Process and system for the production of natural gas by methanation of synthesis gas

Abstract

The present application relates to the field of coal gasification comprehensive application, disclose a method and system for synthesizing natural gas by methanation of synthesis gas. The method comprises: in the presence of catalyst I, the synthesis gas is subjected to methanation reaction to obtain a primary reaction gas, then the primary reaction gas is subjected to primary condensation and gas-liquid separation to obtain a primary gas phase and a primary liquid phase; in the presence of catalyst II, the primary gas phase is subjected to first adiabatic methanation reaction to obtain a secondary reaction gas, then the secondary reaction gas is subjected to secondary condensation and gas-liquid separation to obtain a secondary gas phase and a secondary liquid phase; in the presence of catalyst III, the secondary gas phase is subjected to second adiabatic methanation reaction to obtain a tertiary reaction gas, then the tertiary reaction gas is subjected to tertiary condensation and gas-liquid separation to obtain a methane product gas and a liquid phase material. The combination of the series slurry bed-adiabatic-adiabatic reactor is beneficial to increase the yield of the methane product gas and improve the quality of the methane product gas in combination with the specific catalyst I.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of comprehensive utilization of coal gasification, and in particular to a method and system for synthesizing natural gas by methanation of synthesis gas. BACKGROUND

[0002] Synthesis gas, which is composed of CH4, H2, CO and CO2, is an ideal raw gas for producing SNG / LNG. The synthesis gas can be used to produce natural gas, which can bring good economic and social benefits. In view of the composition of synthesis gas, developing suitable synthesis gas methanation technology is an effective way to realize the utilization of synthesis gas, which is of great significance.

[0003] CN110903870A discloses a process for preparing methane from coal-based synthesis gas in a slurry bed. In this process, the coal-based synthesis gas is exchanged with the gas at the outlet of the methane synthesis reactor, and after being heated, it enters the first methane synthesis reactor. The reacted gas is cooled and separated after heat exchange, and then heated and enters the second methane synthesis reactor for reaction. The gas at the outlet of the reactor has a high temperature, and cooling pipes are arranged in both the first and second methane synthesis reactors. The heat is recovered by a steam generator, and the reaction gas is finally cooled, separated from the condensate, and then sent out of the boundary zone. The two reactors described in the patent are both slurry bed reactors, and the by-produced organic compounds with more than two carbons cannot be effectively separated from the product methane.

[0004] CN109837125A discloses a preparation method and device for substitute natural gas. The method comprises the following steps: 1) part of the raw gas enters the first fixed bed reactor to perform the first methanation reaction, and generates the first reaction gas. The first reaction gas is exchanged with the first heat to generate the first low-temperature gas; 2) the first low-temperature gas and the remaining raw gas enter the second fixed bed reactor to perform the second methanation reaction, and generate the second reaction gas. The second reaction gas is exchanged with the second heat to generate the second low-temperature gas; 3) part of the second low-temperature gas enters the first slurry bed reactor to perform the third methanation reaction, and generates the third reaction gas. The remaining second low-temperature gas enters the second slurry bed reactor to perform the fourth methanation reaction, and generates the fourth reaction gas; 4) the third reaction gas and the fourth reaction gas are combined to generate the mixed reaction gas. The mixed reaction gas is subjected to gas-liquid separation operation to obtain the substitute natural gas. This method has many reactors and a complex process. The parallel process of some reactors has a high requirement for the control of the material flow.

[0005] At present, low-temperature methanation process gradually becomes a new direction of methane production. Low-temperature methanation is widely used in the production of methane due to high chemical equilibrium, large treatment capacity, less equipment and no need of circulation. Slurry bed is a relatively advanced reaction equipment in low-temperature process, the temperature in the reaction zone of which is highly homogenized, and it is extremely difficult to have temperature runaway or local temperature too high, heat removal is fast, and methanation efficiency is high, so the slurry bed process performs excellently in the production of methanation. However, the low-temperature methanation process is limited by catalyst and methanation side reactions, and a large amount of C2+ hydrocarbons are by-produced in the methanation process, and the main side reactions are as follows:

[0006] 2CO + 5H2→ C2H6 + 2H2O

[0007] 2CO + 4H2→ C2H4 + 2H2O

[0008] 3CO + 7H2→ C3H8 + 3H2O

[0009] 4CO + 9H2→ C4H 10 + 4H2O

[0010] The by-produced C2+ hydrocarbons consume the total amount of CO + CO2, and reduce the total purity of product methane, which has a non-negligible impact on the economy of methane production. SUMMARY

[0011] The purpose of the present application is to overcome the problems of the prior art that a large amount of C2 and C2+ hydrocarbons are by-produced in the methanation process, the yield of methane product gas is low, and the quality is poor.

[0012] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a method for synthesizing natural gas by methanation of synthesis gas, which comprises:

[0013] (a) methanation reaction of synthesis gas in the presence of catalyst I to obtain primary reaction gas, then primary condensation of the primary reaction gas, and after gas-liquid separation, primary gas phase and primary liquid phase are obtained; wherein the methanation reaction is carried out in a slurry bed reactor; the catalyst I comprises catalyst particles and a protective agent wrapping the catalyst particles, the catalyst particles contain amorphous nickel and a dispersing agent; the dispersing agent is selected from at least one of alumina, zirconia, magnesia and borax, wherein the crystal form of the zirconia is tetragonal;

[0014] (b) first adiabatic methanation reaction of the primary gas phase in the presence of catalyst II to obtain secondary reaction gas, then secondary condensation of the secondary reaction gas, and after gas-liquid separation, secondary gas phase and secondary liquid phase are obtained;

[0015] (c) performing a second adiabatic methanation reaction on the secondary gas phase in the presence of a catalyst III to obtain a tertiary reaction gas, and then performing a tertiary condensation on the tertiary reaction gas, and after gas-liquid separation, obtaining a methane product gas and a liquid phase material;

[0016] wherein the catalyst II and the catalyst III are the same or different, and each is independently a methanation catalyst.

[0017] The second aspect of the present application provides a system for synthesizing natural gas by methanation of synthesis gas, comprising at least one methanation unit, wherein the methanation unit comprises, in sequence, a first preheater, a slurry bed reactor, a first heat exchanger, a first gas-liquid separator, a second preheater, a first adiabatic reactor, a second heat exchanger, a second gas-liquid separator, a third preheater, a second adiabatic reactor, a third heat exchanger, and a third gas-liquid separator.

[0018] By the above technical solution, the method and system for synthesizing natural gas by methanation of synthesis gas provided by the present application adopt a combination of slurry bed-adiabatic-adiabatic reactors in series. By means of a low-temperature slurry bed reactor and a specific catalyst I, synthesis gas with a higher CO+CO2 content is reacted to obtain a primary gas phase with a lower CO+CO2 content. The CO+CO2 content in the primary gas phase is further reduced by a first adiabatic methanation reaction, and C2 and hydrocarbons above C2 in the primary gas phase are cracked into methane. The secondary gas phase obtained is further refined by a second adiabatic methanation reaction, and finally a methane product gas meeting the national standard is obtained.

[0019] The method shortens the synthesis gas methanation process, does not require a circulating compressor, and has low equipment investment and operating cost. The heat is directly removed from the slurry bed reactor by the heat-conducting medium, without inter-stage heat exchange, thereby saving the heat exchanger. In addition, the low reaction temperature of the slurry bed reactor can slow down the carbon deposition and high-temperature deactivation rate of the catalyst due to high temperature, prolong the service life of the catalyst, and avoid local overheating in the reactor. By controlling the temperature of the first adiabatic methanation reaction or increasing the temperature of the primary gas phase, C2 and hydrocarbons above C2 produced by the methanation reaction in the slurry bed reactor are cracked. The products obtained by cracking are methane. The C2 and hydrocarbons above C2 produced at low temperature in the slurry bed reactor are reasonably utilized. Finally, the secondary gas phase is refined by a second adiabatic methanation reaction. Carbon oxides remaining in the secondary gas phase due to high temperature at a lower reaction equilibrium are converted into methane, and finally a methane product gas is obtained. The method provided by the present application is beneficial to increasing the yield of the methane product gas and improving the quality of the methane product gas. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a system for synthesizing natural gas by methanation of synthesis gas according to an embodiment of the present application;

[0021] Figure 2 is an XRD pattern of the reduction product obtained in step (1) of Preparation Example 1 of the present application;

[0022] Figure 3 is an XRD pattern of the dispersant used in Preparation Example 1 of the present application.

[0023] BRIEF DESCRIPTION OF DRAWINGS

[0024] 1. first preheater 2. slurry bed reactor 3. first heat exchanger

[0025] 4. first gas-liquid separator 5. second preheater 6. first adiabatic reactor

[0026] 7. second heat exchanger 8. second gas-liquid separator 9. third preheater

[0027] 10. second adiabatic reactor 11. third heat exchanger 12. third gas-liquid separator DETAILED DESCRIPTION

[0028] The endpoints of the ranges and any values disclosed herein are not to be understood as limited to the exact values recited as the exact dimensions are not to be construed as being restnicted to only the precise value. It is intended that the description of individual values and ranges nclude all values from the range broadly recited and any value ncluding the end points of the ranges.

