Method for extracting, rectifying and separating 2-methylstyrene in cracked C9 aromatic hydrocarbon

Abstract

The invention belongs to the technical field of ethylene, and relates to a method for extracting, rectifying and separating 2-methylstyrene in cracked C9 aromatic hydrocarbon. Comprising the following steps: (1) introducing a raw material light cracked C9 aromatic hydrocarbon and an extraction agent into an extractive distillation tower for extractive distillation to obtain a fraction rich in mixed aromatic hydrocarbon at the tower top and a fraction rich in 2-methylstyrene at the tower bottom; the extracting agent is a mixed solution of N, N-dimethylformamide and glycerol; and (2) introducing the fraction rich in the mixed aromatic hydrocarbon obtained at the tower top in the step (1) into a solvent recovery tower, obtaining high-purity 2-methylstyrene at the tower top, and returning an extracting agent obtained at the tower bottom to the extractive distillation tower for recycling. The purity and the yield of the 2-methylstyrene separated by the method disclosed by the invention are relatively high.

Description

Technical Field

[0001] The present invention belongs to the technical field of ethylene, and specifically relates to a method for separating 2-methylstyrene from cracked C9 aromatics by extractive distillation. Background Art

[0002] Cracked C9 aromatics are by-products of ethylene plants, accounting for about 10%-20% of the total ethylene production. The traditional process route for the utilization of cracked C9 aromatics generally pre-treats the raw materials, which are divided into light cracked C9 aromatics and heavy cracked C9 aromatics. The light cracked C9 aromatics are hydrogenated and used as solvent oil. Therefore, the effective components in a large amount of cracked C9 aromatics, such as 2-methylstyrene, etc., cannot be fully utilized. However, 2-methylstyrene is a monomer for organic synthesis and an important intermediate for pharmaceutical R & D and synthesis, and its price is expensive. The mass fraction of 2-methylstyrene in cracked C9 aromatics reaches about 15%. Therefore, extracting 2-methylstyrene from cracked C9 has important economic value.

[0003] C9 aromatics are a multi-component mixture. Since the boiling points of 2-methylstyrene and trimethylbenzene are close, it is difficult to separate them by ordinary distillation methods. Gu Zhenggui et al. proposed a scheme for extracting styrene from cracked C9 aromatics by vacuum extractive distillation. The effects of different extractants were investigated, and it was found that the separation performance of modified dimethyl sulfoxide (adding sodium acetate with a mass fraction of 5%) was the best, which has guiding significance for the selection of extractants in the process of separating 2-methylstyrene by extractive distillation.

[0004] At present, there is still a need in the art to develop new extractants for separating 2-methylstyrene from cracked C9 aromatics by extractive distillation. Summary of the Invention

[0005] The purpose of the present invention is to overcome the technical defect that the existing preparation methods cannot separate high-purity 2-methylstyrene from cracked C9 aromatics, and provide a method for separating 2-methylstyrene from cracked C9 aromatics by extractive distillation. This method uses a mixed solvent of N,N-dimethylformamide (DMF) + glycerol (GLY) as an extractant to obtain high-purity 2-methylstyrene.

[0006] The present invention provides a method for separating 2-methylstyrene from cracked C9 aromatics by extractive distillation, including the following steps:

[0007] (1) Feeding the raw material of light cracked C9 aromatics and the extractant into an extractive distillation column for extractive distillation. A fraction rich in mixed aromatics is obtained at the top of the column, and a fraction rich in 2-methylstyrene is obtained at the bottom of the column; the extractant is a mixed solution of N,N-dimethylformamide and glycerol;

[0008] (2) Feed the fraction rich in 2-methylstyrene obtained at the bottom of step (1) into the solvent recovery column. High-purity 2-methylstyrene is obtained at the top of the column, and the extractant is obtained at the bottom and returned to the extractive distillation column for recycling.

