Interfacial tension of edible oils in supercritical carbon dioxide

Interfacial properties essentially influence fluid‐liquid separation processes. Thereby, interfacial tension is an important parameter that is associated with mass transfer and mutual solubility of participating compounds. For this reason, interfacial tension of a virgin olive oil with a known amount of free fatty acids was measured in supercritical carbon dioxide atmosphere at 313 K and 353 K and pressures up to 40 MPa. The obtained values were compared to different oils some of which contain appreciable amounts of volatile components. In general, interfacial tension behaviour is dominated by the effect of pressure, whereas differences between oil compositions are secondary. Besides mutual solubility interfacial tension is supposed to be associated with the compressibility of the dense fluid phase. For predicting mass transfer area some general comments on the colloidal behaviour of systems containing supercritical CO₂ are made     

Interfacial tension of marine lipids in contact with high pressure carbon dioxide

Interfacial tension (IFT) of fish oil triglycerides (TG) and fatty acid ethyl esters (FAEE) in contact with carbon dioxide (CO₂) was measured according to the pendant drop method at 40, 55 and 70 °C and pressures up to 25 MPa. The IFT of both TG and FAEE decreased substantially with CO₂ pressure. The IFT of FAEE vanished at elevated pressures, whereas that of TG decreased to a fairly constant level of about 2 mN/m. The IFT was correlated using a model taking into account the density, pressure and temperature of CO₂, thereby facilitating the calculation of the ideal pendant drop volume as well as the surface excess concentration of CO₂. In the pressure range studied, the pendant drop volume for FAEE decreased with pressure, whereas for TG it increased at elevated presssures due to the predominant effect of buoyancy. Furthermore, the change in IFT over time was determined at 55 °C for TG in contact with CO₂ at pressures up to 11.4 MPa showing a decrease of IFT over time at low pressures, whereas at higher pressures it remained nearly constant. IFT influences drop formation as well as the disintegration of falling films thereby affecting the performance of separation processes.     

Simulations of vapor–liquid phase equilibrium and interfacial tension in the CO2–H2O–NaCl system

Direct interfacial molecular dynamics simulations are used to obtain the phase behavior and interfacial tension of CO₂–H₂O–NaCl mixtures over a broad temperature and pressure range (50°C ≤ T ≤ 250°C, 0 ≤ P ≤ 600 bar) and NaCl concentrations (1–4 mol/kg H₂O). The predictive ability of several existing water (SPC and TIP4P2005), carbon dioxide (EPM2 and TraPPE), and sodium chloride (SD and DRVH) models is studied and compared, using conventional Lorentz–Berthelot combining rules for the unlike‐pair parameters. Under conditions of moderate NaCl molality (～1 mol/kg H₂O), the predictions of the CO₂ solubility in the water‐rich and CO₂‐rich phase resemble those in the CO₂–H₂O system [Liu et al., J Phys Chem B. 2011;115:6629–6635]. Consistent with our previous work, the TraPPE/TIP4P2005 model combination gives the best overall performance in predicting coexistence composition and pressure in the water‐rich phase. Critical assessments are also made on the ranges of temperature and pressure where particular model combinations work better. The dependence of the interfacial tension on temperature and pressure is better predicted by the TraPPE/TIP4P2005 and EPM2/SPC models, whereas the EPM2/TIP4P2005 model overestimates this property by 10–20%, possibly due to the inadequacy of the combining rules. It is also found that the interfacial tension increases with salt concentration, consistent with experimental observations. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3514–3522, 2013     

Reactions of co-adsorbed carbon dioxide and dioxygen at the Mg(0001) surface at low temperatures

X-ray photoelectron spectroscopy has established that molecular dioxygen states are stabilised at a Mg(0001) surface in the presence of physisorbed carbon dioxide at 80 K. The dioxygen–CO₂ complex is highly reactive with low energy reaction pathways to carbonate formation; the latter is subsequently reduced to give surface carbide and oxide at a temperature below 150 K. This revised version was published online in June 2006 with corrections to the Cover Date.     

