A method for separating naphtha by directional adsorption

Abstract

The present application provides a naphtha directional adsorption separation method, and relates to the technical field of petroleum chemical industry.The present application adopts a double desorption agent process flow, uses stronger adsorption force between high carbon alkanes (n-dodecane, n-tetradecane or n-hexadecane) and adsorbents, solves the problems of incomplete desorption of low carbon alkanes desorption agent and low separation yield, and thus significantly improves the separation efficiency of the process.Meanwhile, the use of low carbon alkanes (n-pentane or n-hexane) to replace high carbon alkanes on the adsorbents can avoid the residue of high carbon alkanes on the adsorbents, and affect the recycling of the adsorbents.The present application adopts the double desorption agent process flow, which can ensure high separation efficiency and improve the utilization rate of the adsorbents at the same time.The present application can efficiently separate n-alkanes in naphtha, and the separated n-alkanes can be used as high-quality cracking ethylene (propylene) raw materials;the adsorption residual oil rich in isomeric alkanes, naphthenes and aromatic hydrocarbons can be used as high-quality catalytic reforming aromatic hydrocarbon raw materials.

Description

Technical Field

[0001] This invention relates to the field of petrochemical technology, and in particular to a method for the directional adsorption and separation of naphtha. Background Technology

[0002] Naphtha refers to the light fraction of crude oil distilled at temperatures between the initial boiling point (the point at which it begins distillation under atmospheric pressure) and 200°C (or 180°C), with its hydrocarbon composition ranging from C4 to C10 carbon atoms. In a typical naphtha composition, n-alkanes account for 30%, isoalkanes for 30%, cycloalkanes for 30%, and aromatics for 10%. Traditional petroleum processing employs a fraction management strategy, which involves dividing the crude oil mixture into products with different distillation ranges based on their distillation characteristics, and then assigning them appropriate uses according to their properties. Under this management model, resources are often not utilized most efficiently. For example, naphtha has two main uses in the refining industry, but from the perspective of reaction engineering, the molecular composition of naphtha feedstock has obvious misalignment and inefficient conversion: (1) It is used as a feedstock for steam cracking to produce ethylene, which currently accounts for more than 65% of the ethylene feedstock composition, but the aromatics and cycloalkanes in naphtha are difficult to open the ring and crack, and are prone to coking; (2) It is used as a feedstock for catalytic reforming to produce aromatic products, but in the catalytic reforming reaction, the alkanes in naphtha (content can reach more than 50%) are difficult to cyclize and dehydrogenate to produce aromatics, but instead crack to produce by-products.

[0003] Current research hotspots both domestically and internationally focus on using molecular sieves as adsorbents to separate n-alkanes from non-n-alkanes (isoalkanes, cycloalkanes, and aromatics) in naphtha. Naphtha rich in n-alkanes serves as a high-quality feedstock for steam cracking to produce ethylene, while naphtha rich in non-n-alkanes serves as a high-quality feedstock for catalytic reforming. Companies such as UOP and ExxonMobil have conducted extensive research on this topic internationally.

[0004] Currently, in simulated moving bed adsorption separation processes, n-pentane or n-hexane are commonly used as desorbents. For example, Chinese patent CN102585887A discloses an adsorption separation method for naphtha, in which naphtha is passed into a simulated moving bed adsorption separation device packed with 5A molecular sieves while maintaining a liquid phase. Through a continuous liquid-solid adsorption separation process, using n-pentane or n-hexane as the desorbent, desorbed effluent and adsorbed effluent are obtained. The desorbed effluent and adsorbed effluent are then recovered by the desorbent to obtain desorbed oil rich in n-alkanes and adsorbed oil rich in non-n-alkanes. However, n-pentane and n-alkanes in naphtha have similar adsorption performance on molecular sieves, resulting in incomplete desorption and low separation yield. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for the directional adsorption and separation of naphtha. This invention can achieve highly efficient adsorption and separation of naphtha.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for the directional adsorption and separation of naphtha, comprising the following steps:

[0008] Liquid naphtha was adsorbed using a molecular sieve adsorbent to obtain the adsorbate effluent;

[0009] The molecular sieve adsorbent after adsorption was subjected to a first desorption using a first desorbent to obtain a desorbed effluent.

[0010] A second desorbent is used to perform a second desorption on the molecular sieve adsorbent after the first desorption, and the resulting molecular sieve adsorbent repeats the adsorption process.

