Continuous extractive distillation separation method for p-xylene-butanol mixture
By using sulfolane, N-methylpyrrolidone, and dimethyl sulfoxide as extractants, a continuous extractive distillation method was developed, which solved the problem of separating the azeotropic mixture of p-xylene and butanol. This method achieved efficient and environmentally friendly separation, and significantly improved product purity and extractant recovery efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SINOMA INT ENVIRONMENTAL ENG (BEIJING) CO LTD
- Filing Date
- 2026-02-03
- Publication Date
- 2026-05-12
AI Technical Summary
Existing technologies are insufficient for efficiently separating the azeotropic mixture of p-xylene and butanol. Furthermore, traditional separation methods are energy-intensive and use highly toxic solvents, making it difficult to meet environmental protection requirements and product purity demands.
Using sulfolane, N-methylpyrrolidone, and dimethyl sulfoxide as extractants, a continuous extractive distillation method was employed to establish an "extraction tower-solvent recovery tower" process. The relative volatility of the extractants was controlled, and the solvent was recovered in a closed loop in the desorption section, thereby achieving efficient separation of xylene and butanol.
It achieves efficient separation of xylene-butanol mixtures, with a product purity of over 99.9%. The extractant can be recycled, reducing energy consumption and waste emissions, and meeting the requirements of green and low-carbon production.
Smart Images
Figure CN122010686A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of separation technology, specifically relating to a continuous extractive distillation separation method for a mixture of p-xylene and butanol. Background Technology
[0002] p-Xylene (PX) and butanol (n-BuOH) are important basic chemical raw materials. PX is a core monomer in the polyester industry, with a global annual demand exceeding 70 million tons, and can be used to produce terephthalic acid (PTA). n-BuOH can be used as a solvent, with an annual consumption exceeding 12 million tons. The two are often found in by-product systems such as petroleum refining, forming a 30%-70% mixed system.
[0003] PX and n-BuOH form a minimum azeotrope under normal pressure with an azeotropic temperature of 99.5℃ and an azeotropic composition (mol%) of PX 34.8% / n-BuOH 65.2%. Conventional distillation cannot effectively separate them, and special distillation or coupled separation techniques are required. Therefore, it is difficult to achieve efficient separation.
[0004] Current environmental and regulatory requirements in industrial production influence the selection of separation technologies for PX-n-BuOH azeotropic systems: In terms of carbon emissions and energy consumption, traditional high-energy-consuming separation technologies are facing elimination, while low-energy-consuming extraction and distillation are preferred; in terms of VOCs emission control, to ensure that n-BuOH emissions meet standards, the recovery efficiency of extractants must be increased to over 99.8%; in terms of solvent environmental friendliness, relevant regulations prohibit highly toxic solvents, prompting the application of low-toxicity and recyclable solvents; in terms of product purity, separation technologies must meet the requirements of polyester-grade PX purity ≥99.7% and industrial-grade n-BuOH purity ≥99.5% while controlling impurity residues. Summary of the Invention
[0005] The purpose of this invention is to provide a continuous extraction and distillation separation method for a mixture of xylene and butanol, which effectively overcomes the technical drawbacks of the prior art.
[0006] To achieve the above or other objectives, the present invention is implemented through the following technical solutions.
[0007] A continuous extractive distillation separation method for a xylene-butanol mixture, using any two of sulfolane, N-methylpyrrolidone, and dimethyl sulfoxide as extractants.
[0008] Furthermore, the extractant is a mixture of sulfolane and N-methylpyrrolidone, or a mixture of N-methylpyrrolidone and dimethyl sulfoxide, or a mixture of dimethyl sulfoxide and sulfolane.
[0009] More preferably, when the extractant is a mixture of sulfolane and N-methylpyrrolidone, the mass ratio of sulfolane to N-methylpyrrolidone is 1:(0.4~1.8).
[0010] More preferably, when the extractant is a mixture of N-methylpyrrolidone and dimethyl sulfoxide, the mass ratio of N-methylpyrrolidone to dimethyl sulfoxide is 1:(0.4~1.8). More preferably, when the extractant is a mixture of dimethyl sulfoxide and sulfolane, the mass ratio of dimethyl sulfoxide to sulfolane is 1:(0.4~1.8).
