Whenever industries need to remove solute from fluid then adsorption operation is used like for purification of liquid, gases from moisture, undesired gases from vapour product etc.
What is adsorption?
The phenomenon of the concentration enrichment of chemical substances are the surface of a solid is called adsorption. The substance which adsorbs on solid or fluid is known as adsorbate and the solid on which adsorption operation takes place is known as adsorbent.In adsorption, fluid is contacted with solid. The solute is attracted to a solid surface and removed from the fluid as this way we get the desired purity of fluid.
If the relative volatility of solute in liquid is near to unity then it's very difficult to separate them by distillation, also it will increase capital and operating cost for separation. Hence adsorption also can be used for the gas phase.
Classification of adsorption
Adsorption is classified based on interaction forces between adsorbate and adsorbent which are:(1) Physical Adsorption: In this intermolecular forces of attraction between molecules of adsorbate and adsorbent is weak like van der Waals force. Also known as physisorption.
(2) Chemical Adsorption: If molecules involved chemical interaction forces between adsorbate solute and adsorbent solid then it called chemical Adsorption, also known as chemisorption.
- Adsorbent surface area per unit weight should be high, so forgiven separation adsorbent required is less.
- They must be highly porous material.
- They should be free-flowing for ease of handling.
- They should offer low-pressure drop for the flow of fluid when used in a fixed bed.
- They should have high strength.
- After adsorption operation desorption of solute from the adsorbent is easy.
Most used adsorbents and their general uses are given below:
(1) Activated carbon: used for Removal of colour from sugar solution, drugs, chemicals and also water purification.
(2) Silica gel: used for Removal of moisture from the air or other gases, in gas masks and fractionating hydrocarbon.
(3) Zeolite (molecular sieve): used for Removal of moisture from both gases and liquids.
(4) Bone char: used for Refining of sugar.
(5)Activated clay: Used for decolourizing petroleum products.
(6)Activated alumina: Used for Removal of sulfur from the fluid.
(7) fuller's earth: Also known as natural clay. Used as decolourizer, neutralizer and drying such petroleum products like lubricating oil, vegetable oil, kerosene, gasoline etc.
Applications of adsorption operation are given as :
- Removal of colour from the sugar solution
- Removal of odour impurities from industrial gases.
- To recover valuable solvent vapour from gases, for example, coak oven gas adsorption on a solid surface.
- Removal of unwanted taste and odour.
- To fractionate hydrocarbon gases containing methane, ethane, ethylene, propane and propylene.
Reference
- Principle of mass transfer and separation process by Binay K.Dutta
- Mass transfer-2 K.A ghavane