METHODS FOR CARBON SEQUESTRATION AND MAKING MAGNESIUM-BASED CEMENT

Abstract

A method for producing cement comprises: obtaining a first hydroxide; forming a first carbonate from the first hydroxide; forming a mixture by mixing the first carbonate, magnesium oxide and zeolite; and allowing the mixture to cure to thereby form cement.

Claims

1.-20. (canceled)

21. A method of producing cement, the method comprising: obtaining a first hydroxide by electrolyzing a first brine; forming a first carbonate from the first hydroxide; forming a mixture by mixing the first carbonate, magnesium oxide and zeolite; and allowing the mixture to cure to thereby form cement.

22. A method according to claim 21 wherein forming a mixture by mixing the first carbonate, magnesium oxide and zeolite comprises forming the mixture by mixing the first carbonate, magnesium oxide, zeolite and a second brine.

23. A method according to claim 22 comprising obtaining one or both of the first and the second brine from a waste stream of an industrial process.

24. The method of claim 23 wherein the first and second brine have the same composition.

25. A method according to claim 23 wherein the waste stream comprises a waste stream from at least one of: production of oil and gas, production of potash, production of geothermal energy, and desalination.

26. A method according to claim 21 wherein electrolyzing the first brine comprises applying voltage to the first brine to cause calcium chloride in the first brine to form hydrochloric acid and calcium hydroxide and the first hydroxide comprises the calcium hydroxide formed from electrolyzing the first brine.

27. A method according to claim 21 wherein electrolyzing the first brine comprises applying voltage to the first brine to cause magnesium chloride in the first brine to form hydrochloric acid and magnesium hydroxide and the first hydroxide comprises the magnesium hydroxide formed from electrolyzing the first brine.

28. A method according to claim 21 comprising: obtaining a second hydroxide; forming a second carbonate from the second hydroxide; and wherein: forming the mixture comprises mixing the first carbonate, the second carbonate, magnesium oxide and zeolite.

29. A method according to claim 28 wherein the first hydroxide comprises calcium hydroxide and the first carbonate comprises calcium carbonate and wherein the second hydroxide comprises magnesium hydroxide and the second carbonate comprises magnesium carbonate.

30. A method according to claim 21 wherein forming the first carbonate from the first hydroxide comprises feeding a gas and the first hydroxide into a carbonation reactor, wherein the gas comprises greater than 5% carbon dioxide (by volume).

31. A method according to claim 30 wherein the gas is obtained by treating flue gas from at least one of: an industrial process and a power generation process.

32. A method according to claim 30 wherein the gas is obtained by treating flue gas from synthesis of magnesium oxide.

33. A method according to claim 31 wherein treating the flue gas comprises: separating carbon dioxide from the flue gas; and mixing the separated carbon dioxide with air to form the gas.

34. A method according to claim 33 wherein treating the flue gas further comprises: removing water vapor from the flue gas before separating carbon dioxide from the flue gas.

35. A method according to claim 33 wherein treating flue gas further comprises: cooling the flue gas before separating carbon dioxide from the flue gas.

36. A method according to any claim 33 wherein separating carbon dioxide from the flue gas comprises adsorbing the carbon dioxide with an adsorption zeolite.

37. A method according to claim 36 wherein mixing the separated carbon dioxide with air to form the gas comprises releasing the adsorbed carbon dioxide from the adsorption zeolite into the air to form the gas by heating the adsorption zeolite.

38. A method according to claim 31 wherein the carbonation reactor comprises a rotating packed bed reactor.

39. A method according to claim 21 comprising dewatering the mixture prior to curing to remove dissolved ions from the mixture.

40. A method according to claim 21 wherein the first hydroxide comprises a carbonate-forming metal hydroxide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive.

[0051] FIG. 1 is a flowchart depicting a method of forming magnesium-based cement according to the prior art.

[0052] FIG. 2 is a flowchart depicting a method of forming magnesium-based cement according to an example embodiment of this invention.

[0053] FIG. 3 is a flowchart depicting a system of forming magnesium-based cement according to an example embodiment of this invention.

[0054] FIG. 4 is a flowchart depicting a method of forming CO.sub.2 enriched gas according to an example embodiment of this invention.

[0055] FIG. 5 is a flowchart depicting a system of forming CO.sub.2 enriched gas according to an example embodiment of this invention.

[0056] FIG. 6 is a flowchart depicting a method of forming hydroxides according to an example embodiment of this invention.

[0057] FIG. 7 is a flowchart depicting a system of forming hydroxides according to an example embodiment of this invention.

DESCRIPTION

[0058] Throughout the following description specific details are set forth in order to provide a more thorough understanding to persons skilled in the art. However, well known elements may not have been shown or described in detail to avoid unnecessarily obscuring the disclosure. Accordingly, the description and drawings are to be regarded in an illustrative, rather than a restrictive, sense.

