Systems and methods for electrochemical marine alkalinity enhancement

Abstract

This disclosure relates to using bipolar membrane electrodialysis (BPMED) to enhance the alkalinity of brine, such as seawater, without removing divalent cations that would otherwise cause scaling. In one embodiment, a BPMED is used in which the brine volumetric flow rate through the alkalization chamber is higher than the flow rate through the brine chamber at a given current density, which increases the pH of the brine output while keeping it below the precipitation pH. In one embodiment, the spacers located in the alkalization chamber are thicker than those elsewhere in the BPMED to resist membrane deformation due to the increased hydrostatic pressure in the alkalization chamber at higher flow rates. The brine output with increased alkalinity can be returned to the ocean to mitigate acidification and is capable of capturing atmospheric carbon dioxide.

Description

[0001] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 292,627, filed December 22, 2021, the entire contents of which are incorporated herein by reference.

[0002] field

[0003] This disclosure relates to a method and system for enhancing the alkalinity of fluids, such as brine, like seawater, the results of which can be used for negative emission carbon removal, including returning alkalinity-enhanced brine to the ocean to enhance the ocean's ability to remove carbon dioxide from the air and store it in the ocean in dissolved ionic forms (bicarbonate and carbonate).

[0004] background

[0005] Enhancing the alkalinity of fluids such as brine includes electrochemical ocean alkalinity enhancement (OAE), which involves using electrochemistry to generate alkalinity, which is then added to the ocean in this case, leading to a reduction in ocean acidification and the safe continuation of atmospheric CO2 as bicarbonate ions in the ocean. Utilizing the ocean to capture atmospheric CO2 is often referred to as ocean carbon dioxide removal or ocean CDR.

[0006] Typically, these electrochemical systems utilize electricity and a brine feed stream (seawater, reverse osmosis concentrate, etc.) as input, and the output is the acid and base composition of the introduced salt, for example, converting NaCl in seawater into HCl (acid) and NaOH (base). Bipolar membrane electrodialysis (BPMED) is an electrochemical process that uses an ion-selective membrane between two end electrodes to generate HCl and NaOH from an introduced NaCl-containing brine. If the resulting NaOH and seawater are returned to the ocean, this enhances the ocean's alkalinity, mitigating ocean acidification and improving the ocean's ability to remove CO2 from the atmosphere and safely store it in the ocean in dissolved ionic forms (bicarbonate and carbonate); the resulting HCl can be retained on land for other purposes, such as commercial sale or to improve the reaction rate and storage capacity of CO2 mineralization reactors. Typically, the brine feed stream introduced into BPMED, such as seawater or reverse osmosis concentrate, contains divalent calcium cations (Ca). ++ ) and / or magnesium cations (Mg ++ As pH increases, these divalent cations can form solid calcium and / or magnesium precipitates, such as CaCO3 and / or Mg(OH)2. These precipitates can lead to scaling on the BPMED membrane, resulting in higher energy consumption, shorter membrane life, and frequent BPMED operation interruptions. To date, scaling problems have been addressed by removing these divalent cations before BPMED, typically through pretreatment such as water softening. However, these pretreatments are expensive and increase operational complexity.

[0007] Therefore, there is a need for methods and systems to enhance the alkalinity of fluids such as brine without removing these divalent cations from the feed stream of BPMED.

[0008] Overview

[0009] In one aspect, this disclosure relates to a method for enhancing alkalinity, comprising (i) providing a bipolar membrane electrodialysis apparatus (BPMED) including electrodes and at least one unit comprising a brine compartment, an acid compartment, and an alkaline compartment; (ii) allowing an aqueous brine solution to flow through the alkaline compartment at a first volumetric flow rate (fba) and through the brine compartment at a second volumetric flow rate (fbr), the aqueous brine solution containing at least one divalent cation that precipitates from the aqueous brine solution to form a solid precipitate when the aqueous brine solution is at or above the precipitation pH; (iii) applying a voltage to the BPMED apparatus between the electrodes at a given current density to form an alkaline-enhanced brine product in the alkaline compartment having a pH higher than the pH of the brine but lower than the precipitation pH; (iv) maintaining the first volumetric flow rate through the alkaline compartment at the current density at a flow rate sufficiently greater than the second volumetric flow rate through the brine compartment to maintain the pH of the alkaline-enhanced brine product formed in the alkaline compartment below the precipitation pH; and (v) discharging the alkaline-enhanced brine product from the alkaline compartment.

