Systems and methods for sequestering carbon dioxide

Abstract

Disclosed herein are systems and methods for a method for sequestering carbon dioxide from an aqueous solution comprising aqueous carbon dioxide and carbonates, the method comprising: (i) removing aqueous carbon dioxide from the solution, wherein the solution has a pH below a pH threshold and the aqueous carbon dioxide is removed until the pH of the solution is increased to a pH above the pH threshold, wherein the pH threshold is a pH at which a precipitation threshold of a carbonate salt in the solution is reached; and (ii) reducing the carbonate salt saturation state of the solution to decrease the carbonate salt saturation state to below the precipitation threshold; wherein the aqueous carbon dioxide is sequestered, and acidification and precipitation of carbonates is mitigated, on release of the solution into a body of water.

Description

SYSTEMS AND METHODS FOR SEQUESTERING CARBON DIOXIDEFIELD OF THE INVENTION

[0001] The present disclosure relates to the field of carbon capture and sequestration and, in particular, to improved sequestration methods and systems.BACKGROUND OF THE INVENTION

[0002] Global industrialization has led to increased levels of CO2 emissions, contributing to global warming and ocean acidification. The climate crisis has prompted stringent measures to be proposed by the EPA and other regulatory bodies requiring industrial emitters to capture and store a substantial portion of their CO2 emissions. The need for efficient, cost-effective, and permanent solutions for CO2 capture and sequestration is, therefore, more critical than ever.

[0003] Methods involving the accelerated weathering of limestone (AWL) for CO2 neutralization and storage have been proposed to address this need. United States Patent No. 6,890,497 (Rau et al.) describes a gas / water / calcium carbonate (limestone) reactor process for extracting CO2 from an exhaust gas stream. AWL is a chemical process (1) by which CO2 dissolves in water to form carbonic acid, which in turn dissolves limestone, neutralizing the acid. The resulting aqueous solution contains calcium and bicarbonate ions, which are both common in the ocean and non-toxic.

[0004] The stepwise progression of AWL involves CO2 in the gas phase (atmospheric or flue gas) to be dissolved in the liquid phase (2). The aqueous CO2 will then become hydrated to form carbonic acid (3), which then quickly loses a proton (H+) to become bicarbonate (4). The proton then attacks the limestone surface and causes dissolution turning it into calcium (Ca2+) and bicarbonate (HCO3‘) which can be safely released into seawater.CO2(g) CO2(aq) (2)

[0005] In seawater, these increases in the concentrations of CO2and HCO3‘ equilibrate over time with carbonate (CO3‘) (collectively referred to as dissolved inorganic carbon or DIC). The equilibrium proportions of the various species are a function of pH. At low pH, CO2is the dominant species, at neutral pH HCO3‘ is the dominant species, and at high pH CO32' is the dominant species. As the pH of the solution raises to about 8.1 (which is typical for oceanic surface waters), about 90% of the DIC is bicarbonate, about 10% is carbonate and less than 1% remains as carbon dioxide.

[0006] A known challenge of AWL is that the pH of the treated solution prior to discharge is about 7. At this pH, about 45% of the captured DIC in solution is in the form of CO2, which results in the undesirable effect of ocean acidification and eventual off-gassing of CO2to the atmosphere. Thus AWL has not proven to be a durable method of CO2sequestration.

[0007] A further challenge of AWL is unwanted precipitation of calcium carbonate. To counter the undesired effects of ocean acidification and CO2off-gassing, efforts to remove excess CO2from the solution have been made to raise the pH, and thereby shift a higher percentage of the CO2to bicarbonate or carbonate. In attempting to increase the percentage of captured DIC in the form of bicarbonate or carbonate, this approach results in the increased concentration of carbonate above the level where calcium carbonate precipitation is known to occur in the ocean, and further risking the reversal of chemical process (1) and a loss of the stored carbon and added alkalinity.

[0008] These challenges have resulted in the limited ability of existing sequestration methods to efficiently and effectively provide durable long-term sequestration of CO2 in a solution that does not lead to acidification of the ocean when released.There is, therefore, an existing gap in technology for a method that not only captures CO2 efficiently from various industrial sources but can also ensure that the CO2 remains sequestered from both the ocean and the atmosphere. Moreover, there is a need for methods for ensuring the storage of CO2 in the oceanic environment for extended periods, which is vital for any long-term climate change mitigation strategy.

[0009] This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present disclosure. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present disclosure.SUMMARY OF THE INVENTION

[0010] In accordance with an aspect, there is provided a method for sequestering carbon dioxide from an aqueous solution comprising aqueous carbon dioxide and carbonates, the method comprising: (i) removing aqueous carbon dioxide from the solution, wherein the solution has a pH below a pH threshold and the aqueous carbon dioxide is removed until the pH of the solution is increased to a pH above the pH threshold, wherein the pH threshold is a pH at which a precipitation threshold of a carbonate salt in the solution is reached; and (ii) reducing the carbonate salt saturation state of the solution to decrease the carbonate salt saturation state to below the precipitation threshold; wherein the aqueous carbon dioxide is sequestered, and acidification and precipitation of carbonates is mitigated, on release of the solution into a body of water.

[0011] In some embodiments, the aqueous carbon dioxide is removed until the pH of the solution is increased to ambient pH.

[0012] In some embodiments, the aqueous carbon dioxide is removed until the pH of the solution is increased to a pH of about 8.2.

[0013] In some embodiments, the aqueous carbon dioxide is removed until the pH of the solution is increased to a pH range of about 7 to about 9.

[0014] In some embodiments, removing aqueous carbon dioxide comprises degassing the aqueous carbon dioxide.

[0015] In some embodiments, the degassing comprises vacuum degassing.

[0016] In some embodiments, the degassing comprises using a membrane contactor.

[0017] In some embodiments, the degassing comprises using a liquid-to-liquid membrane contactor, wherein gaseous CO2 is transferred across the membrane from a high pCO2liquid to a low pCO2liquid, producing a liquid solution that is enriched with CO2 and a second liquid solution enriched with bicarbonate.

[0018] In some embodiments, the degassing comprises applying an electrical current in the aqueous carbon dioxide stream to generate gaseous carbon dioxide.

[0019] In some embodiments, the degassing comprises ultrasonic degassing to generate gaseous carbon dioxide.

[0020] In some embodiments, the degassing comprises thermal degassing.

[0021] In some embodiments, the degassing comprises using rotating packed beds.

[0022] In some embodiments, the degassing comprises using chemical swing absorption.

[0023] In some embodiments, the degassing comprises using at least one selective permeable membrane.

[0024] In some embodiments, the degassing comprises using a liquid to liquid membrane contactor.

[0025] In some embodiments, the degassing comprises using microorganisms to metabolize the carbon dioxide.

[0026] In some embodiments, the carbonate salt is calcium carbonate.

[0027] In some embodiments, the carbonate saturation state of the solution is decreased to 60.

[0028] In some embodiments, the carbonate salt saturation state of the solution is decreased to 30.

[0029] In some embodiments, the carbonate salt saturation state of the solution is decreased to 15.

[0030] In some embodiments, the carbonate salt saturation state of the solution is decreased to 18.

[0031] In some embodiments, reducing the carbonate salt saturation state is by diluting the solution with a second solution, the second solution supersaturated with the carbonate salt.

[0032] In some embodiments, decreasing the carbonate salt saturation state of the solution is by diluting the solution with a second solution, the second solution undersaturated with the carbonate salt.

[0033] In some embodiments, removing aqueous carbon dioxide increases DIC concentration in the solution above 55%.

[0034] In some embodiments, the removal of the aqueous carbon dioxide increases the pH of the solution by reducing carbonic acid generated from the aqueous carbon dioxide.

[0035] In some embodiments, the removal of the aqueous carbon dioxide decreases the partial pressure of the aqueous carbon dioxide in the solution to an ambient aqueous carbon dioxide partial pressure.

[0036] In some embodiments, the removal of the aqueous carbon dioxide decreases the partial pressure of the aqueous carbon dioxide in the solution to about an oceanic carbon dioxide partial pressure.

[0037] In some embodiments, the method further includes (iii) releasing the solution into a body of water.

[0038] In some embodiments, the method further includes adjusting the pH of the solution to correspond to a pH of the body of water before the releasing.

[0039] In some embodiments, the solution is released into the body of water at a depth where an ambient pressure of the body of water maintains the carbonate in a dissolved state.

[0040] In some embodiments, the method further includes generating the aqueous carbon dioxide in the solution by capturing gaseous carbon dioxide.

[0041] In some embodiments, about 95% to about 100% of the aqueous carbon dioxide is converted to the carbonates in the solution.

[0042] In accordance with an aspect, there is provided a system for sequestering carbon dioxide from an aqueous solution comprising aqueous carbon dioxide and carbonates, the system comprising: a degassing chamber configured to remove aqueous carbon dioxide from the solution to increase a pH of the solution and increase saturation of carbonates in the solution; and a dilution vessel configured to decrease a carbonate mineral concentration below a precipitation threshold.

[0043] In some embodiments, the carbonate is calcium carbonate.

[0044] In accordance with an aspect, there is provided a system for sequestering carbon dioxide from an aqueous solution comprising aqueous carbon dioxide and a carbonates, the system comprising: a chamber configured to remove aqueous carbon dioxide from a solution to increase a pH of the solution and increase saturation of carbonates in the solution and further configured to decrease a carbonate salt concentration below a precipitation threshold.

[0045] In some embodiments, the carbonate is calcium carbonate.

[0046] In some embodiments, the system further includes a monitoring and control system configured to configure a pH of the solution to reach a target pH level and configured to configure the saturation of carbonates to reach a threshold carbonate saturation level and configured to configure a carbonate salt level to be below a carbonate salt precipitation threshold.

[0047] In accordance with an aspect, there is provided a system for sequestering carbon dioxide, the system comprising: a mixing vessel configured to dissolve a carbonate mineral in solution by conversion of aqueous carbon dioxide into bicarbonate and carbonate ions, the mixing vessel configured to provide the solution to the carbon dioxide removal vessel; a carbon dioxide removal vessel configured to remove a portion of the aqueous carbon dioxide from the solution; and a monitoring and control system configured to configure a pH of the solution to reach a target pH level and configured to configure a carbonate saturation level to reach a threshold carbonate saturation level and configured to configure a carbonate salt level to be below a carbonate salt precipitation threshold.

[0048] In some embodiments, the carbon dioxide removal vessel comprises an air sparger.

[0049] In some embodiments, the carbon dioxide removal vessel comprises a vacuum degasser.

[0050] In some embodiments, the carbon dioxide removal vessel comprises a membrane contactor.

[0051] In some embodiments, the carbon dioxide removal vessel further comprises a gas outlet configured to provide removed carbon dioxide to the mixing vessel.

[0052] In some embodiments, the system further includes a discharge system configured to discharge the solution to a body of water.

[0053] In some embodiments, the discharge system comprises at least one filter, at least one discharge port, and at least one safety valve.

[0054] In some embodiments, there is provided a method for sequestering carbon dioxide, the method including: removing aqueous carbon dioxide from a solution containing carbonates to increase a pH of the solution above a pH threshold, the pH threshold being a pH at which a precipitation threshold of a carbonate salt in the solution is reached; and decreasing a carbonate salt saturation state of the solution below the precipitation threshold. Furthermore, the solution is released into a body of water, namely, the ocean, where the pH of the solution released matches the pH of the body of water, for example, about 8.2 (or in some embodiments, in a range from 7.9 to 9). In some embodiments, when the solution is released into the body of water, the calcium carbonate saturation state is elevated relative to the calcium carbonate saturation state of the body of water, but is under the precipitation threshold of the calcium carbonate or point at which calcium carbonate precipitates in that body of water. In some embodiments, the calcium carbonate saturation state of the solution released is > = 60. In some embodiments, the calcium carbonate saturation state of the solution released is > = 30. In some embodiments, the calcium carbonate saturation state of the solution released is > = 20. In some embodiments, the calcium carbonate saturation state of the solution released is > = 15. In some embodiments, the calcium carbonate saturation state of the solution released is > is in a range from Q = 1 to > = 14. For example, where a precipitation threshold of calcium carbonate is > = 30, the calcium carbonate saturation state can be > = 28 or less (e.g., reduced to that amount by dilution or ion exchange as described herein) and the increase in total alkalinity can be 7000 pmol / kg (see e.g., FIG. 6B for additional example values). Advantageously, a high total alkalinity denotes a higher conversion of carbondioxide to DIC (e.g., bicarbonate) attained. For example, 55% or more of the original aqueous carbon dioxide is converted to DIC in the solution released, according to some embodiments.BRIEF DESCRIPTION OF THE DRAWINGS

[0055] These and other features will become more apparent in the following detailed description in which reference is made to the appended drawings.

