A process for preparing linear alpha-olefins by non-selective polymerization of ethylene

Abstract

The present invention belongs to the field of petrochemical catalysis technology, and relates to a process for non-selective polymerization of ethylene to prepare linear alpha-olefins. The present invention provides a novel process for non-selective polymerization of ethylene to produce linear alpha-olefins from the synthesis of diiminopyridine, until the synthesis of linear alpha-olefins of different carbon numbers by ethylene polymerization reaction with diiminopyridine iron as the main catalyst, and only involves a solvent from beginning to end. The present invention solves the problem of the need to use multiple solvents in the existing process of the catalytic system. The seamless connection of the ligand synthesis step and the ethylene polymerization reaction step is achieved, and the cumbersome post-processing operations (suction filtration, frozen crystallization, suction filtration, frozen crystallization, suction filtration, drying, etc.) after the ligand synthesis in the existing process are omitted. The industrial implementation of the present invention can bring advantages such as high safety, small equipment investment, low energy consumption in the production process, and conducive to reducing the production cost of alpha-olefins.

Description

Technical Field

[0001] The invention belongs to the technical field of petrochemical catalysis and relates to a process for preparing linear alpha-olefins by non-selective polymerization of ethylene. Background Art

[0002] Linear α-olefins are an important product and raw material in the chemical industry, and are widely used. Linear α-olefins with different carbon numbers are used in different fields. C4-C8 linear α-olefins are mainly used as comonomers of polyolefins. They can improve the properties of copolymers. For example, linear polyethylene copolymerized with 1-hexene has excellent properties that are difficult to match with ordinary polyethylene in terms of tensile strength, impact strength, crack resistance and service life; C6-C 10 Linear α-olefins are converted into C7-C 11 Fatty alcohols can be used as plasticizers and special plasticizers for PVC. 10 Linear α-olefins react with anhydrous phthalic acid to produce the corresponding phthalate plasticizers. Plasticizers made with straight-chain alcohols have low volatility, good softness, and good light stability and oxidation stability. 11 -C 14 C 12 -C 15 Alcohol has good biodegradability and is mostly used in the production of detergents. The production of detergent alcohol using linear α-olefins as raw materials also has the advantages of easy carbonylation reaction and easy alkylation reaction with benzene. In fact, the carbonylation reaction of linear α-olefins can produce various oxygen-containing compounds (aldehydes, alcohols, acids, esters, etc.), providing broad space for the development of fragrances, daily chemicals and special fine chemicals; 12 Polyalphaolefin oil (PAO, also known as linear alpha olefin oligomer) made from linear alpha olefin polymerization is the main raw material for synthetic lubricants in the automotive, mechanical and aerospace industries. Synthetic lubricants produced with PAO have the advantages of low viscosity, high viscosity index, low volatility, high flash point, low pour point, good chemical and thermal stability and long service life; C 12 -C 16 Linear α-olefins react with hydrogen bromide in the presence of peroxide to form alkyl bromides, which then react with dimethylamine to form fatty tertiary amines, which further react with hydrogen peroxide to produce amine oxides, which can be used as surfactants. This type of surfactant exhibits non-ionic properties in the neutral and alkaline pH range, and has excellent detergency, biodegradability, and foam stability at low pH. In addition, amine oxides can also be used as components of shampoos, carpet washes, cosmetics, surface cleaners, fine detergents, toothpastes, foam soaps, textile softeners, lubricants, and metal detergents. 14 -C 18The α-olefin sulfonate obtained by direct sulfonation of linear α-olefins and then hydrolysis and neutralization with NaOH is an excellent anionic synthetic detergent. Because the product contains double bonds and hydroxyl groups, it has good solubility, biodegradability, detergency and foaming properties. It is stable in acid, alkali and high temperature, has good color and low odor. It is also effective in cold water and is relatively insensitive to hard water, so it has a broad market. 18 α-olefin sulfonates have significant effects in washing heavy dirt. In addition to daily use, α-olefin sulfonates can also be used in other areas such as oil field drilling fluids, emulsion polymerization in polymer industry, cement plasticizers in concrete, and newspaper ink removers; C 12 -C 30 , especially C 14 -C 24 Linear α-olefins can be used to produce additives for synthetic lubricants. The alkyl side chain of this type of lubricant additive has excellent performance and is mainly divided into three categories. The first category is alkylbenzene produced by alkylation of α-olefin and benzene, which is sulfonated and neutralized to produce calcium, magnesium or barium salts. The second category is alkylphenol synthesized from α-olefin and phenol, which is neutralized to produce calcium, magnesium or barium salts. The third category is a compound containing 5%-20% sulfur produced by mixing α-olefin with oleic acid ester or triglyceride and then vulcanizing.

[0003] With the continuous development of the global economy, the market for high-end polyethylene, detergents, surfactants and lubricants has developed rapidly, driving the rapid growth of the market demand for linear α-olefins. In addition, as CO2 emission reduction actions are gradually launched around the world, high-carbon linear α-olefins are likely to find an unprecedented huge market in the field of phase change energy storage technology. As we all know, phase change energy storage technology is inseparable from energy storage media, namely phase change materials. Phase change materials can be divided into organic phase change materials, inorganic phase change materials and eutectic phase change materials according to their chemical composition. Heat storage materials are the medium for storing and releasing heat energy in heat storage systems and are the core of heat storage systems. The performance of heat storage materials directly determines the performance of heat storage systems. Specifically, the requirements of phase change energy storage technology for phase change materials are as follows: (1) Phase change materials must have a constant heat storage temperature. Heat input or output is often accompanied by temperature changes. If the temperature changes greatly during the heat storage or heat release process of the heat storage system, it will have an adverse effect on the stable operation of the system. Therefore, the heat storage-heat release process of the heat storage material is best achieved under constant temperature conditions; (2) Phase change materials must have high stability, including thermal stability and chemical stability. Thermal stability refers to the fact that the material composition of the heat storage material remains relatively stable during the heating process, thereby avoiding decomposition of the material due to local overheating. Chemical stability refers to the fact that the heat storage material is not easy to react chemically with environmental factors such as light, air, water vapor, and metal containers during use, causing changes in the material composition and thus changing its heat storage characteristics; (3) Phase change materials should be widely available and inexpensive. In large-scale heat storage systems, heat storage materials account for most of the cost; (4) Phase change materials should have a high heat storage density. Heat storage density refers to the amount of heat that can be stored per unit mass or per unit volume of heat storage material. The higher the heat storage density, the less heat storage material the system needs, and the lighter the system weight or the smaller the volume; (5) Phase change materials should have a high thermal conductivity. Thermal conductivity (also known as thermal conductivity) is an important parameter for measuring the heat conduction capacity of a material. It is defined as the amount of heat directly conducted by a material of unit cross-section and length under unit temperature difference and per unit time. Thermal conductivity determines the heat storage and release rate of the heat storage material. Only heat storage materials with high thermal conductivity can quickly absorb and release heat and have a high response rate; (6) Phase change materials must have high reliability. During use, heat storage materials must undergo a long-term cycle of heat storage and heat release. In order to meet the requirement that heat storage materials can operate for a long time, heat storage materials must have the characteristic of small changes in physical properties during multiple cold and hot cycles. Otherwise, the performance of the heat storage system will decrease significantly after long-term use.

[0004] Higher aliphatic hydrocarbons are an important organic phase change material. Paraffin and its higher fatty acid phase change materials are very suitable as phase change energy storage media. Take paraffin as an example: paraffin is a mixture of normal alkanes with a straight-chain structure, and its molecular formula is C2H 2m+2. Paraffin wax releases a large amount of heat when it crystallizes, and the phase change temperature increases with the growth of the carbon chain. Paraffin phase change materials are chemically inactive, have a wide phase change temperature range, are non-corrosive, and have a low melting vapor pressure. Therefore, they can be used as heat storage materials in heat storage systems for a long time. In general, paraffin wax as a phase change material has the advantages of consistent melting, high melting heat, chemical inertness, self-nucleation, and no phase separation. However, industrial-grade paraffin wax is mostly a mixture of alkanes, so industrial-grade paraffin wax often has a melting temperature range rather than a sharp melting point, and is not suitable for use as a phase change energy storage material. In contrast, α-olefins produced by ethylene polymerization can be easily separated to obtain monomer α-olefins with a single carbon number. After hydrogenation, monomer α-olefins with a single carbon number can produce monomer chain alkanes with a single carbon number. Monomer chain alkanes are phase change energy storage paraffin waxes with consistent melting, high melting heat, and chemical inertness.

[0005] Since the melting points and phase change enthalpies of monomer paraffins (chain alkanes) with different carbon numbers are different, monomer α-olefins with different carbon numbers can be used as phase change energy storage materials to meet different needs after hydrogenation. The melting points and phase change enthalpies of some monomer chain alkanes are as follows: 12 (melting point -9.7℃, phase change enthalpy 210J / g); C 13 (melting point -5.4℃, phase change enthalpy 196J / g); C 14 (melting point 5°C, phase change enthalpy 230 J / g); C 15 (melting point 10°C, phase change enthalpy 205 J / g); C 16 (melting point 16.7°C, phase change enthalpy 237 J / g); C 17 (melting point 21.7°C, phase change enthalpy 213 J / g); C 18 (melting point 28°C, phase change enthalpy 244 J / g); C 19 (melting point 32°C, phase change enthalpy 222 J / g); C 20 (melting point 36.7°C, phase change enthalpy 246 J / g); C 21 (melting point 40.2°C, phase change enthalpy 200 J / g); C 22 (melting point 44°C, phase change enthalpy 249 J / g); C 23 (melting point 47.5°C, phase change enthalpy 232 J / g); C 24 (melting point 50.6°C, phase change enthalpy 255 J / g); C 25 (melting point 53.3°C, phase change enthalpy 238 J / g); C 26 (melting point 56.3°C, phase change enthalpy 256 J / g); C 27 (melting point 58.8℃, phase change enthalpy 236J / g); C 28 (melting point 61.6°C, phase change enthalpy 253 J / g); C 29 (melting point 63.4°C, phase change enthalpy 240 J / g); C30 (Melting point 65.4°C, phase change enthalpy 251 J / g).

[0006] Linear α-olefins were initially produced by paraffin cracking. In 1965, Chevron was the first to use thermal cracking to industrialize the production of α-olefins using refined wax as a raw material. The raw material used for wax cracking is generally refined paraffin (deoiled) from the lubricating oil fraction (350-480°C), and the oil content is generally less than 1%. Paraffin and superheated steam undergo thermal cracking reactions in a cracking furnace at about 540°C and a pressure of 0.2-0.4MPa to produce α-olefin products with coexistence of odd and even carbon numbers. C6-C 20 The content of linear α-olefins in the fraction is about 83%-89%. The wax cracking process is simple and mature, does not require a catalyst, and is easy to operate. However, the α-olefins produced by this process route have high impurity contents such as internal olefins, diolefins, and branched olefins, and the coexistence of odd- and even-carbon α-olefins and the close boiling points of adjacent carbon number molecules make separation and purification difficult. Therefore, it is difficult to obtain high-purity monomer olefins, and the product quality is poor, which cannot meet the needs of downstream high-end products such as comonomers and surfactants. In addition, this process route requires refined wax as raw material, the source of raw materials is limited and the price is high, and the yield of α-olefins is low (about 60%), and it lacks economic superiority. Therefore, with the continuous development of the ethylene polymerization production process, the paraffin cracking method has been in a trend of being replaced.

