Continuous Electrodeionization Production of High-Purity Water Withoutwithout Regenerationregeneration Chemicalschemicals

Home , Electrodeionization

Continuous Electrodeionization Production of High-Purity Water withoutwithout RegenerationRegeneration ChemicalsChemicals

by Felice DiMascio, Jonathan Wood, and James M. Fenton

lectrochemical deionization (EDI), Electrodeionization Background of the CEDI process in the 1970s and also called electrodeionization, is a 1980s. Matejka investigated CEDI for process that removes ionizable The concept of electrodeionization the deionization of brackish or tap species from liquids using ioni- has been extensively investigated since water to produce high-purity water. cally active media and an elec- the mid-1950s for various purposes. Several researchers in Israel were also trical potential to influence ionic Walters et al.2 investigated a batch very actively studying electrodeioniza- Etransport. Electrodeionization processes electrodeionization process for the con- tion.13-15 During this time, new devices can be batch or continuous. Contin- centration of radioactive aqueous were being proposed and patents being uous Electrodeionization (CEDI) is an wastes, based on electrolytic regenera- granted to a number of others.16-19 electrodeionization process where the tion of ion exchange resins. The first commercially available ion transport properties of the active In the late 1950s and early 1960s, continuous electrodeionization mod- media are the primary scale-up parame- the theory, design, and operating con- ules and systems were introduced in ters. There are also batch electrodeion- ditions of the CEDI process were inves- 1987 under the trade name Ionpure, ization processes, such as capacitive tigated by Glueckauf.3 He proposed a now sold by U.S. Filter Corporation deionization,1 where the ion capacity theoretical model based on a two-stage (“U.S. Filter”). A more comprehensive properties of the active media are the removal of ions: the diffusive transfer of review of the technical literature on primary sizing parameters. ions from flowing solution to ion electrodeionization is given by Ganzi et CEDI devices combine the use of exchange resin beads and the transfer al.20 A recent review of CEDI tech- ion exchange resins, ion exchange of ions along the chain of ion exchange nology was provided by Henley.21 It is membranes and electrodes without beads. Sammons and Watts4 studied believed that there are more than 1300 the need for regeneration chemicals. the deionization of sodium salt solu- industrial size CEDI installations world- The CEDI cell combines the benefits tions using multi-cell electrodeioniza- wide, about 95% of which have been of ion exchange and electrodialysis tion modules, quantifying the supplied by U.S. Filter. Applications while minimizing the problems asso- relationships between solution concen- have included pharmaceutical, elec- ciated with each of these separate tration, flow rate, and applied current. tronics, power generation, food and technologies. The CEDI cell uses the They experimentally demonstrated beverage, and laboratory. ion exchange resin to provide high CEDI, but they did not define in great ionic conductivity to the normally detail the effects of parameters such as Continuous Electrodeionization high resistance found in the dilute liquid flow velocity, cell width, resin Process compartments of an electrodialysis particle size, and type of resin filling. cell. The resin’s high ionic capacity A Dutch company applied for the The continuous electrodeionization increases the residence time of the first patent for an electrodeionization process employs anion and cation ionic contaminants inside the cell device in 1953. They described an appa- permeable ion exchange membranes, allowing more time for the transport ratus for the deionization of salt-con- with ion exchange resins packed of these ions into the appropriate taining liquids using alternating layers between them. Figure 1 is a typical compartments. The electrodes gen- of anion and cation resins. The patent schematic diagram of the process erate a potential gradient for ionic was granted in 1957.5 A patent was also showing the separate diluting and con- movement within the cell. At granted to Kollsman in 1957,6 centrating compartments and the cation/anion (resin/resin and describing a CEDI apparatus for the direction of ion flow. Applying a DC resin/membrane) interfaces water is purification of acetone. In this time electric potential causes ions to move dissociated into its constituent ions, period and in the 1960s, numerous from one compartment to another, H+ and OH-, which regenerate the patents were granted for various types affecting a separation. Since the con- resins on-line, so there is no down of electrodeionization devices.7-10 centration of ions is reduced in one time or need for regenerative chemi- Matejka11 and Shaposhnik12 compartment and increased in the cals as in ion exchange. extended the investigation into the other, the process can be used for operating conditions and performance either purification or concentration.

26 The Electrochemical Society Interface • Fall 1998 paratively rapid, as shown in Table I.23 CDI® Modules and Systems refer to commercial continuous electrodeionization devices developed and sold by U.S. Filter. U. S. Filter is the dominant manu- facturer of industrial size CEDI. Millipore Corporation manufactures low-flow CEDI devices, under the trade name Elix, for laboratory water purification applications. Recently other companies (Christ Ltd., Electropure Inc., Elga Ltd., Glegg Water Conditioning, and Ionics Inc.) have begun to offer CEDI units, but

FIG.1. presently together represent less than an Schematic of estimated 3% of the total number of CDI process. installed CEDI systems.

