Process and system for synthesis of methanol from carbon dioxide and hydrogen

Abstract

The present application relates to a method for synthesizing methanol from carbon dioxide and hydrogen, comprising: mixing carbon dioxide and hydrogen as reaction feed for a first reaction step, and obtaining a first reaction effluent after the reaction; separating the first reaction effluent to obtain a first methanol product and a first gaseous material; subjecting the first gaseous material to a second reaction step, and obtaining a second reaction effluent after the reaction; and separating the second reaction effluent to obtain a second methanol product and a second gaseous material; wherein the first reaction effluent is exchanged with the reaction feed of the first reaction step or the second reaction step before the separation; or the second reaction effluent is exchanged with the reaction feed of the first reaction step or the second reaction step before the separation. The present application also relates to a system for synthesizing methanol from carbon dioxide and hydrogen.

Description

Technical Field

[0001] This invention belongs to the field of methanol synthesis technology, and in particular relates to a method and system for synthesizing methanol from carbon dioxide and hydrogen. Background Technology

[0002] With continuous societal development, human emissions of greenhouse gases are constantly increasing, exacerbating the greenhouse effect. Carbon dioxide, a major greenhouse gas, is a primary cause of global warming due to its increased atmospheric concentration. Reducing carbon dioxide emissions is one of the most pressing issues that countries worldwide urgently need to address.

[0003] my country's carbon emissions are enormous and growing rapidly. In 2020, my country's annual carbon emission growth rate was 3.4%, which is not only higher than the average growth rate of 2.4% over the past 10 years, but also higher than the 0.5% growth rate during the same period. Faced with this severe situation, my country is vigorously promoting green and low-carbon development, driving the green and low-carbon transformation of its economy, and further shaping a "low-carbon future." In 2020, my country proposed "dual carbon" targets: striving to peak carbon dioxide emissions before 2030 and endeavoring to achieve carbon neutrality before 2060. Peaking carbon emissions and achieving carbon neutrality have become important strategies for my country's development.

[0004] With the introduction of the "dual carbon" target, the chemical utilization of carbon dioxide has attracted widespread attention in the industry. Many chemical companies are accelerating the development of new technologies to promote the resource utilization of carbon dioxide. For example, carbon dioxide can be used as a raw material to produce urea, salicylic acid, methanol, polycarbonate, and other polymer materials and clean fuels. Among these, carbon dioxide hydrogenation is widely considered the most important method for carbon dioxide emission reduction, which is conducive to the sustainable development of energy and the environment. Carbon dioxide hydrogenation not only reduces the amount of carbon dioxide in the atmosphere but also yields fuels and valuable chemical products. Carbon dioxide is a cheap, safe, and renewable carbon source, a basic raw material for C1 chemistry, and can be used to produce organic compounds, materials, and carbohydrates. However, carbon dioxide has not been widely used in industry, mainly due to its thermodynamic stability. Nobel laureate in Chemistry and renowned organic chemist George Ora proposed that using carbon dioxide and "renewable" hydrogen to produce methanol could be a solution to the energy shortage problem. Nobel laureate in Physics Carlo Rubia has also repeatedly suggested using carbon dioxide to produce methanol to replace the currently popular carbon capture and storage method, achieving emission reduction while providing raw materials for industry.

[0005] There are two main routes for the hydrogenation of carbon dioxide to methanol: the direct method and the indirect method. The direct method involves directly hydrogenating carbon dioxide to produce methanol. Due to thermodynamic equilibrium limitations, the equilibrium conversion rate of carbon dioxide is 20%-30%, and the equilibrium yield of methanol is ≤20%. Its advantages are a simple process and mild reaction conditions. The indirect method first converts carbon dioxide to carbon monoxide through a reverse water-gas shift reaction, and then synthesizes methanol from carbon monoxide, carbon dioxide, and hydrogen. This route can overcome the equilibrium limitations, achieving an equilibrium conversion rate of ≥45% for carbon dioxide and an equilibrium yield of ≥40% for methanol.

