A C E Time Profiles of Stirred Tank Reactors Continuously Fed with Reactants and Catalyst under Conditions of Strong Catalyst Deactivation

-Feeding continuously operated stirred tank rectors with reactants and homogeneous catalysts subject to inactivation will usually lead to a limited substrate conversion with increasing space time. However, it is shown that a maximum of conversion may be observed under certain circumstances. Guided by experimental evidence, the theoretical background is discussed for identifying reaction systems for which such conversion maxima at distinct space times may be obtained. The analysis shows that this phenomenon may only be observed if the catalyst undergoes deactivation characterized by a kinetics of less than first order. Therefore, a likely case for experimental verification consists in an enzymic reaction accompanied by proteolytic degradation of the substrate transforming enzyme due to the presence of a protease. INTRODUCTION This communicat ion aims at drawing attention to a special behaviour of continuous stirred tank reactors which, to the knowledge of the authors, has been overlooked so far. The phenomenon of interest is associated with the operation of stirred tank reactors continuously fed with reactants and catalyst, whereby the latter is not retained and undergoes strong deactivation. Interest in this question arose, when the partial hydrolysis of whey proteins by means of the soluble enzymic catalyst trypsin in continuously operated stirred tank reactors was studied (Margot, 1992). Under conditions of strong enzyme deactivation, a distinct maximum conversion occurred in the conversion (NPN: "non-protein nitrogen", solubilized fraction of proteins)-space time profile. For convenience, a typical graph is presented in Fig. 1. Details of the experimental work related to these data will be presented elsewhere. The following discussion will focus on this strange behaviour characterized by a decline of substrate conversion with increasing space time. Because of the complexity of the experimental system studied by Margot (1992), the discussion will emphasize the theoretical background of this phenomenon. +Author to whom correspondence should be addressed. 0.5