Method for preparing green ammonia by green hydrogen under normal pressure
The synthesis of ammonia under normal pressure using a variable frequency microwave reactor and α-Fe catalyst solves the problem of high cost of precious metal catalysts, achieves efficient and safe hydrogen storage and ammonia synthesis, simplifies the process, and reduces production costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- INST OF CHEM IND OF FOREST PROD CHINESE ACAD OF FORESTRY
- Filing Date
- 2024-02-29
- Publication Date
- 2026-05-19
AI Technical Summary
Existing technologies use precious metal catalysts, which are expensive and have limited resources, making it difficult to synthesize ammonia efficiently at low temperatures and normal pressures. Furthermore, the inherent frequency of microwaves is difficult to match efficiently with catalyst materials, resulting in low ammonia synthesis efficiency.
A variable frequency microwave reactor was used, with α-Fe as a microwave absorber and catalyst. The microwave frequency was continuously adjustable in the range of 4200-5525MHz. Ammonia was synthesized under normal pressure through resonance and hot spot effect, and hydrogen and nitrogen were produced by biomass gasification.
It enables safe and environmentally friendly hydrogen storage and ammonia synthesis under normal pressure, improves ammonia yield, reduces reaction pressure and production costs, simplifies the process, and enhances production sustainability.
Smart Images
Figure CN118206134B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of hydrogen storage technology, specifically relating to a method for normally suppressing green hydrogen with green ammonia. Background Technology
[0002] Hydrogen energy is a promising renewable and clean energy source. Hydrogen storage is currently a key technology restricting its development. It typically requires storing and transporting hydrogen in stable compound form, releasing hydrogen energy through compound decomposition during use, thus ensuring its safe utilization. Ammonia is one of the important compounds for hydrogen storage. The Haber-Bosch reaction of N2 and H2 to synthesize ammonia is a crucial hydrogen storage technology and one of the industrially used methods. Because this reaction is entropy-increasing and exothermic, it usually requires a catalyst and high pressure. Industrial production pressures exceed 50 MPa, and temperatures need to be around 500-600℃ to activate the catalyst. Synthesizing ammonia under low-temperature, ambient-pressure conditions using catalyst materials has become a novel green technology. Currently, precious metals such as ruthenium (Ru), rhodium (Rh), and their composite catalysts are mainly used as ammonia synthesis catalysts. However, due to the high cost and limited resources of precious metals, there is an urgent need to develop new, low-cost, and high-performance technologies for low-temperature, ambient-pressure ammonia synthesis.
[0003] Microwave-assisted heating is a novel heating technology that has attracted much attention in recent years. It has been proven that microwaves, due to their uniformity, selectivity, instantaneous high temperature, and direct energy transfer, can promote chemical synthesis, helping to optimize synthesis conditions and improve product yield. However, the natural frequency of microwaves is currently 2450MHz. Due to the unique dielectric properties of different materials, it is difficult to make absorbing materials respond efficiently at this fixed frequency. Summary of the Invention
[0004] To address the aforementioned problems in the existing technology, the technical problem to be solved by the present invention is to provide a method for green hydrogen and green ammonia under normal pressure. This method effectively reduces the reaction pressure by changing the microwave frequency to couple the intrinsic frequency of the catalyst, under the influence of resonance and hot spot effects. Hydrogen and nitrogen undergo a Haber-Bosch reaction at normal pressure to synthesize ammonia, thus achieving safe and green hydrogen storage.
[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:
[0006] A method for synthesizing green hydrogen and green ammonia under normal pressure involves using a frequency conversion microwave reactor under an inert atmosphere, with α-Fe as the microwave absorber and catalyst, and N2 and H2 as the reaction gases, to synthesize the gaseous product ammonia through a reaction at normal pressure.
[0007] The method for pressing green hydrogen with green ammonia under normal pressure has a continuously adjustable microwave frequency in the range of 4200-5525MHz and a power of 100W; preferably, the microwave frequency is 5200-5525MHz.
