Plastic and nonmetallic article shaping or treating: processes – Formation of solid particulate material directly from molten... – By impinging plural liquid masses
Reexamination Certificate
1999-12-16
2002-08-27
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Formation of solid particulate material directly from molten...
By impinging plural liquid masses
C264S012000, C425S007000
Reexamination Certificate
active
06440337
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the controlled formation of particulate products using supercritical fluids. It provides a method and apparatus for the formation of substances in particulate form, and also the particulate product of the method.
BACKGROUND TO THE INVENTION
The invention relates generally to the formation of particles of a substance of interest, from a solution or suspension of that substance in an appropriate vehicle, using a supercritical fluid to extract the vehicle and hence cause precipitation of a particulate product.
More particularly, it concerns modifications to an existing technique for particle formation using supercritical fluids, described in WO-95/01221 and (in a modified form) in WO-96/00610. The technique is known as “SEDS” (Solution Enhanced Dispersion by Supercritical Fluids). Its essence is that a solution or suspension of a substance of interest, in an appropriate vehicle, is co-introduced into a particle formation vessel with a supercritical fluid, in such a way that dispersion and extraction of the vehicle occur substantially simultaneously by the action of the supercritical fluid, and substantially immediately on introduction of the fluids into the vessel. The pressure and temperature inside the particle formation vessel are carefully controlled during this process.
SEDS allows a high degree of control over conditions such as pressure, temperature and fluid flow rates, and over the physical dispersion of the solution/suspension, at the exact point where particle formation occurs (ie, at the point where the vehicle is extracted into the supercritical fluid). It therefore allows excellent control over the size, shape and other physical and/or chemical properties of the particles formed.
The present invention builds on this existing technology. It provides a modification to the SEDS technique, which can lead to greatly improved control over the characteristics of the particulate product.
Accordingly, most of the technical features of SEDS, as disclosed in WO-95/01221 and WO-96/00610, apply also to the present invention. The technical information contained in the earlier publications, as to the execution of SEDS, is also applicable when carrying out the present invention and as such, WO-95/01221 and WO-96/00610 are intended to be read together with the present application.
STATEMENTS OF THE INVENTION
According to a first aspect of the present invention there is provided a method for forming particles of a substance, the method comprising (a) introducing into a particle formation chamber, the temperature and pressure in which are controlled, a first supercritical fluid and a solution or suspension of the substance in a vehicle; (b) simultaneously introducing, into the particle formation chamber, an impinging flow of a second supercritical fluid, at an angle to, and directed at, the direction of flow of the first supercritical fluid; and (c) using either or both of the first and second supercritical fluids to disperse the solution or suspension, and to extract the vehicle from it, substantially simultaneously and substantially immediately on introduction of the fluids into the particle formation chamber.
This method retains all the advantages of the SEDS technique. The simultaneous introduction of the solution or suspension and the supercritical fluids, into a chamber inside which pressure and temperature are controlled, allows a high degree of control of operating parameters at the exact point when the fluids come into contact with one another and therefore at the point of actual particle formation. Importantly, the mechanical action of the supercritical fluids is used to disperse the solution/suspension, whilst at the same time they extract the vehicle from it—because of this, controlling the relative flow rates of the fluids allows accurate control over the size of the fluid elements (eg, droplets) formed on dispersion of the solution/suspension, and hence of the particles formed substantially simultaneously by extraction of the vehicle into the supercritical fluid(s).
However, the method of the present invention allows for greatly improved dispersion of the solution or suspension of the substance of interest, by the additional impinging (preferably counter-current) flow of the second supercritical fluid. This improved dispersion can be attributed to enhanced physical contact between the solution/suspension and the (usually relatively high velocity and therefore also high kinetic energy) supercritical fluids, hence effecting the formation of very fine particles with an extremely narrow size distribution. The two supercritical fluid flows, directed at one another and usually in substantially opposite directions, each transfer their kinetic energy to the solution or suspension, serving to break it up into individual fluid elements; the size and size distribution of these elements can be very closely controlled by adjusting the flow rates of the various fluids and other working conditions such as the temperature and pressure inside the particle formation chamber. The solution/suspension can be subjected to a very high degree of dispersion due to the high overall supercritical fluid velocity (ie, high overall kinetic energy), and its efficient dispersion, at substantially the same time as the vehicle is extracted from it, in turn can provide a high degree of uniformity in the particles formed.
A further advantage of using two supercritical fluid flows, and hence introducing a higher level of kinetic energy into the solution/suspension at or near the point of particle formation, is that particles formed from the solution or suspension can be forced rapidly away from the point of particle formation and hence apparatus blockages (which might otherwise occur in the inlet means used to introduce the fluids into the particle formation chamber) can be reduced or even avoided. The supercritical fluids thus serve to disperse the solution or suspension, to extract the vehicle from it and to remove particulate products from the region of particle formation. The high velocities of the supercritical fluids facilitate quick removal of the particles, ensuring that they cannot reunite with fluid elements, aggregate with one another or otherwise clog up the region of particle formation.
The directions of flow of the first supercritical fluid and the solution or suspension may be substantially parallel, for instance coaxial, as described in WO-95/01221 and WO-96/00610. However, the solution or suspension may in the present invention be introduced at an angle (eg, of up to 90°) to the flow of the first supercritical fluid, so long as it is then dispersed by the supercritical fluid(s) immediately it comes into contact with them. Generally speaking, the directions of flow of all the fluids should be chosen so as to maximise the amount of physical contact between them in the region of particle formation; this in turn serves to maximise the amount of kinetic energy transferred from the supercritical fluids to the solution/suspension and to the particulate products, thus improving dispersion and more efficiently removing particles from areas of potential blockage. The use of two supercritical fluid flows together improves these processes yet further and ensures better control over the mechanism of particle formation.
According to a second aspect, the present invention provides apparatus suitable for carrying out the above described method. The apparatus comprises a particle formation chamber; means for controlling the temperature in the chamber at a desired level; means for controlling the pressure in the chamber at a desired level; first fluid inlet means for the introduction into the chamber of a first supercritical fluid and a solution or suspension of the substance of interest in a vehicle; and second fluid inlet means for introducing simultaneously an impinging flow of a second supercritical fluid, at an angle to, and directed at, the direction of flow of the first supercritical fluid, the apparatus being such as to allow dispersion of the solutio
Hanna Mazen
York Peter
Cagan Felissa H.
Inhale Therapeutic Systems Inc.
Kuhns Allan R.
Rafa Michael J.
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