.     

Equilibrium,interfacial and transport properties of n-alkanes: Towards the simplest coarse grained molecular model

In this work, using molecular dynamics simulations, we have investigated how simple could be a coarse grained molecular model yielding simultaneously equilibrium densities, surface tensions and transport properties of some n-alkanes (from methane to n-decane) along the vapour–liquid equilibrium curve. For that purpose, as an initial model, the fully flexible Lennard–Jones Chain (3 “molecular” parameters) model has been chosen. Using this simple molecular model, good results have been obtained on equilibrium properties of all tested n-alkanes despite a systematic slight overestimation of critical temperatures, critical pressures and surface tensions. In addition, concerning transport properties, good results have been obtained for methane and n-butane except for thermal conductivity in the gas state. For n-heptane and n-decane it has been found that thermal conductivity is systematically underestimated while viscosity is well estimated except at low temperatures. Concerning thermal conductivity, this misevaluation can be corrected if the zero-density thermal conductivity is known. Concerning shear viscosity, it is found that an additional “rigidity” fourth parameter is required to improve the results when dealing with the longest chains at the lowest temperatures.     

Solubility of Disperse Red 82 and modified Disperse Yellow 119 in supercritical carbon dioxide or nitrous oxide with ethanol as a cosolvent

Ethanol was used as a cosolvent to enhance the solubility of disperse dyestuffs in supercritical fluids. In the presence of ethanol, from (1 to 5) mol%, the gas–solid equilibrium data of the Disperse Red 82 and modified Disperse Yellow 119 in supercritical carbon dioxide or nitrous oxide have been measured at temperatures from (353.2 to 393.2) K and pressures from (15.0 to 30.0) MPa. The experimental results show that the solubility increases substantially, up to (9 to 25)-fold, by adding 5 mol% of ethanol to the supercritical fluids. In the presence of cosolvent ethanol, the solubility enhancements in nitrous oxide system are much greater than that in carbon dioxide system for modified Disperse Yellow 119 at the same temperature and pressure. The solubility data were correlated with the Chrastil and the Méndez-Santiago and Teja models. The Méndez-Santiago and Teja model yields slightly better results than Chrastil model.     

Modeling of CO2 Solubility in Selected Imidazolium-Based Ionic Liquids

This study explores the use of COSMO-RS model and Peng-Robinson (PR) equation of state (EoS) to predict the solubility of carbon dioxide (CO₂) in specific ionic liquids (ILs). COSMO-RS was employed to estimate of CO₂ solubility at atmospheric pressure in eight imidazolium-based ILs resulting from the combination of ethyl, butyl, hexyl, and octyl-imidazolium cations with two anions: bis(trifluoromethylsulfonyl)imide ([Tf₂N]) and Trifluoromethanesulfonate ([TFO]). The results indicated relatively acceptable qualitative consistency between the experimental and predicted values. The PR EoS was employed at high pressure by tuning the interaction parameters to fit the experimental data reported in the literature. The model demonstrated excellent accuracy in predicting the solubility of CO₂ at pressure values less than the critical pressure of CO₂; however, at higher pressures, the calculated solubility diverged from the experimental values. Furthermore, the type of anion and cation used in the IL affected the performance of the PR EoS.     

Supercritical CO2 extraction of turmerones from turmeric and high-pressure phase equilibrium of CO2 + turmerones

This work studies the enrichment of turmeric α-β-Ar turmerone using supercritical fluid extractions followed by solid–liquid column partition fractionation. The high-pressure vapor–liquid phase equilibrium of the α-β-Ar turmerone with carbon dioxide was also examined. The purity of α-β-Ar turmerone was increased from 67.7% in extracted oil up to 91.8% in enriched oil, as determined by HPLC analysis. An equilibrium apparatus that comprises two vibrating tube densitometers was then adopted to obtain vapor and liquid equilibrium data for this asymmetric system of α-β-Ar turmerone and carbon dioxide mixture at 313.15 K and 333.15 K. Pressures ranged from 2.82 MPa to 20.80 MPa. Experimental data at elevated pressures were successfully correlated with theoretical methods of Peng–Robinson, Soave–Redlich–Kwong and Patel–Teja equations of state, individually combined with quadratic, Panagiotopoulos–Reid and Adachi–Sugie mixing rules.