Methods and systems for producing natural gas by syngas methanation

Abstract

This invention relates to the field of integrated coal gasification applications, and discloses a method and system for producing natural gas from syngas through methanation. The method includes: in a slurry bed reactor, contacting syngas with a low-temperature methanation catalyst to perform a methanation reaction, obtaining an outlet process gas containing paraffin; and contacting the outlet process gas with catalyst II to perform an adiabatic methanation reaction; wherein catalyst II comprises a paraffin cracking catalyst and a high-temperature methanation catalyst; or, catalyst II is a bifunctional catalyst. This method involves slurry bed methanation of syngas, and the resulting paraffin-containing outlet process gas does not require condensation and dehydration, allowing for direct adiabatic methanation. Furthermore, it can remove trace amounts of paraffin in one step, thus avoiding catalyst deactivation. This reduces intermediate steps and equipment requirements, shortens the syngas methanation process to natural gas production, reduces heat loss due to heating and cooling, and results in low equipment investment and operating costs.

Description

Technical Field

[0001] This invention relates to the field of integrated coal gasification applications, specifically to a method and system for producing natural gas from syngas by methanation. Background Technology

[0002] Syngas, composed of CH4, H2, CO, and CO2, is an ideal feedstock for producing SNG / LNG. Converting syngas into natural gas yields significant economic and social benefits. Developing suitable syngas-to-methane technology, tailored to the composition of syngas, is an effective and crucial approach to utilizing syngas.

[0003] Currently, low-temperature methanation is gradually becoming a new direction for methane production. Due to its higher chemical equilibrium, larger throughput, fewer equipment requirements, and no need for recirculation, low-temperature methanation is widely used in methane production. Slurry bed methanation is a relatively advanced reaction device in low-temperature processes. Its reaction zone exhibits highly uniform temperature, making it extremely difficult for temperatures to runaway or become excessively high. It also features rapid heat transfer and high methanation efficiency, making slurry bed technology excellent in methanation production. However, slurry bed methanation is subject to process limitations. The process gas exiting the slurry bed contains paraffin vapor and paraffin entrained in the liquid droplets. This requires cooling, condensation, and separation, followed by heat exchange and reheating before entering the subsequent refining process. This cooling, condensation, and reheating process requires several pieces of equipment, including condensers, separation tanks, cold water circulation pumps, heat exchangers, and heaters, and involves heat loss and power consumption. The separated paraffin-water mixture increases the pressure on wastewater discharge. If the process gas from the slurry bed outlet enters the subsequent refining stage directly without heat exchange, paraffin wax will accumulate on the surface of the subsequent refining catalyst, forming a phenomenon similar to catalyst waxing, which gradually deactivates the catalyst physically. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems in existing low-temperature methanation methods for producing natural gas, where the slurry bed outlet process gas contains paraffin, which easily deactivates the catalyst and requires multiple dewaxing devices.

[0005] To achieve the above objectives, a first aspect of the present invention provides a method for producing natural gas by methanation of syngas, the method comprising:

[0006] (1) In a slurry bed reactor, the syngas is contacted with catalyst I to carry out a methanation reaction to obtain an outlet process gas containing paraffin; the catalyst I is a low-temperature methanation catalyst.

[0007] (2) The outlet process gas is contacted with catalyst II to carry out an adiabatic methanation reaction;

[0008] The catalyst II comprises a paraffin cracking catalyst and a high-temperature methanation catalyst; the paraffin cracking catalyst comprises a support and an active component and an auxiliary agent supported on the support, wherein the active component is manganese dioxide, the auxiliary agent is La2O3, the support is a magnesium-aluminum composite oxide, the magnesium-aluminum composite oxide comprises MgAl2O4, and the content of MgAl2O4 is 93-100 wt% based on the total amount of the magnesium-aluminum composite oxide; based on the total amount of the paraffin cracking catalyst, the content of the active component is 5-15 wt%, the content of the auxiliary agent is 0.1-2 wt%, and the content of the support is 83-94.9 wt%; or,

[0009] The catalyst II is a bifunctional catalyst, comprising a support and active components I, II, and an auxiliary agent supported on the support. Active component I is nickel and / or nickel oxide, active component II is manganese dioxide, the auxiliary agent is La₂O₃, and the support is a magnesium-aluminum composite oxide comprising MgAl₂O₄. Based on the total amount of the magnesium-aluminum composite oxide, the content of MgAl₂O₄ is 93-100 wt%. Based on the total amount of the bifunctional catalyst, the content of active component I (calculated as nickel) is 10-20 wt%, the content of active component II is 5-15 wt%, the content of the auxiliary agent is 0.1-2 wt%, and the content of the support is 74-85 wt%.

[0010] A second aspect of the present invention provides a system for producing natural gas by syngas methanation, the system comprising a methanation unit and a refining unit connected in series, wherein the methanation unit includes at least one slurry bed reactor, the refining unit includes at least one adiabatic fixed bed reactor, and the outlet of the slurry bed reactor is connected to the inlet of the adiabatic fixed bed reactor.

[0011] Through the above technical solution, the method provided by the present invention performs a slurry-bed methanation reaction on syngas. The resulting paraffin-containing outlet process gas does not need to undergo condensation and dehydration steps and can be directly subjected to an adiabatic methanation reaction (high-temperature purification). The high temperature and heat generated by the adiabatic methanation reaction can meet the reaction process conditions required for the vapor cracking of trace paraffin in the slurry-bed outlet process gas. Using these conditions, and with the action of a catalyst that has both high-temperature methanation catalytic effect and high-temperature dewaxing catalytic effect, the trace paraffin contained in the slurry-bed outlet process gas can be removed without condensation separation.

[0012] The method provided by this invention can remove trace amounts of paraffin from the slurry bed outlet process gas in one step and crack it into small molecule hydrocarbons. This avoids catalyst deactivation due to paraffin covering during subsequent refining processes, reduces intermediate steps and equipment requirements, shortens the process of syngas methanation to natural gas production, reduces heat loss from heating and cooling, and lowers equipment investment and operating costs. Furthermore, since paraffin is cracked into methane, it also helps increase methane production. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of a system for producing natural gas by syngas methanation according to one embodiment of the present invention;

[0014] Figure 2 These are XRD patterns of the carriers prepared in Preparation Example A1 and Preparation Example B1 of this invention;

[0015] Figure 3 This is the XRD pattern of the reduction product obtained in step (S1) of preparation example C1 of the present invention;

[0016] Figure 4 This is the XRD pattern of the dispersant used in preparation example C1 of the present invention.

[0017] Explanation of reference numerals in the attached figures

[0018] 1. Slurry bed reactor 2. Valves

[0019] 3. One-way check valve; 4. Insulated fixed-bed reactor Detailed Implementation

[0020] 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.

[0021] In this invention, unless otherwise stated, the content of each component in the paraffin cracking catalyst and the bifunctional catalyst is calculated by the amount of feed.

[0022] In this invention, unless otherwise stated, the pressure is gauge pressure.

[0023] In this invention, unless otherwise stated, room temperature means 25±2℃.

[0024] As previously stated, the first aspect of this invention provides a method for producing natural gas by methanation of syngas, the method comprising:

[0025] (1) In a slurry bed reactor, the syngas is contacted with catalyst I to carry out a methanation reaction to obtain an outlet process gas containing paraffin; the catalyst I is a low-temperature methanation catalyst.

[0026] (2) The outlet process gas is contacted with catalyst II to carry out an adiabatic methanation reaction;

[0027] The catalyst II comprises a paraffin cracking catalyst and a high-temperature methanation catalyst; the paraffin cracking catalyst comprises a support and an active component and an auxiliary agent supported on the support, wherein the active component is manganese dioxide, the auxiliary agent is La2O3, the support is a magnesium-aluminum composite oxide, the magnesium-aluminum composite oxide comprises MgAl2O4, and the content of MgAl2O4 is 93-100 wt% based on the total amount of the magnesium-aluminum composite oxide; based on the total amount of the paraffin cracking catalyst, the content of the active component is 5-15 wt%, the content of the auxiliary agent is 0.1-2 wt%, and the content of the support is 83-94.9 wt%; or,

[0028] The catalyst II is a bifunctional catalyst, comprising a support and active components I, II, and an auxiliary agent supported on the support. Active component I is nickel and / or nickel oxide, active component II is manganese dioxide, the auxiliary agent is La₂O₃, and the support is a magnesium-aluminum composite oxide comprising MgAl₂O₄. Based on the total amount of the magnesium-aluminum composite oxide, the content of MgAl₂O₄ is 93-100 wt%. Based on the total amount of the bifunctional catalyst, the content of active component I (calculated as nickel) is 10-20 wt%, the content of active component II is 5-15 wt%, the content of the auxiliary agent is 0.1-2 wt%, and the content of the support is 74-85 wt%.

[0029] According to some embodiments of the present invention, in step (2), the catalyst II is a catalyst with high-temperature methanation catalysis and dewaxing catalysis. The catalyst II can be a mixture of two or more catalysts with high-temperature methanation catalysis and high-temperature dewaxing catalysis respectively, or it can be a single catalyst with both high-temperature methanation catalysis and high-temperature dewaxing catalysis.

[0030] According to some embodiments of the present invention, in step (2), the catalyst II comprises a paraffin cracking catalyst and a high-temperature methanation catalyst; the paraffin cracking catalyst comprises a support and an active component and an auxiliary agent supported on the support, wherein the active component is manganese dioxide, the auxiliary agent is La2O3, the support is a magnesium-aluminum composite oxide, the magnesium-aluminum composite oxide comprises MgAl2O4, and the content of MgAl2O4 is 93-100 wt% based on the total amount of the magnesium-aluminum composite oxide;

[0031] Based on the total amount of the paraffin cracking catalyst, the content of the active component is 5-15 wt%, the content of the auxiliary agent is 0.1-2 wt%, and the content of the support is 83-94.9 wt%.

