OA11806A - Electrolytic apparatus, methods for purification of aqueous solutions and synthesis of chemicals. - Google Patents

Abstract

Electropurification of contaminated aqueous media, such as ground water and wastewater from industrial manufacturing facilities like paper mills, food processing plants and textile mills, is readily purified, decolorized and sterilized by improved, more economic open configuration electrolysis cell (10) designs with electrodes (18, 20) comprising a plurality of conductive porous elements in electrical contact with one another. The cells (10) may be divided or undivided, and connected in monopolar or bipolar configuration. When coupled with very narrow capillary gap electrodes (18, 20) more economic operation, particularly when treating solutions of relatively low conductivity is assured. The novel cell design (10) is also useful in the electrosynthesis of chemicals, both organic and inorganic types, such as hypochlorite bleaches and other oxygenated species.

Description

-1- 118 0 6

ELECTROLYTIC APPARATUS, METHODS FOR PURIFICATIONOF AQUEOUS SOLUTIONS AND SYNTHESIS OF CHEMICALS

FIELD OF THE INVENTION

The présent invention relates generally to the purification of aqueous solutions and préparation of useful Chemical products, and more specifically, to electrochemical methods and more efficient, économie and safer electrolytic apparatus for both the electropurification of drinking water, industrial waste waters and contaminated ground water, as well as the.electrochemical» synthesis (electrosynthesis) of useful products, e.g., organicand inorganic Chemicals.

BACKGROUND OF THE INVENTION

Wastewater can be a valuable resource in cities and townswhere population is growing and water supplies are limited. Inaddition to easing the strain on limited fresh water supplies,the reuse of wastewater can improve the quality of streams andlakes by reducing the effluent discharges they receive.Wastewater may be reclaimed and reused for crop and landscapeirrigation, groundwater recharge, or recreational purposes.

The provision of water suitable for drinking is anotheressential of life. The quality of naturally available watervaries from location-to-location, and frequently it is necessaryto remove microorganisms, such as bacteria, fungi, spores andother organisms like crypto sporidium; salts, heavy métal ions,organics and combinations of such contaminants.

Over the past several years, numerous primary, secondary andtertiary processes hâve been employed for the decontamination ofindustrial wastewater, the purification of ground water andtreatment of municipal water supplies rendering them safer fordrinking. They include principally combinations of mechanical andbiological processes, like comminution, sédimentation, sludgedigestion, activated sludge filtration, biological oxidation,nitrification, and so on. Physical and Chemical processes hâvealso been widely used, such as flocculation and coagulation with -2- 118 06

Chemical additives, précipitation, filtration, treatment with

chlorine, ozone, Fenton's reagent, reverse osmosis, UV sterilization, to name but a few.

Numerous electrochemical technologies hâve also beenproposed for the decontamination of industrial wastewater andground water, including treatment of municipal water supplies forconsumption. While growing in popularity, the rôle ofelectrochemistry in water and effluent treatment heretofore hasbeen relatively small compared to some of the mechanical,biological and Chemical processes previously mentioned. In someinstances, alternative technologies were found to be moreéconomie in terms of initial capital costs, and in theconsumption of energy. Too often, earlier electrochemical methodswere not cost compétitive, both in initial capital costs andoperating costs with more traditional methods like chlorination,ozonation, coagulation, and the like.

Earlier electrochemical processes required the introductionof supporting electrolytes as conductivity modifiers which addsto operating costs, and can create further problems with thedisposai of by-products. Electrochemical processes in someinstances hâve been ineffective in treating solutions by reducingconcentrations of contaminants to levels permitted undergovernment régulations. Heretofore, such electrochemicalprocesses hâve often lacked sufficient reliability forconsistently achieving substantially complété mineralization oforganic contaminants, as well as the ability to remove sufficientcolor from industrial waste waters in compliance with governmentrégulations.

Notwithstanding the foregoing shortcomings associated withearlier electrochemical technologies, electrochemistry is stillviewed quite favorably as a primary technology in thedecontamination of aqueous solutions. Accordingly, there is aneed for more efficient and safer electrochemical cellconfigurations and processes for more économie treatment of largevolumes of industrial waste waters, effluent streams and 118 0 6 -3- contaminated ground water, including the decontamination ofmunicipal water supplies making them suitable for drinking. Suchelectrochemical cell configurations should also be useful in theelectrosynthesis of Chemical products.

SUMMARY OF THE INVENTION

The présent invention relates to improved means forelectropurification of aqueous solutions, particularly effluentstreams coraprising waste waters polluted with a broad spectrumof Chemical and biological contaminants, including members fromsuch représentative groups as organic and certain inorganicChemical compounds. Représentative susceptible inorganicpollutants include ammonia, hydrazine, sulfides, sulfites,nitrites, nitrates, phosphites, métal ions, and so on. Includedas organic contaminants are organometallic compounds; dyes fromtextile mills; carbohydrates, fats and proteinaceous substancesfrom food processing plants; effluent streams, such as blackliquor from pulp and paper mills containing lignins and othercolor bodies; general types of water pollutants, includingpathogenic microorganisms, i.e., bacteria, fungi, molds, spores,cysts, protozoa and other infectious agents like viruses; oxygen-demanding wastes, and so on.

While it is impractical to specifically identify by name ailpossible contaminants which may be treated successfully accordingto the claimed methods, it will be understood that languageappearing in the daims, namely "contaminated aqueous electrolytesolution", or variations thereof is intended to encompass ailsusceptible pollutants whether organic, inorganic, métal ions orbiological.

The electropurification methods and apparatus for practicingthis invention are particularly noteworthy in their ability toeffectively purify virtually any aqueous solution comprising oneor more organic, certain inorganic, including hazardous métalions and biological contaminants présent in concentrationsranging from as low as <1 ppm to as high as >300,000 ppm. -4- 118 0 6

Only electricity is required to achieve the desired Chemicalchange in the composition of the contaminant(s), in most cases.The conductivity of tap water is sufficient for operation of theimproved cell design. Hence, it is neither required, nornecessarily désirable to incorporate additives into thecontaminated aqueous solutions to modify the conductivity of thesolution beihg treated to achieve the desired décomposition ofthe pollutant/contaminant. Advantageously, in most instancessolid by-products are not produced in the electropurificationreactions as to create costly disposai problems. The improvedelectrochemical processes of the invention are able to achievecomplété or virtually complété color removal; complétémineralization of organic contaminants and total destruction ofbiological pollutants even in the presence of mixed contaminants,and at a cost which is compétitive with traditional non-electrochemical methods, such as chlorination, ozonation andcoagulation, and thereby meet or exceed government régulations.

Accordingly, it is a principal object of the invention toprovide an electrolysis cell which comprises at least one anodeand at least one cathode as électrodes positioned in anelectrolyzer zone. The électrodes are preferably spacedsufficiently close not only to provide an interelectrode gapcapable of minimizing cell voltage and IR loss, but also toachieve conductivity without the need for extra supportingelectrolytes or current carriers. Means are provided for directlyfeeding electrolyte solutions to the électrodes for distributionthrough the interelectrode gap(s). Means are provided forregulating the residency time of the electrolyte solution in theelectrolyzer zone. When the electrolysis cell is employed inelectropurification the electrolyte would remain in theelectrolyzer zone for a sufficient time interval for modificationof contaminants to occur, ether electrochemically by direct meansand/or by Chemical modification of contaminants to less hazardoussubstances during residency in the cell. Additional means areprovided for collecting treated electrolyte solution descending -5- 11806 from the electrolyzer zone. It is also significant, theelectrolysis cell according to the invention has an "openconfiguration".

In addition to the electrochemical cell of this invention,further means are provided for practical and efficient operation,directly feeding contaminated aqueous electrolyte solution to thecell by pump means or by gravity; pretreatment means for thecontaminated aqueous electrolyte solutions, for example, meansfor aération, pH adjustment, heating, filtering of largerparticulates; as well as means for post-treatment, for example,pH adjustment and cooling, or chlorination to provide residualkill for drinking water applications. In addition, the inventioncontemplâtes in-line monitoring with sensors and microprocessorsfor automatic computer-assisted process control, such as pHsensors, UV and visible light, sensors for biologicalcontaminants, température, etc.

It is still a further object of the invention to provide aSystem for purification of aqueous solutions, which comprises: (i) an electrolysis cell comprising at least oneanode and at least one cathode as électrodes positioned in anelectrolyzer zone. The électrodes are spaced sufficiently closeto one another to provide an interelectrode gap capable ofminimizing cell voltage and IR loss. Also included is a conduitmeans for directly feeding a contaminated aqueous electrolytesolution to the électrodes in the electrolyzer zone. Theelectrolysis cell is characterized by an open configuration. (ii) A control valve means for regulating the flowof contaminated aqueous electrolyte solution to the électrodesdirectly via the conduit means of (i) above. (iii) Means are included for pumping contaminatedaqueous electrolyte solution through the conduit means, and then (iv) rectifier means are included for providinga DC power supply to the electrolysis cell.