[0059] FIG. 1 depicts a method of forming magnesium-based cement (specifically, MOC) according to prior art techniques. Step 1 comprises acquiring a concentrated solution containing magnesium chloride. Magnesium chloride is an ingredient involved in the creation of MOC cement. Water is also an ingredient for MOC cement, hence the aqueous solution of magnesium chloride. Step 2 comprises adding magnesium oxide to the magnesium chloride solution. Given the expense associated with acquiring magnesium oxide, magnesium oxide is preferably added in a stoichiometric ratio to the magnesium chloride and water to limit the amount of unreacted magnesium oxide. As mentioned above, for a phase 5 MOC (which is the phase of MOC cement with a high level of structural integrity), the stoichiometric ratio is 5 parts magnesium oxide to 1 part magnesium chloride to 12 parts water. The mixture from step 2 is then allowed to cure in step 3. The mixture will initially have a slurry-like consistency, but upon curing it will solidify. Curing can take up to 7 days, though the curing time is variable and is a function of at least (but not limited to): temperature, humidity, and shape of the cured mixture (for example, curing the mixture in a cube shaped container will result in a faster curing time than curing the mixture in a spherical container due to a cube's higher surface area to volume ratio).

[0060] There are at least two disadvantages associated with the prior art method of forming cement shown in FIG. 1. A first disadvantage is associated with obtaining a magnesium chloride solution. Ideally, the magnesium chloride solution obtained in step 1 should have as high a purity of magnesium chloride as possible. Impurities (such as calcium ions) reduce the effectiveness of the curing step 3, as such impurities will limit the extent of reaction between magnesium oxide, magnesium chloride, and water. The calcium in solution does not form a 5 MOC structure (or calcium analog) and inhibits the growth of structurally strong cements. A second disadvantage of the FIG. 1 cement formation technique is associated with the carbon intensity of forming magnesium oxide. As mentioned above, production of magnesium oxide is a highly carbon dioxide intensive process, and the FIG. 1 method does not ameliorate the carbon intensity of producing cement.

[0061] Though the flowchart in FIG. 1 shows the procedure for making magnesium oxychloride cement (MOC), an analogous procedure can be followed for making other types of magnesium-based cement. For example, if the ion in solution was magnesium sulfate rather than magnesium chloride, then magnesium oxysulfate (MOS) would form. As mentioned above, magnesium oxysulfate (MOS) is another type of magnesium-based cement.

[0062] One aspect of the invention provides a method for forming cement. FIG. 2 depicts a method 100 for forming cement 112 according to an example embodiment of the invention.

[0063] Step 110 comprises obtaining a CO.sub.2 enriched gas 102 (also referred to simply as gas 102). Gas 102 may be obtained from any suitable source and by any suitable process. In some embodiments, gas 102 is obtained by method 200, described further herein.

[0064] Gas 102 may comprise between approximately 5% CO.sub.2 (by volume) and approximately 100% CO.sub.2 (by volume). Gas 102 may comprise between approximately 5% CO.sub.2 (by volume) and approximately 20% CO.sub.2 (by volume). Gas 102 may comprise between approximately 8% CO.sub.2 (by volume) and approximately 12% CO.sub.2 (by volume). Gas 102 may comprise approximately 10% CO.sub.2 (by volume). In some embodiments, at least a portion of the remaining composition of gas 102 comprises air (e.g. a mixture of primarily nitrogen and oxygen). Gas 102 may comprise some water vapor. In some embodiments, gas 102 comprises less than 10% water vapor (by volume). In some embodiments, gas 102 comprises less than 0.01% water vapor (by volume). In some embodiments, gas 102 comprises less than 0.001% water vapor (by volume).

[0065] Since CO.sub.2 enriched gas 102 may have a concentration of at least as low as approximately 20% CO.sub.2 (by volume), step 110 may avoid the significant energy expenditures (and potential associated release of CO.sub.2 from such energy expenditure) associated with other methods of carbon capture which require increasing the concentration of CO.sub.2 enriched gas 102 (e.g. to concentrations above 20% CO.sub.2 (by volume), above 50% CO.sub.2 (by volume) and/or above 90% CO.sub.2 (by volume)). Further, capital expenditures associated with building infrastructure for producing CO.sub.2 enriched gas 102 obtained in step 110 may be reduced significantly (e.g. as compared to the cost of infrastructure used in other methods of carbon capture to achieve concentrations above 20% CO.sub.2 (by volume), above 50% CO.sub.2 (by volume) and/or above 90% CO.sub.2 (by volume)). This reduction in capital expenditure in turn allows for onsite production of CO.sub.2 enriched gas 102 (e.g. at the same site as where method 100 occurs), thereby also avoiding energy intensive transportation (and otherwise necessary energy intensive compression) of CO.sub.2 enriched gas 102.

[0066] Step 120 comprises obtaining one or more hydroxides 104. Hydroxides 104 may be obtained from any suitable source and by any suitable process. In some embodiments, hydroxides 104 are obtained by method 300, described further herein.