[0032] According to some embodiments of the present invention, preferably, the content of MgAl2O4 is 96-100 wt% based on the total amount of the magnesium-aluminum composite oxide.

[0033] According to some embodiments of the present invention, preferably, the magnesium-aluminum composite oxide further includes MgO and / or Al2O3. The MgO is residual magnesium oxide that has not formed magnesium-aluminum spinel (MgAl2O4); the Al2O3 is residual aluminum oxide that has not formed magnesium-aluminum spinel (MgAl2O4).

[0034] Preferably, based on the total amount of the magnesium-aluminum composite oxide, the content of MgO is 0-5 wt%, preferably 0-3 wt%; and the content of Al2O3 is 0-2 wt%, preferably 0-1 wt%.

[0035] In the preferred embodiment described above, the magnesium-aluminum composite oxide contains a low amount of residual alumina, which helps reduce the number of acidic sites. If there is excessive alumina, during paraffin cracking, the relatively stable α-carbon at acidic sites transforms into more reactive β-carbon, easily causing the growth of carbon nanotubes on the catalyst surface, leading to catalyst deactivation due to carbon buildup. The low residual alumina content in the magnesium-aluminum composite oxide avoids this problem of carbon buildup and deactivation, thus improving the catalyst's activity and lifespan.

[0036] According to some embodiments of the present invention, preferably, the grain size of MgAl2O4 is <20 nm, more preferably 4-15 nm, and even more preferably 5-10 nm. Using the above preferred embodiments helps to improve the dispersion of the active component on the carrier surface and, together with the additives, to fix the active component, preventing the carbon nanotubes from lifting the active component from the carrier and causing it to be lost.

[0037] According to some embodiments of the present invention, preferably, the pore volume of MgAl2O4 is >0.15 mL / g, more preferably 0.25-0.35 mL / g, and more preferably 0.27-0.33 mL / g.

[0038] According to some embodiments of the present invention, preferably, the average pore size of MgAl2O4 is 10-50 nm, more preferably 10-30 nm, and even more preferably 13-20 nm.

[0039] By adopting the above preferred embodiment, the grain size, pore volume and average pore size of MgAl2O4 meet the above conditions, which is beneficial to control the impregnation amount of active components during catalyst preparation, as well as the diffusion of paraffin molecules in the catalyst channels and the escape of paraffin cracking products.

[0040] According to some embodiments of the present invention, preferably, the molar ratio of Mg to Al in the magnesium-aluminum composite oxide is 1:2-2.04.

[0041] According to some embodiments of the present invention, the paraffin cracking catalyst does not require activation, is directly active, and can be used directly.

[0042] According to some embodiments of the present invention, preferably, the paraffin cracking catalyst is prepared by a method comprising the following steps:

[0043] (A1) A mixture containing magnesium oxide, pseudoboehmite and a pore-expanding agent is subjected to a first calcination to obtain a support; wherein the temperature of the first calcination is 800-1000℃;

[0044] (A2) The active component precursor and the auxiliary agent precursor are loaded onto the support, and then the resulting product is subjected to a second calcination; wherein the temperature of the second calcination is lower than the temperature of the first calcination.

[0045] According to some embodiments of the present invention, preferably, in step (A1), the temperature of the first calcination is 850-950°C. Using the above preferred embodiments is more advantageous in increasing the MgAl2O4 content and reducing the Al2O3 content in the magnesium-aluminum composite oxide, thereby reducing carbon deposits generated during paraffin cracking and improving the activity and service life of the catalyst.

[0046] According to some embodiments of the present invention, preferably, in step (A1), the first calcination time is 2-10 hours, more preferably 4-8 hours.

[0047] According to some embodiments of the present invention, preferably, in step (A1), the magnesium oxide is light magnesium oxide, and the average particle size of the light magnesium oxide is 0.06-0.09 mm.

[0048] According to some embodiments of the present invention, preferably, in step (A1), the average particle size of the pseudoboehmite is 0.06-0.09 mm.

[0049] Using the raw materials described in the preferred embodiments above is more conducive to obtaining a carrier that meets the above requirements.

[0050] According to some embodiments of the present invention, preferably, in step (A1), the pore-expanding agent is selected from at least one of oxalic acid, nitric acid, acetic acid and sulfuric acid, preferably nitric acid.

[0051] Preferably, the ratio of the pore-expanding agent to the magnesium oxide is 1 mL: 40-60 g.

[0052] According to some embodiments of the present invention, for ease of molding, preferably, in step (A1), the mixture also contains an adhesive.

[0053] Preferably, the binder is selected from at least one of guar gum powder, stearate and cellulose and their derivatives, and is preferably sodium carboxymethyl cellulose.

[0054] Preferably, the mass ratio of the adhesive to the magnesium oxide is 1:20-25.

[0055] According to some embodiments of the present invention, in order to ensure that the components in the mixture are sufficiently dispersed and have appropriate strength for subsequent molding, preferably, in step (A1), the mixture also contains a solvent.

[0056] Preferably, the solvent is deionized water.

[0057] Preferably, the volume ratio of the solvent to the pore-expanding agent is 80-150:1.

[0058] According to some embodiments of the present invention, preferably, before the first calcination, step (A1) further includes the sequential steps of mixing and grinding, sieving, drying, and shaping. The mixing, grinding, sieving, drying, and shaping steps are all conventional methods for preparing catalysts and can be performed with reference to existing technologies.

[0059] According to some embodiments of the present invention, preferably, in step (A2), the active component precursor is selected from at least one of manganese nitrate, manganese sulfate, and manganese chloride, preferably manganese nitrate. Preferably, the active component precursor is provided in the form of an aqueous solution. Exemplarily, the manganese nitrate may be provided in the form of a 50 wt% aqueous solution of manganese nitrate.

[0060] According to some embodiments of the present invention, preferably, in step (A2), the auxiliary agent precursor is selected from at least one of lanthanum nitrate, lanthanum chloride, and lanthanum sulfate, and preferably lanthanum nitrate. Preferably, the auxiliary agent precursor is provided in the form of an aqueous solution. Exemplarily, the lanthanum nitrate may be provided in the form of a 4 wt% aqueous solution of lanthanum nitrate.

[0061] According to some embodiments of the present invention, preferably, in step (A2), the conditions for the second calcination include: a temperature of 350-500°C, preferably 400-450°C; and a time of 4-10 hours, preferably 4-8 hours.

[0062] According to some embodiments of the present invention, preferably, in step (A2), the loading method is an impregnation method;

[0063] Preferably, the impregnation conditions include: a temperature of 60-80°C and a time of 0.5-2 hours;

[0064] Preferably, the active component precursor is first loaded onto the carrier to obtain an intermediate, and then the auxiliary agent precursor is loaded onto the intermediate. After impregnation, each component needs to be dried and calcined to immobilize the component. The drying can be performed according to existing techniques.

[0065] According to a preferred embodiment of the present invention, in step (A2), the loading step includes:

[0066] (A2-a) The carrier is contacted with the active component precursor for a first impregnation, the resulting product is then filtered, and the resulting solid is then dried and calcined in sequence to obtain an intermediate.

[0067] (A2-b) The intermediate is contacted with the auxiliary precursor for a second impregnation, the resulting product is then filtered, and the resulting solid is then dried and calcined in sequence.

[0068] The conditions for the first impregnation and the second impregnation each independently include: a temperature of 60-80℃ and a time of 0.5-2h; the conditions for the second calcination I and the second calcination II each independently include: a temperature of 350-500℃, preferably 400-450℃ and a time of 4-10h, preferably 4-8h.

[0069] According to some embodiments of the present invention, in step (2), the catalyst II is a bifunctional catalyst. The bifunctional catalyst includes a support and active component I, active component II and an auxiliary agent supported on the support, wherein the active component I is nickel and / or nickel oxide, the active component II is manganese dioxide, the auxiliary agent is La2O3, the support is a magnesium-aluminum composite oxide, the magnesium-aluminum composite oxide includes MgAl2O4, and the content of MgAl2O4 is 93-100 wt% based on the total amount of the magnesium-aluminum composite oxide;

[0070] Based on the total amount of the bifunctional catalyst, the content of active component I (calculated as nickel) is 10-20 wt%, the content of active component II is 5-15 wt%, the content of the promoter is 0.1-2 wt%, and the content of the support is 74-85 wt%.

[0071] According to some embodiments of the present invention, preferably, the content of MgAl2O4 is 96-100 wt% based on the total amount of the magnesium-aluminum composite oxide.

[0072] According to some embodiments of the present invention, the magnesium-aluminum composite oxide preferably further includes MgO and / or Al2O3. The MgO is residual magnesium oxide that has not formed magnesium-aluminum spinel (MgAl2O4); the Al2O3 is residual aluminum oxide that has not formed magnesium-aluminum spinel (MgAl2O4).

[0073] Preferably, based on the total amount of the magnesium-aluminum composite oxide, the content of MgO is 0-5 wt%, preferably 0-3 wt%; and the content of Al2O3 is 0-2 wt%, preferably 0-1 wt%.

[0074] In the preferred embodiment described above, the magnesium-aluminum composite oxide contains a low amount of residual alumina, which helps reduce the number of acidic sites. If there is excessive alumina, during paraffin cracking, the relatively stable α-carbon at acidic sites transforms into more reactive β-carbon, easily causing the growth of carbon nanotubes on the catalyst surface, leading to catalyst deactivation due to carbon buildup. The low residual alumina content in the magnesium-aluminum composite oxide avoids this problem of carbon buildup and deactivation, thus improving the catalyst's activity and lifespan.

