A method and apparatus for separating aromatics from diesel fuel using a liquid-phase simulated moving bed.

Abstract

A method and apparatus for separating aromatics from diesel fuel using a liquid-phase simulated moving bed, wherein the simulated moving bed contains multiple adsorbent beds, and along the flow direction of the circulating material within the simulated moving bed, the material inlet and outlet positions are sequentially: first desorbent (D1), second desorbent (D2), extractant (E), diesel feedstock (F), and raffinate (R). Each of the above-mentioned material inlet or outlet moves one bed layer along the flow direction of the circulating material within the simulated moving bed every step time t. The extractant enters an extractant column for distillation separation, yielding an aromatic-rich component from the bottom of the column. The raffinate enters a raffinate column for distillation separation, yielding a component from which most of the aromatics have been removed from the bottom of the column. The first desorbent is a saturated hydrocarbon, and the second desorbent is a light aromatic hydrocarbon. The method provided by this invention achieves better separation of aromatics and non-aromatics in the feedstock, obtaining aromatics with a purity higher than 97 wt%, and the remaining aromatics in the non-aromatic component being less than 3 wt%.

Description

Technical Field

[0001] This invention relates to the field of aromatic hydrocarbon separation from hydrocarbons, specifically, to a method and apparatus for separating aromatic hydrocarbons from diesel fuel using a liquid-phase simulated moving bed adsorption. Background Technology

[0002] Using a simulated moving bed to separate isomers with very small boiling point differences or two groups of components with different structural characteristics is quite effective. This method achieves countercurrent contact between the liquid and solid phases, improving separation efficiency. Typically, the simulated moving bed device has at least three functional zones, with four zones being more common, and a few having five zones. A typical SMB adsorption separation process includes at least two feed streams (F and D) and at least two discharge streams (E and R).

[0003] US2985589A, US3201491A, US3969223A, US3626020A, US3686342A, US3997620A, US4006197A, and US4326092A disclose methods for separating p-xylene, m-xylene, olefins, and n-alkanes using a simulated moving bed adsorption separation device. The equipment for controlling the flow of materials into and out of the adsorption tower can be a rotary valve or a series of on / off valves.

[0004] Diesel fuel is an important petroleum product, primarily used as fuel for vehicles and ships. Diesel fractions typically have a distillation range of 180–350°C and are mixtures of various hydrocarbons with 10 to 20 carbon atoms or higher, including alkanes, cycloalkanes, and aromatics with different structures. With the rapid rise of new energy vehicles and the growing trend towards green and low-carbon development, the oil refining industry faces overcapacity and urgently needs transformation and upgrading. Some diesel fractions in refineries will be converted into chemical feedstocks for the production of olefins or aromatics.

[0005] One method for treating aromatics in diesel fractions is hydroremoval, typically employing a two-stage hydroremoval process. The catalysts, temperatures, pressures, and processes used are publicly reported in numerous patents, such as CN1115390A, CN1119395A, and CN100478426A. This method requires saturating aromatics under relatively harsh conditions and consumes a large amount of hydrogen.

[0006] Another processing method is to separate aromatics from saturated hydrocarbons, and utilize the two materials separately. The material enriched with aromatics is then processed and used as an aromatic feedstock for the production of BTX (benzene, toluene, xylene). Extraction and separation of aromatics from diesel fuel has been reported earlier, such as in CN102021024A and CN104073291A. However, the separation efficiency of aromatics in diesel fuel extraction is limited. The concentration of extracted aromatics can reach 90% by mass, which is difficult to further increase to over 95% by mass. The amount of residual aromatics in the raffinate is also relatively high, usually above 10% by mass.

