High-pressure fluid-phase equilibria: Experimental methods and systems investigated (2000–2004)
Introduction
For the design and optimization of high-pressure chemical processes and separation operations, information on high-pressure phase equilibria and solubilities is essential. The simulation of petroleum reservoirs, enhanced oil recovery, carbon capture and storage, the transportation and storage of natural gas, refrigeration and heat-pump cycles, and the study of geological processes are other examples for the need of high-pressure phase-equilibrium data. The interest in old and new applications of supercritical fluids [1], [2], [3], like extraction, particle formation, impregnation and dyeing, cleaning, reaction, chromatography, injection molding and extrusion, and electronic chip manufacturing, as well as the interest in ionic liquids and “green solvents”, led to a continuation of the increase in the number of publications concerning high-pressure phase-equilibrium data.
There are many ways to obtain information about the phase behavior of fluid mixtures, but the direct measurement of phase-equilibrium data remains an important source of information, though it is difficult and expensive to take precise experimental data. On the other hand, for a company, it is very often more expensive to use imprecise data or to estimate data a couple of times over the years, if experimental data are not available. There are several review articles about techniques for experimental investigations [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14]. Information about experimental equilibrium data is important, even when thermodynamic models are used to calculate the phase behavior of a mixture. Thermodynamic models can help to reduce the number of experimental data points needed for a special design problem, but very often, at least some experimental data points are needed to adjust interaction parameters of the model [15].
Reviews of high-pressure phase-equilibrium data in the literature have been published by several authors [8], [10], [13], [14], [16], [17], [18], [19], [20], [21], [22], [23], [24]. Some reviews cover a specific topic, like the solubility of certain substances in supercritical carbon dioxide, e.g., Bartle et al. [14] for solids and liquids, Gücli-Üstündag and Temelli [19], [23], [24] for lipids, and Higashi et al. [21] for high-boiling compounds, or for a specific binary system, like Diamond and Akenfiev [22] on carbon dioxide + water. Other reviews cover high-pressure fluid-phase-equilibria data that have been published in a specific periods, e.g., Knapp et al. [17] covering 1900–1980, Fornari et al. [8] covering 1978–1987, Dohrn and Brunner [10] covering 1988–1993, and Christov and Dohrn [13] covering 1994–1999. This work gives an overview about systems for which high-pressure phase-equilibrium data have been published from 2000 to 2004, including vapor–liquid equilibria (VLE), liquid–liquid equilibria (LLE), vapor–liquid–liquid equilibria (VLLE), the solubility of high-boiling substances in supercritical fluids, and the solubility of gases in liquids (GLE). Work on the continuation of the review series is under way, covering the period between 2005 and 2008, and will be published in 2010.
Section snippets
Literature search and evaluation
This survey covers the most important journals in the field of high-pressure phase equilibria, as listed in Table 1; abbreviation of journal titles were used according to ISO 4 [25]. To find candidates for articles that are of interest for this review we used a three-stage search strategy. In Stage 1 we systematically searched the table of contents of all volumes that appeared between 2000 and 2004 of the journals of Table 1, checked in cases of doubt the abstracts and downloaded the article.
Experimental methods
Particularly at high pressures, the measurement of phase equilibria is the most suitable method to determine the phase behavior, which often is far more complex than at ambient and moderate pressures. Due to large deviations from ideal behavior, the prediction of high-pressure phase equilibria is less accurate than at lower pressures. Another difficulty of using predictive methods is the fact that molecules of interest for high-pressure applications, particularly supercritical fluid extraction,
Systems investigated
Almost 700 articles with experimental data on high-pressure phase equilibria were found [143], [144], [145], [146], [147], [148], [149], [150], [151], [152], [153], [154], [155], [156], [157], [158], [159], [160], [161], [162], [163], [164], [165], [166], [167], [168], [169], [170], [171], [172], [173], [174], [175], [176], [177], [178], [179], [180], [181], [182], [183], [184], [185], [186], [187], [188], [189], [190], [191], [192], [193], [194], [195], [196], [197], [198], [199], [200], [201]
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