Ion exchange (ionex) 1 Ion exchange Separation method based on exchange of dissolved ions on functional 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 coordination bonding with ionex. More selective. 2 Advantages 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). 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 3 1
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 acid resin cation exchanging http://www.purolite.cz 4 strong base resin anion exchanging capacity IX - characteristics amount of active groups (multiplied by its charge) in IX related to the IX volume (val.dm -3 ) or mass in dry state (val.kg -1 ) total capacity operating capacity number of active groups in given volume used in given process selectivity preferred bonding of specified ion based on affinity towards IX active group degree of swelling osmotic pressure causes expansion of matrix (active groups fixed in IX decrease its concentration by attracted water) volume changes are important from technological point of view 5 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; D rinsing outlet; E reg. soln inlet; F reg. soln. outlet; G flow distribution 6 2
Treatment of wastes radioactive item concentration and repository 7 Treatment of wastes heavy metal contaminated waste water decontamination of ground water old circuit boards treatment Metsep process pro regeneration of waste HCl in IX column for Zn and Fe separation. http://www.remco.com/ixidx.htm 8 Membrane separation processes 9 3
Membrane separation processes Fundamental principle selective transport of components across the membrane by the driving force. Ions, molecules, colloids, etc. can be transported. Membrane nonideal semi permeable barrier with preferred transport of one component from entering stream to product stream permeability amount of flux across the membrane selectivity ability to separate various items 10 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 blocks Disadvantages/limitation membrane poisons compounds solubility precipitation on membrane surface membrane material requirements, price used membrane treatment concentration polarisation 11 Membrane categorization structure 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) 12 4
Membrane modules flat sheet a) sheet fixed in frame b) circular disc tubular (tubular module) similarity to candle filtration 13 Membrane modules II spiral wound - membranes scrolled hollow fiber 14 Membrane material polymer or ceramics (Sterlitech ) Polyethersulfone Ultrafiltration Membrane D dialysis, EP electrophoresis, GS gas separation, MF microfiltration, NF nanofiltration, RO reverse osmosis, UF ultrafiltration 15 5
Membrane processes driving force conc. gradient pressure gradient el. potential temperature gradient process diffusion, osmosis, dialysis, pervaporation reverse osmosis, ultrafiltartion, microfiltration electrodialysis, electrogravitation, electrophoresis, thermoosmosis, membrane destilation concentrate (retentate) feed permeate (diluate) membrane process scheme 16 Pressure membrane processes driving force - external pressure gradient over membrane Process MF UF NF RO pore size [nm]/ rejected compound size [D] 50-1000 nm 3-50 nm/1000-106 D 1-3 nm/200-1000 D pod 1 nm / pod 200 D smallest rejected compounds suspension, miocroorganisms, colloids macromolecules, organic comp. multivalent salts salts MF -microfiltration, UF - ultrafiltration, NF - nanofiltration, RO - reverse osmosis for waste treatment the most frequent application RO/NF (ions separation) and UF (organic polutants separation) 17 Pressure membrane processes 18 6
Reverse osmosis galvanic Ni plating rinsing water regeneration http://www.gewater.com/library/tp/771_application_of.jsp 19 Ultrafiltration Use significantly lower pressure (0,1-1MPa) than RO - low price suitable for organics polutants (oil, ink, etc.) Prep-Tec UF system 2m 3 / den UF FEED Typical ultrafiltration flexographic ink feed. Total solids % : 0.5-2; average 0.75 Suspended solids (mg/l) : 300-10,000; average 5,600 PH : 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 23 PH : 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 20 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 21 7
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 22 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. 23 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 24 8
Electrodyalysis scheme D - diluate chamber, K- concentrate chamber, AM - anion selective membrane, KM - cation selective membrane 25 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 26 Electrodialysis limitations concentration polarisation fouling of chambers and membrane surface membrane poisons limiting current density pressure drop Possible operation modes Operation: batch feed and bleed one-pass Continuous Batch 27 9
Electrodialyser Single parts together forms stack spacer - separation of membranes possible arrangement of diluate flow space 28 Electrodialyser ED-II Type: ED-II-2/200 Nr. of installed membranes 200 cell pairs, (max. effective area 166 m 2 ) Dimension of the membrane Membranes RALEX AM, CM Dimension of the spacer Spacers work.,electr.,inter. Electrode frame and sealing Electrodes anode,cathode End plates (frames) Dimensions, weights 400x 1600mm, effective 320x 1300mm 200 + 210 pieces 810 x 1610 mm, thickness 1 mm 400 + 4 + 2 pieces, PE 2 pieces PP 10 mm, 2 pieces EPDM 1 mm 4 pieces, Ti + Pt (Ru),stainless-steel 2 pieces, PP 20 mm and stainless-steel 500 x 960 x 1750 mm, empty 600 kg, w.water 850 kg Operation limits: DC el. power Pressure inlet /outlet,difference Flow Temperature TSS F -, (Cl - ) ED-II-2/200 max. 400 V / 120 A operational 50 kpa, max. 80 kpa / max. 10 kpa D, K approx. 10 m 3 /hr at 50 kpa, E min. 3 m 3 /hr operation approx. 30 o C, max. 40 o C max. 10 µm, max. 10 ppm max. 5 ppm in electrode solution MEGA a.s. 29 Electrodialysis of Ni rinse water 30 10
Electrodialysis with bipolar membrane Special arrangement of electrodialyser. Water dissociate inside bipolar membrane and H + a OH - ions are introduced to the neighboring chambers 31 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 32 Electrodeionisation (EDI) 33 11
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. 34 Recommended literature Ullmann's Encyclopedia of Industrial Chemistry Published by Wiley-VCH Verlag GmbH & Co. KGaA Perry's Chemical Engineers' Handbook, by Robert H. Perry and Don W. Green McGraw-Hill Inc. best available techniques BAT, reference documents BREF http://eippcb.jrc.es/ 35 12