Density Of Carbon Dioxide Research Articles

High-temperature vibrational densitometer for high-pressure aggressive media

High-temperature vibrational densitometer for chemically active media was developed. The principle of operation of the densitometer is based on recording and analyzing the natural frequency of a U-shaped high-pressure capillary filled with the test medium. The placement of the capillary in a thermostat capable of maintaining its temperature to within ±0.1°C makes it possible to measure the density and study the phase behavior of aggressive media over pressure and temperature ranges of 0.1–50 MPa and 20–500°C, respectively. Measurements of the carbon dioxide density with the densitometer developed at temperature below, near, and above its critical point (31°C), as well as water density measurements at temperatures up to 375°C demonstrated good agreement with the data from the NIST (National Institute of Standards and Technology) interactive database. The density of a methanol-water mixture was measured at temperatures up to 300°C.

초임계 이산화탄소를 이용하여 감태로부터 Fucoxanthin 농축

Fucoxanthin has been concentrated efficiently using supercritical carbon dioxide. First, fucoxanthin was extracted from Ecklonia cava using solvents. Three solvents, such as medium chain fatty acid (MCFA), medium chain fatty acid ethyl ester, and fatty acid from coconut oil were tested, and MCFA was selected as a suitable solvent to extract fucoxanthin from Ecklonia cava. The concentration was conducted at various pressures and temperatures. In order to concentrate fucoxanthin from extracts, MCFA was eliminated from the extract using supercritical carbon dioxide, and fucoxanthin was concentrated successfully in residue. Optimal conditions for concentrating the fucoxanthin from fucoxanthin extract were 40C at 9.7 MPa, 45C at 11.0 MPa, and 50C at 12.4 MPa, respectively. The density of carbon dioxide affected the concentration of fucoxanthin from fucoxanthin extract. In this optimal conditions, the density for concentrating the fucoxanthin was 600 g/L.

Adsorption Equilibria ofcis-5,8,11,14,17-Eicosapentaenoic Acid Ethyl Ester andcis-4,7,10,13,16,19-Docosahexaenoic Acid Ethyl Ester on C18-Bonded Silica from Supercritical Carbon Dioxide

The adsorption equilibrium of cis-5,8,11,14,17-eicosapentaenoic acid ethyl ester (EPA-EE) and cis-4,7,10,13,16,19-docosahexaenoic acid ethyl ester (DHA-EE) on C18-bonded silica from supercritical carbon dioxide was studied. The adsorption isotherms at (318.15, 328.15, and 338.15) K under pressures corresponding to carbon dioxide densities of (0.497, 0.618, and 0.723) g·mL−1 were determined by a static method. The isotherms were found to be of type II and could be well fitted by the BET equation. The monolayer adsorption amount of EPA-EE was (0.039 to 0.048) mmol·g−1, and that of DHA-EE was (0.040 to 0.063) mmol·g−1. At a given equilibrium molecular fraction of EPA-EE or DHA-EE in the bulk phase, the adsorption amount decreases slightly with temperature but decreases significantly with carbon dioxide density. Under the same conditions, the adsorption amount of DHA-EE is greater than that of EPA-EE. The adsorption isotherms of both EPA-EE and DHA-EE at different temperatures and carbon dioxide densities coincide to a general characteristic curve when they are plotted as a fractional monolayer coverage (q/qm) vs reduced concentration (y/y0). The isochoric heats of adsorption of EPA-EE and DHA-EE were in the range of (10 to 36) kJ·mol−1.

Numerical Modeling of Mass Transfer for Solvent-Carbon Dioxide System at Supercritical (Miscible) Conditions

A numerical procedure of mathematical model for mass transfer between a droplet of organic solvent and a compressed antisolvent is presented for conditions such that the two phases are fully miscible. The model is applicable to the supercritical antisolvent (SAS) method of particle formation. In this process, solute particles precipitate from an organic solution when sprayed into a compressed antisolvent continuum. Effects of operating temperature and pressure on droplet behavior were examined. The CO2 critical locus and the conditions for which the densities of solvent and carbon dioxide are equal are identified. Calculations were performed using Peng-Robinson equation of state. The model equations were put into the form that allowed the application of the Matlab standard solver pdepe. Calculations with toluene, ethanol, acetone (solvents) and carbon dioxide (antisolvent) demonstrated that droplets swell upon interdiffusion when the solvent is denser than the antisolvent and shrink when the antisolvent is denser. Diffusion modeling results might be used for data interpretation or experiments planning of the more complex real SAS process.

