Apparatus and method for separating a mixture of n-hexane, ethyl acetate and acetonitrile

Abstract

This invention relates to an apparatus and method for separating a mixture of n-hexane, ethyl acetate, and acetonitrile. The apparatus includes two side-stream extractive distillation columns, an extractant recovery column, three condensers, three bottom reboilers, two coolers, a mixer, and a distributor. The side-stream outlet of side-stream extractive distillation column SEDC1 is connected to the material inlet of side-stream extractive distillation column SEDC2, and the side-stream outlet of side-stream extractive distillation column SEDC2 is connected to the material inlet of the extractant recovery column. In the three columns, the extractant collected from the bottom of each column is divided into two streams: one stream is reboiled and circulated through a bottom reboiler, and the other stream is collected in the mixer. After mixing in the mixer and splitting by the distributor, the extractant flows through coolers E1 and E2 respectively to the extractant inlets of the two side-stream extractive distillation columns. The material collected from the top of each column is condensed in the condenser and then divided into two streams: one stream is refluxed, and the other stream is produced as a product. This invention effectively separates n-hexane, ethyl acetate, and acetonitrile with good separation efficiency and low energy consumption.

Description

Technical Field

[0001] This invention relates to the field of separating mixtures of n-hexane, ethyl acetate, and acetonitrile, and specifically to an apparatus and method for separating mixtures of n-hexane, ethyl acetate, and acetonitrile. Background Technology

[0002] Hexane is an alkane-based organic solvent with a low boiling point and good solubility, commonly used in laboratory organic synthesis and extraction processes. It is also widely used industrially as an organic solvent in the production of coatings, inks, and rubber. Ethyl acetate is an ester-based organic solvent with high solubility and volatility, thus commonly used in the manufacture of industrial products such as coatings, adhesives, and varnishes. Acetonitrile is a nitrile-based organic solvent with high polarity and solubility, commonly used in organic synthesis and pharmaceutical production, and also industrially used in the production of coatings, plastics, and pharmaceuticals.

[0003] In industrial production processes, waste liquid containing a mixture of n-hexane, ethyl acetate, and acetonitrile is generated. These three substances form a binary azeotropic mixture, which cannot be effectively separated using conventional distillation methods, and the process is energy-intensive.

[0004] Therefore, there is an urgent need to design a device and method with low energy consumption and good separation effect to separate a mixture of n-hexane, ethyl acetate and acetonitrile. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide an apparatus for separating a mixture of n-hexane, ethyl acetate and acetonitrile. Firstly, it solves the problem that the mixture of n-hexane, ethyl acetate and acetonitrile is difficult to separate due to the presence of multiple binary azeotropes. Secondly, it solves the problem of high economic cost in the distillation process.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is: an apparatus for separating a mixture of n-hexane, ethyl acetate, and acetonitrile, comprising two side-stream extractive distillation columns, one extractant recovery column, three condensers, three bottom reboilers, two coolers, one mixer, and one distributor; wherein,

[0007] The side outlet of the side-stream extractive distillation column SEDC1 is connected to the material inlet of the side-stream extractive distillation column SEDC2, and the side outlet of the side-stream extractive distillation column SEDC2 is connected to the material inlet of the extractant recovery column ERC.

[0008] In the three columns—sidestream extractive distillation column SEDC1, sidestream extractive distillation column SEDC2, and extractant recovery column ERC—the extractant collected from the bottom of each column is divided into two streams. One stream is reboiled and circulated through a bottom reboiler, while the other stream converges in the mixer. After being mixed in the mixer and split by the distributor, the extractant then passes through coolers E1 and E2 respectively, reaching the extractant inlets of sidestream extractive distillation columns SEDC1 and SEDC2. The material collected from the top of each column is condensed in a condenser and then divided into two streams: one stream is refluxed, and the other stream is produced as a product.

[0009] To further reduce separation costs, the apparatus for separating a mixture of n-hexane, ethyl acetate, and acetonitrile also includes two intermediate reboilers. The material from the side-stream extractive distillation column is divided into two streams: one stream is reboiled and circulated through an intermediate reboiler, and the other stream goes to the material inlet of the next column.

[0010] To further improve the separation effect, the side-stream extractive distillation column SEDC1 has 40-65 trays, with the material inlet located on trays 20-35, the extractant inlet on trays 10-20, and the side-stream outlet on trays 35-55.

