A method for preparing linear α-olefins by ethylene oligomerization

Abstract

This invention relates to a method for preparing linear α-olefins via ethylene oligomerization. The invention also relates to a method for preparing a catalyst, wherein the method includes the following steps: 1) providing a molecular sieve, adding an active metal promoter to the molecular sieve, and shaping it into a molded body; 2) placing the molded body in a fixed-bed reactor; 3) dissolving a transition metal salt in a first valence state and a bidentate ligand in a solvent to prepare a solution; 4) passing the solution and ethylene through the fixed-bed reactor containing the molded body, thereby loading the transition metal onto the molecular sieve via ion exchange, while the transition metal in the first valence state is reduced by the active metal promoter to a transition metal salt in a second valence state, wherein the second valence state is lower than the first valence state, thus obtaining a catalyst. This invention also relates to a method for ethylene oligomerization using the catalyst.

Description

Technical Field

[0001] This invention relates to a method for preparing linear α-olefins by ethylene oligomerization, specifically, to a method for preparing linear α-olefins by ethylene oligomerization using a supported transition metal ligand catalyst. Background Technology

[0002] Linear α-olefins are straight-chain olefins containing a double bond at the molecule's end, and are important raw materials for the production of various fine chemical products. Linear α-olefins are important monomers for the preparation of low-density polyethylene and high-density polyethylene; they are raw materials for the synthesis of high-grade lubricating oils, high-grade surfactants, and higher alcohols; and they are raw materials for the production of various oil displacement agents and oil additives. In recent years, with the continuous development of the polyolefin industry, the demand for linear α-olefins has grown rapidly. Ethylene oligomerization is the main method for preparing linear α-olefins.

[0003] Currently, there are many industrialized technologies for the production of α-olefin oligomerization. These include the earliest developed one-step technology from Chevron Phillips Chemical Co., Ltd. (CPChem) in the United States, using triethylaluminum as a catalyst; the two-step technology improved by BP in the United Kingdom based on the one-step method; the Shop technology from Shell in the Netherlands, using nickel complexes as catalysts; the Idemitsu technology from Idemitsu Kosan Co., Ltd. in Japan, using zirconium complexes as catalysts; the Linear-1 technology developed by UOP and Union Carbide in the United States, using nickel complexes coordinated with special ligands as catalysts; the α-Sablin technology from Sabic in Saudi Arabia, using zirconium-aluminum bicomponents as catalysts; and the C4-C600 technology from the French Petroleum Institute (IFP), which can produce α-olefin oligomers. 10 AlphaSelect technology for α-olefins and Versipol technology from DuPont in the United States, which uses pyridine diimide iron-based complexes as the main catalyst, are examples of this technology. Currently, the world's production capacity for α-olefins via oligomerization is dominated by the early-developed one-step, two-step, and Shop technologies, which account for over 74% of the total capacity. The Shop technology utilizes isomerization and cross-displacement reactions to convert all ethylene feedstock into the linear α-olefins needed by the market, offering advantages such as low emissions, low pollution, mild operating conditions, and safe operation.

[0004] Shell has reported methods for preparing linear α-olefins via ethylene oligomerization in US patents US4020121, US4472522, and US4503279. These methods utilize a homogeneous catalyst with nickel as the active component, diphenylphosphine benzoate as the ligand, and 1,4-butanediol as the solvent. Sodium borohydride is used as a reducing agent to reduce the active nickel ions. The method employs a continuous reaction. The solvent is reused through distillation regeneration. Residual catalyst is removed from the product by regenerating the solvent and washing with water, thereby inhibiting further polymerization of the olefins, ensuring product quality, and preventing blockages in the production process due to polymer formation.

[0005] UOP Corporation reported a method for producing linear α-olefins by eliminating wax deposition in US Patent 5523508. This method uses transition metal nickel as the catalytic active, diphenyl(2-naphthyl-1-sulfonic acid)phosphine as the ligand, and sodium borohydride as the activator. In this method, a portion of the lighter component of the product, such as C... 12 -C 18 Or C 12 -C 16 The α-olefin is returned to the reaction system, and this component can fully dissolve the heavier product components, thereby avoiding blockage caused by wax deposition.

