System and method for producing green methanol by combining green hydrogen and carbon capture

Abstract

This invention proposes a system and method for synthesizing green methanol using green hydrogen combined with carbon capture. The system includes a water electrolysis separation system, a hydrogen purification system, a methanol reaction system, and a methanol distillation system connected in sequence. The water electrolysis separation system includes an electrolyzer; the hydrogen purification system includes a deoxygenation tower and an adsorption tower; the methanol reaction system includes a methanol synthesis reactor and a circulating compressor, used to mix purified hydrogen with carbon dioxide, pressurize it, and carry out a catalytic reaction to produce crude methanol. After condensation and separation, the non-condensable gas is returned to the methanol synthesis reactor through the circulating compressor; the methanol distillation system includes a pre-distillation tower and a methanol distillation tower, used to distill and purify the crude methanol to obtain refined methanol, thereby solving the problems of traditional methanol production relying on fossil raw materials, complex processes, high energy consumption, large carbon emissions, and the lack of efficient utilization pathways for carbon dioxide obtained from carbon capture in existing technologies.

Description

Technical Field

[0001] This invention relates to a system and method for synthesizing green methanol by combining green hydrogen with carbon capture. Background Technology

[0002] With the global energy structure shifting towards cleaner energy sources, methanol, as an important chemical raw material and clean energy carrier, has broad application prospects in the chemical industry, fuel cells, and energy storage. Traditional methanol production mainly relies on fossil fuels such as coal and natural gas, obtaining syngas (a mixture of CO and H2) through coal gasification or natural gas reforming, which is then used in methanol synthesis to produce the product. While this process is technologically mature, it suffers from high carbon emissions and energy consumption, making it difficult to meet carbon neutrality goals.

[0003] To reduce carbon emissions, a technological route has emerged in recent years that utilizes renewable energy to electrolyze water to produce hydrogen, combined with carbon capture technology to synthesize methanol from carbon dioxide. Chinese patent CN118594415A discloses a system for producing green methanol through carbon dioxide electrolysis. This system integrates a carbon dioxide electrolysis unit with a water electrolysis unit to produce hydrogen, obtaining CO and H2 through electrolysis, followed by methanol synthesis. However, this approach requires the simultaneous operation of two electrolysis units (carbon dioxide electrolysis and water electrolysis), resulting in high system complexity, large equipment investment, and high energy consumption during the carbon dioxide electrolysis process, thus limiting its economic viability.

[0004] Therefore, a green hydrogen combined with carbon capture technology to synthesize green methanol is needed, which has a simple process flow, reasonable equipment investment, and high energy utilization efficiency, so as to achieve efficient utilization of carbon resources and low carbonization of the methanol production process. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a system and method for synthesizing green methanol by combining green hydrogen with carbon capture. This addresses the problems of traditional methanol production relying on fossil fuels, complex processes, high energy consumption, large carbon emissions, and the lack of efficient utilization pathways for carbon dioxide obtained through carbon capture. This objective is achieved as follows:

[0006] This invention proposes a system for synthesizing green methanol by combining green hydrogen with carbon capture, comprising a water electrolysis separation system, a hydrogen purification system, a methanol reaction system, and a methanol distillation system connected in sequence. The water electrolysis separation system includes an electrolytic cell for electrolyzing and separating deionized water to obtain hydrogen and oxygen. The hydrogen purification system includes a deoxygenation tower and an adsorption tower for purifying the hydrogen. The methanol reaction system includes a methanol synthesis reactor and a circulating compressor for mixing the purified hydrogen with carbon dioxide, pressurizing the mixture, and conducting a catalytic reaction to produce crude methanol. After condensation and separation, the non-condensable gas is returned to the methanol synthesis reactor via the circulating compressor. The methanol distillation system includes a pre-distillation tower and a methanol distillation tower for purifying the crude methanol to obtain refined methanol.

[0007] Furthermore, the volume ratio of hydrogen to carbon dioxide is 3.05-4.0.

[0008] Furthermore, the methanol distillation system includes two methanol distillation columns connected in series.

[0009] Furthermore, in the hydrogen purification system, the deoxygenation tower and the adsorption tower are connected in sequence.

[0010] Furthermore, the methanol reaction system also includes a steam generator, which is heat-exchange connected to the methanol synthesis reactor.