[0008] The method described above for suppressing green hydrogen with green ammonia has a reaction volume hourly space velocity (VHSV) of 1200-3600 h⁻¹. -1 The reaction temperature is 290-560℃; preferably, the reaction volume hourly space velocity is 2400-3600 h⁻¹. -1 The reaction temperature is 360-440℃; more preferably, the reaction volume hourly space velocity is 3600 h⁻¹. -1 The reaction temperature is 437℃.
[0009] The method for producing green hydrogen under normal pressure and green ammonia involves preparing the reaction gas H2 using biomass gasification, with H2 volume fraction at 50% and CO2 volume fraction at 10%-30% in the synthesis reaction.
[0010] The method for suppressing green hydrogen and green ammonia involves introducing a carrier gas into the microwave reaction gas to create an inert atmosphere in the microwave reactor.
[0011] In the method for suppressing green ammonia with green hydrogen, the carrier gas is nitrogen or argon.
[0012] The method for suppressing green hydrogen with green ammonia includes the following steps:
[0013] The first step is to fill the quartz tube with quartz wool, slowly loading the α-Fe catalyst into the quartz tube and fixing it with quartz wool.
[0014] The second step is to connect the quartz tube to the microwave reactor, check the airtightness, introduce carrier gas to purge the microwave reaction system and keep the microwave reactor in an inert atmosphere.
[0015] 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 the α-Fe catalyst absorbs the microwave, it begins to heat up. The temperature change of the catalyst bed is detected in real time by an infrared thermometer and a thermal imager on the axial section of a quartz tube.
[0016] Step 4: After reaching and stabilizing the reaction temperature, stop the carrier gas supply and adjust the mass flow meter to control the N2 and H2 to enter the reactor at the predetermined flow rates;
[0017] Step 5: After the reaction is complete, collect the gaseous products.
[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0019] 1. Based on the continuous frequency tuning characteristic of variable frequency microwave, this invention effectively reduces the reaction pressure by changing the microwave frequency to couple the optimal absorption frequency of the catalyst under the influence of resonance and hot spot effects, thereby inducing hydrogen and nitrogen to undergo the Haber-Bosch reaction at normal pressure to synthesize ammonia, thus achieving safe and green hydrogen storage.
[0020] 2. The reaction process of this invention uses a commercial α-Fe catalyst, and the NH3 concentration can reach up to 55.6 ppm. Attached Figure Description
[0021] Figure 1 The graph shows the effect of microwaves and microwave frequencies on ammonia synthesis.
[0022] Figure 2 The graph shows the effect of carrier gas on ammonia synthesis.
[0023] Figure 3 The graph shows the effect of GHSV on ammonia synthesis.
[0024] Figure 4 The graph shows the effect of CO2 volume fraction on ammonia synthesis. Detailed Implementation
[0025] The present invention will be further described below with reference to specific embodiments. The present invention uses a microwave continuous frequency modulation device, which is disclosed in patent application (CN 111117676A) as a microwave continuous frequency modulation synergistic biomass directional depolymerization device and its usage method.
[0026] Example 1
[0027] A method for suppressing green hydrogen with green ammonia, the specific implementation steps of which include:
[0028] The first step is to fill a quartz tube with an inner diameter of 8mm with quartz wool, slowly add 10g of α-Fe into the quartz tube, and fix it with quartz wool; the amount of catalyst used is based on the standard that the filling height covers the infrared temperature measurement range.
[0029] The second step is to connect the quartz tube to the microwave reactor, check the airtightness, purge the reaction system with nitrogen and keep the reactor in an inert atmosphere.
[0030] 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. α-Fe absorbs the 4200MHz microwave and begins to heat up. The microwave power is 100W and the space velocity is 3600h. -1 The temperature change of the catalyst is detected in real time using an infrared thermometer and thermal imager on the axial section of a quartz tube.
