A circulating methanol purification system and process

Abstract

This invention relates to a circulating methanol purification system and process. The system includes at least one distillation-hydrogenation loop, which comprises a methanol distillation column and a hydrogenation reactor connected in a loop. The feed inlet of the hydrogenation reactor is connected to the top outlet of the methanol distillation column, and the feed inlet of the hydrogenation reactor is connected to a hydrogen source. The process includes the following steps: passing an aqueous methanol solution containing impurities into the methanol distillation column, removing impurities such as aldehydes and ketones from the top of the column; removing the concentrated impurities through the hydrogenation reactor, and returning the hydrogenation product to the methanol distillation column for fusel oil separation; collecting high-purity methanol from the side stream of the methanol distillation column, further removing remaining trace impurities, especially aldehydes, through an ion exchanger; the purified methanol can be recycled. Using the purification process of this invention, impurities in the circulating methanol are concentrated, the process is simple with low investment, the impurity conversion rate is high, the service life of the epoxidation catalyst can be significantly extended, and product quality can be improved.

Description

Technical Field

[0001] This invention relates to the field of propylene oxide production, specifically to a circulating methanol purification system and process. Background Technology

[0002] Propylene oxide is the third largest propylene derivative after polypropylene and acrylonitrile. It is an important basic organic chemical synthesis raw material, mainly used in the production of polyethers, propylene glycol, etc. It is also a major raw material for fourth-generation detergent nonionic surfactants, oilfield demulsifiers, and pesticide emulsifiers.

[0003] Currently, the main methods for producing propylene oxide worldwide include the chlorohydrin process, the co-oxidation process (including the ethylbenzene co-oxidation process and the isobutane co-oxidation process), and the direct oxidation process using hydrogen peroxide. Among these, the chlorohydrin process is mature and reliable, but it suffers from severe equipment corrosion, high water consumption, and the discharge of large amounts of wastewater and waste residue during the production process. The co-oxidation process has problems such as a long process, high investment, and the need to co-produce 2.2 to 2.5 tons of styrene or tert-butanol for every ton of propylene oxide produced, as well as constraints on raw material sourcing and product sales. In contrast, the new process of directly oxidizing propylene with hydrogen peroxide on a titanium-silicon molecular sieve catalyst to produce propylene oxide has mild reaction conditions, high product yield, no other co-products, and virtually no pollution. It is an environmentally friendly clean production process and represents the development direction of propylene oxide production technology.

[0004] Methanol is generally used as a solvent in the direct epoxidation reaction of hydrogen peroxide and propylene, dissolving the immiscible hydrogen peroxide and propylene in the same phase for the reaction. In existing processes for the direct epoxidation of propylene to produce propylene oxide, all methanol needs to be recycled back to the epoxidation reactor for reuse. During the epoxidation reaction, in addition to propylene oxide, small but diverse trace impurities such as aldehydes, ketones, acids, ethers, and esters are also generated. If these trace impurities are not effectively removed, some of the aldehyde and ketone impurities will be recycled back to the epoxidation reaction system with methanol, gradually accumulating in the system with continuous methanol circulation. These accumulated impurities will continue to undergo other reactions in the epoxidation reactor, generating even more new impurities. This results in increasingly poor quality propylene oxide and a growing amount of impurities in the recycled methanol. These large amounts of impurities also severely affect the lifespan of the epoxidation catalyst.

[0005] EP-A1122248 discloses a method for processing a product stream from propylene epoxidation, the product stream containing propylene, propylene oxide, methanol, and water. The method involves first separating the product stream in a pre-evaporator into a top distillate containing propylene, propylene oxide, and methanol, and a bottom product containing methanol and water. The methanol in the bottom product is recovered and recycled to the epoxidation reactor. Propylene oxide is obtained from the top product of an extractive distillation column, preferably using water as the extractant. The methanol and water stream obtained from the bottom of the extractive distillation column can be directly recycled to the epoxidation reactor. While this method effectively reduces propylene oxide loss, the activity and selectivity of the epoxidation catalyst decrease significantly in a short period, and a large amount of impurities accumulate during methanol recycling.

