Methanation catalysts, processes for their preparation and use

Abstract

This invention relates to the field of methanation catalysts, disclosing a methanation catalyst, its preparation method, and its applications. The method includes: reducing a nickel precursor in the presence of water using a reducing agent; then, in the presence of a protective agent, mixing the resulting reduction product with a dispersant and allowing it to stand and separate into layers to form a layered liquid; wherein the protective agent is a hydrophobic inert liquid; the layered liquid comprises an upper layer and a lower layer, the upper layer containing the protective agent, and the lower layer containing water and catalyst particles, the catalyst particles containing amorphous nickel and the dispersant; adjusting the pH of the lower layer to 7-9, and then removing the water from the lower layer, so that the protective agent coats the catalyst particles. The active component in this methanation catalyst is amorphous nickel, which, compared to catalysts with crystalline nickel as the active component, improves the hydrogenation capacity of the active component. Furthermore, this methanation catalyst is itself in a reduced state, requiring no reduction before use, making it more suitable for slurry bed reactors.

Description

Technical Field

[0001] This invention relates to the field of methanation catalysts, and more specifically to methanation catalysts, their preparation methods, and applications. Background Technology

[0002] Syngas methanation technology, represented by first-generation methanation reactions using adiabatic reactors, is characterized by long process flows, numerous pieces of equipment, and high reaction temperatures. The Lurgi multi-stage adiabatic methanation process, exemplified by this technology, utilizes a circulating adiabatic primary reaction followed by multiple stages of adiabatic refining. The temperature of the first reactor typically exceeds 600°C, and subsequent refining processes employ at least three adiabatic reactors connected in series to obtain the product methane.

[0003] Methanation is a volume-reducing, strongly exothermic reaction. Second-generation methanation, represented by isothermal reactors, uses lower reaction temperatures to improve equilibrium. Isothermal reactors are typically used as a subsequent purification step after adiabatic reactors. While isothermal reactor purification can reduce the residual carbon monoxide and carbon dioxide content in the adiabatic product gas, existing methanation catalysts still suffer from poor heat and mass transfer performance and instability during isothermal methanation. Furthermore, existing methanation catalysts require pre-activation and reduction before use to reduce the precursor of the active component into a catalytically active metal. However, the temperature of an isothermal reactor is often insufficient to meet the reduction conditions. Therefore, an additional activation and reduction step is needed before the isothermal methanation reaction, leading to higher costs and energy consumption.

[0004] Slurry bed reactors are the third generation of reactors for methanation reactions. They offer higher heat transfer capacity and more stable temperature rise compared to isothermal reactors. Furthermore, the mass transfer rate can be controlled by adjusting the stirring speed, thus controlling the composition of the effluent gas. Moreover, the cost of a slurry bed reactor is significantly lower than that of an isothermal reactor with the same capacity, representing another advancement in methanation equipment. However, methanation catalysts suitable for slurry bed reactors differ from those for fixed-bed catalysts, requiring characteristics such as high catalytic activity, uniform particle size, good dispersibility, and wear resistance. Additionally, slurry beds typically cannot be heated to the catalyst reduction temperature, necessitating pre-reduction of the catalyst before use, making catalyst start-up and replenishment procedures more complex.

[0005] CN101979475A and CN101979476A disclose a slurry-bed methanation process for synthesizing natural gas. This process introduces an inert liquid phase component with high thermal conductivity and high fusibility during the methanation reaction, uniformly dispersing the methanation catalyst in the inert liquid, achieving isothermal bed conditions and thus avoiding the temperature runaway problem that occurs in conventional fixed-bed methanation methods. However, both processes use industrial fixed-bed methanation catalysts, whose particle size, strength, and low-temperature reaction performance cannot adequately meet the requirements of the slurry-bed methanation process. Furthermore, due to the boiling point limitation of the inert liquid phase component, the reaction temperature of the slurry-bed methanation process must be controlled below 320℃, which is insufficient for catalyst reduction. Therefore, this process requires an additional catalyst activation and reduction step at a higher temperature before the reaction, resulting in higher costs and energy consumption.

[0006] CN102872875A discloses a slurry-bed methanation catalyst, its preparation method, and its application. This method introduces an additive to increase the catalyst's low-temperature activity in the methanation reaction, resulting in better catalytic methanation performance within a temperature range of ≤320℃, making it more suitable for slurry-bed methanation processes. However, the introduction of the additive increases the cost. Furthermore, this method requires pre-activation and reduction in a mixed atmosphere of H2 and N2 at 450-650℃ (higher than the reaction temperature of slurry-bed methanation), which also increases cost and energy consumption. Summary of the Invention

[0007] The purpose of this invention is to overcome the problems that existing methanation catalysts require pre-activation and reduction, and that the temperatures of isothermal reactors and slurry bed reactors are not easy to meet the reduction conditions.

[0008] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a methanation catalyst, the method comprising:

[0009] (1) In the presence of water, the nickel precursor is brought into contact with a reducing agent to carry out a reduction reaction to obtain the reduction product;

[0010] (2) In the presence of a protective agent, the reduction product is mixed with a dispersant, and the resulting mixture is allowed to stand and separate into layers to form a layered liquid; wherein the protective agent is a hydrophobic inert liquid; the layered liquid includes an upper liquid and a lower liquid, the upper liquid contains the protective agent, the lower liquid contains water and catalyst particles, the catalyst particles contain amorphous nickel and a dispersant; the dispersant is selected from at least one of alumina, zirconium oxide, magnesium oxide and borax, wherein the zirconium oxide has a tetragonal crystal form;

[0011] (3) Adjust the pH of the lower layer of the stratified liquid to 7-9 using water, and then remove the water from the lower layer of the stratified liquid so that the protective agent coats the catalyst particles to obtain the methanation catalyst.