[0006] Chevron Corporation reported a nickel ylide phosphine catalyst in US patents US4686315 and US4711969. This catalyst, which incorporates a certain amount of alkoxyaluminum during oligomerization, exhibits high reactivity but suffers from difficulty in separating the product from the catalyst and low product selectivity.

[0007] Chinese patent application CN1126107A discloses a catalyst for the oligomerization of ethylene to prepare α-olefins. This invention relates to a novel bimetallic coordination catalyst for the oligomerization of ethylene to prepare α-olefins. The catalyst consists of a divalent nickel compound, zinc metal or a monovalent zinc compound thereof, and a water-soluble bidentate organophosphorus ligand containing P and O.

[0008] Nesterov et al. 【1】 Extensive work has been conducted on the solid-state development of nickel complex catalysts. This work first involves loading tertiary phosphine onto silica gel or alumina. The reaction is as follows:

[0009] (E-OH)2+(EtO)2Si-C2H4-PPh2→(EO-) n Si(OEt) 3-n -C2H4-PPh2+nEtOH n=1,2; E=Si,Al

[0010] The supported silica gel contains 0.25% phosphorus (P), and the alumina contains 0.36% P. The supported silica gel or alumina reacts with Ni(COD)₂ and O=C(Ph)-CH=PPh₃:

[0011]

[0012] Test results for this supported solid-phase catalyst show that, under the same reaction conditions, it can achieve or even exceed the activity of the homogeneous catalyst. However, its selectivity for α-olefins is poor, at only about 92%.

[0013] Marcell Peuckert and Wilhelm Keim [2] A heterogeneous catalyst for the oligomerization of ethylene to linear α-olefins was prepared using polystyrene resin as a solid support and loaded with active nickel. Under reaction conditions of 50-75℃ and 4.0 MPa, a product with a linear α-olefin content of 99% was obtained.

[0014] The current industrial-scale processes for preparing α-olefins by ethylene oligomerization are all homogeneous reaction processes. They all suffer from high heat release during production, which affects product yield and makes product separation difficult. They also require sodium borohydride or aluminum alkoxy as co-catalysts, which reduces the selectivity of the reaction and increases production costs.

[0015] References:

[0016] [1]Nesterov GA,Fink G,Heterogenization of a Homogeneous NickelChelate Ethylene Oligomerization Catalyst,JMol Catal,1991,66:367-372

[0017] [2]Marcell Peuckert and Wilhelm Keim, Journal of Molecular Catalyst, 22 (1984) 289-295 Summary of the Invention

[0018] This section provides a general overview of this disclosure and is not a full disclosure of its entire scope or all of its features.

[0019] Other applicable areas will become apparent from the description provided herein. The descriptions and specific examples in this section are intended to be illustrative only and are not intended to limit the scope of this disclosure.

[0020] The objective of this invention is to propose a novel method for preparing catalysts, wherein the catalysts prepared by this method can be successfully used for the oligomerization of ethylene to prepare linear α-olefins, thereby overcoming some or even all of the aforementioned defects of the prior art.

[0021] According to one aspect of the present invention, a method for preparing a catalyst is provided, wherein the method comprises the following steps:

[0022] 1) Provide molecular sieves, add active metal additives to the molecular sieves, and shape them into a molded body.

[0023] 2) Place the molded body in a fixed-bed reactor.

[0024] 3) Dissolve the transition metal salt in its first valence state and the bidentate ligand in an organic solvent to prepare a solution.

[0025] 4) The solution and ethylene are passed through a fixed-bed reactor loaded with a molded body. Transition metals are loaded onto the molecular sieve through ion exchange, while the transition metals in the first valence state are reduced to the second valence state by an active metal promoter. The second valence state is lower than the first valence state, thus obtaining a catalyst.

[0026] According to one aspect of the present invention, a method for preparing linear α-olefins by ethylene oligomerization using the above-described catalyst is provided.

