Pure components

Compilation of pure-component data including vapor pre s sure s. 

Equation (15) requires only pure-component and binary parameters. 

In modern separation design, a significant part of many phase-equilibrium calculations is the mathematical representation of pure-component and mixture enthalpies. Enthalpy estimates are important not only for determination of heat loads, but also for adiabatic flash and distillation computations. Further, mixture enthalpy data, when available, are useful for extending vapor-liquid equilibria to higher (or lower) temperatures, through the Gibbs-Helmholtz equation. ... 

Enthalpies are referred to the ideal vapor. The enthalpy of the real vapor is found from zero-pressure heat capacities and from the virial equation of state for non-associated species or, for vapors containing highly dimerized vapors (e.g. organic acids), from the chemical theory of vapor imperfections, as discussed in Chapter 3. For pure components, liquid-phase enthalpies (relative to the ideal vapor) are found from differentiation of the zero-pressure standard-state fugacities these, in turn, are determined from vapor-pressure data, from vapor-phase corrections and liquid-phase densities. If good experimental data are used to determine the standard-state fugacity, the derivative gives enthalpies of liquids to nearly the same precision as that obtained with calorimetric data, and provides reliable heats of vaporization. 

The enthalpy of a vapor mixture is obtained first, from zero-pressure heat capacities of the pure components and second, from corrections for the effects of mixing and pressure. 

The enthalpies of vaporization for the pure components are in excellent agreement with experiment, as is the composition of the azeotrope. The enthalpy of the saturated vapor is also in... 

The computation of pure-component and mixture enthalpies is implemented by FORTRAN IV subroutine ENTH, which evaluates the liquid- or vapor-phase molar enthalpy for a system of up to 20 components at specified temperature, pressure, and composition. The enthalpies calculated are in J/mol referred to the ideal gas at 300°K. Liquid enthalpies can be determined either with... 

This chapter presents quantitative methods for calculation of enthalpies of vapor-phase and liquid-phase mixtures. These methods rely primarily on pure-component data, in particular ideal-vapor heat capacities and vapor-pressure data, both as functions of temperature. Vapor-phase corrections for nonideality are usually relatively small. Liquid-phase excess enthalpies are also usually not important. As indicated in Chapter 4, for mixtures containing noncondensable components, we restrict attention to liquid solutions which are dilute with respect to all noncondensable components. 

An apparent systematic error may be due to an erroneous value of one or both of the pure-component vapor pressures as discussed by several authors (Van Ness et al., 1973 Fabries and Renon, 1975 Abbott and Van Ness, 1977). In some cases, highly inaccurate estimates of binary parameters may occur. Fabries and Renon recommend that when no pure-component vapor-pressure data are given, or if the given values appear to be of doubtful validity, then the unknown vapor pressure should be included as one of the adjustable parameters. If, after making these corrections, the residuals again display a nonrandom pattern, then it is likely that there is systematic error present in the measurements. ... 

In the generalized method of Hayden and O Connell (1975), the pure-component and cross second virial coefficients are given by the sum of two contributions... 

Pure-component parameters required in Equations (16) through (23) are... 

These were converted from vapor pressure P to fugacity using the vapor-phase corrections (for pure components), discussed in Chapter 3 then the Poynting correction was applied to adjust to zero pressure ... 

Subroutine PRDTA2. This subroutine reads the pure-component and binary parameters required for the various correlations describing the liquid and vapor phases. All input parameters are printed for verification. 

Tj. is the reduced temperature, T is the critical temperature, is the critical pressure, and is the modified Rackett parameter as given in the supplemental table for pure-component properties. 

B. The next four data cards contain pure-component data for component one. 

C. The next four data cards contain pure-component data for component two. The same format as used in part B is repeated here. 

NMD(1,J) cols 1-6 six-character identification code for component one this must match the code read in with the pure-component data. 

CALCULATE PURE COMPONENT LIQUID FUGACITY AT SPECIFIED TEMP AND ZERO PRESSURE IF IVAP.LE.2 C PURE CCMPDNENT VAPOR PRESSURE IF IVAP.EQ.3... 

GET PURE COMPONENT LIQUID FUGACITIES, FIP 120 CALL PURF[Pg.292]

CALCULATE TEMPERATURE-INDEPENOENT PARAMETERS FOR PURE COMPONENTS... 

PURE calculates pure liquid standard-state fugacities at zero pressure, pure-component saturated liquid molar volume (cm /mole), and pure-component liquid standard-state fugacities at system pressure. Pure-component hypothetical liquid reference fugacities are calculated for noncondensable components. Liquid molar volumes for noncondensable components are taken as zero. 

FO(I) Vector (length 20) of pure-component liquid standard-state fugacities at zero pressure or hypothetical liquid standard-... 

The parameters characterizing pure components and their binary interactions are stored in labeled common blocks /PURE/ and /BINARY/ for a maximum of 100 components (see Appendix E). 

Pure component parameters for 92 components, and as many binary interaction parameters as have been established, are cited in Appendix C. These parameters can be loaded from formated cards, or other input file containing card images, by subroutine PARIN. 

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