[0007] In 1994, South Africa's Sasol successfully put into operation an industrial unit for recovering linear α-olefins (mainly 1-pentene and 1-hexene) from high-temperature FT synthesis products. The raw material cost and utility cost of the Sasol process are relatively low, and it has strong market competitiveness. However, the investment in this process is large, linear α-olefins are only a by-product of high-temperature FT synthesis, and it is impossible to produce a large number of α-olefins of various carbon numbers at the same time. Other methods for producing linear α-olefins include alkane dehydrogenation, but these methods have been eliminated.

[0008] At present, there are many methods for producing α-olefins by ethylene polymerization, such as the Gulf method, the Ethyl method, the SHOP method and the Linde method. Among them, the Guf method, the Ethyl method and the SHOP method were industrialized earlier and the process is relatively mature. The Gulf method is also called the Ziegler one-step method or the Chevron method. This method is the first ethylene polymerization method industrialized by the Gulf Company of the United States (later merged by the Chevron Company) in 1964. The characteristics of this method are that triethylaluminum solution is used as a catalyst (Ziegler type catalyst), and the two-step reaction of chain growth and chain displacement is completed in one reactor, so it is also called the Ziegler one-step process. The Gulf method uses a slender tubular reactor, and ethylene and a hydrocarbon solution of triethylaluminum catalyst are contacted and reacted at 180-220°C and a high pressure of 21MPa. The ethylene single-pass conversion rate is controlled within the range of 60%-75% to reduce the generation of impurities such as branched olefins. The unreacted ethylene is recycled, and the liquid product is treated with a NaOH solution to hydrolyze the triethylaluminum catalyst into sodium aluminate and alkanes. The primary distillation tower in the separation system cuts the product into C4-C8 and C 10+ The two fractions, the C4-C8 fraction at the top of the tower, are separated in the subsequent distillation tower to obtain α-olefins with carbon numbers of C4, C6 and C8. 10+ The fraction was then distilled under reduced pressure to obtain C 10 , C 12 , C 14 , C 16 and C 18 Linear-olefin monomers or mixed fractions. The typical α-olefin carbon number distribution of the Gulf process is: C4 13.9%, C6 14.6%, C8 13.7%, C 10 12.0%, C 12 10.0%、C 14 8.2%, C 16 6.5%, C 18 5.2%, C 20+ 14.9%. The product quality of Gulf process is good, and the content of linear α-olefin varies with the carbon number. The content of linear α-olefin in low carbon (C4-C8) products is greater than 96% (impurities are mainly alkanes, and there are also internal olefins and branched olefins, but no undesirable impurities such as aromatics and dienes), which can be used as comonomers.

[0009] The Ethyl process is also called the Ziegler two-step process. This process was introduced by Ethyl Company in 1971 based on the improvement of the one-step process. The catalyst is still triethylaluminum solution. However, the characteristic of the Ethyl process is that the chain growth and chain displacement reactions are carried out in two steps. The first step reaction is carried out under the conditions of an average reaction temperature of 127°C, 21MPa, and a molar ratio of triethylaluminum to ethylene of 1:19, and the ethylene single-pass conversion rate is about 40%. The product and catalyst of the first step reaction are mixed with the circulating ethylene and supplementary ethylene and then enter the second reactor for chain displacement reaction. The reaction temperature is about 293°C, the pressure is 16MPa, and the residence time is about 0.5s.

[0010] Since ethylene and triethylaluminum react in a stoichiometric ratio in the first chain growth reaction, the catalyst is recycled to reduce the consumption of expensive triethylaluminum. The typical α-olefin carbon number distribution of the Ethyl process is: C4 13%, C6 16%, C8 19%, C 10 18%, C 12 15%, C 14 9%, C 16 6%, C 18 3%, C 20+ 1%. In the two-step process, C6-C 10 The content of linear α-olefins in α-olefins is higher than 96%, but the content of linear α-olefins in α-olefins decreases significantly with the increase of carbon number, while the content of isomeric terminal olefins and internal olefins increases significantly. However, the α-olefin products of the Ethyl process are mainly concentrated in C4-C 12 The light end, C 20+ Only 1%. This is attributed to the carbon number adjustment effect of the two-step reaction.

[0011] The SHOP (Shell Higher Olefins Process) method is a new ethylene polymerization process successfully developed by Shell in 1977. This method uses a zero-valent nickel complex solution coordinated by an organic phosphide (1,4-butanediol as a solvent) as a catalyst. The catalyst has high activity and can directly produce high molecular weight oligomers without a replacement reaction. 1,4-Butanediol is used as a solvent because it has good solubility for the catalyst, but is insoluble in α-olefins, which is conducive to the separation of the catalyst and the product. The ethylene polymerization reaction in the SHOP method is carried out in a series of autoclave reactors at 80-120℃ and 6.8-13.6MPa. Unlike the one-step method and the two-step method, the ethylene polymerization of the SHOP method is a three-phase reaction, namely the catalyst phase, the ethylene gas phase and the α-olefin phase. Once the reaction generates ethylene oligomers, the ethylene oligomers immediately form a new phase, the α-olefin phase, because the solvent is insoluble in them. The unreacted ethylene is recycled into the reactor to continue the reaction. The α-olefin phase is washed with 1,4-butanediol solvent, and after absorbing the small amount of catalyst residue contained therein, it enters the fractionation system for separation. Most of the solvent liquid phase is recycled back to the reactor, and a small part enters the regeneration system to reduce the oxidized nickel with NaBH4. The typical α-olefin carbon number distribution of the SHOP method is: C4 12%, C6 13%, C8 12%, C 10 12%, C 12 10%, C 14 8%, C 16 7%, C 18 6%, C 20+ 20%. It can be seen that the product distribution of the SHOP process is roughly similar to that of the Gulf process and the Ethyl process, but the SHOP process has high catalyst activity, relatively mild reaction conditions, automatic separation of products and catalysts, and the catalyst can be recycled. These advantages make the SHOP process more popular.

[0012] In addition, the SHOP process is also equipped with isomerization and disproportionation units to increase the production of detergent raw materials. The purpose of isomerization is to convert the less useful low-carbon olefins (C4) and C 20+ The fraction was converted to C 11 -C 14 Internal olefins can be used as raw materials for disproportionation reaction to increase the yield of the target product. The isomerization reaction is carried out in the presence of a heterogeneous catalyst MgO under liquid phase conditions of 80-140°C and 0.35-1.7MPa. The purpose of the disproportionation reaction is to convert a high-carbon olefin and a low-carbon olefin into two medium-carbon olefins to increase the yield of the desired carbon number olefins. The disproportionation reaction is a liquid phase reaction with Re2O7 / Al2O3 as the catalyst, and the conditions are similar to the isomerization reaction. When the production purpose of the SHOP method is detergent raw materials, the products with less than C 10and greater than C 19 The fraction is recycled from the separation system to the disproportionation unit. In the product obtained by the disproportionation reaction, when the total olefin content is 99.5%, the content of straight-chain olefins is greater than 96%, while the content of aromatics and dienes is less than 0.1%, and the content of alkanes is less than 0.5%.

[0013] In addition to the above ethylene polymerization process, Idemitsu Petrochemical Company of Japan has also developed a Zr / A1 system ethylene polymerization catalyst and built a 50kt / a linear α-olefin industrial production unit in 1989. Based on the Zr / Al system catalyst, Linde has also developed a series of two-component homogeneous catalyst systems based on soluble zirconium and aluminum organometallic compounds for ethylene polymerization. The reaction temperature of the Linde process is 60-80°C and the reaction pressure is 2.0-3.0MPa. The product distribution can be adjusted according to market demand by changing the ratio of aluminum and zirconium. The used catalyst can be separated and recovered from the product by adsorption method, and the metal can be recycled.

[0014] The above mainly describes the non-selective polymerization process of ethylene. As we all know, Phillips Petroleum Company reported a catalytic process for the trimerization of ethylene to produce 1-hexene in 1995. The process uses a catalyst system of 2-ethylhexanoate chromium / 2,5-dimethylpyrrole / dichloroethylaluminum / triethylaluminum (molar ratio of 1:4:5:15) and cyclohexane solvent to trimerize ethylene at 115°C and 4.8MPa (a small amount of hydrogen is injected into the reactor). In order to prevent the subsequent equipment from fouling due to by-product polymers, n-butanol is immediately introduced at the reactor outlet to deactivate the catalyst. The ethylene conversion rate is 68%-84%, and the selectivity of 1-hexene is 89-93%. The product of this process is relatively simple, the separation process is simplified accordingly, and the purity of 1-hexene is as high as 99%. Obviously, the Phillips process belongs to the selective polymerization process of ethylene, which has a great competitive advantage for the production of ethylene comonomers. However, the Phillips process is not applicable to producers of plasticizers, detergents, surfactants and lubricants.

[0015] In recent years, the development and research of new technologies for the production of α-olefins at home and abroad have mainly focused on two directions: selective polymerization of ethylene and non-selective polymerization.

[0016] Research on the selective oligomerization process of ethylene mainly focuses on the trimerization / tetramerization of ethylene catalyzed by Cr-based catalysts. For example, Anthea Carter (Chemical Communications, 2002, 8: 858-859) found that a catalytic system consisting of a PNP ligand with an ortho-methoxy-substituted aromatic group, a chromium source tetrahydrofuran chromium chloride ([CrCl3(THF)3]), an auxiliary agent methylaluminoxane (MAO) and a toluene solvent can be used for ethylene trimerization. The selectivity for 1-hexene is as high as 90.0% at 80°C and 2MPa. The catalytic activity of the Cr-based catalyst with PNP as a ligand and MAO as a co-catalyst at the same pressure is about two orders of magnitude higher than the reported value of the Phillips catalyst, and the catalyst system has good heat resistance and high stability; Annette Bollmann (J.Am.Chem.Soc.2004,126,45,14712–14713) first reported a Cr catalyst system for the selective synthesis of 1-octene by ethylene tetramerization. This catalyst system also uses a PNP type ligand and a co-catalyst, but this catalyst system is different from the catalyst system reported by Anthea Carter. For example, Annette Bollmann used a catalyst system with a molar ratio of Cr(acac)3:((Ph)2P)2NMe:EAO:TMA=1:1.35:1000:250 in toluene solvent to carry out the polymerization of ethylene. The reaction was carried out at 45°C and 4.5MPa for 30 minutes, and an α-olefin product with a selectivity of up to 70% for 1-octene was obtained. In this example, the Cr source is chromium acetylacetonate, the ligand of the main catalyst is nitrogen methyl bis diphenylphosphine, and there are two co-catalysts, namely ethylaluminoxane and trimethylaluminum.

