Magnesium-mediated electrolytic recycling method and system

Abstract

This invention belongs to the field of green chemistry and carbon neutrality, and discloses a magnesium-mediated electrolytic recycling method and system, comprising: Step 1, pre-activating magnesium raw materials, exposing the activated magnesium to a nitrogen-containing atmosphere under normal pressure and heating conditions to undergo a solid-gas nitridation reaction to generate magnesium nitride, which then reacts with water to undergo hydrolysis to generate ammonia and solid magnesium hydroxide, and collecting the ammonia; Step 2, exposing magnesium hydroxide to a carbon dioxide-containing gas stream, where the magnesium hydroxide reacts with carbon dioxide to generate magnesium carbonate; Step 3, acidifying the magnesium carbonate to release carbon dioxide, obtaining a magnesium ion-containing solution, further pre-treating the magnesium ion-containing solution, and then regenerating it through an electrolytic process to obtain metallic magnesium, which is then returned to Step 1 for recycling. This invention achieves direct ammonia synthesis from air and simultaneous direct air carbon capture under mild conditions.

Description

Technical Field

[0001] This invention belongs to the field of green chemistry and carbon neutrality, and relates to a magnesium-mediated electrolytic cycle method and system. Background Technology

[0002] Ammonia is one of the world's most produced basic chemicals, playing an irreplaceable and crucial role in numerous fields such as agriculture, chemicals, and energy. In the energy sector, ammonia is considered a highly promising clean energy carrier, applicable to energy storage and fuel cells.

[0003] The traditional Haber-Bosch process is currently the mainstream method for industrial ammonia synthesis, playing a crucial role in large-scale ammonia production since its introduction in the early 20th century. However, its synthesis process requires harsh conditions of high temperature (>400℃) and high pressure (>15MPa), placing extremely high demands on equipment materials and manufacturing processes. Furthermore, it relies on fossil fuels for hydrogen production, consuming large quantities of fossil fuels such as coal and natural gas, while simultaneously generating massive amounts of carbon dioxide emissions, posing a serious challenge to global climate change and environmental protection.

[0004] Emerging electrochemical nitrogen fixation technology, based on electrochemical principles, utilizes electrical energy to drive the reduction reaction of nitrogen to synthesize ammonia. It possesses potential advantages such as mild reaction conditions and the elimination of fossil fuels, making it a promising green ammonia synthesis method. However, current electrochemical nitrogen fixation technology faces numerous challenges in practical applications. Among these, the hydrogen evolution reaction (HEP) is a key factor restricting its development. During electrochemical nitrogen fixation, due to the extremely high stability and chemical inertness of nitrogen molecules, the activation energy of its reduction reaction is high, resulting in slow reaction kinetics. In contrast, protons in aqueous solutions more readily gain electrons at the electrode surface to undergo reduction reactions to generate hydrogen, leading to a large number of HEP reactions. These HEP reactions not only consume significant amounts of electrical energy, reducing energy efficiency, but also compete with the nitrogen reduction reaction for active sites, inhibiting ammonia formation and significantly reducing the Faraday efficiency. Faraday efficiency is a crucial indicator of the performance of electrochemical ammonia synthesis; a low Faraday efficiency means that most of the electrical energy is not effectively converted into the chemical energy of ammonia, severely impacting the economic viability and feasibility of electrochemical nitrogen fixation technology. Although researchers have improved Faraday efficiency to some extent by optimizing electrode materials and electrolyte composition, it is still difficult to meet the requirements for industrial application.

[0005] Direct air carbon capture (SACC) technology can directly capture carbon dioxide from the atmosphere; however, the high energy consumption of adsorbent regeneration is a core issue restricting the development of this technology. SACC typically requires the use of specific adsorbents to adsorb carbon dioxide from the atmosphere. Once the adsorbent reaches saturation, it needs to be regenerated to release the captured carbon dioxide and restore its adsorption capacity. Currently used adsorbent regeneration methods consume significant amounts of energy. This high energy consumption not only increases the cost of carbon capture but also offsets some of the carbon reduction benefits, making SACC economically uncompetitive. Furthermore, the cost of the adsorbent is also a crucial factor affecting the development of SACC. Currently, high-performance adsorbent materials are often expensive and have a limited lifespan, further increasing the cost of carbon capture.

