Methyl tert-butyl ether production device
By designing a methyl tert-butyl ether production device including multiple tower devices, the problem that the prior art cannot stably produce type II methyl tert-butyl ether that meets the new chemical methyl tert-butyl ether standards has been solved, and the quality of type I methyl tert-butyl ether products has been improved and the application expansion of high-quality methyl tert-butyl ether is achieved.
Patent Information
- Application Number
- CN202421607555.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-09
- Publication Date
- 2025-05-30
- Estimated Expiration
- 2034-07-09
AI Technical Summary
The prior art cannot stably produce type II methyl tert-butyl ether that meets the new chemical methyl tert-butyl ether standards, and type I methyl tert-butyl ether almost cannot meet the standards, especially it is difficult to effectively control the formation of methyl sec-butyl ether and dimers.
A methyl tert-butyl ether production device including an etherification reactor, a type I methyl tert-butyl ether distillation tower, a catalytic distillation tower, a methanol extraction tower and a methanol recovery tower was designed. The type I methyl tert-butyl ether product was separated by a direct azeotropic distillation reaction of the etherification reactor, and the isobutylene was fully reacted in the catalytic distillation tower to improve the conversion rate.
The quality of type I methyl tert-butyl ether has been improved, and the difficult-to-control indicators in the existing technology have been overcome, such as methyl sec-butyl ether and dimer, and the application range of high-quality methyl tert-butyl ether is expanded for the mixed carbon tetrahydric raw materials to produce high-quality methyl tert-butyl ether.
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Figure CN222918126U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the technical field of petrochemical engineering, and more specifically, to a methyl tert-butyl ether production device. Background Art
[0002] According to the different purposes of the device, the process routes of methyl tert-butyl ether are also different. Generally speaking, it can be divided into refinery-type methyl tert-butyl ether and chemical-type methyl tert-butyl ether. The characteristic of the refinery-type methyl tert-butyl ether process is that the production of methyl tert-butyl ether is the goal, and the product methyl tert-butyl ether is used to blend gasoline to improve the octane number of gasoline. Therefore, the requirements for the purity of methyl tert-butyl ether products and the conversion rate of isobutene are relatively not strict, aiming at less investment, low consumption, and low cost. The so-called chemical-type methyl tert-butyl ether process refers to that through the manufacturing process of methyl tert-butyl ether, the isobutene in the mixed C4 is completely reacted, and the etherified C4 is used as the raw material for producing high-purity 1-butene or methyl ethyl ketone, or the methyl tert-butyl ether product can be decomposed to obtain 99.9% high-purity isobutene for use as a chemical monomer. With the continuous progress of methyl tert-butyl ether technology, the requirements for product quality are also getting higher and higher. The state also timely introduced a new standard for chemical-type methyl tert-butyl ether, SH / T 1834-2022, in 2022. The existing technology cannot meet the need for stable production of type II methyl tert-butyl ether, and almost all type I methyl tert-butyl ether cannot meet the standards.
[0003] Therefore, how to develop a methyl tert-butyl ether production device is an urgent problem to be solved by those skilled in the art. Summary of the Utility Model
[0004] In view of this, the utility model provides a methyl tert-butyl ether production device.
[0005] In order to achieve the above purpose, the utility model adopts the following technical scheme:
[0006] A methyl tert-butyl ether production device includes: an etherification reactor, a type I methyl tert-butyl ether rectification tower, a catalytic distillation tower, a methanol extraction tower, and a methanol recovery tower;
[0007] Wherein, the bottom discharge port of the etherification reactor is connected to the middle feed port of the type I methyl tert-butyl ether rectification tower, the top discharge port of the type I methyl tert-butyl ether rectification tower is connected to the middle feed port of the catalytic distillation tower, the top discharge port of the catalytic distillation tower is connected to the lower feed port of the methanol extraction tower, the bottom discharge port of the methanol extraction tower is connected to the middle feed port of the methanol recovery tower, and the bottom discharge port of the methanol recovery tower is connected to the upper feed port of the methanol extraction tower. The above connection methods are all connected through pipelines;
[0008] The bottom of the above-mentioned type I methyl tert-butyl ether distillation column is provided with a type I methyl tert-butyl ether product discharge port, the bottom of the above-mentioned catalytic distillation column is provided with a blending methyl tert-butyl ether discharge port, and the top of the above-mentioned methanol extraction column is provided with a C4 after ether discharge port.