The purification System may also include sensor means and computerized means for receiving input from the sensor means and -6- 113 0 6 providing output for controlling at least one operating conditionof the System selected from the group consisting of currentdensity, flow rate of contaminated aqueous solution to theelectrolysis cell, température and pH of the contaminated aqueouselectrolyte solution. Optional components include exhaust meansfor further handling of electrochemically produced gaseous by-products; means for pretreatment of the contaminated aqueouselectrolyte solution selected from the group consisting offiltration, pH adjustment and température adjustment.

As previously discussed, the electrochemical cells of thisinvention are especially novel in their "open configuration." Asappearing in the spécification and daims, the expression "openconfiguration" or variations thereof are defined aselectrochemical cell designs adapted for controlled leakage ordischarge of treated and decontaminated aqueous electrolytesolution and gaseous or volatile by-products. The abovedéfinition is also intended to mean the élimination or exclusionof conventional closed electrochemical cells and tank type celldesigns utilizing conventional indirect means for feedingelectrolyte to électrodes. Closed flow type electrochemicalcells, for example, are often fabricated from a plurality ofmachined and injection molded cell frames which are typicallyjoined together under pressure into a non-leaking sealed stackwith gaskets and 0-rings to avoid any leakage of electrolyte fromthe cell. This type of sealed electrochemical cell is typicallyfound in closed plate and frame type cells. Very close fittingtolérances for cell components are required in order to seal thecell and avoid leakage of electrolyte and gases to theatmosphère. Consequently, initial capital costs of suchelectrochemical cells, refurbishment costs, including replacementcosts for damaged cell frames and gasketing from disassémbly ofclosed plate and frame type cells are high.

Because the configuration of the electrochemical cells of this invention is "open", and not sealed, allowing for controlled leakage of aqueous electrolyte solution and gaseous by-products, -7- 113 0 6 sealed cell designs, including gaskets, O-rings and other sealingdevices are eliminated. Instead, cell component parts areretained together in close proximity by various mechanical meanswhen needed, including, for instance, clamps, bolts, ties,straps, or fittings which interact by snapping together, and soon. As a resuit, with the novel open cell concept of thisinvention initial cell costs, renewal and maintenance costs areminimized.

In the open configuration cells of this invention,electrolyte is fed directly to the électrodes in the electrolyzerzone from a feeder which may be positioned centrally relative tothe face of the électrodes, for example, where the contaminatedsolution engages with the électrodes by flowing through verynarrow interelectrode gaps or spaces between the électrodes.During this period the contaminants in the aqueous solution areeither directly converted at the électrodes to less hazardoussubstances and/or through the autogenous génération of Chemicaloxidants or reductants, such as chlorine, bleach, i.e.,hypochlorite; hydrogen, oxygen, or reactive oxygen species, likeozone, peroxide, e.g., hydrogen peroxide, hydroxy radicals, andso on, chemically modified to substances of lesser toxicity, likecarbon dioxide, sulfate, hydrogen, oxygen and nitrogen. In someinstances, depending on the compositional make-up of pollutantsin the solution being treated, it may be désirable to add certainsalts like sodium chloride, iron salts or other catalytic saltsat low concentration to the solution before or during treatmentin the cell. For example, this could be used to generate someactive chlorine to provide a residual level of sterilant in thetreated water, or to produce ferrous iron to promote theformation of Fenton's reagent with added or electrogeneratedhydrogen peroxide. Likewise, oxygen or air may be introducedinto the feed stream to enhance peroxide génération.

Because electrolyte is fed directly to the electrode stackusually under positive pressure, gases such as hydrogen andoxygen generated during electrolysis are less prone to accumulate 118 0 6 -8- over electrode surfaces by forming insulative blankets or pocketsof bubbles. Gas blinding of électrodes produces greater internairésistance to the flow of electricity resulting in higher cellvoltages and greater power consumption. However, with direct flowof electrolyte to the cell, the dynamic flow of solution ininterelectrode gaps, according to this invention, minimizes gasblanketing, and therefore, minimizes cell voltages.

The aqueous solution entering the cell by means of pumpingor gravity feed, cascades over and through availableinterelectrode gaps, and on exiting the electrolyzer zone of thecell through gravitational forces, descends downwardly into a ·réservoir, for post treatment, for example, or discharged, suchas into a natural waterway. Any undissolved gases generated byelectrolysis, in contrast, are vented upwardly from the cell tothe atmosphère or may be drawn into a fume collector or hood, ifnecessary, for collection or further Processing.

While the direct feed "open configuration" electrochemicalcells, as described herein, preferably provide for theélimination of conventional cell housings or tanks, as will bedescribed in greater detail below, the expression "openconfiguration" as appearing in the spécification and daims, inaddition to the foregoing définition, is also intended to includeelectrochemical cell designs wherein the directly fed électrodesare disposed in the interior région of an open tank or open cellhousing. A représentative example of an open tank electrochemicalcell is that disclosed by U.S. Pat. 4,179,347 (Krause et al) usedin a continuous system for disinfecting wastewater streams. Thecell tank has an open top, a bottom wall, sidewalls and spacedélectrodes positioned in the tank interior. Instead of feedingthe contaminated aqueous solution directly to the électrodespositioned in the tank the electrolyte, according to Krause etal, is initially fed to a first end of the tank where interiorbaffles generate currents in the wastewater causing it tocirculate upwardly and downwardly through and between theparallel électrodes. Hence, instead of delivering electrolyte

-9- directly to the electrode stack where under pressure it is forcedthrough interelectrode gaps between adjacent anodes and cathodesaccording to the présent invention, the electrolyte in the opentank cell of Krause et al indirectly engages with the électrodesthrough a flooding effect by virtue of the positioning of theélectrodes in the lower région of the tank where the aqueoussolution résides. This passive, flooding effect is insufficientto achieve the mass transport conditions necessary for efficientdestruction particularly of contaminants when présent in lowconcentrations. Consequently, gaseous by-products of theelectrolysis reaction can and often do resuit in the developmentof a blanket of gas bubbles on electrode surfaces. Thisgenerates elevated cell voltages and greater power consumptiondue to higher internai résistances.

Accordingly, for purposes of this invention the expression"open configuration" as appearing in the spécification and daimsis also intended to include open tank type electrochemical cellswherein the electrode stack is positioned in the interior of anopen tank/housing and includes means for directly feedingcontaminated aqueous solutions to the électrodes. With directfeeding the housing does not serve as a réservoir for thecontaminated aqueous solution which otherwise would passivelyengage the électrodes indirectly by a flooding effect.

For purposes of this invention, it is to be understood theexpression "open configuration" is also intended to allow forsafety devices positioned adjacent to the electrochemical cellsand purification Systems, such as splash guards, shields andcages installed for minimizing the potential for injuries tooperators. Hence, the confinement of the electrolysis cells oran entire water purification System of this invention inside asmall room, for example, is also intended to be within themeaning of "open configuration" as appearing in the spécificationand daims. A further type of electrochemical cell design is disclosed by Beck et al in U.S. Pat. 4,048,047. The Beck et al cell design -10- 118 0 6 comprises a bipolar stack of circular electrode plates separatedby spacers to provide interelectrode gaps ranging from 0.05 to2.0 mm. Liquid electrolyte is fed directly to the electrodeplates through a pipeline into a central opening in the electrodestack and then outwardly so it runs down the outside of thestack. However, the electrode stack is placed in a conjointclosed housing with a covering hood to avoid loss of gaseousreactants, vapors or reaction products. Thus, the closedconfiguration of the Beck et al cell does not meet the criteriaof an "open configuration" cell according to this invention.

While it has been pointed out the "open configuration" ofthe improved, highly économie electrochemical cell designs ofthis invention are based on the élimination of traditional closedcell designs, including plate and frame type cells andconventional tank type cells, as well as traditional partiallyopen tank type cell designs, whether batch or continuous, it isto be understood, the expression "open configuration", asappearing in the spécification and daims, also contemplâteselectrochemical cells which may be modified with various inserts,barriers, partitions, baffles, and the like, in some instancespositioned adjacent to cell électrodes, or their peripheraledges. Such modifications can hâve the effect of alteringelectrolyte circulation and direction, and increaseresidency/retention time, and therefore, affect the residencytime and rate of discharge of electrolyte from the cell.Notwithstanding, such modified electrochemical cells which arepartially open do fall within the intended meaning of "openconfiguration" when the électrodes per se remain substantiallyaccessible. Représentative modified electrochemical cell designswith électrodes which remain substantially accessible that areincluded within the définition for "open configuration" asappearing in the daims include modified, so called "Swiss rollcell" designs wherein, for example, the closed tubularcontainment for the électrodes, which are superimposed onto oneanother and rolled up concentrically, is removed, thereby forming -11- 118 0 6 an "open type Swiss roll cell".

