Pre-reduced methanation catalyst, method for preparing the same and use thereof

Abstract

The present application relates to the technical field of catalyst preparation, and discloses a pre-reduction methanation catalyst and a preparation method and application thereof.The catalyst comprises Ni, alumina and an additive, the additive comprises alkaline earth metal oxide and rare earth metal oxide, the content of nickel is 20-45% by weight based on the total amount of the catalyst in terms of oxide, the number of active centers of the catalyst after re-reduction treatment is 0.01-0.2 mmol of hydrogen gas per gram of catalyst, the re-reduction treatment conditions comprise that the temperature is 300 DEG C, the time is 2 hours, the re-reduction atmosphere is an atmosphere containing hydrogen gas and argon with a hydrogen gas concentration of 10% by volume, and the gas volume ratio is 15000; the catalyst is hollow and has a special shape, and the particle size is 7-16 mm.The catalyst has good activity, stability and good reduction degree, and has good reactivation performance, the reduction time is short in the method, and the reduction passivation efficiency is high.

Description

Technical Field

[0001] This invention relates to the technical field of catalyst preparation, specifically to a pre-reduction methanation catalyst, its preparation method, and its application. Background Technology

[0002] Natural gas is a clean, easily transportable, and safe energy source. With the acceleration of my country's industrialization and urbanization, as well as the implementation of energy conservation and emission reduction policies, the consumption of clean energy sources such as natural gas will increase significantly. Syngas can be obtained through coal or biomass gasification, and then synthesized into synthetic natural gas through methanation, which can increase the supply of natural gas.

[0003] The chemical reaction equation for the syngas methanation reaction is as follows:

[0004] CO + 3H₂ = CH₄ + H₂O ΔH 298 = -206.1 kJ / mol

[0005] CO2 + 4H2 = CH4 + 2H2O ΔH 298 = -165.0 kJ / mol

[0006] This demonstrates that methanation is a strongly exothermic reaction; therefore, rapidly and effectively removing the heat of reaction is a significant challenge. Furthermore, due to the strongly exothermic nature of the reaction, the catalyst bed can experience temperature runaway due to insufficient heat exchange, testing the catalyst's thermal stability. Additionally, the high CO concentration in the reaction system means that CO disproportionation at low temperatures can lead to catalyst deactivation through coking, and even reactor blockage. Therefore, it is necessary to improve the catalyst's activity, resistance to coking, and thermal stability.

[0007] Developing high-performance methanation catalysts and reaction processes for synthetic natural gas with independent intellectual property rights in my country is a crucial way to optimize the energy structure and alleviate the shortage of natural gas supply in my country. Currently, there are many patented technologies for methanation catalysts, but the performance of existing catalysts is not ideal, and their thermal stability is generally low. They can only operate at relatively low temperatures, which is not conducive to the recovery and utilization of reaction heat. Existing methanation catalyst systems still need further improvement, especially the stability and activity of methanation catalysts above 600℃, which require further optimization.

[0008] Catalyst reduction can be performed via external pre-reduction or internal reduction. Generally, methanation catalysts have high reduction temperatures, requiring specialized reduction equipment, making catalyst reduction within the reactor unit difficult. External pre-reduction technology offers numerous advantages, including improved reductant utilization, reduced reductant usage, lower start-up costs, shorter start-up cycles, and ultimately increased economic benefits for the enterprise. The pre-reduced catalyst, after being loaded into the reactor, undergoes low-temperature reactivation before use. For the same catalyst, different reduction and passivation treatments have varying effects on its reaction activity and selectivity. Furthermore, different reduction and passivation treatments are typically employed for different catalysts to achieve optimal activity and selectivity.

[0009] The drawbacks of existing technologies include long reduction times and high hydrogen consumption, resulting in long catalyst processing cycles and high costs, which affect the efficiency of catalyst reduction and passivation. Known passivation methods require long passivation times and produce uneven passivation of the resulting catalyst. Therefore, the industry urgently needs a new pre-reduction methanation catalyst. Summary of the Invention

[0010] The purpose of this invention is to overcome the problems of low reactivity and poor stability of existing syngas methanation catalysts, as well as long pre-reduction time and low reduction-passivation efficiency. This invention provides a pre-reduction high-temperature methanation catalyst, its preparation method, and its application. The catalyst has good activity, stability, and good reducibility, and good reactivation performance. The method has a short reduction time and high reduction-passivation efficiency.

[0011] To achieve the above objectives, the first aspect of the present invention provides a pre-reduction methanation catalyst, wherein the catalyst comprises Ni, alumina, and an additive, the additive comprising alkaline earth metal oxides and rare earth metal oxides; and the content of nickel, based on the total amount of catalyst and calculated as oxides, is 20-45% by weight.

[0012] The catalyst, after re-reduction treatment, has an active center number of 0.01-0.2 mmol hydrogen / g catalyst. The re-reduction treatment conditions include: a temperature of 300℃, a time of 2 hours, and a re-reduction atmosphere containing hydrogen and argon with a hydrogen concentration of 10% by volume, and a gas-to-catalyst volume ratio of 15000. The catalyst is hollow and irregular in shape, with a particle size of 7-16 mm.

[0013] A second aspect of the present invention provides a method for preparing a pre-reduced methanation catalyst, wherein the method comprises:

[0014] (1) Preparation of oxidized catalysts by co-precipitation method;

[0015] The coprecipitation method includes: coprecipitating a water-soluble nickel source, an alumina precursor, and a water-soluble additive in the presence of a precipitant; aging, washing, and optionally drying and / or calcining the resulting reaction mixture; and finally shaping to obtain an oxidized catalyst; wherein the amounts of the water-soluble nickel source, the alumina precursor, and the optional water-soluble additive are such that, based on the total amount of catalyst, the nickel content in the prepared catalyst, calculated as oxides, is 20-45% by weight; the additives include alkaline earth metal oxides and rare earth metal oxides.

[0016] (2) The molded product is subjected to reduction treatment and passivation treatment in sequence; the reduction includes: the reduction treatment is carried out in the presence of hydrogen gas, S1, heating to 400-550℃ at a heating rate of 60-150℃ / hour and holding for 0.5-8 hours; S2, heating to 560-700℃ at a heating rate of 50-120℃ / hour and holding for 0.3-8 hours;

[0017] Once the temperature of the catalyst obtained from the S2 reduction drops below 150°C, the catalyst obtained from the S2 reduction is passivated. The passivation includes continuously introducing oxygen-containing gas at a temperature below 60°C, controlling the passivation temperature to be no higher than 180°C; wherein, the oxygen concentration of the oxygen-containing gas continuously increases.

[0018] The third aspect of the present invention provides a pre-reduced methanation catalyst prepared by the preparation method described in the second aspect.

[0019] The fourth aspect of this invention provides the application of the pre-reduced methanation catalyst described in the first or third aspect in the complete methanation of syngas to produce natural gas.

[0020] The catalyst provided by this invention can improve the dispersion and loading of active metals and enhance the catalyst's reactivity and stability. The resulting catalyst exhibits excellent high-temperature stability and anti-coking properties, enabling long-term continuous and stable operation without deactivation, fully meeting the performance requirements for catalysts in the complete methanation of syngas. The pre-reduction catalyst of this invention has even better performance.

[0021] The inventors of this invention discovered that in the prior art, nickel-aluminum catalysts used in high-temperature and exothermic reactions often undergo high-temperature calcination during the preparation of the oxidized catalyst to improve high-temperature stability, better disperse the active metal, and reduce metal aggregation under high-temperature conditions. This results in a high content of nickel-aluminum spinel in the catalyst. Since nickel-aluminum spinel is difficult to reduce, the reduction step requires a high reduction temperature and a long reduction time, leading to high hydrogen consumption and low reduction efficiency. However, excessively long reduction times and / or excessively high reduction temperatures can easily cause metal grain growth, affecting the number of active sites. Therefore, to obtain catalysts with a high number of active sites, there is an urgent need for a method that can better reduce the metal components in the catalyst at lower temperatures and in shorter time periods. Based on this, the inventors completed this invention.

