Iron-based synthetic ammonia catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of ammonia synthesis catalysts, and particularly relates to an iron-based ammonia synthesis catalyst and a preparation method and application thereof. The preparation method comprises the following steps: (1) carrying out coprecipitation reaction on a ferric salt solution, a mixed solution of auxiliary salt and a precipitant solution; aging the obtained precipitate slurry; the auxiliary agent salt comprises one or more of electronic auxiliary agent salt, barrier auxiliary agent salt and structural auxiliary agent salt; (2) filtering, washing, drying, roasting and crushing the obtained aging product to obtain a dry-based iron precursor; (3) mixing the iron precursor with a binder, adding an adhesive, and processing and molding the obtained mixture into a strip-shaped carrier; after the carrier is aged, the carrier is dried and roasted; and (4) impregnating the roasted product in a potassium salt solution by adopting a pore saturation impregnation method, and then drying and roasting the product to prepare the iron-based synthetic ammonia catalyst. The shape and the strength of the obtained catalyst are controllable, and the activity, the toxicity resistance and the mechanical strength of the catalyst can be improved at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of synthetic ammonia catalysts, and particularly relates to an iron-based synthetic ammonia catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] The raw material gas used in traditional synthetic ammonia is hydrogen and nitrogen. The main catalyst used is a fused iron catalyst, and alumina, calcium oxide, etc. are used as promoters; alternatively, a ruthenium-based catalyst with a noble metal ruthenium as the active component, activated carbon as the carrier, and metal salts such as barium and silver as promoters can be used.

[0003] For example, patent document CN104289217A discloses a ruthenium-based ammonia synthesis catalyst supported on a biomorphic composite oxide and a preparation method thereof. The ammonia synthesis catalyst uses a biomorphic composite oxide as the carrier and metal Ru as the active component. The loading amount of the active component is 0.5 wt% - 12 wt% of the biomorphic composite oxide based on Ru; the biomorphic composite oxide is a biomorphic composite oxide of magnesium and one or more of the following other metals prepared by a biological template: ① alkaline earth metals other than magnesium, ② alkali metals, ③ rare earth metals. The molar ratio of magnesium to the other metal is 50 - 500:1, and the biological template is Chinese fir, filter paper, absorbent cotton, amino acid or protein; the beneficial effects of the invention are mainly reflected in that compared with the existing ruthenium-based ammonia synthesis catalyst with an oxide as the carrier, the catalyst has higher catalytic activity.

[0004] However, the supported ruthenium-based catalyst is easily affected by the carrier, and the obtained catalyst has poor stability.

[0005] For example, patent document CN106799232A discloses a nano-iron modified iron-based ammonia synthesis catalyst prepared by a room-temperature solid-phase reaction, a preparation method thereof, and an application thereof. An iron-based ammonia synthesis catalyst, an iron precursor, and a solid reagent are uniformly mixed, ground, ball-milled or stirred to make the iron precursor react with the solid reagent on the iron-based ammonia synthesis catalyst carrier. After the reaction, the product is filtered, washed, dried, and heat-treated under air, nitrogen, argon or vacuum conditions to obtain the final nano-iron modified iron-based ammonia synthesis catalyst. The nano-iron loading amount is 0.1 wt% - 20 wt%; this patent has the advantages of simple preparation method, easy availability and low price of raw materials, short preparation cycle, low energy consumption, small particle size of the prepared nano-iron, good stability, etc., and improves the high activity and stability of the iron-based ammonia synthesis catalyst.

[0006] Patent document CN113976134A discloses a low-temperature, low-pressure, and highly active ammonia synthesis catalyst. To develop more catalyst types, the ferrous oxide-based catalyst consists of ferrous oxide and a promoter. The promoter includes alumina, potassium oxide, alkaline earth metal oxides, rare earth metal oxides, and transition metal oxides. The raw materials required for each component in the formulated amount are mixed evenly and melted into a liquid state under an atmospheric environment. The obtained liquid melt is quickly discharged into a cooling tank with a water jacket and cooled to below 100°C. The obtained melt block is post-treated to obtain the ferrous oxide-based catalyst. The catalyst prepared by this patent has remarkable characteristics such as high activity, easy reducibility, good heat resistance, strong anti-toxicity, and high mechanical strength under low temperature and low pressure, and is particularly suitable for low-temperature and low-pressure ammonia synthesis processes with obvious energy-saving effects.

[0007] However, the above two prior arts both belong to fused iron catalysts. The specific surface area of the existing fused iron catalysts is small, and the shape is directly broken into granular form without control, resulting in low catalyst activity.

[0008] In view of this, continuing to develop iron-based ammonia synthesis catalysts with excellent performance is a research direction worthy of study. Summary of the Invention

[0009] Aiming at the above problems existing in the prior art, the purpose of the present invention is to provide an iron-based ammonia synthesis catalyst, its preparation method and application. The specific surface area of the obtained iron-based catalyst is increased, the shape and strength of the catalyst are controllable, and the activity, anti-toxicity, and mechanical strength of the catalyst can be improved simultaneously.

