Application of a supported molybdenum-based nitrogen carrier in a chemical looping ammonia synthesis reaction

Abstract

The application belongs to the technical field of ammonia synthesis technology, and specifically discloses application of a supported molybdenum-based nitrogen carrier in a chemical looping ammonia synthesis reaction. The supported molybdenum-based nitrogen carrier is added to a fixed bed reactor, and then hydrogen and a nitrogen-hydrogen mixed gas are alternately introduced to perform the chemical looping ammonia synthesis reaction. The preparation steps of the supported molybdenum-based nitrogen carrier include: mixing methene tetraamine, a molybdate, ammonia water and ZSM-5 molecular sieves, and then performing suction filtration to obtain white precipitates; the white precipitates are dried and ground to obtain a supported precursor; and the supported precursor is pyrolyzed under a protective atmosphere, and then cooled to obtain the supported molybdenum-based nitrogen carrier suitable for the chemical looping ammonia synthesis. The supported molybdenum-based nitrogen carrier prepared by the application is suitable for the chemical looping ammonia synthesis, and has the characteristics of low required temperature for nitrogen fixation-nitrogen release reaction, high utilization rate of lattice nitrogen, good cycle stability and high ammonia production rate.

Description

[0001] The application is a divisional application, the parent application's application number is 202210348758.9, the application date is April 1, 2022, and the invention name is "a supported molybdenum-based nitrogen carrier for chemical looping synthesis of ammonia and a preparation method thereof". TECHNICAL FIELD

[0002] The application relates to the technical field of ammonia synthesis, and particularly relates to application of a supported molybdenum-based nitrogen carrier in a chemical looping synthesis of ammonia reaction. BACKGROUND

[0003] Ammonia can not only be used as a raw material for chemical fertilizers, but also as a good energy carrier. In view of the problems of the traditional H-B process, such as harsh operating conditions, large CO2 emission, and a balance conversion rate of only 15-20%, it is particularly urgent to find a method for synthesizing ammonia under mild conditions. Chemical looping synthesis of ammonia, as a new and environmentally friendly low-pressure ammonia synthesis technology, is favored by researchers. It refers to decoupling the synthesis of ammonia into multiple steps, and completing the chemical looping cycle through the consumption and regeneration of the nitrogen carrier. As the key to chemical looping synthesis of ammonia, the nitrogen carrier plays a role in transferring nitrogen species and energy during the cycle. According to the bonding mode of the nitrogen carrier, the nitrogen carrier can be divided into: ionic nitrogen carrier, covalent nitrogen carrier and transition metal nitrogen carrier.

[0004] The ionic nitrogen carrier has the characteristics of easy preparation, such as Li and Mg, which are well known. Li can generate the corresponding nitride at normal pressure and temperature. Although it is easy to prepare, it is difficult to regenerate in the subsequent steps, and needs to be regenerated through thermal-electric coupling.

[0005] The preparation process of the covalent nitrogen carrier such as AlN requires a carbon reducing agent to regenerate it. The temperature is as high as 1700℃, and the high temperature will cause the nitrogen carrier to form sintering, which is not conducive to gas-solid contact and affects the yield of ammonia. Therefore, some people have made some improvements, such as adding a catalyst, changing the carbon species, etc. Although some results have been achieved, the high reaction temperature is still a major obstacle to the industrialization of the technology.

[0006] The transition metal nitrogen carrier has a rich and variable valence, and can form corresponding oxides / nitrides. Studies have shown that Mn, Mo, Cr, etc. can be used as nitrogen carriers. However, the preparation of Mn and Cr requires a high temperature of 1000℃ for regeneration, and the nitriding time is long, which is not conducive to practical application. Therefore, it is particularly important to explore a method for preparing a nitrogen carrier under mild conditions.

