Production of poly-alpha-olefins

Abstract

The present invention describes a process for producing poly-α-olefins, comprising the steps of providing at least one α-olefin monomer and a catalyst, and reacting the at least one α-olefin monomer in the presence of the catalyst to form a mixture of poly-α-olefins (PAO). The resulting mixture of poly-α-olefins is fractionated into two PAO fractions: a first fraction of PAO having a kinematic viscosity of 5 cSt or less and a second fraction of PAO having a kinematic viscosity greater than 5 cSt. Optionally, a recirculated fraction is also obtained in the fractionation, and at least a portion of the recirculated fraction containing the α-olefin dimer can be recycled back into the reaction steps. The process further includes the step of directly and separately hydrogenating the two resulting PAO fractions to obtain a hydrogenated PAO fraction.

Description

Technical Field

[0001] The present invention relates to a process for producing poly-α-olefins from α-olefin monomers. More specifically, the present invention relates to a process for producing poly-α-olefins in which a product mixture is fractionated into two product fractions, and these product fractions are hydrogenated separately.

[0002] Thus, the present invention provides a simple process which may be a continuous process for producing high-quality poly-α-olefins in good yield and using an optimal process and equipment setup.

Background Art

[0003] Oligomerization reactions of α-olefins to form various grades of components useful in the manufacture of synthetic lubricants are well known. The production process generally includes oligomerization of α-olefin monomers using a catalyst or catalyst complex, removal of the catalyst or catalyst complex from the reaction product, and various post-reaction treatments of the oligomerization product. The oligomerization product is generally referred to as poly-α-olefin (PAO) and can usually be classified in the range of 2 to 100 cSt based on the viscosity measured in cSt units of the product. The viscosities of typical low-viscosity PAO products are 2, 4, 6 or 8 cSt.

[0004] In the oligomerization of α-olefins, dimers, trimers, tetramers, pentamers, etc. are formed. Heavier products, i.e., products with a greater number of monomer units in the oligomer product, naturally have a higher viscosity compared to lighter products. PAO products are used in various applications, and depending on the application, various viscosities and other properties are required for PAO products. Different oligomers may also be mixed to form products with desired properties.

[0005] US4,434,309 describes the oligomerization of low molecular weight α-olefins for the production of synthetic lubricant base stocks. This oligomerization is carried out in the presence of a catalyst, which may be boron trifluoride and a proticity enhancer.

[0006] One important aspect of the manufacturing process is the separation of the catalyst or catalytic complex from the oligomerized product. EP1694439 describes a typical PAO manufacturing process, as well as the separation of a catalytic complex containing boron trifluoride (BF3) and an alcohol from the oligomerized product by vacuum distillation.

[0007] The oligomerized products produced typically need to be hydrogenated to saturate the double bonds still present in the poly-α-olefin (PAO). A typical process sequence for hydrogenating unsaturated products involves hydrogenating the product intermediate immediately after the process reaction section, followed by at least one separation step to obtain the desired saturated product fraction. Alternatively, the product is first separated into various product streams with the desired properties, and these product streams are then hydrogenated. However, this process sequence requires intermediate storage capacity and batch hydrogenation of campaign units.

[0008] In PAO production, there is still a need to develop an optimal process sequence that enables the acquisition of high-quality products with sufficient and economical equipment and process setup, resulting in high plant capacity and minimal downtime. [Overview of the Initiative]