[0009] The present invention uses a mixed solution of N,N-dimethylformamide (DMF) + glycerol (GLY) to continuously separate 2-methylstyrene from cracked C9 aromatics by extractive distillation. The raw material used is light cracked C9 aromatics: First, the light cracked C9 aromatics fraction enters the extractive distillation column, and at the same time, a mixed solution of methylformamide (DMF) + glycerol (GLY) enters the extractive distillation column as the extractant. The separation of 2-methylstyrene is achieved through condition control. Subsequently, the obtained 2-methylstyrene has both a high yield and a high purity. The purity can reach over 90%, and the yield is as high as over 85%.

[0010] Other features and advantages of the present invention will be described in detail in the following specific implementation section. Description of the Drawings

[0011] Figure 1 It is a process flow diagram of a method for separating 2-methylstyrene from cracked C9 aromatics by extractive distillation according to a specific implementation of the present invention.

[0012] Description of the Reference Numerals in the Drawings

[0013] 1 Extractive distillation column; 2 Solvent recovery column;

[0014] a Light cracked C9 aromatics raw material; b Extractant; c 2-Methylstyrene. Specific Implementation

[0015] The following details the specific implementation of the present invention. It should be understood that the specific implementation described herein is only used to illustrate and explain the present invention and is not used to limit the present invention.

[0016] The present invention provides a method for separating 2-methylstyrene from cracked C9 aromatics by extractive distillation, including the following steps:

[0017] (1) Feed the raw material light cracked C9 aromatics and the extractant into the extractive distillation column for extractive distillation. A fraction rich in mixed aromatics is obtained at the top of the column, and a fraction rich in 2-methylstyrene is obtained at the bottom; the extractant is a mixed solution of N,N-dimethylformamide and glycerol;

[0018] (2) Feed the fraction rich in 2-methylstyrene obtained at the bottom of step (1) into the solvent recovery column. High-purity 2-methylstyrene is obtained at the top of the column, and the extractant is obtained at the bottom and returned to the extractive distillation column for recycling.

[0019] According to the present invention, the light cracked C9 aromatic hydrocarbons are the light cracked C9 aromatic hydrocarbons obtained by removing dicyclopentadiene and heavy components from the cracked C9 aromatic hydrocarbons. The heavy components refer to the components with more than 10 carbon atoms in the cracked C9 aromatic hydrocarbons. The light cracked C9 aromatic hydrocarbons refer to the C6-C9 aromatic hydrocarbons in the cracked C9 aromatic hydrocarbons, including aromatic hydrocarbons with 6, 7, 8, and 9 carbon atoms, usually monocyclic aromatic hydrocarbons, such as benzene and its homologues (toluene, ethylbenzene, methyl ethylbenzene), and unsaturated aromatic hydrocarbons.

[0020] The removal of dicyclopentadiene and heavy components can be carried out by various methods well-known in the art. For example, two towers can be used. The first tower is used to depolymerize dicyclopentadiene into cyclopentadiene and remove cyclopentadiene as a light component. The components after removing the light components are fed into the second tower to remove the heavy components, obtaining the light cracked C9 aromatic hydrocarbons.

[0021] The method of the present invention is applicable to cracked C9 aromatic hydrocarbons with a 2-methylstyrene content of 15 wt% or more.

[0022] According to the present invention, controlling the ratio of the two components of the mixed solution helps to obtain a better separation effect. Preferably, the mass ratio of the N,N-dimethylformamide to the glycerol is 0.05-0.5:1, preferably 0.06-0.12:1.

[0023] According to a preferred embodiment of the present invention, the extractant enters from the rectifying section of the extractive distillation column, and the light cracked C9 aromatic hydrocarbons enter from the middle of the extractive distillation column to achieve better countercurrent contact.

[0024] According to a preferred embodiment of the present invention, the feeding temperature of the extractant is 10-30°C and can be normal temperature feeding.

[0025] The amount of the extractant is based on achieving good extractive distillation. Specifically, the mass flow ratio of the extractant to the raw material is 0.1-1.5, preferably 0.4-0.6.

[0026] According to a preferred embodiment of the present invention, the operating conditions of the extractive distillation column include: the number of theoretical plates is 50-90, the operating pressure is 5-20 kPa, the bottom temperature is 300-330°C, and the reflux ratio is 15-25.