[0010] In another aspect, this disclosure relates to a system for enhancing alkalinity, comprising a bipolar membrane electrodialysis apparatus (BPMED) including a cathode and an anode; and at least one unit comprising a brine compartment including a first cation exchange membrane, a brine compartment spacer, and an anion exchange membrane; an alkali compartment including a bipolar membrane, an alkali compartment spacer, and a second cation exchange membrane; and an acid compartment located between the brine compartment and the alkali compartment and including opposite sides of the anion exchange membrane, the acid compartment spacer, and the bipolar membrane; wherein the alkali compartment spacer may be more rigid than the brine compartment spacer and the acid compartment spacer when the alkali compartment spacer is thicker than the brine compartment spacer and the acid compartment spacer.

[0011] In another aspect, the methods and systems disclosed herein provide electrochemical marine alkalinity enhancement, which produces very high-quality “negative emission” carbon removal at a reduced cost by avoiding pretreatment for removing precipitated divalent cations.

[0012] In one practice, the flow-through design of this method and system enables the direct supply of seawater or other aqueous saline solutions (such as reverse osmosis concentrate) into the brine and alkali compartments without pretreatment or removal of divalent cations such as Ca. ++ and Mg ++ The ability. Brief description of the attached diagram

[0014] Figure 1 This is a schematic diagram of one implementation of the method disclosed herein, as well as the BPMED system and method.

[0015] Figure 2 yes Figure 1 A schematic cross-section of the implementation scheme of the BPMED system.

[0016] Figure 3A This is a schematic perspective view of one embodiment of the alkali compartment partition disclosed herein. Figure 3B yes Figure 3A A schematic perspective view of the other side of the alkali compartment partition implementation scheme. Figure 3C This is a schematic side view of another embodiment of the alkali compartment partition of this disclosure.

[0017] Detailed Explanation

[0018] The following detailed description of certain embodiments of this disclosure is made with reference to the accompanying drawings, and does not limit the scope of this disclosure. To ensure a clear understanding of the concept of the invention, explanations of related functions or structures known in the art have been omitted to avoid obscuring the invention with unnecessary detail.

[0019] As used herein, the term “about” indicates that the listed value may be slightly changed, as long as the change does not result in a change that does not conform to the methods or systems described herein. For example, for some elements, the term “about” may refer to a change of ±0.1%, and for others, it may refer to a change of ±1% to ±10%, or any point in between. As used herein, the terms “basic” or “substantial” apply equally when used in a negative sense, and refer to a complete or near-complete action, characteristic, property, state, structure, item, or result. For example, a “basic” flat surface is completely flat or nearly flat such that the effect is the same as its complete flatness. As used herein, any reference to a range of values ​​explicitly includes every value (including fractions and integers) covered by the range and includes the endpoints of the range. For illustrative purposes only, the range “0.0001 to 5000” includes integers such as 5000, 4999, 4998…3, 2, 1; and fractions such as 0.00011, 0.00012…0.1, 0.2, 0.3…1.1, 1.2, 1.3…100.5, 100.6…4900.5, 4990.6, 4990.7.

[0020] The implementation of the system and method described herein avoids the removal of divalent cations before the feed stream is fed into the bipolar membrane electrodialysis unit, and provides a system and method specifically configured to use brine containing divalent cations as input for bipolar membrane electrodialysis.