[0009] Therefore, an object of the present invention is to provide a robust process for obtaining poly-α-olefins in which the product fractionation step and hydrogenation step are optimized. This object of the present invention is achieved by a process characterized by the matters described in the independent claim. Preferred embodiments of the present invention are disclosed in the dependent claims. Therefore, the present invention provides a process for producing poly-α-olefins, the process is a) A step of providing at least one α-olefin monomer and a catalyst, b) A step of reacting the at least one α-olefin monomer in the presence of the catalyst to form a mixture of poly-α-olefins (PAOs), c) A step of fractionating the obtained poly-α-olefin mixture, comprising two PAO fractions: a first fraction of PAO having a kinematic viscosity of 5 cSt or less and a second fraction of PAO having a kinematic viscosity of more than 5 cSt; and optionally, a step of recycling at least a portion back to the reaction step and fractionating into a recycled fraction containing an α-olefin dimer. d) The step of separately hydrogenating the two PAO fractions obtained to obtain a hydrogenated PAO fraction, and e) Optionally, further fractionate at least one of the hydrogenated PAO fractions to obtain a hydrogenated PAO sub-fraction. Includes.

[0010] One advantage of the present invention is to provide a process for producing poly-α-olefins using an optimal process and apparatus setup. In one embodiment, the disclosed process allows for the continuous operation of the oligomerization step and the hydrogenation step with little to no intermediate storage of non-hydrogenated products.

[0011] In the following, the present invention will be described in more detail with reference to the accompanying figures, with reference to preferred embodiments. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic process description of one embodiment of the present invention, which includes an oligomerization step, a fractional distillation step, and a hydrogenation step. [Figure 2] Figure 2 shows the cracking of various hydrogenated PAO products at different temperatures. [Figure 3] Figure 3 shows the fractional distillation temperatures required for various PAO products. [Modes for carrying out the invention]

[0013] Hydrogenating the entire product stream obtained from the process before separation into the final product is usually optimal, especially when the final product is not sensitive to separation conditions. However, poly-α-olefin products (PAOs) have strict product specifications, and these specifications cannot be met if product degradation occurs in the final process step. For this reason, a typical process sequence for poly-α-olefin production provides a hydrogenation step as the final essential process step of the poly-α-olefin treatment, which consequently presents the challenge that all fractionated product intermediates must be hydrogenated separately. This can be done in separate parallel and sequential units for each product, or in a single unit operated in a batch manner on a campaign basis.

[0014] The concept of a beneficial manufacturing process is based on the minimum necessary amount of equipment and an optimal equipment layout, which efficiently and continuously performs the desired once-through process with minimal reprocessing of raw materials and intermediate process flows. The concept of a continuous process allows for the continuous and full utilization of the equipment under designed and optimally controlled operating conditions, thereby minimizing unnecessary process disturbances and equipment maintenance work.

[0015] The concept of batch manufacturing processes has the advantage of allowing the processing of multiple quality products in the same minimal amount of equipment. However, the equipment is labor-intensive to operate and is only fully utilized for a limited time. Furthermore, transient modes in batch manufacturing reduce the overall yield of the product and necessitate reprocessing. Therefore, batch manufacturing is usually only beneficial in small-scale manufacturing processes and only when it is necessary to process multiple types of products in campaign units using the same batch equipment.

[0016] Therefore, the aim of the present invention is to provide solutions to the described problems, relating on the one hand to continuous processes and on the other to batch processes. Accordingly, the object of the present invention is to provide a robust process for obtaining poly-α-olefins, comprising optimal product fractionation and hydrogenation steps. The present invention relates to a process for producing poly-α-olefin (PAO) from α-olefins. The term "α-olefin" here is intended to refer to the same thing as alpha-olefin (alpha-olefin or alfa-olefin), which is a 1-alkene having a double bond at the primary carbon, i.e., the α-carbon. The carbon chain of the α-olefin is preferably linear, i.e., an n-alkene. Unless specifically mentioned that the α-olefin is branched, it is assumed that a linear α-olefin is meant. In one embodiment of the present invention, the α-olefin monomer is C4~C 20 It contains α-olefins, preferably C8-C 12 It contains an α-olefin, and more preferably the monomer is C 10It contains α-olefin (1-decene). Even if the starting material for the oligomerization reaction mainly contains, for example, C10-α-olefin (1-decene), it should be noted that the starting material is not completely pure 1-decene and always contains various amounts of other olefins. Other olefins also react in the oligomerization reaction. Therefore, the poly-α-olefin (PAO) product formed in the oligomerization reaction is always a mixture containing products with different degrees of oligomerization (dimers, trimers, tetramers, etc.) and oligomers from olefin monomers other than the α-olefin mainly selected as the starting material.