[0006] Currently, ammonia synthesis technology and carbon capture technology each have many problems, and there is no technology that can couple nitrogen activation and carbon capture processes in one cycle to achieve "negative carbon" chemical production. Summary of the Invention

[0007] The purpose of this invention is to provide a magnesium-mediated electrolytic cycle method and system to solve the problems of high energy consumption and large carbon emissions in existing ammonia synthesis processes, as well as the high cost and difficulty in effectively integrating direct air carbon capture technology with chemical production.

[0008] To achieve the above objectives, the present invention employs the following technical solution: A magnesium-mediated electrolytic cycling method, comprising: Step 1: Pre-activate the magnesium raw material by exposing the activated magnesium to a nitrogen-containing atmosphere under normal pressure and heating conditions to solidify. The gas nitriding reaction produces magnesium nitride, which then undergoes hydrolysis upon contact with water to produce ammonia and solid magnesium hydroxide. The ammonia is then collected. Step 2: Expose magnesium hydroxide to a gas stream containing carbon dioxide. Magnesium hydroxide reacts with carbon dioxide to form magnesium carbonate. Step 3: Acidify the magnesium carbonate to release carbon dioxide and obtain a solution containing magnesium ions. After further pretreatment of the solution containing magnesium ions, regenerate it through an electrolytic process to obtain metallic magnesium. The obtained metallic magnesium is returned to Step 1 for recycling.

[0009] Furthermore, the purity of the metallic magnesium raw material is 99.0%~99.9%, and the particle size distribution is 1~500μm; Pre-activation treatment methods for magnesium raw materials include dry ball milling, wet ball milling, or surface pickling.

[0010] Furthermore, solid During the nitriding reaction, the atmosphere is 99.99% pure nitrogen, the pressure is 0.05~2.0 MPa, the reaction temperature is 200~400℃, and the reaction time is 1~48h.

[0011] Furthermore, during the hydrolysis reaction, the water is liquid deionized water, water vapor, or a mixture of both, the reaction temperature is 30~150℃, and the reaction time is 0.2~6 h.

[0012] Furthermore, during the carbonization reaction, the temperature is 25~200℃, the pressure is 0.1~1.5 MPa, and the reaction time is 5min~12h.

[0013] Furthermore, the carbon dioxide-containing gas flow includes ambient air, flue gas from coal-fired power plants, tail gas from cement kilns, or tail gas from biogas purification processes, with a carbon dioxide volume concentration of 0.04% to 100% and a gas flow rate of 0.1 to 10 L / min·g.

[0014] Furthermore, the acidification treatment uses inorganic acids, including sulfuric acid solution, hydrochloric acid solution and nitric acid solution with a mass fraction of 5% to 30%; During the acidification process, the temperature is 20~90℃ and the duration is 0.5~5 h. The acid addition is stopped when carbon dioxide is produced and the solution is neutral.

[0015] Furthermore, the pretreatment of the magnesium ion-containing solution includes evaporation and concentration, crystallization purification, and removal of impurity ions. The hot steam generated during the pretreatment is used for solidification in step 1. Nitrification reaction.

[0016] Furthermore, the electrolysis process employs molten salt electrolysis, with the electrolyte system being a mixed molten salt of MgCl2-KCl-NaCl, and the electrolysis temperature being 350~400℃.

[0017] A magnesium-mediated electrolysis cycle system for implementing the steps of the method includes a nitriding reactor, a hydrolysis reactor, a carbon dioxide capture reactor, an acidification reactor, a drying reactor, and a molten salt electrolysis reactor connected in sequence. The molten salt electrolysis reactor is connected to the nitriding reactor via a conveying device. The drying reactor is connected to the hydrolysis reactor. The hydrolysis reactor is connected to an ammonia collection device. The carbon dioxide capture reactor is connected to a gas flow conveying device. The acidification reactor is connected to an acid addition device.