[0056] FIG. 1 is a flowchart of a method for sequestering carbon dioxide, according to some embodiments;

[0057] FIG. 2 is a flowchart of a method for sequestering carbon dioxide, according to some embodiments;

[0058] FIG. 3 is a schematic view of a system for sequestering carbon dioxide, according to some embodiments;

[0059] FIG. 4A is a flowchart of a method for sequestering carbon dioxide, according to some embodiments;

[0060] FIG. 4B is a flowchart of a method for sequestering carbon dioxide, according to some embodiments;

[0061] FIG. 5 is a schematic view of a system for sequestering carbon dioxide, according to some embodiments;

[0062] FIG. 6A is a graph showing calcite saturation versus alkalinity from calcium carbonate dissolution in the solution at different temperatures, according to some embodiments;

[0063] FIG. 6B is a graph showing calcite saturation versus alkalinity from calcium carbonate dissolution in the solution at different temperatures, according to some embodiments;

[0064] FIG. 7A is a graph showing alkalinity from calcium carbonate in the solution over time following carbon dioxide sequestration, according to some embodiments;

[0065] FIG. 7B is a graph showing dissolved inorganic carbon levels in the solution over time following carbon dioxide sequestration, according to some embodiments;

[0066] FIG. 7C is a graph showing carbonate saturation state in the solution overtime following carbon dioxide sequestration, according to some embodiments;

[0067] FIG. 7D is a graph showing pH in the solution over time following carbon dioxide sequestration, according to some embodiments;

[0068] FIG. 7E is a graph showing total alkalinity in the solution over time following carbon dioxide sequestration, according to some embodiments;

[0069] FIG. 7F is a graph showing total alkalinity in the solution over time following carbon dioxide sequestration, according to some embodiments;

[0070] FIG. 8 is a Bjerrum plot of the carbonate equilibrium in seawater, according to some embodiments;

[0071] FIG. 9 is a graph showing CO2 removal targets at different pH values, according to some embodiments;

[0072] FIG. 10 shows a graph of calcite saturation states during degassing of CO2 to reach ambient pH, according to some embodiments;

[0073] FIG. 11 is a graph showing example alkalinity concentrations as a function of flue gas CO2 concentration, according to some embodiments; and

[0074] FIG. 12 is a graph showing the bicarbonate concentration that is expected to be reached per kg of seawater that flows through the CO2 removal step, according to some embodiments.DETAILED DESCRIPTION OF THE INVENTION

[0075] Methods for capturing and storing CO2 include converting the CO2 to dissolved inorganic carbon, consisting of a mix of CO2, HCOs' and COs2' in the ocean. When in water, however, excess CO2 acidifies the ocean until it eventually off gases into the atmosphere over years or decades.

[0076] Both outcomes are undesirable. Acidification of the ocean directly impacts the ocean environment, wildlife, and oceanic ecosystems. CO2 off gassing into the atmosphere, even over years to decades, is a harmful pollutant to the environment. Accordingly, due to these undesirable outcomes, such methods are considered temporary carbon storage and are of lower value to carbon markets.

[0077] The inventors have further observed that the effectiveness of such methods for converting CO2 into durable and non-acidic forms of storage (HCOf and CO32") are further limited by the amount of CO2 that can be durably converted. Specifically, increased concentration levels of calcium carbonate increase the risk of losing the durably stored carbon (HCCh' and CO32) through precipitation of calcium carbonate in the body of water. This risk is exacerbated in that precipitation is easy to observe (e.g., whitening events) but hard to quantify. As such, any level of observable precipitation in the body of water is undesirable.

[0078] It has further been observed that attempts to address the undesirable precipitation of calcium carbonate in the body of water by increasing the concentration of bicarbonate in the solution to a calcium carbonate saturation level that matches the level in the body of water, and then relying on dilution in the body of water to hold the CO2, is ineffective.

[0079] Accordingly, such methods present an unsatisfactory avenue for carbon capture and sequestration in view of their environmental impact arising from the return of stored carbon to gaseous CO2 pollutant and the acidification of oceans. Such methods are, therefore, insufficient.

[0080] The present invention provides a system and method for sequestering carbon dioxide that effectively provides durable long-term sequestration of CO2 in a solution that does not lead to acidification of the ocean or precipitation when released. According to embodiments, there is provided a method for sequestering carbon dioxide that can produce a non-acidic solution containing the sequestered carbon dioxide without the otherwise expected precipitation of carbonate salt at elevated pHs.

[0081] In certain embodiments, the method comprises, at a first step, removing aqueous carbon dioxide from a solution containing carbonates to increase a pH of the solution above a pH threshold at which a precipitation threshold of a carbonate salt in the solution is reached; and, at a second step, decreasing a carbonate salt saturation state of the solution below the precipitation threshold. According to such embodiments, removing the aqueous carbon dioxide from the solution increases the pH of the solution by reducing the production of carbonic acid thereby allowing the solution produced to be less acidic for release into ocean environments. In some embodiments, for example, aqueous carbon dioxide is removed from the solution until the pH of the solution reaches ambient pH. In some embodiments, aqueous carbon dioxide is removed from the solution until the pH of the solution reaches 8.2. In further embodiments, aqueous carbon dioxide is removed from the solution until the pH of the solution reaches a range of 7 to 9.

[0082] According to embodiments, removal of aqueous carbon dioxide from the solution to increase the pH of the solution to target levels allows the solution to be released into the body of water (e.g., ocean) without unduly acidifying the body of water.

[0083] In certain embodiments, aqueous carbon dioxide is removed from the solution until the pH of the solution matches the ocean pH thereby further reducing the amount of aqueous carbon dioxide that off gasses over time in the body of water as the solution reaches equilibrium with the body of water. In some embodiments, the aqueous carbon dioxide is removed from the solution by degassing the aqueous carbon dioxide.According to such embodiments, the concentration of aqueous carbon dioxide in the solution is reduced and further results in less carbonic acid produced by reaction of the carbon dioxide with water in the solution according to chemical process (3) and, ultimately, resulting in a solution that is less acidic or has an increased pH.

[0084] According to embodiments, the method provides for the removal of aqueous carbon dioxide from the solution to reduce the amount of aqueous carbon dioxide that off gasses over time in the body of water as the solution reaches equilibrium with the body of water. In contrast to methods that simply dilute the solution to lower CO2 concentration (or partial pressure) to achieve a higher solution pH, the method provides for the removal of aqueous CO2 to mitigate unexpected ocean acidification.

[0085] In particular, there are two problematic dilution processes, that could result in unexpected ocean acidification. The first is dilution from water that is already equilibrated with atmospheric CO2, like a local body of water. In doing so, while the CO2 concentration may decrease and the pH may rise after dilution, the amount of excess acidity has not changed, since all of the excess CO2 is still in the solution, and while it will slow the rate of CO2 off-gassing, eventually the excess will still off-gas. A similar challenge exists for water that is undersaturated with respect to atmospheric CO2 but that would eventually end up in a body of water that equilibrates with atmospheric CO2. By increasing the level of CO2 in the undersaturated water the CO2 that would have been absorbed into that water once it equilibrates with the atmosphere would stay in the atmosphere, canceling out the carbon captured in the process, thus resulting in an increased atmospheric CO2 concentration (over what would have happened if there was no intervention), which would also result in increased ocean acidification.

[0086] These challenges can be especially problematic in that the impact they would have on the ocean acidification is not directly observable given that you cannot directly monitor the total CO2 level in the ocean at the precision required, and furthermore, it is not readily apparent in common ocean carbonate chemistry modeling tools that deal almost exclusively in concentrations (as needs to be the case when considering the ocean) rather than total amounts. Using dilutionwith undersaturated water (with respect to CO2) as suggested by AWL can thus potentially lead to unexpectedly negative results.

[0087] This is further complicated by the beneficial effects of dilution to help lower the calcium carbonate saturation state to prevent precipitation (versus acidification and off-gassing), meaning there is the potential for these unexpected unobservable acidification side effects when attempting controlling calcium carbonate precipitation. Where conceptually the same challenges could exist for calcium carbonate concentration dilution, what makes it work, and is much less problematic, for calcium carbonate concentrations versus CO2 is that the world has a surplus of CO2 in the atmosphere and ocean, which needs to be removed as, among other impacts, it is causing ocean acidification, which has significantly reduced the carbonate concentration levels in the ocean (see FIG. 8). This means that the oceans need more calcium carbonate, not less, making it unexpectedly advantageous to put a solution in the ocean with calcium carbonate concentrations above ambient levels.

[0088] FIG. 8 shows a Bjerrum plot of carbonate equilibrium in seawater. When CO2 is added to seawater it is converted to carbonic acid, causing pH to decrease. When carbonic acid dissolves calcium carbonate (CaCCh) it converts both the CO2 and the dissolved carbonate (CCh2-) to bicarbonate (HCO3 ), thus lowering the amount of CO2 and increasing the amount of HCO3" in the solution, increasing the pH. As more bicarbonate is added to the solution, an increasing proportion of the dissolved carbon is turned into carbonate. The dashed vertical line marks the current pH level of seawater.

[0089] According to some embodiments, and advantageously, methods disclosed herein can reduce the acid in the solution, as well as reduce excess aqueous carbon dioxide which would otherwise off gas into the atmosphere as an undesired pollutant. Embodiments of the invention further involve the step of decreasing the saturation state of the carbonate salt below the precipitation threshold to advantageously mitigate the precipitation of carbonate.

[0090] In particular, when the pH of the solution is increased to these target levels, a greater concentration of bicarbonate ions are produced (see e.g., FIG. 8 showing a high concentration of bicarbonate ions at pH 7.5-8.5). This is advantageous in that it allows a greater amount of carbon dioxide to be sequestered as durable, non-acidic bicarbonate. The inventors have observed that methods that have attempted to increase the pH of the solution, even before reaching these target levels or before reaching the pHs of ocean water, have the disadvantage that the concentration of carbonate ion also produced is above a precipitation threshold for that pH, thereby causing calcium carbonate to precipitate in the solution. If the pH of the solution is increased (by the removal of carbon dioxide) only up to a point before this precipitation occurs, a further disadvantage observed is that a large amount of aqueous carbon dioxide still remains in the solution. For example, at a pH of about 7, about 45% of the captured DIC in solution is in the form of carbon dioxide, rather than the desired bicarbonate ion.

[0091] Accordingly, at the second step of the method, the saturation state of the calcium carbonate is decreased below this point where precipitation occurs. For example, in some embodiments, this is performed by mixing water from the body of water that the solution is to be released into (e.g., ocean water) with the solution. This can be performed in a dilution vessel, for example. The water mixed into the solution can be undersaturated with calcium carbonate or supersaturated with calcium carbonate, according to various embodiments. Decreasing the saturation state of calcium carbonate advantageously allows a greater concentration of carbonate ion to remain in solution up to a calcium carbonate saturation of up to 60, in the range of 16 to 48, or in the range of 16 and 60, according to various embodiments, all without precipitation of calcium carbonate, thereby allowing the pH to be increased (by removal of aqueous carbon dioxide) to the desired higher target levels (e.g., ambient pH, pH of 8.2, pH of 7-9, etc.). This is advantageous at least in that more carbon dioxide can be durably converted to and sequestered as bicarbonate ion (e.g., greater than the 45% observed by inventors at pH of about 7) as well as that the resulting solution is not acidified, all without the precipitation of calcium carbonate that would be otherwise expected to have already occurred at a lower pH while the pH was being increased by removal of aqueous carbon dioxide. For example, in some embodiments, 45% to 100% ofaqueous carbon dioxide in solution is converted to and sequestered as DIC. In some embodiments, 55% to 95% of aqueous carbon dioxide in solution is converted to and sequestered as DIC. In some embodiments, 55% to 95% of aqueous carbon dioxide in solution is converted to and sequestered as DIC. In some embodiments, 65% to 85% of aqueous carbon dioxide in solution is converted to and sequestered as DIC. In some embodiments, 75% to 80% of aqueous carbon dioxide in solution is converted to and sequestered as DIC. In some embodiments, above 75% aqueous carbon dioxide in solution is converted to and sequestered as DIC. The percentage of DIC achieved by performing embodiments of each method described herein can be selected based on data such as shown in FIG. 9, such as in relation to particular pH or calcium carbonate saturation states achieved in the solution and / or the CO2 concentration in the original CO2 gaseous stream captured in the aqueous solution at the start of methods described herein.

[0092] Accordingly, in some embodiments, the calcium carbonate saturation state in the solution is elevated above the calcium carbonate saturation state of the body of water that the solution is to be released into. This provides an additional advantage of being able to use water from the body of water (e.g., ocean water) that is already supersaturated with calcium carbonate, albeit supersaturated to a lesser degree, in order to dilute the calcium carbonate in the solution.

[0093] Importantly, in some embodiments, the method steps are iterative and can occur simultaneously. For example, in some embodiments, the calcium carbonate saturation state of the solution is decreased (e.g., by dilution) successively as the aqueous carbon dioxide is removed from the solution and the pH and carbonate ion concentration are increased.

[0094] According to some embodiments, this method can be used alone or with various carbon sequestration processes, such as AWL, where the method is applied to remove excess aqueous carbon dioxide in solution after some sequestration of carbon dioxide (e.g., conversion to bicarbonate ion) has already occurred. In some embodiments, this method can be used iteratively to remove excess aqueous carbon dioxide in solution as sequestration of the aqueous carbon dioxide is being performed.Definitions

[0095] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0096] As used herein, the term “about” and “approximately” refers to an approximately + / -10% variation from a given value. It is to be understood that such a variation is always included in any given value provided herein, whether or not it is specifically referred to.

[0097] As used herein, references to singular is understood to mean singular in some embodiments and plural or “at least one” in other embodiments.

[0098] As used herein, unless otherwise specified or understood from the context, references to carbonate, the carbonate, or a carbonate are understood, in some embodiments to include materials, such as bicarbonate (HCCU), carbonate ion (CO32"), limestone, calcite, aragonite, magnesium carbonate, potassium carbonate, and / or other materials that include the carbonate ion, CO32’, such as bound to a cation. As examples, the carbonate can be calcite, aragonite, limestone, dolomite, magnesium carbonate, potassium carbonate, sodium carbonate, or other carbonate. As used herein, unless otherwise specified or understood from the context, a solid carbonate can be a carbonate mineral, such as calcite, aragonite, limestone, dolomite, magnesium carbonate, potassium carbonate, sodium carbonate.

[0099] As used herein, unless otherwise specified or understood from the context, calcium carbonate can be substituted with another carbonate salt, such as limestone, calcite, aragonite, magnesium carbonate, potassium carbonate, and / or other materials that include the carbonate ion, CO32’, such as bound to a cation. Corresponding modifications to the process can be made in view of the carbonate used, according to some embodiments.