It is yet a further object of the invention to provide amore efficient electrochemical cell design which can be used ineffectively treating a wide spectrum of both Chemical andbiological contaminants in aqueous media, but also of varyingconcentration (from less than a few ppm to several thousand ppm)which is both economically compétitive in capital costs and powerconsumption to more conventional water purification Systems. Theelectrochemical Systems and methods of the invention hâve suchsignificantly improved économies, as to be readily adaptable totreating via continuous processes, large volumes of industrialwaste waters from manufacturing facilities, such as Chemicalplants, textile plants, paper mills, food Processing plants, andso on.

Lower cell voltages and higher current densities areachieved with the highly économie, open configuration, especiallywhen configured as monopolar electrochemical cells equipped withélectrodes having narrow capillary interelectrode gaps.Generally, the width of the gap between électrodes issufficiently narrow to achieve conductivity without extrasupporting^electrolytes or current carriers being added to thecontaminated aqueous solutions. Thus, the need for addingsupporting electrolyte to the contaminated aqueous electrolytesolution as supporting current carrier can be avoided.

It is thus a further object of the invention to provide forimproved, more économie and safer continuous, semi-continuous orbatch methods for electropurification of contaminated aqueoussolutions by the steps of: (i) providing an electrolysis cell comprising at least oneanode and at least one cathode as électrodes positioned in anelectrolyzer zone. The électrodes are spaced sufficiently closeto one another to provide an interelectrode gap capable ofminimizing cell voltage and IR loss. Means are provided fordirect feeding a contaminated aqueous solution to the électrodesin the electrolyzer zone. Means are provided for regulating the -12- 118 0 6 residency time of the electrolyte solution in the electrolyzerzone during electrolysis for modification of the contaminants.The electrolysis cell is characterized by "open configuration"as previously described; (ii) directly feeding into the electrolyzer zone of theelectrolysis cell a contaminated aqueous electrolyte solution,and (iii) imposing a voltage across the électrodes of theelectrolysis cell to modify, and preferably destroy thecontaminants in the aqueous electrolyte solution.

It will be understood that generally the process willinclude the step of recovering a purified electrolyte solutionfrom the electrolysis cell. However, the invention contemplâtesdirect delivery of purified aqueous solutions to a watershed, forexample, or optionally to other post-treatment stations.

As previously mentioned, the methods are performed in anopen configuration electrolysis cell which may be eithermonopolar or bipolar configuration. Because of the openconfiguration, as defined herein, the electrochemical cells ofthis invention can be reàdily configured to a monopolar design.This is especially advantageous since higher current densitieswould be désirable in electrolyzing contaminated aqueoussolutions having relatively low conductivities while still alsomaintaining low cell voltages. Likewise, the improvedelectrochemical cells of this invention may hâve a bipolarconfiguration, especially for large installations to minimizebusbar and rectifier costs.

Typically, in the monopolar open cell design electricalconnections are made to each electrode. Whereas in bipolarconfigurations electrical connections are made to the endélectrodes. However, many applications require increasedelectrode surface area, especially in scaling up from alaboratory scale electrochemical cells to pilot scale, andfinally to commercial size open cells. It would be advantageousif in scaling up cells one could achieve a more efficient cell -13- 118 0 6 design for performing the processes of this invention, andminimize capital and operating costs even further.

It is therefore still another principal object to providealternative, more économie embodiments of the open electrolysiscell concept of this invention, wherein faces of multiple porousélectrodes are positioned adjacent to one another and arrangedeither in a vertical plane or superimposed horizontally relativeto one another in the format of a stack. The porous électrodes,usually meshes or screens, are in electrical contact with oneanother, with each electrode stack requiring but a single feederelectrode for introducing a voltage thereto. Hence, by arrangingthe électrodes in these représentative formats, the effectiveelectrode surface area is significantly increased without alsoincreasing the number of external electrical contacts otherwiserequired to the power source. By layering the électrodesconnection costs are minimized, while also realizing capitalsavings in electrode purchases. Other benefits include improvedefficiency of operation with the open cell configuration, reducedpower consumption and lower operating costs, as a resuit of lowercell voltages.

Accordingly, the invention contemplâtes an embodiment of the"open cell" configuration wherein the electrolysis cell comprisesat least one anode and at least one cathode as électrodespositioned in an electrolyzer zone. At least one of theélectrodes comprises a plurality. of conductive porous élémentspositioned adjacent to and in electrical contact with oneanother. Means are provided for directly feeding an aqueouselectrolyte solution to the électrodes in the electrolyzer zone,and for regulating the residency time of the electrolyte solutionin the electrolyzer zone.

As an alternative, the electrode consisting of a pluralityof conductive porous éléments may be in combination with a solid,non-porous conductive electrode element.

Also included is a method for electropurification ofcontaminated aqueous solutions by the steps of: 118 06 -14- (i) providing an open configuration electrolysis cellwith at least one anode and at least one cathode as électrodespositioned in an electrolyzer zone. At least one of theélectrodes comprises a plurality of conductive porous éléments,as for example, mesh or screen, positioned adjacent to and inelectrical contact with one another. Means are provided fordirect feeding a contaminated aqueous electrolyte solution to theélectrodes in the electrolyzer zone. Means are also provided forregulating the residency time of the aqueous electrolyte solutionin the electrolyzer zone for modification of contaminantstherein; (ii) a contaminated aqueous electrolyte solution isintroduced into the electrolysis cell of (i), and (iii) a voltage applied across the électrodes of theelectrolysis cell to modify the contaminants in the electrolytein the aqueous electrolyte solution.

The improved electropurification methods of the inventionalso contemplate the treatment of aqueous solutions contaminatedwith métal ions. Often, they are toxic substances from platingbath effluents, métal stripping baths, biocide formulations andpaints, and may be sequestered by a complexing agent, surfactantor reducing agent. The electropurification methods of theinvention destroy the complexing agent, surface active agent orreducing agent to release the hazardous métal for furthertreatment in the electrolysis cell, or alternatively, forinstance, transferred to a métal recovery cell for plating outmetals from solution.

While the electrolysis cells disclosed herein hâve as aprincipal utility the electropurification of contaminatedsolutions, the "open" cell configuration of this invention canbe readily employed in other useful applications. Représentativeexamples include the electrochemical synthesis of inorganic andorganic compounds, such as iodate and periodate salts, chlorinedioxide, persulfate salts, and dimers via the Kolbe method ofelectrolysis of carboxylic acids, or by electrohydrodimerization 113 06 -15- of activated olefins, the electrolysis of water to form hydrogenand oxygen, and so on.

It is therefore yet a further principal object of theinvention to provide electrosynthesis processes in the productionof useful products, by the steps of: (i) providing an electrolysis cell with an openconfiguration wherein the cell is equipped with at least oneanode and at least one cathode as électrodes positioned in anelectrolyzer zone. At least one of the électrodes comprises aplurality of conductive porous éléments, for example, mesh orscreens, positioned adjacent to and in electrical contact withone another. Means are provided for direct feeding of anelectrolyte solution to the électrodes in the electrolyzer zone.Also included are means for regulating the residency time of theelectrolyte solution in the electrolyzer zone; (ii) introducing into the electrolysis cell of (i) anelectrolyte comprising a solution of an electroactive substrate,such as an inorganic sait, e.g., aqueous solution of an alkalimétal chloride when making bleach, an iodate sait when makingperiodate, an aqueous solution of an acid, etc., and (iii) imposing a voltage across the électrodes of theelectrolysis cell to electrolyze the electrolyte solution to forma useful Chemical product.

