Iron-based catalyst reduction method suitable for catalyzing ammonia decomposition reaction and application of iron-based catalyst reduction method

Abstract

The invention discloses a reduction method of an iron-based catalyst suitable for catalyzing ammonia decomposition reaction and application of the reduction method. The reduction method comprises the following steps: S1, preliminarily reducing the iron-based catalyst at 400-510 DEG C under an ammonia gas atmosphere condition with a certain low volume ratio; s2, increasing the reduction temperature of the catalyst from low temperature to high temperature according to a certain heating rate; and S3, deeply reducing the catalyst at 530-570 DEG C under the condition of a certain high-volume-ratio ammonia gas atmosphere, namely reducing the catalyst to a state with better ammonia decomposition reaction activity. The process is simple, danger caused by traditional hydrogen reduction and pre-reduction type iron-based catalysts is avoided, the risk of excessive water yield in hydrogen reduction is weakened, the reduction time is shorter, the reduction process is simple, and the ammonia gas conversion rate of the reduced catalyst at the reaction temperature of 550 DEG C is larger than 99%.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and in particular to a method for reducing an iron-based catalyst suitable for catalyzing ammonia decomposition reactions and an application thereof. Background Art

[0002] H 2 As a clean, sustainable and renewable energy source, ammonia is the most promising energy carrier to replace fossil fuels and is crucial to achieving decarbonization of energy supply and sustainable development of future energy. 3 ) has attracted extensive attention as a potential hydrogen carrier. The only product of ammonia decomposition is H 2 and nitrogen (N 2 ), no CO is produced x , which helps to separate and purify hydrogen. Ammonia has high energy density (11.50MJ / kg), is easy to liquefy, has advantages such as low cost, safe storage and transportation, and complete infrastructure, and is a very promising H 2 Storage and transport carrier.

[0003] Iron-based catalysts are widely used in ammonia decomposition reactions due to their low price, long service life, and good catalytic activity. Iron-based catalysts are widely used in the ammonia industry and the technology is relatively mature, but most of these manufacturers use traditional processes, that is, using large amounts of hydrogen or pre-reduction to ensure the reduction effect of the catalyst.

[0004] CN1047098C discloses preparing a pre-reduced iron-based catalyst to help the subsequent reduction of the catalyst, but the pre-reduced catalyst is relatively active and will oxidize and generate heat when exposed to the air, causing spontaneous combustion. In order to ensure the safety of transportation and loading of the catalyst, strict control is adopted on the reduced catalyst to perform controlled surface passivation on the catalyst to form a layer of FeO protective film, which invisibly increases the time cost and risk factor. CN104785305B discloses a set of reduction and passivation integrated system, which greatly improves production efficiency, shortens production cycle, and improves the performance of the catalyst. Due to the use of a large amount of hydrogen, the heating rate must be strictly controlled and the water output must be continuously detected in this process. If the temperature rises too fast, the internals of the synthesis tower may be burned.

[0005] CN102329912A discloses a rapid reduction method for direct reduction of iron, which utilizes ammonium phosphate to react with soda lime to produce ammonia, and then generate hydrogen, and the hydrogen reduces ferric oxide, so that the reaction speed is increased and the production speed is accelerated. However, under the conditions of this technical solution, the concentration of hydrogen after decomposing ammonia is only about 25%, while the concentration of hydrogen in the conventional hydrogen reduction of iron oxide process needs to reach more than 60% to achieve the purpose of producing metallic iron, so the feasibility of this technical solution is worth considering. CN112921143A discloses a method for producing hot sponge iron based on direct reduction of iron with ammonia, and ammonia is introduced into a vertical furnace. Ammonia is partially decomposed into hydrogen and nitrogen under the catalysis of iron oxide, and the decomposed hydrogen and undecomposed ammonia react with iron-containing raw materials to generate hot sponge iron and water vapor; the reaction time is more than 3 hours, and a constant temperature of 890-910°C is maintained during the reaction.

[0006] Both of the above solutions are used in industrial iron smelting and need to be heated to 800°C or above. This high temperature is harmful to iron-based catalysts. It will cause particle growth and catalyst sintering, resulting in a reduction in active sites, which will affect the production efficiency of the catalyst in industrial applications. Summary of the invention

[0007] In view of the deficiencies in the prior art, the object of the present invention is to provide an ammonia reduction method and application thereof for catalytic decomposition of ammonia to produce hydrogen, which avoids the dangers of traditional hydrogen reduction and pre-reduction iron-based catalysts and reduces the risk of excessive water output during hydrogen reduction, has a shorter reduction time, a simple reduction process, and an ammonia conversion rate of greater than 99% at a reaction temperature of 550°C.

