KR20040059172A - A process for separating aromatics by extractive distillation and a composite solvent used therein - Google Patents

Abstract

PURPOSE: A solvent mixture for separating aromatic materials for a hydrocarbon mixture and a method for separating the aromatic materials through extractive distillation by using the solvent mixture are provided, to mitigate the condition of collecting process of solvents and to reduce the energy consumption by using a solvent mixture having a higher solubility and a relatively wide viscosity range and to improve the separation yield. CONSTITUTION: The solvent mixture comprises a main solvent, 3-39 wt% of a solubilizing agent and a modifier, wherein the solubilizing agent is selected from a C8-C11 aromatic material or a mixture of two different kinds of C8-C11 aromatic materials, and the carbon number of the lowest molecular weight aromatic material in the solubilizing agent must be greater than that of the highest molecular weight aromatic material in the separated aromatic materials. The content of a modifier is 0.01-10.0 wt% if the solubilizing agent is a C8-C11 aromatic material, and is 0-10.0 wt% if it is a mixture of two different kind of C8-C11 aromatic materials, and the main solvent and the modifier are independently selected from a sulfolane derivative, an N-formyl morpholine and an N-methyl pyrrolidone, wherein the acidity and basicity of the modifier is opposite to those of the main solvent and the sulfolane derivative is represented by the formula (wherein R1, R2, R3 and R4 are independently H, a C1-C10 alkyl group, a C7-C12 arylalkyl group or a C1-C8 alkoxy group).

Description

A process for separating aromatics by extractive distillation and a composite solvent used therein}

Technical Field

The present invention relates to a mixed solvent for separating aromatics from a hydrocarbon mixture by extractive distillation.

Background

Most of the methods of separating aromatics from hydrocarbon mixtures such as catalytically reformed gasoline or hydrogenated pyrolysis gasoline are liquid-liquid extraction and extractive distillation. Of these, the most commonly used optional solvents in liquid-liquid extraction are glycerol or sulfolane derivatives. While liquid-liquid extraction can yield high purity benzene, toluene and xylene (BTX) products in high yield, conventional liquid-liquid extraction methods process raw materials containing 30-70% by weight of aromatics. It is only appropriate. When processing raw materials containing more than 70% aromatics, raffinate oil must be added, which consumes more energy and reduces the efficiency of the device.

Extractive distillation is a method of separating aromatics from hydrocarbon mixtures, utilizing the advantages of solvents having different effects on the relative volatility of the various components in the hydrocarbon mixture. This method eliminates the need to add raffinate oil to the hydrocarbon mixture even when processing raw materials containing a high content of aromatics. The solvent used is usually pure N-formyl morpholine, N-methyl pyrrolidone or sulfolane and the like. For example, US Pat. No. 5,310,480 discloses a method for separating aromatics by extractive evaporation, which separates aromatics from non-aromatics in the feed using only one column comprising a reboiler and a cyclone. The upper part of this column is used for extractive distillation and the lower part is used to recover the solvent. In order to improve the selectivity and relax the conditions in solvent recovery, 0.1-20% by weight of water is added to an optional solvent such as sulfolane derivatives, glycerol or glycerol ether, while solvent recovery is carried out by steam stripping. The patent discloses that the optional solvent for aromatics can be a mixed solvent in which one component is a low molecular weight polyalkylene glycerol and the other component is glycerol ether and the mutual solubility of the two components is 0.1-99% by weight. The aromatics obtained from this extractive distillation cannot directly act as water containing products due to the water-containing solvent and steam stripping used; Therefore, it is necessary to distill further. Due to the limited solubility in water-containing solvents, two liquid phases are easily formed when extracting and distilling a raw material with a low content of aromatics, thereby affecting normal operation. In addition, the water contained in the system tends to corrode the device.

CN1262264A discloses a method using a combination of an extractive distillation method and a liquid-liquid extraction method in which the raw material is distilled in advance to obtain a first fraction containing benzene and a second fraction containing a small amount of benzene. The first fraction is extracted and distilled to obtain a benzene product, and the second fraction is mixed with the raffinate obtained from the extractive distillation and then liquid-liquid extracted to obtain toluene and a small amount of benzene. This method is suitable for developing and improving existing liquid-liquid extraction devices in the refining field because of low raw material constraints, a wide range of applications, low energy consumption and simultaneous recovery of BTX. In this patent, since neither the solvent nor the system contains water at all, 0.1-15% by weight of a C ₈ -C ₁₀ aromatic substance is used as a solubilizer to increase the solubility of the solvent, and in the selective solvent for separating benzene by extractive distillation By adding this, side effects of water in benzene recovery can be avoided. However, the present invention merely utilizes the situation where o-xylene acts as a solubilizer and is limited to extractive distillation of a parallel process.