[0007] In recent years, several methods for separating aromatic hydrocarbons from diesel fuel using simulated moving bed adsorption separation have been disclosed. CN105542835A discloses a method for separating polycyclic aromatic hydrocarbons (PAHs) from diesel fuel using simulated moving bed adsorption separation. Diesel fuel, after pretreatment to remove impurities, enters a simulated moving bed adsorption separation device. PAHs are adsorbed by an adsorbent with selective adsorption capacity, and then the adsorbent is regenerated using a desorbent. Examples show that when the PAH content is in the range of 83.4% to 92.18% by mass, and the PAH removal rate is in the range of 76.2% to 94.23% by mass, a relatively good separation effect can be achieved. CN105349175A discloses a method for simultaneously adsorbing and removing sulfides and aromatics from diesel fuel. The diesel fuel is fed into a simulated moving bed adsorption separation device, where sulfides and aromatics are adsorbed in the adsorption zone, and then regenerated in the regeneration zone by a desorbent to obtain sulfur-containing heavy aromatic components. The aromatic removal rate given in the examples is in the range of 64.1% by mass to 73.1% by mass.

[0008] CN106187666A discloses a C10+ aromatic hydrocarbon adsorption and separation method, which utilizes a simulated moving bed adsorption and separation device with multiple columns in series and employs a metal-modified amorphous aluminosilicate adsorbent to finally obtain aromatic and non-aromatic components; in the embodiments, the aromatic hydrocarbon content of the raw material is 77.5% to 79.8% by mass, and the aromatic hydrocarbon content of the separated aromatic hydrocarbon components is 88.25% to 91.41% by mass. CN109022020A discloses a multi-component adsorption separation method for diesel fuel, which employs two interconnected 16-24 column simulated moving bed adsorption separation devices. In the first adsorption separation device, alkanes in the diesel fuel are separated out. The remaining cycloalkane-aromatic components are separated into three parts in the second adsorption separation device. The cycloalkane is not adsorbed. The aromatics adsorbed by the adsorbent are first replaced by desorbent D1 (one or more of cyclohexane, methylcyclopentane, or methylcyclohexane) to displace the monocyclic aromatics, and then replaced by desorbent D0 (one or more of toluene, ethylbenzene, or p-diethylbenzene) to displace the polycyclic aromatic components.

[0009] Existing technologies can achieve good results in separating polycyclic aromatic hydrocarbons from diesel fuel, but there are still significant shortcomings in separating monocyclic aromatic hydrocarbons and polycyclic aromatic hydrocarbons simultaneously. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a simulated moving bed adsorption separation method and apparatus to achieve effective separation of aromatic hydrocarbons and non-aromatic hydrocarbons in diesel fuel.

[0011] In a first aspect, the present invention provides a method for separating aromatics from diesel fuel using a liquid-phase simulated moving bed. The simulated moving bed is provided with multiple adsorbent beds. Along the flow direction of the circulating material within the simulated moving bed, the entry and exit points of each material are, in sequence, a first desorbent D1, a second desorbent D2, extractant E, diesel feedstock F, and raffinate R. The injection or extraction point of each of the above-mentioned materials moves one bed along the flow direction of the circulating material within the simulated moving bed every step time t. The extractant enters an extractant tower for distillation separation, and a component rich in aromatics is obtained from the bottom of the tower. The raffinate enters a raffinate tower for distillation separation, and a component from which most of the aromatics have been removed is obtained from the bottom of the tower.

[0012] In the method provided by this invention, the first desorbent D1 is a saturated hydrocarbon, and the second desorbent D2 is a light aromatic hydrocarbon. The boiling point of the first desorbent D1 is lower than that of the second desorbent D2. The light aromatic hydrocarbon is selected from one or a mixture of several of benzene, toluene, ethylbenzene, p-xylene, m-xylene, and o-xylene.

[0013] In the method provided by this invention, the diesel feedstock typically refers to hydrocarbon fractions with a distillation range of 180-350°C. Materials with an initial boiling point below 180°C or a final boiling point above 350°C can also be processed. The diesel feedstock contains various aromatic hydrocarbon components with C9 or higher and saturated alkane components.

[0014] Secondly, the present invention provides a liquid-phase simulated moving bed apparatus for separating aromatics from diesel fuel, comprising a simulated moving bed adsorption tower, an extractor tower, and a raffinate tower. The simulated moving bed adsorption tower has multiple adsorbent beds, with pipelines connecting adjacent adsorbent beds to inlet and outlet material pipelines. The material inlet and outlet pipelines are at least a first desorbent material pipeline, a second desorbent material pipeline, an extractor material pipeline, a raw material pipeline, and a raffinate material pipeline, each equipped with a switch valve. The extractor material pipeline is connected to the extractor tower, and the raffinate material pipeline is connected to the raffinate tower. Depending on the needs, the material inlet and outlet pipelines may also include material pipelines for flushing.

