The document provides an overview of various mass transfer processes including liquid-liquid extraction, solid-liquid extraction, rising film evaporation, cooling towers, ion exchange, absorption, adsorption, drying, distillation, and crystallization. For each process, a definition and basic principles are given along with common applications. Diagrams are also included to illustrate some of the key process equipment and flow schemes.

1. © Mujeeb-UR-Rahman
MEHRAN UNIVERSITY OF ENGINEERING AND TECHNOLOGY
JAMSHORO
Department of Chemical Engineering
Mass Transfer Laboratory
Submitted to:
Prof. Abdul Qadeer Laghari
Submitted by:
Mujeeb-UR-Rahman
Roll No. 17CH106

2. © Mujeeb-UR-Rahman
TABLE OF CONTENT
1 LIQUID-LIQUID EXTRACTION
2 SOLID-LIQUID EXTRACTION OR LEACHING
3 RISING FILM EVAPORATOR
4 COOLING TOWER
5 FIXED AND FLUIDIZAD BED
6 ION EXCHANGE
7 ABSORPTION
8 ADSORPTION
9 DRYING
10 DISTILLATION
11 CRYSTILIZATION

3. © Mujeeb-UR-Rahman
LIQUID-LIQUID EXTRACTION
Liquid-Liquid extraction is a process that separates the components mixture based on their
relative solubility in two immiscible or miscible liquid. Liquid-Liquid extraction involves
solute and solvent that are mixing together in order to separates the products. Liquid-Liquid
Extraction (LLE) also known as solvent extraction, is a method to separate compound based
on their relative solubility in two different immiscible liquids, usually water and an organic
solvent.
LLE is a separation process which is based on the distribution of the components to be
separated between two liquid phases.
It depends on the mass transfer of the componentto be extracted from a first liquid phase to
a second one. Liquid-Liquid extraction is the separation method of choice where distillation
fails, e.g., for azeotropic mixtures or temperature sensitive components.
Type of liquid-liquid extraction methods:
 Coalescer
 Settler
 Hydro cyclone
 Centrifugal Extractor
 Flotation
 Liquid-Phase Adsorption
 Column Extractor.
In some cases, the efficiency of a liquid-liquid extraction process canbe strongly improved
by modifying the distribution coefficient. Thus, an organic acid would prefer the non-polar
solvent when not dissociated (at low pH) and the aqueous solvent when dissociated (at high
pH).
Application:
Liquid-liquid extraction is an important separation method in research and chemical
analysis. As a commercial process itis frequently used in the chemical and mining industries
and in the downstream recovery of fermentation products (antibiotics, amino acids,
steroids). Its applications to food are restricted to isolate cases, such as the transfer of
carotenoid pigments from organic solvents to edible oils, or the productionof “terpeneless”
essential citrus oil by extraction the oxygenated compounds ofthe essential oil with aqueous
ethanol.

4. © Mujeeb-UR-Rahman
In liquid-liquid extraction units, mass transfer occurs when the surrounding liquid
react with the droplets. The different densities of the liquid subsequently separate the two
liquids react with the accumulation ofthe droplets from the aboveor below continuous phase
occurs depending on the liquids relative densities. The droplets dispersion at the top and
bottom of the extraction column.
Feed
(CarrierA andSolute C) Extract
(SolventBand
Solute CwithA)
SolventB Raffinate
(CarrierA with
some B and C)
Extraction Unit of Two Inlet Streams (The Liquid Barrier Containing Solute Molecules and
Solvent) and two outlet Streams (Raffinate and Solute-Rich Extract).
Counter Current Extraction Unit
Phase-Setting
and
Coalescing
Section
Mixing and
Contacting
Section

