HK1063440B - Apparatus and method for micron and submicron particle formation - Google Patents

Description

Apparatus for forming micron and submicron particles and method thereof

Technical Field

The present invention relates to an apparatus and method for forming very fine compound particles by fluid anti-solvent precipitation (anti-solvent precipitation). More particularly, but not exclusively, the invention relates to a method of forming small protein particles, for example for pharmaceutical use.

Background

Many industries have interest in producing micron and sub-micron particles for different applications. The need for apparatus and methods for producing micron and submicron particles is particularly apparent in the pharmaceutical field.

There are several reasons for using fine powdered drugs in pharmacology, such as the need to improve bioavailability or the need for specific drug types such as nasal, ophthalmic, injectable and modified release (release), among others.

Conventional methods of particle size reduction, such as grinding, milling, spray drying and freeze drying, have a number of disadvantages, particularly with respect to the principle of biological activity. For example, in the initial stages of freeze-drying, pharmaceutical proteins, buffering organisms and other components tend to concentrate resulting in changes in pH and ionic strength; this may result in protein denaturation. The major limitations of this approach to spray drying are the inherent high cost, thermal degradation, and low efficiency due to low yield and high residual moisture.

In the last decade, different processes have been proposed for the formation of micron and submicron particles by Supercritical fluid (Supercritical fluid) techniques, such as Supercritical Solution Rapid Expansion of RESS, GAS-anti-Solvent recrystallization GAS, Solution Enhanced Dispersion with Supercritical Solution (SEDS), and PGSS.

These methods have received a great deal of attention because uniform particles with diameters less than 1 micron can be obtained. In addition to the fact that these processes allow very good control of the size and morphology of the powder, the compound avoids mechanical and thermal shocks and the powder obtained does not contain any solvent.

Two processes for obtaining fine particles by supercritical fluids are highly regarded: supercritical solution rapid expansion method (RESS) (see Tom, j.w., Debenedetti, p.g., "The formation of bioorganic polymeric microspheres and micro particles by rapid expansion of supercritical fluids" biotechnolog. prog.1991, 7, 403-.

In the supercritical solution rapid expansion process (RESS), the substance used is dissolved in a supercritical fluid and the solution is sprayed through a nozzle into a particle formation vessel: the rapid expansion of the supercritical solution causes the solute to precipitate. In some applications, it is possible to add a subcritical (subcritical) solvent regulator to the supercritical fluid.

One disadvantage of this technique is that even with the use of a conditioning agent, only a few compounds are sufficiently soluble in the supercritical fluid. In addition, the rapid expansion of the supercritical solution through the nozzle causes the condensation of the supercritical fluid and the clogging of the nozzle.

In GAS anti-solution recrystallization (GAS), the solute used is dissolved in a liquid solvent miscible with the supercritical fluid, but the solute cannot be dissolved in the supercritical fluid.

The solution is sprayed through a nozzle into a particle formation vessel that is pressurized by a supercritical fluid. The rapid and delicate contact between the solution and the supercritical fluid causes the solvent to separate from the solution in the supercritical fluid and causes the solute to precipitate out as fine particles. It is possible to increase the solubility of liquid solvents in supercritical fluids using modifiers. GAS anti-solution recrystallization (GAS) overcomes the disadvantages of the Rapid Expansion of Supercritical Solution (RESS) and allows for better control of process parameters.

The key step of GAS anti-solution recrystallization (GAS) is the mixing of the solution with a supercritical fluid: to obtain fine and rapid mixing, it is required that the solution be dispersed in the supercritical fluid in small droplets. Various devices have been proposed for injecting the solution and supercritical fluid into the particle formation vessel to achieve good mixing.

The earliest used simple capillary nozzles with diameters between 0.1mm and 0.2mm (see Dixon, D.J. and Johnston, K.P, Formation of microporus polymer fibers and fibers by precision precipitation with a compressed fluid emulsion, J.App.Polymer Sci., 50, 1929-.

Such a device exhibits a high pressure drop along its length, resulting in poor conversion of pressure to kinetic energy at the capillary outlet.

Debenedetti p.g., Lim g.b., and Prud' Homme R.K (see U.S. patent 006063910, 5/16/2000) use GAS anti-solvent recrystallization (GAS) to form protein microparticles. In this example, the protein solution was sprayed through a laser drilled platinum disk with a diameter of 20 microns and a length of 240 microns into a particle formation vessel containing supercritical fluid injected through the other inlet. The laser drilled platinum disk had an outer diameter of 3mm, a thickness of 0.24mm and a nozzle diameter of 20 microns. This technique has been used to form catalase (catalase) and insulin (0.01% w/v) from ethanol/water (9:1v/v) solutions using carbon dioxide as a supercritical fluid. These experiments were carried out at 8.8MPa and 35 ℃; the flow rate of the supercritical fluid was about 36 g/min and the flow rate of the solution was about 0.35 cc/min.

Laser drilling of the disc brings a major advantage over capillary nozzles: the ratio of the length and diameter of the nozzle is such that the pressure drop is minimal and the energy pressure is almost entirely converted to kinetic energy; in this way, very high solution flow rates and very small droplets can be obtained.

In this method, the inlet of the supercritical fluid is not optimized: solution injection occurs under an almost static supercritical fluid atmosphere with low turbulence.

Subramaniam B, Saim S, Rajewskj R.A. and Stella V. (see Methods for particle atomization and ionization by systematic ionization from organic sources specific for each of the particles contained in the particle-forming vessel, U.S. Pat. No. 5,74029, 23.2.1999) disclose the use of a commercial coaxial converging-diverging (convergent-divergent) nozzle to inject the solution into the particle-forming vessel. The nozzle has a converging-diverging passageway for gas expansion and an internal coaxial capillary tube. The solution injected through the capillary is energized by the expanding gas. The gas expanding in the converging-diverging nozzle may reach supersonic velocities.