[0067] Hydroxides 104 may comprise any suitable hydroxides or anions that react to form a chemical bond with CO.sub.2. Hydroxides 104 may comprise carbonate-forming metal hydroxides. For example, hydroxides 104 may comprise calcium hydroxide (Ca(OH).sub.2), sodium hydroxide (NaOH), magnesium hydroxide (Mg(OH).sub.2) and/or other metal hydroxides. Hydroxides 104 may comprise an aqueous solution of hydroxides. For example, hydroxides 104 may comprise between approximately 80% and 90% water (by volume). Hydroxides 104 may comprise an aqueous solution of hydroxides with pH greater than or equal to approximately 10.

[0068] Step 130 comprises carbonating hydroxides 104 to form carbonates 106. Carbonating hydroxides 104 may comprise reacting hydroxides 104 and gas 102 to form carbonates 106.

[0069] Carbonation at step 130 may occur in a carbonation reactor 114 (see FIG. 3). Carbonation reactor 114 may comprise any suitable carbonation reactor. For example, carbonation reactor 114 may comprise a rotating packed bed reactor, a micro bubble reactor, any gas-injecting or gas-tight mixer and/or the like. Carbonation reactor 114 may comprises a microbubble generator to cycle gas 102 through carbonation reactor 114.

[0070] Gas 102 may be cycled through carbonation reactor 114 until sufficient conversion of hydroxides 104 to carbonates 106 has occurred. For example, gas 102 may be cycled through carbonation reactor 114 until conversion of approximately 75% or more of hydroxides 104 to carbonates 106 has occurred or until conversion of approximately 90% or more of hydroxides 104 to carbonates 106 has occurred.

[0071] Where hydroxides 104 comprise Ca(OH).sub.2, carbonation at step 130 may comprise the formation of a calcium carbonate (CaCO.sub.3) carbonate 106 and water as follows:

Ca(OH).sub.2+CO.sub.2.fwdarw.CaCO.sub.3+H.sub.2O

[0072] Where hydroxides 104 additionally or alternatively comprise Mg(OH).sub.2, carbonation at step 30 may comprise the formation of a magnesium carbonate (MgCO.sub.3) carbonate 106 and water as follows:

Mg(OH).sub.2+CO.sub.2.fwdarw.MgCO.sub.3+H.sub.2O

[0073] As hydroxides 104 may be an aqueous solution and/or the carbonation reactions may form water, carbonates 106 may be an aqueous solution. For example, carbonates 106 may comprise between approximately 80% and 90% water (by volume).

[0074] Step 140 comprises mixing carbonates 106 with remaining cement ingredients 108. Remaining cement ingredients 108 may comprise, for example, magnesium oxide (MgO), additional brine 108A, zeolite (or a zeolite replacement such as, but not limited to, PozGlass) and/or supplementary cementing materials (such as, but not limited to, PozGlass) to form a mixture 118. The inclusion of additional brine 108A at step 140 may assist the cementing process through the formation of magnesium oxychloride and/or magnesium oxysulfate. In some embodiments, remaining cement ingredients 108 do not include additional brine 108A (e.g. where the cementing reaction is predominantly the carbonation of MgO and subsequent dewatering). Some water may be released (e.g. evaporate) from mixture 118 during step 140.

[0075] Brine 108A is preferably sourced from an industrial process. Ideally brine 108A is a waste stream from the production of oil and gas, potash, desalination, geothermal energy and/or the like. Oil and gas, potash, desalination and geothermal energy production all produce brines with high magnesium concentrations (in excess of 10,000 ppm), and high calcium concentrations (in excess of 50,000 ppm). These and other industrial waste streams typically contain high amounts of magnesium and calcium.

[0076] The magnesium content of the waste stream that makes up brine 108A may be in a range between approximately 10,000 ppm and 120,000 ppm and, in some embodiments, in a range between approximately 50,000 ppm and 75,000 ppm. The calcium content of the waste stream that makes up brine 108A may be in a range between approximately 25,000 ppm to 125,000 ppm and, in some embodiments, in a range between approximately 25,000 ppm and 50,000 ppm. In some embodiments, the sodium content of the waste stream that makes up brine 108A may be less than 150,000 ppm and, in some embodiments, less than 10,000 ppm. There may be some sulfate ions in the waste stream. If this is the case (i.e. sulphate ions are present), then during the curing step (discussed further herein), some magnesium oxysulfate will form.

[0077] Mixing carbonates 106 with remaining cement ingredients 108 at step 140 may occur with the aid of any suitable mixing device 116 (see FIG. 3). For example, in some embodiments, mixing device 116 comprises a cement mixer.

[0078] Step 150 is an optional step that comprises dewatering mixture. 118 Dewatering may serve a number of purposes.

[0079] One purpose of the optional step 150 dewatering process may be to remove dissolved ions from mixture 118. As mentioned before, brine 108A may contain ions such as (but not limited to) sodium, potassium, or iron. These ions do not normally form part of the binding phase of magnesium-based cements. Furthermore, these ions will not precipitate out of solution to the same extent as calcium carbonate (e.g. due to the low solubility of calcium carbonate). As such, it may be desirable to remove some of the water from the mixture prior to curing in step 160. Removing some of the water may reduce the total amount of dissolved ions in the curing step, but the concentration of dissolved ions in solution may remain the same.

