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good resentatioon of seperation process
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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
IntroductionIntroduction
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)
IntroductionIntroduction
Withdrawal of energy ( cooling, freezing)Withdrawal of energy ( cooling, freezing) Matter (filter, membrane, chemicals)Matter (filter, membrane, chemicals)
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.
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.
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.)
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.) .)
Distillation theoryand practice
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.
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.
Field Flow Fractionation
Field Flow Field Flow FractionationFractionation
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.
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..
Solid Phase Solid Phase ExtractionExtraction
Solid Phase Solid Phase Micro ExtractionMicro Extraction
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Supercritical Fluids
Supercritical FluidSupercritical FluidExtractionExtraction
Supercritical Fluid Supercritical Fluid ChromatographyChromatography
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Electrophoresis
Capillary Capillary ElectrochromatographyElectrochromatography
Membrane Membrane SeparationsSeparations
Definition: A membrane is a thin barrier which allows selective passage of different species through it.
This selectivity is utilized for separation.
The selectivity is due to:
1.Size
2.Shape
3.Electrostatic charge
4.Diffusivity
5.Physicochemical interactions
6.Volatility
7.Polarity/solubility
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
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
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)
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)
Membrane materialMembrane material InorganicsInorganics
--aluminaalumina --aluminaalumina Borosilicate glassBorosilicate glass Pyrolyzed carbonPyrolyzed carbon Zirconia/stainless steelZirconia/stainless steel Zirconia carbonZirconia carbon
Membrane preparationMembrane preparation
Polymer castingPolymer castingPrecipitation from vapour Precipitation from vapour phasephase
Precipitation by evaporationPrecipitation by evaporationImmersion precipitationImmersion precipitationThermal precipitationThermal precipitation
Membrane preparationMembrane preparation
Other methodsOther methodsStretchingStretchingSinteringSinteringSlip castingSlip castingLeachingLeachingTrack etchingTrack etching
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
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
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
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
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
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
In membrane separations a mixture is separated by using a semi permeable membrane
Membrane SeparationsMembrane Separations
Membrane SeparationsMembrane Separations
which allows one component to move through faster than others resulting in differential transport
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
Membrane SeparationsMembrane Separations
Retentate
Permeate
Feed mixture
Purge(optional)
Membrane
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).
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).
Transport Mechanisms Through Transport Mechanisms Through MembranesMembranes
Solution-diffusionRestricted diffusion
Diffusion through poresBulk flow through pores
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.
MicrofiltrationMicrofiltration and and UltrafiltrationUltrafiltrationRestricted diffusion
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
of smaller components, for example separating a small molecule from solvent.
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).
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
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
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
_ElectrodialysisElectrodialysis
+_+ +- -
Electrode rinse solutionElectrode rinse solution
Feed solution
___
_
++ +
+++
+
Concentrate(brine)
Diluate(less salts)
Anode
Cathode
Cationselectivemembranes
Anionselectivemembranes
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