[0027] Surprisingly, the method according to the invention enables the simple preparation of heterogeneous catalysts, which are advantageously suited for industrial-scale processes of ethylene oligomerization to α-olefins, resulting in favorable thermal diffusion and efficient separation of the catalyst from the product. The catalyst preparation process, as well as the subsequent oligomerization process, eliminates the need for expensive and, in some cases, hazardous co-catalysts such as sodium borohydride or aluminum alkoxy, and also avoids the cumbersome post-treatment of co-catalysts. Furthermore, the heterogeneous catalyst exhibits comparable or even higher catalytic activity and linear α-olefin selectivity than homogeneous catalysts. Attached Figure Description

[0028] Figure 1 A gas chromatogram of a typical product according to the present invention is shown. Detailed Implementation

[0029] In the context of this disclosure, the disclosure of a range includes all values ​​across the entire range and the disclosure of further subdivisions of the range, including the endpoints and subranges given for these ranges.

[0030] This invention relates to the following aspects:

[0031] 1. A method for preparing a catalyst, wherein the method comprises the following steps:

[0032] 1) Provide molecular sieves, add active metal additives to the molecular sieves, and shape them into a molded body.

[0033] 2) Place the molded body in a fixed-bed reactor.

[0034] 3) Dissolve the transition metal salt in its first valence state and the bidentate ligand in a solvent to prepare a solution.

[0035] 4) The solution and ethylene are passed through a fixed-bed reactor loaded with a molded body. Transition metals are loaded onto the molecular sieve by ion exchange, while the transition metals in the first valence state are at least partially reduced to transition metal salts in the second valence state by an active metal promoter, wherein the second valence state is lower than the first valence state, thus obtaining a catalyst.

[0036] 2. According to the method of aspect 1, the fixed-bed reactor is preferably of the tubular type.

[0037] 3. According to any of the foregoing methods, the fixed-bed reactor is preferably a jacketed heat exchanger.

[0038] 4. According to any of the preceding methods, the transition metal salt is selected from nickel chloride, nickel bromide, nickel iodide, nickel nitrate, nickel carbonate, and nickel chlorate, preferably nickel chloride.

[0039] 5. The method according to any of the foregoing aspects, wherein the bidentate ligand is an organophosphorus ligand selected from diphenylphosphonic acid, sodium diphenylphosphonate, diphenylphosphonic acid, sodium diphenylphosphonic acid, diphenylphosphonic acid, and sodium diphenylphosphonate, preferably sodium diphenylphosphonate.

[0040] 6. The method according to any of the foregoing aspects, wherein the organic solvent is selected from cyclopentane, cyclohexane, isooctane, decane, benzene, toluene, ethylbenzene, methanol, ethanol, n-propanol, n-butanol, octanol, dodecyl alcohol, ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, preferably 1,4-butanediol and 2,5-hexanediol, more preferably 1,4-butanediol.

[0041] 7. The method according to any of the foregoing aspects, wherein the molar ratio of metallic nickel to ligand is 0.5-10, preferably 1-3, and most preferably 2.

[0042] 8. In any of the preceding methods, the temperature for ion exchange is 10-50°C, preferably 20-40°C, and most preferably 30°C.

[0043] 9. The method according to any of the foregoing aspects, wherein the partial pressure of ethylene during ion exchange is 0.5-5 MPa, preferably 2-4 MPa, and most preferably 3 MPa.

[0044] 10. In any of the preceding methods, the ion exchange is carried out for a period of 1-20 hours, preferably 5-10 hours, and most preferably 8 hours.

[0045] 11. According to any of the preceding methods, wherein the molecular sieve is selected from X, Y, ZSM-5, L, MCM-22 and MCM-36 molecular sieves, preferably L-type molecular sieve.

[0046] 12. According to any of the preceding methods, the active metal auxiliary is selected from metals Al, Zn, Fe, Cd, and Co, preferably Zn.

[0047] 13. According to the method of aspect 12, the content of said active metal auxiliary is 5-70 wt%, preferably 10-40 wt%, and most preferably 22 wt%, the content being relative to the total weight of the solid catalyst obtained.

[0048] 14. According to any of the foregoing methods, the solid catalyst is formed by compression molding, extrusion molding, and rotational molding. Compression molding is preferred.

[0049] 15. According to any of the foregoing methods, the nickel loading is 0.1% to 5% by weight, preferably 1% to 3% by weight, said loading relative to the total weight of the solid catalyst obtained.