[0021] Figure 1 Schematic diagrams depict methods and systems for enhancing the alkalinity of aqueous brine solutions, as used herein, the term including but not limited to saltwater such as seawater, brackish water, brine derived from desalination processes, or mined salts dissolved to produce brine solutions, such as sodium and / or potassium bicarbonates and / or carbonates. Figure 1 (and Figure 2 The image shows a bipolar membrane electrodialysis apparatus (labeled BPMED) and its cathode and anode, which, in this embodiment shown from left to right, includes at least one acid compartment, a brine compartment, and an alkali compartment. Figure 2 ).exist Figure 1 In the illustrated practice, the inputs to the brine chamber (“brine input”) and the inputs to the alkali chamber (“alkali chamber”) are identical, meaning they both originate from the same brine source, such as some form of aqueous brine feed stream, which may include seawater from the ocean (with a salinity of approximately 35) or reverse osmosis concentrate (with a salinity of approximately 70), which may originate from a desalination facility, or the brine source may originate from some other brine feed stream or process. In one practice, the brine source is the ocean, and the alkalinity-enhanced brine product stream is returned to the ocean to mitigate ocean acidification. In one embodiment, the alkalinity-enhanced brine product stream is combined with a partially desalinated brine output stream for return to the ocean.

[0022] exist Figure 1 In this study, the pH of both the brine and alkali inputs is shown as 8.1, but the pH of either or both inputs can range from pH 6 to 8.5. To date, both the brine and alkali input streams must be pretreated, such as seawater or reverse osmosis concentrate, to remove, for example, calcium (Ca). ++ ) and / or magnesium (Mg ++ The presence of divalent cations, due to the high pH levels (e.g., up to 14) typically encountered in the alkali compartment of the BPMED unit, leads to the precipitation of solid Mg(OH)₂ and CaCO₃ on the membrane within the BPMED, thus significantly reducing performance. Figure 1 In the flow-through systems and methods shown, the removal of these types of divalent cations does not occur or is unnecessary because the volumetric flow rate (f) of the alkali input through the alkali compartment is determined by the current density applied when a voltage is applied across the electrodes. BA The movement relative to OH- ions is large enough to maintain the maximum pH in the alkali compartment (as measured at the alkali compartment outlet) at 8.5 to 8.9, which is below the pH at which precipitation of Mg(OH)2 and CaCO3 solids, as well as other solids, occurs, thus eliminating the need for removal of the associated divalent cations. For typical operating values ​​of current density, this is... Figure 1 The volumetric flow rate through the alkali compartment is relative to the volumetric flow rate through the brine compartment (f)BR ) is large enough to achieve this, i.e., f BA >f BR This is to maintain the pH of the alkaline-enhanced brine product formed in the alkali compartment below the precipitation pH. This can also be achieved at a given volumetric flow rate through the alkali compartment by maintaining a sufficiently low current density to keep the alkali compartment pH below the precipitation threshold.

[0023] exist Figure 1 In the flow-through configuration shown, the acid feed is in a "feed-and-bleed" configuration. As shown, the concentration of the aqueous acid input entering the acid compartment channel is constant, denoted as X%HCl. After passing through the acid compartment of the BPMED unit, the output acid concentration increases to (X+∈)%HCl (labeled "more concentrated acid output"). In the practice shown, a portion of this higher concentration (X+∈)%HCl product acid is then discharged. The discharge rate of the high-concentration acid is matched with the feed rate of deionized water (DI water), resulting in a constant concentration of X%HCl at the acid input. Although in Figure 1 The text describes "DI water," but in cases where the product is HCl in brine (e.g., seawater) or other aqueous solutions instead of DI water, the feed can be an aqueous brine solution (e.g., seawater) or other aqueous solutions. Discharged HCl at a concentration of (X+∈)% can be recovered for other uses, including commercial sale or to improve the reaction rate and storage capacity of a CO2 mineralization reactor.

