Preparation method of medium-high viscosity lubricant base oil

Abstract

The invention provides a preparation method of medium-high viscosity lubricant base oil. The method comprises the following steps: carrying out first polymerization reaction on alpha-olefin in a first polymerization reaction kettle in the presence of a first metallocene catalytic system to obtain a first product containing poly-alpha-olefin; enabling the first product containing poly-alpha-olefin to enter a second polymerization reaction kettle, and carrying out second polymerization reaction in the presence of a second metallocene catalytic system to obtain a second product containing poly-alpha-olefin; and carrying out post-treatment on the second product containing poly-alpha-olefin to obtain the medium-high viscosity lubricant base oil, wherein a main catalyst adopted in the first polymerization reaction is a bridged metallocene catalyst, and a main catalyst adopted in the second polymerization reaction is a limited geometric configuration metallocene catalyst. According to the method disclosed by the invention, through a polymerization process in which two kettles are connected in series, different catalysts are adopted in the two reaction kettles, so that the product yield is improved, the medium-high-viscosity mPAO product with narrow molecular weight distribution is synthesized, and the product quality is improved.

Description

Technical Field

[0001] The invention relates to a method for preparing a medium-high viscosity lubricating oil base oil, and belongs to the technical field of poly-alpha-olefin base oils. Background Art

[0002] Polyalphaolefin (PAO) base oil is a Class IV lubricant base oil. Compared with traditional mineral lubricant base oils (Class I, II, and III base oils), it has the advantages of excellent viscosity-temperature performance, good low-temperature fluidity, excellent high-temperature oxidation resistance, good shear stability, and small evaporation loss. It is especially suitable for extreme environments such as high load, high speed, high vacuum, high radiation, and strong oxidizing media. Viscosity is one of the most important physical properties of PAO base oil. It is customary to set the viscosity at 100°C below 10mm. 2 / s products are called low viscosity PAO base oils, with a viscosity of 10 to 40 mm at 100 °C. 2 / s products are called medium viscosity PAO base oils, and the viscosity at 100℃ is higher than 40mm 2 / s products are called high viscosity PAO base oils.

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

[0004] At present, there are two main process technology routes for producing medium and high viscosity PAO. One is to use aluminum chloride as a polymerization catalyst. The polymerization reaction of this technology usually adopts an intermittent polymerization process, and then the catalyst in the oil is removed by neutralization reaction, and then the final PAO base oil product is obtained by hydrogenation saturation and fractionation process. Another process uses a metallocene catalyst to produce mPAO. The metallocene catalyst is composed of a cyclopentadienyl complex of a transition metal and methylaluminoxane or an ionic activator. The complex formed by these components uses a transition metal with restricted geometric shape as a single active center. Because there is only one active center, this catalyst easily forms one type of molecule, that is, the formed polymer has a narrow molecular weight distribution, and the utilization rate of the catalyst is as high as 100%, so the molecular weight, molecular weight distribution, content of comonomers and their distribution on the main chain of the polymer can be precisely controlled, and polymers with molecular structures that meet application requirements or new polymers with special properties can be produced. Due to the special properties of metallocene catalysts, the mPAO produced has a special molecular structure and excellent performance. Compared with traditional PAO, it has a higher viscosity index (VI) and has obvious advantages in viscosity-temperature performance, low temperature performance, shear stability, etc.

[0005] US6548724B2 discloses a method for preparing low-viscosity metallocene poly-alpha-olefin using metallocene catalysis of 1-decene. This method uses a non-bridged metallocene catalyst, and the synthesized low-viscosity PAO has excellent viscosity-temperature performance, but during the synthesis process, the yield of dimers is as high as 49%. US8207390B2 discloses a method for catalytically synthesizing low-viscosity PAO using an alkyl-substituted biscyclopentadienyl zirconium dichloride and an organic boron compound system. Under a certain temperature and hydrogen pressure, the viscosity of the synthesized product can reach 4.36 mm 2 / s, but the yield of dimer is as high as 47%. US8748361B2 uses a hydrogenated bridged metallocene catalyst - dimethylsilyltetrahydroindenyl zirconium dichloride and an organic boron compound catalytic system to synthesize low-viscosity PAO. At a temperature of 140°C, the viscosity of the product is 6.2 mm 2 / s, at this time, the yield of dimer is about 38.7%, and the activity of the catalyst is about 14kg product / g catalyst. US20150344598A1 uses a hydrogenated vinyl-bridged metallocene catalyst-vinyl tetrahydroindenyl zirconium dichloride and an organic boron compound catalytic system to synthesize low-viscosity PAO. Under a certain hydrogen pressure, the activity of the catalyst can reach 80kg product / g catalyst, but about 5% of the raw materials are saturated to alkanes.