[0075] According to some embodiments of the present invention, preferably, the grain size of MgAl2O4 is <20 nm, more preferably 4-15 nm, and even more preferably 5-10 nm. Using the above preferred embodiments helps to improve the dispersion of the active component on the carrier surface and, together with the additives, to fix the active component, preventing the carbon nanotubes from lifting the active component from the carrier and causing it to be lost.

[0076] According to some embodiments of the present invention, preferably, the pore volume of MgAl2O4 is >0.15 mL / g, more preferably 0.25-0.35 mL / g, and more preferably 0.27-0.33 mL / g.

[0077] According to some embodiments of the present invention, preferably, the average pore size of MgAl2O4 is 10-50 nm, more preferably 10-30 nm, and even more preferably 13-20 nm.

[0078] By adopting the above preferred embodiment, the grain size, pore volume and average pore size of MgAl2O4 meet the above conditions, which is beneficial to control the impregnation amount of active components during catalyst preparation, as well as the diffusion of paraffin molecules in the catalyst channels and the escape of paraffin cracking products.

[0079] According to some embodiments of the present invention, preferably, the molar ratio of Mg to Al in the magnesium-aluminum composite oxide is 1:2-2.04.

[0080] According to some embodiments of the present invention, in the bifunctional catalyst, the active component I is present in the form of nickel and / or nickel oxide. Activation reduction by contact with a reducing gas can reduce the nickel oxide to active nickel.

[0081] According to some embodiments of the present invention, preferably, the bifunctional catalyst is prepared by a method comprising the following steps:

[0082] (B1) A mixture containing magnesium oxide, boehmite and a pore-expanding agent is subjected to a first calcination to obtain a support; wherein the temperature of the first calcination is 800-1000℃;

[0083] (B2) The active component precursor I, the active component precursor II and the auxiliary agent precursor are loaded onto the support, and then the resulting product is subjected to a second calcination; wherein the temperature of the second calcination is lower than the temperature of the first calcination.

[0084] According to some embodiments of the present invention, preferably, in step (B1), the temperature of the first calcination is 850-950°C. Using the above preferred embodiments is more advantageous in increasing the MgAl2O4 content and reducing the Al2O3 content in the magnesium-aluminum composite oxide, thereby reducing carbon deposits generated during paraffin cracking and improving the activity and service life of the catalyst.

[0085] According to some embodiments of the present invention, preferably, in step (B1), the first calcination time is 2-10 hours, more preferably 4-8 hours.

[0086] According to some embodiments of the present invention, preferably, in step (B1), the magnesium oxide is light magnesium oxide, and the average particle size of the light magnesium oxide is 0.06-0.09 mm.

[0087] According to some embodiments of the present invention, preferably, in step (B1), the average particle size of the pseudoboehmite is 0.06-0.09 mm.

[0088] Using the raw materials described in the preferred embodiments above is more conducive to obtaining a carrier that meets the above requirements.

[0089] According to some embodiments of the present invention, preferably, in step (B1), the pore-expanding agent is selected from at least one of oxalic acid, nitric acid, acetic acid and sulfuric acid, preferably nitric acid.

[0090] Preferably, the ratio of the pore-expanding agent to the magnesium oxide is 1 mL: 40-60 g.

[0091] According to some embodiments of the present invention, for ease of molding, preferably, in step (B1), the mixture also contains an adhesive.

[0092] Preferably, the binder is selected from at least one of guar gum powder, stearate and cellulose and their derivatives, and is preferably sodium carboxymethyl cellulose.

[0093] Preferably, the mass ratio of the adhesive to the magnesium oxide is 1:20-25.

[0094] According to some embodiments of the present invention, in order to ensure that the components in the mixture are sufficiently dispersed and have appropriate strength for subsequent molding, preferably, in step (B1), the mixture also contains a solvent.

[0095] Preferably, the solvent is deionized water.

[0096] Preferably, the volume ratio of the solvent to the pore-expanding agent is 80-150:1.

[0097] According to some embodiments of the present invention, preferably, before the first calcination, step (B1) further includes the sequential steps of mixing and grinding, sieving, drying, and shaping. The mixing, grinding, sieving, drying, and shaping steps are all conventional methods for preparing catalysts and can be performed with reference to existing technologies.

[0098] According to some embodiments of the present invention, preferably, in step (B2), the active component precursor I is selected from at least one of nickel nitrate, nickel chloride, and nickel sulfate, preferably nickel nitrate. Preferably, the active component precursor I is provided in the form of an aqueous solution. Exemplarily, the nickel nitrate may be provided in the form of a 60 wt% aqueous solution of nickel nitrate.

[0099] According to some embodiments of the present invention, preferably, in step (B2), the active component precursor II is selected from at least one of manganese nitrate, manganese sulfate, and manganese chloride, preferably manganese nitrate. Preferably, the active component precursor II is provided in the form of an aqueous solution. Exemplarily, the manganese nitrate may be provided in the form of a 50 wt% aqueous solution of manganese nitrate.

[0100] According to some embodiments of the present invention, preferably, in step (B2), the auxiliary agent precursor is selected from at least one of lanthanum nitrate, lanthanum chloride, and lanthanum sulfate, and preferably lanthanum nitrate. Preferably, the auxiliary agent precursor is provided in the form of an aqueous solution. Exemplarily, the lanthanum nitrate may be provided in the form of a 4 wt% aqueous solution of lanthanum nitrate.

[0101] According to some embodiments of the present invention, preferably, in step (B2), the conditions for the second calcination include: a temperature of 350-500°C, preferably 400-450°C; and a time of 4-10 hours, preferably 4-8 hours.

[0102] According to some embodiments of the present invention, preferably, in step (B2), the loading method is an impregnation method;

[0103] Preferably, the impregnation conditions include: a temperature of 60-80°C and a time of 0.5-2 hours;

[0104] Preferably, the active component precursor I is first loaded onto the support to obtain intermediate I, then the active component precursor II is loaded onto intermediate I to obtain intermediate II, and finally the auxiliary agent precursor is loaded onto intermediate II. After impregnation, each component needs to be dried and calcined to fix the component. The drying can be performed according to existing technology.

[0105] According to a preferred embodiment of the present invention, in step (B2), the loading step includes:

[0106] (B2-a) The carrier is contacted with the active component precursor I for a first impregnation, the resulting product is then filtered, and the resulting solid is then dried and calcined in sequence to obtain intermediate I.

[0107] (B2-b) The intermediate I is contacted with the active component precursor II for a second impregnation, and then the resulting product is filtered. The resulting solid is then dried and calcined in the second calcination II to obtain intermediate II.

[0108] (B2-c) The intermediate II is contacted with the auxiliary precursor for a third impregnation, the resulting product is then filtered, and the resulting solid is then dried and calcined in the second calcination III.

[0109] The conditions for the first impregnation, the second impregnation, and the third impregnation each independently include: a temperature of 60-80℃; and a time of 0.5-2h.

[0110] The conditions for the second calcination I, the second calcination II, and the second calcination III each independently include: a temperature of 350-500℃, preferably 400-450℃; and a time of 4-10h, preferably 4-8h.

[0111] According to some embodiments of the present invention, preferably, the method for preparing the bifunctional catalyst further includes: contacting the product obtained from the second calcination in step (B2) with a reducing gas for reduction. This operation enables the reduction of nickel oxide to active nickel.

[0112] Preferably, the reducing gas is hydrogen or a mixture of hydrogen and nitrogen. For example, the mixture may be a mixture with a hydrogen content of 20% by volume and a nitrogen content of 80% by volume.

[0113] Preferably, the reduction conditions include: a temperature of 400-500℃ and a time of 2-6 hours.

[0114] According to some embodiments of the present invention, in step (1), the low-temperature methanation catalyst can be a low-temperature methanation catalyst with methanation catalysis commonly used in the art (usually with an operating temperature of 260-350°C), such as a slurry bed methanation catalyst. There are no particular limitations on this, and all of them can achieve the inventive purpose of the present invention to a certain extent.

[0115] According to a preferred embodiment of the present invention, the low-temperature methanation catalyst comprises catalyst particles and a protective agent encapsulating the catalyst particles. The catalyst particles contain amorphous nickel and a dispersant. The dispersant is a mixture of zirconium oxide and magnesium oxide, wherein the mass ratio of zirconium oxide to magnesium oxide in the mixture is (1-10):1, preferably (3-6):1. The zirconium oxide has a tetragonal crystal form. The low-temperature methanation catalyst using the above preferred embodiment has a stronger hydrogenation capacity.

[0116] According to some embodiments of the present invention, preferably, the XRD pattern of the low-temperature 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 low-temperature methanation catalyst exists in an amorphous structure.

[0117] According to some embodiments of the present invention, there is no particular limitation on the content of the protective agent in the low-temperature methanation catalyst, as long as it is sufficient to encapsulate the catalyst particles to isolate them from oxygen. Preferably, the content of the protective agent in the low-temperature methanation catalyst is 2-4 mL relative to 1 g of catalyst particles. By adopting the above preferred embodiments, it is possible to encapsulate the catalyst particles and isolate them from oxygen with a relatively low content of protective agent.

[0118] When using the aforementioned low-temperature 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 are no particular limitations on this.

[0119] Preferably, the amount of inert heat-conducting medium introduced is such that the loading amount of the low-temperature methanation catalyst and the volume of the inert heat-conducting medium satisfy the following: relative to 1g of catalyst particles, the total amount of protective agent and inert heat-conducting medium in the low-temperature methanation catalyst is 20-100mL, preferably 20-50mL. Alternatively, the content of the protective agent in the low-temperature methanation catalyst can be adjusted to control the loading amount of the low-temperature methanation catalyst, thereby achieving the above requirements for the content of catalyst particles and protective agent.