[0015] The beneficial effects of the method and apparatus for separating aromatics from diesel fuel using a liquid-phase simulated moving bed provided by this invention are as follows:

[0016] The method for separating aromatics from diesel fuel using a simulated moving bed provided by this invention involves injecting two desorbents with significantly different adsorption capacities—a first desorbent and a second desorbent—at different locations on the simulated moving bed. This improves the separation efficiency and reduces desorbent consumption. Using the method provided by this invention, the aromatic content in the separated aromatic fraction from diesel fuel can reach over 95% by mass, while the aromatic content in the non-aromatic fraction can be as low as 3% by mass, demonstrating excellent separation performance.

[0017] The apparatus for separating aromatics from diesel fuel using a simulated moving bed provided by this invention is applicable to the above-described method. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of an adsorption tower for the method of separating aromatics from diesel fuel provided by the present invention.

[0019] Figure 2 This is a schematic diagram of the adsorption tower in a conventional simulated moving bed adsorption separation technology.

[0020] Figure 3 This is a schematic diagram of the material flow direction of the adsorption tower and distillation tower according to the first embodiment of the present invention.

[0021] Figure 4 This is a schematic diagram of the material flow direction of the adsorption tower and distillation tower according to the second embodiment of the present invention.

[0022] Figure 5 This is a schematic diagram showing the relative positions of the materials entering and exiting the simulated moving bed adsorption tower in Example 1.

[0023] Figure label:

[0024] D1 - First desorbent; D2 - Second desorbent; D - Desorbent

[0025] E - Extracted fluid; R - Residual fluid; F - Diesel feedstock

[0026] I - Desorption Zone II - Purification Zone III - Adsorption Zone

[0027] IV-Isolation Zone

[0028] 10 - Adsorption tower; 20 - Extraction liquid tower; 21, 31, 41 - Top discharge of the tower.

[0029] 22, 32 - Side stream discharge; 23, 33, 42 - Bottom discharge; 30 - Residual liquid in the evaporator.

[0030] 40-Desorbent Separation Tower Detailed Implementation

[0031] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0032] In a first aspect, the present invention provides a method for separating aromatics from diesel fuel using a liquid-phase simulated moving bed. The simulated moving bed has multiple adsorbent beds. Along the flow direction of the circulating material within the simulated moving bed, the entry and exit points of each material are, in sequence, a first desorbent D1, a second desorbent D2, extractant E, diesel feedstock F, and raffinate R. The injection or extraction point of each of the above-mentioned materials moves one bed along the flow direction of the circulating material within the simulated moving bed every t seconds. The extractant enters an extractant tower for distillation separation, and a component rich in aromatics is obtained from the bottom of the tower. The raffinate enters a raffinate tower for distillation separation, and a component from which most of the aromatics have been removed is obtained from the bottom of the tower.

[0033] In the method provided by this invention, the diesel feedstock typically refers to hydrocarbon fractions with a distillation range of 180-350°C. Materials with an initial boiling point below 180°C or a final boiling point above 350°C can also be processed. The diesel feedstock contains various aromatic hydrocarbon components with C9 or higher and saturated alkane components. The diesel fraction includes alkanes, cycloalkanes, and aromatics. Among them, the components classified as aromatics include many types: alkylbenzenes, indene and indene derivatives, indene derivatives, naphthalene and naphthalene derivatives, acenaphthenes, fluorene derivatives, and tricyclic aromatics, among which naphthalene and naphthalene derivatives, acenaphthenes, fluorene derivatives, and tricyclic aromatics are collectively referred to as polycyclic aromatic hydrocarbons.