[0029] In the present application, "first", "second", "third" and "primary", "secondary", "tertiary" do not represent the order of precedence, nor do they limit the respective materials or operations, but are merely used to distinguish the respective materials or operations, for example, "primary", "secondary" and "tertiary" in "primary reaction gas", "secondary reaction gas" and "tertiary reaction gas" are merely used to distinguish to indicate that they are not the same reaction gas; "first" and "second" in "first adiabatic methanation reaction" and "second adiabatic methanation reaction" are merely used to distinguish to indicate that they are not the same methanation reaction.

[0030] The first aspect of the present application provides a method for producing natural gas by methanation of synthesis gas, the method comprising:

[0031] (a) subjecting synthesis gas to a methanation reaction in the presence of a catalyst I to obtain a primary reaction gas, then subjecting the primary reaction gas to a primary condensation and gas-liquid separation to obtain a primary gas phase and a primary liquid phase; wherein the methanation reaction is carried out in a slurry bed reactor; the catalyst I comprises catalyst particles and a protective agent wrapping the catalyst particles, the catalyst particles containing amorphous nickel and a dispersing agent; the dispersing agent is selected from at least one of alumina, zirconia, magnesia and borax, wherein the zirconia is in tetragonal crystal form;

[0032] (b) subjecting the primary gas phase to a first adiabatic methanation reaction in the presence of a catalyst II to obtain a secondary reaction gas, then subjecting the secondary reaction gas to a secondary condensation and gas-liquid separation to obtain a secondary gas phase and a secondary liquid phase;

[0033] (c) subjecting the secondary gas phase to a second adiabatic methanation reaction in the presence of a catalyst III to obtain a tertiary reaction gas, then subjecting the tertiary reaction gas to a tertiary condensation and gas-liquid separation to obtain a methane product gas and a liquid phase material;

[0034] wherein the catalyst II and the catalyst III are the same or different, each independently being a methanation catalyst.

[0035] According to some embodiments of the present application, the catalyst I comprises catalyst particles and a protective agent wrapping the catalyst particles, the catalyst particles containing amorphous nickel and a dispersing agent; the dispersing agent is selected from at least one of alumina, zirconia, magnesia and borax, wherein the zirconia is in tetragonal crystal form; the active component in the catalyst I is amorphous nickel, which has stronger hydrogenation capacity.

[0036] According to some embodiments of the present application, preferably, in step (a), the XRD spectrum of the catalyst I has a diffraction peak with a peak width greater than 5° at 2θ = 45 ± 0.2°. This wide diffraction peak is a diffuse peak type formed by amorphous diffuse reflection, which is the main characteristic diffraction peak of amorphous nickel, and the short and wide diffuse peak indicates that the nickel in the methanation catalyst is in an amorphous structure.

[0037] According to some embodiments of the present application, the content of the protective agent in the catalyst I is not particularly limited, as long as the catalyst particles can be wrapped to isolate oxygen. Preferably, the content of the protective agent in the catalyst I is 2-4 mL per 1 g of the catalyst particles. With the above preferred embodiments, the catalyst particles can be wrapped and isolated from oxygen with a small amount of protective agent. When the catalyst I is used, an inert heat-conducting medium can be introduced into a slurry bed reactor to adjust the volume of the slurry (inert heat-conducting medium + protective agent); preferably, the inert heat-conducting medium is the same as the protective agent. The amount of the inert heat-conducting medium introduced can be adjusted according to actual conditions, which is not particularly limited. Preferably, the amount of the inert heat-conducting medium introduced is such that the total amount of the protective agent and the inert heat-conducting medium in the catalyst I is 20-100 mL, preferably 20-50 mL per 1 g of the catalyst particles. The content of the catalyst particles and the protective agent can meet the above requirements by adjusting the content of the protective agent in the catalyst I to control the loading amount of the catalyst I.

[0038] According to some embodiments of the present application, preferably, the content of the amorphous nickel in the catalyst particles is 60-85 wt% and the content of the dispersant is 15-40 wt% based on the total weight of the catalyst particles.

[0039] More preferably, the content of the amorphous nickel in the catalyst particles is 65-75 wt% and the content of the dispersant is 25-35 wt% based on the total weight of the catalyst particles.

[0040] According to some embodiments of the present application, preferably, the dispersant is at least one or more selected from the group consisting of a mixture of zirconium oxide and magnesium oxide, aluminum oxide and borax, more preferably a mixture of zirconium oxide and magnesium oxide, and further preferably, the mass ratio of zirconium oxide to magnesium oxide in the mixture is (1-10): 1, preferably (3-6): 1.

[0041] According to some embodiments of the present application, preferably, the particle size of the dispersant is 100-400 mesh, preferably 120-180 mesh.

[0042] According to some embodiments of the present application, preferably, the protective agent is a hydrophobic inert liquid; more preferably, the protective agent is at least one selected from the group consisting of liquid paraffin, diesel and white oil, and further preferably liquid paraffin.

[0043] According to some embodiments of the present application, preferably, in step (a), the preparation method of the catalyst I comprises:

[0044] (1) a reduction reaction is performed by contacting a nickel precursor with a reducing agent in the presence of water to obtain a reduction product;

[0045] (2) the reduction product is mixed with a dispersing agent in the presence of a protective agent, and the obtained mixture is allowed to stand and separate into layers to form a layered liquid; wherein the layered liquid comprises an upper layer liquid and a lower layer liquid, the upper layer liquid contains the protective agent, and the lower layer liquid contains water and catalyst particles, the catalyst particles contain amorphous nickel and the dispersing agent;

[0046] (3) the pH value of the lower layer liquid in the layered liquid is adjusted to 7-9 using water, and then the water in the lower layer liquid is removed so that the protective agent wraps the catalyst particles.

[0047] According to some embodiments of the present application, in step (1), a reduction reaction is performed by contacting a nickel precursor with a reducing agent in the presence of water to obtain a reduction product. This step can reduce the nickel element in the nickel precursor to metallic nickel, and ultimately obtain a reduction product containing amorphous elemental nickel.

[0048] According to some embodiments of the present application, in step (1), the nickel precursor is a compound containing a nickel element. The type of the nickel precursor is not particularly limited and can be a conventional choice in the art, for example, it can be a conventional water-soluble nickel salt in the art. Preferably, the nickel precursor is selected from at least one of nickel nitrate, nickel chloride and nickel acetate, preferably nickel nitrate.

[0049] According to some embodiments of the present application, in step (1), the type of the 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 borohydride, preferably sodium borohydride and / or potassium borohydride.

[0050] According to some embodiments of the present application, preferably, the molar ratio of the reducing agent to the nickel precursor in terms of nickel element is (1-2.5):1, preferably (1.5-2):1. The above preferred embodiments can further promote the generation of amorphous nickel particles through chemical reduction.

[0051] According to some embodiments of the present application, preferably, in step (1), the nickel precursor is provided in the form of a nickel precursor aqueous solution, more preferably, the concentration of nickel element in the nickel precursor aqueous solution is 0.5-2 mol / L.

[0052] According to some embodiments of the present application, preferably, in step (1), the reducing agent is provided in the form of a reducing agent aqueous solution, more preferably, the concentration of reducing agent in the reducing agent aqueous solution is 1-3 mol / L.

[0053] According to some embodiments of the present application, in order to remove oxygen in the solution, further promote the generation of the reduction product, and meanwhile improve the dispersion of the reduction product, preferably, in step (1), the contacting comprises: under oscillation, adding the aqueous solution of the nickel precursor into the aqueous solution of the reducing agent dropwise. Wherein, the oscillation and the conditions and mode of the dropwise adding can be the conventional selection in the art, and there is no particular limitation as long as the nickel element in the nickel precursor can be reduced to amorphous nickel. For example, the frequency of the oscillation can be 20-50 Hz; and the speed of the dropwise adding can be 2-6 drops per second.

[0054] According to some embodiments of the present application, preferably, in step (1), the conditions of the reduction reaction comprise: the temperature is 15-25℃, and the time is 1-3h.

[0055] According to some embodiments of the present application, in order to make the reduction product precipitate and separate better, preferably, in step (1), after the dropwise adding, a magnetic substance or device can be used to assist the reduction product to precipitate during the reduction reaction.

[0056] According to some embodiments of the present application, in step (2), the reduction product is mixed with the dispersant in the presence of a protective agent, and the obtained mixture is left to separate into layers to form a layered liquid. This step can make the amorphous nickel in the reduction product fully contact with the dispersant, which is conducive to the amorphous nickel fully mixing with the dispersant during the settling process.

