A methanation catalyst suitable for jet recycling process and its preparation method

Abstract

This invention discloses a methanation catalyst suitable for a jet-cycle process and its preparation method. The methanation catalyst for the jet-cycle process mainly consists of the following components by mass percentage: 20-50% nickel oxide, 3-8% magnesium oxide, 1-5% lanthanum oxide, 1-5% cerium oxide, with the balance being a titanium oxide-alumina composite support. The catalyst has a bimodal porous structure with a total pore volume of 0.6-1.3 cm³. 3 / g, the pore size distribution exhibits a bimodal characteristic, including mesopore peaks of 2-10 nm and macropore peaks >60 nm, with macropores larger than 60 nm accounting for 15-30% of the total pore volume and a specific surface area of ​​130-220 m². 2 / g. This catalyst features extremely low bed pressure drop, excellent high space velocity adaptability, and high thermal stability.

Description

Technical Field

[0001] This invention relates to catalyst synthesis processes, and more particularly to a methanation catalyst suitable for jet cycling processes and its preparation method. Background Technology

[0002] Methanation is the core process for converting syngas (mainly composed of CO, CO2, and H2) into synthetic natural gas (SNG). Among numerous methanation processes, the jet-cycle process (see patents CN118746025A and CN101705128A) has attracted widespread attention due to its unique energy-saving advantages. This process replaces the traditional circulating compressor with a Venturi ejector, utilizing the kinetic energy of the high-pressure feed gas to eject the recycled gas after the reaction, which can significantly reduce equipment investment and operating energy consumption.

[0003] However, the jet cycle process places special and stringent requirements on the catalyst, which traditional methanation catalysts cannot meet:

[0004] Extremely low bed pressure drop sensitivity: The ejector's entrainment efficiency is extremely sensitive to changes in intake-side pressure. Catalyst bed pressure drop directly translates into increased back pressure on the recirculation gas side, leading to a decrease in entrainment efficiency. When the pressure drop exceeds the design threshold, it will trigger a series of chain reactions, including a decrease in the recycle ratio, inability to remove reaction heat in a timely manner, and bed overheating, potentially even causing runaway reactions. Therefore, low pressure drop is a fundamental prerequisite for stable operation of the ejector recirculation process, which is fundamentally different from processes with compressors. (Theoretical explanation: In the jet-cycle process, the high-pressure feed gas flow passes through the Venturi injector, where a high-speed jet is generated at the throat, creating a negative pressure zone to entrain the low-pressure circulating gas. The pressure drop (ΔP) of the catalyst bed is directly superimposed on the back pressure on the circulating gas side. According to the working principle of the injector, its entrainment coefficient (the ratio of the entrained gas flow rate to the working gas flow rate) is extremely sensitive to the suction side pressure. Excessive bed pressure drop will reduce the pressure difference between the two gas flows within the injector, thereby significantly reducing the entrainment efficiency, disrupting the cycle ratio designed in the process, and ultimately leading to the accumulation of reaction heat and bed overheating. Therefore, the catalyst must have an extremely low bed pressure drop to ensure the efficient and stable operation of the injector.)

[0005] Excellent high space velocity adaptability: Jet cycle processes typically operate at high cycle ratios, requiring catalysts to maintain high activity at high volumetric space velocities of 10,000-20,000 h⁻¹. Traditional catalysts, guided by high specific surface area and small pore size (2-10 nm), exhibit significant internal diffusion resistance at high gas velocities, preventing reactants from effectively contacting the active sites on the inner surface, leading to a sharp decline in conversion at high space velocities.

[0006] Excellent thermal stability: Adiabatic reaction conditions and potential uneven local airflow distribution can easily lead to hot spots forming in the bed. The catalyst must be able to resist high-temperature (≥650℃) sintering.

[0007] Patent CN102500405A discloses a methanation catalyst with small pore volume (0.3-0.6 cm³ / g) and predominantly mesoporous structure. This leads to a significant increase in bed pressure drop (>0.25 MPa / m) at high space velocities (>10000 h⁻¹). When applied to the jet cycle process, this easily causes problems such as decreased Venturi ejector efficiency, cycle ratio imbalance, and bed overheating. Although patent CN104888826A attempts to optimize the pore structure, it does not involve the systematic construction of macropores >60 nm. The obtained catalyst has an insufficient proportion of macropores and poor pore connectivity. Under simulated jet cycle conditions, its high space velocity (>15000 h⁻¹) activity retention and low pressure drop performance still fail to meet the process requirements.

[0008] In view of this, the present invention is hereby proposed. Summary of the Invention

[0009] To address the problems existing in the prior art, the primary objective of this invention is to provide a methanation catalyst suitable for the jet-cycle process. This catalyst, through targeted macroporous volume, dual-mold structure design, and special composition design, maintains high catalytic activity while significantly reducing bed pressure drop, ensuring efficient and stable operation of the injector. It also possesses excellent high space velocity adaptability, overcoming internal diffusion limitations, and exhibits outstanding anti-sintering capability to adapt to the high-temperature environment of the adiabatic bed. With its extremely low bed pressure drop, excellent high space velocity adaptability, and high thermal stability, it overcomes the shortcomings of existing catalysts that cannot be adapted to this energy-saving process.

[0010] The second objective of this invention is to provide a method for preparing the above-mentioned catalyst, which has a simple process flow, is easy to industrialize, and produces a catalyst with both excellent catalytic activity and internal and external mass transfer performance, achieving a balance between the two.