[0120] 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 65-75% by weight, and the content of dispersant is 25-35% by weight.

[0121] According to some embodiments of the present invention, preferably, the particle size of the dispersant is 100-400 mesh, more preferably 120-180 mesh.

[0122] According to some embodiments of the present invention, preferably, the protective agent is liquid paraffin.

[0123] According to some embodiments of the present invention, preferably, the low-temperature methanation catalyst is prepared by a method comprising the following steps:

[0124] (C1) In the presence of water, the nickel precursor is brought into contact with a reducing agent to carry out a reduction reaction, and the reduction product is obtained;

[0125] (C2) 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 layered liquid comprises an upper liquid and a lower liquid, the upper liquid contains the protective agent, the lower liquid contains water and catalyst particles, and the catalyst particles contain amorphous nickel and a dispersant;

[0126] (C3) 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.

[0127] According to some embodiments of the present invention, in step (C1), a nickel precursor is contacted with a reducing agent in the presence of water to undergo 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.

[0128] According to some embodiments of the present invention, in step (C1), 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.

[0129] According to some embodiments of the present invention, in step (C1), 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.

[0130] According to some embodiments of the present invention, preferably, the molar ratio of the reducing agent to the nickel precursor, calculated as nickel element, is (1-2.5):1, more preferably (1.5-2):1. The above-described preferred embodiments can further promote the formation of amorphous nickel particles through chemical reduction.

[0131] According to some embodiments of the present invention, preferably, in step (C1), the nickel precursor is provided in the form of an aqueous solution of the nickel precursor; more preferably, the concentration of nickel in the aqueous solution of the nickel precursor is 0.5-2 mol / L.

[0132] According to some embodiments of the present invention, preferably, in step (C1), the reducing agent is provided in the form of an aqueous reducing agent solution, more preferably, the concentration of the reducing agent in the aqueous reducing agent solution is 1-3 mol / L.

[0133] According to some embodiments of the present invention, in order to remove oxygen in the solution, further promote the formation of reduction products, and improve the dispersion of reduction products, preferably, in step (C1), 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 are not particularly limited, 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.

[0134] According to some embodiments of the present invention, preferably, in step (C1), the conditions for the reduction reaction include: a temperature of 15-25°C and a time of 1-3 hours.

[0135] According to some embodiments of the present invention, in order to better precipitate and separate the reduction product, preferably, in step (C1), 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.

[0136] According to some embodiments of the present invention, in step (C2), 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 sufficient contact with the dispersant, which is beneficial for the amorphous nickel to be fully mixed with the dispersant during the sedimentation process.

[0137] According to some embodiments of the present invention, in step (C2), 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.

[0138] According to some embodiments of the present invention, the protective agent is liquid paraffin. The protective agent can form a protective layer (upper layer) above the lower liquid after the sedimentation and stratification process, thereby isolating oxidizing substances.

[0139] According to some embodiments of the present invention, preferably, the amount of the protective agent is such that the thickness of the upper liquid is 2-3 cm.

[0140] According to some embodiments of the present invention, in step (C2), the dispersant can serve as a support for the dispersion of the slurry bed catalyst to disperse amorphous nickel and prevent it from floating above the slurry (protective agent). The zirconium oxide has a tetragonal crystal form, which provides 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.

[0141] According to some embodiments of the present invention, preferably, the dispersant is a mixture of zirconium oxide and magnesium oxide, wherein 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 points 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.

[0142] According to a preferred embodiment of the present invention, the mixture of zirconium oxide and magnesium oxide is prepared by a method comprising the following steps:

[0143] Zirconia powder and magnesium oxide powder are sieved separately, selecting particles with a particle size of 100-400 mesh, preferably 120-180 mesh, for blending (the mass ratio of zirconia powder to magnesium oxide powder can be selected as described above). The resulting mixture is then calcined at high temperature, causing the zirconia to transform from a monoclinic to a tetragonal crystal form. The calcined product is then cooled to room temperature in air. The high-temperature calcination conditions may include a temperature of 1200-1300℃ and a time of 4-6 hours. During this process, magnesium oxide protects the zirconia in the mixture, preventing it from degenerating from a tetragonal to a monoclinic crystal form during cooling, thus ensuring that the final mixture contains tetragonal zirconia.

[0144] According to some embodiments of the present invention, preferably, in step (C2), the particle size of the dispersant is 100-400 mesh, more preferably 120-180 mesh.

[0145] According to some embodiments of the present invention, preferably, in step (C2), 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.

[0146] According to some embodiments of the present invention, preferably, in step (C2), 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 include: a temperature of 20-50°C, a time of 20-60 min, and a rotation speed of 200-400 rpm.

[0147] According to some embodiments of the present invention, in step (C3), the pH of the lower layer of the stratified liquid is adjusted to 7-9 using water, and then the water in the lower layer of the stratified liquid is removed, so that the protective agent coats the catalyst particles.

[0148] According to some embodiments of the present invention, preferably, in step (C3), water is used to adjust the pH of the lower layer liquid to 7.5-8.

[0149] According to some embodiments of the present invention, preferably, in step (C3), 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.

[0150] 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.

[0151] More preferably, the method for removing water includes: slowly filtering the stratified 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 reactors.

[0152] According to some embodiments of the present invention, in order to prevent the obtained low-temperature methanation catalyst from being oxidized, it is preferable to store the low-temperature methanation catalyst in a sealed container, for example, by sealing and purging it with nitrogen.

[0153] According to some embodiments of the present invention, preferably, in step (1), the particle size of the low-temperature methanation catalyst is 120-180 mesh.

[0154] According to some embodiments of the present invention, preferably, in step (1), the inert heat-conducting medium in the slurry bed reactor is liquid paraffin and / or solid paraffin; preferably, the boiling point of the liquid paraffin is higher than 300°C; the melting point of the solid paraffin is lower than 260°C and the boiling point is higher than 300°C.

[0155] According to some embodiments of the present invention, preferably, in step (1), the volume ratio of the catalyst I to the inert thermally conductive medium is 1:15-25.

[0156] According to some embodiments of the present invention, preferably, in step (1), the conditions for the methanation reaction include: a temperature of 260-340°C, a pressure of 1-4 MPa, and a volume hourly space velocity of 1500-2000 h⁻¹. -1 The stirring speed is 1000-1500 rpm.

[0157] According to some embodiments of the present invention, preferably, in step (1), the paraffin vapor content in the paraffin-containing outlet process gas is not higher than 2000 ppm, more preferably not higher than 1000 ppm, and more preferably 50-1000 ppm.

[0158] According to some embodiments of the present invention, preferably, the water-to-wax molar ratio in the paraffin-containing outlet process gas is higher than 10.

[0159] According to some embodiments of the present invention, preferably, the paraffin-containing outlet process gas contains 3-5% CO by volume, 7-10% CO2 by volume, 37-55% H2 by volume, 15-26.5% CH4 by volume, and 15-26.5% water vapor by volume.

[0160] According to some embodiments of the present invention, preferably, the pressure of the paraffin-containing outlet process gas is 2.0-4.0 MPa, more preferably 2.5-3.5 MPa; and the temperature is 260-350°C, more preferably 270-320°C.

[0161] According to some embodiments of the present invention, in step (2), the outlet process gas is contacted with catalyst II to undergo an adiabatic methanation reaction. Under the high-temperature methanation catalysis and high-temperature dewaxing catalysis of catalyst II, the upstream slurry-bed syngas methanation process gas containing paraffin wax can directly undergo an adiabatic methanation reaction without cooling or separation. In the above process, methanation and paraffin cracking reactions occur simultaneously, resulting in a high-temperature outlet process gas free of paraffin wax.

[0162] According to some embodiments of the present invention, preferably, in step (2), the volume ratio of the paraffin cracking catalyst to the high-temperature methanation catalyst is 0.5-1:1.

[0163] According to some embodiments of the present invention, in step (2), the high-temperature methanation catalyst can be a conventionally used high-temperature methanation catalyst with methanation catalysis (usually operating at 500-700°C), and there are no particular limitations on this, as they can all achieve the inventive purpose of the present invention to a certain extent. Preferably, the high-temperature methanation catalyst includes a support and an active component and an auxiliary agent supported on the support, wherein the active component is nickel and / or nickel oxide; the support is at least one of alumina, magnesium oxide, magnesium aluminum spinel, zirconium oxide, calcium oxide, and silicon dioxide, preferably magnesium aluminum spinel; and the auxiliary agent is La2O3 and / or CeO2.

[0164] According to a preferred embodiment of the present invention, the high-temperature methanation catalyst is a high-temperature methanation catalyst supported on magnesium aluminum spinel with Ni and La2O3.

[0165] According to some embodiments of the present invention, preferably, in step (2), the content of the active component, calculated as nickel, is 5-20 wt% based on the total amount of the high-temperature methanation catalyst, the content of the auxiliary agent is 0.1-5 wt%, and the content of the support is 75-94.9 wt%.

[0166] According to some embodiments of the present invention, preferably, in step (2), the particle size of the high-temperature methanation catalyst is 20-40 mesh.

[0167] According to some embodiments of the present invention, preferably, in step (2), the conditions for the adiabatic methanation reaction include: a pressure of 2.0-4.0 MPa, preferably 2.5-3.5 MPa; an inlet temperature of 260-350°C, preferably 270-320°C; a hot spot temperature of 500-700°C, preferably 550-650°C; and a volume hourly space velocity of 1000-10000 h⁻¹. -1 Preferably 2000-5000h -1 .

[0168] A second aspect of the present invention provides a system for producing natural gas by syngas methanation, the system comprising a methanation unit and a refining unit connected in series, wherein the methanation unit includes at least one slurry bed reactor, the refining unit includes at least one adiabatic fixed bed reactor, and the outlet of the slurry bed reactor is connected to the inlet of the adiabatic fixed bed reactor.

