WO2001020060A1 - Procedes et appareil permettant de d'effectuer une desionisation electrique de l'eau - Google Patents

Procedes et appareil permettant de d'effectuer une desionisation electrique de l'eau Download PDF

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Publication number
WO2001020060A1
WO2001020060A1 PCT/US2000/024858 US0024858W WO0120060A1 WO 2001020060 A1 WO2001020060 A1 WO 2001020060A1 US 0024858 W US0024858 W US 0024858W WO 0120060 A1 WO0120060 A1 WO 0120060A1
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WIPO (PCT)
Prior art keywords
diluting
channel
cation
exchange material
anion
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PCT/US2000/024858
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English (en)
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WO2001020060A9 (fr
Inventor
Leon Mir
Original Assignee
Leon Mir
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Publication date
Priority claimed from US09/395,327 external-priority patent/US6187162B1/en
Priority claimed from US09/394,170 external-priority patent/US6241866B1/en
Priority claimed from US09/395,313 external-priority patent/US6254753B1/en
Priority claimed from US09/442,525 external-priority patent/US6241867B1/en
Priority claimed from US09/526,658 external-priority patent/US6296751B1/en
Application filed by Leon Mir filed Critical Leon Mir
Priority to AU73678/00A priority Critical patent/AU7367800A/en
Publication of WO2001020060A1 publication Critical patent/WO2001020060A1/fr
Publication of WO2001020060A9 publication Critical patent/WO2001020060A9/fr

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
    • C02F1/469—Treatment of water, waste water, or sewage by electrochemical methods by electrochemical separation, e.g. by electro-osmosis, electrodialysis, electrophoresis
    • C02F1/4693—Treatment of water, waste water, or sewage by electrochemical methods by electrochemical separation, e.g. by electro-osmosis, electrodialysis, electrophoresis electrodialysis
    • C02F1/4695—Treatment of water, waste water, or sewage by electrochemical methods by electrochemical separation, e.g. by electro-osmosis, electrodialysis, electrophoresis electrodialysis electrodeionisation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/42—Electrodialysis; Electro-osmosis ; Electro-ultrafiltration; Membrane capacitive deionization
    • B01D61/44—Ion-selective electrodialysis
    • B01D61/46—Apparatus therefor
    • B01D61/48—Apparatus therefor having one or more compartments filled with ion-exchange material, e.g. electrodeionisation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J47/00—Ion-exchange processes in general; Apparatus therefor
    • B01J47/02—Column or bed processes
    • B01J47/06—Column or bed processes during which the ion-exchange material is subjected to a physical treatment, e.g. heat, electric current, irradiation or vibration
    • B01J47/08—Column or bed processes during which the ion-exchange material is subjected to a physical treatment, e.g. heat, electric current, irradiation or vibration subjected to a direct electric current
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/42—Treatment of water, waste water, or sewage by ion-exchange
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
    • C02F1/4604—Treatment of water, waste water, or sewage by electrochemical methods for desalination of seawater or brackish water
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2201/00—Apparatus for treatment of water, waste water or sewage
    • C02F2201/46—Apparatus for electrochemical processes
    • C02F2201/461—Electrolysis apparatus
    • C02F2201/46105—Details relating to the electrolytic devices
    • C02F2201/46115—Electrolytic cell with membranes or diaphragms

Definitions

  • the invention relates to apparatus and methods for carrying out electrodeionization to purify water.
  • Electrodeionization is a process for removing ions from liquids by sorption of these ions into a solid material capable of exchanging these ions for either hydrogen ions (for cations) or hydroxide ions (for anions) and simultaneous or later removal of the sorbed ions into adjacent compartments by the application of an electric field.
  • the hydrogen and hydroxide ions needed to drive the ion exchange process are created by splitting of water molecules at the interface of anion and cation exchanging solids that contact each other in the orientation that depletes the contact zone of ions, when in the presence of an electric field. This orientation requires that the anion exchanging material face the anode and the cation exchanging material face the cathode.
  • the created hydroxide ions enter the anion exchanging material, and the created hydrogen ions enter the cation exchanging material.
  • the electrodeionization process is commonly carried out in an apparatus consisting of alternating diluting compartments and concentrating compartments separated by anion permeable and cation permeable membranes.
  • the diluting compartments are filled with porous ion exchanging solid materials through which the water to be deionized flows.
  • the ion exchanging materials are commonly mixtures of cation exchanging resins and anion exchanging resins (e.g., U.S. Patent 4,632,745), but alternating layers of these resins have also been described (e.g., U.S. Patents Nos. 5,858,191 and 5,308,467).
  • Ion exchanging materials consisting of woven and non-woven fibers have also been described. (E.g., U.S. Patent No.
  • the compartments adjoining the diluting compartment into which the ions are moved by the applied electric field may be filled with ion exchanging materials or with inert liquid permeable materials.
  • An assembly of one or more pairs of diluting and concentrating compartments, referred to as a "cell pair" is bounded on either side by an anode and a cathode which apply an electric field perpendicular to the general direction of liquid flow. Flow of water is provided past the anode and cathode.
  • the diluting compartments are each bounded on the anode side by an anion permeable membrane and on the cathode side by a cation permeable membrane.
  • the adjacent concentrating compartments are each correspondingly bounded by a cation permeable membrane on the anode side and an anion permeable membrane on the cathode side.
  • the applied electric field causes anions to move from the diluting compartment across the anion permeable membrane into the concentrating compartment nearer the anode and cations to move from the diluting compartment across the cation permeable membrane into the concentrating compartment nearer the cathode.
  • the anions and cations become trapped in the concentrating compartments because the movement of anions toward the anode is blocked by a cation permeable membrane, and the movement of cations toward the cathode is blocked by an anion permeable membrane.
  • a flow of water is set up to remove the ions from the concentrating compartments. The net result of the process is the removal of ions from the water stream flowing through the diluting compartments and their concentration in the water flowing through the concentrating compartments.
  • the removal of the ions from the diluting compartment is a multi-step process involving diffusive steps as well as electrically driven steps.
  • the mobility of ions in the solid material may be on the order of 20 times smaller than their mobility in the solution, the electric field acting on the ions in the two phases is the same, so the product of mobility times concentration times electric field strength, which determines the rate of ion removal, is 50 to 5,000 times as large in the solid ion exchanging material.
  • the mechanism of ion removal from the diluting compartment solution includes two steps.
  • the first step is the diffusion of cations to the cation exchanging solids and the diffusion of anions to the anion exchanging solids.
  • the second step is electrical conduction within the solids phases to the bounding membranes of the diluting compartment. Because the concentration of ions in ion exchanging solids is so high, the process that controls the overall removal of ions is their rate of diffusion from the solution to the surface of the ion exchanging solids.
  • This diffusion rate is a function of three factors; the diffusion rate is proportional to surface area between the ion exchanging solids and the flowing solution, inversely proportional to the thickness of the liquid layer through which the ions must diffuse, and proportional to the difference in concentration of the ions in the bulk of the diluting solution and their concentration next to the ion exchanging solid.
  • the ratio of the surface area to the diffusion distance is inversely proportional to the characteristic dimension of the ion exchanging solid material; the characteristic dimension is particle radius for ion exchange resins and is fiber radius for ion exchange fibers.
