System and method for producing methanol by hydrogenation of carbon dioxide

Abstract

This invention discloses a system and method for producing methanol by carbon dioxide hydrogenation. The system includes a feedstock turbine compressor, a first feedstock gas heat exchanger, a second feedstock gas heat exchanger, an adiabatic reactor, an isothermal reactor, a gas-liquid membrane separator, and a molecular sieve. By setting up an isothermal reactor and utilizing the heat from the product produced by the adiabatic reactor in separate streams, heat coupling between the two reactors is achieved. The unreacted feedstock gas remaining after the adiabatic first-stage reaction is circulated in the isothermal reactor, reducing the size requirements of the adiabatic reactor and improving the overall conversion rate of carbon dioxide. This application solves the problems of high energy consumption in the distillation of by-product water in the carbon dioxide hydrogenation to methanol process, large investment in traditional equipment, serious heat loss, and excessive circulating gas volume in existing technologies.

Description

Technical Field

[0001] This invention relates to the field of methanol preparation technology, and in particular to a system and method for producing methanol by carbon dioxide hydrogenation. Background Technology

[0002] Methanol is the fourth largest basic chemical raw material after ethylene, propylene, and benzene, with a wide range of applications. It can be used to produce various chemical products and also as a fuel. With the development of downstream methanol industries and the widespread use of methanol fuel, methanol demand and production capacity will continue to grow.

[0003] Methanol has multiple synthetic routes. Currently, industrial methanol production mainly uses coal and natural gas as raw materials, producing syngas composed of carbon monoxide and hydrogen. Methanol synthesis consumes fossil fuels and is accompanied by carbon dioxide emissions, with coal-based methanol production being particularly egregious. Taking coal-water slurry gasification for methanol production as an example, without considering the carbon dioxide emissions from utility consumption, approximately 2.2 tons of carbon dioxide are emitted for every ton of methanol produced. Therefore, methanol produced from fossil fuels is classified as "gray methanol."

[0004] Producing green methanol using carbon dioxide and green hydrogen as raw materials not only eliminates carbon dioxide emissions but also absorbs them, making it an important means of carbon reduction. Simultaneously, the reaction of carbon dioxide with green hydrogen to produce methanol is also an effective means of storing green hydrogen and renewable energy. Essentially, it utilizes renewable energy to convert carbon dioxide and water into methanol, storing unstable and intermittent solar energy in easily stored and transportable methanol. Therefore, research on methanol production via carbon dioxide hydrogenation has received widespread attention in recent years. However, traditional carbon dioxide hydrogenation methanol production processes still face problems such as large circulating gas volumes, high equipment investment costs, high energy consumption, and heat waste, which urgently need to be addressed.

[0005] Therefore, it is necessary to propose a system and method for producing methanol by carbon dioxide hydrogenation to solve at least one of the above problems. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a system and method for producing methanol by carbon dioxide hydrogenation, which can solve problems such as high energy consumption in the distillation of by-product water in the production of methanol by carbon dioxide hydrogenation, large investment in equipment for traditional processes, serious heat loss, and excessive circulating gas volume.

[0007] The specific technical solution of the embodiments of the present invention is as follows:

[0008] A system for producing methanol by carbon dioxide hydrogenation, comprising: a feedstock turbine compressor, a first feedstock gas heat exchanger, a second feedstock gas heat exchanger, an adiabatic reactor, an isothermal reactor, a gas-liquid membrane separator, and a molecular sieve; wherein the feedstock turbine compressor is used to compress the feedstock gas to a predetermined pressure range; the first feedstock gas heat exchanger includes: a first inlet for receiving the compressed feedstock gas exiting the feedstock turbine compressor; a first outlet for discharging fluid to the adiabatic reactor; a second inlet for receiving the fluid discharged from the adiabatic reactor; and a second outlet for discharging fluid to the gas-liquid membrane separator; the adiabatic reactor has a first interface for connecting to the first outlet of the first feedstock gas heat exchanger, enabling heat exchange with the first feedstock gas. The gas-liquid membrane separator has a second interface for receiving the output fluids of the first raw material gas heat exchanger, the second raw material gas heat exchanger, and the isothermal reactor; a gas outlet for outputting unreacted raw material gas; and a liquid outlet for outputting crude product to the molecular sieve. The second raw material gas heat exchanger includes a third inlet for receiving the gas output from the gas-liquid membrane separator, a fourth inlet for receiving the output fluid from the adiabatic reactor, a third outlet for outputting fluid to the gas-liquid membrane separator, and a fourth outlet for outputting fluid to the isothermal reactor. The isothermal reactor includes a third interface for receiving the fluid output from the second raw material gas heat exchanger and a fourth interface for outputting fluid to the gas-liquid membrane separator.

[0009] In a preferred embodiment, a gas detector is provided at the inlet of the feedstock turbine compressor or upstream of the inlet, the gas detector being used to detect the molar ratio of carbon dioxide to hydrogen in the feedstock gas.

[0010] In a preferred embodiment, the molar ratio of carbon dioxide to hydrogen in the feed gas is greater than 1:8.