[0012] A second aspect of the present invention provides a methanation catalyst prepared by the preparation method described in the first aspect, the methanation catalyst comprising catalyst particles and a protective agent encapsulating the catalyst particles, the catalyst particles containing amorphous nickel and a dispersant.

[0013] The third aspect of this invention provides the application of the methanation catalyst described in the second aspect in the methanation reaction to prepare synthetic natural gas.

[0014] Through the above technical solution, the preparation method provided by the present invention improves the traditional methanation catalyst preparation method by using a reducing agent to reduce the nickel precursor, then mixing the reduction product with a specific dispersant in the presence of a protective agent, then allowing it to stand and separate into layers, adjusting the pH value of the lower layer in the separated liquid, and finally removing the water in the lower layer, so that the protective agent of the upper layer coats the catalyst particles. The resulting methanation catalyst includes catalyst particles and a protective agent coating the catalyst particles, wherein the catalyst particles contain amorphous nickel and a dispersant.

[0015] The active component of this methanation catalyst is amorphous nickel. Compared with catalysts with crystalline nickel as the active component, this methanation catalyst improves the hydrogenation capacity of the active component. Furthermore, the methanation catalyst itself is in a reduced state, requiring no prior reduction before use, making it more suitable for slurry bed reactors, and suitable for applications with a lifespan not exceeding 15000 h⁻¹. -1 When the volume hourly space velocity and reaction temperature are not higher than 340℃, the conversion rate of carbon monoxide in the synthesis gas can reach 100% and the conversion rate of carbon dioxide can reach 90%. Attached Figure Description

[0016] Figure 1 This is the XRD pattern of the reduction product obtained in step (1) of Embodiment 1 of the present invention;

[0017] Figure 2 This is the XRD pattern of the dispersant used in Example 1 of the present invention. Detailed Implementation

[0018] 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.

[0019] The first aspect of this invention provides a method for preparing a methanation catalyst, the method comprising:

[0020] (1) In the presence of water, the nickel precursor is brought into contact with a reducing agent to carry out a reduction reaction to obtain the reduction product;

[0021] (2) In the presence of a protective agent, the reduction product is mixed with a dispersant, and the resulting mixture is allowed to stand and separate into layers to form a layered liquid; wherein the protective agent is a hydrophobic inert liquid; the layered liquid includes an upper liquid and a lower liquid, the upper liquid contains the protective agent, the lower liquid contains water and catalyst particles, the catalyst particles contain amorphous nickel and a dispersant; the dispersant is selected from at least one of alumina, zirconium oxide, magnesium oxide and borax, wherein the zirconium oxide has a tetragonal crystal form;

[0022] (3) Adjust the pH of the lower layer of the stratified liquid to 7-9 using water, and then remove the water from the lower layer of the stratified liquid so that the protective agent coats the catalyst particles to obtain the methanation catalyst.

[0023] According to some embodiments of the present invention, in step (1), the nickel precursor is contacted with a reducing agent in the presence of water to carry out a reduction reaction, thereby obtaining a reduction product. This step can reduce the nickel element in the nickel precursor to metallic nickel, ultimately yielding a reduction product containing amorphous elemental nickel.

[0024] According to some embodiments of the present invention, in step (1), the nickel precursor is a nickel-containing compound. There is no particular limitation on the type of nickel precursor; it can be a conventional choice in the art, such as a conventional water-soluble nickel salt. Preferably, the nickel precursor is selected from at least one of nickel nitrate, nickel chloride, and nickel acetate, with nickel nitrate being the most preferred.

[0025] According to some embodiments of the present invention, in step (1), the type of reducing agent is not particularly limited and can be a conventional choice in the art, as long as it can reduce the nickel element in the nickel precursor to amorphous nickel. Preferably, the reducing agent is a borohydride, preferably sodium borohydride and / or potassium borohydride.

[0026] According to some embodiments of the present invention, preferably, in step (1), the molar ratio of the reducing agent to the nickel precursor (based on nickel element) is (1-2.5):1, more preferably (1.5-2):1. The above-mentioned preferred embodiments can further promote the formation of amorphous nickel particles through chemical reduction.

[0027] According to some embodiments of the present invention, preferably, in step (1), the nickel precursor is provided in the form of an aqueous solution of the nickel precursor, more preferably, the concentration of nickel element in the aqueous solution of the nickel precursor is 0.5-2 mol / L.

[0028] According to some embodiments of the present invention, preferably, in step (1), the reducing agent is provided in the form of an aqueous solution of reducing agent, more preferably, the concentration of the reducing agent in the aqueous solution of reducing agent is 1-3 mol / L.

[0029] According to some embodiments of the present invention, in order to remove oxygen from the solution, further promote the formation of reduction products, and improve the dispersion of reduction products, preferably, in step (1), the contact includes: adding an aqueous solution of the nickel precursor to an aqueous solution of the reducing agent under oscillation. The oscillation and the dropping conditions and methods can be conventional choices in the art, and there are no particular limitations, as long as the nickel element in the nickel precursor can be reduced to amorphous nickel. For example, the oscillation frequency can be 20-50 Hz; the dropping rate can be 2-6 drops / second.

