Method and system for synthesizing ammonia through plasma coupling thermocatalysis

Abstract

The invention belongs to the technical field of ammonia synthesis, and particularly relates to a method and a system for synthesizing ammonia through plasma coupling thermocatalysis. A method for synthesizing ammonia through plasma coupling thermocatalysis comprises the following steps that raw material gas containing nitrogen and oxygen is converted into gas flow containing nitric oxide through plasma, and nitric oxide source gas is formed after purification; the nitrogen oxide source gas and the hydrogen reducing gas are in contact with a bifunctional catalyst subjected to acid pickling treatment for a thermocatalytic reduction reaction, nitrogen oxide is converted, and ammonia gas is generated; wherein the bifunctional catalyst comprises a platinum metal active component and a barium oxide storage component which are loaded on an alumina carrier.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of synthetic ammonia, and particularly relates to a method and system for synthesizing ammonia by coupling plasma with thermal catalysis. BACKGROUND

[0002] Synthetic ammonia is the basis of modern chemical industry, and its traditional production process mainly relies on the Haber-Bosch method. This process directly reacts nitrogen and hydrogen to generate ammonia gas under high temperature and high pressure conditions through a catalyst. Although this method is mature and has high yield, it is highly dependent on fossil energy, consumes a large amount of energy for hydrogen production and reaction process, and causes a large amount of greenhouse gas emissions, which is contrary to the goal of global carbon neutralization and sustainable development. Therefore, developing a new type of green and low-energy synthetic ammonia technology has become a key issue to be solved in this field.

[0003] In recent years, under the driving of renewable energy, the technology of synthesizing ammonia under mild conditions using plasma has received widespread attention. This method has the advantages of being green, low-carbon, easy to start and stop, and suitable for distributed production. However, the mainstream plasma direct synthesis ammonia technology still faces insurmountable bottlenecks: first, the chemical properties of nitrogen molecules are extremely inert, and the bond energy of N≡N triple bond is extremely high, resulting in a huge energy cost for plasma direct bond breaking, and the electron energy utilization rate and ammonia yield are very low; second, nitrogen and hydrogen coexist in the plasma environment, which will trigger complex competitive reactions and side reactions, leading to unstable reaction paths and limiting its industrial application prospects.

[0004] To avoid the difficulty of directly activating highly inert nitrogen molecules, the indirect synthesis of ammonia by first converting nitrogen to more active nitrogen oxides by plasma and then catalytic reduction shows potential. However, at present, the research of this technical route is mostly in the experimental stage of dispersion and unit separation, lacking efficient integration and synergistic optimization of multiple links such as nitrogen source activation, intermediate conversion, and target product synthesis. Therefore, there is an urgent need in the field to provide a method for synthesizing ammonia that can effectively couple low-temperature plasma activation with thermal catalytic reaction, while ensuring efficient and high-selectivity conversion to ammonia gas. SUMMARY

[0005] The purpose of the present application is to solve the above problems, and provide a method and system for synthesizing ammonia by coupling plasma with thermal catalysis.

[0006] In a first aspect, a method for synthesizing ammonia by coupling plasma with thermal catalysis adopts the following technical solution: A method for synthesizing ammonia by coupling plasma with thermal catalysis, comprising the following steps: The raw material gas containing nitrogen and oxygen is converted into a gas stream containing nitrogen oxides by plasma, and the nitrogen oxide source gas is formed after purification; The nitrogen oxide source gas and the hydrogen reduction gas are contacted with the dual-function catalyst treated by pickling to perform a thermal catalytic reduction reaction, and the nitrogen oxides are converted to generate ammonia gas; The dual-function catalyst comprises a platinum metal active component and a barium oxide storage component supported on an alumina carrier.

[0007] Further, in the pickling process, the hydrogen ion concentration is 4-8 mol / L.

[0008] Further, in the thermal catalytic reduction reaction, the thermal catalytic reduction temperature is 100-700℃, the volume ratio of the nitrogen oxide source gas to the hydrogen reduction gas is 1-10:1, and the total volume flow rate of the nitrogen oxide source gas and the hydrogen reduction gas is 1-10 L / min.

[0009] Further, in the thermal catalytic reduction reaction, the thermal catalytic reduction temperature is 300-700℃, the volume ratio of the nitrogen oxide source gas to the hydrogen reduction gas is 3-10:1, and the total volume flow rate of the nitrogen oxide source gas and the hydrogen reduction gas is 5-10 L / min.

[0010] Further, in the thermal catalytic reduction reaction, the thermal catalytic reduction temperature is 500℃, the volume ratio of the nitrogen oxide source gas to the hydrogen reduction gas is 7:1, and the total volume flow rate of the nitrogen oxide source gas and the hydrogen reduction gas is 5 L / min.

