High-pressure phase equilibrium measurements and thermodynamic modeling for the systems involving CO2, ethyl esters (oleate,stearate, palmitate) and acetone

The aim of this work was to study the phase behavior of systems involving carbon dioxide (CO₂), fatty acid ethyl esters (ethyl oleate, ethyl stearate and ethyl palmitate) and acetone at high pressures. The phase behavior involving these components is an important step regarding the design and optimization of industrial processes based on supercritical conditions, such as biodiesel production and fatty esters fractionation involving supercritical and/or pressurized solvents. In addition, supercritical CO₂ can offer an interesting alternative for glycerol separation in water-free biodiesel purification processes. The binary systems investigated in this work were CO₂ + ethyl oleate, and CO₂ + ethyl stearate and these were compared with the CO₂ + ethyl palmitate system. The ternary CO₂ + ethyl palmitate + acetone was also investigated at two different ethyl palmitate to acetone molar ratios of (1:1) and (1:3). The static synthetic method using a variable-volume view cell was employed to obtain the experimental data in the temperature range of 303.15–353.15 K. Vapor–liquid (VL), liquid–liquid (LL) and vapor–liquid–liquid (VLL) phase transitions were observed in these systems. In the binary systems, the solubility increased with the presence of unsaturation and decreased with the number of carbon atoms in the fatty ester chain. Addition of acetone as well as ethanol eliminated the liquid–liquid immiscibility and reduced the pressure transitions, therefore increasing the solubility of the ester in supercritical CO₂. The experimental data sets for the binary and ternary systems were successfully modeled using the Peng–Robinson equation of state with the classical van der Waals quadratic mixing rule (PR-vdW2) and Wong-Sandler (PR-WS) mixing rule. Both models showed good performance in the phase equilibrium correlations and in predictions for the binary and ternary systems.     

Phase equilibria of linear saturated high molecular mass acids in supercritical ethane

High-pressure phase equilibria of the ethane/acid homologous series for linear saturated acids with between 10 and 22 carbon atoms are investigated. Measurements for ethane with decanoic, undecanoic, dodecanoic, tetradecanoic, hexadecanoic, octadecanoic and docosanoic acid were conducted between 308 and 353 K in the acid mass fraction range of 0.016–0.68. Higher phase transition pressures were measured at higher temperatures and no three-phase regions, or indications thereof, were observed. The measurements revealed that as the number of carbon atoms increased, so the phase transition pressure increased linearly, prompting the compilation of a set of linear pressure–carbon number plots. The observed phase transition pressures for the ethane/acid systems are also lower than that of the CO₂/acids systems, suggesting that ethane is an alternative supercritical solvent to or co-solvent with CO₂ for processes involving high molecular mass acids.     

Phase equlibiria and diffusivity of dense gases in various polyethylenes

The aim of this work was to investigate the properties of polyethylenes (PE) of various densities (low-density and high-density) under pressure of CO₂ and propane. The phase equilibria of PE of different density in presence of CO₂ and in presence of propane in dependence of pressure and temperature were investigated. The phase transitions of PE at atmospheric pressure were determined by differential scanning calorimetry (DSC). Furthermore, phase transitions of polymers under pressure of gases were measured by using an optical high pressure cell. Measurements of phase transition were performed in range of pressure of 1–90 MPa. The results show that melting points of LDPE decreased in presence of CO₂ and in presence of propane. For high-density polyethylene (HDPE) the melting point decrease was observed only in presence of propane, while in presence of CO₂ melting point increases with increasing pressure. The melting points of LDPE and HDPE decrease in average for 10–20 K in presence of propane, while in presence of CO₂ the melting point decrease for both LDPE was lower (5–10 K). Solubility and diffusivity of supercritical CO₂ in two low-density polyethylenes (LDPE) and in high-density polyethylene (HDPE) were measured at temperature 373 K and pressures up to 30 MPa using a magnetic suspension balance (MSB). The solubility data were used for estimating the binary diffusion coefficients. The solubilities increased with increasing density. The diffusion coefficient shows strong CO₂ density and CO₂ solubility dependence. Diffusion coefficient starts to decrease with increasing density and solubility of CO₂.     