[0050] 16. According to one aspect of the invention, a catalyst is provided, which is prepared by the method of any of the foregoing aspects.

[0051] 17. According to one aspect of the invention, the use of the catalyst according to the invention for ethylene oligomerization is provided.

[0052] 18. A method for preparing linear α-olefins by oligomerization of ethylene, the method comprising continuously passing ethylene through a fixed-bed reactor packed with a catalyst to oligomerize and prepare linear α-olefins.

[0053] The catalyst is characterized in that it is prepared by the following method:

[0054] 1) Provide molecular sieves, add active metal additives to the molecular sieves, and shape them into a molded body.

[0055] 2) Place the molded body in a fixed-bed reactor.

[0056] 3) Dissolve the transition metal salt in its first valence state and the bidentate ligand in a solvent to prepare a solution.

[0057] 4) The solution and ethylene are passed through a fixed-bed reactor loaded with a molded body, and the transition metal is loaded onto a molecular sieve. At the same time, the transition metal in the first valence state is at least partially reduced to the second valence state by an active metal auxiliary agent, wherein the second valence state is lower than the first valence state.

[0058] 19. According to the method of the preceding aspect, the temperature of the polymerization reaction is 50-120°C, preferably 70-100°C, and most preferably 90°C.

[0059] 20. The method according to aspect 15 or 16, wherein the pressure of said polymerization reaction is 6-12 MPa, preferably 8-11 MPa, and most preferably 10 MPa.

[0060] I. Catalyst Preparation

[0061] According to one aspect of the present invention, a method for preparing a catalyst is provided, wherein the method comprises the following steps:

[0062] 1) Provide molecular sieves, add active metal additives to the molecular sieves, and shape them into a molded body.

[0063] 2) Place the molded body in a fixed-bed reactor.

[0064] 3) Dissolve the transition metal salt in its first valence state and the bidentate ligand in a solvent to prepare a solution.

[0065] 4) The solution and ethylene are passed through a fixed-bed reactor loaded with a molded body. Transition metals are loaded onto the molecular sieve through ion exchange, while the transition metals in the first valence state are reduced to the second valence state by an active metal promoter. The second valence state is lower than the first valence state, thus obtaining a catalyst.

[0066] In the first step of the catalyst preparation method of the present invention, an active metal additive is added to a molecular sieve, which is then shaped and placed in a fixed-bed reactor. The fixed-bed reactor can be of the tubular, horizontal, vertical, or annular type, preferably tubular. The heat exchange method is preferably a jacketed heat exchange method. The heat exchange medium is not particularly limited and can be a common heat exchange medium in the art, such as water.

[0067] In the context of this invention, molecular sieve refers to hydrated aluminosilicate. The molecular sieves used in this invention include X-type molecular sieves, Y-type molecular sieves, ZSM-5 type molecular sieves, L-type molecular sieves, MCM-22 type molecular sieves, MCM-36 type molecular sieves, etc., with L-type molecular sieves being preferred.

[0068] In the context of the present invention, the active metal promoter includes all metals capable of reducing the transition metal from a first valence state to a second valence state under the conditions of catalyst preparation. The active metal promoters used in the present invention include Al, Zn, Fe, Cd, and Co in metallic form, preferably Zn in metallic form. Zn is preferably in powder form to increase the contact area, which is beneficial to the reduction reaction. The content of the active metal promoter is 5-70 wt%, preferably 10-40 wt%, and most preferably 22 wt%, relative to the total weight of the obtained solid catalyst.

[0069] The solid catalysts used in this invention are formed by compression molding, extrusion molding, and rotational molding. Compression molding is preferred.

[0070] During the molding process, a lubricant may optionally be added to the catalyst to facilitate demolding. Examples of such lubricants include graphite, guar gum, and talc. Graphite is preferred.

[0071] A solution is prepared by dissolving a transition metal salt and an organic bidentate ligand in an organic solvent at a specific ratio. This solution is then passed through a fixed-bed reactor loaded with a molded material under controlled temperature, pressure, and the presence of ethylene, where the transition metal (main catalyst) is loaded onto a molecular sieve via ion exchange. Simultaneously, the transition metal (main catalyst) in its first valence state is at least partially reduced to a second valence state by an active metal promoter. Preferably, the second valence state is lower than the first valence state. The first valence state is preferably +2. The second valence state can be monovalent or zero, preferably zero. The loading amount of the transition metal salt (main catalyst) on the molecular sieve is controlled by adjusting the exchange time.

