Multiphasic supercritical fluids

Flows are typically considered compressible when the density varies by more than 5 to 10 percent. In practice compressible flows are normally limited to gases, supercritical fluids, and multiphase flows containing gases. Liquid flows are normally considerea incompressible, except for certain calculations involved in hydraulie transient analysis (see following) where compressibility effects are important even for nearly incompressible hquids with extremely small density variations. Textbooks on compressible gas flow include Shapiro Dynamics and Thermodynamics of Compre.ssible Fluid Flow, vol. 1 and 11, Ronald Press, New York [1953]) and Zucrow and Hofmann (G .s Dynamics, vol. 1 and 11, Wiley, New York [1976]). 

Flows are typically considered compressible when the density varies by more than 5 to 10 percent. In practice compressible flows are normally limited to gases, supercritical fluids, and multiphase flows... 

Arai M, Fujita S, Shirai M (2009) Multiphase catalytic reactions in/under dense phase C02. J Supercrit Fluids 47(3) 351-356... 

Fundamental studies on the adsorption of supercritical fluids at the gas-solid interface are rarely cited in the supercritical fluid extraction literature. This is most unfortunate since equilibrium shifts induced by gas phase non-ideality in multiphase systems can rarely be totally attributed to solute solubility in the supercritical fluid phase. The partitioning of an adsorbed specie between the interface and gaseous phase can be governed by a complex array of molecular interactions which depend on the relative intensity of the adsorbate-adsorbent interactions, adsorbate-adsorbate association, the sorption of the supercritical fluid at the solid interface, and the solubility of the sorbate in the critical fluid. As we shall demonstrate, competitive adsorption between the sorbate and the supercritical fluid at the gas-solid interface is a significant mechanism which should be considered in the proper design of adsorption/desorption methods which incorporate dense gases as one of the active phases. 

The use of supercritical-fluid-extraction techniques in the fractionation of polysiloxanes has been demonstrated by the data presented. The poly-dispersities of the fractions were comparable with those generally attainable only by anionic-polymerization techniques, with which the incorporation of two functional groups is often difficult to attain. The ability to isolate these well-defined fractions will lead to important fundamental studies on structure-property relationships in multiphase copolymer systems. 

Peters, C.J. Multiphase equilibria in near-critical solvent. In Supercritical Fluids Fundamentals for Application, Kiran, E., Levelt Sengers, J.M.H., Eds. NATO ASI Series, Series E Applied Sciences Vol. 273 Kluwer Academic Publishers, 1994 117-145. 

The supercritical fluids exhibit gas-like viscosities, diffusivities, and liquid-like densities. These favorable transport properties lead to enhanced mass transfer, permeation, and wetting characteristics. The mass transfer limited multiphase reactions will benefit from reduction of a number of phases, as in the case of most oxidation, hydrogenation, or replacement of the more viscous liquid phase with a supercritical or a less viscous expanded liquid phase. The mobility combined with tunability results in effective maintenance of catalyst activity in heterogeneous catalysis. 

There are various possible approaches for multiphase operation of homogeneous catalysis, to improve their usability and recycle processes with organic/organic, organic/aqueous, or fluorous solvent pairs (solvent combinations), non-aqueous ionic solvents, supercritical fluids, and systems with soluble polymers. Figure 2.2 reports a general scheme of the possibilities for homogeneous catalysis. 

Practical Approaches to Multiphase Catalysis Involving Supercritical Fluids 7.4.2.1... 

White, G. L., and C. T. Lira. 1991a. High pressure multiphase equilibria of CO2 with polycyclic aromatic hydrocarbons. Paper presented at the 2d International Symposium on Supercritical Fluids. Boston, MA, May. 

Following the logic of this tree, the multiphase processes on the left-hand side belong among the operations with immobilized catalysts but on liquid supports . The topics of this book are the processes with the liquid supports water, supercritical fluids, ionic liquids, organic liquids, soluble polymers, and fluorous liquids among these, only two processes (Ruhrchemie/Rhone-Poulenc and Shell SHOP) are operative industrially so far. The more important leaves of the family tree are shaded in gray. 

C. J. Peters, "Multiphase Equilibria in Near-Critical Solvents," in Supercritical Fluids Fundamentals for Applications, E. Kiran and J. M. H. Levelt Sengers (eds.), NATO ASI Series E, vol. 273, Kluwer Academic Publishers, Dordrecht, 1994, p. 117. 

A pure compound may be in the state of a gas, solid or liquid (or even multiphase) depending on the pressure and temperature, the interrelationship being shown in Fig. 22.5. Following the vapour pressure curve which separates the gas and liquid states in the direction of increased pressure and temperature leads to an area in which the densities of both phases are identical. A phase that is neither gas nor liquid follows on from the critical point P (shaded area) and this is known as the fluid or supercritical area. The fluid can be used as a mobile phase for chromatography which is then referred to as supercritical fluid chromatography (SFC). 

What makes supercritical fluids so attractive in this domain is their sensitivity to a large number of processing variables in a region where transition from a single or multiphase system into another is rather simple through a variety of paths. 

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