- 12:50 PM

Experience Using Turbidity Probes to Control Commercial-Scale Batch Crystallizations

Richard S. Harner1, Roberta J. Ressler2, James E. Hitt3, Paul A. Larsen3, and Timothy Frank4. (1) Process Analytical, The Dow Chemical Company, 1897 Building, Midland, MI 48674, (2) Manufacturing, Dow AgroSciences, 9330 Zionsville Rd., Indianapolis, IN 48674, (3) Process R&D, The Dow Chemical Company, 1603 Building, Midland, MI 48674, (4) Engineering & Process Sciences Laboratory, Process Separations Discipline, The Dow Chemical Company, 1319 Building, Midland, MI 48674

This presentation will describe how a fiber-optic turbidity probe may be used as an inferential sensor for feedback control of commercial-scale batch crystallizations. The discussion will focus on several unseeded crystallization examples involving cooling or cooling plus addition of antisolvent. In a typical control strategy, the probe is used to detect an initial nucleation event, to track a subsequent digestion step for fines dissolution with potential for modification of nuclei size and purity, and then to monitor a growth period. During these steps, operating variables that affect generation of supersaturation are adjusted to maintain a desired turbidity versus time profile. The profile can be determined in liter-scale experiments and then replicated at the 10,000+ liter commercial scale. Within Dow, this control strategy has proven to be robust and cost-effective for numerous commercial-scale batch crystallizations implemented during the past 20 years, including those with highly fouling or corrosive environments.