TW575658B - Aromatics purification from petroleum streams - Google Patents

Description

575658 A7 B7 V. Description of the invention (1) Background of the invention It is not practical or economical to separate components with close boiling points (such as aromatic hydrocarbons and non-aromatic hydrocarbons) by conventional distillation. An alternative method for separating components close to boiling point is extractive distillation (ED). In the ED column, the polar, non-volatile solvent enters the near-top column, and preferentially associates with the more polar components in the feed mixture, so that the relative volatility of the boiling point close to the components can be meaningfully increased, and separation becomes possible. A co-solvent may be added to improve the solubility or solubility and the overall efficiency of the primary solvent. The volatility (α) is the expression of solvent selectivity and is related to the theoretical number of stages required for separation. As α. Increases, the number of theoretical stages or trays required for separation decreases. This will make separation more practical and reduce energy consumption. However, selecting a solvent / co-solvent pair is difficult and requires actual testing. The basic principles, design, and operation of the ED method are fully discussed in the literature, including: Atkins GT, et al., &Quot; Me Kebei-Sier method for calculation of extraction steamhouse " (Application of Me Cabe-Thiele Method to Extractive Distillation calculations), Chem. Eng · Prog ·, 45 (9), 553-562 (1949); Cambers, JM ,,, Extractive Distillation Design and Application " (Extractive Disillation Design and Application), (: hem. Eng · Prog., 47 (11), 555-565 (1951) '· Hackmuth, KK.,' "Industrial Viewpoints on Separation" Processes), Chem. Eng. Prog., 48 (12), 617-626 (1952); Butler et al., U.S. Patent No. 3,1,14,783; and Perry's Chemical Engineers' Handbook Handbook), 6th edition, Megraw-Hill Book Company, 1984, pages 13-53 to 13-57. This paper is sized to the Chinese National Standard (CNS) A4 (210X 297) (Mm) 575658 A7 B7 V. Description of the invention (2) This is incorporated by reference. We are familiar with the use of extractive distillation to separate aromatics, especially for the separation of benzene, toluene, and xylenes from non-aromatics, where aromatic and non-aromatic compounds have near stagnation points. For example, US patent No. 3,591,490 shows a method for separating aromatic hydrocarbons from a hydroxy mixture using N-methyl-eloramine or dimethylformamide as a solvent. U.S. Patent No. 3,723,526 describes a self-aromatic hydroxy and non- A method for recovering aromatic hydrocarbons from a mixture of aromatic cigarettes. This method mixes the primary fraction 'extracts the distillate from the overhead column and extracts the bottom fraction with sulfolane or other related solvents. US Patent No. 4,053,369 gives a method of extractive distillation' The method uses two kinds of liquid phase operations to optimize the reflux ratio, so that the amount of solvent used is reduced. The solvent should be selected to be highly selective and preferably a cyclobutane-type solvent. US Patent No. 4, 2 7 8, 5 No. 0-5 describes a method for extracting and distilling non-aromatic compound n-hexane with a selective solvent (such as N-methyl said pyridone). Fu-Ming Lee, "Extractive Distillation: Close-Boiling-Point 丨", Chemical Engineering, 112-120 (1998) describes the use of co-solvents to make difficult Separation is more economical and feasible. This paper provides selectivity and solubility of various solvents and their polarity data. The solvent / cosolvent pairs tested in the article include cyclohexanol and ethylene glycol, cyclohexanol and tetraethylene glycol, N- Methyl p-bilonone and ethylene glycol, tetraethylene glycol and N-methyl p-bilonium hydrazone, 3-methylcyclobutane and water, di-n-propyl hydrazone and water, and 3-methylcyclobutane This paper states that 'due to the current limitations on the understanding of the properties of polar components in solution', it is difficult to select a solvent / co-solvent pair, so it must be tested for the solubilization. -5- This paper size applies to Chinese national standards (CNS) A4 size (210 X 297 mm) 575658