[0057] According to some embodiments of the present application, in step (2), the protective agent is a hydrophobic inert liquid, which is immiscible with water, so that the mixture will form a layered liquid during the subsequent standing and separation process, the layered liquid comprises an upper layer liquid and a lower layer liquid; the density of the protective agent is smaller than that of water, and the catalyst particles will sink due to gravity, so that in the layered liquid formed, the upper layer liquid contains the protective agent, the lower layer liquid contains water and catalyst particles, and the catalyst particles contain amorphous nickel and the dispersant.

[0058] According to some embodiments of the present application, the protective agent can be any inert liquid suitable for a slurry bed reactor, preferably, the protective agent is selected from at least one of liquid paraffin, diesel and white oil, and preferably is liquid paraffin. The protective agent can form a protective layer (upper layer liquid) above the lower layer liquid after the standing and separation, so as to isolate the oxidizing substances.

[0059] According to some embodiments of the present application, preferably, the amount of the protective agent is such that the thickness of the upper layer liquid is 2-3cm.

[0060] According to some embodiments of the present application, in step (2), the dispersant is selected from at least one of alumina, zirconia, magnesia and borax, wherein the crystal form of the zirconia is tetragonal. The dispersant can be used as a carrier for dispersing the amorphous nickel in the slurry bed catalyst to prevent the amorphous nickel from floating above the slurry (protectant). The crystal form of the zirconia is tetragonal, which has a better auxiliary hydrogenation effect when the zirconia is in point contact with nickel in the slurry bed. The crystal form of the zirconia can be determined by the XRD spectrum of the catalyst.

[0061] According to some embodiments of the present application, preferably, the dispersant is selected from at least one or more of a mixture of zirconia and magnesia, alumina and borax, more preferably a mixture of zirconia and magnesia, and further preferably, the mass ratio of zirconia to magnesia in the mixture is (1-10):1, preferably (3-6):1, wherein the crystal form of the zirconia is tetragonal. By using the above preferred embodiments, the pH value of the contact point between the amorphous nickel and the dispersant in the slurry bed can be adjusted, and the semi-supported relationship between Zr-Ni can be formed to further promote the methanation catalytic effect.

[0062] According to some embodiments of the present application, more preferably, the method for preparing the mixture of zirconia and magnesia comprises: sieving the zirconia powder and the magnesia powder respectively, selecting particles with a particle size of 100-400 mesh, preferably 120-180 mesh, mixing the particles (the mass ratio of the zirconia powder to the magnesia powder can be selected according to the above), and then calcining the obtained mixture at a high temperature to convert the zirconia from monoclinic crystal form to tetragonal crystal form, and cooling the calcined product to room temperature in air. The high-temperature calcination conditions can include a temperature of 1200-1300℃ and a time of 4-6h. In the above process, the magnesia can protect the zirconia in the mixture from being converted from tetragonal crystal form to monoclinic crystal form during the cooling process, thereby ensuring that the zirconia in the final mixture is in tetragonal crystal form.

[0063] According to some embodiments of the present application, preferably, in step (2), the particle size of the dispersant is 100-400 mesh, preferably 120-180 mesh.

[0064] According to some embodiments of the present application, preferably, in step (2), the mass ratio of the nickel precursor to the dispersant, in terms of nickel element, is (1-10):1, preferably (1.5-5.67):1.

[0065] According to some embodiments of the present application, preferably, in step (2), the mixing is performed under stirring. The stirring condition and mode can be a routine selection in the art, and is not particularly limited. For example, the stirring can be performed using a non-ferromagnetic device. Preferably, the mixing condition includes a temperature of 20-50°C, a time of 20-60 min, and a rotation speed of 200-400 rpm.

[0066] According to some embodiments of the present application, in step (3), the pH value of the lower layer of the layered liquid is adjusted to 7-9 using water, and then the water in the lower layer is removed, so that the protective agent wraps the catalyst particles.

[0067] According to some embodiments of the present application, preferably, in step (3), the pH value of the lower layer is adjusted to 7.5-8 using water.

[0068] According to some embodiments of the present application, preferably, in step (3), the pH value adjusting mode includes washing the lower layer of the layered liquid with water for multiple times until the pH value of the lower layer meets the above-mentioned range. The washing can be performed using a washing liquid conventionally used in the art, such as deionized water.

[0069] Preferably, the washing can be performed by adding water to the lower layer of the layered liquid, and then removing the water. The water removing mode includes performing a solid-liquid separation on the layered liquid to remove the water in the lower layer of the layered liquid. The solid-liquid separation mode is not particularly limited, and can be a routine selection in the art, such as at least one of filtration, centrifugal separation, and gravity sedimentation. It is to be noted that the liquid separated by the solid-liquid separation operation is the water in the lower layer of the layered liquid, and does not include the protective agent in the upper layer, and the remaining product includes the protective agent and the catalyst particles.

[0070] More preferably, the water removing mode includes performing a slow filtration on the layered liquid to filter the water in the lower layer from the bottom, and stopping when the interface of the upper layer is tangent to the filtration outlet, so that the protective agent wraps the catalyst particles. The catalyst particles wrapped by the protective agent have a certain flowability, and are particularly suitable for use in a slurry bed reactor.

[0071] According to some embodiments of the present application, in order to prevent the obtained catalyst I from being oxidized, preferably, the catalyst I is stored in a sealed container, such as being sealed with nitrogen.

[0072] According to some embodiments of the present application, the catalyst II and the catalyst III are the same or different, and each is independently a methanation catalyst. The catalyst II and the catalyst III can be any methanation catalyst conventionally used in the art, and each can achieve the inventive purpose of the present application to a certain extent.

[0073] According to some embodiments of the present application, preferably, in step (b), the catalyst II comprises a carrier and an active component and an auxiliary agent supported on the carrier, wherein the active component is nickel and the auxiliary agent is selected from oxides of La and / or Ce, preferably oxides of La. The above preferred embodiments are advantageous for further reducing the by-produced C2 and C2+ hydrocarbons in the methanation process, increasing the yield of the methane product gas and improving the quality of the methane product gas.

[0074] According to some embodiments of the present application, the carrier in the catalyst II can be any carrier commonly used in the art for supported catalysts, as long as it can support the active component and the auxiliary agent, to some extent, to achieve the object of the present application. In order to further reduce the by-produced C2 and C2+ hydrocarbons in the methanation process, increase the yield of the methane product gas and improve the quality of the methane product gas, preferably, the carrier in the catalyst II is selected from at least one of alumina, zirconia and magnesium aluminate spinel, preferably magnesium aluminate spinel.

[0075] According to some embodiments of the present application, preferably, the content of the active component is 5-25% by weight, the content of the carrier is 75-95% by weight and the content of the auxiliary agent, calculated as oxides, is 0.05-5% by weight, based on the total weight of the catalyst II.

[0076] More preferably, the content of the active component is 10-20% by weight, the content of the carrier is 80-90% by weight and the content of the auxiliary agent, calculated as oxides, is 0.5-1.5% by weight, based on the total weight of the catalyst II.

[0077] According to some embodiments of the present application, preferably, the catalyst II has a working temperature range of 260-700°C, i.e. is a high-temperature methanation catalyst.

[0078] The above preferred embodiments are advantageous for further reducing the by-produced C2 and C2+ hydrocarbons in the methanation process, increasing the yield of the methane product gas and improving the quality of the methane product gas.

[0079] According to a preferred embodiment of the present application, the catalyst II comprises a carrier and an active component and an auxiliary agent supported on the carrier, wherein the active component is nickel, the auxiliary agent is oxides of La and the carrier is magnesium aluminate spinel; the content of the active component is 10-20% by weight, the content of the carrier is 80-90% by weight and the content of the auxiliary agent, calculated as oxides, is 0.5-1.5% by weight, based on the total weight of the catalyst II. The above preferred embodiment is particularly advantageous for further reducing the by-produced C2 and C2+ hydrocarbons in the methanation process, increasing the yield of the methane product gas and improving the quality of the methane product gas.

[0080] According to some embodiments of the present application, the catalyst II can be commercially available or prepared according to the prior art, and there is no particular limitation as long as the catalyst II satisfying the above requirements can be obtained. For example, the catalyst NCJ-1 available from Nanjing Research Institute of Catalysts can be used.

[0081] According to some embodiments of the present application, preferably, in step (c), the catalyst III comprises a carrier and an active component and an auxiliary agent supported on the carrier, wherein the active component is nickel, and the auxiliary agent is selected from oxides of La and / or Ce, preferably oxides of La. The above preferred embodiments are advantageous for further reducing the by-produced C2 and C2+ hydrocarbons in the methanation process, increasing the yield of the methane product gas and improving the quality of the methane product gas.

[0082] According to some embodiments of the present application, the carrier in the catalyst III can be any carrier commonly used in the art for supported catalysts as long as it can support the active component and the auxiliary agent, and to some extent, the purpose of the present application can be achieved. In order to further reduce the by-produced C2 and C2+ hydrocarbons in the methanation process, increase the yield of the methane product gas and improve the quality of the methane product gas, preferably, the carrier in the catalyst III is selected from at least one of alumina, zirconia and magnesium aluminate spinel, preferably alumina.

