Separations as unit operations - Principles of Chemical Separations with Environmental Applications - page 28

Use
Asymptote

Distillation

Gas Absorption

Ext./Azeo.
Dist.

Crystallization

lon Exchange

Solvent Ext.
Adsorption: Gas Feed

Adsorption: Liquid Feed

Membranes: Gas Feed
Membranes: Liquid Feed
Chromatography
Liquid Feed
Field-Induced Separations
Affinity Separation

Supercritical
Gas Abs. / Ext.

Liquid
Membranes

First
Application
Invention

Technology
Asymptote

TECHNOLOGICAL MATURITY

Figure 2.8 Separation technology reliability plot [2]. Reproduced with permis-
sion of the American Institute of Chemical Engineers. Copyright 1987 AIChE.
All rights reserved.

difference alone. The relative ability of the various compounds in the feed stream
to react will directly affect the separation selectivity.
3 Do the easiest separation first. This may seem obvious, but often the starting place is
non-obvious when one is faced with a complex feed mixture to separate. What are some
examples of “easy”?
(a) Simple. If particles are present in a fluid phase, filtration can do the separation of
the two phases. Separation of components in each phase can then be done in a
subsequent step, if needed.
(b) High reliability . Separation steps which have been used for long periods of time
with positive results (high “comfort” factor) would be considered ahead of newer
approaches (see Figure 2.8). Newer approaches are easier to implement further
downstream where their impact on the entire process is less than as the first step.
(c) Remove component which has the highest mole fraction first . If the separation fac-
tors for each component in the feed mixture are approximately equal, the component
with the highest mole fraction is usually the easiest to remove first. An alterna-
tive is to remove the component with the highest volatility first if distillation is
feasible.
(d) When more than one step is required for the separation sequence .
(i) Recover the mass-separating agent and/or dissolved products immediately after
the process step involving a mass-separating agent.
(ii) Do not use a mass-separating agent to remove or recover a mass-separating
agent.