Multiphase Bioreactor Design

oxygen FC40/water 12 Sonsbeek et al., 1992a

octene/water 11.4 Meer, 1993

propenoxide toluene/water 3.5 Brink and Tramper,
1985

butylacetate/water 4.6 Brink and Tramper,
1985

butanal toluene/water 6.9 Kawakami, et al., 1992

hexadecane/water 1.52 Kawakami, et al., 1992

tetraline FC40/water 120 Vermudë, et al., 1994

dodecene/water >5000 Vermudë, et al., 1994

Steroids

Androstenoloneactate Hexane/water 1500 Boeren, et al., 1992

4-Androstene-3,17-
dione

Hexane/water 8.5 Boeren, et al., 1992

dehydroepiandrosterone Hexane/water 24 Boeren, et al., 1992

phenylalanine isobutyl methyl 123 Flashel, et al., 1992

propyl ester keton/water

lower water flux, Figure 12.13a, the difference between both dodecane fluxes is almost
insignificant. At the higher water flux, Figure 12.13b, this difference is a little more
pronounced. A general remark about the difference between a high and low toxic product
concentration can hardly be made: at X·vmax the distribution necessarily for giving an
equal performance is sometimes lower other times higher.

Continuous Operation

Executing a biotransformation continuously in a two-phase fluidised bed without a
recycle is highly inefficient, as the medium flux is high compared to the maximum
substrate conversion rate. Consequently the residence time is short and the conversion
rate is low. Only for fast conversions or high reactors, a high degree of substrate
conversion is possible, and hence a fluidised bed might be attractive. As an example, a
substrate conversion of 1 mol/s, a medium velocity of 0.02 m/s, and a reactor height of 1
m results in conversion of 50 mol, assuming zero-order kinetics. This is 50% of the
attainable conversion at a toxic product concentration of 100 mol/m^3.
Otherwise one should use a set-up with a partial recycle and fresh substrate supply. In
this case the incoming substrate concentration is kept constant. The product concentration
in the medium phase will accumulate until steady state is reached. As the product
concentration increases with an increasing recycle, substrate will be converted to a lesser
amount. Application of an organic solvent, i.e. using a three-phase fluidised bed, will
result in a higher conversion, as we calculated for the following case (the organic solvent
was not recycled): medium flux 0.75×10−^2 m/s, dodecane flux 0.40×10m^2 m/s, hence εs=

Design of liquid-liquid-solid fluidised-bed bioreactors 377