This embodiment of the invention includes methods forelectrosynthesis of a useful product wherein the electrolysiscell is equipped with a porous diaphragm or permselectivemembrane.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the invention and itscharacterizing features reference should now be made to theaccompanying drawings wherein: FIG. 1 is a side elevational view illustrating a first embodiment of a direct feed, open configuration, controlled leakage electrochemical cell of the invention wherein the -16- 118 0 6 électrodes are positioned above a water collection vessel in ahorizontal orientation; FIG. 2 is a side elevational view of the electrochemicalcell of Fig. 1 except the électrodes are in a verticalorientation; FIG. 3 is a side elevational view illustrating a secondembodiment of a direct feed, open configuration, controlledleakage electrochemical cell of the invention wherein theélectrodes are positioned in the interior of an open cellhousing; FIG. 4 is an exploded view of the electrode cell stack ofFig. 1. FIG. 5 is a side elevational view of an electrode stack ofthe invention connected in a monopolar configuration; FIG. 6 is a side elevational view of an electrode stack ofthe invention connected in a bipolar configuration; FIG. 7 is an elevational view of an electrode stackcompartmentalized with a separator; FIG. 8 is a side elevational view of an open electrochemicalcell with stacks of porous électrodes connected in a monopolarconfiguration; FIG. 9 is a side elevational view of an open electrochemicalcell with stacks of porous électrodes connected in a bipolarconfiguration, and

FIG. 10 illustrâtes the results of electropurification ofan aqueous solution of phénol decontaminated according to themethods of the invention, as performed in Example I

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning first to Fig. 1 there is illustrated anelectrochemical cell 10 for purification of contaminated aqueoussolutions, as previously discussed, represented by contaminatedwater 12 passing through inlet 22. The contaminated water 12 istreated in the electrolyzer zone 14 of cell 10 which isillustrated in a fully open configuration allowing gaseous by- 118 06 -17- products of the electrolysis reaction, such as oxygen andhydrogen 16 to be released to the atmosphère. It may be désirablein some instances to collect certain potentially hazardous gasesgenerated during the electrolysis reaction to avoid dischargingto the atmosphère. Chlorine, for example, may be generated at theanode during electrolysis of aqueous effluent streams containingbrine or sea water. Such gases can be recovered, for instance,by a vacuum powered hood device of conventional design (notshown) positioned adjacent to electrochemical cell 10.

The electrolyzer zone 14 includes an electrode stack 17shown in a horizontal orientation in Figs. 1 and 4, and comprisesat least one cathode 18 and at least one anode 20. Anodes 20, forexample, may also serve as end plates 21 for holding an assemblyof électrodes, spacers, and separators, whenever used, into anassembled electrode stack 17. Non-conductive electrode spacers23 positioned between électrodes provide the desiredinterelectrode gap or spacing between adjacent anodes andcathodes. While Figs. 1 &amp; 4 of the drawings may be shown withonly a central cathode with anodes on opposite sides of cathode18, for example, it is to be understood the electrode stacks maybe formed from several alternating anodes, spacers, cathodes, andso on, with bolting means 25 running through the stack and endplates for maintaining the components in a structurally stableassembly.

The end plates, électrodes and spacers may hâve a generallyrectangular geometry. However, any number of possible alternativegeometrical shapes and sizes are within the purview of theinvention, including square, round or circular configurations,to name but a few. Contaminated aqueous electrolyte solutions arefed directly to the électrodes in electrolyzer zone 14 via supplyline 22. Supply line 22 is shown centrally positioned relativeto anode/end plate 21. The électrodes, which may be solid andplanar, are preferably mesh/screen-type materials. This enablesthe aqueous electrolyte solutions entering the electrode stackto directly engage with the électrodes, and in so doing flow -18- 11806 radially across the face of the individual electrode surfaceswithin the stack toward their peripheral edges. In addition, theentering solution usually flows axially, or normal to thelongitudinal axis of the plane of the électrodes, so thecontaminated aqueous solution simultaneously cascades over andthrough the electrode stack in a fountain-like effect to maximizecontact with electrode surfaces in the process. Purified water24, free or virtually free of contaminants exiting electrolyzerzone 14, can be collected in an open tank 26, or funneled intoa discharge line (not shown) for emptying into a naturalwatershed, etc.

It will be understood the direct feed of contaminatedaqueous solutions to the electrolyzer zone need not be centrallypositioned relative to the electrode stack, as illustrated inFigs. 1-4. Alternative direct feed routes include inverting thepoint of feed, so that contaminated aqueous solutions are fedfrom the bottom of the electrode stack, or at an oblique orobtuse angle to the planar surface of the électrodes. Inaddition, the direct feed entry point may also be axial with theedge of the planar surface of the électrodes wherein contaminatedsolution is delivered to the peripheral edge of an electrodestack. A convenient means for regulating the residency tinte of thecontaminated aqueous solution in electrolyzer zone 14 and forcontrolling leakage of decontaminated and purified water 24therefrom can be through valve 28 and/or pumping means ofconventional design (not shown). The flow rate of contaminatedwater directly entering the electrode stack and exiting the stackas decontaminated water can be regulated through manual orautomated flow control valve 28 of standard design. The flow rate(liters/minute)is adjusted, so it is sufficient to provideeffective destruction of pollutants by the time the treatedsolution exits the electrolyzèr zone. Persons of ordinary skillin the art having the benefit of this disclosure will alsorecognize the performance of the electrochemical cells of this 113 0 6 -19- invention may be optimized by alternative means, such asincreasing the path of the solution in the electrolyzer zone. Theinstallation of baffles, for instance, can increase the dwelltime of the solution in the electrolyzer zone. Alternative meansinclude enlarging the surface area of the électrodes for reducingthe residency time in the electrolysis zone. In practice,electrochemists skilled in the art will also recognize theperformance of the cell can be increased with higher currentdensities.

Because of cell geometry, and the ability to convenientlyuse both monopolar and bipolar configurations, practically anyelectrode material can be employed, including metals in the formof fiat sheet, mesh; foam or other materials, such as graphite,vitreous carbon, reticulated vitreous carbon and particulatecarbons. This also includes combinations of electrode materials,such as bilayer éléments comprising two métal layers separatedby appropriate insulating or conductive materials, and so on.

Représentative examples of useful anodes would includethose generally known as, noble métal anodes, dimensionallystable anodes, carbon, vitreous carbon and graphite-containinganodes, doped diamond anodes, substoichiometric titanium oxide-containing anodes and lead oxide-containing anodes. More spécifiereprésentative examples include platinized titanium noble métalanodes; anodes available under the trademark DSA-O2, and otheranodes, such as high surface area type anodes like felts, foams,screens, and the like available from The Electrosynthesis Co,Inc., Lancaster, New York. Other anode materials compriseruthénium oxide on titanium, platinum/iridium on titanium,iridium oxide on titanium, silver oxide on silver métal, tinoxide on titanium, nickel III oxide on nickel, gold,substoichiometric titanium oxides, and particularly the so calledMagneli phase titanium oxides having the formula TiOx wherein xranges from about 1.67 to about 1.9. A preferred specie ofsubstoichiometric titanium oxide is Ti4O7. Magneli phase titaniumoxides and methods of manufacture are described in U.S. Pat. 118 06 -20- 4,422,917 (Hayfield) which teachings are incorporated-by-reference herein. They are also commercially available under thetrademark Ebonex®. Where electrocatalytic métal oxides, likePbO2, RuO2z IrO2, SnO2, Ag2O, Ti4O7 and others are used as anodes,doping such oxides with various cations or anions has been foundto further increase the electrocatalytic oxidation behavior,stability, or conductivity of the decontamination reactions ofthis invention. The sélection of appropriate anode materials ismade by considering such factors as cost, stability of the anodematerial in the solutions being treated and its electrocatalyticproperties for achieving high efficiencies.

Suitable cathode materials include metals, such as lead,silver, steel, nickel, copper, platinum, zinc, tin, etc., as wellas carbon, graphite, Ebonex, various alloys, and so on. Gasdiffusion électrodes are also useful in the methods of thisinvention. In this regard, they may be used as cathodes inconverting oxygen or air to useful amounts of peroxide,minimizing hydrogen évolution and/or for lowering cell voltages.The electrode material, whether anode or cathode, may be coatedwith an electrocatalyst, either low or high surface area. Highersurface area électrodes, for example, expanded métal screens,métal or graphite beads, carbon felts, or reticulated vitreouscarbon are especially useful in achieving higher efficiencies fordestruction of toxic or hazardous substances when présent at lowconcentrations in the aqueous electrolyte.

Spécifie anode and cathode materials are selected on thebasis of cost, stability and electrocatalytic properties. Forexample, persons of ordinary skill in the art of electrochemistrywill recognize which electrode material to select when it isdesired to convert chloride to chlorine; water to ozone, hydroxylradicals or other reactive oxygen species; oxygen or air tohydrogen peroxide or hydroxyl radicals via electrochemicallygenerated Fenton's reagent using for instance, a slowlydissolving iron-containing métal anode; and catalytic réductionof nitrate to nitrogen or of organohalogen compounds to halide -21- 113 0 6 ions and organic moieties of lesser toxicity.

