Supercritical phase equilibrium data

A recirculation apparatus for the determination of high pressure phase equilibrium data for mixtures of water, polar organic liquids and supercritical fluids was constructed and operated for binary and ternary systems with supercritical carbon dioxide. 

Processes for supercritical extraction of oils have been described in numerous literature references, including Paulaitis et al. ( ), Ely and Baker (2), Gerard (3.), Stahl et al. (4K and Robey and Sunder (5). The literature lacks detailed phase equilibrium data on multicomponent essential oils with supercritical solvents in the proximity of the solvent critical temperature. 

Saraf, V. P. Kiran, E., "Supercritical Fluid-Polymer Interactions Phase Equilibrium Data for Solutions of Polystyrenes in n-Butane and n-Pentane," Polymer, 29, 2061 (1988). 

Rovetto, L.J. Bottini, S.B. Peters, C.J. Phase equilibrium data on binary and ternary mixtures of methyl palmitate, hydrogen and propane. J. Supercrit. Fluids 2004, 31, 111-121. 

Static Mode. The system can be used as a static cell to obtain equilibrium data for supercritical carbon dioxide and cold-pressed Valencia orange oil. Using the system as a static cell to obtain phase equilibrium data under supercritical conditions was complicated by two factors 1) trapping small samples without disturbing the equilibrium Is difficult and 2) the small sample size makes subsequent analysis complex. The procedure was as follows. 

Highly promising models were obtained by using so-called G models for cubic equations of state. Apart from the description or precalculation of the behavior of highly polar systems, these models allow supercritical components to be taken into account. A further advantage of these models is that, in addition to phase equilibria, other important quantities such as densities and caloric data can be calculated. The required G values can be obtained either by fitting the parameters of proven G models (e.g., Wilson, NRTL, or UNIQUAC equation) to experimental phase equilibrium data, or with the aid of group-contribution methods such as UNIFAC. 

SA2 Saraf, V.P. and Kiran, E., Supercritical fluid-polymer interactions. Phase equilibrium data for solutions of polystyrenes in n-butane and n-pentane, Polymer, 29, 2061, 1988. 

In summary, the kno vledge of both the phase equilibrium data and the mass transfer kinetics is essential for the speciflcation of supercritical processes. As an example. Figure 8.2 sho vs the vell-kno vn data for solubility of seed oil in CO2 and the corresponding kinetic profile of oil extraction from differently prepared... 

Kalra H, Chung SYK, Chen CJ. 1987. Phase Equilibrium Data for Supercritical Extraction of Lemon Flavors and Palm Oils with CO. Fluid Phase Equil. 36 263-278. 

Additionally, Cho et alP also provided phase equilibrium data of the efliyl lactate + CO2 mixture and more recently, Paninho et al. presented the equilibrium compositions of both liquid and supercritical phases (see Figure 20.4.16) in a wide range of temperatures (313-393K) and pressures (0.4-17 MPa). 

During the 1940s, a large amount of solubility data was obtained by Francis (6, 7), who carried out measurements on hundreds of binary and ternary systems with liquid carbon dioxide just below its critical point. Francis (6, 7) found that liquid carbon dioxide is also an excellent solvent for organic materials and that many of the compounds studied were completely miscible. In 1955, Todd and Elgin (8) reported on phase equilibrium studies with supercritical ethylene and a number of... 

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. 

A model based on a modified mixing rule for the Peng-Robinson equation of state was able to reproduce quantitatively all features of the observed phase equilibrium behavior, with model parameters determined from binary data only. The use of such models may substantially facilitate the task of process design and optimization for separations that utilize supercritical fluids. 

For the design of a process for formation of solid particles using supercritical fluids, data on solid - liquid and vapour - liquid phase equilibrium are essential. PGSS process is only possible for systems where enough gas is solubilized in the liquid. 

Several authors [3-9] studied the solubility of polymers in supercritical fluids due to research on fractionation of polymers. For solubility of SCF in polymers only limited number of experimental data are available till now [e.g. 4,5,10-12], Few data (for PEG S with molar mass up to 1000 g/mol) are available on the vapour-liquid phase equilibrium PEG -CO2 [13]. No data can be found on phase equilibrium solid-liquid for the binary PEG S -CO2. Experimental equipment and procedure for determination of phase equilibrium (vapour -liquid and solid -liquid) in the binary system PEG s -C02 are presented in [14]. It was found that the solubility of C02 in PEG is practically independent from the molecular mass of PEG and is influenced only by pressure and temperature of the system. 

