(548e) Interpretation of FBRM Data At High Crystal Density

Focus Beam Reflectance Measurement (FBRM) can be used in situ to monitor crystallization processes. If such measurements are sufficiently accurate and robust, it should be possible to utilize the FBRM in a scheme to control crystallizer operation. To fulfill this goal, both models for crystallization kinetics and the sensor are needed: the former is part of a population balance or method of moments, while the latter converts the measured chord-length distribution (CLD) to the crystal size distribution (CSD). To identify the sensor model, Yu et al [1] found linearity between chord count and the number of polystyrene particles in an aqueous slurry having low particle density. However, this has not been validated for a broader range of particle density, as is the case in the example system involving batch cooling crystallization of paracetamol from ethanolic solutions.

We have begun expanding the range of particle density coverage with experiments and analysis of paracetamol crystals suspended in a non-solvent, toluene. As crystals at certain sizes are added into toluene continuously, the increase on total count number and chord length histogram are recorded and analyzed to modify the linear relationship between number of chord and number of crystals. Our investigations include the following:

-A regime where linearity holds is identified.

-The linear coefficients are found to be different for different sizes of crystals in the linear regime.

- Linear additivity among different sizes of crystals is studied.

And we also perform Monte Carlo simulation to obtain the linear operator for normalized CSD to normalized CLD [2, 3]. The shape of crystals in the simulation is octahedral, the aspect ratio of which is defined by microscope images and adjusted to fit the measured CLD. The linear coefficients of chord count and the matrix for normalized CLD are combined to formulate a sensor model for FBRM.

Reference:

1.            Yu, Z.Q., P.S. Chow, and R.B.H. Tan, Interpretation of focused beam reflectance measurement (FBRM) data via simulated crystallization. Organic Process Research & Development, 2008. 12(4): p. 646-654.

2.            Ruf, A., J. Worlitschek, and M. Mazzotti, Modeling and experimental analysis of PSD measurements through FBRM. Particle & Particle Systems Characterization, 2000. 17(4): p. 167-179.

3.            Kail, N., W. Marquardt, and H. Briesen, Estimation of particle size distributions from focused beam reflectance measurements based on an optical model. Chemical Engineering Science, 2009. 64(5): p. 984-1000.