Page 329 - Biosystems Engineering

306 Cha pte r Ni ne

Solute in solution
(pressurized form)

Solution

Membrane

Filtrate

FIGURE 9.9 Ultrafi ltration process.
100 percent fat, 100 percent protein, 50 percent lactose, and 50 percent
free minerals.
Liquid Membrane
A liquid membrane is made of liquid that is highly selective. With the
use of carriers for the transport mechanism, specific molecular recog-
nition can be achieved.
There are, in fact, two basic types of liquid membranes: an emul-
sion liquid membrane (ELM), and an immobilized liquid membrane
(ILM), also called a supported liquid membrane

ELM An emulsion liquid membrane may be either oil-in-water (O/W)
or water-in-oil (W/O). W/O emulsion is such that the dispersed phase
or the internal phase is water, and the continuous phase or dispersion
medium is oil. However, O/W emulsion is such that the dispersed
phase or internal phase is oil, and the continuous phase or dispersion
medium is an aqueous base. The liquid membrane separates two mis-
cible liquid phases across it.
An emulsion liquid membrane is made first by making a primary
emulsion (either O/W or W/O) and then dispersing the emulsion
into another phase—either oil or water—this phase is also referred to
as the third or external phase giving rise to a multiple emulsion of
type O/W/O or W/O/W. Multiple emulsions are actually emulsions
within emulsions. The W/O/W emulsion is prepared by incorporating
the emulsion W/O in an aqueous phase.
ELM creates a huge surface area for mass transfer than in other
techniques, and extraction and stripping are achieved simultaneously
in a single operation, unlike conventional solvent extraction. The dis-
advantage of this process, however, is its stability and its tendency to
undergo swelling due to a rapid increase in volume of the internal
phase that finally retards the efficiency of separation.