[0006] CN101386564B describes a process for synthesizing methanol from hydrogen and carbon dioxide. This method connects two identical reactors in series, directly synthesizing methanol from hydrogen and carbon dioxide using a copper-based catalyst. In the first reactor, hydrogen and carbon dioxide react under the action of the copper-based catalyst to produce methanol, water, carbon monoxide, and other products. The first reaction product is condensed and subjected to gas-liquid separation. The liquid phase containing methanol and water is separated as the product, while the gaseous phase containing carbon monoxide, hydrogen, and carbon dioxide enters the second reactor. The reaction continues under the action of the copper-based catalyst to produce methanol, water, and other products. The second reaction product is condensed and subjected to gas-liquid separation. The liquid phase containing methanol and water is separated as the product, while the gaseous phase containing carbon monoxide, hydrogen, and carbon dioxide is returned to the first reactor. In this method, the two reaction systems are identical. The paper "Carbon Dioxide Hydrogenation To Form Methanol via a Reverse-Water-Gas-Shift Reaction" (Ind. Eng. Chem. Res. 1999, 38, 1808-1802) introduces a method for producing methanol by hydrogenation of carbon dioxide. This method uses an indirect approach to produce methanol and mainly includes two isothermal reactors. In the first isothermal reactor, carbon dioxide undergoes a reverse-water-gas shift reaction to produce carbon monoxide. After the reaction product is dehydrated by a separator, part of it is recycled back to the first reactor, while the other part goes to the second isothermal reactor to synthesize methanol. After gas-liquid separation, the liquid crude methanol product is sent to a subsequent distillation column for further purification, while the unreacted gas is returned to the second reactor for recycling. CN113045383A describes an apparatus and process for producing methanol by carbon dioxide hydrogenation. This method includes at least three methanol production units connected in series. Each methanol production unit includes a preheater, a methanol synthesis tower, a methanol water cooler, and a methanol separator. The feed gas mixture is preheated and then enters the methanol synthesis tower for reaction. The reaction product is cooled by heat exchange and the methanol water cooler before entering the methanol separator. The gaseous output from the methanol separator enters the preheater of the next methanol production unit. The second and third stages of the process continue using the same flow as the first stage, yielding methanol-water products. Existing technologies for the direct synthesis of methanol by carbon dioxide hydrogenation suffer from problems such as large gas circulation volumes and insufficient heat utilization. Summary of the Invention

[0007] This invention addresses the shortcomings of existing technologies by providing a method and system for synthesizing methanol from carbon dioxide and hydrogen. The novel method for methanol synthesis features low gas circulation and efficient heat utilization.

[0008] To this end, the first aspect of the present invention provides a method for synthesizing methanol from carbon dioxide and hydrogen, comprising: mixing carbon dioxide and hydrogen as a reaction feed and passing it through a first reaction step; separating the first reaction effluent obtained after the reaction to obtain a first methanol product and a first gaseous material; passing the first gaseous material through a second reaction step; separating the second reaction effluent obtained after the reaction to obtain a second methanol product and a second gaseous material; and exchanging heat between the first reaction effluent and the reaction feeds of the first reaction step and the second reaction step respectively before separation.

[0009] In some embodiments of the present invention, the second reaction effluent is subjected to heat exchange with the reaction feeds of the first reaction step and the second reaction step respectively before separation.

[0010] In some embodiments of the present invention, the first reaction step and the second reaction step are adiabatic reactions or isothermal reactions.

[0011] In some embodiments of the present invention, the first reaction step and the second reaction step are different reactions.

[0012] In some embodiments of the present invention, the first reaction step is an adiabatic reaction, and the second reaction step is an isothermal reaction.

[0013] In some embodiments of the present invention, the reaction pressure of the first reaction step is 5.0-9.0 MPaG.

[0014] In some embodiments of the present invention, the second gaseous material is returned as a recycle gas to the first reaction step.

[0015] In some embodiments of the present invention, a portion of the second gaseous material is returned as recycle gas to the first reaction step.

[0016] In some embodiments of the present invention, the second gaseous material comprises more than 96% by volume as circulating gas.

[0017] In some embodiments of the present invention, the mass ratio of the second gaseous material as circulating gas to the carbon dioxide feed is 1.5-3, preferably 1.8-2.7.

