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 an active component, a carrier and an additive; the carrier comprises alumina, the additive comprises alkaline earth metal oxide and rare earth metal oxide, and the active component is Ni; the content of nickel is 20-65% 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 0.03-0.41 mmol of hydrogen gas per gram of catalyst; the re-reduction treatment conditions comprise a temperature of 280 DEG C, a time of 2 hours, a hydrogen-containing and argon-containing atmosphere with a hydrogen concentration of 10% by volume, and a gas volume ratio of 15000; and the particle size of the catalyst is 1-6 mm.The catalyst has good reduction degree, good reactivation performance, many active centers and good stability.

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] Coal consumption accounts for approximately 70% of primary energy consumption. Natural gas is a clean, easily transportable, and safe energy source. With the acceleration of my country's industrialization and urbanization, and the implementation of energy conservation and emission reduction policies, the consumption proportion of clean energy sources such as natural gas will continue to increase. As industrialization and urbanization continue, the demand for natural gas is growing rapidly. Obtaining syngas through coal or biomass gasification, and then producing synthetic natural gas through methanation, has become an effective way to compensate for insufficient gas supply, increase natural gas supply, and ensure national energy security.

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

[0004] CO + 3H2 = CH4 + H2OΔ H 298 =-206.1 kJ / mol

[0005] CO2 + 4H2 = CH4 + 2H2OΔ H 298 =-165.0 kJ / mol

[0006] This demonstrates that methanation is a strongly exothermic reaction with a very large amount of heat released. 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, posing certain safety risks to production operations. Additionally, the high CO concentration in the reaction system favors CO disproportionation at low temperatures, leading to catalyst deactivation through coking, and potentially even reactor blockage. In addition, improvements in catalyst activity and resistance to coking are still needed.

[0007] Currently, my country only possesses atmospheric pressure methanation technology for producing city gas and methanation catalysts for purifying trace amounts of CO / CO2 and other gases. There are no mature catalysts or supporting processes for methanation in coal-to-natural gas production. Conventional reactors, such as tubular fixed-bed reactors, suffer from various problems in mass and heat transfer. Methanation catalyst reduction can be performed via external pre-reduction or internal reduction. Generally speaking, catalyst reduction within the reactor is difficult to operate; improper operation can cause overheating, leading to catalyst sintering and incalculable economic losses. Catalyst pre-reduction technology offers numerous advantages. External pre-reduction can improve reducing agent utilization, reduce reducing agent dosage, lower start-up costs, shorten start-up cycles, and ultimately increase enterprise economic benefits. The pre-reduced catalyst, after being loaded into the reactor, can be used after low-temperature reactivation. This is particularly suitable for situations where the reduction temperature is significantly higher than the subsequent reaction temperature, eliminating the need for special reactor processing for the reduction reaction.

[0008] For the same catalyst, different reduction and passivation treatments will have different effects on its reaction activity and selectivity. Furthermore, different reduction and passivation treatments are usually used for different catalysts to achieve better activity and selectivity.

[0009] The drawbacks of existing technologies include long catalyst 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 very long passivation times and produce catalysts with uneven passivation.

[0010] Therefore, the industry urgently needs a method for the pre-reduction of methanation catalysts and a pre-reduction catalyst. Summary of the Invention

[0011] The purpose of this invention is to overcome the problems of long reduction time, large hydrogen consumption and low reduction efficiency in the pre-reduction process of catalysts in the prior art, and to provide a pre-reduction methanation catalyst, its preparation method and application. The catalyst has good reducibility, good reactivation performance, many active centers and good stability.

[0012] To achieve the above objectives, a first aspect of the present invention provides a pre-reduction methanation catalyst, wherein the catalyst comprises an active component, a support, and an auxiliary agent; wherein the support comprises alumina, the auxiliary agent comprises alkaline earth metal oxides and rare earth metal oxides, and the active component is Ni; based on the total amount of catalyst and calculated as oxides, the nickel content is 20-65% by weight%.

[0013] The catalyst, after re-reduction treatment, has an active center number of 0.03-0.41 mmol hydrogen / g catalyst. The re-reduction treatment conditions include: a temperature of 280℃, 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 particle size of the catalyst is 1-6 mm.

[0014] A second aspect of the present invention provides a method for preparing a pre-reduced methanation catalyst, wherein the method comprises:

[0015] (1) Preparation of oxidized catalysts by co-precipitation method;

[0016] The coprecipitation method includes: preparing a catalyst precursor by coprecipitating a water-soluble nickel source, a support precursor, and an auxiliary precursor in the presence of a precipitant; aging, washing, and optionally drying and / or calcining the resulting reaction mixture, and optionally pulverizing, to obtain a solid product with a particle size of less than 2500 μm; the support includes alumina, and the auxiliary agent includes alkaline earth metal oxides and rare earth metal oxides.

[0017] (2) The solid product is subjected to reduction treatment and passivation treatment in sequence. The reduction treatment is carried out in the presence of hydrogen gas. The passivation treatment is carried out under the action of a passivating agent. The passivation conditions include: the passivation temperature is not higher than 160°C.

[0018] (3) The product obtained in step (2) is mixed with an optional molding agent and / or lubricant and molded;

[0019] The amounts of the carrier precursor, auxiliary precursor, water-soluble nickel source, forming agent, and lubricant used are such that the nickel content in the prepared catalyst, based on the total amount of catalyst and calculated as oxides, is 20-65% by weight.

[0020] The third aspect of the present invention provides a pre-reduced methanation catalyst prepared by the preparation method described in the second aspect.

[0021] The fourth aspect of this invention provides the application of the pre-reduced methanation catalyst described in the first or third aspect in low-temperature and / or medium-temperature methanation reactions.

