A method and system for atmospheric pressure self-cycling synthesis of ammonia

Abstract

The application belongs to the technical field of new energy, and discloses a method and system for synthesizing ammonia by self-circulation under normal pressure. The method comprises the following steps: first, placing a catalyst in a reactor, introducing a reaction gas, and performing a reaction under the conditions of normal pressure and heating, and collecting a reaction product; the reaction gas comprises nitrogen, hydrogen and a molecular promoter, the molecular promoter is nitrogen oxide, and the amount of the molecular promoter introduced is 1-10 vol.% of the total volume of the reaction gas; then, separating ammonia from the reaction product to obtain an ammonia product and residual gas; and finally, feeding the residual gas back to the reactor to perform self-circulation synthesis of ammonia. By selecting a specific catalyst and optimizing process parameters, NH3 in the reaction product is continuously separated, and the residual reaction gas is continuously fed back to the reactor, so that only hydrogen and nitrogen need to be supplemented into the reaction system, and no new molecular promoter needs to be additionally supplemented, thereby realizing low-cost self-circulation synthesis of ammonia under normal pressure.

Description

Technical Field

[0001] This invention belongs to the field of new energy technology, specifically relating to a method and system for synthesizing ammonia under normal pressure through self-circulation. Background Technology

[0002] Ammonia (NH3) is an important chemical raw material used in the production of fertilizers, soda ash, nitric acid, and other industrial products. It is also an ideal hydrogen storage carrier, possessing advantages such as high hydrogen storage density and mature storage and transportation technologies. Furthermore, ammonia can serve as a "zero-carbon" fuel, with its ideal combustion products being nitrogen and water, without directly emitting carbon dioxide or other carbon-containing greenhouse gases. Ammonia plays a crucial role in modern chemical industry. Since the Haber-Bosch process enabled the industrial production of ammonia in the early 20th century, global synthetic ammonia production has now exceeded 100 million tons.

[0003] However, the industrially used Haber-Bosch ammonia synthesis process requires harsh conditions of high temperature and high pressure (300-500℃ and 15-30MPa), and the production process is energy-intensive (accounting for approximately 2% of global energy consumption) and generates significant carbon emissions (approximately 1.5% of global carbon emissions), exacerbating global environmental pollution and the consumption of traditional fossil fuels. Furthermore, the high temperature and high pressure requirements of Haber-Bosch ammonia synthesis, especially the high pressure of 20-30 MPa, are difficult to reconcile with the current development of distributed clean energy. Therefore, it is urgent to overcome the bottleneck limitations of the high-pressure ammonia synthesis process in the Haber-Bosch process.

[0004] Addressing the limitations of current high-pressure ammonia synthesis, the applicant, in their Chinese invention patent "A Method and Application for Ammonia Synthesis" (application number: 2025114352930), points out that introducing a small amount of nitrogen oxides (such as NO) as a molecular promoter into the reaction system of nitrogen (N2) and hydrogen (H2) can significantly promote the ammonia synthesis reaction under normal pressure, thereby increasing the ammonia yield. This method, applied to an industrial iron catalyst ammonia synthesis system, achieves an ammonia conversion rate of 6% at normal pressure and 450℃, approaching the 10% conversion rate of industrial ammonia synthesis. However, existing nitrogen oxide preparation methods generally employ plasma generators, which are energy-intensive and low-yield processes.

[0005] Therefore, while ensuring ammonia yield, reducing nitrogen oxide consumption is extremely important for the industrial application of the atmospheric pressure molecular promoter ammonia synthesis method. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a method and system for atmospheric pressure self-circulating ammonia synthesis. This method can significantly reduce the consumption of nitrogen oxides while ensuring ammonia yield, and can achieve atmospheric pressure self-circulating ammonia synthesis without replenishing the reaction system with new nitrogen oxides.

[0007] The inventive concept of this invention is as follows: This invention introduces a small amount of nitrogen oxide molecular promoter into the N2 / H2 system. Taking NO as an example, NO, under the action of a catalyst, decomposes to produce active nitrogen (N2). * ) and reactive oxygen species (O * ): (1) The generated N * It reacts with H2 to produce NH3: (2) The generated reactive oxygen species O * It reacts with H2 to produce H2O: (3) At the same time, the generated O * It can also react with N2 to open N. The N triple bond generates new NO and N. * : (4) The new NO and N produced * Then, it enters the reaction system to generate ammonia, realizing the self-circulating synthesis of ammonia under normal pressure. Therefore, in order to reduce the consumption of NO, it is necessary to suppress the side reaction of active oxygen and hydrogen to generate water as much as possible, that is, the occurrence of reaction (3); and at the same time promote the reaction of highly active oxygen activating nitrogen, that is, the occurrence of reaction (4), so as to reduce or even eliminate the need to add new NO to the reaction system, and realize the self-circulating synthesis of ammonia under normal pressure.

