Supercritical Mixtures

Why density augmentation occurs in dilute supercritical solutions. 

Fluctuations in dilute binary supercritical mixtures. Entrainer effect in supercritical mixtures. 

The solubility of solids in mixtures composed of a supercritical fluid and an entrainer. 

A simple equation for the solubility of a solid in a supercritical fluid cosolvent with a gas or another supercritical fluid. 

Cubic equation of state and local composition mixing rules correlations and predictions. Application to the solubility of solids in supercritical solvents. 

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Supercritical Mixtures Dehenedetti-Reid showed that conven-tionaf correlations based on the Stokes-Einstein relation (for hquid phase) tend to overpredict diffusivities in the supercritical state. Nevertheless, they observed that the Stokes-Einstein group D g l/T was constant. Thus, although no general correlation ap es, only one data point is necessaiy to examine variations of fluid viscosity and/or temperature effects. They explored certain combinations of aromatic solids in SFg and COg. 

Murga R, Ruiz R, Beltran S and Cabezas JL. 2000. Extraction of natural complex phenols and tannins from grape seeds by using supercritical mixtures of carbon dioxide and alcohol. J Agric Food Chem... 

Supercritical HF, HC1, and Reactive Supercritical Mixtures Containing the Elements H, C, F,... 

The promising results obtained under batch-wise operation could be confirmed also under continuous-flow conditions. As schematically shown in Fig. 2, the substrate was injected with an HPLC pump into a stream of premixed CO2 and O2 before entering the reactor. The supercritical mixture was bubbled through the stationary PEG phase containing the Pd nanoparticles. 

It could be expected, that combustion reactions and possibly flames can be produced in such dense supercritical mixtures. Technical aspects of hydrothermal oxydation at moderate pressures have already been tested and discussed [7,8]. The study of combustion and flames in supercritical phases offers several possibilities 1. The variation of pressure over wide ranges should influence reaction mechanisms and flame characteristics because the density can be changed from low, gas-like, to high, liquid-like, values. 2. The variable temperature of the dense, fluid environment can have an influence on reactions and flames. 3. The chemical and physical character of this environment can be varied considerably, for example by using supercritical water as the major component, as in the present experiments. Certainly, the knowledge of transport coefficients of gases involved is desirable. For water the viscosity has been determined to... 

Recently, the electrocarboxylations of benzyl and aryl halides and perfluoroalkyl-halides [39] in supercritical mixture or in supercritical carbon dioxide (scC02) and of aryl and benzyl halides in microemulsion [40], were also investigated in order to exploit the possible effect of the use of these solvents on the selectivity of the... 

Substantial evidence suggests that in highly asymmetric supercritical mixtures the local and bulk environment of a solute molecule differ appreciably. The concept of a local density enhancement around a solute molecule is supported by spectroscopic, theoretical, and computational investigations of intermolecular interactions in supercritical solutions. Here we make for the first time direct comparison between local density enhancements determined for the system pyrene in CO2 by two very different methods-fluorescence spectroscopy and molecular dynamics simulation. The qualitative agreement is quite satisfactory, and the results show great promise for an improved understanding at a molecular level of supercritical fluid solutions. 

Experimental, theoretical, and computational investigations of molecular interactions in supercritical mixtures (1-17) have led to a growing body of evidence suggesting that in typical supercritical mixtures the local environment surrounding solute molecules can be considerably different from the bulk. A molecular-based understanding of these systems is essential to develop accurate predictive models of their phase behavior. 

Petsche, I.B., Debenedetti, P.G., "Solute-solvent Interactions in Infinitely Dilute Supercritical Mixtures A Molecular Dynamics Investigation," J. Chem. Phys., 1989, 97(11), 7075. 

Temperature Dependence. In order to understand why CH3OH solvates" faster compared to CH3CN, the dependence of the solvation rate with temperature was investigated. Figure 7 shows the recovered temperature-dependent S(t) traces for PRODAN in the binary supercritical fluid composed of C02 and 1.57 mol% CH3OH. The same experiment was carried out for the supercritical mixture of C02 and CH3CN, and the trend is similar. In all cases, as temperature is increased, the solvent relaxation process becomes, as expected, faster. By determining the rate constants of the relaxation process as described above, we construct Arrhenius plots... 

The bulk solvent strength of binary and ternary supercritical mixtures, measured with the solvatochromic dye Nile Red (E ),... 

With binary and ternary supercritical mixtures as chromatographic mobile phases, solute retention mechanisms are unclear. Polar modifiers produce a nonlinear relationship between the log of solute partition ratios (k ) and the percentage of modifier in the mobile phase. The only form of liquid chromatography (LC) that produces non-linear retention is liquid-solid adsorption chromatography (LSC) where the retention of solutes follows the adsorption isotherm of the polar modifier (6). Recent measurements confirm that extensive adsorption of both carbon dioxide (7,8) and methanol (8,9) occurs from supercritical methanol/carbon dioxide mixtures. Although extensive adsorption of mobile phase components clearly occurs, a classic adsorption mechanism does not appear to describe chromatographic behavior of polar solutes in packed column SFC. 

Mohamed, S. R. Debenedetti, P. G. Prud homme, R. K. Effects of Process Conditions on Crystals Obtained from Supercritical Mixtures. AIChE J. 1989b, 35, 325-328. 

Organic chemists have been attracted for a variety of reasons to supercritical media as an environment for performing reactions. These reasons include, especially for C02 and H20, the environmental friendliness of the medium. The fact that supercritical fluids can be removed without a residue is an advantage. Other advantages include the solubility of gases within supercritical mixtures, the high diffusion rates, and the variable and adjustable density, solvent power, and dielectric constant of the medium. Ordinary gases, such as 02 and H2, are miscible with... 

Myers DJ, Urdahl RS, Cherayil BJ, Fayer MD. Temperature dependence of vibrational lifetimes at the critical density in supercritical mixtures. J Phys Chem 1997 107 9741-9748. 

The rapid expansion of supercritical solutions (RESS) has been explored recently as a novel route for the production of small and monodispersed particles (1-2.). Particle formation involves nucleation, growth and agglomeration. In RESS, nucleation is induced by a rapid decompression growth and agglomeration occur within the expanding solution. The thermodynamics of the supercritical mixture influences the relative importance of these mechanisms, and thus play a key role in sizes or size distribution of final particles. 

Supercritical fluids have no surface tension and, like gases, rapidly diffuse to occupy the entire volume of the system. Like a gas, a SCF also mixes perfectly with other gases. As a result, the concentration of gases within a SCF may be much higher than in liquids. The concentration of hydrogen in a supercritical mixture of hydrogen (85 bar) and carbon dioxide (120 bar) at 50 °C is... 

Debenedetti P. Clustering in dilute, binary supercritical mixtures A fluctuation analysis. Chem. Eng. Sci. 1987 42(9) 2203-2212. 

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