[0030] According to some embodiments of the present invention, preferably, in step (1), the conditions for the reduction reaction include: a temperature of 15-25°C and a time of 1-3 hours.

[0031] According to some embodiments of the present invention, in order to better precipitate and separate the reduction product, preferably, in step (1), after the addition is completed, a magnetic material or device can be used to assist the precipitation of the reduction product during the reduction reaction.

[0032] According to some embodiments of the present invention, in step (2), the reduction product is mixed with a dispersant in the presence of a protective agent, and the resulting mixture is allowed to stand and separate into layers to form a layered liquid. This step allows the amorphous nickel in the reduction product to come into full contact with the dispersant, which is beneficial for the amorphous nickel to be fully mixed with the dispersant during the sedimentation process.

[0033] According to some embodiments of the present invention, in step (2), the protective agent is a hydrophobic inert liquid that is immiscible with water. Therefore, the mixture will form a layered liquid during the subsequent settling and layering process. The layered liquid includes an upper liquid and a lower liquid. The density of the protective agent is less than that of water, and the catalyst particles will sink due to gravity. Therefore, in the layered liquid, the upper liquid contains the protective agent, and the lower liquid contains water and catalyst particles. The catalyst particles contain amorphous nickel and a dispersant.

[0034] According to some embodiments of the present invention, the protective agent can be any inert liquid suitable for a slurry bed reactor. Preferably, the protective agent is selected from at least one of liquid paraffin, diesel oil, and white oil, with liquid paraffin being the most preferred. The protective agent can form a protective layer (upper layer) above the lower liquid after the sedimentation and stratification process to isolate oxidizing substances.

[0035] According to some embodiments of the present invention, preferably, in step (2), the amount of the protective agent is such that the thickness of the upper liquid is 2-3 cm.

[0036] According to some embodiments of the present invention, in step (2), the dispersant is selected from at least one of alumina, zirconium oxide, magnesium oxide, and borax, wherein the zirconium oxide has a tetragonal crystal form. The dispersant can serve as a carrier for dispersing the slurry-bed catalyst to disperse amorphous nickel and prevent it from floating above the slurry (protectant). The tetragonal crystal form of the zirconium oxide provides a better auxiliary hydrogenation effect when it comes into point contact with nickel in the slurry bed. The crystal form of the zirconium oxide can be determined by the XRD pattern of the catalyst.

[0037] According to some embodiments of the present invention, preferably, the dispersant is selected from at least one or more of a mixture of zirconium oxide and magnesium oxide, alumina, and borax, more preferably a mixture of zirconium oxide and magnesium oxide, and even more preferably, the mass ratio of zirconium oxide to magnesium oxide in the mixture is (1-10):1, preferably (3-6):1, wherein the zirconium oxide has a tetragonal crystal form. By employing the above preferred embodiments, the pH value at the contact point between amorphous nickel and the dispersant in the slurry bed can be adjusted, and the Zr-Ni mutual half-loading relationship can further promote the methanation catalytic effect.

[0038] According to some embodiments of the present invention, more preferably, the method for preparing the mixture of zirconium oxide and magnesium oxide includes: sieving zirconium oxide powder and magnesium oxide powder separately, selecting particles with a particle size of 100-400 mesh, preferably 120-180 mesh, for blending (the mass ratio of zirconium oxide powder to magnesium oxide powder can be selected as described above), then subjecting the resulting mixture to high-temperature calcination, causing the zirconium oxide to transform from a monoclinic crystal form to a tetragonal crystal form, and then cooling the calcined product to room temperature in air. The conditions for the high-temperature calcination may include: a temperature of 1200-1300°C and a time of 4-6 hours. In the above process, magnesium oxide can protect the zirconium oxide in the mixture, preventing it from degenerating from a tetragonal crystal form to a monoclinic crystal form during the cooling process, ensuring that the zirconium oxide in the final mixture is tetragonal.

[0039] According to some embodiments of the present invention, preferably, in step (2), the particle size of the dispersant is 100-400 mesh, more preferably 120-180 mesh.

[0040] According to some embodiments of the present invention, preferably, in step (2), the mass ratio of the nickel precursor to the dispersant, calculated as nickel element, is (1-10):1, more preferably (1.5-5.67):1.

[0041] According to some embodiments of the present invention, preferably, in step (2), the mixing can be carried out under stirring conditions. The stirring conditions and methods can be conventional choices in the art and are not particularly limited thereto. For example, non-ferromagnetic equipment can be used for the stirring. Preferably, the mixing conditions may include: a temperature of 20-50°C, a time of 20-60 min, and a rotation speed of 200-400 rpm.

[0042] According to some embodiments of the present invention, in step (3), the pH value of the lower layer liquid in the stratified liquid is adjusted to 7-9 using water, and then the water in the lower layer liquid is removed, so that the protective agent coats the catalyst particles.

[0043] According to some embodiments of the present invention, preferably, in step (3), water is used to adjust the pH of the lower layer liquid to 7.5-8.