[0169] According to some embodiments of the present invention, preferably, the outlet of the slurry bed reactor is connected to the inlet of the adiabatic fixed bed reactor via a pipeline.

[0170] Preferably, along the direction of material flow, the pipeline is also provided with valves and one-way check valves in sequence.

[0171] The method and system for producing natural gas by syngas methanation provided by the present invention will be further described in detail below with reference to the accompanying drawings.

[0172] This invention provides, by way of example, a system for producing natural gas from syngas through methanation, such as... Figure 1 As shown. The system includes a methanation unit and a refining unit connected in series. The methanation unit includes a slurry bed reactor 1, and the refining unit includes an adiabatic fixed bed reactor 4. The outlet of the slurry bed reactor 1 is connected to the inlet of the adiabatic fixed bed reactor 4 via a pipeline. Along the direction of material flow, a valve 2 and a one-way check valve 3 are also installed sequentially on the pipeline.

[0173] The present invention will be described in detail below through embodiments.

[0174] Unless otherwise specified, all raw materials used in the following examples and comparative examples are commercially available products. Among them:

[0175] Light magnesium oxide was purchased from Nanjing Pharmaceutical Company. The grade / type was industrial grade, with a purity >99wt% and an average particle size of 0.063mm.

[0176] The boehmite was purchased from Shandong Aluminum Company, with the model / grade LSi-pfd-7, and its Al2O3 content was 70wt%; the average particle size was 0.09mm.

[0177] Nickel nitrate was purchased from Nanjing Chemical Reagent Factory, model / grade AR, purity >99wt%;

[0178] The high-temperature methanation catalyst was purchased from Sinopec Nanjing Chemical Research Institute Co., Ltd., model / grade NCJ-1; its composition is: Ni: 15% by mass, La2O3: 0.5% by mass, and the remainder is magnesium aluminum spinel; the original particle size of the catalyst was cylindrical particles with a particle size of φ5*5mm, which were ground into particles of 20-40 mesh using a planetary mill.

[0179] Unless otherwise specified, all testing equipment used in the following examples and comparative examples are commercially available.

[0180] The XRD pattern of the support was determined by X-ray diffraction. The powder X-ray diffractometer was purchased from Bruker, model D8 advance.

[0181] The grain size was obtained by X-ray diffraction.

[0182] Pore ​​volume and average pore size were obtained by BET adsorption testing.

[0183] The hydrocarbon content was obtained by chromatographic testing, using an Agilent 8890 three-valve five-column FID analyzer.

[0184] The following preparation examples illustrate the paraffin cracking catalyst and its preparation method provided by the present invention.

[0185] Preparation Example A1

[0186] (S1) Light magnesium oxide (400g), pseudoboehmite (1450g), pore expander, binder, and solvent are brought together and sequentially mixed, milled, sieved, dried, shaped, and subjected to a first calcination to obtain a carrier. The XRD test results are as follows: Figure 2 As shown in the figure, there are obvious characteristic peaks of magnesium aluminum spinel at positions 2θ = 37.2°, 45.4°, and 66.25°, indicating that the main body of the support is magnesium aluminum spinel (MgAl2O4). A characteristic peak of magnesium oxide is present at 2θ = 42.9°, which is sharp but has low intensity. No characteristic peak of aluminum oxide is observed at 2θ = 67.2°. Its composition and property parameters are shown in Table 1; where:

[0187] The conditions for the first roasting were: temperature 900℃; time 6 hours.

[0188] The pore-expanding agent is nitric acid, and its ratio with magnesium oxide is 1 mL: 50 g;

[0189] The binder is sodium carboxymethyl cellulose, and its mass ratio with magnesium oxide is 1:21.6;

[0190] The solvent is deionized water, and its volume ratio with the pore-expanding agent is 100:1.

[0191] The sieve used for sieving was a 10-mesh sieve; the drying conditions were: temperature 120℃; time 6 hours.

[0192] The catalyst particles obtained by molding have a size of Φ5*5mm;

[0193] (S2) The above-mentioned carrier (94g) is contacted with the active component precursor for a first impregnation, and then the resulting product is filtered. The resulting solid is then dried and calcined in sequence to obtain an intermediate; wherein:

[0194] The active component precursor is manganese nitrate, which is provided in the form of a 50 wt% aqueous manganese nitrate solution;

[0195] The conditions for the first immersion were: temperature 70℃; time 2 hours.

[0196] The drying conditions were: temperature 120℃; time 6 hours.

[0197] The conditions for the second calcination I are: temperature 420℃; time 4h;

[0198] (S3) The above intermediate is contacted with the auxiliary precursor for a second impregnation, the resulting product is then filtered, and the resulting solid is subsequently dried and then calcined (II); wherein:

[0199] The auxiliary precursor is lanthanum nitrate, which is provided in the form of a 4 wt% aqueous solution of lanthanum nitrate.

[0200] The conditions for the second impregnation were: temperature 70℃; time 2 hours.

[0201] The drying conditions were: temperature 120℃; time 6 hours.

[0202] The conditions for the second calcination (II) are: temperature 420℃; time 4 hours.

[0203] A paraffin cracking catalyst was obtained, wherein the total amount of the paraffin cracking catalyst was 5% by mass, the content of manganese dioxide was 1% by mass, and the remainder was a support.

[0204] The following preparation examples illustrate the bifunctional catalyst and its preparation method provided by the present invention.

[0205] Preparation Example B1

[0206] (S1) Light magnesium oxide (400g), pseudoboehmite (1450g), pore expander, binder, and solvent are brought together and sequentially mixed, milled, sieved, dried, shaped, and subjected to a first calcination to obtain a carrier. The XRD test results are as follows: Figure 2 As shown in the figure, there are obvious characteristic peaks of magnesium aluminum spinel at positions 2θ = 37.2°, 45.4°, and 66.25°, indicating that the main body of the support is magnesium aluminum spinel (MgAl2O4). A characteristic peak of magnesium oxide is present at 2θ = 42.9°, which is sharp but has low intensity. No characteristic peak of aluminum oxide is observed at 2θ = 67.2°. Its composition and property parameters are shown in Table 1; where:

[0207] The conditions for the first roasting were: temperature 900℃; time 6 hours.

[0208] The pore-expanding agent is nitric acid, and its ratio with magnesium oxide is 1 mL: 50 g;

[0209] The binder is sodium carboxymethyl cellulose, and its mass ratio with magnesium oxide is 1:21.6;

[0210] The solvent is deionized water, and its volume ratio with the pore-expanding agent is 100:1.

[0211] The sieve used for sieving was a 10-mesh sieve; the drying conditions were: temperature 120℃; time 6 hours.

[0212] The catalyst particles obtained by molding have a size of Φ5*5mm;

[0213] (S2) The above-mentioned carrier (149g) is contacted with the active component precursor I for a first impregnation, and then the resulting product is filtered. The resulting solid is then subjected to drying and a second calcination I to obtain intermediate I; wherein:

[0214] The active component precursor I is nickel nitrate, which is provided in the form of a 60 wt% aqueous solution of nickel nitrate;

[0215] The conditions for the first immersion were: temperature 70℃; time 2 hours.

[0216] The drying conditions were: temperature 120℃; time 6 hours.

[0217] The conditions for the second calcination I are: temperature 420℃; time 4h;

[0218] (S3) The above intermediate I is contacted with the active component precursor II for a second impregnation, and then the resulting product is filtered. The resulting solid is then subjected to drying and second calcination II to obtain intermediate II; wherein:

[0219] The active component precursor II is manganese nitrate, which is provided in the form of a 50 wt% aqueous solution of manganese nitrate.

[0220] The conditions for the second impregnation were: temperature 70℃; time 2 hours.

[0221] The drying conditions were: temperature 120℃; time 6 hours.

[0222] The conditions for the second calcination (II) are: temperature 420℃; time 4 hours.

[0223] (S4) The above intermediate II is contacted with the auxiliary precursor for a third impregnation, the resulting product is then filtered, and the resulting solid is subsequently dried and calcined in the second calcination stage III; wherein:

[0224] The auxiliary precursor is lanthanum nitrate, which is provided in the form of a 4 wt% aqueous solution of lanthanum nitrate.

[0225] The conditions for the third impregnation are: temperature 70℃; time 2 hours;

[0226] The drying conditions were: temperature 120℃; time 6 hours.

[0227] The conditions for the second calcination III are: temperature 420℃; time 4h;

[0228] (S5) The product obtained in step (S4) is reduced by contacting hydrogen gas; wherein:

[0229] The reduction conditions were: temperature 450℃; time 4 hours.

[0230] A bifunctional catalyst was obtained, wherein the total amount of the bifunctional catalyst was 15% by mass of nickel, 10% by mass of manganese dioxide, 0.5% by mass of lanthanum oxide, and the remainder was a support.

[0231] Table 1

[0232]

[0233] Note: Mg:Al refers to the molar ratio of Mg and Al in the carrier (calculated from the amount of feed).

[0234] The average pore size and pore volume are the same as those of MgAl2O4.

[0235] The following preparation examples illustrate the low-temperature methanation catalyst and its preparation method provided by the present invention.

[0236] Preparation Example C1

[0237] (S1) In the presence of water, the nickel precursor is brought into contact with a reducing agent to undergo a reduction reaction, yielding the reduction product; wherein:

[0238] 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.

[0239] 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.

[0240] The molar ratio of reducing agent to nickel precursor (based on elemental nickel) is 1.5:1;

[0241] 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.

[0242] 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.