[0022] The preparation method provided by this invention, through the specific reduction process described above combined with a specific passivation process, works synergistically to enable rapid and effective reduction of the metal components in the catalyst at lower temperatures and in shorter time periods. Combined with subsequent appropriate passivation, this improves the performance of the resulting pre-reduced catalyst, resulting in high reduction and passivation efficiency. The obtained pre-reduced catalyst has numerous active sites and can be restored to a catalyst with a high number of active sites at a relatively low re-reduction temperature before application. Furthermore, the preparation method of this invention has low cost and can be applied on a large scale industrially. Detailed Implementation

[0023] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] In this invention, it can be understood that the gas-catalyst ratio refers to the ratio of the volume of gas passing through the catalyst bed to the volume of the catalyst per hour. In the reduction process (or re-reduction process), the gas in the gas-catalyst ratio refers to the reducing gas (i.e., hydrogen-containing gas), and in the passivation process, the gas in the gas-catalyst ratio refers to the passivation gas (i.e., oxygen-containing passivation gas, also known as oxygen-containing gas).

[0025] In this invention, it is understood that the reduction of the catalyst after passivation is called "re-reduction", and the reduction before passivation is called "reduction".

[0026] In this invention, it is understood that the number of active centers was obtained by H2 temperature-programmed desorption (H2-TPD) testing on an Autochem 2950 fully automated high-pressure chemical adsorption instrument manufactured by Micromeritics, USA. The testing method was as follows: 0.2000 g of a 40-60 mesh sample was weighed, and re-activation was first performed under the following conditions: a H2-Ar mixture with a hydrogen content of 10% by volume, a flow rate of 50 mL / min, and a heating rate of 10 °C / min to 300 °C for 2 h. The catalyst after re-reduction was cooled in a H2-Ar mixture with a hydrogen content of 10% by volume until the temperature dropped to 55 °C, then purged with Ar gas at a flow rate of 20 mL / min until the baseline stabilized, and then the H2-TPD experiment was performed. The experimental conditions and procedures for H2-TPD are as follows: the carrier gas is Ar, the carrier gas flow rate is 20 mL / min, the heating rate is 10℃ / min, the final temperature is 400℃, the signal is detected by a thermal conductivity detector (TCD), and the TPD curve is obtained.

[0027] The first aspect of the present invention provides a pre-reduced methanation catalyst, wherein the catalyst comprises Ni, alumina and an additive, the additive comprising alkaline earth metal oxides and rare earth metal oxides; and the content of nickel is 20-45% by weight based on the total amount of catalyst and calculated as oxides.

[0028] The catalyst, after re-reduction treatment, has an active center number of 0.01-0.2 mmol hydrogen / g catalyst. The re-reduction treatment conditions include: a temperature of 300℃, a time of 2 hours, and a re-reduction atmosphere containing hydrogen and argon with a hydrogen concentration of 10% by volume, and a gas-to-catalyst volume ratio of 15000. The catalyst is hollow and irregular in shape, with a particle size of 7-16 mm.

[0029] In this invention, it is understood that the hollow irregular shape refers to an irregular catalyst with a porous structure. For example, when the catalyst is cylindrical, there are pores running through it along the axial direction of the cylinder, that is, the catalyst is a hollow cylinder. In this invention, the specific location of the pores is not specifically limited.

[0030] In this invention, the particle size refers to the maximum straight-line distance between any two different points on the catalyst particle; for example, when the catalyst is a spherical particle, the particle size refers to its diameter.

[0031] In a preferred embodiment, the nickel content is 25-40% by weight, based on the total amount of catalyst and calculated as oxides.

[0032] In a preferred embodiment, the catalyst, after re-reduction treatment, has an active center number of 0.012-0.17 mmol hydrogen / g catalyst, for example, 0.012, 0.014, 0.016, 0.018, 0.02, 0.022, 0.024, 0.026, 0.028, 0.03, 0.032, 0.034, 0.036, 0.038, 0.04, 0.042, 0.044, 0.046, 0.048, 0.05, 0 0.052, 0.054, 0.056, 0.06, 0.062, 0.064, 0.066, 0.068, 0.7, 0.072, 0.074, 0.076, 0.078, 0.8, 0.082, 0.084, 0.086, 0.088, 0.9, 0.092, 0.094, 0.096, 0.1, 0.12, 0.14, 0.16, 0.17 mmol hydrogen / g catalyst, and any range of values ​​consisting of any two of these values.

[0033] In a preferred embodiment, the catalyst is characterized by TPR (Transient Reduction Profile). In the TPR curve, the temperature corresponding to the peak of the low-temperature reduction peak with the largest area is 200-360℃, more preferably 210-350℃. The temperature corresponding to the peak of the low-temperature reduction peak with the largest area in the TPR curve can be used as an indicator to evaluate the regenerability of the passivated catalyst. The lower the temperature corresponding to the peak of the low-temperature reduction peak with the largest area, the easier the catalyst is to regenerate. The pre-reduced syngas complete methanation catalyst provided by this invention has good regenerability; its activity can be restored by re-reduction under relatively low re-reduction treatment conditions, and it has multiple active sites.

[0034] In this invention, the TPR (temperature-programmed reduction) characterization was performed using an Autochem 2950 fully automated high-pressure chemical adsorption instrument manufactured by Micromeritics, USA. The test conditions were as follows: 0.20 g of sample was first heated to 120 °C for dehydration treatment for 1 hour under an Ar gas flow of 50 mL / min at a heating rate of 10 °C / min. After the temperature dropped to 50 °C, the TPR experiment was performed. The TPR experimental conditions and program were as follows: the reducing gas was a H2-Ar mixture with a hydrogen content of 10% by volume, the reducing gas flow rate was 50 mL / min, and the temperature was increased to 900 °C at a heating rate of 10 °C / min. During the above heating process, the signal was detected by a thermal conductivity detector (TCD) to obtain the TPR spectrum curve. The temperature corresponding to the peak value of the low-temperature reduction peak with the largest area in the TPR spectrum curve was used as an indicator to evaluate the regenerability of the passivated catalyst. The lower the temperature corresponding to the peak value of the low-temperature reduction peak with the largest area, the easier the catalyst is to regenerate.

[0035] According to the present invention, preferably, the degree of reduction of the pre-reduced catalyst is 50-95% as characterized by TPR. The pre-reduced catalyst provided by the present invention has a suitable degree of reduction and higher activity.

[0036] In this invention, the method for testing the degree of reduction is as follows: First, the TPR spectrum curve of the pre-reduced catalyst is tested; then, 0.2g of the pre-reduced catalyst is calcined in air at 450°C for 2 hours to obtain the oxidized catalyst. The TPR spectrum curve of the oxidized catalyst is tested according to the TPR testing method described in the first aspect, and the degree of reduction of the pre-reduced catalyst is calculated. Wherein, the degree of reduction = (TPR peak area of ​​the oxidized catalyst under direct reduction - peak area of ​​the pre-reduced catalyst under high temperature unreduced state) / TPR peak area of ​​the oxidized catalyst under direct reduction * 100%.

[0037] In a preferred embodiment, the catalyst contains at least one pore with a diameter greater than 0.5 mm, preferably 0.5-2 mm. It is understood that in this invention, "pore" refers to the pore structure of the aforementioned hollow irregular structure.

[0038] The pre-reduction methanation catalyst provided by this invention has the advantages of multiple active centers and good regeneration performance. When used in the complete methanation process of syngas, it exhibits high catalytic activity and good stability.

[0039] In a preferred embodiment, the alumina is γ-alumina.

[0040] In a preferred embodiment, the alkaline earth metal oxide is selected from at least one of BeO, MgO, CaO, CsO, and BaO.

[0041] In a preferred embodiment, the rare earth metal oxide is selected from at least one of Y2O3, La2O3, CeO2, Pr2O3 and Sm2O3.

[0042] In a preferred embodiment, based on the total amount of catalyst, the content of the alkaline earth metal oxide is 1-13 wt%, the content of the rare earth metal oxide is 1-10 wt%, and the content of the alumina is 40-75 wt%; more preferably, based on the total amount of catalyst, the content of the alkaline earth metal oxide is 4-13 wt%, the content of the rare earth metal oxide is 2-9 wt%, and the content of the alumina is 44-70 wt%. The advantage of this preferred embodiment is good catalyst stability.

