Enzyme Technology
Membrane reactors
The main requirement for a membrane reactor
(MR) is a semipermeable membrane which allows the free passage of the product
molecules but contains the enzyme molecules. A cheap example of such a membrane
is the dialysis membrane used for removing low molecular weight species from
protein preparations. The usual choice for a membrane reactor is a hollow-fibre
reactor consisting of a preformed module containing hundreds of thin tubular
fibres each having a diameter of about 200 mm and a membrane thickness of about
50 mm. Membrane reactors may be used in either batch or continuous mode and
allow the easy separation of the enzyme from the product. They are normally used
with soluble enzymes, avoiding the costs and problems associated with other
methods of immobilisation and some of the diffusion limitations of immobilised
enzymes. If the substrate is able to diffuse through the membrane, it may be
introduced to either side of the membrane with respect to the enzyme, otherwise
it must be within the same compartment as the enzyme, a configuration that
imposes a severe restriction on the flow rate through the reactor, if used in
continuous mode. Due to the ease with which membrane reactor systems may be
established, they are often used for production on a small scale (g to kg),
especially where a multi-enzyme pathway or coenzyme regeneration is needed. They
allow the easy replacement of the enzyme in processes involving particularly
labile enzymes and can also be used for biphasic reactions (see Chapter
7). The
major disadvantage of these reactors concerns the cost of the membranes and
their need to be replaced at regular intervals.
The kinetics of membrane reactors are similar
to those of the batch STR, in batch mode, or the CSTR, in continuous mode (see later). Deviations from these models occur primarily in configurations where the
substrate stream is on the side of the membrane opposite to the enzyme and the
reaction is severely limited by its diffusion through the membrane and the
products' diffusion in the reverse direction. Under these circumstances the
reaction may be even more severely affected by product inhibition or the
limitations of reversibility than is indicated by these models.
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This page was established in 2004 and last updated by Martin
Chaplin on
6 August, 2014
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