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).