(626c) Impact of Seed Particle Size Distribution Uncertainty On the Supersaturation Controlled Batch Cooling Crystallization Time: Experimental and Model Based Evaluation

This project investigates the sources of uncertainty for supersaturation controlled crystallization batch time. Since variation of the seed particle size distribution (PSD) is propagated in the final batch time (assuming constant yield operation), the first part of the contribution presents the systematic evaluation of sieving for seed preparation using the QICPIC from Sympatec and Morphologi G3 from Malvern, units which are based on digital imaging. The second part of the contribution quantifies the impact of seed PSD on the crystallization time considering supersaturation controlled batch cooling operation. This is carried out using a population balance model solved using the method of characteristics which assumes size-dependent crystal growth and constant supersaturation, thus an analytical solution is obtained [1]. The main findings are that the PSD of the powder collected from the sieves is shifted towards large sizes, and does not correspond to the nominal sieve specifications; furthermore, the batch-to-batch variability of sieving is low and often bimodal distributions are obtained due to fines. For a fixed sieving recipe, the crystal shape influences the powder PSD obtained on sieves. Related to the crystallization operation, it is concluded that, for size dependent crystal growth, fines increase the crystallization time with as much as 40%; however if these grow above 50-100 microns filtration problems are avoided. Moreover, the exact PSD of the powder obtained by sieving should be determined by an additional sizing technique to provide high quality initial conditions for on-line, population balance model based PSD estimation applications.

[1] Aamir E, Nagy ZK, Rielly CD. Combined Quadrature Method of Moments and Method of Characteristics Approach for Efficient Solution of Population Balance Models for Dynamic Modeling and Crystal Size Distribution Control of Crystallization Processes, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 48,18,8575-8584,2009