[0018] In some embodiments of the present invention, another portion of the second gaseous material is discharged as purge gas.

[0019] In some embodiments of the present invention, the first reaction discharge is divided into two streams of first reaction discharge before separation; the first stream of first reaction discharge exchanges heat with the first reaction feed of the first reaction step, and the second stream of first reaction discharge exchanges heat with the second reaction feed of the second reaction step.

[0020] In some embodiments of the present invention, the ratio of the mass flow rate of the first reaction discharge to the total mass flow rate of the first reaction discharge is 0.25-0.75, preferably 0.3-0.7.

[0021] In some embodiments of the present invention, the second reaction discharge is divided into two streams of second reaction discharge before separation; the first stream of the second reaction discharge exchanges heat with the second reaction feed of the second reaction step, and the second stream of the second reaction discharge exchanges heat with the first reaction feed of the first reaction step.

[0022] In some embodiments of the present invention, the ratio of the mass flow rate of the first stream of the second reaction discharge to the total mass flow rate of the second reaction discharge is 0.25-0.75, preferably 0.3-0.7.

[0023] In some embodiments of the present invention, the molar ratio of hydrogen to carbon dioxide in the reaction feed is 3-3.5, for example, 3.

[0024] In some embodiments of the present invention, the method includes the following specific steps:

[0025] S1: Carbon dioxide and hydrogen are mixed as reaction feed and passed through an adiabatic reaction step. The adiabatic reaction effluent obtained after the reaction is divided into two streams. The first stream of adiabatic reaction effluent exchanges heat with the adiabatic reaction feed of the adiabatic reaction step, and the second stream of adiabatic reaction effluent exchanges heat with the isothermal reaction feed of the isothermal reaction step.

[0026] S2: The first adiabatic reaction discharge and the second adiabatic reaction discharge are mixed after heat exchange, and then cooled and separated to obtain adiabatic methanol product and adiabatic gaseous material. The adiabatic gaseous material is used as the reaction feed for the isothermal reaction step.

[0027] S3: After cooling and separation, the isothermal reaction effluent yields isothermal methanol product and isothermal gas phase material. The isothermal gas phase material is returned to the adiabatic reaction step as circulating gas.

[0028] In some embodiments of the present invention, the method includes the following specific steps:

[0029] S1: Carbon dioxide and hydrogen are mixed as reaction feed and reacted in an isothermal reaction step. The isothermal reaction effluent obtained after the reaction is cooled and separated to obtain isothermal methanol product and isothermal gas phase material.

[0030] S2: The isothermal gaseous material is used as the reaction feed for the adiabatic reaction step. After the reaction, the adiabatic reaction effluent is divided into two streams. The first stream of the adiabatic reaction effluent exchanges heat with the adiabatic reaction feed for the adiabatic reaction step, and the second stream of the adiabatic reaction effluent exchanges heat with the isothermal reaction feed for the isothermal reaction step.

[0031] S3: The adiabatic reaction outputs of the first and second streams are mixed after heat exchange, and then cooled and separated to obtain adiabatic methanol product and adiabatic gaseous material. The adiabatic gaseous material is returned to the isothermal reaction step as circulating gas.

[0032] In some embodiments of the present invention, the feed temperature of the adiabatic reaction step is 220-260°C.

[0033] In some embodiments of the present invention, the feed temperature of the isothermal reaction step is 220-290°C.

[0034] In some embodiments of the present invention, the catalysts used in the adiabatic reaction step and the isothermal reaction step include methanol synthesis catalysts using hydrogen and carbon dioxide as reactants.

[0035] In some embodiments of the present invention, copper-based catalysts are used in the adiabatic reaction steps and isothermal reaction steps, but not limited to those used in the present invention.

[0036] In some embodiments of the present invention, copper-based catalysts containing copper, zinc, and aluminum are used in the adiabatic reaction steps and isothermal reaction steps, but not limited to those containing copper, zinc, and aluminum.

