A process for synthesizing methanol from carbon dioxide in an adiabatic manner

Abstract

The present invention relates to a process for synthesizing methanol from carbon dioxide in an adiabatic manner. The process comprises the following steps: first, purifying and pre-purifying the gas rich in CO2 to obtain a CO2-rich gas with a CO2 content of ≥98%; then mixing the gas with pure hydrogen to obtain feed gas A, and compressing and deeply purifying feed gas A; the deeply purified feed gas A enters a multi-stage adiabatic methanol synthesis reactor with an external circulation to carry out the reactions of methanol synthesis and reverse water-gas shift; the gas at the outlet of the last-stage adiabatic methanol synthesis reactor is subjected to heat exchange and gas-liquid separation to obtain liquid-phase crude methanol and gas-phase B, etc.; this process utilizes the reactions of coupling the endothermic reverse water-gas shift and the exothermic methanol synthesis in an adiabatic reactor for heat coupling, and at the same time, part of the oxygen atoms in CO2 can be converted into H2O in advance and removed, thereby greatly reducing the H2O content in the isothermal methanol synthesis tower, effectively improving the total conversion rate of CO2, and reducing the investment and energy consumption.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical engineering, and relates to a process for producing methanol from a mixed gas containing CO2, CO, and H2, specifically an adiabatic process for synthesizing methanol from carbon dioxide. Background Art

[0002] It is expected that the global carbon dioxide emissions will reach 37.5 billion tons in 2022. Although the total carbon dioxide emissions in China have decreased, the global share will still reach more than 30%. Therefore, the development of carbon dioxide capture and utilization (CCUS) technology has very important practical significance. Coupled with renewable energy such as solar energy, wind energy, and biomass, hydrogenation of carbon dioxide to methanol has opened up a new way for the green conversion and utilization of carbon dioxide to produce high-value chemicals with a significant carbon reduction effect.

[0003] In recent years, CRI Company in Iceland has developed the ETL green methanol process technology, and built an industrial demonstration device for hydrogenation of carbon dioxide to methanol with a production capacity of 4,000 tons / year in Iceland in 2012 and expanded production in 2015. In September 2022, Anyang Shunbao New Carbon Materials Co., Ltd., which uses the ETL technology of CRI Company in Iceland, put into full operation the project of producing green and low-carbon methanol from CO2 and co-producing LNG. The methanol production scale is 110,000 tons / year. It is the first domestic industrial device for producing methanol from carbon dioxide and also the largest global project for producing green methanol from carbon dioxide.

[0004] In recent years, the technology for hydrogenation of carbon dioxide to methanol independently developed in China has also made great progress. On January 17, 2020, the world's first demonstration project for synthesizing solar fuels with a scale of 1,000 tons, undertaken and completed by the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, was successfully commissioned in the Green Chemical Industry Park of Lanzhou New Area. In 2020, CNOOC Ocean Oil Fudao Co., Ltd., the Shanghai Advanced Research Institute of the Chinese Academy of Sciences, and China Chengda Engineering Co., Ltd. jointly developed the "Key Technology and Engineering Demonstration for Hydrogenation of Carbon Dioxide to Methanol", and built an industrial test device with a production capacity of 5,000 tons / year in July 2020, and passed the on-site 72-hour assessment and acceptance organized by the China Petroleum and Chemical Industry Federation.

[0005] At present, the economic efficiency of the technology for hydrogenation of carbon dioxide to methanol is still at a relatively low level, which limits its large-scale industrial application. The main reason is that CO2 is a chemically inert molecule thermodynamically, and usually high-energy H2 needs to be introduced to promote the activation of CO2. Therefore, compared with the traditional reaction of hydrogenation of CO to synthesize methanol, the conversion efficiency of hydrogenation of CO2 is relatively low under the catalysis of existing copper-based catalysts, which leads to a significant increase in the comprehensive energy consumption of methanol production.

[0006] In the existing CO2 hydrogenation to methanol process, most use one or more isothermal methanol synthesis towers, that is, water-cooled towers or air-cooled towers. To increase the methanol production, it is necessary to significantly increase the methanol synthesis recycle ratio. The increase in the recycle gas volume will inevitably lead to an increase in the energy consumption of the device and the production cost of methanol. CN202122493444.1 discloses a multi-stage synthesis of carbon dioxide to methanol system, which uses a multi-stage isothermal methanol synthesis tower for the process of carbon dioxide hydrogenation to methanol, realizing the efficient conversion of carbon dioxide to synthesize methanol, improving the technical economy of methanol synthesis, and also increasing the investment in the methanol device to a certain extent.