[0083] According to some embodiments of the present application, preferably, the content of the active component is 25-50% by weight, the content of the carrier is 50-75% by weight, and the content of the auxiliary agent in terms of oxides is 0.05-5% by weight, based on the total weight of the catalyst III.

[0084] More preferably, the content of the active component is 35-45% by weight, the content of the carrier is 55-65% by weight, and the content of the auxiliary agent in terms of oxides is 0.5-1% by weight, based on the total weight of the catalyst III.

[0085] According to some embodiments of the present application, preferably, the working temperature range of the catalyst III is 260-450°C, i.e. the catalyst is a low-temperature methanation catalyst.

[0086] The above preferred embodiments are advantageous for further reducing the by-produced C2 and C2+ hydrocarbons in the methanation process, increasing the yield of the methane product gas and improving the quality of the methane product gas.

[0087] According to a preferred embodiment of the present application, the catalyst III comprises a carrier, and an active component and an auxiliary agent supported on the carrier, wherein the active component is nickel, the auxiliary agent is an oxide of La, and the carrier is alumina; the content of the active component is 35-45% by weight, the content of the carrier is 55-65% by weight, and the content of the auxiliary agent in terms of oxide is 0.5-1% by weight, based on the total weight of the catalyst III. The above preferred embodiment is particularly advantageous for further reducing the C2 and C2+ hydrocarbons by-produced in the methanation process, increasing the yield of the methane product gas, and improving the quality of the methane product gas.

[0088] According to some embodiments of the present application, the catalyst III can be commercially available or prepared according to the prior art, and there is no particular limitation thereto, as long as the catalyst III satisfying the above requirements can be obtained. For example, the catalyst III can be a catalyst of NCJ-2 brand available from Nanjing Research Institute of Catalysts.

[0089] According to some embodiments of the present application, preferably, in step (a), the synthesis gas is a purified synthesis gas obtained by purifying and desulfurizing a raw gas for synthesis gas.

[0090] According to some embodiments of the present application, preferably, in step (a), the temperature of the synthesis gas is 250-350°C, preferably 260-300°C. The temperature can be provided by external heating or by reaction heat. For example, a preheater can be used to heat the synthesis gas to the above temperature, and / or a heat exchanger can be used to heat the synthesis gas to the above temperature by exchanging heat with the primary reaction gas.

[0091] According to some embodiments of the present application, the synthesis gas contains H2, CO, CO2, and methane and / or inert gas not participating in the reaction. Preferably, in the synthesis gas, the volume percentage content of H2, CO and CO2 satisfies: H2 / (CO+CO2)=3.0-3.6, preferably 3.1-3.3. The above preferred embodiment is advantageous for adapting the catalyst to the gas ratio of the Texaco coal gas as the gas source, and the hydrogen, carbon monoxide and carbon dioxide contained therein can be approximately regarded as satisfying the stoichiometric ratio.

[0092] According to some embodiments of the present application, preferably, in the synthesis gas, the sum of the volume percentage contents of H2, CO and CO2 is greater than 60%, preferably greater than 75%.

[0093] According to some embodiments of the present application, preferably, the conditions of the methanation reaction include: the reaction temperature is not higher than 340°C, preferably 300-340°C; the reaction pressure is 1-4 MPa, preferably 2.5-3.5 MPa; the volume space velocity is 1500-18000 h-1, preferably 3000-9000 h-1.-1 , preferably 6000-15000h -1 The reaction temperature of the methanation reaction is not more than 340℃, preferably 300-340℃, and a lower reaction temperature is beneficial to promote the methanation reaction equilibrium to move in the positive direction and improve the conversion of hydrogen and carbon oxides. The reaction temperature of the methanation reaction can be controlled by adjusting the stirring speed and the flow rate of the cooling liquid of the slurry bed reactor.

[0094] According to some embodiments of the present application, preferably, the content of hydrogen in the primary gas phase is 20-40% by volume, the content of methane is 40-50% by volume, the total content of CO and CO2 is not more than 11% by volume, and the total content of C2 and hydrocarbons with more than C2 is not more than 4500ppm, based on the total amount of the primary gas phase.

[0095] According to some embodiments of the present application, preferably, the temperature of the primary gas phase in step (b) is 250-600℃, preferably 260-450℃. The temperature can be provided by external heating or by reaction heat, for example, a preheater can be used to heat the primary gas phase to the above-mentioned temperature, and / or a heat exchanger can be used to exchange heat between the secondary reaction gas and the primary gas phase to heat the primary gas phase to the above-mentioned temperature.

[0096] According to some embodiments of the present application, preferably, the conditions of the first adiabatic methanation reaction include: the reaction temperature is 400-650℃, preferably 450-620℃; the reaction pressure is 1-4MPa, preferably 1.5-3.5MPa; the volume space velocity is 3000-18000h -1 , preferably 6000-15000h -1 The reaction temperature of the first adiabatic methanation reaction is 400-650℃, preferably 450-620℃, and using the above-mentioned preferred embodiments, a higher reaction temperature is beneficial to the decomposition of C2 and hydrocarbons with more than C2 into methane.

[0097] According to some embodiments of the present application, preferably, the content of hydrogen in the secondary gas phase is 6-9% by volume, the content of methane is 73-90% by volume, the total content of CO and CO2 is not more than 2% by volume, and the total content of C2 and hydrocarbons with more than C2 is not more than 50ppm, based on the total amount of the secondary gas phase.

[0098] According to some embodiments of the present application, preferably, in step (c), the temperature of the secondary gas phase is 250-400℃, preferably 260-300℃. The temperature can be provided by external heating or by reaction heat. For example, a preheater can be used to heat the secondary gas phase to the above-mentioned temperature, and / or a heat exchanger can be used to heat the secondary gas phase to the above-mentioned temperature by exchanging heat with the tertiary reaction gas.

[0099] According to some embodiments of the present application, preferably, the conditions of the second adiabatic methanation reaction include: a reaction temperature of 260-290℃, preferably 265-290℃; a reaction pressure of 1-4 MPa, preferably 1.5-3.5 MPa; a volume space velocity of 3000-18000 h -1 , preferably 6000-15000 h -1 . The reaction temperature of the second adiabatic methanation reaction is 260-290℃, preferably 265-290℃, and more preferably, the temperature rise of the second adiabatic methanation reaction is controlled to be no more than 10℃. With the above-mentioned preferred embodiments, a lower reaction temperature is conducive to promoting the methanation reaction equilibrium to move in the positive direction, thereby improving the effect of methane refining.

[0100] According to some embodiments of the present application, preferably, in the methane product gas, based on the total amount of the dry gas of the methane product gas, the content of hydrogen is 0-2% by volume; the content of methane is greater than 80% by volume; the total content of CO and CO2 is no more than 0.5% by volume; and the total content of C2 and hydrocarbons with more than C2 is no more than 50 ppm.

[0101] The second aspect of the present application provides a system for synthesizing natural gas by methanation of synthesis gas, the system comprising: at least one methanation unit, wherein the methanation unit comprises, in sequence, a first preheater, a slurry bed reactor, a first heat exchanger, a first gas-liquid separator, a second preheater, a first adiabatic reactor, a second heat exchanger, a second gas-liquid separator, a third preheater, a second adiabatic reactor, a third heat exchanger, and a third gas-liquid separator.

[0102] According to some embodiments of the present application, preferably, the slurry bed reactor is filled with catalyst I, which is used for methanation reaction of synthesis gas to obtain a primary reaction gas.

[0103] According to some embodiments of the present application, the first preheater is used to heat the synthesis gas. The first heat exchanger is used to exchange heat between the primary reaction gas and the synthesis gas. The first gas-liquid separator is used to perform primary condensation on the primary reaction gas, and perform gas-liquid separation on the obtained primary condensation product to obtain a primary gas phase and a primary liquid phase.

[0104] According to some embodiments of the present invention, preferably, the first adiabatic reactor is filled with a catalyst II for subjecting the primary gas phase to a first adiabatic methanation reaction to obtain a secondary reaction gas.

[0105] According to some embodiments of the present invention, the second preheater is used to heat the primary gas phase. The second heat exchanger is used to exchange heat between the secondary reaction gas and the primary gas phase. The second gas-liquid separator is used to perform secondary condensation on the secondary reaction gas and perform gas-liquid separation on the obtained secondary condensate to obtain a secondary gas phase and a secondary liquid phase.

[0106] According to some embodiments of the present invention, preferably, the second adiabatic reactor is filled with a catalyst III for subjecting the secondary gas phase to a second adiabatic methanation reaction to obtain a tertiary reaction gas.

[0107] According to some embodiments of the present invention, the third preheater is used to heat the secondary gas phase. The third heat exchanger is used to exchange heat between the tertiary reaction gas and the secondary gas phase. The third gas-liquid separator is used to perform tertiary condensation on the tertiary reaction gas and perform gas-liquid separation on the obtained tertiary condensate to obtain methane product gas and liquid phase material.