[0011] After the desorbed effluent is recovered by a desorbent, a desorbed oil rich in n-alkanes is obtained; after the adsorbed effluent is recovered by a desorbent, an adsorbed oil rich in isoalkanes, cycloalkanes and aromatics is obtained.

[0012] The first desorbent is n-dodecane, n-tetradecane, or n-hexadecane; the second desorbent is n-pentane or n-hexane.

[0013] Preferably, the liquid naphtha is straight-run naphtha, hydrocracked naphtha, or hydrocracked naphtha.

[0014] Preferably, the molecular sieve adsorbent is one or more of 5A, ZSM-5, UZM-35 and β molecular sieve, and the silica-alumina ratio of the molecular sieve adsorbent is 40 to 200.

[0015] Preferably, the temperatures for adsorption, the first desorption, and the second desorption are independently 100–190°C.

[0016] This invention provides a continuous directional adsorption separation method for naphtha, comprising the following steps:

[0017] A simulated moving bed adsorption separation device is provided, which includes an adsorption zone and a desorption zone arranged in series. The adsorption zone and the desorption zone are respectively provided with multiple separation columns filled with molecular sieve adsorbent. Each separation column is provided with a programmable valve at the inlet and outlet.

[0018] Liquid naphtha is passed into the first separation column of the adsorption zone for adsorption. The adsorbed oil flows out of the simulated moving bed adsorption separation device and is subsequently cooled and desorbed agent recovered to obtain a desolventized adsorbed oil rich in isoalkanes, cycloalkanes and aromatics.

[0019] Simultaneously, a second desorbent is introduced into the next separation column after the liquid naphtha inlet for a second desorption, replacing the first desorbent in the column; a first desorbent is introduced into the first separation column of the desorption zone for a first desorption, replacing the n-alkanes adsorbed by the molecular sieve adsorbent in the column; the desorbed oil produced by the first and second desorption flows out of the simulated moving bed adsorption separation device, and is subsequently cooled and desorbent recovered to obtain desorbed oil rich in n-alkanes; the first desorbent is n-dodecane, n-tetradecane, or n-hexadecane; the second desorbent is n-pentane or n-hexane;

[0020] Then, by switching the liquid naphtha inlet, the second desorbent inlet, and the first desorbent inlet using the programmable valve of the simulated moving bed adsorption separation device, each of them moves forward one separation column, repeating the adsorption and desorption process.

[0021] Preferably, the separation columns are respectively filled in cylindrical tower sections, and the height-to-diameter ratio of a single separation column is 2 to 20:1.

[0022] Preferably, the bed temperature of the simulated moving bed adsorption separation device is 100–190°C.

[0023] Preferably, the feed space velocity of the liquid naphtha is 0.05–1.5 h⁻¹. -1 The feed space velocities of the first and second desorbents are independently 0.05–10 h⁻¹. -1 .

[0024] Preferably, the feed space velocities of the first desorbent and the second desorbent are equal.

[0025] Preferably, the switching time is 700-900 seconds.

[0026] This invention provides a method for directional adsorption separation of naphtha, comprising the following steps: adsorbing liquid naphtha using a molecular sieve adsorbent to obtain an adsorbate effluent; performing a first desorption on the adsorbed molecular sieve adsorbent using a first desorbent to obtain a desorbed effluent; performing a second desorption on the molecular sieve adsorbent after the first desorption using a second desorbent, and repeating the adsorption process on the resulting molecular sieve adsorbent; recovering the desorbed effluent with a desorbent to obtain a desorbed oil rich in n-alkane components; and recovering the adsorbate effluent with a desorbent to obtain an adsorbed oil rich in isoalkanes, cycloalkanes, and aromatics; wherein the first desorbent is n-dodecane, n-tetradecane, or n-hexadecane; and the second desorbent is n-pentane or n-hexane. Compared with existing technologies (e.g., patent CN102585887A) that use n-pentane or n-hexane as the desorbent, this invention has the following advantages:

[0027] This invention combines the advantages and disadvantages of both low-carbon and high-carbon alkanes, employing a dual desorbent process. It utilizes the stronger adsorption force between high-carbon alkanes (n-dodecane, n-tetradecane, or n-hexadecane) and the adsorbent, solving the problems of incomplete desorption and low separation yield associated with the similar adsorption performance of low-carbon alkane desorbents and n-alkanes in naphtha on molecular sieves. This significantly improves the separation efficiency of the process. Simultaneously, replacing the high-carbon alkanes on the adsorbent with low-carbon alkanes (n-pentane or n-hexane) avoids the residue of high-carbon alkanes on the adsorbent, preventing its recycling. This invention's dual desorbent process ensures both high separation efficiency and improved adsorbent utilization. This invention can efficiently separate n-alkanes from naphtha, serving as a high-quality feedstock for ethylene (propylene) production via cracking. The separated absorbent oil, rich in isoalkanes, cycloalkanes, and aromatics, can be used as a high-quality feedstock for catalytic reforming to produce aromatics. This invention achieves dual-objective optimization of ethylene (propylene) and aromatics yields using naphtha as feedstock, significantly improving the utilization efficiency of naphtha resources and fully meeting the demand for naphtha feedstock from the ethylene and aromatics industries. It also achieves dual-objective optimization of low-carbon olefin and aromatics yields using naphtha as feedstock.

[0028] This invention also provides a method for the directional adsorption and separation of naphtha, which adopts a simulated moving bed dual desorbent process flow, with continuous operation, high yield, high product yield, and high molecular sieve utilization, for the directional separation of n-alkane components in naphtha. Attached Figure Description

[0029] Figure 1 This is a flow chart of the continuous directional adsorption and separation process for naphtha in an embodiment of the present invention. Figure 1 1-Naphtha storage tank; 2-First desorbent storage tank; 3-Second desorbent storage tank; 4-Residual oil storage tank; 5-Desorbed oil storage tank; 6-Programmable valve; 7-Separation column; 8-Condenser; 9-Pump. Detailed Implementation

[0030] This invention provides a method for the directional adsorption and separation of naphtha, comprising the following steps:

[0031] Liquid naphtha was adsorbed using a molecular sieve adsorbent to obtain the adsorbate effluent;

[0032] The molecular sieve adsorbent after adsorption was subjected to a first desorption using a first desorbent to obtain a desorbed effluent.

[0033] A second desorbent is used to perform a second desorption on the molecular sieve adsorbent after the first desorption, and the resulting molecular sieve adsorbent repeats the adsorption process.

[0034] After the desorbed effluent is recovered by a desorbent, a desorbed oil rich in n-alkanes is obtained; after the adsorbed effluent is recovered by a desorbent, an adsorbed oil rich in isoalkanes, cycloalkanes and aromatics is obtained.

[0035] The first desorbent is n-dodecane, n-tetradecane, or n-hexadecane; the second desorbent is n-pentane or n-hexane.

[0036] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0037] This invention employs a molecular sieve adsorbent to adsorb liquid naphtha, yielding a residual effluent. In this invention, the liquid naphtha is preferably straight-run naphtha, hydrocracked naphtha, or hydropyrolyzed naphtha. The molecular sieve adsorbent is preferably one or more of 5A, ZSM-5, UZM-35, and β-zeolite, and the silica-to-alumina ratio of the molecular sieve adsorbent is preferably 40–200, more preferably 50–150. This invention does not have specific requirements regarding the source of the molecular sieve adsorbent; it can be commercially available or prepared using methods well-known to those skilled in the art. The adsorption temperature is preferably 100–190°C, more preferably 150–180°C, and even more preferably 170°C. During the adsorption process, n-alkanes (C4–C10) in the naphtha are adsorbed into the molecular sieve channels.

[0038] This invention employs a first desorbent to perform a first desorption of the adsorbed molecular sieve adsorbent, yielding a desorbed effluent. In this invention, the first desorbent is n-dodecane, n-tetradecane, or n-hexadecane. The preferred temperature for the first desorption is 100–190°C, more preferably 150–180°C, and even more preferably 170°C. During the first desorption process, the first desorbent displaces the n-alkanes adsorbed in the molecular sieve, forming the desorbed effluent. This invention utilizes the stronger adsorption force between higher carbon alkanes and the adsorbent to more thoroughly desorb n-alkanes, solving the problems of incomplete desorption and low separation yield associated with the similar adsorption performance of low-carbon alkane desorbents and n-alkanes in naphtha on molecular sieves, thereby significantly improving the separation efficiency of the process.

[0039] This invention employs a second desorbent to perform a second desorption on the molecular sieve adsorbent after the first desorption, and the resulting adsorbent is then subjected to the adsorption process again. In this invention, the second desorbent is n-pentane or n-hexane, and the preferred desorption temperature is 100–190°C, more preferably 150–180°C, and even more preferably 170°C. During the second desorption process, the second desorbent displaces the first desorbent from the adsorbent. When using a high-carbon alkane as the first desorbent, the strong binding force between the high-carbon alkane and the adsorbent, while improving the separation efficiency of n-alkanes, affects the adsorbent's re-adsorption performance for naphtha, resulting in low adsorbent utilization. This invention utilizes low-carbon alkane (n-pentane or n-hexane) to replace the high-carbon alkane on the adsorbent, avoiding the residue of high-carbon alkane on the adsorbent and affecting its recycling. During the repeated adsorption process, the second desorbent is displaced from the adsorbent and flows out with the residual oil.

