Figure 5.6 Integrated design strategy
for two-liquid phase biocatalytic
processes: (a) may need to
compromise on solvent selection to
satisfy solubility constraints; (b)
opportunities for protein/ genetic
engineering; (c) may need to
compromise on reactor operation to
satisfy downstream processing
constraints.
downstream processing step is the separation of the product-containing phase from both
the second phase and the biocatalyst. The favoured technique appears to be the use of
microporous microfiltration membranes to aid dispersed phase coalescence which may be
either ceramic (Conrad and Lee, 1998) or hydrophobic/hydrophilic polymer composites
(Schroen and Woodley, 1997). In both cases it is important that the breakthrough
pressure of the phase to be retained is not exceeded during operation. The use of
centrifugation to directly separate the two bulk liquid phases is unlikely to be successful
given the tendency to form stable emulsions, the low phase density difference and the
small size of the dispersed phase droplets. Thermal pretreatment of the emulsified broth
by either heating (autoclaving at 121°C) or cooling (freezing at −20°C) has been shown
Advances in the selection and design of two-liquid phase biocatalytic reactors 135