[0008] In view of this, the present invention, by selecting specific catalysts (such as iron catalysts) and optimizing process parameters (including the amount of nitrogen oxides and reaction temperature), significantly increases the amount of NH3 generated by the reaction of N2 and H2 under normal pressure. On the other hand, it promotes the generation of nitrogen activated by highly reactive oxygen species and inhibits the side reaction of reactive oxygen species with hydrogen to produce water, thus minimizing or even eliminating the amount of NO required. Simultaneously, NH3 is continuously separated from the reaction products, and the remaining reaction gases are continuously returned to the reactor. Therefore, only hydrogen and nitrogen need to be added to the reaction system, without the need for additional NO, enabling low-cost, atmospheric-pressure self-circulating ammonia synthesis.

[0009] To solve the above-mentioned technical problems, the first aspect of the present invention provides a method for synthesizing ammonia under atmospheric pressure through self-circulation, comprising the following steps: (1) Place the catalyst in the reactor, introduce the reaction gas, carry out the reaction under normal pressure and heating conditions, and collect the reaction products; The reactant gases include nitrogen, hydrogen, and a molecular promoter, wherein the molecular promoter is a nitrogen oxide, and the amount of the molecular promoter introduced is 1-10 vol.% of the total volume of the reactant gases. (2) The reaction product is subjected to ammonia separation to obtain ammonia product and residual gas; (3) The remaining gas is returned to the reactor, and the hydrogen and nitrogen consumed in the reaction are added to the reactor to carry out self-circulating ammonia synthesis.

[0010] In some embodiments of the present invention, in step (1), the amount of the molecular promoter introduced is 2-7 vol.% of the total volume of the reaction gas; for example, it can be any volume content of 2 vol.%, 3 vol.%, 4 vol.%, 5 vol.%, 6 vol.%, or 7 vol.%, or any range between the two. Studies have found that the amount of NO introduced has a significant impact on the self-circulation effect, and a suitable amount can greatly reduce the amount of NO used.

[0011] In some embodiments of the present invention, in step (1), the temperature of the reaction is 350-500°C; for example, it can be any temperature among 350°C, 400°C, 450°C, and 500°C, or any temperature range between two of them.

[0012] In some embodiments of the present invention, the reaction temperature in step (1) is 320-380°C. Studies have found that at relatively lower reaction temperatures, it is more conducive to promoting the generation of highly reactive oxygen species activated nitrogen and inhibiting the side reaction of reactive oxygen species with hydrogen to produce water, thereby reducing the amount of NO consumed in the reaction system.

[0013] In some embodiments of the present invention, in step (1), the catalyst comprises an iron catalyst. Studies have found that iron catalysts are also more effective than other existing catalysts (such as CeO2) in reducing the consumption of NO in the reaction system.

[0014] In some embodiments of the present invention, in step (1), the nitrogen oxide is nitric oxide.

[0015] In some embodiments of the present invention, in step (1), the volume ratio of hydrogen to nitrogen is (0.2-4):1; for example, it can be any volume ratio or any range of the two from 0.2:1, 0.28:1, 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1.

[0016] In some embodiments of the present invention, step (1) further includes a step of treating the catalyst under a reducing atmosphere before introducing the reaction gas, wherein the temperature of the treatment is 500-700°C; for example, it can be any temperature among 500°C, 550°C, 600°C, 650°C, and 700°C or any temperature range between two of them.

[0017] In some embodiments of the present invention, the reducing atmosphere is any one of hydrogen, a hydrogen / nitrogen mixture, a hydrogen / helium mixture, or a hydrogen / argon mixture.

[0018] In some embodiments of the present invention, in step (2), the ammonia separation method can employ commonly used separation methods in the art, such as condensation or liquefaction separation at room temperature and low pressure, where the low pressure is 1-2 MPa. The ammonia product obtained by condensation separation or liquefaction separation at room temperature and low pressure is liquid nitrogen; alternatively, aqueous solution absorption can be used, and the ammonia product obtained by aqueous solution absorption is ammonia water.

[0019] In some embodiments of the present invention, in step (3), the volume ratio of the supplemented hydrogen to nitrogen is 3:1.

[0020] In some embodiments of the present invention, step (3) further includes a step of supplementing the reactor with molecular promoter when the content of molecular promoter in the reaction system is less than 85% of the initial value. The amount of molecular promoter supplemented is 0.1-2 vol.% of the total volume of the reaction gas to ensure the self-circulation effect.