Of spécial importance in the sélection of electrocatalyticanode and cathode materials occurs when treating aqueoussolutions comprising complex mixtures of pollutants whereinelectrode materials may be selected for paired destruction ofpollutants. For example, an aqueous stream contaminated withorganics, microorganisms and nitrate pollutants may be treatedsimultaneously in the same electrochemical cell using paireddestruction methods with a reactive oxygen species generatinganode, such as platinum on niobium or Ebonex for destruction ofmicroorganism and oxidation of organics. In addition, the samecell could also be equipped with a lead or other electrocatalyticcathode material designed for nitrate destruction.

As previously mentioned, non-conductive electrode spacers23 provide the desired interelectrode gap or spacing betweenadjacent anodes and cathodes. The thickness of spacers 23, whichare non-conductive, insulative porous mesh screens fabricatedfrom polymeric materials, such as polyolefins, like polypropyleneand polyethylene, détermines the width of the interelectrode gap.Alternatively, it is permissible to employ ionic polymer spacerswhich can effectively increase the ionic conductivity of thecell, so as to reduce cell voltage and operating costs further.Ion-exchange resins of suitable dimensions, like cation and anionexchange resin beads are held immobile within the gap betweenélectrodes.

For most applications, the interelectrode gap ranges fromnear zéro gap, to avoid electrode shorting, to about 2 mm. Morespecifically, this very small capillary size gap is preferablyless than a millimeter, ranging from 0.1 to <1.0 mm. The verysmall interelectrode gap makes possible the passage of currentthrough relatively non-conductive media. This is the case, forexample, in water contaminated with organic compounds. Thus, withthe présent invention it is now possible to destroy contaminantsin solution without adding any current carrying inorganic saltsto increase the ionic conductivity of the aqueous media. -22- 113 0 6

Furthermore, the very narrow interelectrode gap provides theimportant advantage of lower cell voltages which translates intoreduced power consumption and lower operating costs. Hence, thecombination of open configuration electrochemical cells and very 5 narrow interelectrode gaps of this invention provide for bothlower initial capital costs, as well as lower operating costs.This achievement is especially important in large volumeapplications, as in the purification of drinking water, andwastewater, according to the claimed processes. 10 Fig. 2 represents a further embodiment of the electrochemical cells of this invention wherein the electrolyzerzone 30 is also in an open configuration. The electrolyte 32 isfed directly to the electrode stack 34 which is in a verticalorientation. As a resuit, treated aqueous solution 36 is shown 15 exiting mainly from both the top and bottom peripheral edges ofelectrode stack 34. This may be altered further depending on theuse of baffles, for instance, in controlling residency time forthe solution being treated. Purified solution is collected invessel 38 below electrolyzer zone 30. 20 Fig. 3 represents still a third embodiment of the invention wherein the electrolyzer zone 40 comprises an electrode stack 42,as discussed above, positioned in the interior of an openhousing/tank 44. Housing 44 is open at the top allowing gaseousby-products of the electrolysis reaction, like hydrogen and 25 oxygen, for instance, to be readily discharged into theatmosphère or collected through aid of an appropriate device,such as a hood (not shown) . Aqueous contaminated electrolytesolution 46 is fed directly to electrode stack 42 positioned inopen housing 44, unlike other tank cells wherein the électrodes 3-0 receive solution indirectly as a resuit of their immersion inthe solution delivered to the tank. Purified water 48 cascadingdownwardly as a resuit of gravitational forces collects at thebottom of the interior of housing 44, and is withdrawn.

An important advantage of the open configuration 35 electrochemical cells of this invention résides in their ability -23- 11806 to be readily adaptable to either a monopolar or bipolarconfiguration. In this regard, Fig. 5 illustrâtes a monopolaropen configuration electrochemical cell. In the monopolar cellof Fig. 5, anodes 52, 54 and 56 each require an electricalconnector as a current supply, in this case through a bus 58 asa common "external" supply line. Similarly, cathodes 60 and 62each require an electrical connection shown through a common bus64. It is also characteristic of the monopolar cell design thatboth faces of each electrode are active, with the same polarity.

Because water purification for a municipality, in general,is a large volume application, lowest possible cell voltages areessential in order to minimize power consumption. The openconfiguration, monopolar cell design of the présent invention incombination with very narrow interelectrode gaps offers not onlythe benefits of lower initial capital costs, but also lowoperating costs, due to lower internai résistances, lower cellvoltages and higher current densities. This combination isespecially désirable when treating contaminated aqueous media ofrelatively low conductivity without the addition of inorganicsalts as current carriers in accordance with certain embodimentsof this invention, e.g., aqueous solutions contaminated with non-polar, organic solvents.

The open configuration, monopolar, controlled leakageelectrochemical cells with very narrow interelectrode gaps ofthis invention are particularly unique in light of the Beck etal cells of U.S. pat. 4,048, 047. The closed configuration of theelectrochemical cells of Beck et al make it very difficult andcostly to achieve a monopolar connection with high currentdensities associated with external electrical contacts to eachelectrode. By contrast, with the open configuration of theelectrochemical cells of this invention electrical connectionsto individual électrodes are facilitated, irrespective of whetherthe cell is a monopolar or bipolar design. Thus, the closed,bipolar electrochemical cell configuration of Beck et al wouldnot be économie and cost compétitive with the improved -24- 113 0 6 electrochemical cells of the présent invention, or with othernon-electrochemical technologies used in high volume waterpurification processes.

As previously indicated, the open configuration, controlledleakage electrochemical cells of this invention having verynarrow capillary interelectrode gaps are also readily adaptableto bipolar configuration. Fig. 6 illustrâtes open configurationbipolar cell 70, according to the présent invention, requiringonly two "external" electrical contacts 72 and 74 through two endélectrodes /end plates 76 and 78. Each of inner électrodes 80,82 and 84 of the bipolar cell has a different polarity onopposite sides. While the bipolar cell can be quite économie ineffectively utilizing the same current in each cell of theelectrode stack, one important aspect of the invention relatesto treating solutions by passing a current through relativelynon-conductive media using very narrow interelectrode gaps. Thatis, the contaminated aqueous solutions can hâve relatively lowconductivities, about équivalent to that of tap water. In orderto efficiently treat such solutions it would be désirable tooperate at higher current densities. The monopolar cellconfigurations of the invention enable operating at desired lowcell voltages and high current density. While not specificallyillustrated, it will be understood standard power supplies areutilized in the electrolysis cells of the invention, includingDC power supply, AC power supply, pulsed power supply and batterypower supply.

The invention also contemplâtes open configurationelectrochemical cells with distributor means for contaminatedaqueous electrolyte solutions, such as a length of pipe 81 withmultiple openings or pores, or a feeder tube extending from thecontaminated aqueous electrolyte feed inlet through the depth ofthe electrode stack in the electrolyzer zone. This can providemore uniform flow of solution to the electrode éléments.Especially useful for stacks containing many electrode éléments,these porous tubes of métal or plastic material, of sufficient -25- 118 0 6 porosity, diametar and length, are applicable to monopolar,bipolar, and for example, Swiss roll cells of open configuration.For deep cell stacks with electrode éléments, each of largersurface area, more than one porous feeder tube may be provided,manifolded together with the feed inlet conduit.

The open configuration, bipolar type, controlled leakageelectrochemical cells of the présent invention can be mosteffectively used in the purification of aqueous solutionspossessing greater ionic conductivities than those previouslydiscussed, allowing for economical operation at lower currentdensities. In each instance, the open configuration of theelectrochemical cells of this invention facilitâtes theirelectrical connection, whether the cell is a monopolar or bipolardesign.

Most desirably, large volume applications like waterpurification require low capital and operating costs in order tobe economically attractive. These inventors found that capitalcosts are largely reduced by eliminating the need for précisionmachined components, gasketing, costly membranes and cellseparators. Lower operating costs can be achieved through lowercell voltages from narrow interelectrode gaps and lower IR fromélimination of cell membranes and separators, i.e., undividedelectrochemical cells. The smaller interelectrode gap, however,also makes possible the operation of the cells of this inventionin an organic media, for example, containing low concentrationsof supporting electrolyte, with a variety of electrode, insulatormaterials, and so on. Many of such applications would be readilyadaptable to the open cell configuration of this invention, butwith use of a cell divider forming anolyte and catholytecompartments, such as membranes or cell separators. Examples ofuseful processes for the electrochemical cells of this inventionwould include mediated reactions in electrochemical synthesis inwhich the objective of the membrane or separator would be toprevent réduction of anodically produced species at the cathode,and/or oxidation of cathodically produced species at the anode. -26- 118 06

Fig. 7 is a représentative example of an open configurationelectrochemical 90 having anode/end plates 92 and 94 with centralcathode 96 and cation exchange membranes 98 and 100 positionedbetween the électrodes. Membranes 98 and 100 prevent mixing ofthe anolyte and catholyte in the cell while the solution isallowed to flow through opening 102 in. the center of themembrane.