Also included is at least methyl-2_erol bite. 0- 'The above article does not suggest a novel solvent-falling agent combination that is the subject of the present invention. Therefore, there is a need to develop more suitable solvents and solvent mixtures than are currently known for ED aromatic and non-aromatic hydrocarbon mixtures. $ Summary of the Invention = 发 = Provide an effective method for separating polar aromatic solvents and non-aromatic hydrocarbon mixtures with polar organic solvents or polar organic solvent mixtures by boiling retort. H can use novel polar organic solvents or polar organic solvents = The product is produced by extractive distillation from a mixture containing aromatics and non-aromatics: high-purity aromatics. Other objects and benefits are apparent from the detailed description of the present invention and the scope of additional patent applications. According to a specific embodiment of the present invention, a method for separating one or more aromatic hydrocarbons from one or more non-aromatic smokes uses cyclidine as an extraction solvent to extract a distillation feed mixture in an extractive distillation column, which changes the funeral. The extraction solvent is a co-solvent selected from the group consisting of 3-methylsulfolane, N-ketone, acetophenone, isophorone and morpholine. Brief Description of the Drawings Figure 1 illustrates a preferred embodiment of the extractive distillation method of the present invention. Detailed Description of the Preferred Embodiments Figure 1 illustrates a preferred method and apparatus according to the present invention. A feed mixture containing aromatic and non-aromatic hydrocarbons enters the middle portion of the multi-stage ED column 3 through line 1. The temperature of the feed mixture flowing through line 1 can be adjusted by the control heat exchanger 2 to add heat to the feed mixture or remove it from the feed mixture. -6-This paper size applies to China National Standard (CNS) A4 (210X 297) Mm)

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575658 A7 B7 ____ 5. Description of the invention (4) Heat. The solvent from the solvent storage device 20 enters the ED column 3 through the line 22, and the overhead stream rich in non-aromatic hydrocarbons is taken out from the upper portion of the ED column 3 through the line 4. The overhead stream can be completely passed to a storage device or other processing device, or the overhead stream can be condensed for part of, or in a normal situation, a part of which is returned to the ED column 3 as reflux. The overhead stream passing through line 4 is condensed in condenser 5 to produce a condensed stream. Part of the condensing overhead stream can be returned to the ED column 3 as a return stream through line 6, and the remainder of the condensing overhead stream can be produced, or it can be passed through line 7 to other processing units. The bottom stream is taken out from the lower part of the ED column 3 through line 11. A part of the stream taken out from the bottom of the ED tower 3 can be heated and returned to the ED tower 3. For example, according to a preferred embodiment of the present invention, part of the bottom product stream can be extracted through line 8 and heated in a reboiler 9 and then returned to the lower part of the ED column 3 through line 10. The operating conditions in heat exchanger 2, condenser 5 and reboiler 9 can be controlled by solvent flow through line 2, 2, feed mixture flow through line 1, reflux flow through line 6, and bottom stream flow through line 1 1 Interact to fractionate the feed mixture entering the ED column 3 to produce a non-aromatic hydrocarbon-rich overhead stream and a bottoms stream primarily containing aromatic hydrocarbons and solvents. The bottoms stream through line 11 can be transferred to a reservoir for further processing or preferably passed to another distillation column 13 (commonly referred to as a solvent stripping column). Adjusting the temperature of the bottom stream passing through the line 11 is necessary for effective fractionation (extraction) in the column 13, and this can be performed by appropriately adjusting the heat exchanger 12. The overhead stream, which mainly contains aromatic hydrocarbons, is taken from the upper part of the column 13 through the line 14. The overhead stream can be condensed at least partially in the condenser 15. Self-condenser 1 5 This paper size is in accordance with Chinese National Standard (CNS) A4 (210X 297 mm) 575658 A7 B7 V. Description of the invention A greater alpha difference occurs between the separated components, which allows less distillation stages, The individual components in the feed mixture are separated at low volume back / Watt and lower purity. According to a preferred embodiment of the present invention, at least one aromatic hydrocarbon containing 6 to 10 carbon atoms per molecule and at least one non-aromatic hydrocarbon having a boiling point close to it (preferably containing 5 to 10 carbon atoms per molecule) ) Hydrocarbon feed for extractive distillation process. The boiling points of aromatic hydrocarbons and non-aromatic hydrocarbons to be separated by extractive distillation of the present invention (at atmospheric pressure conditions, that is, about 1 atmosphere) are preferably in the temperature range of about 25 to about 175 ° F, and more preferably about 40 to about 150 °. C. In general, the aromatic hydrocarbons and non-aromatics are close to each other / 's point, and differ by about OU ° C at about 1 atmosphere, preferably 03-3 ° C. In the feed, the aromatic content is preferably about 10-95% by weight (more preferably about 20-80% by weight), and the non-aromatic content is about 5-95% by weight (more preferably about 20%). _ 80% by weight). Non-limiting examples of preferred feeds for non-business families are n-pentane, n-hexane, 2-methylpentane, 3-pentylpentane, n-heptane, 2,2-dimethylpentane, 2, 4.Dimethylpentane, 3,3-dimethylpentane, 2,3-dimethylpentane, 2-methylhexane, 3-methylhexane, 2,2,3-trimethyl Butyl, n-octane, 2-methyloctane, n-nonane and the like and mixtures thereof, especially n-heptane-containing mixtures. Non-limiting examples of preferred feed aromatics are benzene, toluene, m-, ortho- and para-xylene, ethylbenzene, xylene, methyl ethylbenzene, and the like and mixtures thereof. Particularly preferred aromatic hydrocarbons are benzene, toluene and xylene. The co-solvent used preferably contains 4 to 8 carbon atoms per molecule. Non-limiting examples of co-solvents used in the present invention are 3-methylcyclobutane, N-methyl-2 -pyrrolidine -9- This paper size is applicable to the Chinese National Standard (CNS) A4 (21 × 297 mm)