The transition from subsonic to supersonic velocity in the nozzle results in the formation of a Mach (Mach) disk which promotes dispersion of the solution and mixing between the solution and the supercritical fluid. Subramaniam et al propose an inert gas such as helium or a supercritical fluid as an energizing gas (energizing gas). In the cited examples, the authors employed a supercritical fluid as the energized gas.

Although very high energized gas pressure drops, about 40MPa, were required to achieve supersonic velocities, the inventors operated under milder conditions which employed pressure drops of about 40 bar, i.e. 4MPa, so they failed to achieve supersonic velocities. Nevertheless, they claim a significant improvement over traditional GAS anti-solution recrystallization (GAS).

Experimentally, they recrystallized hydrocortisone (hydrocortisone) and camptothecin (camptothecin) to obtain powders ranging from 0.5 μm to 1 μm nanoparticles.

One advantage of this technique is that supercritical fluids improve the ejection of the solution in order to obtain very fine droplets; another advantage is that in a very small region at the outlet of the nozzle, a fine mixing of the solution and the supercritical fluid takes place.

A disadvantage of this technique is that the solution and supercritical fluid mix before entering the particle formation vessel: this condition results in the formation of particles before the fluid enters the particle formation vessel and thus causes the nozzle to become clogged.

Hanna m. and York p. (see international patent 96/00610, 1996, 1/11) propose a new method and a new device to obtain very small particles by supercritical fluid technology called solution-enhanced dispersion with supercritical solution (SEDS).

This process is based on a new coaxial nozzle: the solution was expanded through an internal capillary of 0.25mm diameter; the supercritical fluid expands through an outer coaxial passageway having a tapered end; the diameter of the tapered region at the tip is about 0.2 mm. Mixing between the supercritical fluid and the solution occurs in this tapered region. They also propose the use of a three-way nozzle: a modifier may be added in the added pathway to improve mixing. They employ solution-enhanced dispersion with supercritical solution (SEDS) to precipitate small particles of water-soluble compounds, i.e. sugars such as lactose, maltose, trehalose (trehalase) and sucrose and proteins such as R-TEM beta lactonase.

A conditioning agent, such as methanol or ethanol, is introduced into the particle formation vessel with the solution or through a different inlet.

Such a nozzle can mix the supercritical fluid and the solution well and finely: initial contact of the supercritical fluid and the solution occurs at the end of the cone and the two fluids are ejected from the nozzle outlet at high velocity, the supercritical fluid imparting energy to the liquid solution to disperse it into small droplets in the particle formation vessel.

A disadvantage of this technique is the contact between the supercritical fluid and the solution prior to entering the particle formation vessel; precipitation of the powder may occur in the nozzle and eventually lead to nozzle clogging.

The velocity of the supercritical fluid at the nozzle exit is limited by the large diameter of the nozzle.

British patent GB-a-2322326 provides an improved apparatus for forming particles by the SEDS technique. The apparatus comprising a particle formation vessel and means for introducing a solution of a substance and a supercritical fluid into said particle formation vessel, said means comprising a nozzle having respective passages for the solution and supercritical fluid and separate outlets at downstream ends of the respective passages, whereby in use contact of the solution and supercritical fluid initially occurs in the particle formation vessel downstream of the separate outlets.

Disclosure of Invention

The term "supercritical fluid" means a fluid at or above a critical pressure and temperature.

The term "solvent" means a liquid that is capable of forming a solution with a substance.

The term "substance" means a pharmaceutically acceptable solid that is soluble in a solvent and substantially insoluble in a supercritical fluid.

The term "conditioning agent" means a chemical agent that enhances the solubility of a solvent in a supercritical fluid.

It is an object of the present invention to overcome the above-mentioned disadvantages of the prior art.

In particular, it is an object of the present invention to provide a process for obtaining a fine powder of a substance and an apparatus for producing a fine mixture of a solution of a substance and a supercritical fluid.

Viewed from one aspect the present invention provides apparatus for forming micron and sub-micron particles of a substance by employing GAS anti-solution recrystallisation (GAS), the apparatus comprising a particle formation vessel and means for introducing the substance and a supercritical fluid into said particle formation vessel, said means comprising a nozzle having respective passageways for the solution and supercritical fluid and separate outlets located at the downstream ends of the respective passageways, whereby in use contact of the solution and supercritical fluid initially occurs in the particle formation vessel downstream of the separate outlets, wherein an upstream portion of the passageways having a large diameter provides a supply for a downstream portion having a small diameter.

Viewed from a further aspect the invention provides a nozzle for introducing a solution of a substance and a supercritical fluid into a particle formation vessel and forming micron and submicron particles by employing GAS anti-solution recrystallisation (GAS) method, the nozzle having respective passages for the solution and supercritical fluid and separate outlets located at downstream ends of the respective passages, whereby in use, contact of the solution and supercritical fluid initially occurs in the particle formation vessel downstream of the separate outlets, wherein an upstream portion of the passages having a large diameter feeds a downstream portion having a small diameter.

Viewed from a further aspect the invention provides a process for forming micron and sub-micron particles by employing GAS anti-solvent recrystallisation (GAS) which comprises delivering a supercritical fluid and solution, neat or mixed with a conditioning agent, through a nozzle at controlled pressure and temperature to a particle formation vessel whereby solvent is separated from solution by the supercritical fluid and precipitation of micron and sub-micron particles occurs, wherein the supercritical fluid and solution are fed through respective passages in the nozzle and discharged via separate outlets located at the downstream ends of the respective passages, and contact of the solution and supercritical fluid initially occurs in the particle formation vessel downstream of the separate outlets, wherein upstream portions of the passages having large diameters are fed to downstream portions having small diameters.

