A system for separating aromatics from pyrolysis gasoline

Abstract

The application relates to the field of petroleum chemical industry, in particular to a system for separating and cracking aromatics in gasoline; the system comprises an extraction unit including an extraction tower, an integrated unit including an integrated tower, an integrated reboiler and a xylene refining tower, the bottom of the extraction tower being communicated with the feed inlet of the integrated tower, and the two ends of the integrated reboiler being communicated with the discharge outlets of the integrated tower; the integrated tower comprises a partition plate and a plurality of tower trays, the tower trays are horizontally and spacedly arranged in the integrated tower, the partition plate is arranged in the integrated tower, and the partition plate is arranged perpendicularly to the plane where the tower trays are located; a side-line xylene and toluene extraction section is communicated with the xylene refining tower, the bottom of the extraction tower is communicated with the middle part of the integrated tower, the bottom liquid outlet of the xylene refining tower and the bottom discharge outlet of the integrated tower are both communicated with the middle part of the extraction tower; through the system, high-purity separation and collection of various products of the aromatics in the cracked gasoline can be realized, the process of separating and cracking the aromatics in the gasoline is shortened, and the purity of benzene products, toluene products and xylene products in the aromatics is improved.

Description

Technical Field

[0001] This application relates to the petrochemical field, and more particularly to a system for separating aromatics from cracked gasoline. Background Technology

[0002] Aromatics are essential raw materials for petrochemicals, with benzene, toluene, and xylene being the most important. With the development of the oil refining industry, the demand for aromatics, one of the raw materials required for refining, has been increasing. Therefore, petroleum aromatics have become a major source of aromatics. However, with increasingly stringent environmental regulations, the specifications for petroleum products (such as fuels) are also becoming more stringent, generally requiring an aromatic content of ≤35%, of which the benzene content must be <0.8%. Since aromatics are crucial raw materials for producing petroleum products through refining, it is necessary to separate aromatics from catalytic cracking gasoline (DCC gasoline) and ethylene cracking gasoline during the refining process.

[0003] Since the effective components of DCC gasoline and ethylene cracked gasoline at this stage are the C6-C8 components, based on the differences between aromatics and their main components, sulfolane is generally used as an organic solvent to separate benzene, toluene, and xylene from aromatics. Common separation methods include extraction, aromatic recovery, benzene tower, toluene tower, and xylene tower. Not only is the process lengthy and energy-intensive, but the multi-stage process also results in unsatisfactory final aromatic separation, making it impossible to obtain high-purity benzene, toluene, and xylene products.

[0004] Therefore, how to provide a system for separating aromatics from cracked gasoline, so as to shorten the process of separating aromatics from cracked gasoline and improve the purity of the separated aromatic products, is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] This application provides a system for separating aromatics from cracked gasoline, in order to solve the problems of excessively long extraction and separation processes for aromatics from cracked gasoline and excessively low purity of aromatic products in the prior art.

[0006] In a first aspect, embodiments of this application provide a system for separating aromatics from cracked gasoline, the system comprising:

[0007] An extraction unit, comprising an extraction tower, for extracting cracked gasoline with a lean solvent;

[0008] An integrated unit, comprising an integrated tower, an integrated reboiler, and a xylene refining tower, wherein the bottom of the extraction tower is connected to the feed inlet of the integrated tower, and both ends of the integrated reboiler are connected to the discharge outlet of the integrated tower, so as to realize the recycling of the lean solvent after distillation;

[0009] The integrated tower includes a partition and multiple trays, which are arranged laterally at intervals within the integrated tower to divide the integrated tower into a rectification section, a middle processing section, and a stripping section from top to bottom; the partition is located within the integrated tower and is arranged perpendicular to the plane of the trays to divide the middle processing section into a pre-fractionation section and a side-stream xylene and toluene extraction section;

[0010] The integrated reboiler is connected to the bottom outlet of the integrated column, and both ends of the integrated reboiler are connected to the outlet of the integrated column, so as to realize the heating treatment of the lean solvent after distillation.

[0011] The side-stream xylene and the toluene extraction section are connected to the xylene refining tower. The bottom of the extraction tower and the middle of the integrated tower are connected. The bottom liquid outlet of the xylene refining tower and the bottom discharge outlet of the integrated tower are both connected to the middle of the extraction tower to achieve the recycling of lean solvent.

