Introduction to mass transfer slides

1. Ch.E-306 Mass Transfer
Prof. Dr. Nadeem Feroze
Dr. Masooma Rustam

2. Introduction to mass transfer;
Basic concepts of mass transfer;
Mass conservation equation for single and multi-component mixtures;
Steady state diffusion; Prediction of diffusion coefficient;
Application using diffusion equation;
Theoretical model for mass transfer;
Mass transfer in porous media;
Convective mass transfer with chemical reaction;
Mass transfer across a phase boundary;

3. Ch.E-306 Mass Transfer
Introduction to mass transfer operations;
Selection criteria among different separation process.
Complete design calculations for equilibrium stage processes; Distillation;
Gas Absorption; Leaching and liquid-liquid Extraction; Ion Exchange;
Design calculation for Differential contractors;
Case study taking environmental, manufacturing and economics effect.

4. Resources
 Principles of Mass Transfer and Separation Processes
Binay K. Dutta
 Principles of Mass Transfer
Kal Renganathan Sharma
 Unit Operations of Chemical Engineering
McCabe, Smith and Harriott edition 7
 Chemical Engineering
Richardson and Coulson

5. 01sep to 03 Nov
Week 1 Lecture 1 Introduction to mass transfer
Lecture 2
Week 2 Lecture 1 Basic concepts of mass transfer
Lecture 2
Week 3 Lecture 1 Mass conservation equation for
Lecture 2 single and multi-component mixtures
Week 4 Lecture 1 Steady state diffusion
Lecture 2
Week 5 Lecture 1 Prediction of diffusion coefficient
Lecture 2
Week 6 Lecture 1 Application using diffusion equation
Lecture 2
Week 7 Lecture 1 Theoretical model for mass transfer
Lecture 2
Week 8 Lecture 1 Mass transfer in porous media
Lecture 2
Week 9 Lecture 1 Convective mass transfer with
Lecture 2 chemical reaction
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10 Nov to 5 Jan
Week 10 Lecture 1 Mass transfer across a phase boundary
Lecture 2
Week 11 Lecture 1 Introduction to mass transfer operations
Lecture 2
Week 12 Lecture 1 Selection criteria among different separation
Lecture 2 process
Week 13 Lecture 1 Complete design calculations for equilibrium
Lecture 2 stage processes
Week 14 Lecture 1 Prediction of diffusion coefficient
Lecture 2
Week 15 Lecture 1 Distillation; Gas Absorption;
Lecture 2
Week 16 Lecture 1 Leaching and liquid-liquid Extraction;
Lecture 2 Ion Exchange
Lecture 2
Week17 Lecture 1 Mass transfer in porous media
Lecture 2
Week 18 Lecture 1 Convective mass transfer with
Lecture 2 chemical reaction

6. Introduction to Mass Transfer

7. Solid dissolving in a liquid ??????????????????
This process begins with the dissolution of salt from the surface of each
crystal into the neighboring liquid. The salt in solution is then transported
across the liquid by convection and diffusion. Stir the liquid to hasten the
process of mixing, as sugar to coffee, leading eventually to a uniform solute
concentration everywhere.
Before After
Introduction to Mass Transfer

8.  Aquatic life ……. Aquatic life uses oxygen dissolved in water for
survival and supply of oxygen mostly comes from air
The concentration of oxygen in natural water is less than what it
should be at saturation or at equilibrium. As a result oxygen gets
absorbed in the water of lakes, rivers and oceans.
The phenomenon of transport of oxygen from air to water is a mass
transfer process since it is caused by a concentration driving force.
Introduction to Mass Transfer

9. Introduction to Mass Transfer
Liquid in open pail of water evaporates into air because of the difference
in concentration of water vapor at the water surface and the surrounding
of air.
A drop of blue liquid dye is added to a cup of water. The dye molecules
will diffuse slowly by molecular diffusion to all parts of the water.

10. Consider a tank that is divided into two equal parts by a partition.
Initially, the left half of the tank contains nitrogen N2 gas while the
right half contains O2 at the same temperature and pressure.
When the partition is removed the N2 molecules will start diffusing
into the air while the O2 molecules diffuse into the N2. If we wait
long enough, we will have a homogeneous mixture of N2 and O2 in
the tank.
Introduction to Mass Transfer

11. Mass transfer is a transport of components under a chemical potential
gradient.
•The component moves to the direction of reducing concentration
gradient.
•The transport occurs from a region of higher concentration to lower
concentration.
•Equilibrium is reached when the gradient is zero.
The transport or migration of one constituent from a region of higher
concentration to that of a lower concentration is known as mass transfer.
Introduction to Mass Transfer

12. Mass transfer may occur in a
• Gas mixture
• Liquid solution
• Solid
Mass transfer occurs whenever there is a gradient in the concentration
of a species. The basic mechanisms are the same whether the phase is a
gas, liquid, or solid.
Introduction to Mass Transfer