[0011] To achieve the above objectives, the technical solution of the present invention is as follows:

[0012] This invention provides a methanation catalyst suitable for jet recycling process, which is mainly composed of the following components: by mass percentage, nickel oxide 20-50%, magnesium oxide 3-8%, lanthanum oxide 1-5%, cerium oxide 1-5%, and the balance being a titanium oxide-alumina composite support;

[0013] The catalyst has a bimodal porous structure with a total pore volume of 0.6-1.3 cm³. 3 / g, the pore size distribution exhibits a bimodal characteristic, including mesopore peaks of 2-10 nm and macropore peaks >60 nm, with macropores larger than 60 nm accounting for 15-30% of the total pore volume and a specific surface area of ​​130-220 m². 2 / g.

[0014] Preferably, as a further feasible option, in the titanium oxide-alumina composite carrier, the mass ratio of titanium oxide to alumina is 1: (3-10).

[0015] Preferably, as a further feasible option, the pore size range of the macropore peak is 60-150 nm.

[0016] Preferably, as a further feasible option, the pore connectivity index of the dual-mode pore structure is not less than 0.8, the tortuosity factor is not greater than 2.0, and the lateral pressure strength is not less than 100 N / cm.

[0017] Preferably, as a further feasible option, by mass percentage, nickel oxide 30-45%, magnesium oxide 4-7%, lanthanum oxide 2-4%, cerium oxide 2-4%, and the balance being a titanium oxide-alumina composite carrier.

[0018] The present invention provides a low-pressure-drop, large-pore methanation catalyst suitable for jet-cycle processes. The active component of the catalyst is nickel, with a mass content of 20% to 50% based on NiO oxide. Preferably, the NiO content is 30% to 45%. To improve the catalyst's mechanical strength, thermal stability, and anti-coking properties, a specific auxiliary agent system is introduced. This system includes a structural auxiliary agent MgO, with a mass content of 3% to 8%, used to enhance the thermal stability of the support; and electronic auxiliary agents La2O3 and CeO2, both with a mass content of 1% to 5%. La2O3 is used to modulate the electronic state of the active component Ni, inhibiting deep dehydrogenation reactions, thereby inhibiting coking; CeO2 utilizes its oxygen storage and release capacity to regulate the oxygen potential of the reaction microenvironment, synergistically inhibiting coking. The support is a TiO2-Al2O3 composite support with the remainder. The preferred mass ratio of TiO2 to Al2O3 is 1:(3-10). The introduction of TiO2 not only significantly enhances the structural stability of the support framework under high temperature and high water vapor partial pressure conditions above 650℃ by forming stable Ti-O-Al bonds with Al2O3, thus inhibiting the migration and sintering of nickel grains, but also moderately modulates the surface properties of the support. In conjunction with the Mg-La-Ce promoter system, it more effectively suppresses carbon deposition caused by methanation side reactions (such as the Boudouard reaction). This is one of the core aspects of achieving ultra-long thermal stability in the catalyst of this invention while maintaining low pressure drop and high activity.

[0019] The core feature of the catalyst lies in its unique dual-mode pore structure designed to meet the "low pressure drop, high mass transfer" requirements of the injection cycle process. The physicochemical parameters of the catalyst are as follows:

[0020] Total pore volume: 0.6 cm³ / g to 1.3 cm³ / g, to provide ample space for gas diffusion and effectively reduce internal diffusion resistance. The preferred range is 0.7 cm³ / g to 1.2 cm³ / g.

[0021] Pore ​​size distribution: It exhibits a bimodal characteristic. The first peak is located in the mesoporous region of 2-10 nm, which provides a high specific surface area to support and disperse highly active Ni centers, ensuring intrinsically high catalytic activity. The second main peak is located in the macroporous region of >60 nm, forming a "highway" for rapid gas transport, which greatly alleviates the internal diffusion limitation under high space velocity conditions and significantly reduces bed airflow resistance.

[0022] Macropore proportion: The pore volume contributed by macropores with a pore size greater than 60 nm accounts for 15% to 30% of the total pore volume. This proportion of macropore network is the key to ensuring high space velocity and low pressure drop performance. Its high connectivity allows reactant gases to enter and exit the catalyst quickly.

[0023] Specific surface area: 130 m² 2 / g to 220 m 2 / g, to ensure a sufficient number of active sites.

[0024] Mechanical strength: Lateral compressive strength not less than 100 N / cm to meet the mechanical strength requirements of industrial applications.

[0025] Furthermore, the macroporous structure of the catalyst has high connectivity, with a pore connectivity index of not less than 0.8 and a tortuosity factor of not more than 2.0. This means that the reactant gas can be rapidly transported within the catalyst particles along a path with less resistance. This is the key structural guarantee for achieving the excellent effect of significantly reducing the bed pressure drop compared to traditional catalysts.

[0026] Furthermore, the three ranges of total pore volume (0.6-1.3 cm³ / g), macropore (>60 nm) proportion (15-30%), and specific surface area (130-220 m² / g) are the optimal matching ranges verified by extensive experiments. Beyond these ranges, it is difficult to simultaneously achieve low pressure drop and high activity. For example, experiments show that when the total pore volume is below 0.6 cm³ / g, even with a high macropore proportion, the gas diffusion space is still insufficient, and internal diffusion is significantly restricted at high space velocities; when the total pore volume is above 1.3 cm³ / g, the catalyst's mechanical strength decreases significantly. Similarly, when the macropore proportion is below 15%, the low pressure drop advantage is not obvious, and above 30% leads to excessive loss of specific surface area and the number of active sites.

