High-pressure pipeline synthetic natural gas low-temperature catalytic reaction method

Abstract

The present invention relates to the technical field of synthetic natural gas (SNG) production. Specifically, a high-pressure pipeline-based, low-temperature catalytic reaction method for producing SNG is disclosed. In this method, a specific supported metal catalyst (such as Ni / Al2O3) is activated in a tubular reactor with a hydrogen-nitrogen mixture. The syngas feedstock is preheated, mixed with recycle gas, and then passed into a multi-stage temperature-controlled tubular reactor for a methanation reaction at 180-250°C and 10-15 MPa. The reaction products undergo multi-stage condensation to separate liquid byproducts, and unreacted gases are recycled. By limiting the feed gas composition, providing honeycomb-shaped guide plates to optimize mass transfer, and adjusting the recycle ratio using an online analyzer, this method achieves low-temperature, high-efficiency reaction, reduces energy consumption, suppresses side reactions, improves catalyst life and SNG purity, and allows for the recycling of liquid byproducts, offering significant economic and environmental benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of synthetic natural gas preparation, in particular to a high-pressure pipeline synthetic natural gas low-temperature catalytic reaction method. Background Art

[0002] Synthetic natural gas (SNG), as a clean energy source, plays a vital role in the energy transition. Currently, SNG is primarily produced industrially through methanation reactions. Traditional SNG production methods rely on high-temperature, high-pressure catalytic processes. However, high-temperature reaction conditions (typically exceeding 300°C) not only significantly increase energy consumption but also place extremely high demands on the reactor equipment's high-temperature and high-pressure resistance, significantly increasing equipment investment and maintenance costs. High temperatures also easily trigger side reactions, leading to carbon deposition and other problems, reducing catalyst activity and service life, and impacting the yield and quality of SNG. Furthermore, problems such as uneven gas mixing and difficulty in effectively controlling reaction heat in traditional processes lead to low reaction efficiency, resulting in high SNG production costs and hindering the large-scale development and widespread application of the SNG industry. Therefore, there is an urgent need to develop a process that can efficiently and stably produce SNG under low-temperature conditions to reduce energy consumption, improve product quality, and minimize equipment investment and operating costs. Summary of the Invention

[0003] (1) Technical problems solved

[0004] In view of the deficiencies of the prior art, the present invention provides a high-pressure pipeline-type low-temperature catalytic reaction method for synthesizing natural gas, which solves the problems raised in the above-mentioned background technology.

[0005] (2) Technical solution

[0006] In order to achieve the above object, the present invention discloses a high-pressure pipeline-type low-temperature catalytic reaction method for synthesizing natural gas, which comprises the following steps:

[0007] Step A: placing a supported metal catalyst in a tubular reactor and performing activation treatment with a hydrogen-nitrogen mixed gas at an activation temperature of 300-400° C., a pressure of 5-8 MPa, and an activation time of 3-5 hours;

[0008] Step B: passing the synthesis gas raw material into a preheating device, preheating it to 150-200° C., and mixing it with the circulating gas at a volume ratio of 1:0.8-1.2 to form a reaction mixture;

[0009] Step C, passing the mixed gas from step B into the tubular reactor from step A at a flow rate of 0.5-1.2 m / s, controlling the reaction pressure to 10-15 MPa and the reaction temperature to 180-250° C., to carry out a methanation catalytic reaction;

[0010] Step D: cooling the reaction product step by step through a multi-stage condensation separator, with the first stage condensation temperature being -30 to -10°C and the second stage condensation temperature being -80 to -50°C, separating the liquid by-products and collecting the gaseous synthetic natural gas;

[0011] Step E: The unreacted gas is returned to step B via a booster pump to be mixed with fresh synthesis gas for cyclic reaction, with a circulation ratio of 20%-40%.

[0012] Preferably, the supported metal catalyst in step A is one of Ni / Al2O3, Ru / ZrO2 or Co-Mo / SiO2, the catalyst particle size is 0.5-2 mm, and the specific surface area is 200-400 m2 / g.

