System and method for converting carbon dioxide in gas stream to chemical product of commercial value

Abstract

The invention relates to a system and method for reducing the amount of carbon dioxide contained in a gas stream. The system includes a carbon dioxide absorption and mineralization module configured to convert carbon dioxide, ammoniation solvent, and at least one metal chloride in a gas stream to carbonate and / or bicarbonate and ammonium chloride. The system also includes a mineral separation module configured to separate carbonate and / or bicarbonate from ammonium chloride. Also provided is a solvent regeneration module configured to convert ammonium chloride to chlorine and ammonium hydroxide through a catalyst under the action of heat and oxygen.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Provisional Patent Application No. 63 / 484,194, filed February 10, 2023, the entire contents of which are incorporated herein by reference. Background Art

[0003] The present disclosure relates to a system and method for capturing carbon dioxide (CO2) from a dilute gas stream (including but not limited to flue gas and / or fermentation tail gas) and utilizing the captured CO2 to generate minerals and other commercially valuable chemical products.

[0004] Carbon capture, utilization, and storage (CCUS) can help achieve net-zero emissions from hard-to-abate sources. Two current approaches involve capturing carbon dioxide before it enters the atmosphere. These methods are often referred to as carbon capture and geological storage (CCS) and carbon capture and utilization (CCU), collectively known as carbon capture, utilization, and storage (CCUS).

[0005] These approaches rely on applying carbon capture technologies before the CO2 is emitted, either in power plants or industrial processes. Capture technologies can be broadly divided into three categories: (i) post-conversion capture, in which the CO2 in the exhaust gas is separated from the gas stream; (ii) pre-conversion capture, in which the CO2 is produced as an unwanted intermediate by-product that needs to be removed. In both pre-conversion and post-conversion, the CO2 can be captured using various absorption or adsorption methods, such as absorption using chemical solvents or adsorption onto porous organic frameworks; and (iii) oxyfuel capture, in which the fuel is burned with pure oxygen, resulting in a high-purity CO2 exhaust gas free of nitrogen compounds.

[0006] After capture, the CO2 is compressed and prepared for transport for storage or utilization. The most common storage location is a geological reservoir. However, before CCS can be considered a solution to the problem of excess CO2 in the global atmosphere, a number of challenges must be addressed, including storage options and the cost of injecting CO2 into rock formations. One of the main economic barriers is the lack of financial incentives to store the gas, which has slowed the development and deployment of CCS. However, if captured and activated, CO2 can serve as a versatile chemical feedstock for a variety of industries.

[0007] A viable alternative to storing CO2 is using it as a so-called CO2 feedstock to generate a variety of useful chemical products. Utilization offers the advantage of providing economic incentives to industry over traditional storage methods. By using CO2 as a sustainable chemical feedstock, useful petrochemicals or commercial chemicals can be generated, while also achieving both the removal and utilization of CO2 resources.

[0008] But to be commercially viable, these processes need to be improved to obtain more target products with lower energy consumption and a smaller carbon footprint. As natural raw materials become more difficult to obtain, recycling carbon dioxide and using it for chemical production will become a more attractive option for the industry. Therefore, innovative solutions for the capture of CO2 and the supply of chemical raw materials have important environmental and economic value. The present disclosure relates to systems and methods for capturing and mineralizing carbon dioxide from dilute gas streams to generate basic chemicals such as Cl2 (chlorine). Cl2, as the main raw material for many industrial applications (such as water treatment), is currently produced through the chlor-alkali process, which faces significant environmental challenges. More than 75% of traditional chlor-alkali production in the United States uses asbestos diaphragm electrolysis technology, which exposes workers and the environment to harmful asbestos fibers. In contrast, Germany has implemented regulations since 1994 requiring the complete elimination of asbestos in chlor-alkali production to address its health risks.

[0009] Another challenge is the high energy consumption of chlor-alkali processes, particularly when using the mercury anode process. These processes are among the most energy-intensive in the chemical industry, consuming approximately 3,500 kWh of electricity per ton of chlorine produced. However, switching to membrane electrolysis technology could reduce energy consumption by 15% or more per ton of product, offering significant energy savings potential.

[0010] Furthermore, these processes have significant environmental impacts. Historically, mercury pollution has been caused by the mercury anode process, with many older plants releasing large amounts of mercury into the environment. Furthermore, the chemical industry, including chlor-alkali production, is the third largest source of industrial greenhouse gas emissions due to its high reliance on fossil fuels.

[0011] These challenges highlight the urgent need for the chlor-alkali industry to adopt newer, safer and more energy-efficient technologies. Summary of the Invention

[0012] All examples and features mentioned below can be combined in any technically feasible way.

[0013] In one example, the present disclosure relates to a system and process for capturing and mineralizing carbon dioxide (CO2) from a dilute gas stream. In one example, an absorption and mineralization step is included in which carbon dioxide from a CO2-rich gas stream (e.g., flue gas or fermentation tail gas) is reacted with a solvent. The solvent consists of water, ammonium hydroxide, and an X-chloride salt, where the cation X can be Ca 2+ Mg + 、Na + or K +. During the process, CO2 is mineralized and solid X-carbonate and water-soluble ammonium chloride are produced. These products are combined to form an output stream that flows out of the absorber. The gas, free of CO2, then flows out and leaves the process completely. After the absorption and mineralization steps, the output stream enters a separation unit that removes solid X-carbonate and ammonium chloride from the fluid. The X-carbonate is then removed from the process, while the ammonium chloride is sent to the regeneration process. During the regeneration process, the ammonium chloride reacts with oxygen (such as oxygen from the air), removing chlorine and releasing ammonium hydroxide. The newly produced ammonium hydroxide is then returned to the absorber to be used in combination with fresh X-chloride.