The selective thermal cis-trans isomerization of 1,2-diphenylsulfonyl ethylene in the presence of carbon dioxide

The selective isomerization of cis-1,2-diphenylsulfonyl ethylene to trans-1,2-diphenylsulfonyl ethylene proceeded in supercritical carbon dioxide above 393 K without an addition of catalyst. The product yield increased with increasing temperature and was almost constant against carbon dioxide density. The 73% of product yield was obtained at 493 K and 10 MPa of carbon dioxide pressure for 60 min. The product yield obtained in supercritical carbon dioxide was larger than those obtained in organic solvents. The supercritical carbon dioxide was a dilute solvent compared with organic solvent, which probably reduced the suppression of the reaction by dense solvent. Further, only cis-sulfonyl ethylenes isomerized among several cis-ethylene derivatives. The sulfonyl group played an important role for the isomerization.

Onset of Convection in CO2 Sequestration in Deep Inclined Saline Aquifers

Abstract CO2 sequestration in deep geological formations has been suggested as an option to reduce greenhouse gas emissions. Saline aquifers are one of the most promising options for carbon dioxide storage. It has been shown that the dissolution of CO2 into brine causes the density of the mixture to increase. If the corresponding Rayleigh number of the porous medium is enough to initiate convection currents, the rate of dissolution will increase. Early time dissolution of CO2 in brine is mainly dominated by molecular diffusion, while late time dissolution is predominantly governed by a convective mixing mechanism. In this paper, linear stability analysis of density-driven miscible flow for carbon dioxide sequestration in deep inclined and homogeneous saline aquifers is presented. The effect of inclination and its influence on the pattern of convection cells has been investigated and the results are compared with the horizontal layer. The current analysis provides approximations for the initial wavelength of the convective instabilities and the onset of convection that helps in selecting suitable candidates for geological CO2 sequestration sites. Introduction Carbon dioxide sequestration is the capture and safe storage of carbon dioxide that would otherwise emit to the atmosphere. Sequestration refers to any storage scheme that can keep CO2 out of the atmosphere(1). In general, proposed storage sites of carbon dioxide can be divided into two categories: geological sites and marine sites. Carbon dioxide sequestration in deep geological formations has been suggested as a way of reducing greenhouse gas emissions. Geologic sequestration of CO2 is the capture of CO2 from major sources, transporting it usually by pipeline, and injecting it into underground formations such as oil and gas reservoirs, saline aquifers and unmineable coal seams for a significant period of time(2, 3). Unlike coalbed methane reserves and oil reservoirs, sequestration of CO2 in deep saline aquifers does not produce value-added by-products, but it has other advantages. While there are uncertainties regarding the scope, the world's total capacity to store CO2 deep underground is large(4). Underground formations are generally unused and are available in many parts of the world(5). It has been estimated that deep saline formations in the United States could potentially store up to 500 billion tonnes of CO2. Most existing large CO2 point sources are within easy access to a saline formation injection point and, therefore, sequestration in saline formations is compatible with a strategy of transforming large portions of the existing energy and industrial assets to near-zero carbon emissions via low-cost carbon sequestration retrofits(3). However, it is important to investigate the behaviour of CO2 injected into aquifers for effective and safe use of storage. Geological storage of CO2 as a greenhouse gas mitigation option was proposed in the 1970s(6), but little research was done until the early 1990s when the idea gained credibility through the work of individual research groups(7–10). When CO2 is injected into the formation above its critical temperature and pressure, the density of supercritical carbon dioxide is usually less than brine. This density difference causes CO2 to migrate upwards to the top of the formation under an impermeable caprock.

A Fully Flexible Potential Model for Carbon Dioxide

A fully flexible potential model for carbon dioxide has been developed to predict the vapor-liquid coexistence properties using the NVT-Gibbs ensemble Monte Carlo technique (GEMC). The average absolute deviation between our simulation and the literature experimental data for saturated liquid and vapor densities is 0.3% and 2.0%, respectively. Compared with the experimental data, our calculated results of critical properties (7.39 MPa, 304.04 K, and 0.4679 g·cm −3) are acceptable and are better than those from the rescaling the potential parameters of elementary physical model (EPM2). The agreement of our simulated densities of supercritical carbon dioxide with the experimental data is acceptable in a wide range of pressure and temperature. The radial distribution function estimated at the supercritical conditions suggests that the carbon dioxide is a nonlinear molecule with the C ▪O bond length of 0.117 nm and the O ▪C ▪O bond angle of 176.4°, which are consistent with Car-Parrinello molecular-dynamics (CPMD), whereas the EPM2 model shows large deviation at supercritical state. The predicted self-diffusion coefficients are in agreement with the experiments.