[0011] The side-stream extractive distillation column SEDC2 has 55-70 trays, with the material inlet located on trays 30-45, the extractant inlet on trays 5-10, and the side-stream outlet on trays 45-65.

[0012] The number of trays in the extractant recovery tower ERC is 10-25, and the material inlet is located on the 5th-15th tray.

[0013] The present invention also provides a method for separating a mixture of n-hexane, ethyl acetate, and acetonitrile, based on an apparatus for separating such a mixture, the method comprising:

[0014] In step S1, a mixture of n-hexane, ethyl acetate, and acetonitrile, along with the first extractant, enters the side-stream extractive distillation column SEDC1 through the material inlet and the extractant inlet, respectively. The vapor at the top of the side-stream extractive distillation column SEDC1 is condensed by condenser C1. Subsequently, a portion of the material is refluxed back into the top of the side-stream extractive distillation column SEDC1, while the other portion is collected as n-hexane product. A portion of the liquid material collected from the bottom of the side-stream extractive distillation column SEDC1 is reboiled in the bottom reboiler R1 and then enters the side-stream extractive distillation column SEDC1, while the other portion is collected as extractant.

[0015] In step S2, the material collected from the side-stream outlet of the side-stream extractive distillation column SEDC1 and the second extractant enter the side-stream extractive distillation column SEDC2 through the material inlet and extractant inlet, respectively. After contact and separation, the vapor at the top of the side-stream extractive distillation column SEDC2 is condensed by condenser C2, and a portion of the material is refluxed back to the top of the side-stream extractive distillation column SEDC2, while the other portion is collected as ethyl acetate product. A portion of the liquid material collected from the bottom of the side-stream extractive distillation column SEDC2 is reboiled by the bottom reboiler R2 and then enters the side-stream extractive distillation column SEDC2, while the other portion is collected as extractant.

[0016] In step S3, the material collected from the side-stream outlet of the side-stream extractive distillation column SEDC2 enters the extractant recovery column ERC for separation. After the vapor at the top of the extractant recovery column ERC is condensed by condenser C3, part of the material is returned to the top of the extractant recovery column ERC, and the other part is collected as acetonitrile product. Part of the liquid material collected from the bottom of the extractant recovery column ERC is reboiled by the bottom reboiler R3 and then enters the extractant recovery column ERC, and the other part is collected as extractant.

[0017] In step S4, the extractant and additional extractant collected from the bottom of the three columns—sidestream extractive distillation column SEDC1, sidestream extractive distillation column SEDC2, and extractant recovery column ERC—are sequentially separated into two streams after passing through mixer M and splitter S. One stream is cooled by cooler E1 and then enters sidestream extractive distillation column SEDC1 for recycling, while the other stream is cooled by cooler E2 and then enters sidestream extractive distillation column SEDC2 for recycling.

[0018] To further improve the separation effect, the reflux ratio of the side-stream extractive distillation column SEDC1 is 0.75-1.50;

[0019] The reflux ratio of the side-stream extractive distillation column SEDC2 is 0.55-1.50;

[0020] The reflux ratio of the extractant recovery tower ERC is 0.15-0.95.

[0021] Furthermore, the side-stream extractive distillation column SEDC1 has a column pressure of 0.5-0.9 atm, a top temperature of 50-65℃, and a bottom temperature of 170-190℃.

[0022] The SEDC2 side-stream extractive distillation column operates at atmospheric pressure, with a top temperature of 75-90°C and a bottom temperature of 195-220°C.

[0023] The ERC extractant recovery tower operates at atmospheric pressure, with a top temperature of 80-100℃ and a bottom temperature of 190-220℃.

[0024] Furthermore, the total amount of the extractant is in a molar ratio of 2.35 to 4.50 to the mixture of n-hexane, ethyl acetate, and acetonitrile.

[0025] Furthermore, the molar ratio of the extractant amount in the side-stream extractive distillation column SEDC1 to the extractant amount in the side-stream extractive distillation column SEDC2 is 0.50-2.50.

[0026] Furthermore, the extractant is dimethyl sulfoxide.