[0014] The present disclosure describes a system and method for capturing and mineralizing carbon dioxide (CO2) from a dilute carbon dioxide gas stream (including but not limited to flue gas and / or fermentation tail gas) to generate a commercially valuable product. The disclosed method includes capturing CO2 using a high salinity solution and ammonia and converting it into metal carbonates, including CaCO3, NaHCO3, KHCO3 or other similar carbonates or bicarbonates, and NH4Cl. In some embodiments, the bicarbonate can be further processed and converted into carbonates. In some embodiments, NH4Cl can be converted into NH3 and HCl by heating or the like. In other alternative embodiments, NH4Cl can be converted into NH3 and NaCl, KCl, CaCl2 or similar products by adding NaOH, KOH, Ca(OH)2 or similar hydroxides.

[0015] In some embodiments, the disclosed method uses brine (sodium chloride aqueous solution) and ammonia gas to capture and convert CO2, and the main products generated include sodium carbonate (Na2CO3), HCl (or Cl2), H2O and / or NH4Cl. In some embodiments, the disclosed method uses potassium chloride aqueous solution and ammonia gas to capture and convert CO2, and the main products generated include potassium carbonate (K2CO3), HCl (or Cl2), H2O and / or NH4Cl.

[0016] In some embodiments, the disclosed method uses brine (sodium chloride aqueous solution) and ammonia to capture and convert CO2, and the main products generated include sodium bicarbonate (NaHCO3), HCl (or Cl2), H2O and / or NH4Cl.

[0017] In some embodiments, the disclosed method uses aqueous potassium chloride solution and ammonia gas to capture and convert CO2, and the main products generated include potassium bicarbonate (KHCO3), HCl (or Cl2), H2O and / or NH4Cl.

[0018] In some embodiments, the disclosed method uses an aqueous solution of calcium chloride and ammonia gas to capture and convert CO2, and the main products generated include calcium carbonate (CaCO3), HCl (or Cl2), H2O and / or NH4Cl.

[0019] In some embodiments, sodium bicarbonate, potassium bicarbonate, calcium carbonate, or similar carbonates or bicarbonates produced using the disclosed methods are separated from water-soluble ammonium chloride.

[0020] In some embodiments, sodium bicarbonate or potassium bicarbonate produced using the disclosed methods is converted to sodium carbonate or potassium carbonate, respectively, by heating.

[0021] In some embodiments, ammonium chloride produced using the disclosed methods is converted to hydrochloric acid and ammonia. The resulting hydrochloric acid and ammonia gas mixture can be separated, and the ammonia can then be recovered and used in the disclosed methods.

[0022] In some alternative embodiments, the ammonium chloride is separated and used as a fertilizer or as a product in a fermentation process, and the ammonia used in the disclosed methods serves as a precursor to generate the ammonium chloride.

[0023] In one aspect, a system and method for reducing the carbon dioxide content in a gas stream includes a carbon dioxide absorption and mineralization unit configured to react carbon dioxide, an ammoniated solvent, and at least one metal chloride in the gas stream to produce at least one carbonate or bicarbonate and ammonium chloride; a mineral separation unit configured to separate the carbonate or bicarbonate from the ammonium chloride; and a solvent regeneration unit configured to convert the ammonium chloride into chlorine and ammonium hydroxide using a catalyst, heat, and oxygen.

[0024] Some examples include one or any combination of the above and / or below features.

[0025] In some examples, the solvent regeneration unit is configured to separate HCl from the output of the mineral separation unit and react the HCl with a metal chloride-based catalyst X and oxygen to produce XCl and water. In some examples, the solvent regeneration unit is configured to regenerate the catalyst X by decomposing XCl in the presence of a high-temperature inert gas to produce Cl2. In some examples, the solvent regeneration unit is configured to regenerate the catalyst X by reacting XCl with carbon monoxide to produce phosgene. In some examples, the solvent regeneration unit is configured to regenerate the catalyst X by reacting XCl with water to produce HCl and oxygen.

[0026] Some examples include one or any combination of the above and / or following features. In some examples, the molar ratio of ammonia to HCl in the solvent regeneration unit is greater than 1. In some examples, the solvent regeneration unit is configured to separate HCl from the gas stream by a membrane separation method. In some examples, the system further includes a salt dissolving unit. In some examples, the salt dissolving unit is configured to mix water with salt to form a high salinity solution, which is input to the carbon dioxide absorption and mineralization unit. In some examples, the high salinity solution is CaCl2, MgCl2, NaCl, KCl, or a mixture of two or more aqueous solutions thereof. In some examples, the salt dissolving unit is configured to mix seawater, brackish water, or wastewater with salt to form a high salinity solution, which is input to the carbon dioxide absorption and mineralization unit. In some examples, the high salinity solution is CaCl2, MgCl2, NaCl, KCl, or a mixture of two or more aqueous solutions thereof.

[0027] Some examples include one or any combination of the above and / or following features. In one example, the solvent regeneration unit includes an ammonia absorber configured to mix ammonia from the separation unit with a high-salinity solution to form an ammoniated high-salinity solution; the carbon dioxide absorption and mineralization unit is configured to mix the ammoniated high-salinity solution with a gas stream containing carbon dioxide to generate water-soluble ammonium chloride and carbonates and / or bicarbonates; the mineral separation unit includes a solid-liquid separator configured to separate at least a portion of carbonates and / or bicarbonates from the water-soluble ammonium chloride, wherein the carbonates and / or bicarbonates can be hydrates or anhydrous forms; the solvent regeneration unit further includes a heater configured to evaporate water from the water-soluble ammonium chloride and decompose the ammonium chloride to generate a mixture containing ammonia and HCl; and a water condenser for condensing water vapor generated by the heater to generate liquid water.