[0027] The macroscopic shape of the catalyst particles of the present invention can be clover-shaped, toothed spherical, Raschig ring-shaped, four-hole or five-hole, etc.

[0028] This invention provides a method for preparing a methanation catalyst suitable for a jet-cycle process, comprising the following steps:

[0029] Mix boehmite, titanium source, thermally decomposable organic pore-forming agent, and nitrate solution containing magnesium, lanthanum, and cerium, adjust the pH to 3-5, and knead to form a plastic mass.

[0030] The plastic mass is shaped, dried at 100-120°C, and then calcined in air at 500-700°C for 3-6 hours to obtain the titanium oxide-alumina composite carrier.

[0031] The titanium dioxide-alumina composite carrier is impregnated with an equal volume of nickel-ammonia complex solution, dried, and then calcined at 350-500℃.

[0032] Preferably, as a further feasible option, the titanium source is selected from at least one of tetrabutyl titanate, titanium sulfate, or titanium dioxide sol.

[0033] Preferably, as a further feasible option, the organic pore-forming agent is selected from at least one of polyethylene glycol, starch, and polyvinyl alcohol.

[0034] Preferably, as a further feasible option, the nickel-ammonia complex solution is prepared by mixing nickel nitrate and ammonia water at a nickel to ammonia molar ratio of 1:(2-4), wherein the mass concentration of Ni²⁺ is 10-30wt%.

[0035] Preferably, as a further feasible option, the added mass of the organic pore-forming agent is 8-20% of the dry basis mass of the pseudoboehmite.

[0036] In actual operation, the preparation method of the catalyst of the present invention is carried out according to the following steps:

[0037] (1) Preparation and modification of the carrier precursor: Boehmite powder, a titanium source (such as at least one of tetrabutyl titanate, titanium sulfate, or titanium dioxide sol), a thermally decomposable organic pore-forming agent, and a nitrate solution containing magnesium, lanthanum, and cerium (calculated in amounts based on the final catalyst target composition) are mixed. The organic pore-forming agent is selected from at least one of polyethylene glycol (PEG, molecular weight 2000-15000), starch, and polyvinyl alcohol, and its addition mass is preferably 8% to 20% of the dry basis mass of the boehmite. During the mixing process, a dilute acid solution (such as nitric acid or acetic acid) is slowly added to adjust the pH of the mixture to 3-5, and the mixture is thoroughly kneaded to form a homogeneous mass with good plasticity. In this step, the precursors of Ti, Mg, La, and Ce elements are uniformly dispersed in the alumina precursor (boehmite).

[0038] (2) Molding and framework construction: The plastic agglomerate obtained in step (1) is shaped by extrusion or pressing to obtain catalyst carrier precursor particles with the desired macroscopic shape (such as clover-shaped, toothed spherical, Raschig ring, four-pore or five-pore shape, etc.). The shaped wet particles are dried at 100-120℃ for 4-8 hours to remove physically bound water. Subsequently, in an air atmosphere, the temperature is raised to 500-700℃ at a set heating rate (such as 1-5℃ / min) and calcined at a constant temperature for 3-6 hours. During this process, the organic pore-forming agent is decomposed and burned by heat, leaving a large number of interconnected macropores with controllable size in the titanium oxide-alumina composite framework; at the same time, the compounds of Ti, Mg, La and Ce decompose into oxides and interact with the alumina precursor to form a titanium oxide-alumina composite oxide framework with better thermal stability and higher mechanical strength in situ, thereby obtaining a modified macroporous titanium oxide-alumina composite carrier with a dual-mode pore structure.

[0039] (3) Loading and activation of active components: The pre-prepared nickel-ammonia complex solution was uniformly impregnated onto the modified macroporous titanium dioxide-alumina composite support obtained in step (2) using an equal-volume impregnation method. The nickel-ammonia complex solution was prepared by mixing nickel nitrate and ammonia water in a molar ratio of Ni²⁺:NH₃ = 1:(2-4), wherein the mass concentration of Ni²⁺ was 10wt% to 30wt%. The impregnation process ensured that the support uniformly absorbed the impregnation solution. The impregnated material was dried at 100-120℃ for 4-8 hours, and then calcined in an oxidizing atmosphere (such as air) at 350-500℃ for 3-6 hours. In this step, the nickel-ammonia complex decomposed, and the nickel species were loaded onto the mesoporous and macroporous inner surfaces of the modified macroporous support in the form of highly dispersed nickel oxide (NiO), thus obtaining the final methanation catalyst.

[0040] The catalyst described above is specifically designed for methanation injection recirculation process, which is an adiabatic fixed-bed reaction process. The recirculation of the gas is achieved through a Venturi injector, and the methanation reaction is carried out in a fixed-bed reactor. The operating pressure is 2.0-6.0 MPa, the reactor inlet temperature is 250-350℃, the process space velocity is 5000-20000 h⁻¹, and the recirculation ratio is 1-6.

[0041] Compared with the prior art, the solution of the present invention has the following technical effects:

[0042] (1) Revolutionary low pressure drop performance, fundamentally adaptable to the injection cycle process: This invention constructs a high-proportion (>30%), highly interconnected macroporous network, forming a "highway" for gas flow inside the catalyst particles. At space velocities as high as 15,000-20,000 h⁻¹, the bed pressure drops to below 0.02 MPa, which is more than 60% lower than that of traditional catalysts (>0.05 MPa / m). Low pressure drop is the lifeline for ensuring the efficient and stable operation of the injector. It directly guarantees the realization of the designed cycle ratio, effectively removes the heat of reaction, and prevents the bed from overheating, thus laying the foundation for the "self-balancing" and "low-energy consumption" operation of the entire injection cycle process.

