Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B5/00—Drying solid materials or objects by processes not involving the application of heat
  • F26B5/04—Drying solid materials or objects by processes not involving the application of heat by evaporation or sublimation of moisture under reduced pressure, e.g. in a vacuum
  • F26B5/06—Drying solid materials or objects by processes not involving the application of heat by evaporation or sublimation of moisture under reduced pressure, e.g. in a vacuum the process involving freezing

Definitions

• the present invention relates to a method of controlling nucleation during the freezing step of a freeze drying cycle and, more particularity, to such a method that uses a pressure differential ice fog distribution to trigger a
• the range of nucleation temperatures across the vials is distributed randomly between a temperature near the thermodynamic freezing temperature and some value significantly (e.g., up to about 30°C.) lower than the thermodynamic freezing temperature.
• This distribution of nucleation temperatures causes vial-to-vial variation in ice crystal structure and ultimately the physical properties of the lyophilized product.
• the drying stage of the freeze- drying process must be excessively long to accommodate the range of ice crystal sizes and structures produced by the natural stochastic nucleation phenomenon.
• Nucleation is the onset of a phase transition in a small region of a material.
• the phase transition can be the formation of a crystal from a liquid.
• the crystallization process i.e., formation of solid crystals from a solution
• the crystallization process often associated with freezing of a solution starts with a nucleation event followed by crystal growth.
• Ice crystals can themselves act as nucleating agents for ice formation in sub-cooled aqueous solutions.
• a humid freeze- dryer is filled with a cold gas to produce a vapor suspension of small ice particles.
• the ice particles are transported into the vials and initiate nucleation when they contact the fluid interface.
• the currently used "ice fog” methods do not control the nucleation of multiple vials simultaneously at a controlled time and temperature.
• the nucleation event does not occur concurrently or instantaneously within all vials upon introduction of the cold vapor into the freeze-dryer.
• the ice crystals will take some time to work their way into each of the vials to initiate nucleation, and transport times are likely to be different for vials in different locations within the freeze-dryer.
• implementation of the "ice fog” method would require system design changes as internal convection devices may be required to assist a more uniform distribution of the "ice fog" throughout the freeze-dryer.
• an ice fog is not formed inside the product chamber by the introduction of a cold gas, e.g., liquid nitrogen chilled gas at -196°C, which utilizes the humidity inside the product chamber to produce the suspension of small ice particles in accordance with known methods in the prior art.
• a cold gas e.g., liquid nitrogen chilled gas at -196°C
• These known methods have resulted in increased nucleation time, reduced uniformity of the product in different vials in a freeze drying apparatus, and increased expense and complexity because of the required nitrogen gas chilling apparatus.
• My related invention disclosed in pending Patent Application Serial No. 13/097,219 filed on April 29, 2012 utilizes the pressure differential between the product chamber and a condenser chamber to instantly distribute ice nucleation seeding to trigger controlled ice nucleation in the freeze dryer product chamber.
• the nucleation seeding is generated in the condenser chamber by injecting moisture into the cold condenser. The moisture is injected by releasing vacuum and injecting the moisture into the air entering the condenser. The injected moisture freezes into tiny suspended ice crystals (ice fog) in the condenser chamber.
• the condenser pressure is close to atmosphere, while the product chamber is at a reduced pressure. With the opening of an isolation valve between the chambers, the nucleation seeding in the condenser is injected into the product chamber within several seconds. The nucleation seeding evenly distributes among the super cooled product triggering controlled ice nucleation.
• the larger ice crystals help to achieve consistent nucleation coverage and greatly improve controlled nucleation performance, especially when the product chamber has restriction in gas flow, such as side plates or when the vapor port is located under or above the shelf stack.
• the volume of suspended ice fog in gas form was limited by the condenser volume.
• the physical volume of the condenser is no longer a limitation.
• the thickness of frost can easily be controlled to achieve a desired density of larger ice crystals in the product chamber during nucleation.
• the condensed frost method works with any condensing surface.
• the size of the condensing chamber may be reduced to increase the velocity of the gas in the condenser.
• FIGURE 1 is a schematic view of one embodiment of apparatus for performing the method of the present invention
• FIGURE 2 is a schematic view of a second embodiment of apparatus for performing the method of the present invention connected to a freeze dryer with an internal condenser;
• FIGURE 3 is a schematic view of the second embodiment of the apparatus for performing the method of the present invention connected to a freeze dryer having an external condenser.
• an apparatus 10 for performing the method of the present invention comprises a freeze dryer 12 having one or more shelves 14 for supporting vials of product to be freeze dried.
• a condenser chamber 16 is connected to the freeze dryer 12 by a vapor port 18 having an isolation valve 20 of any suitable construction between the condenser chamber 16 and the freeze dryer 12.
• the isolation valve 20 is constructed to seal vacuum both ways.
• a vacuum pump 22 is connected to the condenser chamber 16 with a valve 21 therebetween of any suitable construction.
• the condenser chamber 16 has a fill valve 24 and a vent valve 27 and filter 28 of any suitable construction and the freeze dryer 12 has a control valve 25 and release valve 26 of any suitable construction.
• the operation of the apparatus 10 in accordance with one embodiment of the method of the present invention is as follows:
• Verify condenser temperature is already at its max low usually -53°C or -85°C.
