System and method for preparing 1-butene by using catalytic C4

Abstract

The invention discloses a system and a method for preparing 1-butene by catalyzing C4, and belongs to the technical field of 1-butene production. According to the technical scheme, the device comprises an etherification reactor, a catalytic distillation tower, a deep etherification reactor, a light component removal tower and a heavy component removal tower which are connected in sequence. According to the method, the catalytic C4 is used as a raw material to prepare the 1-butene, so that the source of the raw material for preparing the 1-butene is widened, the utilization rate of the catalytic C4 is also improved, and the method has a relatively good application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of 1-butene production, and in particular to a system and method for preparing 1-butene by utilizing catalytic carbon tetrachloride. Background Art

[0002] 1-Butene is a C4 monoolefin that can be obtained through a variety of hydrocarbon processing techniques. Currently, the 1-butene in industrial production mainly comes from mixed C4 separation methods and chemical synthesis methods.

[0003] The mixed C4 separation method is a petrochemical production process. Its raw material mixed C4 mainly comes from the catalytic cracking unit of the refinery, the ethylene cracking unit of the chemical plant and the MTO / MTP unit of the coal chemical industry. The butadiene and isobutylene in the mixed C4 are removed by extraction or chemical reaction, and then the C4 fraction other than 1-butene is separated by ultra-precision distillation to obtain a high-purity 1-butene product. However, the raw material source of this technology is limited and the energy consumption is high.

[0004] The chemical synthesis method, namely the ethylene dimerization method, usually uses cracked ethylene to produce 1-butene through dimerization reaction, which is characterized by less impurities and high purity. However, this method has high raw material costs and a long process flow, resulting in a relatively high cost for 1-butene production.

[0005] Chinese invention patent CN105837390A discloses a method for obtaining high-purity 1-butene from a C4 hydrocarbon mixture, specifically a method for obtaining high-purity 1-butene starting from a C4 hydrocarbon mixture containing isobutylene, n-butane, isobutane, 1,3-butadiene, 1-butene, 2-butene and optional C3 and C5 hydrocarbons, which includes the following stages: isobutylene conversion in two stages, each stage including one or more reactors and a subsequent distillation tower for recovering the reaction product; recovering excess alcohol; using at least two distillation towers to recover 1-butene; characterized in that a further conversion stage including one or more reactors in series is used to complete the removal of isobutylene. The disadvantage of this patent is that 1-butene is produced using high-concentration isobutylene and 1-butene as raw materials, and the raw material system mainly targeted is cracked carbon four, and low-concentration catalytic carbon four cannot obtain 1-butene that meets product indicators.

[0006] Chinese invention patent CN112079682A discloses a device and method for producing 1-butene using C4 fraction, specifically, it relates to a device and method for producing 1-butene using C4 fraction, the device comprises a selective hydrogenation unit, an etherification unit and a precision distillation unit arranged in sequence along the material flow direction, and also comprises an extraction pre-fractionation unit, wherein the extraction fractionation unit is arranged between the selective hydrogenation unit and the etherification unit, or connected and arranged after the precision distillation unit, and the extraction fractionation unit is also connected to a 2-butene isomerization unit. Compared with the prior art, the energy consumption of the patent can be reduced by more than 20%, and at the same time, the total conversion rate of 2-butene is high, more than 85%, the total yield of 1-butene is greater than 90%, the raw material application range is wide, and it is particularly suitable for C4 raw materials rich in n-butane. However, low-concentration catalytic C4 raw materials cannot obtain 1-butene that meets product indicators.

[0007] Therefore, in order to solve the above problems, it is necessary to develop a method for obtaining 1-butene that meets product indicators using low-concentration catalytic C4 raw materials, so as to expand the raw material sources for preparing 1-butene. Summary of the invention

[0008] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a system and method for preparing 1-butene using catalytic carbon tetrachloride. The catalytic carbon tetrachloride is used as a raw material to prepare 1-butene, which broadens the source of raw materials for preparing 1-butene and improves the utilization rate of the catalytic carbon tetrachloride, and has good application prospects.

[0009] The technical solution of the present invention is: On the one hand, the present invention provides a system for preparing 1-butene by catalytic C4, comprising an etherification reactor, a catalytic distillation tower, a deep etherification reactor, a light removal tower and a heavy removal tower connected in sequence.

