Asymmetric Polarity Reversal for an Electrolytic - Cation Exchange Module (E-CEM)

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]The present application claims priority to U.S. Provisional Application No. 63/564,048, filed Mar. 12, 2024 and titled “Asymmetric Polarity Reversal for an Electrolytic-Cation Exchange Module (E-CEM) Process”, the disclosure of which is incorporated herein in its entirety for all purposes.

GOVERNMENT LICENSE RIGHTS

[0002]This invention was made with government support under Office of Naval Research contract N00014-21-C-1019 awarded by the Department of the Navy. The government has certain rights in the invention.

BACKGROUND

1. Field of Invention

[0003]Aspects and embodiments disclosed herein are generally directed to electrochemical devices, and more specifically, to electrolytic-cation exchange modules and methods of fabricating and operating same.

2. Discussion of Related Art

[0004]Electrochemical devices that perform processes based on chemical reactions at electrodes are widely used in industrial and municipal implementations. Examples of reactions include:

A. Generation of Sodium Hypochlorite from Sodium Chloride and Water.

2Cl⁻→Cl₂+2e⁻  Reaction at anode:

2Na⁺+2H₂O+2e⁻→2NaOH+H₂  Reaction at cathode:

Cl₂+2OH⁻→ClO⁻+Cl⁻+H₂O  In solution:

NaCl+H₂O→NaOCl+H₂  Overall reaction:

B. Generation of Sodium Hydroxide and Chlorine from Sodium Chloride and Water, with a Cation Exchange Membrane Separating the Anode and the Cathode:

2Cl⁻→Cl₂+2e⁻  Reaction at anode:

2H₂O+2e⁻→2OH⁻+H₂  Reaction at cathode:

2NaCl+2H₂O→2NaOH+Cl₂+H₂  Overall reaction:

SUMMARY

[0005]In accordance with one aspect, there is provided an electrochemical system comprising a first electrode disposed in a first electrode compartment, a second electrode disposed in a second electrode compartment, a center compartment disposed between and separated from the first electrode compartment and the second electrode compartment by cation exchange membranes, an electrical power source electrically coupled to the first electrode and to the second electrode, and a control system configured to perform repeating cycles of causing the electrical power source to apply a positive voltage to the first electrode and a negative voltage to the second electrode for a first amount of time, reverse polarities of the voltages applied to the electrodes after the first amount of time, and maintain the reversed polarities for a second amount of time, the second amount of time being different from the first amount of time.

[0006]In some embodiments, the first amount of time is greater than the second amount of time.

[0007]In some embodiments, the first electrode is formed of a metal core with a coating of one of ruthenium oxide, iridium oxide, or a mixed metal oxide.

[0008]In some embodiments, the first electrode is formed of a corrosion-resistant nickel-based alloy.

[0009]In some embodiments, the system further comprises a source of seawater fluidically couplable to the center compartment.

[0010]In some embodiments, the second amount of time is sufficient to generate an amount of dissolved hydrogen ions at the second electrode to dissolve scale from the second electrode during operation of the electrochemical system with the switched polarities.

[0011]In some embodiments, the second amount of time is sufficient to cause a pH of electrolyte in the second compartment to be at about 4.

[0012]In some embodiments, the first amount of time is sufficient to cause a pH of seawater in the center compartment to be at about 4.

[0013]In some embodiments, the system is configured as an electrolytic-cation exchange module.

[0014]In some embodiments, the system further comprises a source of electrolyte fluidly connectable to the first electrode compartment and to the second electrode compartment.

[0015]In accordance with another aspect, there is provided a method of operating an electrochemical system including a first electrode disposed in a first electrode compartment, a second electrode disposed in a second electrode compartment, a center compartment disposed between and separated from the first compartment and the second compartment by cation exchange membranes. The method comprises performing repeated cycles of applying a first current through the electrodes for a first period of time, reversing the applied current after the first period of time, and applying the reversed current through the electrodes for a second period of time.

[0016]In some embodiments, the first amount of time is greater than the second amount of time.

[0017]In some embodiments, the method further comprises flowing electrolyte with a conductivity of less than about 250 μS/cm through each of the first electrode compartment and the second electrode compartment.

[0018]In some embodiments, the method further comprises flowing seawater through the center compartment.