[0243] The XRD pattern of the reduction product is as follows: Figure 3 As shown in the figure, the nickel contained in the reduction product is amorphous nickel.

[0244] (S2) 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, forming a layered liquid; wherein:

[0245] 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;

[0246] 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 4 As shown in the figure, the zirconium oxide contained in this dispersant has a tetragonal crystal form.

[0247] The mass ratio of nickel precursor to dispersant, calculated based on nickel element, is 3:1;

[0248] The mixing conditions were: temperature 20℃, time 20min, and rotation speed 200rpm.

[0249] (S3) Adjust the pH of the lower layer of the phased 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:

[0250] 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.

[0251] 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.

[0252] In this methanation catalyst, the content of the protective agent is 3 mL relative to 1 g of catalyst particles.

[0253] 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.

[0254] The following examples illustrate the method for producing natural gas from syngas by methanation provided by the present invention, wherein, as follows... Figure 1 The system shown is a syngas methanation system for producing natural gas. The system includes a methanation unit and a refining unit connected in series. The methanation unit includes a slurry bed reactor 1, and the refining unit includes an adiabatic fixed bed reactor 4. The outlet of the slurry bed reactor 1 is connected to the inlet of the adiabatic fixed bed reactor 4 via a pipeline. Along the direction of material flow, a valve 2 and a one-way check valve 3 are also installed in sequence on the pipeline.

[0255] Example 1

[0256] (1) In a slurry bed reactor, the syngas is contacted with catalyst I to undergo a methanation reaction, yielding an outlet process gas containing paraffin; wherein:

[0257] Catalyst I is a low-temperature methanation catalyst;

[0258] The inert heat-conducting medium in the slurry bed reactor is liquid paraffin, which has a boiling point of 300℃;

[0259] The volume ratio of catalyst I to inert thermally conductive medium is 1:20;

[0260] The conditions for the methanation reaction were: temperature 320℃, pressure 3MPa, and volume hourly space velocity (VHSV) 1600h⁻¹. -1 The stirring speed is 1200 rpm;

[0261] The outlet process gas has a pressure of 3.5 MPa, a temperature of 270°C, and a volume hourly space velocity (VHSV) of 5000 h⁻¹ relative to the volume of catalyst II. -1 ;

[0262] The composition of the process gas at the outlet is as follows: CO content 5% by volume, CO2 content 10% by volume, H2 content 55% by volume, CH4 content 15% by volume, water vapor is water spontaneously generated from the slurry bed methanation reaction and carried out by the gas flow, with a content of 15% by volume at equilibrium, and paraffin vapor content of 50 ppm.

[0263] (2) In an adiabatic fixed-bed reactor, the above-mentioned outlet process gas is contacted with catalyst II to carry out an adiabatic methanation reaction; wherein:

[0264] In an adiabatic fixed-bed reactor, 15 mL of a mixture of paraffin cracking catalyst and high-temperature methanation catalyst in a volume ratio of 0.5:1 was packed.

[0265] The paraffin cracking catalyst is the paraffin cracking catalyst prepared in Preparation Example A1;

[0266] The conditions for the adiabatic methanation reaction are: pressure 3 MPa; inlet temperature 270℃; hot spot temperature 700℃; volume hourly space velocity 5000 h⁻¹. -1 ;

[0267] The volumetric composition of the obtained outlet process gas is as follows: CO: 0.6%, CO2: 4.2%, H2: 18.6%, CH4: 39.0%, water vapor: 37.6%, C2 hydrocarbons 520ppm, C3 hydrocarbons 80ppm, C4 hydrocarbons 5ppm, and no hydrocarbons above C5.

[0268] In this embodiment, the outlet process gas of the slurry bed reactor is 75 NL / h, of which the amount of paraffin vapor is 3.75 Ncm. 3 / h, the process gas at the outlet of the adiabatic reactor is free of paraffin. The catalyst is disassembled after 500h of use, dried at 100℃ for 4h and tested. The results are shown in Table 2.

[0269] Example 2

[0270] The method is the same as in Example 1, except that:

[0271] In step (1), the conditions for the methanation reaction are as follows: temperature 300℃, pressure 2.5MPa, and volume hourly space velocity 2000h. -1 The stirring speed was 1200 rpm, and all other parameters remained the same, resulting in a slurry bed outlet process gas with a pressure of 2.7 MPa, a temperature of 320 °C, and a volumetric hourly space velocity of 5000 h⁻¹. -1 ;

[0272] Its volume composition is as follows: CO content 4 vol%, CO2 content 9 vol%, H2 content 48 vol%, CH4 content 19.5 vol%, water vapor comes from water spontaneously generated in the slurry bed methanation reaction, carried out by the gas flow, and its content at equilibrium is 19.4 vol%; paraffin vapor content is 1000 ppm.

[0273] In step (2), the conditions for the adiabatic methanation reaction are as follows: pressure 3.2 MPa; inlet temperature 260℃; hot spot temperature 650℃; volume hourly space velocity 5000 h⁻¹. -1 The rest are the same;

[0274] The volumetric composition of the obtained outlet process gas is as follows: CO: 0.5%, CO2: 4.0%, H2: 18.0%, CH4: 39.7%, water vapor: 37.8%, C2 hydrocarbons 540ppm, C3 hydrocarbons 90ppm, C4 hydrocarbons 10ppm, and no hydrocarbons above C5.

[0275] In this embodiment, the process gas outlet of the slurry bed reactor is 75 NL / h, of which the amount of paraffin vapor is 75 Ncm. 3 / h, the process gas at the outlet of the adiabatic reactor is free of paraffin. The catalyst is disassembled after 500h of use, dried at 100℃ for 4h and tested. The results are shown in Table 2.

[0276] Example 3

[0277] The method is the same as in Example 1, except that:

[0278] In step (1), the conditions for the methanation reaction are as follows: temperature 260℃, pressure 2.75MPa, and volume hourly space velocity 1800h⁻¹. -1 The stirring speed was 1100 rpm, and all other parameters remained the same, resulting in a slurry bed outlet process gas with a pressure of 3.0 MPa, a temperature of 300 °C, and a volumetric hourly space velocity of 2000 h⁻¹. -1 ;

[0279] Its volume composition is as follows: CO content 3 vol%, CO2 content 7 vol%, H2 content 37 vol%, CH4 content 26.5 vol%, water vapor comes from the spontaneous generation of water in the slurry bed methanation reaction, which is carried out by the gas flow and has a content of 26.5 vol% at equilibrium, and paraffin vapor content is 500 ppm.

[0280] In step (2), the conditions for the adiabatic methanation reaction are as follows: pressure 2.8 MPa; inlet temperature 280 °C; hot spot temperature 500 °C; volume hourly space velocity 2000 h⁻¹. -1 The rest are the same;

[0281] The volume composition of the obtained outlet process gas is as follows: CO: 0.3%, CO2: 3.0%, H2: 12.9%, CH4: 42%, water vapor: 41.8%, C2 hydrocarbons: 400ppm, C3 hydrocarbons: 20ppm, C4 hydrocarbons: 1ppm, and no hydrocarbons above C5.

[0282] In this embodiment, the process gas outlet of the slurry bed reactor is 30 NL / h, of which the paraffin vapor content is 15 Ncm³. 3 / h, the process gas at the outlet of the adiabatic reactor is free of paraffin. The catalyst is disassembled after 500h of use, dried at 100℃ for 4h and tested. The results are shown in Table 2.

[0283] Example 4

[0284] The method is the same as in Example 1, except that in step (2), the catalyst packed in the adiabatic fixed-bed reactor is the bifunctional catalyst prepared in Preparation Example B1; the rest are the same.

[0285] The volumetric composition of the obtained outlet process gas is as follows: CO: 0.7%, CO2: 4.4%, H2: 19.7%, CH4: 38.0%, water vapor: 37.2%, C2 hydrocarbons: 560ppm, C3 hydrocarbons: 90ppm, C4 hydrocarbons: 4ppm, and no hydrocarbons above C5.

[0286] In this embodiment, the process gas outlet of the slurry bed reactor is 75 NL / h, of which the paraffin vapor content is 3.75 Ncm³. 3 / h, the process gas at the outlet of the adiabatic reactor is free of paraffin. The catalyst is disassembled after 500h of use, dried at 100℃ for 4h and tested. The results are shown in Table 2.

[0287] Example 5

[0288] The method is the same as in Example 4, except that:

[0289] In step (1), the conditions for the methanation reaction are as follows: temperature 300℃, pressure 3.2MPa, and volume hourly space velocity 1600h. -1 The stirring speed was 1000 rpm, and all other parameters remained the same, resulting in a slurry bed outlet process gas with a pressure of 2.7 MPa, a temperature of 320 °C, and a volumetric hourly space velocity of 5000 h⁻¹. -1 ;

[0290] Its volume composition is as follows: CO content 4 vol%, CO2 content 9 vol%, H2 content 48 vol%, CH4 content 19.5 vol%, water vapor comes from water spontaneously generated in the slurry bed methanation reaction, carried out by the gas flow, and its content at equilibrium is 19.4 vol%; paraffin vapor content is 1000 ppm.

[0291] In step (2), the conditions for the adiabatic methanation reaction are as follows: pressure 3.0 MPa; inlet temperature 290℃; hot spot temperature 650℃; volume hourly space velocity 5000 h⁻¹. -1 The rest are the same;

[0292] The volumetric composition of the obtained outlet process gas is as follows: CO: 0.6%, CO2: 4.1%, H2: 18.2%, CH4: 39.5%, water vapor: approximately 37.6%, C2 hydrocarbons: 530 ppm, C3 hydrocarbons: 85 ppm, C4 hydrocarbons: 15 ppm, and no hydrocarbons above C5.

