33 : :

snoitarapes lacimehCsnoitarapes lacimehC naoleMnaoleM .E notfilC .E notfilC

9991,noitacilbuP9991,noitacilbuP ecneicsretnIecneicsretnI--yeliW AyeliW A

--

. .

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

< TARGET="display">

Supercritical Fluids

Supercritical FluidSupercritical FluidExtractionExtraction

Supercritical Fluid Supercritical Fluid ChromatographyChromatography

< TARGET="display">

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