An integrated system for directly preparing ammonium nitrate nitrogen fertilizer from air without additional electrolyte system

Abstract

This invention relates to an integrated system for directly producing ammonium nitrate nitrogen fertilizer from air without the need for an additional electrolyte system. The system includes an energy supply unit, an air plasma activation unit, a nitrogen oxide absorption and acid production unit, a nitric acid buffer metering unit, a proton exchange membrane electrolysis unit, and an ammonium nitrate collection unit. Air is activated by plasma to generate NO. x The solution is then converted into a strongly acidic nitric acid solution in the absorption tower; it is then pumped into the cathode chamber of the electrolytic cell via a metering pump, where selective reduction occurs at the cathode and water oxidation occurs at the anode, producing protons. These protons migrate to the cathode side via the proton exchange membrane; by adjustment, some NO3 is... ‑ Converted to NH4 + The rest of NO3 ‑ As a counter ion, ammonium nitrate solution is formed in situ. The system of this invention achieves spatiotemporal decoupling between intermittent plasma nitrogen fixation and continuous electrolysis processes, and can be powered by renewable energy sources such as photovoltaics. It features a short process, no need for additional electrolytes, and easy modular scaling.

Description

Technical Field

[0001] This invention belongs to the fields of plasma nitrogen fixation, electrochemical nitrogen cycling and green manufacturing technology of ammonium nitrate, and particularly relates to an integrated system for preparing ammonium nitrate nitrogen fertilizer from air under a strongly acidic nitric acid system. Background Technology

[0002] Ammonium nitrate is an important nitrogen-containing chemical and nitrogen fertilizer raw material. Current industrial production typically relies on the Haber-Bosch ammonia synthesis process and the Ostwald nitric acid production process, followed by the neutralization of ammonia and nitric acid to produce ammonium nitrate. This route involves high temperature, high pressure, and multi-stage gas conversion processes, making it heavily reliant on large-scale centralized plants and fossil fuel infrastructure, and difficult to directly couple with fluctuating renewable energy sources and distributed agricultural scenarios.

[0003] In recent years, the plasma-series electrocatalytic synthesis of ammonium nitrate driven by renewable electricity has attracted widespread attention. Air plasma can activate N2 and O2 under normal pressure to generate nitrogen oxides such as NO and NO2. After absorption by water or absorbent, these form nitrous acid, nitric acid, or corresponding nitrogen-containing ions, which are further electrocatalytically converted to ammonium ions, ultimately forming ammonium nitrate. However, most existing systems require the addition of phosphate buffer, alkaline absorbent, or other supporting electrolytes, which not only increases reagent consumption but may also lead to salt accumulation, product separation difficulties, and process complexity. Furthermore, the intermittent output of the front-end plasma and the continuous electrolysis at the back end still present load matching problems, limiting the continuous and integrated operation of the system.

[0004] Nitrogen oxides generated by plasma can be absorbed and oxidized by water to form nitric acid. If the resulting nitric acid solution is used directly for subsequent electrolysis, the NO3- in it can be utilized. − H + This approach leverages the ionic conductivity of nitrates, eliminating the need for additional PBS, KOH, or other supporting electrolytes, thus reducing steps such as neutralization, pH adjustment, and salt separation. This route holds promise for distributed, on-site preparation of nitrogen-containing products using air, water, and renewable electricity as feedstocks. However, in strongly acidic nitric acid systems, nitrate reduction still faces challenges such as hydrogen evolution competition, catalyst corrosion, and insufficient long-term stability. Furthermore, it requires coordination of nitric acid feedstock, electrolysis conditions, and product composition to achieve continuous and stable ammonium nitrate production.

[0005] Therefore, there is an urgent need to develop an integrated system and method for producing nitric acid directly using plasma without the need for additional supporting electrolytes, and which also has the ability to perform efficient electrocatalytic conversion and continuous operation. Summary of the Invention

[0006] The technical problem solved by this invention is to overcome the problems of existing ammonium nitrate production relying on large-scale fossil energy plants, having complex processes, and being difficult to adapt to renewable energy and distributed agricultural applications.

[0007] In view of the technical problems existing in the prior art, this invention designs an integrated system for the direct production of ammonium nitrate nitrogen fertilizer from air without the need for an additional electrolyte system. This system achieves continuous coupling of the air-to-nitric acid production and ammonium nitrate generation processes through nitric acid buffering and metering and acid-resistant electrocatalytic conversion, realizing the direct conversion of air, water, and renewable energy into ammonium nitrate nitrogen fertilizer without the need for additional supporting electrolytes and external ammonia sources.

[0008] It should be noted that, in this invention, unless otherwise specified, the specific meaning of "comprising" in relation to composition definition and description includes both open-ended meanings such as "comprising," "including," etc., and closed-ended meanings such as "composed of," etc., and similar meanings.