[0021] A second aspect of the present invention provides an atmospheric pressure self-circulating ammonia synthesis system for the above-described atmospheric pressure self-circulating ammonia synthesis method; the atmospheric pressure self-circulating ammonia synthesis system includes a reactor, a condensation assembly, and a circulation pipeline, the circulation pipeline connecting the inlet end and the outlet end of the reactor, and the condensation assembly being disposed on the circulation pipeline.

[0022] In some embodiments of the present invention, the condensation assembly includes an air condenser, a water condenser, and a chiller arranged sequentially along the circulation pipeline. This three-stage condensation ensures effective condensation of the product gases.

[0023] In some embodiments of the present invention, the circulation pipeline is further provided with a first gas sampling port and a second gas sampling port. The first gas sampling port is located at the outlet end of the reactor and is used to sample and detect the product gas. The second gas sampling port is located at the inlet end of the reactor and is used to sample and detect the condensed product gas to determine the reaction gas that needs to be replenished.

[0024] Compared with the prior art, the above-described technical solution of the present invention has at least the following technical effects or advantages: This invention proposes a method for atmospheric pressure self-circulating ammonia synthesis. By introducing a small amount of molecular promoter (such as NO) into the N2 / H2 system, the yield of NH3 produced from the reaction of N2 and H2 under atmospheric pressure is increased. Simultaneously, by selecting a specific catalyst (such as an iron catalyst) and optimizing process parameters (including the amount of nitrogen oxides and reaction temperature), the amount of NH3 produced from the reaction of N2 and H2 under atmospheric pressure is significantly increased. Furthermore, the generation of nitrogen activated by highly reactive oxygen species is promoted, while the side reaction of reactive oxygen species reacting with hydrogen to form water is suppressed, minimizing or even eliminating the amount of NO required. NH3 is continuously separated from the reaction products, and the remaining reaction gases are continuously returned to the reactor. Thus, only hydrogen and nitrogen need to be added to the reaction system, without the need for additional NO, thereby achieving low-cost atmospheric pressure self-circulating ammonia synthesis, which is beneficial for industrial application. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the atmospheric pressure self-circulating ammonia synthesis system of the present invention; Figure 2 The atmospheric pressure ammonia synthesis yield measured in Example 1 of this invention; Figure 3 This is the atmospheric pressure ammonia synthesis yield measured in Comparative Example 1 of this invention; Figure 4 The yield of ammonia synthesized under normal pressure, as measured in Comparative Example 2 of this invention; Figure 5 This is the atmospheric pressure ammonia synthesis yield measured in Comparative Example 3 of this invention; Figure 6 This is the atmospheric pressure ammonia synthesis yield measured in Comparative Example 4 of this invention; Figure 7 This is a schematic diagram of the reaction pathway for atmospheric pressure self-circulating ammonia synthesis according to the present invention; Figure 8 This is a mass spectrometry image of NO signal detected in an atmospheric pressure self-circulating ammonia synthesis system as measured in Example 2 of the present invention. Figure 9 This is a graph showing the change in the yield of ammonia synthesized under normal pressure via self-circulation as measured in Example 2 of the present invention over time. Detailed Implementation

[0026] The present invention will now be described in detail with reference to embodiments to facilitate understanding of the invention by those skilled in the art. It is particularly important to note that the embodiments are merely illustrative of the invention and should not be construed as limiting the scope of protection of the invention. Non-essential improvements and adjustments made to the invention by those skilled in the art based on the above description should still fall within the scope of protection of the invention. Furthermore, all raw materials mentioned below, unless otherwise specified, are commercially available products; all process steps or preparation methods not mentioned in detail are process steps or preparation methods known to those skilled in the art.

[0027] like Figure 1 As shown, the atmospheric pressure self-circulating ammonia synthesis system of the present invention includes a reactor 100, a condensation component 200 and a circulation pipeline 300. The circulation pipeline 300 connects the inlet end and the outlet end of the reactor 100, and the condensation component 200 is disposed on the circulation pipeline 300.

[0028] Reactor 100 is a fixed-bed tubular reactor. The catalyst is packed in three or more layers in the fixed bed. The reaction gases N2, H2, and NO are thoroughly mixed in the mixing tank 400 before being introduced into the catalyst bed of reactor 100. The flow rates of the reaction gases N2, H2, and NO can be controlled by the flow meter 501. A gas venting pipe is also provided at the outlet end of reactor 100 for venting the gas inside reactor 100.