[0108] According to some embodiments of the present invention, the catalyst I, catalyst II and catalyst III can be selected with reference to the above, and will not be described in detail here.

[0109] According to some embodiments of the present invention, preferably, the methanation unit further includes a pretreatment unit, and the pretreatment unit is used to purify and desulfurize the raw gas of the synthesis gas to obtain the purified synthesis gas.

[0110] The method and system for producing natural gas by methanation of synthesis gas provided by the present invention will be further described in detail below with reference to the accompanying drawings.

[0111] The present invention illustratively provides a schematic diagram of a system for producing natural gas from synthesis gas by methanation according to an embodiment of the present invention, as shown in FIG. Figure 1 The system includes a pretreatment unit and a methanation unit, wherein the methanation unit includes a first preheater 1, a slurry bed reactor 2, a first heat exchanger 3, a first gas-liquid separator 4, a second preheater 5, a first adiabatic reactor 6, a second heat exchanger 7, a second gas-liquid separator 8, a third preheater 9, a second adiabatic reactor 10, a third heat exchanger 11, and a third gas-liquid separator 12, which are connected in sequence.

[0112] The slurry bed reactor 2 is filled with catalyst I, the first adiabatic reactor 6 is filled with catalyst II, and the second adiabatic reactor 10 is filled with catalyst III.

[0113] According to a particularly preferred embodiment of the present application, the method for preparing natural gas by methanation of synthesis gas comprises:

[0114] (S1) feeding a raw gas of synthesis gas into a pretreatment unit to perform purification treatment and desulfurization treatment, to obtain a purified synthesis gas;

[0115] (S2) feeding the purified synthesis gas into a slurry bed reactor 2 after heating by a first preheater 1 to perform a methanation reaction, to obtain a primary reaction gas; in a first heat exchanger 3, the primary reaction gas is subjected to heat exchange with the purified synthesis gas;

[0116] (S3) feeding the primary reaction gas after heat exchange into a first gas-liquid separator 4 to perform primary condensation, and after gas-liquid separation, obtaining a primary gas phase and a primary liquid phase;

[0117] (S4) feeding the primary gas phase into a first adiabatic reactor 6 after heating by a second preheater 5 to perform a first adiabatic methanation reaction, to obtain a secondary reaction gas; in a second heat exchanger 7, the secondary reaction gas is subjected to heat exchange with the primary gas phase;

[0118] (S5) feeding the secondary reaction gas after heat exchange into a second gas-liquid separator 8 to perform secondary condensation, and after gas-liquid separation, obtaining a secondary gas phase and a secondary liquid phase;

[0119] (S6) feeding the secondary gas phase into a second adiabatic reactor 10 after heating by a third preheater 9 to perform a second adiabatic methanation reaction, to obtain a tertiary reaction gas; in a third heat exchanger 11, the tertiary reaction gas is subjected to heat exchange with the secondary gas phase;

[0120] (S7) feeding the tertiary reaction gas after heat exchange into a third gas-liquid separator 12 to perform tertiary condensation, and after gas-liquid separation, obtaining a methane product gas and a liquid phase material.

[0121] In the present application, the pressures are all gauge pressures.

[0122] The present application will be described in detail below through examples.

[0123] In the following preparation examples and comparative preparation examples, the raw materials used are all commercially available products, unless otherwise specified.

[0124] In the following preparation examples and comparative preparation examples, the water used is deionized water;

[0125] In the following examples and comparative examples:

[0126] The catalyst II used was purchased from the Nanjing Chemical Research Institute and was NCJ-1. Based on the total weight of the catalyst II, the nickel content in the catalyst was 18% by weight, the lanthanum oxide content was 1.2% by weight, and the remainder was a magnesium aluminum spinel support.

[0127] The catalyst III used was purchased from the Nanjing Chemical Research Institute and was NCJ-2. Based on the total weight of the catalyst III, the nickel content was 40% by weight, the lanthanum oxide content was 0.8% by weight, and the remainder was an alumina support.

[0128] The composition of the catalyst was determined by a Rigaku ZSX Primus II X-ray fluorescence spectrometer (XRF);

[0129] The XRD spectrum of the material was measured by an X-ray diffractometer, and the powder X-ray diffractometer was purchased from Bruker, model D8 advance.

[0130] Preparation Examples 1-2 are used to illustrate the catalyst I provided by the present invention and its preparation method

[0131] Preparation Example 1

[0132] (1) In the presence of water, a nickel precursor is contacted with a reducing agent to perform a reduction reaction to obtain a reduction product; wherein:

[0133] The nickel precursor is nickel nitrate, which is provided in the form of a nickel precursor aqueous solution. The nickel precursor aqueous solution 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 nickel precursor aqueous solution is 1.5mol / L.

[0134] The reducing agent is sodium borohydride, which is provided in the form of an aqueous reducing agent solution, wherein the concentration of sodium borohydride in the aqueous reducing agent solution is 2 mol / L;

[0135] The molar ratio of the reducing agent to the nickel precursor calculated as nickel element is 1.5:1;

[0136] The contacting step is specifically as follows: adding the nickel precursor aqueous solution dropwise to the reducing agent aqueous solution under oscillation; the oscillation frequency is 20 Hz; the dropping speed is 4 drops / second;

[0137] The reduction reaction conditions are: temperature 20°C ± 2°C, time 2 hours; 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 precipitation;

[0138] The XRD pattern of the reduction product is as follows Figure 2 As shown in the figure, it can be seen that the nickel contained in the reduction product is amorphous nickel;

[0139] (2) mixing the reduction product with the dispersant in the presence of the protective agent, and allowing the obtained mixture to stand and separate into layers to form a layered liquid; wherein:

[0140] the protective agent is liquid paraffin; the layered liquid comprises an upper layer liquid and a lower layer liquid, the upper layer liquid contains the protective agent, and the lower layer liquid contains water and catalyst particles containing amorphous nickel and the dispersant; the amount of the protective agent is such that the thickness of the upper layer liquid is 2.5 cm;

[0141] 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 crystal form of the zirconium oxide is tetragonal; the particle size of the dispersant is 120-180 mesh; the preparation process of the dispersant is as follows: the zirconium oxide powder and the magnesium oxide powder are sieved respectively, the particles with a particle size of 120-180 mesh are selected, and then mixed according to the above mass ratio, and then the obtained mixture is calcined at 1300℃ for 4h to convert the zirconium oxide from monoclinic crystal form to tetragonal crystal form, and the calcined product is cooled to room temperature in air; the XRD pattern of the dispersant is shown in Figure 3 , from which it can be seen that the crystal form of the zirconium oxide contained in the dispersant is tetragonal;

[0142] the mass ratio of the nickel precursor to the dispersant, in terms of nickel element, is 3:1;

[0143] the mixing conditions are as follows: temperature is 20℃, time is 20min, and rotation speed is 200rpm.

[0144] (3) adjusting the pH value of the lower layer liquid in the layered liquid to 7.5 using water, and then removing the water in the lower layer liquid to allow the protective agent to wrap the catalyst particles to obtain a catalyst I, which is sealed and filled with nitrogen; wherein:

[0145] the adjustment mode is specifically as follows: the lower layer liquid of the layered liquid is washed with water for multiple times until the pH value of the lower layer liquid is 7.5; the water removal mode is specifically as follows: the layered liquid is slowly filtered to filter out the water in the lower layer liquid from the bottom, and the filtering is stopped when the interface of the upper layer liquid is tangent to the filter outlet, so that the protective agent wraps the catalyst particles.

[0146] The catalyst comprises catalyst particles and protective agent wrapping the catalyst particles, and the catalyst particles contain amorphous nickel and the dispersant; based on the total weight of the catalyst particles, the content of amorphous nickel in the catalyst particles is 75wt%, and the content of the dispersant is 25wt%.

[0147] In the catalyst, the content of the protective agent is 3mL relative to 1g of catalyst particles.

[0148] The XRD detection shows that the methanation catalyst has a diffraction peak with a peak width greater than 5° at 2θ = 45 ± 0.2°, indicating that the nickel in the catalyst is amorphous nickel; and the zirconium oxide contained in the catalyst conforms to the peak type, position and intensity of the tetragonal phase (tetragonal crystal form) in the zirconium oxide standard card.

[0149] Preparation Example 2

[0150] According to the method of Preparation Example 1, except that:

[0151] In step (1), the molar ratio of the reducing agent to the nickel precursor in terms of nickel element is 2:1;

[0152] In step (2), the dispersant is a mixture of zirconium oxide and magnesium oxide, wherein the mass ratio of zirconium oxide to magnesium oxide is 4:1; the mass ratio of the nickel precursor in terms of nickel element to the dispersant is 4:1;

[0153] In step (3), the pH value of the lower layer liquid in the layered liquid is adjusted to 8.0 using water;

[0154] The rest is the same as Preparation Example 1, and a methanation catalyst is obtained, which is sealed and filled with nitrogen.

