Process for preparing methanol by hydrogenating carbon dioxide

Abstract

The process comprises a material mixing unit, a methanol synthesis unit and a three-stage separation and purification unit which are communicated in sequence, the material mixing unit is used for mixing hydrogen and carbon dioxide, and the methanol synthesis unit is used for mixing the hydrogen and the carbon dioxide to generate crude methanol; the third-stage separation and purification unit is used for refining and purifying the crude methanol; the process of preparing methanol can be realized through clean gas carbon dioxide and hydrogen, energy utilization of carbon dioxide can be realized, and the hydrogen energy industry is optimized; high-temperature crude methanol discharged from a methanol synthesizer is used as heat supply, so that cyclic utilization of heat energy is realized; water electrolysis is adopted for hydrogen production, reaction ways are reduced, and energy consumption and generation of by-products are reduced; a three-tower series rectification mode is adopted, operation parameters are optimized, the methanol recovery rate is increased, and the investment cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of methanol production, and in particular to a process for producing methanol by hydrogenating carbon dioxide. Background Art

[0002] In the context of energy structure adjustment, the active development of biogas by-product carbon dioxide resource and energy utilization has attracted much attention, and the path of its conversion into high-value products is particularly important; hydrogen, as a green, pollution-free clean energy, has a wide range of utilization value. However, it has problems such as explosion risk, difficulty in transportation and storage. Methanol, as an important chemical raw material and clean energy carrier, can promote the industrial optimization of carbon dioxide and hydrogen energy as a "carbon carrier" and "hydrogen carrier". Carbon dioxide hydrogenation to methanol is an important way to transform and utilize carbon dioxide and hydrogen energy resources, and it is also one of the key means to achieve the goal of carbon neutrality.

[0003] In the existing process of producing methanol from carbon dioxide, methanol is recovered through multi-stage tower distillation. However, the gas phase at the top of the tower easily carries a large amount of methanol gas, which needs to be filtered before it can be discharged. The cost of treating the methanol mixed gas in the subsequent gas phase is high, affecting the economic efficiency. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a process for producing methanol by hydrogenating carbon dioxide to solve the problem of high gas emission cost in producing methanol.

[0005] Based on the technical problems existing in the background technology, the present invention proposes a process for producing methanol by hydrogenating carbon dioxide, comprising a mixing unit, a methanol synthesis unit, and a three-stage separation and purification unit connected in sequence, wherein the mixing unit is used for mixing hydrogen and carbon dioxide, the methanol synthesis unit is used for mixing hydrogen and carbon dioxide to generate crude methanol, and the three-stage separation and purification unit is used for refining and purifying the crude methanol.

[0006] Preferably, the mixing unit includes a water electrolysis device, a cooling and rewarming device, a primary compressor of raw gas, a secondary compressor of raw gas, an LCO2 storage tank, a heat exchanger, an air-temperature vaporizer and a raw gas buffer tank. The water electrolysis device, the cooling and rewarming device, the primary compressor of raw gas, and the secondary compressor of raw gas are connected in sequence to form a hydrogen mixing unit. The LCO2 storage tank, the heat exchanger, and the air-temperature vaporizer are connected in sequence to form a carbon dioxide mixing unit. The hydrogen mixing unit and the carbon dioxide mixing unit are both connected to the raw gas buffer tank and the hydrogen and carbon dioxide are mixed through the raw gas buffer tank.

[0007] Preferably, the methanol synthesis unit comprises a preheater, a methanol synthesis reactor, a heat exchange group, and a cooler. The raw gas buffer tank, the preheater, the heat exchange group, and the cooler are connected in sequence. The methanol synthesis reactor is connected to the preheater and refluxes to the preheater.

[0008] Preferably, an electric heater is connected to the channel from the preheater to the methanol synthesis reactor.

[0009] Preferably, the three-stage separation and purification unit comprises a gas-liquid separator, a pre-distillation tower, an atmospheric distillation tower, and a vacuum distillation tower, and the cooler, gas-liquid separator, pre-distillation tower, atmospheric distillation tower, and vacuum distillation tower are connected in sequence.

[0010] Preferably, the gas phase end at the top of the gas-liquid separator is connected to the channel between the primary compressor of the raw gas and the secondary compressor of the raw gas.

[0011] Preferably, the gas phase at the top of the pre-distillation tower is connected to a pipeline from the water electrolysis device to the cooling and reheating device.