[0007] The production of methanol from carbon dioxide is to convert CO2 into methanol and water through the methanol synthesis reaction and the reverse water-gas shift reaction (RWGS), that is:

[0008] CO2 + 3H2 → CH3OH + H2O △H 298 0 = -49.43 kJ / mol (1)

[0009] CO2 + H2 → CO + H2O △H 298 0 = 41.13 kJ / mol (2)

[0010] CO + 2H2 →CH3OH △H 298 0 = -90.56kJ / mol (3)

[0011] The hydrogenation of CO2 to methanol is an exothermic reaction, and low temperature and high pressure are favorable for the forward reaction. While RWGS is an endothermic reaction, and high temperature promotes the formation of CO from CO2. RWGS will produce CO, and CO hydrogenation generates methanol.

[0012] Therefore, in order to further improve the technical economy of CO2 hydrogenation to methanol to achieve its large-scale industrial application, in addition to improving the performance level of the CO2 hydrogenation to methanol catalyst, it is also necessary to further optimize the CO2 hydrogenation to methanol process, couple the two CO2 hydrogenation reaction processes of CO2 hydrogenation to methanol and CO2 reverse water-gas shift reaction, so as to achieve the efficient conversion of CO2 to synthesize methanol and significantly reduce the comprehensive energy consumption and device investment of methanol production. Summary of the Invention

[0013] The purpose of the present invention is to provide a process for adiabatic synthesis of methanol from carbon dioxide in view of the problems existing in the prior art. This process can achieve a high conversion rate of the reaction of CO2 with H2 to synthesize methanol and requires less investment.

[0014] In order to achieve the above-mentioned invention purpose, the technical solution adopted by the present invention is as follows:

[0015] A process for synthesizing methanol from carbon dioxide in an adiabatic manner, the process comprising the following steps:

[0016] First, a gas rich in CO2 (such as flue gas, lime kiln gas, blast furnace gas, etc.) is purified and pre-purified to obtain a CO2-rich gas with a CO2 content of greater than or equal to 98%. Hydrogen obtained from electrolyzed water, or hydrogen obtained by purifying industrial by-product gases such as by-product hydrogen from a PDH unit, coke oven gas, and semi-coke tail gas, is mixed with the CO2-rich gas to obtain feed gas A, which is then compressed and deeply purified. The deeply purified feed gas A is heat-exchanged and then enters an adiabatic methanol synthesis reactor with a multi-stage external circulation to carry out the reactions of methanol synthesis and reverse water-gas shift. The gas at the outlet of the last-stage adiabatic methanol synthesis reactor is heat-exchanged and gas-liquid separated. The liquid phase obtains crude methanol, and the gas phase B is compressed and then sent to an isothermal methanol synthesis reactor. The deep methanol synthesis reaction continues in the isothermal methanol synthesis reactor. After the material undergoes the methanol synthesis reaction, it is heat-exchanged and gas-liquid separated again. The liquid phase obtains crude methanol, and the gas phase obtains material gas phase C. Finally, all the crude methanol is sent to a methanol distillation system and refined to obtain a refined methanol product. Part of the gas phase C is sent to a hydrogen recovery device, and the recovered hydrogen is returned as feed gas.

[0017] As a preferred embodiment in this application, the deep purification means that the feed gas A is deeply purified of sulfides and chlorides through a superfine purifier, and the total sulfur in the feed gas is removed to less than 0.01 ppm, and the total chlorine is less than 0.01 ppm. The deep purification agent is preferably the CNJ-5P type superfine purification agent of Southwest Research and Design Institute of Chemical Industry Co., Ltd.

[0018] As a preferred embodiment in this application, the multi-stage adiabatic methanol synthesis reaction with external circulation means that a multi-stage adiabatic methanol synthesis reactor is used to carry out the methanol synthesis reaction of CO2 and the reverse water-gas shift reaction. Gas-liquid separation is carried out between each stage of the methanol synthesis reactor. The gas phase goes to the next-stage methanol synthesis reactor, and the liquid phase is liquefied into crude methanol and sent to the distillation system.

