Device and method for separating aromatic hydrocarbon and non-aromatic hydrocarbon through pressure swing extractive distillation

Abstract

The invention belongs to the field of aromatic hydrocarbon extraction, and relates to a device and a method for separating aromatic hydrocarbon and non-aromatic hydrocarbon through pressure swing extractive distillation. The device comprises a hydrocarbon mixture feeding pipeline, a high-pressure extractive distillation tower, a non-aromatic solvent recovery tower, an aromatic solvent recovery tower and a heat exchanger, the hydrocarbon mixture feeding pipeline is sequentially connected with the heat exchanger and the middle part of the high-pressure extractive distillation tower; the high-pressure extractive distillation tower is provided with a raffinate discharging pipeline and an extract discharging pipeline; the raffinate discharge pipeline is connected with the non-aromatic solvent recovery tower, the non-aromatic solvent recovery tower is provided with a recovered solvent discharge pipeline and a non-aromatic discharge pipeline, and the recovered solvent discharge pipeline is connected with the high-pressure extractive distillation tower; the extract discharge pipeline is connected with an aromatic solvent recovery tower, the aromatic solvent recovery tower is provided with a lean solvent discharge pipeline and an aromatic discharge pipeline, and the lean solvent discharge pipeline is connected with a top tray of the high-pressure extractive distillation tower. A pressure reduction facility is arranged on a raffinate discharging pipeline of the high-pressure extractive distillation tower, and a gas phase enters the non-aromatic solvent recovery tower after being subjected to pressure reduction, so that variable-pressure operation of the front tower and the rear tower is realized. According to the invention, low-solvent-ratio extraction can be realized, and the heat exchange area of lean solvent heat extraction equipment can be reduced.

Description

Technical Field

[0001] The present invention belongs to the field of aromatic hydrocarbon extraction, and in particular relates to a device and method for separating aromatic hydrocarbons and non-aromatic hydrocarbons by pressure swing extraction distillation. Background Art

[0002] The process for extractive distillation to separate aromatics and non-aromatics typically consists of an extractive distillation column and a solvent recovery column. Non-aromatics are obtained at the top of the extractive distillation column, while a mixture of aromatics and solvent is obtained at the bottom. This mixture is then sent to the solvent recovery column for separation of the aromatics and solvent. Aromatics products are obtained at the top of the solvent recovery column, while the extraction solvent is separated at the bottom and returned to the extractive distillation column for recycling.

[0003] There are two functional zones within an extractive distillation tower: the section above the extraction solvent feed port is the non-aromatic desolventizing zone, which separates non-aromatics from the solvent; and the section below the extraction solvent feed port is the extractive distillation zone, which separates aromatics from non-aromatics. The non-aromatic desolventizing zone of the extractive distillation tower is typically equipped with several trays, which, under the action of overhead reflux, separate non-aromatics from the extraction solvent, meeting the solvent content requirements of non-aromatic products while minimizing solvent loss. To maximize aromatic recovery, the extractive distillation zone of the extractive distillation tower typically has the extraction solvent feed port located above the hydrocarbon mixture feed port, with several trays positioned between the two feed ports. The extractant, flowing from top to bottom, countercurrently contacts the ascending gas phase and selectively dissolves the aromatics in the gas phase. The extractive distillation zone utilizes the different solubilities of aromatics and non-aromatics in the extraction solvent to separate aromatics from non-aromatics through an extractive distillation process.

[0004] The non-aromatic desolventizing section of an extractive distillation tower follows the same process principles as conventional distillation. The relative volatility between components increases with decreasing pressure, and a relatively low operating pressure facilitates the separation of non-aromatics from the solvent. The extractive distillation section of an extractive distillation tower follows the same process principles as extractive distillation. The solubility of aromatics in the solvent increases with increasing temperature. Operating the extraction process at a relatively high operating temperature can reduce solvent circulation, corresponding to a relatively high operating pressure in the extractive distillation section. In summary, low pressure facilitates the operation of the non-aromatic desolventizing section, while high pressure facilitates the operation of the extractive distillation section. The two functional zones have opposite pressure expectations. It is difficult to operate the non-aromatic desolventizing section and the aromatic extractive distillation section at different preferred pressures within a single tower.

