Diffusion coefficients and phase equilibria of carbon dioxide–ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) system

This article presents the mutual diffusion coefficients of a carbon dioxide–ionic liquid, [bmim][PF₆], system at temperatures of 313.15 and 323.15 K and pressures of 5 and 8 MPa. In order to estimate the diffusion coefficients, we have carried out experiments to find time-dependent carbon dioxide solubilities in the ionic liquid and then fit a transport model to the data. In a system containing high pressure carbon dioxide and ionic liquid, carbon dioxide dissolves in the liquid until its equilibrium mole fraction is reached. During this process, the position of the liquid–vapour interface and the density of the liquid phase change. To account for the variation in liquid density, an equation fit to the experimental density data is included in the transport model. To track the moving interface, the volume-of-fluid method is used. The diffusivities at dilute concentration and at thermodynamic phase equilibrium are determined and compared with the literature values and those obtained from correlations.     

Solubility of carbon dioxide in ammonium-based ionic liquids: Butyltrimethylammonium bis(trifluoromethylsulfonyl)imide and methyltrioctylammonium bis(trifluoromethylsulfonyl)imide

Solubility results of carbon dioxide (CO₂) in two ammonium-based ionic liquids, butyltrimethylammonium bis(trifluoromethylsulfonyl)imide ([N4,1,1,1][Tf₂N]) and methyltrioctylammonium bis(trifluoromethylsulfonyl)imide ([N1,8,8,8][Tf₂N]), are presented at pressures up to approximately 45 MPa and temperatures ranging from 303.15 K to 343.15 K. The solubility was determined by measuring bubble point pressures of mixtures of CO₂ and ionic liquid using a high-pressure equilibrium apparatus equipped with a variable-volume view cell. Sharp increase of equilibrium pressure was observed at high CO₂ compositions. The CO₂ solubility in ionic liquids increased with the increase of the total length of alkyl chains attached to the ammonium cation of the ionic liquids. The experimental data for the CO₂+ionic liquid systems were correlated using the Peng-Robinson equation of state.     

High pressure phase behaviour of mixtures of hydrogen and the ionic liquid family [cnmim][Tf2N]

The high-pressure solubility of hydrogen gas in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulphonyl)amide ([emim][Tf₂N]) was measured experimentally in an equipment based on the synthetic technique. Measurements were carried out within a temperature range of 310–450 K and pressures up to 15 MPa. Hydrogen solubility was shown to be low in this ionic liquid, reaching a maximum concentration of about 6 mole percent at the highest temperatures and pressures investigated. Hydrogen solubility showed an “inverse” temperature effect, indicating increased solubility at higher temperatures in contrast to other commonly investigated gas solubilities in ionic liquids, such as carbon dioxide. Within the temperature and pressure range investigated, solubility isotherms on a pressure–concentration diagram approximated linear behaviour. It was also shown that the solubility of hydrogen increases as the alkyl side chain of the cation increases in size within the homologous family.     

Phase behavior of 1,3,5-tri-tert-butylbenzene–carbon dioxide binary system

1,3,5-tri-tert-butylbenzene (TTBB) is solid at ambient conditions, and has substantial solubility in liquid and supercritical carbon dioxide. We present the phase behavior of TTBB–CO₂ binary system at temperatures between 298 and 328 K and at pressures up to 20 MPa. Phase diagrams showing the liquid–vapor, solid–liquid and solid–vapor equilibrium envelopes are constructed by pressure–volume–temperature measurements in a variable-volume sapphire cell. TTBB is highly soluble in CO₂ over a wide range of compositions. Single-phase states are achieved at moderate pressures, even with very high TTBB concentrations. For example, at 328 K, a binary system containing TTBB at a concentration of 95% by weight forms a single-phase above 2.04 MPa. TTBB exhibits a significant melting-point depression in the presence of CO₂, 45 K at 3.11 MPa, where the normal melting point of 343 K is reduced to 298 K. With its high solubility in carbon dioxide, TTBB has potential uses as a binder or template in materials forming processes using dense carbon dioxide.     