  • this characteristic dimension can be made as small as possible, commensurate with avoidance of excessive pressure drops or plugging by particles in the water to be treated. Particle diameters on the order of 500 to 600 micrometers are typical, and fiber diameters can be on the order of several tens of microns.
  • the third factor controlling the rate of ion removal is the difference in concentration of the ion being removed between the bulk of the solution and its concentration in the liquid adjacent to the surface of the ion exchanging solid where it is being exchanged for either a hydrogen or a hydroxide ion.
  • the concentration of the ion in question at the surface of the ion exchanging solid is in equilibrium with the concentration of that ion in the solid.
  • the equilibrium concentration is approximately equal to the ratio of the cation concentration to the hydrogen ion concentration in the cation exchanging solid times the concentration of the cation in solution.
  • the equilibrium concentration is approximately equal to the ratio of the anion concentration to the hydroxide ion concentration in the anion exchanging solid times the concentration of the anion in solution.
  • the cation exchanging solid should be predominantly in the hydrogen form, and the anion exchanging solid should be predominantly in the hydroxide form.
  • the two solids are completely in the ionic form rather than in the hydrogen or hydroxide form, there is no concentration difference, and ions will not be removed by this diffusive mechanism.
  • the rate of hydrogen ion and hydroxide ion creation must be both high and spatially uniform.
  • a high average rate of water splitting can be achieved by applying a high voltage drop across the diluting compartment.
  • voltages of between 1 and 5 volts are adequate for the purpose.
  • the achievement of a uniform distribution of water splitting is a more difficult problem and much effort has gone into designing structures that achieve this (e.g., U.S. Patents Nos. 5,858,191, 5,868,915 and 5,308,467).
  • Electrodeionization (EDI) stacks frequently suffer from precipitation of calcium carbonate in the concentrating compartments as well as in the cathode compartment.
  • EDI Electrodeionization
  • Vendors of EDI equipment suggest that the concentration of calcium in the feed to the EDI be limited to very low levels; e.g., less than 0.5 ppm. (U.S. Filter Literature No. US2006). While this concentration can be achieved when the electrodeionization apparatus is fed with reverse osmosis (RO) permeate from an RO system with new membranes, and the RO system is operating properly, the suggested values can be exceeded when these conditions do not hold.
  • RO reverse osmosis
  • the Langelier Saturation Index In order for calcium carbonate to precipitate in solution the Langelier Saturation Index (LSI) has to be positive. In the cathode compartment the pH can be high enough for the LSI to be positive; precipitation of calcium carbonate is therefore to be expected under some circumstances.
  • the LSI of RO permeates is always negative. Even in the EDI brine the concentrations of calcium and bicarbonate are so low that the LSI is still negative, at the prevailing pH. Thus, on the basis of consideration of LSI alone, one would not expect the precipitation of calcium carbonate that occurs within EDI concentrating compartments. This phenomenon is instead explainable based upon local conditions.
  • Carbon dioxide and silica diffuse from solution into the partly regenerated anion resin and react with the OH- to form the HC03-, CO 3 • and HSi03- anions which are moved, along with substantial amounts of OH-, by the applied voltage gradient, into the concentrating compartment.
  • the voltage drop in the diluting compartment has to be high enough, typically 2 to 3 volts, to regenerate some portion of the anion resin by the splitting of water into OH- and H+.
  • the ion exchange resin In an EDI stack operated at a sufficiently high current density, the ion exchange resin will be so highly regenerated that it should be capable of producing water equivalent to that produced by mixed ion exchange beds.
  • the second, more fundamental mechanism that limits the ultimate purity of the water that can be produced by EDI is the imperfect permselectivity of ion exchange membranes; i.e., some cations from the concentrating compartment penetrate the anion membrane and some anions penetrate the cation membrane. In both cases the voltage gradient will then force them into the diluting compartment.
  • the Donnan equation (see ADemineralization by Electrodialysis@ by J.R. Wilson Butterworth Scientific Publications, 1960, p. 56) predicts that the penetration of co-ions into the membranes decreases with a decrease in the concentration of these ions in the concentrating compartment.
  • the parasitic processes are illustrated in Fig. 33, which shows a single concentrating channel 510, having cation permeable membrane 512, anion permeable membrane 514 oriented as indicated between anode 516 and cathode 518.
  • the invention features, in general, electrodeionization apparatus for purifying water.
  • the apparatus includes a cathode, an anode, and a plurality of alternating anion permeable membranes and cation permeable membranes between the cathode and anode that define concentrating and diluting flow channels between adjacent pairs of membranes.
  • the diluting channels include cation exchange materials and anion exchange materials that are fixed in close contacting position with respect to each other and provide conductive paths for cations and anions to the adjacent membranes and provide flow passages for water between the materials.
  • the anion exchange materials and cation exchange materials each have a characteristic dimension that is smaller than the characteristic dimensions of the flow passages.
  • Particular embodiments of the invention may include one or more of the following features.
  • Individual particles of cation exchange material and anion exchange material can be fixed together with a binder in sufficient particle concentration to provide conductive paths for cations and anions.
  • the particles of cation exchange material, anion exchange material and binder can form larger combined particles packed into the diluting flow channel in contacting relation between adjacent membranes.
  • the combined particles are sufficiently large so as to cause an acceptably low pressure drop in the diluting flow channel.
  • the particles of the cation exchange material and the anion exchange material and binder can form filaments provided as a matrix between the adjacent membranes.
  • the openings in the matrix for water flow are larger than the diameter of the filaments.
  • a further alternative is to have particles of cation exchange material, anion exchange material and binder form an open cell foam between adjacent membranes, with the openings in the foam being sufficiently large to provide flow passages through the foam with an acceptably low pressure drop.
  • the fixed ion exchange material could also be provided as cation exchange filaments and anion exchange filaments that are intimately commingled or joined together.
  • the fixed ion exchange materials When the fixed ion exchange materials are in the form of filaments, they can be provided in multiple filament bunches or as multiple filament braids.
  • the strands, made of bunches, braids, or individual filaments, can be fixed with respect to other strands by providing them as a woven fabric, nonwoven (randomly oriented) fabric or extruded netting.
  • the fabric could also be provided by extrusion.
  • the majority of combined particles (also referred to as "macrostructural elements" herein) have dimensions greater than 0.1 mm, and the majority of individual particles of the cation and anion exchange material have dimensions less than 0.1 mm. (When the combined particles do not have pores, the particles can be smaller.)
  • the combined particles preferably are sufficiently large so as to cause an acceptably low pressure drop (e.g., less than 100 psig) in the diluting flow channel.
  • the filaments (as macrostructural elements) can have diameters between 0.1 mm and 3.0 mm.
  • the fabric includes groups of generally parallel filaments, with filaments spaced center-to-center by a distance equal to or greater than the diameter of filaments.
  • the binder used to fix the individual cation and anion particles is preferably a thermoplastic polymer or thermosetting polymer, but can be any water insoluble bonding material.
  • the cation and anion exchange materials are made of styrenic ion exchange resin, acrylic ion exchange resin, phenolic ion exchange resin, or carbohydrate ion exchange resin.
  • the invention features, in general, obtaining an increased velocity in the diluting channels of electrodeionization apparatus by reintroducing a portion of the water from the diluting channel outlet to the diluting channel inlet or using flow diverters in the diluting channel to provide a tortuous path for the flowing water, while keeping the volume of the diluting channel substantially unchanged.