[0005] While overhead reflux is essential for the non-aromatic desolventizing section of the extractive distillation column, it is not only unnecessary but also detrimental to this section. To achieve non-aromatic desolventizing, the non-aromatic desolventizing section must have an internal reflux of liquid material to the extractive distillation section, ideally consisting solely of solvent. The overhead reflux enters the extractive distillation section as an internal reflux below the non-aromatic desolventizing section, where it is heated and re-vaporized on the upper trays before returning to the non-aromatic desolventizing section. This internal reflux of non-aromatic hydrocarbons is detrimental to the operation of the extractive distillation section: 1) This internal reflux, primarily composed of non-aromatic hydrocarbons, is difficult to uniformly mix with the incoming solvent. Furthermore, due to the low solubility of non-aromatic hydrocarbons in the solvent, vapor-liquid-liquid three-phase mass transfer occurs near the trays below the solvent feed. This uneven liquid-liquid mixing compromises the extractive distillation process. 2) A small amount of non-aromatic hydrocarbons will be dissolved by the solvent, which will affect the solvent's ability to dissolve aromatics. Therefore, the extractive distillation zone hopes that the internal reflux from the non-aromatic desolventizing zone is as small as possible. However, in an ordinary distillation tower, this internal reflux is determined by the top reflux, which cannot overcome the above shortcomings.

[0006] CN1541988A proposes a method for separating aromatic hydrocarbons by extractive distillation. A hydrocarbon mixture containing aromatics is pre-fractionated to produce a C6-C7 fraction and a C8 fraction. The resulting C6-C7 fraction is introduced into the middle portion of an extractive distillation column, where it is contacted with a selective solvent introduced from the upper portion for extractive distillation. The aromatic-rich solvent discharged from the bottom of the column enters a recovery column to separate the solvent and aromatics. The non-aromatic desolventizing zone and the extractive distillation zone in this method are carried out within the same column.

[0007] CN108929187A proposes a method for extractive distillation and separation of a target product from a hydrocarbon mixture. The method comprises introducing the hydrocarbon mixture from the middle of an extractive distillation tower, introducing an extractive distillation solvent from the upper portion of the tower, and subjecting the mixture to extractive distillation. Non-target products are discharged from the top of the tower. After water removal, a portion of the solvent is returned to the extractive distillation tower, and the remainder is discharged as a raffinate oil system. The rich solvent, enriched in the target product, discharged from the bottom of the tower enters a solvent recovery tower. The non-aromatic desolventizing zone and the extractive distillation zone in this method are carried out in the same tower.

[0008] CN1923772A proposes a method for recovering aromatic hydrocarbons from a hydrocarbon mixture using extractive distillation. The method involves introducing the hydrocarbon mixture from the middle of an extractive distillation column, introducing the extractive distillation solvent from the upper portion of the column, and providing heating by a heat source at the bottom of the non-aromatic reflux section of the column. This method can reduce the amount of internal reflux from the non-aromatic desolventizing section to the extractive distillation zone to a certain extent, but it is difficult to achieve precise control of the internal reflux.

[0009] In summary, the existing methods for separating aromatics and non-aromatics by extractive distillation cannot achieve the different desired values ​​for operating pressure and non-aromatic internal reflux in the non-aromatic desolventizing zone and the extractive distillation zone. Summary of the Invention

[0010] The purpose of the present invention is to address the deficiencies of the prior art and to propose an apparatus and method for separating aromatic hydrocarbons from non-aromatic hydrocarbons by pressure-swing extraction distillation. The present invention provides two pressure-swing tower systems, namely a high-pressure extraction distillation tower and a non-aromatic solvent recovery tower, to achieve operation of the extraction solvent in the extraction distillation zone at a higher pressure and a higher temperature, thereby increasing the solubility of aromatic hydrocarbons in the extraction solvent and facilitating the extraction and separation of non-aromatic hydrocarbons from aromatic hydrocarbons. The non-aromatic desolventizing zone operates at a lower pressure, increasing the relative volatility between components and facilitating the distillation and separation of non-aromatic hydrocarbons from the solvent. The combination of the two reduces the extraction solvent ratio.

