A method for preparing a medium-high viscosity lubricating oil base oil

Abstract

The application provides a preparation method of a medium-high viscosity lubricating oil base oil. The method comprises the following steps: subjecting alpha-olefins to a first polymerization reaction in a first polymerization reactor in the presence of a first metallocene catalyst system to obtain a first product containing poly-alpha-olefins; subjecting the first product containing poly-alpha-olefins to a second polymerization reaction in a second polymerization reactor in the presence of a second metallocene catalyst system to obtain a second product containing poly-alpha-olefins; and subjecting the second product containing poly-alpha-olefins to post-treatment to obtain the medium-high viscosity lubricating oil base oil; wherein the main catalyst used in the first polymerization reaction is a bridged metallocene catalyst, and the main catalyst used in the second polymerization reaction is a constrained geometry metallocene catalyst. The application uses different catalysts in two reactors through a polymerization process in series, improves the product yield, and synthesizes a medium-high viscosity mPAO product with a narrow molecular weight distribution, thereby improving the product quality.

Description

Technical Field

[0001] This invention relates to a method for preparing medium-to-high viscosity lubricating oil base oil, belonging to the field of polyalphaolefin base oil technology. Background Technology

[0002] Polyalphaolefin (PAO) base oil is a Group IV lubricating oil base oil. Compared with traditional mineral lubricating oil base oils (Groups I, II, and III), it has advantages such as excellent viscosity-temperature properties, good low-temperature fluidity, excellent high-temperature oxidation resistance, good shear stability, and low evaporation loss. It is particularly suitable for extreme environments such as high loads, high speeds, high vacuums, high radiation, and strong oxidizing media. Viscosity is one of the most important physical properties of PAO base oils; conventionally, a viscosity below 100℃ is considered acceptable. 2 The product is called low-viscosity PAO base oil, with a viscosity of 10-40 mm at 100℃. 2 The product is called medium viscosity PAO base oil, with a viscosity higher than 40 mm at 100℃. 2 The product with a viscosity of / s is called high viscosity PAO base oil.

[0003] Medium-to-high viscosity PAO is mainly used in the formulation of automotive and industrial lubricants, and is widely used in fields with extremely demanding operating conditions such as wind power generation, industrial robots, high-speed rail, and high-end equipment. With the continuous development of high-end manufacturing in recent years, the installed capacity of green energy wind power, the mileage of high-speed rail, and the number of industrial robots used have increased rapidly, driving a continuous increase in demand for high-performance medium-to-high viscosity PAO base oils.

[0004] Currently, there are two main process technologies for producing medium-to-high viscosity PAO. One method uses aluminum trichloride as a polymerization catalyst. This technology typically employs a batch polymerization process, followed by a neutralization reaction to remove the catalyst from the oil, and then hydrogenation saturation and fractionation to obtain the final PAO base oil product. The other process uses metallocene catalysts to produce mPAO. Metallocene catalysts consist of transition metal cyclopentadienyl complexes and methylaluminoxanes or ion activators. The complexes formed by these components use a geometrically restricted transition metal as a single active center. Because there is only one active center, this catalyst easily forms a type of molecule, i.e., the resulting polymer has a narrow molecular weight distribution, and the catalyst utilization rate is as high as 100%. Therefore, it is possible to precisely control the molecular weight, molecular weight distribution, comonomer content, and their distribution on the main chain of the polymer, and to produce polymers with molecular structures that meet application requirements or novel polymers with special properties. Due to the special properties of metallocene catalysts, the produced mPAO has a special molecular structure and excellent performance. Compared with traditional PAO, it has a higher viscosity index (VI) and has significant advantages in viscosity-temperature performance, low-temperature performance, and shear stability.

[0005] US6548724B2 discloses a method for preparing low-viscosity metallocene polyalphaolefins (PAOs) from 1-decene using metallocene catalysis. This method employs a non-bridging metallocene catalyst, and the synthesized low-viscosity PAO exhibits excellent viscosity-temperature properties. However, the yield of the dimer reaches a maximum of 49% during the synthesis process. US8207390B2 discloses a method for catalytically synthesizing low-viscosity PAO using an alkyl-substituted dicyclopentadienyl zirconium dichloride and an organoboronide system. Under specific temperature and hydrogen pressure conditions, the viscosity of the synthesized product can reach 4.36 mm. 2 / s, but the yield of the dimer is as high as 47%. US8748361B2 synthesized low-viscosity PAO using a hydrogenated bridged metallocene catalyst-dimethylsilyl tetrahydroindenyl dichloride and organoboronide catalytic system. At a temperature of 140°C, the viscosity of the product was 6.2 mm. 2 / s, at which point the yield of the dimer is approximately 38.7%, and the catalyst activity is approximately 14 kg product / g catalyst. US20150344598A1 synthesized low-viscosity PAO using a hydrogenated vinyl-bridged metallocene catalyst—vinyltetrahydroindenylzirconium dichloride and organoboronide catalytic system. Under a certain hydrogen pressure, the catalyst activity can reach 80 kg product / g catalyst, but about 5% of the feedstock is saturated with alkanes.

[0006] In the aforementioned existing technologies, when using metallocene catalytic systems to synthesize PAO, regardless of whether a non-bridged or bridged catalyst is used, a large amount of dimers are generated. Because the flash point of these dimers is too low, they are unsuitable for use as lubricating oil base oils. Therefore, reducing the selectivity of dimers and increasing the yield of base oil components is crucial to the economic efficiency of the metallocene catalytic synthesis of low-viscosity PAO. To improve the yield of base oil components, many researchers have made technical improvements, either by combining metallocene catalysts with Lewis acid catalysts to increase the overall yield of PAO prepared by metallocene catalysts, or by employing a two-stage process to achieve the synthesis of PAO products of different viscosities from metallocene catalysts.

[0007] CN105885929A discloses a method for synthesizing low-viscosity PAO using a bismetallocene-chain shuttle catalyst system. This method uses coal-derived α-olefins as raw material, which undergo oxygen-containing compound removal treatment to obtain coal-derived α-olefins in an 80℃–240℃ fraction. Low-viscosity PAO is then synthesized using a bismetallocene-chain shuttle catalyst system. This catalytic system employs a mixed metallocene catalyst, comprising a main catalyst and a co-catalyst. The main catalyst is a hybrid bridging and non-bridging catalyst, and the co-catalyst is an organoboride and / or alkylaluminum. The organoboride is N,N-dimethyltetrafluorophenylborate, and the alkylaluminum is triisobutylaluminum. By introducing a chain shuttle, this catalytic system reduces the selectivity of dimers in the product, thereby increasing the yield of lubricating oil base oil components and avoiding the disadvantage of partial saturation of the raw material into alkanes when using hydrogen as a molecular weight regulator.

