Fluid systems, phase equilibrium behavior

The system carbon dioxide - acetone - water was investigated at 313 and 333 K. The system demonstrates several of the general characteristics of phase equilibrium behavior for ternary aqueous systems with a supercritical fluid. These include an extensive LLV region that appears at relatively low pressures. Carbon dioxide exhibits a high selectivity for acetone over water and can be used to extract acetone from dilute aqueous solutions. 

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. 

G. Schneider, Phase Equilibriums in Liquid Systems at High Pressures , Ber. Bunsenges. Physik. Chem., 70, 497-520 (1966). G. M. Schneider, Phase Equilibria in Fluid Mixtures at High Pressures , Adv. Chem. Phys. 17, 1-42 (1970). G. M. Schneider, "Gas-Gas Equilibrium. Fluid Mixtures Under Pressure , Fortschr. Chem. Forsch. 13, 559-600 (1970). G. M. Schneider, Phase Behavior and Critical Phenomena in Fluid Mixtures Under Pressure , Ber. Bunsenges. Physik. Chem. 76, 325-331 (1972). G. M. Schneider in Water A Comprehensive Treatise, Vol II, F. Franks, ed.. Plenum Press, New York, 1973, Ch. 6. 

Chapters 17 and 18 use thermodynamics to describe solutions, with nonelectrolyte solutions described in Chapter 17 and electrolyte solutions described in Chapter 18. Chapter 17 focuses on the excess thermodynamic properties, with the properties of the ideal and regular solution compared with the real solution. Deviations from ideal solution behavior are correlated with the type of interactions in the liquid mixture, and extensions are made to systems with (liquid + liquid) phase equilibrium, and (fluid -I- fluid) phase equilibrium when the mixture involves supercritical fluids. 

Keywords Carbon dioxide Polyethylene glycol Phase behavior Biphasic solvent system Supercritical fluids Phase equilibrium... 

Droplet vaporization is a phenomenon occurring in a gas-liquid system, although only recently have serious efforts been made towards understanding the various hquid-phase processes and their influence on the overall behavior. The problem is a complex, yet interesting and important one. Fundamental research in the interdisciplinary areas of fluid mechanics, chemical kinetics, phase equilibrium analysis, and heat and mass transfer are required to achieve a good understanding of the problem. The following discussions may substantiate this point and stimulate future research efforts. 

So far the KBIs have been calculated for numerous binary systems, and the results were used to examine the solution behavior with regard to (1) local composition, (2) various models for phase equilibrium, (3) preferential solvation, and others One should also mention the use of the KB theory for supercritical fluids and mixtures containing supercritical components and for biochemical issues such as the behavior of a protein in aqueous mixed solvents. ... 

The calculations reported in this paper and a related series of publications indicate that it is now quite feasible to obtain reasonably accurate results for phase equilibria in simple fluid mixtures directly from molecular simulation. What is the possible value of such results Clearly, because of the lack of accurate intermolecular potentials optimized for phase equilibrium calculations for most systems of practical interest, the immediate application of molecular simulation techniques as a replacement of the established modelling methods is not possible (or even desirable). For obtaining accurate results, the intermolecular potential parameters must be fitted to experimental results, in much the same way as parameters for equation-of-state or activity coefficient models. This conclusion is supported by other molecular-simulation based predictions of phase equilibria in similar systems (6). However, there is an important difference between the potential parameters in molecular simulation methods and fitted parameters of thermodynamic models. Molecular simulation calculations, such as the ones reported here, involve no approximations beyond those inherent in the potential models. The calculated behavior of a system with assumed intermolecular potentials is exact for any conditions of pressure, temperature or composition. Thus, if a good potential model for a component can be developed, it can be reliably used for predictions in the absence of experimental information. 

Materials in the macroscopic sense follow laws of continuum models in which the nanoscale phenomenon is accounted for by statistical averages. Continuum models and analysis separate materials into solids (structures) and fluids. Computational solid mechanics and structural mechanics emphasize the analysis of solid materials and its structural design. Computational fluid mechanics treats material behaviors that involve the equilibrium and motion of liquid and gases. A relative new area, called multiphysics, includes materials systems that contain interacting fluids and structures such as phase changes (solidification, melting), or interaction of control, mechanical and electromagnetic (MEMS, sensors, etc.). 

Under very general conditions, it follows from classical statistical mechanics that the equilibrium behavior of our fluid system is adequately described % the behavior of a Gibbskn ensemble of systems characterized by a canonical distribution (in energy) in phase space. This has two immediate consequences. First it specifies the spatial distribution of our N molecule system. The simultaneous probability that some first molecule center hes in the volume element dr whose center is at and etc., and the Nih molecule center lies in the volume element dr f whose center is at is... 

To date little or no thermodynamic modeling of the phase behavior of the ligand/C02 or metal chelate/C02 systems has been conducted. However, in order for supercritical fluid extraction to be considered as a possible replacement for organic solvent extraction, accurate models must be developed to predict the phase behavior of these systems to allow for both equipment and process design. Equation of state (EOS) modeling was chosen here to model the vapor-liquid equilibrium of the P-diketone/C02 systems studied. Cubic EOSs are the most widely used in modeling high pressure and supercritical fluid systems. This is... 

These findings indicate that the control of phase behavior is one of the keys to controlling chemical reactions in near-critical fluids. Phase equilibrium plays an important role in dense fluid reaction systems, because the number of phases in equilibrium and their composition can be changed easily by pressure and temperature, and also as a consequence of the conversion of materials by chemical reactions. 

Both adsorption from a supercritical fluid to an adsorbent and desorption from an adsorbent find applications in supercritical fluid processing.The extrapolation of classical sorption theory to supercritical conditions has merits. The supercritical conditions are believed to necessitate monolayer coverage and density dependent isotherms. Considerable success has been observed by flic authors in working with an equation of state based upon the Tofli isoterm. It is also important to note that the retrograde behavior observed for vapor-hquid phase equilibrium is experimentally observed and predicted for sorptive systems. 

Effect of porous medium on phase behavior. Several authors have studied the effect of the porous medium on the phase behavior of reservoir fluid systems. Russian authors Trebin and Zadora (1968) report a strong influence of the porous medium on the dewpoint pressure and vapor-liquid equilibrium (VLE) of gas condensate systems. The porous medium used by these authors was a silica sand mixture (0.300 to 0.215 mm diameter) ground by a special cutter-pulverizer. Three different packings with permeabilities of 5.6, 0.612, and 0.111 darcies and... 

Tindy and Raynal (1966) measured the bubblepoint pressure of two reservoir crude oils in both an open space (PVT cell) and a porous medium with grain sizes in the range of 160 to 200 microns. The bubble-point pressures of those two crude oils were higher in the porous medium than in a PVT cell by 7 and 4 kg/cm, respectively. Specifically, the bubblepoint pressure of one of the two crude oils measured at 80 C in a PVT cell was 121 kg/cm and the bubblepoint pressure at the same temperature in a porous medium of 160 to 20 microns was 128 kg/cm. On the other hand, when these authors used a mixture of methane and n-heptane, they observed no differences in the saturation pressure. Sigmund et aL (1973) have also investigated the effect of the porous medium on phase behavior of model fluids. Their measurements on dewpoint and bubblepoint pressures showed no effect of the porous medium. The fluid systems used by these authors were Cj/nC. and Ci/nCs. The smallest bead size used was 30 to 40 U.S. mesh. In Example 2.3 presented at the end of this chapter, the effect of interface curvature on dewpoint pressure and equilibrium phase composition will be examined. 

---