[0017] In addition, the following foreign patents disclose the technology of selective polymerization of ethylene to synthesize C6 and C8 α-olefins: U.S. Patent US11298693B2, U.S. Patent US11224870B2, U.S. Patent US11247201B2, U.S. Patent US20220072523A1, and U.S. Patent US20220064080A1.

[0018] On the other hand, in 1998, Brookhart et al. (Journal of the American Chemical Society, 1998, 120 (28): 7143-7144) and Gibson et al. (Chemical Communications, 1998 (7): 849-850) reported respectively a type of ethylene polymerization catalyst system with iron (II) and cobalt (II) ions as central metal atoms and diiminopyridine as ligands. The chelate structure formed by the diiminopyridine ligand and the central atom Fe is shown in Formula 1.

[0019]

[0020] Brookhart et al. obtained an activity of up to 5.0×10- 9 g / molFe·h, and the total selectivity of α-olefins was as high as 99% for ethylene polymerization (reaction time 30 min). Gibson et al. also obtained an activity of up to 1.1×10 8 g / molFe·h ethylene polymerization results (reaction time 60min). Bianchinj et al. (Coordination Chemistry Reviews, 2006, 250: 1391-1418) systematically studied the role of substituents on the diimino pyridine ligand on the basis of previous research. The results showed that the size, nature and regiochemistry of the substituents on the imino aromatic group are crucial to controlling ethylene polymerization. In addition, the public document "Optimization and Influence of Cocatalysts for Iron-based Catalyzed Ethylene Polymerization" (doctoral dissertation, Zhejiang University (2018)) systematically studied the diimino pyridine / ferric acetylacetonate / MAO catalyst system. In this study, the addition of p-bromophenol to the above-mentioned catalytic system to inhibit the production of ethylene wax (iron-based catalysts are highly active, the reaction is difficult to control, and ethylene wax is easily produced) was involved. Under the conditions of toluene as solvent, reaction temperature and pressure of 70°C and 0.7MPa respectively, a catalyst containing p-bromophenol (n [-OH] / n [Al] =0.7) was used to carry out ethylene polymerization reaction (reaction time 1h), and the carbon number distribution of the α-olefin product was as follows: C4 23%, C6 22%, C8 16%, C 10 12%, C 12 8%, C 14 6%, C 16 4%, C 18 3%, C 20+ 6%, the ethylene wax production rate (compared with no addition of p-bromophenol) was reduced by 36wt%, and the activity was as high as 6.17×10 7 g / molFe·h and ethylene polymerization results with a total α-olefin selectivity of up to 99%.

[0021] It can be seen that the ethylene polymerization catalyst system developed by Brookhart et al. and Gibson et al., which uses iron (II) ions as the central metal atom and diiminopyridine as the ligand, is a non-selective ethylene polymerization catalyst system. Compared with the SHOP process catalyst system, the reaction conditions of the diiminopyridine iron catalyst system are very mild and the catalytic activity is extremely high; compared with various Cr catalyst systems for ethylene selective polymerization, the diiminopyridine iron catalyst system can simultaneously generate α-olefin products with different carbon numbers, which is conducive to improving the market adaptability of industrial equipment.

[0022] Through literature research, we found that domestic researchers have done a lot of research on the diimino pyridine iron catalyst system. For example:

[0023] Chinese invention patent CN104109064A (application date: 2013-10-12) discloses a catalyst system for ethylene polymerization. Its technical characteristics are that the main catalyst is a 1,10-phenanthroline condensation iron (II) complex substituted with n-propionyl, the co-catalyst is a solution composed of triethylaluminum and aqueous toluene, and the solvent is 1-hexene. The catalyst system has high ethylene polymerization activity, stable polymerization reaction operation, low toxicity and environmental protection, low catalyst cost and strong practicality.

[0024] Chinese invention patent CN103724146A (application date: 2013-12-20) discloses a method for reducing the polyethylene wax content in ethylene polymerization reaction. Its technical feature is to introduce one or more of ethylene wax inhibitors such as ethers, ketones, lactones, heterocyclic compounds, organic phosphine compounds, mono- or poly-carboxylic acid compounds, and silicon compounds containing at least one Si-OR bond and wherein R is a hydrocarbon group into the catalyst system.

[0025] Chinese invention patent CN107282116A (application date: 2016-03-31) discloses a catalyst system for ethylene polymerization reaction, the technical characteristics of which are that the main catalyst is chloro-2-propionyl-1,10-phenanthroline-2,6-diethylaniline iron (II) complex, the co-catalyst is triethylaluminum, and the solvent is toluene. In addition, tert-butyl hydroperoxide is added to the catalyst system.

[0026] In addition, the following invention patents also involve a diiminopyridine iron type catalyst system, and the invention content is mainly about the ligand molecule: Chinese patent CN1463799A (application date 2002-06-21); Chinese patent CN100512962C (application date 2002-06-21); Chinese patent CN1552525A (application date 2003-12-19); Chinese patent CN100372609C (application date 2005-04-22); Chinese patent CN103008011B (application date 2012-03-19).

[0027] It is well known that the structure of the ligand molecule has a significant impact on the performance of the complex catalyst. The diiminopyridine ligand used in the non-selective oligomerization catalyst of ethylene can be synthesized using aniline and pyridine reactants. Undoubtedly, the ligand synthesis technology not only affects the yield of the ligand, but also affects the quality (purity) of the ligand, and thus affects the performance of the complex catalyst.

[0028] Chinese invention patent CN101580488B (application date: 2008-05-16) discloses a method for synthesizing a diiminopyridine ligand. Its technical characteristics are that 2,6-diacetylpyridine and anilines containing different substituents (o-toluidine, 2-methyl-4-methoxyaniline) are used as reactants, and the reaction of synthesizing the ligand is carried out in anhydrous ether solvent under the protection of slightly positive pressure argon gas, a molecular sieve water absorbent is added to the synthesis reactor, and a small amount of TiCl4 is added dropwise as an acid catalyst. The synthesis reaction is terminated after reacting at the reflux temperature of the solvent for 48 hours. Then the solvent is evaporated, the solid is dissolved in anhydrous ethanol and purified by recrystallization to obtain a ligand product. The ligands obtained with different anilines (o-toluidine, 2-methyl-4-methoxyaniline) reactants can reach a yield of 82%. The synthesized ligand is contacted with Fe(II) chloride in tetrahydrofuran solvent to obtain a complex (main catalyst) that has a catalytic effect on the non-selective polymerization of ethylene, namely, 2,6-diacetylpyridine di(2-methylaniline) iron(II) chloride and 2,6-diacetylpyridine di(2-methyl-4-methoxyaniline) iron(II) chloride. When 2,6-diacetylpyridine di(2-methylaniline) iron(II) chloride is used as the main catalyst for the ethylene polymerization reaction, a complex with a carbon number distribution of C4-C 28 Linear α-olefins between C6-C 20 The ethylene polymerization activity was 1.71×10 7 g / molFe·h, and the α-olefin selectivity was 96.8% (the reaction conditions were: reaction temperature of 50°C, reaction pressure of 1.5 MPa, reaction time of 30 min, and reaction solvent of toluene).

[0029] It is worth noting that in the ethylene polymerization technology disclosed in the above invention patent, as many as four solvents are involved: the synthesis reaction of diiminopyridine is carried out in anhydrous ether solvent (boiling point 34.5°C); the recrystallization and purification process of diiminopyridine uses ethanol solvent (boiling point 78.3°C); the preparation of the main catalyst Fe complex is carried out in tetrahydrofuran solvent (boiling point 66°C); and the ethylene polymerization reaction is carried out in toluene solvent (boiling point 110.6°C). There is no doubt that different solvents have different effects. It is people's inertial thinking to use different solvents in different reactions and separation processes and pursue the optimization of unit operations. However, this approach is not conducive to industrialization. This is mainly because in a factory, the simultaneous use of a large number of low-boiling point solvents (taking into account recycling) will complicate the process and will inevitably increase operating costs and safety risks.

[0030] The public document "Study on Ethylene Oligomerization and Supporting of Iron Acetylacetonate / Bis-Iminopyridine Catalytic System" (Master's thesis, Zhejiang University, 2011) involves the preparation of bi-iminopyridine ligands with different steric hindrance and electronic effects using aniline reactants containing different substituents. The ligands synthesized in this document include: 2,6-bis(1-(anilinoethyl))pyridine (L1), 2,6-bis(1-(2-methylanilinoethyl))pyridine (L2), 2,6-bis(1-(4-methoxy-2-methylanilinoethyl))pyridine (L3), 2,6-bis(1-(4-chloro-2-methylanilinoethyl))pyridine (L4) and 2,6-bis(1-(2-chloro-4-methylanilinoethyl))pyridine (L5). The synthesis methods of the above different ligands are the same. Take the synthesis of L3 ligand as an example: 2,6-diacetylpyridine and 2-methyl-4-methoxyaniline are dissolved in anhydrous ethanol, a small amount of glacial acetic acid is added as a catalyst, and the mixture is heated to reflux for 48 hours. After the reflux reaction is completed, most of the ethanol solvent is removed by vacuum distillation and then frozen and crystallized to obtain the crude L3 ligand product. The crude product is dissolved in ethanol again and recrystallized, and finally the obtained crystals are dried to obtain the L3 ligand product with a yield of about 77%. When the synthesized ligand is used to prepare a diiminopyridine iron complex catalyst and for non-selective polymerization of ethylene, the use of toluene solvent is involved. Among them, the diiminopyridine iron catalyst synthesized with L3 ligand and iron acetylacetonate reacts at 50°C and 0.1MPa for 30 minutes to generate α-olefins with a carbon number distribution of C4-C848.8%, C 10 -C 18 39.0%, C 10 -C 24 47.1% and C 26+ 4.1%, and the ethylene polymerization activity was as high as 2.3×10 6g / molFe·h, and the linear α-olefin selectivity is as high as 98%. In the technology reported in the document, a total of two solvents, ethanol and toluene, are involved. Compared with the existing technology, the types of solvents used are reduced. In particular, the synthesis reaction and post-refining of diiminopyridine are carried out in anhydrous ethanol solvent (boiling point 78.3°C), which can reduce the types of solvents involved in the implementation of this technology and relatively improve the safety of using solvents (ethanol is safer than ether and tetrahydrofuran). However, in addition to using ethanol solvent, toluene solvent is also required when implementing this technology. Toluene solvent (boiling point 110°C) is used as a solvent for ethylene polymerization reaction. Therefore, this technology still has the problem of needing to use many types of solvents. Summary of the invention

[0031] The object of the present invention is to provide a novel process for the non-selective oligomerization of ethylene to produce linear α-olefins, which involves only one solvent from the beginning to the end, starting from the synthesis of diiminopyridine to the polymerization of ethylene using diiminopyridine iron as the main catalyst to synthesize linear α-olefins with different carbon numbers. Specifically, the novel process provided by the present invention is as follows: (1) when synthesizing diiminopyridine ligands using 2,6-diacetylpyridine and aniline as raw materials, toluene with a relatively high boiling point is used as the solvent; (2) the ligand synthesized in the toluene solvent is directly reacted with a toluene solution of a metal central atom precursor such as acetylacetonate iron without complicated post-processing operations such as crystallization separation and drying to obtain a toluene solution of the main catalyst; (3) the toluene solution of the main catalyst and the toluene solution of the co-catalyst methylaluminoxane are used to form a catalyst system for the non-selective oligomerization of ethylene to produce α-olefins with different carbon numbers; (4) the non-selective oligomerization of ethylene is carried out in a high-pressure reactor using the catalyst system to produce a linear α-olefin mixture.

