The reactive precipitation process of procaine benzylpenicillin is reviewed, while such secondary pro-cesses as ageing, agglomeration, breakage, and the effects of operation parameters on crystal size are emphasized. In the reactive precipitation the ageing of particles has a little effect on the process, while the greater effect comes from the agglomeration and breakage of particles, furthermore, the mixing has also notable influence on the product size. All of these provide the bases for further study on reactive precipitation.

The bench-scale cooling crystallization for ternary solution of L-ascorbic acid (Vitamin C) was studied. The solid-liquid phase diagram of Vitamin C-water-ethanol system was obtained on the basis of differential scanning calorimeter (DSC) curves. The heat of crystallization of Vitamin C was calculated with the aid of quantitative analysis. According to the population balance equation under unsteady state, the rates of nucleation and growth were determined. The parameters of crystallization kinetics equations were estimated by regression of experimental data. Crystal morphology and size were determined with x-ray diffraction and TAII Coulter Counter.

The general mathematical model for batch cooling crystallization was established based on the p0opula-tion balance equation considering the change of slurry volume, and simulated with crystallization thermodynamics, kinetics and mass balance employing bed voidage. In the system of vitamin C-water-ethanol, reliability of this model was verified by comparison between simulation results and experimental data. The effects of operation parameters on product quality can be systematically investigated by modeling simulation.

A general expression for the relationship between induction period and supersaturation was developed based on polynuclear approach. Different mechanism of primary nucleation in solution can be illustrated by the expression. The results of induction period determined by laser scattering method shows that the crystallization of ciprofloxacin hydrochloride monohydrate in water/ethanol or aqueous solution is by the mechanism of primary nucleation followed by one-dimensional diffusion growth, and then one-dimensional continuous or "birth and spread" growth on crystal face. The growth mechanism on the crystal face is affected by temperature and solvent.