[0080] Another purpose for optional step 150 dewatering process may be to adjust the ratio of magnesium oxide, magnesium chloride, and water in mixture 118. As mentioned before, the constituents of MOC cement are ideally mixed in a ratio of 5 parts magnesium oxide to 1 part magnesium chloride to 12 parts water, as this will form a phase of MOC cement that has high strength. Too much water may cause less desirable MOC cement phases to form. These are non-exhaustive purposes for dewatering in optional step 150; there may be other purposes for the optional dewatering step 150.

[0081] Step 160 comprises curing mixture 118 to form cement 112. The time spent curing is a function of at least temperature, humidity, and the shape of the curing vessel. In some implementations, curing in step 160 may take time in a range of 72 hours to 7 days. In some implementations, curing in step 160 is performed at a temperature in a range of approximately 20 to 50 C., with currently preferred temperatures in a range of approximately 20 to 30 C. During the step 160 curing process, humidity may be maintained relatively high (e.g. above 90%) for a first period of time (e.g. 18-30 hours) and the humidity may be decreased (e.g. to levels in a range of 50%-80% or to levels of 50%-60%) from 30 hours onward for the remainder of the step 160 curing process.

[0082] As mixture 118 cures to form cement 112, carbonates 106 remain entrained in cement 112, thereby sequestering CO.sub.2 from CO.sub.2 enriched gas 102 in cement 112. While some CO.sub.2 may be released when forming MgO employed at step 140 and/or some CO.sub.2 may be released as mixture 118 cures to form cement 112 (e.g. from limestone decomposing into calcium oxide (CaO) and CO.sub.2), the amount of CO.sub.2 released from forming MgO employed at step 140 and released across steps 140 to 160 may be less than the amount of CO.sub.2 sequestered from CO.sub.2 enriched gas 102 in cement 112 such that cement 112 produced by method 100 may be carbon negative (e.g. method 100 may sequester more CO.sub.2 than it produces/releases).

[0083] During or after step 160, cement 112 may be pressed or extruded into desired shapes for building applications (e.g. precast building applications) such as, for example, siding, floor tiles, wall tiles, etc.

[0084] One aspect of the invention provides a method of obtaining CO.sub.2 enriched gas. FIG. 4 depicts a method 200 of obtaining CO.sub.2 enriched gas 208 according to an example embodiment of the invention. Method 200 may be employed, for example, in block 110 of method 100.

[0085] Step 210 comprises obtaining source gas 202. Source gas 202 could be from a number of sources. For example, source gas 202 could be ambient air, flue gas, compressed air and/or an emission source from an industrial process. Source gas 202 may contain carbon dioxide at a concentration of between approximately 400 ppm and 120,000 ppm. Beyond the desirability that there be carbon dioxide, source gas 202 could have any composition and have a wide array of process stream characteristics. For example, source gas 202 could have high particulate contents, and it could also be at high pressure or temperature. Source gas 202 may contain moisture, oxygen, nitrous oxides, sulfur oxides and/or particulate matter that may either remain entrapped in the final cement mixture (e.g. in the case where method 200 is used in block 110 of method 100) or be passed through the reaction mixture. Source gas 202 may comprise between approximately 0.25% and 1% water vapor (by volume). Source gas 202 may comprise approximately 0.5% water vapor (by volume).

[0086] Source gas 202 may comprise flue gas from the production of magnesium oxide. As mentioned above, the production of magnesium oxide releases substantial amounts of carbon dioxide. Using flue gas from the production of magnesium oxide would be particularly advantageous, as the carbon dioxide created during the production of magnesium oxide could be captured during cement formation method 100.

[0087] Step 220 comprises drying source gas 202 to form dried source gas 204. Step 220 may comprise removing water vapor from source gas 202 to form dried source gas 204. Where source gas 202 already has sufficiently low water vapor content, step 220 may be skipped and source gas 202 may be employed in place of dried source gas 204.

[0088] Source gas 202 may be dried at step 220 with any suitable dryer 212 (see FIG. 5). Dryer 212 may comprise a deliquescent dyer, a desiccant dryer, a membrane dryer, a chiller, a refrigerant dryer, etc. For example, dryer 212 may comprises one or more drying columns packed with one or more microsieves or drying agents (e.g. silica) to absorb and/or adsorb water.

[0089] At step 220, water vapor in source gas 202 may be reduced to less than approximately less than 0.01% water vapor (by volume). In some embodiments, gas water vapor in source gas 202 is reduced to less than approximately 0.001% water vapor (by volume).

[0090] In some embodiments, source gas 202 is provided at step 220 at a temperature of less than 25 C. Source gas 202 may be provided to step 220 at a temperature of less than 15 C. or even less than 0 C.

