Database vapor-liquid equilibria

Having identified discrete components as our criterion, the next problem is how to define the equilibrium of three components. In Chap. 2, for example, the vapor-liquid equilibrium of a flash—a single component transfer between two phases—was derived. A certain quantity of a component, called the y fraction, is vaporized into the vapor phase as an equal amount of the same component, called the x fraction, is dissolved in the liquid phase. The K value (the equilibrium constant of K=y/x) is used to determine the component distribution results. This same logic may be used here. Although we cannot use these same K values, as they do not apply, we can apply another database. 

There are at least 20 physical property databases commercially available as on-line data services. Five of the databases listed include vapor-liquid-equilibrium calculations for mixtures. 

Vapor-Liquid Equilibrium Data Collection (Gmehling et al., 1980). In this DECHEMA data bank, which is available both in more than 20 volumes and electronically, the data from a large fraction of the articles can be found easily. In addition, each set of data has been regressed to determine interaction coefficients for the binary pairs to be used to estimate liquid-phase activity coefficients for the NRTL, UNIQUAC, Wilson, etc., equations. This database is also accessible by process simulators. For example, with an appropriate license agreement, data for use in ASPEN PLUS can be retrieved from the DECHEMA database over the Internet. For nonideal mixtures, the extensive compilation of Gmehling (1994) of azeotropic data is very useful. 

Solvent activities of polymer solutions have been measured for about 60 years now. However, the database for polymer solutions is still modest, in comparison with the enormous amount of data available for mixtures of low-molecular substances. Three explicit databases have been published in the literature up to now. The database prepared by Wen Hao et al. is summarized in two parts of the DECHEMA Chemistry Data Series. Danner and Higtf provided a database and some calculation methods on a floppy disk with their book. WoUfarth prepared the most complete data collection regarding vapor-liquid equilibrium data of polymer solutions. His annually updated electronic database is not commercially available however, personal requests can be made via his e-mail address given above. 

The measurements collected in these volumes provide a database of carefully selected experimental vapor-liquid equilibrium data, which can be used for the testing and development of theoretical models, correlations, and process design software. 

WIC1 Wichterle, I. Linek, J. Wagner, Z. Kehiaian, H.V. Vapor-liquid equilibrium in mixtures and solutions. Bibliographic database. Integrated Electronic Chemical Databases - Vol. II, 140 pp., ELDATA SARL, Paris, 1994. 

The ELBT Program on the CD includes a large, almost exhaustive, bibliographical database, EVLM 2006, giving 13476 references to experimental vapor-liquid equilibrium in mixtures and solution measurements for 20937 two- to nine-component systems. These components are organic or inorganic electrolytes and nonelectrolytes, ionic liquids, alloys, fused salts, polymers and other materials. 

The Vapor-Liquid Equilibrium in Mixtures and Solutions Bibliographic Database covers the literature published between January 1900 and December 1995. It gives references on experimental vapor-liquid, vapor-liquid-liquid, and vapor-liquid-solid equilibrium measurements for 2- to 9-component system.s. Data on 2588 substances (and 80 other materials, e.g., polymers) in 30118 systems from 10878 references are stored in the database. 

Prediction of solubility is also receiving more attention, mostly limited to academic research. In comparison to the vapor-Equid equilibrium situation, which has built an extensive database for reliable prediction (Reid et al. 1977), prediction of solid-liquid equilibrium remains in its early stage (Kolaret al. 2002). However, this field is developing rapidly, and its fuUire potential cannot be overlooked (Tung et al. 2007). 

A chemical s Tb, the temperature at which its vapor pressure equals the ambient pressure, and Tm, the temperature at which its solid and liquid forms are in equilibrium at ambient pressure, are easily located in references and databases. As a result, many of the correlations that have been constructed for property estimations use these parameters as independent variables. The Tb of a chemical can nonetheless provide an indication of the partitioning between gas and liquid phases,53 with the higher values denoting a lower tendency to exist in the vapor phase. The surface tension, y, of a chemical, the ratio of the work done to expand the surface divided by the increase in the surface area, is often used to estimate the VP of liquids in aerosols and in soil capillaries.28 The VP of a chemical is the pressure of a pure chemical vapor that is in equilibrium with the pure liquid or solid, and... 

Volume IV/8C summarizes most of the observed values of densities of unsaturated aliphatic hydrocarbons which include normal and branched alkenes, alkadienes, alkynes, and miscellaneous compounds such as alkatrienes and compounds with double and triple bonds in the crystal and liquid phases that have been reported in the world s scientific hterature. The values Usted have been extracted from the TRC Source Database. These data have been collected by the Thermodynamics Research Center over a period of years and used as a basis for density values listed in the TRC Thermodynamic Tables -Hydrocarbons. An additional literature search was made to locate other data and bring the collection np to date. It is believed that this compilation includes at least 90% of the pertinent data reported in the literature. The usual experimental conditions are in contact with air at one atmosphere below the normal boiling point of the hydrocarbon, and in equilibrium with the vapor phase above the normal boiling point. In the summary tables, temperatures are reported on the Kelvin scale. These were obtained by adding 273.15 to temperatures originally given on the Celsius scale. 

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