[0009] To solve the aforementioned technical problems, the present invention adopts the following solution:

[0010] [First technical solution]

[0011] An integrated system for directly producing ammonium nitrate nitrogen fertilizer from air without the need for an additional electrolyte system includes an energy supply unit, an air plasma activation unit, a nitrogen oxide absorption and acid production unit, a nitric acid buffer metering unit, a proton exchange membrane electrolysis unit, and an ammonium nitrate collection unit connected in sequence.

[0012] The energy supply unit is electrically connected to the air plasma activation unit and the proton exchange membrane electrolysis unit respectively, and is used to supply power to the air plasma activation unit and the proton exchange membrane electrolysis unit;

[0013] The air plasma activation unit is used to convert N2 and O2 in the air into nitrogen oxide gas containing NO and / or NO2;

[0014] The nitrogen oxide absorption and acid generation unit is used to contact the nitrogen oxide gas with water to form a strongly acidic nitric acid solution with HNO3 as the main nitrogen-containing component.

[0015] The nitric acid buffer metering unit is used to store and quantitatively deliver the nitric acid solution to the proton exchange membrane electrolysis unit;

[0016] The proton exchange membrane electrolysis unit includes a cathode chamber, an anode chamber, and a proton exchange membrane disposed between the two. The cathode chamber receives the nitric acid solution and performs an electrocatalytic reduction reaction.

[0017] The ammonium nitrate collection unit is used to collect the ammonium nitrate product generated by the electrocatalytic reaction.

[0018] Furthermore, the energy supply unit includes solar photovoltaic panels, an energy storage / inverter power supply unit, an AC power supply, and a DC power supply;

[0019] The AC power supply powers the air plasma activation unit, and the DC power supply powers the proton exchange membrane electrolysis unit.

[0020] Furthermore, the air plasma activation unit includes a plasma integration device, a gas control valve, and a gas flow meter;

[0021] The plasma integrated device is selected from dielectric barrier discharge device, sliding arc discharge device, or a combination thereof.

[0022] Furthermore, the nitrogen oxide absorption and acid production unit includes an absorption tower, which uses water or a circulating nitric acid aqueous solution as the absorbent to absorb NO. x It is absorbed and oxidized into HNO3;

[0023] The nitric acid buffer metering unit includes a nitric acid storage tank, an inlet valve, and a metering pump arranged in sequence.

[0024] Furthermore, the concentration of the nitric acid aqueous solution is 0.5-2.0 mol / L; the nitric acid aqueous solution is directly used as the cathode reactant and conductive medium, and no additional phosphate buffer, alkaline absorbent or other supporting electrolyte is added.

[0025] Furthermore, the cathode in the cathode chamber is a strong acid nitrate reduction electrode with a conductive, acid-resistant substrate supporting a metal-metal oxide composite active component. The anode is an acid-resistant oxygen evolution electrode.

[0026] Furthermore, in the conductive acid-resistant substrate loaded with metal-metal oxide composite active components, the conductive acid-resistant substrate is titanium felt, the metal oxide is WO3, and the loaded metal is Ru, forming a Ru-WO3 / Ti cathode.

[0027] In this invention, the obtained nitric acid is stored and homogenized in a nitric acid storage tank. The concentration of the nitric acid aqueous solution is preferably 1.0 mol / L.

[0028] In this invention, the air plasma activation unit and the electrolysis unit can operate synchronously or asynchronously. The nitric acid generated by the plasma is first stored in a nitric acid storage tank, and then continuously or intermittently transported to the proton exchange membrane electrolysis unit according to the electrolysis load, thereby realizing the spatiotemporal decoupling of the front-end acid production and the back-end electrocatalytic process.

[0029] The method for preparing the cathode electrode with a conductive and acid-resistant substrate supporting a metal-metal oxide composite active component includes the following steps:

[0030] Step 1: Ti substrate pretreatment

[0031] The Ti substrate was sequentially subjected to acetone, 1-3 mol L... -1The surface is cleaned and pretreated with hydrochloric acid, anhydrous ethanol, and ultrapure water to remove surface oil and oxide layers, resulting in a clean Ti substrate. The Ti substrate is preferably a Ti felt, but Ti mesh, Ti sheets, or other Ti-based materials with good electrical conductivity and acid resistance can also be used.