[0007] At present, there are many patents about the preparation and application of molybdenum nitride, such as CN105719843 discloses a preparation method and application of molybdenum nitride / titanium nitride nanotube array composite material. The patent prepares molybdenum oxide / titanium dioxide nanotube array composite material by anodic oxidation and calcination method, electrochemical deposition method, and then prepares molybdenum nitride / titanium nitride nanotube array composite material by high-temperature nitriding method, and applies the composite material to the electrochemical energy storage of supercapacitor electrode. CN107456988B discloses a supported molybdenum nitride catalyst for guaiacol hydrodeoxygenation reaction. The patent obtains the molybdenum nitride catalyst by pretreating the mesoporous carbon, immersing in ammonium molybdate solution and then high-temperature nitriding. CN105671496B discloses application of molybdenum nitride / titanium boron nitride nanocomposite multilayer coating in mechanical processing industry. The preparation methods of molybdenum nitride involved in the above patents are all high-temperature nitriding methods, which need to combine complex temperature rising procedures and higher temperature to prepare catalysts with excellent performance. CN201810759990 discloses a catalytic nitrogen carrier suitable for chemical chain ammonia synthesis process and a preparation method thereof, and the nitrogen carrier takes titanium oxide as the carrier.

[0008] Therefore, how to provide a low-temperature pyrolysis preparation of supported molybdenum-based nitrogen carrier and a preparation method thereof is a technical problem to be solved by those skilled in the art. SUMMARY

[0009] The purpose of the present application is to provide an application of a supported molybdenum-based nitrogen carrier in a chemical chain ammonia synthesis reaction, so as to solve the defects existing in the prior art.

[0010] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0011] The present application provides an application of a supported molybdenum-based nitrogen carrier in a chemical chain ammonia synthesis reaction, comprising the following steps:

[0012] The supported molybdenum-based nitrogen carrier is added to a fixed bed reactor, and then hydrogen and nitrogen-hydrogen mixed gas are alternately introduced to carry out a chemical chain ammonia synthesis reaction;

[0013] The preparation steps of the supported molybdenum-based nitrogen carrier are as follows:

[0014] (1) The hexamethylenetetramine, molybdate, ammonia water and ZSM-5 molecular sieve are mixed and then suction filtered to obtain white precipitate;

[0015] (2) The white precipitate is sequentially dried and ground to obtain a supported precursor;

[0016] (3) The supported precursor is pyrolyzed under a protective atmosphere to obtain a supported molybdenum-based nitrogen carrier suitable for chemical chain ammonia synthesis;

[0017] The mass ratio of methenamine, molybdate and ammonia is 4-8:4-8:60-100; the mass ratio of the total mass of molybdate and methenamine to the mass of ZSM-5 molecular sieve is 1:1-3, and the mass fraction of the ammonia is 13-17%;

[0018] The particle size of the supported precursor is 200-325 mesh;

[0019] The pyrolysis temperature is 450-550 DEG C, and the pyrolysis time is 2-5 h.

[0020] Preferably, the ratio of the addition amount of the supported molybdenum-based nitrogen carrier to the hydrogen inlet rate and the nitrogen-hydrogen mixed gas inlet rate is 0.1 kg:1 L / min:2 L / min.

[0021] Preferably, the temperature of the chemical looping ammonia synthesis reaction is 400 DEG C.

[0022] Preferably, the volume ratio of nitrogen to hydrogen in the nitrogen-hydrogen mixed gas is 1:1.

[0023] It can be known from the above technical solution that, compared with the prior art, the present application has the following beneficial effects:

[0024] 1. The present application significantly increases more active sites by loading the active components into the molecular sieve through the carrier regulation strategy to improve the ammonia production rate; at the same time, effectively alleviates the sintering problem of the nitrogen carrier, and further improves the cycle effect of the supported nitrogen carrier.

[0025] 2. The present application proposes pyrolysis preparation of molybdenum nitride, i.e. the supported molybdenum-based nitrogen carrier is generated by pyrolysis of the supported precursor under the condition of 400-600 DEG C, compared with the prior art, the temperature is low, the time is short, and the preparation process is simple.

[0026] 3. The nitrogen carrier provided by the present application is cheap and easy to obtain, can be used for ammonia production under mild conditions, and shows good ammonia release performance.

[0027] 4. By adjusting the pyrolysis temperature, the present application can prepare nitrogen carriers with different ammonia production rates, cycle performances and reaction activities to be suitable for different industrial applications.

