Vapor‐liquid equilibrium: Part II. Correlations from P‐x data for 15 systems

Abstract

SCOPEThe apparatus described by Gibbs and Van Ness (1972) has been used systematically to measure solution vapor pressures as a function of liquid composition at 3OoC for 15 binary systems in vapor-liquid equilibrium (VLE). Data reduction by the method described in the preceding paper for P-x data yields correlating equations for the excess Gibbs free energy and the activity coefficients, from which the P-x-y relationship at 3OoC may be calculated. The systems studied are CC&, CHCl3, and CH2C12, each with tetrahydrofuran and with furan; tetrahydrofuran with furan; CH2C12 with methyl acetate, with acetone, and with l,4-dioxane; CHC13 with 1,4-dioxane; pyridine with acetone, with CHC13, and with CH2C12; and n-pentanol with n-hexane. Heat-of-mixing data, which are available in the literature for most of the systems reported, allow extension of these results to other conditions. CONCLUSIONS A N D SIGNIFICANCEThe rapidity with which P-x data may be taken commends the use of such data as the basis for formulation of VLE relationships for binary systems. These are useful in themselves, and they serve also in predictive schemes for multicomponent systems, for which experimental determination is much more tedious.Routine methods of data reduction are available, as reviewed in the preceding paper, and the reliability of the method depends solely on the reliability of the P-x data.Gibbs and Van Ness (1972) demonstrated for the ethanoln-heptane system agreement between results obtained with the present apparatus and data from the literature based on measurements with an equilibrium still. The results presented here are for systems representing a wide range of behavior, from large positive to large negative deviations from ideality.The experimental apparatus used in this work is fully described by Gibbs and Van Ness ( 1972). Liquid solutions of known composition are prepared in a thermostated test cell by volumetric metering of degassed liquids from accurate piston-injectors. Direct measurement of pressure in the cell provides for the solution vapor pressure. The raw data' therefore consist of pairs of values for pressure and liquid mole fraction at constant temperature and cover the full composition range from x1 = 0 to x1 = 1.As indicated by the discussion of P-x data in the preceding paper, the raw data are fit by the least-squares spline-fit procedure of Klaus and Van Ness (1967), and this provides the input for the numerical procedure of Mixon et al. (1965) which yields the g = GE/RT versus x1 relationship in accord with Equation (9b) of the preceding paper. The resulting numerical values of g/xlx2 or of ln(yl/yz) are then fit with respect to x1 by an appro-

Extending the Van Laar Model to Multicomponent Systems

“…These values may be used as a guide to assess the quality of the experimental data when more than one set of data were measured at the same temperature or pressure condition for the same mixture but the RMS errors were quite different. It is also remarkable that the VLE data reported by Byer et al [44] and Van Ness and Abbott [45] for the chloroformtetrahydrofuran system at 30 o C can be accurately represented by the reformulated van Laar equation with a single adjustable parameter.…”

In silico design of solvents for carbon capture with simultaneous optimisation of operating conditions

“…1-3 show the PPC-SAFT prediction of VLE for pure solvents and experimental data while Figs. 4-6 compare the Byer et al (1973), Wu and Sandler (1988), Garriga et al (2006) VLE prediction of binary solvent mixtures using PPC-SAFT with experimental data. Tables 1 and 2 summarise the absolute average deviation (AAD) of the PPC-SAFT predictions of some of the solvents used against available experimental data.…”

Vapor‐liquid equilibrium: Part III. Data reduction with precise expressions for GE

“…In Part I of this series of papers Van Ness et al (1973) described the numerical methods by which one may accomplish the reduction of binary VLE data to yield a correlation for the excess Gibbs function of the liquid phase. Byer et al (1973) in Part I1 demonstrated the effectiveness of the numerical procedure based on P-x data alone for 15 binary systems. There is an additional procedure for the reduction of P-x data, developed by Barker (1953), that was not pursued in these earlier papers.…”

“…In Part I1 of this series of papers on vapor-liquid equilibrium (VLE), Byer et al (1973) reported data for 15 binary systems at 30°C and found that for 14 of these systems the data (P vs. x) were correlated to within the limits of experimental uncertainty through use of the four-suffix Margules equation. On the other hand, none of the currently used G E vs. x expressions served to represent the data for n-pentanol-n-hexane to within experimental precision.…”

“…On the other hand, none of the currently used G E vs. x expressions served to represent the data for n-pentanol-n-hexane to within experimental precision. The inadequacy of these equations in the representation of precise data for certain complex mixtures has prompted us in the past to rely on numerical techniques for data reduction (Van Ness et al, 1973). However, Barker's method for the reduction of P-x data (Barker, 1953) is in principle a more attractive procedure because it is a single-step analytical fitting technique that makes direct use of the measured data.…”