[0011] To achieve the above-mentioned object, a first aspect of the present invention provides a device for separating aromatic hydrocarbons from non-aromatic hydrocarbons by pressure swing extraction distillation, the device comprising: a hydrocarbon mixture feed pipeline, a high-pressure extraction distillation column, a non-aromatic solvent recovery column, an aromatic solvent recovery column, and a heat exchanger;

[0012] The hydrocarbon mixture feed pipeline is sequentially connected to the heat exchanger and the middle part of the high-pressure extractive distillation tower, the top tray of the high-pressure extractive distillation tower is provided with an extraction solvent feed port, the top of the tower is provided with an extract discharge pipeline, and the bottom of the tower is provided with an extract discharge pipeline;

[0013] The extract discharge pipeline is connected to the non-aromatic solvent recovery tower, the bottom of the non-aromatic solvent recovery tower is provided with a recovery solvent discharge pipeline, the top of the tower is provided with a non-aromatic discharge pipeline, the non-aromatic discharge pipeline is connected in sequence to the non-aromatic solvent recovery tower top condenser and the non-aromatic solvent recovery tower top reflux tank and then split into two branches, one of which is used as the non-aromatic product discharge pipeline, and the other is refluxed to the top of the non-aromatic solvent recovery tower, and the recovery solvent discharge pipeline is connected to a high-pressure extractive distillation tower;

[0014] The extract discharge pipeline is connected to the aromatic solvent recovery tower, a lean solvent discharge pipeline is provided at the bottom of the aromatic solvent recovery tower, and an aromatic hydrocarbon discharge pipeline is provided at the top of the tower. The aromatic hydrocarbon discharge pipeline is sequentially connected to the aromatic solvent recovery tower top condenser and the aromatic solvent recovery tower top reflux tank and then divided into two branches, one of which is used as the aromatic hydrocarbon product discharge pipeline, and the other is refluxed to the top of the aromatic solvent recovery tower. The lean solvent discharge pipeline is sequentially connected to the lean solvent waste heat heat exchanger and the heat exchanger and then connected to the top tray of the high-pressure extractive distillation tower;

[0015] The extract discharge pipeline of the high-pressure extractive distillation tower is provided with a decompression facility, and the gas phase enters the non-aromatic solvent recovery tower after being decompressed.

[0016] According to the present invention, preferably, the pressure reducing facility is a control valve.

[0017] Preferably, the non-aromatic solvent recovery tower is provided with a rectifying section, or is provided with a rectifying section and a stripping section.

[0018] According to the present invention, preferably, the high-pressure extractive distillation tower kettle is provided with a high-pressure extractive distillation tower reboiler.

[0019] According to the present invention, preferably, the non-aromatic solvent recovery tower kettle is provided with a non-aromatic solvent recovery tower reboiler.

[0020] According to the present invention, preferably, the aromatic solvent recovery tower kettle is provided with an aromatic solvent recovery tower reboiler.

[0021] According to the present invention, preferably, after the recovered solvent discharge pipeline merges with the hydrocarbon mixture feed pipeline, it is sequentially connected to a heat exchanger and the middle part of a high-pressure extractive distillation tower.

[0022] According to the present invention, preferably, the lean solvent discharge pipeline is connected to the lean solvent waste heat heat exchanger and the heat exchanger in sequence, and then connected to the top tray of the high-pressure extractive distillation tower.

[0023] According to the present invention, preferably, the high-pressure extractive distillation tower has no top condensation and reflux facilities.

[0024] A second aspect of the present invention provides a method for separating aromatic hydrocarbons and non-aromatic hydrocarbons by pressure swing extraction and distillation, which is carried out using the apparatus for separating aromatic hydrocarbons and non-aromatic hydrocarbons by pressure swing extraction and distillation, and comprises the following steps:

[0025] The hydrocarbon mixture enters the high-pressure extractive distillation tower and is extracted by the extraction solvent, and the raffinate is obtained at the top of the tower and the extract is obtained at the bottom of the tower;

[0026] The extract residue enters the non-aromatic solvent recovery tower to separate the non-aromatic hydrocarbons and the solvent, and the recovered solvent is obtained at the bottom of the tower, and the non-aromatic hydrocarbons are obtained at the top of the tower. After the non-aromatic hydrocarbons are condensed, a portion of them is refluxed to the top of the non-aromatic solvent recovery tower, and the other portion is extracted as a non-aromatic hydrocarbon product. The recovered solvent is returned to the high-pressure extractive distillation tower;

[0027] The extract enters the aromatic solvent recovery tower to separate the aromatics from the solvent, and the lean solvent is obtained at the bottom of the tower, and the aromatics are obtained at the top of the tower. After the aromatics are condensed, a portion of them is refluxed to the top of the aromatic solvent recovery tower, and the other portion is extracted as the aromatic product. The lean solvent is cooled by the lean solvent waste heat heat exchanger and the heat exchanger, and then returned to the top tray of the high-pressure extractive distillation tower;

[0028] The operating pressure at the top of the high-pressure extractive distillation tower is 30 to 150 kPa higher than the operating pressure at the feed plate of the non-aromatic solvent recovery tower, and preferably 30 to 130 kPa higher.