[0018] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a magnesium-mediated electrolytic cycle method using atmospheric nitrogen and carbon dioxide as direct raw materials and metallic magnesium as the active medium. The nitriding reaction temperature decreases, the pressure drops to atmospheric pressure, and carbon capture occurs near room temperature and pressure. The electrolytic regeneration process also operates at significantly lower temperatures than traditional molten salt electrolysis of magnesium. Through a chemical-electrochemical coupled cycle, ammonia (NH3) is directly synthesized from air under mild conditions, and direct air carbon capture (DAC) is simultaneously achieved. This overcomes the stringent limitations of traditional processes, offering advantages in both safety and equipment cost. The magnesium-mediated chemical cycle innovatively integrates the two independent reactions of nitrogen fixation and carbon fixation into a single material system. Throughout the cycle, metallic magnesium acts as both a reducing agent for nitrogen activation and a carrier for carbon dioxide capture. Compared to the traditional Haber-Bosch process, this invention offers several advantages: First, it significantly reduces the requirements for reactor materials (e.g., eliminating the need for special hydrogen embrittlement-resistant steel) and structural strength, thereby substantially reducing initial investment and maintenance costs. Second, it greatly enhances the inherent safety of the entire production process, reducing operational risks associated with high pressure and high temperature. Third, it enables the system to start and stop quickly and adjust load flexibly, better adapting to the intermittent power supply characteristics of renewable energy sources. This invention constructs a closed-loop material cycle of "magnesium nitridation—hydrolysis to ammonia production—magnesium-based carbon capture—electrolytic regeneration," where magnesium is cyclically converted between elemental magnesium, magnesium nitride, magnesium hydroxide, magnesium carbonate, and magnesium salts. Theoretically, only a small amount of magnesium lost due to system degradation needs to be replenished. This achieves two major breakthroughs: First, it eliminates the absolute dependence of traditional ammonia synthesis on fossil fuel-based hydrogen production, with hydrogen provided by water and participating in the reaction in situ, eliminating carbon emissions at the source. Second, the reaction medium (magnesium) can be efficiently regenerated and recycled, avoiding the addition and disposal of large amounts of consumable chemicals (such as amine absorbents in traditional carbon capture), significantly reducing raw material costs and waste disposal burden. Meanwhile, the main byproducts of the entire process are high-purity carbon dioxide and oxygen, with no other harmful waste generated, truly achieving green and sustainable chemical synthesis. This transforms the traditional high-energy-consuming and high-emission chemical process into an integrated carbon-negative production pathway, realizing a new paradigm of "carbon-negative chemistry." It shifts the balance between energy consumption and carbon emission reduction from a conflict to a synergistic relationship; for every ton of ammonia produced, approximately 3.2 tons of carbon dioxide can be captured simultaneously. More importantly, the main energy-consuming stage—the electrolytic regeneration of magnesium—can be entirely driven by renewable energy. This means that the entire production process not only achieves net-negative carbon dioxide emissions but also transforms fluctuating renewable energy into high-value chemicals and stable carbon sinks, providing a revolutionary technological path for decarbonization in the chemical industry.

[0019] Furthermore, the purity of the magnesium raw material is specified to be 99.0%~99.9%, and the particle size distribution is 1~500μm. High-purity magnesium raw material can reduce the interference of impurities on the reaction, improve the selectivity and yield of the reaction; a suitable particle size distribution helps to increase the contact area between the raw material and the reactant gas, accelerate the reaction rate, and improve production efficiency.

[0020] Furthermore, various pre-activation treatment methods are provided, such as dry ball milling, wet ball milling, or surface pickling. Dry ball milling and wet ball milling can change the surface morphology and crystal structure of metallic magnesium, increasing its surface activity; surface pickling can remove the oxide layer and impurities on the surface of metallic magnesium, improving its reactivity, thereby creating favorable conditions for subsequent solid-gas nitriding reactions.

[0021] Furthermore, it was clarified that the solid-gas nitriding reaction process uses a nitrogen atmosphere with a purity of 99.99%, a pressure of 0.05–2.0 MPa, a reaction temperature of 200–400 °C, and a reaction time of 1–48 h. A high-purity nitrogen atmosphere can reduce the influence of impurities on the reaction; a suitable pressure and temperature range can optimize reaction kinetics, improving the formation rate and yield of magnesium nitride; and a reasonable reaction time can ensure the reaction proceeds fully while avoiding energy waste and equipment wear caused by over-reaction.

[0022] Furthermore, the water used in the hydrolysis reaction can be liquid deionized water, water vapor, or a mixture of both. The reaction temperature is 30–150°C, and the reaction time is 0.2–6 h. Different forms of water can be selected according to actual production conditions. Liquid deionized water is easy to operate and control, while water vapor can increase the reaction rate. A suitable temperature and reaction time range can ensure the smooth progress of the hydrolysis reaction and the efficient generation of ammonia and solid magnesium hydroxide.

