Method and device for liquid-liquid extraction separation of alpha-olefin and alkane mixture, extraction agent and application

Abstract

The invention belongs to the technical field of alkane and olefin separation, and discloses a method and a device for liquid-liquid extraction separation of an alpha-olefin and alkane mixture, an extraction agent and application, the extraction agent comprises silver hexafluorophosphate, silver tetrafluoroborate, silver trifluoromethanesulfonate, silver bis (fluorosulfonyl) imide, sulfolane, N-methyl pyrrolidone, N, N-dimethylformamide, 1, 2, 4-trimethyl-1, 3-pentanedione, 1, 2, 4-trimethyl-1, 3-pentanedione, 1, 2, 4-trimethyl-1, 3-pentanedione, 1, 2, 4-trimethyl-1, 3-pentanedione, 1, 2, 4-trimethyl-1, 3 the solvent is one or more of 2, 3-dimethyl-2-imidazolinone, gamma-valerolactone, methanol, ethanol, ethylene glycol and glycerol. According to the present invention, the specific composition extraction agent is used for separating the alkane / olefin mixture, the alkane almost does not exist in the organic phase product, the purity of the alpha-olefin product obtained by separation in the single-stage extraction tower is more than 98%, the order of magnitude of the extraction efficiency is improved compared with the other process, and the energy consumption and the separation cost are substantially saved. In addition, an olefin-rich component generated in oil phase product separation flows back to the primary extraction tower to be reused, so that the utilization rate of the raw materials is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of alkane-olefin separation technology, and in particular to a method, apparatus, extractant and application for liquid-liquid extraction to separate a mixture of α-olefins and alkanes. Background Technology

[0002] With the continuous development of my country's petrochemical industry, the requirements for high-quality chemicals are constantly expanding. Alkane / olefin mixtures are a broad-spectrum mixture in the chemical industry, widely present in chemical processes such as Fischer-Tropsch synthesis. For example, the content of α-olefins in Fischer-Tropsch synthetic oil can be as high as 70%. α-olefins are an important chemical product and a key raw material for the production of important fine chemical products such as PAO lubricating oil, which has a very important impact on the chemical industry. Therefore, the efficient separation of α-olefins from alkanes is of great significance.

[0003] However, separating α-olefins and alkanes currently presents certain challenges, as they typically have similar structures and boiling points, making direct distillation an energy-intensive process. If α-olefins could be efficiently separated from alkanes, it would not only fully utilize the added value of α-olefins to improve economic efficiency but also promote the sustainable and healthy development of the coal chemical industry.

[0004] Solvent extraction is one of the mainstream methods for separating alkanes and alkenes. It mainly utilizes the different solubilities of alkanes and alkenes in the extractant to achieve separation. Different process routes exist depending on the choice of extractant. Using silver complexation can make great use of the structural differences between alkenes and alkanes, resulting in excellent separation performance.

[0005] The search revealed the following patent publications related to this invention's patent application: CN114736094A discloses a method for extracting and separating α-olefins from Fischer-Tropsch synthetic oil. This method involves multi-stage countercurrent extraction of the alkanes to be separated and the extractant, followed by secondary separation of the subsequent products to finally obtain the α-olefin product. Selected extractants include N-formylmorpholine, diethyl phthalate, 1-methylimidazolium, and dimethyl sulfoxide. While this method can separate α-olefins in complex systems, the selected extractants are based on differences in solubility, resulting in less than ideal separation efficiency.

[0006] CN103232313A discloses a method for extracting and separating alkanes / olefins. This method involves thoroughly mixing the extractant with the system to be separated and allowing it to stand for phase separation. The extractant may be N-methylpyrrolidone, N-formylmorpholine, 1-methylimidazolium, or γ-valerolactone. The main advantage of this method is its simplicity and reliability; however, its disadvantage is that the separated system is too limited, making it unable to achieve integrated separation of multiple components.

