Methods and apparatus for particle formation

Abstract

The invention provides a method for forming particles of a target substance (26), involving: (a) preparing a solution or suspension of the substance in a vehicle (21) which is or includes either a near-critical fluid (21) or a first supercritical fluid; (b) introducing the solution or suspension into a particle formation vessel (32); and (c) contacting the solution or suspension, in the particle formation vessel, with a second supercritical fluid, under conditions which allow the second supercritical fluid to cause precipitation of particles of the target substance from the solution or suspension; wherein the second supercritical fluid is miscible or substantially miscible with the vehicle and is a fluid in which the target substance is insoluble or substantially insoluble. Also provided is apparatus for use in carrying out an embodiment of the method, including a particle formation vessel and means for controlling the temperature and pressure inside it; a fluid mixing vessel and means for controlling the temperature and pressure inside it; first fluid inlet means for introducing into the fluid mixing vessel a vehicle and a solution of a target substance in a primary solvent, so as to form in the fluid mixing vessel a solution of the substance and the primary solvent in the vehicle; and second fluid inlet means for introducing the solution thus formed, preferably together with a second supercritical fluid, into the particle formation vessel. The invention also provides a particulate product formed using the method.

Description

[0001] This invention relates to the controlled formation of particulate products using supercritical fluids. It provides methods and apparatus for the formation of substances in particulate form, and also particulate products of the methods.BACKGROUND TO THE INVENTION

[0002] It is known to form particles of a substance of interest (a "target substance") by dissolving or suspending it in a suitable vehicle and then using a supercritical fluid anti-solvent to extract the vehicle to cause particle precipitation.

[0003] One particular technique for doing this is known as "SEDS" (Solution Enhanced Dispersion by Supercritical fluids). This is described in WO-95 / 01221 and (in a modified form) in WO-96 / 00610, The essence of SEDS is that a solution or suspension of a target substance, in an appropriate vehicle, is co-introduced into a particle formation vessel with a supercritical fluid anti-solvent having a relatively high flow rate, in such a way that two things happen substantially simulta...

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