[0032] Step 2: Preparation of WO3 / Ti catalytic electrode

[0033] Weigh 15-25 g of sodium tungstate dihydrate (Na₂WO₄·2H₂O) and dissolve it in 800-1000 mL of ultrapure water, stirring for 10 minutes. Then, adjust the pH of the solution to 1-2 using 1-3 M hydrochloric acid. Next, add 20-25 g of anhydrous oxalic acid and 60-70 g of ammonium sulfate to the solution sequentially. After thorough mixing, transfer 30-70 mL of the solution to a high-pressure reactor, add pretreated Ti felt, and heat at 160-180 °C. o The reaction was carried out at C for 16 h. After the reaction was completed and cooled, the catalyst was washed with ultrapure water and dried. It was then subjected to an incubation of 200-500 °C in a 10% H₂ / Ar mixed atmosphere. o Calcination at C for 2 hours resulted in the formation of a WO3 / Ti catalytic electrode.

[0034] Step 3: Preparation of Ru-WO3 / Ti catalytic electrode

[0035] The uncalcined WO3 / Ti catalytic electrode obtained in step 2 was vertically immersed in an aqueous solution of 2-10 mM ruthenium chloride (10-30 mL) and heated to 60-80 °C. o The mixture was stirred vigorously at C for 12 h. After the reaction was complete, the Ru-supported WO3 / Ti composite material was washed with ultrapure water and vacuum dried. It was then subjected to a 10% H2 / Ar mixed atmosphere at 200-500 °C. o Calcination at C for 2 hours resulted in the formation of a Ru-WO3 / Ti catalytic electrode.

[0036] In this invention, the strong acid-resistant WO3 support possesses excellent proton storage and transport capabilities, promoting reverse hydrogen overflow and providing active hydrogen for the NO3-RR process. Simultaneously, WO3 can stably anchor Ru nanoclusters, inhibiting their migration and aggregation. Ru, as the main active site, promotes the adsorption, activation, and hydrogenation conversion of nitrate and nitrogen-containing intermediates. The interfacial synergistic effect of these two components significantly enhances the activity, selectivity, and stability of nitrate reduction.

[0037] [Second Technical Solution]

[0038] A method for preparing ammonium nitrate using the above-described integrated system includes the following steps:

[0039] S1: Air is introduced into the air plasma activation unit, and nitrogen oxide gas is generated under the action of plasma;

[0040] S2: The nitrogen oxide gas is introduced into the nitrogen oxide absorption and acid generation unit, where it is absorbed and oxidized to form a strongly acidic nitric acid solution, which is then stored in the nitric acid buffer metering unit.

[0041] S3: The nitric acid solution is delivered to the cathode chamber of the proton exchange membrane electrolysis unit, where nitrate is electrocatalytically reduced to NH4 without the addition of a supporting electrolyte. + ;

[0042] S4: Generated NH4 + With the remaining NO3 in the system - Ammonium nitrate is formed by combining and the resulting ammonium nitrate solution is then transported to the ammonium nitrate collection unit.

[0043] Step S1 involves introducing air into the plasma integrated device after regulation by a gas control valve and a gas flow meter. Under the action of plasma discharge, N2 and O2 in the air are activated to generate nitrogen oxide gas, mainly composed of NO and NO2.

[0044] Step S2 involves passing the obtained nitrogen oxide gas into an absorption tower, where it comes into full contact with water or a circulating acidic absorbent liquid. Through absorption and oxidation, a strongly acidic nitrogen-containing solution, primarily composed of HNO3, is formed. The resulting nitric acid is then stored and homogenized in a nitric acid storage tank, and its concentration is adjusted to a set level according to subsequent electrolysis requirements.

[0045] Step S3 involves directly using the obtained nitric acid for electrocatalytic conversion, reducing nitrate ions without the addition of an additional supporting electrolyte. The electrocatalytic reaction can be performed using an H-type electrolytic cell or a membrane electrode reactor (MEA); the H-type electrolytic cell is used for evaluating catalytic electrode performance and screening reaction conditions, while the MEA is preferably used for continuous electrolysis and series coupling with a front-end plasma nitric acid production unit.

[0046] Step S4 involves disposing of the NH4 generated during the electrolysis process. + With unreduced NO3 in the system - Ammonium nitrate is formed, and the resulting ammonium nitrate solution is transported to an ammonium nitrate collection unit for storage. The prepared ammonium nitrate solution can be used directly as liquid nitrogen fertilizer, or it can be concentrated, diluted, or further formulated according to actual application needs.

[0047] Furthermore, the preferred operating conditions for plasma activation air in step S1 are a discharge voltage of 6-10 kV and an inlet flow rate of 0.5-1 L / min. -1 The outlet flow rate is 1-3 L / min. -1 .

[0048] In step S3, the electrocatalytic reduction is carried out using an H-type electrolytic cell or a membrane electrode reactor.

[0049] When using an H-type electrolytic cell, the control potential is 0.2 to -0.7 V vs. RHE;

[0050] When using a membrane electrode reactor, the constant current is controlled at 0.5–5 A, and the electrolyte flow rate is 5–10 mL / min.

