Supercritical Fluid Systems Research Articles

超臨界流体を用いたポリマーの混練，成形，加工，リサイクル技術 超臨界流体を用いた成形加工のための基礎物性

Solubility, diffusivity and viscosity in supercritical fluid and polymer systems are reviewed. Supercritical fluids such as carbon dioxide dissolve in polymers at high pressures and plasticize them. The increase in diffusivity and the decrease in viscosity of polymers with dissolved supercritical fluids are due to the plasticizing effect of supercritical fluids. In this article general tendency, data source and theoretical calculation methods of solubility, diffusivity and viscosity are presented for supercritical carbon dioxide and nitrogen in polymers.

The fibre optic reflectometer: A new and simple probe for refractive index and phase separation measurements in gases, liquids and supercritical fluids

A fibre optic reflectometer (FOR) has been developed to monitor refractive index (n) and density (ρ) changes in gases, liquids and supercritical fluids (SCFs). The key operating principle is the measurement of the intensity of light from a light emitting diode, LED, which is reflected from the end of a fibre immersed in the medium. The amount of reflected light depends on the difference between the refractive indices of the fibre and the medium. The refractive index of the medium is related in turn to its density. The FOR is particularly sensitive to phase separation, a key aspect of supercritical fluid systems, because of the density discontinuity which accompanies the separation. This device allows the collection of data with a high spatial (9 μm-fibre diameter) and time (∼0.02 s) resolution. The small size of the fibre optic probe means that it can be put into operating reactors and even catalyst beds. Experiments are described with pure CO2 and CHF3, and mixtures CO2 + cyclohexane and CO2 + MeOH over wide pressure and temperatures ranges. The measurements are in excellent agreement with published data for these systems.

Development and Validation of Spectroscopic Methods for Monitoring Density Changes in Pressurized Gaseous and Supercritical Fluid Systems

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionDevelopment and Validation of Spectroscopic Methods for Monitoring Density Changes in Pressurized Gaseous and Supercritical Fluid SystemsMarc A. Blatchford and Scott L. WallenCite this: Anal. Chem. 2002, 74, 21, 5693Publication Date (Web):September 25, 2002Publication History Published online25 September 2002Published inissue 1 November 2002https://doi.org/10.1021/ac020502qCopyright © 2002 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views202Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (10 KB) Get e-Alerts Get e-Alerts

Development and validation of spectroscopic methods for monitoring density changes in pressurized gaseous and supercritical fluid systems.

The further development of new processes utilizing liquid or supercritical CO2 as a solvent will benefit from the rational design of new CO2-philes. Understanding solvation structures and mechanisms of these molecules is an important part of this process. In such studies, determining the change in density as a function of the measured thermodynamic conditions (pressure and temperature) provides an excellent means of directly monitoring the solution conditions in the detection volume for a given technique. By integrating spectroscopic peaks, changes in area can be used to determine changes in analyte concentration in the detection volume, and thus, it should be possible to monitor the system density in situ. In the present study, we examine the utility of Raman and NMR spectroscopy as a means of following changes in solution density conditions and validate this approach in pure fluids and gases (N2 and CO2) and supercritical fluid mixtures (acetaldehyde vapor in N2). In addition, we present the design of a simple, inexpensive cell for conducting Raman and NMR measurements under moderate pressure conditions.

High‐resolution adsorption isotherms of supercritical carbon dioxide on activated carbon

AbstractSupercritical fluids are attractive solvents for heterogeneous processes, including catalysis and adsorptive separation. However, adsorption processes in the near‐critical region are poorly understood and exhibit unique behavior where the adsorption of the supercritical solvent plays an important role in the solute adsorption. The behavior of supercritical fluids in confined pores has been studied theoretically, but there are few experimental data on their behavior in industrially important microporous materials. The adsorption of carbon dioxide on Calgon F400 activated carbon over a wide range of pressures (0–20 MPa) at temperatures near the critical point of carbon dioxide (30 to 45°C) was studied. Near‐continuous adsorption and desorption isotherms were measured with a new flow gravimetric apparatus with precise control over pressure and temperature. As pressure is increased, the excess adsorption increases sharply at low pressures; then a broad maximum is observed. At temperatures greater than the critical temperature, there is a sharp drop in excess adsorption near the critical region where the density of the bulk fluid increases sharply. A crossover is observed near the critical region where, below a certain pressure, the excess adsorption decreases with temperature, while above the crossover point the trend is reversed. When analyzed as a function of solvent density, the crossover disappears, revealing an anomalous maximum in total adsorption near the critical point similar to the enhanced local density or “charisma” observed in binary solute–supercritical fluid systems. A 2‐D EOS model using the 2‐D Peng‐Robinson EOS was able to qualitatively describe the adsorption behavior over the entire pressure range, but the quantitative agreement was poor in the near‐critical region.

Determination of the Local Environment Surrounding Pyrene in Supercritical Alkanes: A First Step toward Solvation in Supercritical Aviation Fuels

We report quantitative data on the local microenvironment surrounding a model organic solute (pyrene) dissolved in several supercritical components of aviation fuels (n-pentane, n-hexane, n-heptane, n-octane). Toward this end, we use static fluorescence spectroscopy to determine whether these supercritical alkanes influence the local microenvironment surrounding pyrene in a way similar to other supercritical fluids (e.g., CO2, CF3H, C2H6, H2O). Steady-state fluorescence measurements indicate that, in all alkanes studied, there is an increase in local fluid density surrounding the pyrene molecule relative to the fluid bulk density (solute−fluid density augmentation). The maximum in this local density augmentation occurs at approximately one-half the fluid critical density and subsequently decreases at higher fluid densities. These results are fully consistent with observations for pyrene in other supercritical fluid systems (i.e., CO2, H2O). The maximum relative local density augmentation increases with in...