[0010] To achieve the above purpose, the present invention provides the following technical solutions:

[0011] In the first aspect, a preparation method of an iron-based ammonia synthesis catalyst is provided, including the following steps:

[0012] (1) The mixed solution of iron salt solution, promoter salt solution, and precipitant solution is fed in parallel for coprecipitation reaction to obtain a precipitate slurry; then the obtained precipitate slurry is aged.

[0013] Among them, the promoter salt includes one or more of an electronic promoter salt and a barrier promoter salt;

[0014] (2) The aged product obtained in step (1) is filtered, washed, dried, calcined, and crushed to obtain a dry-based iron precursor.

[0015] (3) The dry-based iron precursor is mixed with a binder, and an adhesive is added and mixed evenly. Then the obtained mixture is processed into a carrier. The carrier is preferably a strip-shaped carrier; after the carrier is aged, it is further dried and calcined.

[0016] (4) The calcined product obtained in step (3) is impregnated in a potassium salt solution by the pore saturation impregnation method, and then dried and calcined to obtain an iron-based ammonia synthesis catalyst.

[0017] According to the preparation method provided by the present invention, in some embodiments, the iron salt is selected from one or more of iron nitrate, iron sulfate, and iron chloride.

[0018] In some embodiments, the precipitant is selected from ammonia water and / or ammonium bicarbonate.

[0019] In some embodiments, the potassium salt is selected from potassium nitrate and / or potassium carbonate.

[0020] In some embodiments, the electronic promoter salt is selected from one or more of soluble potassium salts, soluble sodium salts, soluble calcium salts, and soluble magnesium salts, preferably one or more of soluble calcium salts and soluble magnesium salts.

[0021] In some embodiments, the barrier promoter salt is selected from one or more of soluble barium salts, soluble titanium salts, soluble zirconium salts, soluble vanadium salts, soluble chromium salts, soluble nickel salts, soluble copper salts, soluble zinc salts, and soluble cerium salts, preferably one or more of soluble copper salts and soluble zinc salts.

[0022] In some embodiments, the promoter salt is a mixture of an electronic promoter salt and a barrier promoter salt.

[0023] In some embodiments, the promoter salt is a mixture of a soluble copper salt and a soluble calcium salt, or a mixture of a soluble zinc salt and a soluble calcium salt.

[0024] Before contacting and reacting the iron salt, the promoter salt, and the precipitant, a mixed solution of an iron salt solution, a promoter salt, and a precipitant solution within a certain concentration range can be prepared in advance. Before impregnating the carrier, a potassium salt solution within a certain concentration range can be prepared.

[0025] In the present invention, the concentrations of the prepared material flow solutions can be conventional selections in the art. For example, the concentration of the iron salt solution can be 10 - 500 g / L (such as 15 g / L, 30 g / L, 50 g / L, 100 g / L, 200 g / L, 300 g / L, 400 g / L); the concentration of the mixed solution of the auxiliary salt can be 0.1 - 100 g / L (such as 0.5 g / L, 1 g / L, 5 g / L, 10 g / L, 20 g / L, 50 g / L, 80 g / L); the concentration of the precipitant solution can be 10 - 500 g / L (such as 15 g / L, 30 g / L, 50 g / L, 100 g / L, 200 g / L, 300 g / L, 400 g / L). The concentration of the potassium salt solution can be 1 - 100 g / L (such as 2 g / L, 4 g / L, 5 g / L, 10 g / L, 20 g / L, 50 g / L, 80 g / L).

[0026] In some embodiments, the mass ratio of the iron salt to the electronic auxiliary salt is 100:(0.2 - 15), for example, 100:0.3, 100:0.5, 100:0.8, 100:1, 100:2, 100:3, 100:4, 100:5, 100:8, 100:12, and preferably 100:(0.5 - 10).

[0027] In some embodiments, the mass ratio of the iron salt to the barrier auxiliary salt is 100:(0.2 - 15), for example, 100:0.3, 100:0.5, 100:0.8, 100:1, 100:2, 100:3, 100:4, 100:5, 100:8, 100:12, and preferably 100:(0.5 - 10).

[0028] According to the preparation method provided by the present invention, in some embodiments, in step (1), the process conditions of the reaction include: the pH value of the system is 3 - 10 (such as 4, 5, 6, 7, 8, 9), preferably 5 - 10, the reaction temperature is 30 - 90 °C (such as 40 °C, 50 °C, 65 °C, 80 °C), and preferably 60 - 90 °C.

[0029] For example, the pH value of the system can be adjusted by the addition amount of the precipitant or the precipitant solution.

[0030] In some embodiments, in step (1), the process conditions of the aging treatment include: the aging temperature is 30 - 90 °C (such as 40 °C, 50 °C, 65 °C, 80 °C), and the aging time is 0 - 2 h (such as 0.1 h, 0.5 h, 1 h, 1.5 h).