[0010] The catalytic distillation tower is composed of a kettle, a stripping section, one or more reaction beds, a rectifying section and a top reflux condenser; a certain number of catalytic distillation baskets are evenly distributed on the reaction bed, and the catalytic distillation baskets are filled with the same solid catalyst as the etherification reactor, and the solid catalyst is a resin catalyst, a heteropolyacid catalyst or a molecular sieve catalyst.

[0011] Preferably, the solid catalyst is a sulfonic acid type macroporous cation exchange resin catalyst.

[0012] The light-removal tower is a common distillation tower, which mainly serves to separate light components such as isobutane and methanol in C4.

[0013] The deweighting tower is a common distillation tower, which mainly serves to separate 1-butene.

[0014] The methanol extraction tower is mainly used to extract methanol from the top of the light removal tower.

[0015] The methanol recovery tower is mainly used to recover methanol for recycling.

[0016] Preferably, the deep etherification reactor is filled with a resin catalyst having an exchange equivalent greater than 5.4 mmolH+ / g.

[0017] Preferably, the top outlet of the lightness removal tower is connected to the inlet of the methanol extraction tower, the bottom outlet of the methanol extraction tower is connected to the inlet of the methanol recovery tower, and the bottom outlet of the methanol recovery tower is connected to the reflux inlet of the methanol extraction tower.

[0018] On the other hand, the present invention also provides a method for preparing 1-butene by using the above system using catalytic C4, comprising the following steps: S1: Catalytic C4 and methanol enter the etherification reactor together to etherify the isobutylene in the catalytic C4 to produce MTBE; S2: The product at the bottom of the etherification reactor enters the catalytic distillation tower for further reaction, and further etherifies the isobutylene in the catalytic C4 to produce MTBE, which is extracted from the bottom outlet of the catalytic distillation tower; if the top distillate is directly subjected to precise distillation to produce 1-butene, isobutylene will be enriched in 1-butene. If the butene content in the original feed is 10%, isobutylene will be enriched in 1-butene by 10 times, from 0.2% to 2%, and the first-grade 1-butene product cannot be obtained. Therefore, the distillate enters the deep etherification reactor from the top outlet to continue etherifying the isobutylene in the catalytic C4 to produce MTBE; S3: The reaction product of the deep etherification reactor enters the light component removal tower from the bottom outlet, and the light component is extracted from the top outlet. The heavy component enters the heavy component removal tower from the bottom outlet, and the heavy component is extracted from the bottom outlet of the heavy component removal tower. The 1-butene product is extracted from the top outlet.

[0019] Preferably, the method further includes the following methanol recovery step to reduce the amount of methanol in the original feed: S4: the light components extracted from the top of the light removal tower enter the methanol extraction tower, isobutane is extracted from the top outlet, the extracted methanol enters the methanol recovery tower from the bottom outlet, methanol is extracted from the top outlet, and the remaining materials are refluxed to the methanol extraction tower from the bottom outlet.

[0020] The lightness removal tower is pressurized (usually the operating pressure of the lightness removal tower is about 0.5Mpa) to increase the top temperature of the tower to supply heat to the bottom of the heavyness removal tower, reducing the steam heating of the heavyness removal tower and condensing the top of the lightness removal tower, which has the effect of reducing energy consumption and reducing the amount of circulating water.

[0021] Preferably, the reaction temperature of the etherification reactor is 40-80°C, and the air velocity is 1.0-5h -1, the reaction pressure is 0.6-1.2MPa; the top pressure of the catalytic distillation tower is 0.45-0.7MPa, the top temperature is 50-70℃, the reaction section temperature is 60-80℃, the bottom temperature is 130-160℃, and the reflux ratio is 0.5-3; the reaction temperature of the deep etherification reactor is 40-70℃, and the space velocity is 1.0-3h -1 , the reaction pressure is 0.4-1.0MPa; the top pressure of the light removal tower is 1.0-1.5MPa, the top temperature is 90-120℃, and the reflux ratio is 15-40; the top pressure of the heavy removal tower is 0.45-0.7MPa, the top temperature is 50-60℃, and the reflux ratio is 15-40; the top pressure of the methanol extraction tower is 0.4-0.8MPa, the top temperature is 40-60℃, and the methanol concentration in the bottom is 7-10%; the top pressure of the methanol recovery tower is 0.1-0.3MPa, the top temperature is 70-120℃, and the reflux ratio is 5-10.