[0012] Optionally, the extraction unit further includes an extraction reboiler, both ends of which are connected to the extraction column to achieve the recycling of the solvent rich in aromatics.

[0013] Optionally, the extraction unit further includes an extraction condenser, which is connected to the top of the extraction tower. The extraction condenser includes a first outlet and a second outlet. The inlet and the first outlet of the extraction condenser are connected to the top of the extraction tower. The second outlet of the extraction condenser is used to discharge raffinate product that does not contain aromatics.

[0014] Optionally, the integrated unit further includes an integrated condenser, both ends of which are connected to the top of the integrated tower to achieve the distillation of aromatics.

[0015] Optionally, the integrated unit further includes a xylene reboiler, the two ends of which are connected to the two ends of the xylene refining tower to realize the recycling of xylene separated from aromatics.

[0016] Optionally, the operating pressure of the extraction tower is ≤0.1MPa, the operating temperature at the top of the extraction tower is 90℃~110℃, and the operating temperature at the bottom of the extraction tower is 165℃~178℃.

[0017] Optionally, the operating pressure of the rectification section is 20 kPa to 60 kPa; the operating temperature of the rectification section is 45°C to 60°C.

[0018] Optionally, the temperature of the side-line product outlet section is 75℃~90℃; and / or,

[0019] The operating temperature of the stripping section is 165℃~178℃.

[0020] Optionally, the extraction column has 40 to 60 theoretical trays; and / or,

[0021] The theoretical number of trays in the integrated tower is 45 to 75; and / or,

[0022] The theoretical number of trays in the xylene refining column is 5 to 15.

[0023] Optionally, the mass ratio of lean solvent to cracked gasoline in the extraction tower is 2 to 6.

[0024] The technical solutions provided in this application have the following advantages compared with the prior art:

[0025] This application provides a system for separating aromatics from cracked gasoline. By employing an extraction tower, countercurrent contact extraction is carried out between lean solvent cracked gasoline components, ensuring sufficient extraction of aromatics from the C6-C8 fractions. The system then passes through an integrated tower comprising an integrated tower, an integrated reboiler, and a xylene refining tower. The integrated tower performs pre-fractionation, rectification, stripping, and xylene refining on the aromatic-rich solvent. The pre-fractionation section allows for initial separation of the lean solvent and extracted aromatics, while also separating benzene and a portion of the toluene-xylene mixture within the aromatics. The rectification section further separates and collects the benzene from the toluene-xylene mixture. Since benzene has the lowest boiling point, a high-purity benzene product is obtained. Finally, baffles are installed within the integrated tower. This system not only divides the integrated tower into multiple working areas, including a pre-fractionation section, a rectification section, a stripping section, and a side-stream xylene and toluene collection section, but also avoids mixing between the gas and liquid phases, improving the purity of the toluene product. Further stripping allows for more precise separation of aromatics and lean solvents, and further separation of the remaining toluene and xylene in the lean solvent. The separated xylene is then separated from the system via the side-stream xylene and toluene collection sections, and finally passes through a xylene refining tower to improve the purity of the separated xylene. Thus, by using only two main processing towers plus a xylene refining tower, high-purity separation and collection of various aromatic products from cracked gasoline can be achieved, shortening the process for separating aromatics from cracked gasoline and simultaneously improving the purity of benzene, toluene, and xylene products within the aromatics. Attached Figure Description

[0026] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0027] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the system structure provided in the embodiments of this application;

[0029] Figure 2 A schematic diagram of the process system provided as a comparative example in this application;

[0030] Among them, 1-extraction unit, 11-extraction tower, 12-extraction reboiler, 13-extraction condenser, 2-integrated unit, 21-integrated tower, 22-integrated reboiler, 23-partition, 24-tray, 25-integrated condenser, 26-xylene refining tower, 27-xylene reboiler, 3-recovery tower, 4-benzene tower, 5-toluene tower, A-cracked gasoline, B-raffinate oil, C-rich solvent, D-benzene, E-toluene, F-xylene, G-lean solvent, I-pre-fractionation section, II-rectification section, III-side-stream xylene and toluene extraction section, IV-stripping section. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0032] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0033] like Figure 1 As shown in the figure, this application provides a system for separating aromatics from cracked gasoline, the system comprising:

[0034] Extraction unit 1, which includes an extraction tower 11, to achieve extraction of cracked gasoline with lean solvent;

[0035] The integrated unit 2 includes an integrated tower 21, an integrated reboiler 22, and a xylene refining tower. The bottom of the extraction tower 11 is connected to the feed inlet of the integrated tower 21, and both ends of the integrated reboiler 22 are connected to the discharge outlet of the integrated tower 21, so as to realize the recycling of the lean solvent after distillation.

