Separation system of fischer-tropsch based paos base oil crude product and separation method and application thereof

Abstract

A separation system, method, and application for crude Fischer-Tropsch PAO base oil products, the separation system comprising: a storage unit for storing C8-C of the refined Fischer-Tropsch synthesis liquid phase product. 14 The process involves preparing crude Fischer-PAO base oil; a multi-stage molecular distillation unit, each stage comprising a sequentially connected molecular distillation vacuum separator, product cooler, and product storage tank. The molecular distillation vacuum separator is connected to a vacuum system. Between adjacent stages, the heavy fraction outlet of the higher-stage molecular distillation vacuum separator is connected to the feed inlet of the lower-stage unit. By employing different stages of molecular distillation methods for efficient and stable separation of crude Fischer-PAO base oil, multiple PAO products can be produced in a single step. These products can then be used as base oil feedstocks for preparing different grades of lubricating oils, enriching product diversity and achieving economic benefits.

Description

Technical Field

[0001] This invention belongs to the technical field of lubricant preparation, and specifically relates to a separation system, separation method and application of crude Fischer-Tropsch PAO base oil. Background Technology

[0002] PAO (polyalphaolefin) is a commonly used base oil for lubricating oils, typically produced through the synthesis of high-carbon-number alpha-olefins or olefin oligomerization. Traditional PAO synthesis methods utilize high-carbon-number alpha-olefins produced from cracked paraffin or through olefin oligomerization. The crude PAO base oil typically requires full-fraction hydrogenation and fractionation processes to produce different grades of PAO lubricating oil base oils.

[0003] In the prior art, purified Fischer-Tropsch synthesis liquid-phase product C8-C is used. 14 Synthetic PAO lubricating oil base oil is a novel synthetic method, producing a product known as "Fischer-Tropsch PAO synthetic lubricating oil base oil crude product." The advantages of this method are that the Fischer-Tropsch PAO crude product has a wide carbon number distribution, excellent performance, and can produce multiple PAO products in a single step through product separation.

[0004] The separation technology for this "Firtoy PAO synthetic lubricating oil base crude product" presents several key technical challenges. This is due to the use of Firtoy C8-C... 14 As a raw material for PAO synthesis, the produced products have a wider carbon number distribution, with heavier components having higher carbon numbers, thus requiring higher separation temperatures. When using atmospheric or vacuum distillation for separation, the high temperatures easily lead to product oxidation, darkening of color, and reduced product quality. Simultaneously, higher temperatures can also cause the decomposition of high-carbon-number heavy products, resulting in a significant decrease in product yield. Therefore, the separation of crude Fischer-PAO base oils remains a major challenge for industrial production. To address these issues, a new separation method is needed to solve the problem of separating crude Fischer-PAO base oils. Summary of the Invention

[0005] To address the problems of product oxidation, color deepening, and reduced product quality caused by atmospheric or vacuum distillation in existing technologies, as well as the decomposition of high-carbon-number heavy products due to high separation temperatures affecting yield, this invention proposes a separation system, method, and application for crude Fischer-Tropsch PAO base oil. By employing different levels of molecular distillation methods, this invention efficiently and stably separates crude Fischer-Tropsch PAO base oil, enabling the production of multiple PAO products in a single step. These products can be used as base oil raw materials for preparing different grades of lubricating oils, enriching product diversity and achieving economic benefits.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A separation system for crude Fischer-Tropsch PAO base oil products includes:

[0008] Storage unit for storing C8-C, a liquid product from purified Fischer-Tropsch synthesis. 14 The crude product of Fischer-PAO base oil prepared by the process;

[0009] The multi-stage molecular distillation unit includes a molecular distillation vacuum divider, a product cooler, and a product storage tank connected in sequence. The molecular distillation vacuum divider is connected to a vacuum device. Between two adjacent molecular distillation units, the heavy fraction outlet of the molecular distillation vacuum divider of the previous stage is connected to the feed inlet of the molecular distillation vacuum divider of the next stage.