[0027] According to a preferred embodiment of the present invention, the operating conditions of the solvent recovery column include: the number of theoretical plates is 50-80, the operating pressure is atmospheric pressure, the reflux ratio is 5-20, and the bottom temperature is 350-390°C.

[0028] The present invention will be further described below in conjunction with embodiments, but the scope of the present invention is not limited to these embodiments.

[0029] The raw materials used in the following examples are: a light cracked C9 aromatic hydrocarbon fraction obtained by removing dicyclopentadiene and heavy components from cracked C9 containing more than 15% of 2-methylstyrene; the component contents of the light cracked C9 aromatic hydrocarbon fraction are: allylbenzene 5.6%, n-propylbenzene 3.7%, methyl ethylbenzene 28.4%, isopropylbenzene 6.6%, 2-methylstyrene 55.1%, and dicyclopentadiene 0.6%.

[0030] Example 1

[0031] Adopt Figure 1 the process flow method shown to extract and rectify 2-methylstyrene from cracked C9 aromatic hydrocarbons, including the following steps:

[0032] (1) Feed the light cracked C9 aromatic hydrocarbon raw material a and the extractant b into the extractive distillation column 1 for extractive distillation. The extractive distillation column 1 has 80 theoretical plates (counting from top to bottom). The extractant b, which is a DMF+GLY mixed solvent, is fed from the 5th plate, and the light cracked C9 aromatic hydrocarbon raw material a is fed from the 40th plate. The mass ratio of the extractant b to the raw material a is 0.5, and the mass ratio of DMF to GLY is 0.08. The operating conditions of the extractive distillation column 1 include: operating at 15 kPa, with a column bottom temperature of 320 °C and a top reflux ratio of 20. After extractive distillation, a fraction rich in mixed aromatic hydrocarbons is obtained at the top of the extractive distillation column 1, and a fraction rich in 2-methylstyrene is obtained at the bottom;

[0033] (2) Feed the fraction rich in 2-methylstyrene obtained at the bottom in step (1) into the solvent recovery column 2. The operating conditions of the solvent recovery column 2 include: operating at atmospheric pressure, with 60 theoretical plates, a column bottom temperature of 375 °C, and a top reflux ratio of 15. High-purity 2-methylstyrene is obtained at the top of the solvent recovery column 2, and the extractant is obtained at the bottom and returned to the extractive distillation column 1 for recycling.

[0034] Example 2

[0035] Adopt Figure 1 the process flow method shown to extract and rectify 2-methylstyrene from cracked C9 aromatic hydrocarbons, including the following steps:

[0036] (1) Feed the light cracked C9 aromatic hydrocarbon raw material a and the extractant b into the extractive distillation column 1 for extractive distillation. The extractive distillation column 1 has 80 theoretical plates (the plate numbers are counted from top to bottom). Use the DMF+GLY mixed solvent as the extractant b and feed it from the 5th plate, and feed the light cracked C9 aromatic hydrocarbon raw material a from the 40th plate. The mass ratio of the extractant b to the raw material a is 0.5, and the mass ratio of DMF to GLY is 0.15. The operating conditions of the extractive distillation column 1 include: operating at 15 kPa, the bottom temperature is 320 °C, and the top reflux ratio is 20. After extractive distillation, a fraction rich in mixed aromatics is obtained at the top of the extractive distillation column 1, and a fraction rich in 2-methylstyrene is obtained at the bottom;

[0037] (2) Feed the fraction rich in 2-methylstyrene obtained at the bottom in step (1) into the solvent recovery column 2. The operating conditions of the solvent recovery column 2 include: operating at atmospheric pressure, the number of theoretical plates is 60, the bottom temperature is 375 °C, and the top reflux ratio is 15. High-purity 2-methylstyrene is obtained at the top of the solvent recovery column 2, and the extractant is obtained at the bottom and returned to the extractive distillation column 1 for recycling.

