Model validation
The mathematical model described in this work was developed based on
experimental data from our multi-enzyme cascade reaction (Figure 1)
during the first step of laboratory-scale process development. Our model
aims to simulate the cinnamyl cinnamate production process in the
miniplant introduced in figure 2, thereby making time- and
cost-intensive experiments for process optimization obsolete. Therefore,
the model is to be used for mathematical optimization. Prior to process
simulation and optimization, however, our model needs to be validated
using independent experimental data from the miniplant as the consequent
second step of process development. Since the developed mathematical
model is designed to perform dynamic simulations, the start-up phase of
the reactor setup has to be included in the validation process.
All experiments for model validation were performed in the miniplant
described in figure 2 in the previous chapter. 500 ml of a 0.1 M
potassium phosphate buffer at pH 8.0 were used in the continuously
stirred tank reactor (figure 2, A), tempered to 30 °C. This device is
equipped with a SpinChem® reactor, spinning at 400 rpm
and containing 21.3 mg of immobilized ADH and 6.6 mg of immobilized FDH.
250 ml/min are pumped within the water-based cycle through the
extractive centrifuge (figure 2, C), thereby connecting the two cycles.
The organic cycle consists of 500 ml of xylene provided in the buffer
tank (figure 2, B), 100 ml/min of which are pumped via the extractive
centrifuge through the fixed bed reactor (figure 2, D) filled with
12.8 g of Novozym®435 and tempered to 60 °C. Six
different experiments were performed with varying starting
concentrations, to validate our mathematical model using a broad range
of experimental data. Table 4 shows the supplied starting concentrations
of the educts for all six experiments, as well as the achieved molar
yield of CCI after 54 hours of operation with respect to the CAL
starting concentration, calculated according to equation (13).