Adsorption - Basics
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The document discusses adsorption and types of adsorbents. It defines adsorption as the concentration of a solute on the surface of a solid. Porous solids with small pores are commonly used as adsorbents to achieve a large surface area. Common adsorbents include silica gel, activated carbon, alumina, bone char and fuller's earth. Adsorbents are used for applications like gas purification, desiccation, catalysis and separation of inert gases. They must have properties like high surface area, strength and adsorptive ability to be effective.
Adsorption - Basics
- 1. PREPARED BY:- Pritesh Vasoya (130420105057) Vishvaraj Chauhan (130420105058) Vivek Mistry (130420105058)
- 2. Introduction Apllication of adsorption Types of adsorbents Nature of adsorbents
- 3. Adsorption (also known as adsorptive separation) can be simply defined as the concentration of a solute, which may be molecules in a gas stream or a dissolved or suspended substance in a liquid stream, on the surface of a solid. The major applications had been in the separation of solutes from liquid streams and removal of impurities from gas streams. adsorption process is shown by the following figure:-
- 5. The adsorbed solute is called the adsorbate, and the solid material is the adsorbent. To achieve a very large surface area for adsorption per unit volume, highly porous solid adsorbents with small diameter inter-connected pores are used. The adsorbents are less than 5-mm in diameter, with pore sizes of the order of 0.01- mm in diameter. Molecules or atoms or ions in a gas or liquid diffuse to the surface of a solid, where they bond with the solid surface or are held there by weak inter-molecular forces show in the following figure.
- 8. Production of high vacuum In Gas masks :This apparatus is used to adsorb poisonous gases (e.g. oxide of sulphur etc.) and thus purify the air for breathing. For desiccation or dehumidification : These substances can be used to reduce/remove water vapours or moisture present in the air. Silica gel and alumina are used for dehumidification in electronic equipment. Removel of colouring matter from solution : (i) Animal charcoal removes colours of solutions by adsorbing coloured impurities. (ii) Animal charcoal is used as decolouriser in the manufacture of cane sugar.
- 9. Heterogeneous catalysis : Mostly heterogeneous catalytic reactions proceed through the adsorption of gaseous reactants on solid catalyst. For example, (I)Finely powdered nickel is used for the hydrogenation of oils. (ii) Finely divided vanadium pentaoxide is used in the contact process for the manufacture of sulphuric acid. Separation of inert gases : Due to the difference in degree of adsorption of gases by charcoal, a mixture of inert gases can be separated by adsorption on coconut charcoal at different low temperatures.
- 10. 1. Silica gel :- Silica gel is a partially dehydrated polymeric form of collodial silicic acid with the formula SiO2.nH2O. Drying of gases, refrigerants, organic solvents, transformer oils Desiccant in packings and double glazing Dew point control of natural gas 2.Decolourising carbon:- Mixing of vegetable matter with inorganic substances such as calcium chloride, carbonizing and leaching away the inorganic matter.
- 11. They are used for a great variety of purpose, including the decolorizing of solution of sugar ,industrial chemicals, drugs and dry cleaning liquids, water purification, refining of vegetable and animal oils, and in recovery of gold and silver from cyanide ore-leach solution. 3.Bone char:- This is obtained by the destructive distillation of crushed, dried bones at temperatures in the range of 600 C to 900 C. It is used in the refining of sugar and can be reused after washing and burning. 4. Bauxite:- This is a certain form of naturally occurring hydrated alumina which must be activated by heating to temperature varying from 230 to 815 C in order to develop its adsorptive ability.
- 12. It is used for decolorizing petroleum products and for drying gases and can be reactivated by heating. 5.Alumina:- This is hard, hydrated aluminum oxide which is activated by heating to drive off the moisture. The porous product is available as granules or powders, and it is used chiefly as a desiccant for gases and liquids . It can be reactivated for reuse. 6.Fuller’s earths:- These are natural clays,the american varieties coming largely from florida and georgia. They are chiefly magnesium aluminum silicates. The clay is heated and dry during which it develop a porous structure it is ground and screen. It is used for decolorizing, neutralizing, and drying such a petroleum products as a lubricating oil,kerosenes and gasoline.
- 13. 7.Activated clays:- They are bentonite and clays which does not show adsorption ability unless activated. They are treated with sulfuric acid and hydrochloric acid than it is washed dried crushed to fine powder and used. It is discarded after single application. 8.Gas adsorbent carbon:- This is made by carbonizing of coconut shells, fruit pits, coal, lignite, and wood. It muse be activated, essentially a partial oxidation process, by treatment with hot air of steam. It is used for recovery of solvent vapors from gas mixtures, gas masks, collection of gasoline hydrocarbons from natural gas , and the fractionation of hydrocarbon gases.
- 14. 9.Molecular-screening activated carbon:- This is a specially made from with pore opening controlled from 5 to 5.5 A. It is used in fractionating acetylene compounds, alcohols, organic acids, ketones, aldehydes, and many others. 10.Synthetic polymeric adsorbents:- These are porous spherical beads, 0.5 mm in diameter, each bead a collection of microspheres, 10^-4 in diameter. They are used for treating water solutions and are regenerated by leaching with low-molecular –weight alcohols or ketones.
- 15. Adsorbent solids are usually used in granular, varying in size from roughly 12mm in diameter to 50 micrometer. It should not offer high pressure drop. They should be having high strength and hardness so that it does not get crush during handling of the adsorbent. It should be freely flowing. It should have adsorptive ability. It should have large surface per unit weight.
- 16. http://www.emedicalprep.com/study- material/chemistry/surface-chemistry/adsorption- application.html Mass Transfer Operations by Robert E. Treybal