[0100] As used herein, in the context of a molecule being derived from other molecule(s), references to “derived” mean produced directly from or produced after two or more chemical reactions or both.

[0101] As used herein, unless otherwise specified or understood from the context, the term “target pH” refers to a pH value or range of values that is desired to be achieved.

[0102] As used herein, unless otherwise specified or understood from the context, the term “pH threshold” or “threshold pH” refers to a particular pH value or range of values at which a precipitation threshold of a carbonate salt in the solution is reached.

[0103] As used herein, unless otherwise specified or understood from the context, the term “precipitation threshold” is the point (or value relative to that point, such as defined by a set-off value or percentage below or above the point) at which a molecule will precipitate, such as immediately or over a period of time. The precipitation threshold of calcium carbonate can be set, such as with reference to modelling or data such as shown in examples in FIGs. 6A to 6B and FIGs. 7A to 7D, depending on the other parameters desired or present.

[0104] As used herein, unless otherwise specified or understood from the context, the term “ambient pH” refers to the local pH of a body of water such as the ocean that the solution is to be released into.

[0105] As used herein, unless otherwise specified or understood from the context, the term “calcium carbonate saturation threshold” or “calcite saturation threshold” are saturation levels or values that calcium carbonate or calcite are at in a solution, respectively. For example, the saturation level is a numeral times a fully saturated state (of > =1), where the numeral is 60, 50, 40, 30, 20, 24, 18, 12, 6, in a range from 2 to 60, in a range from 8 to 55, in a range from 15 to 45, in a range from 20 to 35, in a range from 10 to 25, or any value within such ranges, according to various embodiments. As used herein, unless otherwise specified or understood from the context,the term “Q” refers to the saturation level or saturation state of a molecule, such as calcium carbonate. Where Q = 1, a solution is fully saturated with the molecule.

[0106] To gain a better understanding of embodiments described herein, the following examples are set forth. It will be understood that these examples are intended to describe illustrative embodiments and are not intended to limit the scope of the present disclosure in any way.METHOD FOR SEQUESTERING CARBON DIOXIDE

[0107] According to embodiments, there is provided a method for enhancing the durability of carbon sequestration while mitigating the undesirable effects of oceanic acidification and precipitation of calcium carbonate. The carbon dioxide can be derived from a gaseous carbon dioxide stream such as output waste from an industrial plant. In some embodiments, carbon dioxide is captured in an aqueous solution such as, for example, AWL. The aqueous carbon dioxide is converted to carbonic acid and bicarbonate according to the example steps denoted by chemical process (2), chemical process (3), chemical process (4), and chemical process (5).Mitigation of Oceanic Acidification and CO 2 Off-Gassins

[0108] FIG. 1 shows an example method for mitigating the undesirable effects of oceanic acidification and CO2 off-gassing in sequestering carbon dioxide from an aqueous carbon dioxide solution, according to some embodiments. In general, carbon dioxide is captured in an aqueous solution containing carbonates. The carbon dioxide can be the source of the carbonates, in some embodiments. At 110, aqueous carbon dioxide is removed from the solution containing carbonates to increase the pH of the solution. In some embodiments, the solution may be prepared using alkalinity, such as metal carbonates and / or hydroxides. In some embodiments, the solution may comprise water.

[0109] In certain embodiments, after some gaseous carbon dioxide is captured in thesolution and, in some embodiments, after the carbon dioxide in solution dissolves an alkaline metal in the solution or otherwise is converted to carbonate(s), excess carbon dioxide is removed according to step 110 to raise the pH of the solution to a target pH or range of pHs. This is distinct from other methods that instead attempt to control the calcium carbonate concentration to match that in the body of water. According to certain embodiments, carbon dioxide is removed from the solution until the solution pH is about the pH(s) of the body of water that the solution is to be released into. In some embodiments, the target pH is between 7.5 and 8.5. In some embodiments, the target pH is between 7 and 8.5. In some embodiments, the target pH is between 7 and 9. In some embodiments, the target pH is between 7.2 and 10. In some embodiments, the target pH is between 8 and 10. In some embodiments, the target pH is between 8 and 11. In some embodiments, the target pH is between 8 and 12. In some embodiments, the target pH is between 8 and 13. In some embodiments, the target pH is between 8 and 14. In some embodiments, the target pH is between 8.1 and 8.4. In further embodiments, the target pH is the same as the pH of the body of water to be released into. In some embodiments, target pH is the pH at which a desired level of carbon dioxide is converted to a desired concentration of DIC such as bicarbonate, according to various embodiments. In some embodiments, the target pH is a pH that is above a threshold pH at which calcium carbonate will precipitate in the particular solution. In other embodiments, the target pH is 8.1.

[0110] According to such embodiments, removal of excess carbon dioxide at step 110, until the pH of the solution matches a target pH, reduces the risk of acidification of the body of water by the solution on release. At the same time, removal of excess CO2 from the solution at step 110 in such embodiments reduces CO2 off-gassing post release (which would occur when the CO2 approaches or reaches equilibrium in the body of water (e.g., ocean water in the environment)) thereby increasing the proportion of dissolved inorganic carbon (DIC) that is durably stored from the captured carbon dioxide. In this way, a greater percentage of the carbon dioxide in solution is sequestered in DIC or carbonate(s).

[0111] In some embodiments, the method includes removing aqueous carbon dioxidefrom a solution containing carbonates to increase a pH of the solution and decreasing the calcium carbonate saturation state of the solution such that it does not exceed a precipitation threshold.

[0112] In some embodiments, the method includes removing aqueous carbon dioxide from a solution containing carbonates to increase a pH of the solution above a pH threshold at which a precipitation threshold of a carbonate salt in the solution is reached. For example, the pH is increased to a target pH according to some embodiments. The target pH can be a pH or range of pHs described here, such as 8.2 or a local pH of a body of water into which the solution is released. As the pH of the solution is increased (before release), as it increases above a pH at which a carbonate salt (calcium carbonate, for example) in the solution will precipitate (e.g., over a undesirably short length of time), the method decreases the calcium carbonate saturation state of the solution such that it does not exceed a precipitation threshold, for example, by diluting the solution until the calcium carbonate concentration is reduced back to below the point at which it will precipitate. This method can occur iteratively and successively such that the carbon dioxide is removed to increase the pH while the calcium carbonate saturation state of the solution is decreased to maintain the calcium carbonate saturation state below a level at which calcium carbonate precipitates.Mitigation of Calcium Carbonate Precipitation

[0113] Increasing the pH of the solution and raising the concentration of carbonates, including carbonate ion (CO32-), in the ocean also increases the risk of precipitation of calcium carbonate (or, in some embodiments, another carbonate salt) from the solution, as seen in FIG. 8. The risk of precipitation is directly related to the calcium carbonate saturation state ( ) which is equal to: = [CO32’] [Ca2+] / Ksp (6) where [CO32-] is the concentration of carbonate ions in seawater, [Ca2+] is the concentration of calcium ions and Ksp is the solubility product.

[0114] When < 1 the solution is undersaturated, and CaCCh dissolution is thermodynamically favored; when = 1, the solution is saturated, and CaCCh is in thermodynamic equilibrium; and when > 1, the solution is supersaturated and CaCCh precipitation is thermodynamically favored. In the ocean, precipitation of CaCCh is kinetically inhibited through various poorly characterized mechanisms, resulting in an ambient Q ~ 4. At this level, precipitation of CaCCh has been demonstrated to occur but it is a slow process. Above the ambient level, one would expect some rate of precipitation to return the solution to its ambient state over time. Given that the mechanisms for triggering a calcium carbonate precipitation event are poorly characterized and even referred to as “highly contested”, and with the impact that an event could have on both the environment and an AWL project, the risk of triggering an event has resulted in AWL embodiments effectively limiting the level of during CO2 removal to that of ambient seawater (or about ~ 4).

[0115] By comparison, in order to remove enough CO2 from solution to reach ambient pH levels for industrial levels of CO2 concentrations, would need to rise to between 16 and 48, depending on the specific CO2 concentration. FIG. 10 shows a graph of example calcite saturation states during degassing of CO2 to reach ambient pH, according to some embodiments. The graph is based on global average ocean conditions, as modeled using CO2SYS.

[0116] While such high saturation levels would seem to risk precipitation, according to some embodiments, unexpectedly and advantageously, the calcite saturation state can be raised to 60 times before precipitation occurs (although almost immediately) or to 30 times for about a day or to 15 for about 2 weeks (see e.g., FIGs. 6A and 6B).

[0117] Accordingly, in some embodiments, CO2 is removed until a calcium carbonate saturation of up to 60 times is reached (depending on the local conditions) and then the calcium carbonate saturation state is quickly reduced at a rate that keeps it ahead of the slower precipitation kinetics. For example, with = 60, local seawater with = 4 can then be used to dilute the solution and quickly lower down to 32 with just 1 : 1 dilution, changing the time frame for precipitation from near instant to about one day. Or, 3: 1 dilution would lower Q down to 18, changing theprecipitation time frame to about 2 weeks. Other dilution ratios can be used and / or selected to configure a desired time to precipitation, according to some embodiments.

[0118] Whereas AWL proposes dilution using undersaturated water to reduce the calcium carbonate saturation state, it does not consider using supersaturated ambient water to reduce the calcium carbonate saturation state, likely because no level of dilution would be able to get it back down to ambient. It also does not address the potential implications of inadvertent ocean acidification from diluting the solution with undersaturated levels of CO2 that are likely to arise.

[0119] In some embodiments, with appropriate local ocean conditions and hydrodynamics, the rapid dilution with local water in the desired time frame possible can occur after the solution has been released into the body of water, whereas in other cases, dilution with local seawater may occur inside of a dilution vessel.

[0120] Other methods of reducing the saturation level can be used in combination or in other embodiments. According to some embodiments, the methods disclosed herein provides an unexpected advantage as prior art attempts would not contemplate that a method that increased the saturation state (e.g., up to 60 times higher) could come with a decreased risk of precipitation and improved ocean health. Given the severely undesirable result of precipitating easily observable calcium carbonate into natural oceanic environments, prior art attempts have prohibitively produced acidic solutions that lose half of the stored carbon rather than raise the saturation state even higher.

[0121] In some embodiments, CO2 is removed from a solution (e.g., containing carbonates), and this process converts bicarbonate to carbonate (according to the equilibrium and chemical processes described herein), which is undesired as it increases the saturation state of the carbonate salt in the solution, thereby risking precipitation of the carbonate salt. Accordingly, in some embodiments, the concentration of bicarbonate is raised, without raising the concentrations of carbonate and calcium (or other appropriate ion) such that they combine and precipitate. For example, in some embodiments, as CO2 is converted to bicarbonate, the method and systemremoves CO2 from the solution (thereby increasing the pH and increasing the concentration of bicarbonate in the solution, the latter of which allows more CO2 to be durably stored and sequestered), while the concentration of carbonate salt (e.g., calcium carbonate) is decreased to below its precipitation threshold, such as by dilution with an additional solution having a lower concentration of carbonate salt (but can still be supersaturated, for example) or by ion exchange replacing a portion of the ions (e.g., calcium ions) with replacement ions that have a higher precipitation threshold or higher solubility when combined with carbonate ions than the ions that they are replacing.

[0122] In some embodiments, aqueous carbon dioxide is removed until the pH of the solution is increased to a target level . The target level can be selected to match or be a desired amount relative to the pH of a body of water where the solution is to be released. For example, the pH of the solution can be increased to the ambient pH of the body of water where the solution is to be released, a fixed amount above ambient up to about 0.3 above ambient, 8.1, about 8.1, about 7 to about 9, or other pH value or range. In some embodiments, the target level of pH is a pH (or a defined value or range relative to) at which precipitation of calcium carbonate occurs or is about to occur, as selected, such as from data shown in FIGs. 6 and 7, depending on the parameters.

[0123] In some embodiments, the target level of pH is selected to reduce the amount of carbon dioxide produced from the carbonate in solution from a return to an equilibrium between the carbonate and the carbon dioxide when the pH of the solution released approaches the ambient pH of the body of water on dilution of the solution in the body of water.

[0124] Increasing the pH at step 110 ordinarily may increase the calcium carbonate saturation state in the solution to be higher than that found in the body of water, which increases the undesirable risk of precipitation of carbonate. For example, removing CO2 at step 101 can cause a reverse reaction leading to the precipitation of calcium carbonate. As precipitation of calcium carbonate is a strongly undesired outcome in sequestering carbon dioxide, the method at step 120 advantageously and unexpectedly allows the pH of the solution to be increased to levels exceedingambient pH for example (step 110) while mitigating the precipitation of carbonate.

[0125] According to embodiments, a method is provided for mitigating the undesirable effect of calcium carbonate precipitation in sequestering carbon dioxide from an aqueous carbon dioxide solution. Referring to FIG. 1, step 120 involves diluting the solution to decrease the calcium carbonate saturation state of the solution. In some embodiments, the solution is diluted by the addition of ambient water taken from a body of water that the solution is to be released into. Other methods for decreasing the calcium carbonate solution state of the solution are further described herein, according to various embodiments.

[0126] According to embodiments, step 120 is performed when the solution’s saturation state of calcium carbonate is above a threshold (e.g., precipitation threshold), which may be likely if the solution is prepared using ambient seawater. In some embodiments, the precipitation threshold is the concentration level or saturation state of calcium carbonate at which the calcium carbonate begins to precipitate. In some embodiments, the precipitation threshold can be a defined amount relative to that concentration level or saturation state.

[0127] In some embodiments, dilution of the solution at step 120 to decrease the calcium carbonate saturation state of the solution can be achieved by the natural dilution of the solution after it is released into a local body of water. For example, this can be where the saturation state of calcium carbonate in solution is elevated above the saturation state of calcium carbonate in the local body of water, even if that local body of water is supersaturated with calcium carbonate.