[0013] Preferably, the activation treatment in step A specifically includes:

[0014] a) Purge the reactor with nitrogen until the oxygen content is less than 50 ppm;

[0015] b) Raise the temperature to the target temperature at a rate of 2-4°C / min and activate at constant temperature;

[0016] c) After activation, purge with inert gas to room temperature.

[0017] Preferably, the H2 / CO molar ratio of the synthesis gas feed in step B is 2.8-3.2, the sulfur content is ≤0.1ppm, and the oxygen content is ≤10ppm.

[0018] Preferably, the tubular reactor in step C is a multi-stage temperature control structure, with the temperature of the front section set to 180-200°C, the middle section to 210-230°C, and the final section to 240-250°C. The temperature difference between each section is adjusted by an external jacket heat exchanger.

[0019] Preferably, in step D, the first-stage condenser uses ethylene glycol aqueous solution as the refrigerant, and the second-stage condenser uses liquid nitrogen for indirect cooling.

[0020] Preferably, an online analyzer is provided in the return path of the circulating gas in step E to monitor the concentrations of H2 and CO in real time and to provide feedback to adjust the circulation ratio.

[0021] Preferably, in step a, the nitrogen purge flow rate is 10-15 L / min, and the purge time is 30-60 min.

[0022] Preferably, in step C, a honeycomb guide plate is provided in the reactor, the porosity is 60-80%, and the guide plate spacing is 50-100 mm.

[0023] Preferably, the liquid by-product separated in step D is subjected to reduced pressure distillation to recover C5+ hydrocarbons, with the distillation temperature being 80-120° C. and the pressure being 0.1-0.5 MPa.

[0024] (3) Beneficial technical effects

[0025] In terms of energy conservation and consumption reduction, by controlling the reaction temperature in the low temperature range of 180-250℃, energy consumption is greatly reduced compared with traditional high-temperature processes, and energy consumption costs are reduced; the tubular reactor with a multi-stage temperature control structure has different temperatures set in the front, middle and end sections, and the temperature difference between each section is adjusted by an external jacket heat exchanger, which can more accurately control the reaction process and enable the reaction to proceed at the most suitable temperature, avoiding unnecessary energy consumption caused by excessively high temperature and further improving energy utilization efficiency.

[0026] In terms of catalyst performance optimization, specific supported metal catalysts (such as Ni / Al2O3, Ru / ZrO2 or Co-Mo / SiO2) are used, and their particle size (0.5-2mm) and specific surface area (200-400m² / g) are limited. Combined with activation treatment with hydrogen and nitrogen mixed gas at 300-400℃, 5-8MPa, and 3-5h, the activity and selectivity of the catalysts are significantly improved, the occurrence of side reactions is effectively suppressed, carbon deposition is reduced, the service life of the catalysts is extended, and the cost of catalyst replacement is reduced.

[0027] In terms of improving reaction efficiency, the synthesis gas raw material and the circulating gas are mixed in a volume ratio of 1:0.8-1.2, with an inlet flow rate of 0.5-1.2m / s, so that the reaction mixture can fully contact the catalyst in the tubular reactor, thereby increasing the reaction rate; the honeycomb guide plates installed in the reactor have a porosity of 60-80% and a guide plate spacing of 50-100mm, which optimizes the gas flow path, enhances the gas-solid mass transfer effect, and further improves the reaction efficiency.

[0028] In terms of product quality assurance, the H2 / CO molar ratio (2.8 - 3.2), sulfur content (≤0.1ppm), and oxygen content (≤10ppm) of the synthesis gas feedstock are strictly controlled, providing ideal reaction conditions for the methanation reaction, reducing the interference of impurities on the reaction, and improving the purity of the synthetic natural gas. The multi-stage condensation separator cools the reaction products step by step, with the first stage condensation temperature ranging from -30 to -10°C and the second stage condensation temperature ranging from -80 to -50°C. This can effectively separate liquid by-products and collect high-purity gas-phase synthetic natural gas. At the same time, the separated liquid by-products are recovered through vacuum distillation to recover C5+ hydrocarbons, realizing the comprehensive utilization of resources.