[0029] The condensation assembly 200 includes an air condenser 201, a water condenser 202, and a chiller 203 arranged sequentially along the circulation pipeline 300. It employs three-stage condensation to ensure effective condensation of the product gas. The product gas undergoes condensation and liquefaction separation via the condensation assembly 200, where the generated NH3 and potential H2O are condensed and liquefied, and then stored in the liquid ammonia storage tank 600. The remaining gas is pressurized by the gas pump 700 and returned to the reactor 100.

[0030] The circulation pipeline 300 is also equipped with a first gas sampling port 301 and a second gas sampling port 302. The first gas sampling port 301 is located at the outlet end of the reactor 100, and the second gas sampling port 302 is located at the inlet end of the reactor 100. Combined with a mass spectrometer, the NO content in the product gas is sampled and analyzed through the first gas sampling port 301, while the N2 and H2 amounts recirculated into the reactor 100 are sampled and analyzed through the second gas sampling port 302. The amount of H2 and N2 consumed in the ammonia synthesis reaction (H2 / N2 = 3 / 1) is replenished to the reactor 100 through a flow meter 502, thus performing self-circulating ammonia synthesis. After multiple cycles, an appropriate amount of NO can be added to ensure efficient ammonia synthesis performance under normal pressure.

[0031] The catalysts used in the following examples and comparative examples are as follows: The industrial iron catalyst was purchased from Qizhong Chemical (Zhengzhou) Co., Ltd., model A110. Cerium oxide (CeO2) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with a purity of 99%.

[0032] Example 1 A method for synthesizing ammonia under normal pressure includes the following steps: Take 0.5g of industrial iron catalyst and load it into a fixed-bed tubular reactor with an inner diameter of 8mm. Use 100mL·min at 500℃. -1After H2 reduction for 4 hours, the temperature was lowered to 350℃, and the reaction gas composition was switched to 20.6 mL·min. -1 N2, 74.4 mL·min -1 H2 and 5 mL·min -1 NO (the amount of NO introduced under these conditions is 5 vol.%) was tested. The reaction tail gas was discharged through 200 mL of a 0.05 mol·L⁻¹ solution. -1 After absorption by dilute sulfuric acid solution, the gas was vented. The tail gas absorbent was quantitatively analyzed using Nessler's reagent method combined with an Agilent Cary 60 UV-Vis spectrophotometer. The reaction gas composition was then changed to 20.6 mL / min. - 1 Ar, 74.4 mL·min -1 H2 and 5 mL·min -1 NO, 20.6mL·min -1 N2, 74.4 mL·min -1 H2 and 5 mL·min -1 Ar was tested, and quantitative analysis was performed using dilute sulfuric acid solution absorption and Nessler's reagent method.

[0033] The yield of ammonia synthesis (NH3 formation rate) is as follows: Figure 2 As shown, under normal pressure and 350℃, the ammonia synthesis yield with the reaction gas composition N2 / H2 / NO=20.6 / 74.4 / 5 using iron catalyst is 1850±50µmol. NH3 ·h -1 ·g cat -1 The ammonia synthesis yield was 470 ± 10 µmol when the reaction gas composition was Ar / H2 / NO = 20.6 / 74.4 / 5. NH3 ·h -1 ·g cat -1 The ammonia synthesis yield was 2 ± 0.1 µmol when the reaction gas composition was N2 / H2 / Ar = 20.6 / 74.4 / 5. NH3 ·h -1 ·g cat -1 Therefore, at normal pressure and 350°C, the ammonia yield increased by NO introduction was 1378 µmol. NH3 ·h -1 ·g cat -1 The yield of NH3 produced by the reaction of H2 and NO under these conditions is 293%, indicating that the reactive oxygen species O3 produced by the cracking of NO in the N2 / H2 / NO system under normal pressure and 350℃ is significantly higher than that produced by the reaction of H2 and NO under these conditions. * It tends to activate N2 to promote the reaction of N2 with H2 to produce NH3 and O.* The reaction of combining with H2 to generate H2O was suppressed, which facilitated the self-circulating ammonia synthesis process.

[0034] Comparative Example 1 Referring to the atmospheric pressure ammonia synthesis method in Example 1, the reaction temperature was increased from 350°C to 400°C.