[0017] The products of the oligomerization reaction of α-olefin monomers are called poly-α-olefins (PAOs), or poly-alfa-olefins (poly-alpha-olefins, polyalphaolefins, or polyalfaolefins). Different oligomerization products can be characterized based on the number of monomer units in the oligomer, i.e., dimers, trimers, tetramers, etc. Oligomerization products can also be characterized based on the viscosity value of the product, expressed in cSt. Typical viscosities of light PAO products include, but are not limited to, kinematic viscosities of 2, 4, 6, 8 cSt units at 100°C.

[0018] PAO products with specific kinematic viscosities, such as 4cSt or 6cSt, are always mixtures of oligomers. This is because a product with a specific kinematic viscosity is desired, and the goal is not to obtain a product with only one type of oligomer. What matters is the properties of the product, not the chemical structure itself. A product with specific properties, such as kinematic viscosity, is desired.

[0019] Therefore, the formed PAO product mixture usually needs to be fractionated in order to obtain a product with desired properties. The oligomerization reaction always produces a mixture of oligomers, and the final PAO product is usually formed by fractionating the PAO reaction mixture to obtain a product with desired properties such as kinematic viscosity and volatility. Fractionation is also usually required to separate low oligomerization products such as unreacted monomers and / or dimers, and these products should be separated from the product mixture and are usually recycled to the oligomerization step. Furthermore, the catalyst or catalyst complex needs to be removed from the product mixture, which is usually carried out before PAO fractionation.

[0020] The oligomerization reaction of α - monomers also requires the presence of a catalyst. In this process, the catalyst can be any suitable catalyst capable of catalyzing the oligomerization of α - monomers to form polyα - oligomers. In one embodiment of the present invention, the catalyst is a catalyst complex comprising a main catalyst and a cocatalyst. The term "catalyst complex" is used herein to refer to a combination of a catalyst and a cocatalyst (which can also be referred to as a protic promoter). The catalyst complex can be a physical mixture, or the catalyst and the cocatalyst may be bonded to each other, or a combination of both. The main catalyst can be an aluminum halide or a boron halide, and preferably, the main catalyst is boron trifluoride (BF3). The cocatalyst can be a C1 - C 10 alcohol, or a C1 - C5 alcohol, and preferably, the cocatalyst is n - butanol.

[0021] The performance and advantages of the present invention do not depend on the α - olefin selected in the oligomerization, or the catalyst or alternative catalyst complex used. However, in one embodiment of the present invention, the monomer is linear 1 - decene, and the catalyst complex is formed from BF3 as the main catalyst and n - butanol as the cocatalyst.

[0022] The process according to the invention comprises reacting at least one α-olefin monomer in an oligomerization reaction in the presence of a catalyst to form a mixture of poly-α-olefins (PAO), and fractionating the resulting mixture into two PAO fractions and optionally a recycle fraction. At least a part of the recycle fraction is recycled to the reaction step for further oligomerization. The recycle fraction usually contains at least dimers, but may also contain unreacted monomers. The recycle fraction may also be in multiple streams, and the separation of the recycle fraction may include multiple separation steps. Prior to the fractionation step for obtaining the PAO fraction(s), the catalyst or catalyst complex, and optionally the unreacted monomers, are removed from the outlet of the product mixture from the oligomerization reaction.

[0023] The mixture of poly-α-olefins obtained in the oligomerization reaction is fractionated in a fractionation step to obtain two PAO fractions.