[0011] Furthermore, it includes the following steps: S1. The mixed feed liquid of p-xylene and butanol is added from the feed inlet of the extraction tower, and the extractant is added from the extractant inlet of the extraction tower for extractive distillation. The vapor rich in butanol is condensed into liquid at the top of the tower by a condenser. Part of it is collected as butanol product, and the other part is returned to the tower as condensate. The bottom product is a mixture containing extractant and p-xylene. S2. The bottom product of the extraction tower is introduced into the feed inlet of the solvent recovery tower. After distillation, the vapor rich in p-xylene rises to the top of the tower and is condensed. The p-xylene product is collected from the top of the tower and introduced into the product tank for storage. The extractant is discharged from the bottom of the solvent recovery tower. S3. The extractant discharged from the bottom of the solvent recovery tower is introduced into the upper part of the extraction tower and recycled.
[0012] Furthermore, the mass ratio of the p-xylene-butanol mixed feed solution to the extractant is 1:(2.2~3.2).
[0013] In this invention, the ratio of p-xylene to butanol in the p-xylene-butanol mixed feed solution can be arbitrary. Preferably, the mass percentage of p-xylene to butanol in the p-xylene-butanol mixed feed solution is (10~40):(60~90).
[0014] Furthermore, the theoretical plate number of the extraction column is 20~32, and the reflux ratio is (1.2~2.6):1.
[0015] Furthermore, the top temperature of the extraction column is 115~120℃, the bottom temperature is 145~165℃, the top pressure is 0.1 MPa, and the total pressure drop of the extraction column is 7~10 kPa.
[0016] Furthermore, the number of feed trays for the extractant added to the extraction tower is 2 to 8, and the number of feed trays for the mixed feed liquid added to the extraction tower is 15 to 30.
[0017] Furthermore, the solvent recovery tower has a theoretical plate number of 12~22, a reflux ratio of (0.6~1.2):1, a top temperature of 135~145℃, a bottom temperature of 165~180℃, and a total pressure drop of 7~10 kPa.
[0018] Furthermore, the number of feed trays in the solvent recovery tower is 7 to 15. The number of trays in the solvent recovery tower refluxed to the extraction tower is 2 to 8.
[0019] In summary, this invention provides a continuous extractive distillation method for a p-xylene-butanol mixture. It establishes a continuous extractive distillation process consisting of an extraction tower and a solvent recovery tower. By utilizing the extractant to control relative volatility and a closed-loop solvent recovery section, it can reduce emissions of waste gas, wastewater, and solid waste while ensuring product purity and stability, aligning with the technological direction of green, low-carbon, and large-scale production. The continuous extractive distillation separation method provided by this invention uses sulfolane, N-methylpyrrolidone, and dimethyl sulfoxide as extractants, which can effectively separate p-xylene-butanol mixtures. The extractants selected in this invention have high separation efficiency, are easy to regenerate, and are environmentally friendly, enabling efficient separation of azeotropic mixtures. Using the method of this invention, the mass fraction of butanol after separation can be ≥99.9%. Attached Figure Description
[0020] Figure 1 This is a schematic diagram of the continuous extractive distillation process for separating a pentafluoroethane-chloropentafluoroethane azeotropic mixture according to the present invention. Component labels are as follows: 1. Extraction column; 11. Feed inlet; 12. Extractant inlet; 13. Top outlet of extraction column; 14. Bottom outlet of extraction column; 2. Solvent recovery column; 21. Inlet of solvent recovery column; 22. Top outlet of solvent recovery column; 23. Bottom outlet of solvent recovery column; 3. Condenser; 4. Reboiler; 5. Heat exchanger. Detailed Implementation
[0021] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.
[0022] See Figure 1 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.
[0023] It should be noted that the terms such as "upper", "lower", "left", "right", "middle" and "one" used in this specification are only for clarity of description and are not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered as part of the scope of the invention.
[0024] The present invention protects a continuous extractive distillation separation method for a mixture of xylene and butanol, which uses any two of sulfolane, N-methylpyrrolidone, and dimethyl sulfoxide as extractants.
[0025] In one example of the present invention, when the extractant is a mixture of sulfolane and N-methylpyrrolidone, the mass ratio of sulfolane to N-methylpyrrolidone is 1:(0.4~1.8).
[0026] In one example of the present invention, when the extractant is a mixture of N-methylpyrrolidone and dimethyl sulfoxide, the mass ratio of N-methylpyrrolidone to dimethyl sulfoxide is 1:(0.4~1.8).