[0072] Due to its unique valence electron structure, transition metal nickel can form a planar quadrilateral structure with bidentate ligands, making it one of the most important catalytic actives for the oligomerization of ethylene into linear α-olefins. The nickel salts used in this method to prepare the catalyst are mainly divalent nickel salts, such as nickel chloride, nickel bromide, nickel iodide, nickel nitrate, nickel carbonate, and nickel chlorate, with nickel chloride being preferred.

[0073] Bidentate ligands mainly refer to PO-type organophosphorus compounds, including diphenylphosphine carboxylic acid, diphenylphosphine acetate, diphenylphosphine benzoic acid, sodium diphenylphosphine carboxate, sodium diphenylphosphine acetate, sodium diphenylphosphine benzoate, potassium diphenylphosphine carboxate, potassium diphenylphosphine acetate, potassium diphenylphosphine benzoate, lithium diphenylphosphine carboxate, lithium diphenylphosphine acetate, lithium diphenylphosphine benzoate, ammonium diphenylphosphine carboxate, ammonium diphenylphosphine acetate, and ammonium diphenylphosphine benzoate, with sodium diphenylphosphine benzoate being the preferred choice.

[0074] The organic solvent can be a nonpolar solvent such as cyclopentane, cyclohexane, isooctane, decane, benzene, toluene, ethylbenzene, etc.; or a polar solvent such as methanol, ethanol, n-propanol, n-butanol, octanol, dodecyl alcohol, ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, etc., preferably 1,4-butanediol, 2,5-hexanediol, etc., more preferably 1,4-butanediol.

[0075] The molar ratio of nickel to ligand added in step 3) is 0.5-10, preferably 1-3, and most preferably 2.

[0076] Molecular sieves possess a large specific surface area, a regular pore structure with adjustable pore size, moderate surface acidity that can be easily adjusted according to reaction requirements, and a strong sieving effect on hydrocarbon molecules. Therefore, they are promising carrier materials for ethylene oligomerization. While not construing as limiting the scope of this invention, it is believed that ethylene can react both inside and on the outer surface of the molecular sieve pores.

[0077] The temperature for nickel ion exchange is 10-50℃, preferably 20-40℃, and most preferably 30℃.

[0078] The partial pressure of ethylene during exchange is 0.5-5 MPa, preferably 2-4 MPa, and most preferably 3 MPa.

[0079] The exchange time is 1-20 hours, preferably 5-10 hours, and most preferably 8 hours.

[0080] In the catalyst obtained according to the method of the present invention, the nickel loading is from 0.1% to 5% by weight, preferably from 0.15% to 3% by weight, relative to the total weight of the obtained solid catalyst.

[0081] The catalyst according to the present invention is generated directly in the reactor in an in-situ manner, thereby avoiding loss, deterioration and contamination of the catalyst during storage and transportation.

[0082] II. Ethylene oligomerization reaction

[0083] According to one aspect of the invention, a method for preparing linear α-olefins via ethylene oligomerization using the above-described catalyst is provided. The disclosure above regarding the catalyst is applicable accordingly to the ethylene oligomerization method according to the invention, and will not be repeated here.

[0084] After the catalyst is prepared, the raw material ethylene is continuously passed through a fixed-bed reactor at a certain space velocity to complete the oligomerization of ethylene to prepare linear α-olefins under certain temperature and pressure conditions.

[0085] The polymerization temperature is 50-120℃, preferably 70-100℃, and most preferably 90℃.

[0086] The reaction pressure of ethylene is 6-12 MPa, preferably 8-11 MPa, and most preferably 10 MPa.

[0087] The method according to the invention typically produces C4 to C 48 Various linear α-olefins were identified, with the product distribution conforming to the Schulz-Flory model. The geometric growth factor K value represents the relative proportion of the product olefins.

[0088]

[0089] The K value of the ethylene oligomer obtained by the method according to the present invention is in the range of 0.40-0.90, preferably in the range of 0.60-0.80.

