Pressure dependency of solubility

The solubilities of many inorganic salts increase with temperature, but a number of compounds of interest in natural waters (CaCOa, CaS04> decrease in solubility with an increase in temperature. Pressure dependence of solubility is slight but must be considered for the extreme pressures encountered at ocean depths. For example, the solubility product of CaCOa will increase with increased pressure (by approximately 0.2 logarithmic units for a pressure of 200 atm). ... 

The pressure dependence of solubility parameter and its hydrogen bonding component for this system, at T=31°C and at a 0.02 mole fraction of 1-propanol, are shown in Figure 2.11. As observed, the hydrogen bonding contribution, even at very low alkanol concentration, is significant in this system. 

On-line SFE-NMR coupling was also reported [151,152], SFE provides some degree of separation by means of solubility and affinity to the matrix. This offers the possibility of transferring analytes directly from the extraction into the NMR probe. Drawbacks in the acquisition of SFE-NMR and SFC-NMR spectra are the elongated spin-lattice relaxation times 7) of protons and the pressure dependence of H NMR chemical shifts [153]. 

Volumes of activation can be unambiguously determined only from the pressure dependence of the rate constants. Attempts to obtain volumes of activation from the correlation of rate constants with the solubility parameter 22 or the cohesive energy density parameter (ced)23, which are related to the internal pressure of solvents, have not led to clear-cut results. 

Figure 10.16 illustrates the solubility of naphthalene in supercritical ethene as a function of temperature at different pressures. In Fig. 10.16 the temperature dependence of solubility is different in different pressure areas. At high pressure, an increase in temperature is followed by an increase in solubility, whereas at lower pressures the opposite effect occurs. 

The reaction rates in this system are presumably first-order in catalyst concentration, as implied by the scaling of product formation rates proportionately to rhodium concentration (90, 92, 93). Responses to several other reaction variables may be found in both the open and patent literature. Fahey has reported studies of catalyst activity at several pressures in tet-raglyme solvent with 2-hydroxypyridine promoter at 230°C (43). He finds that the rate to total products is proportional to the pressure taken to the 3.3 power. A large pressure dependence is also evident in the results shown in Table VII. Analysis of these results indicates that the rate of ethylene glycol formation is greater than third-order in pressure (exponents of 3.2-3.5), and that for methanol formation somewhat less (exponents of 2.3-2.8). The pressure dependence of the total product formation rate is close to third-order. A possible complicating factor in the above comparisons is the increased loss of soluble rhodium species in the lower-pressure experiments, as seen in Table VII. Experiments similar to those of Fahey have also been... 

The dependence of solubility on pressure requires an understanding of the equation of state of hydrothermal solutions saturated with quartz. Systematic P-V-T studies have been conducted.(77) Fig. 4(77) summaries some of this data. As can be seen, behavior is qualitatively like that for pure H2O but with pressures substantially reduced. Pressure in hydrothermal quartz synthesis is established by the initial fraction of the vessel volume (% fill) filled with (OH) solution at the beginning of the growth run. 

In the dual-mode sorption and transport model the pressure-dependence of a (= C/p), P and 0 in gas-glassy polymer systems arises from the pressure-dependent distribution of the sorbed gas molecules between Langmuir sites and Henry s law dissolution. Although k, Dg and are assumed to be constant, the average or effective solubility and diffusion coefficients of the entire ensemble of gas molecules change with pressure as the ratio of Henry s to Langmuir s population, C /C, changes continuously with pressure [eq. (14)]. 

The concentration-dependent models attribute the observed pressure dependence of the solubility and diffusion coefficients to the fact that the presence of sorbed gas in a polymer affects the structural and dynamic properties of the polymer, thus affecting the sorption and transport characteristics of the system (3). On the other hand, in the dual-mode model, the pressure-dependent sorption and transport properties arise from a... 

Air-water partition coefficients and Flenry s law constants are strongly temperature dependent because of the temperature dependencies of vapor pressure and of solubility. FI is also slightly dependent on the temperature dependence of water density and, hence, molar volume. The constants may be concentration dependent because of variations in yw, although the effect is believed to be negligible at low concentrations of non-associating solutes. Noted that these simple relationships break down at high concentrations, i.e., at mole fractions in excess of approximately 0.01. For most environmental situations, the concentrations are (fortunately) usually much lower. For thermodynamic purposes, H is usually preferred, whereas for environmental purposes, H is more convenient. 

At low pressures the solubility of C02 in PEG is low. The increase of the melting point of PEG with (static) pressure outweighs the diminishing effect of C02. In a medium pressure range the reducing effect of C02 dominates. At a further pressure increase, the amount of dissolved C02 in the liquid increases. At the same time pressure dependency of the gas solubility decreases (see fig. 2, slope of 0,05 line and 0,25 line). = higher pressures) again the liquefaction temperature... 

In Figure 2 the experimental solubilities are represented as concentration (pressure) and concentration (density) isotherms for C02 at four different temperatures. The dependence of solubility versus temperature or density is quite usual, as it increases when one of these parameters is raising. C02 is a better solvent for the apolar P-carotene than CC1F,. The lower solvent power of CC1F3 can be explained from its dipole moment (1.7-10 30 C m) [21]. The non-polar C02 enables interactions between the solvent molecule and the solute whereas in the case of CC1F3 these effects are restrained. The thermodynamic background to this particular behavior can e.g. be derived from considerations by Prausnitz et al. [22],... 

The effects of pressure on equilibria in the oceans within depth profiles have been studied mostly in relation to the problem of calcium carbonate saturation in this environment (Millero, 1969 Bemer, 1965 Millero and Bemer, 1972 Edmond and Gieskes, 1970). The early calculations by Owen and Brinkley (1941) concerning the effect of pressure upon ionic equilibria in salt solutions have been extended to studies of BaS04 solubility at different depths (Chow and Goldberg, 1960) and to the pressure dependence of sulfate associations (Fisher, 1972). 

Because of the great depth of the ocean, the most important physical property determining the solubility of carbonate minerals in the sea is pressure. The pressure dependence of the equilibrium constants is related to the difference in volume, AV, occupied by the ions of Ca and in... 

For the prediction of the mixed-gas solubilities from the solubilities of the pure individual gases, the pressure dependence of the binary parameters ku is needed. The Peng—Robinson EOS was used to determine the binary parameters ku. The binary interaction parameter qi2 in the van der Waals mixing rule was taken from ref 28, where it was evaluated for the water-rich phases of water—hydrocarbon and water—carbon dioxide binary mixtures. The calculated binary parameters ku are listed in Table 1. One should note that, as expected for a liquid phase, the above parameters are almost independent of pressure, in contrast to their dependence on pressure in the gaseous phase near the critical point,... 

Isolation Process in the Cross-Over Region. Chimowitz and Pennisi (13) developed a process for the separation and isolation of components from mixtures by operating in the multicomponent temperature-solubility cross-over region. The cross-over point of a pure component (dy/dT)p = 0 represents the pressure at which the dependence of solubility on temperature reverses itself. At lower pressures, the solubility is principally dependent on solvent density - raising temperature decreases density and thus solubility decreases. At higher pressures, solubility is principally dependent on solute sublimation pressure raising the temperature increases sublimation pressure and thus solubility increases. The cross-over point is therefore unique for each solute-solvent system. When there are two solutes, cross-over points occur at different pressures. At an intermediate pressure, the temperature can therefore be manipulated to deposit either component. 

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