[0008] CN103890151A discloses a two-step oligomerization method for preparing low-viscosity PAO as a base raw material for lubricants. The method includes: a first step, oligomerizing a low molecular weight linear α-olefin in the presence of a single-point catalyst; and a second step, oligomerizing at least a portion of the product from the first step in the presence of an oligomerization catalyst. Specifically, in the first oligomerization step, the catalyst, activator, and monomer are contacted in a first reactor to obtain a first reactor effluent, which includes a dimer product (or intermediate PAO dimer), a trimer product (or intermediate PAO trimer), and optionally a higher oligomer product (or intermediate PAO higher oligomer product). The dimer product from the first oligomerization step is characterized by a trisubstituted vinylene olefin content of at least 25 wt%. In the second oligomerization step, the prepared polyα-olefin is characterized by very low viscosity and excellent Noack volatility. Furthermore, in the second step, before the dimer product is fed into the second reactor, at least a portion of the dimer product is separated from the trimer and optionally higher oligomer products. This method requires separation of the products from the first reactor, making the operation cumbersome.

[0009] CN108929186A discloses a method for preparing high viscosity index lubricating oil base oil. The method includes the following steps: under nitrogen protection, a metallocene catalyst, a co-catalyst, hydrogen, and liquid 1-decene monomer are added to a reactor; the mixture is heated to allow for reaction, and the reaction temperature and time are controlled. After the reaction, a boron trifluoride-isopropanol complex is added to allow the unreacted 1-decene monomer to continue reacting, yielding a polyalphaolefin lubricating oil base oil. This method can prepare high-viscosity and ultra-high viscosity index lubricating oil base oils with excellent viscosity-temperature properties (125 at 100℃ and a viscosity index of 238) and good low-temperature fluidity. However, this method uses two catalysts: a metallocene catalyst and a cationic catalyst, and polymerization is carried out in a single reactor, which can easily cause reactor contamination and fails to meet the requirements for using metallocene catalysts.

[0010] CN112159489A discloses a system and method for the polymerization process in the preparation of mPAO. In this system and method, the polymerization reactors are connected in series and parallel in stages of 1 to 8. Fresh and recycled refined α-olefin feedstocks, catalysts, and co-catalysts are first subjected to a polymerization reaction. Hydrogen from outside the reactor is also added to the polymerization reactor. The reaction liquid flows autonomously or enters the next stage polymerization reactor using pressure difference. Using this system and method, the residence time of the polymerization reaction is reduced from 2–20 h to 0.4–6.0 h, the conversion rate of α-olefin feedstock in the polymerization reaction is 90.9–94.7%, and the yield of metallocene PAO primary product is 87.2–90.8%. It can be applied to the polymerization process for preparing mPAO, and can achieve commercial continuous production of metallocene PAO primary product at a nominal scale of 200 tons / year to 20,000 tons / year. However, this process involves multiple reactors in series, and the catalyst and hydrogen are only added in the first step of the reaction, making the reaction process difficult to control.

[0011] As can be seen from the existing technologies described above, when using a metallocene catalyst system to catalyze the polymerization of olefins to prepare mPAO, in order to improve the conversion rate of raw materials and the yield of the target product, a multi-stage series reactor configuration can be used to prepare lubricating oil base oils of different viscosity grades. However, none of the aforementioned existing technologies have conducted comparative analysis on the molecular weight and distribution of the products in the multi-stage series reactors, nor have they conducted in-depth research on the factors affecting the performance of the reaction products and their solutions. Furthermore, when using a multi-stage series reactor to produce mPAO, especially when producing medium-to-high viscosity mPAO, there is a trend that as the viscosity of the reaction system increases, the relative molecular weight of the product decreases and the molecular weight distribution widens. This may be because, under the same polymerization conditions, as the system viscosity increases, the coordination polymerization ability of unreacted monomers with active centers decreases, thus generating products with relatively small molecular weights, leading to a wider molecular weight distribution of the final product.

[0012] Therefore, developing a novel method for preparing medium-to-high viscosity lubricating oil base oil remains one of the urgent problems to be solved in this field. Summary of the Invention

[0013] To address the aforementioned technical problems, the present invention aims to provide a method for preparing medium-to-high viscosity lubricating oil base oil. This invention employs a two-reactor series polymerization process, using different catalysts in the two polymerization reactors, which improves product yield and enables the synthesis of medium-to-high viscosity mPAO products with a narrow molecular weight distribution.

[0014] To achieve the above objectives, the present invention provides a method for preparing a medium-to-high viscosity lubricating oil base oil, comprising the following steps:

[0015] (1) The raw material α-olefin is subjected to a first polymerization reaction in the first polymerization reactor in the presence of a first metallocene catalytic system to obtain a first product containing polyα-olefin;

[0016] (2) The first product containing polyα-olefin is fed into the second polymerization reactor, and a second polymerization reaction is carried out in the presence of the second metallocene catalytic system to obtain the second product containing polyα-olefin.

[0017] (3) The second product containing polyα-olefin is post-treated to obtain the medium-high viscosity lubricating oil base oil;

[0018] The first metallocene catalytic system includes a first main catalyst, a co-catalyst, and an activator; the second metallocene catalytic system includes a second main catalyst, a co-catalyst, and an activator.

[0019] The first main catalyst is a bridged metallocene catalyst; the second main catalyst is a restricted geometry metallocene catalyst.

[0020] In the above preparation method, preferably, the bridged metallocene catalyst includes one or a combination of several of the following: dimethylsilylbis(4,5,6,7-tetrahydro-1-indenyl)zirconia, vinylbis(4,5,6,7-tetrahydro-1-indenyl)zirconia, vinylbis(cyclopentadienyl)zirconia, and dimethylsilylbis(cyclopentadienyl)zirconia.

[0021] In the above preparation method, preferably, the restricted geometry metallocene catalyst includes one or a combination of several of the following: 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-di-tert-butylphenoxy titanium dichloride, 2-(2,3,4,5-tetramethylcyclopentadiene)-4-tert-butyl-6-triphenylmethylphenoxy titanium dichloride, 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-dimethylphenoxy titanium dichloride, 2-(1-indenyl)-4-tert-butyl-6-triphenylmethylphenoxy titanium dichloride, 2-(9-fluorenyl)-4-tert-butyl-6-triphenylmethylphenoxy titanium dichloride, and 2-(9-fluorenyl)-4,6-di-tert-butylphenoxy titanium dichloride.

[0022] In the above preparation method, preferably, the co-catalysts in the first metallocene catalytic system and the second metallocene catalytic system each comprise alkylaluminum. More preferably, the alkylaluminum comprises triisobutylaluminum.