[0044] According to some embodiments of the present invention, preferably, in step (3), adjusting the pH value includes: adding water to the lower layer of the layered liquid and washing repeatedly until the pH value of the lower layer meets the above-mentioned range. The washing can be performed using washing solutions conventionally used in the art, such as deionized water.

[0045] Preferably, the washing can be performed by adding water to the lower layer of the separated liquid and then removing the water. The method of water removal includes solid-liquid separation of the separated liquid to remove the water from the lower layer. There is no particular limitation on the method of solid-liquid separation; it can be any conventional choice in the art, such as at least one of filtration, centrifugation, and gravity sedimentation. It should be noted that the liquid separated by the solid-liquid separation operation is the water from the lower layer of the separated liquid, excluding the protective agent in the upper layer; the remaining products include the protective agent and catalyst particles.

[0046] More preferably, the method for removing water includes: slowly filtering the layered liquid, filtering out the water in the lower layer from below, and stopping when the interface of the upper layer is tangent to the filter outlet, so that the protective agent coats the catalyst particles. The catalyst particles, coated with the protective agent, have a certain degree of fluidity, which is particularly suitable for slurry bed reactions.

[0047] According to some embodiments of the present invention, in order to prevent the obtained methanation catalyst from being oxidized, it is preferable to store the methanation catalyst in a sealed container, for example, by sealing and purging it with nitrogen.

[0048] A second aspect of this invention provides a methanation catalyst prepared by the method described in the first aspect. The methanation catalyst comprises catalyst particles and a protective agent encapsulating the catalyst particles. The catalyst particles contain amorphous nickel and a dispersant. The active component in the methanation catalyst is amorphous nickel, which exhibits stronger hydrogenation capability.

[0049] According to some embodiments of the present invention, preferably, the XRD pattern of the methanation catalyst shows a diffraction peak with a width greater than 5° at 2θ = 45 ± 0.2°. This broad diffraction peak is a diffuse peak formed by amorphous diffuse reflection, which is the main characteristic diffraction peak of amorphous nickel. The short and broad diffuse peak indicates that the nickel in the methanation catalyst exists in an amorphous structure.

[0050] According to some embodiments of the present invention, there is no particular limitation on the amount of the protective agent, as long as it can effectively encapsulate the catalyst particles to isolate them from oxygen. Preferably, in the methanation catalyst, the content of the protective agent is 2-4 mL relative to 1 g of catalyst particles. Using the above preferred embodiments, it is possible to encapsulate the catalyst particles and isolate them from oxygen with a relatively small amount of protective agent. When using the methanation catalyst, an inert thermally conductive medium can be introduced into the slurry bed reactor to adjust the volume of the slurry (inert thermally conductive medium + protective agent); preferably, the inert thermally conductive medium is the same as the protective agent. The amount of inert thermally conductive medium introduced can be adjusted according to actual conditions, and there is no particular limitation thereto. Preferably, the amount of inert thermally conductive medium introduced is such that the loading amount of the methanation catalyst and the volume of the inert thermally conductive medium satisfy the following: relative to 1 g of catalyst particles, the total amount of protective agent and inert thermally conductive medium in the methanation catalyst is 20-100 mL, preferably 20-50 mL. Alternatively, during the preparation of the methanation catalyst, the amount of the protective agent can be adjusted to control the loading amount of the methanation catalyst, thereby achieving the desired content of catalyst particles and protective agent.

[0051] According to some embodiments of the present invention, preferably, based on the total weight of the catalyst particles, the content of amorphous nickel in the catalyst particles is 60-85% by weight, and the content of dispersant is 15-40% by weight.

[0052] More preferably, based on the total weight of the catalyst particles, the catalyst particles contain 65-75% by weight of amorphous nickel and 25-35% by weight of dispersant.

[0053] The third aspect of this invention provides the application of the methanation catalyst described in the second aspect in the methanation reaction to prepare synthetic natural gas.

[0054] The present invention will be described in detail below through embodiments.

[0055] Unless otherwise specified, all raw materials used in the following examples and comparative examples are commercially available products.

[0056] In the following examples and comparative examples, deionized water was used;

[0057] The composition of the catalyst was determined using a Rigaku ZSX Primus II X-ray fluorescence spectrometer (XRF).

[0058] The XRD pattern of the material was determined using an X-ray diffractometer, which was purchased from Bruker as a D8 advance model.

[0059] Examples 1-8 illustrate the methanation catalyst and its preparation method provided by the present invention.

[0060] Example 1

[0061] (1) In the presence of water, the nickel precursor is brought into contact with a reducing agent to undergo a reduction reaction, yielding a reduction product; wherein:

[0062] The nickel precursor is nickel nitrate, which is provided in the form of an aqueous solution of nickel precursor. The aqueous solution of nickel precursor is obtained by dissolving 200g of nickel nitrate pentahydrate (containing 43.5g of nickel element) in deionized water. The concentration of nickel element in the aqueous solution of nickel precursor is 1.5mol / L.

[0063] The reducing agent is sodium borohydride, which is provided in the form of an aqueous reducing agent solution with a concentration of 2 mol / L.

[0064] The molar ratio of reducing agent to nickel precursor (based on elemental nickel) is 1.5:1;

[0065] The contact steps are as follows: under oscillation, the aqueous solution of nickel precursor is added dropwise to the aqueous solution of reducing agent; the oscillation frequency is 20 Hz; the dropping rate is 4 drops / second.