[0043] A second aspect of the present invention provides a method for preparing a pre-reduced methanation catalyst, wherein the method comprises:

[0044] (1) Preparation of oxidized catalysts by co-precipitation method;

[0045] The coprecipitation method includes: coprecipitating a water-soluble nickel source, an alumina precursor, and a water-soluble additive in the presence of a precipitant; aging, washing, and optionally drying and / or calcining the resulting reaction mixture; and finally shaping to obtain an oxidized catalyst; wherein the amounts of the water-soluble nickel source, the alumina precursor, and the optional water-soluble additive are such that, based on the total amount of catalyst, the nickel content in the prepared catalyst, calculated as oxides, is 20-45% by weight; the additives include alkaline earth metal oxides and rare earth metal oxides.

[0046] (2) The molded product is subjected to reduction treatment and passivation treatment in sequence; the reduction includes: the reduction treatment is carried out in the presence of hydrogen gas, S1, heating to 400-550℃ at a heating rate of 60-150℃ / hour and holding for 0.5-8 hours; S2, heating to 560-700℃ at a heating rate of 50-120℃ / hour and holding for 0.3-8 hours;

[0047] Once the temperature of the catalyst obtained from the S2 reduction drops below 150°C, the catalyst obtained from the S2 reduction is passivated. The passivation includes continuously introducing oxygen-containing gas at a temperature below 60°C, controlling the passivation temperature to be no higher than 180°C; wherein, the oxygen concentration of the oxygen-containing gas continuously increases.

[0048] In the preparation method of this invention, the introduction of hydrogen gas (which has good thermal conductivity and diffusion properties, thus improving heat and mass transfer efficiency) during the reduction process enables the catalyst to undergo preliminary reduction while being drained. This reduces the adverse effects of water vapor on the reduction and prevents a decrease in the strength of the oxidized catalyst due to the rapid release of large amounts of water during the reduction process. By controlling the overall reduction time, nickel with a suitable grain size can be obtained, which is beneficial for obtaining a greater number of active centers. Furthermore, with appropriate passivation conditions, a catalyst that is easily regenerated and has many active centers is obtained. These multiple measures collectively improve the performance of the resulting catalyst.

[0049] The catalyst prepared by the method provided by this invention has good stability, making it suitable for use in the high-temperature conditions of a fixed-bed high-temperature methanation reactor, and it also has high activity.

[0050] In this invention, there is no particular limitation on the type of precipitant. Preferably, in step (1), the precipitant is selected from at least one of sodium carbonate, sodium bicarbonate, potassium carbonate, ammonia, and sodium hydroxide.

[0051] In this invention, there is no particular limitation on the type of water-soluble nickel source. Preferably, in step (1), the water-soluble nickel source is selected from at least one of nickel nitrate, acetate and chloride.

[0052] In this invention, there is no particular limitation on the type of water-soluble additive. Preferably, in step (1), the water-soluble additive is selected from at least one of nitrates, acetates, and chlorides containing additives.

[0053] In this invention, there is no particular limitation on the type of alumina precursor. Preferably, in step (1), the alumina precursor is selected from at least one of alumina sol, sodium aluminate, and aluminum nitrate.

[0054] In this invention, the preferred content of Ni and the content of aluminum oxide, rare earth oxides and alkaline earth metal oxides have been described in the first aspect and will not be repeated here.

[0055] In this invention, there are no restrictions on the mixing method of the alumina precursor and the water-soluble additive. For example, the precipitant can be added to a mixed salt solution containing a water-soluble nickel source, an alumina precursor, and a water-soluble additive; alternatively, the mixed salt solution containing the water-soluble nickel source, an alumina precursor, and a water-soluble additive can be added to the precipitant solution; or both can be added concurrently. Preferably, the precipitant is added to a mixed salt solution containing a water-soluble nickel source, an alumina precursor, and a water-soluble additive. The precipitant is preferably introduced in the form of an aqueous solution, preferably at a temperature of 30-70°C. More preferably, the mixed salt solution is prepared by the following process: first, mixing a water-soluble auxiliary agent (preferably in the form of an aqueous solution) and a water-soluble nickel source (preferably in the form of an aqueous solution) (preferably heated to 40-80°C at a stirring speed of 20-150 rpm) to obtain a metal salt mixed solution; then mixing the metal salt mixed solution with an alumina precursor (preferably in the form of an aqueous solution) (preferably stirred at a stirring speed of 20-150 rpm). This invention does not impose any limitations on the concentration of the corresponding aqueous solutions, as long as the corresponding solutes can be dissolved; those skilled in the art can freely choose according to their needs.

[0056] In this invention, the selection range of conditions for the coprecipitation reaction is relatively wide. Preferably, in step (1), the conditions for the coprecipitation reaction include: a reaction temperature of 40-80℃ and a pH of 7-9 when the coprecipitation reaction is completed.

[0057] In this invention, the range of aging conditions is relatively wide. Preferably, in step (1), the aging conditions include: an aging temperature of 30-70°C and a time of 1-8 hours.

[0058] In a preferred embodiment, step (1) includes the drying process comprising:

[0059] The precipitate obtained after washing is dried at 80-180℃ for 2-24 hours;

[0060] Alternatively, the precipitate obtained after washing can be pulped to obtain a slurry with a solid content of 15-50% by weight, and the slurry can be spray-dried.

[0061] In this invention, the pulping is preferably carried out under stirring, and the stirring time is preferably 1-6 hours. It is understood that a solvent is introduced during pulping, preferably water, and the pulp is an aqueous pulp.

[0062] In this invention, there are no particular limitations on the conditions for spray drying. Preferably, the spray drying conditions include: an atomization pressure of 1-5 MPa, an inlet temperature of 250-400°C, an outlet temperature of 80-160°C, and a spray drying time of 2-5 seconds. It is understood that the spray drying is carried out in a spray dryer, and the inlet temperature and outlet temperature are the inlet and outlet temperatures of the spray dryer, respectively.

[0063] In this invention, microspheres are obtained after spray drying, and the microspheres are subsequently calcined and shaped.

[0064] In a preferred embodiment, the calcination conditions include a temperature of 550-750°C and a time of 3-7 hours.

[0065] This invention does not limit the molding method; any commonly used method in the art can be used, such as tableting. Preferably, the molding process includes: mixing the calcined material with a lubricant and a molding agent, and then performing tableting. Those skilled in the art can select existing lubricants and molding agents according to actual needs. The lubricant is, for example, graphite (preferably 2-3% by weight of the product obtained after molding), and the molding agent is, for example, at least one of calcium aluminate cement, alumina, and aluminum silicate (preferably 5-10% by weight of the product obtained after molding). The catalyst particles after tableting have a size of 7-16 mm, are hollow and irregularly shaped, and contain at least one pore with a diameter greater than 0.5 mm, preferably 0.5-2 mm.

[0066] In this invention, the method further includes heating the oxidized catalyst before performing the reduction. The heating can be performed by preheated gas or within a reduction apparatus.

[0067] In a preferred embodiment, in step (2), the reducing atmosphere is hydrogen and optionally a protective gas. In this invention, the protective gas generally refers to a gas that does not participate in the reduction reaction.

[0068] In this invention, there is no particular limitation on the type of protective gas. Preferably, in step (2), the protective gas is at least one of helium, argon, and nitrogen, and more preferably nitrogen.

[0069] In a preferred embodiment, in step (2), the volume concentration of hydrogen in the reducing atmosphere is not less than 5%, and more preferably 5-80%. For example, it can be any value from 10, 12, 15, 20, 25, 30, 35, 40, 45, 55, 60, 65, 70, 75, 80 volume %, or any range between any values.

[0070] In this invention, preferably, the reducing atmosphere is provided by first introducing a protective gas, and then introducing hydrogen. The gas-to-gas ratio in this scheme is based on the reducing atmosphere (i.e., a mixture of hydrogen and a protective gas, also known as a hydrogen-containing gas).

[0071] According to a specific embodiment of the present invention, the method further includes: before the reduction, first replacing the gas in the reduction system with a protective gas to ensure that the O2 content in the reduction system is ≤0.5% by volume, then maintaining the pressure of the reduction system at 0-0.2 MPa (gauge pressure); then introducing a reducing gas (i.e., hydrogen or hydrogen-containing gas) to satisfy the composition of the reducing atmosphere, and then carrying out the reduction according to the reduction process. This preferred embodiment can prevent an explosion caused by excessive oxygen mixing with the reducing gas, ensuring the safe operation of the device.

[0072] More preferably, the method further includes a heat exchange step: the introduced reducing gas (i.e., hydrogen or hydrogen-containing gas) or protective gas is first heat-exchanged with the reduced gas, and then heated. The reduced exhaust gas, after being cooled by heat exchange, is preferentially subjected to gas-liquid separation, and the exhaust gas after water removal can be recycled for the reduction process.

