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.     

Density and viscosity of the binary polyethylene glycol/CO2 systems

Density of CO₂ saturated solutions of polyethylene glycols (PEGs) of different molecular weight was measured in pressure range from 8.0 MPa up to 47.7 MPa at a temperature of 343 K by a volumetric method. To validate the method density of pure CO₂ was measured at different pressures and a temperature of 293 K. The results were compared to the literature data and the accuracy was better than 2%. The density was between 1.17 g/mL for PEG 1000/CO₂ at 14.5 MPa and 1.78 g/mL for the system PEG 4000/CO₂ at 35 MPa. Further, the data were compared to results, obtained by a gravimetric method using magnetic suspension balance (MSB).Viscosity of CO₂ saturated solutions of polyethylene glycols (PEGs) of different molecular weight at different pressures and at a temperature of 343 K was measured using a high pressure view cell. Also a temperature impact on the viscosity of pure PEGs was observed at ambient pressure. After saturating PEG 1500 with 10 MPa of CO₂ pressure its viscosity decreases from 76.6 mPa s to 2.24 mPa s at 333 K. Further addition of CO₂ and increasing the pressure results in even lower viscosity and the highest viscosity reduction was reached at the highest pressure; at 35 MPa viscosity of the system PEG 1500/CO₂ is only 0.665 mPa s.     

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.     

Synthesis,characterization and structure effects of polyethylene glycol bis(2-isopropoxyethyl) dimethyl diphosphates on lanthanides extraction with supercritical carbon dioxide

Three new CO₂-philic open-chain organophosphorous chelating ligands, i.e. ethylene glycol bis(2-isopropoxyethyl) dimethyl diphosphate (EG2IPE), triethylene glycol bis(2-isopropoxyethyl) dimethyl diphosphate (EG3IPE), and tetraethylene glycol bis(2-isopropoxyethyl) dimethyl diphosphate (EG4IPE), were synthesized and characterized. Solubilities of these ligands in scCO₂ were determined at different combinations of temperature (313.15⿿333.15 K) and pressure (9⿿20 MPa), which generally showed considerable solubility in each case. These experimental data are in agreement with computed data via a semi-empirical model, in which the average absolute relative deviations lie in the range of 4.09⿿4.95%. The effect of these ligands on supercritical fluid extraction of selected rare earth metals (La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Gd³⁺, Er³⁺, and Yb³⁺) was investigated at 313.15 K and 20 MPa. The extraction efficiency of this system was found to increase in the order EG4IPE < EG3IPE < EG2IPE with a range from 55% to 79%. The rationale behind different selectivities toward these metals was also discussed in comparison to other traditional organophosphorous agents. A detailed experimental analysis of the complexation patterns by means of a combination of IR, ¹H NMR and ESI-MS has revealed that the interaction of ether oxygen group in EG4IPE with metals and the corresponding extraction mechanism.     

Water and ethanol as co-solvent in supercritical fluid extraction of proanthocyanidins from grape marc: A comparison and a proposal

Supercritical carbon dioxide (SC-CO₂) extraction of grape marc was studied using water (W) and ethanol (EtOH) as co-solvent at 15% (w/w), 100 and 200 MPa, and 313.15, 323.15 and 333.15 K to analyze their influence upon total phenols of the extracts. The overall extraction curves were determined and suggested 10 MPa and 313.15 K as the best operating conditions for SC-CO₂ + 15%W extraction, and 10 MPa and 333.15 K for SC-CO₂ + 15% EtOH. The phenolic yields obtained were 63.4 g/kg of extract for SC-CO₂ + 15% W and 38.8 g/kg of extract for SC-CO₂ + 15% EtOH. An alternative method combining Sc-CO₂ + 15% W extraction, followed by SC-CO₂ + 15% EtOH was tested. This procedure provided the best results allowing to obtain the highest phenolic yield (68.0 g/kg of extract), phenol content (733.6 mg GAE/100 g DM), proanthocyanidins concentration (572.8 mg catechin/100 g DM) and antioxidant activity (2649.6 mg α-tocopherol/100 g DM). SC-CO₂ methods were compared with methanol extraction.     