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k 575658 A7 B7 V. Description of the invention (7 嗣, ethyl alcohol, isophorone, morpholine, and mixtures thereof. The preferred falling aids of the present invention are 3-methylsulfolane and N-methyl · 2-pyrrolidine. According to a preferred embodiment of the present invention, the weight ratio of component (b) (co-solvent) to component (a) (sulfolane) in any solvent that exhibits a synergistic effect in the implementation can be utilized in the extractive distillation process. The weight of component (a) to component (b) is more preferably in the range of about 0.1: 1 to about 20: 1, and more preferably about 0.1: 1 to about 10: 1. The weight ratio of the hydrocarbon feed mixture can be used. The solvent to feed weight is preferably in the range of about 05: 1 to about 40: 1, more preferably about 0.5: 1 to about 20: 1. Tian can choose any Applicable feed inlet position. Generally, from the bottom of the tower, the feed inlet position is within the range of about 2 to about 70%, more preferably about 5 to about 60%, and more preferably about 7 to about 50%. Any suitable solvent inlet position can be selected. Generally, the solvent inlet position is within the range of about 50% to about 99% of the total height of the filling column or the tray, Best from about 70 to about 99%, more preferably from about 80 to about 99%.

Binding may use any applicable return sludge ratio (ie, the weight ratio of the condensed vapor portion returned to the distillation column to the condensed vapor portion taken out as distillate). Generally, the reflux ratio is in the range of about 0: 1 to about 100: 1, preferably about 0: 1 to about 50: 1, and more preferably about 0.1: 1 to about 5: 1.

The wire can be used in a distillation kettle (reboiler) at any suitable temperature. Its temperature is generally from about 4 ° C to about 210 ° C :, preferably about 65 ° C to about 60 ° C. Generally, the button is heated closer to the bottom, and rarely heated near the crotch. Generally, The temperature at the top of the column where the steam enters the condenser is about 40 r to about i5 (rc range -10-

This paper size is in accordance with Chinese National Standard (CNS) A4 specification (210X297 mm) 575658 A7 ____________B7 5. In the description of the invention (8), it is preferably from about 65 ° C to about 120 ° C. Solvents and feeds are usually preheated before they enter a packed or trayed column (typically to a temperature close to the temperature of the corresponding inlet point column). Any suitable pressure may be utilized during extractive distillation. The pressure may be from about 5 to about 100 hours per square inch gauge, preferably from about 8 to about 20 pieces per square inch gauge. The overhead product (taken from the top) contains a smaller volume percentage of aromatic hydrocarbons and a larger volume percentage of non-aromatic hydrocarbons than the feed. Generally, the bottoms product (taken from the bottom) contains more aromatic hydrocarbons than the feed and less non-aromatic hydrocarbons than the feed. The bottom product also contains substantially all of the added solvent, and the added solvent can be separated from the other bottom components by simple distillation, because the solvent usually has a higher boiling point than the other bottom components. The recovered lean solvent is preferably recycled to the ED column. Any suitable packed length or number of trays can be used in the process of the invention for an ED column having a suitable column diameter. The precise column size and design depend on the scale of operation, feed composition, solvent composition, desired recovery and purity of various hydrocarbon products, and the like, and can be easily determined by those skilled in the art. The following examples further illustrate preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Example 1 This example illustrates the synergistic effect of mixing sulfolane (SULF) and 3-methylsulfolane (3 MSULF) in an extractive distillation aromatic / non-aromatic feed mixture compared to the individual components. A mixture of about 50% by weight benzene and 50% by weight n-heptane in a hydrocarbon mixture

