A method for producing polyolefins using mixed α-olefins separated from Fischer-Tropsch synthetic oil

Abstract

The present invention discloses a polyolefin production method using mixed α-olefins obtained by separation of Fischer-Tropsch oil. The method is characterized in that, in the presence of a catalyst, ethylene and mixed α-olefins are polymerized in a reactor to obtain a multi-polymer polymer solution, wherein the mixed α-olefins come from an α-olefin crude separation unit of a Fischer-Tropsch oil device; the obtained polymer solution is fed to a devolatilization unit to obtain a polymer and a mixed stream containing unreacted monomers, a solvent and impurities; the mixed stream passes through the separation unit to obtain recycled ethylene, recycled solvent, recycled α-olefins, oligomers and tail gas, and part of the recycled α-olefins is transported to an α-olefin fine separation unit of a Fischer-Tropsch oil section to obtain α-olefins and internal olefins of different carbon numbers, and the purified α-olefins can be recycled and used to adjust the mass concentration of different α-olefins in the polymerization unit.

Description

Technical Field

[0001] The present invention relates to the technical field of olefin polymerization production, and in particular to a method for producing polyolefins by using mixed alpha-olefins separated from Fischer-Tropsch synthetic oil. Background Art

[0002] Polyolefin products are widely used in pipes, food packaging, automotive parts, films, electrical housings, etc. Different application markets have different requirements for the performance of polyolefin materials. Ordinary polyolefin plastics are usually obtained by ethylene homopolymerization and / or ethylene and a small amount of α-olefin copolymerization. Ethylene and α-olefin copolymers with high α-olefin comonomer content are a type of high-performance polyolefin thermoplastic elastomer. Due to its higher content of comonomers in the molecular chain and lower density, it is widely used in polymer modification, medical and other fields.

[0003] Currently, the industrial production of polyolefin thermoplastic elastomers primarily utilizes a solution process, typically conducted at temperatures between 40°C and 160°C and pressures below 20 MPa. Common comonomers used include 1-butene, 1-hexene, and 1-octene. Patent CN10380999 B discloses a solution polymerization method for ethylene and α-olefins. This method utilizes a mixed solvent of two hydrocarbons, one of which is in a supercritical state at the solution polymerization pressure and temperature. This method reduces the viscosity of the reaction system, thereby reducing the energy consumption required for solvent removal downstream of the polymerization reaction. Solution polymerization offers advantages such as short polymerization times and easy product brand switching. However, its production cost is relatively high, primarily due to the following reasons: 1. The high price of α-olefin raw materials; 2. The high viscosity of the polymer solution makes devolatilization difficult; and 3. α-olefins are subject to isomerization during the polymerization process. For example, patent US 11192969 B2 discloses a method for reducing α-olefin isomerization during polyolefin solution polymerization. Separating the α-olefin from the isomerized olefin is energy-intensive.

[0004] Currently, α-olefins are primarily produced through ethylene oligomerization. This process is simple but produces numerous byproducts, resulting in high energy consumption and poor economic efficiency. Fischer-Tropsch light distillate oils contain significant amounts of α-olefins, typically 40% to 60%. Patent CN 115011376A discloses a method for separating α-olefins from Fischer-Tropsch light distillate oils using a coupled adsorption distillation separation process. This separation of Fischer-Tropsch light distillate oils into α-olefins of varying carbon numbers is accomplished through four steps: fractionation cutting, adsorption deoxygenation, adsorption distillation, and deep distillation. Patent CN114395416A discloses a method for producing polymerization-grade, high-purity long-chain α-olefins using a coupled adsorption separation and internal olefin disproportionation reaction. First, a mixture of long-chain alkanes and olefins is separated using adsorption separation technology. Internal olefin disproportionation is then used to convert the internal olefins into α-olefins. Further deep distillation is performed to obtain α-olefins of varying carbon numbers.

