Phase equilibria in supercritical

Gibbs-Ensemble Monte Carlo Simulations of Phase Equilibria in Supercritical Fluid Mixtures... 

Ekart MP, Brennecke JF, Eckert CA. Molecular analysis of phase equilibria in supercritical fluids. Chapter 3. In Brrmo TJ, Ely JF, eds. Supercritical Fluid Technology. Florida, Boca Raton, FL CRC Press, 1991 163-192. 

Page, S.H., Sumpter, S.R., and Lee, M.L., Fluid phase equilibria in supercritical fluid chromatography with CO2 based mixed mobile phase — a review, J. Microcolumn Separ., 4 (2), 91-122,... 

Various authors reported on such phase equilibria in supercritical solutions of linear PE or LDPE in ethylene (see [90-94]). It is unfortunate, however, that in many cases essential information on the molecular characteristics of the samples used is missing (degree of branching, molar mass distribution) which renders quantitative treatment of the measured phase diagrams impossible. 

Wiesmet V, Weidner E, Behme S et al (2000) Measurement and modelling of high-pressure phase equilibria in the systems polyethylene glycol (PEG)-propane, PEG-nitrogen and PEG-carbon dioxide. J Supercrit Fluids 17(1) 1-12... 

High-Pressure Phase Equilibria in Ternary Fluid Mixtures with a Supercritical Component... 

Experimental results are presented for high pressure phase equilibria in the binary systems carbon dioxide - acetone and carbon dioxide - ethanol and the ternary system carbon dioxide - acetone - water at 313 and 333 K and pressures between 20 and 150 bar. A high pressure optical cell with external recirculation and sampling of all phases was used for the experimental measurements. The ternary system exhibits an extensive three-phase equilibrium region with an upper and lower critical solution pressure at both temperatures. A modified cubic equation of a state with a non-quadratic mixing rule was successfully used to model the experimental data. The phase equilibrium behavior of the system is favorable for extraction of acetone from dilute aqueous solutions using supercritical carbon dioxide. 

For the design of new, innovative processes to separate low-volatile components such as drugs or polymers with supercritical fluids, experimental data are needed. We designed and built a new apparatus capable of investigating phase equilibria in the occuring complex systems up to 200 bar and 250°C. Phase transitions are determined optically. Samples of the coexisting phases even at high concentration and viscosity are taken. Solid particles can be collected. 

Figure 6 Pressure effect on the temperature-induced and gas-assisted melting of tetracosane and PVDF (for more details and explanations, see refs. 26 and 29) (al) and (a2) heat rate evolution during fusion in the presence of supercritical CH and C 2 2 (VF), respectively (bl) fluid phase equilibria in the tetracosane/methane system and (b2) partial p—T phase diagram for the PVDF-VF and PVDF-N2 systems. Note the depression in the melting/crystallization temperatures in the pressure range up to 30 MPa for the tetracosane/CH and PVDF/VF systems...

Competent design of chemical processes requires accurate knowledge of such process variables as the temperature, pressure, composition and phase of the process contents. Current predictive models for phase equilibria Involving supercritical fluids are limited due to the scarcity of data against which to test them. Phase equilibria data for solids In equilibrium with supercritical solvents are particularly sparse. The purpose of this work Is to expand the data base to facilitate the development of such models with emphasis on the melting point depressions encountered when solid mixtures are contacted with supercritical fluids. 

W. B. Street , Phase equilibria in fluid and solid mixtures at high pressure, in Chemical Engineering at Supercritical Fluid Conditions, M. E. Paulaitis, J. M. L. Penninger, R. D. Gray, and P. Davidson (ed.), Ann Arbor Science, Ann Arbor, Michigan, 1983. 

Kikic I, Lora M, Bertucco A. Thermodynamic analysis of three phase equilibria in binary and ternary systems for applications in rapid expansion of a supercritical solution (RESS) particles from gas-saturated solutions (PGSS) and supercritical antisolvent (SAS). Ind Eng Chem Res 1997 36 5507-5515. 

Chen, S. J., and M. Radosz. 1991. High-pressure phase equilibria in binary and ternary systems of alternating poly(ethylene-propylene). Paper presented at the 2d International Symposium on Supercritical Fluids. Boston, MA, May. 

Todd, D. B. 1952. Phase equilibria in systems with supercritical ethylene. Ph.D. diss., Princeton Univ. 