[0022] Preferably, in step S1, the mass percentage of isobutylene in the catalytic C4 is 8%-25%.

[0023] Preferably, in step S1, the molar ratio of isobutylene to methanol in the catalytic C4 is 1:1.15-1.3.

[0024] The present invention further performs deep etherification on the catalytic C4 after etherification-catalytic distillation because: isobutylene and 1-butene have similar boiling points, and when the concentration of 1-butene in the C4 raw material is high, a sufficient amount of 1-butene product can still be obtained by appropriately losing a little 1-butene due to the presence of isobutylene; however, the 1-butene content in the catalytic C4 raw material is low, and the quality of the 1-butene product cannot be achieved at the cost of losing 1-butene, so the amount of isobutylene in the catalytic C4 must be reduced to a level suitable for 1-butene purification.

[0025] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses catalytic C4 as a raw material, and obtains a high-purity 1-butene product through an etherification-catalytic distillation-deep etherification-precision distillation process with methanol. The difference between the present invention and the prior art is that the raw material uses the catalytic C4 with the largest market reserve, so that the raw material source of 1-butene is no longer limited to ethylene cracking C4 and MTO / MTP C4 of coal chemical industry, broadens the source of raw materials, and the scope of technical application is wider, thereby providing a solution to the source of 1-butene for factories or regions that do not have ethylene cracking devices and coal chemical MTO / MTP devices but need 1-butene products, and also improves the utilization rate of catalytic C4, thereby improving corporate benefits. At present, the number of domestic ethylene devices is limited and the distribution area is uneven. The method of producing 1-butene using catalytic C4 as a raw material has good application prospects. The production of 1-butene using catalytic C4 needs to meet the following indicators: the residual amount of isobutylene is ≤0.04%, and the yield of 1-butene is higher than ≥80%. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the present invention.

[0027] In the figure, 1. etherification reactor; 2. catalytic distillation tower; 3. deep etherification reactor; 4. light removal tower; 5. heavy removal tower; 6. methanol extraction tower; 7. methanol recovery tower. DETAILED DESCRIPTION

[0028] In order to enable persons skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0029] like Figure 1 As shown, the system for preparing 1-butene used in the following examples includes an etherification reactor 1, a catalytic distillation column 2, a deep etherification reactor 3, a light removal column 4 and a heavy removal column 5 which are connected in sequence.

[0030] Furthermore, the etherification reactor 1 and the catalytic distillation tower 2 are filled with a solid catalyst, and the solid catalyst is a resin catalyst, a heteropolyacid catalyst or a molecular sieve catalyst.

[0031] Furthermore, the solid catalyst is a sulfonic acid type cation exchange resin catalyst.

[0032] Furthermore, the deep etherification reactor 3 is filled with a resin catalyst having an exchange equivalent greater than 5.4 mmolH+ / g.

[0033] Furthermore, the top outlet of the lightness removal tower 4 is connected to the inlet of the methanol extraction tower 6 , the bottom outlet of the methanol extraction tower 6 is connected to the inlet of the methanol recovery tower 7 , and the bottom outlet of the methanol recovery tower 7 is connected to the reflux inlet of the methanol extraction tower 6 .

[0034] The method for preparing 1-butene by utilizing catalytic carbon four through the above system comprises the following steps: S1: Catalytic C4 and methanol enter the etherification reactor 1 together, so that the isobutylene in the catalytic C4 is etherified to produce MTBE. The conversion rate of the exported isobutylene reaches about 94%, and the isobutylene content is about 1%; S2: The product at the bottom of the etherification reactor 1 enters the catalytic distillation tower 2 for further reaction, and further etherifies the isobutylene in the catalytic C4 to generate MTBE. The content of isobutylene in the C4 after etherification at the top outlet is about 0.2%, and the total conversion rate of isobutylene is about 98.5%. MTBE is extracted from the bottom outlet of the catalytic distillation tower 2, and the distillate enters the deep etherification reactor 3 from the top outlet, so that the isobutylene in the catalytic C4 continues to be etherified to generate MTBE. After deep etherification, the total conversion rate of isobutylene can be stably increased to more than 99.5%; S3: The reaction product of the deep etherification reactor 3 enters the light component removal tower 4 from the bottom outlet, and the light component is extracted from the top outlet. The heavy component enters the heavy component removal tower 5 from the bottom outlet, and the heavy component is extracted from the bottom outlet of the heavy component removal tower 5. The 1-butene product is extracted from the top outlet.

