Ion exchange filter usable in electrochemical systems

Abstract

Provided herein are ion exchange filters comprising a mixed bed of strong acid cation resin in the H form, strong base anion resin in the OH form, and strong base anion resin in the HCO3 form in specific ratios. The eluate provided by the mixed resin bed has greater thermal stability and lower conductivity compared to eluate processed by mixed bed comprising different resin components and ratios. Further provided herein is a method of purifying an aqueous fluid, such as a stream in a fuel cell, a battery, a battery charger, or an electrolytic cell, by contact with the mixed resin bed of the ion exchange filter described herein.

Description

Cross-reference to related applications

[0001] This application is based on 35 USC 365(c) claims priority to European Patent Application No. 24305130, filed on 23 January 2024, which is incorporated herein by reference in its entirety. Technical Field

[0002] This invention relates to the field of ion exchange filters, particularly ion exchange filters having a mixed resin bed, and to the use of these ion exchange filters for purifying aqueous fluids (e.g., streams in fuel cells, batteries, or electrolyzers, such as coolant streams). Furthermore, methods for purifying these aqueous fluids using these ion exchange filters are provided. Background Technology

[0003] This specification references several patents, patent applications, and publications to provide a more comprehensive description of the prior art to which this invention relates. The full disclosure of each of these patents, patent applications, and publications is incorporated herein by reference.

[0004] Electrochemical systems involve converting chemical energy into electrical energy and vice versa through electrochemical reactions. Examples of electrochemical systems include batteries, battery chargers, fuel cells, and electrolyzers. These systems are widely used in a variety of applications, such as portable electronic devices, electric vehicles, and renewable energy technologies.

[0005] A battery converts chemical energy into electrical energy through an electrochemical reaction process between two or more electrodes and an electrolyte. Inside the battery, a chemical reaction occurs to generate a flow of electrons from the negative electrode (anode) to the positive electrode (cathode). This electron flow produces an electric current that can be used to power external devices. The electrolyte acts as the medium for ion transfer between the anode and cathode. As the battery discharges, the chemical reactions that generate the current may begin to slow down, and the battery eventually runs out of power. A battery can be recharged using a charger, which applies an external current that forces the electrochemical reactions to proceed in reverse.

[0006] Coolant is required in batteries and chargers to help control temperatures during charging and discharging. Batteries and chargers can generate excessive heat during operation, especially when they discharge or charge rapidly. This heat can degrade the performance and lifespan of the battery or charger, and in extreme cases, even lead to safety issues such as thermal runaway or explosion. Coolant helps dissipate heat from the battery or charger by absorbing and transferring heat from internal components (such as battery cells or plates), where energy is dissipated as heat rather than potential. Therefore, coolant helps maintain the operating temperature of the battery or charger within a safe range. Additionally, coolant helps prevent the electrolyte from freezing or boiling in extreme temperature environments.

[0007] More specifically, electric vehicle chargers convert alternating current (AC) into direct current (DC) compatible with the electric vehicle's battery. This conversion generates heat. For example, a typical 22 kW AC charger provides enough power in 120 minutes to provide an additional 200 km of driving range. To reduce the charging time for 200 km of range to just 16 minutes, a 150 kW DC charging station would be needed. According to a report from the U.S. Department of Energy, at this power level, and to avoid overheating, an effective and improved thermal management system is required, as the battery pack temperature can rise to over 270°C during a 10-minute fast charge. See, for example, the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy's "Enabling FastCharging: A Technology Gap Assessment," in [reference needed]. https: / / www.energy.gov / sites / prod / files / 2017 / 10 / f38 / XFC%20Technology%20Gap% 20Assessment%20Report_FINAL_10202017.pdf Found there.

[0008] Traditionally, air cooling has been the preferred solution, but liquid cooling has proven to be the most efficient. The heat capacity of water—the ratio of heat absorbed to the resulting temperature change—is 3,500 times that of air. This is one reason why water is up to 10 times more efficient at dissipating heat at its source. Furthermore, liquid cooling allows for the operation of pre-filled systems, which facilitates maintenance, speeds up any necessary replacements, enables rapid initial installations, and accelerates upgrades. Therefore, liquid cooling can be found in many applications, including but not limited to thermal battery packs, vehicle inverters, and power electronics in charging stations.

[0009] The coolant used for liquid cooling in fast chargers is typically a water / glycol mixture. Compared to water alone, using a water / glycol mixture prevents the coolant from freezing and increases its boiling point.

[0010] It is evident that technical malfunctions in battery chargers can generate additional heat. For example, a charger programmed to maintain a constant charging rate will generate excessive heat if the voltage is unstable. Furthermore, impurities will be leached from the plastic surfaces used in the cooling system and from metal components such as coolers. Non-conductive coolants themselves undergo thermal degradation, releasing conductive components into the cooling circuit. Glycolic acid and formic acid are typical examples of formation in the degradation mechanism of ethylene glycol (“monoethylene glycol” or “MEG”), while lactic acid and acetic acid are formed in the degradation mechanism of propylene glycol (“PG”).

[0011] See, for example, AN INVESTIGATION OF THE DEGRADATION OF AQUEOUS ETHYLENEGLYCOL AND PROPYLENE GLYCOL SOLUTIONS USING ION CHROMATOGRAPHY, Walter J. ROSSITER, Jr., McClure GODETTE, Paul W. BROWN, and Kevin G. GALUK, Department of Building Materials, Center for Building Technology, National Bureau of Standards, Gaithersburg, MD 10899, USA; Received May 17, 1984; Revised August 30, 1984; Available online March 5, 2003; Solar Energy Materials, Vol. 11, Nos. 5-6, Jan-February 1985, pp. 455-467. At https: / / doi.org / 10.1016 / 0165-1633(85)90016-4 Available here.