[0011] In a preferred embodiment, the gas-liquid separator includes a housing and a degassing membrane disposed within the housing, the degassing membrane having opposing high-pressure and low-pressure sides, the low-pressure side of the degassing membrane being connected to a vacuum pump.

[0012] In a preferred embodiment, the molecular sieve crystal is a three-dimensional network structure formed by connecting SiO4 and AlO4 tetrahedra through oxygen bridging bonds.

[0013] In a preferred embodiment, the predetermined pressure range is from 4 MPa to 5 MPa.

[0014] In a preferred embodiment, a first multi-way valve is provided downstream of the second port of the adiabatic reactor, the first multi-way valve connecting the second port to the first feed gas heat exchanger and the second feed gas heat exchanger; a second multi-way valve is provided upstream of the first inlet of the gas-liquid film separator, the second multi-way valve connecting the first feed gas heat exchanger, the second feed gas heat exchanger, and the isothermal reactor to the first port of the gas-liquid film separator; a third multi-way valve is provided downstream of the gas outlet of the gas-liquid film separator, the third multi-way valve connecting the gas outlet to the second feed gas heat exchanger and the venting gas discharge pipeline.

[0015] A method for producing methanol from carbon dioxide using the aforementioned system of carbon dioxide hydrogenation, the method comprising:

[0016] After purification, the mixed raw material gas is compressed by the turbine compressor and then undergoes a heat exchange with a portion of the product mixture from the adiabatic reactor before entering the adiabatic reactor for an adiabatic first-stage reaction.

[0017] After the adiabatic first-stage reaction, a partial product mixture is obtained by heat exchange and pressure reduction in the first raw material gasification heat exchanger. The product mixture obtained after heat exchange and pressure reduction is then sent to the gas-liquid membrane separator to separate the unreacted raw material gas from the crude methanol product.

[0018] After separation by the gas-liquid membrane separator, part of the unreacted raw material gas is used as purge gas, and the other part is passed through the second raw material gas heat exchanger and exchanged heat with another part of the product mixture from the adiabatic reactor before entering the isothermal reactor for secondary reaction.

[0019] The product mixture produced by the isothermal reactor and the product mixture produced by the adiabatic reactor after heat exchange and pressure reduction are fed into the gas-liquid membrane separator for degassing to form unreacted raw material gas for recycling.

[0020] The crude methanol, after being degassed by the gas-liquid membrane separator, enters the molecular sieve for dehydration treatment, ultimately yielding a qualified methanol product.

[0021] In a preferred embodiment, the method for producing methanol by carbon dioxide hydrogenation further includes: testing the purified mixed feed gas, and when the molar ratio of carbon dioxide to hydrogen in the mixed feed gas reaches 1:8 or higher, performing the step of: exchanging heat once between the mixed feed gas and a portion of the product mixture from the adiabatic reactor before entering the adiabatic reactor for an adiabatic first-stage reaction.

[0022] In a preferred embodiment, the method for producing methanol by carbon dioxide hydrogenation further includes: passing cooling water through the isothermal reactor to absorb the heat in the isothermal reactor through the cooling water, forming steam which is then output.

[0023] The technical solution of the present invention has the following significant beneficial effects:

[0024] The system and method for producing methanol by carbon dioxide hydrogenation provided in this application utilize the heat from the product produced by the adiabatic reactor in separate streams, achieving coupled heat utilization between the adiabatic and isothermal reactors, thus improving heat utilization efficiency and carbon dioxide conversion rate. The small portion of unreacted feed gas remaining after the adiabatic first-stage reaction is recycled in the isothermal reactor, reducing the size requirements of the adiabatic reactor and increasing the overall carbon dioxide conversion rate. The dehydration rate of the recycled feed gas is improved through a degassing membrane gas-liquid separator, thereby increasing the single-pass conversion rate of carbon dioxide in the isothermal reactor to some extent, further reducing the gas circulation volume and lowering equipment investment costs. Utilizing the difference in kinetic diameter and the strong adsorption affinity of the molecular sieve framework for water, the traditional methanol distillation and dehydration process is replaced, significantly reducing energy consumption and equipment investment costs.

[0025] Specific embodiments of the invention are disclosed in detail with reference to the following description and accompanying drawings, indicating how the principles of the invention can be employed. It should be understood that the embodiments of the invention are not therefore limited in scope. Within the spirit and scope of the appended claims, embodiments of the invention include many changes, modifications, and equivalents. Features described and / or shown for one embodiment may be used in the same or similar manner in one or more other embodiments, combined with features in other embodiments, or substituted for features in other embodiments. Attached Figure Description

[0026] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way. Furthermore, the shapes and proportions of the components in the drawings are merely illustrative to aid in understanding the invention and do not specifically limit the shapes and proportions of the components. Those skilled in the art, guided by the teachings of this invention, can select various possible shapes and proportions to implement the invention according to specific circumstances.

[0027] Figure 1 This is a schematic diagram of a system for producing methanol by carbon dioxide hydrogenation provided in the embodiments of this application;

[0028] Figure 2 This is a schematic flowchart of a method for producing methanol by hydrogenation of carbon dioxide provided in the embodiments of this application.