[0027] In one example of the present invention, when the extractant is a mixture of dimethyl sulfoxide and sulfolane, the mass ratio of dimethyl sulfoxide to sulfolane is 1:(0.4~1.8).
[0028] like Figure 1 As shown, the continuous extractive distillation method of the present invention adopts a continuous extractive distillation process of "extraction tower - solvent recovery tower", including an extraction tower 1 and a solvent recovery tower 2. The extraction tower 1 includes a raw material inlet 11 located in the middle of the extraction tower 1, an extractant inlet 12 located in the upper part of the extraction tower 1, an extraction tower top outlet 13 located at the top of the extraction tower 1, and an extraction tower bottom outlet 14 located at the bottom of the extraction tower 1. The solvent recovery tower 2 includes a solvent recovery tower inlet 21 located in the upper part of the solvent recovery tower 2, a solvent recovery tower top outlet 22 located at the top of the solvent recovery tower 2, and a solvent recovery tower bottom outlet 23 located at the bottom of the solvent recovery tower 2. The bottom outlet 14 of the extraction tower is connected to the inlet 21 of the solvent recovery tower via a pipeline; the bottom outlet 23 of the solvent recovery tower is connected to the inlet 12 of the extractant via a pipeline.
[0029] In one embodiment of the present invention, a condenser 3 is connected to the top outlet 13 of the extraction column via a pipeline. By providing the condenser 3, the collected component vapor at the top outlet 13 of the extraction column can be condensed, thereby collecting the product.
[0030] In one embodiment of the present invention, the bottom outlet 14 of the extraction tower is connected to a reboiler 4 via a pipeline, and the reboiler 4 is connected to the inlet 21 of the solvent recovery tower via a pipeline.
[0031] In one example of the present invention, the solvent recovery tower top outlet 22 at the top of the solvent recovery tower 2 is connected to the condenser 3 via a pipeline.
[0032] In one example of the present invention, a heat exchanger 5 is also connected between the extraction tower bottom outlet 14 and the solvent recovery tower inlet 21 via a pipeline.
[0033] In one example of the present invention, a heat exchanger 5 is also connected between the solvent recovery tower bottom outlet 23 and the extractant inlet 12 via a pipeline.
[0034] The continuous extractive distillation separation method for a mixture of p-xylene and butanol of the present invention includes the following steps: S1. The p-xylene-butanol mixed feed liquid is added from the middle feed inlet 11 of the extraction tower 1, and the extractant is added from the upper extractant inlet 12 of the extraction tower 1 for extractive distillation. The vapor rich in butanol is condensed into liquid at the top of the tower by a condenser. Part of it is collected as butanol product from the top outlet 13 of the extraction tower, and the other part is returned to the tower as condensate. The bottom product is a mixture containing extractant and p-xylene. S2. The bottom product of the extraction tower 1 is introduced into the feed inlet 21 of the solvent recovery tower in the middle of the solvent recovery tower 2 through the bottom outlet 14 of the extraction tower. After distillation, the vapor rich in p-xylene rises to the top of the tower and is condensed. The p-xylene product is collected from the top outlet 22 of the solvent recovery tower and introduced into the product tank for storage. The extractant is discharged from the bottom outlet 23 of the solvent recovery tower. S3. The extractant discharged from the solvent recovery tower bottom outlet 23 is introduced into the upper part of the extraction tower 1 and enters the extraction tower 1 through the extractant inlet 12 for recycling.
[0035] In one example of the present invention, the mass ratio of the p-xylene-butanol mixed feed solution to the extractant is 1:(2.2~3.2).
[0036] In this invention, the ratio of p-xylene to butanol in the p-xylene-butanol mixed feed solution can be arbitrary. In one example of this invention, the mass percentage of p-xylene to butanol in the p-xylene-butanol mixed feed solution is (10~40):(60~90).
[0037] In one example of the present invention, in S1, the theoretical number of trays in extraction column 1 is 20-32, the reflux ratio is (1.2-2.6):1, the top temperature is 115-120°C, the bottom temperature is 145-165°C, the top pressure is 0.1 MPa, and the total pressure drop of the extraction column is 7-10 kPa. The number of trays to which the extractant is added to the feed tray of extraction column 1, i.e., the number of trays at the extractant inlet 12, is 2-8, and the number of trays to which the mixed feed liquid is added to the feed tray of extraction column 1, i.e., the number of trays at the feed inlet 11, is 15-30.
