(420c) Methodological Aspects of On-Line Probes in Batch & Semi Batch Stirred Tanks

On-line measurements of critical processing variables are essential for PAT implementation. The complexity of hydrodynamic flow structure in real laboratory and plant reactors leads to non-uniformity of physical and concentration distributions through many chemical processes. Gradients of temperature or concentration of solid particles, for example, may vary with changes in stirring speed, filling factor and properties of the reaction mixture. Under such conditions, PAT data collected by probes will reflect local concentration and not the overall, or indeed average, of the process in the reactor. Ignoring this effect may lead to misinterpretation of the data and adverse effects on product / process performance. The use of multiple probes in different locations provides only a partial solution and, in particular, does not guarantee performance of dynamic processes. In this paper we present analysis of the impact of hydrodynamics on results of on-line measurements using temperature and particle size (FBRM measurements) as probes. Mathematical simulation of hydrodynamics in stirred tanks is shown to be essential and an effective instrument in the implementation of PAT.