In a conventional method using one extractive distillation solvent, the temperature of the recovery column will not be too high due to constraints on the decomposition temperature of the solvent at the time of solvent recovery; Therefore, the degree of vacuum must be increased to thoroughly separate the aromatics in the solvent and the rich solvent; As a result, the operating strength of the recovery column is relatively high. In addition, extractive distillation solvents often contain O, N or S atoms, because certain polarities are required to increase the selective solubility of aromatics; Thus, the distillation solvent has a certain weak acidity or basicity which gives an aromatic product with a corresponding degree of weak acidity or basicity. Therefore, the product thus obtained must be worked up to neutralize acidity or basicity.

Summary of the Invention

It is an object of the present invention to provide a good mixed solvent which is used to separate aromatics by extractive distillation. Such mixed solvents have higher solubility and relatively wide boiling point regions, which can alleviate process conditions and reduce energy consumption during solvent recovery.

1 is a process flow diagram of an extractive distillation method using a mixed solvent according to the present invention.

Detailed description of the invention

Mixed solvents according to the present invention include a main solvent, a solubilizer and a modifier. The solubilizing agent is a C ₈ - C ₁₁ is any one of an aromatic substance or a carbon number of two different types of C ₈ - is selected from a mixture of C ₁₁ aromatics, in amounts of 3 - is a 39% by weight; The carbon number of the lowest aromatics in the solubilizer must be greater than the carbon number of the highest aromatics in the aromatics to be separated. The solubilizer is selected from any one of C ₈ -C ₁₁ aromatics, and the mixed solvent comprises 0.01 to 10.0% by weight of a modifier; When the solubilizer is selected from a mixture of two C ₈ -C ₁₁ aromatics having different carbon numbers, the mixed solvent comprises from 0 to 10.0% by weight of the modifying agent. The main solvent and the modifier are independently selected from sulfolane derivatives, N-formyl morpholimo and N-methyl pyrrolidone, provided that the acidity and basicity of the modifier are opposite to the main solvent.

The main solvent and the modifier may be selected from sulfolane derivatives, N-formyl morpholino and N-methyl pyrrolidone, respectively. The sulfolane derivatives are represented by the formula:

Wherein R 1, R 2, R 3, R 4 are each independently selected from H, C ₁ -C ₁₀ alkyl, C ₇ -C ₁₂ arylalkyl, C ₁ -C ₈ alkoxy. Preferred solvents are sulfolane, 2-methyl sulfolane or 2,4-dimethylsulfolane.

Solubilizers in mixed solvents according to the invention may increase solubility. The solubilizer is selected according to the composition of the aromatic material to be separated; That is, the solubilizer should have a structure similar to that of the aromatic material so that the solubility of the aromatic material is increased. However, the solubilizer must be different from the aromatic material to be separated to facilitate recovery of the solvent. Typically, all raw materials containing aromatics include benzene and toluene; Thus, the solubilizer is C₈-C₁₁Any one of the aromatics or a mixture of two of them. However, when the raw material contains xylene, the solubilizer is C.₉ Or more aromatic substances, preferably C₉Aromatics, or C₉And C₁₀It should be chosen from mixtures of aromatic substances.

Adding a modifier to the mixed solvent overcomes the problem of separation of the aromatics from the neutrality due to the main solvent. For example, when sulfolane is used as the main solvent, since the sulfolane itself is weakly acidic, the separated aromatic product is also weakly acidic, and therefore, post-treatment of the product is necessary to neutralize acidity. For the same reason, when the weakly basic N-formyl morpholine and N-methyl pyrrolidone are used as main solvents, the isolated product is also weakly basic. Therefore, it is necessary to acidify the product to neutralize the basicity. If an extraction solvent having acid-base opposite to the main solvent is added to the mixed solvent as a modifying agent, the separated aromatic product can be neutralized to avoid post-treatment. Specifically, when sulfolane acts as the main solvent, the modifier is selected from N-formyl morpholine and N-methyl pyrrolidone; If N-formyl morpholine or N-methyl pyrrolidone acts as the main solvent, the modifier is sulfolane.

