Supercritical Fluid Technology - American Chemical Society

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Chapter 1

Fundamental Studies and Applications of Supercritical Fluids A Review 1

Mary Ellen P . McNally and Frank V. Bright 1

Downloaded by UNIV LAVAL on July 14, 2014 | http://pubs.acs.org Publication Date: May 8, 1992 | doi: 10.1021/bk-1992-0488.ch001

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Agricultural Products, Experimental Station, E402/3328B, E . I. du Pont de Nemours and Company, Wilmington, D E 19880-0402 Department of Chemistry, Acheson Hall, State University of New York at Buffalo, Buffalo, N Y 14214 Over the course of the last several years, essential studies have been conducted in a wide variety of areas using supercritical fluids. The continued constructive development of the science employing these fluids is dependent upon a unique bridging of scientists from many disciplines involved in this work. This text, a compilation of several of the papers presented at the ACS meeting in Atlanta in the spring of 1991, attempts to illustrate the numerous scientific endeavors that have been and continue to be pursued. Individually, these works are able to stand alone in their viability. Collectively, they demonstrate the vast interest, the overwhelming potential and the extensive growth that is available. This text is a snap-shot in time since the scientific developments are being driven rapidly by interest, funding and high expectations for the potentials that have been suggested. This introductory chapter presents a brief background synopsis of supercritical fluids in spectroscopic investigations, the loss of impetus in supercritical fluid chromatographic (SFC) developments but its vast potential, and the flourishing future status of supercritical fluid extraction (SFE).

Many physicochemical properties describe a chemical substance or mixture. For example, the boiling point, density, and dielectric constant can all be used to characterize a particular species or system as a solid, liquid, or gas. However, i f 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 (1-14). This single phase is termed a supercritical fluid and is characterized by a critical temperature and pressure (T and P ). Supercritical fluids offer a convenient means to achieve solvating properties which have gas- and liquid-like characteristics without actually changing chemical structure. By proper control of pressure and temperature one can access a significant c

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0097-^156/92/0488-0001$06.00/0 © 1992 American Chemical Society

In Supercritical Fluid Technology; Bright, F., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

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SUPERCRITICAL FLUID

TECHNOLOGY

range of physicochemical properties (density, diffusivity, dielectric constants, etc.) without ever passing through a phase boundary, e.g., changing from gas to liquid form. That is, a supercritical fluid can be considered a continuously adjustable solvent. To illustrate how supercritical fluids compare to gases and liquids, Table 1 compiles some of the more important physicochemical properties of each.

T A B L E 1. Properties of Supercritical Fluids vs. Gases and Liquids(13)

Gas 3

io-

Downloaded by UNIV LAVAL on July 14, 2014 | http://pubs.acs.org Publication Date: May 8, 1992 | doi: 10.1021/bk-1992-0488.ch001

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Density(g/cm ) 2

Diff. Coeff.(cm /s)

IO-

Viscosity(g/cm s)

IO"

1

4

SF 0.1-1 3

10 -10^ 3

10 -10^

Liquid 1 5