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.     

Experimental and molecular modelling study of the three-phase behaviour of (propane + carbon dioxide + water) at reservoir conditions

Acquiring a comprehensive understanding of the phase behaviour of mixtures of crude-oil with carbon dioxide and water is a key input for reservoir engineering in processes of enhanced oil recovery and geological storage of carbon dioxide. To gain an insight, given the very complex nature of crude-oil mixtures, the study of simpler systems is of interest. In this work the system (propane + carbon dioxide + water) has been chosen as a model (light oil fraction + carbon dioxide + water) mixture. Phase equilibrium measurements have been carried out using a quasi-static-analytical high-pressure apparatus that was validated on the system (n-decane + carbon dioxide) in comparison with literature data, and used to study the system (n-decane + carbon dioxide + water) [E. Forte, A. Galindo, J. P.M. Trusler, The Journal of Physical Chemistry B 115 (49) (2011) 14591–14609]. In the present work, new experimental data have been measured for the system (propane + carbon dioxide + water) under conditions of three-phase equilibria. Compositions of the three coexisting phases have been obtained along four isotherms at temperatures from 311 to 353 K and at pressures up to the upper critical end points where the propane-rich and the carbon dioxide-rich phases become critical. The experimental data obtained for the ternary mixture have been compared to the predictions obtained with the statistical associating fluid theory for potentials of variable range (SAFT-VR). The phase behaviour of each pair of binary subsystems has been calculated using this theory and, where applicable, a modification of the Hudson and McCoubrey combining rules has been used to treat the systems predictively. Furthermore, a detailed analysis of the phase behaviour of the ternary mixture has been carried out based on comparison with available data for the constituent binary subsystems, as well as with the previous findings for the ternary (n-decane + carbon dioxide + water). Such comparison is useful to examine the effect that adding a third component has in the mutual solubility of each pair. Remarks relevant to reservoir processing are also highlighted.     

Liquid–liquid equilibria and thermo physical properties for 1-methyl-2-pyrrolidinone + heterocyclic nitrogen compounds + hexadecane systems at 298.15 K

Liquid–liquid equilibrium data for {1-methyl-2-pyrrolidinone (NMP) + heterocyclic nitrogen compounds + hexadecane} systems were analytically determined at 298.15 K and atmospheric pressure using stirred and thermo-regulated cell. The experimental data were modeled with the NRTL and UNIQUAC equations. Besides, the Bachman–Brown correlation was used to ascertain the reliability of the experimental data. Additionally, excess molar volumes (V^E) and deviations in the molar refractivity (ΔR) data at 298.15 K were determined for the {NMP + heterocyclic nitrogen compounds} binary systems using a digital vibrating-tube densimeter and a precision digital refractometer. The V^E and ΔR data were modeled with the Redlich–Kister equation.     

Phase equilibria of (CO2 + H2O + NaCl) and (CO2 + H2O + KCl): Measurements and modeling

We report experimental measurements of the phase behavior of (CO₂ + H₂O + NaCl) and (CO₂ + H₂O + KCl) at temperatures from 323.15 K to 423.15 K, pressure up to 18.0 MPa, and molalities of 2.5 and 4.0 mol kg⁻¹. The present study was made using an analytical apparatus and is the first in which coexisting vapor- and liquid-phase composition data are provided. The new measurements are compared with the available literature data for the solubility of CO₂ in brines, many of which were measured with the synthetic method. Some literature data show large deviations from our results.The asymmetric (γ–φ) approach is used to model the phase behavior of the two systems, with the Peng–Robinson equation of state to describe the vapor phase, and the electrolyte NRTL solution model to describe the liquid phase. The model describes the mixtures in a way that preserves from our previous work on (CO₂ + H₂O) the values of the Henry's law constant and the partial molar volume of CO₂ at infinite dilution Hou et al. [22]. The activity coefficients of CO₂ in the aqueous phase are provided. Additionally, the correlation of Duan et al. [14] for the solubility of CO₂ in brines is tested against our liquid-phase data.     