New correlations predict aqueous solubility and density of carbon dioxide

In this paper, new correlations for predicting density and the solubility of carbon dioxide in pure water as well as the aqueous sodium chloride solutions are developed, where using the generated interaction parameters, the solubility model is applied to correlate the carbon dioxide solubilities in aqueous solutions for temperatures between 300 and 400 K and pressures from 50 to 700 bar. The correlation developed for predicting density of carbon dioxide accurately works for pressures between 25 and 700 bar and temperatures between 293 and 433 K. The results have been compared with the reported data and it was found that there is a good agreement between the prediction results and observed values.

Solubility of p-Toluenesulfonamide in Pure and Modified Supercritical Carbon Dioxide

The experimental equilibrium solubilities of p-toluenesulfonamide (p-TSA) in supercritical carbon dioxide were measured at temperatures between (308.15 and 328.15) K and for pressures from (8.0 to 21.0) MPa using a dynamic flow method. The solubility ranged from a p-TSA mole fraction of 0.97·10−5 (308.15 K, 8.0 MPa) to 5.12·10−5 (328.15 K, 21.0 MPa). The effects of two cosolvents, ethanol and glycol, were investigated at a cosolvent mole concentration of 3.5 %. The results showed that the solubility was greatly enhanced by the presence of both the cosolvents, and ethanol exhibited a higher cosolvent effect. The Peng−Robinson EOS with van der Waals (VDW2) mixing rules was employed to calculate the density of the supercritical carbon dioxide (SC CO2) + ethanol mixture. The solubility data in the absence and presence of cosolvents were correlated by the Chrastil equation and the modified Mendez-Santiago and Teja equation, respectively. Both the correlations yielded satisfactory results, with average absolute...

Preparation of chitosan scaffolds loaded with dexamethasone for tissue engineering applications using supercritical fluid technology

Supercritical fluid impregnation was tested to prepare a new scaffold loaded with a bioactive compound. Dexamethasone is used in osteogenic media to direct the differentiation of stem cells towards the osteogenic lineage. Dexamethasone was impregnated in chitosan scaffolds at different operating conditions, in order to optimize the impregnation process. Pressure and temperature affect the carbon dioxide density and influence the swelling of the polymer and the drug solubility in the fluid phase, therefore these are two important parameters that were studied in this work. Chitosan sponges prepared by freeze drying were impregnated with the active compound at pressures from 8.0 up to 14.0 MPa and temperatures from 35 up to 55 °C. The effect of the impregnation contact time (3 h and 6 h) was also evaluated. From the experiments performed we can conclude that the yield of impregnation is lower when increasing pressure and temperature. The contact time will mainly influence the amount of drug impregnated in the scaffold and for higher contact times the impregnation yield is also higher. Scanning electron microscopy shows particles of dexamethasone in the bulk of the scaffold, which confirms the feasibility of the supercritical fluid impregnation technology for the preparation of delivery devices. The loading capacity of the scaffolds was determined by spectroscopic analysis and the highest loading was achieved for the experiments performed at 8.0 MPa and 35 °C. Furthermore, in vitro drug release studies were carried out and the results show that dexamethasone was sustainably released. Supercritical fluid impregnation proved to be feasible for the preparation of a drug delivery system for bone tissue engineering purposes.

Binary diffusion coefficients for 2,3-dimethylaniline, 2,6-dimethylaniline, 2-methylanisole, 4-methylanisole and 3-nitrotoluene in supercritical carbon dioxide

The measurement and correlation of the experimental binary diffusion coefficients of 2,3-dimethylaniline, 2,6-dimethylaniline, 2-methylanisole, 4-methylanisole and 3-nitrotoluene in supercritical carbon dioxide is reported. Results were obtained using the Taylor-Aris dispersion technique, at 313, 323, and 333 K, and in a pressure range from 15.0 to 35.0 MPa. The diffusivity experimental data were correlated with temperature, pressure and carbon dioxide density and viscosity. Moreover, the experimental results were compared with the values estimated by several semiempirical equations.