[0028] Some examples include one or any combination of the above and / or following features. In some examples, the solvent regeneration unit includes an ammonia absorber configured to mix ammonia with a brine solution to form ammoniated brine. In some examples, the carbon dioxide absorption and mineralization unit is configured to mix the ammoniated brine with a gas stream containing carbon dioxide to produce water-soluble ammonium chloride and carbonates and / or bicarbonates. In some examples, the mineral separation unit includes a solid-liquid separator configured to separate at least a portion of the carbonates and / or bicarbonates from the water-soluble ammonium chloride, wherein the carbonates and / or bicarbonates may be hydrates or anhydrous. In some examples, the system further includes a dryer for removing at least a portion of the water from the hydrated carbonates and / or bicarbonates separated by the solid-liquid separator. In some examples, the solvent regeneration unit further includes a heater configured to evaporate water from the water-soluble ammonium chloride and decompose the ammonium chloride to produce ammonia and HCl. In some examples, the solvent regeneration unit further includes a water condenser for condensing water vapor generated by the heater. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Various aspects of at least one example are discussed below in conjunction with the accompanying drawings, which are not drawn to scale. These drawings are intended to illustrate and further understand the various aspects and examples, are incorporated into and constitute a part of this specification, and are not intended to limit the scope of the invention. In the drawings, identical or nearly identical components shown in various figures may be represented by the same reference numerals or numbers. For clarity, not all components are labeled in every figure. In the drawings:

[0030] Figure 1 It is a schematic diagram of the general form of the system and process of the present invention.

[0031] Figure 2 is a more detailed schematic diagram showing one non-limiting specific example application of the system and process in which calcium chloride is used to generate calcium carbonate (CaCO3) and chlorine gas (Cl2).

[0032] Figure 3 Shown is the rate at which calcium chloride (CaCl2) is converted to calcium carbonate (CaCO3) in flue gas containing different concentrations of carbon dioxide.

[0033] Figure 4 Shown are the rates of ammonia production when the experiments were performed at different temperatures.

[0034] Figure 5 Shown are the average and maximum rates of ammonia formation for packed-bed and fluidized-bed reaction experiments conducted under identical conditions.

[0035] Figure 6The amount of ammonia and hydrochloric acid dissolved in the solution, determined by ion chromatography, is shown over time.

[0036] Figure 7 Shown are the average and maximum rates of chlorine production for experiments conducted at different temperatures, with other parameters remaining the same.

[0037] Figure 8 The average and maximum rates of chlorine production in packed bed and fluidized bed reactions are shown under the same other parameter conditions.

[0038] Figure 9 The average and maximum rates of chlorine formation are shown when the experiments are conducted using different catalyst dosages and the minimum fluidizing oxygen flow rate required for each bed size, while keeping other parameters the same.

[0039] Figure 10 Shown are the measured moles of chlorine dissolved in solution and the estimated total chlorine production based on a 7% solubility of chlorine in water. DETAILED DESCRIPTION

[0040] The examples of materials, systems, methods, and devices discussed herein are not limited to the structural details and component arrangements described below or shown in the accompanying drawings. These systems, methods, and devices can be implemented in other examples and can be practiced or implemented in various ways. The specific implementation examples provided herein are for illustrative purposes only and are not intended to be limiting. The functions, components, elements, and features of any one or more examples described herein should not be construed as inapplicable in other examples.

[0041] The examples disclosed herein may be combined with other examples in any manner consistent with at least one principle disclosed herein, and references to terms such as "one example," "some examples," "alternative examples," "various examples," and "an example" are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic being described may be included in at least one example. The appearances of such terms herein do not necessarily all refer to the same example.

[0042] In addition, the words and terms used herein are for descriptive purposes only and should not be considered limiting. For examples, components, elements, operations or functions in the computer program products, systems and methods involved in this document, if referenced in the singular, multiple implementations should also be included; if referenced in the plural, only one implementation should also be included. Therefore, references in the singular or plural form should not limit the disclosed systems or methods, their components, operations or elements. As used herein, "includes," "comprising," "having," "containing," "involving" and their variations are intended to cover the items listed thereafter and their equivalents as well as additional items. References to "or" can be interpreted as inclusive, so any term described using "or" can represent any, multiple or all of the terms.

[0043] The present disclosure describes a system and method for capturing and converting carbon dioxide (CO2) (as contained in flue gas and / or fermentation tail gas) to generate chemical products with commercial value. The disclosed method includes capturing CO2 using a high salinity solution and ammonia and converting it into CaCO3, MgCO3, NaHCO3, KHCO3 or other similar carbonates or bicarbonates, and NH4Cl. In some embodiments, the bicarbonate can be further processed and converted into carbonate. In some embodiments, NH4Cl can be converted into NH3 and HCl by heating. In other alternative embodiments, NH4Cl can be converted into NH3 and NaCl, KCl, CaCl2 or similar products by adding NaOH, KOH, Ca(OH)2 or similar hydroxides.

[0044] The disclosed systems and methods allow for regeneration of the CO2 absorbent, which can improve efficiency and minimize the amount of by-products generated.

[0045] Figure 1 A general process 10 for converting a CO2-rich gas stream into a CO2-depleted gas stream and commercially valuable chemical products is shown. Process 10 consists of three key equipment packages / steps: step 12, absorption and mineralization of CO2 to produce X-carbonate and ammonium chloride ("Product A"); step 14, separation of X-carbonate and ammonium chloride from the mineralized product stream; and step 16, conversion of ammonium chloride into a solvent that can be reused in step 12 and other products. Note that Figure 1 The numbered boxes in the figure represent the processes and devices used to perform these processes. It will be apparent to those skilled in the art that some processes can be implemented in combination by a single unit or device.

[0046] In some embodiments, the disclosed method uses brine (sodium chloride aqueous solution) and ammonia to capture and convert CO2, and the main products generated in step 12 include sodium carbonate (Na2CO3), HCl (or Cl2), H2O and / or NH4Cl.

[0047] In some embodiments, the disclosed method uses aqueous potassium chloride and ammonia gas to capture and convert CO2, and the main products generated in step 12 include potassium carbonate (K2CO3), HCl (or Cl2), H2O and / or NH4Cl. In embodiments where flue gas is captured and converted, additional products of step 12 may include potassium nitrate (KNO3), potassium nitrite (KNO2), potassium sulfite (K2SO3), potassium metabisulfite (KHSO3), potassium metabisulfate (KHSO4), and potassium sulfate (K2SO4).

