System and method for producing 1-butene using catalytic c4s

Abstract

The application discloses a system and method for preparing 1-butene by using catalytic C4, and belongs to the technical field of 1-butene production. The technical scheme is that the system comprises an etherification reactor, a catalytic distillation column, a deep etherification reactor, a light component removal column and a heavy component removal column which are sequentially connected. The application uses catalytic C4 as raw material to prepare 1-butene, widens the raw material source for preparing 1-butene, improves the utilization rate of catalytic C4, and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of 1-butene production, in particular to a system and method for preparing 1-butene by catalytic carbon four. BACKGROUND

[0002] 1-butene is a carbon four monoolefin, which can be obtained by various hydrocarbon processing processes. Currently, 1-butene in industrial production mainly comes from mixed carbon four separation method and chemical synthesis method.

[0003] The mixed carbon four separation method is a petroleum chemical production process, the raw material mixed carbon four mainly comes from the catalytic cracking device of the oil refinery, the ethylene cracking device of the chemical plant and the MTO / MTP device of the coal chemical industry, the butadiene and isobutene in the mixed carbon four are removed by extraction or chemical reaction method, and then the carbon four fraction except 1-butene is separated by ultra-precision rectification to obtain high-purity 1-butene product. However, this technology has limited raw material sources and high energy consumption.

[0004] The chemical synthesis method, i.e. ethylene dimerization method, usually uses cracked ethylene to prepare 1-butene by dimerization reaction, which has the characteristics of less product impurities and high purity. However, this method has high raw material cost and long process flow, resulting in high cost of 1-butene production.

[0005] Chinese patent CN105837390A discloses a method for obtaining high-purity 1-butene from C4 hydrocarbon mixture, which is a method for obtaining high-purity 1-butene from C4 hydrocarbon mixture containing isobutene, n-butane, isobutane, 1,3-butadiene, 1-butene, 2-butene and optionally C3 and C5 hydrocarbons, which includes the following stages: isobutene conversion is realized in two stages, each stage includes one or more reactors and a distillation column after the reactor for recovering reaction products; recovering excess alcohol; recovering 1-butene by using at least two distillation columns; characterized in that a further conversion stage including one or more reactors in series is also used to complete isobutene removal. The disadvantages of this patent are: high-concentration isobutene and 1-butene are used as raw materials to produce 1-butene, and the main raw material system is cracked carbon four, and low-concentration catalytic carbon four cannot obtain 1-butene meeting product specifications.

[0006] The Chinese invention patent CN112079682A discloses a device and method for producing 1-butene by using carbon four fraction, specifically relates to a device and method for producing 1-butene by using carbon four fraction, the device comprises a selective hydrogenation unit, an etherification unit and a precision rectification unit arranged in sequence along the material flow direction, and further comprises an extraction pre-fractionation unit, wherein the extraction fractionation unit is arranged between the selective hydrogenation unit and the etherification unit, or is connected after the precision rectification unit, and a 2-butene isomerization unit is further connected after the extraction fractionation unit. Compared with the prior art, the energy consumption of the patent can be reduced by more than 20%, 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 the device is particularly suitable for carbon four raw material rich in n-butane. However, 1-butene meeting product indicators cannot be obtained from low-concentration catalytic carbon four raw materials.

[0007] Therefore, in view of the above problems, it is necessary to develop a method for obtaining 1-butene meeting product indicators by using low-concentration catalytic carbon four raw materials, so as to expand the raw material source for preparing 1-butene. SUMMARY

[0008] The technical problem to be solved by the present application is to overcome the shortcomings of the prior art, provide a system and method for preparing 1-butene by using catalytic carbon four, use catalytic carbon four as raw material to prepare 1-butene, broaden the raw material source for preparing 1-butene, improve the utilization rate of catalytic carbon four, and have good application prospect.

[0009] The technical scheme of the present application is as follows:

[0010] In one aspect, the present application provides a system for preparing 1-butene by using catalytic carbon four, which comprises an etherification reactor, a catalytic distillation column, a deep etherification reactor, a light-removing column and a heavy-removing column connected in sequence.