[0040] After obtaining the desorbed effluent and the adsorbed effluent, the present invention recovers the desorbed effluent with a desorbing agent to obtain a desorbed oil rich in n-alkane components; the adsorbed effluent is then recovered with a desorbing agent to obtain an adsorbed oil rich in isoalkanes, cycloalkanes, and aromatics. The present invention does not have any particular requirements for the method of desorbing agent recovery; any method well known to those skilled in the art, such as distillation, can be used.

[0041] This invention, based on molecular management, separates n-alkanes from naphtha, which can be used as high-quality feedstock for ethylene (propylene) production through cracking. It also separates isoalkanes, cycloalkanes, and aromatics from naphtha, which can be used as high-quality feedstock for aromatics production through catalytic reforming. This achieves dual-objective optimization of ethylene (propylene) and aromatics yields using naphtha as feedstock, significantly improving the utilization efficiency of naphtha resources and fully meeting the demand for naphtha feedstock from the ethylene and aromatics industries. Furthermore, it achieves dual-objective optimization of low-carbon olefins and aromatics yields using naphtha as feedstock.

[0042] This invention provides a continuous directional adsorption separation method for naphtha, comprising the following steps:

[0043] A simulated moving bed adsorption separation device is provided, which includes an adsorption zone and a desorption zone arranged in series. The adsorption zone and the desorption zone are provided with multiple separation columns filled with molecular sieve adsorbent. Each separation column is equipped with a programmable valve at its inlet and outlet.

[0044] Liquid naphtha is passed into the first separation column of the adsorption zone for adsorption. The adsorbed oil flows out of the simulated moving bed adsorption separation device and is subsequently cooled and desorbed agent recovered to obtain a desolventized adsorbed oil rich in isoalkanes, cycloalkanes and aromatics.

[0045] Simultaneously, a second desorbent is introduced into the next separation column after the liquid naphtha inlet for a second desorption, replacing the first desorbent in the column; a first desorbent is introduced into the first separation column of the desorption zone for a first desorption, replacing the n-alkanes adsorbed by the molecular sieve adsorbent in the column; the desorbed oil produced by the first and second desorption flows out of the simulated moving bed adsorption separation device, and is subsequently cooled and desorbent recovered to obtain desorbed oil rich in n-alkanes; the first desorbent is n-dodecane, n-tetradecane, or n-hexadecane; the second desorbent is n-pentane or n-hexane;

[0046] Then, by switching the liquid naphtha inlet, the second desorbent inlet, and the first desorbent inlet using the programmable valve of the simulated moving bed adsorption separation device, each of them moves forward one separation column, repeating the adsorption and desorption process.

[0047] The present invention does not have any special requirements for the simulated moving bed adsorption separation device; any simulated moving bed adsorption separation device well known to those skilled in the art can be used.

[0048] In this invention, the separation columns are preferably filled in cylindrical tower sections, and the height-to-diameter ratio of a single separation column is preferably 2 to 20:1, more preferably 10:1.

[0049] In this invention, the molecular sieve adsorbent is preferably the same as the above-described technical solution, and will not be repeated here.

[0050] In this invention, the bed temperature of the simulated moving bed adsorption separation device is preferably 100-190°C, more preferably 150-180°C, and even more preferably 170°C.

[0051] In this invention, the feed space velocity of the liquid naphtha is preferably 0.05 to 1.5 h⁻¹. -1 More preferably, it is 0.17–0.34h. -1 The feed space velocity of the first desorbent and the second desorbent is preferably independently 0.05 to 10 h⁻¹. -1 More preferably, it is 0.68–1.37h. -1 The switching time is preferably 700-900 seconds. In this embodiment of the invention, the feed space velocity of the first desorbent and the second desorbent is more preferably equal, and the switching time is preferably the same.

[0052] In this invention, the cooling temperature of the adsorbed oil and desorbed oil is preferably 10 to 30°C. After cooling, the adsorbed oil and desorbed oil are condensed and liquefied.