[0035] The yield of ammonia synthesis is as follows: Figure 3 As shown, under normal pressure and 400℃, the ammonia synthesis yield with the reaction gas composition N2 / H2 / NO=20.6 / 74.4 / 5 using iron catalyst is 8231±380µmol. NH3 ·h -1 ·g cat -1 The ammonia synthesis yield with a reaction gas composition of Ar / H2 / NO = 20.6 / 74.4 / 5 was 3408 ± 78 µmol. NH3 ·h -1 ·g cat -1 The ammonia synthesis yield with a reaction gas composition of N2 / H2 / Ar = 20.6 / 74.4 / 5 was 33 ± 1 µmol. NH3 ·h -1 ·g cat -1 Therefore, at normal pressure and 400°C, the ammonia yield increased by NO introduction was 4790 µmol. NH3 ·h -1 ·g cat -1 This is 141% of the NH3 yield generated by the reaction of H2 and NO under these conditions. It is evident that when the reaction temperature is raised to 400℃ under normal pressure, the reactive oxygen species O3 produced by the decomposition of NO in the N2 / H2 / NO system... * Compared to Example 1, half of the N2 was used to activate N2 to promote the reaction of N2 and H2 to produce NH3, and the other half was used for O. * When it reacts with H2 to produce H2O, the "self-circulation" effect will be weakened.

[0036] Comparative Example 2 Referring to the atmospheric pressure ammonia synthesis method in Example 1, the reaction temperature was increased from 350°C to 450°C.

[0037] The yield of ammonia synthesis is as follows: Figure 4 As shown, under normal pressure and 450℃, the ammonia synthesis yield with the reaction gas composition N2 / H2 / NO=20.6 / 74.4 / 5 using iron catalyst is 14594±110µmol. NH3 ·h -1 ·g cat -1The ammonia synthesis yield with a reaction gas composition of Ar / H2 / NO = 20.6 / 74.4 / 5 was 7439 ± 189 µmol. NH3 ·h -1 ·g cat -1 The ammonia synthesis yield was 232 ± 23 µmol when the reaction gas composition was N2 / H2 / Ar = 20.6 / 74.4 / 5. NH3 ·h -1 ·g cat -1 Therefore, at normal pressure and 450 °C, the ammonia yield increased by NO introduction was 6923 µmol. NH3 ·h -1 ·g cat -1 This represents 93% of the NH3 yield generated from the reaction of H2 and NO under these conditions. It is evident that further increasing the reaction temperature to 450 °C under normal pressure results in a significant increase in the reactive oxygen species (O3) produced by the decomposition of NO in the N2 / H2 / NO system. * Compared to Example 1, only about one-third of O * Used to activate N2 to promote the reaction of N2 with H2 to produce NH3, with two-thirds of the O * It reacts with H2 to produce H2O, which significantly weakens the "self-circulation" effect.

[0038] Comparative Example 3 Referring to the atmospheric pressure ammonia synthesis method of Example 1, the amount of NO introduced was adjusted from 5 vol.% to 1 vol.%, 2 vol.%, and 8 vol.%, respectively, specifically including the following steps: Take 0.5g of industrial iron catalyst and load it into a fixed-bed tubular reactor with an inner diameter of 8mm. Use 100mL·min at 500℃. -1 After H2 reduction for 4 h, the temperature was lowered to 350℃, and the reaction gas composition was switched to 24.1 mL·min. -1 N2, 74.9 mL·min -1 H2 and 1 mL·min -1 NO (the amount of NO introduced under these conditions is 1 vol.%) was tested. The reaction tail gas was discharged through 200 mL of a 0.05 mol·L⁻¹ solution. -1 After absorption by dilute sulfuric acid solution, the gas was vented. The tail gas absorbent was quantitatively analyzed using Nessler's reagent method combined with an Agilent Cary 60 UV-Vis spectrophotometer. The reaction gas composition was then changed to 24.1 mL / min. - 1 Ar, 74.9 mL·min -1 H2 and 1 mL·min -1 NO, 24.1 mL·min-1 N2, 74.9 mL·min -1 H2 and 1 mL·min -1 Ar was tested, and quantitative analysis was performed using dilute sulfuric acid solution absorption and Nessler's reagent method.

[0039] Similarly, the composition of the reaction gas was changed to 23.2 mL·min -1 N2, 74.8 mL·min -1 H2 and 2 mL·min -1 NO (the amount of NO introduced under these conditions is 2 vol.%) was tested, and the composition of the reaction gas was changed to 23.2 mL·min. -1 Ar, 74.8 mL·min -1 H2 and 2 mL·min -1 NO, 23.2 mL·min -1 N2, 74.8 mL·min -1 H2 and 2 mL·min -1 Ar was used for testing. The reaction gas composition was changed to 18 mL·min. -1 N2, 74 mL·min -1 H2 and 8 mL·min -1 NO (the amount of NO introduced under these conditions is 8 vol.%) was tested, and the composition of the reaction gas was changed to 18 mL·min. -1 Ar, 74 mL·min -1 H2 and 8 mL·min -1 NO, 18 mL·min -1 N2, 74 mL·min -1 H2 and 8 mL·min -1 Ar was used for testing.