[0006] When a metallocene catalytic system is used to synthesize PAO in the above-mentioned prior art, whether a non-bridged catalyst or a bridged catalyst is used, a large amount of dimers will be produced. Since the flash point of the dimer is too low, it is not suitable for use as a lubricating oil base oil. Therefore, reducing the selectivity of the dimer and increasing the yield of the base oil component are crucial to the economic efficiency of the metallocene catalytic synthesis of low-viscosity PAO process. In order to increase the yield of the base oil component, many scholars have made technical improvements, either combining metallocene catalysts with Lewis acid catalysts to increase the overall yield of PAO prepared by metallocene catalysts, or using a two-stage process to achieve metallocene synthesis of PAO products with different viscosities.

[0007] CN105885929A discloses a method for synthesizing low-viscosity PAO using a dual metallocene-chain shuttling agent catalytic system. The method uses coal-based alpha-olefins as raw materials, removes oxygen-containing compounds, obtains 80°C to 240°C fractional coal-based alpha-olefins, and synthesizes low-viscosity PAO using a dual metallocene-chain shuttling agent catalytic system. The catalytic system uses a mixed metallocene catalyst, which includes a main catalyst and a co-catalyst. The main catalyst used is a bridged and non-bridged mixed catalyst, and the co-catalyst is an organic boron compound and / or an alkyl aluminum. The organic boron compound is N,N-dimethyltetrafluorobenzene borate, and the alkyl aluminum is triisobutyl aluminum. The catalytic system reduces the selectivity of dimers in the product by introducing a chain shuttling agent, thereby achieving the purpose of increasing the yield of the lubricating oil base oil component and avoiding the disadvantage that part of the raw material is saturated into alkanes when hydrogen is used as a molecular weight regulator.

[0008] CN103890151A discloses a two-step oligomerization method for preparing low-viscosity PAO used as a lubricant base stock. The method comprises: a first step of oligomerizing low molecular weight linear α-olefins in the presence of a single-site catalyst; a second step of 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, the activator and the monomer are contacted in a first reactor to obtain a first reactor effluent, the effluent comprising a dimer product (or an intermediate PAO dimer), a trimer product (or an intermediate PAO trimer), and optionally a higher oligomer product (or an intermediate PAO higher oligomer product), the dimer product from the first oligomerization being characterized by a trisubstituted vinylidene 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. And in the second step of the method, before the dimer product is fed into the second reactor, at least a portion of the dimer product is separated from the trimer and optional higher oligomer products. This method requires the product of the first reactor to be separated, and the operation is cumbersome.

[0009] CN108929186A discloses a method for preparing a high viscosity index lubricant base oil. The method comprises the following steps: under nitrogen protection, adding a metallocene catalyst, a co-catalyst, hydrogen and a monomer 1-decene liquid into a reactor, heating to react, controlling the reaction temperature and time, adding a boron trifluoride-isopropanol complex after the reaction is completed, and allowing the unreacted 1-decene monomer to continue to react to obtain a poly-alpha-olefin lubricant base oil. The method can prepare a high viscosity and ultra-high viscosity index lubricant base oil with excellent viscosity-temperature performance and good low-temperature fluidity, with a viscosity of 125 at 100°C and a viscosity index of 238. The method uses two catalysts, the first of which is a metallocene catalyst and the second is a cationic catalyst, and the polymerization is carried out in a reactor, which is easy to cause pollution of the reactor and cannot meet the requirements for the use of metallocene catalysts.

[0010] CN112159489A discloses a system and method for preparing a polymerization process in mPAO. In the system and method, the polymerization reactor is connected in series and parallel in 1 to 8 stages, and the fresh and returned refined α-olefin raw materials, catalysts, and co-catalysts are first subjected to polymerization reaction, and hydrogen from outside is also added to the polymerization reactor, and the reaction liquid flows into the next stage polymerization reactor autonomously or by pressure difference. Using this system and method, the residence time of the polymerization reaction is reduced from 2 to 20 hours to 0.4 to 6.0 hours, the conversion rate of α-olefin raw materials in the polymerization reaction is 90.9 to 94.7%, and the yield of the metallocene PAO primary product is 87.2 to 90.8%. It can be applied to the polymerization process for preparing mPAO, and can realize the commercial continuous production of the metallocene PAO primary product on an industrial scale of 200 tons / year to 20,000 tons / year. However, the process involves a multi-reactor series process, and the catalyst and hydrogen are only added in the first step reaction, and the reaction process is difficult to control.

[0011] It can be seen from the above-mentioned prior art that when mPAO is prepared by catalyzing olefin polymerization using a metallocene catalyst system, in order to improve the raw material conversion rate and the yield of the target product, a multi-kettle series connection can be used to prepare lubricating oil base oils of different viscosity grades. However, none of the above-mentioned prior art has conducted a comparative analysis of the product molecular weight and its distribution in the multi-stage series kettle, and has not conducted an in-depth study on the factors and solutions that affect the performance of the reaction products. In addition, when mPAO is produced by using multiple kettles in series, especially when producing medium and high viscosity mPAO, there is a trend that the relative molecular weight of the product becomes smaller and the molecular weight distribution becomes wider as the viscosity of the reaction system increases. This may be because under the same polymerization conditions, the viscosity of the system increases, and the coordination polymerization ability of the unreacted monomer and the active center is reduced, thereby generating a product with a small relative molecular weight, resulting in a widening of the molecular weight distribution of the final product.

