(497f) Effect of Aging On Crystal Breakage in Stirred Vessels

Previous research has shown that crystals often break in stirred vessels due to collisions with the impeller. Since this often causes secondary nuclei, it can change the entire crystal size distribution in a crystallizer. To isolate breakage, it is necessary to prevent dissolution, growth, nucleation and agglomeration from occurring. This is generally done by using a nonsolvent, or by using a saturated solution. The concern with the saturated solution approach is that it does not give true breakage results because aging changes the crystal size distribution. However, the extent of the aging effect is not well studied.

The aging effect was investigated by performing one set of breakage experiments in a stirred vessel with crystals suspended in a saturated solution, and a second set with crystals suspended in a nonsolvent. If aging did not occur, then both sets of experiments should yield the same results. Breakage results from saturated solutions were compared to breakage in nonsolvents to determine if the results were different and if so, to determine how strong an effect aging had on the breakage results. Experiments were performed with a variety of crystals including sodium chloride, pentaerythritol, potash alum, ammonium sulfate, and paracetamol.

Results are presented which show that there can be significant differences between breakage in saturated solutions and breakage in nonsolvents. In general, this indicates that to isolate the mechanism of breakage, it is necessary to perform experiments in nonsolvents.