[0006] Currently, factories typically remove impurities by passing all the aqueous alcohol solution in the unit through hydrogen gas. This results in a large hydrogenation reactor and related equipment, as well as a large amount of catalyst, leading to high energy consumption and relatively low efficiency. Furthermore, unconverted hydrogen peroxide from the epoxidation reaction decomposes in the hydrogenation reactor, producing oxygen. The hydrogen circulation process inevitably leads to oxygen enrichment, posing a significant safety risk. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a simple, efficient, and cost-effective circulating methanol purification system and process that can significantly reduce the impurity content in propylene oxide products while improving the lifespan of epoxidation catalysts.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] To reduce the content of aldehydes and ketones in recycled methanol, prevent their accumulation in the system, improve the quality of propylene oxide products, and extend the service life of epoxidation catalysts, a more cost-effective, safe, and efficient method for removing aldehydes and ketones is needed. The specific solution is as follows:

[0010] A circulating methanol purification system includes at least one distillation-hydrogenation loop, the loop including a methanol distillation column and a hydrogenation reactor connected in a cycle;

[0011] The feed inlet of the hydrogenation reactor is connected to the top outlet of the methanol distillation column; the feed inlet of the hydrogenation reactor is connected to a hydrogen source.

[0012] The outlet of the hydrogenation reactor is connected to the side of the methanol distillation column.

[0013] Furthermore, the system also includes at least one overhead reflux loop, comprising a methanol distillation column, a condenser, an overhead reflux tank, and a circulation pump connected in sequence.

[0014] Furthermore, the aforementioned top reflux circulation loop is located at the top of the methanol distillation column.

[0015] Furthermore, the system also includes at least one hydrogen flash circulation loop, which includes a circulating hydrogenation reactor and a gas-liquid separator.

[0016] Furthermore, the gas flash outlet of the gas-liquid separator is connected to the feed inlet of the hydrogenation reactor, and the liquid flash outlet of the gas-liquid separator is connected to the side of the methanol distillation column.

[0017] Furthermore, the system also includes at least one aldehyde removal stream connected to the side of the methanol distillation column, which includes an ion exchanger for aldehyde removal.

[0018] Furthermore, the system also includes at least one side-feed methanol stream located on the side of the methanol distillation column and / or at least one bottom-circulating stream located in the column reboiler. In order to reduce the fusel oil content in the circulating methanol, it is necessary to reduce the accumulation of ethanol or propanol in the circulating methanol through separate side-feeding.

[0019] A circulating methanol purification process based on the system described above includes the following steps:

[0020] The raw materials are fed into the methanol distillation column via the raw material feed stream;

[0021] The material concentrated at the top of the column flows out of the top stream and is then pressurized by a pump. It is then mixed with the hydrogen stream to form the hydrogenation reaction feed stream, which enters the hydrogenation reactor. At the same time, the material at the bottom of the column flows out of the bottom stream.

[0022] After cooling, the hydrogenation product enters the gas-liquid separator. The flash-evaporated hydrogen is returned to the hydrogenation reactor via the hydrogen circulation stream, while the liquid phase enters the methanol distillation column to further separate fusel oils.

[0023] Some of the methanol in the tower is drawn out from the side, forming an aldehyde removal stream, which enters the ion exchanger to further react and remove the aldehydes, thus purifying the methanol.

[0024] Furthermore, the raw materials include at least methanol and water, and also one or more of ethylene glycol, 1-methoxy-2-propanol, 2-methoxy-1-propanol, formaldehyde, acetaldehyde, or propionaldehyde; the components drawn from the top of the column contain aldehyde and ketone impurities, as well as impurities with boiling points lower than methanol or impurities that azeotropically react with methanol, specifically including methyl formate and / or dimethoxyethane; the wastewater from the bottom of the methanol distillation column containing impurities such as propylene glycol, 1-methoxy-2-propanol, 2-methoxy-1-propanol, and 1-propylene glycol monomethyl ether is discharged downstream for impurity recovery and treatment;

[0025] The theoretical number of plates in the methanol distillation column is 10-100, preferably 40-70, and the theoretical number of plates in the top section is 5-20; the content of aldehyde and ketone impurities extracted from the top of the column accounts for 50-100% of the feed to the methanol distillation column, preferably 70-90%.

[0026] The hydrogenation catalyst in the hydrogenation reactor is a nickel-based catalyst; the hydrogenation reaction temperature is 100-200℃; and the reaction pressure is 1-5 MPa.

