FORMATION OF FINE POWDERS OF CAFFEINE BY RESS

Precipitation of solids resulting from solution supersaturation is wid ely adopted to produce organic and inorganic powders. In fact, the rap id expansion of supercritical solution (RESS) is a new process of part icle formation. Various morphologies and particle sizes can be thus pr oduced: thin films, thin diameter fibers, needles or spherical product s of narrow size distribution. The distinguishing features of this pro cess are the fast attainment of the uniform conditions and of high sup ersaturations in the carrier fluid (supercritical carbon dioxide), whi ch favor the formation of small particles, with narrow distribution. T he expansion of a supercritical solution thus leads to loss of solvent power and hence to solute precipitation. The RESS is described for th e production of fine powders of caffeine from supercritical carbon dio xide upon expansion. There is variety of the fluid solution expansion parameters. The product morphology, however, can vary considerably dep ending on the solution components and the operating conditions used in the process: solute concentration, preexpansion and expansion tempera ture and pressure of extraction have been shown to affect the product characteristics of the formed powder during the process. Optical photo micrographs of the formed particles are compared taking into account t he variation of thermodynamic variables. Finally we discuss the variat ion of the density distribution and the particle sizes along a plate o f deposition.