Carbon dioxide, pressure-density

The parameters that control the leaching process are as follows temperature, carbon dioxide pressure, agitation, slurry density, particle size, and leachant composition. In general the effects of these parameters on a slurry of Mg(OH)2 are as follows ... 

Another indication of the probable incorrectness of the pressure melting explanation is that the variation of the coefficient of friction with temperature for ice is much the same for other solids, such as solid krypton and carbon dioxide [16] and benzophenone and nitrobenzene [4]. In these cases the density of the solid is greater than that of the liquid, so the drop in as the melting point is approached cannot be due to pressure melting. 

The elastomer process is very similar to the Dennis process. It involves a number of steps in which a gas, formerly carbon dioxide and now fluorocarbon, is mixed with a plastisol under pressure. When released to atmospheric pressure, the gas expands the vinyl compounds into a low density, open-ceUed foam which is then fused with heat. 

Solvent Strength of Pure Fluids. The density of a pure fluid is extremely sensitive to pressure and temperature near the critical point, where the reduced pressure, P, equals the reduced temperature, =1. This is shown for pure carbon dioxide in Figure 2. Consider the simple case of the solubihty of a soHd in this fluid. At ambient conditions, the density of the fluid is 0.002 g/cm. Thus the solubiUty of a soHd in the gas is low and is given by the vapor pressure over the total pressure. The solubiUties of Hquids are similar. At the critical point, the density of CO2 is 0.47 g/cm. This value is nearly comparable to that of organic Hquids. The solubiHty of a soHd can be 3—10 orders of magnitude higher in this more Hquid-like CO2. 

Fig. 2. Reduced density, p, versus reduced pressure, P, isotherms for pure carbon dioxide, where the numbers on the curves represent = TjT values.

The fugacity coefficient of thesolid solute dissolved in the fluid phase (0 ) has been obtained using cubic equations of state (52) and statistical mechanical perturbation theory (53). The enhancement factor, E, shown as the quantity ia brackets ia equation 2, is defined as the real solubiUty divided by the solubihty ia an ideal gas. The solubiUty ia an ideal gas is simply the vapor pressure of the sohd over the pressure. Enhancement factors of 10 are common for supercritical systems. Notable exceptions such as the squalane—carbon dioxide system may have enhancement factors greater than 10. Solubihty data can be reduced to a simple form by plotting the logarithm of the enhancement factor vs density, resulting ia a fairly linear relationship (52). 

K, have been tabulated (2). Also given are data for superheated carbon dioxide vapor from 228 to 923 K at pressures from 7 to 7,000 kPa (1—1,000 psi). A graphical presentation of heat of formation, free energy of formation, heat of vaporization, surface tension, vapor pressure, Hquid and vapor heat capacities, densities, viscosities, and thermal conductivities has been provided (3). CompressibiHty factors of carbon dioxide from 268 to 473 K and 1,400—69,000 kPa (203—10,000 psi) are available (4). 

Example. A gas oil having a density of 0.84 grams per milliliter (37°AP1) is stored at 60°C (140°F) under a gas blanket of carbon dioxide (CO2) at a pressure of 1 atmosphere absolute. To estimate the amount of carbon dioxide dissolved in the gas oil at equilibrium, take the following steps ... 

The solubilities of adamantane and diamantane in supercritical (dense) methane, ethane, and carbon dioxide gases have been measured by a number of investigators [35-37] at a few temperatures with various pressures and solvent densities. These measurements are reported in Figs. 9-12. 

DEPENDENCE OF DENSITY ON TEMPERATURE AND PRESSURE FOR SUPERCRITICM." CARBON DIOXIDE... 

Figure 6.4 On the left is a phase diagram for carbon dioxide. Broken lines indicate isotherm crossing at either constant pressure or density. On the right is illustrated the change in solubility of naphthalene as a function of temperature and pressure.

Figure 6.7 Plot of log k against l/T for hexadecane at constant pressure and constant density with carbon dioxide as the nobile phase.

Pressure or density programming is the most popular of the gradient techniques in SFC. Density is the important parameter with respect to retention but pressure is the physical property which is directly monitored by SFC instruments. If enough experimental density-volume-temperature data are available for the mobile phase then a computer-based algorithm can be used to generate specific density programs. Such data are available for only a few mobile phases, such as carbon dioxide and the n-... 

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