[0012] Compared with the prior art, the process for producing methanol by hydrogenating carbon dioxide proposed in the present invention adopts the above technical solution and achieves the following technical effects:

[0013] The present invention can realize the process of producing methanol through clean gaseous carbon dioxide and hydrogen, realize the energy utilization of carbon dioxide, and optimize the hydrogen energy industry; utilize the high-temperature crude methanol produced by the methanol synthesizer as heat supply to realize the recycling of thermal energy; the present invention adopts water electrolysis to produce hydrogen, reduces the reaction pathway, reduces energy consumption and the generation of by-products; the present invention adopts a three-tower series distillation method, optimizes the operating parameters, improves the methanol recovery rate, and reduces the investment cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the process of the present invention.

[0015] In the figure: 100, mixing unit; 200, methanol synthesis unit; 300, three-stage separation and purification unit; 1, water electrolysis device; 2, cooling and reheating device; 3, primary compressor of raw gas; 4, secondary compressor of raw gas; 5, LCO2 storage tank; 6, heat exchanger; 7, air-temperature vaporizer; 8, raw gas buffer tank; 101, hydrogen mixing unit; 102, carbon dioxide mixing unit; 9, preheater; 10, methanol synthesis reactor; 17, heat exchange group; 11, cooler; 16, electric heater; 12, gas-liquid separator; 13, pre-distillation tower; 14, atmospheric distillation tower; 15, vacuum distillation tower. DETAILED DESCRIPTION

[0016] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0017] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0018] Example

[0019] Please refer to Figure 1 The present invention proposes a process for producing methanol by hydrogenating carbon dioxide, comprising a mixing unit 100, a methanol synthesis unit 200, and a three-stage separation and purification unit 300 which are connected in sequence. The mixing unit 100 mixes hydrogen and carbon dioxide to form a mixed gas, and the mixed gas is reversed through the methanol synthesis unit 200 to generate crude methanol, wherein the crude methanol contains a mixture of gas phase and liquid phase. The gas phase mixture is returned to the mixing unit 100 to continue mixing reaction, and the liquid phase mixture is refined into refined methanol through the three-stage separation and purification unit 300. At the same time, the gas phase mixture in the three-stage separation unit is returned to the mixing unit 100 for mixing.

[0020] In a specific embodiment, refer to Figure 1The mixing unit includes a water electrolysis device 1, a cooling and reheating device 2, a raw gas primary compressor 3, a raw gas secondary compressor 4, an LCO2 storage tank 5, a heat exchanger 6, an air-temperature vaporizer 7 and a raw gas buffer tank 8. The water electrolysis device 1, the cooling and reheating device 2, the raw gas primary compressor 3, and the raw gas secondary compressor 4 are sequentially connected to form a hydrogen mixing unit 101, wherein the water electrolysis device 1 is used to produce high-concentration hydrogen, and its oxygen will be discharged into the air. The hydrogen will be reheated to 20-35 degrees through the cooling and reheating device 2 to keep the hydrogen at normal pressure, and then compressed once through the raw gas primary compressor 3 to reduce the gas volume, and then compressed twice through the raw gas secondary compressor 4 to 2.0MPa further reduces the volume and reduces the space occupied; the LCO2 storage tank 5, the heat exchanger 6, and the air-temperature vaporizer 7 are connected in sequence to form a carbon dioxide mixing unit 102. The LCO2 storage tank 5 provides carbon dioxide. The pressure in the LCO2 storage tank 5 is 2.0Mpa and the temperature is -25 degrees. It is converted into gaseous carbon dioxide through heat exchanger 6. The heat exchanger 6 exchanges heat through flowing ethylene glycol antifreeze, and then passes through the air-temperature vaporizer 7 to reheat to 40 degrees and is sent to the raw gas buffer tank 8 for mixing; the hydrogen mixing unit 101 and the carbon dioxide mixing unit 102 formed above are both connected to the raw gas buffer tank 8 and the hydrogen and carbon dioxide are mixed through the raw gas buffer tank 8.

[0021] In a specific embodiment, refer to Figure 1 The methanol synthesis unit 200 includes a preheater 9, a methanol synthesis reactor 10, a heat exchange group 17, and a cooler 11. The raw gas buffer tank 8, the preheater 9, the heat exchange group 17, and the cooler 11 are connected in sequence. The methanol synthesis reactor 10 is connected to the preheater 9 and refluxes to the preheater 9. In this scheme, the preheater 9 can receive the mixed gas from the raw gas buffer tank 8 and heat the mixed gas to 230 degrees. The heated mixed gas reacts in the methanol synthesis reactor 10 to generate methanol. The heat generated by the reaction will be exchanged through the heat exchange group 17. The heat exchange group 17 is connected to the heat exchanger 6 and shares ethylene glycol antifreeze for heat exchange, thereby realizing heat recycling. Then the mixed gas containing methanol is cooled to 40 degrees through the cooler 11.

[0022] In a specific embodiment, refer to Figure 1 An electric heater 16 is connected to the passage from the preheater 9 to the methanol synthesis reactor 10. The electric heater 16 is used during the first operation to heat the passage from the preheater 9 to the methanol synthesis reactor 10.