[0023] In the above preparation method, preferably, the activators in the first metallocene catalytic system and the second metallocene catalytic system each comprise organoborides. More preferably, the organoborides include Ph3CB(C6F5)4 and B(C6F5). 3、 One or more combinations of PhNMe2HB(C6F5)4 and Ph3CB[(CF3)2C6H3]4.

[0024] In the above preparation method, preferably, in the first metallocene catalytic system and the second metallocene catalytic system, the molar ratio of aluminum in the co-catalyst to the transition metal in the main catalyst is 5 to 20.

[0025] In the above preparation method, preferably, in the first metallocene catalytic system and the second metallocene catalytic system, the molar ratio of boron in the activator to the transition metal in the main catalyst is 1 to 5, respectively.

[0026] In the above preparation method, preferably, the raw material α-olefin in step (1) includes fresh and / or recycled raw material α-olefin. Those skilled in the art will understand that recycled raw material α-olefin comes from the α-olefin obtained by post-processing the second product containing polyα-olefin in step (3). The method for separating unreacted α-olefin can employ conventional methods in the art, and this invention does not specifically limit it.

[0027] In the above preparation method, preferably, the feed rate of the α-olefin raw material in step (1) into the first polymerization reactor is 5 to 20 L / h.

[0028] In the above preparation method, preferably, in step (1), the concentration of the first main catalyst in the first metallocene catalytic system is 0.01 to 0.1 mmol / L, based on the volume of the raw material α-olefin in the first polymerization reactor.

[0029] In the above preparation method, preferably, the temperature of the first polymerization reaction in step (1) is 40-100°C and the residence time is 0.5-2h.

[0030] In the above preparation method, preferably, the α-olefin conversion rate in step (1) is 60-80%.

[0031] In the above preparation method, preferably, in step (2), the concentration of the second main catalyst in the second metallocene catalytic system is 0.002 to 0.02 mmol / L, based on the volume of the first product containing polyα-olefin in the second polymerization reactor.

[0032] In the above preparation method, preferably, the temperature of the second polymerization reaction in step (2) is 40-100°C and the residence time is 0.5-2h.

[0033] In the above preparation method, preferably, the α-olefin conversion rate in step (2) is above 90%.

[0034] In the above preparation method, preferably, step (3) specifically includes: when the liquid level in the second polymerization reactor reaches a set value, the second product containing polyα-olefin is transferred to a polymer receiving tank, a terminator is added to the polymer receiving tank to terminate the polymerization reaction, and then the second product containing polyα-olefin is distilled to remove components below 320°C to obtain the medium-high viscosity lubricating oil base oil. The terminator used can be a conventional polymerization reaction terminator in the art, such as acidified ethanol. More preferably, step (3) further includes: distilling the second product containing polyα-olefin to separate α-olefins. The separated α-olefins can be used as part or all of the raw material α-olefins in step (1).

[0035] In the above preparation method, preferably, the medium-high viscosity lubricating oil base oil has a molecular weight distribution of less than 1.8, a pour point below -33℃, and a kinematic viscosity of 40-200 mmHg at 100℃. 2 / s.

[0036] This invention provides a method for preparing medium-to-high viscosity lubricating oil base oil, specifically a method for synthesizing metallocene lubricating oil base oil using a two-reactor series continuous flow polymerization. The method employs a two-reactor series continuous polymerization process. In the first polymerization reactor, fresh and / or recycled α-olefin feedstock undergoes polymerization under the action of a first metallocene catalytic system. The resulting first product containing polyα-olefins enters the second polymerization reactor. In the second polymerization reactor, under the action of a second metallocene catalytic system, polymerization continues to occur, yielding a second product containing polyα-olefins. After post-processing, the medium-to-high viscosity lubricating oil base oil is obtained.

[0037] In existing technologies, when using metallocene catalyst systems to catalyze the polymerization of olefins to prepare mPAO, multiple reactors are usually connected in series to improve the conversion rate of raw materials and the yield of the target product. However, when producing medium-to-high viscosity mPAO, as the conversion rate of raw materials increases, the viscosity of the reaction system increases, and the relative molecular weight of the product decreases and the molecular weight distribution becomes wider. This may be because, under high viscosity systems, due to factors such as mass transfer, the probability of collision between active centers and raw materials decreases, and the chain growth rate is less than the chain transfer rate.

[0038] The technical solution of the present invention achieves at least the following beneficial effects compared with the prior art:

[0039] The method of this invention employs a two-reactor series polymerization process, using different metallocene catalytic systems in the two polymerization reactors. The primary catalyst used in the first polymerization reactor is a bridged metallocene catalyst, while the primary catalyst used in the second polymerization reactor is a restricted geometry metallocene catalyst. The restricted geometry metallocene catalyst has stronger polymerization ability than the bridged metallocene catalyst. Through the synergistic effect of the two catalytic systems and by controlling the polymerization conditions in both reactors, the polymerization intensity is controlled, thereby improving the yield of polyalphaolefin (PAO). Simultaneously, the PAO obtained from the first and second polymerization reactors has similar molecular weights, and the molecular weight distribution of the PAO obtained from the second polymerization reactor is not wider than that from the first polymerization reactor. This ultimately yields a medium-to-high viscosity PAO base oil product with a narrow molecular weight distribution, improving product quality. Furthermore, the method of this invention eliminates the need to separate the product from the first polymerization reactor; instead, the material from the first polymerization reactor directly enters the second polymerization reactor to continue the reaction. Additionally, the method of this invention can obtain mPAO with a narrow molecular weight distribution without hydrogen conditioning, offering the advantage of process simplicity. Detailed Implementation

[0040] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0041] According to a specific embodiment of the present invention, the present invention provides a method for preparing a medium-to-high viscosity lubricating oil base oil, which includes the following steps:

[0042] (1) The raw material α-olefin is subjected to a first polymerization reaction in the first polymerization reactor in the presence of a first metallocene catalytic system to obtain a first product containing polyα-olefin;

[0043] (2) The first product containing polyα-olefin is fed into the second polymerization reactor, and a second polymerization reaction is carried out in the presence of the second metallocene catalytic system to obtain the second product containing polyα-olefin.

[0044] (3) The second product containing polyα-olefin is post-treated to obtain the medium-high viscosity lubricating oil base oil;

[0045] The first metallocene catalytic system includes a first main catalyst, a co-catalyst, and an activator; the second metallocene catalytic system includes a second main catalyst, a co-catalyst, and an activator.

[0046] The first main catalyst is a bridged metallocene catalyst; the second main catalyst is a restricted geometry metallocene catalyst.