5. © Mujeeb-UR-Rahman
Liquid-liquid Extraction Equipment

6. © Mujeeb-UR-Rahman
RISING FILM EVAPORATOR
Rising Film Evaporators operate on a “Thermo-Siphon” principle.
Feed product enters the bottom of the heating tubes and as it heats,
steam begins to form. The upward force of this steam produced during
the boiling causes liquid and vapors to flow upwards in parallel flow.
At the same time the production of vapor increases and the productis
pressed as a thin film on the walls of the tubes, and the liquid rises
upwards.
Steam condenseon the outside ofthe surface of the vertical tubes. The
liquid inside the tubes is brought to a boil, with the vapor generated
occupying the core of the tube. As the fluid moves up the tube, more
vapor is formed, resulting in a higher central-core velocity that forces
the remaining liquid to the tube wall. This leads to a thinner and more
rapidly moving liquid film.as the film moves more rapidly, hat-transfer
coefficient increase and residence time drop.
Preferably used for the evaporation of highly viscous products and
products that have a tendency to foul the heating surface. Can also
operate as high concentrators with single-pass operation.
Since the vapor and liquid both flow in the same direction, the thinning of the liquid film is
not as pronounced as in a falling-film type of evaporator, and the possibility of tube dry out
is less. This makes the rising-film evaporator particularly suited to services having mild
scaling tendencies.
Applications:
Major uses of rising-film evaporators include concentrating black liquors in pulp-and-paper
mills, and concentrating nitrates, spin-bath liquors, electrolytic tinning liquors, etc.
 Concentration of dilute solutions of plant extract in water or organic solvent.
 Re-boiler to distillation Column
 Used as a pre-concentration before final drying up to saturation point for recovery of
solvent from product or waste stream.

7. © Mujeeb-UR-Rahman
CHEMICAL
 Caustic
Caustic sodaand Caustic potash
solution
 Organic Acids
 Inorganic Acids
 Salt Solutions
Ammonium nitrate, ammonium
sulphate, calcium nitrate etc.
 Amine
Urea, diethylene
 Alcohols
Phenol, methanol, ethanol,
Glycerin
 Petroleum products
 Synthetically products
Caprolactum water, synthetic glue,
stabilizer, aromas.
ORGANIC NATURAL PRODUCTS
 Fermentation Broths
 Glue and gelatin
 Emulsion
 Steepwater
Corn, sorghum
PHARMACEUTICAL
 Pharmaceuticalsolutions
Enzymes, antibiotics, drug extracts,
sugar substitutes, sorbitol, sorbose,
gluconates
 Effluents
Leakage of water, oil emulsions,
photographic effluents, etc.
FOOD INDUSTRY
o Milk and milk products
o High protein juices
o Vegetables juices
o Starch product

8. © Mujeeb-UR-Rahman
SOLID-LIQUID EXTRACTION
Definition:
Extraction of a soluble constituent from a solid
by using a liquid solvent.
 In order to separate the desired solute
constituent or remove an undesirable solute
component from the solid phase, the solid is
contacted with a liquid phase.
 When two phases are in intimate contact and
the solute can diffuse from the solid to the
liquid phase, which causes separation of the
components originally in the solid.
In this process the components of a solid mixture
are extracted into a solvent. Solvent comes into
contactwith the solid matrix. A solvent is usually a
liquid that functions to dissolve a substance or
solute. A solute is the substancebeing dissolved by
a solvent. Thus, the solvent would be the liquid and
the solute would be the substance you would like to extract from the solid matrix. Again,
referring to our tea example, the solute would be your green tea extracted while the solvent
would be the hot water.
 Amount of soluble material removed is often greater than ordinary filtration.
 Properties of the solid may change considerably during the leaching process
 Coarse, hard or granular feed solids may disintegrate into pulp or mush when their
content of soluble material is removed.

