An adsorption separation method and system for naphtha

Abstract

A method and system for adsorption separation of naphtha, comprising: naphtha being separated into light naphtha and heavy naphtha via a fractionation tower; the light naphtha entering a first adsorption separation unit, using a first desorbent to separate a first extract and a first raffinate, which are further fractionated to obtain a first extract oil and a first raffinate oil; the heavy naphtha entering a second adsorption separation unit, using a second desorbent to separate a second extract and a second raffinate, which are further fractionated to obtain a second extract oil and a second raffinate oil; wherein the first extract oil is used as the second desorbent, and the second extract oil is used as the first desorbent. The method and system provided by this invention can reduce the cost of desorbents, reduce the energy consumption of desorbent separation, and the process is highly adaptable to raw material composition and product requirements.

Description

Technical Field

[0001] This invention relates to an adsorption separation method and system for whole-fraction naphtha. Specifically, it relates to a method for liquid-phase adsorption separation of n-alkanes from whole-fraction naphtha using simulated moving bed technology. Background Technology

[0002] Naphtha originally referred to the light distillate from crude oil, distilled at temperatures between atmospheric pressure and approximately 200°C. It is a mixture of various hydrocarbons, primarily consisting of C4-C11 n-alkanes, isoalkanes, cycloalkanes, and aromatics. Later, mixtures of hydrocarbons from this distillate fraction from different sources were also called naphtha, such as hydrocracked naphtha, coking naphtha, catalytic cracked naphtha, or oilfield condensate. The content of each component varies in naphtha from different sources, with n-alkanes typically comprising 20%–50% by mass, and non-n-alkanes comprising 50%–80%. Naphtha can be used as a feedstock for steam cracking to produce ethylene, catalytic reforming to produce aromatics, or as a blending component in gasoline.

[0003] When used as feedstock for steam cracking to produce ethylene, the composition of naphtha significantly impacts key indicators such as yield, cycle time, and production cost. n-Alkanes are excellent feedstocks for olefin production, followed by isoalkanes. Aromatics, however, retain their cyclic structure largely under high-temperature cracking conditions and are prone to condensation and coking, making them unsuitable as cracking feedstocks. When used as feedstock in reforming units, cycloalkanes in naphtha readily convert to aromatics, while n-alkanes are least likely to do so. When used for gasoline blending, branched alkanes, cycloalkanes, and aromatics also exhibit significantly higher octane numbers than n-alkanes.

[0004] Therefore, if the n-alkanes in naphtha are separated for steam cracking to produce olefins, and the remaining non-n-alkanes are used for gasoline blending or catalytic reforming, not only can the utilization value of naphtha be significantly improved and energy and material consumption reduced, but the feedstock composition for steam cracking and catalytic reforming is also optimized, which is beneficial to the stable and long-term operation of the unit.

[0005] US4176053A, US4210771A, US4595490A, and US4709116A disclose methods for gas-phase adsorption of low-octane n-alkanes using 5A molecular sieve adsorbents, followed by gas purging to desorb the n-alkanes from the adsorbent and recycling them back for isomerization. The purging gas used is primarily hydrogen. CN1179410A discloses a method for separating iso-alkanes / n-alkanes using gas-phase adsorption, separating n-alkanes from C5 and C6 alkane isomerization products via pressure swing adsorption. These gas-phase adsorption methods are mainly suitable for systems with narrow distillation ranges and low carbon numbers. CN1710030A discloses a method for separating full-fraction naphtha using gas-phase adsorption. Desorption of high-carbon n-alkanes is difficult; therefore, nitrogen purging of the adsorption column at 400°C is required during desorption.

