Method for separating 1-butene in mixed C4

Abstract

The invention provides a method for separating 1-butene in mixed C4, which is characterized in that a dividing wall column in an upper dividing wall form is used for separation, the area ratio of a feeding side to a product extraction side is (1: 9)-(9: 1), a mixed C4 fraction enters the dividing wall column from the middle of the feeding side, the number of theoretical plates of the dividing wall column is 40-200, the operating pressure is 0.1-2Mpa, the tower top temperature is 20-120 DEG C, the tower bottom temperature is 30-200 DEG C, and the 1-butene in the mixed C4 fraction is separated from the dividing wall column. C4 light components are extracted from the tower top of the feeding side, 1-butene-rich components are extracted from the tower top of the product extraction side, part of the 1-butene-rich components are condensed and refluxed, part of the 1-butene-rich components is discharged out of the device, part of the 1-butene-rich components is refluxed to the product extraction side through the tower top, a tower kettle product is heavy C4 components, part of the heavy C4 components is discharged out of the device, and part of the heavy C4 components is refluxed to the dividing wall tower from the tower kettle through the reboiler. The method is short in process flow and high in efficiency, and the obtained 1-butene is high in purity.

Description

Technical Field

[0001] The present invention belongs to the technical field of 1-butene separation, and particularly relates to a method for separating 1-butene from mixed C4. Background Art

[0002] With the development of China's chemical industry, the demand for high-purity 1-butene is increasing day by day. Currently, it is mainly used as a polymerization monomer for linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and poly-1-butene, and can also produce C8 and C12 α-olefins, which are excellent raw materials for preparing surfactants. It also has a wide range of uses in the fields of petrochemical industry, fine chemical industry, medicine, pesticides, etc.

[0003] High-purity 1-butene can be prepared by the ethylene dimerization method. However, since the ethylene dimerization method uses relatively valuable ethylene as a raw material, the cost is relatively high, and generally it is uneconomical. Currently, the mainly adopted method at home and abroad is the ultra-precision rectification method. Its process uses mixed C4 as a raw material. First, butadiene is extracted, then isobutene is removed through an MTBE unit, and after removing a small amount of butadiene and alkynes by hydrogenation, polymerization-grade 1-butene is obtained through the ultra-precision rectification separation method. Since the boiling points of 1-butene, cis-2-butene, and trans-2-butene contained in mixed C4 are not very different, the energy consumption of using the traditional rectification method is relatively high. Therefore, researchers have been committed to seeking an efficient, energy-saving, and low-cost method to replace the existing separation method.

[0004] CN101605873B uses mixed C4 with an isobutene content of less than 10% in the feed, mainly including 1-butene, 2-butene, n-butane, isobutane, etc., and adopts a dividing wall column to recover 1-butene. The essence of the present invention is the concept of two traditional rectification towers, and the thermodynamic equilibrium of the dividing wall column is not truly achieved. It is just a mechanical combination of two traditional towers into one tower. The energy-saving effect of the actual dividing wall column cannot be achieved.

[0005] CN208482029U proposes a device for separating 1-butene from mixed C4 using a dividing wall column. The dividing wall column is realized by an intermediate dividing wall method, including a top common rectification section, a pre-fractionation section, a main tower section, and a bottom common stripping section. 1-Butene is withdrawn from the side line of the main tower. This patent has a shorter separation process for 1-butene, lower energy consumption, less investment, and saves floor space compared with the traditional process. However, in this patent, 1-butene is withdrawn from the side line of the main tower, and the extraction concentration is greatly affected by the top of the tower, and an ultra-high-purity 1-butene product cannot be obtained. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for separating 1-butene from mixed C4, which has a short process flow, high efficiency, and high purity of the obtained 1-butene.

[0007] To achieve the above object, the present invention provides a method for separating 1-butene from mixed C4, which uses a dividing wall column in the form of an upper dividing wall for separation. The area ratio of the feed side to the product withdrawal side is 1:9 to 9:1. The mixed C4 fraction enters the dividing wall column in the middle of the feed side. The number of theoretical plates of the dividing wall column is 40 - 200, the operating pressure is 0.1 - 2 Mpa, the top temperature of the column is 20 - 120 °C, and the bottom temperature of the column is 30 - 200 °C. C4 light components are withdrawn from the top of the feed side of the column, and the 1-butene-rich component is withdrawn from the top of the product withdrawal side of the column. After condensation and reflux, part of the 1-butene-rich component is discharged from the device, and part is refluxed to the product withdrawal side from the top of the column. The bottom product is the heavy C4 component. Part of the heavy C4 component is discharged from the device, and part is refluxed from the bottom of the column to the dividing wall column through a reboiler.