[0009] Furthermore, it also includes: a mixer;
[0010] The above-mentioned mixer is provided with a methanol feed port, a recycled methanol feed port, a mixed C4 feed port and a discharge port. The discharge port of the above-mentioned mixer is connected to the top feed port of the etherification reactor, and the top discharge port of the methanol recovery column is connected to the recycled methanol feed port of the mixer.
[0011] Beneficial effects of adopting the above further technical solution: The mixing of C4 and methanol is poor, and the above technical solution makes the material mixing more uniform.
[0012] Furthermore, the catalyst loaded in the above-mentioned catalytic distillation column is one or several of CDM140, CDM150 or CDM170.
[0013] Beneficial effects of adopting the above further technical solution: The reaction passes through the catalyst, making the reaction in the catalytic distillation column more complete, with low energy consumption and high conversion rate.
[0014] Furthermore, the above-mentioned type I methyl tert-butyl ether distillation column is provided with a top condenser I and a bottom reboiler I. The top discharge port of the above-mentioned type I methyl tert-butyl ether distillation column, the top condenser I and the middle feed port of the catalytic distillation column are connected in sequence.
[0015] Furthermore, the above-mentioned catalytic distillation column is provided with a top condenser II and a bottom reboiler II. The top discharge port of the above-mentioned catalytic distillation column, the top condenser II and the lower feed port of the methanol extraction column are connected in sequence.
[0016] Furthermore, the above-mentioned methanol recovery column is provided with a top condenser III and a bottom reboiler III. The top discharge port of the above-mentioned methanol recovery column, the top condenser III and the recycled methanol feed port of the mixer are connected. The bottom discharge port of the above-mentioned methanol recovery column, the bottom reboiler III and the upper feed port of the methanol extraction column are connected.
[0017] Beneficial effects of the utility model: The utility model aims at producing type I methyl tert-butyl ether products from mixed C4 raw materials, overcomes the drawback that the existing technology cannot produce type I methyl tert-butyl ether, and improves the level of methyl tert-butyl ether equipment. The utility model can expand the application scope of mixed C4 to produce high-quality methyl tert-butyl ether. The product quality of type I methyl tert-butyl ether is much higher than that of type II methyl tert-butyl ether. The existing process cannot produce type I methyl tert-butyl ether by adjusting the process parameters. Although most indicators can be controlled, the indicators that are difficult to control or cannot be effectively controlled are mainly methyl sec-butyl ether and dimers. These two substances are the key to methyl tert-butyl ether not being able to reach type I. For the mixed C4 raw material methyl tert-butyl ether process, the difficulty of the main source of methyl sec-butyl ether and dimers being the catalytic distillation tower is overcome. The utility model directly obtains type I methyl tert-butyl ether product by azeotropic distillation separation from the outlet of the etherification reactor, and the carbon four at the top of the tower enters a catalytic distillation tower to fully react with isobutylene to obtain qualified etherified carbon four for subsequent processing, and the methyl tert-butyl ether at the bottom of the catalytic distillation tower has a low purity and contains more methyl sec-butyl ether and dimer. Such substances have a high octane number and can be used as oil blending. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 The utility model is a schematic diagram of the structure of the methyl tert-butyl ether production device.
[0019] Among them, 1-mixer, 2-etherification reactor, 3-type I methyl tert-butyl ether distillation tower, 4-catalytic distillation tower, 5-methanol extraction tower, 6-methanol recovery tower, 7-tower top condenser one, 8-tower bottom reboiler one, 9-tower top condenser two, 10-tower bottom reboiler two, 11-tower top condenser three, 12-tower bottom reboiler three. DETAILED DESCRIPTION
[0020] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.