[0038] Example 3

[0039] Adopt Figure 1 The shown process flow method for extractive distillation to separate 2-methylstyrene from cracked C9 aromatics includes the following steps:

[0040] (1) Feed the light cracked C9 aromatic hydrocarbon raw material a and the extractant b into the extractive distillation column 1 for extractive distillation. The extractive distillation column 1 has 80 theoretical plates (the plate numbers are counted from top to bottom). Use the DMF+GLY mixed solvent as the extractant b and feed it from the 5th plate, and feed the light cracked C9 aromatic hydrocarbon raw material a from the 40th plate. The mass ratio of the extractant b to the raw material a is 0.4, and the mass ratio of DMF to GLY is 0.18. The operating conditions of the extractive distillation column 1 include: operating at 15 kPa, the bottom temperature is 310 °C, and the top reflux ratio is 20. After extractive distillation, a fraction rich in mixed aromatics is obtained at the top of the extractive distillation column 1, and a fraction rich in 2-methylstyrene is obtained at the bottom;

[0041] (2) Feed the fraction rich in 2-methylstyrene obtained at the bottom in step (1) into the solvent recovery column 2. The operating conditions of the solvent recovery column 2 include: operating at atmospheric pressure, the number of theoretical plates is 60, the bottom temperature is 360 °C, and the top reflux ratio is 15. High-purity 2-methylstyrene is obtained at the top of the solvent recovery column 2, and the extractant is obtained at the bottom and returned to the extractive distillation column 1 for recycling.

[0042] Example 4

[0043] Adopt Figure 1The extraction and rectification process method shown is used to separate 2-methylstyrene from cracked C9 aromatic hydrocarbons, including the following steps:

[0044] (1) Feed the light cracked C9 aromatic hydrocarbon raw material a and the extractant b into the extraction and rectification column 1 for extraction and rectification. The extraction and rectification column 1 has 80 theoretical plates (counting from top to bottom). Using the DMF+GLY mixed solvent as the extractant b, it is fed from the 5th plate, and the light cracked C9 aromatic hydrocarbon raw material a is fed from the 40th plate. The mass ratio of the extractant b to the raw material a is 0.4, and the mass ratio of DMF to GLY is 0.25. The operating conditions of the extraction and rectification column 1 include: operating at 15 kPa, the bottom temperature is 305 °C, and the top reflux ratio is 20. After extraction and rectification, a fraction rich in mixed aromatic hydrocarbons is obtained at the top of the extraction and rectification column 1, and a fraction rich in 2-methylstyrene is obtained at the bottom;

[0045] (2) Feed the fraction rich in 2-methylstyrene obtained at the bottom in step (1) into the solvent recovery column 2. The operating conditions of the solvent recovery column 2 include: operating at atmospheric pressure, the number of theoretical plates is 60, the bottom temperature is 360 °C, and the top reflux ratio is 15. High-purity 2-methylstyrene is obtained at the top of the solvent recovery column 2, and the extractant is obtained at the bottom and returned to the extraction and rectification column 1 for recycling.

[0046] Example 5

[0047] Adopt Figure 1 The extraction and rectification process method shown is used to separate 2-methylstyrene from cracked C9 aromatic hydrocarbons, including the following steps:

[0048] (1) Feed the light cracked C9 aromatic hydrocarbon raw material a and the extractant b into the extraction and rectification column 1 for extraction and rectification. The extraction and rectification column 1 has 80 theoretical plates (counting from top to bottom). Using the DMF+GLY mixed solvent as the extractant b, it is fed from the 5th plate, and the light cracked C9 aromatic hydrocarbon raw material a is fed from the 40th plate. The mass ratio of the extractant b to the raw material a is 0.2, and the mass ratio of DMF to GLY is 0.43. The operating conditions of the extraction and rectification column 1 include: operating at 15 kPa, the bottom temperature is 325 °C, and the top reflux ratio is 20. After extraction and rectification, a fraction rich in mixed aromatic hydrocarbons is obtained at the top of the extraction and rectification column 1, and a fraction rich in 2-methylstyrene is obtained at the bottom;

[0049] (2) Feed the fraction rich in 2-methylstyrene obtained at the bottom in step (1) into the solvent recovery column 2. The operating conditions of the solvent recovery column 2 include: operating at atmospheric pressure, the number of theoretical plates is 60, the bottom temperature is 380 °C, and the top reflux ratio is 15. High-purity 2-methylstyrene is obtained at the top of the solvent recovery column 2, and the extractant is obtained at the bottom and returned to the extraction and rectification column 1 for recycling.