Phase equilibrium data of guaçatonga (Casearia sylvestris) extract + ethanol + CO2 system and encapsulation using a supercritical anti-solvent process

The aim of this research was to investigate the phase equilibrium behavior of a system containing guaçatonga extract + ethanol + CO₂ in order to help define the adequate conditions of temperature and pressure for the co-precipitation process, performed by means of supercritical anti-solvent (SAS) technique. Guaçatonga (Casearia sylvestris) is a native medicinal plant from Brazil, rich in valuable components such as β-caryophyllene, α-humulene and bicyclogermacrene. Phase equilibrium data were obtained by the static method using guaçatonga extract dissolved in ethanol (1:100, wt/wt), at temperatures ranging from 35 to 75 °C and CO₂ mass content from 60 to 90 wt%. It was noticed that the system exhibited solid–vapor–liquid, solid–liquid–liquid and solid–vapor–liquid–liquid transition types and a lower critical solution temperature behavior. Phase behavior study was considered for the definition of the SAS conditions applied for the encapsulation of guaçatonga extract in the biopolymer Pluronic F127. The conditions tested ranged from 80 to 140 bar at 45 °C. At 80 bar only segregated particles of extract and the biopolymer were detected, while at 110 and 140 bar an extract encapsulation was achieved.     

Measurement and modeling of the phase behavior of the (carbon dioxide + water) mixture at temperatures from 298.15 K to 448.15 K

An analytical apparatus has been designed to study the phase behavior of fluid mixtures of relevance to CO₂-enhanced oil recovery and carbon dioxide storage in deep aquifers or depleted oil fields. The fluid phases are circulated by means of a dual-channel magnetically-coupled pump and aliquots may be withdrawn from the re-circulation loops, by means of high-pressure sampling valves, for analysis by gas chromatography. The high-pressure cell is fitted with a special probe that may be rotated in order to draw liquid into the re-circulation loop from different heights within the cell, thereby permitting the study of three-phase vapor–liquid–liquid equilibria. The working temperature range of the apparatus is from (298 to 448) K and the maximum working pressure is 50 MPa.In this work, measurements have been made on the binary system (CO₂ + H₂O) at temperatures from (298.15 to 448.15) K and pressure from (1.5 to 18.0) MPa, and the results are compared with the available literature data. Vapor–liquid–liquid and liquid–liquid equilibrium points were also measured at T = 298.15 K. Standard uncertainties were 0.04 K for temperature, 0.04% of reading for pressure, and typically 3 × 10⁻⁴ and 8 × 10⁻⁴ for the mole fractions in liquid and vapor phases respectively. The results have been correlated by means of an asymmetric approach based on the Peng–Robinson equation of state, for the vapor phase, and an extended form of Henry's law incorporating the NRTL solution model, for the aqueous liquid-phase. The ability of the Krichevsky–Kasarnovsky (KK) approach to correlate the data has also been evaluated.     

High-pressure phase equilibrium data for the l-lactic acid + (propane + ethanol) and the l-lactic acid + (carbon dioxide + ethanol) systems

Biodegradable polymers have received increased attention due to their potential applications in the medicine and food industries; in particular, poly(l-lactic acid) (PLA) is of primary importance because of its biocompatibility and resorbable features. Recently, the synthesis of this biopolymer through the enzyme-catalyzed ring-opening polymerization of l-lactic acid in a compressed fluid has been considered promising. The aim of this work was to report the phase equilibrium data (cloud points) of the l-lactic acid + (propane + ethanol) and the l-lactic acid + (carbon dioxide + ethanol) systems. The phase equilibrium experiments were conducted in a variable-volume view cell employing the static synthetic method. These experiments were conducted in the temperature range of 323.15–353.15 K and at pressures up to 25 MPa; the mass ratio of ethanol to either CO₂ or propane was maintained at 1:9. The l-lactic acid + (propane + ethanol) system exhibited vapor–liquid, liquid–liquid and vapor–liquid–liquid transitions, whereas the l-lactic acid + (carbon dioxide + ethanol) system only exhibited liquid–liquid type transitions.     