[0011] In a second aspect, a system for synthesizing ammonia by plasma-coupled thermal catalysis adopts the following technical solution: A system for synthesizing ammonia by plasma-coupled thermal catalysis adopts the above method to synthesize ammonia; the system comprises: A plasma unit for exciting nitrogen and oxygen in air to generate nitrogen oxides, and an outlet of the plasma unit delivers a gas stream containing nitrogen oxides to a downstream catalytic ammonia synthesis unit; A raw material supply unit connected to the plasma unit and the catalytic ammonia synthesis unit respectively, for delivering air to the plasma unit and delivering hydrogen reduction gas to the catalytic ammonia synthesis unit; The catalytic ammonia synthesis unit is filled with the dual-function catalyst, and is configured to receive the nitrogen oxide source gas and the hydrogen reduction gas formed after purification from the upstream to perform a thermal catalytic reduction reaction on the dual-function catalyst to generate ammonia gas mixture; An ammonia collection unit is connected with the catalytic ammonia synthesis unit, and is configured to receive the ammonia gas mixture delivered by the outlet of the catalytic ammonia synthesis unit, and separate liquid ammonia and a mixture gas containing hydrogen and nitrogen oxides.

[0012] Further, the system further comprises a NO oxidation unit and an oxygen separation unit connected in sequence between the plasma unit and the catalytic ammonia synthesis unit, the inlet of the NO oxidation unit is connected with the outlet of the plasma unit, for receiving the gas stream containing nitrogen oxides and oxidizing NO into NO2; the outlet of the oxygen separation unit is connected with the inlet of the catalytic ammonia synthesis unit, for separating oxygen and forming a nitrogen oxide source gas.

[0013] Further, the system further comprises a hydrogen recovery unit, the inlet of the hydrogen recovery unit is connected with the outlet of the ammonia collection unit, and the outlet of the hydrogen recovery unit is connected with the NO oxidation unit, for recovering and drying hydrogen and delivering the remaining gas to the NO oxidation unit to form a circulation loop.

[0014] Further, the system further comprises a process control module, the process control module further comprises a gas flow regulation unit and a temperature control unit, the gas flow regulation unit is connected with the raw material supply unit, for regulating the preset volume ratio of the nitrogen oxide source gas and the hydrogen reduction gas and the preset total volume flow rate; the temperature control unit is connected with the catalytic ammonia synthesis unit, for controlling and maintaining the preset temperature of the thermal catalytic reduction of the catalytic ammonia synthesis unit.

[0015] Further, the catalytic ammonia synthesis unit is a fixed bed reactor, and the bifunctional catalyst in the fixed bed reactor is filled in the form of a static bed.

[0016] Advantages of the present application: The present application provides a method for synthesizing ammonia by coupling plasma with thermal catalysis, which pre-converts inert nitrogen into active nitrogen oxides under mild conditions by plasma, avoids the high temperature and high pressure of the traditional Haber process and the high energy consumption and bond breaking bottleneck of the plasma direct method, and significantly reduces the energy barrier of nitrogen source activation. By introducing a bifunctional catalyst and coupling the steps of nitrogen oxide capture and catalytic reduction, efficient and highly selective conversion from active nitrogen intermediates to final product ammonia is achieved. By acid washing pretreatment of the catalyst, the microstructure and surface properties of the catalyst are greatly optimized, and the catalytic activity and stability are significantly enhanced, thereby greatly improving the overall ammonia synthesis efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The high-resolution XPS spectrum of the bifunctional catalyst provided for Example 1.

[0018] Figure 2 Surface morphology structure images of the bifunctional catalyst provided for Example 1 after acid washing and non-acid washing treatment.

[0019] Figure 3 Surface morphology change images of the bifunctional catalyst provided for Example 1 before and after treatment with different acid concentrations (33%, 50%, 66%).

[0020] Figure 4 Element mapping distribution images of the bifunctional catalyst provided for Example 1 after acid washing and non-acid washing treatment; (a) non-acid washing catalyst; (b) acid washing catalyst.

[0021] Figure 5 EDS spectrogram of the bifunctional catalyst provided for Example 1 after acid washing and non-acid washing treatment; (a) EDS spectrogram of the non-acid washing catalyst; (b) EDS spectrogram of the acid washing catalyst.

[0022] Figure 6 Test result images of the ammonia synthesis performance of the catalyst under different acid washing concentrations; (a) ammonia synthesis concentration with V NO2(s) :V H2 change; (b) yield, NO2, and H2 conversion rate.

[0023] Figure 7 Test result images of the ammonia synthesis performance of the catalyst under 66% acid washing concentration at different reaction temperatures; (a) ammonia synthesis concentration with temperature change; (b) yield, NO2, and H2 conversion rate.

[0024] Figure 8 Test result images of the ammonia synthesis performance of the catalyst under 66% acid washing concentration with total gas flow change; (a) ammonia synthesis concentration with gas flow change; (b) yield, NO2, and H2 conversion rate.

[0025] Figure 9 Test result images of the ammonia synthesis performance of the catalyst with a length of 100 mm under 66% acid washing concentration at different total gas flow changes; (a) ammonia synthesis concentration with gas flow change; (b) yield, NO2, and H2 conversion rate.