[0012] Therefore, developing a new method for preparing medium-to-high viscosity lubricant base oil is still one of the problems to be solved urgently in this field. Summary of the invention

[0013] In order to solve the above technical problems, the purpose of the present invention is to provide a method for preparing medium-high viscosity lubricant base oil. The present invention adopts a two-reactor series polymerization process and uses different catalysts in the two polymerization reactors, which can improve the product yield and synthesize medium-high viscosity mPAO products with narrow molecular weight distribution.

[0014] In order to achieve the above object, the present invention provides a method for preparing a medium-high viscosity lubricating oil base oil, which comprises the following steps:

[0015] (1) subjecting a raw material α-olefin 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 a poly-α-olefin;

[0016] (2) allowing the first product containing poly-α-olefin to enter a second polymerization reactor, and performing a second polymerization reaction in the presence of a second metallocene catalyst system to obtain a second product containing poly-α-olefin;

[0017] (3) post-treating the second product containing poly-α-olefin to obtain the medium-high viscosity lubricating oil base oil;

[0018] Wherein, the first metallocene catalytic system comprises a first main catalyst, a co-catalyst and an activator; the second metallocene catalytic system comprises a second main catalyst, a co-catalyst and an activator;

[0019] The first procatalyst is a bridged metallocene catalyst; the second procatalyst is a constrained geometry metallocene catalyst.

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

[0021] In the above preparation method, preferably, the constrained geometry metallocene catalyst includes one or a combination of 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-di-tert-butylphenoxytitanium dichloride, 2-(2,3,4,5-tetramethylcyclopentadiene)-4-tert-butyl-6-tritylphenoxytitanium dichloride, 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-dimethylphenoxytitanium dichloride, 2-(1-indenyl)-4-tert-butyl-6-tritylphenoxytitanium dichloride, 2-(9-fluorenyl)-4-tert-butyl-6-tritylphenoxytitanium dichloride and 2-(9-fluorenyl)-4,6-di-tert-butylphenoxytitanium dichloride.

[0022] In the above preparation method, preferably, the cocatalyst in the first metallocene catalyst system and the second metallocene catalyst system respectively comprises an alkyl aluminum. More preferably, the alkyl aluminum comprises triisobutyl aluminum.

[0023] In the above preparation method, preferably, the activators in the first metallocene catalyst system and the second metallocene catalyst system respectively include organic boron compounds. More preferably, the organic boron compounds include Ph3CB(C6F5)4, B(C6F5) 3、 One or a combination of PhNMe2HB(C6F5)4 and Ph3CB[(CF3)2C6H3]4, etc.

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

[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-mentioned preparation method, preferably, the raw material α-olefin in step (1) includes fresh and / or recycled raw material α-olefin. It can be understood by those skilled in the art that the recycled raw material α-olefin comes from the α-olefin separated after post-treatment of the second product containing polyα-olefin in step (3). The method for separating unreacted α-olefin can adopt conventional methods in the art, and the present invention is not particularly limited thereto.

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

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

[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 0.5-2 h.

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

[0031] In the above preparation method, preferably, 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 catalyst system is 0.002-0.02 mmol / L.

[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 0.5-2 h.

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

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

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

[0036] The present invention provides a method for preparing a medium-high viscosity lubricating oil base oil, specifically, a method for synthesizing a metallocene lubricating oil base oil by two-kettle series continuous flow. The method of the present invention adopts two-kettle series continuous polymerization, in the first polymerization reactor, fresh and / or recycled raw material α-olefin is polymerized under the action of the first metallocene catalyst system, and the first product containing polyα-olefin obtained by the reaction enters the second polymerization reactor; in the second polymerization reactor, under the action of the second metallocene catalyst system, the polymerization reaction is continued to obtain a second product containing polyα-olefin; and then after post-treatment, a medium-high viscosity lubricating oil base oil is prepared.

[0037] When the prior art uses a metallocene catalyst system to catalyze olefin polymerization to prepare mPAO, multiple reactors are usually connected in series to improve the raw material conversion rate and the yield of the target product. However, when producing medium- and high-viscosity mPAO, as the raw material conversion rate increases, the viscosity of the reaction system increases, the relative molecular weight of the generated product decreases, and the molecular weight distribution becomes wider. The possible reason is that in a high-viscosity system, due to factors such as mass transfer, the collision probability between the active center and the raw material is reduced, and the chain growth rate is lower than the chain transfer rate.

