High-pressure phase equilibria for the binary system carbon dioxide + benzyl alcohol

The phase equilibria of the carbon dioxide + benzyl alcohol system were measured at 298.15, 306.35 and 313.15 K, under pressures from 1.03 to 16.15 MPa. An upper critical end point (UCEP) of the binary system was identified at 307.45 K and 7.77 MPa and three-phase equilibria were observed along the liquid-liquid-vapor (LLV) equilibrium line between 279.75 and 307.45 K. The experimental data were correlated well by the Peng-Robinson equation of state with two binary parameters. According to the experimental results, the phase behavior of the carbon dioxide + benzyl alcohol system appears to belong to Type-III according to the classification of van Konynenburg and Scott.     

Measurement and prediction of high-pressure vapor-liquid equilibria for binary mixtures of carbon dioxide + n-octane, methanol, ethanol, and perfluorohexane

We report the measurement of high-pressure vapor-liquid equilibrium data for binary mixtures of carbon dioxide + n-octane, +methanol, and +ethanol systems at 313.14 K and carbon dioxide + perfluorohexane at 303.15-323.15 K. The experimental data were collected using a new simple apparatus for measuring high-pressure vapor-liquid equilibria and correlated using a modified SRK equation with the three-parameter conventional mixing rule proposed by Adachi and Sugie. The SAFT-VR equation of state has also been used to predict the phase behavior and found to be in good agreement with experimental data. For the carbon dioxide + methanol, carbon dioxide + ethanol and carbon dioxide + perfluorhexane systems simple Lorentz-Berthelot combining rules can be used to determine the cross interactions and predict the phase behavior. For the carbon dioxide + n-octane system cross interaction parameters fitted to experimental data are needed in order to capture the non-ideal phase behavior exhibited by this system.     

Measurement and correlation of the solid-liquid-gas equilibria for carbon dioxide + normal chain saturated aliphatic hydrocarbon systems

The pressure p-temperature T projections of solid-liquid-gas (S-L-G) three-phase coexistence lines for the carbon dioxide + tetradecanoic acid (C₁₄H₂₈O₂) system, the carbon dioxide + hexadecanoic acid (C₁₆H₃₂O₂) system, and the carbon dioxide + 1-hexadecanol (C₁₆H₃₄O) were measured by the first melting point method in which the initial appearance of the liquid phase was observed. The profiles of the p-T projections of the S-L-G lines for the carbon dioxide + acid systems are similar to each other, the S-L-G equilibria for the carbon dioxide + acid systems are, however, different from that for the carbon dioxide + 1-hexadecanol systems. The experimental p-T projections of the S-L-G lines were also correlated by the Peng-Robinson equation of state and the van der Waals type mixing rules with two binary interaction parameters introduced into attraction term and size terms, respectively. The present model gave good correlation results for all of the experimental S-L-G lines with maximum average absolute relative deviations of 0.075% for the carbon dioxide + tetradecanoic acid system, 0.14% for the carbon dioxide + hexadecanoic acid system and 0.28% for the carbon dioxide + 1-hexadecanol system, respectively.     

Volumetric properties of carbon dioxide + 2-butanol mixtures at 313.15 K

Volumetric properties were measured of carbon dioxide + 2-butanol mixtures at 313.15 K, using the vibrating tube Anton Paar DMA 512P density meter. In the present experiments, no analytical instrument was required. The saturated pressures were also measured of carbon dioxide + 2-butanol mixtures at 313.15 K by the synthetic method. The experimental data obtained were correlated with the density equation, Soave-Redlich-Kwong (SRK) equation of state, and the pseudocubic equation of state.     

Phase equilibria of carbon dioxide + 1-nonanol system at high pressures

Vapor-liquid-equilibria (VLE) and vapor-liquid-liquid equilibria (VLLE) data for the carbon dioxide + 1-nonanol system were measured at 303.15, 308.15, 313.15, 333.15, and 353.15 K. Phase behavior measurements were made in a high-pressure visual cell with variable volume, based on the static-analytic method. The pressure range under investigation was between 1.15 and 103.3 bar. The Soave-Redlich-Kwong (SRK) equation of state (EOS) coupled with both classical van der Waals and a Gibbs excess energy (G^E) mixing rules was used in semi-predictive approaches, in order to represent the complex phase behavior (critical curve, liquid-liquid-vapor (LLV) line, isothermal VLE, LLE, and VLLE) of the system. The topology of phase behavior is correctly predicted.     