[0031] In step (2) of the present invention, both the filtration and washing processes can be achieved by conventional operations in the art, which will not be elaborated here.

[0032] In some embodiments, in step (2), the process conditions for drying include: the drying temperature is 80 - 200 °C (for example, 90 °C, 100 °C, 120 °C, 150 °C, 180 °C), and the drying time is 8 - 24 h (for example, 10 h, 15 h, 18 h, 20 h); the process conditions for roasting include: the roasting temperature is 400 - 600 °C (for example, 420 °C, 450 °C, 500 °C, 550 °C, 580 °C), and the roasting time is 2 - 12 h (for example, 3 h, 5 h, 8 h, 10 h).

[0033] In some embodiments, in step (3), the binder is alumina or silica.

[0034] In some embodiments, in step (3), based on the amount of Fe2O3 in the dry-based iron precursor, the mass ratio of Fe2O3 to the binder is 100:(20 - 80), for example, 100:25, 100:30, 100:50, 100:60, 100:70.

[0035] In some embodiments, based on the amount of Fe2O3 in the dry-based iron precursor, the mass ratio of Fe2O3 to Al2O3 = 100∶(20 - 80), for example, 100:25, 100:30, 100:40, 100:50, 100:60, 100:75; or, the mass ratio of Fe2O3 to SiO2 is 100:(0 - 80), for example, 100:5, 100:10, 100:25, 100:30, 100:40, 100:50, 100:60, 100:75.

[0036] In some embodiments, in step (3), the adhesive is dilute nitric acid; based on the amount of the dry-based iron precursor, the mass of the solute (nitric acid) in the dilute nitric acid is 0.5 - 5.0 wt% of the amount of the dry-based iron precursor, for example, 0.8 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, 4.0 wt%, 4.5 wt%.

[0037] In some embodiments, in step (3), the process conditions for the aging treatment include: the aging temperature is from room temperature to 90 °C (for example, 30 °C, 40 °C, 50 °C, 65 °C, 80 °C), and the aging time is 0 - 2 h (for example, 0.1 h, 0.5 h, 1 h, 1.5 h).

[0038] In some embodiments, in step (3), the process conditions for drying include: the drying temperature is 80 - 200 °C (for example, 90 °C, 100 °C, 120 °C, 150 °C, 180 °C), and the drying time is 3 - 24 h (for example, 4 h, 5 h, 10 h, 15 h, 18 h, 20 h); the process conditions for roasting include: the roasting temperature is 400 - 600 °C (for example, 420 °C, 450 °C, 500 °C, 550 °C, 580 °C), and the roasting time is 2 - 12 h (for example, 3 h, 5 h, 8 h, 10 h).

[0039] In step (4) of the present invention, the process of impregnating the carrier in the impregnating solution can be achieved by conventional means in the art and will not be elaborated here. In some embodiments, in step (4), the roasted product obtained in step (3) can be impregnated in the potassium salt solution by the pore saturation impregnation method with equal volume.

[0040] In some embodiments, in step (4), the process conditions for drying include: the drying temperature is 80 - 200 °C (for example, 90 °C, 100 °C, 120 °C, 150 °C, 180 °C), and the drying time is 3 - 24 h (for example, 4 h, 5 h, 10 h, 15 h, 18 h, 20 h); the process conditions for roasting include: the roasting temperature is 400 - 600 °C (for example, 420 °C, 450 °C, 500 °C, 550 °C, 580 °C), and the roasting time is 2 - 12 h (for example, 3 h, 5 h, 8 h, 10 h).

[0041] In the catalyst obtained after roasting in step (4), the loading amount of potassium oxide can be 0.5 - 10 wt%, such as 1 wt%, 2 wt%, 4 wt%, 5 wt%, 8 wt%.

[0042] In the second aspect, there is provided an iron-based ammonia synthesis catalyst prepared by the preparation method as described above. Based on the total weight of the catalyst being 100 wt%, the components and their content ranges in the catalyst are as follows:

[0043] The content of iron oxide is 40 - 75 wt% (for example, 42 wt%, 45 wt%, 50 wt%, 55 wt%, 62 wt%, 65 wt%, 70 wt%), preferably 40 - 60 wt%;

[0044] The content of potassium oxide is 0.5 - 10 wt% (for example, 1 wt%, 1.5 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 9 wt%), preferably 2 - 8 wt%;

[0045] The content of alumina or silica is 20 - 50 wt% (for example, 22 wt%, 24 wt%, 30 wt%, 35 wt%, 42 wt%, 45 wt%), preferably 25 - 40 wt%;

[0046] The balance is the sum of the contents of each auxiliary component.

[0047] For example, the mass ratio of Fe2O3: electronic auxiliary component: barrier auxiliary component can be 100:(0.5 - 10):(0.5 - 10). Such as, 100:0.5:0.5, 100:1:0.5, 100:2:0.5, 100:5:0.5, 100:10:0.5, 100:0.5:1, 100:0.5:2, 100:0.5:5, 100:0.5:10.