[0051] Furthermore, the nitric acid solution does not require pH adjustment before entering the cathode chamber and is fed directly in a strongly acidic form.

[0052] Step S3: Before the test, add 20 mL min -1 Argon gas was bubbled into the electrolyte to remove excess oxygen and N2, and then the test was performed in an electrolyte environment of 0.25-1.0 M H2SO4 and 0.5-2.0 M HNO3. NO2 was calculated using ion chromatography. - and NH4 + The yields and Faraday efficiencies of H2 and N2 were calculated using gas chromatography.

[0053] [Third technical solution]

[0054] An application of the above-mentioned integrated system in the following scenarios:

[0055] Distributed agricultural nitrogen fertilizer production on-site;

[0056] Nitrogen fertilizer preparation powered by renewable energy sources such as solar, wind, or energy storage;

[0057] Distributed fertilizer supply scenarios in facility agriculture, greenhouse cultivation, hydroponics, smart agriculture, and remote areas;

[0058] It can directly convert air and water into liquid nitrogen fertilizer or solid ammonium nitrate products without the need for additional electrolytes.

[0059] In this invention, the obtained ammonium nitrate solution can be used directly as liquid nitrogen fertilizer, or it can be concentrated, crystallized and separated into solid and liquid forms to obtain ammonium nitrate products.

[0060] This invention provides an integrated system for the direct preparation of ammonium nitrate nitrogen fertilizer from air without the need for an additional electrolyte system. It can directly use strongly acidic nitric acid as the reaction and conductive medium, without the need for additional electrolytes, achieving a continuous conversion from air to ammonium nitrate nitrogen fertilizer. Its specific technical features and beneficial effects are as follows:

[0061] 1. This invention uses air and water as the main raw materials. Nitrogen and oxygen in the air are activated by plasma to generate nitrogen oxides, which are then further absorbed to form nitric acid. The resulting nitric acid is directly used as the nitrogen source and reaction medium for subsequent electrocatalytic reactions. Under strongly acidic conditions, it is electrocatalytically reduced to ammonium ions, which then react with nitrate ions in the system to form ammonium nitrate. This process avoids the high dependence of traditional ammonium nitrate production on the Haber-Bosch ammonia synthesis and Ostwald nitric acid production processes, and eliminates the need for additional fossil-derived ammonia and hydrogen. The system can be powered by renewable energy sources such as solar energy, thereby significantly reducing fossil energy consumption and carbon emissions in the ammonium nitrate production process.

[0062] 2. This invention directly uses the nitric acid absorbent formed by plasma air nitrogen fixation in the subsequent electrocatalytic process, eliminating the need for further neutralization, adjustment to a neutral or alkaline environment, and the addition of buffer salts as electrolytes. Nitric acid simultaneously serves as a nitrogen source, proton source, and conductive medium in the system. During electrocatalysis, some nitrate ions are selectively reduced to ammonium ions, and the remaining nitrate ions further form ammonium nitrate as counterions. This achieves a continuous coupling of "air-to-nitric acid production—nitric acid electrocatalytic conversion—ammonium nitrate formation," reducing intermediate separation, transfer, and reagent addition steps, and improving the overall process integration.

[0063] 3. This invention employs a Ru-WO3 / Ti catalytic electrode, where WO3 provides a stable oxide interface resistant to strong acids and promotes nitrate adsorption activation and interfacial proton transfer; Ru provides highly efficient active hydrogen generation and hydrogenation sites for nitrogen-containing intermediates. The synergistic effect of the Ru-WO3 interface can further regulate the electronic structure of the active sites and the adsorption behavior of reactants, promoting the continuous conversion of nitrate to ammonium. At a potential of -0.3 V vs. RHE, the ammonia Faraday efficiency can reach approximately 90%, and the ammonia formation rate can reach 2.7 mmol / cm². -2 h -1 .

[0064] 4. This invention couples the membrane electrode (MEA) electrolysis unit with the plasma nitric acid production unit in series. Under a constant current of 4 A, it can operate continuously and stably for more than 24 hours, with the ammonia Faraday efficiency maintained at about 70%, and finally obtains about 0.3 mol of ammonium nitrate product.

[0065] 5. The system of this invention is compatible with renewable energy sources such as solar energy and has the potential for modular and distributed applications. Both the plasma unit and the electrocatalytic unit of this invention are electrically driven and can be integrated with solar photovoltaic, wind power, and energy storage power supply systems to achieve renewable energy-driven air nitrogen fixation and ammonium nitrate fertilizer production. This system uses air and water as the main raw materials, eliminating the need for external supply of hydrogen and ammonia, avoiding the complex gas preparation and storage processes in traditional ammonium nitrate production, and reducing production safety risks. Simultaneously, the system features modular structure, mild operating conditions, flexible start-up and shutdown, and easy scalability, allowing for flexible configuration according to agricultural production needs. The resulting ammonium nitrate solution can be directly used as liquid nitrogen fertilizer, suitable for distributed agricultural scenarios such as farmland, greenhouses, hydroponics, and remote areas, realizing on-site production and utilization of nitrogen fertilizer. Attached Figure Description

[0066] Figure 1 This is a schematic diagram of the integrated system for the direct preparation of ammonium nitrate nitrogen fertilizer from air without the need for an additional electrolyte system, according to the present invention.