[0019] As a preferred embodiment in this application, the number of stages of the multi-stage adiabatic methanol synthesis reaction is 1 to 3 stages, more preferably 1 stage.

[0020] As a preferred embodiment in this application, the hydrogen in the reactor before startup is used to ensure that the molar ratio of hydrogen to carbon dioxide entering the adiabatic methanol synthesis reactor is 4 to 12.

[0021] As a preferred embodiment in this application, the inlet temperature of the adiabatic methanol synthesis reactor is 200 to 350 °C, the outlet temperature is 260 to 330 °C, the pressure is 1.5 to 5 MPa.A, and the space velocity is 3000 to 20000 h -1 .

[0022] As a preferred embodiment of the present application, the catalyst filled in the adiabatic methanol reactor is a mixture of a copper-based wide-temperature shift catalyst and a methanol synthesis catalyst, and the mixing ratio by volume is 0.2 to 5:1; the copper-based wide-temperature shift catalyst is preferably the CNGC-2 type copper-based wide-temperature shift catalyst of Southwest Research and Design Institute of Chemical Industry Co., Ltd.

[0023] As a preferred embodiment of the present application, gas phase B is compressed to a pressure of 6 to 10 MPa.A after compression, and then a low-pressure isothermal methanol synthesis reaction is carried out.

[0024] Compared with the prior art, the positive effects of the present invention are reflected in:

[0025] By using a multi-stage adiabatic methanol synthesis reaction process with external circulation, the endothermic reverse shift reaction and the exothermic methanol synthesis reaction are coupled in an adiabatic reactor, realizing heat coupling. The reverse shift reaction can be carried out without external heating. Part of the oxygen atoms in CO2 can be converted into H2O in advance and removed, thus greatly reducing the H2O content in the isothermal methanol synthesis tower, effectively improving the total conversion rate of CO2, and reducing investment and energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic process flow diagram of an adiabatic process for synthesizing methanol from carbon dioxide according to the present invention.

[0027] SPECIFIC EMBODIMENTS EXAMPLES:

[0028] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with specific embodiments. However, this should not be construed as limiting the scope of the above-mentioned subject matter of the present invention to the following embodiments. Without departing from the above-mentioned technical idea of the present invention, various substitutions and changes made according to ordinary technical knowledge and customary means in the art should be included within the scope of the present invention.

[0029] A process for adiabatically synthesizing methanol from carbon dioxide includes the following process steps (see Figure 1 ):

[0030] First, the gas rich in CO2 (such as flue gas, lime kiln gas, blast furnace gas, etc.) is purified and pre-purified to obtain a CO2-rich gas with a CO2 content of greater than or equal to 98% and a total sulfur content of less than 1 ppm. Then this gas is mixed with pure hydrogen or hydrogen-rich gas to obtain feed gas A, which is then compressed and deeply purified. The deeply purified feed gas A is further compressed and then enters an adiabatic methanol synthesis reactor with multiple stages and an external circulation to carry out the reactions of methanol synthesis and reverse shift. The gas at the outlet of the last-stage adiabatic methanol synthesis reactor is subjected to heat exchange and gas-liquid separation. The liquid phase obtains crude methanol, and the gas phase B is compressed and then sent to an isothermal methanol synthesis reactor. In the isothermal methanol synthesis reactor, the methanol synthesis reaction continues. After heat exchange and gas-liquid separation, the liquid phase obtains crude methanol, and the gas phase obtains gas phase C. Finally, all the crude methanol is sent to the methanol distillation system and refined to obtain refined methanol products. Part of gas phase C is sent to the recycle compressor, and the rest is sent to the hydrogen recovery device. In the hydrogen recovery device, the recovered hydrogen is returned as feed gas, and the rest goes to the tail gas treatment device.

[0031] In this article, for gases involving ratios or percentages, they are calculated based on the gas volume.

[0032] Example 1:

[0033] The process flow schematic diagram of this example is shown in Figure 1 .