[0048] In the third aspect, there is provided an iron-based ammonia synthesis catalyst prepared by the preparation method as described above or the application of the iron-based ammonia synthesis catalyst as described above in the ammonia synthesis reaction.

[0049] According to the application provided by the present invention, in some embodiments, the reaction conditions of the ammonia synthesis reaction include: the temperature is 200°C - 500°C (for example, 220°C, 250°C, 300°C, 350°C, 400°C, 450°C), the pressure is 5 MPa - 15 MPa (for example, 6 MPa, 8 MPa, 10 MPa, 12 MPa), and the space velocity is 1000 h -1 -30000 h -1 (1200 h -1 、1500 h -1 、2000 h -1 、4000 h -1 、5000 h -1 、8000 h -1 、10000 h -1 、15000 h -1 、20000 h -1 、25000 h -1 ).

[0050] During the use of the synthetic ammonia catalysts provided by the prior art, the active components of the catalysts will inevitably aggregate, thereby leading to a decrease in activity. In addition, during long-term use, there will also be a problem that the catalysts break into particulate form and cannot be controlled, which will also affect the catalytic activity. Aiming at the requirements that the synthetic ammonia catalysts should have high activity, selectivity and long-term stability, the present invention prepares through a co-precipitation process and adds a complex of different promoter salt components in the co-precipitation process. That is, in the obtained catalysts, by introducing barrier promoter components (such as oxides of titanium, copper, zinc, chromium, nickel, etc.), the aggregation of the active components of the catalysts can be prevented; in order to prevent the decrease in activity caused by the aggregation of the active components, by introducing electronic promoter components (such as oxides of potassium, sodium, calcium, magnesium), the dissociation of nitrogen can be promoted and the reaction activity of ammonia synthesis can be improved; in addition, by adding binder components (such as oxides of silicon or aluminum), the mechanical strength and stability of the catalysts can be improved.

[0051] Compared with the prior art, the excellent effects of the technical solution of the present invention are at least as follows:

[0052] 1) By introducing a variety of promoter salts in the co-precipitation process of the present invention, each promoter component can be more evenly dispersed; the obtained catalysts are easier to reduce, have more active sites and higher activity;

[0053] When the obtained catalysts are applied to the ammonia synthesis reaction, the reaction temperature and pressure can be reduced and the activity of the catalysts can be improved;

[0054] 2) In the preparation method of the present invention, an iron precursor is obtained through the co-precipitation method, and the specific surface area of the obtained iron-based catalysts can be increased (for example, it can be controlled within 50 - 500 m 2 / g), the pore volume and pore diameter are controllable, and its pore volume > 0.1 cm 3 / g (for example, it is 0.1 - 0.5 cm 3 / g);

[0055] 3) The shape, size and strength of the catalysts obtained by the present invention are controllable and can be controlled to the required shape; and the strength of the catalysts is increased by adjusting the binder, which is more beneficial to improving the anti-toxicity and mechanical strength of the catalysts. Detailed Embodiments

[0056] In order to be able to understand the technical features and content of the present invention in detail, the preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described in the examples, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein.

[0057] Unless otherwise specified, the experimental procedures used in the following examples are all conventional methods.

[0058] The materials, reagents, etc. used in the following examples can all be obtained commercially.

[0059] Example 1:

[0060] A method for preparing an iron-based ammonia synthesis catalyst includes the following steps:

[0061] (1) Dissolve 25 kg of ferric nitrate nonahydrate, 0.2 kg of copper nitrate, and 0.4 kg of calcium nitrate in deionized water to prepare a 160-liter mixed salt solution. Dissolve 12.5 kg of ammonia water in deionized water to prepare an 80-liter precipitant solution;

[0062] Pump the prepared mixed salt solution and the prepared precipitant solution into the reaction kettle in parallel, control the temperature in the reaction kettle at 60 °C, control the pH value of the system at 7 by the addition amount of the precipitant solution, and carry out a coprecipitation reaction to obtain a precipitate slurry;

[0063] After precipitation, let the obtained product stand and age at 60 °C for 60 minutes;

[0064] (2) Filter the obtained aged product, wash the filter cake, dry it at 120 °C for 12 h, then calcine it at 500 °C for 5 h, and then ball mill and crush it into powder to obtain a dry-based iron precursor;

[0065] (3) Mix the dry-based iron precursor obtained in step (2) with alumina according to m(dry-based Fe2O3)∶m(Al2O3)=65∶35, and add dilute nitric acid as an adhesive thereto. After mixing, carry out extrusion molding to form a strip-shaped carrier; the addition amount of solute nitric acid during extrusion accounts for 3 wt% of the mass of the dry-based iron precursor;

[0066] The obtained carrier is aged at room temperature for 4 h, then dried at 80 °C for 5 h, and then calcined at 500 °C for 5 h;

[0067] (4) Dissolve 0.2 kg of potassium nitrate in deionized water to prepare a 17-liter potassium salt solution; the calcined product obtained in step (3) is impregnated isovolumetrically in the prepared potassium salt solution by the pore saturation impregnation method, then dried at 80 °C for 4 h, and then calcined at 500 °C for 5 h to obtain a catalyst; the loading mass fraction of potassium oxide in this catalyst is 2 wt%.