[0038] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0039] The method of the present invention adopts a polymerization process of two kettles in series, and different metallocene catalytic systems are used in the two polymerization reactors. The main catalyst used in the first polymerization reactor is a bridged metallocene catalyst, and the main catalyst used in the second polymerization reactor is a restricted geometry metallocene catalyst. The polymerization ability of the restricted geometry metallocene catalyst is stronger than that of the bridged metallocene catalyst. Through the coordinated action of the two catalytic systems, and the polymerization conditions of the two kettles are controlled, and then the polymerization strength of the two kettles is controlled, the yield of the product polyalphaolefin is improved, and the molecular weight of the polyalphaolefin obtained by the first polymerization reactor and the second polymerization reactor is similar, and the molecular weight distribution of the polyalphaolefin obtained by the second polymerization reactor is not widened compared to the first polymerization reactor, and finally a medium-high viscosity polyalphaolefin base oil product with a narrow molecular weight distribution is obtained, which improves the product quality. In addition, the method of the present invention does not need to separate the product of the first polymerization reactor, but allows the material in the first polymerization reactor to directly enter the second polymerization reactor to continue to react. At the same time, the method of the present invention can obtain mPAO with a narrow molecular weight distribution without hydrogen adjustment, which has the advantage of simple process. DETAILED DESCRIPTION

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

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

[0042] (1) subjecting a raw material α-olefin 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 a poly-α-olefin;

[0043] (2) allowing the first product containing poly-α-olefin to enter a second polymerization reactor, and performing a second polymerization reaction in the presence of a second metallocene catalyst system to obtain a second product containing poly-α-olefin;

[0044] (3) post-treating the second product containing poly-α-olefin to obtain the medium-high viscosity lubricating oil base oil;

[0045] Wherein, the first metallocene catalytic system comprises a first main catalyst, a co-catalyst and an activator; the second metallocene catalytic system comprises a second main catalyst, a co-catalyst and an activator;

[0046] The first procatalyst is a bridged metallocene catalyst; the second procatalyst is a constrained geometry metallocene catalyst.

[0047] In some specific embodiments of the present invention, the bridged metallocene catalyst includes one or more combinations of dimethylsilylbis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride, vinylbis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride, vinylbis(cyclopentadienyl)zirconium dichloride and dimethylsilylbis(cyclopentadienyl)zirconium dichloride. These bridged metallocene catalysts can be obtained by commercial purchase or prepared by methods disclosed in the prior art. The bridged metallocene catalyst selected in the present invention is suitable for preparing medium and high viscosity mPAO.

[0048] In some specific embodiments of the present invention, the constrained geometry metallocene catalyst includes one or a combination of 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-di-tert-butylphenoxytitanium dichloride, 2-(2,3,4,5-tetramethylcyclopentadiene)-4-tert-butyl-6-tritylphenoxytitanium dichloride, 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-dimethylphenoxytitanium dichloride, 2-(1-indenyl)-4-tert-butyl-6-tritylphenoxytitanium dichloride, 2-(9-fluorenyl)-4-tert-butyl-6-tritylphenoxytitanium dichloride and 2-(9-fluorenyl)-4,6-di-tert-butylphenoxytitanium dichloride. These constrained geometry metallocene catalysts can be obtained by commercial purchase or prepared by methods disclosed in the prior art, for example, they can be prepared by referring to the method disclosed in "Synthesis, Characterization and Catalytic Properties of Constrained Geometry Metallocene Catalysts" published by Huo Hang (Jilin University, DOI: CNKI: CDMD: 2.1015.597805.). The constrained geometry metallocene catalyst selected in the present invention is suitable for preparing ultra-high viscosity mPAO.

[0049] In some specific embodiments of the present invention, the cocatalysts in the first metallocene catalytic system and the second metallocene catalytic system respectively include alkyl aluminum. Preferably, the alkyl aluminum includes triisobutyl aluminum.

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

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

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

[0053] In some specific embodiments of the present invention, the raw material α-olefin in step (1) includes one or a combination 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. It can be understood by those skilled in the art that the recycled raw material α-olefin comes from the α-olefin separated after post-treatment of the second product containing poly-α-olefin in step (3). The method for separating unreacted α-olefin can adopt conventional methods in the art, and the present invention is not particularly limited thereto.

[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 catalyst system is 0.01-0.1 mmol / L.

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

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

[0059] In some specific embodiments of the present invention, the first product containing poly-α-olefin obtained in step (1) enters the second polymerization reactor by overflow or by using 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 catalyst system is 0.002-0.02 mmol / L.

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

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

[0063] In some specific embodiments of the present invention, in step (1) and step (2), the first polymerization reactor and the second polymerization reactor can be polymerization reactors in the prior art. Preferably, the polymerization reaction temperature in the first polymerization reactor and the second polymerization reactor is controlled by thermocouple heating of heat transfer oil, the heat removal of the polymerization reaction can be removed by circulating cooling water in the inner cooling pipe in 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 of the second polymerization reactor reaches a set value, the second product containing poly-α-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 poly-α-olefin is distilled to remove components below 320° C. to obtain the medium-high viscosity lubricant base oil. The terminator used can be a conventional polymerization terminator in the art, such as acidified ethanol. The second product containing poly-α-olefin can enter the polymer receiving tank by overflow or by using a pressure difference.