[0048] In some embodiments, the disclosed method uses brine (sodium chloride aqueous solution) and ammonia gas to capture and convert CO2, and the main products generated in step 12 include sodium bicarbonate (NaHCO3), HCl (or Cl2), H2O and / or NH4Cl. In some embodiments, the disclosed method uses potassium chloride aqueous solution and ammonia gas to capture and convert CO2, and the main products generated in step 12 include potassium bicarbonate (KHCO3), HCl (or Cl2), H2O and / or NH4Cl.

[0049] In some embodiments, the disclosed method uses an aqueous solution of calcium chloride and ammonia gas to capture and convert CO2, and the main products generated in step 12 include calcium carbonate (CaCO3), HCl (or Cl2), H2O and / or NH4Cl.

[0050] In some embodiments, the sodium bicarbonate, potassium bicarbonate, calcium carbonate, or similar carbonate or bicarbonate salts produced in step 12 using the disclosed methods are separated from the aqueous ammonium chloride solution in step 14.

[0051] In some embodiments, the sodium bicarbonate or potassium bicarbonate produced in step 12 using the disclosed methods is heated and converted to sodium carbonate or potassium carbonate, respectively.

[0052] In some embodiments, ammonium chloride produced in step 12 using the disclosed methods is separated from solution in step 14 and converted into hydrochloric acid and ammonia in step 16. The resulting hydrochloric acid and ammonia gas mixture is separated in step 16, and the ammonia is then recovered for reuse in the disclosed methods.

[0053] about Figure 1In the process 10 shown, in some embodiments, the input of step 12 is a gas stream containing carbon dioxide, an absorbent (e.g., NH4OH), and a high salinity solution (X-Cl). In addition, the gases used for any separation process in steps 14 and 16, including reactants, are also input. In some embodiments, the gases used for the separation process can be N2 and O2. In some embodiments, the gases used for the separation process can be CO and O2. The output of this process is carbonate and / or bicarbonate (e.g., sodium bicarbonate and calcium carbonate, X-CO3), chlorine (Cl2), water, N2, and O2. In some embodiments, the product may include hydrochloric acid (HCl). In some embodiments, the product may include phosgene (COCl2).

[0054] In some embodiments, salt is mixed with water in a salt dissolver (not shown) to produce a high salinity solution. The high salinity solution may also be referred to herein as a brine solution or brine. The salt may be pure NaCl, CaCl2, KCl, or MgCl2, or a mixture of these salts. In some embodiments, calcium chloride may be added to the salt dissolver in one of three forms: anhydrous CaCl2, CaCl2·2H2O, or CaCl2·4H2O. In some embodiments, magnesium chloride may be added to the salt dissolver in one of two forms: anhydrous MgCl2 or MgCl2·6H2O. In some embodiments, the output of the process is a saturated solution of salt at the operating temperature. In some embodiments, the salt dissolver is configured to operate in a wide temperature range of 15-70°C, with a preferred operating temperature range of 25-60°C.

[0055] In some embodiments, seawater or brackish water can be used as the medium in the salt dissolver. Thus, the disclosed methods can be applied in seawater desalination or water treatment processes, as fresh water is one of the products produced by using the disclosed methods.

[0056] Before processing the CO2-containing gas stream, the gas stream temperature can be reduced by transferring heat to other process units. For example, in some embodiments, heat can be transferred to the catalytic process (step 16), which produces NH4OH and Cl2. After the gas stream temperature is reduced, it enters the absorption and mineralization process, step 12.

[0057] In some embodiments, the components that interact in step 12 are a gas stream containing carbon dioxide, NH4OH, and a high-salinity aqueous solution, which may contain NaCl, CaCl2, KCl, or a mixture of these salts. In some embodiments, the high-salinity aqueous solution is prepared by mixing these salts with water in a stirred reactor. In some embodiments, the high-salinity aqueous solution is mixed with ammonia in an ammonia absorber to form an ammoniated solution, which then flows from the top of the absorption tower into the CO2 absorber (step 12) and is countercurrently contacted with the CO2-enriched gas stream entering from the bottom of the tower. The overall reaction between the high-salinity solution, ammonium hydroxide, and CO2, depending on the composition of the high-salinity solution, may be one or more of the following reactions:

[0058] NaCl(aq)+NH4OH+CO2→NaHCO3(s)+NH4Cl(aq) (1)

[0059] CaCl2(aq)+2NH4OH+CO2→CaCO3(s)+2NH4Cl(aq) (2)

[0060] MgCl2(aq)+2NH4OH+CO2→MgCO3(s)+2NH4Cl(aq) (3)

[0061] KCl(aq)+NH4OH+CO2→KHCO3(s)+NH4Cl(aq) (4)

[0062] In some embodiments, the absorption and mineralization unit (step 12) is configured to operate within a wide temperature range of 10-70° C., with a preferred operating temperature range of 15-60° C. As a result of absorbing CO 2 in the absorption and mineralization unit, the CO 2 content in the gas stream can be reduced by at least 30% and up to 99%.

[0063] In some embodiments, biogas is the gas stream entering step 12. Due to the absorption and mineralization, the gas discharged from the absorber is a methane-rich gas stream. In some embodiments, this methane-rich gas stream can be used commercially as renewable natural gas (RNG).

[0064] The solution flowing out of the bottom of the absorber 12 contains aqueous NH4Cl and carbonates and / or bicarbonates (including but not limited to CaCO3, NaHCO3, KHCO3 and MgCO3) and is directed to the separation process / unit 14. Here, the carbonates and / or bicarbonates are separated, and the aqueous NH4Cl is transferred to the heater (regenerator) in the catalytic process / unit 16. In certain embodiments, the mass percentage of solid carbonates and / or bicarbonates discharged from the carbon dioxide absorber in step 12 is between 10% and 50% and enters the solid-liquid separator in step 14. In certain embodiments, the solid-liquid separator in step 14 is composed of or includes a filter or a centrifuge.