[0012] A fuel cell system electrochemically oxidizes fuel (such as hydrogen) with oxygen to produce electricity and water. This system may include several subsystems, such as:

[0013] • Subsystem for managing the flow of hydrogen and oxygen: This subsystem may include a gas compression and control system to deliver the gas to the subsystem for power generation. In some cases, hydrogen is generated on-site using gas reformers, which extract hydrogen from hydrocarbons such as natural gas. Oxygen can be supplied directly from the air.

[0014] • Subsystem for generating electricity: This subsystem typically takes the form of a fuel cell stack, which comprises multiple individual fuel cells. Each unit contains an anode and a cathode separated by an electrolyte and a proton-selective membrane. When hydrogen comes into contact with the anode, it decomposes into protons (H₂O). +(Ions) and electrons. Protons pass through the electrolyte and proton-selective membrane to reach the cathode, where they react with oxygen and electrons from the anode to generate electricity, heat, and water.

[0015] • Subsystem for managing water flow: Water is produced as a product of the electrochemical oxidation of hydrogen in the fuel cell. This water can be released as vapor from the fuel cell stack or condensed and reused in the system, for example, as a coolant or humidifier for incoming air.

[0016] • Liquid coolant subsystem: This subsystem typically includes:

[0017] Devices that exchange heat via liquid coolant: Fuel cells generate heat during their electrochemical oxidation. Heat typically improves fuel cell efficiency, and this can be considered a beneficial mode of operation. However, heat can degrade components such as ion exchange resins, electrolytic membranes, and other building materials. Thermal management is crucial for ensuring fuel cell performance and lifespan. Therefore, a cooling system is essential for maintaining and extending the operation of the electrochemical system. There are no particular limitations on cooling systems suitable for use with the ion exchange filters described herein, and they typically include coolant recirculated in a conduit or pipe between a remote heat exchanger and the fuel cell. The heat exchanger may be in fluid communication with one or more of a radiator, thermal regulator, or bypass device for selectively filtering the circulating coolant. There are no particular limitations on coolants suitable for use with the ion exchange filters described herein, but they typically include low-conductivity fluids such as purified water or aqueous alkylene glycol mixtures. Various additives may be included in the coolant. Other designs and coolants are well known and may also be suitable, including, for example, those described in EP 1791206.

[0018] Devices that process the liquid coolant: During coolant circulation, ions from metals and organic matter from plastic surfaces may diffuse into the coolant, or glycols may thermally degrade into organic acids, such as glycolic acid or formic acid, or both may occur. Each of these mechanisms leads to a gradual increase in the electrical conductivity of the coolant liquid. This conductivity poses safety and reliability risks, and therefore the coolant must be treated to reduce or remove impurities. This treatment is typically carried out using ion exchange resins.

[0019] An electrolyzer performs the electrochemical reduction of water to produce hydrogen and oxygen. An electrolysis system may include several subsystems, such as:

[0020] • Subsystems for managing water flow: Pumps and water quality control systems may be necessary to provide a reliable water supply to the electrolyzer.

[0021] • Subsystem for power consumption: This subsystem is typically in the form of an electrolytic cell containing an anode and a cathode separated by an electrolyte and an ion-selective membrane, such as a proton exchange membrane (PEM). In the case of a proton-selective membrane, when water comes into contact with the anode, it decomposes into hydrogen ions (H+). + Hydrogen ions travel through the electrolyte and proton-selective membrane to the cathode, where they are converted into hydrogen gas. Oxygen is collected at the anode.

[0022] • Subsystem for managing the flow of hydrogen and oxygen: This subsystem may include gas separation, purification and compression, as well as a control system for delivering the gas to its destination.

[0023] • Liquid coolant subsystem: This subsystem typically includes:

[0024] Devices that exchange heat via a liquid coolant: Heat is generated in the electrolyzer due to the resistance of the electrolyte solution to the passage of electricity. Heat typically increases the efficiency of the electrolysis process, and this can be considered a beneficial mode of operation. However, heat can degrade components such as ion exchange resins, electrolytic membranes, and other building materials. Therefore, a cooling system is essential for maintaining and extending the operation of the electrochemical system.

[0025] Some heat is absorbed by the water circulating through the electrolyzer. Typically, not all the water fed into the electrolyzer is converted into hydrogen and oxygen. A portion of the unconverted water can be treated with ion exchange resin to remove contaminants. The converted water can be replenished by the makeup water stream.

[0026] Liquid or air cooling may be additionally employed. There are no particular limitations on the cooling system suitable for use with the ion exchange filter described herein, and it typically includes a coolant recirculated in piping or within pipes between a remote heat exchanger and the electrolyzer. The heat exchanger may be in fluid communication with one or more of a plate heat exchanger, a thermal regulator, or a bypass device for selectively filtering the circulating coolant. There are no particular limitations on the coolant system or loop (which differs from the loop containing the electrolytic feed and product streams), but it typically includes low-conductivity fluids such as purified water. Various additives may be included in the coolant. Other designs and coolants are well known and are available, including several similar designs and coolants to those described in EP 1791206 concerning fuel cells. Water is typically used to transfer heat from the electrolyzer to one or more coolers.

[0027] This typically includes devices for treating the recirculated feedwater or coolant stream through the electrolyzer, which may be contaminated by ions from metal surfaces, organic matter from plastic surfaces, other chemicals, or microorganisms. Such contamination can reduce heat transfer efficiency or lead to blockages, fouling, corrosion, or safety hazards. This treatment is usually carried out using ion exchange resins.