[0026] Figure 10 Test result images of the ammonia synthesis performance of the catalyst with a length of 100 mm under 66% acid washing concentration at different NO2 / H2 volume ratios; (a) ammonia synthesis concentration with V H2 :V NO2 change; (b) yield, NO2, and H2 conversion rate.

[0027] Figure 11 Process schematic diagram of the plasma coupled thermal catalytic ammonia synthesis system provided for Example 7. DETAILED DESCRIPTION

[0028] The method and system for synthesizing ammonia by plasma-coupled thermal catalysis according to the present application are further described in detail below with reference to the following examples. For the sake of brevity and clarity, the present document does not include all possible techniques and embodiments of the present application, and it is understood that any technical features and embodiments within the present examples do not limit the scope of protection of the present application, which includes any alternative technical features and embodiments that can be adopted by those skilled in the art without creative effort. Specifically, any technical features of the present application can be replaced, or any two or more technical features provided by the present application can be combined with each other, and the resulting embodiments should be within the scope of protection of the present application. If the specific techniques and conditions are not specified in the examples, the techniques and conditions described in the literature in the art or according to the product instructions are used, and if the manufacturers of the reagents or instruments are not specified, the reagents or instruments are conventional products that can be purchased on the market.

[0029] EXAMPLE Example 1 Example 1 provides a method for synthesizing ammonia by plasma-coupled thermal catalysis, comprising the following steps: Converting a raw gas containing nitrogen and oxygen into a gas stream containing nitrogen oxides by plasma, and forming a nitrogen oxide source gas after purification; Contacting the nitrogen oxide source gas and a hydrogen reduction gas with a dual-functional catalyst treated by pickling to perform a thermal catalytic reduction reaction, and converting the nitrogen oxides to generate ammonia; The dual-functional catalyst comprises a platinum metal active component and a barium oxide storage component supported on an alumina carrier.

[0030] Example 1 also provides a method for preparing a dual-functional catalyst, comprising the following steps: Commercial alumina particles are selected as the carrier. The carrier is placed in a nitric acid solution and stirred for 4 hours at room temperature for pickling treatment. After pickling, the carrier particles are taken out, washed repeatedly with deionized water until neutral, and then dried in an oven at 120°C for 12 hours.

[0031] An equal-volume impregnation method is used to load the active component. First, a certain amount of barium acetate is dissolved in deionized water to prepare impregnation solution A. The pretreated alumina carrier is added to impregnation solution A and soaked at room temperature for 12 hours, and then dried at 120°C. Subsequently, a certain amount of chloroplatinic acid hexahydrate is dissolved in deionized water to prepare impregnation solution B. The barium-loaded carrier is added to impregnation solution B and soaked for 12 hours, and then dried at 120°C.

[0032] The catalyst precursor loaded with all components was placed in a muffle furnace, and heated to 500°C at a rate of 10°C / min under air atmosphere, and calcined at this temperature for 5 hours. After natural cooling to room temperature, the Pt / BaO / Al2O3 bifunctional catalyst was obtained.

[0033] In order to analyze the surface chemical state and micro-morphology of the Pt / BaO / Al2O3 bifunctional catalyst prepared in the above Example 1, XPS, SEM and EDS characterization were carried out.

[0034] (1) XPS analysis In order to show the X-ray photoelectron spectroscopy (XPS) of the surface element composition and chemical state of the bifunctional catalyst used in this example, the distribution and interaction of the catalyst surface Pt (platinum), Ba (barium), N related species (N2, NO2 - , NO3 - ) were investigated.

[0035] 1. Pt species analysis XPS test showed that the Pt 4f peaks at about 71.2 eV and about 74.5 eV corresponded to Pt 4f 7 / 2 and Pt 4f 5 / 2 , respectively, indicating that Pt mainly existed in the form of metal Pt. In addition, Pt 4d double peaks were observed near 303.8 eV and near 312.3 eV, indicating that Pt 2+ or Pt 4+ species such as PtO or PtO2 may exist on the surface of the catalyst. This indicates that the Pt on the surface of the catalyst has a certain distribution of oxidation state.

[0036] 2. Ba species analysis In the Ba 3d spectrum, Ba 3d 5 / 2 characteristic peaks were observed near 780.1 eV and near 795.5 eV, indicating that Ba mainly existed in the form of Ba 2+ (such as BaO, Ba(NO3)2). Ba as an additive of the catalyst plays a key role in the NO X adsorption and conversion process in this catalytic system, especially in the formation of nitrate (Ba(NO3)2), and the shift of Ba 3d binding energy can reflect the interaction strength with NO X species.

[0037] 3. N related species analysis (NO3 - , NO3 - and N2) The distribution of N1s binding energy peak can further reveal the NO XThe presence of NO2species is observed around 403.5 eV - ; while NO3species is observed around 406.8 eV - The characteristic peaks indicate that the catalyst surface has a strong adsorption capacity for NO X species. In addition, a N2-related peak is observed around 398.2 eV, indicating that there may be a certain amount of N2 residue or nitrogen species conversion path on the catalyst surface.