[0011] The catalytic distillation column is composed of one column kettle, one stripping section, one or more reaction bed layers, one rectification section and one column top reflux condenser; a certain number of catalytic distillation baskets are uniformly distributed in the reaction bed layer, the catalytic distillation basket is filled with the same solid catalyst as the etherification reactor, and the solid catalyst is a resin catalyst, a heteropoly acid catalyst or a molecular sieve catalyst.

[0012] Preferably, the solid catalyst is a sulfonic acid type macroporous cation exchange resin catalyst.

[0013] The light-removing column is a common rectification column, which mainly plays a role in separating light components such as isobutane and methanol in carbon four.

[0014] The heavy-removing column is a common rectification column, which mainly plays a role in separating 1-butene.

[0015] The methanol extraction column mainly functions to extract methanol from the top of the light-removing column.

[0016] The methanol recovery column mainly functions to recycle the recovered methanol.

[0017] Preferably, the deep etherification reactor is filled with a catalyst having an exchange equivalent greater than 5.4 mmol H+ / g resin.

[0018] Preferably, the top outlet of the light-removing column is connected to the inlet of the methanol extraction column, the bottom outlet of the methanol extraction column is connected to the inlet of the methanol recovery column, and the bottom outlet of the methanol recovery column is connected to the reflux inlet of the methanol extraction column.

[0019] In another aspect, the present application also provides a method for preparing 1-butene from catalytic C4 by using the above system, comprising the following steps:

[0020] S1: catalytic C4 and methanol enter the etherification reactor to etherify isobutene in the catalytic C4 to generate MTBE;

[0021] S2: the product at the bottom of the etherification reactor enters the catalytic distillation column for further reaction to etherify isobutene in the catalytic C4 to generate MTBE, which is collected from the bottom outlet of the catalytic distillation column; if the overhead distillate is directly subjected to precision rectification to prepare 1-butene, isobutene will be enriched in 1-butene, and if the butene content in the original feed is 10%, isobutene will be enriched in 1-butene by 10 times, from 0.2% to 2%, and thus the 1-butene product cannot be a first-grade product, therefore, the distillate enters the deep etherification reactor from the top outlet, so that isobutene in the catalytic C4 is further etherified to generate MTBE;

[0022] S3: the reaction product of the deep etherification reactor enters the light-removing column from the bottom outlet, light components are collected from the top outlet, heavy components enter the heavy-removing column from the bottom outlet, heavy components are collected from the bottom outlet of the heavy-removing column, and 1-butene product is collected from the top outlet.

[0023] Preferably, the following methanol recovery step is further included to reduce the amount of methanol in the original feed: S4: the light components collected from the top of the light-removing column enter the methanol extraction column, isobutane is collected from the top outlet, the extracted methanol enters the methanol recovery column from the bottom outlet, methanol is collected from the top outlet, and the remaining material is refluxed to the methanol extraction column from the bottom outlet.

[0024] The light-removing column is operated under pressure (usually at an operating pressure of about 0.5 MPa), the top temperature of the light-removing column is increased to provide heat to the bottom of the heavy-removing column, and the steam heat supply of the heavy-removing column is reduced, thereby reducing energy consumption and the amount of circulating water.

[0025] Preferably, the reaction temperature of the etherification reactor is 40-80℃, the space velocity is 1.0-5h -1 , the reaction pressure is 0.6-1.2MPa; the overhead pressure of the catalytic distillation column is 0.45-0.7MPa, the overhead 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℃, the space velocity is 1.0-3h -1 , the reaction pressure is 0.4-1.0MPa; the overhead pressure of the light-removing column is 1.0-1.5MPa, the overhead temperature is 90-120℃, and the reflux ratio is 15-40; the overhead pressure of the heavy-removing column is 0.45-0.7MPa, the overhead temperature is 50-60℃, and the reflux ratio is 15-40; the overhead pressure of the methanol extraction column is 0.4-0.8MPa, the overhead temperature is 40-60℃, and the methanol concentration at the bottom is 7-10%; the overhead pressure of the methanol recovery column is 0.1-0.3MPa, the overhead temperature is 70-120℃, and the reflux ratio is 5-10.

