Solubility pressure effect

At lower ScF pressures, solubility effects on the extraction process are observed. Figure 3 shows the on-line measurement of the extraction of 7.0 ml of 0.1 M uranium in 6 N nitric acid with ScF CO2 at S0°C, at lower pressures, and... 

FIGURE 12.2 An illustration of the vapor pressure and solubility effects discussed in the text. Components A, B, and C have vapor pressures decreasing from A to B to C and have solubilities in the stationary phase increasing from A to B to C. 

It is most important to know in this connection the compressibility of the substances concerned, at various temperatures, and in both the liquid and the crystalline state, with its dependent constants such as change of. melting-point with pressure, and effect of pressure upon solubility. Other important data are the existence of new pol3miorphic forms of substances the effect of pressure upon rigidity and its related elastic moduli the effect of pressure upon diathermancy, thermal conductivity, specific heat capacity, and magnetic susceptibility and the effect of pressure in modif dng equilibrium in homogeneous as well as heterogeneous systems. 

Another factor that differentiates the solubility of gases from solids and liquids is the effect of pressure. The effect of pressure on gas solubility was studied extensively by a contemporary and close associate of John Dalton named William Henry (1775-1836). Henry s Law states that the solubility of a gas is directly proportional to the partial pressure of that gas over the solution. Stated mathematically, Henry s Law is c = kP, where c is the concentration of the dissolved gas in moles per liter, k is Henry s law constant for the solution, and P is the partial pressure of the gas above the solution. Henry s Law is demonstrated every time a carbonated beverage is opened. During the carbonation process, carbon dioxide is dis-... 

As we have seen in Chapter 9, there are a variety of dissolved solutes in atmospheric particles, which will lower the vapor pressure of droplets compared to that of pure water. As a result, there is great interest in the nature and fraction of water-soluble material in atmospheric particles and their size distribution (e.g., Eichel el al., 1996 Novakov and Corrigan, 1996 Hoffmann et al., 1997). This vapor pressure lowering effect, then, works in the opposite direction to the Kelvin effect, which increases the vapor pressure over the droplet. The two effects are combined in what are known as the Kohler curves, which describe whether an aerosol particle in the atmosphere will grow into a cloud droplet or not under various conditions. 

Schulman (51) on Li, Na, and K stearates. The NH4OH and LiOH curves are similar in shape to the HC1 curve. The CsOH, RbOH, KOH, and NaOH curves are highly expanded, with lower collapse pressures. The NaOH curve seems to exhibit unusually pronounced solubility effects at low surface areas. At areas greater than 50 sq. A. per molecule, the surface pressures for the soaps are still substantial (greater than 5 dynes per cm.), while they fall to near zero for the unionized fatty acid. 

In the supercritical phase, both temperature and pressure play a significant role in determining the extraction efficiency. After the short-lived retrograde solubility effect subsides at about 55-60°C, a transition of the system back to the mass transfer controlled situation will take place where increasing temperature will, once again, bring about a surge in the extraction efficiency. In fact, for the supercritical phase,... 

FACTORS THAT AFFECT SOLUBILITY Effect of Pressure on Solubility... 

To understand any extraction technique it is first necessary to discuss some underlying principles that govern all extraction procedures. The chemical properties of the analyte are important to an extraction, as are the properties of the liquid medium in which it is dissolved and the gaseous, liquid, supercritical fluid, or solid extractant used to effect a separation. Of all the relevant solute properties, five chemical properties are fundamental to understanding extraction theory vapor pressure, solubility, molecular weight, hydrophobicity, and acid dissociation. These essential properties determine the transport of chemicals in the human body, the transport of chemicals in the air water-soil environmental compartments, and the transport between immiscible phases during analytical extraction. 

In the switch from CFC to the more polar HFA propellants, one of the major problems has been inadequate solubility of the surfactants (used to stabilize the micronized drag particles) in the HFA. Solubility can be adjusted within the CFC propellant, e.g. CFC 12 is a far better solvent than CFC 11. However, for HFAs, blends do not exist and so solvency can only be addressed by using a cosolvent such as ethanol. It must be remembered that changing the solvency of the propellant will almost certainly affect the all-important vapor pressure and thus the MM AD, the particle velocity and the deposition site. Alternative stabilizers have been investigated and include PVP, fluorinated surfactants and Poloxamers. In addition to solubility effects, difficulties associated with the use of HFAs also include incompatibility with elastomer components in the metering valves. 