[0068] Example 2:

[0069] A method for preparing an iron-based ammonia synthesis catalyst includes the following steps:

[0070] (1) Dissolve 25 kg of ferric nitrate nonahydrate, 0.8 kg of copper nitrate, and 0.1 kg of calcium nitrate in deionized water to prepare a 160-liter mixed salt solution. Dissolve 12.5 kg of ammonia water in deionized water to prepare an 80-liter precipitant solution;

[0071] Pump the prepared mixed salt solution and the prepared precipitant solution into the reaction kettle in parallel. Control the temperature in the reaction kettle at 30 °C, and control the pH value of the system at 6 by the addition amount of the precipitant solution to carry out the coprecipitation reaction to obtain a precipitate slurry;

[0072] After the precipitation is completed, let the obtained product stand and age at 30 °C for 30 minutes;

[0073] (2) Filter the obtained aged product. After the filter cake is washed, dry it at 120 °C for 12 h, then calcine it at 500 °C for 5 h, and then ball mill and crush it into powder to obtain a dry-based iron precursor;

[0074] (3) Mix the dry-based iron precursor obtained in step (2) with alumina according to m(dry-based Fe2O3)∶m(Al2O3) = 65∶35, and add dilute nitric acid as an adhesive thereto. After mixing, carry out extrusion molding to form a strip-shaped carrier; when extruding, the addition amount of solute nitric acid accounts for 3 wt% of the mass of the dry-based iron precursor;

[0075] The obtained carrier is aged at room temperature for 4 h, then dried at 80 °C for 5 h, and then calcined at 500 °C for 5 h;

[0076] (4) Dissolve 0.2 kg of potassium nitrate in deionized water to prepare a 17-liter potassium salt solution; the calcined product obtained in step (3) is impregnated isovolumetrically with the prepared potassium salt solution by the pore saturation impregnation method, then dried at 80 °C for 4 h, and then calcined at 500 °C for 5 h to obtain a catalyst; the loading mass fraction of potassium oxide in this catalyst is 2 wt%.

[0077] Example 3:

[0078] A preparation method of an iron-based ammonia synthesis catalyst, comprising the following steps:

[0079] (1) Dissolve 25 kg of ferric nitrate nonahydrate, 0.1 kg of copper nitrate, and 1.5 kg of calcium nitrate in deionized water to prepare a 160-liter mixed salt solution. Dissolve 12.5 kg of ammonia water in deionized water to prepare an 80-liter precipitant solution;

[0080] Pump the prepared mixed salt solution and the prepared precipitant solution into the reaction kettle in parallel. Control the temperature in the reaction kettle at 60 °C, and control the pH value of the system at 9 by the addition amount of the precipitant solution to carry out the coprecipitation reaction to obtain a precipitate slurry;

[0081] After precipitation, the obtained product is allowed to stand and age at 60 °C for 30 minutes;

[0082] (2) The obtained aged product is filtered, and the filter cake is washed and then dried at 120 °C for 12 h, calcined at 500 °C for 5 h, and then ball-milled and crushed into a powder to obtain a dry-based iron precursor;

[0083] (3) According to m(dry-based Fe2O3)∶m(Al2O3) = 65∶35, the dry-based iron precursor obtained in step (2) is mixed with alumina, and dilute nitric acid is added thereto as an adhesive. After mixing, it is extruded into a strip-shaped carrier; when extruding, the addition amount of solute nitric acid accounts for 3 wt% of the mass of the dry-based iron precursor;

[0084] The obtained carrier is aged at room temperature for 4 h, then dried at 80 °C for 5 h, and then calcined at 500 °C for 5 h;

[0085] (4) 0.1 kg of potassium carbonate is dissolved in deionized water to prepare a 17-liter potassium salt solution; the calcined product obtained in step (3) is impregnated in the prepared potassium salt solution by the pore saturation impregnation method with equal volume, then dried at 80 °C for 4 h, and then calcined at 500 °C for 5 h to obtain a catalyst; the loading mass fraction of potassium oxide in this catalyst is 2 wt%.

[0086] Example 4:

[0087] The preparation method of the iron-based ammonia synthesis catalyst refers to Example 1, the difference being that the precipitant used in step (1) is ammonium bicarbonate.

[0088] The remaining steps are the same as those in Example 1 to obtain a catalyst.