[0038] In one example of the present invention, the solvent recovery tower 2 has a theoretical number of trays of 12-22, a reflux ratio of (0.6-1.2):1, a top temperature of 135-145°C, a bottom temperature of 165-180°C, and a total pressure drop of 7-10 kPa. The number of feed trays of the solvent recovery tower 2, i.e., the number of trays at the solvent recovery tower inlet 21, is 7-15. The number of trays refluxed from the solvent recovery tower to the extraction tower is 2-8.
[0039] The technical solution of the present invention will be described in detail below through several specific embodiments. Unless otherwise stated, the raw materials and reagents used in the following embodiments are commercially available products, or can be prepared by conventional methods in the art. Unless otherwise specified, the detection methods used in the embodiments of the present invention are conventional detection methods in the industry.
[0040] Example 1
[0041] A continuous extractive distillation separation method for a xylene-butanol mixture, employing as follows: Figure 1 The process flow shown uses N-methylpyrrolidone and dimethyl sulfoxide as extractants in a mass ratio of 1:1.1 at a rate of 3200 kg / h. The mixed feed solution has a throughput of 1000 kg / h and consists of p-xylene (32 wt%) and butanol (68 wt%). The separation method specifically includes the following steps: S1. A mixed feed solution of p-xylene and butanol is added from the middle feed inlet 11 of extraction column 1, and the extractant is added from the upper extractant inlet 12 of extraction column 1 for extractive distillation. The butanol-rich vapor is condensed into liquid at the top of the column by a condenser. Part of it is collected as butanol product from the top outlet 13 of the extraction column, and the other part is refluxed into the column as condensate. The bottom product is a mixture containing extractant and p-xylene. The extraction column 1 has 24 trays. The extractant inlet 12 is located on the 6th tray of the extraction column 1, the feed inlet 11 is located on the 15th tray of the extraction column 1, the reflux ratio is set to 1.5:1, the top temperature is 120℃, the bottom temperature is 145℃, the pressure drop of the extraction column 1 is 7 kPa, and the butanol product collected from the top outlet 13 of the extraction column has a purity >99.99%. S2. The bottom product of extraction tower 1 is introduced into the middle solvent recovery tower inlet 21 of solvent recovery tower 2 through extraction tower bottom outlet 14. After rectification, the vapor rich in p-xylene rises to the top of the tower and condenses. The p-xylene product is collected from the top outlet 22 of the solvent recovery tower and introduced into the product tank for storage, with a purity > 99.99%. The extractant is discharged from the bottom outlet 23 of the solvent recovery tower. The solvent recovery tower 2 has 18 trays. The solvent recovery tower inlet 21 is on the 9th tray of the solvent recovery tower 2. The reflux ratio is 0.9:1. The top temperature of the solvent recovery tower 2 is 135℃ and the bottom temperature is 175℃. When the pressure drop of the solvent recovery tower 2 is 7kPa, the mass fraction of the bottom extractant is > 99.99% and it is refluxed at the 5th tray as a supplement to the solvent. The top distillate is output to the product tank for storage. S3. The extractant discharged from the solvent recovery tower bottom outlet 23 is introduced into the upper part of the extraction tower 1 and enters the extraction tower 1 through the extractant inlet 12 for recycling.
[0042] Example 2
[0043] The separation method in this embodiment is the same as in Embodiment 1, except that: in this embodiment, the extractant is N-methylpyrrolidone and dimethyl sulfoxide, with a dosage of 3200 kg / h and a mass ratio of 1:1.2; the mixed feed liquid processing capacity is 1000 kg / h, and the mixed feed liquid composition is p-xylene (30 wt%) and butanol (70 wt%); the number of trays in extraction column 1 is 28, the extractant inlet 12 is located on the 5th tray of extraction column 1, the feed inlet 11 is located on the 16th tray of extraction column 1, the reflux ratio is set to 1.6:1, the column top temperature is 115°C, the column bottom temperature is 155°C, the column pressure drop is 7 kPa, and the butanol product collected from the top outlet 13 of the extraction column has a purity of >99.99%.
