Patent ID: 7087197

Claim:
A method for preparing a substance in particulate form, the method comprising: introducing into a particle formation vessel, through separate first and second fluid inlets respectively, (a) a solution or suspension of the substance in a fluid and (b) a compressed fluid anti-solvent for the substance; and allowing the compressed fluid anti-solvent to extract the fluid from the solution or suspension to form particles of the substance; wherein the compressed fluid anti-solvent and the solution or suspension enter the particle formation vessel at different locations and meet downstream in the particle formation vessel, the pressure in the particle formation vessel is P 1 and is greater than the critical pressure P c of the anti-solvent, the compressed fluid anti-solvent is introduced through a restricted inlet so as to have a back pressure of P 2 , where P 2 is greater than P 1 , the temperature in the particle formation vessel is T 1 and T 1 is greater than the critical temperature T c of the anti-solvent, the compressed fluid anti-solvent is introduced into the particle formation vessel at a temperature T 2 , where T 2 is greater than T 1 , T 1 and T 2 are such that Joule-Thomson cooling of the compressed fluid anti-solvent as it enters the particle formation vessel does not reduce temperature of the compressed anti-solvent to below that required of it to produce particles, P 1 , P 2 , T 1 and T 2 are such that the compressed fluid anti-solvent has a sonic, near-sonic or supersonic velocity as it enters the particle formation vessel, and T 1 and T 2 are such that the temperature of the compressed fluid anti-solvent does not fall below T c within the particle formation vessel.