[0008] In the method for separating 1-butene from mixed C4 according to the present invention, the non-condensable gas is discharged after the C4 light components withdrawn from the top of the feed side of the column are condensed and refluxed. The liquid phase component after condensation is the isobutane-rich component. Part of it is discharged from the device, and part is refluxed to the feed side from the top of the column.

[0009] In the method for separating 1-butene from mixed C4 according to the present invention, when the alcohol content in the mixed C4 fraction is greater than 3 wt%, water is also introduced into the feed side. The alcohol-water component is withdrawn from the bottom of the feed side of the column. Part of the alcohol-water component is discharged from the device, and part is refluxed from the bottom of the column to the dividing wall column through a reboiler. The heavy C4 component is withdrawn from the bottom of the product withdrawal side of the column.

[0010] In the method for separating 1-butene from mixed C4 according to the present invention, the mixed C4 fraction contains 1-butene, isobutane, n-butane, 2-butene, and alcohol.

[0011] In the method for separating 1-butene from mixed C4 according to the present invention, the area ratio of the feed side to the product withdrawal side is 3:7 to 7:3.

[0012] In the method for separating 1-butene from mixed C4 according to the present invention, the reflux ratio of the 1-butene-rich component is 1 - 40.

[0013] In the method for separating 1-butene from mixed C4 according to the present invention, the reflux ratio of the isobutane-rich component is 1 - 40.

[0014] In the method for separating 1-butene from mixed C4 according to the present invention, the addition amount of water is 2 wt% - 50 wt% of the mass of the mixed C4 fraction.

[0015] In the method for separating 1-butene from mixed C4 according to the present invention, the reflux ratio of the alcohol-water component is 1 - 40.

[0016] Advantages of the present invention:

[0017] This patent uses a dividing wall column to separate 1-butene from mixed C4, and the dividing wall column is implemented by means of a top dividing wall. 1-Butene is withdrawn from the rectifying section on the right side of the main column, and the isobutane product is withdrawn from the pre-fractionating section on the left side of the main column. While ensuring a short separation process, low energy consumption, less investment, and saving floor area, it also ensures high purity of the main product and by-products. Compared with the dividing wall column with the dividing wall in the middle, the top dividing wall divides the rectifying section at the top of the column, reducing the cross-mixing of materials on both sides, ensuring that the overhead product stream is less affected by feed fluctuations, and at the same time defining the reaction conditions in each reaction zone, making the 1-butene product have high purity and stable operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the process flow diagram of a method for separating 1-butene from mixed C4 according to the present invention;

[0019] Figure 2 is the process flow diagram of another method for separating 1-butene from mixed C4 according to the present invention.

[0020] Among them, the reference numerals:

[0021] 1 Mixed C4 fraction; 2 Rich isobutane component out of the unit; 3 Heavy C4 component; 4 Rich 1-butene component out of the unit; 5 Heavy C4 component out of the unit; 6 Dividing wall column; 7 C4 light component; 8 Condenser; 9 Condensed C4 light component; 10 Reflux drum; 11 Non-condensable gas; 12 Reflux pump; 13 Refluxed rich isobutane component; 14 Rich 1-butene component; 15 Condenser; 16 Reflux drum; 17 Refluxed rich 1-butene component; 18 Reboiler; 19 Water; 20 Alcohol-water component; 21 Reboiler; 22 Alcohol-water component out of the unit. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will be specifically described below through examples. It is necessary to point out here that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention according to the above content of the present invention.