[0028] However, in all these electrochemical systems, coolant containing impurities can cause short circuits via conductivity. A short circuit may only result in inefficiency, or it may lead to complete system failure. A short circuit can also cause a dangerous electrical fire. Alternatively, impurities may contaminate the anode, cathode, or membrane, leading to inefficient operation and shortening the system's lifespan. Therefore, it is evident that coolant purification is an important aspect of many electrochemical systems.

[0029] One common method for removing contaminants from coolant streams is ion exchange treatment. Several publications describe the use of ion exchange resins to remove debris and contaminants from coolant streams. See, for example, US 8808931; US ​​7261816; US6673482; US 6663993 and EP 1791206. In particular, US 8808931 describes the use of strong base anion exchange resins in the form of HCO3 to treat fuel cell coolants. The use of HCO3-form anion exchange resins improves the thermal stability of the coolant compared to coolants treated with typically used OH-form anion exchange resins. However, the use of HCO3-form SBA in fuel cell coolants also increases the electrical conductivity of the coolant. As discussed above, increased conductivity is undesirable because it can lead to short circuits, other unsafe conditions, and fuel cell shutdown.

[0030] US 11165074 describes the use of a combination of strong acid cations, strong base anions, and weak base anion exchange resins to treat coolant streams. It is presumed that weak base anion exchange resins can exhibit higher thermal stability than strong base anion exchange resins. However, limitations exist associated with weak base anion exchange resins. For example, in the coolant circuits of fuel cells and batteries used in electric vehicles (EVs), the primary contaminants (weakly associated organic acids, primarily glycolic acid) are associated with the thermal degradation of glycols. Weak base anion exchange resins containing secondary or tertiary amines will not be able to effectively remove weakly acidic ions, such as glycolic acid with a pKa of 3.83, from water using ion exchange at near-neutral or alkaline pH conditions. Specifically, glycolic acid and its derivative impurities do not exist significantly as free acids because the pH exceeds their pKa value. Therefore, under near-neutral pH conditions, the conjugate bases of glycolic acid and its derivative acids cannot protonate the secondary or tertiary amines, thus allowing glycolic acid and other acidic impurities to adsorb onto the weak base resin. Therefore, when the pH of the coolant is close to neutral or slightly alkaline, glycolic acid and related impurities will not be removed from the coolant stream by the weak base anion exchange resin.

[0031] Therefore, there is still a need for ion exchange filters containing resins that have improved thermal stability, produce eluents with low conductivity, and generate aqueous streams with superior purity for use in a variety of electrochemical systems. Summary of the Invention

[0032] Therefore, this document provides electrochemical systems, such as fuel cells, batteries, battery chargers, and electrolyzers, which include ion exchange filters having a mixed bed of a strong acid cation exchange resin in the H-form and a strong base anion exchange resin in the OH-form, a strong base anion exchange resin in the HCO3-form, or a combination of both types of strong base anion exchange resins in a specific ratio. Furthermore, a method for treating coolant water streams, such as coolant water streams from electrochemical systems, using the ion exchange filters described herein is provided. Attached Figure Description

[0033] Figure 1 This is a graph showing the conductivity relative to the total amount of hydroxyglycolic acid (HGA) removed from a 0.1 M aqueous solution. The graph illustrates the conductivity trends in the product streams from different mixed beds used to treat contaminants.

[0034] Figure 2 This is a graph showing the retention rate of toluenetriazole relative to time for different mixed beds. Detailed Implementation

[0035] Mixed-bed resin tanks are typically used to process coolant streams. Mixed beds known in the art typically comprise cationic resins in the H-form and anionic resins in the OH-form.

[0036] There are no particular limitations on the size of the resin beads, and they can be selected based on operating conditions. Preferred anion exchange resins have bead diameters of approximately 300 to 1000 micrometers. Uniform particle size (UPS) resins can be used, or resins with a mixture of various bead sizes can be used, such as those with a Gaussian particle size distribution.

[0037] The high temperatures (approximately 60°C to 105°C) in the cooling loop of an electrochemical system will cause thermal degradation of the anionic functional groups in the OH-form resin, thus shortening the resin life. To minimize the impact of the thermal degradation process, an HCO3-form anion exchange resin can be used. However, when a mixed bed with strong acid cations in the H-form and strong base anions in the HCO3-form is used in the coolant loop, the HCO3 balance causes the coolant conductivity baseline to shift from < 0.1 uS / cm to the range of 1.0 to 5 uS / cm or 0.3–5 uS / cm, which is undesirable. The conductivity is measured using a conductivity probe WTWLR325 / 01 with a 0.1 cm... -1 The battery constant was measured using an inoLab™ Cond 7310P conductivity meter.

[0038] It has been unexpectedly discovered that ion exchange filters comprising mixed beds of ion exchange resins solve the problems of thermal stability and conductivity while maintaining the high water resistivity required for use in electrochemical systems. Typically, water with a resistivity greater than or equal to 12, 15, 17, or 19 MOhm-cm is considered to meet this standard. Resistivity is the reciprocal of conductivity; therefore, it is determined by the same experimental methods as conductivity. The mixed beds described herein comprise, in specific proportions, strong acid cation exchange resins in the H form together with strong base anion exchange resins in the OH form, strong base anion exchange resins in the HCO3 form, or a combination of both types of strong base anion exchange resins.

[0039] Suitable strong acid and strong base ion exchange resins used in this invention, as well as methods for synthesizing such resins, are described in detail in U.S. Patent No. 8,808,931 to Golz et al.; and 6,784,213 to Rohrbach et al.; and the references cited in these patents. Additionally, suitable acid and base resins are commercially available, for example, from DuPont de Nemours, Inc. (hereinafter “DuPont”), Wilmington, Delaware. Furthermore, those skilled in the art will recognize the definitions of various terms used herein to describe ion exchange resins and their uses, such as “makeup water,” “Type I resin,” “Type II resin,” “gel resin,” etc. These terms are also defined and used in product data sheets and other literature publicly available from ion exchange resin manufacturers. See, for example… https: / / www.dupont.com / water / technologies / ion-exchange-ix.html .