[0065] In some specific embodiments of the present invention, step (3) further comprises: distilling the second product containing poly-α-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 method for preparing the medium-high viscosity lubricating oil base oil provided by the present invention may include the following steps:

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

[0068] S2 first polymerization reaction: after nitrogen purging, setting polymerization reaction conditions of two polymerization reactors, using circulating cooling water of inner cooling pipes in two polymerization reactors to cool down, making two polymerization reactors reach a predetermined polymerization reaction temperature, starting the raw material pump and the first metallocene catalyst system pump of the first polymerization reactor, controlling the feed rate, making raw material α-olefin and the first metallocene catalyst system enter the first polymerization reactor, starting stirring, and carrying out the first polymerization reaction, the polymerization reaction temperature is controlled by thermocouple heating heat transfer oil, the heat removal of the polymerization reaction is removed by the circulating cooling water of the inner cooling pipe in 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, and when the liquid level in the first polymerization reactor reaches the overflow port, the first product containing poly-α-olefin in the first polymerization reactor overflows to the second polymerization reactor; wherein, the first main catalyst, co-catalyst, activator, etc. in the first metallocene catalyst system can be dissolved in toluene respectively, formulated into a toluene solution of a certain concentration (for example but not limited to 0.02mmol / mL), and then enter the first polymerization reactor;

[0069] S3 second polymerization reaction: at the same time, start the second metallocene catalyst system pump of the second polymerization reactor, make the second metallocene catalyst system enter the second polymerization reactor, start stirring, carry out the second polymerization reaction, and control the polymerization reaction temperature, residence time, etc. in the same manner as in the first polymerization reactor, and wait for the liquid level in the second polymerization reactor to reach the overflow port, and the second product containing poly-α-olefin in the second polymerization reactor overflows to the polymer receiving tank; wherein the second main catalyst, co-catalyst, activator, etc. in the second metallocene catalyst system can be dissolved in toluene respectively, and prepared into a toluene solution of a certain concentration (for example but not limited to 0.02 mmol / mL), and then enter the second polymerization reactor;

[0070] S4 post-treatment: adding a terminator (such as but not limited to acidified ethanol) to the polymer receiving tank to terminate the polymerization reaction, and then distilling the second product containing poly-α-olefin (for example, vacuum distillation), distilling out the components below 320°C to obtain medium-high viscosity lubricant base oil; the components distilled below 320°C can be further separated to obtain α-olefins for use as recycled raw material 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 of less than -33°C, and a kinematic viscosity of 40 to 200 mm at 100°C. 2 / s.

[0072] The technical scheme of the present invention is specifically described below through examples and comparative examples, but the present invention is not limited to these examples and can of course be implemented in various modifications within the scope of the gist of the present invention.

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

[0074] 1-Decene: Purity is polymerization grade;

[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-butylphenoxytitanium dichloride: purity>99.5%;

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

[0082] 2-(2,3,4,5-Tetramethylcyclopentadienyl)-4-tert-butyl-6-tritylphenoxytitanium dichloride: purity>99.5%;

[0083] 2-(1-indenyl)-4-tert-butyl-6-tritylphenoxytitanium 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 device comprises: two 10L high-pressure autoclave polymerization reactors connected in series.

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

[0090] α-olefin conversion rate: (raw material feed amount - unreacted raw material amount) / raw material feed amount × 100%;

[0091] Product yield: target product mass / raw material feed amount × 100%;

[0092] Molecular weight and molecular weight distribution of the product: measured by PL-GPC220 gel permeation chromatograph at 150°C (refer to SN / T 3002-2011);

[0093] Product viscosity: measured at 100°C using the CAV2200 fully automatic kinematic viscosity tester from Cannon, USA (refer to GB / T 265-1988);

[0094] Pour point of product: DSY-006A petroleum product pour point / cloud point tester produced by Tianjin Shengbo Instrument Co., Ltd. (refer to GB / T3535-2006) is used.

[0095] Example 1

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

[0097] (1) After pretreatment of both polymerization reactors, the temperatures of both polymerization reactors were set to 40° C., a continuous polymerization reaction was started, and the co-catalyst pump, raw material pump, main catalyst pump, and activator pump of the first polymerization reactor were sequentially turned on to carry out a first polymerization reaction; wherein the raw material α-olefin used was 1-decene, and the feed rate of the raw material pump was controlled to be 5 L / h; the main catalyst used was vinyl bis(4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride, and the flow rate was 3 mL / h; the co-catalyst used was triisobutylaluminum, and the flow rate was 15 mL / h; the activator used was Ph3CB(C6F5)4, and the flow rate was 3 mL / h; the residence time of the first polymerization reaction was 2 h; 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 to the second polymerization reactor;

[0098] (2) simultaneously starting the co-catalyst pump, the main catalyst pump, and the 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 poly-α-olefin in the second polymerization reactor overflows to the polymer receiving tank;

[0099] (3) 10 mL of 10% acidified ethanol (i.e., ethanol containing 10% by volume hydrochloric acid) was added to the polymer receiving tank to terminate the polymerization reaction, and then the second product containing poly-α-olefin was distilled to distill out the components below 320° C. to obtain a medium-to-high viscosity lubricant base oil product.