The process according to the invention comprises co-introducing a solution or suspension of the substance in a solvent, a supercritical fluid and, preferably, a conditioning agent into a particle formation vessel. The regulator is a compound soluble in the solvent and the supercritical fluid. The modifier is used when the solvent is substantially immiscible with the supercritical fluid or has low solubility.

The use of a modifier allows better mixing between the solution and the supercritical fluid when the solubility of the solvent in the supercritical fluid is low.

When a modulator is used, the ratio of the modulator flow rate to the solution flow rate must be selected so that there is a significant increase in the solubility of the solvent in the supercritical fluid. The conditioning agent may be introduced with the supercritical fluid, or with the solution, or partially with the supercritical fluid and partially with the solution; the manner in which the conditioning agent is introduced severely affects the extraction of the solvent and the shape of the particles formed.

For the precipitation of starch powder from aqueous solutions using carbon dioxide as the supercritical solvent and ethanol as the conditioning agent, the ratio of the flow rate of the supercritical fluid to the flow rate of the conditioning agent is about 7, while the ratio of the flow rate of the conditioning agent to the flow rate of the solution is about 20.

Thus, in one instance, the solution of the substance and the mixture of supercritical fluid and conditioning agent are introduced separately into the particle formation vessel. Alternatively, the conditioning agent may be mixed with the solution prior to introduction. In another aspect of the process, the conditioning agent is introduced into the particle formation vessel partially with the supercritical fluid and partially with the solution.

If the solvent is immiscible with the supercritical fluid, the solution of the substance in the solvent and the supercritical fluid are separately introduced into the particle formation vessel where mixing of the supercritical fluid with the solution occurs and the solvent is extracted by the supercritical fluid.

Preferably, the substance is a pharmaceutical compound that is soluble in the solvent and the modifying agent and substantially insoluble in the supercritical fluid.

In the particle formation vessel, the solution is mixed with a supercritical fluid and a compound of a conditioning agent, or with a pure supercritical fluid. In this way, the solvent is extracted from the solution and the material precipitates as fine particles.

The key point of the process for forming fine particles is the mixing of the solution with the supercritical fluid: the rapid and fine mixing allows the particles to settle in small diameters and high powder yields can be obtained.

To achieve good mixing, the solution must be dispersed into the supercritical fluid in the form of small droplets, thus providing a high interfacial area for mass transport and a short path for diffusion of the supercritical fluid in the solution droplets, thereby preventing growth of solute particles. In addition, increasing the mass transfer rate between the solution and the supercritical fluid allows operation under mild temperature and pressure conditions. The present invention allows such operation.

Furthermore, the high ratio between the flow rate of the supercritical fluid and the flow rate of the solution allows for a large excess of supercritical fluid to be generated relative to the solution upon their contact, thereby improving the driving force for mass transport of the supercritical fluid into the solution and of the solute into the supercritical fluid.

As noted above, in order to obtain very small droplets of solution, it is necessary that the solution be well dispersed into the supercritical fluid.

The size of the solution droplets formed is determined by the hydrodynamic conditions of the mixing zone and the physical properties of the solution and supercritical solvent, such as viscosity coefficient, surface tension and density. These properties are greatly influenced by the temperature and pressure of the supercritical fluid.

The velocity of the solution and supercritical fluid at the nozzle exit is related to the mass flow rate and the diameter of the exit. In addition, the energy pressure of the solution and supercritical fluid must be converted to kinetic energy with minimal energy loss.

A new nozzle was designed to achieve this goal.

The solution and supercritical fluid, neat or mixed with a conditioning agent, are introduced into the particle formation vessel in a co-current flow through a nozzle that provides distinct outlets for the supercritical fluid and the solution. The contacting of the solution and supercritical fluid initially occurs in a particle formation vessel located downstream of the separate outlet. This minimizes the potential for nozzle blockage by the formed particles. The respective effluents of the supercritical fluid and the solution can be expanded and mixed with each other in the particle formation vessel.

The nozzle body has passages for respective fluids, including a large diameter upstream portion that feeds a small diameter downstream portion. The downstream portion may be short in order to reduce the pressure drop along this portion to better achieve the conversion of pressure into kinetic energy. This overcomes the problems of the nozzles employed in the prior art, which are essentially of a coaxial tubular design, wherein a small diameter is maintained along the entire length of the nozzle, resulting in a significant pressure drop.

The outlets are preferably adjacent to each other, e.g. 3mm from the centre line. The outlet is preferably male.

Preferably, the outlet has a central outlet and a plurality of outer outlets. The central outlet may be for delivery of the supercritical fluid. By providing multiple external outlets, mixing of the supercritical fluid and solution is facilitated. Preferably, the outer outlets are arranged at the same distance from the central outlet. They may therefore lie on the same radius and are preferably equally angularly spaced. This also aids in mixing.

The outlet may be located at the end of a separate pipe or the like. The outlet is preferably formed at the end of the downstream direction of each passage through the nozzle body. The vias may be laser drilled, for example. The nozzle body may be a disc. A preferred arrangement therefore comprises a nozzle in the form of a disc having a centrally located outlet and two or more circumferentially equidistantly spaced outlets equidistant from the centre. All of the outlets communicate with the interior of the particle formation vessel. The solution is preferably introduced into the particle formation vessel through a central outlet, while the supercritical fluid, pure or mixed with the conditioning agent, is introduced through an outer outlet.

The passageway in the nozzle body has an upstream end which, in use, serves to deliver the supercritical fluid and solution respectively. Preferably, the nozzle body is formed with a seal for sealingly separating the respective upstream ends of the passages through the nozzle body. The use of a nozzle body thus allows passageways of a desired size to be formed by drilling or otherwise forming to optimize the flow of fluid, while the passageways may be sealed from each other at their upstream ends. In the case of a central outlet and a plurality of radially outwardly spaced outlets, the seal may be annular, for example an O-ring, and disposed radially outwardly of the central outlet and radially inwardly of the plurality of radially outwardly spaced outlets. Another annular seal is preferably formed outside the plurality of radially outer outlets. Preferably, each seal is embedded within a recess, such as an annular recess, of the nozzle body.

