Method for producing pre-reduction type ammonia synthesis catalyst by using pure hydrogen reduction

Abstract

The invention relates to the technical field of pre-reduction type catalyst production, and discloses a method for producing a pre-reduction type ammonia synthesis catalyst by using pure hydrogen reduction, which comprises the following steps: filling an oxidation state ammonia synthesis catalyst into a reduction tower, and introducing reducing gas for reduction; the reduction process comprises the following stages: a heating stage, an initial reduction stage, a main reduction stage and a later reduction stage; after the reduction process is finished, shielding gas is introduced to replace hydrogen, the temperature of the catalyst is reduced to 50 DEG C or below, then the passivation process is performed, and the pre-reduction type ammonia synthesis catalyst is obtained after the passivation process is finished. According to the pre-reduction type ammonia synthesis catalyst produced through the method, reduction and passivation of the catalyst are sufficient, the reduction quality of the catalyst is stable, the production process is efficient, energy-saving and environmentally friendly, electric energy is saved by 8% or above during production of the pre-reduction type ammonia synthesis catalyst, raw material reducing gas is saved by 25% or above, waste water discharge is avoided, and almost no environmental protection cost exists.

Description

Technical Field

[0001] The invention relates to the technical field of pre-reduction catalyst production, in particular to a method for producing a pre-reduction ammonia synthesis catalyst by reducing with pure hydrogen. Background Art

[0002] In order to shorten the start-up cycle, reduce the start-up costs of enterprises and increase the economic benefits of enterprises, the synthetic ammonia industry mostly uses pre-reduction ammonia synthesis catalysts.

[0003] The temperature reduction of ammonia synthesis catalysts basically uses a hydrogen-nitrogen mixture. The existing problems are: nitrogen is heavier than hydrogen, the system resistance is large during the reduction process, the circulating machine current is large, and the power consumption is high; as the reduction proceeds, the hydrogen and nitrogen in the system generate ammonia and form dilute ammonia water with the discharged water, which needs to be treated to meet the emission standards, thereby increasing the cost of environmental protection treatment; and as the hydrogen in the reducing gas is consumed, fresh reducing gas needs to be added and a large amount of relaxation gas needs to be discharged, increasing the consumption of raw reducing gas.

[0004] In addition, the prior art also has technical problems such as long reduction passivation time of pre-reduction ammonia synthesis catalyst, large reduction gas consumption, large system resistance, resulting in high catalyst production and processing costs and high energy consumption.

[0005] Therefore, there is an urgent need for a method for producing a pre-reduced ammonia synthesis catalyst using pure hydrogen reduction to solve the above technical problems. Summary of the invention

[0006] The purpose of the present invention is to provide a method for producing a pre-reduction ammonia synthesis catalyst by reducing with pure hydrogen in view of the deficiencies in the prior art. By adopting pure hydrogen as reducing gas, the system resistance is reduced and energy consumption is saved. No ammonia is generated in the system, and the discharged water is clean water, which does not need to be treated, thereby reducing environmental protection costs. Only a small amount of reducing gas needs to be added, and there is almost no relaxation gas, thereby reducing the consumption of raw hydrogen.

[0007] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0008] A method for producing a pre-reduction type ammonia synthesis catalyst by pure hydrogen reduction comprises the following steps:

[0009] The oxidized ammonia synthesis catalyst is loaded into the reactor and reduced by introducing reducing gas;

[0010] The restoration process includes the following stages:

[0011] During the heating period, the temperature rises to 330-350°C at a rate of 30-50°C / h;

[0012] In the initial stage of reduction, the temperature rises to 370-380°C at a rate of 5-15°C / h;

[0013] During the main reduction period, the temperature is raised to 450-480°C at a rate of 0-5°C / h;

[0014] In the later stage of reduction, the temperature is raised to 480-500°C at a rate of 0-2°C / h and kept at this temperature for 5-12h;

[0015] After the reduction process is completed, protective gas is introduced to replace hydrogen, and the catalyst temperature is reduced to below 50° C., followed by a passivation process. After the passivation process is completed, a pre-reduced ammonia synthesis catalyst is obtained.