[0043] (2) High activity and high conversion rate at high space velocities: The unique "dual-membrane" structure achieves a synergistic effect of "mesopores maintaining activity and macropores promoting mass transfer". The macroporous network ensures that reactants and products can quickly enter and exit the interior of the catalyst particles, greatly alleviating the internal diffusion limitation; the abundant mesopores provide a huge specific surface area and support highly dispersed nickel active centers. Therefore, even at ultra-high space velocities of 20,000 h⁻¹, the CO conversion rate can still be maintained above 95%, and the CO2 conversion rate exceeds 75%, achieving a balance between high space velocity and high activity.

[0044] (3) Excellent thermal stability and anti-coking ability: The MgO introduced into the support forms a magnesium aluminum spinel structure with Al2O3 during calcination, which significantly enhances the mechanical strength and anti-sintering ability of the support at high temperature. The addition of La2O3 can adjust the electronic state of nickel and inhibit the deep dehydrogenation of the coking precursor; the oxygen storage capacity of CeO2 helps to regulate the reaction microenvironment, promote the water-gas shift reaction, and further inhibit coking. The synergistic effect of the Mg-La-Ce ternary promoter system enables the catalyst to maintain a stable crystal structure and catalytic performance at a hot spot temperature of 650℃, and the activity retention rate exceeds 95% after 1000 hours of operation.

[0045] (4) Significant improvement in overall energy efficiency: Using this catalyst ensures that the injection cycle process operates under optimal conditions. On the one hand, the low pressure drop directly reduces the energy consumption of the feed gas compressor and system circulation; on the other hand, the stable high thermal efficiency and long catalyst life reduce unplanned shutdowns and catalyst replacement frequency, thereby significantly reducing the total life cycle operating cost of the methanation unit. Attached Figure Description

[0046] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0047] Figure 1 This is a pore size distribution curve of the catalyst prepared in Example 1 of the present invention;

[0048] Figure 2 The graph shows the effect of air velocity on pressure drop in Example 1 (C-1) and Comparative Example 1 (D-1);

[0049] Figure 3 This is a schematic diagram of the methanation jetting cycle process of the present invention. Detailed Implementation

[0050] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0051] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0052] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0053] To more clearly illustrate the technical solutions in this invention, specific embodiments are described below.

[0054] Example 1 Preparation of catalyst C-1

[0055] (1) Take 1000g of boehmite (dry basis), add tetrabutyl titanate equivalent to 50g of TiO2, add 150g of polyethylene glycol 6000 (15% of dry basis) as a pore-forming agent, and then add a mixed solution containing magnesium nitrate, lanthanum nitrate and cerium nitrate (calculate the required salt amount according to the final catalyst target content: MgO 5 wt%, La2O3 3 wt%, CeO2 2 wt%). Add dilute nitric acid solution to adjust the pH to 4.0, and knead thoroughly in a kneader for 40 minutes to obtain a uniform plastic clay.

[0056] (2) The mud was dried, granulated, and pressed into sheets using a four-hole mold. Subsequently, it was heated to 600℃ in a muffle furnace at a heating rate of 2℃ / min and calcined in air at this temperature for 4 hours to obtain a modified macroporous TiO2-Al2O3 composite support. According to BET and mercury porosimetry tests, the support had a specific surface area of ​​178 m² / g, a total pore volume of 1.18 cm³ / g, and a distinct bimodal pore size distribution. The most probable pore sizes were 5 nm and 75 nm, respectively, with macropores larger than 60 nm accounting for 25% of the total pore volume.

[0057] (3) Preparation of nickel-ammonia complex impregnation solution: Dissolve 530 g of nickel nitrate hexahydrate in an appropriate amount of deionized water, and slowly add concentrated ammonia water while stirring until the solution turns dark blue and transparent (pH≈9.5, Ni:NH3 molar ratio about 1:3). Finally, adjust the volume to the saturated water absorption volume of the carrier. The mass concentration of Ni²⁺ in the solution is about 25%.

[0058] (4) Place the carrier obtained in step (2) in a rotary impregnation pot and impregnate it with the impregnation solution prepared in step (3) for 2 hours.

[0059] (5) The impregnated material was dried at 120℃ for 6 hours, and then calcined in air at 450℃ for 4 hours to obtain catalyst C-1. XRF analysis showed its final composition to be: NiO 38.5%, MgO 5.0%, La2O3 3.0%, CeO2 2.0%, and the remainder being a TiO2-Al2O3 composite support (of which TiO2 was approximately 4.5%). The specific pore size distribution is as follows: Figure 1 As shown.

[0060] Example 2 Preparation of catalyst C-2

[0061] (1) Take 1000g of pseudoboehmite (dry basis), add a titanium sulfate solution equivalent to 20g of TiO2, add 80g of polyvinyl alcohol 1788 (8% dry basis) as a pore-forming agent, and then add a mixed solution containing magnesium nitrate, lanthanum nitrate and cerium nitrate (calculate the required salt amount based on the final catalyst target content: MgO 3 wt%, La2O3 1 wt%, CeO2 1 wt%). Adjust the pH to 3.5 with dilute nitric acid and knead to form a plastic slurry.