  • the diffusion distance is decreased by increasing the velocity of the water flowing past the ion exchanged particles.
  • Embodiments of the invention may include one or more of the following advantages.
  • a substantially spatially uniform rate of water splitting is achieved in the diluting channels; the uniform rate is conducive to a high and uniform degree of resin regeneration and consequently a high rate of ion removal from the water flowing through the diluting compartments.
  • the uniform regeneration of the anion resin additionally facilitates removal of silica and carbon dioxide.
  • the small size of the ion exchanging particles or filaments insures that numerous and uniformly distributed sites for water splitting are created without creating excessive pressure drops, because the dimension of the passages for water flow can be made larger, without affecting adversely the water splitting properties of the material.
  • the invention features, in general, a packing for an electrodeionization compartment that includes one or more macrostructural elements (e.g., beads, strands, brands or foam) made up of smaller, microstructural elements (e.g., particles or fibers).
  • macrostructural elements e.g., beads, strands, brands or foam
  • microstructural elements e.g., particles or fibers.
  • the microstructural elements are in fixed, close contacting position with respect to each other in the macrostructural elements so as to provide porosity in the macrostructural elements.
  • a majority of the microstructural elements have a characteristic dimension between 5 and 50 micrometers, and the macrostructural elements have a void fraction interior to the macrostructural elements between about 25% and 50%.
  • the invention features electrodeionization apparatus including a cathode, an anode, a plurality of alternating anion permeable membranes and cation permeable membranes between the cathode and anode defining concentrating and diluting flow channels, and ion exchange packing in the diluting flow channels including macrostructural elements and microstructural elements as already described.
  • the microstructural elements can be cation exchange material, anion exchange material or a mixture of the two.
  • the characteristic dimension of the microelements preferably is between 7 and 40 micrometers, and the void fraction is less than 45%.
  • the macrostructural elements when other than a foam, can each have a characteristic dimension between about 0.3 and 3 mm.
  • Microstructural elements in the form of particles can be held together by binder.
  • Macrostructural elements in the form of beads can include particles as microstructural elements held together by binder. Each bead includes micropassages between the particles in a bead and macropassages in the packing between the beads.
  • Macrostructural elements in the form of strands can be single-fiber strands that are porous (e.g., including particles as microelements held together by binder) or strands made up of a plurality of fibers. In both of these cases there will be micropassages between the microelements and macropassages between the strands.
  • the strands can be provided in braids, in which case the braids preferably are oriented so that the longitudinal axes of the strands make an angle of between 30 and 60 degrees with the direction of water flow through the diluting channel.
  • Macrostructural elements in the form of an integral foam element can include particles as microelements that are held together in a porous polymer foam binder.
  • Embodiments of the invention may have one or more of the following advantages.
  • a packing having macroelements made up of a plurality of microelements of specified size and void fraction permits large effective active surface area for the ion exchange material at the same time that pressure drop is maintained at acceptable levels.
  • the microelement size and void fraction provide pores (also referred to as micropassages) between the microelement particles or fibers that are sufficiently large so that adequate quantities of water can flow through these pores under the influence of the pressure gradient established in the diluting compartment by the flow of water through the large channels between the beads, strands or braids. This flowing water supplies the interior of the beads or braids with a much larger quantity of ions than can be supplied by simple diffusion.
  • the invention features, in general, using first and second stages in electrodeionization to purify water including calcium and carbon dioxide and its hydrates.
  • the diluting flow channels of the first stage include only anion exchange material or cation exchange material, and thus remove either carbon dioxide and its hydrates (and other anions) or calcium (and other cations) but not the other.
  • the diluting flow channels of the second stage receive the diluting channel effluent from the first stage and include the other type of exchange resin (or a mixed resin) and remove the oppositely charged ions.
  • the brine effluent from the concentrating flow channels in the first stage is isolated from the second stage, and calcium and carbon dioxide and its hydrates tend to be removed in different stages so as to deter calcium carbonate precipitation in any of the concentrating flow channels.
  • the invention features, in general, using electrodeionization to purify water including calcium and inorganic carbon.
  • the concentrating channels include cation exchange material nearer to the anion membrane than the cation membrane, and pH is lowered at the surface of the anion so as to limit calcium carbonate precipitation in the concentrating flow channel.
  • Each concentrating flow channel can include anion exchange material between the cation membrane and the cation exchange material so that water splitting occurs between the anion exchange material and the cation exchange material.
  • the anion exchange material in the concentrating channel is in a first fixed structure, and the cation exchange material in the concentrating channel is in a second fixed structure.
  • the anion exchange material and cation exchange material in the concentrating channel can directly contact each other, or they can be separated by an a cation membrane, cation/anion membrane pair, or a bipolar membrane. Water splitting occurs at the interface of an anion material or membrane with a cation material or membrane.
  • the anion exchange material or cation exchange material in the concentrating channel can be provided as two layers with a membrane that inhibits mixing of the brine in the anion exchange layer with the brine in the cation exchange layer, such as a dialysis membrane, located between the two layers.
  • This membrane is chosen so as not to increase the electrical resistance of the concentrating compartment unduly.
  • the invention features, in general, using electrodeionization to purify water including calcium and inorganic carbon.
  • the diluting flow channels include a mixture of cation and anion resins.
  • the diluting flow channels can include cation resin only at the diluting inlets.
  • the invention features, in general, using electrodeionization to purify water including calcium and inorganic carbon by flowing the feed to the concentrating compartment first through a region that renders it substantially acidic before it enters a region that contains calcium.
  • the concentrating flow channel includes first and second flow channel portions in overlying relation, with the outlet of the first flow channel being connected to the inlet of the second flow channel.
  • the first flow channel includes an anion resin
  • the second flow channel includes a cation resin.
  • the first flow channel and the second flow channel can be separated by a cation membrane or by a bipolar membrane.
  • the first channel inlets and the second channel outlets can be adjacent to the diluting outlets, and the diluting inlets can be the adjacent to the first channel outlets and the second channel inlets.
  • the first channel inlets and the second channel inlets can be adjacent to the diluting outlets, and the diluting inlets can be adjacent to the first channel outlets and the second channel outlets.
  • the second channel outlet can be connected to divert a portion of its effluent to the first channel inlet in order to maintain a high flow rate without the use of excessive amounts of fresh feed.
  • Embodiments of the invention may include one or more of the following advantages.
  • the tendency of scaling is reduced by modifying the design of the EDI stack without additional unit operations.
  • the invention features, in general, electrodeionization apparatus for purifying water.
  • the apparatus includes a cathode, an anode, and a plurality of alternating anion permeable membranes and cation permeable membranes between the cathode and anode that define concentrating and diluting flow channels between adjacent pairs of membranes.
  • Each concentrating flow channel includes a first guard channel adjacent to the anion permeable membrane, a second guard channel adjacent to the cation permeable membrane, and a brine channel between the first and second guard channels.
  • the first and second guard channels have water with lower concentration of dissolved ions than water in the brine channel so as limit parasitic transfer from a concentrating flow channel to a diluting flow channel.
  • Preferred embodiments of the invention may include one or more of the following features.