[0029] In the present invention, the relatively high operating pressure of the high-pressure extractive distillation tower corresponds to a high solvent extraction temperature, which can reduce the extraction solvent ratio; the two towers can be operated at their own appropriate operating pressures and have relative independence in pressure control.

[0030] The extraction solvent ratio refers to the mass ratio of the extraction solvent to the aromatic hydrocarbons in the hydrocarbon mixture.

[0031] According to the present invention, preferably, the mass ratio of the extraction solvent to the aromatic hydrocarbons in the hydrocarbon mixture is 3.0 to 6.0, preferably 3.0 to 5.5.

[0032] According to the present invention, preferably, the hydrocarbon mixture is introduced into the high-pressure extractive distillation tower from the middle; the extraction solvent is introduced into the high-pressure extractive distillation tower from the top tray, and the extraction solvent contacts the ascending gas phase countercurrently from top to bottom and selectively dissolves the aromatic hydrocarbons in the gas phase material.

[0033] According to the present invention, preferably, the extraction solvent is at least one of sulfolane, N,N-dimethylacetamide, N-methylpyrrolidone and N-formylmorpholine.

[0034] According to the present invention, preferably, the hydrocarbon mixture is hydrocarbons with 5 to 10 carbon atoms.

[0035] According to the present invention, preferably, the high-pressure extractive distillation tower has a theoretical plate number of 30 to 50, a bottom temperature of 165 to 180° C., and an operating pressure at the top of the tower of 0.10 to 0.20 MPaG; the extraction solvent inlet temperature is 100 to 150° C. The high-pressure extractive distillation tower has no top condensation and reflux facilities, and its gas phase (i.e., the top extract residue) enters the non-aromatic solvent recovery tower after passing through a decompression facility. Preferably, the decompression facility is a control valve.

[0036] The non-aromatic solvent recovery tower is provided with a rectifying section, or a rectifying section and a stripping section.

[0037] According to the present invention, preferably, the non-aromatic solvent recovery tower has a theoretical plate number of 5 to 10, a bottom temperature of 100 to 130° C., and a top operating pressure of -0.09 to 0.08 MPaG.

[0038] According to the present invention, preferably, the recovered solvent is first merged with the hydrocarbon mixture, then passes through a heat exchanger to exchange heat with the lean solvent after heat exchange in a lean solvent waste heat extraction heat exchanger, and then returns to the middle of the high-pressure extractive distillation tower.

[0039] The technical solution of the present invention has the following technical effects:

[0040] 1) The present invention provides two pressure-switching tower systems, namely a high-pressure extractive distillation tower and a non-aromatic solvent recovery tower, so that the extraction solvent in the extractive distillation zone is operated at a higher pressure and a higher temperature, thereby increasing the solubility of aromatic hydrocarbons in the extraction solvent and facilitating the extraction separation of non-aromatic hydrocarbons from aromatic hydrocarbons; the non-aromatic desolventizing zone is operated at a lower pressure, increasing the relative volatility between components and facilitating the distillation separation of non-aromatic hydrocarbons from the solvent. The combination of the two realizes low solvent ratio extraction.

[0041] 2) The present invention separates the non-aromatic desolventizing zone and the extractive distillation zone by providing two pressure-switching tower systems, namely a high-pressure extractive distillation tower and a non-aromatic solvent recovery tower, thereby reducing the amount of non-aromatic hydrocarbons refluxed from the non-aromatic desolventizing zone to the extractive distillation zone, avoiding liquid-liquid-vapor three-phase mass transfer, and making the operation more stable.

[0042] 3) The present invention provides two pressure-swing tower systems: a high-pressure extractive distillation tower and a non-aromatic solvent recovery tower. These towers can operate at their own suitable operating pressures, providing independent pressure control and greater operational flexibility. The reflux and reboil rates can be independently adjusted to control the non-aromatic solvent content of the reflux tank at the top of the non-aromatic solvent recovery tower.