[0062] (2) The clay was extruded into 1.5 mm clover-shaped strips and dried at 100 °C for 8 hours. It was then calcined in air at 500 °C for 6 hours to obtain the carrier. The total pore volume was measured to be 0.64 cm³ / g, the pore size distribution showed a bimodal structure, the proportion of macropores larger than 60 nm was about 18%, and the specific surface area was 210 m² / g.

[0063] (3) Prepare nickel-ammonia complex impregnation solution (Ni²⁺ concentration 20%, Ni:NH3 molar ratio 1:2).

[0064] (4) Following steps (4) and (5) of Example 1, after impregnation and drying, the catalyst C-2 was calcined at 400°C for 5 hours. The final composition was: NiO 22.2%, MgO 3.0%, La2O3 1.1%, CeO2 1.0%, and TiO2-Al2O3 composite support (of which TiO2 was about 2%) as the balance.

[0065] Example 3 Preparation of catalyst C-3

[0066] (1) Take 1000g of pseudoboehmite (dry basis), add titanium dioxide sol equivalent to 100g of TiO2, add 200g of soluble starch (accounting for 20% of dry basis) as a pore-forming agent, and then add a mixed solution containing magnesium nitrate, lanthanum nitrate and cerium nitrate (calculate the required salt amount based on the final catalyst target content: MgO 8 wt%, La2O3 5 wt%, CeO2 5 wt%). Adjust the pH to 5.0 with dilute nitric acid and knead to form a plastic slurry.

[0067] (2) The clay was pressed into Raschig rings using a mold and dried at 120°C for 4 hours. It was then calcined in air at 700°C for 3 hours to obtain the carrier. The total pore volume was measured to be 1.28 cm³ / g, with macropores larger than 60 nm accounting for approximately 28%, and a specific surface area of ​​135 m² / g.

[0068] (3) Prepare nickel-ammonia complex impregnation solution (Ni²⁺ concentration 30%, Ni:NH3 molar ratio 1:4).

[0069] (4) Following steps (4) and (5) of Example 1, after impregnation and drying, the catalyst C-3 was calcined at 500°C for 3 hours. The final composition was: NiO 42.8%, MgO 7.9%, La2O3 4.9%, CeO2 4.8%, and the remainder being TiO2-Al2O3 composite support (of which TiO2 was approximately 9%).

[0070] Example 4 Preparation of catalyst C-4

[0071] (1) Take 1000g of boehmite (dry basis), add tetrabutyl titanate equivalent to 70g of TiO2, add 100g of polyethylene glycol 4000 (10% of dry basis) as a pore-forming agent, and then add a mixed solution containing magnesium nitrate, lanthanum nitrate and cerium nitrate (calculate the required salt amount based on the final catalyst target content: MgO 6 wt%, La2O3 2 wt%, CeO2 3 wt%). Adjust the pH to 4.5 with dilute nitric acid and knead to form a plastic slurry.

[0072] (2) The clay was extruded into toothed spheres using a mold and dried at 110°C for 6 hours. It was then calcined in air at 550°C for 5 hours to obtain the carrier. The total pore volume was measured to be 0.95 cm³ / g, with macropores larger than 60 nm accounting for approximately 22%, and a specific surface area of ​​190 m² / g.

[0073] (3) Prepare nickel-ammonia complex impregnation solution (Ni²⁺ concentration 15%, Ni:NH3 molar ratio 1:3.5).

[0074] (4) Following steps (4) and (5) of Example 1, after impregnation and drying, the catalyst C-4 was calcined at 380°C for 5 hours. The final composition was: NiO 28.5%, MgO 6.0%, La2O3 2.1%, CeO2 2.9%, and the balance being TiO2-Al2O3 composite support (of which TiO2 was approximately 6%).

[0075] Example 5 Preparation of catalyst C-5

[0076] (1) Take 1000g of boehmite (dry basis), add tetrabutyl titanate equivalent to 60g of TiO2, add 120g of polyethylene glycol 6000 (12% dry basis) as a pore-forming agent, and then add a mixed solution containing magnesium nitrate, lanthanum nitrate and cerium nitrate (calculate the required salt amount based on the final catalyst target content: MgO 4 wt%, La2O3 1.5 wt%, CeO2 1.0 wt%). Adjust the pH to 4.2 with dilute nitric acid solution, and knead thoroughly in a kneader for 40 minutes to obtain a uniform plastic clay.

[0077] (2) The clay was dried, granulated, and pressed into sheets using a four-hole mold. Subsequently, it was heated to 600℃ in a muffle furnace at a heating rate of 2℃ / min and calcined in air at this temperature for 4 hours to obtain a modified macroporous TiO2-Al2O3 composite support. BET and mercury porosimetry tests showed that the support had a specific surface area of ​​168 m² / g, a total pore volume of 1.05 cm³ / g, and macropores with a diameter greater than 60 nm accounted for 22% of the total pore volume.

[0078] (3) Preparation of high-concentration nickel-ammonia complex impregnation solution: Dissolve 670 g of nickel nitrate hexahydrate in an appropriate amount of deionized water, and slowly add concentrated ammonia water while stirring until the solution turns dark blue and transparent (pH≈9.5, Ni:NH3 molar ratio about 1:3.5). Finally, adjust the volume to the saturated water absorption volume of the carrier. The mass concentration of Ni²⁺ in the solution is about 30%.

[0079] (4) The equal-volume double impregnation method is adopted. After the first impregnation, the material is dried at 100°C for 2 hours, and then the second impregnation is carried out to ensure uniform loading of high nickel content. The total impregnation time is 4 hours.