[0091] At step 230, at least a portion of the CO.sub.2 content of dried source gas 204 is separated from dried source gas 204 to form a CO.sub.2 enriched gas 208. A by-product of step 230 may be a CO.sub.2 depleted source gas 206 (e.g. depleted source gas 206 comprises the remaining content of dried source gas 204 after at least some of the CO.sub.2 content was separated therefrom).

[0092] Any suitable CO.sub.2 separator 214 (see FIG. 5) may be employed at step 230. For example CO.sub.2 separator 214 may comprise a functionalized membrane, or a liquid based spray system containing high affinity CO.sub.2 solutions such as amines, hydroxides, etc. CO.sub.2 separator 214 may employ a solid sorbent material such as, zeolite (e.g. 4A zeolite 13X), activated carbon, or other CO.sub.2 selective material.

[0093] In some embodiments, step 230 occurs in two stages: adsorption of CO.sub.2 and desorption of CO.sub.2. In some embodiments, a CO.sub.2 separator 214 adsorbs CO.sub.2 from dried source gas 206 during a first phase and may then release (e.g. desorb) the adsorbed CO.sub.2 as desired during a second phase. In some embodiments, the second phase is initiated by heating, and/or reducing the pressure within, CO.sub.2 separator 214.

[0094] In some embodiments, CO.sub.2 separator 214 comprises zeolite (e.g. zeolite 13X) which may adsorb CO.sub.2 when at a first temperature and release CO.sub.2 when at a second temperature. For example, dried source gas 204 may be directed into CO.sub.2 separator 214 at the first temperature. Then, after sufficient CO.sub.2 is adsorbed, the remaining CO.sub.2 depleted gas 206 may be released from CO.sub.2 separator 214. The adsorbed CO.sub.2 may then be desorbed to form CO.sub.2 enriched gas 208 by raising the temperature of CO.sub.2 separator 214 to the second temperature. In some embodiments, the first temperature is less than 20 C. In some embodiments, the first temperature is less than 5 C. In some embodiments, the second temperature is between approximately 50 C. and 120 C. In some embodiments, the second temperature is more than 70 C. In some embodiments, the second temperature is approximately 90 C.

[0095] To facilitate removing desorbed CO.sub.2 from CO.sub.2 separator 214 during the second phase and transporting the CO.sub.2 to the next step, a carrier gas 216 may be flushed through CO.sub.2 separator 214. The resultant CO.sub.2 enriched gas 208 may therefore comprises a mixture of CO.sub.2 and carrier gas 216. Carrier gas 216 may comprise air (e.g. a mixture of primarily nitrogen and oxygen).

[0096] CO.sub.2 enriched gas 208 may comprise between approximately 5% CO.sub.2 (by volume) and approximately 100% CO.sub.2 (by volume). CO.sub.2 enriched gas 208 may comprise between approximately 5% CO.sub.2 (by volume) and approximately 20% CO.sub.2 (by volume). CO.sub.2 enriched gas 208 may comprise between approximately 8% CO.sub.2 (by volume) and approximately 12% CO.sub.2 (by volume). CO.sub.2 enriched gas 208 may comprise approximately 10% CO.sub.2 (by volume).

[0097] The CO.sub.2 enriched gas 208 formed by method 200 may be employed as gas 102 for method 100, although this is not mandatory. In some embodiments, CO.sub.2 enriched gas 208 is stored for later usage (e.g. in method 100). In some embodiments, CO.sub.2 enriched gas 208 flows directly to carbonation reactor 114 for use at step 130 of method 100.

[0098] One aspect of the invention provides a method of obtaining hydroxides from a brine. FIG. 6 depicts a method 300 of obtaining hydroxides 306 from a brine 302 according to an example embodiment of the invention. Method 300 may be employed, for example, in block 120 of method 100.

[0099] Step 310 comprises obtaining brine 302. Brine 302 is preferably sourced from an industrial process. Ideally brine 302 is a waste stream from the production of oil and gas, potash, desalination, geothermal energy and/or the like. Oil and gas, potash, desalination and geothermal energy production all produce brines with high magnesium concentrations (in excess of 10,000 ppm), and high calcium concentrations (in excess of 50,000 ppm). These and other industrial waste streams typically contain high amounts of magnesium and calcium.

[0100] The magnesium content of the waste stream that makes up brine 302 may be in a range between approximately 10,000 ppm and 120,000 ppm and, in some embodiments, between approximately 50,000 ppm and 75,000 ppm. The calcium content of the waste stream that makes up brine 302 may be in a range between approximately 25,000 ppm to 125,000 ppm and, in some embodiments, between approximately 25,000 ppm and 50,000 ppm. In some embodiments, the sodium content of the waste stream that makes up brine 302 may be less than 150,000 ppm and, in some embodiments, less than 10,000 ppm. There may be some sulfate ions in the waste stream. If this is the case (i.e. sulphate ions are present), then during the curing step 160 (where method 300 is used in block 120 of method 100), some magnesium oxysulfate will form.