[0036] The integrated tower 21 includes a partition 23 and a plurality of trays 24. The trays 24 are arranged laterally at intervals within the integrated tower 21, so that the integrated tower 21 is divided from top to bottom into a rectification section II, a middle processing section, and a stripping section IV. The partition 23 is disposed within the integrated tower 21 and is arranged perpendicular to the plane of the trays 24, so as to divide the middle processing section into a pre-fractionation section I and a side-stream xylene and toluene extraction section III.

[0037] The integrated reboiler 22 is connected to the bottom outlet of the integrated tower 21, and both ends of the integrated reboiler 22 are connected to the outlet of the integrated tower 21, so as to realize the heating treatment of the lean solvent after distillation.

[0038] The side-stream xylene and the toluene extraction section III are connected to the xylene refining tower 26. The bottom of the extraction tower 11 is connected to the middle of the integrated tower 21. The bottom liquid outlet of the xylene refining tower 26 and the middle discharge outlet of the integrated tower 21 are both connected to the middle of the extraction tower 11 to achieve the recycling of lean solvent.

[0039] In this embodiment of the application, the system includes an extraction unit 11 and an integration unit 22. The extraction unit 11 is used to achieve countercurrent contact between the lean solvent and the cracked gasoline and extract aromatics. The integration unit 22 is then used to process the rich solvent from which the aromatics have been extracted, thereby achieving the separation of benzene, toluene and lean solvent in the aromatics.

[0040] Extraction column 11 is a device that involves counter-current contact between a lean solvent and the C6-C8 components of cracked gasoline within the column. Aromatic hydrocarbons such as benzene, toluene, and xylene in the gasoline components are extracted into the lean solvent. At the top of extraction column 11, aromatic-free alkanes are obtained. These aromatic-free alkanes are referred to in the industry as raffinate, which can be directly discharged from the system for the next process. At the bottom of extraction column 11, an aromatic-rich solvent is obtained. Extraction column 11 can employ liquid-liquid extraction or extractive distillation techniques. When extractive distillation is used, a cooling system is installed at the top of extraction column 11, and a reboiler is installed at the bottom. The trays 24 can be either sieve trays or valve trays.

[0041] Integrated column 21 is a wall-splitting column that integrates the separation of aromatics from the solvent in a solvent-rich environment, as well as the separation of aromatics into products such as benzene and toluene, into a single column. A wall-splitting column is a distillation device with a partition 23 located in the middle of a conventional distillation column. The partition 23 is installed vertically to prevent lateral mixing of the liquid and gas phases on both sides. The internal structure of the wall-splitting column is divided into a rectification section II, a pre-fractionation section I, a side-stream xylene and toluene collection section III, and a stripping section IV. Pre-fractionation section I is separated from the side-stream xylene and toluene collection section III by a partition 23, forming pre-fractionation section I. This section performs rough fractionation on the feed, allowing a mixture of benzene and a portion of toluene and xylene to enter rectification section II for distillation, producing benzene gas. The toluene and xylene mixture is further separated into toluene and xylene in side-stream xylene and toluene collection section III. At this point, the lean solvent and the mixture of toluene and xylene pass through stripping section IV for separation. The lean solvent is collected at the bottom of integrated column 21, while the mixture of toluene and xylene is further separated into toluene and xylene in side-stream xylene and toluene collection section III. This completes the separation of aromatics and lean solvent within the integrated column, yielding a high-purity product. Side-stream xylene and toluene collection section III, together with rectification section II and stripping section IV, constitutes the main column, where light, medium, and heavy components are separated. A condenser is installed at the top of the column, and a reboiler is installed at the bottom. The rich solvent enters the pre-fractionation section I of the integrated tower 21. Benzene is obtained at the top of the tower. Toluene is obtained from the side-stream xylene and the product from the side-stream of toluene collection section III. Xylene is obtained from the bottom of the side-stream xylene and the product from the bottom of toluene collection section III. The bottom of the tower yields the lean solvent recycled back to the extraction tower 11. The integrated tower 21 is a vacuum tower operating under negative pressure. The xylene refining tower 26 is used to refine the xylene produced from the side-stream xylene and toluene collection section III. Since this xylene may contain a small amount of lean solvent, it needs to be removed to obtain a high-purity xylene product. The xylene refining tower 26 can be a plate tower or a packed tower.