超临界二氧化碳萃取低挥发性液体混合物的相平衡

在半连续式实验设备中分别测定了苯甲醇－２－苯乙醇和苯甲酸酯－苯甲醇的等摩尔混合物与超临界ＣＯ２三元系相平衡数据。实验温度分别为３０８．２Ｋ和３１８．２Ｋ，压力范围为８～２０ＭＰａ。实验结果表明：对第一个三元系，两种液体在超临界ＣＯ２中的溶解度与ＣＯ２在液相中溶解行为密切相关；对第二个三元系，较高压力下，超临界流体相中苯甲酸甲酯浓度突然增大，而苯甲醇浓度变化不明显。通过引入考虑分子体积差别的二元作用参数，用Ｐｅｎｇ－Ｒｏｂｉｎｓｏｎ方程对气液平衡数据进行了关联。     

Thermal conductivity of the ionic liquid [HMIm][Tf2N] with compressed carbon dioxide

The liquid thermal conductivity of the ionic liquid (IL), 1-hexyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)amide ([HMIm][Tf₂N]), saturated with compressed vapor and supercritical carbon dioxide was measured over three isotherms (298.15, 323.15, and 348.15 K) and pressures up to approximately 20 MPa using a transient hot-wire technique. Pure [HMIm][Tf₂N] thermal conductivity was also measured over a temperature range of 293.15–353.15 K at ambient pressure and with hydrostatic pressure to approximately 20 MPa. Literature vapor–liquid equilibrium data were used to predict the liquid CO₂ composition at the conditions investigated. Initially, the liquid thermal conductivity slightly decreased with pressure/composition of CO₂ followed by a gradual increase that is mainly attributed to hydrostatic pressure effects. Simple composition-based mixing rules for mixture properties are not qualitatively nor quantitatively accurate. These data could be used to engineer heat transfer equipment required for a variety of proposed IL applications in CO₂ capture, absorption refrigeration, biphasic CO₂/IL reaction platforms, etc.     

The effect of [bmim][Br] on the solubility of carbon dioxide and methane in glycols at pressures up to 14 MPa and temperatures ranging from 303 to 423 K

Solubility data of methane in ethylene glycol and 1-4 butylene glycol and carbon dioxide in ethylene glycol and 1-2 propylene glycol in the presence of the ionic liquid 1-butyl-3-methylimidazolium bromide have been measured in the temperature range (303–423) K at pressures up to 14 MPa. Henry's law constant of each solute in the studied solvent at saturation pressure is given. The experiments were performed in an autoclave type phase equilibrium apparatus using the total pressure method. For mixtures containing carbon dioxide and ethylene glycol no influence was observed. For mixtures containing carbon dioxide and 1-2 propylene glycol it was observed salting-out effect at 303.2 K and 323.2 K and salting-in effect at the remaining temperatures. For mixtures containing methane and ethylene glycol or 1-4 butylene glycol salting-in effect was observed.     

Solubility of Jatropha and Aquilaria oils in supercritical carbon dioxide at elevated pressures

This study investigated experimental equilibrium solubilities of Jatropha curcas and Aquiliaria crassna oils dissolved in supercritical carbon dioxide at temperatures of 318-338 K and pressures of 20, 25, 30, 35 MPa. The highest solubility of J. curcas and A. crassna oil were 29.8 and 28.4 mg L⁻¹, respectively, at 338 K and 35 MPa. The oil solubilities and the concentration of triglycerides both increased with increasing temperature and pressure. Triglyceride molecules surrounded by carbon dioxide molecules may be proposed since solubilities increased with the flux of supercritical carbon dioxide. The solubility of these two oils linearly increased with the density of supercritical carbon dioxide. Experimental data of the oil solubility were successfully correlated by the Chrastil equation.     

Phase equilibrium characteristics of supercritical CO2/poly(ethylene terephthalate) binary system

The solubility of carbon dioxide in poly (ethylene terephthalate) (PET) at high pressure and elevated temperature conditions was investigated for a better understanding of the phase equilibrium characteristics of supercritical CO₂/PET binary system and useful data for the process development of the supercritical fluid dyeing. Based on the principle of pressure decaying, a novel experimental apparatus suitable to high pressure and high temperature measurement was established. The solubilities of CO₂ in PET were measured with the apparatus at temperatures of 110, 120, and 130°C and pressures up to 30.0 MPa. The results show that the solubility of CO₂ in PET increases with the increase of pressure and CO₂ density, respectively, at a constant temperature, whereas it decreases with the increase of temperature at a constant pressure. The Sanchez‐Lacombe equation of state (S‐L EOS) was used to correlate the experimental data. The calculated results are in good agreement with the experimental ones. The average absolute relative derivation (AARD) is less than 3.91%. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