[0028] 5. The nitrogen carrier prepared by the present application can be passivated by 1% O2 without being damaged, and after industrialization of this technology, it is beneficial to the shutdown and maintenance of the reactor, and after maintenance, only low-temperature activation is needed to restore the activity.

[0029] 6. The supported molybdenum-based nitrogen carrier is applied to the chemical looping ammonia synthesis, can be operated at low temperature and normal pressure, has low required temperature for nitrogen fixation-release reaction, high utilization rate of lattice nitrogen, good cycle stability, high ammonia production rate, does not need thick reaction equipment, greatly reduces the energy consumption, and is beneficial to small-scale distributed ammonia production. DETAILED DESCRIPTION

[0030] The application provides a preparation method of a supported molybdenum-based nitrogen carrier suitable for chemical chain synthesis of ammonia, comprising the following steps:

[0031] (1) mixing hexamethylenetetramine, a molybdate, ammonia water and ZSM-5 molecular sieves, and then performing suction filtration to obtain white precipitate;

[0032] (2) sequentially performing drying and grinding on the white precipitate to obtain a supported precursor;

[0033] (3) performing pyrolysis on the supported precursor in a protective atmosphere to obtain the supported molybdenum-based nitrogen carrier suitable for chemical chain synthesis of ammonia.

[0034] In the application, the mixing in step (1) is ultrasonic mixing of the hexamethylenetetramine, the molybdate and the ammonia water to obtain a mixed solution, and then mixing the mixed solution with the ZSM-5 molecular sieves; the power of the ultrasonic mixing is 90-110 Hz, preferably 95-105 Hz, and the time is 5-30 min, preferably 10-15 min; the time for mixing the mixed solution with the ZSM-5 molecular sieves is 0.5-2 h, preferably 1-1.5 h.

[0035] In the application, the mass ratio of the hexamethylenetetramine, the molybdate and the ammonia water is 4-8:4-8:60-100, preferably 8:8:60; the mass ratio of the total mass of the molybdate and the hexamethylenetetramine to the mass of the ZSM-5 molecular sieves is 1:1-3, preferably 1:1.5-2.5, and the mass fraction of the ammonia water is 13-17%, preferably 14-16%.

[0036] In the application, the molybdate is ammonium molybdate, sodium molybdate or potassium molybdate, preferably ammonium molybdate.

[0037] In the application, the temperature for drying in step (2) is 80-120 DEG C, preferably 90-110 DEG C, and the time for drying is 12-24 h, preferably 16-20 h, and the temperature is cooled to room temperature after the drying is completed.

[0038] In the application, the particle size of the supported precursor is 200-325 mesh, preferably 200-300 mesh.

[0039] In the application, the protective atmosphere is nitrogen, argon or helium, preferably nitrogen or argon.

[0040] In the application, the temperature for pyrolysis is 400-600 DEG C, preferably 450-550 DEG C, and the time for pyrolysis is 1-6 h, preferably 2-5 h; the temperature is cooled to room temperature after the pyrolysis is completed.

[0041] The application further provides the supported molybdenum-based nitrogen carrier prepared by the preparation method.

[0042] The technical solutions provided by the application are described in detail below in combination with examples, but they should not be understood as limitations to the protection scope of the application.

[0043] Example 1

[0044] 8 kg of methenamine C6H 12 N4 and 8 kg of ammonium molybdate (NH4) 6Mo7O 24 ·4H2O is dissolved in 60 kg of 15% ammonia water, and ultrasonic treatment is performed for 15 min at an ultrasonic power of 100 Hz; then 16 kg of ZSM-5 molecular sieve is immersed in the solution and stirred for 1 h, and then white precipitate is obtained through suction filtration; the white precipitate is dried at 120 ℃ for 12 h, naturally cooled to room temperature, and then ground into a powder-shaped supported precursor with a fineness of 200 mesh; the precursor is pyrolyzed under an argon atmosphere, the pyrolysis temperature is 500 ℃, the pyrolysis time is 3 h, and then the supported molybdenum-based nitrogen carrier is obtained by naturally cooling to room temperature.

