Case Studies

TRACERCO Diagnostics™ Residence Study

Residence Time Study Boosts Yield

In the manufacture of a chemical intermediate, several streams are mixed together in a stirred tank reactor. The incoming streams are first intimately mixed using several; mixing nozzles. Excessive time in the reactor will generate more by-product resulting in a lower product yield. Tracerco was called in to use its TRACERCO Diagnostics™ Residence Study technique to determine the residence time through the reactor at different mixing speeds and different mixing nozzle configurations. An organic radioisotope was chosen because, in this case, it was unreactive and would simulate the flow of the organic phase in the feed streams. A small amount of the tracer was injected into the stream A.

Radiation detectors were placed at the distribution centre prior to entering the reactor and at the exit pipe for the crude product. As the pulse of radiation passed each detector the radiation counts were plotted graphically and entered into a computer. The resulting curves were integrated to determine the mean residence time. Analysis of the data provided not only reactor residence times, but also the degree of mixing in the form of stirred tank equivalents (STE). Low values of STE represent good mixing characteristics, whereas high values suggest plug flow through the reactor. A combination of mixing nozzle configurations and mixing speeds were identified which minimized both residence time and the STE value. Operating the unit under these conditions resulted in a product yield improvement of 15%.

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