Micronization of phenanthrene using the gas antisolvent process. 1. Experimental study and use of FTIR

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 degrees 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 mu m. 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.