[0019]In some embodiments, the second amount of time is sufficient to generate an amount of dissolved hydrogen ions at the second electrode to dissolve scale from the second electrode during operation of the module with the switched polarities.

[0020]In some embodiments, the second amount of time is sufficient to change a pH of electrolyte in the second compartment to about 4.

[0021]In some embodiments, the first amount of time is sufficient to change a pH of seawater in the center compartment to about 4.

[0022]In accordance with another aspect, there is provided a method of retrofitting an electrochemical system including a first electrode disposed in a first electrode compartment, a second electrode disposed in a second electrode compartment, a center compartment disposed between and separated from the first electrode compartment and the second electrode compartment by cation exchange membranes, an electrical power source electrically coupled to the first electrode and to the second electrode, and a control system. The method comprises reprogramming the control system to perform repeating cycles of applying a first current through the electrodes for a first period of time, reversing the applied current after the first period of time, and applying the reversed current through the electrodes for a second period of time, the second period of time having a different duration than the first period of time.

[0023]In some embodiments, replacing the first electrode includes replacing the first electrode with an electrode formed of a metal core with a coating of one of ruthenium oxide, iridium oxide, or a mixed metal oxide.

[0024]In accordance with another aspect, there is provided a non-transitory computer readable medium having instructions encoded thereon which when executed by a computerized control system of an electrochemical system including a first electrode disposed in a first electrode compartment, a second electrode disposed in a second electrode compartment, a source of electrolyte fluidly connected to the first electrode compartment and to the second electrode compartment, a center compartment disposed between and separated from the first electrode compartment and the second electrode compartment by cation exchange membranes, causes the computerized control system to perform repeating cycles of applying a first current through the electrodes for a first period of time, reversing the applied current after the first period of time, and applying the reversed current through the electrodes for a second period of time, the second period of time having a different duration than the first period of time.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:

[0026]FIG. 1A is a schematic of an embodiment of an electrolytic-cation exchange module (E-CEM) device and process operating with voltage applied across electrodes in a first polarity;

[0027]FIG. 1B is a schematic of the E-CEM device of FIG. 1A operating with voltage applied across electrodes in a second polarity;

[0028]FIG. 2 is a graph of pH values over time in seawater and catholyte in the E-CEM device of FIGS. 1A and 1B operated in accordance with methods disclosed herein;

[0029]FIG. 3 illustrates a control system that may be utilized for embodiments of electrochemical systems disclosed herein;

[0030]FIG. 4 illustrates a memory system for the control system of FIG. 3;

[0031]FIG. 5 is a graph of pH values over time in seawater and catholyte in an E-CEM device in accordance with an example embodiment of the present disclosure; and

[0032]FIG. 6 is a graph of voltage over time for the example embodiment of FIG. 5.

DETAILED DESCRIPTION

[0033]Aspects and embodiments disclosed herein are not limited to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. Aspects and embodiments disclosed herein are capable of being practiced or of being carried out in various ways. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” “having,” “containing,” “involving,” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

[0034]Aspects and embodiments disclosed herein include electrochemical systems, and specifically, electrolytic-cation exchange modules (E-CEM) and systems operated utilizing polarity reversal to increase production of useful products as compared to conventionally operated E-CEM systems.

[0035]An E-CEM is an electrochemical acidification device configured to convert dissolved HCO₃ ions in a seawater feed to CO₂ gas while simultaneously producing H₂ gas through electrolytic dissociation of water. An example of an E-CEM is described in U.S. Pat. No. 9,303,323 B2, which is incorporated herein by reference in its entirety.

[0036]In accordance with one aspect of the present disclosure, there is provided an electrochemical system, for example, an E-CEM, that comprises a first electrode disposed in a first electrode compartment, a second electrode disposed in a second electrode compartment, and a center compartment disposed between and separated from the first electrode compartment and the second electrode compartment by cation exchange membranes. An electrical power source is electrically coupled to the first electrode and to the second electrode. The electrical power source may be a direct current power source configured to provide a constant output current or a constant output voltage. The electrochemical system further comprises a control system configured to perform repeating cycles of causing the electrical power source to apply a positive voltage to the first electrode and a negative voltage to the second electrode for a first amount of time, reverse polarities of the voltages applied to the electrodes after the first amount of time, and maintain the reversed polarities for a second amount of time, the second amount of time being different from the first amount of time. It is to be understood that any switches, relays, or other equipment that enables the reversal of the polarities of the voltages applied to the electrodes shall be considered part of the power supply.