[0022] 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 stability and resistance to coking, enabling long-term continuous and stable operation without deactivation, fully meeting the performance requirements of methanation catalysts. The pre-reduction catalyst of this invention has even better performance.

[0023] The pre-reduced catalyst of this invention can be restored to a catalyst with a high number of active centers at a relatively low temperature, making it applicable to various reactions, reducing start-up time and investment in reduction equipment. The pre-reduced catalyst provided by this invention has a suitable degree of reduction, a large number of active centers, good reactivation performance, and good stability. In existing low-temperature and medium-temperature methanation devices, its activity can be restored under relatively low re-reduction conditions (e.g., a re-reduction temperature of 250°C for 2 hours), making it convenient to use. In contrast, existing pre-reduced catalysts rarely mention re-reduction conditions, but their passivation condition descriptions are generally vague, typically requiring re-reduction at above 250°C for more than 2 hours.

[0024] The preparation method provided by this invention, through the synergistic effect of the specific reduction and passivation processes described above, can rapidly and effectively reduce the metal components in the catalyst at lower temperatures and shorter time periods. Combined with subsequent appropriate passivation, this improves the performance of the obtained 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. Detailed Implementation

[0025] 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.

[0026] 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).

[0027] 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".

[0028] 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 280 °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.

[0029] The first aspect of this invention provides a pre-reduction methanation catalyst, wherein the catalyst comprises an active component, a support, and an auxiliary agent; wherein the support comprises alumina, the auxiliary agent comprises alkaline earth metal oxides and rare earth metal oxides, and the active component is Ni; based on the total amount of catalyst and calculated as oxides, the nickel content is 20-65% by weight%.

[0030] The catalyst, after re-reduction treatment, has an active center number of 0.03-0.41 mmol hydrogen / g catalyst. The re-reduction treatment conditions include: a temperature of 280℃, 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 particle size of the catalyst is 1-6 mm.

[0031] In this invention, it is understood that the catalyst can be at least one of the following shapes: cylindrical, gear-shaped, Raschig ring-shaped, and spherical, all of which can be used 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.

[0032] In a preferred embodiment, the nickel content is 25-60% by weight, based on the total amount of catalyst and calculated as oxides.

[0033] In a preferred embodiment, the number of active centers of the catalyst after re-reduction treatment is 0.025-0.4 mmol hydrogen / g catalyst, for example, it can be any point value among 0.025, 0.05, 0.075, 0.1, 0.125, 0.15, 0.175, 0.2, 0.225, 0.25, 0.275, 0.3, 0.325, 0.35, 0.375, 0.4 mmol hydrogen / g catalyst, as well as any range value composed of any two sets of data.

[0034] In a preferred embodiment, the catalyst is characterized by TPR (thermal reduction profile). In the TPR curve, the temperature corresponding to the peak of the low-temperature reduction peak with the largest area is 180-350℃, more preferably 200-300℃. 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 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.

[0035] 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.

[0036] According to the present invention, preferably, the degree of reduction of the pre-reduced catalyst is 70-95% as characterized by TPR. The pre-reduced catalyst provided by the present invention has a suitable degree of reduction and higher activity.

[0037] 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%.

[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 methanation process, 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] The advantage of using the above preferred embodiment is that it reduces carbon buildup.

[0043] In a preferred embodiment, based on the total amount of catalyst, the content of the alkaline earth metal oxide is 1-10%, the content of the rare earth metal oxide is 1-7 wt%, and the content of the alumina is 25-75 wt%; more preferably, based on the total amount of catalyst, the content of the alkaline earth metal oxide is 4-10 wt%, the content of the rare earth metal oxide is 3-7 wt%, and the content of the alumina is 35-70 wt%. The advantage of this preferred embodiment is reduced carbon buildup.

[0044] A second aspect of the present invention provides a method for preparing a pre-reduced methanation catalyst, wherein the method comprises:

[0045] (1) Preparation of oxidized catalysts by co-precipitation method;

[0046] The coprecipitation method includes: preparing a catalyst precursor by coprecipitating a water-soluble nickel source, a support precursor, and an auxiliary precursor in the presence of a precipitant; aging, washing, and optionally drying and / or calcining the resulting reaction mixture, and optionally pulverizing, to obtain a solid product with a particle size of less than 2500 μm; the support includes alumina, and the auxiliary agent includes alkaline earth metal oxides and rare earth metal oxides.

[0047] (2) The oxidized catalyst is reduced under a reducing atmosphere, wherein the reduction treatment refers to the reduction of the oxidized catalyst in step 1 under a reducing atmosphere;

[0048] (3) The catalyst obtained in step (2) is passivated, calcined and shaped under a passivation atmosphere, wherein the passivation temperature is not higher than 140°C;

[0049] The amounts of the carrier precursor, auxiliary precursor, water-soluble nickel source, forming agent, and lubricant used are such that the nickel content in the prepared catalyst, based on the total amount of catalyst and calculated as oxides, is 20-65% by weight.

[0050] In a preferred embodiment, the amounts of the carrier precursor, auxiliary precursor, 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 25-60% by weight.

[0051] In a preferred embodiment, the amount of the carrier precursor and the auxiliary precursor is such that, based on the total amount of catalyst, the content of the alkaline earth metal oxide is 1-10%, the content of the rare earth metal oxide is 1-7 wt%, and the content of the alumina is 25-75 wt%; more preferably, based on the total amount of catalyst, the content of the alkaline earth metal oxide is 4-10 wt%, the content of the rare earth metal oxide is 3-7 wt%, and the content of the alumina is 35-70 wt%.