[0031] Step 4: After reaching and stabilizing the reaction temperature, stop the nitrogen flow and adjust the mass flow meter to control the gas flow rate into the reactor. The N2 flow rate is 25 ml / min, the H2 flow rate is 75 ml / min, and the pressure is 0.1 MPa. Under standard conditions, the gas density is a constant. The density multiplied by the volumetric flow rate is the mass flow rate. Therefore, the volumetric flow rate under standard conditions is equal to the mass flow rate. The mass flow meter used can directly control the gas to enter the reaction system at a fixed volumetric flow rate.
[0032] Step 5: After reacting for 20 minutes, the gaseous products are collected using a gas sampling bag and analyzed offline in a gas chromatograph.
[0033] The results showed that the NH3 concentration was 21.1 ppm at a reactor temperature of 368℃ and a frequency of 4200MHz.
[0034] Example 2
[0035] In the microwave reactor, the microwave power was set to 100W and the frequency to 4225MHz. Other conditions and implementation steps were the same as in Example 1.
[0036] The reactor temperature was 340℃ and the NH3 concentration was 27.3ppm.
[0037] Example 3
[0038] In the microwave reactor, the microwave power was set to 100W and the frequency to 4450MHz. Other conditions and implementation steps were the same as in Example 1.
[0039] The reactor temperature was 536℃ and the NH3 concentration was 18.4ppm.
[0040] Example 4
[0041] In the microwave reactor, the microwave power was set to 100W and the frequency to 5175MHz. Other conditions and implementation steps were the same as in Example 1.
[0042] The reactor temperature was 290℃ and the NH3 concentration was 20.9ppm.
[0043] Example 5
[0044] 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.
[0045] The reactor temperature was 515℃ and the NH3 concentration was 29.8ppm.
[0046] Example 6
[0047] 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.
[0048] The reactor temperature was 457℃ and the NH3 concentration was 30.1ppm.
[0049] The effect of microwaves and microwave frequencies on ammonia synthesis is described in Examples 1-6, and the results are as follows: Figure 1 As shown.
[0050] With the same catalyst material, different microwave emission frequencies led to significant differences in catalyst performance. At frequencies of 5200 MHz and 5525 MHz, ammonia concentrations increased significantly, reaching 29.8 ppm and 30.1 ppm, respectively. The difference in ammonia yield at different frequencies is mainly due to the high requirement of the absorbing material's properties for microwave frequencies. Matching the microwave frequency with the intrinsic frequency of the absorbing material allows the temperature conditions to effectively promote the reaction. Therefore, the significant increase in ammonia yield is largely attributed to the catalyst's ability to effectively promote electron transfer efficiency during nitrogen molecule activation at the matched microwave frequency. This finding highlights the significant role of microwave technology in the catalytic conversion of ammonia synthesis under low-temperature and low-pressure conditions, providing a feasible approach for more efficient and environmentally friendly ammonia synthesis.
[0051] Example 7
[0052] A method for suppressing green hydrogen with green ammonia, the specific implementation steps of which include:
[0053] The first step is to fill a quartz tube with an inner diameter of 8mm with quartz wool, and slowly fill 10g of α-Fe into the quartz tube and fix it with quartz wool.
[0054] The second step is to connect the quartz tube to the reaction system, check the airtightness, purge the reaction system with argon gas and keep the reactor in an inert atmosphere, with an argon flow rate of 15 ml / min.
[0055] 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. α-Fe absorbs the 5175MHz microwave and begins to heat up. The microwave power is 100W and the space velocity is 3600h. -1 The temperature change of the catalyst is detected in real time using an infrared thermometer and thermal imager on the axial section of a quartz tube.
[0056] Step 4: After reaching and stabilizing the reaction temperature, stop the argon gas supply and adjust the mass flow meter to control the gas flow into the reactor at a predetermined rate; wherein, the reaction pressure is 0.1 MPa, the N2 flow rate is 25 ml / min, and the H2 flow rate is 75 ml / min.
[0057] Step 5: After reacting for 20 minutes, the gaseous products are collected using a gas sampling bag and analyzed offline in a gas chromatograph.