[0042] To ensure that the lean solvent used does not decompose, the bottom of the extraction tower 11 and the integrated tower 21 in this application are heated by steam, heat transfer oil or other media, and the temperature of the heating medium is controlled at 200℃~220℃ to ensure that the operating temperature in the extraction tower 11 and the integrated tower 21 is within the expected range.

[0043] Lean solvents refer to solvents that can extract aromatics from reformed gasoline but have not yet extracted the aromatics, including sulfolane organic solvents.

[0044] Rich solvent refers to a lean solvent from which aromatics have been extracted. The trays 24 of the integrated column 21 are generally set to 45–75, preferably 51–69. Correspondingly, the trays 24 of the extraction column 11 are generally 40–60, preferably 45–50. The xylene purification column 26 theoretically has 5–15 trays 24, preferably 10–15.

[0045] In some optional embodiments, the extraction unit 1 further includes an extraction reboiler 12, both ends of which are connected to the extraction column 11 to achieve the recycling of the solvent rich in aromatics.

[0046] In this embodiment, the extraction unit 1 further includes an extraction reboiler 12, which is used to reboil the rich solvent, so that the rich solvent re-enters the extraction tower 11 for extraction again, thereby enabling the lean solvent to be fully extracted from the C6 to C8 components of the cracked gasoline.

[0047] In some optional embodiments, the extraction unit 1 further includes an extraction condenser 13, which is connected to the top of the extraction tower 11. The extraction condenser 13 includes a first outlet and a second outlet. The inlet and the first outlet of the extraction condenser 13 are connected to the top of the extraction tower 11. The second outlet of the extraction condenser 13 is used to discharge raffinate product that does not contain aromatics.

[0048] In this embodiment, the extraction unit 1 further includes an extraction condenser 13, which is used to condense the non-C6 to C8 components in the cracked gasoline after countercurrent contact to form raffinate components, which are then collected for the next stage. Optionally, the integrated unit 2 also includes an integrated condenser 25, both ends of which are connected to the top of the integrated tower 21 to achieve solvent-rich distillation, thereby enabling the distillation and separation of benzene, toluene, and xylene.

[0049] In some alternative embodiments, the integrated unit 2 further includes an integrated condenser 25, both ends of which are connected to the top of the integrated tower 21 to achieve the distillation of aromatics.

[0050] In this embodiment of the application, the integrated unit 2 further includes an integrated condenser 25, which is used to further separate the mixture of benzene, toluene and xylene separated in the aromatics during the distillation stage, so that the benzene is condensed into liquid and discharged from the integrated tower 21, thus completing the collection of high-purity benzene.

[0051] In some optional embodiments, the integrated unit 2 further includes a xylene reboiler 27, the two ends of which are connected to the two ends of the xylene refining tower 26 to realize the recycling of xylene separated from aromatics.

[0052] In this embodiment of the application, the integrated unit 2 further includes a xylene reboiler 27, which can perform multiple cycles of processing on the separated xylene to ensure that the small amount of solvent-poor xylene is completely processed, thereby obtaining a pure xylene product.

[0053] In some optional embodiments, the operating pressure of the extraction tower 11 is ≤0.1MPa, the operating temperature at the top of the extraction tower 11 is 90℃~110℃, and the operating temperature at the bottom of the extraction tower 11 is 165℃~178℃.