[0065] In step 14, the ammonium chloride in the aqueous solution remaining after solid-liquid separation of the solid carbonate and / or bicarbonate is separated by another separation unit. In certain embodiments, the separator can be a crystallizer or an evaporator. In certain embodiments, a single unit can simultaneously separate carbonate and / or bicarbonate and ammonium chloride from the product generated in step 12. The NH4Cl-rich stream leaving step 14 enters the catalytic process step 16.

[0066] In the catalytic process step 16, the NH4Cl in the enriched stream decomposes into NH3 and HCl at high temperature, with the overall reaction being as follows:

[0067] NH4Cl→HCl(g)+NH3(g) (5)

[0068] In certain embodiments, in step 16, NH is recovered by a catalytic regeneration process, a membrane process, or other separation methods. In certain embodiments, a catalytic regeneration process is used to recover NH from the stream by the following reaction, wherein hydrochloric acid (HCl) reacts with a catalyst (X) and oxygen (ammonia recovery step):

[0069] 4HCl(g)+O2(g)+4X→4XCl+2H2O (6)

[0070] In certain embodiments, the catalyst (X) used in the catalytic process can be a metal chloride, such as nickel chloride, cobalt chloride, CuCl or FeCl2.

[0071] In certain embodiments, the catalyst (X) used in the catalytic process can be a molten alkali metal chloride, such as KCl, NaCl, CuCl, KiCl2, mixed with metal oxides such as Fe, Ni, Co and Cu, as described in U.S. Patent No. 3,627,471 (A).

[0072] In certain embodiments, the catalyst (X) used in the catalytic process may be an activated form of a mixture consisting of a metal suboxide selected from Mn, Fe, Co, Cu and Ni, potassium chloride and copper monochloride, as described in US Pat. No. 3,410,657.

[0073] In certain embodiments, the catalyst used in the catalytic process can be a metal oxide (MO), such as nickel oxide, cobalt oxide or CuO, preferably CuO. As described in U.S. Patent No. 4,959,202A. In certain embodiments, when a metal oxide (such as copper oxide) is used to separate NH3 from a stream, the reaction is as follows:

[0074] 4HCl(g)+2MO→2MCl2+2H2O (7)

[0075] In certain embodiments, the catalyst used in the catalytic process is impregnated onto a support material, such as alumina, silica, or a molecular sieve material, as described in U.S. Patent No. 4,959,202. Impregnation of the catalyst onto these materials can provide different surface structures, thereby affecting the reaction rate.

[0076] In certain embodiments, the ammonia recovery step of the catalytic process operates at a temperature ranging from 180° C. to 450° C., preferably from 180° C. to 300° C. In certain embodiments, the pressure in the ammonia recovery step of the catalytic process may be at least 1 bar and may be as high as 20 bar.

[0077] In certain embodiments, a high temperature inert gas (e.g., N2) is used to release Cl2 from the catalyst used in the ammonia recovery step and restore it to its original state (catalyst regeneration step) by the following reaction:

[0078] 2XCl→2X+Cl2 (8)

[0079] In certain embodiments, when a metal (M) oxide (e.g., copper oxide) is used to separate NH from a stream in the ammonia recovery step of a catalytic process, the catalyst is regenerated using oxygen by the following reaction:

[0080] 2MCl2+O2(g)→2MO+Cl2 (9)

[0081] In certain embodiments, superheated steam is used in the catalyst regeneration step to generate hydrochloric acid (HCl) by the following reaction:

[0082] 4XCl+2H2O→4X+2HCl+O2(g) (10)

[0083] In certain embodiments, CO is used in the catalyst regeneration step to generate phosgene (COCl2) by the following reaction:

[0084] 2XCl+CO→2X+COCl2 (11)

[0085] In certain embodiments, the catalyst regeneration step is operated at a temperature in the broad range of 300-800° C., preferably in the range of 300-500° C. In certain embodiments, the pressure in the catalyst regeneration step may be at least 1 bar and may be as high as 20 bar.

[0086] In certain embodiments, there are two gas streams exiting the catalytic process, one of which is an ammonia-containing gas stream having an ammonia to hydrochloric acid molar ratio greater than 1, and the other is a chlorine-containing gas stream having an ammonia to chlorine molar ratio less than 2.

[0087] In certain embodiments, there are two gas streams exiting the catalytic process, one of which is an ammonia-containing gas stream having a molar ratio of ammonia to hydrochloric acid greater than 1, and the other is a hydrochloric acid-containing gas stream having a molar ratio of ammonia to hydrochloric acid less than 1.

[0088] In certain embodiments, there are two gas streams exiting the catalytic process, one of which is an ammonia-containing gas stream having a molar ratio of ammonia to hydrochloric acid greater than 1, and the other is a phosgene-containing gas stream having a molar ratio of ammonia to phosgene less than 1.

[0089] In certain embodiments, the ammonia-containing gas stream exiting the catalytic process is dissolved in water to generate fresh solvent (NH4OH) for the absorption and mineralization steps, as follows:

[0090] NH3(g)+H2O→NH4OH(aq) (12)

[0091] In certain embodiments, the temperature of the ammonia-containing gas stream exiting the catalytic process can be reduced by transferring heat to other process units before it is recovered. For example, in certain embodiments, heat can be transferred back to the catalytic process to generate NH4OH and Cl2. After the gas stream temperature is reduced, it enters the amination reactor to complete the catalytic process and regenerate the solvent.