[0038] In summary, on the surface of Pt-based catalysts, NO2 - and NO3 - species have different binding energies, and their variation with composition can be explained by metal-support electronic interactions. XPS binding energy analysis shows that the introduction of Ba causes the Pt 4f orbital binding energy to shift to lower energy, indicating that Ba as an electronic additive enhances the electron density of Pt through Pt→Ba charge transfer. This electronic structure modulation significantly affects the adsorption behavior of NO X : the binding energy of NO3 - is slightly higher, confirming the presence of BaO phase, which enhances the electrostatic interaction between the surface basic site and the nitrate anion, thereby increasing the chemical adsorption strength of NO3 - . The simultaneous observation of a decrease in the binding energy of NO2 - indicates that Ba may preferentially stabilize high-valence NO X species. These electronic-level interaction mechanisms provide a theoretical basis for designing NO X storage-reduction catalysts with gradient adsorption characteristics, especially in terms of regulating the synergistic effect of Pt active sites and nitrogen storage components.

[0039] (2) SEM analysis 1. Surface morphology and structure analysis of acid-washed and non-acid-washed dual-function catalysts The microstructure and element distribution of the catalysts before and after acid washing were characterized by scanning electron microscopy (SEM) to analyze the effect of acid washing on the surface structure and element uniformity of the catalysts, as shown in Figure 2 The SEM imaging results show that the surface of the non-acid-washed catalyst is rough, with uneven particle size distribution and obvious agglomeration in some areas. The acid-washed catalyst shows more significant etching characteristics, with some degree of corrosion pits and holes on the surface, indicating that the acid washing process removed some impurities or weakly bound species, causing changes in the surface structure of the catalyst.

[0040] 2. Surface morphology and structure analysis of catalysts with different acid washing concentrations Figure 3Morphology changes of catalyst surface before and after treatment with different acid concentrations (33%, 50%, 66%, concentrated hydrochloric acid and water were configured according to different volume ratios) are shown in the middle. From the reaction before Figure 3 As can be seen from (a)-(c), with the increase of acid concentration, the structure between the particles on the surface of the catalyst gradually changes from dense and regular to porous and loose. Especially under the acid concentration of 66% (d), the surface presents obvious needle-like and strip-like microstructure, indicating that high-concentration acid has strong corrosion ability and can significantly remove surface impurities and expose more active sites. After the reaction Figure 3 Figure 3 (d)-(f) further verifies this trend, that is, high acid concentration can make the original structure of the catalyst surface be etched basically, indicating that acid washing has a significant modification effect on the surface structure.

[0041] In summary, the higher the acid concentration, the more obvious the etching effect, which can effectively enhance the roughness and specific surface area of the catalyst surface. This structural change not only helps to enhance the adsorption capacity of reactant molecules, but also promotes the exposure and utilization of active sites, thereby improving the efficiency of ammonia synthesis reaction to some extent. This result reflects the importance of acid concentration regulation in optimizing the performance of the catalyst.

[0042] (3) EDS spectrum analysis Figure 4 The element mapping distribution of the unacid-washed bifunctional catalyst and the acid-washed bifunctional catalyst is shown. The analysis shows that the distribution of Pt (platinum), Ba (barium) and Al (aluminum) on the unacid-washed catalyst is uneven, and the enrichment phenomenon is obvious in some areas, which may affect the catalytic activity. The distribution of each element in the acid-washed catalyst is more uniform, indicating that acid washing helps to improve the uniformity of the composition of the catalyst, thereby optimizing its catalytic performance. In addition, through Figure 5 The quantitative analysis results of EDS spectrum show that the mass fraction of Pt, Ba and Al on the acid-washed catalyst is higher than that of the unacid-washed sample, which may be due to the removal of inactive components or impurities on the surface by acid washing, improving the exposure of target elements on the catalyst surface and providing more active sites for catalytic reaction.

[0043] In summary, SEM and EDS analysis show that acid washing not only changes the surface microstructure of the catalyst, making it present the etched morphology characteristics, but also improves the uniformity of the distribution of active elements and increases the mass fraction of key catalytic elements such as platinum, barium and aluminum, thereby providing a structural basis for optimizing the activity and stability of the catalyst.

[0044] Example 2 Example 2 is to explore the redox synthesis ammonia performance of the bifunctional catalyst provided in Example 1 under different acid concentrations, wherein C​NO2 (s) =10000 ppm, total gas flow Q = 1 L / min, catalyst size 8 mm / 12.5 g, and the results are shown in Figure 6 (a). Figure 6 It can be seen from (a) that the higher the acid washing concentration of the catalyst (66%>50%>33%), the higher the overall level of NH3 concentration generated at different inlet V NO2(s) :V H2 volume ratios, especially in the high NO X region, indicating that high acid washing treatment helps to expose more active sites and promote the progress of ammonia synthesis reaction. Figure 6 (b) further reveals the reaction rate and hydrogen utilization efficiency of the catalyst at different inlet ratios. It is worth noting that under the condition of high acid washing concentration, the lower the hydrogen ratio (10:1, 4:1), the more obvious the promotion of NH3 generation rate, showing strong catalytic ability. However, with the increase of H2 content, the hydrogen utilization efficiency (η H2 ) increases significantly, indicating that high acid washing treatment not only improves the conversion efficiency of hydrogen by the catalyst, but also improves the economy of the reaction. In summary, high concentration acid washing treatment can significantly enhance the activity of the catalyst surface, thereby improving the efficiency and selectivity of ammonia synthesis reaction; at the same time, by reasonably adjusting the inlet ratio of NO X and H2, the generation rate and resource utilization efficiency of NH3 can be further optimized.

