Variable-frequency microwave induced alpha-Fe low-temperature catalysis method for synthesizing ammonia from water vapor and nitrogen

Abstract

The invention discloses a variable-frequency microwave induced alpha-Fe low-temperature catalysis method for synthesizing ammonia from water vapor and nitrogen, and belongs to the technical field of ammonia synthesis. According to the method, alpha-Fe is taken as a microwave absorbing agent and a bifunctional catalyst, water vapor and nitrogen are introduced, and microwave frequency is regulated to realize low-temperature synthesis of ammonia; and performing catalytic cracking on the water vapor through the alpha-Fe to generate hydrogen, and directly synthesizing ammonia on the surface of the alpha-Fe by the hydrogen generated by cracking and nitrogen. Under the conditions of 310 DEG C and 5525 MHz, the corresponding H2 volume fraction is 58%, and the NH3 concentration reaches 58.7 ppm. According to the method, the single catalyst alpha-Fe is used for catalyzing water splitting and ammonia synthesis at the same time for the first time, thermodynamic limitation is broken through through frequency matching, water splitting and ammonia synthesis are completed under the conditions of normal pressure and the temperature smaller than or equal to 420 DEG C, and the three problems that in a traditional process, energy consumption is high, catalyst oxygen poisoning inactivation is achieved, and a hydrogen source depends on fossil fuel are solved.

Description

Technical Field

[0001] This invention belongs to the field of ammonia synthesis technology, specifically relating to a method for synthesizing ammonia from water vapor and nitrogen using frequency-converted microwave-induced α-Fe low-temperature catalytic synthesis. Background Technology

[0002] Nitrogen fertilizer is a core raw material and a hydrogen energy carrier, and its production scale is directly related to global food security and the energy transition process. The traditional Haber-Bosch process, despite a century of development, still struggles to break free from its deep dependence on fossil fuels—producing 1 ton of ammonia requires 1.2 tons of standard coal and emits over 2 tons of CO2. Replacing carbon-based feedstocks with renewable resources for ammonia production has become an inevitable choice for the green upgrading of the chemical industry. Water resources, due to their large reserves and clean, carbon-free characteristics, are considered an ideal hydrogen source carrier. However, the strong OH bonds in water molecules (bond energy 463 kJ / mol) pose a significant energy barrier to their decomposition: conventional thermocatalysis requires maintaining temperatures above 800℃, with energy costs accounting for 68% of the total ammonia production cost; electrolysis is limited by the scarcity of precious metal catalysts and the bottleneck of cleanliness in electricity production. Even more serious is the fact that the oxygen atoms released from water cracking have strong oxidizing properties, irreversibly poisoning the active sites of iron-based catalysts, making it difficult for the traditional "water-to-hydrogen → ammonia synthesis" series process to operate sustainably in industrial settings.

[0003] Microwave-assisted catalysis exhibits unique advantages in low-temperature reactions. Despite progress in laboratory-scale microwave catalysis, industrial-scale water-based ammonia production still suffers from systemic defects: existing technologies mostly focus on single reactions (hydrogen production or ammonia synthesis), failing to address the energy barrier matching problem between water splitting and ammonia synthesis; the physical separation design of microwave absorbers and catalysts leads to energy loss rates exceeding 60%; and a fundamental solution to oxygen poisoning is particularly lacking. Developing an integrated technology capable of simultaneously achieving low-temperature activation of water molecules, efficient nitrogen-hydrogen coupling, and self-regeneration is the core challenge in overcoming the bottleneck of green ammonia production industrialization, and a key problem that has been explored by those skilled in the art for a long time without success. Summary of the Invention

[0004] One technical problem solved by this invention is to provide a method for low-temperature catalytic synthesis of ammonia from water vapor and nitrogen using α-Fe induced by frequency conversion microwaves. Utilizing the selective heating characteristics of frequency conversion microwaves, α-Fe undergoes a water splitting reaction with water vapor to generate hydrogen; subsequently, the hydrogen and nitrogen react under the action of α-Fe to synthesize ammonia.

[0005] Technical Solution: To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A method for synthesizing ammonia from water vapor and nitrogen using frequency-converting microwave-induced α-Fe low-temperature catalysis is disclosed. α-Fe serves as both a microwave absorber and a bifunctional catalyst, while water vapor and nitrogen are the reactants. Water vapor and nitrogen are introduced into a quartz tube within a microwave reaction chamber via a gas delivery system. The water vapor flows downwards and, upon passing through the α-Fe bed, undergoes a water splitting reaction under microwave irradiation to generate H2 and O2. Subsequently, the generated H2 and N2 undergo an ammonia synthesis reaction under the catalysis of α-Fe.

[0007] The method for synthesizing ammonia from water vapor and nitrogen using frequency-converted microwave-induced α-Fe low-temperature catalytic reaction involves a microwave frequency of 4400-5525MHz, a power of 100W, and a temperature of 310-420℃.

[0008] The method for synthesizing ammonia from water vapor and nitrogen using frequency-converted microwave-induced α-Fe low-temperature catalytic water vapor and nitrogen has a water vapor input rate of 0.15-0.25 mL / min and a nitrogen input rate of 18-22 mL / min in the quartz tube.