[0034] The flow rate of CO2-rich is 40000 Nm 3 / h, which is material 1, and the specific composition is shown in Table 2-1. The flow rate of pure hydrogen is 120000 Nm 3 / h, which is material 2, as shown in Table 2-2 specifically;

[0035] Table 2-1 Composition of CO2-rich (vol%)

[0036] Name <![CDATA[CO2]]> <![CDATA[N2]]> Content / % 99.8 0.2

[0037] Table 2-2 Composition of hydrogen (vol%)

[0038] Name <![CDATA[H2]]> <![CDATA[N2]]> Content / % 99.9 0.1

[0039] (1) CO2 purification and pre-purification

[0040] First, the blast furnace gas rich in CO2 is purified and pre-purified to obtain a CO2 gas with a CO2 content of greater than or equal to 98% and a total sulfur content of less than 1 ppm, which is material 1. The hydrogen from the outside is material 2. Then this part of the CO2 gas is mixed with hydrogen, and the ratio of the flow rate of the CO2 gas to the flow rate of the hydrogen is 1:3 to obtain material A.

[0041] (2) Compression and deep purification

[0042] The mixed gas mixture is first pressurized to 5.1 MPa.A by a centrifugal (or reciprocating) compressor, and the final stage compression is not cooled and directly enters the deep purification unit.

[0043] The deep purification unit uses a deep purification agent mainly composed of copper to deeply remove toxic substances such as sulfur and chlorine in the mixed gas. The total sulfur content is less than 0.01 ppm, and the chlorine content is less than 0.01 ppm, obtaining Material 3.

[0044] (3) Adiabatic methanol synthesis unit

[0045] An adiabatic methanol synthesis process with a first-stage external circulation is adopted. The catalyst filled in the adiabatic methanol reactor is a mixture of a copper-based wide-temperature shift catalyst and a methanol synthesis catalyst, and the mixing ratio by volume is 0.2:1. The molar ratio of CO2 to H2 in Material 4 is 12, the temperature is 280 °C, and the pressure is 5.0 MPa.A. After passing through the adiabatic methanol reactor, Material 5 is obtained, with a temperature of 330 °C and a pressure of 4.90 MPa.A.

[0046] (4) Isothermal methanol synthesis unit

[0047] An isothermal methanol synthesis process with circulation is adopted. The inlet material of the isothermal methanol synthesis reactor is Material 6, with a temperature of 210 °C and a pressure of 10 MPa.A. After passing through the isothermal methanol reactor, Material 7 is obtained, with a temperature of 250 °C and a pressure of 9.80 MPa.A, and the main component is methanol.

[0048] (5) The gaseous material from the isothermal methanol synthesis unit, part goes to the recycle compressor, and the rest goes to a high-pressure pressure swing adsorption or membrane separation device for hydrogen recovery. The recovered hydrogen is mixed with Gas Phase B and then sent to the adiabatic methanol synthesis reactor.

[0049] In this example, the methanol production is 14.44 t / h, and the total conversion rate of CO2 is 97.5%.

[0050] Example 2:

[0051] The process flow schematic diagram of this example is shown in Figure 1 .

[0052] The flow rate of the CO2-rich is 40000 Nm 3 / h, which is Material 1, and the specific composition is shown in Table 2-1. The flow rate of pure hydrogen is 120000 Nm 3 / h, which is Material 2, as shown in Table 2-2 specifically;

[0053] Table 2-1 CO2-rich composition (vol%)

[0054] Name <![CDATA[CO2]]> <![CDATA[N2]]> Content / % 99.8 0.2

[0055] Table 2-2 Hydrogen Composition (vol%)

[0056]

[0057]

[0058] (1) CO2 Purification and Pre-Purification

[0059] First, the blast furnace gas rich in CO2 is purified and refined to obtain CO2 gas with a CO2 content of greater than or equal to 98% and a total sulfur content of less than 1 ppm, which is Material 1. The hydrogen gas from the outside is Material 2. Then, this part of the CO2 gas is mixed with hydrogen gas, and the ratio of the flow rate of the CO2 gas to the flow rate of the hydrogen gas is 1:3 to obtain Material A.

[0060] (2) Compression and Deep Purification

[0061] The mixed gas after mixing is first pressurized to 1.6 MPa.A by a centrifugal (or reciprocating) compressor, and the final-stage compression is directly fed into the deep purification unit without cooling.

[0062] The deep purification unit uses a deep purification agent mainly composed of copper to deeply remove toxic substances such as sulfur and chlorine in the mixed gas, with a total sulfur content of less than 0.01 ppm and a chlorine content of less than 0.01 ppm, to obtain Material 3.