[0045] Example 3 Example 3 is to explore the effect of different thermal catalytic reduction temperatures on ammonia synthesis performance, under the condition of 66% acid washing concentration, C NO2 (s) =10000 ppm, Q = 1 L / min, catalyst size 8 mm / 12.5 g, and the results are shown in Figure 7 (a). Figure 7 It can be observed from (a) that the NH3 concentration increases significantly with the increase of temperature, especially in the low temperature zone (100-500℃), the growth rate is the fastest, indicating that this interval is the key temperature zone for the significant enhancement of reaction activity. However, when the temperature rises above 500℃ (high temperature zone), the increase of NH3 concentration tends to be flat, which may be limited by the reaction equilibrium or thermal stability factors. In addition, the NO2 concentration decreases rapidly with the increase of temperature, and tends to be zero above 200℃, and the NO concentration is always at a very low level in the whole temperature zone, indicating that NO2 is effectively adsorbed and converted, and there is no obvious accumulation of by-products.

[0046] Figure 7 (b) further confirms the above conclusion. The generation rate of NH3 increases rapidly before 500℃, and then enters a plateau period, indicating that the reaction realizes the optimal kinetic matching in the medium temperature zone. The conversion rate of NO2 ηNO2 It also continues to rise with the increase of temperature, further demonstrating that the catalyst can efficiently adsorb NO2 and promote its conversion to NH3. At the same time, the NO generation rate is always very low, indicating that the side reaction path is effectively inhibited.

[0047] Example 4 Example 4 is to explore the change of total gas flow on the performance of ammonia synthesis, under the condition of 66% pickling concentration, C NO2 (s) =10000 ppm, NO 2(s) / H2 volume ratio of 4:1, catalyst size of 8 mm / 12.5 g, and the results are shown in Figure 8 From Figure 8 (a), it can be seen that the NH3 concentration is higher in the low flow area, indicating that the utilization of raw gas is more optimal and the catalytic reaction is more sufficient. However, with the increase of gas flow, the NH3 concentration gradually decreases, and the raw gas NO2 and by-product NO appear, indicating that under the condition of high flow, the raw gas and by-product reaction is not sufficient, which reduces the conversion rate of reactants. Figure 8 (b) further reveals the reaction characteristics under different flow rates. In the low flow area, the generation rate of NH3 (R NH3 ) is relatively low, but the conversion efficiency of raw gas (η NO2 and η H2 ) is high, indicating that the catalyst is more efficient in utilizing reactants under this condition. In the high flow area, although the by-products increase, the generation rate of NH3 significantly increases, indicating that increasing the gas flow can effectively improve the yield of ammonia synthesis. In summary, the experimental results show that the catalyst has higher raw material utilization rate at low flow, while high flow is more conducive to improving the yield of ammonia synthesis.

[0048] Example 5 Example 5 is to explore the performance of ammonia synthesis of large block bifunctional catalyst under the change of different total gas flow, the bifunctional catalyst is treated by 66% pickling concentration, C NO2 (s) =20000 ppm, V NO2(s) :V H2 =4:1, catalyst size of 100 mm / 160 g. The results are shown in Figure 9 As can be seen from Figure 9 (a), in the low gas flow range (1-5 L / min), it can be found that the NH3 concentration is basically stable near a fixed concentration, while in the gas flow range greater than 5 L / min, the NH3 concentration gradually decreases, and NO2 gas appears at the tail gas end, indicating that 5 L / min is the best reaction gas flow of the catalyst. In addition, from Figure 9(b) It is known that the ammonia synthesis rate increases with increasing gas flow, and the rate increases faster at low gas flow. At high gas flow, the rate tends to level off, reaching about 2916 μmol / min at 10 L / min.

[0049] Example 6 Example 6 is to investigate the performance of the bulk dual-function catalyst in the synthesis of ammonia at different NO2 / H2 volume ratios. The dual-function catalyst was treated with 66% acid concentration, C NO2 (s) = 20000 ppm, Q = 1 L / min, catalyst size 100 mm / 160 g. The results are shown in Figure 10 Figure 10 (a) It is known that in the low H2 content region, there is an optimal ammonia synthesis efficiency point at V NO2 / V H2 = 7:1. In the high H2 region, the excess of H2 causes the NH3 concentration and yield to decrease. It is worth noting that the catalyst exhibits optimal performance at a volume ratio of 7:1, with the NH3 yield reaching a peak. This phenomenon is significantly different from that of the shorter catalyst, indicating that the 100 mm length of the catalyst changes the overall adsorption characteristics and reactant capture capacity, allowing effective utilization of reactants even at a higher NO2 proportion.

