Introduction to
Separation Processes
Engr. Ralph John Erwin R. Ornales
Department of Chemical Engineering
Learning Objectives
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To categorize different types of separation processes
and separation techniques.
To learn the role of separation operations in an
industrial chemical process.
To explain what constitutes the separation of a
chemical mixture and enumerate the five general
separation techniques.
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Learning Objectives
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What is Separation?
Separate (definition from dictionary)
◉ To isolate from a mixture; extract
◉ To divide into constituent parts
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What are Separation Processes?
Defined as those operations which transform a mixture of
substances into two or more products which differ from
each other in composition.
◉ A technique to achieve any mass transfer occurrence that
converts a mixture of substances into two or more
individual product mixtures.
◉ The specific separation design may vary depending on
what chemicals are being separated, but the basic design
principles for a given separation method are always the
same.
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Separation Processes
The main goal of separation process is to purify solution. To
do this, we must cause different transport of species or
convection of species so that the purer mixture can be
collected. Most separation processes involve differential
transport.
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Separations
The separation of chemical mixtures into their constituents
has been practiced, as an art, for millennia.
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Separations
including
enrichment,
purification,
isolation,
concentration, and refining, are important to chemists and chemical
engineers.
◉ Chemists use analytical separation methods while chemical
engineers are more concerned with the manufacture of chemicals
using economical, large-scale separation methods.
◉ Separations
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Why Separation Processes are Important?
◉ Almost every element or compound is found naturally in an impure
state such as a mixture of two or more substances. Many times the
need to separate it into its individual components arises.
◉ A typical chemical plant is a chemical reactor surrounded by
separators.
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Applications of Separation Processes
Raw Materials
Physical
Transformation
 Water to distilled
water
 Crude oil to gasoline
 Air to nitrogen gas ;
oxygen gas
 Coconut oil to
cooking oil
 Limestone to gravel
Chemical
Transformation
Product 1
Product 2
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 Water to hydrogen
 Crude oil to
polyester
 Air to ethylene
glycol (antifreeze)
 Coconut oil to
medicinal oil
 Limestone to
cement
Separation Processes
The separation technology involved in crude
oil reforming includes:
◉ Distillation – separates various chemical
component according to volatility.
◉ Alkylation – to react small hydrocarbon
molecules to create larger ones
◉ Catalytic reforming – to modify the
structure of medium-sized hydrocarbons.
◉ Fluid catalytic cracking – to break apart
very large hydrocarbon molecules.
◉ Hydrocracking – to break apart very large
hydrocarbon molecules
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Why Separation?
There are many reasons for wanting pure substances. Some of
these include:
◉ Need for pure material in engineering applications
◉ Preparation of raw materials into their component
◉ Need for pure material for materials processing
◉ Need to remove toxins or inactive components from solutions
(drugs)
◉ Need for ultra-pure samples for testing
◉ Need for analysis of the components of mixture (DNA testing)
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Examples of Separation Processes
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Separation of blood
Purification of drugs
Purification of Au, Ag, Ti
Refining of crude oil
DNA testing
Purification of organic material
Purification of water
Separation of water and waste product of metabolism from
kidney
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1. Industrial Chemical Processes
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Industrial Chemical Processes
A chemical process is conducted in various manners.
Feed
◉ Naturally occurring
raw materials
◉ Plant or animal
matter
Operating Mode
◉ Batch wise
◉ Continuous
◉ Semi continuous
Operations
◉ Key Operations
(chemical reactions,
separations)
◉ Auxiliary operations
(phase separations,
heat addition, heat
removal, shaft work
addition, shaft work
removal, mixing,
dividing, etc.)
◉ Chemical
intermediates
◉ Chemicals of
commerce
◉ Waste products
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Block-flow Diagrams
◉ Used
to represent chemical processes; indicate chemical
reaction and separation steps and, by connecting lines, the major
process streams that flow from one processing step to another.
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Base Units
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2. Mechanism of Separation
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Why Separation is Difficult to Occur?
Second Law of Thermodynamics
◉ Substances are tend to mix
together
naturally
and
spontaneously.