[0043] 4) The present invention achieves a reduction in the extraction solvent ratio by providing two pressure-switching tower systems, namely a high-pressure extraction distillation tower and a non-aromatic solvent recovery tower, thereby reducing the non-aromatic content in the aromatic product and improving the purity of the aromatic product.

[0044] 5) The present invention increases the solvent extraction temperature and thus the extraction solvent inlet temperature, thereby reducing the total temperature difference of the circulating extraction solvent and reducing the heat exchange area of ​​the lean solvent heat extraction equipment.

[0045] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0047] Figure 1 A schematic diagram of an apparatus for separating aromatic hydrocarbons and non-aromatic hydrocarbons by pressure swing extraction distillation provided in Example 1 of the present invention is shown.

[0048] Description of Reference Numerals

[0049] 1. High-pressure extractive distillation tower; 2. Non-aromatic solvent recovery tower; 3. Aromatic solvent recovery tower; 4. Heat exchanger; 5. High-pressure extractive distillation tower reboiler; 6. Non-aromatic solvent recovery tower reboiler; 7. Aromatic solvent recovery tower reboiler; 8. Non-aromatic solvent recovery tower top condenser; 9. Non-aromatic solvent recovery tower top reflux tank; 10. Aromatic solvent recovery tower top condenser; 11. Aromatic solvent recovery tower top reflux tank; 12. Pressure reduction facility; 13. Hydrocarbon mixture; 14. Raffinate; 15. Non-aromatic product; 16. Recovered solvent; 17. Aromatic product; 18. Lean solvent; 19. Extract; 20. Extraction solvent; 21. Lean solvent waste heat extraction heat exchanger. DETAILED DESCRIPTION

[0050] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0051] Example 1

[0052] This embodiment provides a device for separating aromatic hydrocarbons and non-aromatic hydrocarbons by pressure swing extraction distillation, such as Figure 1 As shown, the device comprises: a hydrocarbon mixture feed pipeline, a high-pressure extractive distillation tower 1, a non-aromatic solvent recovery tower 2, an aromatic solvent recovery tower 3 and a heat exchanger 4;

[0053] The hydrocarbon mixture feed pipeline is sequentially connected to the heat exchanger 4 and the middle part of the high-pressure extractive distillation tower 1. The top tray of the high-pressure extractive distillation tower 1 is provided with an extraction solvent feed port, the bottom of the tower is provided with a high-pressure extractive distillation tower reboiler 5, the top of the tower is provided with an extract discharge pipeline, and the bottom of the tower is provided with an extract discharge pipeline;

[0054] The raffinate discharge pipeline is connected to the non-aromatic solvent recovery tower 2, and a decompression facility 12 is provided on the raffinate discharge pipeline, which is a control valve. The non-aromatic solvent recovery tower 2 is provided with a non-aromatic solvent recovery tower reboiler 6 at the bottom of the tower, a recovery solvent discharge pipeline is provided at the bottom of the tower, and a non-aromatic discharge pipeline is provided at the top of the tower. The non-aromatic discharge pipeline is sequentially connected to the non-aromatic solvent recovery tower top condenser 8 and the non-aromatic solvent recovery tower top reflux tank 9, and then divided into two branches, one of which is used as a non-aromatic product discharge pipeline, and the other is refluxed to the top of the non-aromatic solvent recovery tower 2. After the recovery solvent discharge pipeline is connected to the hydrocarbon mixture feed pipeline, it is sequentially connected to the heat exchanger 4 and the middle part of the high-pressure extractive distillation tower 1;

[0055] The extract discharge pipeline is connected to the aromatic solvent recovery tower 3, the aromatic solvent recovery tower 3 is provided with an aromatic solvent recovery tower reboiler 7 at the bottom of the tower, a lean solvent discharge pipeline is provided at the bottom of the tower, and an aromatics discharge pipeline is provided at the top of the tower. The aromatics discharge pipeline is connected to the aromatic solvent recovery tower top condenser 10 and the aromatic solvent recovery tower top reflux tank 11 in sequence, and then divided into two branches, one of which is used as the aromatics product discharge pipeline, and the other is refluxed to the top of the aromatic solvent recovery tower 3. The lean solvent discharge pipeline is connected to the lean solvent waste heat heat exchanger 21, the heat exchanger 4 and the top tower plate of the high-pressure extractive distillation tower 1 in sequence.