[0027] By adopting the above technical solution, this invention successfully separated a mixture of n-hexane, ethyl acetate, and acetonitrile, obtaining high-purity n-hexane, ethyl acetate, and acetonitrile products. The purity of the n-hexane product obtained by this invention is 99.9 mol%, the purity of the ethyl acetate product is 99.9 mol%, the purity of the acetonitrile product is 99.9 mol%, and the purity of the extractant dimethyl sulfoxide is 99.99 mol%. This avoids direct discharge of waste liquid into the environment, reduces the waste of chemical reagents, and saves resources. Compared with the traditional three-tower extractive distillation process, this invention sets up side streams in two extractive distillation towers, reducing the backmixing effect in the traditional extractive distillation process and lowering energy consumption. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the apparatus for separating a mixture of n-hexane, ethyl acetate and acetonitrile according to the present invention. Detailed Implementation

[0029] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0030] like Figure 1 As shown, an apparatus for separating a mixture of n-hexane, ethyl acetate, and acetonitrile includes two side-stream extractive distillation columns, one extractant recovery column, three condensers, three bottom reboilers, two coolers, one mixer, and one splitter; wherein,

[0031] The side outlet of the side-stream extractive distillation column SEDC1 is connected to the material inlet of the side-stream extractive distillation column SEDC2, and the side outlet of the side-stream extractive distillation column SEDC2 is connected to the material inlet of the extractant recovery column ERC.

[0032] In the three columns—sidestream extractive distillation column SEDC1, sidestream extractive distillation column SEDC2, and extractant recovery column ERC—the extractant collected from the bottom of each column is divided into two streams. One stream is reboiled and circulated through a bottom reboiler, while the other stream converges to mixer M. After mixing in mixer M and splitting by distributor S, the extractant flows through coolers E1 and E2 respectively to the extractant inlets of sidestream extractive distillation columns SEDC1 and SEDC2. The material collected from the top of each column is condensed in a condenser and then divided into two streams: one stream is refluxed, and the other stream is produced as a product.

[0033] Specifically, in this embodiment, both side-stream extractive distillation columns use side-stream sampling. The mixture to be separated can directly enter the next column for separation through the side-stream instead of the bottom of the column. Furthermore, both side-stream extractive distillation columns can produce high-concentration extractant at the bottom for recycling. In contrast, the distillation column without side-stream sampling draws a mixture at approximately 200°C from the bottom of the column, which needs to enter the next column for further separation. Since both extractive distillation columns in this embodiment use side-stream sampling, it is more energy-efficient and saves economic costs.

[0034] In one embodiment, such as Figure 1 As shown, the apparatus for separating a mixture of n-hexane, ethyl acetate, and acetonitrile also includes two intermediate reboilers. The material collected from the side-stream extractive distillation column is divided into two streams: one stream is reboiled and circulated through an intermediate reboiler, and the other stream goes to the material inlet of the next column.

[0035] Specifically, in distillation columns, the required heating is provided by reboilers. In distillation columns with side streams, i.e., side-stream extractive distillation columns, the temperature of the bottom product is close to 200°C, requiring expensive high-pressure steam for heating. In this embodiment, an intermediate reboiler is added. The heating required for the side-stream extractive distillation column is divided into two parts: one part for intermediate heating and one part for bottom heating. The total heating amount does not change significantly. The intermediate reboiler can be heated with low-pressure steam, while the bottom product still uses high-pressure steam, but in reduced quantities. Therefore, by adding two intermediate reboilers in this embodiment, the amount of high-pressure steam used can be reduced, thereby further reducing separation costs and demonstrating significant economic benefits and industrial value.

[0036] Among them, such as Figure 1 As shown, the three bottom reboilers are R1, R2 and R3; the three condensers are C1, C2 and C3; and the two intermediate reboilers are IR1 and IR2.

[0037] The SEDC1 side-stream extractive distillation column has 40-65 trays, with the material inlet located on trays 20-35, the extractant inlet on trays 10-20, and the side-stream outlet on trays 35-55.

[0038] The SEDC2 side-stream extractive distillation column has 55-70 trays, with the material inlet located on trays 30-45, the extractant inlet on trays 5-10, and the side-stream outlet on trays 45-65.

[0039] The number of trays in the extractant recovery tower ERC is 10-25, and the material inlet is located on trays 5-15.

[0040] The separation method of the apparatus for separating a mixture of n-hexane, ethyl acetate, and acetonitrile involved in the above embodiments includes:

[0041] In step S1, a mixture of n-hexane, ethyl acetate, and acetonitrile, along with the first extractant, enters the side-stream extractive distillation column SEDC1 through the material inlet and the extractant inlet, respectively. The vapor at the top of the side-stream extractive distillation column SEDC1 is condensed by condenser C1. Subsequently, a portion of the material is refluxed back into the top of the side-stream extractive distillation column SEDC1, while the other portion is collected as n-hexane product. A portion of the liquid material collected from the bottom of the side-stream extractive distillation column SEDC1 is reboiled in the bottom reboiler R1 and then enters the side-stream extractive distillation column SEDC1, while the other portion is collected as extractant.