The outlet is preferably formed downstream of the end of the tapered portion of the nozzle. The passageway may be formed with a tapered portion. Thus, the passageway may have a relatively large diameter upstream portion, e.g. 1mm, followed by a tapered portion to a smaller diameter portion, e.g. 20 microns. The small diameter portion is referred to herein as an orifice. The large diameter portion and the tapered portion may be formed by, for example, mechanical drilling, and the small diameter portion or the small hole may be drilled by laser. The length of the large diameter portion is significantly greater than the length of the orifice, thus allowing the nozzle body to be relatively thick in the direction of flow, e.g., 5mm, and thus easy to operate without causing the orifice to have an excessively long length. The length of the large diameter portion may be, for example, at least 5 times, preferably 10 times, greater than the length of the aperture.

In another design, the small hole with a small diameter may extend the full length of the nozzle body, but this design is not preferred as the nozzle body will have to be thin in the direction of the liquid flow and difficult to handle.

Thus, expansion of the solution and supercritical fluid occurs downstream of the orifice. Preferred apertures are characterized by a length to diameter ratio of 5 to 10. It has advantages of minimizing pressure energy loss on the capillary tube and efficiently converting pressure energy into kinetic energy.

The nozzle preferably has an orifice of diameter 0.02mm to 0.1mm, more preferably 0.02mm to 0.04mm, and a length 0.1mm to 0.2 mm. This size allows very high velocities of the solution and supercritical fluid to be achieved at the exit of the orifice.

In a preferred embodiment, the plurality of supercritical fluid outlets are arranged around the solution outlet and at a very short distance, about 3 mm: this configuration allows the solution to be energized by the supercritical fluid, thus promoting dispersion of the solution into very small droplets, and providing a high interfacial surface between the two phases and rapid extraction of the solvent into the supercritical fluid. These phenomena are particularly effective when the supercritical fluid velocity reaches or exceeds sonic velocity at the outlet. When the supercritical fluid velocity reaches or exceeds the speed of sound, a mach disk is formed which causes the solution to disperse into very fine droplets. This phenomenon is well known and widely used in the supercritical solution Rapid expansion process (RESS) (see Matson d.w., fusion j.l., Petersen r.c., Smith r.d., "Rapid expansion of supercritical fluids solutions: solutions for powders, in films, and fibers" ind. eng. chem. res., 1987, 26, 2298-.

Although the supercritical fluid velocity is small, it is of the order of sonic velocity, and thus a significant enhancement in solution dispersion is obtained (see subramanian b., Saim s., Rajewskj r.a., Stella v., Methods for particulate atomization and ionization from organic soluble inorganic particulate, us patent 5874029, 23/2/1999).

It is known that the downstream pressure, often referred to as the critical pressure, at which a supercritical fluid reaches sonic velocity, has the following relationship to the upstream pressure as the actual fluid adiabatically expands through a converging-diverging nozzle:

wherein P is the upstream pressure, P_cK is the specific heat C of the supercritical fluid at normal pressure_pAnd specific heat C under constant capacity_vThe ratio therebetween. For example, if the supercritical fluid is carbon dioxide, which k is 4.81, and if the downstream pressure is 10MPa, then to achieve sonic velocity, the upstream pressure must be 38.4MPa, i.e. a pressure drop of 28.4MPa is required.

However, for a downstream pressure of 10MPa, it is possible to achieve supercritical fluid velocities on the order of sonic velocity with a pressure drop of 4MPa at 40 ℃.

The speed of sound of a fluid is strongly dependent on pressure and temperature: the minimum value of the sound velocity of carbon dioxide in the supercritical region is 208 m/s under the conditions of 8MPa and 40 ℃. To obtain the advantages of the above phenomena, it is easy to work under these operating conditions when carbon dioxide is used as the supercritical fluid.

The preferred nozzle for use in the apparatus of the present invention has a small hole that is laser drilled. At the orifice exit, the velocity of the supercritical fluid can be estimated from the energy balance between the supercritical fluid path portion (portion 1) upstream of the orifice and the orifice exit portion (portion 2). The energy balance with neglected energy loss can be calculated by the following formula:

H₁+1/2ρ₁υ₁ ²＝H₂+1/2 ρ₂υ₂ ²

wherein H₁And H₂Specific enthalpy of the supercritical fluid at the upstream and downstream of the orifice, respectively; rho₁And ρ₂The density of the supercritical fluid at the upstream and downstream of the orifice, respectively; upsilon is₁And upsilon₂The velocity of the supercritical fluid upstream and downstream of the orifice, respectively.

For the formation of fine powders from aqueous solutions by GAS anti-solution recrystallization (GAS) using carbon dioxide as the supercritical solvent and ethanol as the modifier, it has been found that the optimum operating conditions are a pressure in the range of 8 to 12MPa and a temperature in the range of 35 to 50 ℃. In the experimental apparatus for performing the experimental test, the mass flow rate of the supercritical fluid was 30 g/min, the flow rate of the solution was 0.2 g/min, the mass flow rate of the regulator was 4 g/min, the ratio of the mass flow rates of the supercritical fluid and the regulator was set to 7, the ratio of the mass flow rates of the regulator and the solution was 20, and the velocity of the supercritical fluid at the outlet of the nozzle was about 300 m/sec.

The pressure in the particle formation vessel is between the critical pressure of carbon dioxide and 30MPa, more preferably between 8MPa and 12MPa, and the temperature in the particle formation vessel is between 30 ℃ and 80 ℃, more preferably between 40 ℃ and 50 ℃.