[0128] In some embodiments, the solution is continuously cycled between steps 110 and 120 to iteratively adjust the pH to the desired threshold while ensuring the calcium carbonate saturation state of the solution is maintained at a desired amount below the precipitation threshold. In such embodiments, aqueous carbon dioxide is removed with each cycle through step 110 to continuously increase the pH while the corresponding increase of the calcium carbonate saturation state of the solution is kept below threshold levels (or reduced back down to below thresholdlevels) with each cycle through step 120 to dilute the solution with supersaturated or undersaturated water (with respect to calcium carbonate state) to prevent or reduce precipitation of calcium carbonate. This cycle can be repeated until the pH is raised to a target level (e.g., matching an ambient pH of a body of water that the solution is to be released into) and the saturation level of calcium carbonate in solution is near but does not meet a level where the calcium carbonate will precipitate after release. Advantageously, in some embodiments, this can help prevent precipitation of calcium carbonate during the removal of aqueous carbon dioxide.

[0129] In some embodiments, following step 120, the solution can then be released into the ocean or other natural body of water at a pH that matches the body of water (rather than at an acidic pH harmful to the environment) and without precipitation of calcium carbonate, thereby effectively sequestering carbon dioxide as carbonates, such as bicarbonate (HCCh ) and / or carbonate ion (COs2-), in solution. Advantageously and unexpectedly, the carbonate concentration in the released solution can be higher than the concentration of the same in the body of water without precipitation and while stably and more durably converting a higher amount of the carbon dioxide to carbonates, reducing the amount converted back to carbon dioxide over time, according to some embodiments.

[0130] According to embodiments, the method described herein can be used as a standalone method for sequestering carbon dioxide from an aqueous carbon dioxide solution, or alternatively, can be integrated into an AWL method to further mitigate the undesirable effects of oceanic acidification, CO2 off-gassing, and precipitation in such systems. In some embodiments, steps 110 and step 120 are performed after the conversion of a portion of the carbon dioxide to carbonate(s), such as bicarbonate (HCCh') and / or carbonate ion (COs2-), or otherwise a sequestration of a portion of the carbon dioxide. This method can be performed to increase sequestration of the carbon dioxide, according to some embodiments. This method can be used to remove excess carbon dioxide (e.g., excess aqueous carbon dioxide) after capture and sequestration of a portion of carbon dioxide, according to some embodiments. Carbon dioxide can be sequestered or converted to carbonate(s) according to a process defined by chemical process(2), chemical process (3), chemical process (4) and, in some embodiments, also chemical process (5), according to some embodiments. Carbon dioxide can be converted to carbonate(s) or sequestered according to an accelerated weathering of limestone process, according to some embodiments. In some embodiments, alternatively or in addition, this method can be used directly to capture and sequester carbon dioxide (e.g., directly from flue gas from an industrial process) without any prior capture or sequestration of any portion of the carbon dioxide, according to some embodiments. In these embodiments, step 110 is performed on aqueous carbon dioxide captured from gaseous carbon dioxide, such as from flue gas or other gaseous stream.Integration into A WL Methods

[0131] Referring to FIG. 2, in accordance with certain embodiments, the method can be integrated into an AWL method to further mitigate the undesirable effects of oceanic acidification, CO2 off-gassing, and precipitation in such systems. In some embodiments, the method is instead integrated into other carbon capture or sequestration methods, or used as a standalone carbon sequestration method.

[0132] According to such embodiments, excess CO2 is removed after the CO2 has been captured into the solution and dissolves the alkaline metal (220). Counterintuitive to general AWL practices, in some embodiments, the excess CO2 is removed to the point where the pH matches the local body of water (230) as opposed to matching the calcium carbonate concentration of the body of water, such a pH attained being the target pH. In some embodiments, the target pH attained is above the pH of the local body of water. In some embodiments, this helps prevent acidification of the body of water but has the undesirable effect of carbonate saturation states that are higher than found in the body of water or that are higher than a precipitation threshold of the carbonate salt (e.g., calcium carbonate). The result of these high carbonate saturation states is the risk of undesirable precipitation of calcium carbonate. To address this, at step 240, the calcium carbonate saturation state is controlled such that there is no precipitation once the solution is put into the body of water.

[0133] In some embodiments, after some gaseous carbon dioxide is captured in the solution and, in some embodiments, after the carbon dioxide in solution dissolves an alkaline metal in the solution or otherwise is converted to carbonate(s), excess carbon dioxide is removed according to step 110 until the pH of the solution matches a threshold pH or range of pHs (e.g., the pH(s) of the body of water that the solution is to be released into). This is distinct from other methods that may instead attempt to control the calcium carbonate concentration to match that in the body of water. According to embodiments, carbon dioxide is removed until the pH matches a target pH of 7-9. According to embodiments, carbon dioxide is removed until the pH matches a target pH of 8.2.

[0134] According to such embodiments, removal of excess carbon dioxide at step 110 is performed until the pH of the solution matches a target pH and, accordingly, the method disclosed herein allows the solution to reduce the risk of acidification of the body of water by the solution on release. At the same time, removal of excess CO2 from the solution at step 110 in such embodiments reduces CO2 off gassing thereby also increasing the proportion of dissolved inorganic carbon that is durably stored from the captured carbon dioxide, such as by removing excess CO2 from the solution and preventing it from off-gassing in the ocean. In this way, the proportion of carbonates to CO2 in solution is accordingly higher than expected, which is advantageous at least in that it allows a greater percentage of the carbon dioxide to be sequestered in carbonate(s).Capture of Gaseous Carbon Dioxide

[0135] FIG. 2 shows an example method for sequestering carbon dioxide, according to some embodiments. At 210, CO2 is captured from an industrial source into an aqueous solution that contains carbonates to form a CCh-enriched solution. At 220, the captured CO2 is hydrated to form carbonic acid (H2CO2) as denoted by chemical process (3), which then quickly loses a proton (H+) to become bicarbonate (HCCh') as denoted by chemical process (4). The proton then attacks the limestone surface and causes dissolution turning it into calcium (Ca2+) and bicarbonate (HCO3’) as denoted by chemical process (5). This has the result of increasing the bicarbonate concentration to significantly above that found naturally occurring in the ocean.

[0136] According to some embodiments, gaseous CO2 is first captured from a gaseous CO2 stream (210), such as from a fossil power plant’s emissions or an industrial source. Gaseous CO2 is captured in the solution as aqueous CO2, according to some embodiments. In some embodiments, the gaseous carbon dioxide is captured in an aqueous carbon dioxide stream by bubbling the gaseous carbon dioxide in a bubble column reactor. For example, according to some embodiments, the reactor is designed as a vertical column filled with an aqueous alkaline solution, which serves as the CO2 absorbent. The gaseous CO2 stream, such as flue gases from a power plant, are introduced at the bottom of the column through a series of spargers, which disperse the gas into small bubbles, allowing for a large surface area contact between the gas and the liquid phase. The gaseous CO2 stream can include other gases in addition to CO2 gas.

[0137] As the flue gas bubbles rise through the column, the CO2 in the gas phase diffuses into the solution, which can be an aqueous alkaline solution, where it reacts to form bicarbonate and carbonate species (220). The solution can be an alkaline solution composed of compounds such as calcium carbonate (limestone), calcium oxide (lime), sodium hydroxide, magnesium hydroxide and others. Alkaline solutions are used as they can neutralize the acidity from the carbonic acid, and convert the CO2 to bicarbonate. Use of an alkaline solution can buffer the acidity and facilitate conversion of CO2 to bicarbonate. In some embodiments, metal oxides and hydroxides can be used, such as CaO, MgOH. In some embodiments, using a cation exchange can reduce the calcium level.

[0138] In some embodiments, the bubble column reactor is operated under conditions that favor the transfer of CO2 from the gas phase to the liquid phase. Parameters such as the height of the liquid column, the concentration of the alkaline solution, and the residence time of the gas bubbles are optimized based on the specific properties of the gas stream and the desired level of CO2 capture. The reactor may also include internals such as packing or trays to increase thegas-liquid contact time, enhancing the CO2 capture rate.

[0139] In some embodiments, the bubble column reactor is configured for continuous operation, with the gas stream being constantly fed into the reactor and the CO2 -enriched aqueous solution being continuously drawn off, such as for a next step of removing CO2 from the aqueous solution or degassing the aqueous solution. This constant flow can help enable a steady state of operation, where the concentration of CO2 in the aqueous phase is kept at an optimal level for subsequent processing steps.

[0140] The simple construction and operation of bubble column reactors make them a cost-effective choice for integration with existing power plant infrastructure particularly for the large volumes of CO2 gasses that a power plant emits, according to some embodiments.

[0141] In some embodiments, other methods for capturing the carbon dioxide are used. For example, in some embodiments, the gaseous carbon dioxide is captured as aqueous carbon dioxide using packed bed reactors, where the gas flows through a packed column filled with the alkaline solution, allowing extended contact time for CO2 absorption; fluidized bed reactors, utilizing a fluid-like behavior of the solid-liquid mixture for efficient gas-liquid contact; spray towers, where the alkaline solution is sprayed into a column through which the C Ch-rich gas flows; rotating disc contactors, offering high surface area for gas-liquid interaction through a series of rotating discs; membrane contactors, where semi-permeable membranes facilitate direct contact between the gas and the absorbing solution without actual mixing; and / or jet bubbling reactors, where high-velocity jets of the alkaline solution create fine bubbles for effective CO2 capture. Each of these reactor types offers unique advantages in terms of efficiency, scalability, and adaptability to specific industrial needs for CO2 capture.

[0142] In some embodiments, the CO2 may be captured from emissions of power plants or industrial processes. In some embodiments, the partial pressure of the CO2 (pCCh) from the industrial source may be increased to achieve the desired concentrations of aqueous CO2 for thestep 230. For example, the partial pressure of gaseous carbon dioxide is increased to generate a threshold level of aqueous carbon dioxide. In some embodiments, additional alkalinity may be added to the solution to reach a threshold level of the carbonate in the solution, according to some embodiments. The threshold levels can be predetermined as being acceptable range(s) and / or acceptable value(s) for the particular purpose. For example, FIGs. 6A and 6B show exemplary values, according to some embodiments.

[0143] In some embodiments, an acceptable threshold pCC>2 range where the process is particularly well suited for industrial sources may be between 30,000 and 200,000 micro atmospheres. Above 200,000 p atm the percentage of the captured CO2 that has to be removed to reach the target pH level may be too high to make the process efficient. Whereas below 30,000 p atm, the solubility of CO2 in water may be too low to make the process efficient. In some embodiments, the partial pressure adjustment of CO2 may be achieved using a membrane separation technique.

[0144] In some embodiments, the concentration of alkalinity used varies with local oceanic environmental conditions and pCC>2 pressure in the solution (or from the flue gas). In some embodiments, the alkalinity used (e.g., to generate the aqueous solution in which CO2 is captured) as a function of CO2 concentration can be determined by the use of an ocean carbonate chemistry models, such as CO2SYS, as shown in FIG. 11. FIG. 11 is a graph showing example alkalinity concentrations as a function of flue gas CO2 concentration, according to some embodiments. In some embodiments, for optimal efficiency, sufficient alkalinity should be in the solution to neutralize enough of the CO2 to reach the desired pH levels while ensuring excessive levels of unreacted alkalinity does not waste the alkaline material or exceed total suspended solids requirements for disposal. In some embodiments, the alkalinity adjustment may be achieved by grinding limestone to 50 microns with a ball mill and then mixing it with the solution in a mixing vessel. In some embodiments excess alkalinity is captured and reused, with a smaller size following partial dissolution providing an increased surface area to mass ratio, resulting in improved dissolution rates.

[0145] FIG. 11 shows example total amounts of alkalinity used in a solution depending on the concentration of CO2 gas in the solution, according to some embodiments. According to embodiments, the total alkalinity is in a range from 6500 to 16500. According to embodiments, the total alkalinity is in a range from 7500 to 15500. According to embodiments, the total alkalinity is in a range from 8500 to 14500. According to embodiments, the total alkalinity is in a range from 9500 to 13500. According to embodiments, the total alkalinity is in a range from 10500 to 12500. According to embodiments, the total alkalinity is in a range from 11500 to 12000.Removing Aqueous Carbon Dioxide From the Solution

[0146] According to embodiments, the method for mitigating the undesirable effects of oceanic acidification, CO2 off-gassing, and precipitation in sequestering carbon dioxide can be integrated into an AWL system following the steps 210 and 220 as exemplified in FIG. 2.

[0147] At 230, CO2 is removed from the solution to get the partial pressure of CO2 of the solution closer to, at or below that found naturally occurring in the ocean. For example, the CO2- enriched solution may be subjected to a controlled degassing process to precisely manage the partial pressure of CO2. In some embodiments, removal of CO2 from the solution increases the pH, such as close to, at, or above the CO2 level found in the ocean or other body of water the solution is to be released into. This can help prevent acidification of the body of water upon release of the solution. This can also increase the concentration of carbonates in the solution, such as by increasing the amount of aqueous CO2 that is durably stored as carbonates in the solution. The concentration of CO2 in the solution and / or the desired pH of the solution (or acceptable range(s)) are configured according to various processes described herein.

[0148] In some embodiments, following the capture of gaseous CO2 into aqueous CO2 in the solution (210), bicarbonate is derived from the aqueous carbon dioxide in the solution (220) prior to removing aqueous carbon dioxide in the solution at step 230. For example, a solid carbonate is reacted in the solution with acid derived from the aqueous carbon dioxide to producea bicarbonate, such as according to chemical process (3), chemical process (4), and / or chemical process (5) and / or an accelerated weathering of limestone (or other carbonate) process.