If the solubilizer is selected from C ₈ -C ₁₁ aromatics, the aromatics are either aromatic compounds having the same carbon number or C ₈ aromatics including o-xylene, m-xylene, p-xylene, ethylbenzene or mixed xylenes. A mixture of isomers such as C ₉ aromatics, isopropyl benzene, trimethyl benzene. The solubilizer content in the mixed solvent is preferably 5-30% by weight and the modifier content is preferably 0.1-5.0% by weight.

If the solubilizer is selected from any two mixtures selected from C ₈ -C ₁₁ aromatics having different carbon numbers, the solubilizer content in the mixed solvent is preferably 5-30% by weight and the modifier content is preferably 0 -5.0 wt%, more preferably 0.1-5.0 wt%. Any two mixtures selected from C ₈ -C ₁₁ aromatics having different carbon numbers in the solubilizer are preferably mixtures of C _{8 + n} aromatics and C _{9 + n} aromatics, where n is 0, 1 Or 2). The weight ratio of C _{8 + n} / C _{9 + n} aromatics is 1-50: 1, preferably 1-20: 1, more preferably 1.5-15.0: 1.

Mixed solvents according to the invention are suitable for extractive distillation. Suitable raw materials for extractive distillation are hydrogenated pyrolysis gasoline fractions containing 15-99% by weight of aromatics, reformed oil, coultar oil and the like. The raw material is preferably a hydrocarbon mixture comprising one or two aromatic substances, such as benzene, benzene and toluene, or a raw material comprising toluene and xylene.

A method for separating aromatics by extractive distillation using a mixed solvent according to the method of the present invention,

Introducing a mixed solvent to the top of the column for extractive distillation,

Introducing a hydrocarbon mixture into the middle portion of the column;

Extracting the non-aromatic material from the upper end of the column for extractive distillation,

Introducing a rich solvent comprising an aromatic material into the middle portion of the solvent recovery column at the bottom of the extraction column to separate the aromatic material and the mixed solvent;

Withdrawing the aromatic material thus obtained from the upper end of the recovery column; And

And introducing a mixed solvent taken out from the lower end of the solvent recovery column into an upper end of the recirculating extractive distillation column.

The process conditions of the column for extractive distillation in the extractive distillation process are as follows: the top pressure is 0.10-0.30MPa, the inlet temperature of the lean solvent is 80-130 ° C, the bottom temperature is 130-180 ° C The solvent / raw weight ratio, ie the solvent ratio is 3.0-7.0, the reflux ratio is 0.1-3.0, and the theoretical number of plates is 10-40; The top pressure of the recovery column is 0.04-0.10 MPa, the temperature of the rich solvent is 125-175 ° C, the bottom temperature is 160-190 ° C, the flux ratio is 0.5-2.5, and the theoretical number of plates is 10-25 Dog.

As an example, the reaction flow separating benzene by extractive distillation will be described below with reference to FIG. 1. Raw material for extractive distillation is introduced into the heat exchanger (3) through the line (1), heat exchanged to a predetermined temperature, and then introduced into the middle portion of the column (4) for extractive distillation. The mixed solvent enters the upper part of the column for extractive distillation via line (2). By extractive distillation, the non-aromatic material is withdrawn from the top and enters the condenser 6 via line 5. After condensation and cooling, the non-aromatic material enters the reflux tank 7, part of which is refluxed through line 9 to the column for extractive distillation 4, the other part being routed through line 8. Nate oil is discharged from the device. The rich solvent enters the solvent recovery column 12 via line 11 from the bottom of the extractive distillation column 4. The gas stream at the top of the solvent recovery column 12 enters the condenser 14 via the condensate line 13 and after cooling into the condensate tank 16. A portion of the condensate is refluxed through line 18 to a solvent recovery column and the remaining portion exits the device as benzene product via line 17. The upper end of the condensate tank 16 is connected with the vacuum system 15. The lean solvent obtained at the lower end of the solvent recovery column 12 is introduced into the heat exchanger 3 through the line 20 and recycled to the column 4 for extractive distillation after heat exchange. Both the extractive distillation column 4 and the solvent recovery column 12 are provided with reboilers 10 and 19 at the lower end.