[0053] In this invention, in order to improve the purity of the adsorbed oil, it is preferable to use the obtained adsorbed oil as raw material to be passed back into the simulated moving bed adsorption separation device, and to perform adsorption separation according to the above method. After the desorbent is recovered, the adsorbed oil rich in high concentrations of isoalkanes, cycloalkanes and aromatics is obtained.

[0054] Figure 1 This is a flow chart of the continuous directional adsorption separation process (i.e., simulated moving bed adsorption separation process) for naphtha in this embodiment of the invention. The simulated moving bed adsorption separation device is divided into four regions: Zone I, Zone II, Zone III, and Zone IV. Figure 1 The method for continuous directional adsorption separation of naphtha, as shown in the process, is as follows: The bed temperature of the simulated moving bed adsorption separation device is heated to 100-190℃. Naphtha from naphtha storage tank 1, the first desorbent from the first desorbent storage tank 2, and the second desorbent from the second desorbent storage tank 3 are respectively introduced into the feed inlet (F) and the desorbent inlet (D / E) of the simulated moving bed adsorption separation device filled with molecular sieve adsorbent. The n-alkanes in the naphtha are adsorbed into the molecular sieve channels of the first separation column in the adsorption zone (zone III). The adsorbed oil after adsorption treatment flows out of the simulated moving bed adsorption separation device. In the bed adsorption separation unit, the adsorbent is condensed and liquefied by condenser 8, collected by adsorbent storage tank 4, and then passed through a desorbent recovery tower to obtain desolvated adsorbent oil rich in isoalkanes, cycloalkanes, and aromatics. Simultaneously, a second desorbent is introduced into the next separation column after the naphtha inlet, replacing the first desorbent in the adsorption column. At this time, the first desorbent displaces the n-alkanes adsorbed in the molecular sieve in the desorption zone (Zone I) of the simulated moving bed and is carried out by the desorbed oil outlet (G), condensed and liquefied by condenser 8, collected by desorbed oil storage tank 5, and then passed through a desorbent recovery tower to obtain desorbed oil rich in n-alkanes. Then, the naphtha inlet, the second desorbent inlet, and the first desorbent inlet are all moved forward by one separation column via programmable valve 6, repeating the adsorption-desorption process. After adsorption in Zone III is complete, adsorption proceeds to Zone IV, while desorption occurs in Zone II; then adsorption proceeds to Zone I, while desorption occurs in Zone III; this cycle continues, ensuring a continuous supply of adsorption columns for adsorption.

[0055] This invention employs a programmable valve to simulate a moving bed adsorption separation device, and through a continuous liquid-solid adsorption separation process, using dual desorbents, it achieves continuous directional adsorption separation of naphtha.

[0056] To further illustrate the present invention, the naphtha directional adsorption separation method provided by the present invention will be described in detail below with reference to examples, but these examples should not be construed as limiting the scope of protection of the present invention.

[0057] Example 1

[0058] See Figure 1 The process flow in this embodiment is as follows:

[0059] Liquid naphtha and the desorbent n-dodecane are passed into zones III and I of a separation column packed with ZSM-5 molecular sieves (silicon-to-aluminum ratio of 50), respectively. The n-alkanes in the naphtha are adsorbed into the micropores of the molecular sieve in zone III. The adsorbed oil after adsorption treatment flows out of zone III of the simulated moving bed separation column, is cooled, and is condensed to obtain an adsorbed oil rich in isoalkanes, cycloalkanes, and aromatics. This oil is then sent to a catalytic reforming unit to obtain reforming products such as benzene, toluene, and xylene.

[0060] Meanwhile, the desorbent n-dodecane is desorbed in zone I of the simulated moving bed separation column. The desorbent carrying n-alkanes flows out of zone I of the simulated moving bed separation column. The n-alkanes are condensed and liquefied to obtain desorbed oil rich in n-alkanes. The desorbent n-pentane is then used to replace the n-dodecane in the adsorption column in zone III of the simulated moving bed separation column, next to the naphtha feedstock inlet.

[0061] Then, through the programmable valve, the inlet and outlet positions of the simulated moving bed are moved forward synchronously by the position of one separation column, and the adsorption separation principle is the same as described above.