[0149] Alternatively or in addition, in some embodiments, following the capture of gaseous CO2 into aqueous CO2 in the solution, such as upon exiting the reactor(s) used to effect the capture, the solution is a CCh-enriched aqueous solution containing an increased concentration of aqueous CO2 due to the CO2 capture such as via an absorption process. The solution is then directed to an aqueous carbon dioxide removal step 230. For example, in some embodiments, the solution is provided to a degassing chamber. In some embodiments, in the degassing chamber, the absorbed aqueous CO2 is removed before sequestration in the ocean or other body of water.

[0150] In some embodiments, removing the aqueous carbon dioxide comprises degassing the aqueous carbon dioxide. Carbon dioxide gas is generated from the aqueous carbon dioxide, according to some embodiments. For example, in some embodiments, degassing the aqueous carbon dioxide is by vacuum degassing. An example method of vacuum degassing will now be described according to some embodiments. The process begins by transferring the aqueous carbon dioxide (e.g., CCh-enriched aqueous solution) into a sealed degassing tank. Once sealed, the internal atmosphere of the tank is subjected to a vacuum. The vacuum is created by a vacuum pump, which reduces the pressure within the tank to a predetermined level below atmospheric pressure. This reduction in pressure decreases the solubility of aqueous CO2 in the solution, causing the dissolved CO2 to outgas, or separate, from the liquid phase. In some embodiments, CO2 reduction levels to match ambient pH result in pCO2 levels between 3 and 7 times larger than atmospheric levels for industrial flue gas concentrations, making low grade vacuum pressures of between 0.2 and 0.5 bar sufficient. In some embodiments, about 1 bar can be used.

[0151] The vacuum degassing tank may be equipped with a series of baffles or structured packings that increase the contact surface area between the gas and liquid phases. As the solution flows over these structures, the reduced pCC>2 pressure allows the CO2 to escape more efficiently from the solution. In some embodiments, the rate of flow, pressure settings, and the temperatureof the solution are meticulously controlled to optimize the release of CO2 while maintaining the integrity of the aqueous solution and preventing the excessive loss of alkalinity. In some embodiments, water is combined with the solution in a degassing process to dilute the solution and meticulously control the carbonate saturation state, preventing it from exceeding the saturation threshold.

[0152] This degassing method is particularly advantageous due to its simplicity, efficiency, and the ability to fine-tune the process parameters to accommodate various solution compositions and desired CO2 removal rates and carbonate nucleation timelines, according to some embodiments. In some embodiments, waste heat from an industrial process, like a thermal power plant, or heat from another source, can be used to accelerate rate of degassing by increasing the temperature of the solution. In some embodiments, the water used for dilution also provides cooling of the solution, which can be used to slow the rate of degassing.

[0153] In some embodiments, the aqueous carbon dioxide is circulated to increase exposure of the aqueous carbon dioxide to a lower pressure environment. For example, to enhance the degassing efficiency, the solution may be agitated or circulated within the tank. This can be achieved by a stirring mechanism or a recirculation loop, which helps to release more CO2 by constantly renewing the interface between the solution and the low-pressure environment. The agitation process is carefully managed to prevent the formation of foam or excessive turbulence, which could reduce the efficiency of CO2 removal.

[0154] In some embodiments, degassing the aqueous carbon dioxide is by membrane contactor. In some embodiments, the membrane contactor is a liquid-to-liquid contactor that allows the selective diffusion of aqueous CO2 while acting as a barrier that prevents direct mixing of the two liquid phases. An example method of liquid-to-liquid membrane degassing will now be described according to some embodiments. The process begins by flowing CCh-rich solution on one side of the semi-permeable membrane, while the water from the local body of water flows on the other side. The CO2 concentration gradient between the two liquids drives CO2 gas todiffuse from the CO2 rich solution, across the membrane, and into the CO2 lean solution, where the CO2 is physically absorbed, thus removing CO2 from one solution while enriching the other.

[0155] This liquid-to-liquid membrane contactor method is particularly advantageous as it provides efficient CO2 removal from the solution while maintaining the calcium carbonate concentration in the solution while also providing efficient CO2 capture for a new solution that can be recycled back into the process.

[0156] In some embodiments, degassing the aqueous carbon dioxide is done by air sparging, where ambient air is bubbled through the solution, absorbing gaseous CO2 into the bubbles, which remove it from the solution by buoyancy.

[0157] In some embodiments, other mechanisms for degassing can be used in combination or in the alternative. For example, in some embodiments, the degassing comprises applying an electrical current in the aqueous carbon dioxide stream to generate gaseous carbon dioxide. This can involve use of electrochemical cells where an applied electrical current induces the release of CO2 from the solution. This method allows for precise control over the degassing process and can be fine- tuned based on the specific requirements of the CO2 concentration in the solution. As a further example, the degassing comprises ultrasonic degassing to generate gaseous carbon dioxide, where high-frequency sound waves create microbubbles in the solution, providing a large surface area for CO2 to escape. This method can be particularly effective in rapidly degassing large volumes of solution, making it suitable for industrial-scale applications. Both methods offer the advantages of controlled, efficient CO2 removal while minimizing energy consumption and operational costs, according to some embodiments.

[0158] As further examples, the degassing comprises thermal degassing, where heat is used to increase the solution's temperature, thereby reducing CO2 solubility; rotating packed beds, which utilize centrifugal force to enhance gas-liquid contact and facilitate CO2 escape; chemical swing absorption, where a chemical change induces CO2 release; and / or biological methods,where microorganisms are used to metabolize CO2, converting it into biomass or other compounds. According to various embodiments, each of these methods offers unique advantages in terms of efficiency, energy requirements, and suitability for different scales of operation, providing a range of options for optimizing the degassing step in CO2 capture and storage processes.

[0159] In some embodiments, CO2 is removed from the solution not merely by reducing the pCO2of the solution. Reducing pCO2 may be achieved by dilution with lower pCO2 water and this can reduce the degassing rate post release of the solution into the body of water during equilibration with the water, but may not reduce the total amount of CO2 lost. Accordingly, in some embodiments, advantageously, the CO2 is removed instead of simply reducing the partial pressure of CO2, and this can reduce or prevent degassing after the solution is released into the body of water, as well as raise the pH of the solution (e.g., so as to not acidify the body of water following release of the solution into the body of water). Other methods may attempt to decrease the partial pressure of CO2 without removing the CO2 from the solution, but this disadvantageously may not reduce the total amount of CO2 lost eventually to the atmosphere.Separation o f Degassed Carbon Dioxide from Aqueous Carbon Dioxide and Effect on pH and Carbonate Concentration in Solution

[0160] In some embodiments, gaseous carbon dioxide that is generated from decreasing the partial pressure of the aqueous carbon dioxide is separated from the aqueous carbon dioxide. For example, according to some embodiments, the CO2 gas that is separated from the solution is then collected from the top of the degassing tank. The system decreasing the partial pressure (e.g., a vacuum system) is designed to ensure a continuous flow of gas out of the system (e.g., out of the tank), which can reduce or prevent reintroduction of CO2 into the solution. The collected gaseous CO2 can be directed for further processing, storage, or utilization, as required by the overall carbon capture and storage strategy.

[0161] In some embodiments, the gaseous CO2 is recirculated back into the system and re-captured in solution as aqueous carbon dioxide such as according to CO2 capture methods described herein. Accordingly, in some embodiments, up to 100% of gaseous carbon dioxide (such as from flue gas from an industrial source) can be sequestered as carbonates according to methods described herein. For example, additional aqueous carbon dioxide in the solution is generated using the gaseous carbon dioxide produced from degassing the aqueous carbon dioxide, in some embodiments.

[0162] In some embodiments, the CO2 removed may be reintroduced into the same solution or a new solution. In some embodiments, up to 100% of the CO2 that was captured in the solution may be stored in solution as bicarbonate or carbonate. In some embodiments, about 95% to about 100% of the aqueous carbon dioxide is converted to the carbonates in the solution. In some embodiments, the method sequesters up to 100% of the captured dissolved inorganic carbon that enters the ocean in the sequestration step.

[0163] In some embodiments, the CO2 removed from the solution may be captured and sequestered through another method known in the art. In some embodiments, the CO2 removed from the solution may be captured and used in an external process.

[0164] In some embodiments, removing aqueous carbon dioxide increases the pH of the solution by reducing carbonic acid generated from the aqueous carbon dioxide, such as according to chemical process (3). The pH of the solution can be controlled according to the particular application by controlling the partial pressure of carbon dioxide in the aqueous solution (e.g., controlling the amount of carbon dioxide off gassed from the solution). In some embodiments, the pH of the solution is raised to a target level (e.g., within a range or to a specified value or approximate value). For example, in some embodiments, the partial pressure of the aqueous carbon dioxide is decreased to a level to increase the pH of the solution to an ambient pH. The ambient pH can be a local pH of the body of water that the solution is to be released into, such as the ocean. In some embodiments, the pH of the solution is increased or set to an ambient pH, toan ambient pH or above an ambient pH, at about 8.2, or within a range from about 7 to about 9, about 7.5 to about 8.5, or about 7.9 to about 8.3. The pH of the solution can be raised or set to other pH values or pH ranges, according to various embodiments. In some embodiments, a pH of the solution is adjusted to increase conversion of the aqueous carbon dioxide to the carbonates in the solution. This can be by other methods in addition to or alternatively to decreasing the partial pressure of carbon dioxide. In some embodiments, the pH can be raised by the addition of another stronger source of alkalinity to the solution, such as NaOH, MgOH, and / or other hydroxides.

[0165] In some embodiments, the pH is indirectly controlled by directly controlling the partial pressure of the aqueous carbon dioxide in the solution. For example, in some embodiments, the partial pressure of the aqueous carbon dioxide in the solution is decreased to an ambient aqueous carbon dioxide partial pressure, such as the ambient partial pressure of aqueous carbon dioxide in a body of water that the solution is to be released into. For example, the partial pressure in the solution is decreased to about a partial pressure of carbon dioxide in the ocean.

[0166] Advantageously, in some embodiments, the pH of the solution is controlled to prevent or reduce likelihood of acidification of a body of water that the solution is released into. This can allow for carbon dioxide capture of flue gas from industrial processes that would otherwise be released as pollutant into the environment to be effectively sequestered (e.g., as carbonates in solution) and released directly into the environment such as the ocean without adversely affecting the pH of the ocean. Furthermore, where the pH of the solution is controlled to match the pH of the body of water that the solution is to be released into, this can reduce the amount of aqueous carbon dioxide in the solution that is out-gassed when the solution reaches equilibrium with the body of water. For example, if the pH of the solution were increased to be too much higher than the pH of the body of water that the solution is released into, when the solution’s pH decreases as equilibrium with the body of water is reached, a greater amount of carbonates in the solution can be converted to carbon dioxide and reverse the desired sequestration process. This can be by a reversal of chemical process (3) and / or chemical process (4), which can lead to a reversal of chemical process (2), for example.

[0167] In some embodiments, the concentration of bicarbonate in the solution is increased by removing aqueous carbon dioxide, such as at step 230. For example, removing CO2 from the solution raises the pH of the solution, which shifts the carbonate chemistry equilibrium towards increased levels of bicarbonate, raising the bicarbonate concentration above the level found naturally in a body of water that the solution is to be released into (e.g., the ocean). In some embodiments, as another example in addition or in the alternative, embodiment, the concentration of carbonates in the solution is increased by using a carbonate ion pump. As another example in addition or in the alternative, the concentration of carbonates in the solution is increased by using an ion exchange to replace Ca2+(where calcium carbonate is used) with another ion, such as Mg2+. This reduces the concentration of calcium in the solution, lowering the calcium carbonate saturation state, which can result in additional capacity to hold carbonate in the solution without exceeding the calcium carbonate saturation state threshold, thus increasing the concentration of carbonates in the solution.Decreasing the Calcium Carbonate Concentration in Solution

[0168] At 240, the calcium carbonate saturation state (or saturation state of another carbonate) or calcium carbonate concentration is lowered to below a precipitation threshold. For example, the solution may be diluted with water that has a lower calcium carbonate saturation state in a tank. In some embodiments, advantageously, this allows more carbonates (converted from CO2) to be durably held in the solution without precipitation by increasing the pH of the solution by removing aqueous CO2.

[0169] In some embodiments, the method, at step 240, decreases the calcium carbonate (or, in some embodiments, other carbonate) saturation state of the solution such that it does not exceed a precipitation threshold. The threshold level it is permitted to reach may be determined, such as by a set-off value relative to a saturation state where precipitation occurs, such as over a specified period of time. In some embodiments, the increase in carbonate concentration does not result in precipitation of carbonates in the ocean. In some embodiments, the method may includediluting the treated solution either in a reactor or directly in the ocean to maintain the carbonate in solution. In some embodiments, the solution is mixed with ocean water (or water from another other body of water) to achieve a desired calcium carbonate saturation state before release into the ocean (or other body of water).

[0170] In some embodiments, the capacity of the solution to hold dissolved carbonate may be increased by exchanging at least some of the Ca2+ions (e.g., ions that participate in the reaction shown by chemical process (5)) for more soluble ions, such as Mg2+. In some embodiments, the calcium carbonate saturation state may reach 60 times the saturation point. In some embodiments, the calcium carbonate saturation state is configured to reach a desired saturation threshold, such as selected from the values shown in FIG. 6B or FIG. 6A. Example 1 and FIG. 6B or FIG. 6A include additional examples of calcium carbonate saturation states that can be achieved for various time spans, according to some embodiments. For example, in some embodiments, calcium carbonate saturation states are maintained below and / or reduced to be below = 30. In some embodiments, calcium carbonate saturation states are maintained below and / or reduced to be below = 20. in some embodiments, calcium carbonate saturation states are maintained below and / or reduced to be below = 15. in some embodiments, calcium carbonate saturation states are maintained below and / or reduced to be below = 10. in some embodiments, calcium carbonate saturation states are maintained below and / or reduced to be below = 5. In some embodiments, calcium carbonate saturation states are maintained below and / or reduced to be below = 60. in some embodiments, calcium carbonate saturation states are maintained below and / or reduced to be below = 50. In some embodiments, calcium carbonate saturation states are maintained below and / or reduced to be below = 40. In some embodiments, calcium carbonate saturation states are maintained below a range from = 15 to = 60.