[0054] In this embodiment, the operating pressure, top operating temperature, and bottom operating temperature of the extraction tower 11 are limited. Based on the requirement for countercurrent contact of benzene, toluene, and xylene in the aromatics in the lean solvent, and combined with the specific characteristics of cracked gasoline and lean solvent, the aromatics in the cracked gasoline enter the lean solvent to form a rich solvent, which facilitates the subsequent processing work of the integrated tower 21.

[0055] In some optional embodiments, the operating pressure of the rectification section II is 20 kPa to 60 kPa; the operating temperature of the rectification section II is 45°C to 60°C.

[0056] In this embodiment, the specific operating pressure and temperature of the rectification section II are defined to ensure that the rectification of a mixture of benzene and partial toluene and xylene can proceed smoothly.

[0057] In some optional embodiments, the temperature of the side-line product outlet section III is 75°C to 90°C; and / or,

[0058] The operating temperature of the stripping section is 165℃~178℃.

[0059] In this embodiment of the application, the positive effect of limiting the temperature of the side-stream product outlet section III to 75°C to 90°C is that within this temperature range, toluene and xylene can be ensured to be discharged from the system through the side-stream xylene and toluene outlet section III respectively. Toluene is discharged from the side-stream outlet area of ​​the side-stream xylene and toluene outlet section III, and xylene product is discharged from the lower outlet area of ​​the side-stream xylene and toluene outlet section III.

[0060] In some optional embodiments, the extraction column 11 has 40 to 60 theoretical trays; and / or,

[0061] The theoretical number of trays in the integrated tower 21 is 45 to 75; and / or,

[0062] The theoretical number of trays in the xylene refining column 26 is 5 to 15.

[0063] In this embodiment, the theoretical number of trays in the extraction tower 11, the integrated tower 21, and the xylene purification tower 26 is limited. This ensures sufficient countercurrent contact time between the cracked gasoline and lean solvent in the extraction tower 11, and also ensures the normal operation of each working area in the integrated tower 21. This guarantees the separation effect of benzene, toluene, and xylene in aromatics, as well as the separation purity of benzene and toluene in aromatics. At the same time, it also ensures the purification effect of the separated xylene in the xylene purification tower 26, thereby ensuring the purity and separation efficiency of the product.

[0064] Due to the influence of the actual environment of the unit and the specifications of different reformed gasoline, the actual number of trays is generally higher than the theoretical number of trays.

[0065] In some alternative embodiments, the mass ratio of lean solvent to cracked gasoline in the extraction tower 11 is 2 to 6.

[0066] In the embodiments of this application, the positive effect of limiting the mass ratio of lean solvent to reformed gasoline to 2 to 6 is that within this mass ratio range, it can be ensured that the lean solvent extracts the aromatics from the reformed gasoline, thereby ensuring the collection of benzene and toluene from the aromatics in the subsequent distillation stage.

[0067] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0068] Example 1

[0069] like Figure 1 As shown in the figure, this application provides a system for separating aromatics from cracked gasoline, comprising:

[0070] Extraction unit 1 includes extraction column 11 to achieve extraction of cracked gasoline with lean solvent;

[0071] The integrated unit 2 includes an integrated tower 21, an integrated reboiler 22, and a xylene refining tower 26. The bottom of the extraction tower 11 is connected to the feed inlet of the integrated tower 21, and both ends of the integrated reboiler 22 are connected to the discharge outlet of the integrated tower 21, so as to realize the recycling of the lean solvent after distillation.

[0072] The integrated reboiler 22 is connected to the bottom outlet of the integrated column 21, and both ends of the integrated reboiler 22 are connected to the outlet of the integrated column 21, so as to achieve heating treatment of the lean solvent after distillation.

[0073] The integrated tower 21 includes a partition plate 23 and multiple trays 24. The trays 24 are arranged laterally at intervals within the integrated tower 21, so that the integrated tower 21 is divided from top to bottom into a rectification section II, a middle processing section and a stripping section IV. The partition plate 23 is located within the integrated tower 21 and is arranged perpendicular to the plane of the trays 24, so as to divide the middle processing section into a pre-fractionation section I and a side-stream xylene and toluene extraction section III.

[0074] The side-stream xylene and the toluene extraction section III are connected to the xylene refining tower 26. The bottom of the extraction tower 11 and the middle of the integrated tower 21 are connected. The bottom liquid outlet of the xylene refining tower 26 and the middle discharge outlet of the integrated tower 21 are both connected to the middle of the extraction tower 11 to achieve the recycling of lean solvent.

