A method for catalytically converting methane and nitrogen by plasma to co-produce ammonia, amine compounds and hydrogen

Abstract

The present invention provides a method for co-producing ammonia, amine compounds and hydrogen by plasma catalytic conversion of methane and nitrogen, which involves the activation of nitrogen and methane molecules. Specifically, this method is to apply an alternating current in a mixed gas of methane and nitrogen under the condition of filling a catalytic material to excite a low-temperature plasma, so as to realize the method for co-producing ammonia, amine compounds and hydrogen by the conversion of methane and nitrogen. This method directly utilizes the synergistic effect of the low-temperature plasma and the catalytic material at near room temperature and atmospheric pressure to achieve the efficient activation and directional conversion of nitrogen and methane. In a fixed-bed plasma reactor, the single-pass conversion rate of nitrogen is as high as 3.5%, the conversion rate of methane is 50%, the selectivity of ammonia is 84%, and the total selectivity of methylamine and ethylamine is as high as 16%. The advantages of the present invention are that the preparation process of the catalyst adopted is simple and controllable, the reaction equipment is simple and easy to be scaled up industrially, and the co-production of hydrogen, ammonia and amine compounds is directly realized by using methane and nitrogen under the conditions of atmospheric pressure and near room temperature.

Description

Technical Field

[0001] The present invention relates to the activation and conversion of nitrogen and methane, in particular to a method for the conversion of methane and nitrogen to co-produce hydrogen, ammonia and amine compounds by using a catalyst under low-temperature plasma. Background Art

[0002] Artificial nitrogen fixation is the process of converting elemental nitrogen into compounds under artificial conditions. Ammonia, as the main nitrogen fixation product, is an important raw material for synthesizing many biochemical products such as fertilizers, resins, explosives and drugs. Industrially, ammonia is synthesized through the Haber-Bosch (HB) process, which consumes huge amounts of energy, accounting for about 2% of the global primary energy supply, and has serious carbon emissions. At the same time, the synthesis of ammonia requires the consumption of hydrogen, and hydrogen is usually obtained through steam reforming of methane, with high energy consumption and high carbon emissions. Ammonia is only an important intermediate product for the subsequent synthesis of amine compounds. Therefore, it is of great significance to directly co-produce hydrogen, ammonia and amine compounds from methane and nitrogen under mild conditions. However, nitrogen and methane, especially nitrogen, are one of the two most inert gas molecules in nature due to their small polarity and high symmetry. Therefore, it is very difficult to achieve the catalytic conversion of nitrogen and methane under mild conditions. Low-temperature plasma, such as dielectric barrier discharge, is a good means to activate nitrogen and methane under mild conditions due to its unique non-equilibrium characteristics (electron temperature is much higher than the gas temperature).

[0003] Some recent studies have reported the activation of nitrogen and methane in low-temperature plasma, but the products are mostly hydrocarbon species, with only a very small amount of ammonia and hydrogen cyanide generated, and amine products (such as methylamine, ethylamine) cannot be obtained (Chem. Eng. J. 2018, 345, 67 - 78, J. Phys. D: Appl. Phys. 2018, 51, 315201). At the same time, these studies have shown that the conversion of methane under low-temperature plasma is relatively simple, while the conversion of nitrogen is relatively difficult. Therefore, it is crucial to simultaneously achieve nitrogen adsorption dissociation and the formation of N-H or N-C bonds through the plasma-catalytic process in the presence of a catalyst. Summary of the Invention

[0004] The present invention aims to provide a method for the catalytic conversion of methane and nitrogen by low-temperature plasma to co-produce ammonia, amine compounds and hydrogen.

[0005] The specific steps of the present invention are as follows:

[0006] A method for co-producing ammonia, amine compounds and hydrogen by catalytic conversion of methane and nitrogen at low temperature, comprising: using a low-temperature plasma reaction device, filling a catalytic material between a dielectric tube and an inner electrode, introducing a mixed gas of methane and nitrogen, and applying a sinusoidal alternating current between the inner and outer electrodes at the same time to excite low-temperature plasma between the dielectric tube and the inner electrode, so as to realize the co-conversion of methane and nitrogen to co-produce hydrogen, ammonia and amine compounds.

[0007] Further, in the above technical solution, the catalyst includes at least one of metal oxides or supported catalysts.

[0008] Further, in the above technical solution, the metal oxides include at least one of Al2O3, SiO2, CeO2, MgO, TiO2, ZrO2, WO3.