[0021] The methyl tert-butyl ether production device comprises: an etherification reactor 2, a type I methyl tert-butyl ether distillation tower 3, a catalytic distillation tower 4, a methanol extraction tower 5 and a methanol recovery tower 6;
[0022] Among them, the bottom discharge port of the etherification reactor 2 is connected to the middle feed port of the Type-I methyl tert-butyl ether distillation column 3, the top discharge port of the Type-I methyl tert-butyl ether distillation column 3 is connected to the middle feed port of the catalytic distillation column 4, the top discharge port of the catalytic distillation column 4 is connected to the lower feed port of the methanol extraction column 5, the bottom discharge port of the methanol extraction column 5 is connected to the middle feed port of the methanol recovery column 6, and the bottom discharge port of the methanol recovery column 6 is connected to the upper feed port of the methanol extraction column 5. The connection methods are all through pipelines.
[0023] The bottom of the Type-I methyl tert-butyl ether distillation column 3 is provided with a Type-I methyl tert-butyl ether product discharge port, the bottom of the catalytic distillation column 4 is provided with a blending methyl tert-butyl ether discharge port, and the top of the methanol extraction column 5 is provided with a C4 after ether discharge port.
[0024] In one embodiment, it further includes: a mixer 1;
[0025] The mixer 1 is provided with a methanol feed port, a recycled methanol feed port, a mixed C4 feed port and a discharge port. The discharge port of the mixer 1 is connected to the top feed port of the etherification reactor 2, and the top discharge port of the methanol recovery column 6 is connected to the recycled methanol feed port of the mixer 1.
[0026] In one embodiment, the catalyst loaded in the catalytic distillation column 4 is one or several of CDM140, CDM150 or CDM170.
[0027] In one embodiment, the Type-I methyl tert-butyl ether distillation column 3 is provided with a top condenser 7 and a bottom reboiler 8. The top discharge port of the Type-I methyl tert-butyl ether distillation column 3, the top condenser 7 and the middle feed port of the catalytic distillation column 4 are connected in sequence.
[0028] In one embodiment, the catalytic distillation column 4 is provided with a top condenser 9 and a bottom reboiler 10. The top discharge port of the catalytic distillation column 4, the top condenser 9 and the lower feed port of the methanol extraction column 5 are connected in sequence.
[0029] In one embodiment, the methanol recovery column 6 is provided with a top condenser 11 and a bottom reboiler 12. The top discharge port of the methanol recovery column 6, the top condenser 11 and the recycled methanol feed port of the mixer 1 are connected, and the bottom discharge port of the methanol recovery column 6, the bottom reboiler 12 and the upper feed port of the methanol extraction column 5 are connected.
[0030] The working principle of the device of the present utility model:
[0031] (1) Mixed C4 and methanol enter the mixer 1, are mixed and then enter the etherification reactor 2. In the etherification reactor 2, isobutene reacts with methanol to generate methyl tert-butyl ether. The discharge of the etherification reactor 2 enters the Type-I methyl tert-butyl ether distillation column 3;
[0032] (2) Separate the type-I methyl tert-butyl ether product from C4 and methanol in the type-I methyl tert-butyl ether distillation column 3. The product of type-I methyl tert-butyl ether is obtained by reboiling at the bottom of the column through the bottom reboiler I 8, and C4 and methanol are obtained at the top of the column. The overhead product enters the catalytic distillation column 4 through the overhead condenser I 7 for further reaction;
[0033] (3) In the reaction section of the catalytic distillation column 4, methanol and unreacted isobutene continue to react and are separated. The product of blending methyl tert-butyl ether is obtained by reboiling at the bottom of the column through the bottom reboiler II 10. The C4 containing methanol at the top of the column enters the methanol extraction column 5 through the overhead condenser II 9 for extraction;
[0034] (4) The C4 without methanol is discharged from the top of the methanol extraction column 5. The water containing methanol in the methanol extraction column 5 enters the methanol recovery column 6, and the separation of methanol and extraction water is completed in the methanol recovery column 6;
[0035] (5) The recovered methanol at the top of the methanol recovery column 6 returns to the mixer 1 through the overhead condenser III 11, and the extraction water reboiled at the bottom of the column through the bottom reboiler III 12 returns to the methanol extraction column 5.