[0034] The diesel feedstock is selected from one or more of catalytic cracking diesel, straight-run diesel, and hydrotreated diesel. Hydrotreated diesel fractions, due to their very low levels of impurities such as sulfur and nitrogen, can directly enter the adsorption tower. However, if straight-run diesel fractions directly enter the adsorption tower, the separation performance of the adsorbent will gradually decline. Preferably, before entering the adsorption tower, the straight-run diesel undergoes pretreatment to remove most of the sulfur, nitrogen, and gum.

[0035] In the method provided by this invention, the first desorbent D1 is a saturated hydrocarbon, and the second desorbent D2 is a light aromatic hydrocarbon, wherein the light aromatic hydrocarbon is selected from one or a mixture of several of benzene, toluene, ethylbenzene, p-xylene, m-xylene, and o-xylene. The boiling point of the first desorbent D1 is lower than that of the second desorbent D2, so that the saturated hydrocarbon in the first desorbent and the light aromatic hydrocarbon in the second desorbent can be separated by fractional distillation. For example, if the aromatic hydrocarbon in the second desorbent is benzene, then the saturated hydrocarbon in the first desorbent can be n-hexane, isohexane, cyclopentane, or a mixture of several of these. If the aromatic hydrocarbon in the second desorbent is toluene, then cyclohexane, isoheptane, n-heptane, and methylcyclohexane can all be components in the first desorbent.

[0036] Preferably, the mass flow rate ratio of the first desorbent D1 to the second desorbent D2 is 1.0 to 1.8:1.

[0037] In the method provided by the present invention, the simulated moving bed adsorption tower is provided with 10 to 16 adsorbent beds, and the positions of the first desorbent and the second desorbent entering the adsorption tower are spaced 1 to 2 beds apart;

[0038] Preferably, in the simulated moving bed adsorption tower, the number of beds in the desorption zone, purification zone, adsorption zone, and isolation zone are 3-5, 3-5, 3-5, and 2-3, respectively. Specifically, the adsorbent bed between the first desorbent injection and the extractant collection is the desorption zone; the adsorbent bed between the extractant collection and the feed injection is the purification zone; the adsorbent bed between the feed injection and the raffinate collection is the adsorption zone; and the adsorbent bed between the raffinate collection and the desorbent injection is the isolation zone.

[0039] In the method provided by this invention, the adsorbent is an adsorbent with selective adsorption of aromatics, and this invention is not limited in this regard. Silica gel is preferred as the adsorbent. The silica gel refers to commercially available silica gel adsorbents, which can be modified by acid, alkali, or metal salt treatment, or by reacting with hydroxyl groups on the silica gel surface to introduce various groups to modulate selectivity. It is usually in the form of spherical particles. Preheating is required to remove free moisture, but the surface silanol groups must not be destroyed.

[0040] The adsorbent used in this invention has a significantly higher adsorption selectivity for aromatic hydrocarbons than that for saturated hydrocarbons such as alkanes and cycloalkanes. The adsorption selectivity also varies considerably for different types of aromatic hydrocarbons. Generally, naphthalene and naphthalene derivatives are more selective than alkylbenzenes, tricyclic aromatic hydrocarbons are more selective, and there are also differences among different molecules belonging to the same alkylbenzene class.

[0041] The simulated moving bed used in the adsorption separation process of the method described in this invention comprises one or more adsorption towers, preferably one adsorption tower, each adsorption tower being divided into multiple adsorption bed layers by a grid. The function of the grid is to redistribute material from the upper bed layer to the lower bed layer, to uniformly mix externally introduced material with material from the upper bed layer, and to draw a portion of the material from the upper bed layer out of the adsorption tower. The grid allows liquid to pass through and intercepts adsorbent particles escaping from the adsorbent bed layer; its upper and lower surfaces are generally made of woven wire mesh, sintered metal mesh, or Johnson screen. Material introduced from the outside into a particular bed layer and material drawn out of the adsorption tower from the upper bed layer both enter and exit the adsorption bed layer through pipelines connected to the grid of that bed layer. The injection or extraction point of the material moves one bed layer in the same direction every step time t.