[0006] For materials with a wider distillation range, liquid-phase adsorption separation is a more suitable method. Desorbents are required in liquid-phase adsorption separation, and the choice of desorbent significantly affects the separation performance. CN1476474A discloses an adsorption separation method for obtaining n-alkanes as steam cracking feedstock. The feedstock stream is fractionated into a C5 fraction and a C6 and above fraction fed into an adsorption separation unit; the C5 fraction is used as the desorbent. CN102811984A discloses a method for separating n-alkanes from whole-range naphtha using simulated moving bed adsorption, employing C12 hydrocarbons as the desorbent. Its advantage is that the desorbent is easily separated from the components in the feedstock, thereby reducing the energy consumption for desorbent separation and recycling. CN106433742A discloses a method for adsorbing and separating n-alkanes from distillate oil containing n-alkanes, using a mixture of n-dodecane and n-pentadecane as the desorbent to separate C5-C11 hydrocarbon distillate oil, which can improve the yield of n-alkanes with different carbon numbers. In technological solutions for large-scale industrial production, a crucial aspect is reducing energy consumption. In liquid-phase adsorption separation, the primary energy consumption comes from the separation of the desorbent. While meeting separation requirements, reducing the amount of desorbent used and increasing the boiling point difference between the desorbent and the feedstock are common methods for reducing energy consumption. Desorbents are generally specialized chemicals with high value, and their consumption is a cost that must be controlled in production. Summary of the Invention

[0007] One of the technical problems this invention aims to solve is to provide an adsorption separation method for full-fraction naphtha. This method can reduce the cost of desorbents, reduce the energy consumption of desorbent separation, and the process is highly adaptable to the composition of raw materials and product requirements.

[0008] The second technical problem to be solved by the present invention is to provide an adsorption separation system for full-fraction naphtha.

[0009] A naphtha adsorption separation method involves fractionating naphtha into light naphtha and heavy naphtha. The light naphtha contains most of C5-C6 n-alkanes, while the heavy naphtha contains most of C8-C10 n-alkanes. The light naphtha enters a first adsorption separation unit and, using a first desorbent, is separated to obtain a first extracted oil and a first raffinate oil. The heavy naphtha enters a second adsorption separation unit and, using a second desorbent, is separated to obtain a second extracted oil and a second raffinate oil. The first desorbent is used as the first extracted oil, and the second desorbent is used as the second extracted oil.

[0010] A naphtha adsorption separation system includes a first distillation column, a first adsorption separation device, a second adsorption separation device, and an optional second distillation column. The top discharge line of the first distillation column is connected to the feed inlet of the first adsorption separation device, and the bottom discharge line of the first distillation column is connected to the feed inlet of the second adsorption separation device. Optionally, the oil outlet of the first adsorption separation device and the oil outlet of the second adsorption separation device are connected to the feed inlet of the second distillation column.

[0011] The beneficial effects of the naphtha adsorption separation method and system provided by this invention are as follows:

[0012] The naphtha adsorption separation method provided by this invention cuts full-fraction naphtha into light naphtha rich in C5 / C6 and heavy naphtha rich in C8 / C9 / C10 according to boiling point. The n-alkanes separated from the light naphtha can be used as high-quality feedstock for steam cracking units, while the non-n-alkanes separated from the light naphtha are high-octane components. Alternatively, n-alkanes can be converted into high-octane components, or non-n-alkanes can be converted into n-alkanes as high-quality cracking feedstock, as needed. The n-alkanes separated from the heavy naphtha can be used as high-quality feedstock for steam cracking units, while the non-n-alkanes separated from the heavy naphtha are high-quality reforming feedstock.

[0013] The technical solution of this invention can fully utilize all components in whole-fraction naphtha and can flexibly adapt to various different needs. Attached Figure Description

[0014] Figure 1 This is a schematic flowchart of the first embodiment of the naphtha adsorption separation method of the present invention.

[0015] Figure 2 This is a schematic flowchart of a second embodiment of the naphtha adsorption separation method of the present invention.

[0016] Figure 3 This is a schematic flowchart of the third embodiment of the naphtha adsorption separation method of the present invention.

[0017] Figure 4 This is a schematic diagram of the naphtha adsorption separation method in Comparative Example 1.

[0018] Figure 5 This is a schematic diagram of the naphtha adsorption separation method in Comparative Example 2. Detailed Implementation

[0019] 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.

[0020] In a first aspect, the present invention provides an adsorption separation method for naphtha, comprising: (1) fractionating naphtha into light naphtha and heavy naphtha, wherein the light naphtha contains most of C5-C6 n-alkanes and the heavy naphtha contains most of C8-C10 n-alkanes; (2) the light naphtha enters a first adsorption separation device, and a first desorbent is used to separate a first extracted oil and a first raffinate oil; the heavy naphtha enters a second adsorption separation device, and a second desorbent is used to separate a second extracted oil and a second raffinate oil; wherein the first desorbent is used as the first extracted oil and the second desorbent is used as the second extracted oil.