[0029] Reference numerals in the figures of this application:

[0030] 1. Raw material turbine compressor;

[0031] 21. First raw material gas heat exchanger;

[0032] 211. First entrance;

[0033] 212. First Exit;

[0034] 213. Second entrance;

[0035] 214. Second Exit;

[0036] 22. Second raw material gas heat exchanger;

[0037] 221. The third entrance;

[0038] 222. Fourth entrance;

[0039] 223. Third Exit;

[0040] 224. Fourth Exit;

[0041] 3. Insulated reactor;

[0042] 31. First interface;

[0043] 32. Second interface;

[0044] 4. Isothermal reactor;

[0045] 41. Third interface;

[0046] 42. Fourth interface;

[0047] 5. Gas-liquid membrane separator;

[0048] 51. First import;

[0049] 52. Gas outlet;

[0050] 53. Liquid outlet;

[0051] 6. Molecular sieves;

[0052] 71. First multi-way valve;

[0053] 72. Second multi-way valve;

[0054] 73. Third multi-way valve. Detailed Implementation

[0055] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art fall within the scope defined by the appended claims.

[0056] It should be noted that when an element is referred to as being "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0057] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0058] One of the existing technologies:

[0059] Chinese patent CN216550214U discloses a system for multi-stage synthesis of methanol from carbon dioxide. The specific steps disclosed in this patent are as follows:

[0060] S1: Hydrogen in the raw material gas is compressed and mixed with part of the pressurized vaporized carbon dioxide and the circulating gas, and then enters the methanol synthesis and separation system of stages 1 to n in sequence, where crude methanol is synthesized.

[0061] S2: A portion of the gas generated from the nth stage methanol synthesis and separation system is returned to the first stage methanol synthesis and separation system after compression as recycle gas;

[0062] S3: The remaining gases then enter the (n+1)th stage methanol synthesis and separation system;

[0063] S4: The carbon dioxide supply system runs through each stage of the methanol synthesis and separation system to adjust the carbon-hydrogen ratio of the reaction.

[0064] The aforementioned process involves significant investment in equipment for multi-stage reaction and separation systems. Furthermore, the multi-stage heat exchange, separation, and compression sections further increase the overall power consumption and heat waste. In addition, the separation of a large amount of byproduct water during the carbon dioxide-to-methanol production process results in excessive energy consumption in the distillation section.

[0065] Second existing technology:

[0066] Chinese patent CN116983945 discloses a method and system for producing methanol from carbon dioxide and hydrogen. The specific steps disclosed in this patent are as follows:

[0067] S1: Carbon dioxide gas and hydrogen gas are compressed by carbon dioxide turbine compressor and hydrogen turbine compressor respectively, and then mixed and entered into the preheater for preheating;

[0068] S2: The preheated carbon dioxide gas and hydrogen gas enter the methanol reactor for reaction, and the reaction products enter the preheater as a heat source to preheat the carbon dioxide gas and hydrogen gas.

[0069] S3: The reaction products, after being cooled by the preheater, enter the high-pressure distillation column for distillation;

[0070] S4: The gas phase after distillation in the high-pressure distillation column enters the pressurizing fan through the top of the column and is pressurized. Then it returns to the preheater for preheating and re-enters the methanol reactor to participate in the reaction.

[0071] S5: The bottom liquid phase after distillation in the high-pressure distillation column enters the methanol recovery column for methanol distillation.

[0072] The patent failed to fully utilize thermal coupling to reduce heat loss; in addition, due to the problem of separating a large amount of by-product water in the production of methanol from carbon dioxide, the energy load caused by the distillation section is too large.

[0073] This invention provides a system and method for producing methanol by carbon dioxide hydrogenation, which can solve the problems of high energy consumption in the distillation of by-product water in the production of methanol by carbon dioxide hydrogenation, large investment in equipment in traditional processes, serious heat loss, and excessive circulating gas volume in the prior art.

[0074] Please see Figure 1This application specification provides a system for producing methanol by carbon dioxide hydrogenation. The system may include: a feedstock turbine compressor 1, a first feedstock gas heat exchanger 21, a second feedstock gas heat exchanger 22, an adiabatic reactor 3, an isothermal reactor 4, a gas-liquid membrane separator 5, and a molecular sieve 6. The feedstock turbine compressor 1 is used to compress the feedstock gas to a predetermined pressure range. The first feedstock gas heat exchanger 21 includes: a first inlet 211 for receiving the compressed feedstock gas exiting the feedstock turbine compressor 1; a first outlet 212 for outputting fluid to the adiabatic reactor 3; a second inlet 213 for receiving the fluid output from the adiabatic reactor 3; and a second outlet 214 for outputting fluid to the gas-liquid membrane separator 5. The adiabatic reactor 3 has a first interface 31 for connecting to the first outlet 212 of the first feedstock gas heat exchanger 21, enabling the supply of fluid to the first feedstock gas. The gas heat exchanger 21 and the second raw material gas heat exchanger 22 have a second interface 32 for outputting fluids; the gas-liquid membrane separator 5 has a first inlet 51 for receiving fluids output from the first raw material gas heat exchanger 21, the second raw material gas heat exchanger 22 and the isothermal reactor 4, a gas outlet 52 for outputting unreacted raw material gas, and a liquid outlet 53 for outputting crude product to the molecular sieve 6; the second raw material gas heat exchanger 22 includes: a third inlet 221 for receiving gas output from the gas-liquid membrane separator 5, a fourth inlet 222 for receiving fluid output from the adiabatic reactor 3, a third outlet 223 for outputting fluid to the gas-liquid membrane separator 5, and a fourth outlet 224 for outputting fluid to the isothermal reactor 4; the isothermal reactor 4 includes: a third interface 41 for receiving fluid output from the second raw material gas heat exchanger 22, and a fourth interface 42 for outputting fluid to the gas-liquid membrane separator 5.

