Reactive Crystallization of an Intermediate

Goals Development of a robust process to produce a filterable intermediate with high purity Issues Laboratory operation produced bimodal distributions with unacceptable filtration rates and 

The laboratory process to produce an intermediate in a multistep process involves reaction of two organic compounds that produce a crystalline product as the reaction proceeds and is, therefore, a reactive crystallization. The initial process produced crystalline product that was irregular in shape and difficult to filter. In addition, the chemical purity was severely reduced by contamination with one of the reactants. 

The reaction was carried out by the addition of reagent B to A over the course of 1 hour. In this mode of operation, contamination of the product with reagent A was unacceptable at 4-5% and filtration rates were low (0.36 m /hr-m ). 

Reduction in the amount of A in e product was investigated first by varying die addition scheme. Simultaneous addition of A and B was effective by minimizing the amount of unreacted A in the mixture at all times. A reduction of A contamination was achieved. However, the filtration rate was still unacceptable for scale-up. 

As in Example 10-1, the issue was addressed by seeding and a reduction in the feed rates of the reagents. Seed did not have to be grown separately, as the problem in this example was bimodal dis-tiibution and not initial size. The bimodal distribution is shown in Fig. 10-7a. 

---