Selecting the appropriate thermodynamic model and supplying correct parameters is a key step in solving a simulation problem. The purpose of this chapter is to review the fundamentals of phase equilibria in process simulation. Modem thermodynamic methods make possible the treatment of very complex mixtures, including supercritical and subcritical components, hydrocarbons or polar species, water, etc. Such calculations are impossible by hand or even with spreadsheets. However, the user should be aware that only a good understanding of theoretical bases could ensure reliable results. 

NAG Nagy, I., Loos, Th.W.de, Krenz, R.A., and Heidemami, R.A., High pressure phase equilibria in the systems linear low density polyethylene -1- n-hexane and linear low density polyethylene + n-hexane + ethylene Experimental results and modelling with the Sanchez-Lacombe equation of state, J. Supercrit Fluids, 37,115,2006. 

Since then. Dr. Woldfarth s main researeh has been related to polymer systems. Currently, his research topics are molecular thermodynamics, continuous thermodynamics, phase equilibria in polymer mixtures and solutions, polymers in supercritical fluids, PVT behavior and equations of state, and sorption properties of polymers, about which he has published approximately 100 original papers. He has written the following books Vapor-Liquid Equilibria of Binary Polymer Solutions, CRC Handbook of Thermodynamic Data of Copolymer Solutions, CRC Handbook of Thermodynamic Data of Aqueous Polymer Solutions, CRC Handbook of Thermodynamic Data of Polymer Solutions at Elevated Pressures, CRC Handbook of Enthalpy Data of Polymer-Solvent Systems, and CRC Handbook of Liquid-Liquid Equilibrium Data of Polymer Solutions. 

GR4 Gregg, C.J., Phase equilibria of supercritical fluid solutions of associating polymers in noiqtolar and polar fluids, Ph.D. Thesis, Lehigh University, Bethlehem, 1994. 

Trumpi, H., et al.. High pressure phase equilibria in the system linear low density polyethylene-i-ethylene experimental results and modelling. Journal of Supercritical Fluids, 2003. 27(2) p. 205-214. 

Kikic, I., Lora, M. and Bertucco, A. (1997) A Thermodynamic Analysis of Three-Phase Equilibria in Binary and Ternary Systems for Applications in Rapid Expansion of a Supercritical Solution (RESS), Particles from Gas-Saturated Solutions (PGSS), and Supercritical Antisolvent (SAS), Ind. Eng. Chem. Res. 36,5507-5515. 

J. O. Werling and P. G. Debenedetti, Mass transfer and phase equilibria in the supercritical antisolvent process... 

The first chapter by Levelt Sengers and the second chapter by Schneider and his coworkers introduce the basic concepts on supercritical fluids, fluid mixtures, and provide an overview of applications. Thermodynamics and phase equilibria in binary and ternary mixtures are treated in Chapter 3 by Gauter and Peters. Chapter 4 by Anisimov and Sengers describes the recent developments on crossover phenomena that attempt to bridge the gap between the behavior of fluids asymptotically close to the critical point with behavior away from criticality. 

Licence, R, DeUar, M.P., Wilson, R.G.M. et al. (2004) Large-aperture variable-volume view cell for the determination of phase-equilibria in high pressure systems and supercritical fluids. Review of Scientific Instruments, 75, 3233—3236. 

Chapter 1 (Phase Equilibria in Binary and Ternary Hydro-thermal Systems, V. M. Valyashko, Russia) contains a description of the general trends of sub- and supercritical phase behavioin in binary and ternary systems taking into accoimt both stable and metastable equilibria. A presentation of the various types of phase diagrams aims to show the possible versions of phase transitions under hydrothermal conditions and to help the reader with the determination of where the phase equilibrium occurs in p-T-X space, and what happens to this equilibrium if the parameters of state are changed. Special attention is paid to continuous phase transformations taking place with variations of temperature. 

High-pressure phase equilibria in systems of polymers, solvents, and supercritical gases are in almost all cases modeled using equations of state. A review of equations of state for polymer systems, including a discussion of their theoretical background, has been given by Lambert et al. [6]. One of the first equations of state that was used to model the high-pressure phase behavior of polymer-solvent systems was the Flory equation of state [11, 12]. Patterson and Delmas [10] showed that this equation of state can be used to describe both LCST and UCST phase behavior. The perturbed hard-chain theory (PCHT) was developed by Prausnitz and coworkers [57-59]. It can be considered as an improvement of the approach of Flory... 

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