Phase equilibria for supercritical fluid process design

Abstract

Supercritical fluids (SCF's) are powerful solvents with many unique properties. They have great potential for many extraction processes, but reliable and versatile mathematical models of the phase equilibrium thermodynamics are needed for their use in process design and economic feasibility studies. This paper reviews existing experimental data and analytical methods and attempts to delineate their strengths and limitations. Also discussed are new data needs and possible new directions for a better fundamental understanding of the molecular processes in SCF solutions.

Fundamental Studies and Applications of Supercritical Fluids

“…In the latter studies, the observed spectral shift was more than expected based on the McRae theory (56,57), this was attributed to cluster formation. In other studies, Brennecke and Eckert (5,31,44,45) examined the fluorescence of pyrene in supercritical CQ2, C 2 H^y and CHF 3 . Steady-state emission spectra were used to show density augmentation near the critical point.…”

“…The general conclusion from these studies is that there is local density augmentation (i.e., solvent clustering) about the solute near the critical point. In addition, it has been suggested that there is enhanced solute-solute interactions near the critical point (5,31,(43)(44)(45).…”

“…However, if a substance is heated and maintained above its critical temperature it becomes impossible to liquify it with pressure (1). When pressure is applied to this system a single phase forms that exhibits unique physicochemical properties (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14). This single phase is termed a supercritical fluid and is characterized by a critical temperature and pressure (T c and P c ).…”

“…To illustrate how supercritical fluids compare to gases and liquids, Table 1 compiles some of the more important physicochemical properties of each. <ia 5 Viscosity(g/cm s)…”

“…io- 2 Because of their unique characteristics, supercritical fluids have received a great deal of attention in a number of important scientific fields (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14). Several reasons are given for choosing a supercritical fluid over another solvating system, but choice is governed generally by: 1) the unique solvation and favorable mass transport properties (5) and 2) the ease with which the chemical potential can be varied simply by adjustment of the system pressure and/or temperature (13).…”