[0024] refer to Figure 2 ,This is Figure 1 A schematic cross-section of an embodiment of a BPMED system available in the diagram shows an electrodialysis unit 100 comprising at least one cell triplet (cell 1) including a brine compartment 210, an acid compartment 220, and an alkali compartment 230. However, it may comprise multiple (“N”) such cell triplets connected in series, for example, up to 100 cells or more, having brine compartments 210, 210A…up to 200N, and acid compartments 220, 220A…200N (all not shown) when connected in series, as shown in the configuration of each triplet. Unit 100 includes a cathode 110 and an anode 114, and corresponding electrode compartments 200 and 116, which have end cap membranes 118 and 120 to separate the electrode compartments from the BPMED membrane cell, and may each independently contain components that can serve as… The purchased sulfonated tetrafluoroethylene vinyl fluoropolymer copolymer. Electrodes 110 and 114 may comprise materials known in the art, such as nickel. It is to be understood that, regarding Figure 2 Which films are depicted adjacent to the corresponding electrodes? Multiple configurations are possible, and Figure 2The configuration shown is merely representative in this respect. In one practice, an electrode solution, such as an aqueous solution of sodium hydroxide (NaOH), is allowed to flow through electrode compartments 200 and 116; in this practice, the positively charged electrode 114 causes sodium ions (Na₂O₃) to be released. + Moving across the end cap membrane 120, the negatively charged electrode 110 attracts sodium ions into the electrode compartment 200. Other suitable electrode solutions include sodium sulfate, which is adjusted to acidity by adding sulfuric acid or to alkalinity by adding sodium hydroxide.

[0025] exist Figure 2 In the illustrated embodiment, the brine compartment 210 is defined by a cation exchange membrane (CEM) 130 and an anion exchange membrane (AEM) 150 (which, when multiple or other elements of the BPMED are present and connected in series, are indicated, for example, by letter suffixes, such as 130, 130A…130N; 150, 150A…150N, etc.). Available CEMs include monovalent cation-selective permeation membranes as known in the art, such as, but not limited to, those available as Neosepta CMX-S. Available AEMs include monovalent anion-selective permeation membranes as known in the art, such as, but not limited to, those available as Neosepta ACS. The brine compartment 210 also includes a brine compartment spacer 140, which may contain spacers known in the art, such as polymers, like polyolefins including polypropylene, or silicone compounds, and may be woven or nonwoven, and may have the same or similar external dimensions as the CEM 130 and AEM 150, and a thickness of about 0.15 to about 1.5 mm. Acid compartment 220 is defined by the opposite side of AEM 150 and bipolar membrane (BPM) 170. BPMs available herein include those known in the art, such as, but not limited to, those available as Neosepta BP-1E. Acid compartment 220 also includes acid compartment spacer 160, which may contain the same construction material and dimensions as alkali compartment spacer 140; in one practice, the alkali and acid compartment spacers are substantially identical to avoid or minimize hydrostatic pressure differences that would otherwise occur across the membrane due to volumetric flow rates through adjacent compartments. Typically, when a voltage is applied across cell 100 via electrodes 110, 114, water dissociation within the BPM results in hydrogen ions (H+). + ) is transported from one side of the BPM, while hydroxide ions (OH-) - Transport occurs from the opposite side. Regarding AEM / CEM, these allow negatively charged / positively charged ions to transport across the membrane.

[0026] The alkali compartment 230 is defined by the opposite side of the BPM 170 and the CEM 130A. The cation exchange membrane 130A may be different from or preferably the same as the CEM 130. In one embodiment, the alkali compartment spacer 180 is more rigid than the brine compartment spacer 140 and the acid compartment spacer 160. This is to minimize or prevent undesirable hydrostatic pressure differentials during BPMED operation. In one embodiment, the side of the alkali compartment spacer 180 closest to the bipolar membrane 170 is configured to be more rigid than the side of the alkali compartment spacer 180 opposite to the bipolar membrane 170, for example by including a backing that is more rigid than, for example, the interior of the spacer 180. Furthermore, or specifically in this respect, the thickness of the alkali compartment spacer 180 may be greater than the thickness of the brine compartment spacer 140 and greater than the thickness of the acid compartment spacer 160. For example, the thickness of the alkali compartment spacer 180 may be up to 10 times the thickness of the brine compartment spacer 140 and the acid compartment spacer 160, which may have the same thickness. The alkali compartment spacer 180 may comprise a woven polyolefin, such as polypropylene, or silicone, and may be configured as a mesh. Various embodiments of alkali compartment spacers are depicted in Figure 3.