[0035] Furthermore, the following steps are included: S4: the light components extracted from the top of the light removal tower 4 enter the methanol extraction tower 6, isobutane is extracted from the top outlet, the extracted methanol enters the methanol recovery tower 7 from the bottom outlet, methanol is extracted from the top outlet, and the remaining materials are refluxed to the methanol extraction tower 6 from the bottom outlet.

[0036] Furthermore, the reaction temperature of the etherification reactor 1 is 40-80°C, and the air velocity is 1.0-5h -1 , the reaction pressure is 0.6-1.2MPa; the top pressure of the catalytic distillation tower 2 is 0.45-0.7MPa, the top temperature is 50-70℃, the reaction section temperature is 60-80℃, the bottom temperature is 130-160℃, and the reflux ratio is 0.5-3; the reaction temperature of the deep etherification reactor 3 is 40-70℃, the space velocity is 1.0-3h -1 , the reaction pressure is 0.4-1.0MPa; the top pressure of the light removal tower 4 is 1.0-1.5MPa, the top temperature is 90-120℃, and the reflux ratio is 15-40; the top pressure of the heavy removal tower 5 is 0.45-0.7MPa, the top temperature is 50-60℃, and the reflux ratio is 15-40; the top pressure of the methanol extraction tower 6 is 0.4-0.8MPa, the top temperature is 40-60℃, and the methanol concentration in the bottom is 7-10%; the top pressure of the methanol recovery tower 7 is 0.1-0.3MPa, the top temperature is 70-120℃, and the reflux ratio is 5-10.

[0037] Furthermore, in step S1, the mass percentage of isobutylene in the catalytic C4 is 8%-25%.

[0038] Furthermore, in step S1, the molar ratio of isobutylene to methanol in the catalytic C4 is 1:1.15-1.3.

[0039] Example 1 Among the raw materials used in this embodiment, the mass percentage of isobutylene in the catalytic C4 is 8%, and the molar ratio of isobutylene to methanol is 1:1.15.

[0040] The operating conditions of the etherification reactor 1 are: reaction temperature 40°C, space velocity 1.0h -1 , the reaction pressure is 0.6MPa, so that the reactants and products are both in liquid phase, and the conversion rate of isobutylene can reach more than 95%.

[0041] The operating conditions of the catalytic distillation tower 2 are: the tower top pressure is 0.45MPa, the tower top temperature is 50°C, the reaction section temperature is 60°C, the tower bottom temperature is 130°C, and the reflux ratio is 0.5. Isobutylene continues to react in the reaction section, and the chemical equilibrium is broken by catalytic distillation, so that the reaction continues to proceed. The isobutylene content at the top of the catalytic distillation tower 2 is controlled to 0.2%.

[0042] The operating conditions of deep etherification reactor 3 are: reaction temperature 40°C, space velocity 1.0h -1 The reaction pressure is 0.4 MPa, so that the reactants and products are both in liquid phase, and the mass percentage of outlet isobutylene is 0.03%.

[0043] The operating conditions of the light-removal tower 4 are: the tower top pressure is 1.0 MPa, the tower top temperature is 90°C, and the reflux ratio is 15.

[0044] The operating conditions of the deweighting tower 5 are: the tower top pressure is 0.45 MPa, the tower top temperature is 50°C, and the reflux ratio is 15.

[0045] The operating conditions of the methanol extraction tower 6 are: the tower top pressure is 0.4 MPa, the tower top temperature is 40° C., and the methanol concentration in the tower bottom is controlled to be 7%.

[0046] The operating conditions of the methanol recovery tower 7 are: the tower top pressure is 0.1 MPa, the tower top temperature is 70° C., and the reflux ratio is 5.

[0047] The 1-butene product obtained in this example meets the quality standard, wherein the purity of 1-butene is 99.36%.

[0048] Example 2 Among the raw materials used in this embodiment, the mass percentage of isobutylene in the catalytic C4 is 25%, and the molar ratio of isobutylene to methanol is 1:1.3.