[0089] Example 5:

[0090] The preparation method of the iron-based ammonia synthesis catalyst refers to Example 1, the difference being that the temperature of the coprecipitation reaction in step (1) is 90 °C, and the pH value of the system is controlled to be 7;

[0091] The remaining steps are the same as those in Example 1 to obtain a catalyst.

[0092] Comparative Example 1:

[0093] Mix alumina, potassium oxide, calcium oxide and iron tetroxide evenly to obtain a mixture. Among them, based on the total weight of the mixture being 100 wt%, alumina accounts for 5 wt%, potassium oxide accounts for 3 wt%, calcium oxide accounts for 1.5 wt%, and the balance is iron tetroxide; then load this mixture into a steel furnace with a water jacket, connect two electrodes with leads to make it energized, and rely on the conductivity of the substance and its own resistance to make the mixture conduct electricity and generate heat for melting; after melting for 20 minutes, quickly pour the high-temperature molten material into a cooling tank with a water jacket to cool it to room temperature, and the obtained product is crushed and screened to the required particle size to prepare the catalyst.

[0094] Comparative Example 2:

[0095] A preparation method of an iron-based ammonia synthesis catalyst includes the following steps:

[0096] (1) Dissolve 25 kg of ferric nitrate nonahydrate, 0.2 kg of copper nitrate, and 0.4 kg of calcium nitrate in deionized water to prepare a 160-liter mixed salt solution, and dissolve 12.5 kg of ammonia water in deionized water to prepare an 80-liter precipitant solution;

[0097] Pump the prepared mixed salt solution and the prepared precipitant solution into the reaction kettle in parallel, control the temperature in the reaction kettle at 100 °C, and control the pH value of the system at 12 by the addition amount of the precipitant solution to carry out a precipitation reaction to obtain a precipitate slurry;

[0098] After the precipitation is completed, let the obtained product stand and age at 100 °C for 30 minutes;

[0099] (2) Filter the obtained aged product, wash the filter cake, dry it at 120 °C for 12 h, then calcine it at 500 °C for 5 h, and then ball-mill and crush it into a powder to obtain a dry-based iron precursor;

[0100] (3) Mix the dry-based iron precursor obtained in step (2) with alumina according to m(dry-based Fe2O3)∶m(Al2O3) = 65∶35, and add dilute nitric acid as an adhesive thereto, and after mixing, carry out extrusion molding into a strip-shaped carrier; when extruding, the addition amount of solute nitric acid accounts for 3 wt% of the mass of the dry-based iron precursor;

[0101] The obtained carrier is aged at room temperature for 4 h, then dried at 80 °C for 5 h, and then calcined at 500 °C for 5 h;

[0102] (4) Dissolve 0.2 kg of potassium nitrate in deionized water to prepare a 17-liter potassium salt solution; the calcined product obtained in step (3) is impregnated isovolumetrically with the prepared potassium salt solution by the pore saturation impregnation method, then dried at 80 °C for 4 h, and then calcined at 500 °C for 5 h to prepare the catalyst; the loading mass fraction of potassium oxide in this catalyst is 2 wt%.

[0103] Comparative Example 3:

[0104] A preparation method of an iron-based ammonia synthesis catalyst, comprising the following steps:

[0105] (1) Dissolve 25 kg of ferric nitrate nonahydrate, 0.2 kg of copper nitrate, and 0.4 kg of calcium nitrate in deionized water to prepare a 160-liter mixed salt solution. Dissolve 12.5 kg of ammonia water in deionized water to prepare an 80-liter precipitant solution;

[0106] Pump the prepared mixed salt solution and the prepared precipitant solution into the reaction kettle in parallel, control the temperature in the reaction kettle at 30 °C, and control the pH value of the system at 2 by the addition amount of the precipitant solution to carry out the precipitation reaction to obtain a precipitate slurry;

[0107] After the precipitation is completed, let the obtained product stand and age at 30 °C for 30 minutes;

[0108] (2) Filter the obtained aged product, wash the filter cake, dry it at 120 °C for 12 h, then calcine it at 500 °C for 5 h, and then ball mill and crush it into powder to obtain a dry-based iron precursor;

[0109] (3) Mix the dry-based iron precursor obtained in step (2) with alumina according to m(dry-based Fe2O3)∶m(Al2O3)=65∶35, and add dilute nitric acid as an adhesive thereto. After mixing, extrude and process it into a strip-shaped carrier; the addition amount of solute nitric acid during extrusion accounts for 3 wt% of the mass of the dry-based iron precursor;

[0110] The obtained carrier is aged at room temperature for 4 h, then dried at 80 °C for 5 h, and then calcined at 500 °C for 5 h;

[0111] (4) Dissolve 0.2 kg of potassium nitrate in deionized water to prepare a 17-liter potassium salt solution; the calcined product obtained in step (3) is impregnated isovolumetrically in the prepared potassium salt solution by the pore saturation impregnation method, then dried at 80 °C for 4 h, and then calcined at 500 °C for 5 h to obtain a catalyst; the loading mass fraction of potassium oxide in the catalyst is 2 wt%.

