Handbook of Solvents - George Wypych - ChemTech - Ventech!

21.1 Supercritical solvents 1439
Inherent characteristics of systems
@ supercritical conditions
Sensitivity of responses to process
variables
High pressure
Dominance of physical characteristic
on solvency over chemical
Figure 21.1.12. A generic process flow sheet.
Resulting promise Challenges to be met
Effective recovery of solvents, and
innovative fractionation possibilities
Expansion of solvent spate to environmentally
benign, inexpensive,
and non flammable solvents and
their mixtures
Control and optimization
High capital cost and need for
recovery of mechanical energy
There have been many useful attempts made to classify separation technologies.
Supercritical fluids are applicable with both intra-phase and inter-phase separations. Due to
the ease and flexibility in which a new phase can be formed for regeneration of the solvent,
inter-phase is the more common. Furthermore, material solubility and swelling problems,
particularly with organic-component based membranes, limit inter-phase separations. This
is due to the enhanced solubility of these components in supercritical solvents.
Generic steps involved in a typical chemical process are shown in Figure 21.1.12, with
each separation sub task type identified. Environmental processes are usually dominated by
feed preparation tasks while biochemical processes utilize all of the four subtasks. Blending
is considered a finishing task while splitting is considered a feed preparation task. The objective
criteria used for the separation may vary according to the subtask. For example, in
feed preparation, technical feasibility such as removal of the fines is more appropriate while
the usual economic objectives subject to technical feasibility constraints become the goal
for the purification and finishing stages.
The feed preparation task involves removal of insoluble components and at times
non-condensable compounds. The technology selection and the scheduling of tasks are con-