[0058] The results showed that the NH3 concentration was 28.5 ppm at a reactor temperature of 303℃ and a frequency of 5175MHz.
[0059] Example 8
[0060] 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 7.
[0061] The reactor temperature was 361℃ and the NH3 concentration was 53.4ppm.
[0062] Example 9
[0063] In the microwave reactor, the microwave power was set to 100W and the frequency to 5400MHz, and other conditions and implementation steps were the same as in Example 7.
[0064] The reactor temperature was 368℃ and the NH3 concentration was 47.8ppm.
[0065] Example 10
[0066] 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 7.
[0067] The reactor temperature was 437℃ and the NH3 concentration was 55.6ppm.
[0068] The effect of carrier gas on ammonia synthesis is described in Examples 4-10, and the results are as follows: Figure 1 , 2 As shown.
[0069] The feasibility of frequency-converted microwave-induced atmospheric pressure ammonia synthesis under different carrier gas atmospheres was investigated using the same frequencies of 5175MHz, 5200MHz, and 5525MHz, with argon as the inert gas. The results from the examples show that the introduction of argon has a positive impact on the atmospheric pressure synthesis of ammonia from pure hydrogen and nitrogen, with the ammonia concentration reaching a maximum of 55.6ppm at a microwave frequency of 5525MHz.
[0070] Example 11
[0071] In a variable frequency microwave reactor, α-Fe was used as both a microwave absorber and a catalyst, with a mass of 10 g. The microwave frequency was set to 5525 MHz, the power to 100 W, the pressure to 0.1 MPa, and the space velocity to 1200 h⁻¹. -1 .
[0072] The specific implementation steps are the same as in Example 7.
[0073] The reactor temperature was 437℃ and the NH3 concentration was 12.7ppm.
[0074] Example 12
[0075] In a variable frequency microwave reactor, α-Fe was used as both a microwave absorber and a catalyst, with a mass of 10 g. The microwave frequency was set to 5525 MHz, the power to 100 W, the pressure to 0.1 MPa, and the space velocity to 2400 h⁻¹. -1 .
[0076] The specific implementation steps are the same as in Example 7.
[0077] The reactor temperature was 339℃ and the NH3 concentration was 40.1ppm.
[0078] The effects of GHSV are described in Examples 10-12, and the results are as follows: Figure 3 As shown.
[0079] Under conditions where the microwave frequency is close to the intrinsic frequency of the catalyst, the GHSV is 1200 h. -1 At a concentration of 12.7 ppm, within the same reaction time, with the increase of GHSV, the number of active sites on the catalyst increased, and the yield showed an increasing trend. At a GHSV of 3600 h⁻¹, the yield increased. -1 The ammonia yield reached approximately 55.6 ppm. The increase in yield is due to the fact that, with the increase of GHSV, the amount of gas entering the system to participate in the conversion increases significantly within the same reaction time, thus increasing the overall yield.
[0080] Furthermore, a certain increase in GHSV typically leads to more gas passing through the catalyst surface, increasing the collision frequency of reactant molecules on the catalyst surface and thus promoting the reaction and increasing the reaction rate. However, the yield increase is slow because as GHSV increases, the residence time of gas on the catalyst surface decreases, which may reduce the opportunity for reactant molecules to adsorb and react on the catalyst surface, thereby affecting the reaction rate and conversion.
[0081] GHSV also has a certain impact on system temperature stability. High GHSV may lead to localized temperature increases in the reactor because the gas flow rate is faster and heat transfer is relatively less. This may affect the thermal equilibrium of the reaction, thereby affecting the ammonia yield. Furthermore, high GHSV may increase the catalyst deactivation rate because frequent gas impacts can cause catalyst surface wear, which may negatively impact yield in long-term operation. Therefore, in actual production processes, a comprehensive consideration should be given to balancing temperature stability, gas yield, and catalyst lifespan to achieve economic benefits.