9. © Mujeeb-UR-Rahman
APPLICATIONS:
Extraction of vegetable oils
 Extract oil from peanuts, soybeans, castor beans by using Organic solvent (hexane,
acetone, etc.).
 Removal of nickel salts or gold from their natural solid beds with sulfuric acid
solutions.
Food Industry
 Sugar industry when soluble sucroseis removed by water extraction from sugar
cane or beet.
Pharmaceutical
 Herbal and oil extraction
Miniaturized Solid-Phase Extraction Techniques

10. © Mujeeb-UR-Rahman
COOLING TOWER
INTRODUCTION
Cooling towers are widely used in energy
systems and industrial processes to dissipate
waste heat from hot process streams into the
environment. Heat ejection from the wet cooling
tower occurs as convectional transfer between
water droplets and the surrounding air, and as the
evaporation of a small portion of the water into
the moving air. Therefore, the process involves
both heat and mass transfer.
Cooling towers are used to extract waste heat
from water to atmospheric air.
Cooling towers reject heat from the hot water
circulating through the condenser of a chiller.
There are two basic types of cooling towers.
The theory of cooling: As a water droplet falls
through the tower, air flows past it and cooling
takes place in three ways:
a. A small proportionof heat is lost from the
droplet by radiation of heat from its surface.
b. Approximately a quarter to one-third of the heat transferred is by conduction and
convection between the water and the air the amount of heat transferred depends on
the temperature of water and air.
c. The remainder of the heat transfer is by evaporation. As the air evaporates some of
the water into water vapor, the vapor takes with it the latent heat of evaporation. The
remaining water therefore has a lower heat content than it had originally, and is also
at a lower temperature. The amount of evaporation which takes place depends on a
number of factors;these include the total surface area the water presents to the air (the
reason the packing design is so important), and the amount ofair flowing. The greater
the air flow, the greater the cooling achieved.

11. © Mujeeb-UR-Rahman
Cooling Tower Operation
TYPES OF COOLING TOWERS
Natural draft cooling tower:
The natural draft or hyperbolic cooling tower makes use of the difference in temperature
between the ambient air and the hotter air inside the tower. As hot air moves upwards
through the tower (because hot air rises), fresh coolair is drawn into the tower through an
air inlet at the bottom. Due to the layout of the tower, no fan is required and there is almost
no Circulation of hot air that could affect the performance.
Mechanical draft cooling tower:
Mechanical draft towers have large fans to force or draw air through circulated water. The
water falls downwards over fill surfaces, which help increase the contact time between the
water and the air - this helps maximize heat transfer between the two. Cooling rates of
mechanical draft towers depend upon various parameters such as fan diameter and speed of
operation, fills for system resistance etc.
Mechanical draft towers are available in the following airflow arrangements:
a. Counter flow induced draft.
b. Counter flow forced draft.
c. Cross flow induced draft.

12. © Mujeeb-UR-Rahman
The Industrial Application of Cooling Towers
 Water cooled air compressors.
 Natural gas processing plants
 Power plants
 Food processing plants
 Petrochemical plants
 Semi-conductor plants
 Petroleum refineries and more.
 Plastic Injection & Blow Moulding Machine.
 Die casting machine.
 Refrigeration and chilling plant.
 Cold storage.
 Anodizing processes plant.
 Electrical power generation plant.
 Water cooled air conditioning systems and VAM machines.
Conclusion:
The mass transfer and heat transfer is decreased with increase inlet air humidity and
the objective of usepacking is to increase area of contactbetween water and air. The cooling
tower does not use in the place which the air have high humidity.

13. © Mujeeb-UR-Rahman
Assimilation of molecular species throughout the bulk of the solid or liquid is termed as
absorption.
PROCESS
Absorption occurs when atoms pass through or enter a bulky material. During absorption,
the molecules are entirely dissolved or diffused in the absorbent to form a solution. Once
dissolved, the molecules cannot be separated easily from the absorbent.
It is a bulk phenomenon.
Heat exchange Endothermic process.
It is not affected by temperature.
Rate of reaction it occurs at a uniform rate.
Concentration is same throughout the material.
Gas-liquid absorption Blue spheres are solute molecules.
APPLICATION:
The common commercial uses of absorption cycle are absorption chillers for spacecooling
applications, ice production, cold storage, turbine inlet cooling. High efficiency operation,
environmentally friendly refrigerants, clean-burning fuels and few moving parts that require
maintenance make absorption a very good choice for consumers.
The process of gas absorption by a liquid is used in hydrogenation of oils and carbonation
of beverages.
ABSORPTION