Advantages of CEDI

When compared with conventional resin-based, chemically regenerated deionization equipment, CEDI systems offer a variety of benefits. Most obvious is the elimination of the regeneration process and its associated hazardous regeneration chemicals, acid and caustic. Since CEDI operates through a combination of ion transfer across the resins and membranes, as well as electrochemical regeneration of the outlet FIG. 2. portion of the bed, the resins and CDI process flow schematic. membranes are never fully exhausted. In addition, the CEDI system Under the influence of the electric eration, accounts for the ability of product water quality stays constant field, cations will migrate in the direc- CEDI systems to produce multi-mega- over time, whereas in regenerable tion of the negatively charged cathode, ohm water, much like a continuously deionization, product water quality through the cation-exchange resin, regenerated mixed bed ion-exchange degrades as the resins approach cation-permeable membrane and into column. exhaustion. For those processes the concentrating stream. An anion Most commercially available CEDI requiring deionized (DI) water on permeable membrane on the opposite modules are plate and frame devices a continuous basis, conventional side of that stream prevents further with multiple arrangements of alter- systems must be duplexed, so that one migration, effectively trapping the nating diluting and concentrating system can provide water while the cations in the concentrating stream. compartments, hydraulically in par- other is regenerated. Duplexing adds The process for anion removal is analo- allel and electrically in series, as shown cost, complexity, and size to conven- gous, but in the opposite direction, schematically in FIG. 2. There are tional DI systems. Since CEDI is contin- toward the positively charged anode. presently two sizes of CEDI modules uous, and not a batch process, In continuous electrodeionization available from U.S. Filter. So-called duplexing is not necessary. As a result, for the preparation of deionized water, “industrial” modules can have 30–240 CEDI system footprints are often the process operates in two regimes.22 diluting compartments and are one half of the size of their conven- In the first regime, at higher salinity or capable of flow rates of 2.0–64.0 gpm tional counterparts. at the inlet portion of the resin bed, (0.45–14.5 m3/h). The smaller version, There are significant tangible cost the resins in the diluting streams “compact” CEDI modules, typically benefits associated with the elimination remain in the salt forms, and efficien- have 10–40 diluting compartments of regeneration. The costs of regenera- cies are derived from the resin- and are capable of flow rates of 0.5–4.0 tion labor and chemicals are replaced enhanced electrical conductivity of the gpm (0.1–0.9 m3/h). with a small amount of electrical con- ion-depleting compartments. sumption. A typical CEDI system will In the second regime, at low CEDI Performance Improvements use approximately 1 kW-hr of electricity salinity or at the outlet portion of the to deionize 1,000 gallons from a feed resin bed, the DC electric potential Although about thirty years passed conductivity of 50 µS/cm to 10 MΩ-cm causes water to dissociate into its con- between the invention of electrodeion- resistivity. Since the waste stream constituent ions, H+ and OH-, electro- ization and the commercialization of tains only the feed water contaminants chemically converting the resins to the the continuous electrodeionization at 5–20 times higher concentration, it hydrogen and hydroxide forms. This process, the rate of advancement of the can be discharged without treatment. phenomenon, known as electroregen- U.S. Filter CEDI process has been com- Thus, facilities costs can also be reduced

