Lec3_Mass Transfer Principles and Techniques.ppt

Mass Transfer Principles and Operations

1. MASS TRANSFER OPERATIONS
Principles and Techniques
Lecture No: 3

2. MASS TRANSFER OPERATIONS
• Distillation
• Gas Absorption
• Dehumidification
• Adsorption
• Liquid Extraction
• Leaching
• Crystallization
• Membrane Separation
• etc.

3. PRINCIPLES AND TECHNIQUES

Aim of any Mass Transfer Operation:
 SEPARATION - By Transfer of material from
one homogenous phase to another one.
 Driving Force:
 The basic net unbalance force by which the
required TRANSFORMATION of material can
be carried out.
 Unwanted Situation:
 The condition of equilibrium normally
called PHASE EQUILIBRIA.

4. 1. DISTILLATION
 Aim :
Separation by vaporization a liquid mixture of miscible
and volatile substances into individual components (or
in some cases, into a group of components).
 Driving Force:
Difference in vapor pressures.
 Example:
1.Separation of a mixture of alcohol and water into its
components.
2.Liquid air into N
2
, O
2
and Ar.
3.Crude oil petroleum into gasoline, Kerosene, fuel
oil, and Lubricating stock.

5. 2. GAS ABSORPTION
 Aim :
In this a solute gas is absorbed from an inert gas into a
liquid in which the solute is more or less soluble.
(The solute is subsequently recovered from the liquid
by Distillation, and the absorbing liquid can be either
discarded or reused).
 Driving Force:
Difference in solubility .
 Example:
1.The washing of Ammonia from a mixture of
ammonia and air by means of liquid water.

6. 3. DESORPTION OR STRIPPING
 Aim :
In this a solute is transferred from the
solvent liquid to the gas phase.
 Driving Force:
Difference in solubility .

7. 4. DEHUMIDIFICATION

Aim :
In this a pure liquid is partially removed from
an inert or carrier gas by condensation.
 Driving Force:
Difference in rates of condensation .
 Example:
Removing of moisture from air in AC
Environment.

8. 5. HUMIDIFICATION
 Aim :
In this operation the direction of
transfer is from the liquid to the gas
phase.
 Driving Force:
Difference in concentrations .

9. 6. DRYING
 Aim :
In the Drying of SOLIDS, a liquid, usually
water, is separated by the use of hot, dry gas
(usually air) and so is coupled with the
humidification of the gas phase.
 Driving Force:
Difference in concentrations .

10. 7. MEMBRANE SEPARATION
 Aim :
In membrane separation one component of liquid or
gaseous mixture, passes through a selective membrane
more readily than the other components.
 Driving Force:
Difference in thermodynamic activity, but in many
cases the driving force can be expressed as difference
in concentration or partial pressure.
 Example:
Reverse Osmosis, and Ultrafiltration

11. 8. ADSORPTION
 Aim :
In this a solute is removed from either
a liquid or a gas through contact with a
solid ADSORBANT, the surface of which
has a special affinity for the solute.
 Driving Force:
Difference in affinity of the substances
for a particular adsorbent.

12. 9. LIQUID EXTRACTION
 Aim :
A mixture of two components is treated by a solvent
that preferentially dissolves one or more of the
components in the mixture..
 Driving Force:
Difference in solubility
Important Terms:
Raffinate: The mixture treated.
Extract: Solvent rich phase.
Solute: The component transferred from
raffinate to extract.
Diluetent: The component left behind in the
raffinate.

13. 10. LEACHING
 Aim :
It is the EXTRACTION of Solids. In this a soluble material
is dissolved from its mixture with an inert solid by
means of a liquid solvent. (The dissolved material, or
solute, can then be recovered by crystallization or
evaporation).
 Driving Force:
Difference in solubility

14. 11. CRYSTALLIZATION
 Aim :
It is used to obtain materials in attractive and uniform
crystals of good purity, separating a solute from a melt
or solution and leaving impurities behind.
 Driving Force:
Difference in attractive forces (crystal formation)
Examples:
Manufacturing of Sugar.

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