(41)
where Bi is the Biot number ( The solution of equation (21) with (24) and
(41) as boundary conditions gives the dimensionless concentration profile of the
substrate, from which the total effectiveness factor can be calculated.
Miscellaneous effectsApart from the influence of these factors on the activity of the enzyme, other properties
of the enzyme can change. Thus substrate specificity alters, particularly when using a
high molecular weight substrate, by effect of steric hindrance and diffusional resistances.
The kinetic constants Km and rm of the immobilised enzyme are different from the free
enzyme as a consequence of conformational changes of the immobilised form, which
affect the affinity between enzyme and substrate. The increase of activity energy for
some immobilised enzymes may be attributed to diffusional resistances, mainly in porous
supports.
One of the major properties of the immobilised enzymes is their stability, especially
the operational stability. This enhanced stability is particularly valuable in the continuous
use of immobilised enzymes, in industrial operations.
Such increased stability has been observed in many cases, although a decreased
stability has been observed in a few systems.
IMMOBILISED ENZYME REACTORS
Among the applications of immobilised enzymes, their utilisation in industry is perhaps
the most important and consequently the most frequently discussed.
The use of immobilised enzymes in industrial processes is performed in basic
chemical reactors. A classification of enzyme reactor based on the mode of operation and
the flow characteristics of substrate and product is presented in Table 4.3.
Table 4.3 Classification of enzyme reactors
Mode of operation Flow pattern Type of reactor
Batch Well mixed
Plug flow
Batch stirred tank reactor (BSTR)
Total recycle reactorContinuous Well mixed Continuous stirred tank reactor (CSTR)
CSTR with continuous ultrafiltration membrane
Plug flow Packed bed reactor (PBR)
Fluidized bed reactor (FBR)
Tubular reactor (other)
Hollow fiber reactor
Design and modelling of immobilised biocatalytic reactors 111