[0011] On the other hand, the present invention also proposes a method for synthesizing green methanol by combining green hydrogen with carbon capture, characterized by the following steps: S1: electrolyzing demineralized water in an electrolytic cell to separate hydrogen and oxygen; S2: purifying the hydrogen by sequentially passing it through a deoxygenation tower and an adsorption tower to obtain high-purity hydrogen; S3: mixing the high-purity hydrogen with carbon dioxide, pressurizing and preheating it, and then entering a methanol synthesis reactor for a catalytic reaction to generate crude methanol. After the reaction product is condensed and separated, the non-condensable gas is returned to the methanol synthesis reactor through a circulating compressor; S4: refining the crude methanol by sequentially passing it through a pre-distillation tower and a methanol distillation tower to obtain refined methanol.

[0012] Furthermore, in S1, the electrolysis temperature is 60-90℃ and the electrolysis pressure is 0.1-3.0MPa.

[0013] Furthermore, in S2, the deoxygenation temperature is 20-80℃ and the adsorption pressure is 0.5-2.0MPa.

[0014] Furthermore, in S3, the synthesis reaction temperature is 200-300℃ and the synthesis reaction pressure is 5-10MPa.

[0015] Furthermore, in S4, the operating temperature of the pre-distillation column is 60-80℃, and the operating temperature of the methanol distillation column is 64-66℃.

[0016] Compared with the prior art, the beneficial effects of the present invention are: to realize the direct synthesis of refined methanol from carbon dioxide by green hydrogen and carbon capture, with near-zero carbon emissions in the production process, fundamentally solving the problem of traditional methanol production relying on fossil raw materials and large carbon emissions, and meeting the requirements of carbon neutrality target;

[0017] The process is simple, eliminating the need for traditional carbon monoxide conversion devices and complex impurity separation devices, thus reducing equipment investment and operating costs, resulting in excellent economic efficiency. Attached Figure Description

[0018] Figure 1 This is a pipeline diagram of a system that combines green hydrogen with carbon capture to form green methanol;

[0019] In the diagram: 1. Electrolyzer, 2. Deoxygenation tower, 3. Adsorption tower, 4. Methanol synthesis reactor, 5. Circulating compressor, 6. Steam generator, 7. Pre-distillation tower, 8a. Methanol distillation tower A, 8b. Methanol distillation tower B. Detailed Implementation

[0020] To enhance understanding of the present invention, the present invention will be further described in detail below with reference to embodiments and accompanying drawings. These embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0021] Example 1

[0022] Please refer to Figure 1 In this embodiment, the volume ratio of H2 to CO2 is 3.05, the methanol synthesis reaction temperature is 200℃, the synthesis pressure is 5MPa, the electrolysis temperature is 60℃, the deoxygenation temperature is 20℃, the adsorption pressure is 0.5MPa, the pre-distillation column operating temperature is 60℃, and the methanol distillation column operating temperature is 64℃.

[0023] The specific steps are as follows:

[0024] The demineralized water is pressurized by a feed pump and then sent to electrolytic cell 1. Under electrical drive, an electrolytic reaction occurs, with the reaction equation being: 2H₂O → 2H₂ + O₂. The operating temperature of electrolytic cell 1 is 60℃, and the operating pressure is 0.1MPa. The mixed fluid generated by electrolysis enters a gas-liquid separator to complete the initial separation of hydrogen, oxygen, and residual water. The separated hydrogen enters a hydrogen buffer tank and is sent to the hydrogen purification system as crude hydrogen. The oxygen enters an oxygen buffer tank and is either discharged or recycled. The residual water is returned to electrolytic cell 1 for reuse.

[0025] The crude hydrogen produced by the water electrolysis separation system enters deoxygenation tower 2. Under the action of the deoxygenation catalyst, the trace oxygen in the hydrogen reacts with the hydrogen to produce water. The reaction equation is: 2H2 + O2 → 2H2O. The operating temperature of deoxygenation tower 2 is 20℃. The deoxygenated hydrogen enters adsorption tower 3, which is filled with molecular sieve adsorbent. The water and trace impurity gases in the hydrogen are removed by pressure swing adsorption (PSA). The adsorption pressure is 0.5 MPa. There are three adsorption towers in tower 3, one in adsorption mode and the other two in regeneration mode. The switching is achieved online through a switching valve. The purified high-purity hydrogen is then transported to the methanol reaction system. The hydrogen purity reaches over 99.9%.