Phase equilibria of long chain n-alkanes in supercritical ethane: Review,measurements and prediction

The available sets of data for the phase equilibrium of long chain n-alkanes with 10 or more carbon atoms in supercritical ethane were studied to determine if the phase equilibrium pressure can be predicted from the number of carbon atoms and system temperature. It has previously been shown that for the phase equilibria of heavy n-alkanes in supercritical propane there exists, at constant temperature and mass fraction, a linear relationship between the number of carbon atoms and the bubble/dew point pressure. Published data in the temperature range 310–360 K was obtained from a literature survey and, where required, additional data was measured using a high-pressure equilibrium cell. It was found that linear relationships exist and that these relationships can be used to predict the phase equilibrium pressure within 4% of experimental values.     

Supercritical CO2 extraction of lutein esters from marigold (Tagetes erecta L.) enhanced by ultrasound

As a novel technique, supercritical CO₂ (SC-CO₂) extraction enhanced by ultrasound was applied to the extraction of lutein esters from marigold and the extraction curves were described by Sovová model. The mass transfer coefficient in the solid phase (k_s) increased from 3.1 × 10⁻⁹ to 4.3 × 10⁻⁹ m/s due to ultrasound. The effect of extraction parameters including particle size of matrix, temperature, pressure, flow rate of CO₂, and ultrasonic conditions consisting of power, frequency and irradiation time/interval on the yield of lutein esters were investigated with single factor experiments. The results showed that the yield of lutein esters increased significantly with the presence of ultrasound (p < 0.05). The maximal yield of lutein esters (690 mg/100 g) was obtained for a particle size fraction of 0.245–0.350 mm, extraction pressure of 32.5 MPa, temperature of 55 °C and CO₂ flow rate of 10 kg/h with ultrasonic power of 400 W, ultrasonic frequency of 25 kHz and ultrasonic irradiation time/interval of 6/9 s.     

Phase behavior for the poly(dimethylsiloxane) in supercritical fluid solvents

In this work, cloud-point and bubble-point phase behavior data are reported for the poly(dimethylsiloxane) [PDMSA] in supercritical carbon dioxide, propane, propylene, butane, 1-butene and dimethyl ether (DME). The static-type method, using a variable-volume view cell, was employed to obtain the experimental data at the temperature range for (315.2–454.9) K and pressure up to 55.52 MPa. PDMS (M_w = 38,900) + C₄ cloud-point curves are ～10 MPa lower than the PDMS + C₃ curves at constant temperature of 423 K. Cloud-point curves for the PDMS + solvents system show the lower critical solution temperature (LCST) region.     

Supercritical carbon dioxide separation of fish oil ethyl esters by means of a continuous countercurrent process with an internal reflux

The continuous countercurrent fractionation of fish oil ethyl esters using supercritical carbon dioxide is studied, modelling a process with internal reflux generated by a thermal gradient at the top stage. A methodology for process design is proposed and applied to determine the relationships between the temperature at the top stage (T₁), the number of theoretical stages (N), and the solvent to feed ratio (S/F), with the aim of providing a quantitative comparison with the external reflux process. The internal reflux process is viable and, for stated process specifications (mass fraction and recovery of C20 + C22 ethyl esters of 95%), provides comparable or better results than the external reflux process. For example, operating at 13.3 MPa and 50 °C, and keeping T₁ in the range (66–70) °C, the specifications are attained with N and S/F in the range 16–30 and 88–120, respectively.     

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.     

Sunflower oil hydrogenation on Pd in supercritical solvents: Kinetics and selectivities

The partial hydrogenation of sunflower oil on a few supported Pd catalysts in supercritical (SC) dimethyl ether (DME) as reaction solvent was studied to obtain hydrogenates with low trans C 18:1 and stearic contents.The kinetics was determined on eggshell 0.5% Pd/Al₂O₃ and uniform 2% Pd/C catalysts using a sequential experimental design in a continuous, radial-flow, internal recycle reactor. The operating variables were temperature (456–513 K), pressure (18–23 MPa) and the space-velocity (WHSV = 41–975 h⁻¹). The rotation frequency and the molar feed concentration (oil:H₂:DME) were held constant at 157 rad/s and 1:4:95 mol%, respectively. Kinetic scheme was based on that published before. Some reactor runs were simulated using mixed-flow assumption and the kinetics data for both systems with good results. A comparison was established between the eggshell 0.5% Pd/Al₂O₃ in DME and the data for 2% Pd/C in propane with respect to trans production and stearic formation. trans seems to be lower using 2% Pd/C in propane, while the undesired stearic formation is less on the eggshell 0.5% Pd/Al₂O₃ catalyst in DME. An overview is presented on the merits of the catalysts available for the SCF process in terms of linoleic selectivity and trans yield on a few vegetable fats.     