[0112] Comparative Example 4:

[0113] A preparation method of an iron-based ammonia synthesis catalyst, comprising the following steps:

[0114] (1) Dissolve 25 kg of ferric nitrate nonahydrate, 1.2 kg of copper nitrate, and 2.4 kg of calcium nitrate in deionized water to prepare a 160-liter mixed salt solution. Dissolve 12.5 kg of ammonia water in deionized water to prepare an 80-liter precipitant solution;

[0115] The prepared mixed salt solution and the prepared precipitant solution are pumped into the reaction kettle in parallel by a pump. The temperature in the reaction kettle is controlled at 60 °C, and the pH value of the system is controlled at 7 by the addition amount of the precipitant solution to carry out a coprecipitation reaction to obtain a precipitate slurry.

[0116] After the precipitation is completed, the obtained product is allowed to stand and age at 60 °C for 60 minutes.

[0117] (2) The obtained aged product is filtered. The filter cake is washed and then dried at 120 °C for 12 h, roasted at 500 °C for 5 h, and then ball milled and crushed into powder to obtain a dry-based iron precursor.

[0118] (3) According to m(dry-based Fe2O3)∶m(Al2O3) = 65∶35, the dry-based iron precursor obtained in step (2) is mixed with alumina, and dilute nitric acid is added thereto as an adhesive. After mixing, it is extruded into a strip-shaped carrier; when extruding, the addition amount of solute nitric acid accounts for 3 wt% of the mass of the dry-based iron precursor.

[0119] The obtained carrier is aged at room temperature for 4 h, then dried at 80 °C for 5 h, and roasted at 500 °C for 5 h.

[0120] (4) 0.01 kg of potassium carbonate is dissolved in deionized water to prepare a 17 L potassium salt solution; the calcined product obtained in step (3) is impregnated isovolumetrically in the prepared potassium salt solution by the pore saturation impregnation method, then dried at 80 °C for 4 h, and roasted at 500 °C for 5 h to obtain a catalyst; the loaded mass fraction of potassium oxide in this catalyst is 0.2 wt%.

[0121] Table 1 Composition of the catalysts prepared in each example and comparative example

[0122]

[0123]

[0124] The physical property parameters of the catalysts in each example and comparative example are tested as follows:

[0125] (1) Test process for specific surface area, pore volume and pore diameter: It is measured by a physical adsorption method BET test instrument (the instrument is purchased from Micromeritics, USA, model ASAP).

[0126] (2) Test process for attrition rate: Under the action of the injection of a high-speed air flow, the catalyst is in a fluidized state, and fine powder is generated due to friction between catalyst particles. Through screening and weighing, the attrition rate of the catalyst is calculated.

[0127] Table 2 Physical property parameters of the catalysts prepared in each example and comparative example

[0128] Number <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Pore volume (cm 3 / g)]]> Aperture Wear rate (%) Example 1 254 0.45 9.07 5 Example 2 183 0.38 8.04 5 Example 3 200 0.42 10.05 5 Example 4 230 0.43 10.74 5 Example 5 310 0.52 11.16 5 Comparative Example 1 10 0.02 1.02 6 Comparative Example 2 54 0.31 9.16 5 Comparative Example 3 120 0.35 8.54 5 Comparative Example 4 224 0.46 9.81 5

[0129] Catalyst performance evaluation

[0130] The catalyst prepared as above is applied to the reaction process of ammonia synthesis, and its performance is tested. In the synthesis reactor, hydrogen and nitrogen are reacted in the presence of the catalyst prepared as above. The reaction process of ammonia synthesis is: 3H2 + 2N2 = 2NH3;

[0131] Among them, the process conditions include: the pressure is 5 MPa, the space velocity is 30000 h -1 , the composition of the raw material gas is H2 / N2 = 3:1, and the ammonia concentration at the reactor outlet of the reaction using the catalysts obtained in each example and comparative example is measured respectively.

[0132] Table 3 Performance evaluation results of the catalysts prepared in each example and comparative example

[0133]

[0134] From the test data in the above table, it can be seen that by using the process of the present invention to prepare the catalyst by introducing various promoter salts in the coprecipitation process, each promoter component can be more evenly dispersed; the obtained catalyst is easier to reduce, has more active sites, higher activity, larger specific surface area and pore volume of the catalyst; in addition, with an internal binder and by extrusion molding, the catalyst has high strength; when this catalyst is used in the ammonia synthesis process, the process conditions for ammonia synthesis can be milder and the activity is higher.

[0135] The various embodiments of the present invention have been described above. The above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art without departing from the gist of the present invention.