[0075] In this embodiment of the application, the system for producing methanol by carbon dioxide hydrogenation mainly includes: a raw material turbine compressor 1, a first raw material gas heat exchanger 21, a second raw material gas heat exchanger 22, an adiabatic reactor 3, an isothermal reactor 4, a gas-liquid membrane separator 5, a molecular sieve 6, and necessary pipelines, etc.

[0076] In this embodiment, the raw material turbine compressor 1 is used to compress the purified mixed raw material gas, so that the mixed raw material gas is compressed to a predetermined pressure range after passing through the raw material turbine compressor 1. In this embodiment, the mixed raw material gas can specifically be a mixture of carbon dioxide and hydrogen.

[0077] Specifically, during use, the mixed raw material gas entering the raw material turbine compressor 1 can reach a pressure of 4 MPa to 5 MPa after being compressed by the raw material gas compressor.

[0078] In one embodiment, a gas detector is provided at the inlet of the raw material turbine compressor 1 or upstream of the inlet, the gas detector being used to detect the molar ratio of carbon dioxide to hydrogen in the raw material gas.

[0079] The system for producing methanol by carbon dioxide hydrogenation may also include a controller, and the gas detector may be electrically connected to the controller. The controller may determine whether the molar ratio of carbon dioxide to hydrogen in the current mixed feed gas meets the requirements based on the detection signal obtained by the gas detector.

[0080] Specifically, to ensure the selectivity and conversion rate of carbon dioxide in a single pass, the molar ratio of carbon dioxide to hydrogen in the purified mixed feed gas should be 1:8 or higher. To detect the molar ratio of carbon dioxide to hydrogen in this mixed feed gas, a gas detector can be installed at the inlet of the feed turbine compressor 1 or upstream of the inlet to detect the molar ratio of carbon dioxide to hydrogen in the feed gas, thereby ensuring the carbon-hydrogen ratio of the feed gas.

[0081] Specifically, experimental verification shows that in the process of preparing methanol by carbon dioxide hydrogenation, when the raw material gas at 35°C to 40°C is introduced into the adiabatic reactor 3 for methanol preparation, since the molar ratio of carbon dioxide to hydrogen in the mixed raw material gas reaches more than 1:8, the selectivity and conversion rate of carbon dioxide in a single pass can reach 90%.

[0082] In this embodiment, the basic function of the first raw material gas heat exchanger 21 is to exchange heat with the fluid flowing through it. For example, the first raw material gas heat exchanger 21 can use a portion of the high-temperature fluid (containing a high-temperature product mixture of methanol and a small amount of raw material gas) flowing out of the adiabatic reactor 3 to heat the raw material gas, thereby efficiently utilizing the heat of the products produced in the adiabatic reactor 3.

[0083] Specifically, the first raw material gas heat exchanger 21 includes: a first inlet 211 for receiving the compressed raw material gas flowing out of the outlet of the raw material turbine compressor 1; a first outlet 212 for discharging fluid to the adiabatic reactor 3; a second inlet 213 for receiving the fluid discharged from the adiabatic reactor 3; and a second outlet 214 for discharging fluid to the gas-liquid membrane separator 5. The components of the fluids may vary depending on the reaction time and the composition of the raw material gas, and this application does not impose a single limitation on this.

[0084] In this embodiment, the adiabatic reactor 3 is mainly used for adiabatic primary reaction of the feed gas to produce methanol. The adiabatic reactor 3 has a first interface 31 for connecting to the first outlet 212 of the first feed gas heat exchanger 21, and a second interface 32 for outputting fluid to the first feed gas heat exchanger 21 and the second feed gas heat exchanger 22.

[0085] Downstream of the second port 32 of the adiabatic reactor 3, a first multi-way valve 71 is provided. The first multi-way valve 71 connects the second port 32 to the first feed gas heat exchanger 21 and the second feed gas heat exchanger 22. Using this first multi-way valve 71, the connection between the second port 32 and the first and second feed gas heat exchangers 21 can be controlled according to reaction requirements during the methanol preparation process.

