Martin-christ Epsilon 2-6D LSCplus Manuel d'utilisateur télécharger pdf (Page 21)

Freeze-dryer EPSILON 2-6 LSCplus

2 Layout and mode of operation

Version 10/2012, Rev. 1.6 of 16/12/2014 • sb

Translation of the original operating manual

NOTE

If the product that is to be dried contains solvents or high salt

concentrations, it may start to thaw during the drying process, which is

indicated by clearly visible foaming. In order to prevent this, the product

must be frozen as deeply as possible, e.g. with the aid of liquid nitrogen,

prior to putting it into the unit.

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2.2.2.3 Main drying

When the product is frozen to a sufficiently deep extent, the main drying

phase commences. The vacuum pump is switched on. The pressure inside

the drying chamber will be lowered to the value that corresponds to the

freezing temperature in accordance with the vapour pressure curve above

ice. At the same time, thermal energy will be added to the product. In the

case of products in round-bottom flasks, wide-neck bottles, etc., this is

realised through the environment that is considerably warmer (direct

contact heat), in the case of unheated shelves by way of thermal radiation

from the environment, and in the case of temperature-controlled shelves

directly via the shelves. As a result, the sublimation process starts.

At the beginning of the drying process, the maximum drying rate will be

reached. The more the sublimation area recedes into the product, the

further the produced water vapour must pass through the layers that have

already been dried.

Under certain conditions, it is possible that the vacuum inside the ice

condenser chamber increases during the main drying phase (e.g. from 0.63

mbar to 0.47 mbar) although the valve towards the vacuum pump is closed.

From a physical point of view, this is due to the pumping effect of the ice

condenser ("cryo-pumping effect").

The required drying time depends strongly on the drying vacuum. At 1.0

mbar, one gram of ice takes up a volume of 1 m

of vapour, at 0.1 mbar a

volume of 10 m

of vapour, and at 0.001 mbar a volume of 100 m

. The

closer the vacuum is to the solidification point, the smaller is the resulting

vapour volume. The drying rate increases and the drying time decreases.

The end of the main drying phase is reached, when the product

temperature and the shelf temperature are nearly identical. The

temperature difference between the shelf and the product should be

approximately 3 K to 5 K.

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2.2.2.4 Final drying

Final drying is an option whenever one requires a product with minimal

residual moisture. In the physical sense, this process is a desorption

process, i.e. the removal of adsorptively bound water. Final drying is

performed under the lowest possible final pressure that depends on the ice

condenser temperature in accordance with the vapour pressure curve

above ice as well as on the final vacuum of the vacuum pump that is used.

The process is supported by a higher shelf temperature.

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Martin-christ Epsilon 2-6D LSCplus Manuel d'utilisateur Page 21

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