Mass transfer between the different phases in a 2- or 3-phase system can be presented
schematically as shown in Figure 12.7. To describe mass transfer inside the gel bead we
used Fickian diffusion of substrate and product. For describing the mass transfer from gel
bead interface to the bulk of the medium, we used the film model for substrate as well as
product. The film model was also used for the mass transfer of the product from the bulk
to the interface between medium and organic-solvent droplet. Mass transfer from this
interface to the bulk of the organic-solvent droplet was also described by the film model.
Further it is assumed that the distribution coefficient between gel bead and surrounding
liquid is equal to one. Next, it is assumed that there is thermodynamic
Table 12.1 Hydrodynamic characteristics for a
liquid-fluidised bed and a liquid-liquid-solid
fluidised bed
(^) 2-phase fluidised bed 3-phase fluidised bed
mixing
water
phase
number of tanks-in-series (15) number of tanks-in-series (3)
gel bead
phase
ideally mixed per tank ideally mixed per tank
droplet
phase
- plug flow
hold-up Richardson and Zaki model with experimentally
determined parameters
Experimentally determined,
see Figure 12.6Figure 12.7 Profiles in a multi-phase
system:—product profile, ...substrate
profile
equilibrium at the interface between droplet and medium. The equilibrium distribution at
the interface can be described with a constant distribution coefficient (m):
Design of liquid-liquid-solid fluidised-bed bioreactors 363