[0086] Specifically, the first multi-way valve 71 can be a three-way valve, which can have one inlet connector and two outlet connectors. One inlet connector is connected to the adiabatic reactor 3, and the two outlet connectors are respectively connected to the first raw material gas heat exchanger 21 and the second raw material gas heat exchanger 22.

[0087] In the embodiments of this application, the first multi-way valve 71 can also be in other forms, such as a four-way valve, a five-way valve, or the first multi-way valve 71 can be replaced by a multi-way connector, etc. Of course, the specific configuration of the first multi-way valve 71 can also be in other ways, and is not limited to the above description. Those skilled in the art may make other changes under the guidance of the technical essence of this application, but as long as the function and effect achieved are the same as or similar to those of this application, they should all be covered within the protection scope of this application.

[0088] After being compressed by the raw material gas compressor, the compressed raw material gas can exchange heat with a portion of the methanol mixture (550°C to 650°C) from the adiabatic reactor 3 in the first raw material gas heat exchanger 21 before entering the adiabatic reactor 3 to prepare methanol.

[0089] To detect the temperature of the product exiting the adiabatic reactor 3, a temperature sensor can be installed at the second interface 32 or downstream of the second interface 32. This temperature sensor can be electrically connected to a controller. The controller can determine whether the temperature of the product in the adiabatic reactor 3 has reached the aforementioned temperature range based on the detection signal from the temperature sensor.

[0090] The basic function of the gas-liquid membrane separator 5 is to separate gas and liquid. It has a first inlet 51 for receiving the output fluids of the first raw material gas heat exchanger 21, the second raw material gas heat exchanger 22 and the isothermal reactor 4, a gas outlet 52 for outputting unreacted raw material gas, and a liquid outlet 53 for outputting crude product to the molecular sieve 6.

[0091] A second multi-way valve 72 is provided upstream of the first inlet 51 of the gas-liquid membrane separator 5. The second multi-way valve 72 is used to connect the first raw material gas heat exchanger 21, the second raw material gas heat exchanger 22 and the isothermal reactor 4 to the first interface 31 of the gas-liquid membrane separator 5.

[0092] Specifically, the second multi-way valve 72 can be a four-way valve.

[0093] The four-way valve may have three inlet connectors and one outlet connector. The three inlet connectors are respectively connected to the first raw material gas heat exchanger 21, the second raw material gas heat exchanger 22 and the isothermal reactor 4, and the outlet connector is connected to the first inlet 51 of the gas-liquid film separator 5.

[0094] In the embodiments of this application, the second multi-way valve 72 can also be in other forms, such as a five-way valve, a six-way valve, or the second multi-way valve 72 can be replaced by a multi-way connector, etc. Of course, the specific configuration of the second multi-way valve 72 can also be in other ways, and is not limited to the above description. Those skilled in the art may make other changes under the guidance of the technical essence of this application, but as long as the function and effect achieved are the same as or similar to those of this application, they should all be covered within the protection scope of this application.

[0095] Specifically, the gas-liquid separator may include a housing and a degassing membrane disposed within the housing. The housing is the external structure of the gas-liquid separator, providing support and protection for the degassing membrane. The housing is typically made of corrosion-resistant materials, such as stainless steel or plastic, to adapt to different working environments. The degassing membrane is the core component of the gas-liquid separator, usually made of polymer materials with a special microporous structure. The size and shape of these micropores are carefully designed to allow gas molecules to pass through while blocking liquid molecules. The working principle of the degassing membrane is based on the partial pressure difference of the gas on both sides of the membrane. When a liquid containing gas passes through the degassing membrane, due to the difference in gas partial pressure on both sides of the membrane, gas molecules diffuse from the high-pressure side to the low-pressure side, thereby achieving gas-liquid separation. The degassing membrane has opposing high-pressure and low-pressure sides, and the low-pressure side of the degassing membrane can be connected to a vacuum pump.

[0096] A gas-liquid separator composed of a degassing membrane is used to extract unreacted raw material gas and gas dissolved in crude methanol through vacuum extraction, thereby ensuring a high dehydration rate of the raw material gas. The high dehydration rate of the raw material gas improves the single-pass conversion rate of carbon dioxide in the subsequent isothermal reactor 4 to some extent, thereby further reducing the gas circulation volume and lowering equipment investment costs.

[0097] The molecular sieve 6 is located downstream of the liquid outlet 53 of the gas-liquid separator and is used for dehydration of methanol. Specifically, the crystals of the molecular sieve 6 are a three-dimensional network structure formed by SiO4 and AlO4 tetrahedra linked by oxygen bridges.

[0098] In this embodiment, crude methanol can be purified using molecular sieve 6, replacing the traditional distillation process. The main principle of purifying crude methanol using molecular sieve 6 is as follows: a tightly packed membrane layer is formed by growing type A molecular sieve 6 crystals on a tubular ceramic porous support, utilizing the difference in kinetic diameter between methanol and water molecules to separate alcohol and water; in addition, the silicon-aluminum content (Si / Al = 1) in the molecular sieve 6 framework gives it extremely strong hydrophilicity, allowing type A molecular sieve 6 to permeate and vaporize the inorganic membrane, making it particularly suitable for the dehydration of organic solvents such as methanol.