[0040] The yield of ammonia synthesis is as follows: Figure 5 As shown, under normal pressure and 350℃ conditions, with a NO content of 1 vol.%, the ammonia synthesis yield of iron catalyst in an N2 / H2 / NO atmosphere is 368 ± 7 µmol. NH3 ·h -1 ·g cat -1 The ammonia synthesis yield under an Ar / H2 / NO atmosphere was 93±3µmol. NH3 ·h -1 ·g cat -1 The ammonia synthesis yield under N2 / H2 / Ar atmosphere was 2 ± 0.2 µmol. NH3 ·h -1 ·g cat -1Therefore, the ammonia yield increased by NO introduction was 214 µmol. NH3 ·h -1 ·g cat -1 This is 141% of the NH3 yield generated from the reaction of H2 and NO under these conditions. With a NO introduction amount of 2 vol.%, the ammonia synthesis yield under a N2 / H2 / NO atmosphere is 714 ± 23 µmol. NH3 ·h -1 ·g cat -1 The ammonia synthesis yield under an Ar / H2 / NO atmosphere was 238±8 µmol. NH3 ·h -1 ·g cat -1 The ammonia synthesis yield under N2 / H2 / Ar atmosphere was 2 ± 0.1 µmol. NH3 ·h -1 ·g cat -1 Therefore, the ammonia yield increased by NO introduction was 474 µmol. NH3 ·h -1 ·g cat -1 This is 199% of the NH3 yield generated from the reaction of H2 and NO under these conditions. With an NO introduction amount of 8 vol.%, the ammonia synthesis yield under a N2 / H2 / NO atmosphere is 2076 ± 121 µmol. NH3 ·h -1 ·g cat -1 The ammonia synthesis yield under an Ar / H2 / NO atmosphere was 941 ± 17 µmol. NH3 ·h -1 ·g cat -1 The ammonia synthesis yield under N2 / H2 / Ar atmosphere was 2 ± 0.1 µmol. NH3 ·h -1 ·g cat -1 Therefore, the ammonia yield increased by NO introduction was 1133 µmol. NH3 ·h -1 ·g cat -1 This is 120% of the NH3 yield generated from the reaction of H2 and NO under these conditions. Combined with the results of Example 1, it can be seen that with iron catalyst at atmospheric pressure and 350°C, as the NO introduction amount increases from 1 vol.% to 5 vol.%, the ratio of the NH3 yield increased by NO introduction to the NH3 yield generated from the reaction of H2 and NO (i.e., Δ) is significantly higher. r / r H2 / NOThe gradual increase in NO content indicates that the "self-circulation" effect is continuously strengthening; further increasing the NO introduction amount to 5 vol.%, Δ r / r H2 / NO The fact that the effect decreased instead of increased indicates that the "self-circulation" effect has been weakened. This shows that the appropriate amount of NO introduced has a significant impact on the "self-circulation" effect, with 5 vol.% NO showing the best results.

[0041] Comparative Example 4 Referring to the atmospheric pressure ammonia synthesis method of Example 1, the industrial iron catalyst is replaced with an equal amount of CeO2, specifically including the following steps: Take 0.5 g of CeO2 and pack it into a fixed-bed tubular reactor with an inner diameter of 8 mm. Use 100 mL / min at 700 °C. -1 After H2 treatment for 5 h, the temperature was lowered to 350℃, and the reaction gas composition was switched to 20.6 mL·min. -1 N2, 74.4 mL·min -1 H2 and 5 mL·min -1 NO was tested. The reaction tail gas was passed through 200 mL of a solution with a concentration of 0.05 mol·L⁻¹. -1 After absorption by dilute sulfuric acid solution, the gas was vented. The tail gas absorbent was quantitatively analyzed using Nessler's reagent method combined with an Agilent Cary 60 UV-Vis spectrophotometer. The reaction gas composition was then changed to 20.6 mL / min. -1 Ar, 74.4 mL·min -1 H2 and 5 mL·min -1 NO, 20.6mL·min -1 N2, 74.4 mL·min -1 H2 and 5 mL·min -1 Ar was tested, and quantitative analysis was performed using dilute sulfuric acid solution absorption and Nessler's reagent method.