[0092] Figure 2 A non-limiting process example 30 is shown. Figure 1A more detailed example of the process shown. The absorption and mineralization unit 12a includes a mineralizer 32, in which a CO2-enriched gas stream (such as flue gas or fermentation tail gas) is contacted with a solvent (a mixture of NH4OH and CaCl2) to produce CaCO3, NH4Cl and CO2 removal gas. The CO2 removal gas then flows out and completely leaves the process. After step 32, the CaCO3 in solid form is physically separated from the ammonium chloride aqueous solution by a physical separation process (such as a filtration step 34). The produced CaCO3 slurry can be dried using a dryer 35 as needed and then further used, such as sold to the industrial market or used in other processes. The separation step output of the filter 34 is an ammonium chloride solution, which is fed into a crystallizer 36. The product of the crystallizer is a more concentrated ammonium chloride solution (NH4Cl slurry) and water (containing some residual salts). The water is fed into a mixer 42. The separation process / unit 14a includes a filter 34, a crystallizer 36 and an optional dryer 35.

[0093] The slurry from the crystallizer 36 is heated to 200–350°C in a sublimation unit / step 38 to sublimate the ammonium chloride into ammonia (NH3) and hydrochloric acid (HCl). Unit 38 includes a condenser for condensing the water vapor produced by the heater. The condensed water is sent to unit 42. In step / regenerator 40, the hydrochloric acid reacts with the catalyst in the presence of oxygen to release ammonia. The recovered ammonia flows out as a gas and leaves the regeneration unit. The catalyst is heated to 400–500°C to produce chlorine gas. The water obtained from steps 36 and 38 is mixed with CaCl2 salt in a mixer / step 42 to produce a CaCl2 aqueous solution. The ammonia released from step 40 is then mixed with the CaCl2 aqueous solution (the product of step 42) in an ammoniaation unit (step 44) to produce fresh solvent for the absorption and mineralization process (step 32). Catalytic process 16a includes sublimation 38, regeneration 40, mixer 42, and ammoniaation 44.

[0094] Please note that Figure 2 The numbered boxes in the figure represent the processes and equipment used to perform these processes. It will be apparent to those skilled in the art that some processes can be combined into one unit or device.

[0095] Example

[0096] Example 1: Mineralization

[0097] The first parameter tested was the influence of solvent composition. This effect was examined by conducting mineralization experiments using different solvents in a 3-inch diameter and 36-inch high PVC column. For each mineralization experiment, the column was packed with ceramic particles to help evenly distribute the gas and liquid within the column, and a CO2-enriched feed was introduced into the column via a bubbler located at the bottom of the reactor. Additionally, solvent was added from the top of the column and flowed to an outlet at the bottom. The configuration operated in semi-batch mode, meaning that the solvent was continuously recycled while fresh CO2 was continuously fed into the column. The entire experiment was conducted at room temperature, and the conversion process was tracked by pH. The mineralization process continued until the pH either stopped changing or began to rise. Calibration samples were prepared to determine the pH at different calcium chloride conversion rates.

[0098] The experiment found that the required concentrations of calcium chloride (CaCl2) and ammonium hydroxide (NH4OH) in the solvent were 2.51 and 10.56 molar ratios, respectively (NH4OH had a 110% stoichiometric excess). However, when the concentrations of either were individually reduced by a factor of 10, additional undesirable products were formed when 2.51 molar ratios of CaCl2 were combined with 1.06 molar ratios of NH4OH (CaCl2 was a 374% stoichiometric excess) and 0.251 molar ratios of CaCl2 were combined with 10.56 molar ratios of NH4OH (NH3 was a 1995% stoichiometric excess). This was determined by preparing samples based on the expected conversion of the limiting reagent and developing a pH calibration curve. For excess calcium chloride and ammonium hydroxide, the two sets of samples reached an estimated conversion of 190% and 135%, respectively, indicating that additional products were formed, further changing the pH value. Table 1 lists the expected starting pH, expected 100% conversion pH, actual starting pH, and actual final pH for each solvent ratio tested, and shows that the standard solvent ratio was within the expected pH range, while the final pH of the two significantly excess solvent ratios was outside the expected range.

[0099] Table 1. Comparison of expected and actual pH values ​​under different solvent compositions

[0100]

[0101]

[0102] Another potential influence investigated was the effect of feed CO2 concentration. CO2 compositions of 100%, 75%, and 25% by volume were tested. The results showed that, while the total flow rate remained constant, the rate of calcium carbonate formation decreased as the CO2 concentration decreased. This was expected, as lower concentrations meant a slower CO2 transport rate into the mineralization column. Figure 3The calcium carbonate formation rate was compared at different flue gas concentrations. The composition of the mineralized products was analyzed using carbon, hydrogen, and nitrogen (CHN) elemental analysis, revealing that the carbon dioxide concentration in the feed did not affect the purity of the produced calcium carbonate. Table 2 shows the purity of the calcium carbonate produced at different flue gas concentrations. Minor differences in sample purity were attributed to minor inconsistencies in the washing process.

[0103] Table 2. Purity of calcium carbonate under different volume fractions of carbon dioxide

[0104] Carbon dioxide concentration Calcium carbonate purity <![CDATA[Percentage of captured CO2]]> 100％ 97.8％ 99.4％ 75％ 98.0％ 97.2％ 25％ 99.1％ 97.1％

[0105] Example 2: Crystallization

[0106] Since ammonium chloride is less soluble in water than calcium chloride, crystallization can be used to supersaturate the solution with ammonium chloride while remaining unsaturated with calcium chloride. Once the ammonium chloride is supersaturated, it forms solid crystals that are easily separated from the waste solvent and fed to the regeneration unit.

[0107] To test this hypothesis, a bench-scale forced circulation crystallizer was constructed. Solution was introduced upward from below the liquid surface into the crystallizer, and a stream rich in solid crystals subsequently flowed from the bottom of the crystallizer into an open reservoir. The solution in the reservoir was then pumped back into the crystallizer via a boiling water heat exchanger. The crystallizer was operated at different heat exchanger temperatures, each for one hour. The experiment was terminated once visible crystals formed, and the final solution was collected and the crystals isolated by centrifugation.

