Chemical apparatus and process disinfecting – deodorizing – preser – Process disinfecting – preserving – deodorizing – or sterilizing – Using fluent heat transfer medium other than air
Reexamination Certificate
1999-08-23
2003-08-26
Warden, Sr., Robert J. (Department: 1744)
Chemical apparatus and process disinfecting, deodorizing, preser
Process disinfecting, preserving, deodorizing, or sterilizing
Using fluent heat transfer medium other than air
C422S040000, C422S905000, C062S114000, C062S185000, C062S480000, C165S009100, C165S005000, C165S104270, C165S104210, C165S104320, C252S070000, C134S022180, C134S16900A
Reexamination Certificate
active
06610250
ABSTRACT:
FIELD OF INVENTION
This invention relates to an apparatus for low temperature processing requiring sterilization and methods therefor. More particularly, this invention relates to an apparatus (and methods therefor) using halogenated organic fluids for heat transfer in low temperature processes requiring high temperature (e.g., steam) sterilization.
BACKGROUND
Low temperature processing can generally be described as a dehydration, a chemical reaction, a biological reaction, etc. which occurs in a vessel or chamber at temperatures ranging from about −150° C. to about 0° C. The low temperature processes of particular interest in the present invention occur in a vessel or chamber which requires sterilization (or a high temperature process) at the end of the low temperature processing. Examples of such chambers include, but are not limited to, a vacuum chamber from freeze drying and a chemical or biological reactor.
Freeze drying can generally be described as a process of dehydration or of separating water from matter (e.g., biological matter or chemical matter). A product containing biological or chemical matter is frozen and then subjected to a high vacuum. The water vaporizes without melting (sublimes) leaving behind non-water components.
Generally, freeze drying requires at least four components: a vacuum chamber, a condenser, a pump, and a means for providing the heat of sublimation to the product being dried. The vacuum chamber typically contains a series of thin stainless steel shelves. Product, for example in containers, is placed upon these shelves. The condenser is used to remove the sublimed water vapor. The pump is typically a high powered vacuum pump.
A freeze drying system generally comprises other components such as a means for heat transfer. This heat transfer means may comprise a means for heating and a means for cooling. The freeze drying system typically comprises a sterilization process, especially for pharmaceutical applications.
Freeze drying systems operate over a range of temperatures, but in general the product is completely frozen prior to dehydration. The freezing point of the product may be well below the freezing point of water. For example, the freezing point of the product may be as low as about −50° C. or the operating temperature may be as low as about −50° C.
If sterilization is desired, the freeze drying system may also operate at temperatures around about 120° C. to about 130° C. (i.e., the temperature for high pressure saturated steam which is often used for sterilization).
During dehydration, a heat-transfer fluid is pumped through passages in the shelves of the vacuum chamber providing the heat of sublimation to the product being dried. Following drying, the product is removed from the container and the vacuum chamber may then be sterilized. As discussed, typically a high temperature steam (120° C. to 130° C.) is used for this sterilization process. If the heat-transfer fluid in the passages boils during this sterilization process, the system pressure may rise to a level where the shelves (which are typically thin to ensure adequate heat transfer) are damaged. Thus, selection of heat-transfer fluid is critical.
Heat-transfer fluids used in such applications typically have low viscosities at lower temperatures (i.e., −50° C. for the shelves and −80° C. for the condenser system), but are readily maintained in the liquid phase at the highest operating temperature for the system (which is typically during sterilization). Desirable heat-transfer fluids for freeze drying applications are also non-corrosive, non-toxic, and non-flammable.
Polydimethylsiloxanes (silicone oils) have a suitably wide liquid range and are often used in freeze drying. The average molecular weight of the silicone oil can be selected such that it functions well at temperatures as low as −80° C. At this temperature, the heat-transfer fluid may be pumped through passages in the shelves where the product is being dried. Such a silicone oil has a boiling point significantly above 130° C., thus the passages may be kept full of heat-transfer fluid without the danger of the heat-transfer fluid boiling and causing elevated system pressure. Silicone oils seem to be ideally suited for this type of application. However, they are flammable. There have been instances of silicone oil fires and such fires can cost millions of dollars as well as injury.
As is the case with freeze drying, during low temperature chemical or biological processes, the heat-transfer fluid preferably has good low temperature heat transfer characteristics. Typically, the heat-transfer fluid is pumped through a reactor jacket for heating, cooling, or temperature control. For ease of handling and safety, preferably this fluid is non-toxic and non-flammable. The heat-transfer fluid has similar temperature constraints (i.e., suitable at low temperature processing temperatures and at high temperature sterilization temperatures).
Halogenated organic compounds, such as perfluorocarbons (PFCs), perfluoropolyethers (PFPEs), hydrofluorocarbons (HFCs), chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluoroethers (HFEs), hydrohalofluoroethers (HHFEs), hydrochlorocarbons (HCCs), hydrobromocarbons (HBCs), perfluoroalkyl iodides (PFIs), perfluoroolefins (PFOs), and fluorinated compounds containing at least one aromatic moiety, or mixtures thereof are generally non-toxic and non-flammable. The lower molecular weight compounds tend to have good low temperature heat transfer properties. Additionally, halogenated organic compounds are non-corrosive and very thermally stable.
However, in conventional designs these halogenated organic compounds tend not to be viable candidates as heat-transfer fluids because either their boiling points are too low (leading to excessive system pressure at high temperatures) or their freezing points are too high (leading to freeze up or high viscosity at low temperatures). Candidates, for example, that are liquid at 130° C. or which have acceptable vapor pressures at this temperature tend to be solid or very viscous at −80° C. and thus cannot be used. Similarly, candidates, for example, that may work well at −80° C. tend to have lower boiling points which result in excessive vapor pressures that would prevent their use at 130° C. Typically, these fluids are not used in conventional designs because to maintain the fluid in a liquid state throughout the system/apparatus and throughout the operating temperature range, the system is typically pressurized above the fluid saturation pressure using a compressed gas such as air or nitrogen. This pressure compromises certain components in the apparatus unless they are built to more rigorous design codes which adds cost and may affect performance.
Thus, the need exists for an apparatus which allows volatile halogenated organic compounds having good heat transfer properties at low temperatures, non-corrosivity, non-flammability, low toxicity, etc. to be utilized in low temperature processes requiring high temperature sterilization.
SUMMARY OF THE INVENTION
The present invention provides an apparatus for low temperature processing where the chamber requires sterilization which allows a volatile halogenated organic compound to be effectively used as a heat-transfer fluid. The apparatus of the present invention allows for heat-transfer fluids to be used which have a boiling point of less than about 120° C. Thus, fluids having otherwise desirable traits can be utilized.
The present invention provides an apparatus for low temperature processing and high temperature sterilization comprising: a product; a heat-transfer fluid having a saturation temperature at a system pressure below the sterilization temperature; a chamber requiring sterilization comprising one or more passageway(s) for said heat-transfer fluid wherein said heat-transfer fluid enters and exits said passageway(s) at the lower portion of said chamber; a pump in fluid connection with said passageway(s); and an expansion device sized to acco
Chorbaji Monzer R.
Fagan Lisa M.
Warden, Sr. Robert J.
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