[0066] The conditions for the reduction reaction are: temperature 20℃±2℃, time 2h; during the reduction reaction, after the addition is completed, the product is allowed to precipitate freely, and a magnetic material is used below to assist in the precipitation.

[0067] The XRD pattern of the reduction product is as follows: Figure 1 As shown in the figure, the nickel contained in the reduction product is amorphous nickel.

[0068] (2) In the presence of a protective agent, the reduction product is mixed with a dispersant, and the resulting mixture is allowed to stand and separate into layers to form a layered liquid; wherein:

[0069] The protective agent is liquid paraffin; the layered liquid consists of an upper liquid and a lower liquid, the upper liquid contains the above-mentioned protective agent, and the lower liquid contains water and catalyst particles, the catalyst particles contain amorphous nickel and the above-mentioned dispersant; the amount of protective agent used makes the thickness of the upper liquid 2.5 cm;

[0070] The dispersant is a mixture of zirconium oxide and magnesium oxide, wherein the mass ratio of zirconium oxide to magnesium oxide is 6:1; the zirconium oxide has a tetragonal crystal form; the particle size of the dispersant is 120-180 mesh; the specific preparation process of the dispersant is as follows: zirconium oxide powder and magnesium oxide powder are sieved separately, and particles with a particle size of 120-180 mesh are selected and mixed according to the above mass ratio. Then, the resulting mixture is calcined at 1300℃ for 4 hours to transform the zirconium oxide from a monoclinic crystal form to a tetragonal crystal form, and the calcined product is cooled to room temperature in air; the XRD pattern of the dispersant is shown below. Figure 2 As shown in the figure, the zirconium oxide contained in this dispersant has a tetragonal crystal form.

[0071] The mass ratio of nickel precursor to dispersant, calculated based on nickel element, is 3:1;

[0072] The mixing conditions were: temperature 20℃, time 20min, and rotation speed 200rpm.

[0073] (3) Adjust the pH of the lower layer of the stratified solution to 7.5 using water, then remove the water from the lower layer to allow the protective agent to coat the catalyst particles, obtaining the methanation catalyst, which is then sealed and purged with nitrogen; wherein:

[0074] The adjustment method is as follows: add water to the lower layer of the stratified liquid and wash it multiple times until the pH value of the lower layer is 7.5; the water removal method is as follows: slowly filter the stratified liquid, filter out the water in the lower layer from the bottom, and stop when the interface of the upper layer is tangent to the filter outlet, so that the protective agent coats the catalyst particles.

[0075] The methanation catalyst comprises catalyst particles and a protective agent encapsulating the catalyst particles. The catalyst particles contain amorphous nickel and a dispersant. Based on the total weight of the catalyst particles, the content of amorphous nickel in the catalyst particles is 75% by weight, and the content of dispersant is 25% by weight.

[0076] In this methanation catalyst, the content of the protective agent is 3 mL relative to 1 g of catalyst particles.

[0077] XRD analysis revealed that the methanation catalyst exhibited a diffraction peak with a width greater than 5° at 2θ = 45 ± 0.2°, indicating that the nickel in the methanation catalyst was amorphous. Furthermore, the zirconium oxide contained in the methanation catalyst conformed to the peak shape, position, and intensity of the tetragonal phase (tetragonal crystal form) in the zirconium oxide standard card.

[0078] Example 2

[0079] The method according to Example 1 differs in that:

[0080] In step (1), the molar ratio of the reducing agent to the nickel precursor (based on nickel element) is 2:1;

[0081] The contact steps are as follows: under oscillation, the aqueous solution of nickel precursor is added dropwise to the aqueous solution of reducing agent; the oscillation frequency is 50 Hz; the dropping rate is 3 drops / second; and the reduction reaction time is 1 hour.

[0082] In step (2), the dispersant is a mixture of zirconium oxide and magnesium oxide, wherein the mass ratio of zirconium oxide to magnesium oxide is 3:1; and the mass ratio of nickel precursor to dispersant, calculated as nickel element, is 1.5:1.

[0083] In step (3), water is used to adjust the pH of the lower layer of the stratified liquid to 8.0;

[0084] The rest was the same as in Example 1, and the methanation catalyst was obtained and sealed and purged with nitrogen.

[0085] The methanation catalyst comprises catalyst particles and a protective agent encapsulating the catalyst particles. The catalyst particles contain amorphous nickel and a dispersant. Based on the total weight of the catalyst particles, the content of amorphous nickel in the catalyst particles is 60% by weight and the content of dispersant is 40% by weight.

[0086] In this methanation catalyst, the content of the protective agent is 3 mL relative to 1 g of catalyst particles.

[0087] XRD analysis revealed that the methanation catalyst exhibited a diffraction peak with a width greater than 5° at 2θ = 45 ± 0.2°, indicating that the nickel in the methanation catalyst was amorphous. Furthermore, the zirconium oxide contained in the methanation catalyst conformed to the peak shape, position, and intensity of the tetragonal phase (tetragonal crystal form) in the zirconium oxide standard card.

[0088] Example 3

[0089] The method according to Example 1 differs in that:

[0090] In step (1), the molar ratio of the reducing agent to the nickel precursor (based on nickel element) is 1.75:1;

[0091] The contact steps are as follows: the aqueous solution of nickel precursor is added dropwise to the aqueous solution of reducing agent under oscillation; the oscillation frequency is 40 Hz; the dropping rate is 2 drops / second; and the reduction reaction time is 3 hours.