[0042] In the method provided by this invention, the operating temperature of the simulated moving bed adsorption tower is 20–160°C, preferably 50–120°C; the pressure is 0.5–2.0 MPa; the step time t is 100–350 seconds; the operating pressure of the extractor tower and the raffinate tower is 0.03–0.08 MPa, and the tower top temperature is 40–80°C. All pressures mentioned in this application are gauge pressures.

[0043] In one embodiment of the method of the present invention, the top discharge of the extraction liquid tower and the top discharge of the residual liquid tower enter the desorbent separation tower for separation. At least a portion of the top discharge is recycled back to the adsorption tower as a first desorbent, and at least a portion of the bottom discharge is recycled back to the adsorption tower as a second desorbent.

[0044] In a second embodiment of the method of the present invention, the top discharge of the extractant tower is recycled back to the adsorption tower as the first desorbent, and the side discharge of the extractant tower is recycled back to the adsorption tower as the second desorbent; the top discharge of the raffinate tower is recycled back to the adsorption tower as the first desorbent, and the side discharge of the raffinate tower is recycled back to the adsorption tower as the second desorbent.

[0045] Secondly, the apparatus for separating aromatics from diesel fuel using a liquid-phase simulated moving bed provided by the present invention includes a simulated moving bed adsorption tower, an extractor tower, and a raffinate tower. The simulated moving bed adsorption tower has multiple adsorbent beds, and pipelines connecting adjacent adsorbent beds to inlet and outlet material pipelines are provided. The material inlet and outlet pipelines are at least a first desorbent material pipeline, a second desorbent material pipeline, an extractor material pipeline, a raw material pipeline, and a raffinate material pipeline. Each inlet and outlet material pipeline is equipped with a switch valve. The extractor material pipeline is connected to the extractor tower, and the raffinate material pipeline is connected to the raffinate tower.

[0046] Optionally, the extracting liquid tower is provided with a top outlet, a side outlet, and a bottom outlet; the residual liquid tower is provided with a top outlet, a side outlet, and a bottom outlet; the top outlet of the extracting liquid tower and the top outlet of the residual liquid tower are connected to the first desorbent material pipeline; the side outlet of the extracting liquid and the side outlet of the residual liquid tower are connected to the second desorbent material pipeline.

[0047] Preferably, the extraction liquid tower has 35 to 60 trays, and the side stream outlet is located on the 8th to 21st trays; the residual liquid tower has 35 to 60 trays, and the side stream outlet is located on the 8th to 21st trays.

[0048] Optionally, the top discharge pipeline of the extracting liquid tower and the top discharge pipeline of the residual liquid tower are respectively connected to the feed inlet of the desorbent separation tower, the top discharge pipeline of the desorbent separation tower is connected to the first desorbent material pipeline, and the bottom discharge pipeline of the desorbent separation tower is connected to the second desorbent material pipeline.

[0049] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings, but the drawings do not constitute a limitation on the present invention.

[0050] Appendix Figure 1 A schematic diagram of the adsorption tower for the liquid-phase simulated moving bed method for separating aromatics from diesel fuel provided by this invention is attached. Figure 1As shown, the simulated moving bed adsorption tower has multiple adsorbent beds. Along the flow direction of the circulating material within the simulated moving bed, the entry and exit points of each material are, in sequence, the first desorbent D1, the second desorbent D2, the extractant E, the diesel feedstock F, and the raffinate R. Each injection or extraction point of these materials moves one bed layer along the flow direction of the circulating material within the simulated moving bed every t seconds. Based on the location of the first desorbent D1, the adsorbent bed between the injection of the first desorbent D1 and the extraction of the extractant E is designated as desorption zone I; the adsorbent bed between the extraction of the extractant E and the injection of the diesel feedstock F is designated as purification zone II; the adsorbent bed between the injection of the diesel feedstock F and the extraction of the raffinate R is designated as adsorption zone III; and the adsorbent bed between the extraction of the raffinate R and the injection of the first desorbent D1 is designated as isolation zone. Preferably, the number of simulated moving bed layers is 10 to 16. The entry points of the first desorbent D1 and the second desorbent D2 into the adsorption tower are spaced 1 to 2 bed layers apart.

