Making a total process design and optimising this design for both reactors goes beyond
the scope of this paper. One can also compare both reactors on their performance, i.e.
degree of conversion of the substrate, or synthesis rate of product.
Before we go into a detailed comparison of both bioreactors, the model used for the
calculations is described.
Model DerivationA general total model for the design of a reactor is schematically shown in Figure 12.5.
This model consist of three major parts:
● hydrodynamics of the reactor
● kinetics of the bioconversion
● mass transfer of compounds between the different phases
Figure 12.5 Model outline
Together with mass balances over each phase for the different components, the total
model is complete.
Investigated systemIn our laboratory hydrodynamic studies have been done on a three-phase system
consisting of water, dodecane and gel beads. This system is used as the model system.
Obviously, highly complicated bioconversions can be involved in producing industrially
interesting products, in which more than one substrate and product influence the kinetics.
We have chosen a very simple one-to-one conversion: substrate S gives product P. It is
further assumed that substrate is dissolved in the medium and insoluble in the organic
solvent, transported to the gel bead and then converted to product. The product itself is
transported out of the gel bead to the medium phase and subsequently to the organic
solvent phase.
Design of liquid-liquid-solid fluidised-bed bioreactors 361