[0056] This embodiment also provides a method for separating aromatic hydrocarbons and non-aromatic hydrocarbons by pressure swing extractive distillation, comprising the following steps:

[0057] The hydrocarbon mixture 13 enters the high-pressure extractive distillation tower 1 and is extracted by the extraction solvent 20, and the raffinate 14 is obtained at the top of the tower and the extract 19 is obtained at the bottom of the tower;

[0058] The extract raffinate 14 passes through the decompression device 12 (the decompression device is a control valve) and enters the non-aromatic solvent recovery tower 2 for separation of non-aromatic hydrocarbons and solvent, and a recovered solvent 16 is obtained at the bottom of the tower, and non-aromatic hydrocarbons are obtained at the top of the tower. After the non-aromatic hydrocarbons are condensed, a portion of them is refluxed to the top of the non-aromatic solvent recovery tower 2, and the other portion is extracted as a non-aromatic hydrocarbon product 15. After the recovered solvent 16 is merged with the hydrocarbon mixture 13, it returns to the middle of the high-pressure extractive distillation tower 1;

[0059] The extract 19 enters the aromatic solvent recovery tower 3 for separation of aromatics and solvent, and a lean solvent 18 is obtained at the bottom of the tower, and aromatics are obtained at the top of the tower. After the aromatics are condensed, a portion of them refluxes to the top of the aromatic solvent recovery tower 3, and the other portion is extracted as the aromatic product 17. The lean solvent 18 is cooled by the lean solvent waste heat heat exchanger 21 and the heat exchanger 4, and then returned to the top tray of the high-pressure extractive distillation tower 1.

[0060] The extraction solvent in the high-pressure extractive distillation column is sulfolane. The high-pressure extractive distillation column has 40 theoretical plates; the non-aromatic solvent recovery column has 5 theoretical plates; and the solvent recovery column has 20 theoretical plates. The composition of the hydrocarbon mixture is shown in Table 1.

[0061] Comparative Example 1

[0062] This comparative example was carried out using the apparatus and method of CN1923772A.

[0063] The extractive distillation solvent in the extractive distillation tower is sulfolane.

[0064] The number of theoretical plates of the extractive distillation tower is 45; the number of theoretical plates of the solvent recovery tower is 20.

[0065] The composition of the hydrocarbon mixture is shown in Table 1.

[0066] Table 1

[0067] composition C5 non-aromatic, wt% 1.6 C6 non-aromatic, wt% 18.2 C7 non-aromatic, wt% 10.4 C8 non-aromatic, wt% 4.1 Benzene, wt% 30.1 Toluene, wt% 34.8 C8 aromatics, wt% 0.8 Total, wt% 100.0

[0068] The aromatic hydrocarbons and non-aromatic hydrocarbons in the hydrocarbon mixture in Table 1 were separated according to the methods of Example 1 and Comparative Example 1, respectively. The comparison of the non-aromatic hydrocarbon desolventizing zone is shown in Table 2, the comparison of the extractive distillation zone is shown in Table 3, other comparisons are shown in Table 4, and the product quality indicators and comparisons are shown in Table 5.

[0069] Table 2 Non-aromatic desolventizing zone

[0070]

[0071] Table 3 Extraction distillation zone

[0072]

[0073] Table 4

[0074] Solvent recovery tower Example 1 Comparative Example 1 Tower bottom discharge temperature, ℃ 175 175 Reflux ratio 0.5 0.5

[0075] Table 5

[0076]

[0077] From the comparison results of Tables 2 to 5, it can be seen that both the embodiment and the comparative example can meet the separation requirements, and the aromatic hydrocarbon recovery rate and product quality of the embodiment are improved. The method of the present invention has the following advantages: the tray temperature (solvent extraction temperature) in the high-pressure extractive distillation tower is generally increased by 5 to 19°C, corresponding to a higher aromatic hydrocarbon solubility; although the operating pressure of the high-pressure extractive distillation tower is increased, the extraction solvent ratio is reduced by 16%, the proportion of solvent in the tower bottom material is low, and the tower bottom temperature can be equivalent; the tower pressure of the non-aromatic solvent recovery tower is reduced, and the tower bottom temperature is equivalent, which proves that the non-aromatic content in the tower bottom is reduced; the temperature of the extraction solvent entering the extraction distillation zone is increased by 8°C, and the total temperature difference of the lean solvent heat exchange is reduced by 8°C, reducing the heat exchange area of ​​the lean solvent heat extraction equipment.