[0016] The reducing gas is pure hydrogen.

[0017] Preferably, the particle size of the oxidized ammonia synthesis catalyst is 1 to 30 mm.

[0018] More specifically, the oxidized ammonia synthesis catalyst is prepared for industrial production.

[0019] Preferably, the reduction pressure in the reduction process is 0.3-0.8 MPa, and the reduction space velocity is 2000-10000 h -1 .

[0020] Furthermore, the reduction pressure in the reduction process is preferably 0.5-0.8 MPa, and the reduction space velocity is preferably 3000-6000 h -1 .

[0021] Preferably, the pure hydrogen is hydrogen gas having a hydrogen content of not less than 99.99% (volume percentage).

[0022] Preferably, the water vapor concentration during the heating period is controlled to be no higher than 2.0 g / m 3 The water vapor concentration in the initial reduction period and the main reduction period is controlled to be no higher than 2.5g / m 3 The water vapor concentration is controlled to be no higher than 0.5 g / m 3 .

[0023] Furthermore, the water vapor concentration during the heating period is preferably controlled to be no higher than 1.5 g / m 3 The water vapor concentration in the initial reduction period and the main reduction period is preferably controlled to be no higher than 2.0 g / m 3 In the later stage of reduction, the water vapor concentration is preferably controlled to be no higher than 0.3 g / m 3 .

[0024] Preferably, when the water vapor concentration in the heating period, the initial reduction period, the main reduction period, and the late reduction period is higher than a limit value, it is necessary to reduce the heating rate of this stage or suspend the heating.

[0025] Preferably, the protective gas is at least one of helium, argon, nitrogen and neon.

[0026] Preferably, the passivation process comprises the following steps:

[0027] When the catalyst temperature drops below 50°C and the hydrogen has been completely replaced by the protective gas, add air and control the air velocity at 300-2000h -1 , gradually increase the oxygen content in the protective gas, the catalyst bed temperature does not exceed 60°C during the passivation process, and the final oxygen content is controlled to be 20-21.5% (volume percentage). When there is no temperature rise for 0.5-6 hours, the passivation process is completed.

[0028] Furthermore, during the passivation process, the controlled air velocity is preferably 500 to 1000 h -1 .

[0029] Specifically, the oxygen content is controlled at 0.05-0.2% in the early stage of passivation to prevent excessive temperature rise. The oxygen content is slowly increased to more than 20% in the middle and late stages of passivation, and the catalyst bed temperature is controlled below 60°C. When the final oxygen content is 20-21.5%, and there is no temperature rise for 0.5-6 hours, the passivation process is completed.

[0030] Preferably, the catalyst reduction and catalyst passivation processes are carried out in the same reactor or in different reactors connected in parallel, and the reactor is a fixed bed reactor or a reduction tower.

[0031] Specifically, the same reactor or different reactors connected in parallel means that the method can use one reactor to perform reduction and then passivation; or multiple reactors can be connected in parallel to perform reduction and passivation together.

[0032] The present invention places an oxidized ammonia synthesis catalyst in a reduction tower, uses pure hydrogen as a reducing gas for temperature reduction, stably controls the system reduction temperature, pressure and water vapor concentration, and obtains a product after passivation after reduction. The catalyst is fully reduced and passivated, the catalyst reduction quality is good, and the production process is efficient, energy-saving and environmentally friendly.

