Multiphase Bioreactor Design

CHAPTER TWELVE

DESIGN OF LIQUID-LIQUID-SOLID

FLUIDISED-BED BIOREACTORS

ERIK VAN ZESSEN, ARJEN RINZEMA AND JOHANNES

TRAMPER

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 three-

phase 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.

INTRODUCTION

Advantages of using a liquid-liquid two-phase system in biotransformations have been
discussed (van Sonsbeek et al., 1993; Vermuë and Tramper, 1995a; Tramper et al., 1992;
Adlercreutz, 2000). Depending on the nature of the biotransformations, the reason for
applying a liquid-liquid two-phase system varies. Examples of different