[0007] CN119912312A describes a method and apparatus for separating and purifying aromatics, alkenes, and alkanes. This method combines liquid-liquid extraction and extractive distillation, operating within their respective advantageous ranges. Liquid-liquid extraction separates heavier alkanes with lower solubility, while extractive distillation separates lighter alkanes with relatively higher volatility. Finally, the same solvent is used to achieve efficient separation of aromatics, alkanes, and alkenes. Selected extractants include amides, glycols, glycol ethers, and lactones. However, the apparatus involved in this method is highly complex, requiring substantial investment in equipment for production.

[0008] A comparison reveals fundamental differences between this invention's patent application and the aforementioned patent publications. Therefore, there is an urgent need to invent a novel extractant and separation process that is simple in its equipment and, in particular, exhibits excellent separation efficiency, for the efficient separation of mixtures of alkanes and α-olefins. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method, apparatus, extractant and application for liquid-liquid extraction to separate a mixture of α-olefins and alkanes.

[0010] The technical solution adopted by this invention to solve its technical problem is: A novel combined extractant for the efficient separation of alkanes and alkenes, the extractant comprising one or more of the following: silver hexafluorophosphate, silver tetrafluoroborate, silver trifluoromethanesulfonate, silver difluorosulfonylimide, sulfolane, N-methylpyrrolidone, N,N-dimethylformamide, 1,3-dimethyl-2-imidazolinone, γ-valerol, methanol, ethanol, ethylene glycol, and glycerol.

[0011] Furthermore, the extractant comprises a first component and a second component, wherein the first component is selected from one of silver hexafluorophosphate, silver tetrafluoroborate, silver trifluoromethanesulfonate, and silver difluorosulfonylimide; The second component is selected from one of the following: sulfolane, N,N-dimethylformamide, 1,3-dimethyl-2-imidazolinone, γ-valerol, methanol, ethanol, ethylene glycol, and glycerol.

[0012] Furthermore, the first component and the second component are thoroughly mixed; or, the mass ratio of the first component and the second component is between 0.1 and 4:1.

[0013] Furthermore, the mixing temperature of the first component and the second component is 20-80℃, and the mixing time is 2-12h.

[0014] The method for separating alkanes and alkenes by liquid-liquid extraction using the combined extractant described above includes the following steps: (1) Add a combination of extractants to a mixed system of olefins and alkanes to perform extraction operations, and obtain an oil phase product containing most of the alkanes, raffinate olefins and a small amount of extractant, and an organic phase product containing a large amount of extractant, extracted olefins and a small amount of alkanes. (2) Further separation of the oil phase products yields alkane products, olefins and extractant; (3) Further separate the organic phase products to obtain olefin products and extractant.

[0015] Furthermore, the mass ratio of the combined extractant to the mixture to be separated is 0.2-5:1; Alternatively, the selected mixture system contains at least one set of olefins and alkanes with the same carbon chain length; Alternatively, the extraction operation can be performed at a temperature range of 20-80°C and at an atmospheric pressure. Alternatively, the carbon chain length in the hybrid system is in the range of C5 to C16.

[0016] Furthermore, the extractant obtained in steps (2) and (3) is returned to step (1) for recycling, the olefin-rich phase obtained in step (2) is returned to step (1) as raw material for reuse, and then the other olefins and alkanes are extracted as products.

[0017] Furthermore, the extractant and the mixture are in countercurrent contact; Alternatively, the extraction and separation process in step (1) can be carried out in an extraction tower; Alternatively, the separation operation in step (2) can be carried out in a solvent recovery tower; Alternatively, the separation in steps (2) and (3) can be performed as decompression separation.

[0018] Furthermore, the bottom temperature of the recovery tower is 50-240℃, and the top pressure of the recovery tower is 1-20kPa.

[0019] The application of the combined extractants described above in the separation of alkanes and olefins.