[0108] After the crystallization process, salt crystals formed on the surface near the outlet, and the remaining solution was centrifuged to remove any remaining suspended crystals. Liquid samples were then analyzed by ion chromatography (IC) to determine the concentrations of ammonium, calcium, and chloride ions. The IC results, shown in Table 3, support this hypothesis. After crystallization, the ammonium concentration in the sample decreased, confirming that ammonium formed solid crystals that were removed. However, the calcium concentration increased due to the reduction in solvent volume (solvent evaporation during the crystallization process).

[0109] Table 3. Concentrations of ammonium chloride and calcium chloride in the solvent before and after crystallization

[0110] Initial concentration (mM) Final concentration (mM) calcium chloride 137.3 284.2 Ammonium chloride 753.7 553.1

[0111] By accounting for the loss of solvent due to evaporation, the molar amounts of calcium chloride and ammonium chloride in the sample before and after crystallization can be calculated. Table 4 shows that during the crystallization process, the calcium chloride content in the sample remained constant (with a change rate of 0.4%), while the ammonium chloride content decreased by 65.7%. This confirms that the ammonium chloride crystallized to form solid crystals while the calcium chloride remained dissolved in the solvent. These solid crystals were then collected by filtration, achieving an ammonium chloride recovery rate of 65.7%.

[0112] Table 4. Moles of ammonium chloride and calcium chloride in the solvent before and after crystallization

[0113] Initial concentration (mmol) Final concentration (mmol) calcium chloride 127.0 126.5 Ammonium chloride 697.2 246.1

[0114] Example 3: Solvent Regeneration

[0115] Several parameters can influence the solvent regeneration step. Experimental studies investigated the effects of temperature, bed arrangement, and the salt phase at the time of dosing. These effects were investigated using two experimental setups. The first setup was a fixed-bed reactor filled with catalyst-impregnated alumina pellets and an ammonium chloride salt placed in the center. The reactor was then heated to different temperatures while oxygen was introduced. The second setup was a fluidized-bed setup, in which the pure catalyst was mixed with the salt and fluidized in a columnar reactor heated to the same temperature as the fixed bed, using oxygen as the fluidizing gas. For both sets of experiments, ammonia generation was measured by dissolving the generated ammonia in water and monitoring the pH until the pH either remained constant or began to decrease over time.

[0116] The effect of temperature was tested in a fixed bed at temperatures ranging from 190°C to 240°C. It was found that the rate of ammonia formation increased with increasing temperature. The formation rates at 190°C, 210°C, 230°C, and 240°C were shown in Table 1. Figure 4 and Table 5. Small performance gains were observed between 190°C, 210°C, and 230°C, but both the average and instantaneous maximum rates increased tenfold when the temperature was increased from 230°C to 240°C. This efficiency improvement is expected to be due to the significant increase in the sublimation rate of ammonium chloride between 230°C and 240°C. This increase in sublimation rate significantly increases the amount of hydrochloric acid available to react with the catalyst.

[0117] Table 5. Average and instantaneous maximum ammonia production rates at different temperatures

[0118] temperature Average rate (g / min) Maximum rate (g / min) 190℃ 0.000025 0.000065 210℃ 0.000055 0.000157 230℃ 0.000100 0.000272 240℃ 0.001083 0.003110

[0119] The solvent regeneration process was also tested in a fluidized bed using pure copper chloride (CuCl) as a catalyst. Compared to a fixed bed at the same temperature, the average rate in the fluidized bed was twice as high and the maximum rate was three times as high. A comparison of the two experiments shows that Figure 5 Samples collected during the regeneration of the fluidized bed solvent were analyzed by ion chromatography to verify the presence of the expected ions in solution. Figure 6As shown, the ammonia concentration increases over time, while the chlorine concentration remains constant. This confirms that during solvent regeneration, chlorine is captured by the catalyst while ammonia is released through the reactor. At the end of the experiment, the dissolved hydrochloric acid concentration rises slightly, indicating that at 90 minutes, the amount of fresh catalyst is less than the amount of hydrochloric acid being generated, and the catalyst needs to be regenerated.

[0120] Example 4: Catalyst regeneration

[0121] The copper(II) chloride can then undergo thermal decomposition to produce copper(II) chloride (the original catalyst) and chlorine gas (one of the products of the overall process). The rate of this thermal decomposition is affected by a number of factors. Factors tested experimentally include temperature, fluidization conditions, bed size, grind size, and pre-drying treatment. The two apparatuses used to test solvent regeneration were also used for the catalyst regeneration tests: a fixed bed and a fluidized bed. The key differences are that the operating temperature is increased (starting at 400°C) and no ammonium chloride salt is used. In the fixed bed, the catalyst is impregnated on alumina pellets and maintained at different temperatures while oxygen is introduced; in the fluidized bed, the pure catalyst is fluidized in a column reactor and maintained at different temperatures. Under both operating conditions, the amount of chlorine generated is measured by dissolving chlorine in water and monitoring the pH change (until the pH no longer changes with time or begins to rise).

[0122] Because catalyst regeneration is achieved through thermal decomposition, temperature is the primary control parameter. The regeneration process was performed at various temperatures, ranging from 400°C to 450°C, using a simple fixed bed. The study found that while the reaction can occur as low as 400°C, efficiency increases with increasing temperature. Figure 7 The average and maximum rates of catalyst regeneration experiments conducted at 400°C, 430°C, and 450°C were compared.

[0123] The study also found that fluidizing the system can increase the rate of chlorine generation. This is mainly attributed to two factors: first, the fluidized system uses a smaller particle size catalyst, which increases the specific surface area of ​​the catalyst in the bed; second, the fluidization itself improves the mixing effect and enhances the interaction between the catalyst and the heated wall. These improvements increased the chlorine generation rate by about 10 times. Under the same conditions (fluidization using oxygen and a temperature of 400°C), the average chlorine generation rate of the fixed bed system was 0.108 mg / min per gram of catalyst, and the maximum rate was 0.354 mg / min; while the average rate of the fluidized bed system was 1.896 mg / min and the maximum rate was 7.392 mg / min. A direct comparison of these values ​​can be seen in Figure 8 .