Scott-van Konynenburg phase diagram of carbon dioxide + alkylimidazolium-based ionic liquids

As part of an IUPAC task force, this study was initiated in collaboration with a number of different laboratories throughout the world to help understand the reasons for the discrepancies observed in ionic liquid properties published in literature and to establish an acceptable data bank for the investigated properties of one representative ionic liquid. This study presents experimental high-pressure solubility data of carbon dioxide in the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide within the temperature range of 280-370 K and pressures up to 14 MPa. The data are compared with those obtained in other laboratories and the differences are not alarming. In addition, a discussion is presented on the carbon dioxide + ionic liquid phase behavior according to the classifications of Scott and van Konynenburg. Such an understanding can greatly help to predict what kinds of phase phenomena may be expected of such systems in regions outside those measured experimentally and can be a very valuable map when designing and optimizing processes involving gases and ionic liquids.     

Phase behavior of the poly(neopentyl methacrylate) + supercritical fluid solvents + neopentyl methacrylate system and CO2 + neopentyl methacrylate mixtures at high pressure

High-pressure phase behaviors are measured for the CO₂ + neopentyl methacrylate (NPMA) system at 40, 60, 80, 100, and 120 °C and pressure up to 160 bar. This system exhibits type-I phase behavior with a continuous mixture-critical curve. The experimental results for the CO₂ + NPMA system are modeled using the Peng-Robinson equation of state. Experimental cloud-point data up to the temperature of 180 °C and the pressure of 2000 bar are presented for ternary mixtures of poly(neopentyl methacrylate) [poly(NPMA)] + supercritical solvents + NPMA systems. Cloud-point pressures of poly(NPMA) + CO₂ + NPMA system are measured in the temperature range of 60-180 °C and to pressures as high as 2000 bar with NPMA concentration of 0.0, 5.2, 19.0, 28.1 and 40.2 wt%. It appears that adding 51.2 wt% NPMA to the poly(NPMA) + CO₂ mixture does significantly change the phase behavior. Cloud-point curves are obtained for the binary mixtures of poly(NPMA) in supercritical propane, propylene, butane, 1-butene, and dimethyl ether (DME). The impact of dimethyl ether concentration on the phase behavior of the poly(NPMA) + CO₂ + x wt% DME system is also measured at temperature of 180 °C and pressure range of 36-2000 bar. This system changes the pressure-temperature (P-T) slope of the phase behavior curves from upper critical solution temperature (UCST) region to lower critical solution temperature (LCST) region as the NPMA concentration increases.     

Foaming strategies for bioabsorbable polymers in supercritical fluid mixtures. Part I. Miscibility and foaming of poly(l-lactic acid) in carbon dioxide + acetone binary fluid mixtures

Miscibility and foaming of poly(l-lactic acid) (PLLA) in carbon dioxide + acetone mixtures have been explored over the temperature and pressure ranges from 60 to 180 °C and 14 to 61 MPa. Liquid-liquid phase boundaries were determined in a variable-volume view-cell for polymer concentrations up to 25 wt% PLLA and fluid mixtures containing 67-93 wt% CO₂ over a temperature range from 60 to 180 °C. Even though not soluble in carbon dioxide at pressures tested, the polymer could be completely solubilized in mixtures of carbon dioxide and acetone at modest pressures.Foaming experiments were carried out in different modes. Free-expansions were carried out by exposure and swelling in pure carbon dioxide in a view-cell followed by depressurization. Foaming experiments were also carried out within the confinement of specially designed molds with porous metal surfaces as boundaries to direct the fluid escape path and to generate foams with controlled overall shape and dimensions. These experiments were conducted in pure carbon dioxide and also in carbon dioxide + acetone fluid mixtures over a wide range of temperatures and pressures. Foaming in carbon dioxide + acetone mixtures was limited to 1 and 4 wt% acetone cases. Microstructures were examined using an environmental scanning electron microscope (ESEM). Depending upon the conditions employed, pore diameters ranging from 5 to 400 μm were generated. At a given temperature, smaller pores were promoted when foaming was carried out by depressurization from higher pressures. At a given pressure, smaller pores were generated from expansions at lower temperatures. Foams with larger pores were produced in mixtures of carbon dioxide with acetone.     

