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ContentsContents IntroductionIntroduction
DistillationDistillation Solvent Extraction Solvent Extraction
Solid Phase ExtractionSolid Phase Extraction Solid Phase micro
ExtractionSolid Phase micro Extraction Supercritical Fluid
ExtractionSupercritical Fluid Extraction Supercritical Fluid
ChromatographySupercritical Fluid Chromatography Field Flow
FractionationField Flow Fractionation
ElectrophoresisElectrophoresis Membrane separationsMembrane
separations
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IntroductionIntroduction
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IntroductionIntroduction
In order to affect a separation, separating In order to affect a
separation, separating agents are needed in the form of
either:agents are needed in the form of either:
Energy input (heat, pressure, electricity, Energy input (heat,
pressure, electricity, magnetism, kinetic or potential
energy)magnetism, kinetic or potential energy)
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IntroductionIntroduction
Withdrawal of energy ( cooling, freezing)Withdrawal of energy (
cooling, freezing) Matter (filter, membrane, chemicals)Matter
(filter, membrane, chemicals)
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A separation process is an operationA separation process is an
operationcarried out in a special separation carried out in a
special separation device which transforms a mixture device which
transforms a mixture into at least two product streams into at
least two product streams which are different in composition.which
are different in composition.
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In the separation device, separation In the separation device,
separation takes place due to an imposed takes place due to an
imposed gradient such as temperature, gradient such as temperature,
concentration, pressure or electrical concentration, pressure or
electrical field. field.
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Two important elements of Two important elements of separation
are:separation are:
1.1. Separating agent used (heat, Separating agent used (heat,
pressure, solvent, matter such pressure, solvent, matter such as
resins, filters, adsorbents as resins, filters, adsorbents
etc.)etc.)
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1.1.Principle of separation Principle of separation used,
separation gradient used, separation gradient applied (temperature,
applied (temperature, concentration, chemical concentration,
chemical potential, magnetic field potential, magnetic field
etcetc.) .)
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Distillation theoryand practice
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ClausiusClausius-- ClapeyronClapeyron equationequation
This relationship can be used to determine the This relationship
can be used to determine the HHvapvap from the pfrom the p00 of a
liquid at two temperatures. of a liquid at two temperatures.
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ClausiusClausius-- ClapeyronClapeyron equationequation
An estimate of PAn estimate of P00 can be made of any can be
made of any temperature provided the Htemperature provided the
Hvapvap and the boiling and the boiling point at atmospheric
pressure is known. point at atmospheric pressure is known.
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Field Flow Fractionation
Field Flow Field Flow FractionationFractionation
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Flow FFFFlow FFF
Two crossed flow streams are superimposed on Two crossed flow
streams are superimposed on the same channel.the same channel.
Channel walls are permeable and the pore size Channel walls are
permeable and the pore size determines the lower size limit for
separation.determines the lower size limit for separation.
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Field flow fractionationField flow fractionation
The driving force is the viscous force The driving force is the
viscous force exerted on the particle by the cross streamexerted on
the particle by the cross streambased on sample diameterbased on
sample diameter..
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Solid Phase Solid Phase ExtractionExtraction
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Solid Phase Solid Phase Micro ExtractionMicro Extraction
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Supercritical Fluids
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Supercritical FluidSupercritical FluidExtractionExtraction
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Supercritical Fluid Supercritical Fluid
ChromatographyChromatography
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Electrophoresis
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Capillary Capillary
ElectrochromatographyElectrochromatography
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Membrane Membrane SeparationsSeparations
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Definition: A membrane is a thin barrier which allows selective
passage of different species through it.
This selectivity is utilized for separation.
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The selectivity is due to:
1.Size
2.Shape
3.Electrostatic charge
4.Diffusivity
5.Physicochemical interactions
6.Volatility
7.Polarity/solubility
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Product concentration, i.e. removal of Product concentration,
i.e. removal of solvent from solute/ssolvent from solute/s
Clarification, i.e. removal of particles Clarification, i.e.
removal of particles from fluids, a special case being from fluids,
a special case being sterilization which refers to removal of
sterilization which refers to removal of microorganisms from
fluidsmicroorganisms from fluids
Membrane separation Membrane separation processes:
Applicationsprocesses: Applications
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Removal of solute from solvent, e.g. Removal of solute from
solvent, e.g. desalting, desalination, desalting, desalination,
demineralization, dialysisdemineralization, dialysis
Fractionation, i.e. separation of one Fractionation, i.e.
separation of one solute from anothersolute from another
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Gas separation, i.e. separation of Gas separation, i.e.