[0010] Some technical solutions also include a vacuum condenser and a vacuum buffer tank connected in series to the pipeline between the molecular distillation vacuum divider and the vacuum equipment, wherein the vacuum condenser is used to cool the molecules that overflow from the molecular distillation.

[0011] In some technical solutions, the storage unit includes a crude product buffer container;

[0012] The multi-stage molecular distillation unit includes a first-stage molecular distillation vacuum divider, a second-stage molecular distillation vacuum divider, a third-stage molecular distillation vacuum divider, and a fourth-stage molecular distillation vacuum divider connected in series.

[0013] The feed inlet of the primary molecular distillation vacuum cutter is connected to the crude product buffer tank, and the light fraction outlet of the primary molecular distillation vacuum cutter is connected in sequence to the first cooler and the PAO oligomer storage tank.

[0014] The feed inlet of the secondary molecular distillation vacuum cutter is connected to the heavy fraction outlet of the primary molecular distillation vacuum cutter, and the light fraction outlet of the secondary molecular distillation vacuum cutter is connected in sequence to the second cooler and the PAO2 product storage tank.

[0015] The feed inlet of the three-stage molecular distillation vacuum cutter is connected to the heavy fraction outlet of the two-stage molecular distillation vacuum cutter, and the light fraction outlet of the three-stage molecular distillation vacuum cutter is connected in sequence to the third cooler and the PAO8 product storage tank.

[0016] The feed inlet of the fourth-stage molecular distillation vacuum cutter is connected to the heavy fraction outlet of the third-stage molecular distillation vacuum cutter. The light fraction outlet of the fourth-stage molecular distillation vacuum cutter is connected in sequence to the fourth cooler and the PAO20 product storage tank. The heavy fraction outlet of the fourth-stage molecular distillation vacuum cutter is connected in sequence to the fifth cooler and the PAO40 product storage tank.

[0017] According to another aspect of the present invention, the present invention further provides a method for separating crude Fischer-Tropsch PAO base oil products, suitable for the above-mentioned separation system, comprising the following steps:

[0018] S10: Hydrorefining of crude Fischer-PAO base oil products;

[0019] S21: The crude Fischer-PAO base oil product, which has been hydrotreated, is pumped from the crude product buffer tank to the primary molecular distillation vacuum separator.

[0020] S22: The PAO oligomer product extracted from the light phase line of the primary molecular distillation vacuum separator is cooled to room temperature by the first cooler and then sent to the PAO oligomer storage tank.

[0021] S23: Flow the phase repetition line of the primary molecular distillation vacuum separator into the secondary molecular distillation vacuum separator;

[0022] S24: The PAO2 product extracted from the light phase line of the secondary molecular distillation vacuum separator is cooled to room temperature by the second cooler and then enters the PAO2 product storage tank.

[0023] S25: Flow the phase repetition line of the second-stage molecular distillation vacuum separator into the third-stage molecular distillation vacuum separator;

[0024] S26: The PAO8 product extracted from the light phase line of the three-stage molecular distillation vacuum separator is cooled to room temperature by the third cooler and then sent to the PAO8 product storage tank.

[0025] S27: Flow the phase repetition line of the third-stage molecular distillation vacuum splitter into the fourth-stage molecular distillation vacuum splitter;

[0026] S28: The PAO20 product extracted from the light phase line of the four-stage molecular distillation vacuum separator is cooled to room temperature by the fourth cooler and then sent to the PAO20 product storage tank.

[0027] S29: The PAO40 product extracted from the rephase line of the four-stage molecular distillation vacuum separator is cooled to room temperature by the fifth cooler and then sent to the PAO40 product storage tank.

[0028] Some technical solutions also include the following steps:

[0029] Vacuum condensers are used to cool the overflow molecules from each stage of the molecular distillation vacuum separator in order to improve the vacuum level of each stage of the molecular distillation vacuum separator.

[0030] In some technical solutions, the operating temperature of the primary molecular distillation vacuum separator is 60–90°C, and the processing pressure is 0.5–15 kPa.

[0031] The operating temperature of the two-stage molecular distillation vacuum separator is 100–210℃, and the processing pressure is 100Pa–300Pa.