[0023] Furthermore, the carbonization reaction was specified to be carried out at a temperature of 25–200°C, a pressure of 0.1–1.5 MPa, and a reaction time of 5 min–12 h. Suitable temperature and pressure conditions can promote the carbonization reaction of magnesium hydroxide and carbon dioxide, increasing the efficiency of magnesium carbonate formation; a reasonable reaction time can ensure complete reaction, improving the purity and quality of the product.

[0024] Furthermore, the carbon dioxide-containing gas stream includes ambient air, flue gas from coal-fired power plants, cement kiln tail gas, or biogas purification tail gas, with a carbon dioxide volume concentration of 0.04% to 100% and a gas flow rate of 0.1 to 10 L / min. This broadens the sources of carbon dioxide and improves the flexibility and practicality of carbon capture; a suitable gas flow rate ensures sufficient contact between carbon dioxide and magnesium hydroxide, improving the efficiency of the carbonization reaction.

[0025] Furthermore, the magnesium carbonate is acidified using inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid solutions with a mass fraction of 5%–30% at a temperature of 20–90°C for 0.5–5 hours. Acid addition is stopped when carbon dioxide is produced and the solution becomes neutral. Appropriate acid concentrations and reaction conditions ensure complete acidification of the magnesium carbonate, releasing carbon dioxide. Using a neutral solution as the indicator for stopping acid addition avoids over-acidification, reducing acid waste and environmental impact.

[0026] Furthermore, the pretreatment of the magnesium ion-containing solution includes evaporation and concentration, crystallization purification, and removal of impurity ions. The hot steam generated during pretreatment is used for the solid-gas nitriding reaction. Evaporation and concentration, and crystallization purification can increase the concentration and purity of the magnesium ion-containing solution, providing high-quality raw materials for subsequent electrolysis processes; removing impurity ions can reduce the impact of impurities on the electrolysis process, improve electrolysis efficiency and the quality of metallic magnesium; using the hot steam generated during pretreatment for the solid-gas nitriding reaction achieves energy recycling, reduces energy consumption, and improves the economics of the entire production process.

[0027] Furthermore, the electrolysis process employs molten salt electrolysis, with the electrolyte system being a mixed molten salt of MgCl2-KCl-NaCl, and the electrolysis temperature being 350~400℃. Molten salt electrolysis has advantages such as high current efficiency and low electrode loss; the MgCl2-KCl-NaCl mixed molten salt system has good conductivity and chemical stability, which can reduce the electrolysis temperature and reduce energy consumption; a suitable electrolysis temperature range can ensure the smooth progress of the electrolysis process and efficiently regenerate metallic magnesium.

[0028] This invention also provides a magnesium-mediated electrolytic cycle system, comprising a nitriding reactor, a hydrolysis reactor, a carbon dioxide capture reactor, an acidification reactor, a drying reactor, and a molten salt electrolysis reactor connected in sequence. The molten salt electrolysis reactor is connected to the nitriding reactor via a conveying device, and the drying reactor is connected to the hydrolysis reactor, forming a closed-loop cycle system. Through magnesium-mediated circulation, carbon dioxide capture and ammonia synthesis are achieved. The process has high integration, strong process controllability, and is adaptable to different production scales, significantly reducing raw material consumption and production costs, and improving resource utilization. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a flowchart of the magnesium-mediated electrolytic cycling method of the present invention.

[0031] Figure 2 This is a structural diagram of the magnesium-mediated electrolysis cycle system of the present invention. Detailed Implementation

[0032] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0033] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0034] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0035] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0036] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0037] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0038] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0039] The present invention will now be described in further detail with reference to the accompanying drawings: See Figure 1 This invention provides a magnesium-mediated electrolysis cycle method, specifically comprising the following cyclic steps: Step (1), Magnesium Nitrification and Ammonia Synthesis: First, the magnesium raw material is pre-activated to improve its reactivity. The activated magnesium is placed in a reactor and exposed to a nitrogen atmosphere under normal pressure and heating conditions. The magnesium reacts with nitrogen in a solid-gas nitridation reaction to produce magnesium nitride. Subsequently, the resulting magnesium nitride is brought into contact with water to undergo a hydrolysis reaction, producing gaseous ammonia and solid magnesium hydroxide. The ammonia is collected and used as a product, while the magnesium hydroxide is used as an intermediate product in the next stage.

