High-pressure phase behavior of systems with ionic liquids: measurements and modeling of the binary system fluoroform+1-ethyl-3-methylimidazolium hexafluorophosphate

In order to gain insight into the phase behavior of ionic liquids+supercritical fluids, the phase boundaries of a binary mixture of an air- and water-stable ionic liquid and a supercritical fluid has been studied experimentally. For this purpose, fluoroform (CHF₃) was considered as the supercritical fluid and 1-ethyl-3-methylimidazolium hexafluorophosphate ([emim][PF₆]) was selected as the ionic liquid. A synthetic method was used to measure vapor–liquid and solid–liquid boundaries. Results are reported for CHF₃ concentrations ranging from 10.1 to 99.0 mol%, and within temperature and pressure ranges of 309.3–367.5 K and 1.6–51.6 MPa, respectively. The Peng–Robinson equation of state is used to model this binary system.     

Modeling vapor–liquid equilibrium and liquid–liquid extraction of deep eutectic solvents and ionic liquids using perturbed-chain statistical associating fluid theory equation of state. Part II

This study aims to use perturbed-chain statistical associating fluid theory (PC-SAFT) to describe the phase behavior of systems containing deep eutectic solvents (DESs) and ionic liquids (ILs). The DESs are based on tetrabutylammonium chloride and tetrabutylammonium bromide as hydrogen bond acceptors, and levulinic acid and diethylene glycol as hydrogen bond donors in the mole ratio of 1:2 and 1:4, respectively. Predictions of phase equilibria by PC-SAFT were compared with the results of COnductor like Screening MOdel for Real Solvents (COSMO-RS) and non-random two-liquid (NRTL). In this work, low viscosity ether- and pyridinium-based ILs [E_nPy][NTf₂] and [C_mPy][NTf₂] were used for vapor–liquid equilibrium systems, while 1-(2-methoxyethyl)-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)-amide and 1-propyl-3-methylimidazolium bis{trifluoromethylsulfonyl}imide with n-heptane + thiophene and n-hexane + ethylbenzene were used in the liquid–liquid extraction, respectively. In the last part, the phase behavior of the mixtures of perfluoroalkylalkanes with their linear alkane counterparts was studied and compared with the SAFT-Mie pair potential.     

What is the state of aggregation of ethanol molecules in ethanol–supercritical carbon dioxide mixtures? An FTIR investigation in the full molar fraction range

The evolution of the degree of hydrogen bonding of ethanol molecules in scCO₂–ethanol mixtures for different molar fraction (from 0.5 to 100% in ethanol) in the temperature range 40–200 °C and at two different constant pressures P = 15 and 20 MPa is reported in this paper. For a given pressure, we observe a strong dependence of the degree of hydrogen bonding as a function of temperature and ethanol molar fraction. We emphasize that a detailed knowledge of the degree of hydrogen bonding of ethanol molecules in these binary systems is important for the understanding and the further development of the supercritical fluid technology.     

Phase behavior on the binary and ternary mixtures of poly(isooctyl acrylate) + supercritical fluid solvents + isooctyl acrylate and CO2 + isooctyl acrylate system

Experimental cloud‐point data to the temperature of 180 °C and the pressure up to 2000 bar are presented for ternary mixtures of poly(isooctyl acrylate) + supercritical fluid solvents + isooctyl acrylate systems. Cloud‐point pressures of poly(isooctyl acrylate) + CO₂ + isooctyl acrylate system is measured in the temperature range of 60–180°C and to pressures as high as 2000 bar with isooctyl acrylate concentration of 0–44.5 wt. This system changes the pressure–temperature slope of the phase behavior curves from upper critical solution temperature (UCST) region to lower critical solution temperature (LCST) region as the isooctyl acrylate concentration increases. Poly(isooctyl acrylate) does dissolve in pure CO₂ to the temperature of 180°C and the pressure of 2000 bar. The phase behavior for poly(isooctyl acrylate) + CO₂ + 9.5, 14.8, 30.6, and 41.9 wt % dimethyl ether (DME) mixture show the curve changes from UCST to LCST as the DME concentration increases. Also, the cloud‐point curves are measured for the binary mixtures of poly(isooctyl acrylate) in supercritical propane, propylene, butane, and 1‐butene. High pressure phase behaviors are measured for the CO₂ + isooctyl acrylate system at 40, 60, 80, 100, and 120°C and pressure up to 200 bar. This system exhibits type‐I phase behavior with a continuous mixture‐critical curve. The experimental results for the CO₂ + isooctyl acrylate system are modeled using the Peng‐Robinson equation of state. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Phase behavior of mixture of supercritical CO2 + ionic liquid: Thermodynamic consistency test of experimental data