[0047] In some specific embodiments of the present invention, the bridged metallocene catalyst comprises one or a combination of several of the following: dimethylsilylbis(4,5,6,7-tetrahydro-1-indenyl)zirconia, vinylbis(4,5,6,7-tetrahydro-1-indenyl)zirconia, vinylbis(cyclopentadienyl)zirconia, and dimethylsilylbis(cyclopentadienyl)zirconia. These bridged metallocene catalysts can all be commercially available or prepared using methods disclosed in the prior art. The bridged metallocene catalyst selected in this invention is suitable for preparing medium-to-high viscosity mPAO.

[0048] In some specific embodiments of the present invention, the restricted geometry metallocene catalyst includes one or a combination of several of the following: 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-di-tert-butylphenoxy titanium dichloride, 2-(2,3,4,5-tetramethylcyclopentadiene)-4-tert-butyl-6-triphenylmethylphenoxy titanium dichloride, 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-dimethylphenoxy titanium dichloride, 2-(1-indenyl)-4-tert-butyl-6-triphenylmethylphenoxy titanium dichloride, 2-(9-fluorenyl)-4-tert-butyl-6-triphenylmethylphenoxy titanium dichloride, and 2-(9-fluorenyl)-4,6-di-tert-butylphenoxy titanium dichloride. These restricted geometry metallocene catalysts can all be prepared commercially available or by methods disclosed in existing technologies, such as the method disclosed in "Synthesis, Characterization and Catalytic Properties of Restricted Geometry Metallocene Catalysts" by Huo Hang (Jilin University, DOI:CNKI:CDMD:2.1015.597805.). The restricted geometry metallocene catalyst selected in this invention is suitable for preparing ultra-high viscosity mPAO.

[0049] In some specific embodiments of the present invention, the co-catalysts in the first metallocene catalytic system and the second metallocene catalytic system respectively comprise alkylaluminum. Preferably, the alkylaluminum comprises triisobutylaluminum.

[0050] In some specific embodiments of the present invention, the activators in the first metallocene catalytic system and the second metallocene catalytic system respectively comprise organoborides. Preferably, the organoborides comprise one or a combination of several of Ph3CB(C6F5)4, B(C6F5)3, PhNMe2HB(C6F5)4, and Ph3CB[(CF3)2C6H3]4. The activators in the first metallocene catalytic system and the second metallocene catalytic system may be the same or different. These organoborides can all be obtained commercially or prepared by methods disclosed in the prior art. For example, these organoborides are disclosed in CN101117366A and CN101130467A.

[0051] In some specific embodiments of the present invention, in the first metallocene catalytic system and the second metallocene catalytic system, the molar ratio of aluminum in the co-catalyst to the transition metal in the main catalyst is 5 to 20, respectively. The molar ratio of aluminum to the transition metal in the first metallocene catalytic system and the molar ratio of aluminum to the transition metal in the second metallocene catalytic system may be the same or different.

[0052] In some specific embodiments of the present invention, in the first metallocene catalytic system and the second metallocene catalytic system, the molar ratio of boron in the activator to the transition metal in the main catalyst is 1 to 5, respectively. The molar ratio of boron to the transition metal in the first metallocene catalytic system may be the same as or different from the molar ratio of boron to the transition metal in the second metallocene catalytic system.

[0053] In some specific embodiments of the present invention, the raw material α-olefin in step (1) includes one or a combination of several of 1-decene, 1-octene and dodecene.

[0054] In some specific embodiments of the present invention, the raw material α-olefin in step (1) includes fresh and / or recycled raw material α-olefin. Those skilled in the art will understand that recycled raw material α-olefin comes from the α-olefin separated after post-processing the second product containing polyα-olefin in step (3). The method for separating unreacted α-olefin can employ conventional methods in the art, and the present invention does not specifically limit it.

[0055] In some specific embodiments of the present invention, the feed rate of the raw material α-olefin in step (1) into the first polymerization reactor is 5 to 20 L / h.

[0056] In some specific embodiments of the present invention, in step (1), based on the volume of the raw material α-olefin in the first polymerization reactor, the concentration of the first main catalyst in the first metallocene catalytic system is 0.01 to 0.1 mmol / L.

[0057] In some specific embodiments of the present invention, the temperature of the first polymerization reaction in step (1) is 40 to 100°C and the residence time is 0.5 to 2 hours.

[0058] In some specific embodiments of the present invention, the α-olefin conversion rate in step (1) is 60-80%.

[0059] In some specific embodiments of the present invention, the first product containing polyα-olefin obtained in step (1) is introduced into the second polymerization reactor by overflow or by pressure difference.

[0060] In some specific embodiments of the present invention, in step (2), based on the volume of the first product containing poly-α-olefin in the second polymerization reactor, the concentration of the second main catalyst in the second metallocene catalytic system is 0.002 to 0.02 mmol / L.

[0061] In some specific embodiments of the present invention, the temperature of the second polymerization reaction in step (2) is 40 to 100°C and the residence time is 0.5 to 2 hours.

[0062] In some specific embodiments of the present invention, the α-olefin conversion rate in step (2) is above 90%.

[0063] In some specific embodiments of the present invention, in steps (1) and (2), the first polymerization reactor and the second polymerization reactor can be polymerization reactors of the prior art. Preferably, the polymerization reaction temperature in the first polymerization reactor and the second polymerization reactor is controlled by heating the heat transfer oil with a thermocouple, the heat removal of the polymerization reaction can be removed by the circulating cooling water in the internal cooling pipe of the reactor, and the residence time of the polymerization reaction can be controlled by the flow rate of the raw material α-olefin.

[0064] In some specific embodiments of the present invention, step (3) specifically includes: when the liquid level in the second polymerization reactor reaches a set value, the second product containing polyα-olefin is transferred to a polymer receiving tank, a terminator is added to the polymer receiving tank to terminate the polymerization reaction, and then the second product containing polyα-olefin is distilled to remove components below 320°C to obtain the medium-high viscosity lubricating oil base oil. The terminator used can be a conventional polymerization reaction terminator in the art, such as acidified ethanol. The second product containing polyα-olefin can enter the polymer receiving tank via overflow or by pressure differential.

[0065] In some specific embodiments of the present invention, step (3) further includes: distilling the second product containing polyα-olefin to separate α-olefin. The separated α-olefin can be used as part or all of the raw material α-olefin in step (1).

[0066] More specifically, the preparation method of the medium-to-high viscosity lubricating oil base oil provided by the present invention may include the following steps:

[0067] S1 reactor pretreatment: Before polymerization begins, the first and second polymerization reactors are cleaned with refined cyclohexane at a temperature of 90-120°C for 0.5-1 hour. Then, the two polymerization reactors are purged with high-purity nitrogen to ensure that air and trace amounts of water are removed from them.