[0032] Undoubtedly, when the process provided by the present invention is used for the industrial production of α-olefins, the linear α-olefin mixture generated in the high-pressure reactor can be separated by a conventional separation process to obtain a monomeric α-olefin product. At the same time, a refined toluene solvent can also be obtained from the separation system. The refining of the toluene solvent includes a dehydration and a deoxygenation step. The refined toluene solvent can be recycled in steps (1) to (4).

[0033] The key to the present invention is to timely remove the effect of generated water on the conversion rate of 2,6-diacetylpyridine and aniline reactants when synthesizing the diiminopyridine ligand in a toluene solution. We have found in our exploratory research that if the water generated by the reaction cannot be removed in time, the reaction of 2,6-diacetylpyridine and aniline is difficult to proceed to the end, and the yield of diiminopyridine is low, which will not only reduce the concentration of the effective substance diiminopyridine in the diiminopyridine toluene solution produced in step (1), but also cause the toluene solution of the ligand to contain a large amount of unreacted substances, 2,6-diacetylpyridine and aniline, thereby causing the toluene solution of the ligand to be unable to be used to directly react with the toluene solution of a metal central atom precursor such as acetylacetonate iron to prepare the required diiminopyridine iron (main catalyst) toluene solution. The present invention has found through experiments that when 2,6-diacetylpyridine and aniline react in a toluene solution to synthesize diiminopyridine, using a dehydrating drying agent such as 3A molecular sieve, 4A molecular sieve and 5A molecular sieve to promptly remove moisture from the toluene solvent can significantly promote the conversion of the reactants and the generation of diiminopyridine ligands. Therefore, an ideal diiminopyridine toluene solution can be obtained for directly preparing a toluene solution of a main catalyst, that is, a toluene solution of diiminopyridine iron.

[0034] We have noticed that in the synthesis method of the diiminopyridine ligand disclosed in the Chinese invention patent CN101580488B (application date: 2008-05-16), it is recorded that when the diiminopyridine ligand is synthesized in anhydrous ether solvent using 2,6-diacetylpyridine and aniline containing different substituents (o-toluidine, 2-methyl-4-methoxyaniline) as reactants, a molecular sieve water absorbent is added to the synthesis kettle. However, we have found through experiments that directly adding a molecular sieve molding (such as a commercially available small spherical 4A molecular sieve dehydrating agent) to the reactor for synthesizing diiminopyridine will affect the stirring operation of the synthesis kettle and the molecular sieve molding is easy to pulverize under the action of solvent heat and mechanical stirring. If a powdered molecular sieve dehydrating agent is directly added to the reactor, it will increase the trouble of solid-liquid separation and cause the separation loss of toluene solvent and ligand. More importantly, the added solid-liquid separation link will increase the exposure of the ligand solution to the air, and then the moisture and oxygen in the air will be absorbed by the dry ligand solution, resulting in the loss of function or even complete loss of the catalyst system prepared in step (3). The best way to overcome this problem is to add molecular sieve dehydrating agent particles to the reflux tank of the toluene solvent, and the water generated by the reaction is taken out of the reactor by the toluene vapor, and is removed when it contacts the molecular sieve dehydrating agent in the reflux tank, and the dehydrated toluene solvent will eventually be automatically refluxed to the reactor. This method not only solves the problem of toluene solvent dehydration in the synthesis process of diimino pyridine, but also avoids solid-liquid separation operation. The appropriate amount of molecular sieve dehydrating agent is determined by experiment. The basis for determining the amount of molecular sieve dehydrating agent is to measure the water content of the ligand solution. The final water content in the ligand solution (after the reflux reaction is completed) must be able to meet the needs of directly preparing the main catalyst solution. It is not difficult to understand that in the present invention, if the water content of the ligand solution obtained in step (1) exceeds the standard, it will cause the catalyst system assembled in step (3) to lose function or even completely lose. The molecular sieve dehydrating agent particles are added to the reflux tank of the toluene solvent to avoid the mutual influence between the molecular sieve dehydration and the stirring reaction in the synthesis reactor. The size of the reflux tank can be flexibly set according to the appropriate amount of the molecular sieve dehydrating agent.

[0035] In addition, when the toluene solution of the ligand is prepared by the method provided by the present invention, the reflux reaction of 2,6-diacetylpyridine and aniline is also required to be carried out under the protection of high-purity nitrogen. The purpose of using high-purity nitrogen protection is mainly to prevent air from entering the reactor, which causes the ligand solution to fail to meet the anhydrous and oxygen-free conditions required for the direct assembly of the catalyst system.

[0036] The technical solution of the present invention is as follows:

[0037] A process for preparing linear α-olefins by non-selective polymerization of ethylene, comprising the following steps:

[0038] Step 1: Preparation of toluene solution of bis-iminopyridine ligand

[0039] The diiminopyridine ligand is synthesized by reacting 2,6-diacetylpyridine with aniline raw materials. The synthesis reaction is carried out under the protection of high-purity nitrogen using toluene that has been dehydrated and deoxygenated as solvent, with a reaction pressure of normal pressure and a reaction temperature range of 100-120°C, preferably 110°C (toluene reflux temperature); the reaction time range is 0.5-72h, preferably 3-4h. The water generated during the synthesis of the diiminopyridine ligand is removed by using a type A molecular sieve dehydrating agent molded product filled in a reflux tank. The prepared toluene solution of the diiminopyridine ligand is kept at a constant temperature of not less than 30°C.

[0040] Engineers familiar with this field can select the aniline raw materials according to relevant patent documents and public documents. Such as aniline, o-toluidine, 2-methyl-4-methoxyaniline, 2-methyl-4-chloroaniline, 2-chloro-4-methylaniline, etc. The present invention recommends the use of 2-methyl-4-methoxyaniline. It should be emphasized that although the existing method (such as Example 18 of CN101580488B) tends to use a large excess of 2-methyl-4-methoxyaniline (n 2-甲基-4-甲氧基苯胺 :n 2,6-二乙酰基吡啶 =5:1) to synthesize diiminopyridine, but for the present invention, since the separation process of ligand crystallization is omitted, the reaction product of 2,6-diacetylpyridine and 2-methyl-4-methoxyaniline in toluene solvent is directly used to prepare the main catalyst (diiminopyridine iron) solution, so the molar ratio of the amount of 2-methyl-4-methoxyaniline to the amount of 2,6-diacetylpyridine is required to be close to the theoretical value (2:1). The present invention recommends that the molar ratio of the amount of 2-methyl-4-methoxyaniline to the amount of 2,6-diacetylpyridine is in the range of 3:1-2:1, and the preferred range is 2.5:1-2.2:1. Similarly, the molar ratio of the amount of aniline raw materials to the amount of 2,6-diacetylpyridine is in the range of 3:1-2:1, and the preferred range is 2.5:1-2.2:1.

[0041] In addition, the amount of toluene solvent used must take into account the needs of the synthesis reaction of the diiminopyridine ligand and the requirements for the concentration of the diiminopyridine ligand when the diiminopyridine iron catalyst is subsequently prepared. The present invention recommends that the appropriate range of the amount of toluene solvent used, expressed by the concentration of 2,6-diacetylpyridine, is 0.05-0.5 mol / L, preferably 0.2-0.3 mol / L.

[0042] The A-type molecular sieve used as a dehydrating agent can conveniently select commercially available 3A, 4A or 5A molecular sieve beads. Although other commercial molecular sieves such as X, Y and SAPO-34, as well as non-molecular sieve salts such as NaSO4, also have the function of removing trace water from organic matter, and are therefore theoretically applicable to the present invention, the present invention recommends the use of 3A, 4A or 5A molecular sieve beads from comprehensive considerations of cost, dehydration selectivity and dehydration depth, and regeneration and reuse performance. From the perspective of use effect, there is no essential difference in using 3A, 4A or 5A molecular sieve beads as dehydrating agents. In order to ensure the dehydration effect, the present invention requires that the appropriate amount of A-type molecular sieve added based on the weight of 2,6-diacetylpyridine feed is ≥30 times, preferably ≥40 times.

[0043] Before using the type A molecular sieve as a dehydrating agent, conventional dehydration pretreatment is required. When using type A molecular sieve as a dehydrating agent in industry, after a period of use, the molecular sieve dehydrating agent must be dehydrated and regenerated to ensure the dehydration effect for continued use. Engineers familiar with this field can select the dehydration pretreatment conditions before using the type A molecular sieve, as well as the staged dehydration and regeneration conditions during use based on experience. The dehydration pretreatment of the type A molecular sieve before use and the staged dehydration and regeneration treatment during use can be performed in situ in the reflux tank.

[0044] In order to facilitate the direct use of the toluene solution of the synthesized bis-iminopyridine ligand in the second step, it is necessary to quantitatively sample the toluene solution of the bis-iminopyridine ligand, prepare the bis-iminopyridine ligand sample according to a conventional crystallization method and measure it, and then use nuclear magnetic resonance hydrogen spectrum to quantitatively analyze the bis-iminopyridine content in the ligand sample, so as to backcalculate the synthesis yield of the ligand and the bis-iminopyridine content in the toluene solution of the bis-iminopyridine ligand.

[0045] In addition, it should be noted that engineers familiar with the art can flexibly select the dehydration and deoxygenation methods of toluene solvent according to their own experience and production conditions. For example, in the laboratory, the method of sodium wire distillation (reflux) can be used to remove trace water and oxygen in toluene solvent. In industrial production, 4A molecular sieve drying and dehydrating agent can be used to remove trace moisture in toluene solvent, and commercially available deoxidizer can be used to remove trace dissolved oxygen in toluene solvent. The present invention is not limited to this. As for the protective gas that needs to be used in the synthesis process of the diimino pyridine ligand, its main function is to prevent water vapor and oxygen in the air from invading. Therefore, theoretically, inert gases such as high-purity helium and argon that can achieve this purpose and cannot react chemically with toluene solvent and reactants and ligand products can be used, and the present invention is not limited to this. However, from the perspective of cost and the prospect of industrial application, the present invention recommends the use of high-purity nitrogen as protective gas. In addition to the above, the present invention also particularly points out that the prepared diimino pyridine ligand solution should be stored at an appropriate temperature to prevent diimino pyridine from precipitating from the toluene solvent. Engineers familiar with the art can select the storage temperature of the ligand solution according to the amount of toluene solvent, i.e. the actual concentration of diimino pyridine in the toluene solvent. When the present invention is implemented industrially, the toluene solution of the ligand can be kept at a constant temperature at or near the temperature of ethylene polymerization.