A tunable mixture solvent for poly(?-caprolactone): Acetone + CO2

We report on a tunable, versatile solvent system for poly(?-caprolactone) (PCL). It is shown that acetone + carbon dioxide mixtures are efficient solvents for this biodegradable polymer. Phase behavior and volumetric properties of PCL + acetone + CO₂ mixtures were determined in a variable-volume view cell. Effect of temperature (323-398 K), pressure (0.1-50 MPa), polymer concentration (1-20 wt%), polymer molecular weight (14k and 65k) and carbon dioxide concentration (0-60 wt%) on the liquid-liquid (L-L) phase boundaries and the densities was explored. Complete miscibility of mixtures with polymer concentrations up to 20 wt% could be achieved in the fluid mixtures containing up to 50 wt% carbon dioxide at modest pressures (5-40 MPa). The solutions all showed LCST-type phase behavior. Comparisons with literature data on the miscibility pressures in other solvent mixtures such as dimethyl ether + carbon dioxide or chlorodifluoromethane + carbon dioxide show that complete miscibilities of PCL in acetone + carbon dioxide mixtures are achievable at much lower pressures.The mixture densities were in the range 0.58-1.20 g/cm³. Mixtures with carbon dioxide content more than 20 wt% showed higher sensitivity and larger change in density with pressure. Densities of the polymer solutions were found to increase significantly with PCL concentration. The densities of solutions with different polymer molecular weights were close to each other, with the lower molecular weight polymer samples showing slightly higher densities.A unique contribution of the present paper is the comparison of compressibility and expansivity of the solutions with the corresponding properties of the solvents. Analysis of the data shows that the compressibilities of PCL solutions are lower than that of the acetone + carbon dioxide solvent mixture at temperatures lower than 373 K. At around 373 K, compressibilities become equal to each other and a switchover is observed at higher temperatures. The difference in the isothermal compressibility of the polymer solution and the solvent decreases with pressure, but reaches a plateau value for pressures greater than 25 MPa. Compared to their solvent mixture, the polymer solutions display a higher isobaric expansivity at the same pressure.     

Extension of a compressible lattice model to CO2 + cosolvent + polymer systems

We have recently proposed a compressible lattice model for CO₂ + polymer systems in which CO₂ forms complexes with one or more functional groups in the polymer. Furthermore, we have shown that this model is able to simultaneously correlate phase equilibria, sorption behavior, and glass transition temperatures in such systems. In the present work, we extend the model to ternary CO₂ + cosolvent + polymer systems and demonstrate that cloud point behavior in CO₂ + dimethyl ether + poly (?-caprolactone), CO₂ + dimethyl ether + poly (isopropyl acrylate), and CO₂ + dimethyl ether + poly (isodecyl acrylate) systems can be predicted using parameters obtained from binary data. Our results also suggest that dimethyl ether may form weak complexes with poly (?-caprolactone), poly (isopropyl acrylate), and poly (isodecyl acrylate).     