  • a further anion permeable membrane separates the first guard channel from the brine channel
  • a further cation permeable membrane separates the second guard channel from the brine channel.
  • the first guard channel includes anion exchange material
  • the second guard channel includes cation exchange material.
  • Embodiments of the invention may include one or more of the following advantages.
  • the anion exchange resin in the first guard channel and the additional anion membrane act as a transfer layer for the anions moving to the middle brine channel, while the cation exchange material in the second guard channel and the additional cation membrane act as a transfer layer for the cations moving to the middle brine channel.
  • the water (e.g., feed or purified) flowing through both guard channels keeps the concentration of ions at a very low level and thus virtually eliminates both back-diffusion processes.
  • Fig. 1 is a diagram of electrodeionizing apparatus.
  • Fig. 2 is a diagrammatic plan view of a woven fabric of deionizing material used in a diluting channel of the Fig. 1 apparatus.
  • Fig. 3 is a diagrammatic plan view of a fabric of extruded netting of deionizing material used in a diluting channel of the Fig. 1 apparatus.
  • Fig. 4 is a diagrammatic plan view of a nonwoven fabric of (randomly oriented) strands of deionizing material used in a diluting channel of the Fig. 1 apparatus.
  • Fig. 5 is a diagrammatic elevation of a multifilament strand of deionizing material useful in the Fig. 2, 3 or 4 fabric.
  • Fig. 6 is a diagrammatic elevation of a braided strand of multifilaments of deionizing material useful in the Fig. 2, 3 or 4 fabric.
  • Fig. 7 is a diagrammatic perspective view of a filament that contains cation exchange and anion exchange fibers in a binder and can be used in the Fig. 2, 3 or 4 fabric.
  • Fig. 8 is a diagrammatic vertical sectional view showing the woven fabric of Fig. 2 in a diluting channel of the Fig. 1 device.
  • Fig. 9 is a diagrammatic perspective view of an open cell foam that contains cation exchange and anion exchange materials therein and can be used in a dilutmg channel of the Fig. 1 apparatus.
  • Fig. 10 is a diagrammatic elevation of combined ion exchange particles useful in the diluting channel of the Fig. 1 apparatus.
  • Fig. 11 is diagram showing a partial recirculation loop that can be used with the Fig. 1 apparatus.
  • Fig. 12 is a diagrammatic plan view showing the use of flow diverters in diluting channels of the Fig. 1 apparatus.
  • Fig. 13 is a diagram illustrating a braid structure that permits loose packing of filaments to achieve a desired void fraction.
  • Fig. 14 is a diagram illustrating filaments perpendicular and parallel to direction of flow.
  • Fig. 15 is a diagram illustrating orientation of filaments at an angle to direction of flow to promote flow through micropassages.
  • Fig. 16 is a flow diagram of a single-stage electrodeionizing apparatus.
  • Fig. 17 is a flow diagram of a two-stage electrodeionizing apparatus.
  • Fig. 18 is flow diagram of an alternative two-stage electrodeionizing apparatus.
  • Fig. 19 is a diagram showing the conditions involved in scaling in a concentrating cell of electrodeionization apparatus.
  • Figs. 20-25 are diagrams of alternative embodiments for concenfrating cells useful in the Fig. 1, 2 or 3 apparatus.
  • Figs. 26-30 are diagrams of alternative embodiments for the concentrating and diluting channels of an electrodeionizing apparatus.
  • Fig. 31 is a diagram of pH versus position in concentrating and diluting channels for the embodiment of Fig. 27.
  • Fig. 32 is a diagram of a serpentine flow path in a concentrating channel.
  • Fig. 33 is a diagram illustrating parasitic processes in a single concentrating channel of electrodeionizing apparatus.
  • Fig. 34 is a diagram of a concentrating channel of the Fig. 1 apparatus.
  • electrodeionization apparatus 10 includes cathode 12, anode 14 spaced from cathode 12, and a plurality of alternating anion permeable membranes 16, and cation permeable membranes 18.
  • Diluting channels 20 (“D") are provided between each pair of an anion permeable membrane 16 that faces anode 14 and a cation permeable membrane 18 that faces cathode 12.
  • Concentrating channels 22 (“C") are provided between each pair of an anion permeable membrane 16 that faces cathode 12 and a cation permeable membrane 18 that faces anode 14.
  • Diluting channels 20 and concentrating channels 22 can be about 3.0 mm thick.
  • Fixed ion exchange materials 24 are located in diluting channels 20, and ion exchange materials or other spacers 25 are located in concentrating channels 22. As discussed in detail below, fixed ion exchange materials 24 can take a variety of forms. Cathode 12, anode 14, membranes 16, 18 and spacer materials 25 can be made of components and materials typically used in electrodeionization apparatus, as described, e.g., in the above-referenced patents, which are hereby incorporated by reference. Water flows are provided past cathode 12 and anode 14. As is well known in the art, the components shown on Fig.
  • Diluting channels 20 and concentrating channels 22 are typically between 1.0 mm and 5.0 mm thick, and there typically are 10 to 300 diluting channels.
  • the surface area of each membrane is typically between 0.5 and 5.0 square feet.
  • Fixed ion exchange materials 24 include cation exchange materials and anion exchange materials that are fixed in close contacting position with respect to each other.
  • Fixed ion exchange materials 24 can be provided in strands 26 of combined anion and cation exchange materials in woven fabric 28 (Fig. 2), extruded netting fabric 30 (Fig. 3) and nonwoven fabric 32 of randomly oriented strands 26 (Fig. 4).
  • Fixed ion exchange materials could also be provided by open cell foam 50 (Fig. 9) and by combined exchange particles 60 (Fig. 10).
  • Strands 26 can also take a variety of forms.
  • Strand 26 can be made in the form of bundle 34 of multiple filaments 36, as shown in Fig. 5.
  • Strand 26 can also be in the form of braided strand 38, as shown in Fig. 6; braid 38 is made on a standard braiding machine.
  • Strand 26 can also be in the form of combined exchange particle filament 40, which is made of cation exchange particles 42 (shown white on Fig. 7) and anion exchange particles 44 (shown dark on Fig. 7) that are held together by binder 46.
  • Filaments 36, used in bundle 34 (Fig. 5) could be made of roughly equal, commingled amounts of individual filaments of cation exchange material and individual filaments of anion exchange material.
  • combined exchange particle filaments 40 (Fig. 7), each having cation exchange particles and anion exchange particles, could be used as filaments 36 in bundle 34.
  • Combined exchange particle filaments 40 could similarly be used in making braid 38, using either a single filament 40 or a plurality of filaments 40 in each braided together portion 48 of braid 38.
  • Each portion 48 of braid 38 could also be made of a plurality of commingled filaments of cation exchange material and filaments of anion exchange material.
  • fixed ion exchange materials 24 could also be provided as open cell foam 50, which (like filaments 40) includes cation exchange particles 52, anion exchange particles 54 and binder 56.
  • Open cell foam 50 has an interconnected network of flow passages 58 therethrough.
  • fixed ion exchange materials 24 could also be provided as combined particles 60, made up of cation exchange particles 62 (shown white), anion exchange particles 64 (shown dark) and binder 66.
  • Combined particles 60 are sufficiently large so as to cause an acceptably low pressure drop in diluting flow channels 20 in the space between combined particles 60.