[0024] The two PAO fractions are a first fraction of PAO having a kinematic viscosity of 5 cSt or less and a second fraction of PAO having a kinematic viscosity of more than 5 cSt. The first fraction of PAO having a kinematic viscosity of 5 cSt or less may also be referred to as the light fraction, and the second fraction of PAO having a kinematic viscosity of more than 5 cSt may also be referred to as the heavy fraction. In one embodiment, fractionation of the mixture of poly-α-olefins yields more than two PAO fractions, such as three, four or five PAO fractions.

[0025] In this specification, a PAO fraction having a kinematic viscosity of 5 cSt or less (or PAO fraction) means that the fraction contains a PAO product having a kinematic viscosity of 5 cSt or less as measured at 100°C, i.e., the kinematic viscosity can be up to 5 cSt, for example, 4.5 cSt, 4 cSt, or 3.5 cSt. In one embodiment, the first fraction of the PAO product has a kinematic viscosity of 2 cSt to 5 cSt. Similarly, a PAO fraction having a kinematic viscosity greater than 5 cSt (or PAO fraction) means a PAO product whose measured kinematic viscosity is higher than 5 cSt, for example, 5.5 cSt, 6 cSt, or 6.5 cSt. In one embodiment, the second fraction of the PAO product has a kinematic viscosity greater than 5 cSt up to 10 cSt, or greater than 5 cSt up to 12 cSt. The fraction of PAO product separated as a fraction has one measured kinematic viscosity, and the range of kinematic viscosity for the first and second fractions means that the measured kinematic viscosity of the fraction is within this range.

[0026] Alternatively, in one embodiment, the first PAO fraction has a kinematic viscosity of 4 cSt or less, and the second PAO fraction has a kinematic viscosity greater than 4 cSt. Further alternatively, in one embodiment, the first PAO fraction has a kinematic viscosity of 6 cSt or less, and the second PAO fraction has a kinematic viscosity greater than 6 cSt.

[0027] Typically, in this process for producing poly-α-olefins according to the present invention, three different PAO products with different kinematic viscosities are produced. These three PAO products are, in one embodiment of the present invention, a 2cSt product, a 4cSt product, and either a 6cSt product or an 8cSt product. Thus, the first fraction of the PAO product (light fraction) contains two PAO products, namely the 2cSt product and the 4cSt product, while the second fraction of the PAO product (heavy fraction) contains one PAO product, namely either the 6cSt product or the 8cSt product. Thus, the first PAO fraction having a kinematic viscosity of 5cSt or less typically contains two PAO products, namely the 2cSt product and the 4cSt product. Similarly, the second PAO fraction having a kinematic viscosity greater than 5cSt typically contains one PAO product, namely the 6cSt product or the 8cSt product.

[0028] This process involves fractionating the resulting poly-α-olefin mixture into two PAO fractions and optionally a recirculated fraction, a portion of which may be recycled back into the reaction step, and this recycled fraction contains α-olefin dimers. It is beneficial to perform the fractionation so that two fractions of approximately equal volume are obtained. This means that if separate hydrogenation units are used for the two PAO fractions, the hydrogenation units can be of equal size, and the flow and pathways to the hydrogenation units can be interchangeable. Two fractions of approximately equal size can be obtained by fractionating the PAO product such that one fraction contains a PAO product with a kinematic viscosity of 5 cSt or less, and the second PAO fraction contains a PAO product with a kinematic viscosity greater than 5 cSt.

[0029] Obtaining two fractions is also beneficial because only the light fraction, i.e., the fraction with a kinematic viscosity of 5 cSt or less, needs to be further separated after hydrogenation. This further separation can be carried out under mild processing conditions and therefore does not cause product degradation. On the other hand, the heavy fraction, i.e., the fraction with a kinematic viscosity exceeding 5 cSt, becomes a completely finished product after hydrogenation, and no further product degradation can occur. Separation of the heavy product requires harsher operating conditions, which would result in a higher risk of product degradation.