[0046] Step 2: directly use the toluene solution of the diiminopyridine ligand obtained in the first step to prepare a toluene solution of the main catalyst diiminopyridine iron

[0047] First, a toluene solution of an iron central atom precursor is prepared using dehydrated and deoxygenated toluene as a solvent. Then, the toluene solution of the diiminopyridine ligand obtained in the first step and the toluene solution of the iron central atom precursor are mixed evenly in equimolar amounts at or near the ethylene polymerization temperature under anhydrous and oxygen-free conditions to obtain a toluene solution of the main catalyst diiminopyridine iron.

[0048] The toluene solution of the iron center atom precursor and the toluene solution of the diimino pyridine ligand are mixed according to the metering ratio n 双亚胺基吡啶 :n 铁原子 ≈1:1. The theoretical value of the concentration of diiminopyridine iron in toluene solvent after mixing (≈diiminopyridine concentration≈iron central atom concentration) is in the range of 0.5×10 -4 -1.5×10 -4 mol / L, the preferred range is 0.8×10 -4 -1.2×10 -4mol / L. Engineers familiar with the field can select the iron-centered atom precursor according to reports in patent literature and public literature. For example, iron acetylacetonate, ferric chloride, ferrous chloride and ferrous bromide can be selected as the iron-centered atom precursor.

[0049] Step 3: Using the toluene solution of the main catalyst diimidopyridyl iron prepared in the second step and the toluene solution of the co-catalyst methylaluminoxane (MAO) in a high-pressure reactor used for ethylene polymerization to form a catalyst system for non-selective polymerization of ethylene

[0050] First, a toluene solution of a co-catalyst methylaluminoxane (MAO) is prepared using toluene that has been subjected to a dehydration and deoxygenation treatment as a solvent. Then, under anhydrous and oxygen-free conditions, the toluene solution of the co-catalyst methylaluminoxane (MAO) and the toluene solution of the main catalyst diimidopyridyl iron obtained in the second step are added in order according to metering at or near the ethylene polymerization temperature to a high-pressure reactor used for ethylene polymerization reaction that has been pre-treated by dehydration and deoxygenation in a conventional method and mixed evenly, thereby forming a catalyst system for non-selective ethylene polymerization.

[0051] Wherein, the cocatalyst methylaluminoxane (MAO) can be a commercial product. The commercial product is generally a toluene solution with a MAO content of 10%. Engineers familiar with the art can also synthesize a toluene solution of MAO from trimethylaluminum (TMA) according to the methods reported in patent documents and public documents. For example, a toluene solution of methylaluminoxane (MAO) can be synthesized according to the method provided in the document (Petrochemical Technology and Application, 2009, 27 (06): 526-528.). In addition, the present invention also allows the use of modified methylaluminoxane (MMAO) as a cocatalyst. The modified methylaluminoxane (MMAO) can be a commercial product or can be synthesized by itself. Engineers familiar with the art can synthesize a toluene solution of MMAO from trimethylaluminum (TMA) according to the methods reported in patent documents and public documents. For example, a toluene solution of modified methylaluminoxane (MMAO) can be synthesized according to the method provided in the document (Petrochemical Technology and Application, 2008 (04): 326-328).

[0052] In addition, engineers familiar with the art can select the ratio of the co-catalyst to the main catalyst according to their own experience and specific requirements for the ethylene polymerization reaction (especially the requirements for the activity of the catalyst system). The ratio of the co-catalyst to the main catalyst can also be selected according to reports in patent documents and public documents. The present invention is not limited to this. Engineers familiar with the art can also add an appropriate amount of ethylene wax inhibitor to the ethylene non-selective polymerization catalyst system according to their own experience and specific requirements for the ethylene polymerization reaction (especially the restrictions on the formation of polyethylene wax by ethylene polymerization). For example, referring to the report in Chinese patent CN104961618A (application date: 2015-06-12), at least one of the following substances is added to the ethylene non-selective polymerization catalyst system as an inhibitor for inhibiting the formation of ethylene wax: p-bromophenol, p-chlorophenol and p-fluorophenol. The present invention allows the addition of such additives, but there is no limitation on whether to add such additives. Engineers familiar with the art can flexibly determine the concentration of the main catalyst diimidopyridine iron in the final catalyst system to which various additives are added based on their own experience and specific requirements for the ethylene polymerization reaction (mainly requirements for the activity of the catalyst system). The present invention does not specifically limit this.

[0053] Generally, the preparation of the ethylene non-selective polymerization catalyst system should be carried out in situ in the ethylene polymerization high-pressure reactor. For example, when a small high-pressure reactor is used in the laboratory for the non-selective polymerization of ethylene, before the non-selective polymerization catalyst system of ethylene is prepared in situ, the synthesis reactor should be subjected to the following conventional purification treatment: first, the reactor and its affiliated pipeline system should be treated by high-temperature drying, vacuum replacement and other operations to ensure that the reaction system is free of water and oxygen, and after replacing the reaction system with 110°C high-purity nitrogen twice, the reaction system is replaced once with high-purity ethylene (refined by dehydration and deoxygenation tubes) to put the reaction system in an ethylene environment, and then the reactor is lowered to the reaction temperature of 50°C.

[0054] Step 4: Using the catalyst system prepared in situ in the high-pressure reactor in the third step, a non-selective polymerization reaction of ethylene is carried out in the high-pressure reactor to produce a linear α-olefin mixture.

[0055] Engineers familiar with the art can carry out the reaction of the non-selective polymerization of ethylene to produce a linear α-olefin mixture in a high-pressure reactor according to their own experience or according to the methods provided in patent documents and public documents. For example, Chinese patent CN1401666A (application date: 2001-08-17) describes in detail the reaction method of non-selective polymerization of ethylene to produce a linear α-olefin mixture in a laboratory. The general method is as follows: (1) After the toluene solution of the co-catalyst, the main catalyst and other auxiliary agents are introduced into the reactor in sequence according to the third step to form a catalyst system, ethylene is introduced into the reactor at the reaction temperature to reach the reaction pressure, and the timing reaction can be started. The reaction temperature, pressure and time can be optimized and determined by experiments according to the specific requirements of the catalyst system. For example, the most suitable pressure, temperature and time parameters can be selected within the range of reaction pressure of 0.1 to 3 MPa, reaction temperature of 30 to 70°C and reaction time of 5 to 30 min. The present invention has no specific limitation on this; (2) After the reaction is completed, the high-pressure reactor is first depressurized, and after the actual temperature in the reactor is lower than 50°C, the reactor is opened at normal pressure, all the reactants are taken out, and an appropriate amount of 10% acidified ethanol is added thereto to terminate the reaction.

[0056] The effect of the present invention can be evaluated by the catalyst (Fe) activity of the ethylene polymerization reaction, the linear α-olefin product selectivity and the solid product quality. The reaction product liquid is analyzed by Shimadzu 2014C gas chromatograph, and the chromatographic column model is PONA column (50m×0.2mm×0.2μm). The column temperature is 320°C, the detector is 330°C, the injection port temperature is 330°C, and the temperature is programmed. The internal standard method (the internal standard is n-heptane) is used to quantitatively calculate the linear α-olefin content of different carbon numbers, and the catalyst activity and linear α-olefin selectivity are calculated by weighing the mass of the solid product ethylene wax.

[0057] Beneficial effects of the present invention:

[0058] The alpha-olefin production process provided by the present invention uses only toluene solvent, and the solvent used for synthesizing the diimino pyridine ligand is the same as the solvent for the ethylene polymerization reaction. Therefore, the product liquid obtained in the ligand synthesis step can be directly used to prepare the catalyst for the ethylene polymerization reaction, so that the ligand synthesis step and the ethylene polymerization reaction step are seamlessly connected, and the cumbersome post-processing operations (suction filtration, freezing crystallization, suction filtration, freezing crystallization, suction filtration, drying, etc.) after the ligand synthesis in the existing process method are omitted. The industrial implementation of the present invention can bring advantages such as high safety, small equipment investment, low energy consumption in the production process, and is conducive to reducing the production cost of alpha-olefins. DETAILED DESCRIPTION

[0059] The present invention will be further described below by means of specific examples, but the present invention is not limited by these examples.

[0060] Example 1: This example is used to illustrate that from the synthesis of diaminopyridine to the ethylene polymerization reaction with diaminopyridine iron as the main catalyst, only one solvent, toluene, is used, that is, only one solvent is involved from beginning to end, so that the ligand synthesis step and the ethylene polymerization reaction step are seamlessly connected, and the cumbersome post-processing operations such as crystallization separation after the ligand synthesis in the existing process method are omitted. The toluene solution containing the ligand obtained in the ligand synthesis step is directly used to prepare the main catalyst diaminopyridine iron, which is completely feasible for the ethylene polymerization reaction.

[0061] Step 1: Synthesize the diiminopyridine ligand using 2,6-diacetylpyridine and 2-methyl-4-methoxyaniline as raw materials

[0062] 1) Use a 250mL round-bottom flask as a reactor. After the reactor is replaced with high-purity nitrogen, a rotor is placed in the reactor under the protection of high-purity nitrogen, 30mL of dehydrated and deoxygenated toluene is added as a solvent, and then 1.2g of 2,6-diacetylpyridine and 2mL of 2-methyl-4-methoxyaniline (the molar ratio of 2-methyl-4-methoxyaniline to 2,6-diacetylpyridine is 2.2:1), and then 3 drops of glacial acetic acid are added as a catalyst. A reflux tank is connected above the round-bottom flask, and a spherical condenser is provided above the reflux tank. 50g of pretreated 4A molecular sieve is added to the reflux tank as an adsorbent (the amount of 4A molecular sieve beads added is 41.7 times the amount of 2,6-diacetylpyridine feed (mass)); 2) Start stirring and oil bath heating, and the oil bath temperature is set to 110℃. When the reactor reaches the reflux reaction temperature of 110°C, the timing starts, and the reaction time is set to 3h; 3) After the reaction is completed, the prepared diiminopyridine ligand solution is transferred to the prepared Schleck bottle and stored at a constant temperature of not less than 30°C for use.

