Factor Pitzer’s acentric

For the calculations presented in this paper, we first elected to use three simple cubic equations of state PR-EOS SRK-EOS and RK-EOS. For the pure components, critical properties (Pq, Tq) and Pitzer s acentric factor (ci>) are needed to obtain a and b . Critical properties have been measured for most of the low molecular weight components and are reported by Reid et al. 

Table 11 Critical Properties and Pitzer s Acentric Factor for the Working Materials...

Characterization of the vapor pressure curve was readily accessible in the form of Pitzer s acentric factor. The definition of the acentric factor is... 

TC=CRITICAL TEMPERATURE, K PC=CRITICAL PRESSURE, BAR W PITZER S ACENTRIC FACTOR... 

The approach is predictive, and the only input data required are the critical parameters, molecular weight, Pitzer s acentric factor and, for thermal conductivity, the ideal gas specific heat. 

In terms of this nomenclature, the Soave premultiplier, fta.°, generalized in terms of Pitzer s acentric factor a>, and the reduced temperature Trv is... 

Zc = critical compressibility factor. o) = Pitzer s acentric factor. 

The equation of state uses corresponding states theory to determine the attractive and volume parameters of each species. Therefore, the pure component critical temperature, 7, and critical pressure, are required. The EOS uses a third parameter, viz. Pitzer s acentric factor, (O, (9)... 

For improved accuracy generalized equations of state are complemented with property parameters of individual components. More often are used Hougen-Watson or Lee-Kesler equations of state. In the former the additional parameter is critical compressibility coefficient, in the latter, Pitzer s acentric factor as the indication of their molecular structure. 

If the departure from equation (35) is not too large, it can be treated as a perturbation. The effect of non-central interactions on the second virial coefficient is second order and it is very difficult to distinguish between any of the non-central interactions on the basis of the behaviour of In essence, it is possible to fit the properties of many pure substances to equations based on simple corresponding states and additional terms whose magnitude is proportional to a perturbation parameter that is a measure of the deviation from central forces. One such perturbation parameter is Pitzer s acentric factor. 74,76 another is Rowlinson s In a homologous series the number of carbon atoms in the chain constitutes yet another measure of the perturbation. It can be shown that there is a simple relation between the different factors. ... 

Later Soave (1972) improved on the RK-EOS by replacing the term a/T f with a more general temperature-dependent term a(T) and proposed a simple form for a oj) for all pure substances, taking advantage of the concept of the acentric factor of Pitzer. Pitzer (1939), and Pitzer. et al. (1955), Pitzer s acentric factor, oj, was intended as an additional parameter for the improvement of the corresponding-states principle. The acentric factor is a measure of the difference in molecular structure between a given component and a gas with spherically symmetric molecules with u) — 0 (such as argon). 

The BWRC equation was first tested on nonpolar gases and their mixtures. It is most commonly used in a generalized form [0.49]. The recommended formulas in Ref. [0.49] for the determination of coefficients of Eq. (0.5) are simple functions of critical parameters and of Pitzer s acentric factor (7, Pcr Pi)- In a more general case, it is imperative also to know, for each pair of mixture components, what is termed the constant of binary interaction K j. 

Greenkorn at Purdue have started to work in this area. The group-contribution method necessarily provides only an approximation but for many applications that is sufficient. For practical-minded chemical engineers this new research in applied thermodynamics represents perhaps the most exciting development since Pitzer s acentric factor. 

Pitzer s acentric factor binary interaction parameter... 

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