[0099] A third multi-way valve 73 may be installed downstream of the gas outlet 52 of the gas-liquid membrane separator 5. The third multi-way valve 73 is used to connect the gas outlet 52 to the second raw material gas heat exchanger 22 and the venting gas discharge pipeline.

[0100] The third multi-way valve 73 can be used to control the connection between the gas outlet 52, the second raw material gas heat exchanger 22, and the venting gas discharge pipeline according to the reaction requirements during the preparation of methanol.

[0101] Specifically, the third multi-way valve 73 can be a three-way valve, which can have one inlet connector and two outlet connectors. One inlet connector is connected to the gas-liquid film separator 5, and the two outlet connectors are respectively connected to the second raw material gas heat exchanger 22 and the venting gas discharge pipeline.

[0102] In the embodiments of this application, the third multi-way valve 73 can also be in other forms, such as a four-way valve, a five-way valve, or it can be replaced by a multi-way connector. Of course, the specific configuration of the third multi-way valve 73 can also be in other ways, and is not limited to the above description. Those skilled in the art may make other changes based on the technical essence of this application, but as long as the function and effect achieved are the same as or similar to those of this application, they should all be covered within the protection scope of this application.

[0103] In this embodiment, the basic function of the second raw material gas heat exchanger 22 is to exchange heat with the fluid flowing through it. For example, the second raw material gas heat exchanger 22 can use a portion of the high-temperature fluid (containing a high-temperature product mixture of methanol and a small amount of raw material gas) flowing out of the adiabatic reactor 3 to heat the unreacted raw material gas output from the gas-liquid membrane separator 5, thereby efficiently utilizing the heat of the product produced in the adiabatic reactor 3.

[0104] The second raw material gas heat exchanger 22 includes: a third inlet 221 for receiving unreacted raw material gas output from the gas-liquid membrane separator 5; a fourth inlet 222 for receiving a portion of the high-temperature product mixture output from the adiabatic reactor 3; a third outlet 223 for outputting the cooled product mixture to the gas-liquid membrane separator 5; and a fourth outlet 224 for outputting the heated raw material gas to be reacted to the isothermal reactor 4.

[0105] The isothermal reactor 4 includes a third port 41 for receiving the raw gas output from the second raw gas heat exchanger 22, and a fourth port 42 for outputting the product mixture after the isothermal secondary reaction to the gas-liquid membrane separator 5.

[0106] In this embodiment, by setting up the isothermal reactor 4 and utilizing the heat from the product produced by the adiabatic reactor 3 in separate streams, heat coupling between the two reactors (adiabatic reactor 3 and isothermal reactor 4) is achieved. Specifically, the unreacted raw material gas remaining after the adiabatic first-stage reaction in the adiabatic reactor 3 is recycled in the isothermal reactor 4. This arrangement reduces the size requirements of the adiabatic reactor 3 and improves the overall carbon dioxide conversion rate.

[0107] Overall, the carbon dioxide hydrogenation to methanol system provided in this application utilizes the heat from the product produced by the adiabatic reactor 3 in separate streams, achieving heat coupling between the adiabatic reactor 3 and the isothermal reactor 4, thus improving heat utilization efficiency and carbon dioxide conversion rate. The small portion of unreacted feed gas remaining after the adiabatic first-stage reaction is recycled in the isothermal reactor 4, reducing the size requirements of the adiabatic reactor 3 and improving the overall carbon dioxide conversion rate. The degassing membrane gas-liquid separator improves the dehydration rate of the recycled feed gas, thereby increasing the single-pass carbon dioxide conversion rate in the isothermal reactor 4 to some extent, further reducing the gas circulation volume and lowering equipment investment costs. Utilizing the difference in kinetic diameter and the strong adsorption affinity of the molecular sieve 6 framework for water, the traditional methanol distillation and dehydration process is replaced, significantly reducing energy consumption and equipment investment costs.

[0108] Please see Figure 2 Based on the system for producing methanol by carbon dioxide hydrogenation provided in the above embodiments, this application also provides a method for producing methanol by carbon dioxide hydrogenation, which may include the following steps:

[0109] S11: The purified mixed raw material gas is compressed by the turbine compressor and then undergoes a heat exchange with a portion of the product mixture from the adiabatic reactor 3 before entering the adiabatic reactor 3 for adiabatic first-stage reaction.

[0110] S12: The product mixture generated after the adiabatic first-stage reaction is passed through the first raw material gasification heat exchanger for heat exchange and pressure reduction to obtain a product mixture, and the product mixture obtained after heat exchange and pressure reduction is sent to the gas-liquid membrane separator 5 for separation of unreacted raw material gas and crude methanol product.

[0111] S13: Part of the unreacted raw material gas obtained after separation by the gas-liquid membrane separator 5 is used as purge gas, and the other part is passed through the second raw material gas heat exchanger 22 and exchanged heat with another part of the product mixture from the adiabatic reactor 3 before entering the isothermal reactor 4 for secondary reaction.

