Continuous Separation of Isomers in Fluidized Bed Crystallizers

A fluidized bed process exploiting two coupled crystallizers was studied for continuous preferential crystallization in two ternary systems, namely, ortho -aminobenzoic acid (OABA)/ para -aminobenzoic acid (PABA)/water and l -asparagine monohydrate ( l -asn·H 2 O), d -asparagine monohydrate ( d -asn·H 2 O)/water. A continuous supply of seeds was realized by ultrasonic comminution of crystals, withdrawn from the bottom of the partially conical-shaped fluidized bed crystallizers. Product removal occurred via outlets placed at specific positions in the conical sections of the crystallizers. The crystal size distribution (CSD) as well as the purity of the product crystals reached steady states with purities exceeding 97%. A simplified dynamic model was developed and applied to predict solution concentrations and product CSDs. Results of primary solid–liquid equilibria and metastable zone width studies are also reported.