[0067] Figure 2 SEM, TEM, and XRD images of WO3 / Ti and Ru-WO3 / Ti prepared in Example 1;

[0068] Figure 3 Linear sweep voltammetry (LSV) curves of the Ti-based catalyst prepared in Example 1 of this invention in an H cell, as well as the Faradaic efficiency (FE) and ammonia synthesis performance at different potentials;

[0069] Figure 4 Linear sweep voltammetry (LSV) curves of the Ru-WO3 / Ti catalyst prepared in Example 1 of this invention in a 3 cm × 3 cm membrane electrode reactor, and Faraday efficiency versus ammonia synthesis performance under different electrolyte flow rates and current conditions.

[0070] Figure 5 The operational performance of the plasma-generated nitric acid and strongly acidic nitric acid electrolysis coupling system was studied. Figure 5 a represents the cumulative amount of nitric acid and nitrous acid in the absorbent obtained by plasma-activated air over the reaction time; Figure 5 b and Figure 5 c represents the long-term stability test results of the Ru-WO3 / Ti catalyst prepared in Example 1 in the plasma-coupled electrocatalytic preparation of ammonium nitrate system. Detailed Implementation

[0071] The present invention will be further described below with reference to specific embodiments and accompanying drawings:

[0072] Example 1: Construction and operation of an integrated system for the direct preparation of ammonium nitrate nitrogen fertilizer from air without the need for an additional electrolyte system.

[0073] like Figure 1 As shown, the integrated system consists of 1 solar photovoltaic panel, 2 AC power supply, 3 energy storage / inverter power supply unit, 4 DC power supply, 5 plasma integrated device, 6 gas control valve, 7 gas flow meter, 8 absorption tower, 9 nitric acid storage tank, 10 liquid inlet valve, 11 metering pump, 12 electrolytic cell, 13 cathode chamber, 14 anode chamber, 15 proton exchange membrane and 16 ammonium nitrate storage tank.

[0074] The electrical energy output from photovoltaic panel 1 first enters energy storage / inverter power supply unit 3. One output of power supply unit 3 drives plasma integration device 5 via AC power supply 2, and the other output drives electrolytic cell 12 via DC power supply 4. This power architecture allows the plasma and electrolytic cell to start and stop independently and adapt to changes in illumination.

[0075] Air is metered into the plasma integrated device 5 via gas control valve 6 and gas flow meter 7. The plasma device preferably operates at a 6 kV discharge voltage, and the inlet flow rate can be set to 0.5-3 L / min depending on the device size. The generated NO... x The solution is directly introduced into absorption tower 8 to ensure full contact with water. Absorption tower 8 can be a packed tower or a spray tower structure; the absorbent liquid circulates, allowing NO to be absorbed effectively. x It is gradually transformed and enriched into nitric acid.

[0076] The resulting nitric acid enters the nitric acid storage tank 9. The storage tank 9 is used to average the fluctuations in the acid production rate of the front-end plasma. When electrolysis is required, the inlet valve 10 is opened, and the metering pump 11 continuously feeds the nitric acid into the cathode chamber 13 of the electrolytic cell 12. The anode chamber 14 is filled with aqueous anolyte; a proton exchange membrane 15 is installed between the cathode chamber 13 and the anode chamber 14.

[0077] Under the action of a DC electric field, the cathode NO3 - Stepwise hydrogenation occurs to produce NH4 + Anode water is oxidized to produce O2 and H2. + H + It migrates through the proton exchange membrane 15 to the cathode chamber 13. The electrolytic cell outlet liquid enters the ammonium nitrate storage tank 16.

[0078] By adjusting the nitric acid feed flow rate and total power consumption, some NO3... - Reduced to NH4 + And the remaining NO3 - The ammonium nitrate solution is retained in storage tank 16.

[0079] Characterization of the WO3 / Ti and Ru-WO3 / Ti cathodes and structures in Example 1

[0080] The WO3 / Ti catalytic electrode was prepared by in-situ growth of WO3 nanorods on the surface of Ti felt.

[0081] Specifically, acetone and 3 mol L were used sequentially. -1 Hydrochloric acid, anhydrous ethanol, and ultrapure water were used to clean and pre-treat the Ti felt to remove surface oil and oxide layers, followed by cleaning at 60°C. o C. Vacuum dry for later use.