[0075] The extraction unit 1 also includes an extraction reboiler 12, both ends of which are connected to the extraction tower 11 to achieve the recycling of the solvent rich in aromatics.

[0076] The extraction unit 1 also includes an extraction condenser 13, which is connected to the top of the extraction tower 11. The extraction condenser 13 includes a first outlet and a second outlet. The inlet and the first outlet of the extraction condenser 13 are connected to the top of the extraction tower 11. The second outlet of the extraction condenser 13 is used to discharge raffinate products that do not contain aromatics.

[0077] The integrated unit 2 also includes an integrated condenser 25, both ends of which are connected to the top of the integrated tower 21 to achieve the distillation of aromatics.

[0078] The integrated unit 2 also includes a xylene reboiler 27, which is connected to both ends of the xylene refining tower 26 to achieve the recycling of xylene separated from aromatics.

[0079] Among them, the extraction column 11 has 45 to 50 theoretical trays, the top operating temperature is 105℃ to 109℃, the bottom operating temperature is 170℃ to 174℃, the top operating pressure is 0.04MPa(g) to 0.1MPa(g), and the mass ratio of lean solvent to cracked gasoline is 3 to 4.

[0080] The theoretical number of trays in integrated tower 21 is 51 to 69, the operating temperature at the top of the tower is 50℃ to 55℃, the temperature of the side-stream xylene and toluene extraction section III is 75℃ to 90℃, the operating temperature at the bottom of the tower is 170℃ to 174℃, and the operating pressure at the top of the tower is 20 kPa(a) to 60 kPa(a).

[0081] The xylene refining column 26 has 10 to 15 trays, an operating temperature of 105℃ to 110℃ at the top, an operating temperature of 160℃ to 166℃ at the bottom, and an operating pressure of 30 kPa(a) to 0.04 MPa(a) at the top.

[0082] Example 2

[0083] Comparing Example 2 with Example 1, the difference between Example 2 and Example 1 is as follows:

[0084] The feedstock is a typical DCC gasoline C6-C8 component, as shown in Table 1. The feed rate is 400,000 tons / year, the feed pressure is 0.15 MPa (g), the feed temperature is 110℃, and the mass ratio of lean solvent to cracked gasoline is 4.

[0085] The extraction tower operates at a pressure of 0.04 MPa (g) and requires 86 trays; the integrated tower is a split-wall tower, operating at a pressure of 30 kPa (a), requiring 116 trays; the xylene refining tower operates at atmospheric pressure and requires 20 trays. The system used employs the following... Figure 1 As shown in Table 2, the process parameters are as follows.

[0086] Comparative Example 1

[0087] Comparative Example 1 and Example 3 will be compared. The difference between Comparative Example 1 and Example 3 is as follows:

[0088] The separation process employs an extraction tower 11, a recovery tower 3, a benzene tower 4, and a toluene tower 5.

[0089] The process conditions are as follows: the raw material is a typical DCC gasoline C6-C8 component, the composition of which is shown in Table 1; the feed rate is 400,000 tons / year; the feed pressure is 0.15 MPa (g); the feed temperature is 110℃; and the mass ratio of lean solvent to cracked gasoline is 4.

[0090] Extraction tower 11 operates at a pressure of 0.05 MPa (g) and requires 86 trays; recovery tower 3 operates at a pressure of 30 kPa (a) and requires 34 trays; benzene tower 4 operates at a pressure of 0.07 MPa (g) and requires 66 trays; toluene tower 5 operates at a pressure of 0.4 MPa (g) and requires 66 trays. The system used in the process flow is as follows: Figure 2 As shown in Table 2, the process parameters are as follows.

[0091] Relevant experimental and effect data:

[0092] Separation requirements: Based on the actual separation effects of each embodiment and comparative example, benzene needs to meet the requirements of national standard GB / T3405, with a purity of 99.9% (mass); toluene needs to meet the requirements of national standard GB / T 3406, with a purity of 99.9% (mass); and xylene needs to meet the requirements of national standard GB / T 3406, with a purity of 98.5% (mass).