[0092] In step (2), the dispersant is a mixture of zirconium oxide and magnesium oxide, wherein the mass ratio of zirconium oxide to magnesium oxide is 4:1; and the mass ratio of nickel precursor to dispersant, calculated as nickel element, is 5.67:1.

[0093] In step (3), water is used to adjust the pH of the lower layer of the stratified liquid to 7.7;

[0094] The rest was the same as in Example 1, and the methanation catalyst was obtained and sealed and purged with nitrogen.

[0095] The methanation catalyst comprises catalyst particles and a protective agent encapsulating the catalyst particles. The catalyst particles contain amorphous nickel and a dispersant. Based on the total weight of the catalyst particles, the content of amorphous nickel in the catalyst particles is 85% by weight, and the content of dispersant is 15% by weight.

[0096] In this methanation catalyst, the content of the protective agent is 2 mL relative to 1 g of catalyst particles.

[0097] XRD analysis revealed that the methanation catalyst exhibited a diffraction peak with a width greater than 5° at 2θ = 45 ± 0.2°, indicating that the nickel in the methanation catalyst was amorphous. Furthermore, the zirconium oxide contained in the methanation catalyst conformed to the peak shape, position, and intensity of the tetragonal phase (tetragonal crystal form) in the zirconium oxide standard card.

[0098] Example 4

[0099] The method according to Example 1 differs in that:

[0100] In step (1), the molar ratio of the reducing agent to the nickel precursor (based on nickel element) is 2:1;

[0101] The reduction reaction takes 1.5 hours.

[0102] In step (2), the dispersant is a mixture of zirconium oxide and magnesium oxide, wherein the mass ratio of zirconium oxide to magnesium oxide is 5:1;

[0103] The rest was the same as in Example 1, and the methanation catalyst was obtained and sealed and purged with nitrogen.

[0104] The methanation catalyst comprises catalyst particles and a protective agent encapsulating the catalyst particles. The catalyst particles contain amorphous nickel and a dispersant. Based on the total weight of the catalyst particles, the content of amorphous nickel in the catalyst particles is 75% by weight, and the content of dispersant is 25% by weight.

[0105] In this methanation catalyst, the content of the protective agent is 4 mL relative to 1 g of catalyst particles.

[0106] XRD analysis revealed that the methanation catalyst exhibited a diffraction peak with a width greater than 5° at 2θ = 45 ± 0.2°, indicating that the nickel in the methanation catalyst was amorphous. Furthermore, the zirconium oxide contained in the methanation catalyst conformed to the peak shape, position, and intensity of the tetragonal phase (tetragonal crystal form) in the zirconium oxide standard card.

[0107] Example 5

[0108] The method according to Example 1 differs in that:

[0109] In step (1), the molar ratio of the reducing agent to the nickel precursor (based on nickel element) is 2:1;

[0110] In step (2), the dispersant is a mixture of zirconium oxide and magnesium oxide, wherein the mass ratio of zirconium oxide to magnesium oxide is 4:1; the mass ratio of nickel precursor to dispersant, calculated as nickel element, is 4:1.

[0111] In step (3), water is used to adjust the pH of the lower layer of the stratified liquid to 8.0;

[0112] The rest was the same as in Example 1, and the methanation catalyst was obtained and sealed and purged with nitrogen.

[0113] The methanation catalyst comprises catalyst particles and a protective agent encapsulating the catalyst particles. The catalyst particles contain amorphous nickel and a dispersant. Based on the total weight of the catalyst particles, the content of amorphous nickel in the catalyst particles is 80% by weight, and the content of dispersant is 20% by weight.

[0114] In this methanation catalyst, the content of the protective agent is 2 mL relative to 1 g of catalyst particles.

[0115] XRD analysis revealed that the methanation catalyst exhibited a diffraction peak with a width greater than 5° at 2θ = 45 ± 0.2°, indicating that the nickel in the methanation catalyst was amorphous. Furthermore, the zirconium oxide contained in the methanation catalyst conformed to the peak shape, position, and intensity of the tetragonal phase (tetragonal crystal form) in the zirconium oxide standard card.

[0116] Example 6

[0117] The method according to Example 1 differs in that:

[0118] In step (1), the reduction reaction takes 2.5 hours;

[0119] In step (2), the dispersant is a mixture of zirconium oxide and magnesium oxide, wherein the mass ratio of zirconium oxide to magnesium oxide is 3:1; and the mass ratio of nickel precursor to dispersant, calculated as nickel element, is 5:1.

[0120] The rest was the same as in Example 1, and the methanation catalyst was obtained and sealed and purged with nitrogen.

[0121] The methanation catalyst comprises catalyst particles and a protective agent encapsulating the catalyst particles. The catalyst particles contain amorphous nickel and a dispersant. Based on the total weight of the catalyst particles, the content of amorphous nickel in the catalyst particles is 83.3% by weight, and the content of dispersant is 16.7% by weight.

[0122] In this methanation catalyst, the content of the protective agent is 4 mL relative to 1 g of catalyst particles.

[0123] XRD analysis revealed that the methanation catalyst exhibited a diffraction peak with a width greater than 5° at 2θ = 45 ± 0.2°, indicating that the nickel in the methanation catalyst was amorphous. Furthermore, the zirconium oxide contained in the methanation catalyst conformed to the peak shape, position, and intensity of the tetragonal phase (tetragonal crystal form) in the zirconium oxide standard card.