[0171] In some embodiments, the carbonates in the solution do not precipitate. In some embodiments, the solution is not acidified by the sequestering of the CO2. In some embodiments, the sequestered CO2 may not result in acidification of the ocean. In some embodiments, the sequestered CO2 may be prevented from being released back into the atmosphere. In someembodiments, the method may include performing one or more additional steps.

[0172] In some embodiments, the calcium carbonate saturation is controlled according to the particular application by controlling the concentration of carbonate and calcium in the aqueous solution. In some embodiments, the calcium carbonate saturation state of the solution is lowered once it reaches a threshold level (e.g., within a range or to a specified value or approximate value). For example, in some embodiments, the calcium carbonate concentration of the aqueous solution is decreased to a level where it would not precipitate in the time it spends in the system. In some embodiments, the calcium carbonate concentration of the aqueous solution is decreased to a level where it would not precipitate in the body of water given the expected dilution in the body of water over the time. In some embodiments, the expected saturation states over time are determined by carbonate chemistry models taking into account the environmental conditions of the local body of water and the local hydrodynamics.

[0173] In some embodiments, the calcium carbonate saturation state of the solution is allowed to increase up to 60 times a fully saturated state prior to dilution in a reactor, according to various embodiments. In some embodiments, the saturation state is allowed to increase up to 30 times prior to dilution in a local body of water. In some embodiments, the calcium carbonate precipitation thresholds are determined by experimentation with local seawater in a process similar to Example 1.

[0174] In some embodiments, calcium carbonate (e.g., limestone) is added to the solution to prepare the original solution or facilitate AWL using aqueous carbon dioxide in the solution. In some embodiments, this calcium carbonate can be substituted as carbonate (e.g., another form of carbonate). In some embodiments, the carbonate salt that precipitates in a meaningful volume is calcium carbonate, and the saturation state referenced herein is only the calcium carbonate saturation state. In some embodiments, calcium carbonate or calcium carbonate saturation state refers to any polymorph of calcium carbonate, such as aragonite, calcite, and others.Releasing Solution Into Environment

[0175] At 250, the treated solution is released into the ocean such that the carbonates may be durably stored in the ocean, sequestering the CO2 from both the ocean and the atmosphere.

[0176] In some embodiments, following step 240 in the method, the solution is released into a body of water, such as the ocean or a natural or unnatural body of water. In some embodiments, the pH of the solution is adjusted to correspond to a pH of the body of water before the solution is released. This can be according to step 230 as described herein or, in addition to or in the alternative, in some embodiments, the pH of the solution is further adjusted by other methods, such as addition or removal of compounds, prior to release of the solution to the body of water. For example, in some embodiments, sources of more reactive alkalinity such as NaOH and / or MgOH are used.

[0177] In some embodiments, the solution is released into the body of water via coolant outflow pipes. For example, in some embodiments, releasing the solution into the ocean utilizes the existing infrastructure of an industrial plant’s coolant outflow pipes. These pipes, which typically discharge water used for cooling purposes during the power generation process, provide an efficient conduit for introducing the carbonate saturated solution into the oceanic environment.

[0178] In some embodiments, the solution, after undergoing a degassing process to reduce aqueous CO2 to the desired concentration (e.g., step 230) (which increases a concentration of carbonates in the solution) and decreasing the calcium carbonate saturation state to the desired level (e.g., step 240), is released. In some embodiments, the solution is released by conveying the solution through the power plant’s outflow pipes, which extend into the ocean and are designed to disperse the water into the ocean, ensuring a wide distribution of carbonates in the ocean.

[0179] In some embodiments, the outflow pipes are equipped with diffusers at their terminus, which break up the flow into smaller streams, enhancing the mixing with ocean water. This gradual mixing process helps to dilute the calcium carbonate and match the ocean’s naturalchemistry, facilitating the seamless integration of the treated solution into the ocean without disturbing the local ecosystem.

[0180] In some embodiments, the release process is monitored to ensure threshold levels of metrics are met, such as for compliance with environmental regulations. In some embodiments, pH, temperature, DIC, total alkalinity, pCO2, carbonate concentration, and / or other metrics of the body of water are monitored after the solution is released into the body of water.

[0181] In some embodiments, sensors are used to measure the pH, temperature, and / or carbonate concentration of the discharged solution, such as to monitor whether or confirm that the release does not harm the marine environment. The monitoring data is used for real-time adjustments and is recorded for environmental impact assessment and reporting to regulatory agencies. This can help ensure that the sequestered CO2 remains in the ocean, contributing to the long-term reduction of atmospheric CO2 levels while safeguarding marine life.

[0182] In some embodiments, the method may include monitoring the partial pressure of CO2 in the carbonate-enriched solution to ensure it matches with the desired sequestration parameters. In some embodiments, the solution may be released into the ocean at a depth where the ambient pressure may maintain the carbonate in a dissolved state. In some embodiments, the pH of the aqueous solution is adjusted to optimize CO2 absorption in the carbonate. In some embodiments, the method may be adaptable to different CO2 concentrations and water chemistries. In some embodiments, the sequestration method may be adaptable to variable oceanic conditions, including temperature, pressure, and salinity.

[0183] In some embodiments, a carbon dioxide sequestration system and method removes CO2 from an aqueous carbonate solution to raise the pH of the solution to match that of a local body of water without raising the calcium carbonate saturation state to the point that the carbonate would precipitate out of the solution when dispersed in the local body of water.

[0184] In some embodiments, the carbon dioxide sequestration system includes a monitoring device to measure the pH levels and calcium carbonate saturation state as CO2 is removed. If the calcium carbonate saturation state exceeds a predefined threshold (e.g., reaches near a precipitation threshold), the carbon dioxide sequestration system dilutes the solution with water from a local body of water (or in some embodiments, another solution), which is at ambient levels of pH and may be supersaturated with respect to calcium carbonate. In some embodiments, if the solution is under or oversaturated with respect to CO2 care is taken to ensure inadvertent ocean acidification does not occur. In some embodiments, the solution can be subjected to CO2 removal (e.g., via degassing) to further increase the pH and convert CO2 in the solution to dissolved carbonates in solution. In some embodiments, the solution is then discharged into the body of water only when it has a pH equal to that of the local body of water and a calcium carbonate saturation state that is below a predefined threshold (e.g., below a precipitation threshold or within a threshold range relative to the same), according to some embodiments.SYSTEM FOR SEQUESTERING CARBON DIOXIDE

[0185] It is expected that the described method can be readily integrated into any carbon dioxide sequestration system to further mitigate the undesirable effects of oceanic acidification, CO2 off-gassing, and precipitation in such systems. Exemplary systems illustrating the integration of the described method are provided.

[0186] FIG. 3 shows an example carbon dioxide sequestration system 300, according to some embodiments. Carbon dioxide sequestration system 300 includes a mixing vessel 310, a CO2 removal vessel 320, a monitoring and control system 330, a dilution vessel 340, and a discharge system 350, according to some embodiments.

[0187] In some embodiments, mixing vessel 310 is a sealed vessel designed to contain and treat the aqueous carbonate solution. Mixing vessel 310 is equipped with an inlet for introducing the solution and multiple sensors for monitoring pH and the calcium carbonate saturation state ( ). The sensors for monitoring could measure total alkalinity (TA) of thesolution, dissolved inorganic carbon or pCO2 levels in the solution. When combined with pH, these measurements can be used to track changes in . Monitoring and control system 330 is configured to receive these measurements from mixing vessel 310 and track changes in the same and / or in , according to some embodiments.

[0188] In some embodiments, mixing vessel 310 includes internal components, such as an agitator, that facilitate the dissolution of calcium carbonate and the conversion of CO2 into bicarbonate and carbonate ions. The chamber of mixing vessel 310 is optimized to ensure efficient mixing and chemical reaction equilibrium, according to some embodiments.

[0189] In some embodiments, CO2 removal vessel 320 is a sealed vessel designed to contain the mixed solution and remove excess CO2 from the solution. Equipment for the removal of CO2 from the solution is integrated into the vessel, and could be a(n): air sparger (a diffuser or perforated plate generating fine air bubbles for stripping CO2 from the solution); vacuum degasser (a degassing unit that uses reduced pressure to facilitate CO2 removal); membrane contactor (an apparatus that allows selective CO2 diffusion through a gas-permeable membrane); and / or gas outlet. The gas outlet can be an outlet for the removed gaseous CO2 (and air, if an air sparger is used). This gas can be captured or recycled back into the system, for example by using a wet limestone scrubber to capture the CO2 into an aqueous limestone solution.

[0190] In some embodiments, monitoring and control system 330 includes one or more sensors configured to measure one or more metrics, such as metrics of the aqueous solution, for example, pH, temperature, carbonate saturation level, total alkalinity, partial pressure of molecules such as carbon dioxide, and / or other metric. For example, in some embodiments, monitoring and control system 330 includes a pH sensor configured to continuously measure the pH of the solution and sends real-time data to a control unit; carbonate saturation state sensor configured to continuously measure the carbonate saturation state of the solution and send realtime data to a control unit; and a control unit including a central processor that uses input from the pH sensor and carbonate saturation state sensor to regulate the process and initiate dilution if desired (e.g., to raise or lower the pH and / or carbonate saturate state to target level(s) (e.g.,range(s) or value(s)). The target level(s) can be pre-determined and / or set in real-time based on measured levels of metrics of the environment, such as a body of water that the aqueous solution is to be released into. For example, sensor(s) in dilution vessel 340 or at an intake from outside dilution vessel 340 can be included to measure pH, carbonate saturation level, partial pressure of CO2, and / or other metric of the body of water, and monitoring and control system 330 is configured to increase and / or decrease a corresponding metric(s) or a related metric(s) of the aqueous solution accordingly, such as by diluting solution in dilution vessel 340 until threshold value(s) are met, according to some embodiments.

[0191] In some embodiments, dilution vessel 340 is a sealed vessel configured to contain the aqueous solution with ambient pH or equal to the precipitation threshold. In some embodiments, dilution vessel 340 includes a water intake system and a mixing mechanism. In some embodiments, the water intake system is connected to a local body of water and draws in water that is at ambient pH and carbonate saturation levels, which may be supersaturated with respect to calcium carbonate. In some embodiments, the mixing mechanism is an automated mixing system that is configured to blend the drawn-in ambient water with the treated solution to lower the until it reaches the desired level. The mixing is controlled by monitoring and control system 330 to achieve the desired dilution effect without raising the pH beyond target limits.

[0192] In some embodiments, discharge system 350 includes a filter(s), discharge port(s), and safety valve(s). The filter(s) include filtration components configured to remove solid calcium carbonate and other suspended solids, including any precipitated carbonate, to help meet regulatory requirements or threshold value(s) and to recapture any valuable, unreacted solid carbonate, which could be reused in the carbon sequestration system 300, according to some embodiments. This can be performed to remove suspended solids before release into the ocean to limit nucleation sites. For example, the filter(s) are configured to remove suspended solids from the solution and reduce the number of potential nucleation sites, thus lowering the likelihood of precipitation.

[0193] The discharge port(s) include an outlet for releasing the treated and diluted solution into the local body of water. The discharge is regulated by the monitoring and control system 330, which is configured to maintain or drive the solution to an ambient pH level and a that is below the precipitation threshold (although may be above ambient ), according to some embodiments. In some embodiments, monitoring and control system 330 is configured to maintain or drive the solution to other pH levels and / or levels by controlling the level and / or rate of discharge. The safety valve(s) are configured as a fail-safe mechanism to prevent discharge if either pH or saturation levels are outside the acceptable range (e.g., as measured by monitoring and control system 330, according to some embodiments).

[0194] FIG. 5 shows a further example system for carbon dioxide sequestration, according to some embodiments. As shown, a neutralization reactor replaces mixing vessel 310, and a stabilization reactor combines the functionality of and replaces the CO2 removal vessel 320 (e.g., degassing vessel) and dilution vessel 340, and stabilization reactor is configured to recirculate removed CChback into the solution (e.g., back to neutralization reactor) to convert the removed CCh into carbonates. In some embodiments, absorber column is configured to remove CCh from the solution, and provide the solution to neutralization reactor where the pH of the solution is increased and the solution is provided to stabilization reactor, which is configured to return the solution to an earlier system and / or adjust one or more parameters (metrics) of the solution (e.g., pH, saturation level) or discharge the solution into a body of water. This can be determined and controlled by monitoring and control system 330, such that the solution is only released to the body of water where the pH matches the pH of the body of water (or, in some embodiments, is within a threshold range relative to same) and where the carbonate saturation of the solution is below a precipitation threshold in the body of water.

[0195] Reagents shown may be substituted in other embodiments. For example, a different carbonate mineral may be substituted or used in combination with limestone. Mechanical components shown may be substituted in other embodiments. For example, the ball mill shown may be replaced with a crushing and grinding machine configured to crush and grind limestone.

[0196] The exemplary systems are designed to integrate the described method for mitigating the undesirable effects of oceanic acidification, CO2 off-gassing, and precipitation. FIG. 4A and FIG. 4B show the process steps carried out by such exemplary systems for carbon dioxide sequestration, according to some embodiments.

[0197] At 410 or 4100, CO2 and calcium carbonate solution enters the system, such as a containment vessel or a mixing vessel 310. The CO2 (or a portion thereof) is converted to bicarbonate. For example, in particular, an aqueous carbonate solution that has been enriched with CO2 is introduced into the containment vessel or a mixing vessel 310. In the containment vessel, the CO2 reacts with the water and calcium carbonate to form bicarbonate and carbonate. In some embodiments, a different carbonate other than calcium carbonate is used.