The ratio between the mass flow rates of carbon dioxide and the regulator is between 2 and 40, preferably between 6 and 8, and the ratio between the mass flow rates of the regulator and the aqueous solution is between 5 and 40, preferably between 10 and 25.

As a comparative example as described above, the supercritical fluid may be ethane, ethylene, propane, sulfur hexafluoride, nitrous oxide, chlorotrifluoromethane, monofluoromethane, xenon, and mixtures thereof; the solvent of the solution of the pharmaceutical compound may be a solvent immiscible with the supercritical fluid, such as ethanol, methanol, dimethyl sulfoxide (DMSO), isopropanol, acetone, Tetrahydrofuran (THF), acetic acid, glycol, polyethylene glycol, N-dimethylaniline. The same solvents can be used for the modulator when aqueous solutions of the pharmaceutical compounds are used.

Drawings

Certain preferred embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic flow diagram of an apparatus for performing a process according to the present invention;

FIG. 2 shows a schematic area of a nozzle for performing the process according to the present invention, taken along line A-A in FIG. 3, with portions of the nozzle shown enlarged in circles;

FIG. 3 illustrates a region of the nozzle taken along line B-B in FIG. 2;

FIGS. 4 and 5 show more detailed views similar to FIGS. 2 and 3, respectively;

FIG. 6 shows a cross-sectional view of a nozzle design;

FIGS. 7 and 8 show Scanning Electron Microscope (SEM) microscope lenses of SIGMA alkaline phosphatase (ALP) prepared under the conditions of example 1;

FIGS. 9, 10 and 11 show Scanning Electron Microscope (SEM) microscope lenses of SIGMA lysozyme prepared under the conditions of example 2;

FIGS. 12 and 13 show microscope slides of trehalose prepared under the conditions of example 3; and

figure 14 shows the particle size distribution of trehalose prepared under the conditions of example 3.

Detailed Description

Referring to fig. 1, the apparatus shown includes a particle formation vessel 22. This is a standard reaction vessel with a suitable volume. The temperature in the vessel is kept constant by a heating jacket (heating jack) 21. The pressure in the vessel is controlled by a micro metering valve 25.

The temperature and pressure within the particle formation vessel are measured by thermocouple 29 and pressure transducer 30.

The formed particles are screened through a filter 23. This is a stainless steel basket with a bottom consisting of a 0.5 micron sintered stainless steel disc. A second 0.5 micron filter 24 is placed at the outlet of the vessel.

Supercritical fluid is withdrawn from cylinder 3, condensed by condenser 4 and pumped by pump 8 through line 34 to the particle formation vessel. The supercritical fluid is heated to a desired temperature by preheater 14 and heater 17 before entering the particle formation vessel. The preheater 14 also serves as a pulsation damper (pulsation damper). The supercritical fluid is also filtered through a 0.5 micron filter 15.

The temperature and pressure of the supercritical fluid before entering the precipitation vessel are measured by thermocouple 28 and pressure transducer 43, respectively.

The conditioning agent is withdrawn from tank 2, it is pumped by pump 9 to line 34 and mixed with the supercritical fluid before entering the particle formation vessel. The conditioning agent is also filtered through a 0.5 micron filter 12.

The line 34 is fitted with a relief valve 16.

The solution is withdrawn from tank 1 and it is pumped by pump 10 via line 6 to the particle formation vessel. The solution was also filtered through a 0.5 micron filter 13.

In another version of the process, the conditioning agent may be introduced into the particle formation vessel, in part with the solution and in part with the supercritical fluid.

Supercritical fluid and solution, neat or mixed with a conditioning agent, are delivered to particle formation vessel 22 through nozzle 27.

Downstream of particle formation vessel 22, the supercritical fluid, conditioning agent and solvent mixture is filtered through 0.5 micron filter 24 to screen out particles that have not been previously filtered out by filter 23. The mixture of the supercritical fluid, the regulator and the solvent is decompressed by the micro metering valve 25, and the supercritical solvent is separated from the regulator and the solvent in the separator 26, and its flow rate is measured by the mass flow meter 31 and discharged.

Figures 2 and 3 show a nozzle for performing the process according to the invention. This nozzle is a distinct feature of the process according to the present method.

The nozzle may introduce the solution and the supercritical fluid neat or mixed with the conditioning agent into the particle formation vessel in a co-current flow.

The nozzle provides respective outlets for the supercritical fluid and the solution. The nozzle may be constructed of stainless steel or other suitable material.

The nozzle 27 has a nozzle body shaped as a disk 36 and has a centrally located orifice 39 and two or more circumferentially evenly spaced orifices 41 that are equidistant from the center. The pores communicate with the interior of the particle formation vessel. The solution is introduced into the particle formation vessel through the central orifice, while the supercritical fluid, pure or mixed with a conditioning agent, is introduced into the particle formation vessel through the outer orifices.

The passageway 37 for the solution comprises a hole having a diameter D3. The end of the bore has a taper 40. At the bottom discharge port of the conical tip 40 is a laser drilled orifice 39. The length L1 of the aperture is 5 to 10 times its diameter D1. The diameter D1 may be selected in such a way as to achieve any desired solution velocity at the orifice outlet.

The passageway 38 for the supercritical fluid is a hole having a diameter D4. The end of each hole has a taper 42. At the bottom discharge opening of the conical tip 42 there is a laser drilled orifice 41. The length L2 of the aperture is 5 to 10 times its diameter D2. Diameter D2 may be selected in such a way as to achieve any desired supercritical fluid velocity at the orifice exit.

The ratio between the length L1 or L2 and the diameter D1 or D2 of the orifices 39 and 41 is chosen so as to minimize energy losses and to obtain higher velocities by converting energy pressure into kinetic energy.