[0080] (5) The impregnated material was dried at 120℃ for 6 hours, and then calcined in air at 450℃ for 4 hours to obtain catalyst C-5. XRF analysis showed that its final composition was: NiO 48.5%, MgO 4.0%, La2O3 1.5%, CeO2 1.0%, and TiO2-Al2O3 composite support (of which TiO2 was approximately 4.0%) as the balance. Physical characterization showed that its total pore volume was 0.98 cm3 / g, the proportion of macropores (>60nm) was 21%, the specific surface area was 155 m2 / g, and the lateral compressive strength was 110 N / cm.

[0081] Comparative Example 1: Preparation of Catalyst D-1

[0082] (1) Take 1000g of pseudoboehmite (dry basis), add an appropriate amount of dilute nitric acid solution (concentration 5-10%) to adjust the pH to 2-3, and knead to form a plastic clay. No organic pore-forming agents or precursors such as TiO2, Mg, La, Ce are added.

[0083] (2) The clay material was extruded into cylindrical strips with a diameter of 1.6 mm and dried at 110°C for 4 hours. Subsequently, it was calcined in air at 600°C for 4 hours to obtain a conventional alumina carrier. The pore volume was measured to be 0.52 cm³ / g, the most probable pore size was 15 nm, the specific surface area was 350 m² / g, the pore size distribution showed a unimodal characteristic, and there were basically no macropores >60 nm.

[0084] (3) Prepare a nickel nitrate impregnation solution with a Ni²⁺ mass concentration of 25% and without adding ammonia water for complexation.

[0085] (4) The support obtained in step (2) was impregnated with nickel nitrate solution using the equal-volume impregnation method. After impregnation, it was dried at 120°C for 4 hours and then calcined in air at 450°C for 4 hours to obtain the comparative catalyst D-1. XRF analysis showed that its composition was: 25% NiO, balance Al2O3, and it did not contain MgO, La2O3, CeO2, TiO2 and other additives.

[0086] Comparative Example 2: Preparation of Comparative Catalyst D-2

[0087] (1) Take 1000g of pseudoboehmite (dry basis), without adding any titanium source, add 150g of polyethylene glycol 6000 (15% of dry basis) as a pore-forming agent, and then add a mixed solution containing magnesium nitrate, lanthanum nitrate and cerium nitrate (the amount is the same as in Example 1). The remaining preparation steps (mixing, kneading, molding, drying, calcining, impregnation and activation) are the same as in Example 1 to obtain comparative catalyst D-2. The final composition was determined to be: NiO 38.5%, MgO 5.0%, La2O3 3.0%, CeO2 2.0%, Al2O3 balance, and no TiO2. According to BET test, its total pore volume is 1.15 cm³ / g, the pore size distribution is still bimodal, but the proportion of macropores >60 nm has slightly decreased to 22%, and the specific surface area is 185 m² / g.

[0088] Comparative Example 3: Preparation of Comparative Catalyst D-3

[0089] (1) Take 1000g of boehmite (dry basis), add titanium source and auxiliary salt (same amount as in Example 1), and add 220g of polyethylene glycol 6000 (22% of dry basis) as excess pore-forming agent. By adjusting the kneading and molding process, a high-porosity precursor is obtained. The remaining preparation steps are the same as in Example 1, and comparative catalyst D-3 is obtained. It was determined that its total pore volume is as high as 1.52 cm³ / g, which exceeds the upper limit of the scope of this invention. Its >60 nm macropores account for 32%, but the specific surface area is significantly reduced to 122 m² / g. The lateral pressure strength test showed that its average lateral pressure strength was only 85 N / cm, which is lower than the requirements of this invention.

[0090] Comparative Example 4: Preparation of Comparative Catalyst D-4

[0091] (1) Take 1000g of pseudoboehmite (dry basis), add titanium source and auxiliary salt (same amount as in Example 1), and add only 50g of polyethylene glycol 2000 (5% of dry basis) as a small amount of pore-forming agent. A special low-temperature short-time calcination process (450℃, 2h) is used to suppress macropore formation. The remaining preparation steps are the same as in Example 1, and comparative catalyst D-4 is obtained. It is determined that its total pore volume is 0.72cm³ / g, but the proportion of macropores with a pore size >60 nm is only 9%, which is significantly lower than the lower limit required by this invention. Its specific surface area is 240 m² / g.

[0092] Application and Performance Evaluation

[0093] Performance tests were conducted on a high-pressure micro-reverse-jet cycle simulation evaluation device, which can simulate the working state of a Venturi injector.

[0094] Reaction conditions: Pressure 4.0 MPa, feed gas composition (vol%): H2-60, CO-20, CO2-5, CH4-10, N2-5. The effect of different bed pressure drops on the ejector entrainment coefficient was simulated using a back pressure valve.

[0095] Evaluation indicators: At different space velocities, measure CO / CO2 conversion rate, bed pressure drop, and bed hot spot temperature, and observe the system's ability to achieve a stable cycle ratio (set to 4). Specific process diagrams are shown below. Figure 3 As shown.