[0040] Preferably, the strong acid ion exchange resins used herein are suitable for use in one or more of the following applications: industrial public water supply, condensate polishing, and 18 MOhm-cm water production in the semiconductor industry. More preferably, the strong acid cation exchange resin is characterized by one or more of the following properties: it is a gel-type resin; it is a crosslinked copolymer of styrene and divinylbenzene; it is a sulfonated polymer; it is in protonated (H) form; it can have any particle size distribution, such as uniform or Gaussian particle size distribution, or it can be sieved to achieve different types of particle size distributions; and it has a total ion exchange capacity of about 1.0 to about 2.65, more preferably about 1.5 to about 2.65, and even more preferably about 1.8 to about 2.3 equivalents (eq / L) per liter of resin in H form. The term “total ion exchange capacity” is synonymous with and interchangeable with the terms “total capacity of cation exchange resins,” “total capacity of anion exchange resins,” and “total capacity and salt-dissociation capacity of anion exchange resins,” depending on the cation or anion nature of the resin under discussion. Total ion exchange capacity can be measured according to one or more of the methods listed in ASTM standard number D2187-17 (Standard Test Methods and Practices for Evaluating the Physical and Chemical Properties of Particulate Ion Exchange Resins), or by another suitable method.

[0041] Preferably, the strong base ion exchange resin used herein is also suitable for one or more applications in industrial public water supply, condensate polishing, or 18 MOhm-cm water production in the semiconductor industry. More preferably, the strong base anion exchange resin is characterized by one or more of the following properties: it is a type I resin; it is a gel-type resin; it is a crosslinked copolymer of styrene and divinylbenzene; it is in the form of OH or HCO3; it has a uniform particle size or Gaussian particle size distribution; and it has a total ion exchange capacity in the OH form of about 0.9 to about 1.8, more preferably about 0.9 to about 1.6, and even more preferably about 1.0 to about 1.4 eq / L.

[0042] The mixed bed described herein comprises a strong acid cation exchange resin (SAC) in the H form and a strong base anion exchange resin (SBA) in the OH form or in the form of OH and HCO3. Specifically, when the electrochemical system is a fuel cell, a battery, or a battery charger, the mixed bed comprises:

[0043] a) Strong acid cationic resin in the H form;

[0044] b) Strong base anion exchange resins in the OH form; and

[0045] c) Strong base anion exchange resin in the form of HCO3.

[0046] However, when the electrochemical system is an electrolyzer, the mixed bed comprises:

[0047] a) Strong acid cationic resin in the H form;

[0048] b) Strong base anion exchange resins in the OH form; and optionally...

[0049] c) Strong base anion exchange resin in the form of HCO3.

[0050] The mixed bed is preferably anion-dominated. In other words, in a given volume of the mixed bed, the sum of the volumes of strong base anion exchange resins in the forms of OH and HCO3 is preferably greater than or equal to the volume of strong acid cation exchange resins in the form of H. Preferably, based on the total volume of the mixed bed, the volume of the cation exchange resin is greater than 7.5 vol% and less than 25.0 vol%, greater than 10.3 vol% and less than 25.0 vol%, greater than 15 vol% and less than 20 vol%. Complementarily, based on the total volume of the mixed bed, the volume of one or more anion exchange resins is more preferably greater than 75.0 vol% and less than 92.5 vol%, greater than 75.0 vol% and less than 89.7 vol%, or greater than 80 vol% and less than 85 vol%. The sum of the volume percentages of the resins in the mixed bed is 100 vol%. The term "complementary" as used herein, or in derived forms such as "complementarily," refers to a percentage that sums to 100%, such as 10.3% and 89.7%.

[0051] Preferably, in a given volume of anion-dominant mixed bed, the strong base anion exchange resin has a total ion exchange capacity greater than one equivalent for every equiv / L of the total ion exchange capacity of the strong acid cation exchange resin in the mixture. For example, in a 100 ml mixed bed containing 75 ml of anion exchange resin with an exchange capacity of 1.0 equiv / L and 25 ml of cation exchange resin with an exchange capacity of 2.0 equiv / L, the volume of the mixture comprises 75 x 1 / 25 x 2 = 1.5 equivalents of anion capacity / equivalent of cation capacity.

[0052] More preferably, in a given volume of anion-dominated mixed bed, the following two conditions are met: based on the total volume of the mixed bed, the sum of the volume percentages of one or more strong base anion exchange resins is greater than the volume percentage of strong acid cation exchange resins; and the total ion exchange capacity of one or more strong base anion exchange resins is greater than the total ion exchange capacity of strong acid cation exchange resins. Even more preferably, in a given volume of anion-dominated mixed bed, the molar number of anion exchange sites exceeds the molar number of cation exchange sites.

[0053] Suitable designs for ion exchange cartridges used to purify coolant streams from fuel cells are described, for example, in U.S. Patent No. 8,808,931. Similar design principles can be used to adapt this system for purifying coolant streams from other electrochemical systems, such as batteries, battery chargers, and electrolysis devices.

[0054] Suitable coolants for use in the electrochemical systems described herein are well known in the art. However, in brief, coolants typically comprise water, one or more glycols, or a combination of water and one or more glycols. Suitable glycols include alkylene glycols. Alkylenes can be straight-chain or branched. Preferred alkylenes comprise 2 to 10 carbon atoms, more preferably 2 to 4 carbon atoms, and even more preferably 2 to 3 carbon atoms.