[0073] In a preferred embodiment, the gas-to-powder ratio in step (2) is 700-5000, more preferably 1000-4000.

[0074] In a preferred embodiment, the gas-to-catalyst ratio in stage S1 is 1000-2000, and the gas-to-catalyst ratio in stage S2 is 1500-4000. This preferred embodiment is more conducive to promoting the reduction process of the catalyst, enabling the catalyst to be reduced uniformly and appropriately.

[0075] In a preferred embodiment, the reduction includes: S1, heating to 420-530°C at a heating rate of 80-140°C / hour and holding at that temperature for 1-6 hours; S2, heating to 580-680°C at a heating rate of 60-100°C / hour and holding at that temperature for 1-4 hours.

[0076] According to the present invention, the main equipment for reducing the oxidized catalyst is a reduction furnace. The reducing gas can be passed through once or recycled, preferably recycled. In one specific embodiment, the process flow is as follows: the oxidized catalyst is loaded into the reduction furnace, and hydrogen is added according to the reduction procedure for reduction. The reduction tail gas is dehydrated and then heated for recycling. More specifically: the catalyst is loaded into the pre-reduction reactor, the system is replaced with N2 to ensure that the volume percentage of O2 in the system is ≤0.5%, the compressor is started, the system pressure is maintained at 0.0-2 MPa (gauge pressure), and reduction is carried out according to the heating and hydrogen addition procedure. In the above process operation, the process flow is described as follows: the supplemented reducing gas enters the heat exchanger to exchange heat with the remaining gas after reduction, and then enters the heating furnace for further heating, and then enters the reactor for reduction. The remaining gas exits from the bottom of the reactor and enters the heat exchanger to exchange heat with the cold supplemented reducing gas for cooling. Then, after the water is cooled to 50°C by the inlet condenser, it enters the water separator. The reduced water is separated, compressed by the circulating compressor, dried by the molecular sieve dryer, and then circulated back to the pre-reduction reactor to continue participating in the reduction, saving a large amount of reducing gas.

[0077] In a preferred embodiment, the reduction is carried out at a pressure of 0-0.2 MPa. It should be noted that the pressure is gauge pressure.

[0078] In this invention, it is understood that the passivation temperature not exceeding 180°C means that the passivation temperature of the catalyst bed is not higher than 180°C.

[0079] According to the present invention, in step (2), preferably, the catalyst obtained by reduction in step (2) is passivated after the temperature drops below 150°C.

[0080] In this invention, there are no restrictions on the method of cooling the catalyst obtained by reduction in step (2), as long as the catalyst can be cooled to the required temperature, such as by heat exchange, cold exchange, water cooling, ammonia cooling, etc.

[0081] In this invention, preferably, the method further includes: after the temperature of the catalyst obtained by reduction in step (2) is reduced to below 60°C (preferably below 50°C), it is purged with a protective gas and then passivated.

[0082] In a preferred embodiment, the passivation treatment time in step (2) is 2-30 hours, more preferably 6-25 hours, while the passivation time in the prior art pre-reduction method is generally more than 48 hours.

[0083] In step (2) of this invention, the phrase "the oxygen concentration of the oxygen-containing gas continuously increases" means that the oxygen concentration in the introduced oxygen-containing gas generally shows an upward trend. For example, 1. the oxygen concentration in the introduced oxygen-containing gas can continuously increase (i.e., the oxygen concentration increases at a certain rate); 2. the oxygen concentration in the introduced oxygen-containing gas can be introduced for a certain period of time and then increased. In this case, the oxygen concentration increases in stages. For example, in multiple stages, in one specific implementation, the oxygen concentration in the later stage is higher than the oxygen concentration in the previous stage. In another specific implementation, the oxygen concentration in the first few stages is the same and lower than the oxygen concentration in the subsequent stages, thus showing an overall upward trend.

[0084] The present invention allows for a wide range of possible degrees of increase in the oxygen concentration of the oxygen-containing gas. The increase can be a regular, continuous increase, such as a doubling increase or an exponential increase; or it can be an irregular, continuous increase, for example, the oxygen concentration in the second stage differs from that in the first stage by a factor of 1, the oxygen concentration in the third stage differs from that in the second stage by a factor of 1.2, and the oxygen concentration in the fourth stage differs from that in the third stage by a factor of 2.

[0085] In this invention, preferably, the oxygen concentration of the oxygen-containing gas is increased in stages. In this case, the duration of each stage can be selected within a wide range, as long as it is beneficial to improve the performance of the obtained catalyst. More preferably, during the passivation process, when the oxygen-containing gas introduced in the previous stage makes the oxygen concentration in the passivation outlet gas equal to the oxygen concentration of the introduced oxygen-containing gas, the next stage of introducing oxygen-containing gas is started.

[0086] According to the present invention, preferably, during the passivation process, the oxygen concentration of the oxygen-containing gas increases continuously in at least two stages. It is understood that, in this preferred embodiment, the oxygen concentration of the oxygen-containing gas in the first stage is lower than that in the second stage, the oxygen concentration of the oxygen-containing gas in the second stage is lower than that in the third stage, and so on, continuously increasing. Further, it is understood that the relative multiples of the oxygen concentrations of the oxygen-containing gas in each adjacent pair of stages can be independently the same or different; for example, the relative multiple of the oxygen concentrations of the oxygen-containing gas in the first and second stages is 1.5, and the relative multiple of the oxygen concentrations of the oxygen-containing gas in the second and third stages can be 1.5 or 2.

[0087] More preferably, during the passivation process, the oxygen concentration of the oxygen-containing gas increases continuously in 2-8 stages. For example, the number of stages can be any value among 2, 3, 4, 5, 6, 7, and 8, and more preferably, it increases continuously in 3-6 stages. By adopting the preferred embodiment of the present invention, the catalyst can achieve more uniform passivation, thereby enabling the catalyst to have more reducing active centers after reactivation.

[0088] In a preferred embodiment, in step (2), the passivation treatment, the gas-to-agent ratio is 200-5000, for example, any point value among 300, 400, 500, 1000, 1200, 1500, 2000, 3000, 4000, and 5000, and any point value and range between them, more preferably 500-3000.

[0089] According to the present invention, preferably, in step (2), the gas-to-catalyst ratio in the previous stage of the passivation treatment is not lower than that in the subsequent stage. This preferred embodiment is more conducive to promoting a uniform passivation process of the catalyst and improving passivation efficiency.

[0090] In this invention, the oxidizing gas is preferably a mixture of a protective gas and oxygen, wherein the protective gas is selected from at least one of helium, argon, carbon dioxide and nitrogen.

[0091] In this invention, the method further includes: before the passivation, first introducing a protective gas (preferably carbon dioxide and N2 in a volume ratio of 10-20:1), and then introducing oxygen, so that the amount of oxygen in the passivation atmosphere meets the required oxygen concentration, and then performing the passivation. The passivated gas is reused or directly discharged.

[0092] According to the present invention, when the reduction and passivation are performed using the same equipment, it is preferable to introduce a protective gas after the reduction to replace the hydrogen in the system before performing the passivation.

[0093] In a preferred embodiment, the passivation temperature is preferably kept below 180°C by adjusting the amount of protective gas (preferably carbon dioxide) pumped in.

[0094] In a preferred embodiment, in step (2), the concentration of the oxidizing gas is 0.01-21% by volume.

[0095] In a preferred embodiment, in step (2), the initial oxygen concentration of the oxidizing gas introduced during the passivation treatment is 0.01-1% by volume, more preferably 0.02-0.1% by volume. Using an oxidizing gas with a lower initial oxygen concentration enables uniform and controllable passivation, which is more conducive to obtaining a catalyst that is easy to re-reducible.

[0096] In a preferred embodiment, in step (3), the oxygen concentration of the oxidizing gas introduced in the later stage of the passivation treatment is 2-8 times that of the oxidizing gas introduced in the previous stage. This preferred embodiment enables more uniform and controllable passivation of the catalyst, resulting in a catalyst with more reduction active centers after re-reduction treatment, while also achieving high passivation efficiency.

[0097] In this invention, preferably, in the passivation process, the concentration of the oxidizing gas introduced in the last stage is 21% by volume, that is, air is introduced.