13. Whenever there is concentration difference in a medium, nature tends to
equalize things by forcing a flow from the high to the low concentration
region.
The molecular transport process of mass is characterized by the general
equation:
Rate of transfer process = driving force/resistance
Introduction to Mass Transfer

14.  Studies of heat transfer and mass transfer have more common
and similar approaches but a noticeable difference between
mass transfer and heat transfer are way of contact like direct or
indirect contact. The phases exchanging mass through direct
contact are immiscible or partially miscible.
 If phases are miscible, a selectively permeating barrier may be
placed between them to effect mass transfer without physical
mixing of phases……membrane gas separation
Three fundamental transfer processes:
1. Momentum transfer 2. Heat transfer 3. Mass transfer
Introduction to Mass Transfer

15. Mass transfer may be diffusional or convective.
 A purely diffusional mass transfer phenomenon occurs in the
absence of any macroscopic motion of medium. The migration
of moisture within a grain during drying is purely diffusional.
 Mass transfer occur in a fluid medium which is in some sort of
motion is called convective mass transfer with molecular
diffusion.
Introduction to Mass Transfer

16.  Separation of mixture accounts for about 40 to 70
percent of both capital and operating costs of chemical
industry.
 The cost of separation of high value products from a
dilute solution may entail 90% of the operating cost
of a plant.
Introduction to Mass Transfer

17. Role of Separation Processes in a Chemical Industry
Introduction to Mass Transfer

18. Core separation processes in chemical industry
 Gas absorption and Stripping
 Distillation
 Liquid/liquid and solid liquid extraction
 Drying of wet solid
 Adsorption
 Crystallization
 Membrane separation and separation of multi-
component
Introduction to Mass Transfer

19. Absorption/Stripping
Absorption
Absorption and stripping are two chemical process operations
that normally are coupled in order to remove a minor
component, the solute, from an incoming process gas stream
and then recover that same component in a more concentrated
form.
A carefully selected solvent, in which the solute is selectively
soluble, is fed to the absorber (or “scrubber”), and the rich
solvent is then fed to the stripper, where the solute is
recovered.
Introduction to Mass Transfer

20. Acetone is recovered from air using a water solvent. The acetone–water
solution is then stripped to provide high purity acetone.
Coupled absorption-stripping system

21. Adsorption/Desorption
The ability of transfer of mass from either a gas or a liquid to the surface
of a solid. The adsorption is not a true inter-phase mass transfer operation
because the fluid adheres to the solid surface instead of dissolving in the
solid. A desorption involves the transfer of mass from the solid surface
(adsorbents) to the gas or liquid medium (adsorbates).
Introduction to Mass Transfer

22. Adsorption/Desorption
A few operations of practical applications are
1. Elimination of toxic gases and deodorization of air
2. Recovery of solvents
3. Removal of ions from solution as in demineralization of water
4. Fractionation by selective adsorption of gases, vapours from
gases, vapors from vapors and liquids from liquids and many
other applications.
Introduction to Mass Transfer

23. Extraction
Separation of the constituents of a liquid solution by contact with
another insoluble liquid. The liquid which is added to the solution to
bring about the extraction is known as the solvent. The solution which
is to be extracted is called the feed. The solvent-richen product of the
operation is called the extract and the residual liquid from which the
solute is separated is called the raffinate.
Introduction to Mass Transfer

24. Extraction
Application of extraction
1. The separation of aromatics from kerosene based fuel oils
2. The production of fuels in the nuclear industry
3. The separation of penicillin from fermentation mixtures
Introduction to Mass Transfer

25. Leaching
A treatment of a finely divided solid with a liquid.
Some examples of leaching operations are
1. Oilseed extraction
2. Extraction of sugar beets with hot water
3. Extraction of medicinal compounds from plant roots,
leaves and stems.
Introduction to Mass Transfer

26. Distillation
An operation whereby a liquid mixture of miscible and volatile
substances is separated into individual components or into group of
components by partial vaporization.
Examples
The separation of a mixture of methanol and water into its
components
 Separation of petroleum crude into gasoline, kerosene, fuel oil and
lubricating stock
Introduction to Mass Transfer

27. Humidification
In humidification, the enrichment of vapour content in a gas
stream takes place by passing the gas over a liquid. The
transfer of water from the liquid phase to the gas phase of a
mixture of air and water vapour is a widespread application of
humidification.
Introduction to Mass Transfer

28. Dehumidification
Dehumidification involves the transfer of water vapour from the gas phase to
the liquid phase. Removal of water vapour from air by condensation of a cold
surface.
Example
Condensation of carbon tetrachloride out of a stream of nitrogen
Air dehumidification
Introduction to Mass Transfer