초록
A novel control concept was developed for a two phase biocatalytic oxidoreduction system. The hydrophobic substrate acetophenone dissolved in n-heptane is reduced to (S)-1-phenylethanol by Candida parapsilosis carbonyl reductase 2, immobilized in a polyvinyl alcohol hydrogel. The cofactor NADH is regenerated via formic acid oxidation using likewise immobilized Candida boidinii formate dehydrogenase, increasing the pH-value of the aqueous phase. Therefore, the measured amount of CO<SUB>2</SUB> leaving the reactor is used to calculate the amount of formic acid to be replaced. Experiments lead to unexpectedly poor conversions motivating the development of a holistic process model, which was exclusively based on literature data and did not require parameter fitting. Simulation studies identified the CO<SUB>2</SUB>-solubility in n-heptane as the root cause for the time-lag in co-substrate feed and the resulting pH-shifts leading to poor conversions. They also indicated enzyme activity and stability as improvement targets, and the choice of an organic phase with low CO<SUB>2</SUB>-solubility. Exemplarily, increased buffer concentration to stabilize the pH within the hydrogel resulted in a predicted 13% productivity improvement, which could be validated experimentally, thus highlighting the potential of process models for complex biocatalytic process evaluation.