Those embodiments of the electrochemical cells employinga diaphragm or separator are preferably equipped with ion-exchange membranes, although porous diaphragm type separators canbe used. A broad range of inert materials are commerciallyavailable based on microporous thin films of polyethylene,polypropylene, polyvinylidene-difluoride, polyvinyl chloride,polytetrafluoro-ethylene (PTFE), polymer-asbestos blends and soon, are useful as porous diaphragms or separators.

Useful cationic and anionic type permselective membranes arecommercially available from many manufacturers and suppliers,including such companies as RAI Research Corp., Hauppauge, NY,under the trademark Raipore; E.I. DuPont, Tokuyama Soda, AsahiGlass, and others. Generally, those membranes which areare most preferred because of their overallAn especially useful class of permselective ion exchange membranes are the perfluorosulfonic acid membranes, suchas those available from E.I. DuPont under the Nafion® trademark.The présent invention also contemplâtes membranes and électrodesformed into solid polymer electrolyte composites. That is, atleast one of the électrodes, either anode or cathode or bothanode and cathode, are bonded to the ion exchange membraneforming an intégral component.

While embodiments of the invention previously discussedmention electrode stacks, e.g., 17 and 34 of Figs. 1 and 2, respectively, etc., such electrode stacks are comprised of individual, single anode and single cathode éléments spaced from one another by narrow interelectrode gaps. Fig. 4 illustrâtes représentative electrode stacks in exploded view comprising a fluorinatedstability. 118 0 6 -27- cathode 18 consisting of a single planar screen element havingits own external electrical contact 19. Non-conductive porousspacers 23 on each side of cathode 18 provide the desiredinterelectrode gaps separating the cathode element from adjacentend anodes 20. While Fig. 4 illustrâtes an electrode stack witha single cathode screen positioned between end anodes 20, it isto be understood that larger capacity commercial and semi-commercial pilot scale cells of this invention will usually hâvecell stacks comprising a multiplicity of alternating anodes andcathodes each having an external electrical contact when in amonopolar configuration.

However, those scaled up versions of the electrolysis cellsof this invention requiring increased electrode surface area canachieve this resuit more economically by stacking a plurality ofindividual porous electrode éléments as illustrated by Figs. 8and 9. Multiple electrode éléments consisting of conductiveporous éléments, for example, meshes or screens are positionedadjacent to and in electrical contact with one another in eithermonopolar (Fig. 8} and bipolar (Fig. 9) open cell configurations.

Either or both the anodes and cathodes of the open cellembodiment may hâve the multiple electrode element design. Thatis, an anode stack consisting of multiple electrode éléments areheld together in electrical contact, and may be positionedadjacent to a cathode consisting of a single electrode element,and vice versa. This is best illustrated by Fig. 8, whichconsists of monopolar open cell 104 held between end plates 105with multiple porous anode éléments 106 positioned between singleelement cathodes 108, illustrated as porous cathodes, but mayalso be non-porous plate électrodes. Anodes 106 are separatedfrom cathodes 108 by means of porous non-conductive spacers 107.Advantageously, anode stacks 106 need only a single "feeder"electrode 110 for transferring a voltage on either side to otherelectrode éléments of the same stack in contact therewith. Bystacking electrode éléments in this manner, the effectiveelectrode surface can be significantly increased without -28- 118 06 increasing the number of external electrical contacts 112 to thepower source 113, which would otherwise be required. This notonly minimizes costs for external electrical connectors andcapital costs for électrodes, but also improves efficiency ofoperation resulting in lower cell voltages and reduced powerconsumption for lower operating costs.

The conductive porous éléments of the électrodes may befabricated from métal or carbon, for instance, and can be in theform of perforated métal plates, welded wire cloth, woven wirecloth, expanded métal, carbon felts, woven carbon cloth,reticulated vitreous carbon, including metallic foams, such asnickel foam having sponge-like characteristics. Représentativeexamples of commercially available perforated métal plates arelow carbon steel sheets and micro-etched type 316 stainless Steelsheets with hole patterns which are uniform and accurate in size.Welded wire cloth includes type 304 stainless steel cloth andstainless steel knitted wire mesh. Wire cloth is a woven orwelded material formed from métal wire, and is available in avariety of mesh sizes. Also available is type 304 stainless steelgrade. Expanded métal consists of plates which hâve been slitand stretched. The plates/sheets are lightweight, yet strong dueto the diamond truss pattern of their openings. They arecommonly fabricated from carbon steel and type 304 stainlesssteel.

The invention contemplâtes a combination of different porousmaterials for use as the electrode éléments in a single cell toachieve a combination oxidation/reduction effect, for example.The pore density of the conductive porous éléments of theélectrodes may range from 1 to about 500 mesh/linear inch. Theconductive porous éléments may also hâve an open area rangingfrom about 10 to about 90 percent. Some éléments, such as foamsmay hâve porosities ranging from 1 to 1000 pores/lineal inch anda densities ranging from 5 to about 85 percent. The electrodeéléments may simply be stacked in close electrical contact orwelded together and to the feeder electrode, as appropriate, to -29- 118 0 6 ensure electrical connectivity through ail members of the stack.

Fig. 9 also shows an open electrolysis cell design 114similar to Fig. 8, but in a bipolar configuration shown with ailintermediate electrode stacks 116 consisting of a plurality ofporous electrode éléments. Individual éléments of each electrodestack are in electrical contact with other members of the samestack. Power is routed to the cell through end plate anodes 118.Stacks 116 are spaced from one another by porous spacers 120.

The optimum number of electrode éléments which may be usedwith or without a "feeder" electrode is a function of a numberof variables, including the thickness of each porous electrodeelement, the conductivity of the solution being treated and theoverall optimum cell design. The number of electrode éléments,in addition to the feeder electrode (Fig. 8) may range from 1 to100, and more specifically, 1 to 10 electrode éléments. The"feeder" electrode may be the same material of construction asthe individual electrode éléments, or different, provided thefeeder is stable under electrolysis conditions, and iselectrically conductive.

In the purification of solutions the invention provides forthe treatment of low conductivity media. However, it may benecessary to add very low concentrations of inert, soluble salts,such as alkali métal salts, e.g. sodium or potassium sulfate,chloride, phosphate, to name but a few. Stable quaternaryammonium salts may also be employed. As previously mentioned, ionexchange resin beads of appropriate size can be inserted in thespaces between the électrodes to increase conductivity. Thiswill provide further réductions in cell voltage and totaloperating costs.

Gontaminated solutions entering the cell can range intempérature from near freezing to about boiling, and morespecifically from about 40° to about 90°C. Higher températurescan be bénéficiai in lowering cell voltages and increase ratesof contaminant destruction. Such higher températures can beachieved, if needed, by preheating the incoming solution, heating 118 06 -30- the électrodes, or through IR heating in the cell, especiallywhen solution conductivities are low, as for example inpurification of drinking water. By suitably adjusting the cellvoltage and résidence time in the cell, bénéficiai températuresin the above ranges are possible.

As a preferred embodiment of the invention, as an undividedcell, for the purification of contaminated aqueous solutions avariety of useful anode and cathode species can be generatedduring electrolysis which in turn aid in the Chemical destructionof contaminants and the purification of the aqueous solutions.They include such species as oxygen, ozone, hydrogen peroxide,hydroxyl radical, and other reactive oxygen species. Lesspreferred species, although useful in the process include thegénération of chlorine or hypochlorite (bleach) through theelectrolysis of brine or sea water. While not wishing to be heldto any spécifie mechanism of action for the success of theprocesses in the decontamination, decolorization andsterilization of aqueous solutions contaminated with toxicorganics and microorganisms, several processes, including thosepreviously mentioned, may be occurring simultaneously. Theyinclude, but are not limited to the direct oxidation ofcontaminants at the anode; destruction of contaminants by directréduction at the cathode; oxygénation of the feed stream by microbubbles of oxygen produced at the anode; degasification ofvolatiles in the feed stream by oxygen and hydrogen microbubbles; IR heating in the cell; aération of the water streamexiting the open cell, and so on. A broad range of compounds, microorganisms and otherhazardous substances, such as métal ions as previously discussedare successfully destroyed or removed in the open cellconfiguration of the invention employing the processes asdescribed herein. Représentative examples include aliphaticalcohols, phénols, nitrated or halogenated aromatic compounds,and so on. Color réduction or complété élimination of color canalso be achieved, along with disinfection, including the -31- 118 0 6 destruction of viruses.