[0023] Figure 1 is the process flow diagram of a method for separating 1-butene from mixed C4 according to the present invention. The mixed C4 fraction 1 from outside the battery limit enters from the middle of one side ( Figure 1 for the left side, and can also be the right side as needed) of the dividing wall column 6, and the feed side of the dividing wall column 6 ( Figure 1On the left side of the middle), the C4 light components 7 drawn from the top of the tower enter the reflux drum 10 after being condensed by the condenser 8, and the non-condensable gas 11 is discharged. The liquid phase is the isobutane-rich component. Part of the isobutane-rich component is discharged from the device through the reflux pump 12, and part is refluxed. The isobutane-rich component discharged from the device is used for other purposes, and the refluxed isobutane-rich component flows back from the top of the tower on the feed side to the dividing wall column 6; the heavy C4 fraction 3 (mainly n-butane and 2-butene) is drawn from the bottom of the tower, part of it is pumped out of the device through the pump, and the heavy C4 component 5 discharged from the device is used for other purposes, and part of it returns to the dividing wall column from the bottom of the tower through the reboiler 18; the gas phase at the top of the tower on the product extraction side is the 1-butene-rich component 14, which is partially discharged from the device after passing through the condenser 15 and the reflux drum 16 and then through the pump. The 1-butene-rich component discharged from the device is taken out as a product, and part of it is refluxed as the 1-butene-rich component 17 and flows back from the top of the tower to the dividing wall column 6.

[0024] Figure 2 This is the process flow diagram of another method for separating 1-butene from mixed C4 described in the present invention. The mixed C4 fraction 1 from outside the battery limit enters the dividing wall column 6 from the middle of one side ( Figure 2 On the left side, it can also be the right side according to needs) of the dividing wall column 6. The water 19 from outside the battery limit enters the dividing wall column 6 on the same side as the mixed C4 fraction 1. The bottom fraction of the feed side of the dividing wall column 6 is the alcohol-water component 20, and part of it is discharged from the device. The alcohol-water component 22 discharged from the device is used for other purposes, and part of it returns to the dividing wall column from the bottom of the tower through the reboiler 21; the gas phase at the top of the feed side of the dividing wall column 6 is the C4 light component 7, which is discharged from the device for other purposes; the gas phase at the top of the product extraction side is the 1-butene-rich component 14, which is partially discharged from the device after passing through the condenser 15 and the reflux drum 16 and then through the pump. The 1-butene-rich component 4 discharged from the device is taken out as a product, and part of it is refluxed as the 1-butene-rich component 17 and flows back from the top of the tower to the dividing wall column; the bottom fraction of the product extraction side of the dividing wall column is the heavy C4 component 3 (mainly n-butane and 2-butene), part of it is pumped out of the device through the pump, and the heavy C4 component 5 discharged from the device is used for other purposes, and part of it returns to the dividing wall column from the bottom of the tower through the reboiler 18.

[0025] Table 1 Composition of mixed C4 fraction (low alcohol content)

[0026]

[0027] Table 2 Composition of mixed C4 fraction (high alcohol content)

[0028]

[0029]

[0030] Example 1

[0031] The feed pressure of the mixed C4 fraction is 1 Mpa, the feed temperature is 60 °C, and the feed composition refers to Table 1. Using Figure 1The process flow shown. The number of trays in the dividing wall column is 40. Operating conditions of the dividing wall column: the top pressure on the left side is 0.60 Mpa, the temperature is 40.2 °C, the top pressure on the right side is 0.55 MPa, the temperature is 46.1 °C, the bottom temperature is 56.5 °C, and the area ratio of the feed side to the product withdrawal side of the dividing wall column is 4:6. The reflux ratio of the 1-butene-rich component is 5, and the reflux ratio of the isobutane-rich component is 10. In this example, the mass fraction of 1-butene in the product is over 99%, the alcohol and water content is less than 20 μg / g; the mass fraction of 1-butene in the isobutane product is below 10%; the mass fraction of 1-butene in the n-butane and 2-butene products is below 5%.

[0032] Example 2

[0033] The feed pressure of the mixed C4 fraction is 1 Mpa, the feed temperature is 60 °C, and the feed composition refers to Table 2. The Figure 2 process flow shown is adopted; the feed pressure of water is 1 MPa, the feed temperature is 45 °C, and the feed amount is 5 wt% of the mixed C4 fraction; the number of trays in the dividing wall column is 80. Operating conditions of the dividing wall column: the top pressure on the left side is 0.98 Mpa, the temperature is 62.2 °C, the top pressure on the right side is 0.95 MPa, the temperature is 65.2 °C, the bottom temperature on the left side is the same as that on the right side and is 90.6 °C, and the area ratio of the feed side to the product withdrawal side of the dividing wall column is 2:8. The reflux ratio of the 1-butene-rich component is 15, the reflux ratio of the isobutane-rich component is 25, and the reflux ratio of the alcohol and water component is 5. In this example, the mass fraction of 1-butene in the product is over 99%, the alcohol and water content is less than 30 μg / g; the mass fraction of 1-butene in the isobutane product is below 10%; the mass fraction of 1-butene in the n-butane and 2-butene products is below 5%.