[0100] Wherein, the flow rates of the main catalyst, the co-catalyst and the activator in steps (1) and (2) are all the flow rates of the solutions obtained after they are dissolved in toluene. The concentrations of the toluene solution of the main catalyst, the toluene solution of the co-catalyst and the toluene solution of the activator are all 0.02mmol / mL. The same is true for the following embodiments and comparative examples.

[0101] The conversion rate of the raw material α-olefin and the product yield in step (1) and step (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-high viscosity lubricant base oil. The method is basically the same as that of Example 1, except that: the temperature of the two polymerization reactors is set to 60°C; the feed rate of the raw material 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(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride, with a flow rate of 25mL / h; the triisocyanate used in the first polymerization reactor is 1,2-dimethylsilylbis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride, with a flow rate of 25mL / h; The flow rate of butyl aluminum is 500 mL / h; the activator used in the first polymerization reactor is B(C6F5)3, and the flow rate is 80 mL / h; the main catalyst used in the second polymerization reactor is 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-dimethylphenoxytitanium dichloride, and the flow rate is 5 mL / h; the flow rate of triisobutyl aluminum used in the second polymerization reactor is 400 mL / h; the activator used in the second polymerization reactor is B(C6F5)3, and the flow rate is 100 mL / h.

[0104] The conversion rate of the raw material α-olefin and the product yield in step (1) and step (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] The present embodiment provides a method for preparing a medium-high viscosity lubricating oil base oil. The method is basically the same as Example 1, except that: the temperature of the two polymerization reactors is set to 80°C; the main catalyst used in the first polymerization reactor is vinyl bis (cyclopentadienyl) zirconium dichloride, and the flow rate is 20mL / h; the flow rate of triisobutyl aluminum used in the first polymerization reactor is 400mL / h; the activator used in the first polymerization reactor is Ph3CB[(CF3)2C6H3]4, and the flow rate is 100mL / h; the main catalyst used in the second polymerization reactor is 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-di-tert-butylphenoxy titanium dichloride, and the flow rate is 1mL / h; the flow rate of triisobutyl aluminum used in the second polymerization reactor is 20mL / h; the activator used in the second polymerization reactor is Ph3CB[(CF3)2C6H3]4, and the flow rate is 5mL / h.

[0107] The conversion rate of the raw material α-olefin and the product yield in step (1) and step (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 a medium-high viscosity lubricating oil base oil. This method is basically the same as Example 1, except that: the temperatures of the two polymerization reactors are set to 100°C; the feed rate of the raw material 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 dimethylsilyl bis(cyclopentadienyl) zirconium dichloride, and the flow rate is 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, and the flow rate is 200mL / h; the main catalyst used in the second polymerization reactor is 2-(9-fluorenyl)-4,6-di-tert-butylphenoxytitanium dichloride, and the flow rate is 5mL / h; the flow rate of triisobutylaluminum used in the second polymerization reactor is 25mL / h; the activator used in the second polymerization reactor is Ph3CB(C6F5)4, and the flow rate is 5mL / h.

[0110] The conversion rate of the raw material α-olefin and the product yield in step (1) and step (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-high viscosity lubricating oil base oil. The method is basically the same as that of Example 3, except that: the temperature of the two reactors is 80°C, the main catalyst used in the first polymerization reactor is dimethylsilylbis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride, and the flow rate is 3mL / h; the flow rate of triisobutylaluminum used in the first polymerization reactor is 60mL / h; the activator used in the first polymerization reactor is Ph3CB(C6F5)4, and the flow rate is 15mL / h; the main catalyst used in the second polymerization reactor is 2-(9-fluorenyl)-4,6-di-tert-butylphenoxytitanium dichloride, and the flow rate is 1mL / h; the flow rate of triisobutylaluminum used in the second polymerization reactor is 20mL / h; the activator used in the second polymerization reactor is B(C6F5)3, and the flow rate is 5mL / h.

[0113] The conversion rate of the raw material α-olefin and the product yield in step (1) and step (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-high viscosity lubricating oil base oil. The method is basically the same as that of Example 1, except that: the temperature of the two polymerization reactors is set to 60°C; the feed rate of the raw material 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 vinyl bis (4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride, and the flow rate is 20mL / h; the flow rate of triisobutyl aluminum used in the first polymerization reactor is 10 0mL / h; the activator used in the first polymerization reactor is Ph3CB(C6F5)4, and the flow rate is 20mL / h; the main catalyst used in the second polymerization reactor is 2-(2,3,4,5-tetramethylcyclopentadiene)-4-tert-butyl-6-tritylphenoxytitanium dichloride, and the flow rate is 5mL / h; the flow rate of triisobutylaluminum used in the second polymerization reactor is 25mL / h; the activator used in the second polymerization reactor is Ph3CB[(CF3)2C6H3]4, and the flow rate is 5mL / h.