[0026] Preferably, in step S1, the mass percentage of isobutylene in the catalytic C4 is 8%-25%.

[0027] Preferably, in step S1, the molar ratio of isobutylene to methanol in the catalytic C4 is 1:1.15-1.3.

[0028] The present application continues to perform deep etherification on the catalytic C4 after etherification-catalytic distillation, because the boiling points of isobutylene and 1-butylene are similar, and when the concentration of 1-butylene in the C4 raw material is high, a sufficient amount of 1-butylene product can still be obtained by properly losing a little 1-butylene due to the presence of isobutylene; but when the content of 1-butylene in the catalytic C4 raw material is low, the quality of the 1-butylene product cannot be reached at the expense of 1-butylene, so the amount of isobutylene in the catalytic C4 must be reduced to a suitable degree for 1-butylene purification.

[0029] Compared with the prior art, the present application has the following beneficial effects:

[0030] This invention uses catalytic C4 as a raw material, and together with methanol, undergoes an etherification-catalytic distillation-deep etherification-precision distillation process to obtain high-purity 1-butene. The difference between this invention and existing technologies lies in the use of catalytic C4, the most widely available raw material in the market. This broadens the source of 1-butene beyond ethylene cracking C4 and coal chemical MTO / MTP C4, expanding the application scope of the technology. This provides a solution for factories or regions lacking ethylene cracking or coal chemical MTO / MTP units but requiring 1-butene products, while also improving the utilization rate of catalytic C4, thereby enhancing enterprise efficiency. Currently, the number of ethylene plants in China is limited and their distribution is uneven. The method of using catalytic C4 as a raw material to produce 1-butene has good application prospects. The production of 1-butene using catalytic C4 needs to meet the following indicators: isobutene residue ≤0.04%, 1-butene yield ≥80%. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of the present invention.

[0032] In the diagram, 1 is the etherification reactor; 2 is the catalytic distillation column; 3 is the deep etherification reactor; 4 is the light component removal column; 5 is the heavy component removal column; 6 is the methanol extraction column; and 7 is the methanol recovery column. Detailed Implementation

[0033] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this invention.

[0034] like Figure 1 As shown, the system used in the following examples for preparing 1-butene includes an etherification reactor 1, a catalytic distillation column 2, a deep etherification reactor 3, a light-weight removal column 4, and a heavy-weight removal column 5 connected in sequence.

[0035] Furthermore, the etherification reactor 1 and the catalytic distillation column 2 are filled with solid catalysts, which are resin catalysts, heteropolyacid catalysts or molecular sieve catalysts.

[0036] Furthermore, the solid catalyst is a sulfonic acid-type cation exchange resin catalyst.

[0037] Furthermore, the deep etherification reactor 3 contains a resin catalyst with an exchange equivalent greater than 5.4 mmol H+ / g.

[0038] Furthermore, the top outlet of the light-weight 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.

[0039] The method for preparing 1-butene from catalytic C4 by the system comprises the following steps:

[0040] S1: catalytic C4 and methanol enter the etherification reactor 1 together, so that the isobutene in the catalytic C4 is etherified to generate MTBE, the conversion rate of the outlet isobutene is about 94%, and the isobutene content is about 1%;

[0041] S2: the product at the bottom of the etherification reactor 1 enters the catalytic distillation column 2 to continue the reaction, so that the isobutene in the catalytic C4 is further etherified to generate MTBE, the isobutene content in the outlet ether after the column top is about 0.2%, and the total conversion rate of the isobutene is about 98.5%; the MTBE is collected from the bottom outlet of the catalytic distillation column 2, the distillate enters the deep etherification reactor 3 from the column top outlet, so that the isobutene in the catalytic C4 is continuously etherified to generate MTBE, and the total conversion rate of the isobutene can be stably increased to more than 99.5% after deep etherification;

[0042] S3: the reaction product of the deep etherification reactor 3 enters the light-removing column 4 from the bottom outlet, the light component is collected from the column top outlet, the heavy component enters the heavy-removing column 5 from the bottom outlet, the heavy component is collected from the bottom outlet of the heavy-removing column 5, and the 1-butene product is collected from the column top outlet.

