3 | Product description
Büchi Labortechnik AG
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Operation Manual Lyovapor™ L-300/L-300 Pro
3
Product description
3.1
Description of function
The Lyovapor™ is a freeze-dryer in which frozen samples can be gently dried.
The basis of freeze-drying is sublimation. Sublimation refers to the process whereby
a substance transforms directly from the solid to the gaseous state.
The physical process of sublimation can be explained using the solvent water as an
example.
The water is frozen.
The frozen water is transformed into the gaseous state under vacuum at a
pressure below the triple point.
Thus, freeze-drying takes place in three phases:
1. Freezing phase: the sample is frozen at atmospheric pressure.
2. Main drying phase: heat is applied to the frozen sample under a vacuum. The
frozen water is removed by sublimation.
3. Secondary drying phase (only possible with heatable shelves): the trace levels
of water remaining are removed by heating.
The Lyovapor™ consists of an ice condenser and various top-mount drying racks. The
top-mount drying racks can be chosen to suit the availability of the sample being
dried and the requirements of the end product.
The following top-mount drying racks can be used:
Non-heatable and heatable shelves in rack
Trays in rack
Top-mount rack with manifold valves
3.1.1
Freezing phase
In the freezing phase, the liquid sample is transformed to a solid state. Freezing
takes place under atmospheric pressure using a separate freezer, a liquid nitrogen
bath, or a mixture of dry ice and alcohol.
The end of the freezing phase is reached as soon as the water or solvent contained
in the sample has fully crystallized and the entire sample is solidified.
3.1.2
Main drying phase
In the main drying phase, the ice crystals are removed from the sample by
sublimation. Sublimation in the Lyovapor™ takes place under a vacuum with the
addition of thermal energy.
The vacuum pressure is lowered to the level required for sublimation.
For water that is: less than 6.11mbar.
As the ice condenser is colder than the sample being dried, the vapour pressure in
the area of the ice condenser is lower than in the area of the sample. The water
vapour escaping from the sample therefore flows towards the ice condenser. The
water or solvent vapour condenses on the coil of the ice condenser.
If drying chamber without heating is used, heat transfer takes place by convection
and radiation from the surroundings. Control of the thermal energy transferred is
then difficult.