[0005] As can be seen, the current α-olefin production process is long and expensive, which in turn affects the production cost of polyolefin elastomers. Furthermore, the growing demand for high-end polyolefin materials with excellent performance necessitates the development of new products, such as multi-component copolymers of ethylene and two or more α-olefins. The solution polymerization process for multi-component copolymerization introduces multiple α-olefins and their corresponding internal olefin impurities, making the process longer and more complex, and improving economic efficiency is a major challenge. By combining the compositional distribution characteristics of the mixed α-olefins in Fischer-Tropsch synthetic oils with a coupled process for polyolefin solution polymerization, the goal of reducing production costs and developing new products can be achieved through system integration.

[0006] There is currently no polyolefin process technology for mixed alpha-olefins using Fischer-Tropsch oils. Summary of the Invention

[0007] In order to solve the problems in the prior art, the present invention proposes a method for producing polyolefins using mixed α-olefins separated from Fischer-Tropsch synthetic oil.

[0008] In the present invention, α-olefin refers to a monoolefin with a double bond at the end of the molecular chain, such as 1-butene, 1-hexene, and 1-octene.

[0009] A polymer is a macromolecule composed of multiple monomers linked together by covalent chemical bonds, such as a copolymer of ethylene and a C3 to C12 alpha-olefin monomer.

[0010] A multipolymer is a polymer containing at least three monomers.

[0011] The technical solutions of the present invention are as follows:

[0012] The present invention first provides a method for producing polyolefins using mixed α-olefins separated from Fischer-Tropsch oil, which comprises the following steps:

[0013] a) feeding a catalyst, ethylene, a solvent and a mixed α-olefin into a reactor, causing a polymerization reaction in the reactor, and discharging a multi-component copolymer solution; the mixed α-olefin comprises at least two α-olefins, and the mixed α-olefin is obtained from an α-olefin crude separation unit of a Fischer-Tropsch synthesis oil section;

[0014] b) feeding the polymer solution to a devolatilization unit to obtain a multi-component copolymer and a mixed stream comprising unreacted ethylene, unreacted α-olefin, solvent and impurities;

[0015] c) The mixed stream is passed through a primary separation unit to obtain recycled ethylene, recycled solvent, recycled α-olefins, oligomers, and tail gas; the recycled ethylene, recycled solvent, and a portion of the recycled α-olefins are transported back to the reactor of step a); and the remaining portion of the recycled α-olefins is transported to an α-olefin fine separation unit to obtain α-olefins of different carbon numbers and internal olefins.

[0016] According to a preferred embodiment of the present invention, the α-olefin separation unit in step c) can be the α-olefin separation unit of the Fischer-Tropsch synthesis oil section or the α-olefin separation unit of the polymerization section; the α-olefin separation unit separates α-olefins of different carbon numbers, and the α-olefins of different carbon numbers can be used to adjust the mass concentration of α-olefins of different carbon numbers in the mixed α-olefins of step a). For example, when it is necessary to increase the mass concentration of α-olefins of a certain carbon number in the mixed α-olefins, the α-olefin of that carbon number separated by the α-olefin separation unit can be added to the mixed α-olefins.

[0017] It should be noted that the α-olefin crude separation unit of the Fischer-Tropsch synthesis oil section of the present invention is used to obtain mixed α-olefins of a desired carbon number range. Typically, but not limited to, it can be used to obtain mixed α-olefins of C5 to C7, mixed α-olefins of C6 to C8, or mixed α-olefins of C7 to C9. Preferably, the concentration of any single carbon number α-olefin in the obtained mixed α-olefins is no more than 80 wt%.

[0018] According to a preferred embodiment of the present invention, the separation unit in step c) is a primary separation unit of the polymerization section, and does not include an α-olefin fine separation device capable of separating α-olefins of different carbon numbers, nor does it include an α-olefin fine separation device capable of separating α-olefins and internal olefins of the same carbon number.

[0019] According to a preferred embodiment of the present invention, no more than 50% by mass flow of the recycled α-olefins obtained from the separation unit in step c) is transferred to the α-olefin fine separation unit, preferably no more than 30% by mass flow.