Microwave dielectric properties of BaxLa4Ti3 + xO12 + 3x (x = 0.0–1.0) ceramics

In the BaO–La₂O₃–TiO₂ system, the Ba_nLa₄Ti_3 + nO_12 + 3n homologous compounds exist on the tie line BaTiO₃–La₄Ti₃O₁₂ besides tungstenbronze-type like Ba_6 − 3xR_8 + 2xTi₁₈O₅₄ (R = rare earth) solid solutions. There are four kinds of compounds in the homologous series: n = 0, La₄Ti₃O₁₂; n = 1, BaLa₄Ti₄O₁₅; n = 2, Ba₂La₄Ti₅O₁₈; n = 4, Ba₄La₄Ti₇O₂₄. These compounds have the layered hexagonal perovskite-like structure, which has a common sub-structure in the crystal structure. These compounds have been investigated in our previous studies. In this study, we have investigated the phase relation and the microwave dielectric properties of Ba_xLa₄Ti_3 + xO_12 + 3x ceramics in the range of x between 0.2 and 1.0. With the increase in x, the dielectric constant ɛ_r locates around 45, the quality factor Q × f shows over 80,000 GHz at x = 0.2 and the minimum value of 30,000 GHz at x = 0.9, and the temperature coefficients of resonant frequency τ_f is improved from −17 to −12 ppm/°C. At x = 0.2, the ceramic composition obtained has dielectric constant ɛ_r = 42, the temperature coefficient of the resonant frequency τ_f  = −17 ppm/°C and a high Q × f of 86,000 GHz.     

Experimental measurement and modelling with Aspen Plus® of the phase behaviour of supercritical CO2 + (n-dodecane + 1-decanol + 3,7-dimethyl-1-octanol)

Experimental phase equilibrium data for the systems CO₂ + n-dodecane, CO₂ + 1-decanol and CO₂ + 3,7-dimethyl-1-octanol were used to determine values for binary interaction parameters for use in the RK-ASPEN thermodynamic model in Aspen Plus^®. Bubble and dew point data of the mixtures CO₂ + (n-dodecane + 1-decanol), CO₂ + (n-dodecane + 3,7-dimethyl-1-octanol), CO₂ + (1-decanol + 3,7-dimethyl-1-octanol) and CO₂ + (n-dodecane + 1-decanol + 3,7-dimethyl-1-octanol) were measured experimentally in a static synthetic view cell, and compared to the data predicted by the RK-ASPEN model. The model predicted the phase equilibrium data reasonably well in the low solute concentration region; significant deviation of model predictions from experimental data occurred in the mixture critical and high solute concentration regions due to the exclusion of solute–solute interaction parameters in the model. Distribution coefficients and separation factors were determined for the multi-component mixture and separation of the alkane from the alcohol mixture with a supercritical fluid extraction process was found to be possible.     

Phase equilibria of allyl sulfide + carbon dioxide binary mixtures: Experimental data and thermodynamic modeling

This contribution reports new experimental data on vapor–liquid equilibrium of the binary system diallyl sulfide + carbon dioxide, at temperatures between 275 and 370 K and pressures up to 12 MPa. These data are of interest to study the extraction of Allium oils from garlic and onion, using near-critical CO₂. The experimental data were modeled with a group-contribution equation of state. A (CH₂S) functional group has been defined to represent alkyl and allyl sulfides. Pure group and binary interaction parameters for this new functional group have been determined. Good correlation and prediction of phase equilibrium conditions were obtained.     

Vapor–liquid phase equilibrium of carbon dioxide with mixed solvents of DMSO + ethanol and chloroform + methanol including near critical regions

A visual and volume-variable high-pressure phase equilibrium analyzer was used for measuring the vapor–liquid phase boundaries of the ternary systems containing carbon dioxide and mixed solvents of dimethyl sulfoxide (DMSO) + ethanol or chloroform + methanol at temperatures from 298.15 K to 348.15 K over wide composition ranges including near critical points. Four pseudo-binary systems of carbon dioxide plus mixed solvents with constant molar ratios of DMSO/ethanol = 3/7, 5/5, 7/3, and chloroform/methanol = 1/2, were studied in this work. The critical conditions at each investigated temperature were estimated from the experimental isothermal phase boundaries by interpolation. The Peng–Robinson equation of state with the two-parameter van der Waals mixing rules was applied to calculate the phase boundaries. The experimental values were compared with the predicted results from the Peng–Robinson equation using the binary interaction parameters determined from the vapor–liquid equilibrium data of the constituent binaries. The agreement is reasonably well for carbon dioxide + chloroform + methanol, but obvious overestimations are found near the critical regions of carbon dioxide + DMSO + ethanol, especially at higher temperatures.     

