MODEL IDENTIFICATION OF BATCH COOLING CRYSTALLIZATIONS THROUGH CALORIMETRY AND IMAGE-ANALYSIS

For most batch crystallization processes it remains difficult to obtai n relevant on-line information on both the dissolved solid concentrati on in the liquid phase and the crystal size distribution (CSD). Moreov er, the reported experimental results are generally based upon simplif ied population balance models such as moment equations which are known to contain insufficient information on the CSD. In order to cope with these two difficulties, the aim of this article is to present a new a pproach for parameter estimation and modelling of batch cooling crysta lizations. Measurements of supersaturation were made with a Mettler RC 1 calorimeter coupled with an on-line in situ laser sensor. Estimates of the final CSD were also obtained through image analysis. In additio n to such a measurement strategy, the population balance equations wer e solved to simulate the time variations of the CSD, and used to ident ify nucleation and growth kinetic parameters. In order to evaluate the method, the isothermal crystallization of adipic acid in water was ex perimentally investigated. Profiles of the heat release due to crystal growth were computed from the on-line energy balance of the crystalli zation, and final CSDs were obtained off-line after image analysis. On -line information about the nucleation mechanism was also provided by the laser sensor. Through the fitting of both calorimetric and granulo metric experimental data, these operations allow one to select the app ropriate crystallization kinetic models and to estimate the correspond ing parameters. For the reported batch experiments, the comparison bet ween experimental and simulated variables such as the supersaturation and the final CSD was satisfactory. (C) 1997 Elsevier Science Ltd.