Various models have been applied composed of the Peng‐Robinson equation of state (PR‐EoS) and the Soave‐Redlich‐Kwong equation of state (SRK‐EoS) associated with three mixing rules including the following: Wong‐Sandler (WS), van der Waals one (vdW1), and van der Waals two (vdW2) for phase behavior modeling of mixtures of supercritical CO₂ + different ionic liquids in vapor–liquid equilibrium (VLE) region. It has been found that the PR EoS implying the WS mixing rule can be used as a reliable thermodynamic model to perform a thermodynamic consistency test on the experimental data of phase behaviors of the supercritical CO₂ + ionic liquid systems (19 commonly‐used ionic liquids have been studied). The results show that 40% of the experimental data seem to be thermodynamically consistent, 55.5% seem to be thermodynamically inconsistent, and 4.5% seem to be not fully consistent. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3892–3913, 2013     

Supercritical fluid extraction of ethanol from aqueous solutions

The recovery of ethanol from aqueous solutions was studied by using supercritical carbon dioxide. At 333.2 K and 10.0 MPa, vapor–liquid equilibrium data of the mixture CO₂+ethanol+water were determined. No azeotrope was observed. Theoretical calculation of equilibrium stages was performed and compared with countercurrent column experiments. Separation of extract and solvent was optimized by multistage solvent distillation. The height of one theoretical stage was found to depend on the ethanol content of the liquid phase. Moreover, flooding point measurements were carried out with ethanol+water mixtures of different composition.     

Simultaneous modeling of VLE,LLE and VLLE of CO2 and 1, 2, 3 and 4 alkanol containing mixtures using GC-PPC-SAFT EOS

A polar version of the group contribution PC-SAFT equation of state (GC-PPC-SAFT; Tamouza et al., 2004; NguyenHuynh et al., 2008) combined with a method for correlation/prediction of binary interaction parameters k_ij (NguyenHuynh et al., 2008) is here applied to model vapor–liquid, liquid–liquid and vapor–liquid–liquid phase equilibria of CO₂ + alkanol mixtures simultaneously.A cross-association interaction between CO₂ and alkanol had to be taken into account to model/predict the mixtures equilibria accurately. The cross-association parameters were evaluated using the so-called CR1 mixing rules supported by ab initio computations.Extensive prediction tests on CO₂ + alkanol mixtures involving linear and branched alkanols are carried out. The results obtained showed that in most cases, the correlation and prediction calculations are qualitatively and quantitatively satisfactory: the overall deviations on liquid phase and vapor phase are respectively ΔX = 3–4% and ΔY = 1–2%.     

Monte Carlo simulations of phase behavior and microscopic structure for supercritical CO2 and thiophene mixtures

The phase equilibria of thiophene in supercritical carbon dioxide are calculated by Monte Carlo simulations in Gibbs ensemble using a united atom force field. To validate the simulations, binary vapor–liquid coexistence curves were computed for two different temperatures using Monte Carlo simulations. An excellent agreement between simulations and experimental data is obtained. The effects of pressure on structural properties were studied for thiophene–CO₂ binary mixtures. The radial distribution functions and local composition of thiophene in CO₂ were investigated over a range of pressures. A weak dependence of thiophene structural properties with pressure was observed in supercritical phase. Local solution structure of thiophene in supercritical CO₂ was studied by computing angular–radial distribution functions and spatial distribution functions with three-dimensional probability distributions. The characteristic angular–radial distributions show a mutually parallel arrangement between thiophene plane and CO₂ molecules within the first solvation shell. Spatial distribution functions (SDFs) results show that CO₂ molecules have two higher probability distributions around thiophene molecules located above and below the thiophene ring.     