[0063] (3) Adiabatic Methanol Synthesis Unit

[0064] An adiabatic methanol synthesis process with a single-stage external circulation is adopted. The catalyst filled in the adiabatic methanol reactor is a mixture of a copper-based wide-temperature shift catalyst and a methanol synthesis catalyst, and the mixing ratio by volume is 5:1. The molar ratio of CO2 to H2 in Material 4 is 8, the temperature is 350 °C, and the pressure is 1.5 MPa.A. After passing through the adiabatic methanol reactor, Material 5 is obtained, with a temperature of 260 °C and a pressure of 1.4 MPa.A.

[0065] (4) Isothermal Methanol Synthesis Unit

[0066] An isothermal methanol synthesis process with circulation is adopted. The inlet material of the isothermal methanol synthesis reactor is Material 6, with a temperature of 220 °C and a pressure of 8 MPa.A. After passing through the isothermal methanol reactor, Material 7 is obtained, with a temperature of 260 °C and a pressure of 7.80 MPa.A, and the main component is methanol.

[0067] (5) The gaseous material from the isothermal methanol synthesis unit is partially sent to the recycle compressor, and the rest is sent to a high-pressure pressure swing adsorption or membrane separation device for hydrogen recovery. The recovered hydrogen is mixed with Gas Phase B and then fed into the adiabatic methanol synthesis reactor.

[0068] In this embodiment, the methanol production rate is 14.22 t / h, and the total conversion rate of CO2 is 96%.

[0069] Example 3:

[0070] The process flow schematic diagram of this embodiment is shown in Figure 1 .

[0071] The flow rate of CO2-rich is 40000 Nm 3 / h, which is Material 1, and the specific composition is shown in Table 2-1. The flow rate of pure hydrogen is 120000 Nm 3 / h, which is Material 2, as shown in Table 2-2 for details.

[0072] Table 2-1 Composition of CO2-rich (vol%)

[0073] Name <![CDATA[CO2]]> <![CDATA[N2]]> Content / % 99.8 0.2

[0074] Table 2-2 Composition of hydrogen (vol%)

[0075] Name <![CDATA[H2]]> <![CDATA[N2]]> Content / % 99.9 0.1

[0076] (1) CO2 purification and pre-purification

[0077] First, the blast furnace gas rich in CO2 is purified and refined to obtain CO2 gas with a CO2 content of not less than 98% and a total sulfur content of less than 1 ppm, which is Material 1. The hydrogen from the outside is Material 2. Then, this part of CO2 gas is mixed with hydrogen, and the ratio of the flow rate of CO2 gas to the flow rate of hydrogen is 1:3 to obtain Material A.

[0078] (2) Compression and deep purification

[0079] The mixed gas after mixing is first pressurized to 3.1 MPa.A by a centrifugal (or reciprocating) compressor, and the final stage compression is not cooled and directly enters the deep purification unit.

[0080] The deep purification unit uses a deep purification agent mainly composed of copper to deeply remove toxic substances such as sulfur and chlorine in the mixed gas, with a total sulfur content of less than 0.01 ppm and a chlorine content of less than 0.01 ppm, to obtain Material 3.

[0081] (3) Adiabatic methanol synthesis unit

[0082] An adiabatic methanol synthesis process with a first-stage external circulation is adopted. The catalyst filled in the adiabatic methanol reactor is a mixture of a copper-based wide-temperature shift catalyst and a methanol synthesis catalyst, and the mixing ratio by volume is 2:1. The molar ratio of CO2 to H2 in Material 4 is 8, the temperature is 290 °C, and the pressure is 3.0 MPa.A. After passing through the adiabatic methanol reactor, Material 5 is obtained, with a temperature of 310 °C and a pressure of 2.9 MPa.A.

[0083] (4) Isothermal methanol synthesis unit

[0084] An isothermal methanol synthesis process with recycle is adopted. The inlet material of the isothermal methanol synthesis reactor is Material 6, with a temperature of 220 °C and a pressure of 6.0 MPa.A. After passing through the isothermal methanol reactor, Material 7 is obtained, with a temperature of 250 °C and a pressure of 5.8 MPa.A, and its main component is methanol.

[0085] (5) The gaseous material from the isothermal methanol synthesis unit, part of it goes to the recycle compressor, and the rest goes to the high-pressure pressure swing adsorption or membrane separation device for hydrogen recovery. The recovered hydrogen is mixed with Gas Phase B and then fed into the adiabatic methanol synthesis reactor.