575658

AT B7 V. Description of the invention (9) Solvent-feed weight ratio is added with E D solvent (SULF or 3 MSULF or mixture of different proportions of SULF and 3 MSULF). The entire mixture was heated to its boiling point in the equilibration tank equipped with a reflux condenser to its boiling point for about 20 to 30 minutes. Then use the diaphragm device to draw a small amount of sample from the cell containing the liquid phase of the equilibrium system, and also draw the condensed vapor sample from the diaphragm at a position just below the reflux condenser. Two samples were analyzed. The weight fractions of n-heptane and benzene in the liquid and condensed phases were determined by gas chromatography. Calculate the relative volatility (α) according to formula (1), where n-heptane is component 1 and benzene is component 2. The results are summarized in Table 1.

Table I Relative volatility of solvent S / F (a) 0.0 0.57 without solvent added SULF 3.0 1.97 10% SULF / 90% 3 MSULF 3.0 2.48 25% SULF / 75% 3 MSULF 3.0 2.44 3 MSULF 3.0 2.34 Table 1 shows the data When no solvent is added, because the boiling point of n-heptane (98.4 ° C) is much higher than the boiling point of benzene (80.1 ° C), the relative volatility (α) of n-heptane to benzene is 0.57 (less than 1). When the S / F is 3.0, SULF and 3 MSULF can increase α from 0.57 to about 1.97 and 2.34, respectively, making separation possible in the ED process. In the ED process, the less polar n-heptane is removed as the top product, and the more polar benzene is removed as the bottom product together with the solvent. Therefore, under the solvent, α increases to a number greater than 1.0. Larger α 値 indicates easier separation. Table 1 is also willing to show the synergistic effect of the mixed SULF and 3 MSULF, indicating that for -12- this paper size applies the Chinese National Standard (CNS) A4 specification (210X 297 mm) 575658 A7 B7 V. Description of the invention (10) In the case of alkane and benzene, a better alpha is obtained by using a mixture than a single solvent alone. Unexpectedly for the skilled artist, the solvent / co-solvent mixing of SULF and 3 MSULF produced such a synergistic effect. Example 2 This example demonstrates the synergistic effect of mixing cyclamidine (SULF) and N-methyl-2-pyrrolidone (NMP) in an extractive distillation aromatic / non-aromatic feed mixture versus using the components individually. Add 50% by weight of benzene and 50% by weight of n-heptane in a hydrocarbon-to-feed weight ratio of 3.0 D solvent (SULF to NMP or a different mixture of SULF and NMP). Repeat the experimental steps in the equilibrium cell as in Example.1. Calculate the relative volatility (α) from formula (1), where n-heptane is component 1 and benzene is component 2. The results are shown in Table 2.

Table II Relative volatility (α) of solvent added 0.0 0.57 SULF 3.0 1.97 75% SULF / 25% NMP 3.0 2.48 50 0% SULF / 50% NMP 3.0 2.67 25% SULF / 75% NMP 3.0 2.34 NMP 3.0 2.01 Table II shows that when S / F is 3.0, SULF and NMP can increase α from 0.57 to 2.00 separately, making it possible to separate in the ED process. However, the synergistic effect of mixing SULF and NMP shows that intentionally better results are obtained with a mixture than with a solvent alone. In fact, in the separation of n-heptane -13- this paper size applies the Chinese National Standard (CNS) A4 specification (21 × 297 mm)

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Line 575658 A7 B7 V. Description of the invention (n) and benzene ED process, the solvent mixture shows the maximum efficiency at 50% SULF and 50% NMP. For those skilled in the art, it is difficult to predict that the solvent / co-solvent mixing of SULF and NMP produces such a synergistic effect. Example 3 This example illustrates the effectiveness of SULF and acetophenone (ACTN) when separating aromatic and non-aromatic compounds by extractive distillation. The test series of this example was performed using the apparatus and feed described in Example 1 at an S / F ratio of 3.0. The test results are listed in Table III.