[0050] Comparative Example 1

[0051] The extractive distillation was carried out under the operating conditions of Example 5 to separate 2-methylstyrene from cracked C9 aromatics, except that only DMF solvent was used as the extractant.

[0052] Comparative Example 2

[0053] The extractive distillation was carried out under the operating conditions of Example 5 to separate 2-methylstyrene from cracked C9 aromatics, except that only GLY solvent was used as the extractant.

[0054] Test Example 1

[0055] The yields and purities of 2-methylstyrene obtained in each example and comparative example were tested, and the results are shown in Table 1 below.

[0056] The content of 2-methylstyrene in the raw material was tested in advance.

[0057] The yield was calculated using the following formula:

[0058] Yield of 2-methylstyrene = mass of obtained 2-methylstyrene / content of 2-methylstyrene in the raw material × 100%.

[0059] Table 1

[0060]

[0061] It can be seen from Table 1 that both the purity and yield of 2-methylstyrene separated by the method of the present invention are relatively high.

[0062] The above has described the embodiments of the present invention. The above description is exemplary and not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.

[0063] The endpoints and any values disclosed in this document are not limited to the exact range or value. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this document.

Claims

1. A method for separating 2-methylstyrene from cracked C9 aromatics by extractive distillation, comprising the following steps: (1) Feeding the raw material of light cracked C9 aromatics and the extractant into an extractive distillation column for extractive distillation. A fraction rich in mixed aromatics is obtained at the top of the column, and a fraction rich in 2-methylstyrene is obtained at the bottom of the column; the extractant is a mixed solution of N,N-dimethylformamide and glycerol; (2) Feeding the fraction rich in 2-methylstyrene obtained at the bottom of step (1) into a solvent recovery column. High-purity 2-methylstyrene is obtained at the top of the column, and the extractant is obtained at the bottom of the column and returned to the extractive distillation column for recycling.

2. The method for separating 2-methylstyrene from cracked C9 aromatics by extractive distillation according to claim 1, wherein, The light cracked C9 aromatics are the light cracked C9 aromatics obtained by removing dicyclopentadiene and heavy components from the cracked C9 aromatics.

3. The method for separating 2-methylstyrene and mixed aromatics from light cracked C9 aromatics by extractive distillation according to claim 2, wherein, The heavy components are components having more than 10 carbon atoms.

4. The method for separating 2-methylstyrene and mixed aromatics from light cracked C9 aromatics by extractive distillation according to claim 2, wherein, The light cracked C9 aromatics are C6-C9 aromatics.

5. The method for separating 2-methylstyrene from cracked C9 aromatic hydrocarbons by extractive distillation according to claim 2, wherein, The content of 2-methylstyrene in the cracked C9 aromatics is 15 wt% or more.

6. The method for separating 2-methylstyrene from cracked C9 aromatics by extractive distillation according to claim 1, wherein, The mass ratio of the N,N-dimethylformamide to the glycerol is 0.05-0.5:1, preferably 0.06-0.12:

1.

7. The method for separating 2-methylstyrene from cracked C9 aromatics by extractive distillation according to claim 1, wherein, The extractant enters from the rectifying section of the extractive distillation column, and the feeding temperature of the extractant is 10-30 °C.

8. The method for separating 2-methylstyrene from cracked C9 aromatics by extractive distillation according to claim 1, wherein, The mass flow ratio of the extractant to the raw material is 0.1-1.5, preferably 0.4-0.

6.

9. The method for separating 2-methylstyrene from cracked C9 aromatic hydrocarbons by extractive distillation according to claim 1, wherein, The operating conditions of the extractive distillation column include: the number of theoretical plates is 50-90, the operating pressure is 5-20 kPa, the column bottom temperature is 300-330 °C, and the reflux ratio is 15-25.

10. The method for separating 2-methylstyrene from cracked C9 aromatics by extractive distillation according to claim 1, wherein, The operating conditions of the solvent recovery column include: the number of theoretical plates is 50-80, the operating pressure is atmospheric pressure, the reflux ratio is 5-20, and the column bottom temperature is 350-390 °C.

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