[0021] In the method provided by this invention, the naphtha can be any type of naphtha, preferably one or a mixture of several of the following: straight-run naphtha, hydrocracked naphtha, coking naphtha, catalytic cracked naphtha, and oilfield condensate.

[0022] The content of n-alkanes in naphtha from different sources varies, typically ranging from 20 wt% to 50 wt%.

[0023] The method provided by this invention uses a fractionation tower to separate naphtha into light naphtha and heavy naphtha. The light naphtha contains mostly C5-C6 n-alkanes, and the heavy naphtha contains mostly C8-C10 n-alkanes. Preferably, the operating conditions of the fractionation tower are: pressure 0.1-0.2 MPa, top temperature 40-70°C, and bottom temperature 125-155°C. All pressures mentioned in this application are gauge pressures.

[0024] In the method provided by the present invention, the first adsorption separation device in step (2) is a liquid-phase simulated moving bed adsorption separation device, with an operating temperature of 80-220℃, preferably 100-180℃, and an operating pressure of 0.5-3.0MPa; the second adsorption separation device is a liquid-phase simulated moving bed adsorption separation device, with an operating temperature of 80-220℃, preferably 100-180℃, and an operating pressure of 0.5-3.0MPa.

[0025] In the method provided by the present invention, the adsorbent packed in the first adsorption separation device is a type A molecular sieve; the adsorbent packed in the second adsorption separation device is a type A molecular sieve.

[0026] Preferably, the molar ratio of calcium oxide to sodium oxide in the adsorbent of the first adsorption separation device is greater than 4; the molar ratio of calcium oxide to sodium oxide in the adsorbent of the second adsorption separation device is greater than 4.

[0027] In the method provided by the present invention, C5-C6 n-alkanes are obtained after the first desorbent is separated from the first extract, and C5-C6 non-n-alkanes are obtained after the first raffinate is separated from the first desorbent.

[0028] After separating the second desorbent from the second raffinate, C7-C10 n-alkanes are obtained; after separating the second desorbent from the second raffinate, C7-C10 non-n-alkanes are obtained.

[0029] Preferably, the first extract and the second extract are fed into the same extract distillation column for separation, with the top product being the first extract oil and the bottom product being the second extract oil. The operating conditions of the extract distillation column are: operating pressure of 0.08-0.2 MPa, top temperature of 40-70℃, and bottom temperature of 125-155℃.

[0030] Secondly, the present invention provides a naphtha adsorption separation system, comprising a fractionation tower, a first adsorption separation device, a second adsorption separation device, an extractant distillation tower, a first raffinate distillation tower, and a second raffinate distillation tower. The top discharge line of the fractionation tower is connected to the feed inlet of the first adsorption separation device, and the bottom discharge line of the fractionation tower is connected to the feed inlet of the second adsorption separation device. The extractant outlets of the first and second adsorption separation devices are connected to the feed inlet of the extractant distillation tower. The raffinate outlet of the first adsorption separation device is connected to the first raffinate distillation tower, and the raffinate outlet of the second adsorption separation device is connected to the second raffinate distillation tower.

[0031] In the method provided by this invention, in step (2), the adsorption separation device can consist of one or more adsorption columns and can operate in either the gas phase or the liquid phase. Preferably, it is a simulated moving bed adsorption separation device operating entirely in the liquid phase. The advantages of this device are continuous operation, higher adsorbent utilization efficiency, and a smaller desorption dosage, thereby reducing the investment and operating costs of the device. The operating temperature of the simulated moving bed adsorption separation device is 80–220°C, more preferably 100–180°C. The operating pressure is 0.5–3.0 MPa.

[0032] The simulated moving bed adsorption separation device includes one or more adsorption towers, preferably one adsorption tower. Each adsorption tower is divided into multiple adsorption beds by a grid. The function of the grid is to redistribute material from the upper bed to the lower bed, to mix externally introduced material with material from the upper bed, and to draw a portion of the material from the upper bed out of the adsorption tower. The grid allows liquid to pass through and intercepts adsorbent particles escaping from the adsorbent bed. Its upper and lower surfaces are generally made of woven wire mesh, sintered metal mesh, or Johnson screen. Material introduced from the outside to a particular bed and material drawn out of the adsorption tower from the upper bed both enter and exit through pipelines connected to the grid of that bed.

