Handbook of Solvents - George Wypych - ChemTech - Ventech!

1452 Aydin K. Sunol and Sermin G. Sunol
Figure 21.1.15. A flexible pilot plant for supercritical fluid aided materials processing.
21.1.4.5 Materials processing with supercritical solvents
The material field related applications of supercritical fluids are rapidly developing with exciting
innovative developments continually emerging. The recent increase of activity in the
supercritical field at large is partially due to these new horizons. Supercritical fluids are
used to make highly porous material, aids in making uniform porous or non-porous films, to
deposit solubilized components by diffusion and permeation into porous media resulting in
composites with tailored characteristics or functionalized surfaces, is used to make particles
with desired shape and particle size distribution, is used to encapsulate particles for time release
applications, is used to fractionate macromolecules to desired dispersity and molecular
weight distributions, and soon may be part of our household for cleaning/washing.
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.
One can start with a homogeneous phase and use pressure, temperature, mass separating
agents, other external fields such as electromagnetic or irradiation, to nucleate and
grow, or react or fractionate, to form new material with unique performance characteristics.
In the homogenization step, supercritical fluids are used to solubilize. If solubilization in the
supercritical fluid is not possible, the supercritical fluid can be used to induce phase separation
as an anti-solvent in a subsequent step.
The supercritical fluids are effective in heterogeneous environments as well. They
penetrate into porous environment loaded with additives or, used as a pure supercritical
fluid to clean, dry (extract), coat, impregnate and process (e.g. extrude) a low viscosity solution.
A flexible pilot plant that addresses all the materials processing demands excluding
extrusion is shown in Figure 21.1.15 while the modes for encapsulation and aerogel/impregnation
are expanded upon Figures 21.1.16 and 21.1.17 respectively.