[0036] Example 1
[0037] The methyl tert-butyl ether production device includes: an etherification reactor 2, a type-I methyl tert-butyl ether distillation column 3, a catalytic distillation column 4, a methanol extraction column 5, a methanol recovery column 6, and a mixer 1;
[0038] Among them, the bottom discharge port of the etherification reactor 2 is connected to the middle feed port of the type-I methyl tert-butyl ether distillation column 3, the overhead discharge port of the type-I methyl tert-butyl ether distillation column 3 is connected to the middle feed port of the catalytic distillation column 4, the overhead discharge port of the catalytic distillation column 4 is connected to the lower feed port of the methanol extraction column 5, the bottom discharge port of the methanol extraction column 5 is connected to the middle feed port of the methanol recovery column 6, and the bottom discharge port of the methanol recovery column 6 is connected to the upper feed port of the methanol extraction column 5. The connection methods are all through pipelines;
[0039] The type-I methyl tert-butyl ether distillation column 3 is provided with a type-I methyl tert-butyl ether product discharge port at the bottom, the catalytic distillation column 4 is provided with a blending methyl tert-butyl ether discharge port at the bottom, and the methanol extraction column 5 is provided with a C4 after ether discharge port at the top.
[0040] The mixer 1 is provided with a methanol feed port, a recovered methanol feed port, a mixed C4 feed port, and a discharge port. The discharge port of the mixer 1 is connected to the overhead feed port of the etherification reactor 2, and the overhead discharge port of the methanol recovery column 6 is connected to the recovered methanol feed port of the mixer 1.
[0041] The catalyst loaded in the catalytic distillation column 4 is CDM140.
[0042] The type-I methyl tert-butyl ether distillation column 3 is equipped with a top condenser 7 and a bottom reboiler 8. The top discharge port of the type-I methyl tert-butyl ether distillation column 3, the top condenser 7 and the middle feed port of the catalytic distillation column 4 are connected in sequence.
[0043] The catalytic distillation column 4 is equipped with a top condenser 9 and a bottom reboiler 10. The top discharge port of the catalytic distillation column 4, the top condenser 9 and the lower feed port of the methanol extraction column 5 are connected in sequence.
[0044] The methanol recovery column 6 is equipped with a top condenser 11 and a bottom reboiler 12. The top discharge port of the methanol recovery column 6, the top condenser 11 and the recovered methanol feed port of the mixer 1 are connected. The bottom discharge port of the methanol recovery column 6, the bottom reboiler 12 and the upper feed port of the methanol extraction column 5 are connected.
[0045] Example 2
[0046] Using the device of Example 1, the methyl tert-butyl ether production process includes the following steps:
[0047] (1) Mixed C4 and methanol enter the mixer 1, are mixed and then enter the etherification reactor 2. In the etherification reactor 2, isobutene reacts with methanol to form methyl tert-butyl ether. The discharge from the etherification reactor 2 enters the type-I methyl tert-butyl ether distillation column 3;
[0048] The mass content of isobutene in the raw material mixed C4 is 2%;
[0049] The process parameters of the etherification reactor 2 are set as follows: temperature 35°C, pressure 0.6 MPa, space velocity 1 h -1 , and the alcohol-olefin ratio is 3.0:1;
[0050] (2) In the type-I methyl tert-butyl ether distillation column 3, the type-I methyl tert-butyl ether product is separated from C4 and methanol. The type-I methyl tert-butyl ether product is obtained at the bottom of the column, and C4 and methanol are obtained at the top of the column. The top discharge enters the catalytic distillation column 4 for further reaction;
[0051] The process parameters of the type-I methyl tert-butyl ether distillation column 3 are set as follows: top temperature 50°C, top pressure 0.4 MPa, reflux ratio 0.5:1;
[0052] (3) In the reaction section of the catalytic distillation column 4, methanol and unreacted isobutene continue to react and are separated. The blending methyl tert-butyl ether is obtained at the bottom of the column, and the C4 containing methanol at the top enters the methanol extraction column 5 for extraction;
[0053] The process parameters of the catalytic distillation column 4 are set as follows: top temperature 50°C, top pressure 0.5 MPa, reflux ratio 0.5:1.
[0054] The process parameters of the methanol extraction tower 5 are set as follows: temperature 40°C, pressure 0.4 MPa, and the weight ratio of water to C4 in the methanol extraction tower 5 is 0.1:1.