[0198] At 420 or 4200, CO2 acidifies the solution (e.g., water). This can occur according to chemical processes (3) and (4), for example, when the CO2 is converted to carbonic acid and bicarbonate is produced.

[0199] At 430 or 4300, the calcium carbonate is dissolved. This can occur according to chemical process (5), for example, when acid (e.g., carbonic acid) derived from the CO2 dissolves the carbonate mineral (e.g., calcium carbonate) to produce bicarbonate.

[0200] At 440, the calcium carbonate saturation state increases, and the pH increases. This can occur as bicarbonate is produced from the CO2, for example, according to chemical processes (3), (4), and (5). Steps 410, 420, 430, and 440 can occur concurrently, in some embodiments. For example, CO2 acidifies the water and dissolves the calcium carbonate, which causes the calcium carbonate saturation state to increase towards 1 (fully saturated).

[0201] At 450, the carbonate saturation state is monitored, such as by monitoring and control system 330. As the CO2 dissolves the calcium carbonate and is converted to bicarbonate and carbonate, the calcium carbonate saturation state ( ) rises and is measured by one or more sensors. Monitoring and control system 330 is configured to use this data to ensure the saturation state getssufficiently close to fully saturated ( = 1) before any CO2 removal occurs. In some embodiments, the reaction rate of CO2 to bicarbonate slows as approaches 1, thus there is a trade-off when deciding on the control parameters, between reaching a fully saturated state and the residence time spent in the vessel. Longer residence times require larger vessels while lower saturation states are less efficient at storing carbonate in the water, according to some embodiments. If the saturation level is not near full saturation, monitoring and control system 330 is configured to allow additional carbonate mineral (e.g., calcium carbonate) to dissolve and additional carbonates to be produced (additional conversion of CO2 to bicarbonate and carbonate).

[0202] At 460, CO2 is removed from the solution, such as at CO2 removal vessel 320. For example, in some embodiments, once is sufficiently close to 1 as indicated by the sensor readings, the solution is pumped to the CO2 removal vessel 320 and the CO2 removal process begins (e.g. with an air sparger, vacuum degasser, and / or membrane contactor) to desorb the excess CO2 and raise the solution’s pH to match that of the local body of water. For some seawater, this is about 8.1, for example. In some embodiments, when the carbonate saturation state is sufficiently close to 1 (within a threshold range), the solution is pumped, such as from the mixing vessel 310, to CO2 removal, such as at CO2 removal vessel 320.

[0203] At 470, the saturation state of calcium carbonate in the solution and the pH of the solution increases. For example, the pH rises towards ambient pH and the calcium carbonate saturation level rises towards the precipitation threshold, according to some embodiments. This occurs while CO2 is removed from the solution at step 460, for example. The pH and the calcium carbonate saturation state are monitored, such as by monitoring and control system 330. For example, as CO2 is removed, the carbonate saturation state rises above 1 (e.g. supersaturated) and is continuously measured. In fresh water, above 1, calcium carbonate may tend to precipitate out of solution over time. In seawater, there are natural mechanisms that inhibit this precipitation resulting in an of about 4. For CO2 concentrations consistent with industrial fossil fuel burning processes (> 2% CO2 in the flue gas), raising the pH to that of ambient seawater may lead to an of greater than the supersaturated levels of ambient water. As rises above the ambient level, thelikelihood of precipitation rises and the time to a precipitation event decreases. A specific threshold that takes these factors into consideration is therefore set, such as by the monitoring and control system 330, for the release of the solution. Specifically, the system, such as at monitoring and control system 330, takes into account the current (and expected) environmental conditions of the local body of water and the expected change in over time as it disperses into the body of water. In some embodiments, the monitoring and control system 330 is configured to use this data to help ensure that the pH matches that of the local body of water and that does not exceed the precipitation threshold, either of which could be detrimental on discharge. In some embodiments, instead of calcium carbonate, a different carbonate salt is used.

[0204] At 480, where either the pH in the solution reaches the threshold level or reaches the precipitation threshold, monitoring and control system 330 pumps the solution into the dilution vessel 340. If the ambient pH level has not been reached, monitoring and control system 330 is configured to activate an intake system to draw in water (or other solution) from a local body of water. The ambient water (solution) is mixed with the carbonate solution using an automated mixing mechanism, diluting the solution and, at step 490, lowering to the point where the solution can be returned to step 460, such as by pumping the solution back to the CO2 removal vessel 320 to remove more CO2 and continue raising the pH level. In some embodiments, if the is less than the precipitation threshold (or near), and the pH of the solution is less than or not at the target level (e.g., the ambient pH of the body of water the solution is to be released into as determined by sensor data), the solution is returned to step 460.

[0205] In some embodiments, at 480, instead of dilution such as at dilution vessel 340, the calcium carbonate saturation state in the solution is maintained below a time varying threshold. For example, in some embodiments, some of the calcium ions in solution can be exchanged with ions, such as magnesium, that bind to carbonate ions in the solution and reduce the concentration of calcium carbonate in solution, thereby increasing the capacity of the solution to store additional calcium carbonate and therefore an increased amount of CO2 can be converted to carbonate in the solution.

[0206] Monitoring and control system 330 is configured to help ensure that the dilution maintains below that of precipitation threshold of the local body of water, leveraging feedback from the carbonate saturation sensor to fine-tune the mixing process, according to some embodiments.

[0207] In some embodiments, when the carbonate saturation state reaches the precipitation threshold, the solution is diluted, such as pumped to dilution vessel 340 and supersaturated water from a local body of water (having an ambient carbonate saturation level) is pumped into the dilution vessel 340, and the solution is mixed with the water from the local body of water. Once the carbonate saturation level in the solution is lowered sufficiently below the precipitation threshold, the solution is subjected to CO2 removal, such as by being pumped back to the CO2 removal vessel 320.

[0208] At 495 or 4950, the solution is discharged into the body of water. Once the solution reaches the target pH and Q is below the precipitation threshold for the local body of water, monitoring and control system 330 is configured to release the solution, such as by opening a discharge port, such as of discharge system 350. The discharge is halted if any parameter drifts out of range, activating the safety valve as a precautionary measure, according to some embodiments. In some embodiments, once the pH of the solution reaches an ambient pH (or other target pH range or value), the solution is discharged into the body of water.

[0209] In some embodiments, steps 410 to 495 are performed in the respective vessels and systems shown in FIG. 3, namely, mixing vessel 310, CO2 removal vessel 320, dilution vessel 340, and discharge system 350. In some embodiments, steps 410 to 495 are performed in alternative vessel(s) and / or system(s). For example, in some embodiments, a single vessel can be configured to receive a starting aqueous solution (e.g., containing aqueous CO2 and carbonates or other alkaline material), configured to remove CO2 (such as using apparatuses or methods described herein such as in relation to lowering the partial pressure of CO2), configured to receive intake solution (e.g., water intake from a surrounding body of water that the solution is to be released into), and configured to discharge the solution once pH target levels and / or carbonatesaturation threshold levels are reached. This can be controlled by a monitoring and control system 330, for example. In some embodiments, monitoring and control system 330 is configured to incrementally dilute the solution in the single vessel, while degassing the CO2 in the solution (or otherwise removing the CO2), such that even though the partial pressure of CO2 is decreased, the concentration of the carbonate in the solution does not change.

[0210] To gain a better understanding of the invention described herein, the following examples are set forth. It will be understood that these examples are intended to describe illustrative embodiments of the invention and are not intended to limit the scope of the invention in any way.EXAMPLESEXAMPLE 1: Calcium Carbonate Saturation States

[0211] The Matlab program CO2SYS was used to calculate the calcite saturation state ( ) of seawater at a salinity of 35 under various alkalinity increases due to calcium carbonate dissolution using embodiments of the methods disclosed herein. The modeled calcium concentration of the seawater was altered to reflect an increase in [Ca] per change in alkalinity concentration in the stoichiometric ratio of 1 :2 under calcium carbonate dissolution (e.g., as effected by the dissolution of calcium carbonate by carbon dioxide in the solution during embodiments of methods disclosed herein). In order to reflect how degassing of carbon dioxide (e.g., after release of the solution into the seawater) to different endpoints would affect the calcite saturations state, modeled solutions were equilibrated to either the starting pH or an atmospheric pCO2 of 420 ppm. According to some embodiments, these modelling methods can be used to determine or select a calcium carbonate saturation state to be achieved for the solution (e.g., achieved at a point during operation of the methods or at a point prior to release of the solution into the body of water) based on the desired parameters or context (e.g., desired length of time to precipitation, absence of precipitation, known pH level of seawater, known atmospheric pCC>2 of environment where solution is to be released, or other parameters of the body of water orenvironmental conditions in which the solution is to be released). Similarly, in embodiments where other carbonate salts are used, similar modelling can be performed to select a desired carbonate salt saturation state. For example, in some embodiments, monitoring and control unit 330 is configured to increase a pH of the solution until the desired calcium carbonate saturation state is reached, while actuating dilution of the solution to decrease the calcium carbonate saturation state below a precipitation threshold, the precipitation threshold being the concentration of calcium carbonate at which calcium carbonate will precipitate over a specified period of time.

[0212] For example, in embodiments where it is not desired for calcium carbonate to precipitate until two weeks later, the calcium carbonate saturation state of the final solution before release into the body of water having a specified pCCh or specified pH can be determined, and monitoring and control unit 330 is configured to increase the pH of the solution by removing CO2 until a target pH is reached, the target pH being the pH at which the desired calcium carbonate saturation state is reached. In various embodiments, any calcium carbonate saturation state shown in FIG. 6A or FIG. 6B that is below the precipitation thresholds denoted by the horizontal lines can be selected as the final calcium carbonate saturation states in the solution released.Results

[0213] FIG. 6A is a graph showing calcite saturation versus total alkalinity from calcium carbonate dissolution in the solution, according to some embodiments. FIG. 6B is a graph showing calcite saturation versus alkalinity from calcium carbonate dissolution in the solution, according to some embodiments.

[0214] FIG. 6A and FIG. 6B show the amount of alkalinity added from calcium carbonate dissolution on the y-axis compared to the saturation state of calcite ( ) for seawater at four different temperatures, 5°C, 15°C, 25°C, and 35°C. FIG. 6A shows the saturation state when the solution is equilibrated back to atmospheric pCO2 (420 ppm) while FIG. 6B shows the solution equilibrated back to the initial seawater pH before any alkalinity was added. The calcite saturation state was calculated at a salinity of 35. Calculations were conducted in CO2SYS which wasamended to increase the concentration of calcium equivalent to the amount of calcium carbonate dissolved (e.g., by carbon dioxide through an AWL process using embodiments of methods described herein) to better reflect changes in . The horizontal lines shown represent saturation state thresholds when secondary precipitation has been observed to occur, namely, from top to bottom, = 30 (<1 day), Q = 20 (4 days), and Q = 15 (15 days). Experiments were conducted in the lab to determine temperatures and alkalinity concentrations that matched up with the predicted amount of time the solution was stable in terms of calcium carbonate precipitation according to the present modelling. With the parameters of FIG. 6A, data was collected from those experiments showing that at +3000 TA at 25°C, = 23 (or in a range from 20 to 25), according to some embodiments. With the parameters of FIG. 6A, data was collected from those experiments showing that at +3000 TA at 5°C, = 13 (or in a range from 10 to 15), according to some embodiments. With the parameters of FIG. 6B, data was collected from those experiments showing that at +3000 TA at 25°C, Q = 14 (or in a range from 10 to 15) and that at +14000 TA at 25°C, = 60 (or in a range from 50 to 75) and that at +3000 TA at 5°C, = 5 (or in a range from 2 to 10), according to some embodiments.

[0215] As shown, the +14000 solution began precipitating almost instantaneously once the solution was equilibrated back to a pH of 8.1, while the +3000 solution was still stable except for the pCO2 equilibrated one at 25°C which started to precipitate at four days.EXAMPLE 2: VALUES FOR FURTHER PARAMETERS

[0216] According to some embodiments, artificial seawater was made by mixing deionized water and Instant Ocean Reef Crystals until a salinity of 34.5 was reached. The seawater was placed in Reef Octopus SRO 3000-D Calcium Reactor with coarse Aragonite Reactor Media (ARM). The pH of the calcium reactor was set to different levels to dissolve the aragonitic media and obtain total alkalinity concentrations of -5300 and -16300 pmol kg-1. These concentrations represent increases above natural seawater alkalinity of the same salinity (34.5) of -3000 and -14000 pmol kg-1, respectively. Once the desired alkalinity level was reached, the seawater solution was 0.2 pm filtered and equilibrated back to a pH of 8.1 or the pCO2 of the laboratory(-450 ppm) by bubbling ambient air and pure nitrogen into the solution. The equilibrated solutions were pipetted into 20mL borosilicate crimp top vials that were previously acid washed and UV sterilized. The filled vials were then UV sterilized for an additional 60 minutes before being placed in incubators set at 5 and 25°C. Vials were then destructively sampled over a time series and titrated for total alkalinity using a Metrohm 888 Titrando.Results

[0217] FIG. 7A is a graph showing alkalinity from calcium carbonate in the solution over time following carbon dioxide sequestration, according to some embodiments. FIG. 7B is a graph showing dissolved inorganic carbon levels in the solution over time following carbon dioxide sequestration, according to some embodiments. FIG. 7C is a graph showing carbonate saturation state in the solution over time following carbon dioxide sequestration, according to some embodiments. FIG. 7D is a graph showing pH in the solution over time following carbon dioxide sequestration, according to some embodiments.