[0029] In terms of process stability and intelligent control, an online analyzer is installed in the circulating gas return path to monitor the H2 and CO concentrations in real time and adjust the circulation ratio through feedback. This allows the reaction process to automatically adjust according to changes in gas concentration, ensuring that the reaction is always in the optimal state, thereby improving the stability and reliability of the process. At the same time, the parameters of each step in this method are clear and controllable, which facilitates precise control and large-scale application in industrial production, providing a strong guarantee for the stable and efficient production of synthetic natural gas. DETAILED DESCRIPTION

[0030] To facilitate understanding of the present invention, the present invention will be described in more detail below. Preferred embodiments of the present invention are provided below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present invention.

[0031] Example 1:

[0032] Step A: A supported metal catalyst, Ni / Al2O3, was placed in a tubular reactor. Nitrogen was first purged at 10 L / min for 60 minutes until the oxygen content was <50 ppm. The reactor was then heated to 300°C at a rate of 2°C / min and activated at a constant temperature of 5 MPa for 3 hours. After activation, the reactor was purged with inert gas to room temperature. The catalyst had a particle size of 0.5 mm and a specific surface area of 200 m² / g.

[0033] Step B: Synthesis gas with a H2 / CO molar ratio of 2.8, a sulfur content of ≤0.1 ppm, and an oxygen content of ≤10 ppm is introduced into a preheating device, preheated to 150°C, and mixed with circulating gas at a volume ratio of 1:0.8 to form a reaction mixture.

[0034] Step C: The mixed gas from Step B was passed into the tubular reactor from Step A at a flow rate of 0.5 m / s. The tubular reactor had a multi-stage temperature control structure, with the front section set at 180°C, the middle section at 210°C, and the rear section at 240°C. The temperature difference between the sections was adjusted using an external jacketed heat exchanger. The reaction pressure was controlled at 10 MPa for the methanation catalytic reaction. The reactor was equipped with honeycomb-shaped baffles with a porosity of 60% and a spacing of 50 mm.

[0035] Step D: The reaction product is cooled step by step through a multi-stage condensation separator. The first stage condensation temperature is -30°C, and ethylene glycol aqueous solution is used as the refrigerant; the second stage condensation temperature is -80°C, and liquid nitrogen is used for indirect cooling to separate the liquid by-products and collect the gaseous synthetic natural gas.

[0036] Step E: The unreacted gas is returned to Step B via a booster pump for mixing with fresh synthesis gas for a cyclic reaction. An online analyzer is installed along the return path of the recycled gas to monitor H2 and CO concentrations in real time and adjust the recycle ratio based on feedback, which is set at 20%. The separated liquid by-products are then distilled under reduced pressure to recover C5+ hydrocarbons at 80°C and 0.1 MPa.

[0037] Example 2:

[0038] Step A: A supported metal catalyst, Ru / ZrO2, was placed in a tubular reactor. Nitrogen was purged at a flow rate of 12 L / min for 45 minutes to reduce the oxygen content to <50 ppm. The reactor was then heated to 350°C at a rate of 3°C / min and activated at this temperature for 4 hours at a pressure of 6 MPa. After activation, the reactor was purged with inert gas to room temperature. The catalyst had a particle size of 1 mm and a specific surface area of 300 m² / g.

[0039] Step B: A synthesis gas feedstock having an H2 / CO molar ratio of 3.0, a sulfur content ≤0.1 ppm, and an oxygen content ≤10 ppm is introduced into a preheating device, preheated to 175°C, and mixed with the circulating gas at a volume ratio of 1:1 to obtain a reaction mixture.