[0055] (4) The C4 without methanol is discharged from the top of the methanol extraction tower 5, and the water containing methanol in the methanol extraction tower 5 enters the methanol recovery tower 6, where the separation of methanol and extraction water is completed.
[0056] The process parameters of the methanol recovery tower 6 are set as follows: top temperature 65°C, top pressure 0 MPa, and reflux ratio 5:1.
[0057] (5) The methanol recovered from the top of the methanol recovery tower 6 is returned to the mixer 1, and the extraction water at the bottom of the tower is returned to the methanol extraction tower 5.
[0058] Example 3
[0059] Using the device of Example 1, the methyl tert-butyl ether production process includes the following steps:
[0060] (1) The mixed C4 and methanol enter the mixer 1, and after mixing, enter the etherification reactor 2. In the etherification reactor 2, isobutene reacts with methanol to form methyl tert-butyl ether, and the effluent from the etherification reactor 2 enters the Type-I methyl tert-butyl ether distillation tower 3.
[0061] The mass content of isobutene in the raw material mixed C4 is 50%.
[0062] The process parameters of the etherification reactor 2 are set as follows: temperature 65°C, pressure 1.2 MPa, space velocity 4 h -1 , and the alcohol-olefin ratio is 1.05:1.
[0063] (2) In the Type-I methyl tert-butyl ether distillation tower 3, the Type-I methyl tert-butyl ether product is separated from C4 and methanol. The Type-I methyl tert-butyl ether product is obtained at the bottom of the tower, and C4 and methanol are obtained at the top of the tower. The effluent at the top of the tower enters the catalytic distillation tower 4 for further reaction.
[0064] The process parameters of the Type-I methyl tert-butyl ether distillation tower 3 are set as follows: top temperature 70°C, top pressure 0.8 MPa, and reflux ratio 3.0:1.
[0065] (3) In the reaction section of the catalytic distillation tower 4, methanol and unreacted isobutene continue to react and are separated. The blending methyl tert-butyl ether is obtained at the bottom of the tower, and the C4 containing methanol at the top enters the methanol extraction tower 5 for extraction.
[0066] The process parameters of the catalytic distillation tower 4 are set as follows: top temperature 60°C, top pressure 0.6 MPa, and reflux ratio 3.0:1.
[0067] The process parameters of the methanol extraction tower 5 are set as follows: temperature 50°C, pressure 0.8 MPa, and the weight ratio of water to C4 in the methanol extraction tower 5 is 0.5:1.
[0068] (4) The C4 without methanol is discharged from the top of the methanol extraction tower 5, and the water containing methanol in the methanol extraction tower 5 enters the methanol recovery tower 6, where the separation of methanol and extraction water is completed.
[0069] The process parameters of the methanol recovery tower 6 are set as follows: top temperature 90°C, top pressure 0.3 MPa, and reflux ratio 15:1.
[0070] (5) The methanol recovered from the top of the methanol recovery tower 6 is returned to the mixer 1, and the extraction water at the bottom of the tower is returned to the methanol extraction tower 5.
[0071] Example 4
[0072] Using the device of Example 1, the methyl tert-butyl ether production process includes the following steps:
[0073] (1) The mixed C4 and methanol enter the mixer 1, and after mixing, enter the etherification reactor 2. In the etherification reactor 2, isobutene reacts with methanol to form methyl tert-butyl ether, and the discharge from the etherification reactor 2 enters the type-I methyl tert-butyl ether distillation tower 3.
[0074] The mass content of isobutene in the raw material mixed C4 is 25%.
[0075] The process parameters of the etherification reactor 2 are set as follows: temperature 50°C, pressure 0.8 MPa, space velocity 2 h -1 , and the alcohol-olefin ratio is 1.10:1.
[0076] (2) In the type-I methyl tert-butyl ether distillation tower 3, the type-I methyl tert-butyl ether product is separated from C4 and methanol. The type-I methyl tert-butyl ether product is obtained at the bottom of the tower, and C4 and methanol are obtained at the top of the tower. The discharge at the top of the tower enters the catalytic distillation tower 4 for further reaction.
