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In this study the micronization of phenanthrene from toluene was studied using the gas antisolvent (GAS) recrystallization process. A systematic investigation of the influence of the key GAS process parameters, antisolvent addition rate (1, 20, 50, and 100 mL/min), temperature (25, 45, 55, and 65 °C), solute concentration (25%, 50%, 75%, and 100%), and agitation rate (500, 1000, 2000, and 3500 rpm), was investigated on the particle morphology, size, and size distribution. It was found using laser diffraction that increasing the antisolvent addition rate and the agitation rate, while decreasing the temperature and solute concentration, led to a decrease in the mean particle diameter. Furthermore, a unimodal particle size distribution was obtained at the higher agitation and antisolvent addition rates, but a particle size distribution of a bimodal nature was obtained at the higher temperatures and the lower agitation and antisolvent addition rates. The process parameters could be reproducibly tuned to give a mean particle diameter between 21 and 210 µm. The applicability of on-line attenuated total reflection (ATR) FTIR measurements for an improved understanding of the dynamics of the GAS process was investigated through peak analysis of the in situ ATR-FTIR spectra of phenanthrene. This work also demonstrated that ATR-FTIR on-line monitoring of the solute is a valuable technique for analyzing the GAS crystallization process.

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In the second part of our study, a rigorous mathematical model was developed and simulated using Parsival for the gas antisolvent recrystallization process using phenanthrene-toluenecarbon dioxide as a model system, This model accounts for the governing physical phenomena, i.e., the thermodynamics of near-critical solutions, and the particle formation process controlled by primary and secondary nucleation, and crystal growth. Simulations were performed for changes in the main operating parameters, i.e., the antisolvent addition rate and saturation level. The simulations were performed at a process temperature of 25 °C, while the antisolvent addition rate (Q A ) was varied between 1 and 100 mL/min, and the initial solute concentration was varied between 25% and 100% of the concentration ratio. The model was successfully able to predict/represent the experimental observations phenomenologically. It was shown that the simulation findings were consistent with the experimental results, and good quantitative agreement was achieved.