[0078] While various embodiments of the present invention have been described above, the above description is intended to be illustrative, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A device for separating aromatic hydrocarbons and non-aromatic hydrocarbons by pressure swing extraction distillation, characterized in that: The device comprises: a hydrocarbon mixture feed pipeline, a high-pressure extraction distillation tower (1), a non-aromatic solvent recovery tower (2), an aromatic solvent recovery tower (3) and a heat exchanger (4); The hydrocarbon mixture feed pipeline is sequentially connected to the heat exchanger (4) and the middle part of the high-pressure extractive distillation tower (1); the top tray of the high-pressure extractive distillation tower (1) is provided with an extraction solvent feed port, the top of the tower is provided with an extract discharge pipeline, and the bottom of the tower is provided with an extract discharge pipeline; The raffinate discharge pipeline is connected to a non-aromatic solvent recovery tower (2), a recovery solvent discharge pipeline is provided at the bottom of the non-aromatic solvent recovery tower (2), and a non-aromatic hydrocarbon discharge pipeline is provided at the top of the tower. The non-aromatic hydrocarbon discharge pipeline is connected to a non-aromatic hydrocarbon recovery tower top condenser (8) and a non-aromatic hydrocarbon recovery tower top reflux tank (9) in sequence and then splits into two branches, one of which is used as a non-aromatic hydrocarbon product discharge pipeline, and the other is refluxed to the top of the non-aromatic hydrocarbon solvent recovery tower (2). The recovery solvent discharge pipeline is connected to a high-pressure extractive distillation tower (1); The extract discharge pipeline is connected to the aromatic solvent recovery tower (3), the bottom of the aromatic solvent recovery tower (3) is provided with a lean solvent discharge pipeline, and the top of the tower is provided with an aromatic hydrocarbon discharge pipeline, the aromatic hydrocarbon discharge pipeline is sequentially connected to the aromatic hydrocarbon solvent recovery tower top condenser (10) and the aromatic hydrocarbon solvent recovery tower top reflux tank (11) and then divided into two branches, one of which is used as the aromatic hydrocarbon product discharge pipeline, and the other is refluxed to the top of the aromatic solvent recovery tower (3), the lean solvent discharge pipeline is sequentially connected to the lean solvent waste heat heat exchanger (21) and the heat exchanger (4) and then connected to the top tray of the high-pressure extractive distillation tower (1); A decompression device (12) is provided on the extract discharge pipeline of the high-pressure extractive distillation tower (1), and the gas phase enters the non-aromatic solvent recovery tower (2) after being decompressed.

2. The device for separating aromatic hydrocarbons and non-aromatic hydrocarbons by pressure swing extraction distillation according to claim 1, wherein: The pressure reducing device (12) is a control valve; The non-aromatic solvent recovery tower (2) is provided with a rectifying section, or a rectifying section and a stripping section.

3. The device for separating aromatic hydrocarbons and non-aromatic hydrocarbons by pressure swing extraction distillation according to claim 1, wherein: The high-pressure extractive distillation tower (1) has a tower kettle provided with a high-pressure extractive distillation tower reboiler (5); The non-aromatic solvent recovery tower (2) is provided with a non-aromatic solvent recovery tower reboiler (6) in the bottom of the tower; The aromatic hydrocarbon solvent recovery tower (3) is provided with an aromatic hydrocarbon solvent recovery tower reboiler (7) in the tower bottom.

4. The device for separating aromatic hydrocarbons and non-aromatic hydrocarbons by pressure swing extraction distillation according to claim 1, wherein: After the recovery solvent discharge pipeline is merged with the hydrocarbon mixture feed pipeline, it is sequentially connected to the heat exchanger (4) and the middle part of the high-pressure extraction distillation tower (1); The lean solvent discharge pipeline is connected in sequence to the lean solvent waste heat extraction heat exchanger (21) and the heat exchanger (4), and then connected to the top tray of the high-pressure extractive distillation tower (1).

5. The device for separating aromatic hydrocarbons and non-aromatic hydrocarbons by pressure swing extraction distillation according to claim 1, wherein: The high-pressure extractive distillation tower (1) has no top condensation and reflux facilities.