• the actual gas type and moisture added to the condenser chamber 16 can vary depending on user preference such that there is sufficient moisture content to generate the condensed frost, and is within the knowledge of one skilled in the art.
• the gas and moisture content added to the condenser chamber 16 may be nitrogen or argon with a sufficient amount of moisture added.
• Nozzles, heaters and steam may be used as sources of moisture.
• moisture may be added to the condenser chamber 16 while in a vacuum. The vacuum is then released in the condenser chamber 16 to create a pressure differential with the product chamber 13.
• moisture may be added to the condenser chamber 16 while under a high vacuum (e.g. 1000 mT) and then the pressure may be slowly increased in the condenser chamber 16 until it is above the pressure in the product chamber 13.
• moisture may be added to the condenser chamber while it is under atmospheric pressure or another predetermined pressure that is greater than the pressure (e.g. 50 Torr-300 Torr) in the product chamber.
• the sudden change of pressure creates strong gas turbulence in the condenser chamber which serves to knock off loosely condensed frost on the inner surface thereof and break it into relatively large ice crystals that mix in the gas flow rushing into the product chamber to increase the effectiveness of the nucleation process in the product chamber.
• the ice crystals are rapidly injected into the product chamber 13 where they are distributed evenly across the chamber and into all of the vials.
• the ice crystals serve as nucleation sites for the ice crystals to grow in the sub-cooled solution. With the even distribution, all of the vials nucleate within a short period of time. The nucleation process of all vials will start from top down and finish within a few seconds.
• Figure 2 illustrates a compact condenser 100 connected to a freeze dryer 102 having an internal condenser 104 which is not constructed to produce condensed frost therein and requires an additional seeding chamber and related hardware to be added.
• the freeze dryer 102 comprises a product chamber 106 with shelves 108 therein for supporting the product to be freeze dried.
• the compact condenser 100 comprises a nucleation seeding generation chamber 1 10 having a cold surface or surfaces 112 defining frost condensing surfaces.
• the cold surface 1 12 may be a coil, plate, wall or any suitable shape to provide a large amount of frost condensing surface in the nucleation seeding generation chamber 1 10 of the compact condenser 100.
• a moisture injection nozzle 1 14 extends into the nucleation seeding generation chamber 1 10 and is provided with a moisture injection or fill valve 1 16.
• a venting gas supply line 1 18 having a filter 120 is connected to the nucleation seeding generation chamber 1 10 by a vacuum release or vent valve 122.
• the nucleation seeding generation chamber 1 10 of the compact condenser 100 is connected to the freeze dryer 102 by a nucleation valve 124.
• the flow of gas and moisture into the nucleation seeding generation chamber 1 10 produces condensed frost on the surfaces of the concentric coils, plates, walls or other surfaces 1 12. Since the pressure in the compact condenser 100 is greater than that in the freeze dryer 102, when the nucleation valve 124 and vent valve 122 are opened, strong gas turbulence is created in the nucleation seeding generation chamber 1 10 to remove loosely condensed frost on the inner surfaces of the coils, plates, walls or other surfaces 1 12 therein and to break it into ice crystals that mix in the gas flow rushing into the product chamber 106 to increase the effectiveness of the nucleation process in the product chamber.
• Figure 3 illustrates a compact condenser 200 connected to a freeze dryer 202 having an external condenser 204.
• the construction and operation of the compact condenser 200 is the same as that of the compact condenser 100 shown in Figure 2.
• This method of nucleation is unique by combining an external controllable pre-formation of condensed frost with a sudden pressure differential distribution method. This results in a rapid nucleation event because of the large ice crystals, taking seconds instead of minutes, no matter what size of system it is used on. It gives the user precise control of the time and temperature of nucleation and has the following additional advantages: 1. Pre- formation of condensed frost in the external condenser chamber is controllable to allow the formation of the ice crystals to be easily controlled.
• the pressure differential ratio can also be controlled to optimize the
• This method can guarantee the sealed sterile operation mode for
• the advantage of a uniform nucleation method for the application of freeze drying is a uniform crystal structure and large aligned crystals across all of the vials, thus enabling a reduced primary drying process.
• condensed frost takes up less volume than a suspended ice fog.
• the condensed frost is more stable and can be stored for an extended period of time and used on demand.
• the frost formation environment can be carefully controlled to generate a loosely condensed frost which breaks down into ice crystals by gas turbulence during pressure release by use of a high condenser chamber pressure (e.g., 500 Torr a high volume low velocity gas flow and a warmer condensing surface temperature (e.g., below 0 degrees C).
• a high condenser chamber pressure e.g. 500 Torr a high volume low velocity gas flow and a warmer condensing surface temperature (e.g., below 0 degrees C).
• the larger ice crystals from the condensed frost are denser and stay frozen longer than the gas form of ice fog during the introduction into the product chamber to expedite the nucleation process.
• a more compact condenser can be added to systems that don't have an external condenser or where the existing condenser does not enable building condensed frost, or the existing condenser can't be validated for sterility.
• the condenser can be added to an existing port of sufficient size or by changing the chamber door, for example.

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• Drying Of Solid Materials (AREA)

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• 2014
  • 2014-09-18 JP JP2016557074A patent/JP6389270B2/ja active Active
  • 2014-09-18 ES ES14885084T patent/ES2799600T3/es active Active
  • 2014-09-18 WO PCT/US2014/056192 patent/WO2015138005A1/en active Application Filing
  • 2014-09-18 EP EP14885084.5A patent/EP3117165B1/de active Active
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  • 2014-09-18 CN CN201910394343.3A patent/CN110108097A/zh active Pending
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