[0052] 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.

[0053] 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.

[0054] In this invention, there is no particular limitation on the type of auxiliary agent precursor. Preferably, in step (1), the auxiliary agent precursor is selected from at least one of nitrates, acetates and chlorides containing auxiliary agents.

[0055] In this invention, there is no particular limitation on the type of carrier precursor. Preferably, in step (1), the carrier precursor is selected from at least one of silica sol, water glass, aluminosilicate, sodium aluminate, and aluminum nitrate.

[0056] In this invention, there are no restrictions on the mixing method of the water-soluble nickel source, the carrier precursor, and the auxiliary agent precursor. For example, the precipitant can be added to a mixed salt solution containing the water-soluble nickel source, the carrier precursor, and the auxiliary agent precursor; the mixed salt solution containing the water-soluble nickel source, the carrier precursor, and the auxiliary agent precursor can be added to the precipitant solution; or both can be added concurrently. Preferably, the precipitant is added to the mixed salt solution containing the water-soluble nickel source, the carrier precursor, and the auxiliary agent precursor. 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, an optional auxiliary agent precursor (preferably in the form of an aqueous solution) and a water-soluble nickel source (preferably in the form of an aqueous solution) are mixed (preferably heated to 40-80°C at a stirring speed of 20-150 rpm) to obtain a metal salt mixed solution; then, the metal salt mixed solution is mixed with the carrier precursor (preferably in the form of an aqueous solution) (preferably stirred at a stirring speed of 20-150 rpm). The present invention does not impose any restrictions on the concentration of the corresponding aqueous solutions, as long as the corresponding solute can be dissolved. Those skilled in the art can freely choose according to their needs.

[0057] In this invention, the 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.

[0058] 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.

[0059] In this invention, the range of roasting conditions is relatively wide. Preferably, in step (1), the roasting conditions include: a roasting temperature of 300-500℃ and a roasting time of 2-10 hours.

[0060] In a preferred embodiment, step (1) includes the drying process comprising:

[0061] The precipitate obtained after washing is dried at 80-180℃ for 2-24 hours;

[0062] 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.

[0063] 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.

[0064] 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.

[0065] In this invention, microspheres are obtained after spray drying, and these microspheres are subsequently calcined and shaped. This invention does not limit the shaping method; any commonly used method in the art can be used, such as tableting. Preferably, the shaping process includes: mixing the calcined material with a lubricant and a shaping agent, and then performing tableting. Those skilled in the art can select existing lubricants and shaping agents according to actual needs. The lubricant is, for example, graphite (preferably 2-3% by weight of the product obtained after shaping), and the shaping agent is, for example, at least one of calcium aluminate cement, alumina, and aluminum silicate (preferably 5-10% by weight of the final product). The catalyst particle size after tableting is preferably 1-6 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 hydrogen-containing atmosphere is a mixture of hydrogen and a protective gas.

[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.

[0069] In a preferred embodiment, in step (2), the volume concentration of hydrogen in the reducing atmosphere is 50-90%.

[0070] In a preferred embodiment, in step (2), the reduction process is a single-stage reduction.

[0071] In a preferred embodiment, the single-stage reduction conditions include: heating to 100℃-580℃ at a heating rate of 50-150℃ / hour, pressure of 0-2.0MPa, and holding at that temperature for 0.3-8 hours; more preferably, the single-stage reduction conditions include: heating to 200-550℃ at a heating rate of 50-150℃ / hour, pressure of 0.2-1.8MPa, and holding at that temperature for 0.5-6 hours.

[0072] According to a preferred embodiment of the present invention, the catalyst reduction temperature is preferably 350-550℃, and the reduction residence time is not more than 2 hours, preferably 0.5-2 hours.

[0073] 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.

[0074] In a preferred embodiment, the passivation treatment includes contacting the catalyst reduced in step (2) with a passivating agent at an initial temperature not exceeding 80°C, and controlling the temperature to not exceed 120°C during the passivation process.

[0075] In this invention, the range of passivation treatment methods is relatively wide. Preferably, in step (3), the passivation treatment is selected from gas passivation and / or liquid passivation.

[0076] In a preferred embodiment, in step (3), the passivating agent for gas passivation is an oxidizing gas with an oxygen volume content of 0.01-21%, and the balance is at least one of argon, nitrogen, carbon dioxide and helium. The temperature is controlled not to exceed 120°C during the passivation process.

[0077] In a preferred embodiment, in step (3), the passivating agent for liquid passivation is water or oil.

[0078] In one embodiment of the present invention, the main equipment included in the passivation process is a passivation furnace. The reduction furnace and the passivation furnace can be configured separately or share a common configuration, preferably separately. The passivation gas can pass through once or be recycled, preferably through gas recycling. By optimizing the passivation cooling rate, the passivation efficiency is improved, thereby increasing the overall system efficiency. After catalyst reduction, passivation is performed in the passivation furnace using carbon dioxide or a mixture of carbon dioxide and nitrogen or air. The temperature in the passivation furnace is controlled below 140°C, and the passivated gas is recycled or directly discharged.

[0079] According to one embodiment of the invention, passivation is performed using an oxidizing gas. The reduced catalyst is transferred into a passivation reactor. The passivation steps include: replacing H2 in the system with carbon dioxide or a mixture of carbon dioxide and nitrogen, and rapidly cooling the system. When the volume percentage of H2 in the system is ≤1% and the reactor temperature is below 160°C, O2 is introduced, employing multi-stage passivation. The reactor temperature is maintained below 160°C, preferably below 120°C, by adjusting the carbon dioxide pumping rate.