[0020] The advantages and positive effects of this invention are as follows: 1. The specific composition extractant of this invention is used to separate alkane / olefin mixtures. The organic phase product contains almost no alkanes, and the α-olefin product obtained in a single-stage extraction tower has a purity greater than 98%. Compared with other processes, this represents an order-of-magnitude improvement in extraction efficiency, significantly saving energy and separation costs. Furthermore, the olefin-rich components generated during the separation of the oil phase product are recycled back to the primary extraction tower for reuse, greatly improving the utilization rate of the raw materials.

[0021] 2. The extractant of this invention only needs to be mixed for use. Its hydrogen bonds have the characteristic of spontaneous construction, and can be rapidly constructed based on hydrogen bond linkage. It has the characteristics of simple and reliable preparation process, low corrosiveness to equipment, low requirements for operating conditions, environmental protection and easy recycling.

[0022] 3. The present invention rationally designs the extractant to achieve a shielded state characteristic that makes it almost insoluble in alkanes, while maintaining high-throughput complexation of alkenes. The extractant is based on the self-construction of hydrogen bonds, has a simple synthesis method, and can achieve almost complete shielding of alkanes, thereby achieving an order-of-magnitude improvement in separation efficiency.

[0023] 4. In view of the shortcomings of the prior art, including low separation efficiency, high energy consumption and complex equipment and process, the present invention provides a highly efficient separation method for α-olefins and alkanes. It can achieve extremely efficient separation of olefins with low energy consumption. Compared with conventional extraction, it can achieve a separation selectivity improvement of more than two orders of magnitude. The purity of the α-olefins obtained can be as high as 98% or more.

[0024] 5. The method of this invention involves countercurrent contact between an alkane-olefin mixture and an extractant in an extraction tower to obtain an oil phase product and an organic phase product. The organic phase product is then separated again to obtain α-olefins and the extractant, wherein the α-olefins are collected as the product, and the extractant is recycled back into the extraction tower for reuse. The oil phase product undergoes a second separation to obtain alkanes, olefins, and the extractant, wherein the alkanes are collected as the product, and the olefin-rich phase and the extractant are recycled back into the extraction tower for reuse. This invention, based on a highly efficient combination of extractants and a olefin-rich phase recycling separation method, achieves low-energy and high-efficiency separation of alkanes and aromatics, making it suitable for industrial application. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structural connection of the extraction device in this invention. Detailed Implementation

[0026] The present invention will be further described below with reference to the embodiments. The following embodiments are descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0027] The various experimental operations involved in the specific embodiments are all conventional techniques in the field. For parts not specifically annotated in this document, those skilled in the art can refer to various commonly used reference books, scientific and technological documents or related instructions and manuals prior to the filing date of this invention to carry out the operations.

[0028] This invention provides a novel, highly efficient combined extractant for separating alkanes and alkenes. The composition comprises one or more of the following: silver hexafluorophosphate, silver tetrafluoroborate, silver trifluoromethanesulfonate, silver difluorosulfonylimide, sulfolane, N-methylpyrrolidone, N,N-dimethylformamide, 1,3-dimethyl-2-imidazolinone, γ-valerol, methanol, ethanol, ethylene glycol, and glycerol. The first component of the extractant is selected from one of silver hexafluorophosphate, silver tetrafluoroborate, silver trifluoromethanesulfonate, and silver difluorosulfonylimide; the other component is selected from one of sulfolane, N-methylpyrrolidone, N,N-dimethylformamide, 1,3-dimethyl-2-imidazolinone, γ-valerol, methanol, ethanol, ethylene glycol, and glycerol. The mass ratio of the two components is 0.1-4:1.

[0029] Combinatorial extraction possesses a shielding feature that makes alkanes almost insoluble, while maintaining high-throughput complexation of olefins.

[0030] This invention provides a method for preparing a combined extractant based on hydrogen bond self-construction, with a preparation temperature range of 20-80℃, preferably carried out at room temperature; and a preparation time range of 2-12 hours.