  • Individual cation exchange particles 42, 52 and 62 and anion exchange particles 44, 54 and 64 in filament 40 (Fig. 7), foam 50 (Fig. 9), and combined particle 60 (Fig. 10), respectively, have dimensions (roughly a diameter) of less than 0.1 mm, preferably less than 0.05 mm.
  • Individual filaments 36 in bundle 34 (Fig. 5) and in braided strand 38 are between 0.01 mm and 1.0 mm in diameter.
  • Strands 26, bundles 34, braid 38, combined exchange particle filament 40 and combined particle 60 have diameters between 0.1 mm and 3.0 mm.
  • Particles 42, 44, 62, and 64 are preferably less than 1/3 the diameter of combined exchange particle filament 40 or combined particle 60, respectively.
  • Particles 42, 44, 52, 54, 62, 64 are provided in sufficient particle concentration to provide conductive paths for cations and anions through the bulk filament, foam, or combined particle structure, respectively.
  • the volumetric concentration of the anion plus cation particle should exceed 60% and preferably is about 70% as a fraction of solid material.
  • fixed ion exchange materials 24 there is an intimate fixed, mixture of cation exchanging material and anion exchanging material, and the individual particles or filaments of the exchange materials have a small size.
  • the small size of the ion exchanging particles or filaments and the intimate relationship of the two types of exchange resin insures numerous and uniformly distributed sites for water splitting.
  • Figs. 2-10) there also are relatively large passages for the flow of water (referred to as "macropassages") when compared to the particle size, thus providing good water splitting without excessive pressure drop.
  • the respective ion exchanging materials have a characteristic dimension that is smaller than the characteristic dimensions of the macropassages through which the purified water flows.
  • the characteristic dimension is the radius of the filament.
  • the characteristic dimension is the radius of the individual particles.
  • the macropassages for flow in all examples are not determined by spaces between individual particles or filaments, but instead are determined by the larger dimensions of the overall strands (for Figs. 2-7 and 9) or the combined particles (Fig. 10). As appears from the figures, the macropassages around the larger structures are substantially larger than the dimensions of the individual particles or filaments. As is described in more detail below in reference to Figs.
  • Passages 58 in open cell foam 50 preferably include macropassages that are also substantially larger than the individual cation and anion exchange particles 52, 54 in foam 50 and micropassages to provide increased exposure of the ion exchange surface.
  • Anion and cation exchange filaments 36 and the individual anion and cation exchange filaments used in braid 38 can be made from any of the well-known ion exchange materials, e.g., styrenic ion exchange resin, acrylic ion exchange resin, phenolic ion exchange resin, and carbohydrate ion exchange resin.
  • Individual ion exchange particles 42, 44, 52, 54, 62 and 64 can be made from the same well-known materials.
  • Binder 44 and binder 64 can be any of the well-known thermoplastic polymers or thermosetting polymers used in the manufacture of ion permeable membranes.
  • Binder 54 can be any suitable foam material such as polyurethane.
  • the individual filaments made of either cation exchange resin or anion exchange resin can be made by known techniques, e.g., as described in the above-referenced patents.
  • the combined exchange particle filament 40 and combined particle 60 are made by obtaining (e.g., from a commercially available source) individual anion exchange particles and anion exchange particles in the desired size and approximately equinormal amounts, and then applying the binder 46 and 66 using the same techniques as used for making ion selective membranes, as described in the above-referenced patents.
  • Open cell foam 50 is similarly made by known techniques for open cell material, adding the individual anion and cation exchange particles prior to initiating the reaction that creates the foam.
  • feed and brine are supplied to diluting channels 20 and concentrating channels 22, respectively, at typical flow rates (e.g., 1 to 3 cm sec) and pressure (e.g., 5 to 50 psig), and electric power is supplied to cathode 12 and anode 14 to provide an appropriate current density of 2 to 15 mA square cm and voltage of 1 to 5 volts per cell pair.
  • the feed supplied to the inlets of diluting channels 20 is typically the permeate from a reverse osmosis process.
  • the brine supplied to the inlets of concentrating channels 22 is typically a mixture of the reverse osmosis permeate and brine recirculated from the outlet of the electrodeionization apparatus.
  • the removal of ions from diluting channels 20 includes two steps.
  • the first step is the diffusion of cations to the cation exchanging solids and the diffusion of anions to the anion exchanging solids.
  • the second step is electrical conduction within the solid phases to the bounding membranes of the diluting compartment.
  • the concentration of the ion in question at the surface of the ion exchanging solid is in equilibrium with the concentration of that ion in the solid. It is desired to increase the exchanging sites having hydrogen ions and hydroxide ions to increase the transfer of ions from the liquid to the solid.
  • the regeneration of exchanging sites with hydrogen ions and hydroxide ions is promoted by water splitting. Thus, by providing numerous, uniformly distributed sites for water splitting (the interfaces between individual ion exchanging particles or filaments), the transfer of ions to the solid is promoted. Because transfer to the solid is the limiting step in the removal of ions, the efficiency of apparatus 10 in removing ions is improved.
  • the applied electric field then causes anions on the exchanging material to travel along the anion exchanging material in a conductive path to and through the anion permeable membrane into the concentrating compartment nearer the anode.
  • the applied electric field similarly causes cations to travel along the cation exchanging materials in a conductive path to and through the cation permeable membrane into the concentrating compartment nearer the cathode.
  • the anions and cations become trapped in the concentrating compartments because the movement of anions toward the anode is blocked by a cation permeable membrane, and the movement of cations toward the cathode is blocked by an anion permeable membrane.
  • the removal of ions is improved, and the ion concentration in the deionized output is advantageously decreased without excessive pressure drops.
  • the dimension of the ion exchange beads or braids (also referred to as “macrostructural elements”) need to be quite large in order to avoid high pressure drops, the diffusion of ions from the outer surface of these elements to the interior surface of the constitutive particles or fibrils (also referred to as “microstructural elements”) can be slow. This can lead to the virtually complete capture of the inwardly diffusing ions by the ion exchange resin particles or fibrils nearer this outer surface of the bead or braid and the absence of ions in the interior. If this occurs, the ion exchange surface in the interior is almost completely ineffective in capturing ions, there being no ions to capture. This phenomenon becomes more pronounced as the size of the particles or fibrils becomes smaller.
  • the ions can be effectively delivered to the interior surfaces of the ion exchange materials by providing sufficient pores or micropassages between the particles of ion exchange resin or ion exchange fibrils.
  • the pores need to be large enough so that adequate quantities of water can flow through these pores under the influence of the pressure gradient established in the diluting compartment by the flow of water through the large channels between the beads or braids.
  • This flowing water supplies the interior of the beads or braids with a much larger quantity of ions than can be supplied by simple diffusion.
  • the ion exchange surface in the interior of the beads or braids is in contact with a solution that has an ion concentration almost as high as the ion concentration at the exterior surface of the structure.
  • the entire ion exchange surface is therefore effective in capturing ions, and a major improvement in the efficiency of the EDI stack is obtained.
  • Sufficient pores can be provided in a practical EDI device by controlling the size of the particles and the void fraction within the macrostructural elements. Assuming circular sectioned fibrils or spherical particles, the size of the pores can be estimated in terms of the size of the particles or fibrils and the void fraction within the bead or braid by the following formula:
  • Radius of pore void fraction (l- void fraction)* Radius of (fibril or particle)
  • the flow rate though these interior pores is very sensitive to the pore radius, being proportional to its fourth power.