[0008] The present invention adopts the following technical solution:

[0009] The present invention provides a method for reducing an iron-based catalyst suitable for catalyzing ammonia decomposition reaction, comprising the following steps:

[0010] S1. Preliminary reduction of the iron-based catalyst under low-temperature ammonia atmosphere;

[0011] S2, raising the reduction temperature of the iron-based catalyst from a low temperature to a high temperature at a certain heating rate;

[0012] S3. The iron-based catalyst is deeply reduced under high-temperature ammonia atmosphere conditions, so that the iron-based catalyst can be reduced to a state with better ammonia decomposition reaction activity.

[0013] The low-temperature ammonia atmosphere condition in step S1 is to treat in a mixed atmosphere of ammonia and inert gas, the low-temperature reduction temperature is 400-510°C, the ammonia volume concentration is 20-50%, and the fixed bed reactor is heated to 400-510°C at a heating rate of 3-8°C / min.

[0014] The initial reduction time of the iron-based catalyst in step S1 is 1-5 hours.

[0015] Preferably, the initial reduction time of the iron-based catalyst in step S1 is 2-4 hours.

[0016] The heating rate from low temperature to high temperature in step S2 is 0.5-10°C / min, the proportion of inert gas is increased during the heating process, the volume concentration of ammonia is 10-30%, and the air velocity is 6000-30000h -1 , the heating time is 1-3h.

[0017] The high-temperature ammonia atmosphere condition in step S3 is to treat in a mixed atmosphere of ammonia and inert gas, the high-temperature reduction temperature is 530-570° C., and the ammonia volume concentration is 60-100%.

[0018] The high-temperature reduction time of the iron-based catalyst in step S3 is 2-6 hours.

[0019] The pressure during the reduction process of the iron-based catalyst is 0.1-1.3 MPa.

[0020] The space velocity of the iron-based catalyst reduction reaction is 200-20000h -1 .

[0021] The application of the iron-based catalyst reduced by the above method in the ammonia catalytic reduction reaction is as follows: the ammonia decomposition catalytic reaction is carried out in a fixed bed reactor, the iron-based catalyst is loaded in the fixed bed reactor, ammonia gas is introduced for decomposition reaction, the reaction pressure is 0.1-2MPa, and the reaction volume space velocity is 300-10000h -1 , the reaction temperature is 350-650℃.

[0022] The technical solution of the present invention has the following advantages:

[0023] A. The ammonia reduction method of the iron-based catalyst provided by the present invention avoids the dangers brought by traditional hydrogen reduction and pre-reduction iron-based catalysts and reduces the risk of excessive water output during hydrogen reduction. The reduction time is shorter and the reduction process is simple. The ammonia conversion rate of the reduced catalyst at a reaction temperature of 550°C is greater than 99%.

[0024] B. The process of the present invention is simple, and an iron-based catalyst ammonia reduction system is established, which greatly improves safety, shortens production cycle, and improves the performance of the catalyst. Under certain conditions, the ammonia reduction reaction can effectively directly reduce iron. During the direct reduction process, the gradually generated α-Fe can effectively catalyze the cracking of ammonia into hydrogen at high temperature, and the released hydrogen further promotes the reduction of ferrous oxide to iron. This autocatalytic reaction mechanism provides a way to further improve reaction efficiency and reduce fixed asset investment (such as equipment cost for hydrogen reduction, etc.) and operating expenses (such as equipment maintenance costs, etc.). DETAILED DESCRIPTION

[0025] The technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Embodiment 1:

[0027] This embodiment provides a method for reducing an iron-based catalyst suitable for catalyzing ammonia decomposition reaction, comprising the following steps:

[0028] S1. Weigh 1.4 g of catalyst (volume 0.5 ml) and mix with quartz sand and put into a fixed bed reactor. In an atmosphere of 30% ammonia volume concentration, heat the temperature from room temperature to 450°C at a rate of 5°C / min for initial reduction for 2 h.