An apparatus for phase equilibrium studies of carbon dioxide+heavy hydrocarbon systems

An apparatus for measuring the solubility of gas in liquid and that of liquid or solid in gas has been constructed. The apparatus can be used at system temperatures ranging from 20 to 70°C and at system pressures up to 15 MPa. The solubilities were determined by means of gravimetric measurements. The solubilities measured in this study for the carbon dioxide+n-decane and carbon dioxide + naphthalene systems agree very well with the literature values. The vapor-liquid equilibria of the carbon dioxide+Peace River bitumen system at 45 and 55 °C were studied. The new data indicate that the supercritical-fluid carbon dioxide can extract a fair amount of the light components from Peace River bitumen.     

Solubilities of solids in supercritical fluids

The solubilities of several low-volatility compounds in supercritical fluids were measured. The fluids used were pure carbon dioxide or carbon dioxide modified with small amounts of organic liquids. Some enthalpies of solution of solids in carbon dioxide at a density of 0.80 g/mL are presented. The enthalpy of solution of fluoranthene in carbon dioxide was found to be less endothermic at higher CO₂ density. The order of solubilities in the modified fluids was the same as that in the pure liquid modifiers. The same apparatus was used to measure vapor pressures of some substances as well as solubilities.     

Solubility of fish oil fatty acid ethyl esters in suband supercritical carbon dioxide

Mutual solubilities and K-values of fish oil fatty acid ethyl esters, prepared from sand launce oil, and sub- and supercritical carbon dioxide have been measured in an apparatus originally designed for phase equilibrium, density and gasoil ratio measurements of reservoir fluids. The measurements were performed at pressures from 2 to 22 MPa at temperatures of 283.2, 313.2 and 343.2°K. Experimental temperatures, pressures, solubilities, K-values and densities are reported. The K-values of ethyl myristate, palmitate, oleate, eicosapentaenoate and docosahexaenoate are compared with published experimental binary and/or multicomponent data. Because both vapor and liquid solubilities are reported, such data are applicable in the design of supercritical extraction plants.     

Ternary phase equilibria of the iso-propanol+water+carbon dioxide system at high pressure

Ternary phase diagrams are presented for the system: iso-propanol(IPA)+water+carbon dioxide at temperatures from 15 to 70 °C and pressures from 7 to 17 MPa. The distribution coefficients of IPA between the dense phase carbon dioxide and water changed dramatically with temperature and pressure. In the vicinity of the critical point, distribution coefficients was low, yet at liquid-like densities carbon dioxide had a high affinity for IPA. Selectivity reversal was observed at differing pressures. High selectivity of CO₂ for IPA was achieved in the near-critical liquid and in supercritical carbon dioxide at high pressure.     

An apparatus for high-pressure VLE measurements using a static mixer. Results for (CO2+limonene+citral) and (CO2+limonene+linalool)

A new flow apparatus for high-pressure vapour–liquid equilibrium measurements was assembled. Its main feature is the use of a static mixer followed by a cyclone separator. Phase equilibrium ratios were determined, at 323.2 K and at pressures up to the vicinity of the mixture critical pressure, for the following systems: carbon dioxide+limonene, carbon dioxide+citral, carbon dioxide+linalool, carbon dioxide+limonene+citral and carbon dioxide+limonene+linalool. The results compare well with available literature data.     

Interfacial tension and density measurement of the system corn germ oil – carbon dioxide at low temperatures

In this article, the physical properties of corn germ oil at high pressures of up to 30 MPa and at low temperatures from ?10 °C to 22 °C are presented. We measured the interfacial tension of the commercially available corn germ oil Mazola® and of unrefined corn germ oil in contact with carbon dioxide, as well as the density of carbon dioxide‐saturated corn germ oil. The interfacial tension of refined and unrefined corn germ oil in contact with gaseous carbon dioxide at temperatures above ?10 °C depends on time, while at higher pressures the equilibrium value of the interfacial tension is reached immediately after the formation of the drops or bubbles. The interfacial tension of unrefined corn germ oil in contact with carbon dioxide is higher than the interfacial tension of refined corn germ oil. This fact is explained in this article. The interfacial tension of refined and of unrefined corn germ oil in contact with carbon dioxide decrease with rising pressure and can be described as a function of the carbon dioxide density for the examined temperature range. The density of carbon dioxide‐saturated corn germ oil is linearly dependent on pressure, with a high slope if carbon dioxide is gaseous and with a low slope if carbon dioxide is liquid.     