Response surface optimization of Smyrnium cordifolium Boiss (SCB) oil extraction via supercritical carbon dioxide

In this study, the essential oil of aerial parts of a species of a plant called Smyrnium cordifolium Boiss (SCB) was extracted by supercritical CO₂. The essence was analyzed by the method of GC/MS. Design of experiments was carried out with response surface methodology by Minitab 16 software to optimize four operating variables of supercritical carbon dioxide (SC-CO₂) extraction (pressure, temperature, CO₂ flow rate and extraction dynamic time). This is the first report announcing optimization of the operation of supercritical extraction of SCB in laboratorial conditions. Optimizing process was done to achieve maximum yield extraction. Independent variables were dynamic time (t_d), pressure (P), temperature (T) and flow rate of SC-CO₂ (Q) in the range of 30–150 min, 10–30 MPa, 40–60 °C and 0.5–1.7 ml/min, respectively. The experimental optimal recovery of essential oil (0.8431, w/w%) was obtained at 13.43 MPa, 40 °C, 150 min (dynamic) and 1.7 ml/min (CO₂ flow rate).     

Domain evolution and phase transition dynamics of BaTiO3 ferroelectric single crystal under high pressure with various loading methods: Phase field simulation

The microstructure and macroscopic properties of ferroelectric materials at high pressure are of great interest in both the engineering and scientific arenas. The effect ofthe pressure value, loading time (the time taken for the pressure to increase from atmospheric pressure to the highest pressure) and loading direction on the evolution of domains and the ferroelectric phase transition for a BaTiO₃ single crystal was investigated using a phase field approach. It was found that under symmetrical compression loading the pressure loading time affected the phase transition path and rate but did not affect the phase transition pressure or the ultimate stable phase. For example, at room temperature, even when the loading time increased from 1 ns to 10 μs, the phase transition pressure remained stable at 2.1 GPa, but the phase transition time was prolonged. At −70 °C the orthorhombic–cubic phase transition was induced when the loading pressure was 5 GPa and the loading time was 1 ns, whereas the orthorhombic–tetragonal–cubic phase transition occurred when the loading time increased to 10 μs. In addition, it was found that the application of symmetrical pressure tended to reduce the degree of ferroelectricity, while one-dimensional compression favored the ferroelectric phase.     

Surface chemistry of phase-pure M1 MoVTeNb oxide during operation in selective oxidation of propane to acrylic acid

The surface of a highly crystalline MoVTeNb oxide catalyst for selective oxidation of propane to acrylic acid composed of the M1 phase has been studied by infrared spectroscopy, microcalorimetry, and in situ photoelectron spectroscopy. The acid–base properties of the catalyst have been probed by NH₃ adsorption showing mainly Brønsted acidity that is weak with respect to concentration and strength of sites. Adsorption of propane on the activated catalyst reveals the presence of a high number of energetically homogeneous propane adsorption sites, which is evidenced by constant differential heat of propane adsorption q_diff,initial = 57 kJ mol^?1 until the monolayer coverage is reached that corresponds to a surface density of approximately 3 propane molecules per nm² at 313 K. The decrease of the heat to q_diff,initial = 40 kJ mol^?1 after catalysis implies that the surface is restructured under reaction conditions. The changes have been analyzed with high-pressure in situ XPS while the catalyst was working applying reaction temperatures between 323 and 693 K, different feed compositions containing 0 mol.% and 40 mol.% steam and prolonged reaction times. The catalytic performance during the XPS experiments measured by mass spectrometry is in good agreement with studies in fixed-bed reactors at atmospheric pressure demonstrating that the XPS results taken under operation show the relevant active surface state. The experiments confirm that the surface composition of the M1 phase differs significantly from the bulk implying that the catalytically active sites are no part of the M1 crystal structure and occur on all terminating planes. Acrylic acid formation correlates with surface depletion in Mo⁶⁺ and enrichment in V⁵⁺ sites. In the presence of steam in the feed, the active ensemble for acrylic acid formation appears to consist of V⁵⁺ oxo-species in close vicinity to Te⁴⁺ sites in a Te/V ratio of 1.4. The active sites are formed under propane oxidation conditions and are embedded in a thin layer enriched in V, Te, and Nb on the surface of the structural stable self-supporting M1 phase.     