[0049] The operating conditions of the etherification reactor 1 are: reaction temperature 80°C, space velocity 5h -1 , the reaction pressure is 1.2MPa, so that the reactants and products are both in liquid phase, and the conversion rate of isobutylene can reach more than 95%.

[0050] The operating conditions of the catalytic distillation tower 2 are: the tower top pressure is 0.7 MPa, the tower top temperature is 70°C, the reaction section temperature is 80°C, the tower bottom temperature is 160°C, and the reflux ratio is 3. Isobutylene continues to react in the reaction section, and the chemical equilibrium is broken by catalytic distillation, so that the reaction continues to proceed. The isobutylene content at the top of the catalytic distillation tower 2 is controlled to 0.4%.

[0051] The operating conditions of deep etherification reactor 3 are: reaction temperature 70°C, space velocity 3h -1 The reaction pressure is 1.0 MPa, so that the reactants and products are both in liquid phase, and the mass percentage of outlet isobutylene is 0.02%.

[0052] The operating conditions of the light-removal tower 4 are: the tower top pressure is 1.5 MPa, the tower top temperature is 120°C, and the reflux ratio is 40.

[0053] The operating conditions of the deweighting tower 5 are: the tower top pressure is 0.7 MPa, the tower top temperature is 60°C, and the reflux ratio is 40.

[0054] The operating conditions of the methanol extraction tower 6 are: the tower top pressure is 0.8 MPa, the tower top temperature is 60° C., and the methanol concentration in the tower bottom is controlled to be 10%.

[0055] The operating conditions of the methanol recovery tower 7 are: the tower top pressure is 0.3 MPa, the tower top temperature is 120° C., and the reflux ratio is 10.

[0056] The 1-butene product obtained in this example meets the quality standard, wherein the purity of 1-butene is 99.41%.

[0057] Example 3 Among the raw materials used in this embodiment, the mass percentage of isobutylene in the raw material catalytic carbon four is 15%, and the molar ratio of isobutylene to methanol is 1:1.2.

[0058] The operating conditions of the etherification reactor 1 are: reaction temperature 60°C, space velocity 2h -1 , the reaction pressure is 0.8MPa, so that the reactants and products are both in liquid phase, and the conversion rate of isobutylene can reach more than 95%.

[0059] The operating conditions of the catalytic distillation tower 2 are: the tower top pressure is 0.6MPa, the tower top temperature is 60°C, the reaction section temperature is 70°C, the tower bottom temperature is 140°C, and the reflux ratio is 1. Isobutylene continues to react in the reaction section, and the chemical equilibrium is broken by catalytic distillation, so that the reaction continues to proceed. The isobutylene content at the top of the catalytic distillation tower 2 is controlled to 0.4%.

[0060] The operating conditions of deep etherification reactor 3 are: reaction temperature 50°C, space velocity 2h -1 The reaction pressure is 0.8 MPa, so that the reactants and products are both in liquid phase, and the mass percentage of outlet isobutylene is 0.02%.

[0061] The operating conditions of the light-removal tower 4 are: the tower top pressure is 1.2 MPa, the tower top temperature is 100°C, and the reflux ratio is 20.

[0062] The operating conditions of the deweighting tower 5 are: the tower top pressure is 0.5 MPa, the tower top temperature is 55°C, and the reflux ratio is 25.

[0063] The operating conditions of the methanol extraction tower 6 are: the tower top pressure is 0.5 MPa, the tower top temperature is 50° C., and the methanol concentration in the tower bottom is controlled to be 8%.

[0064] The operating conditions of the methanol recovery tower 7 are: the tower top pressure is 0.2 MPa, the tower top temperature is 100° C., and the reflux ratio is 8.

[0065] The 1-butene product obtained in this example meets the quality standard, wherein the purity of 1-butene is 99.45%.

[0066] Comparative Example 1 The difference from Example 3 is that the overhead distillate of the catalytic distillation tower directly enters the lightness removal tower to start precise distillation. The purity of 1-butene in the final 1-butene product is 97.6%.

[0067] It can be seen from the examples and comparative example 1 that when 1-butene is produced by catalytic C4, if it is directly subjected to precision distillation after etherification and catalytic distillation together with methanol without deep etherification, the purity of 1-butene in the produced 1-butene product will be reduced and cannot reach a level of more than 99%.