[0042] In step S2, the material collected from the side-stream outlet of the side-stream extractive distillation column SEDC1 and the second extractant enter the side-stream extractive distillation column SEDC2 through the material inlet and extractant inlet, respectively. After contact and separation, the vapor at the top of the side-stream extractive distillation column SEDC2 is condensed by condenser C2, and a portion of the material is refluxed back to the top of the side-stream extractive distillation column SEDC2, while the other portion is collected as ethyl acetate product. A portion of the liquid material collected from the bottom of the side-stream extractive distillation column SEDC2 is reboiled by the bottom reboiler R2 and then enters the side-stream extractive distillation column SEDC2, while the other portion is collected as extractant.

[0043] In step S3, the material collected from the side-stream outlet of the side-stream extractive distillation column SEDC2 enters the extractant recovery column ERC for separation. After the vapor at the top of the extractant recovery column ERC is condensed by condenser C3, part of the material is returned to the top of the extractant recovery column ERC, and the other part is collected as acetonitrile product. Part of the liquid material collected from the bottom of the extractant recovery column ERC is reboiled by the bottom reboiler R3 and then enters the extractant recovery column ERC, and the other part is collected as extractant.

[0044] In step S4, the extractant and additional extractant collected from the bottom of the three columns—sidestream extractive distillation column SEDC1, sidestream extractive distillation column SEDC2, and extractant recovery column ERC—are sequentially separated into two streams after passing through mixer M and splitter S. One stream is cooled by cooler E1 and then enters sidestream extractive distillation column SEDC1 for recycling, while the other stream is cooled by cooler E2 and then enters sidestream extractive distillation column SEDC2 for recycling.

[0045] The side-stream extractive distillation column SEDC1 has a pressure of 0.5-0.9 atm, a top temperature of 50-65℃, a bottom temperature of 170-190℃, and a reflux ratio of 0.75-1.50.

[0046] The SEDC2 side-stream extractive distillation column operates at atmospheric pressure, with a top temperature of 75-90℃ and a bottom temperature of 195-220℃; the reflux ratio is 0.55-1.50.

[0047] The extractant recovery tower (ERC) operates at atmospheric pressure, with a top temperature of 80-100℃ and a bottom temperature of 190-220℃; the reflux ratio is 0.15-0.95.

[0048] The extractant can be dimethyl sulfoxide. The molar ratio of the total extractant to the mixture of n-hexane, ethyl acetate, and acetonitrile is 2.35–4.50.

[0049] The molar ratio of the extractant used in the side-stream extractive distillation column SEDC1 to that used in the side-stream extractive distillation column SEDC2 is 0.50-2.50.

[0050] Among them, the total number of trays, material inlet location, extractant inlet, side stream outlet location, and reflux ratio are key factors affecting product purity. In this embodiment, these parameters were obtained through simulation and optimization using ASPENPLUS software.

[0051] The process and effects of the technical solutions involved in the above embodiments will be described in detail below with reference to specific examples.

[0052] Example 1

[0053] The feed flow rate was 100 kmol / h, the temperature was 40℃, the pressure was 1 atm, and the feed contained 25 mol% n-hexane, 55 mol% ethyl acetate, and 20 mol% acetonitrile.

[0054] The SEDC1 sidestream extractive distillation column operates at a pressure of 0.54 atm, has 51 trays, with the feed inlet on the 24th tray, the extractant inlet on the 14th tray, the sidestream outlet on the 39th tray, a reflux ratio of 0.793, an extractant flow rate of 90.24 kmol / h, a sidestream outlet flow rate of 122.97 kmol / h, a top distillate flow rate of 25.025 kmol / h, a top temperature of 50.24℃, and a bottom temperature of 176.09℃.

[0055] The SEDC2 side-stream extractive distillation column operates at a pressure of 1 atm, has 65 trays, with the feed inlet on the 36th tray, the extractant inlet on the 5th tray, the side-stream outlet on the 54th tray, a reflux ratio of 0.575, an extractant flow rate of 143.33 kmol / h, a side-stream outlet flow rate of 47.93 kmol / h, a top distillate flow rate of 55.035 kmol / h, a top temperature of 77.20℃, and a bottom temperature of 196.99℃.