Solubility of 2-ethyl-hexyl-2-ethyl hexanoate in binary and quaternary systems in supercritical carbon dioxide

Binary and quaternary solubility of 2-ethyl-hexyl-2-ethyl hexanoate (2E2E) in supercritical carbon dioxide have been measured at flow rate of 250±10 ml/min, and (a) constant temperature of 313 K in the pressure range of 90–253 bar, (b) constant pressure of 170 bar, in the temperature range of 313–353 K, and (c) constant temperature of 313 K and pressure of 170 bar in flow rate range of 100–300 ml/min. The quaternary solubilities of 2-ethyl-1-hexanol and 2-ethyl hexanoic acid in supercritical carbon dioxide (SC-CO₂) were found to be greater than of 2E2E at pressure of 170 bar, a temperature of 313 K, and a flow rate of 250±10 ml/min. There is an isosolubility range for the mixed-liquid of the acid and the ester. Solubility diminutions (∼69–75%) of 2E2E at different pressures were observed for the quaternary model system compared to the binary system in SC-CO₂.     

Experimental study of methane and carbon dioxide solubility in 1,4 butylene glycol at pressures up to 11 MPa and temperatures ranging from 303 to 423 K

This work reports solubility data of methane and carbon dioxide in 1,4 butylene glycol and the Henry's law constant of each solute in the studied solvent at saturation pressure. The measurements were performed at 303, 323, 373, 398 and 423.15 K and pressures up to 3.8 MPa for mixtures containing carbon dioxide and pressures up to 10.9 MPa for mixtures containing methane. The experiments were performed in an autoclave type phase equilibrium apparatus using a technique based on the total pressure method (synthetic method). All investigated systems show an increase of gas solubility with the increase of pressure. A decrease of carbon dioxide solubility with the increase of temperature and an increase of methane solubility with the increase of temperature were observed. From the variation of solubility with temperature, the partial molar enthalpy and entropy change of each mixture were calculated.     

Cloud point behavior for poly(isodecyl methacrylate)+supercritical solvents+cosolvent and vapor-liquid behavior for CO<Subscript>2</Subscript>+isodecyl methacrylate systems at high pressure

Experimental cloud-point data of binary and ternary mixtures for poly(isodecyl methacrylate) [P(IDMA)] in supercritical carbon dioxide, dimethyl ether (DME), propane, propylene, butane and 1-butene have been studied experimentally using a high pressure variable volume view cell. These systems show the phase behavior at temperature of 308 K to 473 K and pressure up to 255 MPa. The cloud-point curves for the P(IDMA)+CO₂+isodecyl methacrylate (IDMA) are measured in changes of the pressure-temperature (P-T) slope, and with cosolvent concentrations of 0-60.1 wt%. Also, experimental data of phase behaviors for IDMA in supercritical carbon dioxide is obtained at temperature range of 313.2–393.2 K and pressure range of 5.8–22.03 MPa. The experimental results were modeled with the Peng-Robinson equation of state. The location of the P(IDMA)+CO₂ cloud-point curve shifts to lower temperatures and pressures when DME is added to P(IDMA)+CO₂ solution. The P(IDMA)+C₄ hydrocarbons cloud-point curves are ca. 16.0 MPa lower pressures than the P(IDMA)+C₃ hydrocarbons curves at constant temperature. This article is dedicated to Professor Chul Soo Lee in commemoration of his retirement from Department of Chemical and Biological Engineering of Korea University.     

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     

Ionization and Henry’s law constants for volatile,weak electrolyte water pollutants

Data base on ionization and Henry’s law constants up to 673 K are presented by temperature dependent equations for volatile, weak electrolyte water pollutants; ammonia, carbon dioxide, hydrogen sulfide, sulfur dioxide and hydrogen cyanide. In the fitting of ionization constants, various recent sources of experimental isothermal data are mainly utilized, however. Henry’s constants are correlated by two steps: first the vapor pressures, the partial molar volumes at infinite dilution, and the vapor and liquid phase nonidealities based on the vapor-liquid equilibrium conditions are calculated from P-T-x data. And then the calculated Henry’s constants at different isotherms are treated as a function of temperature. Both correlations reproduce actual data accurately up to high temperatures for reliable phase equilibrium calculations.