The Electrochemical Society Interface • Fall 1998 27 since waste neutralization equipment and ventilation for hazardous fumes are not necessary. There are also less tangible cost reductions, which are harder to quan- tify, but clearly favor the use of CEDI systems. By eliminating hazardous chemicals wherever possible, workplace health and safety conditions can be improved. With today’s increasing regulatory influence on the workplace, the storage, use, neutralization, and disposal of hazardous chemicals result in hidden costs associated with moni- FIG.3. All filled toring and paperwork to conform with configuration EPA and OSHA requirements as well as CDI process. the “Right To Know” laws. In addition, the fumes, particularly from acid, often removal have made the CDI process a uous reduction in total organic carbon cause corrosive structural damage to viable alternative for boiler makeup in (TOC).25 The pretreatment scheme is facilities and equipment. power and cogeneration, as well as for similar to that used in the pharmaceu- semiconductor manufacturing. CDI tical industry, as are the placement of Applications in Water Purification systems have also been installed at the RO and CEDI systems. The storage, institutions such as hospitals, universi- distribution, and polishing differ con- The principal use of CEDI systems ties and dialysis centers. siderably from pharmaceutical systems has been in the production of pure or Most of the early CDI systems oper- however, with storage tanks com- ultrapure water for industrial process ated on pretreated tap water and gave monly blanketed with nitrogen gas and use since the first commercial device water quality similar to that produced by sparged continuously with ozone for was introduced in early 1987. U.S. separate-bed deionizers. The current microbial control. The polishing step Filter has installed over 1300 CDI sys- trend is to combine CEDI with reverse includes 185 nm UV light for organic tems worldwide. These range in osmosis (RO) to produce ultrapure, oxidation, followed by polishing flowrate from 1 to 960 gpm. In addi- mixed-bed quality water. Presently, the mixed-bed deionization, 254 nm UV tion, Millipore Corp. has sold over largest user is the pharmaceutical light, 0.5 micron cartridge filtration, 2000 units for low flow rate laboratory industry. One of the reasons for this is and finally 0.1 micron cartridge filtra- applications, less than 100 lph. that when operated properly, CEDI mod- tion. This ultrapure water is distributed Many different industries require ules do not cause proliferation of bac- to the points of use, with a recircula- deionized water, and each has its own teria, and have even in some cases shown tion loop returning unused water to specific requirements for the quantity to be bacteriostatic.24 The number of the storage tank. RO/CDI based sys- and quality of water used. CDI systems installations is more evenly spread out tems have been installed for semicon- are now operating in a variety of indus- among the other market segments. ductor wafer and other rinsing tries, from process feed water in phar- Water of the highest possible purity applications at both manufacturing maceutical, biotechnology and food is also used in the electronics industry and research facilities for many For- and beverage applications to high- for critical rinsing steps in the fabrica- tune 500 companies. The systems typi- quality rinsing water for electronics, tion of semiconductor wafers. Of par- cally meet ASTM specifications for surface finishing and optical glass appli- ticular importance to the electronics “Electronics Grade Water.” cations. More recently, increases in industry is the demonstrated ability of CDI systems have also been used for flowrate capability and improved silica the CEDI system to provide a contin- general industrial applications requiring

TABLE I. CDI® System Technological Milestones

1987 ...... First commercial product ...... 5 gpm and 10 gpm modules

1989 ...... Uniform particle-size ion ...... CO2 removal without chemical feed exchange resins

1991 ...... Improved ion exchange membranes ...... Dissolved SiO2 removal Improved salt removal 1992 ...... 240-compartment module ...... Up to 64 gpm product flow 1993 ...... “Compact” module ...... Resin-filled concentrate compartments Improved performance 1994 ...... Improved ion exchange ...... Better chemical & electrical resistance membranes: polyethylene Heat-weldable

1998 ...... All-filled “industrial” module (FIG. 3)...... Resin-filled concentrate compartments Twice the flow per cell Capable of polarity reversal

28 The Electrochemical Society Interface • Fall 1998 efficient deionization and even higher flow rates. To date, the CEDI process has been mainly applied to water purification. While some systems have been installed for wastewater treatment,26 there may also be nonaqueous applications for CEDI in such areas as food and beverage manufacturing and chemical processing. Some of these applications are presently under investigation, and CEDI equipment is already in use for fruit juice deionization.27 Millipore Corporation has con- tinued to apply electrodeionization to