[0068] S2 First Polymerization Reaction: After nitrogen purging, the polymerization reaction conditions of the two polymerization reactors are set. The internal cooling pipes of the two polymerization reactors are used to circulate cooling water to cool down the reactors and bring them to the predetermined polymerization reaction temperature. The feed pump and the first metallocene catalytic system pump of the first polymerization reactor are started, and the feed rate is controlled to allow the raw material α-olefin and the first metallocene catalytic system to enter the first polymerization reactor. Stirring is started to carry out the first polymerization reaction. The polymerization reaction temperature is controlled by heating the heat transfer oil with a thermocouple. The heat removal of the polymerization reaction is removed by the circulating cooling water in the internal cooling pipes of the first polymerization reactor. The residence time of the polymerization reaction is controlled by the flow rate of the raw material α-olefin. High-purity nitrogen is introduced and the pressure is controlled. When the liquid level in the first polymerization reactor reaches the overflow port, the first product containing polyα-olefin in the first polymerization reactor overflows to the second polymerization reactor. The first main catalyst, co-catalyst, activator, etc. in the first metallocene catalytic system can be dissolved in toluene to prepare a toluene solution of a certain concentration (e.g., but not limited to 0.02 mmol / mL) before entering the first polymerization reactor.

[0069] S3 Second Polymerization Reaction: Simultaneously, the pump of the second metallocene catalytic system in the second polymerization reactor is started, allowing the second metallocene catalytic system to enter the second polymerization reactor. Stirring is started to carry out the second polymerization reaction. The polymerization reaction temperature, residence time, etc. are controlled in the same way as in the first polymerization reactor. When the liquid level in the second polymerization reactor reaches the overflow port, the second product containing polyα-olefin in the second polymerization reactor overflows to the polymer receiving tank. The second main catalyst, co-catalyst, activator, etc. in the second metallocene catalytic system can be dissolved in toluene to prepare a toluene solution of a certain concentration (e.g., but not limited to 0.02 mmol / mL) before entering the second polymerization reactor.

[0070] S4 post-treatment: A terminator (e.g., but not limited to acidified ethanol) is added to the polymer receiving tank to terminate the polymerization reaction. The second product containing polyα-olefin is then distilled (e.g., vacuum distillation) to distill off the component below 320°C, yielding a medium-to-high viscosity lubricating oil base oil. The distilled component below 320°C can be further separated to obtain α-olefins for use as a recycled feedstock for α-olefins.

[0071] In some specific embodiments of the present invention, the medium-high viscosity lubricating oil base oil has a molecular weight distribution of less than 1.8, a pour point below -33°C, and a kinematic viscosity of 40–200 mmHg at 100°C. 2 / s.

[0072] The technical solutions of the present invention are illustrated in detail below through embodiments and comparative examples. However, the present invention is not limited to these embodiments, and various modifications can be made within the scope of the key points of the present invention.

[0073] The raw materials and equipment used in the following embodiments and comparative examples include:

[0074] 1-Decanene: Polymer grade purity;

[0075] Dimethylsilylbis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride: purity > 99.5%;

[0076] 2-(2,3,4,5-Tetramethylcyclopentadiene)-4,6-di-tert-butylphenoxytitanium dichloride: Purity > 99.5%;

[0077] Vinylbis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride: purity > 99.5%;

[0078] 2-(2,3,4,5-Tetramethylcyclopentadiene)-4,6-dimethylphenoxytitanium dichloride: Purity > 99.5%;

[0079] Vinylbis(cyclopentadienyl)zirconium dichloride: Purity > 99.5%;

[0080] 2-(9-fluorenyl)-4,6-di-tert-butylphenoxy titanium dichloride: purity > 99.5%;

[0081] Dimethylsilylbis(cyclopentadienyl)zirconium dichloride: Purity > 99.5%;

[0082] 2-(2,3,4,5-Tetramethylcyclopentadiene)-4-tert-butyl-6-triphenylmethylphenoxytitanium dichloride: Purity > 99.5%;

[0083] 2-(1-Indanyl)-4-tert-butyl-6-triphenylmethylphenoxytitanium dichloride: Purity > 99.5%;

[0084] Triisobutylaluminum: Purity > 99%;

[0085] Ph3CB(C6F5)4: Purity > 99%;

[0086] B(C6F5)3: Purity > 99%;

[0087] Ph3CB[(CF3)2C6H3]4: Purity > 99%;

[0088] The reaction apparatus includes two 10L high-pressure autoclave polymerization reactors connected in series.

[0089] The calculation and measurement methods used in the following examples and comparative examples include:

[0090] α-Olefin conversion: (feed amount - unreacted feed amount) / feed amount × 100%;

[0091] Product yield: Target product quality / Raw material feed amount × 100%;

[0092] Molecular weight and molecular weight distribution of the product: determined using a PL-GPC220 gel permeation chromatograph at 150℃ (refer to SN / T 3002-2011);

[0093] Product viscosity: Measured using a Cannon CAV2200 fully automatic kinematic viscometer at 100℃ (refer to GB / T 265-1988);

[0094] Pour point of the product: The pour point / cloud point tester for petroleum products was tested using the DSY-006A petroleum product pour point / cloud point tester from Tianjin Shengbo Instrument Co., Ltd. (refer to GB / T3535-2006).

[0095] Example 1

[0096] This embodiment provides a method for preparing a medium-to-high viscosity lubricating oil base oil, which includes the following steps:

[0097] (1) After pretreatment of both polymerization reactors, the temperature of both polymerization reactors was set to 40℃ to start continuous polymerization. The co-catalyst pump, raw material pump, main catalyst pump, and activator pump of the first polymerization reactor were turned on in sequence to carry out the first polymerization reaction. The raw material α-olefin used was 1-decene, and the feed rate of the raw material pump was controlled at 5L / h. The main catalyst used was vinylbis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride with a flow rate of 3mL / h. The co-catalyst used was triisobutylaluminum with a flow rate of 15mL / h. The activator used was Ph3CB(C6F5)4 with a flow rate of 3mL / h. The residence time of the first polymerization reaction was 2h. When the liquid level in the first polymerization reactor reached the overflow port, the first product containing polyα-olefin in the first polymerization reactor overflowed into the second polymerization reactor.

[0098] (2) Simultaneously turn on the co-catalyst pump, main catalyst pump, and activator pump of the second polymerization reactor to carry out the second polymerization reaction; the main catalyst used is 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-di-tert-butylphenoxytitanium dichloride with a flow rate of 1 mL / h; the co-catalyst used is triisobutylaluminum with a flow rate of 5 mL / h; the activator used is Ph3CB(C6F5)4 with a flow rate of 1 mL / h; the residence time of the second polymerization reaction is 2 h; when the liquid level in the second polymerization reactor reaches the overflow port, the second product containing polyα-olefin in the second polymerization reactor overflows to the polymer receiving tank;

[0099] (3) Add 10 mL of 10% acidified ethanol (i.e., ethanol containing 10% hydrochloric acid by volume) to the polymer receiving tank to terminate the polymerization reaction. Then, distill the second product containing polyα-olefin to distill off the components below 320°C to obtain a medium-high viscosity lubricating oil base product.