Detailed views of the nozzle used in the present invention are shown in fig. 4 and 5. Small holes may be drilled to a minimum of up to 0.02mm in diameter. Nozzles that have been used to perform experimental tests have small holes with diameters of 0.02mm to 0.04 mm.

In another embodiment of the invention, one or more of the outer apertures are drilled in such a way that their axes converge on the axis of the central aperture. The angle formed by the axis of the outer porthole and the axis of the central porthole is comprised between 1 deg. and 30 deg..

The upper surface of the disc 36 of the nozzle 27 is formed with an inner annular groove 50 surrounding the inlet end of the central passage 37 and an outer annular groove 52 surrounding the inlet end of the passage 38.

Fig. 6 shows an assembly structure of the nozzle 27. The annular groove 50 of the disk 36 is embedded with a first O-ring seal 54 and the outer annular groove 52 is embedded with a second O-ring seal 56. The disk 36 is embedded in a cup 58, and the cup 58 is further embedded with a nozzle block (puzzle block)60, a lower end face of the nozzle block 60 being engaged with the second O-ring 56. The nozzle block 60 is formed with a central bottom chamber 62 at the bottom region of its length, the chamber 62 communicating at its top end with lateral chambers 64. The nozzle block 60 is formed with a central top cavity 66 at the top region of its length. A nozzle cartridge (nozzle brush) 68 extends along the central top chamber 66 and the central bottom chamber 62 and has a bottom end face that engages the first O-ring seal 54. The nozzle barrel 68 is formed with a central barrel bore 70. Another seal (not shown) is typically formed around nozzle cartridge 68 to seal the top of nozzle block 60.

In use, liquid solution is delivered to central bore 70 and flows through disc 36 to the inlet end of central passage 37. The junction between the central bore 70 and the disk 36 is sealed with a first O-ring seal 54. Supercritical fluid, optionally containing a conditioning agent, is delivered to lateral chamber 64 in communication with central bottom chamber 62 and flows through disk 36 to passage 38. The junction between the central bottom cavity 62 and the passageway 38 is sealed on the inside with a first O-ring seal 54 and on the outside with a second O-ring seal 56.

The solution is ejected from the central orifice 39 at high speed and disperses fine droplets that will come into contact with the supercritical fluid. If the velocity of the supercritical fluid is very high, on the order of sonic velocity at the temperature and pressure conditions of operation, the dispersion of the solution liquid spray is greatly enhanced by the supercritical fluid being ejected from the small holes 41. The role of the supercritical fluid to enhance dispersion of the liquid jet of solution is critical and determines the shape, size and yield of the product.

Experimental procedure

The supercritical fluid is delivered to the precipitation vessel by pump 8, and pump 8 can set the flow rate of the supercritical fluid. The temperature of the supercritical fluid flowing in line 35 is set to a higher temperature than the inside of the particle formation vessel by heater 17 in consideration of the decrease in temperature due to expansion through the nozzle orifice. The conditioning agent is then added to the supercritical fluid by pump 9 at a predetermined flow rate. When steady state conditions are achieved, the solution is pumped by pump 10 into the particle formation vessel.

After a certain amount of solution has been fed to the particle formation vessel, pumps 9 and 10 are stopped and only supercritical fluid is fed to the particle formation vessel until the precipitated powder is completely desolventized and conditioned.

The particle formation vessel is depressurized and the powder is recovered.

Examples

The following examples were carried out using the process according to the invention. The apparatus used was similar to that shown in figure 1.

First embodiment

Preparation of alkaline phosphatase (ALP) particles

In the examples, the method of the present invention was used to prepare protein powders by alkaline phosphatase.

A0.2% w/w solution of alkaline phosphatase, manufactured by SIGMA Chemicals, in deionized water was used. Carbon dioxide and ethanol are used for the supercritical fluid and the regulator, respectively.

The solution is fed into particle formation vessel 22 by pump 10 at a flow rate of 0.2 grams per minute. Supercritical carbon dioxide was fed by pump 8 at a flow rate of 30 grams per minute and ethanol was fed by pump 9 at a flow rate of 4 grams per minute into line 34 and mixed with the supercritical fluid prior to entering the particle formation vessel.

The supercritical fluid was injected into the particle formation vessel through four outer orifices of the nozzle, each having a diameter of 0.04 mm. The solution was injected into the particle formation vessel through a central orifice of 0.04mm diameter of the nozzle. All the holes are 0.2mm in length.

The temperature and pressure in the particle formation vessel were maintained at T-40 ℃ and P-10.0 MPa. The precipitated particles are collected on the filter 23 at the bottom of the particle formation vessel, while the supercritical fluid, the regulator and water are collected into the cylinder 26 at atmospheric pressure.

The solution and the supercritical carbon dioxide mixed with the conditioning agent are delivered for 240 minutes and after the solution delivery is stopped, pure carbon dioxide is fed into the particle formation vessel in order to extract residual solvated conditioning agent from the precipitated powder. Typically, to obtain a dry powder, twice the volume of carbon dioxide is used to flush the particle forming vessel.

After depressurization, the particle-forming vessel was opened and the powder was recovered.

The yield of recovered powder was about 70%.

The micrographs of the scanning electron microscope shown in fig. 7 and 8 show that the powder obtained has a nominal diameter of less than 1 μm and has a narrow size distribution.

The residual enzymatic activity of alkaline phosphatase was found to be 90% compared to the unprocessed commercial reagent.

Second embodiment

Preparation of lysozyme particles

In this example, the method of the present invention was used to prepare protein powder by lysozyme.

The lysozyme used was a solution of 0.2% w/w lysozyme, produced by SIGMA Chemicals, dissolved in deionized water. Carbon dioxide and ethanol are used for the supercritical fluid and the regulator, respectively.