[0040] Step C: The mixed gas from Step B was introduced into the tubular reactor from Step A at a flow rate of 0.8 m / s. The temperatures in the front section of the tubular reactor were set at 190°C, the middle section at 220°C, and the rear section at 245°C. The reaction pressure was controlled at 12 MPa for catalytic methanation. The honeycomb baffles in the reactor had a porosity of 70% and a spacing of 75 mm.

[0041] Step D: The reaction product is passed through a multi-stage condensation separator, with the first stage condensation temperature set at -20°C and cooled with ethylene glycol aqueous solution; the second stage condensation temperature is set at -70°C and indirectly cooled with liquid nitrogen to separate the liquid by-products and collect the gaseous synthetic natural gas.

[0042] Step E: The unreacted gas is returned to Step B via a booster pump. An online analyzer on the return path monitors H2 and CO concentrations in real time, adjusting the recycle ratio to 30%. The liquid byproduct is subjected to vacuum distillation to recover C5+ hydrocarbons at 90°C and 0.2 MPa.

[0043] Example 3:

[0044] Step A: Place the supported metal catalyst Co-Mo / SiO2 into a tubular reactor and purge the reactor with nitrogen at a flow rate of 15 L / min for 30 minutes to bring the oxygen content to standard. The temperature is then raised to 400°C at a rate of 4°C / min and activated at a pressure of 8 MPa for 5 hours. After activation, the reactor is purged with inert gas to room temperature. The catalyst has a particle size of 2 mm and a specific surface area of 400 m² / g.

[0045] Step B: Synthesis gas raw material with an H2 / CO molar ratio of 3.2 and sulfur and oxygen contents meeting the requirements is preheated to 200°C and mixed with circulating gas at a volume ratio of 1:1.2 to form a reaction mixture.

[0046] Step C: The mixed gas from Step B was introduced into the tubular reactor from Step A at a flow rate of 1.2 m / s. The reactor temperature was maintained at 200°C in the front section, 230°C in the middle section, and 250°C in the rear section. The reaction pressure was 15 MPa for catalytic methanation. The honeycomb baffles within the reactor had a porosity of 80% and a spacing of 100 mm.

[0047] Step D: The reaction product is condensed in multiple stages, with the first stage being cooled with -10°C ethylene glycol aqueous solution and the second stage being indirectly cooled with -50°C liquid nitrogen, and the liquid by-products are separated and the gas phase synthetic natural gas is collected.

[0048] Step E: The unreacted gas is returned to Step B and monitored and adjusted with an online analyzer at a recycle ratio of 40%. The liquid by-product is subjected to vacuum distillation at 120°C and 0.5 MPa to recover C5+ hydrocarbons.

[0049] Example 4:

[0050] Step A: Using Ni / Al2O3 catalyst, nitrogen purging and other operations are the same as in Example 1, activation temperature is 320°C, pressure is 7 MPa, activation time is 3.5 h, catalyst particle size is 0.8 mm, and specific surface area is 250 m2 / g.

[0051] Step B: The synthesis gas raw material H2 / CO molar ratio is 2.9, and other conditions are the same as those in Example 2. It is preheated to 160°C and mixed with the circulating gas in a volume ratio of 1:0.9.

[0052] Step C: The mixed gas is introduced into the reactor at a flow rate of 0.6 m / s, with the temperature of the front section being 185°C, the middle section being 215°C, the end section being 242°C, and the pressure being 11 MPa. The porosity of the guide plates in the reactor is 65%, and the spacing is 60 mm.

[0053] Step D: The first stage condensation temperature is -25°C, the second stage is -75°C, and the cooling method is the same as in Example 2.

[0054] Step E: The circulation ratio is 25%, the distillation temperature of the liquid by-product is 85° C., and the pressure is 0.15 MPa.

[0055] Example 5:

[0056] Step A: Ru / ZrO2 catalyst, nitrogen purge, etc. are similar to Example 2, activation temperature 360°C, pressure 7 MPa, activation 4.5 h, catalyst particle size 1.2 mm, specific surface area 320 m² / g.

[0057] Step B: Synthesis gas raw material H2 / CO molar ratio is 3.1, preheated to 180°C, and mixed with recycle gas in a volume ratio of 1:1.1.

