Freeze-Drying Process; Preparation; Freezing - Christ Alpha 3-4 LSCbasic Operating Manual

Freeze-dryer Alpha 3-4 LSCbasic
2 Layout and mode of operation

2.2.2

Freeze-drying process


2.2.2.1

Preparation


2.2.2.2

Freezing

NOTE
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18 / 97
The main components of a freeze-dryer are:
•
vacuum drying chamber or drying manifold,
•
vacuum pump for generating a vacuum inside the drying chamber,
•
ice condenser for binding the water vapour that is released by the
product.
The ice condenser chamber must be clean and dry. Any water residues
from a preceding drying run must be removed.
The media drain valve and the aeration valve must be closed.
In the case of units that are equipped with a pressure control valve
(standard on LSCplus and LSCbasic units), the vacuum pump should be
warmed up ("warm-up") for at least 15 minutes prior to the start of the main
drying phase. Do not subject the vacuum pump to condensable gases until
the operating temperature is reached. In this way, the service life of the
vacuum pump can be extended.
At the same time, the ice condenser is pre-cooled ("cool-down"). The ice
condenser temperature does not have any influence on the product
temperature. The sole purpose of the ice condenser is to bind the released
water vapour.
First, the product that is to be dried is frozen. Especially in the case of small
filling quantities, we recommend pre-cooling the shelves as well in order to
prevent the product from thawing during the evacuation.
Two very different structures of the frozen material can be distinguished:
•
crystalline structures with clearly distinguishable crystals
•
amorphous structures with no crystal junctions at all (e.g. glass)
The majority of the freeze-drying products have a crystalline form.
When freezing these kinds of products, one must take into consideration
that too deep and too quick freezing leads to smaller ice crystals, which has
a negative effect on the duration of the drying process.
For every product to be dried, the solidification point must be determined as
a first step. This is the point at which the water that is contained in the
product has completely crystallised. In order to ensure an optimum freeze-
drying process, the product temperature should be approximately 10°C
below the solidification point.
In the case of a solvent-containing product or of a product with a high salt
concentration, the product may thaw during the freeze-drying process.
This is indicated by easily visible foaming. To prevent this, the product
must be frozen down to a very deep temperature, e.g. in liquid nitrogen,
prior to placing it in the freeze-dryer.
Version 11/2018, Rev. 1.2 of 05/03/2019 • sb-pe
Translation of the original operating manuel