[0033] The adsorbent used in the adsorption separation device is a type A molecular sieve. The adsorbent can be in various shapes, such as spherical, cylindrical, or irregular, and the particle size can range from 0.3 mm to 5 mm. The adsorbent used for adsorption separation comprises 80–98% by mass of molecular sieve as the active component and 2–20% by mass of a binder, wherein the binder is selected from alumina, kaolin, bentonite, or attapulgite.

[0034] The materials entering and exiting the adsorption tower include at least the feed (F), desorbent (D), extract (E), and raffinate (R). The feed is naphtha, as mentioned above. The adsorbent has higher adsorption selectivity for n-alkanes in the feed. The desorbent used should have a significant difference in boiling point from the feed, allowing for separation via distillation. The extract is enriched with the adsorbed n-alkanes from the feed and contains a portion of the desorbent. The raffinate contains a smaller amount of n-alkanes; the lower the content, the higher the adsorption and separation efficiency. The main components of the raffinate are the desorbent and the non-n-alkanes from the feed. The extract and raffinate are separated by distillation columns to remove the desorbent for recycling. For the first adsorption unit, the desorbent has a higher boiling point than the feed, and it is separated from the bottom of the distillation column. For the second adsorption unit, the desorbent has a lower boiling point than the feed, and it is separated from the top of the distillation column. In the second adsorption separation unit, a portion of the second extracted oil and desorbent can be discharged together as n-alkane products without further distillation. The reduced circulating desorbent can be replenished from the first extracted oil, thus reducing the energy consumption for desorbent separation. Similarly, in the first adsorption separation unit, a portion of the first extracted oil and desorbent can also be discharged together as n-alkane products without further distillation. The reduced circulating desorbent can be replenished from the second extracted oil, further reducing the energy consumption for desorbent separation.

[0035] The extract distillation column in the first adsorption separation unit and the extract distillation column in the second adsorption separation unit can be combined. At least a portion of the first extract and at least a portion of the second extract enter the same distillation column for distillation separation. The top material can be used as a desorbent in the second adsorption separation unit, and the bottom material can be used as a desorbent in the first adsorption separation unit.

[0036] The adsorption tower is divided into desorption, purification, adsorption, and isolation zones along the material flow direction. The adsorbent bed between the desorbent injection and the extractant collection constitutes the desorption zone; the adsorbent bed between the extractant collection and the feed injection constitutes the purification zone; the adsorbent bed between the feed injection and the raffinate collection constitutes the adsorption zone; and the adsorbent bed between the raffinate collection and the desorbent injection constitutes the isolation zone. The simulated moving bed number is 6–24, preferably 8–12.

[0037] The technical solutions of specific embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings, but the accompanying drawings do not constitute a limitation on the present invention.

[0038] Appendix Figure 1 This is a schematic flowchart illustrating the first embodiment of the naphtha adsorption separation method provided by the present invention. (See attached diagram.) Figure 1 As shown, naphtha feedstock 1 enters the first distillation column 10 for fractionation to obtain light naphtha 11 and heavy naphtha 12. Light naphtha 11 contains mostly C5-C6 n-alkanes, while heavy naphtha 12 contains mostly C8-C10 n-alkanes. Light naphtha 11 enters the first adsorption separation unit 20, preferably a simulated moving bed adsorption separation unit, where a first desorbent 2 is introduced. After adsorption separation, a first extract 21 and a first raffinate 22 are obtained. The first extract 21 enters the first extract distillation column 40, where the top is separated to obtain first extract oil 41, and the bottom is separated via pipeline 42 to obtain the first desorbent. The first raffinate 22 enters the first raffinate distillation column 50, where the top is separated to obtain first raffinate oil 51, and the bottom is separated via pipeline 52 to obtain the first desorbent. The separated first desorbent is recycled back to the first adsorption unit 20 via pipeline 2.

[0039] Heavy naphtha 12 enters the second adsorption separation unit 30, preferably a simulated moving bed adsorption separation unit, where the second desorbent 3 is introduced. After adsorption separation, a second extract 31 and a second raffinate 32 are obtained. The second extract enters the second extract distillation column 60, where the second desorbent is separated from the top and led out through pipeline 61. The bottom product is the second extract oil 62. The second raffinate enters the second raffinate distillation column 70, where the second desorbent 71 is separated from the top and the bottom product is the second raffinate oil 72. The separated second desorbent is recycled back to the second adsorption unit. At least a portion of the first extract oil 41 is recycled into the second desorbent 3, and at least a portion of the second extract oil 62 is recycled into the first desorbent 2.