[0032] The operating temperature of the three-stage molecular distillation vacuum separator is 190–245℃, and the processing pressure is 10Pa–100Pa.

[0033] The operating temperature of the four-stage molecular distillation vacuum separator is 245–265℃, and the processing pressure is 0.5 Pa–15 Pa.

[0034] In some technical solutions, the PAO oligomer product is a distillate component with ≤20 carbon atoms;

[0035] The PAO2 product is a distillate component with a viscosity between 2 and 8 at 100°C.

[0036] The PAO8 product is a distillate component with a viscosity between 8 and 20 at 100°C.

[0037] The PAO20 product is a distillate component with a viscosity between 20 and 40 at 100°C.

[0038] The PAO40 product is a distillate component with a viscosity higher than 40 at 100°C.

[0039] According to another aspect of the present invention, the present invention further provides an application of Fischer-Tropsch PAO base oil crude products, using multiple PAO products produced in one step by the above separation method as raw materials for lubricating oil base oils.

[0040] The present invention, by employing the above technical solution, has at least the following beneficial effects:

[0041] 1. The present invention proposes a separation system for crude PAO base oil products, which separates crude product components with different carbon number compositions by setting up multi-stage molecular distillation units, and can produce multiple PAO products at one time, thereby improving product diversity and obtaining economic benefits;

[0042] 2. The present invention proposes a method for separating crude PAO base oil products. Through four-stage molecular distillation, the crude product components are separated step by step, producing multiple PAO products including PAO2, PAO8, PAO20 and PAO40 products in one step. These products can be used as base oil raw materials for preparing different grades of lubricating oils, thereby increasing economic benefits and enriching product diversity.

[0043] 3. The present invention proposes a separation system and method for crude Fischer-Tropsch PAO base oil products, which sets up vacuum condensers for the overflow molecules of each stage of molecular distillation vacuum separator to condense them, thereby improving the vacuum degree of the molecular distillation vacuum separator and ensuring its stable operation;

[0044] 4. The present invention proposes a method for separating crude Fischer-PAO base oil products. By controlling the operating temperature of each stage of the molecular distillation vacuum separator to be gradually increased and all below 300°C, the method effectively prevents the problem of decreased yield of high carbon number products in crude Fischer-PAO base oil products due to the decomposition of high carbon number heavy components. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings and their markings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a schematic diagram of the separation system for crude Fischer-Tropsch PAO base oil according to an embodiment of the present invention.

[0047] The meanings of the symbols marked in the figure are as follows:

[0048] 1. Crude product buffer tank; 2. Primary molecular distillation vacuum separator; 3. Secondary molecular distillation vacuum separator; 4. Tertiary molecular distillation vacuum separator; 5. Quaternary molecular distillation vacuum separator; 6A. Vacuum condenser; 6B. Product cooler; 7. Vacuum buffer tank; 8. Vacuum equipment; 9. PAO oligomer storage tank; 10. PAO2 product storage tank; 11. PAO8 product storage tank; 12. PAO20 product storage tank; 13. PAO40 product storage tank. Detailed Implementation

[0049] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0050] To keep the drawings concise, each figure only schematically shows the parts relevant to the invention, and these do not represent the actual structure of the product. Furthermore, to facilitate understanding, in some figures, only one of components with the same structure or function is schematically depicted, or only one is labeled. In this document, "one" not only means "only one," but can also mean "more than one."

[0051] It should also be further understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0052] In this document, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0053] Furthermore, in the description of this application, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0054] According to one aspect of the invention, see Figure 1 A separation system for crude Fischer-Tropsch PAO base oil is provided, comprising a storage unit and a multi-stage molecular distillation unit. Specifically, the storage unit includes a crude product buffer tank 1 for storing the C8-C product obtained from the refined Fischer-Tropsch synthesis liquid phase. 14 The crude product of Fischer-PAO base oil is characterized by its high carbon number and wide carbon distribution. A multi-stage molecular distillation unit is used, with each stage containing a sequentially connected molecular distillation vacuum separator, a product cooler 6B, and a product storage tank. The molecular distillation vacuum separator is connected to a vacuum system 8 to regulate the vacuum level of the separation process. The product cooler 6B is connected to the light fraction outlet of the molecular distillation vacuum separator, and the product storage tank is connected to the outlet of the product cooler 6B to collect PAO products of each grade. Between adjacent molecular distillation units, the heavy fraction outlet of the molecular distillation vacuum separator of the previous stage is connected to the feed inlet of the molecular distillation vacuum separator of the next stage, allowing for the step-by-step separation of the crude Fischer-PAO base oil. This produces multiple PAO products in a single step, which are then used as base oil feedstocks for preparing different grades of lubricating oils, enriching product diversity and increasing economic benefits.