High-pressure phase equilibria of systems carbon dioxide + n-eicosane and propane + n-eicosane

In this work we investigated the phase equilibrium behavior of the binary asymmetric systems propane (C3) + n-eicosane (C20) and carbon dioxide (CO₂) + n-eicosane (C20). We used a variable-volume view cell for obtaining fluid–fluid equilibrium (FFE), solid–fluid equilibrium (SFE) and solid–fluid–fluid equilibrium (SFFE) experimental data. We modeled the phase equilibria of both systems using the Peng–Robinson Equation of State for describing the fluid phases and an expression for the fugacity of pure solid n-eicosane with parameters fit to reproduce the pure n-eicosane melting line. We performed the phase equilibrium calculations by implementing path-following methods for tracking entire solid–fluid (SF) and solid–fluid–fluid (SFF) equilibrium curves for binary asymmetric mixtures. This made it possible to obtain complete isoplethic lines or complete three-phase equilibrium lines in single runs. Although the model is relatively simple, it is able to grasp the complex observed behavior for the systems studied here.     

COSMO-RS modeling on the extraction of stimulant drugs from urine sample by the double actions of supercritical carbon dioxide and ionic liquid

This work presents the first research linking chemical engineering and sport science as far as we know. The COSMO-RS (conductor-like screening model for real solvents) model was used to make a priori prediction for the extraction of stimulants from aqueous solution by the double action of supercritical carbon dioxide (SC CO₂) and ionic liquid. It was found that the suitable ionic liquids should have small molecular volume, unbranched group and no sterical shielding effect around anion charge center, and thus [C₂MIM]⁺[OAc]^- is the best among all the ionic liquids investigated. The calculated results from the COSMO-RS model were qualitatively consistent with those from experiments. On this basis, partition coefficients of amphetamine (C9N) and nikethamide (C10N) between aqueous phase and supercritical fluid (or MTBE) phase at different temperatures were calculated. It was shown that the separation efficiency of supercritical extraction with ionic liquid is generally higher than that of traditional liquid-liquid extraction. The modeling present can also be extended to the separation of trace amount of organic substances from aqueous solutions for other purposes.     

Prediction of solubility parameters using the group‐contribution lattice‐fluid theory

A formulation for the solubility parameter based on the group‐contribution, lattice fluid equation of state was derived. The solubility parameters of pure liquid solvents, polymers, copolymers, and liquid mixtures were calculated and compared against the best available data. This investigation was conducted on pure components and mixtures of alkanes, alkenes, ketones, ethers, acetates, alcohols, chlorinated molecules, and cyclic and aromatic solvents. The capabilities of the model to distinguish between two isomers and to predict the solubility parameter of supercritical fluids and their mixtures were also studied. The predicted values are generally good, although the error increases when hydrogen bonding is present. A primary application of the procedure is for the prediction of the solubility parameters of polymers. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 197–206, 2001     

Hydrogenation of vegetable oils using mixtures of supercritical carbon dioxide and hydrogen

Hydrogenation of vegetable oils under supercritical conditions can involve a homogeneous one-phase system, or alternatively two supercritical components in the presence of a condensed phase consisting of oil and a solid catalyst. The former operation is usually conducted in flow reactors while the latter mode is more amenable to stirred, batch-reactor technology. Although many advantages have been cited for the one-phase hydrogenation of oils or oleochemicals using supercritical carbon dioxide or propane, its ultimate productivity is limited by the oil solubility in the supercritical fluid phase as well as unconventional conditions that affect the hydrogenation. In this study, a dead-end reactor has been utilized in conjunction with a head-space consisting of either a binary fluid phase consisting of varying amounts of carbon dioxide mixed with hydrogen or neat hydrogen for comparison purposes. Reaction pressures up to 2000 psi and temperatures in the range of 120–140°C have been utilized with a conventional nickel catalyst to hydrogenate soybean oil. Depending on the chosen reaction conditions, a wide variety of end products can be produced having different iodine values, percentage trans fatty acid content, and dropping points or solid fat indices. Although addition of carbon dioxide to the fluid phase containing hydrogen retards the overall reaction rate in most of the studied cases, the majority of products have low trans fatty acid content, consistent with a nonselective mode of hydrogenation.     