We also examined the pressure (density) effects at 673 K. For metals that were highly reactive (Zr, Mo, Fe, Pd), or relatively unreactive (Y, Eu, Gd, La, Nd, Sm, Ag, Cd, Ba, Sr, Cs, Na), no density effect was observed. For other metals ( Cr, Ce, Pr, Mn, Ni) however, we could observe moderate effects of the pressure (density) on the recovery. As density increased, recoveries decreased. This implies that the solubilities increased or that the reactions shifted to more soluble products with increasing density. At 723 K, the recoveries were found to be independent of density in the range of 0.08 - 0.15 g/cm3. 

As discussed in Chapters 4 and 5, CBPC formation is governed by the oxide solubility. The solubility, in turn, is related to the Gibbs free energy, which is a function of temperature and pressure. As a result, the CBS formulation depends on the downhole temperature and pressure. The effect of the temperature on the solubility has already been discussed in Section 6.4. The pressure effect can be assessed in a similar manner, but as we shall see, it is negligibly small and can be ignored for all practical purposes. 

Cobalt(II,III) sepulchrates have been used in the chemical education [415] and considerable number of the chemical and physicochemical studies as efficient quencher of the phosphorescence [416] and electronic excited states [417, 418], as a reductant in kinetic studies of redox reactions [419, 420], as a model for study of magnetodynamic [421], solvent [422] and pressure [423] effects on the outer-sphere electron-transfer reactions. Transfer chemical potentials (from solubility measurements) [424], electrochemical reduction potentials [425] and ligand-field parameters [426] for cobalt sepulchrates have been calculated. Solvent effect on Co chemical shift of cobalt(III) ion encapsulated in the sepulchrate cavity [427]... 

The process of choosing a random number and calculation of cascading error is repeated 10,000 times, generating a distribution of solubility values relative to the "true" value which can be characterized mathematically, plotted, and used to furnish the likelihood or probability of any particular solubility value in the range being exceeded. Essentially the same steps were followed in simulations for other parameters investigated, even for those on vapor pressure, where effects of temperature variation are compound-specific. 

For this purpose the solubility of several acetylacetonate metallorganic com-potmds in supercritical carbon dioxide at 313 K and pressures up to 62 MPa have been studied. Moreover, the solubility effect of several polar entrainers has been studied along with the effect of process conditions on properties and characteristics of crystals and coatings obtained when expanding and pyrolyzing the above-mentioned supercritical saturated mixtures (Table 13.2). 

The prediction of analyte solubility in a SF is difficult it depends on the SF density and dielectric constant and on the analyte vapor pressure. In addition, the polarities of the SF and the analyte should be as similar as possible in order to improve the solubility. Effects of some variables on analyte solubility are ... 

The region of pressure below the crossover pressure is known as the retrograde region. In this range of pressure, solubility decreases with an increase in temperature because the density of the SCF falls sharply. The decrease in density is sufficient to overcome any increases in solute vapor pressure that would normally lead to an increase in solubility. Above the crossover pressure, the decrease in solvent density is less sensitive to temperature and so solubility increases with temperature because the vapor pressure effect becomes dominant. 

Morel and Hering (1993) state that the calcium carbonate is usually supersaturated in surface waters. Further, pressure has an effect on the free energies on the ions (in this case in the water column, but this is also applicable to high pressure membrane systems) and the solubility is decreased at lower pressures. Solubility of calcite also increases with CO2 partial pressure (which would have increased in the NF stirred cell since air was used to pressurise the system). 

T is temperature, Ak is the change in compressibility caused by the reaction, V indicates partial molal volume, and sub- scripts refer to pressure in atmospheres. Determination of AV would allow calculation of stCOYOACaa) quantity necessary for predicting the direction of tne pressure effect for several geochemical reactions which are difficult to investigate experimentally, for exaniple, mineral formation at sea floor conditions. However, this calculation demands accuracy in knowledge of the atmospheric pressure solubility, and confidence in the reproducibility of the pressure versus solubility plots. 

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