Seader

E. J. Henley and. D. Seader, Equilibrium-Stage Separation Operations in ChemicalEngineering ]ohn. Wiley Sons, Inc., New York, 1981. 

Distillation J. D. Seader, Jeffrey J. Siirola, Scott D. Barnicki... 

J. D. Seader, Ph.D., Professor of Chemical Engineering, University of Utali, Salt Lake City, Utali Fellow, American Institute of Chemical Engineers Member, American Chemical Society Member, American Society for Engineering Education (Section 13, Distillation)... 

Seader, J. D. Computer Modeling of Chemical Processes. AlChE Monog. Ser. No. 15(1985). 

FIG. 13-20 Liqi lid-phase activity coefficients for an ethanol-n-hexane system, [Henleij and Seader, Eqiiilihriiim-Stage Separation Operations in Chemical Engineering, Wileif, New York, 1931 data of Si nor and Weher, J, Chem, Eng, Data, 5, 243-247 (I960).]... 

The results of the analyses for all the various elements commonly encountered in distillation processes are summarized in Table 13-5. Details of the analyses are given by Smith (Design of Equilibrium Stage Processes, McGraw-Hul, New York, 1967) and in a somewhat different form by Henley and Seader (op. cit.). 

FIG. 13-41 Comparison of rigorous calcnlations with Gilliland correlation. [Henley and Seader, Eqnilihrinm-Stage Separation Operations in Chemical Engineering, Wiley, New York, 1981 data of Van Winkle and Todd, Chem. Eng., 78(21), 136 (Sept. 20, 1971) data of Gilliland, Elements of Fractional Distillation, 4th ed., McGraw-Hill, New York, 1950 data of Brown and Maiiin, Trans. Am. Inst. Chem. Eng., 35, 679 (1.93.9) ]... 

The (x, i )), values in Eq. (13-37) are minimum-reflux values, i.e., the overhead concentration that would be produced by the column operating at the minimum reflux with an infinite number of stages. When the light key and the heavy key are adjacent in relative volatihty and the specified spht between them is sharp or the relative volatilities of the other components are not close to those of the two keys, only the two keys will distribute at minimum reflux and the Xi D),n values are easily determined. This is often the case and is the only one considered here. Other cases in which some or all of the nonkey components distribute between distillate and bottom products are discussed in detail by Henley and Seader (op. cit.). 

However, the total number of equilibrium stages N, N/N,n, or the external-reflux ratio can be substituted for one of these three specifications. It should be noted that the feed location is automatically specified as the optimum one this is assumed in the Underwood equations. The assumption of saturated reflux is also inherent in the Fenske and Underwood equations. An important limitation on the Underwood equations is the assumption of constant molar overflow. As discussed by Henley and Seader (op. cit.), this assumption can lead to a prediction of the minimum reflux that is considerably lower than the actual value. No such assumption is inherent in the Fenske equation. An exact calculational technique for minimum reflux is given by Tavana and Hansen [Jnd. E/ig. Chem. Process Des. Dev., 18, 154 (1979)]. A computer program for the FUG method is given by Chang [Hydrocarbon Process., 60(8), 79 (1980)]. The method is best applied to mixtures that form ideal or nearly ideal solutions. 

Calculations were made with the Grayson-Streed modification of the Chao-Seader method for K values and the Lee-Kesler method for enthalpy departures. Initial estimates for stage temperatures and flow rates were as follows, where numbers in parentheses are consistent with specifications ... 

Baird [Comp. Chem. Engng., 9, 593 (1985)]. Since then, they have been applied successfully to problems involving interlinked distillation (Wayburn and Seader, op. cit.), azeotropic and three-phase distillation [Kovach, 111 and Seider, Comp. Chem. Engng., 11,593(1987)], and reac tive distillation [Chang and Seader, Comp. Chem. Engng., 12, 1243 (1988)], when SC and inside-out methods have failed. Today, many computer-aided distillation-design and simulation packages include continuation techniques to make the codes more robust. 

Correlations for estimating overall mass-transfer coefficients can be found in McCabe et al. (1993), Perry and Green (1984), Geankoplis (1983), Henley and Seader (1981), King (1980) and Treybal (1980). 

Henley, E. J. and Seader, J. D. (1981). Equilibrium-Stage Separation Operations in Chemical Engineering. Wiley, New York. 

There are many other specific techniques applicable to particular situations, and these should often be investigated to select the method for developing the vapor-liquid relationships most reliable for the system. These are often expressed in calculation terms as the effective K for the components, i, of a system. Frequently used methods are Chao-Seader, Peng-Robinson, Renon, Redlich-Kwong, Soave Redlich-Kwong, Wilson. 

Henley, E. J. andj. D., Seader, Equilibrium Stage Separations in Chemical Engineering John Wiley and Sons (1981), p. 507. 

Mullis (M10), Bastress (B4), and Carlson and Seader (Cl) have conducted experimental studies to determine the heat-transfer characteristics of typical rocket-exhaust igniters. In these studies, the total rate of heat transfer to the propellant or simulated propellant surface was measured as a function of mass flow rate, geometry, and impingement angle between the igniter exhaust... 

The Scatchard-Hildebrand theory of regular solutions is most attractive because of its simplicity, and it is of special interest here because it has been applied to hydrocarbon mixtures at high pressures (PI 3), leading to the correlation of Chao and Seader (Cl). 

In their correlation, Chao and Seader use the original Redlich-Kwong equation of state for vapor-phase fugacities. For the liquid phase, they use the symmetric convention of normalization for y and partial molar volumes which are independent of composition, depending only on temperature. For the variation of y with temperature and composition, Chao and Seader use the equation of Scatchard and Hildebrand for a multicomponent solution ... 

Although (5 varies with temperature, the quantity [<5, — 5] is insensitive to temperature the solubility parameters used in Eq. (70) were therefore treated as constants. Table III gives some of the solubility parameters used by Chao and Seader. For supercritical components, the solubility parameters were back-calculated from binary-mixture data, as was also done by Shair (P2). 

Solubility Parameters and Liquid Molar Volumes in the Chao-Seader Correlation... 

The correlation of Chao and Seader has been computerized and has been used extensively in the petroleum industry. It provides a useful method for estimating high-pressure vapor-liquid equilibria in hydrocarbon systems over a wide range of temperature, pressure, and composition, and presents a significant improvement over the previously used A -charts first introduced by W. K. Lewis, B. F. Dodge, G. G. Brown, M. Souders, and others (see D6) almost forty years ago. However, the Chao-Seader correlation is unreliable at conditions approaching the critical. Various extensions have been proposed (G2), especially for application at extreme temperatures. 

The method of Chao and Seader is subject to certain limitations, and it is instructive briefly to consider the most serious ones ... 

Chao and Seader assume that the partial molar volumes are independent of composition this assumption is equivalent to saying that at constant temperature and pressure there is no volume change upon mixing the pure liquid components, be they real or hypothetical. The term on the right-hand side of Eq. (46) is assumed to be zero for all temperatures, pressures, and compositions. This assumption is very poor near critical conditions, and is undoubtedly the main reason for the poor performance of the Chao-Seader correlation in the critical region. 

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