Solubility of supercritical gases in organic liquids

Chrastil (1982) [6] demonstrated that the solubility of a substance in a supercritical fluid (SCF) can be correlated with the density of the pure supercritical gas. Therefore, Chrastil's equation permits calculation of the supercritical phase composition of binary SCF + substance mixture based on the knowledge of the supercritical gas density and avoiding the use of equation of state based models.In this work, it is demonstrated that the supercritical fluid density also defines the liquid phase composition of binary systems; a density-dependent relationship is presented to calculate the solubility of supercritical gases in organic liquids. The isothermal solubility of several gases commonly employed in supercritical processing, such as carbon dioxide, methane, and ethane, in different organic liquids, including alkanes, alkenes, alcohols, acids, ketones, esters, terpenes and aromatic compounds, was successfully correlated as a function solely of the pure supercritical fluid density. As an application, pressure vs. composition phase diagrams of binary SCF + substance mixtures were obtained circumventing the use of equation of state models.     

Fluid phase equilibria of the reacting mixture in the dimethyl carbonate synthesis from supercritical CO2

In order to investigate the dimethyl carbonate synthesis from methanol and supercritical CO₂, the thermodynamic behaviour of the reacting mixture, i.e. the quaternary methanol–CO₂–DMC–water mixture, has to be known. The SRK equation of state with MHV2 mixing rules has been chosen to predict fluid phase equilibria in the reactor. The first part of this work is dedicated to the determination of binary interaction parameters, needed in the use of this model. These parameters are deduced from the fitting of experimental data concerning binary or ternary sub-systems existing in the quaternary mixture. Literature data was used for most of the binary sub-systems, but for the DMC–CO₂ and DMC–water mixtures, specific experiments were carried out. The agreement between experimental and predicted fluid phase equilibria was found to be satisfactory. With a view to studying of the operating conditions for the reaction, the thermodynamic model was used to predict fluid phase equilibria in the reactor, by considering several hypothetical feed ratios and conversions. This work shows that CO₂ has to be used in large excess in order to be sure of running the reaction in a homogeneous fluid medium.     

Solubilities of methyl oleate,oleic acid,oleyl glycerols,and oleyl glycerol mixtures in supercritical carbon dioxide

Solubility isotherms for oleic acid and methyl oleate as well as mono-, di-, and trioleylglycerol (MO, DO, and TO) in supercritical fluid CO₂ at 50 and 60°C are reported. Partition coefficients for quaternary (MO-DO-TO-CO₂) mixtures were obtained at 60°C at pressures ranging from 172 to 309 bar. Data indicate that diolein, and especially monoolein, exhibit positive deviation from ideal behavior, possibly due to intermolecular hydrogen bonding. Supercritical fluid CO₂ appears to be a good media for removal of mono- and diacylglycerol by-products from synthetic triglyceride reaction mixtures at moderate temperatures.     

High pressure measurements and molecular modeling of the water content of acid gas containing mixtures

Water content of three carbon dioxide containing natural gas mixtures in equilibrium with an aqueous phase was measured using a dynamic saturation method. Measurements were performed up to high temperatures (477.6 K = 400°F) and pressures (103.4 MPa = 15,000 psia). The perturbed chain form of the statistical associating fluid theory was applied to predict water content of pure carbon dioxide (CO₂), hydrogen sulfide (H₂S), nitrous oxide (N₂O), nitrogen (N₂), and argon (Ar) systems. The theory application was also extended to model water content of acid gas mixtures containing methane (CH₄). To model accurately the liquid‐liquid equilibrium at subcritical conditions, cross association between CO₂, H₂S, and water was included. The agreement between the model predictions and experimental data measured in this work was found to be good up to high temperatures and pressures. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3038–3052, 2015     

Synthesis of higher alcohols from syngas over Zn–Cr–K catalyst in supercritical fluids