High‐pressure viscosity and density of carbon dioxide + pentaerythritol ester mixtures: Measurements and modeling

AbstractThis article reports densities and viscosities up to 60 MPa and from 303.15 to 353.15 K on two binary mixtures of CO2 and lubricant pentaerythritol tetra‐2‐ethylhexanoate with 7.8% and 14.4% mass fraction of lubricant. Because CO2 and the lubricant are not in the same phase at atmospheric pressure and room temperature, a specially‐designed vibrating‐wire apparatus has been used. The experimental data, together with our previous data for six mixtures of CO2 and three polyolesters, have been used to test the predictive and correlation ability of several models: simple mixing laws, the self‐referencing method, and the hard‐sphere and free volume models. In general, it is not possible to predict the viscosity with deviations smaller than 10%. The hard‐sphere model and the self‐referencing model are the more adequate to represent the viscosity of these mixtures. Most of the models studied underestimate the viscosities over the investigated (T,p) range. © 2008 American Institute of Chemical Engineers AIChE J, 2008

A new analysing approach for the structure of density fluctuation of supercriticalfluid

Large scale structural evolution of supercritical carbon dioxide along the isotherm at32 °C was investigated with small-angle neutron scattering. The maximum of the densityfluctuation, the so-called ‘ridge’, was confirmed with Ornstein–Zernike analysis. Toinvestigate the structural change in more detail, the molecular distribution over a largedomain was determined with a newly developed reverse Monte Carlo method.From the molecular distribution obtained, the pair distribution function andcluster-size distribution can be calculated. With increasing density of carbondioxide, the cluster size increases monotonically, whereas the pair distributionfunction for the range of sizes shorter than 10 Å shows a monotonic decrease. From thisresult, it is suggested that the structural change along the isotherm is caused bythe change of balance between growth of clusters and increase of the averagedensity.

Study of acoustical properties of supercritical carbon dioxide using liquid acoustical theory

Molar sound velocity, molar adiabatic compressibility and Van der Waals constant of gaseons, liquid and supercritical carbon dioxide at different temperature and pressure are calculated using liquid acoustical models and data of sound velocity, density, molar volume and adiabatic compressibility of carbon dioxide provided by National Institute of Standards and Technology, USA. The results show that the liquid acoustical models can be used in study acoustical property of supercritical carbon dioxide in wide ranges of temperature and pressure. The surface tension, conglutination and diffusivity at different temperatures and pressures are calculated. And the mutative rules of these physical quantities are analyzed. The data can provide reference for supercritical liquid technique.

Adsorption Equilibria of cis-5,8,11,14,17-Eicosapentaenoic Acid Ethyl Ester and cis-4,7,10,13,16,19-Docosahexaenoic Acid Ethyl Ester from Supercritical Carbon Dioxide on Silica Gel

Adsorption data of cis-5,8,11,14,17-eicosapentaenoic acid ethyl ester (EPA-EE) and cis-4,7,10,13,16,19-docosahexaenoic acid ethyl ester (DHA-EE) from supercritical carbon dioxide on silica gel were determined at temperatures from (319.15 to 340.35) K and carbon dioxide densities from (0.668 to 0.734) g·mL−1 by using the elution by characteristic point (ECP) method. The equilibrium isotherm data were fitted using a Langmuir model. The monolayer adsorption capacity of EPA-EE is 0.130 mmol·g−1, and that of DHA-EE is 0.119 mmol·g−1. The adsorption enthalpy change of EPA-EE is in the range of (34.4 to 38.0) kJ·mol−1, and that of DHA-EE is in the range of (34.4 to 40.6) kJ·mol−1.