Quality of wheat germ oil extracted by liquid and supercritical carbon dioxide

The extraction of wheat germ oil by liquid and supercritical CO₂ is described from the point of view of both operative method and pretreatment of raw material. The best conditions for wheat germ oil extraction are: pressure, 150 bar; temperature, 40°C; and solvent flow rate, 1.5 L/min at standard temperature and pressure. The yields and fatty acid compositions obtained are very similar to those resulting from the conventional extraction process using hexane as solvent (8.0 wt%), although a higher-quality oil is obtained by using CO₂ as solvent (free fatty acids, 12.4%; tocopherol content, 416.7 mg tocopherol/g wheat germ oil). These factors lead to the conclusion that the extraction process using CO₂ could be economically competitive with the conventional process, since it considerably simplifies the oil refinement stages and completely eliminates the solvent distillation stage, which are the most costly processing steps in terms of energy consumption.     

Interfacial tension measurements and evidence of order in high‐density polyethylene melts

Polyethylene (PE) is a widely used product commercially. However, our knowledge is incomplete about the properties of high‐density polyethylene (HDPE) at temperatures above its melting point, where solid crystals disappear. Recently, there has been increasing evidence from rheological, differential scanning calorimetry, and NMR studies that suggests the presence of microstructural order in the bulk of PE melts. In this study, the interfacial tension of HDPE melts in contact with silicone oil was measured with a spinning drop tensiometer in the same temperature range in which phase transitions have been observed in the bulk HDPE. Anomalous temperature dependence of interfacial tension was found between 200 and 230°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 4061–4067, 2003     

Pilot-scale supercritical carbon dioxide extraction and fractionation of wheat germ oil

There is a need for the development of new processing techniques to facilitate vegetable oil extraction and refining while sustaining the nutritional components naturally present in edible oils and reducing the adverse impact of oil processing on the environment. In this study supercritical carbon dioxide (SC−CO₂) extraction and fractionation techniques were examined as alternative methods to obtain wheat germ oil (WGO) of high quality and purity. It was shown that the SC−CO₂ extraction technique is effective in extraction of WGO. There was no significant difference in the FA composition of SC−CO₂- and hexane-extracted WGO. Both hexane-and SC−CO₂-extracted WGO were rich in α-tocopherol. Moisture content of the SC−CO₂-extracted oil was higher than that of the hexane-extracted oil. Solvent/feed ratio had a significant effect on the SC−CO₂ extraction yields. This study demonstrated that supercritical fluid fractionation was a viable process to remove FFA efficiently from both hexane-and SC−CO₂-extracted WGO while retaining bioactive oil components in the final product.     

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.     

Analysis of carbon dioxide gas/liquid mass transfer in aerated stirred vessels using non–Newtonian media

Gas/liquid mass transfer has been investigated in an aerated stirred tank using non‐Newtonian media and carbon dioxide as absorbent and gas phase respectively. The volumetric mass transfer coefficients at different operational variables have been measured. The non‐Newtonian media (liquid phases) used were aqueous solutions of two polymers, carboxymethyl cellulose and alginate sodium salts. The influence upon the mass transfer of the rheological properties, polymer concentration, stirring rate and gas flow rate was studied. Kinematic viscosity and density experimental data were used to calculate the average molecular weight corresponding to the polymers employed. Reasonable agreement was found between the predictions of proposed models and the experimental data. The results shown in the present paper allow us to understand carbon dioxide transfer to a non‐Newtonian liquid phase and to evaluate the effect of the liquid phase characteristics. The equations used in this paper allow accurate simulation of the transfer of a pure gas to a rheologically complex solution. Copyright © 2004 Society of Chemical Industry     

Interfacial tension and the behavior of microemulsions and macroemulsions of water and carbon dioxide with a branched hydrocarbon nonionic surfactant