[0034] Example 3

[0035] The feed pressure of the mixed C4 fraction is 1 Mpa, the feed temperature is 60 °C, and the feed composition refers to Table 1. The Figure 1 process flow shown is adopted; the number of trays in the dividing wall column is 150. Operating conditions of the dividing wall column: the top pressure on the left side is 1.55 Mpa, the temperature is 95.2 °C, the top pressure on the right side is 1.50 MPa, the temperature is 99.7 °C, the bottom temperature is 129.8 °C, and the area ratio of the feed side to the product withdrawal side of the dividing wall column is 5:5. The reflux ratio of the 1-butene-rich component is 25, and the reflux ratio of the isobutane-rich component is 40. In this example, the mass fraction of 1-butene in the product is over 99%, the alcohol and water content is less than 20 μg / g; the mass fraction of 1-butene in the isobutane product is below 10%; the mass fraction of 1-butene in the n-butane and 2-butene products is below 5%.

[0036] Example 4

[0037] The feed pressure of the mixed C4 fraction is 1 Mpa; the feed temperature is 60 °C, and the feed composition refers to Table 1. The Figure 1The process flow shown; the number of trays in the dividing wall column is 200, and the operating conditions of the dividing wall column are as follows: the top pressure on the left side is 1.93 Mpa, the temperature is 115.0 °C, the top pressure on the right side is 1.89 MPa, the temperature is 119.1 °C, the bottom temperature is 155.5 °C, and the area ratio of the feed side and the product withdrawal side of the dividing wall column is 8:2. The reflux ratio of the rich 1-butene component is 40, and the reflux ratio of the rich isobutane component is 5. In this example, the mass fraction of 1-butene in the product is over 99%, and the alcohol and water content is less than 20 μg / g; the mass fraction of 1-butene in the isobutane product is below 10%; the mass fraction of 1-butene in the n-butane and 2-butene products is below 5%.

[0038] Example 5

[0039] The feed pressure of the mixed C4 fraction is 1 Mpa, the feed temperature is 60 °C, and the feed composition refers to Table 2. The Figure 2 process flow shown is adopted. The feed pressure of water is 1 MPa, the feed temperature is 45 °C, and the feed amount is 50 wt% of the mixed C4 fraction; the number of trays in the dividing wall column is 200, and the operating conditions of the dividing wall column are as follows: the top pressure on the left side is 0.60 Mpa, the temperature is 43.1 °C, the top pressure on the right side is 0.58 MPa, the temperature is 49.2 °C, the bottom temperature on the left side is the same as that on the right side, both are 60.1 °C, and the area ratio of the feed side and the product withdrawal side of the dividing wall column is 5:5. The reflux ratio of the rich 1-butene component is 20, the reflux ratio of the rich isobutane component is 20, and the reflux ratio of the alcohol and water component is 35. In this example, the mass fraction of 1-butene in the product is over 99%, and the alcohol and water content is less than 30 μg / g; the mass fraction of 1-butene in the isobutane product is below 10%; the mass fraction of 1-butene in the n-butane and 2-butene products is below 5%.

[0040] Example 6

[0041] The feed pressure of the mixed C4 fraction is 1 Mpa, the feed temperature is 60 °C, and the feed composition refers to Table 2. The Figure 2 process flow shown is adopted; the feed pressure of water is 1 MPa, the feed temperature is 45 °C, and the feed amount is 25 wt% of the mixed C4 fraction; the number of trays in the dividing wall column is 100, and the operating conditions of the dividing wall column are as follows: the top pressure on the left side is 0.80 Mpa, the temperature is 49.1 °C, the top pressure on the right side is 0.77 MPa, the temperature is 52.2 °C, the bottom temperature on the left side is the same as that on the right side, both are 60.1 °C, and the area ratio of the feed side and the product withdrawal side of the dividing wall column is 7:3. The reflux ratio of the rich 1-butene component is 15, the reflux ratio of the rich isobutane component is 10, and the reflux ratio of the alcohol and water component is 10. In this example, the mass fraction of 1-butene in the product is over 99%, and the alcohol and water content is less than 30 μg / g; the mass fraction of 1-butene in the isobutane product is below 10%; the mass fraction of 1-butene in the n-butane and 2-butene products is below 5%.