[0116] The conversion rate of the raw material α-olefin and the product yield in step (1) and step (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-high viscosity lubricant base oil. The method is basically the same as that of Example 1, except that: the temperature of the two polymerization reactors is set to 80°C; the feed rate of the raw material α-olefin in the first polymerization reactor is controlled at 10L / h, the residence time in the first polymerization reactor is 1h, and the residence time in the second polymerization reactor is 1h; 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 6mL / h; the triisobutylene used in the first polymerization reactor is 1,000 mmol / l, and the reaction temperature is 40°C. The flow rate of base aluminum is 120mL / h; the activator used in the first polymerization reactor is B(C6F5)3, and the flow rate is 30mL / h; the main catalyst used in the second polymerization reactor is 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-dimethylphenoxytitanium dichloride, and the flow rate is 2mL / h; the flow rate of triisobutylaluminum used in the second polymerization reactor is 10mL / h; the activator used in the second polymerization reactor is B(C6F5)3, and the flow rate is 30mL / h.

[0119] The conversion rate of the raw material α-olefin and the product yield in step (1) and step (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] The present embodiment provides a method for preparing a medium-high viscosity lubricating oil base oil. The method is basically the same as Example 1, except that: the temperature of the two polymerization reactors is set to 100°C; the main catalyst used in the first polymerization reactor is vinyl bis (cyclopentadienyl) zirconium dichloride, and the flow rate is 20mL / h; the flow rate of triisobutyl aluminum used in the first polymerization reactor is 100mL / h; the activator used in the first polymerization reactor is B (C6F5) 3, and the flow rate is 20mL / h; the main catalyst used in the second polymerization reactor is 2- (1-indenyl) -4- tert-butyl -6-trityl phenoxy titanium dichloride, and the flow rate is 5mL / h; the flow rate of triisobutyl aluminum used in the second polymerization reactor is 5mL / h; the activator used in the second polymerization reactor is B (C6F5) 3, and the flow rate is 25mL / h.

[0122] The conversion rate of the raw material α-olefin and the product yield in step (1) and step (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-high viscosity lubricating oil base oil. The method uses only one polymerization reactor to carry out the polymerization reaction, and comprises the following steps:

[0125] After pretreatment of the polymerization reactor, the temperature of the polymerization reactor is set to 40°C, and the co-catalyst pump, raw material pump, main catalyst pump and activator pump of the polymerization reactor are turned on in sequence to carry out polymerization reaction; the raw material α-olefin used is 1-decene, and the feed rate controlled by the raw material pump is 5L / h; the main catalyst used is vinyl bis(4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride, and the flow rate is 3mL / h; the co-catalyst used is triisobutylaluminum, and the flow rate is 15mL / h; the activator used is Ph3CB(C6F5)4, and the flow rate is 3mL / h; the residence time of the polymerization reaction is 2h; when the liquid level in the polymerization reactor reaches the overflow port, the product containing polyα-olefin in the polymerization reactor overflows to the polymer receiving tank; 10% acidified ethanol is added to the polymer receiving tank to terminate the polymerization reaction, and then the product containing polyα-olefin is distilled to distill out the components below 320°C to obtain a medium-high viscosity lubricant base oil product.

[0126] The conversion rate of the raw material α-olefin and the product yield 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-high viscosity lubricating oil base oil. The method uses only one polymerization reactor for polymerization reaction, and its specific steps are basically the same as those of 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; the activator used is Ph3CB(C6F5)4, with a flow rate of 1 mL / h.

[0129] The conversion rate of the raw material α-olefin and the product yield 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-high viscosity lubricating base oil. The method is basically the same as Example 1, except that the main catalyst used in the second polymerization reactor is vinyl bis (4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride, with a flow rate of 1 mL / h.

[0132] The conversion rate of the raw material α-olefin and the product yield in step (1) and step (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-high viscosity lubricating oil base oil. The method is basically the same as 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 of the raw material α-olefin and the product yield in step (1) and step (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-high viscosity lubricating oil base oil. The method is basically the same as Example 1, except that: the main catalyst used in the first polymerization reactor is 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-di-tert-butylphenoxy titanium dichloride, with a flow rate of 3 mL / h; the main catalyst used in the second polymerization reactor is vinyl bis(4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride, with a flow rate of 1 mL / h.