[0056] The extractant recovery tower operates at an ERC pressure of 1 atm, has 14 trays, a material inlet on the 7th tray, a reflux ratio of 0.197, a top distillate flow rate of 19.985 kmol / h, a top temperature of 81.63℃, and a bottom temperature of 192.05℃.

[0057] After separation, the purity of the n-hexane product was 99.9 mol%; the purity of the ethyl acetate product was 99.9 mol%; and the purity of the acetonitrile product was 99.9 mol%.

[0058] Example 2

[0059] The feed flow rate was 100 kmol / h, the temperature was 40℃, the pressure was 1 atm, and the feed contained 25 mol% n-hexane, 55 mol% ethyl acetate, and 20 mol% acetonitrile.

[0060] The SEDC1 side-stream extractive distillation column operates at a pressure of 0.54 atm, has 58 trays, with the feed inlet on tray 26, the extractant inlet on tray 17, the side-stream outlet on tray 41, a reflux ratio of 0.757, an extractant flow rate of 91.71 kmol / h, a side-stream outlet flow rate of 123.20 kmol / h, a top distillate flow rate of 25.025 kmol / h, a top temperature of 50.24℃, and a bottom temperature of 177.09℃.

[0061] The SEDC2 side-stream extractive distillation column operates at a pressure of 1 atm, has 67 trays, with the feed inlet on the 34th tray, the extractant feed on the 7th tray, the side-stream outlet on the 51st tray, a reflux ratio of 0.593, an extractant flow rate of 144.73 kmol / h, a side-stream outlet flow rate of 47.98 kmol / h, a top distillate flow rate of 55.035 kmol / h, a top temperature of 77.19℃, and a bottom temperature of 197.19℃.

[0062] The extractant recovery tower operates at an ERC pressure of 1 atm, has 17 trays, a material inlet on the 6th tray, a reflux ratio of 0.244, a top distillate flow rate of 19.983 kmol / h, a top temperature of 81.63℃, and a bottom temperature of 192.35℃.

[0063] After separation, the purity of the n-hexane product was 99.9 mol%; the purity of the ethyl acetate product was 99.9 mol%; and the purity of the acetonitrile product was 99.9 mol%.

[0064] Example 3

[0065] The feed flow rate was 100 kmol / h, the temperature was 40℃, the pressure was 1 atm, and the feed contained 25 mol% n-hexane, 55 mol% ethyl acetate, and 20 mol% acetonitrile.

[0066] The SEDC1 side-stream extractive distillation column operates at a pressure of 0.54 atm, has 46 trays, with the feed inlet on the 25th tray, the extractant inlet on the 16th tray, the side-stream outlet on the 37th tray, a reflux ratio of 0.815, an extractant flow rate of 90.66 kmol / h, a side-stream outlet flow rate of 122.62 kmol / h, a top distillate flow rate of 25.025 kmol / h, a top temperature of 50.23℃, and a bottom temperature of 175.36℃.

[0067] The SEDC2 side-stream extractive distillation column operates at a pressure of 1 atm, has 61 trays, with the feed inlet on the 32nd tray, the extractant inlet on the 7th tray, the side-stream outlet on the 50th tray, a reflux ratio of 0.633, an extractant flow rate of 142.35 kmol / h, a side-stream outlet flow rate of 47.25 kmol / h, a top distillate flow rate of 55.035 kmol / h, a top temperature of 77.19℃, and a bottom temperature of 196.63℃.

[0068] The extractant recovery tower operates at an ERC pressure of 1 atm, has 14 trays, feeds from the 6th tray, has a reflux ratio of 0.190, a top distillate flow rate of 19.979 kmol / h, a top temperature of 81.64℃, and a bottom temperature of 192.04℃.

[0069] After separation, the purity of the n-hexane product was 99.9 mol%; the purity of the ethyl acetate product was 99.9 mol%; and the purity of the acetonitrile product was 99.9 mol%.

[0070] Comparative Example 1

[0071] The feed flow rate was 100 kmol / h, the temperature was 40℃, the pressure was 1 atm, and the feed contained 25 mol% n-hexane, 55 mol% ethyl acetate, and 20 mol% acetonitrile.