[0042] The yield of ammonia synthesis is as follows: Figure 6 As shown, the ammonia synthesis yield of CeO2 with a reaction gas composition of N2 / H2 / NO = 20.6 / 74.4 / 5 at atmospheric pressure and 350℃ is 1063±23µmol. NH3 ·h -1 ·g cat -1 The ammonia synthesis yield was 407 ± 8 µmol when the reaction gas composition was Ar / H2 / NO = 20.6 / 74.4 / 5. NH3 ·h -1 ·g cat -1 The ammonia synthesis yield was 1.1 ± 0.01 µmol when the reaction gas composition was N2 / H2 / Ar = 20.6 / 74.4 / 5.NH3 ·h -1 ·g cat -1 Therefore, at normal pressure and 350°C, the ammonia yield increased by NO introduction was 655 µmol. NH3 ·h -1 ·g cat -1 It is 161% of the yield of NH3 produced by the reaction of H2 and NO under these conditions, that is, the Δ yield of CeO2 at atmospheric pressure and 350℃. r / r H2 / NO The figure was 161%, lower than the 293% achieved by the iron catalyst under the same conditions in Example 1, indicating that the "self-circulation" effect of using CeO2 as a catalyst is not as good as that of using the iron catalyst.

[0043] In summary, the ammonia yield promotion effect of iron catalyst in the ammonia synthesis system under normal pressure and at 350-450℃ decreases with increasing reaction temperature. The promotion rate decreased from 293% at 350℃ in Example 1 to 141% at 400℃ in Comparative Example 1, and further to 93% at 450℃ in Comparative Example 2. Therefore, at relatively lower temperatures, such as 320-380℃, the "self-circulation" effect of NO on the ammonia synthesis reaction of N2 and H2 is more significant; under these conditions, the degree of side reaction between NO and H2 is lower, and the consumption of NO is less. Figure 7 As shown, in the N2 / H2 / NO system, reactive oxygen species O2 is generated by the decomposition of NO. * The desired pathway was used extensively to activate N2, thereby promoting the reaction of N2 and H2 to produce NH3, thus avoiding the undesired pathway, i.e., O. * The reaction with H2 produces H2O, which weakens the "self-circulation" effect. The amount of NO introduced has a significant impact on the "self-circulation" effect of the molecular promoter-based ammonia synthesis system; introducing 3-7 vol.% NO yields better results. Furthermore, in Comparative Example 4, using CeO2 as a catalyst, the promotion rate at 350°C was 161%, but its "self-circulation" effect was worse than that of Example 1 using an iron catalyst under the same conditions. Therefore, the choice of catalyst, the amount of NO introduced, and the reaction temperature all have a significant impact on the yield of ammonia synthesis at atmospheric pressure.

[0044] Example 2 A method for synthesizing ammonia under atmospheric pressure through self-circulation includes the following steps: Take 0.5g of industrial iron catalyst and load it into a fixed-bed tubular reactor with an inner diameter of 8mm. Use 100mL·min at 500℃. -1 After H2 reduction for 4 hours, the temperature was lowered to 350℃, and the reaction gas composition was switched to 20.6 mL·min. -1 N2, 74.4 mL·min-1 H2 and 5 mL·min -1 The performance of NO in self-circulating ammonia synthesis was tested. A sample was taken from the first gas sampling port and fed into a mass spectrometer to analyze the NH3 yield and NO content in the product gas after the initial reaction. After condensation, the remaining gas was pressurized by a gas pump and reintroduced into the fixed-bed tubular reactor. A sample was taken from the second gas sampling port and fed into the mass spectrometer to analyze the N2 and H2 content in the remaining gas. After the second reaction, samples were taken from both the first and second gas sampling ports to analyze the NH3 yield, NO, N2, and H2 content in the remaining gas. This process was repeated for two, three, four, five, six, seven, eight, nine, and tenth reactions. The composition of the reaction gas and the replenishment amount during the ten cycles are shown in Table 1.

[0045] Table 1:

[0046] Table 1 shows that the gas composition of the initial reaction of the iron catalyst at normal pressure and 350℃ is N2 / H2 / NO = 20.6 / 74.4 / 5 mL·min -1 After the initial reaction, due to the consumption of H2 and N2 caused by the ammonia synthesis reaction, a small amount of H2 and N2 needs to be added to the reaction conditions for the second to tenth reactions. The amount of H2 added after each reaction is 0.39 mL·min. -1 The amount of N2 replenished after each reaction was 0.13 mL·min. -1 The amount of NO in the reactant gas increased from an initial 5 mL / min. -1 The concentration gradually decreased to 4.36 mL / min after ten reactions. -1 The NO content decreased from 5% to 4.8% accordingly. The NO signal (i.e., the signal with a mass-to-charge ratio m / z of 30) in the initial reaction gas and the gas after ten reactions was detected using a mass spectrometer (Shanghai Jingpuruo, PM-DEMS). The results are as follows: Figure 8 As shown, the mass spectrum signal (m / z) value of NO only ranges from 6.53 × 10⁻⁶. -10 Reduced to 6.14×10 -10 After ten reactions, the NO concentration in the N2 / H2 / NO mixture did not change significantly. Therefore, there is no need to add NO to the reaction system, and the above-described ammonia synthesis process at atmospheric pressure can proceed in a self-circulating manner.