[0027] The ion exchange resin in the ion exchanger is a weak acid ion exchange resin, a strong acid ion exchange resin, a weak base ion exchange resin, or a strong base ion exchange resin, or a combination thereof, and the reaction temperature of the ion exchanger is 40-100℃.

[0028] Furthermore, the process can be operated in single-tower or dual-tower mode. If the process design has no requirements for energy consumption, a single methanol distillation tower can be used; if the process design requires heat integration optimization, the methanol distillation can be split into two towers.

[0029] When a single methanol distillation column is operated, the top pressure is 0.2-1 MPa, preferably 0.5-0.8 MPa; when a dual methanol distillation column is operated, the top pressure of the high-pressure column is 0.5-2 MPa, preferably 1-1.5 MPa, and the top pressure of the low-pressure column is 0.05-0.7 MPa, preferably 0.2-0.5 MPa.

[0030] Compared with existing technologies, this invention concentrates aldehyde and ketone impurities in methanol and combines concentrated impurity hydrogenation with recycled methanol ion exchange resin treatment. This eliminates the safety concerns associated with mixing hydrogen and oxygen. Furthermore, because the amount of material being processed is small and hydrogen can be recycled, the processing cost is low, equipment investment is minimal, impurity removal is effective, and operation is convenient. Using this method, high-purity recycled methanol can be obtained, impurities do not accumulate in the system, the epoxidation catalyst has a long lifespan, and the propylene oxide product has high purity. Attached Figure Description

[0031] Figure 1 A schematic diagram of a single-tower circulating methanol purification system;

[0032] Figure 2 A schematic diagram of a dual-tower circulating methanol purification system;

[0033] The labels in the diagram indicate: T1 - First methanol distillation column, T2 - Second methanol distillation column, R1 - Hydrogenation reactor, R2 - Ion exchanger, V1 - First column top reflux tank, V2 - Gas-liquid separator; V3 - Second column top reflux tank;

[0034] 1-Methanol-water solution; 2-Top material of the column; 3-Cooled top material of the column; 4-Reflux tank discharge; 5-Reflux liquid; 6-Concentrated aldehyde-ketone solution; 7-Feed to the hydrogenation reactor; 8-Fresh hydrogen; 9-Discharge from the hydrogenation reactor; 10-Circulating hydrogen; 11-Fusel alcohol material; 12-Side-collected methanol; 13-Discharge from the ion exchanger; 14-Side-collected fusel alcohol; 15-Bottom wastewater of the column;

[0035] 20-First methanol-water solution; 21-First top material; 22-First cooled top material; 23-First reflux tank discharge; 24-First reflux liquid; 25-First concentrated aldehyde-ketone solution; 26-First hydrogenation reactor feed; 27-First fresh hydrogen; 28-Hydrogenation reactor discharge; 29-First recycled hydrogen; 30-First fusel oil material; 31-First fusel oil material to be removed from the tower; 32-Second fusel oil material to be removed from the tower; 33-First side-collected methanol; 34-First bottom material; 35-Second top material; 36-Second cooled top material; 37-Second reflux tank discharge; 38-Second reflux liquid; 39-Second concentrated aldehyde-ketone solution; 40-Second side-collected methanol; 41-First ion exchanger feed; 42-First ion exchanger discharge; 43-First side-collected fusel oil; 44-First bottom wastewater. Detailed Implementation

[0036] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise defined, all percentages herein are understood to be mass percentages.

[0037] A circulating methanol purification system and process are disclosed. The system includes at least one distillation-hydrogenation circulating loop, which includes a methanol distillation column and a hydrogenation reactor connected in a circulating manner. The feed inlet of the hydrogenation reactor is connected to the top outlet of the methanol distillation column. The feed inlet of the hydrogenation reactor is connected to a hydrogen source. The outlet of the hydrogenation reactor is connected to the side of the methanol distillation column.

[0038] The system also includes at least one overhead reflux loop, comprising a methanol distillation column, a condenser, an overhead reflux tank, and a circulation pump connected in sequence. The overhead reflux loop is located at the top of the methanol distillation column. The system also includes at least one hydrogen flash circulation loop, which comprises a hydrogenation reactor and a gas-liquid separator connected in sequence.