[0055] Additionally, suitable coolants may include numerous additives or stabilizers that reduce or prevent the thermal or oxidative degradation of glycols. Additive packages are typically considered trade secrets by coolant manufacturers. However, coolants may contain one or more of, for example, heat stabilizers and corrosion inhibitors. Additive packages are typically categorized into three groups: IAT (Inorganic Additive Technology), OAT (Organic Additive Technology), and HOAT (Hybrid OAT). OAT and HOAT types have the lowest electrical conductivity and are primarily used in fuel cells and electric vehicles. Pure glycols are colorless, but can be colored with dyes such as rhodamine for liquid identification and leak detection purposes. Therefore, additive packages may further contain dyes. Other suitable additives include heat stabilizers, often described as silica-based, and defoaming additives, often described as silicones or polyols. Suitable corrosion inhibitors to prevent oxidative degradation include azoles, carboxylates, and triazoles.

[0056] Suitable additives and stabilizers, as well as suitable amounts of these additives and stabilizers, are known in the art. See, for example, the Kirk-Othmer Encyclopedia of Chemical Technology and PCT International Application Publication No. WO 2017080542. However, in brief, based on the total weight of the coolant, the total amount of additives and stabilizers in the coolant is preferably less than 5 wt%, less than 3 wt%, less than 2 wt%, or less than 1 wt%.

[0057] Coolants containing glycols will last longer and perform better when additives such as corrosion inhibitors and heat stabilizers remain in the coolant stream. However, when glycols are exposed to high temperatures, they will degrade. Degradation products include low-molecular-weight organic acids, which can cause corrosion on metal surfaces present in the coolant circuit (e.g., aluminum-copper coolers). The dissolved or suspended metals, as corrosion products, catalyze the degradation of one or more glycols in the coolant, thereby increasing the thermal degradation rate of one or more glycols and enhancing the formation of conductive organic acids that promote corrosion.

[0058] This negative feedback loop can be prevented or slowed down by maintaining optimal levels of stabilizer in the coolant. For this reason, stabilized coolants are commercially available, such as Glysantin™ FC G 20-00 / 50, a suppressant, ready-to-use, low-conductivity glycol coolant from BASF SE in Ludwigshafen, Germany (hereinafter referred to as "BASF"). For evidence of the stabilizer's effectiveness, see, for example, BASF's Technische Information TI / EVO e, published in January 2016.

[0059] However, current prior art ion exchange resins in the H / OH form effectively remove these additives from the diol. This phenomenon has been described, for example, by Rossiter et al., cited above. In contrast, the mixed-bed ion exchange resins described herein unexpectedly and advantageously do not remove or remove only small amounts of additives such as corrosion inhibitors and stabilizers from the coolant stream, thereby extending the service life of the coolant and coolant circuit.

[0060] The following describes three preferred embodiments of the mixed-bed ion exchange filter provided herein.

[0061] Example 1 The mixed bed comprises the entire ion exchange resin bed. In this embodiment:

[0062] • The mixed bed is preferably anion-dominated. This can be described as follows: the sum of the volumes of strong base anion exchange resins in OH and HCO3 forms is equal to or greater than the volume of strong acid cation exchange resins in H forms.

[0063] • For anion exchange resins, the proportion of OH form should be in the range of 33 to 75 vol% of the total volume of the anion exchange resin in the mixed bed. This can be further described as follows: the volume of strong base anion exchange resin in OH form is greater than 33% and less than 75% of the sum of the volumes of strong base anion exchange resin in OH form and strong base anion exchange resin in HCO3 form.

[0064] Example 2The ion exchange resin bed comprises a mixed bed section and an unmixed bed section, wherein the unmixed bed section is above the mixed bed section. As used herein, the term "above" refers to an upstream location, and the term "below" refers to a downstream location. It is not necessary for the ion exchange filter to be placed vertically for these terms to apply. For example, in this Example 2, the coolant water flowing through the ion exchange filter first passes through the unmixed bed section, which is above the mixed bed section. Additionally, the mixed bed section is below the unmixed bed section; that is, the water that has passed through the mixed bed section has already passed through the unmixed bed section. In this Example 2:

[0065] • The mixed bed section is preferably anion-dominated. This can be described as follows: the sum of the volumes of strong base anion exchange resins in OH and HCO3 forms is equal to or greater than the volume of strong acid cation exchange resins in H forms.

[0066] • The unmixed bed section is preferably composed of one or more strong base anion exchange resins in the OH form. This resin may be the same as or different from the strong base anion exchange resin in the mixed bed in the OH form.

[0067] • For anion exchange resins in mixed-bed sections, the proportion of OH-form resins should be in the range of 33 to 75 vol%. This can be further described as follows: the volume of strong base anion exchange resin in OH-form is greater than 33% and less than 75% of the sum of the volumes of strong base anion exchange resins in OH-form and strong base anion exchange resins in HCO3-form.

[0068] • The volume of strong base anion exchange resin in the OH form in the mixed bed section is greater than 40% of the sum of the volumes of strong base anion exchange resin in the OH form in the unmixed bed section and the mixed bed section.

[0069] Example 3 The ion exchange resin bed includes a mixed bed section and an unmixed bed section, wherein the unmixed bed section is located below the mixed bed section. In this embodiment:

[0070] • The mixed bed section is preferably anion-dominated. This can be described as follows: for a given volume of mixed bed resin, the sum of the volumes of strong base anion exchange resins in the form of OH and HCO3 is greater than or equal to the volume of strong acid cation exchange resins in the form of H.

[0071] • The unmixed bed section is preferably composed of one or more strong base anion exchange resins in the OH form. This resin may be the same as or different from the strong base anion exchange resin in the mixed bed in the OH form.