An investigation was carried out on the selective synthesis of higher alcohols from syngas in a supercritical fluid (a mixture of C₁₀–C₁₃ alkanes) by using a fixed bed reactor. Experiments were conducted over Zn–Cr–K catalyst in the temperature range of 360–400°C, a partial pressure of syngas of 7.5 MPa and a partial pressure of supercritical medium of 1.78 MPa. Comparison of results in the gas phase with those in the supercritical phase indicated that CO conversion was higher in the supercritical phase reaction. Alcohol selectivity decreased slowly with increasing temperature in the supercritical phase reaction but decreased rapidly in the gas phase reaction, due to the special properties of supercritical fluids (SCF). Product distributions were different in both reaction phases. The introduction of the supercritical medium promoted carbon chain growth and the content of C₂⁺OH was increased. The product distribution features with high methanol content of the gas phase synthesis were changed.     

A predictive method for calculating the solubility of solids in supercritical gases application to apolar mixtures

A thermodynamic method is proposed for calculating the solublities of apolar solids compounds in apolar supercritical gases. The method, analogous to the Hildebrand theory of solids' solubilities in liquid solvents, is mainly based on the application of Scatchard-Hildebrand equation to supercritical fluid mixtures.The derived method is applied to the determination of the ethylene/naphthalene equfiibria at 5 temperatures between 12 and 50°C and over pressure ranges of 50–270 ata. Calculated data are compared with the experimental data by Diepen and Scheffer.Methods for determining the solubility parameters of supercritical gases are discussed. The possibility of extending the proposed theory to polar mixtures of condensed phases in supercritical gases is also indicated.     

Experimental cloud points for polybutadiene + light solvent and polyethylene + light solvent systems at high pressure

The hydrogenation of unsaturated heavy compounds is conventionally carried out in the presence of two fluid phases, because the immiscibility in the binary subsystem ‘hydrogen + heavy substrate’ cannot be overcome by adding a standard solvent. Using a supercritical or quasicritical solvent allows the hydrogen and the unsaturated heavy substrate to dissolve into a single phase. To select the operating conditions of a supercritical reactor, it is necessary to determine the phase boundaries of the subsystems ‘solvent + hydrogen’ and ‘solvent + heavy compound’. In this work, we measured cloud points for binary systems made of polybutadiene (PB) or polyethylene (PE) and a light solvent, i.e., propane or dimethyl ether (DME) or diethyl ether (DEE). The temperature range studied was from 50 to 160 °C for ‘PB + DME’ and ‘PB + Propane’ and from 100 to 190 °C for ‘PB + DEE’ and ‘PE + DEE’. We found that in PB-containing binary systems, at the ranges of conditions of the experiments, the minimum pressure required to guarantee homogeneity, at any temperature, is below 200 bar for DEE, below 300 bar for DME and in the order of 500 bar when using propane as solvent. Our data for ‘PE + DEE’ indicate the need for a minimum pressure of about 240 bar to keep the system within a single phase. The results from this work and from the literature suggest that the use of binary solvent mixtures may be convenient to carry out the supercritical hydrogenation of PB.     

Binary and ternary mixtures of liquid crystals with CO2

Liquid crystals, elongated molecules with a structured liquid phase, may be used as new solvents for CO₂ capture. However, no molecule has been found yet with optimal properties. Therefore, mixtures of two liquid crystals and CO₂ are investigated. Also, the phase behavior of some binary subsystems of the investigated ternary systems is studied for comparison. In the mixtures investigated, 4,4′‐pentyloxycyanobiphenyl + 4,4′‐heptyloxycyanobiphenyl + CO₂ and 4,4′‐propylcyclohexylbenzonitrile + 4,4′‐heptylcyclohexylbenzonitrile + CO₂, the nematic phases form a nematic homogeneous solution and the solid phases form an eutectic system, leading to a material with improved properties for CO₂ capture. Moreover, the ternary mixture of 4,4′‐propylcyclohexylbenzonitrile + 4,4′‐heptylcyclohexylbenzonitrile + CO₂ showed an increased solubility of CO₂ compared with the binary subsystems. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2977–2984, 2015