[0042] Comparative Example 1

[0043] The feed pressure of the mixed C4 fraction is 1 Mpa, the feed temperature is 60 °C, and the feed composition refers to Table 2. The same process flow as Figure 2 is adopted. The difference is that the partition plate in the dividing wall column is located in the middle of the column kettle, and neither the top nor the bottom of the partition plate is connected to the column kettle; the water feed pressure is 1 MPa, the feed temperature is 45 °C, and the feed amount is 25 wt% of the mixed C4 fraction; the number of trays in the dividing wall column is 100; the operating conditions of the dividing wall column are: the top pressure is 2.50 Mpa, the temperature is 150.1 °C, the temperature of the column kettle is 210.2 °C, and the area ratio of both sides of the dividing wall column is 7:3. The reflux ratio of the 1-butene-rich component is 15, the reflux ratio of the isobutane-rich component is 10, and the reflux ratio of the alcohol-water component is 10. In this comparative example of the middle dividing wall column, the mass fraction of the 1-butene product is 97% - 99%, and the alcohol-water content is less than 30 μg / g; the mass fraction of 1-butene in the isobutane product is less than 10%; the mass fraction of 1-butene in the n-butane and 2-butene products is less than 7%.

[0044] Of course, the present invention may also have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention, but these corresponding changes and deformations should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for separating 1-butene from mixed C4, characterized in that, a dividing wall column in the form of an upper dividing wall is used for separation, the area ratio of the feed side to the product extraction side is 1:9 to 9:1, the mixed C4 fraction enters the dividing wall column from the middle of the feed side, the number of theoretical plates of the dividing wall column is 40 - 200, the operating pressure is 0.1 - 2 Mpa, the top temperature of the column is 20 - 120 °C, the bottom temperature of the column is 30 - 200 °C, C4 light components are extracted from the top of the feed side of the column, rich 1-butene components are extracted from the top of the product extraction side of the column, after the rich 1-butene components are condensed and refluxed, part of them are discharged from the device and part are refluxed to the product extraction side from the top of the column, the bottom product of the column is heavy C4 components, part of the heavy C4 components are discharged from the device and part are refluxed from the bottom of the column to the dividing wall column through a reboiler.

2. The method for separating 1-butene from mixed C4 according to claim 1, characterized in that, the non-condensable gas is discharged after the C4 light components extracted from the top of the feed side of the column are condensed and refluxed, the liquid phase component after condensation is rich isobutane component, part of it is discharged from the device and part is refluxed to the feed side from the top of the column.

3. The method for separating 1-butene from mixed C4 according to claim 1, characterized in that, when the alcohol content in the mixed C4 fraction is greater than 3 wt%, water is also introduced into the feed side, the alcohol-water component is extracted from the bottom of the feed side of the column, part of the alcohol-water component is discharged from the device and part is refluxed from the bottom of the column to the dividing wall column through a reboiler, and the heavy C4 component is extracted from the bottom of the product extraction side of the column.

4. The method for separating 1-butene from mixed C4 according to claim 1, characterized in that, the mixed C4 fraction contains 1-butene, isobutane, n-butane, 2-butene and alcohol.

5. The method for separating 1-butene from mixed C4 according to claim 1, characterized in that, the area ratio of the feed side to the product extraction side is 3:7 to 7:

3.

6. The method for separating 1-butene from mixed C4 according to claim 1, characterized in that, the reflux ratio of the rich 1-butene component is 1 - 40.

7. The method for separating 1-butene from mixed C4 according to claim 2, characterized in that, the reflux ratio of the rich isobutane component is 1 - 40.

8. The method for separating 1-butene from mixed C4 according to claim 3, characterized in that, the addition amount of water is 2 wt% - 50 wt% of the mass of the mixed C4 fraction.

9. The method for separating 1-butene from mixed C4 according to claim 3, characterized in that, the reflux ratio of the alcohol-water component is 1 - 40.

Images