[0218] FIGs. 7A to 7D show four parameters measured (total alkalinity (TA), DIC, calcite saturation state, and pH) at an elevated alkalinity of 3000 or more above seawater, at 5°C and 25°C for each of contexts where (i) the pH of the solution once released is equilibrated; and (ii) the pCO2of the solution once released is equilibrated to atmospheric pCO2. According to some embodiments, such experiments and modelling can be used to select various desired parameters (e.g., total alkalinity, pH, pCO2, temperature, DIC of the solution, calcite saturation state) when performing methods described herein, such as steps 110 and 120; steps 210 to 250; steps 4100 to 4950; steps 410 to 495; or using systems described herein, such as shown in FIG. 3 or FIG. 5.

[0219] For example, as shown, according to some embodiments, the only solution to precipitate is the solution at 25°C released in a body of water causing the equilibration of pCO2 (e.g., pCO2equilibrated waters) (shown in FIG. 7A). In contrast, the solution at 5°C released in a body of water causing equilibration of pCO2 equilibration was still stable at 13 days out despite having a similar saturation state as the solution with the method performed at 25°C.EXAMPLE 3: SIMULATION MODELLING OF THE EFFECT OF pH AND CALCIUM CARBONATE SATURATION STATE ON DURABLY STORED CARBON

[0220] FIG. 9 shows example CO2 removal targets according to some embodiments, such as performed at step 110, 230, or 460, or vessel 320 or neutralization reactor in FIG. 5. FIG. 9 shows the percentage of dissolved inorganic carbon that may be durably stored in the ocean as bicarbonate and carbonate as a function of the initial concentration of CO2 in a flue gas.

[0221] The numbers are based on modeling of ocean carbonate chemistry using the CO2SYS software. They assume the solution starts with seawater at a temperature of 16°C, salinity of 35, total alkalinity of 2314 peq / kg, and Ca2+concentration of 10.12 mmol / kg, yielding an initial calcite saturation state of = 3.83 and a pH of 8.03. The simulation uses KI, K2 (the first and second dissociation constants for carbonic acid), each of which are hereby incorporated by reference in their entireties.

[0222] In the cases depicted, in order to illustrate embodiments of the present disclosure, seawater starts equilibrated with atmospheric CO2 at a concentration of 420 ppm and is then fully equilibrated with CO2 at the specified flue gas concentration, then sufficient calcite is added to the solution to raise the calcite saturation state to fully equilibrated ( = 1). Then the level of total Dissolved Inorganic Carbon (DIC) in the solution is reduced until one of the three target levels is achieved (simulating the CO2 removal targeting approach taken according to embodiments, such as at step 110 of FIG. 1). The solution is then diluted with 100 parts of ambient seawater (at the initial conditions specified above) before it is fully equilibrated with atmospheric CO2 at the initial concentration specified above. For example, this dilution simulates step 120, while the equilibration with atmospheric CO2 simulates equilibration with atmospheric CO2 after the solution is released into a body of water such as the ocean and allowed to equilibrate over time.

[0223] The ambient Q case follows the approach taken in the foregoing and, in the modelling shown, allows the calcite saturation state of the solution to rise to the ambient Q = 3.83, using embodiments of the present disclosure.

[0224] The ambient pH case represents an embodiment and, in the modelling shown, allows the pH of the solution to rise to the ambient pH = 8.03, using embodiments of the present disclosure.

[0225] The ambient pH + 0.27 case represents an embodiment and, in the modelling shown, allows the pH of the solution to rise to pH = 8.30, using embodiments of the present disclosure.

[0226] Embodiments of the present disclosure are therefore demonstrated to achieve higher levels of durably stored carbon and, in some embodiments, can store above the 75% level required by the EPA to qualify for 45Q credits and can rise to 100% under certain conditions.EXAMPLE 4: SIMULATION MODELLING OF CALCITE SATURATION STATES DURING DEGASSING OF CO2TO REACH AMBIENT pH

[0227] FIG. 10 shows a graph relating the saturation state of calcite to initial CO2 concentration (from a gaseous CO2 stream prior to capture at the start of methods described herein, such as at step 210). FIG. 10 depicts the maximum calcite saturation state that is expected to be reached when degassing the solution (e.g., at step 110 or 230) to an ambient pH level for a range of initial CO2 concentration levels in a flue gas, according to some embodiments.

[0228] The modelling was performed by following the process outlined in respect of FIG. 9 for the ambient pH case and simulates the calcite saturation state as a function of the CO2 concentration in the initial flue gas.

[0229] These levels can be used to help determine the expected precipitation time frames and to select the appropriate dilution approach, according to some embodiments. For example, any data point shown in FIG. 10 can be selected to select a calcite saturation state to be reached such as to determine a pH target to be reached by the removal of carbon dioxide at step 110 or 230, at the appropriate initial CO2 concentration in the initial flue gas received at the beginning of the method, according to various embodiments.EXAMPLE 5: SIMULATION MODELLING FOR DETERMINING ALKALINITY LEVELS FOR CO2 GAS CONCENTRATION

[0230] FIG. 11 depicts the amount of total alkalinity that is expected to be required to raise the calcite saturation state to saturated for a range of initial CO2 concentration levels in a flue gas.

[0231] The modelling was performed by following the process outlined in respect of FIG. 9 (for all three cases) and simulates the total alkalinity that would be required in solution (inclusive of the initial alkalinity of 2314 peq / kg) to raise the calcite saturation state to a saturated state ( = 1).

[0232] These levels can be used to help determine the expected precipitation time frames and to select the appropriate dilution approach. For example, any data point shown in FIG. 11 can be selected to select a total alkalinity in the solution to be produced such as to determine a pH target to be reached by the removal of carbon dioxide at step 110 or 230, or such as to determine a carbonate concentration level to be reached in the solution by the removal of carbon dioxide at step 110 or 230, each at the appropriate initial CO2 concentration in the initial flue gas received at the beginning of the method, according to various embodiments.EXAMPLE 6 SIMULATION MODELLING FOR DETERMINING BICARBONATE CONCENTRATION

[0233] FIG. 12 depicts the bicarbonate concentration that is expected to be reached per kg of seawater that flows through the CO2 removal step for various CO2 removal targeting strategies using embodiments of methods described herein (e.g., at step 110 or 230).

[0234] The modelling was performed by following the process outlined in respect of FIG. 9 (for all three cases) and simulates the bicarbonate concentrations that can be reached in solution as a function of concentration of CO2 in flue gas.

[0235] In some embodiments, compared to AWL without using methods described herein, a difference therefore lies in CO2 concentrations achieved in the solution (and thus acidity levels and the proportion of DIC that is durably stored). That is, embodiments described herein can achieve a lower CO2 concentration in solution than other methods.

[0236] The disclosures of all patents, patent applications, publications and database entries referenced in this specification are hereby specifically incorporated by reference in their entirety to the same extent as if each such individual patent, patent application, publication and database entry were specifically and individually indicated to be incorporated by reference.

[0237] Although the present disclosure has made reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art. All such modifications as would be apparent to one skilled in the art are intended to be included within the scope of the following claims.

Claims

CLAIMSWhat is claimed is:

1. A method for sequestering carbon dioxide from an aqueous solution comprising aqueous carbon dioxide and carbonates, the method comprising:(i) removing aqueous carbon dioxide from the solution, wherein the solution has a pH below a pH threshold and the aqueous carbon dioxide is removed until the pH of the solution is increased to a pH above the pH threshold, wherein the pH threshold is a pH at which a precipitation threshold of a carbonate salt in the solution is reached; and(ii) reducing the carbonate salt saturation state of the solution to decrease the carbonate salt saturation state to below the precipitation threshold; wherein the aqueous carbon dioxide is sequestered, and acidification and precipitation of carbonates is mitigated, on release of the solution into a body of water.

2. The method of claim 1, wherein the aqueous carbon dioxide is removed until the pH of the solution is increased to ambient pH.

3. The method of claim 1, wherein the aqueous carbon dioxide is removed until the pH of the solution is increased to a pH of about 8.2.

4. The method of claim 1, wherein the aqueous carbon dioxide is removed until the pH of the solution is increased to a pH range of about 7 to about 9.

5. The method of any one of claims 1 to 4, wherein removing aqueous carbon dioxide comprises degassing the aqueous carbon dioxide.

6. The method of claim 5, wherein the degassing comprises vacuum degassing.

7. The method of claim 5, wherein the degassing comprises using a membrane contactor.

8. The method of claim 5, wherein the degassing comprises using a liquid-to-liquid membrane contactor, wherein gaseous CO2 is transferred across the membrane from a high pCO2liquid to a low pCO2liquid, producing a liquid solution that is enriched with CO2and a second liquid solution enriched with bicarbonate.

9. The method of claim 5, wherein the degassing comprises applying an electrical current in the aqueous carbon dioxide stream to generate gaseous carbon dioxide.

10. The method of claim 5, wherein the degassing comprises ultrasonic degassing to generate gaseous carbon dioxide.

11. The method of claim 5, wherein the degassing comprises thermal degassing.

12. The method of claim 5, wherein the degassing comprises using rotating packed beds.

13. The method of claim 5, wherein the degassing comprises using chemical swing absorption.

14. The method of claims 5, wherein the degassing comprises using at least one selective permeable membrane.

15. The method of claim 5, wherein the degassing comprises using a liquid to liquid membrane contactor.

16. The method of claim 5, wherein the degassing comprises using microorganisms to metabolize the carbon dioxide.

17. The method of any one of claims 1 to 16, wherein the carbonate salt is calcium carbonate.

18. The method of any one of claims 1 to 17, wherein the carbonate saturation state of the solution is decreased to 60.

19. The method of any one of claims 1 to 17, wherein the carbonate salt saturation state of the solution is decreased to 30.

20. The method of any one of claims 1 to 17, wherein the carbonate salt saturation state of the solution is decreased to 15.

21. The method of any one of claims 1 to 17, wherein the carbonate salt saturation state of the solution is decreased to 18.

22. The method of any one of claims 1 to 21, wherein reducing the carbonate salt saturation state is by diluting the solution with a second solution, the second solution supersaturated with the carbonate salt.

23. The method of any one of claims 1 to 21, wherein decreasing the carbonate salt saturation state of the solution is by diluting the solution with a second solution, the second solution undersaturated with the carbonate salt.

24. The method of any one of claims 1 to 23, wherein removing aqueous carbon dioxide increases DIC concentration in the solution above 55%.

25. The method of any one of claims 1 to 24, wherein the removal of the aqueous carbon dioxide increases the pH of the solution by reducing carbonic acid generated from the aqueous carbon dioxide.

26. The method of any one of claims 1 to 25, wherein the removal of the aqueous carbon dioxide decreases the partial pressure of the aqueous carbon dioxide in the solution to an ambient aqueous carbon dioxide partial pressure.

27. The method of any one of claims 1 to 25, wherein the removal of the aqueous carbon dioxide decreases the partial pressure of the aqueous carbon dioxide in the solution to about an oceanic carbon dioxide partial pressure.

28. The method of any one of claims 1 to 27, further comprising (iii) releasing the solution into a body of water.

29. The method of claim 28, further comprising adjusting the pH of the solution to correspond to a pH of the body of water before the releasing.

30. The method of claim 28 or 29, wherein the solution is released into the body of water at a depth where an ambient pressure of the body of water maintains the carbonate in a dissolved state.

31. The method of any one of claims 1 to 30, further comprising generating the aqueous carbon dioxide in the solution by capturing gaseous carbon dioxide.

32. The method of any one of claims 1 to 31, wherein about 95% to about 100% of the aqueous carbon dioxide is converted to the carbonates in the solution.

33. A system for sequestering carbon dioxide from an aqueous solution comprising aqueous carbon dioxide and carbonates, the system comprising: a degassing chamber configured to remove aqueous carbon dioxide from the solution to increase a pH of the solution and increase saturation of carbonates in the solution; and a dilution vessel configured to decrease a carbonate mineral concentration below a precipitation threshold.

34. The system of claim 33, wherein the carbonate is calcium carbonate.

35. A system for sequestering carbon dioxide from an aqueous solution comprising aqueous carbon dioxide and a carbonates, the system comprising: a chamber configured to remove aqueous carbon dioxide from a solution to increase a pH of the solution and increase saturation of carbonates in the solution and further configured to decrease a carbonate salt concentration below a precipitation threshold.

36. The system of claim 35, wherein the carbonate is calcium carbonate.

37. The system of claim 35 or 36, further comprising a monitoring and control system configured to configure a pH of the solution to reach a target pH level and configured to configure the saturation of carbonates to reach a threshold carbonate saturation level and configured to configure a carbonate salt level to be below a carbonate salt precipitation threshold.

38. A system for sequestering carbon dioxide, the system comprising: a mixing vessel configured to dissolve a carbonate mineral in solution by conversion of aqueous carbon dioxide into bicarbonate and carbonate ions, the mixing vessel configured to provide the solution to the carbon dioxide removal vessel; a carbon dioxide removal vessel configured to remove a portion of the aqueous carbon dioxide from the solution; and a monitoring and control system configured to configure a pH of the solution to reach a target pH level and configured to configure a carbonate saturation level to reach a threshold carbonate saturation level and configured to configure a carbonate salt level to be below a carbonate salt precipitation threshold.

39. The system of claim 38, wherein the carbon dioxide removal vessel comprises an air sparger.

40. The system of claims 38, wherein the carbon dioxide removal vessel comprises a vacuum degasser.

41. The system of claim 38, wherein the carbon dioxide removal vessel comprises a membrane contactor.

42. The system of any one of claims 38 to 41, wherein the carbon dioxide removal vessel further comprises a gas outlet configured to provide removed carbon dioxide to the mixing vessel.

43. The system of any one of claims 38 to 42, further comprising a discharge system configured to discharge the solution to a body of water.

44. The system of claim 43, wherein the discharge system comprises at least one filter, at least one discharge port, and at least one safety valve.

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