Table III Relative volatility of solvent S / F added (a) 0.0 0.57 SULF 3.0 1.97 75% SULF / 25% ACTN 3.0 2.26 50% SULF / 50% ACTN 3.0 2.01 25% SULF / 75% ACTN 3.0 1.66 ACTN 3.0 1.27 According to the test results in Table 3, it can be inferred that a mixture of SULF and ACTN with a lower percentage (such as approximately 25%) of ACTN can be more effective than SULF or ACTN alone. Surprisingly for this artist, the solvent / co-solvent mixing of SULF and ACTN produced such a synergistic effect. Example 4 This example illustrates the effectiveness of mixing another co-solvent isophorone (ISOP) with SULF in the separation of aromatic and non-aromatic compounds by extractive distillation. · The test series of this example uses the device and feed described in Example 1 again, from 3.0 to -14. This paper size applies the Chinese National Standard (CNS) A4 specification (210 X 297 mm) 575658 A 7 B7 5 Description of the invention (12 S / F ratio. Test results are listed in Table IV.

Table IV Relative volatility of the solvent S / F added (a) 0.0 0.57 SULF 3.0 2.04 75% SULF / 25% ISOP 3.0 2.28 ISOP 3.0 1.16 added without solvent Table IV shows the separation of benzene with a mixture of 75% SULF and 25% ISOP And n-heptane is more effective than using SULF or ISOP alone. Surprisingly for this artist, the solvent / co-solvent mixing of SULF and ISOP produces such a synergistic effect. Example 5 This example shows the effectiveness of SULF and morpholine (MORP) in the separation of aromatic and non-aromatic compounds by extractive distillation. The test series of this example was performed using the apparatus and feed described in Example 1 at an S / F ratio of 3.0. The test results are listed in Table V. Table V Relative volatility of solvent S / F added (a) 0.0 0.57 SULF 3.0 2.04 75% SULF / 25% MORP 3.0 2.27 50% SULF / 50% MORP 3.0 2.13 25% SULF / 75% MORP 3.0 1.73 MORP 3.0 1.44 -15- This paper size applies to China National Standard (CNS) A4 (210 X 297 mm)

Claims (1)