The solution is fed into particle formation vessel 22 by pump 10 at a flow rate of 0.2 grams per minute. Supercritical carbon dioxide was fed by pump 8 at a flow rate of 30 grams per minute and ethanol was fed by pump 9 at a flow rate of 4 grams per minute into line 34 and mixed with the supercritical fluid prior to entering the particle formation vessel.

The supercritical fluid was injected into the particle formation vessel through four outer orifices of the nozzle, each having a diameter of 0.04 mm. The solution was injected into the particle formation vessel through a central orifice of 0.04mm diameter of the nozzle. All the holes are 0.2mm in length.

The temperature and pressure in the particle formation vessel were maintained at 40 ℃ and 10.0MPa, respectively.

The precipitated particles are collected on the filter 23 at the bottom of the particle formation vessel, while the supercritical fluid, the regulator, water and finally the non-precipitated solute are collected in the cylinder 26 at atmospheric pressure.

After a certain amount of solute is fed into the particle formation vessel, pumps 9 and 10 are stopped, and only supercritical fluid is fed into the particle formation vessel in order to dry the precipitated powder: typically, twice the volume of supercritical fluid as the particle formation vessel is required to obtain a dry powder.

At this point, the particle formation vessel may be depressurized and the powder opened and recovered.

The yield of recovered powder was 90%.

The micrographs of the scanning electron microscope shown in fig. 9, 10 and 11 show that the powder obtained has a nominal diameter of less than 1 μm and has a narrow size distribution.

The residual enzymatic activity of alkaline phosphatase was found to be 90% compared to the unprocessed commercial reagent.

Third embodiment

Preparation of trehalose granules

In this example, the process of the invention was used to prepare protein powder from trehalose.

The lysozyme used was a 2% w/w solution of 2% lysozyme, produced by SIGMA Chemicals, Inc., in deionized water. Carbon dioxide and ethanol are used for the supercritical fluid and the regulator, respectively.

The solution is fed into particle formation vessel 22 by pump 10 at a flow rate of 0.2 grams per minute. Supercritical carbon dioxide was fed by pump 8 at a flow rate of 30 grams per minute and ethanol was fed by pump 9 at a flow rate of 4 grams per minute into line 34 and mixed with the supercritical fluid prior to entering the particle formation vessel.

The supercritical fluid was injected into the particle formation vessel through four outer orifices of the nozzle, each having a diameter of 0.04 mm. The solution was injected into the particle formation vessel through a central orifice of 0.04mm diameter of the nozzle. All the holes are 0.2mm in length.

The temperature and pressure in the particle formation vessel were maintained at 40 ℃ and 10.0MPa, respectively.

The precipitated particles are collected on the filter 23 at the bottom of the particle formation vessel, while the supercritical fluid, the regulator, water and finally the non-precipitated solute are collected in the cylinder 26 at atmospheric pressure.

After a certain amount of solute is fed into the particle formation vessel, pumps 9 and 10 are stopped, and only supercritical fluid is fed into the particle formation vessel in order to dry the precipitated powder: typically, twice the volume of the particle formation vessel is required for the supercritical fluid to obtain a dry powder.

At this point, the particle formation vessel may be depressurized and the powder opened and recovered.

The yield of recovered powder was 80%.

Shown in fig. 12 and 13 are micrographs of the obtained powder by scanning electron microscopy.

The particle size distribution shown in FIG. 14 was determined using an Aerosizer mo.3225(TSI-Amherst) and gives an average size of 1.89 μm.

The present invention can be understood in a broader sense. Thus, according to one broad aspect, the present invention provides apparatus for the formation of micron and submicron particles of a substance by the GAS anti-solution recrystallization method (GAS), comprising a particle formation vessel and means for introducing a solution of the substance and a supercritical fluid into said particle formation vessel, characterised in that said means comprises a nozzle having separate outlets for delivering the solution and supercritical fluid respectively.

According to another broad aspect, the invention provides a nozzle for introducing a solution of a substance and a supercritical fluid into a particle formation vessel for forming micron and submicron particles of the substance by a GAS anti-solution recrystallization (GAS) process, characterized in that the nozzle comprises a central outlet for delivering a flow of the solution and a plurality of outer outlets for delivering a flow of either a pure supercritical fluid or a supercritical fluid mixed with a conditioning agent.

According to yet another broad aspect, the present invention provides a process for forming micron and submicron particles of a substance by a GAS anti-solution recrystallization (GAS) process comprising delivering a supercritical fluid and a solution, neat or mixed with a conditioning agent, through separate inlets of a nozzle into a particle formation vessel at a controlled pressure and temperature, thereby being extracted from solution with the supercritical fluid solvent and producing a precipitate of micron and submicron particles.

Claims (29)

1. An apparatus for forming micron and submicron particles of a substance by a gas anti-solution recrystallisation method, comprising a particle formation vessel (22) and means for introducing a solution of the substance and a supercritical fluid into the particle formation vessel (22), said means comprising a nozzle (27) having passageways (37, 38) for the solution and the supercritical fluid respectively and outlets (39, 41) at the downstream ends of the respective passageways, whereby in use contact of the solution and supercritical fluid initially occurs in the particle formation vessel downstream of the separate outlets, wherein the passageways (37, 38) comprise a large diameter upstream portion feeding a small diameter downstream portion,

wherein the substance is a pharmaceutically acceptable solid, soluble in a solvent and substantially insoluble in a supercritical fluid.

2. The apparatus of claim 1, wherein said nozzle (27) has a central outlet (39) and a plurality of outer outlets (41), said central outlet (39) for delivering a flow of solution and said outer outlets (41) for delivering a flow of pure supercritical fluid.

3. The device according to claim 2, wherein said outer outlets (41) are arranged at the same distance from said central outlet (39).

4. Apparatus as claimed in claim 1, 2 or 3, wherein said respective passageway (37, 38) extends through the nozzle body (36).