[0040] Step (2), carbon dioxide capture: The magnesium hydroxide generated in step (1) is exposed to air or a gas flow containing carbon dioxide. The magnesium hydroxide reacts with the carbon dioxide to form magnesium carbonate, thereby achieving direct capture and fixation of carbon dioxide in the atmosphere.

[0041] Step (3), Electrolytic Regeneration and Closed-Loop Cycle of Magnesium: The magnesium carbonate obtained in step (2) is acidified to release carbon dioxide and obtain a solution containing magnesium ions. The solution containing magnesium ions is further pretreated to convert it into a form suitable for electrolysis and regenerated into metallic magnesium through an electrolytic process. The regenerated metallic magnesium is returned to step (1) for recycling, thus forming a complete, closed-loop magnesium-mediated recycling system.

[0042] Preferably, in step (1), the purity of the magnesium raw material ranges from 99.0% to 99.9%, and the particle size distribution is from 1 to 500 μm. The pre-activation treatment of the magnesium includes dry ball milling, wet ball milling, or surface pickling to remove the oxide layer and increase the specific surface area. The dry ball milling time for pre-activation treatment ranges from 2 to 72 h, and the ball milling media are preferably cemented carbide or stainless steel balls, with a ball-to-material mass ratio ranging from 2 to 15:1. After pre-activation, the specific surface area of ​​the magnesium can be increased to more than 1.5 times the initial value.

[0043] Preferably, in step (1), the solid The atmosphere for the gas nitriding reaction is 99.99% high-purity nitrogen gas at a pressure of 0.05~2.0 MPa; solid The operating temperature range of the gas nitriding reactor is 200~400℃, with a preferred temperature window of 300~350℃; solid The duration of the gas nitriding reaction ranges from 1 to 48 hours, and the specific time can be adjusted according to the temperature and the form of magnesium.

[0044] Preferably, in step (1), the water used in the hydrolysis reaction is liquid deionized water, water vapor, or a mixture of both; the temperature control range of the hydrolysis reaction is 30~150℃, and the time range of the hydrolysis reaction is 0.2~6 h, so as to ensure that the magnesium nitride reacts completely.

[0045] In step (1), the generated ammonia gas can be collected by ice-water condensation, dilute acid spray absorption, or molecular sieve adsorption; the byproduct magnesium hydroxide is a loose and porous solid with a bulk density ranging from 0.2 to 1.0 g / cm³. 3 This facilitates the subsequent carbonization reaction.

[0046] Preferably, in step (2), the operating temperature range for magnesium hydroxide to capture carbon dioxide is 25~200℃; the operating pressure range for the carbonization reaction is 0.1~1.5 MPa; the gas flow containing carbon dioxide includes ambient air, flue gas from coal-fired power plants, tail gas from cement kilns, or tail gas from biogas purification; the lower limit of the volume concentration of carbon dioxide is 0.04% (ambient air), and the upper limit can reach 100%; the gas flow rate range is 0.1~10 L / min·g; the reaction contact time range is 5 min~12 h; the capture process can be carried out using a fixed bed, fluidized bed, or moving bed reactor.

[0047] In step (2), the actual carbonization conversion rate of magnesium hydroxide to magnesium carbonate can reach 60%~95%.

[0048] Preferably, in step (3), the acidification treatment of magnesium carbonate uses inorganic acids, including sulfuric acid, hydrochloric acid and nitric acid solutions with a mass fraction of 5% to 30%, preferably hydrochloric acid; the temperature range of the acidification treatment is 20 to 90°C; the duration of the acidification treatment is 0.5 to 5 h, and the acid is stopped when carbon dioxide is generated and the solution is neutral.

[0049] In step (3), the carbon dioxide gas released by the acidification treatment can reach a purity of 97%~99.9%, and can be directly compressed for food-grade or industrial-grade applications. The concentration range of the magnesium ion-containing solution (such as magnesium sulfate solution, magnesium chloride solution and magnesium nitrate solution) obtained after acidification treatment is 0.5~4.0 mol / L.

