AlhudaidaUniversity
Chemical Engineering
Engineering Collage
Dep. Of Chemical Engineering
Advanced Sepration
Prepared by: Mr Ali Abbas
1
Introduction
• . Many of the substances we use everyday were actually once part of
a mixture. ... It turns out that many compounds and elements aren't
found in nature in their pure form, but are found as parts
of mixtures. Separating substances from mixtures is
an important part of chemistry and modern industry.
SO
Why does chemical engineering require the study of
separation techniques?
2
Petroleum Refinery Engineering
Mr. Ali Abbas
Introduction
• separations are crucial in chemical engineering.
• Since separations are ubiquitous in chemical plants and petroleum
refineries, chemical engineers must be familiar with a variety of
separation methods. We will first focus on some of the most
common chemical engineering separation methods: distillation,,
absorption, extraction and many other separations techniques.
3
Petroleum Refinery Engineering
Mr. Ali Abbas
• Separation process –
In chemistry and chemical engineering a separation process is used to
transform a mixture of substances into two or more distinct products. 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.
4
Petroleum Refinery Engineering
Mr. Ali Abbas
• Industrial separation processes are technical procedures which are used in
industry to separate a product from impurities or other products. The
original mixture may either be a natural resource (like ore, oil or sugar cane)
or the product of a chemical reaction (like a drug or an organic solvent).
• Separation processes are of great economic importance as they are
accounting for 40 – 90% of capital and operating costs in industry. The
separation processes of mixtures are including besides others washing,
extraction, pressing, drying, clarification, evaporation, crystallization and
filtration. Often several separation processes are performed successively.
Separation operations are having several different functions:
• Purification of raw materials and products and recovery of by-products
• Recycling of solvents and unconverted reactants
• Removal of contaminants from effluents
5
Petroleum Refinery Engineering
Mr. Ali Abbas
• A heterogeneous mixture (e. g. liquid and solid) can be separated by
mechanical separation processes like filtration or centrifugation.
• Homogeneous mixtures can be separated by molecular separation
processes; these are either equilibrium-based or rate-controlled.
Equilibrium-based processes are operating by the formation of two
immiscible phases with different compositions at equilibrium, an
example is distillation (in distillation the vapor has another
composition than the liquid). Rate-controlled processes are based on
different transport rates of compounds through a medium, examples
are adsorption, ion exchange or crystallization.
6
Petroleum Refinery Engineering
Mr. Ali Abbas
• separation process is a method that converts a mixture or solution
of chemical substances into two or more distinct product mixtures.
• At least one of results of the separation is enriched in one or more of
the source mixture's constituents. In some cases, a separation may
fully divide the mixture into pure constituents. Separations exploit
differences in chemical properties or physical properties (such as size,
shape, mass, density, or chemical affinity) between the constituents
of a mixture.
• Processes are often classified according to the particular differences
they use to achieve separation. If no single difference can be used to
accomplish a desired separation, multiple operations can often be
combined to achieve the desired end.
7
Petroleum Refinery Engineering
Mr. Ali Abbas
Separations
Exploits Differences of Material Properties
• Molecular Property
• Boiling Point
• Freezing Point
• Particle size
• Affinity to a stationary
phase
• Density
• Selective affinity to solid
particles
• Separation Process
• Distillation
• Crystallization
• Filtration
• Chromatography
• Centrifuge
• Adsorption
Separation processes
Generally, separation processes may be classified as either mechanicalphysical separation processes or mass transfer operations.
• Mechanical-physical separation processes (do not require a mass
transfer gradient for the separation)
• Mass transfer operations (based on diffusion and require a mass
transfer gradient for the separation.
9
Petroleum Refinery Engineering
Mr. Ali Abbas
Separation processes
Examples of mechanical-physical separation processes are:
• Size separation.
• Filtration
• Some and not all membrane separation processes
• Sedimentation (Thickening and clarification)
• Evaporation
• Centrifugation
10
Petroleum Refinery Engineering
Mr. Ali Abbas
Separation processes
Examples of mass transfer operations are:
• Distillation
• Crystallization
• Drying
• Liquid-liquid extraction
• Gas absorption
• Membrane separation (Not all membrane separation
processes)
• Adsorption
• Electrolysis
• Chromatography
11
Petroleum Refinery Engineering
Mr. Ali Abbas
Mechanical-physical separation processes
• Separators
A separator is a vessel in which a mixture of fluids that are not
soluble in each other are separated from one another. In the oil field
separators are used to separate gas from liquid. They are also used to
separate two liquids, such as condensate and water or crude oil and
water. There are more separators in oil and gas process facilities than
any other type of process equipment. Sometimes they are called
scrubbers, accumulators, flash tanks etc. All these vessels have the
same function. They separate two or more fluids; usually gas and
liquid. They all operate in the same way
12
Petroleum Refinery Engineering
Mr. Ali Abbas
Separators
Separators are classified in two ways:
• The position of the vessel.