[0020] According to a preferred embodiment of the present invention, the Fischer-Tropsch synthetic oil section includes at least a deoxygenation unit, an alkane-olefin separation unit, an internal olefin disproportionation unit and an α-olefin crude separation unit; wherein the deoxygenation unit is used to remove oxides in the Fischer-Tropsch synthetic oil; the alkane-olefin separation unit is used to separate and obtain mixed alkanes and mixed olefins; the internal olefin disproportionation unit obtains mixed olefins and converts part of the internal olefins into α-olefins under the action of ethylene and a catalyst; and the α-olefin crude separation unit obtains mixed α-olefins in the required carbon number range.

[0021] Furthermore, the Fischer-Tropsch synthesis oil section may also include an alkane separation unit, which obtains a mixed alkane stream and separates it into alkanes with different carbon numbers. Furthermore, the Fischer-Tropsch synthesis oil section may also include an α-olefin fine separation unit, which obtains the mixed α-olefins from the α-olefin crude separation unit and / or the mixed α-olefins from the separation unit in step c) and refines them to obtain α-olefins with different carbon numbers.

[0022] According to a preferred embodiment of the present invention, the mixed α-olefins contain C5 to C7 α-olefins, and the total mass fraction of C5 to C7 α-olefins is not less than 80%, preferably not less than 90%; the total weight content of C5 to C7 α-olefins in the multipolymer is 5-60%, preferably 10-45%.

[0023] According to another preferred embodiment of the present invention, the mixed α-olefins contain C6 to C8 α-olefins, and the total mass fraction of C6 to C8 α-olefins is not less than 80%, preferably not less than 90%; the total weight content of C6 to C8 α-olefins in the multipolymer is 5-60%, preferably 10-45%.

[0024] According to another preferred embodiment of the present invention, the mixed α-olefins contain C7 to C9 α-olefins, and the total mass fraction of C7 to C9 α-olefins is not less than 80%, preferably not less than 90%; the total weight content of C7 to C9 α-olefins in the multipolymer is 5-60%, preferably 10-45%.

[0025] According to a preferred embodiment of the present invention, the mass fraction of the polymer in the polymer solution in the reactor is 5 to 30%, preferably 10 to 20%.

[0026] According to a preferred embodiment of the present invention, the polymerization reaction is operated at a temperature in the range of 80-180° C. and a pressure in the range of 30-200 bar.

[0027] Compared with the prior art, the method of the present invention has the following beneficial effects: the method of the present invention is based on the composition characteristics of the mixed α-olefins of the Fischer-Tropsch synthetic oil, and invents a solution polymerization process for multi-component copolymerization using the mixed α-olefins that have undergone coarse separation as comonomers, and combines the deep distillation unit of the mixed α-olefins to complete separation and purification, which can reduce the overall energy consumption, improve the economic benefits of the process, and obtain new products with different performances.

[0028] In the present invention, the mixed α-olefins of the crudely separated Fischer-Tropsch synthetic oil are transported to the polymerization reaction unit as comonomers, and under the action of a catalyst, polymerization reaction occurs with ethylene to generate a multi-component copolymerized polyolefin. Subsequently, the polymer solution passes through a devolatilization unit to obtain a polymer and unreacted ethylene and α-olefin monomers and some impurities. The polymer is further subjected to steps such as granulation to obtain a final product, which is then passed through a separation unit to obtain reusable ethylene, α-olefin monomers and impurity components to be removed. As known in the art, the polymerization reactor in the solution polymerization process is a single liquid phase, that is, at a certain temperature and pressure, monomers, comonomers, catalysts, polymers, and other hydrocarbon inert impurity components introduced by monomers and comonomers are dissolved in the solvent and flow out of the reactor in the form of a polymer solution to enter a downstream separation and recovery unit. As known in the art, in order to realize the high value utilization of α-olefins in Fischer-Tropsch synthetic oil, it is often necessary to separate high-purity α-olefins, such as polymer-grade α-olefins, from the Fischer-Tropsch synthetic oil, and such a process flow is complicated and requires separation of components such as oxides, alkanes, and internal olefins in the Fischer-Tropsch synthetic oil. It is known in the art that the separation process is a high energy consumption process. For the solution polymerization process of ethylene and α-olefins, reducing the materials entering the separation process is beneficial to reducing energy consumption. However, directly reusing excess materials without separation is not conducive to the removal of inert impurity components. For the high value utilization of α-olefins in Fischer-Tropsch synthetic oil, if α-olefins can be utilized without fine separation, the cost can be reduced. The present method realizes the "low-cost" high value utilization of Fischer-Tropsch synthetic oil by utilizing the demand of the polymerization unit of the polyolefin solution method for mixed α-olefins, and cleverly integrates the separation unit of the Fischer-Tropsch synthetic oil mixed α-olefins and the separation unit of the polyolefin solution method, thereby improving the economy of the process technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The method of the present invention is a multi-component copolymerization polyolefin solution process using crude separation of Fischer-Tropsch synthetic oil and mixed α-olefins as comonomers.