[0009] The method for synthesizing ammonia from water vapor and nitrogen using frequency-converted microwave-induced α-Fe low-temperature catalysis involves a water vapor input rate of 0.2 mL / min and a nitrogen input rate of 20 mL / min into the quartz tube.

[0010] The method for synthesizing ammonia from water vapor and nitrogen using frequency-modulated microwave-induced α-Fe low-temperature catalytic reaction involves a microwave frequency of 4400MHz, a power of 100W, and a reactor temperature of 420℃.

[0011] The method for synthesizing ammonia from water vapor and nitrogen using frequency-modulated microwave-induced α-Fe low-temperature catalytic reaction involves a microwave frequency of 5200MHz, a power of 100W, and a reactor temperature of 390℃.

[0012] The method for synthesizing ammonia from water vapor and nitrogen using frequency-modulated microwave-induced α-Fe low-temperature catalytic reaction involves a microwave frequency of 5525MHz, a power of 100W, and a reactor temperature of 310℃.

[0013] The method for synthesizing ammonia from water vapor and nitrogen using frequency-converted microwave-induced α-Fe low-temperature catalytic reaction includes the following steps:

[0014] The first step is to fill a quartz tube with an inner diameter of 8mm with quartz wool, slowly insert 2g of α-Fe into the quartz tube, and then fix it with quartz wool.

[0015] The second step is to connect the quartz tube to the microwave reaction system, check the airtightness, purge the microwave reaction system with nitrogen gas, and keep the microwave reactor in an inert atmosphere.

[0016] The third step is to turn on the microwave power supply and input the frequency-converted microwave into the microwave resonant cavity through the microwave feed port. After α-Fe absorbs microwaves of different frequencies, it begins to heat up. The temperature change of the catalyst is detected in real time by an infrared thermometer and a thermal imager at the axial section of the quartz tube.

[0017] Step 4: After reaching and stabilizing the reaction temperature, turn on the gas delivery system to introduce water vapor and nitrogen into the quartz tube inside the microwave reaction chamber to start the reaction;

[0018] Step 5: After the reaction is complete, collect the gaseous products.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0020] 1. Revolutionary breakthrough in low-temperature reaction: By precisely matching the microwave frequency with the intrinsic properties of α-Fe, water splitting and ammonia synthesis are simultaneously driven within a temperature window far lower than that of traditional processes, significantly reducing system energy consumption.

[0021] 2. Leap in energy utilization efficiency: The synergistic effect of microwave-catalyst significantly improves the energy conversion rate, enabling clean electrical energy to be efficiently converted into chemical energy, creating a new paradigm for low-carbon ammonia production.

[0022] 3. Broad prospects for industrial applications: The process is compatible with atmospheric pressure operation, and the only byproduct is environmentally friendly oxygen, providing technical support for the construction of distributed green ammonia production bases.

[0023] 4. Simplified process and strong controllability: The single reactor integrates raw material pyrolysis and product synthesis functions, eliminating complex pretreatment and separation units, and significantly reducing equipment investment and operation and maintenance costs.

[0024] 5. This invention is the first to utilize a single catalyst α-Fe to simultaneously catalyze water splitting and ammonia synthesis. By overcoming thermodynamic limitations through frequency matching, the "water splitting and ammonia synthesis" can be completed under normal pressure and ≤420℃ conditions. In a single microwave reaction chamber, the two key reactions can be continuously completed through a simple fixed-bed packing method and unidirectional flow of water vapor and nitrogen.

[0025] 6. Key parameters such as microwave frequency, power (fixed at 100W) and reaction temperature are easily adjustable: The reaction process and product distribution can be precisely controlled by adjusting the frequency as needed (e.g., 4400MHz corresponds to 420℃, 5200MHz corresponds to 390℃, and 5525MHz corresponds to 310℃), resulting in good process stability and strong operability. Attached Figure Description

[0026] Figure 1 The graph shows the effect of microwave frequency on ammonia synthesis.

[0027] Figure 2 The figure shows the effect of microwave frequency on water splitting. Detailed Implementation

[0028] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are implemented based on the technical solutions of the present invention and should be understood as being for illustrative purposes only and not for limiting the scope of the invention. The frequency conversion device used in the embodiments is the device disclosed in patent publication number CN 111117676 B, entitled "A Microwave Continuous Frequency Modulation Coordinated Biomass Directional Depolymerization Device and its Usage Method".

[0029] Example 1

[0030] In a microwave reactor, the microwave power was set to 100W and the frequency to 4400MHz. Utilizing the selective heating characteristics of frequency-converting microwaves, α-Fe underwent a water splitting reaction with water vapor to generate hydrogen. Subsequently, the hydrogen and nitrogen reacted under the action of α-Fe to synthesize ammonia. The α-Fe packing mass was 2g, the water vapor flow rate was 0.2mL / min, and the nitrogen flow rate was 20mL / min. Specific implementation steps included:

[0031] The first step is to fill a quartz tube with an inner diameter of 8mm with quartz wool, slowly insert α-Fe into the quartz tube, and then fix it with quartz wool.