[0037] A second aspect of the present invention provides a system for synthesizing methanol from carbon dioxide and hydrogen, comprising: an adiabatic reactor and an isothermal reactor connected in communication, wherein the adiabatic reactor is connected to a first discharge pipeline and a second discharge pipeline, the ends of the first discharge pipeline and the second discharge pipeline away from the adiabatic reactor being respectively connected to an adiabatic reaction discharge mixing pipeline; and an adiabatic reaction second heat exchanger is provided between the first discharge pipeline and the feed pipeline of the adiabatic reactor.

[0038] In some embodiments of the present invention, an isothermal reaction second heat exchanger is provided between the second discharge pipeline and the feed pipeline of the isothermal reactor.

[0039] In some embodiments of the present invention, the adiabatic reactor is connected to the isothermal reactor via the feed line of the isothermal reactor.

[0040] In some embodiments of the present invention, the isothermal reactor is connected to the adiabatic reactor via a feed line to the adiabatic reactor.

[0041] In some embodiments of the present invention, the system further includes: the adiabatic reactor is connected to the adiabatic reaction gas-liquid separator via an adiabatic reaction discharge mixing pipeline.

[0042] In some embodiments of the present invention, the isothermal reactor is connected to the isothermal gas-liquid separator via an isothermal reaction discharge pipeline.

[0043] In some embodiments of the present invention, the adiabatic reaction gas-liquid separator is connected to the isothermal reactor via the feed line of the isothermal reactor, and the isothermal reaction gas-liquid separator is connected to the feed line of the adiabatic reactor via a circulating gas line.

[0044] In some embodiments of the present invention, the isothermal reaction gas-liquid separator is connected to the adiabatic reactor via the feed pipeline of the adiabatic reactor, and the adiabatic reaction gas-liquid separator is connected to the feed pipeline of the isothermal reactor via the circulating gas pipeline.

[0045] In some embodiments of the present invention, an adiabatic reaction cooler is provided on the adiabatic reaction discharge mixing pipeline.

[0046] In some embodiments of the present invention, an adiabatic reaction first heat exchanger is provided between the adiabatic reaction discharge mixing pipeline and the feed pipeline of the adiabatic reactor.

[0047] In some embodiments of the present invention, an isothermal reaction cooler is provided on the isothermal reaction discharge pipeline.

[0048] In some embodiments of the present invention, an isothermal reaction first heat exchanger is provided between the isothermal reaction discharge pipeline and the isothermal reactor feed pipeline.

[0049] In some embodiments of the present invention, a circulating compressor is provided on the circulating gas pipeline.

[0050] In some embodiments of the present invention, the adiabatic reactor is an axially or radially adiabatic fixed-bed reactor.

[0051] In some embodiments of the present invention, the isothermal reactor is an isothermal tubular fixed-bed reactor.

[0052] Technical effects:

[0053] (1) The present invention directly reacts carbon dioxide and hydrogen to produce methanol by using a combined reaction method of adiabatic reaction and isothermal reaction. By using adiabatic and isothermal reactors and isothermal reactors for the reaction, the gas circulation volume of the reaction system is greatly reduced.

[0054] (2) By adopting an adiabatic reaction scheme, the heat generated by the adiabatic reaction itself is used to heat the inlet materials of the adiabatic reactor and the isothermal reactor to a specified temperature. This avoids the shortcomings of usually requiring the introduction of external heating equipment and energy to heat the inlet materials of the reactor to a specified temperature, reduces equipment investment, improves the overall heat utilization effect and environmental protection level of the system, and achieves better technical results. Attached Figure Description

[0055] Figure 1 This is a schematic diagram of the process flow for the synthesis of methanol from carbon dioxide and hydrogen according to the present invention.

[0056] Figure 2 This is a schematic diagram of the process flow for synthesizing methanol from carbon dioxide and hydrogen according to the present invention, which is consistent with... Figure 1 The difference lies in the different reaction sequences of adiabatic reactors and isothermal reactors.