[0040] Appendix Figure 2 This is a schematic flow chart of a second embodiment of the naphtha adsorption separation method of the present invention. (See attached diagram.) Figure 1 The difference is that a stream of material 36 is separated from the second extract 31, which does not pass through the second extract distillation column 60, and is sent out of the device along with a portion of the second extract oil 62 via pipeline 66.

[0041] Appendix Figure 3 This is a schematic flowchart of the third embodiment of the naphtha adsorption separation method of the present invention. (See attached diagram.) Figure 1 The difference is that a portion of the first extract 21 and a portion of the second extract 31 are introduced into the same extract distillation column 80. The top product of the column is the first extract oil 41, a portion of which is incorporated into the second desorbent 3. The bottom product of the column is the second extract oil 62, a portion of which is incorporated into the first desorbent 2. The other portion is sent out of the device as a product via pipeline 66.

[0042] The following examples further illustrate the technical solution and effects of the naphtha adsorption separation method provided by the present invention, but the present invention is not limited thereto.

[0043] In the examples and comparative examples:

[0044] The naphtha was obtained from the Yanshan Branch of China Petroleum & Chemical Corporation. The specific composition is shown in Table 1, which includes hydrocarbons from C5 to C11, of which n-alkanes account for 28.7% by mass.

[0045] Table 1.

[0046] carbon number n-hydrocarbons Isomers Cycloalkanes Aromatics total 5 5.2 4.4 1.0 0 10.6 6 6.5 7.3 5.5 0.6 19.9 7 5.7 6.4 8.5 1.7 22.3 8 5.1 6.2 6.4 3.3 21 9 4.3 5.3 5.3 2.7 17.6 10 1.9 4.3 1.5 0 7.7 11 0 0.7 0.2 0 0.9 total 28.7 34.6 28.4 8.3 100

[0047] Comparative Example 1

[0048] The naphtha feedstock flow rate is 100t / h.

[0049] The naphtha was processed according to the adsorption and separation method described in CN1476474A. See the attached flowchart. Figure 4Raw material 01 is separated in distillation column 10 to obtain C5 fraction, of which hydrocarbons with five carbon atoms account for 94.7 wt% and n-alkanes account for approximately 51 wt%. At the bottom of the column, a fraction with C6 or higher is obtained, of which hydrocarbons with five carbon atoms account for 1.0 wt% and n-alkanes account for 26.2 wt%. The fraction with C6 or higher is sent to adsorption separation unit 20 via pipeline 12 for processing. The C5 fraction, along with the material recycled from the top of the next two distillation columns via pipeline 11, serves as desorbent 02, yielding extract 21, which contains the desorbent and most of the n-alkanes from the fraction with C6 or higher. A portion of extract 21 enters extract distillation column 30 to separate the desorbent and the n-alkanes from the fraction with C6 or higher. The resulting desorbent is recycled back to adsorption separation unit 20 via pipeline 31. The obtained n-alkanes from the fraction with C6 or higher, 32, are combined with the portion of extract that did not enter distillation column 30 via pipeline 26 to form steam cracking feedstock, which is then led out of the unit via pipeline 36. The raffinate 22 obtained from the adsorption separation unit 20 contains a desorbent and most of the C6 and above are non-n-alkanes. The raffinate 22 enters the raffinate distillation column 40 to separate the desorbent and the raffinate oil. The desorbent is recycled back to the adsorption separation unit 20 through pipeline 41, and the raffinate oil 42 is obtained as a product. It can be sent to the reforming unit for processing, or some of the light components in the raffinate oil can be separated as gasoline blending components, and the remaining materials can be sent to the reforming unit for processing.

[0050] The flow rates and compositions of each stream are shown in Table 2. The C5 fraction discharged from the top of the fractionation tower contains only about 50% n-hydrocarbons, and separating n-pentane and isopentane would be energy-intensive due to the boiling point difference being less than 10°C. The feed 36 sent for steam cracking contains approximately 81% n-hydrocarbons, which is due to the unseparated isohydrocarbons and n-hydrocarbons from C5 merging together in 36.