[0031] The present invention does not impose any particular limitations on the stirring conditions, which can be appropriately selected according to specific circumstances.

[0032] This invention provides a method for separating alkanes and / or α-olefins by liquid-liquid extraction, the method comprising the following steps: (1) The system to be separated is contacted countercurrently with the combined extractant described in this invention in an extraction tower to obtain an organic phase product containing olefins and extractant and an oil phase product containing alkanes, a small amount of olefins and extractant.

[0033] (2) Separate the organic phase products to obtain olefin products and regenerated extractant.

[0034] (3) The oil phase products are separated, and the olefin-rich phase is extracted from the middle line. Alkane products and regenerated extractant are also obtained.

[0035] The regenerated extractant in steps (2) and (3) and the olefin-rich phase in step (3) are returned to step (1) for reuse.

[0036] In a preferred embodiment, the extractant is fed from the top of the extraction column, and the system to be separated is fed from the bottom of the extraction column. In the extraction column, one component of the extractant undergoes a complexation reaction with olefins, carrying the separated olefins downwards to form an organic phase product. During this process, the second component of the extractant acts as a shield, almost completely preventing alkanes from entering the organic phase; the alkane product flows out from the top of the column as an oil phase product.

[0037] In a preferred embodiment, the system to be separated contains a C5-C16 structural range, and the carbon chain lengths of the corresponding alkenes and alkanes are close to or the same, and it can simultaneously contain alkanes and alkenes with multiple carbon numbers. The present invention does not limit the structure of the alkanes; they can be straight-chain alkanes or isomeric alkanes. The alkenes are also not structurally limited; they can be internal alkenes or cyclic alkenes, but both alkanes and alkenes are preferably straight-chain hydrocarbons.

[0038] The present invention does not impose any special restrictions on the source of the system to be separated. It can be Fischer-Tropsch light oil, or other mixtures of alkanes and olefins that meet the conditions, or mixtures of alkanes and olefins with multiple carbon numbers. Preferably, it is Fischer-Tropsch light oil after deoxygenation, with a fraction range of C6-C8.

[0039] In a preferred embodiment, the organic phase product contains only a very small amount of residual alkane. As verified by gas chromatography, the mass of residual alkane is less than 0.01% of the total mass. In this invention, since the residual alkane in the organic phase product is extremely low and can be almost ignored, this invention can achieve an order-of-magnitude improvement in the separation performance of alkane and olefin.

[0040] In a preferred embodiment, the oil phase product contains almost all alkanes, a small amount of unseparated olefins, and extractant. In the oil phase product separation operation, the unseparated olefins are enriched and then collected from the centerline and refluxed back to the extraction tower for reuse. In the final alkane product obtained at the top of the tower, the mass fraction of olefins is less than 3%, the total olefin loss is low, and most of the olefins can be converted into the final product.

[0041] In a preferred embodiment, the extraction tower operates at 20-60°C, preferably room temperature, and at atmospheric pressure. The present invention does not specifically limit the room temperature, and the feed ratio of the extraction tower is 0.2-4.0.

[0042] In a preferred embodiment, the extraction tower is a packed tower with a packing height ranging from 0.2 to 4 meters. There is no special limitation on the type of packing, which can be Raschig rings, Pall rings, etc.

[0043] In a preferred embodiment, the secondary separation operation is carried out under a pressure of 1 kPa-20 kPa and a temperature range of 40-100°C, with the olefin-rich phase being extracted near the middle section.

[0044] Specifically, the relevant preparation and testing methods are as follows: The present invention will be described in detail below through embodiments.

