Clarification & Filtration (Pharmaceutics) notes

Terms used in Filtration

• FILTRATION may be defined as the “Separation of solids from a fluid by means of a porous medium that retains the solids but allows the fluid to pass.
• CLARIFICATION: When solid does not exceed 1.0%, filtration is termed as clarification & filtrate is the primary product.
• STRAINING: The object of filtration is to remove large visible particles using a coarse filtering medium (muslin/cotton wool).
• ULTRA-FILTRATION: Separation of inter-micellar liquid from solid by use of high pressure on a semi-permeable membrane
• SLURRY/FEED: Suspension of solid in liquid to be filtered
• FILTER MEDIUM: Porous medium used to retain/entrap the solids
• FILTER CAKE/RESIDUE: Accumulation of solids on the filter medium
• FILTRATE/EFFLUENT: Clear liquid passing through the filter medium
• CAKE FILTRATION: If the recovery of the solid is desired, the process is called cake filtration.

Factor affecting the rate of filtration

• Factor affecting the rate of filtration
  1. Filtration
  2. Viscosity
  3. Surface area of filter media
  4. Temp.
  5. Particle size
  6. Pore size of filter media
  7. Thickness of cake
  8. Nature of solid materials (porosity of filter cake)

TYPES OF FILTER MEDIA

• TYPES OF FILTER MEDIA
  1. Filter paper (Grade-Coarse, medium & fine)
  2. Glass wool (Corrosive liquids)
  3. Cotton wool
  4. Asbestos(Al. silicate): Corrosive liquids, Alkalinity of filtrate)
  5. Sintered glass: borosilicate glass, Parenteral, corrosive liquid & Oxidising agents)
  6. Membrane filter
  7. Filter cloths

FILTER AIDS:

Substances that reduce the resistance of the filter cake & increase the filtration. (Added to the liquid slurry to be filtered)

Filter aids Should form a porous cake & Insoluble in liquid

Filter aids forms a fine surface deposit- prevent solid from contacting & plugging the supporting filter medium.

Filter aids added by 2 methods:

Materials	Composition	Advantage	Disadvantage
Carbon	Carbon	Filtering strong alkaline solutions	Coarse grade only & Expensive
Cellulose	Cellulose	Higy purity & Excellent chemical resistance	Expensive
Diatomaceous earth	Silica	Wide range; Used for very fine filtration	Slightly soluble than diatomites in acid & alkali
Asbestos	Aluminosilicate	Good retention on coarse screens	More soluble than diatomites in acid & alkali
Perlite	Silica & Aluminosilicate	Wide range; not capable of finest retention	More soluble than diatomites in acid & alkali