 |  Plant Design and Economics for Chemical Engineers, 5/e Max S. Peters,
University of Colorado
Klaus Timmerhaus,
University of Colorado, Boulder
Ronald E. West,
University of Colorado, Boulder
Separation Equipment - Design and Costs
Chapter OverviewS
ince the separation of most mixtures into their constituent chemical species is not
a spontaneous process, separation will require the expenditure of energy or the use
of external forces. Many techniques are available for separating either homogeneous
or heterogeneous mixtures. This chapter examines several of the more widely
used separation techniques.
When the feed mixture is a homogeneous, single-phase solution, a second immiscible
phase must often be developed or added before separation of the chemical species
can be achieved. The second phase is created by the use of an energy-separating agent
and/or the addition of a mass-separating agent. Some of the more important separation
processes besides distillation and absorption include azeotropic and extractive distillation,
stripping, extraction, and crystallization. Design procedures for most of these
separation operations have been incorporated as mathematical models into widely used
commercial computer-aided chemical process simulation and design programs for
steady-state operations.
The use of microporous and nonporous membranes as semipermeable barriers in
the separation process has been receiving considerable attention with numerous applications.
Separation techniques that involve some form of barrier in the separation
process include microfiltration, ultrafiltration, nanofiltration, osmosis, gas separation,
and pervaporation. On the other hand, removal of certain components may be accomplished
more successfully with the use of solid mass-separating agents. Separation
processes that operate in this fashion are adsorption, chromatography, and ion exchange.
Finally, the use of external force fields can sometimes be used to provide the
separation driving force between dissimilar molecules and ions. The use of this concept
leads to another list of separation processes including centrifugation, thermal diffusion,
electrolysis, electrophoresis, and electrodialysis.
When the mixture is heterogeneous, it is often more practical to use some mechanical
process based on gravity, centrifugal force, pressure reduction, or electric and/or
magnetic field to separate the phases. Further separation techniques, if required, can then be applied to each phase. Some of the methods used for the separation of
heterogeneous mixtures include settling and sedimentation, flotation, centrifugation,
drying, evaporation, and filtration.
There are two measures, besides economics, that provide a good insight with
respect to the overall effect of a separation operation. One measure is the recovery percentage
of key products obtained from the feed mixture. The other measure of separation
is product purity. Both measures have served as guides for design engineers in
the selection of suitable separation processes required in industrial processes. These
measures have become even more critical as more recent separations involve the recovery
of very high-cost products requiring particularly high purities from temperature-sensitive
dilute feed streams as, for example, in many biotech and pharmaceutical
separations. |
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2003 McGraw-Hill Higher Education