Claims

1. A preparation method of an iron-based ammonia synthesis catalyst, characterized in that, It includes the following steps: (1) Co-feed an iron salt solution, a mixed solution of promoter salts, and a precipitant solution to carry out a coprecipitation reaction to obtain a precipitate slurry; then age the obtained precipitate slurry; Among them, the promoter salts include one or more of electronic promoter salts and barrier promoter salts; (2) Filter, wash, dry, calcine, and crush the aged product obtained in step (1) to obtain a dry-based iron precursor; (3) Mix the dry-based iron precursor with a binder, add an adhesive and mix evenly, and then process the obtained mixture into a carrier, and the carrier is preferably a strip-shaped carrier; after aging the carrier, perform drying and calcination treatments; (4) Immerse the calcined product obtained in step (3) in a potassium salt solution by pore saturation impregnation method, and then perform drying and calcination to obtain an iron-based ammonia synthesis catalyst.

2. The preparation method according to claim 1, characterized in that, The iron salt is selected from one or more of iron nitrate, iron sulfate, and iron chloride; The precipitant is selected from ammonia water and / or ammonium bicarbonate; The potassium salt is selected from potassium nitrate and / or potassium carbonate.

3. The preparation method according to claim 1, characterized in that The electronic promoter salt is selected from one or more of soluble potassium salts, soluble sodium salts, soluble calcium salts, and soluble magnesium salts, preferably one or more of soluble calcium salts and soluble magnesium salts; and / or The barrier promoter salt is selected from one or more of soluble barium salts, soluble titanium salts, soluble zirconium salts, soluble vanadium salts, soluble chromium salts, soluble nickel salts, soluble copper salts, soluble zinc salts, and soluble cerium salts, preferably one or more of soluble copper salts and soluble zinc salts; Preferably, the promoter salt is a mixture of a soluble copper salt and a soluble calcium salt, or a mixture of a soluble zinc salt and a soluble calcium salt.

4. The preparation method according to claim 1, characterized in that The mass ratio of the iron salt to the electronic promoter salt is 100:(0.2 - 15), preferably 100:(0.5 - 10); The mass ratio of the iron salt to the barrier promoter salt is 100:(0.2 - 15), preferably 100:(0.5 - 10).

5. The preparation method according to claim 1, characterized in that, In step (1), the process conditions of the reaction include: the pH value of the system is 3 - 10, preferably 5 - 10, the reaction temperature is 30 - 90°C, preferably 60 - 90°C; and / or In step (1), the process conditions of the aging treatment include: the aging temperature is 30 - 90°C, and the aging time is 0 - 2h; and / or In step (2), the process conditions of the drying include: the drying temperature is 80 - 200°C, and the drying time is 8 - 24h; the process conditions of the calcination include: the calcination temperature is 400 - 600°C, and the calcination time is 2 - 12h.

6. The preparation method according to claim 1, wherein In step (3), the binder is alumina or silica; Calculated based on the amount of Fe2O3 in the dry-based iron precursor, the mass ratio of Fe2O3 to the binder is 100:(20 - 80); preferably, calculated based on the amount of Fe2O3 in the dry-based iron precursor, the mass ratio of Fe2O3 to Al2O3 = 100∶(20 - 80); or, the mass ratio of Fe2O3 to SiO2 is 100:(0 - 80); The adhesive is dilute nitric acid; based on the amount of the dry-based iron precursor, the mass of the solute in the dilute nitric acid is 0.5 - 5.0 wt% of the amount of the dry-based iron precursor.

7. The preparation method according to claim 1, characterized in that, In step (3), the process conditions for the aging treatment include: the aging temperature is from room temperature to 90 °C, and the aging time is 0 - 2 h; In step (3), the process conditions for the drying include: the drying temperature is 80 - 200 °C, and the drying time is 3 - 24 h; the process conditions for the calcination include: the calcination temperature is 400 - 600 °C, and the calcination time is 2 - 12 h.

8. The preparation method according to any one of claims 1-7, characterized in that, In step (4), the process conditions for the drying include: the drying temperature is 80 - 200 °C, and the drying time is 3 - 24 h; the process conditions for the calcination include: the calcination temperature is 400 - 600 °C, and the calcination time is 2 - 12 h.

9. An iron-based ammonia synthesis catalyst prepared by the preparation method according to any one of claims 1-8, characterized in that, Based on the total weight of the catalyst being 100 wt%, the components and their content ranges in the catalyst are as follows: The content of iron oxide is 40 - 75 wt%, preferably 40 - 60 wt%; The content of potassium oxide is 0.5 - 10 wt%, preferably 2 - 8 wt%; The content of alumina or silica is 20 - 50 wt%, preferably 25 - 40 wt%; The balance is the sum of the contents of each auxiliary component.

10. The application of the iron-based ammonia synthesis catalyst prepared by the preparation method according to any one of claims 1 - 8 or the iron-based ammonia synthesis catalyst according to claim 9 in the ammonia synthesis reaction; Preferably, the reaction conditions for the ammonia synthesis reaction include: The temperature is 200°C - 500°C, the pressure is 5 MPa - 15 MPa, and the space velocity is 1000 h -1 -30000 h -1 .

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