[0009] Further, in the above technical solution, the supported catalyst is a metal supported on at least one of carriers such as metal oxides, carbides, carbon materials, carbon nanotubes, molecular sieves, aerogels.

[0010] Further, in the above technical solution, the metal includes at least one of Pt, Ru, Ir, Pd, Au, Ag, Cu, Fe, Co, Ni.

[0011] Further, in the above technical solution, the material of the dielectric tube includes at least one of polytetrafluoroethylene (PTFE), fluorinated propylene (FEP), ethylene chlorotrifluoroethylene (ECTE), ethylene tetrafluoroethylene (ETFE), soluble polytetrafluoroethylene (PFA), quartz, glass, ceramics.

[0012] Further, in the above technical solution, an outer electrode surrounds the outside of the dielectric tube, and the materials of the inner electrode and the outer electrode can be the same or different, including at least one of Al, Cu, and stainless steel.

[0013] Further, in the above technical solution, the volume ratio of nitrogen in the mixed gas of methane and nitrogen is 10%-80%, and the balance is methane.

[0014] Further, in the above technical solution, the low-temperature plasma conditions are: frequency 5-60 kHz, power 10-200 W.

[0015] Further, in the above technical solution, the conditions for the co-production of hydrogen, ammonia and amine compounds by the conversion of methane and nitrogen are: pressure 0.5-2 atm, time 0.5-8 h, reaction gas flow rate 10-200 mL / min, catalyst bed volume 2-20 cm 3 , reaction temperature 25-100 °C; preferably, the reaction temperature is 25-80 °C and the pressure is 1 atm.

[0016] Application of the above method in co-producing hydrogen, ammonia and amine compounds by converting methane and nitrogen

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] (1) The present invention shows excellent catalytic performance for nitrogen and methane conversion under mild conditions. Under near-room temperature and atmospheric pressure (1 atm) reaction conditions, the single-pass conversion rate of nitrogen is as high as 3.5%, the conversion rate of methane is 50%, among which the selectivity of ammonia is as high as 84%, and the selectivity of methylamine and ethylamine is 16%.

[0019] (2) The catalyst used is a metal oxide or a supported catalyst. The reaction occurs in the gas-solid phase. The plasma atmosphere passes through the catalyst bed, increasing the contact probability between the reactants and the catalyst and improving the catalytic activity of the catalyst.

[0020] (3) Due to the presence of low-temperature plasma, the electron temperature in the system is extremely high (5000 K), while the atmosphere temperature is near room temperature (about 60 °C), which promotes the activation of methane and nitrogen.

[0021] (4) The preparation process of the catalyst used is simple and controllable. At the same time, the equipment is simple and easy to scale up industrially.

[0022] In summary, by using the method and catalyst for directly converting methane and nitrogen by low-temperature plasma to co-produce hydrogen, ammonia and amine compounds provided by the present invention, high plasma catalytic conversion activity of methane and nitrogen can be obtained under near-room temperature and atmospheric pressure, and the catalyst has good catalytic stability and has good industrial application prospects. Detailed implementation mode

[0023] The method and catalyst for directly catalytically converting methane and nitrogen by low-temperature plasma to co-produce hydrogen, ammonia and amine compounds provided by the present invention are further described in detail below, but the present invention is not limited thereby.

[0024] Example 1

[0025] Weigh 3 g of the foam Ni-based catalyst and place it between the quartz reaction tube and the inner high-voltage Al electrode. The outer of the quartz tube is surrounded by a stainless-steel ground electrode. Through the gas pipeline, a methane-nitrogen mixed gas is introduced into the reaction system. The molar ratio of methane / nitrogen is 1:1, the total flow rate is 22 mL / min, the pressure is 1 atm, and the temperature is 25 °C. Before the reaction, the reactor is purged with the methane-nitrogen mixed gas for 15 min, and then the inner and outer electrodes are connected to the plasma generator. Adjust the output signal of the plasma generator to 10 kHz and 38 W, and react for 1 h to conduct the experiment on co-producing hydrogen, ammonia and amine compounds by plasma catalytic conversion of methane and nitrogen. The specific reaction performance is listed in Table 1.