[0138] The conversion rate of the raw material α-olefin and the product yield in step (1) and step (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 producing mPAO by the methods of Examples 1-8 and Comparative Examples 1-5

[0140]

[0141] From the data comparison of Comparative Examples 1-2 and Examples 1-8, it can be seen that Example 1-8 uses two kettles in series for polymerization, which greatly improves the conversion rate of the monomer. This is because the use of two kettles in series is equivalent to extending the reaction residence time, so the conversion rate is improved. From the data comparison of Comparative Examples 3-5 and Examples 1-8, it can be seen that the first polymerization reactor in Example 1-8 uses a bridged metallocene catalyst system, the second polymerization reactor uses a restricted geometry metallocene catalyst system, and the reaction conditions of the two reactors are controlled, and the molecular weight distribution of the obtained product is narrow, lower than 1.8; while the two polymerization reactors in Comparative Example 3 both use a bridged metallocene catalyst system, and the molecular weight distribution of the product is relatively wide, higher than 2.0; the two polymerization reactors in Comparative Example 4 both use a restricted geometry metallocene catalyst system, and the first reactor produces a product with a large molecular weight, and the viscosity of the product becomes larger and the molecular weight distribution becomes wider; Comparative Example 5 uses a restricted geometry metallocene catalyst system in the first polymerization reactor and a bridged metallocene catalyst system in the second polymerization reactor, and the molecular weight of the product is significantly widened. In addition, Examples 1-8 can flexibly obtain a viscosity range of 40 to 200 mm at 100°C by adjusting the catalyst used and the dosage ratio. 2 / s of mPAO products.

[0142] In summary, the method of the present invention adopts a polymerization process with two reactors connected in series. Through the synergistic effect of two catalytic systems, not only the single-pass conversion rate of the raw material α-olefin is improved, the yield of the target product is increased to more than 90%, and the economy of the process is improved, but also a medium-high viscosity polyα-olefin base oil product with an adjustable viscosity range and uniform molecular weight distribution is prepared, thereby improving the product quality.

Claims

1. A method for preparing a medium-high viscosity lubricating oil base oil, comprising the following steps: (1) subjecting a raw material α-olefin 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 a poly-α-olefin; (2) allowing the first product containing poly-α-olefin to enter a second polymerization reactor, and performing a second polymerization reaction in the presence of a second metallocene catalyst system to obtain a second product containing poly-α-olefin; (3) post-treating the second product containing poly-α-olefin to obtain the medium-high viscosity lubricating oil base oil; Wherein, the first metallocene catalytic system comprises a first main catalyst, a co-catalyst and an activator; the second metallocene catalytic system comprises a second main catalyst, a co-catalyst and an activator; The first procatalyst is a bridged metallocene catalyst; the second procatalyst is a constrained geometry metallocene catalyst.

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

3. The preparation method according to claim 1, wherein The constrained geometry metallocene catalyst includes one or a combination of 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-di-tert-butylphenoxytitanium dichloride, 2-(2,3,4,5-tetramethylcyclopentadiene)-4-tert-butyl-6-tritylphenoxytitanium dichloride, 2-(2,3,4,5-tetramethylcyclopentadiene)-4,6-dimethylphenoxytitanium dichloride, 2-(1-indenyl)-4-tert-butyl-6-tritylphenoxytitanium dichloride, 2-(9-fluorenyl)-4-tert-butyl-6-tritylphenoxytitanium dichloride and 2-(9-fluorenyl)-4,6-di-tert-butylphenoxytitanium dichloride.

4. The preparation method according to claim 1, wherein The co-catalysts in the first metallocene catalyst system and the second metallocene catalyst system respectively include alkyl aluminum; Preferably, the aluminum alkyl comprises triisobutylaluminum.

5. The preparation method according to claim 1, wherein The activators in the first metallocene catalyst system and the second metallocene catalyst system respectively include organic boron compounds; Preferably, the organic boron compound includes one or a combination of Ph3CB(C6F5)4, B(C6F5)3, PhNMe2HB(C6F5)4 and Ph3CB[(CF3)2C6H3]4.

6. 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 5-20, respectively.

7. The preparation method according to claim 1 or 5, 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.

8. The preparation method according to claim 1, wherein The raw material α-olefin in step (1) includes fresh and / or recycled raw material α-olefin; Preferably, the feed rate of the raw material α-olefin into the first polymerization reactor in step (1) is 5 to 20 L / h.

9. The preparation method according to claim 1, wherein 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 catalyst system is 0.01 to 0.1 mmol / L.

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

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

12. 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 catalyst system is 0.002-0.02 mmol / L.

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

14. The preparation method according to claim 1, wherein: The conversion rate of α-olefin in step (2) is above 90%.

15. The preparation method according to claim 1, wherein: Step (3) specifically includes: when the liquid level of the second polymerization reactor reaches a set value, the second product containing poly-α-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 poly-α-olefin is distilled to remove components below 320° C. to obtain the medium-high viscosity lubricant base oil.

16. The preparation method according to claim 1, wherein: The medium-high viscosity lubricating oil base oil has a molecular weight distribution of less than 1.8, a pour point of less than -33°C, and a kinematic viscosity of 40 to 200 mm at 100°C. 2 / s.

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