[0062] Five kilograms of straight-run liquid naphtha, containing 30% n-alkanes and with a distillation range of 40–180°C, was passed through a simulated moving bed molecular sieve bed at 170°C. The bed was packed with 3.4 kg of ZSM-5 molecular sieve, had a height of 30 cm, a height-to-diameter ratio of 10:1, and a naphtha feed space velocity of 0.34 h⁻¹. -1 The feed space velocity of the desorbent n-dodecane was 1.37 h⁻¹. -1 The feed space velocity of the desorbent n-pentane was 1.37 h⁻¹. -1 The switching time is 900 seconds. After condensation, the adsorbed intermediate oil and desorbed oil are obtained. The adsorbed intermediate oil and desorbed oil are then subjected to a desorbent recovery (distillation recovery) process to obtain desolventized adsorbed intermediate oil and desolventized desorbed oil. The total mass concentration of isoalkanes, cycloalkanes and aromatics in the desolventized adsorbed intermediate oil is 88%, and the mass concentration of n-alkanes in the desolventized desorbed oil is 99%.

[0063] The solvent-absorbed intermediate oil was fed into a simulated moving bed for re-adsorption and separation, and then subjected to a desorbent recovery process (distillation recovery). The total mass concentration of isoalkanes, cycloalkanes, and aromatics in the obtained solvent-absorbed oil was 94%.

[0064] Since the simulated moving bed consists of several interconnected single columns, naphtha and desorbent must pass through all single columns within one switching cycle to complete separation. Therefore, the molecular sieve bed utilization rate is 100% for the simulated moving bed process. In this embodiment, the annual naphtha processing capacity is 2000 kg / a.

[0065] Example 2

[0066] The process flow of this embodiment is as follows: Figure 1 As shown.

[0067] Five kilograms of straight-run liquid naphtha, containing 30% n-alkanes and with a distillation range of 40–180°C, was passed through a simulated moving bed molecular sieve bed at 150°C. The bed was packed with 3.4 kg of ZSM-5 molecular sieve (silicon-to-alumina ratio of 50), with a bed height of 30 cm and a height-to-diameter ratio of 10:1. The naphtha feed space velocity was 0.17 h⁻¹. -1 The feed space velocity of the desorbent n-tetradecane is 0.68 h⁻¹. -1 The feed space velocity of the desorbent n-hexane is 0.68 h⁻¹. -1 The switching time is 900 seconds. After condensation, adsorption intermediate oil and desorbed oil are obtained. The adsorption intermediate oil and desorbed oil are then subjected to a desorbent recovery process to obtain desolventized adsorption intermediate oil and desolventized desorbed oil. The total mass concentration of isoalkanes, cycloalkanes, and aromatics in the desolventized adsorption intermediate oil is 85%, and the mass concentration of n-alkanes in the desolventized desorbed oil is 95%.

[0068] The solvent-absorbed intermediate oil was used as raw material and fed into a simulated moving bed for re-adsorption and separation. After a desorbent recovery process, the total mass concentration of isoalkanes, cycloalkanes and aromatics in the obtained solvent-absorbed oil was 92%.

[0069] Example 3

[0070] The process flow of this embodiment is as follows: Figure 1 As shown.

[0071] Five kilograms of straight-run liquid naphtha, containing 25% n-alkanes and with a distillation range of 44–180°C, was passed through a simulated moving bed molecular sieve bed at 170°C. The bed was packed with 3.4 kg of ZSM-5 molecular sieve (silicon-to-alumina ratio of 50), with a bed height of 30 cm and a height-to-diameter ratio of 10:1. The naphtha feed space velocity was 0.17 h⁻¹. -1 The feed space velocity of the desorbent n-dodecane is 0.86 h⁻¹. -1 The feed space velocity of the desorbent n-pentane is 0.86 h⁻¹. -1 The switching time is 700 seconds. After condensation, adsorption intermediate oil and desorbed oil are obtained. The adsorption intermediate oil and desorbed oil are then subjected to a desorbent recovery process to obtain desolventized adsorption intermediate oil and desolventized desorbed oil. The total mass concentration of isoalkanes, cycloalkanes, and aromatics in the desolventized adsorption intermediate oil is 88%, and the mass concentration of n-alkanes in the desolventized desorbed oil is 97%.

[0072] The solvent-absorbed intermediate oil was fed into a simulated moving bed for re-adsorption and separation, and after a desorbent recovery process, the total mass concentration of isoalkanes, cycloalkanes and aromatics in the obtained solvent-absorbed oil was 96%.

[0073] Example 4

[0074] The process flow of this embodiment is as follows: Figure 1 As shown.