FIG.4. specialty separations in the pharma- 80 gpm CDI ceutical industry.28-29 ■ system. References low to medium quality deionized water. regenerable resin-based deionization In these cases, the use of RO is not nec- systems. Since the initial commercial- 1. J. C. Farmer, et al., Separation Science and Tech- essary, as CEDI can remove from 95- ization in 1987, CDI systems have nology - Part 1, AIChE, New York (1997). 2. W. R. Walters, D. W. Weisee, and J. L. Marek, 99% of the dissolved ions from pre- found worldwide application in indus- Ind. Eng. Chem., 47 (1), 61 (1955). treated tap water. The pretreatment is tries with the most demanding high 3. E. Glueckauf, British Chemical Engineering, p. quite similar to that of a RO system, purity water requirements such as in 646 (1959). except that an organic scavenger is 4. D. C. Sammon and R. E. Watts, AERE-R3137, the manufacture of pharmaceuticals, Atomic Energy Research Establishment, sometimes required to prevent fouling semiconductors, and high quality (1960). of the CEDI by humic and fulvic acids optics, in surface finishing of electronic 5. H. E. Verkeer, et al., U.K. Pat. 776,469 (1957). found in many surface water sources. 6. P. Kollsman, U.S. Pat. 2,815,320 (1957). components and durable goods, and in 7. F. L. Tye, U.K. Pat. 815,154 (1959). Systems have been installed for such the generation of electric power. Typ- 8. R. G. Pearson, U.S. Pat. 2,794,777 (1957). applications as electrocoat painting, ical of any high technology product of 9. T. R. E. Kressman, U.S. Pat. 2,923,674 (1960). chemical manufacturing, electroplating, this age, CEDI is constantly evolving, 10. E. J. Parsi, U.S. Pat. 3,149,061 (1964). 11. Z. Matejka, J. Appl. Chem. Biotechnol., 21, 117 bottle washing, humidification, and with improvements in deionization (1971). optics manufacturing. performance and increases in single 12. V. A. Shaposhnik, A. K. Reshetnikova, R. I. module flow rate capability arising Zolotareva, I.V. Drobysheva, and N. I. Isaev, Zhurnal Prikladnoi Khimii, 46 (12), 2659 The Future of CEDI Technology with each new generation, such as the (1973). 80 gpm “all-filled” industrial CDI 13. E. Selegny and E. Korngold, U.S. Pat. 3,686,089 The CEDI process has become a module shown in FIG. 4. Future (1972). viable alternative to conventional, 14. E. Korngold, Desalination, 16 (2), 223 (1975). improvements will likely achieve more 15. O. Kedem, Desalination, 16 (1), 105 (1975). 16. T. A. Davis, U.S. Pat. 4,032,452 (1977). 17. R. A. Tejeda, U.S. Pat. 3,869,376 (1975). 18. G. Kunz, U.S. Pat. 4,636,296 (1987). About the Authors 19. A. J. Giuffrida, A. D. Jha, and G. C. Ganzi, U.S. Pat. 4,632,745 (1986). 20. G. C. Ganzi, J. H. Wood, and C. S. Griffin, Felice DiMascio was a Product Development Engineer for U.S. Filter Corp. in Lowell, MA. Environmental Progress, 11, (1), (1992). He holds BS and MS degrees in Chemical Engineering from the University of Connecticut. 21. M. Henley, Ultrapure Water, p. 15, (1997). He is currently working toward a PhD degree in Chemical Engineering at Tufts University. 22. G. C. Ganzi, “The Ionpure Continuous Deion- ization Process: Effect of Electrical Current Mr. DiMascio has a one-year application experience in wastewater treatment and over five Distribution on Performance,” presented at years of product development experience in electrochemical membrane separation process. the 80th Annual AIChE meeting, Wash- He is presently involved in product development for electrochemical equipment at Halox ington, DC, on November 28, 1988. 23. J. Wood and F. DiMascio, “Eight Years of Technologies Corp. in Bridgeport Connecticut. Continuous Electrodeionization,” presented at the Thirteenth Annual Membrane Tech- Jonathan Wood is Applications R&D Manager for U.S. Filter Corp. in Lowell, MA. He nology/Separations Planning Conference, has a BS degree in Chemical Engineering from Worcester Polytechnic Institute and an MS Newton, MA, October 25, 1995. degree in Environmental Engineering from Northeastern University. Mr. Wood has over 20 24. G. C. Ganzi and P. L. Parise, J. of Parenteral Sci- ence and Technology, 44 (4), 231 (1990). years experience in water purification, encompassing research, product development, 25. F. C. Wilkins and P.A. McConnelee, Solid State product management, and technical service. He is presently involved primarily in applica- Technology, August 1988. tions development for electrodeionization and reverse osmosis equipment. Prior to joining 26. S. Sung and J. M. Fenton, Environmental U.S. Filter he spent 10 years with Barnstead Company working with distillation, pure Progress. To be submitted. 27. P. Soria, M. Saporta, and C. Berdun, Fruit Pro- steam generation, and deionization equipment. cessing, p. 368 (1993). 28. J. D. Steen and G. De Los Reyes, “Electrically James M. Fenton is a Professor of Chemical Engineering and Director of the Pollution Enhanced Mixed-Bed Deionization of Sugars, Prevention Research and Development Center at the University of Connecticut (UConn) in Contrast Agents, and Ureas,” presented at the Storrs, CT. He has a BS degree in Chemical Engineering from the University of California, AIChE Annual Meeting, Miami Beach, FL, November 4, 1992. Los Angeles, and MS and PhD degrees in Chemical Engineering from the University of Illi- 29. Y. Egozy and J.D. Steen, “Electrodeionization: nois, Champaign-Urbana. Dr. Fenton has been conducting research in pollution prevention A New Tool for the Purification of Pharmaceu- and environmental engineering through electrolyic processes at UConn since 1984. ticals,” presented at the AIChE Summer National Meeting, Boston, MA, (July 30- August 2, 1995).

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