[0043] Further, the following step is further included: S4: the light component collected from the column top of the light-removing column 4 enters the methanol extraction column 6, the isobutane is collected from the column top outlet, the extracted methanol enters the methanol recovery column 7 from the bottom outlet, the methanol is collected from the column top outlet, and the remaining material is refluxed to the methanol extraction column 6 from the bottom outlet.

[0044] Further, the reaction temperature of the etherification reactor 1 is 40-80 ℃, the space velocity is 1.0-5 h -1 , the reaction pressure is 0.6-1.2 MPa; the column top pressure of the catalytic distillation column 2 is 0.45-0.7 MPa, the column top temperature is 50-70 ℃, the reaction section temperature is 60-80 ℃, the column 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 1.0-3 h -1 , the reaction pressure is 0.4-1.0 MPa; the column top pressure of the light-removing column 4 is 1.0-1.5 MPa, the column top temperature is 90-120 ℃, and the reflux ratio is 15-40; the column top pressure of the heavy-removing column 5 is 0.45-0.7 MPa, the column top temperature is 50-60 ℃, and the reflux ratio is 15-40; the column top pressure of the methanol extraction column 6 is 0.4-0.8 MPa, the column top temperature is 40-60 ℃, and the methanol concentration at the column bottom is 7-10%; the column top pressure of the methanol recovery column 7 is 0.1-0.3 MPa, the column top temperature is 70-120 ℃, and the reflux ratio is 5-10.

[0045] Further, in step S1, the mass percentage of isobutene in the catalytic C4 is 8%-25%.

[0046] Further, in step S1, the molar ratio of isobutene to methanol in the catalytic C4 is 1:1.15-1.3.

[0047] Example 1

[0048] In the raw materials used in this example, the mass percentage of isobutene in the catalytic C4 is 8%, and the molar ratio of isobutene to methanol is 1:1.15.

[0049] The operating conditions of the etherification reactor 1 are: the reaction temperature is 40℃, the space velocity is 1.0h -1 , and the reaction pressure is 0.6MPa, so that the reactants and products are in liquid phase, and the conversion rate of isobutene can reach more than 95%.

[0050] The operating conditions of the catalytic distillation column 2 are: the column top pressure is 0.45MPa, the column top temperature is 50℃, the reaction section temperature is 60℃, the column bottom temperature is 130℃, and the reflux ratio is 0.5. Isobutene continues to react in the reaction section, and the chemical equilibrium is broken through catalytic distillation, so that the reaction continues to proceed deeply, and the isobutene content at the top of the catalytic distillation column 2 is controlled to 0.2%.

[0051] The operating conditions of the deep etherification reactor 3 are: the reaction temperature is 40℃, the space velocity is 1.0h -1 , and the reaction pressure is 0.4MPa, so that the reactants and products are in liquid phase, and the mass percentage of isobutene at the outlet is 0.03%.

[0052] The operating conditions of the light-removing column 4 are: the column top pressure is 1.0MPa, the column top temperature is 90℃, and the reflux ratio is 15.

[0053] The operating conditions of the heavy-removing column 5 are: the column top pressure is 0.45MPa, the column top temperature is 50℃, and the reflux ratio is 15.

[0054] The operating conditions of the methanol extraction column 6 are: the column top pressure is 0.4MPa, the column top temperature is 40℃, and the methanol concentration at the column bottom is controlled to 7%.

[0055] The operating conditions of the methanol recovery column 7 are: the column top pressure is 0.1MPa, the column top temperature is 70℃, and the reflux ratio is 5.

[0056] The 1-butene product obtained in this example meets the superior product index, in which the purity of 1-butene is 99.36%.

[0057] Example 2

[0058] In this embodiment, the mass percentage of isobutylene in the C4 catalyst is 25%, and the molar ratio of isobutylene to methanol is 1:1.3.

[0059] The operating conditions for etherification reactor 1 are: reaction temperature 80℃, space velocity 5h. -1 The reaction pressure is 1.2 MPa, which makes both the reactants and products liquid, and the conversion rate of isobutylene can reach more than 95%.