[0045] 0.1 kg of the prepared supported molybdenum-based nitrogen carrier is used for ammonia release reaction, 1 L / min of H2 and 2 L / min of N2 / H2 are alternately introduced into a fixed bed for 1 h, the hydrogenation temperature is 400 ℃, the reaction time is 1 h, and the ammonia production rate is 21800 μmol / g / h.

[0046] Example 2

[0047] 6 kg of methenamine C6H 12 N4 and 7 kg of sodium molybdate Na2MoO4 are dissolved in 80 kg of 15% ammonia water, and ultrasonic treatment is performed for 20 min at an ultrasonic power of 95 Hz; then 26 kg of ZSM-5 molecular sieve is immersed in the solution and stirred for 2 h, and then white precipitate is obtained through suction filtration; the white precipitate is dried at 80 ℃ for 24 h, naturally cooled to room temperature, and then ground into a powder-shaped precursor with a fineness of 300 mesh; the precursor is pyrolyzed under a nitrogen atmosphere, the pyrolysis temperature is 600 ℃, the pyrolysis time is 6 h, and then the supported molybdenum-based nitrogen carrier is obtained by naturally cooling to room temperature.

[0048] 0.1 kg of the prepared supported molybdenum-based nitrogen carrier is used for ammonia release reaction, 1 L / min of H2 and 2 L / min of N2 / H2 are alternately introduced into a fixed bed for 1 h, the hydrogenation temperature is 400 ℃, the reaction time is 1 h, and the ammonia production rate is 15800 μmol / g / h.

[0049] Example 3

[0050] 4kg of methenamine C6H 12 N4and 6kg of potassium molybdate K2MoO4were dissolved in 100kg of 15% ammonia water under ultrasonic for 30min with ultrasonic power of 105Hz, then 30kg of ZSM-5 molecular sieve was immersed in the solution and stirred for 1.5h, and then white precipitate was obtained by suction filtration; the white precipitate was dried at 100℃ for 16h, naturally cooled to room temperature, and then ground into a powder precursor with fineness of 325 mesh; the precursor was pyrolyzed under helium atmosphere, the pyrolysis temperature was 400℃, the pyrolysis time was 4h, and then naturally cooled to room temperature to obtain the supported molybdenum-based nitrogen carrier.

[0051] The prepared 0.1kg of the supported molybdenum-based nitrogen carrier was subjected to ammonia release reaction, 1L / min of H2and 2L / min of N2 / H2were alternately introduced into the fixed bed for 1h, the hydrogenation temperature was 400℃, the reaction time was 1h, and the ammonia production rate was 19102μmol / g / h.

[0052] Example 4

[0053] 5kg of methenamine C6H 12 N4and 7kg of ammonium molybdate (NH4)6Mo7O 24 ·4H2O were dissolved in 90kg of 15% ammonia water under ultrasonic for 5min with ultrasonic power of 97Hz, then 12kg of ZSM-5 molecular sieve was immersed in the solution and stirred for 0.5h, and then white precipitate was obtained by suction filtration; the white precipitate was dried at 90℃ for 20h, naturally cooled to room temperature, and then ground into a powder precursor with fineness of 250 mesh; the precursor was pyrolyzed under argon atmosphere, the pyrolysis temperature was 600℃, the pyrolysis time was 5h, and then naturally cooled to room temperature to obtain the supported molybdenum-based nitrogen carrier.

[0054] The prepared 0.1kg of the supported molybdenum-based nitrogen carrier was subjected to ammonia release reaction, 1L / min of H2and 2L / min of N2 / H2were alternately introduced into the fixed bed for 1h, the hydrogenation temperature was 400℃, the reaction time was 1h, and the ammonia production rate was 9815μmol / g / h.

