EXPERIMENTAL-EVIDENCE FOR AND PREDICTION OF MICROMIXING EFFECTS IN PRECIPITATION

The influence of micromixing on precipitation is predicted qualitatively for batch or semibatch precipitations by means of a simplified mixing model, which considers primary nucleation as the main process affected significantly by hydrodynamics. Unwanted micromixing effects are avoided to a maximum in a batch configuration designed to have a volume mixing ratio alpha close to unity. Using a semibatch precipitator or a batch with a high alpha value dramatically accentuates mixing interactions. For mixing, changing the feed point location is shown to have much stronger influence than changing the stirring speed and constitutes an efficient test of micro-mixing. Experimental evidences for these conclusions have been established for calcium oxalate monohydrate batch precipitation. In particular, the early seconds of the reaction (when mainly primary nucleation occurs) have been demonstrated as conditioning the subsequent behavior of the precipitation, even for induction times of a few minutes.