Gradients in Liquid, Gas or Solid Fractions

Abstract

Processes consist of different steps. If for example an aerobic conversion takes place in a solid particle the oxygen has to be transferred from the gas phase to the liquid phase and from the liquid phase to the solid phase. The rate of the overall process will be determined by the slowest process. Optimization of the process can be achieved by optimization of the slowest process step. In that case, however, an overview has to be made of all possible process steps. A useful tool for such an inventory is regime analysis. A system with immobilized biocatalysts has a complex behaviour. A complete description of the process for a wide range of conditions is time consuming or even impossible. This argument is valid for most biotechnological processes and a consistent approach to simplify these processes is regime analysis (Moser 1988, Roels 1983). In the regime analysis presented by Schouten et al. (1986), with immobilized Clostridium spp. for isopropanol/ butanol production, the effectiveness factor for the immobilized cells was estimated to be 1. They conclude that the isopropanol/butanol production is not diffusion controlled and the immobilized cells behave as free cells. New for the regime analysis presented here is the addition of a solid third phase with immobilized cells growing in a diffusion-controlled situation.