conventional organic solvents. They also have the potential to act as “designer solvents”
(Freemantle, 1998) as simple structural modifications to either the anion or cation will
alter the physico-chemical properties of the liquid and offer the possibility to design an
ionic liquid system optimised for a particular application. Although their use in
biocatalytic processes is at an early stage, ionic liquids offer us the opportunity to operate
two-phase processes more safely and with reduced environmental impact.
CONCLUSIONS
There has been considerable development in the field of two-liquid phase biocatalysis in
the last decade and some of the developments are outlined in Table 5.5. Two-liquid phase
biocatalysis has matured into a technology with a particular niche in biocatalysis. Given
the increasing interest in the use of biocatalysis to synthesise novel optically pure
compounds it is clear that application of two-liquid phase processes will increase.
Table 5.5 Recent developments in two-liquid phase
biocatalysis
Process feature Development References
Biocatalyst Solvent resistance
Increased activity with non-natural
substrates
de Bont (1998)
Affholter and Arnold
(1999)Organic phase Ionic liquids as solvent replacements Cull et al. (2000)
Reactor Liquid-impelled loop reactor
Dense phase membrane reactors
Tramper et al. (1987)
Doig et al. (1998)Downstream
processing
Membrane-based phase coalescence Conrad and Lee (1998)Alternative technologies exist which may prove preferable in some cases. Most
importantly the use of organic solvents which are environmentally compromising may
now be replaced with ionic liquid media. Likewise the use of designer biocatalysts will
create new opportunities.
ACKNOWLEDGEMENTS
GJL would like to thank Esso and the Royal Academy of Engineering for the award of an
Engineering Fellowship and the Nuffield Foundation for financial support (NUF-NAL).
REFERENCES
Affholter, J. and Arnold F.H. (1999) Engineering a revolution. Chemtech, 29, 34–39.
Advances in the selection and design of two-liquid phase biocatalytic reactors 141