[0051] The evaporate E enters the evaporator column for rectification and separation. A component rich in aromatics is obtained from the bottom of the column, and the top product is a mixture of the first and second desorbents. The raffinate R enters the raffinate column for rectification and separation. A component with most of the aromatics removed is obtained from the bottom of the column, and the top product is a mixture of the first and second desorbents. Both desorbents are further separated and recycled.

[0052] Appendix Figure 2 This is a schematic diagram of an adsorption tower in a conventional simulated moving bed adsorption separation technology. (See attached diagram.) Figure 2 As shown, the adsorption tower of the simulated moving bed is usually divided into desorption zone I, purification zone II, adsorption zone III and isolation zone IV. Only one desorbent D is used. Along the flow direction of the circulating material in the simulated moving bed, the entry and exit points of each material are, in order, desorbent D, extractant E, diesel feedstock F and raffinate R. The injection point or extraction point of each of the above materials moves one bed layer along the flow direction of the circulating material in the simulated moving bed every t seconds.

[0053] Appendix Figure 3 This is a schematic diagram of the material flow direction in the adsorption tower and distillation tower according to the first embodiment of the present invention. (See attached diagram.) Figure 3As shown, diesel feedstock F enters a simulated moving bed adsorption tower 10, along with the first desorbent D1 and the second desorbent D2. The extract E obtained from adsorption tower 10 enters extractor tower 20, containing the first desorbent D1, the second desorbent D2, and enriched aromatic components from the diesel feedstock. The top discharge 21 of extractor tower 20 yields a mixture of the first desorbent D1 and the second desorbent D2 via pipeline; the bottom discharge 23 of extractor tower 20 yields enriched aromatic components from the feedstock. The raffinate R obtained from adsorption tower 10 enters raffinate tower 30, containing the first desorbent D1, the second desorbent D2, and enriched non-aromatic components from the feedstock. The top discharge 31 of raffinate tower 30 yields a mixture of the first desorbent D1 and the second desorbent D2; the bottom discharge 33 of raffinate tower 30 yields enriched non-aromatic components from the feedstock.

[0054] The top discharge 21 of the evaporator and the top discharge 31 of the residue evaporator enter the desorbent separation tower 40 together. The main component of the top discharge 41 is saturated hydrocarbons with lower boiling points, which are recycled back to the adsorption tower as the first desorbent D1. The main component of the bottom discharge 42 is light aromatic hydrocarbons with relatively high boiling points, which are recycled back to the adsorption tower as the second desorbent D2.

[0055] Appendix Figure 4 This is a schematic diagram of the material flow direction in the adsorption tower and distillation tower according to the second embodiment of the present invention. (See attached diagram.) Figure 3 The implementation methods differ in that the top discharge 21 of the extraction liquid tower 20 mainly consists of saturated hydrocarbons with the lowest boiling point, which are recycled back to the adsorption tower 10 as the first desorbent D1; the side discharge 22 of the extraction liquid tower mainly consists of light aromatic hydrocarbons, which are recycled back to the adsorption tower 10 as the second desorbent D2; and the bottom discharge 23 of the extraction liquid tower 20 consists of the aromatic hydrocarbon components enriched in the raw material.

[0056] The top feed 31 of the raffinate tower 30 mainly consists of saturated hydrocarbons with the lowest boiling point, which is recycled back to the adsorption tower 10 as the first desorbent D1; the side feed 32 of the raffinate tower mainly consists of light aromatic hydrocarbons, which is recycled back to the adsorption tower 10 as the second desorbent D2; the bottom feed 33 of the raffinate tower 30 is the non-aromatic components enriched in the raw material.

[0057] The method of the present invention is further illustrated by the following examples, but the present invention is not limited thereto.

[0058] Example 1

[0059] The diesel feedstock processed was straight-run diesel fraction from the Tianjin branch of China Petroleum & Chemical Corporation, with an aromatics content of 23.8% by mass.

[0060] The silica gel adsorbent used is commercially available silica gel with a bulk density of approximately 0.59 kg / L and a BET specific surface area of ​​approximately 630 m².2 / g, consisting of small spheres with a particle size of 0.5–1.0 mm. The simulated moving bed consists of 12 adsorption columns, each filled with approximately 77g of silica gel adsorbent.