[0080] In a preferred embodiment, the reduced catalyst powder is cooled to below 100°C, preferably below 80°C, and a low-concentration oxidizing gas at below 100°C, preferably below 80°C, is introduced. The oxygen concentration is 0.01-21%, preferably 0.05%-19.0%, and most preferably 0.05%-17.0%. A four-stage passivation treatment is preferred: the first stage has an oxygen concentration of 0.05%-0.2%, the second stage has an oxygen concentration of 0.2-1%, the third stage has an oxygen concentration of 1-5%, and the fourth stage has an oxygen concentration of 5-17%. Generally, the time allocation is (4-9):(0.5-1):(0.5-1):(0.2-0.4) for the first passivation stage: second passivation stage: third passivation stage. The passivation operation ends when the reactor temperature stops rising and the inlet and outlet oxygen contents are essentially the same. The total passivation time is generally 0.5-40 hours, depending on the actual situation.

[0081] In this invention, there are no restrictions on the method of cooling the reduced catalyst, as long as the catalyst can be cooled to the required temperature, such as by heat exchange, cold exchange, water cooling, ammonia cooling, etc. In this invention, preferably, the method further includes: in step (2), after cooling the catalyst obtained by reduction in step (1), it is then purged with a protective gas, and then passivation is performed.

[0082] According to the present invention, preferably, the passivation time is 2-30 hours, for example, it can be a range of 2, 5, 10, 15, 20, 25, 30 hours or any two sets of values. In contrast, the passivation time in existing pre-reduction methods is generally over 48 hours. In the present invention, "the oxygen concentration of the oxidizing gas continuously increases" means that the oxygen concentration in the introduced oxidizing gas generally shows an upward trend. For example, 1, the oxygen concentration in the introduced oxidizing gas can continuously increase (i.e., the oxygen concentration increases at a certain rate); 2, the oxygen concentration in the introduced oxidizing gas can be introduced for a stable period of time before increasing. In this case, the oxygen concentration increases in stages. For example, in a multi-stage process, in one specific embodiment, the oxygen concentration in each subsequent stage is higher than that in the previous stage; in another specific embodiment, the oxygen concentration in the first few stages is the same and lower than that in the subsequent stages, thus showing an overall upward trend.

[0083] The present invention allows for a wide range of possible degrees of increase in the oxygen concentration of the oxidizing gas. It can be a regular, continuous increase, for example, 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.

[0084] In this invention, preferably, the oxygen concentration of the oxidizing 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 concentration in the passivation outlet gas is equal to the oxygen concentration of the oxidizing gas introduced in the previous stage, the next stage of oxidizing gas is introduced.

[0085] In a preferred embodiment, in step (3), the passivation treatment is gas passivation, which is carried out in at least three stages, preferably in stages 3-8 with progressively increasing concentrations, more preferably in stages 4-6 with progressively increasing concentrations, wherein the oxygen concentration of the oxidizing gas increases progressively in each stage. It is understood that, in this preferred embodiment, the oxygen concentration of the oxidizing gas in the first stage is lower than that in the second stage, and the oxygen concentration of the oxidizing gas in the second stage is lower than that in the third stage, and so on. Further, it is understood that the relative multiples of the oxygen concentrations of the oxidizing gas in each adjacent stage can be independently the same or different. For example, the relative multiple of the oxygen concentrations of the oxidizing gas in the first and second stages is 1.5, and the relative multiple of the oxygen concentrations of the oxidizing gas in the second and third stages can be 1.5 or 2; no specific limitation is made in this invention.

[0086] In a preferred embodiment, in step (3), the gas-agent ratio in the passivation treatment 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.

[0087] According to the present invention, preferably, in the passivation treatment, the gas-to-catalyst ratio in the first stage is not lower than that in the second stage. This preferred embodiment is more conducive to promoting a uniform passivation process for the catalyst and improving passivation efficiency.

[0088] In this invention, preferably, the oxidizing gas is 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.

[0089] In a preferred embodiment, in step (3), the initial oxygen concentration of the oxidizing gas introduced during the passivation treatment is 0.01-0.2% by volume, preferably 0.02-0.2% 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.

[0090] In a preferred embodiment, in step (3), the oxygen concentration of the oxidizing gas introduced in the later stage of the passivation treatment is 1.8-7 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, and also achieves high passivation efficiency. Preferably, in the passivation process, the concentration of the oxidizing gas introduced in the last stage is 21% by volume, i.e., air is introduced.

[0091] In a preferred embodiment, the reduction treatment is carried out in a reduction reactor, and the passivation treatment is carried out in a passivation reactor. Preferably, the reduction reactor and the passivation reactor are the same reactor or different reactors. It is understood in this invention that the reduction treatment and the passivation treatment can be carried out in the same reactor or two different reactors, or in the same space or different spaces.

[0092] In a preferred embodiment, the reduction reactor and the passivation reactor are each independently selected from at least one of a rotary kiln reactor, a fluidized bed reactor, and a drum reactor.

[0093] 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. During the passivation process, it is preferable to adjust the pumping rate of the protective gas (preferably carbon dioxide) to ensure that the passivation temperature does not exceed 80°C.

[0094] In a preferred embodiment, the method further includes mixing and granulating the passivated catalyst from step (2) with additives to obtain the catalyst. The size of the catalyst particles can be 1-6 mm, and the final shape and size of the catalyst can also be determined according to the application, such as a cylindrical shape with dimensions of 4 mm * 4 mm.

[0095] In a preferred embodiment, the additive is selected from at least one of lubricants, binders, and performance enhancers.

[0096] In a preferred embodiment, the lubricant is selected from at least one of graphite, stearic acid and palmitic acid and metal or alkali metal salts of acids, paraffin oil, ester lubricants and talc.