[0072] • For anion exchange resins in mixed-bed sections, the proportion of OH-form resins should be in the range of 33 to 75 vol%. This can be further described as follows: the volume of strong base anion exchange resin in OH-form is greater than 33% and less than 75% of the sum of the volumes of strong base anion exchange resins in OH-form and strong base anion exchange resins in HCO3-form.

[0073] • The volume of strong base anion exchange resin in the OH form in the mixed bed section is greater than 60% of the sum of the volumes of strong base anion exchange resin in the OH form in the unmixed bed section and the mixed bed section.

[0074] The following examples are provided to further describe the invention in detail. These examples, which illustrate specific embodiments and preferred modes of carrying out the invention as currently considered, are intended to be illustrative and not limiting. Example

[0075] In the following experimental groups, the strong acid cation exchange resins are sulfonated divinylbenzene crosslinked polystyrene gel polymers in the H form, with a total ion exchange capacity equal to or greater than 2.05 equivalences / L. The strong base anion exchange resins are type I divinylbenzene crosslinked polystyrene gel polymers in the OH form, with a total ion exchange capacity equal to or greater than 1.10 equivalences / L. These ion exchange resins are commercially available, for example from DuPont, and represent a wide range of commercially available anion and cation resins characterized by different capacities but similar chemical compositions. The ultrapure water used in these experimental groups has a resistivity of 17 MOhm-cm or greater.

[0076] Experimental group 1: The following completely mixed beds are used to remove contaminants: strong acid cations (SAC) (H2 form) and strong base anions (SBA) (OH and HCO3 forms).

[0077] • The experiment was conducted in a glass column with an inner diameter of 2 cm and a total resin volume of 50 ml. A 380 ppm solution of monoglycolic acid (MGA; a known contaminant in the fuel cell coolant circulation loop) in ultrapure water was prepared.

[0078] The proportion of resin in the mixed bed varies as described in Table 1.

[0079] Before use, rinse the mixed bed with 5 bed volumes (BV; here, 5.50 ml = 250 ml) of ultrapure water. Inject the MGA solution into the top of the mixed bed at a flow rate of 1000 mL / hr (corresponding to 20 BV per hour). Continue injection until the mixed bed resin is exhausted. Exhaustion is reached after approximately 150 bed volumes have passed through the resin, defined by an eluent with a conductivity of at least 5 µS / cm. Discard the first 3 bed volumes of eluent and do not include them in this measurement.

[0080] The results of these experiments are shown in Table 1. The average weighted conductivity of the eluent was calculated as the sum of the conductivity measured for each BV divided by the total number of BVs passing through the mixed bed. The final value of the average weighted conductivity was reported when exhaustion was reached (i.e., when the conductivity of the eluent was 5 µS / cm). For example, when 0–10 BV = 10 µS at 1 µS and 10–20 BV = 20 µS at 2 µS, the weighted average over 20 BVs was equal to (10 + 20 µS) / 20 BV = 1.5 µS. The conductivity of the eluent at the 10th BV was considered the initial conductivity.

[0081] As shown, when the amount of OH-form resin in the mixed bed is between 33 and 75 vol%, the average weighted conductivity remains low. Increasing the vol% OH-form in the mixed bed to above 75 vol% did not further reduce the average weighted conductivity; however, these compositions are expected to reduce the thermal stability of the mixed bed.

[0082] Table 1: Resin composition (fully mixed bed) for processing MGA streams

[0083]

[0084] Experimental group 2: The thermal stability of resins in the following mixed beds: SAC (H form), SBA (OH and HCO3 forms) is assessed by evaluating the resin capacity loss due to thermal aging in the following manner: calculating the difference between the total ion exchange capacity of the thermally aged ion exchange resin and the total ion exchange capacity of the same ion exchange resin before thermal aging, and reporting this difference as a percentage of the original total resin exchange capacity.

[0085] To determine the resin capacity loss due to thermal aging, 200 mL of a mixed resin bed with varying amounts of OH and HCO3 resins was placed in a sealed glass bottle and placed in an oven at 90°C for 500 hours. The thermally aged resin was then regenerated and tested to evaluate its ion exchange capacity. To regenerate the OH and HCO3 resins to the OH form, 10 mL of the OH-form resin was stirred with 20 mL of HCl (1N) for 10 minutes to allow the existing OH sites to react with the HCl. After a 10-minute contact time, NaOH (1N) solution was metered into the remaining supernatant HCl solution (backtied) to pH 7.0. The strong acid cation exchange resin was regenerated with HCl (1N) to fully recover to the H form, and then rinsed with deionized water. The H sites were then released by adding 5 g of NaCl, followed by backtiing with NaOH (1N) solution to pH 7.0.

[0086] The capacity of the mixed resin prior to thermal aging was calculated as the average of the initial capacity of each individual resin in the mixture, weighted by its volume percentage. For example, the initial capacity of the mixed resin in Test 1 was (55 • (initial capacity OH form) + 45 • (initial capacity HCO3 form)) / 100, where the sum of the volume percentages of the OH and HCO3 resins was 100 vol%. The initial thermal capacity was also determined using the method described above. Specifically, the resins were not heated; instead, they were regenerated, and their ion exchange capacity (in equivalents per liter of OH functional groups) was then measured. The results are shown in Table 2. When the volume percentage of OH form exceeded 75 vol%, the capacity loss of the resin due to thermal aging was greater at 90°C.

[0087] Table 2: Thermal stability test results

[0088]

[0089] Experimental group 3: The following contaminants are removed using a mixed bed topped with unmixed OH resin: SAC (H form) and SBA (OH and HCO3 forms).

[0090] • The experiment was conducted in a glass column with an inner diameter of 2 cm and a total resin volume of 50 ml. A 380 ppm solution of hydroxyglycolic acid (HGA, a known contaminant in the fuel cell coolant circulation loop) was prepared in Glysantin™ FC G20 coolant, which is available from BASF and is believed to be a mixture of 50% ethylene glycol and 50% DI water.

