Method and apparatus for the formation of particles

Abstract

The invention provides a method for forming particles of a substance, by co-introducing into a particle formation vessel, in which the temperature and pressure are controlled, of a supercritical fluid; a solution or suspension of the substance in a first vehicle; and a second vehicle which is both substantially miscible with the first vehicle and substantially soluble in the supercritical fluid in such a way that dispersion of the solution or suspension and the second vehicle, and extraction of the vehicles, occur substantially simultaneously and substantially immediately on introduction of the fluids into the vessel, by the action of the supercritical fluid. Preferably the solution suspension of the substance is introduced separately from the second vehicle, in such a way that contact between the solution / suspension and the second vehicle occurs either substantially simultaneously with, or immediately before, their dispersion by the supercritical fluid and extraction of the vehicles by the supercritical fluid. The method allows a high degree of control over the size, shape, crystalline form and other physico-chemical properties of the particulate product. The invention also provides apparatus for carrying out such a method, using a coaxial nozzle to introduce the fluids into the particle formation vessel, and a particulate product made using the method or the apparatus.

Description

[0001] This invention relates to the controlled formation of particulate products using supercritical fluids. It provides a method and apparatus for the formation of a substance in particulate form, and the particulate product of such a method.[0002] The use of supercritical fluids (SCFs) and the properties thereof have been extensively documented; see for instance J. W. Tom and P. G. Debenedetti, "Particle Formation with Supercritical Fluids--A Review", J. Aerosol. Sci., 22 (5), pp555-584,(1991). Briefly, a supercritical fluid can be defined as a fluid at or above its critical pressure (Pc) and critical temperature (Tc) simultaneously. Such fluids have been of considerable interest, not least because of their unique properties. These characteristics include:[0003] High diffusivity, low viscosity and low surface tension compared with liquids.[0004] High compressibility compared with the ideal gas implies large changes in fluid density with only slight changes in pressure, which in t...

AI Technical Summary

Benefits of technology

[0142] The following examples were carried out using a method according to the present invention, and apparatus generally similar to that shown in FIGS. 1-4. They illustrate the versatility of the method of the invention, its usefulness in forming particles of materials which would otherwise be difficult to prepare by supercritical fluid techniques and the advantageous effects which can thereby be achieved.

[0143] The following examples illustrate the successful and controlled formation of crystalline lactose, using carbon dioxide as a supercritical fluid, despite the very low solubility of lactose in conventional CO.sub.2-soluble organic solvents. According to the present invention, two vehicles were used for the lactose, water as the first and an organic solvent (methanol), which is miscible with water and soluble in supercritical carbon dioxide, as the second.

Problems solved by technology

It may be a substance which, though soluble in an appropriate supercritical fluid-soluble solvent, would suffer detrimental effects if dissolved in that solvent prior to particle formation (for instance, a hydrophilic protein), or be otherwise incompatible with such a solvent.

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