[0051] Table 2. Flow rate and composition of each material in Comparative Example 1

[0052]

[0053] The materials requiring distillation include naphtha feedstock and a portion of extract 21, totaling 265.8 t / h; the materials separated from the top of the distillation column include C5 fraction, circulating desorbent 31 and circulating desorbent 41, totaling 90.1 t / h.

[0054] Comparative Example 2

[0055] The composition of the naphtha feedstock flow rate was the same as in Comparative Example 1. The naphtha was processed according to the method described in CN102811984A for separating n-alkanes from the whole-fraction naphtha by adsorption using a simulated moving bed, with C12 n-alkanes as the desorbent.

[0056] See attached document for the process. Figure 5Raw material 01 enters the adsorption separation unit 20 for processing. The desorbent 02 is C12 n-hydrocarbon, resulting in extract 21, which contains the C12 n-hydrocarbon desorbent and most of the n-hydrocarbons from the raw material. Extract 21 enters the extract distillation column 30 to separate the C12 n-hydrocarbon desorbent from the n-hydrocarbons from the raw material, yielding n-hydrocarbons 31 from the raw material. This n-hydrocarbons 31 are used as steam cracking feedstock, yielding C12 n-hydrocarbon desorbent 32, which is recycled back to the adsorption separation unit 20. Extract 21 is obtained from the adsorption separation unit 20... The residual liquid 22, containing C12 n-alkanes desorbent and most of the non-n-alkanes from the feedstock, enters the residual liquid distillation column 40 to separate the C12 n-alkanes desorbent and the non-n-alkanes from the feedstock, yielding C12 n-alkanes desorbent 42, which is recycled back to the adsorption separation unit 20. The non-n-alkanes 41 from the feedstock are obtained as a product, which can be sent to the reforming unit for processing. Alternatively, some of the light components in 41 can be separated as gasoline blending components, and the remaining material can be sent to the reforming unit for further processing. The flow rates and compositions of each material are shown in Table 3.

[0057] Table 3. Material flow rate and composition in Comparative Example 2

[0058]

[0059] The materials requiring distillation include extract and raffinate, totaling 187.2 t / h; the materials separated from the top of the distillation column include extract oil and raffinate oil, totaling 100.0 t / h. C12 n-hydrocarbons are used as the desorbent, a relatively difficult-to-obtain and high-value material. To minimize its loss, the operation of the extract and raffinate distillation columns must be more stringent, limiting the amount of C12 n-hydrocarbon desorbent in the top feed. The energy consumption per unit weight of the material is higher than usual. If the amount of C12 n-hydrocarbon desorbent in the top feed is limited to 0.01%–0.05%, then 0.01–0.05 tons of C12 n-hydrocarbon desorbent will be lost per hour. Based on 8000 hours of production per year, this translates to an annual loss of 80–400 tons of C12 n-hydrocarbon desorbent. If the unit price of C12 n-hydrocarbon desorbent is 20,000 RMB / ton, then the annual desorbent cost is 1.6 million–8 million RMB.

[0060] Example 1

[0061] The naphtha feedstock composition is the same as in Comparative Example 1. Processing is carried out according to the method provided in this invention; the process flow is shown in the appendix. Figure 1 .

[0062] Naphtha feedstock 1 is separated in the first distillation column 10 to obtain light naphtha 11, of which C5 hydrocarbons account for 38.6 wt% and C6 hydrocarbons account for 58.3 wt%; heavy naphtha 12 is obtained at the bottom of the column, of which C5 / C6 hydrocarbons account for 5.3 wt% and n-alkanes account for 23.5 wt%. Light naphtha 11 is sent to the first adsorption separation unit 20 for processing to obtain extract 21 and raffinate 22, with the first desorbent being n-alkanes of C7 or higher. The extract 21 enters the first extract distillation column 40 to separate and obtain the first desorbent 42 and the first extract oil 41. The first desorbent 42 is recycled back to the first adsorption separation unit 20, and the first extract oil 41 is mainly composed of C5 / C6 n-alkanes as steam cracking feedstock. The raffinate 22 enters the first raffinate distillation column 50 to separate and obtain the first desorbent 52, which is recycled back to the adsorption separation unit 20. The first raffinate oil 51 obtained is composed of C5 / C6 non-n-alkanes and is sent out to the device, where it can be used as a blending component for high-octane gasoline.