[0098] In this invention, the reducing gas (i.e., the reducing atmosphere) and the passivating gas (i.e., the oxygen-containing gas) can be used in one go or recycled; preferably, the gas is recycled.

[0099] In this invention, there are no restrictions on the equipment used for reduction. For example, the main equipment for reduction can be a reduction furnace or a reduction reactor. The reduction equipment can be a converter, a moving bed reactor, or a fixed bed reactor. The equipment shape can be cylindrical, double-cone, spherical, etc., or an axial reactor or a radial reactor. A fixed bed reactor is preferred (e.g., a flat cylindrical axial reactor with a height-to-diameter ratio of 0.3-0.8) to minimize the residence of water vapor in the catalyst bed, uniformly reduce the catalyst at different bed positions, and avoid damaging the mechanical strength of the catalyst. This invention also places no restrictions on the equipment used for passivation. For example, the main equipment for passivation can be a passivation furnace. This invention can also be equipped with heat exchangers, cold exchangers, water coolers, ammonia coolers, dryers, regeneration heating furnaces, and circulating fans. The reduction equipment and passivation equipment can be configured separately or shared, preferably shared, and other supporting equipment is also preferably shared.

[0100] The third aspect of the present invention provides a pre-reduced methanation catalyst prepared by the preparation method described in the second aspect.

[0101] The fourth aspect of this invention provides the application of the pre-reduced methanation catalyst described in the first or third aspect in the complete methanation of syngas to produce natural gas.

[0102] The catalyst provided by this invention needs to be reactivated by reduction in the presence of hydrogen before being used in the complete methanation reaction of syngas. The reactivation conditions include: a reduction temperature of 230-400℃, preferably 260-380℃; and a reduction time of 0.5-6 hours, preferably 1-4 hours, and more preferably 2-3 hours. The reactivation can be carried out in pure hydrogen or in a mixture of hydrogen and a protective gas, preferably in pure hydrogen. In a preferred embodiment, the reactivation conditions further include: a space velocity of 1000-2000 h⁻¹. -1 The heating rate is 60-120℃ / hour.

[0103] In a preferred embodiment, the conditions for the complete methanation reaction of the syngas include: a molar ratio of H2:CO:nitrogen of 3-5:0.5-1:1; a reaction temperature of 350-650℃; a pressure of 0-6MPa; and a feed gas space velocity of 1000-120000 h⁻¹. -1 .

[0104] The present invention will be described in detail below through embodiments.

[0105] In this embodiment of the invention, a laser particle size analyzer is used to determine the particle size of the powdered catalyst, and TPR is used to characterize the regenerability of the catalyst. Specifically, the highest temperature corresponding to the low-temperature reduction peak in the TPR spectrum curve is used as an indicator to evaluate the regenerability of the passivated catalyst. The lower the highest temperature of the low-temperature reduction peak, the easier the catalyst is to regenerate.

[0106] Example 1

[0107] (1) Preparation of oxidized catalyst

[0108] Dissolve 80g of Ni(NO3)2·6H2O, 80g of Al(NO3)3·9H2O, and 5.31g of La(NO3)3·6H2O in 500mL of deionized water, and add 2g of magnesium oxide and 2g of calcium oxide to prepare a mixed metal salt solution I. Add 50g of aluminum sol (alumina concentration of 20% by weight) to 100mL of water and stir at 50r / min until homogeneous to obtain a dilute aluminum sol. Mix the mixed metal salt solution and the aluminum sol and stir at 50r / min until homogeneous to obtain the bottom solution of the catalyst precursor. 129.83 g of Na₂CO₃ was dissolved in 500 mL of deionized water to prepare alkaline solution II. The temperature of alkaline solution II was maintained at a constant 70 °C. Mixed salt solution I was gradually added dropwise to alkaline solution II while stirring at 70 r / min until homogeneous. The mixture was allowed to undergo a complete precipitation reaction, with pH = 8 as the titration endpoint. After precipitation, the mixture was stirred thoroughly and aged at 65 °C for 2 hours. The precipitated precursor was washed three times with deionized water. The catalyst composition, by weight percentage, was 43.21% NiO, 44.02% alumina, 4.36% lanthanum oxide, 4.205% magnesium oxide, and 4.205% calcium oxide.

[0109] The filter cake was slurried with a solid content of 40% by weight and stirred for 1.5 hours. The slurry was then sent to a spray dryer with an atomization pressure of 2.5 MPa, an inlet temperature of 330°C, and an outlet temperature of 130°C. The slurry flowed out of the outlet of the spray dryer after 5 seconds, resulting in microspheres with a particle size Dv(90) of 140 micrometers. The dried powder was then calcined at 600°C for 4 hours.

[0110] Then, the product obtained from calcination, graphite (based on the total amount of the product obtained after molding, with graphite accounting for 2% by weight), and calcium aluminate cement (based on the total amount of the product obtained after molding, with calcium aluminate accounting for 8% by weight) are mixed evenly and pressed into hollow cylindrical sheets with a particle size of 8mm × 8mm. Each cylinder has a hole with a diameter of 2mm in the middle, thus obtaining an oxidized catalyst.

[0111] (2) Preparation of pre-reduced methanation catalyst

[0112] The prepared oxidized catalyst was placed in a reactor. First, nitrogen was introduced into the reactor to purge the oxygen until it reached the required level (oxygen content ≤ 0.5% by volume). Then, hydrogen was added to make the hydrogen content in the hydrogen-nitrogen mixture 60% by volume. Then, a multi-stage reduction process was started. In stage S1, the above-mentioned mixture with a gas-to-catalyst ratio of 1500 was introduced, and the temperature of the catalyst was raised to 500°C at a heating rate of 80°C / hour and held at this temperature for 2 hours. In stage S2, the above-mentioned mixture with a gas-to-catalyst ratio of 2500 was introduced. In stage S2-1, the temperature of the catalyst was first raised to 630°C at a heating rate of 70°C / hour and held at this temperature for 2 hours. Then, in stage S2-2, the temperature of the catalyst was raised to 700°C at a heating rate of 60°C / hour and held at this temperature for 1 hour, and the reduction step was completed.

[0113] Then, nitrogen was introduced to replace the hydrogen in the system, and the reduced catalyst was cooled to below 140°C. Under normal pressure, an oxygen-containing gas with an oxygen concentration of 0.5-21 vol% (v / v) composed of air and nitrogen was introduced at a temperature below 45°C. Oxygen-containing gas with oxygen concentrations of 0.5 vol%, 1 vol%, 8 vol%, and 21 vol% was introduced sequentially in four stages. After introducing the oxygen-containing gas in the previous stage, when the oxygen concentration at the gas outlet equaled the oxygen concentration at the gas inlet, the oxygen-containing gas in the next stage was introduced. This process of gradually increasing the oxygen concentration was used for passivation until passivation was complete. The gas-to-catalyst ratio for the first two passivation stages was 1000, and the ratio for the last two passivation stages was 500. The passivation temperature of the catalyst bed was controlled to be below 180°C, and the total passivation time was 16 hours. The passivated catalyst, i.e., the pre-reduced catalyst C1, was obtained.

[0114] Example 2

[0115] Dissolve 70g of Ni(NO3)2·6H2O, 80g of Al(NO3)3·9H2O, and 6g of La(NO3)3·6H2O in 500mL of deionized water, and add 4g of magnesium oxide to prepare a mixed metal salt solution I. Add 60g of aluminum sol (alumina concentration of 20% by weight) to 100mL of water and stir at 50r / min until homogeneous to obtain a dilute aluminum sol. Mix the mixed metal salt solution and the aluminum sol and stir at 70r / min until homogeneous to obtain the bottom solution of the catalyst precursor. 129.83 g of Na₂CO₃ was dissolved in 500 mL of deionized water to prepare alkaline solution II. The temperature of alkaline solution II was maintained at a constant 60 °C. Mixed salt solution I was gradually added dropwise to alkaline solution II while stirring at 70 r / min until homogeneous. The mixture was allowed to undergo a complete precipitation reaction, with pH = 8 as the titration endpoint. After precipitation, the mixture was stirred thoroughly and aged at 55 °C for 2 hours. The precipitated precursor was then washed three times with deionized water. The catalyst composition, by weight percentage, was 38.12% NiO, 48.61% alumina, 4.79% lanthanum oxide, and 8.48% magnesium oxide.