Claims

1. A system for preparing 1-butene by catalytic carbon four, characterized in that: The invention comprises an etherification reactor (1), a catalytic distillation tower (2), a deep etherification reactor (3), a light removal tower (4) and a heavy removal tower (5) which are connected in sequence.

2. The system for preparing 1-butene by catalytic C4 as claimed in claim 1, characterized in that: The etherification reactor (1) and the catalytic distillation tower (2) are filled with a solid catalyst, and the solid catalyst is a resin catalyst, a heteropolyacid catalyst or a molecular sieve catalyst.

3. The system for preparing 1-butene by catalytic C4 as claimed in claim 2, characterized in that: The solid catalyst is a sulfonic acid type cation exchange resin catalyst.

4. The system for preparing 1-butene by catalytic C4 as claimed in claim 1, characterized in that: The deep etherification reactor (3) contains a resin catalyst.

5. The system for preparing 1-butene by catalytic C4 as claimed in claim 1, characterized in that: The top outlet of the light removal tower (4) is connected to the inlet of the methanol extraction tower (6), the bottom outlet of the methanol extraction tower (6) is connected to the inlet of the methanol recovery tower (7), and the bottom outlet of the methanol recovery tower (7) is connected to the reflux inlet of the methanol extraction tower (6).

6. A method for preparing 1-butene by catalyzing carbon tetrachloride using a system as described in any one of claims 1 to 5, characterized in that: The following steps are involved: S1: catalytic C4 and methanol enter the etherification reactor (1) to etherify the isobutylene in the catalytic C4 to produce MTBE; S2: The product at the bottom of the etherification reactor (1) enters the catalytic distillation tower (2) for further reaction, further etherifying the isobutylene in the catalytic C4 to produce MTBE, and the MTBE is taken out from the bottom outlet of the catalytic distillation tower (2), and the distillate enters the deep etherification reactor (3) from the top outlet, so that the isobutylene in the catalytic C4 is further etherified to produce MTBE; S3: The reaction product of the deep etherification reactor (3) enters the light component removal tower (4) from the tower bottom outlet, and the light component is extracted from the tower top outlet. The heavy component enters the heavy component removal tower (5) from the tower bottom outlet, and the heavy component is extracted from the tower bottom outlet of the heavy component removal tower (5). The 1-butene product is extracted from the tower top outlet.

7. The method according to claim 6, characterized in that The following steps are also included: S4: The light components extracted from the top of the light removal tower (4) enter the methanol extraction tower (6), isobutane is extracted from the top outlet, the extracted methanol enters the methanol recovery tower (7) from the bottom outlet, methanol is extracted from the top outlet, and the remaining materials are refluxed to the methanol extraction tower (6) from the bottom outlet.

8. The method according to claim 7, characterized in that The reaction temperature of the etherification reactor (1) is 40-80°C, and the space velocity is 1.0-5h -1 , the reaction pressure is 0.6-1.2MPa; the top pressure of the catalytic distillation tower (2) is 0.45-0.7MPa, the top temperature is 50-70°C, the reaction section temperature is 60-80°C, the bottom temperature is 130-160°C, and the reflux ratio is 0.5-3; the reaction temperature of the deep etherification reactor (3) is 40-70°C, the space velocity is 1.0-3h -1 , the reaction pressure is 0.4-1.0MPa; the top pressure of the light removal tower (4) is 1.0-1.5MPa, the top temperature is 90-120°C, and the reflux ratio is 15-40; the top pressure of the heavy removal tower (5) is 0.45-0.7MPa, the top temperature is 50-60°C, and the reflux ratio is 15-40; the top pressure of the methanol extraction tower (6) is 0.4-0.8MPa, the top temperature is 40-60°C, and the methanol concentration in the bottom of the tower is 7-10%; The top pressure of the methanol recovery tower (7) is 0.1-0.3 MPa, the top temperature is 70-120°C, and the reflux ratio is 5-10.

9. The method according to claim 6, characterized in that In step S1, the mass percentage of isobutylene in the catalytic C4 is 8%-25%.

10. The method according to claim 6, characterized in that In step S1, the molar ratio of isobutylene to methanol in the catalytic C4 is 1:1.15-1.3.

Images