[0057] Icons: 1-Carbon dioxide feedstock, 2-Hydrogen feedstock, 3-Adiabatic reaction feed, 4-First adiabatic reaction discharge, 5-Second adiabatic reaction discharge, 6-Adiabatic methanol feed, 7-Adiabatic gaseous feed, 8-Isothermal reaction feed, 9-Isothermal reaction discharge, 10-Isothermal methanol feed, 11-Isothermal gaseous feed, 12-Circulating gas, 13-Releasing gas, R1-Adiabatic reactor, R2-Isothermal reactor, E1-First adiabatic reaction heat exchanger, E2-Second adiabatic reaction heat exchanger, E3-Adiabatic reaction cooler, E4-First isothermal reaction heat exchanger, E5-Second isothermal reaction heat exchanger, E6-Isothermal reaction cooler, V1-Adiabatic reaction gas-liquid separator, V2-Isothermal reaction gas-liquid separator, K1-Circulating compressor. Detailed Implementation

[0058] To make the present invention easier to understand, the present invention will be further described in detail below with reference to embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of application of the present invention. Unless otherwise specified, the raw materials or components used in the present invention can be obtained commercially or by conventional methods.

[0059] The carbon dioxide used in this invention is either commercially available cylinder gas or high-purity carbon dioxide gas from a factory, and the hydrogen is either commercially available cylinder gas or high-purity hydrogen gas from a factory.

[0060] The process description and implementation examples are all based on Figure 1 The process flow shown is explained below:

[0061] according to Figure 1The process shown involves mixing carbon dioxide feedstock 1 and hydrogen feedstock 2, which then sequentially enter the first adiabatic reaction heat exchanger E1 and the second adiabatic reaction heat exchanger E2. After being heated by heat exchange, the adiabatic reaction feedstock 3 enters the adiabatic reactor R1, where methanol is produced under the action of a catalyst. The adiabatic reaction effluent is divided into two streams: the first stream, adiabatic reaction effluent 4, enters the second adiabatic reaction heat exchanger E2 to heat the adiabatic reaction feedstock 3 to a specified temperature; the second stream, adiabatic reaction effluent 5, enters the second isothermal reaction heat exchanger E5 to heat the isothermal reaction feedstock 8 to a specified temperature. After being cooled by heat exchange, the first stream of adiabatic reaction effluent 4 and the second stream of adiabatic reaction effluent 5 are mixed and sequentially cooled by heat exchange in the first adiabatic reaction heat exchanger E1 and cooled in the adiabatic reaction cooler E3 before entering the adiabatic reaction gas-liquid separator V1 for further processing. Gas-liquid separation: At the bottom of the adiabatic reaction gas-liquid separator V1, adiabatic methanol material 6 is obtained, and at the top of the separator, adiabatic gas phase material 7 is obtained. These materials sequentially enter the first isothermal reaction heat exchanger E4 and the second isothermal reaction heat exchanger E5. After being heated by heat exchange, the isothermal reaction feed 8 enters the isothermal reactor R2, where methanol is generated under the action of a catalyst. The isothermal reaction effluent 9 is sequentially cooled by heat exchange in the first isothermal reaction heat exchanger E4 and cooled by the isothermal reaction cooler E6 before entering the isothermal reaction gas-liquid separator V2 for gas-liquid separation. At the bottom of the isothermal reaction gas-liquid separator V2, isothermal methanol material 10 is obtained, and at the top of the separator, isothermal gas phase material 11 is obtained. Most of the isothermal gas phase material 11 is returned to the adiabatic reactor R1 as circulating gas 12 after being pressurized by the circulating compressor K1, while a small portion is discharged as purge gas 13.

[0062] Example 1

[0063] according to Figure 1 As shown, the carbon dioxide feed rate is 500 mol / h, the hydrogen feed rate is 1500 mol / h, the feed temperature for the adiabatic reaction step is 220℃, and the reaction pressure is 5.0 MPaG. The feed temperature for the isothermal reaction step is also 220℃. Both the adiabatic and isothermal reactors are filled with copper-based catalysts (specifically, the composition is 50% copper, 40% zinc, and 10% aluminum). The ratio of the mass flow rate of the first adiabatic reaction effluent to the total mass flow rate of the adiabatic reaction effluent is 0.75. After heat exchange, cooling, and separation, 97% of the isothermal gaseous material obtained from the isothermal reaction effluent is returned to the adiabatic reactor as recirculated gas, with a recirculation ratio of 2.2 (the ratio of the recirculated gas mass flow rate to the raw carbon dioxide mass flow rate, the same below). The methanol yield is 90.6% (relative to the carbon dioxide feedstock, the same below). The heat exchange required to process each kilogram of raw carbon dioxide is 3393 kJ (the sum of the heat exchange rates of heat exchangers E1, E2, E4, and E5, the same below).