  • the area within the beads or braids is inversely proportional to the radius of the constitutive particles or fibrils.
  • quantity of ions that need to be supplied into the interior of the bead or braid increases with decreasing particle or fibril radius
  • quantity of ions brought by the flow rate of water into the interior of the bead or braid drops sharply with decreasing particle or fibril radius.
  • the void fraction must be increased in order to maintain the pore radius at a reasonable size and the supply of water at a level that matches the potential adsorptive capacity of the ion exchange surface.
  • the void fraction in the interior of the bead in the absence of a binder, would generally be between about 35% and 50%.
  • the bonding agent needed to adhere the small particles to each other, in order to form a bead occupies some of the available void volume. This can reduce the void fraction to levels that seriously reduce the flow of water through the interior of the bead.
  • Such void fractions can be obtained by controlling the amount of binder applied to the particles in making the beads.
  • the prefened range of void fractions internal to the braids has been found to be 25% and 50%. Void fractions in excess of 40% can be obtained, without weakening the structure of the braid, by braiding or ananging the fibrils loosely and bonding the fibers together at regular intervals, as shown in Fig. 13.
  • ion exchange structures composed of braids or similar filamentous ion exchange materials arranged as two approximately perpendicular sets can be further enhanced by employing a preferred orientation with respect to the direction of the pressure gradient, i.e., the direction of water flow. If the axis of one set of the braids is parallel to the pressure gradient, there is effectively no flow through the pores, because there is no component of the pressure gradient along the pores. The interior area of this set of braids is effectively wasted. There is adequate flow through the pores of the other set of braids, oriented in a direction perpendicular to the direction of water flow, because the pressure gradient is oriented along these pores and the effective internal area approaches the geometrical area, as shown in Fig. 14.
  • the average effective internal area for the packing is about 50% of the total geometrical internal area of both sets of braids. If, however, the two sets of braids are oriented so that the axes of the two sets are at an angle of about 45 degrees to the direction of the pressure gradient, the effective area of the packing is about 71% of the geometrical area, as shown in Fig. 15. An angle of 45 degrees is an optimum orientation of the packing, though a range of angles between 30 and 60 degrees is still effective.
  • particles or fibrils whose radii range from about 5 micrometers to 50 micrometers and have internal void fractions between 25% and 45%.
  • the prefened braid should be composed of particles with radii between 5 and 50 micrometers and have a void fraction between 25% and 50%, the braids being oriented at an angle of between 30 and 60 degrees to the direction of the water flow.
  • the ion exchange material can be cation exchange only or anion exchange only in some embodiments; in these cases, the volumetric concentration of the cation or anion exchange resin should exceed 60% and preferably be about 70% as a fraction of solid material.
  • fixed ion exchange material could be usefully used in the concentrating channels 22 as well.
  • a fabric of fixed ion exchange materials 24 could also be made by extrusion.
  • Figs. 11 and 12 Two techniques shown in Figs. 11 and 12.
  • the first involves mixing a portion of the water leaving the diluting channel 20 with the feed water entering channel 20 using recirculating loop 100. This increases the velocity of the water and also results in a dilution of the feed water and thus an improved water purity.
  • the second technique involves providing a serpentine path whose cross section, normal to the flow direction, is smaller than the cross section of the electrodeionization compartments. This is achieved by placing non- permeable obstructions 102 in the flow path so as to create a tortuous path for the flowing water, while keeping the volume of the diluting compartment substantially unchanged.
  • Single-stage electrodeionization apparatus 210 is shown in Fig. 16.
  • Apparatus 210 has a plurality of concenfrating chambers 212 (shown as a single box in Fig. 16) and a plurality of diluting chambers 214 (again shown as a single box) which have both anion exchange resin and cation exchange resin.
  • Feed water 216 (typically the output of RO apparatus) enters inlet 218 of the diluting chambers 214, and is therein converted to deionized water 220 provided at outlet 224.
  • Brine 226 enters inlet 228 of concentrating chambers 212, picks up ions removed from the diluting channels, and leaves outlet 230.
  • single-stage electrodeionization apparatus 210 can be provided with resistance to scaling formation.
  • Two-stage electrodeionization apparatus 232 is shown in Fig. 17.
  • Apparatus 232 has first stage 234 and second stage 236. Both stages 234, 236 have a plurality of concentrating chambers 212 and a plurality of diluting chambers, though diluting chambers 238 of first stage 234 have only cation exchange resin, while diluting chambers 240 of second stage 236 have both anion exchange resin and cation exchange resin.
  • Feed water 216 enters inlet 242 of the diluting chambers 238, and the effluent 244 at the outlet 246 of diluting chambers 238 is connected as the inflow to the inlet 248 of diluting chamber 240 of second stage 236.
  • Brine 226 enters inlet 250 of concentrating chambers 212 of first stage 234, picks up cations removed from the diluting channels, and leaves outlet 230 as brine 252, including Ca++.
  • Water splitting at the interface of the anion membrane with the cation exchange material in the dilutmg channels 238 regenerates the cation resin and replaces the cations that are removed with H+, which converts HC03- in the feed water into C02. This suppresses the transfer of TIC into the concentrating compartment and thus reduces the scaling potential, even though the pH of the concentrating compartment is alkaline.
  • Two-stage apparatus 232 thus inherently provides scaling resistance regardless of the type of design for concentrating channels 212.
  • Two-stage electrodeionization apparatus 262 shown in Fig. 18, is similar to apparatus 232 (Fig. 17) except that the diluting chambers 264 of the first stage have anion exchange resins only, instead of cation exchange resin only as in diluting chambers 238 in Fig. 17.
  • Brine 226 enters inlet 250 of concentrating chambers 212 of first stage 234, picks up anions removed from the diluting channels, and leaves outlet 230 as brine 266, including HCO3-. Water splitting at the interface between the anion exchange resin in channels 264 and the cation membrane renders the diluting channel alkaline. This converts carbon dioxide to bicarbonate and thus results in very complete removal of TIC into the concentrating compartment.
  • the concentrating compartment 212 of first stage 234 is acidic, and hence no scaling can take place within it. It is possible that the LSI in the diluting compartment could become positive, for some feed compositions, and scaling could then take place. Minimization of this possibility requires careful control of the cunent density so as to avoid excessive regeneration of the resin in the diluting compartment.
  • Fresh brine 254 enters inlet 256 of concenfrating chambers 212 of second stage 236, picks up cations (in particular Ca++) and cations not removed in the first stage, and leaves outlet 258 as brine 268, including Ca++.
  • Two-stage apparatus 262 thus inherently provides scaling resistance regardless of the type of design for concentrating channels 212. When one of the anangements shown in Figs. 20-25 is used for concentrating channels 212, even further resistance to scaling can be provided.
  • Fig.l shows the details of the electrodeionization stacks used in single-stage electrodeionization apparatus 210 and in first stage 234 and second stage 236 of two-stage deodorization apparatus 232 and two-stage electrodeionization apparatus 262.
  • Ion exchange materials 24 (Fig. 1) are located in diluting channels 20, and spacers 25 are located in concentrating channels 22.