[0032] The second step is to connect the quartz tube to the microwave reaction system, check the airtightness, purge the microwave reaction system with nitrogen gas, and keep the microwave reactor in an inert atmosphere.

[0033] The third step is to turn on the microwave power supply and input the frequency-converted microwave into the microwave resonant cavity through the microwave feed port. After α-Fe absorbs the microwave, it begins to heat up. The temperature change of the catalyst is detected in real time by an infrared thermometer and a thermal imager at the axial section of the quartz tube.

[0034] Step 4: After reaching and stabilizing the reaction temperature, turn on the gas delivery system to introduce water vapor into the quartz tube inside the microwave reaction chamber to start the reaction;

[0035] Step 5: After the reaction is complete, the gaseous products are collected using a gas sampling bag and analyzed offline in gas chromatography. Ammonia is analyzed using ion chromatography.

[0036] The reactor infrared temperature is 420℃, and the gas component volume fraction is as follows: Figure 1 and Figure 2 As shown, the specific concentrations are: H2: 67%, N2: 29.5%, O2: 3.5%, and NH3 concentration: 25.6 ppm.

[0037] Example 2

[0038] In the microwave reactor, the microwave power was set to 100W and the frequency to 5200MHz. Other conditions and implementation steps were the same as in Example 1.

[0039] The reactor infrared temperature is 390℃, and the gas component volume fraction is as follows: Figure 1 and Figure 2 As shown, the specific values ​​are: H2: 65%, N2: 32%, O2: 3%, and NH3 concentration: 28.3 ppm.

[0040] Example 3

[0041] In the microwave reactor, the microwave power was set to 100W and the frequency to 5525MHz. Other conditions and implementation steps were the same as in Example 1.

[0042] The reactor infrared temperature is 310℃, and the gas component volume fraction is as follows: Figure 1 and Figure 2 As shown, the specific concentrations are: H2: 58%, N2: 40.7%, O2: 1.3%, and NH3 concentration: 58.7 ppm.

[0043] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for synthesizing ammonia from water vapor and nitrogen using frequency-converted microwave-induced α-Fe low-temperature catalysis, characterized in that, Using α-Fe as a microwave absorber and a bifunctional catalyst, and water vapor and nitrogen as reactants, water vapor and nitrogen are introduced into a quartz tube in a microwave reaction cavity. Water vapor passes through the α-Fe bed from top to bottom. Under the action of α-Fe, the water vapor undergoes a water splitting reaction. Subsequently, the hydrogen produced by water splitting reacts with nitrogen to synthesize ammonia.

2. The method for synthesizing ammonia from water vapor and nitrogen using frequency-converted microwave-induced α-Fe low-temperature catalysis according to claim 1, characterized in that, The microwave frequency is 4400-5525MHz, the power is 100W, and the temperature is 310-420℃.

3. The method for synthesizing ammonia from water vapor and nitrogen using frequency-converted microwave-induced α-Fe low-temperature catalysis according to claim 1, characterized in that, The rate at which water vapor is introduced into the quartz tube is 0.15-0.25 mL / min, and the rate at which nitrogen is introduced into the quartz tube is 18-22 mL / min.

4. The method for synthesizing ammonia from water vapor and nitrogen using frequency-converted microwave-induced α-Fe low-temperature catalysis according to claim 1, characterized in that, The rate at which water vapor is introduced into the quartz tube is 0.2 mL / min, and the rate at which nitrogen is introduced into the quartz tube is 20 mL / min.

5. The method for synthesizing ammonia from water vapor and nitrogen using frequency-converted microwave-induced α-Fe low-temperature catalysis according to claim 1, characterized in that, The microwave frequency is 4400MHz, the power is 100W, and the reactor temperature is 420℃.

6. The method for producing hydrogen from biomass steam using microwave staged catalysis according to claim 1, characterized in that, The microwave frequency is 5200MHz, the power is 100W, and the reactor temperature is 390℃.

7. The method for producing hydrogen from biomass steam using microwave staged catalysis according to claim 1, characterized in that, The microwave frequency is 5525MHz, the power is 100W, and the reactor temperature is 310℃.

8. The method for producing hydrogen from biomass steam using microwave staged catalysis according to claim 1, characterized in that, Includes the following steps: The first step is to fill a quartz tube with an inner diameter of 8mm with quartz wool, slowly insert 2g of α-Fe into the quartz tube, and then fix it with quartz wool. The second step is to connect the quartz tube to the microwave reaction system, check the airtightness, purge the microwave reaction system with nitrogen gas, and keep the microwave reactor in an inert atmosphere. The third step is to turn on the microwave power supply and input the frequency-converted microwave into the microwave resonant cavity through the microwave feed port. After α-Fe absorbs microwaves of different frequencies, it begins to heat up. The temperature change of the catalyst is detected in real time by an infrared thermometer and a thermal imager at the axial section of the quartz tube. Step 4: After reaching and stabilizing the reaction temperature, turn on the gas delivery system to introduce water vapor and nitrogen into the quartz tube inside the microwave reaction chamber to start the reaction; Step 5: After the reaction is complete, collect the gaseous products.

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