[0037]The first amount of time may be greater than the second amount of time. In some examples, the first amount of time may be up to ten times the second amount of time.

[0038]The first and second electrodes may be formed from different materials. In some examples, the second electrode includes a coating that is more resistant to reduction when exposed to liquid at basic pH levels than a coating of the first electrode. The first electrode may be formed of a metal core, for example, a titanium core, with a coating of one of ruthenium oxide, iridium oxide, or a mixed metal oxide (e.g., a mixture of a valve metal oxide and a platinum group metal oxide), or may be formed of a corrosion-resistant nickel-based alloy. The second electrode may be formed of platinum-coated titanium.

[0039]The coating's resistance to reduction may be determined by any appropriate method, including, e.g., the lifetime of the electrode. In some embodiments, an indicator of electrode coating degradation may be increased voltage of the cell. For example, in some embodiments, the cell voltage for an electrode having a coating of ruthenium oxide, iridium oxide, or a mixed metal oxide may be markedly higher (e.g., at least 150 mV higher) than the cell voltage for an electrode formed of platinum-coated titanium. Accordingly, if the second electrode is formed of platinum-coated titanium, it may be more resistant to reduction when exposed to liquid at basic pH levels than the coating of the first electrode.

[0040]The center compartment may be supplied with seawater while the first and second electrode compartments may be supplied with electrolyte such as reverse osmosis (RO) product water with a conductivity of less than 250 μS/cm or sodium sulfate solution with a conductivity of between 300 μS/cm and 3000 μS/cm.

[0041]Operation of the electrochemical system with the positive voltage applied to the first electrode and the negative voltage applied to the second electrode during the first amount of time may result in scale, for example, calcium carbonate, magnesium silicate, or other calcium or magnesium compounds to deposit on the second electrode. This scale may increase the electrical resistance across the electrodes of the electrochemical system and reduce operating performance. Operation of the electrochemical system with the negative voltage applied to the first electrode and the positive voltage applied to the second electrode during the second amount of time may result in generation of hydrogen ions and acidification of liquid in the second electrode compartment that may dissolve the scale from the second electrode and restore operating performance of the electrochemical device. The second amount of time and voltage applied across the electrodes during the second amount of time may cause the pH of the liquid in the second electrode compartment to drop to a pH of, for example, about 4. In contrast, the first amount of time and voltage applied across the electrodes during the first amount of time may cause the pH of the seawater in the center compartment to drop to a pH of, for example, about 4.

[0042]In some examples, the current applied across the electrodes of the electrochemical system may be controlled during the first and second time periods, and operation of the electrochemical system may include applying a first current through the electrodes for a first period of time, reversing the applied current after the first period of time, and applying the reversed current through the electrodes for a second period of time.

[0043]Aspects and embodiments disclosed herein also include methods of retrofitting existing electrochemical systems. An existing electrochemical system may include a first electrode disposed in a first electrode compartment, a second electrode disposed in a second electrode compartment, a center compartment disposed between and separated from the first electrode compartment and the second electrode compartment by cation exchange membranes, an electrical power source electrically coupled to the first electrode and to the second electrode, and a control system. Examples of the method of retrofitting the existing electrochemical system may include reprogramming the control system to perform repeating cycles of applying a first current through the electrodes for a first period of time, reversing the applied current after the first period of time, and applying the reversed current through the electrodes for a second period of time. The second period of time may have a different duration than the first period of time. Examples of the method of retrofitting the existing electrochemical system may further include replacing the first electrode with an electrode having a coating that is less resistant to reduction at basic pH levels than a coating of the second electrode.

[0044]Also contemplated herein are examples of non-transitory computer readable media having instructions encoded thereon which when executed by a computerized control system of an electrochemical system cause the electrochemical system to perform any of the methods disclosed herein.

