Ion exchange (ionex) - vscht.czpaidarm/pozp/POZP_MembrEng WEB.pdf · support. Inert support provide...
Transcript of Ion exchange (ionex) - vscht.czpaidarm/pozp/POZP_MembrEng WEB.pdf · support. Inert support provide...
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Ion exchange(ionex)
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Separation method based on exchange of dissolved ions onfunctional groups fixed on matrix .
Ionex (ion exchanger (IX)) - compound able to exchange ions
inorganic (zeolites) and organic materials, nowadays mainly
functionalised organics polymers
Cation exchanger - ionex exchanging positive charged ions
Anion exchanger - ionex exchanging negative charged ions
Chelating ionex - dissolved species are captured by coordinationbonding with ionex. More selective.
Ion exchange
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• enable to capture ions from very diluted solutions and
concentrate them
• selective - special ion exchangers designed to separate only one
type of ions (e.g. nitrates).
Advantages
Disadvantages
- additional chemicals necessary (regeneration) - waste solutions formation
- low efficiency in case of high concentration
- fouling of columns - pretreatment necessary
- risk of biological contamination
- periodically interrupted
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Ion exchangers• inorganic or organic materials , today mainly synthetic
polymers (polystyrene, polyacrylate) (resins)
• form of particles (spheres) – particle size has influence to the kinetics and pressure drop in IX column
• IX matrix – wide polymer molecule forming IX particle
strong base resin – anion exchanging
strong acid resin – cation exchanging
http://www.purolite.cz
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capacity
• amount of active groups (multiplied by its charge) in IX relatedto the IX volume (val.dm-3) or mass in dry state (val.kg-1) – totalcapacity
• operating capacity – number of active groups in given volumeused in given process
IX - characteristics
selectivity
• preferred bonding of specified ion based on affinity towards IXactive group
degree of swelling
• osmotic pressure causes expansion of matrix (active groupsfixed in IX decrease its concentration by attracted water)
• volume changes are important from technological point of view
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Column operation
• most frequent arrangement (filter press principle)
• equilibrium at each level => low output concentrations
• working cycle
sorption – capture of ions
regeneration – displacement of captured ions
rinsing – remaining parts of reg. solution
backwash – to eliminate resin compaction + suspended items removal
IX column: A inlet; B outlet of treated water; C rinsing inlet; Drinsing outlet; E reg. soln inlet; F reg. soln. outlet; G flow distribution
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Treatment of wastes
• radioactive item concentration and repository
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Treatment of wastes
• heavy metal contaminated waste water
• decontamination of ground water
Metsep process pro regeneration of waste HCl in IX column for Zn and Fe separation.
http://www.remco.com/ixidx.htm
old circuit boards treatment
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Membrane separation processes
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Fundamental principle – selective transport of componentsacross the membrane by the driving force. Ions, molecules,colloids, etc. can be transported.
Membrane – nonideal semi permeable barrier with preferredtransport of one component from entering stream to product stream
permeability– amount of flux across the membrane
selectivity– ability to separate various items
Membrane separation processes
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Advantages• separation of components without change of state at ambient
temperature
• simple automation and continuous process
• simple arrangement – easy scalable
• low energy consumption related to “classical methods”
• zero-emission technological blocksDisadvantages/limitation
• membrane poisons
• compounds solubility – precipitation on membrane surface
• membrane material requirements, price
• used membrane treatment
concentration polarisation
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Membrane categorization
• symmetric
structure and pore size same across all membrane thickness
usually formed by one type of material
• asymmetric
separation layer on porous support
one or more materials (composite)
structure
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Membrane modules
• flat sheet
a) sheet fixed in frame
b) circular disc
• tubular (tubular module) –
similarity to candle filtration
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Membrane modules II
• spiral wound - membranes scrolled
• hollow fiber
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polymer or ceramics
Membrane material
D dialysis, EP electrophoresis, GS gas separation, MF microfiltration, NF nanofiltration, RO reverse osmosis, UF ultrafiltration
(Sterlitech™) PolyethersulfoneUltrafiltration Membrane
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Membrane processes
membrane process scheme
feed
concentrate (retentate)
permeate (diluate)
driving force process
conc. gradient diffusion, osmosis, dialysis, pervaporation
pressure gradient reverse osmosis, ultrafiltartion, microfiltration
el. potential electrodialysis, electrogravitation, electrophoresis,
temperature gradient thermoosmosis, membrane destilation
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Pressure membrane processes
driving force - external pressure gradient over membrane
Process pore size [nm]/ rejected compound size [D]
smallest rejected compounds
MF
UFNFRO
50-1000 nm
3-50 nm/1000-106 D1-3 nm/200-1000 Dpod 1 nm / pod 200 D
suspension, miocroorganisms, colloidsmacromolecules, organic comp.multivalent saltssalts
MF -microfiltration, UF - ultrafiltration, NF - nanofiltration, RO - reverse osmosis
• for waste treatment the most frequent application RO/NF(ions separation) andUF (organic polutants separation)
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Pressure membrane processes
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Reverse osmosis
galvanic Ni plating rinsing water regeneration
http://www.gewater.com/library/tp/771_Application_of.jsp
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UltrafiltrationUse significantly lower pressure (0,1-1MPa)
than RO - low price
suitable for organics polutants (oil, ink, etc.)
