Micromixing effects in a two-impinging-jets precipitator

To carry out rapid precipitation on a practical scale the use of a two-impinging-jets (TIJ) mixer was explored in terms of its ability to deliver rapid micromixing. The two-step Bourne reaction scheme between 1-naphthol and diazosulfanilic acid was used to characterize micromixing in the TIJ mixer as a function of hydrodynamics and mixer geometry. The characteristic time for micromixing in this device was at least as small as 65 ms. The larger the jet diameter, the higher the jet Reynolds number required to achieve the same micromixing quality. The micromixing time in the TIJ mixer correlated well as a function of a Damkohler number that led to a scale-up criterion giving an inverse relationship between the micromixing time constant and the 1.5 power of the jet velocity. Finally, the precipitation of Lovastatin was carried out in the TIJ mixer under well and poorly micromixed conditions. The level of micromixing in the precipitator affected the crystal size distribution of the precipitated product only when the rime constant for micromixing was comparable to or larger than the induction time for nucleation of the solute.