[0058] Step C: The mixed gas is introduced into the reactor at a flow rate of 0.9 m / s, with the front section at 195°C, the middle section at 225°C, the end section at 248°C, the pressure at 13 MPa, the porosity of the guide plates at 72%, and the spacing at 80 mm.

[0059] Step D: Condensation temperature of the first stage is -15℃, the second stage is -65℃, and the cooling method remains unchanged.

[0060] Step E: The circulation ratio is 35%, the distillation temperature of the liquid by-product is 100° C., and the pressure is 0.3 MPa.

[0061] Example 6:

[0062] Step A: Co-Mo / SiO2 catalyst, nitrogen purge, etc. as in Example 3, activation temperature 380°C, pressure 6 MPa, activation 4 h, catalyst particle size 1.5 mm, specific surface area 350 m² / g.

[0063] Step B: Synthesis gas raw material H2 / CO molar ratio is 3.0, preheated to 190°C, and mixed with circulating gas in a volume ratio of 1:1.

[0064] Step C: The mixed gas is introduced into the reactor at a flow rate of 1.0 m / s, with the front section at 200°C, the middle section at 230°C, the final section at 250°C, the pressure at 14 MPa, the porosity of the guide plates at 75%, and the spacing at 90 mm.

[0065] Step D: Condensation temperature of the first stage is -20℃, the second stage is -70℃, and the cooling method is the same as before.

[0066] Step E: The circulation ratio is 32%, the distillation temperature of the liquid by-product is 110° C., and the pressure is 0.4 MPa.

[0067] Comparative Example 1:

[0068] Step A: The supported metal catalyst Ni / Al2O3 is placed in a tubular reactor without activation treatment.

[0069] Step B: Synthesis gas with a H2 / CO molar ratio of 2.8, a sulfur content of ≤0.1 ppm, and an oxygen content of ≤10 ppm is introduced into a preheating device, preheated to 150°C, and mixed with circulating gas at a volume ratio of 1:0.8 to form a reaction mixture.

[0070] Step C: The mixed gas from Step B was introduced into the tubular reactor from Step A at a flow rate of 0.5 m / s. The tubular reactor had a multi-stage temperature control structure, with the front section set at 180°C, the middle section at 210°C, and the rear section at 240°C. The temperature difference between the sections was adjusted using an external jacketed heat exchanger. The reaction pressure was controlled at 10 MPa for the catalytic methanation reaction. No honeycomb baffles were installed in the reactor.

[0071] Step D: The reaction product is cooled step by step through a multi-stage condensation separator. The first stage condensation temperature is -30°C, and ethylene glycol aqueous solution is used as the refrigerant; the second stage condensation temperature is -80°C, and liquid nitrogen is used for indirect cooling to separate the liquid by-products and collect the gaseous synthetic natural gas.

[0072] Step E: The unreacted gas is returned to Step B via a booster pump for mixing with fresh synthesis gas for a cyclic reaction. The return path for the recycled gas is not equipped with an online analyzer, and the recycle ratio is set at 20%. The separated liquid by-products are then distilled under reduced pressure to recover C5+ hydrocarbons at 80°C and 0.1 MPa.

[0073] Comparative Example 2:

[0074] Step A: A supported metal catalyst, Ru / ZrO2, was placed in a tubular reactor. Nitrogen was purged at a flow rate of 12 L / min for 45 minutes to reduce the oxygen content to <50 ppm. The reactor was then heated to 350°C at a rate of 3°C / min and activated at this temperature for 4 hours at a pressure of 6 MPa. After activation, the reactor was purged with inert gas to room temperature. The catalyst had a particle size of 1 mm and a specific surface area of 300 m² / g.

[0075] Step B: Synthesis gas with a H2 / CO molar ratio of 3.0, a sulfur content ≤ 0.1 ppm, and an oxygen content ≤ 10 ppm is introduced into a preheating device and preheated to 175°C without mixing with the recycle gas.