[0072] The SEDC1 side-stream extractive distillation column operates at a pressure of 0.54 atm, has 35 trays, with the feed inlet on the 15th tray, the extractant inlet on the 5th tray, the side-stream outlet on the 30th tray, a reflux ratio of 0.552, an extractant flow rate of 92.36 kmol / h, a side-stream outlet flow rate of 120.88 kmol / h, a top distillate flow rate of 25.025 kmol / h, a top temperature of 50.25℃, and a bottom temperature of 128.24℃.

[0073] The SEDC2 side-stream extractive distillation column operates at a pressure of 1 atm, has 50 trays, with the feed inlet on the 25th tray, the extractant inlet on the 3rd tray, the side-stream outlet on the 40th tray, a reflux ratio of 0.725, an extractant flow rate of 140.55 kmol / h, a side-stream outlet flow rate of 48.67 kmol / h, a top distillate flow rate of 55.035 kmol / h, a top temperature of 77.06℃, and a bottom temperature of 195.61℃.

[0074] The extractant recovery tower operates at an ERC pressure of 1 atm, has 8 trays, feeds from the 4th tray, has a reflux ratio of 0.105, a top distillate flow rate of 19.975 kmol / h, a top temperature of 90.10℃, and a bottom temperature of 191.36℃.

[0075] After separation, the purity of the n-hexane product was 99.8 mol%; the purity of the ethyl acetate product was 97.4 mol%; and the purity of the acetonitrile product was 77.2 mol%.

[0076] Comparative Example 2

[0077] The feed flow rate was 100 kmol / h, the temperature was 40℃, the pressure was 1 atm, and the feed contained 25 mol% n-hexane, 55 mol% ethyl acetate, and 20 mol% acetonitrile.

[0078] The SEDC1 sidestream extractive distillation column operates at a pressure of 0.54 atm, has 38 trays, with the feed inlet on the 18th tray, the extractant inlet on the 7th tray, the sidestream outlet on the 33rd tray, a reflux ratio of 0.634, an extractant flow rate of 93.88 kmol / h, a sidestream outlet flow rate of 123.65 kmol / h, a top distillate flow rate of 25.025 kmol / h, a top temperature of 50.25℃, and a bottom temperature of 164.79℃.

[0079] The SEDC2 side-stream extractive distillation column operates at a pressure of 1 atm, has 33 trays, with the feed inlet on the 28th tray, the extractant feed on the 3rd tray, the side-stream outlet on the 43rd tray, a reflux ratio of 1.652, an extractant flow rate of 143.32 kmol / h, a side-stream outlet flow rate of 50.66 kmol / h, a top distillate flow rate of 55.035 kmol / h, a top temperature of 77.24℃, and a bottom temperature of 195.89℃.

[0080] The extractant recovery tower operates at an ERC pressure of 1 atm, has 9 trays, with the material inlet located on the 5th tray. The reflux ratio is 1.262, the top distillate flow rate is 19.968 kmol / h, the top temperature is 82.98℃, and the bottom temperature is 191.55℃.

[0081] After separation, the purity of the n-hexane product was 91.8 mol%; the purity of the ethyl acetate product was 93.8 mol%; and the purity of the acetonitrile product was 95.3 mol%.