[0091] The proportion of resin in the mixed bed varies as described in Table 3.

[0092] Before use, a portion of the mixed bed was rinsed with 5 BV of ultrapure water. HGA solution was injected into the top of the portion of the mixed bed at a flow rate of 1000 mL / hr (corresponding to 20 bed volumes / hour). Injection continued until the mixed bed resin was depleted, as determined by the method described above in Experimental Group 1.

[0093] The results are shown in Table 3. Performance was measured as the amount of bed volume eluted before the 5 µS / cm endpoint, indicating depletion. The results indicate that up to 60 vol% of the OH form can remain in the unmixed bed (or at least 40 vol% of the OH form must be present in the mixed bed) before performance degradation is observed, as the volume of eluent processed through the column decreases before depletion.

[0094] Table 3: Resin composition used to process HGA streams (part of the mixed bed below the unmixed OH resin).

[0095]

[0096] Experimental group 4: The following contaminants are removed using a mixed bed with unmixed OH resin at the bottom: SAC (H form) and SBA (OH and HCO3 forms).

[0097] • The experiment was conducted in a glass column with an inner diameter of 2 cm and a total resin volume of 50 ml. The HGA solution described in Experimental Group 3 was prepared.

[0098] The proportion of resin in the mixed bed varies as described in Table 4.

[0099] Before use, a portion of the mixed bed was rinsed with 5 BV of ultrapure water. HGA solution was injected into the top of the portion of the mixed bed at a flow rate of 1000 mL / hr (corresponding to 20 bed volumes / hour). Injection continued until the mixed bed resin was depleted, as determined by the method described in Experimental Group 1 above.

[0100] The results are shown in Table 4. Performance was measured as the amount of bed volume processed before reaching 5 µS / cm, indicating depletion. The results indicate that up to 40 vol% of the OH form can be retained in an unmixed bed of this configuration (or at least 60 vol% of the OH form must be present in a mixed bed) before performance degradation is observed, as the volume of eluent processed through the column decreases before depletion.

[0101] In summary, these data indicate that there exists an optimal range of relative volumes for HCO3 and OH anion exchange resins that combine high thermal stability and good performance (as measured by resin capacity loss due to thermal aging and average weighted conductivity). There also exists an optimal range of volume percentages for the mixing of OH resins to maintain good performance (as measured by removing a greater amount of impurities before depletion), which surprisingly depends on whether the unmixed bed of OH resins is above or below the mixed bed.

[0102] Table 4: Resin composition used to process HGA streams (partial mixed bed above unmixed OH resin)

[0103]

[0104] Experimental group 5: The following mixed bed is used to remove contaminants: strong acid cations (SAC) in H-form and weak base anions (WBA) in free base form.

[0105] • This experimental group was conducted to provide a comparative example. The experiment was carried out in a glass column with an inner diameter of 2 cm and a total resin volume of 400 ml. The HGA solutions described in experimental groups 3 and 4 were prepared.

[0106] The resin ratio in the mixed bed is 50% SAC and 50% WBA by volume.

[0107] Before use, rinse the mixed bed with 5 BV of ultrapure water. Inject the HGA solution into the top of the mixed bed at a flow rate of 600 bed volumes / hour. Continue injection until the mixed bed resin is depleted, as described in Experimental Group 1 above.

[0108] The result is Figure 1 As shown in the figure, the graph depicts the conductivity as a function of the amount of HGA removed (i.e., absorbed or “loaded”) per liter of resin from the solution (in meq or mmol). Figure 1 Data confirms that the mixed bed containing WBA showed an immediate increase in conductivity compared to a mixed bed containing 50 V% SAC resin mixed with 50 V% SBA resin (in OH or HCO3 form). In contrast, the conductivity of the stream leaving the mixed bed containing OH-form SBA began to increase when the total load capacity exceeded approximately 700 meq / L, and the conductivity of the stream leaving the mixed bed containing HCO3-form SBA began to increase when the total load capacity exceeded approximately 800 meq / L. These results demonstrate the limited benefit of using WBA resin to treat coolant streams contaminated with common byproducts of glycol degradation.

[0109] Advantageously, the mixed resin bed described herein does not remove additives, such as corrosion inhibitors and stabilizers, from the coolant stream. In contrast, prior art strong acid cation / strong base anion (H / OH) mixed beds completely or substantially completely remove additives.

[0110] In particular, Figure 2 The results described herein indicate that the mixed bed of ion exchange resins (SAC resin in H-form, SBA resin in HCO3-form) did not completely remove the stabilizer or reduce the stabilizer concentration below the operating level after operation for 7 h or longer under the following conditions:

[0111] • Resin volume = 50 mL mixed bed

[0112] • Test hydraulic method = In a loop circulation of 1 L toluenetriazole aqueous solution (concentration 1.5 g / L), samples are taken hourly for HPLC analysis at a rate of 20 BV / h (feed with stirring).

[0113] • Coolant samples were analyzed by HPLC using a WATERS™ e2695 separation module equipped with an XSelect HSS T3 5 µm column and operated at 25°C (available from Waters Corp., Milton, Massachusetts). The injection size was 10 μL, and UV detection was at 210 nm. The mobile phase was disodium hydrogen phosphate (Na₂HPO₄, 3.4 g / L at pH 2.7, in a solution of 20 wt% or 20 vol% acetonitrile, with the remainder being water or DI water).

[0114] In contrast, under the same conditions, the existing mixed bed (SAC resin in H form, SBA resin in OH form) removed virtually all of the toluenetriazole from the circulating solution after one hour.