[0030] Figure 2 The invention does not use an integrated method, but uses a solution process for producing α-olefins using Fischer-Tropsch synthetic oil alone and for producing polyolefins using a copolymerization of α-olefin and ethylene.

[0031] Figure 3 Material balance diagram of Example 1.

[0032] Figure 4 Material balance illustration of Comparative Example 1. DETAILED DESCRIPTION

[0033] The present invention will be further described and illustrated below in conjunction with specific embodiments. The embodiments are merely illustrative of the present disclosure and do not limit its scope. The technical features of the various embodiments of the present invention may be combined accordingly, provided that there is no conflict between them.

[0034] like Figure 1 As shown, the embodiment of the present invention provides a solution polymerization method for crude separation of mixed α-olefins using Fischer-Tropsch oil. The unit operations used in this method mainly include the polymerization unit, devolatilization unit, and primary separation unit of the polymerization section, as well as the deoxygenation unit, alkane-olefin separation unit, internal olefin disproportionation unit, α-olefin crude separation unit, and α-olefin fine separation unit of the Fischer-Tropsch oil section. It should be noted that Figure 1 While the α-olefin separation unit is included in the FT-TO process in the process flow diagram, this is not the only implementation method. In fact, the polymerization process can also include an α-olefin separation unit while the FT-TO process does not, or both the polymerization process and the FT-TO process can include α-olefin separation units.

[0035] exist Figure 1 In the process, ethylene monomer, solvent, catalyst and mixed α-olefins obtained from the α-olefin crude separation unit of the Fischer-Tropsch synthesis oil section are transported to the polymerization unit to obtain a polymer solution, and the polymer solution is transported to the devolatilization unit; a polymer and a mixed stream containing unreacted ethylene, unreacted α-olefins, solvent, internal olefins and oligomers are obtained from the devolatilization unit; the mixed stream obtains recycled ethylene, recycled solvent and recycled α-olefins in the separation unit, and part of the oligomers are removed and part of the tail gas is discharged; the recycled ethylene, recycled solvent and part of the recycled α-olefins are transported back to the polymerization unit, and the remaining part of the recycled α-olefins is transported to the α-olefin fine separation unit of the Fischer-Tropsch synthesis oil section. In the Fischer-Tropsch synthetic oil section, the obtained Fischer-Tropsch synthetic oil is transported to the deoxygenation unit to remove oxides; then, it is transported to the alkane-olefin separation unit to obtain mixed alkanes and mixed olefins; the mixed alkanes enter the alkane separation unit for further separation to obtain alkanes with different carbon numbers; the mixed olefins enter the internal olefin disproportionation unit, and under the action of ethylene and a catalyst, part of the internal olefins are converted into α-olefins; then, the mixed olefins enter the α-olefin crude separation unit to obtain mixed α-olefins with the required carbon number. In this embodiment, part of the mixed α-olefins is transported to the polymerization section to participate in the polymerization reaction, and the remaining part enters the α-olefin fine separation unit for further refinement to obtain α-olefins with different carbon numbers; the high-purity α-olefins obtained in the fine separation unit can be used to adjust the composition of the mixed α-olefins entering the polymerization section.