[0063] Step 2: Preparation of toluene solution of main catalyst diiminopyridine iron

[0064] The toluene solution of the main catalyst diiminopyridine iron was directly prepared using the diiminopyridine toluene solution obtained in the first step. First, 50 mL of toluene that had been dehydrated and deoxygenated was taken as a solvent in a glove box, added to a Schleck bottle containing 1.75 mg of acetylacetonate iron, and shaken well to prepare a toluene solution of the iron central atom precursor. Then, under anhydrous and oxygen-free conditions, 28.6 μL of the ligand toluene solution obtained in the first step (the concentration of diiminopyridine was calculated to be 0.175 mol / L by crystallization measurement and nuclear magnetic resonance analysis, so n 双亚胺基吡啶 :n 铁原子≈1:1) and the prepared toluene solution of the iron central atom precursor were mixed at 30°C to obtain a toluene solution of the main catalyst diiminopyridine iron. The theoretical concentration of diiminopyridine iron in toluene solvent is 1.0×10 -4 mol / L (≈bis-iminopyridine concentration ≈ iron central atom concentration).

[0065] Step 3: Preparation of ethylene non-selective oligomerization catalyst system in a high pressure reactor

[0066] The ethylene non-selective polymerization catalyst system is prepared by the toluene solution of the main catalyst prepared in the second step and the toluene solution containing methylaluminoxane (MAO). The preparation of the ethylene non-selective polymerization catalyst system is carried out in situ in the ethylene polymerization autoclave. For this reason, before the catalyst system is introduced into the autoclave, the reactor and its attached pipeline system must first be replaced by operations such as high-temperature drying and vacuum replacement to ensure that the reaction system is anhydrous and oxygen-free, and then the reaction system is replaced with high-purity ethylene (refined by a dehydration and deoxygenation tube) to make the reaction system in an ethylene environment and keep the reactor temperature constant at the ethylene polymerization reaction temperature (50°C). Then in a glove box, 1.662mL of a commercially available solution of methylaluminoxane (10% MAO) is added to a Schreck bottle containing 50mL of a toluene solvent treated with dehydration and deoxygenation, and shaken to prepare a toluene solution of the cocatalyst methylaluminoxane (MAO). Next, under anhydrous and oxygen-free conditions, 50 mL of the prepared toluene solution containing methylaluminoxane (MAO) and 50 mL of the toluene solution of the main catalyst obtained in the second step are successively sucked into a high-pressure reactor in a stirring state, thereby preparing a catalyst system for non-selective polymerization of ethylene.

[0067] Step 4: Non-selective polymerization of ethylene

[0068] 1) After the third step of sequentially introducing the toluene solutions of the co-catalyst and the main catalyst into the reactor to form the catalyst system in situ, ethylene can be directly introduced into the reactor to reach a reaction pressure of 2MPa in this step, and then the reaction time is started for 10 minutes; 2) After the reaction is completed, the high-pressure reactor is first depressurized, and when it is confirmed that the actual temperature in the reactor is lower than 50°C and it is safe to open the reactor, the reactor is carefully opened at normal pressure, all the reactants are taken out, and 2mL of 10% acidified ethanol is added thereto to terminate the reaction. 3) The reactants are centrifuged 2-3 times, and the supernatant is taken for gas chromatography analysis. The solid product obtained by centrifugation is placed in a 50°C oven and dried overnight and then weighed, and the mass of the solid product is 0.91g. According to the chromatographic analysis data, the reaction result is calculated as follows: the catalyst activity is 1.23×10 7 g / molFe·h, linear α-olefin selectivity is 91.16%. The carbon number distribution is C4-C 28Among them, C6 14.95%, C8 20.11%, C 10 17.26%, C 12 13.21%, C 14+ 34.47%.

[0069] Comparative Example 1: This comparative example is used to illustrate that, when the amount of molecular sieve dehydrating agent is appropriate and the ligand synthesis reaction is normal, the diiminopyridine ligand is crystallized from its synthesis solution and dried, and then redissolved in toluene solution for preparing the main catalyst solution and conducting ethylene polymerization reaction. The process steps are cumbersome and will not improve the effect of the ethylene polymerization reaction.

[0070] (1) Example 1 was repeated, but the reaction solution containing the diimino pyridine ligand prepared in the first step was rotary evaporated to remove most of the solvent, and then filtered after crystallization at -18°C overnight, washed with anhydrous ethanol, and recrystallized at -18°C for 4 hours and filtered, and dried at 110°C for 4 hours to obtain a yellow powder of 2,6-di(1-(4-methoxy-2-methylanilino)ethyl)pyridine ligand with a yield of 82%. 1 H NMR(CDCl3 / TMS,δ):8.40(d,2H,Py-mH),7.87(t,1H,Py-pH),6.82(d,2H,Aryl-mH),6.76(m,2H,Aryl -mH), 6.64 (d, 2H, Aryl-oH), 3.82 (s, 6H, Aryl-OCH3), 2.36 (s, 6H, N = C-CH3), 2.14 (s, 6H, Aryl-CH3).

[0071] (2) In a glove box, 0.00225 g of the solid ligand sample was dissolved in 50 mL of anhydrous and oxygen-free toluene solvent to prepare a toluene solution of the ligand (the concentration of diiminopyridine was 1.0 × 10 -4 mol / L). Then, a toluene solution of the main catalyst and the co-catalyst was prepared according to the method described in Example 1, and a catalyst system for non-selective polymerization of ethylene was formed in situ in a high-pressure reactor. The catalyst system was used to carry out non-selective polymerization of ethylene under the reaction conditions described in Example 1, and a solid product mass of 1.37 g was obtained. The reaction result was a catalyst activity of 1.19×10 7 g / molFe·h, linear α-olefin selectivity is 86.27%. The carbon number distribution is C4-C 28 Among them, C6 17.69%, C8 22.61%, C 10 18.06%, C 12 12.49%, C 14+ 29.14%.

[0072] In this comparative example, the actual change brought about by crystallizing the ligand from toluene is to reduce the content of 2,6-diacetylpyridine and 2-methyl-4-methoxyaniline in the catalyst system. However, it can be seen from the comparison of the reaction results that this is not necessary, indicating that when the ligand toluene solution is directly used in Example 1, the small amount of 2,6-diacetylpyridine and 2-methyl-4-methoxyaniline contained therein will not affect the ethylene polymerization reaction.

[0073] Comparative Example 2: This comparative example is used to illustrate that toluene solvent is used instead of anhydrous ethanol to synthesize diiminopyridine ligands and the toluene solution containing the ligand obtained in the ligand synthesis step is directly used to prepare the main catalyst diiminopyridine iron, thereby achieving seamless connection between the ligand synthesis step and the ethylene polymerization reaction step, simplifying the production process of α-olefins, and reducing the types of solvents used in industrial production sites, without adversely affecting the non-selective polymerization of ethylene in the catalyst system.

[0074] (1) Repeat the process of synthesis of the bisiminopyridine ligand, rotary evaporation of the reaction solution, low-temperature crystallization and dissolution recrystallization described in Comparative Example 1, but change the solvent used for the synthesis of the bisiminopyridine ligand to anhydrous ethanol, and do not use 4A molecular sieve as a dehydrating agent in the reaction of synthesizing the ligand. The synthesis yield of the bisiminopyridine ligand is also about 82%. 1 HNMR(CDCl3 / TMS,δ):8.40(d,2H,Py-mH),7.87(t,1H,Py-pH),6.82(d,2H,Aryl-mH),6.76(m,2H,Ary l-mH), 6.64 (d, 2H, Aryl-oH), 3.82 (s, 6H, Aryl-OCH3), 2.36 (s, 6H, N = C-CH3), 2.14 (s, 6H, Aryl-CH3).

[0075] (2) Using the diiminopyridine synthetic sample as a ligand, the operation in step (2) of comparative example 1 was repeated to obtain a solid product mass of 1.45 g. The result of the non-selective polymerization of ethylene was: the catalyst activity was 1.17×10 7 g / molFe·h, linear α-olefin selectivity is 85.20%. The carbon number distribution is C4-C 28 Among them, C6 15.47%, C8 19.56%, C 10 16.61%, C 12 12.60%, C 14+ 35.76%.

[0076] Example 2: This example is used to illustrate that when a diiminopyridine ligand is synthesized in a toluene solvent and the resulting product liquid is directly used to prepare a main catalyst diiminopyridine iron solution, the ratio of the amount of 2-methyl-4-methoxyaniline to the amount of 2,6-diacetylpyridine is allowed to vary within a certain range.

[0077] Example 1 was repeated, but in the first step of ligand synthesis, the molar ratio of 2-methyl-4-methoxyaniline to 2,6-diacetylpyridine was changed to 2:1, 2.5:1 and 3:1, respectively, and the obtained catalyst was used for non-selective polymerization of ethylene. The mass of the solid product was 0.76 g, 1.03 g and 0.89 g, respectively, and the catalyst activity was 6.3×10 6 g / molFe·h, 1.17×10 7 g / molFe·h and 1.15×10 7 g / molFe·h, linear α-olefin selectivities were 88.85%, 86.26% and 87.25% respectively, and the carbon number distribution was C4-C 28 In order, C6 15.16%, C8 19.98%, C 10 15.82%, C 12 13.54%, C 14+ 35.50%; C6 15.62%, C8 20.56%, C 10 15.34%, C 12 12.38%, C 14+ 36.10%; C6 15.36%, C819.88%, C 10 15.97%, C 12 13.08%, C 14+ 35.71%.

[0078] Example 3: This example is used to further illustrate that when a diiminopyridine ligand is synthesized in a toluene solvent and the resulting product liquid is directly used to prepare a main catalyst diiminopyridine iron solution, the concentration of 2,6-diacetylpyridine in the toluene solvent is allowed to vary within a certain range.

[0079] Example 1 was repeated, but in the first step of ligand synthesis, the amount of toluene solvent was changed to 147 mL (the concentration of 2,6-diacetylpyridine in toluene solvent was 0.05 mol / L) and 14.7 mL (the concentration of 2,6-diacetylpyridine in toluene solvent was 0.5 mol / L), and the obtained catalysts were used for ethylene non-selective oligomerization reaction. The solid product masses were 0.76 g and 0.65 g, respectively, and the catalyst activities were 1.23×10 7g / molFe·h and 1.05×10 7 g / molFe·h, linear α-olefin selectivity was 87.15% and 87.65% respectively. The carbon number distribution was C4-C 28 Among them, C6 15.26%, C8 19.99%, C 10 15.52%, C 12 13.58%, C 14+ 35.65% and C6 15.22%, C8 20.09%, C 10 15.42%, C 12 13.67%, C 14+ 35.60%.

[0080] Example 4: This example is used to illustrate that when a diiminopyridine ligand is synthesized in a toluene solvent and the resulting product liquid is directly used to prepare a main catalyst diiminopyridine iron solution, other aniline raw materials can be used to replace 2-methyl-4-methoxyaniline to react with 2,6-diacetylpyridine to prepare a usable diiminopyridine ligand and a main catalyst.