[0077] The process parameters of the type-I methyl tert-butyl ether distillation tower 3 are set as follows: top temperature 60°C, top pressure 0.6 MPa, and reflux ratio 1.0:1.
[0078] (3) In the reaction section of the catalytic distillation tower 4, methanol and unreacted isobutene continue to react and are separated. The blending methyl tert-butyl ether is obtained at the bottom of the tower, and the C4 containing methanol at the top enters the methanol extraction tower 5 for extraction.
[0079] The process parameters of the catalytic distillation tower 4 are set as follows: top temperature 55°C, top pressure 0.55 MPa, and reflux ratio 1.0:1.
[0080] The process parameters of the methanol extraction tower 5 are set as follows: temperature 45°C, pressure 0.5 MPa, and the weight ratio of water to C4 in the methanol extraction tower 5 is 0.3:1.
[0081] (4) The C4 without methanol is discharged from the top of the methanol extraction tower 5, and the water containing methanol in the methanol extraction tower 5 enters the methanol recovery tower 6, where the separation of methanol and extraction water is completed.
[0082] The process parameters of the methanol recovery tower 6 are set as follows: top temperature 70°C, top pressure 0.1 MPa, reflux ratio 10:1.
[0083] (5) The methanol recovered from the top of the methanol recovery tower 6 is returned to the mixer 1, and the extraction water at the bottom of the tower is returned to the methanol extraction tower 5.
[0084] The quality of the type-I methyl tert-butyl ether products obtained in Examples 2 to 4 is shown in Table 1 below.
[0085] Table 1 Quality of the type-I methyl tert-butyl ether products
[0086]
[0087]
[0088] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present utility model. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present utility model. Therefore, the present utility model will not be limited to the embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features disclosed herein.
Claims
1. A methyl tert-butyl ether production device, characterized in that: include: Etherification reactor, type I methyl tert-butyl ether distillation tower, catalytic distillation tower, methanol extraction tower and methanol recovery tower; The bottom discharge port of the etherification reactor is connected to the middle feed port of the type I methyl tert-butyl ether distillation tower, the top discharge port of the type I methyl tert-butyl ether distillation tower is connected to the middle feed port of the catalytic distillation tower, the top discharge port of the catalytic distillation tower is connected to the lower feed port of the methanol extraction tower, the bottom discharge port of the methanol extraction tower is connected to the middle feed port of the methanol recovery tower, and the bottom discharge port of the methanol recovery tower is connected to the upper feed port of the methanol extraction tower, and the connection methods are all connected through pipelines; The bottom of the Type I MTBE distillation tower is provided with a Type I MTBE product discharge port, the bottom of the catalytic distillation tower is provided with an oil-adjusted MTBE discharge port, and the top of the methanol extraction tower is provided with an ether-post-C4 discharge port.
2. A methyl tert-butyl ether production device according to claim 1, characterized in that: Also includes: mixer; The mixer is provided with a methanol feed port, a recovered methanol feed port, a mixed C4 feed port and a discharge port. The discharge port of the mixer is connected to the top feed port of the etherification reactor, and the top discharge port of the methanol recovery tower is connected to the recovered methanol feed port of the mixer.
3. A methyl tert-butyl ether production device according to claim 1, characterized in that: The catalyst loaded in the catalytic distillation tower is one or more of CDM140, CDM150 or CDM170.
4. A methyl tert-butyl ether production device according to claim 1, characterized in that: The type I methyl tert-butyl ether distillation tower is provided with a top condenser and a bottom reboiler. The top discharge port, the top condenser and the middle feed port of the catalytic distillation tower are connected in sequence.
5. The methyl tert-butyl ether production device according to claim 1, characterized in that: The catalytic distillation tower is provided with a second top condenser and a second bottom reboiler. The top discharge port of the catalytic distillation tower, the second top condenser and the lower feed port of the methanol extraction tower are connected in sequence.
6. The methyl tert-butyl ether production device according to claim 1, characterized in that: The methanol recovery tower is provided with a third top condenser and a third bottom reboiler. The top discharge port of the methanol recovery tower, the third top condenser and the recovered methanol feed port of the mixer are connected. The bottom discharge port of the methanol recovery tower, the third bottom reboiler and the upper feed port of the methanol extraction tower are connected.