[0026] High-purity hydrogen produced by the hydrogen purification system and external CO2 are pressurized to 5 MPa by a syngas compressor. They are then mixed in a direct-injection pipeline at a volume ratio of H2 to CO2 of 3.05. The resulting hydrogen-carbon mixture enters a preheater, where it is mixed with circulating gas from the circulating compressor 5 and heated to 200°C. It then enters the methanol synthesis reactor 4, a fixed-bed reactor filled with a methanol synthesis catalyst. Under the action of the catalyst, hydrogen and CO2 react to produce methanol. The main reaction equation is: CO2 + 3CO2 + 2CO2 → 2CO2 + 2CO2 + 2CO2. H2→CH3OH+H2O, the reaction products enter the hot side of steam generator 6, where they exchange heat with the demineralized water on the cold side to recover the reaction heat for steam generation. The steam is then transported to the external steam network. The reaction products after heat exchange enter the gas-liquid separator for gas-liquid separation. The separated liquid phase is crude methanol, which is transported to the methanol distillation system. The separated gas phase is divided into two parts: one part is discharged as purge gas to remove accumulated inert gases from the system; the other part is used as recirculation gas, which is pressurized by recirculation compressor 5 and returned to the preheater to mix with fresh hydrogen-carbon mixture and continue to participate in the reaction. The recirculation ratio is 3.

[0027] The crude methanol produced by the methanol reaction system is pressurized by the feed pump and preheated to 60°C by the feed preheater before entering the pre-distillation column 7. The pre-distillation column 7 operates at a pressure of 0.1 MPa, with a top temperature of 60°C and a bottom temperature of 80°C. This removes light component impurities from the crude methanol, including dissolved gases, ethers, and low-boiling alcohols. The top tail gas is discharged. The product from the pre-distillation column 7 enters the methanol distillation column A8a, which operates at a pressure of 0.1 MPa, with a top temperature of 64°C and a bottom temperature of 100°C. Further removal of water and light component impurities is achieved. The product from methanol distillation column A8a then enters methanol distillation column B8b. Methanol distillation column B8b operates at a pressure of 0.1 MPa, with a top temperature of 64°C and a bottom temperature of 100°C. This further removes heavy component impurities and residual water. Refined methanol is collected from the top of methanol distillation column B8b, cooled, and then enters a product storage tank. The product methanol has a purity of over 99.9% and a water content of less than 0.05%, meeting the standards for electronic-grade methanol. The wastewater from the bottom of the column is transported to an external wastewater treatment system.

[0028] Example 2

[0029] In this embodiment, the volume ratio of H2 to CO2 is 3.5, the methanol synthesis reaction temperature is 250°C, the synthesis pressure is 7 MPa, the electrolysis temperature is 75°C, the deoxygenation temperature is 50°C, the adsorption pressure is 1.0 MPa, the operating temperature of the pre-distillation column 7 is 70°C, and the operating temperature of the methanol distillation column is 65°C.

[0030] The specific steps are as follows:

[0031] The demineralized water is pressurized by a feed pump and then sent to electrolytic cell 1. Under electrical drive, an electrolytic reaction occurs, with the reaction equation being: 2H₂O → 2H₂ + O₂. The operating temperature of electrolytic cell 1 is 75℃, and the operating pressure is 1.0 MPa. The mixed fluid generated by electrolysis enters a gas-liquid separator to complete the initial separation of hydrogen, oxygen, and residual water. The separated hydrogen enters a hydrogen buffer tank and is sent to the hydrogen purification system as crude hydrogen. The oxygen enters an oxygen buffer tank and is either discharged or utilized as a resource. The residual water is returned to electrolytic cell 1 for recycling.

[0032] The crude hydrogen produced by the water electrolysis separation system enters the deoxygenation tower 2. Under the action of the deoxygenation catalyst, the trace oxygen in the hydrogen reacts with the hydrogen to produce water. The operating temperature of the deoxygenation tower 2 is 50℃. The deoxygenated hydrogen enters the adsorption tower 3, where water and trace impurities are removed by pressure swing adsorption. The adsorption pressure is 1.0 MPa. There are three adsorption towers 3, which are switched online by a switching valve. The purified high-purity hydrogen is then transported to the methanol reaction system, with a hydrogen purity of over 99.9%.

[0033] High-purity hydrogen produced by the hydrogen purification system and CO2 from outside the system are pressurized to 7 MPa by a syngas compressor. They are then mixed in the post-discharge pipeline at a volume ratio of H2 to CO2 of 3.5. The resulting hydrogen-carbon mixture enters a preheater, where it is mixed with circulating gas from the circulating compressor 5 and heated to 250°C. It then enters the methanol synthesis reactor 4, a fixed-bed reactor filled with a methanol synthesis catalyst. Under the action of the catalyst, hydrogen and CO2 react to produce methanol. The main reaction equation is: CO2 + 3H2→CH3OH+H2O. The reaction products enter the hot side of steam generator 6 and exchange heat with the demineralized water on the cold side to recover the heat of reaction for steam generation. The reaction products after heat exchange enter the gas-liquid separator for gas-liquid separation. The separated liquid phase is crude methanol, which is sent to the methanol distillation system. The separated gas phase is distributed as a purge gas to remove the inert gas accumulated in the system. The other part is used as a recycle gas, which is pressurized by the recycle compressor 5 and returned to the preheater. It is then mixed with fresh hydrogen-carbon mixture and continues to participate in the reaction. The recycle ratio is 5.