[0045]FIG. 1A is a schematic of an embodiment of an E-CEM device and process operated with voltage applied across the electrodes in a first polarity (Polarity A). The E-CEM device 100 includes three compartments: an anode compartment 110, a center compartment 120, and a cathode compartment 130, separated by cation exchange membranes (CEM) 140. An anode 170 is disposed in the anode compartment 110 opposite a first CEM 140 with the anode 170 and first CEM 140 defining widthwise boundaries of the anode compartment 110. A cathode 180 is disposed in the cathode compartment 130 opposite a second CEM 140 with the cathode 180 and second CEM 140 defining widthwise boundaries of the cathode compartment 130. A source of electrolyte solution (feed or anolyte 190A) is fluidly connectable to the anode compartment 110 and a source of electrolyte solution (feed or catholyte 190C), which may be the same or different from the electrolyte solution for the anode compartment 110 is fluidly connectable to the cathode compartment 130. The feed 190A, 190C to the anode and cathode compartments 110, 130 is a conductive solution, for example, reverse osmosis (RO) product water with a conductivity of less than 250 μS/cm or sodium sulfate solution with a conductivity of between 300 μS/cm and 3000 μS/cm. In some embodiments, the feed 195 to the center compartment 120 is seawater, with a pH of about 8.

[0046]When DC current is applied, hydrogen ions (H⁺) along with oxygen molecules are generated at the anode 170. The H⁺ ions travel from the anolyte 190A through the first CEM 140 to the seawater in center compartment 120, replacing cations such as sodium (Na⁺), calcium (Ca⁺²) and magnesium (Mg⁺²) that are transported from the center compartment 120 to the catholyte 190C through the second CEM 140 bounding the cathode compartment 130. At the cathode 180, water is decomposed to produce hydroxyl ions (OH⁻) and hydrogen gas (H₂). The seawater feed 195 in the center compartment is acidified and bicarbonate ions in the seawater are converted to carbonous acid (H₂CO₂).

[0047]The reactions in the compartments are:

2H₂O→4H⁺+O₂(g)+4e⁻  Anode:

H⁺+HCO₃⁻→H₂CO₃+H₂O+CO₂(g)  Center:

2H₂O+→e⁻→2OH⁻+2H₂(g)  Cathode:

[0048]The production of hydroxyl ions in the catholyte 190C results in an increase in pH. Hardness ions such as calcium and magnesium may precipitate as CaSO₄ and Mg(OH)₂.

[0049]From experimental data, as the module 100 is powered, the voltage drop across the module 100 increases with time. This voltage drop across the module 100 is a sign of hardness ions precipitating and scaling in the cathode compartment 130, particularly on the surface of the cathode 180. Scaling results in increased electrical resistance and cathodic pressure drop. The energy consumption per unit of seawater treated increases.

[0050]Thus, to overcome scaling, cyclic polarity reversal is performed. For example, in one embodiment, the polarity of the electrodes 170, 180 is reversed every 30 minutes, as shown in FIG. 1A and FIG. 1B (Polarity A→Polarity B). After every reversal, the former cathode 180 becomes an anode 170 and the pH in the anode compartment 110 (the former cathode compartment 130) decreases, causing scales on the former cathode 180 to dissolve.

[0051]Under symmetric polarity reversal, the polarity may be switched every 30 minutes, for example. However, it is to be understood that polarity may be switched at other intervals, either shorter or longer than 30 minutes.

[0052]In one embodiment, asymmetric polarity reversal is implemented. In asymmetric polarity reversal, the operating time in one polarity is longer than in the other.

[0053]FIG. 2 shows the results of asymmetrical reversal in one experiment. The pH in the effluents from the seawater compartment and the compartment adjacent to electrode B (the cathode 180 in operation under Polarity A and the anode 170 in operation under Polarity B) are plotted versus time. The E-CEM is first operated in Polarity A. Initially the pH in the seawater is reduced to 3.5-4.5, which is low enough to convert all of the HCO₃ ions to CO₂. The pH in the compartment next to electrode B, which is operating as the cathode 180, increases to 11.5 and remains steady at that value. At time 16:28, noise/spikes appear in the pH values of the seawater effluent, which may be an indication of scale formation in the cathode compartment 130, with resulting decrease in the acidification performance.