• The number of fluids to be separated. (phases) Separators can be
used in the horizontal position or in the vertical position.
The two types of separators most commonly used are:
• Two phase horizontal separator.
• Three phase horizontal separator.
The number of phases tells you the number of separate streams that
leave a separator and not the number of phases that are in the inlet
stream.
13
Petroleum Refinery Engineering
Mr. Ali Abbas
FACTORS THAT CAUSE SEPARATION
14
Petroleum Refinery Engineering
Mr. Ali Abbas
Separators
The normal separator must have certain characteristics which are
essential in field operations and plant processes. These are as follows:
• The separator must be strong enough to withstand operating
pressures.
• The separator must have a space where the heavier components can
be collected. It must also have an easy way to drain them.
• It must have outlets on the top for the gas and vapors and outlets for
relief valves. It must also have manholes for inspections and for
cleaning out the bottom of the vessel.
15
Petroleum Refinery Engineering
Mr. Ali Abbas
Separators
• It must be fitted with a controlling system on the inlet or outlet line.
These controls regulate the working pressure on the separator and
control the plant gas intake. There is also an automatic shut off valve
upstream of this control valve to shut off the gas inlet in case of
emergency.
16
Petroleum Refinery Engineering
Mr. Ali Abbas
THREE PHASE HORIZONTAL SEPARATOR
17
Petroleum Refinery Engineering
Mr. Ali Abbas
SCRUBBERS
18
Petroleum Refinery Engineering
Mr. Ali Abbas
Filtration
• Method used to separate large insoluble solid particles from a liquid
/ solution / gas.
• E.g.
Sand and salt solution
Dust from air
• Apparatus used :
Filter funnel
Filter paper
Beaker / Conical flask
• The filter paper has tiny pores that allow small solvent / liquid /
solute particles to flow through but trap larger solid particles.
• The solid particles trapped within the filter paper is called the
residue, while the solution / liquid which passes through the filter
paper is called the filtrate.
Mixture of
solid and
liquid
Filtration
separates a liquid
from a solid
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 40
Stirring
rod
Funnel
Filter paper
traps solid
Filtrate (liquid
component
of the mixture)
Introduction
Filtration
Filtration may be defined as the separation of solids from liquids by passing a
suspension through a permeable medium which retains the particles.
The suspension of solid and liquid to be filtered is known as the slurry. The
porous medium used to retain the solids is described as the filter medium;
The accumulation of solids on the filter is referred to as the filter cake, while the
clear liquid passing through the filter is the filtrate.
The fluid may be a liquid or a gas.
 the valuable stream from the filter may be the fluid, or the solids, or both.
They are also either continuous or discontinuous,
Schematic diagram of filtration system
Rate of Filtration:
The factors affecting rate of filtration is known as Darcy”s law and may be
expressed as:
dV/dt = KA ∆P / μL
where
V= volume of filtrate
t = time of filtration
K = constant for the filter medium and filter cake
A = area of filter medium
P = pressure drop across the filter medium and filter cake
μ= viscosity of the filtrate
l = thickness of cake.
Rate of Filtration
The fluid passes through the filter medium, which offers resistance to its
passage, under the influence of a force which is the pressure differential
across the filter.
rate of filtration = driving force/resistance
Rate of Filtration:
Factors affecting rate of filtration
1- Permeability coefficient
The constant (K) represents the resistance of both the filter medium and the
filter cake.
As the thickness of the cake increase, the rate of filtration and surface area of
the particles will decrease.
the porosity of the cake, and rigidity or compressibility of the particles could
affect the permeability of the cake.
2- Area of filter medium
The total volume of filtrate flowing from the filter will be proportional to the
area of the filter.
The area can be increased by using larger filters.
 In the rotary drum filter, the continuous removal of the filter cake will give
an infinite area for filtration.
Factors affecting rate of filtration
3- Pressure drop
The rate of filtration is proportional to the pressure difference across both the
filter medium and filter cake.
The pressure drop can be achieved in a number of ways:
1. Gravity: A pressure difference could be obtained by maintaining a head of
slurry above the filter medium. The pressure developed will depend on the
density of the slurry.
2.
Vacuum: The pressure below the filter medium may be reduced below
atmospheric pressure by connecting the filtrate receiver to a vacuum pump
and creating a pressure difference across the filter.