There are many kinds of métal salts in aqueous solutions,including toxic metals in ionic form in plating bath effluents,métal stripping baths, biocide formulations, paints, etc., which 5 are difficult to remove or recover by ion exchange or byconventional Chemical or electrochemical means. Such metalsinclude the precious metals, like platinum, silver and gold, aswell as non-precious metals, such as copper, nickel, cobalt andtin, to name but a few. Government régulations are becoming 10 increasingly strict, as to maximum acceptable levels of thesemetals which may be discharged into our waterways. Thesesolubilized métal solutions are often difficult to treat becauseof other components which may be présent, typically complexingagents, surfactants, reducing agents, and other similar type 15 materials.

Accordingly, the présent invention also contemplâteselectropurification of aqueous solutions contaminated withhazardous métal ions by treating in the open electrolysis cellsdisclosed herein using the methods previously discussed. This 20 includes decontaminating the solutions by métal réduction at thecathodes of the open cell, as well as treating métal ions fromplating bath effluents, métal stripping baths, biocideformulations, paints, and other contaminated industrial aqueoussolutions, wherein the metals are sequestered by various 25 complexing agents, surfactants or reducing agents, for instance.Solution components, including complexing agents are initiallydestroyed electrochemically, greatly facilitating recovery/removal of metals from the solutions. Représentative complexingagents may include cyanides, ferricyanides, thiosulfates, imides, .30 hydroxycarboxylic acids, like tartaric, citric and lactic acids,and so' on. This method effectively releases the ionized métalfor réduction in the cell or for removal/recovery. Alternatively,the partially treated aqueous solution may be treated furtheroutside the open cell using such methods as ion exchange, 35 précipitation with base, by electrolysis in a métal recovery -32- 118 06 electrochemical cell, such as a Renocell™ manufacturée! byRenovare International. This latter method allows métal to beplated onto a high surface area cathode.

The following spécifie examples demonstrate the variousembodiments of the invention, however, it is to be understoodthey are for illustrative purposes only and do not purport to bewholly definitive as to conditions and scope.

EXAMPLE I A monopolar electrochemical cell having an openconfiguration was set up with an electrode stack comprising 316stainless steel end plates each with a diameter of 12.065centimeters and a thickness of 0.95 centimeters. The end plateswere connected as cathodes. A central cathode was also assembledinto the stack and consisted of 316 stainless steel mesh with 7.8x 7.8 openings/linear centimeter, 0.046 centimeter wire diameter,0.081 centimeter opening width and 41 percent open area. Theanodes consisted of two platinum clad niobium électrodesmanufactured by Blake Vincent Metals Corp. of Rhode Island. Theanodes which were clad on both sides of the niobium substrate hada thickness of 635 micrometers, were expanded into a mesh witha thickness of about 0.051 centimeters, with 0.159 centimeterdiamond shaped interstices. The spacers positioned betweenadjacent électrodes were fabricated from polypropylene mesh with8.27 x 8.27 openings/linear centimeter, 0.0398 centimeter threaddiameter, 0.084 centimeter opening and a 46 percent open area wassupplied by McMaster-Carr of Cleveland, Ohio. The gap between theélectrodes was approximately 0.04 centimeters, determined by thethickness of the polypropylene mesh. A schematic of theelectrochemical cell corresponds to Fig. 1 of the drawings,except a hood was omitted. Recirculation of the aqueous solutionbetween the glass collection tank and the cell was effected bymeans of an AC-3C-MD March centrifugal pump at a flow rate ofabout 1 liter/minute. A Sorensen DCR 60-45B power supply was usedto generate the necessary voltage drop across the cell. -33- 118 0 6 A test solution was prepared containing 1 g of phénol in 1liter of tap water. The solution was recirculated through thecell while a constant current of 25 amps was passed. Thesolution which was initially clear turned red after about 2-3minutes into the treatment process, possibly indicating thepresence of quinone-type intermediates. The initial cell voltageof 35 V decreased rapidly to 8-9 V, and the température of thesolution stabilized at about 56-58°C. Samples taken wereanalyzed periodically for total organic carbon (TOC). Theresults, which are shown in Fig.10, appear to suggest thedecrease in TOC is from the phénol probably undergoing complétéoxidation to carbon dioxide which is then eliminated as gas fromthe solution.

EXAMPLE II

In order to demonstrate color réduction in a textileeffluent 1 liter of solution was prepared with tap watercontaining 0.1 g of the textile dye Remazol™ Black B (HoechstCelanese), 0.1 g of the surfactant Tergitol™ 15-S-5 (UnionCarbide) and 1 g of NaCl.

The composition of the test solution was similar to that oftypical effluents produced in textile dyeing processes where evenvery low concentrations of Remazol Black impart very strongcoloration to solutions. Remazol Black is a particularlydifficult to treat textile dye. Heretofore, other methods usedto treat Remazol Black, such as by ozonation or with hypochloritebleach hâve failed to produce satisfactory color réduction.

The above solution containing Remazol Black was electrolyzedin the monopolar cell set up of Example I above, at a constantcurrent of 25 amps. The cell voltage was about 25 V, and thetempérature of the solution reached 52°C. The initial color ofthe solution was dark blue. After 10 minutes of electrolysis thecolor of the solution turned to pink, and after 30 minutes thesolution was virtually colorless. -34- 11806

EXAMPLE III A further experiment was conducted in order to demonstratethe decontamination of ground water. Humic acids are typicalcontaminants of ground water, produced by the décomposition ofvegetable matter. Water containing humic acids is stronglycolored even at low concentrations, and the élimination of thecolor can be difficult. A dark brown solution in tap water was prepared containing30 ppm of the sodium sait of humic acid (Aldrich) without anyadditives to increase the electrical conductivity of thesolution. The solution was recirculated through a monopolarelectrochemical cell similar to that used in Example I, butequipped with only one anode and two cathodes. A constantcurrent of 10 amps was passed for 2.5 hours. The cell voltage was24-25 volts, and the température reached 58°C. At the end of theexperiment the solution was completely clear, demonstrating theeffective destruction of humic acid.

EXAMPLE IV A further experiment was conducted to demonstrate theeffectiveness of the electrolysis cells and methods of thisinvention in the sterilization and Chemical oxygen demand (COD)réduction in effluents from food processing plants. 250 ml of wastewater from a Mexican malt manufacturingcompany was treated using a monopolar, open electrochemical cellsimilar to that employed in Example I, except the total anodearea of 6 cm2. The objectives were to reduce the COD, partial ortotal réduction of the color, élimination of microorganisms andodor. A current of 1 amp was passed for 150 minutes; the initialcell voltage of 22 V dropped to 17.5 V, and the température ofthe solution reached 44°C.

The results are shown in the following Table: -35- 11806 TABLE Initial Final COD 1700 ppm 27 ppm Color Yellow-Orange Clear Microorganisms Active Sterilized Odor Yes No

EXAMPLE V A further experiment was conducted to demonstrate theeffectiveness of the electrolysis cells and methods of thisinvention in the removal of color in a single-pass configuration. A dark purple solution containing methyl violet dye in tapwater at a concentration of 15 ppm was circulated through amonopolar, open electrochemical cell similar to that employed inExample 1, in single-pass mode, at a flow rate of 250 ml/minute.The objective was to achieve total réduction of the color. A current of 25 amp was passed; the cell voltage was 25 V,and the température of the solution reached 65°C.

After a single pass through the cell a clear solution wasobtained.

EXAMPLE VI

An experiment can be conducted to demonstrate the utilityof the open configuration electrochemical cell in theelectrosynthesis of Chemicals, in this instance sodiumhypochlorite.

The electrochemical cell of Example I is modified byreplacing the anodes with catalytic chlorine evolving anodes,such as DSA® anodes manufactured by Eltech Systems. A solutionof brine containing 10g of sodium chloride per liter isintroduced into the electrolyzer zone wherein chlorine isgenerated at the anode and sodium hydroxide is produced at thecathode. The chlorine and caustic soda are allowed to react inthe cell to produce a dilute aqueous solution of sodium -36- hypochlorite bleach. 11806

EXAMPLE VII

To demonstrate the open cell configuration employingélectrodes comprising a plurality of conductive porous élémentspositioned adjacent to and in electrical contact with oneanother, an experiment is performed using the monopolar cellconfiguration illustrated in Fig. 8. The cell is equipped witha Pt/Nb woven mesh anode having 10 strands per linear inch. Twoof the Pt/Nb screens are in electrical contact and stacked ontop of a third Pt/Nb screen, as the feeder electrode, which inturn is connected to the positive terminal of a DC power supply.The cathode element is a single nickel screen connected to thenégative terminal of the DC power supply.