[0116] The filter cake and water were slurried and stirred for 1.5 hours to obtain a slurry with a solid content of 35% by weight. The slurry was then transported to a spray dryer with an atomization pressure of 2.5 MPa, an inlet temperature of 330°C, and an outlet temperature of 130°C. After 5 seconds, the slurry flowed out from the outlet of the spray dryer to obtain microspheres with a particle size Dv(90) of 160 micrometers. The microspheres were then calcined at 650°C for 2 hours. The calcined product was then mixed with graphite (based on the total amount of the product obtained after molding, with a graphite content of 2% by weight) and calcium aluminate cement (based on the total amount of the product obtained after molding, with a calcium aluminate content of 8% by weight). The mixture was then pressed into hollow cylindrical sheets with a particle size of 7×7 mm and a 2 mm diameter hole in the middle of the cylinder to obtain an oxidized catalyst.

[0117] The oxidized catalyst prepared in Example 2 was placed in a reactor. First, nitrogen was introduced into the reactor to purge the oxygen until it met the required oxygen content (oxygen content ≤ 0.5% by volume). Then, hydrogen was added to the reactor to make the hydrogen content in the hydrogen-nitrogen mixture 50% by volume. Then, a multi-stage reduction process was started. In stage S1, the above-mentioned mixture with a gas-to-catalyst ratio of 1500 was introduced, and the temperature of the catalyst was raised to 500°C at a heating rate of 80°C / hour and held at this temperature for 2 hours. In stage S2, the above-mentioned mixture with a gas-to-catalyst ratio of 2500 was introduced. In stage S2-1, the temperature of the catalyst was first raised to 650°C at a heating rate of 70°C / hour and held at this temperature for 2 hours. Then, in stage S2-2, the temperature of the catalyst was raised to 730°C at a heating rate of 60°C / hour and held at this temperature for 1 hour, and the reduction step was completed.

[0118] Then, nitrogen was introduced to replace the hydrogen in the system, and the reduced catalyst was cooled to below 150°C. Under normal pressure, an oxygen-containing gas with an oxygen concentration of 0.5-21 vol% (v / v) composed of air and nitrogen was introduced at a temperature below 60°C. Oxygen-containing gas with oxygen concentrations of 0.5 vol%, 1 vol%, 8 vol%, and 21 vol% was introduced sequentially in four stages. After introducing the oxygen-containing gas in the previous stage, when the oxygen concentration at the gas outlet equaled the oxygen concentration at the gas inlet, the oxygen-containing gas in the next stage was introduced. This process of gradually increasing the oxygen concentration was used for passivation until passivation was complete. The gas-to-catalyst ratio for the first two passivation stages was 1000, and the ratio for the last two passivation stages was 500. The passivation temperature of the catalyst bed was controlled to be below 180°C, and the total passivation time was 15 hours. The passivated catalyst, i.e., the pre-reduced catalyst C2, was obtained.

[0119] Example 3

[0120] The oxidized catalyst prepared in Example 1 was placed in a reactor. First, nitrogen was introduced into the reactor to purge the oxygen until it met the required level (oxygen content ≤ 0.5% by volume). Then, hydrogen was added to make the hydrogen content in the hydrogen-nitrogen mixture 65% by volume. Then, a multi-stage reduction process was started. In stage S1, the above-mentioned mixture with a gas-to-catalyst ratio of 1500 was introduced, and the temperature of the catalyst was raised to 500°C at a heating rate of 80°C / hour and held at this temperature for 2 hours. In stage S2, the above-mentioned mixture with a gas-to-catalyst ratio of 2500 was introduced. In stage S2-1, the temperature of the catalyst was first raised to 650°C at a heating rate of 70°C / hour and held at this temperature for 2 hours. Then, in stage S2-2, the temperature of the catalyst was raised to 730°C at a heating rate of 60°C / hour and held at this temperature for 1 hour, and the reduction step was completed.

[0121] Then, nitrogen was introduced to replace the hydrogen in the system, and the reduced catalyst was cooled to below 150°C. Under normal pressure, oxygen-containing gas, composed of air and nitrogen at a concentration of 0.5-21 vol%, was introduced at a temperature below 45°C. Oxygen-containing gas with concentrations of 0.5 vol%, 1 vol%, 4 vol%, 8 vol%, and 21 vol% was introduced sequentially in five stages. After introducing the oxygen-containing gas in the previous stage, when the oxygen concentration at the gas outlet equaled the oxygen concentration at the gas inlet, the oxygen-containing gas in the next stage was introduced. This process of gradually increasing the oxygen concentration was used for passivation until passivation was complete. The gas-to-catalyst ratio was 1000 for the first two stages of passivation and 500 for the last three stages. The passivation temperature of the catalyst bed was controlled to be below 170°C, and the total passivation time was 15 hours. The passivated catalyst, i.e., the pre-reduced catalyst C3, was obtained.

[0122] Example 4

[0123] The oxidized catalyst prepared in Example 1 was placed in a reactor. First, nitrogen was introduced into the reactor to purge the oxygen until it met the required oxygen content (oxygen content ≤ 0.5% by volume). Then, hydrogen was added to make the hydrogen content in the hydrogen-nitrogen mixture 70% by volume, and the multi-stage reduction process of the catalyst began. In stage S1, the above-mentioned mixture with a gas-to-catalyst ratio of 1500 was introduced, and the temperature of the catalyst was raised to 500°C at a heating rate of 80°C / hour and held at that temperature for 2 hours. In stage S2, the above-mentioned mixture with a gas-to-catalyst ratio of 2500 was introduced, and in stage S2-1, the temperature of the catalyst was first raised to 640°C at a heating rate of 70°C / hour and held at this temperature for 2 hours. Then, in stage S2-2, the temperature of the catalyst was raised to 720°C at a heating rate of 60°C / hour and held at this temperature for 1 hour, and the reduction step ended.

[0124] Then, nitrogen was introduced to replace the hydrogen in the system, and the reduced catalyst was cooled to below 150°C. Under normal pressure, oxygen-containing gas, composed of air and nitrogen at a concentration of 0.5-21 vol%, was introduced at a temperature below 45°C. Oxygen-containing gas with concentrations of 0.5%, 1%, 4%, 8%, and 21 vol% was introduced sequentially in five stages. After introducing the oxygen-containing gas in the previous stage, when the oxygen concentration at the gas outlet equaled the oxygen concentration at the gas inlet, the oxygen-containing gas in the next stage was introduced. This process of gradually increasing the oxygen concentration was used for passivation until passivation was complete. The gas-to-catalyst ratio for the first two passivation stages was 1000, and for the last two stages it was 500. The passivation temperature of the catalyst bed was controlled to be below 170°C, and the total passivation time was 15 hours. The resulting passivated catalyst, i.e., the pre-reduced catalyst C4, was obtained.

[0125] Example 5

[0126] The method of Example 4 was followed, except that stage S2 was different (i.e., only one stage S2 was used). Specifically, the catalyst temperature was raised to 720°C at a heating rate of 60°C / hour and held at this temperature for 2 hours to end the reduction step. The rest was the same as in Example 4. Catalyst number C5.

[0127] Example 6

[0128] The method was carried out according to Example 1, except that the stages of introducing oxygen-containing gas during the passivation process were different. Specifically, oxygen-containing gas with an oxygen concentration of 0.15-21 vol% was introduced in six stages, with oxygen concentrations of 0.15 vol%, 0.3 vol%, 1.0 vol%, 6 vol%, 12 vol%, and 21.0 vol%, respectively. The gas-to-catalyst ratio was 2000 in the first two stages of passivation and 1000 in the last four stages. The total passivation time was 30 hours. Catalyst number C6.

[0129] Comparative Example 1

[0130] Compared to Example 6, the difference lies in the step of first shaping the oxidized catalyst and then performing reduction passivation. Specifically:

[0131] 1. Oxidized catalyst microspheres with a particle size DV(90) of 140 micrometers were prepared according to step 1 of Example 1;

[0132] 2. Based on the total amount of oxides after molding, add 2% by weight of graphite and 8% by weight of calcium aluminate cement, mix evenly, and press into hollow cylindrical sheets with a particle size of 8mm×8mm. The cylinder has a hole with a diameter of 2mm in the middle to obtain the oxidized catalyst.