Interfacial tension measurements and modelling of (carbon dioxide + n-alkane) and (carbon dioxide + water) binary mixtures at elevated pressures and temperatures

Supercritical carbon dioxide (CO₂) is often used as a process fluid for enhanced oil recovery. The storage of carbon dioxide in underground formations is a potential way of mitigating climate change during a transition period to more sustainable energy sources. Combining injection with subsequent trapping of the non-wetting supercritical carbon dioxide phase in the pores of a depleted reservoir is a promising scheme for allowing the continued use of fossil fuels with minimal environmental consequences. The design of such processes is ultimately linked to the confined behaviour of the fluids in question at reservoir conditions, which is largely controlled by interfacial forces. Measurements of the relevant interfacial tensions for systems containing alkanes, carbon dioxide and water are currently limited and inconsistent while models usually fail to capture the pressure dependence of the interfacial tension. In this work, a density functional theory based on the SAFT-VR equation of state was used to predict the interfacial tension of (H₂O + CO₂ + n-alkane) binary systems over wide ranges of temperature and pressure. The comparison with a new set of reported experimental data of three (n-alkane + CO₂) systems at pressures up to the critical points, as well as with the (H₂O + CO₂) system at pressures up to 60 MPa, for a temperature range of (298-443) K, is discussed.     

Phase equilibrium data and thermodynamic modeling of the system propane + NMP + methanol at high pressures

This work reports phase equilibrium data at high pressures for the binary and ternary systems formed by propane + n-methyl-2-pyrrolidone (NMP) + methanol. Phase equilibrium measurements were performed in a high-pressure variable-volume view cell, following the static synthetic method for obtaining the experimental bubble and dew points transition data in the temperature range of 363-393 K, pressures up to 16 MPa and overall molar fraction of the lighter component varying from 0.1 to 0.998. For the systems investigated, vapor-liquid (VLE), liquid-liquid (LLE) and vapor-liquid-liquid (VLLE) phase transitions were visually recorded. Results show that the systems investigated present UCST (upper critical solution temperature) phase transition curves with an UCEP (upper critical end point) at a temperature higher than the propane critical temperature. The experimental data were modeled using the Peng-Robinson equation of state with the Wong-Sandler and the classical quadratic mixing rules, affording a satisfactory representation of the experimental data.     

High pressure phase behavior and density of the carbon dioxide + 1-methylimidazole binary system

The phase behavior of the carbon dioxide + 1-methylimidazole binary system has been investigated in a high-pressure variable-volume view cell using an analytical method. Phase equilibrium data for the system carbon dioxide + 1-methylimidazole was measured at 293.15, 309.75 and 323.15 K. The pressure under investigation was between 2.83 and 14.16 MPa. There coexisted three phases (LLV) of the binary system, which were found in a temperature range of 297.85–313.95 K. The densities of the binary mixture at phase transition points were also measured. The experimental data were correlated well by the Peng–Robinson equation of state with two binary parameters. According to the experimental results, the phase behavior of the binary system might be classified to Type-IV or Type-V according to the classification of six principal types of binary phase diagrams.     

Phase equilibria and glass formation studies in the (1 − x)TeO2-xCdO (0.05 ≤ x ≤ 0.33 mol) system

Phase equilibria and glass formation studies of the (1 − x)TeO₂-xCdO system (0.05 ≤ x ≤ 0.33 mol) were realized by using differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The samples were prepared by applying a conventional melt-quenching technique at 800 °C. The glass formation range of the system was determined as 0.05 ≤ x < 0.15 and the sample containing 10 mol% CdO showed the highest glass stability. Crystallization behavior of the TeO₂-CdO glasses was investigated and formation and/or transformation of different phases were detected for each crystallization reaction. In order to obtain thermal stability of the system, as-cast samples were heat-treated above all crystallization reaction temperatures at 550 °C for 24 h. A binary eutectic: liquid → TeO₂ + CdTe₂O₅ was detected at 638 ± 4 °C. Crystallization behavior of the TeO₂-CdO glasses and microstructural characterization of the TeO₂-CdTe₂O₅ system was realized.     

Measurement of phase equilibria of the systems CO2 + styrene and CO2 + vinyl acetate using different experimental methods

The experimental determination of high-pressure phase equilibria is often the only suitable method to obtain reliable data because high-pressure phase behavior is complex and difficult to predict. This contribution gives a brief classification of applied experimental methods. A new high-pressure apparatus is described, which can be used for phase-equilibrium measurements with different experimental methods, namely the analytical-isothermal method, the synthetic-isothermal method as well as the non-visual- and the visual-synthetic method. The different techniques have been tested for the measurement of the phase behavior of systems containing CO₂ + styrene and CO₂ + vinyl acetate. The measured data were compared with data from literature and discussed in terms of accuracy, advantages and drawbacks of the applied methods.     

