Plastic and nonmetallic article shaping or treating: processes – Formation of solid particulate material directly from molten...
Reexamination Certificate
2001-10-19
2004-12-14
Theisen, Mary Lynn (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Formation of solid particulate material directly from molten...
C264S011000, C264S012000, C264S014000
Reexamination Certificate
active
06830714
ABSTRACT:
This invention relates to a process for producing solid materials in a particulate form, and to an apparatus for performing the process. In particular this invention relates to such a process and apparatus using a substance in a supercritical fluid state.
Certain compressible fluids, e.g. gases, can act as antisolvents. An “antisolvent” is a substance which when mixed with a solvent, such as an organic solvent, reduces the power of the solvent to dissolve solutes. Consequently when an antisolvent is mixed with a solution of a solute in a solvent, the solubility of the solute can be reduced such that the solute precipitates out of solution. For example some compressed gases can act as antisolvents, for example carbon dioxide at pressures above ca. 30 bar. However the antisolvent effect of compressible fluids is most manifest when the fluid is in a supercritical fluid state.
A “supercritical fluid” as referred to herein, is a fluid at or above its critical pressure (Pc) and critical temperature (Tc) simultaneously. Such a fluid is under such conditions whereby its molar volume and solvating power can be significantly altered by varying the temperature and pressure of the fluid. Fluids which are slightly below their actual critical temperature and pressure can also show such characteristics and the term “supercritical fluid”, as used herein also includes such fluids.
The use of supercritical fluids in the production of solid materials in a particulate form has been extensively documented, see for example Tom J. W. and Debenedetti P. G.
“Particle formation with supercritical fluids—A review”
in J. Aerosol Sci. 22(5), 555-584 (1991).
A number of processes for using supercritical fluids in the production of particles are known. These include the Rapid Expansion of Supercritical Solution (“RESS”) process, see for example Tom J. W. and Debenedetti P. G. (op cit), the Gas Anti-Solvent (“GAS”) process, see for example Gallagher P. M. et al,
“Supercritical fluid science and technology”
, ACS Symp. Ser., 406, p334 (1989), and the Solution Enhanced Dispersion using Supercritical Fluids (“SEDS”) process, see for example University of Bradford GB 2322326A, PCT/GB94/01426 and PCT/GB95/01523.
Current GAS processes using supercritical fluids in the production of particles isolate particles of a solute by precipitation from a solution using a supercritical fluid such as carbon dioxide as an antisolvent. They are generally batch processes where the solute product is difficult to remove from the particle formation chamber and where other shortcomings exist. Fine particles resulting from rapid crystallisation processes can undergo crystal growth during the prolonged exposure to the supercritical fluid in these processes and changes to the material can occur during the depressurisation cycle required to harvest the product. Small, well engineered and controlled particles, desirably approaching or below one micron, are difficult to achieve using known supercritical fluid GAS processes of the type referred to above. WO 97/31691 (University of Kansas) discloses a process for particle precipitation and coating using a GAS supercritical fluid process.
Processes such as RESS rely on saturator chambers to dissolve material prior to particle formation. These are semi continuous processes that can last for some hours and again shortcomings exist. As the saturator is depleted the resulting solution can vary in concentration. In addition, the material within the saturator may be subjected to degradation or a change of physical form at the elevated times, temperatures and pressures involved.
In the SEDS process and apparatus a mixture of a supercritical fluid and a solvent is allowed to expand into a downstream particle formation vessel, which is provided with a back pressure regulator. The SEDS process involves a complex nozzle structure and a back pressure regulator.
It is an object of the present invention to provide an alternative, improved process using supercritical fluids in the production of particles, which in part at least solves the problems of these prior art processes. Other objects and advantages of the present invention will be apparent from the following description.
DESCRIPTION OF THE INVENTION
According to this invention, a process for using a compressible fluid antisolvent substance in the production of particles of a material is provided wherein:
a stream of a dispersion of the material in a solvent and a stream of a compressible fluid antisolvent substance are brought into contact with each other so that the streams combine to form a mixture under conditions such that the substance is in a compressible fluid antisolvent state,
the mixture is then caused to flow along a conduit extending downstream from the region where the streams come into contact, toward an orifice opening from the conduit, the pressure and temperature of the mixture in the conduit being such that the compressible fluid antisolvent substance remains in a compressed state over at least part of the length of the conduit,
then the mixture is caused to flow into a downstream region in which the compressible fluid antisolvent substance decompresses into a gaseous state and the material is isolated in a particulate state.
In a second aspect this invention further provides an apparatus suitable for performing the process of this invention.
Such an apparatus may comprise:
means for bringing a stream of a dispersion of the material in a solvent and a stream of a compressible fluid antisolvent substance into contact with each other such that the streams combine to form a mixture under conditions such that the substance is in a compressible fluid antisolvent state,
a conduit extending downstream from the region where the streams come into contact toward an orifice, along which the mixture can flow,
means to cause the pressure and temperature of the mixture in the conduit to be such that the substance remains in a compressed state along at least part of the conduit,
a region in downstream communication with the orifice in which region the pressure and temperature conditions are such that the compressible fluid antisolvent substance decompresses and the material is recovered as a solid.
Preferably in its compressed state the substance is in a compressible fluid antisolvent state.
In a preferred embodiment of this invention the compressible fluid antisolvent substance is in a supercritical fluid state, and when the substance decompresses the substance expands and converts into a gaseous state, and the material is recovered as a solid.
Therefore in this preferred embodiment of the process of the invention, a process for using a supercritical fluid in the production of particles of a material is provided wherein:
a stream of a dispersion of the material in a solvent and a stream of a supercritical fluid substance are brought into contact with each other so that the streams combine to form a mixture under conditions such that the substance is in a supercritical fluid state,
the mixture is then caused to flow along a conduit extending downstream from the region where the streams come into contact, toward an orifice opening from the conduit, the pressure and temperature of the mixture in the conduit being such that the substance remains in a supercritical fluid state over at least part of the length of the conduit,
then the mixture is caused to flow into a downstream region in which the pressure and temperature conditions are such that the substance converts into a gaseous state and the material is isolated in a particulate state.
An apparatus is also provided for performing this preferred process, comprising:
means for bringing a stream of a dispersion of the material in a solvent and a stream of a supercritical fluid substance into contact with each other such that the streams combine to form a mixture under conditions such that the substance is in a supercritical fluid state,
a conduit extending downstream from the region where the streams come into contact toward an orifice, along which the mixture can flow,
means to cause the press
Avontuur Petrus Paulus Cornelis
Merrifield David Roy
Souter Andrew Robert
Valder Christopher Edmund
Warr John Peter
Dinner Dara L.
Kinzig Charles M.
SmithKline Beecham plc
Theisen Mary Lynn
Venetianer Steven
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