Stability and growth of gas hydrates below the ice–hydrate–gas equilibrium line on the P–T phase diagram

Using a previously developed experimental technique, the behavior of small methane and propane hydrate samples formed from water droplets between 0.25 and 2.5 mm in size has been studied in the pressure–temperature area between the ice–hydrate–gas equilibrium line and the supercooled water–hydrate–gas metastable equilibrium line, where ice is a stable phase. The unusual persistence of the hydrates within the area bounded by these lines and the isotherms at T=253 K for methane hydrate or at T=263 K for propane hydrates was observed. This behavior has not previously been reported. For example, in the experiment carried out at 1.9 MPa and 268 K, the methane hydrates existed in a metastable state (the equilibrium pressure at 268 K is 2.17 MPa) for 2 weeks, then immediately dissociated into liquid supercooled water and gas after the pressure was isothermally decreased slightly below the supercooled water–hydrate–gas metastable equilibrium pressure. It was found that dissociation of metastable hydrate into supercooled water and gas was reversible. The lateral hydrate film growth rates of metastable methane and propane hydrates on the surface of supercooled water at a pressure below the ice–hydrate–gas equilibrium pressure were measured. The temperature range within which supercooled water formed during hydrate dissociation can exist and a role of supercooled water in hydrate self-preservation is discussed.     

Laser analyses of mixture formation and the influence of solute on particle precipitation in the SAS process

Laser based Raman and elastic light scattering measurements were performed to study the process of mixture formation and the influence of the solute paracetamol onto the phase behaviour of the pseudo-binary system ethanol/CO₂ in the supercritical antisolvent process. From the Raman based technique, mole fraction and partial density distributions of CO₂ were obtained. The mole fraction distributions indicate a rapid mixture formation with fast supersaturation of the solute. At the same time, the increase of the CO₂ partial density at conditions considerably above the mixture critical point (MCP) indicate a change from a homogeneous supercritical to a multi-phase subcritical flow. This phase change goes along with particle precipitation. Thus, the results of our investigations proof, why past approaches failed to generate amorphous paracetamol nanoparticles with the system paracetamol/ethanol/CO₂ above the MCP. Process parameters like injection pressure (20.0–35.0 MPa), chamber pressure of CO₂ (7.5–17.5 MPa), temperature (313–333 K) and solute concentration (0–5 wt%) were varied.     

Effect of Sn:Ti variations on electric filed induced AFE–FE phase transition in PLZST antiferroelectric ceramics

The effect of Sn:Ti variations on antiferroelectric to ferroelectric phase transition of (Pb_0.97La_0.02)(Zr_0.65Sn_0.35?xTi_x)O₃ (x = 0.08–0.11) ceramics with compositions near antiferroelectric to ferroelectric morphotropic phase boundary was studied. X-ray diffraction showed that all samples were tetragonal phase at room temperature. With the increase of x from 0.08 to 0.1, all samples showed the typical antiferroelectric double loops. The critical value E_AF of the electric-field induced antiferroelectric to ferroelectric phase transition decreased from 64 kV/cm to 38 kV/cm, and the electric field E_FA of induced-ferroelectric to antiferroelectric phase transition decreased from 44 kV/cm to 10 kV/cm. A high polarization of the sample with x = 0.1 can be induced with a lower electric filed. The variations of Sn:Ti ratio had no effect on hysteresis of ΔE (=E_AF ? E_FA), but ΔE reduced with temperature increasing. The virgin sample of which x = 0.11 was intrinsic antiferroelectric phase, but the remanent polarization of induced-ferroelectric phase remained after electric-field was removed at room temperature.     

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.     