[0081] Example 1 was repeated, but in the first step of ligand synthesis, 1.41 mL of aniline, 1.66 mL of o-toluidine, 1.99 mL of 2-methyl-4-chloroaniline, and 1.99 mL of 2-chloro-4-methylaniline were used in order to replace 2-methyl-4-methoxyaniline (the molar ratio of aniline to 2,6-diacetylpyridine was 2.2:1), and the obtained catalyst was used for the non-selective polymerization of ethylene. The masses of the solid products were 1.39 g, 1.17 g, 1.41 g, and 1.39 g, respectively, and the catalyst activities were 1.04×10 7 g / molFe·h, 1.11×10 7 g / molFe·h, 1.38×10 7 g / molFe·h and 1.34×10 7 g / molFe·h, the linear α-olefin selectivities were 86.51%, 85.98%, 85.51% and 85.55% respectively. The carbon number distribution was C4-C 28 In order, they are: C6 15.35%, C8 20.22%, C 10 17.52%, C 12 12.45%, C 14+ 34.46%; C6 15.67%, C820.89%, C 10 17.58%, C 12 12.09%, C 14+ 33.77%; C6 15.25%, C8 20.09%, C10 17.32%, C 12 12.41%, C 14+ 34.93%; C6 15.26%, C8 20.34%, C 10 17.83%, C 12 12.05%, C 14+ 34.52%. From the comparison with Example 1, it can be seen that other anilines are also suitable for preparing diimino pyridine ligands for ethylene oligomerization.

[0082] Example 5: This example is used to illustrate that when synthesizing diiminopyridine ligands in toluene solvent, the amount of molecular sieve dehydrating agent loaded in the reflux tank is allowed to vary within a certain range, which has no obvious effect on the subsequent use of the synthesized ligand solution directly for the preparation of the main catalyst diiminopyridine iron solution and the non-selective polymerization reaction of ethylene.

[0083] Example 1 was repeated, but in the first step of ligand synthesis, the amount of 4A molecular sieve was changed to 30 times and 83 times the amount of 2,6-diacetylpyridine, and the obtained catalyst was used for non-selective polymerization of ethylene. The mass of the solid product was 1.09 g and 0.89 g, respectively, and the catalyst activity was 1.04×10 7 g / molFe·h and 1.23×10 7 g / molFe·h, linear α-olefin selectivity was 87.28% and 86.25% respectively. The carbon number distribution was C4-C 28 Among them, C6 15.34%, C8 19.16%, C 10 17.93%, C 12 12.67%, C 14+ 34.90% and C6 15.23%, C8 20.19%, C 10 16.63%, C 12 12.68%, C 14+ 35.27%.

[0084] Example 6: This example is used to illustrate that when synthesizing diiminopyridine ligands in toluene solvent, there are multiple choices of the type of molecular sieve dehydrating agent loaded in the reflux tank, which has no adverse effect on the subsequent direct use of the synthesized ligand solution for the preparation of the main catalyst diiminopyridine iron solution and the non-selective polymerization reaction of ethylene.

[0085] Example 1 was repeated, but in the first step of ligand synthesis, 4A molecular sieve was replaced by 3A and 5A molecular sieves, and the obtained catalysts were used for non-selective polymerization of ethylene. The mass of the solid product was 1.25 g and 1.05 g, respectively, and the catalyst activity was 1.08×107 g / molFe·h and 8.47×10 6 g / molFe·h, the linear α-olefin selectivity was 88.81% and 86.12% respectively. The carbon number distribution was C4-C 28 Among them, C6 15.20%, C8 20.79%, C 10 16.34%, C 12 12.81%, C 14+ 34.86% and C6 15.72%, C8 20.66%, C 10 15.82%, C 12 12.89%, C 14+ 34.90%. From the comparison with Example 1, it can be seen that 3A molecular sieve and 5A molecular sieve are also suitable for preparing diimino pyridine ligands for ethylene oligomerization reaction.

[0086] Comparative Example 3: This comparative example is used to illustrate that in order to be able to use the diiminopyridine ligand synthesized in toluene solvent directly for the preparation of the main catalyst diiminopyridine iron solution without crystallization separation, the ratio of 2-methyl-4-methoxyaniline to 2,6-diacetylpyridine in the ligand synthesis process should not be too high, otherwise a large amount of excess 2-methyl-4-methoxyaniline is not conducive to the non-selective polymerization reaction of ethylene.

[0087] Example 1 was repeated, but in the first step of ligand synthesis, the molar ratio of 2-methyl-4-methoxyaniline to 2,6-diacetylpyridine was changed to 5:1, and the obtained catalyst was used for non-selective polymerization of ethylene. The mass of the solid product was 1.53 g, and the reaction results were: the catalyst activity was 9.5×10 6 g / molFe·h, linear α-olefin selectivity is 86.25%. The carbon number distribution is C4-C 28 Among them, C6 14.98%, C8 20.67%, C 10 16.03%, C 12 14.11%, C 14+ 34.21%.

[0088] Comparative Example 4: This comparative example is used to illustrate that in order to be able to use the diiminopyridine ligand synthesized in toluene solvent directly for the preparation of the main catalyst diiminopyridine iron solution without crystallization separation, the ratio of 2-methyl-4-methoxyaniline to 2,6-diacetylpyridine in the ligand synthesis process should not be too low, otherwise it will be detrimental to the non-selective polymerization reaction of ethylene.

[0089] Example 1 was repeated, but in the first step of ligand synthesis, the molar ratio of 2-methyl-4-methoxyaniline to 2,6-diacetylpyridine was changed to 1.8:1, and the obtained catalyst was used for non-selective polymerization of ethylene. The mass of the solid product was 1.13 g, and the reaction results were: the catalyst activity was 8.9×10 6 g / molFe·h, linear α-olefin selectivity is 87.95%. The carbon number distribution is C4-C 28 Among them, C6 15.02%, C8 20.16%, C 10 16.73%, C 12 15.01%, C 14+ 33.08%.

[0090] Comparative Example 5: This comparative example is used to illustrate that when synthesizing diiminopyridine ligands in toluene solvent, the amount of molecular sieve dehydrating agent loaded in the reflux tank is too small, which is not conducive to the subsequent direct use of the synthesized ligand solution for the preparation of the main catalyst diiminopyridine iron solution and the non-selective polymerization reaction of ethylene.

[0091] Example 1 was repeated, but in the first step of ligand synthesis, the amount of 4A molecular sieve was changed to 8.3 times the amount of 2,6-diacetylpyridine, and the obtained catalyst was used for non-selective polymerization of ethylene. The mass of the solid product was 1.03 g, and the reaction results were: the catalyst activity was 3.83×10 6 g / molFe·h, linear α-olefin selectivity is 87.25%. The carbon number distribution is C4-C 28 Among them, C6 14.65%, C8 20.72%, C 10 16.56%, C 12 12.99%, C 14+ 35.08%.

[0092] Studies have shown that when synthesizing diiminopyridine ligands in toluene solvent, if the amount of molecular sieve dehydrating agent loaded in the reflux tank is too small, on the one hand, the yield of diiminopyridine ligands will be reduced, and on the other hand, the water content in the toluene solution of the ligand will be too high. These two points are the main reasons for the poor effect of ethylene polymerization reaction.

[0093] Example 7: This example is used to further illustrate that when the diiminopyridine ligand is synthesized in toluene solvent and the resulting product liquid is directly used to prepare the main catalyst diiminopyridine iron solution, the reaction temperature is allowed to vary within a certain range.

[0094] Example 1 was repeated, but in the first step of ligand synthesis, the ligand synthesis temperature was changed to 100°C and 120°C, respectively, and the obtained catalysts were used for non-selective polymerization of ethylene. The solid product masses were 0.45 g and 0.85 g, respectively, and the catalyst activities were 9.6×10 6 g / molFe·h and 1.21×10 7 g / molFe·h, linear α-olefin selectivity was 89.05% and 88.78% respectively. The carbon number distribution was C4-C 28 Among them, C6 15.19%, C8 20.89%, C 10 15.32%, C 12 13.29%, C 14+ 35.31% and C6 15.57%, C8 20.02%, C 10 15.22%, C 12 13.47%, C 14+ 35.72%.

[0095] Example 8: This example is used to further illustrate that when a diiminopyridine ligand is synthesized in a toluene solvent and the resulting product liquid is directly used in the preparation of a main catalyst diiminopyridine iron solution, the reaction time is allowed to vary within a certain range.

[0096] Example 1 was repeated, but in the first step of ligand synthesis, the ligand synthesis time was changed to 0.5 h, 4 h and 72 h, respectively, and the obtained catalysts were used for ethylene non-selective oligomerization. The solid product masses were 0.38 g, 1.03 g and 1.28 g, respectively, and the catalyst activities were 9.03×10 6 g / molFe·h, 1.35×10 7 g / molFe·h and 1.38×10 7 g / molFe·h, the linear α-olefin selectivity is 89.23%, 87.39% and 86.72% respectively. The carbon number distribution is C4-C 28 In order, they are: C6 15.19%, C8 20.72%, C 10 15.08%, C 12 13.28%, C 14+ 35.73%; C6 15.35%, C8 20.62%, C 10 15.95%, C 12 13.06%, C 14+ 35.02%; C6 15.28%, C8 20.69%, C 10 15.35%, C 12 13.72%, C14+ 34.96%.

[0097] Example 9: This example is used to further illustrate that when using the toluene solution of the diiminopyridine ligand obtained in the first step to prepare the toluene solution of the main catalyst diiminopyridine iron, the concentration of diiminopyridine iron in the toluene solvent is allowed to vary within a certain range.

[0098] Example 1 was repeated, but in the second step of preparing the toluene solution of the main catalyst diimino pyridine iron, the amount of toluene solution was changed to 100 mL (the concentration of diimino pyridine iron in toluene solvent after mixing was 0.5×10 - 4 mol / L), 63mL (the concentration of diiminopyridine iron in toluene solvent after mixing is 0.8×10 -4 mol / L), 42mL (the concentration of diiminopyridine iron in toluene solvent after mixing is 1.2×10 -4 mol / L) and 33mL (the concentration of diiminopyridine iron in toluene solvent after mixing is 1.5×10 -4 mol / L), and the obtained catalyst was used for the non-selective oligomerization of ethylene. The mass of the solid product was 1.28g, 0.95g, 1.28g and 1.47g, respectively, and the catalyst activity was 9.62×10 6 g / molFe·h, 1.15×10 7 g / molFe·h, 1.05×10 7 g / molFe·h and 1.18×10 7 g / molFe·h, the linear α-olefin selectivities were 82.71%, 88.56%, 86.57% and 83.91% respectively. The carbon number distribution was C4-C 28 In order, they are: C6 15.29%, C8 20.25%, C 10 15.62%, C 12 13.45%, C 14+ 35.39%; C6 15.28%, C8 20.14%, C 10 15.63%, C 12 13.35%, C 14+ 35.60%; C6 15.01%, C8 20.29%, C 10 15.85%, C 12 13.37%, C 14+ 35.48%; C6 15.23%, C8 20.87%, C 10 15.73%, C 12 13.04%, C14+ 35.13%.

[0099] Example 10: This example is used to further illustrate that when using the toluene solution of the diiminopyridine ligand obtained in the first step to prepare the toluene solution of the main catalyst diiminopyridine iron, other iron central atom precursors can be selected.

