(259d) The Confined Impeller Stirred Tank: Blend Time

The dispersion and dissolution of chemical additives into liquids has to be efficient in order to achieve reasonable industrial yields. Current bench scale tests do not represent properly industrial scale behavior, and turbulence inhomogeneity in bench scale stirred tanks can lead to significant uncertainties about the process mixing requirements. In order to better represent the industrial scale, a new bench scale stirred tank has been developed: the Confined Impeller Stirred Tank (CIST). The CIST provides more uniform intensity of mixing over the volume of the tank and uses a much smaller volume of sample than the traditional stirred tank. The geometry of the CIST allows a more uniform turbulence distribution because the tank is filled with several impellers and therefore the portion occupied by the bulk of the tank is dramatically decreased. The CIST is a narrow and tall tank (T=7.6 cm, H=3T). Three sets of impellers have been used:  the A310, Rushton and Intermig. Sets of five (Rushton and A310) or six (Intermig) impellers of a relatively large diameter (D=T/2 for Rushton and A310 and D=2T/3 for Intermig) were used. The current work assessed the blend time in the CIST using a spectrophotometer. The Reynolds number was varied from 2 000 to 40 000.