[0054]As discussed above, in some embodiments, polarity may be reversed from Polarity A to Polarity B when it is determined that scale is forming in the cathode compartment 130. Such a determination may be made based on, e.g., noise/spikes in the pH values of the seawater effluent, as described above with respect to FIG. 2. In some cases, a signal-to-noise calculation can be used by dividing the difference of peak pH signal by the root mean square (RMS) value of the noise on the background signal. If the ratio exceeds a predetermined value, such as about 10%, the polarity may be changed from A to B. In other embodiments, polarity may be reversed from Polarity A to Polarity B based on an increase in voltage or resistance in the system which, similar to a spike in pH values, may indicate scale formation in the cathode compartment 130. In still other embodiments, pressure drop across the cathode compartment 130 may be measured, and polarity may be reversed from Polarity A to Polarity B based on a predetermined increase in pressure drop, which also may signify scaling in the compartment. Additionally and/or alternatively, based on the electrodes used and/or other known system configurations, a time duration after which scale formation may occur in the compartment may be determined, and the reversal from Polarity A to Polarity B may be set based on this determination. Similarly, the timing of reversal from Polarity B back to Polarity A may also be predetermined in some embodiments.

[0055]When the polarity is reversed to Polarity B, electrode B becomes an anode 170 and the pH from electrode B compartment (formerly cathode compartment 130, now anode compartment 110) decreased from pH 11.5 to about pH 2 as the H⁺ ions generated dissolve the scaling formed during Polarity A. The seawater pH increases to pH 8.4 and around time 16:34:00 starts to decrease. The downward slope of pH can be assumed to be an indication of scale dissolution as the time taken for seawater to reach pH 4 during Polarity B is about the same as the time in Polarity A. Accordingly, the about 4-minute reversal was sufficient to remove scaling and the process is seen to be as efficient in the second Polarity A run as in the first.

[0056]In some embodiments, the switch from Polarity A to Polarity B (and vice versa) does not occur immediately. Instead, there may be a “dead period” during which neither the anode 170 nor the cathode 180 are polarized, thereby enabling the system to stabilize prior to polarity reversal. The duration of the dead period may vary. In some embodiments, the duration of the dead period may be between, e.g., 1 second and 10 minutes. In other embodiments, the duration of the dead period may be between, e.g., 1 minute and 5 minutes.

[0057]In some embodiments, the seawater passing through center compartment 120 during a Polarity B run is directed to, e.g., a separate tank prior to CO₂ extraction for mixing with acidified seawater from previous Polarity A runs. As the pH of the seawater during the Polarity B run does not reach below 6, the carbonates present in the seawater are not completely converted to CO₂ for extraction. Thus, by mixing the seawater from the Polarity B run(s) with one or more previous Polarity A runs having a pH of, e.g., less than 4, the combined seawater in the tank may maintain a pH below about 6, which may be sufficient to convert the carbonates in the combined seawater to CO₂. Alternatively, in another embodiment, the water generated during the Polarity B run(s) may be recycled and mixed with a seawater inlet of the E-CEM, enabling the recycled and mixed water to pass through the E-CEM again for acidification.

[0058]In another embodiment of the present invention, in addition to asymmetrical reversal, the two electrodes may be formed of different materials and/or have different coatings. For example, in one embodiment, electrode A includes a valve metal (e.g., titanium) with a platinum (Pt), iridium (Ir), or ruthenium (Ru) mixed metal oxide (MMO) coating or a Pt/Ir coating, while electrode B has a platinum (Pt) coating.

[0059]The ability to perform under polarity reversal long term is limited to very few electrode materials such as, e.g., platinum (Pt) coated titanium (Ti) substrates (Pt|Ti) or Hastelloy® corrosion-resistant nickel-based alloys. Other electrode materials used in seawater electrodialysis such as, e.g., substrates with mixed metal oxide (MMO) coatings and Magneli-phase titanium anodes are typically not recommended for applications with symmetrical reversal. Some of these electrodes may perform well as a cathode, but the trade-off is their overall durability or lifetime due to gradual reduction of the metal oxide coating.

[0060]Pt|Ti is more expensive than electrodes formed of materials such as ruthenium-oxide on Ti metal (RuO₂|Ti) or iridium-oxide on Ti metal (IrO₂|Ti), so one way to reduce overall electrode cost may be to use only Pt|Ti as cathode 180 in the longer polarity of an asymmetrical reversal process (e.g., Polarity A in the above example) and use a different electrode such as, e.g., a valve metal with Pt, Ir, or Ru MMO coating, for the anode. In this configuration, the different electrode functions as cathode 180 only during operation under Polarity B, which is much shorter than operation under Polarity A.

[0061]Aspects and embodiments disclosed herein may also provide the ability to run the E-CEM continuously long-term, without the need to disassemble for cleaning, while also achieving continuous acidification performance.