[0027] In practice, in a non-restrictive manner and with reference to Figure 1 An aqueous saline solution is allowed to flow through an alkali chamber 230 (alkali input) at a first volumetric flow rate (fba) and through a brine chamber 210 (brine input) at a second volumetric flow rate (fbr). The aqueous saline solution contains at least one divalent cation that precipitates from the aqueous saline solution to form a solid precipitate when the aqueous saline solution is at or above the precipitation pH; representative divalent cations include calcium (Ca). ++ ), magnesium (Mg) ++ Or both; representative solid precipitates include CaCO3, Mg(OH)2, or both. The presence of such Ca and Mg divalent cations can be naturally occurring, such as in seawater and brackish water. The aqueous brine solution (brine input) flowing to brine compartment 210 can be the same as or different from the aqueous brine solution (alkali input) flowing to alkali compartment 220, for example, seawater, reverse osmosis concentrated brine, etc.; and the brine input and alkali input can each originate from the same or different brine sources, which can include, for example, natural seawater bodies (such as the ocean), or sources containing mined salt dissolved to produce the aqueous brine solution. The aqueous brine solution can flow separately from the brine source to each of brine compartment 210 and / or alkali compartment 220 in separate pipelines, or it can flow as follows: Figure 1 The flow is shown in a common pipeline that branches to supply brine compartment 210 and alkali compartment 220, respectively.

[0028] A voltage is applied between electrodes 110 and 114, providing a current density to BPMED 100, thereby forming an alkaline-enhanced brine product in alkaline compartment 230 (and, as understood herein, in alkaline compartments 230A…230N when using a series cell), the alkaline-enhanced brine product having a pH higher than the pH of the aqueous brine feed (alkaline input), but lower than the precipitation pH of the aqueous brine feed containing one or more of the divalent cations. One embodiment for achieving this involves maintaining a first volumetric flow rate (fba) through alkaline compartment 230 at this current density at a flow rate sufficiently greater than the second volumetric flow rate (fbr) through brine compartment 210, so as to maintain the pH of the alkaline-enhanced brine product formed in alkaline compartment 230 below the precipitation pH. In one practice, the first volumetric flow rate (fba) through alkaline compartment 230 is about 1 to about 10 times higher than the second volumetric flow rate (fbr) through brine compartment 210. Figure 2 As shown, the saline compartment 210, acid compartment 220, and alkaline compartment 230 are included in a battery triplet (battery 1 triplet); in one practice, BPMED 100 includes multiple battery triplets connected in series (battery 1 triplet...battery N triplet (not shown)). In one embodiment, the voltage and current density applied across the electrodes to achieve the aforementioned alkalinity enhancement is approximately 1V to approximately 4V per battery triplet, and the current density is approximately 5mA / cm². 2 Approximately 120 mA / cm 2 In one implementation, voltage is used as an early indicator to suggest the need for rapid in-situ cleaning by flushing a portion of the generated acid 510 or 540 through all compartments; the pH output during this cleaning process can be used to improve the voltage feedback signal.

[0029] Non-limiting, the typical pH of the aqueous brine feed for brine input 400 (and for series-connected batteries, brine inputs 400A…400N, not shown) and for alkali input 410 (and for series-connected batteries, alkali inputs 410A…410N) is between about 6 and about 8.5, for example, pH 8.1. The typical precipitation pH of the aqueous brine feed input containing divalent cations of calcium and / or magnesium can be up to pH 14, for example, pH 9 and higher. Non-limiting, the typical pH of the partially desalinated brine output 420 (for series-connected batteries, 420A…420N) from brine compartment 210 (for series-connected batteries, 210A…210N, not shown) is the same as that of input 410, and is between about 6 and about 8.5. Typical values ​​of the alkaline-enhanced brine product 430A (for series-connected cells, 230A…230N) output from alkaline compartment 230 (230A…230N) are between approximately 8.5 and approximately 8.9. In one practice, the first volumetric flow rate (fba) through alkaline compartment 230, relative to the current density, ensures that the pH of alkaline compartment 230 does not exceed 8.5.