[0097] In a preferred embodiment, the binder is selected from at least one of methylcellulose, guar gum, cement, and water.

[0098] In a preferred embodiment, the performance enhancer is selected from at least one of magnesium oxide, calcium oxide, aluminum oxide, silicon carbide, aluminum nitride, and potassium nepheline.

[0099] In a preferred embodiment, the granulation is selected from at least one of ball rolling, tableting and extrusion molding.

[0100] According to one embodiment of the present invention, the passivated catalyst is compounded, mixed, and granulated with a lubricant and additives. After passivation, the metal surface is protected by an oxide film, and compression molding and crushing in air will not cause oxidation of the internal metal; compression molding is preferred. During compression molding, the additives can be selected from metal oxide carrier components, such as those containing Al2O3, ZnO, TiO2, activated carbon, zeolite, clay, natural silicates, or mixtures of two or more of these substances. Based on the catalyst, the lubricant is selected as follows: the lubricant is preferably graphite at 3 wt% or less, and the amount of all additives is preferably 12 wt% or less. The catalyst is molded into the desired shape suitable for the reaction, such as a cylinder, a hollow cylinder, a wheel, a four-hole cylinder, etc.

[0101] The method provided by this invention rapidly reduces smaller particles, thereby ensuring sufficient reduction of oxides in the catalyst, increasing the catalyst's reduction degree, and maintaining small crystal grains. This efficiently reduces the oxidized catalyst to a highly active catalyst precursor. Furthermore, the method offers high efficiency. If a molding step is included, it can simultaneously yield large-particle catalysts that are highly uniform, easily regenerable, and have numerous active sites, thus improving the overall catalyst reactivity and demonstrating promising prospects for industrial applications.

[0102] The third aspect of the present invention provides a pre-reduced methanation catalyst prepared by the preparation method described in the second aspect.

[0103] The fourth aspect of the present invention provides the application of the pre-reduced methanation catalyst described in the first or third aspect in low-temperature and / or medium-temperature methanation reactions.

[0104] The catalyst provided by this invention requires re-reduction activation in the presence of hydrogen before being used in a methanation reaction. The re-reduction conditions include: a reduction temperature of 170-320°C, preferably 200-300°C; and a reduction time of 0.5-6 hours, preferably 1-4 hours, and more preferably 2-3 hours. The re-reduction can be carried out in pure hydrogen or in a mixture of hydrogen and a protective gas, preferably in a pure hydrogen atmosphere. In a preferred embodiment, the re-reduction conditions further include: a space velocity of 1000-2000 h⁻¹. -1 The heating rate is 60-120℃ / hour.

[0105] In a preferred embodiment, the conditions for the methanation reaction include: a molar ratio of H2:CO:nitrogen of 3-15:0.5-1:1; a reaction temperature of 220-400℃; a pressure of 0-6MPa; and a feed gas space velocity of 1000-120000 h⁻¹. -1 .

[0106] The present invention will be described in detail below through embodiments.

[0107] 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.

[0108] Example 1

[0109] (1) Preparation of oxidized catalyst

[0110] 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 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 then washed three times with deionized water. The catalyst, by weight percentage, contained 43.21% NiO, 44.02% alumina, 4.36% lanthanum oxide, 4.205% magnesium oxide, and 4.205% calcium oxide.

[0111] The filter cake was slurried with a solid content of 40% 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 500°C for 4 hours.

[0112] Step 2. Reduction and passivation

[0113] After drying, the powder is passed through a 40-mesh sieve and then transported to a fluidized bed reduction reactor. First, a nitrogen replacement system is introduced into the reactor until the oxygen content is qualified (oxygen content ≤ 0.5% by volume). By controlling the opening of the preheating furnace, a preheating gas of 40% by volume of hydrogen and nitrogen is used to preheat the catalyst bed to 500℃ at 100℃ / hour for 2 hours, with a pressure of 0.2MPa and a gas-to-catalyst ratio of 2000.

[0114] Then, nitrogen is introduced to replace the hydrogen in the system, and the reduced catalyst is cooled to below 55°C. Under normal pressure, an oxygen-containing gas with an oxygen concentration of 0.2-21% by volume, composed of air and nitrogen, is introduced at a gas-to-catalyst ratio of 2000. The oxygen concentration is introduced in six stages, with concentrations of 0.2%, 0.6%, 1.0%, 3.0%, 8.0%, and 21% by volume, respectively. After introducing the oxygen-containing gas from the previous stage, when the oxygen concentration at the gas outlet equals the oxygen concentration at the gas inlet, the oxygen-containing gas from the next stage is introduced. This process of gradually increasing the oxygen concentration is used for passivation until passivation is complete. During this process, the passivation temperature of the catalyst bed is controlled to be below 80°C, resulting in a pre-reduced catalyst.

[0115] Step 3. Shaping

[0116] Based on the total amount of oxides after molding, 2% by weight of graphite and 8% by weight of calcium aluminate cement were added, mixed evenly, and pressed into discs with a particle size of 4×4mm to obtain the molded pre-reduced catalyst C1.

[0117] Example 2

[0118] Compared to Example 1, the only difference is the reduction conditions. The reduction conditions were: increasing the temperature from 120°C / hour to 520°C for 2 hours, with a pressure of 0.2 MPa, a 70% hydrogen-nitrogen mixture, and a gas-to-catalyst ratio of 2500. This yielded a pre-reduced catalyst C2.