◉ All
natural processes take
place to increase the entropy,
or randomness of the universe.
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Mechanism of Separation
A schematic diagram of a general separation process is
shown.
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General Separation Techniques
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How Separations are Achieved?
◉
Enhancing the mass transfer rate by diffusion of
certain species relative to mass transfer of all species
by bulk movement within a particular phase, with the
following considerations which are crucial in
separation operations.
Rate of Separation – governed by mass transfer
Extent of Separation – limited by thermodynamic
equilibrium
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How Separations are Achieved?
The extent of separation achieved depends on the following
properties of species in the different phases present.
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3. Separation by Phase Creation
or Addition
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Separation by Phase Creation or Addition
If the feed mixture is a homogeneous, single-phase solution,
a second immiscible phase must often be developed or
added before separation of chemical species can be
achieved.
◉ The second phase is created by an energy-separating agent
(ESA) and/or added as a mass-separating agent (MSA).
◉ Although separations that use an ESA are generally
preferred, an MSA can make possible a separation that is
not feasible with ESA.
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Disadvantages of MSA
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Need for additional separator to recover the MSA for
recycle
Need for MSA makeup
Possible contamination of the product with the MSA
More difficult design procedures
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Partial Condensation or Vaporization
◉ When the feed mixture includes species
that differ widely in their tendency to
condense or vaporize
◉ Separating agent: heat transfer (ESA)
◉ Example: Recovery of 𝐻2 and 𝑁2 from
ammonia by partial condensation and
high-pressure phase separation
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Flash Vaporization
◉ Caused by reducing the pressure of the
feed with a valve.
◉ The resulting vapor phase is enriched
with respect to the species that are
most volatile while the liquid phase is
enriched with respect to the least
volatile species.
◉ Separating agent: pressure reduction
◉ Example: Recovery of water from sea
water
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Distillation
◉ The
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most widely utilized industrial
separation technique.
When the volatility differences among
species are not sufficiently large.
Involves multiple contacts between
countercurrently flowing liquid and
vapor phases.
Separating agent: ESA and sometimes
work transfer
Example: Purification of styrene
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Extractive Distillation
◉ When
volatility differences between
species to be separated are so small
◉ Separating agent: Liquid solvent (MSA)
and heat transfer (ESA)
◉ Example: Separation of acetone and
methanol
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MSA
Absorption
◉ If the feed is all vapor and the stripping
section of the column is not needed to
achieve the desired operation.
◉ Separating agent: Liquid absorbent
(MSA)
◉ Example: Separation of carbon dioxide
from
combustion
products
by
absorption with aqueous solutions of an
ethanolamine
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Stripping
◉ A liquid mixture is separated, generally
at elevated temperature and ambient
pressure, by contacting liquid feed with
a stripping agent.
◉ Separating agent: Stripping vapor (MSA)
◉ Example: Stream stripping of naphtha,
kerosene, and gas oil side cuts from
crude distillation unit to remove light
ends
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Azeotropic Distillation
◉ Formation
of
minimum-boiling
azeotropic mixtures
◉ Separating agent: Liquid entrainer
(MSA) and heat transfer (ESA)
◉ Example: Separation of acetic acid
from water using n-butyl acetate as
entrainer to form azeotrope with
water
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Liquid-Liquid Extraction
◉ Widely
used when distillation is
impractical, especially when the
mixture
to
be
separated
is
temperature-sensitive.
◉ The solvent selectively dissolves only
one or a fraction of the components in
the feed mixture.
◉ Separating agent: Liquid solvent (MSA)
◉ Example: Recovery of Aromatics
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Liquid-Liquid Extraction (Two Solvents)
◉ Each
solvent has its own specific
selectivity for dissolving the components
of the feed mixture.
◉ Separating agent: Two liquid solvents
(𝑀𝑆𝐴1 and 𝑀𝑆𝐴2 )
◉ Example: Use of propane and cresylic
acid as solvents to separate paraffins
from aromatics and naphthenes
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Leaching
◉ Referred to as solid-liquid extraction
◉ Widely used in the metallurgical, natural
product, and food industries.
◉ To promote diffusion of the solute out of
the solid and into the liquid solvent.