[0036] The present invention provides a method for polymer solution polymerization. Solution polymerization is a well-known method, one of the characteristics of which is that the monomer, comonomer, solvent, catalyst, and polymer obtained by polymerization are a single liquid phase in the reactor. Patents CN103880999 B, CN 101472951 B, and CN 107074995 B all disclose such methods. The solution polymerization method of the present invention is characterized in that the comonomer contains no less than two α-olefins, and the α-olefins are derived from a mixed α-olefin of Fischer-Tropsch synthetic oil. The α-olefin is represented by the formula CH2=CHA, wherein A is a straight-chain hydrocarbon group having 2-10 carbon atoms.

[0037] Polymerization unit includes polymerization reactor, and reactor feed mainly includes ethylene monomer, alpha-olefin comonomer, solvent, catalyst, co-catalyst and hydrogen.As known in the art, ethylene and alpha-olefin polymerization reaction need to be carried out under catalyst action, and catalyst can be one or more of metallocene catalyst, late transition metal catalyst, Ziegler-Natta catalyst, non-metallocene catalyst, FI catalyst known in the art, and co-catalyst can be one or more of methylaluminoxane MAO, modified methylaluminoxane MMAO, ethylaluminoxane EAO, tris (2,4,6-trifluorophenyl) borane.As known in the art, solvent needs to be inert to catalyst system and reactant, and keeps stable during the reaction, and solution polymerization needs a large amount of solvent, maintains ethylene monomer, alpha-olefin comonomer, catalyst, molecular weight regulator and polymer product in reactor in single phase.Pentane, hexane, cyclohexane, heptane, Isopar E are solvents known in the art. As is known in the art, the α-olefin comonomer can be a C3 to C12 α-olefin. α-olefins refer to monoolefins with double bonds at the ends of the molecular chain, such as 1-butene, 1-hexene, and 1-octene. As is known in the art, the addition of a small amount of a substance with a large chain transfer constant can reduce the molecular weight of the polymer. Various suitable chain transfer agents exist, with hydrogen being a common example.

[0038] As is known in the art, solution polymerization reaction temperatures typically range from 80°C to 180°C, and reaction pressures range from 30 to 200 bar. The reactor can be adiabatic, tubular, or loop reactors, or non-adiabatic. After leaving the reactor, the polymer solution enters a devolatilization unit to remove volatile components. Patent CN109563187B describes a method for preheating the polymer solution using a spiral heat exchanger to achieve better devolatilization.

[0039] As is known in the art, a polymer solution devolatilization unit typically comprises a multi-stage devolatilization process. Patent CN114437253A discloses a polymer solution devolatilization method and apparatus comprising first and second flash tanks. Flash separation achieves phase separation by pressure reduction. The vapor stream from the overhead flash tank is conveyed to a heat recovery unit, where it is fully or partially condensed and then conveyed to a recovery unit. The liquid stream from the bottom flash tank is conveyed to the next stage of devolatilization. Unreacted ethylene, α-olefins, and solvent obtained from the devolatilization unit enter a separation unit, where components such as non-condensable tail gas, oligomers, and internal olefins are separated to produce recycled ethylene, solvent, and α-olefins. The separation process in the separation unit typically utilizes a fractionator, i.e., a distillation column, to separate the components based on their boiling point differences. Patent CN108602900B discloses conveying a first vapor stream from the first separator to a first fractionator, and obtaining an overhead stream from the first fractionator as a first recycle stream back to the polymerization reactor.

