engleski

An experimental study of the effect of mixing on the crystallization of borax decahydrate

In this work experiments on batch cooling crystallization of borax decahydrate are reported with purpose to estimate the mixing effects on this process. The importance of mixing was studied in baffled stirred crystallizer with a volume of about 2 L, equipped with straight four blade turbine (4-SBT) cooling at constant cooling rate. The effect of impeller speed and impeller diameter on the metastable zone width, nucleation kinetics and the crystal size distribution were examined respectively. Metastable zone width was determined by visual method, while concentration changes during the process were monitored in line using ion-selective electrode. The nucleation behavior in the batch cooling crystallizer was presented according to Mersmann's criteria. From the results obtained it is evident that the increasing impeller speed and impeller diameter the metastability range decreases. The nucleation rate depends significantly on the turbulence intensity in the crystallizer. The mixing affects the crystal size distributions of the borax and the position of maximum in these distributions. As consequence of an inadequate mixing in the system the agglomeration of final borax crystals appears.

mixing; batch cooling crystallization; borax; metastable zone width; nucleation

nije evidentirano