3.
Pressure: The simplest method being to pump the slurry into the filter under
pressure.
4.
Centrifugal force: The gravitational force could be replaced by centrifugal
force in particle separation,
Factors affecting rate of filtration
4- Viscosity of filtrate
 It would be expect that an increase in the viscosity of the filtrate will
increase the resistance of flow , so that the rate of filtration is inversely
proportional to the viscosity of the fluid.
This problem can be overcome by two methods:
 a- The rate of filtration may be increased by raising the temperature of the
liquid, which lowers its viscosity. However, it is not practicable if
thermolabile materials are involved or if the filtrate is volatile.
b- Dilution is another alternative but the rate must be doubled.
5- Thickness of filter cake
 The rate of flow of the filtrate through the filter cake is inversely
proportional to thickness of the cake.
Preliminary decantation may be useful to decrease the amount of the solids.
Evaporation
• Involves the removal of solvent molecules in solution by heating a
solution until only the solute particles remain i.e. evaporation to dryness .
This is only done if the solute is in volatile / does not decompose on
heating. e.g. sodium chloride
• Or involves the removal of solvent molecules in a solution by heating a
solution until it is saturated, followed by crystallization. Crystals of the salt
are obtained.
Experimental set-up : •
Salt solution
Beaker
Water
Heat
Centrifugation
• Spin sample very rapidly: denser
materials go to bottom (outside)
• Separate blood into serum and
plasma
• Serum (clear)
• Plasma (contains red blood cells
‘RBCs’)
• Check for anemia (lack of iron)
AFTER
Before
Serum
Blood
RBC’s
A
B
C
Mass transfer operations
• The separation is based on differences of certain physical properties
of the constituents such as the boiling and melting points, adsorption
affinities on a certain solid, and diffusion through certain membranes
34
Petroleum Refinery Engineering
Mr. Ali Abbas
Distillation
• Distillation is a process for isolating components from a mixture
based on differences in boiling points. Vapors are generated from
liquids or solids by heating and are then condensed into liquid
products
• Used to separate a mixture of miscible liquids whose boiling points
are far apart
OR
• To separate a solvent from a solution.
e.g. pure water from sea water
• Apparatus :
Distillation flask
Thermometer
Liebig condenser
Boiling stones
• The solvent molecules evaporate on heating and move into the
condenser. The gaseous solvent molecules condense to form liquid
within the condenser.
• The liquid flows out & is collected. This liquid is called the distillate.
A Distillation Apparatus
thermometer
liquid with a solid
dissolved in it
condenser
tube
distilling
flask
Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 282
hose connected to
cold water faucet
receiving
flask
pure
liquid
• The thermometer reading remains constant as the liquid distils off.
• The thermometer reading shows the boiling point of the distillate
• Cool water flows into the condenser from the bottom and flows out from
the top of the condenser. This is to ensure efficient condensation of hot
vapour as the water jacket of the condenser is completely filled with cool
water and residual vapour can be condensed before it leaves the
condenser.
Fractional Distillation
• Used to separate a mixture of miscible liquids whose boiling points
are fairly close
e.g. Crude oil to petroleum fractions
or ethanol and water
• Apparatus :
Round Bottom flask
Fractionating column
Thermometer
Liebig condenser
Boiling stones
Distillation
41
Petroleum Refinery Engineering
Mr. Ali Abbas
• The solvent molecules evaporate on heating and
move into the fractionating column. Cool glass
beads in the column allow the gaseous solvent
molecules to condense to form liquid within the
column.
• As the temperature in the column rises, the liquid
with the lowest boiling point vaporizes and distils
off. The other liquids are trapped by condensation
within the column.
• The liquid with the lower boiling point distils off
and collects as distillate.
• The temperature rises and the next liquid distils off.
The solution is boiled and steam is driven off.
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 39
Salt remains after all water is boiled off.
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 39
No chemical change occurs when salt water is
distilled.
Distillation
(physical method)
Salt
Saltwater solution
(homogeneous mixture)
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 40
Pure water
Separation of a sand-saltwater mixture.
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 40
Separation of Sand from Salt
1.
Gently break up your salt-crusted sand with a plastic spoon.
Follow this flowchart to make a complete separation.
Saltcrusted
sand.
Calculate
weight of
salt.
Weigh the
mixture.
Weigh
sand.
Pour into
heat-resistant
container.
Fill with
water.
Stir and let
settle 1
minute.
Decant
clear
liquid.
Dry
sand.
No
2. How does this flow
chart insure a complete
separation?
Evaporate
to
dryness.
