A good control of both concentration polarisation and fouling effects is essential to
maintain constant mass fluxes, and hence productivity, in membrane reactors.
Another factor that can have an impact in permeate flux is the viscosity of the reaction
medium. Highly concentrated solutions of substrate/product (higher viscosity) will
originate lower permeate fluxes and eventually a lower productivity of the membrane
reactor (Nishizawa et al., 2000).
APPLICATIONS OF ENZYME MEMBRANE REACTORS
Membrane reactors can be used with any biocatalysed reaction with the aim of
developing continuous integrated processes with high productivity. The applications
found in a survey of the scientific literature over the past fifteen years were sorted out
according to the type of reactions investigated, as shown in Table 6.3. Several research
cases within each group are shortly described in Tables 6.4 to 6.10.
Hydrolysis of MacromoleculesThe majority of the first applications of membrane reactors described in the literature
dealt with the enzymatic hydrolysis of macromolecules such as proteins and
carbohydrates—starch and cellulose (Cheryan & Mehaia, 1986). Applications of the
correspondent
Table 6.3 General applications of membrane
bioreactors
Applications
Hydrolysis of macromolecules
Biotransformation of lipids
Reactions with cofactors
Optical resolutions and synthesis of peptides
Biomédical and environmental applications
Conversion of oligosaccharides
other
products can be envisaged mainly in the food industry, with the use of the different
hydrolisates in the supplementation of beverages and food products (Cheryan & Mehaia,
1986). One of the major functions played by the membrane of a reactor in these
applications is the retention of the macromolecular substrates, with the concomitant
increase in reaction rates during continuous operation. This type of reaction can only be
promoted in direct contact membrane reactors (Figure 6.2), where there is no need for the
substrate molecules to diffuse through the membrane in order to reach the enzyme. The
membrane also plays an important role in the selective separation of low molecular
Enzymatic membrane reactors 163