Page 330 - Biosystems Engineering

Bioseparation Pr ocesses 307

Source Receiving
phase phase

FIGURE 9.10 Thin sheet–supported liquid membrane.

Thin–Supported Liquid Membrane
A thin sheet–supported liquid membrane can be used for a labora-
tory scale, but it cannot be scaled up for industrial use (see Fig. 9.10).
Essentially, this is just a porous polymer membrane whose pores are
filled with an organic liquid and carrier, set between the source phase
and the receiving phase, which are being gently stirred.
Hollow Fiber–Supported Liquid Membrane
Supported liquid membrane (SLM) extraction, with flat membrane or
hollow fiber membrane as supporting material for an organic solvent
to form an aqueous−organic solvent−aqueous three-phase system,
has been applied to sampling of various compounds, including weak
acids and bases, as well as metal ions. It is a new versatile tool for
speciation of trace metals, in particular Cu, Pb, and Cd based on a hol-
low fiber–supported liquid membrane. Low plutonium content acidic
waste is generated in nuclear chemical facilities. In this technique for
quantitative separation and recovery of plutonium (Pu) from such
wastes using tri-n-butyl phosphate (TBP) in dodecane as carrier was
successful. Citric acid was successfully separated from an aqueous
solution using this membrane. Tri-n-octylamine diluted in various
organic solvents was used as a complexing agent for facilitated trans-
port of citric acid from an aqueous solution. Pure water and aqueous
sodium hydroxide were used as stripping agents.
In the liquid membrane (Fig. 9.11) the outer shell in made up of
nonporous material restricting the transport of materials inside. The
thin fibers run along the length of the shell inside. The source phase is
piped through the system from top to bottom, and the pores in the
fibers are filled with the organic phase.
The waste liquid containing the carrier was transported across the
receiving phase (may be organic or aqueous), and the receiving phase
is forced out through the sides of the shell. There is rapid transporta-
tion due to surface area and membrane thickness. There are no problems
with leakage and contamination, but the system is highly expensive
and requires intermittent cleaning to remove aqueous and contami-
nant buildup.