[0082] Weigh 22 g of Na₂WO₄·2H₂O and dissolve it in 800 mL of ultrapure water. After stirring for 10 min, use 3 mol L⁻¹ water. -1 The pH of the solution was adjusted to 2 with hydrochloric acid. Then, 25.2 g of anhydrous oxalic acid and 66.7 g of ammonium sulfate were added sequentially, and the mixture was stirred thoroughly. 30 mL of the solution was transferred to a high-pressure reactor, and pretreated Ti felt (1 cm × 4 cm) was added. The reactor was then heated to 180°C. o The hydrothermal reaction was carried out at C for 16 h. After the reaction was completed and cooled to room temperature, the electrode was removed, thoroughly washed with ultrapure water and dried, and then subjected to a 10% H2 / Ar mixed atmosphere at 300 °C. o After heat treatment at C for 2 h, a WO3 / Ti catalytic electrode was obtained.

[0083] The Ru-WO3 / Ti catalytic electrode was prepared by impregnating and loading an uncalcined WO3 / Ti precursor.

[0084] Specifically, the uncalcined WO3 / Ti precursor was vertically immersed in 10 mL of water at a concentration of 6 mmol / L. -1 In an aqueous solution of ruthenium chloride, and at 60 o The mixture was stirred vigorously at C for 12 h. After the reaction was completed, the Ru-supported WO3 / Ti composite material was thoroughly washed with ultrapure water and dried under vacuum. Then, it was heat-treated at 300 °C for 2 h in a 10% H2 / Ar mixed atmosphere to finally obtain the Ru-WO3 / Ti catalytic electrode.

[0085] Figure 2 The SEM, TEM, and XRD characterization results of the Ti felt, WO3 / Ti, and Ru-WO3 / Ti catalytic electrodes prepared in Example 1 of this invention are shown.

[0086] Figure 2 SEM images of ac show that WO3 nanorods grow uniformly and vertically on the Ti felt surface, forming a dense, interwoven seaweed-like array structure; after loading Ru, the overall morphology of the nanorod array remains basically unchanged, indicating that the introduction of Ru did not cause significant damage to the WO3 framework structure.

[0087] Figure 2The TEM images of d further show that Ru nanoparticles were successfully loaded onto the surface of WO3 nanorods, with a relatively uniform distribution, a particle size of about 1 to 2 nm, and formed a rich heterogeneous interface with WO3.

[0088] XRD results further confirmed the formation of the WO3 phase, and no obvious metallic Ru diffraction peaks were observed, indicating that the Ru species has a small grain size and high dispersion.

[0089] Screening of catalytic performance for the reduction of strong acid nitrate

[0090] A system for the electrocatalytic reduction of nitrate to ammonia under strongly acidic conditions was constructed, and the catalytic performance of Ti felt, WO3 / Ti and Ru-WO3 / Ti catalytic electrodes was evaluated.

[0091] In the H-type electrolytic cell, the electrode prepared in Example 1 was used as the working cathode electrode, the Pt sheet was used as the anode, the Ag / AgCl electrode was used as the reference electrode, and the gas outlet of the cathode chamber was connected to a gas chromatograph.

[0092] Before the test, use 20 mL min -1 Ar was introduced into the electrolyte at a flow rate of [value missing] to remove dissolved O2 and N2. During the test, 0.5 M H2SO4 or 1.0 M HNO3 solution was added to the anode and cathode chambers, respectively, to carry out the nitrate reduction reaction. Electrolysis was performed using a potentiostatic method within the range of 0.2 to -0.7 V vs. RHE, with each potential reacting for 30 min.

[0093] After the reaction was completed, NH4 in the cathode electrolyte was determined by ion chromatography. + and NO2 - The content of H2 and N2 generated at the cathode was determined, and the corresponding generation rate and Faraday efficiency were calculated. Gas chromatography was used to determine the generation rate and Faraday efficiency of H2 and N2 generated at the cathode.

[0094] All measured voltages E (Ag / AgCl) All of these are converted into a potential E relative to the reversible hydrogen electrode (RHE). （RHE） E （RHE） =E （Ag / AgCl） +0.01976+0.0592*pH.

[0095] Figure 3 The results show that, compared with Ti felt and WO3 / Ti electrodes, Ru-WO3 / Ti exhibits a higher cathode current density at the same potential, indicating that the introduction of Ru significantly promotes the kinetics of nitrate reduction under strongly acidic conditions. Within the test range of 0.2 to -0.7 V vs. RHE, the NH4+ of Ru-WO3 / Ti... +The formation rates were significantly higher than those of Ti felt and WO3 / Ti, and continued to increase with a negative shift in cathode potential.