[0030] In one embodiment (not shown), at least a portion of the alkaline-enhanced brine product 430A output from the alkali compartment 230 flows directly to a final destination 300, which may include a seawater body, such as the ocean, or involve other processing. Figure 2 In another embodiment shown, a portion or all of the partially desalinated brine product 420 formed in and output from brine compartment 210 is combined with all or at least a portion of the alkaline-enhanced brine product 430A output from alkali compartment 230, and the combined stream flows to a final destination 300, such as the ocean. In one embodiment (not shown), a portion or all of the partially desalinated brine product 420 formed in and output from brine compartment 210 comprises all or a portion of the feed 410 (alkali input) entering alkali compartment 230.

[0031] like Figure 2As shown, an aqueous feed stream 500 containing a first HCl concentration (X% HCl) flows into the acid compartment 220, and an acidified product 510 with a second HCl concentration (denoted as (X+∈)% HCl, where ∈ represents an increase in concentration) greater than the first concentration is formed and discharged from the acid compartment. In one embodiment, a portion of the acidified product feed stream 510 is discharged as 520. An aqueous feed stream 310, which may contain deionized water or an aqueous brine solution, is fed at a rate and amount sufficient to form a feed stream 540 with a first concentration of X% HCl into a feed stream 530 containing the undischarged concentration of (X+∈)% HCl, and then an acid input feed 500 is provided into the acid compartment 220. As understood, when the BPMED unit 100 contains multiple battery triplets, this feed-and-bleed technique can be applied to all acid compartments 220 (up to 200N, not shown). In one practice, a first portion of feed stream 540 is recovered as an HCl product with an HCl concentration of about 0.1M to about 1M; and a second portion of feed stream 540 flows into acid compartment 220 as an acid input feed. In another embodiment, discharge stream 520 containing a second concentration (X+∈)% HCl is recovered as a product or used as feed for other processes.

[0032] In such Figure 2 In another embodiment of this disclosure, the system for enhancing alkalinity includes a bipolar membrane electrodialysis device (BPMED) 100, comprising a cathode 110 and an anode 114; and at least one cell or battery triplet comprising a brine compartment 210, comprising a first cation exchange membrane 130, a brine compartment spacer 140, and an anion exchange membrane 150; an alkali compartment 230, comprising a bipolar membrane 170, an alkali compartment spacer 180, and a second cation exchange membrane 130A; and an acid compartment 220, located between the brine compartment 210 and the alkali compartment 230, and comprising the opposite side of the anion exchange membrane 150, the opposite side of the acid compartment spacer 160, and the opposite side of the bipolar membrane 170. In one practice, such as Figure 2 As shown, the acid compartment 220, the brine compartment 210 and the alkali compartment 230 each have their own inlet and outlet, and each is individually configured for flow-through operation. Figure 2 The system shown may further include one or more flow controllers (not shown) as known in the art to maintain the volumetric flow rate through the alkali compartment at a level greater than the volumetric flow rate through the brine compartment. The BPMES of this system may comprise one or more battery triplets connected in series.

[0033] The alkali compartment spacer 180 is as rigid as or more rigid than the brine compartment spacer 140 and / or the acid compartment spacer 160. In one practice, the alkali side of the alkali compartment spacer 180 near the bipolar membrane 170 is configured to be more rigid than the side of the alkali compartment spacer opposite to the bipolar membrane 170, thus making the alkali compartment spacer more rigid than the brine compartment spacer 140 and the acid compartment spacer 160. Additionally or separately, the thickness of the alkali compartment spacer 180 is greater than the thickness of the brine compartment spacer 140 and greater than the thickness of the acid compartment spacer 160. In this respect, the acid compartment spacer 160 and the brine compartment spacer 160 may have the same or different thicknesses. The typical thicknesses of the acid compartment spacer 160 and the brine compartment spacer 140 are each between about 0.5 and about 1.2 mm. In one practice, the thickness of the alkali compartment spacer 180 is up to 10 times the thickness of the acid compartment spacer and the brine compartment spacer. Non-limitingly, the alkali compartment spacer 180 may comprise a woven polypropylene or silicone mesh.