[0133] 3. The shaped oxidized catalyst from step 2 is fed into a fluidized bed reduction reactor for pre-reduction and passivation. The reduction conditions are the same as in Example 1, except that the number of passivation stages and the oxygen concentration are different. Specifically, the number of passivation stages is one, that is, the reduced catalyst is directly passivated with a reducing gas with an oxygen concentration of 5% by volume, to obtain the pre-reduced catalyst D1.

[0134] Test case

[0135] The performance of the pre-reduction methanation catalyst prepared above was tested, as follows:

[0136] 1. Evaluate the activity of the catalyst

[0137] A. The activity of the catalyst was evaluated by the number of active centers after the catalyst was re-reduced.

[0138] The number of active sites was obtained by H2 temperature-programmed desorption (H2-TPD) testing using an Autochem 2950 fully automated high-pressure chemisorption analyzer manufactured by Micromeritics, USA. The test method was as follows: 0.2000 g of 40-60 mesh sample was weighed and first activated by reduction under the following conditions: a 10 vol% H2-Ar mixture with a flow rate of 50 mL / min, heated to 300 °C for 2 h at a heating rate of 10 °C / min. The reduced catalyst was then cooled in a 10 vol% H2-Ar mixture until it reached 55 °C, at which point Ar gas was switched to purge at a flow rate of 20 mL / min until the baseline stabilized. Then, the H2-TPD experiment was performed. The experimental conditions and program for H2-TPD were: Ar as the carrier gas, a flow rate of 20 mL / min, a heating rate of 10 °C / min, a final temperature of 400 °C, and signal detection using a thermal conductivity detector (TCD) to obtain the TPD curve.

[0139] B. The proportion of catalytically active nickel in the catalyst is characterized by the TPD desorption peak area. The larger the TPD desorption peak area, the higher the proportion of catalytically active nickel in the catalyst. The TPD desorption peak area is obtained from the TPD curve obtained by the above testing method.

[0140] 2. The regenerability of the catalyst is characterized by TPR (thermal reduction profile). Specifically, the highest temperature corresponding to the low-temperature reduction peak in the TPR curve is used as an indicator to evaluate the regenerability of the passivated catalyst. The lower the highest temperature of the low-temperature reduction peak, the easier the catalyst is to regenerate.

[0141] TPR (temperature programmed reduction) characterization was performed using an Autochem 2950 fully automated high-pressure chemical adsorption instrument manufactured by Micromeritics, USA. The test conditions were as follows: 0.20 g of sample was first heated to 120 °C for dehydration treatment for 1 hour under an Ar gas flow of 50 mL / min at a heating rate of 10 °C / min. After the temperature dropped to 50 °C, the TPR experiment was performed. The experimental conditions and program for TPR were as follows: the reducing gas was a H2-Ar mixture with a hydrogen content of 10% by volume, the reducing gas flow rate was 50 mL / min, and the temperature was increased to 900 °C at a heating rate of 10 °C / min. During the above heating process, the signal was detected by a thermal conductivity detector (TCD) to obtain the TPR spectrum curve.

[0142] 3. Obtain the reduction status of the catalyst through the degree of reduction.

[0143] The specific method is as follows: 0.2g of the pre-reduced catalyst is calcined in air at 450℃ for 2 hours to obtain the oxidized catalyst. Then, the TPR spectrum curve of the calcined oxidized catalyst is tested according to the above TPR test method, and the degree of reduction of the pre-reduced catalyst is calculated. Wherein, degree of reduction = (TPR peak area of ​​direct reduction of oxidized catalyst - peak area of ​​high-temperature unreduced pre-reduced catalyst) / TPR peak area of ​​direct reduction of oxidized catalyst * 100%.

[0144] The test results are listed in Table 2.

[0145] Table 2

[0146]

[0147]

[0148] As can be seen from Table 2, the number of active centers of the pre-reduction catalyst prepared by the embodiments of the present invention is better than that of the comparative example, indicating that the pre-reduction methanation catalyst obtained by the method of the present invention contains a higher proportion of catalytically active nickel.

[0149] The reduction and passivation processes in the catalyst preparation of this invention are simple to operate, the passivation effect is controllable, and the regenerability of the catalyst is controllable. After being treated by this invention, the surface of the catalyst is oxidized to form a dense oxide film, which prevents air from penetrating deep into the catalyst interior, facilitating storage and transportation. At the same time, it is easily reduced by H2 during use, and can quickly exhibit high catalytic activity, greatly shortening start-up time and bringing good economic benefits to enterprises.

[0150] Application examples

[0151] To further evaluate the reactivity of the pre-reduction catalyst of this invention, 10 mL of catalyst (particle size 2 mm-4 mm) was loaded into a fixed-bed reactor, along with the catalysts obtained in the above examples and comparative examples. The catalyst provided by this invention requires re-reduction activation in the presence of hydrogen before being used in the syngas methanation reaction. The re-reduction conditions include: at atmospheric pressure in a pure hydrogen atmosphere, with a space velocity of 1500 h⁻¹. -1 After reducing at a constant temperature of 350℃ for 2 hours by raising the temperature at 100℃ / hour, the feed gas (H2 / CO / N2 = 3 / 1 / 1, molar ratio) was switched and the reaction was carried out at 350℃ with a reaction space velocity of 100,000 h⁻¹. -1 The reaction pressure was 2 MPa. The pre-reduced catalysts obtained in the above examples and comparative examples were tested, and the CO conversion rate (X) was measured at 10 h and 100 h, respectively. CO The composition of the exhaust gas was analyzed by online gas chromatography, and the CO conversion rate was calculated. The results are listed in Table 3.

[0152] The carbon deposits were measured using an SC-632 carbon-sulfur analyzer. The amount of carbon deposits after unloading was the difference between the measured value of carbon deposits after unloading and the measured value of carbon deposits after fresh application.

[0153] CO conversion rate is calculated using the following formula:

[0154]

[0155] Where V1 and V2 represent the volume of the raw material gas entering the reaction system and the volume of the tail gas flowing out of the reaction system under standard conditions within a certain time period, respectively; c1 and c2 represent the content of the corresponding substances in the raw material gas and the tail gas, respectively.

[0156] Table 3

[0157] CO conversion rate over 10 hours, % CO conversion rate over 100 hours, % Carbon deposits, % Example 1 99.5 99.4 0.001 Example 2 99.5 99.4 0.001 Example 3 99.9 99.8 0.001 Example 4 99.4 99.3 0.001 Example 5 99.1 99.0 0.001 Example 6 99.5 99.4 0.001 Comparative Example 1 10.4 10.3 0.001

[0158] As can be seen from the comparison of Example 4, the catalyst prepared using the preferred reduction process of the present invention has higher activity, is easier to regenerate, and has high stability. As can be seen from the comparison of Example 1 and Examples 1-6, the catalyst prepared using the preferred scheme of the present invention has high activity.

[0159] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A pre-reduced methanation catalyst, characterized in that, The catalyst comprises Ni, alumina, and additives, including alkaline earth metal oxides and rare earth metal oxides; based on the total amount of catalyst and calculated as oxides, the nickel content is 20-45% by weight. The catalyst, after re-reduction treatment, has an active center number of 0.01-0.2 mmol hydrogen / g catalyst. The re-reduction treatment conditions include: a temperature of 300℃, a time of 2 hours, and a re-reduction atmosphere containing hydrogen and argon with a hydrogen concentration of 10% by volume, and a gas-to-catalyst volume ratio of 15000. The catalyst is hollow and irregular in shape, with a particle size of 7-16 mm. The method for preparing the pre-reduced methanation catalyst includes: (1) Preparation of oxidized catalysts by co-precipitation method; The coprecipitation method includes: coprecipitating a water-soluble nickel source, an alumina precursor, and a water-soluble additive in the presence of a precipitant, aging, washing, and optionally drying and / or calcining the resulting reaction mixture, and finally shaping it to obtain an oxidized catalyst. (2) The oxidized catalyst is subjected to reduction and passivation treatment in sequence; the reduction includes: in the presence of hydrogen gas, S1, heating to 400-550℃ at a heating rate of 60-150℃ / hour and holding for 0.5-8 hours; S2, heating to 560-700℃ at a heating rate of 50-120℃ / hour and holding for 0.3-8 hours; Once the temperature of the catalyst obtained from S2 reduction drops below 150°C, the catalyst obtained from S2 reduction is passivated. The passivation includes continuously introducing oxygen-containing gas at a temperature below 60°C and controlling the passivation temperature to be no higher than 180°C. The passivation process is carried out in at least two stages, and the oxygen concentration of the oxygen-containing gas increases progressively in each stage.