[0050] In step (3), before electrolysis, the magnesium-containing solution can be pretreated by evaporation and concentration, crystallization and purification, and removal of impurity ions. The generated hot steam can be used in step (1) for solidification. The gas nitriding reaction produces ammonia, achieving the recycling of materials and thermal energy.

[0051] Preferably, in step (3), when the electrolysis process uses molten salt electrolysis, the electrolyte system is a MgCl2-KCl-NaCl mixed molten salt, and the operating temperature range is 350~400℃.

[0052] In step (3), the metallic magnesium obtained by electrolytic regeneration is precipitated at the cathode in the form of dendritic, granular or dense layered form; the purity of the regenerated metallic magnesium ranges from 96% to 99.5%, and it can be directly or after simple smelting and returned to step (1) for recycling.

[0053] like Figure 2 As shown, the present invention also provides a magnesium-mediated electrolysis cycle system, comprising a nitriding reactor, a hydrolysis reactor, a carbon dioxide capture reactor, an acidification reactor, a drying reactor, and a molten salt electrolysis reactor connected in sequence. The molten salt electrolysis reactor is connected to the nitriding reactor via a conveying device, and the drying reactor is connected to the hydrolysis reactor, forming a closed-loop cycle system to achieve the steps of the above method. The hydrolysis reactor is connected to an ammonia collection device, through which liquid deionized water, water vapor, or a mixture of both can be introduced to hydrolyze the magnesium nitriding. The carbon dioxide capture reactor is connected to a gas flow conveying device for conveying a gas flow containing carbon dioxide. The acidification reactor is connected to an acid addition device for adding inorganic acid. The cycle system can operate in batch, semi-continuous, or fully continuous modes, and the total magnesium recovery rate (by mass) of the entire cycle system from magnesium carbonate acidification treatment to the return of metallic magnesium regeneration is not less than 95%.

[0054] The technical solution of the present invention will be further described in detail below through specific embodiments: Example 1: First, 99.5% pure magnesium powder with a particle size of 100 μm was pre-activated by dry ball milling under argon protection. Stainless steel balls were used as the milling media, with a ball-to-powder mass ratio of 10:1, and the milling time was 24 h, increasing the specific surface area of ​​the magnesium powder to twice its initial value. The activated magnesium powder was then placed in a high-pressure reactor and reacted at 320℃ for 12 h under a high-purity nitrogen atmosphere (99.99%) at 0.5 MPa pressure to obtain magnesium nitride. Subsequently, this magnesium nitride was hydrolyzed with deionized water at 80℃ for 2 h. The generated ammonia gas was collected using a dilute sulfuric acid absorbent to obtain magnesium hydroxide powder as a byproduct with a bulk density of approximately 0.6 g / cm³. 3 .

[0055] The magnesium hydroxide was loaded into a fixed-bed reactor and subjected to a reaction at 0.3 MPa pressure and 60°C. Flue gas from a coal-fired power plant with a carbon dioxide concentration of 20% was introduced at a gas flow rate of 1 L / min·g. After 3 hours of contact reaction, the carbonization conversion rate of magnesium hydroxide reached 85%, producing magnesium carbonate.

[0056] Subsequently, magnesium carbonate was acidified with a 15% hydrochloric acid solution at 50°C for 2 hours, releasing carbon dioxide gas with a purity greater than 99.5%, and simultaneously obtaining a magnesium chloride solution with a concentration of 2.0 mol / L. After evaporating, concentrating, and purifying the magnesium chloride solution by crystallization, molten salt electrolysis was performed using a MgCl2-KCl-NaCl electrolyte system at 380°C and a cell voltage of 3.8 V. Dendritic magnesium was obtained at the cathode, and after smelting, its purity reached 99.0%. The regenerated magnesium was returned to the solid waste treatment plant. The gas nitriding reaction step is recycled, and the total magnesium recovery rate of the system is calculated to be 96%.