◉ Separating agent: Liquid solvent
◉ Example: Extraction of sucrose from
sugar beets with hot water
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4. Separation by Barrier
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Separation by Barrier
The use of microporous and nonporous
membranes as semipermeable barriers for
difficult and highly selective operations is
rapidly gaining adherents.
◉ For microporous membranes, separation
is effected by differing rates of diffusion
through the pores.
◉ For nonporous membranes, separation
occurs because of differences in both
solubility in the membrane and the rate of
diffusion through the membrane.
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Osmosis
◉ Involves transfer, by a concentration
gradient, of a solvent through a
membrane into a mixture of solute and
solvent.
◉ The membrane is almost nonpermeable
to the solute.
◉ Separating agent: Nonporous membrane
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Reverse Osmosis
◉ Transport of solvent in the opposite
direction and is effected by imposing a
pressure, higher than osmotic pressure
on the feed side.
◉ Separating agent: Nonporous membrane
with pressure gradient
◉ Example: Desalination of sea water
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Dialysis
◉ Transport, by concentration gradient, of
small solute molecules, sometimes
called crystalloids, through a porous
membrane.
◉ Separating agent: Porous membrane
with pressure gradient
◉ Example: Recovery of caustic from
hemicellulose
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Microfiltration
◉ Retention of molecules typically in
the size range from 0.02 𝑡𝑜 10 𝜇𝑚
◉ Separating
agent:
Microporous
membrane with pressure gradient
◉ Example: Removal of bacteria from
drinking water
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Ultrafiltration
◉ Retention of molecules typically in
the size range from 1 𝑡𝑜 20 𝑛𝑚
◉ Separating
agent:
Microporous
membrane with pressure gradient
◉ Example: Separation of whey from
cheese
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Pervaporation
◉ The species being absorbed by and
transported through the nonporous
membrane are evaporated.
◉ Uses lower pressures than RO
◉ Separating
agent:
Nonporous
membrane with pressure gradient
◉ Example: Separation of azeotropic
mixtures
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Gas Permeation
◉ Separation of gas mixtures through
membranes, using pressure as the
driving force
◉ Separating
agent:
Nonporous
membrane with pressure gradient
◉ Example: Hydrogen enrichment
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5. Separation by Solid Agent
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Solid Mass Separating Agent
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Usually in the form of granular material or packing
Acts as an inert support for a thin layer of absorbent or
enters directly into the separation operation by
selective adsorption of, or chemical reaction with,
certain species in the mixture.
The active separating agent eventually becomes
saturated with solute and must be regenerated or
replaced periodically.
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Adsorption
◉ Used to remove components present
in low concentrations in non-adsorbing
solvents or gases and to separate the
components in gas or liquid mixtures
◉ Separating agent: Solid adsorbent
◉ Example: Purification of p-xylene
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Adsorption
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Chromatography
◉ A method for separating the components
of a feed gas or liquid mixture by passing
the feed through a bed of packing.
◉ Separating agent: Solid adsorbent or
liquid adsorbent on a solid support
◉ Example: Separation of xylene isomers
and ethylbenzene
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Ion Exchange
◉ Resembles adsorption in that solid
particles are used and regeneration is
necessary, however involves chemical
reaction.
◉ Separating agent: Resin with ion-active
sites
◉ Example: Demineralization of water
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6. Separation by External Field or
Gradient
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Centrifugation
◉ Establishes
a pressure field that
separates fluid mixtures according to
molecular weight.
◉ Force field or gradient: Centrifugal
force field
◉ Example: Separation of uranium
isotopes
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Electrolysis
◉ When water is decomposed into
hydrogen at the cathode and oxygen
at the anode.
◉ Force field or gradient: Electrical
force field
◉ Example: Concentration of heavy
water
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Electrodialysis
◉ Cation
and
anion-permeable
membranes carry a fixed charge,
preventing the migration of species
of like charge.
◉ Force field or gradient: Electrical
force field and membrane
◉ Example: Desalinization of sea water
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7. Selection of Feasible Separation
Processes
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Important Factors
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Thanks!
ANY QUESTIONS?
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