[0060] The operating conditions for catalytic distillation column 2 are as follows: top pressure 0.7 MPa, top temperature 70℃, reaction section temperature 80℃, bottom temperature 160℃, and reflux ratio 3. Isobutylene continues to react in the reaction section. The chemical equilibrium is broken by catalytic distillation, allowing the reaction to proceed further. The isobutylene content at the top of catalytic distillation column 2 is controlled to 0.4%.

[0061] The operating conditions for deep etherification reactor 3 are: reaction temperature 70℃, space velocity 3h. -1 The reaction pressure was 1.0 MPa, which resulted in both reactants and products being in the liquid phase, and the mass percentage of isobutylene at the outlet was 0.02%.

[0062] The operating conditions for the light-weight removal tower 4 are: top pressure of 1.5 MPa, top temperature of 120℃, and reflux ratio of 40.

[0063] The operating conditions for the deweight removal tower 5 are: top pressure of 0.7 MPa, top temperature of 60℃, and reflux ratio of 40.

[0064] The operating conditions for methanol extraction column 6 are as follows: top pressure of 0.8 MPa, top temperature of 60℃, and methanol concentration at bottom of column controlled at 10%.

[0065] The operating conditions for methanol recovery tower 7 are: top pressure of 0.3 MPa, top temperature of 120℃, and reflux ratio of 10.

[0066] The 1-butene product obtained in this embodiment meets the superior grade index, wherein the purity of 1-butene is 99.41%.

[0067] Example 3

[0068] In this embodiment, the mass percentage of isobutylene in the raw material catalytic C4 is 15%, and the molar ratio of isobutylene to methanol is 1:1.2.

[0069] The operating conditions for etherification reactor 1 are: reaction temperature 60℃, space velocity 2h. -1 The reaction pressure is 0.8 MPa, which makes both the reactants and products liquid, and the conversion rate of isobutylene can reach more than 95%.

[0070] The operating conditions of the catalytic distillation column 2 are: the column top pressure is 0.6 MPa, the column top temperature is 60℃, the reaction section temperature is 70℃, the column bottom temperature is 140℃, and the reflux ratio is 1. The isobutylene continues to react in the reaction section, and the chemical equilibrium is broken by catalytic distillation, so that the reaction continues to proceed deeply, and the isobutylene content at the top of the catalytic distillation column 2 is controlled to 0.4%.

[0071] The operating conditions of the deep etherification reactor 3 are: the reaction temperature is 50℃, the space velocity is 2h -1 -1, and the reaction pressure is 0.8 MPa, so that the reactants and products are in liquid phase, and the mass percentage of isobutylene at the outlet is 0.02%.

[0072] The operating conditions of the light removal column 4 are: the column top pressure is 1.2 MPa, the column top temperature is 100℃, and the reflux ratio is 20.

[0073] The operating conditions of the heavy removal column 5 are: the column top pressure is 0.5 MPa, the column top temperature is 55℃, and the reflux ratio is 25.

[0074] The operating conditions of the methanol extraction column 6 are: the column top pressure is 0.5 MPa, the column top temperature is 50℃, and the methanol concentration at the column bottom is controlled to 8%.

[0075] The operating conditions of the methanol recovery column 7 are: the column top pressure is 0.2 MPa, the column top temperature is 100℃, and the reflux ratio is 8.

[0076] The 1-butene product obtained in this example meets the premium product index, in which the purity of 1-butene is 99.45%.

[0077] Comparative Example 1

[0078] The difference from Example 3 is that the catalytic distillation column top distillate directly enters the light removal column to start precision rectification. The purity of 1-butene in the final obtained 1-butene product is 97.6%.

[0079] From the examples and Comparative Example 1, it can be seen that when catalytic carbon four is used to produce 1-butene, if it is subjected to etherification and catalytic rectification together with methanol and then directly subjected to precision rectification without deep etherification, the purity of 1-butene in the produced 1-butene product will be reduced, and it cannot reach a level of more than 99%.