[0096] Figure 3 The paper presents the product distribution and Faraday efficiency for different electrodes. The Ti felt electrode primarily exhibits the hydrogen evolution reaction, accompanied by a relatively significant NO2 reaction. - Accumulation of intermediate products; after in-situ growth of WO3, the hydrogen evolution side reaction is somewhat suppressed, and NH4... + The improved selectivity indicates that WO3 has proton storage and transfer capabilities, which can promote the continuous hydrogenation conversion of nitrate by active hydrogen.

[0097] In contrast, Ru-WO3 / Ti achieves approximately 85%–95% NH4+ over a wider potential range. + Faraday efficiency and significant inhibition of NO2. - Accumulation indicates that the Ru site and Ru-WO3 interface synergistically promote the continuous hydrogenation of nitrogen-containing intermediates, improving the activity and selectivity of nitrate reduction. Ultimately, an ammonia Faraday efficiency of approximately 90% and an ammonia formation rate of 2.7 mmol / cm² were achieved at -0.3 V vs. RHE potential. -2 h -1 .

[0098] Regarding the flow electrolysis of strongly acidic nitric acid in a membrane electrode reactor

[0099] The scale-up performance of a strongly acidic nitric acid system was investigated using a two-electrode flow electrolyzer.

[0100] Specifically, Ru-WO3 / Ti catalytic electrode and platinum-plated Ti felt were used as the cathode and anode, respectively. The electrolytes for both the cathode and anode were 0.5 M H2SO4 or 1.0 M HNO3 solution, and a proton exchange membrane was used between the cathode and anode.

[0101] like Figure 4 As shown, compared with the H-type electrolytic cell, the NO3 in the flow electrolytic cell... - The RR ammonia production rate was significantly improved, demonstrating good potential for scale-up applications. Subsequently, constant current electrolysis was performed within a current range of 0.5–5 A, with nitric acid feed flow rates set to 5, 7.5, and 10 mL / min. At a total current of 5 A, NH4+... + The generation rate can reach 17.18 mmol h. -1 The ammonia-Faraday efficiency is 73.4%.

[0102] Regarding the operational performance of the plasma-coupled system for nitric acid production and strong acid nitric acid electrolysis

[0103] An air plasma activation unit is connected in series with an absorption tower, using water as the absorbent to continuously absorb NO generated by the plasma.x This forms a nitric acid electrolyte.

[0104] The preferred operating conditions for plasma-activated air are: discharge voltage 6 kV, inlet gas flow rate 1 L / min. -1 Outlet gas flow rate 3 L / min -1 Subsequently, a dual-channel flow pump was used to circulate and deliver the catholyte and anolyte separately at a flow rate of 7.5 mL / min. -1 The long-term stability was tested under a constant current of 4 A. The effective reaction area of ​​the membrane electrode electrolyzer used was 3 cm × 3 cm.

[0105] like Figure 5 As shown, under a constant current of 4 A, NH4 + The Faraday efficiency remained at approximately 60%–72% throughout the 24-hour operation, with NH4 + The cumulative amount increased continuously with reaction time, reaching approximately 300 mmol at 24 h. This was due to the presence of sufficient NO3 in the cathode feed. - The generated NH4 + It can react with the remaining NO3 in the system - It forms ammonium nitrate.

[0106] The above results show that the front-end plasma unit can stably convert nitrogen in the air into nitric acid, the back-end membrane electrode electrolysis unit can operate continuously at a current of 4 A, and the load of the front and back ends can be buffered and matched through the nitric acid storage tank, thereby realizing the continuous and stable synthesis of ammonium nitrate.

[0107] The present invention has been described above by way of example with reference to the embodiments and accompanying drawings. Obviously, the implementation of the present invention is not limited to the above-described manner. Any improvements made by adopting the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other occasions without modification, are all within the protection scope of the present invention.

Claims

1. An integrated system for directly preparing ammonium nitrate nitrogen fertilizer from air without the need for an additional electrolyte system, characterized in that: It includes an energy supply unit, an air plasma activation unit, a nitrogen oxide absorption and acid production unit, a nitric acid buffer metering unit, a proton exchange membrane electrolysis unit, and an ammonium nitrate collection unit connected in sequence. The energy supply unit is electrically connected to the air plasma activation unit and the proton exchange membrane electrolysis unit respectively, and is used to supply power to the air plasma activation unit and the proton exchange membrane electrolysis unit; The air plasma activation unit is used to convert N2 and O2 in the air into nitrogen oxide gas containing NO and / or NO2; The nitrogen oxide absorption and acid generation unit is used to contact the nitrogen oxide gas with water to form a strongly acidic nitric acid solution with HNO3 as the main nitrogen-containing component. The nitric acid buffer metering unit is used to store and quantitatively deliver the nitric acid solution to the proton exchange membrane electrolysis unit; The proton exchange membrane electrolysis unit includes a cathode chamber, an anode chamber, and a proton exchange membrane disposed between the two. The cathode chamber receives the nitric acid solution and performs an electrocatalytic reduction reaction. The ammonium nitrate collection unit is used to collect the ammonium nitrate product generated by the electrocatalytic reaction.