  • ion exchange materials 124 can be fixed ion exchange materials.
  • Spacers 25 can be ion exchange resin or ion inactive, permeable material; examples of different spacer anangements are described in Figs. 20-25.
  • Cathode 12, anode 14, membranes 16 and membranes 18 can be made of components and materials typically used in deodorization apparatus, as described, e.g., in the above-referenced patents, which are hereby incorporated by reference.
  • Fig. 9 shows anion member 316 and the ions involved in scaling in the concenfration channel in the absence of measures to reduce or avoid such scaling as described herein.
  • Figs. 20-25 show six different spacer anangements for the concentrating channels 212 that are designed to provide a reduced pH at the surface of the anion membrane so as to avoid CaCO3 precipitation.
  • the six concentrating channel anangements can be used with any of the three different system configurations of Figs. 16-18.
  • concentrating channel 330 is filled with a layer of anion exchanging material 332 (also refened to as anionic spacer 332) next to the cation permeable membrane 318 and a layer of cation exchanging material 334 (also refened to as cationic spacer 334) next to anion permeable membrane 316.
  • Water splitting takes place at interface 336 of layers 332 and 334. The effect of this water splitting is to render acidic the cation exchange layer 334 and its bounding anion exchange membrane 316, which prevents scale formation at anion exchange membrane 316.
  • the cation exchange material is sufficiently close to the anion membrane so as to provide hydrogen ions to the surface of the anion membrane facing the concentrating flow channel.
  • concentrating channel 340 is similar to concentrating channel 330 (Fig. 20), except that cation permeable membrane 342 is placed between anionic spacer 332 and cationic spacer 334.
  • Membrane 342 creates two separate brine streams, and water splitting now occurs at interface 344 of anionic spacer 332 and cation permeable membrane 342. This creates two separate concentrate streams.
  • the concenfrate stream flowing through the anion exchanging layer contains calcium, is slightly alkaline and contains no TIC and hence cannot scale.
  • the concentrate stream flowing through the cation exchanging layer contains TIC and is slightly acidic, but it contains no calcium and hence cannot scale. This approach provides a very high degree of protection against scaling.
  • concentrating channel 350 is similar to concenfrating channel 340 (Fig. 21) except that anion permeable membrane 352 is placed between anionic spacer 332 and cation permeable membrane 342. Water splitting now takes place between membranes 332 and 342, and cation spacer 334 is again rendered acidic, preventing scale formation at anion membrane 316. These membranes furthermore prevent the fransfer of cations to the acidic brine compartment in spacer 334 and of anions to the basic brine compartment in spacer 332.
  • concentrating channel 360 is similar to concentrating channel 350 (Fig. 22) except that bipolar membrane 362 replaces anion permeable membrane 352 and cation permeable membrane 342. Water splitting now takes place within bipolar membrane 362 at the interface of the cation and anion parts, and cation spacer 334 is again rendered acidic, preventing scale formation at anion membrane 316. Bipolar membrane 362 furthermore prevents the transfer of cations to the acidic brine compartment in spacer 334 and of anions to the basic brine compartment in spacer 332.
  • concentrating compartment 370 shown in Fig. 25, there is direct contact between cationic spacer 334 and anionic spacer 332, and there is dialysis membrane 372 and additional anionic spacer 374 between spacer 332 and cation membrane 318.
  • concentrating compartment 380 shown in Fig. 25, there is direct contact between cationic spacer 334 and anionic spacer 332, and there is dialysis membrane 382 and additional cationic spacer 384 between spacer 332 and cation membrane 318.
  • the dialysis membrane serves to inhibit the mixing of the alkaline portion of the brine, which contains Ca++, with the acidic portion of the brine and thus serves to reduce scaling potential.
  • feed and brine are supplied to diluting channels 214 and concentrating channels 212, respectively, at typical flow rates (e.g., 1-3 cm/sec) and pressure (e.g., 5 to 50 psig), and electric power is supplied to cathode 12 and anode 14 (Fig. 1) to provide an appropriate cunent density of 2 to 15 mA/square cm and voltage of 1 to 5 volts per cell pair.
  • the feed 216 supplied to the inlets 218, 242 (Figs. 16-18) of diluting channels 214 is typically the permeate of reverse osmosis processing.
  • the brine 226 supplied to the inlets of concentrating channels 212 is typically a mixture of the reverse osmosis permeate and brine recirculated from the outlet of the electrodeionization apparatus.
  • the removal of ions from diluting channels 214 includes two steps.
  • the first step is the diffusion of cations to the cation exchanging solids and the diffusion of anions to the anion exchanging solids in the diluting channels.
  • the applied electric field then causes anions on the exchanging material to travel along the anion exchanging material in the diluting channels in a conductive path to and through the anion permeable membrane into the concentrating compartment nearer the anode.
  • the applied electric field similarly causes cations to travel along the cation exchanging materials in the diluting channels in a conductive path to and through the cation permeable membrane into the concentrating compartment nearer the cathode.
  • the anions and cations become frapped in the concentrating compartments because the movement of anions toward the anode is blocked by a cation permeable membrane, and the movement of cations toward the cathode is blocked by an anion permeable membrane.
  • Figs. 26-30 show alternative embodiments for concentrating channels and diluting channels to provide for reduced scaling.
  • This improvement is achieved in two ways.
  • the first approach, shown in Fig. 26, is by ananging the flow of solution in the concentrating stream in a counter-cunent direction to the flow of water through the diluting compartments so that little or no calcium is present at the concentrating side of the anion membrane in the region where scaling has a tendency to occur.
  • the second shown in different embodiments in Figs.
  • FIG. 27-30 is by flowing the water feed to the concenfrating compartment first through a region that renders it substantially acidic before it enters a region that contains calcium.
  • Fig.12 shows stack 400 with diluting channel 402 and concentrating channel 404 (also refened to as “compartments") between anion membranes 406 and cation membrane 408, which are all positioned between anode 410 and cathode 412.
  • the diluting channels and concentrating channels include spacer material, as described above. Water enters the concentrating compartment 404 at concentrating inlet 414 at the same end of the stack that product water leaves the diluting compartment 402 at diluting outlet 416. Concentrate leaves the concenfrating compartment 404 at concentrating outlet 418 at the same end of the stack that feed water enters the diluting compartment 402 at diluting inlet 420.
  • the TIC enters the concenfrating compartment in the middle portion of the diluting flow path at TIC transfer zone 422. It is in this general area that scaling would take place on the concentrating side of the anion membrane 406, because calcium ions in the concentrating channel can diffuse into the high pH region adjacent to the anion membrane 406 where the LSI index is positive. It is known that calcium leaves the diluting compartment 402 and enters the concenfrating compartment 404 primarily at calcium transfer zone 424 at the feed water inlet side near inlet 420, because calcium is a doubly valent ion and is therefore adsorbed preferentially by the cation resin in the diluting compartment. In the flow configuration shown in Fig.
  • the brine stream in concentrating channel 404 does not pick up calcium until it has passed the critical central portion of the flow path, where scaling could otherwise occur.
  • the pH values are closer to neutrality, because, as has been explained above, little water splitting takes place at the feed water entrance end of the stack.
  • Fig. 26 reduces scaling tendencies in a conventional electrodeionization diluting compartment, which contains a mixture of cation and anion resins.