[0050] Figure 10 (b) Further indicates that at the optimal ratio of 7:1, the utilization of hydrogen (η H2 ) also reaches a high level, about 18%. This indicates that not only is the NH3 yield optimal, but the utilization of raw materials is also the most economical. This "double optimization" characteristic is due to the unique surface adsorption kinetics of the bulk catalyst: the longer reaction channel increases the gas residence time, allowing NO2 and H2 to fully contact and react on the catalyst surface, thereby maintaining high efficiency conversion within a wide range of raw material ratios.

[0051] ​In summary, increasing the acid concentration at a low hydrogen ratio can effectively improve the catalytic performance. Compared with 33.3%, the ammonia synthesis yield of the catalyst treated with 50% acid concentration increased by 11.3%, and the ammonia synthesis yield of the catalyst treated with 66.6% acid concentration increased by 25.5%. The ammonia synthesis yield increased with the increase of heating temperature and tended to be stable at 700°C. In addition, the ammonia synthesis yield increased with the increase of gas flow, especially under low gas flow conditions, the yield increased faster; under high gas flow, the growth trend tended to be flat. When the gas flow was 10 L / min, the yield of the 8 mm catalyst was about 1200 μmol / min, and the yield of the 100 mm catalyst was about 2916 μmol / min. Although the large size catalyst was superior in absolute yield, from the perspective of reagent use efficiency per unit mass, the 8 mm catalyst showed higher catalytic efficiency. The optimal hydrogen ratio was related to the size of the catalyst, in which the 8 mm catalyst had higher yield at V NO2(S) :V H2 =4:1, while the 100 mm catalyst performed better at V NO2(S) :V H2 =7:1.

[0052] Example 7 Example 7 provides a system for plasma-coupled thermal catalytic synthesis of ammonia, which adopts the method described above to synthesize ammonia; the system comprises: a plasma unit for exciting nitrogen and oxygen in air to generate nitrogen oxides, and an outlet of the plasma unit delivers a nitrogen oxide-containing gas stream to a downstream catalytic ammonia synthesis unit; a raw material supply unit connected to the plasma unit and the catalytic ammonia synthesis unit respectively, for delivering air to the plasma unit and delivering hydrogen reduction gas to the catalytic ammonia synthesis unit; a catalytic ammonia synthesis unit filled with a bifunctional catalyst, the catalytic ammonia synthesis unit is configured to receive the nitrogen oxide source gas and the hydrogen reduction gas formed by purification from the upstream to undergo a thermal catalytic reduction reaction on the bifunctional catalyst to generate an ammonia gas mixture; an ammonia gas collection unit connected to the catalytic ammonia synthesis unit, the ammonia gas collection unit is configured to receive the ammonia gas mixture delivered by the outlet of the catalytic ammonia synthesis unit to liquefy and separate liquid ammonia and a mixed gas containing hydrogen and nitrogen oxides.

[0053] The present embodiment provides a system for plasma-coupled thermal catalytic synthesis of ammonia, as shown in Figure 11 the system mainly comprises the following units: a raw material supply unit: this unit is composed of an air compressor or a high-pressure air cylinder and a high-purity hydrogen cylinder. Air is connected to the inlet of the plasma unit through a pipeline, and its flow rate is accurately controlled by a mass flow controller (MFC). Hydrogen is connected to the inlet of the catalytic ammonia synthesis unit through a pressure reducing valve and another mass flow controller.

[0054] Plasma unit: a dielectric barrier discharge (DBD) reactor is used. The reactor is composed of two coaxial quartz tubes, the outer wall of the inner tube and the inner wall of the outer tube serve as the high-voltage electrode and the ground electrode, respectively. A high-frequency high-voltage AC power supply is used to power the electrodes. When the air-carrying raw gas flows through the annular space between the two quartz tubes, the gas is excited to generate plasma, and the nitrogen and oxygen in the air react to generate a mixed gas stream containing NO and NO2.

[0055] Catalytic ammonia synthesis unit: the main body of this unit is a tubular fixed-bed reactor, the reaction tube is made of quartz or stainless steel, and the outside is heated by a programmable tubular heating furnace. The inside of the reaction tube is filled with the bifunctional catalyst prepared in Example 1. The nitrogen oxide source gas from the upstream (in this basic system, the gas after the basic purification of the plasma unit outlet gas) and the hydrogen gas from the raw material supply unit are mixed before entering the inlet of the reactor, and then enter the heated zone filled with the catalyst together, and the catalytic reduction reaction occurs at a predetermined temperature to generate a mixed gas containing ammonia, unreacted hydrogen, nitrogen, and byproduct water.