In the case of simultaneous recovery of benzene / toluene by extractive distillation, the raw material is a C ₆ -C ₇ fraction and flows as described above except that a mixture of benzene / toluene is obtained at the top of the recovery column. . The mixture can be further rectified and separated to yield pure benzene and pure toluene. When separating xylene from the C ₈ fraction, the same process as for benzene recovery is carried out, except that the solubilizer used is an aromatic substance of C ₉ or higher. When toluene / xylene is recovered at the same time, the same process as the simultaneous recovery of benzene / toluene is carried out, except that the solubilizer used is an aromatic substance of at least C ₉ .

The mixed solvent according to the present invention has a greatly improved solubility due to the addition of a solubilizer, thereby allowing the mixed solvent to have a sufficiently high recovery rate when recovering the aromatics from a raw material having a low content of aromatics, thereby allowing the application of the apparatus. Becomes wider. The addition of solubilizers can greatly alleviate the process conditions of the solvent recovery column, thereby reducing the adverse effects of impurities, such as sulfur, nitrogen, and oxygen, on the quality of the product resulting from thermal decomposition of the solvent. In addition, since the neutrality of the aromatic product can be ensured by adding the modifier, post-treatment can be omitted.

The mixed solvent according to the present invention does not contain water and since the solvent recovery column does not use stripping water, the aromatic product can be obtained directly without a water separator; This saves energy as well as price, and does not cause water to corrode the device.

The following examples illustrate the invention in more detail.

Example 1

Benzene was recovered from the benzene fraction in hydrogenated pyrolysis gasoline. The composition of the raw material used is shown in Table 2. The mixed solvent used consisted of sulfolane as the main solvent, o-xylene and isopropyl benzene as the solubilizer and N-formyl morpholine as the modifying agent. The content of various components in the mixed solvent is shown in Table 1. The process flow shown in FIG. 1 was used. Process conditions of the extractive distillation column and the solvent recovery column are shown in Table 3. Table 4 shows the separation results of the aromatics.

Example 2

The benzene product was separated from the C ₆ fraction of the reformate via the reaction flow shown in FIG. 1. The main solvent of the mixed solvent was sulfolane, the solubilizers were o-xylene and isopropyl benzene, and the modifier was N-methyl pyrrolidone. The composition of the mixed solvent is shown in Table 1. The composition of the raw material is shown in Table 2. Table 3 shows the process conditions of the extraction column and the solvent recovery column. The aromatics separation results are shown in Table 4.

From Tables 3 and 4, the process of extracting and distilling reformate with a low content of aromatics using the mixed solvent according to the present invention is not only continuously operated under mild conditions but also has a purity of 99.99% and a sulfur content of 0.2 ppm. It can be seen that the phosphorus benzene product produces a high recovery of 99.6%. The aromatics content in the raffinate was as low as 0.32%.

Example 3

Benzene was recovered from the benzene fraction in hydrogenated pyrolysis gasoline. The added raw materials and process conditions were similar to those in Example 1 except that the main solvent in the mixed solvent was sulfolane and the solubilizers were o-xylene and isopropyl benzene and did not contain a modifier. The composition of the mixed solvent is shown in Table 1. The aromatics separation results are shown in Table 4.

Example 4

Benzene was recovered from the benzene fraction of hydrogenated pyrolysis gasoline. The raw materials and process conditions used were similar to those in Example 1 except that the main solvent in the mixed solvent was sulfolane, the solubilizer was o-xylene and the modifier was N-formyl morpholine. The composition of the mixed solvent is shown in Table 1. The aromatics separation results are shown in Table 4.

Comparative example

Benzene was recovered from the benzene fraction of hydrogenated pyrolysis gasoline. The raw materials and process conditions used were similar to those in Example 1, except that a mixed solvent (disclosed in CN1262264A) with a main solvent of sulfolane and a solubilizer of o-xylene was used. The composition of the mixed solvent is shown in Table 1. Table 3 shows the process conditions of the extractive distillation column and the solvent recovery column. The aromatics separation results are shown in Table 4.

From the data of Example 3 and Comparative Example shown in Table 4, the mixed solvent of the present invention comprising two solubilizer compounds compared to the mixed solvent described in CN1262264A containing only one solubilizer component is the benzene product under the same process parameters. It can be seen that the recovery rate can be improved. From the data of Example 4, it can be seen that adding the modifier to the mixed solvent reduces the sulfur content in the benzene product to meet the neutralization requirements. From the data of Examples 1 and 2, the mixed solvent comprising two solubilizers and one modifier not only improves the recovery of aromatics but also reduces the content of sulfur to give a better effect of making the benzene product neutral It can be seen that it provides. The process can be simplified because traces of acidic substances in the neutral benzene product do not have to be recovered from the neutral benzene product by post treatment.

