Carbon dioxide, pressure-density behavior

Calculate the vapor densities (kg/m3) of pure carbon dioxide (C02), propane (C3H8) and butane (C4H10) at 25 °C and pressure of 1 atm. Assume ideal gas behavior. 

Above the crossover pressure, the opposite eifect occurs. This behavior can be understood by considering two opposing effects of temperature on solubility (Chimowitz 2005). The vapor pressure of the solid solute always increases with temperature, while the density (or solvent power) of supercritical carbon dioxide decreases. Below the crossover pressure where the compressibility is larger, the density effect dominates, and the solubility decreases with increasing temperature. At pressures above the crossover pressure, the vapor-pressure effect dominates hence solubility increases with temperature. 

TITc) 2.0, is very high compared to that of carbon dioxide, rR l.l. To overcome ideal gas behavior, it is necessary to compress methane to very high pressures to obtain reasonable methane densities and, hence, solvent power. 

By factoring out solute volatility, the enhancement factor allows comparison of solvent and secondary solute effects. Empirically, there is a linear relationship between the log of the enhancement factor and solvent density. For nonpolar and polar solutes in supercritical carbon dioxide, plots of enhancement factor coincide, indicating that differences in solubility are primarily due to vapor-pressure differences. Nonlinear behavior is noted in the case of high solubilities. The enhancement m pure fluids is relatively independent of solute structure but is sensitive to solvent polarity and density. 

The simplest type of phase behavior to understand is the solubility of a solid solute, such as naphthalene, in a supercritical fluid. When the solute is a crystalline solid, the solid phase may be assumed to be pure and only the supercritical phase is a mixture. Imagine solid naphthalene in a closed vessel under one atmosphere of carbon dioxide at 40°C. The reduced temperature and reduced density of CO2 are 1.03 and 3.7x10 respectively. At this pressure, the gas phase is ideal and the naphthalene solubility is determined by its vapor pressure. As the container volume is decreased isothermally, the solubility initially decreases when the gas phase is still nearly ideal. As the pressure is increased further, however, the gas phase density becomes increasingly nonideal and approaches the mixture critical density (near the critical density of CO2 because the gas phase is still mostly CO2). The reduced density of CO2 increases rapidly near the critical region as shown in Figure 2. The solvent power of CO2 is related to the density which leads to a rapid solubility increase. A brief description of intermolecular interactions is helpful in understanding this behavior. 

ZHA Zhang, W. and Kiran, E., Phase behavior and density of polysulfone in binary fluid mixtures of tetrahydrofuran and carbon dioxide under high pressure miscibility windows, J. Appl. Polym. Sci., 86, 2357, 2002. 

In Fig. 1.5, two projections of the phase behavior of carbon dioxide are shown. In the pressure-temperature phase diagram (Fig. 1.5a), the boihng hne is observed, which separates the vapor and liquid regions and ends in the critical point At the critical point the densities of the equilibrium liquid phase and the saturat-... 

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