Claims

1. A system for producing 1-butene from catalytic C4s, characterized in that, The application relates to a methanol etherification device, which comprises an etherification reactor (1), a catalytic distillation column (2), a deep etherification reactor (3), a light component removal column (4) and a heavy component removal column (5) connected in sequence; the catalytic distillation column (2) is composed of a column kettle, a stripping section, one or more reaction bed layers, a rectification section and a column top reflux condenser; catalytic distillation baskets are uniformly distributed in the reaction bed layers, and the catalytic distillation baskets are filled with solid catalysts which are the same as those in the etherification reactor (1); the deep etherification reactor (3) is filled with a resin catalyst with an exchange equivalent greater than 5.4mmolH + / g resin catalyst; the top outlet of the light component removal column (4) is connected with the inlet of a methanol extraction column (6), the bottom outlet of the methanol extraction column (6) is connected with the inlet of a methanol recovery column (7), the bottom outlet of the methanol recovery column (7) is connected with the reflux inlet of the methanol extraction column (6); the reaction product of the deep etherification reactor (3) enters the light component removal column (4) through the bottom outlet, the light component is taken out through the top outlet, and the heavy component enters the heavy component removal column (5) through the bottom outlet.

2. The system for producing 1-butene using catalytic C4 according to claim 1, wherein, The etherification reactor (1) and the catalytic distillation column (2) are filled with solid catalysts, which are resin catalysts, heteropoly acid catalysts or molecular sieve catalysts.

3. The system for preparing 1-butene using catalytic C4 as described in claim 2, characterized in that, The solid catalysts are sulfonic acid type cation exchange resin catalysts.

4. Process for the production of 1-butene from catalytic C4's by means of a system according to any one of claims 1-3, characterized in that, The method comprises the following steps: S1: catalytic C4 and methanol enter the etherification reactor (1) to etherify isobutylene in the catalytic C4 to generate MTBE; S2: the product at the bottom of the etherification reactor (1) enters the catalytic distillation column (2) to continue the reaction, further etherify isobutylene in the catalytic C4 to generate MTBE, the MTBE is taken out from the bottom outlet of the catalytic distillation column (2), and the distillate enters the deep etherification reactor (3) from the top outlet to continue etherification of isobutylene in the catalytic C4 to generate MTBE; S3: the reaction product of the deep etherification reactor (3) enters the light component removal column (4) from the bottom outlet, the light component is taken out from the top outlet, the heavy component enters the heavy component removal column (5) from the bottom outlet, the heavy component is taken out from the bottom outlet of the heavy component removal column (5), and the 1-butene product is taken out from the top outlet; S4: the light component taken out from the top of the light component removal column (4) enters the methanol extraction column (6), isobutane is taken out from the top outlet, the extracted methanol enters the methanol recovery column (7) from the bottom outlet, the methanol is taken out from the top outlet, and the remaining material is refluxed to the methanol extraction column (6) from the bottom outlet.

5. The method of claim 4, wherein, The reaction temperature of the etherification reactor (1) is 40-80℃, the space velocity is 1.0-5h -1 , the reaction pressure is 0.6-1.2MPa; the overhead pressure of the catalytic distillation column (2) is 0.45-0.7MPa, the overhead 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 overhead pressure of the light-removing column (4) is 1.0-1.5MPa, the overhead temperature is 90-120℃, and the reflux ratio is 15-40; the overhead pressure of the heavy-removing column (5) is 0.45-0.7MPa, the overhead temperature is 50-60℃, and the reflux ratio is 15-40; the overhead pressure of the methanol extraction column (6) is 0.4-0.8MPa, the overhead temperature is 40-60℃, and the methanol concentration at the bottom is 7-10%. The top pressure of the methanol recovery column (7) is 0.1-0.3 MPa, the top temperature is 70-120 DEG C, and the reflux ratio is 5-10.

6. The method of claim 4, wherein, In step S1, the mass percentage of isobutylene in the catalytic C4 is 8%-25%.

7. The method of claim 4, wherein, In step S1, the molar ratio of isobutylene in the catalytic C4 to methanol is 1:1.15-1.3.

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