[0155] The methanation catalyst includes catalyst particles and a protective agent wrapping the catalyst particles, and the catalyst particles contain amorphous nickel and a dispersant; based on the total weight of the catalyst particles, the content of amorphous nickel in the catalyst particles is 80% by weight, and the content of the dispersant is 20% by weight.

[0156] In the methanation catalyst, the content of the protective agent is 2 mL with respect to 1 g of catalyst particles.

[0157] The XRD detection shows that the methanation catalyst has a diffraction peak with a peak width greater than 5° at 2θ = 45 ± 0.2°, indicating that the nickel in the catalyst is amorphous nickel; and the zirconium oxide contained in the catalyst conforms to the peak type, position and intensity of the tetragonal phase (tetragonal crystal form) in the zirconium oxide standard card.

[0158] Comparative Preparation Example 1

[0159] According to the method of Preparation Example 1, except that: in step (2), no dispersant is added;

[0160] The rest is the same as Preparation Example 1, and a catalyst I is obtained, which is sealed and filled with nitrogen.

[0161] The catalyst includes catalyst particles and a protective agent wrapping the catalyst particles, and the catalyst particles are amorphous nickel (i.e., based on the total weight of the catalyst particles, the content of amorphous nickel in the catalyst particles is 100% by weight).

[0162] The XRD detection shows that the catalyst has a diffraction peak with a width of more than 5° at 2θ = 45 ± 0.2°, indicating that the nickel in the catalyst is amorphous nickel.

[0163] Example 1-5 is used to illustrate the method for preparing natural gas by methanation of synthesis gas provided by the present application

[0164] Example 1

[0165] The system for preparing natural gas by methanation of synthesis gas as shown in Figure 1 is used. In the system, the catalyst I filled in the slurry bed reactor 2 is the catalyst I prepared in Preparation Example 1; the filling amount of the catalyst I satisfies that the catalyst particles in the methanation catalyst are 30 g, and the inert heat-conducting medium (of the same type as the protective agent) is introduced, so that the filling amount of the methanation catalyst and the volume amount of the inert heat-conducting medium satisfy that the total amount of the protective agent in the methanation catalyst and the inert heat-conducting medium is 40 mL relative to 1 g of the catalyst particles; the filling amount of the catalyst II in the first adiabatic reactor 6 is 20 mL; and the filling amount of the catalyst III in the second adiabatic reactor 10 is 20 mL. The method for preparing natural gas by methanation of synthesis gas is as follows:

[0166] (S1) The raw gas of the synthesis gas is sent to a pretreatment unit for purification treatment and desulfurization treatment to obtain purified synthesis gas; the temperature of the purified synthesis gas is 40℃, and the volume composition is: hydrogen 67.2%, methane 9.8%, carbon monoxide 17%, carbon dioxide 4%, and nitrogen 2%, wherein the volume percentage contents of H2, CO and CO2 satisfy: H2 / (CO+CO2) = 3.2;

[0167] (S2) The purified synthesis gas is heated to 260℃ by the first preheater 1 and then sent to the slurry bed reactor 2 for methanation reaction to obtain primary reaction gas; the primary reaction gas is heat-exchanged with the purified synthesis gas in the first heat exchanger 3; wherein the conditions of the methanation reaction are: the reaction temperature is 320℃, the reaction pressure is 3 MPa, and the volume space velocity of the purified synthesis gas relative to the catalyst I is 15000 h -1 ;

[0168] (S3) The primary reaction gas after heat exchange is sent to the first gas-liquid separator 4 for primary condensation, and after gas-liquid separation, the first gas phase and the first liquid phase are obtained; the volume composition of the first gas phase is: hydrogen 38%, methane 50%, carbon monoxide 1.3%, carbon dioxide 7%, C2 and above hydrocarbons 3400 ppm, and the rest is nitrogen, based on the volume of dry gas;

[0169] (S4) The primary gas phase is heated to 260° C. in the second preheater 5 and then fed into the first adiabatic reactor 6 for a first adiabatic methanation reaction to obtain a secondary reaction gas; the secondary reaction gas is heat exchanged with the primary gas phase in the second heat exchanger 7; wherein the conditions for the first adiabatic methanation reaction are: a reaction temperature of 450° C., a reaction pressure of 3 MPa, and a volume space velocity of the primary gas phase relative to the catalyst II of 13500 h-1. -1 ;

[0170] (S5) The secondary reaction gas after heat exchange is sent to the second gas-liquid separator 8 for secondary condensation. After gas-liquid separation, a secondary gas phase and a secondary liquid phase are obtained. The volume composition of the secondary gas phase, calculated on a dry gas volume basis, is as follows: 6% hydrogen, 88.4% methane, 0% carbon monoxide, 1.5% carbon dioxide, 40 ppm C2 and higher hydrocarbons, and the remainder nitrogen.

[0171] (S6) The secondary gas phase is heated to 260° C. in the third preheater 9 and then fed into the second adiabatic reactor 10 for a second adiabatic methanation reaction to obtain a tertiary reaction gas; in the third heat exchanger 11, the tertiary reaction gas is heat exchanged with the secondary gas phase; wherein the conditions for the second adiabatic methanation reaction are: a reaction temperature of 290° C., a reaction pressure of 3 MPa, and a volume space velocity of the secondary gas phase relative to the catalyst III of 9000 h / min. -1 ;

[0172] (S7) The tertiary reaction gas after heat exchange is sent to the third gas-liquid separator 12 for tertiary condensation and gas-liquid separation to obtain methane product gas and liquid phase substances; the composition of the methane product gas is: 0.3% hydrogen, 95.1% methane, 0% carbon monoxide, 0.2% carbon dioxide, 42 ppm C2 and higher hydrocarbons, and the balance is nitrogen, based on the volume of dry gas;

[0173] In this embodiment, the flow rate of C2 and C2 hydrocarbons above at the outlet of the slurry bed reactor is 0.612NL / h, and the flow rate of C2 and C2 hydrocarbons above at the outlet of the first adiabatic reactor is 0.0072NL / h. The first adiabatic methanation reaction reduces 98.8% of C2 and C2 hydrocarbons above, and increases the production of methane product gas by 1.5NL / h.

[0174] Example 2

[0175] The system and method of Example 1 are the same, except that the catalyst I loaded into the slurry bed reactor 2 is the catalyst I prepared in Preparation Example 2; the loading amount of the catalyst I is such that the catalyst particles in the methanation catalyst are 30 g, and an inert heat-conducting medium (of the same type as the protective agent) is introduced, so that the loading amount of the methanation catalyst and the volume of the inert heat-conducting medium satisfy the following conditions: the total amount of the protective agent and the inert heat-conducting medium in the methanation catalyst is 30 mL per 1 g of the catalyst particles;

[0176] In step (S2), the conditions of the methanation reaction are as follows: the reaction temperature is 340℃, the reaction pressure is 3 MPa, and the volume space velocity of the purified synthesis gas relative to the catalyst I is 6000 h -1 ;

[0177] In step (S3), the volume composition of the primary gas phase is as follows: hydrogen 40%, methane 47.4%, carbon monoxide 1.5%, carbon dioxide 7.5%, C2 and C2+ hydrocarbons 4500 ppm, and the rest is nitrogen, based on the volume of dry gas;

[0178] In step (S5), the volume composition of the secondary gas phase is as follows: hydrogen 8%, methane 86%, carbon monoxide 0%, carbon dioxide 2%, C2 and C2+ hydrocarbons 50 ppm, and the rest is nitrogen, based on the volume of dry gas;

[0179] In step (S6), the reaction temperature of the second adiabatic methanation reaction is 280℃;

[0180] In step (S7), the composition of the methane product gas is as follows: hydrogen 0.4%, methane 95%, carbon monoxide 0%, carbon dioxide 0.3%, C2 and C2+ hydrocarbons 50 ppm, and the rest is nitrogen, based on the volume of dry gas;

[0181] In this embodiment, the flow rate of C2 and C2+ hydrocarbons at the outlet of the slurry bed reactor is 0.245 NL / h, the flow rate of C2 and C2+ hydrocarbons at the outlet of the first adiabatic reactor is 0.0096 NL / h, the first adiabatic methanation reaction reduces C2 and C2+ hydrocarbons by 99.1%, and the production of methane product gas is increased by 0.5 NL / h.