[0026] Example 2

[0027] Weigh 3 g of SiO2 aerogel catalyst and place it between the quartz reaction tube and the inner high-voltage Al electrode. The quartz tube is surrounded by a stainless-steel ground electrode outside. Pass a methane-nitrogen mixture into the reaction system through a gas pipeline. The molar ratio of methane to nitrogen is 1:1, the total flow rate is 22 mL / min, the pressure is 1 atm, and the temperature is 25 °C. Before the reaction, use the methane-nitrogen mixture to displace the reactor for 15 min. Then connect the inner and outer electrodes to the plasma generator, adjust the output signal of the plasma generator to 10 kHz and 38 W, and react for 1 h to conduct an experiment on the plasma catalytic conversion of methane and nitrogen to co-produce hydrogen, ammonia, and amine compounds. The specific reaction performance is listed in Table 1.

[0028] Example 3

[0029] Weigh 3 g of SiO2-Al2O3 aerogel catalyst and place it between the quartz reaction tube and the inner high-voltage Al electrode. The quartz tube is surrounded by a stainless-steel ground electrode outside. Pass a methane-nitrogen mixture into the reaction system through a gas pipeline. The molar ratio of methane to nitrogen is 1:1, the total flow rate is 22 mL / min, the pressure is 1 atm, and the temperature is 25 °C. Before the reaction, use the methane-nitrogen mixture to displace the reactor for 15 min. Then connect the inner and outer electrodes to the plasma generator, adjust the output signal of the plasma generator to 10 kHz and 38 W, and react for 1 h to conduct an experiment on the plasma catalytic conversion of methane and nitrogen to co-produce hydrogen, ammonia, and amine compounds. The specific reaction performance is listed in Table 1.

[0030] Example 4

[0031] Weigh 3 g of Fe / SiO2-Al2O3 aerogel catalyst and place it between the quartz reaction tube and the inner high-voltage Al electrode. The quartz tube is surrounded by a stainless-steel ground electrode outside. Pass a methane-nitrogen mixture into the reaction system through a gas pipeline. The molar ratio of methane to nitrogen is 1:1, the total flow rate is 22 mL / min, the pressure is 1 atm, and the temperature is 25 °C. Before the reaction, use the methane-nitrogen mixture to displace the reactor for 15 min. Then connect the inner and outer electrodes to the plasma generator, adjust the output signal of the plasma generator to 10 kHz and 38 W, and react for 1 h to conduct an experiment on the plasma catalytic conversion of methane and nitrogen to co-produce hydrogen, ammonia, and amine compounds. The specific reaction performance is listed in Table 1.

[0032] Example 5

[0033] Weigh 3 g of Co / SiO2-Al2O3 aerogel catalyst and place it between the quartz reaction tube and the inner high-voltage Al electrode. A stainless-steel ground electrode is wound around the outside of the quartz tube. Pass a methane-nitrogen mixed gas into the reaction system through the gas pipeline. The molar ratio of methane to nitrogen is 1:1, the total flow rate is 22 mL / min, the pressure is 1 atm, and the temperature is 25 °C. Before the reaction, use the methane-nitrogen mixed gas to displace the reactor for 15 min. Then connect the inner and outer electrodes to the plasma generator, adjust the output signal of the plasma generator to 10 kHz and 38 W, and react for 1 h to conduct an experiment on the plasma-catalytic conversion of methane and nitrogen to co-produce hydrogen, ammonia, and amine compounds. The specific reaction performance is listed in Table 1.

[0034] Example 6

[0035] Weigh 3 g of Ni / SiO2-Al2O3 aerogel catalyst and place it between the quartz reaction tube and the inner high-voltage Al electrode. A stainless-steel ground electrode is wound around the outside of the quartz tube. Pass a methane-nitrogen mixed gas into the reaction system through the gas pipeline. The molar ratio of methane to nitrogen is 1:1, the total flow rate is 22 mL / min, the pressure is 1 atm, and the temperature is 25 °C. Before the reaction, use the methane-nitrogen mixed gas to displace the reactor for 15 min. Then connect the inner and outer electrodes to the plasma generator, adjust the output signal of the plasma generator to 10 kHz and 38 W, and react for 1 h to conduct an experiment on the plasma-catalytic conversion of methane and nitrogen to co-produce hydrogen, ammonia, and amine compounds. The specific reaction performance is listed in Table 1.

[0036] Example 7

[0037] Weigh 3 g of Cu / SiO2-Al2O3 aerogel catalyst and place it between the quartz reaction tube and the inner high-voltage Al electrode. A stainless-steel ground electrode is wound around the outside of the quartz tube. Pass a methane-nitrogen mixed gas into the reaction system through the gas pipeline. The molar ratio of methane to nitrogen is 1:1, the total flow rate is 22 mL / min, the pressure is 1 atm, and the temperature is 25 °C. Before the reaction, use the methane-nitrogen mixed gas to displace the reactor for 15 min. Then connect the inner and outer electrodes to the plasma generator, adjust the output signal of the plasma generator to 10 kHz and 38 W, and react for 1 h to conduct an experiment on the plasma-catalytic conversion of methane and nitrogen to co-produce hydrogen, ammonia, and amine compounds. The specific reaction performance is listed in Table 1.