5. Apparatus as claimed in claim 4, wherein the nozzle body (36) is formed with a seal (54) for sealingly separating the respective upstream ends of the passages through the nozzle body.

6. The device of claim 5, wherein the seal (54) is embedded in a recess (50) in the nozzle body.

7. The apparatus of claim 1 wherein said outlet (39, 41) is formed downstream of a bottom discharge opening of a tapered conical portion (40, 42) of the nozzle.

8. Apparatus according to claim 1, wherein the outlets (39, 41) are located at the downstream end of each orifice, the diameter of the orifices being between 0.02mm and 0.1mm, and the ratio of the length to the diameter of the orifices being between 5 and 10.

9. The device of claim 8, wherein the diameter of the orifice is between 0.02mm and 0.04 mm.

10. The device according to claim 1, wherein the outlets (39, 41) at the downstream end of each orifice are perforated in such a way that their axes converge, the angle formed between the axes being between 1 ° and 30 °.

11. The apparatus of claim 1, further comprising means for introducing a conditioning agent into the particle formation vessel (22) through said nozzle (27);

wherein the modifier refers to a chemical agent for enhancing the solubility of the solvent in the supercritical fluid.

12. The apparatus of claim 1, wherein the respective outlets deliver a flow of solution mixed with a conditioning agent;

wherein the modifier refers to a chemical agent for enhancing the solubility of the solvent in the supercritical fluid.

13. The apparatus of claim 1, wherein the respective outlets deliver a flow of supercritical fluid mixed with a conditioning agent;

wherein the modifier refers to a chemical agent for enhancing the solubility of the solvent in the supercritical fluid.

14. A nozzle for introducing a solution of a substance and a supercritical fluid in a particle formation vessel for forming micron and submicron particles of the substance by a gas anti-solution recrystallisation process, the nozzle comprising passageways (37, 38) for the solution and the supercritical fluid respectively, and outlets (39, 41) at the downstream ends of the respective passageways, whereby in use contact of the solution and supercritical fluid occurs initially downstream of the separate outlets, wherein the passageways (37, 38) comprise a large diameter upstream portion which feeds a small diameter downstream portion,

wherein the substance is a pharmaceutically acceptable solid, soluble in a solvent and substantially insoluble in a supercritical fluid.

15. Nozzle according to claim 14, comprising a central outlet (39) for delivering a flow of solution and a plurality of outer outlets (41) for delivering a flow of pure supercritical fluid or supercritical fluid mixed with a conditioning agent;

wherein the modifier refers to a chemical agent for enhancing the solubility of the solvent in the supercritical fluid.

16. A process for forming micron and submicron particles of a substance by a gas anti-solution recrystallization method, comprising delivering a supercritical fluid neat or mixed with a conditioning agent and a solution of the substance through a nozzle (27) at a controlled pressure and temperature to a particle formation vessel, whereby solvent is extracted from the solution by the supercritical fluid and precipitation of the micron and submicron particles occurs, wherein the supercritical fluid and solution are delivered through respective passageways (37, 38) in the nozzle and exit the nozzle via outlets (39, 41) located on downstream end faces of the respective passageways, and contact of the solution and supercritical fluid initially occurs in the particle formation vessel downstream of the separate outlets, wherein the passageways (37, 38) comprise large diameter upstream portions which feed small diameter downstream portions,

wherein the substance is a pharmaceutically acceptable solid, soluble in a solvent and substantially insoluble in a supercritical fluid; the modifier refers to a chemical agent for enhancing the solubility of a solvent in a supercritical fluid.

17. The process of claim 16 wherein the solution is mixed with a conditioning agent and introduced into the particle formation vessel.

18. The process of claim 16 or 17, wherein the solution is an aqueous solution containing the pharmaceutical compound, the supercritical fluid is carbon dioxide, and the conditioning agent is ethanol.

19. The process of claim 18, wherein the pressure in the particle formation vessel is between the critical pressure of carbon dioxide and 30MPa, and the temperature in the particle formation vessel is between 30 ℃ and 80 ℃.

20. The process of claim 19, wherein the pressure in the particle formation vessel is between 8MPa and 12 MPa.

21. The process of claim 19, wherein the temperature in the particle formation vessel is between 40 ℃ and 50 ℃.

22. The process of claim 19, wherein the ratio between the mass flow rates of carbon dioxide and the modifier is between 2 and 40 and the ratio between the mass flow rates of the modifier and the aqueous solution is between 5 and 40.

23. The process of claim 22, wherein the ratio between the mass flow rates of carbon dioxide and the modifier is between 6 and 8.

24. The process of claim 22, wherein the ratio between the mass flow rates of the conditioning agent and the aqueous solution is between 10 and 25.

25. The process of claim 22, wherein the velocity of the carbon dioxide at the outlet of the passage is on the order of sonic velocity at the temperature and pressure in the particle formation vessel.

26. The process of claim 16 or 17, wherein the solution comprises a pharmaceutical compound and a solvent soluble in the supercritical fluid selected from the group consisting of ethanol, methanol, dimethyl sulfoxide, isopropanol, acetone, tetrahydrofuran, acetic acid, glycol, polyethylene glycol, and N, N-dimethylaniline.

27. The process of claim 16 or 17, wherein said supercritical fluid is selected from the group consisting of ethane, ethylene, propane, sulfur hexafluoride, nitrous oxide, trifluorochloromethane, monofluoromethane, xenon, and mixtures thereof.

28. The process of claim 16 or 17, wherein the modifier is selected from the group consisting of ethanol, methanol, dimethyl sulfoxide, isopropanol, acetone, tetrahydrofuran, acetic acid, glycol, polyethylene glycol, and N, N-dimethylaniline.

29. The process of claim 16, carried out using any of the apparatuses according to claims 1 to 13.