[0182] Example 3

[0183] According to the system and method of Example 1, except that the amount of inert heat-conducting medium introduced into the slurry bed reactor 2 is adjusted so that the amount of methanation catalyst and the volume of inert heat-conducting medium satisfy the following condition: the total amount of protective agent in the methanation catalyst and the inert heat-conducting medium is 20 mL per 1 g of catalyst particles;

[0184] In step (S1), the volume composition of the purified synthesis gas is as follows: hydrogen 60.8%, methane 14.2%, carbon monoxide 14%, carbon dioxide 3%, and nitrogen 8%, wherein the volume percentage content of H2, CO and CO2 satisfies the following condition: H2 / (CO+CO2)=3.6;

[0185] In step (S3), the volume composition of the primary gas phase is as follows: hydrogen 30%, methane 50%, carbon monoxide 1%, carbon dioxide 6.5%, C2 and C2+ hydrocarbons 4000 ppm, and the rest is nitrogen, based on the volume of dry gas;

[0186] In step (S5), the volume composition of the secondary gas phase is: hydrogen 6%, methane 77.5%, carbon monoxide 0%, carbon dioxide 1.5%, C2 and above hydrocarbons 30 ppm, and the rest is nitrogen, based on the volume of dry gas;

[0187] In step (S6), the reaction temperature of the second adiabatic methanation reaction is 270°C;

[0188] In step (S7), the composition of the methane product gas is: hydrogen 0.2%, methane 84.7%, carbon monoxide 0%, carbon dioxide 0.1%, C2 and above hydrocarbons 50 ppm, and the rest is nitrogen, based on the volume of dry gas;

[0189] In this embodiment, the flow rate of C2 and above hydrocarbons at the outlet of the slurry bed reactor is 1.08 NL / h, and the flow rate of C2 and above hydrocarbons at the outlet of the first adiabatic reactor is 0.0135 NL / h, which is reduced by 99% through the first adiabatic methanation reaction, and 2.6 NL / h of methane product gas is increased.

[0190] Example 4

[0191] According to the system and method of Example 2, except that:

[0192] In step (S2), the methanation reaction conditions are: reaction temperature 300°C, reaction pressure 3 MPa, and volume space velocity of purified synthesis gas 10000 h -1 ;

[0193] In step (S3), the volume composition of the primary gas phase is: hydrogen 38.5%, methane 47%, carbon monoxide 3.5%, carbon dioxide 7.5%, C2 and above hydrocarbons 3000 ppm, and the rest is nitrogen, based on the volume of dry gas;

[0194] In step (S4), the reaction temperature of the first adiabatic methanation reaction is 650°C;

[0195] In step (S5), the volume composition of the secondary gas phase is: hydrogen 8%, methane 86%, carbon monoxide 0.1%, carbon dioxide 1.9%, C2 and above hydrocarbons 5 ppm, and the rest is nitrogen, based on the volume of dry gas;

[0196] In step (S6), the reaction temperature of the second adiabatic methanation reaction is 270°C;

[0197] In step (S7), the composition of the methane product gas is: hydrogen 0.3%, methane 95.4%, carbon monoxide 0%, carbon dioxide 0.2%, C2 and above hydrocarbons 5 ppm, and the rest is nitrogen, based on the volume of dry gas;

[0198] In this embodiment, the flow rate of C2 and higher hydrocarbons at the outlet of the slurry bed reactor C2 is 0.9 NL / h, and the flow rate of C2 and higher hydrocarbons at the outlet of the first adiabatic reactor C2 is 0.0015 NL / h, 99.9% of C2 and higher hydrocarbons are reduced by the first adiabatic methanation reaction, and 2.25 NL / h of methane product gas is increased.

[0199] Example 5

[0200] According to the system and method of Example 3, except that:

[0201] In step (S1), the volume composition of the purified synthesis gas is: hydrogen 57.2%, methane 17%, carbon monoxide 13%, carbon dioxide 4.8%, nitrogen 8%, wherein the volume percentage content of H2, CO and CO2 satisfies: H2 / (CO+CO2)=3.2;

[0202] In step (S2), the conditions of the methanation reaction are: the reaction temperature is 330°C, the reaction pressure is 3 MPa, and the volume space velocity of the purified synthesis gas is 6000 h -1 ;

[0203] In step (S3), the volume composition of the primary gas phase is: hydrogen 28.5%, methane 50%, carbon monoxide 0.5%, carbon dioxide 6.5%, C2 and higher hydrocarbons 4500 ppm, and the rest is nitrogen, based on the volume of dry gas;

[0204] In step (S4), the primary gas phase is heated to 450°C by the second preheater 5;

[0205] In step (S5), the volume composition of the secondary gas phase is: hydrogen 6.5%, methane 73.8%, carbon monoxide 0%, carbon dioxide 1.7%, C2 and higher hydrocarbons 15 ppm, and the rest is nitrogen, based on the volume of dry gas;

[0206] In step (S7), the composition of the methane product gas is: hydrogen 0.4%, methane 81%, carbon monoxide 0%, carbon dioxide 0.2%, C2 and higher hydrocarbons 15 ppm, and the rest is nitrogen, based on the volume of dry gas;

[0207] In this embodiment, the flow rate of C2 and higher hydrocarbons at the outlet of the slurry bed reactor C2 is 0.81 NL / h, and the flow rate of C2 and higher hydrocarbons at the outlet of the first adiabatic reactor C2 is 0.0027 NL / h, 99.7% of C2 and higher hydrocarbons are reduced by the first adiabatic methanation reaction, and 1.94 NL / h of methane product gas is increased.

[0208] Comparative Example 1

[0209] The system and method of Example 1 are adopted, except that the catalyst I filled in the slurry bed reactor 2 is the catalyst I prepared in Comparative Preparation 1;

[0210] In step (S3), the volume composition of the primary gas phase is: 45% of hydrogen, 37.8% of methane, 2% of carbon monoxide, 11.5% of carbon dioxide, 8000 ppm of C2 and C2+ hydrocarbons, and the rest is nitrogen, based on the volume of dry gas;

[0211] In step (S5), the volume composition of the secondary gas phase is: 28% of hydrogen, 61.4% of methane, 0.4% of carbon monoxide, 6.7% of carbon dioxide, 120 ppm of C2 and C2+ hydrocarbons, and the rest is nitrogen, based on the volume of dry gas;

[0212] In step (S7), the composition of the methane product gas is: 4.5% of hydrogen, 90% of methane, 0% of carbon monoxide, 1.2% of carbon dioxide, 120 ppm of C2 and C2+ hydrocarbons, and the rest is nitrogen, based on the volume of dry gas;

[0213] In the present comparative example, the flow rate of C2 and C2+ hydrocarbons at the outlet of the slurry bed reactor is 3.6 NL / h, and the flow rate of C2 and C2+ hydrocarbons at the outlet of the first adiabatic reactor is 0.054 NL / h, which is reduced by 98.5% through the first adiabatic methanation reaction, and 8.51 NL / h of methane product gas is produced.

[0214] As can be seen from the above results, the method and system for synthesizing natural gas by methanation of synthesis gas provided by the present application can shorten the process of synthesis gas methanation, reduce the cost, reduce the carbon oxides in the methane product gas, and achieve the purpose of converting C2 and C2+ hydrocarbons in the slurry bed methanation reaction into methane, and the volume content of hydrogen in the methane product gas is not more than 0.5%, the total volume content of carbon oxides is not more than 0.5%, and the methane content is greater than 75%.

[0215] The above describes the preferred embodiments of the present application, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application, and all fall within the protection scope of the present application.

Claims

1. A method for producing natural gas by methanation of synthesis gas, characterized in that: The method comprises: (a) subjecting synthesis gas to a methanation reaction in the presence of a catalyst (I) to obtain a primary reaction gas, then subjecting the primary reaction gas to a primary condensation, and subjecting the primary reaction gas to gas-liquid separation to obtain a primary gas phase and a primary liquid phase; wherein the methanation reaction is conducted in a slurry bed reactor; the catalyst (I) comprises catalyst particles and a protective agent encapsulating the catalyst particles, the catalyst particles containing 60-85% by weight of amorphous nickel and 15-40% by weight of a dispersant; the dispersant is selected from at least one of alumina, zirconia, magnesium oxide, and borax, wherein the zirconia has a tetragonal crystal form; and the protective agent is a hydrophobic inert liquid; (b) subjecting the primary gas phase to a first adiabatic methanation reaction in the presence of catalyst II to obtain a secondary reaction gas, and then subjecting the secondary reaction gas to a secondary condensation and gas-liquid separation to obtain a secondary gas phase and a secondary liquid phase; (c) subjecting the secondary gas phase to a second adiabatic methanation reaction in the presence of catalyst III to obtain a tertiary reaction gas, and then subjecting the tertiary reaction gas to a third-stage condensation and gas-liquid separation to obtain a methane product gas and a liquid phase substance; Wherein, the catalyst II and the catalyst III are the same as or different from each other, and are each independently a methanation catalyst.

2. The method according to claim 1, wherein In step (a), in the XRD spectrum of the catalyst I, there is a diffraction peak with a peak width greater than 5° at 2θ = 45±0.2°; And / or, in the catalyst I, the content of the protective agent is 2-4 mL relative to 1 g of the catalyst particles; and / or, 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; And / or, the method for preparing the mixture of zirconium oxide and magnesium oxide comprises: calcining a mixture obtained by mixing zirconium oxide powder and magnesium oxide powder at high temperature, wherein the high temperature calcination conditions include: a temperature of 1200-1300° C. and a time of 4-6 hours; And / or, the particle size of the dispersant is 100-400 mesh.