[0047] The above ten reactions were conducted with approximately half an hour intervals between each reaction. Further analysis of the reaction products was performed, specifically testing the change in the self-circulating ammonia synthesis yield over 5 hours in a reaction atmosphere with N2 / H2 / NO ratios of 20.6 / 74.4 / 5, supplemented with H2 / N2 at 3 / 1 and NO at 0, under normal pressure and 350°C. Figure 9 As shown. By Figure 9 It can be seen that the ammonia yield of the iron catalyst remains relatively stable within 5 hours, and the total ammonia yield increases with the reaction time, i.e., the number of cycles, with a total ammonia yield of 2 mmol within 1 hour. NH3 ·g cat -1 The total ammonia production within 5 hours was 9.1 mmol. NH3 ·g cat -1 Therefore, this atmospheric pressure ammonia synthesis process can achieve "self-circulation" and produce ammonia efficiently.

[0048] For those skilled in the art, several simple deductions or substitutions can be made without departing from the inventive concept, without requiring creative effort. Therefore, any simple improvements made to this invention by those skilled in the art based on the disclosure of this invention should be within the scope of protection of this invention. The above embodiments are preferred embodiments of this invention, and all processes similar to this invention and equivalent changes should fall within the scope of protection of this invention.

Claims

1. A method for synthesizing ammonia under normal pressure through self-circulation, characterized in that, Includes the following steps: (1) Place the catalyst in the reactor, introduce the reaction gas, carry out the reaction under normal pressure and heating conditions, and collect the reaction products; The reactant gases include nitrogen, hydrogen, and a molecular promoter, wherein the molecular promoter is a nitrogen oxide, and the amount of the molecular promoter introduced is 1-10 vol.% of the total volume of the reactant gases. (2) The reaction product is subjected to ammonia separation to obtain ammonia product and residual gas; (3) The remaining gas is returned to the reactor, and the hydrogen and nitrogen consumed in the reaction are added to the reactor to carry out self-circulating ammonia synthesis.

2. The method for synthesizing ammonia under normal pressure through self-circulation according to claim 1, characterized in that, In step (1), the reaction temperature is 350-500℃; and / or, the catalyst includes an iron catalyst; and / or, the nitrogen oxide is nitric oxide.

3. The method for synthesizing ammonia under normal pressure through self-circulation according to claim 1, characterized in that, In step (1), the volume ratio of hydrogen to nitrogen is (0.2-4):

1.

4. The method for synthesizing ammonia under normal pressure through self-circulation according to claim 1, characterized in that, In step (1), before the reaction gas is introduced, the catalyst is further treated in a reducing atmosphere at a temperature of 500-700°C.

5. The method for synthesizing ammonia under normal pressure through self-circulation according to claim 1, characterized in that, In step (2), the ammonia separation method includes condensation and / or liquefaction separation at room temperature and low pressure, wherein the low pressure is 1-2 MPa.

6. The method for synthesizing ammonia under atmospheric pressure through self-circulation according to claim 1, characterized in that, In step (3), the volume ratio of the supplemented hydrogen to nitrogen is 3:

1.

7. The method for synthesizing ammonia under normal pressure through self-circulation according to claim 1, characterized in that, In step (3), when the content of molecular promoter in the reaction system is less than 85% of the initial value, the step of supplementing the reactor with molecular promoter is also included, and the amount of molecular promoter supplemented is 0.1-2 vol. of the total volume of the reaction gas.

8. An atmospheric pressure self-circulating ammonia synthesis system, characterized in that, The method for atmospheric pressure self-circulating ammonia synthesis according to any one of claims 1-7; the atmospheric pressure self-circulating ammonia synthesis system includes a reactor, a condensation assembly and a circulation pipeline, the circulation pipeline connecting the inlet end and the outlet end of the reactor, and the condensation assembly being disposed on the circulation pipeline.

9. The atmospheric pressure self-circulating ammonia synthesis system according to claim 8, characterized in that, The condensation assembly includes an air condenser, a water condenser, and a refrigeration unit arranged sequentially along the circulation pipeline.

10. The method for synthesizing ammonia under atmospheric pressure through self-circulation according to claim 8, characterized in that, The circulation pipeline is also provided with a first gas sampling port and a second gas sampling port. The first gas sampling port is located at the outlet end of the reactor, and the second gas sampling port is located at the inlet end of the reactor.

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