[0061] Appendix Figure 5 This is a schematic diagram illustrating the relative positions of the materials entering and exiting the simulated moving bed adsorption tower in the embodiment, as shown in the attached diagram. Figure 5 As shown, the simulated moving bed adsorption tower contains the following streams:

[0062] As attached Figure 5 As shown, each small line segment represents an adsorption column, labeled with numbers 1 to 12 respectively. The material flow direction is from column 1 to column 12, flowing to column 12 and then back to column 1. The first desorbent D1 and the second desorbent D2 are separated by one adsorption column. D2 and the extract E are separated by three adsorption columns. The extract E and the feed F are separated by three adsorption columns. The feed F and the raffinate R are separated by three adsorption columns. The raffinate R and the desorbent D1 are separated by two adsorption columns.

[0063] The simulated moving bed operates at a temperature of 80℃ and a pressure of approximately 1.0 MPa. The positions of each material inlet and outlet switch every 320 seconds, returning to their original positions after 12 cycles, thus completing one full cycle.

[0064] The composition and flow rate of each material are as follows:

[0065]

[0066] After the operation stabilized, the extract was analyzed. The aromatic content of the diesel fraction in the extract was 98.2% after normalization. The raffinate was analyzed. The aromatic content of the diesel fraction in the raffinate was 2.8% after normalization.

[0067] As shown in the attached document Figure 3 The method shown separates and recycles two desorbents in the extract and raffinate. The first desorbent D1 and the second desorbent D2 in the extract E are separated from the top of the extract column, and the first desorbent D1 and the second desorbent D2 in the raffinate R are separated from the top of the raffinate column. Both streams are then fed into the desorbent separation column 40. Cyclohexane, with a lower boiling point, is obtained from the top of the column, while toluene is obtained from the bottom. Both streams are then recycled back to the adsorption separation process. This method utilizes conventional distillation operations.

[0068] Example 2

[0069] The method for separating diesel feedstock using a simulated moving bed adsorption tower is the same as in Example 1.

[0070] The difference is that it adopts the method shown in the appendix. Figure 4The method shown separates and recycles two desorbents in the extract and raffinate. No separate desorbent separation tower is used; side streams are provided in both the extract and raffinate towers to obtain cyclohexane from the top. The side streams yield enriched toluene, containing a small amount of cyclohexane. The distillation process of the assumed components was simulated using the process simulation software Aspen Plus.

[0071] Assume that the components in extract E include cyclohexane, toluene, 1,2,3-trimethylbenzene, 1-methylnaphthalene, and dodecylbenzene, as shown in the table below. Tables 2-1, 2-2, and 2-3 present simulation results under different conditions. The number of trays, feed tray position, and side stream exit position are calculated based on theoretical trays. If a 70% tray efficiency is assumed, the actual trays corresponding to the number of trays, feed tray position, and side stream exit position of 40, 26, and 7 under the first separation condition are 57, 37, and 10, respectively.

[0072] Table 2-1 Simulation Results of Liquid Extraction Tower with Side Stream

[0073]

[0074] Table 2-2 Simulation Results of Liquid Extraction Tower with Side Stream

[0075]

[0076]

[0077] Table 2-3 Simulation Results of Liquid Extraction Tower with Side Stream

[0078]

[0079] Assuming that the components in the raffinate R include cyclohexane, toluene, n-decane, n-tetradecane, and n-octadecane, Tables 3-1, 3-2, and 3-3 present the simulation results under different conditions.

[0080] Table 3-1 Simulation Results of a Residual Liquid Tower with Side Stream

[0081]

[0082]

[0083] Table 3-2 Simulation Results of the Residual Liquid Tower with Side Stream

[0084]

[0085] Table 3-3 Simulation Results of the Residual Liquid Tower with Side Stream

[0086]

[0087]

[0088] Separation via a distillation column with a side stream allows for the recycling of a material with a cyclohexane content greater than 90% by mass from the top of the column back to the adsorption column as the first desorbent D1, while a material with a toluene content of approximately 70% by mass from the side stream back to the adsorption column as the second desorbent D2.