[0064] Example 2

[0065] according to Figure 1As shown, the carbon dioxide feed rate is 500 mol / h, the hydrogen feed rate is 1500 mol / h, the feed temperature for the adiabatic reaction step is 240℃, the reaction pressure is 7.0 MPaG, and the feed temperature for the isothermal reaction step is 250℃. Both the adiabatic and isothermal reactors are filled with copper-based catalysts (specifically, the composition is 60% copper, 20% zinc, and 20% aluminum). The ratio of the mass flow rate of the first adiabatic reaction effluent to the total mass flow rate of the adiabatic reaction effluent is 0.6. After heat exchange, cooling, and separation, 97% of the gaseous material obtained from the isothermal reaction effluent is returned to the adiabatic reactor as recirculated gas, with a recirculation ratio of 1.8. The methanol yield is 92.2%, and the heat exchange required to process each kilogram of carbon dioxide feedstock is 3258 kJ.

[0066] Example 3

[0067] according to Figure 1 As shown, the carbon dioxide feed rate is 500 mol / h, the hydrogen feed rate is 1500 mol / h, the feed temperature for the adiabatic reaction step is 260℃, the reaction pressure is 6.0 MPaG, and the feed temperature for the isothermal reaction step is 290℃. Both the adiabatic and isothermal reactors are filled with copper-based catalysts (specifically, the composition is 70% copper, 10% zinc, and 20% aluminum). The ratio of the mass flow rate of the first adiabatic reaction effluent to the total mass flow rate of the adiabatic reaction effluent is 0.25. After heat exchange, cooling, and separation, 98% of the gaseous material obtained from the isothermal reaction effluent is returned to the adiabatic reactor as recirculated gas, with a recirculation ratio of 2.1. The methanol yield is 93.9%, and the heat exchange required to process each kilogram of carbon dioxide feedstock is 4125 kJ.

[0068] Example 4

[0069] according to Figure 1 As shown, the carbon dioxide feed rate is 500 mol / h, the hydrogen feed rate is 1500 mol / h, the feed temperature for the adiabatic reaction step is 230℃, the reaction pressure is 9.0 MPaG, and the feed temperature for the isothermal reaction step is 270℃. Both the adiabatic and isothermal reactors are filled with copper-based catalysts (specifically, the composition is 30% copper, 50% zinc, and 20% aluminum). The ratio of the mass flow rate of the first adiabatic reaction effluent to the total mass flow rate of the adiabatic reaction effluent is 0.4. After heat exchange, cooling, and separation, 98.5% of the gaseous material obtained from the isothermal reaction effluent is returned to the adiabatic reactor as recycle gas. The recycle ratio is 2.2, the methanol yield is 95.1%, and the heat exchange required to process each kilogram of carbon dioxide feed is 3734 kJ.

[0070] Example 5

[0071] according to Figure 1As shown, the carbon dioxide feed rate is 500 mol / h, the hydrogen feed rate is 1500 mol / h, the feed temperature for the adiabatic reaction step is 250℃, the reaction pressure is 8.0 MPaG, and the feed temperature for the isothermal reaction step is 260℃. Both the adiabatic and isothermal reactors are filled with copper-based catalysts (specifically, the composition is 40% copper, 30% zinc, and 30% aluminum). The mass flow rate ratio of the first adiabatic reaction effluent to the total mass flow rate of the adiabatic reaction effluent is 0.5. After heat exchange, cooling, and separation, 99% of the gaseous material obtained from the isothermal reaction effluent is returned to the adiabatic reactor as recirculated gas, with a recirculation ratio of 2.7. The methanol yield is 96.0%, and the heat exchange required to process each kilogram of carbon dioxide feedstock is 4442 kJ.

