fluidised beds. Membrane reactors seem particularly suited to carry out complex
enzymatic transformations, involving, for example, several enzymes, and cofactor
regeneration. They also display unusual geometric characteristics that are particularly
adequate for non-conventional types of media such as organic-aqueous two-phase
systems and reversed micelles. And, the separation possibilities offered by these reactors
open up new perspectives for the development of applications in enzyme engineering.
Considering that process integration and process intensification are becoming more
and more a guiding philosophy in the development of new bioreactor configurations,
membrane reactors constitute ideal systems for developing biotechnology applications
with the coupling of bioconversion with separation process (extractive bioconversions).
In general, membrane reactors represent a step forward in the development of bioreactors
and constitute a new generation of enzymatic reactors. At this stage, however, membrane
reactor possibilities have not been explored to their full extent. The future will probably
bring the development of even more complex enzymatic systems and elaborate
configurations based on these types of reactors, and hopefully the establishment of
processes at the industrial scale. The following lines suggest some topics where research
efforts in the area of membrane reactors may be concentrated in the coming years:
- Exploration of electric potential as a driving force for transport of solutes through
membranes and eventually as an alternative cofactor regenerating technique in
membrane reactors. - Use of membrane reactors in reactions with insoluble substrates and/or products in
order to explore the capability of ultrafiltration membranes to retain solid compounds. - Investigation of membrane reactors in sequential reactions catalyzed by multi-enzymes
acting synergistically. - Improvement in efficiency of membrane reactors by using arrangements in series and
parallel, and developing new module designs. - Use of membrane reactors in the process development of enzymatic synthesis of chiral
drugs. - Development of highly selective membranes (e.g. affinity membranes, chiral
membranes...). - Developments in the field of materials engineering to improve membrane resistance
(mechanical, thermal, chemical). - Miniaturisation in order to develop micro membrane enzymatic reactors of extremely
small dimensions. For instance, implantable devices could find applications in the
biomedical area.
REFERENCES
Adu-Amankwa, B. and Constantinides, A. (1984) Mathematical Modelling of Diffusion and
Reaction in the Hydrolysis of Vegetable Proteins in an Immobilized Enzyme Recycle Reactor.
Biotechnol. Bioeng., 6, 156–166.
Alfani, F., Albanesi, D., Cantarella, M. and Scardi, V. (1982) Effects of Temperature and Shear on
the Activity of Acid Phosphatase in a Tubular Membrane Reactor. Enzyme Microb. Technol., 4,
181–184.
Enzymatic membrane reactors 179