[0034] refer to Figure 3A , 3B And 3C, describes one embodiment of a spacer that can be used as a spacer in an alkali compartment. In Figure 3A and 3B In this embodiment, spacer 700 includes a first side 730 and a second side 750 opposite to the first side. As shown, spacer 700 is generally rectangular, but other geometries are also possible, and has a first end 770 and a second end 780. The spacer may also include through-holes 710 and / or 720 to allow fluid flow in the respective compartments. In one practice, the first side 730 has a first mesh pattern 740, and the second side 750 has a second mesh pattern 760, and the open area of ​​at least a portion of the openings in the first mesh pattern 740 is larger than the open area in the second mesh pattern 760, which, as shown, has a tighter and denser mesh. The openings of the first mesh pattern 740 may be uniform or non-uniform on the first side 730. In one embodiment, the larger open area and mesh design of the first mesh pattern 740 are configured to eliminate non-uniform high pH hotspots near the surface of the spacer membrane. In one embodiment, the openings in the first mesh pattern 740 are configured to provide less fluid resistance than the openings in the second mesh pattern 760. In one practice, the opening of the first mesh pattern 740 widens towards the first end 770. The first mesh pattern 740 and the second mesh pattern 760 may each individually comprise a woven polymer web, such as one derived from a polyolefin like polypropylene, or a silicone web. The woven web may contain overlapping or non-overlapping patterns. Figure 3CThis is another embodiment of a spacer 600 for an alkali compartment. The spacer 600 includes a body 620 (which may include the mesh as described above), a first side 650 and a second side 620, and includes a rigid backing 630 over the first side 650; the rigid backing may be integral with or adhered to the first side. The rigid backing 630 may also be close to the membrane surface (not shown) and is more rigid than the interior of the spacer. As shown, the rigid backing 630 includes a surface 640, which, when used in the alkali compartment of a BPMED, is positioned close to the bipolar membrane. The rigid backing may be... Figure 3A and 3B The open mesh implementation scheme is used in combination. In another practice, the spacer 600 includes a thickness T, which is up to 10 times the thickness of the corresponding spacers used in the brine and acid compartments of BPMED. Non-limitingly, the thickness T can be from about 2 mm to about 12 mm. Example

[0035] Preliminary experiments were conducted to demonstrate that even with divalent ions such as Ca... ++ and Mg ++ In its presence, maintaining the pH of the alkali compartment below 8.7 also prevents solid precipitation within the BPMED system. The BPMED system comprises acid, alkali, and brine tanks and operates in batch mode. The input to BPMED is taken from these tanks, transported through their respective paths within the BPMED system, and then returned to the same tank. In batch mode, the acid continues to become more acidic over time, the alkali continues to become more alkaline over time, and the brine continues to become less salty over time. Table 1 below shows the data from this experiment. The starting solution was 0.5 M NaCl in the acid and brine compartments and 0.5 M "Instant Ocean" in the alkali compartment. Instant Ocean is a commercially available salt mixture designed to simulate seawater, containing approximately the same concentration of divalent cations such as Ca2+ as seawater. ++ and Mg ++ .

[0036] The following rows represent the current and voltage measured on the BPMED system during 10-second intervals when current was applied. During these times, the acid, brine, and alkali solutions continued to flow, but no current was applied. This allowed each tank to be thoroughly mixed after current application, ensuring a homogeneous pH in each tank. The listed pH values ​​are those after pH stabilization. The initiation of precipitation in the system is indicated by the voltage increasing at a given constant current density due to the formation of solid precipitates on the membrane. The following data show that, despite the fact that the alkali solution was seawater without removing divalent cations, the voltage remained constant for 110 minutes at a constant current value when exposed to a pH of up to 8.69 in the alkali compartment. These data suggest that maintaining a sufficiently low pH in this flow-through invention would allow the use of seawater without pretreatment.

