Freeze-drying methods including vacuum freezing
Various implementations of a freeze-drying method are described where the material is cooled by reducing the pressure in a chamber to evaporate and/or sublimate water in the material. In one implementation, the material is dried in the chamber by sublimating ice in the material to water vapor. In another implementation, the freeze-drying method includes actively cooling the chamber. In another implementation, at least a portion of the water vapor is deposited on an actively cooled interior surface of the chamber. In another implementation, the freeze-drying method includes cooling the material to −25° F. or below. In another implementation, the material is cooled at approximately ambient pressure to 30° F. or below and then cooled by reducing the pressure in the chamber.
1. A freeze-drying method comprising:
cooling a material to 32° F. or below in a chamber that is not pressurized and is at approximately ambient pressure to form a first cooled material;
cooling the first cooled material in the chamber to −30° F. or below to form a frozen material, wherein, before reaching −30° F., the first cooled material is cooled at least 10° F. by concurrently: (a) reducing the pressure in the chamber below ambient pressure to evaporate and/or sublimate water in the first cooled material and (b) actively cooling the chamber; and
drying the frozen material in the chamber by sublimating ice in the frozen material to water vapor.
2. The freeze-drying method of claim 1 comprising collecting at least a portion of the water vapor on an interior surface of the chamber.
3. The freeze-drying method of claim 1 comprising cooling the material to 10° F. or below in the chamber at approximately ambient pressure to form the first cooled material.
4. The freeze-drying method of claim 1 wherein cooling the first cooled material in the chamber to form the frozen material comprises reducing the pressure in the chamber from approximately ambient pressure to 2000 mTorr or below in a single step.
5. The freeze-drying method of claim 1 wherein drying the frozen material in the chamber includes heating the frozen material in the chamber to sublimate ice in the frozen material to water vapor.
6. The freeze-drying method of claim 5 wherein cooling the first cooled material in the chamber to form the frozen material comprises cooling the first cooled material to −10° F. or below.
7. The freeze-drying method of claim 1 wherein actively cooling the chamber comprises cooling an interior surface of the chamber to 0° F. or below.
8. The freeze-drying method of claim 5 wherein cooling the first cooled material to form the frozen material comprises cooling the first cooled material at a pressure of 2000 mTorr or below for at least 10 minutes before heating the frozen material in the chamber.
9. The freeze-drying method of claim 5 wherein cooling the material comprises cooling the material at least 15° F.
10. A freeze-drying method comprising:
cooling a material to a first temperature in a chamber that is not pressurized and is at approximately ambient pressure to form a first cooled material, the first temperature being above −25° F.;
cooling the first cooled material from the first temperature to −25° F. or below by reducing the pressure in the chamber below ambient pressure to evaporate and/or sublimate water in the material; and
drying the material in the chamber by sublimating ice in the material to water vapor.
11. The freeze-drying method of claim 10 comprising collecting at least a portion of the water vapor on an interior surface of the chamber.
12. The freeze-drying method of claim 10 wherein the first temperature is 10° F. or below.
13. The freeze-drying method of claim 10 comprising actively cooling an interior surface of the chamber to −30° F. or below.
14. A freeze-drying method comprising:
cooling a material in a chamber by initially cooling the material at approximately ambient pressure and without pressurizing the chamber followed by cooling the material from −15° F. to below −25° F. by reducing the pressure in the chamber below ambient pressure to evaporate and/or sublimate water in the material;
drying the material in the chamber by heating the material and sublimating ice in the material to water vapor; and
collecting at least a portion of the water vapor on an interior surface of the chamber.
15. The freeze-drying method of claim 14 wherein cooling the material in the chamber comprises cooling the material from −10° F. to below −25° F. by reducing the pressure in the chamber.
16. The freeze-drying method of claim 14 wherein:
cooling the material in the chamber includes:
cooling the material at approximately ambient pressure to 30° F. or below to form a first cooled material; and
cooling the first cooled material in the chamber from −15° F. to below −25° F. to form a second cooled material, the first cooled material being cooled by reducing the pressure in the chamber to evaporate and/or sublimate water in the first cooled material; and
drying the material in the chamber includes drying the second cooled material in the chamber by sublimating ice in the second cooled material to water vapor.
17. The freeze-drying method of claim 14 wherein cooling the material in the chamber from −15° F. to below −25° F. comprises reducing the pressure in the chamber to 2000 mTorr or below.
18. The freeze-drying method of claim 17 wherein cooling the material in the chamber from −15° F. to below −25° F. comprises reducing the pressure in the chamber from approximately ambient pressure to 2000 mTorr or below in a single step.
19. The freeze-drying method of claim 14 comprising actively cooling the interior surface of the chamber.
20. A freeze-drying method comprising:
cooling a material in a chamber that is not pressurized and is at approximately ambient pressure to 30° F. or below to form a first cooled material;
cooling the first cooled material in the chamber from −15° F. to below −25° F. to form a second cooled material, the first cooled material being cooled by reducing the pressure below ambient pressure in the chamber to evaporate and/or sublimate water in the first cooled material; and
drying the second cooled material in the chamber by sublimating ice in the second cooled material to water vapor.
21. The freeze-drying method of claim 20 wherein cooling the first cooled material in the chamber to form the second cooled material comprises cooling the first cooled material from −10° F. to below −25° F.
22. The freeze-drying method of claim 20 wherein cooling the first cooled material in the chamber lowers the temperature of the first cooled material at a rate of at least 0.25° F./min from −15° F. to below −25° F.