A model for correlating the solubility of solids in supercritical CO 2

A model for correlating the phase equilibria of solid–supercritical fluid (SCF) systems has been developed. The model is based on the fact that the free solute molecules, the solvent molecules, and the solute–solvent clusters in such a solid–SCF system are in chemical equilibrium. The local density of the solvent surrounding a solute is used as one of the parameters in the model. The validity of the model is verified by correlation of the phase equilibrium data of supercritical CO 2–solid systems reported in the literature. Using the solubility data, the model can be used to estimate the local density and the average number of the solvent molecules in the clusters.

New local composition model and mixing rule for the mixtures asymmetric both in size and energy

A new DDLC (density dependent local composition) model which possesses sound theoretical background describing both size and energy asymmetries of molecules has been developed. Dividing the radial distribution function into packing and attractive effects new local composition model naturally satisfies high and low density boundary conditions and it shows desirable characteristics to represent computer simulated local composition data correctly. Based on the new local composition model, DDLC mixing rule for the cubic equation of state has been derived and utilized to calculate the solubilities of solids in supercritical fluid mixtures. It has been found that new version of DDLC mixing rule shows excellent capabilities to predict solubilities of solids in various supercritical fluid systems including solid mixtures or entrainers.

Integral equation and Monte Carlo simulation studies of clusters in infinitely dilute supercritical solutions

We present a systematic study of both the size and attractive interaction strength effects on solvent clustering in infinitely dilute supercritical solutions. Both integral equation and computer simulation methods are brought to bear. We argue that monitoring the net local solvent density change due to the presence of the solute as well as residual solute chemical potential offers a predictive way of identifying clustering or declustering in infinitely dilute supercritical solutions. Phase diagram-like figures can be obtained, wherein the ‘phase boundaries’ divide the solvent enrichment (or effective attraction) from the solvent depletion (or effective repulsion) region. In conjunction with the corresponding states analyses these diagrams can provide a useful semiquantitative means of predicting the nature of solvation in many supercritical fluid systems.

Predicting and Calculating Complex Phase Equilibrium in Supercritical Fluid Systems with a New Technique

A general approach to multiphase equilibrium calculations with particular application to vapour-liquid-liquid and liquid-liquid-liquid systems is presented. The capabilities of the new technique to correctly predict and calculate complex phase equilibrium are tested on five highly non-ideal systems, relevant to supercritical fluid extraction. The thermodynamic models applied are the recently proposed MHV2 model and the Redlich-Kwong-Soave cubic equation of state.

A modified perturbed hard-sphere equation of state

A modified perturbed hard-sphere equation of state, represented by the Carnahan—Starling equation with the van der Waals attractive part, has been investigated using the Mollerup approach for the energy parameter a for pure substances. The equation has been extended to mixtures, for both vapor—liquid equilibria and solid—supercritical fluid equilibria, using the Boublik—Mansoori equation with the same van der Waals attractive part. The vapor pressure, density, second virial coefficient, specific heat capacity and enthalpy were examined for pure substances. The new equation was also able to predict accurately the vapor pressures of fatty acids. The predictions of both vapor—liquid equilibria and solid—supercritical fluid equilibria, using the one fluid van der Waals mixing rules with one binary interaction parameter, are significantly better than those obtained by cubic equations of state, especially for large molecules. The predictions for solid—supercritical fluid systems were improved by incorporating solute—solute interaction parameters. Density dependent mixing rules were also examined.

Molecular thermodynamic model for solvent-induced glass transitions in polymer—supercritical fluid systems

A molecular thermodynamic approach is described for predicting polymer glass transition temperatures as a function of the amount of gas sorbed by the polymer. The predictive model is based on a lattice theory of polymer solutions and the concept of order parameters, the use of which has been important in the development of macroscopic models and phenomenological analyses of glass transitions. A general definition of the solvent-induced glass transition is given, and then applied within the framework of this lattice model and its order parameters to predict glass transition temperatures for several polymer-compressed CO 2 mixtures. The model is also used to examine a new experimental observation described as retrograde vitrification.

Effect of structure on the cloud-point curves of silicone-based amphiphiles in supercritical carbon dioxide

The use of surfactants in nonpolar supercritical fluid (SCF) systems helps to increase solvating power of the SCF. Although C02 is the most widely used SCF, many commercially available surfactants generally exhibit poor solubility in this fluid. Our goal is to design and synthesize amphiphiles that are both functional and highly CO 2-soluble, and evaluate the relationship between structure and solubility. The basis of the design involves the synthesis of molecules whose hydrophobic groups interact favorably, in a thermodynamic sense, with CO 2 while the hydrophilic group(s) interacts with the chosen solute (water, polar molecules, metals). In this work, we will explore the relationship between structure and solubility of silicone-based amphiphiles in CO 2 via high-pressure phase-behavior experiments. The phase-behavior results clearly indicate that the silicone-based amphiphiles exhibit high CO 2 solubility at temperatures of 313 K and pressures below 40 MPa.

Multiphase behavior of supercritical fluid systems: oil solutions in light hydrocarbon solvents

Etude experimentale de l'equilibre multiphasique de solutions d'huile dans des solvants constitutes d'hydrocarbures legers. Le trace des diagrammes pression-temperature (P-T) montre que les solvants de masse moleculaire faible et les huiles de masse moleculaire elevee favorisent l'extension des cones V-L (vapeur-liquide-liquide). Les compositions d'equilibre des deux phases sont expliquees a l'aide du concept des phenomenes retrogrades et des diagrammes reguliers pression-composition (P-X) et temperature-composition (T-X). Les diagrammes P-T sont egalement utilises pour construire des diagrammes enthalpie-temperature (H-T) dont la signification est discutee