[0044] Solvent recovery tower 2 has 20 trays. The feed inlet 21 is located on the 10th tray of solvent recovery tower 2. The reflux ratio is 1.1:1. The top temperature is 140℃, the bottom temperature is 165℃, and the pressure drop is 8 kPa. The top outlet 22 of the solvent recovery tower collects paraxylene with a purity >99.99%, and the bottom extractant has a mass fraction >99.99% and is refluxed at the 6th tray as a supplement to the solvent. The top distillate is discharged to the product tank for storage.
[0045] Example 3
[0046] The separation method in this embodiment is the same as in Embodiment 1, except that: in this embodiment, the extractant used is dimethyl sulfoxide and sulfolane, with a dosage of 3200 kg / h and a mass ratio of 1:1.3; the mixed feed liquid processing capacity is 1000 kg / h, and the mixed feed liquid composition is p-xylene (34 wt%) and butanol (66 wt%). Extraction column 1 has 26 trays, a pressure drop of 8 kPa, an extractant inlet 12 located on the 5th tray of extraction column 1, a feed inlet 11 located on the 17th tray of extraction column 1, a reflux ratio set to 2:1, a top temperature of 120°C, a bottom temperature of 165°C, and the butanol product collected from the top outlet 13 of the extraction column has a purity >99.99%. Solvent recovery tower 2 has 20 trays. The feed inlet 21 is located on the 9th tray of solvent recovery tower 2. The reflux ratio is 1.2:1. The top temperature is 145℃, the bottom temperature is 180℃, and the pressure drop is 9 kPa. The top outlet 22 of the solvent recovery tower collects paraxylene with a purity >99.99%, and the bottom extractant has a mass fraction >99.99% and is refluxed at the 7th tray as a supplement to the solvent. The top distillate is discharged to the product tank for storage.
[0047] Example 4
[0048] The separation method in this embodiment is the same as in Embodiment 1, except that: in this embodiment, the extractant is sulfolane and N-methylpyrrolidone, with a dosage of 3200 kg / h and a mass ratio of 1:0.4; the mixed feed liquid processing capacity is 1000 kg / h, and the mixed feed liquid composition is p-xylene (35 wt%) and butanol (65 wt%). Extraction column 1 has 26 trays, a pressure drop of 7 kPa, an extractant inlet 12 located on the 5th tray of extraction column 1, a feed inlet 11 located on the 18th tray of extraction column 1, a reflux ratio set to 1.6:1, a top temperature of 120°C, a bottom temperature of 150°C, and the butanol obtained at the top of extraction column 1 has a purity >99.99%. Solvent recovery tower 2 has 22 trays. The feed inlet 21 is located on the 10th tray of solvent recovery tower 2. The reflux ratio is 1:1. The pressure drop of solvent recovery tower 2 is 8 kPa. The top temperature is 140℃ and the bottom temperature is 170℃. The top outlet 22 of solvent recovery tower collects paraxylene with a purity >99.99%. The bottom extractant has a mass fraction >99.99% and is refluxed at the 6th tray as a supplement to the solvent. The top distillate is discharged to the product tank for storage.
[0049] Example 5
[0050] The separation method in this embodiment is the same as in Embodiment 1, except that: in this embodiment, the extractant used is sulfolane and N-methylpyrrolidone, with a dosage of 3200 kg / h and a mass ratio of 1:1.8; the mixed feed liquid processing capacity is 1000 kg / h, and the mixed feed liquid composition is p-xylene (35 wt%) and butanol (65 wt%). The butanol obtained at the top of extraction column 1 has a purity >99.99%. The p-xylene with a purity >99.99% is collected from the top outlet 22 of the solvent recovery column, and the extractant mass fraction at the bottom of solvent recovery column 2 is >99.99% and is refluxed at the 6th tray as a solvent replenishment. The top distillate is discharged to the product tank for storage.
[0051] Example 6
[0052] The separation method in this embodiment is the same as in Embodiment 1, except that: in this embodiment, the extractant used is sulfolane and N-methylpyrrolidone, with a dosage of 3200 kg / h and a mass ratio of 1:1.2; the mixed feed liquid processing capacity is 1000 kg / h, and the mixed feed liquid composition is p-xylene (35 wt%) and butanol (65 wt%). The butanol obtained at the top of extraction column 1 has a purity >99.99%. The p-xylene with a purity >99.99% is collected from the top outlet 22 of the solvent recovery column, and the extractant mass fraction at the bottom of solvent recovery column 2 is >99.99% and is refluxed at the 6th tray as a solvent replenishment. The top distillate is discharged to the product tank for storage.
