Dr. Erdogan Kiran

Supercritical fluid based processes are going to play a major role in chemical engineering practice in the new millennium. There is already intense research in separations, reactions, and materials processing in or with supercritical fluids that tries to take advantage of the special properties of these fluids.

Supercritical fluids are neither gas nor liquid but can be compressed gradually from low to high density. As a result a wide range of properties from gas-like to liquid-like become accessible by these fluids by simple manipulation of pressure and/or temperature. As such, these are tunable fluids that can be customized for a given application. They are ideal for selective and or sequential separations by pressure or density tuning. For example, depending upon the fluid density, the fluid may be tuned to behave as a specific solvent for a specific substance at one pressure, but as a non-solvent at another pressure.

Historically, the pressure-tunable characteristics were first put to commercial practice in the selective extraction in the food industry as in decaffeination of coffee and tea. In the analytical field, these concepts were adopted in supercritical fluid chromatography that is also commercial. The applications have expanded dramatically in the past decade to include a wide range of operations that are encountered in various industries such as the pharmaceuticals, polymers, inorganic materials, and in chemical recycling operations. Among recent developments that are becoming commercial are polymerization, dry cleaning, foaming, and coating processes that use near-critical or supercritical carbon dioxide in the process.

The major interest and motivation in using supercritical fluids stem from the fact that

a) Their physicochemical properties can be conveniently changed by density or pressure-tuning, and can be further modified through compositional tuning when using binary fluid mixtures,

b) They can be used not only as a solvent or diluent, but also as non solvent,

c) They can facilitate recycling of the solvent, removal of the solvent from the products, and the recovery of the products from the solvent, or facilitate the processing of traditional materials.

d) They are easy to adopt for hybrid- or coupled-methodologies such as simultaneous reaction and separation, or simultaneous miscibility, phase separation and property modifications,

e) They can be used as replacement of undesirable solvents and be environmentally benign as is the case with carbon dioxide-based processes.

The research program at Virginia Tech Chemical Engineering department led by Professor Kiran is aimed at

a) generating fundamental data pertaining to the high pressure properties of fluids and mixtures, and

b) developing unique methodologies and techniques for materials synthesis, modification and processing using these fluids with the primary applications focus being on polymer systems.

Professor Kiran's supercritical fluids program at Virginia Tech is internationally recognized for a number of unique contributions. Among these are

1. Founding of the Journal of Supercritical Fluids in 1988. This journal currently a publication of Elsevier Science, has helped identify supercritical fluids as a discipline and has played a major role in its growth.

2. Organization of two NATO sponsored Advanced Study Institutes on Supercritical Fluids and Their Applications which were held in Kemer, Turkey in 1993 and 1998 respectively. Each of these high-level schools brought together more than 100 scientist from around the world to review the current state and future needs. These institutes have been instrumental in helping the next generation of engineers and scientist establish their networking in the community and be current with the most recent advances.

3. Production of two highly pedagogical and comprehensive books on supercritical fluids and their applications that have been developed from the lectures presented at the NATO Advanced Study Institutes.

4. Development of unique experimental high-pressure techniques for thermodynamic, transport and kinetic data generation especially for polymer -fluid systems. Among these are instrumentation for simultaneous measurement of viscosity, density and phase behavior; instrumentation for repeatable pressure-quench experiments and for experimental documentation of the kinetics of phase separation; and development of a unique methodolgy for assessment of experimentally accessible spinodal boundaries, and

5. Development of PIPS (Pressure-induced phase separation) as a new methodology towards production of microstructured materials. This methodolgy is being developed for targeted applications for formation of particles, foams, scaffolds, fibers, membranes, dielectric materials, blends and composites.