Effect of phase transition on the microwave dielectric properties of BiNbO4

BiNbO₄ specimens were transformed from the orthorhombic to triclinic phase at 1040 °C. The calculated intrinsic dielectric properties of the specimens were changed from K = 42, Qf = 15700 GHz in the orthorhombic phase to K = 30, Qf = 8900 GHz in the triclinic phase. The change of Qf value resulted from the increase of the dispersion parameter and modes for nonsymmetrical structure with the phase transition. TCF of the specimens decreased due to the increase of the octahedral distortion of BiNbO₄ with change from the orthorhombic to the triclinic phase. These results are due to the increase of bond valence of BiNbO₄ with the phase transition.     

Supercritical anti-solvent micronization of chromatography purified marigold lutein using hexane and ethyl acetate solvent mixture

This work aims to study supercritical anti-solvent micronization of marigold derived purified lutein that was dissolved in the mixture of hexane and ethyl acetate (70:30 v/v), the solvent used as the mobile phase for chromatographic purification. The results show significant effect of pressure on the morphology of micronized lutein particles. The increase in lutein initial concentration from 1.5 mg/ml to 3.2 mg/ml and the increase in SC-CO₂ flow rate from 15 ml/min to 25 ml/min show no significant effects on the morphology of lutein particles. However, the reduction of mean particle size from about 2 μm to 0.8 μm was observed by increasing SC-CO₂ flow rate. The X-ray diffraction patterns of the micronized lutein particles show apparent amorphous nature, while the Fourier transform infrared spectroscopy results show that no chemical structural changes occurred. Moreover, the solubility of the micronized lutein particles in aqueous solution was found to increase significantly from being almost insoluble to having approximately 20% solubility     

Phase transitions in single crystal tubes formed from C60 molecules under high pressure

Pure single crystal tubes formed from C₆₀ molecules, with a face-centered cubic (fcc) structure were fabricated by a liquid–liquid interfacial precipitation method using C₆₀ powder. A bulk transition from fcc to a simple cubic structure and a surface transition from (1 × 1) to (2 × 2) have been observed around 246 K (bulk transition temperature T_B) and 214 K (surface transition temperature T_S), respectively, during the measurement of the temperature dependence of electrical resistance. The initiation of the two transitions under pressure was investigated using a piston cylinder high pressure apparatus and it was found that both T_B and T_S increase with increasing pressure. And the C₆₀ molecules at the surface of the tube exhibit the same behavior of that in the bulk at a pressure of about 2.1 GPa.     

Phase equilibria of the propylene glycol/CO2 and propylene glycol/ethanol/CO2 systems

The high-pressure vapour–liquid phase equilibria (P–T–x–y) of the binary mixture propylene glycol/CO₂ have been experimentally investigated at temperatures of (398.2, 423.2 and 453.2) K over the pressure range from (2.5 to 55.0) MPa using a static-analytic method. Furthermore, the high-pressure vapour–liquid phase equilibria (P–T–x–y) of the ternary mixture propylene glycol/CO₂/ethanol at constant temperatures of (398.2, 423.2 and 453.2) K and at constant pressure of 15.0 MPa have been determined using a static-analytic method. Initial concentrations of components in propylene glycol (PG)/ethanol (EtOH) mixture vary from 10 up to 90 wt.%. In general, for binary system it was observed that the solubility of CO₂ in the heavy propylene glycol reach phase increases with increasing pressure at constant temperature. On the contrary, the composition of gaseous phase is not influenced by the pressure or the temperature. On average the solubility of PG in light phase of CO₂ amounts to 30 wt.%. The system behaviour at temperature of 398.2 K was investigated up to 70.0 MPa and a single-phase region was not observed. Above the pressure 60.0 MPa a single-phase region of the system was observed for the temperature of 423.2 K. For the temperature of 453.2 K the single-phase was observed above the pressure of 48.0 MPa. For ternary system it was observed that the composition of heavy phase is slightly influenced by the temperature when the mass fraction of EtOH in initial mixture is higher than 50 wt.%. If the mass fraction of PG in initial mixture is higher than 50 wt.%, the composition of heavy phase is not influenced by the temperature anymore. The composition of the PG, EtOH and CO₂ in light phase remains more or less unchanged and it is not influenced by the conditions.