[0030] Surprisingly, fractional distillation into two PAO products, namely a first PAO fraction with a kinematic viscosity of 5 cSt or less and a second PAO fraction with a kinematic viscosity greater than 5 cSt, was found to be beneficial. This is because the light PAO fraction can be further fractionated into two separate PAO products, typically a 2 cSt product and a 4 cSt product, at lower temperatures without product degradation (see examples provided herein). As mentioned above, the heavy PAO fraction is typically the finished product after hydrogenation, and further fractional distillation of the hydrogenated heavy PAO product is not required.

[0031] When heavier PAO products, such as 8cSt products, are desired, the total volume of products decreases and the operating time is extended. However, obtaining two PAO fractions is still beneficial because the desired heavier fraction can be hydrogenated in one hydrogenation unit, while the other lighter fraction, which has a significantly smaller volume when heavier products such as 8cSt products are desired, can be stored in an intermediate storage tank, thereby allowing the other hydrogenation unit to undergo maintenance and upkeep. Therefore, obtaining two PAO fractions and hydrogenating them separately in batches, or having two separate hydrogenation units for the two PAO fractions, enables an end-to-end process with optimal product fractionation and hydrogenation steps for obtaining poly-α-olefins.

[0032] In one embodiment of the present invention, obtaining two PAO fractions enables two hydrogenation apparatuses having separate lines, which are interchangeable with one another, and thus allows catalyst replacement in one hydrogenation unit while the other hydrogenation unit is operating in a continuous end-to-end processing mode.

[0033] The kinematic viscosity of a mixture or fraction of PAO products is a typical method for characterizing mixtures of PAO products and various poly-α-olefins. Those skilled in the art are well familiar with measuring the kinematic viscosity of products such as PAO products. Kinematic viscosity is measured according to ASTM D-445 (latest edition) and is typically measured at temperatures of at least 100°C, 40°C, and 0°C. Kinematic viscosity as used herein is measured at 100°C unless otherwise defined. Kinematic viscosity is given in cSt (centistokes), which is in SI units of mm. 2 Corresponds to / s.

[0034] In this specification, a PAO fraction having a kinematic viscosity of 5 cSt or less, for example, means that the kinematic viscosity of the fraction is 5 cSt or less at 100°C. PAO fractions are usually mixtures of oligomers, and therefore it is useful to define fractions based on their kinematic viscosity rather than using the number of monomer units in the oligomers. Those skilled in the art are well familiar with obtaining PAO fractions having a specific kinematic viscosity, and therefore, a mixture of PAO products can be fractionally distilled to obtain PAO fractions(s) having a specific kinematic viscosity. Fractional distillation can be carried out by any well-known distillation or fractional distillation procedure, such as vacuum distillation.

[0035] The fractional distillation into two PAO fractions can be carried out as distillation under reduced pressure, such that the temperature required to separate, for example, a first PAO fraction having a kinematic viscosity of 5 cSt or less from a second PAO fraction having a kinematic viscosity greater than 5 cSt is a maximum of 280°C, 300°C, or 330°C. The distillation temperature depends on the kinematic viscosity of the bottom fraction and the reduced pressure. The reduced pressure can be 0.2 kPa to 1 kPa at the top of the distillation column.

[0036] The process according to the present invention further includes the step of hydrogenating the two obtained PAO fractions to obtain hydrogenated PAO fractions. The step of hydrogenating the two PAO fractions is performed immediately after fractional distillation, thereby the process includes the step of directly hydrogenating the two obtained PAO fractions and performing separate hydrogenations to obtain hydrogenated PAO fractions. Direct hydrogenation of the two PAO fractions means that the PAO fractions are not subjected to further oligomerization, recirculation to oligomerization, or other chemical modification (modification) of the fractions before being subjected to the hydrogenation step. The hydrogenation of the PAO fractions may be carried out separately and in separate hydrogenation units. Thus, in one embodiment, there are at least two separate hydrogenation units operating in parallel.