[0033] Beneficial effects:

[0034] The method of producing a pre-reduction type ammonia synthesis catalyst by pure hydrogen reduction of the present invention follows the purpose of green chemistry and solves the drawbacks of high energy consumption and high cost of traditional reduction methods. The pre-reduction type ammonia synthesis catalyst produced by the present invention has sufficient reduction and passivation of the catalyst, stable catalyst reduction quality, high efficiency, energy saving and environmental protection in the production process, and the production of the pre-reduction type ammonia synthesis catalyst saves more than 8% of electric energy and more than 25% of raw material reduction gas, has no wastewater discharge and almost no environmental protection cost. DETAILED DESCRIPTION

[0035] The present invention is further described below with reference to specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

[0036] All raw materials of the present invention are not particularly limited in their sources and can be purchased from the market or prepared according to conventional methods well known to those skilled in the art.

[0037] There is no particular limitation on the purity of all raw materials in the present invention, and the present invention preferably adopts the conventional purity used in the art.

[0038] The devices used in the present invention are not particularly limited and can be any of the commonly used devices in the art.

[0039] Comparative Example 1

[0040] The industrial production of oxidized ammonia synthesis catalyst with a particle size of 1.5 to 3 mm 7m 3 Load into the reduction tower, introduce heated hydrogen-nitrogen mixed gas containing 75% hydrogen, adjust the system pressure to 0.6MPa and the air velocity to 3000h -1 , the reducing gas brings heat into the catalyst bed.

[0041] During the heating period, the heating rate was controlled at 35-45℃ / h and the water vapor concentration was controlled not to exceed 1.5g / m 3 When the water vapor concentration is high, reduce the heating rate or stop heating. When the catalyst layer temperature rises to 330-350℃, it enters the initial stage of reduction. At this time, the water vapor concentration is high, adjust the heating rate to 5-15℃ / h, and control the water vapor concentration not higher than 2.0g / m 3 When the catalyst layer temperature rises to 370-380℃, it enters the main reduction period. As the reduction proceeds, the hydrogen content in the circulating gas in the system decreases, and fresh reducing gas needs to be added while the relaxation gas is discharged to maintain the hydrogen content and pressure in the system. The heating rate is adjusted to 0-5℃ / h, and the water vapor concentration is controlled not to be higher than 2.0g / m 3 , continue to heat up to 450-480℃ to enter the late stage of reduction; control the water vapor concentration not higher than 0.3g / m 3 , adjust the heating rate to 0-2℃ / h, heat to 480-500℃, keep warm for 8h, and measure the water vapor concentration to be less than 0.1g / m 3 The restoration is complete.

[0042] After the reduction process is completed, nitrogen is introduced to replace the hydrogen in the exhaust system, and the temperature is reduced to below 50°C at a cooling rate of 35-45°C / h, and the pressure is reduced to normal pressure. The air velocity is controlled at 1000h -1 , gradually add air into the system, control the oxygen content at 0.05-0.2% in the early stage of passivation to prevent excessive temperature rise, slowly increase the oxygen content to more than 20% in the middle and late stages of passivation, and control the catalyst bed temperature below 60°C. When the final oxygen content is 20-21.5% and there is no temperature rise for 3 hours, the passivation process is completed and a pre-reduction ammonia synthesis catalyst is obtained.

[0043] The reduction process of this comparative example 1 consumes a total of 49,000 kWh of electricity and 11,000 Nm of hydrogen-nitrogen mixed gas containing 75% hydrogen. 3 In the middle and late stages of reduction, the hydrogen-nitrogen mixture will partially react on the reduced catalyst at high temperature to generate ammonia, which will form dilute ammonia water with the discharged water. About 6 tons of dilute ammonia water will be discharged as wastewater, which needs to be treated to meet the discharge standards and has certain environmental protection treatment costs.

[0044] Comparative Example 2

[0045] The industrial production of oxidized ammonia synthesis catalyst with a particle size of 3.3 to 4.7 mm 7m 3 Load into the reduction tower, introduce heated hydrogen-nitrogen mixed gas containing 75% hydrogen, adjust the system pressure to 0.7MPa and the air velocity to 5000h -1 , the reducing gas brings heat into the catalyst bed.