575658 A8 B8 C8 D8 No. 090110178 Patent Application Chinese Patent Application for Replacement of the Patent Scope (% August) The scope of benefits „1! '·'! Ί, ——,:.: ',, ...-: f 1 ·„ ':::: .Λ. F 1.-A method for separating at least one aromatic hydrocarbon containing 6-12 faces per stagnation point from a non-aromatic smoke with a stagnation point of at least-by distillation in the presence of solvents A feed comprising at least one aromatic hydrocarbon and at least one non-W hydrocarbon, the solvent mixture includes sulfolane and at least one agent, and the co-solvent is selected from the group consisting of 3-methylsulfolane, N_methyl_2_pyrrole = ketone, ethyl A group of acetophenone, isophorone and morpholine.疋 2 · According to the scope of patent application! The method of claim, wherein the weight ratio of the sulfolane to the 3-methylsulfolidine is in the range of 1: 1 to 2: 1. 3. The method according to item 2 of the scope of patent application, wherein the weight ratio of the sulfolane to the 3-methylcyclobutane is in the range of 1: 1 to 丨:. 4. The method according to item 1 of the scope of patent application, wherein the co-solvent is 3-methylcyclobutane. 5. The method according to item 1 of the scope of the patent application, wherein the co-solvent is n_methyl-2 -pyrrolidone 6. The method according to the item 1 of the scope of patent application, wherein the co-solvent is acetofluorene. 7. The method according to item 1 of the scope of patent application, wherein the co-solvent is isophorous. 8. The method according to item 1 of the scope of patent application, wherein the co-solvent is wood. 9. The method according to item i of the patent application range, wherein 20-80% by weight of the feed mixture is an aromatic hydrocarbon and 20-80% by weight of the feed mixture is a non-aromatic hydrocarbon. 10. The method according to item 1 of the scope of patent application, wherein the paper size of the feed mixture is covered by the Chinese National Standard (CNS) A4 specification (210X 297 mm) 575658 A8 B8 C8 ________ D8 6. The scope of patent application contains at least one Aromatic hydrocarbons containing 6 to 10 carbon atoms per molecule. 11. The method according to item 丨 of the patent application range, wherein the feed mixture contains at least one non-aromatic hydrocarbon having 5 to 10 carbon atoms per molecule. 12. The method according to item 丨 of the patent application range, wherein the extraction solvent / co-solvent mixture and the feed mixture are introduced into the distillation column at a weight ratio of 0.5 to 20 parts by weight of solvent per part of the feed mixture. 13. The method according to item 丨 of the scope of patent application, wherein steam is cooled at the top of the tower and returned to the tower as reflux, steam exits the tower and is collected as overhead products, and the reflux is applied to the overhead products. The weight ratio is from 0.1: 1 to 5: 1. 14. · A method for separating one or more aromatic hydrocarbons from one or more non-aromatic hydrocarbons, wherein the feed mixture is subjected to extractive distillation in an extractive distillation column, and cyclopentane is used as an extraction solvent, and the improvement is that the extraction is performed therein. The solvent also includes at least one co-solvent selected from the group consisting of 3-methylsulfolane, N-methylpyrrolidone, acetophenone, isophorone and morpholine. 15. The method according to item 14 of the scope of patent application, wherein the weight ratio of the sulfolane to the co-solvent is in the range of 0.1: 1 to 20: 1. 16. The method according to item 15 of the scope of patent application, wherein the weight ratio of the sulfolane to the co-solvent is in the range of 0.1: 1 to 10: 1. 17. The method according to item 14 of the scope of patent application, wherein the co-solvent is 3methylcyclobutane. 18. The method according to item 14 of the scope of patent application, wherein the co-solvent is n methyl-2-pyrrolidone. 19. The method according to item 14 of the scope of patent application, wherein the co-solvent is Ethanol -2-This paper size applies Chinese National Standard (CNS) A4 specification (210 X 297 mm) 575658 benzene. Wherein the co-solvent is isophor. Where is the co-solvent? The non 20. The method according to item i 4 of the scope of patent application. 21 · Method according to item 1 * of the scope of patent application. The method of 4 items, wherein 20 to 80% by weight of 20 to 80% by weight of the feed mixture is 22. According to the scope of the patent application, the feed mixture is an aromatic hydrocarbon. 23. The method according to item 14 of the patent application park, wherein the feed mixture contains at least one aromatic warp having 6 to 10 carbon atoms per molecule. 24. The method according to claim 23, wherein the feed mixture comprises at least one non-aromatic hydrocarbon having 5 to 10 carbon atoms per molecule. 25. The method according to item i 4 of the patent application, wherein the extraction solvent / co-solvent and the feed mixture are introduced at a ratio of 0.00 to 20% by weight of solvent per part of the feed mixture. The distillation column. 26. The method according to item i 4 of the scope of patent application, wherein steam is cooled at the top of the tower and returned to the tower as reflux, steam exits the tower and is collected as overhead product, and the reflux is directed to the tower product The weight ratio is from 0 · 1: 1 to 5: 1. 27. A method for separating one or more aromatic hydrocarbons from one or more non-aromatic hydrocarbons, wherein the feed mixture is in an extractive distillation column, and cyclobutane is used as an extraction solvent after extractive distillation, and the improvement is as follows: The extraction solvent also includes N-methyl-2-pyrrolidone as a co-solvent. The solvent and co-solvent mixture is based on the weight of 3 parts of the solvent and co-solvent mixture per part of the feed mixture. CNS) A4 specification (210 X 297 mm) 575658 A8 B8 C8 D8 6. The scope of patent application is introduced to the column, where the feed mixture includes n-heptane and benzene. 28. A method for separating one or more non-aromatic hydrocarbons from one or more non-aromatic hydrocarbons, wherein the feed mixture is in an extractive distillation column, and cyclobutane is used as an extraction solvent after extractive distillation. The extraction solvent also includes 3-methylcyclobutanine as a co-solvent. The solvent and the co-solvent mixture are introduced into the column in a weight ratio of 3 parts of the solvent and the co-solvent mixture per part of the feed mixture, wherein the feed mixture includes Heptane and benzene. -4- This paper size applies to China National Standard (CNS) A4 (210 X 297 mm)