Claims

1. A method for separating aromatics from diesel fuel using a liquid-phase simulated moving bed, characterized in that, The simulated moving bed adsorption tower has multiple adsorbent beds. Along the flow direction of the circulating material in the simulated moving bed, the entry and exit points of each material are, in sequence, the first desorbent (D1), the second desorbent (D2), the extract (E), the diesel feedstock (F), and the raffinate (R). The injection or extraction point of each of the above materials moves one bed along the flow direction of the circulating material in the simulated moving bed every step time t. The extract enters the extract tower for distillation separation, and the component rich in aromatics is obtained from the bottom of the tower. The raffinate enters the raffinate tower for distillation separation, and the component from the bottom of the tower is obtained after most of the aromatics have been removed. The first desorbent is a saturated hydrocarbon, and the second desorbent is a light aromatic hydrocarbon. The boiling point of the saturated hydrocarbon in the first desorbent is lower than the boiling point of the light aromatic hydrocarbon in the second desorbent.

2. The method for separating aromatics from diesel fuel using a liquid-phase simulated moving bed according to claim 1, characterized in that, The diesel feedstock is a hydrocarbon fraction containing multiple aromatic components with more than C9 carbon atoms and saturated alkane components.

3. The method for separating aromatics from diesel fuel using a liquid-phase simulated moving bed according to claim 1, characterized in that, The light aromatic hydrocarbons are selected from one or a mixture of several of benzene, toluene, ethylbenzene, p-xylene, m-xylene and o-xylene.

4. The method for separating aromatics from diesel fuel using a liquid-phase simulated moving bed according to claim 3, characterized in that, The mass flow rate ratio of the first desorbent D1 to the second desorbent D2 is 1.0 to 1.

8.

5. The method for separating aromatics from diesel fuel using a liquid-phase simulated moving bed according to claim 1, characterized in that, The simulated moving bed adsorption tower has 10 to 16 adsorbent beds, and the first desorbent and the second desorbent enter the adsorption tower at intervals of 1 to 2 beds.

6. The method for separating aromatics from diesel fuel using a liquid-phase simulated moving bed according to claim 5, characterized in that, In the simulated moving bed adsorption tower, the number of bed layers in the desorption zone, purification zone, adsorption zone, and isolation zone are 3-5, 3-5, 3-5, and 2-3, respectively.

7. The method for separating aromatics from diesel fuel using a liquid-phase simulated moving bed according to claim 1, characterized in that, The adsorbent is silica gel.

8. The method for separating aromatics from diesel fuel using a liquid-phase simulated moving bed according to any one of claims 1 to 6, characterized in that, The simulated moving bed adsorption tower operates at a temperature of 20~160℃ and a pressure of 0.5~2.0MPa; the step time t is 100-350 seconds; the operating pressure of the extractor and raffinate towers is 0.03~0.08MPa, and the tower top temperature is 40~80℃.

9. The method for separating aromatics from diesel fuel using a liquid-phase simulated moving bed according to claim 8, characterized in that, The operating temperature of the simulated moving bed adsorption tower is 50~120℃.

10. The method for separating aromatics from diesel fuel using a liquid-phase simulated moving bed according to any one of claims 1 to 6, characterized in that, The top discharge from the evaporator and the top discharge from the residual liquid are separated in the desorbent separation tower (40). At least part of the top discharge is recycled back to the adsorption tower as the first desorbent; at least part of the bottom discharge is recycled back to the adsorption tower as the second desorbent.

11. The method for separating aromatics from diesel fuel using a liquid-phase simulated moving bed according to any one of claims 1 to 6, characterized in that, The top discharge from the extractor tower is recycled back to the adsorption tower as the first desorbent, and the side discharge from the extractor tower is recycled back to the adsorption tower as the second desorbent; the top discharge from the raffinate tower is recycled back to the adsorption tower as the first desorbent, and the side discharge from the raffinate tower is recycled back to the adsorption tower as the second desorbent.

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