[0029] S2. After the initial reduction is completed, the volume concentration of ammonia is reduced to 20%, and the temperature is raised to 550°C at a heating rate of 8°C / min;

[0030] S3. After the heating is completed, the ammonia volume concentration is adjusted to 80%, and further reduction is carried out at high temperature for 3 hours.

[0031] S4, after the reduction, at a volume space velocity of 5000h -1 The catalyst was evaluated at 500℃, 550℃ and 560℃ respectively, and the ammonia conversion rate could reach 96% and 99%.

[0032] Embodiment 2:

[0033] This embodiment provides a method for reducing an iron-based catalyst suitable for catalyzing ammonia decomposition reaction, comprising the following steps:

[0034] S1. Weigh 1.4 g of catalyst (volume 0.5 ml) and mix with quartz sand and load into a fixed bed reactor. In an atmosphere of 20% ammonia volume concentration, heat the temperature from room temperature to 400°C at a rate of 8°C / min for initial reduction for 4 hours.

[0035] S2. After the initial reduction is completed, the volume concentration of ammonia is reduced to 10%, and the temperature is raised to 530°C at a heating rate of 4°C / min;

[0036] S3, after the heating is completed, the ammonia volume concentration is adjusted to 60%, and further reduction is carried out at high temperature for 6 hours.

[0037] S4, after the reduction, at a volume space velocity of 5000h -1 The catalyst was evaluated at 570℃, 650℃ and 850℃ respectively, and the ammonia conversion rate could reach 99% and 99%.

[0038] Embodiment 3:

[0039] This embodiment provides a method for reducing an iron-based catalyst suitable for catalyzing ammonia decomposition reaction, comprising the following steps:

[0040] S1. Weigh 1.4 g of catalyst (volume 0.5 ml) and mix with quartz sand and put into a fixed bed reactor. In an atmosphere of 50% ammonia volume concentration, heat the temperature from room temperature to 510°C at a rate of 3°C / min for initial reduction for 5 h.

[0041] S2. After the initial reduction is completed, the volume concentration of ammonia is reduced to 30%, and the temperature is increased to 570°C at a rate of 0.5°C / min;

[0042] S3. After the heating is completed, the ammonia volume concentration is adjusted to 100%, and further reduction is carried out at high temperature for 2 hours.

[0043] S4, after the reduction, at a volume space velocity of 300h -1 The catalyst was evaluated at 500℃, 550℃ and 570℃ respectively, and the ammonia conversion rate could reach 95% and 99%.

[0044] Embodiment 4:

[0045] This embodiment provides a method for reducing an iron-based catalyst suitable for catalyzing ammonia decomposition reaction, comprising the following steps:

[0046] S1. Weigh 1.4 g of catalyst (volume 0.5 ml) and mix with quartz sand and load into a fixed bed reactor. In an atmosphere of 30% ammonia volume concentration, heat the temperature from room temperature to 450°C at a rate of 5°C / min for initial reduction for 1 h.

[0047] S2. After the initial reduction is completed, the volume concentration of ammonia is reduced to 20%, and the temperature is increased to 530°C at a heating rate of 10°C / min;

[0048] S3. After the heating is completed, the ammonia volume concentration is adjusted to 60%, and further reduction is carried out at high temperature for 3 hours.

[0049] S4, after the reduction, at a volume space velocity of 20000h -1 The catalyst was evaluated under 350℃, 350℃ and 450℃ conditions respectively, and the ammonia conversion rate could reach 95% and 96%.

[0050] The oxidized iron-based catalyst used in the present invention is prepared by a molten iron method, the preparation process conditions are simple, the raw materials are easily available, and it is conducive to large-scale production. At the same time, the content of the catalyst components can be optimized by adjusting the ratio of the raw materials, which is conducive to the formation and stability of the active phase.

[0051] In the reduction step of the present invention, in the first reduction step, iron oxide is reduced to ferrous oxide, and low-concentration ammonia can safely remove most of the moisture; in the second step, the proportion of inert gas is increased during the temperature rise process to purge the remaining moisture in the system; in the third step, the ferrous oxide has a small amount of water output during the reduction process, and the reduction risk is low, so high-concentration ammonia can be used to increase the reduction rate. Therefore, ammonia can be quickly reduced under high temperature conditions to shorten the reduction time. Compared with the 30h-45h reduction time of hydrogen, the reduction time of the present invention is only 6-10h, which greatly reduces the reduction energy consumption, reduces the reduction cost, and is more conducive to the application in industrial production.