[0053] Example 7
[0054] The separation method in this embodiment is the same as in Embodiment 1, except that: in this embodiment, the extractant used is dimethyl sulfoxide and N-methylpyrrolidone, with a dosage of 3200 kg / h and a mass ratio of 1:1.8; the mixed feed liquid processing capacity is 1000 kg / h, and the mixed feed liquid composition is p-xylene (30 wt%) and butanol (70 wt%). The butanol obtained at the top of extraction column 1 has a purity >99.99%. The p-xylene with a purity >99.99% is collected from the top outlet 22 of the solvent recovery column, and the extractant mass fraction at the bottom of solvent recovery column 2 is >99.99% and refluxed at the 6th tray as a solvent replenishment. The top distillate is discharged to the product tank for storage.
[0055] Example 8
[0056] The separation method in this embodiment is the same as in Embodiment 1, except that: in this embodiment, the extractant is dimethyl sulfoxide and N-methylpyrrolidone, with a dosage of 2500 kg / h and a mass ratio of 1:0.4; the mixed feed liquid processing capacity is 1000 kg / h, and the mixed feed liquid composition is p-xylene (33 wt%) and butanol (67 wt%). The butanol obtained at the top of extraction column 1 has a purity >99.99%. The p-xylene with a purity >99.99% is collected from the top outlet 22 of the solvent recovery column, and the extractant mass fraction at the bottom of solvent recovery column 2 is >99.99% and is refluxed at the 6th tray as a solvent replenishment. The top distillate is discharged to the product tank for storage.
[0057] Example 9
[0058] The separation method in this embodiment is the same as in Embodiment 1, except that: in this embodiment, the extractant used is dimethyl sulfoxide and sulfolane, with a dosage of 2200 kg / h and a mass ratio of 1:0.4; the mixed feed liquid processing capacity is 1000 kg / h, and the mixed feed liquid composition is p-xylene (33 wt%) and butanol (67 wt%). The butanol obtained at the top of extraction column 1 has a purity >99.99%. The p-xylene with a purity >99.99% is collected from the top outlet 22 of the solvent recovery column, and the extractant mass fraction at the bottom of solvent recovery column 2 is >99.99% and is refluxed at the 6th tray as a solvent replenishment. The top distillate is discharged to the product tank for storage.
[0059] Example 10
[0060] The separation method in this embodiment is the same as in Embodiment 1, except that: in this embodiment, the extractant used is dimethyl sulfoxide and sulfolane, with a dosage of 3000 kg / h and a mass ratio of 1:1.8; the mixed feed liquid processing capacity is 1000 kg / h, and the mixed feed liquid composition is p-xylene (33 wt%) and butanol (67 wt%). The butanol obtained at the top of extraction column 1 has a purity >99.99%. The p-xylene with a purity >99.99% is collected from the top outlet 22 of the solvent recovery column, and the extractant mass fraction at the bottom of solvent recovery column 2 is >99.99% and is refluxed at the 6th tray as a solvent replenishment. The top distillate is discharged to the product tank for storage.
[0061] Comparative Example 1 The separation method in Comparative Example 1 is the same as in Example 1, except that: sulfolane was used as the extractant in Comparative Example 1 at a rate of 3200 kg / h; the feed rate was 1000 kg / h, and the feed composition was p-xylene (34 wt%) and butanol (66 wt%). Extraction column 1 had 30 trays, with the extractant inlet on the 5th tray and the feed inlet on the 22nd tray. The reflux ratio was set to 1.8:1, and the obtained butanol purity was 95.7%. Solvent recovery column 2 had 20 trays, with the H-T1 stream inlet located at the 8th tray. The reflux ratio was 0.8:1, and the bottom extractant mass fraction was 80.9%, which was refluxed at the 6th tray as a solvent replenishment.
[0062] Comparative Example 2 The separation method in Comparative Example 2 is the same as in Example 1, except that: in Comparative Example 2, dimethyl sulfoxide (DMSO) is used as the extractant at a rate of 2500 kg / h; the feed rate is 1000 kg / h, and the feed composition is p-xylene (32 wt%) and butanol (68 wt%). Extraction column 1 has 28 trays, with the extractant feed located on the 4th tray and the feed material on the 20th tray. The reflux ratio is set to 1.6:1, and the obtained butanol has a purity of 96.3%. Solvent recovery column 2 has 18 trays, with the H-T1 feed stream located at the 7th tray of the solvent recovery column at inlet 21. The reflux ratio is 1:1, and the bottom extractant mass fraction is 75.7%, which is then refluxed at the 5th tray as a solvent replenishment.