Measurements of interfacial tensions for 2-ethyl-hexanol-(propylene oxide)∼_4.5-(ethylene oxide)∼₈ (2EH-PO_4.5-EO₈) at the planar water-CO₂ interface and the surfactant distribution coefficient are utilized to explain microemulsion and macroemulsion phase behavior from 24 to 60 °C and 6.9 to 27.6 MPa. A CO₂ captive bubble technique has been developed to measure the interfacial tension γ at a known surfactant concentration in the aqueous phase, with rapid equilibration at the water-CO₂ interface. The surface pressure (γ_o − γ) decreases modestly with density at constant temperature as CO₂ solvates the surfactant tails more effectively, but changes little with temperature at constant density. The area per surfactant at the CO₂-water interface determined from the Gibbs adsorption equation decreases from 250 A²/molecule at 24 °C and 6.9 MPa, to 200 A²/molecule at 27.6 MPa. It was approximately twofold larger than that at the water-air interface, given the much smaller γ_o driving force for surfactant adsorption. For systems with added NaCl, γ decreases with salinity at low CO₂ densities as the surfactant partitions from water towards the W-C interface. At high densities, salt drives the surfactant from the W-C interface to CO₂ and raises γ. Compared with most hydrocarbon surfactants, this dual tail surfactant is unusually CO₂-philic in that it partitions primarily into the CO₂ phase versus the water phase at CO₂ densities above 0.8 g/ml, and produces γ values below 1 mN/m. With this small γ, a middle phase microemulsion and a C/W microemulsion were formed at low temperatures and high CO₂ densities, whereas macroemulsions were formed at other conditions.     

Synthesis of copper–polystyrene nanocomposite particles using water in supercritical carbon dioxide medium and its antimicrobial activity

Copper‐encapsulated polystyrene nanocomposite particles were prepared through ex situ dispersion of Cu nanoparticles into monomer droplets and subsequent polymerization using water in supercritical carbon dioxide (water‐in‐sc‐CO₂) at 70°C. First, colloidal dispersion of copper nanoparticles was synthesized by chemical reduction of copper chloride (CuCl₂) using sodium borohydrate (NaBH₄) as reducing agent. Colloidal dispersion of copper nanoparticles was added slowly during the polymerization of styrene using water‐in‐sc‐CO₂ medium at 70°C and 20.68 MPa. Cu nanoparticle encapsulated polymer particles were characterized by UV, X‐ray diffraction, thermogravimetric analysis, SEM, and TEM. Cu nanoparticles were uniformly distributed inside the polymer matrix during the polymerization process. This work represents a simple way to prepare a variety of metal nanoparticles encapsulated polymer particles using water‐in‐sc‐CO₂ medium. The Cu/polystyrene nanocomposite particles exhibit antimicrobial activity against a number of bacteria. The current work represents a simple, cheap and universal way to prepare a variety of metal–polymer nanocomposite materials. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and characteristics of a novel aliphatic polycarbonate,poly[(propylene oxide)‐co‐(carbon dioxide)‐co‐(γ‐butyrolactone)]

A novel aliphatic polycarbonate, poly[(propylene oxide)‐co‐(carbon dioxide)‐co‐(γ‐butyrolactone)] [P(PO? CO₂? GBL)], was synthesized by the copolymerization of carbon dioxide, propylene oxide (PO) and γ‐butyrolactone (GBL). The resulting copolymers were determined by FTIR and NMR spectral analysis with viscosity‐average molecular weights (M_v) from 50 000 to 120 000 g mol^?1. According to elemental analysis, the calculated data of elemental contents in P(PO? CO₂? GBL)44 were close to the found data. The result showed that GBL was inserted into the backbone of poly[(propylene oxide)‐co‐(carbon dioxide)] successfully. GBL offered an ester structural unit that gave the copolymer better degradability. The correlations between reaction conditions and properties were studied. When GBL content increased, the M_v and the glass transition temperature (T_g) of the copolymers improved relative to an identical copolymer without GBL. Prolonging the reaction time of the copolymerization resulted in increases in M_v and T_g. P(PO? CO₂? GBL) exhibited a high T_g above 40 °C. The rate of backbone degradation increased with increasing GBL content. Copyright © 2005 Society of Chemical Industry     

Determination of 3‐MCPD esters in edible oil – methods of analysis and comparability of results