[0090] Example

[0091] The following embodiments are further illustrative examples of the present invention and are not intended to limit the scope of protection of the present invention. The exemplary embodiments provided below are intended to make this disclosure thorough and to fully convey its scope to those skilled in the art. Numerous specific details, such as examples of specific compositions, components, apparatuses, and methods, are set forth to provide a full understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that the specific details are not required, and the exemplary embodiments may be embodied in many different forms, none of which should be considered as limiting the scope of the present disclosure. In some exemplary embodiments, well-known methods, well-known apparatus structures, and well-known techniques are not described in detail.

[0092] Product composition analysis

[0093] The components were analyzed using gas chromatography. Exemplary gas chromatographic conditions were as follows: a 30m × 0.32mm 0.1µm SE-30 capillary column, injector temperature 300℃, detector temperature 300℃, split ratio 50.00, and column pressure 1.004 psi. Column temperature was programmed: 30℃–200℃ at a rate of 10℃ / min, and 200℃–340℃ at a rate of 3℃ / min.

[0094] Typical product gas chromatograms are as follows: Figure 1 As shown.

[0095] Nickel ion content determination

[0096] Nickel ion content analysis was performed using inductively coupled plasma atomic emission spectrometry (ICP). The instrument used was an Avio 200 ICP-OES. A solid-state RF generator with a power of 750-1500W was employed. The monochromator used a two-dimensional dispersion system with an echelle grating and prism, with a wavelength range of 170-750 nm and a focal length of 200-650 nm. A solid-state detector with a resolution ≤0.003 nm was used.

[0097] Example 1

[0098] Preparation and reaction results of solid catalysts with different types of molecular sieves as supports.

[0099] Weigh out 100g of X, Y, ZSM-5, L, MCM-22, and MCM-36 molecular sieves respectively, add 30g of zinc powder and 5g of graphite to each, and press them into Φ5×5mm tablets using a tablet press. Label them as samples A1, A2, A3, A4, A5, and A6 respectively.

[0100] Weigh 8.5 g of NiCl2·6H2O salt and 5.5 g of sodium diphenylphosphine benzoate and dissolve them in 1000 g of 1,4-butanediol solution to form exchange solution W.

[0101] 100 g of sample A1 was placed in a jacketed heat exchange tubular fixed-bed reactor, and ethylene gas was introduced to maintain the ethylene pressure at 3.0 MPa. The exchange solution W was injected into the reactor using a metering pump at a flow rate of 1000 g / h, and this solution was recycled. The temperature was maintained at 30°C, and the exchange was continued for 8 hours. After the exchange was completed, the ethylene pressure was increased to 9.0 MPa, the reaction temperature was raised to 90°C, and the ethylene feed rate was controlled at 60 g / h.

[0102] The material exiting the fixed-bed reactor first undergoes gas-liquid separation; unreacted ethylene gas is returned to the reaction system for recycling. The α-olefin product in the liquid phase is immiscible with the solvent and naturally separates into layers. The upper layer product is collected for analysis. The lower layer solution is returned to the reaction system for recycling.

[0103] The reaction was carried out continuously for 10 hours, and samples were taken for analysis. The reaction results of sample A1 were obtained.

[0104] Repeat the above process to obtain the reaction results of samples A2, A3, A4, A5, and A6, as shown in Table 1.

[0105] Experimental results show that the solid-phase catalyst prepared using L-type molecular sieves exhibits good reactivity and selectivity.

[0106] Example 2

[0107] Preparation and reaction results of solid catalysts with different active metal additive contents.

[0108] Weigh 100g of L-type molecular sieve, add 5g of graphite, and then add 5g, 10g, 20g, 30g, 40g, and 50g of zinc powder respectively. Press the mixture into Φ5×5mm tablets using a tablet press. Label them as samples B1, B2, B3, A4, B4, and B5 respectively.

[0109] The loading and reaction process of the active component nickel are the same as in Example 1.

[0110] The reaction results are shown in Table 2.

[0111] The catalyst's reactivity initially increases with the addition of zinc, an active metal promoter, before leveling off, while the selectivity of the reaction tends to decrease.