Benzene and toluene were simultaneously recovered from the C ₆ -C ₇ fraction of the hydrogenated pyrolysis gasoline. The process stream shown in FIG. 1 was employed for extractive distillation, and the resulting benzene / toluene mixture was introduced into a rectification column and converted to benzene and toluene products through a rectification process. The main solvent in the mixed solvent used in the extractive distillation column was N-formyl morpholine, the solubilizers were o-xylene and isopropyl benzene and the modifier was sulfolane. The composition of the mixed solvent is shown in Table 1. The composition of the raw material is shown in Table 2. Table 3 shows the process conditions of the extractive distillation column and the solvent recovery column. The aromatic substance separation results are shown in Table 5.

From Tables 3 and 5, benzene / toluene aromatic mixtures having a purity of 99.9% were obtained under relatively mild conditions-that is, the residual pressure at the top in the solvent recovery column was 0.045 MPa, the top temperature was 72 ° C, and the bottom temperature was 186 ° C. It can be seen that the product thus obtained is neutral. The benzene and toluene products meet the high quality standards of GB3405-89 and GB3406-90, respectively. If pure N-formyl morpholine is used as the solvent for extractive distillation, the residual pressure of the recovery column must be 0.038 MPa, the bottom temperature must be 201 ° C., and the mixed aromatic material to obtain the same recovery rate as the aromatic material of the same purity. The nitrogen content in the high to 2-3ppm, which results in a relatively high nitrogen content in the toluene product is relatively high basicity. Therefore, aftertreatment processes such as adsorptive purification of the product with clay should be employed so that neutral product is produced.

Complex Solvent Composition Main solvent (% by weight) Solubilizer (wt%) Modifier (wt%) Example 1 Sulfolane (84.0) o -xylene (11.0) Isopropylbenzene (4.0) N-formylmorpholine (1.0) Example 2 Sulfolan (75.0) o -xylene (17.0) Isopropylbenzene (5.0) N-formylmorpholine (3.0) Example 3 Sulfolane (85.0) o -xylene (14.0) Isopropylbenzene (1.0) Example 4 Sulfolane (84.0) o -xylene (15.8) - N-formylmorpholine (0.2) Example 5 N-formylmorpholine (86.0) Mixed Xylene (6.0) Isopropylbenzene (3.5) Sulfolane (4.5) Comparative example Sulfolane (94.0) o -xylene (6.0) - -

Composition of raw materials, wt% Example 1 Example 2 Example 5 Alkanes C ₅ - 3.56 0.44 C ₆ 4.45 35.40 3.89 C ₇ 1.94 16.99 3.02 Cyclans C ₅ 1.51 0.33 - C ₆ 9.20 2.85 8.24 C ₇ 2.27 0.88 3.34 MCH 0.83 - - Aromatic C ₆ 79.80 39.88 51.52 C ₇ - 0.01 29.55 Total amount 100.00 100.00 100.00

Item Example 1 Example 2 Example 5 Comparative example Extractive distillation Theoretical plate number 29 25 38 29 Solvent ratio 4.5 4.0 5.5 4.5 Inlet solvent temperature, ℃ 90 90 115 90 Top Reflux Ratio 0.3 0.3 0.7 0.3 Upper pressure, MPa 0.1 0.1 0.15 0.1 Lower temperature, ℃ 132 138 175 130 Solvent Recovery Column Theoretical plate number 16 16 16 16 Inlet solvent temperature, ℃ 131 136 174 130 Top Reflux Ratio 1.0 1.5 1.5 1.0 Upper pressure, MPa 0.045 0.08 0.045 0.045 Upper part temperature, ℃ 56 72 72 56 Lower temperature, ℃ 175 170 186 175

Item Example 1 Example 2 Example 3 Example 4 Comparative example Benzene Product Purity, wt% 99.97 99.99 99.97 99.97 99.97 Non-aromatic substance, ppm 300 100 290 300 300 Sulfur, ppm 0.2 0.2 0.5 0.3 One Crystallization temperature, ℃ 5.49 5.50 5.49 5.49 5.49 Neutrality test neutrality neutrality Slightly acidic neutrality Slightly acidic Recovery, Weight% 99.86 99.60 99.87 99.88 99.66 Non-aromatic Product Aromatics, wt% 0.54 0.32 0.51 0.47 1.33 Solvent, ppm <1 <1 <1 <1 <1