[0124] Example 7

[0125] The method according to Example 1 differs in that:

[0126] In step (2), the dispersant is alumina, and it has not undergone high-temperature calcination treatment;

[0127] The rest was the same as in Example 1, and the methanation catalyst was obtained and sealed and purged with nitrogen.

[0128] The methanation catalyst comprises catalyst particles and a protective agent encapsulating the catalyst particles. The catalyst particles contain amorphous nickel and a dispersant. Based on the total weight of the catalyst particles, the content of amorphous nickel in the catalyst particles is 75% by weight, and the content of dispersant is 25% by weight.

[0129] In this methanation catalyst, the content of the protective agent is 3 mL relative to 1 g of catalyst particles.

[0130] XRD analysis revealed that the methanation catalyst exhibited a diffraction peak with a width greater than 5° at 2θ = 45 ± 0.2°, indicating that the nickel in the methanation catalyst was amorphous.

[0131] Example 8

[0132] The method according to Example 1 differs in that:

[0133] In step (2), the dispersant is borax, and it has not undergone high-temperature calcination treatment;

[0134] The rest was the same as in Example 1, and the methanation catalyst was obtained and sealed and purged with nitrogen.

[0135] The methanation catalyst comprises catalyst particles and a protective agent encapsulating the catalyst particles. The catalyst particles contain amorphous nickel and a dispersant. Based on the total weight of the catalyst particles, the content of amorphous nickel in the catalyst particles is 75% by weight, and the content of dispersant is 25% by weight.

[0136] In this methanation catalyst, the content of the protective agent is 3 mL relative to 1 g of catalyst particles.

[0137] XRD analysis revealed that the methanation catalyst exhibited a diffraction peak with a width greater than 5° at 2θ = 45 ± 0.2°, indicating that the nickel in the methanation catalyst was amorphous.

[0138] Comparative Example 1

[0139] The method of Example 1 differs in that: in step (2), no dispersant is added;

[0140] The rest was the same as in Example 1, and the methanation catalyst was obtained and sealed and purged with nitrogen.

[0141] The methanation catalyst comprises catalyst particles and a protective agent encapsulating the catalyst particles. The catalyst particles are amorphous nickel (i.e., based on the total weight of the catalyst particles, the content of amorphous nickel in the catalyst particles is 100% by weight).

[0142] XRD analysis revealed that the methanation catalyst exhibited a diffraction peak with a width greater than 5° at 2θ = 45 ± 0.2°, indicating that the nickel in the methanation catalyst was amorphous.

[0143] Comparative Example 2

[0144] The method according to Example 1 differs in that:

[0145] In step (2), the dispersant is a mixture of zirconium oxide and magnesium oxide, wherein the crystal form of zirconium oxide is monoclinic, that is, the mixture obtained by mixing zirconium oxide powder and magnesium oxide powder in the preparation process of the dispersant is not subjected to high-temperature calcination treatment.

[0146] The rest was the same as in Example 1, and the methanation catalyst was obtained and sealed and purged with nitrogen.

[0147] The methanation catalyst comprises catalyst particles and a protective agent encapsulating the catalyst particles. The catalyst particles contain amorphous nickel and a dispersant. Based on the total weight of the catalyst particles, the content of amorphous nickel in the catalyst particles is 75% by weight, and the content of dispersant is 25% by weight.

[0148] XRD analysis revealed that the methanation catalyst exhibited a diffraction peak with a width greater than 5° at 2θ = 45 ± 0.2°, indicating that the nickel in the methanation catalyst was amorphous. Furthermore, the zirconium oxide contained in the methanation catalyst conformed to the peak shape, position, and intensity of the monoclinic phase (monoclinic crystal form) in the zirconium oxide standard card.

[0149] Test case

[0150] The methanation catalysts prepared in the examples and comparative examples were respectively packed into a slurry bed reactor, with the packing amount satisfying that the catalyst particles in the methanation catalyst are 15g, and an inert heat-conducting medium (the same type as the protective agent) was introduced, so that the packing amount of the methanation catalyst and the volume of the inert heat-conducting medium satisfy that the total amount of protective agent and inert heat-conducting medium in the methanation catalyst is 40mL relative to 1g of catalyst particles.

[0151] Under single-stage slurry bed non-circulating reaction process conditions (volume hourly space velocity as shown in Table 1, inlet temperature 260℃, pressure 3.0MPa, stirring speed 1200r / min), syngas (v / v composition: CO+CO2≤17%, H2 55-60%, remainder methane) was subjected to methanation reaction, and the reaction temperature was controlled below 340℃. The resulting methane product was subjected to performance testing and analysis, and the results are shown in Table 1.

[0152] Table 1

[0153]

[0154]

[0155] Note: Total carbon load is the total volume content of carbon oxides (CO and CO2) in the syngas; CO2 load is the volume content of CO2 in the syngas; residual CO is the CO content in the methane product gas, and residual CO2 is the CO2 content in the methane product gas.

[0156] The above results show that the methanation catalyst prepared by the method provided by this invention has catalyst particles that are already in a reduced state, requiring no reduction before use. This makes it more suitable for slurry bed reactors, especially when the syngas flow rate is no higher than 15000 h⁻¹. -1 With a volume hourly space velocity and a total carbon load not exceeding 17% by volume, carbon monoxide in methane products can be completely converted using a single-stage slurry bed reactor, with a carbon dioxide conversion rate of over 90%.