Measurement of entrainer effects of water and ethanol on solubility of caffeine in supercritical carbon dioxide by FT-IR spectroscopy

The solubilities of caffeine in supercritical CO₂, supercritical CO₂ + water, supercritical CO₂ + ethanol, and supercritical CO₂ + water + ethanol were measured with a circulation-type apparatus combined with an on-line Fourier transform infrared (FT-IR) spectrometer at 313.2 K and 15.0 MPa. The solubilities of caffeine were determined with the peak absorbances of caffeine at 1190 cm⁻¹. The solubilities of caffeine increase until water is saturated in supercritical CO₂. The maximum increase rate is 22%. In CO₂ + caffeine + ethanol system, the solubilities of caffeine increase with increasing the concentration of ethanol. The solubility of caffeine becomes five times when 1000 mol m⁻³ of ethanol is added. In CO₂ + caffeine + water + ethanol system, the solubilities of caffeine are smaller than those with single entrainer of water or ethanol. The shape of the peaks of two CO stretching bands for caffeine were changed by the addition of ethanol. It was confirmed that the interaction species of caffeine interacting with ethanol are produced by deconvolution of the CO stretching bands. The enhancement of solubility for caffeine in supercritical CO₂ by the addition of ethanol is due to the hydrogen bonding between caffeine and ethanol.     

High-pressure phase equilibria of Polystyrene dissolutions in Limonene in presence of CO2

Dissolution with terpenic solvents is presented as an alternative and original route to recycle Polystyrene wastes at room temperature. Limonene was the chosen solvent to carry out the dissolution process because it presents high compatibility with Polystyrene besides being natural, non toxic and relatively low cost. The solvent removal is possible thanks to supercritical CO₂ since it provides high solubility of Limonene and complete PS insolubility at moderated pressures and temperature. In order to determine the proper working conditions to conduct the precipitation of the polymer, accurate knowledge of the phase equilibrium for mixtures of carbon dioxide, Limonene and Polystyrene should be known.In this work, the solubility of Limonene in the ternary system CO₂/Limonene/Polystyrene was determined. The phase equilibrium experiments were conducted in a variable-volume view cell employing the static method. These experiments were carried out in the temperature range of 298.15–313.15 K, at pressures up to 15 MPa and in the concentration range of 0.05–0.80 g PS/ml Limonene. Initially the binary systems were studied by means of equations of state: Peng–Robinson in the case of CO₂/Limonene and Sanchez–Lacombe in the case of Limonene/PS and CO₂/PS. Predicted data were collected together with the experimental to check the agreement and to determine the limits of the ternary system formed by CO₂–Limonene–PS. It is indispensable to determine the behaviour of the ternary system to know completely the fluid phase equilibrium. The results indicate that the solubility of Limonene in the vapour phase is favoured by high pressure and temperature as well as low concentration.     

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.     

Effect of the porous structure in carbon materials for CO2 capture at atmospheric and high-pressure

Activated carbons prepared from petroleum pitch and using KOH as activating agent exhibit an excellent behavior in CO₂ capture both at atmospheric (∼168 mg CO₂/g at 298 K) and high pressure (∼1500 mg CO₂/g at 298 K and 4.5 MPa). However, an exhaustive evaluation of the adsorption process shows that the optimum carbon structure, in terms of adsorption capacity, depends on the final application. Whereas narrow micropores (pores below 0.6 nm) govern the sorption behavior at 0.1 MPa, large micropores/small mesopores (pores below 2.0–3.0 nm) govern the sorption behavior at high pressure (4.5 MPa). Consequently, an optimum sorbent exhibiting a high working capacity for high pressure applications, e.g., pressure-swing adsorption units, will require a poorly-developed narrow microporous structure together with a highly-developed wide microporous and small mesoporous network. The appropriate design of the preparation conditions gives rise to carbon materials with an extremely high delivery capacity ∼1388 mg CO₂/g between 4.5 MPa and 0.1 MPa. Consequently, this study provides guidelines for the design of carbon materials with an improved ability to remove carbon dioxide from the environment at atmospheric and high pressure.     

Investigation of thermodynamic properties of the binary system polyethylene glycol/CO2 using new methods

The solubility and diffusivity of CO₂ in polyethylene glycols (PEGs) of different molecular weight measured by two different methods are discussed in the present work. Before solubility measurements, the melting temperatures of PEG with different molecular weights were determined by means of differential scanning calorimetry. For the purpose of the present study a temperature of 343 K was chosen as the working temperature for both employed methods since all studied polymers are in liquid state at this temperature. All samples were analyzed at isothermal conditions and in the pressure range from 0 MPa up to 30.0 MPa. A set of absorption experiments on the PEG/CO₂ systems was performed using an external balance method. In order to validate results obtained by the new method they were compared to the data obtained at the same process conditions by a method using magnetic suspension balance (MSB).     

