Up to the present, the conventional freeze-drying method for bulk pharmaceticals and other liquid materials has employed a tray/shelf system, while the development of a closed system has been desired for many years, especially for the manufacturing of sterile bulk pharmaceuticals. Seffinga (1964) devised a method, which he called "vertical tube dryer", however, this system was not established due to several drawbacks.
Having restudied Seffinga's method, we have succeeded in eliminating the drawbacks of this method and have developed a closed system for the batch/continuous freeze-drying of liquid materials. Two of the drawbacks of Seffinga's method, namely (a) supercooloing followed by sudden freezing and (b) adherence of dried material to the tube surface, have been eliminated by the formation of an ice lining. Another drawback (c) that a substaintial part of the liquid poured into the chamber must be drained has been solved through multistage frozen layer formation. All of the stage of freeze-drying can be performed using the closed system developed in this study. Further, since the interior dose not have a complicated structure, internal cleaning and steam sterilization can be easily performed. This paper discussed the closed system and the behavior of materials in the freeze-drying process.
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