[0100] In steps (1) and (2), the flow rates of the main catalyst, co-catalyst, and activator are the flow rates of the solutions obtained after dissolving them in toluene. The concentrations of the toluene solutions of the main catalyst, co-catalyst, and activator are all 0.02 mmol / mL. The same applies to the following examples and comparative examples.

[0101] The conversion rate and product yield of the raw material α-olefin in steps (1) and (2) were calculated, and the molecular weight and molecular weight distribution of the product, as well as the viscosity and pour point of the product, were determined. The results are shown in Table 1.

[0102] Example 2

[0103] This embodiment provides a method for preparing a medium-to-high viscosity lubricating oil base. The method is basically the same as in Example 1, except that: the temperature of both polymerization reactors is set to 60°C; the feed rate of the α-olefin in the first polymerization reactor is controlled at 20 L / h, and the residence time in both reactors is 0.5 h; the main catalyst used in the first polymerization reactor is dimethylsilylbis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride, with a flow rate of 25 mL / h; and the catalyst used in the first polymerization reactor is triisocyanate. The flow rate of butylaluminum is 500 mL / h; the activator used in the first polymerization reactor is B(C6F5)3 with a flow rate of 80 mL / h; the main catalyst used in the second polymerization reactor is 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-dimethylphenoxytitanium dichloride with a flow rate of 5 mL / h; the flow rate of triisobutylaluminum used in the second polymerization reactor is 400 mL / h; the activator used in the second polymerization reactor is B(C6F5)3 with a flow rate of 100 mL / h.

[0104] The conversion rate and product yield of the raw material α-olefin in steps (1) and (2) were calculated, and the molecular weight and molecular weight distribution of the product, as well as the viscosity and pour point of the product, were determined. The results are shown in Table 1.

[0105] Example 3

[0106] This embodiment provides a method for preparing a medium-to-high viscosity lubricating oil base. The method is essentially the same as in Example 1, except that: the temperature of both polymerization reactors is set to 80°C; the main catalyst used in the first polymerization reactor is vinylbis(cyclopentadienyl)zirconium dichloride, with a flow rate of 20 mL / h; the flow rate of triisobutylaluminum used in the first polymerization reactor is 400 mL / h; the activator used in the first polymerization reactor is Ph3CB[(CF3)2C6H3]4, with a flow rate of 100 mL / h; the main catalyst used in the second polymerization reactor is 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-di-tert-butylphenoxytitanium dichloride, with a flow rate of 1 mL / h; the flow rate of triisobutylaluminum used in the second polymerization reactor is 20 mL / h; the activator used in the second polymerization reactor is Ph3CB[(CF3)2C6H3]4, with a flow rate of 5 mL / h.

[0107] The conversion rate and product yield of the raw material α-olefin in steps (1) and (2) were calculated, and the molecular weight and molecular weight distribution of the product, as well as the viscosity and pour point of the product, were determined. The results are shown in Table 1.

[0108] Example 4

[0109] This embodiment provides a method for preparing medium-to-high viscosity lubricating oil base oil. The method is basically the same as in Example 1, except that: the temperature of both polymerization reactors is set to 100℃; the feed rate of the α-olefin in the first polymerization reactor is controlled at 20L / h, the residence time in the first polymerization reactor is 0.5h, and the residence time in the second polymerization reactor is 0.5h; the main catalyst used in the first polymerization reactor is dimethylsilylbis(cyclopentadienyl)zirconium dichloride, with a flow rate of 20mL / h; the flow rate of triisobutylaluminum used in the first polymerization reactor is 100mL / h; the activator used in the first polymerization reactor is B(C6F5)3, with a flow rate of 200mL / h; the main catalyst used in the second polymerization reactor is 2-(9-fluorenyl)-4,6-di-tert-butylphenoxytitanium dichloride, with a flow rate of 5mL / h; the flow rate of triisobutylaluminum used in the second polymerization reactor is 25mL / h; and the activator used in the second polymerization reactor is Ph3CB(C6F5)4, with a flow rate of 5mL / h.

[0110] The conversion rate and product yield of the raw material α-olefin in steps (1) and (2) were calculated, and the molecular weight and molecular weight distribution of the product, as well as the viscosity and pour point of the product, were determined. The results are shown in Table 1.

[0111] Example 5

[0112] This embodiment provides a method for preparing a medium-to-high viscosity lubricating oil base. The method is essentially the same as in Example 3, except that: both reactors are set at 80°C; the main catalyst used in the first polymerization reactor is dimethylsilyl bis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride, with a flow rate of 3 mL / h; the flow rate of triisobutylaluminum used in the first polymerization reactor is 60 mL / h; the activator used in the first polymerization reactor is Ph3CB(C6F5)4, with a flow rate of 15 mL / h; the main catalyst used in the second polymerization reactor is 2-(9-fluorenyl)-4,6-di-tert-butylphenoxytitanium dichloride, with a flow rate of 1 mL / h; the flow rate of triisobutylaluminum used in the second polymerization reactor is 20 mL / h; and the activator used in the second polymerization reactor is B(C6F5)3, with a flow rate of 5 mL / h.

[0113] The conversion rate and product yield of the raw material α-olefin in steps (1) and (2) were calculated, and the molecular weight and molecular weight distribution of the product, as well as the viscosity and pour point of the product, were determined. The results are shown in Table 1.

[0114] Example 6

[0115] This embodiment provides a method for preparing a medium-to-high viscosity lubricating oil base. The method is basically the same as in Example 1, except that: the temperature of both polymerization reactors is set to 60°C; the feed rate of the α-olefin in the first polymerization reactor is controlled at 20 L / h, and the residence time in both reactors is 0.5 h; the main catalyst used in the first polymerization reactor is vinylbis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride, with a flow rate of 20 mL / h; the flow rate of triisobutylaluminum used in the first polymerization reactor is 10 mL / h. The flow rate was 0 mL / h; the activator used in the first polymerization reactor was Ph3CB(C6F5)4, with a flow rate of 20 mL / h; the main catalyst used in the second polymerization reactor was 2-(2,3,4,5-tetramethylcyclopentadiene)-4-tert-butyl-6-triphenylmethylphenoxytitanium dichloride, with a flow rate of 5 mL / h; the flow rate of triisobutylaluminum used in the second polymerization reactor was 25 mL / h; the activator used in the second polymerization reactor was Ph3CB[(CF3)2C6H3]4, with a flow rate of 5 mL / h.