[0055] Example 5

[0056] 8kg of methenamine C6H 12N4 and 4kg of sodium molybdate Na2MoO4 are dissolved in 70kg of 15% ammonia water under ultrasonic for 10min, the ultrasonic power is 105Hz, then 24kg of ZSM-5 molecular sieve is immersed in the solution and stirred for 2h, then white precipitate is obtained by suction filtration; the white precipitate is dried at 90℃ for 12h, then naturally cooled to room temperature, and then ground into a powder precursor with a fineness of 270 mesh; the precursor is pyrolyzed under a helium atmosphere, the pyrolysis temperature is 400℃, and the pyrolysis time is 1h, then naturally cooled to room temperature, to obtain a supported molybdenum-based nitrogen carrier.

[0057] 0.1kg of the prepared supported molybdenum-based nitrogen carrier is taken for ammonia release reaction, 1L / min of H2 and 2L / min of N2 / H2 are alternately introduced into a fixed bed for 1h, the hydrogenation temperature is 400℃, the reaction time is 1h, and the ammonia production rate is 8056μmol / g / h.

[0058] Example 6

[0059] 4kg of methenamine C6H 12 N4 and 8kg of potassium molybdate K2MoO4 are dissolved in 100kg of 15% ammonia water under ultrasonic for 25min, the ultrasonic power is 110Hz, then 36kg of ZSM-5 molecular sieve is immersed in the solution and stirred for 1h, then white precipitate is obtained by suction filtration; the white precipitate is dried at 110℃ for 16h, then naturally cooled to room temperature, and then ground into a powder precursor with a fineness of 240 mesh; the precursor is pyrolyzed under a nitrogen atmosphere, the pyrolysis temperature is 500℃, and the pyrolysis time is 2h, then naturally cooled to room temperature, to obtain a supported molybdenum-based nitrogen carrier.

[0060] 0.1kg of the prepared supported molybdenum-based nitrogen carrier is taken for ammonia release reaction, 1L / min of H2 and 2L / min of N2 / H2 are alternately introduced into a fixed bed for 1h, the hydrogenation temperature is 400℃, the reaction time is 1h, and the ammonia production rate is 11708μmol / g / h.

[0061] From the above examples, it can be seen that the application provides a preparation method of a supported molybdenum-based nitrogen carrier suitable for chemical chain synthesis of ammonia, the raw materials are cheap and easy to obtain, can be used for ammonia production under mild conditions, and exhibits good ammonia release performance.

[0062] The above only describes the preferred embodiments of the application, and it should be noted that, for those skilled in the art, without departing from the principles of the application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the application.

Claims

1. Use of a supported molybdenum-based nitrogen carrier in a chemical looping ammonia synthesis reaction, characterized in that, It comprises the following steps: The supported molybdenum-based nitrogen carrier is added to a fixed bed reactor, and then hydrogen and nitrogen-hydrogen mixed gas are alternately introduced to carry out a chemical looping ammonia synthesis reaction. The preparation steps of the supported molybdenum-based nitrogen carrier are as follows: (1) White precipitate is obtained by mixing methenamine, molybdate, ammonia water and ZSM-5 molecular sieve and then performing suction filtration; (2) The white precipitate is sequentially dried and ground to obtain a supported precursor; (3) The supported precursor is pyrolyzed under a protective atmosphere to obtain a supported molybdenum-based nitrogen carrier suitable for chemical looping ammonia synthesis; The mass ratio of methenamine, molybdate and ammonia water is 4-8:4-8:60-100; the total mass of molybdate and methenamine to the mass of ZSM-5 molecular sieve is 1:1-3, and the mass fraction of ammonia water is 13-17%; The particle size of the supported precursor is 200-325 mesh; The pyrolysis temperature is 450-550℃, and the pyrolysis time is 2-5h; The volume ratio of nitrogen to hydrogen in the nitrogen-hydrogen mixed gas is 1:

1.

2. Use of a supported molybdenum-based nitrogen carrier according to claim 1 in a chemical looping ammonia synthesis reaction, characterized in that, The ratio of the addition amount of the supported molybdenum-based nitrogen carrier to the introduction rate of hydrogen and the introduction rate of nitrogen-hydrogen mixed gas is 0.1kg:1L / min:2L / min.

3. Use of a supported molybdenum-based nitrogen carrier according to claim 1 in a chemical looping ammonia synthesis reaction, characterized in that, The temperature of the chemical looping ammonia synthesis reaction is 400℃.