[0075] Five kilograms of straight-run liquid naphtha, containing 30% n-alkanes and with a distillation range of 50–190°C, was passed through a simulated moving bed molecular sieve bed at 170°C. The bed was packed with 3.4 kg of ZSM-5 molecular sieve (silicon-to-alumina ratio of 50), with a bed height of 30 cm and a height-to-diameter ratio of 10:1. The naphtha feed space velocity was 0.34 h⁻¹. -1 The feed space velocity of the desorbent n-dodecane was 1.37 h⁻¹. -1 The feed space velocity of the desorbent n-hexane is 1.37 h⁻¹. -1 The switching time is 900 seconds. After condensation, adsorption intermediate oil and desorbed oil are obtained. The adsorption intermediate oil and desorbed oil are then subjected to a desorbent recovery process to obtain desolventized adsorption intermediate oil and desolventized desorbed oil. The total mass concentration of isoalkanes, cycloalkanes, and aromatics in the desolventized adsorption intermediate oil is 88%, and the mass concentration of n-alkanes in the desolventized desorbed oil is 95%.

[0076] The solvent-absorbed intermediate oil was used as raw material and fed into a simulated moving bed for re-adsorption and separation. After a desorbent recovery process, the total mass concentration of isoalkanes, cycloalkanes and aromatics in the obtained solvent-absorbed oil was 92%.

[0077] Example 5

[0078] The process flow of this embodiment is as follows: Figure 1 As shown.

[0079] Five kilograms of straight-run liquid naphtha, containing 35% n-alkanes and with a distillation range of 50–190°C, was passed through a simulated moving bed molecular sieve bed at 180°C. The bed was packed with 3.4 kg of ZSM-5 molecular sieve (silicon-to-alumina ratio of 50), with a bed height of 30 cm and a height-to-diameter ratio of 10:1. The naphtha feed space velocity was 0.34 h⁻¹. -1 The feed space velocity of the desorbent, n-hexadecane, is 1.37 h⁻¹. -1 The feed space velocity of the desorbent n-pentane was 1.37 h⁻¹. -1 The switching time is 900 seconds. After condensation, adsorption intermediate oil and desorbed oil are obtained. The adsorption intermediate oil and desorbed oil are then subjected to a desorbent recovery process to obtain desolventized adsorption intermediate oil and desolventized desorbed oil. The total mass concentration of isoalkanes, cycloalkanes, and aromatics in the desolventized adsorption intermediate oil is 87%, and the mass concentration of n-alkanes in the desolventized desorbed oil is 98%.

[0080] The solvent-absorbed intermediate oil was used as feedstock and fed into a simulated moving bed for re-adsorption and separation. After a desorbent recovery process, the total mass concentration of isoalkanes, cycloalkanes, and aromatics in the obtained solvent-absorbed oil was 93%.

[0081] Comparative Example 1

[0082] Five kg of straight-run liquid naphtha containing 30% n-alkanes (distillation range 40–180℃) was passed through a fixed-bed molecular sieve at 300℃. The bed was packed with 3.4 kg of ZSM-5 molecular sieve (silicon-to-alumina ratio 50). This process yielded a desorbed oil product rich in alkane and a residual oil product rich in non-alkane, with purity comparable to that obtained from a simulated moving-bed process. The fixed-bed process has an annual naphtha processing capacity of 972 kg / a, and the molecular sieve bed utilization rate is approximately 95% (actual adsorption capacity divided by theoretical adsorption capacity).

[0083] The results show that the annual naphtha processing capacity of the fixed-bed adsorption separation process is only 49% of that of the simulated moving-bed process, and the utilization rate of the fixed-bed molecular sieve bed is also lower than that of the simulated moving-bed process.

[0084] Comparative Example 2

[0085] Five kilograms of straight-run liquid naphtha, containing 30% n-alkanes and with a distillation range of 40–180°C, was passed through a simulated moving bed molecular sieve bed at 170°C. The bed was packed with 3.4 kg of ZSM-5 molecular sieve (silicon-to-alumina ratio of 50), with a bed height of 30 cm and a height-to-diameter ratio of 10:1. The naphtha feed space velocity was 0.34 h⁻¹. -1 Only n-pentane was used as the desorbent, and the n-pentane feed space velocity was 1.37 h⁻¹. -1 The switching time is 900 seconds. After condensation, adsorption intermediate oil and desorbed oil are obtained. The adsorption intermediate oil and desorbed oil are then subjected to a desorbent recovery process to obtain desolventized adsorption intermediate oil and desolventized desorbed oil. The total mass concentration of isoalkanes, cycloalkanes, and aromatics in the adsorption intermediate oil is 76%, and the mass concentration of n-alkanes in the desolventized desorbed oil is 84%.