[0076] Step C: The syngas from Step B was introduced into the tubular reactor from Step A at a flow rate of 0.8 m / s. The temperatures in the front section of the tubular reactor were set at 190°C, the middle section at 220°C, and the rear section at 245°C. The reaction pressure was controlled at 12 MPa for catalytic methanation. The honeycomb baffles in the reactor had a porosity of 70% and a spacing of 75 mm.

[0077] Step D: The reaction product is passed through a multi-stage condensation separator, with the first stage condensation temperature set at -20°C and cooled with ethylene glycol aqueous solution; the second stage condensation temperature is set at -70°C and indirectly cooled with liquid nitrogen to separate the liquid by-products and collect the gaseous synthetic natural gas.

[0078] Step E: No unreacted gas recycling step is provided. The liquid by-product is subjected to reduced pressure distillation to recover C5+ hydrocarbons at a distillation temperature of 90° C. and a pressure of 0.2 MPa.

[0079] Comparative Example 3:

[0080] Step A: Place the supported metal catalyst Co-Mo / SiO2 into a tubular reactor and purge the reactor with nitrogen at a flow rate of 15 L / min for 30 minutes to bring the oxygen content to standard. The temperature is then raised to 400°C at a rate of 4°C / min and activated at a pressure of 8 MPa for 5 hours. After activation, the reactor is purged with inert gas to room temperature. The catalyst has a particle size of 2 mm and a specific surface area of 400 m² / g.

[0081] Step B: Synthesis gas raw material with an H2 / CO molar ratio of 3.2 and sulfur and oxygen contents meeting the requirements is preheated to 200°C and mixed with circulating gas at a volume ratio of 1:1.2 to form a reaction mixture.

[0082] Step C: The mixed gas from Step B was introduced into the tubular reactor from Step A at a flow rate of 1.2 m / s. The tubular reactor did not utilize multi-stage temperature control, but was maintained at a constant temperature of 260°C and a reaction pressure of 15 MPa for the methanation catalytic reaction. The honeycomb-shaped guide plates within the reactor had a porosity of 80% and were spaced 100 mm apart.

[0083] Step D: The reaction product is condensed in multiple stages, with the first stage being cooled with -10°C ethylene glycol aqueous solution and the second stage being indirectly cooled with -50°C liquid nitrogen, and the liquid by-products are separated and the gas phase synthetic natural gas is collected.

[0084] Step E: Unreacted gas is returned to Step B. The online analyzer in the recycle gas return path is not monitored and adjusted in real time, and the recycle ratio is fixed at 40%. The liquid byproduct is distilled under reduced pressure at 120°C and 0.5 MPa to recover C5+ hydrocarbons.

[0085] Comparative Table of Reaction Effects of Examples and Comparative Examples:

[0086]

[0087] As can be seen from the data in the table above, Examples 1-6 achieved high methane yields and relatively low byproduct content due to the rational activation of the catalysts, the use of recycle gas mixing, and multi-stage temperature control. However, Comparative Example 1, in which the catalyst was not activated, resulted in insufficient catalyst activity, a significant decrease in methane yield, and an increase in byproducts. Comparative Example 2, in which recycle gas was not used, prevented the synthesis gas from fully reacting, resulting in a significant decrease in methane yield and an increase in byproduct content. Comparative Example 3 employed a constant temperature, which hindered the optimization of the reaction at different stages, thus affecting methane yield and increasing byproduct content.

[0088] Comparison table of performance of different catalysts:

[0089]

[0090] From the data in this table, we can see that the average methane yield of Ru / ZrO2 catalyst is slightly higher than that of Ni / Al2O3 and Co-Mo / SiO2 catalysts, and the average by-product content is relatively low, indicating that in this reaction system, Ru / ZrO2 catalyst has certain advantages in comprehensive performance, but the performance differences among the three catalysts are not particularly large, and they can all meet the reaction requirements of synthetic natural gas to a certain extent.