[0056] Ammonia collection unit: ammonia is collected by a cold trap method. The ammonia gas mixture from the outlet of the catalytic ammonia synthesis unit first passes through a U-shaped tube or a condenser bottle, which is placed in a low-temperature environment composed of a dewar flask and a refrigerant (such as a dry ice-ethanol mixture or a low-temperature cooling cycle machine) to maintain a temperature of -50°C to -33°C. At this low temperature, ammonia (boiling point -33.34°C) is liquefied and collected at the bottom of the device, while hydrogen, nitrogen, and other gases with very low boiling points remain gaseous and are discharged from the outlet.

[0057] In some embodiments, the system further comprises a NO oxidation unit and an oxygen separation unit connected in sequence between the plasma unit and the catalytic ammonia synthesis unit, the inlet of the NO oxidation unit is connected with the outlet of the plasma unit for receiving the nitrogen oxide-containing gas stream and oxidizing NO to NO2; the outlet of the oxygen separation unit is connected with the inlet of the catalytic ammonia synthesis unit for separating oxygen and forming a nitrogen oxide source gas.

[0058] Between the plasma unit and the catalytic ammonia synthesis unit, a NO oxidation unit and an oxygen separation unit are added. The NOx-containing gas stream from the outlet of the plasma unit first enters the NO oxidation unit. This unit can be a gas mixing chamber in which ozone generated by an ozone generator is introduced. As a strong oxidizing agent, ozone can quickly oxidize NO with relatively low activity in the gas stream to NO2.

[0059] The oxidized gas stream (mainly containing NO2, O2, N2) then enters the oxygen separation unit. This unit uses low-temperature condensation separation method. The temperature of the gas stream is reduced to between -10°C and 20°C by a refrigeration compressor or cooling coil. At this temperature, NO2 is condensed into liquid, while oxygen and nitrogen remain as gas, thus achieving separation. The non-condensed gas is discharged from the system.

[0060] The collected liquid NO2 is accurately metered by a micro pump and re-gasified by a small heating evaporator to form a high-purity nitrogen oxide source gas, which is finally delivered to the catalytic ammonia synthesis unit.

[0061] In some embodiments, the system further comprises a hydrogen recovery unit, the inlet of the hydrogen recovery unit is connected with the outlet of the ammonia collection unit, and the outlet of the hydrogen recovery unit is connected with the NO oxidation unit, for recovering and drying hydrogen and delivering the remaining gas to the NO oxidation unit to form a circulation loop.

[0062] The present embodiment further increases the hydrogen recovery function on the basis of the above-mentioned embodiments, forming a more efficient closed-loop system.

[0063] The hydrogen recovery unit is arranged downstream of the ammonia collection unit. The tail gas (mainly containing unreacted H2 and N2) discharged from the ammonia collection unit (cold trap) and not liquefied first passes through a drying tube filled with molecular sieve or silica gel to remove the trace amount of water that may be entrained therein. The dried gas is pressurized by a diaphragm pump or circulating fan and then re-delivered to the inlet of the NO oxidation unit through a pipeline, mixed with the newly generated NOx-containing gas stream from the plasma unit, and participates in the reaction again as carrier gas or supplementary gas, thus forming a circulation loop, significantly improving the total utilization rate of hydrogen and reducing emissions.

[0064] In some embodiments, the system further comprises a process control module, the process control module further comprises a gas flow regulation unit and a temperature control unit, the gas flow regulation unit is connected with the raw material supply unit, for regulating the preset volume ratio of the nitrogen oxide source gas to the hydrogen reduction gas and the preset total volume flow rate; the temperature control unit is connected with the catalytic ammonia synthesis unit, for controlling and maintaining the preset temperature of the thermal catalytic reduction of the catalytic ammonia synthesis unit.

[0065] The present embodiment configures the process control module for any of the above-mentioned systems to realize automatic and precise operation.

[0066] The implementation of the gas flow regulation unit: high-precision mass flow controllers are installed on the supply lines of air and hydrogen, respectively. They are connected to a central computer or programmable logic controller through data lines. The operator can accurately set and monitor the gas flow entering each reaction unit in real time through the host computer software interface, so as to ensure that the nitrogen oxide source gas and hydrogen reduction gas maintain the best volume ratio (such as 4:1 or 7:1) and the best total volume flow (such as 5 L / min) obtained through experiments.

[0067] The temperature control unit: a thermocouple is installed at the center of the catalyst bed or on the outer wall of the catalytic ammonia synthesis unit (fixed bed reactor). The thermocouple is connected to the proportional-integral-derivative temperature controller that comes with the tubular heating furnace. The operator sets the target thermal catalytic reduction temperature (such as 500℃) on the controller, which will automatically adjust the output power of the heating furnace according to the real-time feedback value of the thermocouple, ensuring that the catalyst bed temperature remains constant at the set value throughout the reaction process, with a temperature control accuracy of ±1℃.

[0068] In some embodiments, the catalytic ammonia synthesis unit is a fixed bed reactor, and the bifunctional catalyst inside is packed in the form of a static bed.