[0093] Table 1. Composition of typical DCC gasoline C6-C8 components (wt%)

[0094]

[0095] Table 2 Process Parameters

[0096]

[0097] As shown in Table 2, the energy can be saved by 25.4% by adopting the process flow and process system of this application.

[0098] As can be seen from the data in Examples 1-3, by using the process system of this invention, high-purity separation and collection of various aromatic products in cracked gasoline can be achieved through only two main processing towers and an additional xylene refining tower 2626, thereby shortening the process of separating aromatics in cracked gasoline and improving the purity of benzene, toluene and xylene products in aromatics.

[0099] To further illustrate the working procedure of this application system, the following is combined with... Figure 1 Further detailed description, but not limited to the embodiments:

[0100] like Figure 1 As shown, the C6-C8 components A of DCC gasoline enter the middle of the extraction tower, while the circulating lean solvent (sulfolane) enters the upper middle part of the extraction tower 11. The two components contact counterclockwise in the extraction tower 11. The lean solvent extracts the aromatics from the gasoline components and is then drawn out from the bottom of the tower as the rich solvent C, entering the integrated tower 21. The top material of the extraction tower 11 is condensed and cooled to obtain the raffinate product without aromatics.

[0101] The rich solvent C enters the lower part of the pre-fractionation section I of the integrated column 21 for coarse separation of aromatics and solvent. The separated aromatics flow upward into the rectification section II for separation of benzene and toluene. The benzene at the top of the column is condensed and refluxed. The benzene product is drawn out from the tray at the top 4-5 layers of the column to ensure that the benzene product is free of water.

[0102] The solvent flows downwards in the pre-fractionation section I into the stripping section IV for fine separation of the solvent and aromatics. The bottom of the column yields a lean solvent free of aromatics, which is returned to the extraction column 11 for recycling. Toluene and xylene are separated in the side-stream xylene and toluene collection section III. Toluene is obtained in the middle of the collection section, while xylene from the bottom enters the xylene refining column 2626 for xylene de-lean solvent removal. The top of the xylene refining column 2626 yields xylene with a purity greater than 98.5% (by mass), while the bottom solvent containing a small amount of aromatics, along with the lean solvent, is returned to the extraction column 11 for recycling.

[0103] Both the bottom of extraction column 11 and the bottom of integrated column 21 are heated by steam. To prevent the decomposition of the solvent sulfolane, the steam temperature is controlled at 200-220℃.

[0104] One or more technical solutions in the embodiments of this application have at least the following technical effects or advantages:

[0105] (1) The system for separating aromatics in cracked gasoline provided in this application uses an integrated tower 21 that is only a wall-breaking tower, replacing the recovery tower 3, benzene tower 4 and toluene tower 5 in the traditional process, reducing the number of towers and their auxiliary facilities by 2, resulting in a shorter process and less land occupation, with a land occupation reduction of about 70%.

[0106] (2) The system for separating aromatics in cracked gasoline provided in this application embodiment avoids the backmixing effect of intermediate components due to the wall-mounted tower structure adopted by the integrated tower 21, and has a high separation efficiency. It can separate four products, including benzene, toluene, xylene and solvent, in one tower. Compared with the conventional process, the utility consumption is reduced by more than 25%.

[0107] (3) The system for separating aromatics from cracked gasoline provided in this application embodiment reduces the number of main equipment by more than 65% and saves more than 50% of the total equipment investment compared with the traditional process.