3. The method according to claim 2, wherein: The dispersant is selected from at least one or more of a mixture of zirconium oxide and magnesium oxide, aluminum oxide and borax.

4. The method according to claim 3, wherein: The dispersant is a mixture of zirconium oxide and magnesium oxide.

5. The method according to claim 4, wherein In the mixture, the mass ratio of zirconium oxide to magnesium oxide is (1-10):

1.

6. The method according to claim 5, wherein: In the mixture, the mass ratio of zirconium oxide to magnesium oxide is (3-6):

1.

7. The method according to claim 2, wherein: The particle size of the zirconium oxide powder and magnesium oxide powder is 100-400 mesh; and / or, the particle size of the dispersant is 120-180 mesh; And / or, the protective agent is selected from at least one of liquid paraffin, diesel and white oil.

8. The method according to claim 7, wherein: The particle size of the zirconium oxide powder and magnesium oxide powder is 120-180 mesh; And / or, the protective agent is liquid paraffin.

9. The method according to any one of claims 1 to 8, wherein: In step (a), the preparation method of the catalyst I comprises: (1) In the presence of water, the nickel precursor is contacted with a reducing agent to undergo a reduction reaction to obtain a reduction product; (2) mixing the reduction product with a dispersant in the presence of a protective agent, and allowing the resulting mixture to stand for stratification to form a stratified liquid; wherein the stratified liquid comprises an upper layer liquid and a lower layer liquid, the upper layer liquid contains the protective agent, the lower layer liquid contains water and catalyst particles, and the catalyst particles contain amorphous nickel and a dispersant; (3) Using water to adjust the pH value of the lower layer liquid in the layered liquid to 7-9, and then removing the water in the lower layer liquid, so that the protective agent wraps the catalyst particles.

10. The method according to claim 9, wherein: In step (1), the nickel precursor is selected from at least one of nickel nitrate, nickel chloride and nickel acetate; and / or, the reducing agent is a borohydride; and / or, the molar ratio of the reducing agent to the nickel precursor calculated as nickel element is (1-2.5):1; And / or, the reduction reaction conditions include: temperature of 15-25° C., time of 1-3 h; And / or, in step (2), the mass ratio of the nickel precursor to the dispersant, calculated as nickel element, is (1-10):1; and / or, the amount of the protective agent is such that the thickness of the upper layer liquid is 2-3 cm; And / or, the mixing conditions include: temperature of 20-50°C, time of 20-60 min, and rotation speed of 200-400 rpm; And / or, in step (3), water is used to adjust the pH value of the lower layer liquid to 7.5-8.

11. The method according to claim 10, wherein: The nickel precursor is nickel nitrate; and / or, the reducing agent is sodium borohydride and / or potassium borohydride; and / or, the molar ratio of the reducing agent to the nickel precursor calculated as nickel element is (1.5-2):1; And / or, the mass ratio of the nickel precursor to the dispersant, calculated as nickel element, is (1.5-5.67):

1.

12. The method according to any one of claims 1 to 8, wherein: In step (b), the catalyst II comprises a carrier and an active component and a promoter supported on the carrier, wherein the active component is nickel and the promoter is selected from oxides of La and / or Ce; and / or the carrier is selected from at least one of alumina, zirconia and magnesia spinel; And / or, the operating temperature range of the catalyst II is 260-700°C.

13. The method according to claim 12, wherein: The auxiliary agent is La oxide; and / or the carrier is magnesium aluminum spinel.

14. The method according to claim 12, wherein: Based on the total weight of the catalyst II, the content of the active component is 5-25% by weight, the content of the carrier is 75-95% by weight, and the content of the auxiliary agent in terms of oxide is 0.05-5% by weight.

15. The method according to claim 14, wherein Based on the total weight of the catalyst II, the content of the active component is 10-20% by weight, the content of the carrier is 80-90% by weight, and the content of the auxiliary agent in terms of oxide is 0.5-1.5% by weight.

16. The method according to any one of claims 1 to 8, wherein: In step (c), the catalyst III comprises a carrier and an active component and a promoter supported on the carrier, wherein the active component is nickel and the promoter is selected from oxides of La and / or Ce; and / or the carrier is selected from at least one of alumina, zirconia and magnesia spinel; And / or, the operating temperature range of the catalyst II is 260-450°C.

17. The method according to claim 16, wherein: The auxiliary agent is La oxide; and / or the carrier is alumina.

18. The method according to claim 16, wherein Based on the total weight of the catalyst III, the content of the active component is 25-50% by weight, the content of the carrier is 50-75% by weight, and the content of the auxiliary agent in terms of oxide is 0.05-5% by weight.

19. The method according to claim 18, wherein Based on the total weight of the catalyst III, the content of the active component is 35-45% by weight, the content of the carrier is 55-65% by weight, and the content of the auxiliary agent in terms of oxide is 0.5-1% by weight.

20. The method according to any one of claims 1 to 8, wherein: In step (a), the synthesis gas is a purified synthesis gas obtained by subjecting the raw synthesis gas to purification and desulfurization treatment; and / or, in step (a), the temperature of the synthesis gas is 250-350°C; and / or, the volume percentages of H2, CO and CO2 in the synthesis gas satisfy the following ratio: H2 / (CO+CO2)=3.0-3.6; and / or, the sum of the volume percentages of H2, CO and CO2 is greater than 60%; And / or, the conditions of the methanation reaction include: a reaction temperature not exceeding 340° C.; a reaction pressure of 1-4 MPa; Volume space velocity is 1500-18000h -1 ; And / or, based on the total amount of dry gas in the primary gas phase, the hydrogen content in the primary gas phase is 20-40 volume%; the methane content is 40-50 volume%; the total content of CO and CO2 does not exceed 11 volume%; and the total content of C2 and C2 and above hydrocarbons does not exceed 4500ppm.

21. The method according to claim 20, wherein The temperature of the synthesis gas is 260-300°C; and / or, the volume percentages of H2, CO and CO2 in the synthesis gas satisfy the following ratio: H2 / (CO+CO2)=3.1-3.3; and / or, the sum of the volume percentages of H2, CO and CO2 is greater than 75%; And / or, the conditions of the methanation reaction include: reaction temperature of 300-340°C; reaction pressure of 2.5-3.5 MPa; volume space velocity of 6000-15000h -1 .

22. The method according to any one of claims 1 to 8, wherein: In step (b), the temperature of the primary gas phase is 250-600°C; And / or, the conditions of the first adiabatic methanation reaction include: reaction temperature of 400-650°C; reaction pressure of 1-4 MPa; volume space velocity of 3000-18000h -1 ; And / or, based on the total amount of dry gas in the secondary gas phase, the hydrogen content in the secondary gas phase is 6-9% by volume; the methane content is 73-90% by volume; the total content of CO and CO2 does not exceed 2% by volume; and the total content of C2 and C2 hydrocarbons above does not exceed 50 ppm.

23. The method according to claim 22, wherein The temperature of the primary gas phase is 260-450°C; And / or, the conditions of the first adiabatic methanation reaction include: reaction temperature of 450-620°C; reaction pressure of 1.5-3.5 MPa; volume space velocity of 6000-15000h -1 .

24. The method according to any one of claims 1 to 8, wherein: In step (c), the temperature of the secondary gas phase is 250-400°C; And / or, the conditions of the second adiabatic methanation reaction include: reaction temperature of 260-290°C; reaction pressure of 1-4 MPa; volume space velocity of 3000-18000 h -1 ; And / or, based on the total amount of dry gas of the methane product gas, the hydrogen content in the methane product gas is 0-2 volume%; the methane content is greater than 80 volume%; the total content of CO and CO2 does not exceed 0.5 volume%; and the total content of C2 and C2+ hydrocarbons does not exceed 50 ppm.

25. The method according to claim 24, wherein The temperature of the secondary gas phase is 260-300°C; And / or, the conditions of the second adiabatic methanation reaction include: reaction temperature of 265-290°C; reaction pressure of 1.5-3.5 MPa; volume space velocity of 6000-15000h -1 .

26. A system for producing natural gas by methanation of synthesis gas, characterized in that: The system is used to implement the method described in any one of claims 1 to 25, and the system includes: at least one methanation unit, wherein the methanation unit includes a first preheater, a slurry bed reactor, a first heat exchanger, a first gas-liquid separator, a second preheater, a first adiabatic reactor, a second heat exchanger, a second gas-liquid separator, a third preheater, a second adiabatic reactor, a third heat exchanger and a third gas-liquid separator connected in sequence.

27. The system of claim 26, wherein: The methanation unit further includes a pretreatment unit, which is used to purify and desulfurize the raw gas of the synthesis gas to obtain purified synthesis gas.

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