[0112] S14: The product mixture produced by the isothermal reactor 4 and the product mixture produced by the adiabatic reactor 3 after heat exchange and pressure reduction are fed into the gas-liquid membrane separator 5 for degassing to form unreacted raw material gas for recycling.

[0113] S15: The crude methanol after degassing by the gas-liquid membrane separator 5 enters the molecular sieve 6 for dehydration treatment, and finally obtains qualified methanol product.

[0114] The method for producing methanol by carbon dioxide hydrogenation further includes: testing the purified mixed feed gas; and when the molar ratio of carbon dioxide to hydrogen in the mixed feed gas reaches 1:8 or higher, performing the following step: exchanging heat once between the mixed feed gas and a portion of the product mixture from the adiabatic reactor 3 before entering the adiabatic reactor 3 for an adiabatic first-stage reaction.

[0115] The method for producing methanol by hydrogenation of carbon dioxide further includes: passing cooling water into the isothermal reactor 4, absorbing the heat in the isothermal reactor 4 through the cooling water, and then outputting steam.

[0116] In one specific implementation, according to Figure 1 As shown, the molar ratio of carbon dioxide to hydrogen in the purified mixed raw material gas should reach 1:8 or higher. This can be ensured by setting up a gas detector.

[0117] Then, the raw material gas at 35°C to 40°C is introduced into the adiabatic reactor 3 to prepare methanol. Due to the high raw material ratio of 1:8, the selectivity and conversion rate of carbon dioxide in a single pass can reach 90%.

[0118] In the process of methanol production, the adiabatic reactor 3 generates a partial methanol mixture at a temperature of 550°C to 650°C. In this application, the heat of this high-temperature fluid is efficiently utilized during the methanol production process in the adiabatic reactor 3. After being compressed to 4 MPa to 5 MPa by the feed gas compressor, the fluid exchanges heat with the 550°C to 650°C partial methanol mixture exiting the adiabatic reactor 3 before entering the adiabatic reactor 3 for methanol production.

[0119] The methanol mixture after heat exchange and pressure reduction enters the gas-liquid membrane separator 5 for separation. The unreacted raw material gas separated by the gas-liquid membrane separator 5 exchanges heat with another portion of the methanol mixture produced by the adiabatic reactor 3 at a temperature between 550°C and 650°C, reducing the temperature to 220°C to 320°C, and then passes it into the isothermal reactor 4 for further reaction. The other portion of the methanol mixture produced by the adiabatic reactor 3 at a temperature between 550°C and 650°C, after heat exchange, is also passed into the gas-liquid membrane separator 5 for separation, thereby achieving a low-volume raw material gas circulation.

[0120] The crude methanol in liquid phase separated by the gas-liquid membrane separator 5 is passed into the molecular sieve 6 to obtain high-purity methanol.

[0121] The heat generated during methanol production in the isothermal reactor 4 is absorbed by a stream of cooling water, which then produces a certain amount of medium-pressure steam for other uses.

[0122] The method for producing methanol from carbon dioxide based on the above-described system for producing methanol from carbon dioxide provided in this application has the following beneficial effects:

[0123] 1. By setting the raw material ratio and dividing the heat of the product produced by the adiabatic reactor 3 for separate utilization, the heat of the adiabatic reactor 3 and the isothermal reactor 4 are coupled and utilized, thereby improving the heat utilization efficiency and the carbon dioxide conversion rate.

[0124] 2. The small portion of unreacted feed gas remaining after the adiabatic first-stage reaction is recycled in the isothermal reactor 4, which reduces the size requirements of the adiabatic reactor 3 and improves the overall conversion rate of carbon dioxide.

[0125] 3. The dehydration rate of the circulating raw material gas is improved by using a degassing membrane gas-liquid separator, which to some extent improves the single-pass reaction conversion rate of carbon dioxide in the isothermal reactor 4, thereby further reducing the gas circulation volume and lowering the equipment investment cost.

[0126] 4. By utilizing the difference in kinetic diameter and the strong affinity of the molecular sieve 6 framework for water, the traditional methanol distillation and dehydration process has been replaced, greatly reducing energy consumption and equipment investment costs.

[0127] It should be noted that in the description of this application, the terms "first," "second," etc., are used only for descriptive purposes and to distinguish similar objects; there is no order between them, nor should they be construed as indicating or implying relative importance. Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more.

[0128] The various embodiments described in this specification are presented in a progressive manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0129] The above are merely a few embodiments of the present invention. Although the embodiments disclosed in the present invention are as described above, the content is only for the purpose of facilitating understanding of the present invention and is not intended to limit the present invention. Any person skilled in the art to which this invention pertains may make any modifications and changes in the form and details of the embodiments without departing from the spirit and scope disclosed in the present invention. However, the patent protection scope of the present invention shall still be determined by the scope defined in the appended claims.