High pressure phase behavior of methanol + ethylene: Experimental measurements and CPA modeling

High pressure–temperature isopleths were obtained, experimentally, for the binary system of methanol + ethylene within a temperature and pressure range of 293–373 K and 38–119 bar, respectively. The experimental results were modeled using the Cubic-Plus-Association (CPA), Peng–Robinson (PR) and Soave–Redlich–Kwong (SRK) equations of state. The ability of the CPA model to predict the phase behavior of methanol + ethylene is much better than the SRK and PR models. However, even though the p–T diagrams indicate that the CPA equation of state correlates well with the experimental results, by increasing ethylene concentrations, the errors of CPA increase due to the solvation that occurs in methanol + ethylene systems. In this work, the effect of solvation is also investigated. Results show that deviations from experimental data are less for CPA with solvation than for the CPA without solvation. Correlations are presented for the binary interaction (k_ij) and the association volume (β^A_iB_j) parameters to model the phase behavior of methanol + ethylene, as both of these parameters were indicated to be temperature-dependent.     

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.     

High pressure densities of carbon dioxide + dipentaerythritol hexaheptanoate: New experimental setup and volumetric behavior

To perform an appropriate selection of the lubricants in air conditioned systems working with carbon dioxide as refrigerant, the thermodynamic behavior of the CO₂ + lubricant systems must be well known. In this work we present a new setup to prepare compressed gas–liquid mixtures and to determine the high pressure density by using an automated densimeter HPM and two syringe pumps. To analyze the reliability of the procedure proposed, we have determined the densities and mixing volumes of four CO₂ + n-decane mixtures. We have found a good agreement with previous literature data. In addition new density values are reported for the binary system CO₂ + dipentaerythritol hexaheptanoate (DiPEC7) at several temperatures and pressures from 10 MPa to 120 MPa.     

Preparation and characterisation of the magneto-electric xBiFeO3–(1 − x)BaTiO3 ceramics

The solid solutions of BiFeO₃–BaTiO₃ have been prepared via solid state with a view to obtaining magnetoelectric properties, i.e. ferroelectric and magnetic activity in the same range of temperatures. Optimum calcination and sintering strategy for obtaining pure perovskite phase, dense ceramics (>97% relative density) and homogeneous microstructures have been determined. The sample of composition 0.7BiFeO₃–0.3BaTiO₃ reported in the present work is pseudo-cubic at room temperature. The permittivity is ɛ_r ≈ 150 at the room temperature and shows a broad ferro-para phase transition at around 175 °C where ɛ_r ≈ 1600. This diffuse maximum of the permittivity, similar to that in relaxors, is due to the chemical inhomogeneity in both A and B sites of the perovskite unit cell ABO₃. Higher losses, tan δ > 1, appear above 200 °C and other different conduction mechanisms start to be active particularly at temperatures higher than 400 °C, when the ceramic becomes conductive. The magnetic properties show a succession of transitions from weak ferro/ferrimagnetism-to-antiferromagnetism and antiferromagnetism-to-paramagnetism at T_N1 ≈ 10 K and T_N2 ≈ 265 K. Below T_N2 the ceramic 0.7BiFeO₃–0.3BaTiO₃ can present magnetoelectric coupling, due to the fact that is simultaneously ferroelectric and antiferromagnetic.     

Measurement and correlation of vapor–liquid equilibra for cyclohexane + ethylene glycol monoisopropyl ether and cyclohexane + ethylene glycol monoisobutyl ether systems

Ethylene glycol monoisopropyl ether (iC₃E₁) and ethylene glycol monoisobutyl ether (iC₄E₁) are nonionic surfactants which have been attracting considerable attention due to inter and intra-molecular association, related to the presence of O and OH in the same molecule. Binary isothermal vapor + liquid equilibrium data were measured for cyclohexane + ethylene glycol monoisopropyl ether and cyclohexane + ethylene glycol monoisobutyl ether systems at four different temperatures ranging from 303.15 K to 333.15 K at 10 K intervals. A static apparatus was used in this study. Two systems show positive deviation from Raoult's law and no azeotrope. The experimental data were correlated well with Peng–Robinson–Stryjek–Vera equation of state using Wong–Sandler mixing rule.     