Structure and electrochemical characterization of electrolytic Ni + Mo + Si composite coatings in an alkaline solution

Ni + Mo + Si coatings were obtained by nickel deposition from a bath containing suspension of molybdenum and silicon powders. These coatings were obtained in galvanostatic conditions, at the current density of j_dep = −0.100 A cm⁻². For determination of the influence of phase composition and surface morphology of obtained coatings on changes of corrosion resistance, these coatings were modified in argon atmosphere by thermal treatment at the temperature of 1100 °C during 1 h. A scanning electron microscope was used for surface morphology characterization of the coatings. Chemical composition of obtained coatings was determined by X-ray fluorescence spectroscopy method. Phase composition investigations were conducted by X-ray diffraction method. It was found that the obtained coatings are composed of three phase structures, i.e., nickel, molybdenum and silicon. Phase composition for the Ni + Mo + Si coatings after thermal treatment is markedly different. The main peaks corresponding to the Ni and Mo coexist with the new ones corresponding to new phases: Mo₅Si₃, NiSi, Mo₂Ni₃Si and Ni₆Mo₆C_1.06.Electrochemical corrosion resistance investigations were carried out in the 5 M KOH, using potentiodynamic and electrochemical impedance spectroscopy methods. On the basis of these investigations it was found that Ni + Mo + Si coatings after thermal treatment are more resistant in alkaline solution than Ni + Mo + Si as-deposited coatings. The reason of this is presence of silicides in the coatings.     

High-pressure gas-liquid equilibrium of the system carbon dioxide-citral at 50 and 70 °C

Measurements of high-pressure gas-liquid equilibria of the binary system carbon dioxide-citral were carried out in the present work. The knowledge of the phase equilibrium behaviour of this system is relevant with regard to the design and optimization of the supercritical deterpenation process. The measurements were carried out at 50 and 70 °C, in the pressure range 7.8-15.6 MPa, by means of a two-chamber gas-phase recirculation apparatus of 340 cm³. Both the liquid and the gas phase composition were measured. The data at 50 °C measured in this work were compared with literature data, whereas no comparison was possible at 70 °C because of their lack. The experimental data measured in this work were successfully correlated by means of a thermodynamic model based on the Peng-Robinson equation of state.     

Drying processes for preparation of titania aerogel using supercritical carbon dioxide

Supercritical carbon dioxide drying was performed for the preparation of titania aerogels from sol–gel routes. The conditions of supercritical carbon dioxide drying were 313–323 K and 7.8–15.5 MPa. The solvents in titania wet gels obtained from the sol–gel routes were replaced by acetone. The titania aerogels obtained from supercritical carbon dioxide drying form needle-like structures. In supercritical carbon dioxide drying, the extraction rates of acetone from the wet gels were measured by using an on-line Fourier transform infrared spectroscope. It was found that the titania aerogels with lower cohesion were induced from the formations of homogenous phase for carbon dioxide + acetone system and the lower extraction rates of acetone. Furthermore, titania films were prepared by the depositions of the titania aerogels on ITO-coated PET substrates. The needle-like aerogels with lower cohesion derive the titania film with high surface area.     

Studies of interfacial layers between 4H-SiC (0 0 0 1) and graphene

The region between epitaxial graphene and the SiC substrate has been investigated. 4H-SiC (0 0 0 1) samples were annealed in a high temperature molecular beam epitaxy system at temperatures between 1100 and 1700 °C. The interfacial layers between the pristine SiC and the graphene layers were studied by X-ray photoelectron spectroscopy. Graphene was found to grow on the SiC surface at temperatures above 1200 °C. Below this temperature, however, sp³ bonded carbon layers were formed with a constant atomic Si concentration. C1s and Si2p core level spectra of the graphene samples suggest that the interface layer we observe has a high carbon concentration and its thickness increases during the graphitization process. A significant concentration of Si atoms is trapped in the interface layer and their concentration also increases during graphitization.