[0293] In this embodiment, the process gas outlet of the slurry bed reactor is 75 NL / h, of which the paraffin vapor content is 75 Ncm. 3 / h, the process gas at the outlet of the adiabatic reactor is free of paraffin. The catalyst is disassembled after 500h of use, dried at 100℃ for 4h and tested. The results are shown in Table 2.

[0294] Comparative Example 1

[0295] The method of Example 2 is the same except that in step (2), only 15 mL of high-temperature methanation catalyst is loaded into the adiabatic fixed-bed reactor;

[0296] The initial output process gas volume composition was as follows: CO: 0.5%, CO2: 4.0%, H2: 18.0%, CH4: 39.7%, water vapor: 37.8%, C2 hydrocarbons: 1200ppm, C3 hydrocarbons: 700ppm, C4 hydrocarbons: 90ppm, with C5 and above hydrocarbons generated. Paraffinic substances were not detected initially.

[0297] In this comparative example, the slurry bed reactor outlet process gas is 75 NL / h, of which the paraffin vapor content is 75 Ncm³. 3 / h, paraffinic substances were detected in the process gas at the outlet of the adiabatic reactor at 350 hours. The catalyst was disassembled after 500 hours of use, dried at 100℃ for 4 hours, and then tested. The results are shown in Table 2.

[0298] Table 2

[0299]

[0300] Note: Fresh sample* refers to a fresh sample of the high-temperature methanation catalyst.

[0301] The results above show that the method provided by this invention for the methanation of syngas to produce natural gas effectively prevents paraffin vapor from covering the pore structure and active sites of the catalyst. Furthermore, the paraffin decomposes thoroughly during the process, and no paraffin blockage of the catalyst pores was observed. In contrast, in the adiabatic methanation reaction, without the use of a paraffin cracking catalyst, the pores of the high-temperature methanation catalyst in Comparative Example 1 were blocked and covered, resulting in a significant reduction in both pore size and surface area. After calcining the paraffin at 450°C, the pore structure essentially returned to its normal size, indicating that the paraffin covering caused catalyst deactivation.

[0302] 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 producing natural gas by methanation of syngas, characterized in that, The method includes: (1) In a slurry bed reactor, the syngas is contacted with catalyst I to carry out a methanation reaction to obtain an outlet process gas containing paraffin; Catalyst I is a low-temperature methanation catalyst, comprising catalyst particles and a protective agent encapsulating the catalyst particles. The catalyst particles contain amorphous nickel and a dispersant; the dispersant is a mixture of zirconium oxide and magnesium oxide; based on the total weight of the catalyst particles, the content of amorphous nickel in the catalyst particles is 65-75% by weight, and the content of the dispersant is 25-35% by weight. (2) In an adiabatic fixed-bed reactor, the outlet process gas is contacted with catalyst II to carry out an adiabatic methanation reaction; The catalyst II comprises a paraffin cracking catalyst and a high-temperature methanation catalyst; the paraffin cracking catalyst comprises a support and an active component and an auxiliary agent supported on the support, wherein the active component is manganese dioxide, the auxiliary agent is La2O3, the support is a magnesium-aluminum composite oxide, and the magnesium-aluminum composite oxide includes MgAl2O4; based on the total amount of the paraffin cracking catalyst, the content of the active component is 5-15 wt%, the content of the auxiliary agent is 0.1-2 wt%, and the content of the support is 83-94.9 wt%; the high-temperature methanation catalyst comprises a support and an active component and an auxiliary agent supported on the support, wherein the active component is nickel and / or nickel oxide; the support is at least one selected from alumina, magnesium oxide, magnesium-aluminum spinel, zirconium oxide, calcium oxide, and silicon dioxide; or... The catalyst II is a bifunctional catalyst, comprising a support and active components I, II, and an additive supported on the support. Active component I is nickel and / or nickel oxide, active component II is manganese dioxide, the additive is La₂O₃, and the support is a magnesium-aluminum composite oxide comprising MgAl₂O₄. Based on the total amount of the bifunctional catalyst, the content of active component I (calculated as nickel) is 10-20 wt%, the content of active component II is 5-15 wt%, the content of the additive is 0.1-2 wt%, and the content of the support is 74-85 wt%. The magnesium-aluminum composite oxide further includes MgO and Al2O3, wherein, based on the total amount of the magnesium-aluminum composite oxide, the content of MgAl2O4 is 93-100wt%, the content of MgO is 0-5wt%, and the content of Al2O3 is 0-2wt%; the grain size of MgAl2O4 is <20nm, the pore volume is >0.15mL / g, and the average pore size is 10-50nm.

2. The method according to claim 1, wherein, Based on the total amount of the magnesium-aluminum composite oxide, the content of MgO is 0-3 wt%, and the content of Al2O3 is 0-1 wt%.

3. The method according to claim 1, wherein, Based on the total amount of the magnesium-aluminum composite oxide, the content of MgAl2O4 is 96-100wt%.

4. The method according to claim 1, wherein, The MgAl2O4 has a grain size of 4-15 nm, a pore volume of 0.25-0.35 mL / g, and an average pore size of 10-30 nm.

5. The method according to claim 4, wherein, The MgAl2O4 has a grain size of 5-10 nm, a pore volume of 0.27-0.33 mL / g, and an average pore size of 13-20 nm.

6. The method according to claim 1, wherein, In the magnesium-aluminum composite oxide, the molar ratio of Mg to Al is 1:2-2.

04.

7. The method according to any one of claims 1-6, wherein, The paraffin cracking catalyst is prepared by a method comprising the following steps: (A1) A mixture containing magnesium oxide, boehmite and a pore-expanding agent is subjected to a first calcination to obtain a support; wherein the temperature of the first calcination is 800-1000℃; (A2) The active component precursor and the auxiliary agent precursor are loaded onto the support described in step (A1), and the resulting product is then subjected to a second calcination; wherein the temperature of the second calcination is lower than the temperature of the first calcination.

8. The method according to claim 7, wherein, In step (A1), the temperature of the first roasting is 850-950℃; the roasting time is 2-10h.

9. The method according to claim 8, wherein, The first roasting time is 4-8 hours.

10. The method according to claim 7, wherein, In step (A1), the magnesium oxide is light magnesium oxide with an average particle size of 0.06-0.09 mm; the pseudoboehmite has an average particle size of 0.06-0.09 mm; and the pore-expanding agent is selected from at least one of oxalic acid, nitric acid, acetic acid, and sulfuric acid.

11. The method according to claim 7, wherein, In step (A1), the ratio of the pore-expanding agent to the magnesium oxide is 1 mL: 40-60 g.

12. The method according to claim 7, wherein, In step (A1), the mixture further contains a binder; the binder is selected from at least one of cellulose and its derivatives, guar gum and stearate.

13. The method according to claim 12, wherein, In step (A1), the mass ratio of the adhesive to the magnesium oxide is 1:20-25.

14. The method according to claim 7, wherein, In step (A2), the active component precursor is selected from at least one of manganese nitrate, manganese sulfate, and manganese chloride; the auxiliary agent precursor is selected from at least one of lanthanum nitrate, lanthanum chloride, and lanthanum sulfate.

15. The method according to claim 7, wherein, In step (A2), the loading method is impregnation; the impregnation conditions include: temperature of 60-80℃; time of 0.5-2h.

16. The method according to claim 7, wherein, In step (A2), the active component precursor is first loaded onto the carrier described in step (A1) to obtain an intermediate, and then the adjuvant precursor is loaded onto the intermediate.

17. The method according to claim 7, wherein, In step (A2), the conditions for the second calcination include: a temperature of 350-500℃ and a time of 4-10h.

18. The method according to claim 17, wherein, The conditions for the second roasting include: a temperature of 400-450℃ and a time of 4-8 hours.

19. The method according to any one of claims 1-6, wherein, The bifunctional catalyst is prepared by a method comprising the following steps: (B1) A mixture containing magnesium oxide, boehmite and a pore-expanding agent is subjected to a first calcination to obtain a support; wherein the temperature of the first calcination is 800-1000℃; (B2) The active component precursor I, the active component precursor II and the auxiliary agent precursor are loaded onto the support described in step (B1), and the resulting product is then subjected to a second calcination; wherein the temperature of the second calcination is lower than the temperature of the first calcination.

20. The method according to claim 19, wherein, In step (B1), the temperature of the first roasting is 850-950℃; the roasting time is 2-10h.

21. The method according to claim 20, wherein, The first roasting time is 4-8 hours.

22. The method according to claim 19, wherein, In step (B1), the magnesium oxide is light magnesium oxide with an average particle size of 0.06-0.09 mm; the pseudoboehmite has an average particle size of 0.06-0.09 mm; and the pore-expanding agent is selected from at least one of oxalic acid, nitric acid, acetic acid, and sulfuric acid.

23. The method according to claim 19, wherein, In step (B1), the ratio of the pore-expanding agent to the magnesium oxide is 1 mL: 40-60 g.

24. The method according to claim 19, wherein, In step (B1), the mixture further contains a binder; the binder is selected from at least one of cellulose and its derivatives, guar gum, and stearate.

25. The method according to claim 24, wherein, In step (B1), the mass ratio of the adhesive to the magnesium oxide is 1:20-25.

26. The method according to claim 19, wherein, In step (B2), the active component precursor I is selected from at least one of nickel nitrate, nickel chloride, and nickel sulfate; The active component precursor II is selected from at least one of manganese nitrate, manganese sulfate and manganese chloride; The auxiliary agent precursor is selected from at least one of lanthanum nitrate, lanthanum chloride, and lanthanum sulfate.

27. The method according to claim 19, wherein, In step (B2), the loading method is impregnation; the impregnation conditions include: temperature of 60-80℃; time of 0.5-2h.

