Evaporation

Definitions:

  • Theoretically: simply evaporation from the surface of theliquid when no boiling occurs.     

• Practically: the removal of liquid from the solution by boiling the liquor in a suitable vessel and   withdrawing the vapor, leaving a concentrated liquid residue.

Factors affecting evaporation:

1.  Temperature: ↑temperature cause↑ rate of evaporation. Thermolable substances should be treated with temperature that will cause the least possible decomposition.

2.  Temperature and moisture contents: some drug decomposed more readily in the presence of moisture especially at high temperature, so the evaporation was carried out first at low temperature then the final at high temperature when only little moisture was remained.

3.  Temperature and time of evaporation: exposure to high temperature for short time may cause less destruction of the active constituent than a lower temperature expose for long time.

4.  Type of products required: Evaporation still or pan for liquid and dry products.                                                            Film evaporator for liquid product.

Equipment:

a. Natural circulation evaporation:

1. Evaporation pan (simplest form)

Advantage: it is simple, cheap, easy to be use, clean and maintain.                   

Disadvantage:

1.   Unsuitable for thermolable material.

2.  Deposition of the solids on the surface of the pan leading to the decomposition of the products.

3.  Saturation of the atmosphere due to the opening of the pan.

Uses: for aqueous and thermo-stable liquid