[0023] In a specific embodiment, refer to Figure 1The three-stage separation and purification unit 300 includes a gas-liquid separator 12, a pre-distillation tower 13, an atmospheric distillation tower 14, and a vacuum distillation tower 15. The cooler 11, the gas-liquid separator 12, the pre-distillation tower 13, the atmospheric distillation tower 14, and the vacuum distillation tower 15 are connected in sequence. In this scheme, the gas-liquid separator 12 receives the gas containing methanol after the reaction of the methanol synthesis unit 200, and separates the gas phase and the liquid phase through the gas-liquid separator 12. The separated liquid phase is first sent to the pre-distillation tower 13 to distill out the carbon dioxide and hydrogen dissolved in the liquid phase, and the liquid phase at the bottom of the pre-distillation tower 13 is sent to the atmospheric distillation tower 14. The distilled gas phase is cooled by the top cooler of the atmospheric distillation tower 14 to obtain refined methanol. The liquid phase at the bottom of the atmospheric distillation tower 14 is sent to the vacuum distillation tower 15, and the top gas phase is cooled by the top cooler of the atmospheric distillation tower 14 to obtain refined methanol.

[0024] In a further embodiment, reference is made to Figure 1 The gas phase separated from the top of the gas-liquid separator 12 will flow back to the inlet of the raw gas secondary compressor 4.

[0025] In a further embodiment, reference is made to Figure 1 The gas phase at the top of the pre-distillation tower 13 is connected to the pipeline between the water electrolysis device 1 and the cooling and reheating device 2. The gas phase distilled from the pre-distillation tower 13 is first cooled by the top cooler of the pre-distillation tower 13 and then refluxed to the cooling and reheating device 2.

[0026] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A process for preparing methanol by hydrogenating carbon dioxide, characterized in that: The invention comprises a mixing unit (100), a methanol synthesis unit (200), and a three-stage separation and purification unit (300) which are connected in sequence. The mixing unit (100) is used for mixing hydrogen and carbon dioxide, the methanol synthesis unit (200) is used for mixing hydrogen and carbon dioxide to generate crude methanol, and the three-stage separation and purification unit (300) is used for refining and purifying the crude methanol.

2. The process for producing methanol by hydrogenation of carbon dioxide according to claim 1, characterized in that: The mixing unit comprises a water electrolysis device (1), a cooling and reheating device (2), a primary raw gas compressor (3), a secondary raw gas compressor (4), an LCO2 storage tank (5), a heat exchanger (6), an air-temperature vaporizer (7) and a raw gas buffer tank (8); the water electrolysis device (1), the cooling and reheating device (2), the primary raw gas compressor (3) and the secondary raw gas compressor (4) are sequentially connected to form a hydrogen mixing unit (101); the LCO2 storage tank (5), the heat exchanger (6) and the air-temperature vaporizer (7) are sequentially connected to form a carbon dioxide mixing unit (102); the hydrogen mixing unit (101) and the carbon dioxide mixing unit (102) are both connected to the raw gas buffer tank (8) and hydrogen and carbon dioxide are mixed through the raw gas buffer tank (8).

3. The process for producing methanol by hydrogenation of carbon dioxide according to claim 2, characterized in that: The methanol synthesis unit (200) comprises a preheater (9), a methanol synthesis reactor (10), a heat exchange group (17), and a cooler (11); the raw gas buffer tank (8), the preheater (9), the heat exchange group (17), and the cooler (11) are connected in sequence; the methanol synthesis reactor (10) is connected to the preheater (9) and refluxes to the preheater (9).

4. The process for producing methanol by hydrogenation of carbon dioxide according to claim 3, characterized in that: An electric heater (16) is connected to the passage from the preheater (9) to the methanol synthesis reactor (10).

5. The process for producing methanol by hydrogenation of carbon dioxide according to claim 3, characterized in that: The three-stage separation and purification unit (300) comprises a gas-liquid separator (12), a pre-distillation tower (13), an atmospheric distillation tower (14), and a vacuum distillation tower (15); the cooler (11), the gas-liquid separator (12), the pre-distillation tower (13), the atmospheric distillation tower (14), and the vacuum distillation tower (15) are connected in sequence.

6. The process for producing methanol by hydrogenation of carbon dioxide according to claim 5, characterized in that: The gas phase end at the top of the gas-liquid separator (12) is connected to the channel between the primary raw gas compressor (3) and the secondary raw gas compressor (4).

7. The process for producing methanol by hydrogenation of carbon dioxide according to claim 5, characterized in that: The gas phase at the top of the pre-distillation tower (13) is connected to a pipeline from the water electrolysis device (1) to the cooling and reheating device (2).

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