Methods for freeze drying
View Patent ↗A method for producing a fog of ice nuclei by introducing a cryogenic fluid and a humid gas stream into a freeze dryer. The cryogenic fluid and humid gas stream will form ice nuclei having a preferred size for introduction into vials contained in the freeze dryer.
1. A method for forming a fog of ice nuclei in a freeze dryer comprising the steps: a) introducing a humid carrier gas into said freeze dryer, thereby forming a water vapor region; b) introducing a cryogenic fluid into said freeze dryer, thereby contacting said humid carrier gas and forming an ice fog region surrounded by said water vapor region; c) introducing a humid carrier gas into said freeze dryer, thereby forming a second water vapor region and said water vapor region and said ice fog region mix to form a mixed growth region; and d) introducing a cryogenic fluid into said freeze dryer, thereby contacting said second water vapor region to produce a second ice fog region within said second water vapor region and said mixed growth region.
2. The method as claimed in claim 1 wherein said freeze dryer comprises at least one means for inputting material and at least one means for venting material.
3. The method as claimed in claim 1 wherein a mixing zone is created at the entrance of said freeze dryer.
4. The method as claimed in claim 1 wherein said freeze dryer contains cold plates and vials on said cold plates.
5. The method as claimed in claim 1 wherein said ice fog region contains ice nuclei.
6. The method as claimed in claim 1 wherein said cryogenic fluid is selected from the group consisting of nitrogen, oxygen, air and argon.
7. The method as claimed in claim 1 wherein said humid gas stream comprises water vapor in nitrogen.
8. The method as claimed in claim 1 where said humid gas stream is selected from the group consisting of steam injection into nitrogen, sparging nitrogen into a water bath and spraying or atomizing water into a nitrogen stream.
9. The method as claimed in claim 1 wherein said ice nuclei grow in size in the mixed growth region.
10. The method as claimed in claim 1 wherein said second ice fog region contains newly generated ice nuclei.
11. The method as claimed in claim 1 wherein said newly generated ice nuclei are uniformly dispersed in said second ice fog region.
12. The method as claimed in claim 1 where said freeze chamber is pressurized to assist in introducing said ice nuclei into said vials.
13. The method as claimed in claim 1 wherein said cryogenic fluid is at a temperature of −20° C. to −180° C.
14. The method as claimed in claim 1 wherein said carrier gas is at a temperature of ambient to −70° C.
15. The method as claimed in claim 1 wherein steps c) and d) are repeated.