[0086] In this embodiment, the methanol production is 13.78 t / h, and the total conversion rate of CO2 is 93%.

[0087] The foregoing basic example of the present invention and its various further selection examples can be freely combined to form multiple embodiments, all of which are the embodiments that can be adopted and claimed by the present invention. In the solution of the present invention, each selection example can be arbitrarily combined with any other basic example and selection example. Those skilled in the art know that there are numerous combinations.

[0088] The above embodiments are only the preferred solutions of the present invention. The implementation manners and protection scope of the present invention are not limited to the above embodiments. Any design and technical solutions using the idea of the present invention belong to the protection scope of the present invention. It should be noted that for those skilled in the art of this technology, several modifications made without departing from the design principle of the present invention should also be regarded as within the protection scope of the present invention. The present invention extends to any new feature or any new combination disclosed in this specification, and any new method or process step or any new combination disclosed.

Claims

1. An adiabatic process for synthesizing methanol from carbon dioxide, characterized in that It includes the following steps: First, the gas rich in CO2 is purified and pre-purified to obtain a CO2-rich gas with a CO2 content of ≥98%; then this gas is mixed with pure hydrogen to obtain feed gas A, and feed gas A is further compressed and deeply purified; the deeply purified feed gas A enters a multi-stage adiabatic methanol synthesis reactor with an external circulation to carry out methanol synthesis and reverse shift reactions; the gas at the outlet of the last-stage adiabatic methanol synthesis reactor is subjected to heat exchange and gas-liquid separation to obtain liquid-phase crude methanol and gas-phase B; gas-phase B is further compressed and then sent to an isothermal methanol synthesis reactor; in the isothermal methanol synthesis reactor, the methanol synthesis reaction continues, and after heat exchange and gas-liquid separation, liquid-phase crude methanol and gas-phase C are obtained; part of gas-phase C is sent to a hydrogen recovery device, and the recovered hydrogen is returned as feed gas, and the remaining gas-phase C enters a recycle compressor to continue as feed; finally, all the crude methanol is sent to a methanol distillation system, and after distillation, refined methanol meeting the national standard requirements is obtained; The multi-stage adiabatic methanol synthesis reaction with an external circulation refers to using multi-stage adiabatic methanol synthesis reactors to carry out methanol synthesis and reverse shift reactions of CO2. Gas-liquid separation is carried out between each stage of methanol synthesis reactors. The gas phase goes to the next-stage methanol synthesis reactor, and the liquid phase is crude methanol and goes to the distillation system; The inlet temperature of the adiabatic methanol synthesis reactor described above is 200 to 350 °C, the outlet temperature is 260 to 330 °C, the pressure is 1.5 to 5 MPa.A, and the space velocity is 3000 to 20000 h -1 ; the number of stages of the adiabatic methanol synthesis reaction with multi-stage external circulation described above is 1 to 3 stages; the catalyst loaded in the adiabatic methanol synthesis reactor is a mixture of a copper-based wide-temperature shift catalyst and a methanol synthesis catalyst, and the volume ratio of the two is 0.2 to 5:

1.

2. The adiabatic process for synthesizing methanol from carbon dioxide according to claim 1, characterized in that, The deep purification means that feed gas A is deeply purified of sulfides and chlorides through an ultra-fine purifier, and the total sulfur in the feed gas is removed to less than 0.01 ppm, and the total chlorine is less than 0.01 ppm.

3. The adiabatic process for synthesizing methanol from carbon dioxide according to claim 1, characterized in that: Utilize the hydrogen in the reactor before start-up operation to ensure that the molar ratio of hydrogen to carbon dioxide entering the adiabatic methanol synthesis reactor is 4 to 12.

4. The adiabatic process for synthesizing methanol from carbon dioxide according to claim 1, characterized in that: Gas-phase B is compressed, and the compressed pressure is 6 to 10 MPa.A, and then a low-pressure isothermal methanol synthesis reaction is carried out.

5. The adiabatic process for synthesizing methanol from carbon dioxide according to claim 1, characterized in that: The number of stages of the multi-stage adiabatic methanol synthesis reaction is 1 stage.

6. The adiabatic process for synthesizing methanol from carbon dioxide according to claim 1, characterized in that: The copper-based wide-temperature shift catalyst is the CNGC-2 type copper-based wide-temperature shift catalyst of Southwest Research and Design Institute of Chemical Industry Co., Ltd.

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