The discovery of fatty acid esters of 3‐chloropropane‐1,2‐diol (3‐MCPD) in edible oil products initiated food monitoring campaigns in many EU Member States. As the determination of 3‐MCPD esters was new to most laboratories, questions on the reliability of the produced analysis data were raised. In response to this, the Institute for Reference Materials and Measurements (IRMM) of the European Commission's Joint Research Centre (JRC) organised a proficiency test on the determination of 3‐chloropropane‐1,2‐diol esters (3‐MCPD esters) in edible oils. The aim of this proficiency test was to scrutinise the capabilities of official food control laboratories, private food control laboratories as well as laboratories from food industry to determine the 3‐MCPD esters content of edible oils. The study was carried out in accordance with “The International Harmonised Protocol for the Proficiency Testing of Analytical Chemistry Laboratories” and ISO Guide 43. The test materials dispatched to the participants were: refined palm oil, extra virgin olive oil spiked with 3‐chloropropane‐1,2‐dioleate and 3‐MCPD standard solution in sodium chloride. Altogether 41 laboratories from 11 EU Member States, Switzerland and Macedonia subscribed for participation in the study. The analysis task was to determine the 3‐MCPD esters content as total 3‐MCPD content of the test samples. Participants were free to choose their analysis methods. In total, 34 laboratories reported results to the organisers of the study. The performance of laboratories in the determination of 3‐MCPD esters in edible oils was expressed by z‐scores. About 56% of the participants performed satisfactorily in the determination of 3‐MCPD esters in palm oil and 85% for the spiked extra virgin olive oil test sample. The study revealed that the direct transesterification of the sample without the prior removal of glycidol esters might lead to strong positive bias.     

Isomeric diacylglycerols – Determination of 1,2‐ and 1,3‐diacylglycerols in virgin olive oil

The “Joint Committee for the Analysis of Fats, Oils, Fatty Products, Related Products and Raw Materials (GA Fett)” has developed the following method for the determination of isomeric diacylglycerols in virgin olive oils to detect the freshness of oils. It is intended to include this method in Section C, Chapter VI of the German Standard Methods.*     

Viscosity measurement and modeling of canola oil and its blend with canola stearin in equilibrium with high pressure carbon dioxide

During enzymatic reactions carried out in supercritical CO₂ (SCCO₂) media, CO₂ can expand the liquid reactant mixture, especially lipid-type substances, due to pressure increase and dissolution of CO₂, causing viscosity reduction, and improvement of the diffusion of reactants and products. For better understanding of the transesterification reaction of canola oil and canola stearin in SCCO₂ media, the viscosity of canola oil at 40, 50, 65, and 75 °C and its blend with canola stearin (30 wt%) at 65 °C in equilibrium with high pressure CO₂ was measured up to 12.4 MPa using a rotational rheometer equipped with a high pressure cell. The solubility of CO₂ in canola oil at 40 and 65 °C and its blend with canola stearin at 65 °C was also determined at pressures of up to 20 MPa using a high pressure view cell. The viscosity of canola oil at 40, 50, 65, and 75 °C and its blend with canola stearin at 65 °C decreased exponentially to 87.2, 84.7, 74.8, 66.2, and 74.2% of its value at atmospheric pressure, respectively, with pressure increase up to 12.4 MPa. The viscosity of the samples decreased with an increase in temperature, but the effect of temperature diminished above 10 MPa. The viscosities of CO₂-expanded canola oil and its blend with canola stearin at 65 °C were similar up to 12.4 MPa. The samples exhibited shear-thickening behavior as the flow behavior index reached almost 1.2 at elevated pressures. The mass fraction of CO₂ in canola oil at 40 and 65 °C and its blend with canola stearin at 65 °C reached 24 and 21% at 20 MPa, respectively. The Grunberg and Nissan model was used to correlate the viscosity of CO₂-expanded lipid samples.     

Interfacial tensions of ethanol-carbon dioxide and ethanol-nitrogen. Dependence of the interfacial tension on the fluid density—prerequisites and physical reasoning

Interfacial tensions in the systems ethanol-carbon dioxide and ethanol-nitrogen are measured. In both systems the interfacial tension decreases with increasing pressure. The interfacial tension in the system ethanol-nitrogen decreases with increasing temperature. In contrast to this, in the system ethanol-carbon dioxide at high pressures an isobaric increase in temperature provokes an increase in interfacial tension. In the system ethanol-carbon dioxide at elevated pressure the density of the carbon dioxide phase is the only influence parameter concerning the interfacial tension. This phenomena can be observed for various other systems with one near critical or supercritical component and a high solubility of this component in the liquid phase and at temperatures above the critical temperature of the gas. For this fact a physical reasoning, which is based on a new concept of partial interfacial tensions, is given. Furthermore, it is stated that the interfacial tension of fatty systems in contact with carbon dioxide has approximately the same dependence on the reduced density (ρ_r=ρ/ρ_c) of the supercritical phase as the interfacial tension of the same systems in contact with ethane. The knowledge of this fact can help to avoid experiments with ethane, which is flammable.     