14. © Mujeeb-UR-Rahman
ADSORPTION
Accumulation of the molecular species at the surface rather than in the bulk of the solid or
liquid is termed as adsorption.
PROCESS
Adsorption is generally classified into physisorption (weak van der Waals forces) and
chemisorption (covalent bonding). It can also be caused by electrostatic attraction. The
molecules are held loosely on the surface of the adsorbent and can be easily removed.
It is a surface phenomenon.
Exothermic process.
It is favored by low temperature.
Rate of Reaction it steadily increases and reaches
equilibrium.
Concentration on the surface of adsorbentis
different from that in the bulk.
Gas-liquid absorption Blue spheres are solute molecules.
APPLICATIONS:
Some of the industrial applications for adsorption are air-conditioning, adsorption chillers,
synthetic resin and water purification. In pharmaceutical industry applications, prolong
neurological exposure to specific drugs or parts thereof. Adsorption of molecules onto
polymer surfaces is used in various applications such as in the development of non-stick
coatings and in various biomedical devices.

15. © Mujeeb-UR-Rahman
DRYING
The process whereby moisture is vaporized from a material and is swept away from the
surface.
Sometimes under vacuum, but normally by means of carrier gas which passes through or
over the material. Commonly, drying is conceived as the removal of water into a hot
airstream, but drying may encompass the removal of any volatile liquid into any heated gas.
A drying process removes the remaining solvent and a final sintering thermal treatment can
be carried out if further polycondensation or densification is needed.
The moist material must obtain heat from its surroundings by convection, radiation or
conduction, or by internal generation suchas dielectric or inductive heating; the moisture in
the body evaporates and the vapor is received by a carrier gas.
Convective drying process
Dehydration is the process of depriving a material of its water or the loss of water as a
constituent. The term is often used in food-drying operations to describe processes which
strive to expel moisture but retain other volatile constituents in the original material, and
which are responsible for valuable aromatic and flavoring properties.
Desiccation implies a more thorough removal of water.
It is applied in the drying of foodstuffs to indicate almost complete dehydration of these
materials forpreservation. The term is also commonly used to describethe thorough removal
of moisture from gases.
While heat may be used to drive off moisture from a wet substance, moisture can be severed
from its host material by the action of pressure gradients. This process is known
as dewatering.

16. © Mujeeb-UR-Rahman
Drying is an energy-intensive operation of some significance.
An airless drying system with heat recovery
Drying only takes place if the wet material contains more moisture than the equilibrium
value for its environment.
The earliest ideas on convective drying implied that liquid moisture diffuses to the exposed
surface of a wet body where it evaporates, the vapor diffusing through the boundary layer
into the bulk of the surrounding air.
This view is clearly unsatisfactory, except for drying of homogeneous materials in which
the moisture is effectively dissolved. Mechanisms ofmoisture movement are generally more
complex. Most materials are composed of sub entities, such as particles and fibers, which
may be loose or held in some kind of matrix.

17. © Mujeeb-UR-Rahman
CRYSTALLIZATION
A process by which a chemical is converted from a liquid
solution into a solid crystalline state. The widespread useof
crystallization within industry is in part due to the fact that
crystallization acts as both a separation and purification
step; almost all chemical processes utilize at least one
crystallization step (either as key separation mechanism or
final product).
How does the crystallizationprocess occur?
The crystallization process consists oftwo major events:
Nucleation:
Molecules gather together in clusters in a defined
manner. Clusters need to be stable under current
experimental conditions to reach the “critical cluster size”
or they will dissolve. It is this point in the crystallization
process that defines the crystal structure.
Crystal Growth:
Nuclei that have successfully achieved the “critical
cluster size” begin to increase in size. Crystal growth is a
dynamic process, with atoms precipitating from solution
and becoming dissolved. Supersaturation and super cooling are two of the most common
driving forces behind crystal formation.