[0119] Example 3

[0120] Compared with Example 1, the only difference is the reduction conditions, specifically:

[0121] After drying, the powder is passed through a 40-mesh sieve and then fed into a fluidized bed reduction reactor. First, a nitrogen purging system is introduced into the reactor until the oxygen content is within acceptable limits (oxygen content ≤ 0.5% by volume). The catalyst bed is then preheated with a 70% hydrogen-nitrogen mixture by controlling the preheating furnace opening, increasing the temperature from 100℃ / hour to 550℃ for 1 hour, at a pressure of 0.2 MPa and a gas-to-catalyst ratio of 2500. This yields a pre-reduced catalyst C3.

[0122] Example 4

[0123] Compared with Example 1, the only difference is the molding step, specifically:

[0124] Based on the total amount of oxides after molding, 2% by weight of graphite and 10% by weight of calcium aluminate cement were added and mixed evenly. Then, the mixture was pressed into discs with a particle size of 5×5mm to obtain the pre-reduced catalyst C4.

[0125] Example 5

[0126] Compared with Example 1, the only difference is the molding step, specifically:

[0127] The catalyst was prepared in the same manner as in Example 1. The difference was that the filter cake was dried at 160°C for 4 hours, then pulverized to a particle size DV(90) of 700 micrometers. After calcination at 500°C for 4 hours in a converter, it was reduced at 500°C for 4 hours under a 40% hydrogen-nitrogen mixed atmosphere. The catalyst was then cooled to 55°C for passivation. During this process, the passivation temperature of the catalyst bed was controlled to be less than 80°C to obtain the pre-reduced catalyst. Based on the total amount of oxides after molding, 2% by weight of graphite and 10% by weight of calcium aluminate cement were added and mixed evenly. The mixture was then pressed into discs with a particle size of 6 mm × 6 mm to obtain the pre-reduced catalyst C5.

[0128] Example 6

[0129] Catalyst C6 was prepared according to the method in Example 1, except that 110 g of Ni(NO3)2·6H2O, 92 g of Al(NO3)3·9H2O, and 5.31 g of La(NO3)3·6H2O were dissolved in 500 mL of deionized water, and 2 g of magnesium oxide and 2 g of calcium oxide were added to prepare a mixed metal salt solution I. 50 g of aluminum sol (alumina concentration of 20% by weight) was added to 100 mL of water, and the mixture was stirred at 50 r / min until homogeneous to obtain a dilute aluminum sol. The mixed metal salt solution and the aluminum sol were then mixed and stirred at 50 r / 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 then washed three times with deionized water. The catalyst composition, by weight percentage, consisted of 57.86% NiO, 25.74% alumina, 6.16% lanthanum oxide, 5.12% magnesium oxide, and 5.12% calcium oxide.

[0130] Example 7

[0131] Compared with Example 1, the only difference is the passivation conditions, specifically:

[0132] The reduced catalyst was then cooled to below 55°C, and an oxygen-containing gas with an oxygen concentration of 0.5-21% by volume, prepared from air and nitrogen and heated to below 60°C, was introduced under normal pressure. At a gas-to-catalyst ratio of 2000, oxygen-containing gas with oxygen concentrations of 0.5%, 1%, 2%, 3%, and 21% by volume was introduced sequentially in five stages. After introducing the oxygen-containing gas from the previous stage, when the oxygen concentration at the gas outlet equaled that at the gas inlet, the oxygen-containing gas from the next stage was introduced. This process of gradually increasing the oxygen concentration was continued until passivation was complete. During this process, the passivation temperature of the catalyst bed was controlled to be below 100°C, resulting in the pre-reduced catalyst C7.

[0133] Comparative Example 1

[0134] Compared to Example 6, the difference lies in the step of first shaping the oxidized catalyst and then performing reduction passivation. Specifically:

[0135] 1. Oxidized catalyst microspheres with a particle size DV (90) of 140 micrometers were prepared according to step 1 of Example 1;

[0136] 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 discs with a particle size of 4×4mm to obtain the molded oxidized catalyst.

[0137] 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 reducing gas at an oxygen concentration of 5% by volume, to obtain the pre-reduced catalyst D1.

[0138] Test case

[0139] The catalyst prepared above was subjected to performance tests, as detailed below:

[0140] 1. Evaluate the activity of the catalyst

[0141] A. The activity of the catalyst was evaluated by the number of active centers after the catalyst was re-reduced.

[0142] The number of active sites was obtained by H2 temperature-programmed desorption (H2-TPD) testing on 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 280 °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.

[0143] 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.

[0144] 2. The regenerability of the catalyst is characterized by TPR (Temperature Reduction Peak). 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.

[0145] 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.

[0146] 3. The reduction status of the catalyst is obtained through the degree of reduction.

[0147] 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 TPR test method described above, and the degree of reduction of the pre-reduced catalyst is calculated. Wherein, the degree of reduction = (TPR peak area of ​​direct reduction of the oxidized catalyst - peak area of ​​the pre-reduced catalyst at high temperature without reduction) / TPR peak area of ​​direct reduction of the oxidized catalyst * 100%.

[0148] The test results are listed in Table 1.

[0149] Table 1

[0150]

[0151] 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.

[0152] Application examples

[0153] To further evaluate the reactivity of the pre-reduction catalyst of the present invention, 10 mL of catalyst (particle size 10-20 mesh) was loaded into a fixed-bed reactor, and the catalysts obtained in the above examples and comparative examples were loaded respectively. The catalyst provided by the present invention needs to be reactivated in the presence of hydrogen before being used in the syngas methanation reaction. The reactivation conditions include: at atmospheric pressure in a pure hydrogen atmosphere, with a space velocity of 1500 h⁻¹. -1 After reducing the temperature to 280℃ at a rate of 100℃ / h for 2 hours, the feed gas was switched (H2 / CO / N2 = 3 / 1 / 1, molar ratio) for the reaction. The reaction temperature was 280℃ and the reaction space velocity was 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 2.