[0045] In the following examples, the separation effect of the extractant is represented by the partition coefficient (D), selectivity coefficient (S), and mass fraction (w%). The partition coefficient is expressed as the ratio of the actual mass fraction of a solute component in the oil phase to that in the organic phase. The selectivity coefficient is expressed as the ratio of the partition coefficients of olefins to those of alkanes. The separation effect of the extractant is quantitatively represented by the partition coefficient; a larger partition coefficient indicates a higher separation flux, and a larger selectivity coefficient indicates a better separation effect. They are expressed by the following formulas: ……………………………………….Equation (1) Equation (2) Among them, D i w represents the partition coefficient of solute component i; i oil Indicates the mass fraction of component i in the oil phase; w i org D represents the mass fraction of component i in the organic phase; S represents the selectivity coefficient; olefin D represents the partition coefficient of olefins. alkane This represents the partition coefficient of alkanes.

[0046] Simulated oils were prepared, corresponding to C6-C8 components and containing their mixed components. The composition of the simulated oils is shown in Table 1 (these five model oils were used in Tables 2-6, representing the mixture composition under different working conditions. The five model oils were separated under different conditions in the five examples, and the corresponding results were obtained). The extraction results are shown in Table 2.

[0047] Table 1

[0048] An apparatus for liquid-liquid extraction and separation of a mixture of α-olefins and alkanes, such as... Figure 1 As shown, the apparatus includes an extraction tower T1, an organic phase separation tower T2, an oil phase separation tower T3, a first centrifugal pump P1, a second centrifugal pump P2, a third centrifugal pump P3, a fourth centrifugal pump P4, a first total condenser A1, a second total condenser A2, a first heat exchanger E1, a second heat exchanger E2, a first reboiler H1, and a second reboiler H2. The extraction tower T1 includes an extraction tower body (not labeled in the figure), with a top inlet 1 and a top outlet 2 connected to the upper part of the extraction tower body, and a bottom inlet 3 and a bottom outlet 4 connected to the lower part of the extraction tower body. The organic phase separation tower T2 includes an organic phase separation tower body (not labeled in the figure), with a top inlet 6 and a top outlet 5 connected to the upper part of the organic phase separation tower body, a bottom inlet 9 connected to the lower part of the organic phase separation tower body, a bottom outlet 7 connected to the bottom of the organic phase separation tower body, and a reflux inlet 8 connected to the upper part of the organic phase separation tower body between the bottom inlet 9 and the bottom outlet 7. The oil phase separation tower T3 includes an oil phase separation tower body (not labeled in the figure), with a top inlet 10 connected to the upper part of the tower body, a top outlet 11 connected to the top of the tower body, a top reflux inlet 12 connected to the top outlet 11, a tower body outlet 15 connected to the upper part of the tower body between the top inlet 10 and the bottom reflux inlet 13, a bottom outlet 14 connected to the bottom of the tower body, and a bottom reflux inlet 13 connected to the lower part of the tower body. The extraction tower T1 has a top inlet 1 that can receive a combined extractant, and a top outlet 2 that is connected to a top inlet 10. The bottom inlet 3 can receive the system to be separated, and a bottom outlet 4 that is connected to a bottom inlet 9. The top outlet 5 is connected to the top inlet 6 of the organic phase separation tower T2 via a first total condenser A1, a first heat exchanger E1, and a third centrifugal pump P3, or discharges olefin product S9. The bottom outlet 7 of the organic phase separation tower T2 is connected to a reflux inlet 8 via a first heat exchanger E1, and is also connected to the top inlet 1 via a first centrifugal pump P1. The top outlet 11 of the oil phase separation tower T3 is connected to the top reflux port 12 via the second total condenser A2, the second heat exchanger E2, and the fourth centrifugal pump P4, or discharges alkane product S8; the tower body outlet 15 is connected to the bottom inlet 3; the bottom outlet 14 is connected to the bottom reflux inlet 13 via the second heat exchanger E2, and the bottom outlet 14 is also connected to the top inlet 1 via the second centrifugal pump P2.