[0112] Example 3

[0113] The effect of different nickel loading on the reaction results.

[0114] The loading of nickel, the active component, on the solid catalyst was controlled by the ion exchange time. Using sample A4 as the solid catalyst, the nickel ion content in the circulating liquid was examined after different exchange times, from which the nickel loading on the solid catalyst could be calculated. Except for the loading time, the nickel loading process and reaction process were the same as in Example 1.

[0115] The loading of nickel on the solid catalyst and the reaction results are shown in Table 3.

[0116] As the exchange time increases, the nickel content on the solid-phase catalyst increases, and the reaction activity increases. After reaching a peak, it shows a downward trend. This is because, on the supported catalyst, the ethylene oligomerization reaction proceeds under the combined action of active nickel and acid centers. Initially, as the nickel loading increases, the number of active metal centers increases, and the polymerization activity increases. When the amount of active nickel increases to a certain level, these nickel ions will cover part of the surface acidity of the molecular sieve, thereby inhibiting the polymerization activity.

[0117] Example 4

[0118] The effect of different reaction temperatures on polymerization reactions.

[0119] Sample A4 was selected as the solid-phase catalyst for evaluating the reaction. The method and process of active metal ion exchange were the same as in Example 1. The effects of different reaction temperatures on activity and selectivity were investigated. The reaction results are shown in Table 4.

[0120] Example 5

[0121] The effect of different reaction pressures on polymerization reactions.

[0122] Sample A4 was selected as the solid-phase catalyst for evaluating the reaction. The method and process of active metal ion exchange were the same as in Example 1. The effects of different reaction pressures on activity and selectivity were investigated. The reaction results are shown in Table 5.

[0123] Ethylene oligomerization is a reaction that reduces the number of molecules, and increasing the reaction pressure is beneficial to the polymerization process. However, excessively high reaction pressure increases the requirements for catalyst strength and reaction equipment, thereby increasing production costs.

[0124] Table 1.

[0125]

[0126] Table 2.

[0127]

[0128] Table 3.

[0129]

[0130] Table 4.

[0131]

[0132] Table 5.

[0133]

[0134] The above description of the embodiments is provided for illustration and description purposes. It is not intended to be exhaustive or limiting of this disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but are interchangeable and applicable to selected embodiments where applicable, even if not explicitly shown or described. It can also be changed in many ways. Such changes should not be considered as a departure from this disclosure, and all such modifications are intended to be included within the scope of this disclosure as defined by the claims.

Claims

1. A method for preparing a catalyst for the oligomerization of ethylene to prepare linear α-olefins, wherein the method comprises the following steps: 1) Provide molecular sieves, add active metal additives to the molecular sieves, and shape them into a molded body. 2) Place the molded body in a fixed-bed reactor. 3) Dissolve the transition metal salt in its first valence state and the bidentate ligand in a solvent to prepare a solution. 4) The solution and ethylene are passed through a fixed-bed reactor loaded with a molded body. Transition metals are loaded onto the molecular sieve via ion exchange, while the transition metals in the first valence state are at least partially reduced to a transition metal salt in the second valence state by an active metal promoter. The second valence state is lower than the first valence state, thus yielding a catalyst. The active metal additives are selected from metals Al, Zn, Fe, Cd, and Co. The transition metal salts mentioned above are selected from nickel chloride, nickel bromide, nickel iodide, nickel nitrate, nickel carbonate, and nickel chlorate. The bidentate ligand is an organophosphorus ligand.

2. The method of claim 1, wherein the fixed-bed reactor is tubular.

3. The method according to claim 1 or 2, wherein the fixed-bed reactor is a jacketed heat exchanger.

4. The method according to claim 1 or 2, wherein the transition metal salt is nickel chloride.

5. The method according to claim 1 or 2, wherein the bidentate ligand is selected from diphenylphosphonic acid, sodium diphenylphosphonate, diphenylphosphonic acid, sodium diphenylphosphonic acid, diphenylphosphonic acid, and sodium diphenylphosphonate.

