Skip to main content

Renin Angiotensin Mechanism.

Filtration: Filter Media.

 

Filter Media:

  • The surface upon which solids are retained in the process of filtration is known as 'filter medium'. 

  • A good filter media should possess the following characteristics:

    • It should not absorb the constituents of the liquid preparation undergoing  filtration.

    • It should be resistant to corrosive action of the liquid.

    • It should have a smooth surface for easy discharge of cake.

    • It should allow free flow of liquid.

    • It should be resistant to chemical reactions with the contents of the liquid to be filtered.

    • It should have sufficient mechanical strength to resist the damage that occurs  during filtration of liquid under pressure.

  • The selection of filter media depends on:

    • The quantity of the material to be filtered.

    • The nature of the product to be filtered i.e. its viscosity etc.

    • The size of the solid particles to be retained on the filter

    • The purpose of filtration e.g. weather sterility required or not?

  • The various filtering media employed for filtration are:

  1. Filter paper : 

  • Filter paper is most commonly used as filter media for  general filtration. 

  • The filter papers are classified as coarse, medium and fine according to their pore size.

  •  For the filtration of  pharmaceutical preparations, a fine grade of filter paper is used. 

  • The main drawback of a filter paper is that it has an absorbing property and also  it sheds fine particles into the filtrate.

  1. Cotton wool : 

  • Cotton wool is generally used for filtering of moderately  coarse particles. 

  • The disadvantage of cotton is that it sheds fine cotton hair  in the filtrate. 

  • This problem can be solved to a large extent by using long staple cotton,  wool of long staple and wetting the cotton wool plug with liquid before its use.

  1. Glass wool : 

  • It consists of fine fibers of glass which are resistant to  corrosive liquids. 

  • So it is used for filtering corrosive liquids, such as  strong acids, alkalies and oxidizing agents e.g. solutions of chromic acid  and potassium permanganate.

  1. Asbestos : 

  • It is used for the same purpose as glass wool.

  • It is commonly  used in gravimetric analysis for collecting fine precipitates which are to be subsequently ignited.
Labels:

Popular posts from this blog

Rate of Drying Curve.

  Definition Drying is defined as the removal of liquid from a product usually with application of heat. Rate of Drying Curve. Drying process can be divided into three periods Initial Adjustment Period. Constant drying rate period. First falling drying rate period. Second falling rate period. Initial Adjustment Period (A-B): Also called the “ Heating up” period . In this period the substance gets heat and increases in temperature. Drying has not yet started. Constant drying rate period (B-C): During this period the temperature of the solid and the rate of drying remain constant. The moisture evaporating from the surface is replaced by water diffusing from the interior of the solid at a rate equal t o the rate of evaporation.  The moisture content at the end of constant rate (point C) is referred to as the critical moisture content (CMC).  At CMC, dry spots start appearing and drying rate starts falling . First falling drying rate period (C-D): This period is also called ...
Read more

Heat Exchangers and Heat Interchangers.

  In pharmaceutical industries many types of equipments are used for transfer of heat, they can be classified as follows, Heat Exchangers. Heat Interchangers. Heat Exchangers: These devices are used for transferring heat from a fluid (Hot Gas or Steam) to another fluid (Liquid) through a metal wall. Heat Interchangers: These devices are used for transferring heat from a One liquid to another liquid or one gas to another gas through a metal wall. HEAT EXCHANGERS; The equipment used for heat transferring are known as heat exchangers. Some of the processes that involves heat transfer in pharmaceutical industries are: Preparation of starch paste (in steam jacketed kettle). Crystallization. Evaporation. Distillation.  Classification of heat exchangers On the basis of transfer of heat, heat exchangers are classified as: Direct transfer type:  The hot and cold fluids are separated by a metal wall through which the heat is transferred from hot fluid to cold fluid. E.g. shell and ...
Read more

Flash Distillation.

  Principle: When a hot mixture is allowed to enter from a high-pressure zone into a low pressure zone, the entire liquid mixture is suddenly vaporized. This process is known as flash vaporization .  During this process, the chamber is cooled.  The less volatile fraction is condensed and the more volatile component remains in the vapor phase .  This process requires time, hence liquid and vapor are kept in intimate contact until equilibrium is achieved. Flash distillation is also called equilibrium distillation because separation of two liquids takes place when liquid and vapor phases are at equilibrium. Equipment used for Flash Distillation: Construction: It consists of a pump, which is connected to a feed reservoir.  Pumps help in pumping the feed into the heating chamber.  The heating chamber is heat supplied by steam.  The other end of the pipe is directly introduced into the vapor-liquid separator through a reducing valve.  The vapor outlet...
Read more