[0157] 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 method for preparing a methanation catalyst, characterized in that, The preparation method includes: (1) In the presence of water, the nickel precursor is brought into contact with a reducing agent to carry out a reduction reaction to obtain the reduction product; (2) In the presence of a protective agent, the reduction product is mixed with a dispersant, and the resulting mixture is allowed to stand and separate into layers to form a layered liquid; wherein the protective agent is a hydrophobic inert liquid; the layered liquid includes an upper liquid and a lower liquid, the upper liquid contains the protective agent, the lower liquid contains water and catalyst particles, the catalyst particles contain amorphous nickel and a dispersant; the dispersant is selected from at least one of alumina, zirconium oxide, magnesium oxide and borax, wherein the zirconium oxide has a tetragonal crystal form; (3) Adjust the pH of the lower layer of the stratified liquid to 7-9 using water, and then remove the water from the lower layer of the stratified liquid so that the protective agent coats the catalyst particles to obtain the methanation catalyst.

2. The preparation method according to claim 1, wherein, In step (1), the nickel precursor is selected from at least one of nickel nitrate, nickel chloride, and nickel acetate; And / or, the reducing agent is a borohydride.

3. The preparation method according to claim 2, wherein, The nickel precursor is nickel nitrate.

4. The preparation method according to claim 2, wherein, The reducing agent is sodium borohydride and / or potassium borohydride.

5. The preparation method according to claim 1, wherein, In step (1), the molar ratio of the reducing agent to the nickel precursor (based on nickel element) is (1-2.5):1; and / or the conditions for the reduction reaction include: a temperature of 15-25°C and a time of 1-3h.

6. The preparation method according to claim 5, wherein, The molar ratio of the reducing agent to the nickel precursor, calculated as nickel, is (1.5-2):

1.

7. The preparation method according to any one of claims 1-6, wherein, In step (2), the protective agent is selected from at least one of liquid paraffin, diesel oil, and white oil; And / or, the particle size of the dispersant is 100-400 mesh.

8. The preparation method according to claim 7, wherein, The protective agent is liquid paraffin.

9. The preparation method according to any one of claims 1-6, wherein, In step (2), the dispersant is selected from at least one or more of a mixture of zirconium oxide and magnesium oxide, aluminum oxide and borax.

10. The preparation method according to claim 9, wherein, The dispersant is a mixture of zirconium oxide and magnesium oxide.

11. The preparation method according to claim 10, wherein, In the mixture, the mass ratio of zirconium oxide to magnesium oxide is (1-10):

1.

12. The preparation method according to claim 11, wherein, In the mixture, the mass ratio of zirconium oxide to magnesium oxide is (3-6):

1.

13. The preparation method according to any one of claims 10-12, wherein, The method for preparing the mixture of zirconium oxide and magnesium oxide includes: calcining the mixture obtained by mixing zirconium oxide powder and magnesium oxide powder at high temperature, wherein the conditions for high temperature calcination include: a temperature of 1200-1300℃ and a time of 4-6h.

14. The preparation method according to claim 13, wherein, The zirconium oxide powder and magnesium oxide powder have a particle size of 100-400 mesh.

15. The preparation method according to claim 14, wherein, The zirconium oxide powder and magnesium oxide powder have a particle size of 120-180 mesh.

16. The preparation method according to claim 7, wherein, The particle size of the dispersant is 120-180 mesh.

17. The preparation method according to any one of claims 1-6, wherein, In step (2), the mass ratio of the nickel precursor to the dispersant, calculated as nickel element, is (1-10):1; And / or, the amount of the protective agent used is such that the thickness of the upper liquid layer is 2-3 cm; And / or, the mixing conditions include: a temperature of 20-50°C, a time of 20-60 min, and a rotation speed of 200-400 rpm.

18. The preparation method according to claim 17, wherein, The mass ratio of the nickel precursor to the dispersant, calculated based on nickel element, is (1.5-5.67):

1.

19. The preparation method according to any one of claims 1-6, wherein, In step (3), water is used to adjust the pH of the lower layer liquid to 7.5-8.

20. A methanation catalyst prepared by the method according to any one of claims 1-19, characterized in that, The methanation catalyst comprises catalyst particles and a protective agent encapsulating the catalyst particles, wherein the catalyst particles contain amorphous nickel and a dispersant.

21. The methanation catalyst according to claim 20, wherein, In the XRD pattern of the methanation catalyst, there is a diffraction peak with a width greater than 5° at 2θ = 45 ± 0.2°. And / or, in the methanation catalyst, the content of the protective agent is 2-4 mL relative to 1 g of the catalyst particles.

22. The methanation catalyst according to claim 20 or 21, wherein, Based on the total weight of the catalyst particles, the catalyst particles contain 60-85% by weight of amorphous nickel and 15-40% by weight of dispersant.

23. The methanation catalyst according to claim 22, wherein, Based on the total weight of the catalyst particles, the catalyst particles contain 65-75% by weight of amorphous nickel and 25-35% by weight of dispersant.

24. The use of the methanation catalyst according to any one of claims 20-23 in the preparation of synthetic natural gas by methanation reaction.

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