Measurement of solid solubilities of diuron in supercritical carbon dioxide and analysis of recrystallization by using the rapid expansion of supercritical solutions process

A semi-flow type apparatus was used to measure the solid solubilities of diuron, an herbicide, in supercritical carbon dioxide (CO2) from 10 to 20 MPa at 308.2, 318.2, and 328.2 K. The mole fraction of solid diuron dissolved in supercritical CO2 was between 8.72 x 10(-7) and 1.63 x 10(-5). The measured solubility data were correlated using three thermodynamic models: the Chrastil equation, Mendez-Santiago and Teja equation, and regular solution model coupled with the Flory-Huggins equation. These models yielded satisfactory results with the average relative deviations being less than 6%. Furthermore, an analysis using the rapid expansion of supercritical solutions CRESS) process was conducted to determine the effects of three operating temperatures on recrystallization of diuron. Three extraction temperatures (T-ext) (308, 318, and 328 K), three pre-expansion temperatures (T-pre) (433, 453, and 473 K), and three post-expansion temperatures (T-post) (273, 293, and 313 K) were used to determine the effect of operating temperatures. A lower post-expansion temperature of 273 K and higher pre-expansion temperature of 473 K were associated with the production of smaller diuron particles with a narrower size distribution. The effect of extraction temperature remained insignificant. The mean particle size of diuron could be successfully reduced to approximately 6 mu m by using the RESS process. (C) 2015 Elsevier B.V. All rights reserved.