[0038] Example 8

[0039] Weigh 3 g of Ni / SiO2 aerogel catalyst and place it between the quartz reaction tube and the inner high-voltage Al electrode. The quartz tube is surrounded by a stainless-steel ground electrode. Pass a methane-nitrogen mixed gas into the reaction system through a gas pipeline. The molar ratio of methane to nitrogen is 1:1, the total flow rate is 22 mL / min, the pressure is 1 atm, and the temperature is 25 °C. Before the reaction, use the methane-nitrogen mixed gas to displace the reactor for 15 min. Then connect the inner and outer electrodes to the plasma generator, adjust the output signal of the plasma generator to 10 kHz and 38 W, and react for 1 h to conduct an experiment on the plasma-catalytic conversion of methane and nitrogen to co-produce hydrogen, ammonia, and amine compounds. The specific reaction performance is listed in Table 1.

[0040] Example 9

[0041] Weigh 3 g of Ni / Al2O3 catalyst and place it between the quartz reaction tube and the inner high-voltage Al electrode. The quartz tube is surrounded by a stainless-steel ground electrode. Pass a methane-nitrogen mixed gas into the reaction system through a gas pipeline. The molar ratio of methane to nitrogen is 1:1, the total flow rate is 22 mL / min, the pressure is 1 atm, and the temperature is 25 °C. Before the reaction, use the methane-nitrogen mixed gas to displace the reactor for 15 min. Then connect the inner and outer electrodes to the plasma generator, adjust the output signal of the plasma generator to 10 kHz and 38 W, and react for 1 h to conduct an experiment on the plasma-catalytic conversion of methane and nitrogen to co-produce hydrogen, ammonia, and amine compounds. The specific reaction performance is listed in Table 1.

[0042] Example 10

[0043] Weigh 3 g of Ni / HZSM-5 catalyst and place it between the quartz reaction tube and the inner high-voltage Al electrode. The quartz tube is surrounded by a stainless-steel ground electrode. Pass a methane-nitrogen mixed gas into the reaction system through a gas pipeline. The molar ratio of methane to nitrogen is 1:1, the total flow rate is 22 mL / min, the pressure is 1 atm, and the temperature is 25 °C. Before the reaction, use the methane-nitrogen mixed gas to displace the reactor for 15 min. Then connect the inner and outer electrodes to the plasma generator, adjust the output signal of the plasma generator to 10 kHz and 38 W, and react for 1 h to conduct an experiment on the plasma-catalytic conversion of methane and nitrogen to produce hydrogen, ammonia, and amine compounds. The specific reaction performance is listed in Table 1.

[0044] Example 11

[0045] Weigh 3 g of Ni / CeO2 catalyst and place it between the quartz reaction tube and the inner high-voltage Al electrode. A stainless-steel ground electrode is wound around the outside of the quartz tube. Pass a methane-nitrogen mixed gas into the reaction system through the gas pipeline. The molar ratio of methane to nitrogen is 1:1, the total flow rate is 22 mL / min, the pressure is 1 atm, and the temperature is 25 °C. Before the reaction, use the methane-nitrogen mixed gas to displace the reactor for 15 min. Then connect the inner and outer electrodes to the plasma generator, adjust the output signal of the plasma generator to 10 kHz and 38 W, and react for 1 h to conduct an experiment on the plasma-catalytic conversion of methane and nitrogen to prepare hydrogen, ammonia, and amine compounds. The specific reaction performance is listed in Table 1.

[0046] Example 12

[0047] Weigh 3 g of Ni / SiO2-Al2O3 aerogel catalyst and place it between the quartz reaction tube and the inner high-voltage Al electrode. A stainless-steel ground electrode is wound around the outside of the quartz tube. Pass a methane-nitrogen mixed gas into the reaction system through the gas pipeline. The molar ratio of methane to nitrogen is 1:1, the total flow rate is 66 mL / min, the pressure is 1 atm, and the temperature is 25 °C. Before the reaction, use the methane-nitrogen mixed gas to displace the reactor for 15 min. Then connect the inner and outer electrodes to the plasma generator, adjust the output signal of the plasma generator to 10 kHz and 38 W, and react for 1 h to conduct an experiment on the plasma-catalytic conversion of methane and nitrogen to prepare hydrogen, ammonia, and amine compounds. The specific reaction performance is listed in Table 1.

