2013 AIChE Annual Meeting

(241c) Determination of Critical Seed Loading From Nucleation Kinetics

Authors

Tseng, Y. T. - Presenter, National Taiwan University
Ward, J. D., National Taiwan University



It has been observed experimentally that in at least some cases, secondary nucleation in batch crystallization can be suppressed by using an adequate seed loading. Kubota and coworkers1–3call this seed loading the critical seed loading and propose a correlation to predict the critical seed loading as a function of seed size. So far, critical seed loading has only been determined experimentally for a limited number of systems. In this contribution, a method is presented for preparing the critical seed loading diagram knowing only the nucleation kinetics for the system in question. This is advantageous because it is much less time-consuming than conducting experiments or developing and solving a complete batch process model including solubility expressions and growth and nucleation rate kinetics.

The results for 43 systems taken from the literature show that there is a great deal of variability in the critical seed loading, and a single correlation is inadequate to describe the relationship between critical seed loading and seed size. For a seed size of 10 microns, seed loading can effectively suppress nucleation in 92% of cases, while for seeds of size 50, 100 and 200 microns, seed loading can suppress nucleation in 74%, 61% and 39% of cases respectively.

Furthermore, the effects of changing process parameters (total batch time and the net crystal yield) can also be readily studied, although they are found to have a small effect compared to seed size. Finally the possibility of using a critical seed length or critical seed surface area for process development instead of critical seed mass is also investigated, however these alternatives are not found to be more attractive than the critical seed mass.

References

  1. Doki N, Kubota N, Yokota M, Chianese A. Determination of critical seed loading ratio for the production of crystals of uni-modal size distribution in batch cooling    crystallization of potassium alum. J Chem Eng Jpn. Jul 2002;35(7):670-676.
  2. Doki N, Kubota N, Sato A, Yokota M, Hamada O, Masumi F. Scaleup experiments on seeded batch cooling crystallization of potassium alum. AIChE J. Dec 1999;45(12):2527-2533.
  3. Jagadesh D, Kubota N, Yokota M, Sato A, Tavare NS. Large and mono-sized product crystals from natural cooling mode batch crystallizer. J Chem Eng Jpn. Oct 1996;29(5):865-873.