[0049] In the separation device, olefin mixture S1 is fed from the bottom of extraction tower T1, and fresh extractant S2 is fed from the top of extraction tower T1. After sufficient countercurrent mass transfer inside the extraction tower, the oil phase S3 to be separated flows out from the top of extraction tower T1 and flows to oil phase separation tower T3 for further separation, while the organic phase S4 to be separated flows out from the bottom of extraction tower T1 and flows to organic phase separation tower T2 for further separation. In organic phase separation tower T2, the extractant flows out from the bottom of the tower as a heavy component and is returned to the top of the extraction tower for reuse as T2 circulating extractant S5. Olefins flow out from the top of the tower as a light component as olefin product S9. In oil phase separation tower T3, the remaining extractant flows out from the bottom of the tower as a heavy component and is returned to the top of the extraction tower for reuse as T3 circulating extractant S6. Olefins and alkanes are enriched at the top of the tower as light components. A portion of the olefin-rich phase S7 is collected from the side stream and returned to the bottom of the extraction tower for reuse as feedstock, while the remaining alkanes are collected from the top of the tower as alkane product S8.

[0050] In all the examples below, the combined extractant components used were prepared by mixing ethylene glycol and silver tetrafluoroborate at a mass ratio of 1:1 at room temperature.

[0051] In all the embodiments below, the operating pressure of the solvent recovery tower is maintained at 20 kPa and the top temperature is set to 70°C.

[0052] Using the above, such as Figure 1 The apparatus shown and the method using the apparatus are used for the efficient separation of alkanes and olefins, with specific parameters described in the following examples.

[0053] Example 1 The system to be separated and the extractant were fed into an extraction tower at a mass ratio of 1:3 for countercurrent extraction. The operating conditions were ambient temperature and pressure, and Raschig rings were used as the packing material with a packing height of 2.5 meters. The extractant was fed from the top of the tower, and the system to be separated was fed from the bottom. The oil phase product was collected at the top of the tower, and the organic phase product was collected at the bottom.

[0054] The organic phase product is fed into a distillation column for distillation. The bottom of the column yields a recycled combined extractant, which is returned to the extraction column. The top of the column directly yields a high-purity olefin product. The specific product purity is shown in Table 2.

[0055] The oil phase product is fed into a distillation column for distillation separation. The recycled extractant obtained at the bottom of the column is returned to the extraction column for reuse. The 30% mass fraction product is collected from the middle line as an olefin-rich phase and returned to the extraction column as a raw material to be fed back from the bottom of the column. The alkane product is obtained at the top of the column, and the purity is shown in Table 2.

[0056] Table 2

[0057] Example 2 The system to be separated and the combined extractant were fed into an extraction tower at a mass ratio of 1:2 for countercurrent extraction. The operating conditions were ambient temperature and pressure, and Raschig rings were used as the packing material with a packing height of 2.5 meters. The combined extractant was fed from the top of the tower, and the system to be separated was fed from the bottom of the tower. The oil phase product was collected at the top of the tower, and the organic phase product was collected at the bottom of the tower.

[0058] The organic phase product is fed into a distillation column for distillation. The bottom of the column yields a recycled combined extractant, which is returned to the extraction column. The top of the column directly yields a high-purity olefin product. The specific product purity is shown in Table 3.

[0059] The oil phase product is fed into a distillation column for distillation separation. The recycled extractant obtained at the bottom of the column is returned to the extraction column for reuse. The 30% mass fraction product is collected from the middle line as an olefin-rich phase and returned to the extraction column as a raw material to be fed back from the bottom of the column. The alkane product is obtained at the top of the column, and the purity is shown in Table 3.

[0060] Table 3

[0061] Example 3 The system to be separated and the extractant were fed into an extraction tower at a 1:1 mass ratio for countercurrent extraction. The operating conditions were ambient temperature and pressure, and Raschig rings were used as the packing material with a packing height of 2.5 meters. The extractant was fed from the top of the tower, while the system to be separated was fed from the bottom. The oil phase product was collected at the top of the tower, and the organic phase product was collected at the bottom.

