The velocity on the surface of the membrane is 10^5 times higher than inside the
membrane pores. These velocities have quite different effects on the properties of the
fluid circulation in the reactor.
By employing Equation 66, the Reynolds number, Re, for the reaction medium at the
membrane surface and inside the membrane pores can be calculated. The ratio of the two
values is in the order of magnitude of 10^12 , the Res being characteristic of a turbulent
regimen, whilst inside the pores the flux has a laminar or viscous property.
CONCLUSIONS
We have now reached a point where we have extensive knowledge of the basic principles
that rule the formation and properties of reversed micelles. Furthermore, a wide number
of structural techniques are now available for the study of microstructure of these systems
and in the near future they will provide more insight at this level. The numerous
advantages of reversed micellar systems make them of special interest for technical
purposes. Industrial application requires the scale-up of systems and the operation of
reactors in a continuous mode. Moreover, it is desirable to define the characteristics of
the reactor in order to control the final quality of products.
This chapter provides the analysis of a MBR both in terms of performance and
hydrodynamics, describing in detail how the flow rate and the recirculation ratio affect
the residence time of substrates and thus the reactor efficiency in continuous operation.
Moreover, the comparison of conversions obtained in MBR when operating in a total
recirculation mode and in continuous operation, as well as the conversion per pass, gave
rise to the general classification of MBR as a global CSTR.
The properties of the membrane account significantly for the interactions with the
biocatalyst. Thus, it is important to relate the differences in degree of permeate and
retentate conversion to the prediction of enzyme distribution. The membrane pores may
retain a fraction of enzyme that is responsible for the product increment in the permeate,
especially with the higher residence time exhibited by this sequential reactor. The
integration of all operating aspects together with the enhancement of product
concentration on permeate and enzyme distribution in the membrane permits the
identification of MBR with a cascade of two CSTRs.
The consequences for biocatalyst stability may be important since the deactivation is
decreased when the enzyme is sheltered inside the membrane pores. Emphasis should be
given to the fact that high shear stress forces, in a strong turbulent regimen, affect the
operational stability whereas in a laminar regimen the half-life is largely improved.
NOMENCLATURE
∆PTM transmembrane pressure (ML−lT−2)
θ hydraulic residence time (T)
τ normalised residence time (ML−^3 T)
η viscosity (ML−^1 T−^1 )
ρ volumetric mass (ML−^3 )Reversed micellar bioreaction systems 227