Item Example 5 Aromatic product (benzene + toluene) Purity, wt% 99.90 Non-aromatic substance, ppm 1000 Nitrogen, ppm <0.5 Neutrality test neutrality Recovery, Weight% 99.6 Non-aromatic product Aromatics, wt% 0.65 Solvent, ppm <1

When the mixed solvent according to the present invention is used to recover the aromatics by extractive distillation, the process conditions at the time of solvent recovery can be relaxed, the yield of the aromatics can be improved, and the separated aromatics can be neutral.

Claims (10)

Main solvents, solubilizers and modifiers, The solubilizing agent C ₈ - C _11, one of the aromatic material or a carbon number of two different types of C ₈ - is selected from a mixture of C ₁₁ aromatic substances in amounts of 3 and 39% by weight, of the lower aromatic material selected from the group consisting of a solubilizing agent The carbon number should be larger than the carbon number of the higher aromatics among the aromatics to be separated, and when the solubilizer is selected from any one of C ₈ -C ₁₁ aromatics, the modifier content is 0.01 to 10.0% by weight and the carbon number is two kinds When selected from a mixture of C ₈ -C ₁₁ aromatic substances of the modifier content is 0 to 10.0% by weight, the main solvent and the modifier is a sulfolane derivative, N-formyl morpholine and N-methyl pyrrolidone Independently selected from the above, except that the acidity and basicity of the modifier is opposite to the main solvent, the sulfolane derivative is characterized by the following formula, Solvent mixture for separating aromatics from the hydrocarbon mixture by distillation Ex. Wherein R 1, R 2, R 3, R 4 are each independently selected from H, C ₁ -C ₁₀ alkyl, C ₇ -C ₁₂ arylalkyl, C ₁ -C ₈ alkoxy. The solubilizer is 5-30% by weight and the modifier content is 0.1-5.0% by weight when the solubilizer is any one selected from C ₈ -C ₁₁ aromatics. Mixed solvents. The solubilizer is 5-30% by weight and the modifier content is 0.01-5.0% when the solubilizer is selected from a mixture of two kinds of C ₈ -C ₁₁ aromatics having different carbon numbers. Mixed solvent, characterized in that%. The method according to claim 1 or 3, wherein the solubilizer is a mixture of C _{8 + n} and C _{9 + n} aromatics, wherein n is 0, 1 or 2 and of the C _{8 + n} / C _{9 + n} mixture A mixed solvent, characterized in that the weight ratio is 1-20: 1. The mixed solvent of claim 4, wherein the weight ratio of the C _{8 + n} / C _{9 + n} mixture is 1.5-15.0: 1. The mixed solvent according to any one of claims 1 to 3, wherein the main solvent is sulfolane and the modifier is selected from N-formyl morpholine and N-methylpyrrolidone. The mixed solvent according to any one of claims 1 to 3, wherein the main solvent is selected from N-formyl morpholine and N-methylpyrrolidone, and the modifier is sulfolane. Introducing a mixed solvent of any one of claims 1 to 3 into the top of the column for extractive distillation; Introducing a hydrocarbon mixture into the middle portion of the column; Extracting the non-aromatic material from the upper end of the extractive distillation column; Introducing a rich solvent including an aromatic material into a middle portion of the solvent recovery column at a lower end of the extractive distillation column to separate the aromatic material and the mixed solvent; Extracting the aromatic material obtained from the upper end of the recovery column; And And recycling the mixed solvent withdrawn from the lower end of the solvent recovery column to the upper end of the column for extractive distillation, thereby recycling the aromatics from the hydrocarbon mixture. The pressure of the upper end of the extractive distillation column is 0.10-0.30 MPa, the inlet temperature of the mixed solvent is 80-130 ° C, the lower end temperature is 130-180 ° C, the solvent ratio is 3.0-7.0 The upper pressure of the recovery column is 0.04-0.10 Mpa, The inlet temperature of the rich solvent is 125-175 ℃, the lower temperature is 160-190 ℃. 9. A process according to claim 8, wherein the aromatic material is benzene, a mixture of benzene and toluene or a mixture of toluene and xylene.