Some binary phase equilibrium and solubility data of limonene and linalool with supercritical C02 can be found in the current literature [11, 12, 13, 14, 15]. However, the different ranges of pressure and/or temperature of these data cause difficulties and inaccuracies to calculate or predict the related compound selectivities. 

In our research, we were led to characterise thermodynamically the mixtures composed of an organic compound and supercritical CO2 in a relatively wide range of temperatures, including several types of phase equilibrium. We looked for a single thermodynamic model which would be predictive (no parameters to adjust to the experimental data), valid for a wide range of temperatures and pressures, and also capable of representing solid-fluid and liquid-fluid equilibria. 

Figure 4 shows a linear dependence of R with the concentration of the drug in the supercritical phase. Taking into account the only data of runs 4, 5 and 6, an equilibrium constant K can be estimated in spite of a relative imprecision. The value thus obtained is K = 8.2 10"3. This equilibrium constant is slightly better than the one obtained for the ethanol (6.4 10 3). This means that for an equal concentration of ocTocopherol acetate in supercritical C02 or ethanol, the impregnation is quantitatively better in the former case. 

Effect of Unlike-Pair Interactions on Phase Behavior. No adjustment of the unlike-pair interaction parameter was necessary for this system to obtain agreement between experimental data and simulation results (this is, however, also true of the cubic equation-of-state that reproduces the properties of this system with an interaction parameter interesting question that is ideally suited for study by simulation is the relationship between observed macroscopic phase equilibrium behavior and the intermolecular interactions in a model system. Acetone and carbon dioxide are mutually miscible above a pressure of approximately 80 bar at this temperature. Many systems of interest for supercritical extraction processes are immiscible up to much higher pressures. In order to investigate the transition to an immiscible system as a function of the strength of the intermolecular forces, we performed a series of calculations with lower strengths of the unlike-pair interactions. Values of - 0.90, 0.80, 0.70 were investigated. 

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. 

Particularly evident is the lack of systematic reports on polymer-mixed solvents data (VLE or LLE) in the open hterature, especially in form of full-phase equilibrium measurements. Most experimental studies for mixed solvent systans have been reported by Chinese and Japanese investigators - and only a few by other investigators. Data are often reported simply as soluble/nonsoluble or as theta temperatures (critical solution temperature at infinite polymer molecular weight). Several reported polymer-mixed solvent data concern supercritical fluid applications (e.g., polypropylene/pen-tane/C02, and PEG/C02/cosolvent ) and bioseparations, especially for systems related to the partitioning of biomolecules in aqueons two-phase systems, which contain PEG and dextran. A recent review for data on solnbihty of gases in glassy polymers is also available. ... 

Elgin, J. C., and J. J. Weinstock. 1959. Phase equilibrium at elevated pressures in ternary systems of ethylene and water with organic liquids Salting out with a supercritical gas. J. Chem. Eng. Data 4 3. 

We first discuss the overall chemical process predicted, followed by a discussion of reaction mechanisms. Under the simulation conditions, the HMX was in a highly reactive dense fluid phase. There are important differences between the dense fluid (supercritical) phase and the solid phase, which is stable at standard conditions. Namely, the dense fluid phase cannot accommodate long-lived voids, bubbles, or other static defects, since it has no surface tension. Instead numerous fluctuations in the local environment occur within a timescale of 10s of femtoseconds. The fast reactivity of the dense fluid phase and the short spatial coherence length make it well suited for molecular dynamics study with a finite system for a limited period of time. Under the simulation conditions chemical reactions occurred within 50 fs. Stable molecular species were formed in less than a picosecond. We report the results of the simulation for up to 55 picoseconds. Figs. 11 (a-d) display the product formation of H2O, N2, CO2 and CO, respectively. The concentration, C(t), is represented by the actual number of product molecules formed at the corresponding time (. Each point on the graphs (open circles) represents a 250 fs averaged interval. The number of the molecules in the simulation was sufficient to capture clear trends in the chemical composition of the species studied. These concentrations were in turn fit to an expression of the form C(/) = C(l- e ), where C is the equilibrium concentration and b is the effective rate constant. From this fit to the data, we estimate effective reaction rates for the formation of H2O, N2, CO2, and CO to be 0.48, 0.08,0.05, and 0.11 ps, respectively. 

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. 

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