2. The methanation catalyst according to claim 1, wherein, Based on the total amount of catalyst, the nickel content is 25-40% by weight, calculated as oxides.

3. The methanation catalyst according to claim 1, wherein, After re-reduction treatment, the catalyst has an active center number of 0.012-0.17 mmol hydrogen / g catalyst.

4. The methanation catalyst according to claim 1, wherein, The catalyst was characterized by TPR. In the TPR curve, the temperature corresponding to the peak of the low-temperature reduction peak with the largest area is 200-360℃.

5. The methanation catalyst according to claim 4, wherein, The catalyst was characterized by TPR. In the TPR curve, the temperature corresponding to the peak of the low-temperature reduction peak with the largest area was 210-350℃.

6. The methanation catalyst according to claim 1, wherein, The catalyst contains at least one pore with a diameter greater than 0.5 mm.

7. The methanation catalyst according to any one of claims 1-6, wherein, The alumina is γ-alumina; And / or, the alkaline earth metal oxide is selected from at least one of BeO, MgO, CaO, CsO and BaO; And / or, the rare earth metal oxide is selected from at least one of Y2O3, La2O3, CeO2, Pr2O3 and Sm2O3.

8. The methanation catalyst according to any one of claims 1-6, wherein, Based on the total amount of catalyst, the content of alkaline earth metal oxide is 1-13 wt%, the content of rare earth metal oxide is 1-10 wt%, and the content of alumina is 40-75 wt%.

9. The methanation catalyst according to claim 8, wherein, Based on the total amount of catalyst, the content of alkaline earth metal oxide is 4-13 wt%, the content of rare earth metal oxide is 2-9 wt%, and the content of alumina is 44-70 wt%.

10. A method for preparing a pre-reduced methanation catalyst, wherein, The method includes: (1) Preparation of oxidized catalysts by co-precipitation method; The coprecipitation method includes: coprecipitating a water-soluble nickel source, an alumina precursor, and a water-soluble additive in the presence of a precipitant; aging, washing, and optionally drying and / or calcining the resulting reaction mixture; and finally molding to obtain an oxidized catalyst; wherein the amounts of the water-soluble nickel source, the alumina precursor, and the optional water-soluble additive are such that, based on the total amount of catalyst and calculated as oxides, the nickel content in the prepared catalyst is 20-45% by weight; and the additives include alkaline earth metal oxides and rare earth metal oxides. (2) The oxidized catalyst is subjected to reduction and passivation treatment in sequence; the reduction includes: the reduction treatment is carried out in the presence of hydrogen gas, S1, heating to 400-550℃ at a heating rate of 60-150℃ / hour and holding for 0.5-8 hours; S2, heating to 560-700℃ at a heating rate of 50-120℃ / hour and holding for 0.3-8 hours; Once the temperature of the catalyst obtained from S2 reduction drops below 150°C, the catalyst obtained from S2 reduction is passivated. The passivation includes continuously introducing oxygen-containing gas at a temperature below 60°C and controlling the passivation temperature to be no higher than 180°C. The passivation process is carried out in at least two stages, and the oxygen concentration of the oxygen-containing gas increases progressively in each stage.

11. The method according to claim 10, wherein, In step (1), the precipitant is selected from at least one of sodium carbonate, sodium bicarbonate, potassium carbonate, ammonia and sodium hydroxide.

12. The method according to claim 10, wherein, In step (1), the water-soluble nickel source is selected from at least one of nickel nitrate, acetate and chloride.

13. The method according to claim 10, wherein, In step (1), the water-soluble adjuvant is selected from at least one of nitrates, acetates and chlorides containing adjuvants.

14. The method of claim 10, wherein, In step (1), the alumina precursor is selected from at least one of alumina sol, sodium aluminate and aluminum nitrate.

15. The method according to claim 10, wherein, The amounts of the alumina precursor, water-soluble additive, water-soluble nickel source, forming agent, and lubricant are such that the nickel content in the prepared catalyst, based on the total amount of catalyst and calculated as oxides, is 25-40% by weight.

16. The method of claim 10, wherein, The amounts of the alumina precursor, water-soluble additive, water-soluble nickel source, forming agent, and lubricant are such that, based on the total amount of catalyst, the content of the alkaline earth metal oxide is 1-13 wt%, the content of the rare earth metal oxide is 1-10 wt%, and the content of alumina is 25-75 wt%.

17. The method according to claim 10 or 16, wherein, Based on the total amount of catalyst, the content of alkaline earth metal oxide is 4-13 wt%, the content of rare earth metal oxide is 2-9 wt%, and the content of alumina is 44-70 wt%.

18. The method according to claim 10, wherein, In step (1), the conditions for the coprecipitation reaction include: a reaction temperature of 40-80℃ and a pH of 7-9 when the coprecipitation reaction is completed.

19. The method according to claim 10, wherein, In step (1), the aging conditions include: an aging temperature of 30-70℃ and a time of 1-8 hours.

20. The method of claim 10, wherein, In step (1), the drying process includes drying the precipitate obtained after washing at 80-180°C for 2-24 hours.

21. The method according to claim 10, wherein, In step (1), the drying process includes pulping the precipitate obtained after washing to obtain a slurry with a solid content of 15-50% by weight, and spray drying the slurry.

22. The method according to claim 21, wherein, The spray drying conditions include: atomization pressure of 1-5 MPa, inlet temperature of 250-400℃, outlet temperature of 80-160℃, and atomization drying time of 2-5 seconds.

23. The method according to claim 10, wherein, In step (1), the roasting conditions include: a temperature of 550-750℃ and a time of 3-7h.

24. The method according to claim 10, wherein, In step (2), the hydrogen-containing gas is hydrogen and optionally a protective gas.

25. The method according to claim 24, wherein, In step (2), the protective gas is at least one of helium, argon and nitrogen.

26. The method according to claim 24, wherein, In step (2), the volume concentration of hydrogen in the hydrogen-containing gas is not less than 5%.

27. The method according to claim 26, wherein, In step (2), the volume concentration of hydrogen is 5-80%.

28. The method according to claim 10, wherein, In step (2), the gas-to-agent ratio in the reduction process is 700-5000.

29. The method according to claim 28, wherein, In step (2), the gas-to-agent ratio in the reduction process is 1000-4000.

30. The method according to claim 29, wherein, In step (2), the gas-to-agent ratio in the reduction process is 1000-2000 in stage S1 and 3000-4000 in stage S2.

31. The method according to claim 10, wherein, The reduction process includes: S1, heating to 420-530℃ at a heating rate of 80-140℃ / hour and holding for 1-6 hours; S2, heating to 580-680℃ at a heating rate of 60-100℃ / hour and holding for 1-4 hours.

32. The method according to claim 10, wherein, In step (2), the passivation treatment takes 2-30 hours.

33. The method according to claim 32, wherein, In step (2), the passivation treatment takes 6-25 hours.

34. The method according to claim 10, wherein, In step (2), the passivation process is carried out in 2-8 stages.

35. The method according to claim 34, wherein, In step (2), the passivation process is carried out in 3-6 stages.

36. The method according to claim 10, wherein, In step (2), the gas-to-agent ratio in the passivation treatment is 200-5000.

37. The method of claim 36, wherein, In step (2), the gas-to-agent ratio in the passivation treatment is 500-3000.

38. The method according to claim 10, wherein, In step (2), the gas-to-agent ratio in the passivation process is not lower than that in the subsequent stage.

39. The method according to claim 10, wherein, In step (2), the concentration of the oxygen-containing gas is 0.01-21% by volume.

40. The method of claim 10, wherein, In step (2), during the passivation process, the initial oxygen concentration of the oxygen-containing gas introduced is 0.01-1 volume.

41. The method according to claim 40, wherein, In step (2), during the passivation process, the initial oxygen concentration of the oxygen-containing gas introduced is 0.02-1 volume.

42. The method according to claim 10, wherein, In step (2), the oxygen concentration of the oxygen-containing gas introduced in the later stage of the passivation treatment is 2-8 times that of the oxygen-containing gas introduced in the previous stage.

43. The pre-reduced methanation catalyst prepared by the preparation method according to any one of claims 10-42.

44. The use of the pre-reduced methanation catalyst according to any one of claims 1-9 and 43 in the complete methanation of syngas to produce natural gas.

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