2. The integrated system for directly preparing ammonium nitrate nitrogen fertilizer from air without the need for an additional electrolyte system, as described in claim 1, is characterized in that: The energy supply unit includes solar photovoltaic panels, an energy storage / inverter power supply unit, an AC power supply, and a DC power supply; The AC power supply powers the air plasma activation unit, and the DC power supply powers the proton exchange membrane electrolysis unit.

3. The integrated system for directly preparing ammonium nitrate nitrogen fertilizer from air without the need for an additional electrolyte system, as described in claim 2, is characterized in that: The air plasma activation unit includes a plasma integration device, a gas control valve, and a gas flow meter; The plasma integrated device is selected from dielectric barrier discharge device, sliding arc discharge device, or a combination thereof.

4. The integrated system for directly preparing ammonium nitrate nitrogen fertilizer from air without the need for an additional electrolyte system, as described in claim 3, is characterized in that: The nitrogen oxide absorption and acid production unit includes an absorption tower, which uses water or a circulating nitric acid solution as the absorbent to absorb NO. x It is absorbed and oxidized into HNO3; The nitric acid buffer metering unit includes a nitric acid storage tank, an inlet valve, and a metering pump arranged in sequence.

5. The integrated system for directly preparing ammonium nitrate nitrogen fertilizer from air without the need for an additional electrolyte system, as described in claim 4, is characterized in that: The concentration of the nitric acid aqueous solution is 0.5-2.0 mol / L; the nitric acid aqueous solution is used directly as the cathode reactant and conductive medium, and no additional phosphate buffer, alkaline absorbent or other supporting electrolyte is added.

6. The integrated system for directly preparing ammonium nitrate nitrogen fertilizer from air without the need for an additional electrolyte system, as described in claim 1, is characterized in that: The cathode in the cathode chamber is a strong acid nitrate reduction electrode with a conductive and acid-resistant substrate and a metal-metal oxide composite active component loaded on it; the anode is an acid-resistant oxygen evolution electrode.

7. The integrated system for directly preparing ammonium nitrate nitrogen fertilizer from air without the need for an additional electrolyte system, as described in claim 6, is characterized in that: In the conductive acid-resistant substrate loaded with metal-metal oxide composite active components, the conductive acid-resistant substrate is titanium felt, the metal oxide is WO3, and the loaded metal is Ru, forming a Ru-WO3 / Ti cathode.

8. A method for preparing ammonium nitrate using the integrated system according to any one of claims 1-7, characterized in that, Includes the following steps: S1: Air is introduced into the air plasma activation unit, and nitrogen oxide gas is generated under the action of plasma; S2: The nitrogen oxide gas is introduced into the nitrogen oxide absorption and acid generation unit, where it is absorbed and oxidized to form a strongly acidic nitric acid solution, which is then stored in the nitric acid buffer metering unit. S3: The nitric acid solution is delivered to the cathode chamber of the proton exchange membrane electrolysis unit, where nitrate is electrocatalytically reduced to NH4 without the addition of a supporting electrolyte. + ; S4: Generated NH4 + With the remaining NO3 in the system - Ammonium nitrate is formed by combining and the resulting ammonium nitrate solution is then transported to the ammonium nitrate collection unit.

9. The method according to claim 8, characterized in that: The preferred operating conditions for plasma activation air in step S1 are a discharge voltage of 6-10 kV and an inlet flow rate of 0.5-1 L / min. -1 The outlet flow rate is 1-3 L / min. -1 ; In step S3, the electrocatalytic reduction is carried out using an H-type electrolytic cell or a membrane electrode reactor. When using an H-type electrolytic cell, the control potential is 0.2 to -0.7 V vs. RHE; When using a membrane electrode reactor, the constant current is controlled at 0.5–5 A, and the electrolyte flow rate is 5–10 mL / min. Furthermore, the nitric acid solution does not require pH adjustment before entering the cathode chamber and is fed directly in a strongly acidic form.

10. An application of the integrated system described in any one of 1-7 in the following scenarios: Distributed agricultural nitrogen fertilizer production on-site; Nitrogen fertilizer preparation powered by renewable energy sources such as solar, wind, or energy storage; Distributed fertilizer supply scenarios in facility agriculture, greenhouse cultivation, hydroponics, smart agriculture, and remote areas; It can directly convert air and water into liquid nitrogen fertilizer or solid ammonium nitrate products without the need for additional electrolytes.

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