Solubility in supercritical

Politzer, P., P. Lane, J. S. Murray, and T. Brinck. 1992a. Investigation of Relationships Between Solute Molecule Surface Electrostatic Potentials and Solubilities in Supercritical Fluids. J. Phys. Chem. 96, 7938. 

Shing, K. S. Chung, S. T., Computer-simulation methods for the calculation of solubility in supercritical extraction systems, J. Phys. Chem. 1987, 91, 1674-1681... 

The formation of relatively ill-defined catalysts for epoxide/C02 copolymerization catalysts, arising from the treatment of ZnO with acid anhydrides or monoesters of dicarboxylic acids, has been described in a patent disclosure.968 Employing the perfluoroalkyl ester acid (342) renders the catalyst soluble in supercritical C02.969 At 110°C and 2,000 psi this catalyst mixture performs similarly to the zinc bisphenolates, producing a 96 4 ratio of polycarbonate polyether linkages, with a turnover of 440 g polymer/g [Zn] and a broad polydispersity (Mw/Mn>4). Related aluminum complexes have also been studied and (343) was found to be particularly active. However, selectivity is poor, with a ratio of 1 3.6 polycarbonate polyether.970... 

Gomez-Prieto MS, Caja MM and Santa-Maria G. 2002. Solubility in supercritical carbon dioxide of the predominant carotenes in tomato skin. J Am Oil Chem Soc 79(9) 897—902. 

Coimbra P, Blanco MR, Silva HSRC, Gil MH, de Sousa HC. (2006) Experimental determination and correlation of artemisinin s solubility in supercritical carbon dioxide. J Chem Eng Data 51 1097-1104. 

Alternatively, we have shown that CO2 can be used to induce miscibility of fluorocarbon-hydrocarbon mixtures (see Figure 1), even those involving polar compounds such as methanol (2). Fluorinated organometallic complexes have been well established to have significant solubility in supercritical CO2, and their use as catalysts in this medium is well developed (10). This allows the homogeneously catalyzed reaction to be carried out in the C02-expanded homogeneous solution. 

Measurements of solubilities in supercritical CO2 corroborated the hypothesis that the nonpolar character of a series of tetraaUsylammonium dialkyl-dithiocarbamate ion pairs was influenced... 

The mole fraction solubilities of ten copper(II) and five chromium(III) P-diketo-nates were measured in SCCO2 with a spectroscopic technique and found to vary over four orders of magnitude. Observed trends indicate that the solubility in supercritical carbon dioxide is strongly dictated by the character of the hydrocarbon or fluorocarbon shell surrounding the central metal atom. A regular solutions approach was used for Cr(acac)°3 to quantitatively attempt to predict the solubility in SCCO2. Solubility... 

An understanding of the phase behavior of a particular system of interest is important because complex results can sometimes occur. A dramatic example, which occurs frequently for solubilities in supercritical systems, is the retrograde behavior. Figure 3 clearly shows the presence of a retrograde region. For an isobaric system at some pressure, such as 12.7 MPa (1841.5 psi), an increase in temperature of a solution of ethylene and naphthalene from 300 to 320 K results in an increase in the equilibrium solubility of naphthalene. This behavior is typical of liquid solvent systems. For the same increase in temperature (300 to 320 K) but at a pressure of 8.1 MPa (1174.5 psi), the solubility of naphthalene decreases by nearly an order of magnitude. Because this latter behavior is the opposite of typical liquid solvents, it is termed retrograde solubility. 

In terms of the solubilities of solutes in a supercritical phase, the following generalizations can be made. Solute solubilities in supercritical fluids approach and sometimes exceed those of liquid solvents as the SCF density increases. Solubilities typically increase as the pressure is increased. Increasing the temperature can cause increases, decreases, or no change in solute solubilities, depending on the temperature effect on solvent density and/or the solute vapor pressure. Also, at constant SCF density, a temperature increase increases the solute solubility (16). 

Powders from organometallics. Fine pigment powders are also possible. Metal alkoxides such as titanium isopropoxide, which is soluble in supercritical ethanol, can undergo rapid expansion spraying to form submicronic titanium dioxide powders. 

The Group 6 compounds glucose and glycine were not tested at the small-scale level because previous work suggested that they would not be soluble in supercritical fluid CO2. Additionally, chloroform was not tested at this level because it is undoubtedly extractable but would pose significant trapping problems because of its relatively high vapor pressure. 

Several other non salt-specific factors, such as pressure and temperature, influence crystallization. In SCWO, the solubility reduces as the temperature increases, owing to the reduction in dielectric constant. For example, sodium chloride s solubility in supercritical water is 824 mg/L at 400°C while at 500 °C it is only 299 mg/L [28], Pressure increase produces an increase in dielectric constant, and it is not infrequent for the precipitated salt to redissolve itself. For example, Foy et al. [24] oxidized chloro-compounds at temperatures around 550°C and 600 bar in these conditions, the dielectric constant is sufficiently high to avoid chloride deposition. 

By utilizing the rapid expansion of supercritical solutions, small-size particles can be produced from materials which are soluble in supercritical solvents. In this process, a solid is dissolved in a pressurized supercritical fluid and the solution is rapidly expanded to some lower pressure level which causes the solid to precipitate. This concept has been demonstrated for a wide variety of materials including polymers, dyes, pharmaceuticals and inorganic substances. 

Lemert, R.M., Johnston, K.P., "Chemical Complexing Agents for Enhanced Solubilities in Supercritical Fluid Carbon Dioxide," submitted to I EC Res., 1990. 

We explain these results based upon the specific arrangement of monomers in the oligomer chain. The exact sequence of monomers will affect their solubility in supercritical COy, therefore, one expects to see more than one envelope for tne MMA oligomers which possess two BA units. In contrast, soft ionization mass spectrometry will not distinguish such isomers. Soft ionization mass spectrometric analysis preceded by SFC separation should yield molecular weight and sequence distribution data on copolymers. 

Although there were some differences on the effects of temperature and pressure according to each particular compound, the free bases of hyoscyamine (1), scopolamine (2), and pseudoephedrine (6) were all found to be highly soluble in supercritical CO,. However, the hydrochloride salts of these compounds were scarcely extracted by pure CO, under any conditions employed. These results were consistent with preliminary evidence indicating that these alkaloids are not extracted from plant materials by pure CO,. This means that the alkaloids in living cells in the plant are not in the form of their free bases but rather as water-soluble salts in the cell vacuole [40]. Therefore, it was necessary to develop a procedure to enhance the solubilities of alkaloidal salts in CO,. 

Lamb, D. M., Barbara, T. M. Jonas, J. NMR Study of Solid Naphthalene Solubilities in Supercritical Carbon Dioxide Near the Upper Critical End Point. J. Phys. Chem. 1986, 90, 4210M215. 

Other extraction methods used in the lipid extraction include supercritical fluid extraction (SFE) and pressurized liquid extraction (PLE). With SEE, good extraction yields have been obtained for nonpolar lipids including ester-ified fatty acids, acylglycerols, and unsaponifiable matter. However, complex polar lipids are only sparingly soluble in supercritical carbon dioxide alone and polar modifiers, such as methanol, ethanol, or even water is required to improve the extraction of polar lipids (10). SFE has been used for the extraction of lipids especially from various food matrices, such as different nuts, edible oils, and seeds (11). The recoveries of lipids in SFE were on the same levels than with conventional solvent extraction methods (12,13), no significant differences between the fatty acids extracted were observed. PLE has also been used in lipid extraction, although only in very few applications (14). The elevated temperatures used in PLE can cause alteration of the lipid composition. 

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