[0057] Example 2: First, 99.9% pure magnesium powder with a particle size of 500 μm was pre-activated by dry ball milling under argon protection. The milling media was cemented carbide, the ball-to-powder mass ratio was 15:1, and the milling time was 2 h, increasing the specific surface area of ​​the magnesium powder to twice its initial value. The activated magnesium powder was then placed in a high-pressure reactor and reacted at 300℃ for 48 h under a high-purity nitrogen (99.99%) atmosphere at 2.0 MPa pressure to obtain magnesium nitride. Subsequently, this magnesium nitride was hydrolyzed with deionized water at 150℃ for 0.2 h. The generated ammonia gas was collected using a dilute sulfuric acid absorbent to obtain magnesium hydroxide powder as a byproduct with a bulk density of approximately 0.8 g / cm³. 3 .

[0058] The magnesium hydroxide was loaded into a fixed-bed reactor. Under the conditions of 0.1 MPa pressure and 200℃, biogas with a carbon dioxide concentration of 40% was introduced to purify the tail gas. The gas flow rate was controlled at 10 L / min·g. After 5 min of contact reaction, the carbonization conversion rate of magnesium hydroxide reached 90%, and magnesium carbonate was generated.

[0059] Subsequently, magnesium carbonate was acidified with a 30% nitric acid solution at 90°C for 0.5 h, releasing carbon dioxide gas with a purity greater than 98%, and simultaneously obtaining a magnesium nitrate solution with a concentration of 3.0 mol / L. After evaporation, concentration, crystallization, and purification of the magnesium nitrate solution, a molten salt electrolysis process was employed, using MgCl2-KCl-NaCl as the electrolyte system, at 350°C and a cell voltage of 3.8 V. Granular precipitated metallic magnesium was obtained at the cathode, and after smelting, its purity reached 99.5%. The regenerated metallic magnesium was returned to the solid waste... The gas nitriding reaction step is recycled, and the total magnesium recovery rate of the system is calculated to be 97%.

[0060] Example 3: First, 99.0% pure magnesium powder with a particle size of 1 μm was pre-activated by wet ball milling under argon protection. Stainless steel balls were used as the milling media, with a ball-to-powder mass ratio of 2:1, and the milling time was 72 h, increasing the specific surface area of ​​the magnesium powder to 2.2 times its initial value. The activated magnesium powder was then placed in a high-pressure reactor and reacted at 350℃ for 1 h under a high-purity nitrogen atmosphere (99.99%) at 0.05 MPa pressure to obtain magnesium nitride. Subsequently, this magnesium nitride was hydrolyzed with deionized water at 30℃ for 6 h. The generated ammonia gas was collected using a dilute sulfuric acid absorbent to obtain magnesium hydroxide powder as a byproduct with a bulk density of approximately 1.0 g / cm³. 3 .

[0061] The magnesium hydroxide was loaded into a fixed-bed reactor and subjected to a reaction at 1.5 MPa pressure and 25°C. Air (carbon dioxide concentration of 0.04%) was introduced and the gas flow rate was controlled at 0.1 L / min·g. After 12 hours of contact reaction, the carbonization conversion rate of magnesium hydroxide reached 80%, producing magnesium carbonate.

[0062] Subsequently, magnesium carbonate was acidified with a 5% sulfuric acid solution at 20°C for 5 hours, releasing carbon dioxide gas with a purity greater than 99.0%, and simultaneously obtaining a magnesium sulfate solution with a concentration of 2.8 mol / L. After evaporating, concentrating, and purifying the magnesium sulfate solution by crystallization, a molten salt electrolysis process was employed, using MgCl2-KCl-NaCl as the electrolyte system, at 400°C and a cell voltage of 3.8 V. The cathode yielded dense, layered precipitated metallic magnesium, which, after smelting, achieved a purity of 98.5%. The regenerated metallic magnesium was returned to the solid waste... The gas nitriding reaction step is recycled, and the total magnesium recovery rate of the system is calculated to be 96.5%.

[0063] Examples 1-3 of this invention achieve a complete closed-loop cycle of "magnesium nitridation-hydrolysis to ammonia production-magnesium-based carbon capture-electrolytic regeneration". Under mild conditions (atmospheric to medium pressure, temperature below 400°C), ammonia was successfully synthesized from nitrogen while simultaneously capturing carbon dioxide. The magnesium nitridation yield (based on magnesium conversion) exceeded 90%, and the ammonia obtained from hydrolysis was efficiently absorbed; the actual CO2 capture capacity of magnesium hydroxide was significant, and the purity of the CO2 released by acidification met industrial utilization standards; the process of obtaining metallic magnesium through electrolytic regeneration was stable, and the regenerated material could be directly reused, resulting in a total magnesium recovery rate of no less than 95%, far exceeding the requirements of general industrial cycles. This process integrates high-energy-consuming ammonia synthesis and carbon capture into one unit, without the need for an external hydrogen source, and the core energy-consuming link (electrolysis) can be coupled with renewable energy, verifying the technical feasibility of the method of this invention in achieving a carbon-negative ammonia synthesis pathway.