X-ray single phase LSGM at 1350 °C

Synthesis of X-ray-phase-pure (La_1−xSr_xGa_1−yMg_yO_3−δ, LSGM, where x = 0.1, y = 0.15 and 0.17) powders were achieved at temperatures as low as 1350 °C via organic precursor method using tartaric acid as the carrier material. LSGM materials were characterized for their phase purity, crystallization and electrical properties. Pellets sintered at 1350 °C for 6 h were single phase and dense (>99%). Electron microscopy analysis of X-ray single-phase pellets revealed MgO precipitates with sizes ranging from 50–300 nm. Phase formation and distribution in this complicated multi-cation-oxide system as a function of temperature were reported and discussed. Amorphous LSGM first crystallizes at 625 °C. However, elimination of undesired phases require higher temperatures. Impedance measurements as a function of temperature up to 545 °C revealed that the X-ray phase pure pellets may have extrapolated ionic conductivity values as high as 0.14–0.16 S/cm at 800 °C. Possible implications of limited MgO solubility on the ionic conductivity are presented.     

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

The experimental solubility of dibenzofuran in near-critical and supercritical carbon dioxide and the solid–liquid–vapor (SLV) equilibrium line for the CO₂ + dibenzofuran system are reported. The built in-house static view cell apparatus used in these measurements is described. The solubility of naphthalene in supercritical CO₂ and the CO₂ + naphthalene SLV line are also determined in order to assess the reliability and accuracy of the measurement technique. The solubility of dibenzofuran in carbon dioxide is determined at 301.3, 309.0, 319.2, 328.7 and 338.2 K in the 6–30 MPa pressure range. Solubility data are correlated using the Chrastil model and the Peng–Robinson equation of state. This equation is also used to predict the CO₂ + dibenzofuran SLV line. Results show the feasibility of using supercritical CO₂ to extract dibenzofuran.     

Phase behavior measurement for poly(isobornyl acrylate) + cosolvent systems in supercritical solvents at high pressure

We have conducted experiments to obtain cloud-point data of binary and ternary mixtures for poly(isobornyl acrylate) [P(IBnA)] (Mw = 100,000) + isobornyl acrylate(IBnA) in supercritical carbon dioxide (CO₂), P(IBnA) (Mw = 100,000) + dimethyl ether (DME) in CO₂, P(IBnA) (Mw = 100,000) in propane and butane, and P(IBnA) (Mw = 1,000,000) in propane, propylene, butane and 1-butene at high pressure conditions. Phase behaviors for these systems were measured at a temperature range from 323.4 K to 474.1 K and pressure up to 296.7 MPa. The cloud-point curves of P(IBnA) (Mw = 100,000) + IBnA and DME in CO₂ change from upper critical solution temperature (UCST) behavior to lower critical solution temperature (LCST) behavior as IBnA and DME concentration increases, and liquid–liquid–vapor phase behavior appears for the P(IBnA) (Mw = 100,000) + CO₂ + 80.3 wt.% IBnA system. Phase behaviors of P(IBnA) and 50 wt.% IBnA in CO₂ and P(IBnA) in propane and butane show the pressure difference in accordance with Mw = 1,000,000 and Mw = 100,000 of P(IBnA). Also, the solubility curves for IBnA in supercritical CO₂ were measured at a temperature range of (313.2–393.2) K and pressure up to 22.86 MPa. The experimental results were modeled with the Peng–Robinson equation of state (PR-EOS) using a mixing rule including two adjustable parameters. The critical property of IBnA is estimated with the Joback–Lyderson method.     

New high Q microwave dielectric ceramics with rock salt structures: (1 − x)Li2TiO3 + xMgO system (0 ≤ x ≤ 0.5)

The structural evolution and microwave dielectric properties of (1 ? x)Li₂TiO₃ + xMgO system (0 ≤ x ≤ 0.5) have been investigated in this paper. The ordering degree decreased with the increase of MgO content. The microcracks and cleavage on (0 0 1) due to the weak Li–O bonds disappeared with the increase of MgO content. The dielectric constant and temperature coefficient of resonant frequency decreased with the increase of MgO content. The Q × f value increased with x up to x = 0.2 and then decreases with the further increase of x. An excellent combined microwave dielectric properties could be obtained when x = 0.24, ?_r = 19.2, Q × f = 106,226 GHz and τ_f = 3.56 ppm/°C.