[0096] Results analysis:

[0097] (1) Low pressure drop and process stability: The catalysts of this invention (C-1 to C-4) benefit from the TiO2-Al2O3 composite support and optimized dual-pore structure. At a high space velocity of 15000 h⁻¹, the bed pressure drop is only 0.015-0.025 MPa / m, and the system can easily maintain the set cycle ratio (4), with a stable reaction temperature. In contrast, the comparative example D-1 has a pressure drop as high as 0.060-0.075 MPa / m under the same conditions. Figure 2As shown in the bed pressure drop comparison chart, within the entire test space velocity range of 5000-20000 h⁻¹, the pressure drop curve of catalyst C-1 of this invention is consistently much lower than that of comparative catalyst D-1 in Comparative Example 1, demonstrating a revolutionary low pressure drop advantage. The huge pressure drop resistance leads to excessively high back pressure on the intake side of the simulated injector, preventing the intake of sufficient circulating gas. The actual circulation ratio drops to approximately 2.5, and the heat of reaction cannot be removed in time, resulting in localized high temperatures (>650℃) in the bed, posing a risk of runaway. The test results of comparative catalyst D-4 (with a macroporous content of only 9%) in Comparative Example 4 have key implications: its bed pressure drop at 15000 h⁻¹ is 0.055 MPa / m, slightly better than the conventional catalyst D-1, but significantly worse than the catalyst of this invention (C-1 is 0.020 MPa / m). This directly proves that only when the proportion of macropores (>60 nm) reaches more than 15% as required by this invention can a highly interconnected pore network be formed that can significantly reduce airflow resistance, thereby achieving the "extremely low bed pressure drop" required by the jet circulation process.

[0098] (2) High space velocity activity: The unique dual-membrane structure of the catalyst of this invention, characterized by "mesoporous structure maintaining activity and macroporous structure promoting mass transfer," exhibits excellent high space velocity activity based on the stable framework provided by the TiO2-Al2O3 composite support. Catalysts C-1, C-3, and C-4 all maintained CO conversion rates above 96% and CO2 conversion rates above 78% at a space velocity of 20,000 h⁻¹. In contrast, Comparative Example D-1, at the same space velocity, suffered from severe internal diffusion limitation due to its small pore volume and uniform pore size, resulting in a CO conversion rate below 75% and a CO2 conversion rate below 55%. Example C-2, due to its low pore volume and macroporous ratio, had a slightly lower CO conversion rate than C-1 at 15,000 h⁻¹, but it was still significantly better than the comparative catalyst D-1 of Comparative Example 1, demonstrating the effectiveness of the present invention.

[0099] (3) Thermal stability and anti-carbon deposition ability: The synergistic effect of the TiO2-Al2O3 composite support and the ternary promoter system of MgO, La2O3, and CeO2 significantly improves the thermal stability and anti-carbon deposition performance of the catalyst. In accelerated aging tests (100 hours of treatment at 650℃ and 10% water vapor atmosphere), the specific surface area and pore volume decay rate of the catalysts C-1, C-3, and C-4 of this invention are all less than 4%, and the side pressure strength retention rate exceeds 90%. After running under simulated industrial conditions for 1000 hours, its activity retention rate exceeds 96%. In contrast, the comparative example D-2 (without TiO2) under the same aging conditions showed a significant decrease in mechanical strength (strength retention rate of only 78%), and the activity retention rate after operation was only 88%, and the carbon deposition amount (1.2 wt%) was twice that of the C-1 catalyst (0.6 wt%). This strongly demonstrates that the introduction of TiO2 plays an irreplaceable role in forming a high-temperature stable composite support framework and synergistically inhibiting carbon deposition. Comparative Example D-1, under the same aging conditions, showed a significant decrease in mechanical strength, with an activity retention rate of less than 75% after operation, and a carbon deposition amount more than three times that of the catalyst of this invention. Furthermore, although the comparative catalyst D-3 (total pore volume 1.52 cm³ / g) of Comparative Example 3 had acceptable initial activity, its lateral compressive strength failed to meet the standard (<100 N / cm) after aging tests, posing a risk of breakage in practical industrial applications. This confirms the necessity of controlling the upper limit of the total pore volume to 1.3 cm³ / g to ensure the long-term operational reliability of the catalyst. The specific performance comparisons of the catalysts in each embodiment and the comparative example are shown in Tables 1-2 below.

[0100] Table 1. Comparison of simulated bed pressure drop data between comparative example (D-1) and the catalyst of the present invention (C-1) at different space velocities.

[0101]

[0102] Table 2. Comprehensive data on catalyst properties and performance of each embodiment and comparative example.

[0103]

[0104] Original particle size catalyst application examples

[0105] The catalyst prepared by the method of the present invention in Example 4 was subjected to a single-tube experiment with a C-4 (toothed spherical) packing of 50 ml of the original particle size. The adiabatic fixed-bed reactor simulated the Venturi injection cycle process, aiming to efficiently convert CO, CO2, and H2 in coke oven gas into CH4, improve its calorific value, and produce qualified synthetic natural gas (SNG).

[0106] (1) Overview of the equipment and process:

[0107] Raw material gas: coke oven gas, with a typical composition (vol%) of: H2 55-60%, CH4 23-28%, CO 5-8%, CO2 1-3%, N2 3-5%, and trace impurities (such as O2, olefins, and sulfides, which are purified to meet the requirements of the catalyst).

[0108] (2) Core process: Coke oven gas injection and circulation methanation process. Simulating the gas composition of the Venturi ejector process, the preheated high-pressure fresh coke oven gas is efficiently mixed with the low-pressure circulating gas from the reactor outlet after cooling and separation, and then enters the reactor.

[0109] (3) Design parameters: The design space velocity is 12000-15000 h⁻¹, and the design circulation ratio is 1-4, in order to adapt to the characteristics of relatively low CO content and high H2 / CO ratio in coke oven gas.