6. The method according to claim 1 or 2, wherein the bidentate ligand is sodium diphenylphosphine benzoate.

7. The method according to claim 1 or 2, wherein the organic solvent is selected from cyclopentane, cyclohexane, isooctane, decane, benzene, toluene, ethylbenzene, methanol, ethanol, n-propanol, n-butanol, octanol, dodecanol, ethylene glycol, propylene glycol, butanediol, pentanediol, and hexanediol.

8. The method according to claim 1 or 2, wherein the organic solvent is selected from 1,4-butanediol and 2,5-hexanediol.

9. The method according to claim 1 or 2, wherein the organic solvent is 1,4-butanediol.

10. The method according to claim 1 or 2, wherein the molar ratio of metallic nickel to the ligand is 0.5-10.

11. The method according to claim 1 or 2, wherein the molar ratio of metallic nickel to the ligand is 1-3.

12. The method according to claim 1 or 2, wherein the molar ratio of metallic nickel to the ligand is 2.

13. The method according to claim 1 or 2, wherein the temperature for ion exchange is 10-50°C.

14. The method according to claim 1 or 2, wherein the temperature for ion exchange is 20-40°C.

15. The method according to claim 1 or 2, wherein the temperature for ion exchange is 30°C.

16. The method according to claim 1 or 2, wherein the partial pressure of ethylene during ion exchange is 0.5-5 MPa.

17. The method according to claim 1 or 2, wherein the partial pressure of ethylene during ion exchange is 2-4 MPa.

18. The method according to claim 1 or 2, wherein the partial pressure of ethylene during ion exchange is 3 MPa.

19. The method of claim 1 or 2, wherein the ion exchange is performed for 1-20 hours.

20. The method of claim 1 or 2, wherein the ion exchange is performed for 5-10 hours.

21. The method of claim 1 or 2, wherein the ion exchange is performed for 8 hours.

22. The method according to claim 1 or 2, wherein the molecular sieves are selected from X, Y, ZSM-5, L, MCM-22 and MCM-36 molecular sieves.

23. The method according to claim 1 or 2, wherein the molecular sieve is an L-type molecular sieve.

24. The method according to claim 1 or 2, wherein the active metal auxiliary is metallic Zn.

25. The method of claim 24, wherein the content of the active metal auxiliary is 5-70 wt%.

26. The method of claim 24, wherein the content of the active metal auxiliary is 10-40 wt%.

27. The method of claim 24, wherein the content of the active metal auxiliary is 22 wt%.

28. The method according to claim 1 or 2, wherein the solid catalyst is formed by compression molding, extrusion molding and rotational molding.

29. The method according to claim 1 or 2, wherein the solid catalyst is formed by compression molding.

30. A method for preparing linear α-olefins by oligomerization of ethylene, the method comprising continuously passing ethylene through a fixed-bed reactor packed with a catalyst to oligomerize and prepare linear α-olefins. Its features are, The catalyst is prepared in the following manner: 1) Provide molecular sieves, add active metal additives to the molecular sieves, and shape them into a molded body. 2) Place the molded body in a fixed-bed reactor. 3) Dissolve the transition metal salt in its first valence state and the bidentate ligand in a solvent to prepare a solution. 4) The solution and ethylene are passed through a fixed-bed reactor loaded with a molded body, and a transition metal is loaded onto a molecular sieve. Simultaneously, the transition metal in its first valence state is at least partially reduced to a second valence state by an active metal auxiliary agent, wherein the second valence state is lower than the first valence state. The active metal additives are selected from metals Al, Zn, Fe, Cd, and Co. The transition metal salts mentioned above are selected from nickel chloride, nickel bromide, nickel iodide, nickel nitrate, nickel carbonate, and nickel chlorate. The bidentate ligand is an organophosphorus ligand.

31. The method of claim 30, wherein the temperature of the polymerization reaction is 50-120°C.

32. The method according to claim 30 or 31, wherein the pressure of the polymerization reaction is 6-12 MPa.

33. The method of claim 30, wherein the temperature of the polymerization reaction is 70-100°C.

34. The method of claim 30, wherein the polymerization reaction is carried out at a temperature of 90°C.

35. The method according to claim 30 or 31, wherein the pressure of the polymerization reaction is 8-11 MPa.

36. The method according to claim 30 or 31, wherein the pressure of the polymerization reaction is 10 MPa.

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