  • the approach is even more effective when used in conjunction with a diluting channel that has the feed end filled with just cation resin.
  • the removal of calcium is more completely confined to the front end of the electrodeionization stack and intrusion of calcium into the cenfral part of the stack, which as explained above, is prone to scaling, is more completely avoided.
  • Fig. 27 shows stack 430, which embodies the second approach mentioned above.
  • Stack 430 has concentrating channels with two compartments 432, 434 therein, similar to the configuration shown above in Figs. 20-25.
  • Water enters the lower channel 432 of the concentrating compartment 404 at the end of the stack where the product water leaves at diluting outlet 416. After flowing through this channel 432 it enters the upper channel 434 of the concentrating compartment 404, as indicated in Fig. 27, and leaves at the same end of the stack as it entered through concentrate outlet 418.
  • the lower channel 432 of the concentrating compartment 404 is acidic because the entry of cations from the upper concentrating compartment 434 is very small as that channel is filled with an anion resin 436, and the conductivity of cations is therefore low.
  • Electrical neutrality in the lower concenfrating compartment 432 is maintained by hydrogen ions, produced by water splitting at the interface of the cation membrane 438 splitting the concentrating compartment 204 and the anion resin 236 filling the upper part 434 of the concentrating compartment 204.
  • the ionic solute in the lower brine compartment 432 consists almost exclusively of the acids of the anion in the feed water, H 2 C0 3 , HC1 and H 2 S0 4 .
  • the stream flowing through the lower brine compartment 432 picks up more and more acid, and at the outlet of this compartment its pH is between 2 and 3.
  • On entering the upper channel 434 of the concenfrating compartment 404 it becomes gradually neutralized by the OH " ions that enter this channel 434 in an amount conesponding exactly to the H + ions that were present in the lower concentrating channel 432. Consequently the pH of the solution in the upper concentrating channel 434 is always acidic and only approaches the pH of the feed water to the electrodeionization apparatus at the concentrating outlet 418.
  • Fig. 28 shows a stack 440 in which the brine stream enters the upper concentrating compartment 434 at the same end of the stack as it enters the lower concentrating compartment 432 by an concentrating inlet 414.
  • Fig. 28 shows a stack 440 in which the brine stream enters the upper concentrating compartment 434 at the same end of the stack as it enters the lower concentrating compartment 432 by an concentrating inlet 414.
  • any combination of entry points is suitable as long as the brine stream enters the upper brine compartment 432 after having passed through enough channels of the lower brine compartment 434 so as to render it acidic.
  • Fig. 29 shows a stack 450 in which a portion of the brine leaving the upper concenfrating channel 434 is recycled to the lower concentrating channel 432.
  • This design may be beneficial in maintaining a high flow rate in the concentrating channels 432, 434, without the use of excessive amounts of water. It does have the drawback of introducing some calcium ions into the scaling prone area of the lower concentrating channel 432 and should therefore be used only when the concentration of calcium in the feed water to the electrodeionization apparatus is low, preferably less than 2 ppm.
  • Fig. 30 shows a stack 460 in which a bipolar membrane 462 is used to generate the H + ions required to render the lower channel 432 acidic.
  • This design can be combined with any of the flow directions previously described in Figs. 27-29.
  • the stack is shown with anion resin in the upper concentrating channel 434 and cation resin the lower concentrating channel 432, it can be used with inert filling material in the channels since the water splitting function that it provides is within the membrane itself and contact with anion exchange resin is not required.
  • Fig. 1 can be subject to parasitic processes as illustrated in Fig. 33, which shows a single concenfrating channel 510, having cation permeable membrane 512, anion permeable membrane 514 oriented as indicated between anode 516 and cathode 518.
  • Fig. 34 shows an anangement that can be used to avoid parasitic process by employing spacers/membrane anangements located in concentrating channels 22 (Fig. 1).
  • the spacer/membrane anangement 525 in each concentrating channel 522 includes cation resin 530, cation permeable membrane 532, spacer 534, anion membrane 536, and anion exchange resin 538.
  • Brine flows through permeable spacer 534 in the central channel 540, while feed or product water, with a concenfration of dissolved ions that is much less than that in the brine, flows at a low flow rate through guard channels 542, 544.
  • cation exchange resin 530 in guard channel 542 acts as a transfer layer for the cations moving to the middle concentrating compartment 540.
  • Anion exchange resin 538 in guard channel 544 acts as a fransfer layer for the anions moving to the middle concentrating compartment 540.
  • a low flow rate of purified water or of feed water through both guard channels 542, 544 keeps the concenfration of ions at a very low level and thus virtually eliminates both back-diffusion processes. This low flow of purified water can serve as make up to the concentrate stream, and thus no decrease in water recovery results.
  • the flow rate through the concentrating compartment positioned between the two guard compartments is designed to carry away the bulk of the ions removed from the diluting compartments.

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Abstract

Cet appareil de désionisation électrique (10) permettant de purifier de l'eau comprend une cathode (12), une anode (14) ainsi que plusieurs membranes alternées perméables aux cations et aux anions (16, 18) définissant des canaux d'écoulement de concentration et de dilution (22, 20) entre des paires de membranes adjacentes. Les canaux de dilution comportent des matériaux d'échange cationique et anionique (24) fixés en contact étroit afin de constituer des chemins conducteurs pour les ions des membranes adjacentes et des circuits d'écoulement pour l'eau entre les matériaux susmentionnés. Le matériau de garnissage peut comporter un ou plusieurs éléments macrostructuraux faits d'éléments microstructuraux plus petits. Il est possible d'utiliser un premier et un second étage pour purifier l'eau, comprenant du calcium, du dioxyde de carbone et ses hydrates, la substance d'échange ionique étant différente dans le canal d'écoulement de chaque étage. Les canaux d'écoulement de concentration peuvent comporter un canal à saumure entre deux canaux de garde.
PCT/US2000/024858 1999-09-13 2000-09-11 Procedes et appareil permettant de d'effectuer une desionisation electrique de l'eau WO2001020060A1 (fr)

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Application Number Priority Date Filing Date Title
AU73678/00A AU7367800A (en) 1999-09-13 2000-09-11 Apparatus and methods for electrodeionization of water

Applications Claiming Priority (10)

Application Number Priority Date Filing Date Title
US09/395,313 1999-09-13
US09/395,327 US6187162B1 (en) 1999-09-13 1999-09-13 Electrodeionization apparatus with scaling control
US09/394,170 1999-09-13
US09/394,170 US6241866B1 (en) 1999-09-13 1999-09-13 Electrodeionization apparatus with fixed ion exchange materials
US09/395,327 1999-09-13
US09/395,313 US6254753B1 (en) 1999-09-13 1999-09-13 High purity electrodeionization
US09/442,525 US6241867B1 (en) 1999-09-13 1999-11-18 Electrodeionization apparatus and packing therefor
US09/442,525 1999-11-18
US09/526,658 2000-03-15
US09/526,658 US6296751B1 (en) 1999-09-13 2000-03-15 Electrodeionization apparatus with scaling control

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WO2016193166A1 (fr) 2015-05-29 2016-12-08 Voltea B.V. Appareil pour l'élimination d'ions à partir d'eau et son procédé de production

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