[0046] The catalyst temperature reduction process and passivation process are the same as those in Comparative Example 1, except that the protective gas is replaced by argon.

[0047] The reduction process of this comparative example 2 consumes a total of 45,000 kWh of electricity and 9,500 Nm of hydrogen-nitrogen mixed gas containing 75% hydrogen. 3 In the middle and late stages of reduction, the hydrogen-nitrogen mixture will partially react on the reduced catalyst at high temperature to generate ammonia, which will form dilute ammonia water with the discharged water. About 5.4 tons of dilute ammonia water will be discharged as wastewater, which needs to be treated to meet the discharge standards and has certain environmental protection treatment costs.

[0048] Example 1

[0049] A method for producing a pre-reduction type ammonia synthesis catalyst by pure hydrogen reduction comprises the following steps:

[0050] The industrial production of oxidized ammonia synthesis catalyst with a particle size of 1.5 to 3 mm 7m 3 Load it into the reduction tower, introduce heated pure hydrogen (hydrogen content not less than 99.99%), adjust the system pressure to 0.6MPa and the air velocity to 3000h -1 , the reducing gas brings heat into the catalyst bed.

[0051] During the heating period, the heating rate was controlled at 35-45℃ / h and the water vapor concentration was controlled not to exceed 1.5g / m 3 When the water vapor concentration is high, reduce the heating rate or stop heating. When the catalyst layer temperature rises to 330-350℃, it enters the initial stage of reduction. At this time, the water vapor concentration is high, adjust the heating rate to 5-15℃ / h, and control the water vapor concentration not higher than 2.0g / m 3When the catalyst layer temperature rises to 370-380℃, it enters the main reduction period. As the reduction proceeds, the hydrogen in the circulating gas in the system is consumed, and fresh pure hydrogen needs to be added while a small amount of relaxation gas is discharged to maintain the pressure in the system. The heating rate is adjusted to 0-5℃ / h, and the water vapor concentration is controlled not to be higher than 2.0g / m 3 , continue to heat up to 450-480℃ to enter the late stage of reduction; control the water vapor concentration not higher than 0.3g / m 3 , adjust the heating rate to 0-2℃ / h, heat to 480-500℃, keep warm for 8h, and measure the water vapor concentration to be less than 0.1g / m 3 The restoration is complete.

[0052] After the reduction process is completed, nitrogen is introduced to replace the hydrogen in the exhaust system, and the temperature is reduced to below 50°C at a cooling rate of 35-45°C / h, and the pressure is reduced to normal pressure. The air velocity is controlled at 1000h -1 , gradually add air into the system, control the oxygen content at 0.05-0.2% in the early stage of passivation to prevent excessive temperature rise, slowly increase the oxygen content to more than 20% in the middle and late stages of passivation, and control the catalyst bed temperature below 60°C. When the final oxygen content is 20-21.5% and there is no temperature rise for 3 hours, the passivation process is completed and a pre-reduction ammonia synthesis catalyst is obtained.

[0053] Compared with comparative example 1, the reduction process of this embodiment 1 consumes a total of 45,000 kWh of electricity, saving 8.16%, and consumes 8,200 Nm of pure hydrogen. 3 , saving 25.45% of the raw reducing gas, and no ammonia is generated during the reduction process, and about 5.5t of water is discharged, which is clean water and does not require treatment.

[0054] Example 2

[0055] A method for producing a pre-reduction type ammonia synthesis catalyst by pure hydrogen reduction comprises the following steps:

[0056] The industrial production of oxidized ammonia synthesis catalyst with a particle size of 3.3 to 4.7 mm 7m 3 Load it into the reduction tower, introduce heated pure hydrogen, adjust the system pressure to 0.7MPa and the air velocity to 5000h -1 , the reducing gas brings heat into the catalyst bed.

[0057] The catalyst temperature reduction process and passivation process are the same as in Example 1, except that the protective gas is replaced by argon.