separation of one gas from anotherone gas from another
PervaporationPervaporation, i.e. removal of , i.e. removal of
volatiles from non volatiles (usually volatiles from non volatiles
(usually solvents)solvents)
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Membrane materialMembrane material Organic polymersOrganic
polymers
Polysulfone (PS)Polysulfone (PS) Polyethersulfone
(PES)Polyethersulfone (PES) Cellulose acetate (CA)Cellulose acetate
(CA) Regenerated celluloseRegenerated cellulose Polyamides
(PA)Polyamides (PA) Polyvinylidedefluoride
(PVDF)Polyvinylidedefluoride (PVDF) Polyacrylonitrile
(PAN)Polyacrylonitrile (PAN)
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Membrane materialMembrane material InorganicsInorganics
--aluminaalumina --aluminaalumina Borosilicate glassBorosilicate
glass Pyrolyzed carbonPyrolyzed carbon Zirconia/stainless
steelZirconia/stainless steel Zirconia carbonZirconia carbon
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Membrane preparationMembrane preparation
Polymer castingPolymer castingPrecipitation from vapour
Precipitation from vapour phasephase
Precipitation by evaporationPrecipitation by
evaporationImmersion precipitationImmersion precipitationThermal
precipitationThermal precipitation
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Membrane preparationMembrane preparation
Other methodsOther
methodsStretchingStretchingSinteringSinteringSlip castingSlip
castingLeachingLeachingTrack etchingTrack etching
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Driving force in membrane Driving force in membrane
processesprocesses
Transmembrane pressure (TMP)Transmembrane pressure (TMP)
Concentration gradientConcentration gradient Chemical
potentialChemical potential Osmotic pressureOsmotic pressure
Electric fieldElectric field Magnetic fieldMagnetic field Partial
pressurePartial pressure pH gradientpH gradient
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Membrane processes Membrane processes primarilyprimarily based
based on species sizeon species size
Microfiltration (MF)Microfiltration (MF)Micron sized poresMicron
sized poresMainly used for particleMainly used for particle--fluid
separationfluid separationTMP: 1 to 50 psigTMP: 1 to 50 psig
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Membrane processes Membrane processes primarilyprimarily based
on based on species sizespecies size
Ultra filtration (UF)Ultra filtration (UF)Pores: 10 Pores: 10
1000 angstroms1000 angstromsUsed for: Concentration, desalting,
Used for: Concentration, desalting,
clarification and fractionationclarification and
fractionationTMP: 10 TMP: 10 100 psig100 psig
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Membrane processes Membrane processes primarilyprimarily based
on based on species sizespecies size
NanofiltrationNanofiltration (NF)(NF) TMP: 40 TMP: 40 200
psig200 psig
Reverse osmosis (RO) Reverse osmosis (RO) TMP: 200 TMP: 200 300
psig300 psig
DialysisDialysisConcentration gradient drivenConcentration
gradient drivenSelectivity based indirectly on Selectivity based
indirectly on sizesize
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Membrane processes based Membrane processes based on principles
other than on principles other than
species sizespecies size
Pervaporation (PV)Pervaporation (PV)Driven by partial
pressureDriven by partial pressureSelectivity depends on volatility
Selectivity depends on volatility and solubility of species in and
solubility of species in membranemembrane
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Gas separationGas separationDriven by partial pressureDriven by
partial pressureSelectivity depends on solubility of Selectivity
depends on solubility of
species in membranespecies in membrane
ElectrodialysisElectrodialysis (ED)(ED)Driven by electric
fieldDriven by electric fieldSelectivity depends of charge
Selectivity depends of charge
exclusionexclusion
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In membrane separations a mixture is separated by using a semi
permeable membrane
Membrane SeparationsMembrane Separations
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Membrane SeparationsMembrane Separations
which allows one component to move through faster than others
resulting in differential transport
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The mixture is separated into a retentate, enriched in the less
mobile species and a permeate,
enriched in the components which move through the membrane
fastest.
MembraneMembrane SeparationsSeparations
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Membrane SeparationsMembrane Separations
Retentate
Permeate
Feed mixture
Purge(optional)
Membrane
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Transport Mechanisms Through Transport Mechanisms Through
MembranesMembranes
Transport Through Membranes: Bulk flow through pores (membrane
is
microporous with pores larger than the mean free path).
Diffusion through pores (pores are large enough for diffusion,
but small relative to the MFP).
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Transport Mechanisms Through Transport Mechanisms Through
MembranesMembranes
Restricted diffusion through pores (if pores are large enough
for some species, but not others).
Solution-diffusion (Diffusion through dense membranes with
diffusantdissolved in polymer matrix).
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Transport Mechanisms Through Transport Mechanisms Through
MembranesMembranes
Solution-diffusionRestricted diffusion
Diffusion through poresBulk flow through pores
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MicrofiltrationMicrofiltration and and
UltrafiltrationUltrafiltration
Microfiltration is based on the restricted diffusion of species
through pores: Larger speciesor particles are restricted from
entering pores of 0.1 to 1 micron in size.
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MicrofiltrationMicrofiltration and and
UltrafiltrationUltrafiltrationRestricted diffusion
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Ultrafiltration is similar, except the pore size is even smaller
(on the order of
the molecule size) and the number of pores small. This allows
for separation
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of smaller components, for example separating a small molecule
from solvent.
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Bulk Flow Through MembranesBulk Flow Through MembranesBulk flow
through pores
L
D
Bulk flow through pores (if membrane is microporous with pores
larger than the mean free path).
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If flow is in the laminar regime then the Reynolds Number NRe
(which is related to the pore and fluid
properties) is less than 2,100:
N Re D 2 , 100
D2
32 L P 0 P
n D2
4
Similar to Darcys Law
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Bulk Flow Through MembranesBulk Flow Through Membranes D
2
32 L P0 P
Note that the the porosity gives the total cross-sectional area
of the flow perpendicular to the flow direction:
n D2
4N Combining:
Velocity Porosity Flux (molar or mass)
A
Density
N (nA) V
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If the pores are not straight or cylindrical then we must modify
this equation by factors that describe
the tortuosity and specific surface area.
N D2
32L P0 P nD4128L P0 P
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_ElectrodialysisElectrodialysis
+_+ +- -
Electrode rinse solutionElectrode rinse solution
Feed solution
___
_
++ +
+++
+
Concentrate(brine)
Diluate(less salts)
Anode
Cathode
Cationselectivemembranes
Anionselectivemembranes
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Osmosis and Reverse OsmosisOsmosis and Reverse Osmosis
A, B, CP1
C C A, B, CP1
C
Membrane(only permeable
to solvent)
InitialCondition
(equal pressures)
EquilibriumCondition
(pressure differencemaintained by
osmotic pressure)
ReverseOsmosis
(Transport againstconcentration gradient
if pressure aboveosmotic pressure)
A, B, CP1 P2
P2P2