[0101] Step 320 comprises electrolyzing brine 302 to form one or more hydroxides 306 and one or more acidic salts 304. Hydroxides 306 may comprise, for example, carbonate-forming metal hydroxides. For example, where brine 302 comprises water and calcium chloride (CaCl.sub.2)), electrolysis of brine 302 may first form hydrogen ions and hydroxide ions. The hydroxide ions and hydrogen ions may then react with the CaCl.sub.2) to form calcium hydroxide (Ca(OH).sub.2) as hydroxide 306 and hydrochloric acid (HCl) as acidic salt 304, as follows:

H.sub.2O.fwdarw.H.sup.++OH.sup.

CaCl.sub.2+2H.sup.++2OH.sup..fwdarw.2HCl+Ca(OH).sub.2

As another example, where brine 302 alternatively or additionally comprises water and magnesium chloride (MgCl.sub.2), electrolysis of brine 302 may first form hydrogen ions and hydroxide ions. The and hydroxide ions and hydrogen ions may then react with the MgCl.sub.2 to form magnesium hydroxide (Mg(OH).sub.2) as hydroxide 306 and hydrochloric acid (HCl) as acidic salt 304, as follows:

H.sub.2O.fwdarw.H.sup.++OH.sup.

MgCl.sub.2+2H.sup.++2OH.sup..fwdarw.2HCl+Mg(OH).sub.2

[0102] Hydroxides 306 produced at step 320 may be an aqueous solution with a ratio of solids to liquid of between approximately 0.01 to 0.5 (by volume). Hydroxides 306 produced at step 320 may be an aqueous solution with a ratio of solids to liquid of approximately 0.5 (by volume).

[0103] Step 320 may employ any suitable electrolyzer 308 (see FIG. 7). Electrolyzer 308 may or may not employ one or more membranes (e.g. to separate hydroxides 306 from acidic salts 304). Electrolyzer 308 may be a continuous flow electrolyzer. In some embodiments, electrolyzer 308 comprises a continuous flow membraneless cell.

[0104] Electrolyzer 308 may comprise an anode and a cathode. For example, electrolyzer 308 may comprise membrane anodes and cathodes to separate hydroxides 306 from acidic salts 304 as they are formed. In some embodiments, electrolyzer 308 comprises an anode of stainless steel iron, graphite carbon, etc. In some embodiments, electrolyzer 308 comprises a cathode of platinum, graphite, titanium or another conductive material suitable for a hydrogen evolution reaction.

[0105] Electrolyzer 308 may apply a voltage to brine 302 (e.g. by applying a voltage across an anode and a cathode inserted at least partially into brine 302). The voltage may be between approximately 0.1V and 10V. The voltage may be between approximately 0.5V and 5V. The voltage applied to brine 302 at step 320 may be chosen to: (1) achieve desired pH levels of hydroxides 306 and acidic salts 304; and/or (2) minimize energy costs associated with step 320. To achieve these goals, the voltage may be increased if the difference in pH between hydroxides 306 and acidic salts 304 is less than seven; the voltage may be decreased if the difference in pH between hydroxides 306 and acidic salts 304 is more than 10; the voltage may be increased if the pH of hydroxides 306 is three or more and/or the pH of acidic salts 304 is 10 or less; and/or the voltage may be decreased if the pH of hydroxides 306 is three or less and/or the pH of acidic salts 304 is 10 or more. These changes in voltage may be effected by a suitably configured controller/processor (not shown) connected to receive signals from pH sensors (not shown) and to a apply voltage signal between the anode and cathode.

[0106] The one or more hydroxides 306 formed by method 300 may be employed as hydroxides 104 for method 100, although this is not mandatory. In some embodiments, hydroxides 306 are stored for later usage (e.g. in method 100). In some embodiments, hydroxides 306 flow directly to carbonation reactor 114 for use at step 130 of method 100.

[0107] In some embodiments, method 100 is combined with one or both of method 200 and method 300 for carbon sequestration through making of magnesium-based cement. The combined method may allow for carbon negative manufacturing of magnesium-based cement with relatively low energy requirements compared to traditional techniques for making magnesium-based cement (e.g. since relatively low concentration CO.sub.2 enriched gas 102 may be employed rather than high concentration CO.sub.2 enriched gas 102 which could require energy intensive purification, compression and/or transportation from an offsite plant). The combined method may allow for carbon negative manufacturing of magnesium-based cement with relatively lower capital cost requirements compared to traditional techniques for making magnesium-based cement (e.g. due to a lack of need of equipment for achieving high concentration CO.sub.2 enriched gas 102).

Interpretation of Terms

[0108] Unless the context clearly requires otherwise, throughout the description and the [0109] comprise, comprising, and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of including, but not limited to; [0110] connected, coupled, or any variant thereof, means any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements can be physical, logical, or a combination thereof; [0111] herein, above, below, and words of similar import, when used to describe this specification, shall refer to this specification as a whole, and not to any particular portions of this specification; [0112] or, in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list; [0113] the singular forms a, an, and the also include the meaning of any appropriate plural forms.

