Multiphase Bioreactor Design

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APPENDIX A DERIVATION OF MASS BALANCES FOR A THREE-

PHASE FLUIDISED BED BIOREACTOR

In a three-phase fluidised bed three different phases are present. Mass balances are
derived for the individual phases. As conversion we took one mol of substrate giving one
mol of product. So, two components are present in the solid phase and the medium phase.
Only product is present in the organic-solvent phase.
The total reactor is divided into a number of vertically stacked ideally stirred tank
reactors, a tanks-in-series model (number of tanks is 3). We took a plug flow model for
the organic-solvent phase. A tank-in-series model was applied with a large enough
number of tanks to mimic plug flow. For simplicity we assumed that the gel beads did not
circulate inside the reactor. Systematically the bioreactor looks as shown in Figure 12.8.
Mass transfer takes place from the medium phase to the gel beads for substrate.
Product is transferred from the gel beads to the medium, and from medium to the organic
solvent.
Mass balances for one tank, including the boundary and initial conditions, read as
follows:
The gel bead
Substrate

r=0, centre of the gel

r=R, edge of the gel bead

Product

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