Claims

1. A system for producing methanol by hydrogenation of carbon dioxide, characterized in that, The system for producing methanol by carbon dioxide hydrogenation includes: a feedstock turbine compressor, a first feedstock gas heat exchanger, a second feedstock gas heat exchanger, an adiabatic reactor, an isothermal reactor, a gas-liquid membrane separator, and a molecular sieve. The raw material turbine compressor is used to compress the raw material gas to a predetermined pressure range; The first raw material gas heat exchanger includes: a first inlet for receiving compressed raw material gas flowing out of the outlet of the raw material turbine compressor, a first outlet for outputting fluid to the adiabatic reactor, a second inlet for receiving fluid output from the adiabatic reactor, and a second outlet for outputting fluid to the gas-liquid membrane separator. The adiabatic reactor has a first interface for connecting to the first outlet of the first feed gas heat exchanger and a second interface for outputting fluid to the first feed gas heat exchanger and the second feed gas heat exchanger. The gas-liquid membrane separator has a first inlet for receiving the output fluids from the first feed gas heat exchanger, the second feed gas heat exchanger, and the isothermal reactor, a gas outlet for outputting unreacted feed gas, and a liquid outlet for outputting crude product to the molecular sieve. The second raw material gas heat exchanger includes: a third inlet for receiving the gas output from the gas-liquid membrane separator, a fourth inlet for receiving the fluid output from the adiabatic reactor, a third outlet for outputting fluid to the gas-liquid membrane separator, and a fourth outlet for outputting fluid to the isothermal reactor. The isothermal reactor includes: a third interface for receiving the fluid output from the second feed gas heat exchanger, and a fourth interface for outputting fluid to the gas-liquid membrane separator. A gas detector is installed at the inlet of the raw material turbine compressor or upstream of the inlet. The gas detector is used to detect the molar ratio of carbon dioxide to hydrogen in the raw material gas. The molar ratio of carbon dioxide to hydrogen in the raw material gas is greater than 1:

8. A first multi-way valve is provided downstream of the second port of the adiabatic reactor, and the first multi-way valve connects the second port to the first feed gas heat exchanger and the second feed gas heat exchanger. A second multi-way valve is provided upstream of the first inlet of the gas-liquid membrane separator. The second multi-way valve is used to connect the first feed gas heat exchanger, the second feed gas heat exchanger, and the isothermal reactor to the first interface of the gas-liquid membrane separator. A third multi-way valve is provided downstream of the gas outlet of the gas-liquid membrane separator. The third multi-way valve is used to connect the gas outlet to the second raw material gas heat exchanger and the venting gas discharge pipeline.

2. The system for producing methanol by carbon dioxide hydrogenation as described in claim 1, characterized in that, The gas-liquid membrane separator includes a housing and a degassing membrane disposed within the housing. The degassing membrane has a high-pressure side and a low-pressure side, and the low-pressure side of the degassing membrane is connected to a vacuum pump.

3. The system for producing methanol by carbon dioxide hydrogenation as described in claim 1, characterized in that, The molecular sieve crystals are a three-dimensional network structure formed by SiO4 and AlO4 tetrahedra linked by oxygen bridge bonds.

4. The system for producing methanol by carbon dioxide hydrogenation as described in claim 1, characterized in that, The predetermined pressure range is from 4 MPa to 5 MPa.

5. A method for producing methanol from carbon dioxide using the system for producing methanol from carbon dioxide according to any one of claims 1 to 4, characterized in that, The method for producing methanol by carbon dioxide hydrogenation includes: After purification, the mixed raw material gas is compressed by a turbine compressor and then undergoes a heat exchange with a portion of the product mixture from the adiabatic reactor before entering the adiabatic reactor for an adiabatic first-stage reaction. After the adiabatic first-stage reaction, a portion of the product mixture is passed through the first raw material gas heat exchanger for heat exchange and pressure reduction to obtain a product mixture. The product mixture obtained after heat exchange and pressure reduction is then sent to the gas-liquid membrane separator to separate the unreacted raw material gas from the crude methanol product. After separation by the gas-liquid membrane separator, part of the unreacted raw material gas is used as purge gas, and the other part is passed through the second raw material gas heat exchanger and exchanged heat with another part of the product mixture from the adiabatic reactor before entering the isothermal reactor for secondary reaction. The product mixture produced by the isothermal reactor and the product mixture produced by the adiabatic reactor after heat exchange and pressure reduction are fed into the gas-liquid membrane separator for degassing to form unreacted raw material gas for recycling. The crude methanol, after being degassed by the gas-liquid membrane separator, enters the molecular sieve for dehydration treatment, and finally obtains a qualified methanol product. The method for producing methanol by carbon dioxide hydrogenation further includes: testing the purified mixed feed gas; and when the molar ratio of carbon dioxide to hydrogen in the mixed feed gas reaches 1:8 or higher, performing the step of: exchanging heat once between the mixed feed gas and a portion of the product mixture from the adiabatic reactor before entering the adiabatic reactor for an adiabatic first-stage reaction.

6. The method for producing methanol by hydrogenation of carbon dioxide as described in claim 5, characterized in that, The method for producing methanol by carbon dioxide hydrogenation further includes: passing cooling water through the isothermal reactor, absorbing the heat in the isothermal reactor through the cooling water, and then outputting steam.

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