[0062]Various operating parameters of the electrochemical systems disclosed herein may be controlled or adjusted by an associated control system or controller based on various parameters measured by various sensors located in different portions of the systems. The controller may be programmed or configured to regulate operating parameters such as flow rate of feed liquids through the anode compartments 110, center compartments 120, and cathode compartments 130 of systems disclosed herein as well as power (voltage, current, and/or polarity) applied across electrodes of systems disclosed herein.

[0063]Various aspects of the controller may be implemented as specialized software executing in a general-purpose computer system 200 such as that shown in FIG. 3. The computer system 200 may include a processor 202 connected to one or more memory devices 204, such as a disk drive, solid state memory, or other device for storing data. Memory 204 is typically used for storing programs and data during operation of the computer system 200. Components of computer system 200 may be coupled by an interconnection mechanism 206, which may include one or more busses (e.g., between components that are integrated within a same machine) and/or a network (e.g., between components that reside on separate discrete machines). The interconnection mechanism 206 enables communications (e.g., data, instructions) to be exchanged between system components of system 200. Computer system 200 also includes one or more input devices 208, for example, a keyboard, mouse, trackball, microphone, touch screen, and one or more output devices 310, for example, a printing device, display screen, and/or speaker.

[0064]The output devices 210 may also comprise valves, pumps, or switches which may be utilized to regulate or maintain flows of the various fluid streams of systems as disclosed herein. One or more sensors 214 may also provide input to the computer system 200. These sensors may include, for example, pressure sensors, chemical concentration sensors, temperature sensors, pH sensors, flow rate sensors, voltage sensors, current sensors, or sensors for any other parameters of interest to the systems disclosed herein. These sensors may be located in any portion of the system where they would be useful. In addition, computer system 200 may contain one or more interfaces (not shown) that connect computer system 200 to a communication network in addition or as an alternative to the interconnection mechanism 206.

[0065]The storage system 212, shown in greater detail in FIG. 4, typically includes a computer readable and writeable nonvolatile recording medium 302 in which signals are stored that define a program to be executed by the processor 202 or information to be processed by the program. The medium may include, for example, a disk or flash memory. Typically, in operation, the processor causes data to be read from the nonvolatile recording medium 302 into another memory 304 that allows for faster access to the information by the processor than does the medium 302. This memory 304 is typically a volatile, random access memory such as a dynamic random access memory (DRAM) or static memory (SRAM). It may be located in storage system 212, as shown, or in memory system 204. The processor 202 generally manipulates the data within the integrated circuit memory 304 and then copies the data to the medium 302 after processing is completed. A variety of mechanisms are known for managing data movement between the medium 302 and the integrated circuit memory element 304, and aspects and embodiments disclosed herein are not limited thereto. Aspects and embodiments disclosed herein are not limited to a particular memory system 304 or storage system 212.

[0066]The computer system may include specially-programmed, special-purpose hardware, for example, an application-specific integrated circuit (ASIC). Aspects and embodiments disclosed herein may be implemented in software, hardware or firmware, or any combination thereof. Further, such methods, acts, systems, system elements and components thereof may be implemented as part of the computer system described above or as an independent component.

[0067]Although computer system 200 is shown by way of example as one type of computer system upon which various aspects and embodiments disclosed herein may be practiced, it should be appreciated that aspects and embodiments disclosed herein are not limited to being implemented on the computer system as shown in FIG. 3. Various aspects and embodiments disclosed herein may be practiced on one or more computers having a different architecture or components than shown in FIG. 3.

[0068]Computer system 200 may be a general-purpose computer system that is programmable using a high-level computer programming language. Computer system 300 may be also implemented using specially programmed, special purpose hardware. In computer system 200, processor 202 is typically a commercially available processor such as the well-known Core™ class processors available from the Intel Corporation. Many other processors are available, including programmable logic controllers. Such a processor usually executes an operating system which may be, for example, the Windows 10, or Windows 11 operating system available from the Microsoft Corporation, the MAC OS System X available from Apple Computer, the Solaris Operating System available from Sun Microsystems, or UNIX available from various sources. Many other operating systems may be used.

[0069]The processor and operating system together define a computer platform for which application programs in high-level programming languages are written. It should be understood that the invention is not limited to a particular computer system platform, processor, operating system, or network. Also, it should be apparent to those skilled in the art that aspects and embodiments disclosed herein are not limited to a specific programming language or computer system. Further, it should be appreciated that other appropriate programming languages and other appropriate computer systems could also be used.