Activation of lipase by sol–gel coating with hydrophobic alkyl‐substituted silicates in supercritical carbon dioxide

BACKGROUND: Sol–gel entrapment of lipases is usually performed in an aqueous solution. A novel method of sol–gel coating of lipase in supercritical carbon dioxide (SC‐CO₂) is proposed. RESULTS: Crude lipase powder (Rhizopus oryzae) coated with hydrophobic silicates, derived from dimethyldimethoxysilane and tetramethoxysilane in SC‐CO₂ at 35 °C and 15 MPa, exhibited 5–7 times higher esterification activity than that prepared via an aqueous sol–gel route. Lipase immobilized in a methyl‐substituted silica monolith was also highly activated by sol–gel coating using the same silica precursors in SC‐CO₂. CONCLUSION: Sol– gel coating in SC‐CO₂, of lipases in powder and immobilized forms with hydrophobic alkyl‐substituted silicates provides an efficient tool for the enhancement of enzymatic activities in non‐aqueous media. Copyright © 2009 Society of Chemical Industry     

Degradation mechanism analysis of Ba0.5Sr0.5Co0.8Fe0.2O3‐δ membranes at intermediate‐low temperatures

The degradation of the permeation flux of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3‐δ membranes has typically been attributed to the phase transformation of the material at intermediate temperatures. In this study, the effect of the interfacial oxygen exchange steps was considered to give an overall view of the degradation mechanism. The changes in the interfacial exchange resistances, bulk resistance, and morphologies of the membranes were investigated via physical characterizations and a permeation model. The interfacial oxygen exchange resistances increased more quickly with time than bulk resistance. Meanwhile, BaSO₄ particles were detected on both surfaces of the membranes, and their contents reached maximum at 650°C. However, after the membrane surfaces were coated by Sm_0.5Sr_0.5CoO_3‐δ porous layers, the interfacial oxygen exchange resistances kept constant and the degradation rates were slowed down. The degradation was predominated by the increase of interfacial oxygen exchange resistances induced by the enrichment of BaSO₄ particles on membrane surfaces. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3879–3888, 2015     

Supercritical antisolvent micronisation of synthetic all‐trans‐β‐carotene with tetrahydrofuran as solvent and carbon dioxide as antisolvent

BACKGROUND: Supercritical antisolvent (SAS) micronisation of synthetic trans ‐β‐carotene was studied using tetrahydrofuran (THF) as solvent and supercritical carbon dioxide (CO₂) as antisolvent, with the objective of increasing its bioavailability and facilitating its dispersion in oil and emulsion formulations as a result of its smaller particle size. The micronised powder was analysed by scanning electron microscopy and high‐performance liquid chromatography. Micronisation experiments were performed in order to evaluate the effects of temperature (308.15–333.15 K), pressure (6.5–13 MPa) and concentration of the liquid solution (6–9 g L^?1). The effect of the supercritical CO₂/THF flow ratio in the range between 4 and 44 (on a mass basis) was also analysed. Determinations of equilibrium concentrations of β‐carotene in the CO₂/THF mixture were also performed. RESULTS: The particle size obtained ranged from 1 to 500 µm, with mean particle diameters around 100 µm. Three types of morphology were found in the precipitated powder: crystalline with superficial pores and leaf‐like appearance; crystalline with regular shapes and blade‐like edges; and crystalline without superficial pores and leaf‐like apearance. The Peng–Robinson equation of state was used to calculate the density of the CO₂/THF binary mixture, and the solubility of β‐carotene in this mixture was correlated with its density. CONCLUSION: The use of the SAS technique to micronise β‐carotene proved to be efficient, and the absence of degradation in the micronised powder allows the industrial application of this technique. Copyright © 2008 Society of Chemical Industry