The electrolyte to be treated consists of 5 g of sodiumchloride added to one liter of an aqueous electroless nickelplating effluent at 60°C, containing 60 g of nickel sait, 25 gsodium hypophosphite, and a COD of 20,000 ppm. Electrolysis isconducted at 55mA/cm2, at a cell voltage of 5.5V until the CODof the effluent drops to about 10 percent of its initial value.The effluent is then treated in an electrochemical cellcontaining a high surface area carbon cathode to plate out mostof the nickel remaining in solution.

This demonstrates the destruction of complexing agents inelectroless plating bath effluent and release of métal ions forrecovery by plating means.

While the invention has been described in conjunction withvarious embodiments, they are illustrative only. Accordingly,many alternatives, modifications and variations will be apparentto persons skilled in the art in light of the foregoing goingdetailed description, and it is therefore intended to embrace ailsuch alternatives and variations as to fall within the spirit andbroad scope of the appended daims.

Claims (40)

118 06 37

1. An electrolysis cell characterized by comprising at leastone anode and at least one cathode as électrodes positioned in anelectrolyzer zone, conduit means for introducing an electrolyteto said électrodes for electrolysis, said electrolysis cell havingan open configuration, and excluding a cell housing intended forretaining an electrolyte solution in said electrolyzer zone.

2. The electrolysis cell of claim 1 wherein said openconfiguration is characterized by controlled leakage ofelectrolyte solution and/or gaseous by-products.

3. The electrolysis cell of claim 1 characterized as aelectropurification cell for treating contaminated aqueoussolutions.

4. The electrolysis cell of claim 1 characterized as anelectrosynthesis cell for production of organic or inorganicChemicals.

5. The electrolysis cell of claim 1 characterized by saidélectrodes connected in a monopolar or bipolar configuration.

6. The electrolysis cell of claim 5 characterized by atleast one of said électrodes comprising a plurality of conductiveporous éléments positioned adjacent to and in electrical contactwith one another.

7. The electrolysis cell of claim 6 characterized by saidconductive porous éléments of said électrodes fabricated frommétal or carbon.

8. The electrolysis cell of claim 6 characterized by saidconductive porous éléments of the électrodes comprised of amaterial independently selected from the group consisting of

38 perforated métal, welded wire cloth, woven wire cloth, expandedmétal, carbon felt, woven carbon cloth, reticulated vitreouscarbon and metallic foam.

9. The electrolysis cell of claim 6 wherein the électrodescomprising a plurality of conductive porous éléments arecharacterized by a feeder electrode and from 1 to 100 additionalconductive porous éléments in electrical connection with saidfeeder electrode.

10. The electrolysis cell of claim 1 wherein said cell isfurther characterized by means for regulating electrolyteresidency time.

11. The electrolysis cell of claim 10 characterized by meansfor uniform distribution of electrolyte solution over saidélectrodes.

12. The electrolysis cell of claim 1 wherein said anodes arecharacterized as electrocatalytic for producing reactive oxygenspecies.

13. The electrolysis cell of claim 12 wherein theelectrocatalytic anodes are characterized by a material ofconstruction selected from the group consisting of nobel métal,tin oxide, lead dioxide, substoichiometric titanium oxide anddoped diamond.

14. The electrolysis cell of claim 1 wherein said cathodesare characterized as electrocatalytic for nitrate destructions.

15. The electrolysis cell of claim 1 wherein said cathodesare characterized as gas diffusion cathodes suitable for réductionof oxygen to water or peroxide. 39 11806*

16. The electrolysis cell of claim 1 characterized as anundivided electrochemical cell.

17. The electrolysis cell of claim 1 characterized by thepresence of a cell divider between said anode and cathode to formanolyte and catholyte compartments.

18. The electrolysis cell of claim 1 characterized by thepresence of at least one sensor selected from the group consistingof Ph, UV light, visible light conductivity, hydrogen andchlorine.

19. The electrolysis cell of claim 1 characterized by thepresence of at least oné power supply selected from the groupconsisting of a DC power supply, AC power supply, pulsed powersupply and battery power supply.

20. The electrolysis cell of claim 1, characterized by thepresence of sensor means and computerized means for receivinginput from said sensor means and providing output for controllingat least one operating condition in said electrolysis cellselected from the group consisting of current density, flow rateof electrolyte solution to said electrolysis cell, température andelectrolyte pH.

21. A method for electropurification of a contaminatedsolution, characterized by the steps which comprise: (i) providing an electrolysis cell comprising at leastone anode and at least one cathode as électrodes positioned in anelectrolyzer zone, conduit means for introducing an electrolyteto said électrodes for electrolysis, said electrolysis cell havingan open configuration, and excluding a cell housing intended forretaining an electrolyte solution in said electrolyzer zone; 40 11306 (ii) introducing into the electrolysis cell acontaminated electrolyte solution, and (iii) imposing a voltage across the électrodes of saidelectrolysis cell to electrolyze the contaminated solution andmodify the contaminants therein.

22. The electropurification method of claim 21 wherein theopen configuration of said electrolysis cell is characterized bycontrolled leakage of electrolyte solution and/or gaseous by-products.

23. The electropurif ication method of claim 21 characterizedby the électrodes of said electrolysis cell connected in amonopolar or bipolar configuration.

24. The electropurif ication method of claim 23 characterizedby at least one of the électrodes of said electrolysis cellcomprising a plurality of conductive porous éléments positionedadjacent to and in electrical contact with one another.

25. The electropurif ication method of claim 21 characterizedby said electrolyte solution comprising contaminants selected fromthe group consisting of organic compounds, inorganic compounds,microorganisms, viruses, métal ions and mixtures thereof.

26. The electropurif ication method of claim 21 characterizedby said electrolyte solution comprising microorganisms selectedfrom the group consisting of bacteria, spores, cysts, protozoa,fungi and mixtures thereof.

27. The electropurif ication method of claim 21 characterizedby the electrolyte solution introduced into the electrolysis cellcomprising a dye or other color producing contaminants, and the 41 11806 modified electrolyte solution recovered from said electrolysiscell is substantially color-free.

28. The electropurification method of claim 21 characterizedby electrolysis being conducted with the introduction of a currentcarrier to the electrolyte solution in an amount sufficient toenhance the destruction of contaminants.

29. The electropurification method of claim 28 wherein thecurrent carrier is an alkaline substance or an acidic substanceselected from the group consisting of acid and acid sait.

30. The electropurif ication method of claim 21 characterizedby the step of adding sufficient sait to the contaminatedelectrolyte solution to provide an active halogen residue in thepurified solution.

31. The electropurif ication method of claim 21 characterizedby the electrolyte solution introduced into the electrolysis cellbeing contaminated with métal ions.

32. The electropurif ication method of claim 31 characterizedby said métal ions which are toxic metals from plating batheffluents, métal stripping baths, biocide formulations and paints,said metals sequestered by a complexing agent, surfactant orreducing agent.

33. The electropurif ication method of claim 32 characterizedby said complexing agent, surfactant or reducing agent beingmodified in the electrolysis cell to release the métal ions forfurther treatment in said electrolysis cell or for transfer to amétal recovery cell. 118 06 42

34. A method for electrosynthesis of Chemicals,characterized by the steps which comprise: (i) providing an electrolysis cell, which comprises atleast one anode and at least one cathode as électrodes positionedin an electrolyzer zone, conduit means for introducing anelectrolyte to said électrodes for electrolysis, said electrolysiscell having an open configuration, and excluding a cell housingintended for retaining an electrolyte solution in saidelectrolyzer zone, (ii) introducing into the electrolysis cell anelectrolyte comprising a solution of an electroactive substrate,and (iii) imposing a voltage across the électrodes of saidelectrolysis cell to electrolyze the electrolyte to form a usefulproduct.

35. The method for electrosynthesis according to claim 34characterized by said électrodes connected in a monopolar orbipolar configuration.

36. The method for electrosynthesis of Chemicals accordingto claim 35 characterized by at least one of said électrodescomprising a plurality of conductive porous éléments positionedadjacent to and in electrical contact with one another.

37. The method for electrosynthesis of Chemicals accordingto claim 36 characterized by said conductive porous éléments ofsaid électrodes fabricated from métal or carbon.

38. The method for electrosynthesis of Chemicals accordingto claim 34 characterized by said electrolyte comprising anaqueous solution of a sait or an acid. 43 11806

39. The method for electrosynthesis of Chemicals accordingto claim 34 characterized by the useful product which is aninorganic or organic compound.

40. The method for electrosynthesis of Chemicals according to claim 34 characterized by the electrolysis cell of (i)comprising a porous diaphragm or permselective membrane. 10