[0058] Compared with comparative example 2, the reduction process of this embodiment 2 consumes a total of 41,000 kWh of electricity, saving 8.89%, and consumes 7,000 Nm of pure hydrogen. 3 , saving 26.32% of the raw reducing gas, and no ammonia is generated during the reduction process, and about 4.9 tons of water is discharged, which is clean water and does not require treatment.

[0059] The technical solution of the present invention is not limited to the above-mentioned specific embodiments. All technical variations made according to the technical solution of the present invention fall within the protection scope of the present invention.

Claims

1. A method for producing a pre-reduction type ammonia synthesis catalyst by pure hydrogen reduction, characterized in that: The following steps are involved: The oxidized ammonia synthesis catalyst is loaded into the reactor and reduced by introducing reducing gas; The reduction process The following phases are included: During the heating period, the temperature rises to 330-350°C at a rate of 30-50°C / h; In the initial stage of reduction, the temperature rises to 370-380°C at a rate of 5-15°C / h; During the main reduction period, the temperature is raised to 450-480°C at a rate of 0-5°C / h; In the later stage of reduction, the temperature is raised to 480-500°C at a rate of 0-2°C / h and kept at this temperature for 5-12h; After the reduction process is completed, protective gas is introduced to replace hydrogen, and the catalyst temperature is reduced to below 50° C., followed by a passivation process. After the passivation process is completed, a pre-reduced ammonia synthesis catalyst is obtained; The reducing gas is pure hydrogen.

2. A method for producing a pre-reduction type ammonia synthesis catalyst by pure hydrogen reduction as claimed in claim 1, characterized in that: The particle size of the oxidized ammonia synthesis catalyst is 1 to 30 mm.

3. A method for producing a pre-reduction type ammonia synthesis catalyst by pure hydrogen reduction as claimed in claim 1, characterized in that: The reduction pressure in the reduction process is 0.3-0.8 MPa, and the reduction space velocity is 2000-10000 h -1 .

4. A method for producing a pre-reduction type ammonia synthesis catalyst by pure hydrogen reduction as claimed in claim 1, characterized in that: The pure hydrogen is hydrogen gas with a hydrogen content of not less than 99.99%.

5. The method for producing a pre-reduction type ammonia synthesis catalyst by pure hydrogen reduction as claimed in claim 1, characterized in that: The water vapor concentration during the heating period is controlled to be no higher than 2.0 g / m 3 The water vapor concentration in the initial reduction period and the main reduction period is controlled to be no higher than 2.5g / m 3 The water vapor concentration is controlled to be no higher than 0.5 g / m 3 .

6. A method for producing a pre-reduction type ammonia synthesis catalyst by pure hydrogen reduction as claimed in claim 5, characterized in that: When the water vapor concentration in the heating period, initial reduction period, main reduction period, and late reduction period is higher than the limit value, it is necessary to reduce the heating rate of this stage or suspend the heating.

7. A method for producing a pre-reduction type ammonia synthesis catalyst by pure hydrogen reduction as claimed in claim 1, characterized in that: The protective gas is at least one of helium, argon, nitrogen and neon.

8. The method for producing a pre-reduction type ammonia synthesis catalyst by pure hydrogen reduction as claimed in claim 1, characterized in that: The passivation process comprises the following steps: When the catalyst temperature drops below 50°C and the hydrogen has been completely replaced by the protective gas, add air and control the air velocity at 300-2000h -1 , gradually increase the oxygen content in the protective gas, the catalyst bed temperature does not exceed 60°C during the passivation process, and the final oxygen content is controlled to be 20-21.5% and maintained for 0.5-6 hours without temperature rise, the passivation process is completed.

9. The method for producing a pre-reduction type ammonia synthesis catalyst by pure hydrogen reduction as claimed in claim 1, characterized in that: The catalyst reduction and catalyst passivation processes are carried out in the same reactor or in different reactors connected in parallel, and the reactor is a fixed bed reactor or a reduction tower.