[0063] Comparative Example 3 The separation method in Comparative Example 3 was the same as in Example 1, except that: the extractant used in Comparative Example 3 was N-methylpyrrolidone, with a dosage of 3200 kg / h; the feed rate was 1000 kg / h, and the feed composition was p-xylene (32 wt%) and butanol (68 wt%). Extraction column 1 had 28 trays, with the extractant inlet on the 4th tray and the feed inlet on the 20th tray. The reflux ratio was set to 1.6:1, and the obtained butanol purity was 95.5%. Solvent recovery column 2 had 18 trays, with the H-T1 stream inlet located at the 7th tray of solvent recovery column 2. The reflux ratio was 1:1, and the bottom extractant mass fraction was 78.9%, which was refluxed at the 5th tray as a solvent replenishment.
[0064] In summary, it can be seen that the extractant used in this invention, a mixture of any two of sulfolane, N-methylpyrrolidone, and dimethyl sulfoxide, can effectively separate the p-xylene-butanol azeotropic mixture. The p-xylene-butanol azeotropic mixture exhibits high separation efficiency, easy regeneration, and environmental friendliness, enabling highly efficient separation of the azeotropic mixture. Through the extractive distillation separation method of this invention, the mass fraction of butanol after separation can reach ≥99.9%, and the mass fraction of the extractant is >99.99%, allowing for recycling.
[0065] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.
Claims
1. A continuous extractive distillation method for separating a mixture of p-xylene and butanol, characterized in that, Any two of sulfolane, N-methylpyrrolidone, and dimethyl sulfoxide can be used as extractants.
2. The preparation method according to claim 1, characterized in that, The extractant is a mixture of sulfolane and N-methylpyrrolidone, with a mass ratio of sulfolane to N-methylpyrrolidone of 1:(0.4~1.8).
3. The preparation method according to claim 1, characterized in that, The extractant is a mixture of N-methylpyrrolidone and dimethyl sulfoxide, with a mass ratio of N-methylpyrrolidone to dimethyl sulfoxide of 1:(0.4~1.8).
4. The preparation method according to claim 1, characterized in that, The extractant is a mixture of dimethyl sulfoxide and sulfolane, with a mass ratio of dimethyl sulfoxide to sulfolane of 1:(0.4~1.8).
5. The preparation method according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1. The mixed feed liquid of p-xylene and butanol is added from the feed inlet of the extraction tower, and the extractant is added from the extractant inlet of the extraction tower for extractive distillation. The vapor rich in butanol is condensed into liquid at the top of the tower by a condenser. Part of it is collected as butanol product, and the other part is returned to the tower as condensate. The bottom product is a mixture containing extractant and p-xylene. S2. The bottom product of the extraction tower is introduced into the feed inlet of the solvent recovery tower. After distillation, the vapor rich in p-xylene rises to the top of the tower and is condensed. The p-xylene product is collected from the top of the tower and introduced into the product tank for storage. The extractant is discharged from the bottom of the solvent recovery tower. S3. The extractant discharged from the bottom of the solvent recovery tower is introduced into the upper part of the extraction tower and recycled.
6. The preparation method according to claim 5, characterized in that, The mass ratio of the p-xylene-butanol mixed feed solution to the extractant is 1:(2.2~3.2).
7. The preparation method according to claim 5, characterized in that, The theoretical plate number of the extraction column is 20~32, and the reflux ratio is (1.2~2.6):
1.
8. The preparation method according to claim 5, characterized in that, The temperature at the top of the extraction column is 115~120℃, the temperature at the bottom of the column is 145~165℃, the pressure at the top of the column is 0.1 MPa, and the total pressure drop of the extraction column is 7~10 kPa.
9. The preparation method according to claim 7, characterized in that, The number of feed trays for the extractant added to the extraction tower is 2 to 8, and the number of feed trays for the mixed feed liquid added to the extraction tower is 15 to 30.
10. The preparation method according to claim 5, characterized in that, The theoretical number of plates in the solvent recovery tower is 12~22, and the reflux ratio is (0.6~1.2):1.