[0040] As is known in the art, Fischer-Tropsch oil is a hydrocarbon mixture obtained by Fischer-Tropsch synthesis of synthesis gas. Industrial Fischer-Tropsch oil technology primarily utilizes two processes: fluidized bed high-temperature synthesis and fixed bed low-temperature synthesis. The primary difference between the two processes is their product distribution. Low-temperature Fischer-Tropsch oil primarily consists of α-olefins, normal alkanes, and oxygenates such as alcohols and ketones. In low-temperature synthetic Fischer-Tropsch oil, the mass fraction of α-olefins is typically 40-60%, and the mass fraction of oxides is 3-10%. Separating α-olefins from Fischer-Tropsch oil typically requires sequential deoxidation and alkene separation. For example, patent CN111100683 A uses a pre-adsorption tower to separate oxides. The active component of the adsorbent is activated carbon, silica gel, resin, or a silicate adsorbent. The pre-adsorption tower simulates a moving bed adsorption separation process. The deoxidized material is then fed into a simulated moving bed adsorption separation system filled with an alkane-olefin separation adsorbent, which selectively separates α-olefins from alkanes. The active component of the alkane-olefin separation adsorbent is 13X zeolite, LTA zeolite, or a composite crystal of the two zeolite molecular sieves. Alkane-olefin adsorption separation is a countercurrent simulated moving bed adsorption separation process. The desorbent used is an alkane, an alkene, or a mixture of alkanes and alkenes. The adsorption separation temperature is 60-150°C, and the purity of the separated α-olefins is greater than 95%. Patent CN115011376A uses adsorption distillation technology to precisely separate alkanes and olefins from the deoxygenated C4-C10 distillate oil, obtaining high-purity α-olefins with a purity of up to 99.5%.

[0041] Example 1

[0042] The material balance was carried out as described. Figure 3As shown, the α-olefins obtained from the Fischer-Tropsch synthesis oil unit are subjected to coarse separation to obtain a mixed α-olefin stream containing C6 to C8, which is then transported to the polymerization unit. The following also enter the polymerization unit: recycled α-olefins, finely separated α-olefins, recycled ethylene, recycled solvent, fresh ethylene, catalyst, hydrogen, and make-up solvent; the reactor adopts a single adiabatic autoclave reactor with a stirring component, a reaction pressure of 70 bar, and a residence time of 10 min; CGC is used as the main catalyst, MAO as the co-catalyst, and hydrogen as the molecular weight regulator; the reactor inlet and outlet temperatures are -15 and 148.5°C, respectively; the polymerization conditions (composition at the reactor outlet) are as follows: Figure 3 As shown, the ethylene concentration is 6wt.%, the 1-hexene concentration is 10wt.%, the 1-heptene concentration is 11wt.%, and the 1-octene concentration is 13wt.%; the separation system adopts a three-stage flash evaporation method, the first stage is a medium-pressure flash evaporation, the flash tank is set at 16bar, and the polymer solution is heated to 200°C by a solution preheater before entering the first-stage flash evaporation; the second stage is a low-pressure flash evaporation, the flash tank is set at 3bar, and the separation temperature is 190°C; the third stage is also a low-pressure flash evaporation, the flash tank is set at 1bar, and the separation temperature is 190°C; the devolatilization unit obtains polymer and recovery stream, and the recovery stream enters the separation unit to remove impurities and non-condensable gas tail gas; the internal olefins contained in the olefin feedstock (mainly 2-hexene , 2-heptene, 2-octene), so this case is simplified to include only one internal olefin, and this method is also applicable to the case of multiple internal olefins) does not participate in the polymer and needs to be removed by separation; it is known in the art that in order to reduce the loss of α-olefins, isomers are usually separated at the cost of higher energy consumption; in Example 1, the recovered streams successively obtain recycled ethylene and recycled solvents, and the oligomers are removed by a deweighting tower (distillation tower); the recovered mixed α-olefins obtained need to remove part of the internal olefins, and 85% of the mass flow of the recovered stream is directly recycled, and the other 15% enters the α-olefin fine separation unit of the Fischer-Tropsch synthetic oil, and part of the stream is obtained from the fine separation unit and circulated to the polymerization unit to adjust the feed composition of the polymerization unit. Part of the information of Example 1 is summarized in Table 1.