[0037] The hydrogenation of PAO products is well known to those skilled in the art, and this process is not limited to any particular hydrogenation process. Typically, hydrogenation is carried out in the presence of a noble metal catalyst or a nickel catalyst, preferably a nickel catalyst. Hydrogenation may be carried out in a fixed-bed reactor. In one embodiment, hydrogenation is carried out under conditions of a hydrogen pressure of 2 MPa to 10 MPa, preferably 2.5 MPa to 8 MPa, more preferably 3 MPa to 6 MPa; and a temperature of 100°C to 320°C, preferably 120°C to 280°C, more preferably 130°C to 250°C. Typically, hydrogen is produced from hydrocarbons 1 m 3 25-500 Nm per unit 3 It is used in such quantities that the liquid space velocity (LHSV) is 0.2 to 10¹ / hour.

[0038] In one embodiment of the present invention, the process further includes an additional fractional distillation step after the hydrogenation of the PAO fraction, in which a plurality of sub-fractions of the hydrogenated PAO fraction are obtained. In one embodiment, the hydrogenated PAO sub-fractions are obtained from a hydrogenated PAO fraction having a kinematic viscosity of 5 cSt or less, and the additional fractional distillation of the sub-fractions is carried out to obtain a first hydrogenated PAO sub-fraction having a kinematic viscosity of about 2 cSt and a second hydrogenated PAO sub-fraction having a kinematic viscosity of about 4 cSt.

[0039] Figure 1 shows a schematic process of one embodiment of the present invention. The oligomerization reaction and catalytic separation of α-olefin monomers are carried out in the oligomerization unit (10) to produce PAO products. The formed PAO products are subjected to fractional distillation (20), where two PAO product fractions are obtained. Prior to the fractional distillation step, the catalyst complex is removed from the product stream (not shown in the figure). A first fraction containing PAO products with kinematic viscosities of 2cSt and 4cSt is obtained, and a second fraction containing PAO products with a kinematic viscosity of 6cSt or 8cSt is obtained. The two PAO fractions are subjected to hydrogenation in separate hydrogenation units, namely, a first hydrogenation unit (30) for the 2cSt and 4cSt PAO product fractions and a second hydrogenation unit (35) for the 6cSt or 8cSt PAO product. From the fractional distillation unit (20), a recirculating dimer stream (25) may be optionally withdrawn, and at least a portion of it may be recycled to the oligomerization reaction unit (10). After the first hydrogenation unit (30), the hydrogenated PAO fractions of the 2cSt and 4cSt PAO products are passed to the second fractional distillation unit (40) to separate the 2cSt PAO product and the 4cSt PAO product.

[0040] Surprisingly, it has been found that it is beneficial to perform fractional distillation into two PAO product fractions before hydrogenation, and to hydrogenate at least two PAO fractions separately or in separate hydrogenation units. This is because the first fractional distillation, primarily to separate the recirculated fraction containing α-olefin dimers, usually needs to be separated from the PAO product mixture before hydrogenation. Also, since fractional distillation of PAO products usually causes cracking, which can lead to the formation of double bonds or similar structures, a hydrogenation step is required after the fractional distillation step. It is particularly advantageous to fractionate the PAO product mixture into exactly two fractions at a kinematic viscosity of 5 cSt and to hydrogenate these fractions directly and separately. The benefit of fractional distillation at this specific kinematic viscosity and the direct and separate hydrogenation of the two resulting PAO fractions is that it ensures that each fraction is hydrogenated under conditions best suited to its respective properties. Specifically, a PAO fraction having a kinematic viscosity of 5 cSt or less may undergo a further fractionation step to obtain two PAO sub-fractions with kinematic viscosities of 2 cSt and 4 cSt, respectively. This further separation may be carried out under mild treatment conditions, as shown in the examples below, thereby preventing degradation of the product.