[0069] The catalytic ammonia synthesis unit uses a fixed bed reactor. The reactor body is a quartz glass tube with an inner diameter of 20 mm and a length of 600 mm. In the center of the quartz tube, spherical or strip-shaped bifunctional catalyst particles prepared according to Example 1 are packed to form a static catalyst bed with a length of 100 mm. At both ends of the bed, quartz wool is used for packing and fixing to prevent gas from blowing the catalyst particles. The entire quartz tube is placed horizontally in the constant temperature zone of the tubular heating furnace. The reaction gas enters from one end, passes through the static catalyst bed, and flows out from the other end after reaction. This structure is simple, has low fluid resistance, is easy to pack and replace catalysts, and is very suitable for the synthesis of ammonia in this application.

[0070] Other different forms of changes or variations can be made by those of ordinary skill in the art based on the above description. Here, it is not necessary or possible to exhaust all embodiments, and the obvious changes or variations derived therefrom are still within the protection scope of the claims of the present application.

Claims

1. A method of plasma-coupled thermal catalytic synthesis of ammonia, characterized in that, The method comprises the following steps: converting a raw gas containing nitrogen and oxygen into a gas stream containing nitrogen oxides by using plasma, and forming a nitrogen oxide source gas after purification; contacting the nitrogen oxide source gas and a hydrogen reduction gas with a dual-function catalyst treated by pickling to perform a thermal catalytic reduction reaction, and converting the nitrogen oxides to generate ammonia gas; The dual-function catalyst comprises a platinum metal active component and a barium oxide storage component supported on an alumina carrier.

2. The method of claim 1, wherein, In the pickling treatment, the hydrogen ion concentration is 4-8 mol / L.

3. The method of claim 2, wherein, In the thermal catalytic reduction reaction, the thermal catalytic reduction temperature is 100-700℃, the volume ratio of the nitrogen oxide source gas to the hydrogen reduction gas is 1-10:1, and the total volume flow rate of the nitrogen oxide source gas and the hydrogen reduction gas is 1-10 L / min.

4. The method of claim 3, wherein, In the thermal catalytic reduction reaction, the thermal catalytic reduction temperature is 300-700℃, the volume ratio of the nitrogen oxide source gas to the hydrogen reduction gas is 3-10:1, and the total volume flow rate of the nitrogen oxide source gas and the hydrogen reduction gas is 5-10 L / min.

5. The method of claim 4, wherein, In the thermal catalytic reduction reaction, the thermal catalytic reduction temperature is 500℃, the volume ratio of the nitrogen oxide source gas to the hydrogen reduction gas is 7:1, and the total volume flow rate of the nitrogen oxide source gas and the hydrogen reduction gas is 5 L / min.

6. A system for the synthesis of ammonia by plasma coupled thermal catalysis, characterized in that, The system comprises: a plasma unit for exciting nitrogen and oxygen in air to generate nitrogen oxides, and an outlet of the plasma unit delivering a gas stream containing nitrogen oxides to a downstream catalytic ammonia synthesis unit; a raw material supply unit connected to the plasma unit and the catalytic ammonia synthesis unit respectively, for delivering air to the plasma unit and delivering a hydrogen reduction gas to the catalytic ammonia synthesis unit; a catalytic ammonia synthesis unit filled with the dual-function catalyst, configured to receive the nitrogen oxide source gas and the hydrogen reduction gas from upstream to perform a thermal catalytic reduction reaction on the dual-function catalyst to generate an ammonia gas mixture; an ammonia gas collection unit connected to the catalytic ammonia synthesis unit, configured to receive the ammonia gas mixture delivered from the outlet of the catalytic ammonia synthesis unit, and to liquefy and separate liquid ammonia and a mixed gas containing hydrogen and nitrogen oxides.

7. The system of claim 6, wherein, The system further comprises a NO oxidation unit and an oxygen separation unit connected in sequence and arranged between the plasma unit and the catalytic ammonia synthesis unit, an inlet of the NO oxidation unit connected to an outlet of the plasma unit for receiving the gas stream containing nitrogen oxides and oxidizing NO to NO2, and an outlet of the oxygen separation unit connected to an inlet of the catalytic ammonia synthesis unit for separating oxygen and forming the nitrogen oxide source gas.

8. The system of claim 7, wherein, The system further comprises a hydrogen recovery unit, an inlet of the hydrogen recovery unit connected to an outlet of the ammonia gas collection unit, and an outlet of the hydrogen recovery unit connected to the NO oxidation unit for recovering and drying hydrogen and delivering the remaining gas to the NO oxidation unit to form a circulation loop.

9. The system of claim 8, wherein, The system further comprises a process control module, which further comprises a gas flow regulating unit and a temperature control unit, the gas flow regulating unit is connected with the raw material supply unit, for regulating the preset volume ratio of the nitrogen oxide source gas and the hydrogen reducing gas and the preset total volume flow rate; The temperature control unit is connected with the catalytic ammonia synthesis unit, for controlling and maintaining the preset temperature of the thermal catalytic reduction of the catalytic ammonia synthesis unit.

10. The system of claim 6, wherein, The catalytic ammonia synthesis unit is a fixed bed reactor, and the bifunctional catalyst in the interior of the fixed bed reactor is filled in the form of a static bed.

Images