Yes
Repeat
3 times?
Wet
sand.
Crystallization
• Method of obtaining crystals of a salt by cooling a hot, saturated salt
solution.
• If the saturated solution is cooled very fast, small crystals are
formed.
• On slow cooling, large crystals are formed.
• To form large & well-shaped crystals, a cold saturated solution is
allowed to evaporate slowly.
• Explanation: Crystallization is the slow precipitation of crystals from
a saturated solution. When it is used to purify an impure solid, the
process is often called fractional crystallization or recrystallization.
You heat a sample of the impure compound with a suitable solvent,
often at its boiling point.
50
Petroleum Refinery Engineering
Mr. Ali Abbas
• Crystallisation is one of the purest means of purification.
• Crystallisation is used in :
- Obtaining salt from sea-water.
- Obtaining sulphur.
- Obtaining pure sugar from industries.
- Obtaining very pure silicon used in
computer chips
ABSORPTION PROCESS
• This process selectively removes a certain gas from a gas mixture
using a liquid absorbent. In the refining industry, this process is used
extensively to free the product gas streams from acid gases (mainly
H2S) either by using a physical or a chemical absorbent.
52
Petroleum Refinery Engineering
Mr. Ali Abbas
Physical Absorption
• In Absorption processes no chemical reaction occurs between the
acid gas and the solvent. The solvent, or absorbent, is a liquid that
selectively absorbs the acid gases and leaves out the hydrocarbons.
• Raw natural gas passes counter currently to the descending solvent.
When the solvent becomes saturated with the acid gases, the
pressure is reduced, and hydrogen sulfide and carbon dioxide are
desorbed. The solvent is then recycled to the absorption tower.
Figure 1-1 shows the Selexol process.
53
Petroleum Refinery Engineering
Mr. Ali Abbas
54
Petroleum Refinery Engineering
Mr. Ali Abbas
ADSORPTION PROCESS
• Adsorption processes use a solid material (adsorbent) possessing a
large surface area and the ability to selectively adsorb a gas or a
liquid on its surface. Examples of adsorbents are silica (SiO2),
anhydrous alumina (Al2O3), and molecular sieves (crystalline
silica/alumina).
• Adsorption processes may be used to remove acid gases from natural
gas and gas streams. For example, molecular sieves are used to
dehydrate natural gas and to reduce its acid gases. Adsorption
processes are also used to separate liquid mixtures. For example,
adsorption of n- paraffins from a lowoctane naphtha fraction.
55
Petroleum Refinery Engineering
Mr. Ali Abbas
SOLVENT EXTRACTION
• Liquid solvents are used to extract either desirable or undesirable
compounds from a liquid mixture. Solvent extraction processes use a
liquid solvent that has a high solvolytic power for certain compounds
in the feed mixture. For example, ethylene glycol has a greater
affinity for aromatic hydrocarbons and extracts them preferentially
from a reformate mixture.
56
Petroleum Refinery Engineering
Mr. Ali Abbas
SOLVENT EXTRACTION
• Propane deasphalting removes asphaltic materials from heavy lube
oil base stocks. These materials reduce the viscosity index of lube
oils. In this process, liquid propane dissolves mainly paraffinic
hydrocarbons and leaves out asphaltic materials. Higher extraction
temperatures favor better separation of the asphaltic components.
57
Petroleum Refinery Engineering
Mr. Ali Abbas
Membrane Separation Processes
• What is the membrane?
an interphase separating two phases and selectively controlling the
transport of materials between those phases.
58
Petroleum Refinery Engineering
Mr. Ali Abbas
Membrane Separation Processes
• Separation processes involving membranes require two bulk phases
that are physically separated by a third phase, the membrane. In all
membrane processes, the feed is separated into two phases: the
permeate (the materials that go through the membrane) and the
retentate (the portion of the feed retained by the membrane). The
transport of materials between the permeate and retentate phases is
controlled by the membrane and the operating conditions. One or
more of the species in the feed mixture are allowed to pass through
the membrane in preference to others, that is to say, the membrane
is selective for these species. The permeate phase is enriched in
these species as the retentate phase is depleted of them.
59
Petroleum Refinery Engineering
Mr. Ali Abbas
• Most commercial membranes consist of thin, selective, active layers
or skins (about 0.1 to 5μm) on porous support layers that provide
mechanical strength. The active and support layers can be formed in
a single operation from a given polymeric material. In the case of
composite membranes, the active layer can be a coating on the
support layer
60
Petroleum Refinery Engineering
Mr. Ali Abbas
61
Petroleum Refinery Engineering
Mr. Ali Abbas
62
Petroleum Refinery Engineering
Mr. Ali Abbas
63
Petroleum Refinery Engineering
Mr. Ali Abbas
Water Molecules
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 8
The decomposition of two water molecules.