[0041] While fractionation into more than two fractions may be beneficial, the cost of having more than two hydrogenation units usually outweighs the benefits of obtaining more than two PAO fractions. If more than two PAO fractions are obtained before hydrogenation, the process should have greater intermediate storage capacity for the PAO fraction, and hydrogenation should be carried out in a semi-batch operation mode. [Examples]

[0042] Example 1 Two PAO products with different kinematic viscosities, namely 4cSt PAO and 8cSt PAO grades, were subjected to tests for their thermal stability. Multiple PAO products were placed in similar autoclaves and positioned in an oven maintained at a constant temperature. The autoclaves were left in the oven for several hours. The amount of product remaining in the autoclaves after the test was recorded. Liquid samples were analyzed by gas chromatography (GC) to quantify the cracking product. The test was repeated for two sets at temperatures of 280°C, 300°C, and 320°C. Some degree of color change was observed in all tests. The measured cracking rates are shown in Figure 2.

[0043] The results clearly show that lowering the temperature reduces the cracking rate almost linearly. It can also be observed that the heavier 8cSt PAO product exhibits a higher tendency to crack. In other words, the longer the oligomeric chain, the more susceptible it becomes to thermal degradation.

[0044] The typical maximum processing temperatures required for fractional distillation of various PAO products are shown in Figure 3 as a function of product grade. It can be concluded that fractional distillation of heavier PAO grades such as 6cSt and 8cSt carries a higher risk of product degradation during processing due to the higher temperatures required for fractional distillation.

[0045] As technology advances, it will be apparent to those skilled in the art that the concept of the present invention can be implemented in a variety of ways. The present invention and its embodiments are not limited to the examples described above and may be modified within the scope of the claims.

Claims

1. A process for producing poly-α-olefins, a) A step of providing at least one α-olefin monomer and a catalyst, b) A step of reacting the at least one α-olefin monomer in the presence of the catalyst to form a mixture of poly-α-olefins (PAOs), c) A step of fractional distillation of the obtained poly-α-olefin mixture, comprising two PAO fractions: a first fraction of PAO having a kinematic viscosity of 5 cSt or less and a second fraction of PAO having a kinematic viscosity of more than 5 cSt; and optionally, a step of recycling at least a portion back to the reaction step and fractionating into a recycled fraction containing an α-olefin dimer. d) The step of separately hydrogenating the two PAO fractions obtained to obtain a hydrogenated PAO fraction, and e) Optionally, further fractionate at least one of the hydrogenated PAO fractions to obtain a hydrogenated PAO sub-fraction. A process that includes this.

2. The process according to claim 1, wherein the two PAO fractions obtained are hydrogenated in separate hydrogenation units.

3. The process according to claim 1 or 2, wherein the process comprises a further fractional distillation step e), the further fractional distillation step e) is performed on the hydrogenated PAO fraction having a kinematic viscosity of 5 cSt or less, to obtain a first hydrogenated PAO sub-fraction having a kinematic viscosity of about 2 cSt and a second hydrogenated PAO sub-fraction having a kinematic viscosity of about 4 cSt.

4. The at least one α-olefin monomer is C ４ ~C ２０ It contains α-olefin, preferably C ８ ~C １２ It contains α-olefin, more preferably C １０ The process according to any one of claims 1 to 3, comprising the α-olefin.

5. The catalyst is a catalyst complex comprising a main catalyst and a co-catalyst, wherein the main catalyst is preferably an aluminum halide or a boron halide, and more preferably the main catalyst is BF ３ And the co-catalyst is preferably C １ ~C １０ The process according to any one of claims 1 to 4, wherein the co-catalyst is selected from alcohols, and more preferably n-butanol.

6. The process according to any one of claims 1 to 5, wherein the hydrogenation is carried out in a fixed-bed reactor in the presence of a noble metal catalyst or a nickel catalyst.

7. The process according to any one of claims 1 to 6, wherein the hydrogenation is carried out at a pressure of 2 MPa to 10 MPa, preferably 2.5 MPa to 8 MPa, more preferably 3 MPa to 6 MPa; and at a temperature of 100°C to 320°C, preferably 120°C to 280°C, more preferably 130°C to 250°C.

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