[0154] 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.

[0155] CO conversion rate is calculated using the following formula:

[0156]

[0157] in, V 1 、V 2 represents the volume of raw gas entering the reaction system and the volume of tail gas flowing out of the reaction system under standard conditions within a certain time period; c 1 、c 2 represents the content of the corresponding substances in the raw gas and the exhaust gas, respectively.

[0158] Table 2

[0159]

[0160] The results in Table 2 show that, compared with the comparative example, the pre-reduction catalyst of the present invention has good activity, and at the same time, it is not prone to carbon deposition and has good stability.

[0161] 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 an active component, a support, and an auxiliary agent; wherein the support comprises alumina, the auxiliary agent comprises alkaline earth metal oxides and rare earth metal oxides, and the active component is Ni; wherein, after re-reduction treatment, the number of active centers in the catalyst is 0.03-0.41 mmol hydrogen / g catalyst, and the re-reduction treatment conditions include: a temperature of 280℃, a time of 2 hours, and a re-reduction atmosphere of 10% by volume hydrogen containing hydrogen and argon, with a gas-to-catalyst volume ratio of 15000; the particle size of the catalyst is 1-6 mm; The method for preparing the pre-reduced methanation catalyst includes: (1) Preparation of oxidized catalysts by co-precipitation method; The coprecipitation method includes: preparing a catalyst precursor by coprecipitating a water-soluble nickel source, a support precursor, and an auxiliary precursor in the presence of a precipitant; aging, washing, and optionally drying and / or calcining the resulting reaction mixture, and pulverizing to obtain a solid product with a particle size of less than 2500 μm; the support includes alumina, and the auxiliary agent includes alkaline earth metal oxides and rare earth metal oxides. (2) The solid product is subjected to reduction treatment and passivation treatment in sequence. The reduction treatment is carried out in the presence of hydrogen gas. The passivation treatment is carried out under the action of a passivating agent. The passivation conditions include: the passivation temperature is not higher than 160°C. (3) The product obtained in step (2) is mixed with an optional molding agent and / or lubricant and molded; The amounts of the carrier precursor, auxiliary precursor, water-soluble nickel source, forming agent, and lubricant used are such that, based on the total amount of catalyst, the nickel content in the prepared catalyst, calculated as oxides, is 20-65% by weight. In step (2), the reduction process is a single-stage reduction; the single-stage reduction conditions include: heating to 100℃-580℃ at a heating rate of 50-150℃ / hour, pressure of 0-2MPa, and holding for 0.3-8 hours. The passivation process is gas passivation and is carried out in at least three stages.

2. The methanation catalyst according to claim 1, wherein, Based on the total amount of catalyst, the nickel content is 25-60% 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 0.025-0.4 mmol hydrogen / g catalyst.

4. The methanation catalyst according to any one of claims 1-3, 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 180-350℃.

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 200-300℃.

6. The methanation catalyst according to any one of claims 1-3, wherein, The catalyst was characterized by TPR, and the degree of reduction of the pre-reduced catalyst was 70-95%.

7. The methanation catalyst according to any one of claims 1-3, wherein, The alumina is γ-alumina.

8. The methanation catalyst according to any one of claims 1-3, wherein, The alkaline earth metal oxide is selected from at least one of BeO, MgO, CaO, CsO and BaO.

9. The methanation catalyst according to any one of claims 1-3, wherein, The rare earth metal oxide is selected from at least one of Y2O3, La2O3, CeO2, Pr2O3 and Sm2O3.

10. The methanation catalyst according to any one of claims 1-3, wherein, Based on the total amount of catalyst, the content of alkaline earth metal oxide is 1-10 wt%, the content of rare earth metal oxide is 1-7 wt%, and the content of alumina is 25-75 wt%.

11. The methanation catalyst according to claim 10, wherein, Based on the total amount of catalyst, the content of alkaline earth metal oxide is 4-10 wt%, the content of rare earth metal oxide is 3-7 wt%, and the content of alumina is 35-70 wt%.

12. 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: preparing a catalyst precursor by coprecipitating a water-soluble nickel source, a support precursor, and an auxiliary precursor in the presence of a precipitant; aging, washing, and optionally drying and / or calcining the resulting reaction mixture, and pulverizing to obtain a solid product with a particle size of less than 2500 μm; the support includes alumina, and the auxiliary agent includes alkaline earth metal oxides and rare earth metal oxides. (2) The solid product is subjected to reduction treatment and passivation treatment in sequence. The reduction treatment is carried out in the presence of hydrogen gas. The passivation treatment is carried out under the action of a passivating agent. The passivation conditions include: the passivation temperature is not higher than 160°C. (3) The product obtained in step (2) is mixed with an optional molding agent and / or lubricant and molded; The amounts of the carrier precursor, auxiliary precursor, water-soluble nickel source, forming agent, and lubricant used are such that, based on the total amount of catalyst, the nickel content in the prepared catalyst, calculated as oxides, is 20-65% by weight. In step (2), the reduction process is a single-stage reduction; the single-stage reduction conditions include: heating to 100℃-580℃ at a heating rate of 50-150℃ / hour, pressure of 0-2MPa, and holding for 0.3-8 hours. The passivation process is gas passivation and is carried out in at least three stages.

13. The method according to claim 12, wherein, The amounts of the carrier precursor, auxiliary precursor, 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 25-60% by weight.