[0086] The solvent-absorbed intermediate oil was fed into a simulated moving bed for re-adsorption and separation, and after a desorbent recovery process, the total mass concentration of isoalkanes, cycloalkanes and aromatics in the obtained solvent-absorbed oil was 82%.

[0087] The results show that when only n-pentane is used as the desorbent, since the adsorption performance of n-alkanes in naphtha and n-pentane on molecular sieves is similar, the total mass concentration of isoalkanes, cycloalkanes and aromatics in the adsorbed oil and the mass concentration of n-alkanes in the desorbed oil are both lower than those obtained when using a dual desorbent process.

[0088] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for directional adsorption separation of naphtha, characterized in that, Includes the following steps: Liquid naphtha is adsorbed using a molecular sieve adsorbent to obtain a residual effluent; the molecular sieve adsorbent is one or more of ZSM-5, UZM-35, and β molecular sieve; The molecular sieve adsorbent after adsorption was subjected to a first desorption using a first desorbent to obtain a desorbed effluent. A second desorbent is used to perform a second desorption on the molecular sieve adsorbent after the first desorption, and the resulting molecular sieve adsorbent repeats the adsorption process. After the desorbed effluent is recovered by a desorbent, a desorbed oil rich in n-alkanes is obtained; after the adsorbed effluent is recovered by a desorbent, an adsorbed oil rich in isoalkanes, cycloalkanes and aromatics is obtained. The first desorbent is n-dodecane, n-tetradecane, or n-hexadecane; the second desorbent is n-pentane or n-hexane.

2. The naphtha-directed adsorption separation method according to claim 1, characterized in that, The liquid naphtha is straight-run naphtha, hydrocracked naphtha, or hydrolyzed naphtha.

3. The naphtha-directed adsorption separation method according to claim 1, characterized in that, The silica-alumina ratio of the molecular sieve adsorbent is 40~200.

4. The naphtha-directed adsorption separation method according to claim 1, characterized in that, The adsorption, first desorption, and second desorption temperatures are independently 100~190℃.

5. A continuous directional adsorption separation method for naphtha, characterized in that, Includes the following steps: A simulated moving bed adsorption separation device is provided, which includes an adsorption zone and a desorption zone arranged in series. The adsorption zone and the desorption zone are respectively provided with multiple separation columns filled with molecular sieve adsorbent. Each separation column is provided with a programmable valve at the inlet and outlet. Liquid naphtha is passed into the first separation column of the adsorption zone for adsorption. The adsorbed oil flows out of the simulated moving bed adsorption separation device and is subsequently cooled and desorbed agent recovered to obtain a desolventized adsorbed oil rich in isoalkanes, cycloalkanes and aromatics. Simultaneously, a second desorbent is introduced into the next separation column after the liquid naphtha inlet for a second desorption, replacing the first desorbent in the column; a first desorbent is introduced into the first separation column of the desorption zone for a first desorption, replacing the n-alkanes adsorbed by the molecular sieve adsorbent in the column; the desorbed oil produced by the first and second desorption flows out of the simulated moving bed adsorption separation device, and is subsequently cooled and desorbent recovered to obtain desorbed oil rich in n-alkanes; the first desorbent is n-dodecane, n-tetradecane, or n-hexadecane; the second desorbent is n-pentane or n-hexane; Then, by switching the liquid naphtha inlet, the second desorbent inlet, and the first desorbent inlet using the programmable valve of the simulated moving bed adsorption separation device, each of them moves forward one separation column, repeating the adsorption and desorption process.

6. The continuous directional adsorption separation method for naphtha according to claim 5, characterized in that, The separation columns are respectively filled in the cylindrical tower sections, and the height-to-diameter ratio of a single separation column is 2~20:

1.

7. The continuous directional adsorption separation method for naphtha according to claim 5, characterized in that, The bed temperature of the simulated moving bed adsorption separation device is 100~190℃.

8. The continuous directional adsorption separation method for naphtha according to claim 5, characterized in that, The feed space velocity of the liquid naphtha is 0.05~1.5h. -1 The feed space velocities of the first and second desorbents are independently 0.05~10 h⁻¹. -1 .

9. The continuous directional adsorption separation method for naphtha according to claim 8, characterized in that, The feed space velocities of the first and second desorbents are equal.

10. The continuous directional adsorption separation method for naphtha according to claim 5 or 8, characterized in that, The switching time is 700~900s.

Images