[0070]One or more portions of the computer system may be distributed across one or more computer systems (not shown) coupled to a communications network. These computer systems also may be general-purpose computer systems. For example, various aspects of the invention may be distributed among one or more computer systems configured to provide a service (e.g., servers) to one or more client computers, or to perform an overall task as part of a distributed system. For example, various aspects and embodiments disclosed herein may be performed on a client-server system that includes components distributed among one or more server systems that perform various functions according to various aspects and embodiments disclosed herein. These components may be executable, intermediate (e.g., IL) or interpreted (e.g., Java) code which communicate over a communication network (e.g., the Internet) using a communication protocol (e.g., TCP/IP). In some embodiments one or more components of the computer system 300 may communicate with one or more other components over a wireless network, including, for example, a cellular telephone network.

[0071]It should be appreciated that the aspects and embodiments disclosed herein are not limited to executing on any particular system or group of systems. Also, it should be appreciated that the aspects and embodiments disclosed herein are not limited to any particular distributed architecture, network, or communication protocol. Various aspects and embodiments disclosed herein may be programmed using an object-oriented programming language, such as SmallTalk, Java, C++, Ada, or C# (C-Sharp). Other object-oriented programming languages may also be used. Alternatively, functional, scripting, and/or logical programming languages may be used, for example, ladder logic. Various aspects and embodiments disclosed herein may be implemented in a non-programmed environment (e.g., documents created in HTML, XML or other format that, when viewed in a window of a browser program, render aspects of a graphical-user interface (GUI) or perform other functions). Various aspects and embodiments disclosed herein may be implemented as programmed or non-programmed elements, or any combination thereof.

Example

[0078]The electrodes used as anode and cathode for the present example were platinum-coated titanium electrodes.

[0079]As shown in FIG. 5, the electrolytic-cation exchange module (E-CEM) was run continuously for four (4) asymmetric polarity cycles. Each polarity reversal was maintained for approximately five (5) minutes. The line pH_e represents the pH of the electrolyte in compartment two of the module, while the line pH_s.w represents the pH of seawater. As observed in the first cycle shown in FIG. 5, the pH_s.w acidified to a pH of about 5 within the first about five (5) minutes, reaching near steady-state thereafter. As is notable in the graph, the pH_s.w started to slightly increase after about 15 mins which may be considered as approaching the end of the first cycle, which may be an indication of scaling in the cathode compartment.

[0080]When the polarity was reversed, the pH_s.w stops acidifying and briefly returned to a pH of about 8 before starting to acidify again. This low pH during Polarity B is believed to dissolve any scale that may have formed on electrode B as the cathode compartment. The downward slope of pH_s.w during this polarity reversal period is believed to confirm that any scaling has been at least partially, if not fully, dissolved.

[0081]As shown in FIG. 5, the polarity reversal cycles were repeated and substantially similar results were observed with each of the subsequent cycles. Thus, the present example exemplifies one aspect of the invention that may involve initiating the polarity reversal when the pH of the seawater from the center compartment is at about 5, or even as the pH approaches 5, e.g., at a pH of about 4.5.

[0082]Referring to FIG. 6, this can also be verified by the reduction in voltage during the polarity reversal, as reduced scaling results in lower resistance. After switching the polarity back to Polarity A (i.e., the second cycle), the pH_s.w begins acidifying in an analogous manner as the first cycle, reaching a pH of 5 within 5 minutes.

[0083]As such, this example provides aspects of the invention that can involve reverting from the reversed polarity, i.e., terminating polarity B and applying polarity A, when the pH of the seawater is less than about 7 or upon detecting acidic conditions in the seawater.

[0084]The phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. As used herein, the term “plurality” refers to two or more items or components. The terms “comprising,” “including,” “carrying,” “having,” “containing,” and “involving,” whether in the written description or the claims and the like, are open-ended terms, i.e., to mean “including but not limited to.” Thus, the use of such terms is meant to encompass the items listed thereafter, and equivalents thereof, as well as additional items. Only the transitional phrases “consisting of” and “consisting essentially of,” are closed or semi-closed transitional phrases, respectively, with respect to the claims. Use of ordinal terms such as “first,” “second,” “third,” and the like in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.