[0055] In a preferred embodiment, a vacuum condenser 6A and a vacuum buffer tank 7 are further included in the pipeline connected in series between the molecular distillation vacuum separator and the vacuum system 8. The vacuum condenser 6A is used to cool the molecules overflowing from the molecular distillation, reducing their entry into the vacuum buffer tank 7. This embodiment can strictly control the ambient vacuum level during the separation process, avoiding product oxidation and deterioration, color darkening, and reduced product quality caused by increased oxygen content.

[0056] In one specific embodiment, the multi-stage molecular distillation unit includes a first-stage molecular distillation vacuum divider 2, a second-stage molecular distillation vacuum divider 3, a third-stage molecular distillation vacuum divider 4, and a fourth-stage molecular distillation vacuum divider 5 connected in series. The feed inlet of the first-stage molecular distillation vacuum divider 2 is connected to the crude product buffer tank 1, and the light fraction outlet of the first-stage molecular distillation vacuum divider 2 is connected in series to the first cooler and the PAO oligomer storage tank 9. The feed inlet of the second-stage molecular distillation vacuum divider 3 is connected to the heavy fraction outlet of the first-stage molecular distillation vacuum divider 2, and the light fraction outlet of the second-stage molecular distillation vacuum divider 3 is connected in series to the second cooler. The PAO2 product storage tank 10 is connected to the PAO2 product storage tank 11. The feed inlet of the tertiary molecular distillation vacuum separator 4 is connected to the heavy fraction outlet of the secondary molecular distillation vacuum separator 3, and the light fraction outlet of the tertiary molecular distillation vacuum separator 4 is connected to the third cooler and the PAO8 product storage tank 11 in sequence. The feed inlet of the quaternary molecular distillation vacuum separator 5 is connected to the heavy fraction outlet of the tertiary molecular distillation vacuum separator 4, and the light fraction outlet of the quaternary molecular distillation vacuum separator 5 is connected to the fourth cooler and the PAO20 product storage tank 12 in sequence. The heavy fraction outlet of the quaternary molecular distillation vacuum separator 5 is connected to the fifth cooler and the PAO40 product storage tank 13 in sequence.

[0057] In the above embodiments, the PAO oligomer product is a distillate component with ≤20 carbon atoms; the PAO2 product is a distillate component with a viscosity between 2 and 8 at 100°C; the PAO8 product is a distillate component with a viscosity between 8 and 20 at 100°C; the PAO20 product is a distillate component with a viscosity between 20 and 40 at 100°C; and the PAO40 product is a distillate component with a viscosity higher than 40 at 100°C.

[0058] In this embodiment, the crude product components are separated step by step through four-stage molecular distillation, producing a variety of PAO products including PAO2, PAO8, PAO20 and PAO40 products in one go. These products can be used as base oil raw materials for preparing different grades of lubricating oils, thereby increasing economic benefits and enriching product diversity.

[0059] According to another aspect of the present invention, a method for separating crude Fischer-Tropsch PAO base oil products is provided, comprising the following steps:

[0060] S10: Hydrorefining of crude Fischer-PAO base oil products;

[0061] S21: The crude Fischer-Tropsch PAO base oil product, which has been hydrorefined, is pumped from the crude product buffer tank to the first-stage molecular distillation vacuum separator 2. In order to improve the vacuum level and reduce the number of molecules entering the downstream vacuum buffer tank 7, the overflowing molecules can be cooled by the vacuum condenser 6A.