6. A method for separating aromatic hydrocarbons and non-aromatic hydrocarbons by pressure swing extractive distillation, characterized in that: The method of separating aromatic hydrocarbons and non-aromatic hydrocarbons by pressure swing extraction distillation according to any one of claims 1 to 5 comprises the following steps: The hydrocarbon mixture (13) enters a high-pressure extractive distillation tower (1) and is extracted by an extraction solvent (20), whereby a raffinate (14) is obtained at the top of the tower and an extract (19) is obtained at the bottom of the tower; The extract (14) enters the non-aromatic solvent recovery tower (2) through the decompression device (12) to separate the non-aromatic hydrocarbons from the solvent, and a recovery solvent (16) is obtained at the bottom of the tower, and non-aromatic hydrocarbons are obtained at the top of the tower. After the non-aromatic hydrocarbons are condensed, a portion of them is refluxed to the top of the non-aromatic solvent recovery tower (2), and the other portion is extracted as a non-aromatic hydrocarbon product (15). The recovery solvent (16) returns to the high-pressure extractive distillation tower (1); The extract (19) enters the aromatic solvent recovery tower (3) to separate the aromatic hydrocarbons from the solvent, and a lean solvent (18) is obtained at the bottom of the tower, and aromatic hydrocarbons are obtained at the top of the tower. After the aromatic hydrocarbons are condensed, a portion of them is refluxed to the top of the aromatic solvent recovery tower (3), and the other portion is extracted as an aromatic hydrocarbon product (17). The lean solvent (18) is cooled by the lean solvent waste heat heat exchanger (21) and the heat exchanger (4), and then returned to the top tray of the high-pressure extractive distillation tower (1); The operating pressure at the top of the high-pressure extractive distillation tower (1) is 30 to 150 kPa higher than the operating pressure of the feed plate of the non-aromatic solvent recovery tower (2).

7. The method for separating aromatic hydrocarbons and non-aromatic hydrocarbons by pressure swing extractive distillation according to claim 6, wherein: The operating pressure at the top of the high-pressure extractive distillation tower (1) is 30 to 130 kPa higher than the operating pressure at the feed plate of the non-aromatic solvent recovery tower (2); The mass ratio of the extraction solvent to the aromatic hydrocarbons in the hydrocarbon mixture is 3.0 to 6.0, preferably 3.0 to 5.

5.

8. The method for separating aromatic hydrocarbons and non-aromatic hydrocarbons by pressure swing extractive distillation according to claim 6, wherein: The hydrocarbon mixture (13) is introduced into the high-pressure extractive distillation tower (1) from the middle; the extraction solvent (20) is introduced into the high-pressure extractive distillation tower (1) from the top tray, and the extraction solvent (20) contacts the ascending gas phase from top to bottom in countercurrent and selectively dissolves aromatic hydrocarbons in the gas phase material; The extraction solvent is at least one of sulfolane, N,N-dimethylacetamide, N-methylpyrrolidone and N-formylmorpholine; The hydrocarbon mixture is hydrocarbons with 5 to 10 carbon atoms.

9. The method for separating aromatic hydrocarbons and non-aromatic hydrocarbons by pressure swing extractive distillation according to claim 6, wherein: The high-pressure extractive distillation tower (1) has a theoretical plate number of 30 to 50, a tower bottom temperature of 165 to 180° C., and a tower top operating pressure of 0.10 to 0.20 MPaG; the extraction solvent inlet temperature is 100 to 150° C.; The non-aromatic solvent recovery tower (2) has a theoretical plate number of 5 to 10, a bottom temperature of 100 to 130° C., and a top operating pressure of -0.09 to 0.08 MPaG; The high-pressure extractive distillation tower (1) has no top condensation and reflux facilities, and its gas phase enters the non-aromatic solvent recovery tower (2) after passing through the decompression facility (12).

10. The method for separating aromatic hydrocarbons and non-aromatic hydrocarbons by pressure swing extractive distillation according to claim 6, wherein: The recovered solvent (16) is first combined with the hydrocarbon mixture (13), then passes through a heat exchanger (4) to exchange heat with the lean solvent (18) after heat exchange in the lean solvent waste heat extraction heat exchanger (21), and then returns to the middle of the high-pressure extractive distillation tower (1).

Images