UF FEED
Typical ultrafiltration flexographic ink feed.Total solids % : 0.5-2; average 0.75 Suspended solids (mg/l) : 300-10,000; average 5,600PH : 5.6-9.3; average 7.5 Chemical Oxygen Demand : 8,000-80,000; average 4,000 Biological Oxygen Demand : 3,340 - 66,000; average 31,000
UF PERMEATE
Typical ultrafiltration of flexographic ink permeates.Total solids % : 0.6-0.62; Suspended solids (mg/l) : 4-40; average 23PH : 4.6-9.3; average 6.8 Chemical Oxygen Demand : 8,00-9,300; average 3,700 Biological Oxygen Demand : 160-6,000; average 2,900
UF CONCENTRATE
Typical practical concentrates of approximately 25% total solids can be achieved via Prep-Tec tubular ultrafiltration systems. Final solids levels of > 30% total solids have been achieved at the expense of more intensive membrane cleaning procedures
Prep-Tec UF system 2m3 / den
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Electromembrane processes
separation of charged ions by migration in electric field.
driving force - electric field
electrodialysis (ED) and electrodeionisation (EDI),
electrophoresis, membrane electrolysis, electrogravitation
suitable for low concentrated solutions treatment
often applied in connection to pressure membrane process
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Ion exchange membranes
ion exchange (ion selective) membrane - foil or sheet prepared from
ion exchanger
main task isn’t ion exchange but selective transport across
charge of active groups in membrane is compensated by ions with
opposite charge - counterions
occurrence of membrane defects causes penetration of ions charged
as active groups fixed in membrane
similarly to ion exchangers:
Cation selective - enables transport of positive charged ions
Anion selective - enables transport of positive charged ions
bipolar - (special kind) membrane consisting from cation and anion
selective layers
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Ione exchange membrane structure
With respect to the structure and preparation way:
Homogeneous - produced by incorporation of active groups to the
polymer film. They are formed only from ion exchanging material.
Most often based on styrenne or vinylpyridine copolymers,
crosslinked by divinylbenzene.
Heterogeneous - dispersion of ion exchanger material in inert
support. Inert support provide mechanical properties and IX material
provide ionic selectivity. Distribution of IX material and optimal
balance between inert matrix and IX material are crucial points in
membrane preparation.
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Electrodialysis
application of direct electric current on dissolved ions cause
migration of ions to the opposite charged electrode.
ion selective membrane enable transport of ions with only one
polarity - cation and anion selective membrane forms together
chambers:
diluate chamber - treated stream
concentrate chamber - stream with concentrated solution
electrodialyser contain hundreds of membrane chambers
arrangement - „filter press“, periodically contains diluate and
concentrate chambers
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Electrodyalysis scheme
D - diluate chamber, K- concentrate chamber, AM - anion selective membrane, KM - cation selective membrane
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Application of electrodialysis
• sea water desalination
• recycling of rinse water in galvanoindustry
• waste water treatment and chemicals recycling in chemical
industry
• radioactive solutions treatment
• desalination of organics compounds (glycerine, CMC)
www.mega.cz
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Electrodialysis limitations• concentration polarisation
• fouling of chambers and membrane surface
• membrane poisons
• limiting current density
• pressure drop
Possible operation modes
Continuous Batch
Operation:• batch• feed and bleed• one-pass
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Electrodialyser
spacer - separation of membranes
Single parts together forms stack
possible arrangement of diluate flow space
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Electrodialyser ED-IIType: ED-II-2/200
Nr. of installed membranes 200 cell pairs, (max. effective area 166 m2)
Dimension of the membrane 400 x 1600 mm, effective 320 x 1300 mm
Membranes– RALEX AM, CM 200 + 210 pieces
Dimension of the spacer 810 x 1610 mm, thickness 1 mm
Spacers– work., electr., inter. 400 + 4 + 2 pieces, PE
Electrode frame and sealing 2 pieces PP 10 mm, 2 pieces EPDM 1 mm
Electrodes– anode, cathode 4 pieces, Ti + Pt (Ru), stainless-steel
End plates (frames) 2 pieces, PP 20 mm and stainless-steel
Dimensions, weights 500 x 960 x 1750 mm, empty 600 kg, w.water850 kg
Operation limits: ED-II-2/200
DC el. power max. 400 V / 120 A
Pressure inlet / outlet,difference operational 50 kPa, max. 80 kPa / max. 10 kPa
Flow D, K approx. 10 m3/hr at 50 kPa, E min. 3 m3/hr
Temperature operationapprox. 30oC, max. 40oC
TSS max. 10µm, max. 10 ppm
F-, (Cl-) max. 5 ppm in electrode solution
MEGA a.s.
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Electrodialysis of Ni rinse water
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Electrodialysis with bipolar membrane
Special arrangement of electrodialyser. Water dissociate inside bipolar membrane and H+ a OH- ions are introduced to the neighboring chambers
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Electrodeionisation (EDI)combination of ion exchange and electrodialysis
continuous process for highly diluted solutions
diluate chamber filled with ion exchanger (mixed bed or selective)
ion exchanger increase conductivity of diluate chamber
ion exchanger is continually regenerated by OH- a H+ ions
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Electrodeionisation (EDI)
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Summary
• all mentioned methods have their own advantages and limitations
• suitable application of any methods need individual judgment
• efficiency increase by methods combination
• in case of waste treatment methods is desired formation of commercially attractive products.
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Recommended literature
• Ullmann's Encyclopedia of Industrial ChemistryPublished by Wiley-VCH Verlag GmbH & Co. KGaA
• Perry's Chemical Engineers' Handbook, by Robert H. Perryand Don W. Green McGraw-Hill Inc.
• best available techniques – BAT, reference documents BREF http://eippcb.jrc.es/