[0124] After confirming that the fluidized system could generate chlorine at a higher rate within a reactor of the same size, the team next tested the maximum catalyst mass that could be used in a single regeneration. To achieve this, the initial catalyst mass was increased from 10 grams to 20 grams, and the oxygen flow rate was increased accordingly to meet the required fluidization conditions. The results showed that doubling the catalyst mass had little effect on the average chlorine generation rate per unit catalyst mass (from 1.896 mg / min to 1.794 mg / min), but the maximum generation rate per unit mass decreased by approximately 20% (from 7.392 mg / min to 5.880 mg / min). Figure 9 The average and maximum formation rates of the two catalysts were compared for their initial mass. This comparison shows that increasing the catalyst mass leads to a slight decrease in the chlorine formation rate per unit mass of catalyst.

[0125] As described above, while various aspects of at least one example have been described, those skilled in the relevant art will readily appreciate that the present invention is susceptible to various modifications, improvements, and variations. Such modifications, improvements, and variations are intended to form part of this specification and are considered to fall within the scope of the present invention. Therefore, the foregoing description and drawings are intended to be illustrative only, and the scope of protection of the present invention should be determined by a reasonable interpretation of the appended claims and their equivalents.

Claims

1. A system for reducing the carbon dioxide content in a gas stream, comprising: a carbon dioxide absorption and mineralization module configured to react carbon dioxide in the gas stream with an ammoniated solvent and at least one metal chloride to produce carbonates and / or bicarbonates, and ammonium chloride; a mineral separation module configured to separate carbonate and bicarbonate from ammonium chloride; as well as A solvent regeneration module is configured to react ammonium chloride, heat, and oxygen using a catalyst to produce chlorine and ammonium hydroxide.

2. The system according to claim 1, wherein: The solvent regeneration module is configured to separate hydrochloric acid (HCl) in the product from the mineral separation module by reacting HCl with a metal chloride-based catalyst X and oxygen to generate XCl and water.

3. The system according to claim 2, characterized in that The solvent regeneration module is configured to regenerate the catalyst X and generate Cl 2 by decomposing XCl in the presence of a high-temperature inert gas.

4. The system according to claim 2, wherein: The solvent regeneration module is configured to regenerate catalyst X by reacting XCl with carbon monoxide to form phosgene (COCl2).

5. The system according to claim 2, wherein: The solvent regeneration module is configured to regenerate catalyst X by reacting XCl with water to generate hydrochloric acid and oxygen.

6. The system according to claim 1, wherein: The molar ratio of ammonia to hydrochloric acid in the solvent regeneration module is greater than 1.

7. The system according to claim 6, characterized in that The solvent regeneration module is configured to separate hydrochloric acid from a gas stream by a membrane separation process.

8. The system according to claim 1, wherein: The system further includes a salt dissolution unit.

9. The system according to claim 8, characterized in that The salt dissolution unit is configured to mix water with salt to form a high-salinity solution, which is input into the carbon dioxide absorption and mineralization module.

10. The system according to claim 9, characterized in that The high-salinity solution is an aqueous solution of CaCl2, MgCl2, NaCl, KCl, or a mixture of two or more thereof.

11. The system according to claim 8, wherein: The salt dissolution unit is configured to mix seawater, brackish water or wastewater with salt to form a high-salinity solution, which is input into the carbon dioxide absorption and mineralization module.

12. The system according to claim 11, wherein: The high-salinity solution is an aqueous solution of CaCl2, MgCl2, NaCl, KCl, or a mixture of two or more thereof.

13. The system according to claim 11, wherein: The solvent regeneration module includes an ammonia absorber configured to mix ammonia from the separation module with the high salinity solution to form an ammoniated high salinity solution; The carbon dioxide absorption and mineralization module is configured to mix the ammoniated high-salinity solution from the ammonia absorber with a gas stream containing carbon dioxide to form an aqueous solution of ammonium chloride and carbonates and / or bicarbonates; The mineral separation module comprises a solid-liquid separator configured to separate at least a portion of carbonates and / or bicarbonates from the aqueous ammonium chloride solution, wherein the carbonates and / or bicarbonates may be hydrated or anhydrous; and The solvent regeneration module further includes a heater configured to evaporate water from the aqueous ammonium chloride solution and decompose the ammonium chloride to form a mixture including ammonia and HCl; and a condenser configured to condense water vapor generated by the heater to generate liquid water.

14. The system according to claim 1, wherein: The solvent regeneration module includes an ammonia absorber configured to mix ammonia with a brine solution to form an ammoniated brine.

15. The system according to claim 14, wherein: The carbon dioxide absorption and mineralization module is configured to mix the ammoniated brine with a carbon dioxide-containing gas stream to form an aqueous ammonium chloride solution and carbonates and / or bicarbonates.

16. The system according to claim 15, characterized in that The mineral separation module includes a solid-liquid separator configured to separate at least a portion of carbonates and / or bicarbonates from the aqueous ammonium chloride solution, wherein the carbonates and / or bicarbonates may be hydrated or anhydrous.

17. The system according to claim 16, wherein: The system further includes a dryer configured to remove at least a portion of water from the hydrated carbonate and / or bicarbonate separated in the solid-liquid separator.

18. The system according to claim 15, wherein: The solvent regeneration module further includes a heater configured to evaporate water from the aqueous ammonium chloride solution and decompose the ammonium chloride to generate ammonia and hydrogen chloride (HCl).

19. The system according to claim 18, wherein: The solvent regeneration module further includes a water condenser configured to condense water vapor generated by the heater.

20. A method for reducing the amount of carbon dioxide contained in a gas stream, comprising the steps of: generating carbonates and / or bicarbonates, and ammonium chloride from the carbon dioxide, the ammoniated solvent, and at least one metal chloride in the gas stream; separating carbonates and bicarbonates from ammonium chloride; and Using a catalyst, ammonium chloride is converted into chlorine and ammonium hydroxide in the presence of heat and oxygen.

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