[0072] Comparative Example 1

[0073] The comparative example uses the same method and system as Example 1, with the only difference being that the adiabatic reactor is replaced with an isothermal reactor. The heat exchange required to process each kilogram of raw material carbon dioxide is 3002 kJ (the sum of the heat exchange of heat exchangers E1 and E4), requiring an external supply of 391 kJ of heating energy to the reaction feed (to compensate for the heat exchange of heat exchangers E2 and E5). The external heating accounts for 11.5% of the total heat of heat exchangers E1, E2, E4, and E5.

[0074] Comparative Example 2

[0075] The comparative example uses the same method and system as Example 1, with the only difference being that only a single isothermal reactor is used. Under the premise of maintaining the same methanol yield as in Example 1, the recycle ratio is 5.0, and the heat exchange required to process each kilogram of raw material carbon dioxide is 3051 kJ (heat exchange of heat exchanger E4). An external heating of 390 kJ is required to supply the reactor feed (to compensate for the heat exchange of heat exchanger E5). The external heating accounts for 11.3% of the total heat of heat exchangers E4 and E5.

[0076] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for synthesizing methanol from carbon dioxide and hydrogen, characterized in that, include: Carbon dioxide and hydrogen are mixed as reaction feed and passed through the first reaction step. The first reaction effluent obtained after the reaction is separated to obtain the first methanol product and the first gaseous material. The first gaseous material is passed through the second reaction step. The second reaction effluent obtained after the reaction is separated to obtain the second methanol product and the second gaseous material. The first reaction effluent is heat exchanged with the reaction feed of the first reaction step and the second reaction step respectively before separation. Alternatively, the effluent from the second reaction step may be heat-exchanged with the feeds from both the first and second reaction steps before separation. The first reaction step and the second reaction step are adiabatic reactions or isothermal reactions; the feed temperature of the adiabatic reaction step is 220-260℃, and the feed temperature of the isothermal reaction step is 220-290℃. The first reaction step is an adiabatic reaction and the second reaction step is an isothermal reaction. The first reaction effluent is divided into two streams before separation. The first stream of the first reaction effluent exchanges heat with the first reaction feed of the first reaction step, and the second stream of the first reaction effluent exchanges heat with the second reaction feed of the second reaction step. Alternatively, the second reaction step is an adiabatic reaction and the first reaction step is an isothermal reaction. The second reaction effluent is divided into two streams before separation. The first stream of the second reaction effluent exchanges heat with the second reaction feed of the second reaction step, and the second stream of the second reaction effluent exchanges heat with the first reaction feed of the first reaction step.

2. The method according to claim 1, characterized in that, The first reaction step is an adiabatic reaction, and the second reaction step is an isothermal reaction.

3. The method according to claim 2, characterized in that, The reaction pressure of the first reaction step is 5.0-9.0 MPaG.

4. The method according to claim 1, characterized in that, The second gaseous material is returned to the first reaction step as a circulating gas.

5. The method according to claim 4, characterized in that, A portion of the second gaseous material is returned as recycle gas to the first reaction step.

6. The method according to claim 5, characterized in that, More than 96% of the volume of the second gas phase material is used as circulating gas.

7. The method according to claim 1, characterized in that, The ratio of the mass flow rate of the first reaction product to the total mass flow rate of the first reaction product is 0.25-0.75; And / or, the ratio of the mass flow rate of the first stream of the second reaction discharge to the total mass flow rate of the second reaction discharge is 0.25-0.

75.

8. The method according to claim 7, characterized in that, The ratio of the mass flow rate of the first reaction discharge to the total mass flow rate of the first reaction discharge is 0.3-0.7; And / or, the ratio of the mass flow rate of the first stream of the second reaction discharge to the total mass flow rate of the second reaction discharge is 0.3-0.

7.

9. The method according to claim 1, characterized in that, The molar ratio of hydrogen to carbon dioxide in the reaction feed is 3-3.

5.