Water
molecules
Diatomic
oxygen molecule +
Diatomic
hydrogen molecules
Electric
current
2 H2O

O2
+
2 H2
Electrolysis
“electro” = electricity
“lysis” = to split
*H1+
H2O(l)
water
Water
Oxygen
gas forms
Hydrogen
gas forms
O2 (g) + 2 H2 (g)
oxygen
*Must add acid catalyst
to conduct electricity
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 32
hydrogen
Source of
direct current
Electrode
Electrolysis of Water
D.C. power
source
oxygen
gas
hydrogen
gas
anode
cathode
Half reaction at the cathode (reduction):
4 H2O + 4 e -  2 H2 + 4 OH 1Half reaction at the anode (oxidation):
2 H2O  O2 + 4 H 1+ + 4 e -
water
Chromatography
• Used to separate and identify components of a complex mixture.
• Advantages :
• Very accurate – trace quantities of impurities can be detected
• Very complex mixtures can be analyzed
• Only small amounts of the mixture is required for analysis
Introduction
Chromatography – Separating Mixtures •
Includes a mobile/stationary phase •
Preparative or Analytical •
Preparative: Separate to use components •
Analytical: Measure relative proportion of •
a substance
5 different types of Chromatography: •
Adsorption •
Partition •
Ion Exchange •
Molecular Exclusion •
Affinity •
Ex: Chromatography in Action
Adsorption Chromatography
When a mobile gas or liquid collects onto a stationary •
solid
Forms a thin layer of molecules •
Solvent travels up adsorbent to meet sample •
Continues upwards as a solvent/solute solution (adsorbate) •
Different compounds in sample •
Different solubilities •
Travels different distances •
Analyze•
Separate
Identify•
Purify•
Mixture
Components
Quantify•
• Chromatography is a laboratory technique for the separation of a
mixture. The mixture is dissolved in a fluid called the mobile
phase, which carries it through a structure holding another material
called the stationary phase. The various constituents of the mixture
travel at different speeds, causing them to separate. The separation is
based on differential partitioning between the mobile and stationary
phases. Subtle differences in a compound's partition
coefficient result in differential retention on the stationary phase and
thus affect the separation.
• Chromatography may be preparative or analytical. The purpose of
preparative chromatography is to separate the components of a
mixture for later use, and is thus a form of purification. Analytical
chromatography is done normally with smaller amounts of material
and is for establishing the presence or measuring the relative
proportions of analytes in a mixture. The two are not mutually
exclusive
72
Petroleum Refinery Engineering
Mr. Ali Abbas
• Technique is based on DIFFERENTIAL SOLUBILITY of the
solutes present in the mixture within the solvent used.
• The component MOST soluble in the solvent moves the
furthest away from the start line.
• The start line is marked in pencil as pencil lead is
insoluble in solvents. Ink, if used, may separate out &
affect the results of chromatography.
• The spots marked (at the start line) should be above the solvent level to
prevent the spots from dissolving in the solvent prior to the start of the
experiment.
• Longer strips of filter paper allow a clearer separation of spots i.e. spots
will be further apart from each other.
• Spots must be as small as possible to prevent overlapping of spots.
• The tube or vessel used to carry out chromatography is usually stoppered
to prevent evaporation of the solvent used.
• Analysis of a chromatogram :
• Single spot formed implies a pure substance
• Two or more spots formed imply presence of a mixture.
• If original spot does not move above the start line, the substances in the spot are
insoluble in the solvent used.
• Rf (retention factor ) is a value used to identify the components in a
mixture.
• The Rf value of a component is fixed for a particular solvent. The Rf value
may vary if different solvents are used.
Distance travelled by spot
from start line
• Rf of a spot =
Distance travelled by solvent
front from start line
•Applications of chromatography:
• In urine analysis – to detect drugs used to enhance performance at sports.
• In food industry – to ensure safety standards of artificial dyes used in food.
Paper Chromatography
Separation by Chromatography
sample
mixture
a chromatographic column
stationary phase
selectively absorbs
components
http://antoine.frostburg.edu/chem/senese/101/matter/slides/sld006.htm
mobile phase
sweeps sample
down column
detector
Separation by Chromatography
sample
mixture
a chromatographic column
stationary phase
selectively absorbs
components
http://antoine.frostburg.edu/chem/senese/101/matter/slides/sld006.htm
mobile phase
sweeps sample
down column
detector