PREPARED BY:-

Pritesh Vasoya (130420105057)

Vishvaraj Chauhan (130420105058)

Vivek Mistry (130420105058)

ADSORPTION

Introduction

Apllication of adsorption

Types of adsorbents

Nature of adsorbents

CONTENT

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:-

INTRODUCTION

 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.

• As shown above, we see that a feed stream containing a contaminated component is passed through a solid adsorbent, and the contaminant component is retained in the adsorbent. Now, if a second liquid feed (known as the desorbent) containing a different component that also has an affinity for adsorbing to the solid adsorbent, there will be competition between the contaminant and this component for the limited number of adsorption sites available. This will result in the removal or desorption of the contaminant component from the solid, as shown in the Figure  below:

 Production of high vacuumIn 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.

APPLICATION OF ADSORPTION

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.

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 oilsDesiccant in packings and double glazingDew 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.

TYPES OF ADSORBENTS

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.

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.

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.

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.

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.

NATURE OF ADSORBENTS

http://www.emedicalprep.com/study-material/chemistry/surface-chemistry/adsorption-application.html

Mass Transfer Operations by Robert E. Treybal

REFERENCE

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