[0052] The ammonia reduction method of the iron-based catalyst provided by the present invention avoids the dangers brought by traditional hydrogen reduction and pre-reduction type iron-based catalysts and reduces the risk of excessive water output during hydrogen reduction. The reduction time is shorter and the reduction process is simple. The ammonia conversion rate of the reduced catalyst at a reaction temperature of 550° C. is greater than 99%.

[0053] The process of the present invention is simple, and an iron-based catalyst ammonia reduction system is established, which greatly improves safety, shortens production cycle, and improves the performance of the catalyst. Under certain conditions, the ammonia reduction reaction can effectively directly reduce iron. During the direct reduction process, the gradually generated α-Fe can effectively catalyze the cracking of ammonia into hydrogen at high temperature, and the released hydrogen further promotes the reduction of ferrous oxide to iron. This autocatalytic reaction mechanism provides a way to further improve reaction efficiency and reduce fixed asset investment (such as equipment cost for hydrogen reduction, etc.) and operating expenses (such as equipment maintenance costs, etc.).

[0054] Any matters not described in the present invention are applicable to the prior art.

[0055] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. However, the obvious changes or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A method for reducing an iron-based catalyst suitable for catalytic ammonia decomposition reaction, characterized in that: The steps include: S1. Preliminary reduction of the iron-based catalyst under low-temperature ammonia atmosphere; S2, raising the reduction temperature of the iron-based catalyst from a low temperature to a high temperature at a certain heating rate; S3. The iron-based catalyst is deeply reduced under high-temperature ammonia atmosphere conditions to reduce the iron-based catalyst to an active state for ammonia decomposition reaction.

2. The method for reducing an iron-based catalyst suitable for catalytic ammonia decomposition reaction according to claim 1, characterized in that: The low-temperature ammonia atmosphere condition in step S1 is treatment in a mixed atmosphere of ammonia and inert gas, the low-temperature reduction temperature is 400-510° C., and the ammonia volume concentration is 20-50%.

3. The method for reducing an iron-based catalyst suitable for catalytic ammonia decomposition reaction according to claim 1, characterized in that: The initial reduction time of the iron-based catalyst in step S1 is 1-5 hours.

4. The method for reducing an iron-based catalyst suitable for catalytic ammonia decomposition reaction according to claim 3, characterized in that: The initial reduction time of the iron-based catalyst in step S1 is 2-4 hours.

5. The method for reducing an iron-based catalyst suitable for catalytic ammonia decomposition reaction according to claim 1, characterized in that: The heating rate from low temperature to high temperature in step S2 is 0.5-10°C / min, the proportion of inert gas is increased during the heating process, the volume concentration of ammonia is 10-30%, and the air velocity is 6000-30000h -1 , the heating time is 1-3h.

6. The method for reducing an iron-based catalyst suitable for catalytic ammonia decomposition reaction according to claim 1, characterized in that: The high-temperature ammonia atmosphere condition in step S3 is to treat in a mixed atmosphere of ammonia and inert gas, the high-temperature reduction temperature is 530-570° C., and the ammonia volume concentration is 60-100%.

7. The method for reducing an iron-based catalyst suitable for catalytic ammonia decomposition reaction according to claim 1, characterized in that: The high-temperature reduction time of the iron-based catalyst in step S3 is 2-6 hours.

8. The method for reducing an iron-based catalyst suitable for catalytic ammonia decomposition reaction according to claim 1, characterized in that: The pressure during the reduction process of the iron-based catalyst is 0.1-1.3 MPa.

9. The method for reducing an iron-based catalyst suitable for catalytic ammonia decomposition reaction according to claim 1, characterized in that: The space velocity of the iron-based catalyst reduction reaction is 200-20000h -1 .

10. Use of the iron-based catalyst reduced by the method according to any one of claims 1 to 9, characterized in that: The ammonia decomposition catalytic reaction is carried out in a fixed bed reactor. The iron-based catalyst is loaded in the fixed bed reactor, and ammonia gas is introduced to carry out the decomposition reaction. The reaction pressure is 0.1-2MPa, and the reaction volume space velocity is 300-10000h -1 , the reaction temperature is 350-650℃.