[0114] Words that indicate directions such as vertical, transverse, horizontal, upward, downward, forward, backward, inward, outward, left, right, front, back, top, bottom, below, above, under, and the like, used in this description and any accompanying claims (where present), depend on the specific orientation of the apparatus described and illustrated. The subject matter described herein may assume various alternative orientations. Accordingly, these directional terms are not strictly defined and should not be interpreted narrowly.

[0115] While processes or blocks are presented in a given order, alternative examples may perform routines having steps, or employ systems having blocks, in a different order, and some processes or blocks may be deleted, moved, added, subdivided, combined, and/or modified to provide alternative or subcombinations. Each of these processes or blocks may be implemented in a variety of different ways. Also, while processes or blocks are at times shown as being performed in series, these processes or blocks may instead be performed in parallel, or may be performed at different times.

[0116] In addition, while elements are at times shown as being performed sequentially, they may instead be performed simultaneously or in different sequences. It is therefore intended that the following claims are interpreted to include all such variations as are within their intended scope.

[0117] Where a component is referred to above, unless otherwise indicated, reference to that component (including a reference to a means) should be interpreted as including as equivalents of that component any component which performs the function of the described component (i.e., that is functionally equivalent), including components which are not structurally equivalent to the disclosed structure which performs the function in the illustrated exemplary embodiments of the invention.

[0118] Specific examples of systems, methods and apparatus have been described herein for purposes of illustration. These are only examples. The technology provided herein can be applied to systems other than the example systems described above. Many alterations, modifications, additions, omissions, and permutations are possible within the practice of this invention. This invention includes variations on described embodiments that would be apparent to the skilled addressee, including variations obtained by: replacing features, elements and/or acts with equivalent features, elements and/or acts; mixing and matching of features, elements and/or acts from different embodiments; combining features, elements and/or acts from embodiments as described herein with features, elements and/or acts of other technology; and/or omitting combining features, elements and/or acts from described embodiments.

[0119] Various features are described herein as being present in some embodiments. Such features are not mandatory and may not be present in all embodiments. Embodiments of the invention may include zero, any one or any combination of two or more of such features. This is limited only to the extent that certain ones of such features are incompatible with other ones of such features in the sense that it would be impossible for a person of ordinary skill in the art to construct a practical embodiment that combines such incompatible features. Consequently, the description that some embodiments possess feature A and some embodiments possess feature B should be interpreted as an express indication that the inventors also contemplate embodiments which combine features A and B (unless the description states otherwise or features A and B are fundamentally incompatible).

