Biomedical Engineering Reference
In-Depth Information
Membrane Morphology
Isotropic
Anisotropic
Dense
Dense/Selective Skin
Porous
Porous Skin
FIGURE 10.1
Basic membrane morphology.
Two basic morphologies of hollow fiber membrane are isotropic and
anisotropic (Figure  10.1). Membrane separation is achieved by using these
morphologies.
The anisotropic configuration is of special value. In the early 1960s, the
development of anisotropic membranes exhibiting a dense, ultrathin skin
on a porous structure provided a momentum to the progress of membrane
separation technology. The semipermeability of the porous morphology is
based essentially on the spatial cross section of the permeating species,
that is, small molecules exhibit a higher permeability rate through the fiber
wall. While the anisotropic morphology of the dense membrane, which
exhibit the dense skin, is obtained through the solution-diffusion mecha-
nism. The permeation species chemically interacts with the polymer matrix
and selectively dissolves in it, resulting in diffusive mass transport along
the chemical potential gradient, as was demonstrated in the pervaporation
process.
Type of the membrane configuration is given in Figure 10.2 .
Hollow fiber is one of the most popular membranes used in industries. It
is because of its several beneficial features that make it attractive for those
industries. Among them are
Modest energy requirement : In the hollow fiber filtration process, no
phase change is involved. Consequently, it needs no latent heat. This
makes the hollow fiber membrane have the potential to replace some
unit operations that consume heat, such as distillation or evapora-
tion columns.
No waste products : Since the basic principle of hollow fiber is filtra-
tion, it does not create any waste from its operation except for the
unwanted component in the feed stream. This can help to decrease
the cost of operation to handle the waste.
Large surface per unit volume : Hollow fiber has a large membrane sur-
face per module volume. Hence, the size of hollow fiber is smaller
than other types of membrane but can give higher performance.
Flexible : Hollow fiber is a flexible membrane; it can carry out the fil-
tration by two ways; it is either is “inside-out” or “outside-in.”
Low operation cost : Hollow fiber needs low operational costs com-
pared to other types of unit operation.
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