[0039] The gas flash outlet of the gas-liquid separator is connected to the feed inlet of the hydrogenation reactor, and the liquid flash outlet of the gas-liquid separator is connected to the side of the methanol distillation column. The system also includes at least one aldehyde removal stream connected to the side of the methanol distillation column, comprising an ion exchanger for aldehyde removal. The system also includes at least one side-feed methanol stream located on the side of the methanol distillation column and / or at least one bottom recycle stream located in the reboiler. To reduce the fusel oil content in the recycled methanol, it is necessary to reduce the accumulation of ethanol or propanol in the recycled methanol through separate side-feeding.

[0040] The specific steps of the circulating methanol purification process are as follows:

[0041] A methanol-water solution containing impurities is passed into a methanol distillation column, where aldehydes, ketones, and other impurities are removed from the top. Methanol distillation can be performed using a single column or a dual column. If the process design has no energy consumption requirements, a single methanol distillation column can be used; if the process design requires integrated heat optimization, methanol distillation can be split into two columns. When the methanol distillation column is operated as a single unit, the top pressure is 0.2-1 MPa, preferably 0.5-0.8 MPa. When the methanol distillation column is operated as a dual column, the top pressure of the high-pressure column is 0.5-2 MPa, preferably 1-1.5 MPa, and the top pressure of the low-pressure column is 0.05-0.7 MPa, preferably 0.2-0.5 MPa. The theoretical number of plates in the methanol distillation column is 10-80, preferably 30-60, and the theoretical number of plates in the top section is 5-20. The component extracted from the top of the column contains aldehydes and ketones, as well as other impurities with boiling points lower than methanol or azeotropic impurities, such as methyl formate and dimethoxyethane. The content of aldehydes and ketones extracted from the top of the column accounts for 50-100% of the methanol distillation column feed, preferably 70-90%.

[0042] Concentrated impurities are removed via a hydrogenation reactor, and the hydrogenation product is returned to a methanol distillation column for fusel oil separation. A nickel-based catalyst is preferred for hydrogenation. The hydrogenation feedstock and hydrogen can simultaneously enter from the top of the reactor and exit from the bottom, or simultaneously enter from the bottom and exit from the top. The hydrogenation reaction temperature is 100-200℃; the reaction pressure is 1-5 MPa. The feedstock at the hydrogenation reactor outlet undergoes gas-liquid separation; the gas phase is returned to the hydrogenation reactor, and the liquid phase enters the methanol distillation column for further separation.

[0043] High-purity methanol is collected from the side stream of the methanol distillation column. This methanol is then further purified by an ion exchanger to remove residual trace impurities, especially aldehydes. The purified methanol can be recycled. The ion exchange resin can be a weakly acidic ion exchange resin, a strong acidic ion exchange resin, a weakly basic ion exchange resin, a strong basic ion exchange resin, or a combination of different resins. The reaction temperature of the ion exchanger is 40-100℃. To reduce the content of fusel oils in the recycled methanol, it is necessary to reduce the accumulation of ethanol or propanol in the recycled methanol by separate side stream collection. The wastewater containing impurities such as propylene glycol, 1-methoxy-2-propanol, 2-methoxy-1-propanol, and 1-propylene glycol monomethyl ether at the bottom of the methanol distillation column is discharged downstream for impurity recovery and treatment.

[0044] Example 1

[0045] like Figure 1 The feed flow rate of methanol distillation column T1 is 500 kg / h, of which methanol accounts for 80%, with the remainder being mostly water. It also contains 2000 ppm ethylene glycol, 1200 ppm 1-methoxy-2-propanol and 2-methoxy-1-propanol, 40 ppm formaldehyde, 250 ppm acetaldehyde + propionaldehyde, and 60 ppm acetone. The methanol distillation column has 50 theoretical plates, and the top pressure is 0.5 MPa. After concentration at the top, the flow rate of the overhead stream 6 is 180 kg / h. After being pressurized by a pump, it is mixed with hydrogen and used as the reaction feed 7 in the hydrogenation reactor R1. The inlet temperature of the hydrogenation reactor is 130℃, and the inlet pressure is 2 MPa. After hydrogenation, the concentrated impurities react with hydrogen to form alcohols with the corresponding number of carbon atoms. The hydrogenation product is cooled and enters the gas-liquid separator V2, where hydrogen flashes out and returns to the hydrogenation reactor. The liquid phase 11 enters the methanol distillation column for further separation of fusel oils. The side-source methanol 12 is extracted from the 14th theoretical plate, which also contains 52 ppm of acetaldehyde and propionaldehyde. Material 12 enters the ion exchanger R2 for further reaction and removal of trace amounts of aldehydes. The feed temperature of the ion exchanger is 40℃, and it is filled with strong acid ion exchange resin. After treatment by the ion exchange resin, the content of acetaldehyde and propionaldehyde is reduced to 6 ppm.