Hydrogen solubility in CO2-expanded 2-propanol and in propane-expanded 2-propanol determined by an acoustic sensor

Hydrogen solubility in CO₂-expanded 2-propanol and in propane-expanded 2-propanol was obtained by an acoustic technique described elsewhere [L. Zevnik, J. Levec, Gas expanded liquids: Determination of the volumetric expansion by an acoustic technique, J. Supercrit. Fluids (2007), in press]. Solubility in CO₂-expanded 2-propanol at expansion coefficients V/V₀ = 2 and 4 was determined at 298 and 313 K. H₂ solubility was determined also in liquid CO₂ at 298 K and partial pressure of H₂ up to 6 MPa. Solubility in propane-expanded 2-propanol with V/V₀ = 2 and 4 was measured at 333, 353 and 393 K. Hydrogen mole fraction in liquid propane was obtained at 333 K and partial pressure of H₂ up to 5 MPa. For both expanded liquids the results show that hydrogen concentration increases with increasing V/V₀ ratio and with increasing temperature. It is demonstrated, however, that the acoustic technique is a reliable method for determination of gas composition and that it can be also implemented in various fields of gas processing.     

Supercritical fluid extraction from Syzygium aromaticum buds: Phase equilibrium,mathematical modeling and antimicrobial activity

Clove essential oil is an important product to food industry because it presents a powerful antioxidant and antimicrobial potential enabling its use for the substitution of synthetic commercial products for food preservation. The objective of this paper is to study the extraction kinetics for predicting operational condition to obtain Syzygium aromaticum essential oil using CO₂ as solvent by means of the introduction of thermodynamic approach into the mathematical modeling of the process. Extractions were performed at 9000 kPa/313.15 K, 10,000 kPa/313.15 K, 9000 kPa/323.15 K, and 10,000 kPa/323.15 K and the essential oil yields obtained were 14.17%, 12.32%, 13.11%, and 14.02%, respectively. To calculate the extract solubility in CO₂ supercritical, the Peng–Robinson EoS coupled with three mixing rules (van der Waals 1, van der Waals 2 and Mathias–Klotz–Prausnitz) was used and a mass transfer model was employed to represent the relationship yield versus extraction time. The mathematical modeling of the process using the calculated solubility presented high concordance with experimental data. The volatile extracts were analyzed by GC/MS and the major compounds were eugenol and β-caryophyllene. Also, minimum inhibitory concentration (MIC) of supercritical extracts was determined with respect to Escherichia coli, Staphylococcus aureus and Enterococcus faecalis by microdilution method. All samples inhibited the bacterial growth, being the extract obtained at 313.15 K/9000 kPa the most effective.     

Characterization of wheat bran oil obtained by supercritical carbon dioxide and hexane extraction

Supercritical carbon dioxide (SC-CO₂) and soxhlet extraction using was carried out to extract oil from wheat bran oil. For SC-CO₂, the pressure and temperature were ranging from 10 to 30 MPa and 313.15–333.15 K. The extraction was performed in a semi batch process with a CO₂ flow rate of 26.81 g/min for 2 h. Wheat bran oil was characterized to investigate the quality. Acid value (AV) and peroxide value (POV) were higher in hexane extracted oil compared to SC-CO₂ extracted oil. Induction period was measured by rancimat test. The oil obtained by SC-CO₂ extraction had higher capability to delay the oxidation by surrounding environment. The DPPH radical scavenging activity was also measured. The SC-CO₂ extracted oil showed higher radical scavenging activity compared to hexane extracted oil.     

Mathematical modelling of phase equilibria for supercritical CO2 and polyethylene glycol of various molecular weights

The Sanchez–Lacombe equation of state and the Statistical Associating Fluid Theory were applied for modelling the phase equilibrium for the polyethylene glycol–CO₂ systems. The Aspen Plus software was used and polyethylene glycol with various molecular weights was investigated. The results were compared with previously obtained experimental values for solubility. The phase equilibrium was calculated at a temperature of 343 K, in the pressure range of 10–30 MPa and for polyethylene glycol molecular weights from 1000 to 100,000 g/mol. The binary interaction parameters for the models were optimized in order to obtain the best fit between the estimated and the experimental gas solubility data. The results suggest that both models are reliable in describing the phase equilibrium of the polyethylene glycol–CO₂ systems at the proposed conditions. Moreover, the molecular weight of the polymer affects the behaviour of the system, as observed from the variation of solubility values and of binary interaction coefficients.     