[0048] Example 13

[0049] Weigh 3 g of Ni / SiO2-Al2O3 aerogel catalyst and place it between the quartz reaction tube and the inner high-voltage stainless-steel electrode. A stainless-steel ground electrode is wound around the outside of the quartz tube. Pass a methane-nitrogen mixed gas into the reaction system through the gas pipeline. The molar ratio of methane to nitrogen is 2:1, the total flow rate is 22 mL / min, the pressure is 1 atm, and the temperature is 25 °C. Before the reaction, use the methane-nitrogen mixed gas to displace the reactor for 15 min. Then connect the inner and outer electrodes to the plasma generator, adjust the output signal of the plasma generator to 10 kHz and 38 W, and react for 1 h to conduct an experiment on the plasma-catalytic conversion of methane and nitrogen to prepare hydrogen, ammonia, and amine compounds. The specific reaction performance is listed in Table 1.

[0050] Comparative Example 1

[0051] Weigh 3 g of Ni / SiO2 - Al2O3 aerogel catalyst and place it between the quartz reaction tube and the inner high - pressure stainless - steel electrode. Surround the quartz tube with a stainless - steel ground electrode. Pass a methane - nitrogen mixture into the reaction system through a gas pipeline. The methane / nitrogen molar ratio is 1:1, the total flow rate is 22 mL / min, the pressure is 1 atm, and the temperature is 25 °C. Before the reaction, use the methane - nitrogen mixture to displace the reactor for 15 min, then heat it up to 60 °C and react for 1 h to conduct an experiment on the plasma - catalytic conversion of methane and nitrogen to prepare hydrogen, ammonia, and amine compounds. The specific reaction performance is listed in Table 1.

[0052] Comparative Example 2

[0053] Surround the quartz tube with a stainless - steel ground electrode. Pass a methane - nitrogen mixture into the reaction system through a gas pipeline. The methane / nitrogen molar ratio is 1:1, the total flow rate is 22 mL / min, the pressure is 1 atm, and the temperature is 25 °C. Before the reaction, use the methane - nitrogen mixture to displace the reactor for 15 min, then connect the inner and outer electrodes to the plasma generator, adjust the output signal of the plasma generator to 10 kHz, 38 W, and react for 1 h to conduct an experiment on the plasma - catalytic conversion of methane and nitrogen to prepare hydrogen, ammonia, and amine compounds. The specific reaction performance is listed in Table 1.

[0054] Table 1

[0055]

[0056]

Claims

1. A method for co-producing ammonia, amine compounds and hydrogen by plasma catalytic conversion of methane and nitrogen, characterized in that: By using a low-temperature plasma reaction device, under the condition that a catalytic material is filled between the dielectric tube and the inner electrode, a mixed gas of methane and nitrogen is introduced and a sinusoidal alternating current is applied, and a low-temperature plasma is excited between the dielectric tube and the inner electrode to realize the co-conversion of methane and nitrogen to co-produce hydrogen, ammonia and amine compounds; The catalytic material is selected from metal oxides or Ni-supported metal oxides; The metal oxides are Al2O3 and SiO2; An outer electrode is surrounded outside the dielectric tube, and the materials of the inner electrode and the outer electrode are the same or different, and are selected from at least one of Al, Cu, and stainless steel; The conditions for low-temperature plasma are: frequency 5 - 60 kHz, power 10 - 200 W; the conditions for the co-conversion of methane and nitrogen to produce hydrogen, ammonia and amine compounds are: pressure 0.5 - 2 atm, time 0.5 - 8 h, reaction gas flow rate 10 - 200 mL / min, catalytic material bed volume 2 - 20 cm 3 , reaction temperature 25 - 100 °C; The volume ratio of nitrogen in the mixed gas of methane and nitrogen is 10%-80%, and the balance is methane.

2. The method according to claim 1, wherein: The material of the dielectric tube is selected from at least one of polytetrafluoroethylene, fluorinated propylene, ethylene trifluorochloroethylene, ethylene tetrafluoroethylene, quartz, glass, and ceramics.

3. Use of the method according to claim 1 in the conversion of methane and nitrogen to co-produce hydrogen, ammonia and amine compounds.

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