[0046] Example 2

[0047] like Figure 1The feed composition of methanol feed tower T1 is the same as in Example 1. The methanol distillation tower has 60 theoretical plates and a top pressure of 0.8 MPa. After concentration at the top of the tower, the flow rate of the overhead stream 6 is 250 kg / h. After being pressurized by a pump, it is mixed with hydrogen and used as the reaction feed 7 of hydrogenation reactor R1. The inlet temperature of the hydrogenation reactor is 125°C and the inlet pressure is 4 MPa. After hydrogenation, the concentrated impurities react with hydrogen to form alcohols with the corresponding number of carbon atoms. The hydrogenation product is cooled and enters the gas-liquid separator V2, where hydrogen flashes out and returns to the hydrogenation reactor. The liquid phase 11 enters the methanol distillation tower for further separation of fusel oils. The side-source methanol 12 is extracted from the 14th theoretical plate, which also contains 44 ppm of acetaldehyde and propionaldehyde. Material 12 enters the ion exchanger R2 for further reaction and removal of trace amounts of aldehydes. The feed temperature of the ion exchanger is 60℃, and it is filled with weakly acidic ion exchange resin. After treatment by the ion exchange resin, the content of acetaldehyde and propionaldehyde is reduced to 12 ppm.

[0048] Example 3

[0049] like Figure 2 The feed composition of methanol feed tower T1 is the same as in Example 1. The methanol distillation tower adopts a dual-tower operation. The methanol-water solution first enters methanol distillation tower 1, with a top pressure of 0.2 MPa. After concentration at the top of the tower, the flow rate of the top stream 25 is 90 kg / h. After mixing with hydrogen, it enters hydrogenation reactor R1, with an inlet temperature of 160°C and an inlet pressure of 5 MPa. After hydrogenation, the concentrated impurities react with hydrogen to form alcohols with the corresponding number of carbon atoms. The hydrogenation product is cooled and enters gas-liquid separator V2, where hydrogen flashes out and returns to the hydrogenation reactor. The liquid phase 31 enters methanol distillation tower T1 for further separation of fusel oils. Side-collected methanol 33 is drawn from the 10th theoretical plate and then sent to ion exchanger R2 for processing. The aqueous alcohol solution 34 from the bottom of methanol distillation column T1 enters methanol distillation column T2 for further separation. The pressure at the top of column T2 is 1 MPa. The overhead stream 39 and stream 25 are combined and enter hydrogenation reactor R1. The effluent 32 from hydrogenation reactor R1 is returned to T2. Methanol 40 from the side stream of T2 is mixed with stream 33. The mixture stream 41 contains 30 ppm of acetaldehyde and propionaldehyde. This stream enters ion exchanger R2 for reaction. The feed temperature of the ion exchanger is 40°C, and it is filled with strongly acidic ion exchange resin. After treatment by the ion exchange resin, the acetaldehyde and propionaldehyde content is reduced to 3 ppm.