[0116] The conversion rate and product yield of the raw material α-olefin in steps (1) and (2) were calculated, and the molecular weight and molecular weight distribution of the product, as well as the viscosity and pour point of the product, were determined. The results are shown in Table 1.

[0117] Example 7

[0118] This embodiment provides a method for preparing a medium-to-high viscosity lubricating oil base. The method is basically the same as in Example 1, except that: the temperature of both polymerization reactors is set to 80℃; the feed rate of the α-olefin in the first polymerization reactor is controlled at 10 L / h, the residence time in the first polymerization reactor is 1 h, and the residence time in the second polymerization reactor is 1 h; the main catalyst used in the first polymerization reactor is dimethylsilylbis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride, with a flow rate of 6 mL / h; and triisobutylene is used in the first polymerization reactor. The flow rate of the base aluminum was 120 mL / h; the activator used in the first polymerization reactor was B(C6F5)3, with a flow rate of 30 mL / h; the main catalyst used in the second polymerization reactor was 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-dimethylphenoxytitanium dichloride, with a flow rate of 2 mL / h; the flow rate of the triisobutylaluminum used in the second polymerization reactor was 10 mL / h; the activator used in the second polymerization reactor was B(C6F5)3, with a flow rate of 30 mL / h.

[0119] The conversion rate and product yield of the raw material α-olefin in steps (1) and (2) were calculated, and the molecular weight and molecular weight distribution of the product, as well as the viscosity and pour point of the product, were determined. The results are shown in Table 1.

[0120] Example 8

[0121] This embodiment provides a method for preparing a medium-to-high viscosity lubricating oil base. The method is essentially the same as in Example 1, except that: the temperature of both polymerization reactors is set to 100°C; the main catalyst used in the first polymerization reactor is vinylbis(cyclopentadienyl)zirconium dichloride, with a flow rate of 20 mL / h; the flow rate of triisobutylaluminum used in the first polymerization reactor is 100 mL / h; the activator used in the first polymerization reactor is B(C6F5)3, with a flow rate of 20 mL / h; the main catalyst used in the second polymerization reactor is 2-(1-indenyl)-4-tert-butyl-6-triphenylmethylphenoxytitanium dichloride, with a flow rate of 5 mL / h; the flow rate of triisobutylaluminum used in the second polymerization reactor is 5 mL / h; the activator used in the second polymerization reactor is B(C6F5)3, with a flow rate of 25 mL / h.

[0122] The conversion rate and product yield of the raw material α-olefin in steps (1) and (2) were calculated, and the molecular weight and molecular weight distribution of the product, as well as the viscosity and pour point of the product, were determined. The results are shown in Table 1.

[0123] Comparative Example 1

[0124] This comparative example provides a method for preparing a medium-to-high viscosity lubricating oil base oil. This method uses only one polymerization reactor for the polymerization reaction and includes the following steps:

[0125] After pretreatment of the polymerization reactor, the temperature of the polymerization reactor was set to 40℃. The co-catalyst pump, feed pump, main catalyst pump, and activator pump of the polymerization reactor were turned on in sequence to carry out the polymerization reaction. The α-olefin used was 1-decene, and the feed rate of the feed pump was controlled at 5L / h. The main catalyst used was vinylbis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride, with a flow rate of 3mL / h. The co-catalyst used was triisobutylaluminum, with a flow rate of 15mL / h. The activator used was Ph3CB(C6F5)4, with a flow rate of 3mL / h. The residence time of the polymerization reaction was 2h. When the liquid level in the polymerization reactor reached the overflow port, the product containing polyα-olefins in the polymerization reactor overflowed into the polymer receiving tank. 10% acidified ethanol was added to the polymer receiving tank to terminate the polymerization reaction. Then, the product containing polyα-olefins was distilled to distill off the components below 320℃ to obtain a medium-high viscosity lubricating oil base oil product.

[0126] The conversion rate and product yield of the α-olefin feedstock were calculated, and the molecular weight and molecular weight distribution of the product, as well as the viscosity and pour point of the product, were determined. The results are shown in Table 1.

[0127] Comparative Example 2

[0128] This comparative example provides a method for preparing a medium-to-high viscosity lubricating oil base. This method uses only one polymerization reactor for the polymerization reaction, and its specific steps are basically the same as those in Comparative Example 1, except that: the main catalyst used is 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-di-tert-butylphenoxytitanium dichloride, with a flow rate of 1 mL / h; the co-catalyst used is triisobutylaluminum, with a flow rate of 5 mL / h; and the activator used is Ph3CB(C6F5)4, with a flow rate of 1 mL / h.

[0129] The conversion rate and product yield of the α-olefin feedstock were calculated, and the molecular weight and molecular weight distribution of the product, as well as the viscosity and pour point of the product, were determined. The results are shown in Table 1.

[0130] Comparative Example 3

[0131] This comparative example provides a method for preparing a medium-to-high viscosity lubricating oil base. The method is basically the same as that in Example 1, except that the main catalyst used in the second polymerization reactor is vinylbis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride, with a flow rate of 1 mL / h.

[0132] The conversion rate and product yield of the raw material α-olefin in steps (1) and (2) were calculated, and the molecular weight and molecular weight distribution of the product, as well as the viscosity and pour point of the product, were determined. The results are shown in Table 1.

[0133] Comparative Example 4

[0134] This comparative example provides a method for preparing a medium-to-high viscosity lubricating oil base. The method is essentially the same as in Example 1, except that the main catalyst used in the first polymerization reactor is 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-di-tert-butylphenoxytitanium dichloride, with a flow rate of 3 mL / h.

[0135] The conversion rate and product yield of the raw material α-olefin in steps (1) and (2) were calculated, and the molecular weight and molecular weight distribution of the product, as well as the viscosity and pour point of the product, were determined. The results are shown in Table 1.

[0136] Comparative Example 5

[0137] This comparative example provides a method for preparing a medium-to-high viscosity lubricating oil base. The method is essentially the same as in Example 1, except that: the main catalyst used in the first polymerization reactor is 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-di-tert-butylphenoxytitanium dichloride, with a flow rate of 3 mL / h; the main catalyst used in the second polymerization reactor is vinylbis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride, with a flow rate of 1 mL / h.

[0138] The conversion rate and product yield of the raw material α-olefin in steps (1) and (2) were calculated, and the molecular weight and molecular weight distribution of the product, as well as the viscosity and pour point of the product, were determined. The results are shown in Table 1.

[0139] Table 1. Results of mPAO production using the methods of Examples 1-8 and Comparative Examples 1-5.

