Phase Equilibrium Data Sources

There are numerous sources of phase equilibrium data available that serve as a database to those developing or improving equations of state. References to these databases are widely available. In addition, new data are added mainly through the Journal of Chemical and Engineering Data and the journal Fluid Phase Equilibria. Next, we give data for two systems so that the reader may practice the estimation methods discussed in this chapter. 

The modified van Laar equation (Black, 1959) extends the applicability of the van Laar equation to many systems, including non-symmetrical and hydrogenbonding binaries. The equation, which is generalized to multi-component mixtures, is expressed in terms of three binary interaction parameters A, and Q (= Cj. These parameters must be determined from binary phase equilibrium data. The modified van Laar equation reduces to the van Laar equation if Q = 0. Refer to the source (Black, 1959) for detailed mathematical formulation of the equation. 

There are a number of sources for phase equilibrium data and computational methods (see E4.1, below). Most of the material focuses on vapor-liquid equilibrium (VLB) since this information is used extensively for distillation, absorption, and stripping. The most complete VLB literature is a series of books by Hala et al. (1967, 1968). Additional information can be found in Hirata et al. (1975) and Gmehling et al. (1979). For light hydrocarbon systems, the Natural Gas Processors Association has published a data book (1972). A very useful and extensive source, including solid-liquid and liquid-liquid as well as VLB information, has been written by Walas (1985). This book contains both source data and methodology and contains sample calculations. 

This chapter will start with a brief overview of SCF processing. Thereafter, a phase behaviour analysis of palmitic acid, methyl palmitate, ethyl palmitate and tripalmitin in CO2, ethane and propane, as well as CO2 together with a co-solvent will be considered. The analysis will investigate phase equilibrium data present in the literature, trends observed the data, a comparison between the phase behaviour of the various derivatives as well as the various solvents, and the effect of a co-solvent. The phase behaviour data will then be used to analyse how SCFF and SCFE can be used to obtain extracts enriched in palmitic acids or its derivatives. In particular this study will consider how SCFF can be used to distinguish between various fatty acids and their derivatives and also between palmitic acid and/or its derivatives and other components present in the sources. Finally, SCFE of palmitic acid containing triglycerides from solid matrices will be considered. The overarching aim of this chapter is thus to show how SCFs can be used to process palmitic acid and its derivatives. 

Figme 5 shows the phase equilibrium data of the system C02/methyl palmitate of both Inomata et al. [48] and Lockemarm [49]. Figure 5 hints towards significant differences between the data sets, yet insufficient information is available to determine which data set us superior. However, the data clearly shows that an increase in temperature results in an increase in phase transition pressure. Due to the scatter in the data and slight inconsistencies between the two sources the exact nature of the relationship between temperature and the phase transition pressure can not be determined. Additional measurements would be required therefore. Both sets of data do, however, indicate that total solubility can be achieved at moderate pressures (less than 25 MPa at temperatures below 343 K). 

Gas solubility has been treated extensively (7). Alethods for the prediction of phase equilibria and actual solubility data have been given (8,9) and correlations of the equilibrium K values of hydrocarbons have been developed and compiled (10). Several good sources for experimental information on gas— and vapor—liquid equilibrium data of nonideal systems are also available (6,11,12). 

The primary data sources are individual publications reporting the results of experimental investigations and supplementary theoretical calculations. The bases for these are calorimetric determinations of enthalpies of reaction, phase transformation and heat capacities, vapor pressure determinations, emf measurements, equilibrium determinations etc. 

The available thermodynamic data are of two types stabihty constants, enthalpy and entropy of reaction for the formation of soluble complexes Th(S04) " " and solubihty data for various solid phases. The two sources are linked because the solubility of the solid phases depends on the chemical speciation, i.e., the sulphate complexes present in the aqueous phase. The analysis of the experimental stability constants has been made using the SIT model however, this method cannot be used to describe the often very high solubility of the solid sulphate phases. In order to describe these data the present review has selected a set of equilibrium constants for the formation of Th(S04) and Th(S04)2(aq) at zero ionic strength based on the SIT model and then used these as constants in a Gibbs energy minimisation code (NONLINT-SIT) for modelling experimental data to determine equilibrium constants for the formation of Th(S04)3 and the solubility products of different thorium sulphate solids phases. 

This four volumes series contains vapor-liquid equilibrium data (i.e., compositions of vapor and liquid phases as functions of temperature and pressure) covering the regions for which experimental measurements exi t. The systems are almost entirely organic. The data have been recalculated Into SI units and have been smoothed in many cases, often using the Redlich-Kister equation. There are detailed references to the source literature and there is an alphabetic index of the systems covered. The four volumes are ... 

Fig. 7.2 Locations of the a- and p-equilibrium transi, the Mg(a ) and M3(a") transi, and the regimes of occurrence of athermal and isothermal to phases in Tl-Nb. Data sources a and p transi, [Molj65, p. 20] (see aiso Fig. 4.10) M3 transi, [Jep70] and [Fuo82] to + P phase data, [Hic69°].

For the compilation of the data published in the literature for the years 1968-1980 inclusive, volumes 70 to 90 of Chemical Abstracts were used as reference sources. The following key words were consulted Section 68 Phase equilibrium Section 70 or 75 Crystallography... 

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