[0063] Heavy naphtha 12 is sent to the second adsorption separation unit 30 for processing, yielding the second extract 31 and the second raffinate 32. The second desorbent is C5 / C6 n-hydrocarbons. The second extract 31 enters the second extract oil distillation column 60 for separation, yielding the second desorbent 61 and the second extract oil 62. The second desorbent 61 is recycled back to the second adsorption separation unit 30, and the second extract oil 62 is mainly used as a feedstock for steam cracking. The second raffinate 32 enters the second raffinate distillation column 70 for separation, yielding the second desorbent 71 and the second raffinate oil 72. The second desorbent 71 is recycled back to the second adsorption separation unit 30, and the second raffinate oil mainly consists of C7 and above non-n-hydrocarbons, serving as a feedstock for the reforming unit. The first extract oil 41 can be added to the second desorbent, and the second extract oil 62 can be added to the first desorbent. The flow rates and compositions of each stream are shown in Table 4.

[0064] Table 4-1. Flow rate and composition of each material in Example 1

[0065]

[0066] Table 4-2. Flow rate and desorbent content of the effluent from the adsorption separation device in Example 1

[0067] Material Number Flow rate, t / h First desorbent content Second desorbent content First extracted fluid 21 22.8 51.5％ / First raffinate 22 43.1 61.8％ / Second extract fluid 31 28.2 / 42.4％ Second raffinate 32 84.3 / 33.2％

[0068] The materials requiring distillation are naphtha feedstock, first extract, first raffinate, second extract, and second raffinate, totaling 278.4 t / h; the materials separated from the top of the distillation column are light naphtha, first extract, first raffinate, second desorbent 61, and second desorbent 71, totaling 94.9 t / h.

[0069] Example 2

[0070] The naphtha feedstock composition is the same as in Comparative Example 1. Processing is carried out according to the method described in this application; the flowchart is attached. Figure 3 The process of raw material distillation and adsorption separation is the same as in Example 1.

[0071] As attached Figure 3 As shown, a portion 26 of the first extract 21 is directly sent to steam cracking, while the remaining material enters the extract distillation tower 80. The treatment of the first raffinate 22 is the same as in Example 1. The first raffinate oil 51 obtained by separation is a C5 / C6 non-n-alkanes, which can be used as a blending component for high-octane gasoline.

[0072] A portion 36 of the second extract 31 is directly sent to steam cracking, while the remaining material enters the extract distillation column 80. After fractionation, the top of the column yields the first extract oil 61, which is recycled back to the second adsorption separation unit 30 as the second desorbent. The bottom of the column yields the second extract oil 62, from which a portion 66 is sent to steam cracking, while the remainder is recycled back to the first adsorption separation unit 20 as the first desorbent. The treatment of the raffinate 32 is the same as in Example 1, yielding the second raffinate oil 72, which is used as feedstock for the reforming unit.

[0073] The flow rates and compositions of naphtha feedstock 1, first desorbent 2, second desorbent 3, light naphtha 11, heavy naphtha 12, first extract 21, first raffinate 22, second extract 31, and second raffinate 32 are the same as in Example 1. The details of the other materials are shown in Table 5.

[0074] Table 5. Flow rate and composition of each material in Example 2

[0075]

[0076]

[0077] The materials requiring distillation are naphtha feedstock, the portion of the first extract 21 minus 26, the first raffinate 22, the portion of the second extract 31 minus 36, and the second raffinate 32, totaling 253.8 t / h; the materials separated from the top of the distillation column are light naphtha 11, the first raffinate 51, the first extract 61, and the second desorbent 71, totaling 84.0 t / h.

[0078] The results of each comparative example and each embodiment are summarized in Table 6.

[0079] Table 6. Comparison of Comparative Examples and Embodiments

[0080]

[0081] As can be seen from the above results, the naphtha adsorption separation method provided by this invention first fractionates the naphtha feedstock into light naphtha containing C5 / C6 fractions and heavy naphtha containing C7 or higher fractions, which are then fed into the first and second adsorption separation units, respectively. The first extracted oil is used as the second desorbent, and the second extracted oil is used as the first desorbent. No external desorbent is required, reducing costs. The obtained n-alkanes have high purity, resulting in high olefin yields when used for steam cracking, leading to better economic benefits. Compared to the material with 81% purity of n-alkanes in Comparative Example 1, the 95% purity n-alkanes used for steam cracking have approximately 3 percentage points higher olefin yields.