Excess molar enthalpies for mixtures of supercritical CO 2 and linalool

Excess molar enthalpies ( H m E ) for mixtures of supercritical CO 2 and linalool were measured at conditions of temperature and pressure typical of supercritical extraction processes: 313.15 and 323.15 K and 7.64, 10.00 and 12.00 MPa. The measurements were carried out using an isothermal high-pressure flow calorimeter. The effects of pressure and temperature on the excess molar enthalpy are large. Mixtures formed by low-density carbon dioxide and linalool show very exothermic mixing and excess molar enthalpies exhibit a minimum in the CO 2-rich region. The lowest H m E values (≈−4000 J mol −1) are observed for mixtures at 313.15 K and 7.64 MPa. Mixtures formed by high-density carbon dioxide and linalool show considerably endothermic mixing (≈400–600 J mol −1) in the linalool-rich region and moderately exothermic mixing for the other compositions. On the other hand, H m E at 7.64 MPa and 313.15 and 323.15 K varies linearly with CO 2 mole fraction in the two-phase region where a gaseous mixture and a liquid mixture of fixed composition, for a given condition of temperature and pressure, are in equilibrium. Results are analyzed in terms of phase equilibria, pure carbon dioxide density and CO 2–terpene molecular interactions. Excess molar enthalpies are simultaneously correlated using the Soave–Redlich–Kwong and Peng–Robinson equations of state and the classical mixing rule. The significance of these large variations of H m E with temperature and pressure in the design of supercritical fluid deterpenation processes is discussed.

Solubility of astaxanthin in supercritical carbon dioxide

The solubility of astaxanthin in carbon dioxide was measured under supercritical conditions of a pressure range from 80 to 300 bar, and temperature range from 303 to 333 K, by using a dynamic flow-type. The solubility of astaxanthin increasing from 0.42×10−5 to 4.89×10−5 with higher temperature and pressure maintains certain density of supercritical carbon dioxide. The solubility data obtained were applied to the Chrastil model, based on the density of carbon dioxide. The data fitted well with the Chrastil model at most experimental conditions.

Viscosity, Density and Excess Volume of Acetone + Carbon Dioxide Mixtures at High Pressures

The densities and viscosities of acetone, carbon dioxide, and acetone + carbon dioxide mixtures containing 10, 25, 50, and 75 wt % carbon dioxide were determined at nominal temperatures of 325, 348, 373, and 398 K and at pressures up to 35 MPa using a falling-cylinder type high-pressure viscometer. The densities of carbon dioxide and acetone + carbon dioxide mixtures were found to show crossovers at around 18 MPa for mixtures with CO2 content less than 50 wt % and at around 23 MPa for mixtures with CO2 content greater than 50 wt % at 325 K, which shifts to higher pressures with temperature. Acetone displayed higher viscosities than the mixtures. At 325 K, the mixtures were found to show negative excess volumes at all compositions for pressures lower than 28 MPa. The excess volumes become less negative with increasing pressure and are positive above 28 MPa for high carbon dioxide content; at pressures above 55 MPa, they become positive for all compositions. Assessments of several mixing rules for viscosity...

Diffusion of Liquid and Supercritical Carbon Dioxide into a Chitosan Sphere

The diffusion and loading of liquid and supercritical carbon dioxide into chitosan spheres with a diameter of 0.5 cm and a mass of 0.055 g was experimentally explored at temperatures of 25, 35, and 45 °C and at fixed carbon dioxide densities of 0.65, 0.75, and 0.85 g/cm3. Loading as high as 1.25 g of carbon dioxide/g of chitosan was achieved. Carbon dioxide loading increased as the carbon dioxide density and temperature each increased. By modeling the loading as unsteady-state radial Fickian diffusion, a diffusion coefficient of carbon dioxide into the chitosan sphere could be obtained at a given exposure temperature and pressure. These diffusion coefficients were on the order of 10-7 m2/s and increased with temperature. Carbon dioxide density did not seem to have a significant effect on the diffusion coefficients, but it did influence the maximum achievable loading.

Supercritical carbon dioxide extraction of acorn oil

Acorn fruit oil of Quercus rotundifolia L. (holm-oak) was extracted with compressed carbon dioxide in the temperature range of 35–60 °C and in the pressure range of 12–21 MPa. The influences of particle size, CO 2 density, solvent flow rate, and extractor geometry were studied. Two different tubular extractors were used: extractor 1 of 0.2 L of capacity, internal diameter D = 45.7 mm, height/diameter ratio H/ D = 1.5, and extractor 2 of 0.09 L of capacity, internal diameter D′ = 21.3 mm, and H′/ D′ = 12. It was found that the yield and the initial extraction rate depend on the carbon dioxide density and superficial velocity, and on the ratio of bed height to D, at the same conditions of temperature, pressure, and particle size. In the beginning of extraction, CO 2 density is the preponderant factor, but after some time of extraction, the fraction of oil directly exposed to the solvent, which is dependent on particle size, becomes the most important factor. The Sovová model was successfully applied to the description of the supercritical extraction curves of acorn oil.