[0091] Comparison table of reaction effects of different circulation ratios:

[0092]

[0093] The table shows that, within a certain range, as the recycle ratio increases, the methane yield initially increases and then slightly decreases. At a recycle ratio of 30%, the methane yield is relatively high, while the byproduct content is relatively low. This indicates that a suitable recycle ratio allows unreacted gas to fully participate in the reaction, improving syngas utilization. However, an excessively high recycle ratio may lead to some adverse factors, affecting the reaction effect.

[0094] Although the embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A high-pressure pipeline-type low-temperature catalytic reaction method for synthesizing natural gas, characterized in that: The method comprises the following steps: Step A: placing a supported metal catalyst in a tubular reactor and performing activation treatment with a hydrogen-nitrogen mixed gas at an activation temperature of 300-400° C., a pressure of 5-8 MPa, and an activation time of 3-5 hours; Step B: passing the synthesis gas raw material into a preheating device, preheating it to 150-200° C., and mixing it with the circulating gas at a volume ratio of 1:0.8-1.2 to form a reaction mixture; Step C, passing the mixed gas from step B into the tubular reactor of step A at a flow rate of 0.5-1.2 m / s, controlling the reaction pressure to 10-15 MPa and the reaction temperature to 180-250° C., to carry out a methanation catalytic reaction; the tubular reactor has a multi-section temperature control structure, with the temperature of the front section set to 180-200° C., the middle section to 210-230° C., and the rear section to 240-250° C., and the temperature difference between each section is adjusted by an external jacket heat exchanger; Step D: cooling the reaction product step by step through a multi-stage condensation separator, with the first stage condensation temperature being -30 to -10°C and the second stage condensation temperature being -80 to -50°C, separating the liquid by-products and collecting the gaseous synthetic natural gas; Step E: returning the unreacted gas to step B via a booster pump for mixing with fresh synthesis gas for cyclic reaction at a circulation ratio of 20%-40%; The supported metal catalyst in step A is one of Ni / Al2O3, Ru / ZrO2 or Co-Mo / SiO2, with a catalyst particle size of 0.5-2 mm and a specific surface area of 200-400 m2 / g; The activation treatment of step A specifically includes: a) Purge the reactor with nitrogen until the oxygen content is less than 50 ppm; b) Raise the temperature to the target temperature at a rate of 2-4°C / min and activate at constant temperature; c) After activation, purge with inert gas to room temperature.

2. The high-pressure pipeline synthetic natural gas low-temperature catalytic reaction method according to claim 1, characterized in that: The H2 / CO molar ratio of the synthesis gas feed in step B is 2.8-3.2, the sulfur content is ≤0.1ppm, and the oxygen content is ≤10ppm.

3. The high-pressure pipeline synthetic natural gas low-temperature catalytic reaction method according to claim 1, characterized in that: In step D, the first-stage condenser uses ethylene glycol aqueous solution as the refrigerant, and the second-stage condenser uses liquid nitrogen for indirect cooling.

4. The high-pressure pipeline synthetic natural gas low-temperature catalytic reaction method according to claim 1, characterized in that: In step E, an online analyzer is set up in the return path of the circulating gas to monitor the H2 and CO concentrations in real time and provide feedback to adjust the circulation ratio.

5. The high-pressure pipeline synthetic natural gas low-temperature catalytic reaction method according to claim 1, characterized in that: In step a, the nitrogen purge flow rate is 10-15 L / min, and the purge time is 30-60 min.

6. The high-pressure pipeline synthetic natural gas low-temperature catalytic reaction method according to claim 1, characterized in that: In step C, a honeycomb guide plate is set in the reactor, with a porosity of 60-80% and a guide plate spacing of 50-100 mm.

7. The high-pressure pipeline synthetic natural gas low-temperature catalytic reaction method according to claim 1, characterized in that: The liquid by-product separated in step D is subjected to reduced pressure distillation to recover C5+ hydrocarbons at a distillation temperature of 80-120° C. and a pressure of 0.1-0.5 MPa.

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