Discuss the theory, construction, and working of freeze drying apparatus

Discuss the theory, construction, and working of freeze drying apparatus
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1 Answer

Answer :

Theory: Freeze drying or sublimation drying consists of simply reducing the temperature & pressure to values below the triple point .(4.579mm of Hg& temp. of 0.0099 c)

• Under these conditions, any heat transferred is used as latent heat & the ice sublimes directly to the vapour state.

• Many pharmaceutical products lose their viability in liquid state & readily deteriorate if dried in air at normal atmospheric pressure.

• These pharmaceutical products may be heat sensitive or they may react readily with oxygen

• Such materials are blood serum, plasma, antibiotics, hormones, bacterial cultures, vaccines, & many foodstuffs.


Construction:

Freeze dryer is composed of four basic components:

A chamber for vacuum drying: Having shelves for keep the material

A vacuum source: vacuum pump is connected to the chamber.

A heat source: heat is provided by conduction or radiation.

A vapour removal system as vacuum pump: The condenser consists of large cooled surface by solid carbon dioxide mixed with acetone or ethanol.


Working: steps involved in freeze drying are

1. Pre-treatment: Solution is concentrated in normal vacuum tray dryer before introducing in the chamber this reduces drying by 8-10 times.

2. Pre-freezing: Ampoules, vials and bottles having aqueous solution are packed and frozen in cold shelves at a temp. below - 500C.

3. Primary drying: The material to be dried is spread to increase the surface area for sublimation.98-99% moisture removed.

4. Secondary drying: Remaining moisture is removed by vacuum drying done at 50- 600C.It takes 10-20 hrs.

5. Packing: Biological products are dried packed in aseptic condition immediately after drying.


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