18. © Mujeeb-UR-Rahman
FIXED AND FLUIDIZED BED
A fluidized bed is a state of a two-phase mixture of particulate solid material and fluid,
which is widely used in many modern technologies for efficient implementation of various
physical and chemical processes.
Fluidized beds have been used in technological processes such as:
cracking and reforming of hydrocarbons (oil), carbonization and gasification of coal, ore
roasting, Fischer-Tropsch synthesis, polyethylene manufacturing, limestone calcining,
aluminum anhydride production, granulation, vinil-chloride production, combustion of
waste, nuclear fuel preparation, combustion of solid, liquid and gaseous fuels, drying,
adsorption, cooling, heating, freezing, conveying, storing and thermal treating of various
particulate solid materials.
The geometrical, physical and aerodynamically properties of particulate solid materials all
affect the onset of fluidization, and the characteristics, behavior and the main parameters of
fluidized beds. The most important solid properties are:
 particle density (not taking porosity into account),
 skeletal (true) density,
 bulk density—mass per unit volume of fixed bed,
 porosity (or void fraction) of the fixed bed—ratio of volume of space between the
particles and the volume of the fixed bed,
 mean equivalent particle diameter—particle characteristic dimension,
 particle shape,
 particle size distribution—probability distribution of particle distribution due to their
size,
 Free fall (or terminal) velocity—velocity of falling particle at which gravitational,
Archimedes and drag forces are in equilibrium.
Forthe exact definition ofthe term "fluidized bed," it is not sufficient to say that the fluidized
bed is astate ofthe two-phasemixture ofthe particulate solid material and the fluid. Between
two limiting states of the mixture—fluid percolation in the vertical direction through a fixed
bed of particulate solids and the free fall of the particles through the stagnant fluid due to
the gravitational force, a variety of different states ofthe solid-fluid two-phasemixture exist.

19. © Mujeeb-UR-Rahman
The common characteristic of all these states in vertical, upward or downward, flow (of
fluid, particles orboth, in the same oroppositedirections) is the existence of fluid-to-particle
relative velocity and drag force.
The fluidized bed characteristics listed above enable its use in various devices for efficient
implementation of physical and chemical processes.
FIXED AND FLUIDIZED BED APPARATUS

20. © Mujeeb-UR-Rahman
DISTILLATION
Distillation is the most widely-used method of separating fluid mixtures on a commercial
scale, it is thus an important part of many processes in the oil and chemical industries.
Many of the tall, thin towers which may be seen in an oil refinery or chemical plant are
distillation columns. The most common column diameter is about 2.5 m, but 6 m diameter
is commonplace and towers of 12 m dia have been built. Column heights may be as much
as 30 m.
The advantages of distillation are:
a) High purity products
b) Economies of scale
c) Well-established technology and
competitive supply of equipment
d) Use of low temperature, low cost
energy
e) Well suited for energy integration into
the surrounding process.
The separation of a mixture by distillation
depends on the difference between the
compositions of a boiling liquid mixture
and the vapor mixture in equilibrium with
the liquid.
DISTILLATION EQUIPMENT

21. © Mujeeb-UR-Rahman
IONEXCHANGE
Ion exchange describes a specific chemical process in which unwanted dissolved ions are
exchanged for other ions with a similar charge.
Ions are atoms or molecules containing a total number of electrons that are not equal to the
total number of protons.
Ion exchange is a water treatment process commonly used for water softening or
demineralization, but it also is used to remove other substances from the water in
processes suchas dealkalization, deionization, and disinfection.
If a substanceis not ionic, such as benzene, it cannot be removed via ion exchange.
Ion Exchange in Drinking WaterTreatment
In the exchange of cations during water treatment, positively charged ions that come into
contact with the ion exchange resin are exchanged with positively charged ions available
on the resin surface, usually sodium.
In the anion exchange process, negatively charged ions are exchanged with negatively
charged ions on the resin surface, usually chloride. Various contaminants — including
nitrate, fluoride, sulfate, and arsenic — can all be removed by anion exchange.