ABSTRACT
Food and Bioprocess Engineering Group, Wageningen University, P.O. Box 8129, 6700 EV Wageningen, The Netherlands
ABSTRACT A liquid-liquid-solid three-phase system is automatically formed, when in one apparatus an immobilised biocatalyst is used for a biotransformation and an organic solvent is used for extraction. The aim of this paper is to show that the application of such a three-phase reactor system for biotransformations strongly inhibited by the product will result in a higher degree of conversion, compared to a conventional reactor system. Thus, different reactor configurations are discussed. These include a simple three-phase fluidised bed, but also more elaborate options, such as variations of a loop reactor. It is concluded that building and operating a three-phase system is nothing more than a minor extension of conventional bioreactors. In the second part of this paper a simple reactor model is developed for a three-phase liquid-liquid-solid fluidised-bed bioreactor. The influence of different parameters is discussed, e.g. the distribution coefficient of product over medium/ organic solvent, the toxic product concentration, and the flux of the organic solvent. In the last part of this paper conditions have been established under which this threephase reactor performs better than a conventional two-phase fluidised bed. At a given maximum substrate conversion rate, the distribution coefficient is determined for which the three-phase fluidised bed performs equally well as the two-phase fluidised bed. It appears already that a low distribution coefficient (larger than 1 but less than 2) suffices for a better operation. If in situ extraction is needed for such a biotransformation, a three-phase fluidised bed, or less simple three-phase bioreactors, are a good choice.