10. The method according to claim 1, characterized in that, The specific steps include the following: S1: Carbon dioxide and hydrogen are mixed as reaction feed and passed through an adiabatic reaction step. The adiabatic reaction effluent obtained after the reaction is divided into two streams. The first stream of adiabatic reaction effluent exchanges heat with the adiabatic reaction feed of the adiabatic reaction step, and the second stream of adiabatic reaction effluent exchanges heat with the isothermal reaction feed of the isothermal reaction step. S2: The first adiabatic reaction discharge and the second adiabatic reaction discharge are mixed after heat exchange, and then cooled and separated to obtain adiabatic methanol product and adiabatic gaseous material. The adiabatic gaseous material is used as the reaction feed for the isothermal reaction step. S3: After cooling and separation, the isothermal reaction effluent yields isothermal methanol product and isothermal gas phase material. The isothermal gas phase material is returned to the adiabatic reaction step as circulating gas. Alternatively, S1: Carbon dioxide and hydrogen are mixed as the reaction feed and reacted in an isothermal reaction step. The isothermal reaction effluent obtained after the reaction is cooled and separated to obtain isothermal methanol product and isothermal gas phase material. S2: The isothermal gaseous material is used as the reaction feed for the adiabatic reaction step. After the reaction, the adiabatic reaction effluent is divided into two streams. The first stream of the adiabatic reaction effluent exchanges heat with the adiabatic reaction feed for the adiabatic reaction step, and the second stream of the adiabatic reaction effluent exchanges heat with the isothermal reaction feed for the isothermal reaction step. S3: The adiabatic reaction outputs of the first and second streams are mixed after heat exchange, and then cooled and separated to obtain adiabatic methanol product and adiabatic gaseous material. The adiabatic gaseous material is returned to the isothermal reaction step as circulating gas.

11. The method according to claim 1, characterized in that, Copper-based catalysts are used in the adiabatic reaction step and the isothermal reaction step.

12. The method according to any one of claims 1-11, characterized in that, The method is carried out in a system for synthesizing methanol from carbon dioxide and hydrogen, the system comprising: an adiabatic reactor and an isothermal reactor connected in communication; the adiabatic reactor is connected to a first discharge pipeline and a second discharge pipeline, the ends of the first and second discharge pipelines away from the adiabatic reactor being respectively connected to an adiabatic reaction discharge mixing pipeline; an adiabatic reaction second heat exchanger is provided between the first discharge pipeline and the feed pipeline of the adiabatic reactor; and / or, an isothermal reaction second heat exchanger is provided between the second discharge pipeline and the feed pipeline of the isothermal reactor.

13. The method according to claim 12, characterized in that, The adiabatic reactor is connected to the isothermal reactor via the feed line of the isothermal reactor; or, the isothermal reactor is connected to the adiabatic reactor via the feed line of the adiabatic reactor.

14. The method according to claim 12, characterized in that, The system further includes: the adiabatic reactor is connected to the adiabatic gas-liquid separator via an adiabatic reaction discharge mixing pipeline; and / or, the isothermal reactor is connected to the isothermal gas-liquid separator via an isothermal reaction discharge pipeline.

15. The method according to claim 14, characterized in that, The adiabatic gas-liquid separator is connected to the isothermal reactor via the feed line of the isothermal reactor, and the isothermal gas-liquid separator is connected to the feed line of the adiabatic reactor via a circulating gas line; or, the isothermal gas-liquid separator is connected to the adiabatic reactor via the feed line of the adiabatic reactor, and the isothermal gas-liquid separator is connected to the feed line of the isothermal reactor via a circulating gas line.

16. The method according to claim 14, characterized in that, An adiabatic reaction cooler is provided on the adiabatic reaction discharge mixing pipeline, and / or an adiabatic reaction first heat exchanger is provided between the adiabatic reaction discharge mixing pipeline and the feed pipeline of the adiabatic reactor; and / or an isothermal reaction cooler is provided on the isothermal reaction discharge pipeline, and / or an isothermal reaction first heat exchanger is provided between the isothermal reaction discharge pipeline and the feed pipeline of the isothermal reactor.

17. The method according to claim 15, characterized in that, A recirculating compressor is installed on the recirculating gas pipeline.

18. The method according to claim 12, characterized in that, The adiabatic reactor is an axially or radially adiabatic fixed-bed reactor; and / or, the isothermal reactor is an isothermal tubular fixed-bed reactor.

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