Phase behavior of supercritical

Our goal in this work is to explore the effects of intermolecular forces on the phase behavior of supercritical systems. For this purpose, it is preferable to use simple intermolecular potential functions, with as few parameters as possible. The Lennard-Jones (6,12) intermolecular potential function,... 

Byun HS, McHugh MA. Impact of free monomer concentration on the phase behavior of supercritical carbon dioxide-polymer mixtures. Ind Eng Chem Res 2000 39 4658-4662. 

Modehng the phase behavior of supercritical gas-polymer mixtures. Macromolecules, 23, 2321, 1990. 

BY2 Byun, H.-S. and Choi, T.-H., Effect of monomer comcentration on the phase behavior of supercritical carbon dioxide-poly(ethyl methacrylate) mixture, J. Korean Ind. Eng. Chem., 11,396, 2000. 

LI1 Li, D., Han, B., Liu, Z., and Zhao, D., Phase behavior of supercritical C02/styrene/ poly(ethylene terephthalate) (PET) system and preparation of polystyrene/PET composites. Polymer, 42, 2331,2001. 

HAR Haruki, M., Matsuura, K., Kaida, Y., Kihara, S.-L, and Takishima, S., Microscopic phase behavior of supercritical carbon dioxide + non-ionic surfactant + water systems at elevated pressures. Fluid Phase Equil, 289, 1, 2010. 

Lam, D.H., JangkamoUculchai, A. and Luks, K.D. (1990) Liquid-liquid-vapor phase equilibrium behavior of certain binary carbon dioxide + n-alkanol mixtures. Fluid Phase Equilibria, 60,131-141. Gurdial, G.S., Foster, N.R., Jimmy Yun, S.L. and Tilly, KJ3. (1993) Phase behavior of supercritical fluid-entrainer systems, in Siqtercritical Fluid Engineering Science, Fundamentals and Applications, E. Kiran and JJ. Brennecke (Eds.), ACS Symposium Series No. 514, pp. 34-45. 

It is clear from the above discussion that the phase behavior of snpercritical aqneous solutions in a complicated matter, bronght on primarily by the decrease in the dielectric constant of water. Un-fortnnately, as is evident from an examination of the literature, the phase behavior of supercritical aqueous solutions is poorly understood, but an appreciation of that behavior is vital for interpreting corrosion and electrochemical phenomena in supercritical aqueous media. 

Phase Behavior. One of the pioneering works detailing the phase behavior of ternary systems of carbon dioxide was presented ia the early 1950s (12) and consists of a compendium of the solubiHties of over 260 compounds ia Hquid (21—26°C) carbon dioxide. This work contains 268 phase diagrams for ternary systems. Although the data reported are for Hquid CO2 at its vapor pressure, they yield a first approximation to solubiHties that may be encountered ia the supercritical region. Various additional sources of data are also available (1,4,7,13). 

A number of theoretical models have been proposed to describe the phase behavior of polymer—supercritical fluid systems, eg, the SAET and LEHB equations of state, and mean-field lattice gas models (67—69). Many examples of polymer—supercritical fluid systems are discussed ia the Hterature (1,3). 

A third motivation for studying gas solubilities in ILs is the potential to use compressed gases or supercritical fluids to separate species from an IL mixture. As an example, we have shown that it is possible to recover a wide variety of solutes from ILs by supercritical CO2 extraction [9]. An advantage of this technology is that the solutes can be removed quantitatively without any cross-contamination of the CO2 with the IL. Such separations should be possible with a wide variety of other compressed gases, such as C2LL6, C2LL4, and SF. Clearly, the phase behavior of the gas in question with the IL is important for this application. 

Polymer-supercritical fluid systems, phase behavior of, 24 11... 

It is well known that the aqueous phase behavior of surfactants is influenced by, for example, the presence of short-chain alcohols [66,78]. These co-surfactants increase the effective value of the packing parameter [67,79] due to a decrease in the area per head group and therefore favor the formation of structures with a lower curvature. It was found that organic dyes such as thymol blue, dimidiiunbromide and methyl orange that are not soluble in pure supercritical CO2, could be conveniently solubihzed in AOT water-in-C02 reverse microemulsions with 2,2,3,3,4,4,5,5-octafluoro-l-pentanol as a co-surfactant [80]. In a recent report [81] the solubilization capacity of water in a Tx-lOO/cyclohexane/water system was foimd to be influenced by the compressed gases, which worked as a co-surfactant. 

Shariati, A. and Peters, C. J., High-pressure phase behavior of systems with ionic liquids Measurements and modeling of the binary system fluoroform + l-ethyl-3-methylimidazolium hexafluorophosphate, /. Supercrit. Fluids, 25, 109, 2003. 

The high-pressure phase behavior of polymer-solvent-supercritical carbon dioxide systems was investigated experimentally The polymers used were poly(methyl methacrylate), polystyrene, polybutadiene, and poly(vinyl ethyl ether) at concentrations ranging from 5 to 10% in mixtures with toluene or tetrahydrofuran. The experiments were conducted for temperatures from 25 to 70°C and pressures up to 2200 psi in a high-pressure cell (Kiamos and Donohue, 1994). 

In their test system, the researchers used the ionic liquid l-butyl-3-methylimidazol-ium hexafluorophosphate (bmim)(PF6), which is stable in the presence of oxygen and water, with naphthalene as a low-volatility model solute. Spectroscopic analysis revealed quantitative recovery of the solute in the supercritical CO2 extract with no contamination from the ionic liquid. They found that CO2 is highly soluble in (bmim)(PF6) reaching a mole fraction of 0.6 at 8 MPa, yet the two phases are not completely miscible. The phase behavior of the ionic liquid-C02 system resembles that of a cross-linked polymer-solvent system (Moerkerke et al., 1998), even though... 

An understanding of the phase behavior of a particular system of interest is important because complex results can sometimes occur. A dramatic example, which occurs frequently for solubilities in supercritical systems, is the retrograde behavior. Figure 3 clearly shows the presence of a retrograde region. For an isobaric system at some pressure, such as 12.7 MPa (1841.5 psi), an increase in temperature of a solution of ethylene and naphthalene from 300 to 320 K results in an increase in the equilibrium solubility of naphthalene. This behavior is typical of liquid solvent systems. For the same increase in temperature (300 to 320 K) but at a pressure of 8.1 MPa (1174.5 psi), the solubility of naphthalene decreases by nearly an order of magnitude. Because this latter behavior is the opposite of typical liquid solvents, it is termed retrograde solubility. 

The last ATR cell described here in detail was designed for the study of catalytic reactions at high pressures and in particular in supercritical fluids. A schematic representation of the design is shown in Fig. 17 (76). An important issue in this type of reaction is the phase behavior of the system, which can have a large influence on the catalytic reaction 77,IS). The cell consists of a horizontal stainless-steel cylinder. It is designed to allow monitoring of the phase behavior via a video camera. For this purpose, one end of the cylinder is sealed with a sapphire window, behind... 

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