[0043] Comparative Example 1

[0044] Comparative Example 1 and Example 1 use the same catalyst, the same polymerization unit operation (same reactor conditions, same output and product) and the same Fischer-Tropsch synthetic oil. The main difference is that Comparative Example 1 is as follows: Figure 2 As shown, the polymerization process ( Figure 2 Part a) and Fischer-Tropsch oil separation section ( Figure 2 The processes in part b) are independent of each other. The Fischer-Tropsch synthetic oil is subjected to coarse separation and fine separation to obtain high-purity α-olefins. The α-olefins used in the polymerization stage are three high-purity α-olefins rather than the mixed α-olefins without fine separation used in the present invention. The material balance of Comparative Example 1 is as follows: Figure 4 As shown, Figure 4 and Figure 3 The main differences in the polymerization section are: Figure 4 In (Comparative Example 1), the mixed α-olefin part obtained from the recovery unit needs to be passed through the α-olefin fine separation unit to separate the internal olefins, while Figure 3 In (Example 1), the separation task is completed by the Fischer-Tropsch synthetic oil device. Part of the information of Example 1 and Comparative Example 1 is summarized in Table 1. It can be seen that Example 1 can reduce the flow rate of mixed α-olefins that need to be finely separated by integrating the α-olefin separation unit of the Fischer-Tropsch synthetic oil section and the separation unit of the polymerization section, which is of great significance for reducing energy consumption and improving economic efficiency. In Example 1, since the mixed α-olefins obtained by the crude separation of the Fischer-Tropsch synthetic oil are directly used for polymerization, the flow rate transported to the α-olefin fine separation unit is only 35.943 kg / h; in Comparative Example 1, the flow stream that needs to be finely separated by α-olefins reaches 84.732 kg / h, including the operation of fine separation of mixed α-olefins in the Fischer-Tropsch synthetic oil section to obtain high-purity α-olefins, and also includes the operation of separating mixed α-olefins in the polymerization section to separate internal olefins.

[0045] Example 2

[0046] Example 2 used the same method as Example 1, except that the α-olefins obtained from the Fischer-Tropsch synthesis oil unit were crudely separated to obtain a mixed α-olefin stream containing C5-C7 (12 kg / h 1-pentene, 0.060 kg / h 2-pentene, 15 kg / h 1-hexene, 0.075 kg / h 2-hexene, 14 kg / h 1-heptene, and 0.070 kg / h 2-heptene). This stream was then fed to a polymerization unit for polymerization under octane solvent. Partial information from Example 2 is summarized in Table 1.

[0047] Comparative Example 2

[0048] Comparative Example 2 and Example 2 use the same catalyst, the same polymerization unit operation (same reactor conditions, same output and product) and the same Fischer-Tropsch synthetic oil. The main difference is that Comparative Example 2 is as follows: Figure 2As shown, the polymerization process and the Fischer-Tropsch oil separation process are independent of each other. The Fischer-Tropsch oil is subjected to coarse separation and fine separation to obtain high-purity α-olefins. The α-olefins used in the polymerization process are three high-purity α-olefins rather than mixed α-olefins obtained by initial separation. Partial information of Example 2 and Comparative Example 2 is summarized in Table 1. It can be seen that Example 2 can reduce the flow rate of mixed α-olefins that require fine separation by integrating the α-olefin separation unit of the Fischer-Tropsch oil section and the separation unit of the polymerization section, which is of great significance for reducing energy consumption and improving economic efficiency. In Example 2, because the mixed α-olefins obtained from the coarse separation of the Fischer-Tropsch oil are directly used for polymerization, the flow rate transported to the α-olefin fine separation unit is only 35.053 kg / h; in Comparative Example 1, the flow stream that requires fine separation of α-olefins reaches 76.304 kg / h, including the operation of fine separation of mixed α-olefins in the Fischer-Tropsch oil section to obtain high-purity α-olefins, and also the operation of separating mixed α-olefins in the polymerization section to separate internal olefins.