28. The method according to claim 19, wherein, In step (B2), the active component precursor I is first loaded onto the carrier in step (B1) to obtain intermediate I, then the active component precursor II is loaded onto intermediate I to obtain intermediate II, and finally the adjuvant precursor is loaded onto intermediate II.

29. The method according to claim 19, wherein, In step (B2), the conditions for the second calcination include: a temperature of 350-500℃ and a time of 4-10h.

30. The method according to claim 29, wherein, The conditions for the second roasting include: a temperature of 400-450℃ and a time of 4-8 hours.

31. The method according to claim 19, wherein, In step (B2), the method further includes: contacting the product obtained from the second calcination in step (B2) with a reducing gas for reduction.

32. The method according to any one of claims 1-6, wherein, In step (1), the mass ratio of zirconium oxide to magnesium oxide in the mixture is (1-10):1; the zirconium oxide has a tetragonal crystal form.

33. The method according to claim 32, wherein, In the mixture, the mass ratio of zirconium oxide to magnesium oxide is (3-6):

1.

34. The method according to any one of claims 1-6, wherein, In step (1), the XRD pattern of the low-temperature methanation catalyst shows a diffraction peak with a width greater than 5° at 2θ = 45±0.2°.

35. The method according to any one of claims 1-6, wherein, In step (1), the content of the protective agent in the low-temperature methanation catalyst is 2-4 mL relative to 1 g of the catalyst particles.

36. The method according to claim 32, wherein, The mixture of zirconium oxide and magnesium oxide is prepared by a method comprising the following steps: The mixture obtained by blending zirconium oxide powder and magnesium oxide powder is subjected to high-temperature calcination. The conditions for high-temperature calcination include a temperature of 1200-1300℃ and a time of 4-6 hours.

37. The method of claim 36, wherein, The zirconium oxide powder and magnesium oxide powder have a particle size of 100-400 mesh.

38. The method according to any one of claims 1-6, wherein, In step (1), the particle size of the dispersant is 100-400 mesh.

39. The method according to any one of claims 1-6, wherein, In step (1), the protective agent is liquid paraffin.

40. The method according to any one of claims 1-6, wherein, In step (1), the particle size of the low-temperature methanation catalyst is 120-180 mesh.

41. The method according to claim 32, wherein, The low-temperature methanation catalyst is prepared by a method comprising the following steps: (C1) In the presence of water, the nickel precursor is brought into contact with a reducing agent to undergo a reduction reaction, yielding the reduction product; (C2) 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 layered liquid comprises an upper liquid and a lower liquid, the upper liquid contains the protective agent, the lower liquid contains water and catalyst particles, and the catalyst particles contain amorphous nickel and a dispersant; (C3) 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.

42. The method according to claim 41, wherein, In step (C1), the nickel precursor is selected from at least one of nickel nitrate, nickel chloride, and nickel acetate.

43. The method according to claim 41, wherein, In step (C1), the reducing agent is a borohydride.

44. The method according to claim 43, wherein, The reducing agent is sodium borohydride and / or potassium borohydride.

45. The method according to claim 41, wherein, In step (C1), the molar ratio of the reducing agent to the nickel precursor, calculated as nickel, is (1-2.5):

1.

46. ​​The method according to claim 41, wherein, In step (C1), the conditions for the reduction reaction include: a temperature of 15-25°C and a time of 1-3 hours.

47. The method according to claim 41, wherein, In step (C2), the mass ratio of the nickel precursor to the dispersant, calculated as nickel element, is (1-10):

1.

48. The method according to claim 41, wherein, In step (C2), the amount of the protective agent used is such that the thickness of the upper liquid layer is 2-3 cm.

49. The method according to claim 41, wherein, In step (C2), the mixing conditions include: a temperature of 20-50°C, a time of 20-60 min, and a rotation speed of 200-400 rpm.

50. The method according to claim 41, wherein, In step (C3), the pH of the lower layer liquid is adjusted to 7.5-8 using water.

51. The method according to any one of claims 1-6, wherein, In step (1), the inert heat-conducting medium in the slurry bed reactor is liquid paraffin and / or solid paraffin.

52. The method according to claim 51, wherein, In step (1), the liquid paraffin has a boiling point higher than 300°C; the solid paraffin has a melting point lower than 260°C and a boiling point higher than 300°C.

53. The method according to claim 51, wherein, In step (1), the volume ratio of the catalyst I to the inert thermally conductive medium is 1:15-25.

54. The method according to any one of claims 1-6, wherein, In step (1), the conditions for the methanation reaction include: a temperature of 260-340℃, a pressure of 1-4 MPa, and a volume hourly space velocity of 1500-2000 h⁻¹. -1 The stirring speed is 1000-1500 rpm.

55. The method according to any one of claims 1-6, wherein, In step (1), the paraffin vapor content in the paraffin-containing outlet process gas is not higher than 2000 ppm.

56. The method according to claim 55, wherein, The paraffin vapor content in the exported process gas containing paraffin is not higher than 1000 ppm.

57. The method according to claim 56, wherein, The paraffin vapor content in the exported process gas containing paraffin is 50-1000 ppm.

58. The method according to any one of claims 1-6, wherein, In step (1), the molar ratio of water vapor to paraffin vapor in the paraffin-containing outlet process gas is higher than 10.

59. The method according to any one of claims 1-6, wherein, In step (1), the paraffin-containing outlet process gas contains 3-5% CO by volume, 7-10% CO2 by volume, 37-55% H2 by volume, 15-26.5% CH4 by volume, and 15-26.5% water vapor by volume.

60. The method according to any one of claims 1-6, wherein, In step (1), the pressure of the paraffin-containing outlet process gas is 2.0-4.0 MPa and the temperature is 260-350℃.

61. The method according to claim 60, wherein, The pressure of the paraffin-containing outlet process gas is 2.5-3.5 MPa, and the temperature is 270-320℃.

62. The method according to any one of claims 1-6, wherein, In step (2), the volume ratio of the paraffin cracking catalyst to the high-temperature methanation catalyst is 0.5-1:

1.

63. The method according to any one of claims 1-6, wherein, In step (2), the support in the high-temperature methanation catalyst is magnesium aluminum spinel; the auxiliary agent is La2O3 and / or CeO2.

64. The method according to any one of claims 1-6, wherein, In step (2), based on the total amount of the high-temperature methanation catalyst, the content of the active component, calculated as nickel, is 5-20 wt%, the content of the auxiliary agent is 0.1-5 wt%, and the content of the support is 75-94.9 wt%.

65. The method according to any one of claims 1-6, wherein, In step (2), the particle size of the high-temperature methanation catalyst is 20-40 mesh.

66. The method according to any one of claims 1-6, wherein, In step (2), the conditions for the adiabatic methanation reaction include: a pressure of 2.0-4.0 MPa, an inlet temperature of 260-350°C, a hot spot temperature of 500-700°C, and a volume hourly space velocity of 1000-10000 h⁻¹. -1 .

67. The method according to claim 66, wherein, The conditions for the adiabatic methanation reaction include: a pressure of 2.5-3.5 MPa, an inlet temperature of 270-320°C, a hot spot temperature of 550-650°C, and a volume hourly space velocity of 2000-5000 h⁻¹. -1 .

68. A system for producing natural gas by methanation of syngas, the system being used to implement the method according to any one of claims 1-67, characterized in that, The system includes a methanation unit and a refining unit connected in series. The methanation unit includes at least one slurry bed reactor, and the refining unit includes at least one adiabatic fixed bed reactor. The outlet of the slurry bed reactor is connected to the inlet of the adiabatic fixed bed reactor. The slurry bed reactor is packed with catalyst I, which is a low-temperature methanation catalyst. The low-temperature methanation catalyst comprises catalyst particles and a protective agent encapsulating the catalyst particles. The catalyst particles contain amorphous nickel and a dispersant; the dispersant is a mixture of zirconium oxide and magnesium oxide. Based on the total weight of the catalyst particles, the amorphous nickel content in the catalyst particles is 65-75% by weight, and the dispersant content is 25-35% by weight. The adiabatic fixed-bed reactor is packed with catalyst II, which includes a paraffin cracking catalyst and a high-temperature methanation catalyst. The paraffin cracking catalyst includes a support and an active component and an auxiliary agent supported on the support, wherein the active component is manganese dioxide, the auxiliary agent is La2O3, and the support is a magnesium-aluminum composite oxide, which includes MgAl2O4. Based on the total amount of the paraffin cracking catalyst, the content of the active component is 5-15 wt%, the content of the auxiliary agent is 0.1-2 wt%, and the content of the support is 83-94.9 wt%. The high-temperature methanation catalyst includes a support and an active component and an auxiliary agent supported on the support, wherein the active component is nickel and / or nickel oxide; the support is at least one of alumina, magnesium oxide, magnesium-aluminum spinel, zirconium oxide, calcium oxide, and silicon dioxide; or... The catalyst II is a bifunctional catalyst, comprising a support and active components I, II, and an additive supported on the support. Active component I is nickel and / or nickel oxide, active component II is manganese dioxide, the additive is La₂O₃, and the support is a magnesium-aluminum composite oxide comprising MgAl₂O₄. Based on the total amount of the bifunctional catalyst, the content of active component I (calculated as nickel) is 10-20 wt%, the content of active component II is 5-15 wt%, the content of the additive is 0.1-2 wt%, and the content of the support is 74-85 wt%. The magnesium-aluminum composite oxide further includes MgO and Al2O3, wherein, based on the total amount of the magnesium-aluminum composite oxide, the content of MgAl2O4 is 93-100wt%, the content of MgO is 0-5wt%, and the content of Al2O3 is 0-2wt%; the grain size of MgAl2O4 is <20nm, the pore volume is >0.15mL / g, and the average pore size is 10-50nm.

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