Claims

1. A method for adsorption separation of naphtha, characterized in that, include: (1) Naphtha is separated into light naphtha and heavy naphtha by a fractionation tower; (2) Light naphtha enters the first adsorption separation unit and is separated by the first desorbent to obtain the first extract and the first raffinate. Part of the first extract is sent out of the unit as n-alkane product, and the other part of the first extract and the first raffinate are further fractionated to obtain the first extract oil and the first raffinate oil. Heavy naphtha enters the second adsorption separation unit, where a second desorbent is used to separate it into a second extract and a second raffinate. Part of the second extract is sent out of the unit as a n-alkane product, while the other part of the second extract and the second raffinate is further fractionated to obtain a second extract oil and a second raffinate oil. The first extract oil is used as the second desorbent, and the second extract oil is used as the first desorbent.

2. The adsorption separation method for naphtha according to claim 1, characterized in that, The operating conditions of the distillation column in step (1) are: pressure of 0.1-0.2 MPa, top temperature of 40-70℃, and bottom temperature of 125-155℃.

3. The adsorption separation method for naphtha according to claim 1 or 2, characterized in that, In step (2), the first adsorption separation device is a liquid-phase simulated moving bed adsorption separation device with an operating temperature of 80-220℃; the second adsorption separation device is a liquid-phase simulated moving bed adsorption separation device with an operating temperature of 80-220℃.

4. The adsorption separation method for naphtha according to claim 3, characterized in that, The first adsorption separation device operates at a temperature of 100–180℃ and an operating pressure of 0.5–3.0 MPa; the second adsorption separation device operates at a temperature of 100–180℃ and an operating pressure of 0.5–3.0 MPa.

5. The adsorption separation method for naphtha according to claim 1 or 2, characterized in that, The first adsorption separation device is filled with type A molecular sieve as the adsorbent; the second adsorption separation device is filled with type A molecular sieve as the adsorbent.

6. The adsorption separation method for naphtha according to claim 5, characterized in that, The molar ratio of calcium oxide to sodium oxide in the adsorbent of the first adsorption separation device is greater than 4; the molar ratio of calcium oxide to sodium oxide in the adsorbent of the second adsorption separation device is greater than 4.

7. The adsorption separation method for naphtha according to claim 1 or 2, characterized in that, After separating the first desorbent from the first extract, C5-C6 n-alkanes are obtained; after separating the first desorbent from the first raffinate, C5-C6 non-n-alkanes are obtained.

8. The adsorption separation method for naphtha according to claim 1 or 2, characterized in that, After separating the second desorbent from the second raffinate, C7-C10 n-alkanes are obtained, and after separating the second desorbent from the second raffinate, C7-C10 non-n-alkanes are obtained.

9. The adsorption separation method for naphtha according to claim 1 or 2, characterized in that, The first and second extracts are fed into the same extract distillation column for separation. The top product of the column is the first extract oil, and the bottom product is the second extract oil.

10. The adsorption separation method for naphtha according to claim 1 or 2, characterized in that, The naphtha feedstock is one or a mixture of several of the following: straight-run naphtha, hydrocracked naphtha, coking naphtha, catalytic cracked naphtha, and oilfield condensate.

11. The adsorption separation method for naphtha according to claim 10, characterized in that, The content of n-alkanes in naphtha feedstock is in the range of 20wt% to 50wt%.

12. A naphtha adsorption separation system, characterized in that, The system includes a fractionation column, a first adsorption separation unit, a second adsorption separation unit, an extractant distillation column, a first raffinate distillation column, and a second raffinate distillation column. The top discharge line of the fractionation column is connected to the feed inlet of the first adsorption separation unit, and the bottom discharge line of the fractionation column is connected to the feed inlet of the second adsorption separation unit. The extractant outlets of the first and second adsorption separation units are connected to the feed inlet of the extractant distillation column, and are respectively led out by devices. The raffinate outlet of the first adsorption separation unit is connected to the first raffinate distillation column, and the raffinate outlet of the second adsorption separation unit is connected to the second raffinate distillation column. The top stream outlet of the extractant distillation column and the top stream outlet of the second raffinate distillation column are connected to the second adsorption separation unit, and the bottom stream outlets of the extractant distillation column and the first raffinate distillation column are connected to the first adsorption separation unit.

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