[0115] While certain preferred embodiments of the invention have been described and specifically illustrated above, they are not intended to limit the invention to such embodiments. Various modifications can be made without departing from the scope and spirit of the invention, as set forth in the following claims.

Claims

1. An apparatus for treating a liquid flow in an electrochemical system, wherein the electrochemical system is a fuel cell, a battery, or a battery charger, the apparatus comprising a mixed bed of ion exchange resin, and the ion exchange resin comprising: a) Strong acid cationic resin in the H form; b) Strong base anion exchange resins in the OH form; and c) Strong base anion exchange resin in the form of HCO3; in, For a given volume of mixed-bed resin, the sum of the volumes of the strong base anion exchange resins in the form of OH and HCO3 is greater than the volume of the strong acid cation exchange resin in the form of H. The total ion exchange capacity of the strong base anion exchange resin in the form of OH and HCO3 is 0.9 to 1.8 equiv / L, and the total ion exchange capacity of the strong acid cation exchange resin in the form of H is 1.0 to 2.65 equiv / L; and The device may optionally further include an unmixed bed of ion exchange resin, the unmixed bed comprising a strong base anion exchange resin in the OH form.

2. The device as claimed in claim 1, wherein, The mixed bed, the unmixed bed, or both the unmixed bed and the mixed bed are characterized by one or more conditions selected from the group consisting of: a) In the mixed bed, the volume of the strong base anion exchange resin in the OH form is greater than 33% of the sum of the volumes of the strong base anion exchange resin in the OH form and the strong base anion exchange resin in the HCO3 form; b) The volume of the strong base anion exchange resin in the OH form is less than 75% of the sum of the volumes of the strong base anion exchange resin in the OH form and the strong base anion exchange resin in the HCO3 form; c) The combined volume of the strong base anion exchange resins in the mixed bed and the unmixed bed in the form of OH and HCO3 is equal to or greater than the volume of the strong acid cation exchange resin in the form of H; d) The volume of the strong base anion exchange resin in the OH form in the mixed bed and the unmixed bed is greater than 33% of the sum of the volumes of the strong base anion exchange resin in the OH form and the strong base anion exchange resin in the HCO3 form in the mixed bed and the unmixed bed; e) The sum of the volumes of the strong base anion exchange resins in the OH form in the mixed bed and the unmixed bed is less than 75% of the combined volume of the strong base anion exchange resins in the OH form and the strong base anion exchange resins in the HCO3 form in the mixed bed and the unmixed bed; f) The volume of the strong base anion exchange resin in the OH form in the mixed bed section is greater than 40% of the sum of the volumes of the strong base anion exchange resin in the OH form in the unmixed bed section and the mixed bed section; and g) The volume of the strong base anion exchange resin in the OH form in the mixed bed section is greater than 60% of the sum of the volumes of the strong base anion exchange resin in the OH form in the unmixed bed section and the mixed bed section.

3. The device as claimed in claim 1 or claim 2, wherein, The liquid stream comprises a mixture of glycol and water; wherein the glycol includes ethylene glycol, propylene glycol, or a combination of ethylene glycol and propylene glycol; and optionally the liquid stream further comprises one or more additives selected from the group consisting of heat stabilizers, defoamers, and corrosion inhibitors.

4. The device as claimed in any of the preceding claims, the device comprising a coolant circuit, wherein the liquid flow is a coolant in the coolant circuit.

5. The device as claimed in any of the preceding claims, wherein, The unmixed bed section is above the mixed bed section.

6. The device as claimed in any one of claims 1 to 4, wherein, The unmixed bed section is below the mixed bed section.

7. An apparatus for treating a liquid stream in an electrolytic cell, the apparatus comprising a mixed bed of ion exchange resin, the mixed bed comprising: Strong acid cation exchange resins in the H form; and Strong base anion exchange resins in the OH form; and optionally... Strong base anion exchange resin in the form of HCO3; and in, For a given volume of mixed-bed resin, the volume of the strong base anion in the OH form or the sum of the volumes of the strong base anion resin in the OH and HCO3 forms is greater than the volume of the strong acid cation resin in the H form. The total ion exchange capacity of the strong base anion exchange resin in the OH form and the optional strong base anion exchange resin in the HCO3 form is 0.9 to 1.8 equiv / L, and the total ion exchange capacity of the strong acid cation exchange resin in the H form is 1.0 to 2.65 equiv / L; and The device may optionally further include an unmixed bed of ion exchange resin, the unmixed bed comprising a strong base anion exchange resin in the OH form.

8. The device as claimed in claim 7, wherein, The liquid stream comprises water and at least one dissolved impurity selected from the group consisting of: anion-rich mixtures of materials classified as total organic carbon; one or more organic acids; and one or more ions selected from the group consisting of boron, silicon dioxide, manganese, nickel, zinc, sodium, potassium, fluorine, chloride, bromine, nitrate, phosphate, and sulfate ions.

9. The apparatus of claim 7 or claim 8, wherein the apparatus includes a coolant circuit, wherein the liquid flow is a coolant in the coolant circuit.

10. The device as claimed in claim 7, claim 8, or claim 9, wherein, The volume of the strong base anion exchange resin in the OH form is equal to or greater than three times the volume of the strong acid cation exchange resin in the H form, or preferably equal to or greater than six times the volume of the strong base anion exchange resin in the H form.

11. A method for treating a liquid flow in an electrochemical system, wherein the electrochemical system is a fuel cell or a storage battery, the method comprising the steps of: Provide the device as claimed in any one of claims 1 to 6; and The liquid flow is brought into contact with the mixed bed of the ion exchange resin.

12. A method for treating a liquid stream in an electrolytic cell, the method comprising the following steps: Provide the device as claimed in any one of claims 7, 8, 9 or 10; and The liquid flow is brought into contact with the mixed bed of the ion exchange resin.

Images