[0064] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A magnesium-mediated electrolytic cycling method, characterized in that, include: Step 1: Pre-activate the magnesium raw material by exposing the activated magnesium to a nitrogen-containing atmosphere under normal pressure and heating conditions to solidify. The gas nitriding reaction produces magnesium nitride, which then undergoes hydrolysis upon contact with water to produce ammonia and solid magnesium hydroxide. The ammonia is then collected. Step 2: Expose magnesium hydroxide to a gas stream containing carbon dioxide. Magnesium hydroxide reacts with carbon dioxide to form magnesium carbonate. Step 3: Acidify the magnesium carbonate to release carbon dioxide and obtain a solution containing magnesium ions. After further pretreatment of the solution containing magnesium ions, regenerate it through an electrolytic process to obtain metallic magnesium. The obtained metallic magnesium is returned to Step 1 for recycling.

2. The magnesium-mediated electrolytic cycling method according to claim 1, characterized in that, The purity of the magnesium raw material is 99.0%~99.9%, and the particle size distribution is 1~500μm; Pre-activation treatment methods for metallic magnesium raw materials include dry ball milling, wet ball milling, or surface pickling.

3. The magnesium-mediated electrolytic cycling method according to claim 1, characterized in that, solid During the nitriding reaction, the atmosphere is 99.99% pure nitrogen, the pressure is 0.05~2.0 MPa, the reaction temperature is 200~400℃, and the reaction time is 1~48h.

4. The magnesium-mediated electrolytic cycling method according to claim 1, characterized in that, During the hydrolysis reaction, the water is liquid deionized water, water vapor, or a mixture of both. The reaction temperature is 30~150℃ and the reaction time is 0.2~6 h.

5. The magnesium-mediated electrolytic cycling method according to claim 1, characterized in that, During the carbonization reaction, the temperature is 25~200℃, the pressure is 0.1~1.5 MPa, and the reaction time is 5min~12h.

6. The magnesium-mediated electrolytic cycling method according to claim 1, characterized in that, The carbon dioxide-containing airflow includes ambient air, flue gas from coal-fired power plants, tail gas from cement kilns, or tail gas from biogas purification processes. The volume concentration of carbon dioxide is 0.04% to 100%, and the airflow velocity is 0.1 to 10 L / min.

7. The magnesium-mediated electrolytic cycling method according to claim 1, characterized in that, The acidification treatment uses inorganic acids, including sulfuric acid solution, hydrochloric acid solution and nitric acid solution with a mass fraction of 5% to 30%; During the acidification process, the temperature is 20~90℃ and the duration is 0.5~5 h. The acid addition is stopped when carbon dioxide is produced and the solution is neutral.

8. The magnesium-mediated electrolytic cycling method according to claim 1, characterized in that, The pretreatment of the magnesium ion-containing solution includes evaporation and concentration, crystallization purification, and removal of impurity ions. The hot steam generated during the pretreatment is used for solidification in step 1. Nitrification reaction.

9. The magnesium-mediated electrolytic cycling method according to claim 1, characterized in that, The electrolysis process uses molten salt electrolysis, with the electrolyte system being a mixed molten salt of MgCl2-KCl-NaCl, and the electrolysis temperature being 350~400℃.

10. A magnesium-mediated electrolytic cycle system, characterized in that, The steps for implementing the method of claim 1 include a nitriding reactor, a hydrolysis reactor, a carbon dioxide capture reactor, an acidification reactor, a drying reactor, and a molten salt electrolysis reactor connected in sequence. The molten salt electrolysis reactor is connected to the nitriding reactor via a conveying device. The drying reactor is connected to the hydrolysis reactor. The hydrolysis reactor is connected to an ammonia collection device. The carbon dioxide capture reactor is connected to a gas flow conveying device. The acidification reactor is connected to an acid addition device.

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