[0110] (4) Statistics after the device has been running stably for 3000 hours:

[0111] It exhibits excellent catalytic performance: at an operating pressure of 3.8 MPa and a mean space velocity of 13500 h⁻¹, the CO conversion rate is consistently >99.5% and the CO₂ conversion rate is consistently >85%.

[0112] The total pressure drop in the catalyst bed was reduced to 5 kPa, far below the design value (40 kPa) and historical data (50 kPa) for similar units using traditional catalysts. This extremely low bed pressure drop ensured the Venturi injector's operating point was extremely stable, with the actual circulation ratio precisely controlled within the optimized range of 1.2-1.6. The heat of reaction was efficiently and smoothly removed, completely avoiding the risk of "runaway temperature" caused by circulation fluctuations.

[0113] The catalyst exhibits outstanding thermal stability and resistance to impurities: the axial and radial temperature distribution of the catalyst bed is uniform, the reactor outlet temperature is controlled between 380-420℃, and the highest hot spot temperature does not exceed 580℃. This demonstrates that the catalyst still possesses excellent resistance to carbon deposition and sintering when dealing with trace amounts of unsaturated hydrocarbons such as olefins and complex compositions that may remain in coke oven gas. Regular sampling analysis shows that the catalyst maintains a good specific surface area and pore structure, with no obvious signs of carbon deposition.

[0114] Significant energy consumption and economic benefits: Compared with similar units using traditional catalysts, the low pressure drop directly leads to a reduction in system energy consumption: the power consumption of the feed gas compressor is reduced by about 7%, and the equivalent power consumption of the entire cycle system is reduced by about 12%.

[0115] The unit has been operating stably for 3000 hours, with no decrease in catalyst activity, and monitoring data (conversion rate, pressure drop, temperature) are highly stable. Based on extrapolation of operating data and periodic sampling analysis, the catalyst's single-cycle lifespan under coke oven gas conditions is expected to exceed 28,000 hours, representing an increase of more than 50% compared to the original conventional catalyst (approximately 12,000-16,000 hours). The reduced catalyst replacement frequency significantly decreases unplanned shutdowns and maintenance costs.

[0116] The low-pressure-drop macroporous catalyst provided by this invention, using titanium oxide-alumina as a composite support, through targeted pore structure (macropores >60 nm, accounting for 15-30%) and composition design, not only perfectly solves the stringent common requirements of "low pressure drop, high mass transfer, high activity, and high thermal stability" for catalysts in the injection cycle process, but also demonstrates excellent adaptability, stability, and economy in the methanation application of coke oven gas, a special feed gas with complex composition and trace impurities.

[0117] Finally, it is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the principles and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A methanation catalyst suitable for a jet-cycle process, characterized in that, It is mainly composed of the following components: by mass percentage, nickel oxide 20-50%, magnesium oxide 3-8%, lanthanum oxide 1-5%, cerium oxide 1-5%, and the balance is titanium oxide-alumina composite carrier; The catalyst has a bimodal porous structure with a total pore volume of 0.6-1.3 cm³. 3 / g, the pore size distribution exhibits a bimodal characteristic, including mesopore peaks of 2-10 nm and macropore peaks >60 nm, with macropores larger than 60 nm accounting for 15-30% of the total pore volume and a specific surface area of ​​130-220 m². 2 / g.

2. The catalyst according to claim 1, characterized in that, In the titanium oxide-alumina composite carrier, the mass ratio of titanium oxide to alumina is 1:(3-10).

3. The catalyst according to claim 1, characterized in that, The pore size range of the macropore peak is 60-150 nm.

4. The catalyst according to claim 1, characterized in that, The pore connectivity index of the dual-mode pore structure is not less than 0.8, the tortuosity factor is not greater than 2.0, and the lateral compressive strength is not less than 100 N / cm.

5. The catalyst according to any one of claims 1-4, characterized in that, By mass percentage, nickel oxide 30-45%, magnesium oxide 4-7%, lanthanum oxide 2-4%, cerium oxide 2-4%, and the balance is a titanium oxide-alumina composite carrier.

6. The method for preparing the methanation catalyst suitable for the jet recycling process according to any one of claims 1-5, characterized in that, Includes the following steps: Mix boehmite, titanium source, thermally decomposable organic pore-forming agent, and nitrate solution containing magnesium, lanthanum, and cerium, adjust the pH to 3-5, and knead to form a plastic mass. The plastic mass is shaped, dried at 100-120°C, and then calcined in air at 500-700°C for 3-6 hours to obtain the titanium oxide-alumina composite carrier. The titanium dioxide-alumina composite carrier is impregnated with an equal volume of nickel-ammonia complex solution, dried, and then calcined at 350-500℃.

7. The method for preparing the methanation catalyst according to claim 6, characterized in that, The titanium source is selected from at least one of tetrabutyl titanate, titanium sulfate, or titanium dioxide sol.

8. The method for preparing the methanation catalyst according to claim 6, characterized in that, The organic pore-forming agent is selected from at least one of polyethylene glycol, starch, and polyvinyl alcohol.

9. The method for preparing the methanation catalyst according to claim 6, characterized in that, The nickel-ammonia complex solution is prepared by mixing nickel nitrate and ammonia water at a nickel to ammonia molar ratio of 1:(2-4), wherein the mass concentration of Ni²⁺ is 10-30wt%.

10. The method for preparing the methanation catalyst according to claim 6, characterized in that, The added organic pore-forming agent is 8-20% of the dry basis mass of the pseudoboehmite.

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