[0120] The invention comprises a number of non-limiting aspects. Non-limiting aspects of the invention include: [0121] 1. A method of producing cement, the method comprising: [0122] obtaining a first hydroxide by electrolyzing a first brine; [0123] forming a first carbonate from the first hydroxide; [0124] forming a mixture by mixing the first carbonate, magnesium oxide and zeolite; and [0125] allowing the mixture to cure to thereby form cement. [0126] 2. A method according to aspect 1 or any other aspect herein wherein forming a mixture by mixing the first carbonate, magnesium oxide and zeolite comprises forming the mixture by mixing the first carbonate, magnesium oxide, zeolite and a second brine. [0127] 3. A method according to aspect 2 or any other aspect herein comprising obtaining the second brine from a waste stream of an industrial process. [0128] 4. A method according to aspect 1 or any other aspect herein comprising obtaining the first brine from a waste stream of an industrial process. [0129] 5. A method according to aspect 1 or any other aspect herein wherein: [0130] forming a mixture by mixing the first carbonate, magnesium oxide and zeolite comprises forming the mixture by mixing the first carbonate, magnesium oxide, zeolite and a second brine; and [0131] the second brine is obtained from the waste stream of the industrial process. [0132] 6. A method according to any one of aspects 4 and 5 or any other aspect herein wherein the waste stream comprises a waste stream from at least one of: production of oil and gas, production of potash, production of geothermal energy, and desalination. [0133] 7. A method according to any one of aspects 1 to 6 or any other aspect herein wherein the first brine comprises a magnesium content of between approximately 10,000 ppm and 120,000 ppm. [0134] 8. A method according to any one of aspects 1 to 7 or any other aspect herein wherein the first brine comprises a calcium content of between approximately 25,000 ppm to 125,000 ppm. [0135] 9. A method according to any one of aspects 1 to 8 or any other aspect herein wherein the first brine comprises a sodium content of less than 150,000 ppm. [0136] 10. A method according to any one of aspects 1, 4 and 6 to 9 or any other aspect herein wherein: [0137] forming a mixture by mixing the first carbonate, magnesium oxide and zeolite comprises forming the mixture by mixing the first carbonate, magnesium oxide, zeolite and a second brine; and [0138] the second brine comprises the same composition as the first brine. [0139] 11. A method according to any one of aspects 1, 4 and 6 to 10 or any other aspect herein wherein electrolyzing the first brine comprises applying voltage to the first brine to cause calcium chloride in the first brine to form hydrochloric acid and calcium hydroxide and the first hydroxide comprises the calcium hydroxide formed from electrolyzing the first brine. [0140] 12. A method according to any one of aspects 1, 4 and 6 to 10 or any other aspect herein wherein electrolyzing the first brine comprises applying voltage to the first brine to cause magnesium chloride in the first brine to form hydrochloric acid and magnesium hydroxide and the first hydroxide comprises the magnesium hydroxide formed from electrolyzing the first brine. [0141] 13. A method according to any one of aspects 1 to 12 or any other aspect herein comprising: [0142] obtaining a second hydroxide; [0143] forming a second carbonate from the second hydroxide; and wherein: [0144] forming the mixture comprises mixing the first carbonate, the second carbonate, magnesium oxide and zeolite. [0145] 14. A method according to aspect 13 or any other aspect herein wherein the first hydroxide comprises calcium hydroxide and the first carbonate comprises calcium carbonate and wherein the second hydroxide comprises magnesium hydroxide and the second carbonate comprises magnesium carbonate. [0146] 15. A method according to any one of aspects 1 to 13 or any other aspect herein wherein forming the first carbonate from the first hydroxide comprises feeding a gas and the first hydroxide into a carbonation reactor, wherein the gas comprises greater than 5% carbon dioxide (by volume). [0147] 16. A method according to any one of aspects 1 to 13 or any other aspect herein wherein forming the first carbonate from the first hydroxide comprises feeding a gas and the first hydroxide into a carbonation reactor, wherein the gas comprises greater than 10% carbon dioxide (by volume). [0148] 17. A method according to any one of aspects 1 to 13 or any other aspect herein wherein forming the first carbonate from the first hydroxide comprises feeding a gas and the first hydroxide into a carbonation reactor, wherein the gas comprises between approximately 10% and 20% carbon dioxide (by volume). [0149] 18. A method according to any one of aspects 15 to 17 or any other aspect herein wherein the gas is obtained by treating flue gas from at least one of: an industrial process and a power generation process. [0150] 19. A method according to any one of aspects 15 to 17 or any other aspect herein wherein the gas is obtained by treating flue gas from the synthesis of magnesium oxide. [0151] 20. A method according to any one of aspects 18 to 19 or any other aspect herein wherein the flue gas has a carbon dioxide content of between approximately 400 ppm and 150,000 ppm by concentration. [0152] 21. A method according to any one of aspects 18 to 20 or any other aspect herein wherein treating the flue gas comprises: [0153] separating carbon dioxide from the flue gas; and [0154] mixing the separated carbon dioxide with air to form the gas. [0155] 22. A method according to aspect 21 or any other aspect herein wherein treating the flue gas comprises: [0156] removing water vapor from the flue gas before separating carbon dioxide from the flue gas. [0157] 23. A method according to any one of aspects 21 and 22 or any other aspect herein wherein treating flue gas comprises: [0158] cooling the flue gas before separating carbon dioxide from the flue gas. [0159] 24. A method according to any one of aspects 21 to 23 or any other aspect herein wherein separating carbon dioxide from the flue gas comprises adsorbing the carbon dioxide with zeolite. [0160] 25. A method according to aspect 24 or any other aspect herein wherein mixing the separated carbon dioxide with air to form the gas comprises releasing the adsorbed carbon dioxide from the zeolite into the air to form the gas. [0161] 26. A method according to aspect 25 or any other aspect herein wherein releasing the adsorbed carbon dioxide into the air to form the gas comprising heating the zeolite and the adsorbed carbon dioxide to release the adsorbed carbon dioxide into the air. [0162] 27. A method according to any one of aspects 15 to 17 or any other aspect herein wherein the carbonation reactor comprises a rotating packed bed reactor. [0163] 28. A method according to any one of aspects 1 to 27 or any other aspect herein comprising dewatering the mixture prior to curing to remove dissolved ions from the mixture. [0164] 29. A method according to any one of aspects 1 to 28 or any other aspect herein wherein the first hydroxide comprises a carbonate-forming metal hydroxide. [0165] 30. A method according to any one of aspects 1 to 28 or any other aspect herein wherein the first hydroxide comprises calcium hydroxide and the first carbonate comprises calcium carbonate. [0166] 31. A method according to any one of aspects 1 to 28 or any other aspect herein wherein the first hydroxide comprises magnesium hydroxide and the first carbonate comprises magnesium carbonate. [0167] 32. Methods comprising any features, combinations of features and/or sub-combinations of features described herein or inferable therefrom. [0168] 33. Apparatus comprising any features, combinations of features and/or sub-combinations of features described herein or inferable therefrom. [0169] 34. Kits comprising any features, combinations of features and/or sub-combinations of features described herein or inferable therefrom.

[0170] It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions, omissions, and sub-combinations as may reasonably be inferred. The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.