[0062] The organic phase product is fed into a distillation column for distillation. The bottom of the column yields a recycled combined extractant, which is returned to the extraction column. The top of the column directly yields a high-purity olefin product. The specific product purity is shown in Table 4.

[0063] The oil phase product is fed into a distillation column for distillation separation. The recycled combined extractant obtained at the bottom of the column is returned to the extraction column for reuse. The 30% mass fraction product is collected from the middle line as an olefin-rich phase and returned to the extraction column as raw material to be fed back from the bottom of the column. The alkane product is obtained at the top of the column, and the purity is shown in Table 4.

[0064] Table 4

[0065] Example 4 The system to be separated and the extractant were fed into an extraction tower at a mass ratio of 2:1 for countercurrent extraction. The operating conditions were ambient temperature and pressure. Raschig rings were used as the packing material, with a packing height of 2.5 meters. The extractant was fed from the top of the tower, while the system to be separated was fed from the bottom. The oil phase product was collected at the top of the tower, and the organic phase product was collected at the bottom.

[0066] The organic phase product is fed into a distillation column for distillation. The bottom of the column yields a recycled combined extractant, which is returned to the extraction column. The top of the column directly yields a high-purity olefin product. The specific product purity is shown in Table 5.

[0067] The oil phase product is fed into a distillation column for distillation separation. The recycled extractant obtained at the bottom of the column is returned to the extraction column for reuse. The 30% mass fraction product is collected from the middle line as an olefin-rich phase and returned to the extraction column as a raw material to be fed back from the bottom of the column. The alkane product is obtained at the top of the column, and the purity is shown in Table 5.

[0068] Table 5

[0069] Example 5 The system to be separated and the extractant were fed into an extraction tower at a mass ratio of 3:1 for countercurrent extraction. The operating conditions were ambient temperature and pressure. Raschig rings were used as the packing material, with a packing height of 2.5 meters. The extractant was fed from the top of the tower, while the system to be separated was fed from the bottom. The oil phase product was collected at the top of the tower, and the organic phase product was collected at the bottom.

[0070] The organic phase product is fed into a distillation column for distillation. The bottom of the column yields a recycled combined extractant, which is returned to the extraction column. The top of the column directly yields a high-purity olefin product. The specific product purity is shown in Table 6.

[0071] The oil phase product is fed into a distillation column for distillation separation. The recycled extractant obtained at the bottom of the column is returned to the extraction column for reuse. The 30% mass fraction product is collected from the middle line as an olefin-rich phase and returned to the extraction column as a raw material to be fed back from the bottom of the column. The alkane product is obtained at the top of the column, and the purity is shown in Table 6.

[0072] Table 6

[0073] As can be seen from the five embodiments, the present invention can directly obtain olefin products with a purity of at least 97% through a single-stage extraction, avoiding the uncertainty of multi-stage extraction and significantly saving equipment and operating costs. Furthermore, it maintains high efficiency in high-olefin separation systems and also possesses high separation capabilities for mixtures of various olefins. The selectivity coefficient can reach up to 1270, representing a two-order-of-magnitude improvement compared to selectivity coefficients in existing literature.

[0074] Comparative Example 1 The system to be separated and sulfolane were fed into an extraction tower at a 1:1 mass ratio for countercurrent extraction. The operating conditions were ambient temperature and pressure, and Raschig rings were used as the packing material with a height of 2.5 meters. The combined extractant was fed from the top of the tower, while the system to be separated was fed from the bottom. The oil phase product was collected at the top of the tower, and the organic phase product was collected at the bottom.

[0075] The organic phase product is fed into a distillation column for distillation. The bottom of the column yields a recycled combined extractant, which is returned to the extraction column. The top of the column directly yields a high-purity olefin product. The specific product purity is shown in Table 7.

[0076] The oil phase product is fed into a distillation column for distillation separation. The recycled extractant obtained at the bottom of the column is returned to the extraction column for reuse. The 30% mass fraction product is collected from the middle line as an olefin-rich phase and returned to the extraction column as a raw material to be fed back from the bottom of the column. The alkane product is obtained at the top of the column, and the purity is shown in Table 7.