[0082] Example 13
[0083] In a variable frequency microwave reactor, α-Fe was used as both a microwave absorber and a catalyst, with a mass of 10 g. The microwave frequency was set to 5525 MHz, the power to 100 W, the pressure to 0.1 MPa, and the space velocity to 2400 h⁻¹. -1 The volume fraction of H2 is 50%; the volume fraction of CO2 is 10%.
[0084] The specific implementation steps are the same as in Example 8.
[0085] The reactor temperature was 487℃ and the NH3 concentration was 21.8ppm.
[0086] Example 14
[0087] In a variable frequency microwave reactor, α-Fe was used as both a microwave absorber and a catalyst, with a mass of 10 g. The microwave frequency was set to 5525 MHz, the power to 100 W, the pressure to 0.1 MPa, and the space velocity to 2400 h⁻¹. -1 The volume fraction of H2 is 50%; the volume fraction of CO2 is 20%.
[0088] The specific implementation steps are the same as in Example 8.
[0089] The reactor temperature was 490℃ and the NH3 concentration was 15.1ppm.
[0090] Example 16
[0091] In a variable frequency microwave reactor, α-Fe was used as both a microwave absorber and a catalyst, with a mass of 10 g. The microwave frequency was set to 5525 MHz, the power to 100 W, the pressure to 0.1 MPa, and the space velocity to 2400 h⁻¹. -1 The volume fraction of H2 is 50%; the volume fraction of CO2 is 30%.
[0092] The specific implementation steps are the same as in Example 8.
[0093] The reactor temperature was 509℃ and the NH3 concentration was 21.8ppm.
[0094] Unlike traditional methods that require pure H2 as a raw material, this method uses hydrogen-rich gas obtained from biomass gasification as the hydrogen source, which then reacts with nitrogen in a catalytic reaction. This process directly generates NH3 at 487-509℃ and atmospheric pressure, eliminating the need for CO2 and hydrogen separation. This approach not only simplifies the biomass hydrogen production process but also reduces separation steps in hydrogen storage, thereby lowering energy consumption and costs. This not only contributes to carbon emission reduction but also enhances the sustainability of the entire production process.
Claims
1. A method for suppressing green hydrogen with green ammonia, characterized in that, A gaseous product, ammonia, was synthesized by a variable frequency microwave reactor under an inert atmosphere, using α-Fe as a microwave absorber and catalyst, and N2 and H2 as reactants, at atmospheric pressure.
2. The method for pressing green hydrogen with green ammonia according to claim 1, characterized in that, The microwave frequency is continuously adjustable in the range of 4200-5525MHz, and the power is 100W.
3. The method for pressing green hydrogen with green ammonia according to claim 1, characterized in that, The reaction volume hourly space velocity is 1200-3600 h⁻¹ -1 The reaction temperature is 290-560℃.
4. The method for pressing green hydrogen with green ammonia according to claim 1, characterized in that, The reaction gas H2 is prepared by biomass gasification. During the ammonia synthesis reaction, the volume fraction of H2 is 50%, and the volume fraction of CO2 is 10%-30%.
5. The method for pressing green hydrogen with green ammonia according to claim 1, characterized in that, A carrier gas is introduced into the microwave reactor to create an inert atmosphere.
6. The method for pressing green hydrogen with green ammonia according to claim 5, characterized in that, The carrier gas is either nitrogen or argon.
7. The method for pressing green hydrogen with green ammonia according to any one of claims 1-6, characterized in that, Includes the following steps: The first step is to fill the quartz tube with quartz wool, slowly loading the α-Fe catalyst into the quartz tube and fixing it with quartz wool. The second step is to connect the quartz tube to the microwave reactor, check the airtightness, introduce carrier gas to purge the microwave reaction system 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 the α-Fe catalyst absorbs the microwave, it begins to heat up, and the temperature change of the catalyst bed is monitored in real time. Step 4: After reaching and stabilizing the reaction temperature, stop the carrier gas supply and introduce N2 and H2. Step 5: After the reaction is complete, collect the gaseous products.