14. The method according to claim 12, wherein, The amount of the carrier precursor and the auxiliary precursor is such that, based on the total amount of catalyst, the content of the alkaline earth metal oxide is 1-10 wt%, the content of the rare earth metal oxide is 1-7 wt%, and the content of the alumina is 25-75 wt%.

15. The method according to claim 14, wherein, The amount of the carrier precursor and the auxiliary precursor used is such that, based on the total amount of catalyst, the content of the alkaline earth metal oxide is 4-10 wt%, the content of the rare earth metal oxide is 3-7 wt%, and the content of the alumina is 35-70 wt%.

16. The method according to any one of claims 12-15, wherein, In step (1), the precipitant is selected from at least one of sodium carbonate, sodium bicarbonate, potassium carbonate, ammonia and sodium hydroxide.

17. The method according to any one of claims 12-15, wherein, In step (1), the water-soluble nickel source is selected from at least one of nickel nitrate, acetate and chloride.

18. The method according to any one of claims 12-15, wherein, In step (1), the auxiliary precursor is selected from at least one of nitrate, acetate and chloride containing auxiliary agents.

19. The method according to any one of claims 12-15, wherein, In step (1), the carrier precursor is selected from at least one of aluminum sol, sodium aluminate and aluminum nitrate.

20. The method according to any one of claims 12-15, 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; And / or, in step (1), the aging conditions include: an aging temperature of 30-70°C and a time of 1-8 hours; And / or, in step (1), the calcination conditions include: a calcination temperature of 300-500℃ and a calcination time of 2-10 hours.

21. The method according to any one of claims 12-15, wherein, In step (1), the drying process includes: The precipitate obtained after washing is dried at 80-180℃ for 2-24 hours; 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.

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

23. The method according to any one of claims 12-15, wherein, In step (2), the hydrogen-containing gas is a mixture of hydrogen and a protective gas.

24. The method according to claim 23, wherein, In step (2), the protective gas is at least one of helium, argon and nitrogen.

25. The method according to any one of claims 12-15, wherein, In step (2), the volume concentration of hydrogen in the hydrogen-containing gas is 50-90%.

26. The method according to any one of claims 12-15, wherein, The single-stage reduction conditions include: heating to 200-550℃ at a heating rate of 50-150℃ / hour, pressure of 0.2-1.8MPa, and holding at that temperature for 0.5-6 hours.

27. The method according to any one of claims 12-15, wherein, In step (2), the passivation process includes contacting the catalyst reduced in step (2) with a passivating agent at an initial temperature not exceeding 80°C, and controlling the temperature not to exceed 120°C during the passivation process.

28. The method according to any one of claims 12-15, wherein, In step (2), the passivating agent for gas passivation is an oxidizing gas with an oxygen volume content of 0.01-21%, and the balance is at least one of argon, nitrogen, carbon dioxide and helium. The temperature is controlled not to exceed 120°C during the passivation process.

29. The method according to any one of claims 12-15, wherein, In step (2), the passivation process is progressively increased in at least 3-8 stages.

30. The method according to claim 29, wherein, In step (2), the passivation process is divided into at least 4-6 stages with increasing oxygen concentration. The passivation process uses an oxidizing gas for passivation, and the oxygen concentration of the oxidizing gas increases in each stage.

31. The method according to any one of claims 12-15, wherein, In step (2), the gas-to-agent ratio in the passivation treatment is 200-5000.

32. The method according to claim 31, wherein, In step (2), the gas-to-agent ratio in the passivation treatment is 500-3000.

33. The method according to any one of claims 12-15, wherein, In step (2), the gas-to-agent ratio in the passivation process is not lower than that in the subsequent stage.

34. The method according to any one of claims 12-15, wherein, In step (2), during the passivation process, the initial oxygen concentration of the oxidizing gas introduced is 0.02-0.2% by volume.

35. The method according to claim 34, wherein, In step (2), during the passivation process, the initial oxygen concentration of the oxidizing gas introduced is 0.05-0.2% by volume.

36. The method according to any one of claims 12-15, wherein, In step (2), the oxygen concentration of the oxidizing gas introduced in the later stage of the passivation process is 1.8-7 times that of the oxygen concentration of the oxidizing gas introduced in the previous stage.

37. The method according to any one of claims 12-15, wherein, The reduction treatment is carried out in a reduction reactor, and the passivation treatment is carried out in a passivation reactor.

38. The method according to claim 37, wherein, The reduction reactor and the passivation reactor may be the same reactor or different reactors.

39. The method according to claim 37, wherein, The reduction reactor and the passivation reactor are each independently selected from at least one of a rotary kiln reactor, a fluidized bed reactor, and a drum reactor.

40. The method according to any one of claims 12-15, wherein, The method further includes: mixing the passivated catalyst from step (2) with additives and granulating them to obtain the catalyst.

41. The method according to claim 40, wherein, The additive is selected from at least one of lubricants, binders, and performance enhancers.

42. The method according to claim 41, wherein, The lubricant is selected from at least one of graphite, stearic acid and palmitic acid and metal or alkali metal salts of acids, paraffin oil, ester lubricants and talc.

43. The method according to claim 41, wherein, The binder is selected from at least one of methylcellulose, guar gum, cement, and water.

44. The method according to claim 41, wherein, The performance-enhancing agent is selected from at least one of magnesium oxide, calcium oxide, aluminum oxide, silicon carbide, aluminum nitride, and potassium nepheline.

45. The method according to claim 40, wherein, The granulation process is selected from at least one of ball rolling, tableting, and extrusion molding.

46. ​​The pre-reduced methanation catalyst prepared by the method of any one of claims 12-45.

47. The use of the pre-reduced methanation catalyst according to any one of claims 1-11, 46 in low-temperature and / or medium-temperature methanation reactions.

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