[0108] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0109] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0110] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for separating aromatics from catalytically cracked gasoline, characterized in that, The system used in the method includes: Extraction unit (1), the extraction unit (1) includes an extraction tower (11) to achieve extraction of cracked gasoline with lean solvent to obtain solvent-rich and raffinate oil; The integrated unit (2) includes an integrated tower (21), an integrated reboiler (22), and a xylene refining tower (26); The integrated tower (21) is a split-wall tower, including a partition plate (23) and multiple trays (24). The trays (24) are arranged horizontally at intervals within the integrated tower (21) so that the integrated tower (21) is divided into a rectification section, a middle processing section and a stripping section from top to bottom. The partition plate (23) is located within the integrated tower (21) and is arranged perpendicular to the plane of the trays (24) to divide the middle processing section into a pre-fractionation section and a side-stream xylene and toluene extraction section. The pre-fractionation section is used for preliminary separation of solvent-rich materials. The side-stream product extracted from the side-stream xylene and toluene extraction section is toluene, and the bottom product extracted from the side-stream xylene and toluene extraction section is xylene. The bottom of the extraction tower (11) is connected to the feed port of the integrated tower (21) to introduce the rich solvent into the pre-fractionation section of the integrated tower (21). The two ends of the integrated reboiler (22) are connected to the discharge port of the integrated tower (21) to heat the lean solvent after distillation. The side-stream xylene and the toluene extraction section are connected to the xylene refining tower (26), the bottom of the extraction tower (11) is connected to the middle of the integrated tower (21), and the bottom liquid outlet of the xylene refining tower (26) and the bottom discharge outlet of the integrated tower (21) are both connected to the middle of the extraction tower (11) to realize the recycling of lean solvent; The extraction tower (11) has a theoretical number of 40 to 60 trays; the integrated tower (21) has a theoretical number of 45 to 75 trays; and the xylene refining tower (26) has a theoretical number of 5 to 15 trays. The method includes the following steps: C6-C8 components of catalytically cracked gasoline are fed into the middle section of an extraction tower, while a circulating lean solvent, sulfolane, is fed into the upper middle section of the extraction tower. The two solvents are in counter-current contact within the extraction tower. The lean solvent extracts the aromatics from the gasoline components and is then drawn from the bottom of the tower as a rich solvent, entering an integrated tower. The top material of the extraction tower is condensed and cooled to obtain a raffinate product free of aromatics. The rich solvent enters the lower part of the pre-fractionation section of the integrated tower for coarse separation of aromatics and solvent. The separated aromatics flow upwards into the rectification section for the separation of benzene and toluene. The benzene at the top of the tower is condensed and refluxed. The solvent is drawn from the trays at the top 4-5 layers of the column. It flows downward in the pre-fractionation section into the stripping section for fine separation of solvent and aromatics. The bottom of the column yields a lean solvent free of aromatics, which is returned to the extraction column for recycling. Toluene and xylene are separated in the side stream xylene and toluene collection sections. Toluene product is obtained in the middle of the collection section, and xylene is obtained at the bottom of the collection section. It enters the xylene refining column for xylene purification to remove the lean solvent. The top of the xylene refining column yields xylene with a mass purity greater than 98.5%, and the solvent containing a small amount of aromatics at the bottom of the column is returned to the extraction column for recycling along with the lean solvent. Both the bottom of the extraction tower and the bottom of the integrated tower are heated by steam, with the steam temperature controlled at 200-220℃. The operating pressure of the extraction column (11) is ≤0.1MPa, the operating temperature of the top of the extraction column (11) is 90℃~110℃, and the operating temperature of the bottom of the extraction column (11) is 165℃~178℃; the operating pressure of the rectification section is 20kPa~60kPa; the operating temperature of the rectification section is 45℃~60℃, the temperature of the side stream product outlet section is 75℃~90℃; the operating temperature of the stripping section is 165℃~178℃, and the mass ratio of lean solvent to cracked gasoline in the extraction column (11) is 2~6.

2. The method according to claim 1, characterized in that, The extraction unit (1) also includes an extraction reboiler (12). Both ends of the extraction reboiler (12) are connected to the extraction tower (11) to realize the recycling of the solvent containing aromatics.

3. The method according to claim 1, characterized in that, The extraction unit (1) further includes an extraction condenser (13), which is connected to the top of the extraction tower (11). The extraction condenser (13) includes a first outlet and a second outlet. The inlet and the first outlet of the extraction condenser (13) are connected to the top of the extraction tower (11). The second outlet of the extraction condenser (13) is used to discharge raffinate products that do not contain aromatics.

4. The method according to claim 1, characterized in that, The integrated unit (2) also includes an integrated condenser (25), both ends of which are connected to the top of the integrated tower (21) to achieve the distillation of aromatics.

5. The method according to claim 1, characterized in that, The integrated unit (2) also includes a xylene reboiler (27), the two ends of which are connected to the two ends of the xylene refining tower (26) to realize the recycling of xylene separated from aromatics.

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