[0082] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for separating a mixture of n-hexane, ethyl acetate, and acetonitrile, characterized in that, The process is based on an apparatus for separating a mixture of n-hexane, ethyl acetate, and acetonitrile. The apparatus includes two side-stream extractive distillation columns, one extractant recovery column, three condensers, three bottom reboilers, two coolers, one mixer, and one splitter. The side outlet of the side-stream extractive distillation column SEDC1 is connected to the material inlet of the side-stream extractive distillation column SEDC2, and the side outlet of the side-stream extractive distillation column SEDC2 is connected to the material inlet of the extractant recovery column ERC. In the three columns—sidestream extractive distillation column SEDC1, sidestream extractive distillation column SEDC2, and extractant recovery column ERC—the extractant collected from the bottom of each column is divided into two streams. One stream is reboiled and circulated through a bottom reboiler, while the other stream converges to the mixer. After being mixed in the mixer and split by the distributor, the extractant then passes through coolers E1 and E2 respectively, reaching the extractant inlets of sidestream extractive distillation columns SEDC1 and SEDC2. The material collected from the top of each column is condensed in a condenser and then divided into two streams: one stream is refluxed, and the other stream is produced as a product. It also includes two intermediate reboilers. The material collected from the side-stream outlet of each side-stream extractive distillation column is divided into two paths: one path is reboiled and circulated through an intermediate reboiler, and the other path reaches the material inlet of the next column. The SEDC1 side-stream extractive distillation column has 40-65 trays, with the material inlet located on trays 20-35, the extractant inlet on trays 10-20, and the side-stream outlet on trays 35-55. The SEDC2 side-stream extractive distillation column has 55-70 trays, with the material inlet located on trays 30-45, the extractant inlet on trays 5-10, and the side-stream outlet on trays 45-65. The number of trays in the extractant recovery tower ERC is 10-25, and the material inlet is located on the 5th-15th tray; The methods include: In step S1, a mixture of n-hexane, ethyl acetate, and acetonitrile, along with the first extractant, enters the side-stream extractive distillation column SEDC1 through the material inlet and the extractant inlet, respectively. The vapor at the top of the side-stream extractive distillation column SEDC1 is condensed by condenser C1. Subsequently, a portion of the material is refluxed back into the top of the side-stream extractive distillation column SEDC1, while the other portion is collected as n-hexane product. A portion of the liquid material collected from the bottom of the side-stream extractive distillation column SEDC1 is reboiled in the bottom reboiler R1 and then enters the side-stream extractive distillation column SEDC1, while the other portion is collected as extractant. In step S2, the material collected from the side-stream outlet of the side-stream extractive distillation column SEDC1 and the second extractant enter the side-stream extractive distillation column SEDC2 through the material inlet and extractant inlet, respectively. After contact and separation, the vapor at the top of the side-stream extractive distillation column SEDC2 is condensed by condenser C2, and a portion of the material is refluxed back to the top of the side-stream extractive distillation column SEDC2, while the other portion is collected as ethyl acetate product. A portion of the liquid material collected from the bottom of the side-stream extractive distillation column SEDC2 is reboiled by the bottom reboiler R2 and then enters the side-stream extractive distillation column SEDC2, while the other portion is collected as extractant. In step S3, the material collected from the side-stream outlet of the side-stream extractive distillation column SEDC2 enters the extractant recovery column ERC for separation. After the vapor at the top of the extractant recovery column ERC is condensed by condenser C3, part of the material is returned to the top of the extractant recovery column ERC, and the other part is collected as acetonitrile product. Part of the liquid material collected from the bottom of the extractant recovery column ERC is reboiled by the bottom reboiler R3 and then enters the extractant recovery column ERC, and the other part is collected as extractant. In step S4, the extractant collected from the bottom of the three columns—sidestream extractive distillation column SEDC1, sidestream extractive distillation column SEDC2, and extractant recovery column ERC—along with additional supplementary extractant, is sequentially separated into two streams after passing through mixer M and splitter S. One stream is cooled by cooler E1 and then recycled into sidestream extractive distillation column SEDC1, while the other stream is cooled by cooler E2 and then recycled into sidestream extractive distillation column SEDC2. The pressure of sidestream extractive distillation column SEDC1 is 0.5–0.9 atm; the extractant is dimethyl sulfoxide. The reflux ratio of the side-stream extractive distillation column SEDC1 is 0.75–1.50; the reflux ratio of the side-stream extractive distillation column SEDC2 is 0.55–1.50; and the reflux ratio of the extractant recovery column ERC is 0.15–0.

95.

2. The method for separating a mixture of n-hexane, ethyl acetate, and acetonitrile according to claim 1, characterized in that, The top temperature of the side-stream extractive distillation column SEDC1 is 50-65℃, and the bottom temperature is 170-190℃. The side-stream extractive distillation column SEDC2 operates at atmospheric pressure, with a top temperature of 75–90°C and a bottom temperature of 195–220°C. The extractant recovery tower ERC operates at atmospheric pressure, with a top temperature of 80–100°C and a bottom temperature of 190–220°C.

3. The method for separating a mixture of n-hexane, ethyl acetate, and acetonitrile according to claim 1, characterized in that, The total amount of the extractant is in a molar ratio of 2.35 to 4.50 to the mixture of hexane, ethyl acetate and acetonitrile.

4. The method for separating a mixture of n-hexane, ethyl acetate, and acetonitrile according to claim 1, characterized in that, The molar ratio of extractant usage in side-stream extractive distillation column SEDC1 to that in side-stream extractive distillation column SEDC2 is 0.50–2.50.

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