[0100] Example 1 was repeated, but in the second step of preparing the toluene solution of the main catalyst diiminopyridine iron, ferric acetylacetonate was replaced by ferric chloride, ferrous chloride and ferrous bromide in sequence, and the obtained catalysts were used for the non-selective polymerization of ethylene. The mass of the solid product was 1.15 g, 0.83 g and 0.63 g, respectively, and the catalyst activity was 9.56×10 6 g / molFe·h, 7.46×10 6 g / molFe·h and 6.92×10 6 g / molFe·h, the linear α-olefin selectivity was 86.21%, 89.13% and 85.73% respectively. The carbon number distribution was C4-C 28 In order, they are: C6 15.28%, C8 20.57%, C 10 15.33%, C 12 13.54%, C 14+ 35.28%; C6 15.18%, C8 20.39%, C 10 15.70%, C 12 13.94%, C 14+ 34.79%; C6 15.13%, C8 20.52%, C 10 15.53%, C 12 13.89%, C 14+ 34.93%.

[0101] Example 11: This example is used to further illustrate that when the non-selective polymerization reaction of ethylene is carried out in the fourth step, the reaction pressure is allowed to vary within a certain range.

[0102] Example 1 was repeated, but in the fourth step, the reaction pressure was changed to 0.1 MPa and 3 MPa, respectively, and the obtained catalyst was used for the non-selective oligomerization of ethylene. The mass of the solid product was 0.27 g and 0.57 g, respectively, and the catalyst activity was 2.73×10 4 g / molFe·h and 8.73×10 6 g / molFe·h, linear α-olefin selectivity was 90.88% and 87.38% respectively. The carbon number distribution was C4-C 28Among them, C6 15.62%, C8 20.96%, C 10 15.36%, C 12 13.22%, C 14+ 34.84% and C6 15.23%, C8 20.18%, C 10 15.82%, C 12 13.36%, C 14+ 35.41%.

[0103] Example 12: This example is used to further illustrate that when the non-selective polymerization of ethylene is carried out in the fourth step, the reaction temperature is allowed to vary within a certain range.

[0104] Example 1 was repeated, but in the fourth step, the reaction temperature was changed to 30°C and 70°C for the non-selective oligomerization of ethylene, and the obtained catalyst was used for the non-selective oligomerization of ethylene. The mass of the solid product was 1.20 g and 2.89 g, respectively, and the catalyst activity was 6.82×10 6 g / molFe·h and 1.62×10 7 g / molFe·h, linear α-olefin selectivity was 87.18% and 78.73% respectively. The carbon number distribution was C4-C 28 Among them, C6 15.32%, C8 20.67%, C 10 15.24%, C 12 13.71%, C 14+ 35.06% and C6 15.24%, C8 20.29%, C 10 15.94%, C 12 13.73%, C 14+ 35.16%.

[0105] Example 13: This example is used to further illustrate that when the non-selective polymerization of ethylene is carried out in the fourth step, the reaction time is allowed to vary within a certain range.

[0106] Example 1 was repeated, but in the fourth step, the reaction time was changed to 5 min and 30 min, respectively, and the obtained catalyst was used for the non-selective polymerization of ethylene. The mass of the solid product was 0.90 g and 1.38 g, respectively, and the catalyst activity was 8.89×10 6 g / molFe·h and 7.29×10 6 g / molFe·h, linear α-olefin selectivity was 87.83% and 83.37% respectively. The carbon number distribution was C4-C 28 Among them, C6 15.18%, C8 20.85%, C10 15.44%, C 12 13.74%, C 14+ 34.83% and C6 15.38%, C8 20.32%, C 10 15.82%, C 12 13.64%, C 14+ 34.84%.

[0107] Example 14: This example is used to illustrate that the method provided by the present invention not only allows the use of toluene solvent instead of anhydrous ethanol to synthesize diiminopyridine ligands, but also allows the toluene solution containing the ligand obtained in the ligand synthesis step to be directly used for the preparation of the main catalyst diiminopyridine iron, thereby achieving seamless connection between the ligand synthesis step and the ethylene polymerization reaction step, simplifying the production process of α-olefins, while reducing the types of solvents used in industrial production sites, and even allowing the addition of additives that can effectively inhibit the formation of ethylene wax by-products to the catalyst system without adversely affecting the non-selective polymerization of ethylene.

[0108] Example 1 was repeated, but in the third step of the catalyst system preparation process, 0.3 g of p-bromophenol was added to the toluene solution of the cocatalyst MAO as an ethylene wax inhibitor. The mass of the solid product was 0.09 g (ethylene wax), and the reaction result became: the catalyst activity was 7.49×10 6 g / molFe·h, linear α-olefin selectivity is 98.56%. The carbon number distribution is C4-C 28 Among them, C6 20.72%, C8 24.84%, C 10 19.10%, C 12 12.69%, C 14+ 22.65%.

Claims

1. A process for preparing linear α-olefins by non-selective oligomerization of ethylene, characterized in that: Here are the steps: Step 1: Preparation of toluene solution of bis-iminopyridine ligand The diiminopyridine ligand is synthesized by reacting 2,6-diacetylpyridine with aniline raw materials; the synthesis reaction is carried out under the protection of high-purity nitrogen using toluene that has been subjected to dehydration and deoxygenation treatment as a solvent, the reaction pressure is normal pressure, the reaction temperature range is 100-120°C, and the reaction time range is 0.5-72h; the water generated during the synthesis of the diiminopyridine ligand is removed by using a type A molecular sieve dehydrating agent molded product filled in a reflux tank; the prepared toluene solution of the diiminopyridine ligand is stored at a constant temperature of not less than 30°C; The concentration of 2,6-diacetylpyridine in toluene solvent is 0.05-0.5 mol / L; The molar ratio of the aniline raw material to 2,6-diacetylpyridine is 3:1-2:1; Based on the weight of 2,6-diacetylpyridine, the amount of type A molecular sieve added is ≥30 times; Type A molecular sieve, as a dehydrating agent, must be pre-treated for dehydration before use; Step 2: directly use the toluene solution of the diiminopyridine ligand obtained in the first step to prepare a toluene solution of the main catalyst diiminopyridine iron First, a toluene solution of an iron central atom precursor is prepared by using toluene that has been subjected to a dehydration and deoxygenation treatment as a solvent; then, the toluene solution of the diiminopyridine ligand obtained in the first step and the toluene solution of the iron central atom precursor are mixed uniformly in equimolar amounts at or near the ethylene polymerization temperature under anhydrous and oxygen-free conditions to obtain a toluene solution of the main catalyst diiminopyridine iron; The concentration of the mixed bis-imino pyridine iron in the toluene solvent ranges from 0.5×10 -4 -1.5×10 -4 mol / L; Step 3: Using the toluene solution of the main catalyst diimidopyridyl iron prepared in the second step and the toluene solution of the co-catalyst methylaluminoxane to form an in-situ catalyst system for non-selective polymerization of ethylene in a high-pressure reactor used for ethylene polymerization reaction First, a toluene solution of a co-catalyst methylaluminoxane is prepared by using toluene that has been subjected to a dehydration and deoxygenation treatment as a solvent; then, under anhydrous and oxygen-free conditions, the toluene solution of the co-catalyst methylaluminoxane and the toluene solution of the main catalyst diimidopyridyl iron obtained in the second step are sequentially added into a high-pressure reactor used for an ethylene polymerization reaction that has been subjected to a dehydration and deoxygenation pretreatment according to metering, at or near an ethylene polymerization temperature, and mixed evenly, thereby forming a catalyst system for non-selective ethylene polymerization; Step 4: Using the catalyst system prepared in situ in the high-pressure reactor in the step 3, a non-selective polymerization reaction of ethylene is carried out to prepare a linear α-olefin mixture.

2. The process for preparing linear α-olefins by non-selective oligomerization of ethylene according to claim 1, characterized in that: In the first step of preparing a toluene solution of the diiminopyridine ligand, any one of aniline, o-toluidine, 2-methyl-4-methoxyaniline, 2-methyl-4-chloroaniline or 2-chloro-4-methylaniline is used as the aniline raw material.

3. The process for preparing linear α-olefins by non-selective oligomerization of ethylene according to claim 1, characterized in that: In the first step of preparing the toluene solution of the bis-imino pyridine ligand, any one of the commercially available 3A, 4A, and 5A molecular sieve beads is used as the A-type molecular sieve dehydrating agent molding.

4. The process for preparing linear α-olefins by non-selective oligomerization of ethylene according to claim 1, characterized in that: In the first step of preparing the toluene solution of the diimino pyridine ligand, the reaction temperature for the ligand synthesis is 110° C. and the reaction time is 3-4 h.

5. The process for preparing linear α-olefins by non-selective oligomerization of ethylene according to claim 1, characterized in that: In the first step of preparing a toluene solution of the diiminopyridine ligand, the molar ratio of the aniline raw material to 2,6-diacetylpyridine is 2.5:1-2.2:

1.

6. The process for preparing linear α-olefins by non-selective oligomerization of ethylene according to claim 1, characterized in that: When preparing the toluene solution of the diimino pyridine ligand in the first step, the amount of type A molecular sieve added is ≥40 times the weight of 2,6-diacetyl pyridine.

7. The process for preparing linear α-olefins by non-selective oligomerization of ethylene according to claim 1, characterized in that: In the second step, a toluene solution of an iron central atom precursor is prepared, and ferric acetylacetonate, ferric chloride, ferrous chloride or ferrous bromide is selected as the iron central atom precursor.

8. The process for preparing linear α-olefins by non-selective oligomerization of ethylene according to claim 1, characterized in that: In the second step, a toluene solution of the iron central atom precursor is prepared. After mixing, the concentration of the diiminopyridine iron in the toluene solvent ranges from 0.8×10 -4 -1.2×10 -4 mol / L.

9. The process for preparing linear α-olefins by non-selective oligomerization of ethylene according to claim 1, characterized in that: In the fourth step, when non-selective polymerization of ethylene is carried out in a high-pressure reactor to prepare a linear α-olefin mixture, the specific method is as follows: (1) after the toluene solutions of the co-catalyst, the main catalyst and other auxiliaries are introduced into the reactor in sequence as described in the third step to form a catalyst system, ethylene is introduced into the reactor at the reaction temperature to reach the reaction pressure, and the timing reaction is started; (2) after the reaction is completed, the high-pressure reactor is first depressurized, and after the actual temperature in the reactor is lower than 50° C., the reactor is opened at normal pressure, all reactants are taken out, and 10% acidified ethanol is added thereto to terminate the reaction.

10. The process for preparing linear α-olefins by non-selective oligomerization of ethylene according to claim 1, characterized in that: In the fourth step, when non-selective polymerization of ethylene is carried out in a high-pressure reactor to produce a linear α-olefin mixture, the reaction pressure is 0.1 to 3 MPa, the reaction temperature is 30 to 70° C., and the reaction time is 5 to 30 min.

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