[0140]

[0141] A comparison of the data from Comparative Examples 1-2 and Examples 1-8 shows that Examples 1-8, employing a two-reactor series polymerization, significantly improved the monomer conversion rate. This is because the two-reactor series polymerization effectively extended the reaction residence time, thus increasing the conversion rate. A comparison of the data from Comparative Examples 3-5 and Examples 1-8 shows that in Examples 1-8, the first polymerization reactor used a bridged metallocene catalytic system, and the second polymerization reactor used a restricted geometry metallocene catalytic system. By controlling the reaction conditions in both reactors, the resulting product had a narrow molecular weight distribution, below 1.8. In contrast, in Comparative Example 3, both polymerization reactors used a bridged metallocene catalytic system, resulting in a wider molecular weight distribution, above 2.0. In Comparative Example 4, both polymerization reactors used a restricted geometry metallocene catalytic system, with the first reactor producing a product with a higher molecular weight, increased viscosity, and a wider molecular weight distribution. In Comparative Example 5, the first polymerization reactor used a restricted geometry metallocene catalytic system, and the second polymerization reactor used a bridged metallocene catalytic system, resulting in a significantly wider molecular weight distribution. Furthermore, by adjusting the catalyst and its dosage ratio, Examples 1-8 can be flexibly adapted to achieve a viscosity range of 40–200 mmHg at 100°C. 2 / s mPAO products.

[0142] In summary, the method of this invention employs a two-stage polymerization process in series. Through the synergistic effect of two catalytic systems, it not only improves the single-pass conversion rate of the raw material α-olefin and the yield of the target product (which exceeds 90%), thus improving the economics of the process, but also produces a medium-to-high viscosity polyα-olefin base oil product with a uniform molecular weight distribution and adjustable viscosity range, thereby improving product quality.

Claims

1. A method for preparing a medium-to-high viscosity lubricating oil base oil, comprising the following steps: (1) The raw material α-olefin is subjected to a first polymerization reaction in the first polymerization reactor in the presence of a first metallocene catalytic system to obtain a first product containing polyα-olefin; (2) The first product containing polyα-olefin is fed into the second polymerization reactor, and a second polymerization reaction is carried out in the presence of the second metallocene catalytic system to obtain the second product containing polyα-olefin. (3) The second product containing polyα-olefin is post-treated to obtain the medium-high viscosity lubricating oil base oil; The first metallocene catalytic system includes a first main catalyst, a co-catalyst, and an activator; the second metallocene catalytic system includes a second main catalyst, a co-catalyst, and an activator. The first main catalyst is a bridged metallocene catalyst; the second main catalyst is a restricted geometry metallocene catalyst.

2. The preparation method according to claim 1, wherein, The bridged metallocene catalyst comprises one or a combination of several of dimethylsilylbis(4,5,6,7-tetrahydro-1-indenyl)zirconia, vinylbis(4,5,6,7-tetrahydro-1-indenyl)zirconia, vinylbis(cyclopentadienyl)zirconia, and dimethylsilylbis(cyclopentadienyl)zirconia.

3. The preparation method according to claim 1, wherein, The restricted geometry metallocene catalysts include one or a combination of several of the following: 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-di-tert-butylphenoxy titanium dichloride, 2-(2,3,4,5-tetramethylcyclopentadiene)-4-tert-butyl-6-triphenylmethylphenoxy titanium dichloride, 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-dimethylphenoxy titanium dichloride, 2-(1-indenyl)-4-tert-butyl-6-triphenylmethylphenoxy titanium dichloride, 2-(9-fluorenyl)-4-tert-butyl-6-triphenylmethylphenoxy titanium dichloride, and 2-(9-fluorenyl)-4,6-di-tert-butylphenoxy titanium dichloride.

4. The preparation method according to claim 1, wherein, The cocatalysts in the first metallocene catalytic system and the second metallocene catalytic system respectively include alkyl aluminum.

5. The preparation method according to claim 4, wherein, The alkylaluminum includes triisobutylaluminum.

6. The preparation method according to claim 1, wherein, The activators in the first metallocene catalytic system and the second metallocene catalytic system respectively include organoborides.

7. The preparation method according to claim 6, wherein, The organoborides include one or a combination of several of Ph3CB(C6F5)4, B(C6F5)3, PhNMe2HB(C6F5)4 and Ph3CB[(CF3)2C6H3]4.

8. The preparation method according to claim 1 or 4, wherein, In the first metallocene catalytic system and the second metallocene catalytic system, the molar ratio of aluminum in the co-catalyst to the transition metal in the main catalyst is 5 to 20, respectively.

9. The preparation method according to claim 1 or 6, wherein, In the first metallocene catalytic system and the second metallocene catalytic system, the molar ratio of boron in the activator to the transition metal in the main catalyst is 1 to 5, respectively.

10. The preparation method according to claim 1, wherein, The feedstock α-olefins in step (1) include fresh and / or recycled feedstock α-olefins.

11. The preparation method according to claim 1, wherein, The feed rate of the α-olefin raw material in step (1) into the first polymerization reactor is 5 to 20 L / h.

12. The preparation method according to claim 1, wherein, In step (1), based on the volume of the α-olefin in the first polymerization reactor, the concentration of the first main catalyst in the first metallocene catalytic system is 0.01 to 0.1 mmol / L.

13. The preparation method according to claim 1, wherein, The temperature of the first polymerization reaction in step (1) is 40 to 100°C, and the residence time is 0.5 to 2 hours.

14. The preparation method according to claim 1, wherein, The α-olefin conversion rate in step (1) is 60-80%.

15. The preparation method according to claim 1, wherein, In step (2), based on the volume of the first product containing poly-α-olefin in the second polymerization reactor, the concentration of the second main catalyst in the second metallocene catalytic system is 0.002 to 0.02 mmol / L.

16. The preparation method according to claim 1, wherein, The temperature of the second polymerization reaction in step (2) is 40-100℃, and the residence time is 0.5-2h.

17. The preparation method according to claim 1, wherein, In step (2), the α-olefin conversion rate is over 90%.

18. The preparation method according to claim 1, wherein, Step (3) specifically includes: when the liquid level in the second polymerization reactor reaches the set value, the second product containing polyα-olefin is transferred to the polymer receiving tank, a terminator is added to the polymer receiving tank to terminate the polymerization reaction, and then the second product containing polyα-olefin is distilled to remove components below 320°C to obtain the medium-high viscosity lubricating oil base oil.

19. The preparation method according to claim 1, wherein, The medium-to-high viscosity lubricating oil base oil has a molecular weight distribution of less than 1.8, a pour point below -33℃, and a kinematic viscosity of 40–200 mmHg at 100℃. 2 / s.

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