1. INTRODUCTION
TO FREEZE-DRYING

2. Freeze-Drying
Also called lyophilisation, it is a drying process where the wet product is first frozen to a solid phase and subsequently dried to vapour phase through sublimation, that is, without passing through the liquid phase, by exposing it to a low partial pressure of water vapour.
Lyo = Solvent Philo = Friend
The lyophilisation process makes the dried product “solvent loving”

3. Basic Concepts (1/4): Phase Diagram
Below the triple point co-ordinates, solid
ice can sublimate to vapour:
Liquid is frozen at atmospheric pressure
2. Pressure is reduced
3. Temperature is raised to promote sublimation from ice to vapour
4. Vapour travels to the ice condenser where it is trapped as ice
5. When drying is finished, trapped ice is melted and drained

4. Basic Concepts (2/4): Vacuum
Vacuum: an enclosed region of space in which the pressure has been reduced (below normal atmospheric pressure)
Atmospheric pressure: mbar
Rough vacuum: mbar mbar
Medium vacuum: 1 mbar mbar
High vacuum: mbar mbar
Ultra-high vacuum < 10-7 mbar
Lyophilisation is normally performed at medium vacuum

5. Basic Concepts (3/4): Eutectic
Above the freezing curve the solution has only one phase and it is liquid
Below the freezing curve there are two phases: pure ice + more concentrated solution
Below the eutectic, there is no liquid phase: everything is solid.
A similar curve is obtained with amorphous materials: eutectic is replaced by glass-transition temperature

6. Basic Concepts (4/4):Vapour Pressure
The vapour pressure of a liquid is the pressure exerted
by its vapour when the liquid and vapour are in dynamic equilibrium.
If a substance is placed in an evacuated, closed container, some of it would vaporise. The pressure in the space above the liquid would increase from zero and eventually stabilise at a constant value: the vapour pressure.
This equilibrium pressure is a function of the temperature of the substance

7. Process Description
Lyophilisation consists in drying a substance removing the solvent (typically water):
freezing the solution below the eutectic temperature (normally 10ºC below)
- sublimating the solvent ice crystals

8. Freeze-Drying Steps Freezing Primary Drying Secondary Drying
Ancillary operations:
Loading / unloading the product
Venting (re-establishing atmospheric pressure) / Backfilling
Defrosting
Cleaning of the unit (CIP)
Sterilisation of the unit (SIP)
HEPA filter integrity testing
Leak test of the unit

9. Freezing
PURPOSE: Cool (freeze) the product achieving a temperature below the eutectic point, getting a crystalline solid (glass state in case of amorphous materials)
An immobilisation of the product is also achieved, avoiding:
Frothing under vacuum
Material shrinkage
Solvent migration
Concentration during drying
Temperature dependent reactions, specially those leading to loss of activity

10. Freezing Rate
It is important to have the correct freezing rate to allow the growth of DENDRITIC ICE CRYSTALS.
When sublimated, there are funnels, allowing vapour to escape.

11. Primary Drying PURPOSE: remove the ice from the product with:
· Minimum damage to the product
· Retention of shape
After the product is frozen at a temperature T1, the chamber is pumped down to a pressure Pc lower than the product saturation vapour pressure Pp.
Sublimation is an endothermic process, latent heat must be provided.
Condenser at a temperature T2 < T1, so that saturation vapour pressure at the condenser Pa < Pc (Pa < Pc < Pp)
Product temperature must be below the collapse temperature.
Primary drying is complete when all the ice has sublimed.
Moisture still remains bound to the product.

12. Switching from Primary Drying to Secondary Drying
Primary drying is complete when:
- The interface disappears at the vial base
- Product and shelf temperature are identical
- Chamber and condenser pressure are identical

13. Secondary Drying
PURPOSE: to remove residual and bound moisture (typically from 10% to less than 2%). Water in the product isn’t crystalline but adsorbed.
Residual water is removed by desorption. Secondary drying time is governed by the water desorption rate from the solid.
This process is temperature dependant and not time dependant. When equilibrium is reached increasing the time is useless.
Product temperature is raised as much as possible without having denaturalisation. Condenser pressure (and so its temperature) must be as low as possible.
Temperature probes now measure real value (but it is useless).

14. Why Freeze-Dry? Minimum damage / loss of activity Low final moisture
Long shelf life
Ease of reconstitution
Possibility of sterile manufacturing
Accurate dosing

15. When to Freeze-Dry? Labile products High value products Sterile drying
Accurate dosing
Reconstitution is difficult
Long shelf life is required
Retention of form

16. Freeze-Drying Applications
Antibiotics
Antitoxins
Bacteria / Viruses
Blood coagulants
Enzymes
Fine chemicals
Hormones / Growth factors
Media
Pathological samples
Pharmaceuticals
Plasma
Reagents
Standards
Tissues
Vaccines
etc...

17. Simplified P&ID of a Freeze Dryer