[0062] S22: The operating temperature of the primary molecular distillation vacuum separator 2 is 60-90℃ and the processing pressure is 0.5-15kPa. The PAO oligomer product extracted from the light phase line of the primary molecular distillation vacuum separator 2 is cooled to room temperature by the first cooler and then sent to the PAO oligomer storage tank 9.

[0063] S23: The recurrent phase line of the primary molecular distillation vacuum separator 2 flows into the secondary molecular distillation vacuum separator 3, with an operating temperature of 100-210℃;

[0064] S24: The operating temperature of the secondary molecular distillation vacuum separator 3 is 100~210℃, and the processing pressure is 100Pa~300Pa. The PAO2 product extracted from the light phase line of the secondary molecular distillation vacuum separator 3 is cooled to room temperature by the second cooler and then enters the PAO2 product storage tank 10.

[0065] S25: The recurrent phase line of the secondary molecular distillation vacuum separator 3 flows into the tertiary molecular distillation vacuum separator 4, with an operating temperature of 190-245℃.

[0066] S26: The operating temperature of the three-stage molecular distillation vacuum separator 4 is 190~245℃, and the processing pressure is 10Pa~100Pa. The PAO8 product extracted from the light phase line of the three-stage molecular distillation vacuum separator 4 is cooled to room temperature by the third cooler and then sent to the PAO8 product storage tank 11.

[0067] S27: The recurrent phase line of the three-stage molecular distillation vacuum separator 4 flows into the four-stage molecular distillation vacuum separator 5, with an operating temperature of 245~265℃.

[0068] S28: The operating temperature of the four-stage molecular distillation vacuum separator 5 is 245 to 265°C, and the processing pressure is 0.5 Pa to 15 Pa. The PAO20 product extracted from the light phase line of the four-stage molecular distillation vacuum separator 5 is cooled to room temperature by the fourth cooler and then sent to the PAO20 product storage tank 12.

[0069] S29: The PAO40 product sampled from the rephase line of the four-stage molecular distillation vacuum separator 5 is cooled to room temperature by the fifth cooler and then sent to the PAO40 product storage tank 13.

[0070] Through the above embodiments, the crude product of Fischer-Tropsch PAO lubricating oil base oil can be separated and processed to obtain a variety of PAO products, thereby meeting different needs and application scenarios.

[0071] Example 1

[0072] The composition of the raw materials to be cut is shown in the table below:

[0073] Table 1. Composition of raw materials to be cut

[0074]

[0075]

[0076] The properties of each grade of PAO product produced using the separation method described above are shown in the table below:

[0077] Table 2. PAO Product Indicators

[0078] product Quality fraction (%) yield Theoretical carbon number Viscosity 100℃ PAO2 10.4 99.1％ 25 Greater than 2 PAO8 14.7 99.5％ 38 Greater than 8 PAO20 58.5 99.5％ 56 Greater than 20 PAO40 16.4 99.8％ 154 Greater than 40

[0079] Example 2

[0080] The composition of the raw materials to be cut is shown in the table below:

[0081] Table 3. Composition of raw materials to be cut

[0082]

[0083] The properties of each grade of PAO product produced using the separation method described above are shown in the table below:

[0084] Table 4. PAO Product Indicators

[0085] product yield carbon number Viscosity 100℃ PAO2 99.5％ 20 Greater than 2 PAO8 99.1％ 32 Greater than 8 PAO20 99.8％ 56 Greater than 20 PAO40 99.9％ 160 Greater than 40

[0086] Comparative Example 1

[0087] The raw materials to be cut in Comparative Example 1 and Example 2 had the same composition. The method used was traditional vacuum distillation. The oligomers were collected from the top of the column, and PAO2, PAO8, and AO20 were collected from the side streams. PAO40 was collected from the bottom of the column. The bottom temperature was 385℃~425℃, the top pressure was 5-20kPa, the side stream temperature of PAO2 was about 220℃, the side stream temperature of PAO8 was about 310℃, and the side stream temperature of PAO20 was about 360℃.