[0049] Table 1 Summary of Examples and Comparative Examples

[0050]

[0051]

[0052] In summary, the present invention utilizes the composition characteristics of mixed α-olefins of Fischer-Tropsch synthetic oil and the demand for different α-olefins in olefin multipolymerization, and proposes a solution process for producing multipolymer polyolefins using mixed α-olefins obtained by crude separation of Fischer-Tropsch synthetic oil. This process can simplify the separation process of α-olefins, reduce energy consumption, and improve economic efficiency.

[0053] The above-described embodiments merely illustrate several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. Persons skilled in the art will readily appreciate that variations and modifications may be made without departing from the scope of the present invention, all of which fall within the scope of protection of the present invention.

Claims

1. A method for producing polyolefins using mixed α-olefins obtained by separation of Fischer-Tropsch synthetic oil, characterized in that The steps include: a) feeding a catalyst, ethylene, a solvent and mixed α-olefins into a reactor, causing a polymerization reaction in the reactor, and discharging a multi-component copolymer solution; the mixed α-olefins include at least two α-olefins, and the mixed α-olefins are obtained from an α-olefin crude separation unit of a Fischer-Tropsch synthesis oil section; b) feeding the polymer solution to a devolatilization unit to obtain a multi-component copolymer and a mixed stream comprising unreacted ethylene, unreacted α-olefin, solvent and impurities; c) The mixed stream passes through the primary separation unit of the polymerization section to obtain recycled ethylene, recycled solvent, recycled α-olefins, oligomers and tail gas; the primary separation unit of the polymerization section does not include α-olefin fine separation equipment that can separate α-olefins with different carbon numbers, nor does it include α-olefin fine separation equipment that can separate α-olefins with the same carbon number and internal olefins; the recycled ethylene, recycled solvent and part of the recycled α-olefins are transported back to the reactor of step a); the remaining part of the recycled α-olefins is transported to the α-olefin fine separation unit of the Fischer-Tropsch synthesis oil section to obtain α-olefins with different carbon numbers and internal olefins.

2. The polyolefin production method according to claim 1, characterized in that In step c), the α-olefin separation unit separates α-olefins of different carbon numbers, and the α-olefins of different carbon numbers are used to adjust the mass concentration of the α-olefins of different carbon numbers in the mixed α-olefins of step a).

3. The polyolefin production method according to claim 1, characterized in that No more than 50% by mass flow of the recycled α-olefins obtained from the separation unit in step c) is sent to the α-olefin fine separation unit.

4. The polyolefin production method according to claim 1, characterized in that The Fischer-Tropsch synthetic oil section at least includes a deoxygenation unit, an alkane-olefin separation unit, an internal olefin disproportionation unit and an α-olefin crude separation unit; wherein the deoxygenation unit is used to remove oxides in the Fischer-Tropsch synthetic oil; the alkane-olefin separation unit is used to separate and obtain mixed alkanes and mixed olefins; the internal olefin disproportionation unit obtains mixed olefins and converts part of the internal olefins into α-olefins under the action of ethylene and a catalyst; and the α-olefin crude separation unit obtains mixed α-olefins in the required carbon number range.

5. The polyolefin production method according to claim 1, characterized in that The mixed α-olefins contain C5-C7 α-olefins, and the total mass fraction of C5-C7 α-olefins is not less than 80%; the total weight content of C5-C7 α-olefins in the multi-polymer is 5-60%.

6. The polyolefin production method according to claim 1, characterized in that The mixed α-olefins contain C6-C8 α-olefins, and the total mass fraction of C6-C8 α-olefins is not less than 80%; the total weight content of C6-C8 α-olefins in the multi-polymer is 5-60%.

7. The polyolefin production method according to claim 1, characterized in that The mixed α-olefins contain C7-C9 α-olefins, and the total mass fraction of C7-C9 α-olefins is not less than 80%; the total weight content of C7-C9 α-olefins in the multi-polymer is 5-60%.

8. The polyolefin production method according to claim 1, characterized in that The mass fraction of the polymer in the polymer solution discharged from the reactor is 5-30%.

9. The polyolefin production method according to claim 1, characterized in that The polymerization reaction is operated at a temperature in the range of 80-180°C and a pressure in the range of 30-200 bar.

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