Saturation acentric factor

An analytical method for the prediction of compressed liquid densities was proposed by Thomson et al. " The method requires the saturated liquid density at the temperature of interest, the critical temperature, the critical pressure, an acentric factor (preferably the one optimized for vapor pressure data), and the vapor pressure at the temperature of interest. All properties not known experimentally maybe estimated. Errors range from about 1 percent for hydrocarbons to 2 percent for nonhydrocarbons. 

Chueh s method for calculating partial molar volumes is readily generalized to liquid mixtures containing more than two components. Required parameters are and flb (see Table II), the acentric factor, the critical temperature and critical pressure for each component, and a characteristic binary constant ktj (see Table I) for each possible unlike pair in the mixture. At present, this method is restricted to saturated liquid solutions for very precise work in high-pressure thermodynamics, it is also necessary to know how partial molar volumes vary with pressure at constant temperature and composition. An extension of Chueh s treatment may eventually provide estimates of partial compressibilities, but in view of the many uncertainties in our present knowledge of high-pressure phase equilibria, such an extension is not likely to be of major importance for some time. 

We see that HF has a very high critical temperature and acentric factor for its molecular weight it also, has the lowest reported critical compressibility of any species. Experimental data for the vapor pressure and the apparent moiecular weight of saturated... 

This work results in correlations which can be used to predict parameters for the RK equation of state for hydrocarbon and other nonpolar components for which the critical pressure, critical temperature, and acentric factor are known or can be estimated. However, the applicability of the correlations to large molecules is unproven because the generalized correlations of physical and thermodynamic properties used to develop Oa and Ob are based on components no heavier than n-decane (acentric factor = 0.4885). Although the predicted parameters are based on properties for the saturated liquid phase, the parameters are applied to both vapor and liquid phases. For components above their critical temperature (a reduced temperature greater than 1.00), the values of fia and Ob determined at a reduced temperature of unity are used. 

Most commonly used are further developments of the cubic van der Waals EOS. This EOS for the first time allowed the description of different phenomena, such as condensation, vaporization, occurrence of the two-phase region and critical phenomena, using only two parameters a and b which take into account the interaction forces between the molecules and the volume of the molecules. The introduction of a further parameter, the acentric factor m, which can be derived from vapor pressure data, leads to a more reliable description of the saturation vapor pressures. 

The ct>a, known as the acentric factor, is a function of the reduced saturated vapor pressure = p /p determined at T = 0.7. CSP is obtained for any constant value of the acentric factor, but more complex expressions are needed for polar, associating liquids [Smith and Van Ness, 1959 Maeso and Solana, 1997 Pai-Panadiker et al., 2002 Kiselev and Ely, 2003 Queimada et al., 2003 Polyakov et al., 2007]. The theoretical analyses lead to the following set of reducing variables [Guggenheim, 1945 Hirschfelder et al., 1954] ... 

For molecules more complex than the noble gases, a third parameter is introduced (Pitzer et al. 1955 Pitzer 1955) to form a three-parameter theory of corresponding states. This is the acentric factor a, which is a function of the acentricity or noncentral nature of the intermolecular forces. It is completely empirical. For simple fluids, it was observed that at a reduced temperature of 0.7, the saturation pressure (i.e., the vapor pressure of the liquid-gas equilibrium) divided by the critical pressure is very close to 1/10, or... 

In developing his expression for Soave used data for saturated fluids with acentric factors up to that of decane his fitting procedure did not extend to supercritical temperatures. In terms of this correlation, a T) in equation (7.19) is given by... 

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