[0050] Example 4

[0051] like Figure 2The feed composition of methanol feed tower T1 is the same as in Example 1. The methanol distillation tower adopts a dual-tower operation. The methanol-water solution first enters methanol distillation tower 1, with a top pressure of 0.5 MPa. After concentration at the top of the tower, the flow rate of the top stream 25 is 100 kg / h. After mixing with hydrogen, it enters hydrogenation reactor R1, with an inlet temperature of 125°C and an inlet pressure of 4 MPa. After hydrogenation, the concentrated impurities react with hydrogen to form alcohols with the corresponding number of carbon atoms. The hydrogenation product is cooled and enters gas-liquid separator V2, where hydrogen flashes out and returns to the hydrogenation reactor. The liquid phase 31 enters methanol distillation tower T1 for further separation of fusel oils. Side-collected methanol 33 is drawn from the 16th theoretical plate and then sent to ion exchanger R2 for processing. The aqueous alcohol solution 34 from the bottom of methanol distillation column T1 enters methanol distillation column T2 for further separation. The pressure at the top of column T2 is 1.5 MPa. The overhead stream 39 and stream 25 are combined and then enter hydrogenation reactor R1. The effluent 32 from hydrogenation reactor R1 is returned to T2. Methanol 40 from the side stream of T2 is mixed with stream 33. The mixture stream 41 contains acetaldehyde + propionaldehyde 36 ppm. This stream enters ion exchanger R2 for reaction. The feed temperature of the ion exchanger is 40℃, and it is filled with weakly acidic ion exchange resin. After treatment by the ion exchange resin, the acetaldehyde + propionaldehyde content is reduced to 8 ppm.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A circulating methanol purification system, characterized in that, The system includes at least one distillation-hydrogenation loop, which includes a methanol distillation column and a hydrogenation reactor connected in a loop. The feed inlet of the hydrogenation reactor is connected to the top outlet of the methanol distillation column; the feed inlet of the hydrogenation reactor is connected to a hydrogen source. The outlet of the hydrogenation reactor is connected to the side of the methanol distillation column; The system also includes at least one overhead reflux loop, comprising a methanol distillation column, a condenser, an overhead reflux tank, and a circulation pump connected in sequence. The system also includes at least one hydrogen flash circulation loop, which includes a circulating hydrogenation reactor and a gas-liquid separator. The system also includes at least one aldehyde removal stream connected to the side of a methanol distillation column, which includes an ion exchanger for aldehyde removal.

2. The circulating methanol purification system according to claim 1, characterized in that, The aforementioned top reflux circulation loop is located at the top of the methanol distillation column.

3. The circulating methanol purification system according to claim 1, characterized in that, The gas flash outlet of the gas-liquid separator is connected to the feed inlet of the hydrogenation reactor, and the liquid flash outlet of the gas-liquid separator is connected to the side of the methanol distillation column.

4. The circulating methanol purification system according to claim 1, characterized in that, The system also includes at least one side-collected methanol stream located on the side of the methanol distillation column and / or at least one bottom-circulating stream located in the column bottom.

5. A circulating methanol purification process based on the system described in any one of claims 1-4, characterized in that, The process includes the following steps: The raw materials are fed into the methanol distillation column via the raw material feed stream; The material concentrated at the top of the column flows out of the top stream and is then pressurized by a pump. It is mixed with the hydrogen stream to form the hydrogenation reaction feed stream, which enters the hydrogenation reactor. At the same time, the material at the bottom of the column flows out of the bottom stream. After cooling, the hydrogenation product enters the gas-liquid separator. The flash-evaporated hydrogen is returned to the hydrogenation reactor via the hydrogen circulation stream, while the liquid phase enters the methanol distillation column to further separate fusel oils. Some methanol in the tower is drawn out from the side, forming an aldehyde removal stream, which enters the ion exchanger to further react and remove the aldehydes, thus purifying the methanol.

6. The circulating methanol purification process according to claim 5, characterized in that, The raw materials include at least methanol and water, and also include one or more of ethylene glycol, 1-methoxy-2-propanol, 2-methoxy-1-propanol, formaldehyde, acetaldehyde, or propionaldehyde; The theoretical number of plates in a methanol distillation column is 10-100, and the theoretical number of plates in the top section is 5-20. The aldehyde and ketone impurities extracted from the top of the column account for 50-100% of the methanol distillation column feed. The hydrogenation catalyst in the hydrogenation reactor is a nickel-based catalyst; the hydrogenation reaction temperature is 100-200℃; and the reaction pressure is 1-5 MPa. The ion exchange resin in the ion exchanger is a weak acid ion exchange resin, a strong acid ion exchange resin, a weak base ion exchange resin, or a strong base ion exchange resin, or a combination thereof, and the reaction temperature of the ion exchanger is 40-100℃.

7. The circulating methanol purification process according to claim 5, characterized in that, Single-tower or dual-tower operation can be used; When a single methanol distillation column is operated, the top pressure is 0.2-1 MPa; when a dual methanol distillation column is operated, the top pressure of the high-pressure column is 0.5-2 MPa, and the top pressure of the low-pressure column is 0.05-0.7 MPa.

8. A circulating methanol purification process according to claim 5 or 7, characterized in that, When the methanol distillation column is operated in a dual-tower configuration, the pressure at the top of the high-pressure tower is 1-1.5 MPa.

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