1. Field of the Invention
This invention relates to fluid bed crystallization systems and more particularly it concerns a novel crystal fracturing arrangement for obtaining improved operation in the growth and recovery of certain types of crystals.
2. Description of the Prior Art
U.S. Pat. No. 3,510,266 describes systems for production of crystals in a fluidized bed using ultrasonic vibrations. In brief, the systems of that patent incorporate a tubular crystalizer column arranged to extend in a generally vertical direction. A supersaturated solution is caused to flow into the column at a location near its lower end and then to flow upwardly through the column. Seed crystals of the solute material initially introduced near the upper end of the column; and these induce additional solute material to come out of the supersaturated solution and onto them. The seed crystals thus grow in size and sink downwardly in the column against the upward liquid flow. At a certain level in the column these crystals collect as a bed of crystals which is kept fluidized by the upward movement of liquid through it. The movement of supersaturated solution over the fluidized crystals causes them to grow. From time to time some of these grown crystals are extracted from the bed. Other crystals, however, grow quite large, and because of their size and weight, they progress down to the bottom of the column. An ultrasonic transducer is located at the bottom of the column; and when the large crystals encounter the transducer they are fractured by the high frequency vibrations which it emits. This results in the production of a great number of smaller crystals which are carried upwardly with the saturated liquid flow in the column. Some of these smaller crystals are extracted as above described while others serve as seed crystals and continue to grow in the column so that the system, when properly controlled, is self seeding.
The system described in U.S. Pat. No. 3,510,266 has been found to be especially effective in the processing of DL-.alpha.-acetamido-.alpha.-vanillyl propionitrile, and similar materials whose crystals are of compact shape and fracture into well defined compact particles.