Lycopene solubility in mixtures of carbon dioxide and ethyl acetate

In order to improve the efficiency of processes using supercritical (sc) carbon dioxide (CO₂) to micronize the carotenoid “lycopene”, it is important to know the solubility of lycopene in mixtures of the organic solvent ethyl acetate (EA) and the antisolvent CO₂ at elevated pressures. The solubility of lycopene has been determined for different temperatures (313–333 K), pressures (12–16 MPa) and CO₂ molar fractions (0.58–1). The obtained data show that CO₂ acts as an antisolvent in the system lycopene/EA/CO₂ in the range of CO₂/EA ratios studied. The solubility of lycopene is rather small with lycopene molar fractions ranging from 0.1 × 10⁻⁶ to 46 × 10⁻⁶. The solubility of lycopene increases with temperature, pressure and EA concentration.     

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.     

Solubility and diffusion coefficient of supercritical-CO2 in polycarbonate and CO2 induced crystallization of polycarbonate

The solubility and diffusion coefficient of supercritical CO₂ in polycarbonate (PC) were measured using a magnetic suspension balance at sorption temperatures that ranged from 75 to 175 °C and at sorption pressures as high as 20 MPa. Above certain threshold pressures, the solubility of CO₂ decreased with time after showing a maximum value at a constant sorption temperature and pressure. This phenomenon indicated the crystallization of PC due to the plasticization effect of dissolved CO₂. A thorough investigation into the dependence of sorption temperature and pressure on the crystallinity of PC showed that the crystallization of PC occurred when the difference between the sorption temperature and the depressed glass transition temperature exceeded 40 °C (T − T_g ≥ 40 °C). Furthermore, the crystallization rate of PC was determined according to Avrami's equation. The crystallization rate increased with the sorption pressure and was at its maximum at a certain temperature under a constant pressure.     

High pressure density and solubility for the CO2 + 1-ethyl-3-methylimidazolium ethylsulfate system

The solubility and density of the CO₂ + 1-ethyl-3-methylimidazolium ethylsulfate system were investigated. The carbon dioxide solubility in the IL was measured in the temperature range 273–413 K, for pressure up to 5 MPa and CO₂ mole fractions ranging from 0.02 to 0.5 using the isochoric method, while the system density was carried out at temperatures ranging from 278.15 K to 398.15 K, pressures from 10 MPa to 120 MPa and 0.2, 0.4, 0.7 and 0.8 CO₂ mole fractions. Similar to what was previously observed for phosphonate-based ILs, the ionic liquid high polarity leads to positive deviations from ideality resulting from unfavorable interactions with the CO₂.The results from the density and solubility derived properties show that the system presents important negative excess molar volumes, over the whole range of compositions and temperatures, and a negative entropy of solvation that suggests an increase in ordering of the solvent molecules surrounding the solute. The observed negative excess molar volumes result from the large difference between the molecular volumes of the species involved, with the small carbon dioxide molecules occupying the empty spaces between the larger IL ions, supporting the notion that the carbon dioxide, upon dissolution, occupies essentially the bulk free volume since the IL does not significantly expand upon gas absorption. These results portray ionic liquids as a porous media, like a soft sponge, with a huge free volume in which large amounts of carbon dioxide are able to accommodate during the dissolution process.     

Extraction of jojoba seed oil using supercritical CO2+ethanol mixture in green and high-tech separation process

In this study, the extraction of jojoba seed oil obtained from jojoba seed using both supercritical CO₂ and supercritical CO₂+ethanol mixtures was investigated. The recovery of jojoba seed oil was performed in a green and high-tech separation process. The extraction operating was carried out at operating pressures of 25, 35 and 45 MPa, operating temperatures of 343 and 363 K, supercritical fluid flow rates of 3.33 × 10⁻⁸, 6.67 × 10⁻⁸ and 13.33 × 10⁻⁸ m³ s⁻¹, entrainer concentrations of 2, 4 and 8 vol.%, and average particle diameters of 4.1 × 10⁻⁴, 6.1 × 10⁻⁴, 8.6 × 10⁻⁴ and 1.2 × 10⁻³ m. It was found that a green chemical modifier such as ethanol could enhance the solubilities, initial extraction rate and extraction yield of jojoba seed oil from the seed matrix as compared to supercritical CO₂. In addition, it was found that the solubility, the initial extraction rate and the extraction yield depended on operating pressure and operating temperature, entrainer concentration, average particle size and supercritical solvent flow rate. The solubility of jojoba seed oil and initial extraction rate increased with temperature at the operating pressures of 35 and 45 MPa and decreased with increasing temperature at the operating pressure of 25 MPa. Furthermore, supercritical fluid extraction involved short extraction time and minimal usage of small amounts entrainer to the CO₂. About 80% of the total jojoba seed oil was extracted during the constant rate period at the pressure of 35 and 45 MPa.