[0034] The crude methanol produced by the methanol reaction system is pressurized by the feed pump and preheated to 70°C by the feed preheater before entering the pre-distillation column 7. The pre-distillation column 7 operates at a pressure of 0.2 MPa, with a top temperature of 70°C and a bottom temperature of 90°C, removing light component impurities from the crude methanol. The top tail gas is discharged. The product from the pre-distillation column 7 enters the methanol distillation column A8a, which operates at a pressure of 0.15 MPa, with a top temperature of 65°C and a bottom temperature of 105°C, further removing water and... Light component impurities are removed from the product of methanol distillation column A8a, which then enters methanol distillation column B8b. Methanol distillation column B8b operates at a pressure of 0.15 MPa, with a top temperature of 65°C and a bottom temperature of 105°C, further removing heavy component impurities and residual moisture. Refined methanol is collected from the top of methanol distillation column B8b, cooled, and then enters a product storage tank. The product methanol has a purity of over 99.9% and a water content of less than 0.05%, meeting the standards for electronic-grade methanol. Wastewater from the bottom of the column is transported to an external wastewater treatment system.

[0035] The two embodiments above demonstrate that, within the parameter range defined by this invention—namely, an H2 to CO2 volume ratio of 3.05–4.0, a synthesis reaction temperature of 200–300°C, a synthesis reaction pressure of 5–10 MPa, and an electrolysis temperature of 60–90°C—high-purity electronic-grade methanol with a purity of over 99.9% can be stably produced. This verifies the reliability of the technical solution and the rationality of the parameter range of this invention.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A system for green hydrogen combined carbon capture to produce green methanol, characterized in that, The system comprises electrolysis water separation system, hydrogen purification system, methanol reaction system and methanol distillation system connected in sequence, the electrolysis water separation system comprises electrolytic cell for electrolysis of desalinated water to separate hydrogen and oxygen, the hydrogen purification system comprises deoxygenation tower and adsorption tower for purifying the hydrogen, the methanol reaction system comprises methanol synthesis reactor and circulating compressor for mixing the purified hydrogen with carbon dioxide, boosting and catalyzing to generate crude methanol, and returning the incondensable gas to the methanol synthesis reactor through the circulating compressor, and the methanol distillation system comprises pre-distillation tower and methanol distillation tower for distilling and purifying the crude methanol to obtain refined methanol.

2. The system for producing green methanol by combining hydrogen and carbon capture according to claim 1, characterized in that, The volume ratio of the hydrogen to the carbon dioxide is 3.05-4.

0.

3. The system for producing green methanol by combining hydrogen and carbon capture according to claim 1, characterized in that, The methanol distillation system comprises two methanol distillation towers connected in series.

4. The system for producing green methanol by combining hydrogen and carbon capture according to claim 1, characterized in that, In the hydrogen purification system, the deoxygenation tower and the adsorption tower are connected in sequence.

5. The system for producing green methanol by combining hydrogen and carbon capture according to claim 1, characterized in that, The methanol reaction system further comprises steam generator in heat exchange connection with the methanol synthesis reactor.

6. A method of green hydrogen combined with carbon capture to produce green methanol, characterized in that, The system comprises the following steps: S1: electrolyzing desalinated water in electrolytic cell to separate hydrogen and oxygen; S2: purifying the hydrogen through deoxygenation tower and adsorption tower in sequence to obtain high-purity hydrogen; S3: mixing the high-purity hydrogen with carbon dioxide, boosting and preheating to enter the methanol synthesis reactor to catalyze to generate crude methanol, and returning the incondensable gas to the methanol synthesis reactor through the circulating compressor after condensing and separating the reaction product; and 7. The method of claim 1, wherein the method is characterized by, S4: distilling the crude methanol through pre-distillation tower and methanol distillation tower in sequence to obtain refined methanol.

8. The method of claim 1, wherein the method is characterized by, In the S1, the electrolysis temperature is 60-90℃, and the electrolysis pressure is 0.1-3.0MPa.

9. The method of claim 1, wherein the method is characterized by, In the S2, the deoxygenation temperature is 20-80℃, and the adsorption pressure is 0.5-2.0MPa.

10. The method of claim 1, wherein the method is characterized by, In the S3, the synthesis reaction temperature is 200-300℃, and the synthesis reaction pressure is 5-10MPa. In the S4, the pre-distillation tower operates at 60-80℃, and the methanol distillation tower operates at 64-66℃.

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