[0037] Voltage (V) Current (A) Time (min) pH of alkaline 7 0.1 0.83 8.05 10 0.3 1 8.05 10 0.3 10 8.27 10 0.3 15 8.36 10 0.3 20 8.41 10 0.3 52 8.5 10 0.3 74 8.51 10 0.3 90.5 8.61 10 0.3 96 8.67 10 0.3 110 8.69

Claims

1. A method for enhancing alkalinity, comprising: (i) Provide a bipolar membrane electrodialysis apparatus comprising electrodes and at least one unit comprising a brine compartment, an acid compartment and an alkali compartment; (ii) Aqueous saline solution is passed through an alkali compartment at a first volume flow rate and through a saline compartment at a second volume flow rate, wherein the aqueous saline solution contains at least one divalent cation that precipitates out of the aqueous saline solution to form a solid precipitate when the aqueous saline solution is at or above the precipitation pH. (iii) Applying a voltage to the bipolar membrane electrodialysis device between the electrodes at a certain current density to form an alkaline-enhanced brine product in the alkali compartment, the pH of which is higher than that of the brine solution but lower than that of the precipitate; (iv) At the current density, the first volume flow rate through the alkali compartment is maintained at a flow rate sufficiently greater than the second volume flow rate through the brine compartment, so as to keep the pH of the alkaline-enhanced brine product formed in the alkali compartment below the precipitation pH. and (v) Discharge the alkaline-enhanced brine product from the alkali compartment.

2. The method according to claim 1, wherein the aqueous saline solutions flowing to the alkali compartment and the brine compartment originate from a brine source, wherein the brine source is the same or different for each of the alkali compartment and the brine compartment.

3. The method according to claim 2, wherein the aqueous salt solution flows directly from the brine source to the alkali compartment, directly to the brine compartment, or directly to both.

4. The method according to claim 1, wherein the brine solution comprises seawater, reverse osmosis concentrated brine, or both.

5. The method according to claim 2, wherein the brine source is a natural seawater body or mined salt dissolved to produce an aqueous brine solution.

6. The method according to claim 1, wherein the divalent cation is selected from calcium (Ca), magnesium (Mg), or both; and the precipitate is selected from CaCO3 or Mg(OH)2 or both.

7. The method of claim 1, wherein the pH of the brine solution is 6 to 8.5; the pH of the precipitate is 8.9 or higher; and the pH of the alkaline-enhanced brine product is 8.5 to 8.

9.

8. The method of claim 1, wherein the first volumetric flow rate is 1 to 10 times higher than the second volumetric flow rate.

9. The method of claim 1, wherein at least a portion of the alkaline-enhanced brine product output from the alkali compartment flows directly into the seawater.

10. The method of claim 1, wherein a partially desalted brine product is formed in and output therefrom the brine compartment, and at least a portion of the desalted brine product output from the brine compartment is combined with at least a portion of the alkaline-enhanced brine product output from the alkali compartment.

11. The method of claim 1, wherein a partially desalted brine product is formed in and output therefrom the brine compartment, and at least a portion of the desalted brine product output from the brine compartment is input into the alkali compartment.

12. The method of claim 10, wherein the combination of the partially desalinated brine product and the alkalinity-enhancing brine product is introduced into the seawater body.

13. The method of claim 10, wherein the desalinated brine product output from the brine compartment has a pH of 8.5 or lower; and the combined desalinated brine product and alkaline-enhanced brine product have a pH of 8.1 to 8.

9.

14. The method of claim 1, wherein the saline compartment, the acid compartment, and the alkali compartment are included in a battery triplet, and the bipolar membrane electrodialysis device comprises a plurality of battery triplets connected in series, wherein the voltage applied across the electrodes is 1V to 4V per battery triplet, and the current density is 5 mA / cm². 2 Up to 120 mA / cm 2 .

15. The method of claim 1, wherein an aqueous stream containing a first HCl concentration is fed into the acid chamber, and an acidification product having a second HCl concentration greater than the first HCl concentration is formed in the acid chamber and discharged therefrom.

16. The method of claim 15, wherein the aqueous feed stream comprises at least a portion of the acidification product output from the acid compartment and a water feed.

17. The method of claim 16, wherein the water feed comprises deionized water or brine.

18. The method of claim 16, wherein a first portion of the aqueous stream is recovered as an HCl product having an HCl concentration of 0.1M to 1M, and a second portion of the aqueous stream flows into the acid compartment.

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