[0077] Table 7

[0078] Comparative Example 1 used sulfolane, a commonly used polar extractant in industry, and operated under the same conditions as in Example 3. Comparing the results of the two groups, it is clear that thanks to the efficient shielding effect of the combined extractant of this invention on alkanes, efficient separation of alkanes and alkenes can be achieved, yielding high-purity products and representing an order-of-magnitude improvement in separation selectivity. In Comparative Example 1, sulfolane relies solely on molecular polarity for separation, making it difficult to distinguish the subtle differences between alkanes and alkenes. Given their miscibility, efficient single-stage separation is difficult to achieve, typically requiring multiple stages in series.

[0079] Although embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the scope of the invention is not limited to the contents disclosed in the embodiments.

Claims

1. A novel combined extractant for the efficient separation of alkanes and olefins, characterized in that: The extractant includes one or more of the following: silver hexafluorophosphate, silver tetrafluoroborate, silver trifluoromethanesulfonate, silver difluorosulfonamide, sulfolane, N-methylpyrrolidone, N,N-dimethylformamide, 1,3-dimethyl-2-imidazolinone, γ-valerol, methanol, ethanol, ethylene glycol, and glycerol.

2. The extractant according to claim 1, characterized in that: The extractant comprises a first component and a second component, wherein the first component is selected from one of silver hexafluorophosphate, silver tetrafluoroborate, silver trifluoromethanesulfonate, and silver difluorosulfonylimide. The second component is selected from one of the following: sulfolane, N,N-dimethylformamide, 1,3-dimethyl-2-imidazolinone, γ-valerol, methanol, ethanol, ethylene glycol, and glycerol.

3. The extractant according to claim 2, characterized in that: The first component and the second component have been thoroughly mixed; or the mass ratio of the first component and the second component is between 0.1 and 4:

1.

4. The extractant according to claim 3, characterized in that: The mixing temperature of the first component and the second component is 20-80℃, and the mixing time is 2-12h.

5. A method for separating alkanes and alkenes by liquid-liquid extraction using the combined extractant as described in any one of claims 1 to 4, characterized in that: Includes the following steps: (1) Add a combination of extractants to a mixed system of olefins and alkanes to perform extraction operations, and obtain an oil phase product containing most of the alkanes, raffinate olefins and a small amount of extractant, and an organic phase product containing a large amount of extractant, extracted olefins and a small amount of alkanes. (2) Further separation of the oil phase products yields alkane products, olefins and extractant; (3) Further separate the organic phase products to obtain olefin products and extractant.

6. The method according to claim 5, characterized in that: The mass ratio of the combined extractant to the mixture to be separated is 0.2-5:1; Alternatively, the selected mixture system contains at least one set of olefins and alkanes with the same carbon chain length; Alternatively, the extraction operation can be performed at a temperature range of 20-80°C and at an atmospheric pressure. Alternatively, the carbon chain length in the hybrid system is in the range of C5 to C16.

7. The method according to claim 5, characterized in that: The extractant obtained in steps (2) and (3) is returned to step (1) for recycling. The olefin-rich phase obtained in step (2) is returned to step (1) as raw material for reuse. Then, the other olefins and alkanes are extracted as products.

8. The method according to any one of claims 5 to 7, characterized in that: The extractant and the mixture are in countercurrent contact; Alternatively, the extraction and separation process in step (1) can be carried out in an extraction tower; Alternatively, the separation operation in step (2) can be carried out in a solvent recovery tower; Alternatively, the separation in steps (2) and (3) can be performed as decompression separation.

9. The method according to claim 8, characterized in that: The temperature at the bottom of the recovery tower is 50-240℃, and the pressure at the top of the recovery tower is 1-20kPa.

10. The use of the combined extractant as described in any one of claims 1 to 4 in the separation of alkanes and olefins.

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