[0088] The product specifications for Comparative Example 1 are shown in the table below:

[0089] Table 5. PAO Product Indicators

[0090] product yield carbon number Viscosity 100℃ PAO2 95.5％ 22 Greater than 2 PAO8 95.4％ 30 Greater than 8 PAO20 80.7％ 58 Greater than 20 PAO40 74.5％ 130 Greater than 40

[0091] The comparison of product indicators between Example 2 and Comparative Example 1 shows that the product yield of Example 2 is improved, with PAO2 and PAO8 yields increasing by about 5%, PAO20 yield increasing by about 20%, and PAO40 yield increasing by about 25%. Furthermore, the PAO40 product has a higher carbon number and better color, indicating less thermally induced decomposition and cracking, resulting in better product performance.

[0092] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A method for separating crude Fischer-Tropsch PAO base oil products, characterized in that, include: Storage unit, including crude product buffer tank, for storing C8-C, the liquid phase product of purified Fischer-Tropsch synthesis. 14 The crude product of Fischer-PAO base oil prepared by the process; A multi-stage molecular distillation unit, comprising a first-stage molecular distillation vacuum divider, a second-stage molecular distillation vacuum divider, a third-stage molecular distillation vacuum divider, and a fourth-stage molecular distillation vacuum divider connected in series. Each stage of the molecular distillation vacuum divider is sequentially connected to a corresponding product cooler and product storage tank, and the heavy fraction outlet of the previous stage molecular distillation vacuum divider is connected to the feed inlet of the next stage molecular distillation vacuum divider. A vacuum condenser and a vacuum buffer tank are installed on the pipeline between the vacuum separators and vacuum equipment at each stage of molecular distillation. The vacuum condenser is used to cool the overflow molecules during each stage of molecular distillation. The separation method includes the following steps: S10: Hydrorefining of crude Fischer-PAO base oil products; S21: The crude Fischer-PAO base oil product, which has been hydrotreated, is pumped from the crude product buffer tank to the primary molecular distillation vacuum separator. S22: The PAO oligomer product extracted from the light phase line of the primary molecular distillation vacuum separator is cooled to room temperature by the first cooler and then sent to the PAO oligomer storage tank. S23: Flow the phase repetition line of the primary molecular distillation vacuum separator into the secondary molecular distillation vacuum separator; S24: The PAO2 product extracted from the light phase line of the secondary molecular distillation vacuum separator is cooled to room temperature by the second cooler and then enters the PAO2 product storage tank. S25: Flow the phase repetition line of the second-stage molecular distillation vacuum separator into the third-stage molecular distillation vacuum separator; S26: The PAO8 product extracted from the light phase line of the three-stage molecular distillation vacuum separator is cooled to room temperature by the third cooler and then sent to the PAO8 product storage tank. S27: Flow the phase repetition line of the third-stage molecular distillation vacuum splitter into the fourth-stage molecular distillation vacuum splitter; S28: The PAO20 product extracted from the light phase line of the four-stage molecular distillation vacuum separator is cooled to room temperature by the fourth cooler and then sent to the PAO20 product storage tank. S29: The PAO40 product sampled from the rephase line of the four-stage molecular distillation vacuum separator is cooled to room temperature by the fifth cooler and then sent to the PAO40 product storage tank. The operating temperature of the first-stage molecular distillation vacuum separator is 60–90℃, and the processing pressure is 0.5–15 kPa; the operating temperature of the second-stage molecular distillation vacuum separator is 100–210℃, and the processing pressure is 100 Pa–300 Pa; the operating temperature of the third-stage molecular distillation vacuum separator is 190–245℃, and the processing pressure is 10 Pa–100 Pa; the operating temperature of the fourth-stage molecular distillation vacuum separator is 245–265℃, and the processing pressure is 0.5 Pa–15 Pa. The PAO oligomer product is a distillate component with ≤20 carbon atoms; the PAO2 product is a distillate component with a viscosity between 2 and 8 at 100°C; the PAO8 product is a distillate component with a viscosity between 8 and 20 at 100°C; the PAO20 product is a distillate component with a viscosity between 20 and 40 at 100°C; and the PAO40 product is a distillate component with a viscosity higher than 40 at 100°C.

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